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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1911.05848 | Dmitry Chirkov | Dmitry Chirkov, Alex Giacomini, Alexey Toporensky | Anisotropic cosmological dynamics in Einstein-Gauss-Bonnet gravity: an
example of dynamical compactification in 7+1 dimensions | 11 pages, 3 figures | Gen. Rel. Grav. 52:30 (2020) | 10.1007/s10714-020-02679-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a particular example of dynamical compactification of an
anisotropic 7+1 dimensional Universe in Einstein - Gauss - Bonnet gravity.
Starting from rather general totally anisotropic initial conditions a Universe
in question evolves towards a product of two isotropic subspaces. The first
subspace expands isotropically, the second represents an "inner" isotropic
subspace with stabilized size. The dynamical evolution does not require
fine-tuning of initial conditions, though it is possible for a particular range
of coupling constants. The corresponding condition have been found analytically
and have been confirmed using numerical integration of equations of motion.
| [
{
"created": "Wed, 13 Nov 2019 22:45:32 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Nov 2019 22:38:03 GMT",
"version": "v2"
},
{
"created": "Wed, 1 Apr 2020 14:19:57 GMT",
"version": "v3"
}
] | 2020-04-02 | [
[
"Chirkov",
"Dmitry",
""
],
[
"Giacomini",
"Alex",
""
],
[
"Toporensky",
"Alexey",
""
]
] | We consider a particular example of dynamical compactification of an anisotropic 7+1 dimensional Universe in Einstein - Gauss - Bonnet gravity. Starting from rather general totally anisotropic initial conditions a Universe in question evolves towards a product of two isotropic subspaces. The first subspace expands isotropically, the second represents an "inner" isotropic subspace with stabilized size. The dynamical evolution does not require fine-tuning of initial conditions, though it is possible for a particular range of coupling constants. The corresponding condition have been found analytically and have been confirmed using numerical integration of equations of motion. |
1203.1702 | Manfred Requardt | Manfred Requardt | Gravitons as Goldstone Modes and the Spontaneous Symmetry Breaking of
Diffeomorphism Invariance | 19 pages, Latex | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We complement investigations of the gauge structure of general relativity
with an analysis of the physical consequences of the spontaneous breaking of
diffeomorphism invariance which manifests itself in e.g. the socalled Einstein
hole problem. We analyze the nature of the gravitons as Goldstone excitations
both in the classical and the quantum case. We show that the metrical field and
the classical space-time manifold play the role of an order parameter field and
order parameter manifold as macroscopic super structures living in an
underlying presumed quantum space-time. We furthermore relate our observations
to possible phase transitions in some pre big-bang era.
| [
{
"created": "Thu, 8 Mar 2012 08:11:48 GMT",
"version": "v1"
}
] | 2012-03-09 | [
[
"Requardt",
"Manfred",
""
]
] | We complement investigations of the gauge structure of general relativity with an analysis of the physical consequences of the spontaneous breaking of diffeomorphism invariance which manifests itself in e.g. the socalled Einstein hole problem. We analyze the nature of the gravitons as Goldstone excitations both in the classical and the quantum case. We show that the metrical field and the classical space-time manifold play the role of an order parameter field and order parameter manifold as macroscopic super structures living in an underlying presumed quantum space-time. We furthermore relate our observations to possible phase transitions in some pre big-bang era. |
1107.0854 | Ioannis Kamaretsos | Ioannis Kamaretsos (Cardiff), Mark Hannam (Cardiff), Sascha Husa
(Palma), and B. S. Sathyaprakash (Cardiff) | Black-hole hair loss: learning about binary progenitors from ringdown
signals | 24 pages, 9 figures, 4 tables, accepted for publication in Physical
Review D | null | 10.1103/PhysRevD.85.024018 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Perturbed Kerr black holes emit gravitational radiation, which (for the
practical purposes of gravitational-wave astronomy) consists of a superposition
of damped sinusoids termed quasi-normal modes. The frequencies and
time-constants of the modes depend only on the mass and spin of the black hole
- a consequence of the no-hair theorem. It has been proposed that a measurement
of two or more quasi-normal modes could be used to confirm that the source is a
black hole and to test if general relativity continues to hold in ultra-strong
gravitational fields. In this paper we propose a practical approach to testing
general relativity with quasi-normal modes. We will also argue that the
relative amplitudes of the various quasi-normal modes encode important
information about the origin of the perturbation that caused them. This helps
in inferring the nature of the perturbation from an observation of the emitted
quasi-normal modes. In particular, we will show that the relative amplitudes of
the different quasi-normal modes emitted in the process of the merger of a pair
of nonspinning black holes can be used to measure the component masses of the
progenitor binary.
| [
{
"created": "Tue, 5 Jul 2011 12:10:38 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Oct 2011 14:24:53 GMT",
"version": "v2"
},
{
"created": "Tue, 10 Jan 2012 19:17:46 GMT",
"version": "v3"
}
] | 2013-05-30 | [
[
"Kamaretsos",
"Ioannis",
"",
"Cardiff"
],
[
"Hannam",
"Mark",
"",
"Cardiff"
],
[
"Husa",
"Sascha",
"",
"Palma"
],
[
"Sathyaprakash",
"B. S.",
"",
"Cardiff"
]
] | Perturbed Kerr black holes emit gravitational radiation, which (for the practical purposes of gravitational-wave astronomy) consists of a superposition of damped sinusoids termed quasi-normal modes. The frequencies and time-constants of the modes depend only on the mass and spin of the black hole - a consequence of the no-hair theorem. It has been proposed that a measurement of two or more quasi-normal modes could be used to confirm that the source is a black hole and to test if general relativity continues to hold in ultra-strong gravitational fields. In this paper we propose a practical approach to testing general relativity with quasi-normal modes. We will also argue that the relative amplitudes of the various quasi-normal modes encode important information about the origin of the perturbation that caused them. This helps in inferring the nature of the perturbation from an observation of the emitted quasi-normal modes. In particular, we will show that the relative amplitudes of the different quasi-normal modes emitted in the process of the merger of a pair of nonspinning black holes can be used to measure the component masses of the progenitor binary. |
1311.6786 | J\"org Hennig | J\"org Frauendiener and J\"org Hennig | Fully pseudospectral solution of the conformally invariant wave equation
near the cylinder at spacelike infinity | 16 pages, 6 figures | Class. Quantum Grav. 31, 085010 (2014) | 10.1088/0264-9381/31/8/085010 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the scalar, conformally invariant wave equation on a
four-dimensional Minkowski background in spherical symmetry, using a fully
pseudospectral numerical scheme. Thereby, our main interest is in a suitable
treatment of spatial infinity, which is represented as a cylinder. We consider
both Cauchy problems, where we evolve data from a Cauchy surface to future null
infinity, as well as characteristic initial value problems with data at past
null infinity, and demonstrate that highly accurate numerical solutions can be
obtained for a small number of grid points.
| [
{
"created": "Tue, 26 Nov 2013 19:41:41 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Apr 2014 01:05:39 GMT",
"version": "v2"
}
] | 2014-04-03 | [
[
"Frauendiener",
"Jörg",
""
],
[
"Hennig",
"Jörg",
""
]
] | We study the scalar, conformally invariant wave equation on a four-dimensional Minkowski background in spherical symmetry, using a fully pseudospectral numerical scheme. Thereby, our main interest is in a suitable treatment of spatial infinity, which is represented as a cylinder. We consider both Cauchy problems, where we evolve data from a Cauchy surface to future null infinity, as well as characteristic initial value problems with data at past null infinity, and demonstrate that highly accurate numerical solutions can be obtained for a small number of grid points. |
gr-qc/0602081 | Tiberiu Harko | C. G. Boehmer, T. Harko | Physics of dark energy particles | 10 pages, no figures; typos corrected, 4 references added; 1
reference added; reference added; entirely revised version, contains new
parts, now 14 pages | Found.Phys.38:216,2008 | 10.1007/s10701-007-9199-4 | null | gr-qc astro-ph hep-th | null | We consider the astrophysical and cosmological implications of the existence
of a minimum density and mass due to the presence of the cosmological constant.
If there is a minimum length in nature, then there is an absolute minimum mass
corresponding to a hypothetical particle with radius of the order of the Planck
length. On the other hand, quantum mechanical considerations suggest a
different minimum mass. These particles associated with the dark energy can be
interpreted as the ``quanta'' of the cosmological constant. We study the
possibility that these particles can form stable stellar-type configurations
through gravitational condensation, and their Jeans and Chandrasekhar masses
are estimated. From the requirement of the energetic stability of the minimum
density configuration on a macroscopic scale one obtains a mass of the order of
10^55 g, of the same order of magnitude as the mass of the universe. This mass
can also be interpreted as the Jeans mass of the dark energy fluid. Furthermore
we present a representation of the cosmological constant and of the total mass
of the universe in terms of `classical' fundamental constants.
| [
{
"created": "Tue, 21 Feb 2006 02:01:32 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Feb 2006 02:28:13 GMT",
"version": "v2"
},
{
"created": "Mon, 24 Apr 2006 02:36:59 GMT",
"version": "v3"
},
{
"created": "Thu, 1 Jun 2006 19:41:33 GMT",
"version": "v4"
},
{
"cr... | 2008-11-26 | [
[
"Boehmer",
"C. G.",
""
],
[
"Harko",
"T.",
""
]
] | We consider the astrophysical and cosmological implications of the existence of a minimum density and mass due to the presence of the cosmological constant. If there is a minimum length in nature, then there is an absolute minimum mass corresponding to a hypothetical particle with radius of the order of the Planck length. On the other hand, quantum mechanical considerations suggest a different minimum mass. These particles associated with the dark energy can be interpreted as the ``quanta'' of the cosmological constant. We study the possibility that these particles can form stable stellar-type configurations through gravitational condensation, and their Jeans and Chandrasekhar masses are estimated. From the requirement of the energetic stability of the minimum density configuration on a macroscopic scale one obtains a mass of the order of 10^55 g, of the same order of magnitude as the mass of the universe. This mass can also be interpreted as the Jeans mass of the dark energy fluid. Furthermore we present a representation of the cosmological constant and of the total mass of the universe in terms of `classical' fundamental constants. |
2301.07973 | \'Alvaro Mozota Frauca | Alvaro Mozota Frauca | Reassessing the problem of time of quantum gravity | To be published in General Relativity and Gravitation | Gen. Relativ. Gravit. 55, 21 (2023) | 10.1007/s10714-023-03067-x | null | gr-qc physics.hist-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper I raise a worry about the most extended resolutions of the
problem of time of canonical quantizations of general relativity. The reason
for this is that these resolutions are based on analogies with deparametrizable
models for which the problem can be solved, while I argue in this paper that
there are good reasons for doubting about these resolutions when the theory is
not deparametrizable, which is the case of general relativity. I introduce an
example of a non-deparametrizable model, a double harmonic oscillator system
expressed by its Jacobi action, and argue that the problem of time for this
model is not solvable, in the sense that its canonical quantization doesn't
lead to the quantum theory of two harmonic oscillators and the standard
resolutions of the problem of time don't work for this case. I argue that as
general relativity is strongly analogous to this model, one should take
seriously the view that the canonical quantization of general relativity
doesn't lead to a meaningful quantum theory. Finally, I comment that this has
an impact on the foundations of different approaches to quantum gravity.
| [
{
"created": "Thu, 19 Jan 2023 10:02:53 GMT",
"version": "v1"
}
] | 2023-01-26 | [
[
"Frauca",
"Alvaro Mozota",
""
]
] | In this paper I raise a worry about the most extended resolutions of the problem of time of canonical quantizations of general relativity. The reason for this is that these resolutions are based on analogies with deparametrizable models for which the problem can be solved, while I argue in this paper that there are good reasons for doubting about these resolutions when the theory is not deparametrizable, which is the case of general relativity. I introduce an example of a non-deparametrizable model, a double harmonic oscillator system expressed by its Jacobi action, and argue that the problem of time for this model is not solvable, in the sense that its canonical quantization doesn't lead to the quantum theory of two harmonic oscillators and the standard resolutions of the problem of time don't work for this case. I argue that as general relativity is strongly analogous to this model, one should take seriously the view that the canonical quantization of general relativity doesn't lead to a meaningful quantum theory. Finally, I comment that this has an impact on the foundations of different approaches to quantum gravity. |
2308.03947 | Ali \"Ovg\"un Dr. | \.Ilim \.Irfan \c{C}imdiker, Ali \"Ovg\"un and Durmu\c{s} Demir | Thin accretion disk images of the black hole in symmergent gravity | 30 pages. Accepted for publication in Classical and Quantum Gravity,
"Special Issue: Focus on Quantum Gravity Phenomenology in the Multi-Messenger
Era: Challenges and Perspectives"
(https://iopscience.iop.org/article/10.1088/1361-6382/aceb45). arXiv admin
note: text overlap with arXiv:1901.05762, arXiv:2002.00589 by other authors | Class. Quantum Grav. 40 (2023) 184001 | 10.1088/1361-6382/aceb45 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this paper, we study circular orbits, effective potential, and
thin-accretion disk of a black hole in symmergent gravity within the
Novikov-Thorne model in a way including the energy flux and temperature
distribution. We determine bounds on symmergent gravity parameters and conclude
that the accretion disk could be used as an astrophysical tool to probe
symmergent gravity.
| [
{
"created": "Mon, 7 Aug 2023 23:28:53 GMT",
"version": "v1"
}
] | 2023-08-09 | [
[
"Çimdiker",
"İlim İrfan",
""
],
[
"Övgün",
"Ali",
""
],
[
"Demir",
"Durmuş",
""
]
] | In this paper, we study circular orbits, effective potential, and thin-accretion disk of a black hole in symmergent gravity within the Novikov-Thorne model in a way including the energy flux and temperature distribution. We determine bounds on symmergent gravity parameters and conclude that the accretion disk could be used as an astrophysical tool to probe symmergent gravity. |
1311.3836 | Alexandre Le Tiec | Alexandre Le Tiec | A Note on Celestial Mechanics in Kerr Spacetime | 7 pages; matches version to appear in Class. Quant. Grav | Class.Quant.Grav.31:097001,2014 | 10.1088/0264-9381/31/9/097001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Hamilton-Jacobi equation for test particles in the Kerr geometry is
separable. Using action-angle variables, we establish several relations between
various physical quantities that characterize bound timelike geodesic orbits
around a spinning black hole, including the particle's rest mass, energy,
angular momentum, mean redshift and fundamental frequencies. These relations
are explicitly checked to hold true in the particular case of equatorial
circular orbits. An application to the gravitational wave-driven, adiabatic
inspiral of extreme-mass-ratio compact binaries is briefly discussed.
| [
{
"created": "Fri, 15 Nov 2013 12:55:25 GMT",
"version": "v1"
},
{
"created": "Fri, 21 Mar 2014 14:11:57 GMT",
"version": "v2"
}
] | 2014-04-21 | [
[
"Tiec",
"Alexandre Le",
""
]
] | The Hamilton-Jacobi equation for test particles in the Kerr geometry is separable. Using action-angle variables, we establish several relations between various physical quantities that characterize bound timelike geodesic orbits around a spinning black hole, including the particle's rest mass, energy, angular momentum, mean redshift and fundamental frequencies. These relations are explicitly checked to hold true in the particular case of equatorial circular orbits. An application to the gravitational wave-driven, adiabatic inspiral of extreme-mass-ratio compact binaries is briefly discussed. |
1109.6324 | Thomas Sotiriou | Thomas P. Sotiriou, Valerio Faraoni | Black holes in scalar-tensor gravity | v1: 4 pages; v2: typos corrected, published version | Phys. Rev. Lett. 108, 081103 (2012) | 10.1103/PhysRevLett.108.081103 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Hawking has proven that black holes which are stationary as the endpoint of
gravitational collapse in Brans--Dicke theory (without a potential) are no
different than in general relativity. We extend this proof to the much more
general class of scalar-tensor and f(R) gravity theories, without assuming any
symmetries apart from stationarity.
| [
{
"created": "Wed, 28 Sep 2011 20:00:03 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Mar 2012 17:31:41 GMT",
"version": "v2"
}
] | 2012-03-07 | [
[
"Sotiriou",
"Thomas P.",
""
],
[
"Faraoni",
"Valerio",
""
]
] | Hawking has proven that black holes which are stationary as the endpoint of gravitational collapse in Brans--Dicke theory (without a potential) are no different than in general relativity. We extend this proof to the much more general class of scalar-tensor and f(R) gravity theories, without assuming any symmetries apart from stationarity. |
gr-qc/0106067 | Shih-Yuin Lin | Shih-Yuin Lin | Classical Aspects of Accelerated Unruh-DeWitt Type Monopole Detectors | 7 pages; typos and references added, minor correction in Sec.IV | null | null | null | gr-qc hep-th | null | We have shown the classical correspondence of Unruh effect in the classical
relativistic electron theory in our previous work (gr-qc/0105051). Here we
demonstrate the analogy between the classical relativistic electron theory and
the classical Unruh-DeWitt type monopole detector theory. The field
configuration generated by a uniformly accelerated detector is worked out. The
classical correspondence of Unruh effect for scalar fields is shown by
calculating the modified energy density for the scalar field around the
detector. We conclude that a classical monopole detector cannot find any
evidence about its acceleration unless it has a finite size.
| [
{
"created": "Thu, 21 Jun 2001 11:48:49 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Jun 2001 12:56:48 GMT",
"version": "v2"
},
{
"created": "Sun, 8 Jul 2001 09:49:31 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Lin",
"Shih-Yuin",
""
]
] | We have shown the classical correspondence of Unruh effect in the classical relativistic electron theory in our previous work (gr-qc/0105051). Here we demonstrate the analogy between the classical relativistic electron theory and the classical Unruh-DeWitt type monopole detector theory. The field configuration generated by a uniformly accelerated detector is worked out. The classical correspondence of Unruh effect for scalar fields is shown by calculating the modified energy density for the scalar field around the detector. We conclude that a classical monopole detector cannot find any evidence about its acceleration unless it has a finite size. |
gr-qc/0608070 | Dr. Anirudh Pradhan | A. Pradhan, J. P. Shahi and C. B. Singh | Cosmological Models of Universe with Variable Deceleration Parameter in
Lyra's Manifold | 11 pages, 3 figures. To appear in Braz. J. Phys | Braz.J.Phys. 36 (2006) 1227-1231 | 10.1590/S0103-97332006000700020 | null | gr-qc | null | FRW models of the universe have been studied in the cosmological theory based
on Lyra's manifold. A new class of exact solutions has been obtained by
considering a time dependent displacement field for variable deceleration
parameter from which three models of the universe are derived (i) exponential
(ii) polynomial and (iii) sinusoidal form respectively. The behaviour of these
models of the universe are also discussed. Finally some possibilities of
further problems and their investigations have been pointed out.
| [
{
"created": "Mon, 14 Aug 2006 11:23:26 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Nov 2006 08:14:18 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Pradhan",
"A.",
""
],
[
"Shahi",
"J. P.",
""
],
[
"Singh",
"C. B.",
""
]
] | FRW models of the universe have been studied in the cosmological theory based on Lyra's manifold. A new class of exact solutions has been obtained by considering a time dependent displacement field for variable deceleration parameter from which three models of the universe are derived (i) exponential (ii) polynomial and (iii) sinusoidal form respectively. The behaviour of these models of the universe are also discussed. Finally some possibilities of further problems and their investigations have been pointed out. |
0912.1823 | Sabine Hossenfelder | Sabine Hossenfelder, Leonardo Modesto, Isabeau Pr\'emont-Schwarz | A model for non-singular black hole collapse and evaporation | 7 pages, 3 figures, references added, replaced with published version | Phys.Rev.D81:044036,2010 | 10.1103/PhysRevD.81.044036 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the formation of a black hole and its subsequent evaporation in a
model employing a minisuperspace approach to loop quantum gravity. In previous
work the static solution was obtained and shown to be singularity-free. Here,
we examine the more realistic dynamical case by generalizing the static case
with help of the Vaidya metric. We track the formation and evolution of trapped
surfaces during collapse and evaporation and examine the buildup of quantum
gravitationally caused stress-energy preventing the formation of a singularity.
| [
{
"created": "Wed, 9 Dec 2009 18:16:54 GMT",
"version": "v1"
},
{
"created": "Mon, 21 Dec 2009 12:05:54 GMT",
"version": "v2"
},
{
"created": "Wed, 24 Feb 2010 17:17:25 GMT",
"version": "v3"
}
] | 2010-04-21 | [
[
"Hossenfelder",
"Sabine",
""
],
[
"Modesto",
"Leonardo",
""
],
[
"Prémont-Schwarz",
"Isabeau",
""
]
] | We study the formation of a black hole and its subsequent evaporation in a model employing a minisuperspace approach to loop quantum gravity. In previous work the static solution was obtained and shown to be singularity-free. Here, we examine the more realistic dynamical case by generalizing the static case with help of the Vaidya metric. We track the formation and evolution of trapped surfaces during collapse and evaporation and examine the buildup of quantum gravitationally caused stress-energy preventing the formation of a singularity. |
gr-qc/9901002 | Aharon Davidson | Aharon Davidson and David Karasik | Cosmic Solenoids: Minimal Cross-Section and Generalized Flux
Quantization | Revtex, 11 twocolumn pages, 3 eps figures (accepted for publication
in Phys. Rev. D) | Phys.Rev. D60 (1999) 045002 | 10.1103/PhysRevD.60.045002 | null | gr-qc astro-ph hep-th | null | A self-consistent general relativistic configuration describing a finite
cross-section magnetic flux tube is constructed. The cosmic solenoid is modeled
by an elastic superconductive surface which separates the Melvin core from the
surrounding flat conic structure. We show that a given amount $\Phi$ of
magnetic flux cannot be confined within a cosmic solenoid of circumferential
radius smaller than $\frac{\sqrt{3G}}{2\pi c^2}\Phi$ without creating a conic
singularity. Gauss-Codazzi matching conditions are derived by means of a
self-consistent action. The source term, representing the surface currents, is
sandwiched between internal and external gravitational surface terms. Surface
superconductivity is realized by means of a Higgs scalar minimally coupled to
projective electromagnetism. Trading the 'magnetic' London phase for a dual
'electric' surface vector potential, the generalized quantization condition
reads: $e/{hc} \Phi + 1/e Q=n$ with $Q$ denoting some dual 'electric' charge,
thereby allowing for a non-trivial Aharonov-Bohm effect. Our conclusions
persist for dilaton gravity provided the dilaton coupling is sub-critical.
| [
{
"created": "Sat, 2 Jan 1999 10:21:26 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Davidson",
"Aharon",
""
],
[
"Karasik",
"David",
""
]
] | A self-consistent general relativistic configuration describing a finite cross-section magnetic flux tube is constructed. The cosmic solenoid is modeled by an elastic superconductive surface which separates the Melvin core from the surrounding flat conic structure. We show that a given amount $\Phi$ of magnetic flux cannot be confined within a cosmic solenoid of circumferential radius smaller than $\frac{\sqrt{3G}}{2\pi c^2}\Phi$ without creating a conic singularity. Gauss-Codazzi matching conditions are derived by means of a self-consistent action. The source term, representing the surface currents, is sandwiched between internal and external gravitational surface terms. Surface superconductivity is realized by means of a Higgs scalar minimally coupled to projective electromagnetism. Trading the 'magnetic' London phase for a dual 'electric' surface vector potential, the generalized quantization condition reads: $e/{hc} \Phi + 1/e Q=n$ with $Q$ denoting some dual 'electric' charge, thereby allowing for a non-trivial Aharonov-Bohm effect. Our conclusions persist for dilaton gravity provided the dilaton coupling is sub-critical. |
1105.0328 | Gamal G.L. Nashed | Gamal G.L. Nashed | Energy and momentum of a spherically symmetric dilaton frame as
regularized by teleparallel gravity | 11 Pages Latex, Accepted for publication in Annalen der Physik | Ann. Phys. (Berlin) 523, No. 6, 450 -- 458 (2011) | 10.1002/andp.201100030 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We calculate energy and momentum of a spherically symmetric dilaton frame
using the gravitational energy-momentum 3-form within the tetrad formulation of
general relativity (GR). The frame we use is characterized by an arbitrary
function $\Upsilon$ with the help of which all the previously found solutions
can be reproduced. We show how the effect of inertia {\it (which is mainly
reproduced from $\Upsilon$)} makes the total energy and momentum always
different from the well known result when we use the Riemannian connection
${{\widetilde \Gamma}_\alpha}^\beta$. On the other hand, when use is made of
the covariant formulation of teleparallel gravity, which implies to take into
account the pure gauge connection, teleparallel gravity always yields the
physically relevant result for the energy and momentum.
