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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0710.4243 | Tolga Birkandan | T. Birkandan, M. Hortacsu | Heun and Mathieu functions as solutions of the Dirac equation | 5 pages, Prepared for the Spanish Relativity Meeting (ERE 2007),
Tenerife, Spain, 10-14 Sep 2007 | EAS Publ.Ser.30:265,2008 | 10.1051/eas:0830041 | null | gr-qc | null | We give examples of where the Heun function exists as solutions of wave
equations encountered in general relativity. While the Dirac equation written
in the background of Nutku helicoid metric yields Mathieu functions as its
solutions in four spacetime dimensions, the trivial generalization to five
dimensions results in the double confluent Heun function. We reduce this
solution to the Mathieu function with some transformations. We must apply
Atiyah-Patodi-Singer spectral boundary conditions to this system since the
metric has a singularity at the origin.
| [
{
"created": "Tue, 23 Oct 2007 11:27:02 GMT",
"version": "v1"
}
] | 2011-08-31 | [
[
"Birkandan",
"T.",
""
],
[
"Hortacsu",
"M.",
""
]
] | We give examples of where the Heun function exists as solutions of wave equations encountered in general relativity. While the Dirac equation written in the background of Nutku helicoid metric yields Mathieu functions as its solutions in four spacetime dimensions, the trivial generalization to five dimensions results in the double confluent Heun function. We reduce this solution to the Mathieu function with some transformations. We must apply Atiyah-Patodi-Singer spectral boundary conditions to this system since the metric has a singularity at the origin. |
1006.0559 | Ali Kaya | Ali Kaya | Cosmological Evolution of Vacuum and Cosmic Acceleration | 22 pages, 2 figures, revtex4, v4: typos corrected | Class.Quant.Grav.27:235022,2010 | 10.1088/0264-9381/27/23/235022 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is known that the unregularized expressions for the stress-energy tensor
components corresponding to subhorizon and superhorizon vacuum fluctuations of
a massless scalar field in a Friedmann-Robertson-Walker background are
characterized by the equation of state parameters w=1/3 and w=-1/3, which are
not sufficient to produce cosmological acceleration. However, the form of the
adiabatically regularized finite stress-energy tensor turns out to be
completely different. By using the fact that vacuum subhorizon modes evolve
nearly adiabatically and superhorizon modes have w=-1/3, we approximately
determine the regularized stress-energy tensor, whose conservation is utilized
to fix the time dependence of the vacuum energy density. We then show that
vacuum energy density grows from zero up to H^4 in about one Hubble time,
vacuum fluctuations give positive acceleration of the order of H^4/M_p^2 and
they can completely alter the cosmic evolution of the universe dominated
otherwise by cosmological constant, radiation or pressureless dust. Although
the magnitude of the acceleration is tiny to explain the observed value today,
our findings indicate that the cosmological backreaction of vacuum fluctuations
must be taken into account in early stages of cosmic evolution.
| [
{
"created": "Thu, 3 Jun 2010 06:26:45 GMT",
"version": "v1"
},
{
"created": "Sat, 28 Aug 2010 09:16:30 GMT",
"version": "v2"
},
{
"created": "Thu, 21 Oct 2010 18:07:27 GMT",
"version": "v3"
},
{
"created": "Thu, 18 Nov 2010 14:51:13 GMT",
"version": "v4"
}
] | 2010-11-19 | [
[
"Kaya",
"Ali",
""
]
] | It is known that the unregularized expressions for the stress-energy tensor components corresponding to subhorizon and superhorizon vacuum fluctuations of a massless scalar field in a Friedmann-Robertson-Walker background are characterized by the equation of state parameters w=1/3 and w=-1/3, which are not sufficient to produce cosmological acceleration. However, the form of the adiabatically regularized finite stress-energy tensor turns out to be completely different. By using the fact that vacuum subhorizon modes evolve nearly adiabatically and superhorizon modes have w=-1/3, we approximately determine the regularized stress-energy tensor, whose conservation is utilized to fix the time dependence of the vacuum energy density. We then show that vacuum energy density grows from zero up to H^4 in about one Hubble time, vacuum fluctuations give positive acceleration of the order of H^4/M_p^2 and they can completely alter the cosmic evolution of the universe dominated otherwise by cosmological constant, radiation or pressureless dust. Although the magnitude of the acceleration is tiny to explain the observed value today, our findings indicate that the cosmological backreaction of vacuum fluctuations must be taken into account in early stages of cosmic evolution. |
gr-qc/0410046 | Sante Carloni | S. Carloni, P. K. S. Dunsby, S. Capozziello and A. Troisi | Cosmological dynamics of R^n gravity | revised and extended version, 35 pages, 12 tables, 14 figures which
are not included and can be found at http://www.mth.uct.ac.za/~peter/Rn | Class.Quant.Grav.22:4839-4868,2005 | 10.1088/0264-9381/22/22/011 | null | gr-qc astro-ph hep-th | null | A detailed analysis of dynamics of cosmological models based on $R^{n}$
gravity is presented. We show that the cosmological equations can be written as
a first order autonomous system and analyzed using the standard techniques of
dynamical system theory. In absence of perfect fluid matter, we find exact
solutions whose behavior and stability are analyzed in terms of the values of
the parameter $n$. When matter is introduced, the nature of the (non-minimal)
coupling between matter and higher order gravity induces restrictions on the
allowed values of $n$. Selecting such intervals of values and following the
same procedure used in the vacuum case, we present exact solutions and analyze
their stability for a generic value of the parameter $n$. From this analysis
emerges the result that for a large set of initial conditions an accelerated
expansion is an attractor for the evolution of the $R^n$ cosmology. When matter
is present a transient almost-Friedman phase can also be present before the
transition to an accelerated expansion.
| [
{
"created": "Mon, 11 Oct 2004 19:45:34 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Oct 2004 08:04:58 GMT",
"version": "v2"
},
{
"created": "Tue, 19 Jul 2005 10:57:54 GMT",
"version": "v3"
},
{
"created": "Wed, 20 Jul 2005 10:06:36 GMT",
"version": "v4"
}
] | 2009-11-10 | [
[
"Carloni",
"S.",
""
],
[
"Dunsby",
"P. K. S.",
""
],
[
"Capozziello",
"S.",
""
],
[
"Troisi",
"A.",
""
]
] | A detailed analysis of dynamics of cosmological models based on $R^{n}$ gravity is presented. We show that the cosmological equations can be written as a first order autonomous system and analyzed using the standard techniques of dynamical system theory. In absence of perfect fluid matter, we find exact solutions whose behavior and stability are analyzed in terms of the values of the parameter $n$. When matter is introduced, the nature of the (non-minimal) coupling between matter and higher order gravity induces restrictions on the allowed values of $n$. Selecting such intervals of values and following the same procedure used in the vacuum case, we present exact solutions and analyze their stability for a generic value of the parameter $n$. From this analysis emerges the result that for a large set of initial conditions an accelerated expansion is an attractor for the evolution of the $R^n$ cosmology. When matter is present a transient almost-Friedman phase can also be present before the transition to an accelerated expansion. |
2205.01705 | Hao-Jui Kuan | Hao-Jui Kuan, Kostas D. Kokkotas | $f$-mode Imprints in Gravitational Waves from Coalescing Binaries
involving Aligned Spinning Neutron Stars | 16 pages, 9 figures, 2 tables. Accepted for publication in PRD | null | 10.1103/PhysRevD.106.064052 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The excitation of $f$-mode in a neutron star member of coalescing binaries
accelerates the merger course, and thereby introduces a phase shift in the
gravitational waveform. Emphasising on the tidal phase shift by aligned,
rotating stars, we provide an accurate, yet economical, method to generate
$f$-mode-involved, pre-merger waveforms using realistic spin-modulated $f$-mode
frequencies for some viable equations of state. We find for slow-rotating stars
that the dephasing effects of the dynamical tides can be uniquely,
EOS-independently determined by the direct observables (chirp mass ${\cal M}$,
symmetric ratio $\eta$ and the mutual tidal deformability ${\tilde \Lambda}$),
while this universality is gradually lost for increasing spin. For binaries
with fast rotating members ($\gtrsim800\text{ Hz}$) the phase shift due to
$f$-mode will exceed the uncertainty in the waveform phase at reasonable
signal-to-noise ($\rho=25$) and cutoff frequency of $\gtrsim400\text{ Hz}$.
Assuming a high cutoff frequency of $10^3\text{ Hz}$ and fast
($\gtrsim800\text{ Hz}$) members, a significant phase shift of $\gtrsim100$
rads has been found. For systems involving a rapidly-spinning star (potentially
the secondary of GW190814), neglecting $f$-mode effect in the waveform
templates can therefore lead to considerable systemic errors in the relevant
analysis. In particular, the dephasing due to $f$-mode is larger than that
caused by equilibrium tides by a factor of $\sim5$, which may lead to a
considerably overestimated tidal deformability if dynamical tidal contribution
is not accounted. The possibility of accompanying precursors flares due to
$f$-mode excitation is also discussed.
| [
{
"created": "Tue, 3 May 2022 18:02:45 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Sep 2022 15:27:54 GMT",
"version": "v2"
}
] | 2022-10-12 | [
[
"Kuan",
"Hao-Jui",
""
],
[
"Kokkotas",
"Kostas D.",
""
]
] | The excitation of $f$-mode in a neutron star member of coalescing binaries accelerates the merger course, and thereby introduces a phase shift in the gravitational waveform. Emphasising on the tidal phase shift by aligned, rotating stars, we provide an accurate, yet economical, method to generate $f$-mode-involved, pre-merger waveforms using realistic spin-modulated $f$-mode frequencies for some viable equations of state. We find for slow-rotating stars that the dephasing effects of the dynamical tides can be uniquely, EOS-independently determined by the direct observables (chirp mass ${\cal M}$, symmetric ratio $\eta$ and the mutual tidal deformability ${\tilde \Lambda}$), while this universality is gradually lost for increasing spin. For binaries with fast rotating members ($\gtrsim800\text{ Hz}$) the phase shift due to $f$-mode will exceed the uncertainty in the waveform phase at reasonable signal-to-noise ($\rho=25$) and cutoff frequency of $\gtrsim400\text{ Hz}$. Assuming a high cutoff frequency of $10^3\text{ Hz}$ and fast ($\gtrsim800\text{ Hz}$) members, a significant phase shift of $\gtrsim100$ rads has been found. For systems involving a rapidly-spinning star (potentially the secondary of GW190814), neglecting $f$-mode effect in the waveform templates can therefore lead to considerable systemic errors in the relevant analysis. In particular, the dephasing due to $f$-mode is larger than that caused by equilibrium tides by a factor of $\sim5$, which may lead to a considerably overestimated tidal deformability if dynamical tidal contribution is not accounted. The possibility of accompanying precursors flares due to $f$-mode excitation is also discussed. |
2011.00031 | Sepideh Bakhoda | Sepideh Bakhoda and Thomas Thiemann | Covariant Origin of the $U(1)^3$ model for Euclidean Quantum Gravity | 26 pages | Class. Quantum Grav. 39 (2022) 025006 | 10.1088/1361-6382/ac37a4 | null | gr-qc hep-lat hep-th math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The utility of the U(1)$^3$ model as a test laboratory for quantum gravity
has recently been emphasized in a recent series of papers due to Varadarajan et
al. The simplification from SU(2) to U(1)$^3$ can be performed simply by hand
within the Hamiltonian formulation by dropping all non-Abelian terms from the
Gauss, spatial diffeomorphism and Hamiltonian constraints respectively.
However, one may ask from which Lagrangian formulation this theory descends.
For the SU(2) theory it is known that one can choose the Palatini action, Holst
action or (anti-)selfdual action (Euclidian signature) as starting point all
leading to equivalent Hamiltonian formulations. In this paper we systematically
analyse this question directly for the U(1)$^3$ theory. Surprisingly, it turns
out that the Abelian analog of the Palatini or Holst formulation is a
consistent but topological theory without propagating degrees of freedom. On
the other hand, a twisted Abelian analog of the (anti-)selfdual formulation
does lead to the desired Hamiltonian formulation. A new aspect of our
derivation is that we work with 1. half-density valued tetrads which simplifies
the analysis, 2. without the simplicity constraint (which admits one undesired
solution that is usually neglected by hand) and 3. without imposing the time
gauge from the beginning. As a byproduct we show that also the non-Abelian
theory admits a twisted (anti-)selfdual formulation. Finally we also derive a
pure connection formulation of Euclidian GR including a cosmological constant
by extending previous work due to Capovilla, Dell, Jacobson and Peldan which
may be an interesting starting point for path integral investigations and
displays (Euclidian) GR as a Yang-Mills theory with non-polynomial Lagrangian.
| [
{
"created": "Fri, 30 Oct 2020 18:22:37 GMT",
"version": "v1"
},
{
"created": "Sun, 19 Dec 2021 15:00:14 GMT",
"version": "v2"
}
] | 2021-12-21 | [
[
"Bakhoda",
"Sepideh",
""
],
[
"Thiemann",
"Thomas",
""
]
] | The utility of the U(1)$^3$ model as a test laboratory for quantum gravity has recently been emphasized in a recent series of papers due to Varadarajan et al. The simplification from SU(2) to U(1)$^3$ can be performed simply by hand within the Hamiltonian formulation by dropping all non-Abelian terms from the Gauss, spatial diffeomorphism and Hamiltonian constraints respectively. However, one may ask from which Lagrangian formulation this theory descends. For the SU(2) theory it is known that one can choose the Palatini action, Holst action or (anti-)selfdual action (Euclidian signature) as starting point all leading to equivalent Hamiltonian formulations. In this paper we systematically analyse this question directly for the U(1)$^3$ theory. Surprisingly, it turns out that the Abelian analog of the Palatini or Holst formulation is a consistent but topological theory without propagating degrees of freedom. On the other hand, a twisted Abelian analog of the (anti-)selfdual formulation does lead to the desired Hamiltonian formulation. A new aspect of our derivation is that we work with 1. half-density valued tetrads which simplifies the analysis, 2. without the simplicity constraint (which admits one undesired solution that is usually neglected by hand) and 3. without imposing the time gauge from the beginning. As a byproduct we show that also the non-Abelian theory admits a twisted (anti-)selfdual formulation. Finally we also derive a pure connection formulation of Euclidian GR including a cosmological constant by extending previous work due to Capovilla, Dell, Jacobson and Peldan which may be an interesting starting point for path integral investigations and displays (Euclidian) GR as a Yang-Mills theory with non-polynomial Lagrangian. |
1811.03283 | Craig J. Hogan | Craig Hogan | Nonlocal Entanglement and Directional Correlations of Primordial
Perturbations on the Inflationary Horizon | Final version, edited to match published version | Phys. Rev. D 99, 063531 (2019) | 10.1103/PhysRevD.99.063531 | FERMILAB-PUB-18-178-A | gr-qc astro-ph.CO quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Models are developed to estimate properties of relic cosmic perturbations
with "spooky" nonlocal correlations on the inflationary horizon, analogous to
those previously posited for information on black hole event horizons. Scalar
curvature perturbations are estimated to emerge with a dimensionless power
spectral density $\Delta_S^2\approx H t_P$, the product of inflationary
expansion rate $H$ with Planck time $t_P$, larger than standard inflaton
fluctuations. Current measurements of the spectrum are used to derive
constraints on parameters of the effective potential in a slow-roll background.
It is shown that spooky nonlocality can create statistically homogeneous and
isotropic primordial curvature perturbations that are initially directionally
antisymmetric. New statistical estimators are developed to study unique
signatures in CMB anisotropy and large scale galaxy surveys.
| [
{
"created": "Thu, 8 Nov 2018 05:58:45 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Nov 2018 21:35:38 GMT",
"version": "v2"
},
{
"created": "Thu, 13 Dec 2018 16:41:50 GMT",
"version": "v3"
},
{
"created": "Thu, 20 Dec 2018 16:27:20 GMT",
"version": "v4"
},
{
"created": "Fri, 4 Jan 2019 18:50:55 GMT",
"version": "v5"
},
{
"created": "Tue, 30 Apr 2019 18:50:25 GMT",
"version": "v6"
}
] | 2019-05-02 | [
[
"Hogan",
"Craig",
""
]
] | Models are developed to estimate properties of relic cosmic perturbations with "spooky" nonlocal correlations on the inflationary horizon, analogous to those previously posited for information on black hole event horizons. Scalar curvature perturbations are estimated to emerge with a dimensionless power spectral density $\Delta_S^2\approx H t_P$, the product of inflationary expansion rate $H$ with Planck time $t_P$, larger than standard inflaton fluctuations. Current measurements of the spectrum are used to derive constraints on parameters of the effective potential in a slow-roll background. It is shown that spooky nonlocality can create statistically homogeneous and isotropic primordial curvature perturbations that are initially directionally antisymmetric. New statistical estimators are developed to study unique signatures in CMB anisotropy and large scale galaxy surveys. |
1203.4534 | Tim-Torben Paetz | Piotr T. Chru\'sciel and Tim-Torben Paetz | The many ways of the characteristic Cauchy problem | 25 pages, a couple of minor changes, version corresponds to the one
published in CQG | Class. Quantum Grav. 29 (2012) 145006 | 10.1088/0264-9381/29/14/145006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We review various aspects of the characteristic initial value problem for the
Einstein equations, presenting new approaches to some of the issues arising.
| [
{
"created": "Tue, 20 Mar 2012 18:18:47 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Jul 2012 09:04:19 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Chruściel",
"Piotr T.",
""
],
[
"Paetz",
"Tim-Torben",
""
]
] | We review various aspects of the characteristic initial value problem for the Einstein equations, presenting new approaches to some of the issues arising. |
gr-qc/0310051 | Michael Kuchiev | M. Yu. Kuchiev | Reflection, radiation and interference for black holes | 10 pages, 1 figure, Revtex | Phys.Rev. D69 (2004) 124031 | 10.1103/PhysRevD.69.124031 | null | gr-qc astro-ph hep-th | null | Black holes are capable of reflection: there is a finite probability for any
particle that approaches the event horizon to bounce back. The albedo of the
black hole depends on its temperature and the energy of the incoming particle.
The reflection shares its physical origins with the Hawking process of
radiation, both of them arise as consequences of the mixing of the incoming and
outgoing waves that takes place on the event horizon.
| [
{
"created": "Thu, 9 Oct 2003 00:15:42 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Kuchiev",
"M. Yu.",
""
]
] | Black holes are capable of reflection: there is a finite probability for any particle that approaches the event horizon to bounce back. The albedo of the black hole depends on its temperature and the energy of the incoming particle. The reflection shares its physical origins with the Hawking process of radiation, both of them arise as consequences of the mixing of the incoming and outgoing waves that takes place on the event horizon. |
2304.11836 | Sizheng Ma | Sizheng Ma, Vijay Varma, Leo C. Stein, Francois Foucart, Matthew D.
Duez, Lawrence E. Kidder, Harald P. Pfeiffer, Mark A. Scheel | Numerical simulations of black hole-neutron star mergers in
scalar-tensor gravity | null | Phys. Rev. D 107, 124051 (2023) | 10.1103/PhysRevD.107.124051 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a numerical-relativity simulation of a black hole - neutron star
merger in scalar-tensor (ST) gravity with binary parameters consistent with the
gravitational wave event GW200115. In this exploratory simulation, we consider
the Damour-Esposito-Farese extension to Brans-Dicke theory, and maximize the
effect of spontaneous scalarization by choosing a soft equation of state and ST
theory parameters at the edge of known constraints. We extrapolate the
gravitational waves, including tensor and scalar (breathing) modes, to future
null-infinity. The numerical waveforms undergo ~ 22 wave cycles before the
merger, and are in good agreement with predictions from post-Newtonian theory
during the inspiral. We find the ST system evolves faster than its
general-relativity (GR) counterpart due to dipole radiation, merging a full
gravitational-wave cycle before the GR counterpart. This enables easy
differentiation between the ST waveforms and GR in the context of parameter
estimation. However, we find that dipole radiation's effect may be partially
degenerate with the NS tidal deformability during the late inspiral stage, and
a full Bayesian analysis is necessary to fully understand the degeneracies
between ST and binary parameters in GR.
| [
{
"created": "Mon, 24 Apr 2023 05:59:16 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Jun 2023 05:48:42 GMT",
"version": "v2"
}
] | 2023-06-29 | [
[
"Ma",
"Sizheng",
""
],
[
"Varma",
"Vijay",
""
],
[
"Stein",
"Leo C.",
""
],
[
"Foucart",
"Francois",
""
],
[
"Duez",
"Matthew D.",
""
],
[
"Kidder",
"Lawrence E.",
""
],
[
"Pfeiffer",
"Harald P.",
""
],
[
"Scheel",
"Mark A.",
""
]
] | We present a numerical-relativity simulation of a black hole - neutron star merger in scalar-tensor (ST) gravity with binary parameters consistent with the gravitational wave event GW200115. In this exploratory simulation, we consider the Damour-Esposito-Farese extension to Brans-Dicke theory, and maximize the effect of spontaneous scalarization by choosing a soft equation of state and ST theory parameters at the edge of known constraints. We extrapolate the gravitational waves, including tensor and scalar (breathing) modes, to future null-infinity. The numerical waveforms undergo ~ 22 wave cycles before the merger, and are in good agreement with predictions from post-Newtonian theory during the inspiral. We find the ST system evolves faster than its general-relativity (GR) counterpart due to dipole radiation, merging a full gravitational-wave cycle before the GR counterpart. This enables easy differentiation between the ST waveforms and GR in the context of parameter estimation. However, we find that dipole radiation's effect may be partially degenerate with the NS tidal deformability during the late inspiral stage, and a full Bayesian analysis is necessary to fully understand the degeneracies between ST and binary parameters in GR. |
0810.5594 | Thomas Sotiriou | Thomas P. Sotiriou | 6+1 lessons from f(R) gravity | Talk given at the 13th Conference on Recent Developments in Gravity
(NEBXIII), Thessaloniki, Greece, 4-6 Jun 2008 | J.Phys.Conf.Ser.189:012039,2009 | 10.1088/1742-6596/189/1/012039 | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There has been a recent stimulus in the study of alternative theories of
gravity lately, mostly triggered from combined motivation coming from
cosmology/astrophysics and high energy physics. Among the proposed theories,
one that has attracted much attention is f(R) gravity. It is certainly
debatable whether such a simplistic modification of General Relativity can
constitute a viable alternative theory of gravitation. However, it is quite
straightforward to see the merits of such a theory when viewed as a toy theory
whose role is to help us understand the implications and difficulties of
beyond-Einstein gravity. Under this perspective, I review some of the main
lessons we seem to have learned from the study of f(R) gravity in the recent
past.
| [
{
"created": "Thu, 30 Oct 2008 23:26:00 GMT",
"version": "v1"
}
] | 2009-11-05 | [
[
"Sotiriou",
"Thomas P.",
""
]
] | There has been a recent stimulus in the study of alternative theories of gravity lately, mostly triggered from combined motivation coming from cosmology/astrophysics and high energy physics. Among the proposed theories, one that has attracted much attention is f(R) gravity. It is certainly debatable whether such a simplistic modification of General Relativity can constitute a viable alternative theory of gravitation. However, it is quite straightforward to see the merits of such a theory when viewed as a toy theory whose role is to help us understand the implications and difficulties of beyond-Einstein gravity. Under this perspective, I review some of the main lessons we seem to have learned from the study of f(R) gravity in the recent past. |
1607.06631 | Abdulla Al Mamon | Abdulla Al Mamon, Kazuharu Bamba and Sudipta Das | Constraints on reconstructed dark energy model from SN Ia and BAO/CMB
observations | Revised version, References added, Accepted for publication in
European Physical Journal C | null | 10.1140/epjc/s10052-016-4590-y | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The motivation of the present work is to reconstruct a dark energy model
through the {\it dimensionless dark energy function} $X(z)$, which is the dark
energy density in units of its present value. In this paper, we have shown that
a scalar field $\phi$ having a phenomenologically chosen $X(z)$ can give rise
to a transition from a decelerated to an accelerated phase of expansion for the
universe. We have examined the possibility of constraining various cosmological
parameters (such as the deceleration parameter and the effective equation of
state parameter) by comparing our theoretical model with the latest Type Ia
Supernova (SN Ia), Baryon Acoustic Oscillations (BAO) and Cosmic Microwave
Background (CMB) radiation observations. Using the joint analysis of the SN
Ia+BAO/CMB dataset, we have also reconstructed the scalar potential from the
parametrized $X(z)$. The relevant potential is found, which comes to be a
polynomial in $\phi$. From our analysis, it has been found that the present
model favors the standard $\Lambda$CDM model within $1\sigma$ confidence level.
