id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2004.12137 | Abolhassan Mohammadi | Abolhassan Mohammadi, Tayeb Golanbari, Salah Nasri, Khaled Saaidi | Brane Constant-roll Inflation | 20 pages, 6 figures; Typos fixed; references added, accepted for
publication in PRD | Phys. Rev. D 101, 123537 (2020) | 10.1103/PhysRevD.101.123537 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The scenario of constant-roll inflation in the frame of the RSII brane
gravity model is considered. Based on the scenario, the smallness of the second
slow-roll parameter is released and it is assumed as a constant which could be
of the order of unity. Applying the Hamilton-Jacobi formalism, the constancy of
the parameter gives a differential equation for the Hubble parameter which
leads to an exact solution for the model. Reconsidering the perturbation
equations we show there are some modified terms appearing in the amplitude of
the scalar perturbations and in turn in the scalar spectral index and
tensor-to-scalar ratio. Comparing the theoretical results of the model with
observational data, the free parameters of the model are determined. Then, the
consistency of the model with the swampland criteria is investigated for the
obtained values of the free parameters. As the final step, the attractor
behavior of the model is considered.
| [
{
"created": "Sat, 25 Apr 2020 13:14:09 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Jun 2020 21:06:18 GMT",
"version": "v2"
},
{
"created": "Wed, 1 Jul 2020 10:32:56 GMT",
"version": "v3"
}
] | 2020-07-08 | [
[
"Mohammadi",
"Abolhassan",
""
],
[
"Golanbari",
"Tayeb",
""
],
[
"Nasri",
"Salah",
""
],
[
"Saaidi",
"Khaled",
""
]
] | The scenario of constant-roll inflation in the frame of the RSII brane gravity model is considered. Based on the scenario, the smallness of the second slow-roll parameter is released and it is assumed as a constant which could be of the order of unity. Applying the Hamilton-Jacobi formalism, the constancy of the parameter gives a differential equation for the Hubble parameter which leads to an exact solution for the model. Reconsidering the perturbation equations we show there are some modified terms appearing in the amplitude of the scalar perturbations and in turn in the scalar spectral index and tensor-to-scalar ratio. Comparing the theoretical results of the model with observational data, the free parameters of the model are determined. Then, the consistency of the model with the swampland criteria is investigated for the obtained values of the free parameters. As the final step, the attractor behavior of the model is considered. |
2207.00878 | Genly Le\'on | Miguel A. Garc\'ia-Aspeitia, Guillermo Fernandez-Anaya, A.
Hern\'andez-Almada, Genly Leon (Catolica del Norte U. and DUT, Durban) and
Juan Maga\~na | Cosmology under the fractional calculus approach | 15 pages, 8 figures. Moderate revision. Matches the version accepted
for publication in MNRAS | null | 10.1093/mnras/stac3006 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Fractional cosmology modifies the standard derivative to Caputo's fractional
derivative of order $\mu$, generating changes in General Relativity. Friedmann
equations are modified, and the evolution of the species densities depends on
$\mu$ and the age of the Universe $t_U$. We estimate stringent constraints on
$\mu$ using cosmic chronometers, Type Ia supernovae, and joint analysis. We
obtain $\mu=2.839^{+0.117}_{-0.193}$ within the $1\sigma$ confidence level
providing a non-standard cosmic acceleration at late times; consequently, the
Universe would be older than the standard estimations. Additionally, we present
a stability analysis for different $\mu$ values. This analysis identifies a
late-time attractor corresponding to a power-law decelerated solution for $\mu
< 2$. Moreover, a non-relativistic critical point exists for $\mu > 1$ and a
sink for $\mu > 2$. This solution is a decelerated power-law if $1 < \mu < 2$
and an accelerated power-law solution if $\mu > 2$, consistent with the mean
values obtained from the observational analysis. Therefore, for both flat FLRW
and Bianchi I metrics, the modified Friedmann equations provide a late cosmic
acceleration under this paradigm without introducing a dark energy component.
This approach could be a new path to tackling unsolved cosmological problems.
| [
{
"created": "Sat, 2 Jul 2022 16:48:06 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Jul 2022 15:11:45 GMT",
"version": "v2"
},
{
"created": "Mon, 17 Oct 2022 14:10:31 GMT",
"version": "v3"
}
] | 2022-10-26 | [
[
"García-Aspeitia",
"Miguel A.",
"",
"Catolica del Norte U. and DUT, Durban"
],
[
"Fernandez-Anaya",
"Guillermo",
"",
"Catolica del Norte U. and DUT, Durban"
],
[
"Hernández-Almada",
"A.",
"",
"Catolica del Norte U. and DUT, Durban"
],
[
"Leon",
"Genly",
"",
"Catolica del Norte U. and DUT, Durban"
],
[
"Magaña",
"Juan",
""
]
] | Fractional cosmology modifies the standard derivative to Caputo's fractional derivative of order $\mu$, generating changes in General Relativity. Friedmann equations are modified, and the evolution of the species densities depends on $\mu$ and the age of the Universe $t_U$. We estimate stringent constraints on $\mu$ using cosmic chronometers, Type Ia supernovae, and joint analysis. We obtain $\mu=2.839^{+0.117}_{-0.193}$ within the $1\sigma$ confidence level providing a non-standard cosmic acceleration at late times; consequently, the Universe would be older than the standard estimations. Additionally, we present a stability analysis for different $\mu$ values. This analysis identifies a late-time attractor corresponding to a power-law decelerated solution for $\mu < 2$. Moreover, a non-relativistic critical point exists for $\mu > 1$ and a sink for $\mu > 2$. This solution is a decelerated power-law if $1 < \mu < 2$ and an accelerated power-law solution if $\mu > 2$, consistent with the mean values obtained from the observational analysis. Therefore, for both flat FLRW and Bianchi I metrics, the modified Friedmann equations provide a late cosmic acceleration under this paradigm without introducing a dark energy component. This approach could be a new path to tackling unsolved cosmological problems. |
2001.05716 | Diego Pavon | Diego Pavon | On the degrees of freedom of a black hole | 8 pages, no figures. Key words: gravity, black holes, statistical
mechanics, equipartition theorem. Comments appreciated | null | null | 523 UAB | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | By examining whether black holes fulfill the theorem of equipartition of
energy we find that the notion of degrees of freedom, previously introduced for
cosmic horizons, is meaningful in the case of Schwarzschild and Kerr black
holes. However, for Reissner-N\"{o}rdstrom and Kerr-Newman black holes this
notion fails.
| [
{
"created": "Thu, 16 Jan 2020 09:45:03 GMT",
"version": "v1"
}
] | 2020-01-24 | [
[
"Pavon",
"Diego",
""
]
] | By examining whether black holes fulfill the theorem of equipartition of energy we find that the notion of degrees of freedom, previously introduced for cosmic horizons, is meaningful in the case of Schwarzschild and Kerr black holes. However, for Reissner-N\"{o}rdstrom and Kerr-Newman black holes this notion fails. |
0807.1689 | Joao Magueijo | Joao Magueijo | Bimetric varying speed of light theories and primordial fluctuations | null | Phys.Rev.D79:043525,2009 | 10.1103/PhysRevD.79.043525 | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We exhibit a varying speed of light (VSL) theory that implements the recently
proposed decaying speed of sound mechanism for generating density fluctuations.
We avail ourselves of bimetric VSL theories, where the speed of gravity differs
from that of light. We first show that a Dirac-Born-Infeld (DBI) type of
$K$-essence has the necessary speed of sound profile to produce (near)
scale-invariant fluctuations. We then examine the map between bimetric and
$K$-essence models: typically the bi-scalar connecting the two metrics is a
$K$-essence field in one of them. Remarkably, the DBI model is found to
perturbatively represent the minimal bimetric model, where the bi-scalar is
Klein-Gordon in the matter frame. But the full non-perturbative bimetric
structure is even simpler: the bi-scalar dynamics should be simply driven by a
cosmological constant in the matter frame, balanced by an opposite cosmological
constant in the gravity frame. Thus the problem of structure formation receives
an elegant and universal solution within bimetric VSL theories, which are known
to also solve the flatness and entropy problems and evade a plethora of
causality concerns.
| [
{
"created": "Thu, 10 Jul 2008 16:01:12 GMT",
"version": "v1"
},
{
"created": "Fri, 29 Jan 2010 17:41:28 GMT",
"version": "v2"
}
] | 2010-01-29 | [
[
"Magueijo",
"Joao",
""
]
] | We exhibit a varying speed of light (VSL) theory that implements the recently proposed decaying speed of sound mechanism for generating density fluctuations. We avail ourselves of bimetric VSL theories, where the speed of gravity differs from that of light. We first show that a Dirac-Born-Infeld (DBI) type of $K$-essence has the necessary speed of sound profile to produce (near) scale-invariant fluctuations. We then examine the map between bimetric and $K$-essence models: typically the bi-scalar connecting the two metrics is a $K$-essence field in one of them. Remarkably, the DBI model is found to perturbatively represent the minimal bimetric model, where the bi-scalar is Klein-Gordon in the matter frame. But the full non-perturbative bimetric structure is even simpler: the bi-scalar dynamics should be simply driven by a cosmological constant in the matter frame, balanced by an opposite cosmological constant in the gravity frame. Thus the problem of structure formation receives an elegant and universal solution within bimetric VSL theories, which are known to also solve the flatness and entropy problems and evade a plethora of causality concerns. |
gr-qc/9508005 | Charles Torre | C. G. Torre (Utah State Univ.) | Spinors, Jets, and the Einstein Equations | to appear in the proceedings of the Sixth Canadian Conference on
General Relativity and Relativistic Astrophysics, 13 pages, uses AMSTeX and
AMSppt.sty | null | null | null | gr-qc | null | Many important features of a field theory, {\it e.g.}, conserved currents,
symplectic structures, energy-momentum tensors, {\it etc.}, arise as tensors
locally constructed from the fields and their derivatives. Such tensors are
naturally defined as geometric objects on the jet space of solutions to the
field equations. Modern results from the calculus on jet bundles can be
combined with a powerful spinor parametrization of the jet space of Einstein
metrics to unravel basic features of the Einstein equations. These techniques
have been applied to computation of generalized symmetries and ``characteristic
cohomology'' of the Einstein equations, and lead to results such as a proof of
non-existence of ``local observables'' for vacuum spacetimes and a uniqueness
theorem for the gravitational symplectic structure.
| [
{
"created": "Thu, 3 Aug 1995 16:35:48 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Torre",
"C. G.",
"",
"Utah State Univ."
]
] | Many important features of a field theory, {\it e.g.}, conserved currents, symplectic structures, energy-momentum tensors, {\it etc.}, arise as tensors locally constructed from the fields and their derivatives. Such tensors are naturally defined as geometric objects on the jet space of solutions to the field equations. Modern results from the calculus on jet bundles can be combined with a powerful spinor parametrization of the jet space of Einstein metrics to unravel basic features of the Einstein equations. These techniques have been applied to computation of generalized symmetries and ``characteristic cohomology'' of the Einstein equations, and lead to results such as a proof of non-existence of ``local observables'' for vacuum spacetimes and a uniqueness theorem for the gravitational symplectic structure. |
2104.14031 | Jiri Horak | Marek Abramowicz, Ji\v{r}\'i Hor\'ak and Kate\v{r}ina
Klimovi\v{c}ov\'a | Wave-fronts of gravitational waves partially trapped in ultra-compact
stars | 4 pages, 3 figures, to appear in proceedings of "Recontres de Moriond
on Gravitation 2021" conference | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We dedicate this work to Dr Omer Blaes, professor of physics at UCSB, on the
occasion of his sixtieth birthday. We have been collaborating now and then with
Dr. Blaes on problems involving oscillations, waves and stability. Happy
birthday, Omer. Enjoy the analytic treatment of damping of the gravitational
waves trapped inside ultra compact stars and its possible connection to Quantum
Gravity in the context of the LIGO-Virgo efforts in accurately measuring
ringdowns and echoes.
| [
{
"created": "Wed, 28 Apr 2021 21:42:08 GMT",
"version": "v1"
}
] | 2021-04-30 | [
[
"Abramowicz",
"Marek",
""
],
[
"Horák",
"Jiří",
""
],
[
"Klimovičová",
"Kateřina",
""
]
] | We dedicate this work to Dr Omer Blaes, professor of physics at UCSB, on the occasion of his sixtieth birthday. We have been collaborating now and then with Dr. Blaes on problems involving oscillations, waves and stability. Happy birthday, Omer. Enjoy the analytic treatment of damping of the gravitational waves trapped inside ultra compact stars and its possible connection to Quantum Gravity in the context of the LIGO-Virgo efforts in accurately measuring ringdowns and echoes. |
gr-qc/0405067 | Norichika Sago | Norichika Sago, Kunihito Ioka, Takashi Nakamura, Ryo Yamazaki | Gravitational Wave Memory of Gamma-Ray Burst Jets | Revtex4, 10 pages, 6 figures, Fig.2 and Fig.3 replaced, minor changes
to text in Sec.I and Sec.V, typos corrected, some reference added, Version to
be published in PRD | Phys.Rev.D70:104012,2004 | 10.1103/PhysRevD.70.104012 | OU-TAP-230, IGPC-04/5-2,KUNS-1916 | gr-qc astro-ph | null | Gamma-Ray Bursts (GRBs) are now considered as relativistic jets. We analyze
the gravitational waves from the acceleration stage of the GRB jets. We show
that (i) the point mass approximation is not appropriate if the opening
half-angle of the jet is larger than the inverse of the Lorentz factor of the
jet, (ii) the gravitational waveform has many step function like jumps, and
(iii) the practical DECIGO and BBO may detect such an event if the GRBs occur
in Local group of galaxy. We found that the light curve of GRBs and the
gravitational waveform are anti-correlated so that the detection of the
gravitational wave is indispensable to determine the structure of GRB jets.
| [
{
"created": "Thu, 13 May 2004 05:03:32 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Nov 2004 10:00:10 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Sago",
"Norichika",
""
],
[
"Ioka",
"Kunihito",
""
],
[
"Nakamura",
"Takashi",
""
],
[
"Yamazaki",
"Ryo",
""
]
] | Gamma-Ray Bursts (GRBs) are now considered as relativistic jets. We analyze the gravitational waves from the acceleration stage of the GRB jets. We show that (i) the point mass approximation is not appropriate if the opening half-angle of the jet is larger than the inverse of the Lorentz factor of the jet, (ii) the gravitational waveform has many step function like jumps, and (iii) the practical DECIGO and BBO may detect such an event if the GRBs occur in Local group of galaxy. We found that the light curve of GRBs and the gravitational waveform are anti-correlated so that the detection of the gravitational wave is indispensable to determine the structure of GRB jets. |
0712.4333 | Anil Zengino\u{g}lu C | An{\i}l Zengino\u{g}lu | Hyperboloidal foliations and scri-fixing | 14 pages, 14 figures. Published version | Class.Quant.Grav.25:145002,2008 | 10.1088/0264-9381/25/14/145002 | AEI-2007-177 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss a gauge choice which allows us to avoid the introduction of
artificial timelike outer boundaries in numerical studies of test fields based
on a 3+1 decomposition of asymptotically flat background spacetimes. The main
idea is to include null infinity in the computational domain by conformally
compactifying the metric on hyperboloidal foliations and fixing the spatial
coordinate location of null infinity, i.e. scri-fixing. We construct such
coordinates explicitly on Minkowski, Schwarzschild and Kerr spacetimes.
| [
{
"created": "Fri, 28 Dec 2007 14:03:57 GMT",
"version": "v1"
},
{
"created": "Tue, 24 Jun 2008 17:31:59 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Zenginoğlu",
"Anıl",
""
]
] | We discuss a gauge choice which allows us to avoid the introduction of artificial timelike outer boundaries in numerical studies of test fields based on a 3+1 decomposition of asymptotically flat background spacetimes. The main idea is to include null infinity in the computational domain by conformally compactifying the metric on hyperboloidal foliations and fixing the spatial coordinate location of null infinity, i.e. scri-fixing. We construct such coordinates explicitly on Minkowski, Schwarzschild and Kerr spacetimes. |
2007.11584 | Carlos A. R. Herdeiro | Nicolas Sanchis-Gual, Miguel Zilh\~ao, Carlos Herdeiro, Fabrizio Di
Giovanni, Jos\'e A. Font, Eugen Radu | Synchronised gravitational atoms from mergers of bosonic stars | 6 pages, 7 figures | Phys. Rev. D 102, 101504 (2020) | 10.1103/PhysRevD.102.101504 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | If ultralight bosonic fields exist in Nature as dark matter, superradiance
spins down rotating black holes (BHs), dynamically endowing them with
equilibrium bosonic clouds, here dubbed synchronised gravitational atoms
(SGAs). The self-gravity of these same fields, on the other hand, can lump them
into (scalar or vector) horizonless solitons known as bosonic stars (BSs). We
show that the dynamics of BSs yields a new channel forming SGAs. We study BS
binaries that merge to form spinning BHs. After horizon formation, the BH spins
up by accreting the bosonic field, but a remnant lingers around the horizon. If
just enough angular momentum is present, the BH spin up stalls precisely as the
remnant becomes a SGA. Different initial data lead to SGAs with different
quantum numbers. Thus, SGAs may form both from superradiance-driven BH spin
down and accretion-driven BH spin up. The latter process, moreover, can result
in heavier SGAs than those obtained from the former: in one example herein,
$\sim 18\%$ of the final system's energy and $\sim 50\%$ of its angular
momentum remain in the SGA. We suggest that even higher values may occur in
systems wherein both accretion and superradiance contribute to the SGA
formation.
| [
{
"created": "Wed, 22 Jul 2020 18:00:00 GMT",
"version": "v1"
}
] | 2020-11-25 | [
[
"Sanchis-Gual",
"Nicolas",
""
],
[
"Zilhão",
"Miguel",
""
],
[
"Herdeiro",
"Carlos",
""
],
[
"Di Giovanni",
"Fabrizio",
""
],
[
"Font",
"José A.",
""
],
[
"Radu",
"Eugen",
""
]
] | If ultralight bosonic fields exist in Nature as dark matter, superradiance spins down rotating black holes (BHs), dynamically endowing them with equilibrium bosonic clouds, here dubbed synchronised gravitational atoms (SGAs). The self-gravity of these same fields, on the other hand, can lump them into (scalar or vector) horizonless solitons known as bosonic stars (BSs). We show that the dynamics of BSs yields a new channel forming SGAs. We study BS binaries that merge to form spinning BHs. After horizon formation, the BH spins up by accreting the bosonic field, but a remnant lingers around the horizon. If just enough angular momentum is present, the BH spin up stalls precisely as the remnant becomes a SGA. Different initial data lead to SGAs with different quantum numbers. Thus, SGAs may form both from superradiance-driven BH spin down and accretion-driven BH spin up. The latter process, moreover, can result in heavier SGAs than those obtained from the former: in one example herein, $\sim 18\%$ of the final system's energy and $\sim 50\%$ of its angular momentum remain in the SGA. We suggest that even higher values may occur in systems wherein both accretion and superradiance contribute to the SGA formation. |
1505.07014 | Caio Macedo | Caio F. B. Macedo, Ednilton S. de Oliveira, Lu\'is C. B. Crispino | Scattering by regular black holes: Planar massless scalar waves
impinging upon a Bardeen black hole | 8 pages, 7 figures. Version to be published in PRD | null | 10.1103/PhysRevD.92.024012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Singularities are common features of general relativity black holes. However,
within general relativity, one can construct black holes that present no
singularities. These regular black hole solutions can be achieved by, for
instance, relaxing one of the energy conditions on the stress energy tensor
sourcing the black hole. Some regular black hole solutions were found in the
context of non-linear electrodynamics, the Bardeen black hole being the first
one proposed. In this paper, we consider a planar massless scalar wave
scattered by a Bardeen black hole. We compare the scattering cross section
computed using a partial-wave description with the classical geodesic
scattering of a stream of null geodesics, as well as with the semi-classical
glory approximation. We obtain that, for some values of the corresponding black
hole charge, the scattering cross section of a Bardeen black hole has a similar
interference pattern of a Reissner-Nordstr\"om black hole.
| [
{
"created": "Tue, 26 May 2015 15:36:20 GMT",
"version": "v1"
},
{
"created": "Fri, 26 Jun 2015 21:24:52 GMT",
"version": "v2"
}
] | 2016-03-08 | [
[
"Macedo",
"Caio F. B.",
""
],
[
"de Oliveira",
"Ednilton S.",
""
],
[
"Crispino",
"Luís C. B.",
""
]
] | Singularities are common features of general relativity black holes. However, within general relativity, one can construct black holes that present no singularities. These regular black hole solutions can be achieved by, for instance, relaxing one of the energy conditions on the stress energy tensor sourcing the black hole. Some regular black hole solutions were found in the context of non-linear electrodynamics, the Bardeen black hole being the first one proposed. In this paper, we consider a planar massless scalar wave scattered by a Bardeen black hole. We compare the scattering cross section computed using a partial-wave description with the classical geodesic scattering of a stream of null geodesics, as well as with the semi-classical glory approximation. We obtain that, for some values of the corresponding black hole charge, the scattering cross section of a Bardeen black hole has a similar interference pattern of a Reissner-Nordstr\"om black hole. |
1204.1483 | Hrvoje Stefancic | Silvije Domazet, Hrvoje Stefancic | Renormalization group scale-setting from the action - a road to modified
gravity theories | v1: 15 pages; v2: shortened to 10 pages, main results unchanged,
published in Class. Quant. Grav | null | 10.1088/0264-9381/29/23/235005 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The renormalization group (RG) corrected gravitational action in
Einstein-Hilbert and other truncations is considered. The running scale of the
renormalization group is treated as a scalar field at the level of the action
and determined in a scale-setting procedure recently introduced by Koch and
Ramirez for the Einstein-Hilbert truncation. The scale-setting procedure is
elaborated for other truncations of the gravitational action and applied to
several phenomenologically interesting cases. It is shown how the logarithmic
dependence of the Newton's coupling on the RG scale leads to exponentially
suppressed effective cosmological constant and how the scale-setting in
particular RG corrected gravitational theories yields the effective $f(R)$
modified gravity theories with negative powers of the Ricci scalar $R$. The
scale-setting at the level of the action at the non-gaussian fixed point in
Einstein-Hilbert and more general truncations is shown to lead to universal
effective action quadratic in Ricci tensor.
| [
{
"created": "Fri, 6 Apr 2012 14:23:38 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Nov 2012 11:02:59 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Domazet",
"Silvije",
""
],
[
"Stefancic",
"Hrvoje",
""
]
] | The renormalization group (RG) corrected gravitational action in Einstein-Hilbert and other truncations is considered. The running scale of the renormalization group is treated as a scalar field at the level of the action and determined in a scale-setting procedure recently introduced by Koch and Ramirez for the Einstein-Hilbert truncation. The scale-setting procedure is elaborated for other truncations of the gravitational action and applied to several phenomenologically interesting cases. It is shown how the logarithmic dependence of the Newton's coupling on the RG scale leads to exponentially suppressed effective cosmological constant and how the scale-setting in particular RG corrected gravitational theories yields the effective $f(R)$ modified gravity theories with negative powers of the Ricci scalar $R$. The scale-setting at the level of the action at the non-gaussian fixed point in Einstein-Hilbert and more general truncations is shown to lead to universal effective action quadratic in Ricci tensor. |
2206.04836 | Shin'ichi Nojiri | G.G.L. Nashed and S. Nojiri | Black Holes with Electric and Magnetic Charges in $F(R)$ Gravity | LaTeX 20 pages, 9 figures, to appear in Fortschritte der Physik -
Progress of Physics | null | 10.1002/prop.202200091 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct spherically symmetric and static solutions in $F(R)$ gravity
coupled with electromagnetic fields. The solutions include new types of black
holes with electric and magnetic charges. We show that the higher-derivative
terms make the curvature singularity much softer than that in the charged black
holes in Einstein's general relativity. We calculate some thermodynamical
quantities of the obtained black holes like entropy, Hawking radiation, and
quasi-local energy and we confirm that the black hole solutions satisfy the
first law of thermodynamics. Finally, we study the stability analysis using the
odd-type mode and show that there are stable black hole solutions and the
radial speed of the parity-odd mode is unit, that is, the speed of light.
| [
{
"created": "Fri, 10 Jun 2022 01:44:46 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Nov 2022 23:01:21 GMT",
"version": "v2"
}
] | 2023-03-22 | [
[
"Nashed",
"G. G. L.",
""
],
[
"Nojiri",
"S.",
""
]
] | We construct spherically symmetric and static solutions in $F(R)$ gravity coupled with electromagnetic fields. The solutions include new types of black holes with electric and magnetic charges. We show that the higher-derivative terms make the curvature singularity much softer than that in the charged black holes in Einstein's general relativity. We calculate some thermodynamical quantities of the obtained black holes like entropy, Hawking radiation, and quasi-local energy and we confirm that the black hole solutions satisfy the first law of thermodynamics. Finally, we study the stability analysis using the odd-type mode and show that there are stable black hole solutions and the radial speed of the parity-odd mode is unit, that is, the speed of light. |
2003.09719 | Wan Cong Ms | Wan Cong, Jiri Bicak, David Kubiznak and Robert B. Mann | Quantum Distinction of Inertial Frames: Local vs. Global | 6 pages, 4 figures | null | 10.1103/PhysRevD.101.104060 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the response function of Unruh-deWitt detectors placed in a flat
spacetime inside a thin matter shell. We show that the response function
distinguishes between the local and global (Minkowski) inertial frames and
picks up the presence of the shell even when the detector is switched on for a
finite time interval within which a light signal cannot travel to the shell and
back as required by a classical measurement. We also analyze how the response
of the detector depends on its location within the shell.
| [
{
"created": "Sat, 21 Mar 2020 18:31:15 GMT",
"version": "v1"
},
{
"created": "Tue, 12 May 2020 01:27:36 GMT",
"version": "v2"
}
] | 2020-06-10 | [
[
"Cong",
"Wan",
""
],
[
"Bicak",
"Jiri",
""
],
[
"Kubiznak",
"David",
""
],
[
"Mann",
"Robert B.",
""
]
] | We study the response function of Unruh-deWitt detectors placed in a flat spacetime inside a thin matter shell. We show that the response function distinguishes between the local and global (Minkowski) inertial frames and picks up the presence of the shell even when the detector is switched on for a finite time interval within which a light signal cannot travel to the shell and back as required by a classical measurement. We also analyze how the response of the detector depends on its location within the shell. |
2108.12930 | Naoki Seto | Naoki Seto | Correlation of Gravitational Wave Background Noises and Statistical Loss
for Angular Averaged Sensitivity Curves | 11 pages, 10 figures | null | 10.1103/PhysRevD.104.063025 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | Gravitational wave backgrounds generate correlated noises to separated
detectors. This correlation can induce statistical losses to actual detector
networks, compared with idealized noise-independent networks. Assuming that the
backgrounds are isotropic, we examine the statistical losses specifically for
the angular averaged sensitivity curves, and derive simple expressions that
depend on the overlap reduction functions and the strength of the background
noises relative to the instrumental noises. For future triangular
interferometers such as ET and LISA, we also discuss preferred network
geometries to suppress the potential statistical losses.
| [
{
"created": "Sun, 29 Aug 2021 22:40:49 GMT",
"version": "v1"
}
] | 2021-09-29 | [
[
"Seto",
"Naoki",
""
]
] | Gravitational wave backgrounds generate correlated noises to separated detectors. This correlation can induce statistical losses to actual detector networks, compared with idealized noise-independent networks. Assuming that the backgrounds are isotropic, we examine the statistical losses specifically for the angular averaged sensitivity curves, and derive simple expressions that depend on the overlap reduction functions and the strength of the background noises relative to the instrumental noises. For future triangular interferometers such as ET and LISA, we also discuss preferred network geometries to suppress the potential statistical losses. |
gr-qc/0008019 | Keith H. Lockitch | Keith H. Lockitch, Nils Andersson, John L. Friedman | The rotational modes of relativistic stars: Analytic results | 36 pages revtex v3.1, 2 eps figures | Phys.Rev. D63 (2001) 024019 | 10.1103/PhysRevD.63.024019 | CGPG-99/12-2 | gr-qc astro-ph | null | We study the r-modes and rotational ``hybrid'' modes of relativistic stars.