| [
{
"created": "Thu, 28 Apr 2011 10:29:55 GMT",
"version": "v1"
}
] | 2011-05-25 | [
[
"Nashed",
"Gamal G. L.",
""
]
] | We calculate energy and momentum of a spherically symmetric dilaton frame using the gravitational energy-momentum 3-form within the tetrad formulation of general relativity (GR). The frame we use is characterized by an arbitrary function $\Upsilon$ with the help of which all the previously found solutions can be reproduced. We show how the effect of inertia {\it (which is mainly reproduced from $\Upsilon$)} makes the total energy and momentum always different from the well known result when we use the Riemannian connection ${{\widetilde \Gamma}_\alpha}^\beta$. On the other hand, when use is made of the covariant formulation of teleparallel gravity, which implies to take into account the pure gauge connection, teleparallel gravity always yields the physically relevant result for the energy and momentum. |
1802.00365 | Burkhard Kleihaus | Xiao Yan Chew, Burkhard Kleihaus, and Jutta Kunz (University of
Oldenburg) | Spinning Wormholes in Scalar-Tensor Theory | null | Phys. Rev. D 97, 064026 (2018) | 10.1103/PhysRevD.97.064026 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider spinning generalizations of the Ellis wormhole in scalar-tensor
theory. Analogous to other compact objects these wormholes can carry a
non-trivial scalarization. We determine the domain of existence of the
scalarized wormholes and investigate the effect of the scalarization on their
properties. Depending on the choice of the coupling function, they may possess
multiple throats and equators in the Jordan frame, while possessing only a
single throat in the Einstein frame.
| [
{
"created": "Thu, 1 Feb 2018 15:58:37 GMT",
"version": "v1"
}
] | 2018-03-28 | [
[
"Chew",
"Xiao Yan",
"",
"University of\n Oldenburg"
],
[
"Kleihaus",
"Burkhard",
"",
"University of\n Oldenburg"
],
[
"Kunz",
"Jutta",
"",
"University of\n Oldenburg"
]
] | We consider spinning generalizations of the Ellis wormhole in scalar-tensor theory. Analogous to other compact objects these wormholes can carry a non-trivial scalarization. We determine the domain of existence of the scalarized wormholes and investigate the effect of the scalarization on their properties. Depending on the choice of the coupling function, they may possess multiple throats and equators in the Jordan frame, while possessing only a single throat in the Einstein frame. |
1511.00627 | Shao-Jiang Wang | Rong-Gen Cai, Shao-Jiang Wang | Dark matter superfluid and DBI dark energy | v1, 4 pages, no figure; v2, 8 pages, 4 figures, numerical
justifications added; v3, references added, final version to match the
published version | Phys. Rev. D 93, 023515 (2016) | 10.1103/PhysRevD.93.023515 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It was shown recently that, without jeopardizing the success of the $\Lambda$
cold dark matter model on cosmic scales, the modified Newtonian dynamics (MOND)
can be derived as an emergent phenomenon when axionlike dark matter particles
condense into superfluid on the galactic scales. We propose in this paper a
Dirac-Born-Infeld (DBI) scalar field conformally coupled to the matter
components. To maintain the success of MOND phenomenon of dark matter
superfluid on the galactic scales, the fifth force introduced by the DBI scalar
should be screened on the galactic scales. It turns out that the screening
effect naturally leads to a simple explanation for a longstanding puzzle that
the MOND critical acceleration coincides with present Hubble scale. This
galactic coincidence problem is solved, provided that the screened DBI scalar
also plays the role of dark energy on the cosmic scales.
| [
{
"created": "Sun, 25 Oct 2015 13:13:15 GMT",
"version": "v1"
},
{
"created": "Mon, 21 Dec 2015 14:07:39 GMT",
"version": "v2"
},
{
"created": "Sat, 23 Jan 2016 01:59:19 GMT",
"version": "v3"
}
] | 2016-01-26 | [
[
"Cai",
"Rong-Gen",
""
],
[
"Wang",
"Shao-Jiang",
""
]
] | It was shown recently that, without jeopardizing the success of the $\Lambda$ cold dark matter model on cosmic scales, the modified Newtonian dynamics (MOND) can be derived as an emergent phenomenon when axionlike dark matter particles condense into superfluid on the galactic scales. We propose in this paper a Dirac-Born-Infeld (DBI) scalar field conformally coupled to the matter components. To maintain the success of MOND phenomenon of dark matter superfluid on the galactic scales, the fifth force introduced by the DBI scalar should be screened on the galactic scales. It turns out that the screening effect naturally leads to a simple explanation for a longstanding puzzle that the MOND critical acceleration coincides with present Hubble scale. This galactic coincidence problem is solved, provided that the screened DBI scalar also plays the role of dark energy on the cosmic scales. |
0810.1491 | Alberto Lobo | P Canizares, A Conchillo, E Garcia-Berro, L Gesa, C Grimani, I Lloro,
A Lobo, I Mateos, M Nofrarias, J Ramos-Castro, J Sanjuan and CF Sopuerta | The diagnostics subsystem on board LISA PathFinder and LISA | 11 pages, 5 figures, pdflatex, prepared for the Proceedings of the
7th International LISA Symposium (Barcelona, Spain, 16-20 June-2008),
submitted to Classical and Quantum Gravity | null | 10.1088/0264-9381/26/9/094005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Data and Diagnostics Subsystem of the LTP hardware and software are at
present essentially ready for delivery. In this presentation we intend to
describe the scientific and technical aspects of this subsystem, which includes
thermal diagnostics, magnetic diagnostics and a Radiation Monitor, as well as
the prospects for their integration within the rest of the LTP. We also sketch
a few lines of progress recently opened up towards the more demanding
diagnostics requirements which will be needed for LISA.
| [
{
"created": "Wed, 8 Oct 2008 17:33:03 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Canizares",
"P",
""
],
[
"Conchillo",
"A",
""
],
[
"Garcia-Berro",
"E",
""
],
[
"Gesa",
"L",
""
],
[
"Grimani",
"C",
""
],
[
"Lloro",
"I",
""
],
[
"Lobo",
"A",
""
],
[
"Mateos",
"I",
""
]... | The Data and Diagnostics Subsystem of the LTP hardware and software are at present essentially ready for delivery. In this presentation we intend to describe the scientific and technical aspects of this subsystem, which includes thermal diagnostics, magnetic diagnostics and a Radiation Monitor, as well as the prospects for their integration within the rest of the LTP. We also sketch a few lines of progress recently opened up towards the more demanding diagnostics requirements which will be needed for LISA. |
2102.02556 | David Burton | C. Fiedler, D.A. Burton | Analogue Hawking temperature of a laser-driven plasma | 12 pages. Green OA version of an article accepted for publication by
Physics Letters A | Phys. Lett. A 403 (2021) 127380 | 10.1016/j.physleta.2021.127380 | null | gr-qc physics.plasm-ph | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We present a method for exploring analogue Hawking radiation using a laser
pulse propagating through an underdense plasma. The propagating fields in the
Hawking effect are local perturbations of the plasma density and laser
amplitude. We derive the dependence of the resulting Hawking temperature on the
dimensionless amplitude of the laser and the behaviour of the spot area of the
laser at the analogue event horizon. We demonstrate one possible way of
obtaining the analogue Hawking temperature in terms of the plasma wavelength,
and our analysis shows that for a high intensity near-IR laser the analogue
Hawking temperature is less than approximately 25K for a reasonable choice of
parameters.
| [
{
"created": "Thu, 4 Feb 2021 11:45:56 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Apr 2021 09:09:22 GMT",
"version": "v2"
}
] | 2021-05-04 | [
[
"Fiedler",
"C.",
""
],
[
"Burton",
"D. A.",
""
]
] | We present a method for exploring analogue Hawking radiation using a laser pulse propagating through an underdense plasma. The propagating fields in the Hawking effect are local perturbations of the plasma density and laser amplitude. We derive the dependence of the resulting Hawking temperature on the dimensionless amplitude of the laser and the behaviour of the spot area of the laser at the analogue event horizon. We demonstrate one possible way of obtaining the analogue Hawking temperature in terms of the plasma wavelength, and our analysis shows that for a high intensity near-IR laser the analogue Hawking temperature is less than approximately 25K for a reasonable choice of parameters. |
1802.02728 | Ryotaro Kase | Ryotaro Kase, Shinji Tsujikawa | Dark energy scenario consistent with GW170817 in theories beyond
Horndeski gravity | 23 pages, 7 figures, published version | Phys. Rev. D 97, 103501 (2018) | 10.1103/PhysRevD.97.103501 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories up to quartic order are
the general scheme of scalar-tensor theories allowing the possibility for
realizing the tensor propagation speed $c_t$ equivalent to 1 on the isotropic
cosmological background. We propose a dark energy model in which the late-time
cosmic acceleration occurs by a simple k-essence Lagrangian analogous to the
ghost condensate with cubic and quartic Galileons in the framework of GLPV
theories. We show that a wide variety of the variation of the dark energy
equation of state $w_{\rm DE}$ including the entry to the region $w_{\rm
DE}<-1$ can be realized without violating conditions for the absence of ghosts
and Laplacian instabilities. The approach to the tracker equation of state
$w_{\rm DE}=-2$ during the matter era, which is disfavored by observational
data, can be avoided by the existence of a quadratic k-essence Lagrangian
$X^2$. We study the evolution of nonrelativistic matter perturbations for the
model $c_t^2=1$ and show that the two quantities $\mu$ and $\Sigma$, which are
related to the Newtonian and weak lensing gravitational potentials
respectively, are practically equivalent to each other, such that $\mu \simeq
\Sigma>1$. For the case in which the deviation of $w_{\rm DE}$ from $-1$ is
significant at a later cosmological epoch, the values of $\mu$ and $\Sigma$
tend to be larger at low redshifts. We also find that our dark energy model can
be consistent with the bounds on the deviation parameter $\alpha_{\rm H}$ from
Horndeski theories arising from the modification of gravitational law inside
massive objects.
| [
{
"created": "Thu, 8 Feb 2018 06:58:31 GMT",
"version": "v1"
},
{
"created": "Wed, 2 May 2018 09:17:48 GMT",
"version": "v2"
}
] | 2018-05-03 | [
[
"Kase",
"Ryotaro",
""
],
[
"Tsujikawa",
"Shinji",
""
]
] | The Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories up to quartic order are the general scheme of scalar-tensor theories allowing the possibility for realizing the tensor propagation speed $c_t$ equivalent to 1 on the isotropic cosmological background. We propose a dark energy model in which the late-time cosmic acceleration occurs by a simple k-essence Lagrangian analogous to the ghost condensate with cubic and quartic Galileons in the framework of GLPV theories. We show that a wide variety of the variation of the dark energy equation of state $w_{\rm DE}$ including the entry to the region $w_{\rm DE}<-1$ can be realized without violating conditions for the absence of ghosts and Laplacian instabilities. The approach to the tracker equation of state $w_{\rm DE}=-2$ during the matter era, which is disfavored by observational data, can be avoided by the existence of a quadratic k-essence Lagrangian $X^2$. We study the evolution of nonrelativistic matter perturbations for the model $c_t^2=1$ and show that the two quantities $\mu$ and $\Sigma$, which are related to the Newtonian and weak lensing gravitational potentials respectively, are practically equivalent to each other, such that $\mu \simeq \Sigma>1$. For the case in which the deviation of $w_{\rm DE}$ from $-1$ is significant at a later cosmological epoch, the values of $\mu$ and $\Sigma$ tend to be larger at low redshifts. We also find that our dark energy model can be consistent with the bounds on the deviation parameter $\alpha_{\rm H}$ from Horndeski theories arising from the modification of gravitational law inside massive objects. |
1912.00601 | Shahab Shahidi | Zahra Haghani and Shahab Shahidi | Cosmology in theories with derivative matter coupling | 13 pages | Phys. Dark Univ. 30 (2020) 100683 | 10.1016/j.dark.2020.100683 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new class of modified gravity theories with a healthy higher order
derivative terms of a function of the matter Lagrangian $f(L_m)$ is considered.
Generally the energy momentum tensor is not conserved, leading to the fifth
force similar to $f(R,T)$ theories. We will however show that in the FRW
background there exists two possibilities corresponding to conservative and
non-conservative cases. Cosmological implications of both cases with different
functions of the matter Lagrangian $f$ will be investigated in details and we
will show that current observational data can be satisfied in this model. The
non-conservative case however, predicts less matter sources at early times and
more deceleration. Evolution of the matter density perturbation in the
longitudinal gauge is also considered for dust matter sources. We will show
that the late time behavior of the matter density perturbation is in agreement
with current observational data at sub-horizon limit.
| [
{
"created": "Mon, 2 Dec 2019 07:14:35 GMT",
"version": "v1"
}
] | 2021-04-19 | [
[
"Haghani",
"Zahra",
""
],
[
"Shahidi",
"Shahab",
""
]
] | A new class of modified gravity theories with a healthy higher order derivative terms of a function of the matter Lagrangian $f(L_m)$ is considered. Generally the energy momentum tensor is not conserved, leading to the fifth force similar to $f(R,T)$ theories. We will however show that in the FRW background there exists two possibilities corresponding to conservative and non-conservative cases. Cosmological implications of both cases with different functions of the matter Lagrangian $f$ will be investigated in details and we will show that current observational data can be satisfied in this model. The non-conservative case however, predicts less matter sources at early times and more deceleration. Evolution of the matter density perturbation in the longitudinal gauge is also considered for dust matter sources. We will show that the late time behavior of the matter density perturbation is in agreement with current observational data at sub-horizon limit. |
2210.01574 | Zhe Feng | Zhe Feng | Charged anisotropic white dwarfs in $f\left({R}, {T}\right)$ gravity | 7 pages, 4 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the context of $f\left(R, T\right) = R + 2 \beta T$ gravity, where $R$ is
the Ricci scalar and $T$ is the trace of the energy-momentum tensor, the
equilibrium structure of charged anisotropic white dwarfs (WDs) is studied. The
stellar equations for the general case are derived and numerical solutions are
found for the Chandrasekhar equation of state (EoS) and a charge density
distribution proportional to the energy density $\rho_{\text{ch}} = \alpha
\rho$. By adjusting different parameters, the properties of the solutions under
various conditions are compared. Most importantly, by going beyond the trivial
WD in GR in various ways, the solutions may exhibit super-Chandrasekhar
behavior. This article is a study of a WD structure, and the results obtained
may have a contrasting effect on astronomical observations such as
superluminous type Ia supernovae.
| [
{
"created": "Fri, 30 Sep 2022 06:34:43 GMT",
"version": "v1"
}
] | 2022-10-05 | [
[
"Feng",
"Zhe",
""
]
] | In the context of $f\left(R, T\right) = R + 2 \beta T$ gravity, where $R$ is the Ricci scalar and $T$ is the trace of the energy-momentum tensor, the equilibrium structure of charged anisotropic white dwarfs (WDs) is studied. The stellar equations for the general case are derived and numerical solutions are found for the Chandrasekhar equation of state (EoS) and a charge density distribution proportional to the energy density $\rho_{\text{ch}} = \alpha \rho$. By adjusting different parameters, the properties of the solutions under various conditions are compared. Most importantly, by going beyond the trivial WD in GR in various ways, the solutions may exhibit super-Chandrasekhar behavior. This article is a study of a WD structure, and the results obtained may have a contrasting effect on astronomical observations such as superluminous type Ia supernovae. |
gr-qc/9705011 | Jack Gegenberg | H. Zaidi and J. Gegenberg | Back Reaction of Hawking Radiation on Black Hole Geometry | Latex file, 15 pages, 4 figures enclosed, uses epsf | Phys.Rev. D57 (1998) 1112-1117 | 10.1103/PhysRevD.57.1112 | null | gr-qc hep-th | null | We propose a model for the geometry of a dynamical spherical shell in which
the metric is asymptotically Schwarzschild, but deviates from Ricci-flatness in
a finite neighbourhood of the shell. Hence, the geometry corresponds to a
`hairy' black hole, with the hair originating on the shell. The metric is
regular for an infalling shell, but it bifurcates, leading to two disconnected
Schwarzschild-like spacetime geometries. The shell is interpreted as either
collapsing matter or as Hawking radiation, depending on whether or not the
shell is infalling or outgoing. In this model, the Hawking radiation results
from tunnelling between the two geometries. Using this model, the back reaction
correction from Hawking radiation is calculated.
| [
{
"created": "Wed, 7 May 1997 14:53:31 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Zaidi",
"H.",
""
],
[
"Gegenberg",
"J.",
""
]
] | We propose a model for the geometry of a dynamical spherical shell in which the metric is asymptotically Schwarzschild, but deviates from Ricci-flatness in a finite neighbourhood of the shell. Hence, the geometry corresponds to a `hairy' black hole, with the hair originating on the shell. The metric is regular for an infalling shell, but it bifurcates, leading to two disconnected Schwarzschild-like spacetime geometries. The shell is interpreted as either collapsing matter or as Hawking radiation, depending on whether or not the shell is infalling or outgoing. In this model, the Hawking radiation results from tunnelling between the two geometries. Using this model, the back reaction correction from Hawking radiation is calculated. |
2101.12108 | Luis Herrera | L. Herrera, A. Di Prisco, J. Ospino | Hyperbolically symmetric static fluids: A general study | 14 pages Revtex. Published in Phys.Rev.D | Physical Review D103, 024037 (2021) | 10.1103/PhysRevD.103.024037 | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/4.0/ | We carry on a comprehensive study on static fluid distributions endowed with
hyperbolical symmetry. Their physical properties are analyzed in detail. The
energy density appears to be necessarily negative, which suggests that any
possible application of this kind of fluids requires extreme physical
conditions where quantum effects are expected to play an important role. Also,
it is found that the fluid distribution cannot fill the region close to the
center of symmetry. Such a region may be represented by a vacuum cavity around
the center. A suitable definition of mass function, as well as the Tolman mass
are explicitly calculated. While the former is positive defined, the latter is
negative in most cases, revealing the repulsive nature of gravitational
interaction. A general approach to obtain exact solutions is presented and some
exact analytical solutions are exhibited.
| [
{
"created": "Thu, 28 Jan 2021 16:51:56 GMT",
"version": "v1"
}
] | 2021-02-03 | [
[
"Herrera",
"L.",
""
],
[
"Di Prisco",
"A.",
""
],
[
"Ospino",
"J.",
""
]
] | We carry on a comprehensive study on static fluid distributions endowed with hyperbolical symmetry. Their physical properties are analyzed in detail. The energy density appears to be necessarily negative, which suggests that any possible application of this kind of fluids requires extreme physical conditions where quantum effects are expected to play an important role. Also, it is found that the fluid distribution cannot fill the region close to the center of symmetry. Such a region may be represented by a vacuum cavity around the center. A suitable definition of mass function, as well as the Tolman mass are explicitly calculated. While the former is positive defined, the latter is negative in most cases, revealing the repulsive nature of gravitational interaction. A general approach to obtain exact solutions is presented and some exact analytical solutions are exhibited. |
gr-qc/0012017 | C. M. zhang | C.M. Zhang | HBO and Periastron Precession around the X-ray Neutron Star
Magnetosphere | 2 pages, 1 figure, submit to Proceedings of The Ninth Marcel Grossman
Meeting on Gen. Rel. and Grav. at Rome, Italy, July, 2000, Eds. Ruffini, R.
(World Sci. Publisher, Singapore) | null | null | null | gr-qc | null | Based on the periastron precession model to account for kHz QPO of the binary
X-ray neutron star, proposed by Stella and Vietri, we ascribe the 15-60 Hz
Quasi Periodic Oscillation (QPO) to the periastron precession frequency of the
orbiting accreted matter at the boundary of magnetosphere-disk of X-ray neutron
star (NS). The obtained conclusions include: all QPO frequencies increase with
increasing the accretion rate. The theoretical relations between 15-60 Hz QPO
(HBO) frequency and the twin kHz QPOs are similar to the measured empirical
formula. Further, the better fitted NS mass by the proposed model is about 1.9
solar masses for the detected LMXBs.
| [
{
"created": "Tue, 5 Dec 2000 12:37:34 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Zhang",
"C. M.",
""
]
] | Based on the periastron precession model to account for kHz QPO of the binary X-ray neutron star, proposed by Stella and Vietri, we ascribe the 15-60 Hz Quasi Periodic Oscillation (QPO) to the periastron precession frequency of the orbiting accreted matter at the boundary of magnetosphere-disk of X-ray neutron star (NS). The obtained conclusions include: all QPO frequencies increase with increasing the accretion rate. The theoretical relations between 15-60 Hz QPO (HBO) frequency and the twin kHz QPOs are similar to the measured empirical formula. Further, the better fitted NS mass by the proposed model is about 1.9 solar masses for the detected LMXBs. |
1205.0258 | Sanved Kolekar | Sanved Kolekar and T. Padmanabhan | Drift, Drag and Brownian motion in the Davies-Unruh bath | v1: 5 pages, no figures, v2: some discussion added, matches published
version | Phys. Rev. D 86, 104057 (2012) | 10.1103/PhysRevD.86.104057 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An interesting feature of the Davies-Unruh effect is that an uniformly
accelerated observer sees an isotropic thermal spectrum of particles even
though there is a preferred direction in this context, determined by the
direction of the acceleration g. We investigate the thermal fluctuations in the
Unruh bath by studying the Brownian motion of particles in the bath, especially
as regards to isotropy. We find that the thermal fluctuations are anisotropic
and induce different frictional drag forces on the Brownian particle depending
on whether it has a drift velocity along the direction of acceleration g or in
a direction transverse to it. Using the fluctuation-dissipation theorem, we
argue that this anisotropy arises due to quantum correlations in the
fluctuations at large correlation time scales.
| [
{
"created": "Tue, 1 May 2012 20:35:04 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Nov 2012 16:58:45 GMT",
"version": "v2"
}
] | 2012-11-29 | [
[
"Kolekar",
"Sanved",
""
],
[
"Padmanabhan",
"T.",
""
]
] | An interesting feature of the Davies-Unruh effect is that an uniformly accelerated observer sees an isotropic thermal spectrum of particles even though there is a preferred direction in this context, determined by the direction of the acceleration g. We investigate the thermal fluctuations in the Unruh bath by studying the Brownian motion of particles in the bath, especially as regards to isotropy. We find that the thermal fluctuations are anisotropic and induce different frictional drag forces on the Brownian particle depending on whether it has a drift velocity along the direction of acceleration g or in a direction transverse to it. Using the fluctuation-dissipation theorem, we argue that this anisotropy arises due to quantum correlations in the fluctuations at large correlation time scales. |
gr-qc/0310102 | Navin Singh | S.C. Tiwari | Unimodular relativity and cosmological constant : Comments | Submitted to Journal of Mathematical Physics; correspondence to
vns_sctiwari@yahoo.com | null | null | null | gr-qc | null | We show that the conclusion that matter stress-energy tensor satisfies the
usual covariant continuity law, and the cosmological constant is still a
constant of integration arrived at by Finkelstein et al (42, 340, 2001) is not
valid.
| [
{
"created": "Wed, 22 Oct 2003 06:37:50 GMT",
"version": "v1"
}
] | 2009-09-29 | [
[
"Tiwari",
"S. C.",
""
]
] | We show that the conclusion that matter stress-energy tensor satisfies the usual covariant continuity law, and the cosmological constant is still a constant of integration arrived at by Finkelstein et al (42, 340, 2001) is not valid. |
1812.08937 | Parampreet Singh | Sahil Saini, Parampreet Singh | Generic absence of strong singularities and geodesic completeness in
modified loop quantum cosmologies | Minor revision to match published version in CQG | Class.Quant.Grav. 36 (2019) 105014 | 10.1088/1361-6382/ab1274 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Different regularizations of the Hamiltonian constraint in loop quantum
cosmology yield modified loop quantum cosmologies, namely mLQC-I and mLQC-II,
which lead to qualitatively different Planck scale physics. We perform a
comprehensive analysis of resolution of various singularities in these modified
loop cosmologies using effective spacetime description and compare with earlier
results in standard loop quantum cosmology. We show that the volume remains
non-zero and finite in finite time evolution for all considered loop
cosmological models. Interestingly, even though expansion scalar and energy
density are bounded due to quantum geometry, curvature invariants can still
potentially diverge due to pressure singularities at a finite volume. These
divergences are shown to be harmless since geodesic evolution does not break
down and no strong singularities are present in the effective spacetimes of
loop cosmologies. Using a phenomenological matter model, various types of
exotic strong and weak singularities, including big rip, sudden, big freeze and
type-IV singularities, are studied. We show that as in standard loop quantum
cosmology, big rip and big freeze singularities are resolved in mLQC-I and
mLQC-II, but quantum geometric effects do not resolve sudden and type-IV
singularities.
| [
{
"created": "Fri, 21 Dec 2018 04:15:35 GMT",
"version": "v1"
},
{
"created": "Thu, 23 May 2019 11:35:21 GMT",
"version": "v2"
}
] | 2019-05-24 | [
[
"Saini",
"Sahil",
""
],
[
"Singh",
"Parampreet",
""
]
] | Different regularizations of the Hamiltonian constraint in loop quantum cosmology yield modified loop quantum cosmologies, namely mLQC-I and mLQC-II, which lead to qualitatively different Planck scale physics. We perform a comprehensive analysis of resolution of various singularities in these modified loop cosmologies using effective spacetime description and compare with earlier results in standard loop quantum cosmology. We show that the volume remains non-zero and finite in finite time evolution for all considered loop cosmological models. Interestingly, even though expansion scalar and energy density are bounded due to quantum geometry, curvature invariants can still potentially diverge due to pressure singularities at a finite volume. These divergences are shown to be harmless since geodesic evolution does not break down and no strong singularities are present in the effective spacetimes of loop cosmologies. Using a phenomenological matter model, various types of exotic strong and weak singularities, including big rip, sudden, big freeze and type-IV singularities, are studied. We show that as in standard loop quantum cosmology, big rip and big freeze singularities are resolved in mLQC-I and mLQC-II, but quantum geometric effects do not resolve sudden and type-IV singularities. |
1507.03382 | B. S. Ratanpal | B. S. Ratanpal, V. O. Thomas and D. M. Pandya | A new class of solutions of anisotropic charged distributions on
pseudo-spheroidal spacetime | 21 pages, 12 figures and 2 tables | Astrophys Space Sci (2015) 360:53 | 10.1007/s10509-015-2568-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present article a new class of exact solutions of Einstein's field
equations for charged anisotropic distribution is obtained on the background of
pseudo-spheroidal spacetime characterized by the metric potential
$g_{rr}=\frac{1+K\frac{r^2}{R^2}}{1+\frac{r^2}{R^2}}$, where $K$ and $R$ are
geometric parameters of the spacetime. The radial pressure $p_r$ and electric
field intensity $E$ are taken in the form $8\pi p_r =
\frac{K-1}{R^2}\frac{\left(1-\frac{r^2}{R^2} \right)}{\left(1+K\frac{r^2}{R^2}
\right)^2}$ and $E^2 =
\frac{\alpha(K-1)\frac{r^2}{R^2}}{R^2\left(1+K\frac{r^2}{R^2} \right)^2}$. The
bounds of geometric parameter $K$ and the parameter $\alpha$ appearing in the
expression of $E^2$ are obtained by imposing the requirements for a physically
acceptable model. It is found that the model is in good agreement with the
observational data of number of compact stars like 4U 1820-30, PSR J1903+327,
4U 1608-52, Vela X-1, PSR J1614-2230, Cen X-3 given by Gangopadhyay {\em{et
al}} [Gangopadhyay T., Ray S., Li X-D., Dey J. and Dey M., {\it Mon. Not. R.