| [
{
"created": "Fri, 22 Jul 2016 11:05:58 GMT",
"version": "v1"
},
{
"created": "Tue, 27 Dec 2016 09:26:35 GMT",
"version": "v2"
}
] | 2017-02-01 | [
[
"Mamon",
"Abdulla Al",
""
],
[
"Bamba",
"Kazuharu",
""
],
[
"Das",
"Sudipta",
""
]
] | The motivation of the present work is to reconstruct a dark energy model through the {\it dimensionless dark energy function} $X(z)$, which is the dark energy density in units of its present value. In this paper, we have shown that a scalar field $\phi$ having a phenomenologically chosen $X(z)$ can give rise to a transition from a decelerated to an accelerated phase of expansion for the universe. We have examined the possibility of constraining various cosmological parameters (such as the deceleration parameter and the effective equation of state parameter) by comparing our theoretical model with the latest Type Ia Supernova (SN Ia), Baryon Acoustic Oscillations (BAO) and Cosmic Microwave Background (CMB) radiation observations. Using the joint analysis of the SN Ia+BAO/CMB dataset, we have also reconstructed the scalar potential from the parametrized $X(z)$. The relevant potential is found, which comes to be a polynomial in $\phi$. From our analysis, it has been found that the present model favors the standard $\Lambda$CDM model within $1\sigma$ confidence level. |
gr-qc/0505108 | Sigbjorn Hervik | Sigbjorn Hervik and Alan Coley | Inhomogeneous perturbations of plane-wave spacetimes | 8 pages, to appear in CQG | Class.Quant.Grav. 22 (2005) 3391-3398 | 10.1088/0264-9381/22/17/002 | null | gr-qc astro-ph hep-th | null | Recently it was shown that the exact cosmological solutions known as the
vacuum plane-wave solutions are late-time attractors for an open set of the
spatially homogeneous Bianchi universes containing a non-inflationary
$\gamma$-law perfect fluid. In this paper we study inhomogeneous perturbations
of these plane-wave spacetimes. By using expansion-normalised scale-invariant
variables we show that these solutions are unstable to generic inhomogeneous
perturbations. The crucial observation for establishing this result is a
divergence of the expansion-normalised frame variables which ultimately leads
to unstable modes.
| [
{
"created": "Fri, 20 May 2005 14:31:17 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Jul 2005 13:44:46 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Hervik",
"Sigbjorn",
""
],
[
"Coley",
"Alan",
""
]
] | Recently it was shown that the exact cosmological solutions known as the vacuum plane-wave solutions are late-time attractors for an open set of the spatially homogeneous Bianchi universes containing a non-inflationary $\gamma$-law perfect fluid. In this paper we study inhomogeneous perturbations of these plane-wave spacetimes. By using expansion-normalised scale-invariant variables we show that these solutions are unstable to generic inhomogeneous perturbations. The crucial observation for establishing this result is a divergence of the expansion-normalised frame variables which ultimately leads to unstable modes. |
gr-qc/0212026 | Mario Novello | M. Novello | Geometrical description of spin-2 fields | null | null | null | null | gr-qc | null | We show that the torsion of a Cartan geometry can be associated to two spin-2
fields. This structure allows a new approach to deal with the proposal of
geometrization of spin-2 fields besides the traditional one dealt with in
General Relativity. We use the associated Hilbert-Einstein Lagrangian $R$ for
generating a dynamics for the fields.
| [
{
"created": "Thu, 5 Dec 2002 17:59:07 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Novello",
"M.",
""
]
] | We show that the torsion of a Cartan geometry can be associated to two spin-2 fields. This structure allows a new approach to deal with the proposal of geometrization of spin-2 fields besides the traditional one dealt with in General Relativity. We use the associated Hilbert-Einstein Lagrangian $R$ for generating a dynamics for the fields. |
gr-qc/0404028 | Belinch\'on Jos\'e Antonio | Jos\'e Antonio Belinch\'on | An excuse for revising a theory of time-varying "constants" | 16 pages, 5 figures. Revtex4. Minor changes in the appendix | null | null | null | gr-qc | null | In this paper we compare the dimensional method with the Lie groups tactic in
order to show the limitations and advantages of each technique. For this
purpose we study in detail a perfect fluid cosmological model with time-varying
"constants" by using dimensional analysis and the symmetry method. We revise
our previous conclusion about the variation of the fine structure constant
finding for example that in the radiation predominance era if $\alpha$ varies
is only due to the variation of $e^{2}\epsilon_{0}^{-1}$ since $c\hbar=const$
in this era.
| [
{
"created": "Wed, 7 Apr 2004 07:37:44 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Jun 2004 16:05:49 GMT",
"version": "v2"
}
] | 2009-09-29 | [
[
"Belinchón",
"José Antonio",
""
]
] | In this paper we compare the dimensional method with the Lie groups tactic in order to show the limitations and advantages of each technique. For this purpose we study in detail a perfect fluid cosmological model with time-varying "constants" by using dimensional analysis and the symmetry method. We revise our previous conclusion about the variation of the fine structure constant finding for example that in the radiation predominance era if $\alpha$ varies is only due to the variation of $e^{2}\epsilon_{0}^{-1}$ since $c\hbar=const$ in this era. |
2205.00875 | Naresh Dadhich | Naresh Dadhich | Fundamental forces and their dynamics | Revamped and published version, Contribution to Professor T.
Padmanabhan memorial volume, GRG Journal | Gen. Relativ. Grav. \{bf 54}, 83 (2022) | 10.1007/s10714-022-02967-8 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this essay, we wish to propose a general principle: \it{the equation of
motion or dynamics of a fundamental force should not be prescribed but instead
be entirely driven by geometry of the appropriate spacetime manifold, and the
equation is then obtained by employing only the geometric property without
appeal to an action.} The motivation for this pronouncement comes from the fact
that the equation of motion of general relativity follows from the geometry of
Riemannian spacetime manifold without appeal to anything else from outside. The
driving differential geometric property is the Bianchi identity satisfied by
the Riemann curvature tensor. Similarly it is geometry of the principal tangent
bundle of fibre spacetime manifold that may account for dynamics of the gauge
vector fields. It is the classical electric force for the Abelian gauge
symmetry group while the non-Abelian symmetry leads to the non-Abelian forces,
the weak and the strong. We shall also reflect on a unified picture of the
basic forces, and the duality correspondences it may inspire.
| [
{
"created": "Fri, 29 Apr 2022 06:32:22 GMT",
"version": "v1"
},
{
"created": "Sun, 7 Aug 2022 07:15:29 GMT",
"version": "v2"
}
] | 2022-08-17 | [
[
"Dadhich",
"Naresh",
""
]
] | In this essay, we wish to propose a general principle: \it{the equation of motion or dynamics of a fundamental force should not be prescribed but instead be entirely driven by geometry of the appropriate spacetime manifold, and the equation is then obtained by employing only the geometric property without appeal to an action.} The motivation for this pronouncement comes from the fact that the equation of motion of general relativity follows from the geometry of Riemannian spacetime manifold without appeal to anything else from outside. The driving differential geometric property is the Bianchi identity satisfied by the Riemann curvature tensor. Similarly it is geometry of the principal tangent bundle of fibre spacetime manifold that may account for dynamics of the gauge vector fields. It is the classical electric force for the Abelian gauge symmetry group while the non-Abelian symmetry leads to the non-Abelian forces, the weak and the strong. We shall also reflect on a unified picture of the basic forces, and the duality correspondences it may inspire. |
gr-qc/9712013 | Nuno Barros e Sa' | Nuno Barros e Sa | Geodesics or autoparallels from a variational principle? | Latex, 13 pages, no figures | null | null | USITP 97-19 | gr-qc | null | Recently it has been argued that autoparallels should be the correct
description of free particle motion in spaces with torsion, and that such
trajectories can be derived from variational principles if these are suitably
adapted. The purpose of this letter is to call attention to the problems that
such attempts raise, namely the requirement of a more elaborate structure in
order to formulate the variational principle and the lack of a Hamiltonian
description for the autoparallel motion. Here is also raised the problem of how
to generalize this proposed new principle to quantum mechanics and to field
theory. Since all applications known of such a principle are equally well
described in terms of geodesics in non-holonomic frames we conclude that there
is no reason to modify the conventional variational principle that leads to
geodesics.
| [
{
"created": "Tue, 2 Dec 1997 14:51:39 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sa",
"Nuno Barros e",
""
]
] | Recently it has been argued that autoparallels should be the correct description of free particle motion in spaces with torsion, and that such trajectories can be derived from variational principles if these are suitably adapted. The purpose of this letter is to call attention to the problems that such attempts raise, namely the requirement of a more elaborate structure in order to formulate the variational principle and the lack of a Hamiltonian description for the autoparallel motion. Here is also raised the problem of how to generalize this proposed new principle to quantum mechanics and to field theory. Since all applications known of such a principle are equally well described in terms of geodesics in non-holonomic frames we conclude that there is no reason to modify the conventional variational principle that leads to geodesics. |
2311.09654 | Shunke Ai | Yikang Chen, Bin Liu, Shunke Ai, Lin Lan, He Gao, Yong Yuan and
Zong-Hong Zhu | On the possibility to detect gravitational waves from post-merger
super-massive neutron stars with a kilohertz detector | 10 pages, 6 figures, 4 tables, accepted for publication on MNRAS | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The detection of a secular post-merger gravitational wave (GW) signal in a
binary neutron star (BNS) merger serves as strong evidence for the formation of
a long-lived post-merger neutron star (NS), which can help constrain the
maximum mass of NSs and differentiate NS equation of states. We specifically
focus on the detection of GW emissions from rigidly rotating NSs formed through
BNS mergers, using several kilohertz GW detectors that have been designed. We
simulate the BNS mergers within the detecting limit of LIGO-Virgo-KARGA O4 and
attempt to find out on what fraction the simulated sources may have a
detectable secular post-merger GW signal. For kilohertz detectors designed in
the same configuration of LIGO A+, we find that the design with peak
sensitivity at approximately $2{\rm kHz}$ is most appropriate for such signals.
The fraction of sources that have a detectable secular post-merger GW signal
would be approximately $0.94\% - 11\%$ when the spindowns of the post-merger
rigidly rotating NSs are dominated by GW radiation, while be approximately
$0.46\% - 1.6\%$ when the contribution of electromagnetic (EM) radiation to the
spin-down processes is non-negligible. We also estimate this fraction based on
other well-known proposed kilohertz GW detectors and find that, with advanced
design, it can reach approximately $12\% - 45\%$ for the GW-dominated spindown
case and $4.7\% - 16\%$ when both the GW and EM radiations are considered.
| [
{
"created": "Thu, 16 Nov 2023 08:12:41 GMT",
"version": "v1"
}
] | 2023-11-17 | [
[
"Chen",
"Yikang",
""
],
[
"Liu",
"Bin",
""
],
[
"Ai",
"Shunke",
""
],
[
"Lan",
"Lin",
""
],
[
"Gao",
"He",
""
],
[
"Yuan",
"Yong",
""
],
[
"Zhu",
"Zong-Hong",
""
]
] | The detection of a secular post-merger gravitational wave (GW) signal in a binary neutron star (BNS) merger serves as strong evidence for the formation of a long-lived post-merger neutron star (NS), which can help constrain the maximum mass of NSs and differentiate NS equation of states. We specifically focus on the detection of GW emissions from rigidly rotating NSs formed through BNS mergers, using several kilohertz GW detectors that have been designed. We simulate the BNS mergers within the detecting limit of LIGO-Virgo-KARGA O4 and attempt to find out on what fraction the simulated sources may have a detectable secular post-merger GW signal. For kilohertz detectors designed in the same configuration of LIGO A+, we find that the design with peak sensitivity at approximately $2{\rm kHz}$ is most appropriate for such signals. The fraction of sources that have a detectable secular post-merger GW signal would be approximately $0.94\% - 11\%$ when the spindowns of the post-merger rigidly rotating NSs are dominated by GW radiation, while be approximately $0.46\% - 1.6\%$ when the contribution of electromagnetic (EM) radiation to the spin-down processes is non-negligible. We also estimate this fraction based on other well-known proposed kilohertz GW detectors and find that, with advanced design, it can reach approximately $12\% - 45\%$ for the GW-dominated spindown case and $4.7\% - 16\%$ when both the GW and EM radiations are considered. |
1111.2672 | Steffen Gielen | Steffen Gielen | The Space of Connections as the Arena for (Quantum) Gravity | Appeared as a review paper in the Special Issue "Loop Quantum Gravity
and Cosmology" of SIGMA; v2: added ref.[9] | SIGMA 7 (2011), 104, 12 pages | 10.3842/SIGMA.2011.104 | AEI-2011-086 | gr-qc hep-th | http://creativecommons.org/licenses/by-nc-sa/3.0/ | We review some properties of the space of connections as the natural arena
for canonical (quantum) gravity, and compare to the case of the superspace of
3-metrics. We detail how a 1-parameter family of metrics on the space of
connections arises from the canonical analysis for general relativity which has
a natural interpretation in terms of invariant tensors on the algebra of the
gauge group. We also review the description of canonical GR as a geodesic
principle on the space of connections, and comment on the existence of a time
variable which could be used in the interpretation of the quantum theory.
| [
{
"created": "Fri, 11 Nov 2011 06:44:42 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Nov 2011 22:54:54 GMT",
"version": "v2"
}
] | 2015-03-19 | [
[
"Gielen",
"Steffen",
""
]
] | We review some properties of the space of connections as the natural arena for canonical (quantum) gravity, and compare to the case of the superspace of 3-metrics. We detail how a 1-parameter family of metrics on the space of connections arises from the canonical analysis for general relativity which has a natural interpretation in terms of invariant tensors on the algebra of the gauge group. We also review the description of canonical GR as a geodesic principle on the space of connections, and comment on the existence of a time variable which could be used in the interpretation of the quantum theory. |
2112.06644 | Hermano Velten | J\'ulio C. Fabris, Marcelo H. Alvarenga, Mahamadou Hamani-Daouda and
Hermano Velten | Nonconservative unimodular gravity: a viable cosmological scenario | 8 pages, 1 figure | null | 10.1140/epjc/s10052-022-10470-2 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | In this work we review the issue of imposing the conservation of the
energy-momentum tensor as a necessary condition to recover the equivalence
between the unimodular gravity and General Relativity (GR) equipped with a
cosmological constant. This procedure is usually interpreted as an {\it ad hoc}
imposition on the unimodular theory's structure. Whereas the consequences of
avoiding the conservation of the total energy-momentum tensor has been already
introduced in the literature, it has been not widely explored so far. We study
an expanding universe sourced by a single effective perfect fluid such that the
null divergence of its energy-momentum tensor is not imposed. As we shall show,
in this scheme, the unimodular theory has its own conservation equation
obtained from the Bianchi identities. We explore the evolution of the
homogeneous and isotropic expanding background and show that a viable
cosmological scenario exists. Also, we consider scalar perturbations with
particular attention given to the gauge issue. We show that contrary to the
traditional unimodular theory where the synchronous and longitudinal
(newtonian) gauge for cosmological perturbations are not permitted, if the
conservation of the energy-momentum is relaxed the scalar perturbations in the
synchronous condition survive and present a growing mode behavior. We study
therefore a new cosmological scenario in which the dynamics of the universe
transits from the radiative phase directly to a accelerated one but allowing
thus for structure formation.
| [
{
"created": "Mon, 13 Dec 2021 13:25:21 GMT",
"version": "v1"
}
] | 2022-06-29 | [
[
"Fabris",
"Júlio C.",
""
],
[
"Alvarenga",
"Marcelo H.",
""
],
[
"Hamani-Daouda",
"Mahamadou",
""
],
[
"Velten",
"Hermano",
""
]
] | In this work we review the issue of imposing the conservation of the energy-momentum tensor as a necessary condition to recover the equivalence between the unimodular gravity and General Relativity (GR) equipped with a cosmological constant. This procedure is usually interpreted as an {\it ad hoc} imposition on the unimodular theory's structure. Whereas the consequences of avoiding the conservation of the total energy-momentum tensor has been already introduced in the literature, it has been not widely explored so far. We study an expanding universe sourced by a single effective perfect fluid such that the null divergence of its energy-momentum tensor is not imposed. As we shall show, in this scheme, the unimodular theory has its own conservation equation obtained from the Bianchi identities. We explore the evolution of the homogeneous and isotropic expanding background and show that a viable cosmological scenario exists. Also, we consider scalar perturbations with particular attention given to the gauge issue. We show that contrary to the traditional unimodular theory where the synchronous and longitudinal (newtonian) gauge for cosmological perturbations are not permitted, if the conservation of the energy-momentum is relaxed the scalar perturbations in the synchronous condition survive and present a growing mode behavior. We study therefore a new cosmological scenario in which the dynamics of the universe transits from the radiative phase directly to a accelerated one but allowing thus for structure formation. |
gr-qc/0401116 | Pierre Martinetti | P. Martinetti | A brief remark on Unruh effect and causality | One reference corrected | J.Phys.Conf.Ser.68:012027,2007 | 10.1088/1742-6596/68/1/012027 | null | gr-qc | null | Unruh effect states that the vacuum of a quantum field theory on Minkovski
space-time looks like a thermal state for an eternal uniformly accelerated
observer. Adaptation to the non eternal case causes a serious problem: if the
thermalization of the vacuum depends on the lifetime of the observer, then in
principle the latest is able to deduce its lifetime from the measurement of the
temperature. This short note aims at underlining that time-energy uncertainty
relation allows to adapt Unruh effect to non-eternal observers without breaking
causality. In particular we show that our adaptation - the diamonds's
temperature- of Bisognano-Wichman approach to Unruh effect is causally
acceptable. This note is self-contained but it is fully meaningful as a
complement to gr-qc/0212074 as well as a comment on gr-qc/0306022.
| [
{
"created": "Wed, 28 Jan 2004 22:36:50 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Feb 2004 12:33:51 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Martinetti",
"P.",
""
]
] | Unruh effect states that the vacuum of a quantum field theory on Minkovski space-time looks like a thermal state for an eternal uniformly accelerated observer. Adaptation to the non eternal case causes a serious problem: if the thermalization of the vacuum depends on the lifetime of the observer, then in principle the latest is able to deduce its lifetime from the measurement of the temperature. This short note aims at underlining that time-energy uncertainty relation allows to adapt Unruh effect to non-eternal observers without breaking causality. In particular we show that our adaptation - the diamonds's temperature- of Bisognano-Wichman approach to Unruh effect is causally acceptable. This note is self-contained but it is fully meaningful as a complement to gr-qc/0212074 as well as a comment on gr-qc/0306022. |
2307.02919 | Francisco Fern\'andez-\'Alvarez | Francisco Fern\'andez-\'Alvarez | Degrees of freedom of gravitational radiation with positive cosmological
constant | 26 pages, 2 figures, typos corrected | Phys. Rev. D 108, 064028 (2023) | 10.1103/PhysRevD.108.064028 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Results on the isolation of the radiative degrees of freedom of the
gravitational field with a positive cosmological constant in full General
Relativity are put forward. Methods employed in a recent geometric
characterisation of gravitational radiation are used and, inspired by
Ashtekar's work on asymptotically flat space-times, a space of connections is
defined. Ground differences emerge due to the space-like character of the
conformal boundary, and one has to put into play a fundamental result by
Friedrich concerning the initial value problem for space-times with a positive
cosmological constant. Based on this, half of the radiative degrees of freedom
are identified; remarkably, they utterly determine the gravitational radiation
content for space-times with algebraically special rescaled Weyl tensor at
infinity. Directions for defining the phase space in the general case are
proposed.
| [
{
"created": "Thu, 6 Jul 2023 11:16:18 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Sep 2023 14:49:52 GMT",
"version": "v2"
}
] | 2023-09-15 | [
[
"Fernández-Álvarez",
"Francisco",
""
]
] | Results on the isolation of the radiative degrees of freedom of the gravitational field with a positive cosmological constant in full General Relativity are put forward. Methods employed in a recent geometric characterisation of gravitational radiation are used and, inspired by Ashtekar's work on asymptotically flat space-times, a space of connections is defined. Ground differences emerge due to the space-like character of the conformal boundary, and one has to put into play a fundamental result by Friedrich concerning the initial value problem for space-times with a positive cosmological constant. Based on this, half of the radiative degrees of freedom are identified; remarkably, they utterly determine the gravitational radiation content for space-times with algebraically special rescaled Weyl tensor at infinity. Directions for defining the phase space in the general case are proposed. |
1302.1190 | Paul Wesson | Paul S. Wesson and James M. Overduin | Wave Mechanics and the Fifth Dimension | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Replacing 4D Minkowski space by 5D canonical space leads to a clearer
derivation of the main features of wave mechanics, including the wave function
and the velocity of de Broglie waves. Recent tests of wave-particle duality
could be adapted to investigate whether de Broglie waves are basically 4D or 5D
in nature.
| [
{
"created": "Mon, 28 Jan 2013 00:22:26 GMT",
"version": "v1"
}
] | 2013-02-06 | [
[
"Wesson",
"Paul S.",
""
],
[
"Overduin",
"James M.",
""
]
] | Replacing 4D Minkowski space by 5D canonical space leads to a clearer derivation of the main features of wave mechanics, including the wave function and the velocity of de Broglie waves. Recent tests of wave-particle duality could be adapted to investigate whether de Broglie waves are basically 4D or 5D in nature. |
gr-qc/0001074 | Roberto Colistete Junior | N. Pinto-Neto, A. F. Velasco, R. Colistete Jr | Quantum Isotropization of the Universe | 10 pages, RevTeX, 3 Postscript figures, uses graficx.sty | Phys.Lett. A277 (2000) 194-204 | 10.1016/S0375-9601(00)00706-4 | null | gr-qc | null | We consider minisuperspace models constituted of Bianchi I geometries with a
free massless scalar field. The classical solutions are always singular (with
the trivial exception of flat space-time), and always anisotropic once they
begin anisotropic. When quantizing the system, we obtain the Wheeler-DeWitt
equation as a four-dimensional massless Klein-Gordon equation. We show that
there are plenty of quantum states whose corresponding bohmian trajectories may
be non-singular and/or presenting large isotropic phases, even if they begin
anisotropic, due to quantum gravitational effects. As a specific example, we
exhibit field plots of bohmian trajectories for the case of gaussian
superpositions of plane wave solutions of the Wheeler-DeWitt equation which
have those properties. These conclusions are valid even in the absence of the
scalar field.
| [
{
"created": "Mon, 24 Jan 2000 14:49:41 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Pinto-Neto",
"N.",
""
],
[
"Velasco",
"A. F.",
""
],
[
"Colistete",
"R.",
"Jr"
]
] | We consider minisuperspace models constituted of Bianchi I geometries with a free massless scalar field. The classical solutions are always singular (with the trivial exception of flat space-time), and always anisotropic once they begin anisotropic. When quantizing the system, we obtain the Wheeler-DeWitt equation as a four-dimensional massless Klein-Gordon equation. We show that there are plenty of quantum states whose corresponding bohmian trajectories may be non-singular and/or presenting large isotropic phases, even if they begin anisotropic, due to quantum gravitational effects. As a specific example, we exhibit field plots of bohmian trajectories for the case of gaussian superpositions of plane wave solutions of the Wheeler-DeWitt equation which have those properties. These conclusions are valid even in the absence of the scalar field. |
1911.05512 | Gonzalo Garc\'ia-Reyes | Gonzalo Garc\'ia-Reyes | Poisson type conformastat spherically symmetric anisotropic fluid
spacetimes | 21 pages, 48 figures | Chinese J. Phys.77, 465-482 (2022) | 10.1016/j.cjph.2022.03.001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct conformastat spherically symmetric spacetimes representing
anisotropic fluid matter distributions from given solutions of the Poisson's
equation of Newtonian gravity and its corresponding circular speed profile. As
simple examples, we present three families of spherically symmetric spacetimes
which we apply in constructing new models of relativistic anisotropic thick
spherical shells, and of relativistic galaxy models composite by a central
spherical bulge, the thick disk and the dark matter halo, writing in this case
the metric in cylindrical coordinates. Moreover, the geodesic motion of test
particles in stable circular orbits around such structures is studied. We build
anisotropic fluid sources for these spacetimes which satisfy all the energy
conditions and the principal stresses are positive quantities (pressure).
| [
{
"created": "Wed, 13 Nov 2019 14:43:47 GMT",
"version": "v1"
},
{
"created": "Wed, 29 Jan 2020 14:49:02 GMT",
"version": "v2"
},
{
"created": "Fri, 31 Jul 2020 14:41:38 GMT",
"version": "v3"
},
{
"created": "Mon, 24 May 2021 13:17:18 GMT",
"version": "v4"
},
{
"created": "Fri, 18 Mar 2022 14:09:56 GMT",
"version": "v5"
}
] | 2022-03-21 | [
[
"García-Reyes",
"Gonzalo",
""
]
] | We construct conformastat spherically symmetric spacetimes representing anisotropic fluid matter distributions from given solutions of the Poisson's equation of Newtonian gravity and its corresponding circular speed profile. As simple examples, we present three families of spherically symmetric spacetimes which we apply in constructing new models of relativistic anisotropic thick spherical shells, and of relativistic galaxy models composite by a central spherical bulge, the thick disk and the dark matter halo, writing in this case the metric in cylindrical coordinates. Moreover, the geodesic motion of test particles in stable circular orbits around such structures is studied. We build anisotropic fluid sources for these spacetimes which satisfy all the energy conditions and the principal stresses are positive quantities (pressure). |
1705.09749 | Valerio Faraoni | Valerio Faraoni (Bishop's University) | Three new roads to the Planck scale | 10 pages, to appear in Am. J. Phys | null | 10.1119/1.4994804 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Three new heuristic derivations of the Planck scale are described. They are
based on basic principles or phenomena of relativistic gravity and quantum
physics. The Planck scale quantities thus obtained are within one order of
magnitude of the "standard" ones. We contemplate the pair creation of causal
bubbles so small that they can be treated as particles, the scattering of a
matter wave off the background curvature of spacetime that it induces, and the
Hawking evaporation of a black hole in a single burst at the Planck scale.
| [
{
"created": "Sat, 27 May 2017 01:09:42 GMT",
"version": "v1"
}
] | 2017-11-22 | [
[
"Faraoni",
"Valerio",
"",
"Bishop's University"
]
] | Three new heuristic derivations of the Planck scale are described. They are based on basic principles or phenomena of relativistic gravity and quantum physics. The Planck scale quantities thus obtained are within one order of magnitude of the "standard" ones. We contemplate the pair creation of causal bubbles so small that they can be treated as particles, the scattering of a matter wave off the background curvature of spacetime that it induces, and the Hawking evaporation of a black hole in a single burst at the Planck scale. |
0904.0033 | Mark Berndtson | Mark V. Berndtson | Harmonic gauge perturbations of the Schwarzschild metric | PhD Thesis, 2007, Department of Physics, University of Colorado,
Boulder. 248 pages, 4 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The satellite observatory LISA will be capable of detecting gravitational
waves from extreme mass ratio inspirals (EMRIs), such as a small black hole
orbiting a supermassive black hole. The gravitational effects of the much
smaller mass can be treated as the perturbation of a known background metric,
here the Schwarzschild metric. The perturbed Einstein field equations form a
system of ten coupled partial differential equations. We solve the equations in
the harmonic gauge, also called the Lorentz gauge or Lorenz gauge. Using
separation of variables and Fourier transforms, we write the frequency domain
solutions in terms of six radial functions which satisfy decoupled ordinary
differential equations. The six functions are the Zerilli and five generalized
Regge-Wheeler functions of spin 2,1,0. We use the solutions to calculate the
gravitational self-force for circular orbits. The self-force gives the first
order perturbative corrections to the equations of motion. Section 1.2 of the
thesis has a more detailed summary.
| [
{
"created": "Tue, 31 Mar 2009 23:38:36 GMT",
"version": "v1"
}
] | 2009-04-02 | [
[
"Berndtson",
"Mark V.",
""
]
] | The satellite observatory LISA will be capable of detecting gravitational waves from extreme mass ratio inspirals (EMRIs), such as a small black hole orbiting a supermassive black hole. The gravitational effects of the much smaller mass can be treated as the perturbation of a known background metric, here the Schwarzschild metric. The perturbed Einstein field equations form a system of ten coupled partial differential equations. We solve the equations in the harmonic gauge, also called the Lorentz gauge or Lorenz gauge. Using separation of variables and Fourier transforms, we write the frequency domain solutions in terms of six radial functions which satisfy decoupled ordinary differential equations. The six functions are the Zerilli and five generalized Regge-Wheeler functions of spin 2,1,0. We use the solutions to calculate the gravitational self-force for circular orbits. The self-force gives the first order perturbative corrections to the equations of motion. Section 1.2 of the thesis has a more detailed summary. |
1411.1986 | Jafar Khodagholizadeh | Fatemeh Ahmadi, Jafar Khodagholizadeh and H.R.Sepangi | Lorentz violation and red shift of gravitational waves in brane-worlds | 12 pages. arXiv admin note: substantial text overlap with
arXiv:gr-qc/0702103; and text overlap with arXiv:arXiv:gr-qc/0305041 by other
author | Astrophys.Space Sci. 342 (2012) 487-492 | 10.1007/s10509-012-1183-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study the speed of gravitational waves in a brane world
scenario and show that if the extra dimension is space-like, the speed of the
propagation of such waves is greater in the bulk than that on the brane.
