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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/0106071 | Robert M. Wald | Sijie Gao and Robert M. Wald | The "physical process" version of the first law and the generalized
second law for charged and rotating black holes | 35 pages; 1 eps figure | Phys.Rev. D64 (2001) 084020 | 10.1103/PhysRevD.64.084020 | null | gr-qc | null | We investigate both the ``physical process'' version of the first law and the
second law of black hole thermodynamics for charged and rotating black holes.
We begin by deriving general formulas for the first order variation in ADM mass
and angular momentum for linear perturbations off a stationary, electrovac
background in terms of the perturbed non-electromagnetic stress-energy, $\delta
T_{ab}$, and the perturbed charge current density, $\delta j^a$. Using these
formulas, we prove the "physical process version" of the first law for charged,
stationary black holes. We then investigate the generalized second law of
thermodynamics (GSL) for charged, stationary black holes for processes in which
a box containing charged matter is lowered toward the black hole and then
released (at which point the box and its contents fall into the black hole
and/or thermalize with the ``thermal atmosphere'' surrounding the black hole).
Assuming that the thermal atmosphere admits a local, thermodynamic description
with respect to observers following orbits of the horizon Killing field, and
assuming that the combined black hole/thermal atmosphere system is in a state
of maximum entropy at fixed mass, angular momentum, and charge, we show that
the total generalized entropy cannot decrease during the lowering process or in
the ``release process''. Consequently, the GSL always holds in such processes.
No entropy bounds on matter are assumed to hold in any of our arguments.
| [
{
"created": "Thu, 21 Jun 2001 17:49:26 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Gao",
"Sijie",
""
],
[
"Wald",
"Robert M.",
""
]
] | We investigate both the ``physical process'' version of the first law and the second law of black hole thermodynamics for charged and rotating black holes. We begin by deriving general formulas for the first order variation in ADM mass and angular momentum for linear perturbations off a stationary, electrovac background in terms of the perturbed non-electromagnetic stress-energy, $\delta T_{ab}$, and the perturbed charge current density, $\delta j^a$. Using these formulas, we prove the "physical process version" of the first law for charged, stationary black holes. We then investigate the generalized second law of thermodynamics (GSL) for charged, stationary black holes for processes in which a box containing charged matter is lowered toward the black hole and then released (at which point the box and its contents fall into the black hole and/or thermalize with the ``thermal atmosphere'' surrounding the black hole). Assuming that the thermal atmosphere admits a local, thermodynamic description with respect to observers following orbits of the horizon Killing field, and assuming that the combined black hole/thermal atmosphere system is in a state of maximum entropy at fixed mass, angular momentum, and charge, we show that the total generalized entropy cannot decrease during the lowering process or in the ``release process''. Consequently, the GSL always holds in such processes. No entropy bounds on matter are assumed to hold in any of our arguments. |
gr-qc/0005074 | Scott M. Hitchcock | Scott Hitchcock | Feynman Clocks, Causal Networks, and The Origin of Hierarchical 'Arrows
of Time' in Complex Systems. Part 1: 'Conjectures' | 53 Pages, No Figures, corrected equations and revised content | null | null | MSUCL-1135 | gr-qc | null | A theory of time as 'information' is outlined using new tools such as Feynman
Clocks (FCs), Collective Excitation Networks (CENs), Sequential Excitation
Networks (SENs), and Plateaus of Complexity (POCs). Applications of this
approach range from the Big Bang to the emergence of 'consciousness'.
| [
{
"created": "Tue, 16 May 2000 23:22:16 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Feb 2001 02:12:10 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Hitchcock",
"Scott",
""
]
] | A theory of time as 'information' is outlined using new tools such as Feynman Clocks (FCs), Collective Excitation Networks (CENs), Sequential Excitation Networks (SENs), and Plateaus of Complexity (POCs). Applications of this approach range from the Big Bang to the emergence of 'consciousness'. |
2112.11738 | Luk\'a\v{s} Polcar | Luk\'a\v{s} Polcar and Otakar Sv\'itek | Phantom scalar field counterpart to Curzon-Chazy spacetime | null | Classical and Quantum Gravity 39 (2022) 185002 | 10.1088/1361-6382/ac8267 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive and analyze phantom scalar field counterpart to Curzon-Chazy
spacetime. Such solution contains wormhole throat while the region inside the
throat behaves like a one-directional time machine. We describe its conformal
structure and non-scalar singularity hidden inside the wormhole. We examine the
results provided by different definitions of mass of spacetime to understand
their value in the presence of phantom matter. The electromagnetic
generalization of this spacetime is as well briefly considered.
| [
{
"created": "Wed, 22 Dec 2021 09:07:03 GMT",
"version": "v1"
},
{
"created": "Mon, 16 May 2022 20:41:35 GMT",
"version": "v2"
},
{
"created": "Mon, 22 Aug 2022 16:18:46 GMT",
"version": "v3"
}
] | 2022-08-23 | [
[
"Polcar",
"Lukáš",
""
],
[
"Svítek",
"Otakar",
""
]
] | We derive and analyze phantom scalar field counterpart to Curzon-Chazy spacetime. Such solution contains wormhole throat while the region inside the throat behaves like a one-directional time machine. We describe its conformal structure and non-scalar singularity hidden inside the wormhole. We examine the results provided by different definitions of mass of spacetime to understand their value in the presence of phantom matter. The electromagnetic generalization of this spacetime is as well briefly considered. |
1209.5358 | T.G Zlosnik | H. F. Westman, T. G. Zlosnik | Cartan gravity, matter fields, and the gauge principle | Updated to match content of published version | null | 10.1016/j.aop.2013.03.012 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravity is commonly thought of as one of the four force fields in nature.
However, in standard formulations its mathematical structure is rather
different from the Yang-Mills fields of particle physics that govern the
electromagnetic, weak, and strong interactions. This paper explores this
dissonance with particular focus on how gravity couples to matter from the
perspective of the Cartan-geometric formulation of gravity. There the
gravitational field is represented by a pair of variables: 1) a `contact
vector' $V^A$ which is geometrically visualized as the contact point between
the spacetime manifold and a model spacetime being `rolled' on top of it, and
2) a gauge connection $A_{\mu}^{\ph\mu AB}$, taken to be valued in the Lie
algebra of SO(2,3) or SO(1,4), which mathematically determines how much the
model spacetime is rotated when rolled. By insisting on two principles, the
{\em gauge principle} and {\em polynomial simplicity}, we show how one can
reformulate the standard matter field actions in a way that is harmonious with
Cartan's geometric construction. This yields a formulation of all matter fields
in terms of first order partial differential equations. We show in detail how
the standard second order formulation can be recovered. Furthermore, the
energy-momentum and spin-density three-forms are naturally combined into a
single object here denoted the spin-energy-momentum three-form. Finally, we
highlight a peculiarity in the mathematical structure of our first-order
formulation of Yang-Mills fields. This suggests a way to unify a U(1) gauge
field with gravity into a SO(1,5)-valued gauge field using a natural
generalization of Cartan geometry in which the larger symmetry group is
spontaneously broken down to $SO(1,3)\times U(1)$. The coupling of this unified
theory to matter fields and possible extensions to non-Abelian gauge fields are
left as open questions.
| [
{
"created": "Mon, 24 Sep 2012 18:33:26 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Apr 2013 06:28:39 GMT",
"version": "v2"
}
] | 2015-06-11 | [
[
"Westman",
"H. F.",
""
],
[
"Zlosnik",
"T. G.",
""
]
] | Gravity is commonly thought of as one of the four force fields in nature. However, in standard formulations its mathematical structure is rather different from the Yang-Mills fields of particle physics that govern the electromagnetic, weak, and strong interactions. This paper explores this dissonance with particular focus on how gravity couples to matter from the perspective of the Cartan-geometric formulation of gravity. There the gravitational field is represented by a pair of variables: 1) a `contact vector' $V^A$ which is geometrically visualized as the contact point between the spacetime manifold and a model spacetime being `rolled' on top of it, and 2) a gauge connection $A_{\mu}^{\ph\mu AB}$, taken to be valued in the Lie algebra of SO(2,3) or SO(1,4), which mathematically determines how much the model spacetime is rotated when rolled. By insisting on two principles, the {\em gauge principle} and {\em polynomial simplicity}, we show how one can reformulate the standard matter field actions in a way that is harmonious with Cartan's geometric construction. This yields a formulation of all matter fields in terms of first order partial differential equations. We show in detail how the standard second order formulation can be recovered. Furthermore, the energy-momentum and spin-density three-forms are naturally combined into a single object here denoted the spin-energy-momentum three-form. Finally, we highlight a peculiarity in the mathematical structure of our first-order formulation of Yang-Mills fields. This suggests a way to unify a U(1) gauge field with gravity into a SO(1,5)-valued gauge field using a natural generalization of Cartan geometry in which the larger symmetry group is spontaneously broken down to $SO(1,3)\times U(1)$. The coupling of this unified theory to matter fields and possible extensions to non-Abelian gauge fields are left as open questions. |
2305.17171 | Thomas W. Baumgarte | Thomas W. Baumgarte, Bernd Br\"ugmann, Daniela Cors, Carsten Gundlach,
David Hilditch, Anton Khirnov, Tom\'a\v{s} Ledvinka, Sarah Renkhoff, and
Isabel Su\'arez Fern\'andez | Critical phenomena in the collapse of gravitational waves | 6 pages, 3 figures | Phys. Rev. Lett. 131, 181401 (2023) | 10.1103/PhysRevLett.131.181401 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Fine-tuning generic but smooth spherically-symmetric initial data for general
relativity to the threshold of dynamical black hole formation creates
arbitrarily large curvatures, mediated by a universal self-similar solution
that acts as an intermediate attractor. For vacuum gravitational waves,
however, these critical phenomena have been elusive. We present, for the first
time, excellent agreement among three independent numerical simulations of this
collapse. Surprisingly, we find no universality, and observe approximate
self-similarity for some families of initial data but not for others.
| [
{
"created": "Fri, 26 May 2023 18:00:09 GMT",
"version": "v1"
}
] | 2024-06-26 | [
[
"Baumgarte",
"Thomas W.",
""
],
[
"Brügmann",
"Bernd",
""
],
[
"Cors",
"Daniela",
""
],
[
"Gundlach",
"Carsten",
""
],
[
"Hilditch",
"David",
""
],
[
"Khirnov",
"Anton",
""
],
[
"Ledvinka",
"Tomáš",
""
],... | Fine-tuning generic but smooth spherically-symmetric initial data for general relativity to the threshold of dynamical black hole formation creates arbitrarily large curvatures, mediated by a universal self-similar solution that acts as an intermediate attractor. For vacuum gravitational waves, however, these critical phenomena have been elusive. We present, for the first time, excellent agreement among three independent numerical simulations of this collapse. Surprisingly, we find no universality, and observe approximate self-similarity for some families of initial data but not for others. |
1312.7652 | Baocheng Zhang | Biao Tang, Baocheng Zhang, Lin Zhou, Jin Wang, and Mingsheng Zhan | Configurations of a new atomic interferometer for gravitational wave
detection | null | RAA 15,333-347 (2015) | 10.1088/1674-4527/15/3/004 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, the configuration using atomic interferometers (AIs) had been
suggested for the detection of gravitational waves. A new AI with some
additional laser pulses for implementing large momentum transfer was also put
forward, in order to improve the influence of shot noise and laser frequency
noise. In the paper, we use the sensitivity function to analyze all possible
configurations of the new AI and to distinguish how many momenta are
transferred in a specific configuration. With the analysis for the new
configuration, we explore the detection scheme of gravitational wave further,
in particular, for the amelioration of the laser frequency noise. We find that
the amelioration is definite in such scheme, but novelly, in some cases the
frequency noise can be canceled completely by using a proper data processing
method.
| [
{
"created": "Mon, 30 Dec 2013 08:54:23 GMT",
"version": "v1"
}
] | 2015-10-20 | [
[
"Tang",
"Biao",
""
],
[
"Zhang",
"Baocheng",
""
],
[
"Zhou",
"Lin",
""
],
[
"Wang",
"Jin",
""
],
[
"Zhan",
"Mingsheng",
""
]
] | Recently, the configuration using atomic interferometers (AIs) had been suggested for the detection of gravitational waves. A new AI with some additional laser pulses for implementing large momentum transfer was also put forward, in order to improve the influence of shot noise and laser frequency noise. In the paper, we use the sensitivity function to analyze all possible configurations of the new AI and to distinguish how many momenta are transferred in a specific configuration. With the analysis for the new configuration, we explore the detection scheme of gravitational wave further, in particular, for the amelioration of the laser frequency noise. We find that the amelioration is definite in such scheme, but novelly, in some cases the frequency noise can be canceled completely by using a proper data processing method. |
1610.06040 | Ezequiel Boero | Ezequiel F. Boero, Osvaldo M. Moreschi | Practical definition of averages of tensors in general relativity | 10 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a definition of tensor fields which are average of tensors over a
manifold, with a straightforward and natural definition of derivative for the
averaged fields; which in turn makes a suitable and practical construction for
the study of averages of tensor fields that satisfy differential equations.
Although we have in mind applications to general relativity, our presentation
is applicable to a general n-dimensional manifold. The definition is based on
the integration of scalars constructed from a physically motivated basis,
making use of the least amount of geometrical structure. We also present
definitions of covariant derivative of the averaged tensors and Lie derivative.
| [
{
"created": "Wed, 19 Oct 2016 14:42:27 GMT",
"version": "v1"
}
] | 2016-10-20 | [
[
"Boero",
"Ezequiel F.",
""
],
[
"Moreschi",
"Osvaldo M.",
""
]
] | We present a definition of tensor fields which are average of tensors over a manifold, with a straightforward and natural definition of derivative for the averaged fields; which in turn makes a suitable and practical construction for the study of averages of tensor fields that satisfy differential equations. Although we have in mind applications to general relativity, our presentation is applicable to a general n-dimensional manifold. The definition is based on the integration of scalars constructed from a physically motivated basis, making use of the least amount of geometrical structure. We also present definitions of covariant derivative of the averaged tensors and Lie derivative. |
2301.09204 | Philip Beltracchi | Philip Beltracchi | Anisotropic Segre [(11)(1,1)] dark energy following a particular
equation of state | Replaced with published version | JCAP09(2023)010 | 10.1088/1475-7516/2023/09/010 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A generally anisotropic equation of state originally derived in the context
of Newman-Janis rotating systems allows for vacuum energy at a specific
density. In this paper we examine the possibility of using that equation of
state for cosmological dark energy. We treat the case of large scale ordering
of the directions of the energy-momentum tensor eigenvectors with a Bianchi
cosmological model, and treat the case where the ordering is random on small
scales with an effectively isotropic FLRW system. We find particular spacetimes
which evolve towards a vacuum energy/ de Sitter like configuration in either
case. In the anisotropic Bianchi case, the system can have behavior reminiscent
of big bounce cosmologies, in which the matter content approaches vacuum energy
at large scale factor and can behave in a variety of ways at small scale
factor. For particular conditions in the effectively isotropic case, we can
evolve between true and false vacuum configurations, or between radiation like
and vacuum energy configurations. We also show how some simpler equations of
state behave under the same assumptions to elucidate the methods for analysis.
| [
{
"created": "Sun, 22 Jan 2023 21:14:49 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Sep 2023 22:28:38 GMT",
"version": "v2"
}
] | 2023-09-08 | [
[
"Beltracchi",
"Philip",
""
]
] | A generally anisotropic equation of state originally derived in the context of Newman-Janis rotating systems allows for vacuum energy at a specific density. In this paper we examine the possibility of using that equation of state for cosmological dark energy. We treat the case of large scale ordering of the directions of the energy-momentum tensor eigenvectors with a Bianchi cosmological model, and treat the case where the ordering is random on small scales with an effectively isotropic FLRW system. We find particular spacetimes which evolve towards a vacuum energy/ de Sitter like configuration in either case. In the anisotropic Bianchi case, the system can have behavior reminiscent of big bounce cosmologies, in which the matter content approaches vacuum energy at large scale factor and can behave in a variety of ways at small scale factor. For particular conditions in the effectively isotropic case, we can evolve between true and false vacuum configurations, or between radiation like and vacuum energy configurations. We also show how some simpler equations of state behave under the same assumptions to elucidate the methods for analysis. |
gr-qc/0001014 | Masafumi Seriu | Masafumi Seriu | Spectral Representation and the Averaging Problem in Cosmology | To appear in General Relativity and Gravitation. The development of a
talk given at South African Relativistic Cosmology Conference, February 1-5
1999, Department of Mathematics and Applied Mathematics, University of Cape
Town, South Africa | Gen.Rel.Grav.32:1473-1485,2000 | 10.1023/A:1001977900785 | null | gr-qc | null | We investigate the averaging problem in cosmology as the problem of
introducing a distance between spaces.
We first introduce the spectral distance, which is a measure of closeness
between spaces defined in terms of the spectra of the Laplacian. Then we define
a space S, the space of all spaces equipped with the spectral distance. We
argue that this space S can be regarded as a metric space and that it also
possess other desirable properties. These facts make the space S a suitable
arena for spacetime physics.
We apply the spectral framework to the averaging problem:
We sketch the model-fitting procedure in terms of the spectral
representation, and also discuss briefly how to analyze the dynamical aspects
of the averaging procedure with this scheme.
In these analyses, we are naturally led to the concept of the apparatus- and
the scale-dependent effective evolution of the universe. These observations
suggest that the spectral scheme seems to be suitable for the quantitative
analysis of the averaging problem in cosmology.
| [
{
"created": "Fri, 7 Jan 2000 06:44:00 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Seriu",
"Masafumi",
""
]
] | We investigate the averaging problem in cosmology as the problem of introducing a distance between spaces. We first introduce the spectral distance, which is a measure of closeness between spaces defined in terms of the spectra of the Laplacian. Then we define a space S, the space of all spaces equipped with the spectral distance. We argue that this space S can be regarded as a metric space and that it also possess other desirable properties. These facts make the space S a suitable arena for spacetime physics. We apply the spectral framework to the averaging problem: We sketch the model-fitting procedure in terms of the spectral representation, and also discuss briefly how to analyze the dynamical aspects of the averaging procedure with this scheme. In these analyses, we are naturally led to the concept of the apparatus- and the scale-dependent effective evolution of the universe. These observations suggest that the spectral scheme seems to be suitable for the quantitative analysis of the averaging problem in cosmology. |
2011.07875 | Vasileios Letsios | Vasileios A. Letsios | The eigenmodes for spinor quantum field theory in global de Sitter
space-time | 33 pages | null | 10.1063/5.0038651 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The mode solutions of the Dirac equation on $N$-dimensional de Sitter
space-time ($dS_{N}$) with $(N-1)$-sphere spatial sections are obtained by
analytically continuing the spinor eigenfunctions of the Dirac operator on the
$N$-sphere ($S^{N}$). The analogs of flat space-time positive frequency modes
are identified and a vacuum is defined. The transformation properties of the
mode solutions under the de Sitter group double cover (Spin($N$,1)) are
studied. We reproduce the expression for the massless spinor Wightman two-point
function in closed form using the mode-sum method. By using this closed-form
expression and taking advantage of the maximal symmetry of $dS_{N}$ we find an
analytic expression for the spinor parallel propagator. The latter is used to
construct the massive Wightman two-point function in closed form.
| [
{
"created": "Mon, 16 Nov 2020 11:24:44 GMT",
"version": "v1"
},
{
"created": "Tue, 17 Nov 2020 18:15:08 GMT",
"version": "v2"
}
] | 2022-06-22 | [
[
"Letsios",
"Vasileios A.",
""
]
] | The mode solutions of the Dirac equation on $N$-dimensional de Sitter space-time ($dS_{N}$) with $(N-1)$-sphere spatial sections are obtained by analytically continuing the spinor eigenfunctions of the Dirac operator on the $N$-sphere ($S^{N}$). The analogs of flat space-time positive frequency modes are identified and a vacuum is defined. The transformation properties of the mode solutions under the de Sitter group double cover (Spin($N$,1)) are studied. We reproduce the expression for the massless spinor Wightman two-point function in closed form using the mode-sum method. By using this closed-form expression and taking advantage of the maximal symmetry of $dS_{N}$ we find an analytic expression for the spinor parallel propagator. The latter is used to construct the massive Wightman two-point function in closed form. |
2206.07794 | Kyriakos Destounis Dr. | Kyriakos Destounis, Giacomo Mascher and Kostas D. Kokkotas | Dynamical behavior of the $C$-metric: charged scalar fields, quasinormal
modes and superradiance | 12 pages, 8 figures, accepted for publication in PRD, updated
references | Phys. Rev. D 105, 124058 (2022) | 10.1103/PhysRevD.105.124058 | null | gr-qc astro-ph.HE hep-th | http://creativecommons.org/licenses/by/4.0/ | The $C$-metric is a boost-symmetric spacetime solution to the vacuum Einstein
field equations which describes black holes that are uniformly accelerated
under the tension of a cosmic string. Only recently the thermodynamics of
accelerating black holes and their modal stability against neutral scalar
perturbations were concisely established. The generalization of accelerating
black holes to incorporate an electric charge, namely the charged $C$-metric,
possess three distinct families of quasinormal mode frequencies; the complex
photon surface quasinormal modes associated with unstable null particles at the
equatorial plane of the photon surface, the purely imaginary acceleration modes
whose existence solely depends on the acceleration of spacetime and the purely
imaginary near-extremal modes which dominate the dynamics of the ringdown at
late times when the event and Cauchy horizon approach each other. We extend the
quasinormal mode analysis to charged scalar fluctuations and find that the
photon surface modes are continuously deformed with respect to their neutral
counterpart as the scalar charge is increased. We further find that the
acceleration and near-extremal families acquire an oscillation frequency when
the scalar charge is introduced. Finally, we study the superradiant
amplification of charged scalar monochromatic waves impinging charged
accelerating black holes. We find that even though the frequency range of
superradiant amplification is lessened due to the acceleration, the
amplification factors are considerably elevated with respect to those
transpiring in Reissner-Nordstr\"om black holes and are maximized when the
scalar charge is significantly large.
| [
{
"created": "Wed, 15 Jun 2022 20:15:57 GMT",
"version": "v1"
},
{
"created": "Sat, 18 Jun 2022 13:38:57 GMT",
"version": "v2"
}
] | 2022-06-24 | [
[
"Destounis",
"Kyriakos",
""
],
[
"Mascher",
"Giacomo",
""
],
[
"Kokkotas",
"Kostas D.",
""
]
] | The $C$-metric is a boost-symmetric spacetime solution to the vacuum Einstein field equations which describes black holes that are uniformly accelerated under the tension of a cosmic string. Only recently the thermodynamics of accelerating black holes and their modal stability against neutral scalar perturbations were concisely established. The generalization of accelerating black holes to incorporate an electric charge, namely the charged $C$-metric, possess three distinct families of quasinormal mode frequencies; the complex photon surface quasinormal modes associated with unstable null particles at the equatorial plane of the photon surface, the purely imaginary acceleration modes whose existence solely depends on the acceleration of spacetime and the purely imaginary near-extremal modes which dominate the dynamics of the ringdown at late times when the event and Cauchy horizon approach each other. We extend the quasinormal mode analysis to charged scalar fluctuations and find that the photon surface modes are continuously deformed with respect to their neutral counterpart as the scalar charge is increased. We further find that the acceleration and near-extremal families acquire an oscillation frequency when the scalar charge is introduced. Finally, we study the superradiant amplification of charged scalar monochromatic waves impinging charged accelerating black holes. We find that even though the frequency range of superradiant amplification is lessened due to the acceleration, the amplification factors are considerably elevated with respect to those transpiring in Reissner-Nordstr\"om black holes and are maximized when the scalar charge is significantly large. |
2106.05750 | Camilo Posada PhD | Zden\v{e}k Stuchl\'ik, Jan Hlad\'ik, Jaroslav Vrba, Camilo Posada | Neutrino trapping in extremely compact Tolman VII spacetimes | 13 pages, 9 figures. To appear in EPJC | Eur. Phys. J. C 81, 529 (2021) | 10.1140/epjc/s10052-021-09309-z | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Extremely compact objects trap gravitational waves or neutrinos, assumed to
move along null geodesics in the trapping regions. The trapping of neutrinos
was extensively studied for spherically symmetric extremely compact objects
constructed under the simplest approximation of the uniform energy density
distribution, with radius located under the photosphere of the external
spacetime; in addition, uniform emissivity distribution of neutrinos was
assumed in these studies. Here we extend the studies of the neutrino trapping
for the case of the extremely compact Tolman VII objects representing the
simplest generalization of the internal Schwarzschild solution with uniform
distribution of the energy density, and the correspondingly related
distribution of the neutrino emissivity that is thus again proportional to the
energy density; radius of such extremely compact objects can overcome the
photosphere of the external Schwarzschild spacetime. In dependence on the
parameters of the Tolman VII spacetimes, we determine the "local" and "global"
coefficients of efficiency of the trapping and demonstrate that the role of the
trapping is significantly stronger than in the internal Schwarzschild
spacetimes. Our results indicate possible influence of the neutrino trapping in
cooling of neutron stars.