Astron. Soc.} {\bf431} (2013) 3216]. When $\alpha = 0$, the model reduces to
the uncharged anisotropic distribution given by Ratanpal {\em et al.} [Ratanpal
B. S., Thomas V. O. and Pandya D. M., arXiv:1506.08512 [gr-qc](2015)]
| [
{
"created": "Mon, 13 Jul 2015 10:12:41 GMT",
"version": "v1"
}
] | 2016-04-07 | [
[
"Ratanpal",
"B. S.",
""
],
[
"Thomas",
"V. O.",
""
],
[
"Pandya",
"D. M.",
""
]
] | In the present article a new class of exact solutions of Einstein's field equations for charged anisotropic distribution is obtained on the background of pseudo-spheroidal spacetime characterized by the metric potential $g_{rr}=\frac{1+K\frac{r^2}{R^2}}{1+\frac{r^2}{R^2}}$, where $K$ and $R$ are geometric parameters of the spacetime. The radial pressure $p_r$ and electric field intensity $E$ are taken in the form $8\pi p_r = \frac{K-1}{R^2}\frac{\left(1-\frac{r^2}{R^2} \right)}{\left(1+K\frac{r^2}{R^2} \right)^2}$ and $E^2 = \frac{\alpha(K-1)\frac{r^2}{R^2}}{R^2\left(1+K\frac{r^2}{R^2} \right)^2}$. The bounds of geometric parameter $K$ and the parameter $\alpha$ appearing in the expression of $E^2$ are obtained by imposing the requirements for a physically acceptable model. It is found that the model is in good agreement with the observational data of number of compact stars like 4U 1820-30, PSR J1903+327, 4U 1608-52, Vela X-1, PSR J1614-2230, Cen X-3 given by Gangopadhyay {\em{et al}} [Gangopadhyay T., Ray S., Li X-D., Dey J. and Dey M., {\it Mon. Not. R. Astron. Soc.} {\bf431} (2013) 3216]. When $\alpha = 0$, the model reduces to the uncharged anisotropic distribution given by Ratanpal {\em et al.} [Ratanpal B. S., Thomas V. O. and Pandya D. M., arXiv:1506.08512 [gr-qc](2015)] |
2104.11236 | Lorenzo Annulli | Lorenzo Annulli, Vitor Cardoso, Leonardo Gualtieri | Applications of the close-limit approximation: horizonless compact
objects and scalar fields | 16 pages, 4 figures. Matches published version in CQG | Class.Quant.Grav. 39 (2022) 10, 105005 | 10.1088/1361-6382/ac6410 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The ability to model the evolution of compact binaries from the inspiral to
coalescence is central to gravitational wave astronomy. Current waveform
catalogues are built from vacuum binary black hole models, by evolving Einstein
equations numerically and complementing them with knowledge from slow-motion
expansions. Much less is known about the coalescence process in the presence of
matter, or in theories other than General Relativity. Here, we explore the
Close Limit Approximation as a powerful tool to understand the coalescence
process in general setups. In particular, we study the head-on collision of two
equal-mass, compact but horizonless objects. Our results show the appearance of
``echoes'' and indicate that a significant fraction of the merger energy goes
into these late-time repetitions. We also apply the Close Limit Approximation
to investigate the effect of colliding black holes on surrounding scalar
fields. Notably, our results indicate that observables obtained through
perturbation theory may be extended to a significant segment of the merger
phase, where in principle only a numerical approach is appropriate.
| [
{
"created": "Thu, 22 Apr 2021 18:00:00 GMT",
"version": "v1"
},
{
"created": "Thu, 19 May 2022 16:26:10 GMT",
"version": "v2"
}
] | 2022-05-20 | [
[
"Annulli",
"Lorenzo",
""
],
[
"Cardoso",
"Vitor",
""
],
[
"Gualtieri",
"Leonardo",
""
]
] | The ability to model the evolution of compact binaries from the inspiral to coalescence is central to gravitational wave astronomy. Current waveform catalogues are built from vacuum binary black hole models, by evolving Einstein equations numerically and complementing them with knowledge from slow-motion expansions. Much less is known about the coalescence process in the presence of matter, or in theories other than General Relativity. Here, we explore the Close Limit Approximation as a powerful tool to understand the coalescence process in general setups. In particular, we study the head-on collision of two equal-mass, compact but horizonless objects. Our results show the appearance of ``echoes'' and indicate that a significant fraction of the merger energy goes into these late-time repetitions. We also apply the Close Limit Approximation to investigate the effect of colliding black holes on surrounding scalar fields. Notably, our results indicate that observables obtained through perturbation theory may be extended to a significant segment of the merger phase, where in principle only a numerical approach is appropriate. |
2010.09173 | Hwajin Eom | Hwajin Eom, Wontae Kim | On thermal radiation of de Sitter space in the semiclassical
Jackiw-Teitelboim model | 16 pages, 1 figure, comments and references added | Gen Relativ Gravit 54, 104 (2022) | 10.1007/s10714-022-02994-5 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In general, the Gibbons-Hawking temperature based on the Euclidean functional
approach shows that de Sitter space in the Bunch-Davies vacuum is globally
thermal. In the exactly soluble semiclassical Jackiw-Teitelboim model, we
investigate thermal property of de Sitter space by taking into account the
quantum back reaction of the geometry. The proper temperature of de Sitter
space in the Bunch-Davies vacuum is found to vanish. In case of a certain
quantum state breaking the de Sitter symmetry, de Sitter space can be made
thermally exited; however, in this case the dilaton singularity cannot be
avoided. Consequently, in the Jackiw-Teitelboim model the proper temperature of
de Sitter space in the Bunch-Davies vacuum turns out to be zero and the
Bunch-Davies vacuum is found to be the only physical vacuum without any naked
singularities.
| [
{
"created": "Mon, 19 Oct 2020 02:29:39 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Jan 2021 07:32:11 GMT",
"version": "v2"
},
{
"created": "Tue, 26 Oct 2021 05:58:48 GMT",
"version": "v3"
},
{
"created": "Thu, 15 Sep 2022 02:44:56 GMT",
"version": "v4"
}
] | 2022-09-16 | [
[
"Eom",
"Hwajin",
""
],
[
"Kim",
"Wontae",
""
]
] | In general, the Gibbons-Hawking temperature based on the Euclidean functional approach shows that de Sitter space in the Bunch-Davies vacuum is globally thermal. In the exactly soluble semiclassical Jackiw-Teitelboim model, we investigate thermal property of de Sitter space by taking into account the quantum back reaction of the geometry. The proper temperature of de Sitter space in the Bunch-Davies vacuum is found to vanish. In case of a certain quantum state breaking the de Sitter symmetry, de Sitter space can be made thermally exited; however, in this case the dilaton singularity cannot be avoided. Consequently, in the Jackiw-Teitelboim model the proper temperature of de Sitter space in the Bunch-Davies vacuum turns out to be zero and the Bunch-Davies vacuum is found to be the only physical vacuum without any naked singularities. |
1905.03227 | Shubham Maheshwari | K. Sravan Kumar, Shubham Maheshwari, Anupam Mazumdar | Perturbations in higher derivative gravity beyond maximally symmetric
spacetimes | 36 pages, 1 figure | Phys. Rev. D 100, 064022 (2019) | 10.1103/PhysRevD.100.064022 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study (covariant) scalar-vector-tensor (SVT) perturbations of infinite
derivative gravity (IDG), at the quadratic level of the action, around
conformally-flat, covariantly constant curvature backgrounds which are not
maximally symmetric spacetimes (MSS). This extends a previous analysis of
perturbations done around MSS, which were shown to be ghost-free. We motivate
our choice of backgrounds which arise as solutions of IDG in the UV, avoiding
big bang and black hole singularities. Contrary to MSS, in this paper we show
that, generically, all SVT modes are coupled to each other at the quadratic
level of the action. We consider simple examples of the full IDG action, and
illustrate this mixing and also a case where the action can be diagonalized and
ghost-free solutions constructed. Our study is widely applicable for both
non-singular cosmology and black hole physics where backgrounds depart from
MSS. In appendices, we provide SVT perturbations around conformally-flat and
arbitrary backgrounds which can serve as a compendium of useful results when
studying SVT perturbations of various higher derivative gravity models.
| [
{
"created": "Wed, 8 May 2019 17:30:30 GMT",
"version": "v1"
}
] | 2019-09-18 | [
[
"Kumar",
"K. Sravan",
""
],
[
"Maheshwari",
"Shubham",
""
],
[
"Mazumdar",
"Anupam",
""
]
] | We study (covariant) scalar-vector-tensor (SVT) perturbations of infinite derivative gravity (IDG), at the quadratic level of the action, around conformally-flat, covariantly constant curvature backgrounds which are not maximally symmetric spacetimes (MSS). This extends a previous analysis of perturbations done around MSS, which were shown to be ghost-free. We motivate our choice of backgrounds which arise as solutions of IDG in the UV, avoiding big bang and black hole singularities. Contrary to MSS, in this paper we show that, generically, all SVT modes are coupled to each other at the quadratic level of the action. We consider simple examples of the full IDG action, and illustrate this mixing and also a case where the action can be diagonalized and ghost-free solutions constructed. Our study is widely applicable for both non-singular cosmology and black hole physics where backgrounds depart from MSS. In appendices, we provide SVT perturbations around conformally-flat and arbitrary backgrounds which can serve as a compendium of useful results when studying SVT perturbations of various higher derivative gravity models. |
2208.12538 | Reginald Christian Bernardo | Reginald Christian Bernardo and Kin-Wang Ng | Stochastic gravitational wave background phenomenology in a pulsar
timing array | 28 pages, 5 figures, discussion improved, to appear in PRD, see
implementation `PTAfast' https://github.com/reggiebernardo/PTAfast | Phys. Rev. D 107, 044007 (2023) | 10.1103/PhysRevD.107.044007 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Pulsar timing offers an independent avenue to test general relativity and
alternative gravity theories. This requires an understanding of how metric
polarizations beyond the familiar transverse tensor ones imprint as a
stochastic gravitational wave background and correlate the arrival time of
radio pulses from a pair of millisecond pulsars. In this work, we focus on an
isotropic stochastic gravitational wave background and present a
straightforward, self-contained formalism for obtaining the power spectrum and
the overlap reduction function, the relevant physical observable in a pulsar
timing array, for generic gravitational degrees of freedom featuring both
transverse and longitudinal modes off the light cone. We additionally highlight
our consideration of finite pulsar distances, which we find significant in two
ways: first, making all the modes well defined, and second, keeping the small
scale power that is contained by pulsars of subdegree separations in the sky.
We discuss this for tensor, vector, and scalar polarizations, for each one
focusing on the angular power spectrum and the overlap reduction function for
an isotropic stochastic gravitational wave background. Our results pave the
road for an efficient numerical method for examining the gravitational wave
induced spatial correlations across millisecond pulsars in a pulsar timing
array.
| [
{
"created": "Fri, 26 Aug 2022 09:54:41 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Jan 2023 10:54:35 GMT",
"version": "v2"
}
] | 2023-02-08 | [
[
"Bernardo",
"Reginald Christian",
""
],
[
"Ng",
"Kin-Wang",
""
]
] | Pulsar timing offers an independent avenue to test general relativity and alternative gravity theories. This requires an understanding of how metric polarizations beyond the familiar transverse tensor ones imprint as a stochastic gravitational wave background and correlate the arrival time of radio pulses from a pair of millisecond pulsars. In this work, we focus on an isotropic stochastic gravitational wave background and present a straightforward, self-contained formalism for obtaining the power spectrum and the overlap reduction function, the relevant physical observable in a pulsar timing array, for generic gravitational degrees of freedom featuring both transverse and longitudinal modes off the light cone. We additionally highlight our consideration of finite pulsar distances, which we find significant in two ways: first, making all the modes well defined, and second, keeping the small scale power that is contained by pulsars of subdegree separations in the sky. We discuss this for tensor, vector, and scalar polarizations, for each one focusing on the angular power spectrum and the overlap reduction function for an isotropic stochastic gravitational wave background. Our results pave the road for an efficient numerical method for examining the gravitational wave induced spatial correlations across millisecond pulsars in a pulsar timing array. |
2210.02861 | Vasilis Oikonomou | V.K. Oikonomou | Effects of a Pre-inflationary de Sitter Bounce on the Primordial
Gravitational Waves in $f(R)$ Gravity Theories | Nuclear Physics B in press. arXiv admin note: text overlap with
arXiv:2209.09781 | null | 10.1016/j.nuclphysb.2022.115985 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we examine the effects of a pre-inflationary de Sitter bounce on
the energy spectrum of the primordial gravitational waves. Specifically we
assume that the Universe is described by several evolution patches, starting
with a de Sitter pre-inflationary bounce which is followed by an quasi-de
Sitter slow-roll inflationary era, followed by a constant equation of state
parameter abnormal reheating era, which is followed by the radiation and matter
domination eras and the late-time acceleration eras. The bounce and the
inflationary era can be realized by vacuum $f(R)$ gravity and the abnormal
reheating and the late-time acceleration eras by the synergy of $f(R)$ gravity
and the prefect matter fluids present. Using well-known reconstruction
techniques we find which $f(R)$ gravity can realize each evolution patch,
except from the matter and radiation domination eras which are realized by the
corresponding matter fluids. Accordingly, we calculate the damping factor of
the primordial de Sitter bounce, and as we show, the signal can be detected by
only one gravitational wave future experiment, in contrast to the case in which
the bounce is absent. We discuss in detail the consequences of our results and
the future perspectives.
| [
{
"created": "Thu, 6 Oct 2022 12:21:10 GMT",
"version": "v1"
}
] | 2022-10-19 | [
[
"Oikonomou",
"V. K.",
""
]
] | In this work we examine the effects of a pre-inflationary de Sitter bounce on the energy spectrum of the primordial gravitational waves. Specifically we assume that the Universe is described by several evolution patches, starting with a de Sitter pre-inflationary bounce which is followed by an quasi-de Sitter slow-roll inflationary era, followed by a constant equation of state parameter abnormal reheating era, which is followed by the radiation and matter domination eras and the late-time acceleration eras. The bounce and the inflationary era can be realized by vacuum $f(R)$ gravity and the abnormal reheating and the late-time acceleration eras by the synergy of $f(R)$ gravity and the prefect matter fluids present. Using well-known reconstruction techniques we find which $f(R)$ gravity can realize each evolution patch, except from the matter and radiation domination eras which are realized by the corresponding matter fluids. Accordingly, we calculate the damping factor of the primordial de Sitter bounce, and as we show, the signal can be detected by only one gravitational wave future experiment, in contrast to the case in which the bounce is absent. We discuss in detail the consequences of our results and the future perspectives. |
1911.00541 | Emanuele Berti | Emanuele Berti | Topical Collection: Testing the Kerr spacetime with gravitational-wave
and electromagnetic observations | Introduction to the General Relativity and Gravitation Topical
Collection "Testing the Kerr spacetime with gravitational-wave and
electromagnetic observations", available at
https://link.springer.com/journal/10714/topicalCollection/AC_9f63b87d155730bc7589edb13e509026 | Gen Relativ Gravit 51, 140 (2019) | 10.1007/s10714-019-2622-2 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | One of the Holy Grails of observational astronomy is to confirm the
prediction that black holes in the Universe are described by the Kerr solution
of Einstein's field equations of general relativity. This Topical Collection
provides a status report of theoretical and experimental progress towards
confirming the "Kerr paradigm" through X-ray astronomy, gravitational lensing,
stellar tidal disruption events, superradiance, and gravitational-wave
observations of black hole binary mergers.
| [
{
"created": "Fri, 1 Nov 2019 18:28:51 GMT",
"version": "v1"
}
] | 2019-11-05 | [
[
"Berti",
"Emanuele",
""
]
] | One of the Holy Grails of observational astronomy is to confirm the prediction that black holes in the Universe are described by the Kerr solution of Einstein's field equations of general relativity. This Topical Collection provides a status report of theoretical and experimental progress towards confirming the "Kerr paradigm" through X-ray astronomy, gravitational lensing, stellar tidal disruption events, superradiance, and gravitational-wave observations of black hole binary mergers. |
gr-qc/9905043 | Kleidis Kostas | K. Kleidis and D. B. Papadopoulos | On the adiabatic expansion of the visible space in a higher-dimensional
Cosmology | LaTex file, 14 pages | Gen.Rel.Grav. 29 (1997) 275 | 10.1023/A:1010264717346 | null | gr-qc | null | In the context of higher-dimensional cosmologies with isotropic visible and
internal space and multi-perfect fluid matter, we study the conditions under
which adiabatic expansion of the visoble external space is possible, when a
time-dependent internal space is present. The analysis is based on a
reinterpretation of the four-dimensional stress-energy tensor in the presence
of the extra dimensions. This modifies the usual adiabatic energy conservation
laws for the visible Universe, leading to a new type of cosmological evolution
which includes large-scale entropy production in four dimensions.
| [
{
"created": "Thu, 13 May 1999 12:38:06 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Kleidis",
"K.",
""
],
[
"Papadopoulos",
"D. B.",
""
]
] | In the context of higher-dimensional cosmologies with isotropic visible and internal space and multi-perfect fluid matter, we study the conditions under which adiabatic expansion of the visoble external space is possible, when a time-dependent internal space is present. The analysis is based on a reinterpretation of the four-dimensional stress-energy tensor in the presence of the extra dimensions. This modifies the usual adiabatic energy conservation laws for the visible Universe, leading to a new type of cosmological evolution which includes large-scale entropy production in four dimensions. |
1601.07395 | Nils Andersson | N. Andersson, S. Wells and J.A. Vickers | Quantised vortices and mutual friction in relativistic superfluids | 9 pages, RevTeX | null | 10.1088/0264-9381/33/24/245010 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the detailed dynamics of an array of quantised superfluid
vortices in the framework of general relativity, as required for quantitative
modelling of realistic neutron star cores. Our model builds on the variational
approach to relativistic (multi-) fluid dynamics, where the vorticity plays a
central role. The description provides a natural extension of, and as it
happens a better insight into, existing Newtonian models. In particular, we
account for the mutual friction associated with scattering of a second "normal"
component in the mixture off of the superfluid vortices.
| [
{
"created": "Wed, 27 Jan 2016 14:55:38 GMT",
"version": "v1"
}
] | 2016-12-07 | [
[
"Andersson",
"N.",
""
],
[
"Wells",
"S.",
""
],
[
"Vickers",
"J. A.",
""
]
] | We consider the detailed dynamics of an array of quantised superfluid vortices in the framework of general relativity, as required for quantitative modelling of realistic neutron star cores. Our model builds on the variational approach to relativistic (multi-) fluid dynamics, where the vorticity plays a central role. The description provides a natural extension of, and as it happens a better insight into, existing Newtonian models. In particular, we account for the mutual friction associated with scattering of a second "normal" component in the mixture off of the superfluid vortices. |
gr-qc/9911037 | Plamen Fiziev | P. P. Fiziev | A Minimal Model for Dilatonic Gravity | 10 pages, LaTeX, no figures. A new Appendex added, new references,
comments and acknowledgments added, typos corrected. Final version: to appear
in Modern Physics Letters A | null | 10.1142/S0217732300002553 | SU-FzF: 4/99 | gr-qc astro-ph hep-ph hep-th | null | We study a new minimal scalar-tensor model of gravity with Brans-Dicke factor
$\omega(\Phi)\equiv 0$ and cosmological factor $\Pi(\Phi)$. The constraints on
$\Pi(\Phi)$ from known gravitational experiments are derived. We show that
almost any time evolution of the scale factor in a homogeneous isotropic
Universe can be obtained via properly chosen $\Pi(\Phi)$ and discuss the
general properties of models of this type.
| [
{
"created": "Wed, 10 Nov 1999 07:40:10 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Jan 2000 12:58:54 GMT",
"version": "v2"
},
{
"created": "Sat, 2 Dec 2000 15:50:59 GMT",
"version": "v3"
}
] | 2009-10-31 | [
[
"Fiziev",
"P. P.",
""
]
] | We study a new minimal scalar-tensor model of gravity with Brans-Dicke factor $\omega(\Phi)\equiv 0$ and cosmological factor $\Pi(\Phi)$. The constraints on $\Pi(\Phi)$ from known gravitational experiments are derived. We show that almost any time evolution of the scale factor in a homogeneous isotropic Universe can be obtained via properly chosen $\Pi(\Phi)$ and discuss the general properties of models of this type. |
1508.05126 | Fay\c{c}al Hammad | Fay\c{c}al Hammad | $f(R)$-Modified Gravity, Wald Entropy, and the Generalized Uncertainty
Principle | 7 pages. Matches the accepted version | Phys. Rev. D 92, 044004 (2015) | 10.1103/PhysRevD.92.044004 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Wald's entropy formula allows one to find the entropy of black holes' event
horizon within any diffeomorphism invariant theory of gravity. When applied to
general relativity, the formula yields the Bekenstein-Hawking result but, for
any other gravitational action that departs from the Hilbert action, the
resulting entropy acquires an additional multiplicative factor that depends on
the global geometry of the background spacetime. On the other hand, the
generalized uncertainty principle (GUP) has extensively been recently used to
investigate corrections to the Bekenstein-Hawking entropy formula, with the
conclusion that the latter always comes multiplied by a factor that depends on
the area of the event horizon. We show, by considering the case of an
$f(R)$-modified gravity, that the usual black hole entropy derivation based on
the GUP might be modified in such a way that the two methods yield the same
corrections to Bekenstein-Hawking formula. The procedure turns out to be an
interesting method for seeking modified gravity theories. Two different
versions of the GUP are used and it is found that only one of them yields a
viable modified gravity model. Conversely, it is possible to find a general
formulation of the GUP that would reproduce Wald entropy formula for any
$f(R)$-theory of gravity.