Therefore, the 4D Lorentz invariance is broken in the gravitational sector. A
comparison is also made between the red shift of such waves and those of the
electromagnetic waves on the brane. Such a comparison is essential for
extracting the signature of the extra dimension and thus clarifying the
question of maximal velocity of gravitational waves in the bulk.
| [
{
"created": "Fri, 7 Nov 2014 17:16:53 GMT",
"version": "v1"
}
] | 2015-06-23 | [
[
"Ahmadi",
"Fatemeh",
""
],
[
"Khodagholizadeh",
"Jafar",
""
],
[
"Sepangi",
"H. R.",
""
]
] | In this paper we study the speed of gravitational waves in a brane world scenario and show that if the extra dimension is space-like, the speed of the propagation of such waves is greater in the bulk than that on the brane. Therefore, the 4D Lorentz invariance is broken in the gravitational sector. A comparison is also made between the red shift of such waves and those of the electromagnetic waves on the brane. Such a comparison is essential for extracting the signature of the extra dimension and thus clarifying the question of maximal velocity of gravitational waves in the bulk. |
2310.03697 | Hossein Mohseni Sadjadi | H. Mohseni Sadjadi | Non-minimally coupled quintessence in the Gauss-Bonnet model, symmetry
breaking, and cosmic acceleration | 14 pages, 5 figures | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a model consisting of a quintessence coupled to the Ricci scalar
and the Gauss-Bonnet invariant. We propose a mechanism for the rising of dark
energy in the matter era, alleviating the coincidence problem. The role of the
Gauss-Bonnet invariant is to restore the initial $Z_2$ symmetry. The Ricci
scalar breaks this symmetry during the Universe's expansion and activates the
quintessence. In our model, the observational constraint on gravitational wave
speed is respected.
| [
{
"created": "Thu, 5 Oct 2023 17:13:30 GMT",
"version": "v1"
}
] | 2023-10-06 | [
[
"Sadjadi",
"H. Mohseni",
""
]
] | We consider a model consisting of a quintessence coupled to the Ricci scalar and the Gauss-Bonnet invariant. We propose a mechanism for the rising of dark energy in the matter era, alleviating the coincidence problem. The role of the Gauss-Bonnet invariant is to restore the initial $Z_2$ symmetry. The Ricci scalar breaks this symmetry during the Universe's expansion and activates the quintessence. In our model, the observational constraint on gravitational wave speed is respected. |
1107.0949 | Jonathan Kommemi | Jonathan Kommemi | The global structure of spherically symmetric charged scalar field
spacetimes | updated to include comments/suggestions from referees; to appear in
Commun. Math. Phys | null | null | null | gr-qc math.AP math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We initiate the mathematical study of spherical collapse of self-gravitating
charged scalar fields. The main result gives a complete characterization of the
future boundary of spacetime, providing a starting point for studying the
cosmic censorship conjectures. In general, the boundary includes two null
components, one emanating from the center of symmetry and the other from the
future limit point of null infinity, joined by an achronal component to which
the area-radius function r extends continuously to zero. Various components of
the boundary, a priori, may be empty and establishing such generic emptiness
would suffice to prove formulations of weak or strong cosmic censorship. As a
simple corollary of the boundary characterization, the present paper rules out
scenarios of 'naked singularity' formation by means of 'super-charging'
(near-)extremal Reissner-Nordstr\"om black holes. The main difficulty in
delimiting the boundary is isolated in proving a suitable global extension
principle that effectively excludes a broad class of singularity formation.
This suggests a new notion of 'strongly tame' matter models, which we introduce
in this paper. The boundary characterization proven here extends to any such
'strongly tame' Einstein-matter system.
| [
{
"created": "Tue, 5 Jul 2011 19:08:34 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Feb 2013 00:08:03 GMT",
"version": "v2"
}
] | 2013-02-13 | [
[
"Kommemi",
"Jonathan",
""
]
] | We initiate the mathematical study of spherical collapse of self-gravitating charged scalar fields. The main result gives a complete characterization of the future boundary of spacetime, providing a starting point for studying the cosmic censorship conjectures. In general, the boundary includes two null components, one emanating from the center of symmetry and the other from the future limit point of null infinity, joined by an achronal component to which the area-radius function r extends continuously to zero. Various components of the boundary, a priori, may be empty and establishing such generic emptiness would suffice to prove formulations of weak or strong cosmic censorship. As a simple corollary of the boundary characterization, the present paper rules out scenarios of 'naked singularity' formation by means of 'super-charging' (near-)extremal Reissner-Nordstr\"om black holes. The main difficulty in delimiting the boundary is isolated in proving a suitable global extension principle that effectively excludes a broad class of singularity formation. This suggests a new notion of 'strongly tame' matter models, which we introduce in this paper. The boundary characterization proven here extends to any such 'strongly tame' Einstein-matter system. |
1405.6116 | Kirill Bronnikov | K.A. Bronnikov, J.C. Fabris, R. Silveira, O.B. Zaslavskii | Dilaton gravity, charged dust, and (quasi-) black holes | revtex4, 4 pages, 1 figure of 3 parts. A brief presentation of main
results (not all) of arXiv:1312.4891 | Phys. Rev. D 89, 107501 (2014) | 10.1103/PhysRevD.89.107501 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider Einstein-Maxwell-dilaton gravity with charged dust and
interaction of the form $P(\chi) F_{\mu\nu} F^{\mu\nu}$, where $P(\chi)$ is an
arbitrary function of the dilaton field $\chi$ that can be normal or phantom.
For any regular $P(\chi)$, static configurations are possible with arbitrary
functions $g_{00} = \exp(2\gamma(x^i))$ ($i=1,2,3$) and $\chi = \chi(\gamma)$,
without any assumption of spatial symmetry. The classical Majumdar-Papapetrou
system is restored by putting $\chi =$ const. Among possible solutions are
black-hole (BH) and quasi-black-hole (QBH) ones. Some general results on BH and
QBH properties are deduced and confirmed by examples. It is found, in
particular, that asymptotically flat BHs and QBHs can exist with positive
energy densities of matter and both scalar and electromagnetic fields.
| [
{
"created": "Fri, 23 May 2014 16:42:37 GMT",
"version": "v1"
}
] | 2014-05-26 | [
[
"Bronnikov",
"K. A.",
""
],
[
"Fabris",
"J. C.",
""
],
[
"Silveira",
"R.",
""
],
[
"Zaslavskii",
"O. B.",
""
]
] | We consider Einstein-Maxwell-dilaton gravity with charged dust and interaction of the form $P(\chi) F_{\mu\nu} F^{\mu\nu}$, where $P(\chi)$ is an arbitrary function of the dilaton field $\chi$ that can be normal or phantom. For any regular $P(\chi)$, static configurations are possible with arbitrary functions $g_{00} = \exp(2\gamma(x^i))$ ($i=1,2,3$) and $\chi = \chi(\gamma)$, without any assumption of spatial symmetry. The classical Majumdar-Papapetrou system is restored by putting $\chi =$ const. Among possible solutions are black-hole (BH) and quasi-black-hole (QBH) ones. Some general results on BH and QBH properties are deduced and confirmed by examples. It is found, in particular, that asymptotically flat BHs and QBHs can exist with positive energy densities of matter and both scalar and electromagnetic fields. |
1610.03540 | Lars Andersson | Lars Andersson, Thomas B\"ackdahl, Pieter Blue | Geometry of black hole spacetimes | Based on lectures given by the first named author at the 2014 Summer
School on Asymptotic Analysis in General Relativity, held at Institut
Fourier, Grenoble. arXiv admin note: text overlap with arXiv:1504.02069 | null | null | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | These notes, based on lectures given at the summer school on Asymptotic
Analysis in General Relativity, collect material on the Einstein equations, the
geometry of black hole spacetimes, and the analysis of fields on black hole
backgrounds. The Kerr model of a rotating black hole in vacuum is expected to
be unique and stable. The problem of proving these fundamental facts provides
the background for the material presented in these notes.
Among the many topics which are relevant for the uniqueness and stability
problems are the theory of fields on black hole spacetimes, in particular for
gravitational perturbations of the Kerr black hole, and more generally, the
study of nonlinear field equations in the presence of trapping. The study of
these questions requires tools from several different fields, including
Lorentzian geometry, hyperbolic differential equations and spin geometry, which
are all relevant to the black hole stability problem.
| [
{
"created": "Tue, 11 Oct 2016 21:31:56 GMT",
"version": "v1"
}
] | 2016-10-13 | [
[
"Andersson",
"Lars",
""
],
[
"Bäckdahl",
"Thomas",
""
],
[
"Blue",
"Pieter",
""
]
] | These notes, based on lectures given at the summer school on Asymptotic Analysis in General Relativity, collect material on the Einstein equations, the geometry of black hole spacetimes, and the analysis of fields on black hole backgrounds. The Kerr model of a rotating black hole in vacuum is expected to be unique and stable. The problem of proving these fundamental facts provides the background for the material presented in these notes. Among the many topics which are relevant for the uniqueness and stability problems are the theory of fields on black hole spacetimes, in particular for gravitational perturbations of the Kerr black hole, and more generally, the study of nonlinear field equations in the presence of trapping. The study of these questions requires tools from several different fields, including Lorentzian geometry, hyperbolic differential equations and spin geometry, which are all relevant to the black hole stability problem. |
gr-qc/0305058 | Tomohiro Harada | Tomohiro Harada, Hideo Iguchi, and Masaru Shibata | Computing gravitational waves from slightly nonspherical stellar
collapse to black hole: Odd-parity perturbation | 31 pages, accepted for publication in Phys. Rev. D, typos and minor
errors corrected | Phys.Rev.D68:024002,2003 | 10.1103/PhysRevD.68.024002 | null | gr-qc astro-ph | null | Nonspherical stellar collapse to a black hole is one of the most promising
gravitational wave sources for gravitational wave detectors. We numerically
study gravitational waves from a slightly nonspherical stellar collapse to a
black hole in linearized Einstein theory. We adopt a spherically collapsing
star as the zeroth-order solution and gravitational waves are computed using
perturbation theory on the spherical background. In this paper we focus on the
perturbation of odd-parity modes. Using the polytropic equations of state with
polytropic indices $n_p=1$ and 3, we qualitatively study gravitational waves
emitted during the collapse of neutron stars and supermassive stars to black
holes from a marginally stable equilibrium configuration. Since the matter
perturbation profiles can be chosen arbitrarily, we provide a few types for
them. For $n_p=1$, the gravitational waveforms are mainly characterized by a
black hole quasinormal mode ringing, irrespective of perturbation profiles
given initially. However, for $n_p=3$, the waveforms depend strongly on the
initial perturbation profiles. In other words, the gravitational waveforms
strongly depend on the stellar configuration and, in turn, on the ad hoc choice
of the functional form of the perturbation in the case of supermassive stars.
| [
{
"created": "Thu, 15 May 2003 14:21:51 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Jun 2003 12:13:18 GMT",
"version": "v2"
}
] | 2010-05-12 | [
[
"Harada",
"Tomohiro",
""
],
[
"Iguchi",
"Hideo",
""
],
[
"Shibata",
"Masaru",
""
]
] | Nonspherical stellar collapse to a black hole is one of the most promising gravitational wave sources for gravitational wave detectors. We numerically study gravitational waves from a slightly nonspherical stellar collapse to a black hole in linearized Einstein theory. We adopt a spherically collapsing star as the zeroth-order solution and gravitational waves are computed using perturbation theory on the spherical background. In this paper we focus on the perturbation of odd-parity modes. Using the polytropic equations of state with polytropic indices $n_p=1$ and 3, we qualitatively study gravitational waves emitted during the collapse of neutron stars and supermassive stars to black holes from a marginally stable equilibrium configuration. Since the matter perturbation profiles can be chosen arbitrarily, we provide a few types for them. For $n_p=1$, the gravitational waveforms are mainly characterized by a black hole quasinormal mode ringing, irrespective of perturbation profiles given initially. However, for $n_p=3$, the waveforms depend strongly on the initial perturbation profiles. In other words, the gravitational waveforms strongly depend on the stellar configuration and, in turn, on the ad hoc choice of the functional form of the perturbation in the case of supermassive stars. |
2210.01552 | Pardyumn Kumar Sahoo | Simran Arora, Aaqid Bhat, P.K. Sahoo | Squared torsion $f(T,\mathcal{T})$ gravity and its cosmological
implications | Fortschr. Phys. accepted version | Fortschr. Phys. 71(2-3) (2023) 2200162 | 10.1002/prop.202200162 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We present the coupling of the torsion scalar $T$ and the trace of
energy-momentum tensor $\mathcal{T}$, which produces new modified
$f(T,\mathcal{T})$ gravity. Moreover, we consider the functional form
$f(T,\mathcal{T}) =\alpha \mathcal{T}+\beta T^2$ where $\alpha$ and $\beta$ are
free parameters. As an alternative to a cosmological constant, the
$f(T,\mathcal{T})$ theory may offer a theoretical explanation of the late-time
acceleration. The recent observational data to the considered model especially
the bounds on model parameters is applied in detail. Furthermore, we analyze
the cosmological behavior of the deceleration, effective equation of state and
total equation of state parameters. However, it is seen that the deceleration
parameter depicts the transition from deceleration to acceleration and the
effective dark sector shows a quintessence-like evolution.
| [
{
"created": "Sun, 2 Oct 2022 09:21:44 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Nov 2022 09:18:46 GMT",
"version": "v2"
}
] | 2023-03-13 | [
[
"Arora",
"Simran",
""
],
[
"Bhat",
"Aaqid",
""
],
[
"Sahoo",
"P. K.",
""
]
] | We present the coupling of the torsion scalar $T$ and the trace of energy-momentum tensor $\mathcal{T}$, which produces new modified $f(T,\mathcal{T})$ gravity. Moreover, we consider the functional form $f(T,\mathcal{T}) =\alpha \mathcal{T}+\beta T^2$ where $\alpha$ and $\beta$ are free parameters. As an alternative to a cosmological constant, the $f(T,\mathcal{T})$ theory may offer a theoretical explanation of the late-time acceleration. The recent observational data to the considered model especially the bounds on model parameters is applied in detail. Furthermore, we analyze the cosmological behavior of the deceleration, effective equation of state and total equation of state parameters. However, it is seen that the deceleration parameter depicts the transition from deceleration to acceleration and the effective dark sector shows a quintessence-like evolution. |
2012.08785 | Che-Yu Chen | Suddhasattwa Brahma, Che-Yu Chen, Dong-han Yeom | Testing loop quantum gravity from observational consequences of
non-singular rotating black holes | 21 pages, 7 figures. Accepted for publication in PRL | Phys. Rev. Lett. 126, 181301 (2021) | 10.1103/PhysRevLett.126.181301 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The lack of rotating black hole models, which are typically found in nature,
in loop quantum gravity (LQG) substantially hinders the progress of testing LQG
from observations. Starting with a non-rotating LQG black hole as a seed
metric, we construct a rotating spacetime using the revised Newman-Janis
algorithm. The rotating solution is non-singular everywhere and it reduces to
the Kerr black hole asymptotically. In different regions of the parameter
space, the solution describes i) a wormhole without event horizon (which, we
show, is almost ruled out by observations), ii) a black hole with a spacelike
transition surface inside the event horizon, or iii) a black hole with a
timelike transition region inside the inner horizon. It is shown how
fundamental parameters of LQG can be constrained by the observational
implications of the shadow cast by this object. The causal structure of our
solution depends crucially only on the spacelike transition surface of the
non-rotating seed metric, while being agnostic about specific details of the
latter, and therefore captures universal features of an effective rotating,
non-singular black hole in LQG.
| [
{
"created": "Wed, 16 Dec 2020 08:04:31 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Apr 2021 18:38:18 GMT",
"version": "v2"
},
{
"created": "Thu, 6 May 2021 17:47:11 GMT",
"version": "v3"
}
] | 2021-05-07 | [
[
"Brahma",
"Suddhasattwa",
""
],
[
"Chen",
"Che-Yu",
""
],
[
"Yeom",
"Dong-han",
""
]
] | The lack of rotating black hole models, which are typically found in nature, in loop quantum gravity (LQG) substantially hinders the progress of testing LQG from observations. Starting with a non-rotating LQG black hole as a seed metric, we construct a rotating spacetime using the revised Newman-Janis algorithm. The rotating solution is non-singular everywhere and it reduces to the Kerr black hole asymptotically. In different regions of the parameter space, the solution describes i) a wormhole without event horizon (which, we show, is almost ruled out by observations), ii) a black hole with a spacelike transition surface inside the event horizon, or iii) a black hole with a timelike transition region inside the inner horizon. It is shown how fundamental parameters of LQG can be constrained by the observational implications of the shadow cast by this object. The causal structure of our solution depends crucially only on the spacelike transition surface of the non-rotating seed metric, while being agnostic about specific details of the latter, and therefore captures universal features of an effective rotating, non-singular black hole in LQG. |
1901.08283 | Gen Ye | Gen Ye and Yun-Song Piao | Bounce in GR and higher-order derivative operators | 3 figures, matched published version in PhysRevD | Phys. Rev. D 99, 084019 (2019) | 10.1103/PhysRevD.99.084019 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recent progress seems to suggest that one must modify General Relativity (GR)
to stably violate the null energy condition and avoid the cosmological
singularity. However, with the higher-order derivative operators of scalar
field (a subclass of the degenerate higher-order scalar-tensor theory), we show
that at energies well below the Planck scale, fully stable nonsingular
cosmologies can actually be implemented within GR.
| [
{
"created": "Thu, 24 Jan 2019 08:40:35 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Oct 2019 03:16:33 GMT",
"version": "v2"
}
] | 2019-10-18 | [
[
"Ye",
"Gen",
""
],
[
"Piao",
"Yun-Song",
""
]
] | Recent progress seems to suggest that one must modify General Relativity (GR) to stably violate the null energy condition and avoid the cosmological singularity. However, with the higher-order derivative operators of scalar field (a subclass of the degenerate higher-order scalar-tensor theory), we show that at energies well below the Planck scale, fully stable nonsingular cosmologies can actually be implemented within GR. |
gr-qc/9805079 | Gerard 't Hooft | G. 't Hooft | TransPlanckian Particles and the Quantization of Time | 12 pages plain tex, 1 figure | Class.Quant.Grav. 16 (1999) 395-405 | 10.1088/0264-9381/16/2/006 | THU-98/22 | gr-qc | null | Trans-Planckian particles are elementary particles accelerated such that
their energies surpass the Planck value. There are several reasons to believe
that trans-Planckian particles do not represent independent degrees of freedom
in Hilbert space, but they are controlled by the cis-Planckian particles. A way
to learn more about the mechanisms at work here, is to study black hole
horizons, starting from the scattering matrix Ansatz.
