id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1912.08712 | Bob Osano | Timothy Oreta and Bob Osano | Post inflationary evolution of inflation-produced, large-scale magnetic
fields using a generalised cosmological Ohm's law and both standard and
modified Maxwell's equations | 25, 1 figure. arXiv admin note: text overlap with arXiv:1412.4806 by
other authors | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In most of the literature on evolution of cosmological magnetic fields, it is
found that large-scale magnetic fields evolve as $B^{2}\propto a^{-4}$
(adiabatic magnetic decay) where $a$ is the cosmological scale factor and $B$
is the cosmological magnetic field. This rapid decay has been considered as the
main obstacle against magnetic fields produced during the inflationary epoch
from surviving until today and seeding the observed fields. However, recent
reports of first ever detection of intergalactic fields, with strengths around
$10^{-6}G$ are a mystery [1-4]. One possible explanation is that large-scale
magnetic fields could have been superadiabatically amplified in their
evolutionary history. Superadiabatic amplification may mean that there is an
actual increase in the strength of the magnetic field or that magnetic
decay-rates are slower than the standard adiabatic magnetic decay rate [5] .
This can be demonstrated if we use the generalised cosmological Ohm's law and
both standard and modified Maxwell field equations; this is the goal of this
study.
| [
{
"created": "Mon, 16 Dec 2019 22:47:02 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Apr 2020 18:40:59 GMT",
"version": "v2"
}
] | 2020-04-23 | [
[
"Oreta",
"Timothy",
""
],
[
"Osano",
"Bob",
""
]
] | In most of the literature on evolution of cosmological magnetic fields, it is found that large-scale magnetic fields evolve as $B^{2}\propto a^{-4}$ (adiabatic magnetic decay) where $a$ is the cosmological scale factor and $B$ is the cosmological magnetic field. This rapid decay has been considered as the main obstacle against magnetic fields produced during the inflationary epoch from surviving until today and seeding the observed fields. However, recent reports of first ever detection of intergalactic fields, with strengths around $10^{-6}G$ are a mystery [1-4]. One possible explanation is that large-scale magnetic fields could have been superadiabatically amplified in their evolutionary history. Superadiabatic amplification may mean that there is an actual increase in the strength of the magnetic field or that magnetic decay-rates are slower than the standard adiabatic magnetic decay rate [5] . This can be demonstrated if we use the generalised cosmological Ohm's law and both standard and modified Maxwell field equations; this is the goal of this study. |
1905.13460 | Andrea Maselli | Giuseppe Gnocchi, Andrea Maselli, Tiziano Abdelsalhin, Nicola
Giacobbo, Michela Mapelli | Bounding Alternative Theories of Gravity with Multi-Band GW Observations | Results updated to match the version in press on Phys. Rev. D | Phys. Rev. D 100, 064024 (2019) | 10.1103/PhysRevD.100.064024 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the constraints on alternative theories of gravity that can be
determined by multi-band observations of gravitational wave signals emitted
from binary black hole coalescences. We focus on three types of General
Relativity modifications induced by a generalised Brans-Dicke theory, and two
classes of quadratic gravity, Einstein-dilaton-Gauss-Bonnet and dynamical
Chern-Simons. Considering a network of space and ground-based detectors,
supplied by a population of spinning binaries black hole, we show how the
multi-band analysis improves the existing bounds on the theory's parameters by
several orders of magnitude, for both pre- and post-Newtonian deviations. Our
results also show the fundamental role played by an interferometer in the
frequency range between LISA and advanced detectors, in constraining possible
deviations from General Relativity.
| [
{
"created": "Fri, 31 May 2019 08:20:51 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Sep 2019 15:21:08 GMT",
"version": "v2"
}
] | 2019-09-18 | [
[
"Gnocchi",
"Giuseppe",
""
],
[
"Maselli",
"Andrea",
""
],
[
"Abdelsalhin",
"Tiziano",
""
],
[
"Giacobbo",
"Nicola",
""
],
[
"Mapelli",
"Michela",
""
]
] | We study the constraints on alternative theories of gravity that can be determined by multi-band observations of gravitational wave signals emitted from binary black hole coalescences. We focus on three types of General Relativity modifications induced by a generalised Brans-Dicke theory, and two classes of quadratic gravity, Einstein-dilaton-Gauss-Bonnet and dynamical Chern-Simons. Considering a network of space and ground-based detectors, supplied by a population of spinning binaries black hole, we show how the multi-band analysis improves the existing bounds on the theory's parameters by several orders of magnitude, for both pre- and post-Newtonian deviations. Our results also show the fundamental role played by an interferometer in the frequency range between LISA and advanced detectors, in constraining possible deviations from General Relativity. |
gr-qc/0608008 | Farhad Darabi | F. Darabi | Classical and quantum wormholes in a flat $\Lambda$-decaying cosmology | 8 pages, 4 figures, accepted for publication in IJTP | Int.J.Theor.Phys.48:961-968,2009 | 10.1007/s10773-008-9869-9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the classical and quantum wormholes for a flat {\it Euclidean}
Friedmann-Robertson-Walker metric with a perfect fluid including an ordinary
matter source plus a source playing the role of dark energy (decaying
cosmological term). It is shown that classical wormholes exist for this model
and the quantum version of such wormholes are consistent with the Hawking-Page
conjecture for quantum wormholes as solutions of the Wheeler-DeWitt equation.
| [
{
"created": "Tue, 1 Aug 2006 12:57:08 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Aug 2006 12:00:03 GMT",
"version": "v2"
},
{
"created": "Sun, 7 Dec 2008 09:09:31 GMT",
"version": "v3"
}
] | 2009-03-24 | [
[
"Darabi",
"F.",
""
]
] | We study the classical and quantum wormholes for a flat {\it Euclidean} Friedmann-Robertson-Walker metric with a perfect fluid including an ordinary matter source plus a source playing the role of dark energy (decaying cosmological term). It is shown that classical wormholes exist for this model and the quantum version of such wormholes are consistent with the Hawking-Page conjecture for quantum wormholes as solutions of the Wheeler-DeWitt equation. |
gr-qc/0111071 | Robert J. Low | Robert J. Low | Light Sheets and the Covariant Entropy Conjecture | 5 pages, to appear in Classical and Quantum Gravity | Class.Quant.Grav.19:L1,2002 | 10.1088/0264-9381/19/1/101 | null | gr-qc hep-th | null | We examine the holography bound suggested by Bousso in his covariant entropy
conjecture, and argue that it is violated because his notion of light sheet is
too generous. We suggest its replacement by a weaker bound.
| [
{
"created": "Wed, 21 Nov 2001 09:25:19 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Low",
"Robert J.",
""
]
] | We examine the holography bound suggested by Bousso in his covariant entropy conjecture, and argue that it is violated because his notion of light sheet is too generous. We suggest its replacement by a weaker bound. |
gr-qc/9605019 | Franz Embacher | Franz Embacher | On the interpretation of quantum cosmology | 86 pages, LaTeX (no figures); in this replaced version, some issues
in the argumentation are formulated more accurate, references are added. The
most important changes are indicated in the LaTeX-file by %%% CORR/END and
/BEGIN | null | null | UWThPh-1996-22 | gr-qc | null | We formulate a ''minimal'' interpretational scheme for fairly general
(minisuperspace) quantum cosmological models. Admitting as few exact
mathematical structure as is reasonably possible at the fundamental level, we
apply approximate WKB-techniques locally in minisuperspace in order to make
contact with the realm of predictions, and propose how to deal with the
problems of mode decomposition and almost-classicality without introducing
further principles. In order to emphasize the general nature of approximate
local quantum mechanical structures, we modify the standard WKB-expansion
method so as to rely on exact congruences of classical paths, rather than a
division of variables into classical and quantum. The only exact mathematical
structures our interpretation needs are the space of solutions of the
Wheeler-DeWitt equation and the Klein-Gordon type indefinite scalar product.
The latter boils down to plus or minus the ordinary quantum mechanical scalar
product in the local quantum structures. According to our approach all further
structures, in particular the concepts encountered in conventional physics,
such as observables, time and unitarity, are approximate. Our interpretation
coincides to some extent with the standard WKB-oriented view, but the way in
which the conventional concepts emerge, and the accuracy at which they are
defined at all, are more transparent. A simpler book-keeping of normalization
issues is automatically achieved. Applying our scheme to the Hawking model, we
find hints that the no-boundary wave function predicts a cosmic catastrophe
with some non-zero probability.
| [
{
"created": "Thu, 9 May 1996 10:16:09 GMT",
"version": "v1"
},
{
"created": "Fri, 10 May 1996 12:27:13 GMT",
"version": "v2"
},
{
"created": "Mon, 20 May 1996 13:56:20 GMT",
"version": "v3"
}
] | 2008-02-03 | [
[
"Embacher",
"Franz",
""
]
] | We formulate a ''minimal'' interpretational scheme for fairly general (minisuperspace) quantum cosmological models. Admitting as few exact mathematical structure as is reasonably possible at the fundamental level, we apply approximate WKB-techniques locally in minisuperspace in order to make contact with the realm of predictions, and propose how to deal with the problems of mode decomposition and almost-classicality without introducing further principles. In order to emphasize the general nature of approximate local quantum mechanical structures, we modify the standard WKB-expansion method so as to rely on exact congruences of classical paths, rather than a division of variables into classical and quantum. The only exact mathematical structures our interpretation needs are the space of solutions of the Wheeler-DeWitt equation and the Klein-Gordon type indefinite scalar product. The latter boils down to plus or minus the ordinary quantum mechanical scalar product in the local quantum structures. According to our approach all further structures, in particular the concepts encountered in conventional physics, such as observables, time and unitarity, are approximate. Our interpretation coincides to some extent with the standard WKB-oriented view, but the way in which the conventional concepts emerge, and the accuracy at which they are defined at all, are more transparent. A simpler book-keeping of normalization issues is automatically achieved. Applying our scheme to the Hawking model, we find hints that the no-boundary wave function predicts a cosmic catastrophe with some non-zero probability. |
0811.4296 | Miodrag Krmar | Vladan Pankovic, Sima Ciganovic, Rade Glavatovic | A Simple, Approximate Method for Analysis of Kerr-Newman Black Hole
Dynamics and Thermodynamics | 8 pages, no figures | null | 10.2298/SAJ0978039P | Ph-18/11-08 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we present a simple, approximate method for analysis of the
basic dynamical and thermodynamical characteristics of Kerr-Newman black hole.
Instead of the complete dynamics of the black hole self-interaction we consider
only such stable (stationary) dynamical situations determined by condition that
black hole (outer) horizon circumference holds the integer number of the
reduced Compton wave lengths corresponding to mass spectrum of a small quantum
system (representing quant of the black hole self-interaction). Then, we show
that Kerr-Newman black hole entropy represents simply the quotient of the sum
of static part and rotation part of mass of black hole on the one hand and
ground mass of small quantum system on the other hand. Also we show that
Kerr-Newman black hole temperature represents the negative value of the
classical potential energy of gravitational interaction between a part of black
hole with reduced mass and small quantum system in the ground mass quantum
state. Finally, we suggest a bosonic great canonical distribution of the
statistical ensemble of given small quantum systems in the thermodynamical
equilibrium with (macroscopic) black hole as thermal reservoir. We suggest
that, practically, only ground mass quantum state is significantly degenerate
while all other, excited mass quantum states are non-degenerate. Kerr-Newman
black hole entropy is practically equivalent to the ground mass quantum state
degeneration. Given statistical distribution admits a rough (qualitative) but
simple modeling of Hawking radiation of the black hole too.
| [
{
"created": "Wed, 26 Nov 2008 13:03:37 GMT",
"version": "v1"
}
] | 2015-05-13 | [
[
"Pankovic",
"Vladan",
""
],
[
"Ciganovic",
"Sima",
""
],
[
"Glavatovic",
"Rade",
""
]
] | In this work we present a simple, approximate method for analysis of the basic dynamical and thermodynamical characteristics of Kerr-Newman black hole. Instead of the complete dynamics of the black hole self-interaction we consider only such stable (stationary) dynamical situations determined by condition that black hole (outer) horizon circumference holds the integer number of the reduced Compton wave lengths corresponding to mass spectrum of a small quantum system (representing quant of the black hole self-interaction). Then, we show that Kerr-Newman black hole entropy represents simply the quotient of the sum of static part and rotation part of mass of black hole on the one hand and ground mass of small quantum system on the other hand. Also we show that Kerr-Newman black hole temperature represents the negative value of the classical potential energy of gravitational interaction between a part of black hole with reduced mass and small quantum system in the ground mass quantum state. Finally, we suggest a bosonic great canonical distribution of the statistical ensemble of given small quantum systems in the thermodynamical equilibrium with (macroscopic) black hole as thermal reservoir. We suggest that, practically, only ground mass quantum state is significantly degenerate while all other, excited mass quantum states are non-degenerate. Kerr-Newman black hole entropy is practically equivalent to the ground mass quantum state degeneration. Given statistical distribution admits a rough (qualitative) but simple modeling of Hawking radiation of the black hole too. |
2406.03353 | Davide Batic | Davide Batic and Denys Dutykh | Quasinormal Modes in Noncommutative Schwarzschild Black Holes: A
Spectral Analysis | 18 pages, 1 figure, 11 tables, one reference corrected | Eur. Phys. J. C 84, 622 (2024) | 10.1140/epjc/s10052-024-12981-6 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We present a comprehensive analysis of quasinormal modes (QNMs) for
noncommutative geometry-inspired Schwarzschild black holes, encompassing both
non-extreme and extreme cases. By employing a spectral method, we calculate the
QNMs in the context of scalar, electromagnetic, and gravitational
perturbations. Our findings not only challenge previous claims in the
literature regarding the instability of these black holes but also reveal
remarkable stability for both non-extreme and extreme Schwarzschild black holes
under various perturbations.
| [
{
"created": "Wed, 5 Jun 2024 15:10:22 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Jun 2024 13:20:32 GMT",
"version": "v2"
}
] | 2024-07-15 | [
[
"Batic",
"Davide",
""
],
[
"Dutykh",
"Denys",
""
]
] | We present a comprehensive analysis of quasinormal modes (QNMs) for noncommutative geometry-inspired Schwarzschild black holes, encompassing both non-extreme and extreme cases. By employing a spectral method, we calculate the QNMs in the context of scalar, electromagnetic, and gravitational perturbations. Our findings not only challenge previous claims in the literature regarding the instability of these black holes but also reveal remarkable stability for both non-extreme and extreme Schwarzschild black holes under various perturbations. |
2406.14157 | David Wiltshire | Marco Galoppo, David L. Wiltshire | Exact solutions for differentially rotating galaxies in general
relativity | 5 pages, 2 figures | null | null | null | gr-qc astro-ph.CO astro-ph.GA hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | A class of stationary axisymmetric solutions of Einstein's equations for
isolated differentially rotating dust sources is presented. The low-energy
asymptotic regime is extracted, requiring a self-consistent coupling of
quasilocal energy and angular momentum. The Raychaudhuri equation reduces to a
balance equation, with two important limits. These limits can be interpreted
empirically for rotationally supported configurations such as galaxies. The net
energy including quasilocal kinetic contributions vanishes on the inner vortex
surface, and the outer rotosurface. These new geometrical objects potentially
shed light on virialization. Whether or not abundant collisionless dark matter
exists, the new solutions suggest that the phenomenology of galactic rotation
curves be fundamentally reconsidered, for consistency with general relativity.
| [
{
"created": "Thu, 20 Jun 2024 09:54:18 GMT",
"version": "v1"
}
] | 2024-06-21 | [
[
"Galoppo",
"Marco",
""
],
[
"Wiltshire",
"David L.",
""
]
] | A class of stationary axisymmetric solutions of Einstein's equations for isolated differentially rotating dust sources is presented. The low-energy asymptotic regime is extracted, requiring a self-consistent coupling of quasilocal energy and angular momentum. The Raychaudhuri equation reduces to a balance equation, with two important limits. These limits can be interpreted empirically for rotationally supported configurations such as galaxies. The net energy including quasilocal kinetic contributions vanishes on the inner vortex surface, and the outer rotosurface. These new geometrical objects potentially shed light on virialization. Whether or not abundant collisionless dark matter exists, the new solutions suggest that the phenomenology of galactic rotation curves be fundamentally reconsidered, for consistency with general relativity. |
1707.02718 | Orlando Luongo | Orlando Luongo | A thermodynamic approach to holographic dark energy | 13 pages, 3 figures, accepted in Adv. High En. Phys | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a method to relate the holographic minimal information density to
the de Broglie's wavelength at a given universe temperature $T$. To figure this
out, we assume that the thermal length of massive and massless constituents
represents the cut-off scale of the holographic principle. To perform our
analysis, we suppose two plausible universe volumes, i.e. the adiabatic and the
horizon volumes, i.e. $V \propto a^3$ and $V \propto H^{-3}$ respectively,
assuming zero spatial curvature. With these choices in mind, we evaluate the
thermal lengths for massive and massless particles and we thus find two
cosmological models associated to late and early cosmological epochs. We
demonstrate that both models depend upon a free term $\beta$ which enters the
temperature parametrization in terms of the redshift $z$. For the two
treatments, we show evolving dark energy terms which can be compared with the
$\omega$CDM quintessence paradigm when the barotropic factor takes the formal
values: $\omega_0=-\frac{1}{3}(2+\beta)$ and $\omega_0=-\frac{1}{3}(1+2\beta)$
respectively for late and early eras. From our analyses, we candidate the two
models as viable alternatives to dark energy determined from thermodynamics in
the field of the holographic principle.
| [
{
"created": "Mon, 10 Jul 2017 07:05:02 GMT",
"version": "v1"
}
] | 2017-07-11 | [
[
"Luongo",
"Orlando",
""
]
] | We propose a method to relate the holographic minimal information density to the de Broglie's wavelength at a given universe temperature $T$. To figure this out, we assume that the thermal length of massive and massless constituents represents the cut-off scale of the holographic principle. To perform our analysis, we suppose two plausible universe volumes, i.e. the adiabatic and the horizon volumes, i.e. $V \propto a^3$ and $V \propto H^{-3}$ respectively, assuming zero spatial curvature. With these choices in mind, we evaluate the thermal lengths for massive and massless particles and we thus find two cosmological models associated to late and early cosmological epochs. We demonstrate that both models depend upon a free term $\beta$ which enters the temperature parametrization in terms of the redshift $z$. For the two treatments, we show evolving dark energy terms which can be compared with the $\omega$CDM quintessence paradigm when the barotropic factor takes the formal values: $\omega_0=-\frac{1}{3}(2+\beta)$ and $\omega_0=-\frac{1}{3}(1+2\beta)$ respectively for late and early eras. From our analyses, we candidate the two models as viable alternatives to dark energy determined from thermodynamics in the field of the holographic principle. |
2405.15558 | BaoYu Tan | BaoYu Tan | EGUP corrected thermodynamics of RN-AdS black hole with quintessence
matter | null | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Reissner-Nordstrom anti de Sitter (RN-AdS) black hole, characterized by
electric charge and negative cosmological constant,exhibits a rich
thermodynamics structure. In this paper, we consider the influence of
quintessence, a hypothetical dark energy component with negative pressure. we
have computed the extended generalized uncertainty principle (EGUP) corrections
to the thermodynamics of RN-AdS black hole, including Hawking temperature, heat
capacity, entropy function and pressure. Furthermore, as a special case of
EGUP, we have computed and compared the result obtained from the generalized
uncertainty principle (GUP) with those from the extended uncertainty principle
(EUP). This work contributes to the understanding of the interplay between
fundamental physics and the macroscopic properties of black holes, offering a
novel perspective on the thermodynamics of RN-AdS black holes in the context of
quintessence and quantum gravity corrections. More importantly, we found that,
unlike in the case of the Reissner-Nordstrom (RN) black hole, the qualitative
behavior for the RN-AdS black hole with quintessence remain largely unchanged,
except for minor differences, at the equation of state parameters w=-1/3 and
w=-2/3. In addition , unlike RN black holes, the phase transition point of
RN-AdS black holes shift to almost zero.
| [
{
"created": "Thu, 23 May 2024 15:49:00 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Jul 2024 02:12:27 GMT",
"version": "v2"
}
] | 2024-07-09 | [
[
"Tan",
"BaoYu",
""
]
] | Reissner-Nordstrom anti de Sitter (RN-AdS) black hole, characterized by electric charge and negative cosmological constant,exhibits a rich thermodynamics structure. In this paper, we consider the influence of quintessence, a hypothetical dark energy component with negative pressure. we have computed the extended generalized uncertainty principle (EGUP) corrections to the thermodynamics of RN-AdS black hole, including Hawking temperature, heat capacity, entropy function and pressure. Furthermore, as a special case of EGUP, we have computed and compared the result obtained from the generalized uncertainty principle (GUP) with those from the extended uncertainty principle (EUP). This work contributes to the understanding of the interplay between fundamental physics and the macroscopic properties of black holes, offering a novel perspective on the thermodynamics of RN-AdS black holes in the context of quintessence and quantum gravity corrections. More importantly, we found that, unlike in the case of the Reissner-Nordstrom (RN) black hole, the qualitative behavior for the RN-AdS black hole with quintessence remain largely unchanged, except for minor differences, at the equation of state parameters w=-1/3 and w=-2/3. In addition , unlike RN black holes, the phase transition point of RN-AdS black holes shift to almost zero. |
gr-qc/9912066 | Draza | Draza Markovic & Stuart Shapiro (University of Illinois at
Urbana-Champaign, Department of Physics) | Gravitational Collapse with a Cosmological Constant | 7 pages, 10 figures; To appear in Phys. Rev. D | Phys.Rev. D61 (2000) 084029 | 10.1103/PhysRevD.61.084029 | null | gr-qc astro-ph | null | We consider the effect of a positive cosmological constant on spherical
gravitational collapse to a black hole for a few simple, analytic cases. We
construct the complete Oppenheimer-Snyder-deSitter (OSdS) spacetime, the
generalization of the Oppenheimer-Snyder solution for collapse from rest of a
homogeneous dust ball in an exterior vacuum. In OSdS collapse, the cosmological
constant may affect the onset of collapse and decelerate the implosion
initially, but it plays a diminishing role as the collapse proceeds. We also
construct spacetimes in which a collapsing dust ball can bounce, or hover in
unstable equilibrium, due to the repulsive force of the cosmological constant.
