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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1511.08583
|
Kenji Tomita
|
Kenji Tomita
|
Fluctuations of the cosmic background radiation appearing in the
10-dimensional cosmological model
|
23 pages, 2 figures
|
Prog. Theor. Exp. Phys. 2015, 123E01 (2015)
|
10.1093/ptep/ptv172
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider a cosmological model starting from (1) the(1+3+6)-dimensional
space-times consisting of the outer space (the 3-dimensional expanding section)
and the inner space (the 6-dimensional section) and reaching (2) the Friedmann
model after the decoupling between the outer space and the inner space, and
derive fluctuations of the background radiation appearing in the above
10-dimensional space-times. For this purpose we first derive the
fluid-dynamical perturbations in the above 10-dimensional space-times,
corresponding to two kinds of curvature perturbations (in the scalar mode) in
the non-viscous case, and next study the quantum fluctuations in the scalar and
tensor modes, appearing at the stage when the perturbations are within the
horizon of the inflating outer space. Lastly we derive the wave-number
dependence of fluctuations (the power spectrum) in the two modes, which formed
at the above decoupling epoch and are observed in the Friedmann stage. It is
found that it can be consistent with the observed spectra of the cosmic
microwave background radiation.
|
[
{
"created": "Fri, 27 Nov 2015 08:32:58 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Dec 2015 04:57:59 GMT",
"version": "v2"
}
] |
2015-12-24
|
[
[
"Tomita",
"Kenji",
""
]
] |
We consider a cosmological model starting from (1) the(1+3+6)-dimensional space-times consisting of the outer space (the 3-dimensional expanding section) and the inner space (the 6-dimensional section) and reaching (2) the Friedmann model after the decoupling between the outer space and the inner space, and derive fluctuations of the background radiation appearing in the above 10-dimensional space-times. For this purpose we first derive the fluid-dynamical perturbations in the above 10-dimensional space-times, corresponding to two kinds of curvature perturbations (in the scalar mode) in the non-viscous case, and next study the quantum fluctuations in the scalar and tensor modes, appearing at the stage when the perturbations are within the horizon of the inflating outer space. Lastly we derive the wave-number dependence of fluctuations (the power spectrum) in the two modes, which formed at the above decoupling epoch and are observed in the Friedmann stage. It is found that it can be consistent with the observed spectra of the cosmic microwave background radiation.
|
gr-qc/0202104
|
David Coule
|
D.H.Coule
|
Entropic issues in contemporary cosmology
|
brief discussion on Poincare recurrence included
|
Int.J.Mod.Phys. D12 (2003) 963-976
|
10.1142/S0218271803003530
| null |
gr-qc hep-th
| null |
Penrose [1] has emphasized how the initial big bang singularity requires a
special low entropy state. We address how recent brane cosmological schemes
address this problem and whether they offer any apparent resolution. Pushing
the start time back to $t=-\infty$ or utilizing maximally symmetric AdS spaces
simply exacerbates or transfers the problem.
Because the entropy of de Sitter space is $S\leq 1/\Lambda$, using the
present acceleration of the universe as a low energy $(\Lambda\sim 10^{-120}$)
inflationary stage, as in cyclic ekpyrotic models, produces a gravitational
heat death after one cycle. Only higher energy driven inflation, together with
a suitable, quantum gravity holography style, restriction on {\em ab initio}
degrees of freedom, gives a suitable low entropy initial state. We question the
suggestion that a high energy inflationary stage could be naturally reentered
by Poincare recurrence within a finite causal region of an accelerating
universe.
We further give a heuristic argument that so-called eternal inflation is not
consistent with the 2nd law of thermodynamics within a causal patch.
|
[
{
"created": "Thu, 28 Feb 2002 19:11:16 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Jul 2002 10:00:41 GMT",
"version": "v2"
},
{
"created": "Mon, 5 Aug 2002 15:48:35 GMT",
"version": "v3"
},
{
"created": "Wed, 18 Sep 2002 16:53:00 GMT",
"version": "v4"
}
] |
2016-08-31
|
[
[
"Coule",
"D. H.",
""
]
] |
Penrose [1] has emphasized how the initial big bang singularity requires a special low entropy state. We address how recent brane cosmological schemes address this problem and whether they offer any apparent resolution. Pushing the start time back to $t=-\infty$ or utilizing maximally symmetric AdS spaces simply exacerbates or transfers the problem. Because the entropy of de Sitter space is $S\leq 1/\Lambda$, using the present acceleration of the universe as a low energy $(\Lambda\sim 10^{-120}$) inflationary stage, as in cyclic ekpyrotic models, produces a gravitational heat death after one cycle. Only higher energy driven inflation, together with a suitable, quantum gravity holography style, restriction on {\em ab initio} degrees of freedom, gives a suitable low entropy initial state. We question the suggestion that a high energy inflationary stage could be naturally reentered by Poincare recurrence within a finite causal region of an accelerating universe. We further give a heuristic argument that so-called eternal inflation is not consistent with the 2nd law of thermodynamics within a causal patch.
|
2009.09319
|
Ran Li
|
Ran Li, Jin Wang
|
Hawking Radiation and $P-v$ Criticality of Charged Dynamical (Vaidya)
Black Hole in Anti-de Sitter Space
| null |
Phys. Lett. B 813 (2021) 136035
|
10.1016/j.physletb.2020.136035
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study Hawking radiation and $P-v$ criticality of charged dynamical
(Vaidya) black hole in Anti-de Sitter (AdS) space. By investigating the near
horizon properties of scalar field, we derive Hawking temperature of dynamical
charged (Vaidya) AdS black hole. Based on this result, by regarding the
cosmological constant as the thermodynamic pressure, we investigate the analogy
between the charged dynamical (Vaidya) AdS black holes in the ensemble with the
fixed charge and van der Waals liquid-gas system in detail, including equation
of state, $P-v$ diagram, critical point, heat capacities and critical exponents
near the critical point. It is shown that the relationship among the critical
pressure, critical volume, and critical temperature gets modified while the
critical exponents are not affected by the dynamical nature of the black hole.
We also find that, when the rate of change of the black hole horizon exceeds
the critical value, the $P-v$ criticality of the charged dynamical (Vaidya) AdS
black hole will disappear.
|
[
{
"created": "Sat, 19 Sep 2020 23:16:37 GMT",
"version": "v1"
}
] |
2020-12-21
|
[
[
"Li",
"Ran",
""
],
[
"Wang",
"Jin",
""
]
] |
We study Hawking radiation and $P-v$ criticality of charged dynamical (Vaidya) black hole in Anti-de Sitter (AdS) space. By investigating the near horizon properties of scalar field, we derive Hawking temperature of dynamical charged (Vaidya) AdS black hole. Based on this result, by regarding the cosmological constant as the thermodynamic pressure, we investigate the analogy between the charged dynamical (Vaidya) AdS black holes in the ensemble with the fixed charge and van der Waals liquid-gas system in detail, including equation of state, $P-v$ diagram, critical point, heat capacities and critical exponents near the critical point. It is shown that the relationship among the critical pressure, critical volume, and critical temperature gets modified while the critical exponents are not affected by the dynamical nature of the black hole. We also find that, when the rate of change of the black hole horizon exceeds the critical value, the $P-v$ criticality of the charged dynamical (Vaidya) AdS black hole will disappear.
|
1501.02104
|
Michal Pirog
|
Piotr Jaranowski, Patryk Mach, Edward Malec and Michal Pirog
|
Virial tests for post-Newtonian stationary black-hole-disk systems
|
6 pages, a talk given at The Spanish Relativity Meeting (Encuentros
Realtivistas Espanoles - ERE), Valencia, 2014
| null |
10.1088/1742-6596/600/1/012011
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We investigated hydrodynamical post-Newtonian models of selfgravitating
stationary black-hole-disk systems. The post-Newtonian scheme presented here
and also in our recent paper is a continuation of previous, purely Newtonian
studies of selfgravitating hydrodynamical disks rotating according to the
Keplerian rotation law. The post-Newtonian relativistic corrections are
significant even at the 1PN level. The 1PN correction to the angular velocity
can be of the order of 10% of its Newtonian value. It can be expressed as a
combination of geometric and hydrodynamical terms. Moreover, in contrast to the
Newtonian Poincare-Wavre theorem, it depends both on the distance from the
rotation axis and the distance from the equatorial plane.
|
[
{
"created": "Fri, 9 Jan 2015 11:17:01 GMT",
"version": "v1"
}
] |
2015-05-20
|
[
[
"Jaranowski",
"Piotr",
""
],
[
"Mach",
"Patryk",
""
],
[
"Malec",
"Edward",
""
],
[
"Pirog",
"Michal",
""
]
] |
We investigated hydrodynamical post-Newtonian models of selfgravitating stationary black-hole-disk systems. The post-Newtonian scheme presented here and also in our recent paper is a continuation of previous, purely Newtonian studies of selfgravitating hydrodynamical disks rotating according to the Keplerian rotation law. The post-Newtonian relativistic corrections are significant even at the 1PN level. The 1PN correction to the angular velocity can be of the order of 10% of its Newtonian value. It can be expressed as a combination of geometric and hydrodynamical terms. Moreover, in contrast to the Newtonian Poincare-Wavre theorem, it depends both on the distance from the rotation axis and the distance from the equatorial plane.
|
1104.4758
|
Orlando Luongo
|
Orlando Luongo, Hernando Quevedo
|
Reconstructing the expansion history of the Universe with a one-fluid
approach
|
revtex4 style, 3 figures
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Assuming that the Universe is filled by one single fluid, we present in the
context of General Relativity a possible explanation for the acceleration of
the Universe. We use ordinary thermodynamics and the fact that small matter
perturbations barely propagate in our Universe, to derive a general solution
for a single fluid in which the speed of sound vanishes. We find a model that
contains $\Lambda$CDM as a special case, and is compatible with current
observational data.
|
[
{
"created": "Mon, 25 Apr 2011 17:59:32 GMT",
"version": "v1"
}
] |
2011-04-26
|
[
[
"Luongo",
"Orlando",
""
],
[
"Quevedo",
"Hernando",
""
]
] |
Assuming that the Universe is filled by one single fluid, we present in the context of General Relativity a possible explanation for the acceleration of the Universe. We use ordinary thermodynamics and the fact that small matter perturbations barely propagate in our Universe, to derive a general solution for a single fluid in which the speed of sound vanishes. We find a model that contains $\Lambda$CDM as a special case, and is compatible with current observational data.
|
1709.00914
|
Massimo Giovannini
|
Massimo Giovannini
|
Quantum coherence of cosmological perturbations
|
10 pages, minor corrected typos; to appear in Mod.Phys. Lett. A
|
Mod. Phys. Lett. A 32, 1750191 (2017)
|
10.1142/S0217732317501917
| null |
gr-qc astro-ph.CO hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The degrees of quantum coherence of cosmological perturbations of different
spins are computed in the large-scale limit and compared with the standard
results holding for a single mode of the electromagnetic field in an optical
cavity. The degree second-order coherence of curvature inhomogeneities (and,
more generally, of the scalar modes of the geometry) reproduces faithfully the
optical limit. For the vector and tensor fluctuations the numerical values of
the normalized degrees of second-order coherence in the zero-time delay limit
are always larger than unity (which is the Poisson benchmark value) but differ
from the corresponding expressions obtainable in the framework of the
single-mode approximation. General lessons are drawn on the quantum coherence
of large-scale cosmological fluctuations.
|
[
{
"created": "Mon, 4 Sep 2017 12:22:53 GMT",
"version": "v1"
},
{
"created": "Tue, 24 Oct 2017 18:58:53 GMT",
"version": "v2"
}
] |
2017-11-09
|
[
[
"Giovannini",
"Massimo",
""
]
] |
The degrees of quantum coherence of cosmological perturbations of different spins are computed in the large-scale limit and compared with the standard results holding for a single mode of the electromagnetic field in an optical cavity. The degree second-order coherence of curvature inhomogeneities (and, more generally, of the scalar modes of the geometry) reproduces faithfully the optical limit. For the vector and tensor fluctuations the numerical values of the normalized degrees of second-order coherence in the zero-time delay limit are always larger than unity (which is the Poisson benchmark value) but differ from the corresponding expressions obtainable in the framework of the single-mode approximation. General lessons are drawn on the quantum coherence of large-scale cosmological fluctuations.
|
gr-qc/0407088
|
Plamen Fiziev
|
P.P.Fiziev
|
On the Solutions of Einstein Equations with Massive Point Source
|
14 pages, latex file, no figures, new essential comments and
references added
| null | null |
SU-04/07-02
|
gr-qc
| null |
We show that Einstein equations are compatible with the presence of massive
point particles and find corresponding two parameter family of their solutions
which depends on the bare mechanical mass $M_0>0$ and the Keplerian mass
$M<M_0$ of the point source of gravity. The global analytical properties of
these solutions in the complex plane define a unique preferable radial variable
of the problem.
|
[
{
"created": "Fri, 23 Jul 2004 15:15:47 GMT",
"version": "v1"
},
{
"created": "Sat, 24 Jul 2004 11:53:14 GMT",
"version": "v2"
},
{
"created": "Thu, 30 Dec 2004 13:18:25 GMT",
"version": "v3"
}
] |
2007-05-23
|
[
[
"Fiziev",
"P. P.",
""
]
] |
We show that Einstein equations are compatible with the presence of massive point particles and find corresponding two parameter family of their solutions which depends on the bare mechanical mass $M_0>0$ and the Keplerian mass $M<M_0$ of the point source of gravity. The global analytical properties of these solutions in the complex plane define a unique preferable radial variable of the problem.
|
gr-qc/0005015
|
Alexander Feinstein
|
Alexander Feinstein
|
Exact Inflationary Solutions from a Superpotential
|
6 pages, no figures
| null | null |
EHU-FT/0006
|
gr-qc
| null |
We propose a novel, potentially useful generating technique for constructing
exact solutions of inflationary scalar field cosmologies with non-trivial
potentials. The generating scheme uses the so-called superpotential and is
inspired by recent studies of similar equations in supergravity. Some exact
solutions are derived, and the physical meaning of the superpotential in these
models is clarified.
|
[
{
"created": "Thu, 4 May 2000 08:15:51 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Feinstein",
"Alexander",
""
]
] |
We propose a novel, potentially useful generating technique for constructing exact solutions of inflationary scalar field cosmologies with non-trivial potentials. The generating scheme uses the so-called superpotential and is inspired by recent studies of similar equations in supergravity. Some exact solutions are derived, and the physical meaning of the superpotential in these models is clarified.
|
1810.01094
|
Paolo Pani
|
Paolo Pani and Leonardo Gualtieri and Tiziano Abdelsalhin and Xisco
Jim\'enez Forteza
|
Magnetic tidal Love numbers clarified
|
v2: 4 pages, one extra equation. Matches the PRD version
|
Phys. Rev. D 98, 124023 (2018)
|
10.1103/PhysRevD.98.124023
| null |
gr-qc astro-ph.HE
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this brief note, we clarify certain aspects related to the magnetic (i.e.,
odd parity or axial) tidal Love numbers of a star in general relativity.
