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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/0002035 | Leonid Grishchuk | L P Grishchuk | Relic Gravitational Waves and Their Detection | 25 pages, 9 figures included, revtex. Based on a talk given at
"Gyros, Clocks, and Interferometers: Testing General Relativity in Space"
(Germany, August 99) | Lect.Notes Phys. 562 (2001) 167-194 | 10.1007/3-540-40988-2_9 | null | gr-qc astro-ph hep-ph | null | The range of expected amplitudes and spectral slopes of relic (squeezed)
gravitational waves, predicted by theory and partially supported by
observations, is within the reach of sensitive gravity-wave detectors. In the
most favorable case, the detection of relic gravitational waves can be achieved
by the cross-correlation of outputs of the initial laser interferometers in
LIGO, VIRGO, GEO600. In the more realistic case, the sensitivity of advanced
ground-based and space-based laser interferometers will be needed. The specific
statistical signature of relic gravitational waves, associated with the
phenomenon of squeezing, is a potential reserve for further improvement of the
signal to noise ratio.
| [
{
"created": "Tue, 8 Feb 2000 19:40:04 GMT",
"version": "v1"
}
] | 2016-12-07 | [
[
"Grishchuk",
"L P",
""
]
] | The range of expected amplitudes and spectral slopes of relic (squeezed) gravitational waves, predicted by theory and partially supported by observations, is within the reach of sensitive gravity-wave detectors. In the most favorable case, the detection of relic gravitational waves can be achieved by the cross-correlation of outputs of the initial laser interferometers in LIGO, VIRGO, GEO600. In the more realistic case, the sensitivity of advanced ground-based and space-based laser interferometers will be needed. The specific statistical signature of relic gravitational waves, associated with the phenomenon of squeezing, is a potential reserve for further improvement of the signal to noise ratio. |
1706.00604 | Alexander B. Balakin | Timur Yu. Alpin and Alexander B. Balakin | Birefringence induced by pp-wave modes in an electromagnetically active
dynamic aether | 13 pages, 0 figures, list of references is modified, misprints
eliminated | The European Physical Journal C: 77, 699 (2017) | 10.1140/epjc/s10052-017-5299-2 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the framework of the Einstein-Maxwell-aether theory we study the
birefringence effect, which can occur in the pp-wave symmetric dynamic aether.
The dynamic aether is considered to be latently birefringent quasi-medium,
which displays this hidden property if and only if the aether motion is
non-uniform, i.e., when the aether flow is characterized by the non-vanishing
expansion, shear, vorticity or acceleration. In accordance with the
dynamo-optical scheme of description of the interaction between electromagnetic
waves and the dynamic aether, we shall model the susceptibility tensors by the
terms linear in the covariant derivative of the aether velocity four-vector.
When the pp-wave modes appear in the dynamic aether, we deal with a
gravitationally induced degeneracy removal with respect to hidden
susceptibility parameters. As a consequence, the phase velocities of
electromagnetic waves possessing orthogonal polarizations do not coincide, thus
displaying the birefringence effect. Two electromagnetic field configurations
are studied in detail: longitudinal and transversal with respect to the aether
pp-wave front. For both cases the solutions are found, which reveal anomalies
in the electromagnetic response on the action of the pp-wave aether mode.
| [
{
"created": "Fri, 2 Jun 2017 09:25:36 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Oct 2017 08:40:13 GMT",
"version": "v2"
}
] | 2017-11-22 | [
[
"Alpin",
"Timur Yu.",
""
],
[
"Balakin",
"Alexander B.",
""
]
] | In the framework of the Einstein-Maxwell-aether theory we study the birefringence effect, which can occur in the pp-wave symmetric dynamic aether. The dynamic aether is considered to be latently birefringent quasi-medium, which displays this hidden property if and only if the aether motion is non-uniform, i.e., when the aether flow is characterized by the non-vanishing expansion, shear, vorticity or acceleration. In accordance with the dynamo-optical scheme of description of the interaction between electromagnetic waves and the dynamic aether, we shall model the susceptibility tensors by the terms linear in the covariant derivative of the aether velocity four-vector. When the pp-wave modes appear in the dynamic aether, we deal with a gravitationally induced degeneracy removal with respect to hidden susceptibility parameters. As a consequence, the phase velocities of electromagnetic waves possessing orthogonal polarizations do not coincide, thus displaying the birefringence effect. Two electromagnetic field configurations are studied in detail: longitudinal and transversal with respect to the aether pp-wave front. For both cases the solutions are found, which reveal anomalies in the electromagnetic response on the action of the pp-wave aether mode. |
0704.3648 | Muhammad Sharif | M. Sharif | Perturbed Self-Similar Massless Scalar Field in Spherically Symmetric
Spaceimes | 15 pages, accepted for publication Int. J. Mod. Phys. A | Int.J.Mod.Phys.A22:4695-4708,2007 | 10.1142/S0217751X07037214 | null | gr-qc | null | In this paper, we investigate the linear perturbations of the spherically
symmetric spacetimes with kinematic self-similarity of the second kind. The
massless scalar field equations are solved which yield the background and an
exact solutions for the perturbed equations. We discuss the boundary conditions
of the resulting perturbed solutions. The possible perturbation modes turn out
to be stable as well as unstable. The analysis leads to the conclusion that
there does not exist any critical solution.
| [
{
"created": "Fri, 27 Apr 2007 02:11:59 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Sharif",
"M.",
""
]
] | In this paper, we investigate the linear perturbations of the spherically symmetric spacetimes with kinematic self-similarity of the second kind. The massless scalar field equations are solved which yield the background and an exact solutions for the perturbed equations. We discuss the boundary conditions of the resulting perturbed solutions. The possible perturbation modes turn out to be stable as well as unstable. The analysis leads to the conclusion that there does not exist any critical solution. |
gr-qc/9912079 | Dieter Brill | Dieter Brill | 2+1-dimensional black holes with momentum and angular momentum | 11 pages, 4 LaTeX figures. Plenary talk presented at the "Journees
Relativistes" in Weimar, September 1999. Submitted to Ann. Phys. (Leipzig) | Annalen Phys.9:217-226,2000 | 10.1002/(SICI)1521-3889(200005)9:3/5<217::AID-ANDP217>3.0.CO;2-H | null | gr-qc | null | Exact solutions of Einstein's equations in 2+1-dimensional anti-de Sitter
space containing any number of black holes are described. In addition to the
black holes these spacetimes can possess ``internal'' structure. Accordingly
the generic spacetime of this type depends on a large number of parameters.
Half of these can be taken as mass parameters, and the rest as the conjugate
(angular) momenta. The time development and horizon structure of some of these
spacetimes are sketched.
| [
{
"created": "Sat, 18 Dec 1999 19:33:55 GMT",
"version": "v1"
}
] | 2017-09-27 | [
[
"Brill",
"Dieter",
""
]
] | Exact solutions of Einstein's equations in 2+1-dimensional anti-de Sitter space containing any number of black holes are described. In addition to the black holes these spacetimes can possess ``internal'' structure. Accordingly the generic spacetime of this type depends on a large number of parameters. Half of these can be taken as mass parameters, and the rest as the conjugate (angular) momenta. The time development and horizon structure of some of these spacetimes are sketched. |
gr-qc/9906011 | Ms. Amita Shaw | S.Biswas, A.Shaw, B.Modak and D.Biswas | Quantum Gravity Equation In Schroedinger Form In Minisuperspace
Description | 11 Pages, ReVTeX, no figure | Gen.Rel.Grav. 32 (2000) 2167-2187 | 10.1023/A:1001902620253 | null | gr-qc | null | We start from classical Hamiltonian constraint of general relativity to
obtain the Einstein-Hamiltonian-Jacobi equation. We obtain a time parameter
prescription demanding that geometry itself determines the time, not the matter
field, such that the time so defined being equivalent to the time that enters
into the Schroedinger equation. Without any reference to the Wheeler-DeWitt
equation and without invoking the expansion of exponent in WKB wavefunction in
powers of Planck mass, we obtain an equation for quantum gravity in
Schroedinger form containing time. We restrict ourselves to a minisuperspace
description. Unlike matter field equation our equation is equivalent to the
Wheeler-DeWitt equation in the sense that our solutions reproduce also the
wavefunction of the Wheeler-DeWitt equation provided one evaluates the
normalization constant according to the wormhole dominance proposal recently
proposed by us.
| [
{
"created": "Thu, 3 Jun 1999 09:01:54 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Biswas",
"S.",
""
],
[
"Shaw",
"A.",
""
],
[
"Modak",
"B.",
""
],
[
"Biswas",
"D.",
""
]
] | We start from classical Hamiltonian constraint of general relativity to obtain the Einstein-Hamiltonian-Jacobi equation. We obtain a time parameter prescription demanding that geometry itself determines the time, not the matter field, such that the time so defined being equivalent to the time that enters into the Schroedinger equation. Without any reference to the Wheeler-DeWitt equation and without invoking the expansion of exponent in WKB wavefunction in powers of Planck mass, we obtain an equation for quantum gravity in Schroedinger form containing time. We restrict ourselves to a minisuperspace description. Unlike matter field equation our equation is equivalent to the Wheeler-DeWitt equation in the sense that our solutions reproduce also the wavefunction of the Wheeler-DeWitt equation provided one evaluates the normalization constant according to the wormhole dominance proposal recently proposed by us. |
1301.7041 | Yasha Neiman | Yasha Neiman | The imaginary part of the gravity action and black hole entropy | 37 pages, 8 figures; v2: sign error corrected; v3: refined the
treatment of Lovelock gravity, added section 3 with expanded discussion,
added references | JHEP 1304 (2013) 071 | 10.1007/JHEP04(2013)071 | IGC-13/1-1 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | As observed recently in arXiv:1212.2922, the action of General Relativity
(GR) in finite spacetime regions has an imaginary part that resembles the
Bekenstein entropy. In this paper, we expand on that argument, with attention
to different causal types of boundaries. This property of the GR action may
open a new approach to the puzzles of gravitational entropy. In particular, the
imaginary action can be evaluated for non-stationary finite regions, where the
notion of entropy is not fully understood. As a first step in constructing the
precise relationship between the imaginary action and entropy, we focus on
stationary black hole spacetimes. There, we identify a class of bounded regions
for which the action's imaginary part precisely equals the black hole entropy.
As a powerful test on the validity of the approach, we also calculate the
imaginary action for Lovelock gravity. The result is related to the
corresponding entropy formula in the same way as in GR.
| [
{
"created": "Tue, 29 Jan 2013 20:03:06 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Feb 2013 18:40:04 GMT",
"version": "v2"
},
{
"created": "Mon, 1 Apr 2013 20:59:07 GMT",
"version": "v3"
}
] | 2013-12-12 | [
[
"Neiman",
"Yasha",
""
]
] | As observed recently in arXiv:1212.2922, the action of General Relativity (GR) in finite spacetime regions has an imaginary part that resembles the Bekenstein entropy. In this paper, we expand on that argument, with attention to different causal types of boundaries. This property of the GR action may open a new approach to the puzzles of gravitational entropy. In particular, the imaginary action can be evaluated for non-stationary finite regions, where the notion of entropy is not fully understood. As a first step in constructing the precise relationship between the imaginary action and entropy, we focus on stationary black hole spacetimes. There, we identify a class of bounded regions for which the action's imaginary part precisely equals the black hole entropy. As a powerful test on the validity of the approach, we also calculate the imaginary action for Lovelock gravity. The result is related to the corresponding entropy formula in the same way as in GR. |
1904.05287 | Steven B. Giddings | Steven B. Giddings | Searching for quantum black hole structure with the Event Horizon
Telescope | 6 pages + refs. v2: a few typos corrected. v3: CERN report number
added. v4: Minor clarification re. apparent EHT image variation | Universe 2019, 5, 201 | 10.3390/universe5090201 | CERN-TH-2019-076 | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The impressive images from the Event Horizon Telescope sharpen the conflict
between our observations of gravitational phenomena and the principles of
quantum mechanics. Two related scenarios for reconciling quantum mechanics with
the existence of black hole-like objects, with "minimal" departure from general
relativity and local quantum field theory, have been explored; one of these
could produce signatures visible to EHT observations. A specific target is
temporal variability of images, with a characteristic time scale determined by
the classical black hole radius. The absence of evidence for such variability
in the initial observational span of seven days is not expected to strongly
constrain such variability. Theoretical and observational next steps towards
investigating such scenarios are outlined.
| [
{
"created": "Wed, 10 Apr 2019 16:42:18 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Apr 2019 08:38:20 GMT",
"version": "v2"
},
{
"created": "Wed, 29 May 2019 08:23:54 GMT",
"version": "v3"
},
{
"created": "Tue, 17 Sep 2019 15:40:39 GMT",
"version": "v4"
}
] | 2019-09-18 | [
[
"Giddings",
"Steven B.",
""
]
] | The impressive images from the Event Horizon Telescope sharpen the conflict between our observations of gravitational phenomena and the principles of quantum mechanics. Two related scenarios for reconciling quantum mechanics with the existence of black hole-like objects, with "minimal" departure from general relativity and local quantum field theory, have been explored; one of these could produce signatures visible to EHT observations. A specific target is temporal variability of images, with a characteristic time scale determined by the classical black hole radius. The absence of evidence for such variability in the initial observational span of seven days is not expected to strongly constrain such variability. Theoretical and observational next steps towards investigating such scenarios are outlined. |
1512.04072 | B. V. Ivanov | B. V. Ivanov | A different approach to anisotropic spherical collapse with shear and
heat radiation | 15 pages, to appear in Int.J.Mod.Phys.D | Int. J. Mod. Phys. D 25, No.4 (2016) 1650049 | 10.1142/S0218271816500498 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In order to study the type of collapse, mentioned in the title, we introduce
a physically meaningful object, called the horizon function. It directly enters
the expressions for many of the stellar characteristics. The main junction
equation, which governs the collapse, transforms into a Riccati equation with
simple coefficients for the horizon function. We integrate this equation in the
geodesic case. The same is done in the general case when one or another of the
coefficients vanish. It is shown how to build classes of star models in this
formulation of the problem and simple solutions are given.
| [
{
"created": "Sun, 13 Dec 2015 15:58:30 GMT",
"version": "v1"
},
{
"created": "Sat, 23 Jan 2016 17:26:49 GMT",
"version": "v2"
}
] | 2016-03-23 | [
[
"Ivanov",
"B. V.",
""
]
] | In order to study the type of collapse, mentioned in the title, we introduce a physically meaningful object, called the horizon function. It directly enters the expressions for many of the stellar characteristics. The main junction equation, which governs the collapse, transforms into a Riccati equation with simple coefficients for the horizon function. We integrate this equation in the geodesic case. The same is done in the general case when one or another of the coefficients vanish. It is shown how to build classes of star models in this formulation of the problem and simple solutions are given. |
1105.6192 | T. Roy Choudhury | T. Roy Choudhury and T. Padmanabhan | Reply to [arXiv:1105.5653]: "Comment on 'Quasinormal modes in
Schwarzschild-de Sitter spacetime: A simple derivation of the level spacing
of the frequencies'" | 2 pages | Phys.Rev.D83:108502,2011 | 10.1103/PhysRevD.83.108502 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explain why the analysis in our paper [Phys. Rev. D 69, 064033 (2004),
arXiv:gr-qc/0311064 ] is relevant and correct.
| [
{
"created": "Tue, 31 May 2011 07:50:31 GMT",
"version": "v1"
}
] | 2011-06-07 | [
[
"Choudhury",
"T. Roy",
""
],
[
"Padmanabhan",
"T.",
""
]
] | We explain why the analysis in our paper [Phys. Rev. D 69, 064033 (2004), arXiv:gr-qc/0311064 ] is relevant and correct. |
1708.09371 | Benito A. Ju\'arez-Aubry | Benito A. Ju\'arez-Aubry, Bernard S. Kay and Daniel Sudarsky | Generally covariant dynamical reduction models and the Hadamard
condition | V2: 20 pages. Some typos corrected and new remarks in the
Introduction. For an extended version of this paper see V1 | Phys. Rev. D 97, 025010 (2018) | 10.1103/PhysRevD.97.025010 | null | gr-qc math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We provide general guidelines for generalizing dynamical reduction models to
curved spacetimes and propose a class of generally covariant relativistic
versions of the GRW model. We anticipate that the collapse operators of our
class of models may play a r\^ole in a yet-to-be-formulated theory of
semiclassical gravity with collapses. We show explicitly that the collapse
operators map a dense domain of states that are initially Hadamard to final
Hadamard states -- a property that we expect will be needed for the
construction of such a semiclassical theory. Finally, we provide a simple
example in which we explicitly compute the violations in energy-momentum due to
the state reduction process and conclude that this violation is of the order of
a parameter of the model -- supposed to be small.
| [
{
"created": "Wed, 30 Aug 2017 17:23:01 GMT",
"version": "v1"
},
{
"created": "Fri, 2 Feb 2018 20:22:39 GMT",
"version": "v2"
}
] | 2018-02-06 | [
[
"Juárez-Aubry",
"Benito A.",
""
],
[
"Kay",
"Bernard S.",
""
],
[
"Sudarsky",
"Daniel",
""
]
] | We provide general guidelines for generalizing dynamical reduction models to curved spacetimes and propose a class of generally covariant relativistic versions of the GRW model. We anticipate that the collapse operators of our class of models may play a r\^ole in a yet-to-be-formulated theory of semiclassical gravity with collapses. We show explicitly that the collapse operators map a dense domain of states that are initially Hadamard to final Hadamard states -- a property that we expect will be needed for the construction of such a semiclassical theory. Finally, we provide a simple example in which we explicitly compute the violations in energy-momentum due to the state reduction process and conclude that this violation is of the order of a parameter of the model -- supposed to be small. |
0904.3949 | Julio Cesar Fabris | C.E.M. Batista, J.C. Fabris and M. Morita | Power spectrum in the Chaplygin gas model: tachyonic, fluid and scalar
field representations | Latex file, 10 pages, 18 figures in EPS format | null | 10.1007/s10714-009-0884-9 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Chaplygin gas model, characterized by an equation of state of the type $p
= - \frac{A}{\rho}$ emerges naturally from the Nambu-Goto action of string
theory. This fluid representation can be recast under the form of a tachyonic
field given by a Born-Infeld type Lagrangian. At the same time, the Chaplygin
gas equation of state can be obtained from a self-interacting scalar field. We
show that, from the point of view of the supernova type Ia data, the three
representations (fluid, tachyonic, scalar field) lead to the same results.
However, concerning the matter power spectra, while the fluid and tachyonic
descriptions lead to exactly the same results, the self-interacting scalar
field representation implies different statistical estimations for the
parameters. In particular, the estimation for the dark matter density parameter
in the fluid representation favors a universe dominated almost completely by
dark matter, while in the self-interacting scalar field representation the
prediction is very closed to that obtained in the $\Lambda$CDM model.
| [
{
"created": "Fri, 24 Apr 2009 22:00:34 GMT",
"version": "v1"
}
] | 2015-05-13 | [
[
"Batista",
"C. E. M.",
""
],
[
"Fabris",
"J. C.",
""
],
[
"Morita",
"M.",
""
]
] | The Chaplygin gas model, characterized by an equation of state of the type $p = - \frac{A}{\rho}$ emerges naturally from the Nambu-Goto action of string theory. This fluid representation can be recast under the form of a tachyonic field given by a Born-Infeld type Lagrangian. At the same time, the Chaplygin gas equation of state can be obtained from a self-interacting scalar field. We show that, from the point of view of the supernova type Ia data, the three representations (fluid, tachyonic, scalar field) lead to the same results. However, concerning the matter power spectra, while the fluid and tachyonic descriptions lead to exactly the same results, the self-interacting scalar field representation implies different statistical estimations for the parameters. In particular, the estimation for the dark matter density parameter in the fluid representation favors a universe dominated almost completely by dark matter, while in the self-interacting scalar field representation the prediction is very closed to that obtained in the $\Lambda$CDM model. |
gr-qc/9712092 | Schubert | Uwe Mueller (Mainz Univ.), Christian Schubert (Argonne), Anton van de
Ven (Hamburg Univ.) | A Closed Formula for the Riemann Normal Coordinate Expansion | 8 pages, standard latex, no figures, minor modifications | Gen.Rel.Grav.31:1759-1768,1999 | 10.1023/A:1026718301634 | DESY 97-254, ANL-HEP-PR-97-99, MZ-TH/97-38 | gr-qc dg-ga hep-th math.DG | null | We derive an integral representation which encodes all coefficients of the
Riemann normal coordinate expansion, and also a closed formula for those
coefficients.
| [
{
"created": "Wed, 24 Dec 1997 00:52:20 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Dec 1999 20:53:34 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Mueller",
"Uwe",
"",
"Mainz Univ."
],
[
"Schubert",
"Christian",
"",
"Argonne"
],
[
"van de Ven",
"Anton",
"",
"Hamburg Univ."
]
] | We derive an integral representation which encodes all coefficients of the Riemann normal coordinate expansion, and also a closed formula for those coefficients. |
1001.3511 | Kirill Bronnikov | Kirill A. Bronnikov, Sergey V. Sushkov | Trapped ghosts: a new class of wormholes | 4.2 pages, 4 figures. Version to appear in CQG | Class. Quantum Grav. 27, 095022 (2010) | 10.1088/0264-9381/27/9/095022 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct examples of static, spherically symmetric wormhole solutions in
general relativity with a minimally coupled scalar field $\phi$ whose kinetic
energy is negative in a restricted region of space near the throat (of
arbitrary size) and positive far from it. Thus in such configurations a "ghost"
is trapped in the strong-field region, which may in principle explain why no
ghosts are observed under usual conditions. Some properties of general wormhole
models with the $\phi$ field are revealed: it is shown that (i) trapped-ghost
wormholes are only possible with nonzero potentials $V(\phi)$; (ii) in twice
asymptotically flat wormholes, a nontrivial potential $V(\phi)$ has an
alternate sign, and (iii) a twice asymptotically flat wormhole which is
mirror-symmetric with respect to its throat has necessarily a zero
Schwarzschild mass at both asymptotics.
| [
{
"created": "Wed, 20 Jan 2010 11:24:10 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Mar 2010 16:06:21 GMT",
"version": "v2"
}
] | 2015-05-18 | [
[
"Bronnikov",
"Kirill A.",
""
],
[
"Sushkov",
"Sergey V.",
""
]
] | We construct examples of static, spherically symmetric wormhole solutions in general relativity with a minimally coupled scalar field $\phi$ whose kinetic energy is negative in a restricted region of space near the throat (of arbitrary size) and positive far from it. Thus in such configurations a "ghost" is trapped in the strong-field region, which may in principle explain why no ghosts are observed under usual conditions. Some properties of general wormhole models with the $\phi$ field are revealed: it is shown that (i) trapped-ghost wormholes are only possible with nonzero potentials $V(\phi)$; (ii) in twice asymptotically flat wormholes, a nontrivial potential $V(\phi)$ has an alternate sign, and (iii) a twice asymptotically flat wormhole which is mirror-symmetric with respect to its throat has necessarily a zero Schwarzschild mass at both asymptotics. |
1904.10794 | Andrej Arbuzov | Andrej B. Arbuzov, Alexander E. Pavlov | Intrinsic Time in Geometrodynamics of Closed Manifolds | 11 pages; format is changed; arXiv admin note: substantial text
overlap with arXiv:1710.01528 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The global time in Geometrodynamics is defined in a covariant under
diffeomorphisms form. An arbitrary static background metric is taken in the
tangent space. The global intrinsic time is identified with the mean value of
the logarithm of the square root of the ratio of the metric determinants. The
procedures of the Hamiltonian reduction and deparametrization of dynamical
systems are implemented. The explored Hamiltonian system appeared to be
non-conservative. The Hamiltonian equations of motion of gravitational field in
the global time are written. Relations between different time intervals
(coordinate, intrinsic, proper) are obtained.
| [
{
"created": "Tue, 23 Apr 2019 07:56:32 GMT",
"version": "v1"
},
{
"created": "Thu, 16 May 2019 14:10:42 GMT",
"version": "v2"
}
] | 2019-05-17 | [
[
"Arbuzov",
"Andrej B.",
""
],
[
"Pavlov",
"Alexander E.",
""
]
] | The global time in Geometrodynamics is defined in a covariant under diffeomorphisms form. An arbitrary static background metric is taken in the tangent space. The global intrinsic time is identified with the mean value of the logarithm of the square root of the ratio of the metric determinants. The procedures of the Hamiltonian reduction and deparametrization of dynamical systems are implemented. The explored Hamiltonian system appeared to be non-conservative. The Hamiltonian equations of motion of gravitational field in the global time are written. Relations between different time intervals (coordinate, intrinsic, proper) are obtained. |
2401.15003 | Ao Guo | Ao Guo, Jun Zhang, Huan Yang | Superradiant clouds may be relevant for close compact object binaries | null | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bosonic fields (within suitable mass range) may be collectively generated by
rotating black holes through the black hole superradiance process. The
resulting black hole is surrounded by a ``cloud" of particles whose wave
function populates the superradiant energy level of the black hole. For
comparable mass ratio binary black hole systems, it has been suggested that
these clouds often deplete at large binary separations because of level mixing
effects. As a result, these clouds may not be dynamically relevant for black
hole and neutron star binaries that enter the LIGO-Virgo-KAGRA and LISA
detection frequency band. In this work, we point out that the common envelope
process during a compact binary evolution may bring the binary to $\sim 0.01$AU
in hundreds to thousands of years, so that depletion caused by certain level
mixings are no longer important. We derive a relevant regime of binary
parameters where the clouds are still present for binary entering the LISA
band, and show that common envelop process does enlarge such parameter regime.