We explore the causal structure of the different spacetimes and identify any
cosmological and black hole event horizons which may be present.
| [
{
"created": "Wed, 15 Dec 1999 23:51:12 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Markovic",
"Draza",
"",
"University of Illinois at\n Urbana-Champaign, Department of Physics"
],
[
"Shapiro",
"Stuart",
"",
"University of Illinois at\n Urbana-Champaign, Department of Physics"
]
] | We consider the effect of a positive cosmological constant on spherical gravitational collapse to a black hole for a few simple, analytic cases. We construct the complete Oppenheimer-Snyder-deSitter (OSdS) spacetime, the generalization of the Oppenheimer-Snyder solution for collapse from rest of a homogeneous dust ball in an exterior vacuum. In OSdS collapse, the cosmological constant may affect the onset of collapse and decelerate the implosion initially, but it plays a diminishing role as the collapse proceeds. We also construct spacetimes in which a collapsing dust ball can bounce, or hover in unstable equilibrium, due to the repulsive force of the cosmological constant. We explore the causal structure of the different spacetimes and identify any cosmological and black hole event horizons which may be present. |
1811.05558 | J. Fernando Abalos | Fernando Abalos and Oscar Reula | On necessary and sufficient conditions for strong hyperbolicity | null | null | 10.1088/1361-6382/ab954c | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we study constant-coefficient first order systems of partial
differential equations and give necessary and sufficient conditions for those
systems to have a well posed Cauchy Problem. In many physical applications, due
to the presence of constraints, the number of equations in the PDE system is
larger than the number of unknowns, thus the standard Kreiss conditions can not
be directly applied to check whether the system admits a well posed initial
value formulation. In this work we find necessary and sufficient conditions
such that there exists a reduced set of equations, of the same dimensionality
as the set of unknowns, which satisfy Kreiss conditions and so are well defined
and properly behaved evolution equations. We do that by studying the systems
using the Kronecker decomposition of matrix pencils and, once the conditions
are meet, finding specific families of reductions which render the system
strongly hyperbolic. We show the power of the theory in some examples: Klein
Gordon, the ADM, and the BSSN equations by writing them as first order systems,
and studying their Kronecker decomposition and general reductions.
| [
{
"created": "Tue, 13 Nov 2018 22:59:55 GMT",
"version": "v1"
},
{
"created": "Mon, 30 Dec 2019 20:17:09 GMT",
"version": "v2"
}
] | 2021-11-17 | [
[
"Abalos",
"Fernando",
""
],
[
"Reula",
"Oscar",
""
]
] | In this work we study constant-coefficient first order systems of partial differential equations and give necessary and sufficient conditions for those systems to have a well posed Cauchy Problem. In many physical applications, due to the presence of constraints, the number of equations in the PDE system is larger than the number of unknowns, thus the standard Kreiss conditions can not be directly applied to check whether the system admits a well posed initial value formulation. In this work we find necessary and sufficient conditions such that there exists a reduced set of equations, of the same dimensionality as the set of unknowns, which satisfy Kreiss conditions and so are well defined and properly behaved evolution equations. We do that by studying the systems using the Kronecker decomposition of matrix pencils and, once the conditions are meet, finding specific families of reductions which render the system strongly hyperbolic. We show the power of the theory in some examples: Klein Gordon, the ADM, and the BSSN equations by writing them as first order systems, and studying their Kronecker decomposition and general reductions. |
1412.6200 | P. A. Gonzalez | Ramon Becar, P. A. Gonzalez, Joel Saavedra and Yerko Vasquez | Greybody Factors of Massive Charged Fermionic Fields in a Charged
Two-Dimensional Dilatonic Black Hole | 14 pages and 7 figures. arXiv admin note: substantial text overlap
with arXiv:1404.6023 | null | 10.1140/epjc/s10052-015-3292-1 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study massive charged fermionic perturbations in the background of a
charged two-dimensional dilatonic black hole, and we solve the Dirac equation
analytically. Then, we compute the reflection and transmission coefficients and
the absorption cross section for massive charged fermionic fields, and we show
that the absorption cross section vanishes at the low and high frequency
limits. However, there is a range of frequencies where the absorption cross
section is not null. Furthermore, we study the effect of the mass and electric
charge of the fermionic field over the absorption cross section.
| [
{
"created": "Fri, 19 Dec 2014 02:34:24 GMT",
"version": "v1"
}
] | 2015-06-23 | [
[
"Becar",
"Ramon",
""
],
[
"Gonzalez",
"P. A.",
""
],
[
"Saavedra",
"Joel",
""
],
[
"Vasquez",
"Yerko",
""
]
] | We study massive charged fermionic perturbations in the background of a charged two-dimensional dilatonic black hole, and we solve the Dirac equation analytically. Then, we compute the reflection and transmission coefficients and the absorption cross section for massive charged fermionic fields, and we show that the absorption cross section vanishes at the low and high frequency limits. However, there is a range of frequencies where the absorption cross section is not null. Furthermore, we study the effect of the mass and electric charge of the fermionic field over the absorption cross section. |
gr-qc/9801012 | Piotr Bizon | Piotr Bizo\'n and Tadeusz Chmaj | Critical Collapse of Skyrmions | 4 pages, 5 Postscript figures, RevTex, typos corrected | Phys.Rev.D58:041501,1998 | 10.1103/PhysRevD.58.041501 | null | gr-qc hep-th | null | We study first order phase transitions in the gravitational collapse of
spherically symmetric skyrmions. Static sphaleron solutions are shown to play
the role of critical solutions separating black-hole spacetimes from
no-black-hole spacetimes. In particular, we find a new type of first order
phase transition where subcritical data do not disperse but evolve towards a
static regular stable solution. We also demonstrate explicitly that the
near-critical solutions depart from the intermediate asymptotic regime along
the unstable manifold of the critical solution.
| [
{
"created": "Tue, 6 Jan 1998 17:24:27 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Jan 1998 15:02:28 GMT",
"version": "v2"
}
] | 2010-01-06 | [
[
"Bizoń",
"Piotr",
""
],
[
"Chmaj",
"Tadeusz",
""
]
] | We study first order phase transitions in the gravitational collapse of spherically symmetric skyrmions. Static sphaleron solutions are shown to play the role of critical solutions separating black-hole spacetimes from no-black-hole spacetimes. In particular, we find a new type of first order phase transition where subcritical data do not disperse but evolve towards a static regular stable solution. We also demonstrate explicitly that the near-critical solutions depart from the intermediate asymptotic regime along the unstable manifold of the critical solution. |
1906.02801 | Abdulmajid Osumanu | Ma\"it\'e Dupuis, Florian Girelli, Abdulmajid Osumanu and Wolfgang
Wieland | First-order formulation of teleparallel gravity and dual loop gravity | 13 pages | Class. Quantum Grav. 37 (2020) 085023 | 10.1088/1361-6382/ab7bb7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There are at least two ways to encode gravity into geometry: Einstein's
general theory of relativity (GR) for the metric tensor, and teleparallel
gravity, where torsion as opposed to curvature encodes the dynamics of the
gravitational degrees of freedom. The main purpose of the paper is to explore
the relation between loop gravity and teleparallel gravity. We argue that these
two formulations of gravity are related to two different discretizations of the
Einstein--Cartan action, which were studied recently in the literature. The
first discretization leads to the \emph{{loop gravity}} kinematical phase space
where the zero torsion condition is enforced {first} and the other is the
\emph{{dual loop gravity}} kinematical phase space where curvature is imposed
to vanish {first}. Our argument is based on the observation that the GR
first-order Einstein--Cartan action can also be seen as a first-order action
for teleparallel gravity up to a boundary term. The results of our paper
suggest that the \emph{dual loop gravity} framework is a natural discretization
of teleparallel gravity, whereas \emph{loop gravity} is naturally related to
the standard GR metric description.
| [
{
"created": "Thu, 6 Jun 2019 20:35:55 GMT",
"version": "v1"
},
{
"created": "Mon, 30 Mar 2020 20:01:59 GMT",
"version": "v2"
}
] | 2020-04-01 | [
[
"Dupuis",
"Maïté",
""
],
[
"Girelli",
"Florian",
""
],
[
"Osumanu",
"Abdulmajid",
""
],
[
"Wieland",
"Wolfgang",
""
]
] | There are at least two ways to encode gravity into geometry: Einstein's general theory of relativity (GR) for the metric tensor, and teleparallel gravity, where torsion as opposed to curvature encodes the dynamics of the gravitational degrees of freedom. The main purpose of the paper is to explore the relation between loop gravity and teleparallel gravity. We argue that these two formulations of gravity are related to two different discretizations of the Einstein--Cartan action, which were studied recently in the literature. The first discretization leads to the \emph{{loop gravity}} kinematical phase space where the zero torsion condition is enforced {first} and the other is the \emph{{dual loop gravity}} kinematical phase space where curvature is imposed to vanish {first}. Our argument is based on the observation that the GR first-order Einstein--Cartan action can also be seen as a first-order action for teleparallel gravity up to a boundary term. The results of our paper suggest that the \emph{dual loop gravity} framework is a natural discretization of teleparallel gravity, whereas \emph{loop gravity} is naturally related to the standard GR metric description. |
1410.2412 | Shahab Shahidi | Zahra Haghani, Nima Khosravi and Shahab Shahidi | The Weyl-Cartan Gauss-Bonnet gravity | 11 pages, 1 figure | Class. Quant Grav. 32 (2015) 215016 | 10.1088/0264-9381/32/21/215016 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we consider the generalized Gauss-Bonnet action in
$4$-dimensional Weyl-Cartan space-time. In this space-time, the presence of
torsion tensor and Weyl vector implies that the generalized Gauss-Bonnet action
will not be a total derivative in four dimension space-time. It will be shown
that the higher than two time derivatives can be removed from the action by
choosing suitable set of parameters. In the special case where only the trace
part of the torsion remains, the model reduces to GR plus two vector fields.
One of which is massless and the other is massive. We will then obtain the
healthy region of the 5-dimensional parameter space of the theory in some
special cases.
| [
{
"created": "Thu, 9 Oct 2014 10:16:06 GMT",
"version": "v1"
},
{
"created": "Sun, 17 Apr 2016 10:45:21 GMT",
"version": "v2"
}
] | 2016-04-19 | [
[
"Haghani",
"Zahra",
""
],
[
"Khosravi",
"Nima",
""
],
[
"Shahidi",
"Shahab",
""
]
] | In this paper, we consider the generalized Gauss-Bonnet action in $4$-dimensional Weyl-Cartan space-time. In this space-time, the presence of torsion tensor and Weyl vector implies that the generalized Gauss-Bonnet action will not be a total derivative in four dimension space-time. It will be shown that the higher than two time derivatives can be removed from the action by choosing suitable set of parameters. In the special case where only the trace part of the torsion remains, the model reduces to GR plus two vector fields. One of which is massless and the other is massive. We will then obtain the healthy region of the 5-dimensional parameter space of the theory in some special cases. |
gr-qc/0604083 | Chang Jun Gao | C.J.Gao and S.N.Zhang | Black Holes in Brans-Dicke Theory with a Cosmological Constant | 5 pages | null | null | null | gr-qc | null | Since the Brans-Dicke theory is conformal related to the dilaton gravity
theory, by applying a conformal transformation to the dilaton gravity theory,
we derived the cosmological constant term in the Brans-Dicke theory and the
physical solution of black holes with the cosmological constant. It is found
that, in four dimensions, the solution is just the Kerr-Newman-de Sitter
solution with a constant scalar field. However, in $n>4$ dimensions, the
solution is not yet the $n$ dimensional Kerr-Newman-de Sitter solution and the
scalar field is not a constant in general. In Brans-Dicke-Ni theory, the
resulting solution is also not yet the Kerr-Newman-de Sitter one even in four
dimensions. The higher dimensional origin of the Brans-Dicke scalar field is
briefly discussed.
| [
{
"created": "Thu, 20 Apr 2006 01:36:36 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Gao",
"C. J.",
""
],
[
"Zhang",
"S. N.",
""
]
] | Since the Brans-Dicke theory is conformal related to the dilaton gravity theory, by applying a conformal transformation to the dilaton gravity theory, we derived the cosmological constant term in the Brans-Dicke theory and the physical solution of black holes with the cosmological constant. It is found that, in four dimensions, the solution is just the Kerr-Newman-de Sitter solution with a constant scalar field. However, in $n>4$ dimensions, the solution is not yet the $n$ dimensional Kerr-Newman-de Sitter solution and the scalar field is not a constant in general. In Brans-Dicke-Ni theory, the resulting solution is also not yet the Kerr-Newman-de Sitter one even in four dimensions. The higher dimensional origin of the Brans-Dicke scalar field is briefly discussed. |
1807.01840 | Kwun Hang Lai | Kwun-Hang Lai, Tjonnie Guang Feng Li | Constraining black-hole horizon effects by LIGO-Virgo detections of
inspiralling binary black holes | 12 pages, 5 figures | Phys. Rev. D 98, 084059 (2018) | 10.1103/PhysRevD.98.084059 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | General relativity predicts mass and spin growth of an inspiralling black
hole due to an energy-momentum flux flowing through the black-hole horizon. The
leading-order terms of this horizon flux introduce 2.5 and 3.5 post-Newtonian
corrections to inspiral motions of binary black holes. The corrections may be
measurable by gravitational waves detectors. Since the proper improvements to
general relativity is still a mystery, it is possible that the true modified
gravity theory introduces negligible direct corrections to the geodesics of
test masses, while near horizon corrections are observable. We introduce a
parameterization to describe arbitrary mass and spin growth of inspiralling
black holes. Comparing signals of gravitational waves and a waveform model with
parameterized horizon flux corrections, deviations from general relativity can
be constrained. We simulate a set of gravitational waves signals following an
astrophysical distribution with horizon flux modifications. Then, we perform a
Bayesian analysis to obtain the expected constraints from the simulated
response of the Advanced LIGO-Virgo detector network to the simulated signals.
We show that the constraint can be improved by stacking multiple detections.
The constraints of modified horizon flux can be used to test a specific class
of modified gravity theories which predict dominant corrections near black-hole
horizons over other types of corrections to general relativity. To support
Hawking's area theorem at 90\% confidence level, over 10000 LIGO-Virgo
detections are required. Within the lifetime of LIGO and Einstein Telescope, a
future ground-based gravitational wave detector, near horizon corrections of
modified gravity theories are potentially detectable if one of the modified
gravity theory is true and the theory predicts a strong correction.
| [
{
"created": "Thu, 5 Jul 2018 04:15:52 GMT",
"version": "v1"
},
{
"created": "Mon, 30 Jul 2018 03:10:17 GMT",
"version": "v2"
},
{
"created": "Fri, 21 Sep 2018 02:39:28 GMT",
"version": "v3"
}
] | 2018-11-07 | [
[
"Lai",
"Kwun-Hang",
""
],
[
"Li",
"Tjonnie Guang Feng",
""
]
] | General relativity predicts mass and spin growth of an inspiralling black hole due to an energy-momentum flux flowing through the black-hole horizon. The leading-order terms of this horizon flux introduce 2.5 and 3.5 post-Newtonian corrections to inspiral motions of binary black holes. The corrections may be measurable by gravitational waves detectors. Since the proper improvements to general relativity is still a mystery, it is possible that the true modified gravity theory introduces negligible direct corrections to the geodesics of test masses, while near horizon corrections are observable. We introduce a parameterization to describe arbitrary mass and spin growth of inspiralling black holes. Comparing signals of gravitational waves and a waveform model with parameterized horizon flux corrections, deviations from general relativity can be constrained. We simulate a set of gravitational waves signals following an astrophysical distribution with horizon flux modifications. Then, we perform a Bayesian analysis to obtain the expected constraints from the simulated response of the Advanced LIGO-Virgo detector network to the simulated signals. We show that the constraint can be improved by stacking multiple detections. The constraints of modified horizon flux can be used to test a specific class of modified gravity theories which predict dominant corrections near black-hole horizons over other types of corrections to general relativity. To support Hawking's area theorem at 90\% confidence level, over 10000 LIGO-Virgo detections are required. Within the lifetime of LIGO and Einstein Telescope, a future ground-based gravitational wave detector, near horizon corrections of modified gravity theories are potentially detectable if one of the modified gravity theory is true and the theory predicts a strong correction. |
2303.07736 | Siba Prasad Das Dr. | K. G. Managave, H. A. Redekar, R. B. Kumbhar, S. P. Das and K. Y.
Rajpure | Nearly Static Magnetized Kerr Black-hole in Non-linear Electrodynamics | 9pages, 12 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We have analyzed the thermodynamics of slowly rotating magnetized Kerr
black-hole, with typical spin parameter $a\le 0.1$ (nearly static) in the
background of non-linear electrodynamics. In particular we have studied the
Bekenstein-Hawking entropy, Hawking temperature, angular momentum, specific
heats and identified regions of parameters for possible phase-transitions. It
turns out that once the stability lost the black-hole never come back to its
original stable position.
| [
{
"created": "Tue, 14 Mar 2023 09:33:40 GMT",
"version": "v1"
}
] | 2023-03-15 | [
[
"Managave",
"K. G.",
""
],
[
"Redekar",
"H. A.",
""
],
[
"Kumbhar",
"R. B.",
""
],
[
"Das",
"S. P.",
""
],
[
"Rajpure",
"K. Y.",
""
]
] | We have analyzed the thermodynamics of slowly rotating magnetized Kerr black-hole, with typical spin parameter $a\le 0.1$ (nearly static) in the background of non-linear electrodynamics. In particular we have studied the Bekenstein-Hawking entropy, Hawking temperature, angular momentum, specific heats and identified regions of parameters for possible phase-transitions. It turns out that once the stability lost the black-hole never come back to its original stable position. |
1803.09933 | Massimiliano Razzano | Massimiliano Razzano, Elena Cuoco | Image-based deep learning for classification of noise transients in
gravitational wave detectors | 25 pages, 8 figures, accepted for publication in Classical and
Quantum Gravity | Razzano, M., and Cuoco, E., 2018, Classical and Quantum Gravity,
Volume 35, Number 9, 2018 | 10.1088/1361-6382/aab793 | null | gr-qc astro-ph.IM cs.CV | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The detection of gravitational waves has inaugurated the era of gravitational
astronomy and opened new avenues for the multimessenger study of cosmic
sources. Thanks to their sensitivity, the Advanced LIGO and Advanced Virgo
interferometers will probe a much larger volume of space and expand the
capability of discovering new gravitational wave emitters. The characterization
of these detectors is a primary task in order to recognize the main sources of
noise and optimize the sensitivity of interferometers. Glitches are transient
noise events that can impact the data quality of the interferometers and their
classification is an important task for detector characterization. Deep
learning techniques are a promising tool for the recognition and classification
of glitches. We present a classification pipeline that exploits convolutional
neural networks to classify glitches starting from their time-frequency
evolution represented as images. We evaluated the classification accuracy on
simulated glitches, showing that the proposed algorithm can automatically
classify glitches on very fast timescales and with high accuracy, thus
providing a promising tool for online detector characterization.
| [
{
"created": "Tue, 27 Mar 2018 07:23:13 GMT",
"version": "v1"
}
] | 2018-04-05 | [
[
"Razzano",
"Massimiliano",
""
],
[
"Cuoco",
"Elena",
""
]
] | The detection of gravitational waves has inaugurated the era of gravitational astronomy and opened new avenues for the multimessenger study of cosmic sources. Thanks to their sensitivity, the Advanced LIGO and Advanced Virgo interferometers will probe a much larger volume of space and expand the capability of discovering new gravitational wave emitters. The characterization of these detectors is a primary task in order to recognize the main sources of noise and optimize the sensitivity of interferometers. Glitches are transient noise events that can impact the data quality of the interferometers and their classification is an important task for detector characterization. Deep learning techniques are a promising tool for the recognition and classification of glitches. We present a classification pipeline that exploits convolutional neural networks to classify glitches starting from their time-frequency evolution represented as images. We evaluated the classification accuracy on simulated glitches, showing that the proposed algorithm can automatically classify glitches on very fast timescales and with high accuracy, thus providing a promising tool for online detector characterization. |
1801.09574 | Dr. Sudhaker Upadhyay | Sudhaker Upadhyay, Saheb Soroushfar and Reza Saffari | Perturbed thermodynamics and thermodynamic geometry of a static black
hole in $f (R)$ gravity | 16 pages, 16 figures, to appear in MPLA | Modern Physics Letters A 36, 2150212 (2021) | 10.1142/S0217732321502126 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we consider a static black hole in $f(R)$ gravity. We
recapitulate the expression for corrected thermodynamic entropy of this black
hole due to small fluctuations around equilibrium. Also, we study the
geometrothermodynamics (GTD) of this black hole and investigate the
adaptability of the curvature scalar of geothermodynamic methods with phase
transition points of this black hole. Moreover, we study the effect of
correction parameter on thermodynamic behaviour of this black hole. We observe
that the singular point of the curvature scalar of Ruppeiner metric coincides
completely with zero point of the heat capacity and the deviation occurs with
increasing correction parameter.
| [
{
"created": "Fri, 26 Jan 2018 16:39:44 GMT",
"version": "v1"
},
{
"created": "Wed, 29 Sep 2021 13:34:36 GMT",
"version": "v2"
}
] | 2021-11-01 | [
[
"Upadhyay",
"Sudhaker",
""
],
[
"Soroushfar",
"Saheb",
""
],
[
"Saffari",
"Reza",
""
]
] | In this paper, we consider a static black hole in $f(R)$ gravity. We recapitulate the expression for corrected thermodynamic entropy of this black hole due to small fluctuations around equilibrium. Also, we study the geometrothermodynamics (GTD) of this black hole and investigate the adaptability of the curvature scalar of geothermodynamic methods with phase transition points of this black hole. Moreover, we study the effect of correction parameter on thermodynamic behaviour of this black hole. We observe that the singular point of the curvature scalar of Ruppeiner metric coincides completely with zero point of the heat capacity and the deviation occurs with increasing correction parameter. |
1710.09581 | Yen-Kheng Lim | Gulmina Zaman Babar, Adil Zaman Babar, and Yen-Kheng Lim | Periodic orbits around a spherically symmetric naked singularity | 14 pages, 7 figures | Phys. Rev. D, 96 084052 (2017) | 10.1103/PhysRevD.96.084052 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The motion of time-like test particles in the Fisher/Janis-Newman-Winicour
(F/JNW) spacetime is studied with the Hamiltonian formulation of the geodesic
equations. The spacetime is characterised by its mass parameter $r_g$ and
scalar field parameter $\nu$. The innermost bound and stable circular orbits
are calculated and the effective potential is analysed. Consistent with
numerical results in earlier literature, for $\nu<1/2$, particles with non-zero
angular momentum encounter an infinite potential barrier, preventing them from
reaching the naked singularity at $r=r_g$. Periodic orbits in the spacetime are
also obtained. Compared to the periodic orbits around the Schwarzschild black
hole, it is found that typically lower energies are required for the same
orbits in the F/JNW spacetime.
| [
{
"created": "Thu, 26 Oct 2017 08:26:00 GMT",
"version": "v1"
}
] | 2017-10-27 | [
[
"Babar",
"Gulmina Zaman",
""
],
[
"Babar",
"Adil Zaman",
""
],
[
"Lim",
"Yen-Kheng",
""
]
] | The motion of time-like test particles in the Fisher/Janis-Newman-Winicour (F/JNW) spacetime is studied with the Hamiltonian formulation of the geodesic equations. The spacetime is characterised by its mass parameter $r_g$ and scalar field parameter $\nu$. The innermost bound and stable circular orbits are calculated and the effective potential is analysed. Consistent with numerical results in earlier literature, for $\nu<1/2$, particles with non-zero angular momentum encounter an infinite potential barrier, preventing them from reaching the naked singularity at $r=r_g$. Periodic orbits in the spacetime are also obtained. Compared to the periodic orbits around the Schwarzschild black hole, it is found that typically lower energies are required for the same orbits in the F/JNW spacetime. |
1604.07106 | Chen Songbai | Songbai Chen, Mei Wang, Jiliang Jing | Testing gravity of a regular and slowly rotating phantom black hole by
quasi-periodic oscillations | 12 paged, 3 figures, Accepted by CQG for publication | Class. Quantum Grav. 33 (2016) 195002 | 10.1088/0264-9381/33/19/195002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We extend firstly the regular phantom black hole solution to a slowly
rotating black hole case and find that the phantom field depresses the angular
velocity of the event horizon and suppresses the super-radiation of black hole.