Magnetic tidal deformations of a compact star had been computed in 2009
independently by Damour and Nagar and by Binnington and Poisson. More recently,
Landry and Poisson showed that the magnetic tidal Love numbers depend on the
assumptions made on the fluid, in particular they are different (and of
opposite sign) if the fluid is assumed to be in static equilibrium or if it is
irrotational. We show that the zero-frequency limit of the Regge-Wheeler
equation forces the fluid to be irrotational. For this reason, the results of
Damour and Nagar are equivalent to those of Landry and Poisson for an
irrotational fluid, and are expected to be the most appropriate to describe
realistic configurations.
|
[
{
"created": "Tue, 2 Oct 2018 07:09:36 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Dec 2018 22:45:05 GMT",
"version": "v2"
}
] |
2018-12-20
|
[
[
"Pani",
"Paolo",
""
],
[
"Gualtieri",
"Leonardo",
""
],
[
"Abdelsalhin",
"Tiziano",
""
],
[
"Forteza",
"Xisco Jiménez",
""
]
] |
In this brief note, we clarify certain aspects related to the magnetic (i.e., odd parity or axial) tidal Love numbers of a star in general relativity. Magnetic tidal deformations of a compact star had been computed in 2009 independently by Damour and Nagar and by Binnington and Poisson. More recently, Landry and Poisson showed that the magnetic tidal Love numbers depend on the assumptions made on the fluid, in particular they are different (and of opposite sign) if the fluid is assumed to be in static equilibrium or if it is irrotational. We show that the zero-frequency limit of the Regge-Wheeler equation forces the fluid to be irrotational. For this reason, the results of Damour and Nagar are equivalent to those of Landry and Poisson for an irrotational fluid, and are expected to be the most appropriate to describe realistic configurations.
|
0910.5377
|
Th. M. Nieuwenhuizen
|
Theo M. Nieuwenhuizen and Vaclav Spicka
|
Bose-Einstein condensed supermassive black holes: a case of renormalized
quantum field theory in curved space-time
|
18 pages Latex Physica E style
| null |
10.1016/j.physe.2009.10.040
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
This paper investigates the question whether a realistic black hole can be in
principal similar to a star, having a large but finite redshift at its horizon.
If matter spreads throughout the interior of a supermassive black hole with
mass $M\sim10^9M_\odot$, it has an average density comparable to air and it may
arise from a Bose-Einstein condensate of densely packed H-atoms. Within the
Relativistic Theory of Gravitation with a positive cosmological constant, a
bosonic quantum field describing H atoms is coupled to the curvature scalar
with dimensionless coupling $\xi$. In the Bose-Einstein condensed groundstate
an exact, self-consistent solution for the metric occurs for a certain large
value of $\xi$, quadratic in the black hole mass. It is put forward that $\xi$
is set by proper choice of the background metric as a first step of a
renormalization approach, while otherwise the non-linearities are small. The
black hole has a hair, the binding energy. Fluctuations about the ground state
are considered.
|
[
{
"created": "Wed, 28 Oct 2009 13:50:51 GMT",
"version": "v1"
}
] |
2015-05-14
|
[
[
"Nieuwenhuizen",
"Theo M.",
""
],
[
"Spicka",
"Vaclav",
""
]
] |
This paper investigates the question whether a realistic black hole can be in principal similar to a star, having a large but finite redshift at its horizon. If matter spreads throughout the interior of a supermassive black hole with mass $M\sim10^9M_\odot$, it has an average density comparable to air and it may arise from a Bose-Einstein condensate of densely packed H-atoms. Within the Relativistic Theory of Gravitation with a positive cosmological constant, a bosonic quantum field describing H atoms is coupled to the curvature scalar with dimensionless coupling $\xi$. In the Bose-Einstein condensed groundstate an exact, self-consistent solution for the metric occurs for a certain large value of $\xi$, quadratic in the black hole mass. It is put forward that $\xi$ is set by proper choice of the background metric as a first step of a renormalization approach, while otherwise the non-linearities are small. The black hole has a hair, the binding energy. Fluctuations about the ground state are considered.
|
1405.6697
|
Camilo Posada
|
Camilo Posada
|
Imbedding a Reissner-Nordstr\"om charged mass into cosmology
|
7 pages
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We present the extension of the method of imbedding a mass into cosmology
proposed by Gautreau, for the case of a Reissner-Nordstr\"om charged mass. We
work in curvature coordinates $(R,T)$ where the coordinate time $T$ is measured
by clocks at fixed points $R = $ const., and geodesic coordinates $(R,\tau)$
where $\tau$ is the time recorded by clocks moving along the radial geodesics.
The Einstein equations are solved for a energy-momentum tensor which is
composed of a cosmological fluid and an electrostatic field outside a radius
$R_{b}$. Inside $R_{b}$ we have a part of cosmological fluid plus a
Reissner-Nordstr\"om charged mass. We offer metrics for a Reissner-Nordstr\"om
charged mass imbedded into different cosmological scenarios with zero
curvature. An important consequence of our results, is that orbits will spiral
when a charged mass is imbedded into a cosmological background. We found the
generalized equation for the change of orbital radius, by using geodesic
coordinates. Some criticism to the Newtonian calculation done by Gautreau for
the orbital spiralling is discussed.
|
[
{
"created": "Mon, 26 May 2014 19:50:42 GMT",
"version": "v1"
}
] |
2014-05-27
|
[
[
"Posada",
"Camilo",
""
]
] |
We present the extension of the method of imbedding a mass into cosmology proposed by Gautreau, for the case of a Reissner-Nordstr\"om charged mass. We work in curvature coordinates $(R,T)$ where the coordinate time $T$ is measured by clocks at fixed points $R = $ const., and geodesic coordinates $(R,\tau)$ where $\tau$ is the time recorded by clocks moving along the radial geodesics. The Einstein equations are solved for a energy-momentum tensor which is composed of a cosmological fluid and an electrostatic field outside a radius $R_{b}$. Inside $R_{b}$ we have a part of cosmological fluid plus a Reissner-Nordstr\"om charged mass. We offer metrics for a Reissner-Nordstr\"om charged mass imbedded into different cosmological scenarios with zero curvature. An important consequence of our results, is that orbits will spiral when a charged mass is imbedded into a cosmological background. We found the generalized equation for the change of orbital radius, by using geodesic coordinates. Some criticism to the Newtonian calculation done by Gautreau for the orbital spiralling is discussed.
|
2408.05581
|
Peter K.F. Kuhfittig
|
Peter K.F. Kuhfittig
|
Thin-shell wormholes admitting conformal motions in spacetimes of
embedding class one
|
10 pages, no figures
|
Int. J. Astron. Astrophys. (IJAA) vol. 14, pp. 162-171, 2024
| null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
This paper discusses the feasibility of thin-shell wormholes in spacetimes of
embedding class one admitting a one-parameter group of conformal motions. It is
shown that the surface energy density $\sigma$ is positive, while the surface
pressure $\mathcal{P}$ is negative, resulting in $\sigma +\mathcal{P}<0$,
thereby signaling a violation of the null energy condition, a necessary
condition for holding a wormhole open. For a Morris-Thorne wormhole, matter
that violates the null energy condition is referred to as "exotic." For the
thin-shell wormholes in this paper, however, the violation has a physical
explanation since it is a direct consequence of the embedding theory in
conjunction with the assumption of conformal symmetry. These properties avoid
the need to hypothesize the existence of the highly problematical exotic
matter.
|
[
{
"created": "Sat, 10 Aug 2024 15:16:25 GMT",
"version": "v1"
}
] |
2024-08-13
|
[
[
"Kuhfittig",
"Peter K. F.",
""
]
] |
This paper discusses the feasibility of thin-shell wormholes in spacetimes of embedding class one admitting a one-parameter group of conformal motions. It is shown that the surface energy density $\sigma$ is positive, while the surface pressure $\mathcal{P}$ is negative, resulting in $\sigma +\mathcal{P}<0$, thereby signaling a violation of the null energy condition, a necessary condition for holding a wormhole open. For a Morris-Thorne wormhole, matter that violates the null energy condition is referred to as "exotic." For the thin-shell wormholes in this paper, however, the violation has a physical explanation since it is a direct consequence of the embedding theory in conjunction with the assumption of conformal symmetry. These properties avoid the need to hypothesize the existence of the highly problematical exotic matter.
|
1908.01195
|
Sanjar Shaymatov
|
Sanjar Shaymatov, Naresh Dadhich, Bobomurat Ahmedov, Mubasher Jamil
|
Five dimensional charged rotating minimally gauged supergravity black
hole cannot be over-spun and/or over-charged in non-linear accretion
|
12 pages, 2 figures; accepted for publication in Eur. Phys. J. C.
Figures and further references have been added
|
Eur. Phys. J. C (2020) 80:481
|
10.1140/epjc/s10052-020-8009-4
| null |
gr-qc astro-ph.HE hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Generally black hole could be over charged/spun violating the weak cosmic
censorship conjecture (WCCC) for linear order accretion while the same is
always restored back for non-linear accretion. The only exception however is
that of a five dimensional rotating black hole with single rotation that cannot
be overspun even at linear order. In this paper we investigate this question
for a five dimensional charged rotating minimally gauged supergravity black
hole and show that it could not be overspun under non-linear accretion and
thereby respecting WCCC. However in the case of single rotation WCCC is however
also respected for linear accretion when angular momentum of accreting particle
is greater than its charge irrespective of relative dominance of charge and
rotation parameters of black hole.
|
[
{
"created": "Sat, 3 Aug 2019 16:14:15 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Mar 2020 13:10:39 GMT",
"version": "v2"
},
{
"created": "Mon, 25 May 2020 23:38:15 GMT",
"version": "v3"
}
] |
2020-05-29
|
[
[
"Shaymatov",
"Sanjar",
""
],
[
"Dadhich",
"Naresh",
""
],
[
"Ahmedov",
"Bobomurat",
""
],
[
"Jamil",
"Mubasher",
""
]
] |
Generally black hole could be over charged/spun violating the weak cosmic censorship conjecture (WCCC) for linear order accretion while the same is always restored back for non-linear accretion. The only exception however is that of a five dimensional rotating black hole with single rotation that cannot be overspun even at linear order. In this paper we investigate this question for a five dimensional charged rotating minimally gauged supergravity black hole and show that it could not be overspun under non-linear accretion and thereby respecting WCCC. However in the case of single rotation WCCC is however also respected for linear accretion when angular momentum of accreting particle is greater than its charge irrespective of relative dominance of charge and rotation parameters of black hole.
|
0811.0756
|
Lorenzo Iorio
|
Lorenzo Iorio
|
On the recently determined anomalous perihelion precession of Saturn
|
LaTex2e, 14 pages, no figures, 2 tables. Accepted by The Astronomical
Journal (AJ)
|
The Astronomical Journal 137 (2009) 3615-3618
|
10.1088/0004-6256/137/3/3615
| null |
gr-qc astro-ph hep-ph physics.space-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The astronomer E.V. Pitjeva, by analyzing with the EPM2008 ephemerides a
large number of planetary observations including also two years (2004-2006) of
normal points from the Cassini spacecraft, phenomenologically estimated a
statistically significant non-zero correction to the usual
Newtonian/Einsteinian secular precession of the longitude of the perihelion of
Saturn, i.e. \Delta\dot\varpi_Sat = -0.006 +/- 0.002 arcsec/cy; the formal,
statistical error is 0.0007 arcsec/cy. It can be explained neither by any of
the standard classical and general relativistic dynamical effects
mismodelled/unmodelled in the force models of the EPM2008 ephemerides nor by
several exotic modifications of gravity recently put forth to accommodate
certain cosmological/astrophysical observations without resorting to dark
energy/dark matter. Both independent analyses by other teams of astronomers and
further processing of larger data sets from Cassini will be helpful in
clarifying the nature and the true existence of the anomalous precession of the
perihelion of Saturn.
