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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0706.3452 | Luis Nunez A | H. Abreu, H. Hernandez and L.A. Nunez | Sound Speeds, Cracking and Stability of Self-Gravitating Anisotropic
Compact Objects | 17 pages, 8 figures, 4 new references added. typos corrected | Class.Quant.Grav.24:4631-4646,2007 | 10.1088/0264-9381/24/18/005 | null | gr-qc | null | Using the the concept of cracking we explore the influence of density
fluctuations and local anisotropy have on the stability of local and non-local
anisotropic matter configurations in general relativity. This concept,
conceived to describe the behaviour of a fluid distribution just after its
departure from equilibrium, provides an alternative approach to consider the
stability of selfgravitating compact objects. We show that potentially unstable
regions within a configuration can be identify as a function of the difference
of propagations of sound along tangential and radial directions. In fact, it is
found that these regions could occur when, at particular point within the
distribution, the tangential speed of sound is greater than radial one.
| [
{
"created": "Sat, 23 Jun 2007 12:15:22 GMT",
"version": "v1"
},
{
"created": "Sun, 22 Jul 2007 16:57:39 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Abreu",
"H.",
""
],
[
"Hernandez",
"H.",
""
],
[
"Nunez",
"L. A.",
""
]
] | Using the the concept of cracking we explore the influence of density fluctuations and local anisotropy have on the stability of local and non-local anisotropic matter configurations in general relativity. This concept, conceived to describe the behaviour of a fluid distribution just after its departure from equilibrium, provides an alternative approach to consider the stability of selfgravitating compact objects. We show that potentially unstable regions within a configuration can be identify as a function of the difference of propagations of sound along tangential and radial directions. In fact, it is found that these regions could occur when, at particular point within the distribution, the tangential speed of sound is greater than radial one. |
2108.05273 | Junji Jia | Zonghai Li, Junji Jia | Kerr-Newman-Jacobi geometry and the deflection of charged massive
particles | 14 pages, 1 figure, to appear in PRD | null | 10.1103/PhysRevD.104.044061 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we investigate the deflection of a charged particle moving in
the equatorial plane of Kerr-Newman spacetime, focusing on weak field limit. To
this end, we use the Jacobi geometry, which can be described in three
equivalent forms, namely Randers-Finsler metric, Zermelo navigation problem,
and $(n+1)$-dimensional stationtary spacetime picture. Based on Randers data
and Gauss-Bonnet theorem, we utilize osculating Riemannian manifold method and
the generalized Jacobi metric method to study the deflection angle,
respectively. In the $(n+1)$-dimensional spacetime picture, the motion of
charged particle follows the null geodesic, and thus we use the standard
geodesic method to calculate the deflection angle. Three methods lead to the
same second-order deflection angle, which is obtained for the first time. The
result shows that the black hole spin $a$ affects the deflection of charged
particles both gravitationally and magnetically at the leading order (order
$\mathcal{O}([M]^2/b^2)$). When $qQ/E<2M$, $a$ will decrease (or increase) the
deflection of prograde (or retrograde) charged signal. If $qQ/E> 2M$, the
opposite happens, and the ray is divergently deflected by the lens. We also
showed that the effect of the magnetic charge of the dyonic Kerr-Newman black
hole on the deflection angle is independent of the particle's charge.
| [
{
"created": "Wed, 11 Aug 2021 15:15:35 GMT",
"version": "v1"
}
] | 2021-09-08 | [
[
"Li",
"Zonghai",
""
],
[
"Jia",
"Junji",
""
]
] | In this paper, we investigate the deflection of a charged particle moving in the equatorial plane of Kerr-Newman spacetime, focusing on weak field limit. To this end, we use the Jacobi geometry, which can be described in three equivalent forms, namely Randers-Finsler metric, Zermelo navigation problem, and $(n+1)$-dimensional stationtary spacetime picture. Based on Randers data and Gauss-Bonnet theorem, we utilize osculating Riemannian manifold method and the generalized Jacobi metric method to study the deflection angle, respectively. In the $(n+1)$-dimensional spacetime picture, the motion of charged particle follows the null geodesic, and thus we use the standard geodesic method to calculate the deflection angle. Three methods lead to the same second-order deflection angle, which is obtained for the first time. The result shows that the black hole spin $a$ affects the deflection of charged particles both gravitationally and magnetically at the leading order (order $\mathcal{O}([M]^2/b^2)$). When $qQ/E<2M$, $a$ will decrease (or increase) the deflection of prograde (or retrograde) charged signal. If $qQ/E> 2M$, the opposite happens, and the ray is divergently deflected by the lens. We also showed that the effect of the magnetic charge of the dyonic Kerr-Newman black hole on the deflection angle is independent of the particle's charge. |
2304.13749 | Alexandre M. Pombo | Alexandre M. Pombo, Jo\~ao M. S. Oliveira, Nuno M. Santos | Scalaroca stars: coupled scalar-Proca solitons | 21 pages, 13 figures, this project was started before the recently
published work ArXiv:2304.08019 | null | 10.1103/PhysRevD.108.044044 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct and explore the physical properties of \textit{scalaroca stars}:
spherically symmetric solitonic solutions made of a complex scalar field $\Phi$
and a complex Proca field $A^\mu$. We restrict our attention to configurations
in which both fields are in the fundamental state and possess an equal mass,
focusing on the cases when ($i$) the scalar and Proca fields are
(non--linearly) super--imposed and do not interact with each other; and ($ii$)
the scalar and Proca fields interact through the term $\alpha |\Phi| ^2 A^\mu
A_\mu$. The solutions are found numerically for the non--interacting case
($\alpha=0$) as well as for both signs of the interaction coupling constant
$\alpha$. While pure ($i.e.$ single--field) Proca/scalar boson stars are the
most/least massive for weakly--interacting fields, one can obtain more massive
solutions for a sufficiently strong interaction. Besides, in the latter case,
solutions can be either in a synchronized state -- in which both fields have
the same frequency -- or in a non--synchronized state. In addition, we observe
that the coupling between the two fields allows solitonic solutions with a real
scalar field. We further comment on the possibility of spontaneous
scalarization and vectorization of the interacting solitonic solution.
| [
{
"created": "Wed, 26 Apr 2023 18:00:03 GMT",
"version": "v1"
}
] | 2023-09-26 | [
[
"Pombo",
"Alexandre M.",
""
],
[
"Oliveira",
"João M. S.",
""
],
[
"Santos",
"Nuno M.",
""
]
] | We construct and explore the physical properties of \textit{scalaroca stars}: spherically symmetric solitonic solutions made of a complex scalar field $\Phi$ and a complex Proca field $A^\mu$. We restrict our attention to configurations in which both fields are in the fundamental state and possess an equal mass, focusing on the cases when ($i$) the scalar and Proca fields are (non--linearly) super--imposed and do not interact with each other; and ($ii$) the scalar and Proca fields interact through the term $\alpha |\Phi| ^2 A^\mu A_\mu$. The solutions are found numerically for the non--interacting case ($\alpha=0$) as well as for both signs of the interaction coupling constant $\alpha$. While pure ($i.e.$ single--field) Proca/scalar boson stars are the most/least massive for weakly--interacting fields, one can obtain more massive solutions for a sufficiently strong interaction. Besides, in the latter case, solutions can be either in a synchronized state -- in which both fields have the same frequency -- or in a non--synchronized state. In addition, we observe that the coupling between the two fields allows solitonic solutions with a real scalar field. We further comment on the possibility of spontaneous scalarization and vectorization of the interacting solitonic solution. |
2012.07813 | Klaus Liegener Dr | Klaus Liegener, {\L}ukasz Rudnicki | Algorithmic approach to Cosmological Coherent State Expectation Values
in LQG | 33 pages; This paper summarizes the results announced at Loops'19
Conference [http://gravity.psu.edu/events/loops19/index-loops19.shtml]. First
draft - minor typos can still be found | Class. Quantum Grav. 38, 205001 (2021) | 10.1088/1361-6382/ac226f | null | gr-qc hep-lat | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the lattice approach to Loop Quantum Gravity on a fixed graph computations
tend to be involved and are rarely analytically manageable. But, when
interested in the expectation values of coherent states on the lattice which
are sharply peaked on isotropic, flat cosmology several simplifications are
possible which reduce the computational effort. We present a step-by-step
algorithm resulting in an analytical expression including up to first order
corrections in the spread of the state. The algorithm is developed in such a
way that it makes the computation straightforward and easy to be implementable
in programming languages such as Mathematica. Exemplarily, we demonstrate how
the algorithm streamlines the road to obtain the expectation value of the
euclidean part of the scalar constraint and as a consistency check perform the
analytic computation as well. To showcase further applications of the
algorithm, we investigate the fate of the effective dynamics program custom in
Loop Cosmology and find that the next-to-leading order corrections can {\it
not} be used as corrections for an effective Hamiltonian.
| [
{
"created": "Mon, 14 Dec 2020 18:46:05 GMT",
"version": "v1"
}
] | 2021-11-01 | [
[
"Liegener",
"Klaus",
""
],
[
"Rudnicki",
"Łukasz",
""
]
] | In the lattice approach to Loop Quantum Gravity on a fixed graph computations tend to be involved and are rarely analytically manageable. But, when interested in the expectation values of coherent states on the lattice which are sharply peaked on isotropic, flat cosmology several simplifications are possible which reduce the computational effort. We present a step-by-step algorithm resulting in an analytical expression including up to first order corrections in the spread of the state. The algorithm is developed in such a way that it makes the computation straightforward and easy to be implementable in programming languages such as Mathematica. Exemplarily, we demonstrate how the algorithm streamlines the road to obtain the expectation value of the euclidean part of the scalar constraint and as a consistency check perform the analytic computation as well. To showcase further applications of the algorithm, we investigate the fate of the effective dynamics program custom in Loop Cosmology and find that the next-to-leading order corrections can {\it not} be used as corrections for an effective Hamiltonian. |
1308.5258 | Cl\'audio Nassif Cruz | Cl\'audio Nassif | On the electrodynamics of moving particles in a quasi flat spacetime
with Lorentz violation and its cosmological implications | 49 pages and 7 figures. arXiv admin note: substantial text overlap
with arXiv:physics/0702095, arXiv:0711.4897.
http://www.worldscientific.com/worldscinet/ijmpd?journalTabs=read. text
overlap with arXiv:0705.1836 by other authors | International Journal of Modern Physics D25:10, p.1-67 (2016) | 10.1142/S0218271816500966 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This research aims to develop a new approach toward a consistent coupling of
electromagnetic and gravitational fields by using an electron that couples with
a weak gravitational potential by means of its electromagnetic field. We find
the value of the tiny coupling constant of gravity with electromagnetic fields,
which depends on the speed of light and a universal minimum speed that
represents the lowest limit of speed for any particle. Such a minimum speed,
unattainable by particles, represents a preferred reference frame associated
with a background field that breaks the Lorentz symmetry. The metric of the
flat spacetime shall include the presence of a uniform vacuum energy density,
which leads to a negative pressure at cosmological scales, i.e., the
cosmological anti-gravity. The tiny values of the cosmological constant and the
vacuum energy density will be successfully obtained in agreement with the
observational data.
| [
{
"created": "Fri, 23 Aug 2013 22:34:17 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Sep 2013 12:11:16 GMT",
"version": "v2"
},
{
"created": "Tue, 14 Oct 2014 17:55:37 GMT",
"version": "v3"
},
{
"created": "Thu, 29 Oct 2015 02:14:51 GMT",
"version": "v4"
},
{
"c... | 2017-01-09 | [
[
"Nassif",
"Cláudio",
""
]
] | This research aims to develop a new approach toward a consistent coupling of electromagnetic and gravitational fields by using an electron that couples with a weak gravitational potential by means of its electromagnetic field. We find the value of the tiny coupling constant of gravity with electromagnetic fields, which depends on the speed of light and a universal minimum speed that represents the lowest limit of speed for any particle. Such a minimum speed, unattainable by particles, represents a preferred reference frame associated with a background field that breaks the Lorentz symmetry. The metric of the flat spacetime shall include the presence of a uniform vacuum energy density, which leads to a negative pressure at cosmological scales, i.e., the cosmological anti-gravity. The tiny values of the cosmological constant and the vacuum energy density will be successfully obtained in agreement with the observational data. |
1904.10333 | Alexander Zhidenko | R. A. Konoplya, A. Zhidenko, A. F. Zinhailo | Higher order WKB formula for quasinormal modes and grey-body factors:
recipes for quick and accurate calculations | 15 pages (revtex), 4 figures | Class. Quantum Grav. 36: 155002 (2019) | 10.1088/1361-6382/ab2e25 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The WKB approach for finding quasinormal modes of black holes, suggested in
[1] by Schutz and Will at the first order and later developed to higher orders
[2-4], became popular during the past decades, because, unlike more
sophisticated numerical approaches, it is automatic for different effective
potentials and mostly provides sufficient accuracy. At the same time, the
seeming simplicity of the WKB approach resulted in appearance of a big number
of partially misleading papers, where the WKB formula was used beyond its scope
of applicability. Here we review various situations in which the WKB formula
can or cannot bring us to reliable conclusions. As the WKB series converges
only asymptotically, there is no mathematically strict criterium for evaluation
of an error. Therefore, here we are trying to introduce a number of practical
recipes instead and summarize cases in which higher WKB orders improve
accuracy. We show that averaging of the Pade approximations, suggested first by
J. Matyjasek and M. Opala [4], leads to much higher accuracy of the WKB
approach, estimate the error and present the automatic code [5] which computes
quasinormal modes and grey-body factors.
| [
{
"created": "Tue, 23 Apr 2019 13:55:18 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Jul 2019 15:48:14 GMT",
"version": "v2"
}
] | 2019-07-15 | [
[
"Konoplya",
"R. A.",
""
],
[
"Zhidenko",
"A.",
""
],
[
"Zinhailo",
"A. F.",
""
]
] | The WKB approach for finding quasinormal modes of black holes, suggested in [1] by Schutz and Will at the first order and later developed to higher orders [2-4], became popular during the past decades, because, unlike more sophisticated numerical approaches, it is automatic for different effective potentials and mostly provides sufficient accuracy. At the same time, the seeming simplicity of the WKB approach resulted in appearance of a big number of partially misleading papers, where the WKB formula was used beyond its scope of applicability. Here we review various situations in which the WKB formula can or cannot bring us to reliable conclusions. As the WKB series converges only asymptotically, there is no mathematically strict criterium for evaluation of an error. Therefore, here we are trying to introduce a number of practical recipes instead and summarize cases in which higher WKB orders improve accuracy. We show that averaging of the Pade approximations, suggested first by J. Matyjasek and M. Opala [4], leads to much higher accuracy of the WKB approach, estimate the error and present the automatic code [5] which computes quasinormal modes and grey-body factors. |
1406.0126 | Alfredo Lopez Ortega | A. Lopez-Ortega | Electromagnetic quasinormal modes of an asymptotically Lifshitz black
hole | 19 pages. Accepted for publication | null | 10.1007/s10714-014-1756-5 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Motivated by the recent interest in the study of the spacetimes that are
asymptotically Lifshitz and in order to extend some previous results, we
calculate exactly the quasinormal frequencies of the electromagnetic field in a
D-dimensional asymptotically Lifshitz black hole. Based on the values obtained
for the quasinormal frequencies we discuss the classical stability of the
quasinormal modes. We also study whether the electromagnetic field possesses
unstable modes in the D-dimensional Lifshitz spacetime.
| [
{
"created": "Sun, 1 Jun 2014 02:30:09 GMT",
"version": "v1"
}
] | 2015-06-19 | [
[
"Lopez-Ortega",
"A.",
""
]
] | Motivated by the recent interest in the study of the spacetimes that are asymptotically Lifshitz and in order to extend some previous results, we calculate exactly the quasinormal frequencies of the electromagnetic field in a D-dimensional asymptotically Lifshitz black hole. Based on the values obtained for the quasinormal frequencies we discuss the classical stability of the quasinormal modes. We also study whether the electromagnetic field possesses unstable modes in the D-dimensional Lifshitz spacetime. |
1101.5419 | Oscar Loaiza-Brito | Filemon Farfan, Ricardo Garcia-Salcedo, Oscar Loaiza-Brito, Claudia
Moreno, Alexander Yakhno | Spherically symmetric solution in a space-time with torsion | (v1) 14 pages, 3 figures. (v2) Version accepted for publication in
General Relativity and Gravitation | null | 10.1007/s10714-011-1293-4 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | By using the method of group analysis, we obtain a new exact evolving and
spherically symmetric solution of the Einstein-Cartan equations of motion,
corresponding to a space-time threaded with a three-form Kalb-Ramond field
strength. The solution describes in its more generic form, a space-time which
scalar curvature vanishes for large distances and for large time. In static
conditions, it reduces to a classical wormhole solution and to a exact solution
with a localized scalar field and a torsion kink, already reported in
literature. In the process we have found evidence towards the construction of
more new solutions.
| [
{
"created": "Fri, 28 Jan 2011 00:39:53 GMT",
"version": "v1"
},
{
"created": "Sun, 23 Oct 2011 22:49:22 GMT",
"version": "v2"
}
] | 2015-05-27 | [
[
"Farfan",
"Filemon",
""
],
[
"Garcia-Salcedo",
"Ricardo",
""
],
[
"Loaiza-Brito",
"Oscar",
""
],
[
"Moreno",
"Claudia",
""
],
[
"Yakhno",
"Alexander",
""
]
] | By using the method of group analysis, we obtain a new exact evolving and spherically symmetric solution of the Einstein-Cartan equations of motion, corresponding to a space-time threaded with a three-form Kalb-Ramond field strength. The solution describes in its more generic form, a space-time which scalar curvature vanishes for large distances and for large time. In static conditions, it reduces to a classical wormhole solution and to a exact solution with a localized scalar field and a torsion kink, already reported in literature. In the process we have found evidence towards the construction of more new solutions. |
1403.0544 | Richard O'Shaughnessy | (1) R. O'Shaughnessy, (2) B. Farr, (1) E. Ochsner, (3) H.S. Cho, (4)
V. Raymond, (5) C. Kim, (3) C.H. Lee ((1) University of Wisconsin-Milwaukee,
(2) Northwestern University, (3) Pusan National University, (4) California
Institute of Technology, (5) Seoul National University) | Parameter Estimation of Gravitational Waves from Precessing BH-NS
Inspirals with higher harmonics | v2: typographical fixes; new subsection | null | 10.1103/PhysRevD.89.102005 | LIGO DCC P1400020 | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Precessing black hole-neutron star (BH-NS) binaries produce a rich
gravitational wave signal, encoding the binary's nature and inspiral
kinematics. Using the lalinference\_mcmc Markov-chain Monte Carlo parameter
estimation code, we use two fiducial examples to illustrate how the geometry
and kinematics are encoded into the modulated gravitational wave signal, using
coordinates well-adapted to precession. Even for precessing binaries, we show
the performance of detailed parameter estimation can be estimated by
"effective" estimates: comparisons of a prototype signal with its nearest
neighbors, adopting a fixed sky location and idealized two-detector network. We
use detailed and effective approaches to show higher harmonics provide nonzero
but small local improvement when estimating the parameters of precessing BH-NS
binaries. That said, we show higher harmonics can improve parameter estimation
accuracy for precessing binaries ruling out approximately-degenerate source
orientations.
Our work illustrates quantities gravitational wave measurements can provide,
such as reliable component masses and the precise orientation of a precessing
short gamma ray burst progenitor relative to the line of sight. "Effective"
estimates may provide a simple way to estimate trends in the performance of
parameter estimation for generic precessing BH-NS binaries in next-generation
detectors. For example, our results suggest that the orbital chirp rate,
precession rate, and precession geometry are roughly-independent observables,
defining natural variables to organize correlations in the high-dimensional
BH-NS binary parameter space.
| [
{
"created": "Mon, 3 Mar 2014 19:55:07 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Apr 2014 15:22:26 GMT",
"version": "v2"
}
] | 2015-06-19 | [
[
"O'Shaughnessy",
"R.",
""
],
[
"Farr",
"B.",
""
],
[
"Ochsner",
"E.",
""
],
[
"Cho",
"H. S.",
""
],
[
"Raymond",
"V.",
""
],
[
"Kim",
"C.",
""
],
[
"Lee",
"C. H.",
""
]
] | Precessing black hole-neutron star (BH-NS) binaries produce a rich gravitational wave signal, encoding the binary's nature and inspiral kinematics. Using the lalinference\_mcmc Markov-chain Monte Carlo parameter estimation code, we use two fiducial examples to illustrate how the geometry and kinematics are encoded into the modulated gravitational wave signal, using coordinates well-adapted to precession. Even for precessing binaries, we show the performance of detailed parameter estimation can be estimated by "effective" estimates: comparisons of a prototype signal with its nearest neighbors, adopting a fixed sky location and idealized two-detector network. We use detailed and effective approaches to show higher harmonics provide nonzero but small local improvement when estimating the parameters of precessing BH-NS binaries. That said, we show higher harmonics can improve parameter estimation accuracy for precessing binaries ruling out approximately-degenerate source orientations. Our work illustrates quantities gravitational wave measurements can provide, such as reliable component masses and the precise orientation of a precessing short gamma ray burst progenitor relative to the line of sight. "Effective" estimates may provide a simple way to estimate trends in the performance of parameter estimation for generic precessing BH-NS binaries in next-generation detectors. For example, our results suggest that the orbital chirp rate, precession rate, and precession geometry are roughly-independent observables, defining natural variables to organize correlations in the high-dimensional BH-NS binary parameter space. |
gr-qc/9805065 | Domenico Giulini | Domenico Giulini | The Generalized Thin-Sandwich Problem and its Local Solvability | 18 pages, Plain TeX | J.Math.Phys. 40 (1999) 2470-2482 | 10.1063/1.532877 | ZU-TH 9/98 | gr-qc | null | We consider Einstein Gravity coupled to dynamical matter consisting of a
gauge field with any compact gauge group and minimally coupled scalar fields.
We investigate the conditions under which a free specification of a spatial
field configuration for the total system and its derivative with respect to
coordinate-time determines a solution to the field equations (generalized
thin-sandwich problem). Sufficient conditions for local solvability (in the
space of fields) are established.
| [
{
"created": "Mon, 18 May 1998 11:37:10 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Giulini",
"Domenico",
""
]
] | We consider Einstein Gravity coupled to dynamical matter consisting of a gauge field with any compact gauge group and minimally coupled scalar fields. We investigate the conditions under which a free specification of a spatial field configuration for the total system and its derivative with respect to coordinate-time determines a solution to the field equations (generalized thin-sandwich problem). Sufficient conditions for local solvability (in the space of fields) are established. |
0801.2673 | Silke Weinfurtner | Silke Weinfurtner, Piyush Jain, Matt Visser, C.W. Gardiner | Cosmological particle production in emergent rainbow spacetimes | null | Class.Quant.Grav.26:065012,2009 | 10.1088/0264-9381/26/6/065012 | null | gr-qc | null | We investigate cosmological particle production in spacetimes where Lorentz
invariance emerges in the infrared limit, but is explicitly broken in the
ultraviolet regime. Our specific model focuses on the boost subgroup that
supports CPT invariance and results in a momentum-dependent dispersion
relation. Motivated by previous studies on spacetimes emerging from a
microscopic substrate, we show how these modifications naturally lead to
momentum-dependent rainbow metrics. Firstly, we investigate the possibility of
reproducing cosmological particle production in spacetimes emerging from real
Bose gases. We have studied the influence of non-perturbative ultraviolet
corrections in time-dependent analogue spacetimes, leading to
momentum-dependent emergent rainbow spacetimes. Within certain limits the
analogy is sufficiently good to simulate relativistic quantum field theory in
time-dependent classical backgrounds, and the quantum effects are approximately
robust against the model-dependent modifications. Secondly, we analyze how
significantly the particle production process deviates from the common picture.
While very low-energy modes do not see the difference at all, some modes
"re-enter the Hubble horizon" during the inflationary epoch, and extreme
ultraviolet modes are completely insensitive to the expansion.
| [
{
"created": "Thu, 17 Jan 2008 02:40:21 GMT",
"version": "v1"
}
] | 2009-03-27 | [
[
"Weinfurtner",
"Silke",
""
],
[
"Jain",
"Piyush",
""
],
[
"Visser",
"Matt",
""
],
[
"Gardiner",
"C. W.",
""
]
] | We investigate cosmological particle production in spacetimes where Lorentz invariance emerges in the infrared limit, but is explicitly broken in the ultraviolet regime. Our specific model focuses on the boost subgroup that supports CPT invariance and results in a momentum-dependent dispersion relation. Motivated by previous studies on spacetimes emerging from a microscopic substrate, we show how these modifications naturally lead to momentum-dependent rainbow metrics. Firstly, we investigate the possibility of reproducing cosmological particle production in spacetimes emerging from real Bose gases. We have studied the influence of non-perturbative ultraviolet corrections in time-dependent analogue spacetimes, leading to momentum-dependent emergent rainbow spacetimes. Within certain limits the analogy is sufficiently good to simulate relativistic quantum field theory in time-dependent classical backgrounds, and the quantum effects are approximately robust against the model-dependent modifications. Secondly, we analyze how significantly the particle production process deviates from the common picture. While very low-energy modes do not see the difference at all, some modes "re-enter the Hubble horizon" during the inflationary epoch, and extreme ultraviolet modes are completely insensitive to the expansion. |
2403.03147 | Giovanni Maria Tomaselli | Giovanni Maria Tomaselli, Thomas F.M. Spieksma, Gianfranco Bertone | The resonant history of gravitational atoms in black hole binaries | 36+9 pages, 16 figures | null | null | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Rotating black holes can produce superradiant clouds of ultralight bosons.