| [
{
"created": "Thu, 10 Jun 2021 13:58:25 GMT",
"version": "v1"
}
] | 2021-06-23 | [
[
"Stuchlík",
"Zdeněk",
""
],
[
"Hladík",
"Jan",
""
],
[
"Vrba",
"Jaroslav",
""
],
[
"Posada",
"Camilo",
""
]
] | Extremely compact objects trap gravitational waves or neutrinos, assumed to move along null geodesics in the trapping regions. The trapping of neutrinos was extensively studied for spherically symmetric extremely compact objects constructed under the simplest approximation of the uniform energy density distribution, with radius located under the photosphere of the external spacetime; in addition, uniform emissivity distribution of neutrinos was assumed in these studies. Here we extend the studies of the neutrino trapping for the case of the extremely compact Tolman VII objects representing the simplest generalization of the internal Schwarzschild solution with uniform distribution of the energy density, and the correspondingly related distribution of the neutrino emissivity that is thus again proportional to the energy density; radius of such extremely compact objects can overcome the photosphere of the external Schwarzschild spacetime. In dependence on the parameters of the Tolman VII spacetimes, we determine the "local" and "global" coefficients of efficiency of the trapping and demonstrate that the role of the trapping is significantly stronger than in the internal Schwarzschild spacetimes. Our results indicate possible influence of the neutrino trapping in cooling of neutron stars. |
2111.15148 | Michael Good | Michael R.R. Good and Eric V. Linder | Quantum power: a Lorentz invariant approach to Hawking radiation | 4 pages, 3 figures | Eur. Phys. J. C 82, 204 (2022) | 10.1140/epjc/s10052-022-10167-6 | null | gr-qc hep-th quant-ph | http://creativecommons.org/licenses/by/4.0/ | Particle radiation from black holes has an observed emission power depending
on the surface gravity $\kappa = c^4/(4GM)$ as \begin{equation}\nonumber
P_{\textrm{black hole}} \sim \frac{\hbar \kappa^2}{6\pi c^2} = \frac{\hbar
c^6}{96\pi G^2 M^2}\,,\end{equation} while both the radiation from accelerating
particles and moving mirrors (accelerating boundaries) obey similar
relativistic Larmor powers, \begin{equation}\nonumber P_{\textrm{electron}}=
\frac{q^2\alpha^2}{6\pi \epsilon_0 c^3}\,, \quad P_{\textrm{mirror}}
=\frac{\hbar \alpha^2}{6\pi c^2}\,, \end{equation} where $\alpha$ is the
Lorentz invariant proper acceleration. This equivalence between the Lorentz
invariant powers suggests a close relation that could be used to understand
black hole radiation. We show that an accelerating mirror with a prolonged
metastable acceleration plateau can provide a unitary, thermal,
energy-conserved analog model for black hole decay.
| [
{
"created": "Tue, 30 Nov 2021 06:13:34 GMT",
"version": "v1"
}
] | 2022-03-09 | [
[
"Good",
"Michael R. R.",
""
],
[
"Linder",
"Eric V.",
""
]
] | Particle radiation from black holes has an observed emission power depending on the surface gravity $\kappa = c^4/(4GM)$ as \begin{equation}\nonumber P_{\textrm{black hole}} \sim \frac{\hbar \kappa^2}{6\pi c^2} = \frac{\hbar c^6}{96\pi G^2 M^2}\,,\end{equation} while both the radiation from accelerating particles and moving mirrors (accelerating boundaries) obey similar relativistic Larmor powers, \begin{equation}\nonumber P_{\textrm{electron}}= \frac{q^2\alpha^2}{6\pi \epsilon_0 c^3}\,, \quad P_{\textrm{mirror}} =\frac{\hbar \alpha^2}{6\pi c^2}\,, \end{equation} where $\alpha$ is the Lorentz invariant proper acceleration. This equivalence between the Lorentz invariant powers suggests a close relation that could be used to understand black hole radiation. We show that an accelerating mirror with a prolonged metastable acceleration plateau can provide a unitary, thermal, energy-conserved analog model for black hole decay. |
1803.06946 | Gauranga Samanta | Koijam Manihar Singh, Gauranga C. Samanta | Dark energy and its manifestations | 13 pages, 6 figures, Accepted in New Astronomy. arXiv admin note:
text overlap with arXiv:1701.00748 by other authors | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a four dimensional manifold formalism we study the evolutionary behavior
as well as the ultimate fate of the universe, in the course of which the
contribution of dark energy in these phases are investigated. At one stage we
get a situation (a condition) where the dark energy contained dominates other
types of energies available in this universe. In the model universes we obtain
here the dark energy is found to be of $\Lambda$CDM and quintessence
types-which bear testimony to being real universes. In one of the cases where
the equation of state between the fluid pressure and density is of the type of
the van der Waals equation, it is found that our universe may end in dust. And,
also, it is seen that the behavior of the deceleration parameter is almost
compatible with the recent observation.
| [
{
"created": "Mon, 19 Mar 2018 14:18:27 GMT",
"version": "v1"
},
{
"created": "Sat, 7 Apr 2018 14:08:10 GMT",
"version": "v2"
},
{
"created": "Sat, 10 Nov 2018 13:50:10 GMT",
"version": "v3"
}
] | 2018-11-13 | [
[
"Singh",
"Koijam Manihar",
""
],
[
"Samanta",
"Gauranga C.",
""
]
] | In a four dimensional manifold formalism we study the evolutionary behavior as well as the ultimate fate of the universe, in the course of which the contribution of dark energy in these phases are investigated. At one stage we get a situation (a condition) where the dark energy contained dominates other types of energies available in this universe. In the model universes we obtain here the dark energy is found to be of $\Lambda$CDM and quintessence types-which bear testimony to being real universes. In one of the cases where the equation of state between the fluid pressure and density is of the type of the van der Waals equation, it is found that our universe may end in dust. And, also, it is seen that the behavior of the deceleration parameter is almost compatible with the recent observation. |
2303.18046 | Antoni Ramos-Buades | Antoni Ramos-Buades, Alessandra Buonanno, H\'ector Estell\'es,
Mohammed Khalil, Deyan P. Mihaylov, Serguei Ossokine, Lorenzo Pompili, Mahlet
Shiferaw | SEOBNRv5PHM: Next generation of accurate and efficient multipolar
precessing-spin effective-one-body waveforms for binary black holes | null | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Spin precession is one of the key physical effects that could unveil the
origin of the compact binaries detected by ground- and space-based
gravitational-wave (GW) detectors, and shed light on their possible formation
channels. Efficiently and accurately modeling the GW signals emitted by these
systems is crucial to extract their properties. Here, we present SEOBNRv5PHM, a
multipolar precessing-spin waveform model within the effective-one-body (EOB)
formalism for the full signal (i.e. inspiral, merger and ringdown) of binary
black holes (BBHs). In the non-precessing limit, the model reduces to
SEOBNRv5HM, which is calibrated to $442$ numerical-relativity (NR) simulations,
13 waveforms from BH perturbation theory, and non-spinning energy flux from
second-order gravitational self-force theory. We remark that SEOBNRv5PHM is not
calibrated to precessing-spin NR waveforms from the Simulating eXtreme
Spacetimes Collaboration. We validate SEOBNRv5PHM by computing the
unfaithfulness against 1543 precessing-spin NR waveforms, and find that for
99.8% (84.4%) of the cases, the maximum value, in the total mass range 20-300
$M_\odot$, is below 3% (1%). These numbers reduce to 95.3% (60.8%) when using
the previous version of the SEOBNR family, SEOBNRv4PHM, and to 78.2% (38.3%)
when using the state-of-the-art frequency-domain multipolar precessing-spin
phenomenological IMRPhenomXPHM model. Due to much better computational
efficiency of SEOBNRv5PHM compared to SEOBNRv4PHM, we are also able to perform
extensive Bayesian parameter estimation on synthetic signals and GW events
observed by LIGO-Virgo detectors. We show that SEOBNRv5PHM can be used as a
standard tool for inference analyses to extract astrophysical and cosmological
information of large catalogues of BBHs.
| [
{
"created": "Fri, 31 Mar 2023 13:28:57 GMT",
"version": "v1"
}
] | 2023-04-03 | [
[
"Ramos-Buades",
"Antoni",
""
],
[
"Buonanno",
"Alessandra",
""
],
[
"Estellés",
"Héctor",
""
],
[
"Khalil",
"Mohammed",
""
],
[
"Mihaylov",
"Deyan P.",
""
],
[
"Ossokine",
"Serguei",
""
],
[
"Pompili",
"Lorenzo... | Spin precession is one of the key physical effects that could unveil the origin of the compact binaries detected by ground- and space-based gravitational-wave (GW) detectors, and shed light on their possible formation channels. Efficiently and accurately modeling the GW signals emitted by these systems is crucial to extract their properties. Here, we present SEOBNRv5PHM, a multipolar precessing-spin waveform model within the effective-one-body (EOB) formalism for the full signal (i.e. inspiral, merger and ringdown) of binary black holes (BBHs). In the non-precessing limit, the model reduces to SEOBNRv5HM, which is calibrated to $442$ numerical-relativity (NR) simulations, 13 waveforms from BH perturbation theory, and non-spinning energy flux from second-order gravitational self-force theory. We remark that SEOBNRv5PHM is not calibrated to precessing-spin NR waveforms from the Simulating eXtreme Spacetimes Collaboration. We validate SEOBNRv5PHM by computing the unfaithfulness against 1543 precessing-spin NR waveforms, and find that for 99.8% (84.4%) of the cases, the maximum value, in the total mass range 20-300 $M_\odot$, is below 3% (1%). These numbers reduce to 95.3% (60.8%) when using the previous version of the SEOBNR family, SEOBNRv4PHM, and to 78.2% (38.3%) when using the state-of-the-art frequency-domain multipolar precessing-spin phenomenological IMRPhenomXPHM model. Due to much better computational efficiency of SEOBNRv5PHM compared to SEOBNRv4PHM, we are also able to perform extensive Bayesian parameter estimation on synthetic signals and GW events observed by LIGO-Virgo detectors. We show that SEOBNRv5PHM can be used as a standard tool for inference analyses to extract astrophysical and cosmological information of large catalogues of BBHs. |
gr-qc/0110111 | Lars Andersson | Lars Andersson (University of Miami), Vincent Moncrief (Yale
University) | Elliptic-hyperbolic systems and the Einstein equations | 29 pages, several minor corrections, submitted to Ann. H. Poincare | Annales Henri Poincare 4 (2003) 1-34 | null | null | gr-qc math.AP | null | The Einstein evolution equations are studied in a gauge given by a
combination of the constant mean curvature and spatial harmonic coordinate
conditions. This leads to a coupled quasilinear elliptic--hyperbolic system of
evolution equations. We prove that the Cauchy problem is locally strongly
well--posed and that a continuation principle holds. For initial data
satisfying the Einstein constraint and gauge conditions, the solutions to the
elliptic-hyperbolic system defined by the gauge fixed Einstein evolution
equations are shown to give vacuum spacetimes.
| [
{
"created": "Thu, 25 Oct 2001 21:25:28 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Dec 2001 19:25:25 GMT",
"version": "v2"
},
{
"created": "Thu, 21 Feb 2002 22:25:23 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Andersson",
"Lars",
"",
"University of Miami"
],
[
"Moncrief",
"Vincent",
"",
"Yale\n University"
]
] | The Einstein evolution equations are studied in a gauge given by a combination of the constant mean curvature and spatial harmonic coordinate conditions. This leads to a coupled quasilinear elliptic--hyperbolic system of evolution equations. We prove that the Cauchy problem is locally strongly well--posed and that a continuation principle holds. For initial data satisfying the Einstein constraint and gauge conditions, the solutions to the elliptic-hyperbolic system defined by the gauge fixed Einstein evolution equations are shown to give vacuum spacetimes. |
gr-qc/0201046 | Piotr Bizon | P. Bizo\'n and A. Wasserman | On the existence of self-similar spherically symmetric wave maps coupled
to gravity | 15 pages, LaTex | Class.Quant.Grav.19:3309-3322,2002 | 10.1088/0264-9381/19/12/313 | null | gr-qc math-ph math.MP | null | We present a detailed analytical study of spherically symmetric self-similar
solutions in the SU(2) sigma model coupled to gravity. Using a shooting
argument we prove that there is a countable family of solutions which are
analytic inside the past self-similarity horizon. In addition, we show that for
sufficiently small values of the coupling constant these solutions possess a
regular future self-similarity horizon and thus are examples of naked
singularities. One of the solutions constructed here has been recently found as
the critical solution at the threshold of black hole formation.
| [
{
"created": "Mon, 14 Jan 2002 20:05:45 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Bizoń",
"P.",
""
],
[
"Wasserman",
"A.",
""
]
] | We present a detailed analytical study of spherically symmetric self-similar solutions in the SU(2) sigma model coupled to gravity. Using a shooting argument we prove that there is a countable family of solutions which are analytic inside the past self-similarity horizon. In addition, we show that for sufficiently small values of the coupling constant these solutions possess a regular future self-similarity horizon and thus are examples of naked singularities. One of the solutions constructed here has been recently found as the critical solution at the threshold of black hole formation. |
1103.0891 | Saibal Ray | R. N. Tiwari and Saibal Ray | A class of solutions for Einstein field equations with spatially varying
cosmological constant in spherically symmetric anisotropic source | 5 Latex pages | Indian J. pure appl. Math., 27, 907 - 911 (1996) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work a class of interior solution for Einstein field equations
corresponding to a spherically symmetric anisotropic fluid sphere has been
obtained under the assumption that the cosmological constant is spatially
variable. The solution obtained has the characteristics that the pressure and
the cosmological parameter vanish at the centre and at the boundary with a
maximum value somewhere inside the body. It has been argued that a variable $
\Lambda $ is as much important physically in Astrophysics as in Cosmology.
| [
{
"created": "Fri, 4 Mar 2011 13:19:10 GMT",
"version": "v1"
}
] | 2011-03-07 | [
[
"Tiwari",
"R. N.",
""
],
[
"Ray",
"Saibal",
""
]
] | In this work a class of interior solution for Einstein field equations corresponding to a spherically symmetric anisotropic fluid sphere has been obtained under the assumption that the cosmological constant is spatially variable. The solution obtained has the characteristics that the pressure and the cosmological parameter vanish at the centre and at the boundary with a maximum value somewhere inside the body. It has been argued that a variable $ \Lambda $ is as much important physically in Astrophysics as in Cosmology. |
1712.00901 | Hwa-Tung Nieh | H.T. Nieh | Torsion in Gauge Theory | null | Phys. Rev. D 97, 044027 (2018) | 10.1103/PhysRevD.97.044027 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The potential conflict between torsion and gauge symmetry in the
Riemann-Cartan curved space-time was noted by Kibble in his 1961 pioneering
paper, and has since been discussed by many authors. Kibble suggested that, to
preserve gauge symmetry, one should forgo the covariant derivative in favor of
the ordinary derivative in the definition of the field strength F_{\mu}{\nu}
for massless gauge theories, while for massive vector fields covariant
derivatives should be adopted. This view was further emphasized by Hehl and
collaborators in their influential 1976 review paper. We address the question
of whether this deviation from normal procedure of forgoing covariant
derivatives in curved spacetime with torsion could give rise to inconsistencies
in the theory, such as the quantum renormalizability of a realistic interacting
theory. We demonstrate in this note the one-loop renormalizability of a
realistic gauge theory of gauge bosons interacting with Dirac spinors, such as
the SU(3) chromodynamics, for the case of a curved Riemann-Cartan spacetime
with totally anti-symmetric torsion. This affirmative confirmation is one step
towards providing justification for the assertion that the flat-space
definition of the gauge field strength should be adopted as the proper
definition.
| [
{
"created": "Mon, 4 Dec 2017 04:44:03 GMT",
"version": "v1"
},
{
"created": "Sat, 6 Jan 2018 16:57:46 GMT",
"version": "v2"
}
] | 2018-02-28 | [
[
"Nieh",
"H. T.",
""
]
] | The potential conflict between torsion and gauge symmetry in the Riemann-Cartan curved space-time was noted by Kibble in his 1961 pioneering paper, and has since been discussed by many authors. Kibble suggested that, to preserve gauge symmetry, one should forgo the covariant derivative in favor of the ordinary derivative in the definition of the field strength F_{\mu}{\nu} for massless gauge theories, while for massive vector fields covariant derivatives should be adopted. This view was further emphasized by Hehl and collaborators in their influential 1976 review paper. We address the question of whether this deviation from normal procedure of forgoing covariant derivatives in curved spacetime with torsion could give rise to inconsistencies in the theory, such as the quantum renormalizability of a realistic interacting theory. We demonstrate in this note the one-loop renormalizability of a realistic gauge theory of gauge bosons interacting with Dirac spinors, such as the SU(3) chromodynamics, for the case of a curved Riemann-Cartan spacetime with totally anti-symmetric torsion. This affirmative confirmation is one step towards providing justification for the assertion that the flat-space definition of the gauge field strength should be adopted as the proper definition. |
gr-qc/9606007 | null | A.Y. Shiekh (ICTP) | Can the Equivalence Principle Survive Quantization? | 10 Pages LaTeX, Plenary lecture at the International Workshop on
AntiMatter Gravity and AntiHydrogen Spectroscopy, Molise, Italy May 96 (to be
published in the proceedings). References updated | HyperfineInteract.109:105,1997 | 10.1023/A:1012693030982 | null | gr-qc hep-ph hep-th | null | It is well known that Einstein gravity is non-renormalizable; however a
generalized approach is proposed that leads to Einstein gravity {\it after}
renormalization. This them implies that at least one candidate for quantum
gravity treats all matter on an equal footing with regard to the gravitational
behaviour.
| [
{
"created": "Wed, 5 Jun 1996 11:16:27 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Jun 1996 07:22:49 GMT",
"version": "v2"
}
] | 2009-10-28 | [
[
"Shiekh",
"A. Y.",
"",
"ICTP"
]
] | It is well known that Einstein gravity is non-renormalizable; however a generalized approach is proposed that leads to Einstein gravity {\it after} renormalization. This them implies that at least one candidate for quantum gravity treats all matter on an equal footing with regard to the gravitational behaviour. |
2402.02039 | Alberto Escalante | Alberto Escalante (Puebla U., Inst. Fis.), P. Fernando Oca\~na
Garc\'ia (Puebla U., Inst. Fis.) | Hamiltonian analysis for perturbative $\lambda R$ gravity | null | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Hamiltonian analysis for the linearized $\lambda R$ gravity around the
Minkowski background is performed. The first-class and second-class constraints
for arbitrary values of $\lambda$ are presented, and two physical degrees of
freedom are reported. In addition, we remove the second-class constraints, and
the generalized Dirac brackets are constructed; then, the equivalence between
General Relativity and the $\lambda R$ theory is shown.
| [
{
"created": "Sat, 3 Feb 2024 05:27:52 GMT",
"version": "v1"
},
{
"created": "Sat, 6 Apr 2024 16:00:22 GMT",
"version": "v2"
}
] | 2024-04-09 | [
[
"Escalante",
"Alberto",
"",
"Puebla U., Inst. Fis."
],
[
"García",
"P. Fernando Ocaña",
"",
"Puebla U., Inst. Fis."
]
] | The Hamiltonian analysis for the linearized $\lambda R$ gravity around the Minkowski background is performed. The first-class and second-class constraints for arbitrary values of $\lambda$ are presented, and two physical degrees of freedom are reported. In addition, we remove the second-class constraints, and the generalized Dirac brackets are constructed; then, the equivalence between General Relativity and the $\lambda R$ theory is shown. |
gr-qc/0607080 | Atsushi Taruya | Atsushi Taruya | Probing anisotropies of gravitational-wave backgrounds with a
space-based interferometer III: Reconstruction of a high-frequency skymap | 15 pages, 10 figures, A version with high-resolution figures is
available at
http://www-utap.phys.s.u-tokyo.ac.jp/~ataruya/paper/ms_skymap3.pdf | Phys.Rev.D74:104022,2006 | 10.1103/PhysRevD.74.104022 | null | gr-qc astro-ph | null | We develop a numerical scheme to make a high-frequency skymap of
gravitational-wave backgrounds (GWBs) observed via space-based interferometer.
Based on the cross-correlation technique, the intensity distribution of
anisotropic GWB can be directly reconstructed from the time-ordered data of
cross-correlation signals, with full knowledge of detector's antenna pattern
functions. We demonstrate how the planned space interferometer, LISA, can make
a skymap of GWB for a specific example of anisotropic signals. At the frequency
higher than the characteristic frequency $f_*=1/(2\pi L)$, where $L$ is the
arm-length of the detector, the reconstructed skymap free from the instrumental
noise potentially reaches the angular resolution up to the multipoles
$\ell\sim10$. The presence of instrumental noises degrades the angular
resolution. The resultant skymap has angular resolution with multipoles
$\ell\leq 6\sim7$ for the anisotropic signals with signal-to-noise ratio
S/N$>5$.
| [
{
"created": "Thu, 20 Jul 2006 14:41:26 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Taruya",
"Atsushi",
""
]
] | We develop a numerical scheme to make a high-frequency skymap of gravitational-wave backgrounds (GWBs) observed via space-based interferometer. Based on the cross-correlation technique, the intensity distribution of anisotropic GWB can be directly reconstructed from the time-ordered data of cross-correlation signals, with full knowledge of detector's antenna pattern functions. We demonstrate how the planned space interferometer, LISA, can make a skymap of GWB for a specific example of anisotropic signals. At the frequency higher than the characteristic frequency $f_*=1/(2\pi L)$, where $L$ is the arm-length of the detector, the reconstructed skymap free from the instrumental noise potentially reaches the angular resolution up to the multipoles $\ell\sim10$. The presence of instrumental noises degrades the angular resolution. The resultant skymap has angular resolution with multipoles $\ell\leq 6\sim7$ for the anisotropic signals with signal-to-noise ratio S/N$>5$. |
gr-qc/9808032 | Alberto Saa | Alberto Saa | Comment on ``Theorem for nonrotating singularity-free universes'' | 1 page, to appear in Phys.Rev.Lett | Phys.Rev.Lett. 81 (1998) 5031 | 10.1103/PhysRevLett.81.5031 | null | gr-qc | null | We show that Raychaudhuri's recently proposed theorem on nonrotating
universes cannot be used to rule out realistic singularity-free descriptions of
the universe, as suggested by him in PRL 80, 654 (1998).
| [
{
"created": "Tue, 11 Aug 1998 16:45:21 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Saa",
"Alberto",
""
]
] | We show that Raychaudhuri's recently proposed theorem on nonrotating universes cannot be used to rule out realistic singularity-free descriptions of the universe, as suggested by him in PRL 80, 654 (1998). |
1708.07191 | Carsten Gundlach | Carsten Gundlach | The Einstein-Vlasov system in spherical symmetry II: spherical
perturbations of static solutions | null | Phys. Rev. D 96, 084008 (2017) | 10.1103/PhysRevD.96.084008 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We reduce the equations governing the spherically symmetric perturbations of
static spherically symmetric solutions of the Einstein-Vlasov system (with
either massive or massless particles) to a single stratified wave equation
$-\psi_{,tt}=H\psi$, with $H$ containing second derivatives in radius, and
integrals over energy and angular momentum. We identify an inner product with
respect to which $H$ is symmetric, and use the Ritz method to approximate the
lowest eigenvalues of $H$ numerically. For two representative background
solutions with massless particles we find a single unstable mode with a growth
rate consistent with the universal one found by Akbarian and Choptuik in
nonlinear numerical time evolutions.
| [
{
"created": "Wed, 23 Aug 2017 21:19:36 GMT",
"version": "v1"
}
] | 2017-10-11 | [
[
"Gundlach",
"Carsten",
""
]
] | We reduce the equations governing the spherically symmetric perturbations of static spherically symmetric solutions of the Einstein-Vlasov system (with either massive or massless particles) to a single stratified wave equation $-\psi_{,tt}=H\psi$, with $H$ containing second derivatives in radius, and integrals over energy and angular momentum. We identify an inner product with respect to which $H$ is symmetric, and use the Ritz method to approximate the lowest eigenvalues of $H$ numerically. For two representative background solutions with massless particles we find a single unstable mode with a growth rate consistent with the universal one found by Akbarian and Choptuik in nonlinear numerical time evolutions. |
gr-qc/0210089 | Alfredo Sandoval-Villalbazo | A. Sandoval-Villalbazo and L.S. Garcia-Colin | Cosmological bulk viscosity, the Burnett regime, and the BGK equation | 9 pages, submitted to CQG | null | null | null | gr-qc | null | Einstein's field equations in FRW space-times are coupled to the BGK equation
in order to derive the stress energy tensor including dissipative effects up to
second order in the thermodynamical forces. The space-time is assumed to be
matter-dominated, but in a low density regime for which a second order
(Burnett) coefficient becomes relevant. Cosmological implications of the
solutions, as well as the physical meaning of transport coefficients in an
isotropic homogeneous universe are discussed.
| [
{
"created": "Fri, 25 Oct 2002 18:44:10 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sandoval-Villalbazo",
"A.",
""
],
[
"Garcia-Colin",
"L. S.",
""
]
] | Einstein's field equations in FRW space-times are coupled to the BGK equation in order to derive the stress energy tensor including dissipative effects up to second order in the thermodynamical forces. The space-time is assumed to be matter-dominated, but in a low density regime for which a second order (Burnett) coefficient becomes relevant. Cosmological implications of the solutions, as well as the physical meaning of transport coefficients in an isotropic homogeneous universe are discussed. |
2106.00843 | Radouane Gannouji | M. Sami and Radouane Gannouji | Spontaneous symmetry breaking in the late Universe and glimpses of early
Universe phase transitions \`a la baryogenesis | Invited review by IJMPD. Extended version of review with new topics:
dynamics of electroweak phase transition, issues related to baryogenesis with
technical details on sphalerons, bubble nucleation and baryon asymmetry
mechanisms beyond standard model; title is modified accordingly | null | 10.1142/S0218271821300056 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Spontaneous symmetry breaking is the foundation of electroweak unification
and serves as an integral part of the model building beyond the standard model
of particle physics and it also finds interesting applications in the late
Universe. We review development related to obtaining the late cosmic
acceleration from spontaneous symmetry breaking in the Universe at large
scales. This phenomenon is best understood through Ginzburg-Landau theory of
phase transitions which we briefly describe. Hereafter, we present elements of
spontaneous symmetry breaking in relativistic field theory. We then discuss the
"symmetron" scenario-based upon symmetry breaking in the late Universe which is
realized by using a specific form of conformal coupling. However, the model is
faced with "NO GO" for late time acceleration due to local gravity constraints.
