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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2304.12126 | Yu Shi | Dawei Wu, Shan-Chang Tang, Yu Shi | Birth and death of entanglement between two accelerating Unruh-DeWitt
detectors coupled with a scalar field | 25 pages | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We consider two accelerating Unruh-DeWitt detectors coupled linearly or
quadratically with a scalar field. We show that entanglement can be created by
acceleration, and is divergent only when the two detectors coincide. For linear
coupling, entanglment decreases monotonically with the increase of
acceleration. For quadratic coupling, entanglement behaves non-monotonically.
| [
{
"created": "Mon, 24 Apr 2023 14:30:33 GMT",
"version": "v1"
}
] | 2023-04-25 | [
[
"Wu",
"Dawei",
""
],
[
"Tang",
"Shan-Chang",
""
],
[
"Shi",
"Yu",
""
]
] | We consider two accelerating Unruh-DeWitt detectors coupled linearly or quadratically with a scalar field. We show that entanglement can be created by acceleration, and is divergent only when the two detectors coincide. For linear coupling, entanglment decreases monotonically with the increase of acceleration. For quadratic coupling, entanglement behaves non-monotonically. |
2003.00458 | Shao-Wen Wei | Shao-Wen Wei, Yu-Xiao Liu | New insights into thermodynamics and microstructure of AdS black holes | 4 pages, 1 figure. Invited News & Views by Science Bulletin | Science Bulletin 65 (2020) 259-261 | 10.1016/j.scib.2019.11.020 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, black hole thermodynamics and phase transition have been studied in
the extended phase space. Besides the VdW-like phase transition, more
interesting phase transitions were found. More interestingly, combining with
the thermodynamic geometry, the microstructure of black holes was
investigated.In this paper, we give a brief review of recent progress on this
subject.
| [
{
"created": "Sun, 1 Mar 2020 10:29:00 GMT",
"version": "v1"
}
] | 2020-03-03 | [
[
"Wei",
"Shao-Wen",
""
],
[
"Liu",
"Yu-Xiao",
""
]
] | Recently, black hole thermodynamics and phase transition have been studied in the extended phase space. Besides the VdW-like phase transition, more interesting phase transitions were found. More interestingly, combining with the thermodynamic geometry, the microstructure of black holes was investigated.In this paper, we give a brief review of recent progress on this subject. |
gr-qc/0109037 | Alan Barnes | Alan Barnes | On the Symmetries of the Edgar-Ludwig Metric | Plain TeX, 7 pages, No figures | Class.Quant.Grav. 18 (2001) 5287-5292 | 10.1088/0264-9381/18/23/321 | null | gr-qc | null | The conformal Killing equations for the most general (non-plane wave)
conformally flat pure radiation field are solved to find the conformal Killing
vectors. As expected fifteen independent conformal Killing vectors exist, but
in general the metric admits no Killing or homothetic vectors. However for
certain special cases a one-dimensional group of homotheties or motions may
exist and in one very special case, overlooked by previous investigators, a
two-dimensional homethety group exists. No higher dimensional groups of motions
or homotheties are admitted by these metrics.
| [
{
"created": "Tue, 11 Sep 2001 14:02:12 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Barnes",
"Alan",
""
]
] | The conformal Killing equations for the most general (non-plane wave) conformally flat pure radiation field are solved to find the conformal Killing vectors. As expected fifteen independent conformal Killing vectors exist, but in general the metric admits no Killing or homothetic vectors. However for certain special cases a one-dimensional group of homotheties or motions may exist and in one very special case, overlooked by previous investigators, a two-dimensional homethety group exists. No higher dimensional groups of motions or homotheties are admitted by these metrics. |
2005.12985 | Mohammad M. Sheikh-Jabbari | K. Hajian, S. Liberati, M.M. Sheikh-Jabbari, M.H. Vahidinia | On Black Hole Temperature in Horndeski Gravity | 9 pages, no figure, v3: Minor changes to match the published version | Phys. Lett. B812 (2020) 136002 | 10.1016/j.physletb.2020.136002 | IPM/P-2020/023 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been observed that for black holes in certain family of Horndeski
gravity theories Wald's entropy formula does not lead to the correct first law
for black hole thermodynamics. For this family of Horndeski theories speeds of
propagation of gravitons and photons are in general different and gravitons
move on an effective metric different than the one seen by photons. We show
that the temperature of the black hole should be modified from surface gravity
over $2\pi$ to include effects of this effective metric. The modified
temperature, with the entropy unambiguously computed by the solution phase
space method, yields the correct first law. Our results have far reaching
implications for the Hawking radiation and species problem, going beyond the
Horndeski theories.
| [
{
"created": "Tue, 26 May 2020 19:08:26 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Jun 2020 18:48:13 GMT",
"version": "v2"
},
{
"created": "Sun, 20 Dec 2020 09:40:40 GMT",
"version": "v3"
}
] | 2020-12-22 | [
[
"Hajian",
"K.",
""
],
[
"Liberati",
"S.",
""
],
[
"Sheikh-Jabbari",
"M. M.",
""
],
[
"Vahidinia",
"M. H.",
""
]
] | It has been observed that for black holes in certain family of Horndeski gravity theories Wald's entropy formula does not lead to the correct first law for black hole thermodynamics. For this family of Horndeski theories speeds of propagation of gravitons and photons are in general different and gravitons move on an effective metric different than the one seen by photons. We show that the temperature of the black hole should be modified from surface gravity over $2\pi$ to include effects of this effective metric. The modified temperature, with the entropy unambiguously computed by the solution phase space method, yields the correct first law. Our results have far reaching implications for the Hawking radiation and species problem, going beyond the Horndeski theories. |
gr-qc/0009076 | Larry Ford | L.H. Ford and Thomas A. Roman | Classical Scalar Fields and the Generalized Second Law | 25 pages, 2 figures; paper substantially rewritten, major changes in
the conclusions | Phys.Rev. D64 (2001) 024023 | 10.1103/PhysRevD.64.024023 | null | gr-qc hep-th | null | It has been shown that classical non-minimally coupled scalar fields can
violate all of the standard energy conditions in general relativity. Violations
of the null and averaged null energy conditions obtainable with such fields
have been suggested as possible exotic matter candidates required for the
maintenance of traversable wormholes. In this paper, we explore the possibility
that if such fields exist, they might be used to produce large negative energy
fluxes and macroscopic violations of the generalized second law (GSL) of
thermodynamics. We find that it appears to be very easy to produce large
magnitude negative energy fluxes in flat spacetime. However we also find,
somewhat surprisingly, that these same types of fluxes injected into a black
hole do {\it not} produce violations of the GSL. This is true even in cases
where the flux results in a decrease in the area of the horizon. We demonstrate
that two effects are responsible for the rescue of the GSL: the acausal
behavior of the horizon and the modification of the usual black hole entropy
formula by an additional term which depends on the scalar field.
| [
{
"created": "Thu, 21 Sep 2000 18:01:15 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Mar 2001 00:43:10 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Ford",
"L. H.",
""
],
[
"Roman",
"Thomas A.",
""
]
] | It has been shown that classical non-minimally coupled scalar fields can violate all of the standard energy conditions in general relativity. Violations of the null and averaged null energy conditions obtainable with such fields have been suggested as possible exotic matter candidates required for the maintenance of traversable wormholes. In this paper, we explore the possibility that if such fields exist, they might be used to produce large negative energy fluxes and macroscopic violations of the generalized second law (GSL) of thermodynamics. We find that it appears to be very easy to produce large magnitude negative energy fluxes in flat spacetime. However we also find, somewhat surprisingly, that these same types of fluxes injected into a black hole do {\it not} produce violations of the GSL. This is true even in cases where the flux results in a decrease in the area of the horizon. We demonstrate that two effects are responsible for the rescue of the GSL: the acausal behavior of the horizon and the modification of the usual black hole entropy formula by an additional term which depends on the scalar field. |
1802.02519 | Lisa Glaser | Lisa Glaser | The Ising model coupled to 2d orders | 25 pages, 28 figures | null | 10.1088/1361-6382/aab139 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we make first steps in coupling matter to causal set theory
in the path integral. We explore the case of the Ising model coupled to the 2d
discrete Einstein Hilbert action, restricted to the 2d orders. We probe the
phase diagram in terms of the Wick rotation parameter \b{eta} and the Ising
coupling j and find that the matter and the causal sets together give rise to
an interesting phase structure. The couplings give rise to five different
phases. The causal sets take on random or crystalline characteristics as
described in [1] and the Ising model can be correlated or uncorrelated on the
random ordes and correlated, uncorrelated or anti-correlated on the crystalline
orders. We find that at least one new phase transition arises, in which the
Ising spins push the causal set into the crystalline phase.
| [
{
"created": "Wed, 7 Feb 2018 16:53:15 GMT",
"version": "v1"
}
] | 2018-03-28 | [
[
"Glaser",
"Lisa",
""
]
] | In this article we make first steps in coupling matter to causal set theory in the path integral. We explore the case of the Ising model coupled to the 2d discrete Einstein Hilbert action, restricted to the 2d orders. We probe the phase diagram in terms of the Wick rotation parameter \b{eta} and the Ising coupling j and find that the matter and the causal sets together give rise to an interesting phase structure. The couplings give rise to five different phases. The causal sets take on random or crystalline characteristics as described in [1] and the Ising model can be correlated or uncorrelated on the random ordes and correlated, uncorrelated or anti-correlated on the crystalline orders. We find that at least one new phase transition arises, in which the Ising spins push the causal set into the crystalline phase. |
1604.01959 | Sergey Yu. Vernov | A.Yu. Kamenshchik, E.O. Pozdeeva, A. Tronconi, G. Venturi, S.Yu.
Vernov | General solutions of integrable cosmological models with non-minimal
coupling | 6 pages | Phys. Part. Nuclei Lett. 14 (2017) 382 | 10.1134/S1547477117020169 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the integrable model with minimally and non-minimally coupled scalar
fields and the correspondence of their general solutions. Using the model with
a minimally coupled scalar field and a the constant potential as an example we
demonstrate the difference between the general solutions of the corresponding
models in the Jordan and the Einstein frames.
| [
{
"created": "Thu, 7 Apr 2016 11:27:03 GMT",
"version": "v1"
}
] | 2017-03-24 | [
[
"Kamenshchik",
"A. Yu.",
""
],
[
"Pozdeeva",
"E. O.",
""
],
[
"Tronconi",
"A.",
""
],
[
"Venturi",
"G.",
""
],
[
"Vernov",
"S. Yu.",
""
]
] | We study the integrable model with minimally and non-minimally coupled scalar fields and the correspondence of their general solutions. Using the model with a minimally coupled scalar field and a the constant potential as an example we demonstrate the difference between the general solutions of the corresponding models in the Jordan and the Einstein frames. |
1401.4093 | Gerard Clement | Gerard Clement and Alessandro Fabbri | Comment on `Critical scalar field collapse in AdS$_3$: an analytical
approach' | 5 pages, reference added, version to be published in Classical and
Quantum Gravity | Class. Quantum Grav. 31 (2014) 098001 | 10.1088/0264-9381/31/9/098001 | LAPTH-002/14 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We comment on the derivation of an analytical solution presented in
arXiv:1309.1629, show that it belongs to a family of separable solutions
previously constructed in arXiv:gr-qc/0109002, and question its relevance to
critical collapse.
| [
{
"created": "Thu, 16 Jan 2014 17:09:59 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Mar 2014 09:05:39 GMT",
"version": "v2"
},
{
"created": "Thu, 3 Apr 2014 11:01:46 GMT",
"version": "v3"
}
] | 2015-06-18 | [
[
"Clement",
"Gerard",
""
],
[
"Fabbri",
"Alessandro",
""
]
] | We comment on the derivation of an analytical solution presented in arXiv:1309.1629, show that it belongs to a family of separable solutions previously constructed in arXiv:gr-qc/0109002, and question its relevance to critical collapse. |
1409.8454 | Matthew J. Lake Dr | Tiberiu Harko and Matthew J. Lake | Cosmic strings in $f\left(R,L_m\right)$ gravity | 20 pages, no figures. Published version | Eur. Phys. J. C 75, no. 2, 60 (2015) | 10.1140/epjc/s10052-015-3287-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider Kasner-type static, cylindrically symmetric interior string
solutions in the $f\left(R,L_m\right)$ theory of modified gravity. The physical
properties of the string are described by an anisotropic energy-momentum tensor
satisfying the condition $T_t^t=T_z^z$; that is, the energy density of the
string along the $z$-axis is equal to minus the string tension. As a first step
in our study we obtain the gravitational field equations in the
$f\left(R,L_m\right)$ theory for a general static, cylindrically symmetric
metric, and then for a Kasner-type metric, in which the metric tensor
components have a power law dependence on the radial coordinate $r$. String
solutions in two particular modified gravity models are investigated in detail.
The first is the so-called "exponential" modified gravity, in which the
gravitational action is proportional to the exponential of the sum of the Ricci
scalar and matter Lagrangian, and the second is the "self-consistent model",
obtained by explicitly determining the gravitational action from the field
equations under the assumption of a power law dependent matter Lagrangian. In
each case, the thermodynamic parameters of the string, as well as the precise
form of the matter Lagrangian, are explicitly obtained.
| [
{
"created": "Tue, 30 Sep 2014 09:48:50 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Oct 2014 12:07:21 GMT",
"version": "v2"
},
{
"created": "Sat, 17 Jan 2015 11:45:47 GMT",
"version": "v3"
},
{
"created": "Sun, 27 Sep 2015 12:07:01 GMT",
"version": "v4"
}
] | 2015-10-07 | [
[
"Harko",
"Tiberiu",
""
],
[
"Lake",
"Matthew J.",
""
]
] | We consider Kasner-type static, cylindrically symmetric interior string solutions in the $f\left(R,L_m\right)$ theory of modified gravity. The physical properties of the string are described by an anisotropic energy-momentum tensor satisfying the condition $T_t^t=T_z^z$; that is, the energy density of the string along the $z$-axis is equal to minus the string tension. As a first step in our study we obtain the gravitational field equations in the $f\left(R,L_m\right)$ theory for a general static, cylindrically symmetric metric, and then for a Kasner-type metric, in which the metric tensor components have a power law dependence on the radial coordinate $r$. String solutions in two particular modified gravity models are investigated in detail. The first is the so-called "exponential" modified gravity, in which the gravitational action is proportional to the exponential of the sum of the Ricci scalar and matter Lagrangian, and the second is the "self-consistent model", obtained by explicitly determining the gravitational action from the field equations under the assumption of a power law dependent matter Lagrangian. In each case, the thermodynamic parameters of the string, as well as the precise form of the matter Lagrangian, are explicitly obtained. |
2310.06592 | David Venhoek | Wim Beenakker, David Venhoek | Accelerating decay with acceleration | null | null | null | null | gr-qc hep-ph hep-th quant-ph | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We investigate accelerated Unruh-deWitt detectors as a model for particle
decay. We find non-trivial decay rates, including a pattern of peaks in decay
rate that extends to lower accelerations. Applying our model to the alpha decay
of $\mathrm{^{210}Po}$, we find that effects could be observed with an
acceleration of $a\approx 10^{26} \frac{\mathrm{m}}{\mathrm{s}^2}$ as long as
that acceleration is controlled to within 1 percent. Although still out of
reach of current experimental setups, other decay processes at lower energy,
such as beta decay, could result in the peaks we find being within range of
future experiments.
| [
{
"created": "Tue, 10 Oct 2023 12:58:36 GMT",
"version": "v1"
}
] | 2023-10-11 | [
[
"Beenakker",
"Wim",
""
],
[
"Venhoek",
"David",
""
]
] | We investigate accelerated Unruh-deWitt detectors as a model for particle decay. We find non-trivial decay rates, including a pattern of peaks in decay rate that extends to lower accelerations. Applying our model to the alpha decay of $\mathrm{^{210}Po}$, we find that effects could be observed with an acceleration of $a\approx 10^{26} \frac{\mathrm{m}}{\mathrm{s}^2}$ as long as that acceleration is controlled to within 1 percent. Although still out of reach of current experimental setups, other decay processes at lower energy, such as beta decay, could result in the peaks we find being within range of future experiments. |
1307.6652 | Alberto Garcia-Diaz | Alberto A. Garcia-Diaz | Three dimensional stationary cyclic symmetric Einstein-Maxwell
solutions; energy, mass, momentum, and algebraic tensors characteristics | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The main purpose of this contribution is to determine physical and
geometrical characterizations of whole classes of stationary cyclic symmetric
gravitational fields coupled to Maxwell electromagnetic fields within the
$(2+1)$-dimensional gravity. The physical characterization is based on the
determination of the local and global energy-momentum-mass quantities using the
Brown-York approach. As far as to the algebraic-geometrical characterization is
concerned, the eigenvalue problem for the electromagnetic field,
energy-momentum and Cotton tensors is solved and their types are established.
The families of Einstein-Maxwell solutions to be considered are: all uniform
electromagnetic solutions possessing electromagnetic fields with vanishing
covariant derivatives (stationary uniform and spinning Clement classes), all
fields having constant electromagnetic field and energy-momentum tensors'
invariants (Kamata-Koikawa solutions), the whole classes of hybrid
electromagnetic Ayon-Cataldo-Garcia solutions, a new family of stationary
electromagnetic solutions, the electrostatic and magnetostatic solutions with
Peldan limit, the Clement spinning charged metric, the
Martinez-Teitelboim-Zanelli black hole solution, and Dias-Lemos electromagnetic
solution.
| [
{
"created": "Thu, 25 Jul 2013 07:57:31 GMT",
"version": "v1"
}
] | 2013-07-26 | [
[
"Garcia-Diaz",
"Alberto A.",
""
]
] | The main purpose of this contribution is to determine physical and geometrical characterizations of whole classes of stationary cyclic symmetric gravitational fields coupled to Maxwell electromagnetic fields within the $(2+1)$-dimensional gravity. The physical characterization is based on the determination of the local and global energy-momentum-mass quantities using the Brown-York approach. As far as to the algebraic-geometrical characterization is concerned, the eigenvalue problem for the electromagnetic field, energy-momentum and Cotton tensors is solved and their types are established. The families of Einstein-Maxwell solutions to be considered are: all uniform electromagnetic solutions possessing electromagnetic fields with vanishing covariant derivatives (stationary uniform and spinning Clement classes), all fields having constant electromagnetic field and energy-momentum tensors' invariants (Kamata-Koikawa solutions), the whole classes of hybrid electromagnetic Ayon-Cataldo-Garcia solutions, a new family of stationary electromagnetic solutions, the electrostatic and magnetostatic solutions with Peldan limit, the Clement spinning charged metric, the Martinez-Teitelboim-Zanelli black hole solution, and Dias-Lemos electromagnetic solution. |
2305.07329 | Piotr T. Chru\'sciel | Piotr T. Chru\'sciel | Remarks on stationary vacuum black holes | null | null | null | Preprint UWThPh-2023-18 | gr-qc math.DG | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We finish the proof of the no-hair theorem for stationary, analytic,
connected, suitably regular, four dimensional vacuum black holes. We show how
to define the surface gravity and the angular velocity of horizons without
assuming analyticity. We point out that, under the usual regularity conditions,
vacuum near-horizon geometries are Kerrian without assuming analyticity.
| [
{
"created": "Fri, 12 May 2023 09:14:03 GMT",
"version": "v1"
}
] | 2023-05-15 | [
[
"Chruściel",
"Piotr T.",
""
]
] | We finish the proof of the no-hair theorem for stationary, analytic, connected, suitably regular, four dimensional vacuum black holes. We show how to define the surface gravity and the angular velocity of horizons without assuming analyticity. We point out that, under the usual regularity conditions, vacuum near-horizon geometries are Kerrian without assuming analyticity. |
2404.07075 | Lang Liu | Zu-Cheng Chen and Lang Liu | Constraints on Inflation with Null Energy Condition Violation from
Advanced LIGO and Advanced Virgo's First Three Observing Runs | 11 pages, 1 figures, title changed as required by the Editor,
accepted by JCAP; | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The null energy condition (NEC) is a cornerstone of general relativity, and
its violation could leave observable imprints in the cosmic gravitational wave
spectrum. Theoretical models suggest that NEC violations during inflation can
amplify the primordial tensor power spectrum, leading to distinct features in
the stochastic gravitational wave background (SGWB). In this work, we search
for these NEC-violating signatures in the SGWB using data from Advanced LIGO
and Advanced Virgo's first three observing runs. Our analysis reveals no
statistically significant evidence of such signals, allowing us to place
stringent upper limits on the tensor power spectrum amplitude, $P_{T,2}$,
during the second inflationary stage. Specifically, we find that $P_{T,2}
\lesssim 0.15$ at a $95\%$ confidence level. Notably, this upper limit is
consistent with constraints derived from pulsar timing array observations,
reinforcing the hypothesis that NEC violations during inflation could explain
the signal detected by pulsar timing arrays. Our findings contribute to a
deeper understanding of the early Universe and highlight the potential of
current and future gravitational wave experiments in probing the physics of
inflation and NEC violations.
| [
{
"created": "Wed, 10 Apr 2024 15:05:44 GMT",
"version": "v1"
},
{
"created": "Sun, 19 May 2024 15:39:38 GMT",
"version": "v2"
}
] | 2024-05-21 | [
[
"Chen",
"Zu-Cheng",
""
],
[
"Liu",
"Lang",
""
]
] | The null energy condition (NEC) is a cornerstone of general relativity, and its violation could leave observable imprints in the cosmic gravitational wave spectrum. Theoretical models suggest that NEC violations during inflation can amplify the primordial tensor power spectrum, leading to distinct features in the stochastic gravitational wave background (SGWB). In this work, we search for these NEC-violating signatures in the SGWB using data from Advanced LIGO and Advanced Virgo's first three observing runs. Our analysis reveals no statistically significant evidence of such signals, allowing us to place stringent upper limits on the tensor power spectrum amplitude, $P_{T,2}$, during the second inflationary stage. Specifically, we find that $P_{T,2} \lesssim 0.15$ at a $95\%$ confidence level. Notably, this upper limit is consistent with constraints derived from pulsar timing array observations, reinforcing the hypothesis that NEC violations during inflation could explain the signal detected by pulsar timing arrays. Our findings contribute to a deeper understanding of the early Universe and highlight the potential of current and future gravitational wave experiments in probing the physics of inflation and NEC violations. |
gr-qc/0112073 | Andrzej Woszczyna | Z. Golda and A.Woszczyna | Anomalous dispersion of density waves in the early universe with
positive cosmological constant | 7 pages | null | null | null | gr-qc | null | Density perturbations in the flat (K=0) Robertson-Walker universe with
radiation ($p=\epsilon/3$) and positive cosmological constant ($\Lambda>0$) are
investigated. The phenomenon of anomalous dispersion of acoustic waves on
$\Lambda$ is discussed.
| [
{
"created": "Thu, 27 Dec 2001 00:50:09 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Golda",
"Z.",
""
],
[
"Woszczyna",
"A.",
""
]
] | Density perturbations in the flat (K=0) Robertson-Walker universe with radiation ($p=\epsilon/3$) and positive cosmological constant ($\Lambda>0$) are investigated. The phenomenon of anomalous dispersion of acoustic waves on $\Lambda$ is discussed. |
2305.15105 | Giorgio Di Russo | Massimo Bianchi, Giorgio Di Russo, Alfredo Grillo, Jose Francisco
Morales, Giuseppe Sudano | On the stability and deformability of top stars | null | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Topological stars, or top stars for brevity, are smooth horizonless static
solutions of Einstein-Maxwell theory in 5-d that reduce to spherically
symmetric solutions of Einstein-Maxwell-Dilaton theory in 4-d. We study linear
scalar perturbations of top stars and argue for their stability and
deformability. We tackle the problem with different techniques including WKB
approximation, numerical analysis, Breit-Wigner resonance method and quantum
Seiberg-Witten curves. We identify three classes of quasi-normal modes
corresponding to prompt-ring down modes, long-lived meta-stable modes and what
we dub `blind' modes. All mode frequencies we find have negative imaginary
parts, thus suggesting linear stability of top stars. Moreover we determine the
tidal Love and dissipation numbers encoding the response to tidal deformations
and, similarly to black holes, we find zero value in the static limit but,
contrary to black holes, we find non-trivial dynamical Love numbers and
vanishing dissipative effects at linear order. For the sake of illustration in
a simpler context, we also consider a toy model with a piece-wise constant
potential and a centrifugal barrier that captures most of the above features in
a qualitative fashion.
| [
{
"created": "Wed, 24 May 2023 12:48:14 GMT",
"version": "v1"
},
{
"created": "Fri, 1 Sep 2023 10:12:22 GMT",
"version": "v2"
}
] | 2023-09-04 | [
[
"Bianchi",
"Massimo",
""
],
[
"Di Russo",
"Giorgio",
""
],
[
"Grillo",
"Alfredo",
""
],
[
"Morales",
"Jose Francisco",
""
],
[
"Sudano",
"Giuseppe",
""
]
] | Topological stars, or top stars for brevity, are smooth horizonless static solutions of Einstein-Maxwell theory in 5-d that reduce to spherically symmetric solutions of Einstein-Maxwell-Dilaton theory in 4-d. We study linear scalar perturbations of top stars and argue for their stability and deformability. We tackle the problem with different techniques including WKB approximation, numerical analysis, Breit-Wigner resonance method and quantum Seiberg-Witten curves. We identify three classes of quasi-normal modes corresponding to prompt-ring down modes, long-lived meta-stable modes and what we dub `blind' modes. All mode frequencies we find have negative imaginary parts, thus suggesting linear stability of top stars. Moreover we determine the tidal Love and dissipation numbers encoding the response to tidal deformations and, similarly to black holes, we find zero value in the static limit but, contrary to black holes, we find non-trivial dynamical Love numbers and vanishing dissipative effects at linear order. For the sake of illustration in a simpler context, we also consider a toy model with a piece-wise constant potential and a centrifugal barrier that captures most of the above features in a qualitative fashion. |
0801.2641 | Kiyoshi Shiraishi | Teruki Hanada, Kazuhiko Shinoda and Kiyoshi Shiraishi (Yamaguchi
University) | Multi-graviton theory in vierbein formalism | 4 pages, no figure. A presentation given at JGRG17 (Nagoya, Japan),
to appear in the proceedings | null | null | null | gr-qc hep-th | null | Recently, multi-graviton theory on a simple closed circuit graph
corresponding to the $S^1$ compactification of the Kaluza-Klein (KK) theory has
been considered. In the present paper, we extend this theory to that on a
general graph and study what modes of particles are included. Furthermore, we
generalize it in a possible non-linear theory based on the vierbein formalism
and study cosmological solutions.
| [
{
"created": "Thu, 17 Jan 2008 10:30:22 GMT",
"version": "v1"
}
] | 2008-01-18 | [
[
"Hanada",
"Teruki",
"",
"Yamaguchi\n University"
],
[
"Shinoda",
"Kazuhiko",
"",
"Yamaguchi\n University"
],
[
"Shiraishi",
"Kiyoshi",
"",
"Yamaguchi\n University"
]
] | Recently, multi-graviton theory on a simple closed circuit graph corresponding to the $S^1$ compactification of the Kaluza-Klein (KK) theory has been considered. In the present paper, we extend this theory to that on a general graph and study what modes of particles are included. Furthermore, we generalize it in a possible non-linear theory based on the vierbein formalism and study cosmological solutions. |
gr-qc/9908075 | Israel Quiroz | Israel Quiros, Rolando Bonal and Rolando Cardenas (Dpto.Fisica.