When the black hole is part of a binary system, its cloud can undergo
resonances and ionization. These processes leave a distinct signature on the
gravitational waveform that depends on the cloud's properties. To determine the
state of the cloud by the time the system enters the band of future millihertz
detectors, we study the chronological sequence of resonances encountered during
the inspiral. For the first time, we consistently take into account the
nonlinearities induced by the orbital backreaction and we allow the orbit to
have generic eccentricity and inclination. We find that the resonance
phenomenology exhibits striking new features. Resonances can "start" or "break"
above critical thresholds of the parameters, which we compute analytically, and
induce dramatic changes in eccentricity and inclination. Applying these results
to realistic systems, we find two possible outcomes. If the binary and the
cloud are sufficiently close to counter-rotating, the cloud survives in its
original state until the system enters in band; otherwise, the cloud is
destroyed during a resonance at large separations, but leaves an imprint on the
eccentricity and inclination. In both scenarios, we characterize the
observational signatures, with particular focus on future gravitational wave
detectors.
| [
{
"created": "Tue, 5 Mar 2024 17:38:19 GMT",
"version": "v1"
},
{
"created": "Sat, 30 Mar 2024 10:46:31 GMT",
"version": "v2"
}
] | 2024-04-02 | [
[
"Tomaselli",
"Giovanni Maria",
""
],
[
"Spieksma",
"Thomas F. M.",
""
],
[
"Bertone",
"Gianfranco",
""
]
] | Rotating black holes can produce superradiant clouds of ultralight bosons. When the black hole is part of a binary system, its cloud can undergo resonances and ionization. These processes leave a distinct signature on the gravitational waveform that depends on the cloud's properties. To determine the state of the cloud by the time the system enters the band of future millihertz detectors, we study the chronological sequence of resonances encountered during the inspiral. For the first time, we consistently take into account the nonlinearities induced by the orbital backreaction and we allow the orbit to have generic eccentricity and inclination. We find that the resonance phenomenology exhibits striking new features. Resonances can "start" or "break" above critical thresholds of the parameters, which we compute analytically, and induce dramatic changes in eccentricity and inclination. Applying these results to realistic systems, we find two possible outcomes. If the binary and the cloud are sufficiently close to counter-rotating, the cloud survives in its original state until the system enters in band; otherwise, the cloud is destroyed during a resonance at large separations, but leaves an imprint on the eccentricity and inclination. In both scenarios, we characterize the observational signatures, with particular focus on future gravitational wave detectors. |
2003.05342 | Andronikos Paliathanasis | Andronikos Paliathanasis | Dynamics of Chiral Cosmology | 20 pages, 10 figures, 1 table, version accepted for publication in
Classical and Quantum Gravity | Class. Quantum Grav. 37 (2020) 19, 195014 | 10.1088/1361-6382/aba667 | null | gr-qc astro-ph.CO hep-ph | http://creativecommons.org/licenses/by/4.0/ | We perform a detailed analysis for the dynamics of Chiral cosmology in a
spatially flat Friedmann-Lema\^{\i}tre-Robertson-Walker universe with a mixed
potential term. The stationary points are categorized in four families.
Previous results in the literature are recovered while new phases in the
cosmological evolution are found. From our analysis we find nine different
cosmological solutions, the eight describe scaling solutions, where the one is
that of a pressureless fluid, while only one de Sitter solution is recovered.
| [
{
"created": "Wed, 11 Mar 2020 14:58:05 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Jul 2020 06:41:06 GMT",
"version": "v2"
},
{
"created": "Wed, 13 Oct 2021 05:50:53 GMT",
"version": "v3"
}
] | 2021-10-14 | [
[
"Paliathanasis",
"Andronikos",
""
]
] | We perform a detailed analysis for the dynamics of Chiral cosmology in a spatially flat Friedmann-Lema\^{\i}tre-Robertson-Walker universe with a mixed potential term. The stationary points are categorized in four families. Previous results in the literature are recovered while new phases in the cosmological evolution are found. From our analysis we find nine different cosmological solutions, the eight describe scaling solutions, where the one is that of a pressureless fluid, while only one de Sitter solution is recovered. |
1505.03863 | Jose' P. S. Lemos | Jos\'e P. S. Lemos, Vilson T. Zanchin | Sharp bounds on the radius of relativistic charged spheres: Guilfoyle's
stars saturate the Buchdahl-Andr\'easson bound | 10 pages, 3 figures | Classical and Quantum Gravity 32, 135009 (2015) | 10.1088/0264-9381/32/13/135009 | null | gr-qc astro-ph.SR hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Buchdahl, by imposing a few physical assumptions on the matter, i.e., its
density is a nonincreasing function of the radius and the fluid is a perfect
fluid, and on the configuration, such as the exterior is the Schwarzschild
solution, found that the radius $r_0$ to mass $m$ ratio of a star would obey
the Buchdahl bound $r_0/m\geq9/4$. He noted that the bound was saturated by the
Schwarzschild interior solution, the solution with $\rho_{\rm m}(r)= {\rm
constant}$, where $\rho_{\rm m}(r)$ is the energy density of the matter at $r$,
when the central central pressure blows to infinity. Generalizations of this
bound have been studied. One generalization was given by Andr\'easson by
including electrically charged matter and imposing that $p+2p_T \leq\rho_{\rm
m}$, where $p$ is the radial pressure and $p_T$ the tangential pressure. His
bound is given by $r_0/m\geq9/\left(1+\sqrt{1+3\,q^2/r_0^2}\right)^{2}$, the
Buchdahl-Andr\'easson bound, with $q$ being the star's total electric charge.
Following Andr\'easson's proof, the configuration that saturates the Buchdahl
bound is an uncharged shell, rather than the Schwarzschild interior solution.
By extension, the configurations that saturate the Buchdahl-Andr\'easson bound
are charged shells. One expects then, in turn, that there should exist an
electrically charged equivalent to the interior Schwarzschild limit. We find
here that this equivalent is provided by the equation $\rho_{\rm m}(r) +
{Q^2(r)}/ {\left(8\pi\,r^4\right)}= {\rm constant}$, where $Q(r)$ is the
electric charge at $r$. This equation was put forward by Cooperstock and de la
Cruz, and Florides, and realized in Guilfoyle's stars. When the central
pressure goes to infinity Guilfoyle's stars are configurations that saturate
the Buchdahl-Andr\'easson bound. It remains to find a proof in Buchdahl's
manner such that these configurations are the limiting configurations of the
bound.
| [
{
"created": "Thu, 14 May 2015 20:00:30 GMT",
"version": "v1"
}
] | 2016-03-23 | [
[
"Lemos",
"José P. S.",
""
],
[
"Zanchin",
"Vilson T.",
""
]
] | Buchdahl, by imposing a few physical assumptions on the matter, i.e., its density is a nonincreasing function of the radius and the fluid is a perfect fluid, and on the configuration, such as the exterior is the Schwarzschild solution, found that the radius $r_0$ to mass $m$ ratio of a star would obey the Buchdahl bound $r_0/m\geq9/4$. He noted that the bound was saturated by the Schwarzschild interior solution, the solution with $\rho_{\rm m}(r)= {\rm constant}$, where $\rho_{\rm m}(r)$ is the energy density of the matter at $r$, when the central central pressure blows to infinity. Generalizations of this bound have been studied. One generalization was given by Andr\'easson by including electrically charged matter and imposing that $p+2p_T \leq\rho_{\rm m}$, where $p$ is the radial pressure and $p_T$ the tangential pressure. His bound is given by $r_0/m\geq9/\left(1+\sqrt{1+3\,q^2/r_0^2}\right)^{2}$, the Buchdahl-Andr\'easson bound, with $q$ being the star's total electric charge. Following Andr\'easson's proof, the configuration that saturates the Buchdahl bound is an uncharged shell, rather than the Schwarzschild interior solution. By extension, the configurations that saturate the Buchdahl-Andr\'easson bound are charged shells. One expects then, in turn, that there should exist an electrically charged equivalent to the interior Schwarzschild limit. We find here that this equivalent is provided by the equation $\rho_{\rm m}(r) + {Q^2(r)}/ {\left(8\pi\,r^4\right)}= {\rm constant}$, where $Q(r)$ is the electric charge at $r$. This equation was put forward by Cooperstock and de la Cruz, and Florides, and realized in Guilfoyle's stars. When the central pressure goes to infinity Guilfoyle's stars are configurations that saturate the Buchdahl-Andr\'easson bound. It remains to find a proof in Buchdahl's manner such that these configurations are the limiting configurations of the bound. |
gr-qc/0608063 | Jose Luis Flores | Jose L. Flores | The Causal Boundary of spacetimes revisited | 37 pages, 10 figures; Definition 6.1 slightly modified; multiple
minor changes; one figure added and another replaced | Commun.Math.Phys.276:611-643,2007 | 10.1007/s00220-007-0345-9 | null | gr-qc | null | We present a new development of the causal boundary of spacetimes, originally
introduced by Geroch, Kronheimer and Penrose. Given a strongly causal spacetime
(or, more generally, a chronological set), we reconsider the GKP ideas to
construct a family of completions with a chronology and topology extending the
original ones. Many of these completions present undesirable features, like
those appeared in previous approaches by other authors. However, we show that
all these deficiencies are due to the attachment of an ``excessively big''
boundary. In fact, a notion of ``completion with minimal boundary'' is then
introduced in our family such that, when we restrict to these minimal
completions, which always exist, all previous objections disappear. The optimal
character of our construction is illustrated by a number of satisfactory
properties and examples.
| [
{
"created": "Fri, 11 Aug 2006 17:18:29 GMT",
"version": "v1"
},
{
"created": "Sun, 20 Aug 2006 07:51:55 GMT",
"version": "v2"
},
{
"created": "Wed, 7 Mar 2007 12:35:33 GMT",
"version": "v3"
},
{
"created": "Thu, 6 Sep 2007 07:03:40 GMT",
"version": "v4"
}
] | 2008-11-26 | [
[
"Flores",
"Jose L.",
""
]
] | We present a new development of the causal boundary of spacetimes, originally introduced by Geroch, Kronheimer and Penrose. Given a strongly causal spacetime (or, more generally, a chronological set), we reconsider the GKP ideas to construct a family of completions with a chronology and topology extending the original ones. Many of these completions present undesirable features, like those appeared in previous approaches by other authors. However, we show that all these deficiencies are due to the attachment of an ``excessively big'' boundary. In fact, a notion of ``completion with minimal boundary'' is then introduced in our family such that, when we restrict to these minimal completions, which always exist, all previous objections disappear. The optimal character of our construction is illustrated by a number of satisfactory properties and examples. |
gr-qc/9903082 | Manuela Campanelli | Manuela Campanelli (Max-Planck-Institut fuer Gravitationsphysik,
Albert-Einstein-Institut, Potsdam, Germany) | Black hole collisions: how far can perturbation theory go? | 6 pages, Latex, uses moriond.sty, proceedings of the talk given at
the Moriond 99' euroconference | null | null | null | gr-qc | null | The computation of gravitational radiation generated by the coalescence of
inspiralling binary black holes is nowdays one of the main goals of numerical
relativity. Perturbation theory has emerged as an ubiquitous tool for all those
dynamical evolutions where the two black holes start close enough to each
other, to be treated as single distorted black hole (close limit
approximation), providing at the same time useful benchmarks for full numerical
simulations. Here we summarize the most recent developments to study evolutions
of perturbations around rotating (Kerr) black holes. The final aim is to
generalize the close limit approximation to the most general case of two
rotating black holes in orbit around each other, and thus provide reliable
templates for the gravitational waveforms in this regime. For this reason it
has become very important to know if these predictions can actually be trusted
to larger separation parameters (even in the region where the holes have
distinct event horizons). The only way to extend the range of validity of the
linear approximation is to develop the theory of second order perturbations
around a Kerr hole, by generalizing the Teukolsky formalism.
| [
{
"created": "Sun, 21 Mar 1999 10:40:24 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Campanelli",
"Manuela",
"",
"Max-Planck-Institut fuer Gravitationsphysik,\n Albert-Einstein-Institut, Potsdam, Germany"
]
] | The computation of gravitational radiation generated by the coalescence of inspiralling binary black holes is nowdays one of the main goals of numerical relativity. Perturbation theory has emerged as an ubiquitous tool for all those dynamical evolutions where the two black holes start close enough to each other, to be treated as single distorted black hole (close limit approximation), providing at the same time useful benchmarks for full numerical simulations. Here we summarize the most recent developments to study evolutions of perturbations around rotating (Kerr) black holes. The final aim is to generalize the close limit approximation to the most general case of two rotating black holes in orbit around each other, and thus provide reliable templates for the gravitational waveforms in this regime. For this reason it has become very important to know if these predictions can actually be trusted to larger separation parameters (even in the region where the holes have distinct event horizons). The only way to extend the range of validity of the linear approximation is to develop the theory of second order perturbations around a Kerr hole, by generalizing the Teukolsky formalism. |
2004.07752 | Xian Gao | Xian Gao and Yu-Min Hu | Higher derivative scalar-tensor theory and spatially covariant gravity:
the correspondence | 19 pages | Phys. Rev. D 102, 084006 (2020) | 10.1103/PhysRevD.102.084006 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the correspondence between generally covariant higher
derivative scalar-tensor theory and spatially covariant gravity theory. The
building blocks are the scalar field and spacetime curvature tensor together
with their generally covariant derivatives for the former, and the spatially
covariant geometric quantities together with their spatially covariant
derivatives for the later. In the case of a single scalar degree of freedom,
they are transformed to each other by gauge fixing and recovering procedures,
of which we give the explicit expressions. We make a systematic classification
of all the scalar monomials in the spatially covariant gravity according to the
total number of derivatives up to $d=4$, and their correspondence to the
scalar-tensor monomials. We discusse the possibility of using spatially
covariant monomials to generate ghostfree higher derivative scalar-tensor
theories. We also derive the covariant 3+1 decomposition without fixing any
specific coordinate, which will be useful when performing a covariant
Hamiltonian analysis.
| [
{
"created": "Thu, 16 Apr 2020 16:37:15 GMT",
"version": "v1"
}
] | 2020-10-07 | [
[
"Gao",
"Xian",
""
],
[
"Hu",
"Yu-Min",
""
]
] | We investigate the correspondence between generally covariant higher derivative scalar-tensor theory and spatially covariant gravity theory. The building blocks are the scalar field and spacetime curvature tensor together with their generally covariant derivatives for the former, and the spatially covariant geometric quantities together with their spatially covariant derivatives for the later. In the case of a single scalar degree of freedom, they are transformed to each other by gauge fixing and recovering procedures, of which we give the explicit expressions. We make a systematic classification of all the scalar monomials in the spatially covariant gravity according to the total number of derivatives up to $d=4$, and their correspondence to the scalar-tensor monomials. We discusse the possibility of using spatially covariant monomials to generate ghostfree higher derivative scalar-tensor theories. We also derive the covariant 3+1 decomposition without fixing any specific coordinate, which will be useful when performing a covariant Hamiltonian analysis. |
0803.4446 | Tomasz Pawlowski | Eloisa Bentivegna, Tomasz Pawlowski | Anti-deSitter universe dynamics in LQC | Revtex4, 29 pages, 20 figures, typos corrected | Phys.Rev.D77:124025,2008 | 10.1103/PhysRevD.77.124025 | IGC-08/3-3 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A model for a flat isotropic universe with a negative cosmological constant
$\Lambda$ and a massless scalar field as sole matter content is studied within
the framework of Loop Quantum Cosmology. By application of the methods
introduced for the model with $\Lambda=0$, the physical Hilbert space and the
set of Dirac observables are constructed. As in that case, the scalar field
plays here the role of an emergent time. The properties of the system are found
to be similar to those of the $k=1$ FRW model: for small energy densities, the
quantum dynamics reproduces the classical one, whereas, due to modifications at
near-Planckian densities, the big bang and big crunch singularities are
replaced by a quantum bounce connecting deterministically the large
semiclassical epochs. Thus in Loop Quantum Cosmology the evolution is
qualitatively cyclic.
| [
{
"created": "Mon, 31 Mar 2008 14:19:27 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Apr 2008 16:06:28 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Bentivegna",
"Eloisa",
""
],
[
"Pawlowski",
"Tomasz",
""
]
] | A model for a flat isotropic universe with a negative cosmological constant $\Lambda$ and a massless scalar field as sole matter content is studied within the framework of Loop Quantum Cosmology. By application of the methods introduced for the model with $\Lambda=0$, the physical Hilbert space and the set of Dirac observables are constructed. As in that case, the scalar field plays here the role of an emergent time. The properties of the system are found to be similar to those of the $k=1$ FRW model: for small energy densities, the quantum dynamics reproduces the classical one, whereas, due to modifications at near-Planckian densities, the big bang and big crunch singularities are replaced by a quantum bounce connecting deterministically the large semiclassical epochs. Thus in Loop Quantum Cosmology the evolution is qualitatively cyclic. |
gr-qc/0302004 | Tomohiro Harada | Tomohiro Harada | Self-Similar Solutions, Critical Behavior and Convergence to Attractor
in Gravitational Collapse | 14 pages, invited review talk given at the 12th Workshop on General
Relativity and Gravitation, Nov 25-28, 2002, Tokyo, Japan | null | null | WU-AP/156/03 | gr-qc | null | General relativity as well as Newtonian gravity admits self-similar solutions
due to its scale-invariance. This is a review on these self-similar solutions
and their relevance to gravitational collapse. In particular, our attention is
mainly paid on the crucial role of self-similar solutions in the critical
behavior and attraction in gravitational collapse.
| [
{
"created": "Mon, 3 Feb 2003 10:23:53 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Harada",
"Tomohiro",
""
]
] | General relativity as well as Newtonian gravity admits self-similar solutions due to its scale-invariance. This is a review on these self-similar solutions and their relevance to gravitational collapse. In particular, our attention is mainly paid on the crucial role of self-similar solutions in the critical behavior and attraction in gravitational collapse. |
2406.13690 | Pabitra Tripathy | Pabitra Tripathy | Lower bound of black hole hair in pure Lovelock theory of gravity | 6 pages, 1 figure | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | As an alternative to the "no hair conjecture," the "no short hair conjecture"
for hairy black holes was established earlier. This theorem stipulates that
hair must be present above 3/2 of the event horizon radius for a hairy black
hole. It is assumed that the nonlinear behavior of the matter field plays a key
role in the presence of such hair. Subsequently, it was established that the
hair must extend beyond the photon sphere of the corresponding black hole. We
have investigated the validity of the "no short hair conjecture" in pure
Lovelock gravity. Our analysis has shown that irrespective of dimensionality
and Lovelock order, the hair of a static, spherically symmetric black hole
extends at least up to the photon sphere.
| [
{
"created": "Wed, 19 Jun 2024 16:42:13 GMT",
"version": "v1"
}
] | 2024-06-21 | [
[
"Tripathy",
"Pabitra",
""
]
] | As an alternative to the "no hair conjecture," the "no short hair conjecture" for hairy black holes was established earlier. This theorem stipulates that hair must be present above 3/2 of the event horizon radius for a hairy black hole. It is assumed that the nonlinear behavior of the matter field plays a key role in the presence of such hair. Subsequently, it was established that the hair must extend beyond the photon sphere of the corresponding black hole. We have investigated the validity of the "no short hair conjecture" in pure Lovelock gravity. Our analysis has shown that irrespective of dimensionality and Lovelock order, the hair of a static, spherically symmetric black hole extends at least up to the photon sphere. |
2105.02289 | Claudia Moreno | Jaime Mendoza Hernandez, Mauricio Bellini, Claudia Moreno | Space-time waves from a collapsing universe with a gravitational
attractor | 10 pages, 2 figures | Physics of the Dark Universe, 30 (2020) 100703 | 10.1016/j.dark.2020.100703 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a collapsing system attracted by a spherically symmetric
gravitational source, with an increasing mass, that generates back-reaction
effects that are the source of space-time waves. As an example, we consider an
exponential collapse and the space-time waves emitted during this collapse due
to the back-reaction effects, originated by geometrical deformation driven by
the increment of the gravitational attracting mass during the collapse.
| [
{
"created": "Wed, 5 May 2021 19:15:04 GMT",
"version": "v1"
}
] | 2021-05-07 | [
[
"Hernandez",
"Jaime Mendoza",
""
],
[
"Bellini",
"Mauricio",
""
],
[
"Moreno",
"Claudia",
""
]
] | We study a collapsing system attracted by a spherically symmetric gravitational source, with an increasing mass, that generates back-reaction effects that are the source of space-time waves. As an example, we consider an exponential collapse and the space-time waves emitted during this collapse due to the back-reaction effects, originated by geometrical deformation driven by the increment of the gravitational attracting mass during the collapse. |
1512.05713 | Mauricio Bellini | Jes\'us Mart\'in Romero, Mauricio Bellini, Jos\'e Edgar Madriz Aguilar | Gravitational waves from a Weyl-Integrable manifold: a new formalism | Accepted in Physics of the Dark Universe | null | null | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the variational principle over an Hilbert-Einstein like action for
an extended geometry taking into account torsion and non-metricity. By
extending the semi-Riemannian geometry, we obtain an effective energy-momentum
tensor which can be interpreted as physical sources. As an application we
develop a new manner to obtain the gravitational wave equations on a
Weyl-integrable manifold taking into account the non-metricity and non-trivial
boundary conditions on the minimization of the action, which can be identified
as possible sources for the cosmological constant and provides two different
equations for gravitational waves. We examine gravitational waves in a
pre-inflationary cosmological model.
| [
{
"created": "Thu, 17 Dec 2015 18:34:07 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Mar 2016 00:19:48 GMT",
"version": "v2"
},
{
"created": "Tue, 29 Mar 2016 17:50:34 GMT",
"version": "v3"
}
] | 2016-03-30 | [
[
"Romero",
"Jesús Martín",
""
],
[
"Bellini",
"Mauricio",
""
],
[
"Aguilar",
"José Edgar Madriz",
""
]
] | We study the variational principle over an Hilbert-Einstein like action for an extended geometry taking into account torsion and non-metricity. By extending the semi-Riemannian geometry, we obtain an effective energy-momentum tensor which can be interpreted as physical sources. As an application we develop a new manner to obtain the gravitational wave equations on a Weyl-integrable manifold taking into account the non-metricity and non-trivial boundary conditions on the minimization of the action, which can be identified as possible sources for the cosmological constant and provides two different equations for gravitational waves. We examine gravitational waves in a pre-inflationary cosmological model. |
gr-qc/0202030 | Alfredo Sandoval-Villalbazo | Ana Laura Garc\'ia-Perciante, Alfredo Sandoval-Villalbazo, and L.S.
Garc\'ia Col\'in | A six dimensional analysis of Maxwell's Field Equations | 8 pages, RevTex. Submitted to Revista Mexicana de F\'{i}sica | null | null | null | gr-qc | null | A framework based on an extension of Kaluza's original idea of using a five
dimensional space to unify gravity with electromagnetism is used to analyze
Maxwell\'{}s field equations. The extension consists in the use of a six
dimensional space in which all equations of electromagnetism may be obtained
using only Einstein's field equation. Two major advantages of this approach to
electromagnetism are discussed, a full symmetric derivation for the wave
equations for the potentials and a natural inclusion of magnetic monopoles
without using any argument based on singularities.
| [
{
"created": "Fri, 8 Feb 2002 17:08:19 GMT",
"version": "v1"
}
] | 2016-08-16 | [
[
"García-Perciante",
"Ana Laura",
""
],
[
"Sandoval-Villalbazo",
"Alfredo",
""
],
[
"Colín",
"L. S. García",
""
]
] | A framework based on an extension of Kaluza's original idea of using a five dimensional space to unify gravity with electromagnetism is used to analyze Maxwell\'{}s field equations. The extension consists in the use of a six dimensional space in which all equations of electromagnetism may be obtained using only Einstein's field equation. Two major advantages of this approach to electromagnetism are discussed, a full symmetric derivation for the wave equations for the potentials and a natural inclusion of magnetic monopoles without using any argument based on singularities. |
1803.05833 | Willians Barreto | W. Barreto, P. C.M. Clemente, H. P. de Oliveira, B. Rodriguez-Mueller | Rio: A new computational framework for accurate initial data of binary
black holes | 15 pages, 6 figures; updated version to appear in Gen. Rel. Grav | Gen Relativ Gravit (2018) 50: 71 | 10.1007/s10714-018-2393-1 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a computational framework (Rio) in the ADM 3+1 approach for
numerical relativity. This work enables us to carry out high resolution
calculations for initial data of two arbitrary black holes. We use the
transverse conformal treatment, the Bowen-York and the puncture methods. For
the numerical solution of the Hamiltonian constraint we use the domain
decomposition and the spectral decomposition of Galerkin-Collocation. The
nonlinear numerical code solves the set of equations for the spectral modes
using the standard Newton-Raphson method, LU decomposition and Gaussian
quadratures. We show the convergence of the Rio code. This code allows for easy
deployment of large calculations. We show how the spin of one of the black
holes is manifest in the conformal factor.
| [
{
"created": "Thu, 15 Mar 2018 16:10:17 GMT",
"version": "v1"
},
{
"created": "Thu, 12 Apr 2018 20:12:49 GMT",
"version": "v2"
},
{
"created": "Wed, 23 May 2018 12:49:41 GMT",
"version": "v3"
}
] | 2018-06-12 | [
[
"Barreto",
"W.",
""
],
[
"Clemente",
"P. C. M.",
""
],
[
"de Oliveira",
"H. P.",
""
],
[
"Rodriguez-Mueller",
"B.",
""
]
] | We present a computational framework (Rio) in the ADM 3+1 approach for numerical relativity. This work enables us to carry out high resolution calculations for initial data of two arbitrary black holes. We use the transverse conformal treatment, the Bowen-York and the puncture methods. For the numerical solution of the Hamiltonian constraint we use the domain decomposition and the spectral decomposition of Galerkin-Collocation. The nonlinear numerical code solves the set of equations for the spectral modes using the standard Newton-Raphson method, LU decomposition and Gaussian quadratures. We show the convergence of the Rio code. This code allows for easy deployment of large calculations. We show how the spin of one of the black holes is manifest in the conformal factor. |
gr-qc/0112078 | Helio V. Fagundes | Helio V. Fagundes (Instituto de Fisica Teorica, Universidade Estadual
Paulista, Sao Paulo, Brazil) | Exploring the global topology of the universe | 4 pages. Contribution to the XXII Brazilian National Meeting on
Particles and Fields, Sao Lourenco, October 2001 | Braz.J.Phys. 32 (2002) 891-894 | null | null | gr-qc astro-ph hep-th | null | In this talk work done by our group on cosmic topology is reviewed. It ranges
from early attempts to solve a famous controversy about quasars through the
multiplicity of images, to quantum cosmology in this context and an application
to QED renormalization.
