id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1701.01032 | Sumanta Chakraborty | Sumanta Chakraborty and Soumitra SenGupta | Gravity stabilizes itself | Revised Version, 19 pages, no figures | Eur. Phys. J. C 77, 573 (2017) | 10.1140/epjc/s10052-017-5138-5 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that a possible resolution to the stabilization of an extra spatial
dimension (radion) can be obtained solely in the context of gravitational
dynamics itself without the necessity of introducing any external stabilizing
field. In this scenario the stabilized value of the radion field gets
determined in terms of the parameters appearing in the higher curvature
gravitational action. Furthermore, the mass of the radion field and its
coupling to the standard model fields are found to be in the weak scale
implying possible signatures in the TeV scale colliders. Some resulting
implications are also discussed.
| [
{
"created": "Fri, 30 Dec 2016 21:00:28 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Aug 2017 04:43:05 GMT",
"version": "v2"
}
] | 2017-08-30 | [
[
"Chakraborty",
"Sumanta",
""
],
[
"SenGupta",
"Soumitra",
""
]
] | We show that a possible resolution to the stabilization of an extra spatial dimension (radion) can be obtained solely in the context of gravitational dynamics itself without the necessity of introducing any external stabilizing field. In this scenario the stabilized value of the radion field gets determined in terms of the parameters appearing in the higher curvature gravitational action. Furthermore, the mass of the radion field and its coupling to the standard model fields are found to be in the weak scale implying possible signatures in the TeV scale colliders. Some resulting implications are also discussed. |
gr-qc/0403034 | Mihalis Dafermos | Mihalis Dafermos and Igor Rodnianski | A note on boundary value problems for black hole evolutions | 8 pages, 3 figures | null | null | null | gr-qc | null | In recent work of Allen at. al., heuristic and numerical arguments were put
forth to suggest that boundary value problems for black hole evolution, where
an appropriate Sommerfeld radiation condition is imposed, would fail to produce
Price law tails. The interest in this issue lies in its possible implications
for numerical relativity, where black hole evolution is typically studied in
terms of such boundary formulations. In this note, it is shown rigorously that
indeed, Price law tails do not arise in this case, i.e. that Sommerfeld (and
more general) radiation conditions lead to decay faster than any polynomial
power. Our setting is the collapse of a spherically symmetric self-gravitating
scalar field. We allow an additional gravitationally coupled Maxwell field. The
proof also applies to the easier problem of a spherically symmetric solution of
the wave equation on a Schwarzschild or Reissner-Nordstrom background. The
method relies on previous work of the authors.
| [
{
"created": "Mon, 8 Mar 2004 18:12:14 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Dafermos",
"Mihalis",
""
],
[
"Rodnianski",
"Igor",
""
]
] | In recent work of Allen at. al., heuristic and numerical arguments were put forth to suggest that boundary value problems for black hole evolution, where an appropriate Sommerfeld radiation condition is imposed, would fail to produce Price law tails. The interest in this issue lies in its possible implications for numerical relativity, where black hole evolution is typically studied in terms of such boundary formulations. In this note, it is shown rigorously that indeed, Price law tails do not arise in this case, i.e. that Sommerfeld (and more general) radiation conditions lead to decay faster than any polynomial power. Our setting is the collapse of a spherically symmetric self-gravitating scalar field. We allow an additional gravitationally coupled Maxwell field. The proof also applies to the easier problem of a spherically symmetric solution of the wave equation on a Schwarzschild or Reissner-Nordstrom background. The method relies on previous work of the authors. |
2204.00662 | Abhirup Ghosh | Abhirup Ghosh (for the LIGO Scientific--Virgo--Kagra Collaborations) | Summary of Tests of General Relativity with GWTC-3 | 8 pages, 3 figures, contribution to the 2022 Gravitation session of
the 56th Rencontres de Moriond; summary of arXiv:2112.06861 | null | null | LIGO-P2200097 | gr-qc astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Observations of gravitational waves (GWs) by the advanced LIGO--Virgo
detectors provide us with ground breaking opportunities to test predictions of
Einstein's theory of general relativity (GR) in the strong field regime. In
this article, we summarise the nine tests of GR performed on the new GW signals
included in the third GW transient catalog, GWTC-3. These tests include overall
and self-consistency checks of the signal with the data; tests of the GW
generation, propagation and polarizations; and probes of the nature of the
remnant object by testing the BH ringdown hypothesis and searching for
post-merger echoes. The results from the new events are combined with those
previously published wherever possible. We do not find any statistically
significant deviation from GR and set the most stringent bounds yet on possible
departures from theory.
| [
{
"created": "Fri, 1 Apr 2022 19:01:26 GMT",
"version": "v1"
}
] | 2022-04-05 | [
[
"Ghosh",
"Abhirup",
"",
"for the LIGO Scientific--Virgo--Kagra Collaborations"
]
] | Observations of gravitational waves (GWs) by the advanced LIGO--Virgo detectors provide us with ground breaking opportunities to test predictions of Einstein's theory of general relativity (GR) in the strong field regime. In this article, we summarise the nine tests of GR performed on the new GW signals included in the third GW transient catalog, GWTC-3. These tests include overall and self-consistency checks of the signal with the data; tests of the GW generation, propagation and polarizations; and probes of the nature of the remnant object by testing the BH ringdown hypothesis and searching for post-merger echoes. The results from the new events are combined with those previously published wherever possible. We do not find any statistically significant deviation from GR and set the most stringent bounds yet on possible departures from theory. |
1109.3010 | Muhammad Sharif | M. Sharif and H. Rizwana Kausar | Effects of f(R) Model on the Dynamical Instability of Expansionfree
Gravitational Collapse | 26 pages, no figure. arXiv admin note: text overlap with
arXiv:1108.2666 | JCAP 07(2011)022 | 10.1088/1475-7516/2011/07/022 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Dark energy models based on f(R) theory have been extensively studied in
literature to realize the late time acceleration. In this paper, we have chosen
a viable f(R) model and discussed its effects on the dynamical instability of
expansionfree fluid evolution generating a central vacuum cavity. For this
purpose, contracted Bianchi identities are obtained for both the usual matter
as well as dark source. The term dark source is named to the higher order
curvature corrections arising from f(R) gravity. The perturbation scheme is
applied and different terms belonging to Newtonian and post Newtonian regimes
are identified. It is found that instability range of expansionfree fluid on
external boundary as well as on internal vacuum cavity is independent of
adiabatic index $\Gamma$ but depends upon the density profile, pressure
anisotropy and f(R) model.
| [
{
"created": "Wed, 14 Sep 2011 07:42:30 GMT",
"version": "v1"
}
] | 2015-05-30 | [
[
"Sharif",
"M.",
""
],
[
"Kausar",
"H. Rizwana",
""
]
] | Dark energy models based on f(R) theory have been extensively studied in literature to realize the late time acceleration. In this paper, we have chosen a viable f(R) model and discussed its effects on the dynamical instability of expansionfree fluid evolution generating a central vacuum cavity. For this purpose, contracted Bianchi identities are obtained for both the usual matter as well as dark source. The term dark source is named to the higher order curvature corrections arising from f(R) gravity. The perturbation scheme is applied and different terms belonging to Newtonian and post Newtonian regimes are identified. It is found that instability range of expansionfree fluid on external boundary as well as on internal vacuum cavity is independent of adiabatic index $\Gamma$ but depends upon the density profile, pressure anisotropy and f(R) model. |
1206.2702 | Shin'ichi Nojiri | E. Elizalde, A.N. Makarenko, S. Nojiri, V.V. Obukhov, and S.D.
Odintsov | Multiple $\Lambda$CDM cosmology with string landscape features and
future singularities | LaTeX 11 pages, 10 figures | null | 10.1007/s10509-012-1339-4 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Multiple $\Lambda$CDM cosmology is studied in a way that is formally a
classical analog of the Casimir effect. Such cosmology corresponds to a
time-dependent dark fluid model or, alternatively, to its scalar field
presentation, and it motivated by the string landscape picture. The future
evolution of the several dark energy models constructed within the scheme is
carefully investigated. It turns out to be almost always possible to choose the
parameters in the models so that they match the most recent and accurate
astronomical values. To this end, several universes are presented which mimick
(multiple) $\Lambda$CDM cosmology but exhibit Little Rip, asymptotically de
Sitter, or Type I, II, III, and IV finite-time singularity behavior in the far
future, with disintegration of all bound objects in the cases of Big Rip,
Little Rip and Pseudo-Rip cosmologies.
| [
{
"created": "Wed, 13 Jun 2012 02:29:45 GMT",
"version": "v1"
}
] | 2015-06-05 | [
[
"Elizalde",
"E.",
""
],
[
"Makarenko",
"A. N.",
""
],
[
"Nojiri",
"S.",
""
],
[
"Obukhov",
"V. V.",
""
],
[
"Odintsov",
"S. D.",
""
]
] | Multiple $\Lambda$CDM cosmology is studied in a way that is formally a classical analog of the Casimir effect. Such cosmology corresponds to a time-dependent dark fluid model or, alternatively, to its scalar field presentation, and it motivated by the string landscape picture. The future evolution of the several dark energy models constructed within the scheme is carefully investigated. It turns out to be almost always possible to choose the parameters in the models so that they match the most recent and accurate astronomical values. To this end, several universes are presented which mimick (multiple) $\Lambda$CDM cosmology but exhibit Little Rip, asymptotically de Sitter, or Type I, II, III, and IV finite-time singularity behavior in the far future, with disintegration of all bound objects in the cases of Big Rip, Little Rip and Pseudo-Rip cosmologies. |
gr-qc/9804053 | null | S. Capozziello, R. de Ritis, A.A. Marino | Recovering the effective cosmological constant in extended gravity
theories | 24 pages, Latex, submitted to Gen.Rel.and Grav | Gen.Rel.Grav.30:1247-1272,1998 | 10.1023/A:1026651129626 | null | gr-qc | null | In the framework of extended gravity theories, we discuss the meaning of a
time dependent "cosmological constant" and give a set of conditions to recover
asymptotic de Sitter behaviour for a class of cosmological models independently
of initial data. To this purpose we introduce a time-dependent (effective)
quantity which asymptotically becomes the true cosmological constant. We will
deal with scalar-tensor, fourth and higher than fourth-order theories.
| [
{
"created": "Wed, 22 Apr 1998 10:28:45 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Capozziello",
"S.",
""
],
[
"de Ritis",
"R.",
""
],
[
"Marino",
"A. A.",
""
]
] | In the framework of extended gravity theories, we discuss the meaning of a time dependent "cosmological constant" and give a set of conditions to recover asymptotic de Sitter behaviour for a class of cosmological models independently of initial data. To this purpose we introduce a time-dependent (effective) quantity which asymptotically becomes the true cosmological constant. We will deal with scalar-tensor, fourth and higher than fourth-order theories. |
gr-qc/0603124 | Jerome Perez | Jerome Perez | Dynamics of Anisotropic Universes | 12 pages, 6 figures, Proceedings of the Albert Einstein Century
International Conference, held in Paris, France, July 18-22, 2005. to be
published in AIP | null | 10.1063/1.2399648 | null | gr-qc | null | We present a general study of the dynamical properties of Anisotropic Bianchi
Universes in the context of Einstein General Relativity. Integrability results
using Kovalevskaya exponents are reported and connected to general knowledge
about Bianchi dynamics. Finally, dynamics toward singularity in Bianchi type
VIII and IX universes are showed to be equivalent in some precise sence.
| [
{
"created": "Thu, 30 Mar 2006 12:51:31 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Perez",
"Jerome",
""
]
] | We present a general study of the dynamical properties of Anisotropic Bianchi Universes in the context of Einstein General Relativity. Integrability results using Kovalevskaya exponents are reported and connected to general knowledge about Bianchi dynamics. Finally, dynamics toward singularity in Bianchi type VIII and IX universes are showed to be equivalent in some precise sence. |
1810.00978 | Alexander B. Balakin | Alexander B. Balakin and Dmitry E. Groshev | Polarization and stratification of axionically active plasma in a dyon
magnetosphere | 20 pages, 4 figures, the revised version published in Phys.Rev.D | Phys. Rev. D 99, 023006 (2019) | 10.1103/PhysRevD.99.023006 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The state of a static spherically symmetric relativistic axionically active
multi-component plasma in the gravitational, magnetic and electric fields of an
axionic dyon is studied in the framework of the Einstein - Maxwell - Boltzmann
- axion theory. We assume that the equations of axion electrodynamics, the
covariant relativistic kinetic equations, and the equation for the axion field
with modified Higgs-type potential are nonlinearly coupled; the gravitational
field in the dyon exterior is assumed to be fixed and to be of the
Reissner-Nordstr\"om type. We introduce the extended Lorentz force, which acts
on the particles in the axionically active plasma, and analyze the consequences
of this generalization. The analysis of exact solutions, obtained in the
framework of this model for the relativistic Boltzmann electron-ion and
electron-positron plasmas, as well as, for degenerated zero-temperature
electron gas, shows that the phenomena of polarization and stratification can
appear in plasma, attracting attention to the axionic analog of the known
Pannekoek-Rosseland effect.
| [
{
"created": "Mon, 1 Oct 2018 21:00:20 GMT",
"version": "v1"
},
{
"created": "Sat, 12 Jan 2019 10:37:23 GMT",
"version": "v2"
}
] | 2019-01-16 | [
[
"Balakin",
"Alexander B.",
""
],
[
"Groshev",
"Dmitry E.",
""
]
] | The state of a static spherically symmetric relativistic axionically active multi-component plasma in the gravitational, magnetic and electric fields of an axionic dyon is studied in the framework of the Einstein - Maxwell - Boltzmann - axion theory. We assume that the equations of axion electrodynamics, the covariant relativistic kinetic equations, and the equation for the axion field with modified Higgs-type potential are nonlinearly coupled; the gravitational field in the dyon exterior is assumed to be fixed and to be of the Reissner-Nordstr\"om type. We introduce the extended Lorentz force, which acts on the particles in the axionically active plasma, and analyze the consequences of this generalization. The analysis of exact solutions, obtained in the framework of this model for the relativistic Boltzmann electron-ion and electron-positron plasmas, as well as, for degenerated zero-temperature electron gas, shows that the phenomena of polarization and stratification can appear in plasma, attracting attention to the axionic analog of the known Pannekoek-Rosseland effect. |
1708.00404 | Lionel London | Lionel London, Sebastian Khan, Edward Fauchon-Jones, Cecilio Garc\'ia,
Mark Hannam, Sascha Husa, Xisco Jim\'enez Forteza, Chinmay Kalaghatgi, Frank
Ohme, Francesco Pannarale | First higher-multipole model of gravitational waves from spinning and
coalescing black-hole binaries | 4 pages, 4 figures | Phys. Rev. Lett. 120, 161102 (2018) | 10.1103/PhysRevLett.120.161102 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational-wave observations of binary black holes currently rely on
theoretical models that predict the dominant multipoles (l,m) of the radiation
during inspiral, merger and ringdown. We introduce a simple method to include
the subdominant multipoles to binary black hole gravitational waveforms, given
a frequency-domain model for the dominant multipoles. The amplitude and phase
of the original model are appropriately stretched and rescaled using
post-Newtonian results (for the inspiral), perturbation theory (for the
ringdown), and a smooth transition between the two. No additional tuning to
numerical-relativity simulations is required. We apply a variant of this method
to the non-precessing PhenomD model. The result, PhenomHM, constitutes the
first higher-multipole model of spinning black-hole binaries, and currently
includes the (l,m) = (2,2), (3,3), (4,4), (2,1), (3,2), (4,3) radiative
moments. Comparisons with numerical-relativity waveforms demonstrate that
PhenomHM is more accurate than dominant-multipole-only models for all binary
configurations, and typically improves the measurement of binary properties.
| [
{
"created": "Tue, 1 Aug 2017 16:07:48 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Aug 2017 09:14:46 GMT",
"version": "v2"
},
{
"created": "Fri, 22 Dec 2017 14:15:55 GMT",
"version": "v3"
},
{
"created": "Thu, 18 Jan 2018 18:57:05 GMT",
"version": "v4"
}
] | 2018-04-25 | [
[
"London",
"Lionel",
""
],
[
"Khan",
"Sebastian",
""
],
[
"Fauchon-Jones",
"Edward",
""
],
[
"García",
"Cecilio",
""
],
[
"Hannam",
"Mark",
""
],
[
"Husa",
"Sascha",
""
],
[
"Forteza",
"Xisco Jiménez",
""
... | Gravitational-wave observations of binary black holes currently rely on theoretical models that predict the dominant multipoles (l,m) of the radiation during inspiral, merger and ringdown. We introduce a simple method to include the subdominant multipoles to binary black hole gravitational waveforms, given a frequency-domain model for the dominant multipoles. The amplitude and phase of the original model are appropriately stretched and rescaled using post-Newtonian results (for the inspiral), perturbation theory (for the ringdown), and a smooth transition between the two. No additional tuning to numerical-relativity simulations is required. We apply a variant of this method to the non-precessing PhenomD model. The result, PhenomHM, constitutes the first higher-multipole model of spinning black-hole binaries, and currently includes the (l,m) = (2,2), (3,3), (4,4), (2,1), (3,2), (4,3) radiative moments. Comparisons with numerical-relativity waveforms demonstrate that PhenomHM is more accurate than dominant-multipole-only models for all binary configurations, and typically improves the measurement of binary properties. |
gr-qc/0209068 | Marcello Ortaggio | Marcello Ortaggio (Trento) and Jiri Podolsky (Prague) | Impulsive waves in electrovac direct product spacetimes with Lambda | 6 pages, 1 figure, LaTeX 2e. To appear in Class. Quantum Grav | Class.Quant.Grav. 19 (2002) 5221-5227 | 10.1088/0264-9381/19/20/313 | null | gr-qc hep-th | null | A complete family of non-expanding impulsive waves in spacetimes which are
the direct product of two 2-spaces of constant curvature is presented. In
addition to previously investigated impulses in Minkowski, (anti-)Nariai and
Bertotti-Robinson universes, a new explicit class of impulsive waves which
propagate in the exceptional electrovac Plebanski-Hacyan spacetimes with a
cosmological constant Lambda is constructed. In particular, pure gravitational
waves generated by null particles with an arbitrary multipole structure are
described. The metrics are impulsive members of a more general family of the
Kundt spacetimes of type II. The well-known pp-waves are recovered for
Lambda=0.
| [
{
"created": "Fri, 20 Sep 2002 10:20:11 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Ortaggio",
"Marcello",
"",
"Trento"
],
[
"Podolsky",
"Jiri",
"",
"Prague"
]
] | A complete family of non-expanding impulsive waves in spacetimes which are the direct product of two 2-spaces of constant curvature is presented. In addition to previously investigated impulses in Minkowski, (anti-)Nariai and Bertotti-Robinson universes, a new explicit class of impulsive waves which propagate in the exceptional electrovac Plebanski-Hacyan spacetimes with a cosmological constant Lambda is constructed. In particular, pure gravitational waves generated by null particles with an arbitrary multipole structure are described. The metrics are impulsive members of a more general family of the Kundt spacetimes of type II. The well-known pp-waves are recovered for Lambda=0. |
2002.08682 | Wen-Biao Han | Qian-Yun Yun, Wen-Biao Han, Gang Wang, Shu-Cheng Yang | Investigating eccentricities of the binary black hole signals from the
LIGO-Virgo catalog GWTC-1 | 9 pages, 6 figures, 3 tables | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the first Gravitational-Wave Transient Catalogue of LIGO and Virgo, all
events are announced having zero eccentricity. In the present paper, we
investigate the performance of SEOBNRE which is a spin-aligned eccentric
waveform model in time-domain. By comparing with all the eccentric waveforms in
SXS library, we find that the SEOBNRE coincides perfectly with numerical
relativity data. Employing the SEOBNRE, we re-estimate the eccentricities of
all black hole merger events. We find that most of these events allow a
possibility for existence of initial eccentricities at 10 Hz band, but are
totally circularized at the observed frequency ($ \gtrsim 20$ Hz). The upcoming
update of LIGO and the next generation detector like as Einstein Telescope,
will observe the gravitational waves starting at 10 Hz or even lower. If the
eccentricity exists at the lower frequency, it may significantly support the
dynamical formation mechanism taking place in globular clusters.
| [
{
"created": "Thu, 20 Feb 2020 11:28:27 GMT",
"version": "v1"
}
] | 2020-02-21 | [
[
"Yun",
"Qian-Yun",
""
],
[
"Han",
"Wen-Biao",
""
],
[
"Wang",
"Gang",
""
],
[
"Yang",
"Shu-Cheng",
""
]
] | In the first Gravitational-Wave Transient Catalogue of LIGO and Virgo, all events are announced having zero eccentricity. In the present paper, we investigate the performance of SEOBNRE which is a spin-aligned eccentric waveform model in time-domain. By comparing with all the eccentric waveforms in SXS library, we find that the SEOBNRE coincides perfectly with numerical relativity data. Employing the SEOBNRE, we re-estimate the eccentricities of all black hole merger events. We find that most of these events allow a possibility for existence of initial eccentricities at 10 Hz band, but are totally circularized at the observed frequency ($ \gtrsim 20$ Hz). The upcoming update of LIGO and the next generation detector like as Einstein Telescope, will observe the gravitational waves starting at 10 Hz or even lower. If the eccentricity exists at the lower frequency, it may significantly support the dynamical formation mechanism taking place in globular clusters. |
0704.2013 | Marcelo Alves | M. Alves | The conical singularity method and the energy-momentum tensor near the
black hole horizon using the Kruskal coordinates | null | Mod.Phys.Lett.A22:3057-3063,2007 | 10.1142/S0217732307023651 | null | gr-qc hep-th | null | We apply the conical singularity method to the two dimensional version of the
Schwarzschild metric to obtain the Kruskal coordinates of the black hole in a
very simple and direct way. Then we make use of this metric in an approximated
version and calculate the expected value of energy-momentum tensor of a
massless quantum field near the horizon, resulting in regular expressions for
its components.
| [
{
"created": "Mon, 16 Apr 2007 13:34:49 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Alves",
"M.",
""
]
] | We apply the conical singularity method to the two dimensional version of the Schwarzschild metric to obtain the Kruskal coordinates of the black hole in a very simple and direct way. Then we make use of this metric in an approximated version and calculate the expected value of energy-momentum tensor of a massless quantum field near the horizon, resulting in regular expressions for its components. |
gr-qc/0702048 | Mayeul Arminjon | Mayeul Arminjon | Dirac-type equations in a gravitational field, with vector wave function | 35 pages. Version accepted for publication in Foundations of Physics.