| [
{
"created": "Tue, 4 Aug 2015 21:38:19 GMT",
"version": "v1"
}
] | 2015-08-24 | [
[
"Hammad",
"Fayçal",
""
]
] | Wald's entropy formula allows one to find the entropy of black holes' event horizon within any diffeomorphism invariant theory of gravity. When applied to general relativity, the formula yields the Bekenstein-Hawking result but, for any other gravitational action that departs from the Hilbert action, the resulting entropy acquires an additional multiplicative factor that depends on the global geometry of the background spacetime. On the other hand, the generalized uncertainty principle (GUP) has extensively been recently used to investigate corrections to the Bekenstein-Hawking entropy formula, with the conclusion that the latter always comes multiplied by a factor that depends on the area of the event horizon. We show, by considering the case of an $f(R)$-modified gravity, that the usual black hole entropy derivation based on the GUP might be modified in such a way that the two methods yield the same corrections to Bekenstein-Hawking formula. The procedure turns out to be an interesting method for seeking modified gravity theories. Two different versions of the GUP are used and it is found that only one of them yields a viable modified gravity model. Conversely, it is possible to find a general formulation of the GUP that would reproduce Wald entropy formula for any $f(R)$-theory of gravity. |
gr-qc/0512099 | Wenbiao Liu | Wenbiao Liu | New Coordinates for BTZ Black Hole and Hawking Radiation via Tunnelling | null | Phys.Lett. B634 (2006) 541-544 | 10.1016/j.physletb.2006.01.028 | null | gr-qc | null | Hawking radiation can usefully be viewed as a semi-classical tunnelling
process that originates at the black hole horizon. For the stationary
axisymmetric BTZ black hole, a generalized Painleve coordinate system
(Painleve-BTZ coordinates) is introduced, and Hawking radiation as tunnelling
under the effect of self-gravitation is investigated. The corrected radiation
is obtained which is not precise thermal spectrum. The result is consistent
with the underlying unitary theory. Moreover, Bekenstein-Hawking entropy of BTZ
black hole is not necessarily corrected when we choose appropriate coordinate
system to study the tunnelling effect.
| [
{
"created": "Fri, 16 Dec 2005 14:21:30 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Liu",
"Wenbiao",
""
]
] | Hawking radiation can usefully be viewed as a semi-classical tunnelling process that originates at the black hole horizon. For the stationary axisymmetric BTZ black hole, a generalized Painleve coordinate system (Painleve-BTZ coordinates) is introduced, and Hawking radiation as tunnelling under the effect of self-gravitation is investigated. The corrected radiation is obtained which is not precise thermal spectrum. The result is consistent with the underlying unitary theory. Moreover, Bekenstein-Hawking entropy of BTZ black hole is not necessarily corrected when we choose appropriate coordinate system to study the tunnelling effect. |
1808.06939 | Lorenzo Sebastiani | L. Sebastiani, L. Vanzo, S. Zerbini | On a WKB formula for echoes | 27 pages, references added, accepted in IJGMMP | null | 10.1142/S0219887819501810 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present an unified approach for the study of idealized gravitational
compact objects like wormholes and horizonless stars, here simulated by the
presence of boundary conditions at a deeply inner wall. At classical level,
namely neglecting quantum effects, the presence of the wall leads to
characteristic echoes following the usual ringdown phase, such that it can
discriminate black holes from other horizonless, and probably exotic, compact
objects. With regard to this issue, an analytical though approximated
expression for the complex frequencies of the quasinormal echoes is found and
discussed. At quantum level, we show that static wormholes do not radiate.
| [
{
"created": "Mon, 20 Aug 2018 08:41:23 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Mar 2019 09:58:51 GMT",
"version": "v2"
},
{
"created": "Wed, 18 Sep 2019 07:32:46 GMT",
"version": "v3"
},
{
"created": "Tue, 8 Oct 2019 12:06:24 GMT",
"version": "v4"
}
] | 2019-11-07 | [
[
"Sebastiani",
"L.",
""
],
[
"Vanzo",
"L.",
""
],
[
"Zerbini",
"S.",
""
]
] | We present an unified approach for the study of idealized gravitational compact objects like wormholes and horizonless stars, here simulated by the presence of boundary conditions at a deeply inner wall. At classical level, namely neglecting quantum effects, the presence of the wall leads to characteristic echoes following the usual ringdown phase, such that it can discriminate black holes from other horizonless, and probably exotic, compact objects. With regard to this issue, an analytical though approximated expression for the complex frequencies of the quasinormal echoes is found and discussed. At quantum level, we show that static wormholes do not radiate. |
1001.4228 | Catherine Meusburger | Angel Ballesteros, Francisco J. Herranz, Catherine Meusburger | Three-dimensional gravity and Drinfel'd doubles: spacetimes and
symmetries from quantum deformations | 12 pages; minor changes, additional references | Phys.Lett.B687:375-381,2010 | 10.1016/j.physletb.2010.03.043 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show how the constant curvature spacetimes of 3d gravity and the
associated symmetry algebras can be derived from a single quantum deformation
of the 3d Lorentz algebra sl(2,R). We investigate the classical Drinfel'd
double of a "hybrid" deformation of sl(2,R) that depends on two parameters
(\eta,z). With an appropriate choice of basis and real structure, this
Drinfel'd double agrees with the 3d anti-de Sitter algebra. The deformation
parameter \eta is related to the cosmological constant, while z is identified
with the inverse of the speed of light and defines the signature of the metric.
We generalise this result to de Sitter space, the three-sphere and 3d
hyperbolic space through analytic continuation in \eta and z; we also
investigate the limits of vanishing \eta and z, which yield the flat spacetimes
(Minkowski and Euclidean spaces) and Newtonian models, respectively.
| [
{
"created": "Sun, 24 Jan 2010 08:17:47 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Mar 2010 12:46:39 GMT",
"version": "v2"
}
] | 2010-04-30 | [
[
"Ballesteros",
"Angel",
""
],
[
"Herranz",
"Francisco J.",
""
],
[
"Meusburger",
"Catherine",
""
]
] | We show how the constant curvature spacetimes of 3d gravity and the associated symmetry algebras can be derived from a single quantum deformation of the 3d Lorentz algebra sl(2,R). We investigate the classical Drinfel'd double of a "hybrid" deformation of sl(2,R) that depends on two parameters (\eta,z). With an appropriate choice of basis and real structure, this Drinfel'd double agrees with the 3d anti-de Sitter algebra. The deformation parameter \eta is related to the cosmological constant, while z is identified with the inverse of the speed of light and defines the signature of the metric. We generalise this result to de Sitter space, the three-sphere and 3d hyperbolic space through analytic continuation in \eta and z; we also investigate the limits of vanishing \eta and z, which yield the flat spacetimes (Minkowski and Euclidean spaces) and Newtonian models, respectively. |
1610.09329 | Izzet Sakalli | G. Tokgoz and I. Sakalli | Stationary Scalar Clouds Around Maximally Rotating Linear Dilaton Black
Holes | Accepted for publication in Classical and Quantum Gravity | Class. Quantum Grav. 34 (2017) 125007 | 10.1088/1361-6382/aa6858 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the wave dynamics of a charged massive scalar field
propagating in a maximally rotating (extremal) linear dilaton black hole
geometry. We prove the existence of a discrete and infinite family of
resonances describing non-decaying stationary scalar configurations (clouds)
enclosing these rapidly rotating black holes. The results obtained signal the
potential stationary scalar field distributions (dark matter) around the
extremal linear dilaton black holes. In particular, we analytically compute the
effective heights of those clouds above the center of the black hole.
| [
{
"created": "Fri, 28 Oct 2016 18:05:58 GMT",
"version": "v1"
},
{
"created": "Mon, 31 Oct 2016 09:19:41 GMT",
"version": "v2"
},
{
"created": "Sat, 17 Dec 2016 11:50:04 GMT",
"version": "v3"
},
{
"created": "Wed, 22 Mar 2017 17:04:24 GMT",
"version": "v4"
}
] | 2017-09-07 | [
[
"Tokgoz",
"G.",
""
],
[
"Sakalli",
"I.",
""
]
] | We investigate the wave dynamics of a charged massive scalar field propagating in a maximally rotating (extremal) linear dilaton black hole geometry. We prove the existence of a discrete and infinite family of resonances describing non-decaying stationary scalar configurations (clouds) enclosing these rapidly rotating black holes. The results obtained signal the potential stationary scalar field distributions (dark matter) around the extremal linear dilaton black holes. In particular, we analytically compute the effective heights of those clouds above the center of the black hole. |
gr-qc/0502070 | Takeshi Chiba | Takeshi Chiba | Generalized Gravity and a Ghost | 8 pages, a reference added | JCAP 0503 (2005) 008 | 10.1088/1475-7516/2005/03/008 | null | gr-qc astro-ph | null | We show that generalized gravity theories involving the curvature invariants
of the Ricci tensor and the Riemann tensor as well as the Ricci scalar are
equivalent to multi- scalar-tensor gravities with four derivatives terms. By
expanding the action around a vacuum spacetime, the action is reduced to that
of the Einstein gravity with four derivative terms, and consequently there
appears a massive spin-2 ghost in such generalized gravity theories in addition
to a massive spin-0 field.
| [
{
"created": "Tue, 15 Feb 2005 02:15:20 GMT",
"version": "v1"
},
{
"created": "Tue, 22 Mar 2005 01:53:10 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Chiba",
"Takeshi",
""
]
] | We show that generalized gravity theories involving the curvature invariants of the Ricci tensor and the Riemann tensor as well as the Ricci scalar are equivalent to multi- scalar-tensor gravities with four derivatives terms. By expanding the action around a vacuum spacetime, the action is reduced to that of the Einstein gravity with four derivative terms, and consequently there appears a massive spin-2 ghost in such generalized gravity theories in addition to a massive spin-0 field. |
1512.01919 | Tao Wang | Tian-Yi Zhao, Towe Wang | Membrane paradigm of black holes in Chern-Simons modified gravity | 16 pages, author information updated | null | 10.1088/1475-7516/2016/06/019 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The membrane paradigm of black hole is studied in the Chern-Simons modified
gravity. Derived with the action principle a la Parikh-Wilczek, the stress
tensor of membrane manifests a rich structure arising from the Chern-Simons
term. The membrane stress tensor, if related to the bulk stress tensor in a
special form, obeys the low-dimensional fluid continuity equation and the
Navier-Stokes equation. This paradigm is applied to spherically symmetric
static geometries, and in particular, the Schwarzschild black hole, which is a
solution of a large class of dynamical Chern-Simons gravity.
| [
{
"created": "Mon, 7 Dec 2015 06:04:17 GMT",
"version": "v1"
},
{
"created": "Sun, 10 Apr 2016 06:11:11 GMT",
"version": "v2"
},
{
"created": "Sun, 5 Jun 2016 07:47:49 GMT",
"version": "v3"
}
] | 2016-06-15 | [
[
"Zhao",
"Tian-Yi",
""
],
[
"Wang",
"Towe",
""
]
] | The membrane paradigm of black hole is studied in the Chern-Simons modified gravity. Derived with the action principle a la Parikh-Wilczek, the stress tensor of membrane manifests a rich structure arising from the Chern-Simons term. The membrane stress tensor, if related to the bulk stress tensor in a special form, obeys the low-dimensional fluid continuity equation and the Navier-Stokes equation. This paradigm is applied to spherically symmetric static geometries, and in particular, the Schwarzschild black hole, which is a solution of a large class of dynamical Chern-Simons gravity. |
gr-qc/0310015 | T. R. Mongan | T. R. Mongan | Vacuum dominance and holography | 5 pages, no figures | null | null | null | gr-qc astro-ph hep-ph | null | A cosmological event horizon develops in a vacuum-dominated Friedmann
universe. The Schwarschild radius of the vacuum energy within the horizon
equals the horizon radius. Black hole thermodynamics and the holographic
conjecture indicate a finite number of degrees of freedom within the horizon.
The average energy per degree of freedom equals the energy of a massless
quantum with wavelength of the horizon circumference. This suggests identifying
the degrees of freedom with the presence or absence, in each Planck area on one
horizon quadrant, of a 0S2 vibrational mode of the horizon with the z axis
passing through that area. Pressure waves on the horizon (the superposition of
0S2 vibrational modes) can be envisioned to propagate into the observable
universe within the horizon at the speed of light. So, the vacuum energy and
pressure throughout the observable universe could (in principle) be determined
from the vacuum equation of state.
| [
{
"created": "Thu, 2 Oct 2003 17:50:45 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Mongan",
"T. R.",
""
]
] | A cosmological event horizon develops in a vacuum-dominated Friedmann universe. The Schwarschild radius of the vacuum energy within the horizon equals the horizon radius. Black hole thermodynamics and the holographic conjecture indicate a finite number of degrees of freedom within the horizon. The average energy per degree of freedom equals the energy of a massless quantum with wavelength of the horizon circumference. This suggests identifying the degrees of freedom with the presence or absence, in each Planck area on one horizon quadrant, of a 0S2 vibrational mode of the horizon with the z axis passing through that area. Pressure waves on the horizon (the superposition of 0S2 vibrational modes) can be envisioned to propagate into the observable universe within the horizon at the speed of light. So, the vacuum energy and pressure throughout the observable universe could (in principle) be determined from the vacuum equation of state. |
2111.05857 | Wenbin Lin | Hiroaki Nakajima and Wenbin Lin | New Chandrasekhar transformation in Kerr spacetime | 14 pages, accepted for publication in PRD | null | 10.1103/PhysRevD.105.064036 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We construct a new type of Chandrasekhar transformation in Kerr spacetime
using the different tortoise coordinate, which is useful for exact analysis to
study Teukolsky equation with arbitrary frequency. We also give the
interpretation of our transformation using the formalism of the quantum
Seiberg-Witten geometry.
| [
{
"created": "Wed, 10 Nov 2021 15:07:12 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Feb 2022 13:51:23 GMT",
"version": "v2"
},
{
"created": "Fri, 4 Mar 2022 01:44:18 GMT",
"version": "v3"
}
] | 2022-04-06 | [
[
"Nakajima",
"Hiroaki",
""
],
[
"Lin",
"Wenbin",
""
]
] | We construct a new type of Chandrasekhar transformation in Kerr spacetime using the different tortoise coordinate, which is useful for exact analysis to study Teukolsky equation with arbitrary frequency. We also give the interpretation of our transformation using the formalism of the quantum Seiberg-Witten geometry. |
1803.04802 | Fabrizio Di Giovanni | Fabrizio Di Giovanni, Nicolas Sanchis-Gual, Carlos A. R. Herdeiro,
Jos\'e A. Font | Dynamical formation of Proca stars and quasi-stationary solitonic
objects | null | Phys. Rev. D 98, 064044 (2018) | 10.1103/PhysRevD.98.064044 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We perform fully non-linear numerical simulations within the spherically
symmetric Einstein-(complex)Proca system. Starting with Proca field
distributions that obey the Hamiltonian, momentum and Gaussian constraints, we
show that the self-gravity of the system induces the formation of compact
objects, which, for appropriate initial conditions, asymptotically approach
stationary soliton-like solutions known as Proca stars. The excess energy of
the system is dissipated by the mechanism of \textit{gravitational cooling} in
analogy to what occurs in the dynamical formation of scalar boson stars. We
investigate the dependence of this process on the phase difference between the
real and imaginary parts of the Proca field, as well as on their relative
amplitudes. Within the timescales probed by our numerical simulations the
process is qualitatively insensitive to either choice: the phase difference and
the amplitude ratio are conserved during the evolution. Thus, whereas a truly
stationary object is expected to be approached only in the particular case of
equal amplitudes and opposite phases, quasi-stationary compact solitonic
objects are, nevertheless, formed in the general case.
| [
{
"created": "Tue, 13 Mar 2018 13:45:52 GMT",
"version": "v1"
},
{
"created": "Sat, 15 Jun 2019 09:08:09 GMT",
"version": "v2"
}
] | 2019-06-18 | [
[
"Di Giovanni",
"Fabrizio",
""
],
[
"Sanchis-Gual",
"Nicolas",
""
],
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Font",
"José A.",
""
]
] | We perform fully non-linear numerical simulations within the spherically symmetric Einstein-(complex)Proca system. Starting with Proca field distributions that obey the Hamiltonian, momentum and Gaussian constraints, we show that the self-gravity of the system induces the formation of compact objects, which, for appropriate initial conditions, asymptotically approach stationary soliton-like solutions known as Proca stars. The excess energy of the system is dissipated by the mechanism of \textit{gravitational cooling} in analogy to what occurs in the dynamical formation of scalar boson stars. We investigate the dependence of this process on the phase difference between the real and imaginary parts of the Proca field, as well as on their relative amplitudes. Within the timescales probed by our numerical simulations the process is qualitatively insensitive to either choice: the phase difference and the amplitude ratio are conserved during the evolution. Thus, whereas a truly stationary object is expected to be approached only in the particular case of equal amplitudes and opposite phases, quasi-stationary compact solitonic objects are, nevertheless, formed in the general case. |
1209.5085 | Bernard S. Kay | Bernard S. Kay (York) | Modern foundations for thermodynamics and the stringy limit of black
hole equilibria | 5 pages | null | null | null | gr-qc cond-mat.stat-mech hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We recall the existing string theory understanding of black hole entropy and
argue it is incomplete but we put forward a modified version, based on the
author's 'matter-gravity entanglement hypothesis', which, we claim, gives a
more satisfactory understanding and also a resolution to the Information Loss
Puzzle. This hypothesis pictures a black hole equilibrium as an, overall pure,
state, with given energy, consisting of a black hole with its (mostly matter)
atmosphere in a box and identifies the black hole's entropy with the pure
state's matter-gravity entanglement entropy. We assume this equilibrium goes
over, at weak string-coupling, to a pure state with similar energy consisting
of a long string with a stringy atmosphere and that the matter-gravity
entanglement entropy goes over to the entanglement entropy between
(approximately) the long string and the stringy atmosphere. We also recall
recent work (in a non-gravitational context) towards modern foundations for
thermodynamics, where, in place of a total microcanonical ensemble, one assumes
that a total system, consisting of a small (sub)system and an energy bath, is
in a (random) pure state with energy in a given narrow range and shows that the
small subsystem will then find itself in a thermal state. We present a new set
of formulae, obtained in a companion paper, which generalize the setting of
that work to cases where the system and energy bath are of comparable size. We
apply these formulae to a model for our string equilibrium where the densities
of states of the long string (replacing our energy bath) and stringy atmosphere
(replacing our system) both grow exponentially. We find, for our picture of
black hole equilibrium, a temperature of the order of the Hawking temperature
and an entropy of the order of the Hawking entropy thus adding to the evidence
for the viablity of our matter-gravity entanglement hypothesis.
| [
{
"created": "Sun, 23 Sep 2012 17:05:25 GMT",
"version": "v1"
}
] | 2012-09-25 | [
[
"Kay",
"Bernard S.",
"",
"York"
]
] | We recall the existing string theory understanding of black hole entropy and argue it is incomplete but we put forward a modified version, based on the author's 'matter-gravity entanglement hypothesis', which, we claim, gives a more satisfactory understanding and also a resolution to the Information Loss Puzzle. This hypothesis pictures a black hole equilibrium as an, overall pure, state, with given energy, consisting of a black hole with its (mostly matter) atmosphere in a box and identifies the black hole's entropy with the pure state's matter-gravity entanglement entropy. We assume this equilibrium goes over, at weak string-coupling, to a pure state with similar energy consisting of a long string with a stringy atmosphere and that the matter-gravity entanglement entropy goes over to the entanglement entropy between (approximately) the long string and the stringy atmosphere. We also recall recent work (in a non-gravitational context) towards modern foundations for thermodynamics, where, in place of a total microcanonical ensemble, one assumes that a total system, consisting of a small (sub)system and an energy bath, is in a (random) pure state with energy in a given narrow range and shows that the small subsystem will then find itself in a thermal state. We present a new set of formulae, obtained in a companion paper, which generalize the setting of that work to cases where the system and energy bath are of comparable size. We apply these formulae to a model for our string equilibrium where the densities of states of the long string (replacing our energy bath) and stringy atmosphere (replacing our system) both grow exponentially. We find, for our picture of black hole equilibrium, a temperature of the order of the Hawking temperature and an entropy of the order of the Hawking entropy thus adding to the evidence for the viablity of our matter-gravity entanglement hypothesis. |
gr-qc/9704060 | Burkhard Kleihaus | Burkhard Kleihaus and Jutta Kunz (Universit\"at Oldenburg) | Static black hole solutions with axial symmetry | 14 pages, including 4 postscript figures, LaTeX | Phys.Rev.Lett. 79 (1997) 1595-1598 | 10.1103/PhysRevLett.79.1595 | null | gr-qc hep-th | null | We construct a new class of asymptotically flat black hole solutions in
Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theory. These black hole
solutions are static, and they have a regular event horizon. However, they
possess only axial symmetry. Like their regular counterparts, the black hole
solutions are characterized by two integers, the winding number $n$ and the
node number $k$ of the gauge field functions.
| [
{
"created": "Wed, 23 Apr 1997 09:43:35 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Kleihaus",
"Burkhard",
"",
"Universität Oldenburg"
],
[
"Kunz",
"Jutta",
"",
"Universität Oldenburg"
]
] | We construct a new class of asymptotically flat black hole solutions in Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theory. These black hole solutions are static, and they have a regular event horizon. However, they possess only axial symmetry. Like their regular counterparts, the black hole solutions are characterized by two integers, the winding number $n$ and the node number $k$ of the gauge field functions. |
2008.04553 | Xiangdong Zhang | Xiangdong Zhang, Jinsong Yang and Yongge Ma | Canonical loop quantization of the lowest-order projectable Horava
gravity | 8 pages, published version for PRD | Phys. Rev. D 102, 124060 (2020) | 10.1103/PhysRevD.102.124060 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The Hamiltonian formulation of the lowest-order projectable Horava gravity,
namely the so-called $\lambda$-$R$ gravity, is studied. Since a preferred
foliation has been chosen in projectable Horava gravity, there is no local
Hamiltonian constraint in the theory. In contrast to general relativity, the
constraint algebra of $\lambda$-$R$ gravity forms a Lie algebra. By canonical
transformations, we further obtain the connection-dynamical formalism of the
$\lambda$-R gravity theories with real $su(2)$-connections as configuration
variables. This formalism enables us to extend the scheme of non-perturbative
loop quantum gravity to the $\lambda$-$R$ gravity. While the quantum
kinematical framework is the same as that for general relativity, the
Hamiltonian constraint operator of loop quantum $\lambda$-$R$ gravity can be
well defined in the diffeomorphism-invariant Hilbert space. Moreover, by
introducing a global dust degree of freedom to represent a dynamical time, a
physical Hamiltonian operator with respect to the dust can be defined and the
physical states satisfying all the constraints are obtained.