We also probe the dependence of quasi-periodic oscillations frequencies in
relativistic precession model on the phantom parameter. With the observation
data of GRO J1655-40, we make a constraint on the parameters of the regular and
slowly rotating phantom black hole. Our results show that although the best-fit
value of the phantom parameter $b$ is small, the allowed value of $b$ in the
$1\sigma$ region is $b<0.619$, which means that the phantom theoretical model
can not be excluded by the constraint from quasi-periodic oscillations with the
observation data of GRO J1655-40.
| [
{
"created": "Mon, 25 Apr 2016 01:55:19 GMT",
"version": "v1"
},
{
"created": "Fri, 19 Aug 2016 07:52:36 GMT",
"version": "v2"
}
] | 2016-09-20 | [
[
"Chen",
"Songbai",
""
],
[
"Wang",
"Mei",
""
],
[
"Jing",
"Jiliang",
""
]
] | We extend firstly the regular phantom black hole solution to a slowly rotating black hole case and find that the phantom field depresses the angular velocity of the event horizon and suppresses the super-radiation of black hole. We also probe the dependence of quasi-periodic oscillations frequencies in relativistic precession model on the phantom parameter. With the observation data of GRO J1655-40, we make a constraint on the parameters of the regular and slowly rotating phantom black hole. Our results show that although the best-fit value of the phantom parameter $b$ is small, the allowed value of $b$ in the $1\sigma$ region is $b<0.619$, which means that the phantom theoretical model can not be excluded by the constraint from quasi-periodic oscillations with the observation data of GRO J1655-40. |
1410.0115 | Vladimir S. Manko | V.S. Manko, J.D. Sanabria-G\'omez | Comment on "Generalized black diholes" | 4 pages, 1 figure; last item of initial version removed at referee's
request | Phys. Rev. D 91: 088501, 2015 | 10.1103/PhysRevD.91.088501 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that a recent solution published by Cabrera-Munguia et al. is
physically inconsistent since the quantity $\sigma$ it involves does not have a
correct limit $R\to\infty$.
| [
{
"created": "Wed, 1 Oct 2014 06:17:24 GMT",
"version": "v1"
},
{
"created": "Thu, 5 Nov 2015 21:59:54 GMT",
"version": "v2"
}
] | 2015-11-09 | [
[
"Manko",
"V. S.",
""
],
[
"Sanabria-Gómez",
"J. D.",
""
]
] | We show that a recent solution published by Cabrera-Munguia et al. is physically inconsistent since the quantity $\sigma$ it involves does not have a correct limit $R\to\infty$. |
gr-qc/0105076 | Gerald Vones | Gerald Vones | R0 Cosmology ? | 11 pages, 1 figure | null | null | null | gr-qc | null | It is postulated that the action of the FRW-universe is the cosmological term
of Einsteins theory (no curvature term - R0 Cosmology). The expansion equation
emerging from the embedding of this most simple brane world with variable speed
of light is deduced. The universal dimensionless coupling constant of gravity
is addressed. Some implications on the deep problems of cosmology are
discussed.
| [
{
"created": "Mon, 21 May 2001 13:09:13 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Vones",
"Gerald",
""
]
] | It is postulated that the action of the FRW-universe is the cosmological term of Einsteins theory (no curvature term - R0 Cosmology). The expansion equation emerging from the embedding of this most simple brane world with variable speed of light is deduced. The universal dimensionless coupling constant of gravity is addressed. Some implications on the deep problems of cosmology are discussed. |
1204.5331 | Parthasarathi Majumdar | Parthasarathi Majumdar | Critical mass of neutron stars : a new view | 11 Pages Latex 2e, 4 eps figures | null | null | null | gr-qc astro-ph.SR hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The issue of the critical mass of neutron stars, with respect to
gravitational collapse to black holes, is reexamined from the perspective of
thermal stability of quantum horizons. Postulating the existence of a tiny,
{\it embryonic}, isolated horizon, hidden deep inside a gravitationally
contracting neutron star, the critical mass is seen to emerge from the
extrapolation of the criterion of thermal stability of quantum isolated
horizons derived earlier by us, to such a `hidden' horizon, as a condition of
its stability and growth (through formation of {\it trapping} or {\it
dynamical} horizons), eventually leading to an equilibrium isolated horizon
engulfing the entire star. The perspective is based on aspects of Loop Quantum
Gravity, and in contrast to extant analyses in the neutron star literature,
uses neither classical spacetime metrics nor details of strong neucleonic
interactions at supranuclear densities, thus delineating the essential role of
quantum gravitation in black hole formation.
| [
{
"created": "Tue, 24 Apr 2012 11:03:25 GMT",
"version": "v1"
}
] | 2012-04-30 | [
[
"Majumdar",
"Parthasarathi",
""
]
] | The issue of the critical mass of neutron stars, with respect to gravitational collapse to black holes, is reexamined from the perspective of thermal stability of quantum horizons. Postulating the existence of a tiny, {\it embryonic}, isolated horizon, hidden deep inside a gravitationally contracting neutron star, the critical mass is seen to emerge from the extrapolation of the criterion of thermal stability of quantum isolated horizons derived earlier by us, to such a `hidden' horizon, as a condition of its stability and growth (through formation of {\it trapping} or {\it dynamical} horizons), eventually leading to an equilibrium isolated horizon engulfing the entire star. The perspective is based on aspects of Loop Quantum Gravity, and in contrast to extant analyses in the neutron star literature, uses neither classical spacetime metrics nor details of strong neucleonic interactions at supranuclear densities, thus delineating the essential role of quantum gravitation in black hole formation. |
gr-qc/0610147 | Ying-Qiu Gu | Ying-Qiu Gu | A Cosmological Model with Dark Spinor Source | 13 pages, no figure, to appear in IJMPA | Int.J.Mod.Phys.A22:4667-4678,2007 | 10.1142/S0217751X07037925 | null | gr-qc astro-ph | null | In this paper, we discuss the system of Friedman-Robertson-Walker metric
coupling with massive nonlinear dark spinors in detail, where the thermodynamic
movement of spinors is also taken into account. The results show that, the
nonlinear potential of the spinor field can provide a tiny negative pressure,
which resists the Universe to become singular. The solution is oscillating in
time and closed in space, which approximately takes the following form $$
g_{\mu\nu}=\bar R^2(1-\delta\cos t)^2\diag(1,-1,-\sin^2r ,-\sin^2r
\sin^2\theta), $$ with $\bar R= (1\sim 2)\times 10^{12}$ light year, and
$\delta=0.96\sim 0.99$. The present time is about $t\sim 18^\circ$.
| [
{
"created": "Sun, 29 Oct 2006 11:01:42 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Nov 2006 02:08:55 GMT",
"version": "v2"
},
{
"created": "Mon, 8 Oct 2007 00:41:07 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Gu",
"Ying-Qiu",
""
]
] | In this paper, we discuss the system of Friedman-Robertson-Walker metric coupling with massive nonlinear dark spinors in detail, where the thermodynamic movement of spinors is also taken into account. The results show that, the nonlinear potential of the spinor field can provide a tiny negative pressure, which resists the Universe to become singular. The solution is oscillating in time and closed in space, which approximately takes the following form $$ g_{\mu\nu}=\bar R^2(1-\delta\cos t)^2\diag(1,-1,-\sin^2r ,-\sin^2r \sin^2\theta), $$ with $\bar R= (1\sim 2)\times 10^{12}$ light year, and $\delta=0.96\sim 0.99$. The present time is about $t\sim 18^\circ$. |
2006.02189 | Oleg Zaslavskii | O. B. Zaslavskii | Negative energy states in the Reissner-Nordstr\"om metric | 6 pages | Mod. Phys. Lett. A. 36 (2021) 2150120 | 10.1142/S0217732321501200 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider electrogeodesics on which the energy $E<0$ in the
Reissner-Nordstr\"{o}m metric. It is shown that outside the horizon there is
exactly one turning point inside the ergoregion for such particles. This
entails that such a particle passes through an infinite chain of black-white
hole regions or terminates in the singularity. These properties are relevant
for two scenarios of high energy collisions in which the presence of white
holes is essential.
| [
{
"created": "Wed, 3 Jun 2020 11:56:12 GMT",
"version": "v1"
}
] | 2021-06-23 | [
[
"Zaslavskii",
"O. B.",
""
]
] | We consider electrogeodesics on which the energy $E<0$ in the Reissner-Nordstr\"{o}m metric. It is shown that outside the horizon there is exactly one turning point inside the ergoregion for such particles. This entails that such a particle passes through an infinite chain of black-white hole regions or terminates in the singularity. These properties are relevant for two scenarios of high energy collisions in which the presence of white holes is essential. |
1001.5349 | Tiberiu Harko | T. Harko | The matter Lagrangian and the energy-momentum tensor in modified gravity
with non-minimal coupling between matter and geometry | 6 pages, accepted for publication in PRD; references added | Phys.Rev.D81:044021,2010 | 10.1103/PhysRevD.81.044021 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that in modified $f(R)$ type gravity models with non-minimal coupling
between matter and geometry, both the matter Lagrangian, and the
energy-momentum tensor, are completely and uniquely determined by the form of
the coupling. This result is obtained by using the variational formulation for
the derivation of the equations of motion in the modified gravity models with
geometry-matter coupling, and the Newtonian limit for a fluid obeying a
barotropic equation of state. The corresponding energy-momentum tensor of the
matter in modified gravity models with non-minimal coupling is more general
than the usual general-relativistic energy-momentum tensor for perfect fluids,
and it contains a supplementary, equation of state dependent term, which could
be related to the elastic stresses in the body, or to other forms of internal
energy. Therefore, the extra-force induced by the coupling between matter and
geometry never vanishes as a consequence of the thermodynamic properties of the
system, or for a specific choice of the matter Lagrangian, and it is non-zero
in the case of a fluid of dust particles.
| [
{
"created": "Fri, 29 Jan 2010 08:11:41 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Feb 2010 07:47:35 GMT",
"version": "v2"
}
] | 2010-05-27 | [
[
"Harko",
"T.",
""
]
] | We show that in modified $f(R)$ type gravity models with non-minimal coupling between matter and geometry, both the matter Lagrangian, and the energy-momentum tensor, are completely and uniquely determined by the form of the coupling. This result is obtained by using the variational formulation for the derivation of the equations of motion in the modified gravity models with geometry-matter coupling, and the Newtonian limit for a fluid obeying a barotropic equation of state. The corresponding energy-momentum tensor of the matter in modified gravity models with non-minimal coupling is more general than the usual general-relativistic energy-momentum tensor for perfect fluids, and it contains a supplementary, equation of state dependent term, which could be related to the elastic stresses in the body, or to other forms of internal energy. Therefore, the extra-force induced by the coupling between matter and geometry never vanishes as a consequence of the thermodynamic properties of the system, or for a specific choice of the matter Lagrangian, and it is non-zero in the case of a fluid of dust particles. |
1702.07526 | Luigi Seveso | Luigi Seveso, Valerio Peri, Matteo G.A. Paris | Does universality of free-fall apply to the motion of quantum probes? | poster contribution to the Eighth International Workshop DICE2016
"Spacetime - Matter - Quantum Mechanics", September 12-16, 2016 | null | 10.1088/1742-6596/880/1/012067 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Can quantum-mechanical particles propagating on a fixed spacetime background
be approximated as test bodies satisfying the weak equivalence principle? We
ultimately answer the question in the negative but find that, when universality
of free-fall is assessed locally, a nontrivial agreement between quantum
mechanics and the weak equivalence principle exists. Implications for mass
sensing by quantum probes are discussed in some details.
| [
{
"created": "Fri, 24 Feb 2017 10:22:55 GMT",
"version": "v1"
}
] | 2017-09-13 | [
[
"Seveso",
"Luigi",
""
],
[
"Peri",
"Valerio",
""
],
[
"Paris",
"Matteo G. A.",
""
]
] | Can quantum-mechanical particles propagating on a fixed spacetime background be approximated as test bodies satisfying the weak equivalence principle? We ultimately answer the question in the negative but find that, when universality of free-fall is assessed locally, a nontrivial agreement between quantum mechanics and the weak equivalence principle exists. Implications for mass sensing by quantum probes are discussed in some details. |
gr-qc/9806059 | Julio Cesar Fabris | J.C. Fabris (1), R. Kerner (2) and J. Tossa (3) ((1) Departamento de
Fisica, Universidade Federal do Espirito Santo, (2) Laboratoire de
Gravitation et Cosmologie Relativistes, Universite Pierre et Marie Curie, (3)
IMSP, Universite du Benin) | Perturbative analysis of generalized Einstein's theories | 14 pages, Latex file | Int.J.Mod.Phys. D9 (2000) 111-125 | 10.1142/S0218271800000116 | DF/UFES-P003/98 | gr-qc | null | The hypothesis that the energy-momentum tensor of ordinary matter is not
conserved separately, leads to a non-adiabatic expansion and, in many cases, to
an Universe older than usual. This may provide a solution for the entropy and
age problems of the Standard Cosmological Model. We consider two different
theories of this type, and we perform a perturbative analysis, leading to
analytical expressions for the evolution of gravitational waves, rotational
modes and density perturbations. One of these theories exhibits satisfactory
properties at this level, while the other one should be discarded.
| [
{
"created": "Fri, 12 Jun 1998 15:06:26 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Fabris",
"J. C.",
""
],
[
"Kerner",
"R.",
""
],
[
"Tossa",
"J.",
""
]
] | The hypothesis that the energy-momentum tensor of ordinary matter is not conserved separately, leads to a non-adiabatic expansion and, in many cases, to an Universe older than usual. This may provide a solution for the entropy and age problems of the Standard Cosmological Model. We consider two different theories of this type, and we perform a perturbative analysis, leading to analytical expressions for the evolution of gravitational waves, rotational modes and density perturbations. One of these theories exhibits satisfactory properties at this level, while the other one should be discarded. |
gr-qc/0505013 | Alfredo Macias | Alfredo Macias, Hernando Quevedo, and Alberto Sanchez | Gowdy $T^3$ Cosmological Models in N=1 Supergravity | 25 pages and 2 figures | null | 10.1063/1.2399683 | null | gr-qc | null | We investigate the canonical quantization of supergravity N=1 in the case of
a midisuperspace described by Gowdy $T^3$ cosmological models. The quantum
constraints are analyzed and the wave function of the universe is derived
explicitly. Unlike the minisuperspace case, we show the existence of physical
states in midisuperspace models. The analysis of the wave function of the
universe leads to the conclusion that the classical curvature singularity
present in the evolution of Gowdy models is removed at the quantum level due to
the presence of the Rarita-Schwinger field.
| [
{
"created": "Tue, 3 May 2005 03:15:50 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Macias",
"Alfredo",
""
],
[
"Quevedo",
"Hernando",
""
],
[
"Sanchez",
"Alberto",
""
]
] | We investigate the canonical quantization of supergravity N=1 in the case of a midisuperspace described by Gowdy $T^3$ cosmological models. The quantum constraints are analyzed and the wave function of the universe is derived explicitly. Unlike the minisuperspace case, we show the existence of physical states in midisuperspace models. The analysis of the wave function of the universe leads to the conclusion that the classical curvature singularity present in the evolution of Gowdy models is removed at the quantum level due to the presence of the Rarita-Schwinger field. |
1602.08164 | Changjun Gao | Changjun Gao and You-Gen Shen | Exact solutions in f(R) theory of gravity | 8 pages, 2 figures,accepted by GRG | General Relativity and Gravitation, 48(10), 1-15, 2016 | 10.1007/s10714-016-2128-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We find a new method for looking for the static and spherically symmetric
solutions in $F(R)$ theory of gravity. With this method, a number of new
solutions in terms of the analytic functions are obtained. We hope this
investigation may be of some help in the searching for some other solutions in
$F(R)$ theory of gravity.
| [
{
"created": "Fri, 26 Feb 2016 01:21:45 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Mar 2016 10:58:55 GMT",
"version": "v2"
},
{
"created": "Wed, 2 Mar 2016 12:33:35 GMT",
"version": "v3"
},
{
"created": "Tue, 29 Mar 2016 07:13:42 GMT",
"version": "v4"
},
{
"created": "Fri, 12 Aug 2016 11:27:17 GMT",
"version": "v5"
},
{
"created": "Thu, 1 Sep 2016 02:47:24 GMT",
"version": "v6"
}
] | 2016-09-15 | [
[
"Gao",
"Changjun",
""
],
[
"Shen",
"You-Gen",
""
]
] | We find a new method for looking for the static and spherically symmetric solutions in $F(R)$ theory of gravity. With this method, a number of new solutions in terms of the analytic functions are obtained. We hope this investigation may be of some help in the searching for some other solutions in $F(R)$ theory of gravity. |
gr-qc/0012095 | Vladimir M. Khatsymovsky | V M Khatsymovsky | Continuous matter fields in Regge calculus | 4 pages, LaTeX | Phys.Lett. B504 (2001) 356-358 | 10.1016/S0370-2693(01)00295-7 | null | gr-qc | null | We find that the continuous matter fields are ill-defined in Regge calculus
in the physical 4D theory since the corresponding effective action has infinite
terms unremovable by the UV renormalisation procedure. These terms are
connected with the singular nature of the curvature distribution in Regge
calculus, namely, with the presence in d>2 dimensions of the (d-3)-dimensional
simplices where the (d-2)-dimensional ones carrying different conical
singularities are meeting. Possible resolution of this difficulty is
discretisation of matter fields in Regge background.
| [
{
"created": "Tue, 26 Dec 2000 13:22:49 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Khatsymovsky",
"V M",
""
]
] | We find that the continuous matter fields are ill-defined in Regge calculus in the physical 4D theory since the corresponding effective action has infinite terms unremovable by the UV renormalisation procedure. These terms are connected with the singular nature of the curvature distribution in Regge calculus, namely, with the presence in d>2 dimensions of the (d-3)-dimensional simplices where the (d-2)-dimensional ones carrying different conical singularities are meeting. Possible resolution of this difficulty is discretisation of matter fields in Regge background. |
1911.06988 | Zi-Yu Tang | Zi-Yu Tang, Bin Wang, and Eleftherios Papantonopoulos | Exact charged black hole solutions in D-dimensions in f(R) gravity | 25 pages, 4 figures, accepted in EPJC | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider Maxwell-f(R) gravity and obtain an exact charged black hole
solution with dynamic curvature in D-dimensions. Considering a spherically
symmetric metric ansatz and without specifying the form of f(R) we fnd a
general black hole solution in D-dimensions. This general black hole solution
can be reduced to the Reissner-Nordstr\"om (RN) black hole in D-dimensions in
Einstein gravity and to the known charged black hole solutions with constant
curvature in f(R) gravity. Restricting the parameters of the general solution
we get polynomial solutions which reveal novel properties when compared to RN
black holes. Specifcally we study the solution in (3 + 1)-dimensions in which
the form of f(R) can be solved explicitly giving a dynamic curvature and
compare it with the RN black hole. We also carry out a detailed study of its
thermodynamics.
| [
{
"created": "Sat, 16 Nov 2019 08:15:03 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Apr 2021 09:09:15 GMT",
"version": "v2"
}
] | 2021-04-07 | [
[
"Tang",
"Zi-Yu",
""
],
[
"Wang",
"Bin",
""
],
[
"Papantonopoulos",
"Eleftherios",
""
]
] | We consider Maxwell-f(R) gravity and obtain an exact charged black hole solution with dynamic curvature in D-dimensions. Considering a spherically symmetric metric ansatz and without specifying the form of f(R) we fnd a general black hole solution in D-dimensions. This general black hole solution can be reduced to the Reissner-Nordstr\"om (RN) black hole in D-dimensions in Einstein gravity and to the known charged black hole solutions with constant curvature in f(R) gravity. Restricting the parameters of the general solution we get polynomial solutions which reveal novel properties when compared to RN black holes. Specifcally we study the solution in (3 + 1)-dimensions in which the form of f(R) can be solved explicitly giving a dynamic curvature and compare it with the RN black hole. We also carry out a detailed study of its thermodynamics. |
1907.07661 | Jos\'e Domingo Vela Arba\~nil | Jos\'e D. V. Arba\~nil, Geanderson A. Carvalho, Ronaldo V. Lobato,
Rubens M. Marinho Jr. and Manuel Malheiro | Extra dimensions' influence on the equilibrium and radial stability of
strange quark stars | 10 Pages, 8 figures | null | 10.1103/PhysRevD.100.024035 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the influence of extra dimensions on the static equilibrium
configurations and stability against radial perturbations. For this purpose, we
solve stellar structure equations and radial perturbation equations, both
modified for a $d$-dimensional spacetime ($d\geq4$) considering that spacetime
outside the object is described by a Schwarzschild-Tangherlini metric. These
equations are integrated considering a MIT bag model equation of state extended
for $d\geq4$. We show that the spacetime dimension influences both the
structure and stability of compact objects. For an interval of central energy
densities $\rho_{cd}\,G_d$ and total masses $MG_d/(d-3)$, we show that the
stars gain more stability when the dimension is increased. In addition, the
maximum value of $M{G_d}/(d-3)$ and the zero eigenfrequency of oscillation are
found with the same value of $\rho_{cd}\,G_d$; i.e., the peak value of
$M{G_d}/(d-3)$ marks the onset of instability. This indicates that the
necessary and sufficient conditions to recognize regions constructed by stable
and unstable equilibrium configurations against radial perturbations are,
respectively, $dM/d\rho_{cd}>0$ and $dM/d\rho_{cd}<0$. We obtain that some
physical parameter of the compact object in a $d$-dimensional spacetime, such
as the radius and the mass, depend of the normalization. Finally, within the
Newtonian framework, the results show that compact objects with adiabatic index
$\Gamma_1\geq2(d-2)/(d-1)$ are stable against small radial perturbations.
| [
{
"created": "Wed, 17 Jul 2019 17:46:34 GMT",
"version": "v1"
}
] | 2019-07-18 | [
[
"Arbañil",
"José D. V.",
""
],
[
"Carvalho",
"Geanderson A.",
""
],
[
"Lobato",
"Ronaldo V.",
""
],
[
"Marinho",
"Rubens M.",
"Jr."
],
[
"Malheiro",
"Manuel",
""
]
] | We analyze the influence of extra dimensions on the static equilibrium configurations and stability against radial perturbations. For this purpose, we solve stellar structure equations and radial perturbation equations, both modified for a $d$-dimensional spacetime ($d\geq4$) considering that spacetime outside the object is described by a Schwarzschild-Tangherlini metric. These equations are integrated considering a MIT bag model equation of state extended for $d\geq4$. We show that the spacetime dimension influences both the structure and stability of compact objects. For an interval of central energy densities $\rho_{cd}\,G_d$ and total masses $MG_d/(d-3)$, we show that the stars gain more stability when the dimension is increased. In addition, the maximum value of $M{G_d}/(d-3)$ and the zero eigenfrequency of oscillation are found with the same value of $\rho_{cd}\,G_d$; i.e., the peak value of $M{G_d}/(d-3)$ marks the onset of instability. This indicates that the necessary and sufficient conditions to recognize regions constructed by stable and unstable equilibrium configurations against radial perturbations are, respectively, $dM/d\rho_{cd}>0$ and $dM/d\rho_{cd}<0$. We obtain that some physical parameter of the compact object in a $d$-dimensional spacetime, such as the radius and the mass, depend of the normalization. Finally, within the Newtonian framework, the results show that compact objects with adiabatic index $\Gamma_1\geq2(d-2)/(d-1)$ are stable against small radial perturbations. |
gr-qc/0610109 | Dmitri Burlankov E | D. Burlankov | "Dark energy" as conformal dynamics of space | 2 pages | null | null | null | gr-qc | null | The exact solution for dynamic of conform-flat space homogeneous since
dynamic equation is given. Conform mode of space metric changing in Global time
theory has negative energy density. Swap of energy to this mode from another
ones lead to increasing of Universe homogeneity although probability of this
swap from local objects is negligibly small. Conform mode is corresponding to
"dark energy" in observation astronomy.
| [
{
"created": "Mon, 23 Oct 2006 07:58:07 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Burlankov",
"D.",
""
]
] | The exact solution for dynamic of conform-flat space homogeneous since dynamic equation is given. Conform mode of space metric changing in Global time theory has negative energy density. Swap of energy to this mode from another ones lead to increasing of Universe homogeneity although probability of this swap from local objects is negligibly small. Conform mode is corresponding to "dark energy" in observation astronomy. |
gr-qc/0105021 | Sergio De Filippo | Sergio De Filippo | Nonrelativistic field theoretic setting for gravitational
self-interactions | The statement about the finite character of the ensuing field theory
is more transparent | null | null | null | gr-qc | null | It is shown that a recently proposed model for the gravitational interaction
in non relativistic quantum mechanics is the instantaneous action at a distance
limit of a field theoretic model containing a negative energy field. It reduces
to the Schroedinger-Newton theory in a suitable mean field approximation. While
both the exact model and its approximation lead to estimates for localization
lengths, only the former gives rise to an explicit non unitary dynamics
accounting for the emergence of the classical behavior of macroscopic bodies.
| [
{
"created": "Mon, 7 May 2001 21:21:27 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Jul 2001 17:11:32 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"De Filippo",
"Sergio",
""
]
] | It is shown that a recently proposed model for the gravitational interaction in non relativistic quantum mechanics is the instantaneous action at a distance limit of a field theoretic model containing a negative energy field. It reduces to the Schroedinger-Newton theory in a suitable mean field approximation. While both the exact model and its approximation lead to estimates for localization lengths, only the former gives rise to an explicit non unitary dynamics accounting for the emergence of the classical behavior of macroscopic bodies. |
1010.0962 | Tomohiro Harada | Tomohiro Harada and Masashi Kimura | Collision of an innermost stable circular orbit particle around a Kerr
black hole | 24 pages, 2 figures, accepted for publication in Physical Review D,
minor correction | Phys.Rev.D83:024002,2011 | 10.1103/PhysRevD.83.024002 | RUP-10-3, OCU-PHYS 338, AP-GR 82 | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive a general formula for the center-of-mass (CM) energy for the
near-horizon collision of two particles of the same rest mass on the equatorial
plane around a Kerr black hole. We then apply this formula to a particle which
plunges from the innermost stable circular orbit (ISCO) and collides with
another particle near the horizon. It is found that the maximum value of the CM
energy $E_{\rm cm}$ is given by $E_{\rm cm}/(2m_{0})\simeq
1.40/\sqrt[4]{1-a_{*}^{2}}$ for a nearly maximally rotating black hole, where
$m_{0}$ is the rest mass of each particle and $a_{*}$ is the nondimensional
Kerr parameter. This coincides with the known upper bound for a particle which
begins at rest at infinity within a factor of 2. Moreover, we also consider the
collision of a particle orbiting the ISCO with another particle on the ISCO and
find that the maximum CM energy is then given by $E_{\rm cm}/(2m_{0})\simeq
1.77/\sqrt[6]{1-a_{*}^{2}}$. In view of the astrophysical significance of the
ISCO, this result implies that particles can collide around a rotating black
hole with an arbitrarily high CM energy without any artificial fine-tuning in
an astrophysical context if we can take the maximal limit of the black hole
spin or $a_{*}\to 1$. On the other hand, even if we take Thorne's bound on the
spin parameter into account, highly or moderately relativistic collisions are
expected to occur quite naturally, for $E_{\rm cm}/(2m_{0})$ takes 6.95
(maximum) and 3.86 (generic) near the horizon and 4.11 (maximum) and 2.43
(generic) on the ISCO for $a_{*}=0.998$. This implies that high-velocity
collisions of compact objects are naturally expected around a rapidly rotating
supermassive black hole. Implications to accretion flows onto a rapidly
rotating black hole are also discussed.