As in Newtonian gravity, the spectrum of low-frequency rotational modes is
highly sensitive to the stellar equation of state. If the star and its
perturbations obey the same one-parameter equation of state (as with isentropic
stars), there exist {\it no pure r-modes at all} - no modes whose limit, for a
star with zero angular velocity, is an axial-parity perturbation. Rotating
stars of this kind similarly have no pure g-modes, no modes whose spherical
limit is a perturbation with polar parity and vanishing perturbed pressure and
density. We compute the post-Newtonian corrections to the $l=m$ r-modes of
isentropic and non-isentropic uniform density stars.
| [
{
"created": "Tue, 8 Aug 2000 21:59:22 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Lockitch",
"Keith H.",
""
],
[
"Andersson",
"Nils",
""
],
[
"Friedman",
"John L.",
""
]
] | We study the r-modes and rotational ``hybrid'' modes of relativistic stars. As in Newtonian gravity, the spectrum of low-frequency rotational modes is highly sensitive to the stellar equation of state. If the star and its perturbations obey the same one-parameter equation of state (as with isentropic stars), there exist {\it no pure r-modes at all} - no modes whose limit, for a star with zero angular velocity, is an axial-parity perturbation. Rotating stars of this kind similarly have no pure g-modes, no modes whose spherical limit is a perturbation with polar parity and vanishing perturbed pressure and density. We compute the post-Newtonian corrections to the $l=m$ r-modes of isentropic and non-isentropic uniform density stars. |
1402.5921 | Ronald Adler | Ronald J. Adler | A quantum theory of distance along a curve | 27 pages, 3 figures; includes added reference and acknowledgements,
corrected typos and phrases, results unchanged | null | null | null | gr-qc math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a quantum theory of distances along a curve, based on a linear
line element that is equal to the operator square root of the quadratic metric
of Riemannian geometry. Since the linear line element is an operator, we treat
it according to the rules of quantum mechanics and interpret its eigenvalues as
physically observable distances; the distance eigenvalues are naturally
quantized. There are both positive and negative eigenvalues, which requires
interpretation. Multi-element curves are defined as direct sums of line
elements, and behave much like systems of spin half electrons in a magnetic
field. For a curve of many elements an entropy and energy and temperature are
quite naturally defined, leading via standard statistical thermodynamics to a
relation between the most probable curve length and temperature. That relation
may be viewed as a universal heat-shrinking property of curves. At this stage
of the theory we do not include bodies or particles in the mix, do not suggest
field equations for the quantum geometry, and questions of interpretation
remain. The theory might conceivably be testable using observations of the
early Universe, when the temperature of space was presumably quite high. In
particular cosmogenesis may be thought of as time stopping at an infinite
temperature as we go backwards in time to the beginning.
| [
{
"created": "Thu, 13 Feb 2014 23:57:15 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Apr 2014 17:34:04 GMT",
"version": "v2"
}
] | 2014-05-06 | [
[
"Adler",
"Ronald J.",
""
]
] | We present a quantum theory of distances along a curve, based on a linear line element that is equal to the operator square root of the quadratic metric of Riemannian geometry. Since the linear line element is an operator, we treat it according to the rules of quantum mechanics and interpret its eigenvalues as physically observable distances; the distance eigenvalues are naturally quantized. There are both positive and negative eigenvalues, which requires interpretation. Multi-element curves are defined as direct sums of line elements, and behave much like systems of spin half electrons in a magnetic field. For a curve of many elements an entropy and energy and temperature are quite naturally defined, leading via standard statistical thermodynamics to a relation between the most probable curve length and temperature. That relation may be viewed as a universal heat-shrinking property of curves. At this stage of the theory we do not include bodies or particles in the mix, do not suggest field equations for the quantum geometry, and questions of interpretation remain. The theory might conceivably be testable using observations of the early Universe, when the temperature of space was presumably quite high. In particular cosmogenesis may be thought of as time stopping at an infinite temperature as we go backwards in time to the beginning. |
1911.09902 | Huaifan Li | Xiong-Ying Guo, Huai-Fan Li, Li-Chun Zhang, Ren Zhao | Continuous phase transition and microstructure of charged AdS black hole
with quintessence | 25 pages,4 figures,added refs. arXiv admin note: text overlap with
arXiv:1901.04703 | Eur. Phys. J. C (2020) 80:168 | 10.1140/epjc/s10052-019-7601-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Previously, the Maxwell equal-area law has been used to discuss the
conditions satisfied by the phase transition of charged AdS black holes with
cloud of string and quintessence, and it was concluded that black holes have
phase transition similar to that of vdW system. The phase transition depends on
the electric potential of the black hole and is not the one between a large
black hole and a small black hole. On the basis of this result, we study the
relation between the latent heat of the phase transition and the parameter of
dark energy, and use the Landau continuous phase transition theory to discuss
the critical phenomenon of the black hole with quintessence and give the
critical exponent. By introducing the number density of the black hole
molecules, some properties of the microstructure of black holes are studied in
terms of a phase transition. It is found that the electric charge of the black
hole and the normalization parameter related to the density of quintessence
field play a key role in phase transition. By constructing the binary fluid
model of the black hole molecules, we also discuss the microstructure of
charged AdS black holes with a cloud of strings and quintessence.
| [
{
"created": "Fri, 22 Nov 2019 07:38:55 GMT",
"version": "v1"
},
{
"created": "Tue, 26 Nov 2019 10:57:36 GMT",
"version": "v2"
},
{
"created": "Fri, 28 Feb 2020 09:49:51 GMT",
"version": "v3"
}
] | 2020-03-02 | [
[
"Guo",
"Xiong-Ying",
""
],
[
"Li",
"Huai-Fan",
""
],
[
"Zhang",
"Li-Chun",
""
],
[
"Zhao",
"Ren",
""
]
] | Previously, the Maxwell equal-area law has been used to discuss the conditions satisfied by the phase transition of charged AdS black holes with cloud of string and quintessence, and it was concluded that black holes have phase transition similar to that of vdW system. The phase transition depends on the electric potential of the black hole and is not the one between a large black hole and a small black hole. On the basis of this result, we study the relation between the latent heat of the phase transition and the parameter of dark energy, and use the Landau continuous phase transition theory to discuss the critical phenomenon of the black hole with quintessence and give the critical exponent. By introducing the number density of the black hole molecules, some properties of the microstructure of black holes are studied in terms of a phase transition. It is found that the electric charge of the black hole and the normalization parameter related to the density of quintessence field play a key role in phase transition. By constructing the binary fluid model of the black hole molecules, we also discuss the microstructure of charged AdS black holes with a cloud of strings and quintessence. |
2312.08392 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | Supporting traversable wormholes: the case for noncommutative geometry | 9 pages, no figures. arXiv admin note: substantial text overlap with
arXiv:2312.05266 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | While wormholes may be just as good a prediction of Einstein's theory as
black holes, they are subject to severe restrictions from quantum field theory.
In particular, a wormhole can only be held open by violating the null energy
condition, calling for the existence of "exotic matter," a condition that many
researchers consider completely unphysical, enough to rule out macroscopic
traversable wormholes. An equally serious problem is the enormous radial
tension at the throat of a typical Morris-Thorne wormhole unless the wormhole
has an extremely large throat size. It has been proposed that noncommutative
geometry, an offshoot of string theory, may be the proper tool for addressing
these issues. The purpose of this paper is two-fold: (1) to refine previous
arguments to make a stronger and more detailed case for this proposal and (2)
to obtain a complete wormhole solution from the given conditions.
| [
{
"created": "Tue, 12 Dec 2023 16:32:05 GMT",
"version": "v1"
},
{
"created": "Sun, 21 Jan 2024 21:13:05 GMT",
"version": "v2"
},
{
"created": "Sun, 5 May 2024 21:34:01 GMT",
"version": "v3"
}
] | 2024-05-07 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | While wormholes may be just as good a prediction of Einstein's theory as black holes, they are subject to severe restrictions from quantum field theory. In particular, a wormhole can only be held open by violating the null energy condition, calling for the existence of "exotic matter," a condition that many researchers consider completely unphysical, enough to rule out macroscopic traversable wormholes. An equally serious problem is the enormous radial tension at the throat of a typical Morris-Thorne wormhole unless the wormhole has an extremely large throat size. It has been proposed that noncommutative geometry, an offshoot of string theory, may be the proper tool for addressing these issues. The purpose of this paper is two-fold: (1) to refine previous arguments to make a stronger and more detailed case for this proposal and (2) to obtain a complete wormhole solution from the given conditions. |
gr-qc/0611020 | Janne Hogdahl | Kari Enqvist, Janne Hogdahl, Sami Nurmi, Filippo Vernizzi | Covariant generalization of cosmological perturbation theory | Minor changes to match the version published in PRD. RevTex, 22
pages, 1 figure | Phys.Rev.D75:023515,2007 | 10.1103/PhysRevD.75.023515 | HIP-2006-48/TH | gr-qc astro-ph | null | We present an approach to cosmological perturbations based on a covariant
perturbative expansion between two worldlines in the real inhomogeneous
universe. As an application, at an arbitrary order we define an exact scalar
quantity which describes the inhomogeneities in the number of e-folds on
uniform density hypersurfaces and which is conserved on all scales for a
barotropic ideal fluid. We derive a compact form for its conservation equation
at all orders and assign it a simple physical interpretation. To make a
comparison with the standard perturbation theory, we develop a method to
construct gauge-invariant quantities in a coordinate system at arbitrary order,
which we apply to derive the form of the n-th order perturbation in the number
of e-folds on uniform density hypersurfaces and its exact evolution equation.
On large scales, this provides the gauge-invariant expression for the curvature
perturbation on uniform density hypersurfaces and its evolution equation at any
order.
| [
{
"created": "Fri, 3 Nov 2006 15:18:53 GMT",
"version": "v1"
},
{
"created": "Mon, 15 Jan 2007 14:14:20 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Enqvist",
"Kari",
""
],
[
"Hogdahl",
"Janne",
""
],
[
"Nurmi",
"Sami",
""
],
[
"Vernizzi",
"Filippo",
""
]
] | We present an approach to cosmological perturbations based on a covariant perturbative expansion between two worldlines in the real inhomogeneous universe. As an application, at an arbitrary order we define an exact scalar quantity which describes the inhomogeneities in the number of e-folds on uniform density hypersurfaces and which is conserved on all scales for a barotropic ideal fluid. We derive a compact form for its conservation equation at all orders and assign it a simple physical interpretation. To make a comparison with the standard perturbation theory, we develop a method to construct gauge-invariant quantities in a coordinate system at arbitrary order, which we apply to derive the form of the n-th order perturbation in the number of e-folds on uniform density hypersurfaces and its exact evolution equation. On large scales, this provides the gauge-invariant expression for the curvature perturbation on uniform density hypersurfaces and its evolution equation at any order. |
0711.0576 | Sergey Paston | S.A. Paston, V.A. Franke | Canonical formulation of the embedded theory of gravity equivalent to
Einstein's General Relativity | LaTeX, 17 pages | Theor.Math.Phys.153:1581-1595,2007; Teor.Mat.Fiz.153:271-288,2007 | 10.1007/s11232-007-0134-9 | null | gr-qc hep-th | null | We study the approach in which independent variables describing gravity are
functions of the space-time embedding into a flat space of higher dimension. We
formulate a canonical formalism for such a theory in a form, which requires
imposing additional constraints, which are a part of Einstein's equations. As a
result, we obtain a theory with an eight-parameter gauge symmetry. This theory
becomes equivalent to Einstein's general relativity either after partial gauge
fixing or after rewriting the metric in the form that is invariant under the
additional gauge transformations. We write the action for such a theory.
| [
{
"created": "Mon, 5 Nov 2007 08:59:42 GMT",
"version": "v1"
}
] | 2010-03-09 | [
[
"Paston",
"S. A.",
""
],
[
"Franke",
"V. A.",
""
]
] | We study the approach in which independent variables describing gravity are functions of the space-time embedding into a flat space of higher dimension. We formulate a canonical formalism for such a theory in a form, which requires imposing additional constraints, which are a part of Einstein's equations. As a result, we obtain a theory with an eight-parameter gauge symmetry. This theory becomes equivalent to Einstein's general relativity either after partial gauge fixing or after rewriting the metric in the form that is invariant under the additional gauge transformations. We write the action for such a theory. |
gr-qc/0101101 | Vladimir V. Dyadichev | D.V. Gal'tsov and V.V. Dyadichev | Solitons in Non-Abelian Born-Infeld Theory | 2pges, LaTeX, Contribution to the 9th Marcel Grossmann meeting (MG9),
Rome, July 2000 | null | 10.1142/9789812777386_0181 | DTP-MSU-0020 | gr-qc | null | Born-Infeld generalization of the Yang-Mills action suggested by the
superstring theory gives rise to modification of previously known as well as to
some new classical soliton solutions. Earlier it was shown that within the
model with the usual trace over the group generators classical glueballs exist
which form an infinite sequence similar to the Bartnik-McKinnon family of the
Einstein-Yang-Mills solutions. Here we give the generalization of this result
to the 'realistic' model with the symmetrized trace and show the existence of
excited monopoles (in presence of triplet Higgs) which can be regarded as a
non-linear superposition of monopoles and sphalerons.
| [
{
"created": "Fri, 26 Jan 2001 12:21:14 GMT",
"version": "v1"
}
] | 2017-08-23 | [
[
"Gal'tsov",
"D. V.",
""
],
[
"Dyadichev",
"V. V.",
""
]
] | Born-Infeld generalization of the Yang-Mills action suggested by the superstring theory gives rise to modification of previously known as well as to some new classical soliton solutions. Earlier it was shown that within the model with the usual trace over the group generators classical glueballs exist which form an infinite sequence similar to the Bartnik-McKinnon family of the Einstein-Yang-Mills solutions. Here we give the generalization of this result to the 'realistic' model with the symmetrized trace and show the existence of excited monopoles (in presence of triplet Higgs) which can be regarded as a non-linear superposition of monopoles and sphalerons. |
1207.3715 | Eugen Radu | Eugen Radu and Bintoro Subagyo | Spinning scalar solitons in anti-de Sitter spacetime | 12 pages, 4 figures | null | 10.1016/j.physletb.2012.09.050 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present spinning Q-balls and boson stars in four dimensional anti-de
Sitter spacetime. These are smooth, horizonless solutions for gravity coupled
to a massive complex scalar field with a harmonic dependence on time and the
azimuthal angle. Similar to the flat spacetime configurations, the angular
momentum is quantized. We find that a class of solutions with a
self-interaction potential has a limit corresponding to static solitons with
axial symmetry only. An exact solution describing spherically symmetric Q-balls
in a fixed AdS background is also discussed.
| [
{
"created": "Mon, 16 Jul 2012 16:01:13 GMT",
"version": "v1"
}
] | 2015-06-05 | [
[
"Radu",
"Eugen",
""
],
[
"Subagyo",
"Bintoro",
""
]
] | We present spinning Q-balls and boson stars in four dimensional anti-de Sitter spacetime. These are smooth, horizonless solutions for gravity coupled to a massive complex scalar field with a harmonic dependence on time and the azimuthal angle. Similar to the flat spacetime configurations, the angular momentum is quantized. We find that a class of solutions with a self-interaction potential has a limit corresponding to static solitons with axial symmetry only. An exact solution describing spherically symmetric Q-balls in a fixed AdS background is also discussed. |
gr-qc/9708061 | M. B. Paranjape | A. Edery M. B. Paranjape | Cosmological sector for localized mass and spin in 2+1 dimensional
topologically massive gravity | 8 pages, no figures | Phys.Lett.B415:344-348,1997 | 10.1016/S0370-2693(97)01221-5 | UdeM-GPP-TH-97-45 | gr-qc | null | The cosmological sector to the full non-linear topologically massive gravity
(TMG) is obtained for localized sources of mass $m$ and spin $\sigma$ besides
the asymptotically spinning conical flat sector previously obtained. In a small
region near but outside the sources, the metric resembles the spinning conical
flat metric, but we find that the mass $m$ creates a negative deficit angle of
$3m$ as opposed to $m$. Furthermore, it is not possible to recover the results
of pure Einstein gravity in the limit $\mu \to \infty$ unlike the flat sector.
| [
{
"created": "Mon, 25 Aug 1997 19:44:42 GMT",
"version": "v1"
}
] | 2008-12-30 | [
[
"Paranjape",
"A. Edery M. B.",
""
]
] | The cosmological sector to the full non-linear topologically massive gravity (TMG) is obtained for localized sources of mass $m$ and spin $\sigma$ besides the asymptotically spinning conical flat sector previously obtained. In a small region near but outside the sources, the metric resembles the spinning conical flat metric, but we find that the mass $m$ creates a negative deficit angle of $3m$ as opposed to $m$. Furthermore, it is not possible to recover the results of pure Einstein gravity in the limit $\mu \to \infty$ unlike the flat sector. |
1412.6467 | Matthew Robbins | Saurya Das, Matthew P. G. Robbins, Mark A. Walton | Generalized Uncertainty Principle Corrections to the Simple Harmonic
Oscillator in Phase Space | minor revisions; included journal reference | Canadian Journal of Physics, 2016, 94(1): 139-146 | 10.1139/cjp-2015-0456 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compute Wigner functions for the harmonic oscillator including corrections
from generalized uncertainty principles (GUPs), and study the corresponding
marginal probability densities and other properties. We show that the GUP
corrections to the Wigner functions can be significant, and comment on their
potential measurability in the laboratory.
| [
{
"created": "Fri, 19 Dec 2014 18:07:15 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Jul 2015 17:26:18 GMT",
"version": "v2"
},
{
"created": "Tue, 26 Jan 2016 21:16:25 GMT",
"version": "v3"
}
] | 2016-01-28 | [
[
"Das",
"Saurya",
""
],
[
"Robbins",
"Matthew P. G.",
""
],
[
"Walton",
"Mark A.",
""
]
] | We compute Wigner functions for the harmonic oscillator including corrections from generalized uncertainty principles (GUPs), and study the corresponding marginal probability densities and other properties. We show that the GUP corrections to the Wigner functions can be significant, and comment on their potential measurability in the laboratory. |
gr-qc/0610006 | Jose Luis Jaramillo | J.L. Jaramillo, M. Ansorg, F. Limousin | Numerical implementation of isolated horizon boundary conditions | 11 pages, 5 figures, references added and corrected | Phys.Rev.D75:024019,2007 | 10.1103/PhysRevD.75.024019 | null | gr-qc | null | We study the numerical implementation of a set of boundary conditions derived
from the isolated horizon formalism, and which characterize a black hole whose
horizon is in quasi-equilibrium. More precisely, we enforce these geometrical
prescriptions as inner boundary conditions on an excised sphere, in the
numerical resolution of the Conformal Thin Sandwich equations. As main results,
we firstly establish the consistency of including in the set of boundary
conditions a "constant surface gravity" prescription, interpretable as a lapse
boundary condition, and secondly we assess how the prescriptions presented
recently by Dain et al. for guaranteeing the well-posedness of the Conformal
Transverse Traceless equations with quasi-equilibrium horizon conditions extend
to the Conformal Thin Sandwich elliptic system. As a consequence of the latter
analysis, we discuss the freedom of prescribing the expansion associated with
the ingoing null normal at the horizon.
| [
{
"created": "Mon, 2 Oct 2006 10:11:13 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Oct 2006 10:17:44 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Jaramillo",
"J. L.",
""
],
[
"Ansorg",
"M.",
""
],
[
"Limousin",
"F.",
""
]
] | We study the numerical implementation of a set of boundary conditions derived from the isolated horizon formalism, and which characterize a black hole whose horizon is in quasi-equilibrium. More precisely, we enforce these geometrical prescriptions as inner boundary conditions on an excised sphere, in the numerical resolution of the Conformal Thin Sandwich equations. As main results, we firstly establish the consistency of including in the set of boundary conditions a "constant surface gravity" prescription, interpretable as a lapse boundary condition, and secondly we assess how the prescriptions presented recently by Dain et al. for guaranteeing the well-posedness of the Conformal Transverse Traceless equations with quasi-equilibrium horizon conditions extend to the Conformal Thin Sandwich elliptic system. As a consequence of the latter analysis, we discuss the freedom of prescribing the expansion associated with the ingoing null normal at the horizon. |
gr-qc/0201097 | Dag Østvang | Dag {\O}stvang | Spherically Symmetric, Metrically Static, Isolated Systems in
Quasi-Metric Gravity | 34 pages; v2: connection changed; v3: extended and local conservation
laws changed; v4: major revision; v5: accepted for publication in G&C, v6:
must have non-universal gravitational coupling; v7: fully coupled theory
implemented; v8: fully coupled theory abandoned; v11: inconsistent equation
replaced (oh well). arXiv admin note: substantial text overlap with
arXiv:gr-qc/0111110 | Grav.Cosmol.13:1-15,2007 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The gravitational field exterior respectively interior to a spherically
symmetric, isolated body made of perfect fluid is examined within the
quasi-metric framework (QMF). It is required that the gravitational field is
"metrically static", meaning that it is static except for the effects of the
global cosmic expansion on the spatial geometry. Dynamical equations for the
gravitational field are set up and an exact solution is found for the exterior
part. Besides, equations of motion applying to inertial test particles moving
in the exterior gravitational field are set up. By construction, the
gravitational field of the system is not static with respect to the cosmic
expansion. This means that the radius of the source increases and that
distances between circular orbits of inertial test particles increase according
to the Hubble law. Moreover, it is shown that if this model of an expanding
gravitational field is taken to represent the gravitational field of the Sun
(or isolated planetary systems), this has no serious consequences for
observational aspects of planetary motion. On the contrary some observational
facts of the Earth-Moon system are naturally explained within the QMF. Finally,
the QMF predicts different secular increases for two different gravitational
coupling parameters. But such secular changes are neither present in the
Newtonian limit of the quasi-metric equations of motion nor in the Newtonian
limit of the quasi-metric field equations valid inside metrically static
sources. Thus standard interpretations of space experiments testing the secular
variation of G are explicitly theory-dependent and do not apply to the QMF.
| [
{
"created": "Thu, 31 Jan 2002 16:59:13 GMT",
"version": "v1"
},
{
"created": "Fri, 3 Feb 2023 15:01:35 GMT",
"version": "v10"
},
{
"created": "Wed, 20 Mar 2024 15:28:38 GMT",
"version": "v11"
},
{
"created": "Sat, 4 May 2002 17:29:54 GMT",
"version": "v2"
},
{
"created": "Thu, 3 Apr 2003 21:25:43 GMT",
"version": "v3"
},
{
"created": "Wed, 19 Oct 2005 17:26:07 GMT",
"version": "v4"
},
{
"created": "Sat, 10 Feb 2007 12:50:32 GMT",
"version": "v5"
},
{
"created": "Fri, 9 May 2014 05:07:06 GMT",
"version": "v6"
},
{
"created": "Wed, 28 Nov 2018 16:05:19 GMT",
"version": "v7"
},
{
"created": "Mon, 17 Feb 2020 15:06:47 GMT",
"version": "v8"
},
{
"created": "Tue, 22 Dec 2020 11:52:13 GMT",
"version": "v9"
}
] | 2024-03-21 | [
[
"Østvang",
"Dag",
""
]
] | The gravitational field exterior respectively interior to a spherically symmetric, isolated body made of perfect fluid is examined within the quasi-metric framework (QMF). It is required that the gravitational field is "metrically static", meaning that it is static except for the effects of the global cosmic expansion on the spatial geometry. Dynamical equations for the gravitational field are set up and an exact solution is found for the exterior part. Besides, equations of motion applying to inertial test particles moving in the exterior gravitational field are set up. By construction, the gravitational field of the system is not static with respect to the cosmic expansion. This means that the radius of the source increases and that distances between circular orbits of inertial test particles increase according to the Hubble law. Moreover, it is shown that if this model of an expanding gravitational field is taken to represent the gravitational field of the Sun (or isolated planetary systems), this has no serious consequences for observational aspects of planetary motion. On the contrary some observational facts of the Earth-Moon system are naturally explained within the QMF. Finally, the QMF predicts different secular increases for two different gravitational coupling parameters. But such secular changes are neither present in the Newtonian limit of the quasi-metric equations of motion nor in the Newtonian limit of the quasi-metric field equations valid inside metrically static sources. Thus standard interpretations of space experiments testing the secular variation of G are explicitly theory-dependent and do not apply to the QMF. |
1007.2790 | John F. Donoghue | Thibault Damour and John F. Donoghue | Phenomenology of the Equivalence Principle with Light Scalars | 5 pages | Class.Quant.Grav.27:202001,2010 | 10.1088/0264-9381/27/20/202001 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Light scalar particles with couplings of sub-gravitational strength, which
can generically be called 'dilatons', can produce violations of the equivalence
principle. However, in order to understand experimental sensitivities one must
know the coupling of these scalars to atomic systems. We report here on a study
of the required couplings. We give a general Lagrangian with five independent
dilaton parameters and calculate the "dilaton charge" of atomic systems for
each of these. Two combinations are particularly important. One is due to the
variations in the nuclear binding energy, with a sensitivity scaling with the
atomic number as $A^{-1/3}$. The other is due to electromagnetism. We compare
limits on the dilaton parameters from existing experiments.