| [
{
"created": "Sun, 30 Dec 2001 14:29:18 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Fagundes",
"Helio V.",
"",
"Instituto de Fisica Teorica, Universidade Estadual\n Paulista, Sao Paulo, Brazil"
]
] | In this talk work done by our group on cosmic topology is reviewed. It ranges from early attempts to solve a famous controversy about quasars through the multiplicity of images, to quantum cosmology in this context and an application to QED renormalization. |
gr-qc/0606081 | Aleksandar Mikovic | A. Mikovic | Errata to "Flat Spacetime Vacuum in Loop Quantum Gravity" | 3 pages, 1 figure | Class.Quant.Grav.23:5459-5462,2006 | 10.1088/0264-9381/23/17/C01 | null | gr-qc | null | We give the correct expressions for the spin network evaluations proposed in
Class. Quant. Grav. 21 (2004) 3909 as the coefficients of the quantum gravity
vacuum wavefunction in the spin network basis.
| [
{
"created": "Mon, 19 Jun 2006 15:39:54 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Mikovic",
"A.",
""
]
] | We give the correct expressions for the spin network evaluations proposed in Class. Quant. Grav. 21 (2004) 3909 as the coefficients of the quantum gravity vacuum wavefunction in the spin network basis. |
gr-qc/9906112 | Michael Martin Nieto | John D. Anderson, Philip A. Laing, Eunice L. Lau, Anthony S. Liu,
Michael Martin Nieto, and Slava G. Turyshev | Anderson et al. Reply (to the Comment by Katz on Pioneer 10/11) | LaTex, 3 pages, Phys. Rev. Lett. (to be published) | Phys.Rev.Lett. 83 (1999) 1893 | 10.1103/PhysRevLett.83.1893 | LA-UR-98-5522 | gr-qc astro-ph | null | We conclude that Katz's proposal (anisotropic heat reflection off of the back
of the spacecraft high-gain antennae, the heat coming from the RTGs) does not
provide enough power and so can not explain the Pioneer anomaly.
| [
{
"created": "Tue, 29 Jun 1999 03:11:38 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Anderson",
"John D.",
""
],
[
"Laing",
"Philip A.",
""
],
[
"Lau",
"Eunice L.",
""
],
[
"Liu",
"Anthony S.",
""
],
[
"Nieto",
"Michael Martin",
""
],
[
"Turyshev",
"Slava G.",
""
]
] | We conclude that Katz's proposal (anisotropic heat reflection off of the back of the spacecraft high-gain antennae, the heat coming from the RTGs) does not provide enough power and so can not explain the Pioneer anomaly. |
1204.1859 | Wei-Tou Ni | Wei-Tou Ni | Equivalence Principles, Lense-Thirring Effects, and Solar-System Tests
of Cosmological Models | 7 pages, 1 table, plenary talk presented at ICGAC10 (Xth
International Conference on Gravitation, Astrophysics and Cosmology),
Quy-Nhon, Vietnam, December 17-22, 2011 | null | null | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this talk, we review the empirical status for modern gravitational
theories with emphases on (i) Equivalence Principles; (ii) Lense-Thirring
effects and the implications of Gravity Probe B experiment; (iii) Solar-System
Tests of Cosmological Models.
| [
{
"created": "Mon, 9 Apr 2012 11:37:53 GMT",
"version": "v1"
}
] | 2012-04-10 | [
[
"Ni",
"Wei-Tou",
""
]
] | In this talk, we review the empirical status for modern gravitational theories with emphases on (i) Equivalence Principles; (ii) Lense-Thirring effects and the implications of Gravity Probe B experiment; (iii) Solar-System Tests of Cosmological Models. |
1506.01101 | Miftachul Hadi | Miftachul Hadi, Malcolm Anderson, Andri Husein | The Gravitational Field of a Twisted Skyrmion String | 5 pages, no figure, presented at ICMNS Bandung, Indonesia, 2 Nov 2014
and submitted to AIP Conference Proceedings | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study the gravitational field of a straight string generated
from a class of nonlinear sigma models, specifically the Skyrme model with a
twist (the twisted Skyrmion string). The twist term, mkz, is included to
stabilize the vortex solution. To model the effects of gravity, we replace the
Minkowski tensor, $\eta^{\mu\nu}$, in the standard Skyrme Lagrangian density
with a space-time metric tensor, $g^{\mu\nu}$, assumed to be static and
cylindrically symmetric. The Einstein equations for the metric and field
components are then derived. This work is still in progress.
| [
{
"created": "Wed, 3 Jun 2015 01:18:44 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Jun 2015 00:44:06 GMT",
"version": "v2"
},
{
"created": "Mon, 13 Jul 2015 08:03:28 GMT",
"version": "v3"
}
] | 2015-07-14 | [
[
"Hadi",
"Miftachul",
""
],
[
"Anderson",
"Malcolm",
""
],
[
"Husein",
"Andri",
""
]
] | In this paper we study the gravitational field of a straight string generated from a class of nonlinear sigma models, specifically the Skyrme model with a twist (the twisted Skyrmion string). The twist term, mkz, is included to stabilize the vortex solution. To model the effects of gravity, we replace the Minkowski tensor, $\eta^{\mu\nu}$, in the standard Skyrme Lagrangian density with a space-time metric tensor, $g^{\mu\nu}$, assumed to be static and cylindrically symmetric. The Einstein equations for the metric and field components are then derived. This work is still in progress. |
1804.11198 | Mohamed Bennai | A. Safsafi and I. Khay and F. Salamate and H. Chakir and M. Bennai | On Chaplygin Gas Braneworld Inflation with Monomial Potential | 7 figures. arXiv admin note: text overlap with arXiv:0805.1005 by
other authors | null | null | null | gr-qc | http://creativecommons.org/publicdomain/zero/1.0/ | In this paper we study the Chaplygin gas model as a candidate for inflation
in the framework of the Randall Sundrum type-II braneworld model. We consider
the original and generalized Chaplygin gas model in the presence of monomial
potential. The inflationary spectrum perturbation parameters are reformulated
and evaluated in the high-energy limit and we found that they depend on several
parameters. We also showed that these perturbation parameters are widely
compatible with the recent Planck data for a particular choice of the
parameters space of the model. A suitable observational central value of
$n_{s}\simeq $ $0.965$ is also obtained in the case of original and generalized
Chaplygin gas.
| [
{
"created": "Thu, 26 Apr 2018 11:22:16 GMT",
"version": "v1"
}
] | 2018-05-01 | [
[
"Safsafi",
"A.",
""
],
[
"Khay",
"I.",
""
],
[
"Salamate",
"F.",
""
],
[
"Chakir",
"H.",
""
],
[
"Bennai",
"M.",
""
]
] | In this paper we study the Chaplygin gas model as a candidate for inflation in the framework of the Randall Sundrum type-II braneworld model. We consider the original and generalized Chaplygin gas model in the presence of monomial potential. The inflationary spectrum perturbation parameters are reformulated and evaluated in the high-energy limit and we found that they depend on several parameters. We also showed that these perturbation parameters are widely compatible with the recent Planck data for a particular choice of the parameters space of the model. A suitable observational central value of $n_{s}\simeq $ $0.965$ is also obtained in the case of original and generalized Chaplygin gas. |
0809.0052 | Catherine Meusburger | C. Meusburger | Quantum double and $\kappa$-Poincar\'e symmetries in (2+1)-gravity and
Chern-Simons theory | 11 pages, no figures, expanded version of talk at the conference
Theory Canada 4, references and explanations added, typos corrected | Canadian Journal of Physics 87 (2009), 245-250 | 10.1139/P08-076 | pi-qg-87 | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We review the role of Drinfeld doubles and kappa-Poincare symmetries in
quantised (2+1)-gravity and Chern-Simons theory. We discuss the conditions
under which a given Hopf algebra symmetry is compatible with a Chern-Simons
theory and determine this compatibility explicitly for the Drinfeld doubles and
kappa-Poincare symmetries associated with the isometry groups of (2+1)-gravity.
In particular, we explain that the usual kappa-Poincare symmetries with a
timelike deformation are not directly associated with (2+1)-gravity. These
kappa-Poincare symmetries are linked to Chern-Simons theory only in the de
Sitter case, and the relevant Chern-Simons theory is physically inequivalent to
(2+1)-gravity.
| [
{
"created": "Sat, 30 Aug 2008 10:38:22 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Sep 2008 11:36:14 GMT",
"version": "v2"
}
] | 2023-06-13 | [
[
"Meusburger",
"C.",
""
]
] | We review the role of Drinfeld doubles and kappa-Poincare symmetries in quantised (2+1)-gravity and Chern-Simons theory. We discuss the conditions under which a given Hopf algebra symmetry is compatible with a Chern-Simons theory and determine this compatibility explicitly for the Drinfeld doubles and kappa-Poincare symmetries associated with the isometry groups of (2+1)-gravity. In particular, we explain that the usual kappa-Poincare symmetries with a timelike deformation are not directly associated with (2+1)-gravity. These kappa-Poincare symmetries are linked to Chern-Simons theory only in the de Sitter case, and the relevant Chern-Simons theory is physically inequivalent to (2+1)-gravity. |
2404.15808 | Sohan Kumar Jha | Sohan Kumar Jha | Observational signature of Lorentz violation in Kalb-Ramond field model
and Bumblebee model: A comprehensive comparative study | null | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | This article is devoted to the comparative study of the effects of the
Lorentz symmetry violation (LV) arising in Kalb-Ramond (KR) and Bumblebee (BM)
field models. We study optical appearance with accretion, Quasinormal modes,
ringdown waveforms, Hawking radiation, and weak gravitational lensing. The
horizon radius, photon radius, and the critical impact parameter for KR BHs
decrease with the LV parameter $\a$. In contrast, they remain independent of
the BM parameter $\b$ and have values the same as those for \s BH. We find that
a KR BH is brighter than a \s or BM BH for static and infalling accretion. The
BM BH, on the other hand, is brighter than a \s BH when the accretion is static
but becomes darker for an infalling accretion. Our investigation into
quasinormal modes (QNMs) and ringdown waveforms provides deeper insight into
the difference in observational imprints of LV parameters. It reveals that GWs
emitted by KR BHs have larger frequencies and decay faster than those emitted
by \s or BM BHs for scalar and electromagnetic perturbations. We then study the
greybody factor (GF) and power emitted for both BHs. The Hawking temperature is
higher for a KR BM and lower for a BM BH than a \s BH. It also reveals that the
transmission probability decreases with $\a$ and $\b$. A comparison of GFs for
KR and BM BHs reveals that the transmission probability is higher for BM BH. We
also study the effect of LV on the power emitted in the form of Hawking
radiation. Power received by an asymptotic observer is larger for a KR BH. We
obtain higher-order corrections in the deflection angle and graphically
illustrate the impact of $\a$ and $\b$. We observe that a light ray gets
deflected most from its path when passing by a \s BH, and the deflection is
least when it passes by a KR BH. Our study conclusively shows that we can
differentiate between KR and BM BHs based on astrophysical observations.
| [
{
"created": "Wed, 24 Apr 2024 11:13:28 GMT",
"version": "v1"
}
] | 2024-04-25 | [
[
"Jha",
"Sohan Kumar",
""
]
] | This article is devoted to the comparative study of the effects of the Lorentz symmetry violation (LV) arising in Kalb-Ramond (KR) and Bumblebee (BM) field models. We study optical appearance with accretion, Quasinormal modes, ringdown waveforms, Hawking radiation, and weak gravitational lensing. The horizon radius, photon radius, and the critical impact parameter for KR BHs decrease with the LV parameter $\a$. In contrast, they remain independent of the BM parameter $\b$ and have values the same as those for \s BH. We find that a KR BH is brighter than a \s or BM BH for static and infalling accretion. The BM BH, on the other hand, is brighter than a \s BH when the accretion is static but becomes darker for an infalling accretion. Our investigation into quasinormal modes (QNMs) and ringdown waveforms provides deeper insight into the difference in observational imprints of LV parameters. It reveals that GWs emitted by KR BHs have larger frequencies and decay faster than those emitted by \s or BM BHs for scalar and electromagnetic perturbations. We then study the greybody factor (GF) and power emitted for both BHs. The Hawking temperature is higher for a KR BM and lower for a BM BH than a \s BH. It also reveals that the transmission probability decreases with $\a$ and $\b$. A comparison of GFs for KR and BM BHs reveals that the transmission probability is higher for BM BH. We also study the effect of LV on the power emitted in the form of Hawking radiation. Power received by an asymptotic observer is larger for a KR BH. We obtain higher-order corrections in the deflection angle and graphically illustrate the impact of $\a$ and $\b$. We observe that a light ray gets deflected most from its path when passing by a \s BH, and the deflection is least when it passes by a KR BH. Our study conclusively shows that we can differentiate between KR and BM BHs based on astrophysical observations. |
1710.02403 | Marius Adrian Oancea | Claudio F. Paganini, Marius A. Oancea | Smoothness of the future and past trapped sets in Kerr-Newman-Taub-NUT
spacetimes | 11 pages, 1 figure. This article is intended as a research article,
and supersedes arXiv:1611.06927, which was only intended as lecture notes, so
there is significant overlap of the definitions | null | 10.1088/1361-6382/aaaa5b | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the sets of future/past trapped null geodesics in the exterior
region of a sub-extremal Kerr-Newman-Taub-NUT spacetime. We show that, from the
point of view of any timelike observer outside of such a black hole, trapping
can be understood as two smooth sets of spacelike directions on the celestial
sphere of the observer.
| [
{
"created": "Fri, 6 Oct 2017 13:32:50 GMT",
"version": "v1"
}
] | 2018-03-14 | [
[
"Paganini",
"Claudio F.",
""
],
[
"Oancea",
"Marius A.",
""
]
] | We consider the sets of future/past trapped null geodesics in the exterior region of a sub-extremal Kerr-Newman-Taub-NUT spacetime. We show that, from the point of view of any timelike observer outside of such a black hole, trapping can be understood as two smooth sets of spacelike directions on the celestial sphere of the observer. |
gr-qc/0612044 | Kazuhiro Yamamoto | Kazuhiro Yamamoto, Masaki Ando, Keita Kawabe, Kimio Tsubono | A theoretical approach to thermal noise caused by an inhomogeneously
distributed loss -- Physical insight by the advanced modal expansion | 10 pages, 4 figures | Phys.Rev.D75:082002,2007 | 10.1103/PhysRevD.75.082002 | null | gr-qc physics.ins-det | null | We modified the modal expansion, which is the traditional method used to
calculate thermal noise. This advanced modal expansion provides physical
insight about the discrepancy between the actual thermal noise caused by
inhomogeneously distributed loss and the traditional modal expansion. This
discrepancy comes from correlations between the thermal fluctuations of the
resonant modes. The thermal noise spectra estimated by the advanced modal
expansion are consistent with the results of measurements of thermal
fluctuations caused by inhomogeneous losses.
| [
{
"created": "Thu, 7 Dec 2006 13:38:46 GMT",
"version": "v1"
},
{
"created": "Tue, 24 Apr 2007 08:11:41 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Yamamoto",
"Kazuhiro",
""
],
[
"Ando",
"Masaki",
""
],
[
"Kawabe",
"Keita",
""
],
[
"Tsubono",
"Kimio",
""
]
] | We modified the modal expansion, which is the traditional method used to calculate thermal noise. This advanced modal expansion provides physical insight about the discrepancy between the actual thermal noise caused by inhomogeneously distributed loss and the traditional modal expansion. This discrepancy comes from correlations between the thermal fluctuations of the resonant modes. The thermal noise spectra estimated by the advanced modal expansion are consistent with the results of measurements of thermal fluctuations caused by inhomogeneous losses. |
0905.2575 | Gilles Esposito-Farese | Gilles Esposito-Farese | Motion in alternative theories of gravity | 28 pages, 12 figures, lecture given at the "School on Mass" (Orleans,
France, June 2008), uses Springer's "svmult.cls" | Fundam.Theor.Phys.162:461-489,2011 | 10.1007/978-90-481-3015-3 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Although general relativity (GR) passes all present experimental tests with
flying colors, it remains important to study alternative theories of gravity
for several theoretical and phenomenological reasons that we recall in these
lecture notes. The various possible ways of modifying GR are presented, and we
notably show that the motion of massive bodies may be changed even if one
assumes that matter is minimally coupled to the metric as in GR. This is
illustrated with the particular case of scalar-tensor theories of gravity,
whose Fokker action is discussed, and we also mention the consequences of the
no-hair theorem on the motion of black holes. The finite size of the bodies
modifies their motion with respect to pointlike particles, and we give a simple
argument showing that the corresponding effects are generically much larger in
alternative theories than in GR. We also discuss possible modifications of
Newtonian dynamics (MOND) at large distances, which have been proposed to avoid
the dark matter hypothesis. We underline that all the previous classes of
alternatives to GR may a priori be used to predict such a phenomenology, but
that they generically involve several theoretical and experimental
difficulties.
| [
{
"created": "Fri, 15 May 2009 16:00:04 GMT",
"version": "v1"
}
] | 2011-02-28 | [
[
"Esposito-Farese",
"Gilles",
""
]
] | Although general relativity (GR) passes all present experimental tests with flying colors, it remains important to study alternative theories of gravity for several theoretical and phenomenological reasons that we recall in these lecture notes. The various possible ways of modifying GR are presented, and we notably show that the motion of massive bodies may be changed even if one assumes that matter is minimally coupled to the metric as in GR. This is illustrated with the particular case of scalar-tensor theories of gravity, whose Fokker action is discussed, and we also mention the consequences of the no-hair theorem on the motion of black holes. The finite size of the bodies modifies their motion with respect to pointlike particles, and we give a simple argument showing that the corresponding effects are generically much larger in alternative theories than in GR. We also discuss possible modifications of Newtonian dynamics (MOND) at large distances, which have been proposed to avoid the dark matter hypothesis. We underline that all the previous classes of alternatives to GR may a priori be used to predict such a phenomenology, but that they generically involve several theoretical and experimental difficulties. |
1807.10141 | Daphne O. Klemme | Vincent Moncrief and James Isenberg | Symmetries of Cosmological Cauchy Horizons with Non-Closed Orbits | 55 pages. arXiv admin note: substantial text overlap with
arXiv:0805.1451 | null | 10.1007/s00220-019-03571-9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider analytic, vacuum spacetimes that admit compact, non-degenerate
Cauchy horizons. Many years ago we proved that, if the null geodesic generators
of such a horizon were all \textit{closed} curves, then the enveloping
spacetime would necessarily admit a non-trivial, horizon-generating Killing
vector field. Using a slightly extended version of the Cauchy-Kowaleski theorem
one could establish the existence of infinite dimensional, analytic families of
such `generalized Taub-NUT' spacetimes and show that, generically, they
admitted \textit{only} the single (horizon-generating) Killing field alluded to
above. In this article we relax the closure assumption and analyze vacuum
spacetimes in which the generic horizon generating null geodesic densely fills
a 2-torus lying in the horizon. In particular we show that, aside from some
highly exceptional cases that we refer to as `ergodic', the non-closed
generators always have this (densely 2-torus-filling) geometrical property in
the analytic setting.
By extending arguments we gave previously for the characterization of the
Killing symmetries of higher dimensional, stationary black holes we prove that
analytic, 4-dimensional, vacuum spacetimes with such (non-ergodic) compact
Cauchy horizons always admit (at least) two independent, commuting Killing
vector fields of which a special linear combination is horizon generating. We
also discuss the \textit{conjectures} that every such spacetime with an
\textit{ergodic} horizon is trivially constructable from the flat Kasner
solution by making certain `irrational' toroidal compactifications and that
degenerate compact Cauchy horizons do not exist in the analytic case.
| [
{
"created": "Wed, 25 Jul 2018 13:43:41 GMT",
"version": "v1"
}
] | 2019-10-23 | [
[
"Moncrief",
"Vincent",
""
],
[
"Isenberg",
"James",
""
]
] | We consider analytic, vacuum spacetimes that admit compact, non-degenerate Cauchy horizons. Many years ago we proved that, if the null geodesic generators of such a horizon were all \textit{closed} curves, then the enveloping spacetime would necessarily admit a non-trivial, horizon-generating Killing vector field. Using a slightly extended version of the Cauchy-Kowaleski theorem one could establish the existence of infinite dimensional, analytic families of such `generalized Taub-NUT' spacetimes and show that, generically, they admitted \textit{only} the single (horizon-generating) Killing field alluded to above. In this article we relax the closure assumption and analyze vacuum spacetimes in which the generic horizon generating null geodesic densely fills a 2-torus lying in the horizon. In particular we show that, aside from some highly exceptional cases that we refer to as `ergodic', the non-closed generators always have this (densely 2-torus-filling) geometrical property in the analytic setting. By extending arguments we gave previously for the characterization of the Killing symmetries of higher dimensional, stationary black holes we prove that analytic, 4-dimensional, vacuum spacetimes with such (non-ergodic) compact Cauchy horizons always admit (at least) two independent, commuting Killing vector fields of which a special linear combination is horizon generating. We also discuss the \textit{conjectures} that every such spacetime with an \textit{ergodic} horizon is trivially constructable from the flat Kasner solution by making certain `irrational' toroidal compactifications and that degenerate compact Cauchy horizons do not exist in the analytic case. |
gr-qc/0605151 | Hakan Andreasson | Hakan Andreasson | On static shells and the Buchdahl inequality for the spherically
symmetric Einstein-Vlasov system | 20 pages, Latex | Commun. Math. Phys. 274:409-425,2007 | 10.1007/s00220-007-0285-4 | null | gr-qc math-ph math.MP | null | In a previous work \cite{An1} matter models such that the energy density
$\rho\geq 0,$ and the radial- and tangential pressures $p\geq 0$ and $q,$
satisfy $p+q\leq\Omega\rho, \Omega\geq 1,$ were considered in the context of
Buchdahl's inequality. It was proved that static shell solutions of the
spherically symmetric Einstein equations obey a Buchdahl type inequality
whenever the support of the shell, $[R_0,R_1], R_0>0,$ satisfies $R_1/R_0<1/4.$
Moreover, given a sequence of solutions such that $R_1/R_0\to 1,$ then the
limit supremum of $2M/R_1$ was shown to be bounded by
$((2\Omega+1)^2-1)/(2\Omega+1)^2.$ In this paper we show that the hypothesis
that $R_1/R_0\to 1,$ can be realized for Vlasov matter, by constructing a
sequence of static shells of the spherically symmetric Einstein-Vlasov system
with this property. We also prove that for this sequence not only the limit
supremum of $2M/R_1$ is bounded, but that the limit is
$((2\Omega+1)^2-1)/(2\Omega+1)^2=8/9,$ since $\Omega=1$ for Vlasov matter.