By compactifying one of the three physical spacial dimensions, the scattering
matrix Ansatz can be exploited more efficiently than before. The algebra of
operators on a black hole horizon allows for a few distinct representations. It
is found that this horizon can be seen as being built up from string bits with
unit lengths, each of which being described by a representation of the SO(2,1)
Lorentz group. We then demonstrate how the holographic principle works for this
case, by constructing the operators corresponding to a field in space-time. The
parameter t turns out to be quantized in Planckian units, divided by the period
R of the compactified dimension.
| [
{
"created": "Wed, 20 May 1998 16:19:24 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Hooft",
"G. 't",
""
]
] | Trans-Planckian particles are elementary particles accelerated such that their energies surpass the Planck value. There are several reasons to believe that trans-Planckian particles do not represent independent degrees of freedom in Hilbert space, but they are controlled by the cis-Planckian particles. A way to learn more about the mechanisms at work here, is to study black hole horizons, starting from the scattering matrix Ansatz. By compactifying one of the three physical spacial dimensions, the scattering matrix Ansatz can be exploited more efficiently than before. The algebra of operators on a black hole horizon allows for a few distinct representations. It is found that this horizon can be seen as being built up from string bits with unit lengths, each of which being described by a representation of the SO(2,1) Lorentz group. We then demonstrate how the holographic principle works for this case, by constructing the operators corresponding to a field in space-time. The parameter t turns out to be quantized in Planckian units, divided by the period R of the compactified dimension. |
2308.09508 | Jakkrit Sangtawee | Saikat Chakraborty, Khamphee Karwan and Jakkrit Sangtawee | Observational predictions of inflationary model in spatially covariant
gravity with two tensorial degrees of freedom for gravity | 18 pages | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the inflationary model constructed from a Spatially Covariant
Gravity (SCG). The Lagrangian for the SCG in our consideration is expressed as
the polynomial of irreducible SCG monomials where the total number of
derivatives of each monomial is two, and the theory propagates two tensorial
degrees of freedom of gravity up to the first order in cosmological
perturbations. The condition for having two tensorial degrees of freedom
studied earlier in literature for such theories is derived in vacuum. We extend
the condition for having two tensorial degrees of freedom to the case where a
scalar field is included by imposing a gauge-fixing. We apply the resulting SCG
to describe inflationary universe. The observational predictions such as the
scalar spectral index and tensor-to-scalar ratio from this model are
investigated. We find that the tensor-to-scalar ratio in this model can either
be in the order of unity or be small depending on the parameter of the model.
| [
{
"created": "Fri, 18 Aug 2023 12:36:53 GMT",
"version": "v1"
}
] | 2023-08-22 | [
[
"Chakraborty",
"Saikat",
""
],
[
"Karwan",
"Khamphee",
""
],
[
"Sangtawee",
"Jakkrit",
""
]
] | We study the inflationary model constructed from a Spatially Covariant Gravity (SCG). The Lagrangian for the SCG in our consideration is expressed as the polynomial of irreducible SCG monomials where the total number of derivatives of each monomial is two, and the theory propagates two tensorial degrees of freedom of gravity up to the first order in cosmological perturbations. The condition for having two tensorial degrees of freedom studied earlier in literature for such theories is derived in vacuum. We extend the condition for having two tensorial degrees of freedom to the case where a scalar field is included by imposing a gauge-fixing. We apply the resulting SCG to describe inflationary universe. The observational predictions such as the scalar spectral index and tensor-to-scalar ratio from this model are investigated. We find that the tensor-to-scalar ratio in this model can either be in the order of unity or be small depending on the parameter of the model. |
gr-qc/0607075 | Benjamin Bahr | Benjamin Bahr, Thomas Thiemann | Approximating the physical inner product of Loop Quantum Cosmology | 35 pages | Class.Quant.Grav.24:2109-2138,2007 | 10.1088/0264-9381/24/8/011 | null | gr-qc | null | In this article, we investigate the possibility of approximating the physical
inner product of constrained quantum theories. In particular, we calculate the
physical inner product of a simple cosmological model in two ways: Firstly, we
compute it analytically via a trick, secondly, we use the complexifier coherent
states to approximate the physical inner product defined by the master
constraint of the system. We will find that the approximation is able to
recover the analytic solution of the problem, which solidifies hopes that
coherent states will help to approximate solutions of more complicated
theories, like loop quantum gravity.
| [
{
"created": "Wed, 19 Jul 2006 19:49:20 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Bahr",
"Benjamin",
""
],
[
"Thiemann",
"Thomas",
""
]
] | In this article, we investigate the possibility of approximating the physical inner product of constrained quantum theories. In particular, we calculate the physical inner product of a simple cosmological model in two ways: Firstly, we compute it analytically via a trick, secondly, we use the complexifier coherent states to approximate the physical inner product defined by the master constraint of the system. We will find that the approximation is able to recover the analytic solution of the problem, which solidifies hopes that coherent states will help to approximate solutions of more complicated theories, like loop quantum gravity. |
gr-qc/0010099 | Wanas | M. I. Wanas | Parameterized Absolute Parallelism: A Geometry for Physical Applications | 17 pages Tex file | Turk.J.Phys. 24 (2000) 473-488 | null | null | gr-qc | null | Absolute parallelism (AP) geometry is frequently used for physical
applications. Although it is wider than Riemannian geometry, it has two main
defects. The first is that its path equation does not represent physical
trajectories of any test particle. The second is the identical vanishing of its
curvature tensor. The present work shows that parameterizing this geometry
would solve the two problems. Furthermore, the resulting parameterized
AP-structure is more general than both the conventional AP-structure and the
Riemannian structure. Also, it is shown that it can be reduced to one or the
other, of these two geometric structures, in some special cases. The structure
obtained is more appropriate for physical applications, especially in
constructing field theories gauging gravity.
| [
{
"created": "Thu, 26 Oct 2000 13:43:25 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Wanas",
"M. I.",
""
]
] | Absolute parallelism (AP) geometry is frequently used for physical applications. Although it is wider than Riemannian geometry, it has two main defects. The first is that its path equation does not represent physical trajectories of any test particle. The second is the identical vanishing of its curvature tensor. The present work shows that parameterizing this geometry would solve the two problems. Furthermore, the resulting parameterized AP-structure is more general than both the conventional AP-structure and the Riemannian structure. Also, it is shown that it can be reduced to one or the other, of these two geometric structures, in some special cases. The structure obtained is more appropriate for physical applications, especially in constructing field theories gauging gravity. |
1108.6157 | Mohammad Reza Tanhayi Ahari | Mohammad Reza Tanhayi, Mohsen Fathi and Mohammad Vahid Takook | Observable Quantities in Weyl Gravity | to be appear in MPLA | Mod. Phys. Lett. A 26, No. 32 (2011) 2403 | 10.1142/S0217732311036759 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, the cosmological "constant" and the Hubble parameter are
considered in the Weyl theory of gravity, by taking them as functions of $r$
and $t$, respectively. Based on this theory and in the linear approximation, we
obtain the values of $H_0$ and $\Lambda_0$ which are in good agreement with the
known values of the parameters for the current state of the universe.
| [
{
"created": "Wed, 31 Aug 2011 08:34:22 GMT",
"version": "v1"
}
] | 2015-05-30 | [
[
"Tanhayi",
"Mohammad Reza",
""
],
[
"Fathi",
"Mohsen",
""
],
[
"Takook",
"Mohammad Vahid",
""
]
] | In this paper, the cosmological "constant" and the Hubble parameter are considered in the Weyl theory of gravity, by taking them as functions of $r$ and $t$, respectively. Based on this theory and in the linear approximation, we obtain the values of $H_0$ and $\Lambda_0$ which are in good agreement with the known values of the parameters for the current state of the universe. |
1605.00261 | Abdul Jawad | Abdul Jawad, Sadaf Butt and Shamaila Rani | Dynamics of Warm Chaplygin Gas Inflationary Models With Quartic
Potential | 21 pages; 3 figures | Eur. Phys. J. C 76 (2016) 274 | 10.1140/epjc/s10052-016-4121-x | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Warm inflationary universe models in the context of generalized chaplygin
gas, modified chaplygin gas, generalized cosmic chaplygin gas are being
studied. The dissipative coefficient of the form $\Gamma\propto T$, weak and
strong dissipative regimes are being considered. We use quartic potential
$\frac{\lambda_{*}\phi^{4}}{4}$, which is ruled out by current data in cold
inflation but in our models it is analyzed that it is in agreement with the
WMAP$9$ and latest Planck data. In these scenarios, the power spectrum,
spectral index, and tensor to scalar ratio are being examined under the slow
roll approximation. We show the dependence of tensor scalar ratio $r$ on
spectral index $n_{s}$ and observe that the range of tensor scalar ratio is
$r<0.05$ in generalized chaplygin gas, $r<0.15$ in modified chaplygin gas, and
$r<0.12$ in generalized cosmic chaplygin gas models. Our results are in
agreement with recent observational data like WMAP$9$ and latest Planck data.
| [
{
"created": "Sun, 1 May 2016 14:46:09 GMT",
"version": "v1"
}
] | 2016-10-27 | [
[
"Jawad",
"Abdul",
""
],
[
"Butt",
"Sadaf",
""
],
[
"Rani",
"Shamaila",
""
]
] | Warm inflationary universe models in the context of generalized chaplygin gas, modified chaplygin gas, generalized cosmic chaplygin gas are being studied. The dissipative coefficient of the form $\Gamma\propto T$, weak and strong dissipative regimes are being considered. We use quartic potential $\frac{\lambda_{*}\phi^{4}}{4}$, which is ruled out by current data in cold inflation but in our models it is analyzed that it is in agreement with the WMAP$9$ and latest Planck data. In these scenarios, the power spectrum, spectral index, and tensor to scalar ratio are being examined under the slow roll approximation. We show the dependence of tensor scalar ratio $r$ on spectral index $n_{s}$ and observe that the range of tensor scalar ratio is $r<0.05$ in generalized chaplygin gas, $r<0.15$ in modified chaplygin gas, and $r<0.12$ in generalized cosmic chaplygin gas models. Our results are in agreement with recent observational data like WMAP$9$ and latest Planck data. |
2004.14865 | Yurii Ignat'ev | Yu. G. Ignat'ev | The Method of Self-Consistent Field and Macroscopical Einstein Equations
for the Early Universe | 19 page, 39 references. arXiv admin note: text overlap with
arXiv:1908.03488 | Theor. and Math. Physics, 204 (2020) 927 | 10.1134/S0040577920070077 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The complete theory of cosmological evolution's macroscopic description is
constructed with a help of self-consistent field. The theory includes a
subsystem of linear equations of perturbations' evolution and nonlinear
macroscopic Einstein equations and equations of a scalar field. We provide
examples of system's solution which show the principal difference of the
cosmological models of the early Universe built on homogenous and locally
fluctuating scalar fields. {\bf Keywords}: macroscopic gravitation,
self-consistent field, cosmological model, scalar fields, averaging of local
fluctuations, asymptotical behavior, cosmological singularity.
| [
{
"created": "Wed, 29 Apr 2020 14:22:18 GMT",
"version": "v1"
}
] | 2020-07-09 | [
[
"Ignat'ev",
"Yu. G.",
""
]
] | The complete theory of cosmological evolution's macroscopic description is constructed with a help of self-consistent field. The theory includes a subsystem of linear equations of perturbations' evolution and nonlinear macroscopic Einstein equations and equations of a scalar field. We provide examples of system's solution which show the principal difference of the cosmological models of the early Universe built on homogenous and locally fluctuating scalar fields. {\bf Keywords}: macroscopic gravitation, self-consistent field, cosmological model, scalar fields, averaging of local fluctuations, asymptotical behavior, cosmological singularity. |
2201.05183 | Sujoy Modak | Saurya Das, Sujoy K. Modak | A novel mechanism for probing the Planck scale with wavepackets
following general distributions | v2, 27 pages, 6 improved figures, matches published version in
European Physical Journal Plus | Eur. Phys. J. Plus (2023) 138: 366 | 10.1140/epjp/s13360-023-03990-7 | null | gr-qc hep-th quant-ph | http://creativecommons.org/licenses/by/4.0/ | It was also shown recently that GUP predicts potentially measurable
corrections to the `doubling time' of freely moving Gaussian atomic and
molecular wavepackets with a favorable combination of three parameters, {\it
e.g.} mass, initial width and mean velocity of a travelling wavepacket.
However, it is well known that such wavepackets can come with various shapes
which correspond to variety of distributions. In this article, we generalize
our earlier work for an {\it arbitrary distribution} and thereby accommodate
any shape of the wavepacket. Mathematically, we build this formalism by
exploiting a duality between quantum and statistical mechanics, by which
(quantum mechanical) expectation values of the momentum operator can be
expressed in terms of the derivatives of the characteristic functions of the
dual statistical description. Equipped with this result, we go one step further
and numerically study a few physical distributions. We find that large organic
(TPPF152) wavepacket following the generalized normal distribution with
parameter $\kappa=0.5$ offers one of the best-case scenarios, effectively
scanning the whole GUP parameter space with current technologies. Although we
do not say that the minimal length has to be near or at the Planck value, we
mange improving our previous studies to scan the minimal length signatures down
to hundred times the Planck value.
| [
{
"created": "Thu, 13 Jan 2022 19:29:44 GMT",
"version": "v1"
},
{
"created": "Sun, 6 Aug 2023 05:05:15 GMT",
"version": "v2"
}
] | 2023-08-08 | [
[
"Das",
"Saurya",
""
],
[
"Modak",
"Sujoy K.",
""
]
] | It was also shown recently that GUP predicts potentially measurable corrections to the `doubling time' of freely moving Gaussian atomic and molecular wavepackets with a favorable combination of three parameters, {\it e.g.} mass, initial width and mean velocity of a travelling wavepacket. However, it is well known that such wavepackets can come with various shapes which correspond to variety of distributions. In this article, we generalize our earlier work for an {\it arbitrary distribution} and thereby accommodate any shape of the wavepacket. Mathematically, we build this formalism by exploiting a duality between quantum and statistical mechanics, by which (quantum mechanical) expectation values of the momentum operator can be expressed in terms of the derivatives of the characteristic functions of the dual statistical description. Equipped with this result, we go one step further and numerically study a few physical distributions. We find that large organic (TPPF152) wavepacket following the generalized normal distribution with parameter $\kappa=0.5$ offers one of the best-case scenarios, effectively scanning the whole GUP parameter space with current technologies. Although we do not say that the minimal length has to be near or at the Planck value, we mange improving our previous studies to scan the minimal length signatures down to hundred times the Planck value. |
2108.13384 | Claudia Lazzaro | G. Vedovato, E. Milotti, G.A. Prodi, S. Bini, M. Drago, V. Gayathri,
O. Halim, C.Lazzaro, D. Lopez, A. Miani, B. O'Brian, F. Salemi, M.
Szczepanczyk, S. Tiwari, A. Virtuoso, S. Klimenko | Minimally-modeled search of higher multipole gravitational-wave
radiation in compact binary coalescence | null | null | 10.1088/1361-6382/ac45da | null | gr-qc | http://creativecommons.org/licenses/by-nc-nd/4.0/ | As the Advanced LIGO and Advanced Virgo interferometers, soon to be joined by
the KAGRA interferometer, increase their sensitivity, they detect an
ever-larger number of gravitational waves with a significant presence of higher
multipoles in addition to the dominant $(2, 2)$ multipole. These higher
multipoles can be detected with different approaches, such as the
minimally-modeled burst search methods, and here we discuss one such approach
based on the coherent WaveBurst pipeline (cWB). During the inspiral phase the
higher multipoles produce chirps whose instantaneous frequency is a multiple of
the dominant (2, 2) multipole, and here we describe how cWB can be used to
detect these spectral features. The search is performed within suitable regions
of the time-frequency representation; their shape is determined by optimizing
the Receiver Operating Characteristics. This novel method has already been used
in the GW190814 discovery paper (Astrophys. J. Lett. 896 L44) and is very fast
and flexible. Here we describe in full detail the procedure used to detect the
(3,3) multipole in GW190814 as well as searches for other higher multipoles
during the inspiral phase, and apply it to another event that displays higher
multipoles, GW190412, replicating the results obtained with different methods.
The procedure described here can be used for the fast analysis of higher
multipoles and to support the findings obtained with the model-based Bayesian
parameter estimates
| [
{
"created": "Mon, 30 Aug 2021 17:10:21 GMT",
"version": "v1"
}
] | 2022-02-09 | [
[
"Vedovato",
"G.",
""
],
[
"Milotti",
"E.",
""
],
[
"Prodi",
"G. A.",
""
],
[
"Bini",
"S.",
""
],
[
"Drago",
"M.",
""
],
[
"Gayathri",
"V.",
""
],
[
"Halim",
"O.",
""
],
[
"Lazzaro",
"C.",
""
],
[
"Lopez",
"D.",
""
],
[
"Miani",
"A.",
""
],
[
"O'Brian",
"B.",
""
],
[
"Salemi",
"F.",
""
],
[
"Szczepanczyk",
"M.",
""
],
[
"Tiwari",
"S.",
""
],
[
"Virtuoso",
"A.",
""
],
[
"Klimenko",
"S.",
""
]
] | As the Advanced LIGO and Advanced Virgo interferometers, soon to be joined by the KAGRA interferometer, increase their sensitivity, they detect an ever-larger number of gravitational waves with a significant presence of higher multipoles in addition to the dominant $(2, 2)$ multipole. These higher multipoles can be detected with different approaches, such as the minimally-modeled burst search methods, and here we discuss one such approach based on the coherent WaveBurst pipeline (cWB). During the inspiral phase the higher multipoles produce chirps whose instantaneous frequency is a multiple of the dominant (2, 2) multipole, and here we describe how cWB can be used to detect these spectral features. The search is performed within suitable regions of the time-frequency representation; their shape is determined by optimizing the Receiver Operating Characteristics. This novel method has already been used in the GW190814 discovery paper (Astrophys. J. Lett. 896 L44) and is very fast and flexible. Here we describe in full detail the procedure used to detect the (3,3) multipole in GW190814 as well as searches for other higher multipoles during the inspiral phase, and apply it to another event that displays higher multipoles, GW190412, replicating the results obtained with different methods. The procedure described here can be used for the fast analysis of higher multipoles and to support the findings obtained with the model-based Bayesian parameter estimates |
2306.14162 | Gamal G.L. Nashed | Shin'ichi Nojiri and G.G.L. Nashed | Hayward black hole in scalar-Einstein-Gauss-Bonnet gravity in four
dimensions | 13 pages 2 figures, To appear in Phys. Rev. D | null | 10.1103/PhysRevD.108.024014 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In the framework of scalar-Einstein-Gauss-Bonnet gravity, we construct the
model which realizes the Hayward black hole and discuss the absence of ghosts
in this model. Because Hayward black hole has two horizons but no curvature
singularity, it may solve the problem of the information loss that might be
generated by black holes. The Gauss-Bonnet term appears as a stringy
correction, and therefore, our results might indicate that the stringy
correction would solve the information loss problem.
| [
{
"created": "Sun, 25 Jun 2023 08:12:42 GMT",
"version": "v1"
}
] | 2023-07-19 | [
[
"Nojiri",
"Shin'ichi",
""
],
[
"Nashed",
"G. G. L.",
""
]
] | In the framework of scalar-Einstein-Gauss-Bonnet gravity, we construct the model which realizes the Hayward black hole and discuss the absence of ghosts in this model. Because Hayward black hole has two horizons but no curvature singularity, it may solve the problem of the information loss that might be generated by black holes. The Gauss-Bonnet term appears as a stringy correction, and therefore, our results might indicate that the stringy correction would solve the information loss problem. |
1801.03428 | Mushtaq Ahmad Sial | M. Farasat Shamir, Mushtaq Ahmad | Gravastars in $f(\mathcal{G},T)$ Gravity | 26 pages, 5 figures, revised version, to appear in PRD | Phys. Rev. D 97, 104031 (2018) | 10.1103/PhysRevD.97.104031 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This work proposes a stellar model under Gauss-Bonnet $f(\mathcal{G}, T)$
gravity with the conjecture theorised by Mazur and Mottola, well known as the
gravitational vacuum stars (gravastars). By taking into account the
$f(\mathcal{G},T)$ stellar model, the structure of the gravastar with its
exclusive division of three different regions namely, (i) the core interior
region (ii) the junction region (shell), and (iii) the exterior region, has
been investigated with reference to the existence of energy density, pressure,
ultra-relativistic plasma, and repulsive forces. The different physical
features like, the equation of the state parameter, length of the shell,
entropy, energy-thickness relation of the gravastar shell model have been
discussed. Also, some other physically valid aspects have been presented with
the connection to non-singular and event-horizon free gravastar solutions,
which in contrast to a black hole solution, might be stable without containing
any information paradox.
| [
{
"created": "Wed, 10 Jan 2018 15:46:54 GMT",
"version": "v1"
},
{
"created": "Tue, 22 May 2018 12:53:43 GMT",
"version": "v2"
}
] | 2018-05-24 | [
[
"Shamir",
"M. Farasat",
""
],
[
"Ahmad",
"Mushtaq",
""
]
] | This work proposes a stellar model under Gauss-Bonnet $f(\mathcal{G}, T)$ gravity with the conjecture theorised by Mazur and Mottola, well known as the gravitational vacuum stars (gravastars). By taking into account the $f(\mathcal{G},T)$ stellar model, the structure of the gravastar with its exclusive division of three different regions namely, (i) the core interior region (ii) the junction region (shell), and (iii) the exterior region, has been investigated with reference to the existence of energy density, pressure, ultra-relativistic plasma, and repulsive forces. The different physical features like, the equation of the state parameter, length of the shell, entropy, energy-thickness relation of the gravastar shell model have been discussed. Also, some other physically valid aspects have been presented with the connection to non-singular and event-horizon free gravastar solutions, which in contrast to a black hole solution, might be stable without containing any information paradox. |
1202.1397 | Puxun Wu | Kaituo Zhang, Puxun Wu, Hongwei Yu | Oscillating universe in the DGP braneworld | 25 pages, 24 figures. To appear in PRD | Phys. RevD. 85. 043521 (2012) | 10.1103/PhysRevD.85.043521 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | With a method in which the Friedmann equation is written in a form such that
evolution of the scale factor can be treated as that of a particle in a
"potential", we classify all possible cosmic evolutions in the DGP braneworld
scenario with the dark radiation term retained. By assuming that the energy
component is pressureless matter, radiation or vacuum energy, respectively, we
find that in the matter or vacuum energy dominated case, the scale factor has a
minimum value $a_0$. In the matter dominated case, the big bang singularity can
be avoided in some special circumstances, and there may exist an oscillating
universe or a bouncing one. If the cosmic scale factor is in the oscillating
region initially, the universe may undergo an oscillation. After a number of
oscillations, it may evolve to the bounce point through quantum tunneling and
then expand. However, if the universe contracts initially from an infinite
scale, it can turn around and then expand forever. In the vacuum energy
dominated case, there exists a stable Einstein static state to avoid the big
bang singularity. However, in certain circumstances in the matter or vacuum
energy dominated case, a new kind of singularity may occur at $a_0$ as a result
of the discontinuity of the scale factor. In the radiation dominated case, the
universe may originate from the big bang singularity, but a bouncing universe
which avoids this singularity is also possible.
| [
{
"created": "Tue, 7 Feb 2012 11:34:52 GMT",
"version": "v1"
}
] | 2012-10-12 | [
[
"Zhang",
"Kaituo",
""
],
[
"Wu",
"Puxun",
""
],
[
"Yu",
"Hongwei",
""
]
] | With a method in which the Friedmann equation is written in a form such that evolution of the scale factor can be treated as that of a particle in a "potential", we classify all possible cosmic evolutions in the DGP braneworld scenario with the dark radiation term retained. By assuming that the energy component is pressureless matter, radiation or vacuum energy, respectively, we find that in the matter or vacuum energy dominated case, the scale factor has a minimum value $a_0$. In the matter dominated case, the big bang singularity can be avoided in some special circumstances, and there may exist an oscillating universe or a bouncing one. If the cosmic scale factor is in the oscillating region initially, the universe may undergo an oscillation. After a number of oscillations, it may evolve to the bounce point through quantum tunneling and then expand. However, if the universe contracts initially from an infinite scale, it can turn around and then expand forever. In the vacuum energy dominated case, there exists a stable Einstein static state to avoid the big bang singularity. However, in certain circumstances in the matter or vacuum energy dominated case, a new kind of singularity may occur at $a_0$ as a result of the discontinuity of the scale factor. In the radiation dominated case, the universe may originate from the big bang singularity, but a bouncing universe which avoids this singularity is also possible. |
1012.2188 | Mattias Dahl | Mattias Dahl, Romain Gicquaud, Emmanuel Humbert | A limit equation associated to the solvability of the vacuum Einstein
constraint equations using the conformal method | Proposition 1.6 changed, error in the proof of this result in the
previous version of the article | Duke Math. J. 161, no. 14 (2012), 2669-2697 | 10.1215/00127094-1813182 | null | gr-qc math.AP math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Let $(M,g)$ be a compact Riemannian manifold on which a trace-free and
divergence-free $\sigma \in W^{1,p}$ and a positive function $\tau \in
W^{1,p}$, $p > n$, are fixed. In this paper, we study the vacuum Einstein
constraint equations using the well known conformal method with data $\sigma$
and $\tau$. We show that if no solution exists then there is a non-trivial
solution of another non-linear limit equation on $1$-forms. This last equation
can be shown to be without solutions no solution in many situations. As a
corollary, we get existence of solutions of the vacuum Einstein constraint
equation under explicit assumptions which in particular hold on a dense set of
metrics $g$ for the $C^0$-topology.
| [
{
"created": "Fri, 10 Dec 2010 07:02:14 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Jan 2011 15:57:30 GMT",
"version": "v2"
}
] | 2019-12-19 | [
[
"Dahl",
"Mattias",
""
],
[
"Gicquaud",
"Romain",
""
],
[
"Humbert",
"Emmanuel",
""
]
] | Let $(M,g)$ be a compact Riemannian manifold on which a trace-free and divergence-free $\sigma \in W^{1,p}$ and a positive function $\tau \in W^{1,p}$, $p > n$, are fixed. In this paper, we study the vacuum Einstein constraint equations using the well known conformal method with data $\sigma$ and $\tau$. We show that if no solution exists then there is a non-trivial solution of another non-linear limit equation on $1$-forms. This last equation can be shown to be without solutions no solution in many situations. As a corollary, we get existence of solutions of the vacuum Einstein constraint equation under explicit assumptions which in particular hold on a dense set of metrics $g$ for the $C^0$-topology. |
1506.03443 | Ujjal Debnath | Behnam Pourhassan and Ujjal Debnath | Particle Acceleration in Rotating Modified Hayward and Bardeen Black
Holes | 11 pages, 18 figures | Gravitation and Cosmology 25 (2019) 196 | 10.1134/S0202289319020129 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we consider rotating modified Hayward and rotating modified
Bardeen black holes as particle accelerators. We investigate the center of mass
energy of two colliding neutral particles with same rest masses falling from
rest at infinity to near the horizons of the mentioned black holes. We
investigate the range of the particle's angular momentum and the orbit of the
particle. We also investigate the center of mass energy for extremal black
hole.
| [
{
"created": "Wed, 10 Jun 2015 16:08:47 GMT",
"version": "v1"
},
{
"created": "Mon, 29 Jun 2015 13:08:04 GMT",
"version": "v2"
},
{
"created": "Tue, 30 Jun 2015 09:24:26 GMT",
"version": "v3"
}
] | 2019-06-25 | [
[
"Pourhassan",
"Behnam",
""
],
[
"Debnath",
"Ujjal",
""
]
] | In this paper we consider rotating modified Hayward and rotating modified Bardeen black holes as particle accelerators. We investigate the center of mass energy of two colliding neutral particles with same rest masses falling from rest at infinity to near the horizons of the mentioned black holes. We investigate the range of the particle's angular momentum and the orbit of the particle. We also investigate the center of mass energy for extremal black hole. |
1903.02389 | Vladimir Dergachev Ph.D. | Vladimir Dergachev, Maria Alessandra Papa, Benjamin Steltner,
Heinz-Bernd Eggenstein | Loosely coherent search in LIGO O1 data for continuous gravitational
waves from Terzan 5 and the galactic center | null | Phys. Rev. D 99, 084048 (2019) | 10.1103/PhysRevD.99.084048 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We report results of a search for continuous gravitational waves from a
region covering the globular cluster Terzan 5 and the galactic center.