| [
{
"created": "Tue, 11 Aug 2020 07:03:38 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Dec 2020 02:57:29 GMT",
"version": "v2"
}
] | 2021-01-01 | [
[
"Zhang",
"Xiangdong",
""
],
[
"Yang",
"Jinsong",
""
],
[
"Ma",
"Yongge",
""
]
] | The Hamiltonian formulation of the lowest-order projectable Horava gravity, namely the so-called $\lambda$-$R$ gravity, is studied. Since a preferred foliation has been chosen in projectable Horava gravity, there is no local Hamiltonian constraint in the theory. In contrast to general relativity, the constraint algebra of $\lambda$-$R$ gravity forms a Lie algebra. By canonical transformations, we further obtain the connection-dynamical formalism of the $\lambda$-R gravity theories with real $su(2)$-connections as configuration variables. This formalism enables us to extend the scheme of non-perturbative loop quantum gravity to the $\lambda$-$R$ gravity. While the quantum kinematical framework is the same as that for general relativity, the Hamiltonian constraint operator of loop quantum $\lambda$-$R$ gravity can be well defined in the diffeomorphism-invariant Hilbert space. Moreover, by introducing a global dust degree of freedom to represent a dynamical time, a physical Hamiltonian operator with respect to the dust can be defined and the physical states satisfying all the constraints are obtained. |
2303.06270 | Vasilis Oikonomou | V.K. Oikonomou | Static Neutron Stars Perspective of Quadratic and Induced Inflationary
Attractor Scalar-tensor Theories | CQG Accepted | null | 10.1088/1361-6382/acc2a7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This study focuses on the static neutron star perspective for two types of
cosmological inflationary attractor theories, namely the induced inflationary
attractors and the quadratic inflationary attractors. The two cosmological
models can be discriminated cosmologically, since one of the two does not
provide a viable inflationary phenomenology, thus in this paper we investigate
the predictions of these theories for static neutron stars, mainly focusing on
the mass and radii of neutron stars. We aim to demonstrate that although the
models have different inflationary phenomenology, the neutron star
phenomenology predictions of the two models are quite similar. We solve
numerically the Tolman-Oppenheimer-Volkoff equations in the Einstein frame
using a powerful double shooting numerical technique, and after deriving the
mass-radius graphs for three types of polytropic equations of state, we derive
the Jordan frame mass and radii. With regard the equations of state we use
polytropic equation of state with the small density part being either the WFF1,
the APR or the intermediate stiffness equation of state SLy. The results of our
models will be confronted with quite stringent recently developed constraints
on the radius of neutron stars with specific mass. As we show, the only
equation of state which provides results compatible with the constraints is the
SLy, for both the quadratic and induced inflation attractors. Thus nowadays,
scalar-tensor descriptions of neutron stars are quite scrutinized due to the
growing number of constraining observations, which eventually may also
constrain theories of inflation.
| [
{
"created": "Sat, 11 Mar 2023 01:13:07 GMT",
"version": "v1"
}
] | 2023-03-29 | [
[
"Oikonomou",
"V. K.",
""
]
] | This study focuses on the static neutron star perspective for two types of cosmological inflationary attractor theories, namely the induced inflationary attractors and the quadratic inflationary attractors. The two cosmological models can be discriminated cosmologically, since one of the two does not provide a viable inflationary phenomenology, thus in this paper we investigate the predictions of these theories for static neutron stars, mainly focusing on the mass and radii of neutron stars. We aim to demonstrate that although the models have different inflationary phenomenology, the neutron star phenomenology predictions of the two models are quite similar. We solve numerically the Tolman-Oppenheimer-Volkoff equations in the Einstein frame using a powerful double shooting numerical technique, and after deriving the mass-radius graphs for three types of polytropic equations of state, we derive the Jordan frame mass and radii. With regard the equations of state we use polytropic equation of state with the small density part being either the WFF1, the APR or the intermediate stiffness equation of state SLy. The results of our models will be confronted with quite stringent recently developed constraints on the radius of neutron stars with specific mass. As we show, the only equation of state which provides results compatible with the constraints is the SLy, for both the quadratic and induced inflation attractors. Thus nowadays, scalar-tensor descriptions of neutron stars are quite scrutinized due to the growing number of constraining observations, which eventually may also constrain theories of inflation. |
0908.0579 | Koji Uryu | Koji Uryu, Francois Limousin, John L. Friedman, Eric Gourgoulhon,
Masaru Shibata | Non-conformally flat initial data for binary compact objects | 22 pages, 7 figures | Phys.Rev.D80:124004,2009 | 10.1103/PhysRevD.80.124004 | DPUR-TH-18 | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new method is described for constructing initial data for a binary
neutron-star (BNS) system in quasi-equilibrium circular orbit. Two formulations
for non-conformally flat data, waveless (WL) and near-zone helically symmetric
(NHS), are introduced; in each formulation, the Einstein-Euler system, written
in 3+1 form on an asymptotically flat spacelike hypersurface, is exactly solved
for all metric components, including the spatially non-conformally flat
potentials, and for irrotational flow. A numerical method applicable to both
formulations is explained with an emphasis on the imposition of a spatial gauge
condition. Results are shown for solution sequences of irrotational BNS with
matter approximated by parametrized equations of state that use a few segments
of polytropic equations of state. The binding energy and total angular momentum
of solution sequences computed within the conformally flat --
Isenberg-Wilson-Mathews (IWM) -- formulation are closer to those of the third
post-Newtonian (3PN) two point particles up to the closest orbits, for the more
compact stars, whereas sequences resulting from the WL/NHS formulations deviate
from the 3PN curve even more for the sequences with larger compactness. We
think it likely that this correction reflects an overestimation in the IWM
formulation as well as in the 3PN formula, by $\sim 1$ cycle in the
gravitational wave phase during the last several orbits. The work suggests that
imposing spatial conformal flatness results in an underestimate of the
quadrupole deformation of the components of binary neutron-star systems in the
last few orbits prior to merger.
| [
{
"created": "Wed, 5 Aug 2009 05:21:50 GMT",
"version": "v1"
},
{
"created": "Thu, 8 Oct 2009 04:53:04 GMT",
"version": "v2"
}
] | 2013-05-29 | [
[
"Uryu",
"Koji",
""
],
[
"Limousin",
"Francois",
""
],
[
"Friedman",
"John L.",
""
],
[
"Gourgoulhon",
"Eric",
""
],
[
"Shibata",
"Masaru",
""
]
] | A new method is described for constructing initial data for a binary neutron-star (BNS) system in quasi-equilibrium circular orbit. Two formulations for non-conformally flat data, waveless (WL) and near-zone helically symmetric (NHS), are introduced; in each formulation, the Einstein-Euler system, written in 3+1 form on an asymptotically flat spacelike hypersurface, is exactly solved for all metric components, including the spatially non-conformally flat potentials, and for irrotational flow. A numerical method applicable to both formulations is explained with an emphasis on the imposition of a spatial gauge condition. Results are shown for solution sequences of irrotational BNS with matter approximated by parametrized equations of state that use a few segments of polytropic equations of state. The binding energy and total angular momentum of solution sequences computed within the conformally flat -- Isenberg-Wilson-Mathews (IWM) -- formulation are closer to those of the third post-Newtonian (3PN) two point particles up to the closest orbits, for the more compact stars, whereas sequences resulting from the WL/NHS formulations deviate from the 3PN curve even more for the sequences with larger compactness. We think it likely that this correction reflects an overestimation in the IWM formulation as well as in the 3PN formula, by $\sim 1$ cycle in the gravitational wave phase during the last several orbits. The work suggests that imposing spatial conformal flatness results in an underestimate of the quadrupole deformation of the components of binary neutron-star systems in the last few orbits prior to merger. |
1405.3827 | Atsushi Higuchi | Rafael P. Bernar, Lu\'is C. B. Crispino, Atsushi Higuchi | Infrared-finite graviton two-point function in static de Sitter space | 17 pages, REVTeX, references corrected | Phys. Rev. D 90, 024045 (2014) | 10.1103/PhysRevD.90.024045 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study quantum gravitational perturbations in the static patch of de Sitter
space. In particular, we determine the symplectic inner product of these
perturbations and use it to write down the graviton two-point function in the
state analogous to the Bunch-Davies vacuum in a certain gauge. We find this
two-point function to be infrared-finite and time-translation invariant.
| [
{
"created": "Thu, 15 May 2014 12:56:27 GMT",
"version": "v1"
},
{
"created": "Fri, 16 May 2014 17:49:46 GMT",
"version": "v2"
}
] | 2014-07-23 | [
[
"Bernar",
"Rafael P.",
""
],
[
"Crispino",
"Luís C. B.",
""
],
[
"Higuchi",
"Atsushi",
""
]
] | We study quantum gravitational perturbations in the static patch of de Sitter space. In particular, we determine the symplectic inner product of these perturbations and use it to write down the graviton two-point function in the state analogous to the Bunch-Davies vacuum in a certain gauge. We find this two-point function to be infrared-finite and time-translation invariant. |
gr-qc/9507010 | Jerose Martin | Y. Kubyshin and J. Martin | Limits on Kaluza-Klein Models from COBE Results | 9 pages, Latex, one figure available on request at the following
adress: jmartin@ccr.jussieu.fr | null | null | UB-ECM-PF 95/13, LGCR 95/06/05, DAMTP R95/35 | gr-qc | null | The large-angular-scale anisotropy of the cosmic microwave background
radiation in multidimensional cosmological models (Kaluza-Klein models) is
studied. Limits on parameters of the models imposed by the experimental data
are obtained. It is shown that in principle there is a room for Kaluza-Klein
models as possible candidates for the description of the Early Universe.
However, the obtained limits are very restrictive and none of the concrete
models, analyzed in the article, satisfy them.
| [
{
"created": "Wed, 5 Jul 1995 15:22:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Kubyshin",
"Y.",
""
],
[
"Martin",
"J.",
""
]
] | The large-angular-scale anisotropy of the cosmic microwave background radiation in multidimensional cosmological models (Kaluza-Klein models) is studied. Limits on parameters of the models imposed by the experimental data are obtained. It is shown that in principle there is a room for Kaluza-Klein models as possible candidates for the description of the Early Universe. However, the obtained limits are very restrictive and none of the concrete models, analyzed in the article, satisfy them. |
gr-qc/0607071 | Miguel Gustavo de Campos Batista | M. de Campos | A study of gravitational collapse with decaying of the vacuum energy | 9 pages, 3 figures | null | null | null | gr-qc | null | We study the gravitational collapse of a dust dark matter star in a
$\Lambda$-background. We consider two distinct cases: First we do not have a
dark matter and dark energy coupling; second, we consider that $\Lambda $ decay
in dark particles. The approach adopted assumes a modified matter expansion
rate and we have formation of a black hole, since that, we have the formation
of an apparent horizon. A brief comparison of the process of the matter
condensation using the gravitational collapse approach and the linear scalar
perturbation theory is considered.
| [
{
"created": "Tue, 18 Jul 2006 15:26:36 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Sep 2006 22:56:58 GMT",
"version": "v2"
},
{
"created": "Tue, 7 Nov 2006 15:12:01 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"de Campos",
"M.",
""
]
] | We study the gravitational collapse of a dust dark matter star in a $\Lambda$-background. We consider two distinct cases: First we do not have a dark matter and dark energy coupling; second, we consider that $\Lambda $ decay in dark particles. The approach adopted assumes a modified matter expansion rate and we have formation of a black hole, since that, we have the formation of an apparent horizon. A brief comparison of the process of the matter condensation using the gravitational collapse approach and the linear scalar perturbation theory is considered. |
gr-qc/0001093 | Garcia | L.C.Garcia de Andrade | On String Cosmology and de Sitter inflation with massless dilatons and
dynamical torsion | Latex file Kb | null | null | null | gr-qc | null | Variation of the 4-D string cosmology action with dynamical torsion and
massless dilatons lead to an expression of torsion in terms of massless
dilatons in the case of de Sitter inflation.The solution is approximated
according to the COBE data.
| [
{
"created": "Fri, 28 Jan 2000 12:03:04 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"de Andrade",
"L. C. Garcia",
""
]
] | Variation of the 4-D string cosmology action with dynamical torsion and massless dilatons lead to an expression of torsion in terms of massless dilatons in the case of de Sitter inflation.The solution is approximated according to the COBE data. |
2208.08098 | Mohammad Vahid Takook | M.V. Takook | Conceptual and technical challenges of quantum gravity | 17 pages, typos corrected | Int. J. Theor. Phys., 59 (2020) 2540 | 10.1007/s10773-020-04520-2 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The appearance of infinity together with collapsing quantum state due to the
observation or interaction, which are two challenging features of quantum field
theory, become very serious problems in quantum gravity as well as in quantum
geometry of space-time. These problems can be divided into two categories:
technical and conceptual parts. In the technical aspect, the biggest problem
comes from the definition of the point, which constructs classical geometry. By
changing the point definition, the technical problem may be approximately
bypassed, and a mathematical formulation of quantum geometry may be found. On
the other hand, the conceptual problem comes from the quantum state collapse
due to the observation since the entanglement between the observer and gravity
cannot be eliminated in the presence of gravity. The conceptual part does not
depend on the techniques which are employed. As much as possible, we try to
discuss these problems by rediscovering the perception and understanding of a
phenomenon for an observer in quantum theory.
| [
{
"created": "Wed, 17 Aug 2022 06:23:42 GMT",
"version": "v1"
}
] | 2023-04-14 | [
[
"Takook",
"M. V.",
""
]
] | The appearance of infinity together with collapsing quantum state due to the observation or interaction, which are two challenging features of quantum field theory, become very serious problems in quantum gravity as well as in quantum geometry of space-time. These problems can be divided into two categories: technical and conceptual parts. In the technical aspect, the biggest problem comes from the definition of the point, which constructs classical geometry. By changing the point definition, the technical problem may be approximately bypassed, and a mathematical formulation of quantum geometry may be found. On the other hand, the conceptual problem comes from the quantum state collapse due to the observation since the entanglement between the observer and gravity cannot be eliminated in the presence of gravity. The conceptual part does not depend on the techniques which are employed. As much as possible, we try to discuss these problems by rediscovering the perception and understanding of a phenomenon for an observer in quantum theory. |
1711.06859 | Seema Satin | Seema Satin | Induced Perturbations and Stochastic effects in Collapsing Relativistic
Stars | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a modified model for relativistic stars which are usually
represented by perfect fluids. Fluctuations of the stress tensor act as source
in the modified Einstein's equation, giving it a Langevin equation form. The
occurrence of these fluctuations is attributed to the microphysics of the
interior of the star and their contribution to statistical properties of the
fluid and the induced metric perturbations are argued to be of significance. We
also discuss the response of fluctuations of the stress tensor in the interior
of the star and possible developments towards fluctuation-dissipation theorem
issues in curved spacetime. The aim and further directions of research
envisioned are discussed intermittently throughout the manuscript and towards
the end.
| [
{
"created": "Sat, 18 Nov 2017 13:23:14 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Dec 2017 13:39:58 GMT",
"version": "v2"
}
] | 2017-12-07 | [
[
"Satin",
"Seema",
""
]
] | We present a modified model for relativistic stars which are usually represented by perfect fluids. Fluctuations of the stress tensor act as source in the modified Einstein's equation, giving it a Langevin equation form. The occurrence of these fluctuations is attributed to the microphysics of the interior of the star and their contribution to statistical properties of the fluid and the induced metric perturbations are argued to be of significance. We also discuss the response of fluctuations of the stress tensor in the interior of the star and possible developments towards fluctuation-dissipation theorem issues in curved spacetime. The aim and further directions of research envisioned are discussed intermittently throughout the manuscript and towards the end. |
1905.05612 | Pameli Saha Ms. | Pameli Saha and Ujjal Debnath | Collision of particles near charged MSW black hole in 2 + 1 dimensions | 14 pages, 12 figures | Modern Physics Letters A, Vol. 34 (2019) 1950127 | 10.1142/S021773231950127X | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Here, we explore the dynamics of particle near the horizon of charged
Mandal-Sengupta-Wadia (MSW) black hole in 2+1 dimensions. It results analysis
of angular momentum and potential energy for null and time-like geodesics. We
also appraise the high center-of-mass energy of coming particles from rest at
infinity near the horizon of the charged MSW black hole in 2+1 dimension for
the extremal case. Finally, we study the ISCO and MBCO radii for this type of
black hole.
| [
{
"created": "Sat, 11 May 2019 12:23:51 GMT",
"version": "v1"
}
] | 2019-05-15 | [
[
"Saha",
"Pameli",
""
],
[
"Debnath",
"Ujjal",
""
]
] | Here, we explore the dynamics of particle near the horizon of charged Mandal-Sengupta-Wadia (MSW) black hole in 2+1 dimensions. It results analysis of angular momentum and potential energy for null and time-like geodesics. We also appraise the high center-of-mass energy of coming particles from rest at infinity near the horizon of the charged MSW black hole in 2+1 dimension for the extremal case. Finally, we study the ISCO and MBCO radii for this type of black hole. |
0811.4592 | Hristu Culetu | Hristu Culetu | Comments on : Frame dragging anomalies for rotating bodies | 3 pages, no figures, 2 references and comments added | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that Collas and Klein (ArXiv : 0811.2471 [gr-qc]) wrongly
concluded that "negative frame dragging" phenomenon takes place at all finite
$r$ and $z$ coordinate values . We argue that a test particle with zero angular
momentum counter-rotates with respect to the source in the "time machine"
region only. In addition, Bonnor's spacetime has an event horizon at $r_{H}$ =
0.
| [
{
"created": "Thu, 27 Nov 2008 17:13:46 GMT",
"version": "v1"
},
{
"created": "Sun, 28 Dec 2008 12:31:43 GMT",
"version": "v2"
}
] | 2008-12-28 | [
[
"Culetu",
"Hristu",
""
]
] | It is shown that Collas and Klein (ArXiv : 0811.2471 [gr-qc]) wrongly concluded that "negative frame dragging" phenomenon takes place at all finite $r$ and $z$ coordinate values . We argue that a test particle with zero angular momentum counter-rotates with respect to the source in the "time machine" region only. In addition, Bonnor's spacetime has an event horizon at $r_{H}$ = 0. |
1301.1073 | Carlos A. R. Herdeiro | F. S. Coelho, C. Herdeiro, C. Rebelo and M. O. P. Sampaio | Radiation from a D-dimensional collision of shock waves: an insight
allowed by the D parameter | 3 pages; contribution to the proceedings of the Thirteenth Marcel
Grossmann Meeting, Stockholm University, Sweden, 1-7 July, 2012; based on a
talk in the AT1 "Higher Dimensional General Relativity" parallel session | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the radiation emitted in a collision of shock waves, in
D-dimensional General Relativity (GR), and describe a remarkably simple
pattern, hinting at a more fundamental structure, unveiled by the introduction
of the parameter D.
| [
{
"created": "Sun, 6 Jan 2013 22:58:08 GMT",
"version": "v1"
}
] | 2013-01-08 | [
[
"Coelho",
"F. S.",
""
],
[
"Herdeiro",
"C.",
""
],
[
"Rebelo",
"C.",
""
],
[
"Sampaio",
"M. O. P.",
""
]
] | We consider the radiation emitted in a collision of shock waves, in D-dimensional General Relativity (GR), and describe a remarkably simple pattern, hinting at a more fundamental structure, unveiled by the introduction of the parameter D. |
2205.08865 | Suman Ghosh | Vivek Sharma and Suman Ghosh | Geodesic Congruences in 5D Warped Ellis-Bronnikov Spacetimes | 19+5 preprint pages, 11 figures; references added, version accepted
in EPJ Plus | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study the timelike geodesic congruences in the generalized Ellis-Bronnikov
spacetime (4D-GEB) and in recently proposed 5D model where a 4D-GEB is embedded
in a warped geometry (5D-WGEB) and conduct a comparative study. Analytical
expressions of ESR variables (for 4D geometries) are found which reveal the
role of the wormhole parameter. In more general 4D and 5D scenarios geodesic
equation, geodesic deviation equation and Raychaudhury equations are solved
numerically. The evolution of cross-sectional area of the congruences of
timelike geodesics (orthogonal to the geodesic flow lines) projected on
2D-surfaces yield an interesting perspective and shows the effects of the
wormhole parameter and growing/decaying warp factors. Presence of warping
factor triggers rotation or accretion even in the absence of initial congruence
rotation. Presence of rotation in the congruence is also found to be playing a
crucial role which we discuss in detail.
| [
{
"created": "Wed, 18 May 2022 11:17:16 GMT",
"version": "v1"
},
{
"created": "Fri, 20 May 2022 04:23:43 GMT",
"version": "v2"
},
{
"created": "Fri, 12 Aug 2022 07:53:55 GMT",
"version": "v3"
}
] | 2022-08-15 | [
[
"Sharma",
"Vivek",
""
],
[
"Ghosh",
"Suman",
""
]
] | We study the timelike geodesic congruences in the generalized Ellis-Bronnikov spacetime (4D-GEB) and in recently proposed 5D model where a 4D-GEB is embedded in a warped geometry (5D-WGEB) and conduct a comparative study. Analytical expressions of ESR variables (for 4D geometries) are found which reveal the role of the wormhole parameter. In more general 4D and 5D scenarios geodesic equation, geodesic deviation equation and Raychaudhury equations are solved numerically. The evolution of cross-sectional area of the congruences of timelike geodesics (orthogonal to the geodesic flow lines) projected on 2D-surfaces yield an interesting perspective and shows the effects of the wormhole parameter and growing/decaying warp factors. Presence of warping factor triggers rotation or accretion even in the absence of initial congruence rotation. Presence of rotation in the congruence is also found to be playing a crucial role which we discuss in detail. |
2403.15205 | Jean-Luc Lehners | Jean-Luc Lehners and Jerome Quintin | Delicate curvature bounces in the no-boundary wave function and in the
late universe | 26 pages, 14 figures | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Theoretical considerations motivate us to consider vacuum energy to be able
to decay and to assume that the spatial geometry of the universe is closed.