Title changed. Introduction expanded: detailed discussion of i) the vector
Dirac wave function and ii) the status of the equivalence principle, main
section (Sect. 2) improved by introducing the specific connection earlier
(see Theorem 1), and other improvements accounting for the referees' remarks | Found.Phys.38:1020-1045,2008 | 10.1007/s10701-008-9249-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An analysis of the classical-quantum correspondence shows that it needs to
identify a preferred class of coordinate systems, which defines a torsionless
connection. One such class is that of the locally-geodesic systems,
corresponding to the Levi-Civita connection. Another class, thus another
connection, emerges if a preferred reference frame is available. From the
classical Hamiltonian that rules geodesic motion, the correspondence yields two
distinct Klein-Gordon equations and two distinct Dirac-type equations in a
general metric, depending on the connection used. Each of these two equations
is generally-covariant, transforms the wave function as a four-vector, and
differs from the Fock-Weyl gravitational Dirac equation (DFW equation). One
obeys the equivalence principle in an often-accepted sense, whereas the DFW
equation obeys that principle only in an extended sense.
| [
{
"created": "Thu, 8 Feb 2007 14:22:16 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Mar 2007 17:13:45 GMT",
"version": "v2"
},
{
"created": "Wed, 27 Jun 2007 14:40:55 GMT",
"version": "v3"
},
{
"created": "Tue, 14 Oct 2008 09:26:01 GMT",
"version": "v4"
}
] | 2008-12-18 | [
[
"Arminjon",
"Mayeul",
""
]
] | An analysis of the classical-quantum correspondence shows that it needs to identify a preferred class of coordinate systems, which defines a torsionless connection. One such class is that of the locally-geodesic systems, corresponding to the Levi-Civita connection. Another class, thus another connection, emerges if a preferred reference frame is available. From the classical Hamiltonian that rules geodesic motion, the correspondence yields two distinct Klein-Gordon equations and two distinct Dirac-type equations in a general metric, depending on the connection used. Each of these two equations is generally-covariant, transforms the wave function as a four-vector, and differs from the Fock-Weyl gravitational Dirac equation (DFW equation). One obeys the equivalence principle in an often-accepted sense, whereas the DFW equation obeys that principle only in an extended sense. |
1011.4933 | Sergey S. Kokarev | Sergey S. Kokarev | Complementarity of Kinematics and Geometry in General Relativity Theory | The paper is developed version of talk, presented at the conference
RusGrav-2010 (June 2010, Moscow), submitted to GRG | null | 10.1134/S0202289311040086 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Relations between kinematics, geometry and law of reference frame motion are
considered. We show, that kinematical tensors define geometry up to a space
functional arbitrariness when integrability condition for spin tensor is
satisfied. Some aspects of geometrization principle and geometrical
conventionalism of Poincare are discussed in a light of the obtained results.
| [
{
"created": "Mon, 22 Nov 2010 20:52:21 GMT",
"version": "v1"
}
] | 2015-05-20 | [
[
"Kokarev",
"Sergey S.",
""
]
] | Relations between kinematics, geometry and law of reference frame motion are considered. We show, that kinematical tensors define geometry up to a space functional arbitrariness when integrability condition for spin tensor is satisfied. Some aspects of geometrization principle and geometrical conventionalism of Poincare are discussed in a light of the obtained results. |
1811.07676 | Hamed Pejhan | Hamed Pejhan, Surena Rahbardehghan, Mohammad Enayati, Kazuharu Bamba,
and Anzhong Wang | `Hidden' symmetry of linearized gravity in de Sitter space | 6 pages, no figure, version accepted for publication in Physics
Letters B | Phys. Lett. B 795 (2019) 220-224 | 10.1016/j.physletb.2019.06.012 | FU-PCG-51 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We demonstrate that the linearized Einstein gravity in de Sitter (dS)
spacetime besides the evident symmetries also possesses the additional (local)
symmetry $h_{\mu\nu}\rightarrow h_{\mu\nu} + {\cal E}_{\mu\nu}\chi$, where
${\cal E}_{\mu\nu}$ is a spin-two projector tensor and $\chi$ is an arbitrary
constant function. We argue that an anomalous symmetry associated with this
hitherto `hidden' property of the existing physics is indeed at the origin of
`dS breaking' in linearized quantum gravity.
| [
{
"created": "Mon, 19 Nov 2018 13:35:39 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Apr 2019 00:58:10 GMT",
"version": "v2"
},
{
"created": "Sun, 9 Jun 2019 10:32:21 GMT",
"version": "v3"
},
{
"created": "Thu, 20 Jun 2019 06:18:58 GMT",
"version": "v4"
}
] | 2019-06-27 | [
[
"Pejhan",
"Hamed",
""
],
[
"Rahbardehghan",
"Surena",
""
],
[
"Enayati",
"Mohammad",
""
],
[
"Bamba",
"Kazuharu",
""
],
[
"Wang",
"Anzhong",
""
]
] | We demonstrate that the linearized Einstein gravity in de Sitter (dS) spacetime besides the evident symmetries also possesses the additional (local) symmetry $h_{\mu\nu}\rightarrow h_{\mu\nu} + {\cal E}_{\mu\nu}\chi$, where ${\cal E}_{\mu\nu}$ is a spin-two projector tensor and $\chi$ is an arbitrary constant function. We argue that an anomalous symmetry associated with this hitherto `hidden' property of the existing physics is indeed at the origin of `dS breaking' in linearized quantum gravity. |
gr-qc/0103055 | Jeremy Nicholas Butterfield | J. N. Butterfield | The End of Time? | 48 pages Latex. A shortened version will appear in 'The British
Journal for Philosophy of Science' | null | null | null | gr-qc | null | I discuss J. Barbour's Machian theories of dynamics, and his proposal that a
Machian perspective enables one to solve the problem of time in quantum
geometrodynamics (by saying that there is no time). I concentrate on his recent
book 'The End of Time' (1999).
| [
{
"created": "Thu, 15 Mar 2001 17:12:03 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Butterfield",
"J. N.",
""
]
] | I discuss J. Barbour's Machian theories of dynamics, and his proposal that a Machian perspective enables one to solve the problem of time in quantum geometrodynamics (by saying that there is no time). I concentrate on his recent book 'The End of Time' (1999). |
1210.2973 | Christian Pfeifer | Christian Pfeifer, Mattias N. R. Wohlfarth | Finsler spacetimes and gravity | Conference proceedings "Relativity and Gravitation - 100 years after
Einstein in Prague", 5 pages | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the geometry of spacetime based on a non-metric, Finslerian,
length measure, which, in terms of physics, represents a generalized clock. Our
defnition of Finsler spacetimes ensure a well defined notion of causality, a
precise description of observers and a geometric background for field theories.
Moreover we present our Finsler geometric extension of the Einstein equations,
which determine the geometry of Finsler spacetimes dynamically.
| [
{
"created": "Wed, 10 Oct 2012 16:35:02 GMT",
"version": "v1"
}
] | 2012-10-11 | [
[
"Pfeifer",
"Christian",
""
],
[
"Wohlfarth",
"Mattias N. R.",
""
]
] | We consider the geometry of spacetime based on a non-metric, Finslerian, length measure, which, in terms of physics, represents a generalized clock. Our defnition of Finsler spacetimes ensure a well defined notion of causality, a precise description of observers and a geometric background for field theories. Moreover we present our Finsler geometric extension of the Einstein equations, which determine the geometry of Finsler spacetimes dynamically. |
1510.02592 | Joanna Ja{\l}mu\.zna | Joanna Ja{\l}mu\.zna, Carsten Gundlach, Tadeusz Chmaj | Scalar field critical collapse in 2+1 dimensions | 27 pages | Phys. Rev. D 92, 124044 (2015) | 10.1103/PhysRevD.92.124044 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We carry out numerical experiments in the critical collapse of a spherically
symmetric massless scalar field in 2+1 spacetime dimensions in the presence of
a negative cosmological constant and compare them against a new theoretical
model. We approximate the true critical solution as the $n=4$ Garfinkle
solution, matched at the lightcone to a Vaidya-like solution, and corrected to
leading order for the effect of $\Lambda<0$. This approximation is only $C^3$
at the lightcone and has three growing modes. We {\em conjecture} that
pointwise it is a good approximation to a yet unknown true critical solution
that is analytic with only one growing mode (itself approximated by the top
mode of our amended Garfinkle solution). With this conjecture, we predict a
Ricci-scaling exponent of $\gamma=8/7$ and a mass-scaling exponent of
$\delta=16/23$, compatible with our numerical experiments.
| [
{
"created": "Fri, 9 Oct 2015 08:51:02 GMT",
"version": "v1"
}
] | 2015-12-30 | [
[
"Jałmużna",
"Joanna",
""
],
[
"Gundlach",
"Carsten",
""
],
[
"Chmaj",
"Tadeusz",
""
]
] | We carry out numerical experiments in the critical collapse of a spherically symmetric massless scalar field in 2+1 spacetime dimensions in the presence of a negative cosmological constant and compare them against a new theoretical model. We approximate the true critical solution as the $n=4$ Garfinkle solution, matched at the lightcone to a Vaidya-like solution, and corrected to leading order for the effect of $\Lambda<0$. This approximation is only $C^3$ at the lightcone and has three growing modes. We {\em conjecture} that pointwise it is a good approximation to a yet unknown true critical solution that is analytic with only one growing mode (itself approximated by the top mode of our amended Garfinkle solution). With this conjecture, we predict a Ricci-scaling exponent of $\gamma=8/7$ and a mass-scaling exponent of $\delta=16/23$, compatible with our numerical experiments. |
1411.7887 | Paul Frampton | Paul H. Frampton | Bang or Bounce | 6 pages | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Following up an earlier suggestion of how the Tolman Entropy Conundrum (TEC)
can be solved in a cyclic cosmology using the Come Back Empty (CBE) assumption
with phantom dark energy, here we show how the same CBE strategy may work with
a cosmological constant in the expansion era. As in the earlier case, this
leads to a multiverse, actually an infiniverse, with the concomitant issues of
predictivity and testability. Here we show how extreme flatness and homogeneity
at the bounce are natural properties of the contraction era, interestingly
without any necessity for an inflationary era at the beginning of the present
expansion. Essential ingredients in the solution of TEC are CBE contraction and
a careful treatment of what is meant by the visible universe.
| [
{
"created": "Wed, 26 Nov 2014 16:55:15 GMT",
"version": "v1"
}
] | 2014-12-01 | [
[
"Frampton",
"Paul H.",
""
]
] | Following up an earlier suggestion of how the Tolman Entropy Conundrum (TEC) can be solved in a cyclic cosmology using the Come Back Empty (CBE) assumption with phantom dark energy, here we show how the same CBE strategy may work with a cosmological constant in the expansion era. As in the earlier case, this leads to a multiverse, actually an infiniverse, with the concomitant issues of predictivity and testability. Here we show how extreme flatness and homogeneity at the bounce are natural properties of the contraction era, interestingly without any necessity for an inflationary era at the beginning of the present expansion. Essential ingredients in the solution of TEC are CBE contraction and a careful treatment of what is meant by the visible universe. |
gr-qc/0212002 | Giovanni Amelino-Camelia | Giovanni Amelino-Camelia | Improved limit on quantum-spacetime modifications of Lorentz symmetry
from observations of gamma-ray blazars | Published version [New J.Phys. 6 (2004) 188]. Title changed. Several
changes made during the long editing period. Revised commentary on
Crab-nebula synchrotron-radiation analysis reflects differences between
astro-ph/0212190v1 and astro-ph/0309681 (astro-ph/0212190v1 made a strong
claim which was softened in astro-ph/0309681). Added cautionary Comments also
relevant for the analysis of the gamma-ray threshold, the cosmic-ray GZK
threshold and photon stability | New J.Phys.6:188,2004 | 10.1088/1367-2630/6/1/188 | null | gr-qc | null | In the quantum-gravity literature there has been interest in the possibility
that quantum properties of spacetime might affect the energy/momentum
dispersion relation. The most used test theory for data analysis is based on a
modification of the laws of propagation proposed in astro-ph/9712103 [Nature
393,763], and the present best limit on the quantum-gravity scale was obtained
in gr-qc/9810044 [Phys.Rev.Lett.83,2108]. I derive an improved limit using
recent experimental information on absorption by the infrared diffuse
extragalactic background of $\gamma$-rays emitted by blazars. Foreseeable more
accurate determinations of the absorption levels could achieve Planck-scale
sensitivity. As a corollary I also show that, contrary to the recent claim of
astro-ph/0208507v3, the test theory here considered does not allow decays of
photons into electron-positron pairs, and I expose the limitations of
phenomenological proposals, such as the one reported in astro-ph/0212190, in
which one attempts to infer limits on the kinematic theory here considered
through the ad hoc introduction of a dynamical framework.
| [
{
"created": "Sat, 30 Nov 2002 00:07:16 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Jan 2003 21:21:29 GMT",
"version": "v2"
},
{
"created": "Thu, 30 Dec 2004 15:49:54 GMT",
"version": "v3"
}
] | 2011-09-13 | [
[
"Amelino-Camelia",
"Giovanni",
""
]
] | In the quantum-gravity literature there has been interest in the possibility that quantum properties of spacetime might affect the energy/momentum dispersion relation. The most used test theory for data analysis is based on a modification of the laws of propagation proposed in astro-ph/9712103 [Nature 393,763], and the present best limit on the quantum-gravity scale was obtained in gr-qc/9810044 [Phys.Rev.Lett.83,2108]. I derive an improved limit using recent experimental information on absorption by the infrared diffuse extragalactic background of $\gamma$-rays emitted by blazars. Foreseeable more accurate determinations of the absorption levels could achieve Planck-scale sensitivity. As a corollary I also show that, contrary to the recent claim of astro-ph/0208507v3, the test theory here considered does not allow decays of photons into electron-positron pairs, and I expose the limitations of phenomenological proposals, such as the one reported in astro-ph/0212190, in which one attempts to infer limits on the kinematic theory here considered through the ad hoc introduction of a dynamical framework. |
1702.00315 | Yafet Sanchez Sanchez | Yafet Sanchez Sanchez, Cesar Merlin and Ricardo Reynoso Fuentes | Lorentzian surfaces and the curvature of the Schmidt metric | null | null | null | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The b-boundary is a mathematical tool used to attach a topological boundary
to incomplete Lorentzian manifolds using a Riemaniann metric called the Schmidt
metric on the frame bundle. In this paper, we give the general form of the
Schmidt metric in the case of Lorentzian surfaces. Furthermore, we write the
Ricci scalar of the Schmidt metric in terms of the Ricci scalar of the
Lorentzian manifold and give some examples. Finally, we discuss some
applications to general relativity.
| [
{
"created": "Wed, 1 Feb 2017 15:32:19 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Nov 2017 08:17:29 GMT",
"version": "v2"
},
{
"created": "Sun, 1 Apr 2018 21:25:34 GMT",
"version": "v3"
}
] | 2018-04-03 | [
[
"Sanchez",
"Yafet Sanchez",
""
],
[
"Merlin",
"Cesar",
""
],
[
"Fuentes",
"Ricardo Reynoso",
""
]
] | The b-boundary is a mathematical tool used to attach a topological boundary to incomplete Lorentzian manifolds using a Riemaniann metric called the Schmidt metric on the frame bundle. In this paper, we give the general form of the Schmidt metric in the case of Lorentzian surfaces. Furthermore, we write the Ricci scalar of the Schmidt metric in terms of the Ricci scalar of the Lorentzian manifold and give some examples. Finally, we discuss some applications to general relativity. |
1604.02762 | M. B. Paranjape | A. Landry and M. B. Paranjape | Graviton laser | 8 pages, no figures, submitted to the 2016 Gravity Research
Foundation Essay Competiton | null | 10.1142/S0218271816440168 | UdeM-GPP-TH-16-250 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the possibility of creating a graviton laser. The lasing medium
would be a system of contained, ultra cold neutrons. Ultra cold neutrons are a
quantum mechanical system that interacts with gravitational fields and with the
phonons of the container walls. It is possible to create a population inversion
by pumping the system using the phonons. We compute the rate of spontaneous
emission of gravitons and the rate of the subsequent stimulated emission of
gravitons. The gain obtainable is directly proportional to the density of the
lasing medium and the fraction of the population inversion. The applications of
a graviton laser would be interesting.
| [
{
"created": "Mon, 11 Apr 2016 00:24:53 GMT",
"version": "v1"
}
] | 2016-11-23 | [
[
"Landry",
"A.",
""
],
[
"Paranjape",
"M. B.",
""
]
] | We consider the possibility of creating a graviton laser. The lasing medium would be a system of contained, ultra cold neutrons. Ultra cold neutrons are a quantum mechanical system that interacts with gravitational fields and with the phonons of the container walls. It is possible to create a population inversion by pumping the system using the phonons. We compute the rate of spontaneous emission of gravitons and the rate of the subsequent stimulated emission of gravitons. The gain obtainable is directly proportional to the density of the lasing medium and the fraction of the population inversion. The applications of a graviton laser would be interesting. |
gr-qc/0012052 | Kayll Lake | Nicos Pelavas, Nicholas Neary and Kayll Lake | Properties of the instantaneous Ergo Surface of a Kerr Black Hole | 15 pages, 11 figures, also on the web at
http://grtensor.phy.queensu.ca/ergo/ | Class.Quant.Grav. 18 (2001) 1319-1332 | 10.1088/0264-9381/18/7/314 | null | gr-qc astro-ph | null | This paper explores properties of the instantaneous ergo surface of a Kerr
black hole. The surface area is evaluated in closed form. In terms of the mass
($m$) and angular velocity ($a$), to second order in $a$, the area of the ergo
surface is given by $16 \pi m^2 + 4 \pi a^2$ (compared to the familiar $16 \pi
m^2 - 4 \pi a^2$ for the event horizon). Whereas the total curvature of the
instantaneous event horizon is $4 \pi$, on the ergo surface it ranges from $4
\pi$ (for $a=0$) to 0 (for $a=m$) due to conical singularities on the axis
($\theta=0,\pi$) of deficit angle $2 \pi (1-\sqrt{1-(a/m)^2})$. A careful
application of the Gauss-Bonnet theorem shows that the ergo surface remains
topologically spherical. Isometric embeddings of the ergo surface in Euclidean
3-space are defined for $0 \leq a/m \leq 1$ (compared to $0 \leq a/m \leq
\sqrt{3}/2$ for the horizon).
| [
{
"created": "Fri, 15 Dec 2000 02:48:19 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Mar 2001 18:31:31 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Pelavas",
"Nicos",
""
],
[
"Neary",
"Nicholas",
""
],
[
"Lake",
"Kayll",
""
]
] | This paper explores properties of the instantaneous ergo surface of a Kerr black hole. The surface area is evaluated in closed form. In terms of the mass ($m$) and angular velocity ($a$), to second order in $a$, the area of the ergo surface is given by $16 \pi m^2 + 4 \pi a^2$ (compared to the familiar $16 \pi m^2 - 4 \pi a^2$ for the event horizon). Whereas the total curvature of the instantaneous event horizon is $4 \pi$, on the ergo surface it ranges from $4 \pi$ (for $a=0$) to 0 (for $a=m$) due to conical singularities on the axis ($\theta=0,\pi$) of deficit angle $2 \pi (1-\sqrt{1-(a/m)^2})$. A careful application of the Gauss-Bonnet theorem shows that the ergo surface remains topologically spherical. Isometric embeddings of the ergo surface in Euclidean 3-space are defined for $0 \leq a/m \leq 1$ (compared to $0 \leq a/m \leq \sqrt{3}/2$ for the horizon). |
2304.12644 | Wenfu Cao | Wen-Fu Cao, Wen-Fang Liu, Xin Wu | Parameter constraints from shadows of Kerr-Newman-dS black holes with
cloud strings and quintessence | 30 pages, 10 figures | General Relativity and Gravitation (2023) 55:120 | 10.1007/s10714-023-03169-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The motion of photons around the Kerr-Newman-dS black hole surrounded by
quintessence and a cloud of strings is investigated. The existence of the
Carter constant leads to that of unstable circular photon orbits on a
two-dimensional plane not limited to the equatorial plane and unstable
spherical photon orbits in the three-dimensional space. These circular or
spherical photon orbits can determine two impact parameters, which are used to
calculate black hole shadows. For the case of a spherically symmetric
nonrotating black hole, the black hole shadow is circular and its size is
independent of an observation angle and a plane on which a circular photon
orbit exists. The shadow sizes are significantly influenced by the parameters
involving the cloud of strings, quintessence parameter, magnitude of
quintessential state parameter, and cosmological constant. When the black hole
is spinning and axially symmetric, the black hole shadow is dependent on the
observation angle. The effects of the parameters excluding the spin parameter
on the sizes of black hole shadows in the rotating case are similar to those in
the nonrotating case. Based on the Event Horizon Telescope observations of
M87*, the constraint of the curvature radius is used to constrain these
parameters. For slowly rotating black holes, the allowed regions of the
parameters including the cosmological constant are given.
| [
{
"created": "Tue, 25 Apr 2023 08:22:11 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Jun 2023 11:06:03 GMT",
"version": "v2"
},
{
"created": "Mon, 30 Oct 2023 00:44:57 GMT",
"version": "v3"
}
] | 2023-10-31 | [
[
"Cao",
"Wen-Fu",
""
],
[
"Liu",
"Wen-Fang",
""
],
[
"Wu",
"Xin",
""
]
] | The motion of photons around the Kerr-Newman-dS black hole surrounded by quintessence and a cloud of strings is investigated. The existence of the Carter constant leads to that of unstable circular photon orbits on a two-dimensional plane not limited to the equatorial plane and unstable spherical photon orbits in the three-dimensional space. These circular or spherical photon orbits can determine two impact parameters, which are used to calculate black hole shadows. For the case of a spherically symmetric nonrotating black hole, the black hole shadow is circular and its size is independent of an observation angle and a plane on which a circular photon orbit exists. The shadow sizes are significantly influenced by the parameters involving the cloud of strings, quintessence parameter, magnitude of quintessential state parameter, and cosmological constant. When the black hole is spinning and axially symmetric, the black hole shadow is dependent on the observation angle. The effects of the parameters excluding the spin parameter on the sizes of black hole shadows in the rotating case are similar to those in the nonrotating case. Based on the Event Horizon Telescope observations of M87*, the constraint of the curvature radius is used to constrain these parameters. For slowly rotating black holes, the allowed regions of the parameters including the cosmological constant are given. |
gr-qc/0504095 | Sergiu Vacaru I. | Sergiu I. Vacaru | Nonholonomic Deformations of Disk Solutions and Algebroid Symmetries in
Einstein and Extra Dimension Gravity | latex2e, 66 pages (Appendix on 26 pages) | null | null | null | gr-qc astro-ph hep-th math-ph math.DG math.MP | null | In this article we consider nonholonomic deformations of disk solutions in
general relativity to generic off-diagonal metrics defining knew classes of
exact solutions in 4D and 5D gravity. These solutions possess Lie algebroid
symmetries and local anisotropy and define certain generalizations of manifolds
with Killing and/ or Lie algebra symmetries. For Lie algebroids, there are
structures functions depending on variables on a base submanifold and it is
possible to work with singular structures defined by the 'anchor' map. This
results in a number of new physical implications comparing with the usual
manifolds possessing Lie algebra symmetries defined by structure constants. The
spacetimes investigated here have two physically distinct properties: First,
they can give rise to disk type configurations with angular/ time/ extra
dimension gravitational polarizations and running constants. Second, they
define static, stationary or moving disks in nontrivial solitonic backgrounds,
with possible warped factors, additional spinor and/or noncommutative
symmetries. Such metrics may have nontrivial limits to 4D gravity with
vanishing, or nonzero torsion. The work develops the results of Ref.
gr-qc/0005025 and emphasizes the solutions with Lie algebroid symmetries
following similar constructions for solutions with noncommutative symmetries
gr-qc/0307103.