When the binary separation further decreases due to gravitational wave
radiation, we discuss the impact of possible cloud mass transfer between the
binary objects.
| [
{
"created": "Fri, 26 Jan 2024 17:04:59 GMT",
"version": "v1"
},
{
"created": "Thu, 9 May 2024 08:56:11 GMT",
"version": "v2"
},
{
"created": "Fri, 26 Jul 2024 04:32:02 GMT",
"version": "v3"
}
] | 2024-07-29 | [
[
"Guo",
"Ao",
""
],
[
"Zhang",
"Jun",
""
],
[
"Yang",
"Huan",
""
]
] | Bosonic fields (within suitable mass range) may be collectively generated by rotating black holes through the black hole superradiance process. The resulting black hole is surrounded by a ``cloud" of particles whose wave function populates the superradiant energy level of the black hole. For comparable mass ratio binary black hole systems, it has been suggested that these clouds often deplete at large binary separations because of level mixing effects. As a result, these clouds may not be dynamically relevant for black hole and neutron star binaries that enter the LIGO-Virgo-KAGRA and LISA detection frequency band. In this work, we point out that the common envelope process during a compact binary evolution may bring the binary to $\sim 0.01$AU in hundreds to thousands of years, so that depletion caused by certain level mixings are no longer important. We derive a relevant regime of binary parameters where the clouds are still present for binary entering the LISA band, and show that common envelop process does enlarge such parameter regime. When the binary separation further decreases due to gravitational wave radiation, we discuss the impact of possible cloud mass transfer between the binary objects. |
1705.02382 | James Edholm | Aindri\'u Conroy, James Edholm | Newtonian Potential and Geodesic Completeness in Infinite Derivative
Gravity | 7 pages, 3 figures | Phys. Rev. D 96, 044012 (2017) | 10.1103/PhysRevD.96.044012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recent study has shown that a non-singular oscillating potential, a feature
of Infinite Derivative Gravity (IDG) theories, matches current experimental
data better than the standard GR potential. In this work we show that this
non-singular oscillating potential can be given by a wider class of theories
which allows the defocusing of null rays, and therefore geodesic completeness.
We consolidate the conditions whereby null geodesic congruences may be made
past-complete, via the Raychaudhuri Equation, with the requirement of a
non-singular Newtonian potential in an IDG theory. In so doing, we examine a
class of Newtonian potentials characterised by an additional degree of freedom
in the scalar propagator, which returns the familiar potential of General
Relativity at large distances.
| [
{
"created": "Fri, 5 May 2017 20:01:21 GMT",
"version": "v1"
},
{
"created": "Tue, 9 May 2017 21:47:30 GMT",
"version": "v2"
}
] | 2017-08-16 | [
[
"Conroy",
"Aindriú",
""
],
[
"Edholm",
"James",
""
]
] | Recent study has shown that a non-singular oscillating potential, a feature of Infinite Derivative Gravity (IDG) theories, matches current experimental data better than the standard GR potential. In this work we show that this non-singular oscillating potential can be given by a wider class of theories which allows the defocusing of null rays, and therefore geodesic completeness. We consolidate the conditions whereby null geodesic congruences may be made past-complete, via the Raychaudhuri Equation, with the requirement of a non-singular Newtonian potential in an IDG theory. In so doing, we examine a class of Newtonian potentials characterised by an additional degree of freedom in the scalar propagator, which returns the familiar potential of General Relativity at large distances. |
0912.5286 | Salvatore Capozziello | Salvatore Capozziello, Mariafelicia De Laurentis, Arturo Stabile | Axially symmetric solutions in f(R)-gravity | 13 pages, 1 figure, to appear in Classical and Quantum Gravity 2010 | Class.Quant.Grav.27:165008,2010 | 10.1088/0264-9381/27/16/165008 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Axially symmetric solutions for f (R)-gravity can be derived starting from
exact spherically sym- metric solutions achieved by Noether symmetries. The
method takes advantage of a complex coordi- nate transformation previously
developed by Newman and Janis in General Relativity. An example is worked out
to show the general validity of the approach. The physical properties of the
solution are also considered.
| [
{
"created": "Tue, 29 Dec 2009 10:14:17 GMT",
"version": "v1"
},
{
"created": "Sat, 29 May 2010 16:06:02 GMT",
"version": "v2"
}
] | 2014-11-20 | [
[
"Capozziello",
"Salvatore",
""
],
[
"De Laurentis",
"Mariafelicia",
""
],
[
"Stabile",
"Arturo",
""
]
] | Axially symmetric solutions for f (R)-gravity can be derived starting from exact spherically sym- metric solutions achieved by Noether symmetries. The method takes advantage of a complex coordi- nate transformation previously developed by Newman and Janis in General Relativity. An example is worked out to show the general validity of the approach. The physical properties of the solution are also considered. |
2307.06474 | Daniela Doneva | Daniela D. Doneva, Llibert Arest\'e Sal\'o, Katy Clough, Pau Figueras,
Stoytcho S. Yazadjiev | Testing the limits of scalar-Gauss-Bonnet gravity through nonlinear
evolutions of spin-induced scalarization | 23 pages, 10 figure, 1 table | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quadratic theories of gravity with second order equations of motion provide
an interesting model for testing deviations from general relativity in the
strong gravity regime. However, they can suffer from a loss of hyperbolicity,
even for initial data that is in the weak coupling regime and free from any
obvious pathology. This effect has been studied in a variety of cases including
isolated black holes and binaries. Here we explore the loss of hyperbolicity in
spin-induced scalarization of isolated Kerr black holes in a
scalar-Gauss-Bonnet theory of gravity, employing the modified CCZ4 formulation
that has recently been developed. We find that, as in previous studies,
hyperbolicity is lost when the scalar field and its gradients become large, and
identify the breakdown in our evolutions with the physical modes of the purely
gravitational sector. We vary the gauge parameters and find the results to be
independent of their value. This, along with our use of a different gauge
formulation to previous works, supports the premise that the loss of
hyperbolicity is dominated by the physical modes. Since scalar-Gauss-Bonnet
theories can be viewed as effective field theories (EFTs), we also examine the
strength of the coupling during the evolution. We find that at the moment when
hyperbolicity is lost the system is already well within the regime where the
EFT is no longer valid. This reinforces the idea that the theories should only
be applied within their regime of validity, and not treated as complete
theories in their own right.
| [
{
"created": "Wed, 12 Jul 2023 22:10:32 GMT",
"version": "v1"
}
] | 2023-07-14 | [
[
"Doneva",
"Daniela D.",
""
],
[
"Saló",
"Llibert Aresté",
""
],
[
"Clough",
"Katy",
""
],
[
"Figueras",
"Pau",
""
],
[
"Yazadjiev",
"Stoytcho S.",
""
]
] | Quadratic theories of gravity with second order equations of motion provide an interesting model for testing deviations from general relativity in the strong gravity regime. However, they can suffer from a loss of hyperbolicity, even for initial data that is in the weak coupling regime and free from any obvious pathology. This effect has been studied in a variety of cases including isolated black holes and binaries. Here we explore the loss of hyperbolicity in spin-induced scalarization of isolated Kerr black holes in a scalar-Gauss-Bonnet theory of gravity, employing the modified CCZ4 formulation that has recently been developed. We find that, as in previous studies, hyperbolicity is lost when the scalar field and its gradients become large, and identify the breakdown in our evolutions with the physical modes of the purely gravitational sector. We vary the gauge parameters and find the results to be independent of their value. This, along with our use of a different gauge formulation to previous works, supports the premise that the loss of hyperbolicity is dominated by the physical modes. Since scalar-Gauss-Bonnet theories can be viewed as effective field theories (EFTs), we also examine the strength of the coupling during the evolution. We find that at the moment when hyperbolicity is lost the system is already well within the regime where the EFT is no longer valid. This reinforces the idea that the theories should only be applied within their regime of validity, and not treated as complete theories in their own right. |
2203.06588 | Pritam Nanda | Pritam Nanda, Chiranjeeb Singha, Pabitra Tripathy, Amit Ghosh | Hawking radiation as quantum mechanical reflection | 9 pages and 3 figures, accepted for publication in General Relativity
and Gravitation | null | 10.1007/s10714-022-03007-1 | null | gr-qc | http://creativecommons.org/licenses/by-sa/4.0/ | In this article, we explore an alternative derivation of Hawking radiation.
Instead of the field-theoretic derivation, we have suggested a simpler
calculation based on quantum mechanical reflection from a one-dimensional
potential. The reflection coefficient shows an exponential fall in energy
which, in comparison with the Boltzmann probability distribution, yields a
temperature. The temperature is the same as Hawking temperature for spherically
symmetric black holes. The derivation gives an exact local calculation of
Hawking temperature that involves a region lying entirely outside the horizon.
This is a crucial difference from the tunneling calculation, where it is
necessary to involve a region inside the horizon.
| [
{
"created": "Sun, 13 Mar 2022 06:40:08 GMT",
"version": "v1"
},
{
"created": "Thu, 29 Sep 2022 17:43:13 GMT",
"version": "v2"
}
] | 2022-10-14 | [
[
"Nanda",
"Pritam",
""
],
[
"Singha",
"Chiranjeeb",
""
],
[
"Tripathy",
"Pabitra",
""
],
[
"Ghosh",
"Amit",
""
]
] | In this article, we explore an alternative derivation of Hawking radiation. Instead of the field-theoretic derivation, we have suggested a simpler calculation based on quantum mechanical reflection from a one-dimensional potential. The reflection coefficient shows an exponential fall in energy which, in comparison with the Boltzmann probability distribution, yields a temperature. The temperature is the same as Hawking temperature for spherically symmetric black holes. The derivation gives an exact local calculation of Hawking temperature that involves a region lying entirely outside the horizon. This is a crucial difference from the tunneling calculation, where it is necessary to involve a region inside the horizon. |
2008.05597 | Li Li | Li Li | On Thermodynamics of AdS Black Holes with Scalar Hair | 15 pages, 2 figures; v2: minor changes, reference added; v3: revised
version, to appear in PLB; v4: typos corrected in the left plots of Figures.
1 and 2 | null | 10.1016/j.physletb.2021.136123 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been known that in the presence of a scalar hair there would be a
distinct additional contribution to the first law of black hole thermodynamics.
While it has been checked in many examples, a deeper understanding of this
issue is necessary. The thermodynamics of AdS black holes in Einstein-scalar
gravity is studied by using the standard holographic renormalization procedure
and the variation of the Hamiltonian via the Wald formalism. It is found that
the first law requires a modification by including an additional term that has
a particular form $\sim\left<O\right>\delta \phi_s$, with $\phi_s$ and
$\left<O\right>$ a new pair of thermodynamic conjugate variables. $\phi_s$ is
the leading source term of the asymptotic fall-off of the scalar field near the
AdS boundary, and $\left<O\right>$ is precisely the response of the dual scalar
operator from the holographic point of view. Some hairy black holes are
constructed explicitly to check the first law of thermodynamics as well as the
thermodynamic relations.
| [
{
"created": "Wed, 12 Aug 2020 23:05:52 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Sep 2020 03:26:09 GMT",
"version": "v2"
},
{
"created": "Tue, 2 Feb 2021 01:22:58 GMT",
"version": "v3"
},
{
"created": "Thu, 27 Jan 2022 02:48:11 GMT",
"version": "v4"
}
] | 2022-01-28 | [
[
"Li",
"Li",
""
]
] | It has been known that in the presence of a scalar hair there would be a distinct additional contribution to the first law of black hole thermodynamics. While it has been checked in many examples, a deeper understanding of this issue is necessary. The thermodynamics of AdS black holes in Einstein-scalar gravity is studied by using the standard holographic renormalization procedure and the variation of the Hamiltonian via the Wald formalism. It is found that the first law requires a modification by including an additional term that has a particular form $\sim\left<O\right>\delta \phi_s$, with $\phi_s$ and $\left<O\right>$ a new pair of thermodynamic conjugate variables. $\phi_s$ is the leading source term of the asymptotic fall-off of the scalar field near the AdS boundary, and $\left<O\right>$ is precisely the response of the dual scalar operator from the holographic point of view. Some hairy black holes are constructed explicitly to check the first law of thermodynamics as well as the thermodynamic relations. |
1904.04368 | Thomas Zannias | Jose Felix Salazar and Thomas Zannias | On Extended Thermodynamics: From Classical to the Relativistic Regime | An extended version of arXiv:1904.04368v2 [gr-qc]. New version
contains 90 pages,no figures,new sections and two new Appendixes added to the
previous version. In this electronic version new proofs and new references
added and various misprints are corrected from the published version | International Journal of Modern Physics D Vol. 29, No. 15, 2030010
(2020) | 10.1142/S0218271820300104 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The recent monumental detection of gravitational waves by LIGO, the
subsequent detection by the LIGO/VIRGO observatories of a binary neutron star
merger seen in the gravitational wave signal $GW170817$,the first photo of the
event horizon of the supermassive black hole at the center of the $M87$ galaxy
released by the EHT telescope and the ongoing experiments on Relativistic Heavy
Ion Collisions at the BNL and at the CERN, demonstrate that we are witnessing
the second golden era of observational relativistic gravity. These new
observational breakthroughs, although in the long run would influence our views
regarding this Kosmos, in the short run, they suggest that relativistic
dissipative fluids (or magnetofluids) and relativistic continuous media play an
important role on astrophysical-and also subnuclear-scales. This realization
brings into the frontiers of current research theories of irreversible
thermodynamics of relativistic continuous media.
Motivated by these considerations, in this paper, we summarize the progress
that has been made in the last few decades in the field of non equilibrium
thermodynamics of relativistic continuous media. For coherence and completeness
purposes, we begin with a brief description of the balance laws for classical
(Newtonian) continuous media and introduce the classical irreversible
thermodynamics (CIT) and the role of the local-equilibrium postulate within
this theory. Tangentially, we touch the program of rational thermodynamics
(RT), the Clausius-Duhem inequality, the theory of constitutive relations and
the emergence of the entropy principle and its role in the description of
continuous media.
| [
{
"created": "Mon, 8 Apr 2019 21:31:46 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Jul 2019 18:02:10 GMT",
"version": "v2"
},
{
"created": "Fri, 8 Oct 2021 17:58:29 GMT",
"version": "v3"
}
] | 2021-10-11 | [
[
"Salazar",
"Jose Felix",
""
],
[
"Zannias",
"Thomas",
""
]
] | The recent monumental detection of gravitational waves by LIGO, the subsequent detection by the LIGO/VIRGO observatories of a binary neutron star merger seen in the gravitational wave signal $GW170817$,the first photo of the event horizon of the supermassive black hole at the center of the $M87$ galaxy released by the EHT telescope and the ongoing experiments on Relativistic Heavy Ion Collisions at the BNL and at the CERN, demonstrate that we are witnessing the second golden era of observational relativistic gravity. These new observational breakthroughs, although in the long run would influence our views regarding this Kosmos, in the short run, they suggest that relativistic dissipative fluids (or magnetofluids) and relativistic continuous media play an important role on astrophysical-and also subnuclear-scales. This realization brings into the frontiers of current research theories of irreversible thermodynamics of relativistic continuous media. Motivated by these considerations, in this paper, we summarize the progress that has been made in the last few decades in the field of non equilibrium thermodynamics of relativistic continuous media. For coherence and completeness purposes, we begin with a brief description of the balance laws for classical (Newtonian) continuous media and introduce the classical irreversible thermodynamics (CIT) and the role of the local-equilibrium postulate within this theory. Tangentially, we touch the program of rational thermodynamics (RT), the Clausius-Duhem inequality, the theory of constitutive relations and the emergence of the entropy principle and its role in the description of continuous media. |
1508.06727 | Ramon Herrera | Ramon Herrera and Roberto G. Perez | Approach to exact solutions of cosmological perturbations: Tachyon field
inflation | 19 pages and 4 figures | Phys. Rev. D 93, 063516 (2016) | 10.1103/PhysRevD.93.063516 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An inflationary universe scenario in the context of tachyon field is studied.
This study is done from an ansantz for the effective potential of cosmological
perturbations $U(\eta)$. We describe in great detail the analytical solutions
of the scalar and tensor perturbations for two different ansantz in the
effective potential of cosmological perturbations; the Easther's model and an
effective potential similar to power law inflation. Also we find from the
background equations that the effective tachyonic potential $V(\varphi)$, in
both models satisfy the properties of a tachyonic potential. We consider the
recent data from the Planck data to constrain the parameters in our effective
potential of cosmological perturbations.
| [
{
"created": "Thu, 27 Aug 2015 05:55:47 GMT",
"version": "v1"
}
] | 2016-03-23 | [
[
"Herrera",
"Ramon",
""
],
[
"Perez",
"Roberto G.",
""
]
] | An inflationary universe scenario in the context of tachyon field is studied. This study is done from an ansantz for the effective potential of cosmological perturbations $U(\eta)$. We describe in great detail the analytical solutions of the scalar and tensor perturbations for two different ansantz in the effective potential of cosmological perturbations; the Easther's model and an effective potential similar to power law inflation. Also we find from the background equations that the effective tachyonic potential $V(\varphi)$, in both models satisfy the properties of a tachyonic potential. We consider the recent data from the Planck data to constrain the parameters in our effective potential of cosmological perturbations. |
1010.3416 | Volker Perlick | Volker Perlick | Gravitational Lensing from a Spacetime Perspective | 120 pages, 31 figures; submitted to Living Reviews in Relativity;
updated version of http://www.livingreviews.org/lrr-2004-9 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The theory of gravitational lensing is reviewed from a spacetime perspective,
without quasi-Newtonian approximations. More precisely, the review covers all
aspects of gravitational lensing where light propagation is described in terms
of lightlike geodesics of a metric of Lorentzian signature. It includes the
basic equations and the relevant techniques for calculating the position, the
shape, and the brightness of images in an arbitrary general-relativistic
spacetime. It also includes general theorems on the classification of caustics,
on criteria for multiple imaging, and on the possible number of images. The
general results are illustrated with examples of spacetimes where the lensing
features can be explicitly calculated, including the Schwarzschild spacetime,
the Kerr spacetime, the spacetime of a straight string, plane gravitational
waves, and others.
| [
{
"created": "Sun, 17 Oct 2010 14:38:29 GMT",
"version": "v1"
}
] | 2010-10-19 | [
[
"Perlick",
"Volker",
""
]
] | The theory of gravitational lensing is reviewed from a spacetime perspective, without quasi-Newtonian approximations. More precisely, the review covers all aspects of gravitational lensing where light propagation is described in terms of lightlike geodesics of a metric of Lorentzian signature. It includes the basic equations and the relevant techniques for calculating the position, the shape, and the brightness of images in an arbitrary general-relativistic spacetime. It also includes general theorems on the classification of caustics, on criteria for multiple imaging, and on the possible number of images. The general results are illustrated with examples of spacetimes where the lensing features can be explicitly calculated, including the Schwarzschild spacetime, the Kerr spacetime, the spacetime of a straight string, plane gravitational waves, and others. |
gr-qc/9509055 | Joseph David Romano | Joseph D. Romano and Charles G. Torre | Internal Time Formalism for Spacetimes with Two Killing Vectors | 36 pages, TeX | Phys.Rev. D53 (1996) 5634-5650 | 10.1103/PhysRevD.53.5634 | null | gr-qc | null | The Hamiltonian structure of spacetimes with two commuting Killing vector
fields is analyzed for the purpose of addressing the various problems of time
that arise in canonical gravity. Two specific models are considered: (i)
cylindrically symmetric spacetimes, and (ii) toroidally symmetric spacetimes,
which respectively involve open and closed universe boundary conditions. For
each model canonical variables which can be used to identify points of space
and instants of time, {\it i.e.}, internally defined spacetime coordinates, are
identified. To do this it is necessary to extend the usual ADM phase space by a
finite number of degrees of freedom. Canonical transformations are exhibited
that identify each of these models with harmonic maps in the parametrized field
theory formalism. The identifications made between the gravitational models and
harmonic map field theories are completely gauge invariant, that is, no
coordinate conditions are needed. The degree to which the problems of time are
resolved in these models is discussed.
| [
{
"created": "Thu, 28 Sep 1995 19:23:42 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Romano",
"Joseph D.",
""
],
[
"Torre",
"Charles G.",
""
]
] | The Hamiltonian structure of spacetimes with two commuting Killing vector fields is analyzed for the purpose of addressing the various problems of time that arise in canonical gravity. Two specific models are considered: (i) cylindrically symmetric spacetimes, and (ii) toroidally symmetric spacetimes, which respectively involve open and closed universe boundary conditions. For each model canonical variables which can be used to identify points of space and instants of time, {\it i.e.}, internally defined spacetime coordinates, are identified. To do this it is necessary to extend the usual ADM phase space by a finite number of degrees of freedom. Canonical transformations are exhibited that identify each of these models with harmonic maps in the parametrized field theory formalism. The identifications made between the gravitational models and harmonic map field theories are completely gauge invariant, that is, no coordinate conditions are needed. The degree to which the problems of time are resolved in these models is discussed. |
1810.03204 | Luca Guido Molinari | Salvatore Capozziello, Carlo Alberto Mantica and Luca Guido Molinari | Cosmological perfect-fluids in f(R) gravity | 13 pages, final version | Int. J. Geom. Meth. Mod. Phys. 16 (2019) 1950008 | 10.1142/S0219887819500087 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that an n-dimensional generalized Robertson-Walker (GRW) space-time
with divergence-free conformal curvature tensor exhibits a perfect fluid
stress-energy tensor for any f(R) gravity model. Furthermore we prove that a
conformally flat GRW space-time is still a perfect fluid in both f(R) and
quadratic gravity where other curvature invariants are considered.
| [
{
"created": "Sun, 7 Oct 2018 20:34:06 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Nov 2018 13:14:59 GMT",
"version": "v2"
}
] | 2018-11-08 | [
[
"Capozziello",
"Salvatore",
""
],
[
"Mantica",
"Carlo Alberto",
""
],
[
"Molinari",
"Luca Guido",
""
]
] | We show that an n-dimensional generalized Robertson-Walker (GRW) space-time with divergence-free conformal curvature tensor exhibits a perfect fluid stress-energy tensor for any f(R) gravity model. Furthermore we prove that a conformally flat GRW space-time is still a perfect fluid in both f(R) and quadratic gravity where other curvature invariants are considered. |
gr-qc/9610044 | Renaud Parentani | R. Parentani | Time dependent Green functions from Wheeler De Witt solutions | 25 pages, latex, no figures | Nucl.Phys. B492 (1997) 475-500 | 10.1016/S0550-3213(97)80042-9 | LPTENS 96/45 | gr-qc | null | The aim of this article is twofold. First we examine from a new angle the
question of recovery of time in quantum cosmology. We construct Green functions
for matter fields from the solutions of the Wheeler De Witt equation. For
simplicity we work in a mini-superspace context. By evaluating these Green
functions in a first order development of the energy ``increment'' induced by
matrix elements of field operators, we show that the background geometry is the
solution of Einstein equations driven by the mean matter energy and that it is
this background which determines the time lapses separating the field
operators. Then, by studying higher order corrections, we clarify the nature of
the small dimensionless parameters which guarantee the validity of the
approximations used. In this respect, we show that the formal expansion in the
inverse Planck mass which is sometime presented as the ``standard procedure''
is illegitimate. Secondly, by the present analysis of Green functions, we
prepare the study of quantum matter transitions in quantum cosmology. In a next
article, we show that the time parametrization of transition amplitudes appears
for the same reasons that it appeared in this article. This proves that the
background is dynamically determined by the transition under examination.
| [
{
"created": "Mon, 21 Oct 1996 09:35:40 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Parentani",
"R.",
""
]
] | The aim of this article is twofold. First we examine from a new angle the question of recovery of time in quantum cosmology. We construct Green functions for matter fields from the solutions of the Wheeler De Witt equation. For simplicity we work in a mini-superspace context. By evaluating these Green functions in a first order development of the energy ``increment'' induced by matrix elements of field operators, we show that the background geometry is the solution of Einstein equations driven by the mean matter energy and that it is this background which determines the time lapses separating the field operators. Then, by studying higher order corrections, we clarify the nature of the small dimensionless parameters which guarantee the validity of the approximations used. In this respect, we show that the formal expansion in the inverse Planck mass which is sometime presented as the ``standard procedure'' is illegitimate. Secondly, by the present analysis of Green functions, we prepare the study of quantum matter transitions in quantum cosmology. In a next article, we show that the time parametrization of transition amplitudes appears for the same reasons that it appeared in this article. This proves that the background is dynamically determined by the transition under examination. |
gr-qc/0202012 | John W. Moffat | J. W. Moffat | Bimetric Gravity Theory, Varying Speed of Light and the Dimming of
Supernovae | 22 pages, Latex file. No figures. Corrected typos. Added reference.
Further references added. Further corrections. To be published in Int. J.
Mod. Phys. D, 2002 | Int.J.Mod.Phys.D12:281-298,2003 | 10.1142/S0218271803002366 | null | gr-qc astro-ph hep-ph hep-th | null | In the bimetric scalar-tensor gravitational theory there are two frames
associated with the two metrics {\hat g}_{\mu\nu} and g_{\mu\nu}, which are
linked by the gradients of a scalar field \phi. The choice of a comoving frame
for the metric {\hat g}_{\mu\nu} or g_{\mu\nu} has fundamental consequences for
local observers in either metric spacetimes, while maintaining diffeomorphism
invariance. When the metric g_{\mu\nu} is chosen to be associated with comoving
coordinates, then the speed of light varies in the frame with the metric {\hat
g}_{\mu\nu}. Observers in this frame see the dimming of supernovae because of
the increase of the luminosity distance versus red shift, due to an increasing
speed of light in the early universe. Moreover, in this frame the scalar field
\phi describes a dark energy component in the Friedmann equation for the cosmic
scale without acceleration. If we choose {\hat g}_{\mu\nu} to be associated
with comoving coordinates, then an observer in the g_{\mu\nu} metric frame will
observe the universe to be accelerating and the supernovae will appear to be
farther away. The theory predicts that the gravitational constant G can vary in
spacetime, while the fine-structure constant \alpha=e^2/\hbar c does not vary.