Universidad Central de Las Villas. Santa Clara. Cuba.) | Brans-Dicke-type theories and avoidance of the cosmological singularity | 9 pages, LaTeX, no figures. Improved version accepted for publication
in PRD | Phys.Rev. D62 (2000) 044042 | 10.1103/PhysRevD.62.044042 | null | gr-qc hep-th | null | We tudy flat Friedmann-Robertson-Walker cosmology in Brans-Dicke-type
theories of gravitation with minimal coupling between the scalar field and the
matter fields in the Einstein frame (general relativity with an extra scalar
field) for arbitrary values of the Brans-Dicke parameter $\omega>-{3/2}$. It is
shown that the cosmological singularity occuring in the Einstein frame
formulation of this theory is removed in the Jordan frame in the range
$-{3/2}<\omega<\leq-{4/3}$. This result is interpreted in the ligth of a
viewpoint (first presented in reference gr-qc/9905071) asserting that both
Jordan frame and Einstein frame formulations of general relativity are
physically equivalent. The implications of the obtained result for string
theory are outlined.
| [
{
"created": "Mon, 30 Aug 1999 22:24:06 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Dec 1999 15:02:23 GMT",
"version": "v2"
},
{
"created": "Mon, 21 Feb 2000 12:57:26 GMT",
"version": "v3"
}
] | 2009-10-31 | [
[
"Quiros",
"Israel",
"",
"Dpto.Fisica.\n Universidad Central de Las Villas. Santa Clara. Cuba."
],
[
"Bonal",
"Rolando",
"",
"Dpto.Fisica.\n Universidad Central de Las Villas. Santa Clara. Cuba."
],
[
"Cardenas",
"Rolando",
"",
"Dpto.Fisica.\n Universidad Central de Las Villas. Santa Clara. Cuba."
]
] | We tudy flat Friedmann-Robertson-Walker cosmology in Brans-Dicke-type theories of gravitation with minimal coupling between the scalar field and the matter fields in the Einstein frame (general relativity with an extra scalar field) for arbitrary values of the Brans-Dicke parameter $\omega>-{3/2}$. It is shown that the cosmological singularity occuring in the Einstein frame formulation of this theory is removed in the Jordan frame in the range $-{3/2}<\omega<\leq-{4/3}$. This result is interpreted in the ligth of a viewpoint (first presented in reference gr-qc/9905071) asserting that both Jordan frame and Einstein frame formulations of general relativity are physically equivalent. The implications of the obtained result for string theory are outlined. |
0810.5686 | Florian Kuhnel | Florian Kuhnel, Dominik J. Schwarz | Stochastic Inflation and Replica Field Theory | 15 pages, 14 figures | Phys.Rev.D79:044009,2009 | 10.1103/PhysRevD.79.044009 | BI-TP 2008/33 | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We adopt methods from statistical field theory to stochastic inflation. For
the example of a free test field in de Sitter and power-law inflation, the
power spectrum of long-wavelength fluctuations is computed. We study its
dependence on the shape of the filter that separates long from short wavelength
modes. While for filters with infinite support the phenomenon of dimensional
reductions is found on large super-horizon scales, filters with compact support
return a scale-invariant power spectrum in the infra-red. Features of the power
spectrum, induced by the filter, decay within a few e-foldings. Thus the
late-time power spectrum is independent of the filter details.
| [
{
"created": "Fri, 31 Oct 2008 13:41:05 GMT",
"version": "v1"
}
] | 2011-02-01 | [
[
"Kuhnel",
"Florian",
""
],
[
"Schwarz",
"Dominik J.",
""
]
] | We adopt methods from statistical field theory to stochastic inflation. For the example of a free test field in de Sitter and power-law inflation, the power spectrum of long-wavelength fluctuations is computed. We study its dependence on the shape of the filter that separates long from short wavelength modes. While for filters with infinite support the phenomenon of dimensional reductions is found on large super-horizon scales, filters with compact support return a scale-invariant power spectrum in the infra-red. Features of the power spectrum, induced by the filter, decay within a few e-foldings. Thus the late-time power spectrum is independent of the filter details. |
0910.0023 | Mariusz Dabrowski P. | Mariusz P. Dabrowski and Tomasz Denkiewicz | Exotic-singularity-driven dark energy | 10 pages, 9 figures, contribution to "Invisible Universe", paris
29.06-3.07.09, to appear in AIP Conference Proceedings | AIP Conf.Proc.1241:561-570,2010 | 10.1063/1.3462686 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss various types of exotic (non-standard) singularities in the
Universe: a Big-Rip (BR or type I), a Sudden Future Singularity (SFS or type
II), a Generalized Sudden Future Singularity, a Finite Scale Factor singularity
(FSF or type III), a Big-Separation (BS or type IV) and a $w$-singularity. They
are characterized by violation of all or some of the energy conditions which
results in a blow-up of all or some of the physical quantities: the scale
factor, the energy density, the pressure, and the barotropic index. We relate
the emergence of these singularities with physical theories (superstring,
brane, higher-order gravity, loop quantum cosmology). We show how the models
involving exotic singularities may serve as dark energy by applying the
observational data. In particular, we show that some of these exotic
singularities (though being of a weak type according to relativistic
definitions) may occur in the near future of the universe.
| [
{
"created": "Wed, 30 Sep 2009 20:27:01 GMT",
"version": "v1"
}
] | 2014-11-20 | [
[
"Dabrowski",
"Mariusz P.",
""
],
[
"Denkiewicz",
"Tomasz",
""
]
] | We discuss various types of exotic (non-standard) singularities in the Universe: a Big-Rip (BR or type I), a Sudden Future Singularity (SFS or type II), a Generalized Sudden Future Singularity, a Finite Scale Factor singularity (FSF or type III), a Big-Separation (BS or type IV) and a $w$-singularity. They are characterized by violation of all or some of the energy conditions which results in a blow-up of all or some of the physical quantities: the scale factor, the energy density, the pressure, and the barotropic index. We relate the emergence of these singularities with physical theories (superstring, brane, higher-order gravity, loop quantum cosmology). We show how the models involving exotic singularities may serve as dark energy by applying the observational data. In particular, we show that some of these exotic singularities (though being of a weak type according to relativistic definitions) may occur in the near future of the universe. |
0908.0215 | Luca Lusanna | David Alba and Luca Lusanna | Charged Particles and the Electro-Magnetic Field in Non-Inertial Frames
of Minkowski Spacetime: II. Applications: Rotating Frames, Sagnac Effect,
Faraday Rotation, Wrap-up Effect | This paper and the second one are an adaptation of arXiv 0812.3057
for publication on Int.J.Geom. Methods in Modern Phys. 36p | Int.J.Geom.Methods Mod.Phys.07 2010:185-213,2010 | 10.1142/S0219887810004051 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We apply the theory of non-inertial frames in Minkowski space-time, developed
in the previous paper, to various relevant physical systems. We give the 3+1
description without coordinate-singularities of the rotating disk and the
Sagnac effect, with added comments on pulsar magnetosphere and on a
relativistic extension of the Earth-fixed coordinate system. Then we study
properties of Maxwell equations in non-inertial frames like the wrap-up effect
and the Faraday rotation in astrophysics.
| [
{
"created": "Mon, 3 Aug 2009 09:44:44 GMT",
"version": "v1"
}
] | 2014-11-20 | [
[
"Alba",
"David",
""
],
[
"Lusanna",
"Luca",
""
]
] | We apply the theory of non-inertial frames in Minkowski space-time, developed in the previous paper, to various relevant physical systems. We give the 3+1 description without coordinate-singularities of the rotating disk and the Sagnac effect, with added comments on pulsar magnetosphere and on a relativistic extension of the Earth-fixed coordinate system. Then we study properties of Maxwell equations in non-inertial frames like the wrap-up effect and the Faraday rotation in astrophysics. |
2003.10859 | Yasutaka Koga | Yasutaka Koga | Photon surfaces as pure tension shells: Uniqueness of thin shell
wormholes | 22 pages, 3 figures | Phys. Rev. D 101, 104022 (2020) | 10.1103/PhysRevD.101.104022 | RUP-20-10 | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Thin shell wormholes are constructed by joining two asymptotically flat
spacetimes along their inner boundaries. The junction conditions imposed on the
spacetimes specify the equation of state of the matter called thin shell
distributed along the joined boundaries. Barcelo and Visser (2000) reported
that spherically symmetric thin shell wormholes have their shells, namely the
wormhole throats, on the photon spheres if the wormholes are $Z_2$-symmetric
across the throats and the shells are of pure tension. In this paper, first, we
consider general joined spacetimes (JSTs) and show that any $Z_2$-symmetric
pure-tensional JST (Z2PTJST) of $\Lambda$-vacuum has its shell on a photon
surface, a generalized object of photon spheres, without assuming any other
symmetries. The class of Z2PTJSTs also includes, for example, brane world
models with the shells being the branes we live in. Second, we investigate the
shell stability of Z2PTJSTs by analyzing the stability of the corresponding
photon surfaces. Finally, applying the uniqueness theorem of photon spheres by
Cederbaum (2015), we establish the uniqueness theorem of static wormholes of
Z2PTJST.
| [
{
"created": "Tue, 24 Mar 2020 14:07:19 GMT",
"version": "v1"
},
{
"created": "Fri, 26 Jun 2020 10:23:26 GMT",
"version": "v2"
}
] | 2020-06-29 | [
[
"Koga",
"Yasutaka",
""
]
] | Thin shell wormholes are constructed by joining two asymptotically flat spacetimes along their inner boundaries. The junction conditions imposed on the spacetimes specify the equation of state of the matter called thin shell distributed along the joined boundaries. Barcelo and Visser (2000) reported that spherically symmetric thin shell wormholes have their shells, namely the wormhole throats, on the photon spheres if the wormholes are $Z_2$-symmetric across the throats and the shells are of pure tension. In this paper, first, we consider general joined spacetimes (JSTs) and show that any $Z_2$-symmetric pure-tensional JST (Z2PTJST) of $\Lambda$-vacuum has its shell on a photon surface, a generalized object of photon spheres, without assuming any other symmetries. The class of Z2PTJSTs also includes, for example, brane world models with the shells being the branes we live in. Second, we investigate the shell stability of Z2PTJSTs by analyzing the stability of the corresponding photon surfaces. Finally, applying the uniqueness theorem of photon spheres by Cederbaum (2015), we establish the uniqueness theorem of static wormholes of Z2PTJST. |
gr-qc/0107060 | B. V. Ivanov | B.V.Ivanov | Integrable cases of gravitating static isothermal fluid spheres | 13 pages, revtex | J.Math.Phys. 43 (2002) 1029 | 10.1063/1.1431259 | null | gr-qc | null | It is shown that different approaches towards the solution of the Einstein
equations for a static spherically symmetric perfect fluid with a gamma-law
equation of state lead to an Abel differential equation of the second kind. Its
only integrable cases at present are flat spacetime, de Sitter solution and its
Buchdahl transform, Einstein static universe and the Klein-Tolman solution.
| [
{
"created": "Tue, 17 Jul 2001 09:53:47 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Ivanov",
"B. V.",
""
]
] | It is shown that different approaches towards the solution of the Einstein equations for a static spherically symmetric perfect fluid with a gamma-law equation of state lead to an Abel differential equation of the second kind. Its only integrable cases at present are flat spacetime, de Sitter solution and its Buchdahl transform, Einstein static universe and the Klein-Tolman solution. |
1203.0691 | John Klauder | John R. Klauder | Recent Results Regarding Affine Quantum Gravity | 32 pages, new features in this alternative approach to quantize
gravity, minor typos plus an improved argument in Sec. 9 suggested by Karel
Kuchar | null | 10.1063/1.4739555 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recent progress in the quantization of nonrenormalizable scalar fields has
found that a suitable non-classical modification of the ground state wave
function leads to a result that eliminates term-by-term divergences that arise
in a conventional perturbation analysis. After a brief review of both the
scalar field story and the affine quantum gravity program, examination of the
procedures used in the latter surprisingly shows an analogous formulation which
already implies that affine quantum gravity is not plagued by divergences that
arise in a standard perturbation study. Additionally, guided by the projection
operator method to deal with quantum constraints, trial reproducing kernels are
introduced that satisfy the diffeomorphism constraints. Furthermore, it is
argued that the trial reproducing kernels for the diffeomorphism constraints
may also satisfy the Hamiltonian constraint as well.
| [
{
"created": "Sat, 3 Mar 2012 22:16:22 GMT",
"version": "v1"
},
{
"created": "Tue, 3 Jul 2012 14:12:02 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Klauder",
"John R.",
""
]
] | Recent progress in the quantization of nonrenormalizable scalar fields has found that a suitable non-classical modification of the ground state wave function leads to a result that eliminates term-by-term divergences that arise in a conventional perturbation analysis. After a brief review of both the scalar field story and the affine quantum gravity program, examination of the procedures used in the latter surprisingly shows an analogous formulation which already implies that affine quantum gravity is not plagued by divergences that arise in a standard perturbation study. Additionally, guided by the projection operator method to deal with quantum constraints, trial reproducing kernels are introduced that satisfy the diffeomorphism constraints. Furthermore, it is argued that the trial reproducing kernels for the diffeomorphism constraints may also satisfy the Hamiltonian constraint as well. |
1302.4486 | Rafael Porto | Chad R. Galley and Rafael A. Porto | Gravitational self-force in the ultra-relativistic limit: The 'large-N'
expansion | 12+23 pages, 24 figures. Paper substantially extended with more
details on the formalism and computations. Submitted to JHEP | null | 10.1007/JHEP11(2013)096 | null | gr-qc astro-ph.CO astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the gravitational self-force using the effective field theory
formalism. We show that in the ultra-relativistic limit \gamma \to \infty, with
\gamma the boost factor, many simplifications arise. Drawing parallels with the
large N limit in quantum field theory, we introduce the parameter 1/N =
1/\gamma^2 and show that the effective action admits a well defined expansion
in powers of \lambda = N\epsilon, at each order in 1/N, where \epsilon = E_m/M
and E_m=\gamma m is the (kinetic) energy of the small mass. Moreover, we show
that diagrams with nonlinear bulk interactions first enter at O(\lambda^2/N^2)
and only diagrams with nonlinearities in the worldline couplings, which are
significantly easier to compute, survive in the large N/ultra-relativistic
limit. Finally, we derive the self-force to O(\lambda^4/N) and provide
expressions for some conservative quantities for circular orbits.
| [
{
"created": "Mon, 18 Feb 2013 23:55:28 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Sep 2013 10:45:25 GMT",
"version": "v2"
}
] | 2015-06-15 | [
[
"Galley",
"Chad R.",
""
],
[
"Porto",
"Rafael A.",
""
]
] | We study the gravitational self-force using the effective field theory formalism. We show that in the ultra-relativistic limit \gamma \to \infty, with \gamma the boost factor, many simplifications arise. Drawing parallels with the large N limit in quantum field theory, we introduce the parameter 1/N = 1/\gamma^2 and show that the effective action admits a well defined expansion in powers of \lambda = N\epsilon, at each order in 1/N, where \epsilon = E_m/M and E_m=\gamma m is the (kinetic) energy of the small mass. Moreover, we show that diagrams with nonlinear bulk interactions first enter at O(\lambda^2/N^2) and only diagrams with nonlinearities in the worldline couplings, which are significantly easier to compute, survive in the large N/ultra-relativistic limit. Finally, we derive the self-force to O(\lambda^4/N) and provide expressions for some conservative quantities for circular orbits. |
gr-qc/0406028 | Andrzej Okolow | Andrzej Okolow | Hilbert space built over connections with a non-compact structure group | 45 pages, no figures, LaTeX2e, the discussion of results extended | Class.Quant.Grav. 22 (2005) 1329-1360 | 10.1088/0264-9381/22/7/009 | null | gr-qc | null | Quantization of general relativity in terms of SL(2,C)-connections (i.e. in
terms of the complex Ashtekar variables) is technically difficult because of
the non-compactness of SL(2,C). The difficulties concern the construction of a
diffeomorphism invariant Hilbert space structure on the space of cylindrical
functions of the connections. We present here a 'toy' model of such a Hilbert
space built over connections whose structure group is the group of real
numbers. We show that in the case of any Hilbert space built analogously over
connections with any non-compact structure group (this includes some models
presented in the literature) there exists an obstacle which does not allow to
define a *-representation of cylindrical functions on the Hilbert space by the
multiplication map which is the only known way to define a diffeomorphism
invariant representation of the functions.
| [
{
"created": "Tue, 8 Jun 2004 11:36:55 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Mar 2005 00:04:10 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Okolow",
"Andrzej",
""
]
] | Quantization of general relativity in terms of SL(2,C)-connections (i.e. in terms of the complex Ashtekar variables) is technically difficult because of the non-compactness of SL(2,C). The difficulties concern the construction of a diffeomorphism invariant Hilbert space structure on the space of cylindrical functions of the connections. We present here a 'toy' model of such a Hilbert space built over connections whose structure group is the group of real numbers. We show that in the case of any Hilbert space built analogously over connections with any non-compact structure group (this includes some models presented in the literature) there exists an obstacle which does not allow to define a *-representation of cylindrical functions on the Hilbert space by the multiplication map which is the only known way to define a diffeomorphism invariant representation of the functions. |
1311.4358 | Christodoulakis Theodosios | N. Dimakis, T. Christodoulakis, Petros A. Terzis | FLRW metric $f(R)$ cosmology with a perfect fluid by generating
integrals of motion | LaTex2e source file, 24 pages, no figures | null | 10.1016/j.geomphys.2013.12.001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the context of metric f(R) gravity, we consider a FLRW space-time, filled
with a perfect fluid described by a barotropic equation of state (p = \gamma
\rho). We give the equivalent mini-superspace description and use the
reparametrization invariance of the resulting Lagrangian to work in the
equivalent constant potential description. At that point, we restrict our
analysis to those models for which the ensuing scaled mini-superspace is
maximally symmetric. Those models exhibit the maximum number of autonomous
integrals of motion linear in the momenta, which are constructed by the Killing
vectors of the respective mini-supermetric. The integrals of motion are used to
analytically solve the equations of the corresponding models. Finally, a brief
description of the properties of the resulting Hubble parameters is given.
| [
{
"created": "Mon, 18 Nov 2013 12:53:04 GMT",
"version": "v1"
}
] | 2015-06-17 | [
[
"Dimakis",
"N.",
""
],
[
"Christodoulakis",
"T.",
""
],
[
"Terzis",
"Petros A.",
""
]
] | In the context of metric f(R) gravity, we consider a FLRW space-time, filled with a perfect fluid described by a barotropic equation of state (p = \gamma \rho). We give the equivalent mini-superspace description and use the reparametrization invariance of the resulting Lagrangian to work in the equivalent constant potential description. At that point, we restrict our analysis to those models for which the ensuing scaled mini-superspace is maximally symmetric. Those models exhibit the maximum number of autonomous integrals of motion linear in the momenta, which are constructed by the Killing vectors of the respective mini-supermetric. The integrals of motion are used to analytically solve the equations of the corresponding models. Finally, a brief description of the properties of the resulting Hubble parameters is given. |
gr-qc/0406122 | Joan Josep Ferrando | Bartolom\'e Coll and Joan Josep Ferrando | Local thermal equilibrium and ideal gas Stephani universes | 20 pages | Gen.Rel.Grav. 37 (2005) 557-573 | 10.1007/s10714-005-0042-y | null | gr-qc | null | The Stephani universes that can be interpreted as an ideal gas evolving in
local thermal equilibrium are determined. Five classes of thermodynamic schemes
are admissible, which give rise to five classes of regular models and three
classes of singular models. No Stephani universes exist representing an exact
solution to a classical ideal gas (one for which the internal energy is
proportional to the temperature). But some Stephani universes may approximate a
classical ideal gas at first order in the temperature: all of them are
obtained. Finally, some features about the physical behavior of the models are
pointed out.
| [
{
"created": "Wed, 30 Jun 2004 14:18:42 GMT",
"version": "v1"
}
] | 2016-08-16 | [
[
"Coll",
"Bartolomé",
""
],
[
"Ferrando",
"Joan Josep",
""
]
] | The Stephani universes that can be interpreted as an ideal gas evolving in local thermal equilibrium are determined. Five classes of thermodynamic schemes are admissible, which give rise to five classes of regular models and three classes of singular models. No Stephani universes exist representing an exact solution to a classical ideal gas (one for which the internal energy is proportional to the temperature). But some Stephani universes may approximate a classical ideal gas at first order in the temperature: all of them are obtained. Finally, some features about the physical behavior of the models are pointed out. |
0804.2082 | Juan Manuel Garcia-Islas | J.Manuel Garcia-Islas | BTZ Black Hole Entropy: A spin foam model description | 10 pages, 2 figures, Final Version | Class.Quant.Grav.25:245001,2008 | 10.1088/0264-9381/25/24/245001 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a microscopical explanation of the entropy of the BTZ black hole
using discrete spin foam models of quantum gravity. The entropy of a black hole
is given in geometrical terms which lead us to think that its statistical
description must be given in terms of a quantum geometry. In this paper we
present it in terms of spin foam geometrical observables at the horizon of the
black hole.
| [
{
"created": "Sun, 13 Apr 2008 19:24:53 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Dec 2008 06:51:44 GMT",
"version": "v2"
}
] | 2008-12-18 | [
[
"Garcia-Islas",
"J. Manuel",
""
]
] | We present a microscopical explanation of the entropy of the BTZ black hole using discrete spin foam models of quantum gravity. The entropy of a black hole is given in geometrical terms which lead us to think that its statistical description must be given in terms of a quantum geometry. In this paper we present it in terms of spin foam geometrical observables at the horizon of the black hole. |
0912.0542 | Genly Le\'on | Genly Leon, Yoelsy Leyva, Emmanuel N. Saridakis, Osmel Martin and
Rolando Cardenas | Falsifying Field-based Dark Energy Models | 64 pages, 12 figures, invited review for Nova Science Publishers, as
a chapter of the book Dark Energy: Theories, Developments and Implications | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We survey the application of specific tools to distinguish amongst the wide
variety of dark energy models that are nowadays under investigation. The first
class of tools is more mathematical in character: the application of the theory
of dynamical systems to select the better behaved models, with appropriate
attractors in the past and future. The second class of tools is rather
physical: the use of astrophysical observations to crack the degeneracy of
classes of dark energy models. In this last case the observations related with
structure formation are emphasized both in the linear and non-linear regimes.