We argue that the problem can be circumvented by using the massless $\lambda
\phi^4$ theory coupled to massive neutrino matter. As for the early Universe,
spontaneous symmetry breaking finds its interesting applications in the study
of electroweak phase transition. To this effect, we first discuss in detail,
the Ginzburg-Landau theory of first order phase transitions and then apply it
to electroweak phase transition including technical discussions on bubble
nucleation and sphaleron transitions. We provide a pedagogical expositions of
dynamics of electroweak phase transition and emphasize the need to go beyond
the standard model of particle physics for addressing the baryogenesis problem.
Review ends with a brief discussion on Affleck-Dine mechanism and spontaneous
baryogenesis. Appendixes include technical details on essential ingredients of
baryogenesis, sphaleron solution, one loop finite temperature effective
potential and dynamics of bubble nucleation.
| [
{
"created": "Tue, 1 Jun 2021 22:47:29 GMT",
"version": "v1"
},
{
"created": "Thu, 29 Jul 2021 16:32:53 GMT",
"version": "v2"
}
] | 2021-11-17 | [
[
"Sami",
"M.",
""
],
[
"Gannouji",
"Radouane",
""
]
] | Spontaneous symmetry breaking is the foundation of electroweak unification and serves as an integral part of the model building beyond the standard model of particle physics and it also finds interesting applications in the late Universe. We review development related to obtaining the late cosmic acceleration from spontaneous symmetry breaking in the Universe at large scales. This phenomenon is best understood through Ginzburg-Landau theory of phase transitions which we briefly describe. Hereafter, we present elements of spontaneous symmetry breaking in relativistic field theory. We then discuss the "symmetron" scenario-based upon symmetry breaking in the late Universe which is realized by using a specific form of conformal coupling. However, the model is faced with "NO GO" for late time acceleration due to local gravity constraints. We argue that the problem can be circumvented by using the massless $\lambda \phi^4$ theory coupled to massive neutrino matter. As for the early Universe, spontaneous symmetry breaking finds its interesting applications in the study of electroweak phase transition. To this effect, we first discuss in detail, the Ginzburg-Landau theory of first order phase transitions and then apply it to electroweak phase transition including technical discussions on bubble nucleation and sphaleron transitions. We provide a pedagogical expositions of dynamics of electroweak phase transition and emphasize the need to go beyond the standard model of particle physics for addressing the baryogenesis problem. Review ends with a brief discussion on Affleck-Dine mechanism and spontaneous baryogenesis. Appendixes include technical details on essential ingredients of baryogenesis, sphaleron solution, one loop finite temperature effective potential and dynamics of bubble nucleation. |
1609.01868 | Soumya Chakrabarti | Soumya Chakrabarti and Narayan Banerjee | Scalar field collapse in a conformally flat spacetime | 14 pages, 3 figures | null | 10.1140/epjc/s10052-017-4740-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The collapse scenario of a scalar field along with a perfect fluid
distribution is investigated for a conformally flat spacetime. The theorem for
the integrability of an anharmonic oscillator has been utilized. For a pure
power law potential of the form ${\phi}^{n+1}$, it is found that a central
singularity is formed which is covered by an apparent horizon for $n>0$ and
$n<-3$. Some numerical results have also been presented for a combination of
two different powers of $\phi$ in the potential.
| [
{
"created": "Wed, 7 Sep 2016 08:11:51 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Feb 2017 07:46:02 GMT",
"version": "v2"
}
] | 2017-04-05 | [
[
"Chakrabarti",
"Soumya",
""
],
[
"Banerjee",
"Narayan",
""
]
] | The collapse scenario of a scalar field along with a perfect fluid distribution is investigated for a conformally flat spacetime. The theorem for the integrability of an anharmonic oscillator has been utilized. For a pure power law potential of the form ${\phi}^{n+1}$, it is found that a central singularity is formed which is covered by an apparent horizon for $n>0$ and $n<-3$. Some numerical results have also been presented for a combination of two different powers of $\phi$ in the potential. |
1906.03630 | Edward Anderson | Edward Anderson | A Local Resolution of the Problem of Time. V. Combining Temporal and
Configurational Relationalism for Finite Theories | 18 pages including 4 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | As we have known comprehensively since the early 1990's works of Isham and
Kucha\v{r}, The Problem of Time mostly concerns interferences between its many
facets. Having introduced the local facets in Articles I to IV, we now show how
Article I's approach to Temporal Relationalism can be combined with Article
II's to Configurational Relationalism. This requires reformulating some of the
Principles of Dynamics to be Temporal Relationalism implementing, a strategy
which we follow through in each subsequent Article. All in all, around half of
the Principles of Dynamics needs to be rewritten to solve this noted,
50-year-old and hitherto unresolved foundational problem. This stands as
sufficient reason to render new resultant Principles of Dynamics - `TRiPoD' - a
significant and worthwhile development of the Principles of Dynamics. This
amounts to taking Jacobi's action principle more seriously than Jacobi himself
did, or any authors in between: to constitute a new starting point for the
entirety of the Principles of Dynamics is to be reworked. This can moreover be
viewed as a mild recategorization necessitated by the Problem of Time. While
mathematically simple to carry out, it requires quite a lot of conceptual
developments, by which it is both prudent and useful exposition to present this
first for finite rather than Field Theoretic examples in the current Article.
Article VI then extends this approach to Field Theory and GR.
| [
{
"created": "Sun, 9 Jun 2019 12:54:38 GMT",
"version": "v1"
}
] | 2019-06-11 | [
[
"Anderson",
"Edward",
""
]
] | As we have known comprehensively since the early 1990's works of Isham and Kucha\v{r}, The Problem of Time mostly concerns interferences between its many facets. Having introduced the local facets in Articles I to IV, we now show how Article I's approach to Temporal Relationalism can be combined with Article II's to Configurational Relationalism. This requires reformulating some of the Principles of Dynamics to be Temporal Relationalism implementing, a strategy which we follow through in each subsequent Article. All in all, around half of the Principles of Dynamics needs to be rewritten to solve this noted, 50-year-old and hitherto unresolved foundational problem. This stands as sufficient reason to render new resultant Principles of Dynamics - `TRiPoD' - a significant and worthwhile development of the Principles of Dynamics. This amounts to taking Jacobi's action principle more seriously than Jacobi himself did, or any authors in between: to constitute a new starting point for the entirety of the Principles of Dynamics is to be reworked. This can moreover be viewed as a mild recategorization necessitated by the Problem of Time. While mathematically simple to carry out, it requires quite a lot of conceptual developments, by which it is both prudent and useful exposition to present this first for finite rather than Field Theoretic examples in the current Article. Article VI then extends this approach to Field Theory and GR. |
1006.5747 | Marcelo Salgado | Luisa G. Jaime, Leonardo Patino, and Marcelo Salgado | Robust approach to f(R) gravity | 5 pages; 2 figures (4 panels); minor corrections to match the
published version; panel added | Phys.Rev.D83:024039,2011 | 10.1103/PhysRevD.83.024039 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider metric f(R) theories of gravity without mapping them to their
scalar-tensor counterpart, but using the Ricci scalar itself as an "extra"
degree of freedom. This approach avoids then the introduction of a scalar-field
potential that might be ill defined (not single valued). In order to explicitly
show the usefulness of this method, we focus on static and spherically
symmetric spacetimes and deal with the recent controversy about the existence
of extended relativistic objects in certain class of f(R) models.
| [
{
"created": "Wed, 30 Jun 2010 00:14:20 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Oct 2010 00:06:11 GMT",
"version": "v2"
},
{
"created": "Mon, 31 Jan 2011 23:27:02 GMT",
"version": "v3"
}
] | 2011-02-15 | [
[
"Jaime",
"Luisa G.",
""
],
[
"Patino",
"Leonardo",
""
],
[
"Salgado",
"Marcelo",
""
]
] | We consider metric f(R) theories of gravity without mapping them to their scalar-tensor counterpart, but using the Ricci scalar itself as an "extra" degree of freedom. This approach avoids then the introduction of a scalar-field potential that might be ill defined (not single valued). In order to explicitly show the usefulness of this method, we focus on static and spherically symmetric spacetimes and deal with the recent controversy about the existence of extended relativistic objects in certain class of f(R) models. |
1807.00724 | Emanuel Gallo | Gabriel Crisnejo, Emanuel Gallo and Adam Rogers | Finite distance corrections to the light deflection in a gravitational
field with a plasma medium | 31 pages. Substantial additions. New section added, new theorem
proved and a broader discussion on the deflection of light in the extended
solar corona plasma model | Phys. Rev. D 99, 124001 (2019) | 10.1103/PhysRevD.99.124001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The aim of the present work is twofold: first, we present general remarks
about the application of recent procedures to compute the deflection angle in
spherically symmetric and asymptotically flat spacetimes, taking into account
finite distance corrections based on the Gauss-Bonnet theorem. Second, and as
the main part of our work, we apply this powerful technique to compute
corrections to the deflection angle produced by astrophysical configurations in
the weak gravitational regime when a plasma medium is taken into account. For
applications, we use these methods to introduce new general formulae for the
bending angle of light rays in plasma environments in different astrophysical
scenarios, generalizing previously known results. We also present new and
useful formulae for the separation angle between the images of two sources when
they are lensed by an astrophysical object surrounded by plasma. In particular,
for the case of an homogeneous plasma we study these corrections for the case
of light rays propagating near astrophysical objects described in the weak
gravitational regime by a Parametrized-Post-Newtonian (PPN) metric which takes
into account the mass of the objects and a possible quadrupole moment. Even
when our work concentrates on finite distances corrections to the deflection
angle, we also obtain as particular cases of our expressions new formulae which
are valid for the more common assumption of infinite distance between receiver,
lens and source. We also consider the presence of an inhomogeneous plasma media
introducing as particular cases of our general results explicit expressions for
particular charge number density profiles.
| [
{
"created": "Mon, 2 Jul 2018 15:00:12 GMT",
"version": "v1"
},
{
"created": "Tue, 3 Jul 2018 23:20:42 GMT",
"version": "v2"
},
{
"created": "Tue, 21 Aug 2018 20:21:58 GMT",
"version": "v3"
},
{
"created": "Thu, 6 Sep 2018 17:28:01 GMT",
"version": "v4"
},
{
"crea... | 2019-06-12 | [
[
"Crisnejo",
"Gabriel",
""
],
[
"Gallo",
"Emanuel",
""
],
[
"Rogers",
"Adam",
""
]
] | The aim of the present work is twofold: first, we present general remarks about the application of recent procedures to compute the deflection angle in spherically symmetric and asymptotically flat spacetimes, taking into account finite distance corrections based on the Gauss-Bonnet theorem. Second, and as the main part of our work, we apply this powerful technique to compute corrections to the deflection angle produced by astrophysical configurations in the weak gravitational regime when a plasma medium is taken into account. For applications, we use these methods to introduce new general formulae for the bending angle of light rays in plasma environments in different astrophysical scenarios, generalizing previously known results. We also present new and useful formulae for the separation angle between the images of two sources when they are lensed by an astrophysical object surrounded by plasma. In particular, for the case of an homogeneous plasma we study these corrections for the case of light rays propagating near astrophysical objects described in the weak gravitational regime by a Parametrized-Post-Newtonian (PPN) metric which takes into account the mass of the objects and a possible quadrupole moment. Even when our work concentrates on finite distances corrections to the deflection angle, we also obtain as particular cases of our expressions new formulae which are valid for the more common assumption of infinite distance between receiver, lens and source. We also consider the presence of an inhomogeneous plasma media introducing as particular cases of our general results explicit expressions for particular charge number density profiles. |
2009.06580 | Abhijit Chakraborty | H. E. Camblong, A. Chakraborty, C. R. Ordonez | Near-horizon aspects of acceleration radiation by free fall of an atom
into a black hole | 23 pages, 2 figures, Accepted to be published in PRD | Phys. Rev. D 102, 085010 (2020) | 10.1103/PhysRevD.102.085010 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A two-level atom freely falling towards a Schwarzschild black hole was
recently shown to detect radiation in the Boulware vacuum in an insightful
paper [M. O. Scully et al., Proc. Natl. Acad. Sci. U.S.A. 115, 8131 (2018)].
The two-state atom acts as a dipole detector and its interaction with the field
can be modeled using a quantum optics approach. The relative acceleration
between the scalar field and the detector causes the atom to detect the
radiation. In this paper, we show that this acceleration radiation is driven by
the near-horizon physics of the black hole. This insight reinforces the
relevance of near-horizon conformal quantum mechanics for all the physics
associated with the thermodynamic properties of the black hole. We additionally
highlight the conformal aspects of the radiation that is given by a Planck
distribution with the Hawking temperature.
| [
{
"created": "Mon, 14 Sep 2020 17:11:14 GMT",
"version": "v1"
}
] | 2020-10-28 | [
[
"Camblong",
"H. E.",
""
],
[
"Chakraborty",
"A.",
""
],
[
"Ordonez",
"C. R.",
""
]
] | A two-level atom freely falling towards a Schwarzschild black hole was recently shown to detect radiation in the Boulware vacuum in an insightful paper [M. O. Scully et al., Proc. Natl. Acad. Sci. U.S.A. 115, 8131 (2018)]. The two-state atom acts as a dipole detector and its interaction with the field can be modeled using a quantum optics approach. The relative acceleration between the scalar field and the detector causes the atom to detect the radiation. In this paper, we show that this acceleration radiation is driven by the near-horizon physics of the black hole. This insight reinforces the relevance of near-horizon conformal quantum mechanics for all the physics associated with the thermodynamic properties of the black hole. We additionally highlight the conformal aspects of the radiation that is given by a Planck distribution with the Hawking temperature. |
1512.03010 | Elizabeth Winstanley | Ben L. Shepherd and Elizabeth Winstanley | Dyons and dyonic black holes in ${\mathfrak {su}}(N)$
Einstein-Yang-Mills theory in anti-de Sitter space-time | 18 pages, 16 figures, minor revisions, references added, accepted for
publication in Physical Review D | Phys. Rev. D 93, 064064 (2016) | 10.1103/PhysRevD.93.064064 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present new spherically symmetric, dyonic soliton and black hole solutions
of the ${\mathfrak {su}}(N)$ Einstein-Yang-Mills equations in four-dimensional
asymptotically anti-de Sitter space-time. The gauge field has nontrivial
electric and magnetic components and is described by $N-1$ magnetic gauge field
functions and $N-1$ electric gauge field functions. We explore the phase space
of solutions in detail for ${\mathfrak {su}}(2)$ and ${\mathfrak {su}}(3)$
gauge groups. Combinations of the electric gauge field functions are monotonic
and have no zeros; in general the magnetic gauge field functions may have
zeros. The phase space of solutions is extremely rich, and we find solutions in
which the magnetic gauge field functions have more than fifty zeros. Of
particular interest are solutions for which the magnetic gauge field functions
have no zeros, which exist when the negative cosmological constant has
sufficiently large magnitude. We conjecture that at least some of these
nodeless solutions may be stable under linear, spherically symmetric,
perturbations.
| [
{
"created": "Wed, 9 Dec 2015 19:39:37 GMT",
"version": "v1"
},
{
"created": "Mon, 21 Mar 2016 03:04:27 GMT",
"version": "v2"
}
] | 2016-03-30 | [
[
"Shepherd",
"Ben L.",
""
],
[
"Winstanley",
"Elizabeth",
""
]
] | We present new spherically symmetric, dyonic soliton and black hole solutions of the ${\mathfrak {su}}(N)$ Einstein-Yang-Mills equations in four-dimensional asymptotically anti-de Sitter space-time. The gauge field has nontrivial electric and magnetic components and is described by $N-1$ magnetic gauge field functions and $N-1$ electric gauge field functions. We explore the phase space of solutions in detail for ${\mathfrak {su}}(2)$ and ${\mathfrak {su}}(3)$ gauge groups. Combinations of the electric gauge field functions are monotonic and have no zeros; in general the magnetic gauge field functions may have zeros. The phase space of solutions is extremely rich, and we find solutions in which the magnetic gauge field functions have more than fifty zeros. Of particular interest are solutions for which the magnetic gauge field functions have no zeros, which exist when the negative cosmological constant has sufficiently large magnitude. We conjecture that at least some of these nodeless solutions may be stable under linear, spherically symmetric, perturbations. |
1811.03369 | Alessio Baldazzi | Alessio Baldazzi, Roberto Percacci and Vedran Skrinjar | Wicked metrics | null | null | 10.1088/1361-6382/ab187d | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There are various ways of defining the Wick rotation in a gravitational
context. There are good arguments to view it as an analytic continuation of the
metric, instead of the coordinates. We focus on one very general definition and
argue that it is incompatible with the requirement of preserving the field
equations and the symmetries at global level: in some cases the Euclidean
metric cannot be defined on the original Lorentzian manifold but only on a
submanifold. This phenomenon is related to the existence of horizons, as
illustrated in the cases of the de Sitter and Schwarzschild metrics.
| [
{
"created": "Thu, 8 Nov 2018 11:55:05 GMT",
"version": "v1"
}
] | 2019-05-22 | [
[
"Baldazzi",
"Alessio",
""
],
[
"Percacci",
"Roberto",
""
],
[
"Skrinjar",
"Vedran",
""
]
] | There are various ways of defining the Wick rotation in a gravitational context. There are good arguments to view it as an analytic continuation of the metric, instead of the coordinates. We focus on one very general definition and argue that it is incompatible with the requirement of preserving the field equations and the symmetries at global level: in some cases the Euclidean metric cannot be defined on the original Lorentzian manifold but only on a submanifold. This phenomenon is related to the existence of horizons, as illustrated in the cases of the de Sitter and Schwarzschild metrics. |
2311.07900 | Dmitry Korotkin | Dmitry Korotkin and Henning Samtleben | Integrability and Einstein's Equations | null | null | null | null | gr-qc hep-th math-ph math.MP nlin.SI | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Integrable structures arise in general relativity when the spacetime
possesses a pair of commuting Killing vectors admitting 2-spaces orthogonal to
the group orbits. The physical interpretation of such spacetimes depends on the
norm of the Killing vectors. They include stationary axisymmetric spacetimes,
Einstein-Rosen waves with two polarizations, Gowdy models, and colliding plane
gravitational waves.
We review the general formalism of linear systems with variable spectral
parameter, solution generating techniques, and various classes of exact
solutions. In the case of the Einstein-Rosen waves, we also discuss the Poisson
algebra of charges and its quantization.
This is an invited contribution to the 2nd edition of the Encyclopedia of
Mathematical Physics.
| [
{
"created": "Tue, 14 Nov 2023 04:19:33 GMT",
"version": "v1"
}
] | 2023-11-17 | [
[
"Korotkin",
"Dmitry",
""
],
[
"Samtleben",
"Henning",
""
]
] | Integrable structures arise in general relativity when the spacetime possesses a pair of commuting Killing vectors admitting 2-spaces orthogonal to the group orbits. The physical interpretation of such spacetimes depends on the norm of the Killing vectors. They include stationary axisymmetric spacetimes, Einstein-Rosen waves with two polarizations, Gowdy models, and colliding plane gravitational waves. We review the general formalism of linear systems with variable spectral parameter, solution generating techniques, and various classes of exact solutions. In the case of the Einstein-Rosen waves, we also discuss the Poisson algebra of charges and its quantization. This is an invited contribution to the 2nd edition of the Encyclopedia of Mathematical Physics. |
1911.11495 | Salah Nasri | Hemza Azri and Salah Nasri | Entropy Production in Affine Inflation | To appear in PRD | Phys. Rev. D 101, 064073 (2020) | 10.1103/PhysRevD.101.064073 | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Multiple scalar fields nonminimally interacting through pure affine gravity
are considered to generate primordial perturbations during an inflationary
phase. The couplings considered give rise to two distinct sources of entropy
perturbations that may not be suppressed in the long wavelength limit. The
first is merely induced by the presence of more than one scalar and arises even
in the minimal coupling limit. The second source however is restricted to
nonminimal interaction. Unlike the case of metric gravity, and due to the
absence of anisotropic stresses, the second source disappears for single
scalar, showing that nonminimal couplings become relevant to non-adiabatic
perturbations only when more than one scalar field are considered. Hence the
notion of adiabaticity is not affected by the transition to minimal coupling
contrary to the metric gravity case where it is confused by changing the
frames. Precise data that might be able to neatly track different sources of
isocurvature modes, if any, must not only distinguish between different models
of inflation but also determine the most viable approach to gravity which
underlies the inflationary dynamics itself.
| [
{
"created": "Tue, 26 Nov 2019 12:31:56 GMT",
"version": "v1"
},
{
"created": "Sat, 14 Mar 2020 08:14:26 GMT",
"version": "v2"
}
] | 2020-04-02 | [
[
"Azri",
"Hemza",
""
],
[
"Nasri",
"Salah",
""
]
] | Multiple scalar fields nonminimally interacting through pure affine gravity are considered to generate primordial perturbations during an inflationary phase. The couplings considered give rise to two distinct sources of entropy perturbations that may not be suppressed in the long wavelength limit. The first is merely induced by the presence of more than one scalar and arises even in the minimal coupling limit. The second source however is restricted to nonminimal interaction. Unlike the case of metric gravity, and due to the absence of anisotropic stresses, the second source disappears for single scalar, showing that nonminimal couplings become relevant to non-adiabatic perturbations only when more than one scalar field are considered. Hence the notion of adiabaticity is not affected by the transition to minimal coupling contrary to the metric gravity case where it is confused by changing the frames. Precise data that might be able to neatly track different sources of isocurvature modes, if any, must not only distinguish between different models of inflation but also determine the most viable approach to gravity which underlies the inflationary dynamics itself. |
2109.11476 | David Prinz | David Prinz and Alexander Schmeding | Lie Theory for Asymptotic Symmetries in General Relativity: The NU Group | 37 pages, article; minor revisions; version to appear in Classical
and Quantum Gravity | Class. Quantum Grav. 39 (2022) 155005 | 10.1088/1361-6382/ac776c | null | gr-qc math-ph math.GR math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the Newman--Unti (NU) group from the viewpoint of
infinite-dimensional geometry. The NU group is a topological group in a natural
coarse topology, but it does not become a manifold and hence a Lie group in
this topology. To obtain a manifold structure we consider a finer Whitney-type
topology. This turns the unit component of the NU group into an
infinite-dimensional Lie group. We then study the Lie theoretic properties of
this group. Surprisingly, the group operations of the full NU group become
discontinuous, whence the NU group does not support a Lie group structure. The
NU group contains the Bondi--Metzner--Sachs (BMS) group as a subgroup, whose
Lie group structure was constructed in a previous article. It is well known
that the NU Lie algebra splits into a direct sum of Lie ideals of the Lie
algebras of the BMS group and conformal rescalings of scri. However, the lack
of a Lie group structure on the NU group implies that the BMS group cannot be
embedded as a Lie subgroup therein.
| [
{
"created": "Thu, 23 Sep 2021 16:30:00 GMT",
"version": "v1"
},
{
"created": "Sun, 26 Sep 2021 09:33:22 GMT",
"version": "v2"
},
{
"created": "Wed, 29 Jun 2022 16:30:01 GMT",
"version": "v3"
}
] | 2022-07-11 | [
[
"Prinz",
"David",
""
],
[
"Schmeding",
"Alexander",
""
]
] | We study the Newman--Unti (NU) group from the viewpoint of infinite-dimensional geometry. The NU group is a topological group in a natural coarse topology, but it does not become a manifold and hence a Lie group in this topology. To obtain a manifold structure we consider a finer Whitney-type topology. This turns the unit component of the NU group into an infinite-dimensional Lie group. We then study the Lie theoretic properties of this group. Surprisingly, the group operations of the full NU group become discontinuous, whence the NU group does not support a Lie group structure. The NU group contains the Bondi--Metzner--Sachs (BMS) group as a subgroup, whose Lie group structure was constructed in a previous article. It is well known that the NU Lie algebra splits into a direct sum of Lie ideals of the Lie algebras of the BMS group and conformal rescalings of scri. However, the lack of a Lie group structure on the NU group implies that the BMS group cannot be embedded as a Lie subgroup therein. |
1908.08599 | Kamran Derakhshani | Kamran Derakhshani | Black Body Radiation in Moving Frames | arXiv admin note: The authorship for this submission is currently in
dispute | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The problem of black body radiation, when measured by a moving observer, has
a pivotal role in relativistic thermodynamics. Mutually, it depends on the
thermodynamical definition of the thermal equilibrium and temperature of moving
bodies, i.e. under a Lorentz transformation, and also in a gravitational field.