| [
{
"created": "Tue, 5 Oct 2010 18:12:11 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Dec 2010 03:00:59 GMT",
"version": "v2"
},
{
"created": "Wed, 5 Jan 2011 04:47:39 GMT",
"version": "v3"
}
] | 2011-10-21 | [
[
"Harada",
"Tomohiro",
""
],
[
"Kimura",
"Masashi",
""
]
] | We derive a general formula for the center-of-mass (CM) energy for the near-horizon collision of two particles of the same rest mass on the equatorial plane around a Kerr black hole. We then apply this formula to a particle which plunges from the innermost stable circular orbit (ISCO) and collides with another particle near the horizon. It is found that the maximum value of the CM energy $E_{\rm cm}$ is given by $E_{\rm cm}/(2m_{0})\simeq 1.40/\sqrt[4]{1-a_{*}^{2}}$ for a nearly maximally rotating black hole, where $m_{0}$ is the rest mass of each particle and $a_{*}$ is the nondimensional Kerr parameter. This coincides with the known upper bound for a particle which begins at rest at infinity within a factor of 2. Moreover, we also consider the collision of a particle orbiting the ISCO with another particle on the ISCO and find that the maximum CM energy is then given by $E_{\rm cm}/(2m_{0})\simeq 1.77/\sqrt[6]{1-a_{*}^{2}}$. In view of the astrophysical significance of the ISCO, this result implies that particles can collide around a rotating black hole with an arbitrarily high CM energy without any artificial fine-tuning in an astrophysical context if we can take the maximal limit of the black hole spin or $a_{*}\to 1$. On the other hand, even if we take Thorne's bound on the spin parameter into account, highly or moderately relativistic collisions are expected to occur quite naturally, for $E_{\rm cm}/(2m_{0})$ takes 6.95 (maximum) and 3.86 (generic) near the horizon and 4.11 (maximum) and 2.43 (generic) on the ISCO for $a_{*}=0.998$. This implies that high-velocity collisions of compact objects are naturally expected around a rapidly rotating supermassive black hole. Implications to accretion flows onto a rapidly rotating black hole are also discussed. |
gr-qc/0011086 | Spiros Cotsakis | Spiros Cotsakis and John Miritzis | Scalar-tensor $\sigma$-cosmologies | Research announcement, 2 pages, submitted for publication in the MG9
Proceedings | null | null | null | gr-qc | null | We show that the scalar-tensor $\sigma$-model action is conformally
equivalent to general relativity with a minimally coupled wavemap with a
particular target metric. Inflation on the source manifold is then shown to
occur in a natural way due both to the arbitrary curvature couplings and the
wavemap self-interactions.
| [
{
"created": "Fri, 24 Nov 2000 10:45:09 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Jan 2001 11:19:23 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Cotsakis",
"Spiros",
""
],
[
"Miritzis",
"John",
""
]
] | We show that the scalar-tensor $\sigma$-model action is conformally equivalent to general relativity with a minimally coupled wavemap with a particular target metric. Inflation on the source manifold is then shown to occur in a natural way due both to the arbitrary curvature couplings and the wavemap self-interactions. |
2004.08111 | Maurizio Gasperini | P. Conzinu, M. Gasperini and G. Marozzi | Primordial Black Holes from Pre-Big Bang inflation | 26 pages, two figures. Many new references and a few comments added.
Version accepted for publication in JCAP | null | 10.1088/1475-7516/2020/08/031 | BA-TH/800-20 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the possibility of producing a significant fraction of dark matter
in the form of primordial black holes in the context of the pre-big bang
inflationary scenario. We take into account, to this purpose, the enhancement
of curvature perturbations possibly induced by a variation of the sound-speed
parameter $c_s$ during the string phase of high-curvature inflation. After
imposing all relevant observational constraints, we find that the considered
class of models is compatible with the production of a large amount of
primordial black holes in the mass range relevant to dark matter, provided the
sound-speed parameter is confined in a rather narrow range of values, $0.003 <
c_s < 0.01$.
| [
{
"created": "Fri, 17 Apr 2020 08:34:34 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Jul 2020 12:28:22 GMT",
"version": "v2"
}
] | 2020-08-19 | [
[
"Conzinu",
"P.",
""
],
[
"Gasperini",
"M.",
""
],
[
"Marozzi",
"G.",
""
]
] | We discuss the possibility of producing a significant fraction of dark matter in the form of primordial black holes in the context of the pre-big bang inflationary scenario. We take into account, to this purpose, the enhancement of curvature perturbations possibly induced by a variation of the sound-speed parameter $c_s$ during the string phase of high-curvature inflation. After imposing all relevant observational constraints, we find that the considered class of models is compatible with the production of a large amount of primordial black holes in the mass range relevant to dark matter, provided the sound-speed parameter is confined in a rather narrow range of values, $0.003 < c_s < 0.01$. |
gr-qc/0611047 | Serguei Krasnikov | S. Krasnikov | Unconventional string-like singularities in flat spacetime | Draft. References and comments are welcome. v2. Section 3 is intact,
the rest is made briefer and clearer. A couple of references are added. v3.
Insignificant correstions. The published version | Phys.Rev.D76:024010,2007 | 10.1103/PhysRevD.76.024010 | null | gr-qc | null | The conical singularity in flat spacetime is mostly known as a model of the
cosmic string or the wedge disclination in solids. Its another, equally
important, function is to be a representative of quasiregular singularities.
From all these of views it seems interesting to find out whether there exist
other similar singularities. To specify what "similar" means I introduce the
notion of the string-like singularity, which is, roughly speaking, an
absolutely mild singularity concentrated on a curve or on a 2-surface S
(depending on whether the space is three- of four-dimensional). A few such
singularities are already known: the aforementioned conical singularity, two
its Lorentzian versions, the "spinning string", the "screw dislocation", and
Tod's spacetime. In all these spacetimes S is a straight line (or a plane) and
one may wonder if this is an inherent property of the string-like
singularities. The aim of this paper is to construct string-like singularities
with less trivial S. These include flat spacetimes in which S is a spiral, or
even a loop. If such singularities exist in nature (in particular, as an
approximation to gravitational field of strings) their cosmological and
astrophysical manifestations must differ drastically from those of the
conventional cosmic strings. Likewise, being realized as topological defects in
crystals such loops and spirals will probably also have rather unusual
properties.
| [
{
"created": "Tue, 7 Nov 2006 15:06:38 GMT",
"version": "v1"
},
{
"created": "Sat, 28 Apr 2007 23:29:41 GMT",
"version": "v2"
},
{
"created": "Tue, 22 Apr 2008 17:18:28 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Krasnikov",
"S.",
""
]
] | The conical singularity in flat spacetime is mostly known as a model of the cosmic string or the wedge disclination in solids. Its another, equally important, function is to be a representative of quasiregular singularities. From all these of views it seems interesting to find out whether there exist other similar singularities. To specify what "similar" means I introduce the notion of the string-like singularity, which is, roughly speaking, an absolutely mild singularity concentrated on a curve or on a 2-surface S (depending on whether the space is three- of four-dimensional). A few such singularities are already known: the aforementioned conical singularity, two its Lorentzian versions, the "spinning string", the "screw dislocation", and Tod's spacetime. In all these spacetimes S is a straight line (or a plane) and one may wonder if this is an inherent property of the string-like singularities. The aim of this paper is to construct string-like singularities with less trivial S. These include flat spacetimes in which S is a spiral, or even a loop. If such singularities exist in nature (in particular, as an approximation to gravitational field of strings) their cosmological and astrophysical manifestations must differ drastically from those of the conventional cosmic strings. Likewise, being realized as topological defects in crystals such loops and spirals will probably also have rather unusual properties. |
1709.01162 | Mauricio Bellini | Luis Santiago Ridao, Marcos Ramiro Alfredo Arcod\'ia, Mauricio Bellini | Gravitons emission during pre-inflation from unified spinor fields | Version accepted in Eur. Phys. J. Plus. arXiv admin note: substantial
text overlap with arXiv:1703.01355 | null | null | null | gr-qc hep-lat hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We obtain the equation that describe the conditions of quantization for
neutral massless bosons on an arbitrary curved space-time, obtained using a
particular theoretical formalism developed in a previous work\cite{MM}. In
particular, we study the emission of neutral massless $(1, 2)\hbar$-spin bosons
during pre-inflation using the recently introduced unified spinor field theory.
We conclude that during pre-inflation (which is governed by an vacuum equation
of state), is emitted gravitational radiation, which could be detected in the
future, as primordial gravitational radiation.
| [
{
"created": "Thu, 31 Aug 2017 19:38:51 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Oct 2017 17:46:55 GMT",
"version": "v2"
},
{
"created": "Mon, 19 Feb 2018 15:54:22 GMT",
"version": "v3"
},
{
"created": "Fri, 2 Nov 2018 16:20:21 GMT",
"version": "v4"
}
] | 2019-09-19 | [
[
"Ridao",
"Luis Santiago",
""
],
[
"Arcodía",
"Marcos Ramiro Alfredo",
""
],
[
"Bellini",
"Mauricio",
""
]
] | We obtain the equation that describe the conditions of quantization for neutral massless bosons on an arbitrary curved space-time, obtained using a particular theoretical formalism developed in a previous work\cite{MM}. In particular, we study the emission of neutral massless $(1, 2)\hbar$-spin bosons during pre-inflation using the recently introduced unified spinor field theory. We conclude that during pre-inflation (which is governed by an vacuum equation of state), is emitted gravitational radiation, which could be detected in the future, as primordial gravitational radiation. |
gr-qc/9406044 | Jeff Greensite | A. Carlini and J. Greensite | Fundamental Constants and the Problem of Time | 46 pages + 5 figures, LaTex, NBI-HE-94-31 | Phys.Rev. D52 (1995) 936-960 | 10.1103/PhysRevD.52.936 | null | gr-qc hep-th | null | We point out that for a large class of parametrized theories, there is a
constant in the constrained Hamiltonian which drops out of the classical
equations of motion in configuration space. Examples include the mass of a
relativistic particle in free fall, the tension of the Nambu string, and
Newton's constant for the case of pure gravity uncoupled to matter or other
fields. In the general case, the classically irrelevant constant is
proportional to the ratio of the kinetic and potential terms in the
Hamiltonian. It is shown that this ratio can be reinterpreted as an {\it
unconstrained} Hamiltonian, which generates the usual classical equations of
motion. At the quantum level, this immediately suggests a resolution of the
"problem of time" in quantum gravity. We then make contact with a recently
proposed transfer matrix formulation of quantum gravity and discuss the
semiclassical limit. In this formulation, it is argued that a physical state
can obey a (generalized) Poincar\'e algebra of constraints, and still be an
approximate eigenstate of 3-geometry. Solutions of the quantum evolution
equations for certain minisuperspace examples are presented. An implication of
our proposal is the existence of a small, inherent uncertainty in the
phenomenological value of Planck's constant.
| [
{
"created": "Fri, 24 Jun 1994 13:58:39 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Carlini",
"A.",
""
],
[
"Greensite",
"J.",
""
]
] | We point out that for a large class of parametrized theories, there is a constant in the constrained Hamiltonian which drops out of the classical equations of motion in configuration space. Examples include the mass of a relativistic particle in free fall, the tension of the Nambu string, and Newton's constant for the case of pure gravity uncoupled to matter or other fields. In the general case, the classically irrelevant constant is proportional to the ratio of the kinetic and potential terms in the Hamiltonian. It is shown that this ratio can be reinterpreted as an {\it unconstrained} Hamiltonian, which generates the usual classical equations of motion. At the quantum level, this immediately suggests a resolution of the "problem of time" in quantum gravity. We then make contact with a recently proposed transfer matrix formulation of quantum gravity and discuss the semiclassical limit. In this formulation, it is argued that a physical state can obey a (generalized) Poincar\'e algebra of constraints, and still be an approximate eigenstate of 3-geometry. Solutions of the quantum evolution equations for certain minisuperspace examples are presented. An implication of our proposal is the existence of a small, inherent uncertainty in the phenomenological value of Planck's constant. |
1209.6261 | Alexander V. Balakin | A.B. Balakin and L.V. Grunskaya | Axion electrodynamics and dark matter fingerprints in the terrestrial
magnetic and electric fields | 26 pages, accepted for publication in the journal Reports on
Mathematical Physics | Reports on Math.Phys. 71 (2013) 45-67 | 10.1016/S0034-4877(13)60021-X | null | gr-qc astro-ph.EP math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider mathematical aspects of the axion electrodynamics in application
to the problem of evolution of geomagnetic and terrestrial electric fields,
which are coupled by relic axions born in the early Universe and
(hypothetically) forming now the cold dark matter. We find axionic analogs of
the Debye potentials, well-known in the standard Faraday - Maxwell
electrodynamics, and discuss exact solutions to the equations of the axion
electrodynamics describing the state of axionically coupled electric and
magnetic fields in a spherical resonator Earth-Ionosphere. We focus on the
properties of the specific electric and magnetic oscillations, which appeared
as a result of the axion-photon coupling in the dark matter environment. We
indicate such electric and magnetic field configurations as longitudinal
electro-magnetic clusters.
| [
{
"created": "Thu, 27 Sep 2012 15:51:09 GMT",
"version": "v1"
}
] | 2015-06-11 | [
[
"Balakin",
"A. B.",
""
],
[
"Grunskaya",
"L. V.",
""
]
] | We consider mathematical aspects of the axion electrodynamics in application to the problem of evolution of geomagnetic and terrestrial electric fields, which are coupled by relic axions born in the early Universe and (hypothetically) forming now the cold dark matter. We find axionic analogs of the Debye potentials, well-known in the standard Faraday - Maxwell electrodynamics, and discuss exact solutions to the equations of the axion electrodynamics describing the state of axionically coupled electric and magnetic fields in a spherical resonator Earth-Ionosphere. We focus on the properties of the specific electric and magnetic oscillations, which appeared as a result of the axion-photon coupling in the dark matter environment. We indicate such electric and magnetic field configurations as longitudinal electro-magnetic clusters. |
gr-qc/0111095 | Bernard F. Schutz | Bernard F. Schutz | Lighthouses of Gravitational Wave Astronomy | 19 pages, for conference proceedings Lighthouses of the Universe,
Garching, August 2001 | null | 10.1007/10856495_29 | AEI-2001-139 | gr-qc | null | Gravitational wave detectors capable of making astronomical observations
could begin to operate within the next year, and over the next 10 years they
will extend their reach out to cosmological distances, culminating in the space
mission LISA. A prime target of these observatories will be binary systems,
especially those whose orbits shrink measurably during an observation period.
These systems are standard candles, and they offer independent ways of
measuring cosmological parameters. LISA in particular could identify the epoch
at which star formation began and, working with telescopes making
electromagnetic observations, measure the Hubble flow at redshifts out to 4 or
more with unprecedented accuracy.
| [
{
"created": "Wed, 28 Nov 2001 08:05:31 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Schutz",
"Bernard F.",
""
]
] | Gravitational wave detectors capable of making astronomical observations could begin to operate within the next year, and over the next 10 years they will extend their reach out to cosmological distances, culminating in the space mission LISA. A prime target of these observatories will be binary systems, especially those whose orbits shrink measurably during an observation period. These systems are standard candles, and they offer independent ways of measuring cosmological parameters. LISA in particular could identify the epoch at which star formation began and, working with telescopes making electromagnetic observations, measure the Hubble flow at redshifts out to 4 or more with unprecedented accuracy. |
1711.11320 | Dennis R\"atzel | Dennis R\"atzel, Fabienne Schneiter, Daniel Braun, Tupac Bravo,
Richard Howl, Maximilian P.E. Lock, Ivette Fuentes | Frequency spectrum of an optical resonator in a curved spacetime | 17 pages, 8 figures, 5 pages appendices | null | 10.1088/1367-2630/aac0ac | null | gr-qc physics.ins-det physics.optics physics.space-ph quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The effect of gravity and proper acceleration on the frequency spectrum of an
optical resonator - both rigid or deformable - is considered in the framework
of general relativity. The optical resonator is modeled either as a rod of
matter connecting two mirrors or as a dielectric rod whose ends function as
mirrors. Explicit expressions for the frequency spectrum are derived for the
case that it is only perturbed slightly. For a deformable resonator, the
perturbation of the frequency spectrum depends on the speed of sound in the rod
supporting the mirrors. A connection is found to a relativistic concept of
rigidity when the speed of sound approaches the speed of light. In contrast,
the corresponding result for the assumption of Born rigidity is recovered when
the speed of sound becomes infinite. The results presented in this article can
be used as the basis for the description of optical and opto-mechanical systems
in a curved spacetime. We apply our results to the examples of a uniformly
accelerating resonator and an optical resonator in the gravitational field of a
small moving sphere. Our approach is not limited to weak gravitational fields,
which we exemplify by its application to the fictitious situation of an optical
resonator falling into a black hole.
| [
{
"created": "Thu, 30 Nov 2017 11:18:14 GMT",
"version": "v1"
}
] | 2018-06-13 | [
[
"Rätzel",
"Dennis",
""
],
[
"Schneiter",
"Fabienne",
""
],
[
"Braun",
"Daniel",
""
],
[
"Bravo",
"Tupac",
""
],
[
"Howl",
"Richard",
""
],
[
"Lock",
"Maximilian P. E.",
""
],
[
"Fuentes",
"Ivette",
""
]
] | The effect of gravity and proper acceleration on the frequency spectrum of an optical resonator - both rigid or deformable - is considered in the framework of general relativity. The optical resonator is modeled either as a rod of matter connecting two mirrors or as a dielectric rod whose ends function as mirrors. Explicit expressions for the frequency spectrum are derived for the case that it is only perturbed slightly. For a deformable resonator, the perturbation of the frequency spectrum depends on the speed of sound in the rod supporting the mirrors. A connection is found to a relativistic concept of rigidity when the speed of sound approaches the speed of light. In contrast, the corresponding result for the assumption of Born rigidity is recovered when the speed of sound becomes infinite. The results presented in this article can be used as the basis for the description of optical and opto-mechanical systems in a curved spacetime. We apply our results to the examples of a uniformly accelerating resonator and an optical resonator in the gravitational field of a small moving sphere. Our approach is not limited to weak gravitational fields, which we exemplify by its application to the fictitious situation of an optical resonator falling into a black hole. |
gr-qc/9802058 | Bozhidar Zakhariev Iliev | Bozhidar Z. Iliev (Institute for Nuclear Research and Nuclear Energy,
Bulgarian Academy of Sciences, Sofia, Bulgaria) | On metric-connection compatibility and the signature change of
space-time | 18 standard LaTeX 2e pages. The packages AMS-LaTeX and amsfonts are
required | Physica Scripta, vol.66, No.6, pp.401-409, 2002 | 10.1238/Physica.Regular.066a00401 | null | gr-qc math-ph math.DG math.MP | null | We discuss and investigate the problem of existence of metric-compatible
linear connections for a given space-time metric which is, generally, assumed
to be semi-pseudo-Riemannian. We prove that under sufficiently general
conditions such connections exist iff the rank and signature of the metric are
constant. On this base we analyze possible changes of the space-time signature.
| [
{
"created": "Sun, 22 Feb 1998 13:15:57 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Iliev",
"Bozhidar Z.",
"",
"Institute for Nuclear Research and Nuclear Energy,\n Bulgarian Academy of Sciences, Sofia, Bulgaria"
]
] | We discuss and investigate the problem of existence of metric-compatible linear connections for a given space-time metric which is, generally, assumed to be semi-pseudo-Riemannian. We prove that under sufficiently general conditions such connections exist iff the rank and signature of the metric are constant. On this base we analyze possible changes of the space-time signature. |
gr-qc/0111076 | Guest User | G. S. Khadekar and Shilpa Samdurkar (Department of Mathematics, Nagpur
University, Nagpur, India) | Higher Dimensional Cosmological Model in Space-Time-Mass (STM) Theory of
Gravitation | latex 4 pages, no figure | null | null | null | gr-qc | null | A new class of non-static higher dimensional vacuum solutions in space-time
-mass (STM) theory of gravity is found. This solution represent expanding
universe without big bang singularity and the higher dimension of these models
shrinks as they expands.
| [
{
"created": "Thu, 22 Nov 2001 14:08:44 GMT",
"version": "v1"
},
{
"created": "Thu, 29 Nov 2001 10:11:23 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Khadekar",
"G. S.",
"",
"Department of Mathematics, Nagpur\n University, Nagpur, India"
],
[
"Samdurkar",
"Shilpa",
"",
"Department of Mathematics, Nagpur\n University, Nagpur, India"
]
] | A new class of non-static higher dimensional vacuum solutions in space-time -mass (STM) theory of gravity is found. This solution represent expanding universe without big bang singularity and the higher dimension of these models shrinks as they expands. |
gr-qc/0209074 | Nematollah Riazi | Nematollah Riazi and Hassan Niad | Gravitating Isovector Solitons | 10 pages, 4 figures | null | null | null | gr-qc | null | We formulate the nonlinear isovector model in a curved background, and
calculate the spherically symmetric solutions for weak and strong coupling
regimes. The usual belief that gravity does not have appreciable effects on the
structure of solitons will be examined, in the framework of the calculated
solutions, by comparing the flat-space and curved-space solutions. It turns out
that in the strong coupling regime, gravity has essential effects on the
solutions. Masses of the self-gravitating solitons are calculated numerically
using the Tolman expression, and its behavior as a function of the coupling
constant of the model is studied.
| [
{
"created": "Sat, 21 Sep 2002 01:29:09 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Riazi",
"Nematollah",
""
],
[
"Niad",
"Hassan",
""
]
] | We formulate the nonlinear isovector model in a curved background, and calculate the spherically symmetric solutions for weak and strong coupling regimes. The usual belief that gravity does not have appreciable effects on the structure of solitons will be examined, in the framework of the calculated solutions, by comparing the flat-space and curved-space solutions. It turns out that in the strong coupling regime, gravity has essential effects on the solutions. Masses of the self-gravitating solitons are calculated numerically using the Tolman expression, and its behavior as a function of the coupling constant of the model is studied. |
1608.04925 | Hedvika Kadlecova | Hedvika Kadlecov\'a and Ond\v{r}ej Klimo and Stefan Weber and Georg
Korn | Gravitational wave generation by interaction of high power lasers with
matter. Part II: Ablation and Piston models | 22 pages, 32 images. arXiv admin note: substantial text overlap with
arXiv:1602.08904 | null | null | null | gr-qc hep-th physics.plasm-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze theoretical models of gravitational waves generation in the
interaction of high intensity laser with matter, namely ablation and piston
models. We analyse the generated gravitational waves in linear approximation of
gravitational theory. We derive the analytical formulas and estimates for the
metric perturbations and the radiated power of generated gravitational waves.