| [
{
"created": "Wed, 20 Apr 2005 21:20:35 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Vacaru",
"Sergiu I.",
""
]
] | In this article we consider nonholonomic deformations of disk solutions in general relativity to generic off-diagonal metrics defining knew classes of exact solutions in 4D and 5D gravity. These solutions possess Lie algebroid symmetries and local anisotropy and define certain generalizations of manifolds with Killing and/ or Lie algebra symmetries. For Lie algebroids, there are structures functions depending on variables on a base submanifold and it is possible to work with singular structures defined by the 'anchor' map. This results in a number of new physical implications comparing with the usual manifolds possessing Lie algebra symmetries defined by structure constants. The spacetimes investigated here have two physically distinct properties: First, they can give rise to disk type configurations with angular/ time/ extra dimension gravitational polarizations and running constants. Second, they define static, stationary or moving disks in nontrivial solitonic backgrounds, with possible warped factors, additional spinor and/or noncommutative symmetries. Such metrics may have nontrivial limits to 4D gravity with vanishing, or nonzero torsion. The work develops the results of Ref. gr-qc/0005025 and emphasizes the solutions with Lie algebroid symmetries following similar constructions for solutions with noncommutative symmetries gr-qc/0307103. |
0806.1037 | Ian Hinder | Ian Hinder, Frank Herrmann, Pablo Laguna and Deirdre Shoemaker | Comparisons of eccentric binary black hole simulations with
post-Newtonian models | 15 pages, 7 figures. Replaced extrapolation of fit parameters with
values at earliest time - results unchanged. Corrected equation typos in
Section IIa. Other minor changes. Corresponds to PRD version | Phys.Rev.D82:024033,2010 | 10.1103/PhysRevD.82.024033 | IGC-08/6-1 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the first comparison between numerical relativity (NR) simulations
of an eccentric binary black hole system with corresponding post-Newtonian (PN)
results. We evolve an equal-mass, non-spinning configuration with an initial
eccentricity e ~ 0.1 for 21 gravitational wave cycles before merger, and find
agreement in the gravitational wave phase with an adiabatic eccentric PN model
with 2 PN radiation reaction within 0.1 radians for 10 cycles. The NR and PN
phase difference grows to 0.7 radians by 5 cycles before merger. We find that
these results can be obtained by expanding the eccentric PN expressions in
terms of the frequency-related variable x = (omega M)^{2/3} with M the total
mass of the binary. When using instead the mean motion n = 2 \pi /P, where P is
the orbital period, the comparison leads to significant disagreements with NR.
| [
{
"created": "Thu, 5 Jun 2008 19:52:43 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Aug 2010 13:41:40 GMT",
"version": "v2"
}
] | 2014-11-18 | [
[
"Hinder",
"Ian",
""
],
[
"Herrmann",
"Frank",
""
],
[
"Laguna",
"Pablo",
""
],
[
"Shoemaker",
"Deirdre",
""
]
] | We present the first comparison between numerical relativity (NR) simulations of an eccentric binary black hole system with corresponding post-Newtonian (PN) results. We evolve an equal-mass, non-spinning configuration with an initial eccentricity e ~ 0.1 for 21 gravitational wave cycles before merger, and find agreement in the gravitational wave phase with an adiabatic eccentric PN model with 2 PN radiation reaction within 0.1 radians for 10 cycles. The NR and PN phase difference grows to 0.7 radians by 5 cycles before merger. We find that these results can be obtained by expanding the eccentric PN expressions in terms of the frequency-related variable x = (omega M)^{2/3} with M the total mass of the binary. When using instead the mean motion n = 2 \pi /P, where P is the orbital period, the comparison leads to significant disagreements with NR. |
2310.04150 | Hyerim Noh | Jai-chan Hwang and Hyerim Noh | On graviton-photon conversions in magnetic environments | 8 pages, no figure, to appear in Phys. Dark. Univ | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Graviton-photon conversions in a given external electric or magnetic field,
known as the Gertsenshtein mechanism, are usually treated using the
four-potential for photons. In terms of the electric and magnetic (EM) fields,
however, proper identification of the fields in curved spacetime is important.
By misidentifying the fields in Minkowski form, as is often practiced in the
literature, we show that the final equation for photon conversion is correct in
transverse-tracefree gauge only for planar gravitational waves in a uniform and
constant external field. Even in the former method, to recover the EM fields
from the four-potential in curved spacetime, one should properly take into
account the metric involved in the relation. By including the metric
perturbation in the graviton conversion equation, we show that a magnetic
environment can cause tachyonic instability term in gravitational wave
equation.
| [
{
"created": "Fri, 6 Oct 2023 10:49:23 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Jan 2024 00:41:20 GMT",
"version": "v2"
}
] | 2024-01-23 | [
[
"Hwang",
"Jai-chan",
""
],
[
"Noh",
"Hyerim",
""
]
] | Graviton-photon conversions in a given external electric or magnetic field, known as the Gertsenshtein mechanism, are usually treated using the four-potential for photons. In terms of the electric and magnetic (EM) fields, however, proper identification of the fields in curved spacetime is important. By misidentifying the fields in Minkowski form, as is often practiced in the literature, we show that the final equation for photon conversion is correct in transverse-tracefree gauge only for planar gravitational waves in a uniform and constant external field. Even in the former method, to recover the EM fields from the four-potential in curved spacetime, one should properly take into account the metric involved in the relation. By including the metric perturbation in the graviton conversion equation, we show that a magnetic environment can cause tachyonic instability term in gravitational wave equation. |
2301.07289 | Mohd Salman | Musavvir Ali, Mohammad Salman, and Sezgin Altay Demirbag | Impact of symmetry inheritance on conformally flat spacetime | null | null | null | null | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by-nc-sa/4.0/ | The goal of this research paper is to investigate curvature inheritance
symmetry in conformally flat spacetime. Curvature inheritance symmetry in
conformally flat spacetime is shown to be a conformal motion. We have proven
that a conformally flat spacetime reduces to Einstein spacetime if admits
curvature inheritance symmetry. A few results on conformally flat spacetimes
that obey Einstein's field equation with or without a cosmological constant, if
admits the curvature inheritance symmetry. The energy-momentum tensor is to be
covariantly constant in a 4-dimensional relativistic perfect fluid spacetime
which is also conformally flat spacetime, admits curvature inheritance, and
obeys Einstein's field equations in the presence of a cosmological constant.
Moreover, it is also obtained that such spacetimes with perfect fluid satisfy
the the vacuum-like equation of state consecutively it is dark matter. Finally,
in the third part of the article, the case compatible with all Theorems from
Theorem \ref{Th2.1} to Theorem \ref{Th2.5n} is shown. On the other hand, it has
also been emphasized that it is an example of de Sitter spacetime. It has been
demonstrated that this spacetime also has a conformal killing vector.
| [
{
"created": "Wed, 18 Jan 2023 03:39:34 GMT",
"version": "v1"
},
{
"created": "Wed, 3 Jul 2024 18:17:04 GMT",
"version": "v2"
}
] | 2024-07-08 | [
[
"Ali",
"Musavvir",
""
],
[
"Salman",
"Mohammad",
""
],
[
"Demirbag",
"Sezgin Altay",
""
]
] | The goal of this research paper is to investigate curvature inheritance symmetry in conformally flat spacetime. Curvature inheritance symmetry in conformally flat spacetime is shown to be a conformal motion. We have proven that a conformally flat spacetime reduces to Einstein spacetime if admits curvature inheritance symmetry. A few results on conformally flat spacetimes that obey Einstein's field equation with or without a cosmological constant, if admits the curvature inheritance symmetry. The energy-momentum tensor is to be covariantly constant in a 4-dimensional relativistic perfect fluid spacetime which is also conformally flat spacetime, admits curvature inheritance, and obeys Einstein's field equations in the presence of a cosmological constant. Moreover, it is also obtained that such spacetimes with perfect fluid satisfy the the vacuum-like equation of state consecutively it is dark matter. Finally, in the third part of the article, the case compatible with all Theorems from Theorem \ref{Th2.1} to Theorem \ref{Th2.5n} is shown. On the other hand, it has also been emphasized that it is an example of de Sitter spacetime. It has been demonstrated that this spacetime also has a conformal killing vector. |
2305.18031 | Panagiotis Dorlis | Panagiotis Dorlis, Nick E. Mavromatos and Sotirios-Neilos Vlachos | Bypassing Bekenstein's no-scalar-hair theorem without violating the
energy conditions | 16 pages, 8 figures | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this work we establish in a rigorous manner, and a model independent way,
the conditions for bypassing Bekenstein's no-scalar-hair theorem for static,
spherically symmetric, and asymptotically flat black holes, while maintaining
the validity of the energy conditions. Specifically, we argue that a hidden
assumption in the theorem, namely the vanishing of the quantity $\mathcal{G} =
\mathcal{E} + T^\theta\!_\theta$, where $\mathcal{E}$ is the energy density and
$T^\theta\!_\theta$ the corresponding component of the energy-momentum tensor
of the scalar field theory, can be relaxed. Indeed, if $\mathcal{G}$ is
positive, as a consequence of the assumption on the validity of the energy
conditions, then scalar hair is potentially allowed in the black hole's
exterior, consistently with the gravitational equations and the generic
properties of the (non-trivial) energy momentum tensor. As an explicit example,
in which such a behaviour is realised, we discuss the well known model of a
(3+1)-dimensional Schwarzschild black hole coupled to a spontaneously broken
Yang-Mills $SU (2)$ gauge theory interacting with a Higgs scalar. We present a
rather novel approach to obtain analytical black hole solutions for this system
(in contrast to the numerical ones in the existing literature) by applying an
appropriate perturbative treatment whereby the black hole configuration is
derived as a result of backreaction of Higgs and gauge fields onto an initially
fixed flat spacetime. The massive nature of the scalar and gauge fields in this
example requires a special treatment, because of their asymptotic form, which
we discuss in some detail.
| [
{
"created": "Mon, 29 May 2023 11:52:09 GMT",
"version": "v1"
}
] | 2023-05-30 | [
[
"Dorlis",
"Panagiotis",
""
],
[
"Mavromatos",
"Nick E.",
""
],
[
"Vlachos",
"Sotirios-Neilos",
""
]
] | In this work we establish in a rigorous manner, and a model independent way, the conditions for bypassing Bekenstein's no-scalar-hair theorem for static, spherically symmetric, and asymptotically flat black holes, while maintaining the validity of the energy conditions. Specifically, we argue that a hidden assumption in the theorem, namely the vanishing of the quantity $\mathcal{G} = \mathcal{E} + T^\theta\!_\theta$, where $\mathcal{E}$ is the energy density and $T^\theta\!_\theta$ the corresponding component of the energy-momentum tensor of the scalar field theory, can be relaxed. Indeed, if $\mathcal{G}$ is positive, as a consequence of the assumption on the validity of the energy conditions, then scalar hair is potentially allowed in the black hole's exterior, consistently with the gravitational equations and the generic properties of the (non-trivial) energy momentum tensor. As an explicit example, in which such a behaviour is realised, we discuss the well known model of a (3+1)-dimensional Schwarzschild black hole coupled to a spontaneously broken Yang-Mills $SU (2)$ gauge theory interacting with a Higgs scalar. We present a rather novel approach to obtain analytical black hole solutions for this system (in contrast to the numerical ones in the existing literature) by applying an appropriate perturbative treatment whereby the black hole configuration is derived as a result of backreaction of Higgs and gauge fields onto an initially fixed flat spacetime. The massive nature of the scalar and gauge fields in this example requires a special treatment, because of their asymptotic form, which we discuss in some detail. |
0805.4660 | Takeshi Chiba | Takeshi Chiba | Initial Conditions for Vector Inflation | 12 pages, 5 figures, version to be published in JCAP | JCAP 0808:004,2008 | 10.1088/1475-7516/2008/08/004 | null | gr-qc astro-ph hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, a model of inflation using non-minimally coupled massive vector
fields has been proposed. For a particular choice of non-minimal coupling
parameter and for a flat FRW model, the model is reduced to the model of
chaotic inflation with massive scalar field. We study the effect of non-zero
curvature of the universe on the onset of vector inflation. We find that in a
curved universe the dynamics of vector inflation can be different from chaotic
inflation, and the fraction of the initial conditions leading to inflationary
solutions is reduced compared with the chaotic inflation case.
| [
{
"created": "Fri, 30 May 2008 02:34:06 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Jul 2008 02:10:20 GMT",
"version": "v2"
},
{
"created": "Tue, 5 Aug 2008 03:00:27 GMT",
"version": "v3"
}
] | 2014-11-18 | [
[
"Chiba",
"Takeshi",
""
]
] | Recently, a model of inflation using non-minimally coupled massive vector fields has been proposed. For a particular choice of non-minimal coupling parameter and for a flat FRW model, the model is reduced to the model of chaotic inflation with massive scalar field. We study the effect of non-zero curvature of the universe on the onset of vector inflation. We find that in a curved universe the dynamics of vector inflation can be different from chaotic inflation, and the fraction of the initial conditions leading to inflationary solutions is reduced compared with the chaotic inflation case. |
2306.13286 | Deyou Chen | Deyou Chen, Yucheng He, Jun Tao | Topological classes of higher-dimensional black holes in massive gravity | 21 pages, 13 figures | Eur. Phys. J. C (2023) 83:872 | 10.1140/epjc/s10052-023-11983-0 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this paper, we study topological numbers for five-, six- and
seven-dimensional anti-de Sitter black holes in the ghost-free massive gravity.
We find that when the black holes are charged, they have the same topological
number. The topological numbers for the uncharged black holes are 0 or 1, and
the specific values are determined by the values of the black holes'
parameters. Since $k$ and $c_ 0^2c_2 m^2 $ appear together in the generalized
free energy in the form of $k +c_ 0^2c_2 m^2 $, where $k$ characterizes the
horizon curvature and $c_2 m^2 $ is the coefficient of the second term of
massive potential associated with the graviton mass, this result is applicable
to the black holes with the spherical, Ricci flat or hyperbolic horizons. This
work shows that the parameters of the ghost-free massive gravity play an
important role in topological classes of black holes.
| [
{
"created": "Fri, 23 Jun 2023 04:21:11 GMT",
"version": "v1"
},
{
"created": "Tue, 27 Jun 2023 11:40:39 GMT",
"version": "v2"
},
{
"created": "Fri, 7 Jul 2023 04:59:03 GMT",
"version": "v3"
},
{
"created": "Wed, 10 Jul 2024 08:15:09 GMT",
"version": "v4"
}
] | 2024-07-11 | [
[
"Chen",
"Deyou",
""
],
[
"He",
"Yucheng",
""
],
[
"Tao",
"Jun",
""
]
] | In this paper, we study topological numbers for five-, six- and seven-dimensional anti-de Sitter black holes in the ghost-free massive gravity. We find that when the black holes are charged, they have the same topological number. The topological numbers for the uncharged black holes are 0 or 1, and the specific values are determined by the values of the black holes' parameters. Since $k$ and $c_ 0^2c_2 m^2 $ appear together in the generalized free energy in the form of $k +c_ 0^2c_2 m^2 $, where $k$ characterizes the horizon curvature and $c_2 m^2 $ is the coefficient of the second term of massive potential associated with the graviton mass, this result is applicable to the black holes with the spherical, Ricci flat or hyperbolic horizons. This work shows that the parameters of the ghost-free massive gravity play an important role in topological classes of black holes. |
gr-qc/0311029 | Choquet-Bruhat | Yvonne Choquet-Bruhat | Einstein constraints on n dimensional compact manifolds | Article for the volume "Space time safari" in honor of Vincent
Moncrief | Class.Quant.Grav.21:S127-S152,2004 | null | null | gr-qc | null | We give a general survey of the solution of the Einstein constraints by the
conformal method on n dimensional compact manifolds. We prove some new results
about solutions with low regularity (solutions in $H_{2}$ when n=3), and
solutions with unscaled sources.
| [
{
"created": "Sat, 8 Nov 2003 15:22:24 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Choquet-Bruhat",
"Yvonne",
""
]
] | We give a general survey of the solution of the Einstein constraints by the conformal method on n dimensional compact manifolds. We prove some new results about solutions with low regularity (solutions in $H_{2}$ when n=3), and solutions with unscaled sources. |
2403.15847 | Tayyaba Naz | Adnan Malik, Tayyaba Naz, Aimen Rauf, M. Farasat Shamir, Z. Yousaf | $f(R, T)$ Gravity Bouncing Universe with Cosmological Parameters | 18 pages, 10 figures | Eur. Phys. J. Plus 139 (2024) 276 | 10.1140/epjp/s13360-024-05006-4 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The basic aim of this manuscript is to investigate the cosmological solutions
in the context of the modified $f(R, T)$ theory of gravity, where $R$ is the
Ricci scalar and $T$ is the trace of the energy-momentum tensor. For our
current work, we consider the Friedmann-Robertson-Walker space-time for finding
the solutions of field equations. We investigate the nature of universe by
considering acceleration expansion of universe, ultra relativistic universe,
sub-relativistic universe, dust universe, radiation universe, stiff universe.
Moreover, we apply the power law technique by taking two different $f(R, T)$
gravity models to observe the expanding nature of the universe. The bouncing
scenario is also discussed by choosing some particular values of the model
parameters and observed the energy conditions, which are satisfied for a
successful bouncing model. It is also concluded that some solutions in $f(R,
T)$ theory of gravity supports the concept of exotic matter and accelerated
expansion of the universe due to a large amount of negative pressure.
| [
{
"created": "Sat, 23 Mar 2024 13:51:25 GMT",
"version": "v1"
}
] | 2024-03-26 | [
[
"Malik",
"Adnan",
""
],
[
"Naz",
"Tayyaba",
""
],
[
"Rauf",
"Aimen",
""
],
[
"Shamir",
"M. Farasat",
""
],
[
"Yousaf",
"Z.",
""
]
] | The basic aim of this manuscript is to investigate the cosmological solutions in the context of the modified $f(R, T)$ theory of gravity, where $R$ is the Ricci scalar and $T$ is the trace of the energy-momentum tensor. For our current work, we consider the Friedmann-Robertson-Walker space-time for finding the solutions of field equations. We investigate the nature of universe by considering acceleration expansion of universe, ultra relativistic universe, sub-relativistic universe, dust universe, radiation universe, stiff universe. Moreover, we apply the power law technique by taking two different $f(R, T)$ gravity models to observe the expanding nature of the universe. The bouncing scenario is also discussed by choosing some particular values of the model parameters and observed the energy conditions, which are satisfied for a successful bouncing model. It is also concluded that some solutions in $f(R, T)$ theory of gravity supports the concept of exotic matter and accelerated expansion of the universe due to a large amount of negative pressure. |
1906.05185 | Leonardo Modesto | Qiang Li, Leonardo Modesto | Galactic rotation curves in Einstein's conformal gravity | 17 pages, 8 figures | null | null | null | gr-qc astro-ph.GA hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show quantitatively that an exact solution of Einstein's conformal gravity
can explain very well the galactic rotation curves for a sample of 104 galaxies
without need for dark matter or other exotic modification of gravity. The
metric is an overall rescaling of the Schwarzschild-de Sitter spacetime as
required by Weyl conformal invariance, which has to be spontaneously broken,
and the velocity of the stars depends only on two universal parameters
determined on the base of the observational data.
| [
{
"created": "Wed, 12 Jun 2019 14:55:05 GMT",
"version": "v1"
}
] | 2019-06-13 | [
[
"Li",
"Qiang",
""
],
[
"Modesto",
"Leonardo",
""
]
] | We show quantitatively that an exact solution of Einstein's conformal gravity can explain very well the galactic rotation curves for a sample of 104 galaxies without need for dark matter or other exotic modification of gravity. The metric is an overall rescaling of the Schwarzschild-de Sitter spacetime as required by Weyl conformal invariance, which has to be spontaneously broken, and the velocity of the stars depends only on two universal parameters determined on the base of the observational data. |
1708.09760 | Vedran Skrinjar | Carlos M. Nieto, Roberto Percacci, Vedran Skrinjar | Split Weyl transformations in quantum gravity | null | Phys. Rev. D 96, 106019 (2017) | 10.1103/PhysRevD.96.106019 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss various realizations of the Weyl group in the background field
expansion of quantum gravity, in the presence of a cutoff, as required in
applications of the functional renormalization group. In order to study the
background--dependence, special attention is given to split gauge
transformations, which act on the background field and fluctuation keeping the
total metric unchanged. The results generalize previous works on global and
local scale transformations.
| [
{
"created": "Thu, 31 Aug 2017 14:54:04 GMT",
"version": "v1"
}
] | 2017-12-06 | [
[
"Nieto",
"Carlos M.",
""
],
[
"Percacci",
"Roberto",
""
],
[
"Skrinjar",
"Vedran",
""
]
] | We discuss various realizations of the Weyl group in the background field expansion of quantum gravity, in the presence of a cutoff, as required in applications of the functional renormalization group. In order to study the background--dependence, special attention is given to split gauge transformations, which act on the background field and fluctuation keeping the total metric unchanged. The results generalize previous works on global and local scale transformations. |
1201.0806 | Vladimir Khatsymovsky | V. M. Khatsymovsky | First order representation of the Faddeev formulation of gravity | 9 pages | Class.Quant.Grav.30:095006,2013 | 10.1088/0264-9381/30/9/095006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study Faddeev formulation of gravity, in which the metric is composed of
vector fields or the tetrad of the ten-dimensional fields, $f^A_\lambda$, where
$\lambda = 1, 2, 3, 4$ and $A = 1, ..., 10$ is vector index w. r. t. the
Euclidean (or Minkowsky) ten-dimensional spacetime. We propose representation
of the type of the Cartan-Weyl one. It is based on extending the set of
variables by introducing the infinitesimal SO(10) connection. Excluding this
connection via equations of motion we reproduce the original Faddeev action. A
peculiar feature of this representation is occurrence of the local SO(10)
symmetry violating condition so that SO(10) symmetry is only global one in full
correspondence with that the original Faddeev formulation just possesses SO(10)
symmetry w. r. t. the global SO(10) rotation of the Euclidean ten-dimensional
spacetime. We also consider analog of the Barbero-Immirzi parameter which can
be naturally introduced in the considered representation.
| [
{
"created": "Wed, 4 Jan 2012 02:20:08 GMT",
"version": "v1"
}
] | 2015-12-10 | [
[
"Khatsymovsky",
"V. M.",
""
]
] | We study Faddeev formulation of gravity, in which the metric is composed of vector fields or the tetrad of the ten-dimensional fields, $f^A_\lambda$, where $\lambda = 1, 2, 3, 4$ and $A = 1, ..., 10$ is vector index w. r. t. the Euclidean (or Minkowsky) ten-dimensional spacetime. We propose representation of the type of the Cartan-Weyl one. It is based on extending the set of variables by introducing the infinitesimal SO(10) connection. Excluding this connection via equations of motion we reproduce the original Faddeev action. A peculiar feature of this representation is occurrence of the local SO(10) symmetry violating condition so that SO(10) symmetry is only global one in full correspondence with that the original Faddeev formulation just possesses SO(10) symmetry w. r. t. the global SO(10) rotation of the Euclidean ten-dimensional spacetime. We also consider analog of the Barbero-Immirzi parameter which can be naturally introduced in the considered representation. |
2111.08713 | Grant Remmen | Grant N. Remmen | Exploration of a Singular Fluid Spacetime | 25 pages, 6 figures | Gen.Rel.Grav.53:101,2021 | 10.1007/s10714-021-02873-5 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the properties of a special class of singular solutions for a
self-gravitating perfect fluid in general relativity: the singular isothermal
sphere. For arbitrary constant equation-of-state parameter $w=p/\rho$, there
exist static, spherically-symmetric solutions with density profile $\propto
1/r^2$, with the constant of proportionality fixed to be a special function of
$w$. Like black holes, singular isothermal spheres possess a fixed
mass-to-radius ratio independent of size, but no horizon cloaking the curvature
singularity at $r=0$. For $w=1$, these solutions can be constructed from a
homogeneous dilaton background, where the metric spontaneously breaks spatial
homogeneity. We study the perturbative structure of these solutions, finding
the radial modes and tidal Love numbers, and also find interesting properties
in the geodesic structure of this geometry. Finally, connections are discussed
between these geometries and dark matter profiles, the double copy, and
holographic entropy, as well as how the swampland distance conjecture can
obscure the naked singularity.
| [
{
"created": "Tue, 16 Nov 2021 19:00:00 GMT",
"version": "v1"
}
] | 2021-11-18 | [
[
"Remmen",
"Grant N.",
""
]
] | We investigate the properties of a special class of singular solutions for a self-gravitating perfect fluid in general relativity: the singular isothermal sphere. For arbitrary constant equation-of-state parameter $w=p/\rho$, there exist static, spherically-symmetric solutions with density profile $\propto 1/r^2$, with the constant of proportionality fixed to be a special function of $w$. Like black holes, singular isothermal spheres possess a fixed mass-to-radius ratio independent of size, but no horizon cloaking the curvature singularity at $r=0$. For $w=1$, these solutions can be constructed from a homogeneous dilaton background, where the metric spontaneously breaks spatial homogeneity. We study the perturbative structure of these solutions, finding the radial modes and tidal Love numbers, and also find interesting properties in the geodesic structure of this geometry. Finally, connections are discussed between these geometries and dark matter profiles, the double copy, and holographic entropy, as well as how the swampland distance conjecture can obscure the naked singularity. |
gr-qc/0508050 | Eran Rosenthal | Eran Rosenthal | Regularization of the second-order gravitational perturbations produced
by a compact object | 12 pages, discussion expanded, to be published in Phys. Rev. D Rapid
Communication | Phys.Rev. D72 (2005) 121503 | 10.1103/PhysRevD.72.121503 | null | gr-qc | null | The equations for the second-order gravitational perturbations produced by a
compact-object have highly singular source terms at the point particle limit.