Thus, static shells of Vlasov matter can have $2M/R_1$ arbitrary close to
$8/9,$ which is interesting in view of \cite{AR2}, where numerical evidence is
presented that 8/9 is an upper bound of $2M/R_1$ of any static solution of the
spherically symmetric Einstein-Vlasov system.
| [
{
"created": "Wed, 31 May 2006 16:12:07 GMT",
"version": "v1"
}
] | 2011-08-04 | [
[
"Andreasson",
"Hakan",
""
]
] | In a previous work \cite{An1} matter models such that the energy density $\rho\geq 0,$ and the radial- and tangential pressures $p\geq 0$ and $q,$ satisfy $p+q\leq\Omega\rho, \Omega\geq 1,$ were considered in the context of Buchdahl's inequality. It was proved that static shell solutions of the spherically symmetric Einstein equations obey a Buchdahl type inequality whenever the support of the shell, $[R_0,R_1], R_0>0,$ satisfies $R_1/R_0<1/4.$ Moreover, given a sequence of solutions such that $R_1/R_0\to 1,$ then the limit supremum of $2M/R_1$ was shown to be bounded by $((2\Omega+1)^2-1)/(2\Omega+1)^2.$ In this paper we show that the hypothesis that $R_1/R_0\to 1,$ can be realized for Vlasov matter, by constructing a sequence of static shells of the spherically symmetric Einstein-Vlasov system with this property. We also prove that for this sequence not only the limit supremum of $2M/R_1$ is bounded, but that the limit is $((2\Omega+1)^2-1)/(2\Omega+1)^2=8/9,$ since $\Omega=1$ for Vlasov matter. Thus, static shells of Vlasov matter can have $2M/R_1$ arbitrary close to $8/9,$ which is interesting in view of \cite{AR2}, where numerical evidence is presented that 8/9 is an upper bound of $2M/R_1$ of any static solution of the spherically symmetric Einstein-Vlasov system. |
2003.01589 | Jorge Pullin | Rodolfo Gambini, Saeed Rastgoo, Jorge Pullin | Gravitation in terms of observables 2: the algebra of fundamental
observables | 21 pages, RevTex, 4 figures | null | 10.1088/1361-6382/ab8eb8 | LSU-REL-030320 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a previous paper, we showed how to use the techniques of the group of
loops to formulate the loop approach to gravity proposed by Mandelstam in the
1960's. Those techniques allow to overcome some of the difficulties that had
been encountered in the earlier treatment. In this approach, gravity is
formulated entirely in terms of Dirac observables without constraints, opening
attractive new possibilities for quantization. In this paper we discuss the
Poisson algebra of the resulting Dirac observables, associated with the
intrinsic components of the Riemann tensor. This provides an explicit
realization of the non-local algebra of observables for gravity that several
authors have conjectured.
| [
{
"created": "Tue, 3 Mar 2020 15:22:15 GMT",
"version": "v1"
}
] | 2020-08-26 | [
[
"Gambini",
"Rodolfo",
""
],
[
"Rastgoo",
"Saeed",
""
],
[
"Pullin",
"Jorge",
""
]
] | In a previous paper, we showed how to use the techniques of the group of loops to formulate the loop approach to gravity proposed by Mandelstam in the 1960's. Those techniques allow to overcome some of the difficulties that had been encountered in the earlier treatment. In this approach, gravity is formulated entirely in terms of Dirac observables without constraints, opening attractive new possibilities for quantization. In this paper we discuss the Poisson algebra of the resulting Dirac observables, associated with the intrinsic components of the Riemann tensor. This provides an explicit realization of the non-local algebra of observables for gravity that several authors have conjectured. |
2006.14349 | Peng Wang | Peng Wang, Houwen Wu, Haitang Yang, and Feiyu Yao | Extended Phase Space Thermodynamics for Black Holes in a Cavity | v1: 20 pages, 9 figures; v2: 21 pages, 9 figures, references added | null | 10.1007/JHEP09(2020)154 | CTP-SCU/2020021 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we extend the phase space of black holes enclosed by a
spherical cavity of radius $r_{B}$ to include $V\equiv4\pi r_{B}^{3}/3$ as a
thermodynamic volume. The thermodynamic behavior of Schwarzschild and
Reissner-Nordstrom (RN) black holes is then investigated in the extended phase
space. In a canonical ensemble at constant pressure, we find that the
aforementioned thermodynamic behavior is remarkably similar to that of the
anti-de Sitter (AdS) counterparts with the cosmological constant being
interpreted as a pressure. Specifically, a first-order Hawking-Page-like phase
transition occurs for a Schwarzschild black hole in a cavity. The phase
structure of a RN black hole in a cavity shows a strong resemblance to that of
the van der Waals fluid. Our results may provide a new perspective for the
extended thermodynamics of AdS black holes by analogy with black holes in a
cavity.
| [
{
"created": "Thu, 25 Jun 2020 12:46:50 GMT",
"version": "v1"
},
{
"created": "Sun, 5 Jul 2020 09:29:05 GMT",
"version": "v2"
}
] | 2020-10-28 | [
[
"Wang",
"Peng",
""
],
[
"Wu",
"Houwen",
""
],
[
"Yang",
"Haitang",
""
],
[
"Yao",
"Feiyu",
""
]
] | In this paper, we extend the phase space of black holes enclosed by a spherical cavity of radius $r_{B}$ to include $V\equiv4\pi r_{B}^{3}/3$ as a thermodynamic volume. The thermodynamic behavior of Schwarzschild and Reissner-Nordstrom (RN) black holes is then investigated in the extended phase space. In a canonical ensemble at constant pressure, we find that the aforementioned thermodynamic behavior is remarkably similar to that of the anti-de Sitter (AdS) counterparts with the cosmological constant being interpreted as a pressure. Specifically, a first-order Hawking-Page-like phase transition occurs for a Schwarzschild black hole in a cavity. The phase structure of a RN black hole in a cavity shows a strong resemblance to that of the van der Waals fluid. Our results may provide a new perspective for the extended thermodynamics of AdS black holes by analogy with black holes in a cavity. |
1507.08225 | Neslihan Oflaz | Ozgur Akarsu, Tekin Dereli, Neslihan Oflaz | Accelerated Expansion of the Universe in a Higher Dimensional Modified
Gravity with Euler-Poincar\'e Terms | 1+19 pages, no figures and tables; matches the version published in
Classical and Quantum Gravity | Classical and Quantum Gravity 32 (2015) 215009 | 10.1088/0264-9381/32/21/215009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A higher dimensional modified gravity theory with an action that includes
dimensionally continued Euler-Poincar\'e forms up to second order in curvatures
is considered. The variational field equations are derived. Matter in the
universe at large scales is modeled by a fluid satisfying an equation of state
with dimensional dichotomy. We study solutions that describe higher dimensional
steady state cosmologies with constant volume for which the three dimensional
external space is expanding at an accelerated rate while the (compact) internal
space is contracting. We showed that the second order Euler-Poincar\'e term in
the constructions of higher dimensional steady state cosmologies could be
crucial.
| [
{
"created": "Wed, 29 Jul 2015 17:09:23 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Oct 2015 18:27:18 GMT",
"version": "v2"
}
] | 2015-10-14 | [
[
"Akarsu",
"Ozgur",
""
],
[
"Dereli",
"Tekin",
""
],
[
"Oflaz",
"Neslihan",
""
]
] | A higher dimensional modified gravity theory with an action that includes dimensionally continued Euler-Poincar\'e forms up to second order in curvatures is considered. The variational field equations are derived. Matter in the universe at large scales is modeled by a fluid satisfying an equation of state with dimensional dichotomy. We study solutions that describe higher dimensional steady state cosmologies with constant volume for which the three dimensional external space is expanding at an accelerated rate while the (compact) internal space is contracting. We showed that the second order Euler-Poincar\'e term in the constructions of higher dimensional steady state cosmologies could be crucial. |
2312.13075 | Bogeun Gwak | Junsu Park, Bogeun Gwak | Bound on Lyapunov exponent in Kerr-Newman-de Sitter black holes by a
charged particle | 35 pages, 34 figures | null | 10.1007/JHEP04(2024)023 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the bound on the Lyapunov exponents by a charged particle in
Kerr-Newman-de Sitter black holes using analytic and numerical methods. We
determine whether the Lyapunov exponent can exceed the bound by an electrically
charged particle with an angular momentum. Our tests are applied to the de
Sitter spacetime by the positive cosmological constant such as
Reissner-Nordstr\"{o}m-de Sitter, Kerr-de Sitter, and Kerr-Newman-de Sitter
black holes. In particular, we consider Nariai and ultracold limits on these
black holes for our tests. From our analysis results, there remain violations
on the bound under the positive cosmological constant, and electric charge and
angular momentum of the particle significantly impact the Lyapunov exponent.
| [
{
"created": "Wed, 20 Dec 2023 14:56:09 GMT",
"version": "v1"
}
] | 2024-04-08 | [
[
"Park",
"Junsu",
""
],
[
"Gwak",
"Bogeun",
""
]
] | We investigate the bound on the Lyapunov exponents by a charged particle in Kerr-Newman-de Sitter black holes using analytic and numerical methods. We determine whether the Lyapunov exponent can exceed the bound by an electrically charged particle with an angular momentum. Our tests are applied to the de Sitter spacetime by the positive cosmological constant such as Reissner-Nordstr\"{o}m-de Sitter, Kerr-de Sitter, and Kerr-Newman-de Sitter black holes. In particular, we consider Nariai and ultracold limits on these black holes for our tests. From our analysis results, there remain violations on the bound under the positive cosmological constant, and electric charge and angular momentum of the particle significantly impact the Lyapunov exponent. |
gr-qc/9411046 | Karen Brewster | Abhay Ashtekar and Jerzy Lewandowski | Projective Techniques and Functional Integration | 36 pages, latex, no figures, Preprint CGPG/94/10-6 | J.Math.Phys.36:2170-2191,1995 | 10.1063/1.531037 | null | gr-qc hep-th | null | A general framework for integration over certain infinite dimensional spaces
is first developed using projective limits of a projective family of compact
Hausdorff spaces. The procedure is then applied to gauge theories to carry out
integration over the non-linear, infinite dimensional spaces of connections
modulo gauge transformations. This method of evaluating functional integrals
can be used either in the Euclidean path integral approach or the Lorentzian
canonical approach. A number of measures discussed are diffeomorphism invariant
and therefore of interest to (the connection dynamics version of) quantum
general relativity. The account is pedagogical; in particular prior knowledge
of projective techniques is not assumed. (For the special JMP issue on
Functional Integration, edited by C. DeWitt-Morette.)
| [
{
"created": "Thu, 17 Nov 1994 14:58:55 GMT",
"version": "v1"
}
] | 2010-11-01 | [
[
"Ashtekar",
"Abhay",
""
],
[
"Lewandowski",
"Jerzy",
""
]
] | A general framework for integration over certain infinite dimensional spaces is first developed using projective limits of a projective family of compact Hausdorff spaces. The procedure is then applied to gauge theories to carry out integration over the non-linear, infinite dimensional spaces of connections modulo gauge transformations. This method of evaluating functional integrals can be used either in the Euclidean path integral approach or the Lorentzian canonical approach. A number of measures discussed are diffeomorphism invariant and therefore of interest to (the connection dynamics version of) quantum general relativity. The account is pedagogical; in particular prior knowledge of projective techniques is not assumed. (For the special JMP issue on Functional Integration, edited by C. DeWitt-Morette.) |
1005.2999 | Don Marolf | Donald Marolf | The dangers of extremes | 6 pages, 5 figures, 3rd place in 2010 Gravity Research Foundation
Essay Competition | Gen.Rel.Grav.42:2337-2343,2010 | 10.1007/s10714-010-1027-z | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | While extreme black hole spacetimes with smooth horizons are known at the
level of mathematics, we argue that the horizons of physical extreme black
holes are effectively singular. Test particles encounter a singularity the
moment they cross the horizon, and only objects with significant back-reaction
can fall across a smooth (now non-extreme) horizon. As a result, classical
interior solutions for extreme black holes are theoretical fictions that need
not be reproduced by any quantum mechanical model. This observation suggests
that significant quantum effects might be visible outside extreme or nearly
extreme black holes. It also suggests that the microphysics of such black holes
may be very different from that of their Schwarzschild cousins.
| [
{
"created": "Mon, 17 May 2010 19:12:22 GMT",
"version": "v1"
}
] | 2015-03-17 | [
[
"Marolf",
"Donald",
""
]
] | While extreme black hole spacetimes with smooth horizons are known at the level of mathematics, we argue that the horizons of physical extreme black holes are effectively singular. Test particles encounter a singularity the moment they cross the horizon, and only objects with significant back-reaction can fall across a smooth (now non-extreme) horizon. As a result, classical interior solutions for extreme black holes are theoretical fictions that need not be reproduced by any quantum mechanical model. This observation suggests that significant quantum effects might be visible outside extreme or nearly extreme black holes. It also suggests that the microphysics of such black holes may be very different from that of their Schwarzschild cousins. |
gr-qc/9710101 | Grant J. Mathews | G. J. Mathews, P. Marronetti, J. R. Wilson | Relativistic Studies of Close Neutron Star Binaries | 3 pages, Submitted to Proceesings of 8th Marcel Grossmann Meeting on
General Relativity | null | null | null | gr-qc | null | We discuss (3+1) dimensional general relativistic hydrodynamic simulations of
close neutron star binary systems. The relativistic field equations are solved
at each time slice with a spatial 3-metric chosen to be conformally flat.
Against this solution the hydrodynamic variables and gravitational radiation
are allowed to respond. We have studied four physical processes which occur as
the stars approach merger. These include: 1) the relaxation to a hydrodynamic
state of almost no spin; 2) relativistically driven compression, heating, and
neutrino emission; 3) collapse to two black holes; and 4) orbit inspiral
occurring at a lower frequency than previously expected. We give a brief
account of the physical origin of these effects and an explanation of why they
do not appear in models based upon, 1PN hydrodynamics, a weak field multipole
expansion, a tidal analysis, or a rigidly corotating velocity field. The
implication of these results for gravity wave detectors is also discussed.
| [
{
"created": "Tue, 21 Oct 1997 15:38:27 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Mathews",
"G. J.",
""
],
[
"Marronetti",
"P.",
""
],
[
"Wilson",
"J. R.",
""
]
] | We discuss (3+1) dimensional general relativistic hydrodynamic simulations of close neutron star binary systems. The relativistic field equations are solved at each time slice with a spatial 3-metric chosen to be conformally flat. Against this solution the hydrodynamic variables and gravitational radiation are allowed to respond. We have studied four physical processes which occur as the stars approach merger. These include: 1) the relaxation to a hydrodynamic state of almost no spin; 2) relativistically driven compression, heating, and neutrino emission; 3) collapse to two black holes; and 4) orbit inspiral occurring at a lower frequency than previously expected. We give a brief account of the physical origin of these effects and an explanation of why they do not appear in models based upon, 1PN hydrodynamics, a weak field multipole expansion, a tidal analysis, or a rigidly corotating velocity field. The implication of these results for gravity wave detectors is also discussed. |
gr-qc/9702057 | Wang Anzhong | Anzhong Wang, J.F. Villas da Rocha, and N.O. Santos | Gravitational collapse of massless scalar field and radiation fluid | Two figures have been removed, and the text has been re-written. To
appear in Phys. Rev. D | Phys.Rev.D56:7692-7699,1997 | 10.1103/PhysRevD.56.7692 | null | gr-qc | null | Several classes of conformally-flat and spherically symmetric exact solutions
to the Einstein field equations coupled with either a massless scalar field or
a radiation fluid are given, and their main properties are studied. It is found
that some represent the formation of black holes due to the gravitational
collapse of the matter fields. When the spacetimes have continuous
self-similarity (CSS), the masses of black holes take a scaling form $M_{BH}
\propto (P - P^{*})^{\gamma}$, where $\gamma = 0.5$ for massless scalar field
and $\gamma = 1$ for radiation fluid. The reasons for the difference between
the values of $\gamma$ obtained here and those obtained previously are
discussed. When the spacetimes have neither CSS nor DSS (Discrete
self-similarity), the masses of black holes always turn on with finite non-zero
values.
| [
{
"created": "Wed, 26 Feb 1997 19:45:52 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Sep 1997 17:21:45 GMT",
"version": "v2"
}
] | 2009-07-07 | [
[
"Wang",
"Anzhong",
""
],
[
"da Rocha",
"J. F. Villas",
""
],
[
"Santos",
"N. O.",
""
]
] | Several classes of conformally-flat and spherically symmetric exact solutions to the Einstein field equations coupled with either a massless scalar field or a radiation fluid are given, and their main properties are studied. It is found that some represent the formation of black holes due to the gravitational collapse of the matter fields. When the spacetimes have continuous self-similarity (CSS), the masses of black holes take a scaling form $M_{BH} \propto (P - P^{*})^{\gamma}$, where $\gamma = 0.5$ for massless scalar field and $\gamma = 1$ for radiation fluid. The reasons for the difference between the values of $\gamma$ obtained here and those obtained previously are discussed. When the spacetimes have neither CSS nor DSS (Discrete self-similarity), the masses of black holes always turn on with finite non-zero values. |
gr-qc/0405086 | Joachim Moortgat | Joachim Moortgat, Jan Kuijpers | Gravitational waves in magnetized relativistic plasmas | 12 pages, 5 figures; Accepted for publication in Phys. Rev. D | Phys.Rev. D70 (2004) 023001 | 10.1103/PhysRevD.70.023001 | null | gr-qc astro-ph | null | We study the propagation of gravitational waves (GW) in a uniformly
magnetized plasma at arbitrary angles to the magnetic field. No a priori
assumptions are made about the temperature, and we consider both a plasma at
rest and a plasma flowing out at ultra-relativistic velocities. In the 3+1
orthonormal tetrad description, we find that all three fundamental
low-frequency plasma wave modes are excited by the GW. Alfven waves are excited
by a x polarized GW, whereas the slow and fast magneto-acoustic modes couple to
the + polarization. The slow mode, however, doesn't interact coherently with
the GW. The most relevant wave mode is the fast magneto-acoustic mode which in
a strongly magnetized plasma has a vanishingly small phase lag with respect to
the GW allowing for coherent interaction over large length scales. When the
background magnetic field is almost, but not entirely, parallel to the GW's
direction of propagation even the Alfven waves grow to first order in the GW
amplitude. Finally, we calculate the growth of the magneto-acoustic waves and
the damping of the GW.
| [
{
"created": "Mon, 17 May 2004 10:10:03 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Moortgat",
"Joachim",
""
],
[
"Kuijpers",
"Jan",
""
]
] | We study the propagation of gravitational waves (GW) in a uniformly magnetized plasma at arbitrary angles to the magnetic field. No a priori assumptions are made about the temperature, and we consider both a plasma at rest and a plasma flowing out at ultra-relativistic velocities. In the 3+1 orthonormal tetrad description, we find that all three fundamental low-frequency plasma wave modes are excited by the GW. Alfven waves are excited by a x polarized GW, whereas the slow and fast magneto-acoustic modes couple to the + polarization. The slow mode, however, doesn't interact coherently with the GW. The most relevant wave mode is the fast magneto-acoustic mode which in a strongly magnetized plasma has a vanishingly small phase lag with respect to the GW allowing for coherent interaction over large length scales. When the background magnetic field is almost, but not entirely, parallel to the GW's direction of propagation even the Alfven waves grow to first order in the GW amplitude. Finally, we calculate the growth of the magneto-acoustic waves and the damping of the GW. |
1609.00745 | Yurii Ignat'ev | Yurii Ignat'ev | Qualitative Analysis and Numerical Simulation of Equations of the
Standard Cosmological Model | 27 pages, 28 figures, 8 references | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | On the basis of qualitative theory of differential equations it is shown that
dynamic system based on the system of Einstein - Klein - Gordon equations with
regard to Friedman Universe has a stable center corresponding to zero values of
scalar potential and its derivative at infinity. Thus, the cosmological model
based on single massive classical scalar field in infinite future would give a
flat Universe. The carried out numerical simulation of the dynamic system
corresponding to the system of Einstein - Klein - Gordon equations showed that
at great times of the evolution the invariant cosmological acceleration has a
microscopic oscillating character ($T\sim 2\pi mt$), while macroscopic value of
the cosmological acceleration varies from $+1$ at inflation stage after which
if decreases fast to $-1/2$ (non-relativistic stage), and then slowly tends to
$-1$ (ultrarelativistic stage).
| [
{
"created": "Thu, 18 Aug 2016 17:05:44 GMT",
"version": "v1"
}
] | 2016-09-06 | [
[
"Ignat'ev",
"Yurii",
""
]
] | On the basis of qualitative theory of differential equations it is shown that dynamic system based on the system of Einstein - Klein - Gordon equations with regard to Friedman Universe has a stable center corresponding to zero values of scalar potential and its derivative at infinity. Thus, the cosmological model based on single massive classical scalar field in infinite future would give a flat Universe. The carried out numerical simulation of the dynamic system corresponding to the system of Einstein - Klein - Gordon equations showed that at great times of the evolution the invariant cosmological acceleration has a microscopic oscillating character ($T\sim 2\pi mt$), while macroscopic value of the cosmological acceleration varies from $+1$ at inflation stage after which if decreases fast to $-1/2$ (non-relativistic stage), and then slowly tends to $-1$ (ultrarelativistic stage). |
gr-qc/0006052 | Mohammad Vahid Takook | Mohammad Vahid Takook | A Natural Renormalization of the One-Loop Effective Action for Scalar
Field in Curved Space-time | 5 pages, LaTeX; typos corrected, some details added, reference added | Int.J.Mod.Phys. E14 (2005) 219-224 | null | null | gr-qc | null | It has been shown that the negative norm states necessarily appear in a
covariant quantization of the free minimally coupled scalar field in de Sitter
space [1,2]. In this process ultraviolet and infrared divergences have been
automatically eliminated [3]. A natural renormalization of the one-loop
interacting quantum field in Minkowski space-time ($\lambda\phi^4$ theory) has
been achieved through the consideration of the negative norm states [4].
One-loop effective action for scalar field in a general curved space-time has
been calculated by this method and a natural renormalization procedure in the
one-loop approximation has been established.
| [
{
"created": "Wed, 14 Jun 2000 06:27:43 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Jun 2000 07:05:46 GMT",
"version": "v2"
},
{
"created": "Mon, 16 Oct 2000 11:03:07 GMT",
"version": "v3"
},
{
"created": "Mon, 9 May 2005 08:34:27 GMT",
"version": "v4"
}
] | 2007-05-23 | [
[
"Takook",
"Mohammad Vahid",
""
]
] | It has been shown that the negative norm states necessarily appear in a covariant quantization of the free minimally coupled scalar field in de Sitter space [1,2]. In this process ultraviolet and infrared divergences have been automatically eliminated [3]. A natural renormalization of the one-loop interacting quantum field in Minkowski space-time ($\lambda\phi^4$ theory) has been achieved through the consideration of the negative norm states [4]. One-loop effective action for scalar field in a general curved space-time has been calculated by this method and a natural renormalization procedure in the one-loop approximation has been established. |
1309.0177 | Joshua S. Schiffrin | Stephen R. Green, Joshua S. Schiffrin, Robert M. Wald | Dynamic and Thermodynamic Stability of Relativistic, Perfect Fluid Stars | 59 pages; v2: a few minor revisions made and several references
added; v3: a few minor changes | Class. Quantum Grav. 31 (2014) 035023 | 10.1088/0264-9381/31/3/035023 | null | gr-qc astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider perfect fluid bodies (stars) in general relativity, characterized
by particle number density and entropy per particle. A star is said to be in
dynamic equilibrium if it is a stationary, axisymmetric solution to the
Einstein-fluid equations with circular flow. We prove that for a star in
dynamic equilibrium, the necessary and sufficient condition for thermodynamic
equilibrium (extremum of total entropy S) is constancy of angular velocity
(\Omega), redshifted temperature, and redshifted chemical potential. Friedman
previously identified positivity of canonical energy, E, as a criterion for
dynamic stability and argued that all rotating stars are dynamically unstable
to sufficiently nonaxisymmetric perturbations (the CFS instability), so our
main focus is on axisymmetric stability. We show that for a star in dynamic
equilibrium, mode stability holds with respect to all axisymmetric
perturbations if E is positive on a certain subspace, V, of axisymmetric
Lagrangian perturbations that, in particular, have no Lagrangian change in
angular momentum density. Conversely, if E fails to be positive on V, then
there exist perturbations that can't become asymptotically stationary at late
times. We further show that for a star in thermodynamic equilibrium, the
canonical energy in the rotating frame, E_r, is related to second order changes
in ADM mass, M, and angular momentum, J, by E_r = \delta^2 M - \Omega \delta^2
J. Thus, positivity of E_r for perturbations with \delta J = 0 is a necessary
condition for thermodynamic stability (local maximum of S). For axisymmetric
perturbations we have E = E_r, so a necessary condition for thermodynamic
stability with respect to axisymmetric perturbations is positivity of E on all
perturbations with \delta J = 0, not merely on the perturbations in V. Many of
our results are in close parallel to results of Hollands and Wald for the
theory of black holes.
| [
{
"created": "Sun, 1 Sep 2013 03:30:34 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Dec 2013 16:57:50 GMT",
"version": "v2"
},
{
"created": "Mon, 23 Dec 2013 02:47:52 GMT",
"version": "v3"
}
] | 2014-01-22 | [
[
"Green",
"Stephen R.",
""
],
[
"Schiffrin",
"Joshua S.",
""
],
[
"Wald",
"Robert M.",
""
]
] | We consider perfect fluid bodies (stars) in general relativity, characterized by particle number density and entropy per particle. A star is said to be in dynamic equilibrium if it is a stationary, axisymmetric solution to the Einstein-fluid equations with circular flow. We prove that for a star in dynamic equilibrium, the necessary and sufficient condition for thermodynamic equilibrium (extremum of total entropy S) is constancy of angular velocity (\Omega), redshifted temperature, and redshifted chemical potential. Friedman previously identified positivity of canonical energy, E, as a criterion for dynamic stability and argued that all rotating stars are dynamically unstable to sufficiently nonaxisymmetric perturbations (the CFS instability), so our main focus is on axisymmetric stability. We show that for a star in dynamic equilibrium, mode stability holds with respect to all axisymmetric perturbations if E is positive on a certain subspace, V, of axisymmetric Lagrangian perturbations that, in particular, have no Lagrangian change in angular momentum density. Conversely, if E fails to be positive on V, then there exist perturbations that can't become asymptotically stationary at late times. We further show that for a star in thermodynamic equilibrium, the canonical energy in the rotating frame, E_r, is related to second order changes in ADM mass, M, and angular momentum, J, by E_r = \delta^2 M - \Omega \delta^2 J. Thus, positivity of E_r for perturbations with \delta J = 0 is a necessary condition for thermodynamic stability (local maximum of S). For axisymmetric perturbations we have E = E_r, so a necessary condition for thermodynamic stability with respect to axisymmetric perturbations is positivity of E on all perturbations with \delta J = 0, not merely on the perturbations in V. Many of our results are in close parallel to results of Hollands and Wald for the theory of black holes. |
0903.0395 | Sam Dolan Dr | Marc Casals, Sam R. Dolan, Adrian C. Ottewill and Barry Wardell | Self-Force Calculations with Matched Expansions and Quasinormal Mode
Sums | Added references, corrected minor typos. 43 pages, 20 figures | Phys.Rev.D79:124043,2009 | 10.1103/PhysRevD.79.124043 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the first application of the Poisson-Wiseman-Anderson method of
matched expansions, to compute the self-force acting on a point particle moving
in a curved spacetime. The method uses two expansions for the Green function,
valid in `quasilocal' and `distant past' regimes, which are matched within the
normal neighbourhood. We perform our calculation in a static region of the
spherically symmetric Nariai spacetime (dS_2 x S^2), on which scalar
perturbations are governed by a radial equation with a P\"oschl-Teller
potential. We combine (i) a very high order quasilocal expansion, and (ii) an
expansion in quasinormal modes, to determine the Green function globally. We
show it is singular everywhere on the null wavefront (even outside the normal
neighbourhood), and apply asymptotic methods to determine its singular
structure. We find the Green function undergoes a transition every time the
null wavefront passes through a caustic: the singular part follows a repeating
four-fold sequence $\delta(\sigma)$, $1/\pi \sigma$, $-\delta(\sigma)$, $-1/\pi
\sigma$ etc., where $\sigma$ is Synge's world function.