Furthermore we investigate the characteristics of polarization and the
behaviour of test particles in the presence of gravitational wave which will be
important for the detection.
| [
{
"created": "Wed, 17 Aug 2016 11:15:15 GMT",
"version": "v1"
}
] | 2016-08-18 | [
[
"Kadlecová",
"Hedvika",
""
],
[
"Klimo",
"Ondřej",
""
],
[
"Weber",
"Stefan",
""
],
[
"Korn",
"Georg",
""
]
] | We analyze theoretical models of gravitational waves generation in the interaction of high intensity laser with matter, namely ablation and piston models. We analyse the generated gravitational waves in linear approximation of gravitational theory. We derive the analytical formulas and estimates for the metric perturbations and the radiated power of generated gravitational waves. Furthermore we investigate the characteristics of polarization and the behaviour of test particles in the presence of gravitational wave which will be important for the detection. |
gr-qc/9410047 | null | L.H. Ford | Gravitons and Lightcone Fluctuations | 18pp, LATEX, TUTP-94-15 | Phys.Rev.D51:1692-1700,1995 | 10.1103/PhysRevD.51.1692 | null | gr-qc hep-th | null | Gravitons in a squeezed vacuum state, the natural result of quantum creation
in the early universe or by black holes, will introduce metric fluctuations.
These metric fluctuations will introduce fluctuations of the lightcone. It is
shown that when the various two-point functions of a quantized field are
averaged over the metric fluctuations, the lightcone singularity disappears for
distinct points. The metric averaged functions remain singular in the limit of
coincident points. The metric averaged retarded Green's function for a massless
field becomes a Gaussian which is nonzero both inside and outside of the
classical lightcone. This implies some photons propagate faster than the
classical light speed, whereas others propagate slower. The possible effects of
metric fluctuations upon one-loop quantum processes are discussed and
illustrated by the calculation of the one-loop electron self-energy.
| [
{
"created": "Mon, 31 Oct 1994 21:49:00 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Ford",
"L. H.",
""
]
] | Gravitons in a squeezed vacuum state, the natural result of quantum creation in the early universe or by black holes, will introduce metric fluctuations. These metric fluctuations will introduce fluctuations of the lightcone. It is shown that when the various two-point functions of a quantized field are averaged over the metric fluctuations, the lightcone singularity disappears for distinct points. The metric averaged functions remain singular in the limit of coincident points. The metric averaged retarded Green's function for a massless field becomes a Gaussian which is nonzero both inside and outside of the classical lightcone. This implies some photons propagate faster than the classical light speed, whereas others propagate slower. The possible effects of metric fluctuations upon one-loop quantum processes are discussed and illustrated by the calculation of the one-loop electron self-energy. |
2111.00712 | Supakchai Ponglertsakul | Piyabut Burikham, Sitthichai Pinkanjanarod and Supakchai Ponglertsakul | Slowly Rotating Neutron Star with Holographic Multiquark Core: I-Love-Q
Relations | 9 pages, 7 figures | null | 10.1103/PhysRevD.105.104018 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Moment of inertia ($I$), rotational~(tidal) Love number ($\lambda^{\rm
(rot)}$) and quadrupole moment ($Q$) of slowly rotating massive neutron
star~(NS) with holographic multiquark~(MQ) core are computed in comparison to
pure MQ star. The Chiral Effective Theory~(CET) stiff equation of state~(EoS)
is used in the crust of the neutron star. The dimensionless multipole moments
$\bar{I},\bar{\lambda}^{\rm (rot)}, \bar{Q}$ are found to be independent of the
rotation parameters and determined completely by the zeroth-order star profile.
Universal ``I-Love-Q'' relations found by Yagi and Yunes [1,2] are mostly
preserved even in the presence of the MQ core. Tidal deformation parameter
$\bar{\lambda}^{\rm (tid)}$ is also explored in connection with $\bar{I},
\bar{\lambda}^{\rm (rot)}, \bar{Q}$, two kinds of universal I-Love-Q relations
are verified. However, the unique kink in the plots of multipoles with respect
to mass and compactness of the population of neutron stars can reveal the
existence of massive NS with the MQ core.
| [
{
"created": "Mon, 1 Nov 2021 05:40:02 GMT",
"version": "v1"
}
] | 2022-05-25 | [
[
"Burikham",
"Piyabut",
""
],
[
"Pinkanjanarod",
"Sitthichai",
""
],
[
"Ponglertsakul",
"Supakchai",
""
]
] | Moment of inertia ($I$), rotational~(tidal) Love number ($\lambda^{\rm (rot)}$) and quadrupole moment ($Q$) of slowly rotating massive neutron star~(NS) with holographic multiquark~(MQ) core are computed in comparison to pure MQ star. The Chiral Effective Theory~(CET) stiff equation of state~(EoS) is used in the crust of the neutron star. The dimensionless multipole moments $\bar{I},\bar{\lambda}^{\rm (rot)}, \bar{Q}$ are found to be independent of the rotation parameters and determined completely by the zeroth-order star profile. Universal ``I-Love-Q'' relations found by Yagi and Yunes [1,2] are mostly preserved even in the presence of the MQ core. Tidal deformation parameter $\bar{\lambda}^{\rm (tid)}$ is also explored in connection with $\bar{I}, \bar{\lambda}^{\rm (rot)}, \bar{Q}$, two kinds of universal I-Love-Q relations are verified. However, the unique kink in the plots of multipoles with respect to mass and compactness of the population of neutron stars can reveal the existence of massive NS with the MQ core. |
gr-qc/0104071 | Elena Cuoco | Elena Cuoco, Giovanni Losurdo, Giovanni Calamai, Leonardo Fabbroni,
Massimo Mazzoni, Ruggero Stanga, Gianluca Guidi, Flavio Vetrano | Noise parametric identification and whitening for LIGO 40-meter
interferometer data | 11 pages, 15 figures, accepted for publication by Physical Review D | Phys.Rev.D64:122002,2001 | 10.1103/PhysRevD.64.122002 | null | gr-qc | null | We report the analysis we made on data taken by Caltech 40-meter prototype
interferometer to identify the noise power spectral density and to whiten the
sequence of noise. We concentrate our study on data taken in November 1994, in
particular we analyzed two frames of data: the 18nov94.2.frame and the
19nov94.2.frame.
We show that it is possible to whiten these data, to a good degree of
whiteness, using a high order whitening filter. Moreover we can choose to
whiten only restricted band of frequencies around the region we are interested
in, obtaining a higher level of whiteness.
| [
{
"created": "Mon, 23 Apr 2001 13:27:08 GMT",
"version": "v1"
},
{
"created": "Fri, 31 Aug 2001 08:15:29 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Cuoco",
"Elena",
""
],
[
"Losurdo",
"Giovanni",
""
],
[
"Calamai",
"Giovanni",
""
],
[
"Fabbroni",
"Leonardo",
""
],
[
"Mazzoni",
"Massimo",
""
],
[
"Stanga",
"Ruggero",
""
],
[
"Guidi",
"Gianluca",
""
],
[
"Vetrano",
"Flavio",
""
]
] | We report the analysis we made on data taken by Caltech 40-meter prototype interferometer to identify the noise power spectral density and to whiten the sequence of noise. We concentrate our study on data taken in November 1994, in particular we analyzed two frames of data: the 18nov94.2.frame and the 19nov94.2.frame. We show that it is possible to whiten these data, to a good degree of whiteness, using a high order whitening filter. Moreover we can choose to whiten only restricted band of frequencies around the region we are interested in, obtaining a higher level of whiteness. |
1601.06337 | Ambrish Raghoonundun | Ambrish M. Raghoonundun and David W. Hobill | The Geometrical Structure of the Tolman VII solution | To be submitted to classical and quantum gravity | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Tolman~VII solution, an exact analytic solution to the spherically
symmetric, static Einstein equations with a perfect fluid source, has many
characteristics that make it interesting for modelling high density physical
astronomical objects. Here we supplement those characteristics with the
geometrical tensors that this solution possess, and find that the Weyl,
Riemann, and Ricci tensor components show unexpected mathematical behaviour
that change depending on physically motivated parameters, even though the mass
of the modelled objects is fixed. We show these features firstly through tensor
components, and then through the scalars in the null tetrad formalism of
Newmann and Penrose. The salient conclusion of this analysis is the intimate
relationship between the Tolman~VII solution and the constant density
Schwarzschild interior solution: the former being a straight forward
generalization of the latter while eschewing the unphysical constant density.
| [
{
"created": "Sun, 24 Jan 2016 02:38:08 GMT",
"version": "v1"
}
] | 2016-01-26 | [
[
"Raghoonundun",
"Ambrish M.",
""
],
[
"Hobill",
"David W.",
""
]
] | The Tolman~VII solution, an exact analytic solution to the spherically symmetric, static Einstein equations with a perfect fluid source, has many characteristics that make it interesting for modelling high density physical astronomical objects. Here we supplement those characteristics with the geometrical tensors that this solution possess, and find that the Weyl, Riemann, and Ricci tensor components show unexpected mathematical behaviour that change depending on physically motivated parameters, even though the mass of the modelled objects is fixed. We show these features firstly through tensor components, and then through the scalars in the null tetrad formalism of Newmann and Penrose. The salient conclusion of this analysis is the intimate relationship between the Tolman~VII solution and the constant density Schwarzschild interior solution: the former being a straight forward generalization of the latter while eschewing the unphysical constant density. |
1910.09415 | Ben Kain | Emanuel Daka, Nhon N. Phan, and Ben Kain | Perturbing the ground state of Dirac stars | 17 pages, 8 figures | null | 10.1103/PhysRevD.100.084042 | Phys. Rev. D 100, 084042 (2019) | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Dirac stars are self-gravitating configurations of spin-1/2 fermions in which
the fermions are described by the Dirac equation. After a detailed review of
the derivation of the equations and their static solutions, we present an
in-depth dynamical stability analysis of the ground state similar to previous
studies for boson stars. We confirm that there exist both stable and unstable
branches of static solutions and show that weakly perturbed Dirac stars from
the unstable branch migrate to the stable branch. We also show that strongly
perturbed Dirac stars from the stable branch migrate to the stable branch if
their mass is below a critical value. If their mass is above the critical value
they can migrate to the stable branch or collapse and form a black hole. For
strongly perturbed Dirac stars from the unstable branch we show that the
addition of even a small amount of mass leads to collapse, while if we decrease
their mass they migrate to the stable branch.
| [
{
"created": "Mon, 21 Oct 2019 14:45:22 GMT",
"version": "v1"
}
] | 2020-01-08 | [
[
"Daka",
"Emanuel",
""
],
[
"Phan",
"Nhon N.",
""
],
[
"Kain",
"Ben",
""
]
] | Dirac stars are self-gravitating configurations of spin-1/2 fermions in which the fermions are described by the Dirac equation. After a detailed review of the derivation of the equations and their static solutions, we present an in-depth dynamical stability analysis of the ground state similar to previous studies for boson stars. We confirm that there exist both stable and unstable branches of static solutions and show that weakly perturbed Dirac stars from the unstable branch migrate to the stable branch. We also show that strongly perturbed Dirac stars from the stable branch migrate to the stable branch if their mass is below a critical value. If their mass is above the critical value they can migrate to the stable branch or collapse and form a black hole. For strongly perturbed Dirac stars from the unstable branch we show that the addition of even a small amount of mass leads to collapse, while if we decrease their mass they migrate to the stable branch. |
gr-qc/0203040 | Horst R. Beyer | Horst R. Beyer | Results on the spectrum of R-Modes of slowly rotating relativistic stars | null | Class.Quant.Grav. 23 (2006) 2409-2426 | null | null | gr-qc astro-ph math-ph math.MP | null | The paper considers the spectrum of axial perturbations of slowly uniformly
rotating general relativistic stars in the framework of Y. Kojima. In a first
step towards a full analysis only the evolution equations are treated but not
the constraint. Then it is found that the system is unstable due to a continuum
of non real eigenvalues. In addition the resolvent of the associated generator
of time evolution is found to have a special structure which was discussed in a
previous paper. From this structure it follows the occurrence of a continuous
part in the spectrum of oscillations at least if the system is restricted to a
finite space as is done in most numerical investigations. Finally, it can be
seen that higher order corrections in the rotation frequency can qualitatively
influence the spectrum of the oscillations. As a consequence different
descriptions of the star which are equivalent to first order could lead to
different results with respect to the stability of the star.
| [
{
"created": "Tue, 12 Mar 2002 16:49:46 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Beyer",
"Horst R.",
""
]
] | The paper considers the spectrum of axial perturbations of slowly uniformly rotating general relativistic stars in the framework of Y. Kojima. In a first step towards a full analysis only the evolution equations are treated but not the constraint. Then it is found that the system is unstable due to a continuum of non real eigenvalues. In addition the resolvent of the associated generator of time evolution is found to have a special structure which was discussed in a previous paper. From this structure it follows the occurrence of a continuous part in the spectrum of oscillations at least if the system is restricted to a finite space as is done in most numerical investigations. Finally, it can be seen that higher order corrections in the rotation frequency can qualitatively influence the spectrum of the oscillations. As a consequence different descriptions of the star which are equivalent to first order could lead to different results with respect to the stability of the star. |
2405.07484 | Aaqid Bhat | Aaqid Bhat, Raja Solanki, P.K. Sahoo | Extended Bose-Einstein condensate dark matter in $f(Q)$ gravity | GRG published version | General Relativity and Gravitation, 56 (2024) 63 | 10.1007/s10714-024-03247-3 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this article, we attempt to explore the dark sector of the universe i.e.
dark matter and dark energy, where the dark energy components are related to
the modified $f(Q)$ Lagrangian, particularly a power law function $f(Q)= \gamma
\left(\frac{Q}{Q_0}\right)^n$, while the dark matter component is described by
the Extended Bose-Einstein Condensate (EBEC) equation of state for dark matter,
specifically, $p = \alpha \rho + \beta \rho^2$. We find the corresponding
Friedmann-like equations and the continuity equation for both dark components
along with an interacting term, specifically $\mathcal{Q} = 3b^2H \rho$, which
signifies the energy exchange between the dark sector of the universe. Further,
we derive the analytical expression of the Hubble function, and then we find
the best-fit values of free parameters utilizing the Bayesian analysis to
estimate the posterior probability and the Markov Chain Monte Carlo (MCMC)
sampling technique corresponding to CC+Pantheon+SH0ES samples. In addition, to
examine the robustness of our MCMC analysis, we perform a statistical
assessment using the Akaike Information Criterion (AIC) and Bayesian
Information Criterion (BIC). Further from the evolutionary profile of the
deceleration parameter and the energy density, we obtain a transition from the
decelerated epoch to the accelerated expansion phase, with the present
deceleration parameter value as $q(z=0)=q_0=-0.56^{+0.04}_{-0.03}$ ($68 \%$
confidence limit), that is quite consistent with cosmological observations. In
addition, we find the expected positive behavior of the effective energy
density. Finally, by examining the sound speed parameter, we find that the
assumed theoretical $f(Q)$ model is thermodynamically stable.
| [
{
"created": "Mon, 13 May 2024 05:58:01 GMT",
"version": "v1"
}
] | 2024-05-24 | [
[
"Bhat",
"Aaqid",
""
],
[
"Solanki",
"Raja",
""
],
[
"Sahoo",
"P. K.",
""
]
] | In this article, we attempt to explore the dark sector of the universe i.e. dark matter and dark energy, where the dark energy components are related to the modified $f(Q)$ Lagrangian, particularly a power law function $f(Q)= \gamma \left(\frac{Q}{Q_0}\right)^n$, while the dark matter component is described by the Extended Bose-Einstein Condensate (EBEC) equation of state for dark matter, specifically, $p = \alpha \rho + \beta \rho^2$. We find the corresponding Friedmann-like equations and the continuity equation for both dark components along with an interacting term, specifically $\mathcal{Q} = 3b^2H \rho$, which signifies the energy exchange between the dark sector of the universe. Further, we derive the analytical expression of the Hubble function, and then we find the best-fit values of free parameters utilizing the Bayesian analysis to estimate the posterior probability and the Markov Chain Monte Carlo (MCMC) sampling technique corresponding to CC+Pantheon+SH0ES samples. In addition, to examine the robustness of our MCMC analysis, we perform a statistical assessment using the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC). Further from the evolutionary profile of the deceleration parameter and the energy density, we obtain a transition from the decelerated epoch to the accelerated expansion phase, with the present deceleration parameter value as $q(z=0)=q_0=-0.56^{+0.04}_{-0.03}$ ($68 \%$ confidence limit), that is quite consistent with cosmological observations. In addition, we find the expected positive behavior of the effective energy density. Finally, by examining the sound speed parameter, we find that the assumed theoretical $f(Q)$ model is thermodynamically stable. |
1708.07383 | Behnam Pourhassan | J. Sadeghi, B. Pourhassan, and F. Rahimi | Logarithmic corrections of charged hairy black hole in (2+1) dimension | 10 pages | Can. J. Phys. 92 (2014) 1638 | 10.1139/cjp-2014-0229 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a charged black hole with a scalar field that is coupled to
gravity in (2 + 1)-dimensions. We compute the logarithmic corrections to the
corresponding system using two approaches. In the first method we take
advantage of thermodynamic properties. In the second method we use the metric
function that is suggested by conformal field theory. Finally, we compare the
results of the two approaches.
| [
{
"created": "Wed, 23 Aug 2017 12:24:28 GMT",
"version": "v1"
}
] | 2017-08-25 | [
[
"Sadeghi",
"J.",
""
],
[
"Pourhassan",
"B.",
""
],
[
"Rahimi",
"F.",
""
]
] | We consider a charged black hole with a scalar field that is coupled to gravity in (2 + 1)-dimensions. We compute the logarithmic corrections to the corresponding system using two approaches. In the first method we take advantage of thermodynamic properties. In the second method we use the metric function that is suggested by conformal field theory. Finally, we compare the results of the two approaches. |
2308.01498 | P. A. Gonzalez | P. A. Gonz\'alez, Marco Olivares, Yerko V\'asquez, J. R. Villanueva | Timelike geodesics for five-dimensional Schwarzschild and
Reissner-Nordstr\"om Anti-de Sitter black holes | 15 pages, and 15 figures | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The timelike structure of the five-dimensional Schwarzschild and
Reissner-Nordstr\"om Anti-de Sitter black holes is studied in detail. Different
kinds of motion are allowed and studied by using an adequate effective
potential. Then, by solving the corresponding equations of motion, several
trajectories and orbits are described in terms of Weierstrass elliptic
functions and elementary functions for neutral particles.
| [
{
"created": "Thu, 3 Aug 2023 01:50:12 GMT",
"version": "v1"
}
] | 2023-08-04 | [
[
"González",
"P. A.",
""
],
[
"Olivares",
"Marco",
""
],
[
"Vásquez",
"Yerko",
""
],
[
"Villanueva",
"J. R.",
""
]
] | The timelike structure of the five-dimensional Schwarzschild and Reissner-Nordstr\"om Anti-de Sitter black holes is studied in detail. Different kinds of motion are allowed and studied by using an adequate effective potential. Then, by solving the corresponding equations of motion, several trajectories and orbits are described in terms of Weierstrass elliptic functions and elementary functions for neutral particles. |
2301.12164 | Cosimo Bambi | Jiahao Tao, Shafqat Riaz, Biao Zhou, Askar B. Abdikamalov, Cosimo
Bambi, Daniele Malafarina | Testing the $\delta$-Kerr metric with black hole X-ray data | 17 pages, 7 figures. v2: refereed version | Phys. Rev. D 108, 083036 (2023) | 10.1103/PhysRevD.108.083036 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The spacetime around astrophysical black holes is thought to be described by
the Kerr solution. However, even within general relativity, there is not yet a
proof that the final product of the complete collapse of an uncharged body can
only be a Kerr black hole. We can thus speculate on the possibility that the
spacetime around astrophysical black holes may be described by other solutions
of the Einstein Equations and we can test such a hypothesis with observations.
In this work, we consider the $\delta$-Kerr metric, which is an exact solution
of the field equations in vacuum and can be obtained from a non-linear
superposition of the Kerr metric with a static axially symmetric solution,
often referred to as the $\delta$-metric. The parameter $\delta=1+q$ quantifies
the departure of the source from the Kerr metric and for $q=0$ we recover the
Kerr solution. From the analysis of the reflection features in the X-ray
spectrum of the Galactic black hole in EXO 1846-031, we find $-0.1 < q < 0.7$
(90% CL), which is consistent with the hypothesis that the spacetime around the
compact object in EXO 1846-031 is a Kerr black hole but does not entirely rule
out the $\delta$-Kerr metric.
| [
{
"created": "Sat, 28 Jan 2023 11:31:47 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Oct 2023 14:19:24 GMT",
"version": "v2"
}
] | 2023-10-26 | [
[
"Tao",
"Jiahao",
""
],
[
"Riaz",
"Shafqat",
""
],
[
"Zhou",
"Biao",
""
],
[
"Abdikamalov",
"Askar B.",
""
],
[
"Bambi",
"Cosimo",
""
],
[
"Malafarina",
"Daniele",
""
]
] | The spacetime around astrophysical black holes is thought to be described by the Kerr solution. However, even within general relativity, there is not yet a proof that the final product of the complete collapse of an uncharged body can only be a Kerr black hole. We can thus speculate on the possibility that the spacetime around astrophysical black holes may be described by other solutions of the Einstein Equations and we can test such a hypothesis with observations. In this work, we consider the $\delta$-Kerr metric, which is an exact solution of the field equations in vacuum and can be obtained from a non-linear superposition of the Kerr metric with a static axially symmetric solution, often referred to as the $\delta$-metric. The parameter $\delta=1+q$ quantifies the departure of the source from the Kerr metric and for $q=0$ we recover the Kerr solution. From the analysis of the reflection features in the X-ray spectrum of the Galactic black hole in EXO 1846-031, we find $-0.1 < q < 0.7$ (90% CL), which is consistent with the hypothesis that the spacetime around the compact object in EXO 1846-031 is a Kerr black hole but does not entirely rule out the $\delta$-Kerr metric. |
1310.1067 | Muhammad Zubair | M. Sharif, M. Zubair | Cosmology of Holographic and New Agegraphic $f(R,T)$ Models | 27 pages, 12 figures | J. Phys. Soc. Jpn. 82(2013)064001 | 10.7566/JPSJ.82.064001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the $f(R,T)$ theory, where $R$ is the scalar curvature and $T$ is
the trace of energy-momentum tensor, as an effective description for the
holographic and new agegraphic dark energy and reconstruct the corresponding
$f(R,T)$ functions. In this study, we concentrate on two particular models of
$f(R,T)$ gravity namely, $R+2A(T)$ and $B(R)+\lambda{T}$. We conclude that the
derived $f(R,T)$ models can represent phantom or quintessence regimes of the
universe which are compatible with the current observational data. In addition,
the conditions to preserve the generalized second law of thermodynamics are
established.
| [
{
"created": "Thu, 29 Aug 2013 11:28:45 GMT",
"version": "v1"
}
] | 2013-10-04 | [
[
"Sharif",
"M.",
""
],
[
"Zubair",
"M.",
""
]
] | We consider the $f(R,T)$ theory, where $R$ is the scalar curvature and $T$ is the trace of energy-momentum tensor, as an effective description for the holographic and new agegraphic dark energy and reconstruct the corresponding $f(R,T)$ functions. In this study, we concentrate on two particular models of $f(R,T)$ gravity namely, $R+2A(T)$ and $B(R)+\lambda{T}$. We conclude that the derived $f(R,T)$ models can represent phantom or quintessence regimes of the universe which are compatible with the current observational data. In addition, the conditions to preserve the generalized second law of thermodynamics are established. |
gr-qc/9806029 | Hector F. Hernandez G. | H. Hernandez, L. A. Nunez and U. Percoco | Nonlocal Equation of State in General Relativistic Radiating Spheres | 19 pages, Revtex, 1 Postscript Figure | Class.Quant.Grav.16:871-896,1999 | 10.1088/0264-9381/16/3/017 | null | gr-qc | null | We show that under particular circumstances a general relativistic
spherically symmetric bounded distribution of matter could satisfy a nonlocal
equation of state. This equation relates, at a given point, the components of
the corresponding energy momentum tensor not only as function at that point,
but as a functional throughout the enclosed configuration. We have found that
these types of dynamic bounded matter configurations, with constant
gravitational potentials at the surface, admit a Conformal Killing Vector and
fulfill the energy conditions for anisotropic imperfect fluids. We also present
several analytical and numerical models satisfying these equations of state
which collapse as reasonable radiating anisotropic spheres in general
relativity.