The problem of cosmological horizons as viewed in the two frames is discussed.
| [
{
"created": "Tue, 5 Feb 2002 19:40:15 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Feb 2002 22:09:14 GMT",
"version": "v2"
},
{
"created": "Thu, 14 Mar 2002 17:26:02 GMT",
"version": "v3"
},
{
"created": "Thu, 28 Mar 2002 23:21:55 GMT",
"version": "v4"
},
{
"cr... | 2014-11-17 | [
[
"Moffat",
"J. W.",
""
]
] | In the bimetric scalar-tensor gravitational theory there are two frames associated with the two metrics {\hat g}_{\mu\nu} and g_{\mu\nu}, which are linked by the gradients of a scalar field \phi. The choice of a comoving frame for the metric {\hat g}_{\mu\nu} or g_{\mu\nu} has fundamental consequences for local observers in either metric spacetimes, while maintaining diffeomorphism invariance. When the metric g_{\mu\nu} is chosen to be associated with comoving coordinates, then the speed of light varies in the frame with the metric {\hat g}_{\mu\nu}. Observers in this frame see the dimming of supernovae because of the increase of the luminosity distance versus red shift, due to an increasing speed of light in the early universe. Moreover, in this frame the scalar field \phi describes a dark energy component in the Friedmann equation for the cosmic scale without acceleration. If we choose {\hat g}_{\mu\nu} to be associated with comoving coordinates, then an observer in the g_{\mu\nu} metric frame will observe the universe to be accelerating and the supernovae will appear to be farther away. The theory predicts that the gravitational constant G can vary in spacetime, while the fine-structure constant \alpha=e^2/\hbar c does not vary. The problem of cosmological horizons as viewed in the two frames is discussed. |
1709.02787 | Nikolaos Stergioulas | Gabriele Bozzola, Nikolaos Stergioulas, Andreas Bauswein | Universal relations for differentially rotating relativistic stars at
the threshold to collapse | 8 pages, 8 figures, submitted to MNRAS | null | 10.1093/mnras/stx3002 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A binary neutron star merger produces a rapidly and differentially rotating
compact remnant whose lifespan heavily affects the electromagnetic and
gravitational emissions. Its stability depends on both the equation of state
(EOS) and the rotation law and it is usually investigated through numerical
simulations. Nevertheless, by means of a sufficient criterion for secular
instability, equilibrium sequences can be used as a computationally inexpensive
way to estimate the onset of dynamical instability, which, in general, is close
to the secular one. This method works well for uniform rotation and relies on
the location of turning points: stellar models that are stationary points in a
sequence of equilibrium solutions with constant rest mass or angular momentum.
Here, we investigate differentially rotating models (using a large number of
equations of state and different rotation laws) and find that several universal
relations between properly scaled gravitational mass, rest mass and angular
momentum of the turning-point models that are valid for uniform rotation, are
insensitive to the degree of differential rotation, to high accuracy.
| [
{
"created": "Fri, 8 Sep 2017 17:40:40 GMT",
"version": "v1"
}
] | 2017-12-27 | [
[
"Bozzola",
"Gabriele",
""
],
[
"Stergioulas",
"Nikolaos",
""
],
[
"Bauswein",
"Andreas",
""
]
] | A binary neutron star merger produces a rapidly and differentially rotating compact remnant whose lifespan heavily affects the electromagnetic and gravitational emissions. Its stability depends on both the equation of state (EOS) and the rotation law and it is usually investigated through numerical simulations. Nevertheless, by means of a sufficient criterion for secular instability, equilibrium sequences can be used as a computationally inexpensive way to estimate the onset of dynamical instability, which, in general, is close to the secular one. This method works well for uniform rotation and relies on the location of turning points: stellar models that are stationary points in a sequence of equilibrium solutions with constant rest mass or angular momentum. Here, we investigate differentially rotating models (using a large number of equations of state and different rotation laws) and find that several universal relations between properly scaled gravitational mass, rest mass and angular momentum of the turning-point models that are valid for uniform rotation, are insensitive to the degree of differential rotation, to high accuracy. |
gr-qc/0411021 | Marco Bruni | Andrea Passamonti, Marco Bruni, Leonardo Gualtieri, Carlos F. Sopuerta | Coupling of radial and non-radial oscillations of Neutron stars | 4 pages. Proceedings of the NATO Advanced Study Institute on the
Electromagnetic Spectrum of Neutron Stars, Marmaris, Turkey, June 2004 | null | null | null | gr-qc astro-ph | null | This is a progress report on our study of the coupling of first-order radial
and non-radial relativistic perturbations of a static spherical star. Our goal
is to investigate the effects of this coupling on the gravitational wave signal
of neutron stars. In particular, we are looking for the existence of resonances
and parametric amplifications, changes in the damping time of non-radial
oscillations, etc. To that end, we have developed a formalism that introduces
gauge invariant quantities to describe the coupling. Their equations have the
same structure as the equations for first-order non-radial perturbations plus
some source terms, which makes them very appealing for time domain studies.
| [
{
"created": "Wed, 3 Nov 2004 23:05:30 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Passamonti",
"Andrea",
""
],
[
"Bruni",
"Marco",
""
],
[
"Gualtieri",
"Leonardo",
""
],
[
"Sopuerta",
"Carlos F.",
""
]
] | This is a progress report on our study of the coupling of first-order radial and non-radial relativistic perturbations of a static spherical star. Our goal is to investigate the effects of this coupling on the gravitational wave signal of neutron stars. In particular, we are looking for the existence of resonances and parametric amplifications, changes in the damping time of non-radial oscillations, etc. To that end, we have developed a formalism that introduces gauge invariant quantities to describe the coupling. Their equations have the same structure as the equations for first-order non-radial perturbations plus some source terms, which makes them very appealing for time domain studies. |
gr-qc/9804029 | Bernard Julia | B. Julia and S. Silva (ENS Paris) | Currents and Superpotentials in classical gauge invariant theories I.
Local results with applications to Perfect Fluids and General Relativity | 64 pages, LaTeX. Version 2 has two more references and one misprint
corrected. Accepted in Classical and Quantum Gravity | Class.Quant.Grav. 15 (1998) 2173-2215 | 10.1088/0264-9381/15/8/006 | LPTENS/98/06 | gr-qc hep-th | null | E. Noether's general analysis of conservation laws has to be completed in a
Lagrangian theory with local gauge invariance. Bulk charges are replaced by
fluxes of superpotentials. Gauge invariant bulk charges may subsist when
distinguished one-dimensional subgroups are present. As a first illustration we
propose a new {\it Affine action} that reduces to General Relativity upon gauge
fixing the dilatation (Weyl 1918 like) part of the connection and elimination
of auxiliary fields. It allows a comparison of most gravity superpotentials and
we discuss their selection by the choice of boundary conditions. A second and
independent application is a geometrical reinterpretation of the convection of
vorticity in barotropic nonviscous fluids. We identify the one-dimensional
subgroups responsible for the bulk charges and thus propose an impulsive
forcing for creating or destroying selectively helicity. This is an example of
a new and general Forcing Rule.
| [
{
"created": "Fri, 10 Apr 1998 10:50:53 GMT",
"version": "v1"
},
{
"created": "Thu, 28 May 1998 15:12:45 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Julia",
"B.",
"",
"ENS Paris"
],
[
"Silva",
"S.",
"",
"ENS Paris"
]
] | E. Noether's general analysis of conservation laws has to be completed in a Lagrangian theory with local gauge invariance. Bulk charges are replaced by fluxes of superpotentials. Gauge invariant bulk charges may subsist when distinguished one-dimensional subgroups are present. As a first illustration we propose a new {\it Affine action} that reduces to General Relativity upon gauge fixing the dilatation (Weyl 1918 like) part of the connection and elimination of auxiliary fields. It allows a comparison of most gravity superpotentials and we discuss their selection by the choice of boundary conditions. A second and independent application is a geometrical reinterpretation of the convection of vorticity in barotropic nonviscous fluids. We identify the one-dimensional subgroups responsible for the bulk charges and thus propose an impulsive forcing for creating or destroying selectively helicity. This is an example of a new and general Forcing Rule. |
2012.00297 | Roger Hurtado PhD | Roger Hurtado and Robel Arenas | Hypergeometric viable models in $f(R)$ gravity | 10 pages, 3 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A cosmologically viable hypergeometric model in the modified gravity theory
$f(R)$ is found from the need for asintoticity towards $\Lambda$CDM, the
existence of an inflection point in the $f(R)$ curve, and the conditions of
viability given by the phase space curves $(m, r)$, where $m$ and $r$ are
characteristic functions of the model. To analyze the constraints associated
with the viability requirements, the models were expressed in terms of a
dimensionless variable, i.e. $R\to x$ and $f(R)\to y(x)=x+h(x)+\lambda$, where
$h(x)$ represents the deviation of the model from General Relativity. Using the
geometric properties imposed by the inflection point, differential equations
were constructed to relate $h'(x)$ and $h''(x)$, and the solutions found were
Starobinsky (2007) and Hu-Sawicki type models, nonetheless, it was found that
these differential equations are particular cases of a hypergeometric
differential equation, so that these models can be obtained from a general
hypergeometric model. The parameter domains of this model were analyzed to make
the model viable.
| [
{
"created": "Tue, 1 Dec 2020 06:37:04 GMT",
"version": "v1"
}
] | 2020-12-02 | [
[
"Hurtado",
"Roger",
""
],
[
"Arenas",
"Robel",
""
]
] | A cosmologically viable hypergeometric model in the modified gravity theory $f(R)$ is found from the need for asintoticity towards $\Lambda$CDM, the existence of an inflection point in the $f(R)$ curve, and the conditions of viability given by the phase space curves $(m, r)$, where $m$ and $r$ are characteristic functions of the model. To analyze the constraints associated with the viability requirements, the models were expressed in terms of a dimensionless variable, i.e. $R\to x$ and $f(R)\to y(x)=x+h(x)+\lambda$, where $h(x)$ represents the deviation of the model from General Relativity. Using the geometric properties imposed by the inflection point, differential equations were constructed to relate $h'(x)$ and $h''(x)$, and the solutions found were Starobinsky (2007) and Hu-Sawicki type models, nonetheless, it was found that these differential equations are particular cases of a hypergeometric differential equation, so that these models can be obtained from a general hypergeometric model. The parameter domains of this model were analyzed to make the model viable. |
1107.5802 | Joao Paulo Pitelli Manoel | J.P.M. Pitelli and P.S. Letelier | Modeling the quantum evolution of the universe through classical matter | updated version as accepted by Gen. Relativ. Gravit | General Relativity and Gravitation, 2013 | 10.1007/s10714-013-1531-z | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is well known that the canonical quantization of the
Friedmann-Lema\^itre-Robertson-Walker (FLRW) filled with a perfect fluid leads
to nonsingular universes which, for later times, behave as their classical
counterpart. This means that the expectation value of the scale factor $<a>(t)$
never vanishes and, as $t\to\infty$, we recover the classical expression for
the scale factor. In this paper, we show that such universes can be reproduced
by classical cosmology given that the universe is filled with an exotic matter.
In the case of a perfect fluid, we find an implicit equation of state (EoS). We
then show that this single fluid with an implict EoS is equivalent to two
non-interacting fluids, one of them representing stiff matter with negative
energy density. In the case of two non-interacting scalar fields, one of them
of the phantom type, we find their potential energy. In both cases we find that
quantum mechanics changes completely the configuration of matter for small
values of time, by adding a fluid or a scalar field with negative energy
density. As time passes, the density of negative energy decreases and we
recover the ordinary content of the classical universe. The more the initial
wave function of the universe is concentrated around the classical big bang
singularity, the more it is necessary to add negative energy, since this type
of energy will be responsible for the removal of the classical singularity.
| [
{
"created": "Thu, 28 Jul 2011 19:32:49 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Aug 2011 18:48:33 GMT",
"version": "v2"
},
{
"created": "Wed, 8 May 2013 15:07:39 GMT",
"version": "v3"
}
] | 2013-05-09 | [
[
"Pitelli",
"J. P. M.",
""
],
[
"Letelier",
"P. S.",
""
]
] | It is well known that the canonical quantization of the Friedmann-Lema\^itre-Robertson-Walker (FLRW) filled with a perfect fluid leads to nonsingular universes which, for later times, behave as their classical counterpart. This means that the expectation value of the scale factor $<a>(t)$ never vanishes and, as $t\to\infty$, we recover the classical expression for the scale factor. In this paper, we show that such universes can be reproduced by classical cosmology given that the universe is filled with an exotic matter. In the case of a perfect fluid, we find an implicit equation of state (EoS). We then show that this single fluid with an implict EoS is equivalent to two non-interacting fluids, one of them representing stiff matter with negative energy density. In the case of two non-interacting scalar fields, one of them of the phantom type, we find their potential energy. In both cases we find that quantum mechanics changes completely the configuration of matter for small values of time, by adding a fluid or a scalar field with negative energy density. As time passes, the density of negative energy decreases and we recover the ordinary content of the classical universe. The more the initial wave function of the universe is concentrated around the classical big bang singularity, the more it is necessary to add negative energy, since this type of energy will be responsible for the removal of the classical singularity. |
gr-qc/0305065 | Ujjal Debnath | Subenoy Chakraborty, N. C. Chakraborty and Ujjal Debnath | A Quintessence Problem in Brans-Dicke Theory with Varying Speed of Light | 8 Latex pages, 6 figures, Revtex style | Int.J.Mod.Phys.D12:325-335,2003 | 10.1142/S0218271803002792 | null | gr-qc | null | It is shown that minimally coupled scalar field in Brans-Dicke theory with
varying speed of light can solve the quintessence problem and it is possible to
have a non-decelerated expansion of the present universe with BD-theory for
anisotropic models without any matter.
| [
{
"created": "Fri, 16 May 2003 15:49:35 GMT",
"version": "v1"
}
] | 2008-11-07 | [
[
"Chakraborty",
"Subenoy",
""
],
[
"Chakraborty",
"N. C.",
""
],
[
"Debnath",
"Ujjal",
""
]
] | It is shown that minimally coupled scalar field in Brans-Dicke theory with varying speed of light can solve the quintessence problem and it is possible to have a non-decelerated expansion of the present universe with BD-theory for anisotropic models without any matter. |
0806.1328 | \"Ozg\"ur Acik | \"O. A\c{c}{\i}k, \"U. Ertem, M. \"Onder and A. Ver\c{c}in | First-order symmetries of Dirac equation in curved background: a unified
dynamical symmetry condition | 13 pages, put into sections and subsections format, added a
conclusion part. Published version | Class.Quant.Grav.26:075001,2009 | 10.1088/0264-9381/26/7/075001 | null | gr-qc hep-th math-ph math.MP | http://creativecommons.org/licenses/by/3.0/ | It has been shown that, for all dimensions and signatures, the most general
first-order linear symmetry operators for the Dirac equation including
interaction with Maxwell field in curved background are given in terms of
Killing-Yano (KY) forms. As a general gauge invariant condition it is found
that among all KY-forms of the underlying (pseudo) Riemannian manifold, only
those which Clifford commute with the Maxwell field take part in the symmetry
operator. It is also proved that associated with each KY-form taking part in
the symmetry operator, one can define a quadratic function of velocities which
is a geodesic invariant as well as a constant of motion for the classical
trajectory. Some geometrical and physical implications of the existence of
KY-forms are also elucidated.
| [
{
"created": "Sun, 8 Jun 2008 13:47:42 GMT",
"version": "v1"
},
{
"created": "Tue, 3 Mar 2009 14:04:16 GMT",
"version": "v2"
}
] | 2010-05-12 | [
[
"Açık",
"Ö.",
""
],
[
"Ertem",
"Ü.",
""
],
[
"Önder",
"M.",
""
],
[
"Verçin",
"A.",
""
]
] | It has been shown that, for all dimensions and signatures, the most general first-order linear symmetry operators for the Dirac equation including interaction with Maxwell field in curved background are given in terms of Killing-Yano (KY) forms. As a general gauge invariant condition it is found that among all KY-forms of the underlying (pseudo) Riemannian manifold, only those which Clifford commute with the Maxwell field take part in the symmetry operator. It is also proved that associated with each KY-form taking part in the symmetry operator, one can define a quadratic function of velocities which is a geodesic invariant as well as a constant of motion for the classical trajectory. Some geometrical and physical implications of the existence of KY-forms are also elucidated. |
2402.06836 | Aaron Johnson | Aaron D. Johnson, Katerina Chatziioannou, Will M. Farr | Source Confusion from Neutron Star Binaries in Ground-Based
Gravitational Wave Detectors is Minimal | 20 pages, 9 figures, 4 tables | null | 10.1103/PhysRevD.109.084015 | null | gr-qc astro-ph.HE astro-ph.IM | http://creativecommons.org/licenses/by/4.0/ | Upgrades beyond the current second generation of ground-based gravitational
wave detectors will allow them to observe tens of thousands neutron star and
black hole binaries. Given the typical minute-to-hour duration of neutron star
signals in the detector frequency band, a number of them will overlap in the
time-frequency plane resulting in a nonzero cross-correlation. We examine
source confusion arising from overlapping signals whose time-frequency tracks
cross. Adopting the median observed merger rate of $100$ Gpc$^{-3}$yr$^{-1}$,
each neutron star binary signal overlaps with an average of 42(4)[0.5] other
signals when observed from 2(5)[10] Hz. The vast majority of overlaps occur at
low frequencies where the inspiral evolution is slow: 91% of time-frequency
overlaps occur in band below 5 Hz. The combined effect of overlapping signals
does not satisfy the central limit theorem and source confusion cannot be
treated as stationary, Gaussian noise: on average 0.91(0.17)[0.05] signals are
present in a single adaptive time-frequency bin centered at 2(5)[10] Hz. We
quantify source confusion under a realistic neutron star binary population and
find that parameter uncertainty typically increases by less than 1% unless
there are overlapping signals whose detector-frame chirp mass difference is
$\lesssim 0.01 M_{\odot}$ and the overlap frequency is $\gtrsim$ 40 Hz. Out of
$1\times10^6$ simulated signals, 0.14% fall within this region of
detector-frame chirp mass differences, but their overlap frequencies are
typically lower than 40 Hz. Source confusion for ground-based detectors, where
events overlap instantaneously is significantly milder than the equivalent LISA
problem, where many classes of events overlap for the lifetime of the mission.
| [
{
"created": "Fri, 9 Feb 2024 23:54:47 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Apr 2024 19:36:17 GMT",
"version": "v2"
}
] | 2024-04-11 | [
[
"Johnson",
"Aaron D.",
""
],
[
"Chatziioannou",
"Katerina",
""
],
[
"Farr",
"Will M.",
""
]
] | Upgrades beyond the current second generation of ground-based gravitational wave detectors will allow them to observe tens of thousands neutron star and black hole binaries. Given the typical minute-to-hour duration of neutron star signals in the detector frequency band, a number of them will overlap in the time-frequency plane resulting in a nonzero cross-correlation. We examine source confusion arising from overlapping signals whose time-frequency tracks cross. Adopting the median observed merger rate of $100$ Gpc$^{-3}$yr$^{-1}$, each neutron star binary signal overlaps with an average of 42(4)[0.5] other signals when observed from 2(5)[10] Hz. The vast majority of overlaps occur at low frequencies where the inspiral evolution is slow: 91% of time-frequency overlaps occur in band below 5 Hz. The combined effect of overlapping signals does not satisfy the central limit theorem and source confusion cannot be treated as stationary, Gaussian noise: on average 0.91(0.17)[0.05] signals are present in a single adaptive time-frequency bin centered at 2(5)[10] Hz. We quantify source confusion under a realistic neutron star binary population and find that parameter uncertainty typically increases by less than 1% unless there are overlapping signals whose detector-frame chirp mass difference is $\lesssim 0.01 M_{\odot}$ and the overlap frequency is $\gtrsim$ 40 Hz. Out of $1\times10^6$ simulated signals, 0.14% fall within this region of detector-frame chirp mass differences, but their overlap frequencies are typically lower than 40 Hz. Source confusion for ground-based detectors, where events overlap instantaneously is significantly milder than the equivalent LISA problem, where many classes of events overlap for the lifetime of the mission. |
gr-qc/0411132 | Stoytcho Yazadjiev | Stoytcho S. Yazadjiev | Charged perfect fluid configurations with a dilaton field | 9 pages, LaTex, v2 typos corrected | Mod.Phys.Lett.A20:821-831,2005 | 10.1142/S0217732305017056 | null | gr-qc | null | We examine static charged perfect fluid configurations in the presence of a
dilaton field. A method for construction of interior solutions is given. An
explicit example of an interior solution which matches continuously the
external Gibbons-Maeda-Garfinkle-Horowitz-Strominger solution is presented.
Extremely charged perfect fluid configurations with a dilaton are also
examined. We show that there are two types of extreme configurations. For each
type the field equations are reduced to a single nonlinear equation on a space
of a constant curvature. In the particular case of a perfect fluid with a
linear equation of state, the field equations of the first type configurations
are reduced to a Helmlotz equation on a space with a constant curvature. An
explicit example of an extreme configuration is given and discussed.
| [
{
"created": "Sun, 28 Nov 2004 11:22:41 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Dec 2004 09:37:20 GMT",
"version": "v2"
}
] | 2010-11-05 | [
[
"Yazadjiev",
"Stoytcho S.",
""
]
] | We examine static charged perfect fluid configurations in the presence of a dilaton field. A method for construction of interior solutions is given. An explicit example of an interior solution which matches continuously the external Gibbons-Maeda-Garfinkle-Horowitz-Strominger solution is presented. Extremely charged perfect fluid configurations with a dilaton are also examined. We show that there are two types of extreme configurations. For each type the field equations are reduced to a single nonlinear equation on a space of a constant curvature. In the particular case of a perfect fluid with a linear equation of state, the field equations of the first type configurations are reduced to a Helmlotz equation on a space with a constant curvature. An explicit example of an extreme configuration is given and discussed. |
gr-qc/0108022 | Ioannis Kouletsis | Ioannis Kouletsis and Karel. V. Kuchar | Diffeomorphisms as Symplectomorphisms in History Phase Space: Bosonic
String Model | 45 pages, no figures | Phys.Rev. D65 (2002) 125026 | 10.1103/PhysRevD.65.125026 | null | gr-qc | null | The structure of the history phase space $\cal G$ of a covariant field system
and its history group (in the sense of Isham and Linden) is analyzed on an
example of a bosonic string. The history space $\cal G$ includes the time map
$\sf T$ from the spacetime manifold (the two-sheet) $\cal Y$ to a
one-dimensional time manifold $\cal T$ as one of its configuration variables. A
canonical history action is posited on $\cal G$ such that its restriction to
the configuration history space yields the familiar Polyakov action. The
standard Dirac-ADM action is shown to be identical with the canonical history
action, the only difference being that the underlying action is expressed in
two different coordinate charts on $\cal G$. The canonical history action
encompasses all individual Dirac-ADM actions corresponding to different choices
$\sf T$ of foliating $\cal Y$. The history Poisson brackets of spacetime fields
on $\cal G$ induce the ordinary Poisson brackets of spatial fields in the
instantaneous phase space ${\cal G}_{0}$ of the Dirac-ADM formalism. The
canonical history action is manifestly invariant both under spacetime
diffeomorphisms Diff$\cal Y$ and temporal diffeomorphisms Diff$\cal T$. Both of
these diffeomorphisms are explicitly represented by symplectomorphisms on the
history phase space $\cal G$. The resulting classical history phase space
formalism is offered as a starting point for projection operator quantization
and consistent histories interpretation of the bosonic string model.
| [
{
"created": "Wed, 8 Aug 2001 10:15:29 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Aug 2001 09:49:55 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Kouletsis",
"Ioannis",
""
],
[
"Kuchar",
"Karel. V.",
""
]
] | The structure of the history phase space $\cal G$ of a covariant field system and its history group (in the sense of Isham and Linden) is analyzed on an example of a bosonic string. The history space $\cal G$ includes the time map $\sf T$ from the spacetime manifold (the two-sheet) $\cal Y$ to a one-dimensional time manifold $\cal T$ as one of its configuration variables. A canonical history action is posited on $\cal G$ such that its restriction to the configuration history space yields the familiar Polyakov action. The standard Dirac-ADM action is shown to be identical with the canonical history action, the only difference being that the underlying action is expressed in two different coordinate charts on $\cal G$. The canonical history action encompasses all individual Dirac-ADM actions corresponding to different choices $\sf T$ of foliating $\cal Y$. The history Poisson brackets of spacetime fields on $\cal G$ induce the ordinary Poisson brackets of spatial fields in the instantaneous phase space ${\cal G}_{0}$ of the Dirac-ADM formalism. The canonical history action is manifestly invariant both under spacetime diffeomorphisms Diff$\cal Y$ and temporal diffeomorphisms Diff$\cal T$. Both of these diffeomorphisms are explicitly represented by symplectomorphisms on the history phase space $\cal G$. The resulting classical history phase space formalism is offered as a starting point for projection operator quantization and consistent histories interpretation of the bosonic string model. |
1603.06146 | Carlos A. R. Herdeiro | Emanuele Berti, Vitor Cardoso, Luis C. B. Crispino, Leonardo
Gualtieri, Carlos Herdeiro and Ulrich Sperhake | Numerical Relativity and High Energy Physics: Recent Developments | 46 pages, 6 figures; Submitted to a Special Issue of IJMPD on
Selected Papers of the III Amazonian Symposium on Physics | null | 10.1142/S0218271816410224 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We review recent progress in the application of numerical relativity
techniques to astrophysics and high-energy physics. We focus on some
developments that took place within the "Numerical Relativity and High Energy
Physics" network, a Marie Curie IRSES action that we coordinated, namely: spin
evolution in black hole binaries, high-energy black hole collisions, compact
object solutions in scalar-tensor gravity, superradiant instabilities and hairy
black hole solutions in Einstein's gravity coupled to fundamental fields, and
the possibility to gain insight into these phenomena using analog gravity
models.
| [
{
"created": "Sat, 19 Mar 2016 21:19:04 GMT",
"version": "v1"
}
] | 2016-08-17 | [
[
"Berti",
"Emanuele",
""
],
[
"Cardoso",
"Vitor",
""
],
[
"Crispino",
"Luis C. B.",
""
],
[
"Gualtieri",
"Leonardo",
""
],
[
"Herdeiro",
"Carlos",
""
],
[
"Sperhake",
"Ulrich",
""
]
] | We review recent progress in the application of numerical relativity techniques to astrophysics and high-energy physics. We focus on some developments that took place within the "Numerical Relativity and High Energy Physics" network, a Marie Curie IRSES action that we coordinated, namely: spin evolution in black hole binaries, high-energy black hole collisions, compact object solutions in scalar-tensor gravity, superradiant instabilities and hairy black hole solutions in Einstein's gravity coupled to fundamental fields, and the possibility to gain insight into these phenomena using analog gravity models. |
2110.04610 | Kirill Kobialko | Kirill Kobialko and Dmitri Gal'tsov | Photon regions in stationary axisymmetric spacetimes and umbilic
conditions | 14 pages, to be submitted to the Proceedings of the 16th Marcel
Grossmann meeting | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the fundamentals of the recently proposed geometric description of
photon regions in terms of foliation into fundamental photon hypersurfaces,
which satisfies the umbilic condition for the subbundle of the tangent bundle
defined by the generalized impact parameter.
| [
{
"created": "Sat, 9 Oct 2021 16:49:56 GMT",
"version": "v1"
}
] | 2021-10-12 | [
[
"Kobialko",
"Kirill",
""
],
[
"Gal'tsov",
"Dmitri",
""
]
] | We present the fundamentals of the recently proposed geometric description of photon regions in terms of foliation into fundamental photon hypersurfaces, which satisfies the umbilic condition for the subbundle of the tangent bundle defined by the generalized impact parameter. |
1908.00017 | Venkatesa Chandrasekaran | Venkatesa Chandrasekaran, Kartik Prabhu | Symmetries, charges and conservation laws at causal diamonds in general
relativity | v2: minor clarifications; v1: 27 pages, 1 figure | JHEP 10 (2019) 229 | 10.1007/JHEP10(2019)229 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the covariant phase space of vacuum general relativity at the null
boundary of causal diamonds. The past and future components of such a null
boundary each have an infinite-dimensional symmetry algebra consisting of
diffeomorphisms of the $2$-sphere and boost supertranslations corresponding to
angle-dependent rescalings of affine parameter along the null generators.