At this limit the standard retarded solutions to these equations are
ill-defined. Here we construct well-defined and physically meaningful solutions
to these equations. These solutions are important for practical calculations:
the planned gravitational-wave detector LISA requires preparation of waveform
templates for the potential gravitational-waves. Construction of templates with
desired accuracy for extreme mass ratio binaries, in which a compact-object
inspirals towards a supermassive black-hole, requires calculation of the
second-order gravitational perturbations produced by the compact-object.
| [
{
"created": "Thu, 11 Aug 2005 20:16:41 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Oct 2005 20:56:54 GMT",
"version": "v2"
},
{
"created": "Fri, 2 Dec 2005 16:43:48 GMT",
"version": "v3"
}
] | 2009-11-11 | [
[
"Rosenthal",
"Eran",
""
]
] | The equations for the second-order gravitational perturbations produced by a compact-object have highly singular source terms at the point particle limit. At this limit the standard retarded solutions to these equations are ill-defined. Here we construct well-defined and physically meaningful solutions to these equations. These solutions are important for practical calculations: the planned gravitational-wave detector LISA requires preparation of waveform templates for the potential gravitational-waves. Construction of templates with desired accuracy for extreme mass ratio binaries, in which a compact-object inspirals towards a supermassive black-hole, requires calculation of the second-order gravitational perturbations produced by the compact-object. |
2311.13839 | Farruh Atamurotov | G. Mustafa, S. K. Maurya, A. Ditta, Saibal Ray, Farruh Atamurotov | Circular orbits and accretion disk around AdS black holes surrounded by
dark fluid with Chaplygin-like equation of state | 22 pages, 12 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present work we study the geodesic motion and accretion process of a
test particle near an Anti-de Sitter (ADS) BH surrounded by a dark fluid with a
Chaplygin-like equation. Within the defined paradigm, we investigate on the
equatorial plane and examine circular geodesics along with their features
related to stabilities, radiation energy flux, oscillations and orbits. The
general form of the fluid accretion onto the AdS BH through dynamical analysis
and mass expansion also has discussed in a depth. Additionally, a few more
interesting topics, e.g. the effective potential, angular momentum, specific
energy, radiation energy and epicyclic frequencies have also been examined
thoroughly. All the attributes are physically acceptable within the
observational signatures and ranges.
| [
{
"created": "Thu, 23 Nov 2023 07:53:35 GMT",
"version": "v1"
}
] | 2023-11-27 | [
[
"Mustafa",
"G.",
""
],
[
"Maurya",
"S. K.",
""
],
[
"Ditta",
"A.",
""
],
[
"Ray",
"Saibal",
""
],
[
"Atamurotov",
"Farruh",
""
]
] | In the present work we study the geodesic motion and accretion process of a test particle near an Anti-de Sitter (ADS) BH surrounded by a dark fluid with a Chaplygin-like equation. Within the defined paradigm, we investigate on the equatorial plane and examine circular geodesics along with their features related to stabilities, radiation energy flux, oscillations and orbits. The general form of the fluid accretion onto the AdS BH through dynamical analysis and mass expansion also has discussed in a depth. Additionally, a few more interesting topics, e.g. the effective potential, angular momentum, specific energy, radiation energy and epicyclic frequencies have also been examined thoroughly. All the attributes are physically acceptable within the observational signatures and ranges. |
gr-qc/9905033 | Daisuke Ida | Daisuke Ida and Sean A. Hayward | How much negative energy does a wormhole need? | 6 pages, no figures | Phys.Lett. A260 (1999) 175-181 | 10.1016/S0375-9601(99)00518-6 | null | gr-qc | null | It is known that traversible wormholes require negative energy density. We
here argue how much negative energy is needed for wormholes, using a local
analysis which does not assume any symmetry. and in particular allows dynamic
(non-stationary) but non-degenerate wormholes. We find that wormholes require
two constraints on the energy density, given by two independent components of
the Einstein equation.
| [
{
"created": "Tue, 11 May 1999 08:45:34 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Nov 1999 16:03:27 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Ida",
"Daisuke",
""
],
[
"Hayward",
"Sean A.",
""
]
] | It is known that traversible wormholes require negative energy density. We here argue how much negative energy is needed for wormholes, using a local analysis which does not assume any symmetry. and in particular allows dynamic (non-stationary) but non-degenerate wormholes. We find that wormholes require two constraints on the energy density, given by two independent components of the Einstein equation. |
1905.05561 | Zaim Slimane | Slimane Zaim and Hadjar Rezki | Thermodynamic Properties of Yukawa-Schwarzschild Black Hole in
Non-commutative Gauge Gravity | 12 pages, 4 figures | Gravitation and Cosmology 26 (3), 200-207 (2020) | 10.1134/S0202289320030135 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we construct a non-commutative gauge theory for the deformed
metric corresponding to the modified structure of a gravitational field in the
case of Yukawa-Schwarzschild non-commutative space-time. The thermodynamic
properties and corrections to the gravitational force on the horizon of a
non-commutative Yukawa-Schwarzschild black hole are analysed.
| [
{
"created": "Tue, 14 May 2019 12:44:20 GMT",
"version": "v1"
}
] | 2022-06-15 | [
[
"Zaim",
"Slimane",
""
],
[
"Rezki",
"Hadjar",
""
]
] | In this paper we construct a non-commutative gauge theory for the deformed metric corresponding to the modified structure of a gravitational field in the case of Yukawa-Schwarzschild non-commutative space-time. The thermodynamic properties and corrections to the gravitational force on the horizon of a non-commutative Yukawa-Schwarzschild black hole are analysed. |
2407.04762 | Alessandro Nagar | Alessandro Nagar, Sebastiano Bernuzzi, Danilo Chiaramello, Veronica
Fantini, Rossella Gamba, Mattia Panzeri, and Piero Rettegno | Effective-one-body waveform model for noncircularized, planar,
coalescing black hole binaries II: high accuracy by improving logarithmic
terms in resummations | 14 pages, 9 figures. Submitted to Phys. Rev. D | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Effective-one-body (EOB) models are based on analytical building blocks that,
mathematically, are truncated Taylor series with logarithms. These polynomials
are usually resummed using Pad\'e approximants obtained first assuming that the
logarithms are constant, and then replacing them back into the resulting
rational functions. A recent study pointed out that this procedure introduces
spurious logarithmic terms when the resummed functions are reexpanded. We
therefore explore analytically more consistent resummation schemes. Here we
update the TEOBResumS-Dali waveform model for spin-aligned, noncircularized,
coalescing black hole binaries by systematically implementing new (still Pad\'e
based) resummations for all EOB functions. Once the model is informed by 51
Numerical Relativity simulations this new approach proves key in lowering the
maximum EOB/NR unfaithfulness $\bar{F}_{\rm EOBNR}^{\rm max}$ for the
$\ell=m=2$ mode (with the Advanced LIGO noise in the total mass range
$10-200M_{\odot}$) over the whole Simulating eXtreme Spacetimes catalog of 534
waveforms. A median mismatch of $3.418\times 10^{-4}$ is achieved, which is a
marked improvement on the previous value, $1.06\times 10^{-3}$. The largest
value, $\bar{\cal F}^{\rm max}_{\rm EOBNR}\sim 10^{-2}$, is found for an
equal-mass, equal-spin simulation with dimensionless spins $\sim +0.994$; only
six configurations (all equal-mass, and with equal spins larger than $+0.97$)
are above $5\times 10^{-3}$. Results for eccentric binaries are similarly
excellent (well below $10^{-2}$ and mostly around $10^{-3}$). For scattering
configurations, we find an unprecedented EOB/NR agreement ($<1\%$) for
relatively small values of the scattering angle, though differences
progressively increase as the threshold of immediate capture is approached.
| [
{
"created": "Fri, 5 Jul 2024 18:00:00 GMT",
"version": "v1"
}
] | 2024-07-09 | [
[
"Nagar",
"Alessandro",
""
],
[
"Bernuzzi",
"Sebastiano",
""
],
[
"Chiaramello",
"Danilo",
""
],
[
"Fantini",
"Veronica",
""
],
[
"Gamba",
"Rossella",
""
],
[
"Panzeri",
"Mattia",
""
],
[
"Rettegno",
"Piero",
... | Effective-one-body (EOB) models are based on analytical building blocks that, mathematically, are truncated Taylor series with logarithms. These polynomials are usually resummed using Pad\'e approximants obtained first assuming that the logarithms are constant, and then replacing them back into the resulting rational functions. A recent study pointed out that this procedure introduces spurious logarithmic terms when the resummed functions are reexpanded. We therefore explore analytically more consistent resummation schemes. Here we update the TEOBResumS-Dali waveform model for spin-aligned, noncircularized, coalescing black hole binaries by systematically implementing new (still Pad\'e based) resummations for all EOB functions. Once the model is informed by 51 Numerical Relativity simulations this new approach proves key in lowering the maximum EOB/NR unfaithfulness $\bar{F}_{\rm EOBNR}^{\rm max}$ for the $\ell=m=2$ mode (with the Advanced LIGO noise in the total mass range $10-200M_{\odot}$) over the whole Simulating eXtreme Spacetimes catalog of 534 waveforms. A median mismatch of $3.418\times 10^{-4}$ is achieved, which is a marked improvement on the previous value, $1.06\times 10^{-3}$. The largest value, $\bar{\cal F}^{\rm max}_{\rm EOBNR}\sim 10^{-2}$, is found for an equal-mass, equal-spin simulation with dimensionless spins $\sim +0.994$; only six configurations (all equal-mass, and with equal spins larger than $+0.97$) are above $5\times 10^{-3}$. Results for eccentric binaries are similarly excellent (well below $10^{-2}$ and mostly around $10^{-3}$). For scattering configurations, we find an unprecedented EOB/NR agreement ($<1\%$) for relatively small values of the scattering angle, though differences progressively increase as the threshold of immediate capture is approached. |
1410.0509 | Jose Luis Jaramillo | Jos\'e Luis Jaramillo | Black hole horizons and quantum charged particles | 5 pages, no figures | null | 10.1088/0264-9381/32/13/132001 | null | gr-qc hep-th math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We point out a structural similarity between the characterization of black
hole apparent horizons as stable marginally outer trapped surfaces (MOTS) and
the quantum description of a non-relativistic charged particle moving in given
magnetic and electric fields on a closed surface. Specifically, the spectral
problem of the MOTS-stability operator corresponds to a stationary quantum
particle with a formal fine-structure constant $\alpha$ of negative sign. We
discuss how such analogy enriches both problems, illustrating this with the
insights into the MOTS-spectral problem gained from the analysis of the
spectrum of the quantum charged particle Hamiltonian.
| [
{
"created": "Thu, 2 Oct 2014 10:56:55 GMT",
"version": "v1"
}
] | 2015-06-17 | [
[
"Jaramillo",
"José Luis",
""
]
] | We point out a structural similarity between the characterization of black hole apparent horizons as stable marginally outer trapped surfaces (MOTS) and the quantum description of a non-relativistic charged particle moving in given magnetic and electric fields on a closed surface. Specifically, the spectral problem of the MOTS-stability operator corresponds to a stationary quantum particle with a formal fine-structure constant $\alpha$ of negative sign. We discuss how such analogy enriches both problems, illustrating this with the insights into the MOTS-spectral problem gained from the analysis of the spectrum of the quantum charged particle Hamiltonian. |
2310.07368 | Elisa Maggio | Elisa Maggio | Probing the horizon of black holes with gravitational waves | 14 pages, 5 figures, contribution to the book "Modified and Quantum
Gravity - From theory to experimental searches on all scales" | Lecture Notes in Physics, vol 1017, Springer (2023) | 10.1007/978-3-031-31520-6_9 | null | gr-qc astro-ph.HE hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | Gravitational waves open the possibility to investigate the nature of compact
objects and probe the horizons of black holes. Some models of modified gravity
predict the presence of horizonless and singularity-free compact objects. Such
dark compact objects would emit a gravitational-wave signal which differs from
the standard black hole scenario. In this chapter, we overview the
phenomenology of dark compact objects by analysing their characteristic
frequencies in the ringdown and the emission of gravitational-wave echoes in
the postmerger signal. We show that future gravitational-wave detectors will
allow us to perform model-independent tests of the black hole paradigm.
| [
{
"created": "Wed, 11 Oct 2023 10:36:38 GMT",
"version": "v1"
}
] | 2023-10-12 | [
[
"Maggio",
"Elisa",
""
]
] | Gravitational waves open the possibility to investigate the nature of compact objects and probe the horizons of black holes. Some models of modified gravity predict the presence of horizonless and singularity-free compact objects. Such dark compact objects would emit a gravitational-wave signal which differs from the standard black hole scenario. In this chapter, we overview the phenomenology of dark compact objects by analysing their characteristic frequencies in the ringdown and the emission of gravitational-wave echoes in the postmerger signal. We show that future gravitational-wave detectors will allow us to perform model-independent tests of the black hole paradigm. |
1311.1455 | Sharmanthie Fernando | Sharmanthie Fernando | String black hole: Can it be a particle accelerator ? | 17 pages and 10 figures, journal reference added | Genera Relativity and Gravitation Vol 46, (2014) 1634 | 10.1007/s10714-013-1634-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we have studied the possibility of the center-of-mass energy of
two particles colliding near the horizon of a static charged black hole in
string theory. Various cases corresponding to the electric charge and the
angular momentum of the particles were considered. The studies were done for
the general black hole as well as for the extreme black hole. There were two
scenarios where the center-of-mass energy reach very large values if the
appropriate properties of the particles are chosen.
| [
{
"created": "Wed, 6 Nov 2013 17:38:54 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Aug 2014 12:40:12 GMT",
"version": "v2"
}
] | 2015-06-17 | [
[
"Fernando",
"Sharmanthie",
""
]
] | In this paper we have studied the possibility of the center-of-mass energy of two particles colliding near the horizon of a static charged black hole in string theory. Various cases corresponding to the electric charge and the angular momentum of the particles were considered. The studies were done for the general black hole as well as for the extreme black hole. There were two scenarios where the center-of-mass energy reach very large values if the appropriate properties of the particles are chosen. |
1606.03413 | Bob Osano | Bob Osano and Patrick W M Adams | Toward the analogue of thermally generated electromagnetic fields | 7 pages, 6 figures | Journal of Mathematical Physics 58, 093101 (2017) | 10.1063/1.5001338 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Magnetic and vorticity fields evolution equations are known to obey the same
equation when effects of dissipation and sources terms are negligible. We
investigate the analogy between the two fields for non-vanishing dissipation
and sources. In addition to the Reynolds (Re)and Prandtl (Pr_M) numbers, we
define a new number (S_M) that is given by the ratio of the diffusive term to
the Biermann battery term and which allows for a different classification of
magnetised fluid behaviour. Numerical simulations of the two fields are then
carried out given a parameter space made of Reynolds, Prandtl and Source
numbers. We find it appropriate to present and discuss the findings against
Prandtl numbers given that these provide the link between viscous and magnetic
diffusion. Our simulations indicate that there exists a range of Prandtl
numbers for which the fields remain analogues which raises the important
question of how far the analogy goes.
| [
{
"created": "Fri, 10 Jun 2016 18:15:42 GMT",
"version": "v1"
},
{
"created": "Sat, 28 Oct 2017 16:19:08 GMT",
"version": "v2"
}
] | 2017-10-31 | [
[
"Osano",
"Bob",
""
],
[
"Adams",
"Patrick W M",
""
]
] | Magnetic and vorticity fields evolution equations are known to obey the same equation when effects of dissipation and sources terms are negligible. We investigate the analogy between the two fields for non-vanishing dissipation and sources. In addition to the Reynolds (Re)and Prandtl (Pr_M) numbers, we define a new number (S_M) that is given by the ratio of the diffusive term to the Biermann battery term and which allows for a different classification of magnetised fluid behaviour. Numerical simulations of the two fields are then carried out given a parameter space made of Reynolds, Prandtl and Source numbers. We find it appropriate to present and discuss the findings against Prandtl numbers given that these provide the link between viscous and magnetic diffusion. Our simulations indicate that there exists a range of Prandtl numbers for which the fields remain analogues which raises the important question of how far the analogy goes. |
1411.1836 | Ravindra Saraykar Dr. | R V Saraykar and Sujatha Janardhan | Causal and Topological Aspects in Special and General Theory of
Relativity | 33 pages, expanded version of the article arXiv:1208.4580, published
in 'Gravitation and Cosmology' | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we present a review of a geometric and algebraic approach to
causal cones and describe cone preserving transformations and their
relationship with the causal structure related to special and general
relativity. We describe Lie groups, especially matrix Lie groups, homogeneous
and symmetric spaces and causal cones and certain implications of these
concepts in special and general relativity, related to causal structure and
topology of space-time. We compare and contrast the results on causal relations
with those in the literature for general space-times and compare these
relations with K-causal maps. We also describe causal orientations and their
implications for space-time topology and discuss some more topologies on
space-time which arise as an application of domain theory. For the sake of
completeness, we reproduce proofs of certain theorems which we proved in our
earlier work.
| [
{
"created": "Fri, 7 Nov 2014 05:57:59 GMT",
"version": "v1"
}
] | 2014-11-10 | [
[
"Saraykar",
"R V",
""
],
[
"Janardhan",
"Sujatha",
""
]
] | In this article we present a review of a geometric and algebraic approach to causal cones and describe cone preserving transformations and their relationship with the causal structure related to special and general relativity. We describe Lie groups, especially matrix Lie groups, homogeneous and symmetric spaces and causal cones and certain implications of these concepts in special and general relativity, related to causal structure and topology of space-time. We compare and contrast the results on causal relations with those in the literature for general space-times and compare these relations with K-causal maps. We also describe causal orientations and their implications for space-time topology and discuss some more topologies on space-time which arise as an application of domain theory. For the sake of completeness, we reproduce proofs of certain theorems which we proved in our earlier work. |
1707.09664 | Antonin Coutant | Antonin Coutant, Silke Weinfurtner | Low frequency analogue Hawking radiation: The Bogoliubov-de Gennes model | 27 pages, 4 figures. v2: typo corrected, few clarifications,
references added | Phys. Rev. D 97, 025006 (2018) | 10.1103/PhysRevD.97.025006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analytically study the low-frequency properties of the analogue Hawking
effect in Bose-Einstein condensates. We show that in one-dimensional flows
displaying an analogue horizon, the Hawking effect is dominant in the
low-frequency regime. This happens despite non vanishing greybody factors, that
is, the coupling of the Hawking mode and its partner to the mode propagating
with the flow. To show this, we obtained analytical expressions for the
scattering coefficients, in general flows and taking into account the full
Bogoliubov dispersion relation. We discuss the obtained expressions for the
greybody factors. In particular, we show that they can be significantly
decreased if the flow obeys a conformal coupling condition. We argue that in
the presence of a small but non-zero temperature, reducing greybody factors
greatly facilitates the observation of entanglement, that is, establishing that
the state of the Hawking mode and its partner is non-separable.
| [
{
"created": "Sun, 30 Jul 2017 20:16:29 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Jan 2018 17:23:48 GMT",
"version": "v2"
}
] | 2018-01-15 | [
[
"Coutant",
"Antonin",
""
],
[
"Weinfurtner",
"Silke",
""
]
] | We analytically study the low-frequency properties of the analogue Hawking effect in Bose-Einstein condensates. We show that in one-dimensional flows displaying an analogue horizon, the Hawking effect is dominant in the low-frequency regime. This happens despite non vanishing greybody factors, that is, the coupling of the Hawking mode and its partner to the mode propagating with the flow. To show this, we obtained analytical expressions for the scattering coefficients, in general flows and taking into account the full Bogoliubov dispersion relation. We discuss the obtained expressions for the greybody factors. In particular, we show that they can be significantly decreased if the flow obeys a conformal coupling condition. We argue that in the presence of a small but non-zero temperature, reducing greybody factors greatly facilitates the observation of entanglement, that is, establishing that the state of the Hawking mode and its partner is non-separable. |
2407.19508 | Joshi Ashok B | Ashok B. Joshi, Dipanjan Dey, Pankaj S. Joshi and Vivekkumar R. Tank | Tidal forces in collapsing compact objects | 13 pages, 5 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this work, we investigate tidal forces in the Lemaitre-Tolman-Bondi (LTB)
metric, focusing on both hidden and locally visible singularities. We discuss
the strength of these singularities in terms of deformationally strong
singularities. Specifically, we analyze tidal forces in LTB spacetime,
calculating radial and angular tidal forces and Jacobi fields for the radially
co-moving shell. To provide a comparative study, we consider both homogeneous
and inhomogeneous cases. The matter field distribution at one-time slice can
differ significantly from another, highlighting the potential for
time-dependent tidal deformation as a distinct observational signature. We
focus on a specific feature: the time-varying maximum of stretching in the
radial tidal force, which we term the "critical tidal boundary." In the
inhomogeneous case, close to singularity time ($t<t_{s}$), the magnitudes of
tidal forces vary substantially, with significant differences in compressive
and stretching forces within a small physical radius $R(t,r)$. The resulting
singularity in the LTB metrics at the end state of gravitational collapse
appears to be an Ori-strong singularity, characterized by infinite tidal
deformation.