| [
{
"created": "Fri, 5 Jun 1998 16:35:58 GMT",
"version": "v1"
}
] | 2011-07-19 | [
[
"Hernandez",
"H.",
""
],
[
"Nunez",
"L. A.",
""
],
[
"Percoco",
"U.",
""
]
] | We show that under particular circumstances a general relativistic spherically symmetric bounded distribution of matter could satisfy a nonlocal equation of state. This equation relates, at a given point, the components of the corresponding energy momentum tensor not only as function at that point, but as a functional throughout the enclosed configuration. We have found that these types of dynamic bounded matter configurations, with constant gravitational potentials at the surface, admit a Conformal Killing Vector and fulfill the energy conditions for anisotropic imperfect fluids. We also present several analytical and numerical models satisfying these equations of state which collapse as reasonable radiating anisotropic spheres in general relativity. |
2402.02497 | Jo\~ao Cavedagne Lobato | Jo\~ao C. Lobato and Maur\'icio O. Calv\~ao | Gravitational wave energy momentum-tensor in reduced Horndeski theories | null | null | 10.1103/PhysRevD.109.044004 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | We generalize, imposing the field equations only at dominant order, the
Isaacson formula for the gravitational wave (GW) energy-momentum tensor (EMT)
to the class of Horndeski theories in which the tensor modes travel at the
speed of light (reduced Horndeski theories) and scalar waves are present. We
discuss important particular cases such as: theories where scalar waves are
also luminal and theories in which the transverse-traceless gauge can be
achieved in an arbitrary open set. The vanishing of the trace of the
gravitational wave energy-momentum tensor is obtained for theories in which all
wave perturbations propagate at the speed of light. The trace is shown not to
vanish trivially in other cases. We obtain, as a particular case of our general
result, the GW EMTs, in a Brans-Dicke theory, both in the Einstein frame,
recovering previous results in the literature, and in the Jordan frame, thereby
showing the GW EMT is not conformally invariant. We further prove that there
exists a subclass of reduced Horndeski theories where, in contrast to general
relativity, the divergence of the GW EMT does not vanish even after the
imposition of the full equations of motion, assuming an eikonal solution.
| [
{
"created": "Sun, 4 Feb 2024 14:11:53 GMT",
"version": "v1"
}
] | 2024-02-06 | [
[
"Lobato",
"João C.",
""
],
[
"Calvão",
"Maurício O.",
""
]
] | We generalize, imposing the field equations only at dominant order, the Isaacson formula for the gravitational wave (GW) energy-momentum tensor (EMT) to the class of Horndeski theories in which the tensor modes travel at the speed of light (reduced Horndeski theories) and scalar waves are present. We discuss important particular cases such as: theories where scalar waves are also luminal and theories in which the transverse-traceless gauge can be achieved in an arbitrary open set. The vanishing of the trace of the gravitational wave energy-momentum tensor is obtained for theories in which all wave perturbations propagate at the speed of light. The trace is shown not to vanish trivially in other cases. We obtain, as a particular case of our general result, the GW EMTs, in a Brans-Dicke theory, both in the Einstein frame, recovering previous results in the literature, and in the Jordan frame, thereby showing the GW EMT is not conformally invariant. We further prove that there exists a subclass of reduced Horndeski theories where, in contrast to general relativity, the divergence of the GW EMT does not vanish even after the imposition of the full equations of motion, assuming an eikonal solution. |
1605.04811 | Laszlo B. Szabados | L\'aszl\'o B Szabados | The evanescence of rest masses and electric charge in black holes | the results are included in arXiv:1603.06997v3 | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The classical Einstein-Standard Model system with conformally invariant
coupling of the Higgs field to gravity is investigated in nearly Schwarzschild
black holes. We show that, in the presence of Kantowski-Sachs symmetries, there
is a finite critical value of the mean curvature such that on spacelike
hypersurfaces with greater mean curvature the Higgs sector does not have any
symmetry breaking vacuum state. Hence, according to the Standard Model of
particle physics, the gauge and spinor fields do not have rest mass and
electric charge. Therefore, particles falling into a nearly Schwarzschild black
hole lose their mass and charge in the "reverse" Brout-Englert-Higgs mechanism.
| [
{
"created": "Mon, 16 May 2016 15:45:55 GMT",
"version": "v1"
},
{
"created": "Mon, 29 May 2017 23:57:53 GMT",
"version": "v2"
}
] | 2017-05-31 | [
[
"Szabados",
"László B",
""
]
] | The classical Einstein-Standard Model system with conformally invariant coupling of the Higgs field to gravity is investigated in nearly Schwarzschild black holes. We show that, in the presence of Kantowski-Sachs symmetries, there is a finite critical value of the mean curvature such that on spacelike hypersurfaces with greater mean curvature the Higgs sector does not have any symmetry breaking vacuum state. Hence, according to the Standard Model of particle physics, the gauge and spinor fields do not have rest mass and electric charge. Therefore, particles falling into a nearly Schwarzschild black hole lose their mass and charge in the "reverse" Brout-Englert-Higgs mechanism. |
0812.1059 | Friedrich W. Hehl | Friedrich W. Hehl (U of Cologne and U of Missouri-Columbia) and Bahram
Mashhoon (U of Missouri-Columbia) | Nonlocal Gravity Simulates Dark Matter | 5 pages RevTex, v3: new material and references added, abstract
somewhat extended | Phys.Lett.B673:279-282,2009 | 10.1016/j.physletb.2009.02.033 | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A nonlocal generalization of Einstein's theory of gravitation is constructed
within the framework of the translational gauge theory of gravity. In the
linear approximation, the nonlocal theory can be interpreted as linearized
general relativity but in the presence of "dark matter" that can be simply
expressed as an integral transform of matter. It is shown that this approach
can accommodate the Tohline-Kuhn treatment of the astrophysical evidence for
dark matter.
| [
{
"created": "Fri, 5 Dec 2008 00:41:18 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Dec 2008 21:18:05 GMT",
"version": "v2"
},
{
"created": "Tue, 3 Feb 2009 17:09:50 GMT",
"version": "v3"
}
] | 2009-03-24 | [
[
"Hehl",
"Friedrich W.",
"",
"U of Cologne and U of Missouri-Columbia"
],
[
"Mashhoon",
"Bahram",
"",
"U of Missouri-Columbia"
]
] | A nonlocal generalization of Einstein's theory of gravitation is constructed within the framework of the translational gauge theory of gravity. In the linear approximation, the nonlocal theory can be interpreted as linearized general relativity but in the presence of "dark matter" that can be simply expressed as an integral transform of matter. It is shown that this approach can accommodate the Tohline-Kuhn treatment of the astrophysical evidence for dark matter. |
1108.1988 | Bob Coecke | Bob Coecke and Raymond Lal | Time-asymmetry of probabilities versus relativistic causal structure: an
arrow of time | 4 pages, some figures; replaces arXiv:1010.4572 [quant-ph] | Phys. Rev. Lett. 108, 200403 (2012) | 10.1103/PhysRevLett.108.200403 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There is an incompatibility between the symmetries of causal structure in
relativity theory and the signaling abilities of probabilistic devices with
inputs and outputs: while time-reversal in relativity will not introduce the
ability to signal between spacelike separated regions, this is not the case for
probabilistic devices with space-like separated input-output pairs. We
explicitly describe a non-signaling device which becomes a perfect signaling
device under time-reversal, where time-reversal can be conceptualized as
playing backwards a videotape of an agent manipulating the device. This leads
to an arrow of time that is identifiable when studying the correlations of
events for spacelike separated regions. Somewhat surprisingly, although
time-reversal of Popuscu-Roerlich boxes also allows agents to signal, it does
not yield a perfect signaling device. Finally, we realize time-reversal using
post-selection, which could lead experimental implementation.
| [
{
"created": "Tue, 9 Aug 2011 17:21:23 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Sep 2011 13:49:45 GMT",
"version": "v2"
}
] | 2014-05-19 | [
[
"Coecke",
"Bob",
""
],
[
"Lal",
"Raymond",
""
]
] | There is an incompatibility between the symmetries of causal structure in relativity theory and the signaling abilities of probabilistic devices with inputs and outputs: while time-reversal in relativity will not introduce the ability to signal between spacelike separated regions, this is not the case for probabilistic devices with space-like separated input-output pairs. We explicitly describe a non-signaling device which becomes a perfect signaling device under time-reversal, where time-reversal can be conceptualized as playing backwards a videotape of an agent manipulating the device. This leads to an arrow of time that is identifiable when studying the correlations of events for spacelike separated regions. Somewhat surprisingly, although time-reversal of Popuscu-Roerlich boxes also allows agents to signal, it does not yield a perfect signaling device. Finally, we realize time-reversal using post-selection, which could lead experimental implementation. |
gr-qc/9905048 | Nikolaos Mavromatos | John.Ellis, N.E. Mavromatos and D.V. Nanopoulos | Search for Quantum Gravity | 7 pages LATEX, no figures, Awarded First Prize in the Gravity
Research Foundation Essay Competition for 1999 | Gen.Rel.Grav.31:1257-1262,1999 | 10.1023/A:1026720723556 | null | gr-qc astro-ph hep-ph hep-th | null | A satisfactory theory of quantum gravity may necessitate a drastic
modification of our perception of space-time, by giving it a foamy structure at
distances comparable to the Planck length. It is argued in this essay that the
experimental detection of such structures may be a realistic possibility in the
foreseeable future. After a brief review of different theoretical approaches to
quantum gravity and the relationships between them, we discuss various possible
experimental tests of the quantum nature of space-time. Observations of photons
from distant astrophysical sources such as Gamma-Ray Bursters and laboratory
experiments on neutral kaon decays may be sensitive to quantum-gravitational
effects if they are only minimally suppressed. Experimental limits from the
Whipple Observatory and the CPLEAR Collaboration are already probing close to
the Planck scale, and significant increases in sensitivity are feasible.
| [
{
"created": "Fri, 14 May 1999 15:52:40 GMT",
"version": "v1"
}
] | 2009-09-11 | [
[
"Ellis",
"John.",
""
],
[
"Mavromatos",
"N. E.",
""
],
[
"Nanopoulos",
"D. V.",
""
]
] | A satisfactory theory of quantum gravity may necessitate a drastic modification of our perception of space-time, by giving it a foamy structure at distances comparable to the Planck length. It is argued in this essay that the experimental detection of such structures may be a realistic possibility in the foreseeable future. After a brief review of different theoretical approaches to quantum gravity and the relationships between them, we discuss various possible experimental tests of the quantum nature of space-time. Observations of photons from distant astrophysical sources such as Gamma-Ray Bursters and laboratory experiments on neutral kaon decays may be sensitive to quantum-gravitational effects if they are only minimally suppressed. Experimental limits from the Whipple Observatory and the CPLEAR Collaboration are already probing close to the Planck scale, and significant increases in sensitivity are feasible. |
1510.02560 | Shao-Wen Wei | Shao-Wen Wei, Yu-Xiao Liu, Chun-E Fu | Null geodesics and gravitational lensing in a nonsingular spacetime | 15 pages, 5 figures, 1 table | Adv.High Energy Phys. 2015 (2015) 454217 | 10.1155/2015/454217 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, the null geodesics and gravitational lensing in a nonsingular
spacetime are investigated. According to the nature of the null geodesics, the
spacetime is divided into several cases. In the weak deflection limit, we find
the influence of the nonsingularity parameter $q$ on the positions and
magnifications of the images is negligible. In the strong deflection limit, the
coefficients and observables for the gravitational lensing in a nonsingular
black hole background and a weakly nonsingular spacetime are obtained.
Comparing these results, we find that, in a weakly nonsingular spacetime, the
relativistic images have smaller angular position and relative magnification,
but larger angular separation than that of a nonsingular black hole. These
results might offer a way to probe the spacetime nonsingularity parameter and
put a bound on it by the astronomical instruments in the near future.
| [
{
"created": "Fri, 9 Oct 2015 03:32:02 GMT",
"version": "v1"
}
] | 2015-10-12 | [
[
"Wei",
"Shao-Wen",
""
],
[
"Liu",
"Yu-Xiao",
""
],
[
"Fu",
"Chun-E",
""
]
] | In this paper, the null geodesics and gravitational lensing in a nonsingular spacetime are investigated. According to the nature of the null geodesics, the spacetime is divided into several cases. In the weak deflection limit, we find the influence of the nonsingularity parameter $q$ on the positions and magnifications of the images is negligible. In the strong deflection limit, the coefficients and observables for the gravitational lensing in a nonsingular black hole background and a weakly nonsingular spacetime are obtained. Comparing these results, we find that, in a weakly nonsingular spacetime, the relativistic images have smaller angular position and relative magnification, but larger angular separation than that of a nonsingular black hole. These results might offer a way to probe the spacetime nonsingularity parameter and put a bound on it by the astronomical instruments in the near future. |
gr-qc/0004012 | Luc Blanchet | Luc Blanchet | Post-Newtonian Gravitational Radiation | 46 pages, in Einstein's Field Equations and Their Physical
Implications, B. Schmidt (Ed.), Lecture Notes in Physics, Springer | Lect.Notes Phys.540:225-272,2000 | null | null | gr-qc | null | 1 Introduction 2 Multipole Decomposition 3 Source Multipole Moments 4
Post-Minkowskian Approximation 5 Radiative Multipole Moments 6 Post-Newtonian
Approximation 7 Point-Particles 8 Conclusion
| [
{
"created": "Tue, 4 Apr 2000 16:01:33 GMT",
"version": "v1"
}
] | 2011-07-19 | [
[
"Blanchet",
"Luc",
""
]
] | 1 Introduction 2 Multipole Decomposition 3 Source Multipole Moments 4 Post-Minkowskian Approximation 5 Radiative Multipole Moments 6 Post-Newtonian Approximation 7 Point-Particles 8 Conclusion |
2110.00556 | Nephtal\'i Eliceo Mart\'inez P\'erez | N.E. Mart\'inez-P\'erez, C. Ram\'irez and V. V\'azquez-B\'aez | 1D Supergravity FLRW Model of Starobinsky | 17 pages, 2 figures | Universe 2021, 7(11), 449 | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We study two homogeneous supersymmetric extensions for the $f(R)$ modified
gravity model of Starobinsky with the FLRW metric. The actions are defined in
terms of a superfield $\mathcal{R}$ that contains the FLRW scalar curvature.
One model has N=1 local supersymmetry, and its bosonic sector is the
Starobinsky action; the other action has N=2, its bosonic sector contains, in
additional to Starobinsky, a massive scalar field without self-interaction. As
expected, the bosonic sectors of these models are consistent with cosmic
inflation, as we show by solving numerically the classical dynamics. Inflation
is driven by the $R^2$ term during the large curvature regime. In the N=2 case,
the additional scalar field remains in a low energy state during inflation.
Further, by means of an additional superfield, we write equivalent
tensor-scalar-like actions from which we can give the Hamiltonian formulation.
| [
{
"created": "Fri, 1 Oct 2021 17:35:38 GMT",
"version": "v1"
},
{
"created": "Sat, 20 Nov 2021 21:53:16 GMT",
"version": "v2"
}
] | 2021-11-23 | [
[
"Martínez-Pérez",
"N. E.",
""
],
[
"Ramírez",
"C.",
""
],
[
"Vázquez-Báez",
"V.",
""
]
] | We study two homogeneous supersymmetric extensions for the $f(R)$ modified gravity model of Starobinsky with the FLRW metric. The actions are defined in terms of a superfield $\mathcal{R}$ that contains the FLRW scalar curvature. One model has N=1 local supersymmetry, and its bosonic sector is the Starobinsky action; the other action has N=2, its bosonic sector contains, in additional to Starobinsky, a massive scalar field without self-interaction. As expected, the bosonic sectors of these models are consistent with cosmic inflation, as we show by solving numerically the classical dynamics. Inflation is driven by the $R^2$ term during the large curvature regime. In the N=2 case, the additional scalar field remains in a low energy state during inflation. Further, by means of an additional superfield, we write equivalent tensor-scalar-like actions from which we can give the Hamiltonian formulation. |
gr-qc/0501048 | Alfredo Macias | Claus Laemmerzahl, Alfredo Macias, and Holger Mueller | Lorentz invariance violation and charge (non--)conservation: A general
theoretical frame for extensions of the Maxwell equations | To appear in Physical Review D | Phys.Rev.D71:025007,2005 | 10.1103/PhysRevD.71.025007 | null | gr-qc | null | All quantum gravity approaches lead to small modifications in the standard
laws of physics which lead to violations of Lorentz invariance. One particular
example is the extended standard model (SME). Here, a general phenomenological
approach for extensions of the Maxwell equations is presented which turns out
to be more general than the SME and which covers charge non--conservation
(CNC), too. The new Lorentz invariance violating terms cannot be probed by
optical experiments but need, instead, the exploration of the electromagnetic
field created by a point charge or a magnetic dipole. Some scalar--tensor
theories and higher dimensional brane theories predict CNC in four dimensions
and some models violating Special Relativity have been shown to be connected
with CNC and its relation to the Einstein Equivalence Principle has been
discussed. Due to this upcoming interest, the experimental status of electric
charge conservation is reviewed. Up to now there seem to exist no unique tests
of charge conservation. CNC is related to the precession of polarization, to a
modification of the $1/r$--Coulomb potential, and to a time-dependence of the
fine structure constant. This gives the opportunity to describe a dedicated
search for CNC.
| [
{
"created": "Fri, 14 Jan 2005 18:20:29 GMT",
"version": "v1"
}
] | 2011-07-19 | [
[
"Laemmerzahl",
"Claus",
""
],
[
"Macias",
"Alfredo",
""
],
[
"Mueller",
"Holger",
""
]
] | All quantum gravity approaches lead to small modifications in the standard laws of physics which lead to violations of Lorentz invariance. One particular example is the extended standard model (SME). Here, a general phenomenological approach for extensions of the Maxwell equations is presented which turns out to be more general than the SME and which covers charge non--conservation (CNC), too. The new Lorentz invariance violating terms cannot be probed by optical experiments but need, instead, the exploration of the electromagnetic field created by a point charge or a magnetic dipole. Some scalar--tensor theories and higher dimensional brane theories predict CNC in four dimensions and some models violating Special Relativity have been shown to be connected with CNC and its relation to the Einstein Equivalence Principle has been discussed. Due to this upcoming interest, the experimental status of electric charge conservation is reviewed. Up to now there seem to exist no unique tests of charge conservation. CNC is related to the precession of polarization, to a modification of the $1/r$--Coulomb potential, and to a time-dependence of the fine structure constant. This gives the opportunity to describe a dedicated search for CNC. |
1402.2785 | Dmitry Shogin | Dmitry Shogin and Sigbj{\o}rn Hervik | Dynamics of tilted Bianchi models of types III, IV, V in presence of
diffusion | 26 pages, 8 figures | Class. Quant. Grav. 32 (2015) 055008 | 10.1088/0264-9381/32/5/055008 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the three types of class B Bianchi cosmologies filled with a
tilted perfect fluid undergoing velocity diffusion in a scalar field
background. We consider the two most importantcases: dust and radiation. A
complete numerical integration of the Einstein field equations coupled with the
diffusion equations is done to demonstrate how the presence of diffusion can
affect the dynamics of cosmological evolution, where the most attention is paid
to changes to the late-time behaviour. We show that aside from quantitative
effects, diffusion can result in significant qualitative differences. For
example, the cosmologies may recollapse if diffusion is sufficiently strong, or
evolve towards the de Sitter state otherwise. In constrast to the diffusionless
case, radiation isotropizes in presence of diffusion, and the tilt decreases
exponentially at later times: $V\sim e^{-0.25\tau}$; also, we determine the
decay rates of energy density, which become slower when the diffusion term is
non-zero.
| [
{
"created": "Wed, 12 Feb 2014 11:03:16 GMT",
"version": "v1"
},
{
"created": "Sat, 6 Dec 2014 09:43:37 GMT",
"version": "v2"
}
] | 2015-02-05 | [
[
"Shogin",
"Dmitry",
""
],
[
"Hervik",
"Sigbjørn",
""
]
] | We investigate the three types of class B Bianchi cosmologies filled with a tilted perfect fluid undergoing velocity diffusion in a scalar field background. We consider the two most importantcases: dust and radiation. A complete numerical integration of the Einstein field equations coupled with the diffusion equations is done to demonstrate how the presence of diffusion can affect the dynamics of cosmological evolution, where the most attention is paid to changes to the late-time behaviour. We show that aside from quantitative effects, diffusion can result in significant qualitative differences. For example, the cosmologies may recollapse if diffusion is sufficiently strong, or evolve towards the de Sitter state otherwise. In constrast to the diffusionless case, radiation isotropizes in presence of diffusion, and the tilt decreases exponentially at later times: $V\sim e^{-0.25\tau}$; also, we determine the decay rates of energy density, which become slower when the diffusion term is non-zero. |
gr-qc/9907012 | Sungwon | S.-W. Kim and S. P. Kim | The traversable wormhole with classical scalar fields | 10 pages, Revtex. | Phys.Rev. D58 (1998) 087703 | 10.1103/PhysRevD.58.087703 | null | gr-qc | null | We study the Lorentzian static traversable wormholes coupled to quadratic
scalar fields. We also obtain the solutions of the scalar fields and matters in
the wormhole background and find that the minimal size of the wormhole should
be quantized under the appropriate boundary conditions for the positive
non-minimal massive scalar field.
| [
{
"created": "Mon, 5 Jul 1999 05:03:53 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Kim",
"S. -W.",
""
],
[
"Kim",
"S. P.",
""
]
] | We study the Lorentzian static traversable wormholes coupled to quadratic scalar fields. We also obtain the solutions of the scalar fields and matters in the wormhole background and find that the minimal size of the wormhole should be quantized under the appropriate boundary conditions for the positive non-minimal massive scalar field. |
2104.06005 | Christiane Klein | Christiane Klein and Jochen Zahn | The renormalized charged scalar current in the Reissner-Nordstr\"om-de
Sitter spacetime | 12 pages, 5 figures, version as accepted for PRD | Phys. Rev. D 104, 025009 (2021) | 10.1103/PhysRevD.104.025009 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We perform a Hadamard point-split renormalization of the current density
$j_\nu$ of a charged scalar field in a Reissner-Nordstr\"om-de Sitter
spacetime. We compute numerically the expectation values of the components
$j_r$ and $j_t$ in the Unruh state in the exterior region and study their
dependence on the field parameters and the position.
| [
{
"created": "Tue, 13 Apr 2021 08:15:11 GMT",
"version": "v1"
},
{
"created": "Fri, 16 Jul 2021 06:55:08 GMT",
"version": "v2"
}
] | 2021-07-19 | [
[
"Klein",
"Christiane",
""
],
[
"Zahn",
"Jochen",
""
]
] | We perform a Hadamard point-split renormalization of the current density $j_\nu$ of a charged scalar field in a Reissner-Nordstr\"om-de Sitter spacetime. We compute numerically the expectation values of the components $j_r$ and $j_t$ in the Unruh state in the exterior region and study their dependence on the field parameters and the position. |
1302.6983 | Jose Geraldo Pereira | J. G. Pereira | Teleparallelism: A New Insight Into Gravity | Chapter to appear in "Handbook of Spacetime", edited by A. Ashtekar
and V. Petcov (Springer, Berlin, 2013). V2: misprints corrected, references
updated | null | 10.1007/978-3-642-41992-8_11 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Teleparallel gravity, a gauge theory for the translation group, turns up as
fully equivalent to Einstein's general relativity. In spite of this
equivalence, it provides a whole new insight into gravitation. It breaks
several paradigms related to the geometric approach of general relativity, and
introduces new concepts in the description of the gravitational interaction.