Associated to these symmetries are charges and fluxes obtained from the
covariant phase space formalism using the prescription of Wald and Zoupas. By
analyzing the behavior of the spacetime metric near the corners of the causal
diamond, we show that the fluxes are also Hamiltonian generators of the
symmetries on the phase space. In particular, the supertranslation fluxes yield
an infinite family of boost Hamiltonians acting on the gravitational data of
causal diamonds. We show that the smoothness of the vector fields representing
such symmetries at the bifurcation edge of the causal diamond implies suitable
matching conditions between the symmetries on the past and future components of
the null boundary. Similarly, the smoothness of the spacetime metric implies
that the fluxes of all such symmetries is conserved between the past and future
components of the null boundary. This establishes an infinite set of
conservation laws for finite subregions in gravity analogous to those at null
infinity. We also show that the symmetry algebra at the causal diamond has a
non-trivial center corresponding to constant boosts. The central charges
associated to these constant boosts are proportional to the area of the
bifurcation edge, for any causal diamond, in analogy with the Wald entropy
formula.
| [
{
"created": "Wed, 31 Jul 2019 18:00:04 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Nov 2019 16:58:11 GMT",
"version": "v2"
}
] | 2019-11-12 | [
[
"Chandrasekaran",
"Venkatesa",
""
],
[
"Prabhu",
"Kartik",
""
]
] | We study the covariant phase space of vacuum general relativity at the null boundary of causal diamonds. The past and future components of such a null boundary each have an infinite-dimensional symmetry algebra consisting of diffeomorphisms of the $2$-sphere and boost supertranslations corresponding to angle-dependent rescalings of affine parameter along the null generators. Associated to these symmetries are charges and fluxes obtained from the covariant phase space formalism using the prescription of Wald and Zoupas. By analyzing the behavior of the spacetime metric near the corners of the causal diamond, we show that the fluxes are also Hamiltonian generators of the symmetries on the phase space. In particular, the supertranslation fluxes yield an infinite family of boost Hamiltonians acting on the gravitational data of causal diamonds. We show that the smoothness of the vector fields representing such symmetries at the bifurcation edge of the causal diamond implies suitable matching conditions between the symmetries on the past and future components of the null boundary. Similarly, the smoothness of the spacetime metric implies that the fluxes of all such symmetries is conserved between the past and future components of the null boundary. This establishes an infinite set of conservation laws for finite subregions in gravity analogous to those at null infinity. We also show that the symmetry algebra at the causal diamond has a non-trivial center corresponding to constant boosts. The central charges associated to these constant boosts are proportional to the area of the bifurcation edge, for any causal diamond, in analogy with the Wald entropy formula. |
gr-qc/9905009 | Zahid Zakir | Zahid Zakir (CTPA) | New Equations for Gravitation with Riemann Tensor and 4-Index
Energy-Momentum Tensors for Gravitation and Matter | Published in: "Z.Zakir (2003) Structure of Space-Time and Matter.
CTPA, Tashkent" | Theor. Phys. Astrophys. and Cosmol. 5 (2010) 14 | 10.9751/TPAC.3600-017 | null | gr-qc | null | A generalized version of the Einstein equations in the 4-index form,
containing the Riemann tensor linearly, is derived. It is shown, that the
gravitational energy-momentum density tensor outside a source is represented
across the Weyl tensor vanishing at the 2-index contraction. The 4-index
energy-momentum density tensor for matter also is constructed.
| [
{
"created": "Mon, 3 May 1999 19:57:01 GMT",
"version": "v1"
},
{
"created": "Tue, 4 May 1999 04:06:22 GMT",
"version": "v2"
},
{
"created": "Sun, 4 Jul 1999 21:19:55 GMT",
"version": "v3"
},
{
"created": "Fri, 17 Oct 2003 13:27:04 GMT",
"version": "v4"
}
] | 2012-10-09 | [
[
"Zakir",
"Zahid",
"",
"CTPA"
]
] | A generalized version of the Einstein equations in the 4-index form, containing the Riemann tensor linearly, is derived. It is shown, that the gravitational energy-momentum density tensor outside a source is represented across the Weyl tensor vanishing at the 2-index contraction. The 4-index energy-momentum density tensor for matter also is constructed. |
2106.11066 | Anindya Biswas | Anindya Biswas | Joule-Thomson expansion of $AdS$ black holes in
Einstein-power-Yang-Mills gravity | 17 pages, 25 figures, comments are welcome | null | 10.1088/1402-4896/ac2b42 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this paper we study Joule-Thomson $(JT)$ expansion of non-linearly charged
$AdS$ black holes in Einstein-power-Yang-Mills (EPYM) gravity in $D$
dimensions. Within the framework of extended phase space thermodynamics we
identify the cosmological constant as thermodynamic pressure and the black hole
mass with the enthalpy and derive the Joule-Thomson coefficient $\mu$.
Furthermore we have presented equations for inversion curves and the exact
expression for the minimum inversion temperature. We also have calculated the
ratio between the minimum of inversion $T_i^{min}$ and the critical temperature
$T_c$ and obtained the analytic expression for the ratio
$\frac{T_i^{min}}{T_c}$ that depends explicitly on the non-linearity parameter
$q$ and dimension $D$. We consider the isenthalpic curves in the $T- P$ plane
for different values of the fixed black hole mass and obtain heating and
cooling region. Finally we have dealt with two limiting masses which
characterizes the process of Joule-Thomson expansion in the $EPYM$ black holes.
| [
{
"created": "Thu, 17 Jun 2021 21:32:54 GMT",
"version": "v1"
}
] | 2021-11-17 | [
[
"Biswas",
"Anindya",
""
]
] | In this paper we study Joule-Thomson $(JT)$ expansion of non-linearly charged $AdS$ black holes in Einstein-power-Yang-Mills (EPYM) gravity in $D$ dimensions. Within the framework of extended phase space thermodynamics we identify the cosmological constant as thermodynamic pressure and the black hole mass with the enthalpy and derive the Joule-Thomson coefficient $\mu$. Furthermore we have presented equations for inversion curves and the exact expression for the minimum inversion temperature. We also have calculated the ratio between the minimum of inversion $T_i^{min}$ and the critical temperature $T_c$ and obtained the analytic expression for the ratio $\frac{T_i^{min}}{T_c}$ that depends explicitly on the non-linearity parameter $q$ and dimension $D$. We consider the isenthalpic curves in the $T- P$ plane for different values of the fixed black hole mass and obtain heating and cooling region. Finally we have dealt with two limiting masses which characterizes the process of Joule-Thomson expansion in the $EPYM$ black holes. |
1009.0521 | Alessandro Nagar | Luca Baiotti, Thibault Damour, Bruno Giacomazzo, Alessandro Nagar and
Luciano Rezzolla | Analytic modelling of tidal effects in the relativistic inspiral of
binary neutron stars | 4 pages, 2 figures. Version published in Phys. Rev. Lett | Phys.Rev.Lett.105:261101,2010 | 10.1103/PhysRevLett.105.261101 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | To detect the gravitational-wave (GW) signal from binary neutron stars and
extract information about the equation of state of matter at nuclear density,
it is necessary to match the signal with a bank of accurate templates. We
present the two longest (to date) general-relativistic simulations of
equal-mass binary neutron stars with different compactnesses, C=0.12 and
C=0.14, and compare them with a tidal extension of the effective-one-body
(EOB)model. The typical numerical phasing errors over the $\simeq 22$ GW cycles
are $\Delta \phi\simeq \pm 0.24$ rad. By calibrating only one parameter
(representing a higher-order amplification of tidal effects), the EOB model can
reproduce, within the numerical error, the two numerical waveforms essentially
up to the merger. By contrast, the third post-Newtonian Taylor-T4 approximant
with leading-order tidal corrections dephases with respect to the numerical
waveforms by several radians.
| [
{
"created": "Thu, 2 Sep 2010 19:55:46 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Dec 2010 15:41:59 GMT",
"version": "v2"
}
] | 2010-12-28 | [
[
"Baiotti",
"Luca",
""
],
[
"Damour",
"Thibault",
""
],
[
"Giacomazzo",
"Bruno",
""
],
[
"Nagar",
"Alessandro",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | To detect the gravitational-wave (GW) signal from binary neutron stars and extract information about the equation of state of matter at nuclear density, it is necessary to match the signal with a bank of accurate templates. We present the two longest (to date) general-relativistic simulations of equal-mass binary neutron stars with different compactnesses, C=0.12 and C=0.14, and compare them with a tidal extension of the effective-one-body (EOB)model. The typical numerical phasing errors over the $\simeq 22$ GW cycles are $\Delta \phi\simeq \pm 0.24$ rad. By calibrating only one parameter (representing a higher-order amplification of tidal effects), the EOB model can reproduce, within the numerical error, the two numerical waveforms essentially up to the merger. By contrast, the third post-Newtonian Taylor-T4 approximant with leading-order tidal corrections dephases with respect to the numerical waveforms by several radians. |
2211.09886 | Carolina Benone | Haroldo C. D. Lima Junior, Carolina L. Benone, Lu\'is C. B. Crispino | Scalar scattering by black holes and wormholes | null | Eur. Phys. J. C 82 (2022) 7, 638 | 10.1140/epjc/s10052-022-10576-7 | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | We study the scattering of monochromatic planar scalar waves in a geometry
that interpolates between the Schwarzschild solution, regular black holes and
traversable wormhole spacetimes. We employ the partial waves approach to
compute the differential scattering cross section of the regular black hole, as
well as of the wormhole solutions. We compare our full numerical results with
the classical geodesic scattering and the glory approximation, obtaining
excellent agreement in the appropriate regime of validity of such
approximations. We obtain that the differential scattering cross section for
the regular black hole case is similar to the Schwarzschild result.
Notwithstanding, the results for wormholes can be very distinctive from the
black hole ones. In particular, we show that the differential scattering cross
section for wormholes considerably decreases at large scattering angles for
resonant frequencies.
| [
{
"created": "Thu, 17 Nov 2022 20:48:56 GMT",
"version": "v1"
}
] | 2022-11-21 | [
[
"Junior",
"Haroldo C. D. Lima",
""
],
[
"Benone",
"Carolina L.",
""
],
[
"Crispino",
"Luís C. B.",
""
]
] | We study the scattering of monochromatic planar scalar waves in a geometry that interpolates between the Schwarzschild solution, regular black holes and traversable wormhole spacetimes. We employ the partial waves approach to compute the differential scattering cross section of the regular black hole, as well as of the wormhole solutions. We compare our full numerical results with the classical geodesic scattering and the glory approximation, obtaining excellent agreement in the appropriate regime of validity of such approximations. We obtain that the differential scattering cross section for the regular black hole case is similar to the Schwarzschild result. Notwithstanding, the results for wormholes can be very distinctive from the black hole ones. In particular, we show that the differential scattering cross section for wormholes considerably decreases at large scattering angles for resonant frequencies. |
1607.00118 | Yoshimasa Kurihara | Yoshimasa Kurihara | Geometrothermodynamics for Black holes and de Sitter Space | 14 pages | General Relativity and Gravitation 50 (2) (2018) 20 | 10.1007/s10714-018-2341-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this report, a general method to extract thermodynamic quantities from
solutions of the Einstein equation is developed. In 1994, Wald established that
the entropy of a black hole could be identified as a Noether charge associated
with a Killing vector of a global space-time (pseudo-Riemann) manifold. We
reconstruct Wald's method using geometrical language, e.g$.$, via differential
forms defined on the local space-time (Minkowski) manifold. Concurrently, the
abstract thermodynamics are also reconstructed using geometrical terminology,
which is parallel to general relativity. The correspondence between the
thermodynamics and general relativity can be seen clearly by comparing the two
expressions. This comparison requires a modification of Wald's method.
The new method is applied to Schwarzschild, Kerr, and Kerr--Newman black
holes and de Sitter space. The results are consistent with previous results
obtained using various independent methods. This strongly supports the validity
of the area theorem for black holes.
| [
{
"created": "Fri, 1 Jul 2016 06:21:33 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Dec 2016 08:54:59 GMT",
"version": "v2"
},
{
"created": "Thu, 2 Feb 2017 15:11:06 GMT",
"version": "v3"
},
{
"created": "Mon, 6 Mar 2017 16:35:03 GMT",
"version": "v4"
},
{
"crea... | 2018-01-29 | [
[
"Kurihara",
"Yoshimasa",
""
]
] | In this report, a general method to extract thermodynamic quantities from solutions of the Einstein equation is developed. In 1994, Wald established that the entropy of a black hole could be identified as a Noether charge associated with a Killing vector of a global space-time (pseudo-Riemann) manifold. We reconstruct Wald's method using geometrical language, e.g$.$, via differential forms defined on the local space-time (Minkowski) manifold. Concurrently, the abstract thermodynamics are also reconstructed using geometrical terminology, which is parallel to general relativity. The correspondence between the thermodynamics and general relativity can be seen clearly by comparing the two expressions. This comparison requires a modification of Wald's method. The new method is applied to Schwarzschild, Kerr, and Kerr--Newman black holes and de Sitter space. The results are consistent with previous results obtained using various independent methods. This strongly supports the validity of the area theorem for black holes. |
gr-qc/9309012 | James Hartle | James B. Hartle | Unitarity and Causality in Generalized Quantum Mechanics for Non-Chronal
Spacetimes | 40pages, UCSBTH92-04 | Phys.Rev. D49 (1994) 6543-6555 | 10.1103/PhysRevD.49.6543 | null | gr-qc hep-th | null | Spacetime must be foliable by spacelike surfaces for the quantum mechanics of
matter fields to be formulated in terms of a unitarily evolving state vector
defined on spacelike surfaces. When a spacetime cannot be foliated by spacelike
surfaces, as in the case of spacetimes with closed timelike curves, a more
general formulation of quantum mechanics is required. In such generalizations
the transition matrix between alternatives in regions of spacetime where states
{\it can} be defined may be non-unitary. This paper describes a generalized
quantum mechanics whose probabilities consistently obey the rules of
probability theory even in the presence of such non-unitarity. The usual notion
of state on a spacelike surface is lost in this generalization and familiar
notions of causality are modified. There is no signaling outside the light
cone, no non-conservation of energy, no ``Everett phones'', and probabilities
of present events do not depend on particular alternatives of the future.
However, the generalization is acausal in the sense that the existence of
non-chronal regions of spacetime in the future can affect the probabilities of
alternatives today. The detectability of non-unitary evolution and violations
of causality in measurement situations are briefly considered. The evolution of
information in non-chronal spacetimes is described.
| [
{
"created": "Mon, 13 Sep 1993 22:08:57 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Hartle",
"James B.",
""
]
] | Spacetime must be foliable by spacelike surfaces for the quantum mechanics of matter fields to be formulated in terms of a unitarily evolving state vector defined on spacelike surfaces. When a spacetime cannot be foliated by spacelike surfaces, as in the case of spacetimes with closed timelike curves, a more general formulation of quantum mechanics is required. In such generalizations the transition matrix between alternatives in regions of spacetime where states {\it can} be defined may be non-unitary. This paper describes a generalized quantum mechanics whose probabilities consistently obey the rules of probability theory even in the presence of such non-unitarity. The usual notion of state on a spacelike surface is lost in this generalization and familiar notions of causality are modified. There is no signaling outside the light cone, no non-conservation of energy, no ``Everett phones'', and probabilities of present events do not depend on particular alternatives of the future. However, the generalization is acausal in the sense that the existence of non-chronal regions of spacetime in the future can affect the probabilities of alternatives today. The detectability of non-unitary evolution and violations of causality in measurement situations are briefly considered. The evolution of information in non-chronal spacetimes is described. |
gr-qc/0209056 | Nicholas G. Phillips | Nicholas G Phillips and B. L. Hu | Noise Kernel and Stress Energy Bi-Tensor of Quantum Fields in Hot Flat
Space and Gaussian Approximation in the Optical Schwarzschild Metric | 21 pages, RevTeX 4 | Phys.Rev. D67 (2003) 104002 | 10.1103/PhysRevD.67.104002 | null | gr-qc | null | Continuing our investigation of the regularization of the noise kernel in
curved spacetimes [N. G. Phillips and B. L. Hu, Phys. Rev. D {\bf 63}, 104001
(2001)] we adopt the modified point separation scheme for the class of optical
spacetimes using the Gaussian approximation for the Green functions a la
Bekenstein-Parker-Page. In the first example we derive the regularized noise
kernel for a thermal field in flat space. It is useful for black hole
nucleation considerations. In the second example of an optical Schwarzschild
spacetime we obtain a finite expression for the noise kernel at the horizon and
recover the hot flat space result at infinity. Knowledge of the noise kernel is
essential for studying issues related to black hole horizon fluctuations and
Hawking radiation backreaction. We show that the Gaussian approximated Green
function which works surprisingly well for the stress tensor at the
Schwarzschild horizon produces significant error in the noise kernel there. We
identify the failure as occurring at the fourth covariant derivative order.
| [
{
"created": "Tue, 17 Sep 2002 18:10:06 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Phillips",
"Nicholas G",
""
],
[
"Hu",
"B. L.",
""
]
] | Continuing our investigation of the regularization of the noise kernel in curved spacetimes [N. G. Phillips and B. L. Hu, Phys. Rev. D {\bf 63}, 104001 (2001)] we adopt the modified point separation scheme for the class of optical spacetimes using the Gaussian approximation for the Green functions a la Bekenstein-Parker-Page. In the first example we derive the regularized noise kernel for a thermal field in flat space. It is useful for black hole nucleation considerations. In the second example of an optical Schwarzschild spacetime we obtain a finite expression for the noise kernel at the horizon and recover the hot flat space result at infinity. Knowledge of the noise kernel is essential for studying issues related to black hole horizon fluctuations and Hawking radiation backreaction. We show that the Gaussian approximated Green function which works surprisingly well for the stress tensor at the Schwarzschild horizon produces significant error in the noise kernel there. We identify the failure as occurring at the fourth covariant derivative order. |
2203.09092 | Alfredo Herrera-Aguilar | Pritam Banerjee, Alfredo Herrera-Aguilar, Mehrab Momennia and Ulises
Nucamendi | Mass and spin of Kerr black holes in terms of observational quantities:
The dragging effect on the redshift | 14 pages in latex, 3 figures | Phys. Rev. D 105 (2022) 124037 | 10.1103/PhysRevD.105.124037 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we elaborate on the development of a general relativistic
formalism that allows one to analytically express the mass and spin parameters
of the Kerr black hole in terms of observational data: the total redshift and
blueshift of photons emitted by geodesic massive particles revolving the black
hole and their orbital parameters. Thus, we present concise closed formulas for
the mass and spin parameters of the Kerr black hole in terms of few directly
observed quantities in the case of equatorial circular orbits either when the
black hole is static or is moving with respect to a distant observer.
Furthermore, we incorporate the gravitational dragging effect generated by the
rotating nature of the Kerr black hole into the analysis and elucidate its
non-trivial contribution to the expression for the light bending parameter and
the frequency shifts of photons emitted by orbiting particles that renders
simple symmetric expressions for the kinematic redshift and blueshift. We also
incorporate the dependency of the frequency shift on the azimuthal angle, a
fact that allows one to express the total redshift/blueshift along any point of
the orbit of the revolving particle for the cases when the black hole is both
static or moving with respect to us. These formulas allow one to compute the
Kerr black hole parameters by applying this general relativistic formalism to
astrophysical systems like the megamaser accretion disks orbiting supermassive
black holes at the core of active galactic nuclei. Our results open a new
window to implement parameter estimation studies to constrain black hole
variables, and they can be generalized to black hole solutions beyond Einstein
gravity.
| [
{
"created": "Thu, 17 Mar 2022 05:27:52 GMT",
"version": "v1"
},
{
"created": "Sun, 26 Jun 2022 00:13:44 GMT",
"version": "v2"
}
] | 2022-06-30 | [
[
"Banerjee",
"Pritam",
""
],
[
"Herrera-Aguilar",
"Alfredo",
""
],
[
"Momennia",
"Mehrab",
""
],
[
"Nucamendi",
"Ulises",
""
]
] | In this work, we elaborate on the development of a general relativistic formalism that allows one to analytically express the mass and spin parameters of the Kerr black hole in terms of observational data: the total redshift and blueshift of photons emitted by geodesic massive particles revolving the black hole and their orbital parameters. Thus, we present concise closed formulas for the mass and spin parameters of the Kerr black hole in terms of few directly observed quantities in the case of equatorial circular orbits either when the black hole is static or is moving with respect to a distant observer. Furthermore, we incorporate the gravitational dragging effect generated by the rotating nature of the Kerr black hole into the analysis and elucidate its non-trivial contribution to the expression for the light bending parameter and the frequency shifts of photons emitted by orbiting particles that renders simple symmetric expressions for the kinematic redshift and blueshift. We also incorporate the dependency of the frequency shift on the azimuthal angle, a fact that allows one to express the total redshift/blueshift along any point of the orbit of the revolving particle for the cases when the black hole is both static or moving with respect to us. These formulas allow one to compute the Kerr black hole parameters by applying this general relativistic formalism to astrophysical systems like the megamaser accretion disks orbiting supermassive black holes at the core of active galactic nuclei. Our results open a new window to implement parameter estimation studies to constrain black hole variables, and they can be generalized to black hole solutions beyond Einstein gravity. |
gr-qc/9709005 | Madjid Aboolhassani | Majid Abolhasani and Mehdi Golshani | Bohmian Time Versus Probabilistic Time | 8 pages, Revtex, no figures | null | null | null | gr-qc | null | One of the basic peoblems of quantum cosmology is the problem of time.