| [
{
"created": "Fri, 16 Jul 2010 15:11:17 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Jul 2010 00:12:33 GMT",
"version": "v2"
}
] | 2011-03-28 | [
[
"Damour",
"Thibault",
""
],
[
"Donoghue",
"John F.",
""
]
] | Light scalar particles with couplings of sub-gravitational strength, which can generically be called 'dilatons', can produce violations of the equivalence principle. However, in order to understand experimental sensitivities one must know the coupling of these scalars to atomic systems. We report here on a study of the required couplings. We give a general Lagrangian with five independent dilaton parameters and calculate the "dilaton charge" of atomic systems for each of these. Two combinations are particularly important. One is due to the variations in the nuclear binding energy, with a sensitivity scaling with the atomic number as $A^{-1/3}$. The other is due to electromagnetism. We compare limits on the dilaton parameters from existing experiments. |
1212.2204 | Martin Bojowald | Stephon Alexander, Martin Bojowald, Antonino Marciano, David Simpson | Electric Time in Quantum Cosmology | 19 pages, 5 figures | Class. Quantum Grav. 30 (2013) 155024 | 10.1088/0264-9381/30/15/155024 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Effective quantum cosmology is formulated with a realistic global internal
time given by the electric vector potential. New possibilities for the quantum
behavior of space-time are found, and the high-density regime is shown to be
very sensitive to the specific form of state realized.
| [
{
"created": "Mon, 10 Dec 2012 20:59:45 GMT",
"version": "v1"
}
] | 2015-06-12 | [
[
"Alexander",
"Stephon",
""
],
[
"Bojowald",
"Martin",
""
],
[
"Marciano",
"Antonino",
""
],
[
"Simpson",
"David",
""
]
] | Effective quantum cosmology is formulated with a realistic global internal time given by the electric vector potential. New possibilities for the quantum behavior of space-time are found, and the high-density regime is shown to be very sensitive to the specific form of state realized. |
1402.6613 | Brajesh Gupt | Peter Diener, Brajesh Gupt, Parampreet Singh | Numerical simulations of a loop quantum cosmos: robustness of the
quantum bounce and the validity of effective dynamics | 47 pages, 26 figures; References updated. Minor changes to match the
version published in CQG | Class. Quantum Grav. 31 105015 (2014) | 10.1088/0264-9381/31/10/105015 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A key result of isotropic loop quantum cosmology is the existence of a
quantum bounce which occurs when the energy density of the matter field
approaches a universal maximum close to the Planck density. Though the bounce
has been exhibited in various matter models, due to severe computational
challenges some important questions have so far remained unaddressed. These
include the demonstration of the bounce for widely spread states, its detailed
properties for the states when matter field probes regions close to the Planck
volume and the reliability of the continuum effective spacetime description in
general. In this manuscript we rigorously answer these questions using the
Chimera numerical scheme for the isotropic spatially flat model sourced with a
massless scalar field. We show that as expected from an exactly solvable model,
the quantum bounce is a generic feature of states even with a very wide spread,
and for those which bounce much closer to the Planck volume. We perform a
detailed analysis of the departures from the effective description and find
some expected, and some surprising results. At a coarse level of description,
the effective dynamics can be regarded as a good approximation to the
underlying quantum dynamics unless the states correspond to small scalar field
momenta, in which case they bounce closer to the Planck volume, or are very
widely spread. Quantifying the amount of discrepancy between the quantum and
the effective dynamics, we find that the departure between them depends in a
subtle and non-monotonic way on the field momentum and different fluctuations.
Interestingly, the departures are generically found to be such that the
effective dynamics overestimates the spacetime curvature, and underestimates
the volume at the bounce.
| [
{
"created": "Wed, 26 Feb 2014 17:07:10 GMT",
"version": "v1"
},
{
"created": "Fri, 16 May 2014 16:41:36 GMT",
"version": "v2"
}
] | 2015-06-18 | [
[
"Diener",
"Peter",
""
],
[
"Gupt",
"Brajesh",
""
],
[
"Singh",
"Parampreet",
""
]
] | A key result of isotropic loop quantum cosmology is the existence of a quantum bounce which occurs when the energy density of the matter field approaches a universal maximum close to the Planck density. Though the bounce has been exhibited in various matter models, due to severe computational challenges some important questions have so far remained unaddressed. These include the demonstration of the bounce for widely spread states, its detailed properties for the states when matter field probes regions close to the Planck volume and the reliability of the continuum effective spacetime description in general. In this manuscript we rigorously answer these questions using the Chimera numerical scheme for the isotropic spatially flat model sourced with a massless scalar field. We show that as expected from an exactly solvable model, the quantum bounce is a generic feature of states even with a very wide spread, and for those which bounce much closer to the Planck volume. We perform a detailed analysis of the departures from the effective description and find some expected, and some surprising results. At a coarse level of description, the effective dynamics can be regarded as a good approximation to the underlying quantum dynamics unless the states correspond to small scalar field momenta, in which case they bounce closer to the Planck volume, or are very widely spread. Quantifying the amount of discrepancy between the quantum and the effective dynamics, we find that the departure between them depends in a subtle and non-monotonic way on the field momentum and different fluctuations. Interestingly, the departures are generically found to be such that the effective dynamics overestimates the spacetime curvature, and underestimates the volume at the bounce. |
gr-qc/0401107 | Miguel Lorente | P. Kramer, M. Lorente | Surface embedding, topology and dualization for spin networks | LaTeX 17 pages, 6 eps figures (late submission to arxiv.org) | J.Phys.A35:8563-8574,2002 | 10.1088/0305-4470/35/40/314 | null | gr-qc | null | Spin networks are graphs derived from 3nj symbols of angular momentum. The
surface embedding, the topology and dualization of these networks are
considered. Embeddings into compact surfaces include the orientable sphere S^2
and the torus T, and the not orientable projective space P^2 and Klein's bottle
K. Two families of 3nj graphs admit embeddings of minimal genus into S^2 and
P^2. Their dual 2-skeletons are shown to be triangulations of these surfaces.
| [
{
"created": "Tue, 27 Jan 2004 18:11:58 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Kramer",
"P.",
""
],
[
"Lorente",
"M.",
""
]
] | Spin networks are graphs derived from 3nj symbols of angular momentum. The surface embedding, the topology and dualization of these networks are considered. Embeddings into compact surfaces include the orientable sphere S^2 and the torus T, and the not orientable projective space P^2 and Klein's bottle K. Two families of 3nj graphs admit embeddings of minimal genus into S^2 and P^2. Their dual 2-skeletons are shown to be triangulations of these surfaces. |
gr-qc/0505050 | Badiali Jean Pierre | J.P. Badiali | Entropy: From Black Holes to Ordinary Systems | null | J.Phys. A39 (2006) 7175-7186 | 10.1088/0305-4470/39/23/001 | null | gr-qc | null | Several results of black holes thermodynamics can be considered as firmly
founded and formulated in a very general manner. From this starting point we
analyse in which way these results may give us the opportunity to gain a better
understanding in the thermodynamics of ordinary systems for which a
pre-relativistic description is sufficient. First, we investigated the
possibility to introduce an alternative definition of the entropy basically
related to a local definition of the order in a spacetime model rather than a
counting of microstates. We show that such an alternative approach exists and
leads to the traditional results provided an equilibrium condition is assumed.
This condition introduces a relation between a time interval and the reverse of
the temperature. We show that such a relation extensively used in the black
hole theory, mainly as a mathematical trick, has a very general and physical
meaning here; in particular its derivation is not related to the existence of a
canonical density matrix. Our dynamical approach of thermodynamic equilibrium
allows us to establish a relation between action and entropy and we show that
an identical relation exists in the case of black holes. The derivation of such
a relation seems impossible in the Gibbs ensemble approach of statistical
thermodynamics. From these results we suggest that the definition of entropy in
terms of order in spacetime should be more general that the Boltzmann one based
on a counting of microstates. Finally we point out that these results are
obtained by reversing the traditional route going from the Schr\"{o}dinger
equation to statistical thermodynamics.
| [
{
"created": "Wed, 11 May 2005 15:56:58 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Badiali",
"J. P.",
""
]
] | Several results of black holes thermodynamics can be considered as firmly founded and formulated in a very general manner. From this starting point we analyse in which way these results may give us the opportunity to gain a better understanding in the thermodynamics of ordinary systems for which a pre-relativistic description is sufficient. First, we investigated the possibility to introduce an alternative definition of the entropy basically related to a local definition of the order in a spacetime model rather than a counting of microstates. We show that such an alternative approach exists and leads to the traditional results provided an equilibrium condition is assumed. This condition introduces a relation between a time interval and the reverse of the temperature. We show that such a relation extensively used in the black hole theory, mainly as a mathematical trick, has a very general and physical meaning here; in particular its derivation is not related to the existence of a canonical density matrix. Our dynamical approach of thermodynamic equilibrium allows us to establish a relation between action and entropy and we show that an identical relation exists in the case of black holes. The derivation of such a relation seems impossible in the Gibbs ensemble approach of statistical thermodynamics. From these results we suggest that the definition of entropy in terms of order in spacetime should be more general that the Boltzmann one based on a counting of microstates. Finally we point out that these results are obtained by reversing the traditional route going from the Schr\"{o}dinger equation to statistical thermodynamics. |
1603.00637 | Yi Xie | Shan-Shan Zhao and Yi Xie | Strong field gravitational lensing by a charged Galileon black hole | null | JCAP07(2016)007 | 10.1088/1475-7516/2016/07/007 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Strong field gravitational lensings are dramatically disparate from those in
the weak field by representing relativistic images due to light winds one to
infinity loops around a lens before escaping. We study such a lensing caused by
a charged Galileon black hole, which is expected to have possibility to evade
no-hair theorem. We calculate the angular separations and time delays between
different relativistic images of the charged Galileon black hole. All these
observables can potentially be used to discriminate a charged Galileon black
hole from others. We estimate the magnitudes of these observables for the
closest supermassive black hole Sgr A*. The strong field lensing observables of
the charged Galileon black hole can be close to those of a tidal
Reissner-Nordstr\"{o}m black hole or those of a Reissner-Nordstr\"{o}m black
hole. It will be helpful to distinguish these black holes if we can separate
the outermost relativistic images and determine their angular separation,
brightness difference and time delay, although it requires techniques beyond
the current limit.
| [
{
"created": "Wed, 2 Mar 2016 09:54:52 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Jun 2016 14:01:17 GMT",
"version": "v2"
}
] | 2016-07-11 | [
[
"Zhao",
"Shan-Shan",
""
],
[
"Xie",
"Yi",
""
]
] | Strong field gravitational lensings are dramatically disparate from those in the weak field by representing relativistic images due to light winds one to infinity loops around a lens before escaping. We study such a lensing caused by a charged Galileon black hole, which is expected to have possibility to evade no-hair theorem. We calculate the angular separations and time delays between different relativistic images of the charged Galileon black hole. All these observables can potentially be used to discriminate a charged Galileon black hole from others. We estimate the magnitudes of these observables for the closest supermassive black hole Sgr A*. The strong field lensing observables of the charged Galileon black hole can be close to those of a tidal Reissner-Nordstr\"{o}m black hole or those of a Reissner-Nordstr\"{o}m black hole. It will be helpful to distinguish these black holes if we can separate the outermost relativistic images and determine their angular separation, brightness difference and time delay, although it requires techniques beyond the current limit. |
2012.09888 | Ammar Kasem | Ammar Kasem and Shaaban Khalil | Quantum Cosmology with vector torsion | null | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We extend the treatment of quantum cosmology to a manifold with torsion. We
adopt a model of Einstein-Cartan-Sciama-Kibble compatible with the cosmological
principle. The universe wavefunction will be subject to a
$\mathcal{PT}$-symmetric Hamiltonian. With a vanishing energy-momentum tensor,
the universe evolution in the semiclassical and classical regimes is shown to
reflect a two-stage inflationary process induced by torsion.
| [
{
"created": "Thu, 17 Dec 2020 19:12:31 GMT",
"version": "v1"
}
] | 2020-12-22 | [
[
"Kasem",
"Ammar",
""
],
[
"Khalil",
"Shaaban",
""
]
] | We extend the treatment of quantum cosmology to a manifold with torsion. We adopt a model of Einstein-Cartan-Sciama-Kibble compatible with the cosmological principle. The universe wavefunction will be subject to a $\mathcal{PT}$-symmetric Hamiltonian. With a vanishing energy-momentum tensor, the universe evolution in the semiclassical and classical regimes is shown to reflect a two-stage inflationary process induced by torsion. |
2406.08501 | \'Alvaro Mozota Frauca | \'Alvaro Mozota Frauca | Foundational Issues in Group Field Theory | null | Found Phys 54, 33 (2024) | 10.1007/s10701-024-00763-9 | null | gr-qc physics.hist-ph | http://creativecommons.org/licenses/by/4.0/ | In this paper I offer an introduction to group field theory (GFT) and to some
of the issues affecting the foundations of this approach to quantum gravity. I
first introduce covariant GFT as the theory that one obtains by interpreting
the amplitudes of certain spin foam models as Feynman amplitudes in a
perturbative expansion. However, I argue that it is unclear that this
definition of GFTs amounts to something beyond a computational rule for finding
these transition amplitudes and that GFT doesn't seem able to offer any new
insight into the foundations of quantum gravity. Then, I move to another
formulation of GFT which I call canonical GFT and which uses the standard
structures of quantum mechanics. This formulation is of extended use in
cosmological applications of GFT, but I argue that it is only heuristically
connected with the covariant version and spin foam models. Moreover, I argue
that this approach is affected by a version of the problem of time which raises
worries about its viability. Therefore, I conclude that there are serious
concerns about the justification and interpretation of GFT in either version of
it.
| [
{
"created": "Wed, 22 May 2024 08:10:55 GMT",
"version": "v1"
}
] | 2024-06-14 | [
[
"Frauca",
"Álvaro Mozota",
""
]
] | In this paper I offer an introduction to group field theory (GFT) and to some of the issues affecting the foundations of this approach to quantum gravity. I first introduce covariant GFT as the theory that one obtains by interpreting the amplitudes of certain spin foam models as Feynman amplitudes in a perturbative expansion. However, I argue that it is unclear that this definition of GFTs amounts to something beyond a computational rule for finding these transition amplitudes and that GFT doesn't seem able to offer any new insight into the foundations of quantum gravity. Then, I move to another formulation of GFT which I call canonical GFT and which uses the standard structures of quantum mechanics. This formulation is of extended use in cosmological applications of GFT, but I argue that it is only heuristically connected with the covariant version and spin foam models. Moreover, I argue that this approach is affected by a version of the problem of time which raises worries about its viability. Therefore, I conclude that there are serious concerns about the justification and interpretation of GFT in either version of it. |
gr-qc/0212087 | Gilad Gour | Gilad Gour | Extensive Entropy Bounds | 8 pages, revtex, To appear in Phys. Rev. D | Phys.Rev. D67 (2003) 127501 | 10.1103/PhysRevD.67.127501 | null | gr-qc cond-mat.stat-mech hep-th quant-ph | null | It is shown that, for systems in which the entropy is an extensive function
of the energy and volume, the Bekenstein and the holographic entropy bounds
predict new results. More explicitly, the Bekenstein entropy bound leads to the
entropy of thermal radiation (the Unruh-Wald bound) and the spherical entropy
bound implies the "causal entropy bound". Surprisingly, the first bound shows a
close relationship between black hole physics and the Stephan-Boltzmann law
(for the energy and entropy flux densities of the radiation emitted by a hot
blackbody). Furthermore, we find that the number of different species of
massless fields is bounded by $\sim 10^{4}$.
| [
{
"created": "Fri, 20 Dec 2002 20:47:30 GMT",
"version": "v1"
},
{
"created": "Mon, 28 Apr 2003 21:03:29 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Gour",
"Gilad",
""
]
] | It is shown that, for systems in which the entropy is an extensive function of the energy and volume, the Bekenstein and the holographic entropy bounds predict new results. More explicitly, the Bekenstein entropy bound leads to the entropy of thermal radiation (the Unruh-Wald bound) and the spherical entropy bound implies the "causal entropy bound". Surprisingly, the first bound shows a close relationship between black hole physics and the Stephan-Boltzmann law (for the energy and entropy flux densities of the radiation emitted by a hot blackbody). Furthermore, we find that the number of different species of massless fields is bounded by $\sim 10^{4}$. |
gr-qc/0307084 | Cosimo Stornaiolo | V.I. Manko, G. Marmo, C. Stornaiolo | Radon transform of Wheeler-De Witt equation and tomography of quantum
states of the universe | 22 pages LaTeX, some minor corrections, new references added,
submitted to General Relativity and Gravitation | Gen.Rel.Grav. 37 (2005) 99-114 | 10.1007/s10714-005-0005-3 | null | gr-qc | null | The notion of standard positive probability distribution function (tomogram)
which describes the quantum state of universe alternatively to wave function or
to density matrix is introduced. Connection of the tomographic probability
distribution with the Wigner function of the universe and with the star-product
(deformation) quantization procedure is established.
Using the Radon transform the Wheeler-De Witt generic equation for the
probability function is written in tomographic form. Some examples of the
Wheeler-DeWitt equation in the minisuperspace are elaborated explicitly for a
homogeneous isotropic cosmological models. Some interpretational aspects of the
probability description of the quantum state are discussed.
| [
{
"created": "Thu, 17 Jul 2003 15:46:03 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Apr 2004 09:57:01 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Manko",
"V. I.",
""
],
[
"Marmo",
"G.",
""
],
[
"Stornaiolo",
"C.",
""
]
] | The notion of standard positive probability distribution function (tomogram) which describes the quantum state of universe alternatively to wave function or to density matrix is introduced. Connection of the tomographic probability distribution with the Wigner function of the universe and with the star-product (deformation) quantization procedure is established. Using the Radon transform the Wheeler-De Witt generic equation for the probability function is written in tomographic form. Some examples of the Wheeler-DeWitt equation in the minisuperspace are elaborated explicitly for a homogeneous isotropic cosmological models. Some interpretational aspects of the probability description of the quantum state are discussed. |
2405.19282 | Edward Kurianovich | E. A. Kurianovich, A.I. Mikhailov, I. V. Volovich | On the theory of relativistic Brownian motion | null | p-Adic Numbers, Ultrametric Analysis and Applications 16 (2024) 2 | null | null | gr-qc math.PR | http://creativecommons.org/licenses/by/4.0/ | The approach to the theory of a relativistic random process is considered by
the path integral method as Brownian motion taking into account the boundedness
of speed. An attempt was made to build a relativistic analogue of the Wiener
measure as a weak limit of finite-difference approximations. A formula has been
proposed for calculating the probability particle transition during
relativistic Brownian motion. Calculations were carried out by three different
methods with identical results. Along the way, exact and asymptotic formulas
for the volume of some parts and sections of an N-1-dimensional unit cube were
obtained. They can have independent value.
| [
{
"created": "Wed, 29 May 2024 17:14:34 GMT",
"version": "v1"
}
] | 2024-05-30 | [
[
"Kurianovich",
"E. A.",
""
],
[
"Mikhailov",
"A. I.",
""
],
[
"Volovich",
"I. V.",
""
]
] | The approach to the theory of a relativistic random process is considered by the path integral method as Brownian motion taking into account the boundedness of speed. An attempt was made to build a relativistic analogue of the Wiener measure as a weak limit of finite-difference approximations. A formula has been proposed for calculating the probability particle transition during relativistic Brownian motion. Calculations were carried out by three different methods with identical results. Along the way, exact and asymptotic formulas for the volume of some parts and sections of an N-1-dimensional unit cube were obtained. They can have independent value. |
2206.12671 | Carlos A. S. Almeida | F. C. E. Lima, A. R. P. Moreira, and C. A. S. Almeida | Properties of black hole vortex in Einstein's gravity | 22 pages, 7 captioned figures. Enhanced version to appear in European
Physical Journal Plus | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We investigate the influence of the matter field and the gauge field on the
metric functions of the AdS$_3$ spacetime of the Maxwell-Higgs model. By
considering a matter field with a solitonic profile with the ability to adjust
the field variable from kink to compact-like configurations, the appearance of
black hole solutions is noticed for an event horizon at $r_{+} \approx 1.5$. An
interesting result is displayed when analyzing the influence of matter field
compactification on the metric functions. As we obtain compact-like field
configurations the metric functions tend to a ``linearized behavior''. However,
the compactification of the field does not change the structure of the horizon
of the magnetic black hole vortex. With the ADM formalism, the mass of the
black hole vortex is calculated, and its numerical results are presented. By
analyzing the so-called ADM mass, it is observed that the mass of the black
hole vortex increases as the cosmological constant becomes more negative, and
this coincides with the vortex core becoming smaller. Nonetheless, this mass
tends to decrease as the solitonic profile of the matter field becomes more
compacted. Then, the black hole temperature study is performed using the
tunneling formalism. In this case, it is perceived that the cosmological
constant, and the $\alpha$-parameter, will influence the Bekenstein-Hawking
temperature. In other words, the temperature of the structure increases as
these parameters increase.
| [
{
"created": "Sat, 25 Jun 2022 15:27:31 GMT",
"version": "v1"
},
{
"created": "Sun, 30 Apr 2023 18:39:01 GMT",
"version": "v2"
}
] | 2023-05-02 | [
[
"Lima",
"F. C. E.",
""
],
[
"Moreira",
"A. R. P.",
""
],
[
"Almeida",
"C. A. S.",
""
]
] | We investigate the influence of the matter field and the gauge field on the metric functions of the AdS$_3$ spacetime of the Maxwell-Higgs model. By considering a matter field with a solitonic profile with the ability to adjust the field variable from kink to compact-like configurations, the appearance of black hole solutions is noticed for an event horizon at $r_{+} \approx 1.5$. An interesting result is displayed when analyzing the influence of matter field compactification on the metric functions. As we obtain compact-like field configurations the metric functions tend to a ``linearized behavior''. However, the compactification of the field does not change the structure of the horizon of the magnetic black hole vortex. With the ADM formalism, the mass of the black hole vortex is calculated, and its numerical results are presented. By analyzing the so-called ADM mass, it is observed that the mass of the black hole vortex increases as the cosmological constant becomes more negative, and this coincides with the vortex core becoming smaller. Nonetheless, this mass tends to decrease as the solitonic profile of the matter field becomes more compacted. Then, the black hole temperature study is performed using the tunneling formalism. In this case, it is perceived that the cosmological constant, and the $\alpha$-parameter, will influence the Bekenstein-Hawking temperature. In other words, the temperature of the structure increases as these parameters increase. |
2004.00336 | Carlos A. R. Herdeiro | Carlos A. R. Herdeiro and Eugen Radu | Spherical electro-vacuum black holes with resonant, scalar $Q$-hair | 18 pages, 5 figures; v2. typos corrected, matches published version | null | 10.1140/epjc/s10052-020-7976-9 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The asymptotically flat, spherical, electro-vacuum black holes (BHs) are
shown to support static, spherical configurations of a gauged,
self-interacting, scalar field, minimally coupled to the geometry. Considering
a $Q$-ball type potential for the scalar field, we dub these configurations
$Q$-clouds, in the test field approximation. The clouds exist under a resonance
condition, at the threshold of (charged) superradiance. This is similar to the
stationary clouds supported by Kerr BHs, which exist for a synchronisation
condition, at the threshold of (rotational) superradiance. In contrast with the
rotating case, however, $Q$-clouds require the scalar field to be massive and
self-interacting; no similar clouds exist for massive but free scalar fields.
First, considering a decoupling limit, we construct $Q$-clouds around
Schwarzschild and Reissner-Nordstr\"om BHs, showing there is always a mass gap.