The purpose of this chapter is to explore some of these concepts, as well as
discuss possible consequences for gravitation, mainly those that could be
relevant for the quantization of the gravitational field.
| [
{
"created": "Wed, 27 Feb 2013 20:31:12 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Aug 2014 16:36:19 GMT",
"version": "v2"
}
] | 2015-06-15 | [
[
"Pereira",
"J. G.",
""
]
] | Teleparallel gravity, a gauge theory for the translation group, turns up as fully equivalent to Einstein's general relativity. In spite of this equivalence, it provides a whole new insight into gravitation. It breaks several paradigms related to the geometric approach of general relativity, and introduces new concepts in the description of the gravitational interaction. The purpose of this chapter is to explore some of these concepts, as well as discuss possible consequences for gravitation, mainly those that could be relevant for the quantization of the gravitational field. |
1506.01271 | Walter Simon | Piotr Bizo\'n, Stefan Pletka and Walter Simon | Initial data for rotating cosmologies | 22p; corrects typos of version 3, and of published version | Class. Quantum Grav. 32 (2015) 175015 | 10.1088/0264-9381/32/17/175015 | UWThPh-2015-15 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We revisit the construction of maximal initial data on compact manifolds in
vacuum with positive cosmological constant via the conformal method. We
discuss, extend and apply recent results of Hebey et al. [19] and Premoselli
[31] which yield existence, non-existence, (non-)uniqueness and
(linearisation-) stability of solutions of the Lichnerowicz equation, depending
on its coefficients. We then focus on so-called $(t,\varphi)$-symmetric data as
"seed manifolds", and in particular on Bowen-York data on the round hypertorus
$\mathbb{S}^2 \times \mathbb{S}$ (a slice of Nariai) and on Kerr-deSitter. In
the former case, we clarify the bifurcation structure of the axially symmetric
solutions of the Lichnerowicz equation in terms of the angular momentum as
bifurcation parameter, using a combination of analytical and numerical
techniques. As to the latter example, we show how dynamical data can be
constructed in a natural way via conformal rescalings of Kerr-deSitter data.
| [
{
"created": "Wed, 3 Jun 2015 15:04:47 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Jun 2015 16:39:06 GMT",
"version": "v2"
},
{
"created": "Fri, 28 Aug 2015 15:08:29 GMT",
"version": "v3"
},
{
"created": "Fri, 18 Mar 2016 10:44:36 GMT",
"version": "v4"
}
] | 2016-03-21 | [
[
"Bizoń",
"Piotr",
""
],
[
"Pletka",
"Stefan",
""
],
[
"Simon",
"Walter",
""
]
] | We revisit the construction of maximal initial data on compact manifolds in vacuum with positive cosmological constant via the conformal method. We discuss, extend and apply recent results of Hebey et al. [19] and Premoselli [31] which yield existence, non-existence, (non-)uniqueness and (linearisation-) stability of solutions of the Lichnerowicz equation, depending on its coefficients. We then focus on so-called $(t,\varphi)$-symmetric data as "seed manifolds", and in particular on Bowen-York data on the round hypertorus $\mathbb{S}^2 \times \mathbb{S}$ (a slice of Nariai) and on Kerr-deSitter. In the former case, we clarify the bifurcation structure of the axially symmetric solutions of the Lichnerowicz equation in terms of the angular momentum as bifurcation parameter, using a combination of analytical and numerical techniques. As to the latter example, we show how dynamical data can be constructed in a natural way via conformal rescalings of Kerr-deSitter data. |
gr-qc/9910112 | null | M. A. Clayton and J. W. Moffat | Scalar-Tensor Gravity Theory For Dynamical Light Velocity | 14 pages latex file. Additional material added. Accepted for
publication in Physics Letters B | Phys.Lett. B477 (2000) 269-275 | 10.1016/S0370-2693(00)00192-1 | UTPT-99 | gr-qc astro-ph hep-ph | null | A gravity theory is developed with the metric ${\hat g}_{\mu\nu}=
{g}_{\mu\nu}+B\partial_\mu\phi\partial_\nu\phi$. In the present universe the
additional contribution from the scalar field in the metric ${\hat g}_{\mu\nu}$
can generate an acceleration in the expansion of the universe, without negative
pressure and with a zero cosmological constant. In this theory, gravitational
waves will propagate at a different speed from non-gravitational waves. It is
suggested that gravitational wave experiments could test this observational
signature.
| [
{
"created": "Sun, 31 Oct 1999 22:09:24 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Feb 2000 22:41:13 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Clayton",
"M. A.",
""
],
[
"Moffat",
"J. W.",
""
]
] | A gravity theory is developed with the metric ${\hat g}_{\mu\nu}= {g}_{\mu\nu}+B\partial_\mu\phi\partial_\nu\phi$. In the present universe the additional contribution from the scalar field in the metric ${\hat g}_{\mu\nu}$ can generate an acceleration in the expansion of the universe, without negative pressure and with a zero cosmological constant. In this theory, gravitational waves will propagate at a different speed from non-gravitational waves. It is suggested that gravitational wave experiments could test this observational signature. |
1710.03438 | Andrzej Rostworowski | Piotr Bizo\'n, Andrzej Rostworowski | Gravitational turbulent instability of AdS${}_5$ | talk given at Strings2014, Princeton, June 2014 | Acta Phys.Polon. B48 (2017) 1375 | 10.5506/APhysPolB.48.1375 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the problem of stability of anti-de Sitter spacetime in five
dimensions under small purely gravitational perturbations satisfying the
cohomogeneity-two biaxial Bianchi IX ansatz. In analogy to spherically
symmetric scalar perturbations, we observe numerically a black hole formation
on the time-scale $\mathcal{O}(\varepsilon^{-2})$, where $\varepsilon$ is the
size of the perturbation.
| [
{
"created": "Tue, 10 Oct 2017 08:08:36 GMT",
"version": "v1"
}
] | 2017-10-11 | [
[
"Bizoń",
"Piotr",
""
],
[
"Rostworowski",
"Andrzej",
""
]
] | We consider the problem of stability of anti-de Sitter spacetime in five dimensions under small purely gravitational perturbations satisfying the cohomogeneity-two biaxial Bianchi IX ansatz. In analogy to spherically symmetric scalar perturbations, we observe numerically a black hole formation on the time-scale $\mathcal{O}(\varepsilon^{-2})$, where $\varepsilon$ is the size of the perturbation. |
1408.5324 | Chen Songbai | Songbai Chen, Jiliang Jing | Dynamical evolution of a vector field perturbation coupling to Einstein
tensor | 19 pages; 10 figures. Title is changed and the mistakes are
corrected. Accepted by PRD for publication. arXiv admin note: text overlap
with arXiv:1307.7459 | Phys.Rev. D 90, 124059 (2014) | 10.1103/PhysRevD.90.124059 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We have investigated the wave dynamics of a vector field perturbation
coupling to Einstein tensor in the four-dimensional Reissner-Nordstr\"{o}m
black hole spacetime. Our results show that besides the dependence on the
coupling between the vector field and Einstein tensor, the wave dynamic
equation of the vector field perturbation strongly depends on the parity of the
perturbation itself, which is quite different from that of the usual vector
field perturbation without the coupling in the four-dimensional spacetime.
Moreover, we also find that the vector field perturbation with odd parity grows
with exponential rate if the coupling strength is stronger than certain a
critical value. However, the vector field perturbation with even parity always
decays in the Reissner-Nordstr\"{o}m black hole spacetime.
| [
{
"created": "Fri, 22 Aug 2014 15:25:21 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Dec 2014 02:49:37 GMT",
"version": "v2"
}
] | 2015-06-22 | [
[
"Chen",
"Songbai",
""
],
[
"Jing",
"Jiliang",
""
]
] | We have investigated the wave dynamics of a vector field perturbation coupling to Einstein tensor in the four-dimensional Reissner-Nordstr\"{o}m black hole spacetime. Our results show that besides the dependence on the coupling between the vector field and Einstein tensor, the wave dynamic equation of the vector field perturbation strongly depends on the parity of the perturbation itself, which is quite different from that of the usual vector field perturbation without the coupling in the four-dimensional spacetime. Moreover, we also find that the vector field perturbation with odd parity grows with exponential rate if the coupling strength is stronger than certain a critical value. However, the vector field perturbation with even parity always decays in the Reissner-Nordstr\"{o}m black hole spacetime. |
0806.3289 | Galin Gyulchev | Galin N. Gyulchev, Stoytcho S. Yazadjiev | Gravitational Lensing by Rotating Naked Singularities | 35 pages, 30 figures | Phys.Rev.D78:083004,2008 | 10.1103/PhysRevD.78.083004 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We model massive compact objects in galactic nuclei as stationary,
axially-symmetric naked singularities in the Einstein-massless scalar field
theory and study the resulting gravitational lensing. In the weak deflection
limit we study analytically the position of the two weak field images, the
corresponding signed and absolute magnifications as well as the centroid up to
post-Newtonian order. We show that there are a static post-Newtonian
corrections to the signed magnification and their sum as well as to the
critical curves, which are function of the scalar charge. The shift of the
critical curves as a function of the lens angular momentum is found, and it is
shown that they decrease slightingly for the weakly naked and vastly for the
strongly naked singularities with the increase of the scalar charge. The
point-like caustics drift away from the optical axis and do not depend on the
scalar charge. In the strong deflection limit approximation we compute
numerically the position of the relativistic images and their separability for
weakly naked singularities. All of the lensing quantities are compared to
particular cases as Schwarzschild and Kerr black holes as well as
Janis--Newman--Winicour naked singularities.
| [
{
"created": "Thu, 19 Jun 2008 18:10:42 GMT",
"version": "v1"
}
] | 2008-12-18 | [
[
"Gyulchev",
"Galin N.",
""
],
[
"Yazadjiev",
"Stoytcho S.",
""
]
] | We model massive compact objects in galactic nuclei as stationary, axially-symmetric naked singularities in the Einstein-massless scalar field theory and study the resulting gravitational lensing. In the weak deflection limit we study analytically the position of the two weak field images, the corresponding signed and absolute magnifications as well as the centroid up to post-Newtonian order. We show that there are a static post-Newtonian corrections to the signed magnification and their sum as well as to the critical curves, which are function of the scalar charge. The shift of the critical curves as a function of the lens angular momentum is found, and it is shown that they decrease slightingly for the weakly naked and vastly for the strongly naked singularities with the increase of the scalar charge. The point-like caustics drift away from the optical axis and do not depend on the scalar charge. In the strong deflection limit approximation we compute numerically the position of the relativistic images and their separability for weakly naked singularities. All of the lensing quantities are compared to particular cases as Schwarzschild and Kerr black holes as well as Janis--Newman--Winicour naked singularities. |
1704.05790 | Maxime Van de Moortel | Maxime Van de Moortel | Stability and instability of the sub-extremal Reissner-Nordstr\"om black
hole interior for the Einstein-Maxwell-Klein-Gordon equations in spherical
symmetry | 46 pages, 4 figures Correction of a few typos. Version accepted for
publication in Communications in Mathematical Physics | null | 10.1007/s00220-017-3079-3 | null | gr-qc math-ph math.AP math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show non-linear stability and instability results in spherical symmetry
for the interior of a charged black hole -approaching a sub-extremal
Reissner-Nordstr\"om background fast enough at infinity- in presence of a
massive and charged scalar field, motivated by the strong cosmic censorship
conjecture in that setting :
1. Stability : We prove that spherically symmetric characteristic initial
data to the Einstein-Maxwell- Klein-Gordon equations approaching a
Reissner-Nordstr\"om background with a sufficiently decaying polynomial decay
rate on the event horizon gives rise to a space-time possessing a Cauchy
horizon in a neighbourhood of time-like infinity. Moreover if the decay is even
stronger, we prove that the spacetime metric admits a continuous extension to
the Cauchy horizon. This generalizes the celebrated stability result of
Dafermos for Einstein-Maxwell-real-scalar-field in spherical symmetry.
2. Instability : We prove that for the class of space-times considered in the
stability part, whose scalar field in addition obeys a polynomial averaged-L^2
(consistent) lower bound on the event horizon, the scalar field obeys an
integrated lower bound transversally to the Cauchy horizon. As a consequence we
prove that the non-degenerate energy is infinite on any null surface crossing
the Cauchy horizon and the curvature of a geodesic vector field blows up at the
Cauchy horizon near time-like infinity. This generalizes an instability result
due to Luk and Oh for Einstein-Maxwell-real-scalar-field in spherical symmetry.
This instability of the black hole interior can also be viewed as a step
towards the resolution of the C^2 strong cosmic censorship conjecture for
one-ended asymptotically initial data.
| [
{
"created": "Wed, 19 Apr 2017 15:59:40 GMT",
"version": "v1"
},
{
"created": "Thu, 4 May 2017 03:31:00 GMT",
"version": "v2"
},
{
"created": "Fri, 17 Nov 2017 19:36:57 GMT",
"version": "v3"
}
] | 2018-03-14 | [
[
"Van de Moortel",
"Maxime",
""
]
] | We show non-linear stability and instability results in spherical symmetry for the interior of a charged black hole -approaching a sub-extremal Reissner-Nordstr\"om background fast enough at infinity- in presence of a massive and charged scalar field, motivated by the strong cosmic censorship conjecture in that setting : 1. Stability : We prove that spherically symmetric characteristic initial data to the Einstein-Maxwell- Klein-Gordon equations approaching a Reissner-Nordstr\"om background with a sufficiently decaying polynomial decay rate on the event horizon gives rise to a space-time possessing a Cauchy horizon in a neighbourhood of time-like infinity. Moreover if the decay is even stronger, we prove that the spacetime metric admits a continuous extension to the Cauchy horizon. This generalizes the celebrated stability result of Dafermos for Einstein-Maxwell-real-scalar-field in spherical symmetry. 2. Instability : We prove that for the class of space-times considered in the stability part, whose scalar field in addition obeys a polynomial averaged-L^2 (consistent) lower bound on the event horizon, the scalar field obeys an integrated lower bound transversally to the Cauchy horizon. As a consequence we prove that the non-degenerate energy is infinite on any null surface crossing the Cauchy horizon and the curvature of a geodesic vector field blows up at the Cauchy horizon near time-like infinity. This generalizes an instability result due to Luk and Oh for Einstein-Maxwell-real-scalar-field in spherical symmetry. This instability of the black hole interior can also be viewed as a step towards the resolution of the C^2 strong cosmic censorship conjecture for one-ended asymptotically initial data. |
gr-qc/0608065 | Jose M. M. Senovilla | Jos\'e M.M. Senovilla | The universal 'energy' operator | 13 pages, no figures; minor improvements and corrections. This is a
larger, expanded version, containing proofs and explanations not available in
the short Note to be published in CQG | Class.Quant.Grav. 23 (2006) 7143-7148 | 10.1088/0264-9381/23/23/N01 | null | gr-qc | null | The "positive square" of any tensor is presented in a universal and unified
manner, valid in Lorentzian manifolds of arbitrary dimension, and independently
of any (anti)-symmetry properties of the tensor. For rank-m tensors, the
positive square has rank 2m. Positive here means future, that is to say,
satisfying the dominant property. The standard energy-momentum and super-energy
tensors are recovered as appropriate parts of the general square. A richer
structure of principal null directions arises.
| [
{
"created": "Sat, 12 Aug 2006 16:08:25 GMT",
"version": "v1"
},
{
"created": "Thu, 5 Oct 2006 09:03:17 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Senovilla",
"José M. M.",
""
]
] | The "positive square" of any tensor is presented in a universal and unified manner, valid in Lorentzian manifolds of arbitrary dimension, and independently of any (anti)-symmetry properties of the tensor. For rank-m tensors, the positive square has rank 2m. Positive here means future, that is to say, satisfying the dominant property. The standard energy-momentum and super-energy tensors are recovered as appropriate parts of the general square. A richer structure of principal null directions arises. |
2103.17108 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | On wormholes in spacetimes of embedding class one | 8 pages, no figures | Fund. J. Math. Phys., vol. 9, pages 21-33, 2021 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An $n$-dimensional Riemannian space is said to be of embedding class $m$ if
$n+m$ is the lowest dimension of the flat space in which the given space can be
embedded. A spherically symmetric spacetime of class two can be reduced to
class one by a suitable transformation of coordinates. Applied to wormholes,
given a well-defined shape function $b=b(r)$, the resulting wormhole has an
event horizon and is therefore nontraversable. On a macroscopic scale, $b(r)$
can be replaced by $m(r)$, the effective mass of a spherical star of radius $r$
with $m(0)=0$, to yield a valid solution. Spacetimes of embedding class one
have been used successfully for modeling compact stellar objects. On a
microscopic scale, one can invoke noncommutative geometry to obtain a charged
nontraversable wormhole, i.e., an Einstein-Rosen bridge, and hence a model for
a charged particle.
| [
{
"created": "Wed, 31 Mar 2021 14:24:43 GMT",
"version": "v1"
},
{
"created": "Sat, 10 Apr 2021 15:03:58 GMT",
"version": "v2"
}
] | 2021-04-13 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | An $n$-dimensional Riemannian space is said to be of embedding class $m$ if $n+m$ is the lowest dimension of the flat space in which the given space can be embedded. A spherically symmetric spacetime of class two can be reduced to class one by a suitable transformation of coordinates. Applied to wormholes, given a well-defined shape function $b=b(r)$, the resulting wormhole has an event horizon and is therefore nontraversable. On a macroscopic scale, $b(r)$ can be replaced by $m(r)$, the effective mass of a spherical star of radius $r$ with $m(0)=0$, to yield a valid solution. Spacetimes of embedding class one have been used successfully for modeling compact stellar objects. On a microscopic scale, one can invoke noncommutative geometry to obtain a charged nontraversable wormhole, i.e., an Einstein-Rosen bridge, and hence a model for a charged particle. |
2106.05097 | Le\"ila Haegel | Le\"ila Haegel | Searching for new physics during gravitational waves propagation | Contribution to the 2021 Gravitation session of the 55th Rencontres
de Moriond | null | null | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/4.0/ | The direct detection of gravitational waves by ground-based interferometers
opened an unprecedented channel to probe alternative theories of gravitation.
Several theories predict a dispersion of the gravitational waves during their
propagation, distorting the signals observed by LIGO and Virgo compared to
their predictions from general relativity. Such dispersion could induce a
modification of the luminosity distance inferred with gravitational radiation
with regards to electromagnetic radiation. By analysing two multimessenger
events, we set constraints on a large class of proposed theories, including
extra-dimensional and scalar-tensor theories. The multimessenger events are the
binary neutron star merger GW170817 associated to GRB170817A, and the binary
black hole merger GW190521 with postulated candidate electromagnetic
counterpart ZTF19abanrhr. Without relying on multimessenger emission, a class
of proposed theories predict a frequency-dependent dispersion of the
gravitational waves breaking Lorentz invariance. By analysing 31 GW events from
binary-black holes coalescence, we constrain several coefficients
parameterising Lorentz violation, including the best constraint on the graviton
mass.
| [
{
"created": "Wed, 9 Jun 2021 14:22:46 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Jun 2021 14:08:33 GMT",
"version": "v2"
},
{
"created": "Tue, 29 Jun 2021 15:55:33 GMT",
"version": "v3"
}
] | 2021-06-30 | [
[
"Haegel",
"Leïla",
""
]
] | The direct detection of gravitational waves by ground-based interferometers opened an unprecedented channel to probe alternative theories of gravitation. Several theories predict a dispersion of the gravitational waves during their propagation, distorting the signals observed by LIGO and Virgo compared to their predictions from general relativity. Such dispersion could induce a modification of the luminosity distance inferred with gravitational radiation with regards to electromagnetic radiation. By analysing two multimessenger events, we set constraints on a large class of proposed theories, including extra-dimensional and scalar-tensor theories. The multimessenger events are the binary neutron star merger GW170817 associated to GRB170817A, and the binary black hole merger GW190521 with postulated candidate electromagnetic counterpart ZTF19abanrhr. Without relying on multimessenger emission, a class of proposed theories predict a frequency-dependent dispersion of the gravitational waves breaking Lorentz invariance. By analysing 31 GW events from binary-black holes coalescence, we constrain several coefficients parameterising Lorentz violation, including the best constraint on the graviton mass. |
gr-qc/0407028 | Carlos Bessa | C. H. G. Bessa and J. A. S. Lima | On the existence of turning points in D-dimensionsal Schwarzschild-de
Sitter and anti-de Sitter spacetimes | 7 pages, no figures, accepted for publication in IJMPD | Int.J.Mod.Phys. D13 (2004) 1217-1222 | 10.1142/S0218271804005341 | null | gr-qc | null | We investigate the motion of a test particle in a d-dimensional, spherically
symmetric and static space-time supported by a mass $M$ plus a $\Lambda$-term.
The motion is strongly dependent on the sign of $\Lambda$. In Schwarzschild-de
Sitter (SdS) space-time ($\Lambda > 0$), besides the physical singularity at
$r=0$ there are cases with two horizons and two turning points, one horizon and
one turning point and the complete absence of horizon and turning points. For
Schwarzschild-Anti de Sitter (SAdS) space-time ($\Lambda < 0$) the horizon
coordinate is associated to a unique turning point.
| [
{
"created": "Wed, 7 Jul 2004 20:03:30 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Bessa",
"C. H. G.",
""
],
[
"Lima",
"J. A. S.",
""
]
] | We investigate the motion of a test particle in a d-dimensional, spherically symmetric and static space-time supported by a mass $M$ plus a $\Lambda$-term. The motion is strongly dependent on the sign of $\Lambda$. In Schwarzschild-de Sitter (SdS) space-time ($\Lambda > 0$), besides the physical singularity at $r=0$ there are cases with two horizons and two turning points, one horizon and one turning point and the complete absence of horizon and turning points. For Schwarzschild-Anti de Sitter (SAdS) space-time ($\Lambda < 0$) the horizon coordinate is associated to a unique turning point. |
1704.01476 | Amir Masoud Ghezelbash | A. M. Ghezelbash, V. Kumar | Exact helicoidal and catenoidal solutions in Einstein-Maxwell theory | 16 pages, 8 figures, typos corrected, references added | Phys. Rev. D95, 124045 (2017) | 10.1103/PhysRevD.95.124045 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present several new exact solutions in five and higher dimensional
Einstein-Maxwell theory by embedding the Nutku instanton. The metric functions
for the five-dimensional solutions depend only on a radial coordinate and on
two spatial coordinates for the six and higher dimensional solutions. The six
and higher dimensional metric functions are convoluted-like integrals of two
special functions. We find that the solutions are regular almost everywhere and
some spatial sections of the solution describe wormhole handles. We also find a
class of exact and nonstationary convoluted-like solutions to the
Einstein-Maxwell theory with a cosmological constant.
| [
{
"created": "Wed, 5 Apr 2017 15:16:18 GMT",
"version": "v1"
},
{
"created": "Wed, 12 Apr 2017 11:44:05 GMT",
"version": "v2"
}
] | 2017-10-04 | [
[
"Ghezelbash",
"A. M.",
""
],
[
"Kumar",
"V.",
""
]
] | We present several new exact solutions in five and higher dimensional Einstein-Maxwell theory by embedding the Nutku instanton. The metric functions for the five-dimensional solutions depend only on a radial coordinate and on two spatial coordinates for the six and higher dimensional solutions. The six and higher dimensional metric functions are convoluted-like integrals of two special functions. We find that the solutions are regular almost everywhere and some spatial sections of the solution describe wormhole handles. We also find a class of exact and nonstationary convoluted-like solutions to the Einstein-Maxwell theory with a cosmological constant. |
1302.6506 | Hoang Nguyen | Hoang Ky Nguyen | Toward a theory of curvature-scaling gravity | 68 pages, 1 figure | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A salient feature of Horava gravity is the anisotropic time variable. We
propose an alternative construction of the spacetime manifold which naturally
enables time anisotropy. We promote the role of curvature: the Ricci scalar R
at a given point sets the length scales for physical processes - including
gravity - in the local inertial frames enclosing that point. The manifold is a
patchwork of local regions; each region is Lorentz invariant and adopts a local
scale a_R defined as a_R = 1/sqrt|R|. In each local patch, the length scales of
physical processes are measured relatively to a_R, and only their dimensionless
ratios partake in the dynamics of physical processes. Time anisotropy arises by
requiring that the form - but not necessarily the parameters - of physical laws
be unchanged under variations of the local a_R as one moves on the manifold.
The time scaling is found to be dt ~ a_R^(3/2) whereas the spatial part scales
as dx ~ a_R.
We show how to conjoin the local patches of the manifold in a way which
respects causality and special relativity, as well as the equivalence and
general covariance principles. All of Einstein's insights are preserved but the
parameters of physical laws are only valid locally and become functions of the
prevailing Ricci scalar. This alternative construction of the manifold permits
a unique choice for the Lagrangian of gravity coupled with matter. Curvature is
actively involved in the dynamics of physical processes by setting the scale
for them.