Surprisingly, even after more than a century, relativistic thermodynamics is
not a mature theory and is still an open problem without a consensus. This
article is a brief review of the evolution of this theory with a special focus
on the black body radiation in moving frames. As an application, we use the
results in the most interesting topics of the quantum field theory in curved
space: Hawking radiation, and Unruh effect.
| [
{
"created": "Thu, 22 Aug 2019 21:12:18 GMT",
"version": "v1"
}
] | 2019-09-26 | [
[
"Derakhshani",
"Kamran",
""
]
] | The problem of black body radiation, when measured by a moving observer, has a pivotal role in relativistic thermodynamics. Mutually, it depends on the thermodynamical definition of the thermal equilibrium and temperature of moving bodies, i.e. under a Lorentz transformation, and also in a gravitational field. Surprisingly, even after more than a century, relativistic thermodynamics is not a mature theory and is still an open problem without a consensus. This article is a brief review of the evolution of this theory with a special focus on the black body radiation in moving frames. As an application, we use the results in the most interesting topics of the quantum field theory in curved space: Hawking radiation, and Unruh effect. |
1611.07192 | Martin Zofka | Ji\v{r}\'i Ryzner, Martin \v{Z}ofka | Extremally charged line | 16 pages, 7 figures | Class. Quant. Gravity 33 (2016) 245005 | 10.1088/0264-9381/33/24/245005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the properties of a static, cylindrically symmetric
Majumdar-Papapetrou-type solution of Einstein-Maxwell equations. We locate its
singularities, establish its algebraic type, find its asymptotic properties and
weak-field limit, study the structure of electrogeodesics, and determine the
mass and charge of its sources. We provide an interpretation of the spacetime
and discuss the parameter appearing in the metric.
| [
{
"created": "Tue, 22 Nov 2016 08:26:11 GMT",
"version": "v1"
}
] | 2016-12-07 | [
[
"Ryzner",
"Jiří",
""
],
[
"Žofka",
"Martin",
""
]
] | We investigate the properties of a static, cylindrically symmetric Majumdar-Papapetrou-type solution of Einstein-Maxwell equations. We locate its singularities, establish its algebraic type, find its asymptotic properties and weak-field limit, study the structure of electrogeodesics, and determine the mass and charge of its sources. We provide an interpretation of the spacetime and discuss the parameter appearing in the metric. |
1612.05830 | Dan Vollick | Dan N. Vollick | Null Surfaces in Static Space-times | null | European Physics Journal Plus 130, 157 (2015) | 10.1140/epjp/i2015-15157-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper I consider surfaces in a space-time with a Killing vector
$\xi^{\alpha}$ that is time-like and hypersurface orthogonal on one side of the
surface. The Killing vector may be either time-like or space-like on the other
side of the surface. It has been argued that the surface is null if
$\xi_{\alpha}\xi^{\alpha}\rightarrow 0$ as the surface is approached from the
static region. This implies that, in a coordinate system adapted to $\xi$,
surfaces with $g_{tt}=0$ are null. In spherically symmetric space-times the
condition $g^{rr}=0$ instead of $g_{tt}=0$ is sometimes used to locate null
surfaces.
In this paper I examine the arguments that lead to these two different
criteria and show that both arguments are incorrect. A surface $\xi=$ constant
has a normal vector whose norm is proportional to $\xi_{\alpha}\xi^{\alpha}$.
This lead to the conclusion that surfaces with $\xi_{\alpha}\xi^{\alpha}=0$ are
null. However, the proportionality factor generally diverges when $g_{tt}=0$,
leading to a different condition for the norm to be null. In static spherically
symmetric space-times this condition gives $g^{rr}=0$, not $g_{tt}=0$.
The problem with the condition $g^{rr}=0$ is that the coordinate system is
singular on the surface. One can either use a nonsingular coordinate system or
examine the induced metric on the surface to determine if it is null. By using
these approaches it is shown that the correct criteria is $g_{tt}=0$. I also
examine the condition required for the surface to be nonsingular.
| [
{
"created": "Sat, 17 Dec 2016 22:18:14 GMT",
"version": "v1"
}
] | 2016-12-20 | [
[
"Vollick",
"Dan N.",
""
]
] | In this paper I consider surfaces in a space-time with a Killing vector $\xi^{\alpha}$ that is time-like and hypersurface orthogonal on one side of the surface. The Killing vector may be either time-like or space-like on the other side of the surface. It has been argued that the surface is null if $\xi_{\alpha}\xi^{\alpha}\rightarrow 0$ as the surface is approached from the static region. This implies that, in a coordinate system adapted to $\xi$, surfaces with $g_{tt}=0$ are null. In spherically symmetric space-times the condition $g^{rr}=0$ instead of $g_{tt}=0$ is sometimes used to locate null surfaces. In this paper I examine the arguments that lead to these two different criteria and show that both arguments are incorrect. A surface $\xi=$ constant has a normal vector whose norm is proportional to $\xi_{\alpha}\xi^{\alpha}$. This lead to the conclusion that surfaces with $\xi_{\alpha}\xi^{\alpha}=0$ are null. However, the proportionality factor generally diverges when $g_{tt}=0$, leading to a different condition for the norm to be null. In static spherically symmetric space-times this condition gives $g^{rr}=0$, not $g_{tt}=0$. The problem with the condition $g^{rr}=0$ is that the coordinate system is singular on the surface. One can either use a nonsingular coordinate system or examine the induced metric on the surface to determine if it is null. By using these approaches it is shown that the correct criteria is $g_{tt}=0$. I also examine the condition required for the surface to be nonsingular. |
2004.06605 | Tiberiu Harko | Bruno J. Barros, Bogdan D\v{a}nil\v{a}, Tiberiu Harko, Francisco S. N.
Lobo | Black hole and naked singularity geometries supported by three-form
fields | 19 pages, 22 figures; minor modifications, accepted for publication
in EPJC | Eur. Phys. J. C 80, 617 (2020) | 10.1140/epjc/s10052-020-8178-1 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate static and spherically symmetric solutions in a gravity theory
that extends the standard Hilbert-Einstein action with a Lagrangian constructed
from a three-form field $A_{\alpha \beta \gamma}$, which is related to the
field strength and a potential term. The field equations are derived from a
variational principle and are obtained explicitly for a static and spherically
symmetric geometry in vacuum. For the case of the vanishing three-form field
potential the gravitational field equations can be solved exactly. However, for
arbitrary potentials, due to their mathematical complexity, numerical
approaches are adopted in studying the behavior of the metric functions and the
three-form field. To this effect, the field equations are reformulated in a
dimensionless form and are solved numerically by introducing a suitable
independent radial coordinate. We detect the formation of a black hole from the
presence of a Killing horizon for the time-like Killing vector in the metric
tensor components. Several models, corresponding to different functional forms
of the three-field potential, namely, the Higgs and exponential type, are
considered. In particular, naked singularity solutions are also obtained for
the exponential potential case. Finally, the thermodynamic properties of these
black hole solutions, such as the horizon temperature, specific heat, entropy
and evaporation time due to the Hawking luminosity, are also investigated in
detail.
| [
{
"created": "Tue, 14 Apr 2020 15:40:04 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Jun 2020 09:39:32 GMT",
"version": "v2"
}
] | 2020-07-15 | [
[
"Barros",
"Bruno J.",
""
],
[
"Dǎnilǎ",
"Bogdan",
""
],
[
"Harko",
"Tiberiu",
""
],
[
"Lobo",
"Francisco S. N.",
""
]
] | We investigate static and spherically symmetric solutions in a gravity theory that extends the standard Hilbert-Einstein action with a Lagrangian constructed from a three-form field $A_{\alpha \beta \gamma}$, which is related to the field strength and a potential term. The field equations are derived from a variational principle and are obtained explicitly for a static and spherically symmetric geometry in vacuum. For the case of the vanishing three-form field potential the gravitational field equations can be solved exactly. However, for arbitrary potentials, due to their mathematical complexity, numerical approaches are adopted in studying the behavior of the metric functions and the three-form field. To this effect, the field equations are reformulated in a dimensionless form and are solved numerically by introducing a suitable independent radial coordinate. We detect the formation of a black hole from the presence of a Killing horizon for the time-like Killing vector in the metric tensor components. Several models, corresponding to different functional forms of the three-field potential, namely, the Higgs and exponential type, are considered. In particular, naked singularity solutions are also obtained for the exponential potential case. Finally, the thermodynamic properties of these black hole solutions, such as the horizon temperature, specific heat, entropy and evaporation time due to the Hawking luminosity, are also investigated in detail. |
1303.1135 | Adam Chudecki Dr | Adam Chudecki and Maciej Przanowski | Killing Symmetries in $\mathcal{H}$-Spaces with $\Lambda$ | null | Jouournal of Mathematical Physics, 54, 102503, (2013) | 10.1063/1.4826346 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | All Killing symmetries in complex $\mathcal{H}$-spaces with $\Lambda$ in
terms of the Pleba\'nski - Robinson - Finley coordinate system are found. All
$\mathcal{H}$-metrics with $\Lambda$ admitting a null Killing vector are
explicitly given. It is shown that the problem of non-null Killing vector
reduces to looking for solution of the Boyer - Finley - Pleba\'nski (Toda
field) equation
| [
{
"created": "Tue, 5 Mar 2013 18:38:49 GMT",
"version": "v1"
}
] | 2013-10-28 | [
[
"Chudecki",
"Adam",
""
],
[
"Przanowski",
"Maciej",
""
]
] | All Killing symmetries in complex $\mathcal{H}$-spaces with $\Lambda$ in terms of the Pleba\'nski - Robinson - Finley coordinate system are found. All $\mathcal{H}$-metrics with $\Lambda$ admitting a null Killing vector are explicitly given. It is shown that the problem of non-null Killing vector reduces to looking for solution of the Boyer - Finley - Pleba\'nski (Toda field) equation |
2107.09578 | Parthapratim Pradhan | Parthapratim Pradhan | Energy Formula for Newman-Unti-Tamburino class of Black Holes | Accepted in General Relativity and Gravitation~(Letter) | Gen. Relativ. Gravit. 53, 69 (2021) | 10.1007/s10714-021-02836-w | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We compute the \emph{surface energy~(${\cal E}_{s}^{\pm}$), the rotational
energy~(${\cal E}_{r}^{\pm}$) and the electromagnetic energy~(${\cal
E}_{em}^{\pm}$)} for Newman-Unti-Tamburino~(NUT) class of black hole having the
event horizon~(${\cal H}^{+}$) and the Cauchy horizon~(${\cal H}^{-}$).
Remarkably, we find that the \emph{mass parameter can be expressed as sum of
three energies i. e. $M={\cal E}_{s}^{\pm}+{\cal E}_{r}^{\pm}+{\cal
E}_{em}^{\pm}$}. It has been \emph{tested} for Taub-NUT black hole,
Reissner-Nordstr\"{o}m-Taub-NUT black hole, Kerr-Taub-NUT black hole and
Kerr-Newman-Taub-NUT black hole. In each case of black hole, we find that
\emph{the sum of these energies is equal to the Komar mass}. It is plausible
only due to the introduction of new conserved charges i.e. $J_{N}=M\,N$~(where
$M=m$ is the Komar mass and $N=n$ is the gravitomagnetic charge), which is
closely analogue to the Kerr-like angular momentum parameter $J=a\,M$.
| [
{
"created": "Tue, 20 Jul 2021 15:47:41 GMT",
"version": "v1"
}
] | 2021-07-21 | [
[
"Pradhan",
"Parthapratim",
""
]
] | We compute the \emph{surface energy~(${\cal E}_{s}^{\pm}$), the rotational energy~(${\cal E}_{r}^{\pm}$) and the electromagnetic energy~(${\cal E}_{em}^{\pm}$)} for Newman-Unti-Tamburino~(NUT) class of black hole having the event horizon~(${\cal H}^{+}$) and the Cauchy horizon~(${\cal H}^{-}$). Remarkably, we find that the \emph{mass parameter can be expressed as sum of three energies i. e. $M={\cal E}_{s}^{\pm}+{\cal E}_{r}^{\pm}+{\cal E}_{em}^{\pm}$}. It has been \emph{tested} for Taub-NUT black hole, Reissner-Nordstr\"{o}m-Taub-NUT black hole, Kerr-Taub-NUT black hole and Kerr-Newman-Taub-NUT black hole. In each case of black hole, we find that \emph{the sum of these energies is equal to the Komar mass}. It is plausible only due to the introduction of new conserved charges i.e. $J_{N}=M\,N$~(where $M=m$ is the Komar mass and $N=n$ is the gravitomagnetic charge), which is closely analogue to the Kerr-like angular momentum parameter $J=a\,M$. |
gr-qc/0702030 | Abhay Ashtekar | Abhay Ashtekar | An Introduction to Loop Quantum Gravity Through Cosmology | 20 pages, 4 figures, Introductory Review. Section IV expanded and
references added | Nuovo Cim.B122:135-155,2007 | 10.1393/ncb/i2007-10351-5 | IGPG-07/01-02, NSF-KITP-07-05 | gr-qc | null | This introductory review is addressed to beginning researchers. Some of the
distinguishing features of loop quantum gravity are illustrated through loop
quantum cosmology of FRW models. In particular, these examples illustrate: i)
how `emergent time' can arise; ii) how the technical issue of solving the
Hamiltonian constraint and constructing the \emph{physical} sector of the
theory can be handled; iii) how questions central to the Planck scale physics
can be answered using such a framework; and, iv) how quantum geometry effects
can dramatically change physics near singularities and yet naturally turn
themselves off and reproduce classical general relativity when space-time
curvature is significantly weaker than the Planck scale.
| [
{
"created": "Mon, 5 Feb 2007 22:26:44 GMT",
"version": "v1"
},
{
"created": "Tue, 15 May 2007 19:33:18 GMT",
"version": "v2"
}
] | 2010-11-11 | [
[
"Ashtekar",
"Abhay",
""
]
] | This introductory review is addressed to beginning researchers. Some of the distinguishing features of loop quantum gravity are illustrated through loop quantum cosmology of FRW models. In particular, these examples illustrate: i) how `emergent time' can arise; ii) how the technical issue of solving the Hamiltonian constraint and constructing the \emph{physical} sector of the theory can be handled; iii) how questions central to the Planck scale physics can be answered using such a framework; and, iv) how quantum geometry effects can dramatically change physics near singularities and yet naturally turn themselves off and reproduce classical general relativity when space-time curvature is significantly weaker than the Planck scale. |
1104.2910 | Daniele Regoli | Daniele Regoli | The relation between Geometry and Matter in classical and quantum
Gravity and Cosmology | PhD thesis, 179 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The present thesis is divided into two main research areas: Classical
Cosmology and (Loop) Quantum Gravity. The first part concerns cosmological
models with one phantom and one scalar field, that provide the
`super-accelerated' scenario not excluded by observations, thus exploring
alternatives to the standard LambdaCDM scenario. The second part concerns the
spinfoam approach to (Loop) Quantum Gravity, which is an attempt to provide a
`sum-over-histories' formulation of gravitational quantum transition
amplitudes: the research here presented focuses on the face amplitude of a
generic spinfoam model for Quantum Gravity.
| [
{
"created": "Thu, 14 Apr 2011 20:08:44 GMT",
"version": "v1"
},
{
"created": "Mon, 18 Apr 2011 12:47:27 GMT",
"version": "v2"
}
] | 2015-03-19 | [
[
"Regoli",
"Daniele",
""
]
] | The present thesis is divided into two main research areas: Classical Cosmology and (Loop) Quantum Gravity. The first part concerns cosmological models with one phantom and one scalar field, that provide the `super-accelerated' scenario not excluded by observations, thus exploring alternatives to the standard LambdaCDM scenario. The second part concerns the spinfoam approach to (Loop) Quantum Gravity, which is an attempt to provide a `sum-over-histories' formulation of gravitational quantum transition amplitudes: the research here presented focuses on the face amplitude of a generic spinfoam model for Quantum Gravity. |
0706.0115 | Ouali Taoufik | A. Errahmani, T. Ouali | Late time acceleration in 3-brane Brans-Dicke cosmology | null | Mod.Phys.Lett.A23:3095-3111,2008 | 10.1142/S0217732308026881 | null | gr-qc | null | In order to investigate more features of the Brans-Dicke cosmology in the
five-dimensional space-time, we explore the solutions of its dynamiacal
systems. A behavior of the universe in its early and late time by means of the
scale factor is considered. As a results, we show that it is possible to avoid
the big rip singularity and to cross the phantom divide line. Furthermore, we
review the dark energy component of the universe and its agreement with the
observation data for this 3-brane Brans Dicke cosmology by means of the
cosmological parameters.
| [
{
"created": "Fri, 1 Jun 2007 10:17:48 GMT",
"version": "v1"
},
{
"created": "Sat, 19 Jan 2008 08:30:21 GMT",
"version": "v2"
},
{
"created": "Tue, 11 Mar 2008 21:18:11 GMT",
"version": "v3"
}
] | 2008-12-25 | [
[
"Errahmani",
"A.",
""
],
[
"Ouali",
"T.",
""
]
] | In order to investigate more features of the Brans-Dicke cosmology in the five-dimensional space-time, we explore the solutions of its dynamiacal systems. A behavior of the universe in its early and late time by means of the scale factor is considered. As a results, we show that it is possible to avoid the big rip singularity and to cross the phantom divide line. Furthermore, we review the dark energy component of the universe and its agreement with the observation data for this 3-brane Brans Dicke cosmology by means of the cosmological parameters. |
1603.04732 | Simon Garruto | Lorenzo Fatibene, Simon Garruto | Principal Symbol of Euler-Lagrange Operators | Some improvements | null | 10.1088/0264-9381/33/14/145012 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We shall introduce the principal symbol for Euler-Lagrange operators and use
them to charac- terise well-posed initial value problems. We shall clarify how
constraints can arise in Lagrangian covariant theories by extending the
standard treatment in GR. Finally, we sketch a quantization procedure based on
what done in LQG.
| [
{
"created": "Tue, 15 Mar 2016 15:59:33 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Jun 2016 10:43:40 GMT",
"version": "v2"
}
] | 2016-06-29 | [
[
"Fatibene",
"Lorenzo",
""
],
[
"Garruto",
"Simon",
""
]
] | We shall introduce the principal symbol for Euler-Lagrange operators and use them to charac- terise well-posed initial value problems. We shall clarify how constraints can arise in Lagrangian covariant theories by extending the standard treatment in GR. Finally, we sketch a quantization procedure based on what done in LQG. |
gr-qc/0605099 | Alexey Boyarsky | V.A. Berezin, A. Boyarsky and A.Yu. Neronov | On the Mechanism of Hawking Radiation | This is arXiv submission of the paper published in the Russian
journal Gravitation and Cosmology in 1999 | Gravitation & Cosmology, Vol. 5 (1999), pp. 16-22 | null | null | gr-qc | null | In this paper we derived Hawking radiation as a tuneling of massless
particles through a non-singular horizon in the s-wave approximation. The back
reaction of emitted modes on the background black hole geometry is
self-consistently taken into account. This is arXive copy of the paper
published in the Russian journal "Gravitation and Cosmology" in 1999.
| [
{
"created": "Wed, 17 May 2006 12:49:02 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Berezin",
"V. A.",
""
],
[
"Boyarsky",
"A.",
""
],
[
"Neronov",
"A. Yu.",
""
]
] | In this paper we derived Hawking radiation as a tuneling of massless particles through a non-singular horizon in the s-wave approximation. The back reaction of emitted modes on the background black hole geometry is self-consistently taken into account. This is arXive copy of the paper published in the Russian journal "Gravitation and Cosmology" in 1999. |
2401.10975 | Samarjit Chakraborty | Samarjit Chakraborty | On the thermodynamic aspects of gravity | 190 pages, This Ph.D. thesis has been accepted | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Here the Weyl curvature hypothesis is examined using the gravitational
entropy (GE). We have considered the family of C-metric accelerating black
holes and evaluated their corresponding gravitational entropy. Then we studied
the GE in some isotropic and anisotropic cosmologies utilizing the definition
proposed by Clifton, Ellis, and Tavakol, where the Bel-Robinson tensor is used
to determine the energy-momentum tensor of the free gravitational field. We
checked whether, in the vicinity of the initial cosmic singularity, the ratio
of the energy density of free gravity to that of matter density goes to zero or
not. We showed that whenever this is true, the gravitational entropy increases
monotonically with the structure formation of the universe and discussed the
conditions of validity for the Weyl curvature hypothesis. Subsequently, the
next part of the thesis deals with the validity of two different proposals of
gravitational entropy (GE) in traversable wormhole systems. We found that the
GE proposals do provide us with a consistent measure of GE in several wormhole
solutions. In the later portion of the thesis, we examined the validity of the
generalized second law of thermodynamics (GSLT) in an expanding FRW universe
filled with different variants of the Chaplygin gas. Lastly, we studied the
evolution of the FRW universe in the presence of variable modified Chaplygin
gas and obtained its temperature and other parameters as a function of the
redshift. Finally, the thesis is concluded.
| [
{
"created": "Fri, 19 Jan 2024 18:50:07 GMT",
"version": "v1"
}
] | 2024-01-23 | [
[
"Chakraborty",
"Samarjit",
""
]
] | Here the Weyl curvature hypothesis is examined using the gravitational entropy (GE). We have considered the family of C-metric accelerating black holes and evaluated their corresponding gravitational entropy. Then we studied the GE in some isotropic and anisotropic cosmologies utilizing the definition proposed by Clifton, Ellis, and Tavakol, where the Bel-Robinson tensor is used to determine the energy-momentum tensor of the free gravitational field. We checked whether, in the vicinity of the initial cosmic singularity, the ratio of the energy density of free gravity to that of matter density goes to zero or not. We showed that whenever this is true, the gravitational entropy increases monotonically with the structure formation of the universe and discussed the conditions of validity for the Weyl curvature hypothesis. Subsequently, the next part of the thesis deals with the validity of two different proposals of gravitational entropy (GE) in traversable wormhole systems. We found that the GE proposals do provide us with a consistent measure of GE in several wormhole solutions. In the later portion of the thesis, we examined the validity of the generalized second law of thermodynamics (GSLT) in an expanding FRW universe filled with different variants of the Chaplygin gas. Lastly, we studied the evolution of the FRW universe in the presence of variable modified Chaplygin gas and obtained its temperature and other parameters as a function of the redshift. Finally, the thesis is concluded. |
gr-qc/9704039 | Toshifumi Sakaguchi | Toshifumi Sakaguchi | Against ``Against Many-Worlds Interpretations'' | 6 pages, REVTeX, no figures | null | null | null | gr-qc quant-ph | null | The paper entitled ``Against Many-Worlds Interpretations'' by A. Kent, which
has recently been submitted to the e-Print archive (gr-qc/9703089) contained
some misconceptions. The claims on Everett's many-worlds interpretation are
quoted and answered.
| [
{
"created": "Tue, 15 Apr 1997 14:02:42 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sakaguchi",
"Toshifumi",
""
]
] | The paper entitled ``Against Many-Worlds Interpretations'' by A. Kent, which has recently been submitted to the e-Print archive (gr-qc/9703089) contained some misconceptions. The claims on Everett's many-worlds interpretation are quoted and answered. |
2005.09458 | Rikpratik Sengupta | Prasenjit Paul, Rikpratik Sengupta, Saibal Ray | Modified Power law Inflation: solution to the graceful exit problem and
improvement of dark energy models | 14 pages; Replacement restores version 1 of arXiv:2005.09458 which
was incorrectly replaced | Chinese Physics C 2022 | 10.1088/1674-1137/acaec0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study power law inflation (PLI) with a monomial potential and find a novel
exact solution. It is well known that conventional PLI with exponential
potential is inconsistent with the Planck data. Unlike the standard PLI,
present model does not suffer from graceful exit problem and it agrees fairly
well with recent observations. We have calculated the spectral index and the
tensor-to-scalar ratio which are in very good agreement with recent
observational data and also comparable with other modified inflationary models.
A technique has been used which shows that the large cosmological constant
reduces with expansion of the Universe in case of the power law inflation. The
coupling of the inflaton with gravitation is the main point in this technique.