We exemplify several studies based on our research, such as quintom and
quinstant dark energy ones. Quintom dark energy paradigm is a hybrid
construction of quintessence and phantom fields, which does not suffer from
fine-tuning problems associated to phantom field and additionally it preserves
the scaling behavior of quintessence. Quintom dark energy is motivated on
theoretical grounds as an explanation for the crossing of the phantom divide,
i.e. the smooth crossing of the dark energy state equation parameter below the
value -1. On the other hand, quinstant dark energy is considered to be formed
by quintessence and a negative cosmological constant, the inclusion of this
later component allows for a viable mechanism to halt acceleration. We comment
that the quinstant dark energy scenario gives good predictions for structure
formation in the linear regime, but fails to do that in the non-linear one, for
redshifts larger than one. We comment that there might still be some degree of
arbitrariness in the selection of the best dark energy models.
| [
{
"created": "Wed, 2 Dec 2009 22:16:25 GMT",
"version": "v1"
}
] | 2009-12-05 | [
[
"Leon",
"Genly",
""
],
[
"Leyva",
"Yoelsy",
""
],
[
"Saridakis",
"Emmanuel N.",
""
],
[
"Martin",
"Osmel",
""
],
[
"Cardenas",
"Rolando",
""
]
] | We survey the application of specific tools to distinguish amongst the wide variety of dark energy models that are nowadays under investigation. The first class of tools is more mathematical in character: the application of the theory of dynamical systems to select the better behaved models, with appropriate attractors in the past and future. The second class of tools is rather physical: the use of astrophysical observations to crack the degeneracy of classes of dark energy models. In this last case the observations related with structure formation are emphasized both in the linear and non-linear regimes. We exemplify several studies based on our research, such as quintom and quinstant dark energy ones. Quintom dark energy paradigm is a hybrid construction of quintessence and phantom fields, which does not suffer from fine-tuning problems associated to phantom field and additionally it preserves the scaling behavior of quintessence. Quintom dark energy is motivated on theoretical grounds as an explanation for the crossing of the phantom divide, i.e. the smooth crossing of the dark energy state equation parameter below the value -1. On the other hand, quinstant dark energy is considered to be formed by quintessence and a negative cosmological constant, the inclusion of this later component allows for a viable mechanism to halt acceleration. We comment that the quinstant dark energy scenario gives good predictions for structure formation in the linear regime, but fails to do that in the non-linear one, for redshifts larger than one. We comment that there might still be some degree of arbitrariness in the selection of the best dark energy models. |
1006.2755 | Sergey Kozyrev | S.M. Kozyrev | Curious interior solutions of general relativity | 6 pages | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article, we provide a discussion on a composite class of exact static
spherically symmetric vacuum solutions of Einstein's equations. We construct
the composite solution of Einstein field equation by match the interior vacuum
metric in Schwarzschild original gauge, to the exterior vacuum metric in
isotropic gauge, at a junction surface. This approach allows us to associate
rigorously with both gauges as a same "space", which is a unique differentiable
manifold M^4
| [
{
"created": "Mon, 14 Jun 2010 16:28:22 GMT",
"version": "v1"
}
] | 2010-06-15 | [
[
"Kozyrev",
"S. M.",
""
]
] | In this article, we provide a discussion on a composite class of exact static spherically symmetric vacuum solutions of Einstein's equations. We construct the composite solution of Einstein field equation by match the interior vacuum metric in Schwarzschild original gauge, to the exterior vacuum metric in isotropic gauge, at a junction surface. This approach allows us to associate rigorously with both gauges as a same "space", which is a unique differentiable manifold M^4 |
gr-qc/0303001 | Theodore A. Jacobson | T. Jacobson, S. Liberati, and D. Mattingly | Comments on ``Improved limit on quantum-spacetime modifications of
Lorentz symmetry from observations of gamma-ray blazars" | 4 pages | null | null | null | gr-qc astro-ph hep-ph hep-th | null | We address several criticisms by Amelino-Camelia of our recent analyses of
two observational constraints on Lorentz violation at order E/M_{Planck}. In
particular, we emphasize the role of effective field theory in our analysis of
synchrotron radiation, and we strengthen the justification for the constraint
coming from photon annihilation.
| [
{
"created": "Sat, 1 Mar 2003 05:07:21 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Jacobson",
"T.",
""
],
[
"Liberati",
"S.",
""
],
[
"Mattingly",
"D.",
""
]
] | We address several criticisms by Amelino-Camelia of our recent analyses of two observational constraints on Lorentz violation at order E/M_{Planck}. In particular, we emphasize the role of effective field theory in our analysis of synchrotron radiation, and we strengthen the justification for the constraint coming from photon annihilation. |
2206.02193 | Truong Xuan Pham | Truong Xuan Pham | Peeling for tensorial wave equations on Schwarzschild spacetime | 22 pages, Reviews in Mathematical Physics, 2023. arXiv admin note:
text overlap with arXiv:2006.02888 | Reviews in Mathematical Physics, 2023 | 10.1142/S0129055X2350023X | null | gr-qc math-ph math.AP math.DG math.MP | http://creativecommons.org/licenses/by/4.0/ | In this paper, we establish the asymptotic behaviour along outgoing and
incoming radial geodesics, i.e., the peeling property for the tensorial
Fackrell-Ipser and spin $\pm 1$ Teukolsky equations on Schwarzschild spacetime.
Our method combines a conformal compactification with vector field techniques
to prove the two-side estimates of the energies of tensorial fields through the
future and past null infinity $\mathscr{I}^\pm$ and the initial Cauchy
hypersurface $\Sigma_0 = \left\{ t=0 \right\}$ in a neighbourhood of spacelike
infinity $i_0$ far away from the horizon and future timelike infinity. Our
results obtain the optimal initial data which guarantees the peeling at all
orders.
| [
{
"created": "Sun, 5 Jun 2022 14:39:36 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Jun 2022 07:59:03 GMT",
"version": "v2"
},
{
"created": "Wed, 14 Jun 2023 09:54:09 GMT",
"version": "v3"
},
{
"created": "Tue, 26 Sep 2023 00:37:13 GMT",
"version": "v4"
}
] | 2023-09-28 | [
[
"Pham",
"Truong Xuan",
""
]
] | In this paper, we establish the asymptotic behaviour along outgoing and incoming radial geodesics, i.e., the peeling property for the tensorial Fackrell-Ipser and spin $\pm 1$ Teukolsky equations on Schwarzschild spacetime. Our method combines a conformal compactification with vector field techniques to prove the two-side estimates of the energies of tensorial fields through the future and past null infinity $\mathscr{I}^\pm$ and the initial Cauchy hypersurface $\Sigma_0 = \left\{ t=0 \right\}$ in a neighbourhood of spacelike infinity $i_0$ far away from the horizon and future timelike infinity. Our results obtain the optimal initial data which guarantees the peeling at all orders. |
1406.0417 | Sumanta Chakraborty | Sumanta Chakraborty | Equilibrium configuration of perfect fluid orbiting around black holes
in some classes of alternative gravity theories | 29 pages; 4 figures; Thoroughly Revised; Matches Published Version | Class. Quantum Grav. 32 075007 (2015) | 10.1088/0264-9381/32/7/075007 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The hydrodynamic behaviour of perfect fluid orbiting around black holes in
spherically symmetric spacetime for various alternative gravity theories has
been investigated. For this purpose we have assumed an uniform distribution for
the angular momentum density of the rotating perfect fluid. The contours of
equipotential surfaces are illustrated in order to obtain the nature of inflow
and outflow of matters. It has been noticed that, the marginally stable
circular orbits originating from decreasing angular momentum density lead to
closed equipotential surfaces along with cusp allowing existence of accretion
disks. On the other hand, the growing part of angular momentum density exhibits
central rings for which stable configurations are possible. However inflow of
matter is prohibited. Among the solutions discussed in this work, the charged
$F(R)$ gravity and Einstein-Maxwell-Gauss-Bonnet solution exhibit inflow and
outflow of matter with central rings present. These varied accretion disk
structure of perfect fluid attribute these spacetimes astrophysical importance.
The effect of higher curvature terms predominantly arises from region near the
black hole horizon. Hence the structural difference of accretion disk in
modified gravity theories with comparison to general relativity may act as an
experimental probe for these alternative gravity theories.
| [
{
"created": "Fri, 9 May 2014 11:28:24 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Mar 2015 11:17:23 GMT",
"version": "v2"
}
] | 2015-03-11 | [
[
"Chakraborty",
"Sumanta",
""
]
] | The hydrodynamic behaviour of perfect fluid orbiting around black holes in spherically symmetric spacetime for various alternative gravity theories has been investigated. For this purpose we have assumed an uniform distribution for the angular momentum density of the rotating perfect fluid. The contours of equipotential surfaces are illustrated in order to obtain the nature of inflow and outflow of matters. It has been noticed that, the marginally stable circular orbits originating from decreasing angular momentum density lead to closed equipotential surfaces along with cusp allowing existence of accretion disks. On the other hand, the growing part of angular momentum density exhibits central rings for which stable configurations are possible. However inflow of matter is prohibited. Among the solutions discussed in this work, the charged $F(R)$ gravity and Einstein-Maxwell-Gauss-Bonnet solution exhibit inflow and outflow of matter with central rings present. These varied accretion disk structure of perfect fluid attribute these spacetimes astrophysical importance. The effect of higher curvature terms predominantly arises from region near the black hole horizon. Hence the structural difference of accretion disk in modified gravity theories with comparison to general relativity may act as an experimental probe for these alternative gravity theories. |
2208.07695 | Elena Kopteva | Stupka A.A., Kopteva E.M., Saliuk M.A., Bormotova I.M | Virial theorem for a cloud of stars obtained from Jeans equations with
the second correlation moments | null | null | 10.1140/epjc/s10052-023-11737-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A hydrodynamic model for small acoustic oscillations in a cloud of stars is
built, taking into account the self-consistent gravitational field in
equilibrium with a non-zero second correlation moment. It is assumed that the
momentum flux density tensor should include the analog of the anisotropic
pressure tensor and the second correlation moment of both longitudinal and
transverse gravitational field strength. The non-relativistic temporal equation
for the second correlation moment of the gravitational field strength is
derived from the Einstein equations using the first-order post-Newtonian
approximation. One longitudinal and two transverse branches of acoustic
oscillations are found in a homogeneous and isotropic star cloud. The
requirement for the velocity of transverse oscillations to be zero provides the
boundary condition for the stability of the cloud. The critical radius of the
spherical cloud of stars is obtained, which is precisely consistent with the
virial theorem.
| [
{
"created": "Tue, 16 Aug 2022 12:05:53 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Feb 2023 15:12:11 GMT",
"version": "v2"
},
{
"created": "Mon, 5 Jun 2023 14:19:33 GMT",
"version": "v3"
}
] | 2023-07-26 | [
[
"A.",
"Stupka A.",
""
],
[
"M.",
"Kopteva E.",
""
],
[
"A.",
"Saliuk M.",
""
],
[
"M",
"Bormotova I.",
""
]
] | A hydrodynamic model for small acoustic oscillations in a cloud of stars is built, taking into account the self-consistent gravitational field in equilibrium with a non-zero second correlation moment. It is assumed that the momentum flux density tensor should include the analog of the anisotropic pressure tensor and the second correlation moment of both longitudinal and transverse gravitational field strength. The non-relativistic temporal equation for the second correlation moment of the gravitational field strength is derived from the Einstein equations using the first-order post-Newtonian approximation. One longitudinal and two transverse branches of acoustic oscillations are found in a homogeneous and isotropic star cloud. The requirement for the velocity of transverse oscillations to be zero provides the boundary condition for the stability of the cloud. The critical radius of the spherical cloud of stars is obtained, which is precisely consistent with the virial theorem. |
1602.04188 | Mikhail M. Ivanov | Diego Blas, Mikhail M. Ivanov, Ignacy Sawicki and Sergey Sibiryakov | On constraining the speed of gravitational waves following GW150914 | 3 pages, 1 figure, references added | Pisma Zh.Eksp.Teor.Fiz. 103 (2016) no.10, 708-710; JETP Lett. 103
(2016) no.10, 624-626 | 10.7868/S0370274X16100039, 10.1134/S0021364016100040 | CERN-TH-2016-034, INR-TH-2016-005 | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We point out that the observed time delay between the detection of the signal
at the Hanford and Livingston LIGO sites from the gravitational wave event
GW150914 places an upper bound on the speed of propagation of gravitational
waves, $c_{gw}\lesssim 1.7$ in the units of speed of light. Combined with the
lower bound from the absence of gravitational Cherenkov losses by cosmic rays
that rules out most of subluminal velocities, this gives a model-independent
double-sided constraint $1\lesssim c_{gw}\lesssim 1.7$. We compare this result
to model-specific constraints from pulsar timing and cosmology.
| [
{
"created": "Fri, 12 Feb 2016 19:58:31 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Mar 2016 08:35:39 GMT",
"version": "v2"
}
] | 2016-08-09 | [
[
"Blas",
"Diego",
""
],
[
"Ivanov",
"Mikhail M.",
""
],
[
"Sawicki",
"Ignacy",
""
],
[
"Sibiryakov",
"Sergey",
""
]
] | We point out that the observed time delay between the detection of the signal at the Hanford and Livingston LIGO sites from the gravitational wave event GW150914 places an upper bound on the speed of propagation of gravitational waves, $c_{gw}\lesssim 1.7$ in the units of speed of light. Combined with the lower bound from the absence of gravitational Cherenkov losses by cosmic rays that rules out most of subluminal velocities, this gives a model-independent double-sided constraint $1\lesssim c_{gw}\lesssim 1.7$. We compare this result to model-specific constraints from pulsar timing and cosmology. |
2306.09052 | Yizhou Lu | Sebastian Garcia-Saenz, Yizhou Lu, Zhiming Shuai | Scalar-Induced Gravitational Waves from Ghost Inflation and Parity
Violation | 36pages | Phys.Rev. D108 (2023) no.12, 123507 | 10.1103/PhysRevD.108.123507 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We calculate the scalar-induced gravitational wave energy density in the
theory of Ghost Inflation, assuming scale invariance and taking into account
both the power spectrum- and trispectrum-induced contributions. For the latter
we consider the leading cubic and quartic couplings of the comoving curvature
perturbation in addition to two parity-violating quartic operators. In the
parity-even case, we find the relative importance of the trispectrum-induced
signal to be suppressed by the requirement of perturbativity, strengthening a
no-go theorem recently put forth. The parity-odd signal, even though also bound
to be small, is non-degenerate with the Gaussian contribution and may in
principle be comparable to the parity-even non-Gaussian part, thus potentially
serving as a probe of the Ghost Inflation scenario and of parity violating
physics during inflation.
| [
{
"created": "Thu, 15 Jun 2023 11:22:00 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Nov 2023 04:46:05 GMT",
"version": "v2"
}
] | 2023-12-06 | [
[
"Garcia-Saenz",
"Sebastian",
""
],
[
"Lu",
"Yizhou",
""
],
[
"Shuai",
"Zhiming",
""
]
] | We calculate the scalar-induced gravitational wave energy density in the theory of Ghost Inflation, assuming scale invariance and taking into account both the power spectrum- and trispectrum-induced contributions. For the latter we consider the leading cubic and quartic couplings of the comoving curvature perturbation in addition to two parity-violating quartic operators. In the parity-even case, we find the relative importance of the trispectrum-induced signal to be suppressed by the requirement of perturbativity, strengthening a no-go theorem recently put forth. The parity-odd signal, even though also bound to be small, is non-degenerate with the Gaussian contribution and may in principle be comparable to the parity-even non-Gaussian part, thus potentially serving as a probe of the Ghost Inflation scenario and of parity violating physics during inflation. |
1609.04488 | Shahram Jalalzadeh | M. Fathi, S. Jalalzadeh and P.V. Moniz | Classical Universe emerging from quantum cosmology without horizon and
flatness problems | 21 pages, 1 figure, to appear in European Physical Journal C | null | 10.1140/epjc/s10052-016-4373-5 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We apply the complex de Broglie-Bohm formulation of quantum mechanics [1] to
a spatially closed homogeneous and isotropic early Universe whose matter
content are radiation and dust perfect fluids. We then show that an expanding
classical Universe can emerge from an oscillating (with complex scale factor)
quantum Universe without singularity. Furthermore, the Universe obtained in
this process has no horizon or flatness problems.
| [
{
"created": "Thu, 15 Sep 2016 01:35:11 GMT",
"version": "v1"
}
] | 2016-10-12 | [
[
"Fathi",
"M.",
""
],
[
"Jalalzadeh",
"S.",
""
],
[
"Moniz",
"P. V.",
""
]
] | We apply the complex de Broglie-Bohm formulation of quantum mechanics [1] to a spatially closed homogeneous and isotropic early Universe whose matter content are radiation and dust perfect fluids. We then show that an expanding classical Universe can emerge from an oscillating (with complex scale factor) quantum Universe without singularity. Furthermore, the Universe obtained in this process has no horizon or flatness problems. |
1206.2055 | Lee Hodgkinson | Lee Hodgkinson and Jorma Louko | Static, stationary and inertial Unruh-DeWitt detectors on the BTZ black
hole | 31 pages, 28 figures. v3: minor corrections and clarifications | Phys. Rev. D 86, 064031 (2012) | 10.1103/PhysRevD.86.064031 | NSF-KITP-12-121 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine an Unruh-DeWitt particle detector coupled to a scalar field in
three-dimensional curved spacetime. We first obtain a regulator-free expression
for the transition probability in an arbitrary Hadamard state, working within
first-order perturbation theory and assuming smooth switching, and we show that
both the transition probability and the instantaneous transition rate remain
well defined in the sharp switching limit. We then analyse a detector coupled
to a massless conformally coupled field in the Hartle-Hawking vacua on the
Banados-Teitelboim-Zanelli black hole, under both transparent and reflective
boundary conditions at the infinity. A selection of stationary and
freely-falling detector trajectories are examined, including the co-rotating
trajectories, for which the response is shown to be thermal. Analytic results
in a number of asymptotic regimes, including those of large and small mass, are
complemented by numerical results in the interpolating regimes. The boundary
condition at infinity is seen to have a significant effect on the transition
rate.
| [
{
"created": "Sun, 10 Jun 2012 20:31:45 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Jun 2012 16:58:36 GMT",
"version": "v2"
},
{
"created": "Thu, 4 Oct 2012 09:06:24 GMT",
"version": "v3"
}
] | 2012-10-09 | [
[
"Hodgkinson",
"Lee",
""
],
[
"Louko",
"Jorma",
""
]
] | We examine an Unruh-DeWitt particle detector coupled to a scalar field in three-dimensional curved spacetime. We first obtain a regulator-free expression for the transition probability in an arbitrary Hadamard state, working within first-order perturbation theory and assuming smooth switching, and we show that both the transition probability and the instantaneous transition rate remain well defined in the sharp switching limit. We then analyse a detector coupled to a massless conformally coupled field in the Hartle-Hawking vacua on the Banados-Teitelboim-Zanelli black hole, under both transparent and reflective boundary conditions at the infinity. A selection of stationary and freely-falling detector trajectories are examined, including the co-rotating trajectories, for which the response is shown to be thermal. Analytic results in a number of asymptotic regimes, including those of large and small mass, are complemented by numerical results in the interpolating regimes. The boundary condition at infinity is seen to have a significant effect on the transition rate. |
2206.05993 | Jose M. Isidro | P. Fernandez de Cordoba, R. Gallego Torrome, S. Gavasso and J.M.
Isidro | On the cosmological constant of flat FLRW spacetime | 12 pages, refs. added, discussion expanded | null | null | null | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | We consider an exponentially expanding, flat,
Friedmann-Lemaitre-Robertson-Walker (FLRW) Universe filled with a free
Schroedinger field. The probability fluid of the latter is used to mimic the
cosmological fluid (baryonic plus dark matter), thus providing the matter
density and pressure terms in the corresponding Friedmann-Lemaitre equations.
We first obtain the eigenfunctions of the Laplacian operator on flat FLRW
space. A quantum operator qualifying as a cosmological constant is defined to
act on the Schroedinger field. We then compute the matrix representing the
cosmological constant in the basis of Laplacian eigenfunctions. For an estimate
of the orders of magnitude involved it suffices to determine the expectation
values of this operator. The expectation value that best fits the
experimentally measured value of the cosmological constant allows us to
identify the quantum state of the Schroedinger field that best represents the
matter contents (baryonic and dark) of the current Universe. Finally, the
operator inverse (modulo dimensional factors) to the one representing the
cosmological constant provides a measure of the gravitational Boltzmann entropy
of the Universe. We compute its matrix in the basis of Laplacian eigenfunctions
and verify that the expectation values of this entropy operator comply with the
upper bound set by the holographic principle.
| [
{
"created": "Mon, 13 Jun 2022 09:29:05 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Sep 2022 08:32:26 GMT",
"version": "v2"
}
] | 2022-09-13 | [
[
"de Cordoba",
"P. Fernandez",
""
],
[
"Torrome",
"R. Gallego",
""
],
[
"Gavasso",
"S.",
""
],
[
"Isidro",
"J. M.",
""
]
] | We consider an exponentially expanding, flat, Friedmann-Lemaitre-Robertson-Walker (FLRW) Universe filled with a free Schroedinger field. The probability fluid of the latter is used to mimic the cosmological fluid (baryonic plus dark matter), thus providing the matter density and pressure terms in the corresponding Friedmann-Lemaitre equations. We first obtain the eigenfunctions of the Laplacian operator on flat FLRW space. A quantum operator qualifying as a cosmological constant is defined to act on the Schroedinger field. We then compute the matrix representing the cosmological constant in the basis of Laplacian eigenfunctions. For an estimate of the orders of magnitude involved it suffices to determine the expectation values of this operator. The expectation value that best fits the experimentally measured value of the cosmological constant allows us to identify the quantum state of the Schroedinger field that best represents the matter contents (baryonic and dark) of the current Universe. Finally, the operator inverse (modulo dimensional factors) to the one representing the cosmological constant provides a measure of the gravitational Boltzmann entropy of the Universe. We compute its matrix in the basis of Laplacian eigenfunctions and verify that the expectation values of this entropy operator comply with the upper bound set by the holographic principle. |
2304.06546 | Omar Mustafa | Omar Mustafa | Fine tuning of rainbow gravity functions and Klein-Gordon particles in
cosmic string rainbow gravity spacetime | 15 pages, 7 figures. arXiv admin note: substantial text overlap with
arXiv:2301.05464, arXiv:2301.12370 | null | null | null | gr-qc astro-ph.HE hep-ph | http://creativecommons.org/licenses/by/4.0/ | We argue that, as long as relativistic quantum particles are in point, the
variable $y=E/E_p$ of the rainbow functions pair $g_{_{0}} (y)$ and $g_{_{1}}
(y)$ should be fine tuned into $y=|E|/E_p$, where $E_p$ is the Planck's energy
scale. Otherwise, the rainbow functions will be only successful to describe the
rainbow gravity effect on relativistic quantum particles and the anti-particles
will be left unfortunate. Under such fine tuning, we consider Klein-Gordon (KG)
particles in cosmic string rainbow gravity spacetime in a non-uniform magnetic
field (i.e., $\mathbf{B}=\mathbf{\nabla }\times \mathbf{A}=\frac{3}{2}B_{\circ
}r\,\hat{z}$ ). Then we consider KG-particles in cosmic string rainbow gravity
spacetime in a uniform magnetic field (i.e., $\mathbf{B}=\mathbf{\nabla }\times
\mathbf{A}=\frac{1}{2}B_{\circ }\,\hat{z}$ ). Whilst the former effectively
yields KG-oscillators, the later effectively yields KG-Coulombic particles. We
report on the effects of rainbow gravity on both KG-oscillators and Coulombic
particles using four pairs of rainbow functions: (i) $% g_{_{0}}\left( y\right)
=1$, $g_{_{1}}\left( y\right) =\sqrt{1-\epsilon y^{2}% }$, (ii) $g_{_{0}}\left(
y\right) =1$, $g_{_{1}}\left( y\right) =\sqrt{% 1-\epsilon y}$, (iii)
$g_{_{0}}\left( y\right) =g_{_{1}}\left( y\right) =\left( 1-\epsilon y\right)
^{-1}$, and (iv) $g_{_{0}}\left( y\right) =\left( e^{\epsilon y}-1\right)
/\epsilon y$, $g_{_{1}}\left( y\right) =1$, where $y=|E|/E_p$ and $\epsilon$ is
the rainbow parameter. It is interesting to report that, all KG particles' and
anti-particles' energies are symmetric about $E=0$ value (a natural
relativistic quantum mechanical tendency), and a phenomenon of energy states to
fly away and disappear from the spectrum is observed for the rainbow functions
pair (iii) at $\gamma=\epsilon m/E_p=1$.