The matched expansion method provides new insight into the non-local
properties of the self-force; we find the contribution from the segment of the
worldline lying outside the normal neighbourhood is significant. We compute the
scalar self-force acting on a static particle, and validate against an
alternative method. Finally, we discuss wave propagation on black hole
spacetimes (where any expansion in quasinormal modes will be augmented by a
branch cut integral) and predict that the Green function in Schwarzschild
spacetime will inherit the four-fold singular structure found here.
| [
{
"created": "Tue, 3 Mar 2009 20:52:41 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Mar 2009 21:58:03 GMT",
"version": "v2"
},
{
"created": "Tue, 10 Mar 2009 20:38:33 GMT",
"version": "v3"
}
] | 2009-07-09 | [
[
"Casals",
"Marc",
""
],
[
"Dolan",
"Sam R.",
""
],
[
"Ottewill",
"Adrian C.",
""
],
[
"Wardell",
"Barry",
""
]
] | We present the first application of the Poisson-Wiseman-Anderson method of matched expansions, to compute the self-force acting on a point particle moving in a curved spacetime. The method uses two expansions for the Green function, valid in `quasilocal' and `distant past' regimes, which are matched within the normal neighbourhood. We perform our calculation in a static region of the spherically symmetric Nariai spacetime (dS_2 x S^2), on which scalar perturbations are governed by a radial equation with a P\"oschl-Teller potential. We combine (i) a very high order quasilocal expansion, and (ii) an expansion in quasinormal modes, to determine the Green function globally. We show it is singular everywhere on the null wavefront (even outside the normal neighbourhood), and apply asymptotic methods to determine its singular structure. We find the Green function undergoes a transition every time the null wavefront passes through a caustic: the singular part follows a repeating four-fold sequence $\delta(\sigma)$, $1/\pi \sigma$, $-\delta(\sigma)$, $-1/\pi \sigma$ etc., where $\sigma$ is Synge's world function. The matched expansion method provides new insight into the non-local properties of the self-force; we find the contribution from the segment of the worldline lying outside the normal neighbourhood is significant. We compute the scalar self-force acting on a static particle, and validate against an alternative method. Finally, we discuss wave propagation on black hole spacetimes (where any expansion in quasinormal modes will be augmented by a branch cut integral) and predict that the Green function in Schwarzschild spacetime will inherit the four-fold singular structure found here. |
gr-qc/0702005 | P. S. Negi | P. S. Negi | The Stability of an Isentropic Model for a Gaseous Relativistic Star | 9 pages (including 1 table); accepted for publication in GRG | Gen.Rel.Grav.39:529-534,2007 | 10.1007/s10714-007-0402-x | null | gr-qc | null | We show that the isentropic subclass of Buchdahl's exact solution for a
gaseous relativistic star is stable and gravitationally bound for all values of
the compactness ratio $u [\equiv (M/R)$, where $M$ is the total mass and $R$ is
the radius of the configuration in geometrized units] in the range, $0 < u \leq
0.20$, corresponding to the {\em regular} behaviour of the solution. This
result is in agreement with the expectation and opposite to the earlier claim
found in the literature.
| [
{
"created": "Thu, 1 Feb 2007 11:51:11 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Negi",
"P. S.",
""
]
] | We show that the isentropic subclass of Buchdahl's exact solution for a gaseous relativistic star is stable and gravitationally bound for all values of the compactness ratio $u [\equiv (M/R)$, where $M$ is the total mass and $R$ is the radius of the configuration in geometrized units] in the range, $0 < u \leq 0.20$, corresponding to the {\em regular} behaviour of the solution. This result is in agreement with the expectation and opposite to the earlier claim found in the literature. |
1410.7132 | Arunava Bhadra Dr. | Tamal Sarkar, Shubhrangshu Ghosh and Arunava Bhadra | Newtonian analogue of Schwarzschild de-Sitter spacetime: Influence on
the local kinematics in galaxies | 25 pages, 12 figures | Physical Review D, Volume 90, Issue 6, id.063008, 2014 | 10.1103/PhysRevD.90.063008 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The late time accelerated expansion of the Universe demands that even in
local galactic-scales it is desirable to study astrophysical phenomena,
particularly relativistic accretion related phenomena in massive galaxies or in
galaxy mergers and the dynamics of the kiloparsecs-scale structure and beyond,
in the local-galaxies in Schwarzschild-de Sitter (SDS) background, rather than
in Schwarzschild or Newtonian paradigm. Owing to the complex and nonlinear
character of the underlying magnetohydrodynamical equations in general
relativistic (GR) regime, it is quite useful to have an Newtonian analogous
potential containing all the important GR features that allows to treat the
problem in Newtonian framework for study of accretion and its related
processes. From the principle of conserved Hamiltonian of the test particle
motion, here, a three dimensional Newtonian analogous potential has been
obtained in spherical geometry corresponding to SDS/Schwarzschild anti-de
Sitter (SADS) spacetime, that reproduces almost all of the GR features in its
entirety with remarkable accuracy. The derived potential contains an explicit
velocity dependent term of the test particle that renders an approximate
relativistic modification of Newtonian like potential. The complete orbital
dynamics around SDS geometry and the epicyclic frequency corresponding to SDS
metric have been extensively studied in the Newtonian framework using the
derived potential. Applying the derived analogous potential it is found that
the current accepted value of $\Lambda \sim 10^{-56} \rm cm^{-2}$ moderately
influences both sonic radius as well as Bondi accretion rate, especially for
spherical accretion with smaller values of adiabatic constant and temperature,
which might have interesting consequences on the stability of accretion disk in
AGNs/radio galaxies.
| [
{
"created": "Mon, 27 Oct 2014 06:32:13 GMT",
"version": "v1"
}
] | 2014-10-28 | [
[
"Sarkar",
"Tamal",
""
],
[
"Ghosh",
"Shubhrangshu",
""
],
[
"Bhadra",
"Arunava",
""
]
] | The late time accelerated expansion of the Universe demands that even in local galactic-scales it is desirable to study astrophysical phenomena, particularly relativistic accretion related phenomena in massive galaxies or in galaxy mergers and the dynamics of the kiloparsecs-scale structure and beyond, in the local-galaxies in Schwarzschild-de Sitter (SDS) background, rather than in Schwarzschild or Newtonian paradigm. Owing to the complex and nonlinear character of the underlying magnetohydrodynamical equations in general relativistic (GR) regime, it is quite useful to have an Newtonian analogous potential containing all the important GR features that allows to treat the problem in Newtonian framework for study of accretion and its related processes. From the principle of conserved Hamiltonian of the test particle motion, here, a three dimensional Newtonian analogous potential has been obtained in spherical geometry corresponding to SDS/Schwarzschild anti-de Sitter (SADS) spacetime, that reproduces almost all of the GR features in its entirety with remarkable accuracy. The derived potential contains an explicit velocity dependent term of the test particle that renders an approximate relativistic modification of Newtonian like potential. The complete orbital dynamics around SDS geometry and the epicyclic frequency corresponding to SDS metric have been extensively studied in the Newtonian framework using the derived potential. Applying the derived analogous potential it is found that the current accepted value of $\Lambda \sim 10^{-56} \rm cm^{-2}$ moderately influences both sonic radius as well as Bondi accretion rate, especially for spherical accretion with smaller values of adiabatic constant and temperature, which might have interesting consequences on the stability of accretion disk in AGNs/radio galaxies. |
gr-qc/9703028 | Carlos Barcelo Seron | Carlos Barcelo, Luis J. Garay | Quantum fields in anti-de Sitter wormholes | RevTeX 3.01, 4 pages, no figures | Phys.Rev. D57 (1998) 5291-5294 | 10.1103/PhysRevD.57.5291 | null | gr-qc | null | We study the effects of asymptotically anti-de Sitter wormholes in low-energy
field theory and give a general prescription for obtaining the local effective
interaction terms induced by them. The choice of vacuum for the matter fields
selects a basis of the Hilbert space of anti-de Sitter wormholes whose elements
can be interpreted as states containing a given number of particles. This
interpretation is subject to the same kind of ambiguity in the definition of
particle as that arising from quantum field theory in curved spacetime.
| [
{
"created": "Tue, 11 Mar 1997 13:13:58 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Mar 1998 16:13:38 GMT",
"version": "v2"
}
] | 2009-10-30 | [
[
"Barcelo",
"Carlos",
""
],
[
"Garay",
"Luis J.",
""
]
] | We study the effects of asymptotically anti-de Sitter wormholes in low-energy field theory and give a general prescription for obtaining the local effective interaction terms induced by them. The choice of vacuum for the matter fields selects a basis of the Hilbert space of anti-de Sitter wormholes whose elements can be interpreted as states containing a given number of particles. This interpretation is subject to the same kind of ambiguity in the definition of particle as that arising from quantum field theory in curved spacetime. |
0712.3775 | Charles Suggs | D. Grumiller and R. Jackiw | Liouville gravity from Einstein gravity | 15 pages, uses diagrams.sty; v2: edited HTML version of abstract,
added reference | null | null | MIT-CTP-3925 | gr-qc hep-th math-ph math.MP | null | We show that Liouville gravity arises as the limit of pure Einstein gravity
in 2+epsilon dimensions as epsilon goes to zero, provided Newton's constant
scales with epsilon. Our procedure - spherical reduction, dualization, limit,
dualizing back - passes several consistency tests: geometric properties,
interactions with matter and the Bekenstein-Hawking entropy are as expected
from Einstein gravity.
| [
{
"created": "Fri, 21 Dec 2007 19:09:31 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Dec 2007 18:01:23 GMT",
"version": "v2"
}
] | 2011-11-10 | [
[
"Grumiller",
"D.",
""
],
[
"Jackiw",
"R.",
""
]
] | We show that Liouville gravity arises as the limit of pure Einstein gravity in 2+epsilon dimensions as epsilon goes to zero, provided Newton's constant scales with epsilon. Our procedure - spherical reduction, dualization, limit, dualizing back - passes several consistency tests: geometric properties, interactions with matter and the Bekenstein-Hawking entropy are as expected from Einstein gravity. |
gr-qc/0011077 | Pavel Krtous | Pavel Krtous | Sum-Over-Histories Quantization of Relativistic Particle | 47 pages, 3 figures, LaTeX2e | Class.Quant.Grav. 21 (2004) 1519-1558 | 10.1088/0264-9381/21/6/017 | null | gr-qc | null | Sum-over-histories quantization of particle-like theory in curved space is
discussed. It is reviewed that the propagator satisfies the Schrodinger
equation respective wave equation with a Laplace-like operator. The exact
dependence of the operator on the choice of measure is shown.
Next, modifications needed for a manifold with a boundary are introduced, and
the exact form of the equation for the propagator is derived. It is shown that
the Laplace-like operator contains some distributional terms localized on the
boundary. These terms induce proper boundary conditions for the propagator.
This choice of boundary conditions is explained as a consequence of a
measurement of particles on the boundary.
The interaction with sources inside of the domain and sources on the boundary
is also discussed.
| [
{
"created": "Wed, 22 Nov 2000 13:05:53 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Krtous",
"Pavel",
""
]
] | Sum-over-histories quantization of particle-like theory in curved space is discussed. It is reviewed that the propagator satisfies the Schrodinger equation respective wave equation with a Laplace-like operator. The exact dependence of the operator on the choice of measure is shown. Next, modifications needed for a manifold with a boundary are introduced, and the exact form of the equation for the propagator is derived. It is shown that the Laplace-like operator contains some distributional terms localized on the boundary. These terms induce proper boundary conditions for the propagator. This choice of boundary conditions is explained as a consequence of a measurement of particles on the boundary. The interaction with sources inside of the domain and sources on the boundary is also discussed. |
1808.00503 | Christian Knoll | Jose Luis Bl\'azquez-Salcedo, Christian Knoll | Solutions of the massive Dirac equation in the near-horizon metric of
the extremal five dimensional Myers-Perry black hole with equal angular
momenta | null | Phys. Rev. D 99, 024026 (2019) | 10.1103/PhysRevD.99.024026 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study massive Dirac fields in the background of the near-horizon limit of
the extremal Myers-Perry black hole in five dimensions. We consider the case in
which both angular momenta have equal magnitude. The resulting Dirac equation
can be decoupled into an angular and a radial part. The solution of the angular
part results in some algebraic relations that determine completely the angular
quantum numbers of the fermionic field. The radial part can be analytically
solved in terms of special functions, which allow us to analyze the
near-horizon radial current of the Dirac field.
| [
{
"created": "Wed, 1 Aug 2018 18:39:42 GMT",
"version": "v1"
}
] | 2019-01-23 | [
[
"Blázquez-Salcedo",
"Jose Luis",
""
],
[
"Knoll",
"Christian",
""
]
] | We study massive Dirac fields in the background of the near-horizon limit of the extremal Myers-Perry black hole in five dimensions. We consider the case in which both angular momenta have equal magnitude. The resulting Dirac equation can be decoupled into an angular and a radial part. The solution of the angular part results in some algebraic relations that determine completely the angular quantum numbers of the fermionic field. The radial part can be analytically solved in terms of special functions, which allow us to analyze the near-horizon radial current of the Dirac field. |
1604.01837 | Ali \"Ovg\"un | A. \"Ovg\"un | Inflation and Acceleration of the Universe by Nonlinear Magnetic
Monopole Fields | two column, 6 pages, 2 figures, final published version | Eur. Phys. J. C (2017) 77: 105 | 10.1140/epjc/s10052-017-4673-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Despite impressive phenomenological successes, cosmological models are
incomplete without an understanding of what happened at the big bang
singularity. Maxwell electrodynamics, considered as a source of the classical
Einstein field equations, leads to the singular isotropic Friedmann solutions.
In the context of Friedmann-Robertson-Walker (FRW) spacetime, we show that
singular behavior does not occur for a class of nonlinear generalizations of
the electromagnetic theory for strong fields. A new mathematical model is
proposed for which the analytical nonsingular extension of FRW solutions is
obtained by using the nonlinear magnetic monopole fields.
| [
{
"created": "Thu, 7 Apr 2016 00:24:56 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Jun 2016 00:03:26 GMT",
"version": "v2"
},
{
"created": "Sun, 5 Feb 2017 23:50:50 GMT",
"version": "v3"
},
{
"created": "Wed, 8 Feb 2017 11:10:27 GMT",
"version": "v4"
},
{
"crea... | 2017-02-17 | [
[
"Övgün",
"A.",
""
]
] | Despite impressive phenomenological successes, cosmological models are incomplete without an understanding of what happened at the big bang singularity. Maxwell electrodynamics, considered as a source of the classical Einstein field equations, leads to the singular isotropic Friedmann solutions. In the context of Friedmann-Robertson-Walker (FRW) spacetime, we show that singular behavior does not occur for a class of nonlinear generalizations of the electromagnetic theory for strong fields. A new mathematical model is proposed for which the analytical nonsingular extension of FRW solutions is obtained by using the nonlinear magnetic monopole fields. |
2105.04479 | Georgios Antoniou | Georgios Antoniou, Antoine Leh\'ebel, Giulia Ventagli, Thomas P.
Sotiriou | Black hole scalarization with Gauss-Bonnet and Ricci scalar couplings | 8 pages, 8 figures | Phys. Rev. D 104, 044002 (2021) | 10.1103/PhysRevD.104.044002 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Spontaneous scalarization is a gravitational phenomenon in which deviations
from general relativity arise once a certain threshold in curvature is
exceeded, while being entirely absent below that threshold. For black holes,
scalarization is known to be triggered by a coupling between a scalar and the
Gauss-Bonnet invariant. A coupling with the Ricci scalar, which can trigger
scalarization in neutron stars, is instead known to not contribute to the onset
of black hole scalarization, and has so far been largely ignored in the
literature when studying scalarized black holes. In this paper, we study the
combined effect of both these couplings on black hole scalarization. We show
that the Ricci coupling plays a significant role in the properties of
scalarized solutions and their domain of existence. This work is an important
step in the construction of scalarization models that evade binary pulsar
constraints and have general relativity as a cosmological late-time attractor,
while still predicting deviations from general relativity in black hole
observations.
| [
{
"created": "Mon, 10 May 2021 16:19:48 GMT",
"version": "v1"
},
{
"created": "Mon, 6 Sep 2021 18:34:34 GMT",
"version": "v2"
}
] | 2021-09-08 | [
[
"Antoniou",
"Georgios",
""
],
[
"Lehébel",
"Antoine",
""
],
[
"Ventagli",
"Giulia",
""
],
[
"Sotiriou",
"Thomas P.",
""
]
] | Spontaneous scalarization is a gravitational phenomenon in which deviations from general relativity arise once a certain threshold in curvature is exceeded, while being entirely absent below that threshold. For black holes, scalarization is known to be triggered by a coupling between a scalar and the Gauss-Bonnet invariant. A coupling with the Ricci scalar, which can trigger scalarization in neutron stars, is instead known to not contribute to the onset of black hole scalarization, and has so far been largely ignored in the literature when studying scalarized black holes. In this paper, we study the combined effect of both these couplings on black hole scalarization. We show that the Ricci coupling plays a significant role in the properties of scalarized solutions and their domain of existence. This work is an important step in the construction of scalarization models that evade binary pulsar constraints and have general relativity as a cosmological late-time attractor, while still predicting deviations from general relativity in black hole observations. |
2205.02122 | Benrong Mu | Xiaobo Guo, Yuhang Lu, Benrong Mu and Peng Wang | Probing Phase Structure of Black Holes with Lyapunov Exponents | 14 pages, 7 figures | null | 10.1007/JHEP08(2022)153 | CTP-SCU/2022008 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We conjecture that there exists a relationship between Lyapunov exponents and
black hole phase transitions. To support our conjecture, Lyapunov exponents of
the motion of particles and ring strings are calculated for
Reissner-Nordstr\"{o}m-AdS black holes. When a phase transition occurs, the
Lyapunov exponents become multivalued, and branches of the Lyapunov exponents
coincide with black hole phases. Moreover, the discontinuous change in the
Lyapunov exponents can be treated as an order parameter, and has a critical
exponent of $1/2$ near the critical point. Our findings reveal that Lyapunov
exponents can be an efficient tool to study phase structure of black holes.
| [
{
"created": "Wed, 4 May 2022 15:23:40 GMT",
"version": "v1"
},
{
"created": "Thu, 26 May 2022 15:00:04 GMT",
"version": "v2"
}
] | 2022-09-07 | [
[
"Guo",
"Xiaobo",
""
],
[
"Lu",
"Yuhang",
""
],
[
"Mu",
"Benrong",
""
],
[
"Wang",
"Peng",
""
]
] | We conjecture that there exists a relationship between Lyapunov exponents and black hole phase transitions. To support our conjecture, Lyapunov exponents of the motion of particles and ring strings are calculated for Reissner-Nordstr\"{o}m-AdS black holes. When a phase transition occurs, the Lyapunov exponents become multivalued, and branches of the Lyapunov exponents coincide with black hole phases. Moreover, the discontinuous change in the Lyapunov exponents can be treated as an order parameter, and has a critical exponent of $1/2$ near the critical point. Our findings reveal that Lyapunov exponents can be an efficient tool to study phase structure of black holes. |
gr-qc/9912105 | R. G. Viswakarma | R. G. Vishwakarma (IUCAA) | A study of the angular size-redshift relation for models in which
$\Lambda$ decays as the energy density | LaTex, 15 pages including 2 figures (Revised version appeared in CQG) | Class.Quant.Grav. 17 (2000) 3833-3842 | 10.1088/0264-9381/17/18/317 | null | gr-qc | null | By modifying the Chen and Wu ansatz, we have investigated some Friedmann
models in which $\Lambda$ varies as $\rho$. In order to test the consistency of
the models with observations, we study the angular size - redshift relation for
256 ultracompact radio sources selected by Jackson and Dodgson. The angular
sizes of these sources were determined by using very long-baseline
interferometry in order to avoid any evolutionary effects. The models fit the
data very well and require an accelerating universe with a positive
cosmological constant. Open, flat and closed models are almost equally
probable, though the open model provides a comparatively better fit to the
data. The models are found to have intermediate density and imply the existence
of dark matter, though not as much as in the canonical Einstein-de Sitter
model.
| [
{
"created": "Fri, 24 Dec 1999 11:25:50 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Feb 2001 15:31:03 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Vishwakarma",
"R. G.",
"",
"IUCAA"
]
] | By modifying the Chen and Wu ansatz, we have investigated some Friedmann models in which $\Lambda$ varies as $\rho$. In order to test the consistency of the models with observations, we study the angular size - redshift relation for 256 ultracompact radio sources selected by Jackson and Dodgson. The angular sizes of these sources were determined by using very long-baseline interferometry in order to avoid any evolutionary effects. The models fit the data very well and require an accelerating universe with a positive cosmological constant. Open, flat and closed models are almost equally probable, though the open model provides a comparatively better fit to the data. The models are found to have intermediate density and imply the existence of dark matter, though not as much as in the canonical Einstein-de Sitter model. |
1704.03708 | Nistor Nicolaevici | Nistor Nicolaevici | Excitation of an inertial Unruh detector in the Minkowski vacuum: a
numerical calculation using spherical modes | 29 pages, 10 figures; submitted to Proceedings of TIM 17 Physics
Conference | null | 10.1063/1.5017428 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the excitation of a finite-length inertial Unruh detector in the
Minkowski vacuum with an adiabatic switch on of the interaction in the infinite
past and a sudden switch off at finite times, and obtain the excitation
probability via a numerical calculation using the expansion of the quantum
field in spherical modes. We evaluate first the excitation probabilities for
the final states of the field with one particle per mode, and then we sum over
the modes. An interesting feature is that, despite of the inertial trajectory
and of the vacuum state of the field, the multipole components of the
excitation probability are time-dependent quantities. We make clear how the
multipole sum yields the time-independent probability characteristic to an
inertial trajectory. In passing, we point out that the excitation probability
for a sudden switch on of the interaction in the infinite past is precisely
twice as large as that for an adiabatic switch on. The procedure can be easily
extended to obtain the response of the detector along radial trajectories in
spherically symmetric spacetimes.
| [
{
"created": "Wed, 12 Apr 2017 11:16:39 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Apr 2017 20:29:32 GMT",
"version": "v2"
}
] | 2018-01-17 | [
[
"Nicolaevici",
"Nistor",
""
]
] | We consider the excitation of a finite-length inertial Unruh detector in the Minkowski vacuum with an adiabatic switch on of the interaction in the infinite past and a sudden switch off at finite times, and obtain the excitation probability via a numerical calculation using the expansion of the quantum field in spherical modes. We evaluate first the excitation probabilities for the final states of the field with one particle per mode, and then we sum over the modes. An interesting feature is that, despite of the inertial trajectory and of the vacuum state of the field, the multipole components of the excitation probability are time-dependent quantities. We make clear how the multipole sum yields the time-independent probability characteristic to an inertial trajectory. In passing, we point out that the excitation probability for a sudden switch on of the interaction in the infinite past is precisely twice as large as that for an adiabatic switch on. The procedure can be easily extended to obtain the response of the detector along radial trajectories in spherically symmetric spacetimes. |
gr-qc/9806014 | Gabrielle Allen | Gabrielle Allen, Karen Camarda, Edward Seidel | Evolution of Distorted Black Holes: A Perturbative Approach | 20 pages, 10 figures, Submitted to Phys. Rev. D | null | null | null | gr-qc | null | We consider a series of distorted black hole initial data sets, and develop
techniques to evolve them using the linearized equations of motion for the
gravitational wave perturbations on a Schwarzschild background. We apply this
to 2D and 3D distorted black hole spacetimes. In 2D, waveforms for different
modes of the radiation are presented, comparing full nonlinear evolutions for
different axisymmetric l-modes with perturbative evolutions. We show how
axisymmetric black hole codes solving the full, nonlinear Einstein equations
are capable of very accurate evolutions, and also how these techniques aid in
studying nonlinear effects. In 3D we show how the initial data for the
perturbation equations can be computed, and we compare with analytic solutions
given from a perturbative expansion of the initial value problem. In addition
to exploring the physics of these distorted black hole data sets, in particular
allowing an exploration of linear, nonlinear, and mode mixing effects, this
approach provides an important testbed for any fully nonlinear numerical code
designed to evolve black hole spacetimes in 2D or 3D.
| [
{
"created": "Wed, 3 Jun 1998 16:07:07 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Jun 1998 12:07:56 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Allen",
"Gabrielle",
""
],
[
"Camarda",
"Karen",
""
],
[
"Seidel",
"Edward",
""
]
] | We consider a series of distorted black hole initial data sets, and develop techniques to evolve them using the linearized equations of motion for the gravitational wave perturbations on a Schwarzschild background. We apply this to 2D and 3D distorted black hole spacetimes. In 2D, waveforms for different modes of the radiation are presented, comparing full nonlinear evolutions for different axisymmetric l-modes with perturbative evolutions. We show how axisymmetric black hole codes solving the full, nonlinear Einstein equations are capable of very accurate evolutions, and also how these techniques aid in studying nonlinear effects. In 3D we show how the initial data for the perturbation equations can be computed, and we compare with analytic solutions given from a perturbative expansion of the initial value problem. In addition to exploring the physics of these distorted black hole data sets, in particular allowing an exploration of linear, nonlinear, and mode mixing effects, this approach provides an important testbed for any fully nonlinear numerical code designed to evolve black hole spacetimes in 2D or 3D. |
1008.4805 | Giacomo Mauro D'Ariano | Giacomo Mauro D'Ariano and Alessandro Tosini | Space-time and special relativity from causal networks | 4 pages and 4 figures | null | null | null | gr-qc hep-th math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show how the Minkowskian space-time emerges from a topologically
homogeneous causal network, presenting a simple analytical derivation of the
Lorentz transformations, with metric as pure event-counting. The derivation
holds generally for d=1 space dimension, however, it can be extended to d>1 for
special causal networks.
| [
{
"created": "Fri, 27 Aug 2010 20:46:15 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Sep 2010 06:15:27 GMT",
"version": "v2"
}
] | 2010-09-27 | [
[
"D'Ariano",
"Giacomo Mauro",
""
],
[
"Tosini",
"Alessandro",
""
]
] | We show how the Minkowskian space-time emerges from a topologically homogeneous causal network, presenting a simple analytical derivation of the Lorentz transformations, with metric as pure event-counting. The derivation holds generally for d=1 space dimension, however, it can be extended to d>1 for special causal networks. |
gr-qc/0610037 | Francesco Cianfrani dr | Francesco Cianfrani, Giovanni Montani | The electro-weak model as a phenomenological issue of multidimensions | 3 pages, proceedings of the XI Marcel Grossmann meeting on
Relativistic Astrophysics, July 23-29, 2006, Berlin | null | null | null | gr-qc | null | We consider Kaluza-Klein theories as candidates for the unification of
gravity and the electro-weak model. In particular, we fix how to reproduce
geometrically the interaction between fermions and gauge bosons, in the low
energy limit.
| [
{
"created": "Mon, 9 Oct 2006 15:57:44 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Cianfrani",
"Francesco",
""
],
[
"Montani",
"Giovanni",
""
]
] | We consider Kaluza-Klein theories as candidates for the unification of gravity and the electro-weak model. In particular, we fix how to reproduce geometrically the interaction between fermions and gauge bosons, in the low energy limit. |
1711.06209 | Andrea Giugno | Andrea Giugno, Andrea Giusti, Alexis Helou | Horizon quantum fuzziness for non-singular black holes | 17 pages, no figures | null | 10.1140/epjc/s10052-018-5715-2 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the extent of quantum gravitational effects in the internal region
of non-singular, Hayward-like solutions of Einstein's field equations according
to the formalism known as Horizon Quantum Mechanics. We grant a microscopic
description to the horizon by considering a huge number of soft, off-shell
gravitons, which superimpose in the same quantum state, as suggested by Dvali
and Gomez. In addition to that, the constituents of such a configuration are
understood as loosely confined in a binding harmonic potential. A simple
analysis shows that the resolution of a central singularity through quantum
physics does not tarnish the classical description, which is bestowed upon this
extended self-gravitating system by General Relativity. Finally, we estimate
the appearance of an internal horizon as being negligible, because of the
suppression of the related probability caused by the large number of virtual
gravitons.