Continuous gravitational waves are expected from fast-spinning, slightly
non-axisymmetric isolated neutron stars as well as more exotic objects. The
regions that we target are believed to be unusually abundant in neutron stars.
We use a new loosely coherent search method that allows to reach unprecedented
levels of sensitivity for this type of search. The search covers the frequency
band 475-1500 Hz and frequency time derivatives in the range of [-3e-8, +1e-9]
Hz/s, which is a parameter range not explored before with the depth reached by
this search.
As to be expected with only a few months of data from the same observing run,
it is very difficult to make a confident detection of a continuous signal over
such a large parameter space. A list of parameter space points that passed all
the thresholds of this search is provided. We follow-up the most significant
outlier on the newly released O2 data and cannot confirm it. We provide upper
limits on the gravitational wave strength of signals as a function of signal
frequency.
| [
{
"created": "Wed, 6 Mar 2019 14:06:22 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Apr 2019 20:54:35 GMT",
"version": "v2"
}
] | 2019-05-08 | [
[
"Dergachev",
"Vladimir",
""
],
[
"Papa",
"Maria Alessandra",
""
],
[
"Steltner",
"Benjamin",
""
],
[
"Eggenstein",
"Heinz-Bernd",
""
]
] | We report results of a search for continuous gravitational waves from a region covering the globular cluster Terzan 5 and the galactic center. Continuous gravitational waves are expected from fast-spinning, slightly non-axisymmetric isolated neutron stars as well as more exotic objects. The regions that we target are believed to be unusually abundant in neutron stars. We use a new loosely coherent search method that allows to reach unprecedented levels of sensitivity for this type of search. The search covers the frequency band 475-1500 Hz and frequency time derivatives in the range of [-3e-8, +1e-9] Hz/s, which is a parameter range not explored before with the depth reached by this search. As to be expected with only a few months of data from the same observing run, it is very difficult to make a confident detection of a continuous signal over such a large parameter space. A list of parameter space points that passed all the thresholds of this search is provided. We follow-up the most significant outlier on the newly released O2 data and cannot confirm it. We provide upper limits on the gravitational wave strength of signals as a function of signal frequency. |
2012.06401 | Andrzej Sitarz | Arkadiusz Bochniak and Andrzej Sitarz | On stability of Friedmann-Lema\^itre-Robertson-Walker solutions in
doubled geometries | 20 pages | Phys. Rev. D 103, 044041 (2021) | 10.1103/PhysRevD.103.044041 | null | gr-qc hep-th math-ph math.MP math.QA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Motivated by the models of geometry with discrete spaces as additional
dimensions we investigate the stability of cosmological solutions in models
with two metrics of the Friedmann-Lema\^itre-Robertson-Walker type. We propose
an effective gravity action that couples the two metrics in a similar manner as
in the bimetric theory of gravity and analyse whether standard solutions with
identical metrics are stable under small perturbations.
| [
{
"created": "Fri, 11 Dec 2020 14:59:42 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Jan 2022 08:55:21 GMT",
"version": "v2"
}
] | 2022-01-12 | [
[
"Bochniak",
"Arkadiusz",
""
],
[
"Sitarz",
"Andrzej",
""
]
] | Motivated by the models of geometry with discrete spaces as additional dimensions we investigate the stability of cosmological solutions in models with two metrics of the Friedmann-Lema\^itre-Robertson-Walker type. We propose an effective gravity action that couples the two metrics in a similar manner as in the bimetric theory of gravity and analyse whether standard solutions with identical metrics are stable under small perturbations. |
gr-qc/9504042 | Chopin Soo | Chopin Soo | Self-dual variables, positive semi-definite action, and discrete
transformations in four-dimensional quantum gravity | 22 pages, LaTeX. Minor corrections. (To appear in Phys. Rev. D.) | Phys.Rev.D52:3484-3493,1995 | 10.1103/PhysRevD.52.3484 | CGPG-95/4-3 | gr-qc hep-th | null | A positive semi-definite Euclidean action for arbitrary four-topologies can
be constructed by adding appropriate Yang-Mills and topological terms to the
Samuel-Jacobson-Smolin action of gravity with (anti)self-dual variables.
Moreover, on-shell, the (anti)self-dual sector of the new theory corresponds
precisely to all Einstein manifolds in four dimensions. The Lorentzian
signature action, and its analytic continuations are also considered. A
self-contained discussion is given on the effects of discrete transformations
C, P and T on the Samuel-Jacobson-Smolin action, and other proposed actions
which utilize self- or anti-self-dual variables as fundamental variables in the
description of four-dimensional gravity.
| [
{
"created": "Tue, 25 Apr 1995 17:43:20 GMT",
"version": "v1"
},
{
"created": "Fri, 30 Jun 1995 21:46:36 GMT",
"version": "v2"
}
] | 2011-07-19 | [
[
"Soo",
"Chopin",
""
]
] | A positive semi-definite Euclidean action for arbitrary four-topologies can be constructed by adding appropriate Yang-Mills and topological terms to the Samuel-Jacobson-Smolin action of gravity with (anti)self-dual variables. Moreover, on-shell, the (anti)self-dual sector of the new theory corresponds precisely to all Einstein manifolds in four dimensions. The Lorentzian signature action, and its analytic continuations are also considered. A self-contained discussion is given on the effects of discrete transformations C, P and T on the Samuel-Jacobson-Smolin action, and other proposed actions which utilize self- or anti-self-dual variables as fundamental variables in the description of four-dimensional gravity. |
2004.01243 | Akash Kumar Mishra | Akash K Mishra | Quasinormal modes and Strong Cosmic Censorship in the regularised 4D
Einstein-Gauss-Bonnet gravity | 19 pages, 3 figures | Gen. Relat. Grav. 52 (2020) 106 | 10.1007/s10714-020-02763-2 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The fate of strong cosmic censorship is ultimately linked to the
extendibility of perturbation across the Cauchy Horizon and known to be
violated in the near extremal region of a charged de Sitter black hole. Similar
violations can also be realized in higher curvature theories, with the strength
of violation becoming stronger as compared to general relativity. In this work,
we extend this analysis further to study the validity of strong cosmic
censorship conjecture in the context of the regularised four-dimensional
Einstein Gauss-Bonnet theory with respect to both scalar and electromagnetic
perturbation. We also study the late time tails of scalar fields.
| [
{
"created": "Thu, 2 Apr 2020 20:02:35 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Nov 2020 16:56:56 GMT",
"version": "v2"
}
] | 2020-11-10 | [
[
"Mishra",
"Akash K",
""
]
] | The fate of strong cosmic censorship is ultimately linked to the extendibility of perturbation across the Cauchy Horizon and known to be violated in the near extremal region of a charged de Sitter black hole. Similar violations can also be realized in higher curvature theories, with the strength of violation becoming stronger as compared to general relativity. In this work, we extend this analysis further to study the validity of strong cosmic censorship conjecture in the context of the regularised four-dimensional Einstein Gauss-Bonnet theory with respect to both scalar and electromagnetic perturbation. We also study the late time tails of scalar fields. |
2206.03824 | Olivier Minazzoli | Olivier Minazzoli | Quantum of action in entangled relativity | 4 pages. v3: substantial rearrangements of the content. Comments
still welcome | null | null | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this letter, I show that Planck's quantum of action $\hbar$ varies
proportionally to Newton's constant $G$ in entangled relativity, which
manifests an explicit connection between the quantum and the gravitational
worlds. On the other hand, the quantum parameter that appears in the phase of
the path integral formulation of the theory is a quantum of energy squared
$\epsilon^2$ -- instead of a quantum of action. I show that the value of this
quantum of energy is set to be the Planck energy by the \textit{semiclassical}
limit of the theory for which the gravitational interaction can safely be
assumed to be classical and to vary slowly with respect to the time-scale of
quantum phenomena. It follows that there is no fundamental notion of elementary
units of time and space in this theory, providing an interesting circumstantial
evidence that this theory might be well behaved at the Planck energy scale.
| [
{
"created": "Wed, 8 Jun 2022 11:47:39 GMT",
"version": "v1"
},
{
"created": "Tue, 3 Jan 2023 16:13:22 GMT",
"version": "v2"
},
{
"created": "Wed, 15 Feb 2023 09:57:50 GMT",
"version": "v3"
}
] | 2023-02-21 | [
[
"Minazzoli",
"Olivier",
""
]
] | In this letter, I show that Planck's quantum of action $\hbar$ varies proportionally to Newton's constant $G$ in entangled relativity, which manifests an explicit connection between the quantum and the gravitational worlds. On the other hand, the quantum parameter that appears in the phase of the path integral formulation of the theory is a quantum of energy squared $\epsilon^2$ -- instead of a quantum of action. I show that the value of this quantum of energy is set to be the Planck energy by the \textit{semiclassical} limit of the theory for which the gravitational interaction can safely be assumed to be classical and to vary slowly with respect to the time-scale of quantum phenomena. It follows that there is no fundamental notion of elementary units of time and space in this theory, providing an interesting circumstantial evidence that this theory might be well behaved at the Planck energy scale. |
1107.2316 | Benjamin Lenoir | Benjamin Lenoir, Bruno Christophe, Agn\`es L\'evy, Bernard Foulon,
Serge Reynaud, Jean-Michel Courty, Brahim Lamine, Hansj\"org Dittus, Tim van
Zoest, Claus L\"ammerzahl, Hanns Selig, Sylvie L\'eon-Hirtz, Richard
Biancale, Gilles M\'etris, Frank Sohl, Peter Wohl | Odyssey 2 : A mission toward Neptune and Triton to test General
Relativity | 61st International Astronautical Congress (Prague, Czech Republic -
September 2010), 7 pages | 61st International Astronautical Congress, (IAC, 2011)
IAC-10.A3.6.5 | null | null | gr-qc astro-ph.EP physics.ins-det | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Odyssey 2 will be proposed in December 2010 for the next call of M3 missions
for Cosmic Vision 2015-2025. This mission, under a Phase 0 study performed by
CNES, will aim at Neptune and Triton. Two sets of objectives will be pursued.
The first one is to perform a set of gravitation experiments at the Solar
System scale. Experimental tests of gravitation have always shown good
agreement with General Relativity. There are however drivers to continue
testing General Relativity, and to do so at the largest possible scales. From a
theoretical point of view, Einstein's theory of gravitation shows
inconsistencies with a quantum description of Nature and unified theories
predict deviations from General Relativity. From an observational point of
view, as long as dark matter and dark energy are not observed through other
means than their gravitational effects, they can be considered as a
manifestation of a modification of General Relativity at cosmic scales. The
scientific objectives are to: (i) test the gravitation law at the Solar System
scale; (ii) measure the Eddington parameter; and (iii) investigate the
navigation anomalies during fly-bys. To fulfil these objectives, the following
components are to be on board the spacecraft: (i) the Gravity Advanced Package
(GAP), which is an electrostatic accelerometer to which a rotating stage is
added; (ii) radio-science; (iii) laser ranging, to improve significantly the
measure of the Eddington parameter. The second set of objectives is to enhance
our knowledge of Neptune and Triton. Several instruments dedicated to
planetology are foreseen: camera, spectrometer, dust and particle detectors,
and magnetometer. Depending on the ones kept, the mission could provide
information on the gravity field, the atmosphere and the magnetosphere of the
two bodies as well as on the surface geology of Triton and on the nature of the
planetary rings around Neptune.
| [
{
"created": "Tue, 12 Jul 2011 15:11:52 GMT",
"version": "v1"
}
] | 2014-09-16 | [
[
"Lenoir",
"Benjamin",
""
],
[
"Christophe",
"Bruno",
""
],
[
"Lévy",
"Agnès",
""
],
[
"Foulon",
"Bernard",
""
],
[
"Reynaud",
"Serge",
""
],
[
"Courty",
"Jean-Michel",
""
],
[
"Lamine",
"Brahim",
""
],
[
"Dittus",
"Hansjörg",
""
],
[
"van Zoest",
"Tim",
""
],
[
"Lämmerzahl",
"Claus",
""
],
[
"Selig",
"Hanns",
""
],
[
"Léon-Hirtz",
"Sylvie",
""
],
[
"Biancale",
"Richard",
""
],
[
"Métris",
"Gilles",
""
],
[
"Sohl",
"Frank",
""
],
[
"Wohl",
"Peter",
""
]
] | Odyssey 2 will be proposed in December 2010 for the next call of M3 missions for Cosmic Vision 2015-2025. This mission, under a Phase 0 study performed by CNES, will aim at Neptune and Triton. Two sets of objectives will be pursued. The first one is to perform a set of gravitation experiments at the Solar System scale. Experimental tests of gravitation have always shown good agreement with General Relativity. There are however drivers to continue testing General Relativity, and to do so at the largest possible scales. From a theoretical point of view, Einstein's theory of gravitation shows inconsistencies with a quantum description of Nature and unified theories predict deviations from General Relativity. From an observational point of view, as long as dark matter and dark energy are not observed through other means than their gravitational effects, they can be considered as a manifestation of a modification of General Relativity at cosmic scales. The scientific objectives are to: (i) test the gravitation law at the Solar System scale; (ii) measure the Eddington parameter; and (iii) investigate the navigation anomalies during fly-bys. To fulfil these objectives, the following components are to be on board the spacecraft: (i) the Gravity Advanced Package (GAP), which is an electrostatic accelerometer to which a rotating stage is added; (ii) radio-science; (iii) laser ranging, to improve significantly the measure of the Eddington parameter. The second set of objectives is to enhance our knowledge of Neptune and Triton. Several instruments dedicated to planetology are foreseen: camera, spectrometer, dust and particle detectors, and magnetometer. Depending on the ones kept, the mission could provide information on the gravity field, the atmosphere and the magnetosphere of the two bodies as well as on the surface geology of Triton and on the nature of the planetary rings around Neptune. |
2107.05797 | Baofei Li | Kristina Giesel, Bao-Fei Li, Parampreet Singh | Non-singular quantum gravitational dynamics of an LTB dust shell model:
the role of quantization prescriptions | 20 pages and 5 figures | null | 10.1103/PhysRevD.104.106017 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study some consequences of the loop quantization of the outermost dust
shell in the Lema\^itre-Tolman-Bondi spacetime with a homogeneous dust density
using different quantization strategies motivated by loop quantum gravity.
Prior work has dealt with loop quantizing this model by employing holonomies
and the triads, following the procedure in standard loop quantum cosmology. In
this work we compare this quantization with the one in which holonomies and
gauge-covariant fluxes are used. While both of the quantization schemes resolve
the central singularity, they lead to different mass gaps at which a trapped
surface forms. This trapped surface which is matched to an exterior generalized
Vaidya spacetime disappears when the density of the dust shell is in the Planck
regime. We find that the quantization based on holonomies and gauge-covariant
fluxes generically results in an asymmetric evolution of the dust shell in
which the effective mass associated with the white hole as seen by an external
observer is $2/\pi$ of the one for the black hole. This effective difference in
masses results from difference in the classical limits in pre- and post-bounce
regimes in the two quantizations. This distinctive feature rules out formation
of any black hole-white hole twin in presence of gauge-covariant flux
modifications which is in contrast to the quantization using holonomies and
triads where the gravitational collapse always leads to a black hole-white hole
twins. In another striking difference, for the quantization based on holonomies
and gauge-covariant fluxes there can be situations in which during a
non-singular collapse only a black hole forms without a white hole.
| [
{
"created": "Tue, 13 Jul 2021 00:56:22 GMT",
"version": "v1"
}
] | 2021-12-15 | [
[
"Giesel",
"Kristina",
""
],
[
"Li",
"Bao-Fei",
""
],
[
"Singh",
"Parampreet",
""
]
] | We study some consequences of the loop quantization of the outermost dust shell in the Lema\^itre-Tolman-Bondi spacetime with a homogeneous dust density using different quantization strategies motivated by loop quantum gravity. Prior work has dealt with loop quantizing this model by employing holonomies and the triads, following the procedure in standard loop quantum cosmology. In this work we compare this quantization with the one in which holonomies and gauge-covariant fluxes are used. While both of the quantization schemes resolve the central singularity, they lead to different mass gaps at which a trapped surface forms. This trapped surface which is matched to an exterior generalized Vaidya spacetime disappears when the density of the dust shell is in the Planck regime. We find that the quantization based on holonomies and gauge-covariant fluxes generically results in an asymmetric evolution of the dust shell in which the effective mass associated with the white hole as seen by an external observer is $2/\pi$ of the one for the black hole. This effective difference in masses results from difference in the classical limits in pre- and post-bounce regimes in the two quantizations. This distinctive feature rules out formation of any black hole-white hole twin in presence of gauge-covariant flux modifications which is in contrast to the quantization using holonomies and triads where the gravitational collapse always leads to a black hole-white hole twins. In another striking difference, for the quantization based on holonomies and gauge-covariant fluxes there can be situations in which during a non-singular collapse only a black hole forms without a white hole. |
gr-qc/9508024 | Alejandro Jakubi | Luis P. Chimento and Alejandro S. Jakubi | Scalar Field Cosmologies with Viscous Fluid | 8 pages, LaTeX. To be published in International Journal of Modern
Physics D | Int.J.Mod.Phys. D5 (1996) 313-318 | 10.1142/S0218271896000217 | null | gr-qc | null | We investigate cosmological models with a free scalar field and a viscous
fluid. We find exact solutions for a linear and nonlinear viscosity pressure.
Both yield singular and bouncing solutions. In the first regime, a de Sitter
stage is asymptotically stable, while in the second case we find power-law
evolutions for vanishing cosmological constant.
| [
{
"created": "Tue, 8 Aug 1995 22:44:17 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Chimento",
"Luis P.",
""
],
[
"Jakubi",
"Alejandro S.",
""
]
] | We investigate cosmological models with a free scalar field and a viscous fluid. We find exact solutions for a linear and nonlinear viscosity pressure. Both yield singular and bouncing solutions. In the first regime, a de Sitter stage is asymptotically stable, while in the second case we find power-law evolutions for vanishing cosmological constant. |
gr-qc/0201071 | L. C. Garcia de Andrade | L.C. Garcia de Andrade (Departamento de Fisica Teorica-IF-UERJ) | Gravitational Stability of inflaton and torsion in
Einstein-Cartan-Klein-Gordon cosmology with kinky potentials | Latex file | null | null | null | gr-qc | null | Gravitational stability of torsion and inflaton field in a four-dimensional
spacetime de Sitter solution in scalar-tensor cosmology where Cartan torsion
propagates is investigated in detail. Inflaton and torsion evolution equations
are derived by making use of a Lagrangean method. Stable and unstable modes for
torsion and inflatons are found to be dependent of the background torsion and
inflaton fields. Present astrophysical observations favour a stable mode for
torsion since this would explain why no relic torsion imprint has been found on
the Cosmic Background Radiation in the universe.
| [
{
"created": "Mon, 21 Jan 2002 23:51:44 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"de Andrade",
"L. C. Garcia",
"",
"Departamento de Fisica Teorica-IF-UERJ"
]
] | Gravitational stability of torsion and inflaton field in a four-dimensional spacetime de Sitter solution in scalar-tensor cosmology where Cartan torsion propagates is investigated in detail. Inflaton and torsion evolution equations are derived by making use of a Lagrangean method. Stable and unstable modes for torsion and inflatons are found to be dependent of the background torsion and inflaton fields. Present astrophysical observations favour a stable mode for torsion since this would explain why no relic torsion imprint has been found on the Cosmic Background Radiation in the universe. |
0711.1299 | Alberto Carrasco Ferreira | Alberto Carrasco, Marc Mars | On marginally outer trapped surfaces in stationary and static spacetimes | 22 pages, 3 figures; 1 reference added, 1 figure changed, other minor
changes | Class.Quant.Grav.25:055011,2008 | 10.1088/0264-9381/25/5/055011 | null | gr-qc | null | In this paper we prove that for any spacelike hypersurface containing an
untrapped barrier in a stationary spacetime satisfying the null energy
condition, any marginally outer trapped surface cannot lie in the exterior
region where the stationary Killing vector is timelike. In the static case we
prove that any marginally outer trapped surface cannot penetrate into the
exterior region where the static Killing vector is timelike. In fact, we prove
these result at an initial data level, without even assuming existence of a
spacetime. The proof relies on a powerful theorem by Andersson and Metzger on
existence of an outermost marginally outer trapped surface.
| [
{
"created": "Thu, 8 Nov 2007 16:32:03 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Nov 2007 13:08:47 GMT",
"version": "v2"
}
] | 2011-03-28 | [
[
"Carrasco",
"Alberto",
""
],
[
"Mars",
"Marc",
""
]
] | In this paper we prove that for any spacelike hypersurface containing an untrapped barrier in a stationary spacetime satisfying the null energy condition, any marginally outer trapped surface cannot lie in the exterior region where the stationary Killing vector is timelike. In the static case we prove that any marginally outer trapped surface cannot penetrate into the exterior region where the static Killing vector is timelike. In fact, we prove these result at an initial data level, without even assuming existence of a spacetime. The proof relies on a powerful theorem by Andersson and Metzger on existence of an outermost marginally outer trapped surface. |
gr-qc/9702051 | John Baez | John C. Baez | Degenerate Solutions of General Relativity from Topological Field Theory | 16 pages LaTeX, uses diagram.sty and auxdefs.sty macros, 2
encapsulated Postscript figures | Commun.Math.Phys. 193 (1998) 219-231 | 10.1007/s002200050326 | null | gr-qc hep-th math.QA q-alg | null | Working in the Palatini formalism, we describe a procedure for constructing
degenerate solutions of general relativity on 4-manifold M from certain
solutions of 2-dimensional BF theory on any framed surface Sigma embedded in M.
In these solutions the cotetrad field e (and thus the metric) vanishes outside
a neighborhood of Sigma, while inside this neighborhood the connection A and
the field E = e ^ e satisfy the equations of 4-dimensional BF theory. Moreover,
there is a correspondence between these solutions and certain solutions of
2-dimensional BF theory on Sigma. Our construction works in any signature and
with any value of the cosmological constant. If M = R x S for some 3-manifold
S, at fixed time our solutions typically describe `flux tubes of area': the
3-metric vanishes outside a collection of thickened links embedded in S, while
inside these thickened links it is nondegenerate only in the two transverse
directions. We comment on the quantization of the theory of solutions of this
form and its relation to the loop representation of quantum gravity.
| [
{
"created": "Tue, 25 Feb 1997 03:15:21 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Baez",
"John C.",
""
]
] | Working in the Palatini formalism, we describe a procedure for constructing degenerate solutions of general relativity on 4-manifold M from certain solutions of 2-dimensional BF theory on any framed surface Sigma embedded in M. In these solutions the cotetrad field e (and thus the metric) vanishes outside a neighborhood of Sigma, while inside this neighborhood the connection A and the field E = e ^ e satisfy the equations of 4-dimensional BF theory. Moreover, there is a correspondence between these solutions and certain solutions of 2-dimensional BF theory on Sigma. Our construction works in any signature and with any value of the cosmological constant. If M = R x S for some 3-manifold S, at fixed time our solutions typically describe `flux tubes of area': the 3-metric vanishes outside a collection of thickened links embedded in S, while inside these thickened links it is nondegenerate only in the two transverse directions. We comment on the quantization of the theory of solutions of this form and its relation to the loop representation of quantum gravity. |
gr-qc/9404064 | null | Lajos Di\'osi | Comments on Omn\`es' Model for Uniqueness of Data | 5 pages Latex, 30-April-1994 | Phys.Lett. 192A (1994) 301-303 | 10.1016/0375-9601(94)90263-1 | null | gr-qc | null | Standard methods of the theory of permanent state reduction are shown to
offer an alternative realization of Omn\`es' project. Our proposal, as simple
as Omn\`es' one, possesses closed master equation for the ensemble density
operator, assuring causality.
| [
{
"created": "Sat, 30 Apr 1994 18:13:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Diósi",
"Lajos",
""
]
] | Standard methods of the theory of permanent state reduction are shown to offer an alternative realization of Omn\`es' project. Our proposal, as simple as Omn\`es' one, possesses closed master equation for the ensemble density operator, assuring causality. |
1604.04718 | Anna Nakonieczna | Anna Nakonieczna, Dong-han Yeom | Scalar field as an intrinsic time measure in coupled dynamical
matter-geometry systems. II. Electrically charged gravitational collapse | 31 pages, 15 figures | JHEP05(2016)155 | 10.1007/JHEP05(2016)155 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Investigating the dynamics of gravitational systems, especially in the regime
of quantum gravity, poses a problem of measuring time during the evolution. One
of the approaches to this issue is using one of the internal degrees of freedom
as a time variable. The objective of our research was to check whether a scalar
field or any other dynamical quantity being a part of a coupled multi-component
matter-geometry system can be treated as a `clock' during its evolution. We
investigated a collapse of a self-gravitating electrically charged scalar field
in the Einstein and Brans-Dicke theories using the 2+2 formalism. Our findings
concentrated on the spacetime region of high curvature existing in the vicinity
of the emerging singularity, which is essential for the quantum gravity
applications. We investigated several values of the Brans-Dicke coupling
constant and the coupling between the Brans-Dicke and the electrically charged
scalar fields. It turned out that both evolving scalar fields and a function
which measures the amount of electric charge within a sphere of a given radius
can be used to quantify time nearby the singularity in the dynamical spacetime
part, in which the apparent horizon surrounding the singularity is spacelike.