| [
{
"created": "Thu, 13 Apr 2023 13:56:45 GMT",
"version": "v1"
}
] | 2023-04-14 | [
[
"Mustafa",
"Omar",
""
]
] | We argue that, as long as relativistic quantum particles are in point, the variable $y=E/E_p$ of the rainbow functions pair $g_{_{0}} (y)$ and $g_{_{1}} (y)$ should be fine tuned into $y=|E|/E_p$, where $E_p$ is the Planck's energy scale. Otherwise, the rainbow functions will be only successful to describe the rainbow gravity effect on relativistic quantum particles and the anti-particles will be left unfortunate. Under such fine tuning, we consider Klein-Gordon (KG) particles in cosmic string rainbow gravity spacetime in a non-uniform magnetic field (i.e., $\mathbf{B}=\mathbf{\nabla }\times \mathbf{A}=\frac{3}{2}B_{\circ }r\,\hat{z}$ ). Then we consider KG-particles in cosmic string rainbow gravity spacetime in a uniform magnetic field (i.e., $\mathbf{B}=\mathbf{\nabla }\times \mathbf{A}=\frac{1}{2}B_{\circ }\,\hat{z}$ ). Whilst the former effectively yields KG-oscillators, the later effectively yields KG-Coulombic particles. We report on the effects of rainbow gravity on both KG-oscillators and Coulombic particles using four pairs of rainbow functions: (i) $% g_{_{0}}\left( y\right) =1$, $g_{_{1}}\left( y\right) =\sqrt{1-\epsilon y^{2}% }$, (ii) $g_{_{0}}\left( y\right) =1$, $g_{_{1}}\left( y\right) =\sqrt{% 1-\epsilon y}$, (iii) $g_{_{0}}\left( y\right) =g_{_{1}}\left( y\right) =\left( 1-\epsilon y\right) ^{-1}$, and (iv) $g_{_{0}}\left( y\right) =\left( e^{\epsilon y}-1\right) /\epsilon y$, $g_{_{1}}\left( y\right) =1$, where $y=|E|/E_p$ and $\epsilon$ is the rainbow parameter. It is interesting to report that, all KG particles' and anti-particles' energies are symmetric about $E=0$ value (a natural relativistic quantum mechanical tendency), and a phenomenon of energy states to fly away and disappear from the spectrum is observed for the rainbow functions pair (iii) at $\gamma=\epsilon m/E_p=1$. |
1905.04111 | Sujoy Modak | Sujoy K. Modak | Cosmological Particle Creation Beyond de Sitter | Invited Review Article to IJMPD (published); 33 pages, 7 figures;
Based on author's previous articles arXiv:1308.4976, arXiv:1802.03833 and
arXiv:1806.00972 | International Journal of Modern Physics D Vol. 28 (2019) 1930015 | 10.1142/S0218271819300155 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Over the years, de Sitter spacetime has been a central focus, in studies
involving quantum fields, for its importance in the early and late expansion
stages of the universe. While de Sitter spacetime closely mimics
characteristics of the inflationary and dark energy dominated universe it does
not help to understand the radiation and matter dominated expansions. In this
review, we revisit some recent works, involving the author, which study
gravitational particle creation beyond the de Sitter stage. Specifically, we
present novel aspects of particle creation in the radiation dominated universe,
and then provide an analysis of time evolution of the primordial (Bunch-Davies)
vacuum state, its particle excitation and quantum versus classical behavior of
field modes, in a multi stage universe, comprising of, (i) the inflationary de
Sitter, (ii) the radiation dominated and, (iii) the late dark energy dominated
stages.
| [
{
"created": "Wed, 8 May 2019 21:00:25 GMT",
"version": "v1"
},
{
"created": "Fri, 31 May 2019 04:18:52 GMT",
"version": "v2"
},
{
"created": "Fri, 9 Jul 2021 03:05:14 GMT",
"version": "v3"
}
] | 2021-07-12 | [
[
"Modak",
"Sujoy K.",
""
]
] | Over the years, de Sitter spacetime has been a central focus, in studies involving quantum fields, for its importance in the early and late expansion stages of the universe. While de Sitter spacetime closely mimics characteristics of the inflationary and dark energy dominated universe it does not help to understand the radiation and matter dominated expansions. In this review, we revisit some recent works, involving the author, which study gravitational particle creation beyond the de Sitter stage. Specifically, we present novel aspects of particle creation in the radiation dominated universe, and then provide an analysis of time evolution of the primordial (Bunch-Davies) vacuum state, its particle excitation and quantum versus classical behavior of field modes, in a multi stage universe, comprising of, (i) the inflationary de Sitter, (ii) the radiation dominated and, (iii) the late dark energy dominated stages. |
gr-qc/0703030 | Antonios Tsokaros A. | Antonios A. Tsokaros, Koji Uryu | Numerical method for binary black hole/neutron star initial data: Code
test | 19 pages, 18 figures | Phys.Rev.D75:044026,2007 | 10.1103/PhysRevD.75.044026 | null | gr-qc | null | A new numerical method to construct binary black hole/neutron star initial
data is presented. The method uses three spherical coordinate patches; Two of
these are centered at the binary compact objects and cover a neighborhood of
each object; the third patch extends to the asymptotic region. As in the
Komatsu-Eriguchi-Hachisu method, nonlinear elliptic field equations are
decomposed into a flat space Laplacian and a remaining nonlinear expression
that serves in each iteration as an effective source. The equations are solved
iteratively, integrating a Green's function against the effective source at
each iteration. Detailed convergence tests for the essential part of the code
are performed for a few types of selected Green's functions to treat different
boundary conditions. Numerical computation of the gravitational potential of a
fluid source, and a toy model for a binary black hole field are carefully
calibrated with the analytic solutions to examine accuracy and convergence of
the new code. As an example of the application of the code, an initial data set
for binary black holes in the Isenberg-Wilson-Mathews formulation is presented,
in which the apparent horizons are located using a method described in Appendix
A.
| [
{
"created": "Mon, 5 Mar 2007 22:15:16 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Tsokaros",
"Antonios A.",
""
],
[
"Uryu",
"Koji",
""
]
] | A new numerical method to construct binary black hole/neutron star initial data is presented. The method uses three spherical coordinate patches; Two of these are centered at the binary compact objects and cover a neighborhood of each object; the third patch extends to the asymptotic region. As in the Komatsu-Eriguchi-Hachisu method, nonlinear elliptic field equations are decomposed into a flat space Laplacian and a remaining nonlinear expression that serves in each iteration as an effective source. The equations are solved iteratively, integrating a Green's function against the effective source at each iteration. Detailed convergence tests for the essential part of the code are performed for a few types of selected Green's functions to treat different boundary conditions. Numerical computation of the gravitational potential of a fluid source, and a toy model for a binary black hole field are carefully calibrated with the analytic solutions to examine accuracy and convergence of the new code. As an example of the application of the code, an initial data set for binary black holes in the Isenberg-Wilson-Mathews formulation is presented, in which the apparent horizons are located using a method described in Appendix A. |
2105.08556 | Philip D. Mannheim | Philip D. Mannheim | Critique of the use of geodesics in astrophysics and cosmology | 51 pages. In flat space normals to wavefronts are geodesic. We show
that the curved space generalization is to curved space wavefront normals,
and in curved space these normals do not have to be geodesic. This is the
final version, which is to appear in Classical and Quantum Gravity | null | 10.1088/1361-6382/ac8140 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Since particles obey wave equations, in general one is not free to postulate
that particles move on the geodesics associated with test particles. Rather,
for this to be the case one has to be able to derive such behavior starting
from the equations of motion that the particles obey, and to do so one can
employ the eikonal approximation. To see what kind of trajectories might occur
we explore the domain of support of the propagators associated with the wave
equations. For a minimally coupled massless scalar field the domain of support
in curved space is shown to not be restricted to the light cone, while for a
conformally coupled massless scalar field the curved space domain is only
restricted to the light cone if it propagates in a conformal to flat
background. Consequently, eikonalization does not in general lead to null
geodesics for curved space massless rays even though it does lead to straight
line trajectories in flat spacetime. Equal remarks apply to the massless
conformal invariant Maxwell equations. However, for massive particles one does
obtain standard geodesic behavior this way, since they do not propagate on the
light cone to begin with. Thus depending on how big the curvature actually is,
in principle, even if not necessarily in practice, the standard
null-geodesic-based gravitational bending formula and the general behavior of
propagating light rays are in need of modification in regions with high enough
curvature. We show that relativistic eikonalization has an intrinsic
light-front structure, and show that eikonalization in a theory with local
conformal symmetry leads to trajectories that are only globally conformally
symmetric. Normals to wavefronts follow the eikonal trajectories, with these
trajectories being the trajectories along which energy and momentum are
transported.
| [
{
"created": "Tue, 18 May 2021 14:40:34 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Jun 2021 19:28:34 GMT",
"version": "v2"
},
{
"created": "Fri, 9 Jul 2021 13:10:28 GMT",
"version": "v3"
},
{
"created": "Tue, 20 Jul 2021 20:06:54 GMT",
"version": "v4"
},
{
"created": "Sun, 1 Aug 2021 14:42:53 GMT",
"version": "v5"
},
{
"created": "Mon, 23 Aug 2021 13:20:58 GMT",
"version": "v6"
},
{
"created": "Mon, 8 Aug 2022 13:08:21 GMT",
"version": "v7"
}
] | 2022-12-07 | [
[
"Mannheim",
"Philip D.",
""
]
] | Since particles obey wave equations, in general one is not free to postulate that particles move on the geodesics associated with test particles. Rather, for this to be the case one has to be able to derive such behavior starting from the equations of motion that the particles obey, and to do so one can employ the eikonal approximation. To see what kind of trajectories might occur we explore the domain of support of the propagators associated with the wave equations. For a minimally coupled massless scalar field the domain of support in curved space is shown to not be restricted to the light cone, while for a conformally coupled massless scalar field the curved space domain is only restricted to the light cone if it propagates in a conformal to flat background. Consequently, eikonalization does not in general lead to null geodesics for curved space massless rays even though it does lead to straight line trajectories in flat spacetime. Equal remarks apply to the massless conformal invariant Maxwell equations. However, for massive particles one does obtain standard geodesic behavior this way, since they do not propagate on the light cone to begin with. Thus depending on how big the curvature actually is, in principle, even if not necessarily in practice, the standard null-geodesic-based gravitational bending formula and the general behavior of propagating light rays are in need of modification in regions with high enough curvature. We show that relativistic eikonalization has an intrinsic light-front structure, and show that eikonalization in a theory with local conformal symmetry leads to trajectories that are only globally conformally symmetric. Normals to wavefronts follow the eikonal trajectories, with these trajectories being the trajectories along which energy and momentum are transported. |
1112.2966 | Laszlo B. Szabados | L\'aszl\'o B. Szabados | Mass, gauge conditions and spectral properties of the Sen-Witten and
3-surface twistor operators in closed universes | 34 pages, final version, appearing in Class. Quantum Grav | null | 10.1088/0264-9381/29/9/095001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A non-negative expression, built from the norm of the 3-surface twistor
operator and the energy-momentum tensor of the matter fields on a spacelike
hypersurface, is found which, in the asymptotically flat/hyperboloidal case,
provides a lower bound for the ADM/Bondi--Sachs mass, while on closed
hypersurfaces it gives the first eigenvalue of the Sen--Witten operator. Also
in the closed case, its vanishing is equivalent to the existence of non-trivial
solutions of Witten's gauge condition. Moreover, it is vanishing if and only if
the closed data set is in a flat spacetime with toroidal spatial topology. Thus
it provides a positive definite measure of the strength of the gravitational
field (with physical dimension mass) on closed hypersurfaces, i.e. some sort of
the total mass of closed universes.
| [
{
"created": "Tue, 13 Dec 2011 17:15:35 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Apr 2012 14:26:10 GMT",
"version": "v2"
}
] | 2015-06-03 | [
[
"Szabados",
"László B.",
""
]
] | A non-negative expression, built from the norm of the 3-surface twistor operator and the energy-momentum tensor of the matter fields on a spacelike hypersurface, is found which, in the asymptotically flat/hyperboloidal case, provides a lower bound for the ADM/Bondi--Sachs mass, while on closed hypersurfaces it gives the first eigenvalue of the Sen--Witten operator. Also in the closed case, its vanishing is equivalent to the existence of non-trivial solutions of Witten's gauge condition. Moreover, it is vanishing if and only if the closed data set is in a flat spacetime with toroidal spatial topology. Thus it provides a positive definite measure of the strength of the gravitational field (with physical dimension mass) on closed hypersurfaces, i.e. some sort of the total mass of closed universes. |
1408.7009 | Joel Saavedra | P. A. Gonzalez, Eleftherios Papantonopoulos, Joel Saavedra, Yerko
Vasquez | Extremal Hairy Black Holes | 17 pages. Match with the journal version accepted by JHEP. arXiv
admin note: substantial text overlap with arXiv:1309.2161 | null | 10.1007/JHEP11(2014)011 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a gravitating system consisting of a scalar field minimally
coupled to gravity with a self-interacting potential and an U(1)
electromagnetic field. Solving the coupled Einstein-Maxwell-scalar system we
find exact hairy charged black hole solutions with the scalar field regular
everywhere. We go to the zero temperature limit and we study the effect of the
scalar field on the near horizon geometry of an extremal black hole. We find
that except a critical value of the charge of the black hole there is also a
critical value of the charge of the scalar field beyond of which the extremal
black hole is destabilized. We study the thermodynamics of these solutions and
we find that if the space is flat then at low temperature the
Reissner-Nordstr\"om black hole is thermodynamically preferred, while if the
space is AdS the hairy charged black hole is thermodynamically preferred at low
temperature.
| [
{
"created": "Fri, 29 Aug 2014 13:07:00 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Sep 2014 15:02:46 GMT",
"version": "v2"
},
{
"created": "Fri, 24 Oct 2014 12:00:39 GMT",
"version": "v3"
}
] | 2015-06-22 | [
[
"Gonzalez",
"P. A.",
""
],
[
"Papantonopoulos",
"Eleftherios",
""
],
[
"Saavedra",
"Joel",
""
],
[
"Vasquez",
"Yerko",
""
]
] | We consider a gravitating system consisting of a scalar field minimally coupled to gravity with a self-interacting potential and an U(1) electromagnetic field. Solving the coupled Einstein-Maxwell-scalar system we find exact hairy charged black hole solutions with the scalar field regular everywhere. We go to the zero temperature limit and we study the effect of the scalar field on the near horizon geometry of an extremal black hole. We find that except a critical value of the charge of the black hole there is also a critical value of the charge of the scalar field beyond of which the extremal black hole is destabilized. We study the thermodynamics of these solutions and we find that if the space is flat then at low temperature the Reissner-Nordstr\"om black hole is thermodynamically preferred, while if the space is AdS the hairy charged black hole is thermodynamically preferred at low temperature. |
gr-qc/0310016 | Itai Seggev | Itai Seggev | Dynamics in Stationary, Non-Globally Hyperbolic Spacetimes | 18 pages, 1 figure, AMSLaTeX; v2: expanded discussion of field
quantization, new Proposition 3.1, revised Theorem 4.2, corrected typos, and
updated references | Class.Quant.Grav. 21 (2004) 2651-2668 | 10.1088/0264-9381/21/11/010 | null | gr-qc | null | Classically, the dynamics in a non-globally hyperbolic spacetime is ill
posed. Previously, a prescription was given for defining dynamics in static
spacetimes in terms of a second order operator acting on a Hilbert space
defined on static slices. The present work extends this result by giving a
similar prescription for defining dynamics in stationary spacetimes obeying
certain mild assumptions. The prescription is defined in terms of a first order
operator acting on a different Hilbert space from the one used in the static
prescription. It preserves the important properties of the earlier one: the
formal solution agrees with the Cauchy evolution within the domain of
dependence, and smooth data of compact support always give rise to smooth
solutions. In the static case, the first order formalism agrees with second
order formalism (using specifically the Friedrichs extension). Applications to
field quantization are also discussed.
| [
{
"created": "Thu, 2 Oct 2003 19:56:06 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Nov 2003 20:56:53 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Seggev",
"Itai",
""
]
] | Classically, the dynamics in a non-globally hyperbolic spacetime is ill posed. Previously, a prescription was given for defining dynamics in static spacetimes in terms of a second order operator acting on a Hilbert space defined on static slices. The present work extends this result by giving a similar prescription for defining dynamics in stationary spacetimes obeying certain mild assumptions. The prescription is defined in terms of a first order operator acting on a different Hilbert space from the one used in the static prescription. It preserves the important properties of the earlier one: the formal solution agrees with the Cauchy evolution within the domain of dependence, and smooth data of compact support always give rise to smooth solutions. In the static case, the first order formalism agrees with second order formalism (using specifically the Friedrichs extension). Applications to field quantization are also discussed. |
2105.06420 | Stephen C. Anco | Stephen C. Anco, Jordan Fazio | Analogue of a Laplace-Runge-Lenz vector for particle orbits (timelike
geodesics) in Schwarzschild spacetime | 42 pages; 15 figures. Major revision and material on LRL vector at
spatial infinity | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In Schwarzschild spacetime, the timelike geodesic equations, which define
particle orbits, have a well-known formulation as a dynamical system in
coordinates adapted to the timelike hypersurface containing the geodesic. For
equatorial geodesics, the resulting dynamical system is shown to possess a
conserved angular quantity and two conserved temporal quantities, whose
properties and physical meaning are analogues of the conserved
Laplace-Runge-Lenz vector, and its variant known as Hamilton's vector, in
Newtonian gravity. When a particle orbit is projected into the spatial
equatorial plane, the angular quantity yields the coordinate angle at which the
orbit has either a turning point (where the radial velocity is zero) or a
centripetal point (where the radial acceleration is zero). This is the same
property as the angle of the respective Laplace-Runge-Lenz and Hamilton vectors
in the plane of motion in Newtonian gravity. The temporal quantities yield the
coordinate time and the proper time at which those points are reached on the
orbit. In general, for orbits that have a single turning point, the three
quantities are globally constant; for orbits that possess more than one turning
point, the temporal quantities are just locally constant as they jump at every
successive turning point, while the angular quantity similarly jumps only if an
orbit is precessing. This is analogous to the properties of a generalized
Laplace-Runge-Lenz vector and generalized Hamilton's vector which are known to
exist for precessing orbits in post-Newtonian gravity. The angular conserved
quantity can be used to define a direct analogue of these vectors at spatial
infinity.
| [
{
"created": "Thu, 13 May 2021 16:55:26 GMT",
"version": "v1"
},
{
"created": "Thu, 23 Feb 2023 22:26:50 GMT",
"version": "v2"
},
{
"created": "Tue, 1 Aug 2023 21:11:37 GMT",
"version": "v3"
}
] | 2023-08-03 | [
[
"Anco",
"Stephen C.",
""
],
[
"Fazio",
"Jordan",
""
]
] | In Schwarzschild spacetime, the timelike geodesic equations, which define particle orbits, have a well-known formulation as a dynamical system in coordinates adapted to the timelike hypersurface containing the geodesic. For equatorial geodesics, the resulting dynamical system is shown to possess a conserved angular quantity and two conserved temporal quantities, whose properties and physical meaning are analogues of the conserved Laplace-Runge-Lenz vector, and its variant known as Hamilton's vector, in Newtonian gravity. When a particle orbit is projected into the spatial equatorial plane, the angular quantity yields the coordinate angle at which the orbit has either a turning point (where the radial velocity is zero) or a centripetal point (where the radial acceleration is zero). This is the same property as the angle of the respective Laplace-Runge-Lenz and Hamilton vectors in the plane of motion in Newtonian gravity. The temporal quantities yield the coordinate time and the proper time at which those points are reached on the orbit. In general, for orbits that have a single turning point, the three quantities are globally constant; for orbits that possess more than one turning point, the temporal quantities are just locally constant as they jump at every successive turning point, while the angular quantity similarly jumps only if an orbit is precessing. This is analogous to the properties of a generalized Laplace-Runge-Lenz vector and generalized Hamilton's vector which are known to exist for precessing orbits in post-Newtonian gravity. The angular conserved quantity can be used to define a direct analogue of these vectors at spatial infinity. |
gr-qc/9303005 | null | C. Farina, J. Gamboa and A. J. Segui-Santonja | Motion and Trajectories of Particles Around Three-Dimensional Black
Holes | Plain TeX, 9pp, IPNO-TH 93/06, DFTUZ 93/01 | Class.Quant.Grav.10:L193-L200,1993 | 10.1088/0264-9381/10/11/001 | null | gr-qc | null | The motion of relativistic particles around three dimensional black holes
following the Hamilton-Jacobi formalism is studied. It follows that the
Hamilton-Jacobi equation can be separated and reduced to quadratures in analogy
with the four dimensional case. It is shown that: a) particles are trapped by
the black hole independently of their energy and angular momentum, b) matter
alway falls to the centre of the black hole and cannot understake a motion with
stables orbits as in four dimensions. For the extreme values of the angular
momentum of the black hole, we were able to find exact solutions of the
equations of motion and trajectories of a test particle.
| [
{
"created": "Tue, 2 Mar 1993 14:54:42 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Farina",
"C.",
""
],
[
"Gamboa",
"J.",
""
],
[
"Segui-Santonja",
"A. J.",
""
]
] | The motion of relativistic particles around three dimensional black holes following the Hamilton-Jacobi formalism is studied. It follows that the Hamilton-Jacobi equation can be separated and reduced to quadratures in analogy with the four dimensional case. It is shown that: a) particles are trapped by the black hole independently of their energy and angular momentum, b) matter alway falls to the centre of the black hole and cannot understake a motion with stables orbits as in four dimensions. For the extreme values of the angular momentum of the black hole, we were able to find exact solutions of the equations of motion and trajectories of a test particle. |
1210.7388 | Wei-Tou Ni | K.G. Arun, Bala R. Iyer and Wei-Tou Ni | Fifth ASTROD Symposium and Outlook of Direct Gravitational-Wave
Detection | 8 pages, 5 figures | Asia Pacific Physics Newsletter Vol. 01, No. 02, pp. 6-11, 2012
(http://www.worldscientific.com/sda/1042/appn-v1n2.pdf) | null | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | From July 11 to July 13, 2012, Raman Research Institute (Bangalore, India)
hosted the Fifth International ASTROD Symposium on Laser Astrodynamics, Space
Test of Relativity and Gravitational-Wave Astronomy. This is a report on the
symposium with an exposition of the outlook of direct gravitational-wave
detection.
| [
{
"created": "Sun, 28 Oct 2012 01:04:43 GMT",
"version": "v1"
}
] | 2012-10-30 | [
[
"Arun",
"K. G.",
""
],
[
"Iyer",
"Bala R.",
""
],
[
"Ni",
"Wei-Tou",
""
]
] | From July 11 to July 13, 2012, Raman Research Institute (Bangalore, India) hosted the Fifth International ASTROD Symposium on Laser Astrodynamics, Space Test of Relativity and Gravitational-Wave Astronomy. This is a report on the symposium with an exposition of the outlook of direct gravitational-wave detection. |
2106.09037 | Sergio Hern\'andez-Cuenca | {\AA}smund Folkestad and Sergio Hern\'andez-Cuenca | Conformal Rigidity from Focusing | 12 pages | Class. Quant. Grav. 38 (2021) 21, 215005 | 10.1088/1361-6382/ac27ef | MIT-CTP/5307 | gr-qc hep-th math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The null curvature condition (NCC) is the requirement that the Ricci
curvature of a Lorentzian manifold be nonnegative along null directions, which
ensures the focusing of null geodesic congruences. In this note, we show that
the NCC together with the causal structure significantly constrain the metric.