| [
{
"created": "Thu, 16 Nov 2017 17:30:16 GMT",
"version": "v1"
}
] | 2018-04-04 | [
[
"Giugno",
"Andrea",
""
],
[
"Giusti",
"Andrea",
""
],
[
"Helou",
"Alexis",
""
]
] | We study the extent of quantum gravitational effects in the internal region of non-singular, Hayward-like solutions of Einstein's field equations according to the formalism known as Horizon Quantum Mechanics. We grant a microscopic description to the horizon by considering a huge number of soft, off-shell gravitons, which superimpose in the same quantum state, as suggested by Dvali and Gomez. In addition to that, the constituents of such a configuration are understood as loosely confined in a binding harmonic potential. A simple analysis shows that the resolution of a central singularity through quantum physics does not tarnish the classical description, which is bestowed upon this extended self-gravitating system by General Relativity. Finally, we estimate the appearance of an internal horizon as being negligible, because of the suppression of the related probability caused by the large number of virtual gravitons. |
1407.2862 | Andrzej Krasi\'nski | Andrzej Krasi\'nski | Mimicking acceleration in the constant-bang-time Lema\^{\i}tre -- Tolman
model: Shell crossings, density distributions and light cones | 13 pages, 13 figures. New secs. X and XI added, secs. I, II, V, IX
and the old XI(now XIII) re-edited to accommodate the new material, Figs. 3,
8 and old 11 (now 10) redrawn, old Fig. 10 removed. The extensions were
inspired by the referee. New text matches that accepted for Phys. Rev. D | Phys. Rev. D 90, 064021 (2014) | 10.1103/PhysRevD.90.064021 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Lema\^{\i}tre -- Tolman model with $\Lambda = 0$ and constant bang time
that imitates the luminosity distance -- redshift relation of the $\Lambda$CDM
model using the energy function $E$ alone contains shell crossings. In this
paper, the location in spacetime and the consequences of existence of the
shell-crossing set (SCS) are investigated. The SCS would come into view of the
central observer only at $t \approx 1064 T$ to the future from now, where $T$
is the present age of the Universe, but would not leave any recognizable trace
in her observations. Light rays emitted near to the SCS are blueshifted at the
initial points, but the blueshift is finite, and is overcompensated by
later-induced redshifts if the observer is sufficiently far. The local
blueshifts cause that $z$ along a light ray is not a monotonic function of the
comoving radial coordinate $r$. As a consequence, the angular diameter distance
$D_A$ and the luminosity distance $D_L$ from the central observer fail to be
functions of $z$; the relations $D_A(z)$ and $D_L(z)$ are multiple-valued in a
vicinity of the SCS. The following quantities are calculated and displayed: (1)
The distribution of mass density on a few characteristic hypersurfaces of
constant time; some of them intersect the SCS. (2) The distribution of density
along the past light cone of the present central observer. (3) A few light
cones intersecting the SCS at characteristic instants. (4) The redshift
profiles along several light cones. (5) The extremum-redshift hypersurface. (6)
The $D_A(z)$ and $D_L(z)$ relations. (7) The last scattering time and its
comparison with the $\Lambda$CDM last scattering epoch.
| [
{
"created": "Thu, 10 Jul 2014 16:50:53 GMT",
"version": "v1"
},
{
"created": "Sun, 13 Jul 2014 17:07:22 GMT",
"version": "v2"
},
{
"created": "Wed, 10 Sep 2014 11:39:56 GMT",
"version": "v3"
}
] | 2014-09-17 | [
[
"Krasiński",
"Andrzej",
""
]
] | The Lema\^{\i}tre -- Tolman model with $\Lambda = 0$ and constant bang time that imitates the luminosity distance -- redshift relation of the $\Lambda$CDM model using the energy function $E$ alone contains shell crossings. In this paper, the location in spacetime and the consequences of existence of the shell-crossing set (SCS) are investigated. The SCS would come into view of the central observer only at $t \approx 1064 T$ to the future from now, where $T$ is the present age of the Universe, but would not leave any recognizable trace in her observations. Light rays emitted near to the SCS are blueshifted at the initial points, but the blueshift is finite, and is overcompensated by later-induced redshifts if the observer is sufficiently far. The local blueshifts cause that $z$ along a light ray is not a monotonic function of the comoving radial coordinate $r$. As a consequence, the angular diameter distance $D_A$ and the luminosity distance $D_L$ from the central observer fail to be functions of $z$; the relations $D_A(z)$ and $D_L(z)$ are multiple-valued in a vicinity of the SCS. The following quantities are calculated and displayed: (1) The distribution of mass density on a few characteristic hypersurfaces of constant time; some of them intersect the SCS. (2) The distribution of density along the past light cone of the present central observer. (3) A few light cones intersecting the SCS at characteristic instants. (4) The redshift profiles along several light cones. (5) The extremum-redshift hypersurface. (6) The $D_A(z)$ and $D_L(z)$ relations. (7) The last scattering time and its comparison with the $\Lambda$CDM last scattering epoch. |
2212.08647 | Franco Fiorini | Franco Fiorini | Chronology protection in $f(T)$ gravity: the case of Gott's pair of
moving cosmic strings | 6 pages, 2 figures | Universe (2024) 10, 52 | 10.3390/universe10010052 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | As a consequence of the spacetime structure, defined by the tetrad field
instead of the metric tensor alone, $f(T)$ gravity seems to harbor its own
chronology protection agency. When Gott's pair of moving cosmic strings is
considered, it is shown that the requirement of having a global parallelization
-- i.e. a global smooth field of tetrads -- drastically restrict the form of
the tetrads on the junction surface between the two strings. The junction
conditions on the tetrad field are satisfied only if the corresponding boosts
needed to put the strings in motion are null on the matching surface. This
seems to throw overboard Gott's construction from the outset without the need
of analyzing the divergence of the expectation value of the energy momentum
tensor on the Cauchy horizon, evading in this way bothering quarrels concerning
the choice of vacuum.
| [
{
"created": "Fri, 16 Dec 2022 18:47:14 GMT",
"version": "v1"
}
] | 2024-01-24 | [
[
"Fiorini",
"Franco",
""
]
] | As a consequence of the spacetime structure, defined by the tetrad field instead of the metric tensor alone, $f(T)$ gravity seems to harbor its own chronology protection agency. When Gott's pair of moving cosmic strings is considered, it is shown that the requirement of having a global parallelization -- i.e. a global smooth field of tetrads -- drastically restrict the form of the tetrads on the junction surface between the two strings. The junction conditions on the tetrad field are satisfied only if the corresponding boosts needed to put the strings in motion are null on the matching surface. This seems to throw overboard Gott's construction from the outset without the need of analyzing the divergence of the expectation value of the energy momentum tensor on the Cauchy horizon, evading in this way bothering quarrels concerning the choice of vacuum. |
1505.05329 | Cosimo Bambi | Nan Lin, Zilong Li, Jake Arthur, Rachel Asquith, Cosimo Bambi | Testing SgrA$^*$ with the spectrum of its accretion structure | 1+11 pages, 5 figures. v2: refereed version. Corrected a problem in
the code and found somewhat different conclusions | JCAP 1509:038,2015 | 10.1088/1475-7516/2015/09/038 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | SgrA$^*$ is the supermassive black hole candidate at the center of the Galaxy
and an ideal laboratory to test general relativity. Following previous work by
other authors, we use the Polish doughnut model to describe an optically thin
and constant angular momentum ion torus in hydrodynamical equilibrium and model
the accretion structure around SgrA$^*$. The radiation mechanisms are
bremsstrahlung, synchrotron emission, and inverse Compton scattering. We
compute the spectrum as seen by a distant observer in Kerr and non-Kerr
spacetimes and we study how an accurate measurement can constrain possible
deviations form the Kerr solution. As in the case of emission from a thin
accretion disk, we find a substantial degeneracy between the determination of
the spin and of possible deviations from the Kerr geometry, even when the
parameters of the ion torus are fixed. This means that this technique cannot
independently test the nature of SgrA$^*$ even in the presence of good data and
with the systematics under control. However, it might do it in combination with
other measurements (black hole shadow, radio pulsar, etc.).
| [
{
"created": "Wed, 20 May 2015 11:46:45 GMT",
"version": "v1"
},
{
"created": "Mon, 14 Sep 2015 15:07:55 GMT",
"version": "v2"
}
] | 2015-12-02 | [
[
"Lin",
"Nan",
""
],
[
"Li",
"Zilong",
""
],
[
"Arthur",
"Jake",
""
],
[
"Asquith",
"Rachel",
""
],
[
"Bambi",
"Cosimo",
""
]
] | SgrA$^*$ is the supermassive black hole candidate at the center of the Galaxy and an ideal laboratory to test general relativity. Following previous work by other authors, we use the Polish doughnut model to describe an optically thin and constant angular momentum ion torus in hydrodynamical equilibrium and model the accretion structure around SgrA$^*$. The radiation mechanisms are bremsstrahlung, synchrotron emission, and inverse Compton scattering. We compute the spectrum as seen by a distant observer in Kerr and non-Kerr spacetimes and we study how an accurate measurement can constrain possible deviations form the Kerr solution. As in the case of emission from a thin accretion disk, we find a substantial degeneracy between the determination of the spin and of possible deviations from the Kerr geometry, even when the parameters of the ion torus are fixed. This means that this technique cannot independently test the nature of SgrA$^*$ even in the presence of good data and with the systematics under control. However, it might do it in combination with other measurements (black hole shadow, radio pulsar, etc.). |
1807.06353 | Andronikos Paliathanasis | Michael Tsamparlis and Andronikos Paliathanasis | The generic model of General Relativity | 55 pages, no figures | Arab. J. Math. 8, 201 (2019) | 10.1007/s40065-019-0239-7 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We develop a generic spacetime model in General Relativity which can be used
to build any gravitational model within General Relativity. The generic model
uses two types of assumptions: (a) Geometric assumptions additional to the
inherent geometric identities of the Riemannian geometry of spacetime and (b)
Assumptions defining a class of observers by means of their 4-velocity $u^{a}$
which is a unit timelike vector field. The geometric assumptions as a rule
concern symmetry assumptions (the so called collineations). The latter
introduces the 1+3 decomposition of tensor fields in spacetime. The 1+3
decomposition results in two major results. The 1+3 decomposition of $u_{a;b}$
defines the kinematic variables of the model (expansion, rotation, shear and
4-acceleration) and defines the kinematics of the gravitational model. The 1+3
decomposition of the energy momentum tensor representing all gravitating matter
introduces the dynamic variables of the model (energy density, the isotropic
pressure, the momentum transfer or heat flux vector and the traceless tensor of
the anisotropic pressure) as measured by the defined observers and define the
dynamics of he model. The symmetries assumed by the model act as constraints on
both the kinematical and the dynamical variables of the model. As a second
further development of the generic model we assume that in addition to the
4-velocity of the observers $u_{a}$ there exists a second universal vector
field $n_{a}$ in spacetime so that one has a so called double congruence
$(u_{a},n_{a})$ which can be used to define the 1+1+2 decomposition of tensor
fields. The 1+1+2 decomposition leads to an extended kinematics concerning both
fields building the double congruence and to a finer dynamics involving more
physical variables.
| [
{
"created": "Tue, 17 Jul 2018 11:27:27 GMT",
"version": "v1"
}
] | 2021-06-15 | [
[
"Tsamparlis",
"Michael",
""
],
[
"Paliathanasis",
"Andronikos",
""
]
] | We develop a generic spacetime model in General Relativity which can be used to build any gravitational model within General Relativity. The generic model uses two types of assumptions: (a) Geometric assumptions additional to the inherent geometric identities of the Riemannian geometry of spacetime and (b) Assumptions defining a class of observers by means of their 4-velocity $u^{a}$ which is a unit timelike vector field. The geometric assumptions as a rule concern symmetry assumptions (the so called collineations). The latter introduces the 1+3 decomposition of tensor fields in spacetime. The 1+3 decomposition results in two major results. The 1+3 decomposition of $u_{a;b}$ defines the kinematic variables of the model (expansion, rotation, shear and 4-acceleration) and defines the kinematics of the gravitational model. The 1+3 decomposition of the energy momentum tensor representing all gravitating matter introduces the dynamic variables of the model (energy density, the isotropic pressure, the momentum transfer or heat flux vector and the traceless tensor of the anisotropic pressure) as measured by the defined observers and define the dynamics of he model. The symmetries assumed by the model act as constraints on both the kinematical and the dynamical variables of the model. As a second further development of the generic model we assume that in addition to the 4-velocity of the observers $u_{a}$ there exists a second universal vector field $n_{a}$ in spacetime so that one has a so called double congruence $(u_{a},n_{a})$ which can be used to define the 1+1+2 decomposition of tensor fields. The 1+1+2 decomposition leads to an extended kinematics concerning both fields building the double congruence and to a finer dynamics involving more physical variables. |
0904.0781 | Sunil Maharaj | S. Thirukkanesh, S. D. Maharaj | Charged relativistic spheres with generalized potentials | 22 pages, To appear in Math. Meth. Appl. Sci | Math.Methods Appl.Sci.32:684-701,2009 | 10.1002/mma.1060 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new class of exact solutions of the Einstein-Maxwell system is found in
closed form. This is achieved by choosing a generalised form for one of the
gravitational potentials and a particular form for the electric field
intensity. For specific values of the parameters it is possible to write the
new series solutions in terms of elementary functions. We regain well known
physically reasonable models. A physical analysis indicates that the model may
be used to describe a charged sphere. The influence of the electromagnetic
field on the gravitational interaction is highlighted.
| [
{
"created": "Sun, 5 Apr 2009 14:26:09 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Thirukkanesh",
"S.",
""
],
[
"Maharaj",
"S. D.",
""
]
] | A new class of exact solutions of the Einstein-Maxwell system is found in closed form. This is achieved by choosing a generalised form for one of the gravitational potentials and a particular form for the electric field intensity. For specific values of the parameters it is possible to write the new series solutions in terms of elementary functions. We regain well known physically reasonable models. A physical analysis indicates that the model may be used to describe a charged sphere. The influence of the electromagnetic field on the gravitational interaction is highlighted. |
2407.13583 | Martin Bojowald | Martin Bojowald and Erick I. Duque | Emergent modified gravity: Polarized Gowdy model on a torus | 55 pages, two figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | New covariant theories of emergent modified gravity exist not only in
spherically symmetric models, as previously found, but also in polarized Gowdy
systems that have a local propagating degree of freedom. Several explicit
versions are derived here, depending on various modification functions. These
models do not have instabilities from higher time derivatives, and a large
subset is compatible with gravitational waves and minimally coupled massless
matter fields travelling at the same speed. Interpreted as models of loop
quantum gravity, covariant Hamiltonian constraints derived from the covariance
conditions found in polarized Gowdy systems are more restricted than those in
spherical symmetry, requiring new forms of holonomy modifications with an
anisotropy dependence that has not been considered before. Assuming homogeneous
space, the models provide access to the full anisotropy parameters of modified
Bianchi I dynamics, in which case different fates of the classical singularity
are realized depending on the specific class of modifications.
| [
{
"created": "Thu, 18 Jul 2024 15:25:33 GMT",
"version": "v1"
}
] | 2024-07-19 | [
[
"Bojowald",
"Martin",
""
],
[
"Duque",
"Erick I.",
""
]
] | New covariant theories of emergent modified gravity exist not only in spherically symmetric models, as previously found, but also in polarized Gowdy systems that have a local propagating degree of freedom. Several explicit versions are derived here, depending on various modification functions. These models do not have instabilities from higher time derivatives, and a large subset is compatible with gravitational waves and minimally coupled massless matter fields travelling at the same speed. Interpreted as models of loop quantum gravity, covariant Hamiltonian constraints derived from the covariance conditions found in polarized Gowdy systems are more restricted than those in spherical symmetry, requiring new forms of holonomy modifications with an anisotropy dependence that has not been considered before. Assuming homogeneous space, the models provide access to the full anisotropy parameters of modified Bianchi I dynamics, in which case different fates of the classical singularity are realized depending on the specific class of modifications. |
2109.08921 | Yong-Ming Huang | Yong-Ming Huang, Yu Tian and Xiao-Ning Wu | Collapsing dust thin shells in Einstein-Gauss-Bonnet gravity | null | The European Physical Journal C volume 82, Article number: 183
(2022) | 10.1140/epjc/s10052-022-10075-9 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate gravitational collapse of a spherically symmetric thin shell
in the Einstein-Gauss-Bonnet (EGB) gravity. Under the recently proposed 4D
limit, we find that the collapsing shell will be bounced back at a small
radius, without forming a singularity. This bouncing behavior is similar to
those of a test particle and a homogeneous spherical dust star, in accordance
with the expectation that the Gauss-Bonnet term will modify the small scale
behavior of the Einstein gravity. We analyze the causal structure of the
dynamic spacetime that represents the bouncing process, finding that the thin
shell has an oscillation behavior on the Penrose diagram, which means that the
thin shell results in a novel type of black hole with respect to observers
outside the event horizon that the collapse forms. We also find that the weak
cosmic censorship conjecture holds in this model. Further implications of such
a regular gravitational collapse are discussed.
| [
{
"created": "Sat, 18 Sep 2021 12:40:44 GMT",
"version": "v1"
},
{
"created": "Sun, 6 Mar 2022 09:03:28 GMT",
"version": "v2"
},
{
"created": "Tue, 8 Mar 2022 03:44:15 GMT",
"version": "v3"
}
] | 2022-03-09 | [
[
"Huang",
"Yong-Ming",
""
],
[
"Tian",
"Yu",
""
],
[
"Wu",
"Xiao-Ning",
""
]
] | We investigate gravitational collapse of a spherically symmetric thin shell in the Einstein-Gauss-Bonnet (EGB) gravity. Under the recently proposed 4D limit, we find that the collapsing shell will be bounced back at a small radius, without forming a singularity. This bouncing behavior is similar to those of a test particle and a homogeneous spherical dust star, in accordance with the expectation that the Gauss-Bonnet term will modify the small scale behavior of the Einstein gravity. We analyze the causal structure of the dynamic spacetime that represents the bouncing process, finding that the thin shell has an oscillation behavior on the Penrose diagram, which means that the thin shell results in a novel type of black hole with respect to observers outside the event horizon that the collapse forms. We also find that the weak cosmic censorship conjecture holds in this model. Further implications of such a regular gravitational collapse are discussed. |
1912.09340 | Lukas Weih | Lukas R. Weih, Matthias Hanauske, Luciano Rezzolla | Postmerger Gravitational-Wave Signatures of Phase Transitions in Binary
Mergers | 6 pages, 4 figures, includes supplemental material, matches version
accepted to PRL | Phys. Rev. Lett. 124, 171103 (2020) | 10.1103/PhysRevLett.124.171103 | null | gr-qc astro-ph.HE nucl-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | With the first detection of gravitational waves from a binary system of
neutron stars, GW170817, a new window was opened to study the properties of
matter at and above nuclear-saturation density. Reaching densities a few times
that of nuclear matter and temperatures up to $100\,\rm{MeV}$, such mergers
also represent potential sites for a phase transition (PT) from confined
hadronic matter to deconfined quark matter. While the lack of a postmerger
signal in GW170817 has prevented us from assessing experimentally this
scenario, two theoretical studies have explored the postmerger
gravitational-wave signatures of PTs in mergers of binary systems of neutron
stars. We here extend and complete the picture by presenting a novel signature
of the occurrence of a PT. More specifically, using fully general-relativistic
hydrodynamic simulations and employing a suitably constructed equation of state
that includes a PT, we present the occurrence of a "delayed PT", i.e. a PT that
develops only some time after the merger and produces a metastable object with
a quark-matter core, i.e. a hypermassive hybrid star. Because in this scenario,
the postmerger signal exhibits two distinct fundamental gravitational-wave
frequencies -- before and after the PT -- the associated signature promises to
be the strongest and cleanest among those considered so far, and one of the
best signatures of the production of quark matter in the present Universe.
| [
{
"created": "Thu, 19 Dec 2019 16:23:15 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Apr 2020 16:06:43 GMT",
"version": "v2"
}
] | 2020-05-01 | [
[
"Weih",
"Lukas R.",
""
],
[
"Hanauske",
"Matthias",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | With the first detection of gravitational waves from a binary system of neutron stars, GW170817, a new window was opened to study the properties of matter at and above nuclear-saturation density. Reaching densities a few times that of nuclear matter and temperatures up to $100\,\rm{MeV}$, such mergers also represent potential sites for a phase transition (PT) from confined hadronic matter to deconfined quark matter. While the lack of a postmerger signal in GW170817 has prevented us from assessing experimentally this scenario, two theoretical studies have explored the postmerger gravitational-wave signatures of PTs in mergers of binary systems of neutron stars. We here extend and complete the picture by presenting a novel signature of the occurrence of a PT. More specifically, using fully general-relativistic hydrodynamic simulations and employing a suitably constructed equation of state that includes a PT, we present the occurrence of a "delayed PT", i.e. a PT that develops only some time after the merger and produces a metastable object with a quark-matter core, i.e. a hypermassive hybrid star. Because in this scenario, the postmerger signal exhibits two distinct fundamental gravitational-wave frequencies -- before and after the PT -- the associated signature promises to be the strongest and cleanest among those considered so far, and one of the best signatures of the production of quark matter in the present Universe. |
1301.4486 | Wojciech Zakrzewski | P.C. Stichel and W.J. Zakrzewski | Nonstandard approach to gravity for the dark sector of the Universe | null | null | 10.3390/e15020559 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We summarize the present state of research on the darkon fuid as a model for
the dark sector of the Universe. Nonrelativistic massless particles are
introduced as a realization of the Galilei group in an enlarged phase space.
The additional degrees of freedom allow for a nonstandard, minimal coupling to
gravity respecting Einstein's equivalence principle. Extended to a
self-gravitating fluid the Poisson equation for the gravitational potential
contains a dynamically generated effective gravitational mass density of either
sign. The equations of motion (EOMs) contain no free parameters and are
invariant w.r.t. Milne gauge transformations. Fixing the gauge eliminates the
unphysical degrees of freedom. The resulting Lagrangian possesses no free
particle limit. The particles it describes, darkons, exist only as fluid
particles of a self-gravitating fluid. This darkon fluid realizes the zero-mass
Galilean algebra extended by dilations with dynamical exponent z = 5/3. We
reduce the EOMs to Friedmann-like equations, derive conserved quantities and a
unique Hamiltonian dynamics by implementing dilation symmetry. By the Casimir
of the Poisson-bracket (PB)-algebra we foliate the phase space and construct a
Lagrangian in reduced phase space. We solve the Friedmann-like equations with
the transition redshift and the value of the Casimir as integration constants.
We obtain a deceleration phase for the early Universe and an acceleration phase
for the late Universe in agreement with observations. Steady state equations in
the spherically symmetric case may model a galactic halo. Numerical solutions
of a nonlinear differential equation for the gravitational potential lead to
predictions for the dark matter (DM) part of the rotation curves (RCs) of
galaxies in qualitative agreement with observational data. We also present a
general covariant generalization of the model.
| [
{
"created": "Fri, 18 Jan 2013 20:33:38 GMT",
"version": "v1"
}
] | 2016-11-04 | [
[
"Stichel",
"P. C.",
""
],
[
"Zakrzewski",
"W. J.",
""
]
] | We summarize the present state of research on the darkon fuid as a model for the dark sector of the Universe. Nonrelativistic massless particles are introduced as a realization of the Galilei group in an enlarged phase space. The additional degrees of freedom allow for a nonstandard, minimal coupling to gravity respecting Einstein's equivalence principle. Extended to a self-gravitating fluid the Poisson equation for the gravitational potential contains a dynamically generated effective gravitational mass density of either sign. The equations of motion (EOMs) contain no free parameters and are invariant w.r.t. Milne gauge transformations. Fixing the gauge eliminates the unphysical degrees of freedom. The resulting Lagrangian possesses no free particle limit. The particles it describes, darkons, exist only as fluid particles of a self-gravitating fluid. This darkon fluid realizes the zero-mass Galilean algebra extended by dilations with dynamical exponent z = 5/3. We reduce the EOMs to Friedmann-like equations, derive conserved quantities and a unique Hamiltonian dynamics by implementing dilation symmetry. By the Casimir of the Poisson-bracket (PB)-algebra we foliate the phase space and construct a Lagrangian in reduced phase space. We solve the Friedmann-like equations with the transition redshift and the value of the Casimir as integration constants. We obtain a deceleration phase for the early Universe and an acceleration phase for the late Universe in agreement with observations. Steady state equations in the spherically symmetric case may model a galactic halo. Numerical solutions of a nonlinear differential equation for the gravitational potential lead to predictions for the dark matter (DM) part of the rotation curves (RCs) of galaxies in qualitative agreement with observational data. We also present a general covariant generalization of the model. |
1211.0222 | Jansen Formiga | J. B. Formiga | On the accelerated observer's proper coordinates and the rigid motion
problem in Minkowski spacetime | The text has been changed in order to change the focus of the paper.
The focus is now on the problem of rigid motion in Minkowski spacetime and
the role played by accelerated observers. This paper has been published in
volume 43 of the Brazilian Journal of Physics | null | 10.1007/s13538-013-0157-7 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Physicists have been interested in accelerated observers for quite some time.
Since the advent of special relativity, many authors have tried to understand
these observers in the framework of Minkowski spacetime. One of the most
important issues related to these observers is the problematic definition of
rigid motion. In this paper, I write the metric in terms of the Frenet-Serret
curvatures and the proper coordinate system of a general accelerated observer.