Then, we make the $Q$-clouds backreact, and construct fully non-linear
solutions of the Einstein-Maxwell-gauged scalar system describing spherical,
charged BHs with resonant, scalar $Q$-hair. Amongst other properties, we
observe there is non-uniqueness of charged BHs in this model and the $Q$-hairy
BHs can be entropically preferred over Reissner-Nordstr\"om, for the same
charge to mass ratio; some $Q$-hairy BH solutions can be overcharged. We also
discuss how some well known no-hair theorems in the literature, applying to
electro-vacuum plus minimally coupled scalar fields, are circumvented by this
new type of BHs.
| [
{
"created": "Wed, 1 Apr 2020 10:56:04 GMT",
"version": "v1"
},
{
"created": "Mon, 11 May 2020 13:42:28 GMT",
"version": "v2"
}
] | 2020-06-24 | [
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Radu",
"Eugen",
""
]
] | The asymptotically flat, spherical, electro-vacuum black holes (BHs) are shown to support static, spherical configurations of a gauged, self-interacting, scalar field, minimally coupled to the geometry. Considering a $Q$-ball type potential for the scalar field, we dub these configurations $Q$-clouds, in the test field approximation. The clouds exist under a resonance condition, at the threshold of (charged) superradiance. This is similar to the stationary clouds supported by Kerr BHs, which exist for a synchronisation condition, at the threshold of (rotational) superradiance. In contrast with the rotating case, however, $Q$-clouds require the scalar field to be massive and self-interacting; no similar clouds exist for massive but free scalar fields. First, considering a decoupling limit, we construct $Q$-clouds around Schwarzschild and Reissner-Nordstr\"om BHs, showing there is always a mass gap. Then, we make the $Q$-clouds backreact, and construct fully non-linear solutions of the Einstein-Maxwell-gauged scalar system describing spherical, charged BHs with resonant, scalar $Q$-hair. Amongst other properties, we observe there is non-uniqueness of charged BHs in this model and the $Q$-hairy BHs can be entropically preferred over Reissner-Nordstr\"om, for the same charge to mass ratio; some $Q$-hairy BH solutions can be overcharged. We also discuss how some well known no-hair theorems in the literature, applying to electro-vacuum plus minimally coupled scalar fields, are circumvented by this new type of BHs. |
1003.1680 | Sergei Winitzki | Sergei Winitzki | Observability of the total inflationary expansion | 11 pages, RevTeX, no figures | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I consider the question of possible observability of the total number of
e-folds accumulated during the epoch of inflation. The total number of
observable e-folds has been previously constrained by the de Sitter entropy
after inflation, assuming that the null energy condition (NEC) holds. The NEC
is violated by upward fluctuations of the local Hubble rate, which occur with
high probability in the fluctuation-dominated regime of inflation. These
fluctuations lead at late times to the formation of black holes and thus limit
the observability of inflationary evolution. I compute the maximum number
<Delta N> of e-folds that can be observed in principle through measurements of
the CMB at arbitrarily late times (if the dark energy disappears). The
calculation also provides a reasonably precise definition of the boundary of
the fluctuation-dominated regime, with an uncertainty of a few percent. In
simple models of single-field inflation compatible with current CMB
observations, I find <Delta N> of order 10^5. This upper bound on the
observable e-folds, although model-dependent, is much smaller than the de
Sitter entropy after inflation. The method of calculation can be used in other
models of single-field inflation.
| [
{
"created": "Mon, 8 Mar 2010 17:16:42 GMT",
"version": "v1"
}
] | 2010-03-09 | [
[
"Winitzki",
"Sergei",
""
]
] | I consider the question of possible observability of the total number of e-folds accumulated during the epoch of inflation. The total number of observable e-folds has been previously constrained by the de Sitter entropy after inflation, assuming that the null energy condition (NEC) holds. The NEC is violated by upward fluctuations of the local Hubble rate, which occur with high probability in the fluctuation-dominated regime of inflation. These fluctuations lead at late times to the formation of black holes and thus limit the observability of inflationary evolution. I compute the maximum number <Delta N> of e-folds that can be observed in principle through measurements of the CMB at arbitrarily late times (if the dark energy disappears). The calculation also provides a reasonably precise definition of the boundary of the fluctuation-dominated regime, with an uncertainty of a few percent. In simple models of single-field inflation compatible with current CMB observations, I find <Delta N> of order 10^5. This upper bound on the observable e-folds, although model-dependent, is much smaller than the de Sitter entropy after inflation. The method of calculation can be used in other models of single-field inflation. |
gr-qc/9912007 | Mamdouh Wanas | M.I. Wanas and M.E. Kahil | Quantum Features of Non-Symmetric Geometries | Eight pages Latex file, published in GRG, vol.31, 1921, (1999) | Gen.Rel.Grav. 31 (1999) 1921 | 10.1023/A:1026743007086 | null | gr-qc | null | Paths in an appropriate geometry are usually used as trajectories of test
particles in geometric theories of gravity. It is shown that non-symmetric
geometries possess some interesting quantum features. Without carrying out any
quantization schemes, paths in such geometries are naturally quantized. Two
different non-symmetric geometries are examined for these features. It is
proved that, whatever the non-symmetric geometry is, we always get the same
quantum features. It is shown that these features appear only in the pure
torsion term (the anti-symmetric part of the affine connection) of the path
equations. The vanishing of the torsion leads to the disappearance of these
features, regardless of the symmetric part of the connection. It is suggested
that, in order to be consistent with the results of experiments and
observations, torsion term in path equations should be parametrized using an
appropriate parameter.
| [
{
"created": "Thu, 2 Dec 1999 12:57:12 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Wanas",
"M. I.",
""
],
[
"Kahil",
"M. E.",
""
]
] | Paths in an appropriate geometry are usually used as trajectories of test particles in geometric theories of gravity. It is shown that non-symmetric geometries possess some interesting quantum features. Without carrying out any quantization schemes, paths in such geometries are naturally quantized. Two different non-symmetric geometries are examined for these features. It is proved that, whatever the non-symmetric geometry is, we always get the same quantum features. It is shown that these features appear only in the pure torsion term (the anti-symmetric part of the affine connection) of the path equations. The vanishing of the torsion leads to the disappearance of these features, regardless of the symmetric part of the connection. It is suggested that, in order to be consistent with the results of experiments and observations, torsion term in path equations should be parametrized using an appropriate parameter. |
1704.02747 | Ken-Ichi Nakao | Yumi Akai and Ken-ichi Nakao | Non-linear stability of a brane wormhole | 32 pages, 10 figure. arXiv admin note: substantial text overlap with
arXiv:1306.6917 | Phys. Rev. D 96, 024033 (2017) | 10.1103/PhysRevD.96.024033 | OCU-PHYS-461, AP-GR-136 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analytically study the non-linear stability of a spherically symmetric
wormhole supported by an infinitesimally thin brane of negative tension, which
has been devised by Barcelo and Visser. We consider a situation in which a thin
spherical shell composed of dust falls into an initially static wormhole; The
dust shell plays a role of the non-linear disturbance. The self-gravity of the
falling dust shell is completely taken into account through Israel's formalism
of the metric junction. When the dust shell goes through the wormhole, it
necessarily collides with the brane supporting the wormhole. We assume the
interaction between these shells is only gravity and show the condition under
which the wormhole stably persists after the dust shell goes through it.
| [
{
"created": "Mon, 10 Apr 2017 08:06:55 GMT",
"version": "v1"
},
{
"created": "Thu, 27 Apr 2017 07:56:14 GMT",
"version": "v2"
}
] | 2017-07-26 | [
[
"Akai",
"Yumi",
""
],
[
"Nakao",
"Ken-ichi",
""
]
] | We analytically study the non-linear stability of a spherically symmetric wormhole supported by an infinitesimally thin brane of negative tension, which has been devised by Barcelo and Visser. We consider a situation in which a thin spherical shell composed of dust falls into an initially static wormhole; The dust shell plays a role of the non-linear disturbance. The self-gravity of the falling dust shell is completely taken into account through Israel's formalism of the metric junction. When the dust shell goes through the wormhole, it necessarily collides with the brane supporting the wormhole. We assume the interaction between these shells is only gravity and show the condition under which the wormhole stably persists after the dust shell goes through it. |
2210.09823 | Jean-David Pailleron | Jean-David Pailleron | A class of solutions to the conformal constraint equations on compact
manifolds with apparent horizon boundary conditions | 42 pages | null | null | null | gr-qc math.AP math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This article is dedicated to solving the Einstein constraint equations with
apparent horizon boundaries and freely specified mean curvature. The main
novelty is that we study the conformal constraint equations assuming only low
regularity.
| [
{
"created": "Tue, 18 Oct 2022 13:04:32 GMT",
"version": "v1"
}
] | 2022-10-19 | [
[
"Pailleron",
"Jean-David",
""
]
] | This article is dedicated to solving the Einstein constraint equations with apparent horizon boundaries and freely specified mean curvature. The main novelty is that we study the conformal constraint equations assuming only low regularity. |
2307.04873 | Francisco X. Linares Cede\~no | Francisco X. Linares Cede\~no and Ulises Nucamendi | Gauge fixing in cosmological perturbations of Unimodular Gravity | 32 pages, new text and references added. Version accepted for
publication in JCAP | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | With focus on the cosmological evolution of linear perturbations of matter
and geometry, we calculate the equivalent expressions to that of the Newtonian
and Synchronous gauges within the framework of Unimodular Gravity, being these
two gauges commonly used and implemented in Boltzmann codes. An important
aspect of our analysis is the inclusion of the energy-momentum current
violation, as well as its perturbations. Moreover, for the first time we
demonstrate that it is possible to fix both gauges consistently, although as it
has been already noticed in previous literature, neither of them is recovered
in the sense of the dynamics given in General Relativity for matter and metric
fluctuations. Specifically, we show that since the unimodular constraint at the
level of linear perturbations lead to only one degree of freedom of scalar
modes of metric fluctuations, the dynamics in Unimodular Gravity forces to keep
the anisotropic stress in the Newtonian gauge, whereas the cold dark matter
comoving frame can not be set in the Synchronous gauge. The physical
implications on the density contrast of cold dark matter is reviewed, and the
Sachs-Wolfe effect is obtained and compared with previous results in the
literature of cosmological perturbations in Unimodular Gravity.
| [
{
"created": "Mon, 10 Jul 2023 19:50:36 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Jul 2023 18:55:31 GMT",
"version": "v2"
},
{
"created": "Tue, 3 Oct 2023 16:54:36 GMT",
"version": "v3"
}
] | 2023-10-04 | [
[
"Cedeño",
"Francisco X. Linares",
""
],
[
"Nucamendi",
"Ulises",
""
]
] | With focus on the cosmological evolution of linear perturbations of matter and geometry, we calculate the equivalent expressions to that of the Newtonian and Synchronous gauges within the framework of Unimodular Gravity, being these two gauges commonly used and implemented in Boltzmann codes. An important aspect of our analysis is the inclusion of the energy-momentum current violation, as well as its perturbations. Moreover, for the first time we demonstrate that it is possible to fix both gauges consistently, although as it has been already noticed in previous literature, neither of them is recovered in the sense of the dynamics given in General Relativity for matter and metric fluctuations. Specifically, we show that since the unimodular constraint at the level of linear perturbations lead to only one degree of freedom of scalar modes of metric fluctuations, the dynamics in Unimodular Gravity forces to keep the anisotropic stress in the Newtonian gauge, whereas the cold dark matter comoving frame can not be set in the Synchronous gauge. The physical implications on the density contrast of cold dark matter is reviewed, and the Sachs-Wolfe effect is obtained and compared with previous results in the literature of cosmological perturbations in Unimodular Gravity. |
2312.00706 | Vojtech Pravda | Marcello Ortaggio, Vojtech Pravda, Alena Pravdova | Kerr-Schild double copy for Kundt spacetimes of any dimension | 26 pages, minor changes, new references added, matches version to
appear in JHEP | J. High Energy Phys. 2024, 69 (2024) | 10.1007/JHEP02(2024)069 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that vacuum type N Kundt spacetimes in an arbitrary dimension admit a
Kerr-Schild (KS) double copy. This is mostly done in a coordinate-independent
way using the higher-dimensional Newman-Penrose formalism. We also discuss two
kinds of non-uniqueness of an electromagnetic field corresponding to a given KS
metric (i.e., its single copy) - these originate, respectively, from the
rescaling freedom in the KS vector and from the non-uniqueness of the splitting
of the KS metric in the flat part and the KS part. In connection to this, we
show that the subset of KS pp-waves admits both null and non-null
electromagnetic single copies. Since vacuum type N Kundt spacetimes are
universal solutions of virtually any higher-order gravities and null fields in
such backgrounds are immune to higher-order electromagnetic corrections, the
KS-Kundt double copy demonstrated in the present paper also applies to large
classes of modified theories.
| [
{
"created": "Fri, 1 Dec 2023 16:42:01 GMT",
"version": "v1"
},
{
"created": "Fri, 9 Feb 2024 16:39:53 GMT",
"version": "v2"
}
] | 2024-02-15 | [
[
"Ortaggio",
"Marcello",
""
],
[
"Pravda",
"Vojtech",
""
],
[
"Pravdova",
"Alena",
""
]
] | We show that vacuum type N Kundt spacetimes in an arbitrary dimension admit a Kerr-Schild (KS) double copy. This is mostly done in a coordinate-independent way using the higher-dimensional Newman-Penrose formalism. We also discuss two kinds of non-uniqueness of an electromagnetic field corresponding to a given KS metric (i.e., its single copy) - these originate, respectively, from the rescaling freedom in the KS vector and from the non-uniqueness of the splitting of the KS metric in the flat part and the KS part. In connection to this, we show that the subset of KS pp-waves admits both null and non-null electromagnetic single copies. Since vacuum type N Kundt spacetimes are universal solutions of virtually any higher-order gravities and null fields in such backgrounds are immune to higher-order electromagnetic corrections, the KS-Kundt double copy demonstrated in the present paper also applies to large classes of modified theories. |
1604.04734 | Joao Paulo Morais Graca | J. P. Morais Gra\c{c}a, Godonou I. Salako and V. B. Bezerra | Quasinormal modes of a black hole with a cloud of strings in
Einstein-Gauss-Bonnet gravity | 15 pages, 7 figures; To appear in IJMPD | null | 10.1142/S0218271817501139 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The quasinormal modes for a scalar field in the background spacetime
corresponding to a black hole, with a cloud of strings, in
Einstein-Gauss-Bonnet gravity, and the tensor quasinormal modes corresponding
to perturbations in such spacetime, were both calculated using the WKB
approximation. In the obtained results we emphasize the role played by the
parameter associated with the string cloud, comparing them with the results
already obtained for the Boulware-Deser metric. We also study how the
Gauss-Bonnet correction to general relativity affects the results for the
quasinormal modes, comparing them with the same background in general
relativity.
| [
{
"created": "Sat, 16 Apr 2016 12:07:03 GMT",
"version": "v1"
},
{
"created": "Sun, 9 Apr 2017 23:46:56 GMT",
"version": "v2"
}
] | 2023-02-22 | [
[
"Graça",
"J. P. Morais",
""
],
[
"Salako",
"Godonou I.",
""
],
[
"Bezerra",
"V. B.",
""
]
] | The quasinormal modes for a scalar field in the background spacetime corresponding to a black hole, with a cloud of strings, in Einstein-Gauss-Bonnet gravity, and the tensor quasinormal modes corresponding to perturbations in such spacetime, were both calculated using the WKB approximation. In the obtained results we emphasize the role played by the parameter associated with the string cloud, comparing them with the results already obtained for the Boulware-Deser metric. We also study how the Gauss-Bonnet correction to general relativity affects the results for the quasinormal modes, comparing them with the same background in general relativity. |
2311.17198 | Akshay Ghalsasi | Akshay Ghalsasi | Amplifying the Chirp: Using Deep Learning (U-Nets) to filter signal from
noise in LIGO data | 20 pages, 9 figures, comments welcome | null | null | PITT-PACC-2322 | gr-qc astro-ph.CO astro-ph.IM hep-ph | http://creativecommons.org/licenses/by/4.0/ | The direct detection of gravitational waves by LIGO has heralded a new era
for astronomy and physics. Typically the gravitational waves observed by LIGO
are dominated by noise. In this work we use Deep Convolutional Neural Networks
(specifically U-Nets) to filter a clean signal from noisy data. We present two
realizations of U-Net filters, the Noise2Clean U-Net filter which is trained
using noisy and clean realizations of the same signal, as well as Noise2Noise
U-Net which is trained on two separate noisy realization of the same signal. We
find that the U-Nets successfully filter signal from noise. We also benchmark
the performance of U-Nets by using them to detect the binary presence or
absence of gravitational wave signals in data.
| [
{
"created": "Tue, 28 Nov 2023 20:04:27 GMT",
"version": "v1"
}
] | 2023-11-30 | [
[
"Ghalsasi",
"Akshay",
""
]
] | The direct detection of gravitational waves by LIGO has heralded a new era for astronomy and physics. Typically the gravitational waves observed by LIGO are dominated by noise. In this work we use Deep Convolutional Neural Networks (specifically U-Nets) to filter a clean signal from noisy data. We present two realizations of U-Net filters, the Noise2Clean U-Net filter which is trained using noisy and clean realizations of the same signal, as well as Noise2Noise U-Net which is trained on two separate noisy realization of the same signal. We find that the U-Nets successfully filter signal from noise. We also benchmark the performance of U-Nets by using them to detect the binary presence or absence of gravitational wave signals in data. |
1502.00811 | Danylo Yerokhin | Yu.L. Bolotin, V.A. Cherkaskiy, O.A. Lemets, D.A. Yerokhin and L.G.
Zazunov | Cosmology In Terms Of The Deceleration Parameter. Part I | 67 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1104.4458, arXiv:1409.3352, arXiv:0708.3414, arXiv:gr-qc/0508052,
arXiv:astro-ph/0402278, arXiv:astro-ph/0104349, arXiv:0807.0207 by other
authors | null | null | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the early seventies, Alan Sandage defined cosmology as the search for two
numbers: Hubble parameter ${{H}_{0}}$ and deceleration parameter ${{q}_{0}}$.
The first of the two basic cosmological parameters (the Hubble parameter)
describes the linear part of the time dependence of the scale factor. Treating
the Universe as a dynamical system it is natural to assume that it is
non-linear: indeed, linearity is nothing more than approximation, while
non-linearity represents the generic case. It is evident that future models of
the Universe must take into account different aspects of its evolution. As soon
as the scale factor is the only dynamical variable, the quantities which
determine its time dependence must be essentially present in all aspects of the
Universe' evolution. Basic characteristics of the cosmological evolution, both
static and dynamical, can be expressed in terms of the parameters ${{H}_{0}}$
and ${{q}_{0}}$. The very parameters (and higher time derivatives of the scale
factor) enable us to construct model-independent kinematics of the cosmological
expansion.
Time dependence of the scale factor reflects main events in history of the
Universe. Moreover it is the deceleration parameter who dictates the expansion
rate of the Hubble sphere and determines the dynamics of the observable galaxy
number variation: depending on the sign of the deceleration parameter this
number either grows (in the case of decelerated expansion), or we are going to
stay absolutely alone in the cosmos (if the expansion is accelerated).
The intended purpose of the report is reflected in its title --- "Cosmology
in terms of the deceleration parameter". We would like to show that practically
any aspect of the cosmological evolution is tightly bound to the deceleration
parameter.
| [
{
"created": "Tue, 3 Feb 2015 11:11:11 GMT",
"version": "v1"
}
] | 2015-02-04 | [
[
"Bolotin",
"Yu. L.",
""
],
[
"Cherkaskiy",
"V. A.",
""
],
[
"Lemets",
"O. A.",
""
],
[
"Yerokhin",
"D. A.",
""
],
[
"Zazunov",
"L. G.",
""
]
] | In the early seventies, Alan Sandage defined cosmology as the search for two numbers: Hubble parameter ${{H}_{0}}$ and deceleration parameter ${{q}_{0}}$. The first of the two basic cosmological parameters (the Hubble parameter) describes the linear part of the time dependence of the scale factor. Treating the Universe as a dynamical system it is natural to assume that it is non-linear: indeed, linearity is nothing more than approximation, while non-linearity represents the generic case. It is evident that future models of the Universe must take into account different aspects of its evolution. As soon as the scale factor is the only dynamical variable, the quantities which determine its time dependence must be essentially present in all aspects of the Universe' evolution. Basic characteristics of the cosmological evolution, both static and dynamical, can be expressed in terms of the parameters ${{H}_{0}}$ and ${{q}_{0}}$. The very parameters (and higher time derivatives of the scale factor) enable us to construct model-independent kinematics of the cosmological expansion. Time dependence of the scale factor reflects main events in history of the Universe. Moreover it is the deceleration parameter who dictates the expansion rate of the Hubble sphere and determines the dynamics of the observable galaxy number variation: depending on the sign of the deceleration parameter this number either grows (in the case of decelerated expansion), or we are going to stay absolutely alone in the cosmos (if the expansion is accelerated). The intended purpose of the report is reflected in its title --- "Cosmology in terms of the deceleration parameter". We would like to show that practically any aspect of the cosmological evolution is tightly bound to the deceleration parameter. |
1512.08623 | Patrick Das Gupta | Patrick Das Gupta and Eklavya Thareja | Supermassive Black Holes from self-gravitating Bose-Einstein Condensates
comprised of Ultra-light Bosonic Dark Matter | Presented the paper in ICGC 2015, IISER, Mohali, India, as well as in
GR21, July 2016, Columbia University, USA | Classical and Quantum Gravity, Volume 34, Number 3 (2017) | 10.1088/1361-6382/aa51fc | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Observed active galactic nuclei at redshifts $\gtrsim 6$ suggest that
supermassive black holes (SMBHs) had formed early on. Accretion of matter onto
remnants of Population III stars leading to SMBHs is a very slow process, and
therefore, such models encounter difficulties in explaining quasars detected at
$ z \gtrsim 6$. In this paper, we invoke collapse of dark bosonic halo matter,
existing initially in self-gravitating Bose-Einstein condensate (BEC) phase, to
lead to formation of SMBH. Making use of Gross-Pitaevskii equation and
employing a Gaussian trial wavefunction, we determine the time dependence of
its parameters and thereby, track the time evolution of the wavefunction. If
the condensate, made up of identical dark bosons of mass $m$, collapses to form
a black hole of mass $M_{eff}$ as soon as the former's effective size shrinks
below the corresponding Schwarzschild radius, a simple inequality $ m \ M_{eff}
\gtrsim 0.64 \ m^2_{Pl} $ can be derived, that ensues from a competition
between attractive self-gravity and quantum repulsion arising due to
uncertainty principle. We show that formation of SMBHs takes place on dynamical
time scales $\sim 10^8$ yrs. Existence of ultra-light ($m \sim 10^{-23} \
\mbox{eV}$) dark bosons not only can lead to SMBHs of mass $\sim 10^{12} \
M_\odot$ at $ z > 6$ but also such particles can masquerade both as dark matter
as well as dark energy. Discovery of aligned radio-jets in the ELAIS-N1 GMRT
deep field leads us to make simple estimates to demonstrate that vortices of a
rotating BEC that collapse to form black holes can give rise to SMBHs with
aligned spins on scales exceeding cluster size length scales, each with angular
momentum $J \lesssim 3.6 \ n_W \frac {G M^2} {c}$, where $n_W$ and $M$ are the
winding number and mass of a vortex, respectively.
| [
{
"created": "Tue, 29 Dec 2015 08:53:20 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Apr 2016 15:09:31 GMT",
"version": "v2"
},
{
"created": "Wed, 16 Nov 2016 06:02:20 GMT",
"version": "v3"
}
] | 2018-12-27 | [
[
"Gupta",
"Patrick Das",
""
],
[
"Thareja",
"Eklavya",
""
]
] | Observed active galactic nuclei at redshifts $\gtrsim 6$ suggest that supermassive black holes (SMBHs) had formed early on. Accretion of matter onto remnants of Population III stars leading to SMBHs is a very slow process, and therefore, such models encounter difficulties in explaining quasars detected at $ z \gtrsim 6$. In this paper, we invoke collapse of dark bosonic halo matter, existing initially in self-gravitating Bose-Einstein condensate (BEC) phase, to lead to formation of SMBH. Making use of Gross-Pitaevskii equation and employing a Gaussian trial wavefunction, we determine the time dependence of its parameters and thereby, track the time evolution of the wavefunction. If the condensate, made up of identical dark bosons of mass $m$, collapses to form a black hole of mass $M_{eff}$ as soon as the former's effective size shrinks below the corresponding Schwarzschild radius, a simple inequality $ m \ M_{eff} \gtrsim 0.64 \ m^2_{Pl} $ can be derived, that ensues from a competition between attractive self-gravity and quantum repulsion arising due to uncertainty principle. We show that formation of SMBHs takes place on dynamical time scales $\sim 10^8$ yrs. Existence of ultra-light ($m \sim 10^{-23} \ \mbox{eV}$) dark bosons not only can lead to SMBHs of mass $\sim 10^{12} \ M_\odot$ at $ z > 6$ but also such particles can masquerade both as dark matter as well as dark energy. Discovery of aligned radio-jets in the ELAIS-N1 GMRT deep field leads us to make simple estimates to demonstrate that vortices of a rotating BEC that collapse to form black holes can give rise to SMBHs with aligned spins on scales exceeding cluster size length scales, each with angular momentum $J \lesssim 3.6 \ n_W \frac {G M^2} {c}$, where $n_W$ and $M$ are the winding number and mass of a vortex, respectively. |
2103.15906 | Christian Boehmer | Christian G. Boehmer, Erik Jensko | Modified gravity: a unified approach | 34 pages, 2 figures; v2 minor changes, references added; v3 final
changes, published version | Phys. Rev. D 104, 024010 (2021) | 10.1103/PhysRevD.104.024010 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Starting from the original Einstein action, sometimes called the Gamma
squared action, we propose a new setup to formulate modified theories of
gravity. This can yield a theory with second order field equations similar to
those found in other popular modified gravity models. Using a more general
setting the theory gives fourth order equations. This model is based on the
metric alone and does not require more general geometries. It is possible to
show that our new theory and the recently proposed $f(Q)$ gravity models are
equivalent at the level of the action and at the level of the field equations,
provided that appropriate boundary terms are taken into account. Our theory can
also match up with $f(R)$ gravity which is an expected result. Perhaps more
surprisingly, we can also show that this equivalence extends to $f(T)$ gravity
at the level of the action and its field equations, provided that appropriate
boundary terms are taken in account. While these three theories are
conceptually different and are based on different geometrical settings, we can
establish the necessary conditions under which their field equations are
indistinguishable. The final part requires matter to couple minimally to
gravity. Through this work we emphasise the importance played by boundary terms
which are at the heart of our approach.
| [
{
"created": "Mon, 29 Mar 2021 19:37:06 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Apr 2021 14:54:39 GMT",
"version": "v2"
},
{
"created": "Thu, 8 Jul 2021 11:55:34 GMT",
"version": "v3"
}
] | 2021-07-14 | [
[
"Boehmer",
"Christian G.",
""
],
[
"Jensko",
"Erik",
""
]
] | Starting from the original Einstein action, sometimes called the Gamma squared action, we propose a new setup to formulate modified theories of gravity. This can yield a theory with second order field equations similar to those found in other popular modified gravity models. Using a more general setting the theory gives fourth order equations. This model is based on the metric alone and does not require more general geometries. It is possible to show that our new theory and the recently proposed $f(Q)$ gravity models are equivalent at the level of the action and at the level of the field equations, provided that appropriate boundary terms are taken into account. Our theory can also match up with $f(R)$ gravity which is an expected result. Perhaps more surprisingly, we can also show that this equivalence extends to $f(T)$ gravity at the level of the action and its field equations, provided that appropriate boundary terms are taken in account. While these three theories are conceptually different and are based on different geometrical settings, we can establish the necessary conditions under which their field equations are indistinguishable. The final part requires matter to couple minimally to gravity. Through this work we emphasise the importance played by boundary terms which are at the heart of our approach. |
1112.6381 | A Khodam-Mohammadi | Antonio Pasqua, A. Khodam-Mohammadi, Mubasher Jamil, R. Myrzakulov | Interacting Ricci Dark Energy with Logarithmic Correction | 24 pages, accepted for publication in 'Astrophysics and Space
Science, DOI:10.1007/s10509-012-1031-8' | Astrophysics and Space Science: Volume 340, 199-208, (2012) | 10.1007/s10509-012-1031-8 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Motivated by the holographic principle, it has been suggested that the dark
energy density may be inversely proportional to the area $A$ of the event
horizon of the universe. However, such a model would have a causality problem.