Using them in this respect in the asymptotic spacetime region is possible only
when both fields are present in the system and, moreover, they are coupled to
each other. The only nonzero component of the Maxwell field four-potential
cannot be used to quantify time during the considered process in the
neighborhood of the whole central singularity. None of the investigated
dynamical quantities is a good candidate for measuring time nearby the Cauchy
horizon, which is also singular due to the mass inflation phenomenon.
| [
{
"created": "Sat, 16 Apr 2016 10:36:01 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Jun 2016 07:01:15 GMT",
"version": "v2"
}
] | 2016-06-06 | [
[
"Nakonieczna",
"Anna",
""
],
[
"Yeom",
"Dong-han",
""
]
] | Investigating the dynamics of gravitational systems, especially in the regime of quantum gravity, poses a problem of measuring time during the evolution. One of the approaches to this issue is using one of the internal degrees of freedom as a time variable. The objective of our research was to check whether a scalar field or any other dynamical quantity being a part of a coupled multi-component matter-geometry system can be treated as a `clock' during its evolution. We investigated a collapse of a self-gravitating electrically charged scalar field in the Einstein and Brans-Dicke theories using the 2+2 formalism. Our findings concentrated on the spacetime region of high curvature existing in the vicinity of the emerging singularity, which is essential for the quantum gravity applications. We investigated several values of the Brans-Dicke coupling constant and the coupling between the Brans-Dicke and the electrically charged scalar fields. It turned out that both evolving scalar fields and a function which measures the amount of electric charge within a sphere of a given radius can be used to quantify time nearby the singularity in the dynamical spacetime part, in which the apparent horizon surrounding the singularity is spacelike. Using them in this respect in the asymptotic spacetime region is possible only when both fields are present in the system and, moreover, they are coupled to each other. The only nonzero component of the Maxwell field four-potential cannot be used to quantify time during the considered process in the neighborhood of the whole central singularity. None of the investigated dynamical quantities is a good candidate for measuring time nearby the Cauchy horizon, which is also singular due to the mass inflation phenomenon. |
gr-qc/9906117 | J. W. van Holten | J.W. van Holten | Cyclotron motion in a gravitational-wave background | 9 pages, no figures | null | null | NIKHEF/99-019 | gr-qc | null | We examine the motion of a relativistic charged particle in a constant
magnetic field perturbed by gravitational waves incident along the direction of
the magnetic field. We apply a generalized energy conservation law to compute
the variations of the kinetic energy of the particle during passage of the
waves. We also explicitly compute the change in the orbit due to a wave with
constant curvature.
| [
{
"created": "Tue, 29 Jun 1999 13:59:40 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"van Holten",
"J. W.",
""
]
] | We examine the motion of a relativistic charged particle in a constant magnetic field perturbed by gravitational waves incident along the direction of the magnetic field. We apply a generalized energy conservation law to compute the variations of the kinetic energy of the particle during passage of the waves. We also explicitly compute the change in the orbit due to a wave with constant curvature. |
gr-qc/9701053 | Anders H\"oglund | S. Brian Edgar (University of Link\"oping), Garry Ludwig (University
of Alberta) | Integration in the GHP formalism III: Finding all conformally flat
radiation metrics as an example of an `optimal situation' | 22 pages, plain TeX | Gen.Rel.Grav. 29 (1997) 1309-1328 | 10.1023/A:1018820031537 | null | gr-qc | null | Held has proposed an integration procedure within the GHP formalism built
around four real, functionally independent, zero-weighted scalars. He suggests
that such a procedure would be particularly simple for the `optimal situation',
when the formalism directly supplies the full quota of four scalars of this
type; a spacetime without any Killing vectors would be such a situation. Wils
has recently obtained a metric which he claims is the only conformally flat,
pure radiation metric which is not a plane wave; this metric has been shown by
Koutras to admit no Killing vectors, in general. Therefore, as a simple
illustration of the GHP integration procedure, we obtain systematically the
complete class of conformally flat, pure radiation metrics. Our result shows
that the conformally flat, pure radiation metrics, which are not plane waves,
are a larger class than Wils has obtained.
| [
{
"created": "Fri, 24 Jan 1997 11:02:11 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Edgar",
"S. Brian",
"",
"University of Linköping"
],
[
"Ludwig",
"Garry",
"",
"University\n of Alberta"
]
] | Held has proposed an integration procedure within the GHP formalism built around four real, functionally independent, zero-weighted scalars. He suggests that such a procedure would be particularly simple for the `optimal situation', when the formalism directly supplies the full quota of four scalars of this type; a spacetime without any Killing vectors would be such a situation. Wils has recently obtained a metric which he claims is the only conformally flat, pure radiation metric which is not a plane wave; this metric has been shown by Koutras to admit no Killing vectors, in general. Therefore, as a simple illustration of the GHP integration procedure, we obtain systematically the complete class of conformally flat, pure radiation metrics. Our result shows that the conformally flat, pure radiation metrics, which are not plane waves, are a larger class than Wils has obtained. |
0907.3941 | Sante Carloni Dr | Sante Carloni, Emilio Elizalde, Sergei Odintsov | Conformal Transformations in Cosmology of Modified Gravity: the
Covariant Approach Perspective | 26 pages, 8 figures | Gen.Rel.Grav.42:1667-1705,2010 | 10.1007/s10714-010-0936-1 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The 1+3 covariant approach and the covariant gauge-invariant approach to
perturbations are used to analyze in depth conformal transformations in
cosmology. Such techniques allow us to obtain very interesting insights on the
physical content of these transformations, when applied to non-standard
gravity. The results obtained lead to a number of general conclusions on the
change of some key quantities describing any two conformally related
cosmological models. In particular, it is shown that the physics in the
Einstein frame has characteristics which are completely different from those in
the Jordan frame. Even if some of the geometrical properties of the cosmology
are preserved (homogeneous and isotropic Universes are mapped into homogeneous
and isotropic universes), it can happen that decelerating cosmologies are
mapped into accelerated ones. Differences become even more pronounced when
first-order perturbations are considered: from the 1+3 equations it is seen
that first-order vector and tensor perturbations are left unchanged in their
structure by the conformal transformation, but this cannot be said of the
scalar perturbations, which include the matter density fluctuations. Behavior
in the two frames of the growth rate, as well as other evolutionary features,
like the presence or absence of oscillations, etc., appear to be different too.
The results obtained are then explicitly interpreted and verified with the help
of some clarifying examples based on $f(R)$-gravity cosmologies.
| [
{
"created": "Thu, 23 Jul 2009 14:29:35 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Oct 2009 14:26:23 GMT",
"version": "v2"
}
] | 2014-11-20 | [
[
"Carloni",
"Sante",
""
],
[
"Elizalde",
"Emilio",
""
],
[
"Odintsov",
"Sergei",
""
]
] | The 1+3 covariant approach and the covariant gauge-invariant approach to perturbations are used to analyze in depth conformal transformations in cosmology. Such techniques allow us to obtain very interesting insights on the physical content of these transformations, when applied to non-standard gravity. The results obtained lead to a number of general conclusions on the change of some key quantities describing any two conformally related cosmological models. In particular, it is shown that the physics in the Einstein frame has characteristics which are completely different from those in the Jordan frame. Even if some of the geometrical properties of the cosmology are preserved (homogeneous and isotropic Universes are mapped into homogeneous and isotropic universes), it can happen that decelerating cosmologies are mapped into accelerated ones. Differences become even more pronounced when first-order perturbations are considered: from the 1+3 equations it is seen that first-order vector and tensor perturbations are left unchanged in their structure by the conformal transformation, but this cannot be said of the scalar perturbations, which include the matter density fluctuations. Behavior in the two frames of the growth rate, as well as other evolutionary features, like the presence or absence of oscillations, etc., appear to be different too. The results obtained are then explicitly interpreted and verified with the help of some clarifying examples based on $f(R)$-gravity cosmologies. |
1108.1728 | Dario Bettoni | Dario Bettoni, Stefano Liberati, Lorenzo Sindoni | Extended LCDM: generalized non-minimal coupling for dark matter fluids | 15 pages, more references added, minor changes, accepted for
publication on JCAP | JCAP11(2011)007 | 10.1088/1475-7516/2011/11/007 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we discuss a class of models that address the issue of
explaining the gravitational dynamics at the galactic scale starting from a
geometric point of view. Instead of claiming the existence of some hidden
coupling between dark matter and baryons, or abandoning the existence of dark
matter itself, we consider the possibility that dark matter and gravity have
some non trivial interaction able to modify the dynamics at astrophysical
scales. This interaction is implemented assuming that dark matter gets
non--minimally coupled with gravity at suitably small scales and late times.
After showing the predictions of the model in the Newtonian limit we also
discuss the possible origin of it non-minimal coupling. This investigation
seems to suggest that phenomenological mechanisms envisaged for the dark matter
dynamics, such as the Bose--Einstein condensation of dark matter halos, could
be connected to this class of models.
| [
{
"created": "Mon, 8 Aug 2011 15:05:05 GMT",
"version": "v1"
},
{
"created": "Fri, 21 Oct 2011 12:06:32 GMT",
"version": "v2"
}
] | 2011-11-10 | [
[
"Bettoni",
"Dario",
""
],
[
"Liberati",
"Stefano",
""
],
[
"Sindoni",
"Lorenzo",
""
]
] | In this paper we discuss a class of models that address the issue of explaining the gravitational dynamics at the galactic scale starting from a geometric point of view. Instead of claiming the existence of some hidden coupling between dark matter and baryons, or abandoning the existence of dark matter itself, we consider the possibility that dark matter and gravity have some non trivial interaction able to modify the dynamics at astrophysical scales. This interaction is implemented assuming that dark matter gets non--minimally coupled with gravity at suitably small scales and late times. After showing the predictions of the model in the Newtonian limit we also discuss the possible origin of it non-minimal coupling. This investigation seems to suggest that phenomenological mechanisms envisaged for the dark matter dynamics, such as the Bose--Einstein condensation of dark matter halos, could be connected to this class of models. |
1606.01801 | Philipp Roser | Philipp Roser and Antony Valentini | Cosmological history in York time: inflation and perturbations | 10 pages, 1 figure | null | 10.1007/s10714-016-2180-9 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The constant mean extrinsic curvature on a spacelike slice may constitute a
physically preferred time coordinate, `York time'. One line of enquiry to probe
this idea is to understand processes in our cosmological history in terms of
York time. Following a review of the theoretical motivations, we focus on
slow-roll inflation and the freezing and Hubble re-entry of cosmological
perturbations. We show how the mathematical account of these processes is
distinct from the conventional account in terms of standard cosmological or
conformal time. We also consider the cosmological York-timeline more broadly
and contrast it with the conventional cosmological timeline.
| [
{
"created": "Mon, 6 Jun 2016 15:59:17 GMT",
"version": "v1"
}
] | 2017-01-25 | [
[
"Roser",
"Philipp",
""
],
[
"Valentini",
"Antony",
""
]
] | The constant mean extrinsic curvature on a spacelike slice may constitute a physically preferred time coordinate, `York time'. One line of enquiry to probe this idea is to understand processes in our cosmological history in terms of York time. Following a review of the theoretical motivations, we focus on slow-roll inflation and the freezing and Hubble re-entry of cosmological perturbations. We show how the mathematical account of these processes is distinct from the conventional account in terms of standard cosmological or conformal time. We also consider the cosmological York-timeline more broadly and contrast it with the conventional cosmological timeline. |
gr-qc/9506024 | Leonid V. Verozub | L.V.Verozub | Gravitational-Wave Detector for a Space Laboratory | 11 pages, Latex 2.O9, 2 figures (inside Latex file) | null | null | null | gr-qc | null | A new method of gravitational- waves detection in the $10^{-2}\div 10^{-1}
Hz$ band for a space laboratory is proposed based on the use of the Kozorez
effect in the magnetic interaction of superconducting solenoids.
| [
{
"created": "Sat, 10 Jun 1995 16:29:30 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Jun 1995 20:15:20 GMT",
"version": "v2"
},
{
"created": "Wed, 14 Jun 1995 21:40:07 GMT",
"version": "v3"
}
] | 2008-06-24 | [
[
"Verozub",
"L. V.",
""
]
] | A new method of gravitational- waves detection in the $10^{-2}\div 10^{-1} Hz$ band for a space laboratory is proposed based on the use of the Kozorez effect in the magnetic interaction of superconducting solenoids. |
1903.06028 | Elsa Teixeira | Elsa M. Teixeira, Ana Nunes and Nelson J. Nunes | Conformally Coupled Tachyonic Dark Energy | 18 pages, 7 figures. V3: Matches published version | Phys. Rev. D 100, 043539 (2019) | 10.1103/PhysRevD.100.043539 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present and study a conformally coupled dark energy model, characterised
by an interaction between a tachyon field $\phi$, with an inverse square
potential $V (\phi)$, and the matter sector. A detailed analysis of the
cosmological outcome reveals different possibilities, in contrast with the
previously studied uncoupled model, for which there exists only one stable
critical point that gives late-time acceleration of the Universe. The
introduction of the coupling translates into an energy exchange between the
fluids. We find the interesting possibility of the emergence of a new fixed
point, which is a scaling solution and an attractor of the system. In this
case, it is possible to describe an everlasting Universe with $\Omega_{\phi}
\simeq 0.7$, therefore alleviating the cosmic coincidence problem. However, we
find that, in order for the evolution to be cosmologically viable, there is the
need to introduce one uncoupled matter species, dominant at early times.
| [
{
"created": "Tue, 12 Mar 2019 17:54:11 GMT",
"version": "v1"
},
{
"created": "Tue, 3 Sep 2019 22:37:41 GMT",
"version": "v2"
},
{
"created": "Thu, 5 Sep 2019 12:34:00 GMT",
"version": "v3"
}
] | 2019-09-06 | [
[
"Teixeira",
"Elsa M.",
""
],
[
"Nunes",
"Ana",
""
],
[
"Nunes",
"Nelson J.",
""
]
] | We present and study a conformally coupled dark energy model, characterised by an interaction between a tachyon field $\phi$, with an inverse square potential $V (\phi)$, and the matter sector. A detailed analysis of the cosmological outcome reveals different possibilities, in contrast with the previously studied uncoupled model, for which there exists only one stable critical point that gives late-time acceleration of the Universe. The introduction of the coupling translates into an energy exchange between the fluids. We find the interesting possibility of the emergence of a new fixed point, which is a scaling solution and an attractor of the system. In this case, it is possible to describe an everlasting Universe with $\Omega_{\phi} \simeq 0.7$, therefore alleviating the cosmic coincidence problem. However, we find that, in order for the evolution to be cosmologically viable, there is the need to introduce one uncoupled matter species, dominant at early times. |
2105.04239 | Adolfo Cisterna A.C | Adolfo Cisterna, Carla Henr\'iquez-B\'aez, Nicol\'as Mora and Leonardo
Sanhueza | Quasitopological electromagnetism: Reissner-Nordstr\"om black strings in
Einstein and Lovelock gravities | References added. Matches published version | Phys. Rev. D 104, 064055 (2021) | 10.1103/PhysRevD.104.064055 | null | gr-qc hep-th | http://creativecommons.org/publicdomain/zero/1.0/ | In this work, we provide consistent compactifications of Einstein-Maxwell and
Einstein-Maxwell-Lovelock theories on direct product spacetimes of the form
$\mathcal{M}_D=\mathcal{M}_d\times\mathcal{K}^{p}$, where $\mathcal{K}^p$ is a
Euclidean internal manifold of constant curvature. For these compactifications
to take place, it is required the distribution of a precise flux of $p$-forms
over the internal manifold. The dynamic of the $p$-forms are demanded to be
controlled by two types of interaction. First, by specific couplings with the
curvature tensor and, second, by a suitable interaction with the
electromagnetic field of the $d$-dimensional brane, the latter being dictated
by a modification of the recently proposed theory of Quasitopological
Electromagnetism. The field equations of the corresponding compactified
theories, which are of second order, are solved and general homogenous charged
black p-branes are constructed. We explicitly provide homogenous
Reissner-Nordstr\"om black strings and black p-branes in Einstein-Maxwell
theory and homogenous charged Boulware-Deser black p-branes for quadratic and
cubic Maxwell-Lovelock gravities.
| [
{
"created": "Mon, 10 May 2021 10:11:37 GMT",
"version": "v1"
},
{
"created": "Thu, 13 May 2021 09:46:00 GMT",
"version": "v2"
},
{
"created": "Fri, 24 Sep 2021 08:22:15 GMT",
"version": "v3"
}
] | 2021-09-29 | [
[
"Cisterna",
"Adolfo",
""
],
[
"Henríquez-Báez",
"Carla",
""
],
[
"Mora",
"Nicolás",
""
],
[
"Sanhueza",
"Leonardo",
""
]
] | In this work, we provide consistent compactifications of Einstein-Maxwell and Einstein-Maxwell-Lovelock theories on direct product spacetimes of the form $\mathcal{M}_D=\mathcal{M}_d\times\mathcal{K}^{p}$, where $\mathcal{K}^p$ is a Euclidean internal manifold of constant curvature. For these compactifications to take place, it is required the distribution of a precise flux of $p$-forms over the internal manifold. The dynamic of the $p$-forms are demanded to be controlled by two types of interaction. First, by specific couplings with the curvature tensor and, second, by a suitable interaction with the electromagnetic field of the $d$-dimensional brane, the latter being dictated by a modification of the recently proposed theory of Quasitopological Electromagnetism. The field equations of the corresponding compactified theories, which are of second order, are solved and general homogenous charged black p-branes are constructed. We explicitly provide homogenous Reissner-Nordstr\"om black strings and black p-branes in Einstein-Maxwell theory and homogenous charged Boulware-Deser black p-branes for quadratic and cubic Maxwell-Lovelock gravities. |
1312.3617 | Paul McGrath | Paul L. McGrath, Melanie Chanona, Richard J. Epp, Michael J. Koop and
Robert B. Mann | Post-Newtonian Conservation Laws in Rigid Quasilocal Frames | 22 pages, 2 figures | null | 10.1088/0264-9381/31/9/095006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In recent work we constructed completely general conservation laws for energy
and linear and angular momentum of extended systems in general relativity based
on the notion of a rigid quasilocal frame (RQF). We argued at a fundamental
level that these RQF conservation laws are superior to conservation laws based
on the local stress-energy-momentum tensor of matter because (1) they do not
rely on spacetime symmetries and (2) they properly account for both matter and
gravitational effects. Moreover, they provide simple, exact, operational
expressions for fluxes of gravitational energy and linear and angular momentum.
In this paper we derive the form of these laws in a general first
post-Newtonian (1PN) approximation, and then apply these approximate laws to
the problem of gravitational tidal interactions. We obtain formulas for tidal
heating and tidal torque that agree with the literature, but without resorting
to the use of pseudotensors. We describe the physical mechanism of these tidal
interactions not in the traditional terms of a Newtonian gravitational force,
but in terms of a much simpler and universal mechanism that is an exact,
quasilocal manifestation of the equivalence principle in general relativity. As
concrete examples, we look at the tidal heating of Jupiter's moon Io and
angular momentum transfer in the Earth-Moon system that causes a gradual
spin-down of the Earth and recession of the Moon. In both examples we find
agreement with observation.
| [
{
"created": "Thu, 12 Dec 2013 20:38:21 GMT",
"version": "v1"
},
{
"created": "Fri, 10 Jan 2014 20:13:38 GMT",
"version": "v2"
}
] | 2015-06-18 | [
[
"McGrath",
"Paul L.",
""
],
[
"Chanona",
"Melanie",
""
],
[
"Epp",
"Richard J.",
""
],
[
"Koop",
"Michael J.",
""
],
[
"Mann",
"Robert B.",
""
]
] | In recent work we constructed completely general conservation laws for energy and linear and angular momentum of extended systems in general relativity based on the notion of a rigid quasilocal frame (RQF). We argued at a fundamental level that these RQF conservation laws are superior to conservation laws based on the local stress-energy-momentum tensor of matter because (1) they do not rely on spacetime symmetries and (2) they properly account for both matter and gravitational effects. Moreover, they provide simple, exact, operational expressions for fluxes of gravitational energy and linear and angular momentum. In this paper we derive the form of these laws in a general first post-Newtonian (1PN) approximation, and then apply these approximate laws to the problem of gravitational tidal interactions. We obtain formulas for tidal heating and tidal torque that agree with the literature, but without resorting to the use of pseudotensors. We describe the physical mechanism of these tidal interactions not in the traditional terms of a Newtonian gravitational force, but in terms of a much simpler and universal mechanism that is an exact, quasilocal manifestation of the equivalence principle in general relativity. As concrete examples, we look at the tidal heating of Jupiter's moon Io and angular momentum transfer in the Earth-Moon system that causes a gradual spin-down of the Earth and recession of the Moon. In both examples we find agreement with observation. |
2202.08442 | Bob Holdom | Bob Holdom | 2-2-holes simplified | 17 pages, 3 figures | Physics Letters B 830 (2022) 137142 | 10.1016/j.physletb.2022.137142 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Quadratic gravity illustrates how a replacement for black holes can emerge
from a UV completion of gravity. 2-2-holes are extremely compact horizonless
objects with an entropy $S_{22}$ due to trapped normal matter, and in this way
they are conceptually easy to understand. But the field equations are
cumbersome and the numerical analysis has so far been restricted to relatively
small size solutions. Here we show how the properties of arbitrarily large
2-2-holes can be found, including the time delay for gravitational wave echoes
and the result $T_\infty S_{22}=M/2$. The starting point is to formulate the
metric in terms of the tortoise coordinate, and to have one of the two metric
functions be a conformal factor. A large conformally-related volume becomes
associated with the interior of a 2-2-hole. We also discuss implications for
the weak gravity conjecture.
| [
{
"created": "Thu, 17 Feb 2022 04:18:48 GMT",
"version": "v1"
},
{
"created": "Wed, 11 May 2022 02:21:55 GMT",
"version": "v2"
}
] | 2022-05-12 | [
[
"Holdom",
"Bob",
""
]
] | Quadratic gravity illustrates how a replacement for black holes can emerge from a UV completion of gravity. 2-2-holes are extremely compact horizonless objects with an entropy $S_{22}$ due to trapped normal matter, and in this way they are conceptually easy to understand. But the field equations are cumbersome and the numerical analysis has so far been restricted to relatively small size solutions. Here we show how the properties of arbitrarily large 2-2-holes can be found, including the time delay for gravitational wave echoes and the result $T_\infty S_{22}=M/2$. The starting point is to formulate the metric in terms of the tortoise coordinate, and to have one of the two metric functions be a conformal factor. A large conformally-related volume becomes associated with the interior of a 2-2-hole. We also discuss implications for the weak gravity conjecture. |
1805.11024 | Douglas A. Singleton | J.A.S Lima and Douglas Singleton | Matter-antimatter asymmetry and other cosmological puzzles via running
vacuum cosmologies | 11 pages revtex4. Accepted for publication in IJMPD | null | 10.1142/S0218271818430162 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Current astronomical observations are successfully explained by the present
cosmological paradigm based on the concordance model ($\Lambda_0$CDM +
Inflation). However, such a scenario is composed of a heterogeneous mix of
ingredients for describing the different stages of cosmological evolution.
Particularly, it does not give an unified explanation connecting the early and
late time accelerating inflationary regimes which are separated by many aeons.