Then, I use this approach to create a systematic way to construct a rigid
motion in Minkowski spacetime. Finally, I exemplify the benefits of this
procedure by applying it to two well-known observers, namely, the Rindler and
the rotating ones, and also by creating a set of observers that, perhaps, may
be interpreted as a rigid cylinder which rotates while accelerating along the
axis of rotation.
| [
{
"created": "Thu, 1 Nov 2012 16:47:54 GMT",
"version": "v1"
},
{
"created": "Sat, 24 Aug 2013 18:00:26 GMT",
"version": "v2"
},
{
"created": "Thu, 3 Oct 2013 11:58:53 GMT",
"version": "v3"
}
] | 2013-10-04 | [
[
"Formiga",
"J. B.",
""
]
] | Physicists have been interested in accelerated observers for quite some time. Since the advent of special relativity, many authors have tried to understand these observers in the framework of Minkowski spacetime. One of the most important issues related to these observers is the problematic definition of rigid motion. In this paper, I write the metric in terms of the Frenet-Serret curvatures and the proper coordinate system of a general accelerated observer. Then, I use this approach to create a systematic way to construct a rigid motion in Minkowski spacetime. Finally, I exemplify the benefits of this procedure by applying it to two well-known observers, namely, the Rindler and the rotating ones, and also by creating a set of observers that, perhaps, may be interpreted as a rigid cylinder which rotates while accelerating along the axis of rotation. |
1005.4569 | Alan Pavan Bendasoli | A. B. Pavan | Analysis of geometries with closed timelike curves | PhD thesis (in Portuguese), Advisor: Prof. Dr. Elcio Abdalla, 155
pages, 31 figures, May 2010 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This work deals with the analysis of cylindrically symmetric and stationary
space-times $\mathcal{C}_{t}$ with closed timelike curves. The equation of
motion describing the evolution of a massive scalar field in a
$\mathcal{C}_{t}$ space-time is obtained. A class of space-times with closed
timelike curves describing cosmic strings and cylinders is studied in detail.
In such space-times, both massive particles as well as photons can reach the
non-causal region. Geodesics and closed timelike curves are calculated and
investigated. We have observed that massive particles and photons describe,
essentially, two kinds of trajectories: confined orbits and scattering states.
The analysis of the light cones show us clearly the intersection between future
and past inside the non-causal region. Exact solutions for the equation of
motion of massive scalar field propagating in cosmic strings and cylinder
space-times are presented. Quasinormal modes for the scalar field have been
calculated in static and rotating cosmic cylinders. We found unstable modes in
the rotating cases. Rotating as well as static cosmic strings, i.e., without
regular interior solutions, do not display quasinormal modes for the scalar
field. We conclude presenting a conjecture relating closed timelike curves and
space-time instability.
| [
{
"created": "Tue, 25 May 2010 13:23:38 GMT",
"version": "v1"
}
] | 2010-05-26 | [
[
"Pavan",
"A. B.",
""
]
] | This work deals with the analysis of cylindrically symmetric and stationary space-times $\mathcal{C}_{t}$ with closed timelike curves. The equation of motion describing the evolution of a massive scalar field in a $\mathcal{C}_{t}$ space-time is obtained. A class of space-times with closed timelike curves describing cosmic strings and cylinders is studied in detail. In such space-times, both massive particles as well as photons can reach the non-causal region. Geodesics and closed timelike curves are calculated and investigated. We have observed that massive particles and photons describe, essentially, two kinds of trajectories: confined orbits and scattering states. The analysis of the light cones show us clearly the intersection between future and past inside the non-causal region. Exact solutions for the equation of motion of massive scalar field propagating in cosmic strings and cylinder space-times are presented. Quasinormal modes for the scalar field have been calculated in static and rotating cosmic cylinders. We found unstable modes in the rotating cases. Rotating as well as static cosmic strings, i.e., without regular interior solutions, do not display quasinormal modes for the scalar field. We conclude presenting a conjecture relating closed timelike curves and space-time instability. |
1210.3629 | Robert Mann | S. H. Hendi, R. B. Mann, N. Riazi, and B. Eslam Panah | Eguchi-Hanson like space-times in F(R) gravity | Latex, 20 pages, 6 figures | Phys. Rev. D86 104034 (2012) | 10.1103/PhysRevD.86.104034 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a model of $F(R)$ gravity in which exponential and power
corrections to Einstein-$\Lambda$ gravity are included. We show that this model
has 4-dimensional Eguchi-Hanson type instanton solutions in Euclidean space. We
then seek solutions to the five dimensional equations for which space-time
contains a hypersurface corresponding to the Eguchi-Hanson space. We obtain
analytic solutions of the $F(R)$ gravitational field equations, and by assuming
certain relationships between the model parameters and integration constants,
find several classes of exact solutions. Finally, we investigate the asymptotic
behavior of the solutions and compute the second derivative of the $F(R)$
function with respect to the Ricci scalar to confirm Dolgov-Kawasaki stability.
| [
{
"created": "Fri, 12 Oct 2012 20:15:11 GMT",
"version": "v1"
}
] | 2015-06-11 | [
[
"Hendi",
"S. H.",
""
],
[
"Mann",
"R. B.",
""
],
[
"Riazi",
"N.",
""
],
[
"Panah",
"B. Eslam",
""
]
] | We consider a model of $F(R)$ gravity in which exponential and power corrections to Einstein-$\Lambda$ gravity are included. We show that this model has 4-dimensional Eguchi-Hanson type instanton solutions in Euclidean space. We then seek solutions to the five dimensional equations for which space-time contains a hypersurface corresponding to the Eguchi-Hanson space. We obtain analytic solutions of the $F(R)$ gravitational field equations, and by assuming certain relationships between the model parameters and integration constants, find several classes of exact solutions. Finally, we investigate the asymptotic behavior of the solutions and compute the second derivative of the $F(R)$ function with respect to the Ricci scalar to confirm Dolgov-Kawasaki stability. |
1409.0760 | Amare Abebe | Amare Abebe | Breaking the cosmological background degeneracy by two-fluid
perturbations in f(R) gravity | 17 pages, 19 figures | Int. J. Mod. Phys. D Vol. 24, No. 7 (2015) 1550053 | 10.1142/S0218271815500534 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | One of the exact solutions of f(R) theories of gravity in the presence of
different forms of matter exactly mimics the LCDM solution of general
relativity at the background level. In this work we study the evolution of
scalar cosmological perturbations in the covariant and gauge-invariant
formalism and show that although the background in such a model is
indistinguishable from the standard LCDM cosmology, this degeneracy is broken
at the level of first-order perturbations. This is done by predicting different
rates of structure formation in LCDM and the f(R) model both in the complete
and quasi\hs static regimes.
| [
{
"created": "Tue, 2 Sep 2014 15:37:29 GMT",
"version": "v1"
},
{
"created": "Wed, 3 Sep 2014 18:13:44 GMT",
"version": "v2"
},
{
"created": "Mon, 27 Apr 2015 12:03:29 GMT",
"version": "v3"
}
] | 2015-04-28 | [
[
"Abebe",
"Amare",
""
]
] | One of the exact solutions of f(R) theories of gravity in the presence of different forms of matter exactly mimics the LCDM solution of general relativity at the background level. In this work we study the evolution of scalar cosmological perturbations in the covariant and gauge-invariant formalism and show that although the background in such a model is indistinguishable from the standard LCDM cosmology, this degeneracy is broken at the level of first-order perturbations. This is done by predicting different rates of structure formation in LCDM and the f(R) model both in the complete and quasi\hs static regimes. |
gr-qc/0211065 | David Delphenich | D. H. Delphenich | The Geometric Origin of the Madelung Potential | 19 pages | null | null | null | gr-qc | null | Madelung's hydrodynamical forms of the Schrodinger equation and the
Klein-Gordon equation are presented. The physical nature of the quantum
potential is explored. It is demonstrated that the geometrical origin of the
quantum potential is in the scalar curvature of the of the metric that defines
the kinetic energy density for an extended particle and that the quantization
of circulation (Bohr-Sommerfeld) is a consequence of associating an
SO(2)-reduction of the Lorentz frame bundle with wave motion. The Madelung
equations are then cast in a basis-free form in terms of exterior differential
forms in such a way that they represent the equations for a timelike solution
to the conventional wave equations whose rest mass density satisfies a
differential equation of the "Klein-Gordon minus nonlinear term" type. The role
of non-zero vorticity is briefly examined.
| [
{
"created": "Tue, 19 Nov 2002 16:10:33 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Delphenich",
"D. H.",
""
]
] | Madelung's hydrodynamical forms of the Schrodinger equation and the Klein-Gordon equation are presented. The physical nature of the quantum potential is explored. It is demonstrated that the geometrical origin of the quantum potential is in the scalar curvature of the of the metric that defines the kinetic energy density for an extended particle and that the quantization of circulation (Bohr-Sommerfeld) is a consequence of associating an SO(2)-reduction of the Lorentz frame bundle with wave motion. The Madelung equations are then cast in a basis-free form in terms of exterior differential forms in such a way that they represent the equations for a timelike solution to the conventional wave equations whose rest mass density satisfies a differential equation of the "Klein-Gordon minus nonlinear term" type. The role of non-zero vorticity is briefly examined. |
gr-qc/0207064 | Marcelo Alves | M.Alves | String Cosmology in the Jackiw-Telteiboim Model with Quantum Corrections | 8 pages, no figures | Class.Quant.Grav. 19 (2002) 4505-4510 | 10.1088/0264-9381/19/17/302 | null | gr-qc hep-th | null | This note deals with the possibility of non-trivial cosmological solutions
given by quantum corrections in the framework of the Jackiw-Telteiboim model to
the bidimensional gravity. The resulting model shows that the quantum
corrections transform, in some cases, the classical solution into a more
interesting one with initial singularity.
| [
{
"created": "Wed, 17 Jul 2002 18:39:47 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Alves",
"M.",
""
]
] | This note deals with the possibility of non-trivial cosmological solutions given by quantum corrections in the framework of the Jackiw-Telteiboim model to the bidimensional gravity. The resulting model shows that the quantum corrections transform, in some cases, the classical solution into a more interesting one with initial singularity. |
2005.08338 | Grigoris Panotopoulos | Grigoris Panotopoulos | Quasinormal modes of charged black holes in higher-dimensional
Einstein-power-Maxwell theory | Reference added. It belongs to Axioms' Special Issue: "Theory and
Mathematical Aspects of Black Holes". It contains material from
arXiv:1711.04146, arXiv:1904.10847, arXiv:1910.08538 | Axioms 2020, 9(1), 33 | 10.3390/axioms9010033 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compute the quasinormal frequencies for scalar perturbations of charged
black holes in five-dimensional Einstein-power-Maxwell theory. The impact on
the spectrum of the electric charge of the black holes, of the angular degree,
of the overtone number, and of the mass of the test scalar field is
investigated in detail. The quasinormal spectra in the eikonal limit are
computed as well for several different space-time dimensionalities.
| [
{
"created": "Sun, 17 May 2020 18:47:25 GMT",
"version": "v1"
},
{
"created": "Sun, 7 Jun 2020 16:02:29 GMT",
"version": "v2"
}
] | 2020-07-02 | [
[
"Panotopoulos",
"Grigoris",
""
]
] | We compute the quasinormal frequencies for scalar perturbations of charged black holes in five-dimensional Einstein-power-Maxwell theory. The impact on the spectrum of the electric charge of the black holes, of the angular degree, of the overtone number, and of the mass of the test scalar field is investigated in detail. The quasinormal spectra in the eikonal limit are computed as well for several different space-time dimensionalities. |
2006.14570 | Yacine Ali-Ha\"imoud | Yacine Ali-Ha\"imoud, Tristan L. Smith and Chiara M. F. Mingarelli | Fisher formalism for anisotropic gravitational-wave background searches
with pulsar timing arrays | Version accepted for publication in PRD after minor changes.
Follow-up paper on applications: arXiv:2010.13958 | Phys. Rev. D 102, 122005 (2020) | 10.1103/PhysRevD.102.122005 | null | gr-qc astro-ph.IM physics.data-an | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Pulsar timing arrays (PTAs) are currently the only experiments directly
sensitive to gravitational waves with decade-long periods. Within the next five
to ten years, PTAs are expected to detect the stochastic gravitational-wave
background (SGWB) collectively sourced by inspiralling supermassive black hole
binaries. It is expected that this background is mostly isotropic, and current
searches focus on the monopole part of the SGWB. Looking ahead, anisotropies in
the SGWB may provide a trove of additional information both on known and
unknown astrophysical and cosmological sources. In this paper, we build a
simple yet realistic Fisher formalism for anisotropic SGWB searches with PTAs.
Our formalism is able to accommodate realistic properties of PTAs, and allows
simple and accurate forecasts. We illustrate our approach with an idealized PTA
consisting of identical, isotropically distributed pulsars. In a companion
paper, we apply our formalism to current PTAs and show that it can be a
powerful tool to guide and optimize real data analysis.
| [
{
"created": "Thu, 25 Jun 2020 17:16:20 GMT",
"version": "v1"
},
{
"created": "Mon, 30 Nov 2020 19:43:22 GMT",
"version": "v2"
}
] | 2021-01-04 | [
[
"Ali-Haïmoud",
"Yacine",
""
],
[
"Smith",
"Tristan L.",
""
],
[
"Mingarelli",
"Chiara M. F.",
""
]
] | Pulsar timing arrays (PTAs) are currently the only experiments directly sensitive to gravitational waves with decade-long periods. Within the next five to ten years, PTAs are expected to detect the stochastic gravitational-wave background (SGWB) collectively sourced by inspiralling supermassive black hole binaries. It is expected that this background is mostly isotropic, and current searches focus on the monopole part of the SGWB. Looking ahead, anisotropies in the SGWB may provide a trove of additional information both on known and unknown astrophysical and cosmological sources. In this paper, we build a simple yet realistic Fisher formalism for anisotropic SGWB searches with PTAs. Our formalism is able to accommodate realistic properties of PTAs, and allows simple and accurate forecasts. We illustrate our approach with an idealized PTA consisting of identical, isotropically distributed pulsars. In a companion paper, we apply our formalism to current PTAs and show that it can be a powerful tool to guide and optimize real data analysis. |
1608.07806 | Vasilis Oikonomou | S. Nojiri, S.D. Odintsov, V.K. Oikonomou | Viable Mimetic Completion of Unified Inflation-Dark Energy Evolution in
Modified Gravity | PRD Accepted | null | 10.1103/PhysRevD.94.104050 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we demonstrate that a unified description of early and
late-time acceleration is possible in the context of mimetic $F(R)$ gravity. We
study the inflationary era in detail and demonstrate that it can be realized
even in mimetic $F(R)$ gravity where traditional $F(R)$ gravity fails to
describe the inflation. By using standard methods we calculated the spectral
index of primordial curvature perturbations and the scalar-to-tensor ratio. We
use two $F(R)$ gravity models and as it turns out, for both the models under
study the observational indices are compatible with both the latest Planck and
the BICEP2/Keck array data. Finally, the graceful exit from inflation is
guaranteed by the existence of growing curvature perturbations when the
slow-roll era ends.
| [
{
"created": "Sun, 28 Aug 2016 13:02:18 GMT",
"version": "v1"
},
{
"created": "Sun, 6 Nov 2016 13:16:57 GMT",
"version": "v2"
}
] | 2016-12-21 | [
[
"Nojiri",
"S.",
""
],
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
]
] | In this paper, we demonstrate that a unified description of early and late-time acceleration is possible in the context of mimetic $F(R)$ gravity. We study the inflationary era in detail and demonstrate that it can be realized even in mimetic $F(R)$ gravity where traditional $F(R)$ gravity fails to describe the inflation. By using standard methods we calculated the spectral index of primordial curvature perturbations and the scalar-to-tensor ratio. We use two $F(R)$ gravity models and as it turns out, for both the models under study the observational indices are compatible with both the latest Planck and the BICEP2/Keck array data. Finally, the graceful exit from inflation is guaranteed by the existence of growing curvature perturbations when the slow-roll era ends. |
1711.00585 | Igor Khavkine | Igor Khavkine | Explicit triangular decoupling of the separated vector wave equation on
Schwarzschild into scalar Regge-Wheeler equations | v2: improved notation, fixed some inconsistent formulas; close to
published version, with minor further corrections. v1: 20 pages, no figures;
contribution to the proceedings of the workshop "Non-regular spacetime
geometry" held in Florence, Italy, 20-22 Jun 2017 | J. Phys.: Conf. Ser. 968, 012006 (2018) | 10.1088/1742-6596/968/1/012006 | null | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | We consider the vector wave equation on the Schwarzschild spacetime, which
can be considered as coming from the harmonic (or Lorenz) gauge fixed Maxwell
equations. After a separation of variables, the radial mode equations form a
complicated system of coupled linear ODEs. We outline a precise abstract
strategy to decouple this system into triangular form, where the diagonal
blocks consist of spin-$s$ scalar Regge-Wheeler equations, with $s=0$ or $1$.
This strategy is then implemented to give an explicit transformation of the
radial mode equations (with nonzero frequency and angular momentum) into this
triangular form. Our decoupling goes a step further than previous results in
the literature by making the triangular form explicit and reducing it as much
as possible. Also, with the help of our abstractly formulated decoupling
strategy, we have significantly streamlined both the presentation of the final
results and the intermediate calculations. Finally, we note that the vector
wave equation is a simple model for more complicated equations, like harmonic
(or de Donder) gauge fixed linearized gravity, and backgrounds, like Kerr,
where we expect the same abstract decoupling strategy to work as well.
| [
{
"created": "Thu, 2 Nov 2017 01:26:42 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Apr 2018 14:14:44 GMT",
"version": "v2"
}
] | 2018-04-11 | [
[
"Khavkine",
"Igor",
""
]
] | We consider the vector wave equation on the Schwarzschild spacetime, which can be considered as coming from the harmonic (or Lorenz) gauge fixed Maxwell equations. After a separation of variables, the radial mode equations form a complicated system of coupled linear ODEs. We outline a precise abstract strategy to decouple this system into triangular form, where the diagonal blocks consist of spin-$s$ scalar Regge-Wheeler equations, with $s=0$ or $1$. This strategy is then implemented to give an explicit transformation of the radial mode equations (with nonzero frequency and angular momentum) into this triangular form. Our decoupling goes a step further than previous results in the literature by making the triangular form explicit and reducing it as much as possible. Also, with the help of our abstractly formulated decoupling strategy, we have significantly streamlined both the presentation of the final results and the intermediate calculations. Finally, we note that the vector wave equation is a simple model for more complicated equations, like harmonic (or de Donder) gauge fixed linearized gravity, and backgrounds, like Kerr, where we expect the same abstract decoupling strategy to work as well. |
2302.01564 | Hrishikesh Chakrabarty | Hrishikesh Chakrabarty, Auttakit Chatrabhuti, Daniele Malafarina,
Bhuddhanubhap Silasan, Takol Tangphati | Effects of gravitational lensing by Kaluza-Klein black holes on neutrino
oscillations | 13 pages, 6 figures, matches published version | JCAP 08 (2023) 018 | null | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | We study gravitational lensing of neutrinos in a Kaluza-Klein black hole
spacetime and compare the oscillation probabilities of neutrinos with the case
of lensing by black holes in General Relativity. We show that measuring
neutrino oscillations in curved spacetimes may allow us to distinguish the two
kinds of black holes. This promises to become an useful tool for future
measurements of the properties of black hole candidates and possibly help to
constrain the validity of alternative theories of gravity.
| [
{
"created": "Fri, 3 Feb 2023 06:24:34 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Aug 2023 09:53:10 GMT",
"version": "v2"
}
] | 2023-08-17 | [
[
"Chakrabarty",
"Hrishikesh",
""
],
[
"Chatrabhuti",
"Auttakit",
""
],
[
"Malafarina",
"Daniele",
""
],
[
"Silasan",
"Bhuddhanubhap",
""
],
[
"Tangphati",
"Takol",
""
]
] | We study gravitational lensing of neutrinos in a Kaluza-Klein black hole spacetime and compare the oscillation probabilities of neutrinos with the case of lensing by black holes in General Relativity. We show that measuring neutrino oscillations in curved spacetimes may allow us to distinguish the two kinds of black holes. This promises to become an useful tool for future measurements of the properties of black hole candidates and possibly help to constrain the validity of alternative theories of gravity. |
2004.13693 | Francisco Cabral | Francisco Cabral, Francisco S. N. Lobo, Diego Rubiera-Garcia | The cosmological principle in theories with torsion: The case of
Einstein-Cartan-Dirac-Maxwell gravity | V2: 11 pages, published version | JCAP 10 (2020) 057 | 10.1088/1475-7516/2020/10/057 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We address the implementation of the cosmological principle, that is, the
assumption of homogeneity and isotropy in the spatial distribution of matter in
the Universe, within the context of Einstein-Cartan theory including minimal
couplings of both Dirac and Maxwell fields to torsion. This theory gives rise
to new physical effects in environments of high spin densities while leaving
the vacuum dynamics unaffected. Our approach is to impose the cosmological
principle from the onset to the geometrical degrees of freedom (metric and
torsion functions), which constrains the torsion components and the
corresponding correction terms in the Friedmann-like equations and in the
resulting fermionic and bosonic (non-linear) dynamics. We derive the
corresponding cosmological dynamics for the geometrical and matter degrees of
freedom and discuss the validity of this approach.
| [
{
"created": "Tue, 28 Apr 2020 17:49:46 GMT",
"version": "v1"
},
{
"created": "Sun, 1 Nov 2020 23:59:15 GMT",
"version": "v2"
}
] | 2020-11-03 | [
[
"Cabral",
"Francisco",
""
],
[
"Lobo",
"Francisco S. N.",
""
],
[
"Rubiera-Garcia",
"Diego",
""
]
] | We address the implementation of the cosmological principle, that is, the assumption of homogeneity and isotropy in the spatial distribution of matter in the Universe, within the context of Einstein-Cartan theory including minimal couplings of both Dirac and Maxwell fields to torsion. This theory gives rise to new physical effects in environments of high spin densities while leaving the vacuum dynamics unaffected. Our approach is to impose the cosmological principle from the onset to the geometrical degrees of freedom (metric and torsion functions), which constrains the torsion components and the corresponding correction terms in the Friedmann-like equations and in the resulting fermionic and bosonic (non-linear) dynamics. We derive the corresponding cosmological dynamics for the geometrical and matter degrees of freedom and discuss the validity of this approach. |
2208.01400 | Muhammad Sharif | M. Sharif and Saba Naz | Impact of Charge on Gravastars in $f(\mathfrak{R},\mathcal{T}^{2})$
Gravity | 20 pages, 4 figures | Mod. Phys. Lett. A 37(2022)2250065 | 10.1142/S0217732322500651 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper studies the influence of charge on a compact stellar structure
also regarded as vacuum condensate star in the background of
$f(\mathfrak{R},\mathcal{T}^{2})$ gravity. This object is considered the
alternate of black hole whose structure involves three distinct regions, i.e.,
interior, exterior and thin-shell. We analyze these domains of a gravastar for
a particular model of this modified theory. In the inner region of a gravastar,
the considered equation of state defines that energy density is equal to
negative pressure which is the cause of repulsive force on the spherical shell.