|
[
{
"created": "Wed, 5 Nov 2008 15:54:42 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Nov 2008 15:06:57 GMT",
"version": "v2"
},
{
"created": "Sun, 9 Nov 2008 13:52:08 GMT",
"version": "v3"
},
{
"created": "Wed, 24 Dec 2008 20:36:53 GMT",
"version": "v4"
}
] |
2009-02-24
|
[
[
"Iorio",
"Lorenzo",
""
]
] |
The astronomer E.V. Pitjeva, by analyzing with the EPM2008 ephemerides a large number of planetary observations including also two years (2004-2006) of normal points from the Cassini spacecraft, phenomenologically estimated a statistically significant non-zero correction to the usual Newtonian/Einsteinian secular precession of the longitude of the perihelion of Saturn, i.e. \Delta\dot\varpi_Sat = -0.006 +/- 0.002 arcsec/cy; the formal, statistical error is 0.0007 arcsec/cy. It can be explained neither by any of the standard classical and general relativistic dynamical effects mismodelled/unmodelled in the force models of the EPM2008 ephemerides nor by several exotic modifications of gravity recently put forth to accommodate certain cosmological/astrophysical observations without resorting to dark energy/dark matter. Both independent analyses by other teams of astronomers and further processing of larger data sets from Cassini will be helpful in clarifying the nature and the true existence of the anomalous precession of the perihelion of Saturn.
|
1607.06222
|
Bethan Cropp
|
Bethan Cropp, Swastik Bhattacharya, S. Shankaranarayanan
|
Hints of quantum gravity from the horizon fluid
|
v2: This version accepted to PRD, 10 pages
|
Phys. Rev. D 95, 024006 (2017)
|
10.1103/PhysRevD.95.024006
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
For many years researchers have tried to glean hints about quantum gravity
from black hole thermodynamics. However, black hole thermodynamics suffers from
the problem of Universality --- at leading order, several approaches with
different microscopic degrees of freedom lead to Bekenstein-Hawking entropy. We
attempt to bypass this issue by using a minimal statistical mechanical model
for the horizon fluid based on Damour-Navier-Stokes (DNS) equation. For
stationary asymptotically flat black hole spacetimes in General Relativity, we
show explicitly that at equilibrium the entropy of the horizon fluid is the
Bekenstein-Hawking entropy. Further we show that, for the bulk viscosity of the
fluctuations of the horizon fluid to be identical to Damour, a confinement
scale exists for these fluctuations, implying quantization of the horizon area.
The implications and possible mechanisms from the fluid point of view are
discussed.
|
[
{
"created": "Thu, 21 Jul 2016 07:56:00 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Dec 2016 06:43:07 GMT",
"version": "v2"
}
] |
2017-01-11
|
[
[
"Cropp",
"Bethan",
""
],
[
"Bhattacharya",
"Swastik",
""
],
[
"Shankaranarayanan",
"S.",
""
]
] |
For many years researchers have tried to glean hints about quantum gravity from black hole thermodynamics. However, black hole thermodynamics suffers from the problem of Universality --- at leading order, several approaches with different microscopic degrees of freedom lead to Bekenstein-Hawking entropy. We attempt to bypass this issue by using a minimal statistical mechanical model for the horizon fluid based on Damour-Navier-Stokes (DNS) equation. For stationary asymptotically flat black hole spacetimes in General Relativity, we show explicitly that at equilibrium the entropy of the horizon fluid is the Bekenstein-Hawking entropy. Further we show that, for the bulk viscosity of the fluctuations of the horizon fluid to be identical to Damour, a confinement scale exists for these fluctuations, implying quantization of the horizon area. The implications and possible mechanisms from the fluid point of view are discussed.
|
2003.10125
|
Masataka Tsuchiya
|
Masataka Tsuchiya, Chul-Moon Yoo, Yasutaka Koga, Tomohiro Harada
|
Sonic Point and Photon Surface
|
34 pages
|
Phys. Rev. D 102, 044057 (2020)
|
10.1103/PhysRevD.102.044057
|
RUP-20-8
|
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The sonic point/photon surface correspondence is thoroughly investigated in a
general setting. First, we investigate a sonic point of a transonic steady
perfect fluid flow in a general stationary spacetime, particularly focusing on
the radiation fluid. The necessary conditions that the flow must satisfy at a
sonic point are derived as conditions for the kinematical quantities of the
congruence of streamlines in analogy with the de Laval nozzle equation in fluid
mechanics. We compare the conditions for a sonic point with the notion of a
photon surface, which can be defined as a timelike totally umbilical
hypersurface. As a result, we find that, for the realization of the sonic
point/photon surface correspondence, the speed of sound $v_{\rm s}$ must be
given by $1/\sqrt{d}$ with $d$ being the spatial dimension of the spacetime.
For the radiation fluid ($v_{\rm s}=1/\sqrt{d}$), we confirm that a part of the
conditions is shared by the sonic point and the photon surface. However, in
general, a Bondi surface, a set of sonic points, does not necessarily coincide
with a photon surface. Additional assumptions, such as a spatial symmetry, are
essential to the realization of the sonic point/photon surface correspondence
in all known examples.
|
[
{
"created": "Mon, 23 Mar 2020 08:23:33 GMT",
"version": "v1"
}
] |
2020-09-09
|
[
[
"Tsuchiya",
"Masataka",
""
],
[
"Yoo",
"Chul-Moon",
""
],
[
"Koga",
"Yasutaka",
""
],
[
"Harada",
"Tomohiro",
""
]
] |
The sonic point/photon surface correspondence is thoroughly investigated in a general setting. First, we investigate a sonic point of a transonic steady perfect fluid flow in a general stationary spacetime, particularly focusing on the radiation fluid. The necessary conditions that the flow must satisfy at a sonic point are derived as conditions for the kinematical quantities of the congruence of streamlines in analogy with the de Laval nozzle equation in fluid mechanics. We compare the conditions for a sonic point with the notion of a photon surface, which can be defined as a timelike totally umbilical hypersurface. As a result, we find that, for the realization of the sonic point/photon surface correspondence, the speed of sound $v_{\rm s}$ must be given by $1/\sqrt{d}$ with $d$ being the spatial dimension of the spacetime. For the radiation fluid ($v_{\rm s}=1/\sqrt{d}$), we confirm that a part of the conditions is shared by the sonic point and the photon surface. However, in general, a Bondi surface, a set of sonic points, does not necessarily coincide with a photon surface. Additional assumptions, such as a spatial symmetry, are essential to the realization of the sonic point/photon surface correspondence in all known examples.
|
1304.4313
|
Florian Beyer
|
Florian Beyer, Leon Escobar
|
Graceful exit from inflation for minimally coupled Bianchi A scalar
field models
|
37 pages, 26 figures; matches the version published in CQG
|
Class. Quantum Grav. 30 (2013) 195020
|
10.1088/0264-9381/30/19/195020
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider the dynamics of Bianchi A scalar field models which undergo
inflation. The main question is under which conditions does inflation come to
an end and is succeeded by a decelerated epoch. This so-called "graceful exit"
from inflation is an important ingredient in the standard model of cosmology,
but is, at this stage, only understood for restricted classes of solutions. We
present new results obtained by a combination of analytical and numerical
techniques.
|
[
{
"created": "Tue, 16 Apr 2013 02:31:54 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Sep 2013 01:07:02 GMT",
"version": "v2"
}
] |
2013-09-20
|
[
[
"Beyer",
"Florian",
""
],
[
"Escobar",
"Leon",
""
]
] |
We consider the dynamics of Bianchi A scalar field models which undergo inflation. The main question is under which conditions does inflation come to an end and is succeeded by a decelerated epoch. This so-called "graceful exit" from inflation is an important ingredient in the standard model of cosmology, but is, at this stage, only understood for restricted classes of solutions. We present new results obtained by a combination of analytical and numerical techniques.
|
gr-qc/9909056
|
Ioannis Raptis
|
Ioannis Raptis
|
A Non-Classical Linear Xenomorph as a Model for Quantum Causal Space
|
LaTeX 2.09, 20 pages
| null | null | null |
gr-qc
| null |
A quantum picture of the causal structure of Minkowski space M is presented.
The mathematical model employed to this end is a non-classical version of the
classical topos {H} of real quaternion algebras used elsewhere to organize the
perceptions of spacetime events of a Boolean observer into M. Certain key
properties of this new quantum topos are highlighted by contrast against the
corresponding ones of its classical counterpart {H} modelling M and are seen to
accord with some key features of the algebraically quantized causal set
structure.
|
[
{
"created": "Mon, 20 Sep 1999 14:36:02 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Raptis",
"Ioannis",
""
]
] |
A quantum picture of the causal structure of Minkowski space M is presented. The mathematical model employed to this end is a non-classical version of the classical topos {H} of real quaternion algebras used elsewhere to organize the perceptions of spacetime events of a Boolean observer into M. Certain key properties of this new quantum topos are highlighted by contrast against the corresponding ones of its classical counterpart {H} modelling M and are seen to accord with some key features of the algebraically quantized causal set structure.
|
1906.09648
|
Konstantinos Dimopoulos
|
Konstantinos Dimopoulos and Leonora Donaldson-Wood
|
Warm Quintessential Inflation
|
14 pages, 2 figures, published version
| null |
10.1016/j.physletb.2019.07.017
| null |
gr-qc astro-ph.CO hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We introduce warm quintessential inflation and study it in the weak
dissipative regime. We consider the original quintessential inflation model,
which approximates quartic chaotic inflation at early times and thawing quartic
inverse-power-law quintessence at present. We find that the model successfully
accounts for both inflation and dark energy observations, while it naturally
reheats the Universe, thereby overcoming a major problem of quintessential
inflation model-building.
|
[
{
"created": "Sun, 23 Jun 2019 20:50:29 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Jul 2019 21:21:14 GMT",
"version": "v2"
},
{
"created": "Tue, 9 Jul 2019 16:06:37 GMT",
"version": "v3"
}
] |
2019-07-17
|
[
[
"Dimopoulos",
"Konstantinos",
""
],
[
"Donaldson-Wood",
"Leonora",
""
]
] |
We introduce warm quintessential inflation and study it in the weak dissipative regime. We consider the original quintessential inflation model, which approximates quartic chaotic inflation at early times and thawing quartic inverse-power-law quintessence at present. We find that the model successfully accounts for both inflation and dark energy observations, while it naturally reheats the Universe, thereby overcoming a major problem of quintessential inflation model-building.
|
2212.09495
|
Aaron Held
|
Astrid Eichhorn and Aaron Held
|
Black holes in asymptotically safe gravity and beyond
|
invited chapter for the book ''Regular Black Holes: Towards a New
Paradigm of the Gravitational Collapse''; comments welcome
| null | null | null |
gr-qc astro-ph.HE
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Asymptotically safe quantum gravity is an approach to quantum gravity that
achieves formulates a standard quantum field theory for the metric. Therefore,
even the deep quantum gravity regime, that is expected to determine the true
structure of the core of black holes, is described by a spacetime metric. The
essence of asymptotic safety lies in a new symmetry of the theory -- quantum
scale symmetry -- which characterizes the short-distance regime of quantum
gravity. It implies the absence of physical scales. Therefore, the Newton
coupling, which corresponds to a scale, namely the Planck length, must vanish
asymptotically in the short-distance regime. This implies a weakening of the
gravitational interaction, from which a resolution of classical spacetime
singularities can be expected. In practise, properties of black holes in
asymptotically safe quantum gravity cannot yet be derived from first
principles, but are constructed using a heuristic procedure known as
Renormalization Group improvement. The resulting asymptotic-safety inspired
black holes have been constructed both for vanishing and for nonvanishing spin
parameter. They are characterized by (i) the absence of curvature
singularities, (ii) a more compact event horizon and photon sphere, (iii) a
second (inner) horizon even at vanishing spin and (iv) a cold remnant as a
possible final product of the Hawking evaporation. Observations can start to
constrain the quantum-gravity scale that can be treated as a free parameter in
asymptotic-safety inspired black holes. For slowly-spinning black holes,
constraints from the EHT and X-ray observations can only constrain
quantum-gravity scales far above the Planck length. In the limit of
near-critical spin, asymptotic-safety inspired black holes may ``light up" in a
way the ngEHT may be sensitive to, even for a quantum-gravity scale equalling
the Planck length.
|
[
{
"created": "Mon, 19 Dec 2022 14:29:38 GMT",
"version": "v1"
}
] |
2022-12-20
|
[
[
"Eichhorn",
"Astrid",
""
],
[
"Held",
"Aaron",
""
]
] |
Asymptotically safe quantum gravity is an approach to quantum gravity that achieves formulates a standard quantum field theory for the metric. Therefore, even the deep quantum gravity regime, that is expected to determine the true structure of the core of black holes, is described by a spacetime metric. The essence of asymptotic safety lies in a new symmetry of the theory -- quantum scale symmetry -- which characterizes the short-distance regime of quantum gravity. It implies the absence of physical scales. Therefore, the Newton coupling, which corresponds to a scale, namely the Planck length, must vanish asymptotically in the short-distance regime. This implies a weakening of the gravitational interaction, from which a resolution of classical spacetime singularities can be expected. In practise, properties of black holes in asymptotically safe quantum gravity cannot yet be derived from first principles, but are constructed using a heuristic procedure known as Renormalization Group improvement. The resulting asymptotic-safety inspired black holes have been constructed both for vanishing and for nonvanishing spin parameter. They are characterized by (i) the absence of curvature singularities, (ii) a more compact event horizon and photon sphere, (iii) a second (inner) horizon even at vanishing spin and (iv) a cold remnant as a possible final product of the Hawking evaporation. Observations can start to constrain the quantum-gravity scale that can be treated as a free parameter in asymptotic-safety inspired black holes. For slowly-spinning black holes, constraints from the EHT and X-ray observations can only constrain quantum-gravity scales far above the Planck length. In the limit of near-critical spin, asymptotic-safety inspired black holes may ``light up" in a way the ngEHT may be sensitive to, even for a quantum-gravity scale equalling the Planck length.