Combining both aspects leads to the possibility that the universe, or certain
regions thereof, can collapse and subsequently undergo a curvature bounce. This
may have occurred in the very early universe, in a pre-inflationary phase. We
discuss the construction of the corresponding no-boundary instantons and show
that they indeed reproduce a bouncing history of the universe, interestingly
with a small and potentially observable departure from classicality during the
contracting phase. Such an early bouncing history receives a large weighting
and provides competition for a more standard inflationary branch of the wave
function. Curvature bounces may also occur in the future. We discuss the
conditions under which they may take place, allowing for density fluctuations
in the matter distribution in the universe. Overall, we find that curvature
bounces require a delicate combination of matter content and initial conditions
to occur, though with significant consequences if these conditions are met.
| [
{
"created": "Fri, 22 Mar 2024 13:46:56 GMT",
"version": "v1"
}
] | 2024-03-25 | [
[
"Lehners",
"Jean-Luc",
""
],
[
"Quintin",
"Jerome",
""
]
] | Theoretical considerations motivate us to consider vacuum energy to be able to decay and to assume that the spatial geometry of the universe is closed. Combining both aspects leads to the possibility that the universe, or certain regions thereof, can collapse and subsequently undergo a curvature bounce. This may have occurred in the very early universe, in a pre-inflationary phase. We discuss the construction of the corresponding no-boundary instantons and show that they indeed reproduce a bouncing history of the universe, interestingly with a small and potentially observable departure from classicality during the contracting phase. Such an early bouncing history receives a large weighting and provides competition for a more standard inflationary branch of the wave function. Curvature bounces may also occur in the future. We discuss the conditions under which they may take place, allowing for density fluctuations in the matter distribution in the universe. Overall, we find that curvature bounces require a delicate combination of matter content and initial conditions to occur, though with significant consequences if these conditions are met. |
1012.1695 | Subenoy Chakraborty | Subenoy Chakraborty, Nairwita Mazumder, Ritabrata Biswas | Hawking radiation as tunnelling from the trapping horizon of a general
non-static spherically symmetric space-time | 8pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using tunnelling approach, Hawking radiation is derived for a general class
of non-static spherically symmetric space time. The standard tunnelling rate
formula is obtained using the unified first law of thermodynamics on the
trapping horizon and Hawking temperature is measured by an Kodama observer
inside the horizon.
| [
{
"created": "Wed, 8 Dec 2010 07:12:36 GMT",
"version": "v1"
}
] | 2010-12-09 | [
[
"Chakraborty",
"Subenoy",
""
],
[
"Mazumder",
"Nairwita",
""
],
[
"Biswas",
"Ritabrata",
""
]
] | Using tunnelling approach, Hawking radiation is derived for a general class of non-static spherically symmetric space time. The standard tunnelling rate formula is obtained using the unified first law of thermodynamics on the trapping horizon and Hawking temperature is measured by an Kodama observer inside the horizon. |
1305.2662 | Ronaldo S. S. Vieira | Ronaldo S. S. Vieira, Patricio S. Letelier | Thin-disk models in an Integrable Weyl-Dirac theory | 18 pages, 3 figures; accepted in General Relativity and Gravitation | Gen. Relativ. Gravit. (2014) 46:1641 | 10.1007/s10714-013-1641-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct a class of static, axially symmetric solutions representing
razor-thin disks of matter in an Integrable Weyl-Dirac theory proposed in
Found. Phys. 29, 1303 (1999). The main differences between these solutions and
the corresponding general relativistic one are analyzed, focusing on the
behavior of physical observables (rotation curves of test particles, density
and pressure profiles). We consider the case in which test particles move on
Weyl geodesics. The same rotation curve can be obtained from many different
solutions of the Weyl-Dirac theory, although some of these solutions present
strong qualitative differences with respect to the usual general relativistic
model (such as the appearance a ring-like density profile). In particular, for
typical galactic parameters all rotation curves of the Weyl-Dirac model present
Keplerian fall-off. As a consequence, we conclude that a more thorough analysis
of the problem requires the determination of the gauge function $\beta$ on
galactic scales, as well as restrictions on the test-particle behavior under
the action of the additional fields introduced by this theory.
| [
{
"created": "Mon, 13 May 2013 02:55:27 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Feb 2014 21:46:41 GMT",
"version": "v2"
}
] | 2014-02-13 | [
[
"Vieira",
"Ronaldo S. S.",
""
],
[
"Letelier",
"Patricio S.",
""
]
] | We construct a class of static, axially symmetric solutions representing razor-thin disks of matter in an Integrable Weyl-Dirac theory proposed in Found. Phys. 29, 1303 (1999). The main differences between these solutions and the corresponding general relativistic one are analyzed, focusing on the behavior of physical observables (rotation curves of test particles, density and pressure profiles). We consider the case in which test particles move on Weyl geodesics. The same rotation curve can be obtained from many different solutions of the Weyl-Dirac theory, although some of these solutions present strong qualitative differences with respect to the usual general relativistic model (such as the appearance a ring-like density profile). In particular, for typical galactic parameters all rotation curves of the Weyl-Dirac model present Keplerian fall-off. As a consequence, we conclude that a more thorough analysis of the problem requires the determination of the gauge function $\beta$ on galactic scales, as well as restrictions on the test-particle behavior under the action of the additional fields introduced by this theory. |
2008.04609 | Chen Lan | Chen Lan, Yan-Gang Miao and Hao Yang | Quasinormal Modes and Thermodynamics of Regular Black Holes | published version | Nucl. Phys. B 971 (2021) 115539 | 10.1016/j.nuclphysb.2021.115539 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | By applying the dimensionless scheme, we investigate the quasinormal modes
and phase transitions analytically for three types of regular black holes. The
universal deviations to the first law of mechanics in regular black holes are
proved. Meanwhile, we verify that second order phase transitions and Davies
points still exist in these three models. In addition, we calculate their
quasinormal modes in the eikonal limit by applying the light ring/quasinormal
mode correspondence, and discuss the spiral-like shapes and the relations
between the quasinormal modes and phase transitions. As the main result, we
show that spiral-like shapes in the complex frequency plane are closely related
to the parameterization, namely in some particular units the spiral-like shapes
will emerge in the models, which may not be of the spiral behaviors reported by
other authors. We also discover a universal property of regular black holes,
i.e., the imaginary parts of their QNMs do not vanish for the extreme cases,
which does not appear in singular black holes, such as the Reissner-Nordstr\"om
and Kerr black holes, etc.
| [
{
"created": "Tue, 11 Aug 2020 10:09:40 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Aug 2020 13:47:43 GMT",
"version": "v2"
},
{
"created": "Thu, 9 Sep 2021 01:39:23 GMT",
"version": "v3"
}
] | 2022-05-13 | [
[
"Lan",
"Chen",
""
],
[
"Miao",
"Yan-Gang",
""
],
[
"Yang",
"Hao",
""
]
] | By applying the dimensionless scheme, we investigate the quasinormal modes and phase transitions analytically for three types of regular black holes. The universal deviations to the first law of mechanics in regular black holes are proved. Meanwhile, we verify that second order phase transitions and Davies points still exist in these three models. In addition, we calculate their quasinormal modes in the eikonal limit by applying the light ring/quasinormal mode correspondence, and discuss the spiral-like shapes and the relations between the quasinormal modes and phase transitions. As the main result, we show that spiral-like shapes in the complex frequency plane are closely related to the parameterization, namely in some particular units the spiral-like shapes will emerge in the models, which may not be of the spiral behaviors reported by other authors. We also discover a universal property of regular black holes, i.e., the imaginary parts of their QNMs do not vanish for the extreme cases, which does not appear in singular black holes, such as the Reissner-Nordstr\"om and Kerr black holes, etc. |
1411.6218 | Hao Wei | Xiao-Peng Yan, De-Zi Liu, Hao Wei | Age Problem in Lemaitre-Tolman-Bondi Void Models | 17 pages, 9 figures, revtex4; v2: discussions added, Phys. Lett. B in
press; v3: published version | Phys.Lett.B742:149-159,2015 | 10.1016/j.physletb.2015.01.029 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | As is well known, one can explain the current cosmic acceleration by
considering an inhomogeneous and/or anisotropic universe (which violates the
cosmological principle), without invoking dark energy or modified gravity. The
well-known one of this kind of models is the so-called
Lema\^{\i}tre-Tolman-Bondi (LTB) void model, in which the universe is
spherically symmetric and radially inhomogeneous, and we are living in a
locally underdense void centered nearby our location. In the present work, we
test various LTB void models with some old high redshift objects (OHROs).
Obviously, the universe cannot be younger than its constituents. We find that
an unusually large $r_0$ (characterizing the size of the void) is required to
accommodate these OHROs in LTB void models. There is a serious tension between
this unusually large $r_0$ and the much smaller $r_0$ inferred from other
observations (e.g. SNIa, CMB and so on). However, if we instead consider the
lowest limit 1.7\,Gyr for the quasar APM 08279+5255 at redshift $z=3.91$, this
tension could be greatly alleviated.
| [
{
"created": "Sun, 23 Nov 2014 10:00:00 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Jan 2015 10:15:00 GMT",
"version": "v2"
},
{
"created": "Tue, 3 Feb 2015 10:00:00 GMT",
"version": "v3"
}
] | 2015-02-04 | [
[
"Yan",
"Xiao-Peng",
""
],
[
"Liu",
"De-Zi",
""
],
[
"Wei",
"Hao",
""
]
] | As is well known, one can explain the current cosmic acceleration by considering an inhomogeneous and/or anisotropic universe (which violates the cosmological principle), without invoking dark energy or modified gravity. The well-known one of this kind of models is the so-called Lema\^{\i}tre-Tolman-Bondi (LTB) void model, in which the universe is spherically symmetric and radially inhomogeneous, and we are living in a locally underdense void centered nearby our location. In the present work, we test various LTB void models with some old high redshift objects (OHROs). Obviously, the universe cannot be younger than its constituents. We find that an unusually large $r_0$ (characterizing the size of the void) is required to accommodate these OHROs in LTB void models. There is a serious tension between this unusually large $r_0$ and the much smaller $r_0$ inferred from other observations (e.g. SNIa, CMB and so on). However, if we instead consider the lowest limit 1.7\,Gyr for the quasar APM 08279+5255 at redshift $z=3.91$, this tension could be greatly alleviated. |
1112.2886 | Sylvain Carrozza | Sylvain Carrozza | Singular topologies in the Boulatov model | 4 pages; proceedings of Loops'11 (May 2011, Madrid); v2: minor
modifications matching published version | J. Phys.: Conf. Ser. 360 012045 (2012) | 10.1088/1742-6596/360/1/012045 | AEI-2011-105 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Through the question of singular topologies in the Boulatov model, we
illustrate and summarize some of the recent advances in Group Field Theory.
| [
{
"created": "Tue, 13 Dec 2011 13:33:24 GMT",
"version": "v1"
},
{
"created": "Thu, 28 Jun 2012 13:50:32 GMT",
"version": "v2"
}
] | 2012-06-29 | [
[
"Carrozza",
"Sylvain",
""
]
] | Through the question of singular topologies in the Boulatov model, we illustrate and summarize some of the recent advances in Group Field Theory. |
1608.05281 | Petr Tretyakov | Petr V. Tretyakov | Stability in higher-derivative matter fields theories | null | null | 10.1140/epjc/s10052-016-4355-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss possible instabilities in higher-derivative matter fields
theories. These theories has two free parameters $\beta_1$ and $\beta_4$. By
using dynamical system approach we explicitly demonstrate that for stability of
Minkowski space in expanding Universe it is need condition $\beta_4<0$. By
using quantum field theory approach we also find additional restriction for
parameters $\beta_1>-\frac{1}{3}\beta_4$ which is need to avoid tachyon-like
instability.
| [
{
"created": "Thu, 18 Aug 2016 14:47:29 GMT",
"version": "v1"
}
] | 2016-10-12 | [
[
"Tretyakov",
"Petr V.",
""
]
] | We discuss possible instabilities in higher-derivative matter fields theories. These theories has two free parameters $\beta_1$ and $\beta_4$. By using dynamical system approach we explicitly demonstrate that for stability of Minkowski space in expanding Universe it is need condition $\beta_4<0$. By using quantum field theory approach we also find additional restriction for parameters $\beta_1>-\frac{1}{3}\beta_4$ which is need to avoid tachyon-like instability. |
2404.10855 | Christopher Helmerich | Christopher Helmerich, Jared Fuchs, Alexey Bobrick, Brandon Melcher,
Luke Sellers, Gianni Martire | Warp Factory: A Numerical Toolkit for the Analysis and Optimization of
Warp Drive Geometries | 34 pages, 34 figures, Published in AIAA SCITECH 2023 Forum | null | 10.2514/6.2023-0553 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The last few decades of warp drive research have focused on analytic methods
to explore warp solutions to Einstein's field equations. These analytic
solutions tend to favor simple metric forms which are easier to analyze but
limit the space of exploration. In addition, all solutions to date have
involved unphysical qualities, such as negative energy, violation of energy
conditions, or enormous energy requirements. In an effort to explore the space
of physically meaningful warp drives, the Advanced Propulsion Laboratory (APL)
at Applied Physics has developed Warp Factory, a toolkit written in MATLAB for
numerically analyzing and optimizing warp drive geometries. Warp Factory
consists of a series of three primary modules: the solver, the analyzer, and
the optimizer. Together, these modules allow users to solve the Einstein field
equations, compute energy conditions and scalars, and perturbatively optimize
general metrics. Finally, the toolkit offers insightful 2D and 3D
visualizations of general metrics and stress-energy tensors. The methods used
in Warp Factory, along with their application in evaluating and optimizing
common metrics, are discussed. With Warp Factory, APL hopes to accelerate warp
research and bring us one step closer to physical and realizable warp drives.
| [
{
"created": "Tue, 16 Apr 2024 19:09:23 GMT",
"version": "v1"
}
] | 2024-04-18 | [
[
"Helmerich",
"Christopher",
""
],
[
"Fuchs",
"Jared",
""
],
[
"Bobrick",
"Alexey",
""
],
[
"Melcher",
"Brandon",
""
],
[
"Sellers",
"Luke",
""
],
[
"Martire",
"Gianni",
""
]
] | The last few decades of warp drive research have focused on analytic methods to explore warp solutions to Einstein's field equations. These analytic solutions tend to favor simple metric forms which are easier to analyze but limit the space of exploration. In addition, all solutions to date have involved unphysical qualities, such as negative energy, violation of energy conditions, or enormous energy requirements. In an effort to explore the space of physically meaningful warp drives, the Advanced Propulsion Laboratory (APL) at Applied Physics has developed Warp Factory, a toolkit written in MATLAB for numerically analyzing and optimizing warp drive geometries. Warp Factory consists of a series of three primary modules: the solver, the analyzer, and the optimizer. Together, these modules allow users to solve the Einstein field equations, compute energy conditions and scalars, and perturbatively optimize general metrics. Finally, the toolkit offers insightful 2D and 3D visualizations of general metrics and stress-energy tensors. The methods used in Warp Factory, along with their application in evaluating and optimizing common metrics, are discussed. With Warp Factory, APL hopes to accelerate warp research and bring us one step closer to physical and realizable warp drives. |
2206.12699 | Riccardo Della Monica | Riccardo Della Monica, Ivan de Martino, Mariafelicia de Laurentis | Constraining MOdified Gravity with the S2 Star | Proceeding of the conference Alternative Gravities and Fundamental
Cosmology (ALTECOSMOFUN'21) | Universe 2022, 8(2) | 10.3390/universe8020137 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We have used publicly available kinematic data for the S2 star to constrain
the parameter space of MOdified Gravity. Integrating geodesics and using a
Markov Chain Monte Carlo algorithm we have provided with the first constraint
on the scales of the Galactic Centre for the parameter $\alpha$ of the theory,
which represents the fractional increment of the gravitational constant $G$
with respect to its Newtonian value. Namely, $\alpha \lesssim 0.662$ at 99.7%
confidence level (where $\alpha = 0$ reduces the theory to General Relativity).
| [
{
"created": "Sat, 25 Jun 2022 17:12:15 GMT",
"version": "v1"
}
] | 2022-06-28 | [
[
"Della Monica",
"Riccardo",
""
],
[
"de Martino",
"Ivan",
""
],
[
"de Laurentis",
"Mariafelicia",
""
]
] | We have used publicly available kinematic data for the S2 star to constrain the parameter space of MOdified Gravity. Integrating geodesics and using a Markov Chain Monte Carlo algorithm we have provided with the first constraint on the scales of the Galactic Centre for the parameter $\alpha$ of the theory, which represents the fractional increment of the gravitational constant $G$ with respect to its Newtonian value. Namely, $\alpha \lesssim 0.662$ at 99.7% confidence level (where $\alpha = 0$ reduces the theory to General Relativity). |
1507.02621 | Mir Faizal | Fay\c{c}al Hammad, Mir Faizal | A Logarithmic Correction in the Entropy Functional Formalism | 12 pages, 0 figures, Accepted for publication in Int. J. Mod. Phys. D | Int. J. Mod. Phys. D 25, 1650080 (2016) | 10.1142/S0218271816500802 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The entropy functional formalism allows one to recover general relativity,
modified gravity theories, as well as the Bekenstein-Hawking entropy formula.
In most approaches to quantum gravity, the Bekenstein-Hawking's entropy formula
acquires a logarithmic correction term. As such terms occur almost universally
in most approaches to quantum gravity, we analyze the effect of such terms on
the entropy functional formalism. We demonstrate that the leading correction to
the micro-canonical entropy in the entropy functional formalism can be used to
recover modified theories of gravity already obtained with an uncorrected
micro-canonical entropy. Furthermore, since the entropy functional formalism
reproduces modified gravity, the rise of gravity-dependent logarithmic
corrections turns out to be one way to impose constraints on these theories of
modified gravity. The constraints found here for the simple case of an
F(R)-gravity are the same as those obtained in the literature from cosmological
considerations.
| [
{
"created": "Mon, 6 Jul 2015 23:14:31 GMT",
"version": "v1"
},
{
"created": "Sat, 19 Dec 2015 17:29:55 GMT",
"version": "v2"
},
{
"created": "Sat, 16 Apr 2016 22:12:38 GMT",
"version": "v3"
}
] | 2016-06-24 | [
[
"Hammad",
"Fayçal",
""
],
[
"Faizal",
"Mir",
""
]
] | The entropy functional formalism allows one to recover general relativity, modified gravity theories, as well as the Bekenstein-Hawking entropy formula. In most approaches to quantum gravity, the Bekenstein-Hawking's entropy formula acquires a logarithmic correction term. As such terms occur almost universally in most approaches to quantum gravity, we analyze the effect of such terms on the entropy functional formalism. We demonstrate that the leading correction to the micro-canonical entropy in the entropy functional formalism can be used to recover modified theories of gravity already obtained with an uncorrected micro-canonical entropy. Furthermore, since the entropy functional formalism reproduces modified gravity, the rise of gravity-dependent logarithmic corrections turns out to be one way to impose constraints on these theories of modified gravity. The constraints found here for the simple case of an F(R)-gravity are the same as those obtained in the literature from cosmological considerations. |
1608.05249 | Xiao Zhang | Yaohua Wang, Xiao Zhang | Nonexistence of time-periodic solutions of the Dirac equation in
nonextreme Kerr-Newman-AdS spacetime | 13 pages, submitted | null | null | null | gr-qc math.CA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In non-extreme Kerr-Newman-AdS spacetime, we prove that there is no
nontrivial Dirac particle which is $L^p$ for $0<p\leq\frac{4}{3}$ with
arbitrary eigenvalue $\lambda$, and for $\frac{4}{3}<p\leq\frac{4}{3-2q}$,
$0<q<\frac{3}{2}$ with eigenvalue $|\lambda|>|Q|+q \kappa $, outside and away
from the event horizon. By taking $q=\frac{1}{2}$, we show that there is no
normalizable massive Dirac particle with mass greater than
$|Q|+\frac{\kappa}{2} $ outside and away from the event horizon in non-extreme
Kerr-Newman-AdS spacetime, and they must either disappear into the black hole
or escape to infinity, and this recovers the same result of Belgiorno and
Cacciatori in the case of $Q=0$ obtained by using spectral methods.
Furthermore, we prove that any Dirac particle with eigenvalue
$|\lambda|<\frac{\kappa}{2} $ must be $L^2$ outside and away from the event
horizon.
| [
{
"created": "Thu, 18 Aug 2016 12:09:39 GMT",
"version": "v1"
}
] | 2016-08-19 | [
[
"Wang",
"Yaohua",
""
],
[
"Zhang",
"Xiao",
""
]
] | In non-extreme Kerr-Newman-AdS spacetime, we prove that there is no nontrivial Dirac particle which is $L^p$ for $0<p\leq\frac{4}{3}$ with arbitrary eigenvalue $\lambda$, and for $\frac{4}{3}<p\leq\frac{4}{3-2q}$, $0<q<\frac{3}{2}$ with eigenvalue $|\lambda|>|Q|+q \kappa $, outside and away from the event horizon. By taking $q=\frac{1}{2}$, we show that there is no normalizable massive Dirac particle with mass greater than $|Q|+\frac{\kappa}{2} $ outside and away from the event horizon in non-extreme Kerr-Newman-AdS spacetime, and they must either disappear into the black hole or escape to infinity, and this recovers the same result of Belgiorno and Cacciatori in the case of $Q=0$ obtained by using spectral methods. Furthermore, we prove that any Dirac particle with eigenvalue $|\lambda|<\frac{\kappa}{2} $ must be $L^2$ outside and away from the event horizon. |
1903.01542 | Luca Buoninfante | Luca Buoninfante, Anupam Mazumdar | Nonlocal star as a blackhole mimicker | 12 pages. V2: references added, typos fixed. V3: accepted for
publication in PRD | Phys. Rev. D 100, 024031 (2019) | 10.1103/PhysRevD.100.024031 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the context of ghost-free, infinite derivative gravity, we will provide a
quantum mechanical framework in which we can describe astrophysical objects
devoid of curvature singularity and event horizon. In order to avoid ghosts and
singularity, the gravitational interaction has to be nonlocal, therefore, we
call these objects as nonlocal stars. Quantum mechanically a nonlocal star is a
self-gravitational bound system of many gravitons interacting nonlocally.
Outside the nonlocal star the spacetime is well described by the Schwarzschild
metric, while inside we have a non-vacuum spacetime metric which tends to be
conformally flat at the origin. Remarkably, in the most compact scenario the
radius of a nonlocal star is of the same order of the Buchdahl limit, therefore
slightly larger than the Schwarzschild radius, such that there can exist a
photosphere. These objects live longer than a Schwarzschild blackhole and they
are very good absorbers, due to the fact that the number of available states is
larger than that of a blackhole. As a result nonlocal stars, not only can be
excellent blackhole mimickers, but can also be considered as dark matter
candidates. In particular, nonlocal stars with masses below $10^{14}$g can be
made stable compared to the age of the Universe.
| [
{
"created": "Mon, 4 Mar 2019 21:19:49 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Mar 2019 08:14:08 GMT",
"version": "v2"
},
{
"created": "Mon, 1 Jul 2019 07:58:19 GMT",
"version": "v3"
}
] | 2019-07-24 | [
[
"Buoninfante",
"Luca",
""
],
[
"Mazumdar",
"Anupam",
""
]
] | In the context of ghost-free, infinite derivative gravity, we will provide a quantum mechanical framework in which we can describe astrophysical objects devoid of curvature singularity and event horizon. In order to avoid ghosts and singularity, the gravitational interaction has to be nonlocal, therefore, we call these objects as nonlocal stars. Quantum mechanically a nonlocal star is a self-gravitational bound system of many gravitons interacting nonlocally. Outside the nonlocal star the spacetime is well described by the Schwarzschild metric, while inside we have a non-vacuum spacetime metric which tends to be conformally flat at the origin. Remarkably, in the most compact scenario the radius of a nonlocal star is of the same order of the Buchdahl limit, therefore slightly larger than the Schwarzschild radius, such that there can exist a photosphere. These objects live longer than a Schwarzschild blackhole and they are very good absorbers, due to the fact that the number of available states is larger than that of a blackhole. As a result nonlocal stars, not only can be excellent blackhole mimickers, but can also be considered as dark matter candidates. In particular, nonlocal stars with masses below $10^{14}$g can be made stable compared to the age of the Universe. |
gr-qc/9710116 | Haret Rosu | H.C. Rosu | Black holes and radiometry | 7pp | Mod.Phys.Lett. A8 (1993) 3429-3434 | 10.1142/S0217732393003846 | IFUG-R7-93 | gr-qc | null | Following Grischuk and Sidorov [Phys. Rev. D 42 (1990) 3413] in putting the
Bogolubov-Hawking coefficient of Schwarzschild black-holes in the squeezing
perspective, we provide a short discussion of Schwarzschild black holes as
radiometric standards
| [
{
"created": "Mon, 27 Oct 1997 22:46:46 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Rosu",
"H. C.",
""
]
] | Following Grischuk and Sidorov [Phys. Rev. D 42 (1990) 3413] in putting the Bogolubov-Hawking coefficient of Schwarzschild black-holes in the squeezing perspective, we provide a short discussion of Schwarzschild black holes as radiometric standards |
gr-qc/0303045 | Lars Andersson | Lars Andersson and Vincent Moncrief | Future complete vacuum spacetimes | 31 pages, latex, amsart | in '50 years of the Cauchy problem in General Relativity', eds.