In this work, we consider the entropy-corrected version of the holographic dark
energy model in the non-flat FRW universe and we propose to replace the future
event horizon area with the inverse of the Ricci scalar curvature. We obtain
the equation of state (EoS) parameter $\omega_{\Lambda}$, the deceleration
parameter $q$ and $\Omega_D'$ in the presence of interaction between Dark
Energy (DE) and Dark Matter (DM). Moreover, we reconstruct the potential and
the dynamics of the tachyon, K-essence, dilaton and quintessence scalar field
models according to the evolutionary behavior of the interacting
entropy-corrected holographic dark energy model.
| [
{
"created": "Thu, 29 Dec 2011 19:05:21 GMT",
"version": "v1"
},
{
"created": "Thu, 23 Feb 2012 07:02:40 GMT",
"version": "v2"
},
{
"created": "Thu, 1 Mar 2012 09:19:49 GMT",
"version": "v3"
},
{
"created": "Sat, 3 Mar 2012 20:10:57 GMT",
"version": "v4"
}
] | 2012-06-06 | [
[
"Pasqua",
"Antonio",
""
],
[
"Khodam-Mohammadi",
"A.",
""
],
[
"Jamil",
"Mubasher",
""
],
[
"Myrzakulov",
"R.",
""
]
] | Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area $A$ of the event horizon of the universe. However, such a model would have a causality problem. In this work, we consider the entropy-corrected version of the holographic dark energy model in the non-flat FRW universe and we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We obtain the equation of state (EoS) parameter $\omega_{\Lambda}$, the deceleration parameter $q$ and $\Omega_D'$ in the presence of interaction between Dark Energy (DE) and Dark Matter (DM). Moreover, we reconstruct the potential and the dynamics of the tachyon, K-essence, dilaton and quintessence scalar field models according to the evolutionary behavior of the interacting entropy-corrected holographic dark energy model. |
2407.14954 | Erick Ivan Duque Gonzalez | Erick I. Duque | Emergent electromagnetism | 66 pages | null | null | null | gr-qc hep-ph | http://creativecommons.org/licenses/by/4.0/ | We introduce the concept of emergent electric field. This is distinguished
from the fundamental one in that the emergent electric field directly appears
in observations through the Lorentz force, while the latter enters the phase
space as the canonical momentum of the electromagnetic field. In Hamiltonian
classical electromagnetism this concept naturally appears after introducing the
topological $\theta$ term. Furthermore, we show that in the spherically
symmetric model the concept of emergent electric field allows us to formulate a
modified theory of electromagnetism that is otherwise impossible. The relation
between the fundamental and the emergent electric fields is derived from the
imposition of general covariance of the electromagnetic strength tensor, which
is a nontrivial task in the canonical formulation the modified theory is based
on. We couple this theory to emergent modified gravity, where a similar
distinction between spacetime and gravity is made such that the spacetime,
which defines the observable geometry, is an emergent field composed of the
fundamental gravitational field. In this more encompassing emergent field
theory coupling gravity and electromagnetism, we show that the spherically
symmetric model contains a nonsingular black hole solution where not only
modified gravity but also modified electromagnetism is crucial for a robust
singularity resolution and to avoid the existence of (super)extermal black
holes.
| [
{
"created": "Sat, 20 Jul 2024 18:14:37 GMT",
"version": "v1"
}
] | 2024-07-23 | [
[
"Duque",
"Erick I.",
""
]
] | We introduce the concept of emergent electric field. This is distinguished from the fundamental one in that the emergent electric field directly appears in observations through the Lorentz force, while the latter enters the phase space as the canonical momentum of the electromagnetic field. In Hamiltonian classical electromagnetism this concept naturally appears after introducing the topological $\theta$ term. Furthermore, we show that in the spherically symmetric model the concept of emergent electric field allows us to formulate a modified theory of electromagnetism that is otherwise impossible. The relation between the fundamental and the emergent electric fields is derived from the imposition of general covariance of the electromagnetic strength tensor, which is a nontrivial task in the canonical formulation the modified theory is based on. We couple this theory to emergent modified gravity, where a similar distinction between spacetime and gravity is made such that the spacetime, which defines the observable geometry, is an emergent field composed of the fundamental gravitational field. In this more encompassing emergent field theory coupling gravity and electromagnetism, we show that the spherically symmetric model contains a nonsingular black hole solution where not only modified gravity but also modified electromagnetism is crucial for a robust singularity resolution and to avoid the existence of (super)extermal black holes. |
gr-qc/0604013 | Parampreet Singh | Abhay Ashtekar, Tomasz Pawlowski, Parampreet Singh | Quantum Nature of the Big Bang: An Analytical and Numerical
Investigation | Revised version to appear in Physical Review D. References added and
typos corrected | Phys.Rev.D73:124038,2006 | 10.1103/PhysRevD.73.124038 | IGPG-06/03-2 | gr-qc hep-th | null | Analytical and numerical methods are developed to analyze the quantum nature
of the big bang in the setting of loop quantum cosmology. They enable one to
explore the effects of quantum geometry both on the gravitational and matter
sectors and significantly extend the known results on the resolution of the big
bang singularity. Specifically, the following results are established for the
homogeneous isotropic model with a massless scalar field: i) the scalar field
is shown to serve as an internal clock, thereby providing a detailed
realization of the `emergent time' idea; ii) the physical Hilbert space, Dirac
observables and semi-classical states are constructed rigorously; iii) the
Hamiltonian constraint is solved numerically to show that the big bang is
replaced by a big bounce. Thanks to the non-perturbative, background
independent methods, unlike in other approaches the quantum evolution is
deterministic across the deep Planck regime. Our constructions also provide a
conceptual framework and technical tools which can be used in more general
models. In this sense, they provide foundations for analyzing physical issues
associated with the Planck regime of loop quantum cosmology as a whole.
| [
{
"created": "Tue, 4 Apr 2006 19:03:37 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Apr 2006 18:29:12 GMT",
"version": "v2"
},
{
"created": "Mon, 19 Jun 2006 17:54:59 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Ashtekar",
"Abhay",
""
],
[
"Pawlowski",
"Tomasz",
""
],
[
"Singh",
"Parampreet",
""
]
] | Analytical and numerical methods are developed to analyze the quantum nature of the big bang in the setting of loop quantum cosmology. They enable one to explore the effects of quantum geometry both on the gravitational and matter sectors and significantly extend the known results on the resolution of the big bang singularity. Specifically, the following results are established for the homogeneous isotropic model with a massless scalar field: i) the scalar field is shown to serve as an internal clock, thereby providing a detailed realization of the `emergent time' idea; ii) the physical Hilbert space, Dirac observables and semi-classical states are constructed rigorously; iii) the Hamiltonian constraint is solved numerically to show that the big bang is replaced by a big bounce. Thanks to the non-perturbative, background independent methods, unlike in other approaches the quantum evolution is deterministic across the deep Planck regime. Our constructions also provide a conceptual framework and technical tools which can be used in more general models. In this sense, they provide foundations for analyzing physical issues associated with the Planck regime of loop quantum cosmology as a whole. |
2105.11690 | Jafar Khodagholizadeh | Jafar Khodagholizadeh, Amir H. Abbassi, Ali Vahedi and Komeil Babaei | Gravitational Waves in a Closed Spacetime via Deviation Equation | 22 pages, 11 figures | Results in Physics, Volume 26, July 2021, 104347 | 10.1016/j.rinp.2021.104347 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Within the closed universe, we obtain the amplitude and frequency of
gravitational waves in the terms of discrete wave numbers, wave propagation
time, and cosmological constant using the deviation equation in the first-order
perturbed metric. We demonstrate that the cosmological constant effect on GWs
is only seen in the early universe. Also, by considering the time evolution of
a gravitational wave in a closed spacetime, we investigate its effect on a
circle of nearby massless particles, which will be compared with this case in
the flat spacetime. Expanding the universe has effective damping on GWs; thus,
we suggest it can be used as a tool to characterize the large-scale curvature
of the universe
| [
{
"created": "Tue, 25 May 2021 06:15:05 GMT",
"version": "v1"
}
] | 2021-05-27 | [
[
"Khodagholizadeh",
"Jafar",
""
],
[
"Abbassi",
"Amir H.",
""
],
[
"Vahedi",
"Ali",
""
],
[
"Babaei",
"Komeil",
""
]
] | Within the closed universe, we obtain the amplitude and frequency of gravitational waves in the terms of discrete wave numbers, wave propagation time, and cosmological constant using the deviation equation in the first-order perturbed metric. We demonstrate that the cosmological constant effect on GWs is only seen in the early universe. Also, by considering the time evolution of a gravitational wave in a closed spacetime, we investigate its effect on a circle of nearby massless particles, which will be compared with this case in the flat spacetime. Expanding the universe has effective damping on GWs; thus, we suggest it can be used as a tool to characterize the large-scale curvature of the universe |
2101.07147 | Vladimir Khatsymovsky | V.M. Khatsymovsky | On the Kerr metric in a synchronous reference frame | 9 pages, 1 figure | Int. J. Mod. Phys. D, Volume No. 30, Issue No. 10, Article No.
2150071, Year 2021 | 10.1142/S0218271821500711 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Kerr metric is considered in a synchronous frame of reference obtained by
using proper time and initial conditions for particles that freely move along a
certain set of trajectories as coordinates. Modifying these coordinates in a
certain way (keeping their interpretation as initial values at large
distances), we still have a synchronous frame and the direct analogue of the
Lemaitre metric, the singularities of which are exhausted by the physical Kerr
singularity (the singularity ring).
| [
{
"created": "Mon, 18 Jan 2021 16:28:23 GMT",
"version": "v1"
}
] | 2021-08-26 | [
[
"Khatsymovsky",
"V. M.",
""
]
] | The Kerr metric is considered in a synchronous frame of reference obtained by using proper time and initial conditions for particles that freely move along a certain set of trajectories as coordinates. Modifying these coordinates in a certain way (keeping their interpretation as initial values at large distances), we still have a synchronous frame and the direct analogue of the Lemaitre metric, the singularities of which are exhausted by the physical Kerr singularity (the singularity ring). |
0804.0153 | Selcuk Bayin | Selcuk S. Bayin | Friedmann Thermodynamics and the Geometry of the Universe | Key note speech delivered in the International Conference on
Efficiency, Costs, Optimization, Simulation and Environmental Impact of
Energy Systems, ECOS'95 and ASME | Proceedings of ECOS' 95 and ASME, Y.A. Gogus, Y.A. Ozturk, G.
Tsatsaronis (eds.) Vol.1, pg. 3, 1995 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a recent article we have introduced Friedmann thermodynamics, where
certain geometric parameters in Friedmann models are treated like their
thermodynamic counterparts (temperature, entropy, Gibbs potential etc.). This
model has the advantage of allowing us to determine the geometry of the
universe by thermodynamic stability arguments. In this article we review
connections between thermodynamics, geometry and cosmology.
| [
{
"created": "Tue, 1 Apr 2008 12:12:36 GMT",
"version": "v1"
}
] | 2008-04-02 | [
[
"Bayin",
"Selcuk S.",
""
]
] | In a recent article we have introduced Friedmann thermodynamics, where certain geometric parameters in Friedmann models are treated like their thermodynamic counterparts (temperature, entropy, Gibbs potential etc.). This model has the advantage of allowing us to determine the geometry of the universe by thermodynamic stability arguments. In this article we review connections between thermodynamics, geometry and cosmology. |
1010.5837 | Bei Lok Hu | B. L. Hu | Gravity and Nonequilibrium Thermodynamics of Classical Matter | 25 pages essay. Invited Talk at Mariofest, March 2010, Rosario,
Argentina. Festschrift to appear as an issue of IJMPD | Int.J.Mod.Phys.D20:697-716,2011 | 10.1142/S0218271811019049 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Renewed interest in deriving gravity (more precisely, the Einstein equations)
from thermodynamics considerations [1, 2] is stirred up by a recent proposal
that 'gravity is an entropic force' [3] (see also [4]). Even though I find the
arguments justifying such a claim in this latest proposal rather ad hoc and
simplistic compared to the original one I would unreservedly support the call
to explore deeper the relation between gravity and thermodynamics, this having
the same spirit as my long-held view that general relativity is the
hydrodynamic limit [5, 6] of some underlying theories for the microscopic
structure of spacetime - all these proposals, together with that of [7, 8],
attest to the emergent nature of gravity [9]. In this first paper of two we set
the modest goal of studying the nonequilibrium thermodynamics of classical
matter only, bringing afore some interesting prior results, without invoking
any quantum considerations such as Bekenstein-Hawking entropy, holography or
Unruh effect. This is for the sake of understanding the nonequilibrium nature
of classical gravity which is at the root of many salient features of black
hole physics. One important property of gravitational systems, from
self-gravitating gas to black holes, is their negative heat capacity, which is
the source of many out-of-the ordinary dynamical and thermodynamic features
such as the non-existence in isolated systems of thermodynamically stable
configurations, which actually provides the condition for gravitational
stability. A related property is that, being systems with long range
interaction, they are nonextensive and relax extremely slowly towards
equilibrium. Here we explore how much of the known features of black hole
thermodynamics can be derived from this classical nonequilibrium perspective. A
sequel paper will address gravity and nonequilibrium thermodynamics of quantum
fields [10].
| [
{
"created": "Thu, 28 Oct 2010 01:36:56 GMT",
"version": "v1"
}
] | 2011-05-25 | [
[
"Hu",
"B. L.",
""
]
] | Renewed interest in deriving gravity (more precisely, the Einstein equations) from thermodynamics considerations [1, 2] is stirred up by a recent proposal that 'gravity is an entropic force' [3] (see also [4]). Even though I find the arguments justifying such a claim in this latest proposal rather ad hoc and simplistic compared to the original one I would unreservedly support the call to explore deeper the relation between gravity and thermodynamics, this having the same spirit as my long-held view that general relativity is the hydrodynamic limit [5, 6] of some underlying theories for the microscopic structure of spacetime - all these proposals, together with that of [7, 8], attest to the emergent nature of gravity [9]. In this first paper of two we set the modest goal of studying the nonequilibrium thermodynamics of classical matter only, bringing afore some interesting prior results, without invoking any quantum considerations such as Bekenstein-Hawking entropy, holography or Unruh effect. This is for the sake of understanding the nonequilibrium nature of classical gravity which is at the root of many salient features of black hole physics. One important property of gravitational systems, from self-gravitating gas to black holes, is their negative heat capacity, which is the source of many out-of-the ordinary dynamical and thermodynamic features such as the non-existence in isolated systems of thermodynamically stable configurations, which actually provides the condition for gravitational stability. A related property is that, being systems with long range interaction, they are nonextensive and relax extremely slowly towards equilibrium. Here we explore how much of the known features of black hole thermodynamics can be derived from this classical nonequilibrium perspective. A sequel paper will address gravity and nonequilibrium thermodynamics of quantum fields [10]. |
gr-qc/9503067 | Carlo Rovelli | Carlo Rovelli | OUTLINE OF A GENERALLY COVARIANT QUANTUM FIELD THEORY AND A QUANTUM
THEORY OF GRAVITY | Latex file, 33 pages | J.Math.Phys.36:6529-6547,1995 | 10.1063/1.531255 | null | gr-qc | null | We study a tentative generally covariant quantum field theory, denoted the
T-Theory, as a tool to investigate the consistency of quantum general
relativity. The theory describes the gravitational field and a minimally
coupled scalar field; it is based on the loop representation, and on a certain
number of quantization choices. Four-dimensional diffeomorphism-invariant
quantum transition probabilities can be computed from the theory. We present
the explicit calculation of the transition probability between two volume
eigenstates as an example. We discuss the choices on which the T-theory relies,
and the possibilities of modifying them.
| [
{
"created": "Sat, 1 Apr 1995 14:45:13 GMT",
"version": "v1"
}
] | 2010-11-01 | [
[
"Rovelli",
"Carlo",
""
]
] | We study a tentative generally covariant quantum field theory, denoted the T-Theory, as a tool to investigate the consistency of quantum general relativity. The theory describes the gravitational field and a minimally coupled scalar field; it is based on the loop representation, and on a certain number of quantization choices. Four-dimensional diffeomorphism-invariant quantum transition probabilities can be computed from the theory. We present the explicit calculation of the transition probability between two volume eigenstates as an example. We discuss the choices on which the T-theory relies, and the possibilities of modifying them. |
2210.14049 | Naritaka Oshita | Naritaka Oshita and Daichi Tsuna | Slowly Decaying Ringdown of a Rapidly Spinning Black Hole: Probing the
No-Hair Theorem by Small Mass-Ratio Mergers with LISA | 8 pages, 8 figures, version accepted for publication in PRD | Phys. Rev. D 108, 104031 (2023) | 10.1103/PhysRevD.108.104031 | RIKEN-iTHEMS-Report-22, RESCEU-19/22, YITP-23-155 | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | The measurability of multiple quasinormal (QN) modes, including overtones and
higher harmonics, with the Laser Interferometer Space Antenna is investigated
by computing the gravitational wave (GW) signal induced by an intermediate or
extreme mass ratio merger involving a supermassive black hole (SMBH). We
confirm that the ringdown of rapidly spinning black holes are long-lived, and
higher harmonics of the ringdown are significantly excited for mergers of small
mass ratios. We investigate the measurability and separability of the QN modes
for such mergers and demonstrate that the observation of GWs from rapidly
rotating SMBHs has an advantage for detecting superposed QN modes and testing
the no-hair theorem of black holes.
| [
{
"created": "Tue, 25 Oct 2022 14:28:48 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Nov 2023 06:23:46 GMT",
"version": "v2"
}
] | 2023-12-01 | [
[
"Oshita",
"Naritaka",
""
],
[
"Tsuna",
"Daichi",
""
]
] | The measurability of multiple quasinormal (QN) modes, including overtones and higher harmonics, with the Laser Interferometer Space Antenna is investigated by computing the gravitational wave (GW) signal induced by an intermediate or extreme mass ratio merger involving a supermassive black hole (SMBH). We confirm that the ringdown of rapidly spinning black holes are long-lived, and higher harmonics of the ringdown are significantly excited for mergers of small mass ratios. We investigate the measurability and separability of the QN modes for such mergers and demonstrate that the observation of GWs from rapidly rotating SMBHs has an advantage for detecting superposed QN modes and testing the no-hair theorem of black holes. |
gr-qc/0605067 | Tatyana P. Shestakova | T. P. Shestakova | Cosmological solutions for the Universe filled with matter in various
states and gauge invariance | 8 pages, talk presented at the International Conference on
Gravitation, Cosmology and Astrophysics dedicated to 90th anniversary of K.
P. Staniukovich, Moscow, March 2006 | Grav.Cosmol. 12 (2006) 223-226 | null | null | gr-qc | null | We explore at phenomenological level a model of the Universe filled with
various kinds of matter characterized by different equations of state. We show
that introducing of each kind of matter is equivalent to a certain choice of a
gauge condition, the gauge condition describing a medium with a given equation
of state. The case of a particular interest is when one kind of matter (de
Sitter false vacuum) dominates at the early stage of the Universe evolution
while another kind (radiation, or ultrarelativistic gas) dominates at its later
stage. We can, therefore, consider different asymptotic regimes for the early
and later stages of the Universe existence. These regimes are described by
solutions to the Wheeler - DeWitt equation for the Universe with matter in that
given state, and, at the same time, in the "extended phase space" approach to
quantum geometrodynamics the regimes are described by solutions to a
Schrodinger equation associated with a choice of some gauge condition. It is
supposed that, from the viewpoint of the observer located at the later stage of
the Universe evolution, solutions for a Lambda-dominated early Universe would
decay.
| [
{
"created": "Thu, 11 May 2006 11:57:18 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Shestakova",
"T. P.",
""
]
] | We explore at phenomenological level a model of the Universe filled with various kinds of matter characterized by different equations of state. We show that introducing of each kind of matter is equivalent to a certain choice of a gauge condition, the gauge condition describing a medium with a given equation of state. The case of a particular interest is when one kind of matter (de Sitter false vacuum) dominates at the early stage of the Universe evolution while another kind (radiation, or ultrarelativistic gas) dominates at its later stage. We can, therefore, consider different asymptotic regimes for the early and later stages of the Universe existence. These regimes are described by solutions to the Wheeler - DeWitt equation for the Universe with matter in that given state, and, at the same time, in the "extended phase space" approach to quantum geometrodynamics the regimes are described by solutions to a Schrodinger equation associated with a choice of some gauge condition. It is supposed that, from the viewpoint of the observer located at the later stage of the Universe evolution, solutions for a Lambda-dominated early Universe would decay. |
1811.04327 | Javier Olmedo | Javier Olmedo and Emanuele Alesci | Power spectrum of primordial perturbations for an emergent universe in
quantum reduced loop gravity | 28 pages, 8 figures | null | 10.1088/1475-7516/2019/04/030 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the dynamics and predictions of a new emergent-universe model
recently derived within Quantum Reduced Loop Gravity and based on the so-called
statistical regularization scheme. These effective geometries show a dynamical
transition from a stationary spacetime, with nearly constant scale factor at
very early times, to a late-time semiclassical phase well approximated by a
classical Friedmann-Robertson-Walker spacetime. We show that this is always the
case when the matter content is a minimally coupled scalar field subject to a
quadratic potential, including the massless case. Besides, a finite period of
(nearly) exponential expansion in the semiclassical region can take place.
Hence, we incorporate cosmological scalar and tensor perturbations, with a
well-defined dynamics, and compute their power spectra at the end of inflation.
We show that they are nearly scale invariant up to some scale where scale
invariance is broken. Besides, they show qualitative differences with respect
to the bouncing scenario of Loop Quantum Cosmology at scales where the scale
invariance is broken. Nevertheless, the tensor-to-scalar ratio remains
approximately constant even for modes well affected by the background
evolution.
| [
{
"created": "Sun, 11 Nov 2018 00:20:20 GMT",
"version": "v1"
}
] | 2019-04-24 | [
[
"Olmedo",
"Javier",
""
],
[
"Alesci",
"Emanuele",
""
]
] | We study the dynamics and predictions of a new emergent-universe model recently derived within Quantum Reduced Loop Gravity and based on the so-called statistical regularization scheme. These effective geometries show a dynamical transition from a stationary spacetime, with nearly constant scale factor at very early times, to a late-time semiclassical phase well approximated by a classical Friedmann-Robertson-Walker spacetime. We show that this is always the case when the matter content is a minimally coupled scalar field subject to a quadratic potential, including the massless case. Besides, a finite period of (nearly) exponential expansion in the semiclassical region can take place. Hence, we incorporate cosmological scalar and tensor perturbations, with a well-defined dynamics, and compute their power spectra at the end of inflation. We show that they are nearly scale invariant up to some scale where scale invariance is broken. Besides, they show qualitative differences with respect to the bouncing scenario of Loop Quantum Cosmology at scales where the scale invariance is broken. Nevertheless, the tensor-to-scalar ratio remains approximately constant even for modes well affected by the background evolution. |
gr-qc/0408088 | Daniel Hofmann | D. Hofmann and W. Kummer | Effective Action and Hawking Flux from Covariant Perturbation Theory | 26 pages | Eur.Phys.J. C40 (2005) 275-286 | 10.1140/epjc/s2005-02129-9 | TUW-04-20 | gr-qc | null | The computation of the radiation flux related to the Hawking temperature of a
Schwarzschild Black Hole or another geometric background is still well-known to
be fraught with a number of delicate problems. In spherical reduction, as shown
by one of the present authors (W. K.) with D.V. Vassilevich, the correct black
body radiation follows when two ``basic components'' (conformal anomaly and a
``dilaton'' anomaly) are used as input in the integrated energy-momentum
conservation equation. The main new element in the present work is the use of a
quite different method, the covariant perturbation theory of Barvinsky and
Vilkovisky, to establish directly the full effective action which determines
these basic components. In the derivation of W. K. and D.V. Vassilevich the
computation of the dilaton anomaly implied one potentially doubtful
intermediate step which can be avoided here. Moreover, the present approach
also is sensitive to IR (renormalisation) effects. We realize that the
effective action naturally leads to expectation values in the Boulware vacuum
which, making use of the conservation equation, suffice for the computation of
the Hawking flux in other quantum states, in particular for the relevant Unruh
state. Thus, a rather comprehensive discussion of the effects of (UV and IR)
renormalisation upon radiation flux and energy density is possible.
| [
{
"created": "Thu, 26 Aug 2004 21:46:06 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Hofmann",
"D.",
""
],
[
"Kummer",
"W.",
""
]
] | The computation of the radiation flux related to the Hawking temperature of a Schwarzschild Black Hole or another geometric background is still well-known to be fraught with a number of delicate problems. In spherical reduction, as shown by one of the present authors (W. K.) with D.V. Vassilevich, the correct black body radiation follows when two ``basic components'' (conformal anomaly and a ``dilaton'' anomaly) are used as input in the integrated energy-momentum conservation equation. The main new element in the present work is the use of a quite different method, the covariant perturbation theory of Barvinsky and Vilkovisky, to establish directly the full effective action which determines these basic components. In the derivation of W. K. and D.V. Vassilevich the computation of the dilaton anomaly implied one potentially doubtful intermediate step which can be avoided here. Moreover, the present approach also is sensitive to IR (renormalisation) effects. We realize that the effective action naturally leads to expectation values in the Boulware vacuum which, making use of the conservation equation, suffice for the computation of the Hawking flux in other quantum states, in particular for the relevant Unruh state. Thus, a rather comprehensive discussion of the effects of (UV and IR) renormalisation upon radiation flux and energy density is possible. |
2002.08048 | Huiquan Li | Huiquan Li and Jiancheng Wang | Towards the merger of Hawking radiating black holes | 17 pages, no figure | null | 10.1142/S0218271821500607 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the merger process of binary black holes with Hawking radiation
taken into account. Besides the redshifted radiation to infinity, binary black
holes can exchange radiation between themselves, which is first redshifted and
then blueshifted when it propagates from one hole to the other. The exchange
rate should be large when the temperature-divergent horizons are penetrating
each other to form a single horizon with unique temperature. This will cause
non-negligible mass and angular momentum transfer between the black holes
during the merging process of the horizons. We further argue in the large mass
ratio limit that the light hole whose local evaporation is enhanced by the
competing redshift-blueshift effects will probably evaporate or decay
completely before reaching the the horizon of the heavy one. We also discuss
the possibility of testing Hawking radiation and even exploring the information
loss puzzle in gravitational wave observations.
| [
{
"created": "Wed, 19 Feb 2020 08:23:44 GMT",
"version": "v1"
},
{
"created": "Mon, 11 May 2020 15:46:57 GMT",
"version": "v2"
},
{
"created": "Thu, 3 Jun 2021 13:59:37 GMT",
"version": "v3"
}
] | 2021-07-21 | [
[
"Li",
"Huiquan",
""
],
[
"Wang",
"Jiancheng",
""
]
] | We discuss the merger process of binary black holes with Hawking radiation taken into account. Besides the redshifted radiation to infinity, binary black holes can exchange radiation between themselves, which is first redshifted and then blueshifted when it propagates from one hole to the other. The exchange rate should be large when the temperature-divergent horizons are penetrating each other to form a single horizon with unique temperature. This will cause non-negligible mass and angular momentum transfer between the black holes during the merging process of the horizons. We further argue in the large mass ratio limit that the light hole whose local evaporation is enhanced by the competing redshift-blueshift effects will probably evaporate or decay completely before reaching the the horizon of the heavy one. We also discuss the possibility of testing Hawking radiation and even exploring the information loss puzzle in gravitational wave observations. |
2006.15622 | She-Sheng Xue | She-Sheng Xue | Massive particle pair production and oscillation in Friedman Universe:
reheating energy and entropy, and cold dark matter | The final version to appear in the European Physical Journal C. 41
pages and 11 captioned figures. Secs 2-3, holographic and massive pair plasma
state; Sec. 5 cosmological model; Sec. 6-10 reheating | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Suppose that the early Universe starts with a cosmological $\Lambda$-term
originating from quantum spacetime at the Planck scale. Dark energy drives
inflation and reheating by reducing its value for massive particle-antiparticle
pairs production and oscillation, resulting in a holographic and massive pair
plasma state. The back-and-forth reaction of dark energy and massive pairs
slows inflation to its end and starts reheating by rapidly producing stable and
unstable pairs. We introduce the Boltzmann-type rate equation describing the
back-and-forth reaction. It forms a close set with Friedman equations and
reheating equations for unstable pairs decay to relativistic particles. The
numerical solutions show preheating, massive pairs dominated and genuine
reheating episodes. We obtain the reheating temperature and entropy in terms of
the tensor-to-scalar ratio $0 < r < 0.047$ consistently with observations.