|
2105.12423
|
Sauvik Sen
|
Sauvik Sen
|
Hawking radiation for a (2+1)-dimensional spinning black hole and the
issue of tunneling
|
Errors noticed in the governing equations
| null | null | null |
gr-qc hep-th math-ph math.MP quant-ph
|
http://creativecommons.org/publicdomain/zero/1.0/
|
We examine Hawking radiation for a (2+1)-dimensional spinning black hole and
study the interesting possibility of tunneling through the event horizon which
acts as a classically forbidden barrier. Our finding shows it to be much lower
than its nonrotating counterpart. We further explore the associated
thermodynamics in terms of Hawking temperature and give estimates of black hole
parameters like the surface gravity and entropy.
|
[
{
"created": "Wed, 26 May 2021 09:24:51 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Jun 2021 09:56:21 GMT",
"version": "v2"
},
{
"created": "Thu, 18 Nov 2021 02:53:59 GMT",
"version": "v3"
}
] |
2021-11-19
|
[
[
"Sen",
"Sauvik",
""
]
] |
We examine Hawking radiation for a (2+1)-dimensional spinning black hole and study the interesting possibility of tunneling through the event horizon which acts as a classically forbidden barrier. Our finding shows it to be much lower than its nonrotating counterpart. We further explore the associated thermodynamics in terms of Hawking temperature and give estimates of black hole parameters like the surface gravity and entropy.
|
2401.08346
|
Tony Rothman
|
Peter Anninos, Tony Rothman and Andrea Palessandro
|
Graviton-Photon Oscillations in an Expanding Universe
|
27 pages, no figures
|
Physics of the Dark Universe Volume 44, May 2024, 101480
|
10.1016/j.dark.2024.101480
| null |
gr-qc astro-ph.CO
|
http://creativecommons.org/licenses/by/4.0/
|
Through the Gertsenshtein effect, the presence of a large external B-field
may allow photons and gravitons to mix in a way that resembles neutrino
oscillations and is even more similar to axion-photon mixing. Assuming a
background B-field (or any field that behaves like one), we examine the
Gertsenshtein mechanism in the context of FLRW expanding universe models, as
well as de Sitter space. The conformal invariance of Maxwell's equations and
the conformal noninvariance of the Einstein equations preclude the operation of
the Gertsenshtein effect at all scales. In general we find for the matter- and
radiation-dominated cases, graviton-oscillations are possible only at late
conformal times or when the wavelengths are much shorter than the horizon
($k\eta \gg 1$), but that the time-dependent oscillations eventually damp out
in any case. The presence of charged particles additionally damps out the
oscillations. For the de Sitter universe, we find that oscillations are
possible only at early conformal times ($\eta \ll H^{-1}$) and for wavelengths
short compared to the Hubble radius, but eventually freeze in when wavelengths
become longer than the Hubble radius. In principle a Gertsenshtein-like
mechanism might influence the balance of particle species in an inflationary
phase before freezing in; however, we find that in all our models the mixing
length is larger than the Hubble radius. We discuss several possible remedies
to this situation.
|
[
{
"created": "Tue, 16 Jan 2024 13:27:25 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Apr 2024 21:49:28 GMT",
"version": "v2"
}
] |
2024-04-03
|
[
[
"Anninos",
"Peter",
""
],
[
"Rothman",
"Tony",
""
],
[
"Palessandro",
"Andrea",
""
]
] |
Through the Gertsenshtein effect, the presence of a large external B-field may allow photons and gravitons to mix in a way that resembles neutrino oscillations and is even more similar to axion-photon mixing. Assuming a background B-field (or any field that behaves like one), we examine the Gertsenshtein mechanism in the context of FLRW expanding universe models, as well as de Sitter space. The conformal invariance of Maxwell's equations and the conformal noninvariance of the Einstein equations preclude the operation of the Gertsenshtein effect at all scales. In general we find for the matter- and radiation-dominated cases, graviton-oscillations are possible only at late conformal times or when the wavelengths are much shorter than the horizon ($k\eta \gg 1$), but that the time-dependent oscillations eventually damp out in any case. The presence of charged particles additionally damps out the oscillations. For the de Sitter universe, we find that oscillations are possible only at early conformal times ($\eta \ll H^{-1}$) and for wavelengths short compared to the Hubble radius, but eventually freeze in when wavelengths become longer than the Hubble radius. In principle a Gertsenshtein-like mechanism might influence the balance of particle species in an inflationary phase before freezing in; however, we find that in all our models the mixing length is larger than the Hubble radius. We discuss several possible remedies to this situation.
|
1012.5375
|
Kiyoshi Shiraishi
|
Nahomi Kan (Yamaguchi Junior College), Takuya Maki (Japan Women's
College of Physical Education) and Kiyoshi Shiraishi (Yamaguchi University)
|
Weyl invariant Dirac-Born-Infeld-Einstein theory
|
4 pages. To appear in the Proceedings of 20th Workshop in General
Relativity and Gravitation in Japan (JGRG20), held in Yukawa Institute for
Theoretical Physics, Kyoto University, Kyoto, Japan (21 - 25 September 2010)
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider a Weyl invariant extension of Dirac-Born-Infeld type gravity. An
appropriate choice of the metric hides the scalar degree of freedom which is
required by the local scale invariance of the action at the first sight, and
then a vector field acquires mass. Moreover, nonminimal couplings of the vector
field and curvatures are induced, which may be suitable to the vector inflation
scenario.
|
[
{
"created": "Fri, 24 Dec 2010 09:45:19 GMT",
"version": "v1"
}
] |
2010-12-27
|
[
[
"Kan",
"Nahomi",
"",
"Yamaguchi Junior College"
],
[
"Maki",
"Takuya",
"",
"Japan Women's\n College of Physical Education"
],
[
"Shiraishi",
"Kiyoshi",
"",
"Yamaguchi University"
]
] |
We consider a Weyl invariant extension of Dirac-Born-Infeld type gravity. An appropriate choice of the metric hides the scalar degree of freedom which is required by the local scale invariance of the action at the first sight, and then a vector field acquires mass. Moreover, nonminimal couplings of the vector field and curvatures are induced, which may be suitable to the vector inflation scenario.
|
2201.06722
|
Glauber Carvalho Dorsch
|
Glauber C. Dorsch and Lucas E. A. Porto
|
An introduction to gravitational waves through electrodynamics: a
quadrupole comparison
|
26 pages, 4 figures
| null |
10.1088/1361-6404/ac4645
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We present a pedagogical introduction to some key computations in
gravitational waves via a side-by-side comparison with the quadrupole
contribution of electromagnetic radiation. Subtleties involving gauge choices
and projections over transverse modes in the tensorial theory are made clearer
by direct analogy with the vectorial counterpart. The power emitted by the
quadrupole moment in both theories is computed, and the similarities as well as
the origins of eventual discrepancies are discussed. Finally, we analyze the
stability of bound systems under radiation emission, and discuss how the
strength of the interactions can be established this way. We use the results to
impose an anthropic bound on Newton's constant of order $G\lesssim 3\times
10^4\, G_\text{obs}$, which is on par with similar constraints from stellar
formation.
|
[
{
"created": "Tue, 18 Jan 2022 03:52:34 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Jan 2022 17:45:05 GMT",
"version": "v2"
}
] |
2022-01-31
|
[
[
"Dorsch",
"Glauber C.",
""
],
[
"Porto",
"Lucas E. A.",
""
]
] |
We present a pedagogical introduction to some key computations in gravitational waves via a side-by-side comparison with the quadrupole contribution of electromagnetic radiation. Subtleties involving gauge choices and projections over transverse modes in the tensorial theory are made clearer by direct analogy with the vectorial counterpart. The power emitted by the quadrupole moment in both theories is computed, and the similarities as well as the origins of eventual discrepancies are discussed. Finally, we analyze the stability of bound systems under radiation emission, and discuss how the strength of the interactions can be established this way. We use the results to impose an anthropic bound on Newton's constant of order $G\lesssim 3\times 10^4\, G_\text{obs}$, which is on par with similar constraints from stellar formation.
|
2209.04669
|
Vasilis Oikonomou
|
V.K. Oikonomou, Pyotr Tsyba, Olga Razina
|
Probing our Universe's Past Using Earth's Geological and Climatological
History and Shadows of Galactic Black Holes
|
Invited article accepted in the journal Universe, special issue
''Modified Gravity Approaches to the Tensions of LCDM''
| null | null | null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this short review, we discuss how Earth's climatological and geological
history and also how the shadows of galactic black holes might reveal our
Universe's past evolution. Specifically we point out that a pressure
singularity that occurred in our Universe's past might have left its imprint on
Earth's geological and climatological history and on the shadows of
cosmological black holes. Our approach is based on the fact that the $H_0$
tension problem may be resolved if some sort of abrupt physics change occurred
in our Universe $70-150\,$Myrs ago, an abrupt change that deeply affected the
Cepheid parameters. We review how such an abrupt physics change might have been
caused in our Universe by a smooth passage of it through a pressure finite-time
singularity. Such finite-time singularities might occur in modified gravity and
specifically in $F(R)$ gravity, so we show how modified gravity might drive
this type of evolution, without resorting to peculiar cosmic fluids or scalar
fields. The presence of such a pressure singularity can distort the elliptic
trajectories of bound objects in the Universe, causing possible geological and
climatological changes on Earth, if its elliptic trajectory around the Sun
might have changed. Also, such a pressure singularity affects directly the
circular photon orbits around supermassive galactic black holes existing at
cosmological redshift distances, thus the shadows of some cosmological black
holes at redshifts $z\leq 0.01$, might look different in shape, compared with
the SgrA* and M87* supermassive black holes. This feature however can be
checked experimentally in the very far future.
|
[
{
"created": "Sat, 10 Sep 2022 14:05:29 GMT",
"version": "v1"
}
] |
2022-09-13
|
[
[
"Oikonomou",
"V. K.",
""
],
[
"Tsyba",
"Pyotr",
""
],
[
"Razina",
"Olga",
""
]
] |
In this short review, we discuss how Earth's climatological and geological history and also how the shadows of galactic black holes might reveal our Universe's past evolution. Specifically we point out that a pressure singularity that occurred in our Universe's past might have left its imprint on Earth's geological and climatological history and on the shadows of cosmological black holes. Our approach is based on the fact that the $H_0$ tension problem may be resolved if some sort of abrupt physics change occurred in our Universe $70-150\,$Myrs ago, an abrupt change that deeply affected the Cepheid parameters. We review how such an abrupt physics change might have been caused in our Universe by a smooth passage of it through a pressure finite-time singularity. Such finite-time singularities might occur in modified gravity and specifically in $F(R)$ gravity, so we show how modified gravity might drive this type of evolution, without resorting to peculiar cosmic fluids or scalar fields. The presence of such a pressure singularity can distort the elliptic trajectories of bound objects in the Universe, causing possible geological and climatological changes on Earth, if its elliptic trajectory around the Sun might have changed. Also, such a pressure singularity affects directly the circular photon orbits around supermassive galactic black holes existing at cosmological redshift distances, thus the shadows of some cosmological black holes at redshifts $z\leq 0.01$, might look different in shape, compared with the SgrA* and M87* supermassive black holes. This feature however can be checked experimentally in the very far future.
|
0810.2530
|
Leor Barack
|
Norichika Sago, Leor Barack and Steven Detweiler
|
Two approaches for the gravitational self force in black hole spacetime:
Comparison of numerical results
|
11 pages; minor typos corrected; final version to be published in PRD
|
Phys.Rev.D78:124024,2008
|
10.1103/PhysRevD.78.124024
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Recently, two independent calculations have been presented of finite-mass
("self-force") effects on the orbit of a point mass around a Schwarzschild
black hole. While both computations are based on the standard mode-sum method,
they differ in several technical aspects, which makes comparison between their
results difficult--but also interesting. Barack and Sago [Phys. Rev. D {\bf
75}, 064021 (2007)] invoke the notion of a self-accelerated motion in a
background spacetime, and perform a direct calculation of the local self force
in the Lorenz gauge (using numerical evolution of the perturbation equations in
the time domain); Detweiler [Phys. Rev. D {\bf 77}, 124026 (2008)] describes
the motion in terms a geodesic orbit of a (smooth) perturbed spacetime, and
calculates the metric perturbation in the Regge--Wheeler gauge (using
frequency-domain numerical analysis). Here we establish a formal correspondence
between the two analyses, and demonstrate the consistency of their numerical
results. Specifically, we compare the value of the conservative $O(\mu)$ shift
in $u^t$ (where $\mu$ is the particle's mass and $u^t$ is the Schwarzschild $t$
component of the particle's four-velocity), suitably mapped between the two
orbital descriptions and adjusted for gauge. We find that the two analyses
yield the same value for this shift within mere fractional differences of $\sim
10^{-5}$--$10^{-7}$ (depending on the orbital radius)--comparable with the
estimated numerical error.
|
[
{
"created": "Tue, 14 Oct 2008 19:44:00 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Dec 2008 16:42:22 GMT",
"version": "v2"
}
] |
2010-05-12
|
[
[
"Sago",
"Norichika",
""
],
[
"Barack",
"Leor",
""
],
[
"Detweiler",
"Steven",
""
]
] |
Recently, two independent calculations have been presented of finite-mass ("self-force") effects on the orbit of a point mass around a Schwarzschild black hole. While both computations are based on the standard mode-sum method, they differ in several technical aspects, which makes comparison between their results difficult--but also interesting. Barack and Sago [Phys. Rev. D {\bf 75}, 064021 (2007)] invoke the notion of a self-accelerated motion in a background spacetime, and perform a direct calculation of the local self force in the Lorenz gauge (using numerical evolution of the perturbation equations in the time domain); Detweiler [Phys. Rev. D {\bf 77}, 124026 (2008)] describes the motion in terms a geodesic orbit of a (smooth) perturbed spacetime, and calculates the metric perturbation in the Regge--Wheeler gauge (using frequency-domain numerical analysis). Here we establish a formal correspondence between the two analyses, and demonstrate the consistency of their numerical results. Specifically, we compare the value of the conservative $O(\mu)$ shift in $u^t$ (where $\mu$ is the particle's mass and $u^t$ is the Schwarzschild $t$ component of the particle's four-velocity), suitably mapped between the two orbital descriptions and adjusted for gauge. We find that the two analyses yield the same value for this shift within mere fractional differences of $\sim 10^{-5}$--$10^{-7}$ (depending on the orbital radius)--comparable with the estimated numerical error.
|
gr-qc/9609073
|
Fernando Lombardo
|
Fernando C. Lombardo and Francisco D. Mazzitelli
|
Einstein-Langevin Equations from Running Coupling Constants
|
10 pages, RevTex file, no figures
|
Phys.Rev.D55:3889-3892,1997
|
10.1103/PhysRevD.55.3889
| null |
gr-qc
| null |
The Einstein-Langevin equations take into account the backreaction of quantum
matter fields on the background geometry. We present a derivation of these
equations to lowest order in a covariant expansion in powers of the curvature.