Other challenges to the concordance model include: a singularity at early times
or the emergence of the Universe from the quantum gravity regime, the
"graceful" exit from inflation to the standard radiation phase, as well as, the
coincidence and cosmological constant problems. We show here that a simple
running vacuum model or a time-dependent vacuum may provide insight to some of
the above open questions (including a complete cosmic history), and also can
explain the observed matter-antimatter asymmetry just after the initial
deflationary period.
| [
{
"created": "Thu, 24 May 2018 05:03:06 GMT",
"version": "v1"
}
] | 2018-08-29 | [
[
"Lima",
"J. A. S",
""
],
[
"Singleton",
"Douglas",
""
]
] | Current astronomical observations are successfully explained by the present cosmological paradigm based on the concordance model ($\Lambda_0$CDM + Inflation). However, such a scenario is composed of a heterogeneous mix of ingredients for describing the different stages of cosmological evolution. Particularly, it does not give an unified explanation connecting the early and late time accelerating inflationary regimes which are separated by many aeons. Other challenges to the concordance model include: a singularity at early times or the emergence of the Universe from the quantum gravity regime, the "graceful" exit from inflation to the standard radiation phase, as well as, the coincidence and cosmological constant problems. We show here that a simple running vacuum model or a time-dependent vacuum may provide insight to some of the above open questions (including a complete cosmic history), and also can explain the observed matter-antimatter asymmetry just after the initial deflationary period. |
0803.1980 | Larry Ford | R. T. Thompson and L. H. Ford | Enhanced Black Hole Horizon Fluctuations | 35 pages, 2 figures | Phys.Rev.D78:024014,2008 | 10.1103/PhysRevD.78.024014 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the possible role of quantum horizon fluctuations on black hole
radiance, especially whether they can invalidate Hawking's analysis based upon
transplanckian modes. We are particularly concerned with ``enhanced''
fluctuations produced by gravitons or matter fields in squeezed vacuum states
sent into the black hole after the collapse process. This allows for the
possibility of increasing the fluctuations well above the vacuum level. We find
that these enhanced fluctuations could significantly alter stimulated emission
but have little effect upon the spontaneous emission. Thus the thermal
character of the Hawking radiation is remarkably robust.
| [
{
"created": "Thu, 13 Mar 2008 14:49:30 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Thompson",
"R. T.",
""
],
[
"Ford",
"L. H.",
""
]
] | We discuss the possible role of quantum horizon fluctuations on black hole radiance, especially whether they can invalidate Hawking's analysis based upon transplanckian modes. We are particularly concerned with ``enhanced'' fluctuations produced by gravitons or matter fields in squeezed vacuum states sent into the black hole after the collapse process. This allows for the possibility of increasing the fluctuations well above the vacuum level. We find that these enhanced fluctuations could significantly alter stimulated emission but have little effect upon the spontaneous emission. Thus the thermal character of the Hawking radiation is remarkably robust. |
gr-qc/0406114 | Tomislav Prokopec | Bjorn Garbrecht and Tomislav Prokopec (Heidelberg University) | Energy Density in Expanding Universes as Seen by Unruh's Detector | 15 pages, 1 figure | Phys.Rev. D70 (2004) 083529 | 10.1103/PhysRevD.70.083529 | HD-THEP-04-26 | gr-qc astro-ph hep-th | null | We consider the response of an Unruh detector to scalar fields in an
expanding space-time. When combining transition elements of the scalar field
Hamiltonian with the interaction operator of detector and field, one finds at
second order in time-dependent perturbation theory a transition amplitude,
which actually dominates in the ultraviolet over the first order contribution.
In particular, the detector response faithfully reproduces the particle number
implied by the stress-energy of a minimally coupled scalar field, which is
inversely proportional to the energy of a scalar mode. This finding disagrees
with the contention that in de Sitter space, the response of the detector drops
exponentially with particle energy and therefore indicates a thermal spectrum.
| [
{
"created": "Mon, 28 Jun 2004 15:02:25 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Garbrecht",
"Bjorn",
"",
"Heidelberg University"
],
[
"Prokopec",
"Tomislav",
"",
"Heidelberg University"
]
] | We consider the response of an Unruh detector to scalar fields in an expanding space-time. When combining transition elements of the scalar field Hamiltonian with the interaction operator of detector and field, one finds at second order in time-dependent perturbation theory a transition amplitude, which actually dominates in the ultraviolet over the first order contribution. In particular, the detector response faithfully reproduces the particle number implied by the stress-energy of a minimally coupled scalar field, which is inversely proportional to the energy of a scalar mode. This finding disagrees with the contention that in de Sitter space, the response of the detector drops exponentially with particle energy and therefore indicates a thermal spectrum. |
0903.3733 | Edward Porter | Jonathan R. Gair, Edward K. Porter | Cosmic Swarms: A search for Supermassive Black Holes in the LISA data
stream with a Hybrid Evolutionary Algorithm | submitted to Classical & Quantum Gravity. 19 pages, 4 figures | Class.Quant.Grav.26:225004,2009 | 10.1088/0264-9381/26/22/225004 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe a hybrid evolutionary algorithm that can simultaneously search
for multiple supermassive black hole binary (SMBHB) inspirals in LISA data. The
algorithm mixes evolutionary computation, Metropolis-Hastings methods and
Nested Sampling. The inspiral of SMBHBs presents an interesting problem for
gravitational wave data analysis since, due to the LISA response function, the
sources have a bi-modal sky solution. We show here that it is possible not only
to detect multiple SMBHBs in the data stream, but also to investigate
simultaneously all the various modes of the global solution. In all cases, the
algorithm returns parameter determinations within $5\sigma$ (as estimated from
the Fisher Matrix) of the true answer, for both the actual and antipodal sky
solutions.
| [
{
"created": "Sun, 22 Mar 2009 16:05:23 GMT",
"version": "v1"
}
] | 2010-02-03 | [
[
"Gair",
"Jonathan R.",
""
],
[
"Porter",
"Edward K.",
""
]
] | We describe a hybrid evolutionary algorithm that can simultaneously search for multiple supermassive black hole binary (SMBHB) inspirals in LISA data. The algorithm mixes evolutionary computation, Metropolis-Hastings methods and Nested Sampling. The inspiral of SMBHBs presents an interesting problem for gravitational wave data analysis since, due to the LISA response function, the sources have a bi-modal sky solution. We show here that it is possible not only to detect multiple SMBHBs in the data stream, but also to investigate simultaneously all the various modes of the global solution. In all cases, the algorithm returns parameter determinations within $5\sigma$ (as estimated from the Fisher Matrix) of the true answer, for both the actual and antipodal sky solutions. |
2308.08580 | Muhammad Sharif | M. Sharif and Arooj Fatima | Impact of Charge on Traversable Wormhole Solutions in $f(R,T)$ Theory | 21 pages, 5 figures | Eur. Phys. J. Plus 138(2023)721 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper examines the effects of charge on traversable wormhole structure
in $f(R,T)$ theory. For this purpose, we use the embedding class-I approach to
build a wormhole shape function from the static spherically symmetric
spacetime. The developed shape function satisfies all the required conditions
and connects two asymptotically flat regions of spacetime. We consider
different models of this modified theory to examine the traversable wormhole
solutions through null energy condition and also check their stable state. We
conclude that viable and stable wormhole solutions are obtained under the
influence of charge in this gravitational theory.
| [
{
"created": "Wed, 16 Aug 2023 13:36:51 GMT",
"version": "v1"
}
] | 2023-08-21 | [
[
"Sharif",
"M.",
""
],
[
"Fatima",
"Arooj",
""
]
] | This paper examines the effects of charge on traversable wormhole structure in $f(R,T)$ theory. For this purpose, we use the embedding class-I approach to build a wormhole shape function from the static spherically symmetric spacetime. The developed shape function satisfies all the required conditions and connects two asymptotically flat regions of spacetime. We consider different models of this modified theory to examine the traversable wormhole solutions through null energy condition and also check their stable state. We conclude that viable and stable wormhole solutions are obtained under the influence of charge in this gravitational theory. |
1206.1128 | Li Qin | Li Qin, Yongge Ma | Coherent State Functional Integral in Loop Quantum Cosmology:
Alternative Dynamics | 10 pages. arXiv admin note: substantial text overlap with
arXiv:1110.5480 | Modern Phys. Lett. A, 27 (2012) 1250078 | 10.1142/S0217732312500782 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Coherent state functional integral for the minisuperspace model of loop
quantum cosmology is studied. By the well-established canonical theory, the
transition amplitude in the path integral representation of loop quantum
cosmology with alternative dynamics can be formulated through group averaging.
The effective action and Hamiltonian with higher-order quantum corrections are
thus obtained. It turns out that for a non-symmetric Hamiltonian constraint
operator, the Moyal (star)-product emerges naturally in the effective
Hamiltonian. For the corresponding symmetric Hamiltonian operator, the resulted
effective theory implies a possible quantum cosmological effect in large scale
limit in the alternative dynamical scenario, which coincides with the result in
canonical approach. Moreover, the first-order modified Friedmann equation still
contains the particular information of alternative dynamics and hence admits
the possible phenomenological distinction between the different proposals of
quantum dynamics.
| [
{
"created": "Wed, 6 Jun 2012 06:37:37 GMT",
"version": "v1"
}
] | 2012-06-07 | [
[
"Qin",
"Li",
""
],
[
"Ma",
"Yongge",
""
]
] | Coherent state functional integral for the minisuperspace model of loop quantum cosmology is studied. By the well-established canonical theory, the transition amplitude in the path integral representation of loop quantum cosmology with alternative dynamics can be formulated through group averaging. The effective action and Hamiltonian with higher-order quantum corrections are thus obtained. It turns out that for a non-symmetric Hamiltonian constraint operator, the Moyal (star)-product emerges naturally in the effective Hamiltonian. For the corresponding symmetric Hamiltonian operator, the resulted effective theory implies a possible quantum cosmological effect in large scale limit in the alternative dynamical scenario, which coincides with the result in canonical approach. Moreover, the first-order modified Friedmann equation still contains the particular information of alternative dynamics and hence admits the possible phenomenological distinction between the different proposals of quantum dynamics. |
1202.0853 | Pablo Jimeno Romero | J. A. R. Cembranos, A. de la Cruz-Dombriz, P. Jimeno Romero | Modified spinning black holes | 4 pages, 6 figures, Contribution to the ERE2011 Spanish Relativity
Meeting, Madrid 2011 | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the context of f(R) modified gravity theories we determine that the black
holes existence is determined by the sign of a parameter dependent of the mass,
the charge, the spin and the scalar curvature. We obtain the different
astrophysical objects derived from the presence of different horizons.
Thermodynamics for this kind of black holes is studied for negative values of
the curvature, revealing that we can distinguish between two kinds of BH: fast
and slow.
| [
{
"created": "Sat, 4 Feb 2012 01:09:15 GMT",
"version": "v1"
}
] | 2012-02-07 | [
[
"Cembranos",
"J. A. R.",
""
],
[
"de la Cruz-Dombriz",
"A.",
""
],
[
"Romero",
"P. Jimeno",
""
]
] | In the context of f(R) modified gravity theories we determine that the black holes existence is determined by the sign of a parameter dependent of the mass, the charge, the spin and the scalar curvature. We obtain the different astrophysical objects derived from the presence of different horizons. Thermodynamics for this kind of black holes is studied for negative values of the curvature, revealing that we can distinguish between two kinds of BH: fast and slow. |
2002.03394 | P. A. Gonzalez | P. A. Gonz\'alez, Marco Olivares, Eleftherios Papantonopoulos and
Yerko V\'asquez | Constraints on Scalar-Tensor Theory of Gravity by Solar System Tests | Version accepted for publication in EPJC | null | 10.1140/epjc/s10052-020-08536-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the motion of particles in the background of a scalar-tensor theory
of gravity in which the scalar field is kinetically coupled to Einstein tensor.
We constrain the value of the derivative parameter $z$ through solar system
tests. By considering the perihelion precession we obtain the constrain
$\sqrt{z}/m_p > 2.6\times 10^{12}$ m, the gravitational red-shift
$\frac{\sqrt{z}}{m_{p}}>2.7\times10^{\,10}$ m, the deflection of light
$\sqrt{z}/m_p > 1.6 \times 10^{11}$ m, and the gravitational time delay
$\sqrt{z}/m_p > 7.9 \times 10^{12}$ m; thereby, our results show that it is
possible to constrain the value of the $z$ parameter in agreement with the
observational tests that have been considered.
| [
{
"created": "Sun, 9 Feb 2020 16:16:28 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Oct 2020 01:08:11 GMT",
"version": "v2"
}
] | 2020-12-02 | [
[
"González",
"P. A.",
""
],
[
"Olivares",
"Marco",
""
],
[
"Papantonopoulos",
"Eleftherios",
""
],
[
"Vásquez",
"Yerko",
""
]
] | We study the motion of particles in the background of a scalar-tensor theory of gravity in which the scalar field is kinetically coupled to Einstein tensor. We constrain the value of the derivative parameter $z$ through solar system tests. By considering the perihelion precession we obtain the constrain $\sqrt{z}/m_p > 2.6\times 10^{12}$ m, the gravitational red-shift $\frac{\sqrt{z}}{m_{p}}>2.7\times10^{\,10}$ m, the deflection of light $\sqrt{z}/m_p > 1.6 \times 10^{11}$ m, and the gravitational time delay $\sqrt{z}/m_p > 7.9 \times 10^{12}$ m; thereby, our results show that it is possible to constrain the value of the $z$ parameter in agreement with the observational tests that have been considered. |
1405.4634 | Bibhas Majhi Ranjan | Bibhas Ranjan Majhi | Vacuum condition and the relation between response parameter and anomaly
coefficient in (1+3) dimensions | Comments added, to appear in JHEP | JHEP 1408(2014)045 | 10.1007/JHEP08(2014)045 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The role of Israel-Hartle-Hawking vacuum is discussed for anomalous fluid in
presence of both the gauge and gravitational anomalies in ($1+3$) dimensions. I
show that imposition of this vacuum condition leads to the relation
$\tilde{c}_{4d}=-8\pi^2c_m$ between the response parameter ($\tilde{c}_{4d}$)
and the anomaly coefficient ($c_m$). This establishes a connection between the
coefficients appearing in a first order and a third order derivative terms in
the constitutive relation.
| [
{
"created": "Mon, 19 May 2014 08:17:41 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Jul 2014 18:41:32 GMT",
"version": "v2"
}
] | 2014-08-08 | [
[
"Majhi",
"Bibhas Ranjan",
""
]
] | The role of Israel-Hartle-Hawking vacuum is discussed for anomalous fluid in presence of both the gauge and gravitational anomalies in ($1+3$) dimensions. I show that imposition of this vacuum condition leads to the relation $\tilde{c}_{4d}=-8\pi^2c_m$ between the response parameter ($\tilde{c}_{4d}$) and the anomaly coefficient ($c_m$). This establishes a connection between the coefficients appearing in a first order and a third order derivative terms in the constitutive relation. |
1710.03945 | Mingzhe Li | Liuyuan Shen, Yicen Mou, Yunlong Zheng, Mingzhe Li | Direct couplings of mimetic dark matter and their cosmological effects | 8 pages, references are updated, the version to be published in
Chinese Physics C | null | 10.1088/1674-1137/42/1/015101 | USTC-ICTS-17-09 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The original mimetic model was proposed to take the role of dark matter. In
this paper we consider possible direct interactions of the mimetic dark matter
with other matter in the universe, especially the standard model particles such
as baryons and photons. By imposing shift symmetry, the mimetic dark matter
field can only have derivative couplings. We discuss the possibilities of
generating baryon number asymmetry and cosmic birefringence in the universe
based on the derivative couplings of the mimetic dark matter to baryons and
photons.
| [
{
"created": "Wed, 11 Oct 2017 07:36:20 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Oct 2017 13:03:57 GMT",
"version": "v2"
}
] | 2018-01-17 | [
[
"Shen",
"Liuyuan",
""
],
[
"Mou",
"Yicen",
""
],
[
"Zheng",
"Yunlong",
""
],
[
"Li",
"Mingzhe",
""
]
] | The original mimetic model was proposed to take the role of dark matter. In this paper we consider possible direct interactions of the mimetic dark matter with other matter in the universe, especially the standard model particles such as baryons and photons. By imposing shift symmetry, the mimetic dark matter field can only have derivative couplings. We discuss the possibilities of generating baryon number asymmetry and cosmic birefringence in the universe based on the derivative couplings of the mimetic dark matter to baryons and photons. |
2402.11439 | Javier Roulet | Javier Roulet and Tejaswi Venumadhav | Inferring Binary Properties from Gravitational Wave Signals | 28 pages, 3 figures. Accepted for publication in Annual Review of
Nuclear and Particle Science. v2: GW200115 reanalyzed in Figure 2, to fix an
issue with corrupted high-frequency data; plus minor edits | null | 10.1146/annurev-nucl-121423-100725 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This review provides a conceptual and technical survey of methods for
parameter estimation of gravitational wave signals in ground-based
interferometers such as LIGO and Virgo. We introduce the framework of Bayesian
inference and provide an overview of models for the generation and detection of
gravitational waves from compact binary mergers, focusing on the essential
features that are observable in the signals. Within the traditional
likelihood-based paradigm, we describe various approaches for enhancing the
efficiency and robustness of parameter inference. This includes techniques for
accelerating likelihood evaluations, such as heterodyne/relative binning,
reduced-order quadrature, multibanding and interpolation. We also cover methods
to simplify the analysis to improve convergence, via reparametrization,
importance sampling and marginalization. We end with a discussion of recent
developments in the application of likelihood-free (simulation-based) inference
methods to gravitational wave data analysis.
| [
{
"created": "Sun, 18 Feb 2024 03:30:32 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Jun 2024 00:11:25 GMT",
"version": "v2"
}
] | 2024-07-01 | [
[
"Roulet",
"Javier",
""
],
[
"Venumadhav",
"Tejaswi",
""
]
] | This review provides a conceptual and technical survey of methods for parameter estimation of gravitational wave signals in ground-based interferometers such as LIGO and Virgo. We introduce the framework of Bayesian inference and provide an overview of models for the generation and detection of gravitational waves from compact binary mergers, focusing on the essential features that are observable in the signals. Within the traditional likelihood-based paradigm, we describe various approaches for enhancing the efficiency and robustness of parameter inference. This includes techniques for accelerating likelihood evaluations, such as heterodyne/relative binning, reduced-order quadrature, multibanding and interpolation. We also cover methods to simplify the analysis to improve convergence, via reparametrization, importance sampling and marginalization. We end with a discussion of recent developments in the application of likelihood-free (simulation-based) inference methods to gravitational wave data analysis. |
1909.05804 | Anuradha Gupta | Anuradha Gupta, Davide Gerosa, K. G. Arun, Emanuele Berti, Will Farr,
B. S. Sathyaprakash | Black holes in the low mass gap: Implications for gravitational wave
observations | 8 pages, 4 figures, 1 table. v4: matches the version accepted for
publication in Phys. Rev. D | null | 10.1103/PhysRevD.101.103036 | LIGO-P1900271 | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Binary neutron-star mergers will predominantly produce black-hole remnants of
mass $\sim 3-4\,M_{\odot}$, thus populating the putative \emph{low mass gap}
between neutron stars and stellar-mass black holes. If these low-mass black
holes are in dense astrophysical environments, mass segregation could lead to
"second-generation" compact binaries merging within a Hubble time. In this
paper, we investigate possible signatures of such low-mass compact binary
mergers in gravitational-wave observations. We show that this unique population
of objects, if present, will be uncovered by the third-generation
gravitational-wave detectors, such as Cosmic Explorer and Einstein Telescope.
Future joint measurements of chirp mass ${\cal M}$ and effective spin
$\chi_{\rm eff}$ could clarify the formation scenario of compact objects in the
low mass gap. As a case study, we show that the recent detection of GW190425
(along with GW170817) favors a double Gaussian mass model for neutron stars,
under the assumption that the primary in GW190425 is a black hole formed from a
previous binary neutron star merger.
| [
{
"created": "Thu, 12 Sep 2019 17:01:12 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Jan 2020 00:42:31 GMT",
"version": "v2"
},
{
"created": "Wed, 5 Feb 2020 21:16:49 GMT",
"version": "v3"
},
{
"created": "Thu, 7 May 2020 19:15:39 GMT",
"version": "v4"
}
] | 2020-06-10 | [
[
"Gupta",
"Anuradha",
""
],
[
"Gerosa",
"Davide",
""
],
[
"Arun",
"K. G.",
""
],
[
"Berti",
"Emanuele",
""
],
[
"Farr",
"Will",
""
],
[
"Sathyaprakash",
"B. S.",
""
]
] | Binary neutron-star mergers will predominantly produce black-hole remnants of mass $\sim 3-4\,M_{\odot}$, thus populating the putative \emph{low mass gap} between neutron stars and stellar-mass black holes. If these low-mass black holes are in dense astrophysical environments, mass segregation could lead to "second-generation" compact binaries merging within a Hubble time. In this paper, we investigate possible signatures of such low-mass compact binary mergers in gravitational-wave observations. We show that this unique population of objects, if present, will be uncovered by the third-generation gravitational-wave detectors, such as Cosmic Explorer and Einstein Telescope. Future joint measurements of chirp mass ${\cal M}$ and effective spin $\chi_{\rm eff}$ could clarify the formation scenario of compact objects in the low mass gap. As a case study, we show that the recent detection of GW190425 (along with GW170817) favors a double Gaussian mass model for neutron stars, under the assumption that the primary in GW190425 is a black hole formed from a previous binary neutron star merger. |
2208.02965 | Yitian Chen | Yitian Chen, Prayush Kumar, Neev Khera, Nils Deppe, Arnab Dhani,
Michael Boyle, Matthew Giesler, Lawrence E. Kidder, Harald P. Pfeiffer, Mark
A. Scheel, and Saul A. Teukolsky | Multipole moments on the common horizon in a binary-black-hole
simulation | 23 pages, 17 figures, 2 tables | null | 10.1103/PhysRevD.106.124045 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct the covariantly defined multipole moments on the common horizon
of an equal-mass, non-spinning, quasicircular binary-black-hole system. We see
a strong correlation between these multipole moments and the gravitational
waveform. We find that the multipole moments are well described by the
fundamental quasinormal modes at sufficiently late times. For each multipole
moment, at least two fundamental modes of different $\ell$ are detectable in
the best model. These models provide faithful estimates of the true mass and
spin of the remnant black hole. We also show that by including overtones, the
$\ell=m=2$ mass multipole moment admits an excellent quasinormal-mode
description at all times after the merger. This demonstrates the perhaps
surprising power of perturbation theory near the merger.
| [
{
"created": "Fri, 5 Aug 2022 03:29:05 GMT",
"version": "v1"
}
] | 2023-01-11 | [
[
"Chen",
"Yitian",
""
],
[
"Kumar",
"Prayush",
""
],
[
"Khera",
"Neev",
""
],
[
"Deppe",
"Nils",
""
],
[
"Dhani",
"Arnab",
""
],
[
"Boyle",
"Michael",
""
],
[
"Giesler",
"Matthew",
""
],
[
"Kidder",
"Lawrence E.",
""
],
[
"Pfeiffer",
"Harald P.",
""
],
[
"Scheel",
"Mark A.",
""
],
[
"Teukolsky",
"Saul A.",
""
]
] | We construct the covariantly defined multipole moments on the common horizon of an equal-mass, non-spinning, quasicircular binary-black-hole system. We see a strong correlation between these multipole moments and the gravitational waveform. We find that the multipole moments are well described by the fundamental quasinormal modes at sufficiently late times. For each multipole moment, at least two fundamental modes of different $\ell$ are detectable in the best model. These models provide faithful estimates of the true mass and spin of the remnant black hole. We also show that by including overtones, the $\ell=m=2$ mass multipole moment admits an excellent quasinormal-mode description at all times after the merger. This demonstrates the perhaps surprising power of perturbation theory near the merger. |
1611.00018 | Yi-Zen Chu | Yi-Zen Chu | More On Cosmological Gravitational Waves And Their Memories | 84 pages, 1 figure | null | 10.1088/1361-6382/aa8392 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We extend recent theoretical results on the propagation of linear
gravitational waves (GWs), including their associated memories, in spatially
flat Friedmann--Lema\^{i}tre--Robertson--Walker (FLRW) universes, for all
spacetime dimensions higher than 3. By specializing to a cosmology driven by a
perfect fluid with a constant equation-of-state $w$ -- conformal re-scaling,
dimension-reduction and Nariai's ansatz may then be exploited to obtain
analytic expressions for the graviton and photon Green's functions, allowing
their causal structure to be elucidated. When $0 < w \leq 1$, the
gauge-invariant scalar mode admits wave solutions, and like its tensor
counterpart, likely contributes to the tidal squeezing and stretching of the
space around a GW detector. In addition, scalar GWs in 4D radiation dominated
universes -- like tensor GWs in 4D matter dominated ones -- appear to yield a
tail signal that does not decay with increasing spatial distance from the
source. We then solve electromagnetism in the same cosmologies, and point out a
tail-induced electric memory effect. Finally, in even dimensional Minkowski
backgrounds higher than 2, we make a brief but explicit comparison between the
linear GW memory generated by point masses scattering off each other on unbound
trajectories and the linear Yang-Mills memory generated by color point charges
doing the same -- and point out how there is a "double copy" relation between
the two.
| [
{
"created": "Mon, 31 Oct 2016 20:05:53 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Nov 2016 08:13:52 GMT",
"version": "v2"
},
{
"created": "Tue, 10 Jan 2017 00:29:04 GMT",
"version": "v3"
},
{
"created": "Fri, 11 Aug 2017 05:57:29 GMT",
"version": "v4"
}
] | 2017-09-27 | [
[
"Chu",
"Yi-Zen",
""
]
] | We extend recent theoretical results on the propagation of linear gravitational waves (GWs), including their associated memories, in spatially flat Friedmann--Lema\^{i}tre--Robertson--Walker (FLRW) universes, for all spacetime dimensions higher than 3. By specializing to a cosmology driven by a perfect fluid with a constant equation-of-state $w$ -- conformal re-scaling, dimension-reduction and Nariai's ansatz may then be exploited to obtain analytic expressions for the graviton and photon Green's functions, allowing their causal structure to be elucidated. When $0 < w \leq 1$, the gauge-invariant scalar mode admits wave solutions, and like its tensor counterpart, likely contributes to the tidal squeezing and stretching of the space around a GW detector. In addition, scalar GWs in 4D radiation dominated universes -- like tensor GWs in 4D matter dominated ones -- appear to yield a tail signal that does not decay with increasing spatial distance from the source. We then solve electromagnetism in the same cosmologies, and point out a tail-induced electric memory effect. Finally, in even dimensional Minkowski backgrounds higher than 2, we make a brief but explicit comparison between the linear GW memory generated by point masses scattering off each other on unbound trajectories and the linear Yang-Mills memory generated by color point charges doing the same -- and point out how there is a "double copy" relation between the two. |
1905.10801 | Dr. Anirudh Pradhan | Gopi Kant Goswami, Anirudh Pradhan and Aroonkumar Beesham | A Dark Energy Quintessence Model of the Universe | 10 pages, 6 figures | Mod. Phys. Lett. A, Vol. 35, No. 04, 10 Feb (2020), 2050002 | 10.1142/S0217732320500029 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this paper, we have presented a model of the FLRW universe filled with
matter and dark energy fluids, by assuming an ansatz that deceleration
parameter is a linear function of the Hubble constant. This results in a
time-dependent DP having decelerating-accelerating transition phase of the
universe. This is a quintessence model $\omega_{(de)}\geq -1$. The quintessence
phase remains for the period $(0 \leq z \leq 0.5806)$. The model is shown to
satisfy current observational constraints. Various cosmological parameters
relating to the history of the universe have been investigated.