Stable massive pairs represent cold dark matter particles and weakly interact
with dark energy. The resultant cold dark matter abundance $\Omega_c\sim
10^{-1}$ is about a constant in time.
| [
{
"created": "Sun, 28 Jun 2020 14:36:58 GMT",
"version": "v1"
},
{
"created": "Mon, 3 May 2021 08:59:43 GMT",
"version": "v2"
},
{
"created": "Tue, 17 Jan 2023 17:54:26 GMT",
"version": "v3"
},
{
"created": "Mon, 17 Apr 2023 09:03:31 GMT",
"version": "v4"
}
] | 2023-04-18 | [
[
"Xue",
"She-Sheng",
""
]
] | Suppose that the early Universe starts with a cosmological $\Lambda$-term originating from quantum spacetime at the Planck scale. Dark energy drives inflation and reheating by reducing its value for massive particle-antiparticle pairs production and oscillation, resulting in a holographic and massive pair plasma state. The back-and-forth reaction of dark energy and massive pairs slows inflation to its end and starts reheating by rapidly producing stable and unstable pairs. We introduce the Boltzmann-type rate equation describing the back-and-forth reaction. It forms a close set with Friedman equations and reheating equations for unstable pairs decay to relativistic particles. The numerical solutions show preheating, massive pairs dominated and genuine reheating episodes. We obtain the reheating temperature and entropy in terms of the tensor-to-scalar ratio $0 < r < 0.047$ consistently with observations. Stable massive pairs represent cold dark matter particles and weakly interact with dark energy. The resultant cold dark matter abundance $\Omega_c\sim 10^{-1}$ is about a constant in time. |
1906.03790 | Marcony Silva Cunha | C.R. Muniz, H.R. Christiansen, M.S. Cunha, H.S. Vieira | Exact solutions of the Wheeler-DeWitt equation with ordering term in a
dark energy scenario | 16 pages, improved figures, some new relevant conclusions, references
added | Physics of the Dark Universe, v28, 100547 (2020) | 10.1016/j.dark.2020.100547 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the quantum evolution of the universe in the presence of two
types of dark energies. First, we consider the phantom class ($\omega<-1$)
which would be responsible for a super-accelerated cosmic expansion, and then
we apply the procedure to an ordinary $\Lambda>0$ vacuum ($\omega=-1$). This is
done by analytically solving the Wheeler-DeWitt equation with ordering term
(WdW) in the cosmology of Friedmann-Robertson-Walker. In this paper, we find
exact solutions in the scale factor $a$ and the ordering parameter $q$. For
$q=1$ it is shown that the universe has a high probability of evolving from a
big bang singularity. On the other hand, for $q = 0$ the solution indicates
that an initial singularity is unlikely. Instead, the universe has maximal
probability of starting with a finite well-defined size which we compute
explicitly at primordial times. We also study the time evolution of the scale
factor by means of the Hamilton-Jacobi equation and show that an ultimate big
rip singularity emerges explicitly from our solutions. The phantom scenario
thus predicts a dramatic end in which the universe would reach an infinite
scale factor in a finite cosmological time as pointed by Caldwell et al. in a
classical setup. Finally, we solve the WdW equation with ordinary constant dark
energy and show that in this case the universe does not rip apart in a finite
era.
| [
{
"created": "Mon, 10 Jun 2019 04:24:08 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Oct 2019 23:10:22 GMT",
"version": "v2"
},
{
"created": "Fri, 20 Mar 2020 17:20:39 GMT",
"version": "v3"
}
] | 2022-04-11 | [
[
"Muniz",
"C. R.",
""
],
[
"Christiansen",
"H. R.",
""
],
[
"Cunha",
"M. S.",
""
],
[
"Vieira",
"H. S.",
""
]
] | We investigate the quantum evolution of the universe in the presence of two types of dark energies. First, we consider the phantom class ($\omega<-1$) which would be responsible for a super-accelerated cosmic expansion, and then we apply the procedure to an ordinary $\Lambda>0$ vacuum ($\omega=-1$). This is done by analytically solving the Wheeler-DeWitt equation with ordering term (WdW) in the cosmology of Friedmann-Robertson-Walker. In this paper, we find exact solutions in the scale factor $a$ and the ordering parameter $q$. For $q=1$ it is shown that the universe has a high probability of evolving from a big bang singularity. On the other hand, for $q = 0$ the solution indicates that an initial singularity is unlikely. Instead, the universe has maximal probability of starting with a finite well-defined size which we compute explicitly at primordial times. We also study the time evolution of the scale factor by means of the Hamilton-Jacobi equation and show that an ultimate big rip singularity emerges explicitly from our solutions. The phantom scenario thus predicts a dramatic end in which the universe would reach an infinite scale factor in a finite cosmological time as pointed by Caldwell et al. in a classical setup. Finally, we solve the WdW equation with ordinary constant dark energy and show that in this case the universe does not rip apart in a finite era. |
1211.2913 | Guido Pizzella | R. de Sangro, G. Finocchiaro, P.Patteri, M. Piccolo, G. Pizzella | Measuring Propagation Speed of Coulomb Fields | 23 pages, 15 figures | null | null | null | gr-qc physics.acc-ph physics.gen-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The problem of gravity propagation has been subject of discussion for quite a
long time: Newton, Laplace and, in relatively more modern times, Eddington
pointed out that, if gravity propagated with finite velocity, planets motion
around the sun would become unstable due to a torque originating from time lag
of the gravitational interactions.
Such an odd behavior can be found also in electromagnetism, when one computes
the propagation of the electric fields generated by a set of uniformly moving
charges. As a matter of fact the Li\'enard-Weichert retarded potential leads to
a formula indistinguishable from the one obtained assuming that the electric
field propagates with infinite velocity. Feyman explanation for this apparent
paradox was based on the fact that uniform motions last indefinitely.
To verify such an explanation, we performed an experiment to measure the
time/space evolution of the electric field generated by an uniformely moving
electron beam. The results we obtain on such a finite lifetime kinematical
state seem compatible with an electric field rigidly carried by the beam
itself.
| [
{
"created": "Tue, 13 Nov 2012 08:35:20 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Nov 2014 09:23:07 GMT",
"version": "v2"
}
] | 2014-11-11 | [
[
"de Sangro",
"R.",
""
],
[
"Finocchiaro",
"G.",
""
],
[
"Patteri",
"P.",
""
],
[
"Piccolo",
"M.",
""
],
[
"Pizzella",
"G.",
""
]
] | The problem of gravity propagation has been subject of discussion for quite a long time: Newton, Laplace and, in relatively more modern times, Eddington pointed out that, if gravity propagated with finite velocity, planets motion around the sun would become unstable due to a torque originating from time lag of the gravitational interactions. Such an odd behavior can be found also in electromagnetism, when one computes the propagation of the electric fields generated by a set of uniformly moving charges. As a matter of fact the Li\'enard-Weichert retarded potential leads to a formula indistinguishable from the one obtained assuming that the electric field propagates with infinite velocity. Feyman explanation for this apparent paradox was based on the fact that uniform motions last indefinitely. To verify such an explanation, we performed an experiment to measure the time/space evolution of the electric field generated by an uniformely moving electron beam. The results we obtain on such a finite lifetime kinematical state seem compatible with an electric field rigidly carried by the beam itself. |
2403.17278 | Julio Cesar Fabris | J\'ulio C. Fabris and Richard Kerner | A unimodular Kaluza-Klein theory | Latex file, 19 pages, 2 figures | null | null | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | Unimodular gravity became an object of increasing interest in the late
$80$-ties and was recently used in primordial Universe modeling with
cosmological constant, in the context of the Brans-Dicke gravity including
scalar field. In the present article we investigate the possibility of imposing
the unimodular condition within the $5$-dimensional Kaluza-Klein theory
including the scalar field. The variational principle is formulated in $5$
dimensions first, and dimensional reduction is applied to the resulting set of
equations. A cosmological model based on these equations is then presented and
discussed.
| [
{
"created": "Mon, 25 Mar 2024 23:48:19 GMT",
"version": "v1"
}
] | 2024-03-27 | [
[
"Fabris",
"Júlio C.",
""
],
[
"Kerner",
"Richard",
""
]
] | Unimodular gravity became an object of increasing interest in the late $80$-ties and was recently used in primordial Universe modeling with cosmological constant, in the context of the Brans-Dicke gravity including scalar field. In the present article we investigate the possibility of imposing the unimodular condition within the $5$-dimensional Kaluza-Klein theory including the scalar field. The variational principle is formulated in $5$ dimensions first, and dimensional reduction is applied to the resulting set of equations. A cosmological model based on these equations is then presented and discussed. |
gr-qc/0602099 | Yaneer Bar-Yam | Yaneer Bar-Yam | ZM theory I: Introduction and Lorentz covariance | 15 pages, 2 figures | null | null | NECSI Report 2006-02-01 | gr-qc | null | We consider defining time as a function of a cyclical field, an abstraction
of a clock. The definition of time corresponds to a novel interpretation of the
relationship between space-time coordinates of observers at different locations
in space. As a first test of the utility of this definition, we show that it
leads to a Lorentz covariant description of space-time. This derivation of
Lorenz covariance provides a starting point for considering more general
constructions that relate to physical laws. The definition of time couples time
to space, making time not orthogonal to space, and making dynamics a result of
geometry, providing a vehicle for curved space-time theories that generalize
general relativity.
| [
{
"created": "Fri, 24 Feb 2006 17:29:32 GMT",
"version": "v1"
}
] | 2009-09-29 | [
[
"Bar-Yam",
"Yaneer",
""
]
] | We consider defining time as a function of a cyclical field, an abstraction of a clock. The definition of time corresponds to a novel interpretation of the relationship between space-time coordinates of observers at different locations in space. As a first test of the utility of this definition, we show that it leads to a Lorentz covariant description of space-time. This derivation of Lorenz covariance provides a starting point for considering more general constructions that relate to physical laws. The definition of time couples time to space, making time not orthogonal to space, and making dynamics a result of geometry, providing a vehicle for curved space-time theories that generalize general relativity. |
1905.04814 | Artymowski Michal | Vahid Kamali, Micha{\l} Artymowski and Mohammad Reza Setare | Constant roll warm inflation in high dissipative regime | 17 pages, 2 figures, published version | null | 10.1088/1475-7516/2020/07/002 | JCAP07(2020)002 | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Constant-roll warm inflation is introduced in this work. A novel approach to
finding an exact solution for Friedman equations coupled to scalar field
equation of motion is presented for cold inflation and is extended to warm
inflation with the constant dissipative parameter $Q=\frac{\Gamma}{3H}$. The
evolution of the primordial inhomogeneities of a scalar field in a thermal bath
is also studied. The $1\sigma$ consistency between the theoretical predictions
of the model and observational constraints has been proven for a range of $Q$
and $\beta=\frac{\ddot{\phi}}{3H\phi}$ (constant rate of inflaton roll). In
addition, we briefly investigate the possible enhancement of super-horizon
perturbations beyond the slow-roll approximation.
| [
{
"created": "Mon, 13 May 2019 00:11:13 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Jul 2020 07:01:55 GMT",
"version": "v2"
}
] | 2020-07-17 | [
[
"Kamali",
"Vahid",
""
],
[
"Artymowski",
"Michał",
""
],
[
"Setare",
"Mohammad Reza",
""
]
] | Constant-roll warm inflation is introduced in this work. A novel approach to finding an exact solution for Friedman equations coupled to scalar field equation of motion is presented for cold inflation and is extended to warm inflation with the constant dissipative parameter $Q=\frac{\Gamma}{3H}$. The evolution of the primordial inhomogeneities of a scalar field in a thermal bath is also studied. The $1\sigma$ consistency between the theoretical predictions of the model and observational constraints has been proven for a range of $Q$ and $\beta=\frac{\ddot{\phi}}{3H\phi}$ (constant rate of inflaton roll). In addition, we briefly investigate the possible enhancement of super-horizon perturbations beyond the slow-roll approximation. |
0905.2442 | Alan Coley | A.A. Coley | Cosmological Observations: Averaging on the Null Cone | null | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The universe is not isotropic or spatially homogeneous on local scales. The
averaging of local inhomogeneities in general relativity can lead to
significant dynamical effects on the evolution of the universe and on the
interpretation of cosmological data. In particular, all deductions about
cosmology are based on light paths; averaging can have an important effect on
photon propagation and hence cosmological observations. It would be desirable
to describe the physical effects of averaging in terms of observational
quantities and focussing on the behaviour of light. Data (e.g., matter terms,
such as the density or galaxy number counts, which are already expressed as
averaged quantities) is given on the null cone. Therefore, it is
observationally meaningful to consider light-cone averages of quantities. In
principle, we wish to describe the cosmological equations on the null cone, and
hence we need to construct the averaged geometry on the null cone. However, we
argue that it is still necessary to average the full Einstein field equations
to obtain suitably averaged equations on the null cone. Since it is not the
geometry per se that appears in the observational relations, we discuss whether
it is possible to covariantly `average' just a subset of the evolution
equations on the null cone, focussing on relevant observational quantities. We
present an averaged version of the scalar null Raychaudhuri equation, which may
be a useful first step in this regard.
| [
{
"created": "Thu, 14 May 2009 23:05:35 GMT",
"version": "v1"
}
] | 2009-05-19 | [
[
"Coley",
"A. A.",
""
]
] | The universe is not isotropic or spatially homogeneous on local scales. The averaging of local inhomogeneities in general relativity can lead to significant dynamical effects on the evolution of the universe and on the interpretation of cosmological data. In particular, all deductions about cosmology are based on light paths; averaging can have an important effect on photon propagation and hence cosmological observations. It would be desirable to describe the physical effects of averaging in terms of observational quantities and focussing on the behaviour of light. Data (e.g., matter terms, such as the density or galaxy number counts, which are already expressed as averaged quantities) is given on the null cone. Therefore, it is observationally meaningful to consider light-cone averages of quantities. In principle, we wish to describe the cosmological equations on the null cone, and hence we need to construct the averaged geometry on the null cone. However, we argue that it is still necessary to average the full Einstein field equations to obtain suitably averaged equations on the null cone. Since it is not the geometry per se that appears in the observational relations, we discuss whether it is possible to covariantly `average' just a subset of the evolution equations on the null cone, focussing on relevant observational quantities. We present an averaged version of the scalar null Raychaudhuri equation, which may be a useful first step in this regard. |
1712.02210 | Vilson T. Zanchin | Jos\'e D. V. Arba\~nil, Vilson T. Zanchin | Relativistic polytropic spheres with electric charge: Compact stars,
compactness and mass bounds, and quasiblack hole configurations | 15 pages, 15 figures | Phys. Rev. D 97, 104045 (2018) | 10.1103/PhysRevD.97.104045 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the static stellar equilibrium configurations ofuncharged and
charged spheres composed by a relativistic polytropic fluid, and compare with
those of spheres composed by a non-relativistic polytropic fluid, the later
case already being studied in a previous work [J. D. Arba\~nil, P. S. Lemos, V.
T. Zanchin, Phys. Rev. D \textbf{88}, 084023 (2013)]. In the relativistic fluid
case, a relativistic polytropic equation of state, $p=\omega\delta^{\gamma}$,
is assumedd. Here, $\delta=\rho-p/(\gamma-1)$, with $\delta$ and $\rho$ being
the rest mass density and the energy density, respectively, and $\omega$ and
$\gamma$ are respectively the polytropic constant and the polytropic exponent.
We assume that the charge density $\rho_e$ is proportional to the energy
density $\rho$, $\rho_e = \alpha\, \rho$, with $\alpha$ being a constant such
that $0\leq |\alpha|\leq 1$. Some properties of the charged spheres such as
mass, total electric charge, radius, redshift, and the speed of sound are
analyzed. The dependence of such properties with the polytropic exponent is
also investigated. In addition, some limits that arise in general relativity,
such as the Chandrasekhar limit, the Oppenheimer-Volkoff limit, the Buchdahl
bound and the Buchdahl-Andr\'easson bound, i.e., the Buchdahl bound for the
electric case, are studied. As in a charged non-relativistic polytropic sphere,
the charged relativistic polytropic sphere with $\gamma\to\infty$ and $\alpha
\to 1$ saturates the Buchdahl-Andr\'easson bound, thus indicating that it
reaches the quasiblack hole configuration. We show by means of numerical
analysis that, as expected, the major differences between the two cases appear
in the high energy density region.
| [
{
"created": "Wed, 6 Dec 2017 14:49:29 GMT",
"version": "v1"
}
] | 2018-05-30 | [
[
"Arbañil",
"José D. V.",
""
],
[
"Zanchin",
"Vilson T.",
""
]
] | We study the static stellar equilibrium configurations ofuncharged and charged spheres composed by a relativistic polytropic fluid, and compare with those of spheres composed by a non-relativistic polytropic fluid, the later case already being studied in a previous work [J. D. Arba\~nil, P. S. Lemos, V. T. Zanchin, Phys. Rev. D \textbf{88}, 084023 (2013)]. In the relativistic fluid case, a relativistic polytropic equation of state, $p=\omega\delta^{\gamma}$, is assumedd. Here, $\delta=\rho-p/(\gamma-1)$, with $\delta$ and $\rho$ being the rest mass density and the energy density, respectively, and $\omega$ and $\gamma$ are respectively the polytropic constant and the polytropic exponent. We assume that the charge density $\rho_e$ is proportional to the energy density $\rho$, $\rho_e = \alpha\, \rho$, with $\alpha$ being a constant such that $0\leq |\alpha|\leq 1$. Some properties of the charged spheres such as mass, total electric charge, radius, redshift, and the speed of sound are analyzed. The dependence of such properties with the polytropic exponent is also investigated. In addition, some limits that arise in general relativity, such as the Chandrasekhar limit, the Oppenheimer-Volkoff limit, the Buchdahl bound and the Buchdahl-Andr\'easson bound, i.e., the Buchdahl bound for the electric case, are studied. As in a charged non-relativistic polytropic sphere, the charged relativistic polytropic sphere with $\gamma\to\infty$ and $\alpha \to 1$ saturates the Buchdahl-Andr\'easson bound, thus indicating that it reaches the quasiblack hole configuration. We show by means of numerical analysis that, as expected, the major differences between the two cases appear in the high energy density region. |
1003.5357 | Robert C. Myers | Robert C. Myers and Brandon Robinson | Black Holes in Quasi-topological Gravity | 33 pages, 4 figures; two references added | JHEP 1008:067,2010 | 10.1007/JHEP08(2010)067 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct a new gravitational action which includes cubic curvature
interactions and which provides a useful toy model for the holographic study of
a three parameter family of four- and higher-dimensional CFT's. We also
investigate the black hole solutions of this new gravity theory. Further we
examine the equations of motion of quasi-topological gravity. While the full
equations in a general background are fourth-order in derivatives, we show that
the linearized equations describing gravitons propagating in the AdS vacua
match precisely the second-order equations of Einstein gravity.
| [
{
"created": "Sun, 28 Mar 2010 10:39:15 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Jun 2010 14:07:25 GMT",
"version": "v2"
}
] | 2014-11-20 | [
[
"Myers",
"Robert C.",
""
],
[
"Robinson",
"Brandon",
""
]
] | We construct a new gravitational action which includes cubic curvature interactions and which provides a useful toy model for the holographic study of a three parameter family of four- and higher-dimensional CFT's. We also investigate the black hole solutions of this new gravity theory. Further we examine the equations of motion of quasi-topological gravity. While the full equations in a general background are fourth-order in derivatives, we show that the linearized equations describing gravitons propagating in the AdS vacua match precisely the second-order equations of Einstein gravity. |
2308.00917 | Tayyab Naseer | M. Sharif, Tayyab Naseer | Cosmological Solutions through Gravitational Decoupling in
$f(\mathcal{R},\mathcal{T},\mathcal{R}_{\mathrm{a}\mathrm{b}}\mathcal{T}^{\mathrm{a}\mathrm{b}})$
Gravity | 30 pages, 10 figures | Gen. Relativ. Gravit. 55(2023)87 | 10.1007/s10714-023-03135-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we adopt minimal gravitational decoupling scheme to extend a
non-static spherically symmetric isotropic composition to anisotropic interior
in
$f(\mathcal{R},\mathcal{T},\mathcal{R}_{\mathrm{a}\mathrm{b}}\mathcal{T}^{\mathrm{a}\mathrm{b}})$
theory. A geometric deformation is applied only on $g_{rr}$ metric component
through which the modified field equations are separated into two sets, each of
them correspond to their parent (seed and newly added) source. An isotropic
model suggested by the Friedmann-Lemaitre-Robertson-Walker metric is adopted to
reduce the unknowns in the first set. We then obtain an isotropic solution by
making use of a linear equation of state and a particular form of the scale
factor. A density-like constraint is chosen to solve the other sector
containing the deformation function and multiple components of an additional
matter source. Further, the graphical interpretation of the developed model is
carried out to analyze how a decoupling parameter and modified gravity
influence the evolutionary phases of the universe. It is concluded that only
the radiation-dominated era meets stability criteria everywhere in this
matter-geometry coupled theory.
| [
{
"created": "Wed, 2 Aug 2023 03:14:52 GMT",
"version": "v1"
}
] | 2023-08-03 | [
[
"Sharif",
"M.",
""
],
[
"Naseer",
"Tayyab",
""
]
] | In this paper, we adopt minimal gravitational decoupling scheme to extend a non-static spherically symmetric isotropic composition to anisotropic interior in $f(\mathcal{R},\mathcal{T},\mathcal{R}_{\mathrm{a}\mathrm{b}}\mathcal{T}^{\mathrm{a}\mathrm{b}})$ theory. A geometric deformation is applied only on $g_{rr}$ metric component through which the modified field equations are separated into two sets, each of them correspond to their parent (seed and newly added) source. An isotropic model suggested by the Friedmann-Lemaitre-Robertson-Walker metric is adopted to reduce the unknowns in the first set. We then obtain an isotropic solution by making use of a linear equation of state and a particular form of the scale factor. A density-like constraint is chosen to solve the other sector containing the deformation function and multiple components of an additional matter source. Further, the graphical interpretation of the developed model is carried out to analyze how a decoupling parameter and modified gravity influence the evolutionary phases of the universe. It is concluded that only the radiation-dominated era meets stability criteria everywhere in this matter-geometry coupled theory. |
gr-qc/0611131 | Shailesh Kulkarni | Rabin Banerjee, Subir Ghosh and Shailesh Kulkarni | Remarks on the Generalized Chaplygin Gas | References addeded | Phys.Rev.D75:025008,2007 | 10.1103/PhysRevD.75.025008 | null | gr-qc hep-th | null | We have developed an action formulation for the Generalized Chaplygin Gas
(GCG). The most general form for the nonrelativistic GCG action is derived
consistent with the equation of state. We have also discussed a relativistic
formulation for GCG by providing a detailed analysis of the Poincare algebra.