Chrusciel and Friedrich, Birkhauser, Basel, 2004, pp. 299-330 | null | null | gr-qc | null | In this paper we prove a global existence theorem, in the direction of
cosmological expansion, for sufficiently small perturbations of a family of
spatially compact variants of the $k=-1$ Friedmann--Robertson--Walker vacuum
spacetime. We use a special gauge defined by constant mean curvature slicing
and a spatial harmonic coordinate condition, and develop energy estimates
through the use of the Bel-Robinson energy and its higher order
generalizations. In addition to the smallness condition on the data, we need a
topological constraint on the spatial manifold to exclude the possibility of a
non--trivial moduli space of flat spacetime perturbations, since the latter
could not be controlled by curvature--based energies such as those of
Bel--Robinson type. Our results also demonstrate causal geodesic completeness
of the perturbed spacetimes (in the expanding direction) and establish precise
rates of decay towards the background solution which serves as an attractor
asymptotically.
| [
{
"created": "Tue, 11 Mar 2003 21:38:20 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Andersson",
"Lars",
""
],
[
"Moncrief",
"Vincent",
""
]
] | In this paper we prove a global existence theorem, in the direction of cosmological expansion, for sufficiently small perturbations of a family of spatially compact variants of the $k=-1$ Friedmann--Robertson--Walker vacuum spacetime. We use a special gauge defined by constant mean curvature slicing and a spatial harmonic coordinate condition, and develop energy estimates through the use of the Bel-Robinson energy and its higher order generalizations. In addition to the smallness condition on the data, we need a topological constraint on the spatial manifold to exclude the possibility of a non--trivial moduli space of flat spacetime perturbations, since the latter could not be controlled by curvature--based energies such as those of Bel--Robinson type. Our results also demonstrate causal geodesic completeness of the perturbed spacetimes (in the expanding direction) and establish precise rates of decay towards the background solution which serves as an attractor asymptotically. |
gr-qc/0609130 | Yi Ling | Yi Ling, Song He and Hongbao Zhang | The kinematics of particles moving in rainbow spacetime | 5 pages | Mod.Phys.Lett.A22:2931-2938,2007 | 10.1142/S0217732307022980 | null | gr-qc | null | The kinematics of particles moving in rainbow spacetime is studied in this
paper. In particular the geodesics of a massive particle in rainbow flat
spacetime is obtained when the semi-classical effect of its own energy on the
background is taken into account. We show that in general the trajectory of a
freely falling particle remains unchanged which is still a straight line as in
the flat spacetime. The implication to the Unruh effect in rainbow flat
spacetime is also discussed.
| [
{
"created": "Thu, 28 Sep 2006 01:11:36 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Ling",
"Yi",
""
],
[
"He",
"Song",
""
],
[
"Zhang",
"Hongbao",
""
]
] | The kinematics of particles moving in rainbow spacetime is studied in this paper. In particular the geodesics of a massive particle in rainbow flat spacetime is obtained when the semi-classical effect of its own energy on the background is taken into account. We show that in general the trajectory of a freely falling particle remains unchanged which is still a straight line as in the flat spacetime. The implication to the Unruh effect in rainbow flat spacetime is also discussed. |
1805.10472 | Matsuno Satsuki | Hideki Ishihara, Satsuki Matsuno, Haruki Nakamura | Black holes submerged in Anti-de Sitter space | 33 page, 19 figures | null | null | OCU-PHYS-480 AP-GR-145 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Suppose a one-dimensional isometry group acts on a space, we can consider a
submergion induced by the isometry, namely we obtain an orbit space by
identification of points on the orbit of the group action. We study the causal
structure of the orbit space for Anti-de Sitter space (AdS) explicitely. In the
case of AdS$_3$, we found a variety of black hole structure, and in the case of
AdS$_5$, we found a static four-dimensional black hole, and a spacetime which
has two-dimensional black hole as a submanifold.
| [
{
"created": "Sat, 26 May 2018 12:46:37 GMT",
"version": "v1"
}
] | 2018-05-29 | [
[
"Ishihara",
"Hideki",
""
],
[
"Matsuno",
"Satsuki",
""
],
[
"Nakamura",
"Haruki",
""
]
] | Suppose a one-dimensional isometry group acts on a space, we can consider a submergion induced by the isometry, namely we obtain an orbit space by identification of points on the orbit of the group action. We study the causal structure of the orbit space for Anti-de Sitter space (AdS) explicitely. In the case of AdS$_3$, we found a variety of black hole structure, and in the case of AdS$_5$, we found a static four-dimensional black hole, and a spacetime which has two-dimensional black hole as a submanifold. |
2208.14768 | Subenoy Chakraborty | Ayanendu Dutta, Dhritimalya Roy, and Subenoy Chakraborty | The role of closed timelike curves in particle motion within Van Stockum
space-time: A generalization | null | Int. J. Mod. Phys. D 31 (13), 2250096 (2022) | 10.1142/S0218271822500961 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The present work analyses the particle motion in the Van Stockum space-time
considering the existence of closed timelike curves. Test particles with or
without angular momentum are studied in the present geometry. It is found that
only non-zero angular momentum test particles exist in the neighborhood of
closed timelike curves. The minimum particle energy and the range of backward
time jump in closed timelike geodesics are studied within a Cauchy horizon.
Finally, a general prescription for CTC and CTG has been presented with
appropriate examples.
| [
{
"created": "Wed, 31 Aug 2022 10:53:15 GMT",
"version": "v1"
}
] | 2024-06-06 | [
[
"Dutta",
"Ayanendu",
""
],
[
"Roy",
"Dhritimalya",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | The present work analyses the particle motion in the Van Stockum space-time considering the existence of closed timelike curves. Test particles with or without angular momentum are studied in the present geometry. It is found that only non-zero angular momentum test particles exist in the neighborhood of closed timelike curves. The minimum particle energy and the range of backward time jump in closed timelike geodesics are studied within a Cauchy horizon. Finally, a general prescription for CTC and CTG has been presented with appropriate examples. |
gr-qc/9907047 | Vadim O. Ustiansky | A.V.Toporensky and V.O. Ustiansky | Dynamics of Bianchi IX universe with massive scalar field | 15 pages with 2 eps figures and 3 gif figures | null | null | null | gr-qc | null | The dynamics of the Bianchi IX cosmological model with minimally coupled
massive real scalar field is studied. The possibility of non-singular
transition from contraction to expansion is shown. A set of initial conditions
that lead to non-singular solutions is studied numerically.
| [
{
"created": "Tue, 13 Jul 1999 09:17:51 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Toporensky",
"A. V.",
""
],
[
"Ustiansky",
"V. O.",
""
]
] | The dynamics of the Bianchi IX cosmological model with minimally coupled massive real scalar field is studied. The possibility of non-singular transition from contraction to expansion is shown. A set of initial conditions that lead to non-singular solutions is studied numerically. |
2207.12155 | Alessandro Pesci | Alessandro Pesci | Information content and minimum-length metric: A drop of light | 40 pages, 1 figure, contribution to the special issue of GERG
dedicated to the memory of Prof. Thanu Padmanabhan | Gen. Rel. Grav. 54 (2022) 72 | 10.1007/s10714-022-02960-1 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the vast amount of results linking gravity with thermodynamics,
statistics, information, a path is described which tries to explore this
connection from the point of view of (non)locality of the gravitational field.
First the emphasis is put on that well-known thermodynamic results related to
null hypersurfaces (i.e. to lightsheets and to generalized covariant entropy
bound) can be interpreted as implying an irreducible intrinsic nonlocality of
gravity. This nonlocality even if possibly concealed at ordinary
scales(depending on which matter is source of the gravitational field, and
which matter we use to probe the latter) unavoidably shows up at the smallest
scales, read the Planck length $l_p$, whichever are the circumstances we are
considering. Some consequences are then explored of this nonlocality when
embodied in the fabric itself of spacetime by endowing the latter with a
minimum length $L$, in particular the well-known and intriguing fact that this
brings to get the field equations, and all of gravity with it, as a
statistical-mechanical result. This is done here probing the neighborhood of a
would-be (in ordinary spacetime) generic event through lightsheets (instead of
spacelike or timelike geodesic congruences as in other accounts) from it. The
tools for these derivations are nonlocal quantities, and among them the
minimum-length Ricci scalar stands out both for providing micro degrees of
freedom for gravity in the statistical account and for the fact that
intriguingly the ordinary, or `classical', Ricci scalar can not be recovered
from it in the $L\to 0$ limit. Emphasis is put on that classical gravity is
generically obtained this way for $\hbar\ne 0$, but not in the $\hbar\to 0$
limit (the statistically derived field equations become singular in this
limit), adding to previous results in this sense. (truncated Abstract; see the
paper for full Abstract)
| [
{
"created": "Mon, 25 Jul 2022 12:56:16 GMT",
"version": "v1"
}
] | 2022-07-26 | [
[
"Pesci",
"Alessandro",
""
]
] | In the vast amount of results linking gravity with thermodynamics, statistics, information, a path is described which tries to explore this connection from the point of view of (non)locality of the gravitational field. First the emphasis is put on that well-known thermodynamic results related to null hypersurfaces (i.e. to lightsheets and to generalized covariant entropy bound) can be interpreted as implying an irreducible intrinsic nonlocality of gravity. This nonlocality even if possibly concealed at ordinary scales(depending on which matter is source of the gravitational field, and which matter we use to probe the latter) unavoidably shows up at the smallest scales, read the Planck length $l_p$, whichever are the circumstances we are considering. Some consequences are then explored of this nonlocality when embodied in the fabric itself of spacetime by endowing the latter with a minimum length $L$, in particular the well-known and intriguing fact that this brings to get the field equations, and all of gravity with it, as a statistical-mechanical result. This is done here probing the neighborhood of a would-be (in ordinary spacetime) generic event through lightsheets (instead of spacelike or timelike geodesic congruences as in other accounts) from it. The tools for these derivations are nonlocal quantities, and among them the minimum-length Ricci scalar stands out both for providing micro degrees of freedom for gravity in the statistical account and for the fact that intriguingly the ordinary, or `classical', Ricci scalar can not be recovered from it in the $L\to 0$ limit. Emphasis is put on that classical gravity is generically obtained this way for $\hbar\ne 0$, but not in the $\hbar\to 0$ limit (the statistically derived field equations become singular in this limit), adding to previous results in this sense. (truncated Abstract; see the paper for full Abstract) |
1411.1839 | Sudipta Das | Sudipta Das, Souvik Pramanik, Subir Ghosh | Effects of a Maximal Energy Scale in Thermodynamics for Photon Gas and
Construction of Path Integral | This is a review article based on our works arXiv:1002.0192,
arXiv:0908.0413, arXiv:1205.3919; v2: text overlap with gr-qc/0207085 removed | SIGMA 10 (2014), 104, 26 pages | 10.3842/SIGMA.2014.104 | null | gr-qc hep-th | http://creativecommons.org/licenses/by-nc-sa/3.0/ | In this article, we discuss some well-known theoretical models where an
observer-independent energy scale or a length scale is present. The presence of
this invariant scale necessarily deforms the Lorentz symmetry. We study
different aspects and features of such theories about how modifications arise
due to this cutoff scale. First we study the formulation of energy-momentum
tensor for a perfect fluid in doubly special relativity (DSR), where an energy
scale is present. Then we go on to study modifications in thermodynamic
properties of photon gas in DSR. Finally we discuss some models with
generalized uncertainty principle (GUP).
| [
{
"created": "Fri, 7 Nov 2014 06:19:27 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Nov 2014 14:38:51 GMT",
"version": "v2"
}
] | 2014-11-14 | [
[
"Das",
"Sudipta",
""
],
[
"Pramanik",
"Souvik",
""
],
[
"Ghosh",
"Subir",
""
]
] | In this article, we discuss some well-known theoretical models where an observer-independent energy scale or a length scale is present. The presence of this invariant scale necessarily deforms the Lorentz symmetry. We study different aspects and features of such theories about how modifications arise due to this cutoff scale. First we study the formulation of energy-momentum tensor for a perfect fluid in doubly special relativity (DSR), where an energy scale is present. Then we go on to study modifications in thermodynamic properties of photon gas in DSR. Finally we discuss some models with generalized uncertainty principle (GUP). |
gr-qc/9606048 | null | Mariano Cadoni | The dualities of 3D dilaton gravity | 15 pages, LaTex file, no figures | Phys.Rev.D54:7378-7385,1996 | 10.1103/PhysRevD.54.7378 | INFNCA-TH9610 | gr-qc hep-th | null | We investigate Brans-Dicke dilaton gravity theories in 2+1 dimensions. We
show that the reduced field equations for solutions with diagonal metric and
depending only on one spacetime coordinate have a continuous O(2) symmetry.
Using this symmetry we derive general static and cosmological solutions of the
theory. The action of the discrete group O(2,Z) on the space of the solutions
is discussed. Three-dimensional string effective theory and three-dimensional
general relativity are discussed in detail. In particular, we find that the
previously discovered black string solution is dual to a spacetime with a
conical singularity.
| [
{
"created": "Mon, 17 Jun 1996 11:21:54 GMT",
"version": "v1"
}
] | 2011-09-09 | [
[
"Cadoni",
"Mariano",
""
]
] | We investigate Brans-Dicke dilaton gravity theories in 2+1 dimensions. We show that the reduced field equations for solutions with diagonal metric and depending only on one spacetime coordinate have a continuous O(2) symmetry. Using this symmetry we derive general static and cosmological solutions of the theory. The action of the discrete group O(2,Z) on the space of the solutions is discussed. Three-dimensional string effective theory and three-dimensional general relativity are discussed in detail. In particular, we find that the previously discovered black string solution is dual to a spacetime with a conical singularity. |
1606.07173 | Francisco Frutos-Alfaro Dr. rer. nat. | Francisco Frutos-Alfaro and Michael Soffel | On Relativistic Multipole Moments of Stationary Spacetimes | null | Royal Society Open Science. 5: 180640, 2018 | 10.1098/rsos.180640 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Among the known exact solutions of Einstein vacuum field equations the
Manko-Novikov and the Quevedo-Mashhoon metrics might be suitable ones for the
description of the exterior gravitational field of some real non-collapsed
body. A new proposal to represent such exterior field is the stationary
q-metric. In this contribution, we computed by means of the
Fodor-Hoenselaers-Perjes formalism the lowest ten relativistic multipole
moments of these metrics. Corresponding moments were derived for the static
vacuum solutions of Gutsunayev-Manko and Hernandez-Martin. A direct comparison
between the multipole moments of these non-isometric spacetimes is given.
| [
{
"created": "Thu, 23 Jun 2016 03:36:33 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Jul 2016 01:31:13 GMT",
"version": "v2"
},
{
"created": "Tue, 4 Oct 2016 14:48:09 GMT",
"version": "v3"
},
{
"created": "Thu, 29 Nov 2018 20:17:03 GMT",
"version": "v4"
},
{
"cr... | 2019-09-17 | [
[
"Frutos-Alfaro",
"Francisco",
""
],
[
"Soffel",
"Michael",
""
]
] | Among the known exact solutions of Einstein vacuum field equations the Manko-Novikov and the Quevedo-Mashhoon metrics might be suitable ones for the description of the exterior gravitational field of some real non-collapsed body. A new proposal to represent such exterior field is the stationary q-metric. In this contribution, we computed by means of the Fodor-Hoenselaers-Perjes formalism the lowest ten relativistic multipole moments of these metrics. Corresponding moments were derived for the static vacuum solutions of Gutsunayev-Manko and Hernandez-Martin. A direct comparison between the multipole moments of these non-isometric spacetimes is given. |
2004.10503 | Teng Zhang | Teng Zhang, Denis Martynov, Andreas Freise, and Haixing Miao | Quantum Squeezing Schemes for Heterodyne Readout | null | Phys. Rev. D 101, 124052 (2020) | 10.1103/PhysRevD.101.124052 | null | gr-qc physics.ins-det | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Advanced gravitational-wave detectors are limited by quantum noise in their
most sensitive frequency band. Quantum noise suppression techniques, such as
the application of the quantum squeezed state of light, have been actively
studied in the context of homodyne readouts. In this paper, we consider quantum
squeezing schemes for the heterodyne readouts. This is motivated by a
successful suppression of the higher-order-mode content by stable recycling
cavities in advanced detectors. The heterodyne readout scheme requires precise
tuning of the interferometer parameters and a broadband squeezing source, but
is conceptually simple and elegant. We further show that it is compatible with
the frequency-dependent squeezing, which reduces both the shot noise and the
radiation-pressure noise. We propose a test of the heterodyne readout with
squeezing in Advanced LIGO. This can serve as a pathfinder not only for the
implementation in future detectors, such as Einstein Telescope and Cosmic
Explorer, but also for general high-precision optical measurements.
| [
{
"created": "Wed, 22 Apr 2020 11:34:37 GMT",
"version": "v1"
}
] | 2020-07-01 | [
[
"Zhang",
"Teng",
""
],
[
"Martynov",
"Denis",
""
],
[
"Freise",
"Andreas",
""
],
[
"Miao",
"Haixing",
""
]
] | Advanced gravitational-wave detectors are limited by quantum noise in their most sensitive frequency band. Quantum noise suppression techniques, such as the application of the quantum squeezed state of light, have been actively studied in the context of homodyne readouts. In this paper, we consider quantum squeezing schemes for the heterodyne readouts. This is motivated by a successful suppression of the higher-order-mode content by stable recycling cavities in advanced detectors. The heterodyne readout scheme requires precise tuning of the interferometer parameters and a broadband squeezing source, but is conceptually simple and elegant. We further show that it is compatible with the frequency-dependent squeezing, which reduces both the shot noise and the radiation-pressure noise. We propose a test of the heterodyne readout with squeezing in Advanced LIGO. This can serve as a pathfinder not only for the implementation in future detectors, such as Einstein Telescope and Cosmic Explorer, but also for general high-precision optical measurements. |
gr-qc/9911111 | John A. Gowan | John A. Gowan | A Spacetime Map of the Universe | 29 pages. Revision: conceptual restatement of spatial size of
universe in text | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A geometric spacetime map of the universe is presented, addressing problems
inherent in deep space observations and cosmology. Implications for the
observer's perspective, the cosmological "horizon" and "flatness" problem,
"inflation", and the recently observed accelerating expansion of the Universe
are discussed.
| [
{
"created": "Sat, 27 Nov 1999 18:38:22 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Apr 2009 13:30:07 GMT",
"version": "v10"
},
{
"created": "Wed, 1 Jul 2009 19:12:05 GMT",
"version": "v11"
},
{
"created": "Sun, 20 Nov 2011 22:22:47 GMT",
"version": "v12"
},
{
"... | 2011-11-22 | [
[
"Gowan",
"John A.",
""
]
] | A geometric spacetime map of the universe is presented, addressing problems inherent in deep space observations and cosmology. Implications for the observer's perspective, the cosmological "horizon" and "flatness" problem, "inflation", and the recently observed accelerating expansion of the Universe are discussed. |
1506.07049 | John Langford | Dean P. Foster and John Langford and Gabe Perez-Giz | Orbiting Radiation Stars | Updated draft | null | 10.1088/0264-9381/33/5/055002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a numerical solution to Einstein's equation for a compact object
composed of null particles. The solution avoids quantum scale regimes and hence
neither relies upon nor ignores the interaction of quantum mechanics and
gravitation. The solution exhibits a deep gravitational well yet remains
singularity free. In fact, the solution is geometrically flat in the vicinity
of the origin with the flat region being of any desirable scale. The solution
is also observationally distinct from a black hole because a photon from
infinity aimed at an object centered on the origin passes through the origin
and escapes to infinity with a time delay.
| [
{
"created": "Tue, 23 Jun 2015 15:28:56 GMT",
"version": "v1"
},
{
"created": "Sun, 20 Mar 2016 14:48:43 GMT",
"version": "v2"
}
] | 2016-03-22 | [
[
"Foster",
"Dean P.",
""
],
[
"Langford",
"John",
""
],
[
"Perez-Giz",
"Gabe",
""
]
] | We study a numerical solution to Einstein's equation for a compact object composed of null particles. The solution avoids quantum scale regimes and hence neither relies upon nor ignores the interaction of quantum mechanics and gravitation. The solution exhibits a deep gravitational well yet remains singularity free. In fact, the solution is geometrically flat in the vicinity of the origin with the flat region being of any desirable scale. The solution is also observationally distinct from a black hole because a photon from infinity aimed at an object centered on the origin passes through the origin and escapes to infinity with a time delay. |
1906.11550 | Naveena Kumara A | A. Naveena Kumara, C.L. Ahmed Rizwan, Deepak Vaid, K.M. Ajith | Critical Behaviour and Microscopic Structure of Charged AdS Black Hole
with a Global Monopole in Extended and Alternate Phase Spaces | 38 pages, 8 figures, comments are welcome! | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A detailed discussion on phase transition and microscopic structure of
charged AdS black hole with a global monopole is presented in both extended and
alternate phase spaces. In the analysis of critical behaviour, the classical
van der Waals analogy is drawn from isotherms which is followed by Gibbs free
energy study and coexistence curves. In both spaces, the symmetry breaking
parameter $\eta$ acts as a hindrance for critical behaviour. The crux of van
der Waals like behaviour is investigated by looking at the microscopic
structure of the black hole via thermodynamic Ruppeiner geometry. The Ruppeiner
invariant scalar behaves differently in extended and alternate spaces. The
monopole parameter influences the microscopic structure of the black hole,
which in turn, affects the critical behaviour. The effect is significant at the
maximal strength of the monopole parameter.
| [
{
"created": "Thu, 27 Jun 2019 11:18:34 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Jul 2019 15:46:44 GMT",
"version": "v2"
},
{
"created": "Mon, 6 Jan 2020 15:41:19 GMT",
"version": "v3"
}
] | 2020-01-07 | [
[
"Kumara",
"A. Naveena",
""
],
[
"Rizwan",
"C. L. Ahmed",
""
],
[
"Vaid",
"Deepak",
""
],
[
"Ajith",
"K. M.",
""
]
] | A detailed discussion on phase transition and microscopic structure of charged AdS black hole with a global monopole is presented in both extended and alternate phase spaces. In the analysis of critical behaviour, the classical van der Waals analogy is drawn from isotherms which is followed by Gibbs free energy study and coexistence curves. In both spaces, the symmetry breaking parameter $\eta$ acts as a hindrance for critical behaviour. The crux of van der Waals like behaviour is investigated by looking at the microscopic structure of the black hole via thermodynamic Ruppeiner geometry. The Ruppeiner invariant scalar behaves differently in extended and alternate spaces. The monopole parameter influences the microscopic structure of the black hole, which in turn, affects the critical behaviour. The effect is significant at the maximal strength of the monopole parameter. |
2308.16001 | Thanasis Giannakopoulos | Thanasis Giannakopoulos | Characteristic formulations of general relativity and applications | 179 pages, PhD Thesis, supplementary material at
https://github.com/ThanasisGiannakopoulos/PhD-thesis-supp | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | General relativity can describe various gravitational systems of
astrophysical relevance, like black holes and neutron stars, or even strongly
coupled systems through the holographic duality. The characteristic initial
(boundary) value problem has numerous applications in general relativity
involving numerical studies and is often formulated using Bondi-like
coordinates. Well-posedness of the resulting systems of partial differential
equations, however, remains an open question. The answer to this question
affects the accuracy, and potentially the reliability of conclusions drawn from
numerical studies based on such formulations. In the first part of this thesis,
we expand our understanding of the hyperbolicity and well-posedness of
Bondi-like free evolution systems. We show that several prototype Bondi-like
formulations are only weakly hyperbolic and examine the root cause of this
result. Consequently, the characteristic initial (boundary) value problem of
general relativity in these gauges is rendered ill-posed in the simplest norms
one would like to employ. We discuss the implications of this result in
accurate gravitational waveform modeling methods and work towards the
construction of alternative norms that might be more appropriate. We also
present numerical tests that demonstrate weak hyperbolicity in practice and
highlight important features to perform them effectively. In the second part,
we turn our attention to applications of these formulations to the qualitative
behavior of strongly coupled systems via holography.
| [
{
"created": "Wed, 30 Aug 2023 12:41:19 GMT",
"version": "v1"
}
] | 2023-08-31 | [
[
"Giannakopoulos",
"Thanasis",
""
]
] | General relativity can describe various gravitational systems of astrophysical relevance, like black holes and neutron stars, or even strongly coupled systems through the holographic duality. The characteristic initial (boundary) value problem has numerous applications in general relativity involving numerical studies and is often formulated using Bondi-like coordinates. Well-posedness of the resulting systems of partial differential equations, however, remains an open question. The answer to this question affects the accuracy, and potentially the reliability of conclusions drawn from numerical studies based on such formulations. In the first part of this thesis, we expand our understanding of the hyperbolicity and well-posedness of Bondi-like free evolution systems. We show that several prototype Bondi-like formulations are only weakly hyperbolic and examine the root cause of this result. Consequently, the characteristic initial (boundary) value problem of general relativity in these gauges is rendered ill-posed in the simplest norms one would like to employ. We discuss the implications of this result in accurate gravitational waveform modeling methods and work towards the construction of alternative norms that might be more appropriate. We also present numerical tests that demonstrate weak hyperbolicity in practice and highlight important features to perform them effectively. In the second part, we turn our attention to applications of these formulations to the qualitative behavior of strongly coupled systems via holography. |
2101.12196 | Kyriakos Destounis Dr. | Christoforos Vlachos, Eleftherios Papantonopoulos, Kyriakos Destounis | Echoes of Compact Objects in Scalar-Tensor Theories of Gravity | 15 pages + references, 7 figures, accepted for publication in PRD | Phys. Rev. D 103, 044042 (2021) | 10.1103/PhysRevD.103.044042 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Scalar-tensor theory predicts solutions to the gravitational field equations
which describe compact objects in the presence of a non-minimally coupled
scalar field to the Einstein tensor. These objects are black holes with scalar
hair and wormholes supporting scalar phantom matter. The evolution of test
fields in fixed asymptotically-flat backgrounds of exotic compact objects leads
to the formation of echoes in the ringdown signal, which designate the
existence of trapping regions close to the event horizon. Here, we consider
minimally-coupled test scalar fields propagating on compact object solutions of
the Horndeski action, which possess an effective cosmological constant, leading
to anti-de Sitter asymptotics, and show that echoes can form in the ringdown
waveform due to the entrapment of test fields between the photon sphere and the
effective asymptotic boundary. Although the presence of an event horizon leads
to the usual echoes with decaying amplitude, signifying modal stability of the
scalarized black hole considered, we find that test scalar fields propagating
on a scalarized wormhole solution give rise to echoes of constant and equal
amplitude to that of the initial ringdown, indicating the existence of normal
modes. Finally, we find that, near extremality, the test field exhibits a
concatenation of echoes; the primary ones are associated with the trapping
region between the photon sphere and the effective anti-de Sitter boundary
while the secondary ones are linked to the existence of a potential well at the
throat of the wormhole.