In the intermediate shell, pressure and energy density are equal and contain
ultra-relativistic fluid. The inward-directed gravitational pull of thin-shell
counterbalance the force exerted by the inner region of a gravastar allowing
the formation of a singularity-free object. The Reissner-Nordstrom metric
presents the outer vacuum spherical domain. Moreover, we discuss the impact of
the charge on physical attributes of a gravastar such as the equation of state
parameter, entropy, proper length and energy. We conclude that singularity-free
solutions of charged gravastar are physically consistent in this modified
theory.
| [
{
"created": "Mon, 1 Aug 2022 07:27:06 GMT",
"version": "v1"
}
] | 2022-08-10 | [
[
"Sharif",
"M.",
""
],
[
"Naz",
"Saba",
""
]
] | This paper studies the influence of charge on a compact stellar structure also regarded as vacuum condensate star in the background of $f(\mathfrak{R},\mathcal{T}^{2})$ gravity. This object is considered the alternate of black hole whose structure involves three distinct regions, i.e., interior, exterior and thin-shell. We analyze these domains of a gravastar for a particular model of this modified theory. In the inner region of a gravastar, the considered equation of state defines that energy density is equal to negative pressure which is the cause of repulsive force on the spherical shell. In the intermediate shell, pressure and energy density are equal and contain ultra-relativistic fluid. The inward-directed gravitational pull of thin-shell counterbalance the force exerted by the inner region of a gravastar allowing the formation of a singularity-free object. The Reissner-Nordstrom metric presents the outer vacuum spherical domain. Moreover, we discuss the impact of the charge on physical attributes of a gravastar such as the equation of state parameter, entropy, proper length and energy. We conclude that singularity-free solutions of charged gravastar are physically consistent in this modified theory. |
1010.1367 | Christian Boehmer | Christian G. Boehmer, Atifah Mussa | Charged perfect fluids in the presence of a cosmological constant | 14 pages, 2 figures; revised version, one subsection removed, minor
changes throughout the text | Gen.Rel.Grav.43:3033-3046,2011 | 10.1007/s10714-011-1223-5 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the static and spherically symmetric field equations of general
relativity for charged perfect fluid spheres in the presence of a cosmological
constant. Following work by Florides (1983) we find new exact solutions of the
field equations, and discuss their mass radius ratios. These solutions, for
instance, require the charged Nariai metric to be the vacuum part of the
spacetime. We also find charged generalizations of the Einstein static universe
and speculate that the smallness problem of the cosmological constant might
become less problematic if charge is taken into account.
| [
{
"created": "Thu, 7 Oct 2010 08:30:26 GMT",
"version": "v1"
},
{
"created": "Sun, 21 Aug 2011 18:35:24 GMT",
"version": "v2"
}
] | 2011-10-19 | [
[
"Boehmer",
"Christian G.",
""
],
[
"Mussa",
"Atifah",
""
]
] | We consider the static and spherically symmetric field equations of general relativity for charged perfect fluid spheres in the presence of a cosmological constant. Following work by Florides (1983) we find new exact solutions of the field equations, and discuss their mass radius ratios. These solutions, for instance, require the charged Nariai metric to be the vacuum part of the spacetime. We also find charged generalizations of the Einstein static universe and speculate that the smallness problem of the cosmological constant might become less problematic if charge is taken into account. |
1311.5931 | Francesco Pannarale | Francesco Pannarale | Black hole remnant of black hole-neutron star coalescing binaries with
arbitrary black hole spin | 11 pages, 2 figures, 3 tables | Phys. Rev. D 89, 044045 (2014) | 10.1103/PhysRevD.89.044045 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A model for determining the dimensionless spin parameter and mass of the
black hole remnant of black hole-neutron star mergers with arbitrary initial
black hole spin angular momentum, binary mass ratio, and neutron star mass and
cold equation of state is formulated. Tests against numerical-relativity
results are carried out, showing that both the dimensionless spin parameter and
the final mass are accurately reproduced. For the first time, the behaviour of
both quantities and of the l = 2, m = 2, n = 0 quasinormal mode frequency is
inspected throughout the parameter space. Predictions of this frequency may be
exploited to guide gravitational wave modelling and detection efforts, and to
extract physical information from detected gravitational wave signals that
would help us break degeneracies between binary black hole and black
hole-neutron star systems, improve our understanding of compact binary
formation, and constrain the neutron star equation of state.
| [
{
"created": "Fri, 22 Nov 2013 23:56:28 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Mar 2014 14:29:57 GMT",
"version": "v2"
}
] | 2014-03-11 | [
[
"Pannarale",
"Francesco",
""
]
] | A model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with arbitrary initial black hole spin angular momentum, binary mass ratio, and neutron star mass and cold equation of state is formulated. Tests against numerical-relativity results are carried out, showing that both the dimensionless spin parameter and the final mass are accurately reproduced. For the first time, the behaviour of both quantities and of the l = 2, m = 2, n = 0 quasinormal mode frequency is inspected throughout the parameter space. Predictions of this frequency may be exploited to guide gravitational wave modelling and detection efforts, and to extract physical information from detected gravitational wave signals that would help us break degeneracies between binary black hole and black hole-neutron star systems, improve our understanding of compact binary formation, and constrain the neutron star equation of state. |
gr-qc/0103017 | Yakov Itin | Yakov Itin | Conserved currents for general teleparallel models | 22 pages, 3 figures | null | 10.1142/S0217751X02011928 | null | gr-qc | null | The obstruction for the existence of an energy momentum tensor for the
gravitational field is connected with differential-geometric features of the
Riemannian manifold. It has not to be valid for alternative geometrical
structures. In this article a general 3-parameter class of teleparallel models
is considered. The field equation turns out to have a form completely similar
to the Maxwell field equation $d*\F^a=\T^a$. By applying the Noether procedure,
the source 3-form $\T^a$ is shown to be connected with the diffeomorphism
invariance of the Lagrangian. Thus the source of the coframe field is
interpreted as the total conserved energy-momentum current of the system. A
reduction of the conserved current to the Noether current and the Noether
charge for the coframe field is provided. An energy-momentum tensor for the
coframe field is defined in a diffeomorphism invariant and a translational
covariant way. The total energy-momentum current of a system is conserved. Thus
a redistribution of the energy-momentum current between material and coframe
(gravity) field is possible in principle, unlike as in GR. The energy-momentum
tensor is calculated for various teleparallel models: the pure Yang-Mills type
model, the anti-Yang-Mills type model and the generalized teleparallel
equivalent of GR. The latter case can serve as a very close alternative to the
GR description of gravity.
| [
{
"created": "Tue, 6 Mar 2001 17:21:12 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Itin",
"Yakov",
""
]
] | The obstruction for the existence of an energy momentum tensor for the gravitational field is connected with differential-geometric features of the Riemannian manifold. It has not to be valid for alternative geometrical structures. In this article a general 3-parameter class of teleparallel models is considered. The field equation turns out to have a form completely similar to the Maxwell field equation $d*\F^a=\T^a$. By applying the Noether procedure, the source 3-form $\T^a$ is shown to be connected with the diffeomorphism invariance of the Lagrangian. Thus the source of the coframe field is interpreted as the total conserved energy-momentum current of the system. A reduction of the conserved current to the Noether current and the Noether charge for the coframe field is provided. An energy-momentum tensor for the coframe field is defined in a diffeomorphism invariant and a translational covariant way. The total energy-momentum current of a system is conserved. Thus a redistribution of the energy-momentum current between material and coframe (gravity) field is possible in principle, unlike as in GR. The energy-momentum tensor is calculated for various teleparallel models: the pure Yang-Mills type model, the anti-Yang-Mills type model and the generalized teleparallel equivalent of GR. The latter case can serve as a very close alternative to the GR description of gravity. |
gr-qc/9403023 | Osamu Yasuda 0426-77-1111x3376 | Osamu Yasuda | A test of a kind of the equivalence principle by long-baseline
neutrino-oscillation experiments | LaTeX, 7 pages and 5 figures appended as uuencoded PostScript files,
TMUP-HEL-9404 | null | null | null | gr-qc | null | Possible breakdown of the universality of the gravitational couplings to
different neutrino flavors can be tested in long-baseline neutrino-oscillation
experiments, such as a proposed experiment at SOUDAN 2 or one at the DUMAND
project. Such a breakdown could be detected with sensitivity to the order of
$10^{-14}$ or $10^{-15}$. For generic case of neutrino oscillations, it is
emphasized that one can identify the spin of the particle which mediates the
force causing the oscillation, by investigating the energy spectrum of the
outgoing charged leptons. (based on talk presented at the Workshop on General
Relativity and Gravitation held at Univ. of Tokyo, January 17-20, 1994)
| [
{
"created": "Fri, 11 Mar 1994 03:35:25 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Yasuda",
"Osamu",
""
]
] | Possible breakdown of the universality of the gravitational couplings to different neutrino flavors can be tested in long-baseline neutrino-oscillation experiments, such as a proposed experiment at SOUDAN 2 or one at the DUMAND project. Such a breakdown could be detected with sensitivity to the order of $10^{-14}$ or $10^{-15}$. For generic case of neutrino oscillations, it is emphasized that one can identify the spin of the particle which mediates the force causing the oscillation, by investigating the energy spectrum of the outgoing charged leptons. (based on talk presented at the Workshop on General Relativity and Gravitation held at Univ. of Tokyo, January 17-20, 1994) |
2208.03661 | Yong Song | Yong Song and Chuanyu Zhang | Quasi-local studies of the particle surfaces and their stability in
general spacetimes | 15 pages, accepted for publication in European Physical Journal C | null | 10.1140/epjc/s10052-022-11143-w | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this paper, enlightened by the definition of the photon surface given by
Claudel, Virbhadra and Ellis, we give a quasi-local definition of the particle
surface. From this definition, one can study the evolution of the circular
orbits in general spacetime. Especially, we pointed out that this definition
can be used to get the spherical circular orbits in stationary spacetimes which
cannot be got by the definition of Claudel, Virbhadra and Ellis. Further, we
give a condition to exclude the particle surface in spacetime without gravity.
Simultaneously, we give a quasi-local definition of the stability of the
particle surface in general spacetime. From this definition, one can get the
evolution equation of the innermost stable circular orbit (ISCO) in general
spacetime. To verify the correctness of these definitions, we studied the
circular orbits in some special cases and the results are all consistent with
the previous results.
| [
{
"created": "Sun, 7 Aug 2022 07:52:36 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Jan 2023 06:10:24 GMT",
"version": "v2"
}
] | 2023-02-08 | [
[
"Song",
"Yong",
""
],
[
"Zhang",
"Chuanyu",
""
]
] | In this paper, enlightened by the definition of the photon surface given by Claudel, Virbhadra and Ellis, we give a quasi-local definition of the particle surface. From this definition, one can study the evolution of the circular orbits in general spacetime. Especially, we pointed out that this definition can be used to get the spherical circular orbits in stationary spacetimes which cannot be got by the definition of Claudel, Virbhadra and Ellis. Further, we give a condition to exclude the particle surface in spacetime without gravity. Simultaneously, we give a quasi-local definition of the stability of the particle surface in general spacetime. From this definition, one can get the evolution equation of the innermost stable circular orbit (ISCO) in general spacetime. To verify the correctness of these definitions, we studied the circular orbits in some special cases and the results are all consistent with the previous results. |
2312.00769 | Kam To Billy Sievers | Kam To Billy Sievers, Liam Newhook, Sarah Muth, Ivan Booth, Robie A.
Hennigar, Hari K. Kunduri | Marginally Outer Trapped Tori in Black Hole Spacetimes | 14 pages, 16 figures | null | 10.1103/PhysRevD.109.124023 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | During a binary black hole merger, multiple intermediary marginally outer
trapped tubes connect the initial pair of apparent horizons with the final
(single) apparent horizon. The marginally outer trapped surfaces (MOTSs) that
foliate these tubes can have complicated geometries as well as non-spherical
topologies. In particular, toroidal MOTSs form inside both of the original
black holes during the early stages of a head-on merger that starts from
time-symmetric initial data [1]. We show that toroidal MOTSs also form in the
maximal analytic extension of the Schwarzschild spacetime as Kruskal time
advances from the $T=0$ moment of time symmetry. As for the merger simulations,
they cross the Einstein-Rosen bridge and are tightly sandwiched between the
apparent horizons in the two asymptotic regions at early times. This strongly
suggests that their formation is a consequence of the initial conditions rather
than merger physics. Finally, we consider MOTSs of spherical topology in the
Kruskal-Szekeres slicing and study their properties. All of these are contained
within the apparent horizon but some do not enclose the wormhole.
| [
{
"created": "Fri, 1 Dec 2023 18:47:56 GMT",
"version": "v1"
}
] | 2024-06-14 | [
[
"Sievers",
"Kam To Billy",
""
],
[
"Newhook",
"Liam",
""
],
[
"Muth",
"Sarah",
""
],
[
"Booth",
"Ivan",
""
],
[
"Hennigar",
"Robie A.",
""
],
[
"Kunduri",
"Hari K.",
""
]
] | During a binary black hole merger, multiple intermediary marginally outer trapped tubes connect the initial pair of apparent horizons with the final (single) apparent horizon. The marginally outer trapped surfaces (MOTSs) that foliate these tubes can have complicated geometries as well as non-spherical topologies. In particular, toroidal MOTSs form inside both of the original black holes during the early stages of a head-on merger that starts from time-symmetric initial data [1]. We show that toroidal MOTSs also form in the maximal analytic extension of the Schwarzschild spacetime as Kruskal time advances from the $T=0$ moment of time symmetry. As for the merger simulations, they cross the Einstein-Rosen bridge and are tightly sandwiched between the apparent horizons in the two asymptotic regions at early times. This strongly suggests that their formation is a consequence of the initial conditions rather than merger physics. Finally, we consider MOTSs of spherical topology in the Kruskal-Szekeres slicing and study their properties. All of these are contained within the apparent horizon but some do not enclose the wormhole. |
1804.07955 | Cosimo Bambi | Yuexin Zhang, Menglei Zhou, Cosimo Bambi | Iron line spectroscopy of black holes in asymptotically safe gravity | 9 pages, 6 figures. v2: refereed version | Eur. Phys. J. C (2018) 78:376 | 10.1140/epjc/s10052-018-5875-0 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the iron line shape expected in the reflection spectrum of accretion
disks around black holes in asymptotically safe gravity. We compare the results
of our simulations with the iron line shapes expected in the reflection
spectrum of accretion disks around Kerr black holes to see if the technique of
iron line spectroscopy can be used as a tool to test asymptotically safe
gravity. Our analysis shows that current X-ray facilities are surely unable to
distinguish black holes in asymptotically safe gravity from black holes in
Einstein's gravity. In the case of the next generation of X-ray missions, which
promise to provide unprecedented high quality data, the question remains open
because it cannot be addressed within our simplified model.
| [
{
"created": "Sat, 21 Apr 2018 12:28:19 GMT",
"version": "v1"
},
{
"created": "Fri, 4 May 2018 11:27:24 GMT",
"version": "v2"
}
] | 2018-05-17 | [
[
"Zhang",
"Yuexin",
""
],
[
"Zhou",
"Menglei",
""
],
[
"Bambi",
"Cosimo",
""
]
] | We study the iron line shape expected in the reflection spectrum of accretion disks around black holes in asymptotically safe gravity. We compare the results of our simulations with the iron line shapes expected in the reflection spectrum of accretion disks around Kerr black holes to see if the technique of iron line spectroscopy can be used as a tool to test asymptotically safe gravity. Our analysis shows that current X-ray facilities are surely unable to distinguish black holes in asymptotically safe gravity from black holes in Einstein's gravity. In the case of the next generation of X-ray missions, which promise to provide unprecedented high quality data, the question remains open because it cannot be addressed within our simplified model. |
2103.11698 | Jo\~ao Lu\'is Rosa | Jo\~ao Lu\'is Rosa | Junction conditions and thin-shells in perfect-fluid $f\left(R,T\right)$
gravity | 21 pages | Phys. Rev. D 103, 104069 (2021) | 10.1103/PhysRevD.103.104069 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we derive the junction conditions for the matching between two
spacetimes at a separation hypersurface in the perfect-fluid version of
$f\left(R,T\right)$ gravity, not only in the usual geometrical representation
but also in a dynamically equivalent scalar-tensor representation. We start
with the general case in which a thin-shell separates the two spacetimes at the
separation hypersurface, for which the general junction conditions are deduced,
and the particular case for smooth matching is considered when the
stress-energy tensor of the thin-shell vanishes. The set of junction conditions
is similar to the one previously obtained for $f\left(R\right)$ gravity but
features also constraints in the continuity of the trace of the stress-energy
tensor $T_{ab}$ and its partial derivatives, which force the thin-shell to
satisfy the equation of state of radiation $\sigma=2p_t$. As a consequence, a
necessary and sufficient condition for spherically symmetric thin-shells to
satisfy all the energy conditions is the positivity of its energy density
$\sigma$. For specific forms of the function $f\left(R,T\right)$, the
continuity of $R$ and $T$ ceases to be mandatory but a gravitational
double-layer arises at the separation hypersurface. The Martinez thin-shell
system and a thin-shell surrounding a central black-hole are provided as
examples of application.
| [
{
"created": "Mon, 22 Mar 2021 10:05:54 GMT",
"version": "v1"
},
{
"created": "Fri, 28 May 2021 15:39:34 GMT",
"version": "v2"
}
] | 2021-06-02 | [
[
"Rosa",
"João Luís",
""
]
] | In this work we derive the junction conditions for the matching between two spacetimes at a separation hypersurface in the perfect-fluid version of $f\left(R,T\right)$ gravity, not only in the usual geometrical representation but also in a dynamically equivalent scalar-tensor representation. We start with the general case in which a thin-shell separates the two spacetimes at the separation hypersurface, for which the general junction conditions are deduced, and the particular case for smooth matching is considered when the stress-energy tensor of the thin-shell vanishes. The set of junction conditions is similar to the one previously obtained for $f\left(R\right)$ gravity but features also constraints in the continuity of the trace of the stress-energy tensor $T_{ab}$ and its partial derivatives, which force the thin-shell to satisfy the equation of state of radiation $\sigma=2p_t$. As a consequence, a necessary and sufficient condition for spherically symmetric thin-shells to satisfy all the energy conditions is the positivity of its energy density $\sigma$. For specific forms of the function $f\left(R,T\right)$, the continuity of $R$ and $T$ ceases to be mandatory but a gravitational double-layer arises at the separation hypersurface. The Martinez thin-shell system and a thin-shell surrounding a central black-hole are provided as examples of application. |
gr-qc/9602039 | Glenn D. Starkman | Neil J. Cornish (Case Western Reserve Univ.), David N. Spergel
(Princeton U. and U of Maryland) and Glenn D. Starkman (C.W.R.U.) | Circles in the Sky: Finding Topology with the Microwave Background
Radiation | 6 pages, 1 latex file, no figures | Class.Quant.Grav. 15 (1998) 2657-2670 | null | CWRU-P1-96 | gr-qc | null | If the universe is finite and smaller than the distance to the surface of
last scatter, then the signature of the topology of the universe is writ on the
microwave background sky. Previous efforts to search for this topology have
focused on one particular model: a toroidal flat universe. We show how both the
high degree of spatial symmetry of this topology and the integrability of its
geodesics make it unreliable as a paradigmatic example, and discuss why
topology on scales significantly smaller than the horizon are not ruled out by
previous analyses focussing on this special case. We show that in these small
universes the microwave background will be identified at the intersections of
the surface of last scattering as seen by different ``copies'' of the observer.
Since the surface of last scattering is a sphere, these intersections will be
circles, regardless of the background geometry or topology. We therefore
propose a statistic that is sensitive to all small finite homogeneous
topologies. Here, small means that the distance to the surface of last scatter
is smaller than the ``periodicity scale'' of the universe.
| [
{
"created": "Tue, 20 Feb 1996 20:22:31 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Feb 1996 22:25:07 GMT",
"version": "v2"
}
] | 2016-02-09 | [
[
"Cornish",
"Neil J.",
"",
"Case Western Reserve Univ."
],
[
"Spergel",
"David N.",
"",
"Princeton U. and U of Maryland"
],
[
"Starkman",
"Glenn D.",
"",
"C.W.R.U."
]
] | If the universe is finite and smaller than the distance to the surface of last scatter, then the signature of the topology of the universe is writ on the microwave background sky. Previous efforts to search for this topology have focused on one particular model: a toroidal flat universe. We show how both the high degree of spatial symmetry of this topology and the integrability of its geodesics make it unreliable as a paradigmatic example, and discuss why topology on scales significantly smaller than the horizon are not ruled out by previous analyses focussing on this special case. We show that in these small universes the microwave background will be identified at the intersections of the surface of last scattering as seen by different ``copies'' of the observer. Since the surface of last scattering is a sphere, these intersections will be circles, regardless of the background geometry or topology. We therefore propose a statistic that is sensitive to all small finite homogeneous topologies. Here, small means that the distance to the surface of last scatter is smaller than the ``periodicity scale'' of the universe. |
gr-qc/0208010 | null | John C. Baez, J. Daniel Christensen and Greg Egan | Asymptotics of 10j symbols | 25 pages LaTeX with 8 encapsulated Postscript figures. v2 has various
clarifications and better page breaks. v3 is the final version, to appear in
Classical and Quantum Gravity, and has a few minor corrections and additional
references | Class.Quant.Grav.19:6489,2002 | 10.1088/0264-9381/19/24/315 | null | gr-qc | null | The Riemannian 10j symbols are spin networks that assign an amplitude to each
4-simplex in the Barrett-Crane model of Riemannian quantum gravity. This
amplitude is a function of the areas of the 10 faces of the 4-simplex, and
Barrett and Williams have shown that one contribution to its asymptotics comes
from the Regge action for all non-degenerate 4-simplices with the specified
face areas. However, we show numerically that the dominant contribution comes
from degenerate 4-simplices. As a consequence, one can compute the asymptotics
of the Riemannian 10j symbols by evaluating a `degenerate spin network', where
the rotation group SO(4) is replaced by the Euclidean group of isometries of
R^3. We conjecture formulas for the asymptotics of a large class of Riemannian
and Lorentzian spin networks in terms of these degenerate spin networks, and
check these formulas in some special cases. Among other things, this conjecture
implies that the Lorentzian 10j symbols are asymptotic to 1/16 times the
Riemannian ones.
| [
{
"created": "Mon, 5 Aug 2002 10:36:35 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Aug 2002 21:10:31 GMT",
"version": "v2"
},
{
"created": "Mon, 4 Nov 2002 20:31:11 GMT",
"version": "v3"
}
] | 2014-11-17 | [
[
"Baez",
"John C.",
""
],
[
"Christensen",
"J. Daniel",
""
],
[
"Egan",
"Greg",
""
]
] | The Riemannian 10j symbols are spin networks that assign an amplitude to each 4-simplex in the Barrett-Crane model of Riemannian quantum gravity. This amplitude is a function of the areas of the 10 faces of the 4-simplex, and Barrett and Williams have shown that one contribution to its asymptotics comes from the Regge action for all non-degenerate 4-simplices with the specified face areas. However, we show numerically that the dominant contribution comes from degenerate 4-simplices. As a consequence, one can compute the asymptotics of the Riemannian 10j symbols by evaluating a `degenerate spin network', where the rotation group SO(4) is replaced by the Euclidean group of isometries of R^3. We conjecture formulas for the asymptotics of a large class of Riemannian and Lorentzian spin networks in terms of these degenerate spin networks, and check these formulas in some special cases. Among other things, this conjecture implies that the Lorentzian 10j symbols are asymptotic to 1/16 times the Riemannian ones. |
1710.06620 | Salvatore Capozziello | G. G. L. Nashed and S. Capozziello | Charged Anti-de Sitter BTZ black holes in Maxwell-$f(T)$ gravity | 15 pages, accepted for publication in IJMPA | null | 10.1142/S0217751X18500768 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Inspired by the BTZ formalism, we discuss the Maxwell-$f(T)$ gravity in
(2+1)-dimensions. The main task is to derive exact solutions for a special form
of $f(T)=T+\epsilon T^2$, with $T$ being the torsion scalar of
Weitzenb$\ddot{\mbox{o}}$ck geometry. To this end, a triad field is applied to
the equations of motion of charged $f(T)$ and sets of circularly symmetric
non-charged and charged solutions have been derived. We show that, in the
charged case, the monopole-like and the ${\it ln}$ terms are linked by a
correlative constant despite of known results in teleparallel geometry and its
extensions [39]. Furthermore, it is possible to show that the event horizon is
not identical with the Cauchy horizon due to such a constant. The singularities
and the horizons of these black holes are examined: they are new and have no
analogue in literature due to the fact that their curvature singularities are
soft. We calculate the energy content of these solutions by using the general
vector form of the energy-momentum within the framework of $f(T) $ gravity.
Finally, some thermodynamical quantities, like entropy and Hawking temperature,
are derived.
| [
{
"created": "Wed, 18 Oct 2017 08:35:24 GMT",
"version": "v1"
},
{
"created": "Sat, 14 Apr 2018 16:05:34 GMT",
"version": "v2"
}
] | 2018-05-23 | [
[
"Nashed",
"G. G. L.",
""
],
[
"Capozziello",
"S.",
""
]
] | Inspired by the BTZ formalism, we discuss the Maxwell-$f(T)$ gravity in (2+1)-dimensions. The main task is to derive exact solutions for a special form of $f(T)=T+\epsilon T^2$, with $T$ being the torsion scalar of Weitzenb$\ddot{\mbox{o}}$ck geometry. To this end, a triad field is applied to the equations of motion of charged $f(T)$ and sets of circularly symmetric non-charged and charged solutions have been derived. We show that, in the charged case, the monopole-like and the ${\it ln}$ terms are linked by a correlative constant despite of known results in teleparallel geometry and its extensions [39]. Furthermore, it is possible to show that the event horizon is not identical with the Cauchy horizon due to such a constant. The singularities and the horizons of these black holes are examined: they are new and have no analogue in literature due to the fact that their curvature singularities are soft. We calculate the energy content of these solutions by using the general vector form of the energy-momentum within the framework of $f(T) $ gravity. Finally, some thermodynamical quantities, like entropy and Hawking temperature, are derived. |
1507.06308 | Rajeev Kumar Jain | Alessandro Codello and Rajeev Kumar Jain | On the covariant formalism of the effective field theory of gravity and
leading order corrections | v1: 35 pages, 3 figures; v2: 32 pages, 3 figures, title slightly
changed, minor corrections, published in Classical and Quantum Gravity | Class. Quantum Grav. 33, 225006 (2016) | 10.1088/0264-9381/33/22/225006 | CP3-Origins-2015-28 DNRF90 and DIAS-2015-28 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct the covariant effective field theory of gravity as an expansion
in inverse powers of the Planck mass, identifying the leading and
next-to-leading quantum corrections. We determine the form of the effective
action for the cases of pure gravity with cosmological constant as well as
gravity coupled to matter. By means of heat kernel methods we renormalize and
compute the leading quantum corrections to quadratic order in a curvature
expansion. The final effective action in our covariant formalism is generally
non-local and can be readily used to understand the phenomenology on different
spacetimes. In particular, we point out that on curved backgrounds the
observable leading quantum gravitational effects are less suppressed than on
Minkowski spacetime.
| [
{
"created": "Wed, 22 Jul 2015 20:00:34 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Nov 2016 11:13:31 GMT",
"version": "v2"
}
] | 2016-11-08 | [
[
"Codello",
"Alessandro",
""
],
[
"Jain",
"Rajeev Kumar",
""
]
] | We construct the covariant effective field theory of gravity as an expansion in inverse powers of the Planck mass, identifying the leading and next-to-leading quantum corrections. We determine the form of the effective action for the cases of pure gravity with cosmological constant as well as gravity coupled to matter. By means of heat kernel methods we renormalize and compute the leading quantum corrections to quadratic order in a curvature expansion. The final effective action in our covariant formalism is generally non-local and can be readily used to understand the phenomenology on different spacetimes. In particular, we point out that on curved backgrounds the observable leading quantum gravitational effects are less suppressed than on Minkowski spacetime. |
gr-qc/0511058 | Hector H. Hernandez | Martin Bojowald, Hector H. Hernandez, Hugo A Morales-Tecotl | Perturbative Degrees of Freedom in Loop Quantum Gravity: Anisotropies | 32 pages | Class.Quant.Grav.23:3491-3516,2006 | 10.1088/0264-9381/23/10/017 | AEI-2005-170, NI05064 | gr-qc hep-th | null | The relation between an isotropic and an anisotropic model in loop quantum
cosmology is discussed in detail, comparing the strict symmetry reduction with
a perturbative implementation of symmetry. While the latter cannot be done in a
canonical manner, it allows to consider the dynamics including the role of
small non-symmetric degrees of freedom for the symmetric evolution. This serves
as a model for the general situation of perturbative degrees of freedom in a
background independent quantization such as loop quantum gravity, and for the
more complicated addition of perturbative inhomogeneities. While being crucial
for cosmological phenomenology, it is shown that perturbative non-symmetric
degrees of freedom do not allow definitive conclusions for the singularity
issue and in such a situation could even lead to wrong claims.
| [
{
"created": "Fri, 11 Nov 2005 10:33:23 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Bojowald",
"Martin",
""
],
[
"Hernandez",
"Hector H.",
""
],
[
"Morales-Tecotl",
"Hugo A",
""
]
] | The relation between an isotropic and an anisotropic model in loop quantum cosmology is discussed in detail, comparing the strict symmetry reduction with a perturbative implementation of symmetry. While the latter cannot be done in a canonical manner, it allows to consider the dynamics including the role of small non-symmetric degrees of freedom for the symmetric evolution. This serves as a model for the general situation of perturbative degrees of freedom in a background independent quantization such as loop quantum gravity, and for the more complicated addition of perturbative inhomogeneities. While being crucial for cosmological phenomenology, it is shown that perturbative non-symmetric degrees of freedom do not allow definitive conclusions for the singularity issue and in such a situation could even lead to wrong claims. |
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