The basic assumption here is that the two metric tensors in the gravitational
and the inflaton parts correspond to different conformal frames which is in
contradiction with the conventional power law inflation where the inflaton
directly coupled with the background metric tensor. This fact has direct
application to different dark energy models and assisted quintessence theory.
| [
{
"created": "Sun, 17 May 2020 19:26:28 GMT",
"version": "v1"
},
{
"created": "Sun, 13 Feb 2022 16:10:47 GMT",
"version": "v2"
},
{
"created": "Tue, 23 Aug 2022 07:48:22 GMT",
"version": "v3"
},
{
"created": "Tue, 6 Sep 2022 13:22:36 GMT",
"version": "v4"
}
] | 2023-01-02 | [
[
"Paul",
"Prasenjit",
""
],
[
"Sengupta",
"Rikpratik",
""
],
[
"Ray",
"Saibal",
""
]
] | We study power law inflation (PLI) with a monomial potential and find a novel exact solution. It is well known that conventional PLI with exponential potential is inconsistent with the Planck data. Unlike the standard PLI, present model does not suffer from graceful exit problem and it agrees fairly well with recent observations. We have calculated the spectral index and the tensor-to-scalar ratio which are in very good agreement with recent observational data and also comparable with other modified inflationary models. A technique has been used which shows that the large cosmological constant reduces with expansion of the Universe in case of the power law inflation. The coupling of the inflaton with gravitation is the main point in this technique. The basic assumption here is that the two metric tensors in the gravitational and the inflaton parts correspond to different conformal frames which is in contradiction with the conventional power law inflation where the inflaton directly coupled with the background metric tensor. This fact has direct application to different dark energy models and assisted quintessence theory. |
1509.03720 | Sergio Zerbini | Yevgeniya Rabochaya and Sergio Zerbini | A note on a mimetic scalar-tensor cosmological model | 9 pages | null | 10.1140/epjc/s10052-016-3926-y | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A specific Horndeski scalar-gravity mimetic model is investigated within a
FLWR space-time. The mimetic scalar field is implemented via a Lagrangian
multiplier, and it is shown that the model has equations of motion formally
similar to the original simpler mimetic matter model of
Chamseddine-Mukhanov-Vikman. Several exact solutions describing inflation,
bounces, future time singularities are presented and discussed.
| [
{
"created": "Sat, 12 Sep 2015 08:01:29 GMT",
"version": "v1"
}
] | 2016-03-23 | [
[
"Rabochaya",
"Yevgeniya",
""
],
[
"Zerbini",
"Sergio",
""
]
] | A specific Horndeski scalar-gravity mimetic model is investigated within a FLWR space-time. The mimetic scalar field is implemented via a Lagrangian multiplier, and it is shown that the model has equations of motion formally similar to the original simpler mimetic matter model of Chamseddine-Mukhanov-Vikman. Several exact solutions describing inflation, bounces, future time singularities are presented and discussed. |
1605.01979 | Joao Paulo Manoel Pitelli | J.P.M. Pitelli | Quantum Cosmology in $(1+1)$-dimensional Ho\v{r}ava-Lifshitz theory of
gravity | 8 pages. To appear in Phys. Rev. D | null | 10.1103/PhysRevD.93.104024 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a recent paper [Phys. Rev. D 92:084012, 2015], the author studied the
classical $(1+1)$-dimensional Friedmann-Robertson-Walker (FRW) universe filled
with a perfect fluid in Ho\v{r}ava-Lifshitz (HL) theory of gravity. This theory
is dynamical due to the anisotropic scaling of space and time. It also
resembles the Jackiw-Teitelboim model, in which a dilatonic degree of freedom
is necessary for dynamics. In this paper, I will give one step further in the
understanding of (1+1)-dimensional HL cosmology by means of the quantization of
the FRW universe filled with a perfect fluid with equation of state (EoS)
$p=w\rho$. The fluid will be introduced in the model via Schutz formalism and
Dirac's algorithm will be used for quantization. It will be shown that the
Schr\"odinger equation for the wave function of the universe has the following
properties: for $w=1$ (radiation fluid), the characteristic potential will be
exponential, resembling Liouville quantum mechanics; for $w\neq 1$, a
characteristic inverse square potential appears in addition to a regular
polynomial which depends on the EoS. Explict solutions for a few cases of
interesting will be found and the expectation value of the scale factor will be
calculated. As in usual quantum cosmology, it will be shown that the quantum
theory smooth out the big-bang singularity, but the classical behavior of the
universe is recovered in the low-energy limit.
| [
{
"created": "Fri, 6 May 2016 15:51:43 GMT",
"version": "v1"
}
] | 2016-05-25 | [
[
"Pitelli",
"J. P. M.",
""
]
] | In a recent paper [Phys. Rev. D 92:084012, 2015], the author studied the classical $(1+1)$-dimensional Friedmann-Robertson-Walker (FRW) universe filled with a perfect fluid in Ho\v{r}ava-Lifshitz (HL) theory of gravity. This theory is dynamical due to the anisotropic scaling of space and time. It also resembles the Jackiw-Teitelboim model, in which a dilatonic degree of freedom is necessary for dynamics. In this paper, I will give one step further in the understanding of (1+1)-dimensional HL cosmology by means of the quantization of the FRW universe filled with a perfect fluid with equation of state (EoS) $p=w\rho$. The fluid will be introduced in the model via Schutz formalism and Dirac's algorithm will be used for quantization. It will be shown that the Schr\"odinger equation for the wave function of the universe has the following properties: for $w=1$ (radiation fluid), the characteristic potential will be exponential, resembling Liouville quantum mechanics; for $w\neq 1$, a characteristic inverse square potential appears in addition to a regular polynomial which depends on the EoS. Explict solutions for a few cases of interesting will be found and the expectation value of the scale factor will be calculated. As in usual quantum cosmology, it will be shown that the quantum theory smooth out the big-bang singularity, but the classical behavior of the universe is recovered in the low-energy limit. |
2403.10278 | Dongze Sun | Dongze Sun, Michael Boyle, Keefe Mitman, Mark A. Scheel, Leo C. Stein,
Saul A. Teukolsky, Vijay Varma | Optimizing post-Newtonian parameters and fixing the BMS frame for
numerical-relativity waveform hybridizations | 21 pages, 22 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Numerical relativity (NR) simulations of binary black holes provide precise
waveforms, but are typically too computationally expensive to produce waveforms
with enough orbits to cover the whole frequency band of gravitational-wave
observatories. Accordingly, it is important to be able to hybridize NR
waveforms with analytic, post-Newtonian (PN) waveforms, which are accurate
during the early inspiral phase. We show that to build such hybrids, it is
crucial to both fix the Bondi-Metzner-Sachs (BMS) frame of the NR waveforms to
match that of PN theory, and optimize over the PN parameters. We test such a
hybridization procedure including all spin-weighted spherical harmonic modes
with $|m|\leq \ell$ for $\ell\leq 8$, using 29 NR waveforms with mass ratios
$q\leq 10$ and spin magnitudes $|\chi_1|, |\chi_2|\leq 0.8$. We find that for
spin-aligned systems, the PN and NR waveforms agree very well. The difference
is limited by the small nonzero orbital eccentricity of the NR waveforms, or
equivalently by the lack of eccentric terms in the PN waveforms. To maintain
full accuracy of the simulations, the matching window for spin-aligned systems
should be at least 5 orbits long and end at least 15 orbits before merger. For
precessing systems, the errors are larger than for spin-aligned cases. The
errors are likely limited by the absence of precession-related spin-spin PN
terms. Using $10^5\,M$ long NR waveforms, we find that there is no optimal
choice of the matching window within this time span, because the hybridization
result for precessing cases is always better if using earlier or longer
matching windows. We provide the mean orbital frequency of the smallest
acceptable matching window as a function of the target error between the PN and
NR waveforms and the black hole spins.
| [
{
"created": "Fri, 15 Mar 2024 13:19:57 GMT",
"version": "v1"
}
] | 2024-03-18 | [
[
"Sun",
"Dongze",
""
],
[
"Boyle",
"Michael",
""
],
[
"Mitman",
"Keefe",
""
],
[
"Scheel",
"Mark A.",
""
],
[
"Stein",
"Leo C.",
""
],
[
"Teukolsky",
"Saul A.",
""
],
[
"Varma",
"Vijay",
""
]
] | Numerical relativity (NR) simulations of binary black holes provide precise waveforms, but are typically too computationally expensive to produce waveforms with enough orbits to cover the whole frequency band of gravitational-wave observatories. Accordingly, it is important to be able to hybridize NR waveforms with analytic, post-Newtonian (PN) waveforms, which are accurate during the early inspiral phase. We show that to build such hybrids, it is crucial to both fix the Bondi-Metzner-Sachs (BMS) frame of the NR waveforms to match that of PN theory, and optimize over the PN parameters. We test such a hybridization procedure including all spin-weighted spherical harmonic modes with $|m|\leq \ell$ for $\ell\leq 8$, using 29 NR waveforms with mass ratios $q\leq 10$ and spin magnitudes $|\chi_1|, |\chi_2|\leq 0.8$. We find that for spin-aligned systems, the PN and NR waveforms agree very well. The difference is limited by the small nonzero orbital eccentricity of the NR waveforms, or equivalently by the lack of eccentric terms in the PN waveforms. To maintain full accuracy of the simulations, the matching window for spin-aligned systems should be at least 5 orbits long and end at least 15 orbits before merger. For precessing systems, the errors are larger than for spin-aligned cases. The errors are likely limited by the absence of precession-related spin-spin PN terms. Using $10^5\,M$ long NR waveforms, we find that there is no optimal choice of the matching window within this time span, because the hybridization result for precessing cases is always better if using earlier or longer matching windows. We provide the mean orbital frequency of the smallest acceptable matching window as a function of the target error between the PN and NR waveforms and the black hole spins. |
2207.01979 | Mihai Marciu C | Mihai Marciu | A two-field dark energy model with cubic contractions of the Riemann
tensor | null | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | The paper proposes a novel cosmological model based on a two-field scenario,
where the two fields are independently coupled with a specific invariant, based
on cubic contractions of the Riemann tensor. After obtaining the modified
Friedmann equations and the specific Klein-Gordon relations, the investigation
studies the corresponding physical features by adopting the linear stability
theory in a quintom scenario case where the coupling functions and potential
energies have an exponential behavior. The corresponding investigation revealed
a high complexity of the phase space structure, with various stationary points
which can explain different aspects in the evolution of our Universe, the
matter dominated epoch, and the late time accelerated stage. The present model
can represent a viable solution to the dark energy problem due to the high
complexity of the phase space and the existence of the scaling solutions.
| [
{
"created": "Tue, 5 Jul 2022 11:46:53 GMT",
"version": "v1"
}
] | 2022-07-06 | [
[
"Marciu",
"Mihai",
""
]
] | The paper proposes a novel cosmological model based on a two-field scenario, where the two fields are independently coupled with a specific invariant, based on cubic contractions of the Riemann tensor. After obtaining the modified Friedmann equations and the specific Klein-Gordon relations, the investigation studies the corresponding physical features by adopting the linear stability theory in a quintom scenario case where the coupling functions and potential energies have an exponential behavior. The corresponding investigation revealed a high complexity of the phase space structure, with various stationary points which can explain different aspects in the evolution of our Universe, the matter dominated epoch, and the late time accelerated stage. The present model can represent a viable solution to the dark energy problem due to the high complexity of the phase space and the existence of the scaling solutions. |
1703.03696 | Paolo Pani | Elisa Maggio, Paolo Pani, Valeria Ferrari | Exotic Compact Objects and How to Quench their Ergoregion Instability | v3: 14 pages, 9 figures; further clarifications added, new appendix
on the superspinar case, results unchanged. Accepted in Phys. Rev. D | Phys. Rev. D 96, 104047 (2017) | 10.1103/PhysRevD.96.104047 | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational-wave astronomy can give us access to the structure of black
holes, potentially probing microscopic or even Planckian corrections at the
horizon scale, as those predicted by some quantum-gravity models of exotic
compact objects. A generic feature of these models is the replacement of the
horizon by a reflective surface. Objects with these properties are prone to the
so-called ergoregion instability when they spin sufficiently fast. We
investigate in detail a simple model consisting of scalar perturbations of a
Kerr geometry with a reflective surface near the horizon. The instability
depends on the spin, on the compactness, and on the reflectivity at the
surface. The instability time scale increases only logarithmically in the
black-hole limit and, for a perfectly reflecting object, this is not enough to
prevent the instability from occurring on dynamical time scales. However, we
find that an absorption rate at the surface as small as 0.4% (reflectivity
coefficient as large as $|{\cal R}|^2=0.996$) is sufficient to quench the
instability completely. Our results suggest that exotic compact objects are not
necessarily ruled out by the ergoregion instability.
| [
{
"created": "Fri, 10 Mar 2017 14:29:47 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Jul 2017 15:28:03 GMT",
"version": "v2"
},
{
"created": "Tue, 7 Nov 2017 01:20:39 GMT",
"version": "v3"
}
] | 2017-12-07 | [
[
"Maggio",
"Elisa",
""
],
[
"Pani",
"Paolo",
""
],
[
"Ferrari",
"Valeria",
""
]
] | Gravitational-wave astronomy can give us access to the structure of black holes, potentially probing microscopic or even Planckian corrections at the horizon scale, as those predicted by some quantum-gravity models of exotic compact objects. A generic feature of these models is the replacement of the horizon by a reflective surface. Objects with these properties are prone to the so-called ergoregion instability when they spin sufficiently fast. We investigate in detail a simple model consisting of scalar perturbations of a Kerr geometry with a reflective surface near the horizon. The instability depends on the spin, on the compactness, and on the reflectivity at the surface. The instability time scale increases only logarithmically in the black-hole limit and, for a perfectly reflecting object, this is not enough to prevent the instability from occurring on dynamical time scales. However, we find that an absorption rate at the surface as small as 0.4% (reflectivity coefficient as large as $|{\cal R}|^2=0.996$) is sufficient to quench the instability completely. Our results suggest that exotic compact objects are not necessarily ruled out by the ergoregion instability. |
2406.07613 | Jorge Castelo Mourelle | Christoph Adam, Jorge Castelo Mourelle, Etevaldo dos Santos Costa
Filho, Carlos A. R. Herdeiro and Andrzej Wereszczynski | Universal Relations for Rotating Scalar and Vector Boson Stars | 23 pages, 22 figures. We made some corrections | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Bosonic stars represent a hypothetical exotic type of compact stellar objects
that could be observed from the gravitational signal of coalescing binaries in
current and future gravitational wave detectors. There are two main families of
bosonic stars, which depend on the nature that governs the particles that build
them: Einstein-Klein-Gordon and Proca Stars. We study the multipolar structure
for both families of rotating objects, using realistic potentials with the aim
of finding possible universal relations and, thus, a method that allows us to
distinguish between these and other compact objects in the gravitational wave
paradigm. We also show how certain relevant observables can be obtained for
these hypothetical but well-motivated astrophysical objects.
| [
{
"created": "Tue, 11 Jun 2024 18:00:02 GMT",
"version": "v1"
},
{
"created": "Fri, 2 Aug 2024 14:05:59 GMT",
"version": "v2"
}
] | 2024-08-05 | [
[
"Adam",
"Christoph",
""
],
[
"Mourelle",
"Jorge Castelo",
""
],
[
"Filho",
"Etevaldo dos Santos Costa",
""
],
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Wereszczynski",
"Andrzej",
""
]
] | Bosonic stars represent a hypothetical exotic type of compact stellar objects that could be observed from the gravitational signal of coalescing binaries in current and future gravitational wave detectors. There are two main families of bosonic stars, which depend on the nature that governs the particles that build them: Einstein-Klein-Gordon and Proca Stars. We study the multipolar structure for both families of rotating objects, using realistic potentials with the aim of finding possible universal relations and, thus, a method that allows us to distinguish between these and other compact objects in the gravitational wave paradigm. We also show how certain relevant observables can be obtained for these hypothetical but well-motivated astrophysical objects. |
0712.3982 | David Wiltshire | David L. Wiltshire | Gravitational energy and cosmic acceleration | 9 pages, 2 figures. An essay which received Honorable Mention in the
2007 GRF Essay Competition. To appear in a special issue of Int. J. Mod.
Phys. D | Int.J.Mod.Phys.D17:641-649,2008 | 10.1142/S0218271808012383 | null | gr-qc astro-ph | null | Cosmic acceleration is explained quantitatively, as an apparent effect due to
gravitational energy differences that arise in the decoupling of bound systems
from the global expansion of the universe. "Dark energy" is a misidentification
of those aspects of gravitational energy which by virtue of the equivalence
principle cannot be localised, namely gradients in the energy due to the
expansion of space and spatial curvature variations in an inhomogeneous
universe. A new scheme for cosmological averaging is proposed which solves the
Sandage-de Vaucouleurs paradox. Concordance parameters fit supernovae
luminosity distances, the angular scale of the sound horizon in the CMB
anisotropies, and the effective comoving baryon acoustic oscillation scale seen
in galaxy clustering statistics. Key observational anomalies are potentially
resolved, and unique predictions made, including a quantifiable variance in the
Hubble flow below the scale of apparent homogeneity.
| [
{
"created": "Mon, 24 Dec 2007 10:04:12 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Wiltshire",
"David L.",
""
]
] | Cosmic acceleration is explained quantitatively, as an apparent effect due to gravitational energy differences that arise in the decoupling of bound systems from the global expansion of the universe. "Dark energy" is a misidentification of those aspects of gravitational energy which by virtue of the equivalence principle cannot be localised, namely gradients in the energy due to the expansion of space and spatial curvature variations in an inhomogeneous universe. A new scheme for cosmological averaging is proposed which solves the Sandage-de Vaucouleurs paradox. Concordance parameters fit supernovae luminosity distances, the angular scale of the sound horizon in the CMB anisotropies, and the effective comoving baryon acoustic oscillation scale seen in galaxy clustering statistics. Key observational anomalies are potentially resolved, and unique predictions made, including a quantifiable variance in the Hubble flow below the scale of apparent homogeneity. |
0705.2047 | Yuri Shtanov | Kirill Krasnov, Yuri Shtanov | Non-Metric Gravity II: Spherically Symmetric Solution, Missing Mass and
Redshifts of Quasars | 39 pages, 2 figures, text slightly extended, references added | Class.Quant.Grav.25:025002,2008 | 10.1088/0264-9381/25/2/025002 | null | gr-qc astro-ph hep-th | null | We continue the study of the non-metric theory of gravity introduced in
hep-th/0611182 and gr-qc/0703002 and obtain its general spherically symmetric
vacuum solution. It respects the analog of the Birkhoff theorem, i.e., the
vacuum spherically symmetric solution is necessarily static. As in general
relativity, the spherically symmetric solution is seen to describe a black
hole. The exterior geometry is essentially the same as in the Schwarzschild
case, with power-law corrections to the Newtonian potential. The behavior
inside the black-hole region is different from the Schwarzschild case in that
the usual spacetime singularity gets replaced by a singular surface of a new
type, where all basic fields of the theory remain finite but metric ceases to
exist. The theory does not admit arbitrarily small black holes: for small
objects, the curvature on the would-be horizon is so strong that non-metric
modifications prevent the horizon from being formed. The theory allows for
modifications of gravity of very interesting nature. We discuss three physical
effects, namely, (i) correction to Newton's law in the neighborhood of the
source, (ii) renormalization of effective gravitational and cosmological
constants at large distances from the source, and (iii) additional redshift
factor between spatial regions of different curvature. The first two effects
can be responsible, respectively, for the observed anomaly in the acceleration
of the Pioneer spacecraft and for the alleged missing mass in spiral galaxies
and other astrophysical objects. The third effect can be used to propose a
non-cosmological explanation of high redshifts of quasars and gamma-ray bursts.
| [
{
"created": "Mon, 14 May 2007 22:55:46 GMT",
"version": "v1"
},
{
"created": "Mon, 15 Oct 2007 21:02:03 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Krasnov",
"Kirill",
""
],
[
"Shtanov",
"Yuri",
""
]
] | We continue the study of the non-metric theory of gravity introduced in hep-th/0611182 and gr-qc/0703002 and obtain its general spherically symmetric vacuum solution. It respects the analog of the Birkhoff theorem, i.e., the vacuum spherically symmetric solution is necessarily static. As in general relativity, the spherically symmetric solution is seen to describe a black hole. The exterior geometry is essentially the same as in the Schwarzschild case, with power-law corrections to the Newtonian potential. The behavior inside the black-hole region is different from the Schwarzschild case in that the usual spacetime singularity gets replaced by a singular surface of a new type, where all basic fields of the theory remain finite but metric ceases to exist. The theory does not admit arbitrarily small black holes: for small objects, the curvature on the would-be horizon is so strong that non-metric modifications prevent the horizon from being formed. The theory allows for modifications of gravity of very interesting nature. We discuss three physical effects, namely, (i) correction to Newton's law in the neighborhood of the source, (ii) renormalization of effective gravitational and cosmological constants at large distances from the source, and (iii) additional redshift factor between spatial regions of different curvature. The first two effects can be responsible, respectively, for the observed anomaly in the acceleration of the Pioneer spacecraft and for the alleged missing mass in spiral galaxies and other astrophysical objects. The third effect can be used to propose a non-cosmological explanation of high redshifts of quasars and gamma-ray bursts. |
gr-qc/9711046 | Ubi Wichoski | R. Opher and U. F. Wichoski | On a Theory for Nonminimal Gravitational-Electromagnetic Coupling
Consistent with Observational Data | 4 pages, no figures, LaTeX (uses mprocl.sty). To appear in the
Proceedings of the Eighth Marcel Grossmann Meeting (Jerusalem, Israel, June
1997) | null | null | BROWN-HET-2001 | gr-qc | null | The idea that the seed primordial magnetic fields can be explained by the
nonminimal coupling between gravitational and electromagnetic fields is
discussed. The predicted values of the magnetic field of the spiral galaxies
are in agreement with the observations.
| [
{
"created": "Fri, 14 Nov 1997 21:09:19 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Opher",
"R.",
""
],
[
"Wichoski",
"U. F.",
""
]
] | The idea that the seed primordial magnetic fields can be explained by the nonminimal coupling between gravitational and electromagnetic fields is discussed. The predicted values of the magnetic field of the spiral galaxies are in agreement with the observations. |
2012.03431 | Mustapha Azreg-A\"inou | Mustapha Azreg-A\"inou | Rotating cosmological cylindrical wormholes in GR and TEGR sourced by
anisotropic fluids | 8 twocolumn pages, 2 figures, references added. Extended version | Physics of the Dark Universe 32 (2021) 100802 | 10.1016/j.dark.2021.100802 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | Given an anisotropic fluid source, we determine in closed forms, upon solving
the field equations of general relativity (GR) and teleparallel gravity (TEGR)
coupled to a cosmological constant, cylindrically symmetric four-dimensional
cosmological rotating wormholes, satisfying all local energy conditions, and
cosmological rotating solutions with two axes of symmetry at finite proper
distance. These solutions have the property that their angular velocity is
proportional to the cosmological constant.
| [
{
"created": "Mon, 7 Dec 2020 03:03:44 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Mar 2021 02:02:13 GMT",
"version": "v2"
}
] | 2021-03-17 | [
[
"Azreg-Aïnou",
"Mustapha",
""
]
] | Given an anisotropic fluid source, we determine in closed forms, upon solving the field equations of general relativity (GR) and teleparallel gravity (TEGR) coupled to a cosmological constant, cylindrically symmetric four-dimensional cosmological rotating wormholes, satisfying all local energy conditions, and cosmological rotating solutions with two axes of symmetry at finite proper distance. These solutions have the property that their angular velocity is proportional to the cosmological constant. |
1402.4557 | Eric Greenwood | Eric Greenwood | Time dependent particle production and particle number in cosmological
de Sitter space | 19 pages | null | 10.1142/S0218271815500315 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we consider the occupation number of induced quasi-particles
produced during a time-dependent process using three-different methods:
Instantaneous diagonalization, Bogolyubov transformation between two different
vacua, and the Unruh-de Witt detector. Here we consider the Hamiltonian for a
time-dependent Harmonic oscillator, with time-dependent mass and frequency. We
derive the occupation number of the induced quasi-particles using the invariant
operator method; in deriving the occupation number we also point out and make
the connection between the Functional Schr\"odinger formalism, quantum kinetic
equation, and Bogolyubov transformation between two different Fock space basis
at equal times and explain the role in which the invariant operator plays.
Using the flat FRW chart of de Sitter spacetime, we show that the different
methods lead to different results: Instantaneous diagonalization leads to a
power law distribution, while the Bogolyubov transformation and Unruh-de Witt
detector both lead to thermal distributions. It is shown that the source of the
discrepancy between the instantaneous diagonalization and Bogolyubov methods is
the fact that there is no notion of well-defined particles in the out vacuum
due to a divergent term. In the Bogolyubov method, this divergent term cancels
leading to the thermal distribution, while in the instantaneous diagonalization
there is no such cancelation. However, to obtain the thermal distribution in
the usual Bogolyubov method, one must use the large mass limit. On physical
grounds, one should expect that only the modes which have been allowed to
sample the horizon would be thermal, thus in the large mass limit these modes
are well within the horizon and, even though they do grow, they remain well
within the horizon due to the mass. Thus one should not expect a thermal
distribution since the modes won't have a chance to thermalize.
| [
{
"created": "Wed, 19 Feb 2014 04:20:31 GMT",
"version": "v1"
}
] | 2015-06-18 | [
[
"Greenwood",
"Eric",
""
]
] | In this paper we consider the occupation number of induced quasi-particles produced during a time-dependent process using three-different methods: Instantaneous diagonalization, Bogolyubov transformation between two different vacua, and the Unruh-de Witt detector. Here we consider the Hamiltonian for a time-dependent Harmonic oscillator, with time-dependent mass and frequency. We derive the occupation number of the induced quasi-particles using the invariant operator method; in deriving the occupation number we also point out and make the connection between the Functional Schr\"odinger formalism, quantum kinetic equation, and Bogolyubov transformation between two different Fock space basis at equal times and explain the role in which the invariant operator plays. Using the flat FRW chart of de Sitter spacetime, we show that the different methods lead to different results: Instantaneous diagonalization leads to a power law distribution, while the Bogolyubov transformation and Unruh-de Witt detector both lead to thermal distributions. It is shown that the source of the discrepancy between the instantaneous diagonalization and Bogolyubov methods is the fact that there is no notion of well-defined particles in the out vacuum due to a divergent term. In the Bogolyubov method, this divergent term cancels leading to the thermal distribution, while in the instantaneous diagonalization there is no such cancelation. However, to obtain the thermal distribution in the usual Bogolyubov method, one must use the large mass limit. On physical grounds, one should expect that only the modes which have been allowed to sample the horizon would be thermal, thus in the large mass limit these modes are well within the horizon and, even though they do grow, they remain well within the horizon due to the mass. Thus one should not expect a thermal distribution since the modes won't have a chance to thermalize. |
0805.2665 | Marek Szydlowski | Marek Szydlowski, Pawel Tambor | Dynamical Emergence of FRW Cosmological Models | 8ssmmp.cls, 14 pages, 3 figures; rev. 2: added section on emergence
from bifurcation; rev. 3: reorganized and shortened text; transition from the
LCDM to CDM model was explicitly shown, for this aim it was used the theorem
on smooth dependence of solution on initial conditions and change of
parameters. In: B. Dragovich, I. Salom (eds) Proceedings of the 8th
Mathematical Physics Meeting: Summer School and Conference on Modern
Mathematical Physics. August 24-31, 2014, Belgrade, Serbia. Institute of
Physics, Belgrade, 2015 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recent astronomical observations strongly indicate that the current Universe
is undergoing an accelerated phase of expansion. The discovery of this fact was
unexpected and resulted in the comeback of cosmological constant. The
conception of standard cosmological model has its roots in this context. The
paper relates to the methodological status of effective theories in the context
of cosmological investigations. We argue that the standard cosmological model
(LCDM model) as well as the CDM have a status of effective theories only,
similarly to the standard model of particle physics. The LCDM model is studied
from the point of view of the methodological debate on reductionism and
epistemological emergence in the science. It is shown in the paper that
bifurcation as well as structural instability notion can be useful in the
detection of emergence the LCDM model from the CDM model. We demonstrate that
the structural stability of the LCDM model can explain the flexibility of the
model to accommodation of the observational data. We show that LCDM model can
be derived from CDM as the bifurcation. It is an example of acausal derivation
of Lambda term. The case study of emergence of LCDM model suggests that it can
be understood in terms of bifurcation and structural stability issue. The
reduction from the upper models represented in terms of dynamical system to
low-level ones can be realized in any case by application of a mathematical
limit (boundary crossing) with respect to the model parameter. It is a simple
consequence of mathematical theorem about smooth dependence solutions with
respect to time, initial condition and the parameters.
| [
{
"created": "Sat, 17 May 2008 11:49:05 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Jan 2009 11:17:09 GMT",
"version": "v2"
},
{
"created": "Thu, 29 Oct 2015 12:46:54 GMT",
"version": "v3"
}
] | 2015-10-30 | [
[
"Szydlowski",
"Marek",
""
],
[
"Tambor",
"Pawel",
""
]
] | Recent astronomical observations strongly indicate that the current Universe is undergoing an accelerated phase of expansion. The discovery of this fact was unexpected and resulted in the comeback of cosmological constant. The conception of standard cosmological model has its roots in this context. The paper relates to the methodological status of effective theories in the context of cosmological investigations. We argue that the standard cosmological model (LCDM model) as well as the CDM have a status of effective theories only, similarly to the standard model of particle physics. The LCDM model is studied from the point of view of the methodological debate on reductionism and epistemological emergence in the science. It is shown in the paper that bifurcation as well as structural instability notion can be useful in the detection of emergence the LCDM model from the CDM model. We demonstrate that the structural stability of the LCDM model can explain the flexibility of the model to accommodation of the observational data. We show that LCDM model can be derived from CDM as the bifurcation. It is an example of acausal derivation of Lambda term. The case study of emergence of LCDM model suggests that it can be understood in terms of bifurcation and structural stability issue. The reduction from the upper models represented in terms of dynamical system to low-level ones can be realized in any case by application of a mathematical limit (boundary crossing) with respect to the model parameter. It is a simple consequence of mathematical theorem about smooth dependence solutions with respect to time, initial condition and the parameters. |
0709.2051 | Eugenio Bianchi | Eugenio Bianchi, Leonardo Modesto | The perturbative Regge-calculus regime of Loop Quantum Gravity | 43 pages, typos corrected, version accepted by Nucl.Phys.B | Nucl.Phys.B796:581-621,2008 | 10.1016/j.nuclphysb.2007.12.011 | null | gr-qc hep-th | null | The relation between Loop Quantum Gravity and Regge calculus has been pointed
out many times in the literature. In particular the large spin asymptotics of
the Barrett-Crane vertex amplitude is known to be related to the Regge action.