| [
{
"created": "Sun, 28 Jul 2024 15:05:17 GMT",
"version": "v1"
}
] | 2024-07-30 | [
[
"Joshi",
"Ashok B.",
""
],
[
"Dey",
"Dipanjan",
""
],
[
"Joshi",
"Pankaj S.",
""
],
[
"Tank",
"Vivekkumar R.",
""
]
] | In this work, we investigate tidal forces in the Lemaitre-Tolman-Bondi (LTB) metric, focusing on both hidden and locally visible singularities. We discuss the strength of these singularities in terms of deformationally strong singularities. Specifically, we analyze tidal forces in LTB spacetime, calculating radial and angular tidal forces and Jacobi fields for the radially co-moving shell. To provide a comparative study, we consider both homogeneous and inhomogeneous cases. The matter field distribution at one-time slice can differ significantly from another, highlighting the potential for time-dependent tidal deformation as a distinct observational signature. We focus on a specific feature: the time-varying maximum of stretching in the radial tidal force, which we term the "critical tidal boundary." In the inhomogeneous case, close to singularity time ($t<t_{s}$), the magnitudes of tidal forces vary substantially, with significant differences in compressive and stretching forces within a small physical radius $R(t,r)$. The resulting singularity in the LTB metrics at the end state of gravitational collapse appears to be an Ori-strong singularity, characterized by infinite tidal deformation. |
gr-qc/0610008 | Diego Pavon | Diego Pavon | Holographic dark energy and late cosmic acceleration | 6 pages, no figures, contribution to the Proceedings of IRGAC-06 | J.Phys.A40:6865-6870,2007 | 10.1088/1751-8113/40/25/S31 | null | gr-qc | null | It has been persuasively argued that the number of the effective degrees of
freedom of a macroscopic system is proportional to its area rather than to its
volume. This entails interesting consequences for cosmology. Here we present a
model based on this "holographic principle" that accounts for the present stage
of accelerated expansion of the Universe and significantly alleviates the
coincidence problem also for non-spatially flat cosmologies. Likewise, we
comment on a recently proposed late transition to a fresh decelerated phase.
| [
{
"created": "Mon, 2 Oct 2006 16:08:23 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Pavon",
"Diego",
""
]
] | It has been persuasively argued that the number of the effective degrees of freedom of a macroscopic system is proportional to its area rather than to its volume. This entails interesting consequences for cosmology. Here we present a model based on this "holographic principle" that accounts for the present stage of accelerated expansion of the Universe and significantly alleviates the coincidence problem also for non-spatially flat cosmologies. Likewise, we comment on a recently proposed late transition to a fresh decelerated phase. |
2012.01320 | Lijing Shao | Rui Xu, Yong Gao, Lijing Shao | Precession of spheroids under Lorentz violation and observational
consequences for neutron stars | 16 pages, 12 figures; accepted by PRD | Phys. Rev. D 103, 084028 (2021) | 10.1103/PhysRevD.103.084028 | null | gr-qc astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Standard-Model Extension (SME) is an effective-field-theoretic framework
that catalogs all Lorentz-violating field operators. The anisotropic correction
from the minimal gravitational SME to Newtonian gravitational energy for
spheroids is studied, and the rotation of rigid spheroids is solved with
perturbation method and numerical approach. The well-known forced precession
solution given by Nordtvedt in the parameterized post-Newtonian formalism is
recovered and applied to two observed solitary millisecond pulsars to set
bounds on the coefficients for Lorentz violation in the SME framework. A
different solution, which describes the rotation of an otherwise
free-precessing star in the presence of Lorentz violation, is found, and its
consequences on pulsar signals and continuous gravitational waves (GWs) emitted
by neutron stars (NSs) are investigated. The study provides new possible tests
of Lorentz violation once free-precessing NSs are firmly identified in the
future.
| [
{
"created": "Wed, 2 Dec 2020 16:49:26 GMT",
"version": "v1"
},
{
"created": "Sun, 13 Dec 2020 08:41:52 GMT",
"version": "v2"
},
{
"created": "Tue, 2 Mar 2021 00:59:23 GMT",
"version": "v3"
}
] | 2021-04-20 | [
[
"Xu",
"Rui",
""
],
[
"Gao",
"Yong",
""
],
[
"Shao",
"Lijing",
""
]
] | The Standard-Model Extension (SME) is an effective-field-theoretic framework that catalogs all Lorentz-violating field operators. The anisotropic correction from the minimal gravitational SME to Newtonian gravitational energy for spheroids is studied, and the rotation of rigid spheroids is solved with perturbation method and numerical approach. The well-known forced precession solution given by Nordtvedt in the parameterized post-Newtonian formalism is recovered and applied to two observed solitary millisecond pulsars to set bounds on the coefficients for Lorentz violation in the SME framework. A different solution, which describes the rotation of an otherwise free-precessing star in the presence of Lorentz violation, is found, and its consequences on pulsar signals and continuous gravitational waves (GWs) emitted by neutron stars (NSs) are investigated. The study provides new possible tests of Lorentz violation once free-precessing NSs are firmly identified in the future. |
2407.08217 | Dipankar Laya | Dipankar Laya, Roshni Bhaumik, Sourav Dutta, Subenoy Chakraborty | A description of classical and quantum cosmology for a single scalar
field torsion gravity | 16 Pages, 4 figures | Modern Physics Letters A Vol. 38, Nos. 22 & 23 (2023) 2350109 (15
pages) | 10.1142/S0217732323501092 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In the background of homogeneous and isotropic flat FLRW space-time, both
classical and quantum cosmology has been studied for teleparallel dark energy
(DE) model. Using Noether symmetry analysis, not only the symmetry vector but
also the coupling function in the Lagrangian and the potential of the scalar
field has been determined. Also symmetry analysis identifies a cyclic variable
in the Lagrangian along the symmetry vector and as a result the Lagrangian
simplifies to a great extend so that classical solution is obtained.
Subsequently, in quantum cosmology Wheeler-DeWitt(WD) equation has been
constructed and the quantum version of the conserved momenta corresponding to
Noether symmetry identifies the periodic part of the wave function of the
universe and as a result the Wheeler-DeWitt equation becomes solvable. Finally,
quantum description shows finite non-zero probability at the classical big-bang
singularity.
| [
{
"created": "Thu, 11 Jul 2024 06:34:02 GMT",
"version": "v1"
}
] | 2024-07-12 | [
[
"Laya",
"Dipankar",
""
],
[
"Bhaumik",
"Roshni",
""
],
[
"Dutta",
"Sourav",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | In the background of homogeneous and isotropic flat FLRW space-time, both classical and quantum cosmology has been studied for teleparallel dark energy (DE) model. Using Noether symmetry analysis, not only the symmetry vector but also the coupling function in the Lagrangian and the potential of the scalar field has been determined. Also symmetry analysis identifies a cyclic variable in the Lagrangian along the symmetry vector and as a result the Lagrangian simplifies to a great extend so that classical solution is obtained. Subsequently, in quantum cosmology Wheeler-DeWitt(WD) equation has been constructed and the quantum version of the conserved momenta corresponding to Noether symmetry identifies the periodic part of the wave function of the universe and as a result the Wheeler-DeWitt equation becomes solvable. Finally, quantum description shows finite non-zero probability at the classical big-bang singularity. |
2008.12526 | Gihyuk Cho | Gihyuk Cho | Analytic expression of perturbations of Schwarzschild spacetime via
Homotopy Analysis Method | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper derives the analytic and practicable expression of general
solution of vacuum Regge-Wheeler equation via Homotopy Analysis Method.
| [
{
"created": "Fri, 28 Aug 2020 07:41:33 GMT",
"version": "v1"
}
] | 2020-08-31 | [
[
"Cho",
"Gihyuk",
""
]
] | This paper derives the analytic and practicable expression of general solution of vacuum Regge-Wheeler equation via Homotopy Analysis Method. |
1112.2478 | Matthew Lake Dr | Matthew Lake and Teruaki Suyama | Evolution of FLRW spacetime after the birth of a cosmic string | 16 pages, 2 figures, published version | Phys. Rev. D 85, 083521 (2012) | 10.1103/PhysRevD.85.083521 | RESCEU-34/11 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the evolution of an initially FLRW universe after the formation
of a long, straight, cosmic string with arbitrary tension and mass per unit
length. The birth of the string sources scalar and tensor-type perturbations in
the background metric and both density and velocity perturbations in the
background fluid, which compensate for the string mass and maintain energy
conservation. The former generate the deficit angle within the light cone of
the string and a gravitational shock front at the cosmological horizon, whereas
the latter are confined within the sound cone. We study the properties of the
metric within each region of the resulting spacetime and give the explicit
coordinate transformations which demonstrate non-violation of causality. This
paper generalizes the work of previous studies for the Nambu-Goto string.
| [
{
"created": "Mon, 12 Dec 2011 09:31:06 GMT",
"version": "v1"
},
{
"created": "Tue, 1 May 2012 06:01:16 GMT",
"version": "v2"
}
] | 2013-05-30 | [
[
"Lake",
"Matthew",
""
],
[
"Suyama",
"Teruaki",
""
]
] | We consider the evolution of an initially FLRW universe after the formation of a long, straight, cosmic string with arbitrary tension and mass per unit length. The birth of the string sources scalar and tensor-type perturbations in the background metric and both density and velocity perturbations in the background fluid, which compensate for the string mass and maintain energy conservation. The former generate the deficit angle within the light cone of the string and a gravitational shock front at the cosmological horizon, whereas the latter are confined within the sound cone. We study the properties of the metric within each region of the resulting spacetime and give the explicit coordinate transformations which demonstrate non-violation of causality. This paper generalizes the work of previous studies for the Nambu-Goto string. |
2008.01588 | S Habib Mazharimousavi | S. Habib Mazharimousavi and M. Halilsoy | Colliding waves in a model of nonlinear electrodynamics | No figure, 7 pages. Final version, published in Classical and Quantum
Gravity | Class. Quantum Grav. 37 (2020) 137001 (8pp) | 10.1088/1361-6382/ab9516 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bell-Szekeres (BS) solution for colliding electromagnetic waves in
Einstein-Maxwell (EM) theory describes also colliding waves in nonlinear
electrodynamics (NED) with an emergent cosmological constant. Our NED model
covers the first leading orders to the well-known Heisenberg-Euler (HE) type in
a particular gauge of pure magnetic field. Prior to the problem of collision we
obtain dyonic solution for the considered NED theory in a conformally flat
spacetime which has both electric and magnetic fields with constant invariants.
Our sole finding is that null currents inevitably arise in the process of
collision of plane waves in the HE type NED theory.
| [
{
"created": "Mon, 3 Aug 2020 15:50:54 GMT",
"version": "v1"
}
] | 2020-08-05 | [
[
"Mazharimousavi",
"S. Habib",
""
],
[
"Halilsoy",
"M.",
""
]
] | Bell-Szekeres (BS) solution for colliding electromagnetic waves in Einstein-Maxwell (EM) theory describes also colliding waves in nonlinear electrodynamics (NED) with an emergent cosmological constant. Our NED model covers the first leading orders to the well-known Heisenberg-Euler (HE) type in a particular gauge of pure magnetic field. Prior to the problem of collision we obtain dyonic solution for the considered NED theory in a conformally flat spacetime which has both electric and magnetic fields with constant invariants. Our sole finding is that null currents inevitably arise in the process of collision of plane waves in the HE type NED theory. |
1005.5460 | Seth A. Major | Seth A. Major | Shape in an Atom of Space: Exploring quantum geometry phenomenology | 14 pages, 7 figures; v2 references added | Class.Quant.Grav.27:225012,2010 | 10.1088/0264-9381/27/22/225012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A phenomenology for the deep spatial geometry of loop quantum gravity is
introduced. In the context of a simple model, an atom of space, it is shown how
purely combinatorial structures can affect observations. The angle operator is
used to develop a model of angular corrections to local, continuum flat-space
3-geometries. The physical effects involve neither breaking of local Lorentz
invariance nor Planck scale suppression, but rather reply on only the
combinatorics of SU(2) recoupling. Bhabha scattering is discussed as an example
of how the effects might be observationally accessible.
| [
{
"created": "Sat, 29 May 2010 15:16:41 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Jun 2010 20:27:41 GMT",
"version": "v2"
}
] | 2014-11-21 | [
[
"Major",
"Seth A.",
""
]
] | A phenomenology for the deep spatial geometry of loop quantum gravity is introduced. In the context of a simple model, an atom of space, it is shown how purely combinatorial structures can affect observations. The angle operator is used to develop a model of angular corrections to local, continuum flat-space 3-geometries. The physical effects involve neither breaking of local Lorentz invariance nor Planck scale suppression, but rather reply on only the combinatorics of SU(2) recoupling. Bhabha scattering is discussed as an example of how the effects might be observationally accessible. |
2005.04747 | Jose Edgar Madriz Aguilar Dr. | Jos\'e Edgar Madriz Aguilar, J. Zamarripa, M. Montes, J. A. Licea, C.
De Loza and A. Peraza | Extending $\Lambda(t)-$CDM to the inflationary epoch using dynamical
foliations and a pre-inflationary vacuum energy from 5D geometrical vacuum as
a unifying mechanism | 8 pages, no figures. This is a revised version | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this letter assuming a 5D quantum pre-inflationary vacuum energy, we
propose a manner to extend some $\Lambda(t)$-CDM models to the inflationary
period by using dynamical foliations of the five-dimensional (5D) Ricci-flat
space-time manifold, regarding a non-compact extra space-like coor\-dinate. In
this formalism we achieve also a geometrical unification of inflation and the
present acce\-le\-rating epoch. In this approach inflation is generated by a
pre-inflationary quantum vacuum energy that maintains the 5D classical vacuum
on cosmological scales. We obtain from geometrical conditions that we can model
the presence of the pre-inflationary vacuum energy in 4D as a dynamical
cosmological constant. The 4D inflationary period results to be governed by a
power law expansion and for certain values of some parameters of the model we
obtain an spectral index satisfying $0.9607\leq n_s\leq 0.9691$ and a scalar to
tensor ratio $r=0.098$, values that fit well according to Planck 2018 results.
The 4D inflationary potential is induced for the 5D geometry and the 4D
pre-inflationary potential is determined by the model. We show thatin this
theoretical framework the present acceleration in the expansion of the universe
can be explained due to a remanent of this pre-inflationary vacuum energy
scaled to the present epoch and that its description can be done with the same
$\Lambda(t)$. In this period we obtain a deceleration parameter in agreement
with Planck 2018 data under certain restrictions of the parameters of the
model. From the geometrical point of view $\Lambda(t)$ is depending on the
dynamical foliation of the 5D space-time manifold.
| [
{
"created": "Sun, 10 May 2020 18:44:10 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Aug 2021 00:01:41 GMT",
"version": "v2"
}
] | 2021-08-20 | [
[
"Aguilar",
"José Edgar Madriz",
""
],
[
"Zamarripa",
"J.",
""
],
[
"Montes",
"M.",
""
],
[
"Licea",
"J. A.",
""
],
[
"De Loza",
"C.",
""
],
[
"Peraza",
"A.",
""
]
] | In this letter assuming a 5D quantum pre-inflationary vacuum energy, we propose a manner to extend some $\Lambda(t)$-CDM models to the inflationary period by using dynamical foliations of the five-dimensional (5D) Ricci-flat space-time manifold, regarding a non-compact extra space-like coor\-dinate. In this formalism we achieve also a geometrical unification of inflation and the present acce\-le\-rating epoch. In this approach inflation is generated by a pre-inflationary quantum vacuum energy that maintains the 5D classical vacuum on cosmological scales. We obtain from geometrical conditions that we can model the presence of the pre-inflationary vacuum energy in 4D as a dynamical cosmological constant. The 4D inflationary period results to be governed by a power law expansion and for certain values of some parameters of the model we obtain an spectral index satisfying $0.9607\leq n_s\leq 0.9691$ and a scalar to tensor ratio $r=0.098$, values that fit well according to Planck 2018 results. The 4D inflationary potential is induced for the 5D geometry and the 4D pre-inflationary potential is determined by the model. We show thatin this theoretical framework the present acceleration in the expansion of the universe can be explained due to a remanent of this pre-inflationary vacuum energy scaled to the present epoch and that its description can be done with the same $\Lambda(t)$. In this period we obtain a deceleration parameter in agreement with Planck 2018 data under certain restrictions of the parameters of the model. From the geometrical point of view $\Lambda(t)$ is depending on the dynamical foliation of the 5D space-time manifold. |
1606.01147 | Huibert Het Lam | Huibert het Lam and Tomislav Prokopec | Singularities in FLRW Spacetimes | null | null | 10.1016/j.physletb.2017.10.070 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We point out that past-incompleteness of geodesics in FLRW spacetimes does
not necessarily imply that these spacetimes start from a singularity. Namely,
if a test particle that follows such a trajectory has a non-vanishing velocity,
its energy was super-Planckian at some time in the past if it kept following
that geodesic. That indicates a breakdown of the particle's description, which
is why we should not consider those trajectories for the definition of an
initial singularity. When one only considers test particles that do not have
this breakdown of their trajectory, it turns out that the only singular FLRW
spacetimes are the ones that have a scale parameter that vanishes at some
initial time.
| [
{
"created": "Fri, 3 Jun 2016 15:40:09 GMT",
"version": "v1"
}
] | 2017-12-06 | [
[
"Lam",
"Huibert het",
""
],
[
"Prokopec",
"Tomislav",
""
]
] | We point out that past-incompleteness of geodesics in FLRW spacetimes does not necessarily imply that these spacetimes start from a singularity. Namely, if a test particle that follows such a trajectory has a non-vanishing velocity, its energy was super-Planckian at some time in the past if it kept following that geodesic. That indicates a breakdown of the particle's description, which is why we should not consider those trajectories for the definition of an initial singularity. When one only considers test particles that do not have this breakdown of their trajectory, it turns out that the only singular FLRW spacetimes are the ones that have a scale parameter that vanishes at some initial time. |
1310.5933 | Ahmet Baykal | Ahmet Baykal | Variational derivatives of gravitational actions | References are reordered and updated. Minor changes in the abstract | Eur. Phys. J. Plus (2013) 128: 125 | 10.1140/epjp/i2013-13125-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A method of calculation for the variational derivatives for gravitational
actions in the pseudo-Riemannian case is proposed as a practical variant of the
first order formalism with constraints. The method is then used to derive the
metric field equations for a generic $f(R)$ model.
| [
{
"created": "Tue, 22 Oct 2013 14:25:23 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Oct 2013 15:07:25 GMT",
"version": "v2"
}
] | 2013-10-30 | [
[
"Baykal",
"Ahmet",
""
]
] | A method of calculation for the variational derivatives for gravitational actions in the pseudo-Riemannian case is proposed as a practical variant of the first order formalism with constraints. The method is then used to derive the metric field equations for a generic $f(R)$ model. |
2111.14351 | Yevgeny Stadnik | Yevgeny V. Stadnik | Comment on ''Quantum sensor networks as exotic field telescopes for
multi-messenger astronomy'' | 10 pages, 1 figure. Added rebuttal to arXiv:2112.02653v1 on page 9.
Comment remains unchanged from v1 | Nature Astronomy 8, 434 (2024) | 10.1038/s41550-024-02245-4 | null | gr-qc astro-ph.IM hep-ph physics.atom-ph quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the recent work [Dailey et al., Nature Astronomy 5, 150 (2021)], it was
claimed that networks of quantum sensors can be used as sensitive
multi-messenger probes of astrophysical phenomena that produce intense bursts
of relativistic bosonic waves which interact non-gravitationally with ordinary
matter. The most promising possibility considered in [Ibid.] involved
clock-based searches for quadratic scalar-type interactions, with greatly
diminished reach in the case of magnetometer-based searches for
derivative-pseudoscalar-type interactions and clock-based searches for linear
scalar-type interactions. In this note, we point out that the aforementioned
work overlooked the ''back action'' of ordinary matter on scalar waves with
quadratic interactions and that accounting for back-action effects can
drastically affect the detection prospects of clock networks. In particular,
back action can cause strong screening of scalar waves near Earth's surface and
by the apparatus itself, rendering clock experiments insensitive to
extraterrestrial sources of relativistic scalar waves. Additionally,
back-action effects can retard the propagation of scalar waves through the
interstellar and intergalactic media, significantly delaying the arrival of
scalar waves at Earth compared to their gravitational-wave counterparts and
thereby preventing multi-messenger astronomy on human timescales.
| [
{
"created": "Mon, 29 Nov 2021 07:08:14 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Dec 2021 10:07:51 GMT",
"version": "v2"
}
] | 2024-04-24 | [
[
"Stadnik",
"Yevgeny V.",
""
]
] | In the recent work [Dailey et al., Nature Astronomy 5, 150 (2021)], it was claimed that networks of quantum sensors can be used as sensitive multi-messenger probes of astrophysical phenomena that produce intense bursts of relativistic bosonic waves which interact non-gravitationally with ordinary matter. The most promising possibility considered in [Ibid.] involved clock-based searches for quadratic scalar-type interactions, with greatly diminished reach in the case of magnetometer-based searches for derivative-pseudoscalar-type interactions and clock-based searches for linear scalar-type interactions. In this note, we point out that the aforementioned work overlooked the ''back action'' of ordinary matter on scalar waves with quadratic interactions and that accounting for back-action effects can drastically affect the detection prospects of clock networks. In particular, back action can cause strong screening of scalar waves near Earth's surface and by the apparatus itself, rendering clock experiments insensitive to extraterrestrial sources of relativistic scalar waves. Additionally, back-action effects can retard the propagation of scalar waves through the interstellar and intergalactic media, significantly delaying the arrival of scalar waves at Earth compared to their gravitational-wave counterparts and thereby preventing multi-messenger astronomy on human timescales. |
1905.02380 | Pablo Le\'on | C. Las Heras and P. Le\'on | New algorithms to obtain analytical solutions of Einstein's equations in
isotropic coordinates | 14 pages, 24 figures, results were improved | null | 10.1140/epjc/s10052-019-7507-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The main objective of this work, is to show two inequivalent methods to
obtain new spherical symmetric solutions of Einstein's Equations with
anisotropy in the pressures in isotropic coordinates. This was done inspired by
the MGD method, which is known to be valid for line elements in Schwarzschild
coordinates. As example, we obtained four analytical solutions using Gold III
as seed solution. Two solutions, out of four, (one for each algorithm), satisfy
the physical acceptability conditions.
| [
{
"created": "Tue, 7 May 2019 06:46:46 GMT",
"version": "v1"
},
{
"created": "Thu, 9 May 2019 03:12:19 GMT",
"version": "v2"
},
{
"created": "Tue, 19 Nov 2019 16:49:32 GMT",
"version": "v3"
}
] | 2020-01-08 | [
[
"Heras",
"C. Las",
""
],
[
"León",
"P.",
""
]
] | The main objective of this work, is to show two inequivalent methods to obtain new spherical symmetric solutions of Einstein's Equations with anisotropy in the pressures in isotropic coordinates. This was done inspired by the MGD method, which is known to be valid for line elements in Schwarzschild coordinates. As example, we obtained four analytical solutions using Gold III as seed solution. Two solutions, out of four, (one for each algorithm), satisfy the physical acceptability conditions. |
1309.2698 | Kazuharu Bamba | Kazuharu Bamba, Salvatore Capozziello, Mariafelicia De Laurentis,
Shin'ichi Nojiri and Diego S\'aez-G\'omez | No further gravitational wave modes in $F(T)$ gravity | 7 pages, no figure, version accepted for publication in Physics
Letters B | Physics Letters B 727 (2013) 194-198 | 10.1016/j.physletb.2013.10.022 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explore the possibility of further gravitational wave modes in $F(T)$
gravity, where $T$ is the torsion scalar in teleparallelism. It is explicitly
demonstrated that gravitational wave modes in $F(T)$ gravity are equivalent to
those in General Relativity. This result is achieved by calculating the
Minkowskian limit for a class of analytic function of $F(T)$. This consequence
is also confirmed by the preservative analysis around the flat background in
the weak field limit with the scalar-tensor representation of $F(T)$ gravity.