In particular, we prove that any conformal rescaling of a vacuum spacetime
introduces either geodesic incompleteness or negative null curvature, provided
the conformal factor is non-constant on at least one complete null geodesic. In
the context of bulk reconstruction in AdS/CFT, our results combined with the
technique of light-cone cuts can be used in vacuum spacetimes to reconstruct
the full metric in regions probed by complete null geodesics reaching the
boundary. For non-vacuum spacetimes, our results constrain the conformal
factor, giving an approximate reconstruction of the metric.
| [
{
"created": "Wed, 16 Jun 2021 18:00:02 GMT",
"version": "v1"
}
] | 2021-10-15 | [
[
"Folkestad",
"Åsmund",
""
],
[
"Hernández-Cuenca",
"Sergio",
""
]
] | The null curvature condition (NCC) is the requirement that the Ricci curvature of a Lorentzian manifold be nonnegative along null directions, which ensures the focusing of null geodesic congruences. In this note, we show that the NCC together with the causal structure significantly constrain the metric. In particular, we prove that any conformal rescaling of a vacuum spacetime introduces either geodesic incompleteness or negative null curvature, provided the conformal factor is non-constant on at least one complete null geodesic. In the context of bulk reconstruction in AdS/CFT, our results combined with the technique of light-cone cuts can be used in vacuum spacetimes to reconstruct the full metric in regions probed by complete null geodesics reaching the boundary. For non-vacuum spacetimes, our results constrain the conformal factor, giving an approximate reconstruction of the metric. |
2402.15323 | Octavian Micu | Octavian Micu | Dynamical stability of bootstrapped Newtonian stars | 17 pages, 3 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We investigate the dynamical stability of bootstrapped Newtonian stars
following homologous adiabatic perturbations, focusing on objects of low or
intermediate compactness. The results show that for stars with homogeneous
densities these perturbations induce some oscillatory behaviour regardless of
their compactness, density and adiabatic index, which makes them dynamically
stable. In the case or polytropes with density profiles approximated by
Gaussian distributions, both stable and unstable behaviours are possible. It
was also shown that in the limit in which the density profile of the Gaussian
density distribution flattens out, the parameter space for which the
perturbations result in an oscillatory behaviour increases, which is in
agreement with the case of stars with homogeneous densities.
| [
{
"created": "Fri, 23 Feb 2024 13:42:55 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Aug 2024 09:22:24 GMT",
"version": "v2"
}
] | 2024-08-08 | [
[
"Micu",
"Octavian",
""
]
] | We investigate the dynamical stability of bootstrapped Newtonian stars following homologous adiabatic perturbations, focusing on objects of low or intermediate compactness. The results show that for stars with homogeneous densities these perturbations induce some oscillatory behaviour regardless of their compactness, density and adiabatic index, which makes them dynamically stable. In the case or polytropes with density profiles approximated by Gaussian distributions, both stable and unstable behaviours are possible. It was also shown that in the limit in which the density profile of the Gaussian density distribution flattens out, the parameter space for which the perturbations result in an oscillatory behaviour increases, which is in agreement with the case of stars with homogeneous densities. |
1007.4846 | Paulo Laerte Natti | Mario Goto, Paulo Laerte Natti and Erica Regina Takano Natti | On the equivalence principle and gravitational and inertial mass
relation of classical charged particles | null | Class.Quant.Grav.27:025005,2010 | 10.1088/0264-9381/27/2/025005 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that the locally constant force necessary to get a stable hyperbolic
motion regime for classical charged point particles, actually, is a combination
of an applied external force and of the electromagnetic radiation reaction
force. It implies, as the strong Equivalence Principle is valid, that the
passive gravitational mass of a charged point particle should be slight greater
than its inertial mass. An interesting new feature that emerges from the
unexpected behavior of the gravitational and inertial mass relation, for
classical charged particles, at very strong gravitational field, is the
existence of a critical, particle dependent, gravitational field value that
signs the validity domain of the strong Equivalence Principle. For electron and
proton, these critical field values are $g_{c}\simeq 4.8\times 10^{31}m/s^{2}$
and $g_{c}\simeq 8.8\times 10^{34}m/s^{2}$, respectively.
| [
{
"created": "Tue, 27 Jul 2010 23:30:11 GMT",
"version": "v1"
}
] | 2014-11-21 | [
[
"Goto",
"Mario",
""
],
[
"Natti",
"Paulo Laerte",
""
],
[
"Natti",
"Erica Regina Takano",
""
]
] | We show that the locally constant force necessary to get a stable hyperbolic motion regime for classical charged point particles, actually, is a combination of an applied external force and of the electromagnetic radiation reaction force. It implies, as the strong Equivalence Principle is valid, that the passive gravitational mass of a charged point particle should be slight greater than its inertial mass. An interesting new feature that emerges from the unexpected behavior of the gravitational and inertial mass relation, for classical charged particles, at very strong gravitational field, is the existence of a critical, particle dependent, gravitational field value that signs the validity domain of the strong Equivalence Principle. For electron and proton, these critical field values are $g_{c}\simeq 4.8\times 10^{31}m/s^{2}$ and $g_{c}\simeq 8.8\times 10^{34}m/s^{2}$, respectively. |
2306.11797 | Shreejit Jadhav | Shreejit Jadhav, Mihir Shrivastava, Sanjit Mitra | Towards a robust and reliable deep learning approach for detection of
compact binary mergers in gravitational wave data | 22 pages, 22 figures | Mach. Learn.: Sci. Technol. 4 045028 (2023) | 10.1088/2632-2153/ad0938 | null | gr-qc astro-ph.HE cs.LG | http://creativecommons.org/licenses/by/4.0/ | The ability of deep learning (DL) approaches to learn generalised signal and
noise models, coupled with their fast inference on GPUs, holds great promise
for enhancing gravitational-wave (GW) searches in terms of speed, parameter
space coverage, and search sensitivity. However, the opaque nature of DL models
severely harms their reliability. In this work, we meticulously develop a DL
model stage-wise and work towards improving its robustness and reliability.
First, we address the problems in maintaining the purity of training data by
deriving a new metric that better reflects the visual strength of the 'chirp'
signal features in the data. Using a reduced, smooth representation obtained
through a variational auto-encoder (VAE), we build a classifier to search for
compact binary coalescence (CBC) signals. Our tests on real LIGO data show an
impressive performance of the model. However, upon probing the robustness of
the model through adversarial attacks, its simple failure modes were
identified, underlining how such models can still be highly fragile. As a first
step towards bringing robustness, we retrain the model in a novel framework
involving a generative adversarial network (GAN). Over the course of training,
the model learns to eliminate the primary modes of failure identified by the
adversaries. Although absolute robustness is practically impossible to achieve,
we demonstrate some fundamental improvements earned through such training, like
sparseness and reduced degeneracy in the extracted features at different layers
inside the model. We show that these gains are achieved at practically zero
loss in terms of model performance on real LIGO data before and after GAN
training. Through a direct search on 8.8 days of LIGO data, we recover two
significant CBC events from GWTC-2.1, GW190519_153544 and GW190521_074359. We
also report the search sensitivity obtained from an injection study.
| [
{
"created": "Tue, 20 Jun 2023 18:00:05 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Nov 2023 21:17:16 GMT",
"version": "v2"
}
] | 2023-11-15 | [
[
"Jadhav",
"Shreejit",
""
],
[
"Shrivastava",
"Mihir",
""
],
[
"Mitra",
"Sanjit",
""
]
] | The ability of deep learning (DL) approaches to learn generalised signal and noise models, coupled with their fast inference on GPUs, holds great promise for enhancing gravitational-wave (GW) searches in terms of speed, parameter space coverage, and search sensitivity. However, the opaque nature of DL models severely harms their reliability. In this work, we meticulously develop a DL model stage-wise and work towards improving its robustness and reliability. First, we address the problems in maintaining the purity of training data by deriving a new metric that better reflects the visual strength of the 'chirp' signal features in the data. Using a reduced, smooth representation obtained through a variational auto-encoder (VAE), we build a classifier to search for compact binary coalescence (CBC) signals. Our tests on real LIGO data show an impressive performance of the model. However, upon probing the robustness of the model through adversarial attacks, its simple failure modes were identified, underlining how such models can still be highly fragile. As a first step towards bringing robustness, we retrain the model in a novel framework involving a generative adversarial network (GAN). Over the course of training, the model learns to eliminate the primary modes of failure identified by the adversaries. Although absolute robustness is practically impossible to achieve, we demonstrate some fundamental improvements earned through such training, like sparseness and reduced degeneracy in the extracted features at different layers inside the model. We show that these gains are achieved at practically zero loss in terms of model performance on real LIGO data before and after GAN training. Through a direct search on 8.8 days of LIGO data, we recover two significant CBC events from GWTC-2.1, GW190519_153544 and GW190521_074359. We also report the search sensitivity obtained from an injection study. |
2311.17639 | Gungwon Kang | Yeong-Bok Bae, Chan Park, Edwin J. Son, Sang-Hyeon Ahn, Minjoong
Jeong, Gungwon Kang, Chunglee Kim, Dong Lak Kim, Jaewan Kim, Whansun Kim,
Hyung Mok Lee, Yong-Ho Lee, Ronald S. Norton, John J. Oh, Sang Hoon Oh, and
Ho Jung Paik | A superconducting tensor detector for mid-frequency gravitational waves:
its multi-channel nature and main astrophysical targets | 35 pages, 8 figures, 4 tables | null | null | null | gr-qc astro-ph.IM hep-ex hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Mid-frequency band gravitational-wave detectors will be complementary for the
existing Earth-based detectors (sensitive above 10 Hz or so) and the future
space-based detectors such as LISA, which will be sensitive below around 10
mHz. A ground-based superconducting omnidirectional gravitational radiation
observatory (SOGRO) has recently been proposed along with several design
variations for the frequency band of 0.1 to 10 Hz. For three conceptual designs
of SOGRO (e.g., pSOGRO, SOGRO and aSOGRO), we examine their multi-channel
natures, sensitivities and science cases. One of the key characteristics of the
SOGRO concept is its six detection channels. The response functions of each
channel are calculated for all possible gravitational wave polarizations
including scalar and vector modes. Combining these response functions, we also
confirm the omnidirectional nature of SOGRO. Hence, even a single SOGRO
detector will be able to determine the position of a source and polarizations
of gravitational waves, if detected. Taking into account SOGRO's sensitivity
and technical requirements, two main targets are most plausible: gravitational
waves from compact binaries and stochastic backgrounds. Based on assumptions we
consider in this work, detection rates for intermediate-mass binary black holes
(in the mass range of hundreds up to $10^{4}$ $M_\odot$) are expected to be
$0.0014-2.5 \,\, {\rm yr}^{-1}$. In order to detect stochastic gravitational
wave background, multiple detectors are required. Two aSOGRO detector networks
may be able to put limits on the stochastic background beyond the indirect
limit from cosmological observations.
| [
{
"created": "Wed, 29 Nov 2023 13:53:44 GMT",
"version": "v1"
}
] | 2023-11-30 | [
[
"Bae",
"Yeong-Bok",
""
],
[
"Park",
"Chan",
""
],
[
"Son",
"Edwin J.",
""
],
[
"Ahn",
"Sang-Hyeon",
""
],
[
"Jeong",
"Minjoong",
""
],
[
"Kang",
"Gungwon",
""
],
[
"Kim",
"Chunglee",
""
],
[
"Kim",
"Dong Lak",
""
],
[
"Kim",
"Jaewan",
""
],
[
"Kim",
"Whansun",
""
],
[
"Lee",
"Hyung Mok",
""
],
[
"Lee",
"Yong-Ho",
""
],
[
"Norton",
"Ronald S.",
""
],
[
"Oh",
"John J.",
""
],
[
"Oh",
"Sang Hoon",
""
],
[
"Paik",
"Ho Jung",
""
]
] | Mid-frequency band gravitational-wave detectors will be complementary for the existing Earth-based detectors (sensitive above 10 Hz or so) and the future space-based detectors such as LISA, which will be sensitive below around 10 mHz. A ground-based superconducting omnidirectional gravitational radiation observatory (SOGRO) has recently been proposed along with several design variations for the frequency band of 0.1 to 10 Hz. For three conceptual designs of SOGRO (e.g., pSOGRO, SOGRO and aSOGRO), we examine their multi-channel natures, sensitivities and science cases. One of the key characteristics of the SOGRO concept is its six detection channels. The response functions of each channel are calculated for all possible gravitational wave polarizations including scalar and vector modes. Combining these response functions, we also confirm the omnidirectional nature of SOGRO. Hence, even a single SOGRO detector will be able to determine the position of a source and polarizations of gravitational waves, if detected. Taking into account SOGRO's sensitivity and technical requirements, two main targets are most plausible: gravitational waves from compact binaries and stochastic backgrounds. Based on assumptions we consider in this work, detection rates for intermediate-mass binary black holes (in the mass range of hundreds up to $10^{4}$ $M_\odot$) are expected to be $0.0014-2.5 \,\, {\rm yr}^{-1}$. In order to detect stochastic gravitational wave background, multiple detectors are required. Two aSOGRO detector networks may be able to put limits on the stochastic background beyond the indirect limit from cosmological observations. |
2307.13099 | Jay Tasson | Anarya Ray, Pinchen Fan, Vincent F. He, Malachy Bloom, Suyu Michael
Yang, Jay D. Tasson, and Jolien D. E. Creighton | Measuring Gravitational Wave Speed and Lorentz Violation with the First
Three Gravitational-Wave Catalogs | 17 pages, 4 figures, 3 tables | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The speed of gravitational waves $v_g$ can be measured with the time delay
between gravitational-wave detectors. Our study provides a more precise
measurement of $v_g$ using gravitational-wave signals only, compared with
previous studies. We select 52 gravitational-wave events that were detected
with high confidence by at least two detectors in the first three observing
runs (O1, O2, and O3) of Advanced LIGO and Advanced Virgo. We use Markov chain
Monte Carlo and nested sampling to estimate the $v_g$ posterior distribution
for each of those events. We then combine their posterior distributions to find
the 90% credible interval of the combined $v_g$ distribution for which we
obtain $0.99^{+0.02}_{-0.02}c$ without the use of more accurate sky
localization from the electromagnetic signal associated with GW170817.
Restricting attention to the 50 binary black hole events generates the same
result, while the use of the electromagnetic sky localization for GW170817
gives a tighter constraint of $0.99^{+0.01}_{-0.02}c$. The abundance of
gravitational wave events allows us to apply hierarchical Bayesian inference on
the posterior samples to simultaneously constrain all nine coefficients for
Lorentz violation in the nondispersive, nonbirefringent limit of the
gravitational sector of the Standard-Model Extension test framework. We compare
the hierarchical Bayesian inference method with other methods of combining
limits on Lorentz violation in the gravity sector that are found in the
literature.
| [
{
"created": "Mon, 24 Jul 2023 19:41:13 GMT",
"version": "v1"
}
] | 2023-07-26 | [
[
"Ray",
"Anarya",
""
],
[
"Fan",
"Pinchen",
""
],
[
"He",
"Vincent F.",
""
],
[
"Bloom",
"Malachy",
""
],
[
"Yang",
"Suyu Michael",
""
],
[
"Tasson",
"Jay D.",
""
],
[
"Creighton",
"Jolien D. E.",
""
]
] | The speed of gravitational waves $v_g$ can be measured with the time delay between gravitational-wave detectors. Our study provides a more precise measurement of $v_g$ using gravitational-wave signals only, compared with previous studies. We select 52 gravitational-wave events that were detected with high confidence by at least two detectors in the first three observing runs (O1, O2, and O3) of Advanced LIGO and Advanced Virgo. We use Markov chain Monte Carlo and nested sampling to estimate the $v_g$ posterior distribution for each of those events. We then combine their posterior distributions to find the 90% credible interval of the combined $v_g$ distribution for which we obtain $0.99^{+0.02}_{-0.02}c$ without the use of more accurate sky localization from the electromagnetic signal associated with GW170817. Restricting attention to the 50 binary black hole events generates the same result, while the use of the electromagnetic sky localization for GW170817 gives a tighter constraint of $0.99^{+0.01}_{-0.02}c$. The abundance of gravitational wave events allows us to apply hierarchical Bayesian inference on the posterior samples to simultaneously constrain all nine coefficients for Lorentz violation in the nondispersive, nonbirefringent limit of the gravitational sector of the Standard-Model Extension test framework. We compare the hierarchical Bayesian inference method with other methods of combining limits on Lorentz violation in the gravity sector that are found in the literature. |
2212.05536 | Bahram Mashhoon | Javad Tabatabaei, Shant Baghram, and Bahram Mashhoon | Local Limit of Nonlocal Gravity: A Teleparallel Extension of General
Relativity | 30 pages; v2: expanded discussion of the modified flat model
regarding H_0 tension; v3: treatment expanded, presentation improved | Monthly Notices of the Royal Astronomical Society 530, 795-811
(2024) | 10.1093/mnras/stae830 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | We describe a general constitutive framework for a teleparallel extension of
the general theory of relativity. This approach goes beyond the teleparallel
equivalent of general relativity (TEGR) by broadening the analogy with the
electrodynamics of media. In particular, the main purpose of this paper is to
investigate in detail a local constitutive extension of TEGR that is the local
limit of nonlocal gravity (NLG). Within this framework, we study the modified
FLRW cosmological models. Of these, the most cogent turns out to be the
modified Cartesian flat model which is shown to be inconsistent with the
existence of a positive cosmological constant. Moreover, dynamic dark energy
and other components of the modified Cartesian flat model evolve differently
with the expansion of the universe as compared to the standard flat
cosmological model. The observational consequences of the modified Cartesian
flat model are briefly explored and it is shown that the model is capable of
resolving the H_0 tension.
| [
{
"created": "Sun, 11 Dec 2022 16:25:52 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Apr 2023 19:52:03 GMT",
"version": "v2"
},
{
"created": "Fri, 17 Nov 2023 11:22:33 GMT",
"version": "v3"
},
{
"created": "Thu, 11 Apr 2024 16:20:43 GMT",
"version": "v4"
}
] | 2024-04-12 | [
[
"Tabatabaei",
"Javad",
""
],
[
"Baghram",
"Shant",
""
],
[
"Mashhoon",
"Bahram",
""
]
] | We describe a general constitutive framework for a teleparallel extension of the general theory of relativity. This approach goes beyond the teleparallel equivalent of general relativity (TEGR) by broadening the analogy with the electrodynamics of media. In particular, the main purpose of this paper is to investigate in detail a local constitutive extension of TEGR that is the local limit of nonlocal gravity (NLG). Within this framework, we study the modified FLRW cosmological models. Of these, the most cogent turns out to be the modified Cartesian flat model which is shown to be inconsistent with the existence of a positive cosmological constant. Moreover, dynamic dark energy and other components of the modified Cartesian flat model evolve differently with the expansion of the universe as compared to the standard flat cosmological model. The observational consequences of the modified Cartesian flat model are briefly explored and it is shown that the model is capable of resolving the H_0 tension. |
0710.0214 | Hamid Reza Sepangi | K. Atazadeh and H. R. Sepangi | Curvature corrections in DGP brane cosmology | 11 pages, 2 figures | JCAP0709:020,2007 | 10.1088/1475-7516/2007/09/020 | null | gr-qc hep-th | null | We consider a DGP inspired brane scenario where the action on the brane is
augmented by a function of the Ricci scalar, ${\cal L}(R)$. The cosmological
implications that such a scenario entails are examined for $R^{n}$ and shown to
be consistent with a universe expanding with power-law acceleration. It is
shown that two classes of solutions exist for the usual FRW metric and small
Hubble radii. When the Hubble radius becomes larger, we either have a
transition to a fully 5D regime or to a self-inflationary solution which
produces a late accelerated expansion such that the radius becomes a function
of $n$.
| [
{
"created": "Mon, 1 Oct 2007 06:55:25 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Atazadeh",
"K.",
""
],
[
"Sepangi",
"H. R.",
""
]
] | We consider a DGP inspired brane scenario where the action on the brane is augmented by a function of the Ricci scalar, ${\cal L}(R)$. The cosmological implications that such a scenario entails are examined for $R^{n}$ and shown to be consistent with a universe expanding with power-law acceleration. It is shown that two classes of solutions exist for the usual FRW metric and small Hubble radii. When the Hubble radius becomes larger, we either have a transition to a fully 5D regime or to a self-inflationary solution which produces a late accelerated expansion such that the radius becomes a function of $n$. |
1102.0053 | Sourav Bhattacharya | Sourav Bhattacharya and Amitabha Lahiri | No hair theorems for stationary axisymmetric black holes | v2, 10pp; minor changes, added references | Phys.Rev.D83:124017,2011 | 10.1103/PhysRevD.83.124017 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a non-perturbative proof of the no hair theorems corresponding to
scalar and Proca fields for stationary axisymmetric de Sitter black hole
spacetimes. Our method also applies to asymptotically flat and under a
reasonable assumption, to asymptotically anti-de Sitter spacetimes.
| [
{
"created": "Tue, 1 Feb 2011 01:46:26 GMT",
"version": "v1"
},
{
"created": "Fri, 20 May 2011 05:35:56 GMT",
"version": "v2"
}
] | 2011-06-24 | [
[
"Bhattacharya",
"Sourav",
""
],
[
"Lahiri",
"Amitabha",
""
]
] | We present a non-perturbative proof of the no hair theorems corresponding to scalar and Proca fields for stationary axisymmetric de Sitter black hole spacetimes. Our method also applies to asymptotically flat and under a reasonable assumption, to asymptotically anti-de Sitter spacetimes. |
1709.05223 | Ho Lee | Ho Lee, Ernesto Nungesser | Late-time behaviour of the Einstein-Boltzmann system with a positive
cosmological constant | null | null | 10.1088/1361-6382/aa9c8f | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study the Einstein-Boltzmann system for Israel particles
with a positive cosmological constant. We consider spatially homogeneous
solutions of Bianchi types except IX and obtain future global existence and
asymptotic behaviour of solutions to the Einstein-Boltzmann system. The result
shows that the solutions converge to the de Sitter solution at late times.
| [
{
"created": "Fri, 15 Sep 2017 14:08:51 GMT",
"version": "v1"
}
] | 2017-12-27 | [
[
"Lee",
"Ho",
""
],
[
"Nungesser",
"Ernesto",
""
]
] | In this paper we study the Einstein-Boltzmann system for Israel particles with a positive cosmological constant. We consider spatially homogeneous solutions of Bianchi types except IX and obtain future global existence and asymptotic behaviour of solutions to the Einstein-Boltzmann system. The result shows that the solutions converge to the de Sitter solution at late times. |
2302.08804 | Massimiliano Rinaldi | Matteo Fontana and Massimiliano Rinaldi | Stress-energy tensor correlations across regular black holes horizons | Version accepted for publication in PRD | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Hawking radiation can be regarded as a spontaneous and continuous creation of
virtual particle-antiparticle pairs outside the event horizon of a black hole
where strong tidal forces prevent the annihilation: the particle escapes to
infinity contributing to the Hawking flux, while its corresponding antiparticle
partner enters the event horizon and ultimately reaches the singularity. The
aim of this paper is to investigate the energy density correlations between the
Hawking particles and their partners across the event horizon of two models of
non-singular black holes by calculating the two-point correlation function of
the density operator of a massless scalar field. This analysis is motivated by
the fact that in acoustic black holes particle-partner correlations are
signalled by the presence of a peak in the equal time density-density
correlator. Performing the calculation in a Schwarzschild black hole it was
shown in [1] that the peak does not appear, mainly because of the singularity.