In this paper we study a semiclassical regime of Loop Quantum Gravity and show
that it admits an effective description in terms of perturbative
area-Regge-calculus. The regime of interest is identified by a class of states
given by superpositions of four-valent spin networks, peaked on large spins.
As a probe of the dynamics in this regime, we compute explicitly two- and
three-area correlation functions at the vertex amplitude level. We find that
they match with the ones computed perturbatively in area-Regge-calculus with a
single 4-simplex, once a specific perturbative action and measure have been
chosen in the Regge-calculus path integral. Correlations of other geometric
operators and the existence of this regime for other models for the dynamics
are briefly discussed.
| [
{
"created": "Thu, 13 Sep 2007 12:02:14 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Dec 2007 09:41:32 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Bianchi",
"Eugenio",
""
],
[
"Modesto",
"Leonardo",
""
]
] | The relation between Loop Quantum Gravity and Regge calculus has been pointed out many times in the literature. In particular the large spin asymptotics of the Barrett-Crane vertex amplitude is known to be related to the Regge action. In this paper we study a semiclassical regime of Loop Quantum Gravity and show that it admits an effective description in terms of perturbative area-Regge-calculus. The regime of interest is identified by a class of states given by superpositions of four-valent spin networks, peaked on large spins. As a probe of the dynamics in this regime, we compute explicitly two- and three-area correlation functions at the vertex amplitude level. We find that they match with the ones computed perturbatively in area-Regge-calculus with a single 4-simplex, once a specific perturbative action and measure have been chosen in the Regge-calculus path integral. Correlations of other geometric operators and the existence of this regime for other models for the dynamics are briefly discussed. |
2107.03406 | Kinjalk Lochan | Kinjalk Lochan and T. Padmanabhan | A nested sequence of comoving Rindler frames, the corresponding vacuum
states, and the local nature of acceleration temperature | 9 pages of main discussion + 6 pages of Appendix, 2 figures | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Bogoliubov transformation connecting the standard inertial frame mode
functions to the standard mode functions defined in the Rindler frame $R_0$,
leads to the result that the inertial vacuum appears as a thermal state with
temperature $T_0=a_0/2\pi$ where $a_0$ is the acceleration parameter of $R_0$.
We construct an infinite family of nested Rindler-like coordinate systems $R_1,
R_2, ...$ within the right Rindler wedge, with time coordinates $\tau_1,
\tau_2, ...,$ and acceleration parameters $a_1, a_2, ...$ by shifting the
origin along the inertial $x$-axis by amounts $\ell_1, \ell_2,\cdots$. We show
that, apart from the inertial vacuum, the Rindler vacuum of the frame $R_n$
also appears to be a thermal state in the frame $R_{n+1}$ with the temperature
$a_{n+1}/2\pi$. In fact, the Rindler frame $R_{n+1}$ attributes to all the
Rindler vacuum states of $R_1, R_2, ... R_n$, as well as to the inertial vacuum
state, the same temperature $a_{n+1}/2\pi$. The frame with the shift $\ell$ and
the corresponding acceleration parameter $a(\ell)$ can be thought of as a
Rindler frame which is instantaneously comoving with the Einstein's elevator
moving with a variable acceleration. Our result suggests that the quantum
temperature associated with such an Einstein's elevator is the same as that
defined in the comoving Rindler frame. The shift parameters $\ell_j$ are
crucial for the inequivalent character of these vacua and encode the fact that
Rindler vacua are not invariant under spatial translation. We further show that
our result is discontinuous in an essential way in the coordinate shift
parameters. Similar structures can be introduced in the right wedge of any
spacetime with bifurcate Killing horizon, like, for e.g., Schwarzschild
spacetime. This has important implications for quantum gravity when flat
spacetime is treated as the ground state of quantum gravity.
| [
{
"created": "Wed, 7 Jul 2021 18:00:04 GMT",
"version": "v1"
}
] | 2021-07-09 | [
[
"Lochan",
"Kinjalk",
""
],
[
"Padmanabhan",
"T.",
""
]
] | The Bogoliubov transformation connecting the standard inertial frame mode functions to the standard mode functions defined in the Rindler frame $R_0$, leads to the result that the inertial vacuum appears as a thermal state with temperature $T_0=a_0/2\pi$ where $a_0$ is the acceleration parameter of $R_0$. We construct an infinite family of nested Rindler-like coordinate systems $R_1, R_2, ...$ within the right Rindler wedge, with time coordinates $\tau_1, \tau_2, ...,$ and acceleration parameters $a_1, a_2, ...$ by shifting the origin along the inertial $x$-axis by amounts $\ell_1, \ell_2,\cdots$. We show that, apart from the inertial vacuum, the Rindler vacuum of the frame $R_n$ also appears to be a thermal state in the frame $R_{n+1}$ with the temperature $a_{n+1}/2\pi$. In fact, the Rindler frame $R_{n+1}$ attributes to all the Rindler vacuum states of $R_1, R_2, ... R_n$, as well as to the inertial vacuum state, the same temperature $a_{n+1}/2\pi$. The frame with the shift $\ell$ and the corresponding acceleration parameter $a(\ell)$ can be thought of as a Rindler frame which is instantaneously comoving with the Einstein's elevator moving with a variable acceleration. Our result suggests that the quantum temperature associated with such an Einstein's elevator is the same as that defined in the comoving Rindler frame. The shift parameters $\ell_j$ are crucial for the inequivalent character of these vacua and encode the fact that Rindler vacua are not invariant under spatial translation. We further show that our result is discontinuous in an essential way in the coordinate shift parameters. Similar structures can be introduced in the right wedge of any spacetime with bifurcate Killing horizon, like, for e.g., Schwarzschild spacetime. This has important implications for quantum gravity when flat spacetime is treated as the ground state of quantum gravity. |
1503.04186 | Carlos Augusto Romero Filho | J. E. Madriz Aguilar, C. Romero, J. B. Fonseca-Neto, T. S. Almeida, J.
B. Formiga | (2+1)-Dimensional Gravity in Weyl Integrable Spacetime | 9 pages. arXiv admin note: text overlap with arXiv:1201.1469,
arXiv:1101.5333 | null | 10.1088/0264-9381/32/21/215003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate (2+1)-dimensional gravity in a Weyl integrable spacetime
(WIST). We show that, unlike general relativity, this scalar-tensor theory has
a Newtonian limit for any dimension and that in three dimensions the congruence
of world lines of particles of a pressureless fluid has a non-vanishing
geodesic deviation. We present and discuss a class of static vacuum solutions
generated by a circularly symmetric matter distribution that for certain values
of the parameter w corresponds to a space-time with a naked singularity at the
center of the matter distribution. We interpret all these results as being a
direct consequence of the space-time geometry.
| [
{
"created": "Fri, 13 Mar 2015 18:51:38 GMT",
"version": "v1"
}
] | 2015-10-21 | [
[
"Aguilar",
"J. E. Madriz",
""
],
[
"Romero",
"C.",
""
],
[
"Fonseca-Neto",
"J. B.",
""
],
[
"Almeida",
"T. S.",
""
],
[
"Formiga",
"J. B.",
""
]
] | We investigate (2+1)-dimensional gravity in a Weyl integrable spacetime (WIST). We show that, unlike general relativity, this scalar-tensor theory has a Newtonian limit for any dimension and that in three dimensions the congruence of world lines of particles of a pressureless fluid has a non-vanishing geodesic deviation. We present and discuss a class of static vacuum solutions generated by a circularly symmetric matter distribution that for certain values of the parameter w corresponds to a space-time with a naked singularity at the center of the matter distribution. We interpret all these results as being a direct consequence of the space-time geometry. |
gr-qc/0207111 | Hanno Sahlmann | Hanno Sahlmann | Some results concerning the representation theory of the algebra
underlying loop quantum gravity | LaTeX, 14 pages, no figures. v2: corrected a minor issue with the
mathematical reasoning, updated references; article is now identical to
published version | J. Math. Phys. 52:012502,2011 | 10.1063/1.3525705 | AEI-2002-056 | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Important characteristics of the loop approach to quantum gravity are a
specific choice of the algebra A of observables and of a representation of A on
a measure space over the space of generalized connections. This representation
is singled out by its elegance and diffeomorphism covariance.
Recently, in the context of the quest for semiclassical states, states of the
theory in which the quantum gravitational field is close to some classical
geometry, it was realized that it might also be worthwhile to study different
representations of the algebra A of observables.
The content of the present note is the observation that under some mild
assumptions, the mathematical structure of representations of A can be analyzed
rather effortlessly, to a certain extent: Each representation can be labeled by
sets of functions and measures on the space of (generalized) connections that
fulfill certain conditions.
These considerations are however mostly of mathematical nature. Their
physical content remains to be clarified, and physically interesting examples
are yet to be constructed.
| [
{
"created": "Mon, 29 Jul 2002 15:32:20 GMT",
"version": "v1"
},
{
"created": "Fri, 21 Jan 2011 02:44:20 GMT",
"version": "v2"
}
] | 2011-01-27 | [
[
"Sahlmann",
"Hanno",
""
]
] | Important characteristics of the loop approach to quantum gravity are a specific choice of the algebra A of observables and of a representation of A on a measure space over the space of generalized connections. This representation is singled out by its elegance and diffeomorphism covariance. Recently, in the context of the quest for semiclassical states, states of the theory in which the quantum gravitational field is close to some classical geometry, it was realized that it might also be worthwhile to study different representations of the algebra A of observables. The content of the present note is the observation that under some mild assumptions, the mathematical structure of representations of A can be analyzed rather effortlessly, to a certain extent: Each representation can be labeled by sets of functions and measures on the space of (generalized) connections that fulfill certain conditions. These considerations are however mostly of mathematical nature. Their physical content remains to be clarified, and physically interesting examples are yet to be constructed. |
1610.09283 | Saugata Mitra | Saugata Mitra, Subhajit Saha and Subenoy Chakraborty | Universal thermodynamics in different gravity theories: Conditions for
generalized second law of thermodynamics and thermodynamical equilibrium on
the horizons | null | Annals of Physics 355, 1 (2015) | 10.1016/j.aop.2015.01.025 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The present work deals with a detailed study of universal thermodynamics in
different modified gravity theories. The validity of the generalized second law
of thermodynamics (GSLT) and thermodynamical equilibrium (TE) of the Universe
bounded by a horizon (apparent/event) in f(R)-gravity, Einstein-Gauss-Bonnet
gravity, RS-II brane scenario and DGP brane model has been investigated. In the
perspective of recent observational evidences, the matter in the Universe is
chosen as interacting holographic dark energy model. The entropy on the
horizons are evaluated from the validity of the unified first law and as a
result there is a correction (in integral form) to the usual Bekenstein
entropy. The other thermodynamical parameter namely temperature on the horizon
is chosen as the recently introduced corrected Hawking temperature. The above
thermodynamical analysis is done for homogeneous and isotropic flat FLRW model
of the Universe. The restrictions for the validity of GSLT and the TE are
presented in tabular form for each gravity theory. Finally, due to complicated
expressions, the validity of GSLT and TE are also examined from graphical
representation, using three Planck data sets.
| [
{
"created": "Thu, 27 Oct 2016 08:12:30 GMT",
"version": "v1"
}
] | 2016-11-02 | [
[
"Mitra",
"Saugata",
""
],
[
"Saha",
"Subhajit",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | The present work deals with a detailed study of universal thermodynamics in different modified gravity theories. The validity of the generalized second law of thermodynamics (GSLT) and thermodynamical equilibrium (TE) of the Universe bounded by a horizon (apparent/event) in f(R)-gravity, Einstein-Gauss-Bonnet gravity, RS-II brane scenario and DGP brane model has been investigated. In the perspective of recent observational evidences, the matter in the Universe is chosen as interacting holographic dark energy model. The entropy on the horizons are evaluated from the validity of the unified first law and as a result there is a correction (in integral form) to the usual Bekenstein entropy. The other thermodynamical parameter namely temperature on the horizon is chosen as the recently introduced corrected Hawking temperature. The above thermodynamical analysis is done for homogeneous and isotropic flat FLRW model of the Universe. The restrictions for the validity of GSLT and the TE are presented in tabular form for each gravity theory. Finally, due to complicated expressions, the validity of GSLT and TE are also examined from graphical representation, using three Planck data sets. |
gr-qc/0310094 | Dumitru Baleanu | D. Baleanu | Hamilton-Jacobi formalism of the massive Yang-Mills theory revisited | LATEX, 8 pages | Nuovo Cim.B118:197-203,2003 | null | null | gr-qc hep-th | null | Using Hamilton-Jacobi formalism we investigated the massive Yang-Mills theory
on both extended and reduced phase-space. The integrability conditions were
discussed and the actions were calculated.
| [
{
"created": "Sun, 19 Oct 2003 10:55:46 GMT",
"version": "v1"
}
] | 2010-11-11 | [
[
"Baleanu",
"D.",
""
]
] | Using Hamilton-Jacobi formalism we investigated the massive Yang-Mills theory on both extended and reduced phase-space. The integrability conditions were discussed and the actions were calculated. |
2402.09435 | Hamed Hadi | H. Hadi, R. Naderi | Gravitational memory effects of black bounces and a traversable wormhole | null | Eur. Phys. J. C (2024) 84:343 | 10.1140/epjc/s10052-024-12718-5 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Black bounces are spacetimes that can be interpreted as either black holes or
wormholes depending on specific parameters. In this study, we examine the
Simpson-Visser and Bardeen-type solutions as black bounces and investigate the
gravitational wave in the background of these solutions. We then explore the
displacement and velocity memory effects by analyzing the deviation of two
neighboring geodesics and their derivatives influenced by the magnetic charge
parameter a. This investigation aims to trace the magnetic charge in the
gravitational memory effect. Additionally, we consider another family of
traversable wormhole solutions obtained from non-exotic matter sources to trace
the electric charge Q_e in the gravitational memory effect, which can be
determined from the far field asymptotic. Furthermore, this research aims to
explore the gravitational memory effect related to the variation in Bondi mass
for the Simpson-Visser and Bardeen-Type black bounces. The investigation will
also be conducted on a traversable wormhole solution that does not require any
exotic field. This study holds importance in not only identifying compact
objects such as wormholes through gravitational memory effects but also in
observing the charge Qe, which offers a tangible manifestation of Wheeler's
idea of "electric charge without charge."
| [
{
"created": "Fri, 26 Jan 2024 17:44:11 GMT",
"version": "v1"
},
{
"created": "Tue, 21 May 2024 07:27:04 GMT",
"version": "v2"
}
] | 2024-05-22 | [
[
"Hadi",
"H.",
""
],
[
"Naderi",
"R.",
""
]
] | Black bounces are spacetimes that can be interpreted as either black holes or wormholes depending on specific parameters. In this study, we examine the Simpson-Visser and Bardeen-type solutions as black bounces and investigate the gravitational wave in the background of these solutions. We then explore the displacement and velocity memory effects by analyzing the deviation of two neighboring geodesics and their derivatives influenced by the magnetic charge parameter a. This investigation aims to trace the magnetic charge in the gravitational memory effect. Additionally, we consider another family of traversable wormhole solutions obtained from non-exotic matter sources to trace the electric charge Q_e in the gravitational memory effect, which can be determined from the far field asymptotic. Furthermore, this research aims to explore the gravitational memory effect related to the variation in Bondi mass for the Simpson-Visser and Bardeen-Type black bounces. The investigation will also be conducted on a traversable wormhole solution that does not require any exotic field. This study holds importance in not only identifying compact objects such as wormholes through gravitational memory effects but also in observing the charge Qe, which offers a tangible manifestation of Wheeler's idea of "electric charge without charge." |
gr-qc/0411026 | M. Meyer | S. Deser | How Special Relativity Determines the Signs of the Nonrelativistic,
Coulomb and Newtonian, Forces | 8 pages. Amplified version, to appear in Am. J. Phys | Am J Phys 73 6 (2005) | 10.1119/1.1898503 | BRX TH-549 | gr-qc physics.class-ph | null | We show that the empirical signs of the fundamental {\it static}
Coulomb/Newton forces are dictated by the seemingly unrelated requirement that
the photons/gravitons in the respective underlying Maxwell/Einstein physics be
stable. This linkage, which is imposed by special relativity, is manifested
upon decomposing the corresponding fields and sources in a gauge-invariant way,
and without appeal to static limits. The signs of these free field excitation
energies determine those of the instantaneous forces between sources; opposite
Coulomb/Newton signs are direct consequences of the Maxwell/Einstein free
excitations' odd/even spins.
| [
{
"created": "Thu, 4 Nov 2004 16:54:52 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Feb 2005 15:46:50 GMT",
"version": "v2"
}
] | 2009-11-19 | [
[
"Deser",
"S.",
""
]
] | We show that the empirical signs of the fundamental {\it static} Coulomb/Newton forces are dictated by the seemingly unrelated requirement that the photons/gravitons in the respective underlying Maxwell/Einstein physics be stable. This linkage, which is imposed by special relativity, is manifested upon decomposing the corresponding fields and sources in a gauge-invariant way, and without appeal to static limits. The signs of these free field excitation energies determine those of the instantaneous forces between sources; opposite Coulomb/Newton signs are direct consequences of the Maxwell/Einstein free excitations' odd/even spins. |
1606.06331 | Alexander B. Balakin | Alexander B. Balakin | Electrodynamics of a Cosmic Dark Fluid | 39 pages, 0 figures, replaced by the version published in MDPI
Journal "Symmetry" (Special Issue: Symmetry: Feature Papers 2016); typos
corrected | Symmetry (2016) 8(7), 56 | 10.3390/sym8070056 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cosmic Dark Fluid is considered as a non-stationary medium, in which
electromagnetic waves propagate, and magneto-electric field structures emerge
and evolve. A medium - type representation of the Dark Fluid allows us to
involve into analysis the concepts and mathematical formalism elaborated in the
framework of classical covariant electrodynamics of continua, and to
distinguish dark analogs of well-known medium-effects, such as optical
activity, pyro-electricity, piezo-magnetism, electro- and magneto-striction and
dynamo-optical activity. The Dark Fluid is assumed to be formed by a duet of a
Dark Matter (a pseudoscalar axionic constituent) and Dark Energy (a scalar
element); respectively, we distinguish electrodynamic effects induced by these
two constituents of the Dark Fluid. The review contains discussions of ten
models, which describe electrodynamic effects induced by Dark Matter and/or
Dark Energy. The models are accompanied by examples of exact solutions to the
master equations, correspondingly extended; applications are considered for
cosmology and space-times with spherical and pp-wave symmetries. In these
applications we focused the attention on three main electromagnetic phenomena
induced by the Dark Fluid: first, emergence of Longitudinal Magneto-Electric
Clusters; second, generation of anomalous electromagnetic responses; third,
formation of Dark Epochs in the Universe history.
| [
{
"created": "Mon, 20 Jun 2016 21:01:10 GMT",
"version": "v1"
},
{
"created": "Wed, 29 Jun 2016 21:17:27 GMT",
"version": "v2"
}
] | 2016-07-01 | [
[
"Balakin",
"Alexander B.",
""
]
] | Cosmic Dark Fluid is considered as a non-stationary medium, in which electromagnetic waves propagate, and magneto-electric field structures emerge and evolve. A medium - type representation of the Dark Fluid allows us to involve into analysis the concepts and mathematical formalism elaborated in the framework of classical covariant electrodynamics of continua, and to distinguish dark analogs of well-known medium-effects, such as optical activity, pyro-electricity, piezo-magnetism, electro- and magneto-striction and dynamo-optical activity. The Dark Fluid is assumed to be formed by a duet of a Dark Matter (a pseudoscalar axionic constituent) and Dark Energy (a scalar element); respectively, we distinguish electrodynamic effects induced by these two constituents of the Dark Fluid. The review contains discussions of ten models, which describe electrodynamic effects induced by Dark Matter and/or Dark Energy. The models are accompanied by examples of exact solutions to the master equations, correspondingly extended; applications are considered for cosmology and space-times with spherical and pp-wave symmetries. In these applications we focused the attention on three main electromagnetic phenomena induced by the Dark Fluid: first, emergence of Longitudinal Magneto-Electric Clusters; second, generation of anomalous electromagnetic responses; third, formation of Dark Epochs in the Universe history. |
1109.4315 | Edmund Schluessel | Edmund R. Schluessel | Long-wavelength gravitational waves and cosmic acceleration | 80 pages, 2 figures | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Strong long-scale gravitational waves can explain cosmic acceleration within
the context of general relativity without resorting to the assumption of exotic
forms of matter such as quintessence. The existence of these gravitational
waves in sufficient strength to cause observed acceleration can be compatible
with the cosmic microwave background under reasonable physical circumstances.
An instance of the Bianchi IX cosmology is demonstrated which also explains the
alignment of low-order multipoles observed in the CMB. The model requires a
closed cosmology but is otherwise not strongly constrained. Recommendations are
made for further observations to verify and better constrain the model.
| [
{
"created": "Tue, 20 Sep 2011 15:08:09 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Sep 2011 22:24:29 GMT",
"version": "v2"
}
] | 2011-09-23 | [
[
"Schluessel",
"Edmund R.",
""
]
] | Strong long-scale gravitational waves can explain cosmic acceleration within the context of general relativity without resorting to the assumption of exotic forms of matter such as quintessence. The existence of these gravitational waves in sufficient strength to cause observed acceleration can be compatible with the cosmic microwave background under reasonable physical circumstances. An instance of the Bianchi IX cosmology is demonstrated which also explains the alignment of low-order multipoles observed in the CMB. The model requires a closed cosmology but is otherwise not strongly constrained. Recommendations are made for further observations to verify and better constrain the model. |
1911.03695 | Sergey Rubin | J\'ulio C. Fabris, Arkady A. Popov, Sergey G. Rubin | Multidimensional gravity with higher derivatives and inflation | 12 pages | Phys.Lett.B, 806, 135458, 2020 | 10.1016/j.physletb.2020.135458 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We elaborate on the inflationary model starting from multidimensional
Lagrangian and gravity with second-order curvature terms. The effective scalar
field is related to the Ricci scalar of extra dimensions. It is shown that the
Kretschmann and the Ricci tensor square terms dominate during inflation. The
observable values of the spectral index and the tensor-to-scalar ratio are
obtained for specific values of the model parameters.
| [
{
"created": "Sat, 9 Nov 2019 14:15:36 GMT",
"version": "v1"
}
] | 2020-06-05 | [
[
"Fabris",
"Júlio C.",
""
],
[
"Popov",
"Arkady A.",
""
],
[
"Rubin",
"Sergey G.",
""
]
] | We elaborate on the inflationary model starting from multidimensional Lagrangian and gravity with second-order curvature terms. The effective scalar field is related to the Ricci scalar of extra dimensions. It is shown that the Kretschmann and the Ricci tensor square terms dominate during inflation. The observable values of the spectral index and the tensor-to-scalar ratio are obtained for specific values of the model parameters. |
1706.05584 | N\'estor Ortiz | N\'estor Ortiz and Olivier Sarbach | Cauchy horizon stability in a collapsing spherical dust cloud. II:
Energy bounds for test fields and odd-parity gravitational perturbations | 27 pages, 3 figures. Conclusion improved. References added. Matches
published version | Class.Quant.Grav. 35 (2018) no.2, 025010 | 10.1088/1361-6382/aa8e70 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the stability of the Cauchy horizon associated with a globally
naked, shell-focussing singularity arising from the complete gravitational
collapse of a spherical dust cloud. In previous work, we have studied the
dynamics of spherical test scalar fields on such a background. In particular,
we proved that such fields cannot develop any divergences which propagate along
the Cauchy horizon. In the present work, we extend our analysis to the more
general case of test fields without symmetries and to linearized gravitational
perturbations with odd parity. To this purpose, we first consider test fields
possessing a divergence-free stress-energy tensor satisfying the dominant
energy condition, and we prove that a suitable energy norm is uniformly bounded
in the domain of dependence of the initial slice. In particular, this result
implies that free-falling observers co-moving with the dust particles measure a
finite energy of the field, even as they cross the Cauchy horizon at points
lying arbitrarily close to the central singularity. Next, for the case of
Klein-Gordon fields, we derive point-wise bounds from our energy estimates
which imply that the scalar field cannot diverge at the Cauchy horizon, except
possibly at the central singular point. Finally, we analyze the behaviour of
odd-parity, linear gravitational and dust perturbations of the collapsing
spacetime. Similarly to the scalar field case, we prove that the relevant
gauge-invariant combinations of the metric perturbations stay bounded away from
the central singularity, implying that no divergences can propagate in the
vacuum region. Our results are in accordance with previous numerical studies
and analytic work in the self-similar case.
| [
{
"created": "Sat, 17 Jun 2017 22:20:15 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Jan 2018 22:00:46 GMT",
"version": "v2"
}
] | 2018-01-09 | [
[
"Ortiz",
"Néstor",
""
],
[
"Sarbach",
"Olivier",
""
]
] | We analyze the stability of the Cauchy horizon associated with a globally naked, shell-focussing singularity arising from the complete gravitational collapse of a spherical dust cloud. In previous work, we have studied the dynamics of spherical test scalar fields on such a background. In particular, we proved that such fields cannot develop any divergences which propagate along the Cauchy horizon. In the present work, we extend our analysis to the more general case of test fields without symmetries and to linearized gravitational perturbations with odd parity. To this purpose, we first consider test fields possessing a divergence-free stress-energy tensor satisfying the dominant energy condition, and we prove that a suitable energy norm is uniformly bounded in the domain of dependence of the initial slice. In particular, this result implies that free-falling observers co-moving with the dust particles measure a finite energy of the field, even as they cross the Cauchy horizon at points lying arbitrarily close to the central singularity. Next, for the case of Klein-Gordon fields, we derive point-wise bounds from our energy estimates which imply that the scalar field cannot diverge at the Cauchy horizon, except possibly at the central singular point. Finally, we analyze the behaviour of odd-parity, linear gravitational and dust perturbations of the collapsing spacetime. Similarly to the scalar field case, we prove that the relevant gauge-invariant combinations of the metric perturbations stay bounded away from the central singularity, implying that no divergences can propagate in the vacuum region. Our results are in accordance with previous numerical studies and analytic work in the self-similar case. |
gr-qc/0412005 | J. Ponce de Leon | J. Ponce de Leon | Transition from decelerated to accelerated cosmic expansion in
braneworld universes | In V2 typos are corrected and one reference is added for section 1.