Various solutions have been proposed for this problem. One approach is to use
the Bohmian time. Another Approach is to use the probabilistic time which was
recently introduced by Castagnino. We consider both of these definitions as
generalizations of a semi-classical time and compare them for a mini-super
space.
| [
{
"created": "Wed, 3 Sep 1997 10:10:08 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Abolhasani",
"Majid",
""
],
[
"Golshani",
"Mehdi",
""
]
] | One of the basic peoblems of quantum cosmology is the problem of time. Various solutions have been proposed for this problem. One approach is to use the Bohmian time. Another Approach is to use the probabilistic time which was recently introduced by Castagnino. We consider both of these definitions as generalizations of a semi-classical time and compare them for a mini-super space. |
2205.12942 | James Wheeler | James Wheeler | On the Definition of Black Holes: Bridging the Gap Between Black Holes
and Singularities | 35 pages, 14 figures | null | 10.1016/j.aop.2023.169356 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A novel perspective on defining black holes designed to be more broadly
applicable outside of asymptotically flat spacetimes, in the context of
classical general relativity, is presented, discussed, and characterized. The
construction formalizes the heuristic idea that black holes are the "past
Cauchy development of the set of singularities". As such, the formulation
depends in a critical way on the identification of singularities, which has
been treated in the literature through various boundary constructions. While
many of the known boundary constructions (e.g. Schmidt's b-boundary or Geroch's
g-boundary) could in principal be cited as underlying one's notion of a black
hole, well-known topological concerns leads us to take the perspective that
Scott and Szekeres' abstract boundary provides the most natural choice. The
framework is utilized to put forward a general, non-IVP formulation of the Weak
Cosmic Censorship Conjecture.
| [
{
"created": "Wed, 25 May 2022 17:45:47 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Feb 2023 21:58:42 GMT",
"version": "v2"
}
] | 2023-06-06 | [
[
"Wheeler",
"James",
""
]
] | A novel perspective on defining black holes designed to be more broadly applicable outside of asymptotically flat spacetimes, in the context of classical general relativity, is presented, discussed, and characterized. The construction formalizes the heuristic idea that black holes are the "past Cauchy development of the set of singularities". As such, the formulation depends in a critical way on the identification of singularities, which has been treated in the literature through various boundary constructions. While many of the known boundary constructions (e.g. Schmidt's b-boundary or Geroch's g-boundary) could in principal be cited as underlying one's notion of a black hole, well-known topological concerns leads us to take the perspective that Scott and Szekeres' abstract boundary provides the most natural choice. The framework is utilized to put forward a general, non-IVP formulation of the Weak Cosmic Censorship Conjecture. |
2308.08997 | Mikhail Khlopunov | M. Khlopunov | Non-local tails in radiation in odd dimensions | 44 pages, 15 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Huygens principle violation in a spacetime of odd dimensions leads to the
fact that the retarded massless fields of localised sources depend on their
history of motion preceding the retarded time. This non-local character of
retarded fields should result into the formation of tail signals in the
radiation of localised sources. In particular, in gravity theories with odd
number of extra spacetime dimensions the gravitational radiation of binary
systems should contain the tail terms. In this work, we demonstrate the
presence of tail signal in radiation within a simple model of scalar field
interacting with the point charge moving on elliptical orbit in three
dimensions. We find that the tail term results into the characteristic
dependence of radiation power of the charge on time. In particular, its
extremum points do not correspond to the moments when the charge passes the
pericenter and apocenter of the orbit, in contrast with the four-dimensional
theory. We obtain the formulae for the shifts of radiation power extremum
points up to the contributions quadratic in the orbital eccentricity. We also
compute the spectral distribution of radiation power of the charge. We find
that in three dimensions the charge on elliptical orbit radiates into the lower
harmonics of the spectrum, compared to the four-dimensional theory. We
conjecture that in higher dimensions the character of spectral distributions is
opposite - the charge mainly radiates into the higher harmonics of the
spectrum.
| [
{
"created": "Thu, 17 Aug 2023 14:09:02 GMT",
"version": "v1"
}
] | 2023-08-23 | [
[
"Khlopunov",
"M.",
""
]
] | Huygens principle violation in a spacetime of odd dimensions leads to the fact that the retarded massless fields of localised sources depend on their history of motion preceding the retarded time. This non-local character of retarded fields should result into the formation of tail signals in the radiation of localised sources. In particular, in gravity theories with odd number of extra spacetime dimensions the gravitational radiation of binary systems should contain the tail terms. In this work, we demonstrate the presence of tail signal in radiation within a simple model of scalar field interacting with the point charge moving on elliptical orbit in three dimensions. We find that the tail term results into the characteristic dependence of radiation power of the charge on time. In particular, its extremum points do not correspond to the moments when the charge passes the pericenter and apocenter of the orbit, in contrast with the four-dimensional theory. We obtain the formulae for the shifts of radiation power extremum points up to the contributions quadratic in the orbital eccentricity. We also compute the spectral distribution of radiation power of the charge. We find that in three dimensions the charge on elliptical orbit radiates into the lower harmonics of the spectrum, compared to the four-dimensional theory. We conjecture that in higher dimensions the character of spectral distributions is opposite - the charge mainly radiates into the higher harmonics of the spectrum. |
2003.04305 | Guo-Ping Li | Xin-Yun Hu, Ke-Jian He, Zhong-Hua Li, Guo-Ping Li | Thermodynamics and weak cosmic censorship conjecture of charged AdS
black hole in the Rastall gravity with pressure | 4 figures; accepted by Chin.Phys. B | null | 10.1088/1674-1056/ab7daa | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Treating the cosmological constant as a dynamical variable, we investigate
the thermodynamics and weak cosmic censorship conjecture (WCCC) of a charged
AdS black hole (BH) in the Rastall gravity. We determine the energy momentum
relation of charged fermion at the horizon of the BH by using the Dirac
equation. Based on this relation, we show that the first law of thermodynamics
(FLT) still holds as a fermion is absorbed by the BH. However, the entropy of
both the extremal and near-extremal BH decreases in the irreversible process,
which means that the second law of thermodynamics (SLT) is violated.
Furthermore, we verify the validity of the WCCC by the minimum values of the
metric function h(r) at its final state. For the extremal charged AdS BH in the
Rastall gravity, we find that the WCCC is valid always since the BH is extreme.
While for the case of near-extremal BH, we find the WCCC could be violable in
the extended phase space (EPS), depending on the value of the parameters of the
BH and their variations.
| [
{
"created": "Sat, 7 Mar 2020 08:16:59 GMT",
"version": "v1"
}
] | 2020-06-24 | [
[
"Hu",
"Xin-Yun",
""
],
[
"He",
"Ke-Jian",
""
],
[
"Li",
"Zhong-Hua",
""
],
[
"Li",
"Guo-Ping",
""
]
] | Treating the cosmological constant as a dynamical variable, we investigate the thermodynamics and weak cosmic censorship conjecture (WCCC) of a charged AdS black hole (BH) in the Rastall gravity. We determine the energy momentum relation of charged fermion at the horizon of the BH by using the Dirac equation. Based on this relation, we show that the first law of thermodynamics (FLT) still holds as a fermion is absorbed by the BH. However, the entropy of both the extremal and near-extremal BH decreases in the irreversible process, which means that the second law of thermodynamics (SLT) is violated. Furthermore, we verify the validity of the WCCC by the minimum values of the metric function h(r) at its final state. For the extremal charged AdS BH in the Rastall gravity, we find that the WCCC is valid always since the BH is extreme. While for the case of near-extremal BH, we find the WCCC could be violable in the extended phase space (EPS), depending on the value of the parameters of the BH and their variations. |
gr-qc/9802028 | Shinji Mukohyama | Shinji Mukohyama, Masafumi Seriu and Hideo Kodama | Entanglement thermodynamics | Latex, 6 pages, Presented at 7th Workshop on General Relativity and
Gravitation, Kyoto, Japan, 27-30 Oct 1997 | null | null | null | gr-qc | null | Entanglement entropy is a statistical entropy measuring information loss due
to coarse-graining corresponding to a spatial division of a system. In this
paper we construct a thermodynamics (entanglement thermodynamics) which
includes the entanglement entropy as the entropy variable, for a massless
scalar field in Minkowski, Schwarzschild and Reissner-Nordstr{\"o}m spacetimes
to understand the statistical origin of black-hole thermodynamics. It is shown
that the entanglement thermodynamics in Minkowski spacetime differs
significantly from black-hole thermodynamics. On the contrary, the entanglement
thermodynamics in Schwarzschild and Reissner-Nordstr{\"o}m spacetimes has close
relevance to black-hole thermodynamics.
| [
{
"created": "Fri, 13 Feb 1998 08:05:13 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Mukohyama",
"Shinji",
""
],
[
"Seriu",
"Masafumi",
""
],
[
"Kodama",
"Hideo",
""
]
] | Entanglement entropy is a statistical entropy measuring information loss due to coarse-graining corresponding to a spatial division of a system. In this paper we construct a thermodynamics (entanglement thermodynamics) which includes the entanglement entropy as the entropy variable, for a massless scalar field in Minkowski, Schwarzschild and Reissner-Nordstr{\"o}m spacetimes to understand the statistical origin of black-hole thermodynamics. It is shown that the entanglement thermodynamics in Minkowski spacetime differs significantly from black-hole thermodynamics. On the contrary, the entanglement thermodynamics in Schwarzschild and Reissner-Nordstr{\"o}m spacetimes has close relevance to black-hole thermodynamics. |
2201.11784 | K{\i}van\c{c} \.Ibrahim \"Unl\"ut\"urk | K{\i}van\c{c} \.I. \"Unl\"ut\"urk and Cem Yeti\c{s}mi\c{s}o\u{g}lu | A model of non-minimally coupled gravitation and electromagnetism in
(1+2) dimensions | This work is dedicated to Tekin Dereli for his 72nd birthday and will
soon appear in his Festschrift in J. Phys. Conf. Ser | null | 10.1088/1742-6596/2191/1/012021 | null | gr-qc hep-th | http://creativecommons.org/licenses/by-nc-nd/4.0/ | Following earlier works of Dereli and collaborators, we study a three
dimensional toy model where we extend the topologically massive gravity with
electrodynamics by the most general $RF^2$-type non-minimal coupling terms.
Here $R$ denotes the possible curvature terms and $F$ denotes the
electromagnetic 2-form. We derive the variational field equations and look for
exact solutions on constant negative curvature space-times with a constant,
self-dual electromagnetic field. The notion of self-dual electromagnetic fields
in three dimensions is introduced by Dereli and collaborators in the study of
exact solutions of models with gravity-electromagnetism couplings. We note the
conditions that the parameters of the model have to satisfy for these self-dual
solutions to exist.
| [
{
"created": "Thu, 27 Jan 2022 19:53:22 GMT",
"version": "v1"
}
] | 2022-02-23 | [
[
"Ünlütürk",
"Kıvanç İ.",
""
],
[
"Yetişmişoğlu",
"Cem",
""
]
] | Following earlier works of Dereli and collaborators, we study a three dimensional toy model where we extend the topologically massive gravity with electrodynamics by the most general $RF^2$-type non-minimal coupling terms. Here $R$ denotes the possible curvature terms and $F$ denotes the electromagnetic 2-form. We derive the variational field equations and look for exact solutions on constant negative curvature space-times with a constant, self-dual electromagnetic field. The notion of self-dual electromagnetic fields in three dimensions is introduced by Dereli and collaborators in the study of exact solutions of models with gravity-electromagnetism couplings. We note the conditions that the parameters of the model have to satisfy for these self-dual solutions to exist. |
2108.13463 | Yen-Wei Liu | Yi-Zen Chu and Yen-Wei Liu | Cherenkov Gravitational Radiation During the Radiation Era | 22 pages, 3 figures; version accepted for publication in Universe | Universe 2021, 7(11), 437 | 10.3390/universe7110437 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cherenkov radiation may occur whenever the source is moving faster than the
waves it generates. In a radiation dominated universe, with equation-of-state
$w = 1/3$, we have recently shown that the Bardeen scalar-metric perturbations
contribute to the linearized Weyl tensor in such a manner that its wavefront
propagates at acoustic speed $\sqrt{w}=1/\sqrt{3}$. In this work, we explicitly
compute the shape of the Bardeen Cherenkov cone and wedge generated
respectively by a supersonic point mass (approximating a primordial black hole)
and a straight Nambu-Goto wire (approximating a cosmic string) moving
perpendicular to its length. When the black hole or cosmic string is moving at
ultra-relativistic speeds, we also calculate explicitly the sudden surge of
scalar-metric induced tidal forces on a pair of test particles due to the
passing Cherenkov shock wave. These forces can stretch or compress, depending
on the orientation of the masses relative to the shock front's normal.
| [
{
"created": "Mon, 30 Aug 2021 18:18:40 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Nov 2021 07:29:15 GMT",
"version": "v2"
}
] | 2021-11-18 | [
[
"Chu",
"Yi-Zen",
""
],
[
"Liu",
"Yen-Wei",
""
]
] | Cherenkov radiation may occur whenever the source is moving faster than the waves it generates. In a radiation dominated universe, with equation-of-state $w = 1/3$, we have recently shown that the Bardeen scalar-metric perturbations contribute to the linearized Weyl tensor in such a manner that its wavefront propagates at acoustic speed $\sqrt{w}=1/\sqrt{3}$. In this work, we explicitly compute the shape of the Bardeen Cherenkov cone and wedge generated respectively by a supersonic point mass (approximating a primordial black hole) and a straight Nambu-Goto wire (approximating a cosmic string) moving perpendicular to its length. When the black hole or cosmic string is moving at ultra-relativistic speeds, we also calculate explicitly the sudden surge of scalar-metric induced tidal forces on a pair of test particles due to the passing Cherenkov shock wave. These forces can stretch or compress, depending on the orientation of the masses relative to the shock front's normal. |
gr-qc/9706050 | Uwe Guenther | U. Guenther, A. Zhuk | Gravitational excitons from extra dimensions | Revised version --- 12 references added, Introduction enlarged, 20
pages, LaTeX, to appear in Phys.Rev.D56 (15.11.97) | Phys.Rev.D56:6391-6402,1997 | 10.1103/PhysRevD.56.6391 | null | gr-qc astro-ph hep-th | null | Inhomogeneous multidimensional cosmological models with a higher dimensional
space-time manifold are investigated under dimensional reduction. In the
Einstein conformal frame, small excitations of the scale factors of the
internal spaces near minima of an effective potential have a form of massive
scalar fields in the external space-time. Parameters of models which ensure
minima of the effective potentials are obtained for particular cases and masses
of gravitational excitons are estimated.
| [
{
"created": "Mon, 16 Jun 1997 22:07:36 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Sep 1997 09:39:41 GMT",
"version": "v2"
}
] | 2011-09-09 | [
[
"Guenther",
"U.",
""
],
[
"Zhuk",
"A.",
""
]
] | Inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold are investigated under dimensional reduction. In the Einstein conformal frame, small excitations of the scale factors of the internal spaces near minima of an effective potential have a form of massive scalar fields in the external space-time. Parameters of models which ensure minima of the effective potentials are obtained for particular cases and masses of gravitational excitons are estimated. |
2309.15778 | Adailton Araújo Filho | A. A. Ara\'ujo Filho, J. A. A. S. Reis, H. Hassanabadi | Exploring antisymmetric tensor effects on black hole shadows and
quasinormal frequencies | 32 pages, 6 figures and 6 tables -- accepted for publication in
Journal of Cosmology and Astroparticle Physics | JCAP 05 (2024) 029 | 10.1088/1475-7516/2024/05/029 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This study explores the impact of antisymmetric tensor effects on spherically
symmetric black holes, investigating photon spheres, shadows, emission rate and
quasinormal frequencies in relation to a parameter which triggers the Lorentz
symmetry breaking. We examine these configurations without and with the
presence of a cosmological constant. In the first scenario, the Lorentz
violation parameter, denoted as $\lambda$, plays a pivotal role in reducing
both the photon sphere and the shadow radius, while also leading to a damping
effect on quasinormal frequencies. Conversely, in the second scenario, as the
values of the cosmological constant ($\Lambda$) increase, we observe an
expansion in the shadow radius. Also, we provide the constraints of the shadows
based on the analysis observational data obtained from the Event Horizon
Telescope (EHT) focusing on Sagittarius $A^{*}$ shadow images. Additionally,
with the increasing $\Lambda$, the associated gravitational wave frequencies
exhibit reduced damping modes.
| [
{
"created": "Wed, 27 Sep 2023 16:52:47 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Nov 2023 15:53:49 GMT",
"version": "v2"
},
{
"created": "Tue, 26 Mar 2024 17:49:49 GMT",
"version": "v3"
}
] | 2024-05-03 | [
[
"Filho",
"A. A. Araújo",
""
],
[
"Reis",
"J. A. A. S.",
""
],
[
"Hassanabadi",
"H.",
""
]
] | This study explores the impact of antisymmetric tensor effects on spherically symmetric black holes, investigating photon spheres, shadows, emission rate and quasinormal frequencies in relation to a parameter which triggers the Lorentz symmetry breaking. We examine these configurations without and with the presence of a cosmological constant. In the first scenario, the Lorentz violation parameter, denoted as $\lambda$, plays a pivotal role in reducing both the photon sphere and the shadow radius, while also leading to a damping effect on quasinormal frequencies. Conversely, in the second scenario, as the values of the cosmological constant ($\Lambda$) increase, we observe an expansion in the shadow radius. Also, we provide the constraints of the shadows based on the analysis observational data obtained from the Event Horizon Telescope (EHT) focusing on Sagittarius $A^{*}$ shadow images. Additionally, with the increasing $\Lambda$, the associated gravitational wave frequencies exhibit reduced damping modes. |
1812.02547 | Alessandro Tronconi | Alexander Y. Kamenshchik, Alessandro Tronconi, Tereza Vardanyan,
Giovanni Venturi | Non-Canonical Inflation and Primordial Black Holes Production | 14 pages, 1 figure. References added. Final version published on PLB | null | 10.1016/j.physletb.2019.02.036 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a mechanism for the amplification of the inflationary scalar
perturbation when the inflaton field action is non-canonical, i.e. the inflaton
kinetic term has a non-standard form. For such a case the speed of sound of the
perturbations generated during inflation is less than one and in general
changes with time. Furthermore in such models, even when the scalar field
potential is negligible, diverse inflationary attractors may exist. The
possible effects of a speed of sound approaching zero during some stage of
inflation may lead to a large amplification for the amplitude of the scalar
spectrum which, on horizon re-entry during the radiation dominated phase, can
collapse and form primordial black holes (PBH) of a mass $M_{\rm BH}\sim
10^{-15}M_{\odot}$ which may constitute a large fraction of the total Dark
Matter (DM) today.
| [
{
"created": "Thu, 6 Dec 2018 14:26:43 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Feb 2019 13:31:26 GMT",
"version": "v2"
}
] | 2019-03-27 | [
[
"Kamenshchik",
"Alexander Y.",
""
],
[
"Tronconi",
"Alessandro",
""
],
[
"Vardanyan",
"Tereza",
""
],
[
"Venturi",
"Giovanni",
""
]
] | We study a mechanism for the amplification of the inflationary scalar perturbation when the inflaton field action is non-canonical, i.e. the inflaton kinetic term has a non-standard form. For such a case the speed of sound of the perturbations generated during inflation is less than one and in general changes with time. Furthermore in such models, even when the scalar field potential is negligible, diverse inflationary attractors may exist. The possible effects of a speed of sound approaching zero during some stage of inflation may lead to a large amplification for the amplitude of the scalar spectrum which, on horizon re-entry during the radiation dominated phase, can collapse and form primordial black holes (PBH) of a mass $M_{\rm BH}\sim 10^{-15}M_{\odot}$ which may constitute a large fraction of the total Dark Matter (DM) today. |
2107.05880 | Andronikos Paliathanasis | Andronikos Paliathanasis | Dynamics in interacting scalar-torsion theory | 19 pages, 4 figures, to appear in Universe, Special Issue: "Probing
the Dark Universe with Theory and Observations" | Universe 2021, 7(7), 244 | 10.3390/universe7070244 | null | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | In a spatially flat \ Friedmann--Lema\^{\i}tre--Robertson--Walker background
space we consider a scalar-torsion gravitational model which has similar
properties with the dilaton theory. This teleparallel model is invariant under
a discrete transformation similar to the Gasperini-Veneziano duality
transformation. Moreover, in the gravitational Action integral we introduce the
Lagrangian function of a pressureless fluid source which is coupled to the
teleparallel dilaton field. This specific gravitational theory with interaction
in the dark sector of the universe is investigated by using methods of the
dynamical system analysis. We calculate that the theory provides various areas
of special interest for the evolution of the cosmological history. Inflationary
scaling solutions and the de Sitter universe is recovered. Furthermore, we
calculate that there exist an attractor which provides a stable solution where
the two fluid components, the scalar field and the pressureless matter,
contribute in the cosmological fluid. This solution is of special interest
because it can describe the present epoch. Finally, the qualitative evolution
of the cosmographic parameters is discussed.
| [
{
"created": "Tue, 13 Jul 2021 07:05:11 GMT",
"version": "v1"
},
{
"created": "Fri, 16 Jul 2021 07:29:14 GMT",
"version": "v2"
}
] | 2021-07-19 | [
[
"Paliathanasis",
"Andronikos",
""
]
] | In a spatially flat \ Friedmann--Lema\^{\i}tre--Robertson--Walker background space we consider a scalar-torsion gravitational model which has similar properties with the dilaton theory. This teleparallel model is invariant under a discrete transformation similar to the Gasperini-Veneziano duality transformation. Moreover, in the gravitational Action integral we introduce the Lagrangian function of a pressureless fluid source which is coupled to the teleparallel dilaton field. This specific gravitational theory with interaction in the dark sector of the universe is investigated by using methods of the dynamical system analysis. We calculate that the theory provides various areas of special interest for the evolution of the cosmological history. Inflationary scaling solutions and the de Sitter universe is recovered. Furthermore, we calculate that there exist an attractor which provides a stable solution where the two fluid components, the scalar field and the pressureless matter, contribute in the cosmological fluid. This solution is of special interest because it can describe the present epoch. Finally, the qualitative evolution of the cosmographic parameters is discussed. |
2101.03520 | Silvia Vicentini | Silvia Vicentini, Massimiliano Rinaldi | Vacuum decay and quadratic gravity: the massive case | calculation details added, comments added, to appear in GERG; 31
pages | Gen Relativ Gravit 54, 22 (2022) | 10.1007/s10714-022-02907-6 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | False vacuum decay in field theory may be formulated as a boundary value
problem in Euclidean space. In a previous work, we studied its solution in
single scalar field theories with quadratic gravity and used it to find
obstructions to vacuum decay. For simplicity, we focused on massless scalar
fields and false vacua with a flat geometry. In this paper, we generalize those
findings to massive scalar fields with the same gravitational interactions,
namely an Einstein-Hilbert term, a quadratic Ricci scalar, and a non-minimal
coupling. We find that the scalar field reaches its asymptotic value faster
than in the massless case, in principle allowing for a wider range of theories
that may accommodate vacuum decay. Nonetheless, this hardly affects the
viability of the bounce in the scenarios here considered. We also briefly
consider other physically interesting theories by including higher-order
kinetic terms and changing the number of spacetime dimensions.
| [
{
"created": "Sun, 10 Jan 2021 10:58:56 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Feb 2021 11:15:09 GMT",
"version": "v2"
},
{
"created": "Mon, 26 Jul 2021 12:05:09 GMT",
"version": "v3"
},
{
"created": "Fri, 4 Feb 2022 10:49:44 GMT",
"version": "v4"
}
] | 2022-02-22 | [
[
"Vicentini",
"Silvia",
""
],
[
"Rinaldi",
"Massimiliano",
""
]
] | False vacuum decay in field theory may be formulated as a boundary value problem in Euclidean space. In a previous work, we studied its solution in single scalar field theories with quadratic gravity and used it to find obstructions to vacuum decay. For simplicity, we focused on massless scalar fields and false vacua with a flat geometry. In this paper, we generalize those findings to massive scalar fields with the same gravitational interactions, namely an Einstein-Hilbert term, a quadratic Ricci scalar, and a non-minimal coupling. We find that the scalar field reaches its asymptotic value faster than in the massless case, in principle allowing for a wider range of theories that may accommodate vacuum decay. Nonetheless, this hardly affects the viability of the bounce in the scenarios here considered. We also briefly consider other physically interesting theories by including higher-order kinetic terms and changing the number of spacetime dimensions. |
2203.11165 | Ali Aghamohammadi | Zahra Ghadiri, Ali Aghamohammadi and Abdollah Refaei | Constraints of anisotropy on warm power-law inflation in light of Planck
results | 16 page, 6 figures | Iranian Journal of Astronomy and Astrophysics 2021 | 10.22128/IJAA.2021.479.1103 | Vol. 8, No. 1, Spring 2021 | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this article, we examine the effects of anisotropy on a model of canonical
warm inflation with the power-law potential. The results of this model are
compared to Planck satellite observational data. Using a conventional local
scalar fi?eld in the Bianchi type I metric, the slow-roll conditions and the
suitable regions, where the free parameters of the model show a good agreement
with Planck results, are investigated in detail. Following the usual
calculations for warm inflationary approaches, the early universe in two
different dissipative regimes, namely the weak dissipative and the strong
dissipative ones, is investigated. In this regard, the slow-roll parameters and
their observational indices in both regimes are obtained and finally, it is
shown that this model is in good agreement with observatio
| [
{
"created": "Mon, 21 Mar 2022 17:44:36 GMT",
"version": "v1"
}
] | 2022-05-05 | [
[
"Ghadiri",
"Zahra",
""
],
[
"Aghamohammadi",
"Ali",
""
],
[
"Refaei",
"Abdollah",
""
]
] | In this article, we examine the effects of anisotropy on a model of canonical warm inflation with the power-law potential. The results of this model are compared to Planck satellite observational data. Using a conventional local scalar fi?eld in the Bianchi type I metric, the slow-roll conditions and the suitable regions, where the free parameters of the model show a good agreement with Planck results, are investigated in detail. Following the usual calculations for warm inflationary approaches, the early universe in two different dissipative regimes, namely the weak dissipative and the strong dissipative ones, is investigated. In this regard, the slow-roll parameters and their observational indices in both regimes are obtained and finally, it is shown that this model is in good agreement with observatio |
gr-qc/9801051 | S. Antoci | S. Antoci | Microscopic Fields and Macroscopic Averages in Einstein's Unified Field
Theory | 22 pages, plain TeX | AnnalesFond.Broglie21:11-38,1996 | null | null | gr-qc | null | The relation between microscopic and macroscopic entities in the generally
covariant theories is considered, and it is argued that a sensible definition
of the macroscopic averages requires a restriction of the allowed
transformations of coordinates. Spacetime averages of the geometric objects of
Einstein's unified field theory are then defined, and the reconstruction of
some features of macroscopic reality from hypothetic microscopic structures is
attempted. It is shown how a fluctuating microscopic behaviour of the metric
field can rule the constitutive relation for electromagnetism both in vacuo and
in nondispersive material media. Moreover, if both the metric and the skew
tensor density that represents the electric displacement and the magnetic field
are assumed to possess a wavy microscopic structure, nonvanishing generalized
force densities can appear in the continuum. They originate from a resonance
process, in which at least three waves need to be involved. This process only
occurs if the wavevectors fulfil the three-wave resonance condition, so
ubiquitous in quantum physics. The wavy behaviour of the metric is essential
for the occurrence of this resonance phenomenon.