It is then interesting to consider what happens when the singularity is not
present. In the Hayward and Simpson-Visser non-singular black holes we show
that the density-density correlator remains finite when the partner particle
approaches the hypersurface that replaces the singularity, opening the
possibility that partner-particle correlations can propagate towards other
regions of spacetime instead of being lost in a singularity.
| [
{
"created": "Fri, 17 Feb 2023 10:57:18 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Nov 2023 13:33:35 GMT",
"version": "v2"
}
] | 2023-11-14 | [
[
"Fontana",
"Matteo",
""
],
[
"Rinaldi",
"Massimiliano",
""
]
] | Hawking radiation can be regarded as a spontaneous and continuous creation of virtual particle-antiparticle pairs outside the event horizon of a black hole where strong tidal forces prevent the annihilation: the particle escapes to infinity contributing to the Hawking flux, while its corresponding antiparticle partner enters the event horizon and ultimately reaches the singularity. The aim of this paper is to investigate the energy density correlations between the Hawking particles and their partners across the event horizon of two models of non-singular black holes by calculating the two-point correlation function of the density operator of a massless scalar field. This analysis is motivated by the fact that in acoustic black holes particle-partner correlations are signalled by the presence of a peak in the equal time density-density correlator. Performing the calculation in a Schwarzschild black hole it was shown in [1] that the peak does not appear, mainly because of the singularity. It is then interesting to consider what happens when the singularity is not present. In the Hayward and Simpson-Visser non-singular black holes we show that the density-density correlator remains finite when the partner particle approaches the hypersurface that replaces the singularity, opening the possibility that partner-particle correlations can propagate towards other regions of spacetime instead of being lost in a singularity. |
1607.04481 | Riccardo Moriconi | Riccardo Moriconi, Giovanni Montani, Salvatore Capozziello | Big-bounce cosmology from quantum gravity: The case of a cyclical
Bianchi I universe | 15 pages, 9 figures | Phys. Rev. D 94, 023519, 2016 | 10.1103/PhysRevD.94.023519 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyse the classical and quantum dynamics of a Bianchi I model in the
presence of a small negative cosmological constant characterizing its evolution
in term of the dust-time dualism. We demonstrate that in a canonical metric
approach, the cosmological singularity is removed in correspondence to a
positive defined value of the dust energy density. Furthermore, the quantum
Big-Bounce is connected to the Universe turning point via a well-defined
semiclassical limit. Then we can reliably infer that the proposed scenario is
compatible with a cyclical Universe picture. We also show how, when the
contribution of the dust energy density is sufficiently high, the proposed
scenario can be extended to the Bianchi IX cosmology and therefore how it can
be regarded as a paradigm for the generic cosmological model. Finally, we
investigate the origin of the observed cut-off on the cosmological dynamics,
demonstrating how the Big-Bounce evolution can be mimicked by the same
semiclassical scenario, where the negative cosmological constant is replaced
via a polymer discretization of the Universe volume. A direct proportionality
law between such two parameters is then established.
| [
{
"created": "Fri, 15 Jul 2016 12:32:53 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Sep 2016 10:29:45 GMT",
"version": "v2"
}
] | 2016-09-02 | [
[
"Moriconi",
"Riccardo",
""
],
[
"Montani",
"Giovanni",
""
],
[
"Capozziello",
"Salvatore",
""
]
] | We analyse the classical and quantum dynamics of a Bianchi I model in the presence of a small negative cosmological constant characterizing its evolution in term of the dust-time dualism. We demonstrate that in a canonical metric approach, the cosmological singularity is removed in correspondence to a positive defined value of the dust energy density. Furthermore, the quantum Big-Bounce is connected to the Universe turning point via a well-defined semiclassical limit. Then we can reliably infer that the proposed scenario is compatible with a cyclical Universe picture. We also show how, when the contribution of the dust energy density is sufficiently high, the proposed scenario can be extended to the Bianchi IX cosmology and therefore how it can be regarded as a paradigm for the generic cosmological model. Finally, we investigate the origin of the observed cut-off on the cosmological dynamics, demonstrating how the Big-Bounce evolution can be mimicked by the same semiclassical scenario, where the negative cosmological constant is replaced via a polymer discretization of the Universe volume. A direct proportionality law between such two parameters is then established. |
2210.00900 | Mohd Salman | Absos Ali Shaikh, Musavvir Ali, Mohammad Salman and Fusun Ozen Zengin | Curvature inheritance symmetry on M-projectively flat spacetimes | null | International Journal of Geometric Methods in Modern Physics(2023) | 10.1142/S0219887823500883 | 2350088 | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | The paper aims to investigate curvature inheritance symmetry in
M-projectively flat spacetimes. It is shown that the curvature inheritance
symmetry in M-projectively flat spacetime is a conformal motion. We have proved
that M- projective curvature tensor follows the symmetry inheritance property
along a vector field $\xi$, when spacetime admits the conditions of both
curvature inheritance symmetry and conformal motion or motion along the vector
field $\xi$. Also, we have derived some results for M-projectively flat
spacetime with perfect fluid following the Einstein field equations with a
cosmological term and admitting the curvature inheritance symmetry along the
vector field $\xi$. We have shown that an M-projectively flat perfect fluid
spacetime obeying the Einstein field equations with a cosmological term and
admitting the curvature inheritance symmetry along a vector field $\xi$ is
either a vacuum or satisfies the vacuum-like equation of state. We have also
shown that such spacetimes with the energy momentum tensor of an
electromagnetic field distribution do not admit any curvature symmetry of
general relativity. Finally, an example of M-projectively flat spacetime has
been exhibited.
| [
{
"created": "Fri, 30 Sep 2022 11:51:42 GMT",
"version": "v1"
}
] | 2023-02-02 | [
[
"Shaikh",
"Absos Ali",
""
],
[
"Ali",
"Musavvir",
""
],
[
"Salman",
"Mohammad",
""
],
[
"Zengin",
"Fusun Ozen",
""
]
] | The paper aims to investigate curvature inheritance symmetry in M-projectively flat spacetimes. It is shown that the curvature inheritance symmetry in M-projectively flat spacetime is a conformal motion. We have proved that M- projective curvature tensor follows the symmetry inheritance property along a vector field $\xi$, when spacetime admits the conditions of both curvature inheritance symmetry and conformal motion or motion along the vector field $\xi$. Also, we have derived some results for M-projectively flat spacetime with perfect fluid following the Einstein field equations with a cosmological term and admitting the curvature inheritance symmetry along the vector field $\xi$. We have shown that an M-projectively flat perfect fluid spacetime obeying the Einstein field equations with a cosmological term and admitting the curvature inheritance symmetry along a vector field $\xi$ is either a vacuum or satisfies the vacuum-like equation of state. We have also shown that such spacetimes with the energy momentum tensor of an electromagnetic field distribution do not admit any curvature symmetry of general relativity. Finally, an example of M-projectively flat spacetime has been exhibited. |
gr-qc/9902055 | Amos Ori | Amos Ori | Remark on the strength of singularities with a C^0 metric | 3 pages, LaTeX | null | null | null | gr-qc | null | Recently Nolan constructed a spherically-symmetric spacetime admitting a
spacelike curvature singularity with a regular C^0 metric. We show here that
this singularity is in fact weak.
| [
{
"created": "Thu, 18 Feb 1999 21:36:33 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Ori",
"Amos",
""
]
] | Recently Nolan constructed a spherically-symmetric spacetime admitting a spacelike curvature singularity with a regular C^0 metric. We show here that this singularity is in fact weak. |
gr-qc/0702082 | David Wiltshire | David L. Wiltshire | Cosmic clocks, cosmic variance and cosmic averages | 72 pages, 5 figures; v4 cosmetic fixes to match published paper, New
J. Phys. Focus Issue on Dark Energy; further summary at
http://www2.phys.canterbury.ac.nz/~dlw24/universe/ | NewJ.Phys.9:377,2007 | 10.1088/1367-2630/9/10/377 | null | gr-qc astro-ph hep-ph hep-th | null | Cosmic acceleration is explained quantitatively, purely in general
relativity, as an apparent effect due to quasilocal gravitational energy
differences that arise in the decoupling of bound systems from the global
expansion of the universe. "Dark energy" is recognised as a misidentification
of those aspects of gravitational energy which by virtue of the equivalence
principle cannot be localised, namely gradients in the energy associated with
the expansion of space and spatial curvature variations in an inhomogeneous
universe, as we observe. Gravitational energy differences between observers in
bound systems, such as galaxies, and volume-averaged comoving locations within
voids in freely expanding space can be so large that the time dilation between
the two significantly affects the parameters of any effective homogeneous
isotropic model one fits to the universe. A new approach to cosmological
averaging is presented, which implicitly solves the Sandage-de Vaucouleurs
paradox. When combined with a nonlinear scheme for cosmological evolution with
back-reaction via the Buchert equations, a new observationally viable
quantitative model of the universe is obtained. The expansion age is increased,
allowing more time for structure formation. The baryon density fraction
obtained from primordial nucleosynthesis bounds can be significantly larger,
yet consistent with primordial lithium abundance measurements. The angular
scale of the first Doppler peak in the CMB anisotropy spectrum fits the new
model despite an average negative spatial curvature at late epochs, resolving
the anomaly associated with ellipticity in the CMB anisotropies. A number of
other testable consequences are discussed, with the potential to profoundly
change the whole of theoretical and observational cosmology. [Abridged]
| [
{
"created": "Thu, 15 Feb 2007 20:34:13 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Mar 2007 20:45:58 GMT",
"version": "v2"
},
{
"created": "Tue, 18 Sep 2007 04:37:33 GMT",
"version": "v3"
},
{
"created": "Thu, 1 Nov 2007 04:18:11 GMT",
"version": "v4"
}
] | 2008-11-26 | [
[
"Wiltshire",
"David L.",
""
]
] | Cosmic acceleration is explained quantitatively, purely in general relativity, as an apparent effect due to quasilocal gravitational energy differences that arise in the decoupling of bound systems from the global expansion of the universe. "Dark energy" is recognised as a misidentification of those aspects of gravitational energy which by virtue of the equivalence principle cannot be localised, namely gradients in the energy associated with the expansion of space and spatial curvature variations in an inhomogeneous universe, as we observe. Gravitational energy differences between observers in bound systems, such as galaxies, and volume-averaged comoving locations within voids in freely expanding space can be so large that the time dilation between the two significantly affects the parameters of any effective homogeneous isotropic model one fits to the universe. A new approach to cosmological averaging is presented, which implicitly solves the Sandage-de Vaucouleurs paradox. When combined with a nonlinear scheme for cosmological evolution with back-reaction via the Buchert equations, a new observationally viable quantitative model of the universe is obtained. The expansion age is increased, allowing more time for structure formation. The baryon density fraction obtained from primordial nucleosynthesis bounds can be significantly larger, yet consistent with primordial lithium abundance measurements. The angular scale of the first Doppler peak in the CMB anisotropy spectrum fits the new model despite an average negative spatial curvature at late epochs, resolving the anomaly associated with ellipticity in the CMB anisotropies. A number of other testable consequences are discussed, with the potential to profoundly change the whole of theoretical and observational cosmology. [Abridged] |
1505.02448 | Edward Anderson | Edward Anderson | Spherical Relationalism | 8 pages, including 2 figs | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper considers passing from the usual $\mathbb{R}^d$ model of absolute
space to $\mathbb{S}^d$ at the level of relational particle models. Both
approaches' $d = 1$ cases are rather simpler than their $d \geq 2$ cases, with
$N$ particles in $\mathbb{S}^1$ admitting a straightforward reduction with
shape space $\mathbb{T}^{N - 1}$. The $\mathbb{S}^2$ and $\mathbb{S}^3$ cases -
observed skies and the simplest closed GR cosmologies respectively -- are also
considered, the latter in the contexts of both static and dynamical radius of
the model universe. The space of relational triangles on $\mathbb{S}^2$ is
hyperbolic 3-space $\mathbb{H}^3$. Overall, by passing to a closed underlying
absolute space, and then to dynamical notion of space, we close some of the
modelling gaps between relational particle models and geometrodynamics or its
inhomogeneous perturbative regime of interest in cosmology. Quantum
counterparts are also outlined, for use as model arenas of quantum cosmology.
These models are useful in further considerations of both classical and quantum
background independence.
| [
{
"created": "Sun, 10 May 2015 22:11:49 GMT",
"version": "v1"
}
] | 2015-05-12 | [
[
"Anderson",
"Edward",
""
]
] | This paper considers passing from the usual $\mathbb{R}^d$ model of absolute space to $\mathbb{S}^d$ at the level of relational particle models. Both approaches' $d = 1$ cases are rather simpler than their $d \geq 2$ cases, with $N$ particles in $\mathbb{S}^1$ admitting a straightforward reduction with shape space $\mathbb{T}^{N - 1}$. The $\mathbb{S}^2$ and $\mathbb{S}^3$ cases - observed skies and the simplest closed GR cosmologies respectively -- are also considered, the latter in the contexts of both static and dynamical radius of the model universe. The space of relational triangles on $\mathbb{S}^2$ is hyperbolic 3-space $\mathbb{H}^3$. Overall, by passing to a closed underlying absolute space, and then to dynamical notion of space, we close some of the modelling gaps between relational particle models and geometrodynamics or its inhomogeneous perturbative regime of interest in cosmology. Quantum counterparts are also outlined, for use as model arenas of quantum cosmology. These models are useful in further considerations of both classical and quantum background independence. |
2210.10907 | Liu Zhao | Song Liu, Xin Hao, Shaofan Liu, and Liu Zhao | Covariant transport equation and gravito-conductivity in generic
stationary spacetimes | 16 pages. v2: misc corrections and new subsection on weak field
limit. v3: version published in EPJC | EPJC 82:1100, 2022 | 10.1140/epjc/s10052-022-11093-3 | null | gr-qc cond-mat.stat-mech hep-th | http://creativecommons.org/licenses/by/4.0/ | We find a near detailed balance solution to the relativistic Boltzmann
equation under the relaxation time approximation with a collision term which
differs from the Anderson-Witting model and is dependent on the stationary
observer. Using this new solution, we construct an explicit covariant transport
equation for the particle flux in response to the generalized temperature and
chemical potential gradients in generic stationary spacetimes, with the
transport tensors characterized by some integral functions in the chemical
potential and the relativistic coldness. To illustrate the application of the
transport equation we study probe systems in Rindler and Kerr spacetimes and
analyze the asymptotic properties of the gravito-conductivity tensor in the
near horizon limit. It turns out that both the longitudinal and lateral parts
(if present) of the gravito-conductivity tend to be divergent in the near
horizon limit. In the weak field limit, our results coincide with with the
non-relativistic gravitational transport equation which follows from the direct
application of the Drude model.
| [
{
"created": "Wed, 19 Oct 2022 22:13:52 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Oct 2022 16:55:37 GMT",
"version": "v2"
},
{
"created": "Wed, 7 Dec 2022 00:01:09 GMT",
"version": "v3"
}
] | 2022-12-08 | [
[
"Liu",
"Song",
""
],
[
"Hao",
"Xin",
""
],
[
"Liu",
"Shaofan",
""
],
[
"Zhao",
"Liu",
""
]
] | We find a near detailed balance solution to the relativistic Boltzmann equation under the relaxation time approximation with a collision term which differs from the Anderson-Witting model and is dependent on the stationary observer. Using this new solution, we construct an explicit covariant transport equation for the particle flux in response to the generalized temperature and chemical potential gradients in generic stationary spacetimes, with the transport tensors characterized by some integral functions in the chemical potential and the relativistic coldness. To illustrate the application of the transport equation we study probe systems in Rindler and Kerr spacetimes and analyze the asymptotic properties of the gravito-conductivity tensor in the near horizon limit. It turns out that both the longitudinal and lateral parts (if present) of the gravito-conductivity tend to be divergent in the near horizon limit. In the weak field limit, our results coincide with with the non-relativistic gravitational transport equation which follows from the direct application of the Drude model. |
1207.4353 | Andrea Dapor | Michal Artymowski, Andrea Dapor, Tomasz Pawlowski | Inflation from non-minimally coupled scalar field in loop quantum
cosmology | Clarity improved. Replaced with revised version accepted in JCAP | null | 10.1088/1475-7516/2013/06/010 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The FRW model with non-minimally coupled massive scalar field has been
investigated in LQC framework. Considered form of the potential and coupling
allows applications to Higgs driven inflation. Out of two frames used in the
literature to describe such systems: Jordan and Einstein frame, the latter one
is applied. Specifically, we explore the idea of the Einstein frame being the
natural 'environment' for quantization and the Jordan picture having an
emergent nature. The resulting dynamics qualitatively modifies the standard
bounce paradigm in LQC in two ways: (i) the bounce point is no longer marked by
critical matter energy density, (ii) the Planck scale physics features the
'mexican hat' trajectory with two consecutive bounces and rapid expansion and
recollapse between them. Furthermore, for physically viable coupling strength
and initial data the subsequent inflation exceeds 60 e-foldings.
| [
{
"created": "Wed, 18 Jul 2012 12:03:48 GMT",
"version": "v1"
},
{
"created": "Fri, 17 May 2013 13:17:33 GMT",
"version": "v2"
},
{
"created": "Mon, 20 May 2013 12:14:56 GMT",
"version": "v3"
}
] | 2015-06-05 | [
[
"Artymowski",
"Michal",
""
],
[
"Dapor",
"Andrea",
""
],
[
"Pawlowski",
"Tomasz",
""
]
] | The FRW model with non-minimally coupled massive scalar field has been investigated in LQC framework. Considered form of the potential and coupling allows applications to Higgs driven inflation. Out of two frames used in the literature to describe such systems: Jordan and Einstein frame, the latter one is applied. Specifically, we explore the idea of the Einstein frame being the natural 'environment' for quantization and the Jordan picture having an emergent nature. The resulting dynamics qualitatively modifies the standard bounce paradigm in LQC in two ways: (i) the bounce point is no longer marked by critical matter energy density, (ii) the Planck scale physics features the 'mexican hat' trajectory with two consecutive bounces and rapid expansion and recollapse between them. Furthermore, for physically viable coupling strength and initial data the subsequent inflation exceeds 60 e-foldings. |
2201.03583 | Marko Toros | Sougato Bose, Anupam Mazumdar, Martine Schut, and Marko Toro\v{s} | Mechanism for the quantum natured gravitons to entangle masses | Accepted for publication in PRD; 13 pages | Phys. Rev. D 105, 106028 (2022) | 10.1103/PhysRevD.105.106028 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper points out the importance of the quantum nature of the
gravitational interaction with matter in a linearized theory of quantum gravity
induced entanglement of masses (QGEM). We will show how the quantum interaction
entangles the steady states of a closed system (eigenstates) of two test masses
placed in the harmonic traps, and how such a quantum matter-matter interaction
emerges from an underlying quantum gravitational field. We will rely upon
quantum perturbation theory highlighting the critical assumptions for
generating a quantum matter-matter interaction and showing that a classical
gravitational field does not render such an entanglement. We will consider two
distinct examples; one where the two harmonic oscillators are static and the
other where the harmonic oscillators are non-static. In both the cases it is
the quantum nature of the gravitons interacting with the harmonic oscillators
that are responsible for creating an entangled state with the ground and the
excited states of harmonic oscillators as the Schmidt basis. We will compute
the concurrence as a criterion for the above entanglement and highlight the
role of the spin-2 nature of the graviton for entangling the two harmonic
oscillators.
| [
{
"created": "Mon, 10 Jan 2022 19:00:06 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Feb 2022 18:41:50 GMT",
"version": "v2"
},
{
"created": "Wed, 18 May 2022 15:36:08 GMT",
"version": "v3"
}
] | 2022-06-03 | [
[
"Bose",
"Sougato",
""
],
[
"Mazumdar",
"Anupam",
""
],
[
"Schut",
"Martine",
""
],
[
"Toroš",
"Marko",
""
]
] | This paper points out the importance of the quantum nature of the gravitational interaction with matter in a linearized theory of quantum gravity induced entanglement of masses (QGEM). We will show how the quantum interaction entangles the steady states of a closed system (eigenstates) of two test masses placed in the harmonic traps, and how such a quantum matter-matter interaction emerges from an underlying quantum gravitational field. We will rely upon quantum perturbation theory highlighting the critical assumptions for generating a quantum matter-matter interaction and showing that a classical gravitational field does not render such an entanglement. We will consider two distinct examples; one where the two harmonic oscillators are static and the other where the harmonic oscillators are non-static. In both the cases it is the quantum nature of the gravitons interacting with the harmonic oscillators that are responsible for creating an entangled state with the ground and the excited states of harmonic oscillators as the Schmidt basis. We will compute the concurrence as a criterion for the above entanglement and highlight the role of the spin-2 nature of the graviton for entangling the two harmonic oscillators. |
0801.4257 | Hossein Farajollahi | Hossein Farajollahi | Time and Dirac Observables in Friedmann Cosmologies | 11 pages | Int.J.Theor.Phys.47:1479-1489,2008 | 10.1007/s10773-007-9628-3 | null | gr-qc | null | A cosmological time variable is emerged from the Hamiltonian formulation of
Friedmann model to measure the evolution of dynamical observables in the
theory. A set of observables has been identified for the theory on the null
hypersurfaces that its evolution is with respect to the volume clock introduced
by the cosmological time variable.
| [
{
"created": "Mon, 28 Jan 2008 12:41:17 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Farajollahi",
"Hossein",
""
]
] | A cosmological time variable is emerged from the Hamiltonian formulation of Friedmann model to measure the evolution of dynamical observables in the theory. A set of observables has been identified for the theory on the null hypersurfaces that its evolution is with respect to the volume clock introduced by the cosmological time variable. |
gr-qc/0012064 | Esposito Giampiero | Giampiero Esposito and Cosimo Stornaiolo | The Role of Elliptic Operators in the Initial-Value Problem for General
Relativity | 9 pages, Latex | null | null | DSF preprint 2000/40 | gr-qc | null | The Arnowitt-Deser-Misner (ADM) equations are deeply intertwined with
discrete spectral resolutions of an elliptic operator of Laplace type
associated with the spacelike hypersurfaces which foliate the space-time
manifold, and the non-linearities of the four-dimensional hyperbolic theory are
mapped into the potential term occurring in this operator. The ADM equations
are here re-expressed as a coupled first-order system for the induced metric
and the trace-free part of the extrinsic-curvature tensor, and their
formulation in terms of integral equations is studied.
| [
{
"created": "Mon, 18 Dec 2000 15:07:05 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Esposito",
"Giampiero",
""
],
[
"Stornaiolo",
"Cosimo",
""
]
] | The Arnowitt-Deser-Misner (ADM) equations are deeply intertwined with discrete spectral resolutions of an elliptic operator of Laplace type associated with the spacelike hypersurfaces which foliate the space-time manifold, and the non-linearities of the four-dimensional hyperbolic theory are mapped into the potential term occurring in this operator. The ADM equations are here re-expressed as a coupled first-order system for the induced metric and the trace-free part of the extrinsic-curvature tensor, and their formulation in terms of integral equations is studied. |
2009.10948 | Vilson T. Zanchin | Angel D. D. Masa, Enesson S. de Oliveira, Vilson T. Zanchin | Stability of regular black holes and other compact objects with a
charged de Sitter core and a surface matter layer | 25 pages, 18 figures (reduced from 27 figures/first version of the
manuscript), new references added | Phys. Rev. D 103, 104051 (2021) | 10.1103/PhysRevD.103.104051 | null | gr-qc astro-ph.HE astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The stability and other physical properties of a class of regular black
holes, quasiblack holes, and other electrically charged compact objects are
investigated in the present work. The compact objects are obtained by solving
the Einstein-Maxwell system of equations assuming spherical symmetry in a
static spacetime. The spacetime is split in two regions by a spherical surface
of coordinate radius $a$. The interior region contains a nonisotropic charged
fluid with a de Sitter type equation of state, $p_r = -\rho_m$, $p_r$ and
$\rho_m$ being respectively the radial pressure and the energy density of the
fluid. The charge distribution is chosen as a well behaved power-law function.
The exterior region is the electrovacuum Reissner-Nordstr\"om metric, which is
joined to the interior metric through a spherical thin shell (a thin matter
layer) placed at the radius $a$. The matter of the shell is assumed to be a
perfect fluid satisfying a linear barotropic equation of state, ${\cal
P}=\omega\sigma$, with ${\cal P}$ and $\sigma$ being respectively the pressure
and energy density of the shell, with $\omega$ being a constant. The exact
solutions obtained are analyzed in some detail by exploring the interesting
regions of parameter space, complementing the analysis of previous works on
similar models. This is the first important contribution of the present study.
The stability of the solutions are then investigated considering perturbations
around the equilibrium position of the shell. This is the second and the most
important contribution of this work. We find that there are stable objects in
relatively large regions of the parameter space. In particular, there are
stable regular black holes for all values of the parameter $\omega$ of
interest. Other stable ultracompact objects as quasiblack holes, gravastars,
and even overcharged stars are allowed in certain regions of the parameter
space.
| [
{
"created": "Wed, 23 Sep 2020 06:35:30 GMT",
"version": "v1"
},
{
"created": "Sat, 12 Dec 2020 21:54:20 GMT",
"version": "v2"
},
{
"created": "Wed, 11 Aug 2021 02:25:53 GMT",
"version": "v3"
}
] | 2021-08-12 | [
[
"Masa",
"Angel D. D.",
""
],
[
"de Oliveira",
"Enesson S.",
""
],
[
"Zanchin",
"Vilson T.",
""
]
] | The stability and other physical properties of a class of regular black holes, quasiblack holes, and other electrically charged compact objects are investigated in the present work. The compact objects are obtained by solving the Einstein-Maxwell system of equations assuming spherical symmetry in a static spacetime. The spacetime is split in two regions by a spherical surface of coordinate radius $a$. The interior region contains a nonisotropic charged fluid with a de Sitter type equation of state, $p_r = -\rho_m$, $p_r$ and $\rho_m$ being respectively the radial pressure and the energy density of the fluid. The charge distribution is chosen as a well behaved power-law function. The exterior region is the electrovacuum Reissner-Nordstr\"om metric, which is joined to the interior metric through a spherical thin shell (a thin matter layer) placed at the radius $a$. The matter of the shell is assumed to be a perfect fluid satisfying a linear barotropic equation of state, ${\cal P}=\omega\sigma$, with ${\cal P}$ and $\sigma$ being respectively the pressure and energy density of the shell, with $\omega$ being a constant. The exact solutions obtained are analyzed in some detail by exploring the interesting regions of parameter space, complementing the analysis of previous works on similar models. This is the first important contribution of the present study. The stability of the solutions are then investigated considering perturbations around the equilibrium position of the shell. This is the second and the most important contribution of this work. We find that there are stable objects in relatively large regions of the parameter space. In particular, there are stable regular black holes for all values of the parameter $\omega$ of interest. Other stable ultracompact objects as quasiblack holes, gravastars, and even overcharged stars are allowed in certain regions of the parameter space. |
gr-qc/9403015 | Miquel Dorca. Fisica Teorica Uab. | Miquel Dorca, Enric Verdaguer | Particle creation in a colliding plane wave spacetime: wave packet
quantization | 23, latex, figures available by fax | Phys.Rev. D50 (1994) 2631-2644 | 10.1103/PhysRevD.50.2631 | UAB-FT-334 | gr-qc | null | We use wave packet mode quantization to compute the creation of massless
scalar quantum particles in a colliding plane wave spacetime. The background
spacetime represents the collision of two gravitational shock waves followed by
trailing gravitational radiation which focus into a Killing-Cauchy horizon. The
use of wave packet modes simplifies the problem of mode propagation through the
different spacetime regions which was previously studied with the use of
monocromatic modes. It is found that the number of particles created in a given
wave packet mode has a thermal spectrum with a temperature which is inversely
proportional to the focusing time of the plane waves and which depends on the
mode trajectory.
| [
{
"created": "Wed, 9 Mar 1994 15:13:40 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Dorca",
"Miquel",
""
],
[
"Verdaguer",
"Enric",
""
]
] | We use wave packet mode quantization to compute the creation of massless scalar quantum particles in a colliding plane wave spacetime. The background spacetime represents the collision of two gravitational shock waves followed by trailing gravitational radiation which focus into a Killing-Cauchy horizon. The use of wave packet modes simplifies the problem of mode propagation through the different spacetime regions which was previously studied with the use of monocromatic modes. It is found that the number of particles created in a given wave packet mode has a thermal spectrum with a temperature which is inversely proportional to the focusing time of the plane waves and which depends on the mode trajectory. |
2002.02435 | Jorge Ananias Neto | Everton M. C. Abreu, Jorge Ananias Neto, Ed\'esio M. Barboza Jr.,
Albert C. R. Mendes and Br\'aulio B. Soares | On the equipartition theorem and black holes nongaussian entropies | Revised version. To appear in MPLA | null | 10.1142/S0217732320502661 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this Letter we have shown that, from the standard thermodynamic functions,
the mathematical form of an equipartition theorem may be related to the
algebraic expression of a particular entropy initially chosen to describe the
black hole thermodynamics. Namely, we have different equipartition expressions
for distinct statistics. To this end, four different mathematical expressions
for the entropy have been selected to demonstrate our objective. Furthermore, a
possible phase transition is observed in the heat capacity behavior of the
Tsallis and Cirto entropy model.
| [
{
"created": "Thu, 6 Feb 2020 18:36:40 GMT",
"version": "v1"
},
{
"created": "Fri, 7 Aug 2020 19:56:16 GMT",
"version": "v2"
}
] | 2020-11-18 | [
[
"Abreu",
"Everton M. C.",
""
],
[
"Neto",
"Jorge Ananias",
""
],
[
"Barboza",
"Edésio M.",
"Jr."