To appear in General Relativity and Gravitation | Gen.Rel.Grav.38:61-81,2006 | 10.1007/s10714-005-0209-6 | null | gr-qc | null | Braneworld theory provides a natural setting to treat, at a classical level,
the cosmological effects of vacuum energy. Non-static extra dimensions can
generally lead to a variable vacuum energy, which in turn may explain the
present accelerated cosmic expansion. We concentrate our attention in models
where the vacuum energy decreases as an inverse power law of the scale factor.
These models agree with the observed accelerating universe, while fitting
simultaneously the observational data for the density and deceleration
parameter. The redshift at which the vacuum energy can start to dominate
depends on the mass density of ordinary matter. For Omega = 0.3, the transition
from decelerated to accelerated cosmic expansion occurs at z approx 0.48 +/-
0.20, which is compatible with SNe data. We set a lower bound on the
deceleration parameter today, namely q > - 1 + 3 Omega/2, i.e., q > - 0.55 for
Omega = 0.3. The future evolution of the universe crucially depends on the time
when vacuum starts to dominate over ordinary matter. If it dominates only
recently, at an epoch z < 0.64, then the universe is accelerating today and
will continue that way forever. If vacuum dominates earlier, at z > 0.64, then
the deceleration comes back and the universe recollapses at some point in the
distant future. In the first case, quintessence and Cardassian expansion can be
formally interpreted as the low energy limit of our model, although they are
entirely different in philosophy. In the second case there is no correspondence
between these models and ours.
| [
{
"created": "Thu, 2 Dec 2004 04:00:13 GMT",
"version": "v1"
},
{
"created": "Sun, 2 Oct 2005 02:21:32 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"de Leon",
"J. Ponce",
""
]
] | Braneworld theory provides a natural setting to treat, at a classical level, the cosmological effects of vacuum energy. Non-static extra dimensions can generally lead to a variable vacuum energy, which in turn may explain the present accelerated cosmic expansion. We concentrate our attention in models where the vacuum energy decreases as an inverse power law of the scale factor. These models agree with the observed accelerating universe, while fitting simultaneously the observational data for the density and deceleration parameter. The redshift at which the vacuum energy can start to dominate depends on the mass density of ordinary matter. For Omega = 0.3, the transition from decelerated to accelerated cosmic expansion occurs at z approx 0.48 +/- 0.20, which is compatible with SNe data. We set a lower bound on the deceleration parameter today, namely q > - 1 + 3 Omega/2, i.e., q > - 0.55 for Omega = 0.3. The future evolution of the universe crucially depends on the time when vacuum starts to dominate over ordinary matter. If it dominates only recently, at an epoch z < 0.64, then the universe is accelerating today and will continue that way forever. If vacuum dominates earlier, at z > 0.64, then the deceleration comes back and the universe recollapses at some point in the distant future. In the first case, quintessence and Cardassian expansion can be formally interpreted as the low energy limit of our model, although they are entirely different in philosophy. In the second case there is no correspondence between these models and ours. |
gr-qc/0410086 | Allan Joseph Michael Medved | A.J.M. Medved | A brief commentary on black hole entropy | 4 pages, Revtex; (v2) some mistaken terminology is corrected | null | null | null | gr-qc | null | It is commonplace, in the literature, to find that the Bekenstein-Hawking
entropy has been endowed with having an explicit statistical interpretation. In
the following essay, we discuss why such a viewpoint warrants a certain degree
of caution.
| [
{
"created": "Mon, 18 Oct 2004 19:53:41 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Oct 2004 00:40:54 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Medved",
"A. J. M.",
""
]
] | It is commonplace, in the literature, to find that the Bekenstein-Hawking entropy has been endowed with having an explicit statistical interpretation. In the following essay, we discuss why such a viewpoint warrants a certain degree of caution. |
2206.14733 | Cosimo Bambi | Jiale Gu, Shafqat Riaz, Askar B. Abdikamalov, Dimitry Ayzenberg,
Cosimo Bambi | Probing bumblebee gravity with black hole X-ray data | 9 pages, 5 figures. v2: refereed version | Eur. Phys. J. C (2022) 82:708 | 10.1140/epjc/s10052-022-10686-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bumblebee gravity is one of the simplest gravity theories with spontaneous
Lorentz symmetry breaking. Since we know a rotating black hole solution in
bumblebee gravity, we can potentially test this model with the available
astrophysical observations of black holes. In this work, we construct a
reflection model in bumblebee gravity and we use our model to analyze the
reflection features of a NuSTAR spectrum of the Galactic black hole EXO
1846-031 in order to constrain the Lorentz-violating parameter $\ell$. We find
that the analysis of the reflection features in the spectrum of EXO 1846-031
cannot constrain the parameter $\ell$ because of a very strong degeneracy
between the estimates of $\ell$ and of the black hole spin parameter $a_*$.
Such a degeneracy may be broken by combining other observations.
| [
{
"created": "Wed, 29 Jun 2022 15:56:21 GMT",
"version": "v1"
},
{
"created": "Mon, 15 Aug 2022 07:29:42 GMT",
"version": "v2"
}
] | 2022-08-16 | [
[
"Gu",
"Jiale",
""
],
[
"Riaz",
"Shafqat",
""
],
[
"Abdikamalov",
"Askar B.",
""
],
[
"Ayzenberg",
"Dimitry",
""
],
[
"Bambi",
"Cosimo",
""
]
] | Bumblebee gravity is one of the simplest gravity theories with spontaneous Lorentz symmetry breaking. Since we know a rotating black hole solution in bumblebee gravity, we can potentially test this model with the available astrophysical observations of black holes. In this work, we construct a reflection model in bumblebee gravity and we use our model to analyze the reflection features of a NuSTAR spectrum of the Galactic black hole EXO 1846-031 in order to constrain the Lorentz-violating parameter $\ell$. We find that the analysis of the reflection features in the spectrum of EXO 1846-031 cannot constrain the parameter $\ell$ because of a very strong degeneracy between the estimates of $\ell$ and of the black hole spin parameter $a_*$. Such a degeneracy may be broken by combining other observations. |
1510.00851 | Karthik Shankar | Karthik H. Shankar | Horizonless, singularity-free, compact shells satisfying NEC | 14 pages, 1 figure | Gen.Rel.Grav. 49 (2017) no.2, 33 | 10.1007/s10714-017-2196-9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational collapse singularities are undesirable, yet inevitable to a
large extent in General Relativity. When matter satisfying null energy
condition collapses to the extent a closed trapped surface is formed, a
singularity is inevitable according to Penrose's singularity theorem. Since
positive mass vacuum solutions are generally black holes with trapped surfaces
inside the event horizon, matter cannot collapse to an arbitrarily small size
without generating a singularity. However, in modified theories of gravity
where positive mass vacuum solutions are naked singularities with no trapped
surfaces, it is reasonable to expect that matter can collapse to an arbitrarily
small size without generating a singularity. Here we examine this possibility
in the context of a modified theory of gravity with torsion in an extra
dimension. We study singularity-free static shell solutions to evaluate the
validity of the null energy condition on the shell. We find that with
sufficiently high pressure, matter can be collapsed to arbitrarily small size
without violating the null energy condition and without producing a
singularity.
| [
{
"created": "Sat, 3 Oct 2015 17:45:20 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Feb 2017 18:33:50 GMT",
"version": "v2"
}
] | 2020-03-09 | [
[
"Shankar",
"Karthik H.",
""
]
] | Gravitational collapse singularities are undesirable, yet inevitable to a large extent in General Relativity. When matter satisfying null energy condition collapses to the extent a closed trapped surface is formed, a singularity is inevitable according to Penrose's singularity theorem. Since positive mass vacuum solutions are generally black holes with trapped surfaces inside the event horizon, matter cannot collapse to an arbitrarily small size without generating a singularity. However, in modified theories of gravity where positive mass vacuum solutions are naked singularities with no trapped surfaces, it is reasonable to expect that matter can collapse to an arbitrarily small size without generating a singularity. Here we examine this possibility in the context of a modified theory of gravity with torsion in an extra dimension. We study singularity-free static shell solutions to evaluate the validity of the null energy condition on the shell. We find that with sufficiently high pressure, matter can be collapsed to arbitrarily small size without violating the null energy condition and without producing a singularity. |
1702.06991 | Subhajit Saha | Subenoy Chakraborty and Subhajit Saha | Quantum Tunnelling for Hawking Radiation from Both Static and Dynamic
Black Holes | 15 pages | Advances in High Energy Physics 2014, 168487 (2014) | 10.1155/2014/168487 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The paper deals with Hawking radiation from both a general static black hole
and a nonstatic spherically symmetric black hole. In case of static black hole,
tunnelling of nonzero mass particles is considered and due to complicated
calculations, quantum corrections are calculated only up to the first order.
The results are compared with those for massless particles near the horizon. On
the other hand, for dynamical black hole, quantum corrections are incorporated
using the Hamilton-Jacobi method beyond semiclassical approximation. It is
found that different order correction terms satisfy identical differential
equation and are solved by a typical technique. Finally, using the law of black
hole mechanics, a general modified form of the black hole entropy is obtained
considering modified Hawking temperature.
| [
{
"created": "Sat, 18 Feb 2017 16:53:46 GMT",
"version": "v1"
}
] | 2017-02-24 | [
[
"Chakraborty",
"Subenoy",
""
],
[
"Saha",
"Subhajit",
""
]
] | The paper deals with Hawking radiation from both a general static black hole and a nonstatic spherically symmetric black hole. In case of static black hole, tunnelling of nonzero mass particles is considered and due to complicated calculations, quantum corrections are calculated only up to the first order. The results are compared with those for massless particles near the horizon. On the other hand, for dynamical black hole, quantum corrections are incorporated using the Hamilton-Jacobi method beyond semiclassical approximation. It is found that different order correction terms satisfy identical differential equation and are solved by a typical technique. Finally, using the law of black hole mechanics, a general modified form of the black hole entropy is obtained considering modified Hawking temperature. |
1612.05480 | Jaume Haro | Llibert Arest\'e Sal\'o, Jaume Amor\'os and Jaume de Haro | Qualitative study in Loop Quantum Cosmology | 12 pages, 7 figures. Version accepted for publication in CQG | Class.Quant.Grav. 34 (2017) no.23, 235001 | 10.1088/1361-6382/aa9311 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This work contains a detailed qualitative analysis, in General Relativity and
in Loop Quantum Cosmology, of the dynamics in the associated phase space of a
scalar field minimally coupled with gravity, whose potential mimics the
dynamics of a perfect fluid with a linear Equation of State (EoS). Dealing with
the orbits (solutions) of the system, we will see that there are analytic ones,
which lead to the same dynamics as the perfect fluid, and our goal is to check
their stability, depending on the value of the EoS parameter, i.e., to show
whether the other orbits converge or diverge to these analytic solutions at
early and late times.
| [
{
"created": "Fri, 16 Dec 2016 14:23:47 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Dec 2016 11:45:25 GMT",
"version": "v2"
},
{
"created": "Fri, 13 Oct 2017 07:03:07 GMT",
"version": "v3"
}
] | 2017-11-09 | [
[
"Saló",
"Llibert Aresté",
""
],
[
"Amorós",
"Jaume",
""
],
[
"de Haro",
"Jaume",
""
]
] | This work contains a detailed qualitative analysis, in General Relativity and in Loop Quantum Cosmology, of the dynamics in the associated phase space of a scalar field minimally coupled with gravity, whose potential mimics the dynamics of a perfect fluid with a linear Equation of State (EoS). Dealing with the orbits (solutions) of the system, we will see that there are analytic ones, which lead to the same dynamics as the perfect fluid, and our goal is to check their stability, depending on the value of the EoS parameter, i.e., to show whether the other orbits converge or diverge to these analytic solutions at early and late times. |
gr-qc/0304057 | Bei-Lok Hu | B. L. Hu, Albert Roura, Sukanya Sinha, E. Verdaguer | Quantum Noise and Fluctuations in Gravitation and Cosmology | 16 pages Latex; small changes in a couple of footnotes | null | 10.1117/12.488949 | umdpp 03-045 | gr-qc | null | We give a short update of our research program on nonequilibrium statistical
field theory applied to quantum processes in the early universe and black
holes, as well as the development of stochastic gravity theory as an extension
of semiclassical gravity and an intermediary in the 'bottom-up' approach to
quantum gravity.
| [
{
"created": "Tue, 15 Apr 2003 13:16:13 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Apr 2003 18:59:02 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Hu",
"B. L.",
""
],
[
"Roura",
"Albert",
""
],
[
"Sinha",
"Sukanya",
""
],
[
"Verdaguer",
"E.",
""
]
] | We give a short update of our research program on nonequilibrium statistical field theory applied to quantum processes in the early universe and black holes, as well as the development of stochastic gravity theory as an extension of semiclassical gravity and an intermediary in the 'bottom-up' approach to quantum gravity. |
gr-qc/0404100 | Jorma Louko | Jorma Louko, Alberto Molgado | Refined algebraic quantisation with the triangular subgroup of SL(2,R) | 30 pages. LaTeX with amsfonts, amsmath, amssymb. (v4: Typos
corrected. Published version.) | Int.J.Mod.Phys. D14 (2005) 1131 | 10.1142/S0218271805006894 | null | gr-qc hep-th math-ph math.MP | null | We investigate refined algebraic quantisation with group averaging in a
constrained Hamiltonian system whose gauge group is the connected component of
the lower triangular subgroup of SL(2,R). The unreduced phase space is
T^*R^{p+q} with p>0 and q>0, and the system has a distinguished classical
o(p,q) observable algebra. Group averaging with the geometric average of the
right and left invariant measures, invariant under the group inverse, yields a
Hilbert space that carries a maximally degenerate principal unitary series
representation of O(p,q). The representation is nontrivial iff (p,q) is not
(1,1), which is also the condition for the classical reduced phase space to be
a symplectic manifold up to a singular subset of measure zero. We present a
detailed comparison to an algebraic quantisation that imposes the constraints
in the sense H_a Psi = 0 and postulates self-adjointness of the o(p,q)
observables. Under certain technical assumptions that parallel those of the
group averaging theory, this algebraic quantisation gives no quantum theory
when (p,q) = (1,2) or (2,1), or when p>1, q>1 and p+q is odd.
| [
{
"created": "Fri, 23 Apr 2004 17:33:11 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Dec 2004 13:17:11 GMT",
"version": "v2"
},
{
"created": "Mon, 6 Jun 2005 17:52:50 GMT",
"version": "v3"
},
{
"created": "Mon, 15 Aug 2005 09:52:13 GMT",
"version": "v4"
}
] | 2009-11-10 | [
[
"Louko",
"Jorma",
""
],
[
"Molgado",
"Alberto",
""
]
] | We investigate refined algebraic quantisation with group averaging in a constrained Hamiltonian system whose gauge group is the connected component of the lower triangular subgroup of SL(2,R). The unreduced phase space is T^*R^{p+q} with p>0 and q>0, and the system has a distinguished classical o(p,q) observable algebra. Group averaging with the geometric average of the right and left invariant measures, invariant under the group inverse, yields a Hilbert space that carries a maximally degenerate principal unitary series representation of O(p,q). The representation is nontrivial iff (p,q) is not (1,1), which is also the condition for the classical reduced phase space to be a symplectic manifold up to a singular subset of measure zero. We present a detailed comparison to an algebraic quantisation that imposes the constraints in the sense H_a Psi = 0 and postulates self-adjointness of the o(p,q) observables. Under certain technical assumptions that parallel those of the group averaging theory, this algebraic quantisation gives no quantum theory when (p,q) = (1,2) or (2,1), or when p>1, q>1 and p+q is odd. |
1009.1136 | Steven Carlip | Steven Carlip | The Small Scale Structure of Spacetime | 14 pages, two eps figures; to appear in Foundations of Space and
Time, edited by George Ellis, Jeff Murugan, Amanda Weltman (Cambridge
University Press) | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Several lines of evidence hint that quantum gravity at very small distances
may be effectively two-dimensional. I summarize the evidence for such
``spontaneous dimensional reduction,'' and suggest an additional argument
coming from the strong-coupling limit of the Wheeler-DeWitt equation. If this
description proves to be correct, it suggests a fascinating relationship
between small-scale quantum spacetime and the behavior of cosmologies near an
asymptotically silent singularity.
| [
{
"created": "Mon, 6 Sep 2010 19:47:59 GMT",
"version": "v1"
}
] | 2010-09-07 | [
[
"Carlip",
"Steven",
""
]
] | Several lines of evidence hint that quantum gravity at very small distances may be effectively two-dimensional. I summarize the evidence for such ``spontaneous dimensional reduction,'' and suggest an additional argument coming from the strong-coupling limit of the Wheeler-DeWitt equation. If this description proves to be correct, it suggests a fascinating relationship between small-scale quantum spacetime and the behavior of cosmologies near an asymptotically silent singularity. |
gr-qc/0310070 | Joan Josep Ferrando | Joan Josep Ferrando and Juan Antonio S\'aez | Type I vacuum solutions with aligned Papapetrou fields: an intrinsic
characterization | 14 pages; v2: added new section, references and table | J.Math.Phys. 47 (2006) 112501 | 10.1063/1.2363258 | null | gr-qc | null | We show that Petrov type I vacuum solutions admitting a Killing vector whose
Papapetrou field is aligned with a principal bivector of the Weyl tensor are
the Kasner and Taub metrics, their counterpart with timelike orbits and their
associated windmill-like solutions, as well as the Petrov homogeneous vacuum
solution. We recover all these metrics by using an integration method based on
an invariant classification which allows us to characterize every solution. In
this way we obtain an intrinsic and explicit algorithm to identify them.
| [
{
"created": "Tue, 14 Oct 2003 13:30:08 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Nov 2006 14:34:43 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Ferrando",
"Joan Josep",
""
],
[
"Sáez",
"Juan Antonio",
""
]
] | We show that Petrov type I vacuum solutions admitting a Killing vector whose Papapetrou field is aligned with a principal bivector of the Weyl tensor are the Kasner and Taub metrics, their counterpart with timelike orbits and their associated windmill-like solutions, as well as the Petrov homogeneous vacuum solution. We recover all these metrics by using an integration method based on an invariant classification which allows us to characterize every solution. In this way we obtain an intrinsic and explicit algorithm to identify them. |
gr-qc/9811055 | Laszlo A. Gergely | L\'aszl\'o \'A. Gergely, Zolt\'an Perj\'es and M\'aty\'as Vas\'uth | Spin effects in radiating compact binaries | 4 pages, 1 figure, sprocl.sty included, to appear in the Proceedings
of the ERES98 Conference | null | null | null | gr-qc | null | We review and summarize our results concerning the influence of the spins of
a compact binary system on the motion of the binary and on its gravitational
reaction. We describe briefly our method which lead us to compute the secular
changes in the post-Newtonian motion and the averaged radiative losses. Our
description is valid to 1.5 post-Newtonian order. All spin-orbit and some
spin-spin effects are considered which contribute at this accuracy. This
approach enabled us to give both the evolutions of the constants of the
nonradiative motion and of the relevant angular variables under radiation
reaction.
| [
{
"created": "Tue, 17 Nov 1998 14:54:59 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Gergely",
"László Á.",
""
],
[
"Perjés",
"Zoltán",
""
],
[
"Vasúth",
"Mátyás",
""
]
] | We review and summarize our results concerning the influence of the spins of a compact binary system on the motion of the binary and on its gravitational reaction. We describe briefly our method which lead us to compute the secular changes in the post-Newtonian motion and the averaged radiative losses. Our description is valid to 1.5 post-Newtonian order. All spin-orbit and some spin-spin effects are considered which contribute at this accuracy. This approach enabled us to give both the evolutions of the constants of the nonradiative motion and of the relevant angular variables under radiation reaction. |
1911.09519 | Iver Brevik | I. Brevik and A. V. Timoshkin | Viscous Fluid Holographic Bounce | 10 pages; to appear in International Journal of Geometric Methods in
Modern Physics | Int. J. Geometric Methods in Mod. Phys. 2050023 (2020) | 10.1142/S0219887820500231 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate bounce cosmological models in the presence of a viscous fluid,
making use of generalized holographic cutoffs introduced by Nojiri and Odintsov
(2017). We consider both an exponential, a power-law, and a double exponential
form for the scale factor. By use of these models we calculate expressions for
infrared cutoffs analytically, such that they correspond to the particle
horizon at the bounce. Finally we derive the energy conservation equation, from
the holographic point of view. In that way the relationship between the viscous
fluid bounce and the holographic bounce is demonstrated.
| [
{
"created": "Thu, 21 Nov 2019 15:06:09 GMT",
"version": "v1"
}
] | 2019-12-25 | [
[
"Brevik",
"I.",
""
],
[
"Timoshkin",
"A. V.",
""
]
] | We investigate bounce cosmological models in the presence of a viscous fluid, making use of generalized holographic cutoffs introduced by Nojiri and Odintsov (2017). We consider both an exponential, a power-law, and a double exponential form for the scale factor. By use of these models we calculate expressions for infrared cutoffs analytically, such that they correspond to the particle horizon at the bounce. Finally we derive the energy conservation equation, from the holographic point of view. In that way the relationship between the viscous fluid bounce and the holographic bounce is demonstrated. |
2111.01130 | Jean Pierre Gazeau | Gilles Cohen-Tannoudji and Jean-Pierre Gazeau | Cold Dark Matter: A Gluonic Bose--Einstein Condensate in Anti-de Sitter
Space Time | This article belongs to the Special Issue Selected Papers from the
1st International Electronic Conference on Universe (ECU 2021) | Universe 2021 | 10.3390/universe7110402 | null | gr-qc | http://creativecommons.org/publicdomain/zero/1.0/ | In the same way as the realization of some of the famous gedanken experiments
imagined by the founding fathers of quantum mechanics has recently led to the
current renewal of the interpretation of quantum physics, it seems that the
most recent progresses of observational astrophysics can be interpreted as the
realization of some cosmological gedanken experiments such as the removal from
the universe of the whole visible matter or the cosmic time travel leading to a
new cosmological standard model. This standard model involves two dark
components of the universe, dark energy and dark matter. Whereas dark energy is
usually associated with the cosmological constant, we propose to explain dark
matter as a pure QCD effect, namely a gluonic Bose Einstein condensate,
following the transition from the quark gluon plasma phase to the colorless
hadronic phase.