| [
{
"created": "Wed, 11 Sep 2013 00:10:25 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Oct 2013 01:17:54 GMT",
"version": "v2"
}
] | 2013-11-14 | [
[
"Bamba",
"Kazuharu",
""
],
[
"Capozziello",
"Salvatore",
""
],
[
"De Laurentis",
"Mariafelicia",
""
],
[
"Nojiri",
"Shin'ichi",
""
],
[
"Sáez-Gómez",
"Diego",
""
]
] | We explore the possibility of further gravitational wave modes in $F(T)$ gravity, where $T$ is the torsion scalar in teleparallelism. It is explicitly demonstrated that gravitational wave modes in $F(T)$ gravity are equivalent to those in General Relativity. This result is achieved by calculating the Minkowskian limit for a class of analytic function of $F(T)$. This consequence is also confirmed by the preservative analysis around the flat background in the weak field limit with the scalar-tensor representation of $F(T)$ gravity. |
2401.06845 | Alexandre Toubiana | Alexandre Toubiana, Jonathan R. Gair | Indistinguishability criterion and estimating the presence of biases | Correction of a small typo in the evaluation of the fitting factor of
P\"urrer & Haster. What was reported was 2(1-fitting factor) | null | null | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In these notes, we comment on the standard indistinguishability criterion
often used in the gravitational wave community to set accuracy requirements on
waveforms. Revisiting the hypotheses under which it is derived, we propose a
correction to it. Moreover, we outline how the approach we proposed in a recent
work in the context of tests of general relativity can be used for this same
purpose.
| [
{
"created": "Fri, 12 Jan 2024 19:00:01 GMT",
"version": "v1"
},
{
"created": "Thu, 18 Jan 2024 09:18:56 GMT",
"version": "v2"
}
] | 2024-01-19 | [
[
"Toubiana",
"Alexandre",
""
],
[
"Gair",
"Jonathan R.",
""
]
] | In these notes, we comment on the standard indistinguishability criterion often used in the gravitational wave community to set accuracy requirements on waveforms. Revisiting the hypotheses under which it is derived, we propose a correction to it. Moreover, we outline how the approach we proposed in a recent work in the context of tests of general relativity can be used for this same purpose. |
gr-qc/0504063 | Niklas Rohr | Niklas Rohr and Claes Uggla | Conformal regularization of Einstein's field equations | New title plus corrections and text added. To appear in CQG | Class.Quant.Grav. 22 (2005) 3775-3787 | 10.1088/0264-9381/22/17/026 | null | gr-qc | null | To study asymptotic structures, we regularize Einstein's field equations by
means of conformal transformations. The conformal factor is chosen so that it
carries a dimensional scale that captures crucial asymptotic features. By
choosing a conformal orthonormal frame we obtain a coupled system of
differential equations for a set of dimensionless variables, associated with
the conformal dimensionless metric, where the variables describe ratios with
respect to the chosen asymptotic scale structure. As examples, we describe some
explicit choices of conformal factors and coordinates appropriate for the
situation of a timelike congruence approaching a singularity. One choice is
shown to just slightly modify the so-called Hubble-normalized approach, and one
leads to dimensionless first order symmetric hyperbolic equations. We also
discuss differences and similarities with other conformal approaches in the
literature, as regards, e.g., isotropic singularities.
| [
{
"created": "Thu, 14 Apr 2005 12:13:59 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Jul 2005 14:21:35 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Rohr",
"Niklas",
""
],
[
"Uggla",
"Claes",
""
]
] | To study asymptotic structures, we regularize Einstein's field equations by means of conformal transformations. The conformal factor is chosen so that it carries a dimensional scale that captures crucial asymptotic features. By choosing a conformal orthonormal frame we obtain a coupled system of differential equations for a set of dimensionless variables, associated with the conformal dimensionless metric, where the variables describe ratios with respect to the chosen asymptotic scale structure. As examples, we describe some explicit choices of conformal factors and coordinates appropriate for the situation of a timelike congruence approaching a singularity. One choice is shown to just slightly modify the so-called Hubble-normalized approach, and one leads to dimensionless first order symmetric hyperbolic equations. We also discuss differences and similarities with other conformal approaches in the literature, as regards, e.g., isotropic singularities. |
2103.12017 | Ronaldo S. S. Vieira | Ronaldo S. S. Vieira, Javier Ramos-Caro, Alberto Saa | Post-Newtonian Hamiltonian dynamics: applications to stationary
spacetimes and statistical mechanics | 9 pages, no figures | null | null | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Although the post-Newtonian Lagrangian formalism is widely used in
relativistic dynamical and statistical studies of test bodies moving around
arbitrary mass distributions, the corresponding general Hamiltonian formalism
is still relatively uncommon, being restricted basically to the case of N-body
problems. Here, we present a consistent Hamiltonian formalism for the dynamics
of test particles in spacetimes with arbitrary energy-momentum distributions in
the first post-Newtonian (1PN) approximation. We apply our formalism to orbital
motion in stationary axisymmetric spacetimes and obtain the 1PN relativistic
corrections to the radial and vertical epicyclic frequencies for quasi-circular
equatorial motion, a result potentially interesting for galactic dynamics. For
the case of razor-thin disk configurations, we obtain an approximated third
integral which could be used to determine analytically the envelope of nearly
equatorial orbits. One of the main advantages of this 1PN analysis is the
explicit presence of frame-dragging effects in all pertinent expressions,
allowing some qualitative predictions in rotating spacetimes. We finish
discussing the 1PN collisionless Boltzmann equation in terms of the Hamiltonian
canonical variables and its relation with previous results in the literature.
| [
{
"created": "Mon, 22 Mar 2021 17:15:25 GMT",
"version": "v1"
}
] | 2021-03-23 | [
[
"Vieira",
"Ronaldo S. S.",
""
],
[
"Ramos-Caro",
"Javier",
""
],
[
"Saa",
"Alberto",
""
]
] | Although the post-Newtonian Lagrangian formalism is widely used in relativistic dynamical and statistical studies of test bodies moving around arbitrary mass distributions, the corresponding general Hamiltonian formalism is still relatively uncommon, being restricted basically to the case of N-body problems. Here, we present a consistent Hamiltonian formalism for the dynamics of test particles in spacetimes with arbitrary energy-momentum distributions in the first post-Newtonian (1PN) approximation. We apply our formalism to orbital motion in stationary axisymmetric spacetimes and obtain the 1PN relativistic corrections to the radial and vertical epicyclic frequencies for quasi-circular equatorial motion, a result potentially interesting for galactic dynamics. For the case of razor-thin disk configurations, we obtain an approximated third integral which could be used to determine analytically the envelope of nearly equatorial orbits. One of the main advantages of this 1PN analysis is the explicit presence of frame-dragging effects in all pertinent expressions, allowing some qualitative predictions in rotating spacetimes. We finish discussing the 1PN collisionless Boltzmann equation in terms of the Hamiltonian canonical variables and its relation with previous results in the literature. |
0806.2177 | Chen Songbai | Songbai Chen, Bin Wang, Jiliang Jing | Scalar emission in a rotating G\"{o}del black hole | 14 pages, 4 figures, This version accepted for publication in Phys.
Rev. D contains a minor modification and two new references | Phys.Rev.D78:064030,2008 | 10.1103/PhysRevD.78.064030 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the absorption probability and Hawking radiation of the scalar field
in the rotating G\"{o}del black hole in minimal five-dimensional gauged
supergravity. We find that G\"{o}del parameter $j$ imprints in the greybody
factor and Hawking radiation. It plays a different role from the angular
momentum of the black hole in the Hawking radiation and super-radiance. These
information can help us know more about rotating G\"{o}del black holes in
minimal five-dimensional gauged supergravity.
| [
{
"created": "Fri, 13 Jun 2008 02:26:38 GMT",
"version": "v1"
},
{
"created": "Sat, 23 Aug 2008 07:36:43 GMT",
"version": "v2"
}
] | 2009-02-20 | [
[
"Chen",
"Songbai",
""
],
[
"Wang",
"Bin",
""
],
[
"Jing",
"Jiliang",
""
]
] | We study the absorption probability and Hawking radiation of the scalar field in the rotating G\"{o}del black hole in minimal five-dimensional gauged supergravity. We find that G\"{o}del parameter $j$ imprints in the greybody factor and Hawking radiation. It plays a different role from the angular momentum of the black hole in the Hawking radiation and super-radiance. These information can help us know more about rotating G\"{o}del black holes in minimal five-dimensional gauged supergravity. |
1001.0381 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | Some remarks on exact wormhole solutions | 3 pages, no figures | Adv.Stud.Theor.Phys.5:365,2011 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Exact wormhole solutions, while eagerly sought after, often have the
appearance of being overly specialized or highly artificial. A case for the
possible existence of traversable wormholes would be more compelling if an
abundance of solutions could be found. It is shown in this note that for many
of the wormhole geometries in the literature, the exact solutions obtained
imply the existence of large sets of additional solutions.
| [
{
"created": "Sun, 3 Jan 2010 15:34:27 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Dec 2010 18:56:11 GMT",
"version": "v2"
},
{
"created": "Fri, 6 May 2011 20:59:50 GMT",
"version": "v3"
},
{
"created": "Sun, 12 Jun 2011 23:16:01 GMT",
"version": "v4"
},
{
"cre... | 2011-06-22 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | Exact wormhole solutions, while eagerly sought after, often have the appearance of being overly specialized or highly artificial. A case for the possible existence of traversable wormholes would be more compelling if an abundance of solutions could be found. It is shown in this note that for many of the wormhole geometries in the literature, the exact solutions obtained imply the existence of large sets of additional solutions. |
1501.01765 | Manabendra Sharma | Sukanta Panda and Manabendra Sharma | Anisotropic Bouncing Scenario in $F(X)-V(\phi)$ model | 13 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1406.3992 | null | 10.1007/s10509-015-2594-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the cosmology of a class of model with noncanonical scalar
field and matter in an anisotropic time dependent background. Writing the
Einstein Equations in terms of dimensionless dynamical variables appropriately
defined for bouncing solutions, we find all the fixed points. From the bouncing
conditions and stability of fixed points, solutions describing non singular
bounce are obtained.
| [
{
"created": "Thu, 8 Jan 2015 08:34:48 GMT",
"version": "v1"
}
] | 2016-02-17 | [
[
"Panda",
"Sukanta",
""
],
[
"Sharma",
"Manabendra",
""
]
] | We investigate the cosmology of a class of model with noncanonical scalar field and matter in an anisotropic time dependent background. Writing the Einstein Equations in terms of dimensionless dynamical variables appropriately defined for bouncing solutions, we find all the fixed points. From the bouncing conditions and stability of fixed points, solutions describing non singular bounce are obtained. |
2109.13554 | Takeshi Fukuyama | Takeshi Fukuyama | Revisiting the Origin of the Universe and the Arrow of Time | 11pages, 3 figures. Comments are added | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We reconsider the old but yet unsolved problems, origin of the universe and
the arrow of time. We show that only the closed universe is free from the
singularity with the arrow of time symmetric with respect to the maximal size
of the cosmic scale. The Wheeler-DeWitt equation is explicitly solved to obtain
the local dynamical times. Corresponding to these local dynamical times, the
thermodynamic arrow of time is proved to coincide with the arrows of dynamical
time and of expanding universe (cosmological time). The proof is explicitly
shown in two-dimensional spacetime.
| [
{
"created": "Tue, 28 Sep 2021 08:20:22 GMT",
"version": "v1"
},
{
"created": "Wed, 18 Jan 2023 05:32:45 GMT",
"version": "v2"
}
] | 2023-01-19 | [
[
"Fukuyama",
"Takeshi",
""
]
] | We reconsider the old but yet unsolved problems, origin of the universe and the arrow of time. We show that only the closed universe is free from the singularity with the arrow of time symmetric with respect to the maximal size of the cosmic scale. The Wheeler-DeWitt equation is explicitly solved to obtain the local dynamical times. Corresponding to these local dynamical times, the thermodynamic arrow of time is proved to coincide with the arrows of dynamical time and of expanding universe (cosmological time). The proof is explicitly shown in two-dimensional spacetime. |
1402.1343 | Abhishek Majhi | Abhishek Majhi | Black Hole Entropy from indistinguishable quantum geometric excitations | 7 pages, 4 figures | Advances in High Energy Physics, vol. 2016, Article ID 2903867, 7
pages, 2016 | 10.1155/2016/2903867 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In loop quantum gravity, the quantum geometry of a black hole horizon consist
of discrete non-perturbative quantum geometric excitations (or punctures)
labeled by spins, which are responsible for the quantum area of the horizon. If
these punctures are compared to a gas of particles, then the spins associated
with the punctures can be viewed as single puncture area levels analogous to
single particle energy levels. Consequently, if we {\it assume} these punctures
to be {\it indistinguishable}, the microstate count for the horizon resembles
that of Bose-Einstein counting formula for gas of particles. For the
Bekenstein-Hawking area law(BHAL) to follow from the entropy calculation in the
large area limit, the Barbero-Immirzi parameter($\g$) approximately takes a
constant value.
| [
{
"created": "Thu, 6 Feb 2014 13:06:52 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Feb 2014 02:21:06 GMT",
"version": "v2"
},
{
"created": "Sat, 21 Nov 2015 03:13:38 GMT",
"version": "v3"
}
] | 2016-11-07 | [
[
"Majhi",
"Abhishek",
""
]
] | In loop quantum gravity, the quantum geometry of a black hole horizon consist of discrete non-perturbative quantum geometric excitations (or punctures) labeled by spins, which are responsible for the quantum area of the horizon. If these punctures are compared to a gas of particles, then the spins associated with the punctures can be viewed as single puncture area levels analogous to single particle energy levels. Consequently, if we {\it assume} these punctures to be {\it indistinguishable}, the microstate count for the horizon resembles that of Bose-Einstein counting formula for gas of particles. For the Bekenstein-Hawking area law(BHAL) to follow from the entropy calculation in the large area limit, the Barbero-Immirzi parameter($\g$) approximately takes a constant value. |
1907.05095 | Alexandre Gavrilik | A.M. Gavrilik, A.V. Nazarenko | Statistics effects in extremal black holes ensemble | v2: 15 pages, 3 figures; refs., text and explanations added to match
reviewers' suggestions, accepted for publication by Int. J. Mod. Phys. A | Int. J. Mod. Phys. A Vol. 34, No. 32, 1950215 (2019) | 10.1142/S0217751X19502154 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the grand canonical ensemble of the static and extremal black
holes, when the equivalence of the electric charge and mass of individual black
hole is postulated. Assuming uniform distribution of black holes in space, we
are finding the effective mass of test particle and mean time dilation at the
admissible points of space, taking into account the gravitational action of
surrounding black holes. Having specified the statistics that governs extremal
black holes, we study its effect on those quantities. Here, the role of
statistics is to assign a statistical weight to the configurations of certain
fixed number of black holes. We borrow these weights from Bose-Einstein,
Fermi-Dirac, classical and infinite statistics. Using mean field approximation,
the aforementioned characteristics are calculated and visualized, what permits
us to draw the conclusions on visible effect of each statistics.
| [
{
"created": "Thu, 11 Jul 2019 10:42:18 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Nov 2019 18:45:06 GMT",
"version": "v2"
}
] | 2020-10-12 | [
[
"Gavrilik",
"A. M.",
""
],
[
"Nazarenko",
"A. V.",
""
]
] | We consider the grand canonical ensemble of the static and extremal black holes, when the equivalence of the electric charge and mass of individual black hole is postulated. Assuming uniform distribution of black holes in space, we are finding the effective mass of test particle and mean time dilation at the admissible points of space, taking into account the gravitational action of surrounding black holes. Having specified the statistics that governs extremal black holes, we study its effect on those quantities. Here, the role of statistics is to assign a statistical weight to the configurations of certain fixed number of black holes. We borrow these weights from Bose-Einstein, Fermi-Dirac, classical and infinite statistics. Using mean field approximation, the aforementioned characteristics are calculated and visualized, what permits us to draw the conclusions on visible effect of each statistics. |
gr-qc/0605061 | Nikodem Poplawski | Nikodem J. Poplawski | Propagating torsion in the Einstein frame | 10 pages; published version | J.Math.Phys. 47 (2006) 112504 | 10.1063/1.2365788 | null | gr-qc | null | The Einstein-Cartan-Saa theory of torsion modifies the spacetime volume
element so that it is compatible with the connection. The condition of
connection compatibility gives constraints on torsion, which are also necessary
for the consistence of torsion, minimal coupling, and electromagnetic gauge
invariance. To solve the problem of positivity of energy associated with the
torsionic scalar, we reformulate this theory in the Einstein conformal frame.
In the presence of the electromagnetic field, we obtain the
Hojman-Rosenbaum-Ryan-Shepley theory of propagating torsion with a different
factor in the torsionic kinetic term.
| [
{
"created": "Wed, 10 May 2006 19:50:28 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Oct 2006 05:26:10 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Poplawski",
"Nikodem J.",
""
]
] | The Einstein-Cartan-Saa theory of torsion modifies the spacetime volume element so that it is compatible with the connection. The condition of connection compatibility gives constraints on torsion, which are also necessary for the consistence of torsion, minimal coupling, and electromagnetic gauge invariance. To solve the problem of positivity of energy associated with the torsionic scalar, we reformulate this theory in the Einstein conformal frame. In the presence of the electromagnetic field, we obtain the Hojman-Rosenbaum-Ryan-Shepley theory of propagating torsion with a different factor in the torsionic kinetic term. |
0712.2831 | Ricardo E. Gamboa Saravi | Ricardo E. Gamboa Saravi | Static plane symmetric relativistic fluids and empty repelling singular
boundaries | 9 pages, 1 figure, accepted for publication in Classical and Quantum
Gravity | Class.Quant.Grav.25:045005,2008 | 10.1088/0264-9381/25/4/045005 | null | gr-qc | null | We present a detailed analysis of the general exact solution of Einstein's
equation corresponding to a static and plane symmetric distribution of matter
with density proportional to pressure. We study the geodesics in it and we show
that this simple spacetime exhibits very curious properties. In particular, it
has a free of matter repelling singular boundary and all geodesics bounce off
it.
| [
{
"created": "Tue, 18 Dec 2007 15:34:58 GMT",
"version": "v1"
}
] | 2008-11-11 | [
[
"Saravi",
"Ricardo E. Gamboa",
""
]
] | We present a detailed analysis of the general exact solution of Einstein's equation corresponding to a static and plane symmetric distribution of matter with density proportional to pressure. We study the geodesics in it and we show that this simple spacetime exhibits very curious properties. In particular, it has a free of matter repelling singular boundary and all geodesics bounce off it. |
1308.2962 | Manuel Rodrigues | M. E. Rodrigues, I. G. Salako, M. J. S. Houndjo and J. Tossa | Locally Rotationally Symmetric Bianchi Type-I cosmological model in
$f(T)$ gravity: from early to Dark Energy dominated universe | 20 pages, 10 figures, Accepted for publication in International
Journal of Modern Physics D (IJMPD) | Int. J. Mod. Phys. D 23, 1450004 (2014) | 10.1142/S0218271814500047 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the locally rotational symmetry Bianchi type-I dark energy model in
the framework of $f(T)$ theory of gravity, where $T$ denotes the torsion
scalar. A viable cosmological model is undertaken and the isotropization of
this latter is checked, yielding a result that reflects the real evolution of
our universe. Moreover, still in the anisotropic optic, a more complicated
$f(T)$ model is obtained from the cosmological reconstruction scheme and the
analysis shows that the universe is more anisotropic at the beginning if the
terms of higher order in $T$ are not considered. This means that the non-linear
model should be favoured by observational data.
| [
{
"created": "Tue, 13 Aug 2013 14:05:52 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Sep 2013 19:47:18 GMT",
"version": "v2"
}
] | 2014-01-13 | [
[
"Rodrigues",
"M. E.",
""
],
[
"Salako",
"I. G.",
""
],
[
"Houndjo",
"M. J. S.",
""
],
[
"Tossa",
"J.",
""
]
] | We study the locally rotational symmetry Bianchi type-I dark energy model in the framework of $f(T)$ theory of gravity, where $T$ denotes the torsion scalar. A viable cosmological model is undertaken and the isotropization of this latter is checked, yielding a result that reflects the real evolution of our universe. Moreover, still in the anisotropic optic, a more complicated $f(T)$ model is obtained from the cosmological reconstruction scheme and the analysis shows that the universe is more anisotropic at the beginning if the terms of higher order in $T$ are not considered. This means that the non-linear model should be favoured by observational data. |
1610.08093 | Ahmad Sheykhi | M. Abdollahi Zadeh, A. Sheykhi and H. Moradpour | Holographic dark energy with the sign-changeable interaction term | 9 pages, 11 figures | IJMPD Vol. 26, No. 8 (2017) 1750080 | 10.1142/S0218271817500808 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We use three IR cutoffs, including the future event horizon, the Hubble and
Granda-Oliveros (GO) cutoffs, to construct three holographic models of dark
energy. Additionally, we consider a Friedmann-Robertson-Walker (FRW) universe
filled by a dark matter (DM) and a dark energy that interact with each other
through a mutual sign-changeable interaction. Thereinafter, we address the
evolution of the some cosmological parameters, such as the equation of state
and dimensionless density parameters of dark energy as well as the deceleration
parameter, during the cosmic evolution from the matter dominated era until the
late time acceleration. We observe that a holographic dark energy (HDE) model
with Hubble cutoff interacting with DM may be in line with the current
universe. Our study shows that models with the future event horizon as the IR
cutoff or the GO cutoff are in good agreement with the observational data. In
fact, we find out that these obtained models can predict the universe
transition from a deceleration phase to the acceleration one in a compatible
way with observations. The three obtained models may also allow the equation of
state parameter to cross the phantom line, a result which depends on the values
of the system's constants such as the value of the interaction coupling
constant.