For massless fields, the equations are completely determined by the running
coupling constants of the theory.
|
[
{
"created": "Mon, 30 Sep 1996 17:04:07 GMT",
"version": "v1"
}
] |
2014-11-17
|
[
[
"Lombardo",
"Fernando C.",
""
],
[
"Mazzitelli",
"Francisco D.",
""
]
] |
The Einstein-Langevin equations take into account the backreaction of quantum matter fields on the background geometry. We present a derivation of these equations to lowest order in a covariant expansion in powers of the curvature. For massless fields, the equations are completely determined by the running coupling constants of the theory.
|
gr-qc/0412045
|
Juan A. Valiente-Kroon
|
J. A. Valiente Kroon
|
Time asymmetric spacetimes near null and spatial infinity. II.
Expansions of developments of initial data sets with non-smooth conformal
metrics
|
Second part of gr-qc/0408062, 23 pages
|
Class.Quant.Grav. 22 (2005) 1683-1707
|
10.1088/0264-9381/22/9/015
| null |
gr-qc
| null |
This article uses the conformal Einstein equations and the conformal
representation of spatial infinity introduced by Friedrich to analyse the
behaviour of the gravitational field near null and spatial infinity for the
development of initial data which are, in principle, non-conformally flat and
time asymmetric. This article is the continuation of the investigation started
in Class. Quantum Grav. 21 (2004) 5457-5492, where only conformally flat
initial data sets were considered. For the purposes of this investigation, the
conformal metric of the initial hypersurface is assumed to have a very
particular type of non-smoothness at infinity in order to allow for the
presence of non-Schwarzschildean initial data sets in the class under study.
The calculation of asymptotic expansions of the development of these initial
data sets reveals --as in the conformally flat case-- the existence of a
hierarchy of obstructions to the smoothness of null infinity which are
expressible in terms of the initial data. This allows for the possibility of
having spacetimes where future and past null infinity have different degrees of
smoothness. A conjecture regarding the general structure of the hierarchy of
obstructions is presented.
|
[
{
"created": "Fri, 10 Dec 2004 10:03:08 GMT",
"version": "v1"
}
] |
2009-11-10
|
[
[
"Kroon",
"J. A. Valiente",
""
]
] |
This article uses the conformal Einstein equations and the conformal representation of spatial infinity introduced by Friedrich to analyse the behaviour of the gravitational field near null and spatial infinity for the development of initial data which are, in principle, non-conformally flat and time asymmetric. This article is the continuation of the investigation started in Class. Quantum Grav. 21 (2004) 5457-5492, where only conformally flat initial data sets were considered. For the purposes of this investigation, the conformal metric of the initial hypersurface is assumed to have a very particular type of non-smoothness at infinity in order to allow for the presence of non-Schwarzschildean initial data sets in the class under study. The calculation of asymptotic expansions of the development of these initial data sets reveals --as in the conformally flat case-- the existence of a hierarchy of obstructions to the smoothness of null infinity which are expressible in terms of the initial data. This allows for the possibility of having spacetimes where future and past null infinity have different degrees of smoothness. A conjecture regarding the general structure of the hierarchy of obstructions is presented.
|
2103.13980
|
K. Sravan Kumar
|
K. Sravan Kumar, Shubham Maheshwari, Anupam Mazumdar and Jun Peng
|
An anisotropic bouncing universe in non-local gravity
|
18 pages, 1 figure, 1 table. We dedicate this work to the memory of
John D. Barrow. v2 matches the one published in JCAP
|
JCAP07(2021)025
|
10.1088/1475-7516/2021/07/025
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
We show that it is possible to realize a cosmological bouncing solution in an
anisotropic but homogeneous Bianchi-I background in a class of non-local,
infinite derivative theories of gravity. We show that the anisotropic shear
grows slower than in general relativity during the contraction phase, peaks to
a finite value at the bounce point, and then decreases as the universe
asymptotes towards isotropy and homogeneity, and ultimately to de Sitter. Along
with a cosmological constant, the matter sector required to drive such a bounce
is found to consist of three components - radiation, stiff matter and
$k$-matter (whose energy density decays like the inverse square of the average
scale factor). Generically, $k$-matter exerts anisotropic pressures. We will
test the bouncing solution in local and non-local gravity and show that in the
latter case it is possible to simultaneously satisfy positivity of energy
density and, at least in the late time de Sitter phase, avoid the introduction
of propagating ghost/tachyonic modes.
|
[
{
"created": "Thu, 25 Mar 2021 17:12:36 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Jul 2021 07:23:02 GMT",
"version": "v2"
}
] |
2021-07-20
|
[
[
"Kumar",
"K. Sravan",
""
],
[
"Maheshwari",
"Shubham",
""
],
[
"Mazumdar",
"Anupam",
""
],
[
"Peng",
"Jun",
""
]
] |
We show that it is possible to realize a cosmological bouncing solution in an anisotropic but homogeneous Bianchi-I background in a class of non-local, infinite derivative theories of gravity. We show that the anisotropic shear grows slower than in general relativity during the contraction phase, peaks to a finite value at the bounce point, and then decreases as the universe asymptotes towards isotropy and homogeneity, and ultimately to de Sitter. Along with a cosmological constant, the matter sector required to drive such a bounce is found to consist of three components - radiation, stiff matter and $k$-matter (whose energy density decays like the inverse square of the average scale factor). Generically, $k$-matter exerts anisotropic pressures. We will test the bouncing solution in local and non-local gravity and show that in the latter case it is possible to simultaneously satisfy positivity of energy density and, at least in the late time de Sitter phase, avoid the introduction of propagating ghost/tachyonic modes.
|
gr-qc/0002049
|
Frederick J. Ernst
|
I. Hauser and F. J. Ernst
|
Proof of a generalized Geroch conjecture for the hyperbolic Ernst
equation
|
75 pages (plus optional table of contents). Sign errors in elliptic
case equations (1A.13), (1A.15) and (1A.25) are corrected. Not relevant to
proof contained in paper
|
Gen.Rel.Grav.33:195-293,2001
|
10.1023/A:1002701301339
| null |
gr-qc
| null |
We enunciate and prove here a generalization of Geroch's famous conjecture
concerning analytic solutions of the elliptic Ernst equation. Our
generalization is stated for solutions of the hyperbolic Ernst equation that
are not necessarily analytic, although it can be formulated also for solutions
of the elliptic Ernst equation that are nowhere axis-accessible.
|
[
{
"created": "Mon, 14 Feb 2000 15:55:50 GMT",
"version": "v1"
},
{
"created": "Sun, 15 Oct 2000 12:10:25 GMT",
"version": "v2"
}
] |
2008-11-26
|
[
[
"Hauser",
"I.",
""
],
[
"Ernst",
"F. J.",
""
]
] |
We enunciate and prove here a generalization of Geroch's famous conjecture concerning analytic solutions of the elliptic Ernst equation. Our generalization is stated for solutions of the hyperbolic Ernst equation that are not necessarily analytic, although it can be formulated also for solutions of the elliptic Ernst equation that are nowhere axis-accessible.
|
0709.4588
|
Leor Barack
|
Leor Barack, Darren A. Golbourn and Norichika Sago
|
m-Mode Regularization Scheme for the Self Force in Kerr Spacetime
|
17 pages. Minor typos corrected; version to appear in PRD
|
Phys.Rev.D76:124036,2007
|
10.1103/PhysRevD.76.124036
| null |
gr-qc astro-ph
| null |
We present a new, simple method for calculating the scalar, electromagnetic,
and gravitational self forces acting on particles in orbit around a Kerr black
hole. The standard ``mode-sum regularization'' approach for self-force
calculations relies on a decomposition of the full (retarded) perturbation
field into multipole modes, followed by the application of a certain
mode-by-mode regularization procedure. In recent years several groups have
developed numerical codes for calculating black hole perturbations directly in
2+1 dimensions (i.e., decomposing the azimuthal dependence into $m$-modes, but
refraining from a full multipole decomposition). Here we formulate a practical
scheme for constructing the self force directly from the 2+1-dimensional
$m$-modes. While the standard mode-sum method is serving well in calculations
of the self force in Schwarzschild geometry, the new scheme should allow a more
efficient treatment of the Kerr problem.
|
[
{
"created": "Fri, 28 Sep 2007 12:00:45 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Dec 2007 11:21:29 GMT",
"version": "v2"
}
] |
2008-11-26
|
[
[
"Barack",
"Leor",
""
],
[
"Golbourn",
"Darren A.",
""
],
[
"Sago",
"Norichika",
""
]
] |
We present a new, simple method for calculating the scalar, electromagnetic, and gravitational self forces acting on particles in orbit around a Kerr black hole. The standard ``mode-sum regularization'' approach for self-force calculations relies on a decomposition of the full (retarded) perturbation field into multipole modes, followed by the application of a certain mode-by-mode regularization procedure. In recent years several groups have developed numerical codes for calculating black hole perturbations directly in 2+1 dimensions (i.e., decomposing the azimuthal dependence into $m$-modes, but refraining from a full multipole decomposition). Here we formulate a practical scheme for constructing the self force directly from the 2+1-dimensional $m$-modes. While the standard mode-sum method is serving well in calculations of the self force in Schwarzschild geometry, the new scheme should allow a more efficient treatment of the Kerr problem.
|
gr-qc/0102099
|
Roberto Colistete Junior
|
R. Kerner, J.W. van Holten, R. Colistete Jr
|
Relativistic Epicycles : another approach to geodesic deviations
|
23 pages, LaTeX, 2 Postscript figures. Version substantially improved
to be published in Classical and Quantum Gravity, with : additional figure,
references, rewritten text, minor corrections, etc
|
Class.Quant.Grav. 18 (2001) 4725-4742
|
10.1088/0264-9381/18/22/302
| null |
gr-qc astro-ph
| null |
We solve the geodesic deviation equations for the orbital motions in the
Schwarzschild metric which are close to a circular orbit. It turns out that in
this particular case the equations reduce to a linear system, which after
diagonalization describes just a collection of harmonic oscillators, with two
characteristic frequencies. The new geodesic obtained by adding this solution
to the circular one, describes not only the linear approximation of Kepler's
laws, but gives also the right value of the perihelion advance (in the limit of
almost circular orbits). We derive also the equations for higher-order
deviations and show how these equations lead to better approximations,
including the non-linear effects. The approximate orbital solutions are then
inserted into the quadrupole formula to estimate the gravitational radiation
from non-circular orbits.
|
[
{
"created": "Thu, 22 Feb 2001 16:25:16 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Sep 2001 15:51:52 GMT",
"version": "v2"
}
] |
2009-11-07
|
[
[
"Kerner",
"R.",
""
],
[
"van Holten",
"J. W.",
""
],
[
"Colistete",
"R.",
"Jr"
]
] |
We solve the geodesic deviation equations for the orbital motions in the Schwarzschild metric which are close to a circular orbit. It turns out that in this particular case the equations reduce to a linear system, which after diagonalization describes just a collection of harmonic oscillators, with two characteristic frequencies. The new geodesic obtained by adding this solution to the circular one, describes not only the linear approximation of Kepler's laws, but gives also the right value of the perihelion advance (in the limit of almost circular orbits). We derive also the equations for higher-order deviations and show how these equations lead to better approximations, including the non-linear effects. The approximate orbital solutions are then inserted into the quadrupole formula to estimate the gravitational radiation from non-circular orbits.
|
1808.00172
|
Tanmoy Paul
|
Tanmoy Paul and Soumitra SenGupta
|
Dynamical suppression of spacetime torsion
|
EPJC accepted
| null |
10.1140/epjc/s10052-019-7109-5
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
A surprising feature of our present four dimensional universe is that its
evolution appears to be governed solely by spacetime curvature without any
noticeable effect of spacetime torsion. In the present paper, we give a
possible explanation of this enigma through ``cosmological evolution'' of
spacetime torsion in the backdrop of a higher dimensional braneworld scenario.