In vacuo our theory takes the form of R^2 gravity and adopts a larger set of
solutions superseding those of Einstein-Hilbert action R. We provide two
solutions: one solution connects our work to Mannheim's theory of galactic
rotation curves; the other leads to novel properties for Schwarzschild black
holes. We apply the theory to address problems in cosmology and discuss its
implications in quantum gravity.
| [
{
"created": "Tue, 26 Feb 2013 17:24:05 GMT",
"version": "v1"
}
] | 2013-02-27 | [
[
"Nguyen",
"Hoang Ky",
""
]
] | A salient feature of Horava gravity is the anisotropic time variable. We propose an alternative construction of the spacetime manifold which naturally enables time anisotropy. We promote the role of curvature: the Ricci scalar R at a given point sets the length scales for physical processes - including gravity - in the local inertial frames enclosing that point. The manifold is a patchwork of local regions; each region is Lorentz invariant and adopts a local scale a_R defined as a_R = 1/sqrt|R|. In each local patch, the length scales of physical processes are measured relatively to a_R, and only their dimensionless ratios partake in the dynamics of physical processes. Time anisotropy arises by requiring that the form - but not necessarily the parameters - of physical laws be unchanged under variations of the local a_R as one moves on the manifold. The time scaling is found to be dt ~ a_R^(3/2) whereas the spatial part scales as dx ~ a_R. We show how to conjoin the local patches of the manifold in a way which respects causality and special relativity, as well as the equivalence and general covariance principles. All of Einstein's insights are preserved but the parameters of physical laws are only valid locally and become functions of the prevailing Ricci scalar. This alternative construction of the manifold permits a unique choice for the Lagrangian of gravity coupled with matter. Curvature is actively involved in the dynamics of physical processes by setting the scale for them. In vacuo our theory takes the form of R^2 gravity and adopts a larger set of solutions superseding those of Einstein-Hilbert action R. We provide two solutions: one solution connects our work to Mannheim's theory of galactic rotation curves; the other leads to novel properties for Schwarzschild black holes. We apply the theory to address problems in cosmology and discuss its implications in quantum gravity. |
2108.02468 | Oliver Buchmueller | Leonardo Badurina, Oliver Buchmueller, John Ellis, Marek Lewicki,
Christopher McCabe, Ville Vaskonen | Prospective Sensitivities of Atom Interferometers to Gravitational Waves
and Ultralight Dark Matter | Chapter contribution to the theme issue Quantum Technologies in
Particle Physics for publication in Philosophical Transactions of the Royal
Society A. 18 pages and 12 figures | Phil. Trans. R. Soc. A.380 20210060, 2022 | 10.1098/rsta.2021.0060 | AION-REPORT/2021-04, KCL-PH-TH/2021-61, CERN-TH-2021-116 | gr-qc astro-ph.HE hep-ex hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We survey the prospective sensitivities of terrestrial and space-borne atom
interferometers (AIs) to gravitational waves (GWs) generated by cosmological
and astrophysical sources, and to ultralight dark matter. We discuss the
backgrounds from gravitational gradient noise (GGN) in terrestrial detectors,
and also binary pulsar and asteroid backgrounds in space-borne detectors. We
compare the sensitivities of LIGO and LISA with those of the 100m and 1km
stages of the AION terrestrial AI project, as well as two options for the
proposed AEDGE AI space mission with cold atom clouds either inside or outside
the spacecraft, considering as possible sources the mergers of black holes and
neutron stars, supernovae, phase transitions in the early Universe, cosmic
strings and quantum fluctuations in the early Universe that could have
generated primordial black holes. We also review the capabilities of AION and
AEDGE for detecting coherent waves of ultralight scalar dark matter.
| [
{
"created": "Thu, 5 Aug 2021 09:16:43 GMT",
"version": "v1"
},
{
"created": "Tue, 28 Dec 2021 10:44:26 GMT",
"version": "v2"
}
] | 2021-12-30 | [
[
"Badurina",
"Leonardo",
""
],
[
"Buchmueller",
"Oliver",
""
],
[
"Ellis",
"John",
""
],
[
"Lewicki",
"Marek",
""
],
[
"McCabe",
"Christopher",
""
],
[
"Vaskonen",
"Ville",
""
]
] | We survey the prospective sensitivities of terrestrial and space-borne atom interferometers (AIs) to gravitational waves (GWs) generated by cosmological and astrophysical sources, and to ultralight dark matter. We discuss the backgrounds from gravitational gradient noise (GGN) in terrestrial detectors, and also binary pulsar and asteroid backgrounds in space-borne detectors. We compare the sensitivities of LIGO and LISA with those of the 100m and 1km stages of the AION terrestrial AI project, as well as two options for the proposed AEDGE AI space mission with cold atom clouds either inside or outside the spacecraft, considering as possible sources the mergers of black holes and neutron stars, supernovae, phase transitions in the early Universe, cosmic strings and quantum fluctuations in the early Universe that could have generated primordial black holes. We also review the capabilities of AION and AEDGE for detecting coherent waves of ultralight scalar dark matter. |
gr-qc/0308060 | Wung-Hong Huang | Wung-Hong Huang | Effects of the Shear Viscosity on the Character of Cosmological
Evolution | null | J.Math.Phys. 31 (1990) 659-663 | 10.1063/1.528901 | null | gr-qc hep-th | null | Bianchi type I cosmological models are studied that contain a stiff fluid
with a shear viscosity that is a power function of the energy density, such as
$\zeta = \alpha \epsilon^n$. These models are analyzed by describing the
cosmological evolutions as the trajectories in the phase plane of Hubble
functions. The simple and exact equations that determine these flows are
obtained when $n$ is an integer. In particular, it is proved that there is no
Einstein initial singularity in the models of $0\leq n < 1$. Cosmologies are
found to begin with zero energy density and in the course of evolution the
gravitational field will create matter. At the final stage, cosmologies are
driven to the isotropic Fnedmann universe. It is also pointed out that although
the anisotropy will always be smoothed out asymptotically, there are solutions
that simultaneously possess non-positive and non-negative Hubble functions for
all time. This means that the cosmological dimensional reduction can work even
if the matter fluid having shear viscosity. These characteristics can also be
found in any-dimensional models.
| [
{
"created": "Tue, 19 Aug 2003 15:03:31 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Aug 2003 15:00:42 GMT",
"version": "v2"
}
] | 2016-08-31 | [
[
"Huang",
"Wung-Hong",
""
]
] | Bianchi type I cosmological models are studied that contain a stiff fluid with a shear viscosity that is a power function of the energy density, such as $\zeta = \alpha \epsilon^n$. These models are analyzed by describing the cosmological evolutions as the trajectories in the phase plane of Hubble functions. The simple and exact equations that determine these flows are obtained when $n$ is an integer. In particular, it is proved that there is no Einstein initial singularity in the models of $0\leq n < 1$. Cosmologies are found to begin with zero energy density and in the course of evolution the gravitational field will create matter. At the final stage, cosmologies are driven to the isotropic Fnedmann universe. It is also pointed out that although the anisotropy will always be smoothed out asymptotically, there are solutions that simultaneously possess non-positive and non-negative Hubble functions for all time. This means that the cosmological dimensional reduction can work even if the matter fluid having shear viscosity. These characteristics can also be found in any-dimensional models. |
2406.19224 | David Marcos Andrade Acosta Mr. | Vicente A. Ar\'evalo, David Andrade, Clara Rojas | Time evolution of Von Neumann entropy for a Kerr-Taub-NUT black hole | null | null | null | null | gr-qc | http://creativecommons.org/publicdomain/zero/1.0/ | In this work, we study the evolution of an evaporating black hole, described
by the Kerr--Taub--NUT metric, which emits scalar particles. We found that
allowing the black hole to radiate massless scalar particles increases the
angular momentum loss rate while decreasing the loss rate of the NUT parameter
and black hole mass. In fact, it means that angular momentum will disappear
faster than the other black hole parameters (mass and NUT parameter) during the
evaporation process. We also calculate the time evolution of the mass, angular
momentum, and NUT parameter in order to get the evolution of the Von Neumann
entropy of the black hole. We found that the entropy follows approximately the
so-called Page curve, where the $\beta$ parameter, which quantifies the amount
of radiation, affects the evaporation process. Implying that high $\beta$
values accelerate the evaporation process of a Kerr--Taub--NUT black hole.
| [
{
"created": "Thu, 27 Jun 2024 14:49:22 GMT",
"version": "v1"
}
] | 2024-06-28 | [
[
"Arévalo",
"Vicente A.",
""
],
[
"Andrade",
"David",
""
],
[
"Rojas",
"Clara",
""
]
] | In this work, we study the evolution of an evaporating black hole, described by the Kerr--Taub--NUT metric, which emits scalar particles. We found that allowing the black hole to radiate massless scalar particles increases the angular momentum loss rate while decreasing the loss rate of the NUT parameter and black hole mass. In fact, it means that angular momentum will disappear faster than the other black hole parameters (mass and NUT parameter) during the evaporation process. We also calculate the time evolution of the mass, angular momentum, and NUT parameter in order to get the evolution of the Von Neumann entropy of the black hole. We found that the entropy follows approximately the so-called Page curve, where the $\beta$ parameter, which quantifies the amount of radiation, affects the evaporation process. Implying that high $\beta$ values accelerate the evaporation process of a Kerr--Taub--NUT black hole. |
gr-qc/0511086 | Mohammad Mansouryar | Mohammad Mansouryar | On a macroscopic traversable spacewarp in practice | 44 pages, 8 Boxes of Figs, typos and one box corrected, one formula
and some links along with some new notes added, some references changed | null | null | null | gr-qc | null | A design of a configuration for violation of the averaged null energy
condition (ANEC) and consequently other classic energy conditions (CECs), is
presented. The methods of producing effective exotic matter (EM) for a
traversable wormhole (TW) are discussed. Also, the approaches of less necessity
of TWs to EM are considered. The result is, TW and similar structures; i.e.,
warp drive (WD) and Krasnikov tube are not just theoretical subjects for
teaching general relativity (GR) or objects only an advanced civilization would
be able to manufacture anymore, but a quite reachable challenge for current
technology. Besides, a new compound metric is introduced as a choice for
testing in the lab.
| [
{
"created": "Wed, 16 Nov 2005 13:31:52 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Jan 2006 16:50:09 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Mansouryar",
"Mohammad",
""
]
] | A design of a configuration for violation of the averaged null energy condition (ANEC) and consequently other classic energy conditions (CECs), is presented. The methods of producing effective exotic matter (EM) for a traversable wormhole (TW) are discussed. Also, the approaches of less necessity of TWs to EM are considered. The result is, TW and similar structures; i.e., warp drive (WD) and Krasnikov tube are not just theoretical subjects for teaching general relativity (GR) or objects only an advanced civilization would be able to manufacture anymore, but a quite reachable challenge for current technology. Besides, a new compound metric is introduced as a choice for testing in the lab. |
gr-qc/0206044 | Dr. Haret Rosu | H.C. Rosu, O. Cornejo, M. Reyes, D. Jimenez | Linear second-order differential equations for barotropic FRW
cosmologies | 6 pages, no figures | null | 10.1023/B:IJTP.0000006019.28659.88 | null | gr-qc | null | Simple linear second-order differential equations have been written down for
FRW cosmologies with barotropic fluids by Faraoni. His results have been
extended by Rosu, who employed techniques belonging to nonrelativistic
supersymmetry to obtain time-dependent adiabatic indices. Further extensions
are presented here using the known connection between the linear second-order
differential equations and Dirac-like equations in the same supersymmetric
context. These extensions are equivalent to adding an imaginary part to the
adiabatic index which is proportional to the mass parameter of the Dirac
spinor. The natural physical interpretation of the imaginary part is related to
the particular dissipation and instabilities of the barotropic FRW
hydrodynamics that are introduced by means of this supersymmetric scheme
| [
{
"created": "Sat, 15 Jun 2002 23:56:53 GMT",
"version": "v1"
},
{
"created": "Sun, 15 Dec 2002 06:13:29 GMT",
"version": "v2"
}
] | 2016-08-31 | [
[
"Rosu",
"H. C.",
""
],
[
"Cornejo",
"O.",
""
],
[
"Reyes",
"M.",
""
],
[
"Jimenez",
"D.",
""
]
] | Simple linear second-order differential equations have been written down for FRW cosmologies with barotropic fluids by Faraoni. His results have been extended by Rosu, who employed techniques belonging to nonrelativistic supersymmetry to obtain time-dependent adiabatic indices. Further extensions are presented here using the known connection between the linear second-order differential equations and Dirac-like equations in the same supersymmetric context. These extensions are equivalent to adding an imaginary part to the adiabatic index which is proportional to the mass parameter of the Dirac spinor. The natural physical interpretation of the imaginary part is related to the particular dissipation and instabilities of the barotropic FRW hydrodynamics that are introduced by means of this supersymmetric scheme |
2309.04622 | Hao-Jui Kuan | Hao-Jui Kuan, Kostas D. Kokkotas | The Last Three Seconds: Packed Message delivered by Tides in Binary
Neutron Star Mergers | 8 pages, 2 figures, 3 tables, 1 appendix. Accepted for publication in
PRD | null | null | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is known that the leading-order tidal effects in gravitational waveforms
can be quantified by tidal deformability, while higher order terms, e.g.,
harmonic overtones of Love number and dynamical tides, have not been
well-investigated yet. The concept of a ``form factor'', which is different
from while resembles the effective tidal deformability, for the tidal
interactions between neutron stars in coalescing binaries is illustrated here.
The form factor effectively incorporates the contribution of dynamical tides.
The dependence of tidal form factor on tidal deformability, spins, and
inclination angles is modeled and expressed in a closed form.
| [
{
"created": "Fri, 8 Sep 2023 22:22:56 GMT",
"version": "v1"
}
] | 2023-09-12 | [
[
"Kuan",
"Hao-Jui",
""
],
[
"Kokkotas",
"Kostas D.",
""
]
] | It is known that the leading-order tidal effects in gravitational waveforms can be quantified by tidal deformability, while higher order terms, e.g., harmonic overtones of Love number and dynamical tides, have not been well-investigated yet. The concept of a ``form factor'', which is different from while resembles the effective tidal deformability, for the tidal interactions between neutron stars in coalescing binaries is illustrated here. The form factor effectively incorporates the contribution of dynamical tides. The dependence of tidal form factor on tidal deformability, spins, and inclination angles is modeled and expressed in a closed form. |
gr-qc/0205040 | Edward Malec | Janusz Karkowski, Edward Malec and Zdobyslaw Swierczynski | How loud can Schwarzschild black holes ring? | 4 pages, 5 figures | Acta Phys.Polon. B34 (2003) 59-68 | null | null | gr-qc | null | A numerical procedure is described for the maximization of the energy
diffusion due to the backscattering of the gravitational radiation. The
obtained maxima are solutions dominated by low frequency waves. They give rise
to robust gravitational ringing, with amplitudes of the order of the original
signal.
| [
{
"created": "Fri, 10 May 2002 11:38:31 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Karkowski",
"Janusz",
""
],
[
"Malec",
"Edward",
""
],
[
"Swierczynski",
"Zdobyslaw",
""
]
] | A numerical procedure is described for the maximization of the energy diffusion due to the backscattering of the gravitational radiation. The obtained maxima are solutions dominated by low frequency waves. They give rise to robust gravitational ringing, with amplitudes of the order of the original signal. |
0805.2503 | Francesco Cianfrani dr | F. Cianfrani, O.M. Lecian, G. Montani | Fundamentals and recent developments in non-perturbative canonical
Quantum Gravity | 95 pages, a section and a new reference have been added | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The aim of this review is to provide a detailed account of the physical
content emerging from this story of the canonical approach to Quantum Gravity.
All the crucial steps in our presentation have a pedagogical character,
providing the reader with the necessary tools to become involved in the field.
Such a pedagogical aspect is then balanced and completed by subtle discussions
on specific topics which we regard as relevant for the physical insight they
outline on the treated questions. Our analysis is not aimed at convincing the
reader about a pre-constituted point of view, bu instead our principal goal is
to review the picture of Canonical Quantum Gravity on the basis of the concrete
facts at the ground of its clear successes, but also of its striking
shortcomings.
| [
{
"created": "Fri, 16 May 2008 11:43:16 GMT",
"version": "v1"
},
{
"created": "Thu, 12 Jun 2008 14:28:08 GMT",
"version": "v2"
}
] | 2008-06-12 | [
[
"Cianfrani",
"F.",
""
],
[
"Lecian",
"O. M.",
""
],
[
"Montani",
"G.",
""
]
] | The aim of this review is to provide a detailed account of the physical content emerging from this story of the canonical approach to Quantum Gravity. All the crucial steps in our presentation have a pedagogical character, providing the reader with the necessary tools to become involved in the field. Such a pedagogical aspect is then balanced and completed by subtle discussions on specific topics which we regard as relevant for the physical insight they outline on the treated questions. Our analysis is not aimed at convincing the reader about a pre-constituted point of view, bu instead our principal goal is to review the picture of Canonical Quantum Gravity on the basis of the concrete facts at the ground of its clear successes, but also of its striking shortcomings. |
gr-qc/9605065 | Claus Laemmerzahl | Claus L\"ammerzahl | On the Equivalence Principle in Quantum Theory | 17 pages, LaTex, includes 1 eps figure, To appear in Gen. Rel. Grav | Gen.Rel.Grav. 28 (1996) 1043 | 10.1007/BF02113157 | null | gr-qc | null | The role of the equivalence principle in the context of non-relativistic
quantum mechanics and matter wave interferometry, especially atom beam
interferometry, will be discussed. A generalised form of the weak equivalence
principle which is capable of covering quantum phenomena too, will be proposed.
It is shown that this generalised equivalence principle is valid for matter
wave interferometry and for the dynamics of expectation values. In addition,
the use of this equivalence principle makes it possible to determine the
structure of the interaction of quantum systems with gravitational and inertial
fields. It is also shown that the path of the mean value of the position
operator in the case of gravitational interaction does fulfill this generalised
equivalence principle.
| [
{
"created": "Wed, 29 May 1996 14:09:14 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Lämmerzahl",
"Claus",
""
]
] | The role of the equivalence principle in the context of non-relativistic quantum mechanics and matter wave interferometry, especially atom beam interferometry, will be discussed. A generalised form of the weak equivalence principle which is capable of covering quantum phenomena too, will be proposed. It is shown that this generalised equivalence principle is valid for matter wave interferometry and for the dynamics of expectation values. In addition, the use of this equivalence principle makes it possible to determine the structure of the interaction of quantum systems with gravitational and inertial fields. It is also shown that the path of the mean value of the position operator in the case of gravitational interaction does fulfill this generalised equivalence principle. |
2402.13360 | Juan M. Z\'arate Pretel | Cl\'esio E. Mota, Juan M. Z. Pretel and C\'esar O. V. Flores | Neutron stars in $f(R,L_m,T)$ gravity | 10 pages, 5 figures. New figures and minor improvements added;
version accepted for publication in EPJC | Eur. Phys. J. C 84 (2024) 673 | 10.1140/epjc/s10052-024-13042-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This study explores the behavior of compact stars within the framework of
$f(R,L_m,T)$ gravity, focusing on the functional form $f(R,L_m,T) = R + \alpha
TL_m$. The modified Tolman-Oppenheimer-Volkoff (TOV) equations are derived and
numerically solved for several values of the free parameter $\alpha$ by
considering both quark and hadronic matter -- described by realistic equations
of state (EoSs). Furthermore, the stellar structure equations are adapted for
two different choices of the matter Lagrangian density (namely, $L_m= p$ and
$L_m= -\rho$), laying the groundwork for our numerical analysis. As expected,
we recover the traditional TOV equations in General Relativity (GR) when
$\alpha \rightarrow 0$. Remarkably, we found that the two choices for $L_m$
have appreciably different effects on the mass-radius diagrams. Results
showcase the impact of $\alpha$ on compact star properties, while final remarks
summarize key findings and discuss implications, including compatibility with
observational data from NGC 6397's neutron star. Overall, this research
enhances comprehension of $f(R,L_m,T)$ gravity's effects on compact star
internal structures, offering insights for future investigations.
| [
{
"created": "Tue, 20 Feb 2024 20:34:04 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Jun 2024 02:02:42 GMT",
"version": "v2"
}
] | 2024-07-09 | [
[
"Mota",
"Clésio E.",
""
],
[
"Pretel",
"Juan M. Z.",
""
],
[
"Flores",
"César O. V.",
""
]
] | This study explores the behavior of compact stars within the framework of $f(R,L_m,T)$ gravity, focusing on the functional form $f(R,L_m,T) = R + \alpha TL_m$. The modified Tolman-Oppenheimer-Volkoff (TOV) equations are derived and numerically solved for several values of the free parameter $\alpha$ by considering both quark and hadronic matter -- described by realistic equations of state (EoSs). Furthermore, the stellar structure equations are adapted for two different choices of the matter Lagrangian density (namely, $L_m= p$ and $L_m= -\rho$), laying the groundwork for our numerical analysis. As expected, we recover the traditional TOV equations in General Relativity (GR) when $\alpha \rightarrow 0$. Remarkably, we found that the two choices for $L_m$ have appreciably different effects on the mass-radius diagrams. Results showcase the impact of $\alpha$ on compact star properties, while final remarks summarize key findings and discuss implications, including compatibility with observational data from NGC 6397's neutron star. Overall, this research enhances comprehension of $f(R,L_m,T)$ gravity's effects on compact star internal structures, offering insights for future investigations. |
1801.08344 | Sante Carloni Dr | Stefano Vignolo, Roberto Cianci, Sante Carloni | On the junction conditions in $f(R)$-gravity with torsion | 13 pages | Class.Quant.Grav. 35 (2018) no.9, 095014 | 10.1088/1361-6382/aab6fe | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Junction conditions are discussed within the framework of $f(R)$-gravity with
torsion. After deriving general junction conditions, the cases of coupling to a
Dirac field and a spin fluid are explicitly dealt with. The main differences
with respect to Einstein--Cartan--Sciama--Kibble theory $\left(f(R)=R\right)$
are outlined.
| [
{
"created": "Thu, 25 Jan 2018 10:50:53 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Mar 2018 17:41:31 GMT",
"version": "v2"
},
{
"created": "Thu, 19 Apr 2018 12:19:35 GMT",
"version": "v3"
}
] | 2018-04-20 | [
[
"Vignolo",
"Stefano",
""
],
[
"Cianci",
"Roberto",
""
],
[
"Carloni",
"Sante",
""
]
] | Junction conditions are discussed within the framework of $f(R)$-gravity with torsion. After deriving general junction conditions, the cases of coupling to a Dirac field and a spin fluid are explicitly dealt with. The main differences with respect to Einstein--Cartan--Sciama--Kibble theory $\left(f(R)=R\right)$ are outlined. |
1102.0616 | Cosimo Bambi | Cosimo Bambi | Constraint on the quadrupole moment of super-massive black hole
candidates from the estimate of the mean radiative efficiency of AGN | 4 pages, 2 figures. v2: refereed version | Phys.Rev.D83:103003,2011 | 10.1103/PhysRevD.83.103003 | IPMU11-0013 | gr-qc astro-ph.CO astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The super-massive objects at the center of many galaxies are commonly thought
to be black holes. In 4-dimensional general relativity, a black hole is
completely specified by its mass $M$ and by its spin angular momentum $J$. All
the higher multipole moments of the gravitational field depend in a very
specific way on these two parameters. For instance, the mass quadrupole moment
is $Q = - J^2/M$. If we can estimate $M$, $J$, and $Q$ for the super-massive
objects in galactic nuclei, we over-constrain the theory and we can test the
black hole hypothesis. While there are many works studying how this can be done
with future observations, in this paper a constraint on the quadrupole moment
of these objects is obtained by using the current estimate of the mean
radiative efficiency of AGN. In terms of the anomalous quadrupole moment $q$,
the bound is $-2.01 < q < 0.14$.
| [
{
"created": "Thu, 3 Feb 2011 08:16:37 GMT",
"version": "v1"
},
{
"created": "Tue, 3 May 2011 08:02:02 GMT",
"version": "v2"
}
] | 2011-05-12 | [
[
"Bambi",
"Cosimo",
""
]
] | The super-massive objects at the center of many galaxies are commonly thought to be black holes. In 4-dimensional general relativity, a black hole is completely specified by its mass $M$ and by its spin angular momentum $J$. All the higher multipole moments of the gravitational field depend in a very specific way on these two parameters. For instance, the mass quadrupole moment is $Q = - J^2/M$. If we can estimate $M$, $J$, and $Q$ for the super-massive objects in galactic nuclei, we over-constrain the theory and we can test the black hole hypothesis. While there are many works studying how this can be done with future observations, in this paper a constraint on the quadrupole moment of these objects is obtained by using the current estimate of the mean radiative efficiency of AGN. In terms of the anomalous quadrupole moment $q$, the bound is $-2.01 < q < 0.14$. |
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