| [
{
"created": "Mon, 24 Oct 2016 19:20:54 GMT",
"version": "v1"
}
] | 2017-06-06 | [
[
"Zadeh",
"M. Abdollahi",
""
],
[
"Sheykhi",
"A.",
""
],
[
"Moradpour",
"H.",
""
]
] | We use three IR cutoffs, including the future event horizon, the Hubble and Granda-Oliveros (GO) cutoffs, to construct three holographic models of dark energy. Additionally, we consider a Friedmann-Robertson-Walker (FRW) universe filled by a dark matter (DM) and a dark energy that interact with each other through a mutual sign-changeable interaction. Thereinafter, we address the evolution of the some cosmological parameters, such as the equation of state and dimensionless density parameters of dark energy as well as the deceleration parameter, during the cosmic evolution from the matter dominated era until the late time acceleration. We observe that a holographic dark energy (HDE) model with Hubble cutoff interacting with DM may be in line with the current universe. Our study shows that models with the future event horizon as the IR cutoff or the GO cutoff are in good agreement with the observational data. In fact, we find out that these obtained models can predict the universe transition from a deceleration phase to the acceleration one in a compatible way with observations. The three obtained models may also allow the equation of state parameter to cross the phantom line, a result which depends on the values of the system's constants such as the value of the interaction coupling constant. |
2211.08477 | Abhishek Hegade K R | Abhishek Hegade K R, Justin L. Ripley, and Nicol\'as Yunes | Where and why does Einstein-Scalar-Gauss-Bonnet theory break down? | matches published version | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a systematic exploration of the loss of predictivity in
Einstein-scalar-Gauss-Bonnet (ESGB) gravity. We first formulate a gauge
covariant method of characterizing the breakdown of the hyperbolicity of the
equations of motion in the theory. With this formalism, we show that strong
geodesic focusing leads to the breakdown of hyperbolicity, and the latter is
unrelated to the violation of the null convergence condition. We then
numerically study the hyperbolicity of the equations during gravitational
collapse for two specific ESGB gravity theories: "shift symmetric Gauss-Bonnet
gravity" and a version of the theory that admits "spontaneously scalarized"
black holes. We devise a "phase space" model to describe the end states for a
given class of initial data. Using our phase space picture, we demonstrate that
the two theories we consider remain predictive (hyperbolic) for a range of GB
couplings. The range of couplings, however, is small, and thus, the presence of
"spontaneously scalarized" solutions requires fine-tuning of initial data. Our
results, therefore, cast doubt as to whether scalarized black hole solutions
can be realistically realized in Nature even if ESGB gravity happened to be the
correct gravitational description.
| [
{
"created": "Tue, 15 Nov 2022 20:03:38 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Feb 2023 21:42:25 GMT",
"version": "v2"
},
{
"created": "Mon, 1 May 2023 17:43:51 GMT",
"version": "v3"
}
] | 2023-05-02 | [
[
"R",
"Abhishek Hegade K",
""
],
[
"Ripley",
"Justin L.",
""
],
[
"Yunes",
"Nicolás",
""
]
] | We present a systematic exploration of the loss of predictivity in Einstein-scalar-Gauss-Bonnet (ESGB) gravity. We first formulate a gauge covariant method of characterizing the breakdown of the hyperbolicity of the equations of motion in the theory. With this formalism, we show that strong geodesic focusing leads to the breakdown of hyperbolicity, and the latter is unrelated to the violation of the null convergence condition. We then numerically study the hyperbolicity of the equations during gravitational collapse for two specific ESGB gravity theories: "shift symmetric Gauss-Bonnet gravity" and a version of the theory that admits "spontaneously scalarized" black holes. We devise a "phase space" model to describe the end states for a given class of initial data. Using our phase space picture, we demonstrate that the two theories we consider remain predictive (hyperbolic) for a range of GB couplings. The range of couplings, however, is small, and thus, the presence of "spontaneously scalarized" solutions requires fine-tuning of initial data. Our results, therefore, cast doubt as to whether scalarized black hole solutions can be realistically realized in Nature even if ESGB gravity happened to be the correct gravitational description. |
2109.01931 | Oleksandr Stashko | O.S. Stashko, V.I. Zhdanov | Singularities in static spherically symmetric configurations of General
Relativity with strongly nonlinear scalar fields | null | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | There are a number of publications on relativistic objects dealing either
with black holes or naked singularities in the center. Here we show that there
exist static spherically symmetric solutions of Einstein equations with a
strongly nonlinear scalar field, which allow the appearance of singularities of
a new type (``spherical singularities'') outside the center of curvature
coordinates. As the example, we consider a scalar field potential
$\sim$$\sinh(\phi^{2n}),\,n>2$, which grows rapidly for large field values. The
space-time is assumed to be asymptotically flat. We fulfill a numerical
investigation of solutions with different $n$ for different parameters, which
define asymptotic properties at spatial infinity. Depending on the
configuration parameters, we show that the distribution of the stable circular
orbits of test bodies around the configuration is either similar to that in the
case of the Schwarzschild solution (thus mimicking an ordinary black hole), or
it contains additional rings of unstable orbits.
| [
{
"created": "Sat, 4 Sep 2021 20:56:00 GMT",
"version": "v1"
},
{
"created": "Sun, 3 Oct 2021 10:59:43 GMT",
"version": "v2"
}
] | 2021-10-05 | [
[
"Stashko",
"O. S.",
""
],
[
"Zhdanov",
"V. I.",
""
]
] | There are a number of publications on relativistic objects dealing either with black holes or naked singularities in the center. Here we show that there exist static spherically symmetric solutions of Einstein equations with a strongly nonlinear scalar field, which allow the appearance of singularities of a new type (``spherical singularities'') outside the center of curvature coordinates. As the example, we consider a scalar field potential $\sim$$\sinh(\phi^{2n}),\,n>2$, which grows rapidly for large field values. The space-time is assumed to be asymptotically flat. We fulfill a numerical investigation of solutions with different $n$ for different parameters, which define asymptotic properties at spatial infinity. Depending on the configuration parameters, we show that the distribution of the stable circular orbits of test bodies around the configuration is either similar to that in the case of the Schwarzschild solution (thus mimicking an ordinary black hole), or it contains additional rings of unstable orbits. |
1303.4992 | Jan Zschoche | Jan Zschoche | The Chaplygin Gas Equation of State for the Quantized Free Scalar Field
on Cosmological Spacetimes | 33 pages; paper shortened, comments added | null | 10.1007/s00023-013-0281-5 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We try to answer the question whether the quantized free scalar field on a
spatially flat Friedmann-Robertson-Walker (FRW) spacetime is a matter model
that can induce a Chaplygin gas equation of state. For this purpose we first
describe how one can obtain every possible homogeneous and isotropic Hadamard
(HIH) state once any such state is given. We also identify a condition on the
scale factor sufficient to entail the existence of a simple HIH state $-$ this
state is constructed explicitly and can thence be used as a starting point for
constructing all HIH states. Furthermore, we employ these results to show that
on an FRW spacetime with non-positive constant scalar curvature there is, with
one exception, no Chaplygin gas equation of state compatible with any HIH
state. Finally, we argue that the semi-classical Einstein equation and the
Chaplygin gas equation of state can presumably not be consistently solved for
the quantized free scalar field.
| [
{
"created": "Wed, 20 Mar 2013 16:57:15 GMT",
"version": "v1"
},
{
"created": "Fri, 2 Aug 2013 09:23:20 GMT",
"version": "v2"
}
] | 2013-08-05 | [
[
"Zschoche",
"Jan",
""
]
] | We try to answer the question whether the quantized free scalar field on a spatially flat Friedmann-Robertson-Walker (FRW) spacetime is a matter model that can induce a Chaplygin gas equation of state. For this purpose we first describe how one can obtain every possible homogeneous and isotropic Hadamard (HIH) state once any such state is given. We also identify a condition on the scale factor sufficient to entail the existence of a simple HIH state $-$ this state is constructed explicitly and can thence be used as a starting point for constructing all HIH states. Furthermore, we employ these results to show that on an FRW spacetime with non-positive constant scalar curvature there is, with one exception, no Chaplygin gas equation of state compatible with any HIH state. Finally, we argue that the semi-classical Einstein equation and the Chaplygin gas equation of state can presumably not be consistently solved for the quantized free scalar field. |
1310.5064 | Elizabeth Winstanley | Elizabeth Winstanley | Kermions | 6 pages, 2 figures, minor changes, contribution to the Proceedings of
the Karl Schwarzschild Meeting (Frankfurt, July 22-26, 2013) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the framework of quantum field theory in curved space-time, we study the
quantization of a massless fermion field on a non-extremal Kerr black hole. The
key theme in this note is the fundamental difference between scalar and fermion
fields for the process of defining quantum states. In particular, we define two
new states for fermions on Kerr which cannot be defined for quantum scalar
fields on Kerr. These two states are the analogues of the standard Boulware and
Hartle-Hawking states on a Schwarzschild black hole.
| [
{
"created": "Fri, 18 Oct 2013 15:50:05 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Oct 2013 11:02:19 GMT",
"version": "v2"
}
] | 2013-10-31 | [
[
"Winstanley",
"Elizabeth",
""
]
] | In the framework of quantum field theory in curved space-time, we study the quantization of a massless fermion field on a non-extremal Kerr black hole. The key theme in this note is the fundamental difference between scalar and fermion fields for the process of defining quantum states. In particular, we define two new states for fermions on Kerr which cannot be defined for quantum scalar fields on Kerr. These two states are the analogues of the standard Boulware and Hartle-Hawking states on a Schwarzschild black hole. |
2208.02927 | Marissa Walker | Marissa Walker, Vijay Varma, Geoffrey Lovelace, Mark A. Scheel | Numerical-relativity surrogate modeling with nearly extremal black-hole
spins | null | null | 10.1088/1361-6382/acb3a7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Numerical relativity (NR) simulations of binary black hole (BBH) systems
provide the most accurate gravitational wave predictions, but at a high
computational cost -- especially when the black holes have nearly extremal
spins (i.e. spins near the theoretical upper limit) or very unequal masses.
Recently, the technique of Reduced Order Modeling (ROM) has enabled the
construction of surrogate models trained on an existing set of NR waveforms.
Surrogate models enable the rapid computation of the gravitational waves
emitted by BBHs. Typically these models are used for interpolation to compute
gravitational waveforms for BBHs with mass ratios and spins within the bounds
of the training set. Because simulations with nearly extremal spins are so
technically challenging, surrogate models almost always rely on training sets
with only moderate spins. In this paper, we explore how well surrogate models
can extrapolate to nearly extremal spins when the training set only includes
moderate spins. For simplicity, we focus on one-dimensional surrogate models
trained on NR simulations of BBHs with equal masses and equal, aligned spins.
We assess the performance of the surrogate models at higher spin magnitudes by
calculating the mismatches between extrapolated surrogate model waveforms and
NR waveforms, by calculating the differences between extrapolated and NR
measurements of the remnant black-hole mass, and by testing how the surrogate
model improves as the training set extends to higher spins. We find that while
extrapolation in this one-dimensional case is viable for current detector
sensitivities, surrogate models for next-generation detectors should use
training sets that extend to nearly extremal spins.
| [
{
"created": "Thu, 4 Aug 2022 23:13:20 GMT",
"version": "v1"
}
] | 2023-02-15 | [
[
"Walker",
"Marissa",
""
],
[
"Varma",
"Vijay",
""
],
[
"Lovelace",
"Geoffrey",
""
],
[
"Scheel",
"Mark A.",
""
]
] | Numerical relativity (NR) simulations of binary black hole (BBH) systems provide the most accurate gravitational wave predictions, but at a high computational cost -- especially when the black holes have nearly extremal spins (i.e. spins near the theoretical upper limit) or very unequal masses. Recently, the technique of Reduced Order Modeling (ROM) has enabled the construction of surrogate models trained on an existing set of NR waveforms. Surrogate models enable the rapid computation of the gravitational waves emitted by BBHs. Typically these models are used for interpolation to compute gravitational waveforms for BBHs with mass ratios and spins within the bounds of the training set. Because simulations with nearly extremal spins are so technically challenging, surrogate models almost always rely on training sets with only moderate spins. In this paper, we explore how well surrogate models can extrapolate to nearly extremal spins when the training set only includes moderate spins. For simplicity, we focus on one-dimensional surrogate models trained on NR simulations of BBHs with equal masses and equal, aligned spins. We assess the performance of the surrogate models at higher spin magnitudes by calculating the mismatches between extrapolated surrogate model waveforms and NR waveforms, by calculating the differences between extrapolated and NR measurements of the remnant black-hole mass, and by testing how the surrogate model improves as the training set extends to higher spins. We find that while extrapolation in this one-dimensional case is viable for current detector sensitivities, surrogate models for next-generation detectors should use training sets that extend to nearly extremal spins. |
gr-qc/0207063 | Sergio De Filippo | Filippo Maimone, Sergio De Filippo | Nonunitary Newtonian Gravity | 6 pages, to appear in Proceedings of the First International
Conference on Quantum Limits to the Second Law, July 29-31, 2002, University
of San Diego, San Diego, CA | AIP Conf.Proc. 643 (2003) 379-384 | null | null | gr-qc | null | It is shown that the Newtonian limit of a stable realization of HD gravity
leads to a sharp transition, around 10^{11} proton masses, from the wavelike
properties of microscopic particles to the classical behaviour of macroscopic
bodies. Besides, due to nonunitarity, a pure state is expected to evolve into a
microcanonical ensamble leading to thermal equilibrium even for truly closed
systems.
| [
{
"created": "Wed, 17 Jul 2002 13:30:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Maimone",
"Filippo",
""
],
[
"De Filippo",
"Sergio",
""
]
] | It is shown that the Newtonian limit of a stable realization of HD gravity leads to a sharp transition, around 10^{11} proton masses, from the wavelike properties of microscopic particles to the classical behaviour of macroscopic bodies. Besides, due to nonunitarity, a pure state is expected to evolve into a microcanonical ensamble leading to thermal equilibrium even for truly closed systems. |
2311.08073 | Giuseppe Fanizza | Giuseppe Fanizza, Giovanni Marozzi, Matheus Medeiros | $\delta N$ formalism on the past light-cone | 33 pages, no figures. References and comments added. Accepted for
publication in General Relativity and Gravitation | Gen. Rel. Grav. 56, 53 (2024) | 10.1007/s10714-024-03239-3 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | We apply the gradient expansion approximation to the light-cone gauge,
obtaining a separate universe picture at non-linear order in perturbation
theory within this framework. Thereafter, we use it to generalize the $\delta
N$ formalism in terms of light-cone perturbations. As a consistency check, we
demonstrate the conservation of the gauge invariant curvature perturbation on
uniform density hypersurface $\zeta$ at the completely non-linear level. The
approach studied provides a self-consistent framework to connect at non-linear
level quantities from the primordial universe, such as $\zeta$, written in
terms of the light-cone parameters, to late time observables.
| [
{
"created": "Tue, 14 Nov 2023 10:51:51 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Apr 2024 16:02:36 GMT",
"version": "v2"
}
] | 2024-05-07 | [
[
"Fanizza",
"Giuseppe",
""
],
[
"Marozzi",
"Giovanni",
""
],
[
"Medeiros",
"Matheus",
""
]
] | We apply the gradient expansion approximation to the light-cone gauge, obtaining a separate universe picture at non-linear order in perturbation theory within this framework. Thereafter, we use it to generalize the $\delta N$ formalism in terms of light-cone perturbations. As a consistency check, we demonstrate the conservation of the gauge invariant curvature perturbation on uniform density hypersurface $\zeta$ at the completely non-linear level. The approach studied provides a self-consistent framework to connect at non-linear level quantities from the primordial universe, such as $\zeta$, written in terms of the light-cone parameters, to late time observables. |
gr-qc/0510019 | Leor Barack | Leor Barack and Carlos O. Lousto | Perturbations of Schwarzschild black holes in the Lorenz gauge:
Formulation and numerical implementation | 29 pages, 21 eps figures | Phys.Rev. D72 (2005) 104026 | 10.1103/PhysRevD.72.104026 | null | gr-qc | null | We reformulate the theory of Schwarzschild black hole perturbations in terms
of the metric perturbation in the Lorenz gauge. In this formulation, each
tensor-harmonic mode of the perturbation is constructed algebraically from 10
scalar functions, satisfying a set of 10 wavelike equations, which are
decoupled at their principal parts. We solve these equations using numerical
evolution in the time domain, for the case of a pointlike test particle set in
a circular geodesic orbit around the black hole. Our code uses characteristic
coordinates, and incorporates a constraint damping scheme. The
axially-symmetric, odd-parity modes of the perturbation are obtained
analytically. The approach developed here is especially advantageous in
applications requiring knowledge of the local metric perturbation near a point
particle; in particular, it offers a useful framework for calculations of the
gravitational self force.
| [
{
"created": "Wed, 5 Oct 2005 18:41:05 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Nov 2005 17:01:47 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Barack",
"Leor",
""
],
[
"Lousto",
"Carlos O.",
""
]
] | We reformulate the theory of Schwarzschild black hole perturbations in terms of the metric perturbation in the Lorenz gauge. In this formulation, each tensor-harmonic mode of the perturbation is constructed algebraically from 10 scalar functions, satisfying a set of 10 wavelike equations, which are decoupled at their principal parts. We solve these equations using numerical evolution in the time domain, for the case of a pointlike test particle set in a circular geodesic orbit around the black hole. Our code uses characteristic coordinates, and incorporates a constraint damping scheme. The axially-symmetric, odd-parity modes of the perturbation are obtained analytically. The approach developed here is especially advantageous in applications requiring knowledge of the local metric perturbation near a point particle; in particular, it offers a useful framework for calculations of the gravitational self force. |
gr-qc/9402022 | H. Shinkai | Hisa-aki SHINKAI and Kei-ichi MAEDA | Generality of Inflation in a Planar Universe | 16 pages, LaTeX style, WU-AP/34/93(revised version). Figures are
available (hard copies) upon requests [62L508@cfi.waseda.ac.jp (H.Shinkai)] | Phys.Rev. D49 (1994) 6367-6378 | 10.1103/PhysRevD.49.6367 | null | gr-qc | null | We study a generality of an inflationary scenario by integrating the Einstein
equations numerically in a plane-symmetric spacetime. We consider the
inhomogeneous spacetimes due to (i) localized gravitational waves with a
positive cosmological constant $\Lambda$, and (ii) an inhomogeneous inflaton
field $\Phi$ with a potential $\frac12 m^2 \Phi^2$. For the case (i), we find
that any initial inhomogeneities are smoothed out even if waves collide, so
that we conclude that inhomogeneity due to gravitational waves do not prevent
the onset of inflation. As for the case (ii), if the mean value of the inflaton
field is initially as large as the condition in an isotropic and homogeneous
inflationary model (i.e., the mean value is larger than several times Planck
mass), the field is soon homogenized and the universe always evolves into de
Sitter spacetime. These support the cosmic no hair conjecture in a planar
universe. We also discuss the effects of an additional massless scalar field,
which is introduced to set initial data in usual analysis.
| [
{
"created": "Thu, 10 Feb 1994 01:19:51 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"SHINKAI",
"Hisa-aki",
""
],
[
"MAEDA",
"Kei-ichi",
""
]
] | We study a generality of an inflationary scenario by integrating the Einstein equations numerically in a plane-symmetric spacetime. We consider the inhomogeneous spacetimes due to (i) localized gravitational waves with a positive cosmological constant $\Lambda$, and (ii) an inhomogeneous inflaton field $\Phi$ with a potential $\frac12 m^2 \Phi^2$. For the case (i), we find that any initial inhomogeneities are smoothed out even if waves collide, so that we conclude that inhomogeneity due to gravitational waves do not prevent the onset of inflation. As for the case (ii), if the mean value of the inflaton field is initially as large as the condition in an isotropic and homogeneous inflationary model (i.e., the mean value is larger than several times Planck mass), the field is soon homogenized and the universe always evolves into de Sitter spacetime. These support the cosmic no hair conjecture in a planar universe. We also discuss the effects of an additional massless scalar field, which is introduced to set initial data in usual analysis. |
1412.2605 | Behnam Pourhassan | B. Pourhassan | Extended Chaplygin Gas in Horava-Lifshitz Gravity | 18 pages, 3 figures, Accepted for Publication in Physics of the Dark
Universe | Physics of the Dark Universe 13 (2016) 132 | 10.1016/j.dark.2016.06.002 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we investigate cosmological models of the extended Chaplygin
gas in a universe governed by Horava-Lifshitz gravity. The equation of state
for an extended Chaplygin gas is a $(n+2)$-variable equation determined by
$A_{n}$, $\alpha$, and $B$. In this work, we are interested to the case of
second order $(n=2)$ equation of state which recovers quadratic barotropic
equation of state. In that case there are four free parameters. We solve
conservation equation approximately and obtain energy density in terms of scale
factor with mentioned free parameters. Under some assumptions we relate free
parameters to each other to have only one free independent parameter $(A_{2})$.
It help us to obtain explicit expression for energy density in terms of scale
factor. The allowed values of the second order extended Chaplygin gas parameter
is fixed using the recent astrophysical and cosmological observational data.