| [
{
"created": "Thu, 15 Jan 1998 09:29:21 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Antoci",
"S.",
""
]
] | The relation between microscopic and macroscopic entities in the generally covariant theories is considered, and it is argued that a sensible definition of the macroscopic averages requires a restriction of the allowed transformations of coordinates. Spacetime averages of the geometric objects of Einstein's unified field theory are then defined, and the reconstruction of some features of macroscopic reality from hypothetic microscopic structures is attempted. It is shown how a fluctuating microscopic behaviour of the metric field can rule the constitutive relation for electromagnetism both in vacuo and in nondispersive material media. Moreover, if both the metric and the skew tensor density that represents the electric displacement and the magnetic field are assumed to possess a wavy microscopic structure, nonvanishing generalized force densities can appear in the continuum. They originate from a resonance process, in which at least three waves need to be involved. This process only occurs if the wavevectors fulfil the three-wave resonance condition, so ubiquitous in quantum physics. The wavy behaviour of the metric is essential for the occurrence of this resonance phenomenon. |
1108.4242 | Shinji Tsujikawa | Antonio De Felice, Tsutomu Kobayashi, Shinji Tsujikawa | Effective gravitational couplings for cosmological perturbations in the
most general scalar-tensor theories with second-order field equations | 12 pages, no figures | Phys.Lett.B706:123-133, 2011 | 10.1016/j.physletb.2011.11.028 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the Horndeski's most general scalar-tensor theories the equations of
scalar density perturbations are derived in the presence of non-relativistic
matter minimally coupled to gravity. Under a quasi-static approximation on
sub-horizon scales we obtain the effective gravitational coupling $G_{eff}$
associated with the growth rate of matter perturbations as well as the
effective gravitational potential $\Phi_{eff}$ relevant to the deviation of
light rays. We then apply our formulas to a number of modified gravitational
models of dark energy--such as those based on f(R) theories, Brans-Dicke
theories, kinetic gravity braidings, covariant Galileons, and field derivative
couplings with the Einstein tensor. Our results are useful to test the
large-distance modification of gravity from the future high-precision
observations of large-scale structure, weak lensing, and cosmic microwave
background.
| [
{
"created": "Mon, 22 Aug 2011 06:57:00 GMT",
"version": "v1"
},
{
"created": "Sat, 26 Nov 2011 15:23:17 GMT",
"version": "v2"
}
] | 2015-05-30 | [
[
"De Felice",
"Antonio",
""
],
[
"Kobayashi",
"Tsutomu",
""
],
[
"Tsujikawa",
"Shinji",
""
]
] | In the Horndeski's most general scalar-tensor theories the equations of scalar density perturbations are derived in the presence of non-relativistic matter minimally coupled to gravity. Under a quasi-static approximation on sub-horizon scales we obtain the effective gravitational coupling $G_{eff}$ associated with the growth rate of matter perturbations as well as the effective gravitational potential $\Phi_{eff}$ relevant to the deviation of light rays. We then apply our formulas to a number of modified gravitational models of dark energy--such as those based on f(R) theories, Brans-Dicke theories, kinetic gravity braidings, covariant Galileons, and field derivative couplings with the Einstein tensor. Our results are useful to test the large-distance modification of gravity from the future high-precision observations of large-scale structure, weak lensing, and cosmic microwave background. |
1809.00795 | Masashi Kimura | Masashi Kimura and Takahiro Tanaka | Stability analysis of black holes by the $S$-deformation method for
coupled systems | 26 pages, 9 figures, v2: minor revisions, v3: minor revisions, to
appear in Classical and Quantum Gravity | null | 10.1088/1361-6382/ab0193 | KUNS-2735, YITP-18-97 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a simple method to prove the linear mode stability of a black hole
when the perturbed field equations take the form of a system of coupled
Schr\"odinger equations. The linear mode stability of the spacetime is
guaranteed by the existence of an appropriate $S$-deformation. Such an
$S$-deformation is related to the Riccati transformation of a solution to the
Schr\"odinger system with zero energy. We apply this formalism to some examples
and numerically study their stability.
| [
{
"created": "Tue, 4 Sep 2018 04:50:27 GMT",
"version": "v1"
},
{
"created": "Wed, 12 Sep 2018 05:20:27 GMT",
"version": "v2"
},
{
"created": "Fri, 25 Jan 2019 06:23:10 GMT",
"version": "v3"
}
] | 2019-02-20 | [
[
"Kimura",
"Masashi",
""
],
[
"Tanaka",
"Takahiro",
""
]
] | We propose a simple method to prove the linear mode stability of a black hole when the perturbed field equations take the form of a system of coupled Schr\"odinger equations. The linear mode stability of the spacetime is guaranteed by the existence of an appropriate $S$-deformation. Such an $S$-deformation is related to the Riccati transformation of a solution to the Schr\"odinger system with zero energy. We apply this formalism to some examples and numerically study their stability. |
0708.0450 | Hiroyuki Nakano | Hiroyuki Nakano, Kunihito Ioka | Second Order Quasi-Normal Mode of the Schwarzschild Black Hole | 23 pages, no figure | Phys.Rev.D76:084007,2007 | 10.1103/PhysRevD.76.084007 | null | gr-qc astro-ph | null | We formulate and calculate the second order quasi-normal modes (QNMs) of a
Schwarzschild black hole (BH). Gravitational wave (GW) from a distorted BH, so
called ringdown, is well understood as QNMs in general relativity. Since QNMs
from binary BH mergers will be detected with high signal-to-noise ratio by GW
detectors, it is also possible to detect the second perturbative order of QNMs,
generated by nonlinear gravitational interaction near the BH. In the BH
perturbation approach, we derive the master Zerilli equation for the metric
perturbation to second order and explicitly regularize it at the horizon and
spatial infinity. We numerically solve the second order Zerilli equation by
implementing the modified Leaver's continued fraction method. The second order
QNM frequencies are found to be twice the first order ones, and the GW
amplitude is up to $\sim 10%$ that of the first order for the binary BH
mergers. Since the second order QNMs always exist, we can use their detections
(i) to test the nonlinearity of general relativity, in particular the no-hair
theorem, (ii) to remove fake events in the data analysis of QNM GWs and (iii)
to measure the distance to the BH.
| [
{
"created": "Fri, 3 Aug 2007 03:13:51 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Nakano",
"Hiroyuki",
""
],
[
"Ioka",
"Kunihito",
""
]
] | We formulate and calculate the second order quasi-normal modes (QNMs) of a Schwarzschild black hole (BH). Gravitational wave (GW) from a distorted BH, so called ringdown, is well understood as QNMs in general relativity. Since QNMs from binary BH mergers will be detected with high signal-to-noise ratio by GW detectors, it is also possible to detect the second perturbative order of QNMs, generated by nonlinear gravitational interaction near the BH. In the BH perturbation approach, we derive the master Zerilli equation for the metric perturbation to second order and explicitly regularize it at the horizon and spatial infinity. We numerically solve the second order Zerilli equation by implementing the modified Leaver's continued fraction method. The second order QNM frequencies are found to be twice the first order ones, and the GW amplitude is up to $\sim 10%$ that of the first order for the binary BH mergers. Since the second order QNMs always exist, we can use their detections (i) to test the nonlinearity of general relativity, in particular the no-hair theorem, (ii) to remove fake events in the data analysis of QNM GWs and (iii) to measure the distance to the BH. |
1809.10935 | Aya Iyonaga | Aya Iyonaga, Kazufumi Takahashi, Tsutomu Kobayashi | Extended Cuscuton: Formulation | 18 pages | JCAP 12 (2018) 002 | 10.1088/1475-7516/2018/12/002 | RUP-18-30 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Among single-field scalar-tensor theories, there is a special class called
"cuscuton," which is represented as some limiting case of k-essence in general
relativity. This theory has a remarkable feature that the number of propagating
degrees of freedom is only two in the unitary gauge in contrast to ordinary
scalar-tensor theories with three degrees of freedom. We specify a general
class of theories with the same property as the cuscuton in the context of the
beyond Horndeski theory, which we dub as the extended cuscuton. We also study
cosmological perturbations in the presence of matter in these extended cuscuton
theories.
| [
{
"created": "Fri, 28 Sep 2018 09:48:51 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Dec 2018 08:03:17 GMT",
"version": "v2"
}
] | 2018-12-06 | [
[
"Iyonaga",
"Aya",
""
],
[
"Takahashi",
"Kazufumi",
""
],
[
"Kobayashi",
"Tsutomu",
""
]
] | Among single-field scalar-tensor theories, there is a special class called "cuscuton," which is represented as some limiting case of k-essence in general relativity. This theory has a remarkable feature that the number of propagating degrees of freedom is only two in the unitary gauge in contrast to ordinary scalar-tensor theories with three degrees of freedom. We specify a general class of theories with the same property as the cuscuton in the context of the beyond Horndeski theory, which we dub as the extended cuscuton. We also study cosmological perturbations in the presence of matter in these extended cuscuton theories. |
gr-qc/9510047 | Luis J. Garay | Carlos Barcelo, Luis J. Garay, Pedro F. Gonzalez-Diaz, Guillermo A.
Mena Marugan | Asymptotically anti-de Sitter wormholes | 10 pages, RevTeX 3.0, LaTeX 2.09 | Phys.Rev. D53 (1996) 3162-3171 | 10.1103/PhysRevD.53.3162 | Imperial/TP/95--96/06 | gr-qc | null | Starting with a procedure for dealing with general asymptotic behaviors, we
construct a quantum theory for asymptotically anti-de Sitter wormholes. We
follow both the path integral formalism and the algebraic quantization program
proposed by Ashtekar. By adding suitable surface terms, the Euclidean action of
the asymptoically anti-de Sitter wormholes can be seen to be finite and gauge
invariant. This action determines an appropriate variational problem for
wormholes. We also obtain the wormhole wave functions of the gravitational
model and show that all the physical states of the quantum theory are
superpositions of wormhole states.
| [
{
"created": "Tue, 24 Oct 1995 15:20:37 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Barcelo",
"Carlos",
""
],
[
"Garay",
"Luis J.",
""
],
[
"Gonzalez-Diaz",
"Pedro F.",
""
],
[
"Marugan",
"Guillermo A. Mena",
""
]
] | Starting with a procedure for dealing with general asymptotic behaviors, we construct a quantum theory for asymptotically anti-de Sitter wormholes. We follow both the path integral formalism and the algebraic quantization program proposed by Ashtekar. By adding suitable surface terms, the Euclidean action of the asymptoically anti-de Sitter wormholes can be seen to be finite and gauge invariant. This action determines an appropriate variational problem for wormholes. We also obtain the wormhole wave functions of the gravitational model and show that all the physical states of the quantum theory are superpositions of wormhole states. |
1602.04969 | Guillem Dom\`enech | Guillem Dom\`enech and Misao Sasaki | Stationary bubbles: information loss paradox? | Parallel talk given at the 2nd LeCosPA Symposium: Everything about
Gravity | null | 10.1142/9789813203952_0080 | YITP-16-12 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The main purpose of this work is to build classically stationary bubbles,
within the thin-shell formalism, which are unstable under quantum effects; they
either collapse into a black hole or expand. Thus, the final state can be
thought of a superposition of geometries. We point out that, from a quantum
mechanical point of view, there is no issue with a loss of information in such
configuration. A classical observer sees a definite geometry and, hence, finds
an effective loss of information. Although it does not cover all possible
cases, we emphasise the role of semi-classical gravitational effects, mediated
by instatons, in alleviating/solving the information loss paradox.
| [
{
"created": "Tue, 16 Feb 2016 10:02:26 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Feb 2016 02:03:18 GMT",
"version": "v2"
}
] | 2019-02-27 | [
[
"Domènech",
"Guillem",
""
],
[
"Sasaki",
"Misao",
""
]
] | The main purpose of this work is to build classically stationary bubbles, within the thin-shell formalism, which are unstable under quantum effects; they either collapse into a black hole or expand. Thus, the final state can be thought of a superposition of geometries. We point out that, from a quantum mechanical point of view, there is no issue with a loss of information in such configuration. A classical observer sees a definite geometry and, hence, finds an effective loss of information. Although it does not cover all possible cases, we emphasise the role of semi-classical gravitational effects, mediated by instatons, in alleviating/solving the information loss paradox. |
2108.01533 | Alexander Zakharov | Alexander F. Zakharov | Constraints on a tidal charge of the supermassive black hole in M87*
with the EHT observations in April 2017 | 8 pages, 1 figure, revised according to the version published in
Universe | Universe vol. 8, issue 3, id. 141 (2022) | 10.3390/universe8030141 | null | gr-qc astro-ph.CO astro-ph.GA | http://creativecommons.org/publicdomain/zero/1.0/ | More than two years ago the Event Horizon Telescope collaboration presented
the first image reconstruction around the shadow for the supermassive black
hole in M87*. It gives an opportunity to evaluate the shadow size. Recently,
the Event Horizon Telescope collaboration constrained parameters ("charges") of
spherical symmetrical metrics of black holes from an estimated allowed interval
for shadow radius from observations of M87* in 2017. Earlier, analytical
expressions for the shadow radius as a function of charge (including a tidal
one) in the case of Reissner--Nordstr\"om metric have been obtained. Some time
ago, Bin-Nun proposed to apply a Reissner--Nordstr\"om metric with a tidal
charge as an alternative to the Schwarzschild metric in Sgr~A*. If we assume
that a Reissner--Nordstr\"om black hole with a tidal charge exists in M87*,
therefore, based on results of the shadow size evaluation for M87* done by the
Event Horizon Telescope collaboration we constrain a tidal charge. Similarly,
we evaluate a tidal charge from shadow size estimates for Sgr~A*.
| [
{
"created": "Tue, 3 Aug 2021 14:32:55 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Mar 2022 07:51:59 GMT",
"version": "v2"
}
] | 2022-03-08 | [
[
"Zakharov",
"Alexander F.",
""
]
] | More than two years ago the Event Horizon Telescope collaboration presented the first image reconstruction around the shadow for the supermassive black hole in M87*. It gives an opportunity to evaluate the shadow size. Recently, the Event Horizon Telescope collaboration constrained parameters ("charges") of spherical symmetrical metrics of black holes from an estimated allowed interval for shadow radius from observations of M87* in 2017. Earlier, analytical expressions for the shadow radius as a function of charge (including a tidal one) in the case of Reissner--Nordstr\"om metric have been obtained. Some time ago, Bin-Nun proposed to apply a Reissner--Nordstr\"om metric with a tidal charge as an alternative to the Schwarzschild metric in Sgr~A*. If we assume that a Reissner--Nordstr\"om black hole with a tidal charge exists in M87*, therefore, based on results of the shadow size evaluation for M87* done by the Event Horizon Telescope collaboration we constrain a tidal charge. Similarly, we evaluate a tidal charge from shadow size estimates for Sgr~A*. |
2408.03793 | Paolo Massimo Bassani | Paolo M Bassani, Joao Magueijo and Shinji Mukohyama | Violations of energy conservation in Horava-Lifshitz gravity: a new
ingredient in the dark matter puzzle | null | null | null | null | gr-qc astro-ph.GA | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We investigate the interplay between Horava-Lifshitz (HL) gravity and more
general theories where the local Hamiltonian constraint is lost, for example
due to the time variability of the Lagrangian (e.g. via its parameters) where
time is defined on a foliation according to a prescription mimicking Lambda and
4-volume time in unimodualr gravity. In one direction we subject the multitude
of parameters in HL to this variability game, mimicking RG flow in a
cosmological setting. In the opposite direction, we examine the evolution on
the left-over Hamiltonian should the HL algebra of constraints be still
applicable, rather than the algebra of General Relativity being restored.
Within the projectable theory, the non-vanishing Hamiltonian can be
reinterpreted as a pressureless fluid. Unlike in theories with similar
variability based on GR, violations of stress-energy tensor conservation
persist, and these are computed here for the full class of projectable HL
models. The phenomenological implications are examined: remarkably the driven
solutions resulting from these energy conservation violations have the correct
profiles to flatten the galactic rotation curves in a toy model. Unfortunately
this interesting remark does not survive closer scrutiny: neither is the driven
solution an attractor, nor does it have the right sign for acceptable values of
the HL parameter, certainly for the simplest terms examined. Yet, in this paper
we have established a new ingredient in the dark matter mystery, the
possibility of energy conservation violation.
| [
{
"created": "Wed, 7 Aug 2024 14:19:45 GMT",
"version": "v1"
}
] | 2024-08-08 | [
[
"Bassani",
"Paolo M",
""
],
[
"Magueijo",
"Joao",
""
],
[
"Mukohyama",
"Shinji",
""
]
] | We investigate the interplay between Horava-Lifshitz (HL) gravity and more general theories where the local Hamiltonian constraint is lost, for example due to the time variability of the Lagrangian (e.g. via its parameters) where time is defined on a foliation according to a prescription mimicking Lambda and 4-volume time in unimodualr gravity. In one direction we subject the multitude of parameters in HL to this variability game, mimicking RG flow in a cosmological setting. In the opposite direction, we examine the evolution on the left-over Hamiltonian should the HL algebra of constraints be still applicable, rather than the algebra of General Relativity being restored. Within the projectable theory, the non-vanishing Hamiltonian can be reinterpreted as a pressureless fluid. Unlike in theories with similar variability based on GR, violations of stress-energy tensor conservation persist, and these are computed here for the full class of projectable HL models. The phenomenological implications are examined: remarkably the driven solutions resulting from these energy conservation violations have the correct profiles to flatten the galactic rotation curves in a toy model. Unfortunately this interesting remark does not survive closer scrutiny: neither is the driven solution an attractor, nor does it have the right sign for acceptable values of the HL parameter, certainly for the simplest terms examined. Yet, in this paper we have established a new ingredient in the dark matter mystery, the possibility of energy conservation violation. |
gr-qc/9903027 | Massar Serge | S. Massar and R. Parentani | How the Change in Horizon Area Drives Black Hole Evaporation | 26 pages latex, extensively revised version of gr-qc/9801043.
Definitive version to be published in Nucl. Phys. B | Nucl.Phys. B575 (2000) 333-356 | 10.1016/S0550-3213(00)00067-5 | THU-98/03 and ULB-TH/99-05 | gr-qc hep-th | null | We rephrase the derivation of black hole radiation so as to take into
account, at the level of transition amplitudes, the change of the geometry
induced by the emission process. This enlarged description reveals that the
dynamical variables which govern the emission are the horizon area and its
conjugate time variable. Their conjugation is established through the boundary
term at the horizon which must be added to the canonical action of general
relativity in order to obtain a well defined action principle when the area
varies. These coordinates have already been used by Teitelboim and
collaborators to compute the partition function of a black hole. We use them to
show that the probability to emit a particle is given by $e^{- \Delta A/4}$
where $\Delta A$ is the decrease in horizon area induced by the emission. This
expression improves Hawking result which is governed by a temperature (given by
the surface gravity) in that the specific heat of the black hole is no longer
neglected. The present derivation of quantum black hole radiation is based on
the same principles which are used to derive the first law of classical black
hole thermodynamics. Moreover it also applies to quantum processes associated
with cosmological or acceleration horizons. These two results indicate that not
only black holes but all event horizons possess an entropy which governs
processes according to quantum statistical thermodynamics.
| [
{
"created": "Mon, 8 Mar 1999 09:26:38 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Jan 2000 10:15:28 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Massar",
"S.",
""
],
[
"Parentani",
"R.",
""
]
] | We rephrase the derivation of black hole radiation so as to take into account, at the level of transition amplitudes, the change of the geometry induced by the emission process. This enlarged description reveals that the dynamical variables which govern the emission are the horizon area and its conjugate time variable. Their conjugation is established through the boundary term at the horizon which must be added to the canonical action of general relativity in order to obtain a well defined action principle when the area varies. These coordinates have already been used by Teitelboim and collaborators to compute the partition function of a black hole. We use them to show that the probability to emit a particle is given by $e^{- \Delta A/4}$ where $\Delta A$ is the decrease in horizon area induced by the emission. This expression improves Hawking result which is governed by a temperature (given by the surface gravity) in that the specific heat of the black hole is no longer neglected. The present derivation of quantum black hole radiation is based on the same principles which are used to derive the first law of classical black hole thermodynamics. Moreover it also applies to quantum processes associated with cosmological or acceleration horizons. These two results indicate that not only black holes but all event horizons possess an entropy which governs processes according to quantum statistical thermodynamics. |
1708.05600 | Gr\'egoire Martinon | Gr\'egoire Martinon | The instability of anti-de Sitter space-time | Topical review, 58 pages, 37 figures, 1 table | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this review, we retrace the recent progress in the anti-de Sitter (AdS)
instability problem. By instability we mean that for large classes of initial
data, any perturbation of AdS space-time, however small, leads to the formation
of a black hole. Since the seminal work of Bizo\'n and Rostworowski in 2011,
many different kinds of numerical experiments were performed in asymptotically
AdS space-times, unveiling a very intricate structure of the instability. In
particular, many efforts were dedicated to the search of islands of stability,
i.e.\ families of initial data that resist black hole formation. Many
analytical and numerical tools were deployed to disentangle stable from
unstable initial data, and shed new light on the necessary and sufficient
conditions for collapse. Recently, research beyond spherical symmetry became
more and more engaged. This is a very promising channel of investigation toward
a deeper understanding of the gravitational dynamics in asymptotically AdS
space-times.
| [
{
"created": "Fri, 18 Aug 2017 13:29:09 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Aug 2017 15:43:04 GMT",
"version": "v2"
},
{
"created": "Mon, 18 Sep 2017 12:39:05 GMT",
"version": "v3"
}
] | 2017-09-19 | [
[
"Martinon",
"Grégoire",
""
]
] | In this review, we retrace the recent progress in the anti-de Sitter (AdS) instability problem. By instability we mean that for large classes of initial data, any perturbation of AdS space-time, however small, leads to the formation of a black hole. Since the seminal work of Bizo\'n and Rostworowski in 2011, many different kinds of numerical experiments were performed in asymptotically AdS space-times, unveiling a very intricate structure of the instability. In particular, many efforts were dedicated to the search of islands of stability, i.e.\ families of initial data that resist black hole formation. Many analytical and numerical tools were deployed to disentangle stable from unstable initial data, and shed new light on the necessary and sufficient conditions for collapse. Recently, research beyond spherical symmetry became more and more engaged. This is a very promising channel of investigation toward a deeper understanding of the gravitational dynamics in asymptotically AdS space-times. |
1406.1541 | Sergey Pavluchenko A. | Fabrizio Canfora, Alex Giacomini, and Sergey A. Pavluchenko | Cosmological dynamics of gravitating hadron matter | 20 pages, 5 figures; typos corrected and a comment added in the last
section. Version accepted for publication in Phys. Rev. D | Phys. Rev. D 90, 043516 (2014) | 10.1103/PhysRevD.90.043516 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Anisotropic cosmologies are studied in the case where the matter source is
given by the Skyrme model which is an effective description of low energy QCD.
The dynamical evolution of the Kantowski-Sachs and Bianchi-I universes are
analyzed in depth. In both situations in order for solutions to exist and at
the same time to avoid finite time future singularities, bounds on the value of
the cosmological constant and on the values of the Skyrme couplings must be
set. The upper bound on the cosmological constant, which depends also on the
initial conditions is closely related to the fact that the baryons appear below
1 GeV. The upper bound on the cosmological constant is actually 72 orders of
magnitudes lower than the standard estimations from quantum field theory. The
lower bound on the cosmological constant and the bounds on the Skyrme couplings
are due to the peculiar combination of nonlinear terms in the Skyrme model. It
is worth to point out that bounds on the Skyrme couplings occur in similar
fashion both for the Kantowski-Sachs and for the Bianchi-I models which are
topologically completely different. Our results suggest that this behavior is
intrinsic to the coupling of the Skyrme field to gravity rather than on a
specific cosmological model.
| [
{
"created": "Thu, 5 Jun 2014 23:01:15 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Aug 2014 12:52:03 GMT",
"version": "v2"
}
] | 2014-08-19 | [
[
"Canfora",
"Fabrizio",
""
],
[
"Giacomini",
"Alex",
""
],
[
"Pavluchenko",
"Sergey A.",
""
]
] | Anisotropic cosmologies are studied in the case where the matter source is given by the Skyrme model which is an effective description of low energy QCD. The dynamical evolution of the Kantowski-Sachs and Bianchi-I universes are analyzed in depth. In both situations in order for solutions to exist and at the same time to avoid finite time future singularities, bounds on the value of the cosmological constant and on the values of the Skyrme couplings must be set. The upper bound on the cosmological constant, which depends also on the initial conditions is closely related to the fact that the baryons appear below 1 GeV. The upper bound on the cosmological constant is actually 72 orders of magnitudes lower than the standard estimations from quantum field theory. The lower bound on the cosmological constant and the bounds on the Skyrme couplings are due to the peculiar combination of nonlinear terms in the Skyrme model. It is worth to point out that bounds on the Skyrme couplings occur in similar fashion both for the Kantowski-Sachs and for the Bianchi-I models which are topologically completely different. Our results suggest that this behavior is intrinsic to the coupling of the Skyrme field to gravity rather than on a specific cosmological model. |
1210.8430 | Alexander Zhidenko | R. A. Konoplya, A. Zhidenko | Radiation processes in the vicinity of non-Schwarzschild and non-Kerr
black holes | 12 pages, 5 figures | Phys. Rev. D 87, 024044 (2013) | 10.1103/PhysRevD.87.024044 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Usually alternative theories of gravity imply deviations from the well-known
Kerr space-time, a model of an isolated black hole in General Relativity. In
the dominant order, the deformed Kerr metric, free of closed time-like curves
outside the event horizon, has been suggested recently by Johannsen and
Psaltis. It has a single deformation parameter which is not constrained by the
current observations, allowing, thereby, for a kind of unified and simple
phenomenological description of black holes in various theories of gravity.