| [
{
"created": "Fri, 24 Nov 2006 10:55:37 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Nov 2006 05:35:54 GMT",
"version": "v2"
}
] | 2016-08-31 | [
[
"Banerjee",
"Rabin",
""
],
[
"Ghosh",
"Subir",
""
],
[
"Kulkarni",
"Shailesh",
""
]
] | We have developed an action formulation for the Generalized Chaplygin Gas (GCG). The most general form for the nonrelativistic GCG action is derived consistent with the equation of state. We have also discussed a relativistic formulation for GCG by providing a detailed analysis of the Poincare algebra. |
gr-qc/0208084 | Janusz Garecki | Janusz Garecki (Institute of Physics, U. of Szczecin) | Einsteinian Strengths and Dynamical Degrees of Freedom for Alternative
Gravity Theories | 19 pages, no figures, LaTeX + RevTeX, Talk delivered at the
International Conference: "Ideas of Albert Abraham Michelson in Mathematical
Physics", Stefan Banach International Mathematical Center, August 4 - 11,
2002, Bedlevo, Poland | null | null | null | gr-qc | null | In this paper we present the results of our calculations of the Einsteinian
strengths S_E(d) and numbers dynamical degrees of freedom N_{DF}(d) for
alternative gravity theories in d >= 4 dimensions. In the first part we
consider the numbers S_E(d) and N_{DF}(d) for metric-compatible and quadratic
in curvature (or quadratic in curvature and in torsion) gravity. We show that
in the entire set of the metric-compatible quadratic gravity in d >= 4
dimensions the 2-nd order Einstein-Gauss-Bonnet theory has the smallest numbers
S_E(d) and N_{DF}(d), i.e., this quadratic theory of gravity has the strongest
field equations. From the physical point of view this theory is the best one
quadratic and metric-compatible theory of gravity in d >= 4 dimensions.
| [
{
"created": "Tue, 27 Aug 2002 14:47:41 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Garecki",
"Janusz",
"",
"Institute of Physics, U. of Szczecin"
]
] | In this paper we present the results of our calculations of the Einsteinian strengths S_E(d) and numbers dynamical degrees of freedom N_{DF}(d) for alternative gravity theories in d >= 4 dimensions. In the first part we consider the numbers S_E(d) and N_{DF}(d) for metric-compatible and quadratic in curvature (or quadratic in curvature and in torsion) gravity. We show that in the entire set of the metric-compatible quadratic gravity in d >= 4 dimensions the 2-nd order Einstein-Gauss-Bonnet theory has the smallest numbers S_E(d) and N_{DF}(d), i.e., this quadratic theory of gravity has the strongest field equations. From the physical point of view this theory is the best one quadratic and metric-compatible theory of gravity in d >= 4 dimensions. |
1810.07356 | Ernesto Contreras | Ernesto Contreras, \'Angel Rinc\'on and J. M. Ram\'irez-Velasquez | Relativistic dust accretion onto a scale--dependent polytropic black
hole | 5 pages, 2 figures | Eur. Phys. J. C (2019) 79:53 | 10.1140/epjc/s10052-019-6601-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we study steady and spherical relativistic dust accretion onto a
static and spherically symmetric scale--dependent black hole. In particular we
consider a polytropic scale--dependent black hole as a central object and
obtain that the radial velocity profile and the energy density are affected
when scale--dependence of the central object is taken into account and such a
deviation is controlled by the so called running parameters of the
scale--dependence models.
| [
{
"created": "Wed, 17 Oct 2018 02:23:37 GMT",
"version": "v1"
},
{
"created": "Thu, 18 Oct 2018 00:36:55 GMT",
"version": "v2"
}
] | 2019-04-01 | [
[
"Contreras",
"Ernesto",
""
],
[
"Rincón",
"Ángel",
""
],
[
"Ramírez-Velasquez",
"J. M.",
""
]
] | In this work we study steady and spherical relativistic dust accretion onto a static and spherically symmetric scale--dependent black hole. In particular we consider a polytropic scale--dependent black hole as a central object and obtain that the radial velocity profile and the energy density are affected when scale--dependence of the central object is taken into account and such a deviation is controlled by the so called running parameters of the scale--dependence models. |
1710.04181 | Jos\'e Andr\'e Louren\c{c}o | Jos\'e A. Louren\c{c}o, Jos\'e A. Helay\"el Neto, Wesley Spalenza | Topological Gravity on $(D,N)-$Shift Superspace Formulation | null | Adv. High Energy Phys. 2018 (2018) 2786081 | 10.1155/2018/2786081 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this contribution, we re-assess the subject of topological gravity by
following the Shift Supersymmetry formalism. The gauge-fixing of the theory
goes under the Batallin-Vilkovisky (BV) prescription based on a diagram that
contains both ghost and anti-ghost superfields, associated to the
super-vielbein and the super-Lorentz connection. We extend the formulation of
the topological gravity action to an arbitrary number of dimensions of the
shift superspace by adopting a formulation based on the gauge-fixing for
BF-type models.
| [
{
"created": "Wed, 11 Oct 2017 17:23:20 GMT",
"version": "v1"
},
{
"created": "Tue, 8 May 2018 22:47:22 GMT",
"version": "v2"
},
{
"created": "Thu, 28 Jun 2018 18:20:10 GMT",
"version": "v3"
}
] | 2018-08-09 | [
[
"Lourenço",
"José A.",
""
],
[
"Neto",
"José A. Helayël",
""
],
[
"Spalenza",
"Wesley",
""
]
] | In this contribution, we re-assess the subject of topological gravity by following the Shift Supersymmetry formalism. The gauge-fixing of the theory goes under the Batallin-Vilkovisky (BV) prescription based on a diagram that contains both ghost and anti-ghost superfields, associated to the super-vielbein and the super-Lorentz connection. We extend the formulation of the topological gravity action to an arbitrary number of dimensions of the shift superspace by adopting a formulation based on the gauge-fixing for BF-type models. |
gr-qc/9509007 | null | Giampiero Esposito | Hamiltonian Structure of a Friedmann-Robertson-Walker Universe with
Torsion | 16 pages, plain-tex, published in Nuovo Cimento B, Volume 104, pages
199-212, year 1989 | NuovoCim.B104:199-212,1989; Erratum-ibid.B106:1315,1991 | 10.1007/BF02906317 | DAMTP R 89/9 | gr-qc | null | We study a $R^{2}$ model of gravity with torsion in a closed
Friedmann-Robertson-Walker universe. The model is cast in Hamiltonian form
subtracting from the original Lagrangian the total time derivative of
$f_{K}f_{R}$, where $f_{K}$ is proportional to the trace of the extrinsic
curvature tensor, and $f_{R}$ is obtained differentiating the Lagrangian with
respect to the highest derivative. Torsion is found to lead to a primary
constraint linear in the momenta and a secondary constraint quadratic in the
momenta, and the full field equations are finally worked out in detail.
Problems to be studied for further research are the solution of these equations
and the quantization of the model. One could then try to study a new class of
quantum cosmological models with torsion.
| [
{
"created": "Wed, 6 Sep 1995 06:04:21 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Esposito",
"Giampiero",
""
]
] | We study a $R^{2}$ model of gravity with torsion in a closed Friedmann-Robertson-Walker universe. The model is cast in Hamiltonian form subtracting from the original Lagrangian the total time derivative of $f_{K}f_{R}$, where $f_{K}$ is proportional to the trace of the extrinsic curvature tensor, and $f_{R}$ is obtained differentiating the Lagrangian with respect to the highest derivative. Torsion is found to lead to a primary constraint linear in the momenta and a secondary constraint quadratic in the momenta, and the full field equations are finally worked out in detail. Problems to be studied for further research are the solution of these equations and the quantization of the model. One could then try to study a new class of quantum cosmological models with torsion. |
2403.00916 | Maarten Grothus | Maarten Grothus, V. Vilasini | Characterizing Signalling: Connections between Causal Inference and
Space-time Geometry | 24 + 24 pages, 10 figures. This work includes significantly improved
versions of initial results presented in MG's master's thesis
arXiv:2211.03593. Comments welcome! | null | null | null | gr-qc math-ph math.MP math.ST quant-ph stat.TH | http://creativecommons.org/licenses/by/4.0/ | Causality is pivotal to our understanding of the world, presenting itself in
different forms: information-theoretic and relativistic, the former linked to
the flow of information, the latter to the structure of space-time. Leveraging
a framework introduced in PRA, 106, 032204 (2022), which formally connects
these two notions in general physical theories, we study their interplay. Here,
information-theoretic causality is defined through a causal modelling approach.
First, we improve the characterization of information-theoretic signalling as
defined through so-called affects relations. Specifically, we provide
conditions for identifying redundancies in different parts of such a relation,
introducing techniques for causal inference in unfaithful causal models (where
the observable data does not "faithfully" reflect the causal dependences). In
particular, this demonstrates the possibility of causal inference using the
absence of signalling between certain nodes. Second, we define an
order-theoretic property called conicality, showing that it is satisfied for
light cones in Minkowski space-times with $d>1$ spatial dimensions but violated
for $d=1$. Finally, we study the embedding of information-theoretic causal
models in space-time without violating relativistic principles such as no
superluminal signalling (NSS). In general, we observe that constraints imposed
by NSS in a space-time and those imposed by purely information-theoretic causal
inference behave differently. We then prove a correspondence between conical
space-times and faithful causal models: in both cases, there emerges a parallel
between these two types of constraints. This indicates a connection between
informational and geometric notions of causality, and offers new insights for
studying the relations between the principles of NSS and no causal loops in
different space-time geometries and theories of information processing.
| [
{
"created": "Fri, 1 Mar 2024 19:00:45 GMT",
"version": "v1"
}
] | 2024-03-05 | [
[
"Grothus",
"Maarten",
""
],
[
"Vilasini",
"V.",
""
]
] | Causality is pivotal to our understanding of the world, presenting itself in different forms: information-theoretic and relativistic, the former linked to the flow of information, the latter to the structure of space-time. Leveraging a framework introduced in PRA, 106, 032204 (2022), which formally connects these two notions in general physical theories, we study their interplay. Here, information-theoretic causality is defined through a causal modelling approach. First, we improve the characterization of information-theoretic signalling as defined through so-called affects relations. Specifically, we provide conditions for identifying redundancies in different parts of such a relation, introducing techniques for causal inference in unfaithful causal models (where the observable data does not "faithfully" reflect the causal dependences). In particular, this demonstrates the possibility of causal inference using the absence of signalling between certain nodes. Second, we define an order-theoretic property called conicality, showing that it is satisfied for light cones in Minkowski space-times with $d>1$ spatial dimensions but violated for $d=1$. Finally, we study the embedding of information-theoretic causal models in space-time without violating relativistic principles such as no superluminal signalling (NSS). In general, we observe that constraints imposed by NSS in a space-time and those imposed by purely information-theoretic causal inference behave differently. We then prove a correspondence between conical space-times and faithful causal models: in both cases, there emerges a parallel between these two types of constraints. This indicates a connection between informational and geometric notions of causality, and offers new insights for studying the relations between the principles of NSS and no causal loops in different space-time geometries and theories of information processing. |
gr-qc/0105117 | Matthew F. Parry | Matthew Parry and Richard Easther | Inhomogeneity and Nonlinear Preheating | Talk given at Marcel Grossmann Meeting IX. 3 pages, 1 figure | null | 10.1142/9789812777386_0451 | null | gr-qc astro-ph hep-ph | null | We investigated the possibility that nonlinear gravitational effects
influence the preheating era after inflation, using numerical solutions of the
inhomogeneous Einstein field equations. We compared our results to perturbative
calculations and to solutions of the nonlinear field equations in a rigid
(unperturbed) spacetime, in order to isolate gravitational phenomena. We
confirm the broad picture of preheating obtained from the nonlinear field
equations in a rigid background, but find gravitational effects have a
measurable impact on the dynamics. The longest modes in the simulation grow
much more rapidly in the relativistic calculation than with a rigid background.
We used the Weyl tensor to quantify the departure from homogeneity in the
universe. We saw no evidence for the sort of gravitational collapse that leads
to the formation of primordial black holes.
| [
{
"created": "Wed, 30 May 2001 18:57:53 GMT",
"version": "v1"
}
] | 2017-08-23 | [
[
"Parry",
"Matthew",
""
],
[
"Easther",
"Richard",
""
]
] | We investigated the possibility that nonlinear gravitational effects influence the preheating era after inflation, using numerical solutions of the inhomogeneous Einstein field equations. We compared our results to perturbative calculations and to solutions of the nonlinear field equations in a rigid (unperturbed) spacetime, in order to isolate gravitational phenomena. We confirm the broad picture of preheating obtained from the nonlinear field equations in a rigid background, but find gravitational effects have a measurable impact on the dynamics. The longest modes in the simulation grow much more rapidly in the relativistic calculation than with a rigid background. We used the Weyl tensor to quantify the departure from homogeneity in the universe. We saw no evidence for the sort of gravitational collapse that leads to the formation of primordial black holes. |
1910.13094 | Tsuyoshi Houri | Tsuyoshi Houri, Norihiro Tanahashi, Yukinori Yasui | Hidden symmetry and the separability of the Maxwell equation on the
Wahlquist spacetime | 13 pages, 2 figures, v2: typos corrected | null | 10.1088/1361-6382/ab6e8a | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine hidden symmetry and its relation to the separability of the
Maxwell equation on the Wahlquist spacetime. After seeing that the Wahlquist
spacetime is a type-D spacetime whose repeated principal null directions are
shear-free and geodesic, we show that the spacetime admits three gauged
conformal Killing-Yano (GCKY) tensors which are in a relation with torsional
conformal Killing-Yano tensors. As a by-product, we obtain an ordinary CKY
tensor. We also show that thanks to the GCKY tensors, the Maxwell equation
reduces to three Debye equations, which are scalar-type equations, and two of
them can be solved by separation of variables.
| [
{
"created": "Tue, 29 Oct 2019 05:46:20 GMT",
"version": "v1"
},
{
"created": "Fri, 1 Nov 2019 09:07:58 GMT",
"version": "v2"
}
] | 2020-04-08 | [
[
"Houri",
"Tsuyoshi",
""
],
[
"Tanahashi",
"Norihiro",
""
],
[
"Yasui",
"Yukinori",
""
]
] | We examine hidden symmetry and its relation to the separability of the Maxwell equation on the Wahlquist spacetime. After seeing that the Wahlquist spacetime is a type-D spacetime whose repeated principal null directions are shear-free and geodesic, we show that the spacetime admits three gauged conformal Killing-Yano (GCKY) tensors which are in a relation with torsional conformal Killing-Yano tensors. As a by-product, we obtain an ordinary CKY tensor. We also show that thanks to the GCKY tensors, the Maxwell equation reduces to three Debye equations, which are scalar-type equations, and two of them can be solved by separation of variables. |
gr-qc/9312030 | Jim McCarthy | T. Damour, S. Deser and J. McCarthy | Nonsymmetric Gravity has Unacceptable Global Asymptotics | 10 pages, ADP-93-221/M20 | null | null | null | gr-qc | null | We analyze the radiative aspects of nonsymmetric gravity theory to show that,
in contrast to General Relativity, its nonstationary solutions cannot
simultaneously exhibit acceptable asymptotic behavior at both future and past
null infinity: good behavior at future null infinity is only possible through
the use of advanced potentials with concomitant unphysical behavior at past
null infinity.
| [
{
"created": "Mon, 20 Dec 1993 04:42:55 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Damour",
"T.",
""
],
[
"Deser",
"S.",
""
],
[
"McCarthy",
"J.",
""
]
] | We analyze the radiative aspects of nonsymmetric gravity theory to show that, in contrast to General Relativity, its nonstationary solutions cannot simultaneously exhibit acceptable asymptotic behavior at both future and past null infinity: good behavior at future null infinity is only possible through the use of advanced potentials with concomitant unphysical behavior at past null infinity. |
1708.04761 | Dao-Jun Liu | Yang Huang, Dao-Jun Liu, Xiang-hua Zhai and Xin-zhou Li | Massive charged Dirac fields around Reissner-Nordstr\"om black holes:
quasibound states and long-lived modes | 9 pages, 5 figures, accepted for publication in PRD | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The behavior of a massive charged test Dirac field in the background of a
Reissner-Nordstr\"om black hole is investigated. Especially, we obtain the
frequencies of quasibound states by solving the Dirac equation numerically both
in time and frequency domain. Our results suggest that although the absence of
superradiance excludes the existence of stationary solutions for massive Dirac
fields, it is still possible to find arbitrarily long-lived solutions.
| [
{
"created": "Wed, 16 Aug 2017 03:38:57 GMT",
"version": "v1"
}
] | 2017-08-17 | [
[
"Huang",
"Yang",
""
],
[
"Liu",
"Dao-Jun",
""
],
[
"Zhai",
"Xiang-hua",
""
],
[
"Li",
"Xin-zhou",
""
]
] | The behavior of a massive charged test Dirac field in the background of a Reissner-Nordstr\"om black hole is investigated. Especially, we obtain the frequencies of quasibound states by solving the Dirac equation numerically both in time and frequency domain. Our results suggest that although the absence of superradiance excludes the existence of stationary solutions for massive Dirac fields, it is still possible to find arbitrarily long-lived solutions. |
1403.1984 | Genly Le\'on | Genly Leon | Phase Space of Anisotropic $R^n$ Cosmologies | Prepared for the First Caribbean Symposium on Nuclear and
Astroparticle Physics - STARS2011 | Int. J. Mod. Phys. E, 20, 19 (2011) | 10.1142/S0218301311040037 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct general anisotropic cosmological scenarios governed by an
$f(R)=R^n$ gravitational sector. Focusing then on some specific geometries, and
modelling the matter content as a perfect fluid, we perform a phase-space
analysis. We analyze the possibility of accelerating expansion at late times,
and additionally, we determine conditions for the parameter $n$ for the
existence of phantom behavior, contracting solutions as well as of cyclic
cosmology. Furthermore, we analyze if the universe evolves towards the future
isotropization without relying on a cosmic no-hair theorem. Our results
indicate that anisotropic geometries in modified gravitational frameworks
present radically different cosmological behaviors compared to the simple
isotropic scenarios.
| [
{
"created": "Sat, 8 Mar 2014 16:28:28 GMT",
"version": "v1"
}
] | 2014-03-11 | [
[
"Leon",
"Genly",
""
]
] | We construct general anisotropic cosmological scenarios governed by an $f(R)=R^n$ gravitational sector. Focusing then on some specific geometries, and modelling the matter content as a perfect fluid, we perform a phase-space analysis. We analyze the possibility of accelerating expansion at late times, and additionally, we determine conditions for the parameter $n$ for the existence of phantom behavior, contracting solutions as well as of cyclic cosmology. Furthermore, we analyze if the universe evolves towards the future isotropization without relying on a cosmic no-hair theorem. Our results indicate that anisotropic geometries in modified gravitational frameworks present radically different cosmological behaviors compared to the simple isotropic scenarios. |
1702.05716 | Sung-Jin Oh | Jonathan Luk, Sung-Jin Oh | Strong cosmic censorship in spherical symmetry for two-ended
asymptotically flat initial data II. The exterior of the black hole region | 132 pages, 10 figures; minor revisions; version accepted for
publication | null | null | null | gr-qc math-ph math.AP math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is the second and last paper of a two-part series in which we prove the
$C^2$-formulation of the strong cosmic censorship conjecture for the
Einstein-Maxwell-(real)-scalar-field system in spherical symmetry for two-ended
asymptotically flat data. In the first paper (arXiv:1702.05715), we showed that
the maximal globally hyperbolic future development of an admissible
asymptotically flat Cauchy initial data set is $C^2$-future-inextendible
provided that an $L^2$-averaged (inverse) polynomial lower bound for the
derivative of the scalar field holds along each horizon. In this paper, we show
that this lower bound is indeed satisfied for solutions arising from a generic
set of Cauchy initial data. Roughly speaking, the generic set is open with
respect to a (weighted) $C^1$ topology and is dense with respect to a
(weighted) $C^\infty$ topology. The proof of the theorem is based on extensions
of the ideas in our previous work on the linear instability of
Reissner-Nordstr\"om Cauchy horizon, as well as a new large data asymptotic
stability result which gives good decay estimates for the difference of the
radiation fields for small perturbations of an arbitrary solution.
| [
{
"created": "Sun, 19 Feb 2017 08:20:17 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Feb 2019 03:51:25 GMT",
"version": "v2"
}
] | 2019-02-25 | [
[
"Luk",
"Jonathan",
""
],
[
"Oh",
"Sung-Jin",
""
]
] | This is the second and last paper of a two-part series in which we prove the $C^2$-formulation of the strong cosmic censorship conjecture for the Einstein-Maxwell-(real)-scalar-field system in spherical symmetry for two-ended asymptotically flat data. In the first paper (arXiv:1702.05715), we showed that the maximal globally hyperbolic future development of an admissible asymptotically flat Cauchy initial data set is $C^2$-future-inextendible provided that an $L^2$-averaged (inverse) polynomial lower bound for the derivative of the scalar field holds along each horizon. In this paper, we show that this lower bound is indeed satisfied for solutions arising from a generic set of Cauchy initial data. Roughly speaking, the generic set is open with respect to a (weighted) $C^1$ topology and is dense with respect to a (weighted) $C^\infty$ topology. The proof of the theorem is based on extensions of the ideas in our previous work on the linear instability of Reissner-Nordstr\"om Cauchy horizon, as well as a new large data asymptotic stability result which gives good decay estimates for the difference of the radiation fields for small perturbations of an arbitrary solution. |
0908.1693 | Mohammad Sami | I. Thongkool, M. Sami, S. Rai Choudhury | How delicate are the $f(R)$ gravity models with disappearing
cosmological constant? | 5 pages and no figures, minor clarification added, final version to
appear in PRD | Phys.Rev.D80:127501,2009 | 10.1103/PhysRevD.80.127501 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider stability of spherically symmetric solutions in $f(R)$ gravity
model proposed by Starobinsky. We find that the model suffers from a severe
fine tuning problem when applied to compact objects like neutron stars. The
problem can be remedied by introducing a cut off on the mass of the scalar
degree of freedom present in the model. A new mass scale associated with
neutron stars density is then required for the stabilities of $f(R)$ gravity
solutions inside relativistic stars.
| [
{
"created": "Wed, 12 Aug 2009 12:45:47 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Nov 2009 04:50:20 GMT",
"version": "v2"
}
] | 2010-03-25 | [
[
"Thongkool",
"I.",
""
],
[
"Sami",
"M.",
""
],
[
"Choudhury",
"S. Rai",
""
]
] | We consider stability of spherically symmetric solutions in $f(R)$ gravity model proposed by Starobinsky. We find that the model suffers from a severe fine tuning problem when applied to compact objects like neutron stars. The problem can be remedied by introducing a cut off on the mass of the scalar degree of freedom present in the model. A new mass scale associated with neutron stars density is then required for the stabilities of $f(R)$ gravity solutions inside relativistic stars. |
2402.06114 | Lehel Csillag | Lehel Csillag, Tiberiu Harko | Semi-Symmetric Metric Gravity: from the Friedmann-Schouten geometry with
torsion to dynamical dark energy models | 17 pages, 10 figures, major revision; new Section and references
added | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present paper we introduce a geometric generalization of standard
general relativity, based on a geometry initially introduced by Friedmann and
Schouten in 1924, through the notion of a semi-symmetric connection. The
semi-symmetric connection is a particular connection that extends the
Levi-Civita one, by allowing for the presence of torsion. While the
mathematical landscape of the semi-symmetric metric connections is
well-explored, their physical implications remain to be investigated. After
presenting in detail the differential geometric aspects of the geometries with
semi-symmetric metric connection, we formulate the Einstein field equations,
which contain additional terms induced by the presence of the specific form of
torsion we are studying. We consider the cosmological applications of the
theory by deriving the generalized Friedmann equations, which also include some
supplementary terms as compared to their general relativistic counterparts and
can be interpreted as a geometric type dark energy. To evaluate the proposed
theory, we consider three cosmological models - the first with constant
effective density and pressure, the second with the dark energy satisfying a
linear equation of state, and a third one one with a polytropic equation of
state. We compare the predictions of the semi-symmetric metric gravitational
theory with the observational data for the Hubble function, and with the
predictions of the standard $\Lambda$CDM model. Our findings indicate that the
semi-symmetric metric cosmological models give a good description of the
observational data, and for certain values of the model parameters, they can
reproduce almost exactly the predictions of the $\Lambda$CDM paradigm.
Consequently, Friedmann's initially proposed geometry emerges as a credible
alternative to standard general relativity, in which dark energy has a purely
geometric origin.
| [
{
"created": "Fri, 9 Feb 2024 00:37:28 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Feb 2024 20:41:04 GMT",
"version": "v2"
},
{
"created": "Thu, 4 Apr 2024 13:44:22 GMT",
"version": "v3"
}
] | 2024-04-05 | [
[
"Csillag",
"Lehel",
""
],
[
"Harko",
"Tiberiu",
""
]
] | In the present paper we introduce a geometric generalization of standard general relativity, based on a geometry initially introduced by Friedmann and Schouten in 1924, through the notion of a semi-symmetric connection. The semi-symmetric connection is a particular connection that extends the Levi-Civita one, by allowing for the presence of torsion. While the mathematical landscape of the semi-symmetric metric connections is well-explored, their physical implications remain to be investigated. After presenting in detail the differential geometric aspects of the geometries with semi-symmetric metric connection, we formulate the Einstein field equations, which contain additional terms induced by the presence of the specific form of torsion we are studying. We consider the cosmological applications of the theory by deriving the generalized Friedmann equations, which also include some supplementary terms as compared to their general relativistic counterparts and can be interpreted as a geometric type dark energy. To evaluate the proposed theory, we consider three cosmological models - the first with constant effective density and pressure, the second with the dark energy satisfying a linear equation of state, and a third one one with a polytropic equation of state. We compare the predictions of the semi-symmetric metric gravitational theory with the observational data for the Hubble function, and with the predictions of the standard $\Lambda$CDM model. Our findings indicate that the semi-symmetric metric cosmological models give a good description of the observational data, and for certain values of the model parameters, they can reproduce almost exactly the predictions of the $\Lambda$CDM paradigm. Consequently, Friedmann's initially proposed geometry emerges as a credible alternative to standard general relativity, in which dark energy has a purely geometric origin. |
1101.2634 | Lorenzo Iorio | Lorenzo Iorio | Constraints on the location of a putative distant massive body in the
Solar System from recent planetary data | LaTex2e, 21 pages. 1 figure, 1 table. Uncited references deleted.