],
[
"Mendes",
"Albert C. R.",
""
],
[
"Soares",
"Bráulio B.",
""
]
] | In this Letter we have shown that, from the standard thermodynamic functions, the mathematical form of an equipartition theorem may be related to the algebraic expression of a particular entropy initially chosen to describe the black hole thermodynamics. Namely, we have different equipartition expressions for distinct statistics. To this end, four different mathematical expressions for the entropy have been selected to demonstrate our objective. Furthermore, a possible phase transition is observed in the heat capacity behavior of the Tsallis and Cirto entropy model. |
gr-qc/0702020 | Dmitri Vassiliev | Dmitri Vassiliev | A teleparallel representation of the Weyl Lagrangian | Submitted to the Proceedings of the Eleventh Marcel Grossmann Meeting | Proceedings of the Eleventh Marcel Grossmann Meeting on General
Relativity (in 3 volumes, editors H.Kleinert and R.T.Jantzen, series editor
R.Ruffini), World Scientific, 2008, part B, p. 1245-1247. | null | null | gr-qc math.DG | null | The main result of the paper is a new representation of the Weyl Lagrangian
(massless Dirac Lagrangian). As the dynamical variable we use the coframe, i.e.
an orthonormal tetrad of covector fields. We write down a simple Lagrangian -
wedge product of axial torsion with a lightlike element of the coframe - and
show that variation of the resulting action with respect to the coframe
produces the Weyl equation. The advantage of our approach is that it does not
require the use of spinors, Pauli matrices or covariant differentiation. The
only geometric concepts we use are those of a metric, differential form, wedge
product and exterior derivative. Our result assigns a variational meaning to
the tetrad representation of the Weyl equation suggested by J.B.Griffiths and
R.A.Newing.
| [
{
"created": "Sat, 3 Feb 2007 18:38:39 GMT",
"version": "v1"
}
] | 2009-10-03 | [
[
"Vassiliev",
"Dmitri",
""
]
] | The main result of the paper is a new representation of the Weyl Lagrangian (massless Dirac Lagrangian). As the dynamical variable we use the coframe, i.e. an orthonormal tetrad of covector fields. We write down a simple Lagrangian - wedge product of axial torsion with a lightlike element of the coframe - and show that variation of the resulting action with respect to the coframe produces the Weyl equation. The advantage of our approach is that it does not require the use of spinors, Pauli matrices or covariant differentiation. The only geometric concepts we use are those of a metric, differential form, wedge product and exterior derivative. Our result assigns a variational meaning to the tetrad representation of the Weyl equation suggested by J.B.Griffiths and R.A.Newing. |
1509.02476 | Tomi Koivisto | Jose Beltr\'an Jim\'enez, Tomi S. Koivisto | Spacetimes with vector distortion: Inflation from generalised Weyl
geometry | 5 pages, 1 table, 0 figures. V2: Added the general quadratic theory | null | 10.1016/j.physletb.2016.03.047 | NORDITA-2015-100 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Spacetime with general linear vector distortion is introduced. Thus, the
torsion and the nonmetricity of the affine connection are assumed to be
proportional to a vector field (and not its derivatives). The resulting
two-parameter family of non-Riemannian geometries generalises the conformal
Weyl geometry and some other interesting special cases. Taking into account the
leading order quadratic curvature correction to the Einstein-Hilbert action
results uniquely in the one-parameter extension of the Starobinsky inflation
known as the alpha-attractor. The most general quadratic curvature action
introduces, in addition to the canonical vector kinetic term, novel ghost-free
vector-tensor interactions.
| [
{
"created": "Tue, 8 Sep 2015 18:07:26 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Jan 2016 16:20:05 GMT",
"version": "v2"
}
] | 2016-03-23 | [
[
"Jiménez",
"Jose Beltrán",
""
],
[
"Koivisto",
"Tomi S.",
""
]
] | Spacetime with general linear vector distortion is introduced. Thus, the torsion and the nonmetricity of the affine connection are assumed to be proportional to a vector field (and not its derivatives). The resulting two-parameter family of non-Riemannian geometries generalises the conformal Weyl geometry and some other interesting special cases. Taking into account the leading order quadratic curvature correction to the Einstein-Hilbert action results uniquely in the one-parameter extension of the Starobinsky inflation known as the alpha-attractor. The most general quadratic curvature action introduces, in addition to the canonical vector kinetic term, novel ghost-free vector-tensor interactions. |
2004.00003 | Emanuele Berti | F\'elix-Louis Juli\'e, Emanuele Berti | $d+1$ formalism in Einstein-scalar-Gauss-Bonnet gravity | 10 pages. v2: fixed references, no changes to the main text | Phys. Rev. D 101, 124045 (2020) | 10.1103/PhysRevD.101.124045 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the $d+1$ formulation of Einstein-scalar-Gauss-Bonnet (ESGB)
theories in dimension $D=d+1$ and for arbitrary (spacelike or timelike)
slicings. We first build an action which generalizes those of
Gibbons-Hawking-York and Myers to ESGB theories, showing that they can be
described by a Dirichlet variational principle. We then generalize the
Arnowitt-Deser-Misner (ADM) Lagrangian and Hamiltonian to ESGB theories, as
well as the resulting $d+1$ decomposition of the equations of motion. Unlike
general relativity, the canonical momenta of ESGB theories are nonlinear in the
extrinsic curvature. This has two main implications: (i) the ADM Hamiltonian is
generically multivalued, and the associated Hamiltonian evolution is not
predictable; (ii) the "$d+1$" equations of motion are quasilinear, and they may
break down in strongly curved, highly dynamical regimes. Our results should be
useful to guide future developments of numerical relativity for ESGB gravity in
the nonperturbative regime.
| [
{
"created": "Mon, 30 Mar 2020 18:00:01 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Apr 2020 16:32:39 GMT",
"version": "v2"
}
] | 2020-07-01 | [
[
"Julié",
"Félix-Louis",
""
],
[
"Berti",
"Emanuele",
""
]
] | We present the $d+1$ formulation of Einstein-scalar-Gauss-Bonnet (ESGB) theories in dimension $D=d+1$ and for arbitrary (spacelike or timelike) slicings. We first build an action which generalizes those of Gibbons-Hawking-York and Myers to ESGB theories, showing that they can be described by a Dirichlet variational principle. We then generalize the Arnowitt-Deser-Misner (ADM) Lagrangian and Hamiltonian to ESGB theories, as well as the resulting $d+1$ decomposition of the equations of motion. Unlike general relativity, the canonical momenta of ESGB theories are nonlinear in the extrinsic curvature. This has two main implications: (i) the ADM Hamiltonian is generically multivalued, and the associated Hamiltonian evolution is not predictable; (ii) the "$d+1$" equations of motion are quasilinear, and they may break down in strongly curved, highly dynamical regimes. Our results should be useful to guide future developments of numerical relativity for ESGB gravity in the nonperturbative regime. |
1601.07952 | Ettore Minguzzi | E. Minguzzi | Special coordinate systems in pseudo-Finsler geometry and the
equivalence principle | 20 pages | Journal of Geometry and Physics 114 (2017) 336--347 | 10.1016/j.geomphys.2016.12.013 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Special coordinate systems are constructed in a neighborhood of a point or of
a curve. Taylor expansions can then be easily inferred for the metric, the
connection, or the Finsler Lagrangian in terms of curvature invariants. These
coordinates circumvent the difficulties of the normal and Fermi coordinates in
Finsler geometry, which in general are not sufficiently differentiable. They
are obtained applying the usual constructions to the pullback of a horizontally
torsionless connection. The results so obtained are easily specialized to the
Berwald or Chern-Rund connections and have application in the study of the
equivalence principle in Finslerian extensions of general relativity.
| [
{
"created": "Fri, 29 Jan 2016 00:07:17 GMT",
"version": "v1"
}
] | 2017-02-27 | [
[
"Minguzzi",
"E.",
""
]
] | Special coordinate systems are constructed in a neighborhood of a point or of a curve. Taylor expansions can then be easily inferred for the metric, the connection, or the Finsler Lagrangian in terms of curvature invariants. These coordinates circumvent the difficulties of the normal and Fermi coordinates in Finsler geometry, which in general are not sufficiently differentiable. They are obtained applying the usual constructions to the pullback of a horizontally torsionless connection. The results so obtained are easily specialized to the Berwald or Chern-Rund connections and have application in the study of the equivalence principle in Finslerian extensions of general relativity. |
0901.1258 | Zurab Silagadze | Z.K. Silagadze | Quantum gravity, minimum length and Keplerian orbits | 4 pages, revtex4, version to be published in Phys. Lett. A | Phys.Lett.A373:2643-2645,2009 | 10.1016/j.physleta.2009.05.053 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We conjecture that the modified commutation relations suggested in the
context of quantum gravity (QG) persist also in the classical limit, if the
momentum of the classical object is not too large, and calculate the
corresponding perihelion precession rate for Keplerian orbits.
| [
{
"created": "Fri, 9 Jan 2009 15:39:24 GMT",
"version": "v1"
},
{
"created": "Sun, 11 Jan 2009 04:15:14 GMT",
"version": "v2"
},
{
"created": "Thu, 28 May 2009 07:39:05 GMT",
"version": "v3"
}
] | 2009-07-24 | [
[
"Silagadze",
"Z. K.",
""
]
] | We conjecture that the modified commutation relations suggested in the context of quantum gravity (QG) persist also in the classical limit, if the momentum of the classical object is not too large, and calculate the corresponding perihelion precession rate for Keplerian orbits. |
1911.06110 | Qingdi Wang | Qingdi Wang and William G. Unruh | How the cosmological constant is hidden by Planck scale curvature
fluctuations | 5 pages. v2 corrected some nonessential misunderstandings on the
letter Phys. Rev. Lett. 123, 131302(2019) presented in the beginning of
Sec.II of v1. v3 has further important revisions | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is argued in a recent letter Phys. Rev. Lett. 123, 131302(2019) that the
effect of a large cosmological constant can be naturally hidden in Planck scale
curvature fluctuations. We point out that there are problems with the author's
arguments. The hiding of the cosmological constant proposed in the letter by
choosing a suitable lapse function is just an illusion maintained by external
forces. In particular, it can not be achieved if the cosmological constant is
positive. Fortunately, it works for a negative cosmological constant in a
different way, and, interestingly, the sign of the cosmological constant just
needs to be negative to make the average spatial curvature $\langle R\rangle$
small.
| [
{
"created": "Wed, 13 Nov 2019 09:00:58 GMT",
"version": "v1"
},
{
"created": "Mon, 18 Nov 2019 11:15:43 GMT",
"version": "v2"
},
{
"created": "Mon, 25 Nov 2019 06:20:01 GMT",
"version": "v3"
}
] | 2019-11-26 | [
[
"Wang",
"Qingdi",
""
],
[
"Unruh",
"William G.",
""
]
] | It is argued in a recent letter Phys. Rev. Lett. 123, 131302(2019) that the effect of a large cosmological constant can be naturally hidden in Planck scale curvature fluctuations. We point out that there are problems with the author's arguments. The hiding of the cosmological constant proposed in the letter by choosing a suitable lapse function is just an illusion maintained by external forces. In particular, it can not be achieved if the cosmological constant is positive. Fortunately, it works for a negative cosmological constant in a different way, and, interestingly, the sign of the cosmological constant just needs to be negative to make the average spatial curvature $\langle R\rangle$ small. |
1009.2266 | Merab Gogberashvili Prof | Merab Gogberashvili and Igor Kanatchikov | On the fine structure constant in the Machian universe | 6 pages, Some modifications in text and formulas were done,
discussion and references added | null | null | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Within the Machian model of the universe the dark energy is identified with
the Machian energy of collective gravitational interactions of all particles
inside the horizon. It is shown that the fine structure constant can be
expressed in terms of the observed radiative, baryon and dark energy densities
of the universe and the densities of various matter components are interrelated
via it.
| [
{
"created": "Sun, 5 Sep 2010 15:01:05 GMT",
"version": "v1"
},
{
"created": "Sun, 26 Sep 2010 17:57:01 GMT",
"version": "v2"
}
] | 2010-09-28 | [
[
"Gogberashvili",
"Merab",
""
],
[
"Kanatchikov",
"Igor",
""
]
] | Within the Machian model of the universe the dark energy is identified with the Machian energy of collective gravitational interactions of all particles inside the horizon. It is shown that the fine structure constant can be expressed in terms of the observed radiative, baryon and dark energy densities of the universe and the densities of various matter components are interrelated via it. |
1512.02947 | Jan Ostrowski | Jan J. Ostrowski, Boudewijn F. Roukema | On the Green and Wald formalism | Contribution to the proceedings of MG14 | null | 10.1142/9789813226609_0264 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Backreaction in the cosmological context is a longstanding problem that is
especially important in the present era of precise cosmology. The standard
model of a homogeneous background plus density perturbations is most probably
oversimplified and is expected to fail to fully account for the near-future
observations of sub-percent precision. From a theoretical point of view, the
problem of backreaction is very complicated and deserves careful examination.
Recently, Green and Wald claimed in a series of papers to have developed a
formalism to properly describe the influence of density inhomogeneities on
average properties of the Universe, i.e., the backreaction effect. A brief
discussion of this framework is presented, focussing on its drawbacks and on
misconceptions that have arisen during the "backreaction debate".
| [
{
"created": "Wed, 9 Dec 2015 17:15:20 GMT",
"version": "v1"
}
] | 2017-12-27 | [
[
"Ostrowski",
"Jan J.",
""
],
[
"Roukema",
"Boudewijn F.",
""
]
] | Backreaction in the cosmological context is a longstanding problem that is especially important in the present era of precise cosmology. The standard model of a homogeneous background plus density perturbations is most probably oversimplified and is expected to fail to fully account for the near-future observations of sub-percent precision. From a theoretical point of view, the problem of backreaction is very complicated and deserves careful examination. Recently, Green and Wald claimed in a series of papers to have developed a formalism to properly describe the influence of density inhomogeneities on average properties of the Universe, i.e., the backreaction effect. A brief discussion of this framework is presented, focussing on its drawbacks and on misconceptions that have arisen during the "backreaction debate". |
1010.2052 | Yuri Pavlov | A. A. Grib, Yu. V. Pavlov | On particles collisions near rotating black holes | LaTeX, 5 pages, 1 figure. arXiv admin note: substantial text overlap
with arXiv:1004.0913 | Grav. Cosmol.17:42-46, 2011 | 10.1134/S0202289311010099 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Scattering of particles with different masses and energy in the gravitational
field of rotating black holes is considered as outside as inside the black
hole. Expressions for scattering energy of particles in the centre of mass
system are obtained. It is shown that scattering energy of particles in the
centre of mass system can obtain very large values not only for extremal black
holes but also for nonextremal ones if one takes into account multiple
scattering. Numerical estimates for the time needed for the particle to get
ultrarelativistic energy are given.
| [
{
"created": "Mon, 11 Oct 2010 10:05:10 GMT",
"version": "v1"
}
] | 2014-11-05 | [
[
"Grib",
"A. A.",
""
],
[
"Pavlov",
"Yu. V.",
""
]
] | Scattering of particles with different masses and energy in the gravitational field of rotating black holes is considered as outside as inside the black hole. Expressions for scattering energy of particles in the centre of mass system are obtained. It is shown that scattering energy of particles in the centre of mass system can obtain very large values not only for extremal black holes but also for nonextremal ones if one takes into account multiple scattering. Numerical estimates for the time needed for the particle to get ultrarelativistic energy are given. |
1611.00431 | Ethan Honda | Ethan P. Honda | RN-AdS Nontopoligical Solitons in Broken Einstein-Maxwell-Higgs Theory | 20 pages, 27 figures, 2 tables | null | 10.1103/PhysRevD.95.024032 | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Results are presented from numerical simulations of the
Einstein-Maxwell-Higgs equations with a broken U(1) symmetry. Coherent
nontopological soliton solutions are shown to exist that separate an Anti-de
Sitter (AdS) true vacuum interior from a Reissner-Nordstrom (RN) false vacuum
exterior. The stability of these bubble solutions is tested by perturbing the
charge of the coherent solution and evolving the time-dependent equations of
motion. In the weak gravitational limit, the short-term stability depends on
the sign of $(\omega/ Q) \, \partial_\omega Q$, similar to q-balls. The
long-term end state of the perturbed solutions demonstrates a rich structure
and is visualized using "phase diagrams." Regions of both stability and
instability are shown to exist for $\kappa_g \lesssim 0.015$, while solutions
with $\kappa_g \gtrsim 0.015$ were observed to be entirely unstable. Threshold
solutions are shown to demonstrate time-scaling laws, and the space separating
true and false vacuum end states is shown to be fractal in nature, similar to
oscillons. Coherent states with superextremal charge-to-mass ratios are shown
to exist and observed to collapse or expand, depending on the sign of the
charge perturbation. Expanding superextremal bubbles induce a phase transition
to the true AdS vacuum, while collapsing superextremal bubbles can form
nonsingular strongly gravitating solutions with superextremal RN exteriors.
| [
{
"created": "Wed, 2 Nov 2016 00:31:25 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Jan 2017 01:43:13 GMT",
"version": "v2"
}
] | 2017-03-08 | [
[
"Honda",
"Ethan P.",
""
]
] | Results are presented from numerical simulations of the Einstein-Maxwell-Higgs equations with a broken U(1) symmetry. Coherent nontopological soliton solutions are shown to exist that separate an Anti-de Sitter (AdS) true vacuum interior from a Reissner-Nordstrom (RN) false vacuum exterior. The stability of these bubble solutions is tested by perturbing the charge of the coherent solution and evolving the time-dependent equations of motion. In the weak gravitational limit, the short-term stability depends on the sign of $(\omega/ Q) \, \partial_\omega Q$, similar to q-balls. The long-term end state of the perturbed solutions demonstrates a rich structure and is visualized using "phase diagrams." Regions of both stability and instability are shown to exist for $\kappa_g \lesssim 0.015$, while solutions with $\kappa_g \gtrsim 0.015$ were observed to be entirely unstable. Threshold solutions are shown to demonstrate time-scaling laws, and the space separating true and false vacuum end states is shown to be fractal in nature, similar to oscillons. Coherent states with superextremal charge-to-mass ratios are shown to exist and observed to collapse or expand, depending on the sign of the charge perturbation. Expanding superextremal bubbles induce a phase transition to the true AdS vacuum, while collapsing superextremal bubbles can form nonsingular strongly gravitating solutions with superextremal RN exteriors. |
1408.3928 | Sunandan Gangopadhyay | Abhijit Dutta, Sunandan Gangopadhyay | Thermodynamics of black holes and the symmetric generalized uncertainty
principle | References added | Int .J . Theor Phys. 55 (2016) 2746 | 10.1007/s10773-015-2907-5 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we have investigated the thermodynamics of Schwarzschild black
holes using the symmetric generalized uncertainty principle which contains
correction terms involving momentum and position uncertainty. We obtain the
mass-temperature relation and the heat capacity of the black hole using which
we compute the critical and remnant masses. The entropy is found to satisfy the
area law upto leading order corrections from the symmetric generalized
uncertainty principle.
| [
{
"created": "Mon, 18 Aug 2014 08:34:30 GMT",
"version": "v1"
},
{
"created": "Sat, 23 Aug 2014 05:10:31 GMT",
"version": "v2"
}
] | 2016-05-11 | [
[
"Dutta",
"Abhijit",
""
],
[
"Gangopadhyay",
"Sunandan",
""
]
] | In this paper, we have investigated the thermodynamics of Schwarzschild black holes using the symmetric generalized uncertainty principle which contains correction terms involving momentum and position uncertainty. We obtain the mass-temperature relation and the heat capacity of the black hole using which we compute the critical and remnant masses. The entropy is found to satisfy the area law upto leading order corrections from the symmetric generalized uncertainty principle. |
gr-qc/0008022 | Dr G. A. Jaroszkiewicz | George Jaroszkiewicz (School of Mathematical Sciences, University of
Nottingham, UK) | Causal Implication and the Origin of Time Dilation | 11 pages, 1 eps figure. Second replacement amends the diagram | null | null | null | gr-qc | null | We discuss the emergence of time dilation as a normal feature expected of any
system where a central processor may have to wait one or more clock cycles
before concluding a local calculation. We show how the process of causal
implication in a typical Newtonian cellular automaton leads naturally to
Lorentz transformations and invariant causal structure.
| [
{
"created": "Wed, 9 Aug 2000 15:47:10 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Aug 2000 10:50:45 GMT",
"version": "v2"
},
{
"created": "Mon, 21 Aug 2000 20:25:26 GMT",
"version": "v3"
}
] | 2009-09-25 | [
[
"Jaroszkiewicz",
"George",
"",
"School of Mathematical Sciences, University of\n Nottingham, UK"
]
] | We discuss the emergence of time dilation as a normal feature expected of any system where a central processor may have to wait one or more clock cycles before concluding a local calculation. We show how the process of causal implication in a typical Newtonian cellular automaton leads naturally to Lorentz transformations and invariant causal structure. |
gr-qc/0208065 | James M. Overduin | T. Fukui, J. M. Overduin | Dynamics of a Generalized Cosmological Scalar-Tensor Theory | 13 pages | Int.J.Mod.Phys. D11 (2002) 669-684 | 10.1142/S0218271802001901 | null | gr-qc | null | A generalized scalar-tensor theory is investigated whose cosmological term
depends on both a scalar field and its time derivative. A correspondence with
solutions of five-dimensional Space-Time-Matter theory is noted. Analytic
solutions are found for the scale factor, scalar field and cosmological term.