| [
{
"created": "Sun, 26 May 2019 13:14:08 GMT",
"version": "v1"
},
{
"created": "Tue, 20 Aug 2019 11:21:54 GMT",
"version": "v2"
}
] | 2021-08-02 | [
[
"Goswami",
"Gopi Kant",
""
],
[
"Pradhan",
"Anirudh",
""
],
[
"Beesham",
"Aroonkumar",
""
]
] | In this paper, we have presented a model of the FLRW universe filled with matter and dark energy fluids, by assuming an ansatz that deceleration parameter is a linear function of the Hubble constant. This results in a time-dependent DP having decelerating-accelerating transition phase of the universe. This is a quintessence model $\omega_{(de)}\geq -1$. The quintessence phase remains for the period $(0 \leq z \leq 0.5806)$. The model is shown to satisfy current observational constraints. Various cosmological parameters relating to the history of the universe have been investigated. |
gr-qc/9605048 | Dave Nicholson | D. Nicholson, et al. (University of Wales, Cardiff, UK.) | Results of the First Coincident Observations by Two
Laser-Interferometric Gravitational Wave Detectors | 11 pages, 2 postscript figures | Phys.Lett.A218:175-180,1996 | 10.1016/0375-9601(96)00438-0 | null | gr-qc | null | We report an upper bound on the strain amplitude of gravitational wave bursts
in a waveband from around 800Hz to 1.25kHz. In an effective coincident
observing period of 62 hours, the prototype laser interferometric gravitational
wave detectors of the University of Glasgow and Max Planck Institute for
Quantum Optics, have set a limit of 4.9E-16, averaging over wave polarizations
and incident directions. This is roughly a factor of 2 worse than the
theoretical best limit that the detectors could have set, the excess being due
to unmodelled non-Gaussian noise. The experiment has demonstrated the viability
of the kind of observations planned for the large-scale interferometers that
should be on-line in a few years time.
| [
{
"created": "Wed, 22 May 1996 10:59:56 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Nicholson",
"D.",
""
]
] | We report an upper bound on the strain amplitude of gravitational wave bursts in a waveband from around 800Hz to 1.25kHz. In an effective coincident observing period of 62 hours, the prototype laser interferometric gravitational wave detectors of the University of Glasgow and Max Planck Institute for Quantum Optics, have set a limit of 4.9E-16, averaging over wave polarizations and incident directions. This is roughly a factor of 2 worse than the theoretical best limit that the detectors could have set, the excess being due to unmodelled non-Gaussian noise. The experiment has demonstrated the viability of the kind of observations planned for the large-scale interferometers that should be on-line in a few years time. |
gr-qc/9912110 | Kiyoshi Shiraishi | Mitsuru Ooho and Kiyoshi Shiraishi (Yamaguchi University) | Multi-centered Solutions with a (very special) Warped Compactification | LaTeX, 4 pages, no figure, Presented at 9th Workshop on General
Relativity and Gravitation, Hiroshima, Japan, Nov 3-6, 1999. References added | null | null | null | gr-qc | null | We find an exact solution for multi-black strings in the brane world with
warped compactification.
| [
{
"created": "Tue, 28 Dec 1999 08:03:30 GMT",
"version": "v1"
},
{
"created": "Sun, 16 Jan 2000 11:23:14 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Ooho",
"Mitsuru",
"",
"Yamaguchi University"
],
[
"Shiraishi",
"Kiyoshi",
"",
"Yamaguchi University"
]
] | We find an exact solution for multi-black strings in the brane world with warped compactification. |
1202.5911 | K G Arun | K. G. Arun (Chennai Mathematical Instt) | Generic bounds on dipolar gravitational radiation from inspiralling
compact binaries | Matches with the published version | Class. Quant. Grav. 29, 075011 (2012) | 10.1088/0264-9381/29/7/075011 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Various alternative theories of gravity predict dipolar gravitational
radiation in addition to quadrupolar radiation. We show that gravitational wave
(GW) observations of inspiralling compact binaries can put interesting
constraints on the strengths of the dipole modes of GW polarizations. We put
forward a physically motivated gravitational waveform for dipole modes, in the
Fourier domain, in terms of two parameters: one which captures the relative
amplitude of the dipole mode with respect to the quadrupole mode ($\alpha$) and
the other a dipole term in the phase ($\beta$). We then use this two parameter
representation to discuss typical bounds on their values using GW measurements.
We obtain the expected bounds on the amplitude parameter $\alpha$ and the phase
parameter $\beta$ for Advanced LIGO (AdvLIGO) and Einstein Telescope (ET) noise
power spectral densities using Fisher information matrix. AdvLIGO and ET may at
best bound $\alpha$ to an accuracy of $\sim10^{-2}$ and $\sim10^{-3}$ and
$\beta$ to an accuracy of $\sim10^{-5}$ and $\sim10^{-6}$ respectively.
| [
{
"created": "Mon, 27 Feb 2012 12:36:57 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Mar 2012 09:00:48 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Arun",
"K. G.",
"",
"Chennai Mathematical Instt"
]
] | Various alternative theories of gravity predict dipolar gravitational radiation in addition to quadrupolar radiation. We show that gravitational wave (GW) observations of inspiralling compact binaries can put interesting constraints on the strengths of the dipole modes of GW polarizations. We put forward a physically motivated gravitational waveform for dipole modes, in the Fourier domain, in terms of two parameters: one which captures the relative amplitude of the dipole mode with respect to the quadrupole mode ($\alpha$) and the other a dipole term in the phase ($\beta$). We then use this two parameter representation to discuss typical bounds on their values using GW measurements. We obtain the expected bounds on the amplitude parameter $\alpha$ and the phase parameter $\beta$ for Advanced LIGO (AdvLIGO) and Einstein Telescope (ET) noise power spectral densities using Fisher information matrix. AdvLIGO and ET may at best bound $\alpha$ to an accuracy of $\sim10^{-2}$ and $\sim10^{-3}$ and $\beta$ to an accuracy of $\sim10^{-5}$ and $\sim10^{-6}$ respectively. |
1510.08770 | Anzhong Wang | J. Gariel, N.O. Santos, and Anzhong Wang | Kerr Geodesics Following the Axis of Symmetry | revtex4, no figures and tables. Gen. Relativ. Grav. 48 (2016) 66 | Gen. Relativ. Grav. 48 (2016) 66 | 10.1007/s10714-016-2061-2 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present here the general expressions for the acceleration of massive test
particles along the symmetry axis of the Kerr metric, and then study the main
properties of this acceleration in different regions of the spacetime. In
particular, we show that there exists a region near the black hole in which the
gravitational field is repulsive. We provide possible physical interpretations
about the role of this effect in terms of the different conserved parameters.
The studies of these geodesics are important not only to understand better the
structure of the Kerr spacetime but also to its use as a possible mechanism for
the production of extragalactic jets. Our results are obtained with the help of
expressing the geodesics of the Kerr spacetime in terms of the Weyl
coordinates.
| [
{
"created": "Thu, 29 Oct 2015 16:35:55 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Apr 2016 16:06:02 GMT",
"version": "v2"
},
{
"created": "Fri, 6 May 2016 00:47:10 GMT",
"version": "v3"
}
] | 2016-05-09 | [
[
"Gariel",
"J.",
""
],
[
"Santos",
"N. O.",
""
],
[
"Wang",
"Anzhong",
""
]
] | We present here the general expressions for the acceleration of massive test particles along the symmetry axis of the Kerr metric, and then study the main properties of this acceleration in different regions of the spacetime. In particular, we show that there exists a region near the black hole in which the gravitational field is repulsive. We provide possible physical interpretations about the role of this effect in terms of the different conserved parameters. The studies of these geodesics are important not only to understand better the structure of the Kerr spacetime but also to its use as a possible mechanism for the production of extragalactic jets. Our results are obtained with the help of expressing the geodesics of the Kerr spacetime in terms of the Weyl coordinates. |
1005.2507 | Edward Anderson | Edward Anderson | Scaled Triangleland Model of Quantum Cosmology | references added | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In scaled relational particle mechanics, only relative times, relative angles
and relative separations are meaningful. It arose in the study of the absolute
versus relative motion debate. It has then turned out to be a useful toy model
of classical and quantum general relativity, such as for investigating
conceptual strategies for the problem of time. This paper studies the
3-particle 2-d scaled relational particle model, for which the configurations
are scaled triangles. The configuration space for these is R^3 with a
conformally flat metric thereupon (it is the cone over the corresponding shape
space S^2. I use multiple harmonic oscillator type potentials and other
potentials suggested by analogy with cosmology, and solve for some of these by
using a partial analogy with the treatment of the atom in spherical and
parabolic coordinates. Spherical coordinates are here the total moment of
inertia $I$ for radius and two pure-shape coordinates. These are \Theta, a
function of the ratio of the two relative separations of subsystems, and \Phi,
the relative angle between the two subsystems. Parabolic coordinates are \Phi
again and twice the partial moments of inertia of each subsystem. I interpret
these solutions using 1) a `Bohr moment of inertia' for the model universe
(playing the role of the scalefactor). 2) Expectations and spreads of sizes and
shapes. 3) Superimposing the probability density function on the labelled
tessellation of the configuration space that encodes meaningful subregions such
as collinear configurations, equilateral triangles and isosceles triangles.
Applications include hidden time, emergent semiclassical time, timeless and
histories theory problem of time strategies, and comparing reduced and Dirac
methods of quantization.
| [
{
"created": "Fri, 14 May 2010 12:26:17 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Jun 2010 18:30:22 GMT",
"version": "v2"
},
{
"created": "Sat, 11 Sep 2010 12:29:52 GMT",
"version": "v3"
},
{
"created": "Mon, 18 Oct 2010 12:35:36 GMT",
"version": "v4"
}
] | 2015-03-17 | [
[
"Anderson",
"Edward",
""
]
] | In scaled relational particle mechanics, only relative times, relative angles and relative separations are meaningful. It arose in the study of the absolute versus relative motion debate. It has then turned out to be a useful toy model of classical and quantum general relativity, such as for investigating conceptual strategies for the problem of time. This paper studies the 3-particle 2-d scaled relational particle model, for which the configurations are scaled triangles. The configuration space for these is R^3 with a conformally flat metric thereupon (it is the cone over the corresponding shape space S^2. I use multiple harmonic oscillator type potentials and other potentials suggested by analogy with cosmology, and solve for some of these by using a partial analogy with the treatment of the atom in spherical and parabolic coordinates. Spherical coordinates are here the total moment of inertia $I$ for radius and two pure-shape coordinates. These are \Theta, a function of the ratio of the two relative separations of subsystems, and \Phi, the relative angle between the two subsystems. Parabolic coordinates are \Phi again and twice the partial moments of inertia of each subsystem. I interpret these solutions using 1) a `Bohr moment of inertia' for the model universe (playing the role of the scalefactor). 2) Expectations and spreads of sizes and shapes. 3) Superimposing the probability density function on the labelled tessellation of the configuration space that encodes meaningful subregions such as collinear configurations, equilateral triangles and isosceles triangles. Applications include hidden time, emergent semiclassical time, timeless and histories theory problem of time strategies, and comparing reduced and Dirac methods of quantization. |
gr-qc/0107100 | Spiros Cotsakis | Spiros Cotsakis and John Miritzis | A note on wavemap-tensor cosmologies | 8 pages, LaTeX, to appear in the Proceedings of the 2nd Hellenic
Cosmology Workshop, National Observatory of Athens, April 21-22, 2001,
(Kluwer 2001) | null | 10.1007/978-94-010-0622-4_7 | null | gr-qc | null | We examine theories of gravity which include finitely many coupled scalar
fields with arbitrary couplings to the curvature (wavemaps). We show that the
most general scalar-tensor $\sigma$-model action is conformally equivalent to
general relativity with a minimally coupled wavemap with a particular target
metric. Inflation on the source manifold is then shown to occur in a novel way
due to the combined effect of arbitrary curvature couplings and wavemap
self-interactions. A new interpretation of the conformal equivalence theorem
proved for such `wavemap-tensor' theories through brane-bulk dynamics is also
discussed.
| [
{
"created": "Tue, 31 Jul 2001 07:29:32 GMT",
"version": "v1"
}
] | 2016-02-01 | [
[
"Cotsakis",
"Spiros",
""
],
[
"Miritzis",
"John",
""
]
] | We examine theories of gravity which include finitely many coupled scalar fields with arbitrary couplings to the curvature (wavemaps). We show that the most general scalar-tensor $\sigma$-model action is conformally equivalent to general relativity with a minimally coupled wavemap with a particular target metric. Inflation on the source manifold is then shown to occur in a novel way due to the combined effect of arbitrary curvature couplings and wavemap self-interactions. A new interpretation of the conformal equivalence theorem proved for such `wavemap-tensor' theories through brane-bulk dynamics is also discussed. |
1907.08525 | Vladim\'ir Balek | Matej S\'aren\'y, Vladim\'ir Balek | Effect of black hole--plasma system on light beams | 20 pages, 16 figures | Gen. Rel. Grav. 51:141 (2019) | 10.1007/s10714-019-2629-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the paper we discuss propagation of light around Kerr black hole
surrounded by non-magnetized cold plasma with infinite conductivity. For that
purpose, we use equations for propagation of light rays obtained within Synge's
approach in the approximation of geometrical optics. We derive equation of
deviation of a ray propagating close to the reference ray, which is a
generalization of the well-known Jacobi equation, and use it to calculate the
modification of angular distribution of stars observed close to a black hole
surrounded by plasma, compared to the uniform star distribution that would be
seen without black hole or plasma. We place the observer in the equatorial
plane of the Kerr black hole and try various choices of plasma distributions
described by mathematically simple formulae. Key features of star distribution
on a local sky near the black hole are identified and the influence of plasma
on them is discussed.
| [
{
"created": "Fri, 19 Jul 2019 14:26:09 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Oct 2019 19:37:14 GMT",
"version": "v2"
},
{
"created": "Wed, 6 Nov 2019 19:15:44 GMT",
"version": "v3"
}
] | 2019-11-13 | [
[
"Sárený",
"Matej",
""
],
[
"Balek",
"Vladimír",
""
]
] | In the paper we discuss propagation of light around Kerr black hole surrounded by non-magnetized cold plasma with infinite conductivity. For that purpose, we use equations for propagation of light rays obtained within Synge's approach in the approximation of geometrical optics. We derive equation of deviation of a ray propagating close to the reference ray, which is a generalization of the well-known Jacobi equation, and use it to calculate the modification of angular distribution of stars observed close to a black hole surrounded by plasma, compared to the uniform star distribution that would be seen without black hole or plasma. We place the observer in the equatorial plane of the Kerr black hole and try various choices of plasma distributions described by mathematically simple formulae. Key features of star distribution on a local sky near the black hole are identified and the influence of plasma on them is discussed. |
1008.0520 | Jan Holland | Jan Holland | Non-existence of toroidal cohomogeneity-1 near horizon geometries | 8 pages | Annales Henri Poincare 15 (2014) 407-414 | 10.1007/s00023-013-0244-x | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We prove that $D\geq 5$ dimensional stationary, non-static near horizon
geometries with (D-3) rotational symmetries subject to the vacuum Einstein
equations including a cosmological constant cannot have toroidal horizon
topology. In D=4 dimensions the same result is obtained under the assumption of
a non-negative cosmological constant.
| [
{
"created": "Tue, 3 Aug 2010 11:10:43 GMT",
"version": "v1"
}
] | 2014-02-04 | [
[
"Holland",
"Jan",
""
]
] | We prove that $D\geq 5$ dimensional stationary, non-static near horizon geometries with (D-3) rotational symmetries subject to the vacuum Einstein equations including a cosmological constant cannot have toroidal horizon topology. In D=4 dimensions the same result is obtained under the assumption of a non-negative cosmological constant. |
2108.06378 | Robert J. Scherrer | S. David Storm and Robert J. Scherrer | Observational constraints on inflection point quintessence with a cubic
potential | 8 pages, 4 figures, added discussion of cyclic models | Phys. Lett. B, 829, 137126 (2022) | 10.1016/j.physletb.2022.137126 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the simplest inflection point quintessence model, with a potential
given by $V(\phi) = V_0 + V_3 \phi^3$. This model can produce either asymptotic
de Sitter expansion or transient acceleration, and we show that it does not
correspond to either pure freezing or thawing behavior. We derive observational
constraints on the initial value of the scalar field, $\phi_i$, and $V_3/V_0$
and find that small values of either $\phi_i$ or $V_3/V_0$ are favored. While
most of the observationally-allowed parameter space yields asymptotic de Sitter
evolution, there is a small region, corresponding to large $V_3/V_0$ and small
$\phi_i$, for which the current accelerated expansion is transient. The latter
behavior is potentially consistent with a cyclic universe.
| [
{
"created": "Fri, 13 Aug 2021 20:04:58 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Dec 2021 20:09:49 GMT",
"version": "v2"
},
{
"created": "Thu, 28 Apr 2022 17:30:10 GMT",
"version": "v3"
}
] | 2022-08-08 | [
[
"Storm",
"S. David",
""
],
[
"Scherrer",
"Robert J.",
""
]
] | We examine the simplest inflection point quintessence model, with a potential given by $V(\phi) = V_0 + V_3 \phi^3$. This model can produce either asymptotic de Sitter expansion or transient acceleration, and we show that it does not correspond to either pure freezing or thawing behavior. We derive observational constraints on the initial value of the scalar field, $\phi_i$, and $V_3/V_0$ and find that small values of either $\phi_i$ or $V_3/V_0$ are favored. While most of the observationally-allowed parameter space yields asymptotic de Sitter evolution, there is a small region, corresponding to large $V_3/V_0$ and small $\phi_i$, for which the current accelerated expansion is transient. The latter behavior is potentially consistent with a cyclic universe. |
gr-qc/9402025 | Jemal Guven | Riccardo Capovilla and Jemal Guven | Super-Minisuperspace and New Variables | 16 pages, CIEA-GR-9401 | Class.Quant.Grav.11:1961-1970,1994 | 10.1088/0264-9381/11/8/004 | null | gr-qc | null | We consider the specialization to spatially homogenous solutions of the
Jacobson formulation of N=1 canonical supergravity in terms of Ashtekar's new
variables.
We find that the classical Poisson algebra of the supersymmetry constraints
is preserved by this specialization only for Bianchi type A models. The
quantization of supersymmetric Bianchi type A models is carried out in the
triad representation. We find the physical states of this quantum theory. Since
we are missing a suitable inner product on these physical states, our results
are only formal.
| [
{
"created": "Fri, 11 Feb 1994 23:46:35 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Capovilla",
"Riccardo",
""
],
[
"Guven",
"Jemal",
""
]
] | We consider the specialization to spatially homogenous solutions of the Jacobson formulation of N=1 canonical supergravity in terms of Ashtekar's new variables. We find that the classical Poisson algebra of the supersymmetry constraints is preserved by this specialization only for Bianchi type A models. The quantization of supersymmetric Bianchi type A models is carried out in the triad representation. We find the physical states of this quantum theory. Since we are missing a suitable inner product on these physical states, our results are only formal. |
gr-qc/9706059 | Farhad Ghaboussi | F. Ghaboussi | Foundation of The Two dimensional Quantum Theory of Gravity | 24 pages, Latex, a revised version | null | null | null | gr-qc | null | The two dimensional substructure of general relativity and gravity, and the
two dimensional geometry of quantum effect by black hole are disclosed. Then
the canonical quantization of the two dimensional theory of gravity is
performed. It is shown that the resulting uncertainty relations can explain
black hole quantum effects. A quantum gravitational length is also derived
which can clarify the origin of Planck length.
| [
{
"created": "Thu, 19 Jun 1997 13:56:26 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Aug 1997 11:32:21 GMT",
"version": "v2"
},
{
"created": "Thu, 16 Jul 1998 12:02:11 GMT",
"version": "v3"
}
] | 2008-02-03 | [
[
"Ghaboussi",
"F.",
""
]
] | The two dimensional substructure of general relativity and gravity, and the two dimensional geometry of quantum effect by black hole are disclosed. Then the canonical quantization of the two dimensional theory of gravity is performed. It is shown that the resulting uncertainty relations can explain black hole quantum effects. A quantum gravitational length is also derived which can clarify the origin of Planck length. |
gr-qc/0101087 | Ali Mostafazadeh | A. Mostafazadeh | Cosmological Adiabatic Geometric Phase of a Scalar Field in a Bianchi
Spacetime | Presented in the IX Regional Conference on Mathematical Physics Ref:
Turkish J. Phys. 24, 411-128 (2000) | Turk.J.Phys. 24 (2000) 411-428 | null | null | gr-qc | null | A two-component formulation of the Klein-Gordon equation is used to
investigate the cyclic and noncyclic adiabatic geometric phases due to
spatially homogeneous (Bianchi) cosmological models. It is shown that no
adiabatic geometric phases arise for Bianchi type I models. For general Bianchi
type IX models the problem of the adiabatic geometric phase is shown to be
equivalent to the one for nuclear quadrupole interactions of a spin. For these
models nontrivial non-Abelian adiabatic geometrical phases may occur in
general.
| [
{
"created": "Mon, 22 Jan 2001 12:15:55 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Mostafazadeh",
"A.",
""
]
] | A two-component formulation of the Klein-Gordon equation is used to investigate the cyclic and noncyclic adiabatic geometric phases due to spatially homogeneous (Bianchi) cosmological models. It is shown that no adiabatic geometric phases arise for Bianchi type I models. For general Bianchi type IX models the problem of the adiabatic geometric phase is shown to be equivalent to the one for nuclear quadrupole interactions of a spin. For these models nontrivial non-Abelian adiabatic geometrical phases may occur in general. |
2301.09147 | Yaqi Zhao | Y. Zhao, Yifu Cai, S. Das, G. Lambiase, E.N. Saridakis, E.C. Vagenas | Quasinormal Modes in Noncommutative Schwarzschild black holes | 15 pages, 7 figures | Nucl. Phys. B 1004 (2024) 116545 | 10.1016/j.nuclphysb.2024.116545 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the quasinormal modes of a massless scalar field in a
Schwarzschild black hole, which is deformed due to noncommutative corrections.
We introduce the deformed Schwarzschild black hole solution, which depends on
the noncommutative parameter $\Theta$. We then extract the master equation as a
Schr\"odinger-like equation, giving the explicit expression of the effective
potential which is modified due to the noncommutative corrections. After that,
we solve the master equation numerically. The significance of these results is
twofold. Firstly, our results can be related to the detection of gravitational
waves by the near future gravitational wave detectors, such as LISA, which will
have a significantly increased accuracy. In particular, these observed
gravitational waves produced by binary strong gravitational systems have
oscillating modes which can provide valuable information. Secondly, our results
can serve as an additional tool to test the predictions of GR, as well as to
examine the possible detection of this kind of gravitational corrections.
| [
{
"created": "Sun, 22 Jan 2023 16:04:49 GMT",
"version": "v1"
},
{
"created": "Fri, 17 May 2024 06:23:18 GMT",
"version": "v2"
}
] | 2024-05-20 | [
[
"Zhao",
"Y.",
""
],
[
"Cai",
"Yifu",
""
],
[
"Das",
"S.",
""
],
[
"Lambiase",
"G.",
""
],
[
"Saridakis",
"E. N.",
""
],
[
"Vagenas",
"E. C.",
""
]
] | We investigate the quasinormal modes of a massless scalar field in a Schwarzschild black hole, which is deformed due to noncommutative corrections. We introduce the deformed Schwarzschild black hole solution, which depends on the noncommutative parameter $\Theta$. We then extract the master equation as a Schr\"odinger-like equation, giving the explicit expression of the effective potential which is modified due to the noncommutative corrections. After that, we solve the master equation numerically. The significance of these results is twofold. Firstly, our results can be related to the detection of gravitational waves by the near future gravitational wave detectors, such as LISA, which will have a significantly increased accuracy. In particular, these observed gravitational waves produced by binary strong gravitational systems have oscillating modes which can provide valuable information. Secondly, our results can serve as an additional tool to test the predictions of GR, as well as to examine the possible detection of this kind of gravitational corrections. |
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