Our results reveal that the torsion field may had a significant value at early
phase of our universe, but gradually decreased with the expansion of the
universe. This leads to a negligible footprint of torsion in our present
visible universe. We also show that at an early epoch, when the amplitude of
the torsion field was not suppressed, our universe underwent through an
inflationary stage having a graceful exit within a finite time. To link the
model with observational constraints, we also determine the spectral index for
curvature perturbation ($n_s$) and tensor to scalar ratio ($r$) in the present
context, which match with the results of $Planck$ 2018 (combining with BICEP-2
Keck-Array) data \cite{Planck}.
|
[
{
"created": "Wed, 1 Aug 2018 05:35:35 GMT",
"version": "v1"
},
{
"created": "Sat, 6 Jul 2019 17:02:01 GMT",
"version": "v2"
}
] |
2019-09-04
|
[
[
"Paul",
"Tanmoy",
""
],
[
"SenGupta",
"Soumitra",
""
]
] |
A surprising feature of our present four dimensional universe is that its evolution appears to be governed solely by spacetime curvature without any noticeable effect of spacetime torsion. In the present paper, we give a possible explanation of this enigma through ``cosmological evolution'' of spacetime torsion in the backdrop of a higher dimensional braneworld scenario. Our results reveal that the torsion field may had a significant value at early phase of our universe, but gradually decreased with the expansion of the universe. This leads to a negligible footprint of torsion in our present visible universe. We also show that at an early epoch, when the amplitude of the torsion field was not suppressed, our universe underwent through an inflationary stage having a graceful exit within a finite time. To link the model with observational constraints, we also determine the spectral index for curvature perturbation ($n_s$) and tensor to scalar ratio ($r$) in the present context, which match with the results of $Planck$ 2018 (combining with BICEP-2 Keck-Array) data \cite{Planck}.
|
gr-qc/9603047
|
Rudolf Poppe
|
Andre' Lukas and Rudolf Poppe
|
Decoherence in Pre-Big-Bang Cosmology
|
15 pages, 2 postscript figures included
|
Mod.Phys.Lett. A12 (1997) 597-612
|
10.1142/S0217732397000625
|
TUM-HEP 240/96, SFB-375/87
|
gr-qc hep-th
| null |
We analyze the quantum cosmology of the simplest pre--big--bang model without
dilaton potential. In addition to the minisuperspace variables we include
inhomogeneous dilaton fluctuations and determine their wave function on a
semiclassical background. This wave function is used to calculate the reduced
density matrix and to find criteria for the loss of decoherence. It is shown
that coherence between different backgrounds can always be achieved by a
specific choice of vacua though generically decoherence can be expected. In
particular, we discuss the implications of these results on the ``exit
problem'' of pre--big--bang cosmology.
|
[
{
"created": "Mon, 25 Mar 1996 16:50:11 GMT",
"version": "v1"
}
] |
2009-10-28
|
[
[
"Lukas",
"Andre'",
""
],
[
"Poppe",
"Rudolf",
""
]
] |
We analyze the quantum cosmology of the simplest pre--big--bang model without dilaton potential. In addition to the minisuperspace variables we include inhomogeneous dilaton fluctuations and determine their wave function on a semiclassical background. This wave function is used to calculate the reduced density matrix and to find criteria for the loss of decoherence. It is shown that coherence between different backgrounds can always be achieved by a specific choice of vacua though generically decoherence can be expected. In particular, we discuss the implications of these results on the ``exit problem'' of pre--big--bang cosmology.
|
0803.1998
|
Alexis Larranaga
|
Alexis Larranaga
|
On the Thermodynamical Relation between Rotating Charged BTZ Black Holes
and Effective String Theory
|
9 pages
|
Commun.Theor.Phys.50:1341-1344,2008
|
10.1088/0253-6102/50/6/19
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper we study the first law of thermodynamics for the (2+1)
dimensional rotating charged BTZ black hole considering a pair of
thermodinamical systems constructed with the two horizons of this solution. We
show that these two systems are similar to the right and left movers of string
theory and that the temperature associated with the black hole is the harmonic
mean of the temperatures associated with these two systems.
|
[
{
"created": "Thu, 13 Mar 2008 16:08:09 GMT",
"version": "v1"
}
] |
2009-01-14
|
[
[
"Larranaga",
"Alexis",
""
]
] |
In this paper we study the first law of thermodynamics for the (2+1) dimensional rotating charged BTZ black hole considering a pair of thermodinamical systems constructed with the two horizons of this solution. We show that these two systems are similar to the right and left movers of string theory and that the temperature associated with the black hole is the harmonic mean of the temperatures associated with these two systems.
|
gr-qc/0005108
|
Elizabeth Winstanley
|
Adrian C. Ottewill and Elizabeth Winstanley
|
Divergence of a quantum thermal state on Kerr space-time
|
7 pages, revtex, no figures
|
Phys.Lett. A273 (2000) 149-152
|
10.1016/S0375-9601(00)00487-4
|
OUTP-00-23-P
|
gr-qc
| null |
We present a simple proof, using the conservation equations, that any quantum
stress tensor on Kerr space-time which is isotropic in a frame which rotates
rigidly with the angular velocity of the event horizon must be divergent at the
velocity of light surface. We comment on our result in the light of the absence
of a `true Hartle-Hawking' vacuum for Kerr.
|
[
{
"created": "Wed, 24 May 2000 13:59:23 GMT",
"version": "v1"
}
] |
2009-10-31
|
[
[
"Ottewill",
"Adrian C.",
""
],
[
"Winstanley",
"Elizabeth",
""
]
] |
We present a simple proof, using the conservation equations, that any quantum stress tensor on Kerr space-time which is isotropic in a frame which rotates rigidly with the angular velocity of the event horizon must be divergent at the velocity of light surface. We comment on our result in the light of the absence of a `true Hartle-Hawking' vacuum for Kerr.
|
1305.4524
|
Andrew J. S. Hamilton
|
A. J. S. Hamilton
|
The Black Hole Particle Accelerator as a Machine to make Baby Universes
|
7 pages, 2 figures. NO honorable mention in the 2013 Essay
Competition of the Gravity Research Foundation
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
General relativity predicts that the inner horizon of an astronomically
realistic rotating black hole is subject to the mass inflation instability. The
inflationary instability acts like a gravity-powered particle accelerator of
extraordinary power, accelerating accreted streams of particles along the
principal outgoing and ingoing null directions at the inner horizon to
collision energies that would, if nothing intervened, typically exceed
exponentially the Planck energy. The inflationary instability is fueled by
ongoing accretion, and is occurring inevitably in essentially every black hole
in our Universe. This extravagant machine, the Black Hole Particle Accelerator,
has the hallmarks of a device to make baby universes. Since collisions are most
numerous inside supermassive black holes, reproductive efficiency requires our
Universe to make supermassive black holes efficiently, as is observed.
|
[
{
"created": "Mon, 20 May 2013 13:25:36 GMT",
"version": "v1"
}
] |
2013-05-21
|
[
[
"Hamilton",
"A. J. S.",
""
]
] |
General relativity predicts that the inner horizon of an astronomically realistic rotating black hole is subject to the mass inflation instability. The inflationary instability acts like a gravity-powered particle accelerator of extraordinary power, accelerating accreted streams of particles along the principal outgoing and ingoing null directions at the inner horizon to collision energies that would, if nothing intervened, typically exceed exponentially the Planck energy. The inflationary instability is fueled by ongoing accretion, and is occurring inevitably in essentially every black hole in our Universe. This extravagant machine, the Black Hole Particle Accelerator, has the hallmarks of a device to make baby universes. Since collisions are most numerous inside supermassive black holes, reproductive efficiency requires our Universe to make supermassive black holes efficiently, as is observed.
|
2402.15854
|
Krishnendu De Dr.
|
Young Jin Suh, Krishnendu De and Uday Chand De
|
Impact of projective curvature tensor in $f\left(R,G\right)$,
$f\left(R,T\right)$ and $f\left(R,L_{m}\right)$-gravity
| null |
International journal of geometric methods in modern physics 2024,
|
10.1142/S0219887824500622
| null |
gr-qc math.DG
|
http://creativecommons.org/licenses/by/4.0/
|
This article concerns with the characterization of a spacetime and modified
gravity, such as $f\left(R,G\right)$, $f\left(R,T\right)$ and
$f\left(R,L_{m}\right)$-gravity equipped with the projective curvature tensor.
We establish that a projectively flat perfect fluid spacetime represents dark
energy era. Also, we prove that a projectively flat perfect fluid spacetime is
either locally isometric to Minkowski spacetime or a de-Sitter spacetime.
Furthermore, it is shown that a perfect fluid spacetime permitting harmonic
projective curvature tensor becomes a generalized Robertson-Walker spacetime
and is of Petrov type $I$, $D$ or $O$. Lastly, we investigate the effect of
projectively flat perfect fluid spacetime solutions in $f\left(R,G\right)$,
$f\left(R,T\right)$ and $f\left(R,L_{m}\right)$-gravity, respectively. We also
investigate the spacetime as a $f\left(R,G\right)$-gravity solution of and use
the flat Friedmann-Robertson-Walker metric to establish a relation among jerk,
snap, and deceleration parameters. Numerous energy conditions are studied in
terms of Ricci scalar with the model $f\left(R,G\right)=\exp(R)+\alpha
\left(6G\right)^{\beta}$. For this model, the strong energy condition is
violated but the weak, dominant and null energy conditions are fulfilled, which
is in excellent accordance with current observational investigations that show
the universe is now accelerating.
|
[
{
"created": "Sat, 24 Feb 2024 16:50:51 GMT",
"version": "v1"
}
] |
2024-02-27
|
[
[
"Suh",
"Young Jin",
""
],
[
"De",
"Krishnendu",
""
],
[
"De",
"Uday Chand",
""
]
] |
This article concerns with the characterization of a spacetime and modified gravity, such as $f\left(R,G\right)$, $f\left(R,T\right)$ and $f\left(R,L_{m}\right)$-gravity equipped with the projective curvature tensor. We establish that a projectively flat perfect fluid spacetime represents dark energy era. Also, we prove that a projectively flat perfect fluid spacetime is either locally isometric to Minkowski spacetime or a de-Sitter spacetime. Furthermore, it is shown that a perfect fluid spacetime permitting harmonic projective curvature tensor becomes a generalized Robertson-Walker spacetime and is of Petrov type $I$, $D$ or $O$. Lastly, we investigate the effect of projectively flat perfect fluid spacetime solutions in $f\left(R,G\right)$, $f\left(R,T\right)$ and $f\left(R,L_{m}\right)$-gravity, respectively. We also investigate the spacetime as a $f\left(R,G\right)$-gravity solution of and use the flat Friedmann-Robertson-Walker metric to establish a relation among jerk, snap, and deceleration parameters. Numerous energy conditions are studied in terms of Ricci scalar with the model $f\left(R,G\right)=\exp(R)+\alpha \left(6G\right)^{\beta}$. For this model, the strong energy condition is violated but the weak, dominant and null energy conditions are fulfilled, which is in excellent accordance with current observational investigations that show the universe is now accelerating.
|
0906.0145
|
Yubei Yue
|
Yubei Yue and Bin Chen
|
K-Inflation with a Dark Energy Coupling
|
8 pages, 1 figure
|
Phys.Rev.D81:023506,2010
|
10.1103/PhysRevD.81.023506
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
It is usually thought that the quintessence as a fundamental scalar field was
already present during the inflationary epoch. While there are various models
in which the quintessence couples to other species, it is attractive to
anticipate a coupling between the quintessence and the inflaton in the very
early universe as well. We consider such a coupling in the context of
k-inflation. The coupling function and the potential of the quintessence are
chosen to be of power law forms. We show such a coupling affects the speed of
sound for the inflaton field as well as the power spectra of perturbations.
|
[
{
"created": "Sun, 31 May 2009 11:15:50 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Sep 2009 16:48:40 GMT",
"version": "v2"
},
{
"created": "Thu, 29 Oct 2009 05:08:36 GMT",
"version": "v3"
},
{
"created": "Sun, 20 Dec 2009 14:39:37 GMT",
"version": "v4"
}
] |
2010-04-06
|
[
[
"Yue",
"Yubei",
""
],
[
"Chen",
"Bin",
""
]
] |
It is usually thought that the quintessence as a fundamental scalar field was already present during the inflationary epoch. While there are various models in which the quintessence couples to other species, it is attractive to anticipate a coupling between the quintessence and the inflaton in the very early universe as well. We consider such a coupling in the context of k-inflation. The coupling function and the potential of the quintessence are chosen to be of power law forms. We show such a coupling affects the speed of sound for the inflaton field as well as the power spectra of perturbations.
|
gr-qc/0406096
|
Achilles D. Speliotopoulos
|
A. D. Speliotopoulos and R. Y. Chiao
|
Differing Calculations of the Response of Matter-wave Interferometers to
Gravitational Waves
|
36 pages, 2 figures, written in RevTeX, submitted to Physical Review
D
| null | null | null |
gr-qc
| null |
There now exists in the literature two different expressions for the phase
shift of a matter-wave interferometer caused by the passage of a gravitation
wave. The first, a commonly accepted expression that was first derived in the
1970s, is based on the traditional geodesic equation of motion (EOM) for a test
particle. The second, a more recently derived expression, is based on the
geodesic deviation EOM. The power-law dependence on the frequency of the
gravitational wave for both expressions for the phase shift is different, which
indicates fundamental differences in the physics on which these calculations
are based. Here we compare the two approaches by presenting a series of
side-by-side calculations of the phase shift for one specific
matter-wave-interferometer configuration that uses atoms as the interfering
particle. By looking at the low-frequency limit of the different expressions
for the phase shift obtained, we find that the phase shift calculated via the
geodesic deviation EOM is correct, and the ones calculated via the geodesic EOM
are not.