Models with free parameters of order unity are consistent with recent
observational data and could be relevant to both the dark-matter and
cosmological-"constant" problems.
| [
{
"created": "Thu, 22 Aug 2002 16:07:48 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Fukui",
"T.",
""
],
[
"Overduin",
"J. M.",
""
]
] | A generalized scalar-tensor theory is investigated whose cosmological term depends on both a scalar field and its time derivative. A correspondence with solutions of five-dimensional Space-Time-Matter theory is noted. Analytic solutions are found for the scale factor, scalar field and cosmological term. Models with free parameters of order unity are consistent with recent observational data and could be relevant to both the dark-matter and cosmological-"constant" problems. |
gr-qc/9709037 | Neil John Cornish | Neil J. Cornish (Cambridge), Janna J. Levin (UC Berkeley) | The mixmaster universe is unambiguously chaotic | 3 pages, 2 figures. To appear in the proceedings of the Eighth Marcel
Grossmann Meeting, Jerusalem, June 1997 (WSP) | null | null | DAMTP-R97-49 | gr-qc | null | The Mixmaster or Bianchi IX cosmological model has become one of the
archetypal settings for studying gravitational dynamics. The past decade has
seen a vigourous debate about whether or not the Mixmaster's dynamics is
chaotic. In this talk we review our recent work in uncovering a chaotic
invariant set of orbits in the Mixmaster phase space, and how we used this
discovery to prove the dynamics is chaotic.
| [
{
"created": "Mon, 15 Sep 1997 12:42:42 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Cornish",
"Neil J.",
"",
"Cambridge"
],
[
"Levin",
"Janna J.",
"",
"UC Berkeley"
]
] | The Mixmaster or Bianchi IX cosmological model has become one of the archetypal settings for studying gravitational dynamics. The past decade has seen a vigourous debate about whether or not the Mixmaster's dynamics is chaotic. In this talk we review our recent work in uncovering a chaotic invariant set of orbits in the Mixmaster phase space, and how we used this discovery to prove the dynamics is chaotic. |
2210.10154 | Remigiusz Durka | Remigiusz Durka, Jerzy Kowalski-Glikman | A tale of two theories of gravity in asymptotically Anti-de Sitter
spacetime | 22 pages, v2 (improved version prepared for publication with the
extended supplement file and new references added) | null | 10.1007/JHEP02(2023)029 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider two BF formulations of the theory of gravity with a negative
cosmological constant, of Plebanski and of MacDowell-Mansouri. Both give the
standard Einstein equations in the bulk but differ in expressions of edge
charges. We compute the asymptotic charges explicitly in both theories for
AdS-Schwarzschild, AdS-Kerr, and AdS-Taub--NUT solutions. We find that while in
the case of the Plebanski theory the charges are divergent, they are finite for
MacDowell-Mansouri theory. Furthermore, we show that in the case of the
arbitrary asymptotically AdS spacetimes, MacDowell--Mansouri asymptotic
charges, action, and symplectic form are all finite. Therefore
MacDowell-Mansouri theory of gravity in asymptotically AdS spaces does not need
any counterterms.
| [
{
"created": "Tue, 18 Oct 2022 20:36:41 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Oct 2022 17:49:54 GMT",
"version": "v2"
}
] | 2023-02-15 | [
[
"Durka",
"Remigiusz",
""
],
[
"Kowalski-Glikman",
"Jerzy",
""
]
] | We consider two BF formulations of the theory of gravity with a negative cosmological constant, of Plebanski and of MacDowell-Mansouri. Both give the standard Einstein equations in the bulk but differ in expressions of edge charges. We compute the asymptotic charges explicitly in both theories for AdS-Schwarzschild, AdS-Kerr, and AdS-Taub--NUT solutions. We find that while in the case of the Plebanski theory the charges are divergent, they are finite for MacDowell-Mansouri theory. Furthermore, we show that in the case of the arbitrary asymptotically AdS spacetimes, MacDowell--Mansouri asymptotic charges, action, and symplectic form are all finite. Therefore MacDowell-Mansouri theory of gravity in asymptotically AdS spaces does not need any counterterms. |
1901.06952 | Mu-Tao Wang | Po-Ning Chen, Mu-Tao Wang, Ye-Kai Wang, and Shing-Tung Yau | Quasi-local mass at null infinity in Bondi-Sachs coordinates | 11 pages | null | null | null | gr-qc math-ph math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There are two important statements regarding the Trautman-Bondi mass at null
infinity: one is the positivity, and the other is the Bondi mass loss formula,
which are both global in nature. In this note, we compute the limit of the
Wang-Yau quasi-local mass on unit spheres at null infinity of an asymptotically
flat spacetime in the Bondi-Sachs coordinates. The quasi-local mass leads to a
local description of the radiation that is purely gravitational at null
infinity. In particular, the quasi-local mass is evaluated in terms of the news
function of the Bondi-Sachs coordinates.
| [
{
"created": "Mon, 21 Jan 2019 15:10:55 GMT",
"version": "v1"
}
] | 2019-01-23 | [
[
"Chen",
"Po-Ning",
""
],
[
"Wang",
"Mu-Tao",
""
],
[
"Wang",
"Ye-Kai",
""
],
[
"Yau",
"Shing-Tung",
""
]
] | There are two important statements regarding the Trautman-Bondi mass at null infinity: one is the positivity, and the other is the Bondi mass loss formula, which are both global in nature. In this note, we compute the limit of the Wang-Yau quasi-local mass on unit spheres at null infinity of an asymptotically flat spacetime in the Bondi-Sachs coordinates. The quasi-local mass leads to a local description of the radiation that is purely gravitational at null infinity. In particular, the quasi-local mass is evaluated in terms of the news function of the Bondi-Sachs coordinates. |
0707.3395 | Marko Vojinovic | Milovan Vasilic, Marko Vojinovic | Classical Spinning Branes in Curved Backgrounds | null | JHEP 0707:028,2007 | 10.1088/1126-6708/2007/07/028 | null | gr-qc hep-th | null | The dynamics of a classical branelike object in a curved background is
derived from the covariant stress-energy conservation of the brane matter. The
world sheet equations and boundary conditions are obtained in the pole-dipole
approximation, where nontrivial brane thickness gives rise to its intrinsic
angular momentum. It is shown that intrinsic angular momentum couples to both,
the background curvature and the brane orbital degrees of freedom. The whole
procedure is manifestly covariant with respect to spacetime diffeomorphisms and
world sheet reparametrizations. In addition, two extra gauge symmetries are
discovered and utilized. The examples of the point particle and the string in 4
spacetime dimensions are analyzed in more detail. A particular attention is
paid to the Nambu-Goto string with massive spinning particles attached to its
ends.
| [
{
"created": "Mon, 23 Jul 2007 19:51:48 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Feb 2008 15:13:20 GMT",
"version": "v2"
}
] | 2010-01-15 | [
[
"Vasilic",
"Milovan",
""
],
[
"Vojinovic",
"Marko",
""
]
] | The dynamics of a classical branelike object in a curved background is derived from the covariant stress-energy conservation of the brane matter. The world sheet equations and boundary conditions are obtained in the pole-dipole approximation, where nontrivial brane thickness gives rise to its intrinsic angular momentum. It is shown that intrinsic angular momentum couples to both, the background curvature and the brane orbital degrees of freedom. The whole procedure is manifestly covariant with respect to spacetime diffeomorphisms and world sheet reparametrizations. In addition, two extra gauge symmetries are discovered and utilized. The examples of the point particle and the string in 4 spacetime dimensions are analyzed in more detail. A particular attention is paid to the Nambu-Goto string with massive spinning particles attached to its ends. |
1506.00487 | Marek Czachor | Diederik Aerts, Marek Czachor, Maciej Kuna | Crystallization of space: Space-time fractals from fractal arithmetic | version accepted in Chaos, Solitons & Fractals | Chaos, Solitons and Fractals 83 (2016) 201-211 | 10.1016/j.chaos.2015.12.004 | null | gr-qc math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Fractals such as the Cantor set can be equipped with intrinsic arithmetic
operations (addition, subtraction, multiplication, division) that map the
fractal into itself. The arithmetics allows one to define calculus and algebra
intrinsic to the fractal in question, and one can formulate classical and
quantum physics within the fractal set. In particular, fractals in space-time
can be generated by means of homogeneous spaces associated with appropriate Lie
groups. The construction is illustrated by explicit examples.
| [
{
"created": "Mon, 1 Jun 2015 13:28:56 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Jun 2015 10:53:41 GMT",
"version": "v2"
},
{
"created": "Wed, 9 Dec 2015 17:39:26 GMT",
"version": "v3"
}
] | 2016-01-20 | [
[
"Aerts",
"Diederik",
""
],
[
"Czachor",
"Marek",
""
],
[
"Kuna",
"Maciej",
""
]
] | Fractals such as the Cantor set can be equipped with intrinsic arithmetic operations (addition, subtraction, multiplication, division) that map the fractal into itself. The arithmetics allows one to define calculus and algebra intrinsic to the fractal in question, and one can formulate classical and quantum physics within the fractal set. In particular, fractals in space-time can be generated by means of homogeneous spaces associated with appropriate Lie groups. The construction is illustrated by explicit examples. |
0808.2225 | Richard Umstaetter | Richard Umstaetter, Renate Meyer, Nelson Christensen | A Bayesian method to set upper limits on the strength of a periodic
gravitational wave signal from the remnant of SN1987A: possible applications
in LIGO searches | 11 pages, 3 figures (1, 2a,b, 3a,b,c,d) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a method that assesses the theoretical detection limit of a
Bayesian Markov chain Monte Carlo search for a periodic gravitational wave
signal emitted by a neutron star. Inverse probability yields an upper limit
estimate for the strength when a signal could not be detected in an observed
data set. The proposed method is based on Bayesian model comparison that
automatically quantifies Occam s Razor. It limits the complexity of a model by
favoring the most parsimonious model that explains the data. By comparing the
model with a signal from a pulsar to the null model that assumes solely noise,
we derive the detection probability and an estimate for the upper limit that a
search, for example, for a narrow-band emission for SN1987a, might yield on
data at the sensitivity of LIGO data for an observation time of one year.
| [
{
"created": "Sat, 16 Aug 2008 00:53:51 GMT",
"version": "v1"
}
] | 2008-08-19 | [
[
"Umstaetter",
"Richard",
""
],
[
"Meyer",
"Renate",
""
],
[
"Christensen",
"Nelson",
""
]
] | We present a method that assesses the theoretical detection limit of a Bayesian Markov chain Monte Carlo search for a periodic gravitational wave signal emitted by a neutron star. Inverse probability yields an upper limit estimate for the strength when a signal could not be detected in an observed data set. The proposed method is based on Bayesian model comparison that automatically quantifies Occam s Razor. It limits the complexity of a model by favoring the most parsimonious model that explains the data. By comparing the model with a signal from a pulsar to the null model that assumes solely noise, we derive the detection probability and an estimate for the upper limit that a search, for example, for a narrow-band emission for SN1987a, might yield on data at the sensitivity of LIGO data for an observation time of one year. |
0809.1272 | Mahmood Roshan | Mahmood Roshan and Fatimah Shojai | Palatini f(R) gravity and Noether symmetry | 4 pages,to appear in physics letters B | Phys.Lett.B668:238-240,2008 | 10.1016/j.physletb.2008.08.036 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study Palatini f(R) cosmology using Noether symmetry approach for the
matter dominated universe. In order to construct a point-like Lagrangian in the
flat FRW space time, we use the dynamical equivalence between f(R) gravity and
scalar-tensor theories. The existence of Noether symmetry of the cosmological
f(R) Lagrangian helps us to find out the form of f(R) and the exact solutions
for cosmic scale factor. We show that this symmetry always exist for f(R)~R^n
and the Noether constant is a function of the Newton's gravitational constant
and the current matter content of the universe.
| [
{
"created": "Mon, 8 Sep 2008 04:41:37 GMT",
"version": "v1"
}
] | 2011-05-19 | [
[
"Roshan",
"Mahmood",
""
],
[
"Shojai",
"Fatimah",
""
]
] | We study Palatini f(R) cosmology using Noether symmetry approach for the matter dominated universe. In order to construct a point-like Lagrangian in the flat FRW space time, we use the dynamical equivalence between f(R) gravity and scalar-tensor theories. The existence of Noether symmetry of the cosmological f(R) Lagrangian helps us to find out the form of f(R) and the exact solutions for cosmic scale factor. We show that this symmetry always exist for f(R)~R^n and the Noether constant is a function of the Newton's gravitational constant and the current matter content of the universe. |
gr-qc/0610087 | Eugen Radu | Yves Brihaye, Eugen Radu and D. H. Tchrakian | Einstein-Yang-Mills solutions in higher dimensional de Sitter spacetime | 17 pages, 8 figures | Phys.Rev.D75:024022,2007 | 10.1103/PhysRevD.75.024022 | null | gr-qc hep-th | null | We consider particle-like and black holes solutions of the
Einstein-Yang-Mills system with positive cosmological constant in d>4 spacetime
dimensions. These configurations are spherically symmetric and present a
cosmological horizon for a finite value of the radial coordinate, approaching
asymptotically the de Sitter background. In the usual Yang--Mills case we find
that the mass of these solutions, evaluated outside the cosmological horizon at
future/past infinity generically diverges for d>4. Solutions with finite mass
are found by adding to the action higher order gauge field terms belonging to
the Yang--Mills hierarchy. A discussion of the main properties of these
solutions and their differences from those to the usual Yang-Mills model, both
in four and higher dimensions is presented.
| [
{
"created": "Tue, 17 Oct 2006 16:29:50 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Dec 2006 13:35:57 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Brihaye",
"Yves",
""
],
[
"Radu",
"Eugen",
""
],
[
"Tchrakian",
"D. H.",
""
]
] | We consider particle-like and black holes solutions of the Einstein-Yang-Mills system with positive cosmological constant in d>4 spacetime dimensions. These configurations are spherically symmetric and present a cosmological horizon for a finite value of the radial coordinate, approaching asymptotically the de Sitter background. In the usual Yang--Mills case we find that the mass of these solutions, evaluated outside the cosmological horizon at future/past infinity generically diverges for d>4. Solutions with finite mass are found by adding to the action higher order gauge field terms belonging to the Yang--Mills hierarchy. A discussion of the main properties of these solutions and their differences from those to the usual Yang-Mills model, both in four and higher dimensions is presented. |
2407.15069 | Andronikos Paliathanasis | Andronikos Paliathanasis | Dipole Cosmology in $f(Q)$-gravity | 26 pages, 6 figures, to appear in Physics Dark Universe | null | null | null | gr-qc astro-ph.CO hep-ph math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | Symmetric teleparallel $f(Q)$-gravity allows for the presence of a perfect
fluid with a tilted velocity in the Kantowski-Sachs geometry. In this dipole
model, we consider an ideal gas and we investigate the evolution of the
physical parameters. The tilt parameter is constrained by the nonlinear
function $f(Q)$ through the non-diagonal equations of the field equations. We
find that the dynamics always reduce to the vacuum solutions of STEGR. This
includes the Kasner universe, when no cosmological term is introduced by the
$f(Q)$ function, and the isotropic de Sitter universe, where $f\left( Q\right)
$ plays the role of the cosmological constant. In the extreme tilt limit, the
universe is consistently anisotropic and accelerated. However, the final
solution matches that of STEGR.
| [
{
"created": "Sun, 21 Jul 2024 05:57:31 GMT",
"version": "v1"
}
] | 2024-07-23 | [
[
"Paliathanasis",
"Andronikos",
""
]
] | Symmetric teleparallel $f(Q)$-gravity allows for the presence of a perfect fluid with a tilted velocity in the Kantowski-Sachs geometry. In this dipole model, we consider an ideal gas and we investigate the evolution of the physical parameters. The tilt parameter is constrained by the nonlinear function $f(Q)$ through the non-diagonal equations of the field equations. We find that the dynamics always reduce to the vacuum solutions of STEGR. This includes the Kasner universe, when no cosmological term is introduced by the $f(Q)$ function, and the isotropic de Sitter universe, where $f\left( Q\right) $ plays the role of the cosmological constant. In the extreme tilt limit, the universe is consistently anisotropic and accelerated. However, the final solution matches that of STEGR. |
1404.3421 | Bruno Arderucio Costa | Bruno Arderucio | Superradiance: Classical, Relativistic and Quantum Aspects | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Several physical systems can be treated as a scattering process, and, for
these processes, a natural observed quantity arises: the ratio between the
reflected and incident intensities, known as the reflection coefficient. This
dissertation is concerned with the phenomenon known as superradiance, that is,
when this coefficient is larger than unity.
We shall explore many examples of such systems, and, more importantly, we
shall also see how, apart from the interest in its own right, superradiance is
related to a number of important current research physical issues. We begin
with a small survey of important results on chapter one. On chapter two, we
establish a general criteria to decide whether or not superradiant scattering
is observed based on the linear, second order, homogeneous ordinary
differential equation (ODE) or linear, first order homogeneous systems of ODEs
which describes the process and we shall give an example of system in which
superradiance is observed. On chapter three, we focus on spinning black hole
superradiance, we shall describe how one can compute explicitly the reflection
coefficient for different spin waves. Chapter four is dedicated to the
relations with thermodynamics. We develop what is meant by black hole
thermodynamics, particularly the so-called first and second law of black hole
thermodynamics, and apply them in the context of superradiance, so we can
generalise some of the results from chapter three to more general black holes.
Finally, on chapter five, we explore many of the quantum aspects of
superradiance, including the relation with the Klein paradox, and the quantum
version of black hole superradiance, for the later we will explain briefly how
one usually quantise fields in curved space-time. A further connection with
thermodynamics is explored. Thorough all this text we analyse the connection
between superradiance and spin and statistics.
| [
{
"created": "Sun, 13 Apr 2014 20:20:02 GMT",
"version": "v1"
},
{
"created": "Sat, 12 Jul 2014 19:07:16 GMT",
"version": "v2"
}
] | 2014-07-15 | [
[
"Arderucio",
"Bruno",
""
]
] | Several physical systems can be treated as a scattering process, and, for these processes, a natural observed quantity arises: the ratio between the reflected and incident intensities, known as the reflection coefficient. This dissertation is concerned with the phenomenon known as superradiance, that is, when this coefficient is larger than unity. We shall explore many examples of such systems, and, more importantly, we shall also see how, apart from the interest in its own right, superradiance is related to a number of important current research physical issues. We begin with a small survey of important results on chapter one. On chapter two, we establish a general criteria to decide whether or not superradiant scattering is observed based on the linear, second order, homogeneous ordinary differential equation (ODE) or linear, first order homogeneous systems of ODEs which describes the process and we shall give an example of system in which superradiance is observed. On chapter three, we focus on spinning black hole superradiance, we shall describe how one can compute explicitly the reflection coefficient for different spin waves. Chapter four is dedicated to the relations with thermodynamics. We develop what is meant by black hole thermodynamics, particularly the so-called first and second law of black hole thermodynamics, and apply them in the context of superradiance, so we can generalise some of the results from chapter three to more general black holes. Finally, on chapter five, we explore many of the quantum aspects of superradiance, including the relation with the Klein paradox, and the quantum version of black hole superradiance, for the later we will explain briefly how one usually quantise fields in curved space-time. A further connection with thermodynamics is explored. Thorough all this text we analyse the connection between superradiance and spin and statistics. |
1110.5885 | Lorenzo Sindoni | Daniele Oriti, Roberto Pereira, Lorenzo Sindoni | Coherent states in quantum gravity: a construction based on the flux
representation of LQG | 24 pages, 2 figures; Revised version to match the published one. Some
references added. Discussion of the resolution of the identity included | null | 10.1088/1751-8113/45/24/244004 | AEI-2011-076 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | As part of a wider study of coherent states in (loop) quantum gravity, we
introduce a modification to the standard construction, based on the recently
introduced (non-commutative) flux representation. The resulting quantum states
have some welcomed features, in particular concerning peakedness properties,
when compared to other coherent states in the literature.
| [
{
"created": "Wed, 26 Oct 2011 19:19:24 GMT",
"version": "v1"
},
{
"created": "Fri, 20 Apr 2012 15:57:35 GMT",
"version": "v2"
}
] | 2015-05-30 | [
[
"Oriti",
"Daniele",
""
],
[
"Pereira",
"Roberto",
""
],
[
"Sindoni",
"Lorenzo",
""
]
] | As part of a wider study of coherent states in (loop) quantum gravity, we introduce a modification to the standard construction, based on the recently introduced (non-commutative) flux representation. The resulting quantum states have some welcomed features, in particular concerning peakedness properties, when compared to other coherent states in the literature. |
1609.03331 | Luis Herrera | L. Herrera, A. Di Prisco, J. Ospino | The spacetime outside a source of gravitational radiation: The axially
symmetric null fluid | 11 pages Latex. arXiv admin note: text overlap with arXiv:1609.02841.
Typos corrected, to appear in Eur. Phys. J. C | Eur. Phys. J. C, 76, 603, (2016) | 10.1140/epjc/s10052-016-4457-2 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We carry out a study of the exterior of an axially and reflection symmetric
source of gravitational radiation. The exterior of such a source is filled with
a null fluid produced by the dissipative processes inherent to the emission of
gravitational radiation, thereby representing a generalization of the Vaidya
metric for axially and reflection symmetric spacetimes. The role of the
vorticity, and its relationship with the presence of gravitational radiation is
put in evidence. The spherically symmetric case (Vaidya) is, asymptotically,
recovered within the context of the $1+3$ formalism.
| [
{
"created": "Mon, 12 Sep 2016 10:20:15 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Nov 2016 16:00:35 GMT",
"version": "v2"
}
] | 2016-11-23 | [
[
"Herrera",
"L.",
""
],
[
"Di Prisco",
"A.",
""
],
[
"Ospino",
"J.",
""
]
] | We carry out a study of the exterior of an axially and reflection symmetric source of gravitational radiation. The exterior of such a source is filled with a null fluid produced by the dissipative processes inherent to the emission of gravitational radiation, thereby representing a generalization of the Vaidya metric for axially and reflection symmetric spacetimes. The role of the vorticity, and its relationship with the presence of gravitational radiation is put in evidence. The spherically symmetric case (Vaidya) is, asymptotically, recovered within the context of the $1+3$ formalism. |
2105.06153 | Pradip Mukherjee | Pradip Mukherjee and Abdus Sattar | Hamiltonian analysis of the Schroedinger field coupled with dynamic
non-relativistic gravity | 17 pages, Latex. arXiv admin note: text overlap with arXiv:1810.06244 | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Using the recently mooted Galilean gauge theory we have constructed the model
for the Schroedinger field interacting wuth gravity which is also dynamical.
The dynamics of gravity is dictated by the Newtonian action in the
Newton-Cartan spacetime. The theory is highly constrained . An elaborate
analysis of the constraints of the theory have been performed. The symmetries
are explicitly verified and the uniqueness of the model has been established.
To the best of our knowledge both the model and its constraints structure are
unique in the literature
| [
{
"created": "Thu, 13 May 2021 09:10:03 GMT",
"version": "v1"
}
] | 2021-09-20 | [
[
"Mukherjee",
"Pradip",
""
],
[
"Sattar",
"Abdus",
""
]
] | Using the recently mooted Galilean gauge theory we have constructed the model for the Schroedinger field interacting wuth gravity which is also dynamical. The dynamics of gravity is dictated by the Newtonian action in the Newton-Cartan spacetime. The theory is highly constrained . An elaborate analysis of the constraints of the theory have been performed. The symmetries are explicitly verified and the uniqueness of the model has been established. To the best of our knowledge both the model and its constraints structure are unique in the literature |
0801.2896 | Serge Reynaud | Serge Reynaud, Brahim Lamine, Loic Duchayne, Peter Wolf, Marc-Thierry
Jaekel | Bounds on gravitational wave backgrounds from large distance clock
comparisons | 10 pages, 8 figures, minor amendments | Phys.Rev.D77:122003,2008 | 10.1103/PhysRevD.77.122003 | null | gr-qc astro-ph quant-ph | null | Our spacetime is filled with gravitational wave backgrounds that constitute a
fluctuating environment created by astrophysical and cosmological sources.
Bounds on these backgrounds are obtained from cosmological and astrophysical
data but also by analysis of ranging and Doppler signals from distant
spacecraft. We propose here a new way to set bounds on those backgrounds by
performing clock comparisons between a ground clock and a remote spacecraft
equipped with an ultra-stable clock, rather than only ranging to an onboard
transponder. This technique can then be optimized as a function of the signal
to be measured and the dominant noise sources, leading to significant
improvements on present bounds in a promising frequency range where different
theoretical models are competing. We illustrate our approach using the SAGAS
project which aims to fly an ultra stable optical clock in the outer solar
system.
| [
{
"created": "Fri, 18 Jan 2008 14:29:54 GMT",
"version": "v1"
},
{
"created": "Fri, 23 May 2008 12:56:17 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Reynaud",
"Serge",
""
],
[
"Lamine",
"Brahim",
""
],
[
"Duchayne",
"Loic",
""
],
[
"Wolf",
"Peter",
""
],
[
"Jaekel",
"Marc-Thierry",
""
]
] | Our spacetime is filled with gravitational wave backgrounds that constitute a fluctuating environment created by astrophysical and cosmological sources. Bounds on these backgrounds are obtained from cosmological and astrophysical data but also by analysis of ranging and Doppler signals from distant spacecraft. We propose here a new way to set bounds on those backgrounds by performing clock comparisons between a ground clock and a remote spacecraft equipped with an ultra-stable clock, rather than only ranging to an onboard transponder. This technique can then be optimized as a function of the signal to be measured and the dominant noise sources, leading to significant improvements on present bounds in a promising frequency range where different theoretical models are competing. We illustrate our approach using the SAGAS project which aims to fly an ultra stable optical clock in the outer solar system. |
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