Here we consider a number of classical and quantum phenomena of radiation in
the vicinity of such deformed Schwarzschild-like and Kerr-like black holes:
spiralling of particles into black holes, decay of fields propagating in the
black hole's background, Hawking radiation. In particular, we calculate some
quantitative characteristics of the above phenomena, such as the binding energy
of particles, quasinormal modes, late-time tails of fields of various spin,
intensity of Hawking radiation. The binding energy released when a particle
goes over from a given stable orbit in the equatorial plane to the innermost
stable one is calculated for such non-Kerr black holes. Due to inseparability
of the wave equations in the general case, the perturbations and stability of
scalar, Dirac, and electromagnetic fields are analyzed for vanishing rotation
only. The dependence of the radiation phenomena on the deformation parameter is
discussed.
| [
{
"created": "Wed, 31 Oct 2012 18:33:02 GMT",
"version": "v1"
},
{
"created": "Sat, 3 Nov 2012 15:08:26 GMT",
"version": "v2"
},
{
"created": "Wed, 9 Jan 2013 16:15:42 GMT",
"version": "v3"
}
] | 2013-02-06 | [
[
"Konoplya",
"R. A.",
""
],
[
"Zhidenko",
"A.",
""
]
] | Usually alternative theories of gravity imply deviations from the well-known Kerr space-time, a model of an isolated black hole in General Relativity. In the dominant order, the deformed Kerr metric, free of closed time-like curves outside the event horizon, has been suggested recently by Johannsen and Psaltis. It has a single deformation parameter which is not constrained by the current observations, allowing, thereby, for a kind of unified and simple phenomenological description of black holes in various theories of gravity. Here we consider a number of classical and quantum phenomena of radiation in the vicinity of such deformed Schwarzschild-like and Kerr-like black holes: spiralling of particles into black holes, decay of fields propagating in the black hole's background, Hawking radiation. In particular, we calculate some quantitative characteristics of the above phenomena, such as the binding energy of particles, quasinormal modes, late-time tails of fields of various spin, intensity of Hawking radiation. The binding energy released when a particle goes over from a given stable orbit in the equatorial plane to the innermost stable one is calculated for such non-Kerr black holes. Due to inseparability of the wave equations in the general case, the perturbations and stability of scalar, Dirac, and electromagnetic fields are analyzed for vanishing rotation only. The dependence of the radiation phenomena on the deformation parameter is discussed. |
2307.08503 | Faizuddin Ahmed | Faizuddin Ahmed | Geodesics motion of test particles around Schwarzschild-Klinkhamer
wormhole with topological defects and gravitational lensing | 23 pages, 8 figures, published in Journal of Cosmology and
Astroparticle Physics (https://doi.org/10.1088/1475-7516/2023/11/010) | JCAP11(2023)010 | 10.1088/1475-7516/2023/11/010 | null | gr-qc astro-ph.HE hep-th | http://creativecommons.org/licenses/by/4.0/ | This study investigates the geodesic motion of test particles, both massless
and massive, within a Schwarzschild-Klinkhamer (SK) wormhole space-time. We
specifically consider the influence of cosmic strings on the system and analyze
the effective potential, and observing that the presence of a cosmic string
parameter alters it for null and time-like geodesics. Moreover, we calculate
the deflection angle for null geodesics, and demonstrate that the cosmic string
modifies this angle and induces a shift in the results. Additionally, we extend
our investigation in this SK-wormhole space-time but with a global monopole. We
explore the geodesic motion of test particles in this scenario and find that
the effective potential is affected by the global monopole. Similarly, we
determine the deflection angle for null geodesics and show that the global
monopole parameter introduces modifications to this angle. Lastly, we present
several known solutions for space-times involving cosmic strings and global
monopoles within the framework of this SK-wormhole.
| [
{
"created": "Mon, 17 Jul 2023 14:06:00 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Jul 2023 04:26:53 GMT",
"version": "v2"
},
{
"created": "Tue, 7 Nov 2023 15:48:00 GMT",
"version": "v3"
}
] | 2023-11-08 | [
[
"Ahmed",
"Faizuddin",
""
]
] | This study investigates the geodesic motion of test particles, both massless and massive, within a Schwarzschild-Klinkhamer (SK) wormhole space-time. We specifically consider the influence of cosmic strings on the system and analyze the effective potential, and observing that the presence of a cosmic string parameter alters it for null and time-like geodesics. Moreover, we calculate the deflection angle for null geodesics, and demonstrate that the cosmic string modifies this angle and induces a shift in the results. Additionally, we extend our investigation in this SK-wormhole space-time but with a global monopole. We explore the geodesic motion of test particles in this scenario and find that the effective potential is affected by the global monopole. Similarly, we determine the deflection angle for null geodesics and show that the global monopole parameter introduces modifications to this angle. Lastly, we present several known solutions for space-times involving cosmic strings and global monopoles within the framework of this SK-wormhole. |
gr-qc/0101050 | Dirk Puetzfeld | Dirk Puetzfeld, Romualdo Tresguerres | A cosmological model in Weyl-Cartan spacetime | 19 pages, 5 figures, typos corrected, uses IOP style file | Class.Quant.Grav. 18 (2001) 677-694 | 10.1088/0264-9381/18/4/308 | null | gr-qc | null | We present a cosmological model for early stages of the universe on the basis
of a Weyl-Cartan spacetime. In this model, torsion $T^{\alpha}$ and
nonmetricity $Q_{\alpha \beta}$ are proportional to the vacuum polarization.
Extending earlier work of one of us (RT), we discuss the behavior of the cosmic
scale factor and the Weyl 1-form in detail. We show how our model fits into the
more general framework of metric-affine gravity (MAG).
| [
{
"created": "Mon, 15 Jan 2001 14:05:43 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Mar 2001 13:12:06 GMT",
"version": "v2"
}
] | 2009-04-03 | [
[
"Puetzfeld",
"Dirk",
""
],
[
"Tresguerres",
"Romualdo",
""
]
] | We present a cosmological model for early stages of the universe on the basis of a Weyl-Cartan spacetime. In this model, torsion $T^{\alpha}$ and nonmetricity $Q_{\alpha \beta}$ are proportional to the vacuum polarization. Extending earlier work of one of us (RT), we discuss the behavior of the cosmic scale factor and the Weyl 1-form in detail. We show how our model fits into the more general framework of metric-affine gravity (MAG). |
2108.03385 | Gast\'on Creci | Gast\'on Creci, Tanja Hinderer, Jan Steinhoff | Tidal response from scattering and the role of analytic continuation | v5, corrected typos, 29 pages, 2 figures | Phys. Rev. D 104 (12 Dec. 2021), p. 124061 | 10.1103/PhysRevD.104.124061 | null | gr-qc astro-ph.HE astro-ph.SR hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The tidal response of a compact object is a key gravitational-wave observable
encoding information about its interior. This link is subtle due to the
nonlinearities of general relativity. We show that considering a scattering
process bypasses challenges with potential ambiguities, as the tidal response
is determined by the asymptotic in- and outgoing waves at null infinity. As an
application of the general method, we analyze scalar waves scattering off a
nonspinning black hole and demonstrate that the low-frequency expansion of the
tidal response reproduces known results for the Love number and absorption. In
addition, we discuss the definition of the response based on gauge-invariant
observables obtained from an effective action description, and clarify the role
of analytic continuation for robustly (i) extracting the response and the
physical information it contains, and (ii) distinguishing high-order
post-Newtonian corrections from finite-size effects in a binary system. Our
work is important for interpreting upcoming gravitational-wave data for
subatomic physics of ultradense matter in neutron stars, probing black holes
and gravity, and looking for beyond-standard-model fields.
| [
{
"created": "Sat, 7 Aug 2021 07:34:00 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Sep 2021 11:30:52 GMT",
"version": "v2"
},
{
"created": "Wed, 22 Dec 2021 16:36:43 GMT",
"version": "v3"
},
{
"created": "Tue, 22 Mar 2022 13:38:58 GMT",
"version": "v4"
},
{
"cr... | 2022-10-26 | [
[
"Creci",
"Gastón",
""
],
[
"Hinderer",
"Tanja",
""
],
[
"Steinhoff",
"Jan",
""
]
] | The tidal response of a compact object is a key gravitational-wave observable encoding information about its interior. This link is subtle due to the nonlinearities of general relativity. We show that considering a scattering process bypasses challenges with potential ambiguities, as the tidal response is determined by the asymptotic in- and outgoing waves at null infinity. As an application of the general method, we analyze scalar waves scattering off a nonspinning black hole and demonstrate that the low-frequency expansion of the tidal response reproduces known results for the Love number and absorption. In addition, we discuss the definition of the response based on gauge-invariant observables obtained from an effective action description, and clarify the role of analytic continuation for robustly (i) extracting the response and the physical information it contains, and (ii) distinguishing high-order post-Newtonian corrections from finite-size effects in a binary system. Our work is important for interpreting upcoming gravitational-wave data for subatomic physics of ultradense matter in neutron stars, probing black holes and gravity, and looking for beyond-standard-model fields. |
0812.0399 | Viqar Husain | Viqar Husain, R. B. Mann | Thermodynamics and phases in quantum gravity | 6 pages, 1 figure; matches published version | Class.Quant.Grav.26:075010,2009 | 10.1088/0264-9381/26/7/075010 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We give an approach for studying quantum gravity effects on black hole
thermodynamics. This combines a quantum framework for gravitational collapse
with quasi-local definitions of energy and surface gravity. Our arguments
suggest that (i) the specific heat of a black hole becomes positive after a
phase transition near the Planck scale,(ii) its entropy acquires a logarithmic
correction, and (iii) the mass loss rate is modified such that Hawking
radiation stops near the Planck scale. These results are due essentially to a
realization of fundamental discreteness in quantum gravity, and are in this
sense potentially theory independent.
| [
{
"created": "Tue, 2 Dec 2008 00:38:03 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Jun 2009 15:58:04 GMT",
"version": "v2"
}
] | 2010-05-12 | [
[
"Husain",
"Viqar",
""
],
[
"Mann",
"R. B.",
""
]
] | We give an approach for studying quantum gravity effects on black hole thermodynamics. This combines a quantum framework for gravitational collapse with quasi-local definitions of energy and surface gravity. Our arguments suggest that (i) the specific heat of a black hole becomes positive after a phase transition near the Planck scale,(ii) its entropy acquires a logarithmic correction, and (iii) the mass loss rate is modified such that Hawking radiation stops near the Planck scale. These results are due essentially to a realization of fundamental discreteness in quantum gravity, and are in this sense potentially theory independent. |
0806.4482 | Bindu Anubha Bambah | K. V. S. Shiv Chaitanya and Bindu A Bambah | Squeezed States and Affleck Dine Baryogenesis | 8 pages 9 figures | Phys.Rev.D78:063525,2008 | 10.1103/PhysRevD.78.063525 | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quantum fluctuations in the post inflationary Affleck-Dine baryogenesis model
are studied. The squeezed states formalism is used to give evolution equations
for the particle and anti-particle modes in the early universe. The role of
expansion and parametric amplification of the quantum fluctuations on the
baryon asymmetry produced is investigated.
| [
{
"created": "Fri, 27 Jun 2008 10:46:01 GMT",
"version": "v1"
},
{
"created": "Sun, 29 Jun 2008 10:29:50 GMT",
"version": "v2"
}
] | 2009-02-23 | [
[
"Chaitanya",
"K. V. S. Shiv",
""
],
[
"Bambah",
"Bindu A",
""
]
] | Quantum fluctuations in the post inflationary Affleck-Dine baryogenesis model are studied. The squeezed states formalism is used to give evolution equations for the particle and anti-particle modes in the early universe. The role of expansion and parametric amplification of the quantum fluctuations on the baryon asymmetry produced is investigated. |
1003.1686 | Laur J\"arv | Laur J\"arv, Piret Kuusk and Margus Saal | Potential dominated scalar-tensor cosmologies in the general relativity
limit: phase space view | 15 pages, 12 figures | Phys.Rev.D81:104007,2010 | 10.1103/PhysRevD.81.104007 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the potential dominated era of
Friedmann-Lemaitre-Robertson-Walker flat cosmological models in the framework
of general Jordan frame scalar-tensor theories of gravity with arbitrary
coupling functions, and focus upon the phase space of the scalar field. To
study the regime suggested by the local weak field tests (i.e. close to the
so-called limit of general relativity) we propose a nonlinear approximation
scheme, solve for the phase trajectories, and provide a complete classification
of possible phase portraits. We argue that the topology of trajectories in the
nonlinear approximation is representative of those of the full system, and thus
can tell for which scalar-tensor models general relativity functions as an
attractor.
| [
{
"created": "Mon, 8 Mar 2010 17:56:26 GMT",
"version": "v1"
}
] | 2010-05-25 | [
[
"Järv",
"Laur",
""
],
[
"Kuusk",
"Piret",
""
],
[
"Saal",
"Margus",
""
]
] | We consider the potential dominated era of Friedmann-Lemaitre-Robertson-Walker flat cosmological models in the framework of general Jordan frame scalar-tensor theories of gravity with arbitrary coupling functions, and focus upon the phase space of the scalar field. To study the regime suggested by the local weak field tests (i.e. close to the so-called limit of general relativity) we propose a nonlinear approximation scheme, solve for the phase trajectories, and provide a complete classification of possible phase portraits. We argue that the topology of trajectories in the nonlinear approximation is representative of those of the full system, and thus can tell for which scalar-tensor models general relativity functions as an attractor. |
2006.09209 | Mikhail Katanaev | D. E. Afanasev and M. O. Katanaev | Global properties of warped solutions in General Relativity with an
electromagnetic field and a cosmological constant. II | 32 pages, 18 figures | Phys. Rev. D, 101 (2020) 124025 | 10.1103/PhysRevD.101.124025 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider general relativity with cosmological constant minimally coupled
to the electromagnetic field and assume that the four-dimensional space-time
manifold is a warped product of two surfaces with Lorentzian and Euclidean
signature metrics. Field equations imply that at least one of the surfaces must
be of constant curvature leading to the symmetry of the metric (``spontaneous
symmetry emergence''). We classify all global solutions in the case when the
Lorentzian surface is of constant curvature. These solutions are invariant with
respect to the Lorentz SO(1,2) or Poincare IO(1,1) groups acting on the
Lorentzian surface.
| [
{
"created": "Sun, 14 Jun 2020 18:03:53 GMT",
"version": "v1"
}
] | 2020-06-17 | [
[
"Afanasev",
"D. E.",
""
],
[
"Katanaev",
"M. O.",
""
]
] | We consider general relativity with cosmological constant minimally coupled to the electromagnetic field and assume that the four-dimensional space-time manifold is a warped product of two surfaces with Lorentzian and Euclidean signature metrics. Field equations imply that at least one of the surfaces must be of constant curvature leading to the symmetry of the metric (``spontaneous symmetry emergence''). We classify all global solutions in the case when the Lorentzian surface is of constant curvature. These solutions are invariant with respect to the Lorentz SO(1,2) or Poincare IO(1,1) groups acting on the Lorentzian surface. |
2103.04218 | Fabio Dahia | J. M. Rocha and F. Dahia | Neutron interferometry and tests of short-range modifications of gravity | null | Phys. Rev. D 103, 124014 (2021) | 10.1103/PhysRevD.103.124014 | null | gr-qc nucl-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider tests of short-distance modifications of gravity based on neutron
interferometry in the scenario of large extra dimensions. Avoiding the
non-computability problem in the calculation of the internal gravitational
potential of extended sources, typical of models with zero-width brane, we
determine the neutron optical potential associated with the higher-dimension
gravitational interaction between the incident neutron and a material medium in
the context of thick brane theories. Proceeding this way, we identify the
physical quantity of the extra dimension model that the neutron interferometry
is capable of constraining. We also consider interferometric experiments in
which the phase shifter is an electric field, as in the test of the
Aharanov-Casher effect. We argue that this experiment, with this non-baryonic
source, can be viewed as a test of the short-range behavior of Post-Newtonian
parameters that measure the capacity of the pressure and the internal energy
for producing gravity.
| [
{
"created": "Sun, 7 Mar 2021 00:29:41 GMT",
"version": "v1"
}
] | 2021-06-16 | [
[
"Rocha",
"J. M.",
""
],
[
"Dahia",
"F.",
""
]
] | We consider tests of short-distance modifications of gravity based on neutron interferometry in the scenario of large extra dimensions. Avoiding the non-computability problem in the calculation of the internal gravitational potential of extended sources, typical of models with zero-width brane, we determine the neutron optical potential associated with the higher-dimension gravitational interaction between the incident neutron and a material medium in the context of thick brane theories. Proceeding this way, we identify the physical quantity of the extra dimension model that the neutron interferometry is capable of constraining. We also consider interferometric experiments in which the phase shifter is an electric field, as in the test of the Aharanov-Casher effect. We argue that this experiment, with this non-baryonic source, can be viewed as a test of the short-range behavior of Post-Newtonian parameters that measure the capacity of the pressure and the internal energy for producing gravity. |
1806.09433 | Eduardo Bittencourt | Eduardo Bittencourt, Vanessa P Freitas, Jos\'e M Salim, Grasiele B
Santos | Radiating Spherical Collapse for an Inhomogeneous Interior Solution | 17 pages, 5 figures | null | 10.1007/s10714-019-2511-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the problem of gravitational collapse considering the matching of
an exterior region described by the Vaidya's metric and an interior region
described by a spherically symmetric shear-free inhomogeneous geometry sourced
by a viscous fluid. We establish initial and final conditions for the process
in order that the outcome be a non-singular object, when this is possible, and
check how it depends on the fulfillment of the energy conditions. We then apply
explicitly the matching procedure to the cases of linear and nonlinear
Lagrangians describing electromagnetic fields inside the star, and analyze how
the different behaviors for the scale factor of the interior geometry produce
singular or nonsingular final stages of the collapse depending on the range
where the initial conditions lie.
| [
{
"created": "Mon, 25 Jun 2018 13:10:01 GMT",
"version": "v1"
}
] | 2019-02-13 | [
[
"Bittencourt",
"Eduardo",
""
],
[
"Freitas",
"Vanessa P",
""
],
[
"Salim",
"José M",
""
],
[
"Santos",
"Grasiele B",
""
]
] | We analyze the problem of gravitational collapse considering the matching of an exterior region described by the Vaidya's metric and an interior region described by a spherically symmetric shear-free inhomogeneous geometry sourced by a viscous fluid. We establish initial and final conditions for the process in order that the outcome be a non-singular object, when this is possible, and check how it depends on the fulfillment of the energy conditions. We then apply explicitly the matching procedure to the cases of linear and nonlinear Lagrangians describing electromagnetic fields inside the star, and analyze how the different behaviors for the scale factor of the interior geometry produce singular or nonsingular final stages of the collapse depending on the range where the initial conditions lie. |
1409.3751 | Aleksandar Mikovic | Aleksandar Mikovic and Miguel A. Oliveira | Canonical formulation of Poincare BFCG theory and its quantization | 17 pages, errors corrected and new references added | null | 10.1007/s10714-015-1900-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We find the canonical formulation of the Poincare BFCG theory in terms of the
spatial 2-connection and its canonically conjugate momenta. We show that the
Poincare BFCG action is dynamically equivalent to the BF action for the
Poincare group and we find the canonical transformation relating the two. We
study the canonical quantization of the Poincare BFCG theory by passing to the
Poincare-connection basis. The quantization in the 2-connection basis can be
then achieved by performing a Fourier transform. We also briefly discuss how to
approach the problem of constructing a basis of spin-foam states, which are the
categorical generalization of the spin-network states from Loop Quantum
Gravity.
| [
{
"created": "Fri, 12 Sep 2014 14:33:12 GMT",
"version": "v1"
},
{
"created": "Sun, 29 Mar 2015 07:17:20 GMT",
"version": "v2"
}
] | 2015-06-22 | [
[
"Mikovic",
"Aleksandar",
""
],
[
"Oliveira",
"Miguel A.",
""
]
] | We find the canonical formulation of the Poincare BFCG theory in terms of the spatial 2-connection and its canonically conjugate momenta. We show that the Poincare BFCG action is dynamically equivalent to the BF action for the Poincare group and we find the canonical transformation relating the two. We study the canonical quantization of the Poincare BFCG theory by passing to the Poincare-connection basis. The quantization in the 2-connection basis can be then achieved by performing a Fourier transform. We also briefly discuss how to approach the problem of constructing a basis of spin-foam states, which are the categorical generalization of the spin-network states from Loop Quantum Gravity. |
1804.02821 | Suddhasattwa Brahma | Suddhasattwa Brahma and Dong-han Yeom | Effective black-to-white hole bounces: The cost of surgery | 18 pages, 8 figures | Class.Quant.Grav. 35 (2018) no.20, 205007 | 10.1088/1361-6382/aae1df | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate possible geometries allowing transitions from a black hole to
a white hole spacetime, by placing a space-like thin shell between them. Such
proposals have been advanced recently to account for singularity-resolution in
black-hole spacetimes. This space-like shell can be extended to be outside the
event horizon and, thereby, reproduce some of the features of these proposals.
On the other hand, if the space-like shell is confined fully within the
horizon, then it results in a bounce near a space-like singularity inside the
black hole. For both cases, the null energy condition is necessarily violated,
at least effectively, due to introduction of quantum effects. If the shell,
with a non-trivial negative tension, extends beyond the event horizon, then one
can see effects of quantum gravity modifications even outside the horizon as a
cost of such a space-like surgery. Naturally, one needs to consider whether
these types of manufactured spacetimes violates any known laws of nature,
allowing for reasonable assumptions. After critically comparing our results
with several models in the literature, we reiterate a new way to avoid such
black-hole singularities without leaving a white-hole remnant via a quantum
bounce.
| [
{
"created": "Mon, 9 Apr 2018 05:47:07 GMT",
"version": "v1"
}
] | 2018-10-18 | [
[
"Brahma",
"Suddhasattwa",
""
],
[
"Yeom",
"Dong-han",
""
]
] | We investigate possible geometries allowing transitions from a black hole to a white hole spacetime, by placing a space-like thin shell between them. Such proposals have been advanced recently to account for singularity-resolution in black-hole spacetimes. This space-like shell can be extended to be outside the event horizon and, thereby, reproduce some of the features of these proposals. On the other hand, if the space-like shell is confined fully within the horizon, then it results in a bounce near a space-like singularity inside the black hole. For both cases, the null energy condition is necessarily violated, at least effectively, due to introduction of quantum effects. If the shell, with a non-trivial negative tension, extends beyond the event horizon, then one can see effects of quantum gravity modifications even outside the horizon as a cost of such a space-like surgery. Naturally, one needs to consider whether these types of manufactured spacetimes violates any known laws of nature, allowing for reasonable assumptions. After critically comparing our results with several models in the literature, we reiterate a new way to avoid such black-hole singularities without leaving a white-hole remnant via a quantum bounce. |
gr-qc/9507031 | Dadhich | L.K. Patel, N. Dadhich and A. Beesham | String-Dust Distributions with the Kerr-NUT symmetry | 15 pages, TeX version. tex error corrected | null | null | IUCAA-17/95 | gr-qc | null | We attempt to solve the Einstein equations for string dust and null flowing
radiation for the general axially symmetric metric, which we believe is being
done for the first time. We obtain the string-dust and radiating
generalizations of the Kerr and the NUT solutions. There also occurs an
interesting case of radiating string-dust which arises from string-dust
generalization of Vaidya's solution of a radiating star.
| [
{
"created": "Fri, 14 Jul 1995 14:45:07 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Jul 1995 16:24:15 GMT",
"version": "v2"
},
{
"created": "Fri, 21 Jul 1995 11:50:30 GMT",
"version": "v3"
}
] | 2008-02-03 | [
[
"Patel",
"L. K.",
""
],
[
"Dadhich",
"N.",
""
],
[
"Beesham",
"A.",
""
]
] | We attempt to solve the Einstein equations for string dust and null flowing radiation for the general axially symmetric metric, which we believe is being done for the first time. We obtain the string-dust and radiating generalizations of the Kerr and the NUT solutions. There also occurs an interesting case of radiating string-dust which arises from string-dust generalization of Vaidya's solution of a radiating star. |
1909.12873 | Damiano Anselmi | Damiano Anselmi and Antonio Marino | Fakeons and microcausality: light cones, gravitational waves and the
Hubble constant | 24 pages; CQG | Class. Quantum Grav. 37 (2020) 095003 | 10.1088/1361-6382/ab78d2 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The concept of fake particle, or "fakeon", allows us to make sense of quantum
gravity as an ultraviolet complete theory, by renouncing causality at very
small distances. We investigate whether the violation of microcausality can be
amplified or detected in the most common settings. We show that it is actually
short range for all practical purposes. Due to our experimental limitations,
the violation does not propagate along the light cones or by means of
gravitational waves. In some cases, the universe even conspires to make the
effect disappear. For example, the positivity of the Hubble constant appears to
be responsible for the direction of time in the early universe.
| [
{
"created": "Fri, 27 Sep 2019 18:56:06 GMT",
"version": "v1"
},
{
"created": "Sat, 28 Mar 2020 22:37:03 GMT",
"version": "v2"
}
] | 2020-04-08 | [
[
"Anselmi",
"Damiano",
""
],
[
"Marino",
"Antonio",
""
]
] | The concept of fake particle, or "fakeon", allows us to make sense of quantum gravity as an ultraviolet complete theory, by renouncing causality at very small distances. We investigate whether the violation of microcausality can be amplified or detected in the most common settings. We show that it is actually short range for all practical purposes. Due to our experimental limitations, the violation does not propagate along the light cones or by means of gravitational waves. In some cases, the universe even conspires to make the effect disappear. For example, the positivity of the Hubble constant appears to be responsible for the direction of time in the early universe. |
1404.3787 | Sang Pyo Kim | Sang Pyo Kim (Kunsan Natl. Univ.) | Geometric Origin of Pair Production by Electric Field in de Sitter Space | LaTex 4 pages, Invited talk at ICGAC11, Almaty, Kazakhstan, October
1-5, 2013 | null | 10.1134/S0202289314030104 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The particle production in a de Sitter space provides an interesting model to
understand the curvature effect on Schwinger pair production by a constant
electric field or Schwinger mechanism on the de Sitter radiation. For that
purpose, we employ the recently introduced complex analysis method, in which
the quantum evolution in the complex time explains the pair production via the
geometric transition amplitude and gives the pair-production rate as the
contour integral. We compare the result by the contour integral with that of
the phase-integral method.
| [
{
"created": "Tue, 15 Apr 2014 00:43:22 GMT",
"version": "v1"
}
] | 2015-06-19 | [
[
"Kim",
"Sang Pyo",
"",
"Kunsan Natl. Univ."