|
[
{
"created": "Wed, 23 Jun 2004 21:36:55 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Speliotopoulos",
"A. D.",
""
],
[
"Chiao",
"R. Y.",
""
]
] |
There now exists in the literature two different expressions for the phase shift of a matter-wave interferometer caused by the passage of a gravitation wave. The first, a commonly accepted expression that was first derived in the 1970s, is based on the traditional geodesic equation of motion (EOM) for a test particle. The second, a more recently derived expression, is based on the geodesic deviation EOM. The power-law dependence on the frequency of the gravitational wave for both expressions for the phase shift is different, which indicates fundamental differences in the physics on which these calculations are based. Here we compare the two approaches by presenting a series of side-by-side calculations of the phase shift for one specific matter-wave-interferometer configuration that uses atoms as the interfering particle. By looking at the low-frequency limit of the different expressions for the phase shift obtained, we find that the phase shift calculated via the geodesic deviation EOM is correct, and the ones calculated via the geodesic EOM are not.
|
2012.03517
|
Dmitry Chirkov
|
Dmitry Chirkov, Alex Giacomini, Sergey A. Pavluchenko, Alexey
Toporensky
|
Cosmological solutions in Einstein-Gauss-Bonnet gravity with static
curved extra dimensions
|
27 pages, 8 figures
|
Eur. Phys. J. C 81, 136 (2021)
|
10.1140/epjc/s10052-021-08934-y
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper we perform systematic investigation of all possible solutions
with static compact extra dimensions and expanding three-dimensional subspace
(``our Universe''). Unlike previous papers, we consider extra-dimensional
subspace to be constant-curvature manifold with both signs of spatial
curvature. We provide a scheme how to build solutions in all possible number of
extra dimensions and perform stability analysis for the solutions found. Our
study suggests that the solutions with negative spatial curvature of extra
dimensions are always stable while those with positive curvature are stable for
a narrow range of the parameters and the width of this range shrinks with
growth of the number of extra dimensions. This explains why in the previous
papers we detected compactification in the case of negative curvature but the
case of positive curvature remained undiscovered. Another interesting feature
which distinguish cases with positive and negative curvatures is that the
latter do not coexist with maximally-symmetric solutions (leading to
``geometric frustration'' of a sort) while the former could -- this difference
is noted and discussed.
|
[
{
"created": "Mon, 7 Dec 2020 08:15:54 GMT",
"version": "v1"
}
] |
2021-04-22
|
[
[
"Chirkov",
"Dmitry",
""
],
[
"Giacomini",
"Alex",
""
],
[
"Pavluchenko",
"Sergey A.",
""
],
[
"Toporensky",
"Alexey",
""
]
] |
In this paper we perform systematic investigation of all possible solutions with static compact extra dimensions and expanding three-dimensional subspace (``our Universe''). Unlike previous papers, we consider extra-dimensional subspace to be constant-curvature manifold with both signs of spatial curvature. We provide a scheme how to build solutions in all possible number of extra dimensions and perform stability analysis for the solutions found. Our study suggests that the solutions with negative spatial curvature of extra dimensions are always stable while those with positive curvature are stable for a narrow range of the parameters and the width of this range shrinks with growth of the number of extra dimensions. This explains why in the previous papers we detected compactification in the case of negative curvature but the case of positive curvature remained undiscovered. Another interesting feature which distinguish cases with positive and negative curvatures is that the latter do not coexist with maximally-symmetric solutions (leading to ``geometric frustration'' of a sort) while the former could -- this difference is noted and discussed.
|
1905.08276
|
Jishnu Suresh
|
Sambit Panda, Swetha Bhagwat, Jishnu Suresh and Sanjit Mitra
|
Stochastic gravitational wave background mapmaking using regularised
deconvolution
|
14 pages, 8 figures and 1 table
|
Phys. Rev. D 100, 043541 (2019)
|
10.1103/PhysRevD.100.043541
| null |
gr-qc astro-ph.IM
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Obtaining a faithful source intensity distribution map of the sky from noisy
data demands incorporating known information of the expected signal, especially
when the signal is weak compared to the noise. We introduce a widely used
procedure to incorporate these priors through a Bayesian regularisation scheme
in the context of map-making of the anisotropic stochastic GW background
(SGWB). Specifically, we implement the quadratic form of regularizing function
with varying strength of regularization and study its effect on image
restoration for different types of the injected source intensity distribution
in simulated LIGO data. We find that regularization significantly enhances the
quality of reconstruction, especially when the intensity of the source is weak,
and dramatically improves the stability of deconvolution. We further study the
quality of reconstruction as a function of regularization constant. While in
principle this constant is dependent on the data set, we show that the
deconvolution process is robust against the choice of the constant, as long as
it is chosen from a broad range of values obtained by the method presented
here.
|
[
{
"created": "Mon, 20 May 2019 18:05:58 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Jun 2019 12:30:50 GMT",
"version": "v2"
}
] |
2019-09-04
|
[
[
"Panda",
"Sambit",
""
],
[
"Bhagwat",
"Swetha",
""
],
[
"Suresh",
"Jishnu",
""
],
[
"Mitra",
"Sanjit",
""
]
] |
Obtaining a faithful source intensity distribution map of the sky from noisy data demands incorporating known information of the expected signal, especially when the signal is weak compared to the noise. We introduce a widely used procedure to incorporate these priors through a Bayesian regularisation scheme in the context of map-making of the anisotropic stochastic GW background (SGWB). Specifically, we implement the quadratic form of regularizing function with varying strength of regularization and study its effect on image restoration for different types of the injected source intensity distribution in simulated LIGO data. We find that regularization significantly enhances the quality of reconstruction, especially when the intensity of the source is weak, and dramatically improves the stability of deconvolution. We further study the quality of reconstruction as a function of regularization constant. While in principle this constant is dependent on the data set, we show that the deconvolution process is robust against the choice of the constant, as long as it is chosen from a broad range of values obtained by the method presented here.
|
2008.05285
|
Gabriel R. Bengochea
|
Gabriel R. Bengochea, Gabriel Le\'on, Philip Pearle, Daniel Sudarsky
|
Discussions about the landscape of possibilities for treatments of
cosmic inflation involving continuous spontaneous localization models
|
13 pages, 1 Appendix. Minor changes in title and abstract
|
Eur. Phys. J. C 80, 1021 (2020)
|
10.1140/epjc/s10052-020-08599-z
| null |
gr-qc astro-ph.CO quant-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this work we consider a wide variety of alternatives opened when applying
the continuous spontaneous localization (CSL) dynamical collapse theory to the
inflationary era. The definitive resolution of many of the issues discussed
here will have to await, not only for a general relativistic CSL theory, but
for a fully workable theory of quantum gravity. Our concern here is to explore
these issues, and to warn against premature conclusions. This exploration
includes: two different approaches to deal with quantum field theory and
gravitation, the identification of the collapse-generating operator and the
general nature and values of the parameters of the CSL theory. All the choices
connected with these issues have the potential to dramatically alter the
conclusions one can draw. We also argue that the incompatibilities found in a
recent paper, between the CSL parameter values and the CMB observational data,
are associated with specific choices made for the extrapolation to the
cosmological context of the CSL theory (as it is known to work in
non-relativistic laboratory situations) which do not represent the most natural
ones.
|
[
{
"created": "Tue, 11 Aug 2020 03:11:21 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Nov 2020 02:26:50 GMT",
"version": "v2"
}
] |
2020-11-09
|
[
[
"Bengochea",
"Gabriel R.",
""
],
[
"León",
"Gabriel",
""
],
[
"Pearle",
"Philip",
""
],
[
"Sudarsky",
"Daniel",
""
]
] |
In this work we consider a wide variety of alternatives opened when applying the continuous spontaneous localization (CSL) dynamical collapse theory to the inflationary era. The definitive resolution of many of the issues discussed here will have to await, not only for a general relativistic CSL theory, but for a fully workable theory of quantum gravity. Our concern here is to explore these issues, and to warn against premature conclusions. This exploration includes: two different approaches to deal with quantum field theory and gravitation, the identification of the collapse-generating operator and the general nature and values of the parameters of the CSL theory. All the choices connected with these issues have the potential to dramatically alter the conclusions one can draw. We also argue that the incompatibilities found in a recent paper, between the CSL parameter values and the CMB observational data, are associated with specific choices made for the extrapolation to the cosmological context of the CSL theory (as it is known to work in non-relativistic laboratory situations) which do not represent the most natural ones.
|
gr-qc/0009001
|
Abel Camacho Quintana
|
Abel Camacho Quintana (Astrophysikalisches Institut Potsdam)
|
Group-theoretical structure of quantum measurements and equivalence
principle
|
13 pages, accepted in Modern Physics Letters A
|
Mod.Phys.Lett. A15 (2000) 1461-1470
|
10.1142/S0217732300001882
| null |
gr-qc quant-ph
| null |
The transverse group associated to some continuous quantum measuring
processes is analyzed in the presence of nonvanishing gravitational fields.
This is done considering, as an exmaple, the case of a particle whose
coordinates are being monitored. Employing the so called restricted path
integral formalism, it will be shown that the measuring process could always
contain information concerning the gravitational field. In other words, it
seems that with the presence of a measuring process the equivalence principle
may, in some cases, break down. The relation between the breakdown of the
equivalence principle, at quantum level, and the fact that the gravitational
field could act always as a decoherence environment, is also considered. The
phenomena of quantum beats of quantum optics will allow us to consider the
possibility that the experimental corroboration of the equivalence principle at
quantum level could be taken as an indirect evidence in favor of the
quantization of the gravitational field, i.e., the quantum properties of this
field avoid the violation of the equivalence principle.
|
[
{
"created": "Fri, 1 Sep 2000 03:12:52 GMT",
"version": "v1"
}
] |
2009-10-31
|
[
[
"Quintana",
"Abel Camacho",
"",
"Astrophysikalisches Institut Potsdam"
]
] |
The transverse group associated to some continuous quantum measuring processes is analyzed in the presence of nonvanishing gravitational fields. This is done considering, as an exmaple, the case of a particle whose coordinates are being monitored. Employing the so called restricted path integral formalism, it will be shown that the measuring process could always contain information concerning the gravitational field. In other words, it seems that with the presence of a measuring process the equivalence principle may, in some cases, break down. The relation between the breakdown of the equivalence principle, at quantum level, and the fact that the gravitational field could act always as a decoherence environment, is also considered. The phenomena of quantum beats of quantum optics will allow us to consider the possibility that the experimental corroboration of the equivalence principle at quantum level could be taken as an indirect evidence in favor of the quantization of the gravitational field, i.e., the quantum properties of this field avoid the violation of the equivalence principle.
|
2012.09075
|
Jose Geraldo Pereira
|
J. G. Pereira and D. F. L\'opez
|
An Improved Framework for Quantum Gravity
|
15 pages, no figures
|
Universe 6 (2020) 243
|
10.3390/universe6120243
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
General relativity has two fundamental problems that render it unsuitable for
tackling the gravitational field's quantization. The first problem is the lack
of a genuine gravitational variable representing gravitation only, inertial
forces apart. The second problem is its incompatibility with quantum mechanics,
a problem inherited from the more fundamental conflict of special relativity
with quantum mechanics. A procedure to overcome these difficulties is outlined,
which amounts to replacing general relativity with its teleparallel equivalent
and the Poincar\'e-invariant special relativity with the de Sitter-invariant
special relativity. Those replacements give rise to the de Sitter-modified
teleparallel gravity, which does not have the two mentioned problems. It can
thus be considered an improved alternative approach to quantum gravity.
|
[
{
"created": "Wed, 16 Dec 2020 16:56:39 GMT",
"version": "v1"
}
] |
2020-12-17
|
[
[
"Pereira",
"J. G.",
""
],
[
"López",
"D. F.",
""
]
] |
General relativity has two fundamental problems that render it unsuitable for tackling the gravitational field's quantization. The first problem is the lack of a genuine gravitational variable representing gravitation only, inertial forces apart. The second problem is its incompatibility with quantum mechanics, a problem inherited from the more fundamental conflict of special relativity with quantum mechanics. A procedure to overcome these difficulties is outlined, which amounts to replacing general relativity with its teleparallel equivalent and the Poincar\'e-invariant special relativity with the de Sitter-invariant special relativity. Those replacements give rise to the de Sitter-modified teleparallel gravity, which does not have the two mentioned problems. It can thus be considered an improved alternative approach to quantum gravity.
|
1612.02484
|
Freddy Cueva Solano
|
Freddy Cueva Solano
|
Exploring the effects of a double reconstruction on the growth rate of
cosmic structure, using current observational data
|
22 pages, 6 figures and 7 tables, Prepared for submission to PRD
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Based on General Relativity (GR) we consider two different cosmological
scenarios in where reconstruct the energy exchange (Q) between cold dark matter
(DM) fluid and dark energy (DE) fluid, which is modelled with a DE varying
equation of state (EoS) parameter {\omega}. We here investigate the main
cosmological effects on the growth rate of matter density perturbations
(f{\sigma}8), on the effective Hubble friction term (Heff ), on the effective
Newton constant (Geff ) and on the growth index of the linear matter
fluctuations ({\gamma}). Our study demonstrates that in the coupled models the
evolution of these quantities are modified with respect to the predictions in
the uncoupled models, and therefore could be used to distinguish among coupled
DE scenarios. Finally, we also perform a combined statistical analysis using
current observational data (geometric and dynamical probes) to put more
stringent constraints on the parameters space of the cosmic scenarios studied.
|
[
{
"created": "Wed, 7 Dec 2016 23:27:39 GMT",
"version": "v1"
}
] |
2016-12-09
|
[
[
"Solano",
"Freddy Cueva",
""
]
] |
Based on General Relativity (GR) we consider two different cosmological scenarios in where reconstruct the energy exchange (Q) between cold dark matter (DM) fluid and dark energy (DE) fluid, which is modelled with a DE varying equation of state (EoS) parameter {\omega}. We here investigate the main cosmological effects on the growth rate of matter density perturbations (f{\sigma}8), on the effective Hubble friction term (Heff ), on the effective Newton constant (Geff ) and on the growth index of the linear matter fluctuations ({\gamma}). Our study demonstrates that in the coupled models the evolution of these quantities are modified with respect to the predictions in the uncoupled models, and therefore could be used to distinguish among coupled DE scenarios. Finally, we also perform a combined statistical analysis using current observational data (geometric and dynamical probes) to put more stringent constraints on the parameters space of the cosmic scenarios studied.
|
gr-qc/0210007
|
Roland Steinbauer
|
Jiri Podolsky, Roland Steinbauer
|
Geodesics in spacetimes with expanding impulsive gravitational waves
|
12 pages, Revtex, final version
|
Phys.Rev. D67 (2003) 064013
|
10.1103/PhysRevD.67.064013
| null |
gr-qc
| null |
We study geodesic motion in expanding spherical impulsive gravitational waves
propagating in a Minkowski background. Employing the continuous form of the
metric we find and examine a large family of geometrically preferred geodesics.