Thermodynamics of the model investigated based on the first and second law of
thermodynamics.
| [
{
"created": "Mon, 8 Dec 2014 15:31:12 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Apr 2015 08:54:46 GMT",
"version": "v2"
},
{
"created": "Sat, 11 Jul 2015 06:25:05 GMT",
"version": "v3"
},
{
"created": "Sat, 25 Jun 2016 07:23:55 GMT",
"version": "v4"
}
] | 2016-07-08 | [
[
"Pourhassan",
"B.",
""
]
] | In this paper, we investigate cosmological models of the extended Chaplygin gas in a universe governed by Horava-Lifshitz gravity. The equation of state for an extended Chaplygin gas is a $(n+2)$-variable equation determined by $A_{n}$, $\alpha$, and $B$. In this work, we are interested to the case of second order $(n=2)$ equation of state which recovers quadratic barotropic equation of state. In that case there are four free parameters. We solve conservation equation approximately and obtain energy density in terms of scale factor with mentioned free parameters. Under some assumptions we relate free parameters to each other to have only one free independent parameter $(A_{2})$. It help us to obtain explicit expression for energy density in terms of scale factor. The allowed values of the second order extended Chaplygin gas parameter is fixed using the recent astrophysical and cosmological observational data. Thermodynamics of the model investigated based on the first and second law of thermodynamics. |
0711.1207 | Shabbir Ghulam | Ghulam Shabbir, Shaukat Iqbal | A note on proper conformal vector fields in cylindrically symmetric
static space-times | 5 pages | null | null | null | gr-qc | null | A study of proper conformal vector field in non conformally flat
cylindrically symmetric static space-times is given by using direct integration
technique. Using the above mentioned technique we have shown that a very
special class of the above space-time admits proper conformal vector field.
| [
{
"created": "Thu, 8 Nov 2007 06:26:32 GMT",
"version": "v1"
}
] | 2007-11-09 | [
[
"Shabbir",
"Ghulam",
""
],
[
"Iqbal",
"Shaukat",
""
]
] | A study of proper conformal vector field in non conformally flat cylindrically symmetric static space-times is given by using direct integration technique. Using the above mentioned technique we have shown that a very special class of the above space-time admits proper conformal vector field. |
2006.16017 | Aditya Tamar | Aditya Tamar | On Challenges to Separability of the Dirac Equation in Kerr Geometry
under Compact Hyperboloidal Coordinates | 10 pages, Submitted to IJP. Comments on the validity of the result
are especially encouraged | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Dirac equation governs the behaviour of spin-1/2 particles. The
equation's separability into decoupled radial and angular differential
equations is a crucial step in analytical and numerical computations of
quantities like eigenvalues, quasinormal modes and bound states. However, this
separation has been performed in co-ordinate systems that are not well-behaved
in either limiting regions of $r \rightarrow r_{horizon}$, $r \rightarrow
r_\infty$ or both. In particular, the extensively used Boyer-Lindquist
co-ordinates contains unphysical features of spacetime geometry for both
$r_{horizon}$ and $r_\infty$. Therefore, motivated by the recently developed
compact hyperboloidal co-ordinate system for Kerr Black Holes that is well
behaved in these limiting regions, we attempt the separation of the Dirac
equation. We first construct a null tetrad suitable for the separability
analysis under the Newman-Penrose formalism. Then, an unexpected result is
shown that by using the standard separability procedure based on the mode
ansatz under this tetrad, the Dirac equation does not decouple into radial and
angular equationsPossible reasons for this behaviour as well as importance of
proving separability for various computations are discussed.
| [
{
"created": "Mon, 29 Jun 2020 13:01:12 GMT",
"version": "v1"
},
{
"created": "Wed, 1 Jul 2020 12:07:16 GMT",
"version": "v2"
}
] | 2020-07-02 | [
[
"Tamar",
"Aditya",
""
]
] | The Dirac equation governs the behaviour of spin-1/2 particles. The equation's separability into decoupled radial and angular differential equations is a crucial step in analytical and numerical computations of quantities like eigenvalues, quasinormal modes and bound states. However, this separation has been performed in co-ordinate systems that are not well-behaved in either limiting regions of $r \rightarrow r_{horizon}$, $r \rightarrow r_\infty$ or both. In particular, the extensively used Boyer-Lindquist co-ordinates contains unphysical features of spacetime geometry for both $r_{horizon}$ and $r_\infty$. Therefore, motivated by the recently developed compact hyperboloidal co-ordinate system for Kerr Black Holes that is well behaved in these limiting regions, we attempt the separation of the Dirac equation. We first construct a null tetrad suitable for the separability analysis under the Newman-Penrose formalism. Then, an unexpected result is shown that by using the standard separability procedure based on the mode ansatz under this tetrad, the Dirac equation does not decouple into radial and angular equationsPossible reasons for this behaviour as well as importance of proving separability for various computations are discussed. |
gr-qc/0611013 | Jesus Martin-Martin | J. A. Cabezas, J. Martin-Martin, A. Molina, E. Ruiz | An approximate global solution of Einstein's equations for a finite body | 32 pages, no figures. Submitted to GRG | Gen.Rel.Grav.39:707-736,2007 | 10.1007/s10714-007-0414-6 | null | gr-qc | null | We obtain an approximate global stationary and axisymmetric solution of
Einstein's equations which can be considered as a simple star model: a
self-gravitating perfect fluid ball with constant mass density rotating in
rigid motion. Using the post-Minkowskian formalism (weak-field approximation)
and considering rotation as a perturbation (slow-rotation approximation), we
find approximate interior and exterior (asymptotically flat) solutions to this
problem in harmonic and quo-harmonic coordinates. In both cases, interior and
exterior solutions are matched, in the sense of Lichnerowicz, on the surface of
zero pressure to obtain a global solution. The resulting metric depends on
three arbitrary constants: mass density, rotational velocity and the star
radius at the non-rotation limit. The mass, angular momentum, quadrupole moment
and other constants of the exterior metric are determined by these three
parameters. It is easy to show that this type of fluid cannot be a source of
the Kerr metric
| [
{
"created": "Thu, 2 Nov 2006 12:41:09 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Cabezas",
"J. A.",
""
],
[
"Martin-Martin",
"J.",
""
],
[
"Molina",
"A.",
""
],
[
"Ruiz",
"E.",
""
]
] | We obtain an approximate global stationary and axisymmetric solution of Einstein's equations which can be considered as a simple star model: a self-gravitating perfect fluid ball with constant mass density rotating in rigid motion. Using the post-Minkowskian formalism (weak-field approximation) and considering rotation as a perturbation (slow-rotation approximation), we find approximate interior and exterior (asymptotically flat) solutions to this problem in harmonic and quo-harmonic coordinates. In both cases, interior and exterior solutions are matched, in the sense of Lichnerowicz, on the surface of zero pressure to obtain a global solution. The resulting metric depends on three arbitrary constants: mass density, rotational velocity and the star radius at the non-rotation limit. The mass, angular momentum, quadrupole moment and other constants of the exterior metric are determined by these three parameters. It is easy to show that this type of fluid cannot be a source of the Kerr metric |
1407.6405 | Raissa Mendes | Raissa F. P. Mendes, George E. A. Matsas, Daniel A. T. Vanzella | Instability of nonminimally coupled scalar fields in the spacetime of
slowly rotating compact objects | 11 pages, 6 figures | Phys. Rev. D 90, 044053 (2014) | 10.1103/PhysRevD.90.044053 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Nonminimally coupled free scalar fields may be unstable in the spacetime of
compact objects. Such instability can be triggered by classical seeds or, more
simply, by quantum fluctuations giving rise to the so-called {\em vacuum
awakening effect}. Here, we investigate how the parameter space which
characterizes the instability is affected when the object gains some rotation.
For this purpose, we focus on the stability analysis of nonminimally coupled
scalar fields in the spacetime of slowly spinning matter shells.
| [
{
"created": "Wed, 23 Jul 2014 23:04:18 GMT",
"version": "v1"
}
] | 2014-09-16 | [
[
"Mendes",
"Raissa F. P.",
""
],
[
"Matsas",
"George E. A.",
""
],
[
"Vanzella",
"Daniel A. T.",
""
]
] | Nonminimally coupled free scalar fields may be unstable in the spacetime of compact objects. Such instability can be triggered by classical seeds or, more simply, by quantum fluctuations giving rise to the so-called {\em vacuum awakening effect}. Here, we investigate how the parameter space which characterizes the instability is affected when the object gains some rotation. For this purpose, we focus on the stability analysis of nonminimally coupled scalar fields in the spacetime of slowly spinning matter shells. |
0903.3832 | Carlo Rovelli | Carlo Rovelli | "Forget time" | 'First Community Prize' of the FQXi 'The Nature of Time' Essay
Contest | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Following a line of research that I have developed for several years, I argue
that the best strategy for understanding quantum gravity is to build a picture
of the physical world where the notion of time plays no role. I summarize here
this point of view, explaining why I think that in a fundamental description of
nature we must "forget time", and how this can be done in the classical and in
the quantum theory. The idea is to develop a formalism that treats dependent
and independent variables on the same footing. In short, I propose to interpret
mechanics as a theory of relations between variables, rather than the theory of
the evolution of variables in time.
| [
{
"created": "Mon, 23 Mar 2009 19:59:42 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Mar 2009 23:07:18 GMT",
"version": "v2"
},
{
"created": "Fri, 27 Mar 2009 20:27:58 GMT",
"version": "v3"
}
] | 2009-03-27 | [
[
"Rovelli",
"Carlo",
""
]
] | Following a line of research that I have developed for several years, I argue that the best strategy for understanding quantum gravity is to build a picture of the physical world where the notion of time plays no role. I summarize here this point of view, explaining why I think that in a fundamental description of nature we must "forget time", and how this can be done in the classical and in the quantum theory. The idea is to develop a formalism that treats dependent and independent variables on the same footing. In short, I propose to interpret mechanics as a theory of relations between variables, rather than the theory of the evolution of variables in time. |
2404.08243 | Zheng-Wen Long | Hao Chen, Meng-Yao Zhang, Hassan Hassanabadi and Zheng-Wen Long | Thermodynamic topology of Phantom AdS Black Holes in Massive Gravity | 10pages, 19 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we explore the thermodynamic topology of phantom AdS black
holes in the context of massive gravity. To this end, we evaluate these black
holes in two distinct ensembles: the canonical and grand canonical ensembles
(GCE). We begin by examining the topological charge linked to the critical
point and confirming the existence of a conventional critical point $(CP_{1})$
in the canonical ensemble (CE), this critical point has a topological charge of
$-1$ and acts as a point of phase annihilation, this situation can only be
considered within the context of the classical Einstein-Maxwell (CEM) theory
$(\eta=1)$, while no critical point is identified in the GCE. Furthermore, we
consider black holes as a topological defect within the thermodynamic space. To
gain an understanding of the local and global topological configuration of this
defect, we will analyze its winding numbers, and observe that the total
topological charge in the CE consistently remains at $1$. When the system
experiences a pressure below the critical threshold, it gives rise to the
occurrence of annihilation and generation points. The value of electric
potential determines whether the total topological charge in the GCE is zero or
one. As a result, we detect a point of generation point or absence of
generation/annihilation point. Based on our analysis, it can be inferred that
ensembles significantly impact the topological class of phantom AdS black holes
in massive gravity.
| [
{
"created": "Fri, 12 Apr 2024 05:12:22 GMT",
"version": "v1"
}
] | 2024-04-15 | [
[
"Chen",
"Hao",
""
],
[
"Zhang",
"Meng-Yao",
""
],
[
"Hassanabadi",
"Hassan",
""
],
[
"Long",
"Zheng-Wen",
""
]
] | In this work, we explore the thermodynamic topology of phantom AdS black holes in the context of massive gravity. To this end, we evaluate these black holes in two distinct ensembles: the canonical and grand canonical ensembles (GCE). We begin by examining the topological charge linked to the critical point and confirming the existence of a conventional critical point $(CP_{1})$ in the canonical ensemble (CE), this critical point has a topological charge of $-1$ and acts as a point of phase annihilation, this situation can only be considered within the context of the classical Einstein-Maxwell (CEM) theory $(\eta=1)$, while no critical point is identified in the GCE. Furthermore, we consider black holes as a topological defect within the thermodynamic space. To gain an understanding of the local and global topological configuration of this defect, we will analyze its winding numbers, and observe that the total topological charge in the CE consistently remains at $1$. When the system experiences a pressure below the critical threshold, it gives rise to the occurrence of annihilation and generation points. The value of electric potential determines whether the total topological charge in the GCE is zero or one. As a result, we detect a point of generation point or absence of generation/annihilation point. Based on our analysis, it can be inferred that ensembles significantly impact the topological class of phantom AdS black holes in massive gravity. |
gr-qc/0111080 | Sushant G. Ghosh | S.G. Ghosh (Science College, Nagpur, India) and R. V. Saraykar (Nagpur
University, Nagpur, India) | Higher dimensional radiation collapse and cosmic censorship | 4 pages, ReVTeX, Phys Rev D Vol 62 107502 (2000) | Phys.Rev.D62:107502,2000 | 10.1103/PhysRevD.62.107502 | null | gr-qc | null | We study the occurrence of naked singularities in the spherically symmetric
collapse of radiation shells in a higher dimensional spacetime. The necessary
conditions for the formation of a naked singularity or a black hole are
obtained. The naked singularities are found to be strong in the Tipler's sense
and thus violating cosmic censorship conjecture.
| [
{
"created": "Sat, 24 Nov 2001 09:49:25 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Ghosh",
"S. G.",
"",
"Science College, Nagpur, India"
],
[
"Saraykar",
"R. V.",
"",
"Nagpur\n University, Nagpur, India"
]
] | We study the occurrence of naked singularities in the spherically symmetric collapse of radiation shells in a higher dimensional spacetime. The necessary conditions for the formation of a naked singularity or a black hole are obtained. The naked singularities are found to be strong in the Tipler's sense and thus violating cosmic censorship conjecture. |
gr-qc/0312068 | Albert V. Minkevich | A. V. Minkevich | Problem of Cosmological Singularity, Inflationary Cosmology and Gauge
Theories of Gravitation | 16 pages, LaTeX2e, some additions are made | null | null | null | gr-qc astro-ph hep-th | null | Problem of cosmological singularity is discussed in the framework of gauge
theories of gravitation. Generalizing cosmological Friedmann equations (GCFE)
for homogeneous isotropic models including scalar fields and usual gravitating
matter are introduced. It is shown that by certain restrictions on equation of
state of gravitating matter and indefinite parameter of GCFE generic feature of
inflationary cosmological models of flat, open and closed type is their regular
bouncing character.
| [
{
"created": "Mon, 15 Dec 2003 17:05:19 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Dec 2003 09:04:02 GMT",
"version": "v2"
},
{
"created": "Mon, 29 Dec 2003 15:12:02 GMT",
"version": "v3"
},
{
"created": "Thu, 5 Feb 2004 16:56:30 GMT",
"version": "v4"
}
] | 2007-05-23 | [
[
"Minkevich",
"A. V.",
""
]
] | Problem of cosmological singularity is discussed in the framework of gauge theories of gravitation. Generalizing cosmological Friedmann equations (GCFE) for homogeneous isotropic models including scalar fields and usual gravitating matter are introduced. It is shown that by certain restrictions on equation of state of gravitating matter and indefinite parameter of GCFE generic feature of inflationary cosmological models of flat, open and closed type is their regular bouncing character. |
0708.0457 | Oyvind Gron | Oyvind G. Gron | The Principle of Relativity and Inertial Dragging | 17 pages | Am.J.Phys.77:373-380,2009 | 10.1119/1.2996480 | null | gr-qc | null | Machs principle and the principle of relativity have been discussed by H. I.
Hartman and C. Nissim-Sabat in this journal. Several phenomena were said to
violate the principle of relativity as applied to rotating motion. These claims
have recently been contested. However, in neither of these articles have the
general relativistic phenomenon of inertial dragging been invoked, and no
calculation have been offered by either side to substantiate their claims. Here
I discuss the possible validity of the principle of relativity for rotating
motion within the context of the general theory of relativity, and point out
the significance of inertial dragging in this connection. Although my main
points are of a qualitative nature, I also provide the necessary calculations
to demonstrate how these points come out as consequences of the general theory
of relativity
| [
{
"created": "Fri, 3 Aug 2007 06:19:18 GMT",
"version": "v1"
}
] | 2009-04-24 | [
[
"Gron",
"Oyvind G.",
""
]
] | Machs principle and the principle of relativity have been discussed by H. I. Hartman and C. Nissim-Sabat in this journal. Several phenomena were said to violate the principle of relativity as applied to rotating motion. These claims have recently been contested. However, in neither of these articles have the general relativistic phenomenon of inertial dragging been invoked, and no calculation have been offered by either side to substantiate their claims. Here I discuss the possible validity of the principle of relativity for rotating motion within the context of the general theory of relativity, and point out the significance of inertial dragging in this connection. Although my main points are of a qualitative nature, I also provide the necessary calculations to demonstrate how these points come out as consequences of the general theory of relativity |
2307.16292 | Sayantani Lahiri | Sayantani Lahiri, Claus Laemmerzahl | Stationary equilibrium torus supported by Weyssenhoff ideal spin fluid
in Schwarzschild spacetime -- I: Case of constant specific angular momentum
distribution | 15 pages, 16 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We consider a non-self-gravitating geometrically thick torus described by
Weyssenhoff ideal spin fluid in a black hole spacetime. The Weyssenhof spin
fluid shares the same symmetries of the background geometry, i,e. stationarity
and axisymmetry and further describes circular orbital motion in the black hole
spacetime. We further assume that assume the alignment of the spin is
perpendicular to the equatorial plane. Under this setup, we determine the
integrability conditions of the general relativistic momentum conservation
equation of Weyssenhoff ideal spin fluid using the Frenkel spin supplementary
condition. In the light of the integrability conditions, we then present
stationary equilibrium solutions of the spin fluid torus with constant specific
angular momentum distributions around the Schwarzschild black hole by
numerically solving the general relativistic momentum conservation equation.
Our study reveals that both the iso-pressure and iso-density surfaces of torus
get significantly modified in comparison to the ideal fluid torus without a
spin fluid, owing to the spin tensor and its coupling to the curvature of the
Schwarzschild black hole. In fact, the size of the torus is also found to be
enhanced (diminished) depending on positive (negative) magnitude of spin
parameter $s_0$. We finally estimate the magnitude of $s_0$ by assuming the
torus to be composed of spin-1/2 particles.
| [
{
"created": "Sun, 30 Jul 2023 18:01:02 GMT",
"version": "v1"
}
] | 2023-08-01 | [
[
"Lahiri",
"Sayantani",
""
],
[
"Laemmerzahl",
"Claus",
""
]
] | We consider a non-self-gravitating geometrically thick torus described by Weyssenhoff ideal spin fluid in a black hole spacetime. The Weyssenhof spin fluid shares the same symmetries of the background geometry, i,e. stationarity and axisymmetry and further describes circular orbital motion in the black hole spacetime. We further assume that assume the alignment of the spin is perpendicular to the equatorial plane. Under this setup, we determine the integrability conditions of the general relativistic momentum conservation equation of Weyssenhoff ideal spin fluid using the Frenkel spin supplementary condition. In the light of the integrability conditions, we then present stationary equilibrium solutions of the spin fluid torus with constant specific angular momentum distributions around the Schwarzschild black hole by numerically solving the general relativistic momentum conservation equation. Our study reveals that both the iso-pressure and iso-density surfaces of torus get significantly modified in comparison to the ideal fluid torus without a spin fluid, owing to the spin tensor and its coupling to the curvature of the Schwarzschild black hole. In fact, the size of the torus is also found to be enhanced (diminished) depending on positive (negative) magnitude of spin parameter $s_0$. We finally estimate the magnitude of $s_0$ by assuming the torus to be composed of spin-1/2 particles. |
gr-qc/9810030 | Vesselin Petkov | Vesselin Petkov | On the gravitational redshift | 4 pages, LaTeX; As it turns out that an overlooked consequence of
Einstein's elevator thought experiment - that the propagation of light in a
gravitational field is anisotropic - can be rigorously derived in the
framework of general relativity, the gravitational redshift is now discussed
in terms of that consequence | Chap. 7.7 of "Relativity and the Nature of Spacetime," 2nd ed
(Springer, 2009) | null | null | gr-qc | null | The purpose of this paper is twofold - to demonstrate that in the
gravitational redshift it is the frequency a photon that is constant, and to
describe the mechanism responsible for the change of its wavelength.
| [
{
"created": "Thu, 8 Oct 1998 07:18:32 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Jan 2000 02:04:28 GMT",
"version": "v10"
},
{
"created": "Fri, 21 Jan 2000 05:56:20 GMT",
"version": "v11"
},
{
"created": "Sun, 23 Jan 2000 23:58:53 GMT",
"version": "v12"
},
{
... | 2011-11-18 | [
[
"Petkov",
"Vesselin",
""
]
] | The purpose of this paper is twofold - to demonstrate that in the gravitational redshift it is the frequency a photon that is constant, and to describe the mechanism responsible for the change of its wavelength. |
1507.00291 | Sabir Ramazanov Dr. | Sabir Ramazanov | Initial Conditions for Imperfect Dark Matter | 16 pages; major revision, references added, conclusions unchanged | JCAP12(2015)007 | 10.1088/1475-7516/2015/12/007 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss initial conditions for the recently proposed Imperfect Dark Matter
(Modified Dust). We show that they are adiabatic under fairly moderate
assumptions about the cosmological evolution of the Universe at the relevant
times.
| [
{
"created": "Tue, 30 Jun 2015 14:01:39 GMT",
"version": "v1"
},
{
"created": "Thu, 29 Oct 2015 12:47:40 GMT",
"version": "v2"
}
] | 2015-12-09 | [
[
"Ramazanov",
"Sabir",
""
]
] | We discuss initial conditions for the recently proposed Imperfect Dark Matter (Modified Dust). We show that they are adiabatic under fairly moderate assumptions about the cosmological evolution of the Universe at the relevant times. |
1308.5573 | Javad Taghizadeh firouzjaee | Javad T. Firouzjaee | Comment on "Inflation with a graceful exit and entrance driven by
Hawking radiation" | null | Physical Review D 89, 068301 (2014) | 10.1103/PhysRevD.89.068301 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/3.0/ | Modak and Singleton [Phys. Rev. D 86, 123515 (2012)] have presented
Hawking-like radiation for cosmological inflation which has a natural "turn on"
and a natural "turn off" mechanism. This Hawking-like radiation results in an
effective negative pressure "fluid" which leads to a rapid period of expansion
in the very early Universe. We discuss that the turn on mechanism can not
happen for FRW model in early universe because its horizon is apparent horizon
not event horizon. Hence, we cannot apply geometric optic approximation which
is a necessary condition for tunneling method. It was shown that this model
predict a value for $\frac{\rho}{m_{pl}^4}$ which is bigger than the COBE
normalization constraint in the Cosmic Microwave Background (CMB) at the
horizon exit.
| [
{
"created": "Mon, 26 Aug 2013 13:14:52 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Apr 2014 06:44:49 GMT",
"version": "v2"
}
] | 2015-06-17 | [
[
"Firouzjaee",
"Javad T.",
""
]
] | Modak and Singleton [Phys. Rev. D 86, 123515 (2012)] have presented Hawking-like radiation for cosmological inflation which has a natural "turn on" and a natural "turn off" mechanism. This Hawking-like radiation results in an effective negative pressure "fluid" which leads to a rapid period of expansion in the very early Universe. We discuss that the turn on mechanism can not happen for FRW model in early universe because its horizon is apparent horizon not event horizon. Hence, we cannot apply geometric optic approximation which is a necessary condition for tunneling method. It was shown that this model predict a value for $\frac{\rho}{m_{pl}^4}$ which is bigger than the COBE normalization constraint in the Cosmic Microwave Background (CMB) at the horizon exit. |
1304.2125 | Narayan Banerjee | Shubhayu Chatterjee and Narayan Banerjee | Modified Ricci flow and asymptotically non-flat spaces | 5 pages, no figure | Canadian Journal of Physics, vol 91, p198-200 (2013) | 10.1139/cjp-2012-0262 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The present work extends the application of a modified Ricci flow equation to
an asymptotically non flat space, namely Marder's cylindrially symmetric space.
It is found that the flow equation has a solution at least in a particular
case.
| [
{
"created": "Mon, 8 Apr 2013 07:41:45 GMT",
"version": "v1"
}
] | 2015-06-15 | [
[
"Chatterjee",
"Shubhayu",
""
],
[
"Banerjee",
"Narayan",
""
]
] | The present work extends the application of a modified Ricci flow equation to an asymptotically non flat space, namely Marder's cylindrially symmetric space. It is found that the flow equation has a solution at least in a particular case. |
gr-qc/0211014 | Cuauhtemoc Campuzano Vargas | Alberto A. Garcia and Cuauhtemoc Campuzano | All Static Circularly Symmetric Perfect Fluid Solutions of 2+1 Gravity | revtex4, 8 pages | Phys.Rev. D67 (2003) 064014 | 10.1103/PhysRevD.67.064014 | null | gr-qc | null | Via a straightforward integration of the Einstein equations with cosmological
constant, all static circularly symmetric perfect fluid 2+1 solutions are
derived. The structural functions of the metric depend on the energy density,
which remains in general arbitrary. Spacetimes for fluids fulfilling linear and
polytropic state equations are explicitly derived; they describe, among others,
stiff matter, monatomic and diatomic ideal gases, nonrelativistic degenerate
fermions, incoherent and pure radiation. As a by--product, we demonstrate the
uniqueness of the constant energy density perfect fluid within the studied
class of metrics. A full similarity of the perfect fluid solutions with
constant energy density of the 2+1 and 3+1 gravities is established.
| [
{
"created": "Tue, 5 Nov 2002 03:48:02 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Garcia",
"Alberto A.",
""
],
[
"Campuzano",
"Cuauhtemoc",
""
]
] | Via a straightforward integration of the Einstein equations with cosmological constant, all static circularly symmetric perfect fluid 2+1 solutions are derived. The structural functions of the metric depend on the energy density, which remains in general arbitrary. Spacetimes for fluids fulfilling linear and polytropic state equations are explicitly derived; they describe, among others, stiff matter, monatomic and diatomic ideal gases, nonrelativistic degenerate fermions, incoherent and pure radiation. As a by--product, we demonstrate the uniqueness of the constant energy density perfect fluid within the studied class of metrics. A full similarity of the perfect fluid solutions with constant energy density of the 2+1 and 3+1 gravities is established. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.