]
] | The particle production in a de Sitter space provides an interesting model to understand the curvature effect on Schwinger pair production by a constant electric field or Schwinger mechanism on the de Sitter radiation. For that purpose, we employ the recently introduced complex analysis method, in which the quantum evolution in the complex time explains the pair production via the geometric transition amplitude and gives the pair-production rate as the contour integral. We compare the result by the contour integral with that of the phase-integral method. |
2010.02754 | Saeed Ullah Khan | Saeed Ullah Khan and Jingli Ren | Particle dynamics around a dyonic charged black hole | 15 pages, 7 figures | Chinese Journal of Physics 2020 | 10.1016/j.cjph.2020.08.027 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article, we study the circular motion of particles and the well-known
Penrose mechanism around a Kerr-Newman-Kasuya black hole spacetime. The inner
and outer horizons, as well as ergosurfaces of the said black hole, are briefly
examined under the effect of spin and dyonic charge. Moreover, by limiting our
exploration to the equatorial plane, we discuss the characteristics of circular
geodesics and investigate both photons, as well as marginally stable circular
orbits. It is noted that black hole charge diminishing the radii of photon and
marginally stable circular orbits. To investigate the nature of particle
dynamics, we studied the effective potential and Lyapunov exponent. While
inspecting the process of energy extraction, we derived the Wald inequality,
which can help us to locate the energy limits of the Penrose process.
Furthermore, we have found expressions for the negative energy states and the
efficiency of energy extraction. The obtained result illustrates that both
black hole rotation and dyonic charge contributes to the efficiency of energy
extraction.
| [
{
"created": "Sun, 4 Oct 2020 09:52:21 GMT",
"version": "v1"
}
] | 2020-10-07 | [
[
"Khan",
"Saeed Ullah",
""
],
[
"Ren",
"Jingli",
""
]
] | In this article, we study the circular motion of particles and the well-known Penrose mechanism around a Kerr-Newman-Kasuya black hole spacetime. The inner and outer horizons, as well as ergosurfaces of the said black hole, are briefly examined under the effect of spin and dyonic charge. Moreover, by limiting our exploration to the equatorial plane, we discuss the characteristics of circular geodesics and investigate both photons, as well as marginally stable circular orbits. It is noted that black hole charge diminishing the radii of photon and marginally stable circular orbits. To investigate the nature of particle dynamics, we studied the effective potential and Lyapunov exponent. While inspecting the process of energy extraction, we derived the Wald inequality, which can help us to locate the energy limits of the Penrose process. Furthermore, we have found expressions for the negative energy states and the efficiency of energy extraction. The obtained result illustrates that both black hole rotation and dyonic charge contributes to the efficiency of energy extraction. |
1811.09844 | William Barker Mr | William E V Barker, Anthony N Lasenby, Michael P Hobson, William J
Handley | Static energetics in gravity | Replaced with published version. 19 pages, 2 figures | null | 10.1063/1.5082730 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A stress-energy tensor for linear gravity adapted to the harmonic gauge was
recently proposed by Butcher, Hobson and Lasenby. By removing gauge constraints
and imposing full metrical GR, we find a natural generalisation to the
pseudotensor of Einstein. M{\o}ller's pseudotensor is an alternative to that of
Einstein formulated using tetrads. We obtain the pseudotensor of M{\o}ller for
gauge theory gravity (GTG) using a variational approach, identifying a
potentially interesting recipe for constructing conserved currents in that
theory. We show that in static, spherical spacetimes with a central
gravitational mass M{\o}ller's pseudotensor describes gravitational
stress-energy as if the gravitational potential were a scalar (i.e.
Klein-Gordon) field coupled to a gravitational mass density on the Minkowski
background. The old Newtonian formula successfully describes the potential of
even strong fields in this picture. The Newtonian limit of this effect was
previously observed in the tensor of Butcher; we recover a local virial theorem
in this limit. We demonstrate using the `Schwarzschild star' solution for an
incompressible perfect fluid ball.
| [
{
"created": "Sat, 24 Nov 2018 14:27:11 GMT",
"version": "v1"
},
{
"created": "Thu, 5 Mar 2020 16:57:22 GMT",
"version": "v2"
}
] | 2020-03-06 | [
[
"Barker",
"William E V",
""
],
[
"Lasenby",
"Anthony N",
""
],
[
"Hobson",
"Michael P",
""
],
[
"Handley",
"William J",
""
]
] | A stress-energy tensor for linear gravity adapted to the harmonic gauge was recently proposed by Butcher, Hobson and Lasenby. By removing gauge constraints and imposing full metrical GR, we find a natural generalisation to the pseudotensor of Einstein. M{\o}ller's pseudotensor is an alternative to that of Einstein formulated using tetrads. We obtain the pseudotensor of M{\o}ller for gauge theory gravity (GTG) using a variational approach, identifying a potentially interesting recipe for constructing conserved currents in that theory. We show that in static, spherical spacetimes with a central gravitational mass M{\o}ller's pseudotensor describes gravitational stress-energy as if the gravitational potential were a scalar (i.e. Klein-Gordon) field coupled to a gravitational mass density on the Minkowski background. The old Newtonian formula successfully describes the potential of even strong fields in this picture. The Newtonian limit of this effect was previously observed in the tensor of Butcher; we recover a local virial theorem in this limit. We demonstrate using the `Schwarzschild star' solution for an incompressible perfect fluid ball. |
1807.04671 | Sergey Paston | R.V. Ilin, S.A. Paston | Exact relation between canonical and metric energy-momentum tensors for
higher derivative tensor field theories | LaTeX, 11 pages | European Physical Journal Plus (2019) 134: 21 | 10.1140/epjp/i2019-12359-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the relation between canonical and metric energy-momentum tensors
for field theories with actions that can depend on the higher derivatives of
tensor fields in a flat spacetime. In order to obtain it we use a modification
of the Noether's procedure for curved space-time. For considered case the
difference between these two tensors turns out to have more general form than
for theories with no more than first order derivatives. Despite this fact we
prove that the difference between corresponding integrals of motion still has
the form of integral over 2-dimensional surface that is infinitely remote in
the spacelike directions.
| [
{
"created": "Thu, 12 Jul 2018 15:25:32 GMT",
"version": "v1"
}
] | 2019-01-14 | [
[
"Ilin",
"R. V.",
""
],
[
"Paston",
"S. A.",
""
]
] | We discuss the relation between canonical and metric energy-momentum tensors for field theories with actions that can depend on the higher derivatives of tensor fields in a flat spacetime. In order to obtain it we use a modification of the Noether's procedure for curved space-time. For considered case the difference between these two tensors turns out to have more general form than for theories with no more than first order derivatives. Despite this fact we prove that the difference between corresponding integrals of motion still has the form of integral over 2-dimensional surface that is infinitely remote in the spacelike directions. |
gr-qc/9912047 | Jorge L. Cervantes-Cota | Jorge L. Cervantes Cota | Bianchi V inflation in the Brans-Dicke theory? | 28 pages, 6 figuras | Class.Quant.Grav.16:3903-3922,1999 | 10.1088/0264-9381/16/12/309 | null | gr-qc | null | It is shown some exact solutions in the Brans-Dicke (BD) theory for a Bianchi
V metric having the property of inflationary expansion, graceful exit, and
asymptotic evolution to a Friedmann-Robertson-Walker (FRW) open model. It is
remarkable that an inflationary behaviour can occur, even without a
cosmological potential or constant. However, the horizon and flatness problems
cannot be solve within the standard BD theory because the inflationary period
is severely restricted by the value of the BD parameter $\omega$.
| [
{
"created": "Fri, 10 Dec 1999 22:40:00 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Cota",
"Jorge L. Cervantes",
""
]
] | It is shown some exact solutions in the Brans-Dicke (BD) theory for a Bianchi V metric having the property of inflationary expansion, graceful exit, and asymptotic evolution to a Friedmann-Robertson-Walker (FRW) open model. It is remarkable that an inflationary behaviour can occur, even without a cosmological potential or constant. However, the horizon and flatness problems cannot be solve within the standard BD theory because the inflationary period is severely restricted by the value of the BD parameter $\omega$. |
2002.00834 | Klaus Liegener Dr | Andrea Dapor, Klaus Liegener | Modifications to Gravitational Wave Equation from Canonical Quantum
Gravity | 9 pages, 3 figures | EPJC 80, no. 741 (2020) | 10.1140/epjc/s10052-020-8333-8 | null | gr-qc astro-ph.CO hep-lat hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is expected that the quantum nature of spacetime leaves its imprint in all
semiclassical gravitational systems, at least in certain regimes, including
gravitational waves. In this paper we investigate such imprints on
gravitational waves within a specific framework: space is assumed to be
discrete (in the form of a regular cubic lattice), and this discrete geometry
is quantised following Dirac's canonical quantisation scheme. The semiclassical
behavior is then extracted by promoting the expectation value of the
Hamiltonian operator on a semiclassical state to an effective Hamiltonian.
Considering a family of semiclassical states representing small tensor
perturbations to Minkowski background, we derive a quantum-corrected effective
wave equation. The deviations from the classical gravitational wave equation
are found to be encoded in a modified dispersion relation and controlled by the
discreteness parameter of the underlying lattice. For finite discretisations,
several interesting effects appear: we investigate the thermodynamical
properties of these modified gravitons and, under certain assumptions, derive
the tensor power spectrum of the cosmic microwave background. The latter is
found to deviate from the classical prediction, in that an amplification of UV
modes takes place. We discuss under what circumstances such effect can be in
agreement with observations.
| [
{
"created": "Mon, 3 Feb 2020 15:47:01 GMT",
"version": "v1"
}
] | 2021-11-01 | [
[
"Dapor",
"Andrea",
""
],
[
"Liegener",
"Klaus",
""
]
] | It is expected that the quantum nature of spacetime leaves its imprint in all semiclassical gravitational systems, at least in certain regimes, including gravitational waves. In this paper we investigate such imprints on gravitational waves within a specific framework: space is assumed to be discrete (in the form of a regular cubic lattice), and this discrete geometry is quantised following Dirac's canonical quantisation scheme. The semiclassical behavior is then extracted by promoting the expectation value of the Hamiltonian operator on a semiclassical state to an effective Hamiltonian. Considering a family of semiclassical states representing small tensor perturbations to Minkowski background, we derive a quantum-corrected effective wave equation. The deviations from the classical gravitational wave equation are found to be encoded in a modified dispersion relation and controlled by the discreteness parameter of the underlying lattice. For finite discretisations, several interesting effects appear: we investigate the thermodynamical properties of these modified gravitons and, under certain assumptions, derive the tensor power spectrum of the cosmic microwave background. The latter is found to deviate from the classical prediction, in that an amplification of UV modes takes place. We discuss under what circumstances such effect can be in agreement with observations. |
2311.13715 | Eric Ling | Eric Ling and Argam Ohanyan | Examples of cosmological spacetimes without CMC Cauchy surfaces | 25 pages, 2 figures; final version agrees with published version | null | 10.1007/s11005-024-01843-7 | CPH-GEOTOP-DNRF151; CF21-0680 | gr-qc math.DG | http://creativecommons.org/licenses/by/4.0/ | CMC (constant mean curvature) Cauchy surfaces play an important role in
mathematical relativity as finding solutions to the vacuum Einstein constraint
equations is made much simpler by assuming CMC initial data. However, in [2]
Bartnik constructed a cosmological spacetime without a CMC Cauchy surface whose
spatial topology is the connected sum of two three-dimensional tori. Similarly,
in [9], Chru\'sciel, Isenberg, and Pollack constructed a vacuum cosmological
spacetime without CMC Cauchy surfaces whose spatial topology was also the
connected sum of two tori. In this article, we enlarge the known number of
spatial topologies for cosmological spacetimes without CMC Cauchy surfaces by
generalizing Bartnik's construction. Specifically, we show that there are
cosmological spacetimes without CMC Cauchy surfaces whose spatial topologies
are the connected sum of any compact oriented Euclidean or hyperbolic
three-manifold with any another compact oriented Euclidean or hyperbolic
three-manifold. We work with the Tolman-Bondi class of metrics and prove gluing
results for variable marginal conditions, which allows for smooth gluing of
Schwarzschild to FLRW models.
| [
{
"created": "Wed, 22 Nov 2023 22:19:44 GMT",
"version": "v1"
},
{
"created": "Wed, 31 Jul 2024 11:13:53 GMT",
"version": "v2"
}
] | 2024-08-01 | [
[
"Ling",
"Eric",
""
],
[
"Ohanyan",
"Argam",
""
]
] | CMC (constant mean curvature) Cauchy surfaces play an important role in mathematical relativity as finding solutions to the vacuum Einstein constraint equations is made much simpler by assuming CMC initial data. However, in [2] Bartnik constructed a cosmological spacetime without a CMC Cauchy surface whose spatial topology is the connected sum of two three-dimensional tori. Similarly, in [9], Chru\'sciel, Isenberg, and Pollack constructed a vacuum cosmological spacetime without CMC Cauchy surfaces whose spatial topology was also the connected sum of two tori. In this article, we enlarge the known number of spatial topologies for cosmological spacetimes without CMC Cauchy surfaces by generalizing Bartnik's construction. Specifically, we show that there are cosmological spacetimes without CMC Cauchy surfaces whose spatial topologies are the connected sum of any compact oriented Euclidean or hyperbolic three-manifold with any another compact oriented Euclidean or hyperbolic three-manifold. We work with the Tolman-Bondi class of metrics and prove gluing results for variable marginal conditions, which allows for smooth gluing of Schwarzschild to FLRW models. |
2002.08160 | Ksh Newton Singh | Ksh. Newton Singh, Abdelghani Errehymy, Farook Rahaman and Mohammed
Daoud | Exploring physical properties of compact stars in $f(R,T)-$gravity: An
embedding approach | 26 Pages, 14 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Solving field equations exactly in $f(R,T)$ gravity is one of the difficult
task. To do so, many authors have adopted different methods such as assuming
both the metric functions, an equation of state (EoS) and a metric function
etc. However, such methods may not always lead to well-behaved solutions and
thereby rejection of the solutions may happen after complete calculations.
Indeed, very recent works on embedding class one methods suggested that the
chances of arriving at the well behaved-solution is very high thereby inspired
us to used it. In class one approach, we have to ansatz one of the metric
potentials and the other can be obtain from the Karmarkar condition. In this
paper, we are proposing new class one solution which is well-behaved in all
physical points of view. We have analyzed the nature of the solution by tuning
the $f(R,T)-$coupling parameter $\chi$ and found that the solution results into
stiffer EoS for $\chi=-1$ than $\chi=1$. This is because for lesser values of
$\chi$, velocity of sound is more, higher $M_{max}$ in $M-R$ curve and the EoS
parameter $\omega$ is larger. The solution satisfy the causality condition,
energy conditions, stable and static under radial perturbations (static
stability criterion) and in equilibrium (modified TOV-equation). The resulting
$M-R$ diagram from this solution is well fitted with observed values of few
compact stars such as PSR J1614-2230, Vela X-1, Cen X-3 and SAX J1808.4-3658.
Therefore, for different values of $\chi$, we have predicted the corresponding
radii and their respective moment of inertia from the $M-I$ curve.
| [
{
"created": "Sat, 15 Feb 2020 16:04:03 GMT",
"version": "v1"
}
] | 2020-02-20 | [
[
"Singh",
"Ksh. Newton",
""
],
[
"Errehymy",
"Abdelghani",
""
],
[
"Rahaman",
"Farook",
""
],
[
"Daoud",
"Mohammed",
""
]
] | Solving field equations exactly in $f(R,T)$ gravity is one of the difficult task. To do so, many authors have adopted different methods such as assuming both the metric functions, an equation of state (EoS) and a metric function etc. However, such methods may not always lead to well-behaved solutions and thereby rejection of the solutions may happen after complete calculations. Indeed, very recent works on embedding class one methods suggested that the chances of arriving at the well behaved-solution is very high thereby inspired us to used it. In class one approach, we have to ansatz one of the metric potentials and the other can be obtain from the Karmarkar condition. In this paper, we are proposing new class one solution which is well-behaved in all physical points of view. We have analyzed the nature of the solution by tuning the $f(R,T)-$coupling parameter $\chi$ and found that the solution results into stiffer EoS for $\chi=-1$ than $\chi=1$. This is because for lesser values of $\chi$, velocity of sound is more, higher $M_{max}$ in $M-R$ curve and the EoS parameter $\omega$ is larger. The solution satisfy the causality condition, energy conditions, stable and static under radial perturbations (static stability criterion) and in equilibrium (modified TOV-equation). The resulting $M-R$ diagram from this solution is well fitted with observed values of few compact stars such as PSR J1614-2230, Vela X-1, Cen X-3 and SAX J1808.4-3658. Therefore, for different values of $\chi$, we have predicted the corresponding radii and their respective moment of inertia from the $M-I$ curve. |
gr-qc/0612053 | Yury F. Pirogov | Yu. F. Pirogov | Minimal metagravity vs. dark matter and/or dark energy | 6 pages, a typo corrected | Phys.Atom.Nucl.70:2148-2151,2007; Phys.Atom.Nucl.71:1650,2008 | 10.1134/S1063778807120162 10.1134/S1063778808090226 | null | gr-qc astro-ph hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The minimal metagravity theory, explicitly violating the general covariance
but preserving the unimodular one, is applied to study the evolution of the
isotropic homogeneous Universe. The massive scalar graviton, contained in the
theory in addition to the massless tensor one, is treated as a source of the
dark matter and/or dark energy. The modified Friedmann equation for the scale
factor of the Universe is derived. The question wether the minimal metagravity
can emulate the LCDM concordance model, valid in General Relativity, is
discussed.
| [
{
"created": "Fri, 8 Dec 2006 17:16:37 GMT",
"version": "v1"
},
{
"created": "Sun, 10 Dec 2006 13:04:55 GMT",
"version": "v2"
},
{
"created": "Wed, 11 Apr 2007 14:00:55 GMT",
"version": "v3"
},
{
"created": "Thu, 5 Jun 2008 18:06:09 GMT",
"version": "v4"
}
] | 2008-11-26 | [
[
"Pirogov",
"Yu. F.",
""
]
] | The minimal metagravity theory, explicitly violating the general covariance but preserving the unimodular one, is applied to study the evolution of the isotropic homogeneous Universe. The massive scalar graviton, contained in the theory in addition to the massless tensor one, is treated as a source of the dark matter and/or dark energy. The modified Friedmann equation for the scale factor of the Universe is derived. The question wether the minimal metagravity can emulate the LCDM concordance model, valid in General Relativity, is discussed. |
0802.4047 | T. Damour | Thibault Damour | Introductory lectures on the Effective One Body formalism | 22 pages, 3 figures, lectures given at the Second ICRANet
Stueckelberg Workshop on Relativistic Field Theories (Pescara, Italy,
September 3-8, 2007); to be published in the International Journal of Modern
Physics A | Int.J.Mod.Phys.A23:1130-1148,2008 | 10.1142/S0217751X08039992 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Effective One Body (EOB) formalism is an analytical approach which aims
at providing an accurate description of the motion and radiation of coalescing
binary black holes. We present a brief review of the basic elements of this
approach.
| [
{
"created": "Wed, 27 Feb 2008 17:04:27 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Damour",
"Thibault",
""
]
] | The Effective One Body (EOB) formalism is an analytical approach which aims at providing an accurate description of the motion and radiation of coalescing binary black holes. We present a brief review of the basic elements of this approach. |
2108.00161 | Jay Solanki | Jay Solanki and Bhashin Thakore | A New Class of Analytical Solutions Describing Anisotropic Neutron Stars
in General Relativity | null | Int. J. Mod. Phys. D, vol. 30, no. 12, p. 2150091, 2021 | 10.1142/S0218271821500917 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | A new class of solutions describing analytical solutions for compact stellar
structures has been developed within the tenets of General Relativity.
Considering the inherent anisotropy in compact stars, a stable and causal model
for realistic anisotropic neutron stars was obtained using the general theory
of relativity. Assuming a physically acceptable non-singular form of one metric
potential and radial pressure containing the curvature parameter $R$, the
constant $k$, and the radius $r$, analytical solutions to Einstein's field
equations for anisotropic matter distribution were obtained. Taking the value
of $k$ as -0.44, it was found that the proposed model obeys all necessary
physical conditions, and it is potentially stable and realistic. The model also
exhibits a linear equation of state, which can be applied to describe compact
stars.
| [
{
"created": "Sat, 31 Jul 2021 06:33:19 GMT",
"version": "v1"
}
] | 2021-10-14 | [
[
"Solanki",
"Jay",
""
],
[
"Thakore",
"Bhashin",
""
]
] | A new class of solutions describing analytical solutions for compact stellar structures has been developed within the tenets of General Relativity. Considering the inherent anisotropy in compact stars, a stable and causal model for realistic anisotropic neutron stars was obtained using the general theory of relativity. Assuming a physically acceptable non-singular form of one metric potential and radial pressure containing the curvature parameter $R$, the constant $k$, and the radius $r$, analytical solutions to Einstein's field equations for anisotropic matter distribution were obtained. Taking the value of $k$ as -0.44, it was found that the proposed model obeys all necessary physical conditions, and it is potentially stable and realistic. The model also exhibits a linear equation of state, which can be applied to describe compact stars. |
gr-qc/0202057 | Joel Smoller | Joel A. Smoller | The Interaction of Gravity with Other Fields | 25 pages, LaTeX | null | null | null | gr-qc | null | We consider the interaction of gravity, as expressed by Einstein's Equations
of General Relativity, to other force fields. We describe some recent results,
discussing both the mathematics, and the physical interpretations. These
results concern both elementary particles, as well as cosmological models.
(This paper describes joint work variously done with with F. Finster, N.
Kamran, B. Temple, and S.-T. Yau.)
| [
{
"created": "Fri, 15 Feb 2002 20:07:37 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Smoller",
"Joel A.",
""
]
] | We consider the interaction of gravity, as expressed by Einstein's Equations of General Relativity, to other force fields. We describe some recent results, discussing both the mathematics, and the physical interpretations. These results concern both elementary particles, as well as cosmological models. (This paper describes joint work variously done with with F. Finster, N. Kamran, B. Temple, and S.-T. Yau.) |
0903.0083 | Ilya Kirnos Vasilyevich | Ilya V. Kirnos, Andrew N. Makarenko | Accelerating cosmologies in Lovelock gravity with dilaton | 23 pages | null | 10.2174/1874381101003010037 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | For the description of the Universe expansion, compatible with observational
data, a model of modified gravity - Lovelock gravity with dilaton - is
investigated. D-dimensional space with 3- and (D-4)-dimensional maximally
symmetric subspaces is considered. Space without matter and space with perfect
fluid are under test. In various forms of the theory under way (third order
without dilaton and second order - Einstein-Gauss-Bonnet gravity - with dilaton
and without it) stationary, power-law, exponential and exponent-of-exponent
form cosmological solutions are obtained. Last two forms include solutions
which are clear to describe accelerating expansion of 3-dimensional subspace.
Also there is a set of solutions describing cosmological expansion which does
not tend to isotropization in the presence of matter.
| [
{
"created": "Sat, 28 Feb 2009 15:48:11 GMT",
"version": "v1"
}
] | 2015-05-13 | [
[
"Kirnos",
"Ilya V.",
""
],
[
"Makarenko",
"Andrew N.",
""
]
] | For the description of the Universe expansion, compatible with observational data, a model of modified gravity - Lovelock gravity with dilaton - is investigated. D-dimensional space with 3- and (D-4)-dimensional maximally symmetric subspaces is considered. Space without matter and space with perfect fluid are under test. In various forms of the theory under way (third order without dilaton and second order - Einstein-Gauss-Bonnet gravity - with dilaton and without it) stationary, power-law, exponential and exponent-of-exponent form cosmological solutions are obtained. Last two forms include solutions which are clear to describe accelerating expansion of 3-dimensional subspace. Also there is a set of solutions describing cosmological expansion which does not tend to isotropization in the presence of matter. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.