Expired link removed and replaced with published references. At press in
Celestial Mechanics and Dynamical Astronomy | Celest.Mech.Dyn.Astron.112:117-130,2012 | 10.1007/s10569-011-9386-7 | null | gr-qc astro-ph.EP physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analytically work out the long-term variations caused on the motion of a
planet orbiting a star by a very distant, pointlike massive object X. Apart
from the semi-major axis a, all the other Keplerian osculating orbital elements
experience long-term variations which are complicated functions of the orbital
configurations of both the planet itself and of X. We infer constraints on the
minimum distance d_X at which X may exist by comparing our prediction of the
long-term variation of the longitude of the perihelion \varpi to the latest
empirical determinations of the corrections \Delta\dot\varpi to the standard
Newtonian/Einsteinian secular precessions of several solar system planets
recently estimated by independent teams of astronomers. We obtain the following
approximate lower bounds on dX for the assumed masses of X quoted in brackets:
150 - 200 au (m_Mars), 250 - 450 au (0.7 m_Earth), 3500 - 4500 au (4 m_Jup).
| [
{
"created": "Thu, 13 Jan 2011 19:07:43 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Jan 2011 15:46:13 GMT",
"version": "v2"
},
{
"created": "Wed, 19 Jan 2011 19:30:13 GMT",
"version": "v3"
},
{
"created": "Fri, 19 Aug 2011 18:47:19 GMT",
"version": "v4"
},
{
"created": "Thu, 20 Oct 2011 13:35:28 GMT",
"version": "v5"
},
{
"created": "Wed, 14 Dec 2011 15:30:44 GMT",
"version": "v6"
}
] | 2015-03-17 | [
[
"Iorio",
"Lorenzo",
""
]
] | We analytically work out the long-term variations caused on the motion of a planet orbiting a star by a very distant, pointlike massive object X. Apart from the semi-major axis a, all the other Keplerian osculating orbital elements experience long-term variations which are complicated functions of the orbital configurations of both the planet itself and of X. We infer constraints on the minimum distance d_X at which X may exist by comparing our prediction of the long-term variation of the longitude of the perihelion \varpi to the latest empirical determinations of the corrections \Delta\dot\varpi to the standard Newtonian/Einsteinian secular precessions of several solar system planets recently estimated by independent teams of astronomers. We obtain the following approximate lower bounds on dX for the assumed masses of X quoted in brackets: 150 - 200 au (m_Mars), 250 - 450 au (0.7 m_Earth), 3500 - 4500 au (4 m_Jup). |
2112.05651 | Philip Lynch | Philip Lynch, Maarten van de Meent and Niels Warburton | Eccentric self-forced inspirals into a rotating black hole | 46 pages, 12 figures | Class. Quantum Grav. 39:145004 (2022) | 10.1088/1361-6382/ac7507 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We develop the first model for extreme mass-ratio inspirals (EMRIs) into a
rotating massive black hole driven by the gravitational self-force. Our model
is based on an action angle formulation of the method of osculating geodesics
for eccentric, equatorial (i.e., spin-aligned) motion in Kerr spacetime. The
forcing terms are provided by an efficient spectral interpolation of the
first-order gravitational self-force in the outgoing radiation gauge. We apply
a near-identity (averaging) transformation to eliminate all dependence of the
orbital phases from the equations of motion, while maintaining all secular
effects of the first-order gravitational self-force at post-adiabatic order.
This implies that the model can be evolved without having to resolve all
$\mathcal{O}(10^5)$ orbit cycles of an EMRI, yielding an inspiral model that
can be evaluated in less than a second for any mass-ratio. In the case of a
non-rotating central black hole, we compare inspirals evolved using self-force
data computed in the Lorenz and radiation gauges. We find that the two gauges
generally produce differing inspirals with a deviation of comparable magnitude
to the conservative self-force correction. This emphasizes the need for
including the (currently unknown) dissipative second order self-force to obtain
gauge independent, post-adiabatic waveforms.
| [
{
"created": "Fri, 10 Dec 2021 16:28:02 GMT",
"version": "v1"
},
{
"created": "Wed, 3 Aug 2022 16:09:03 GMT",
"version": "v2"
}
] | 2022-08-04 | [
[
"Lynch",
"Philip",
""
],
[
"van de Meent",
"Maarten",
""
],
[
"Warburton",
"Niels",
""
]
] | We develop the first model for extreme mass-ratio inspirals (EMRIs) into a rotating massive black hole driven by the gravitational self-force. Our model is based on an action angle formulation of the method of osculating geodesics for eccentric, equatorial (i.e., spin-aligned) motion in Kerr spacetime. The forcing terms are provided by an efficient spectral interpolation of the first-order gravitational self-force in the outgoing radiation gauge. We apply a near-identity (averaging) transformation to eliminate all dependence of the orbital phases from the equations of motion, while maintaining all secular effects of the first-order gravitational self-force at post-adiabatic order. This implies that the model can be evolved without having to resolve all $\mathcal{O}(10^5)$ orbit cycles of an EMRI, yielding an inspiral model that can be evaluated in less than a second for any mass-ratio. In the case of a non-rotating central black hole, we compare inspirals evolved using self-force data computed in the Lorenz and radiation gauges. We find that the two gauges generally produce differing inspirals with a deviation of comparable magnitude to the conservative self-force correction. This emphasizes the need for including the (currently unknown) dissipative second order self-force to obtain gauge independent, post-adiabatic waveforms. |
0705.2987 | Helge Mueller-Ebhardt | Henning Rehbein, Helge Mueller-Ebhardt, Kentaro Somiya, Chao Li, Roman
Schnabel, Karsten Danzmann, Yanbei Chen | Local readout enhancement for detuned signal-recycling interferometers | null | Phys.Rev.D76:062002,2007 | 10.1103/PhysRevD.76.062002 | null | gr-qc | null | Motivated by the optical-bar scheme of Braginsky, Gorodetsky and Khalili, we
propose to add to a high power detuned signal-recycling interferometer a local
readout scheme which measures the motion of the arm-cavity front mirror. At low
frequencies this mirror moves together with the arm-cavity end mirror, under
the influence of gravitational waves. This scheme improves the low-frequency
quantum-noise-limited sensitivity of optical-spring interferometers
significantly and can be considered as a incorporation of the optical-bar
scheme into currently planned second-generation interferometers. On the other
hand it can be regarded as an extension of the optical bar scheme. Taking
compact-binary inspiral signals as an example, we illustrate how this scheme
can be used to improve the sensitivity of the planned Advanced LIGO
interferometer, in various scenarios, using a realistic classical-noise budget.
We also discuss how this scheme can be implemented in Advanced LIGO with
relative ease.
| [
{
"created": "Mon, 21 May 2007 14:33:59 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Jun 2007 12:56:49 GMT",
"version": "v2"
},
{
"created": "Wed, 22 Aug 2007 15:32:48 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Rehbein",
"Henning",
""
],
[
"Mueller-Ebhardt",
"Helge",
""
],
[
"Somiya",
"Kentaro",
""
],
[
"Li",
"Chao",
""
],
[
"Schnabel",
"Roman",
""
],
[
"Danzmann",
"Karsten",
""
],
[
"Chen",
"Yanbei",
""
]
] | Motivated by the optical-bar scheme of Braginsky, Gorodetsky and Khalili, we propose to add to a high power detuned signal-recycling interferometer a local readout scheme which measures the motion of the arm-cavity front mirror. At low frequencies this mirror moves together with the arm-cavity end mirror, under the influence of gravitational waves. This scheme improves the low-frequency quantum-noise-limited sensitivity of optical-spring interferometers significantly and can be considered as a incorporation of the optical-bar scheme into currently planned second-generation interferometers. On the other hand it can be regarded as an extension of the optical bar scheme. Taking compact-binary inspiral signals as an example, we illustrate how this scheme can be used to improve the sensitivity of the planned Advanced LIGO interferometer, in various scenarios, using a realistic classical-noise budget. We also discuss how this scheme can be implemented in Advanced LIGO with relative ease. |
gr-qc/0310116 | Scott Noble | Scott C. Noble (University of Illinois at Urbana-Champaign) | A Numerical Study of Relativistic Fluid Collapse | 228 pages, 66 Postscript figures, Ph.D. Thesis, the University of
Texa s at Austin, uses utdiss2.sty v5 | null | null | null | gr-qc astro-ph | null | We investigate the dynamics of self-gravitating, spherically-symmetric
distributions of fluid through numerical means. In particular, systems
involving neutron star models driven far from equilibrium in the strong-field
regime of general relativity are studied. Hydrostatic solutions of Einstein's
equations using a stiff, polytropic equation of state are used for the stellar
models. Many of the scenarios we examine involve highly-relativistic flows that
require improvements upon previously published numerical methods to simulate.
Here our particular focus is on the physical behavior of the coupled
fluid-gravitational system at the threshold of black hole formation--so-called
black hole critical phenomena. To investigate such phenomena starting from
conditions representing stable stars, we must drive the star far from its
initial stable configuration. We use one of two different mechanisms to do
this: setting the initial velocity profile of the star to be in-going, or
collapsing a shell of massless scalar field onto the star. Both of these
approaches give rise to a large range of dynamical scenarios that the star may
follow. These scenarios have been extensively surveyed by using different
initial star solutions, and by varying either the magnitude of the velocity
profile or the amplitude of the scalar field pulse. In addition to illuminating
the critical phenomena associated with the fluid collapse, the resulting phase
diagram of possible outcomes provides an approximate picture of the stability
of neutron stars to large, external perturbations that may occur in nature.
| [
{
"created": "Tue, 28 Oct 2003 00:53:36 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Noble",
"Scott C.",
"",
"University of Illinois at Urbana-Champaign"
]
] | We investigate the dynamics of self-gravitating, spherically-symmetric distributions of fluid through numerical means. In particular, systems involving neutron star models driven far from equilibrium in the strong-field regime of general relativity are studied. Hydrostatic solutions of Einstein's equations using a stiff, polytropic equation of state are used for the stellar models. Many of the scenarios we examine involve highly-relativistic flows that require improvements upon previously published numerical methods to simulate. Here our particular focus is on the physical behavior of the coupled fluid-gravitational system at the threshold of black hole formation--so-called black hole critical phenomena. To investigate such phenomena starting from conditions representing stable stars, we must drive the star far from its initial stable configuration. We use one of two different mechanisms to do this: setting the initial velocity profile of the star to be in-going, or collapsing a shell of massless scalar field onto the star. Both of these approaches give rise to a large range of dynamical scenarios that the star may follow. These scenarios have been extensively surveyed by using different initial star solutions, and by varying either the magnitude of the velocity profile or the amplitude of the scalar field pulse. In addition to illuminating the critical phenomena associated with the fluid collapse, the resulting phase diagram of possible outcomes provides an approximate picture of the stability of neutron stars to large, external perturbations that may occur in nature. |
0804.0357 | Patricio S. Letelier | Valeria M. Rosa and Patricio S. Letelier | A Comment on Bonnor-Steadman Closed Timelike Curves | 2 pages, RevTex, minor corrections | Gen.Rel.Grav.41:571-573,2009 | 10.1007/s10714-008-0687-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The existence and stability closed timelike curves in a Bonnor-Ward spacetime
without torsion line singularities is shown by exhibiting particular examples.
| [
{
"created": "Wed, 2 Apr 2008 14:13:58 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Apr 2008 13:35:51 GMT",
"version": "v2"
}
] | 2009-03-12 | [
[
"Rosa",
"Valeria M.",
""
],
[
"Letelier",
"Patricio S.",
""
]
] | The existence and stability closed timelike curves in a Bonnor-Ward spacetime without torsion line singularities is shown by exhibiting particular examples. |
gr-qc/9906107 | Ruth A. W. Gregory | Caroline Santos and Ruth Gregory | Vortices and black holes in dilatonic gravity | 16 pages revtex, published version | Phys. Rev. D 61, 024006 (1999) | 10.1103/PhysRevD.61.024006 | DTP/99/49 | gr-qc hep-ph hep-th | null | We study analytically black holes pierced by a thin vortex in dilatonic
gravity for an arbitrary coupling of the vortex to the dilaton in an arbitrary
frame. We show that the horizon of the charged black hole supports the
long-range fields of the Nielsen-Olesen vortex that can be considered as black
hole hair for both massive and massless dilatons. We also prove that extremal
black holes exhibit a flux expulsion phenomenon for a sufficiently thick
vortex. We consider the gravitational back-reaction of the thin vortex on the
spacetime geometry and dilaton, and discuss under what circumstances the vortex
can be used to smooth out the singularities in the dilatonic C-metrics. The
effect of the vortex on the massless dilaton is to generate an additional
dilaton flux across the horizon.
| [
{
"created": "Fri, 25 Jun 1999 19:12:56 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Apr 2000 14:08:33 GMT",
"version": "v2"
}
] | 2016-08-25 | [
[
"Santos",
"Caroline",
""
],
[
"Gregory",
"Ruth",
""
]
] | We study analytically black holes pierced by a thin vortex in dilatonic gravity for an arbitrary coupling of the vortex to the dilaton in an arbitrary frame. We show that the horizon of the charged black hole supports the long-range fields of the Nielsen-Olesen vortex that can be considered as black hole hair for both massive and massless dilatons. We also prove that extremal black holes exhibit a flux expulsion phenomenon for a sufficiently thick vortex. We consider the gravitational back-reaction of the thin vortex on the spacetime geometry and dilaton, and discuss under what circumstances the vortex can be used to smooth out the singularities in the dilatonic C-metrics. The effect of the vortex on the massless dilaton is to generate an additional dilaton flux across the horizon. |
0905.0661 | Aharon Davidson | Aharon Davidson and Shimon Rubin | Zero Cosmological Constant from Normalized General Relativity | 5 PRD pages; | Class.Quant.Grav.26:235019,2009 | 10.1088/0264-9381/26/23/235019 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Normalizing the Einstein-Hilbert action by the volume functional makes the
theory invariant under constant shifts in the Lagrangian. The associated field
equations then resemble unimodular gravity whose otherwise arbitrary
cosmological constant is now determined as a Machian universal average. We
prove that an empty space-time is necessarily Ricci tensor flat, and
demonstrate the vanishing of the cosmological constant within the scalar field
paradigm. The cosmological analysis, carried out at the mini-superspace level,
reveals a vanishing cosmological constant for a Universe which cannot be closed
as long as gravity is attractive. Finally, we give an example of a normalized
theory of gravity which does give rise to a non-zero cosmological constant.
| [
{
"created": "Tue, 5 May 2009 18:08:30 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Jul 2009 12:45:18 GMT",
"version": "v2"
},
{
"created": "Wed, 14 Oct 2009 08:42:56 GMT",
"version": "v3"
}
] | 2017-04-06 | [
[
"Davidson",
"Aharon",
""
],
[
"Rubin",
"Shimon",
""
]
] | Normalizing the Einstein-Hilbert action by the volume functional makes the theory invariant under constant shifts in the Lagrangian. The associated field equations then resemble unimodular gravity whose otherwise arbitrary cosmological constant is now determined as a Machian universal average. We prove that an empty space-time is necessarily Ricci tensor flat, and demonstrate the vanishing of the cosmological constant within the scalar field paradigm. The cosmological analysis, carried out at the mini-superspace level, reveals a vanishing cosmological constant for a Universe which cannot be closed as long as gravity is attractive. Finally, we give an example of a normalized theory of gravity which does give rise to a non-zero cosmological constant. |
0911.1890 | Xin Li | X. Li and Z. Chang | Kinematics in Randers-Finsler geometry and secular increase of the
astronomical unit | 10 pages, 2 tables | null | 10.1088/1674-1137/35/10/005 | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/3.0/ | Kinematics in Finsler space is investigated. It is showed that the result
based on the kinematics with a special Finsler structure is in good agreement
with the reported value of secular trend in the astronomical unit, $d{\rm
AU}/dt=15\pm4[{\rm m/century}]$. The space deformation parameter $\lambda$ in
this special structure is very small with scale of $10^{-6}$ and should be a
constant. This fact is consistent with the reported value of an anomalous
secular eccentricity variation of the Moon's orbit.
| [
{
"created": "Tue, 10 Nov 2009 11:52:38 GMT",
"version": "v1"
}
] | 2015-05-14 | [
[
"Li",
"X.",
""
],
[
"Chang",
"Z.",
""
]
] | Kinematics in Finsler space is investigated. It is showed that the result based on the kinematics with a special Finsler structure is in good agreement with the reported value of secular trend in the astronomical unit, $d{\rm AU}/dt=15\pm4[{\rm m/century}]$. The space deformation parameter $\lambda$ in this special structure is very small with scale of $10^{-6}$ and should be a constant. This fact is consistent with the reported value of an anomalous secular eccentricity variation of the Moon's orbit. |
gr-qc/9701014 | Ruth A. W. Gregory | Ruth Gregory and Caroline Santos | Cosmic strings in dilaton gravity | 24 pages plain TEX, 4 figures -- references amended, some additional
comments added, version to appear in journal | Phys.Rev.D56:1194-1203,1997 | 10.1103/PhysRevD.56.1194 | DTP/97/1 | gr-qc astro-ph hep-th | null | We examine the metric of an isolated self-gravitating abelian-Higgs vortex in
dilatonic gravity for arbitrary coupling of the vortex fields to the dilaton.
We look for solutions in both massless and massive dilaton gravity. We compare
our results to existing metrics for strings in Einstein and Jordan-Brans-Dicke
theory. We explore the generalization of Bogomolnyi arguments for our vortices
and comment on the effects on test particles.
| [
{
"created": "Thu, 9 Jan 1997 17:39:20 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Jun 1997 13:17:12 GMT",
"version": "v2"
}
] | 2011-09-09 | [
[
"Gregory",
"Ruth",
""
],
[
"Santos",
"Caroline",
""
]
] | We examine the metric of an isolated self-gravitating abelian-Higgs vortex in dilatonic gravity for arbitrary coupling of the vortex fields to the dilaton. We look for solutions in both massless and massive dilaton gravity. We compare our results to existing metrics for strings in Einstein and Jordan-Brans-Dicke theory. We explore the generalization of Bogomolnyi arguments for our vortices and comment on the effects on test particles. |
gr-qc/9711088 | Kostas Kokkotas | Nils Andersson (Washington University) and Kostas D. Kokkotas
(Aristotle University of Thessaloniki) | Towards gravitational-wave asteroseismology | 11 pages, 8 figures, mn.sty | Mon.Not.Roy.Astron.Soc.299:1059-1068,1998 | 10.1046/j.1365-8711.1998.01840.x | AUTH-GRAV-97-03 | gr-qc astro-ph | null | We present new results for pulsating neutron stars. We have calculated the
eigenfrequencies of the modes that one would expect to be the most important
gravitational-wave sources: the fundamental fluid f-mode, the first pressure
p-mode and the first gravitational-wave w-mode, for twelve realistic equations
of state. From this numerical data we have inferred a set of ``empirical
relations'' between the mode-frequencies and the parameters of the star (the
radius R and the mass M). Some of these relation prove to be surprisingly
robust, and we show how they can be used to extract the details of the star
(radius, mass, eos) from observed modes with errors no larger than a few
percent.
| [
{
"created": "Fri, 28 Nov 1997 15:45:02 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Andersson",
"Nils",
"",
"Washington University"
],
[
"Kokkotas",
"Kostas D.",
"",
"Aristotle University of Thessaloniki"
]
] | We present new results for pulsating neutron stars. We have calculated the eigenfrequencies of the modes that one would expect to be the most important gravitational-wave sources: the fundamental fluid f-mode, the first pressure p-mode and the first gravitational-wave w-mode, for twelve realistic equations of state. From this numerical data we have inferred a set of ``empirical relations'' between the mode-frequencies and the parameters of the star (the radius R and the mass M). Some of these relation prove to be surprisingly robust, and we show how they can be used to extract the details of the star (radius, mass, eos) from observed modes with errors no larger than a few percent. |
2404.00867 | Paul Steinhardt | Anna Ijjas, Paul J. Steinhardt, David Garfinkle and William G. Cook | Smoothing and flattening the universe through slow contraction versus
inflation | 18 pages, 6 figures, 1 table | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a systematic study, we use an equivalent pair of improved numerical
relativity codes based on a tetrad-formulation of the classical Einstein-scalar
field equations to examine whether slow contraction or inflation (or both) can
resolve the homogeneity, isotropy and flatness problems. Our finding, based on
a set of gauge/frame invariant diagnostics, is that slow contraction robustly
and rapidly smooths and flattens spacetime beginning from initial conditions
that are outside the perturbative regime of the flat Friedmann-Robertson-Walker
metric, whereas inflation fails these tests. We present new numerical evidence
supporting the conjecture that the combination of ultralocal evolution and an
effective equation-of-state with pressure much greater than energy density is
the key to having robust and rapid smoothing. The opposite of ultralocality
occurs in expanding spacetimes, which is the leading obstruction to smoothing
following a big bang.
| [
{
"created": "Mon, 1 Apr 2024 02:26:28 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Apr 2024 11:14:36 GMT",
"version": "v2"
}
] | 2024-04-03 | [
[
"Ijjas",
"Anna",
""
],
[
"Steinhardt",
"Paul J.",
""
],
[
"Garfinkle",
"David",
""
],
[
"Cook",
"William G.",
""
]
] | In a systematic study, we use an equivalent pair of improved numerical relativity codes based on a tetrad-formulation of the classical Einstein-scalar field equations to examine whether slow contraction or inflation (or both) can resolve the homogeneity, isotropy and flatness problems. Our finding, based on a set of gauge/frame invariant diagnostics, is that slow contraction robustly and rapidly smooths and flattens spacetime beginning from initial conditions that are outside the perturbative regime of the flat Friedmann-Robertson-Walker metric, whereas inflation fails these tests. We present new numerical evidence supporting the conjecture that the combination of ultralocal evolution and an effective equation-of-state with pressure much greater than energy density is the key to having robust and rapid smoothing. The opposite of ultralocality occurs in expanding spacetimes, which is the leading obstruction to smoothing following a big bang. |
1904.00260 | Daniele Vernieri | In\^es Terrucha, Daniele Vernieri, Jos\'e P. S. Lemos | Covariant action for bouncing cosmologies in modified Gauss-Bonnet
gravity | 8 pages | Annals of Physics 404 (2019) 39 | 10.1016/j.aop.2019.02.010 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cyclic universes with bouncing solutions are candidates for solving the big
bang initial singularity problem. Here we seek bouncing solutions in a modified
Gauss-Bonnet gravity theory, of the type $R+f(G)$, where $R$ is the Ricci
scalar, $G$ is the Gauss-Bonnet term, and $f$ some function of it. In finding
such a bouncing solution we resort to a technique that reduces the order of the
differential equations of the $R+f(G)$ theory to second order equations. As
general relativity is a theory whose equations are of second order, this order
reduction technique enables one to find solutions which are perturbatively
close to general relativity. We also build the covariant action of the order
reduced theory.
| [
{
"created": "Sat, 30 Mar 2019 17:37:06 GMT",
"version": "v1"
}
] | 2019-04-02 | [
[
"Terrucha",
"Inês",
""
],
[
"Vernieri",
"Daniele",
""
],
[
"Lemos",
"José P. S.",
""
]
] | Cyclic universes with bouncing solutions are candidates for solving the big bang initial singularity problem. Here we seek bouncing solutions in a modified Gauss-Bonnet gravity theory, of the type $R+f(G)$, where $R$ is the Ricci scalar, $G$ is the Gauss-Bonnet term, and $f$ some function of it. In finding such a bouncing solution we resort to a technique that reduces the order of the differential equations of the $R+f(G)$ theory to second order equations. As general relativity is a theory whose equations are of second order, this order reduction technique enables one to find solutions which are perturbatively close to general relativity. We also build the covariant action of the order reduced theory. |
2008.08704 | Tao Zhu | Tao Zhu and Anzhong Wang | Observational tests of the self-dual spacetime in loop quantum gravity | 9 pages, 1 table; version to appear in Phys. Rev. D | Phys. Rev. D 102, 124042 (2020) | 10.1103/PhysRevD.102.124042 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The self-dual spacetime was derived from the mini-superspace approach, based
on the polymerization quantization procedure in loop quantum gravity (LQG). Its
deviation from the Schwarzschild spacetime is characterized by the polymeric
function $P$, purely due to the geometric quantum effects from LQG. In this
paper, we consider the observational constraints imposed on $P$ by using the
solar system experiments and observations. For this purpose, we calculate in
detail the effects of $P$ on astronomical observations conducted in the Solar
system, including the deflection angle of light by the Sun, gravitational time
delay, perihelion advance, and geodetic precession. The observational
constraints are derived by confronting the theoretical predictions with the
most recent observations. Among these constraints, we find that the tightest
one comes from the measurement of the gravitational time delay by the Cassini
mission, which yields $0<P<5.5\times 10^{-6}$. In addition, we also discuss the
potential constraint that can be obtained in the near future by the joint
European-Japanese BepiColombo project and show that it could significantly
improve the current constraints.
| [
{
"created": "Wed, 19 Aug 2020 23:37:15 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Dec 2020 02:38:29 GMT",
"version": "v2"
}
] | 2021-01-04 | [
[
"Zhu",
"Tao",
""
],
[
"Wang",
"Anzhong",
""
]
] | The self-dual spacetime was derived from the mini-superspace approach, based on the polymerization quantization procedure in loop quantum gravity (LQG). Its deviation from the Schwarzschild spacetime is characterized by the polymeric function $P$, purely due to the geometric quantum effects from LQG. In this paper, we consider the observational constraints imposed on $P$ by using the solar system experiments and observations. For this purpose, we calculate in detail the effects of $P$ on astronomical observations conducted in the Solar system, including the deflection angle of light by the Sun, gravitational time delay, perihelion advance, and geodetic precession. The observational constraints are derived by confronting the theoretical predictions with the most recent observations. Among these constraints, we find that the tightest one comes from the measurement of the gravitational time delay by the Cassini mission, which yields $0<P<5.5\times 10^{-6}$. In addition, we also discuss the potential constraint that can be obtained in the near future by the joint European-Japanese BepiColombo project and show that it could significantly improve the current constraints. |
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