Our approach not only allows us to assume a ratio Dark/Visible equal to 11/2
but also provides gluons (and di-gluons, viewed as quasi-particles) with an
extra mass of vibrational nature. Such an interpretation would comfort the idea
that, apart from the violation of the matter/antimatter symmetry satisfying the
Sakharov's conditions, the reconciliation of particle physics and cosmology
needs not the recourse to any ad hoc fields, particles or hidden variables.
| [
{
"created": "Sat, 30 Oct 2021 17:55:18 GMT",
"version": "v1"
},
{
"created": "Thu, 18 Nov 2021 10:45:31 GMT",
"version": "v2"
}
] | 2021-11-19 | [
[
"Cohen-Tannoudji",
"Gilles",
""
],
[
"Gazeau",
"Jean-Pierre",
""
]
] | In the same way as the realization of some of the famous gedanken experiments imagined by the founding fathers of quantum mechanics has recently led to the current renewal of the interpretation of quantum physics, it seems that the most recent progresses of observational astrophysics can be interpreted as the realization of some cosmological gedanken experiments such as the removal from the universe of the whole visible matter or the cosmic time travel leading to a new cosmological standard model. This standard model involves two dark components of the universe, dark energy and dark matter. Whereas dark energy is usually associated with the cosmological constant, we propose to explain dark matter as a pure QCD effect, namely a gluonic Bose Einstein condensate, following the transition from the quark gluon plasma phase to the colorless hadronic phase. Our approach not only allows us to assume a ratio Dark/Visible equal to 11/2 but also provides gluons (and di-gluons, viewed as quasi-particles) with an extra mass of vibrational nature. Such an interpretation would comfort the idea that, apart from the violation of the matter/antimatter symmetry satisfying the Sakharov's conditions, the reconciliation of particle physics and cosmology needs not the recourse to any ad hoc fields, particles or hidden variables. |
0803.3641 | Jiri Kovar | Zdenek Stuchlik and Jiri Kovar | Pseudo-Newtonian gravitational potential for Schwarzschild-de Sitter
spacetimes | 17 pages, 11 figures, accepted by International Journal of Modern
Physics D (2008) | null | 10.1142/S021827180801373X | null | gr-qc astro-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Pseudo-Newtonian gravitational potential describing the gravitational field
of static and spherically symmetric black holes in the universe with a
repulsive cosmological constant is introduced. In order to demonstrate the
accuracy of the pseudo-Newtonian approach, the related effective potential for
test-particle motion is constructed and compared with its general relativistic
counterpart given by the Schwarzschild-de Sitter geometry. The results indicate
that such an approach could be useful in applications of developed Newtonian
theories of accretion discs in astrophysically interesting situations in large
galactic structures for the Schwarzschild-de Sitter spacetimes with the
cosmological parameter y=(1/3)\Lambda M^2<10^{-6}.
| [
{
"created": "Tue, 25 Mar 2008 22:19:59 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Stuchlik",
"Zdenek",
""
],
[
"Kovar",
"Jiri",
""
]
] | Pseudo-Newtonian gravitational potential describing the gravitational field of static and spherically symmetric black holes in the universe with a repulsive cosmological constant is introduced. In order to demonstrate the accuracy of the pseudo-Newtonian approach, the related effective potential for test-particle motion is constructed and compared with its general relativistic counterpart given by the Schwarzschild-de Sitter geometry. The results indicate that such an approach could be useful in applications of developed Newtonian theories of accretion discs in astrophysically interesting situations in large galactic structures for the Schwarzschild-de Sitter spacetimes with the cosmological parameter y=(1/3)\Lambda M^2<10^{-6}. |
gr-qc/9611032 | Piotr Chrusciel | P.T. Chrusciel and G.J. Galloway | ``Nowhere'' differentiable horizons | 28 pages, Latex with pstricks and graphicx, 4 ps figures | Commun.Math.Phys. 193 (1998) 449-470 | 10.1007/s002200050336 | null | gr-qc | null | It is folklore knowledge amongst general relativists that horizons are well
behaved, continuously differentiable hypersurfaces except perhaps on a
negligible subset one needs not to bother with. We show that this is not the
case, by constructing a Cauchy horizon, as well as a black hole event horizon,
which contain no open subset on which they are differentiable.
| [
{
"created": "Tue, 12 Nov 1996 17:36:57 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Chrusciel",
"P. T.",
""
],
[
"Galloway",
"G. J.",
""
]
] | It is folklore knowledge amongst general relativists that horizons are well behaved, continuously differentiable hypersurfaces except perhaps on a negligible subset one needs not to bother with. We show that this is not the case, by constructing a Cauchy horizon, as well as a black hole event horizon, which contain no open subset on which they are differentiable. |
1711.08501 | Emanuel Gallo | Emanuel Gallo and Osvaldo M. Moreschi | Constructing balanced equations of motion for particles in general
relativity: the harmonic gauge case | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Based in the framework of article (arXiv:1609.02110), where we have presented
the general problems one encounters in the construction of balanced equations
of motions for particles in relativistic theories of gravity, we present in
this work the explicit balanced equations of motion for a compact object in
general relativity in the harmonic gauge.
| [
{
"created": "Wed, 22 Nov 2017 20:49:52 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Mar 2018 14:14:14 GMT",
"version": "v2"
}
] | 2018-03-15 | [
[
"Gallo",
"Emanuel",
""
],
[
"Moreschi",
"Osvaldo M.",
""
]
] | Based in the framework of article (arXiv:1609.02110), where we have presented the general problems one encounters in the construction of balanced equations of motions for particles in relativistic theories of gravity, we present in this work the explicit balanced equations of motion for a compact object in general relativity in the harmonic gauge. |
1110.0041 | Jerzy Matyjasek | Jerzy Matyjasek and Katarzyna Zwierzchowska | Semiclassical lukewarm black holes | null | null | 10.1103/PhysRevD.85.024009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The perturbative solutions to the semiclassical Einstein field equations
describing spherically-symmetric and static lukewarm black hole are
constructed. The source term is composed of the (classical) stress-energy
tensor of the electromagnetic field and the renormalized stress-energy tensor
of the quantized massive scalar field in a large mass limit. We used two
different parametrizations. In the first parametrization we calculated the
zeroth-order solution. Subsequently, making use of the quantum part of the
total stress-energy tensor constructed in the classical background we
calculated the corrections to the metric potentials and the corrections to the
horizons. This procedure can be thought of as switching the quantized field on
and analyzing its influence on the classical background via the back-reaction.
In the second parametrization we are looking for a self-consistent lukewarm
solution from the very beginning. This requires knowledge of a generic tensor
which depends functionally on the metric tensor. The transformation formulas
relating the line element in both parametrizations are given.
| [
{
"created": "Fri, 30 Sep 2011 22:03:12 GMT",
"version": "v1"
}
] | 2015-05-30 | [
[
"Matyjasek",
"Jerzy",
""
],
[
"Zwierzchowska",
"Katarzyna",
""
]
] | The perturbative solutions to the semiclassical Einstein field equations describing spherically-symmetric and static lukewarm black hole are constructed. The source term is composed of the (classical) stress-energy tensor of the electromagnetic field and the renormalized stress-energy tensor of the quantized massive scalar field in a large mass limit. We used two different parametrizations. In the first parametrization we calculated the zeroth-order solution. Subsequently, making use of the quantum part of the total stress-energy tensor constructed in the classical background we calculated the corrections to the metric potentials and the corrections to the horizons. This procedure can be thought of as switching the quantized field on and analyzing its influence on the classical background via the back-reaction. In the second parametrization we are looking for a self-consistent lukewarm solution from the very beginning. This requires knowledge of a generic tensor which depends functionally on the metric tensor. The transformation formulas relating the line element in both parametrizations are given. |
gr-qc/9911120 | Vladimir Dzhunushaliev | V.Dzhunushaliev and D.Singleton | Experimental test for 5th dimension in Kaluza-Klein gravity | 4 pages, 4 figures, Talk given at the Third Meeting on Constrained
Dynamics and Quantum Gravity, Villasimius (Sardinia), September 13-17, 1999 | Nucl.Phys.Proc.Suppl. 88 (2000) 225-228 | 10.1016/S0920-5632(00)00772-6 | null | gr-qc hep-th | null | Several electric/magnetic charged solutions (dyons) to 5D Kaluza-Klein
gravity on the principal bundle are reviewed. Here we examine the possibility
that these solutions can act as quantum virtual wormholes in spacetime foam
models. By applying a sufficently large, external electric and/or magnetic
field it may be possible to ``inflate'' these solutions from a quantum to a
classical state. This effect could lead to a possible experimental signal for
higher dimensions in multidimensional gravity.
| [
{
"created": "Tue, 30 Nov 1999 08:58:50 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Dzhunushaliev",
"V.",
""
],
[
"Singleton",
"D.",
""
]
] | Several electric/magnetic charged solutions (dyons) to 5D Kaluza-Klein gravity on the principal bundle are reviewed. Here we examine the possibility that these solutions can act as quantum virtual wormholes in spacetime foam models. By applying a sufficently large, external electric and/or magnetic field it may be possible to ``inflate'' these solutions from a quantum to a classical state. This effect could lead to a possible experimental signal for higher dimensions in multidimensional gravity. |
0707.0726 | Carsten Gundlach | David Garfinkle, Carsten Gundlach, David Hilditch | Comments on Bona-Masso type slicing conditions in long-term black hole
evolutions | 14 pages, LaTex, psfrag | Class.Quant.Grav.25:075007,2008 | 10.1088/0264-9381/25/7/075007 | null | gr-qc | null | We review in generality why time-independent endstates can be reached in
black hole and collapse simulations, with and without excision. We characterise
the Killing states of the Bona-Masso slicing condition with time derivative
along the normals to the slice ("BMn") as solutions of a mixed
elliptic/hyperbolic differential equation on the slice. We show numerically
that these steady states can be reached as end states from typical initial data
with excision but can be reached with the puncture method only if the puncture
is not numerically well resolved. During the evolution, BMn slicings often form
gauge shocks. It may be that these are not seen in current 3D simulations only
through lack of resolution, although we expect that they can be avoided with
some care. Finally we point out that excision with BMn as currently implemented
is ill-posed and therefore not expected to converge; this can be cured. In
technical appendixes, we derive the equations of pure gauge systems on a fixed
spacetime, and bring the BSSN/NOR equations into 3-dimensional tensor form
suitable for multiple coordinate patches or spherical polar coordinates.
| [
{
"created": "Thu, 5 Jul 2007 07:36:32 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Garfinkle",
"David",
""
],
[
"Gundlach",
"Carsten",
""
],
[
"Hilditch",
"David",
""
]
] | We review in generality why time-independent endstates can be reached in black hole and collapse simulations, with and without excision. We characterise the Killing states of the Bona-Masso slicing condition with time derivative along the normals to the slice ("BMn") as solutions of a mixed elliptic/hyperbolic differential equation on the slice. We show numerically that these steady states can be reached as end states from typical initial data with excision but can be reached with the puncture method only if the puncture is not numerically well resolved. During the evolution, BMn slicings often form gauge shocks. It may be that these are not seen in current 3D simulations only through lack of resolution, although we expect that they can be avoided with some care. Finally we point out that excision with BMn as currently implemented is ill-posed and therefore not expected to converge; this can be cured. In technical appendixes, we derive the equations of pure gauge systems on a fixed spacetime, and bring the BSSN/NOR equations into 3-dimensional tensor form suitable for multiple coordinate patches or spherical polar coordinates. |
1811.02014 | Christian Knoll | Jose Luis Bl\'azquez-Salcedo and Christian Knoll | Quasinormal modes of Dirac spinors in the background of rotating black
holes in four and five dimensions | 16 pages, 7 figures | Class. Quantum Grav. 36 105012 (2019) | 10.1088/1361-6382/ab1882 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the quasinormal modes of massive Dirac spinors in the background of
rotating black holes. In particular, we consider the Kerr geometry as well as
the five dimensional Myers-Perry spacetime with equal angular momenta. We
decouple the equations using the standard methods from the literature. In the
five dimensional Myers-Perry black hole the angular equation is solved
analytically. Using the continued fraction method, we calculate the spectrum of
quasinormal modes for the ground modes and first excited modes. We analyze, in
a systematic way, its dependence on the different parameters of the black hole
and fermionic field. We compare our values with previous results available in
the literature for Kerr and for the static limit. The numerical results show
several differences between the four and five dimensional cases. For instance,
in five dimensions the symmetry between the positive and negative (real)
frequency of the modes breaks down, which results in a richer spectrum.
| [
{
"created": "Mon, 5 Nov 2018 20:08:16 GMT",
"version": "v1"
},
{
"created": "Fri, 30 Nov 2018 11:38:53 GMT",
"version": "v2"
}
] | 2019-04-30 | [
[
"Blázquez-Salcedo",
"Jose Luis",
""
],
[
"Knoll",
"Christian",
""
]
] | We study the quasinormal modes of massive Dirac spinors in the background of rotating black holes. In particular, we consider the Kerr geometry as well as the five dimensional Myers-Perry spacetime with equal angular momenta. We decouple the equations using the standard methods from the literature. In the five dimensional Myers-Perry black hole the angular equation is solved analytically. Using the continued fraction method, we calculate the spectrum of quasinormal modes for the ground modes and first excited modes. We analyze, in a systematic way, its dependence on the different parameters of the black hole and fermionic field. We compare our values with previous results available in the literature for Kerr and for the static limit. The numerical results show several differences between the four and five dimensional cases. For instance, in five dimensions the symmetry between the positive and negative (real) frequency of the modes breaks down, which results in a richer spectrum. |
0812.4993 | Clovis Jacinto de Matos | Clovis Jacinto de Matos | Testing Loop Quantum Gravity and Electromagnetic Dark Energy in
Superconductors | 13 pages, 2 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In 1989 Cabrera and Tate reported an anomalous excess of mass of the Cooper
pairs in rotating thin Niobium rings. So far, this experimental result never
received a proper theoretical explanation in the context of superconductor's
physics. In the present work we argue that what Cabrera and Tate interpreted as
an anomalous excess of mass can also be associated with a deviation from the
classical gravitomagnetic Larmor theorem due to the presence of dark energy in
the superconductor, as well as with the discrete structure of the area of the
superconducting Niobium ring as predicted by Loop Quantum Gravity. From Cabrera
and Tate measurements we deduce that the quantization of spacetime in
superconducting circular rings occurs at the Planck-Einstein scale $l_{PE} =
(\hbar G/c^3 \Lambda)^{1/4}\sim 3.77\times 10 ^{-5} m$, instead of the Planck
scale $l_{P} =(\hbar G / c^3)^{1/2}=1.61 \times 10 ^{-35} m$, with an Immirzi
parameter which depends on the specific critical temperature of the
superconducting material and on the area of the ring. The stephan-Boltzmann law
for quantized areas delimited by superconducting rings is predicted, and an
experimental concept based on the electromagnetic black-body radiation emitted
by this surfaces, is proposed to test loop quantum gravity and electromagnetic
dark energy in superconductors.
| [
{
"created": "Tue, 30 Dec 2008 01:48:58 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Aug 2009 15:05:58 GMT",
"version": "v2"
}
] | 2009-08-06 | [
[
"de Matos",
"Clovis Jacinto",
""
]
] | In 1989 Cabrera and Tate reported an anomalous excess of mass of the Cooper pairs in rotating thin Niobium rings. So far, this experimental result never received a proper theoretical explanation in the context of superconductor's physics. In the present work we argue that what Cabrera and Tate interpreted as an anomalous excess of mass can also be associated with a deviation from the classical gravitomagnetic Larmor theorem due to the presence of dark energy in the superconductor, as well as with the discrete structure of the area of the superconducting Niobium ring as predicted by Loop Quantum Gravity. From Cabrera and Tate measurements we deduce that the quantization of spacetime in superconducting circular rings occurs at the Planck-Einstein scale $l_{PE} = (\hbar G/c^3 \Lambda)^{1/4}\sim 3.77\times 10 ^{-5} m$, instead of the Planck scale $l_{P} =(\hbar G / c^3)^{1/2}=1.61 \times 10 ^{-35} m$, with an Immirzi parameter which depends on the specific critical temperature of the superconducting material and on the area of the ring. The stephan-Boltzmann law for quantized areas delimited by superconducting rings is predicted, and an experimental concept based on the electromagnetic black-body radiation emitted by this surfaces, is proposed to test loop quantum gravity and electromagnetic dark energy in superconductors. |
0807.0347 | Salvatore Capozziello | H. Motavali, S. Capozziello, M. Rowshan Almeh Jog | Scalar-tensor cosmology with R^{-1} curvature correction by Noether
Symmetry | 7 pages | Phys.Lett.B666:10-15,2008 | 10.1016/j.physletb.2008.06.058 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss scalar-tensor cosmology with an extra $R^{-1}$ correction by the
Noether Symmetry Approach. The existence of such a symmetry selects the forms
of the coupling $\omega(\phi)$, of the potential $V(\phi)$ and allows to obtain
physically interesting exact cosmological solutions.
| [
{
"created": "Wed, 2 Jul 2008 13:34:58 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Motavali",
"H.",
""
],
[
"Capozziello",
"S.",
""
],
[
"Jog",
"M. Rowshan Almeh",
""
]
] | We discuss scalar-tensor cosmology with an extra $R^{-1}$ correction by the Noether Symmetry Approach. The existence of such a symmetry selects the forms of the coupling $\omega(\phi)$, of the potential $V(\phi)$ and allows to obtain physically interesting exact cosmological solutions. |
1902.08219 | Prashant Kocherlakota Mr. | Prashant Kocherlakota and Pankaj S. Joshi | An Approach to Stability Analyses in General Relativity via Symplectic
Geometry | 15 pages, 1 figure. Arab. J. Math. (2019) | null | 10.1007/s40065-019-0266-4 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We begin with a review of the statements of non-linear, linear and mode
stability of autonomous dynamical systems in classical mechanics, using
symplectic geometry. We then discuss what the phase space and the Hamiltonian
of general relativity are, what constitutes a dynamical system, and
subsequently draw a formal analogy between the notions of stability in these
two theories. Our approach here is pedagogical and geometric, and considerably
simplifies a formal understanding of the statements regarding the stability of
stationary solutions of general relativity. In particular, the governing
equations of motion of a Hamiltonian dynamical system are simply the flow
equations of the associated symplectic Hamiltonian vector field, defined on
phase space, and the non-linear stability analysis of its critical points have
simply to do with the divergence of its flow there. Further, the linear
stability of a critical point is related to the properties of the tangent flow
of the Hamiltonian vector field. Further, we posit that a study of the
genericity of a particular black hole or naked singularity spacetime forming as
an endstate of gravitational collapse is equivalent to an inquiry of how
sensitive the orbits of the symplectic Hamiltonian vector field of general
relativity are to changes in initial data. We demonstrate this by conducting a
restricted non-linear stability analysis of the formation of a Schwarzschild
black hole, working in the usual initial value formulation of general
relativity.
| [
{
"created": "Thu, 21 Feb 2019 19:11:43 GMT",
"version": "v1"
},
{
"created": "Thu, 26 Sep 2019 11:46:58 GMT",
"version": "v2"
}
] | 2020-08-10 | [
[
"Kocherlakota",
"Prashant",
""
],
[
"Joshi",
"Pankaj S.",
""
]
] | We begin with a review of the statements of non-linear, linear and mode stability of autonomous dynamical systems in classical mechanics, using symplectic geometry. We then discuss what the phase space and the Hamiltonian of general relativity are, what constitutes a dynamical system, and subsequently draw a formal analogy between the notions of stability in these two theories. Our approach here is pedagogical and geometric, and considerably simplifies a formal understanding of the statements regarding the stability of stationary solutions of general relativity. In particular, the governing equations of motion of a Hamiltonian dynamical system are simply the flow equations of the associated symplectic Hamiltonian vector field, defined on phase space, and the non-linear stability analysis of its critical points have simply to do with the divergence of its flow there. Further, the linear stability of a critical point is related to the properties of the tangent flow of the Hamiltonian vector field. Further, we posit that a study of the genericity of a particular black hole or naked singularity spacetime forming as an endstate of gravitational collapse is equivalent to an inquiry of how sensitive the orbits of the symplectic Hamiltonian vector field of general relativity are to changes in initial data. We demonstrate this by conducting a restricted non-linear stability analysis of the formation of a Schwarzschild black hole, working in the usual initial value formulation of general relativity. |
0905.0020 | Peter Shawhan | LIGO Scientific Collaboration: B. P. Abbott, et al | Search for gravitational-wave bursts in the first year of the fifth LIGO
science run | v3: various figure and text edits; submitted to PRD; 26 pages | Phys.Rev.D80:102001,2009 | 10.1103/PhysRevD.80.102001 | LIGO-P080056 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the results obtained from an all-sky search for gravitational-wave
(GW) bursts in the 64-2000 Hz frequency range in data collected by the LIGO
detectors during the first year (November 2005 - November 2006) of their fifth
science run. The total analyzed livetime was 268.6 days. Multiple hierarchical
data analysis methods were invoked in this search. The overall sensitivity
expressed in terms of the root-sum-square (rss) strain amplitude h_{rss} for
gravitational-wave bursts with various morphologies was in the range of 6 times
10^{-22} Hz^{-1/2} to a few times 10^{-21} Hz^{-1/2}. No GW signals were
observed and a frequentist upper limit of 3.6 events per year on the rate of
strong GW bursts was placed at the 90% confidence level. As in our previous
searches, we also combined this rate limit with the detection efficiency for
selected waveform morphologies to obtain event rate versus strength exclusion
curves. In sensitivity, these exclusion curves are the most stringent to date.
| [
{
"created": "Fri, 1 May 2009 00:14:26 GMT",
"version": "v1"
},
{
"created": "Tue, 12 May 2009 22:11:21 GMT",
"version": "v2"
},
{
"created": "Wed, 27 May 2009 13:56:57 GMT",
"version": "v3"
},
{
"created": "Tue, 20 Oct 2009 06:23:26 GMT",
"version": "v4"
}
] | 2009-12-04 | [
[
"LIGO Scientific Collaboration",
"",
""
],
[
"Abbott",
"B. P.",
""
]
] | We present the results obtained from an all-sky search for gravitational-wave (GW) bursts in the 64-2000 Hz frequency range in data collected by the LIGO detectors during the first year (November 2005 - November 2006) of their fifth science run. The total analyzed livetime was 268.6 days. Multiple hierarchical data analysis methods were invoked in this search. The overall sensitivity expressed in terms of the root-sum-square (rss) strain amplitude h_{rss} for gravitational-wave bursts with various morphologies was in the range of 6 times 10^{-22} Hz^{-1/2} to a few times 10^{-21} Hz^{-1/2}. No GW signals were observed and a frequentist upper limit of 3.6 events per year on the rate of strong GW bursts was placed at the 90% confidence level. As in our previous searches, we also combined this rate limit with the detection efficiency for selected waveform morphologies to obtain event rate versus strength exclusion curves. In sensitivity, these exclusion curves are the most stringent to date. |
1301.1728 | Joel Saavedra | Samuel Lepe and Joel Saavedra | On Ho\v{r}ava-Lifshitz Cosmology | 11 pages, major revision | null | 10.1007/s10509-014-1793-2 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss some aspects of the Horava-Lifshitz cosmology with different
matter components considered as dominants at different stages of the cosmic
evolution (each stage is represented by an equation of state
pressure/density=constant). We compare cosmological solutions from this theory
with their counterparts of General Relativity (Friedmann cosmology). At early
times, the Horava- Lifshitz cosmology contains a curvature-dependent dominant
term which is stiff matter-reminiscent and this fact motivates to discuss, in
some detail, this term beside the usual stiff matter component
(pressure=density) if we are thinking in the role that this fluid could have
played early in the framework of the holographic cosmology. Nevertheless, we
show that an early stiff matter component is of little relevance in
Horava-Lifshitz cosmology.
| [
{
"created": "Wed, 9 Jan 2013 00:44:14 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Mar 2013 13:13:05 GMT",
"version": "v2"
},
{
"created": "Tue, 30 Jul 2013 20:14:53 GMT",
"version": "v3"
}
] | 2015-06-12 | [
[
"Lepe",
"Samuel",
""
],
[
"Saavedra",
"Joel",
""
]
] | We discuss some aspects of the Horava-Lifshitz cosmology with different matter components considered as dominants at different stages of the cosmic evolution (each stage is represented by an equation of state pressure/density=constant). We compare cosmological solutions from this theory with their counterparts of General Relativity (Friedmann cosmology). At early times, the Horava- Lifshitz cosmology contains a curvature-dependent dominant term which is stiff matter-reminiscent and this fact motivates to discuss, in some detail, this term beside the usual stiff matter component (pressure=density) if we are thinking in the role that this fluid could have played early in the framework of the holographic cosmology. Nevertheless, we show that an early stiff matter component is of little relevance in Horava-Lifshitz cosmology. |
2303.12556 | Jo\~ao Lu\'is Rosa | A.S. Lob\~ao, Jo\~ao Lu\'is Rosa, D. Bazeia | Scalar-tensor representation to $f(R,T)-$brane with Gauss-Bonnet gravity | 11 pages, 7 figures | Int.J.Mod.Phys.A (2023) 2350171 | 10.1142/S0217751X23501713 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we generalize the analysis of the $f(R,T)-$brane via the
inclusion of a term proportional to the Gauss-Bonnet invariant. We consider an
action of the form $F(R,G,T)=f(R,T)+\alpha G$, where $T$ is the trace of the
stress-energy tensor, $R$ is the Ricci scalar, and $\alpha$ is a real parameter
that controls the contribution of the Gauss-Bonnet invariant $G$. We introduce
the first-order formalism to obtain solutions for the source field of the brane
in the special case where $f(R,T)=R+\beta T$ and illustrate its procedure with
an application to the sine-Gordon model. We also investigate the general case
of the $f(R,T)-$brane via the use of the scalar-tensor formalism, where we also
use the first-order formalism to obtain solutions. Finally, we investigate the
linear stability of the brane under tensor perturbations of the the modified
Einstein's field equations. Our results indicate that the Gauss-Bonnet term may
induce qualitatively different behaviors of the quantities on the brane,
provided that its contribution is large enough.
| [
{
"created": "Wed, 22 Mar 2023 13:37:37 GMT",
"version": "v1"
}
] | 2024-01-17 | [
[
"Lobão",
"A. S.",
""
],
[
"Rosa",
"João Luís",
""
],
[
"Bazeia",
"D.",
""
]
] | In this paper, we generalize the analysis of the $f(R,T)-$brane via the inclusion of a term proportional to the Gauss-Bonnet invariant. We consider an action of the form $F(R,G,T)=f(R,T)+\alpha G$, where $T$ is the trace of the stress-energy tensor, $R$ is the Ricci scalar, and $\alpha$ is a real parameter that controls the contribution of the Gauss-Bonnet invariant $G$. We introduce the first-order formalism to obtain solutions for the source field of the brane in the special case where $f(R,T)=R+\beta T$ and illustrate its procedure with an application to the sine-Gordon model. We also investigate the general case of the $f(R,T)-$brane via the use of the scalar-tensor formalism, where we also use the first-order formalism to obtain solutions. Finally, we investigate the linear stability of the brane under tensor perturbations of the the modified Einstein's field equations. Our results indicate that the Gauss-Bonnet term may induce qualitatively different behaviors of the quantities on the brane, provided that its contribution is large enough. |
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