| [
{
"created": "Thu, 28 Jan 2021 18:56:02 GMT",
"version": "v1"
}
] | 2021-02-24 | [
[
"Vlachos",
"Christoforos",
""
],
[
"Papantonopoulos",
"Eleftherios",
""
],
[
"Destounis",
"Kyriakos",
""
]
] | Scalar-tensor theory predicts solutions to the gravitational field equations which describe compact objects in the presence of a non-minimally coupled scalar field to the Einstein tensor. These objects are black holes with scalar hair and wormholes supporting scalar phantom matter. The evolution of test fields in fixed asymptotically-flat backgrounds of exotic compact objects leads to the formation of echoes in the ringdown signal, which designate the existence of trapping regions close to the event horizon. Here, we consider minimally-coupled test scalar fields propagating on compact object solutions of the Horndeski action, which possess an effective cosmological constant, leading to anti-de Sitter asymptotics, and show that echoes can form in the ringdown waveform due to the entrapment of test fields between the photon sphere and the effective asymptotic boundary. Although the presence of an event horizon leads to the usual echoes with decaying amplitude, signifying modal stability of the scalarized black hole considered, we find that test scalar fields propagating on a scalarized wormhole solution give rise to echoes of constant and equal amplitude to that of the initial ringdown, indicating the existence of normal modes. Finally, we find that, near extremality, the test field exhibits a concatenation of echoes; the primary ones are associated with the trapping region between the photon sphere and the effective anti-de Sitter boundary while the secondary ones are linked to the existence of a potential well at the throat of the wormhole. |
gr-qc/0304012 | Niklas Rohr | J. Mark Heinzle, N. Rohr, C. Uggla | Spherically symmetric relativistic stellar structures | 23 pages, 25 figures (compressed), LaTeX | Class.Quant.Grav. 20 (2003) 4567-4586 | 10.1088/0264-9381/20/21/004 | null | gr-qc astro-ph | null | We investigate relativistic spherically symmetric static perfect fluid models
in the framework of the theory of dynamical systems. The field equations are
recast into a regular dynamical system on a 3-dimensional compact state space,
thereby avoiding the non-regularity problems associated with the
Tolman-Oppenheimer-Volkoff equation. The global picture of the solution space
thus obtained is used to derive qualitative features and to prove theorems
about mass-radius properties. The perfect fluids we discuss are described by
barotropic equations of state that are asymptotically polytropic at low
pressures and, for certain applications, asymptotically linear at high
pressures. We employ dimensionless variables that are asymptotically homology
invariant in the low pressure regime, and thus we generalize standard work on
Newtonian polytropes to a relativistic setting and to a much larger class of
equations of state. Our dynamical systems framework is particularly suited for
numerical computations, as illustrated by several numerical examples, e.g., the
ideal neutron gas and examples that involve phase transitions.
| [
{
"created": "Wed, 2 Apr 2003 08:56:42 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Heinzle",
"J. Mark",
""
],
[
"Rohr",
"N.",
""
],
[
"Uggla",
"C.",
""
]
] | We investigate relativistic spherically symmetric static perfect fluid models in the framework of the theory of dynamical systems. The field equations are recast into a regular dynamical system on a 3-dimensional compact state space, thereby avoiding the non-regularity problems associated with the Tolman-Oppenheimer-Volkoff equation. The global picture of the solution space thus obtained is used to derive qualitative features and to prove theorems about mass-radius properties. The perfect fluids we discuss are described by barotropic equations of state that are asymptotically polytropic at low pressures and, for certain applications, asymptotically linear at high pressures. We employ dimensionless variables that are asymptotically homology invariant in the low pressure regime, and thus we generalize standard work on Newtonian polytropes to a relativistic setting and to a much larger class of equations of state. Our dynamical systems framework is particularly suited for numerical computations, as illustrated by several numerical examples, e.g., the ideal neutron gas and examples that involve phase transitions. |
gr-qc/0001068 | Sean A. Hayward | Sean A. Hayward | Gravitational waves from quasi-spherical black holes | 4 revtex pages, 2 eps figures | Phys.Rev.D61:101503,2000 | 10.1103/PhysRevD.61.101503 | null | gr-qc | null | A quasi-spherical approximation scheme, intended to apply to coalescing black
holes, allows the waveforms of gravitational radiation to be computed by
integrating ordinary differential equations.
| [
{
"created": "Fri, 21 Jan 2000 17:56:59 GMT",
"version": "v1"
}
] | 2009-12-30 | [
[
"Hayward",
"Sean A.",
""
]
] | A quasi-spherical approximation scheme, intended to apply to coalescing black holes, allows the waveforms of gravitational radiation to be computed by integrating ordinary differential equations. |
1606.04356 | Ramil Izmailov | Kamal K. Nandi, Alexander A. Potapov, Ramil Izmailov, Amarjit Tamang
and James C. Evans | Stability and instability of Ellis and phantom wormholes: Are there
ghosts? | 43 pages, 5 figures | Phys. Rev. D 93, 104044 (2016) | 10.1103/PhysRevD.93.104044 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is concluded in the literature that Ellis wormhole is unstable under small
perturbations and would decay either to the Schwarzschild black hole or expand
away to infinity. While this deterministic conclusion of instability is
correct, we show that the Ellis wormhole reduces to Schwarzschild black hole
\textit{only} when the Ellis solution parameter $\gamma $ assumes a complex
value $-i$. We shall then reexamine stability of Ellis and phantom wormholes
from the viewpoint of local and asymptotic observers by using a completely
different approach, viz., we adapt Tangherlini's nondeterministic, prequantal
statistical simulation about photon motion in the real optical medium to an
effective medium reformulation of motions obtained via Hamilton's
optical-mechanical analogy in a gravity field. A crucial component of
Tangherlini's idea is the observed increase of momentum of the photons entering
a real medium. We show that this fact has a heuristic parallel in the effective
medium\ version of the Pound-Rebka experiment in gravity. Our conclusion is
that there is a non-zero probability that Ellis and phantom wormholes could
appear stable or unstable depending on the location of observers and on the
values of $\gamma$, leading to the possibility of \textit{ghost wormholes}
(like ghost stars). The Schwarzschild horizon, however, would always appear
certainly stable ($R=1$, $T=0$) to observers regardless of their location.
Phantom wormholes of bounded mass in the extreme limit $a\rightarrow -1$ are
also shown to be stable just as the Schwarzschild black hole is. We shall
propose a thought experiment showing that our non-deterministic results could
be numerically translated into observable deterministic signatures of ghost
wormholes.
| [
{
"created": "Mon, 6 Jun 2016 07:27:03 GMT",
"version": "v1"
}
] | 2016-06-22 | [
[
"Nandi",
"Kamal K.",
""
],
[
"Potapov",
"Alexander A.",
""
],
[
"Izmailov",
"Ramil",
""
],
[
"Tamang",
"Amarjit",
""
],
[
"Evans",
"James C.",
""
]
] | It is concluded in the literature that Ellis wormhole is unstable under small perturbations and would decay either to the Schwarzschild black hole or expand away to infinity. While this deterministic conclusion of instability is correct, we show that the Ellis wormhole reduces to Schwarzschild black hole \textit{only} when the Ellis solution parameter $\gamma $ assumes a complex value $-i$. We shall then reexamine stability of Ellis and phantom wormholes from the viewpoint of local and asymptotic observers by using a completely different approach, viz., we adapt Tangherlini's nondeterministic, prequantal statistical simulation about photon motion in the real optical medium to an effective medium reformulation of motions obtained via Hamilton's optical-mechanical analogy in a gravity field. A crucial component of Tangherlini's idea is the observed increase of momentum of the photons entering a real medium. We show that this fact has a heuristic parallel in the effective medium\ version of the Pound-Rebka experiment in gravity. Our conclusion is that there is a non-zero probability that Ellis and phantom wormholes could appear stable or unstable depending on the location of observers and on the values of $\gamma$, leading to the possibility of \textit{ghost wormholes} (like ghost stars). The Schwarzschild horizon, however, would always appear certainly stable ($R=1$, $T=0$) to observers regardless of their location. Phantom wormholes of bounded mass in the extreme limit $a\rightarrow -1$ are also shown to be stable just as the Schwarzschild black hole is. We shall propose a thought experiment showing that our non-deterministic results could be numerically translated into observable deterministic signatures of ghost wormholes. |
1607.03689 | Matthew J. Lake Dr | Matthew J. Lake | Which quantum theory must be reconciled with gravity? (And what does it
mean for black holes?) | 38 pages, 5 figures. Invited contribution to the Universe special
issue "Open questions in black hole physics" (Gonzalo J. Olmo, Ed.). Matches
published version | Universe 2016, 2(4), 24 | 10.3390/universe2040024 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the nature of quantum properties in non-relativistic quantum
mechanics (QM) and relativistic QFTs, and examine the connection between formal
quantization schemes and intuitive notions of wave-particle duality. Based on
the map between classical Poisson brackets and their associated commutators,
such schemes give rise to quantum states obeying canonical dispersion
relations, obtained by substituting the de Broglie relations into the relevant
(classical) energy-momentum relation. In canonical QM, this yields a dispersion
relation involving $\hbar$ but not $c$, whereas the canonical relativistic
dispersion relation involves both. Extending this logic to the canonical
quantization of the gravitational field gives rise to loop quantum gravity, and
a map between classical variables containing $G$ and $c$, and associated
commutators involving $\hbar$. This naturally defines a "wave-gravity duality",
suggesting that a quantum wave packet describing {\it self-gravitating matter}
obeys a dispersion relation involving $G$, $c$ and $\hbar$. We propose an
ansatz for this relation, which is valid in the semi-Newtonian regime of both
QM and general relativity. In this limit, space and time are absolute, but
imposing $v_{\rm max} = c$ allows us to recover the standard expressions for
the Compton wavelength $\lambda_C$ and the Schwarzschild radius $r_S$ within
the same ontological framework. The new dispersion relation is based on
"extended" de Broglie relations, which remain valid for slow-moving bodies of
{\it any} mass $m$. These reduce to canonical form for $m \ll m_P$, yielding
$\lambda_C$ from the standard uncertainty principle, whereas, for $m \gg m_P$,
we obtain $r_S$ as the natural radius of a self-gravitating quantum object.
Thus, the extended de Broglie theory naturally gives rise to a unified
description of black holes and fundamental particles in the semi-Newtonian
regime.
| [
{
"created": "Wed, 13 Jul 2016 12:07:20 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Oct 2016 11:22:04 GMT",
"version": "v2"
}
] | 2016-10-21 | [
[
"Lake",
"Matthew J.",
""
]
] | We consider the nature of quantum properties in non-relativistic quantum mechanics (QM) and relativistic QFTs, and examine the connection between formal quantization schemes and intuitive notions of wave-particle duality. Based on the map between classical Poisson brackets and their associated commutators, such schemes give rise to quantum states obeying canonical dispersion relations, obtained by substituting the de Broglie relations into the relevant (classical) energy-momentum relation. In canonical QM, this yields a dispersion relation involving $\hbar$ but not $c$, whereas the canonical relativistic dispersion relation involves both. Extending this logic to the canonical quantization of the gravitational field gives rise to loop quantum gravity, and a map between classical variables containing $G$ and $c$, and associated commutators involving $\hbar$. This naturally defines a "wave-gravity duality", suggesting that a quantum wave packet describing {\it self-gravitating matter} obeys a dispersion relation involving $G$, $c$ and $\hbar$. We propose an ansatz for this relation, which is valid in the semi-Newtonian regime of both QM and general relativity. In this limit, space and time are absolute, but imposing $v_{\rm max} = c$ allows us to recover the standard expressions for the Compton wavelength $\lambda_C$ and the Schwarzschild radius $r_S$ within the same ontological framework. The new dispersion relation is based on "extended" de Broglie relations, which remain valid for slow-moving bodies of {\it any} mass $m$. These reduce to canonical form for $m \ll m_P$, yielding $\lambda_C$ from the standard uncertainty principle, whereas, for $m \gg m_P$, we obtain $r_S$ as the natural radius of a self-gravitating quantum object. Thus, the extended de Broglie theory naturally gives rise to a unified description of black holes and fundamental particles in the semi-Newtonian regime. |
2112.01235 | Georgios Kraniotis | G. V. Kraniotis | Curvature Invariants for accelerating Kerr-Newman black holes in
(anti-)de Sitter spacetime | LaTeX file 48 pages, 22eps figures, v3 new results, figures added,v4
typo fixed, v5 version published in Classical and Quantum Gravity | Class.Quantum Grav. 39 (2022) 145002 | 10.1088/1361-6382/ac750a | null | gr-qc astro-ph.GA hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The curvature scalar invariants of the Riemann tensor are important in
General Relativity because they allow a manifestly coordinate invariant
characterisation of certain geometrical properties of spacetimes such as, among
others, curvature singularities, gravitomagnetism. We calculate explicit
analytic expressions for the set of Zakhary-McIntosh curvature invariants for
accelerating Kerr-Newman black holes in (anti-)de Sitter spacetime as well as
for the Kerr-Newman-(anti-)de Sitter black hole. These black hole metrics
belong to the most general type D solution of the Einstein-Maxwell equations
with a cosmological constant. Explicit analytic expressions for the
Euler-Poincare density invariant, which is relevant for the computation of the
Euler-Poincare characteristic $\chi(M)$, and the Kretschmann scalar are also
provided for both cases. We perform a detailed plotting of the curvature
invariants that reveal a rich structure of the spacetime geometry surrounding
the singularity of a rotating, electrically charged and accelerating black hole
. These graphs also help us in an exact mathematical way to explore the
interior of these black holes. Our explicit closed form expressions show that
the above gravitational backgrounds possess a non-trivial Hirzebruch signature
density. Possible physical applications of this property for the
electromagnetic duality anomaly in curved spacetimes that can spoil helicity
conservation are briefly discussed.
| [
{
"created": "Thu, 2 Dec 2021 13:48:13 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Dec 2021 10:33:20 GMT",
"version": "v2"
},
{
"created": "Thu, 17 Feb 2022 17:26:05 GMT",
"version": "v3"
},
{
"created": "Thu, 24 Feb 2022 12:07:03 GMT",
"version": "v4"
},
{
"cr... | 2022-07-13 | [
[
"Kraniotis",
"G. V.",
""
]
] | The curvature scalar invariants of the Riemann tensor are important in General Relativity because they allow a manifestly coordinate invariant characterisation of certain geometrical properties of spacetimes such as, among others, curvature singularities, gravitomagnetism. We calculate explicit analytic expressions for the set of Zakhary-McIntosh curvature invariants for accelerating Kerr-Newman black holes in (anti-)de Sitter spacetime as well as for the Kerr-Newman-(anti-)de Sitter black hole. These black hole metrics belong to the most general type D solution of the Einstein-Maxwell equations with a cosmological constant. Explicit analytic expressions for the Euler-Poincare density invariant, which is relevant for the computation of the Euler-Poincare characteristic $\chi(M)$, and the Kretschmann scalar are also provided for both cases. We perform a detailed plotting of the curvature invariants that reveal a rich structure of the spacetime geometry surrounding the singularity of a rotating, electrically charged and accelerating black hole . These graphs also help us in an exact mathematical way to explore the interior of these black holes. Our explicit closed form expressions show that the above gravitational backgrounds possess a non-trivial Hirzebruch signature density. Possible physical applications of this property for the electromagnetic duality anomaly in curved spacetimes that can spoil helicity conservation are briefly discussed. |
gr-qc/9611037 | Philip Mannheim | Philip D. Mannheim (University of Connecticut) | Classical Underpinnings of Gravitationally Induced Quantum Interference | LaTeX, 8 pages plus two figures in one postscript file | null | null | UCONN 96-08, October 1996 | gr-qc quant-ph | null | We show that the gravitational modification of the phase of a neutron beam
(the COW experiment) has a classical origin, being due to the time delay which
classical particles experience in traversing a background gravitational field.
Similarly, we show that classical light waves also undergo a phase shift in
traversing a gravitational field. We show that the COW experiment respects the
equivalence principle even in the presence of quantum mechanics.
| [
{
"created": "Wed, 13 Nov 1996 15:17:50 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Mannheim",
"Philip D.",
"",
"University of Connecticut"
]
] | We show that the gravitational modification of the phase of a neutron beam (the COW experiment) has a classical origin, being due to the time delay which classical particles experience in traversing a background gravitational field. Similarly, we show that classical light waves also undergo a phase shift in traversing a gravitational field. We show that the COW experiment respects the equivalence principle even in the presence of quantum mechanics. |
1402.5198 | J\"org Hennig | J\"org Hennig | Geometric relations for rotating and charged AdS black holes | 10 pages | Class. Quantum Grav. 31, 135005 (2014) | 10.1088/0264-9381/31/13/135005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive mass-independent equations and inequalities for Kerr-Newman-anti-de
Sitter black holes. In particular, we obtain an equation that relates electric
charge, angular momentum and the areas of the event and Cauchy horizons. An
area-angular momentum-charge inequality is derived from this formula, which
becomes an equality in the degenerate limit. The same equation is shown to hold
for arbitrary degenerate black holes, which might, for example, be surrounded
by matter.
| [
{
"created": "Fri, 21 Feb 2014 03:44:09 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Jun 2014 02:49:00 GMT",
"version": "v2"
}
] | 2014-06-17 | [
[
"Hennig",
"Jörg",
""
]
] | We derive mass-independent equations and inequalities for Kerr-Newman-anti-de Sitter black holes. In particular, we obtain an equation that relates electric charge, angular momentum and the areas of the event and Cauchy horizons. An area-angular momentum-charge inequality is derived from this formula, which becomes an equality in the degenerate limit. The same equation is shown to hold for arbitrary degenerate black holes, which might, for example, be surrounded by matter. |
2310.11827 | B. S. Ratanpal | Rinkal Patel and B. S. Ratanpal | A various equation of state for anisotropic models of compact star | 28 pages and 15 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We obtain models of compact stars having pressure anisotropy on Finch-Skea
spacetime by considering generalized equation of state (EoS), whose particular
cases are linear, quadratic, polytropic, chaplygin and colour - flavor
locked(CFL) equation of states. The physical viability of models are tested for
strange star candidate 4U 1820 - 30 having mass M = 1.58Mass of the sun and
radius R = 9.1 km. All the models are physically plausible.
| [
{
"created": "Wed, 18 Oct 2023 09:28:16 GMT",
"version": "v1"
}
] | 2023-10-19 | [
[
"Patel",
"Rinkal",
""
],
[
"Ratanpal",
"B. S.",
""
]
] | We obtain models of compact stars having pressure anisotropy on Finch-Skea spacetime by considering generalized equation of state (EoS), whose particular cases are linear, quadratic, polytropic, chaplygin and colour - flavor locked(CFL) equation of states. The physical viability of models are tested for strange star candidate 4U 1820 - 30 having mass M = 1.58Mass of the sun and radius R = 9.1 km. All the models are physically plausible. |
1908.04754 | Ayan Banerjee | Ayan Banerjee, Ksh. Newton Singh, M. K. Jasim and Farook Rahaman | Conformally symmetric traversable wormholes in $f(R,T)$ gravity | 10 pages and 9 figures, version published in Annals of Physics:
comments added and typos fixed | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | To find more deliberate $f(R, T)$ astrophysical solutions, we proceed by
studying wormhole geometries under the assumption of spherical symmetry and the
existence of a conformal Killing symmetry to attain the more acceptable
astrophysical results. To do this, we consider a more plausible and simple
model $f(R,T)=R+2\chi T$, where $R$ is the Ricci scalar and $T= -\rho+p_r+2p_t$
denotes the trace of the energy-momentum tensor of the matter content. We
explore and analyze two cases separately. In the first part, wormhole solutions
are constructed for the matter sources with isotropic pressure. However, the
obtained solution does not satisfy the required wormhole conditions. In the
second part, we introduce an EoS relating with pressure (radial and lateral)
and density. We constrain the models with phantom energy EoS i.e. $\omega= p_r/
\rho < -1$, consequently violating the null energy condition. Next, we analyze
the model via $p_t= n p_r $. Several physical properties and characteristics of
these solutions are investigated which are consistent with previous references
about wormholes. We mainly focus on energy conditions (NEC, WEC and SEC) and
consequently for supporting the respective wormhole geometries in details. In
both cases it is found that the energy density is positive as seen by any
static observer. To support the theoretical results, we also plotted several
figures for different parameter values of the model that helps us to confirm
the predictions. Finally, the volume integral quantifier, which provides useful
information about the total amount of exotic matter required to maintain a
traversable wormhole is discussed briefly.
| [
{
"created": "Sat, 10 Aug 2019 12:37:29 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Aug 2020 12:04:11 GMT",
"version": "v2"
}
] | 2020-08-21 | [
[
"Banerjee",
"Ayan",
""
],
[
"Singh",
"Ksh. Newton",
""
],
[
"Jasim",
"M. K.",
""
],
[
"Rahaman",
"Farook",
""
]
] | To find more deliberate $f(R, T)$ astrophysical solutions, we proceed by studying wormhole geometries under the assumption of spherical symmetry and the existence of a conformal Killing symmetry to attain the more acceptable astrophysical results. To do this, we consider a more plausible and simple model $f(R,T)=R+2\chi T$, where $R$ is the Ricci scalar and $T= -\rho+p_r+2p_t$ denotes the trace of the energy-momentum tensor of the matter content. We explore and analyze two cases separately. In the first part, wormhole solutions are constructed for the matter sources with isotropic pressure. However, the obtained solution does not satisfy the required wormhole conditions. In the second part, we introduce an EoS relating with pressure (radial and lateral) and density. We constrain the models with phantom energy EoS i.e. $\omega= p_r/ \rho < -1$, consequently violating the null energy condition. Next, we analyze the model via $p_t= n p_r $. Several physical properties and characteristics of these solutions are investigated which are consistent with previous references about wormholes. We mainly focus on energy conditions (NEC, WEC and SEC) and consequently for supporting the respective wormhole geometries in details. In both cases it is found that the energy density is positive as seen by any static observer. To support the theoretical results, we also plotted several figures for different parameter values of the model that helps us to confirm the predictions. Finally, the volume integral quantifier, which provides useful information about the total amount of exotic matter required to maintain a traversable wormhole is discussed briefly. |
0902.0346 | Matt Visser | Matt Visser (Victoria University of Wellington), Carlos Barcelo
(Astrophysics Institute of Andalusia), Stefano Liberati (SISSA and INFN,
Trieste), Sebastiano Sonego (University of Udine) | Small, dark, and heavy: But is it a black hole? | 17 pages, 8 figures. Technical seminar at the workshop "Black Holes
in General Relativity and String Theory", 24-30 August, 2008, Veli Losinj,
Croatia; V2: one reference added | PoS BHs,GRandStrings 2008:010,2008 | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Astronomers have certainly observed things that are small, dark, and heavy.
But are these objects really black holes in the sense of general relativity?
The consensus opinion is simply "yes", and there is very little "wriggle room".
We discuss one of the specific alternatives.
| [
{
"created": "Mon, 2 Feb 2009 19:51:07 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Feb 2009 20:55:15 GMT",
"version": "v2"
}
] | 2010-02-16 | [
[
"Visser",
"Matt",
"",
"Victoria University of Wellington"
],
[
"Barcelo",
"Carlos",
"",
"Astrophysics Institute of Andalusia"
],
[
"Liberati",
"Stefano",
"",
"SISSA and INFN,\n Trieste"
],
[
"Sonego",
"Sebastiano",
"",
"University of Udi... | Astronomers have certainly observed things that are small, dark, and heavy. But are these objects really black holes in the sense of general relativity? The consensus opinion is simply "yes", and there is very little "wriggle room". We discuss one of the specific alternatives. |
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