For the special class of axially symmetric spacetimes with the spherical
impulse generated by a snapping cosmic string we give a detailed physical
interpretation of the motion of test particles.
|
[
{
"created": "Wed, 2 Oct 2002 14:55:47 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Apr 2003 11:08:05 GMT",
"version": "v2"
}
] |
2009-11-07
|
[
[
"Podolsky",
"Jiri",
""
],
[
"Steinbauer",
"Roland",
""
]
] |
We study geodesic motion in expanding spherical impulsive gravitational waves propagating in a Minkowski background. Employing the continuous form of the metric we find and examine a large family of geometrically preferred geodesics. For the special class of axially symmetric spacetimes with the spherical impulse generated by a snapping cosmic string we give a detailed physical interpretation of the motion of test particles.
|
1601.02235
|
Guido Magnano
|
Guido Magnano
|
Nonlinear Gravitational Lagrangians revisited
|
Variational principles and conservation laws in General Relativity -
Workshop in memory of Prof. Mauro Francaviglia - Torino, June 25th-26th, 2015
| null |
10.1142/S0219887816400065
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The Legendre transformation method, applied in 1987 to deal with purely
metric gravitational Lagrangians with nonlinear dependence on the Ricci tensor,
is extended to metric-affine models and is shown to provide a concise and
insightful comparison of the dynamical content of the two variational
frameworks.
|
[
{
"created": "Sun, 10 Jan 2016 17:16:54 GMT",
"version": "v1"
}
] |
2016-09-21
|
[
[
"Magnano",
"Guido",
""
]
] |
The Legendre transformation method, applied in 1987 to deal with purely metric gravitational Lagrangians with nonlinear dependence on the Ricci tensor, is extended to metric-affine models and is shown to provide a concise and insightful comparison of the dynamical content of the two variational frameworks.
|
2210.01138
|
Johanna N. Borissova
|
Johanna N. Borissova, Alessia Platania
|
Formation and evaporation of quantum black holes from the decoupling
mechanism in quantum gravity
|
v5: some more typos fixed
| null |
10.1007/JHEP03(2023)046
|
NORDITA 2022-069
|
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We propose a new method to account for quantum-gravitational effects in
cosmological and black hole spacetimes. At the core of our construction is the
"decoupling mechanism": when a physical infrared scale overcomes the effect of
the regulator implementing the Wilsonian integration of fluctuating modes, the
renormalization group flow of the scale-dependent effective action freezes out,
so that at the decoupling scale the latter approximates the standard quantum
effective action. Identifying the decoupling scale allows to access terms in
the effective action that were not part of the original truncation and thus to
study leading-order quantum corrections to field equations and their solutions.
Starting from the Einstein-Hilbert truncation, we exploit for the first time
the decoupling mechanism in quantum gravity to investigate the dynamics of
quantum-corrected black holes from formation to evaporation. Our findings are
in qualitative agreement with previous results in the context of
renormalization group improved black holes, but additionally feature novel
properties reminiscent of higher-derivative operators with specific non-local
form factors.
|
[
{
"created": "Mon, 3 Oct 2022 18:00:03 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Oct 2022 19:08:30 GMT",
"version": "v2"
},
{
"created": "Tue, 21 Mar 2023 23:01:59 GMT",
"version": "v3"
},
{
"created": "Mon, 8 May 2023 13:03:41 GMT",
"version": "v4"
},
{
"created": "Tue, 23 May 2023 13:43:05 GMT",
"version": "v5"
}
] |
2023-05-24
|
[
[
"Borissova",
"Johanna N.",
""
],
[
"Platania",
"Alessia",
""
]
] |
We propose a new method to account for quantum-gravitational effects in cosmological and black hole spacetimes. At the core of our construction is the "decoupling mechanism": when a physical infrared scale overcomes the effect of the regulator implementing the Wilsonian integration of fluctuating modes, the renormalization group flow of the scale-dependent effective action freezes out, so that at the decoupling scale the latter approximates the standard quantum effective action. Identifying the decoupling scale allows to access terms in the effective action that were not part of the original truncation and thus to study leading-order quantum corrections to field equations and their solutions. Starting from the Einstein-Hilbert truncation, we exploit for the first time the decoupling mechanism in quantum gravity to investigate the dynamics of quantum-corrected black holes from formation to evaporation. Our findings are in qualitative agreement with previous results in the context of renormalization group improved black holes, but additionally feature novel properties reminiscent of higher-derivative operators with specific non-local form factors.
|
2402.18993
|
Philipp Dorau
|
Philipp Dorau, Rainer Verch
|
Kodama-like Vector Fields in Axisymmetric Spacetimes
|
24 pages, 1 figure. v2: extended analysis of Kerr-Vaidya-de Sitter,
removed misconception regarding the ADM definition of mass, minor revisions
|
Class. Quantum Grav. 41 145008 (2024)
|
10.1088/1361-6382/ad51c3
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We extend the concept of the Kodama symmetry, a quasi-local time translation
symmetry for dynamical spherically symmetric spacetimes, to a specific class of
dynamical axisymmetric spacetimes, namely the families of Kerr-Vaidya and
Kerr-Vaidya-de Sitter spacetimes. We study some geometrical properties of the
asymptotically flat Kerr-Vaidya metric, such as the Brown-York mass and the
Einstein tensor. Furthermore, we propose a generalization of the Kerr-Vaidya
metric to an asymptotic de Sitter background. We show that for these classes of
dynamical axisymmetric black hole spacetimes, there exists a timelike vector
field that exhibits similar properties to the Kodama vector field in spherical
symmetry. This includes the construction of a covariantly conserved current and
a corresponding locally conserved charge, which in the Kerr-Vaidya case
converges to the Brown-York mass in the asymptotically flat region.
|
[
{
"created": "Thu, 29 Feb 2024 09:46:37 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Jun 2024 11:41:17 GMT",
"version": "v2"
}
] |
2024-07-12
|
[
[
"Dorau",
"Philipp",
""
],
[
"Verch",
"Rainer",
""
]
] |
We extend the concept of the Kodama symmetry, a quasi-local time translation symmetry for dynamical spherically symmetric spacetimes, to a specific class of dynamical axisymmetric spacetimes, namely the families of Kerr-Vaidya and Kerr-Vaidya-de Sitter spacetimes. We study some geometrical properties of the asymptotically flat Kerr-Vaidya metric, such as the Brown-York mass and the Einstein tensor. Furthermore, we propose a generalization of the Kerr-Vaidya metric to an asymptotic de Sitter background. We show that for these classes of dynamical axisymmetric black hole spacetimes, there exists a timelike vector field that exhibits similar properties to the Kodama vector field in spherical symmetry. This includes the construction of a covariantly conserved current and a corresponding locally conserved charge, which in the Kerr-Vaidya case converges to the Brown-York mass in the asymptotically flat region.
|
1305.3260
|
Mauricio Bellini
|
Pablo Alejandro S\'anchez, Mauricio Bellini (IFIMAR - Mar del Plata
University and CONICET)
|
Inflationary dark energy from a condensate of spinors in a 5D vacuum
|
Final version to be published in a special number of IJMPD. Essay
awarded by the Gravity Research Foundation with the Honorable Mention -
Annual Essays Competition 2013
| null | null | null |
gr-qc hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
What is the physical origin of dark energy? Could this energy be originated
by other fields than the inflaton? In this work we explore the possibility that
the expansion of the universe can be driven by a condensate of spinors. These
spinors are free of interactions on 5D relativistic vacuum in an extended de
Sitter spacetime. The extra coordinate is considered as noncompact. After
making a static foliation on the extra coordinate, we obtain an effective 4D
(inflationary) de Sitter expansion which describes an inflationary universe. In
view of our results we conclude that the condensate of spinors here studied
could be an interesting candidate to explain the presence of dark energy in the
early universe.
|
[
{
"created": "Tue, 14 May 2013 19:41:08 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Jul 2013 21:06:28 GMT",
"version": "v2"
},
{
"created": "Wed, 9 Oct 2013 12:00:01 GMT",
"version": "v3"
},
{
"created": "Wed, 16 Oct 2013 22:15:53 GMT",
"version": "v4"
}
] |
2013-10-18
|
[
[
"Sánchez",
"Pablo Alejandro",
"",
"IFIMAR - Mar del Plata\n University and CONICET"
],
[
"Bellini",
"Mauricio",
"",
"IFIMAR - Mar del Plata\n University and CONICET"
]
] |
What is the physical origin of dark energy? Could this energy be originated by other fields than the inflaton? In this work we explore the possibility that the expansion of the universe can be driven by a condensate of spinors. These spinors are free of interactions on 5D relativistic vacuum in an extended de Sitter spacetime. The extra coordinate is considered as noncompact. After making a static foliation on the extra coordinate, we obtain an effective 4D (inflationary) de Sitter expansion which describes an inflationary universe. In view of our results we conclude that the condensate of spinors here studied could be an interesting candidate to explain the presence of dark energy in the early universe.
|
gr-qc/0512057
|
Diego Pavon
|
Jose P. Mimoso, Ana Nunes and Diego Pavon
|
Asymptotic behavior of the warm inflation scenario with viscous pressure
|
31 pages, 2 figures, 3 tables. PACS numbers: 98.80Cq, 47.75+f
|
Phys.Rev. D73 (2006) 023502
|
10.1103/PhysRevD.73.023502
| null |
gr-qc
| null |
We analyze the dynamics of models of warm inflation with general dissipative
effects. We consider phenomenological terms both for the inflaton decay rate
and for viscous effects within matter. We provide a classification of the
asymptotic behavior of these models and show that the existence of a late-time
scaling regime depends not only on an asymptotic behavior of the scalar field
potential, but also on an appropriate asymptotic behavior of the inflaton decay
rate. There are scaling solutions whenever the latter evolves to become
proportional to the Hubble rate of expansion regardless of the steepness of the
scalar field exponential potential. We show from thermodynamic arguments that
the scaling regime is associated to a power-law dependence of the
matter-radiation temperature on the scale factor, which allows a mild variation
of the temperature of the matter/radiation fluid. We also show that the late
time contribution of the dissipative terms alleviates the depletion of matter,
and increases the duration of inflation.
|
[
{
"created": "Fri, 9 Dec 2005 11:29:55 GMT",
"version": "v1"
}
] |
2009-11-11
|
[
[
"Mimoso",
"Jose P.",
""
],
[
"Nunes",
"Ana",
""
],
[
"Pavon",
"Diego",
""
]
] |
We analyze the dynamics of models of warm inflation with general dissipative effects. We consider phenomenological terms both for the inflaton decay rate and for viscous effects within matter. We provide a classification of the asymptotic behavior of these models and show that the existence of a late-time scaling regime depends not only on an asymptotic behavior of the scalar field potential, but also on an appropriate asymptotic behavior of the inflaton decay rate. There are scaling solutions whenever the latter evolves to become proportional to the Hubble rate of expansion regardless of the steepness of the scalar field exponential potential. We show from thermodynamic arguments that the scaling regime is associated to a power-law dependence of the matter-radiation temperature on the scale factor, which allows a mild variation of the temperature of the matter/radiation fluid. We also show that the late time contribution of the dissipative terms alleviates the depletion of matter, and increases the duration of inflation.
|
2407.18509
|
Sohan Kumar Jha
|
Sohan Kumar Jha
|
Shadow, ISCO, Quasinormal modes, Hawking spectrum, Weak Gravitational
lensing, and parameter estimation of a Schwarzschild Black Hole Surrounded by
a Dehnen Type Dark Matter Halo
|
corrected version
| null | null | null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
We consider \s black hole (BH) embedded in a Dehnen-$(1,4,0)$ type dark
matter halo (DDM) with two additional parameters - core radius $r_s$ and core
density $\rs$ apart from mass $M$. We analyze the event horizon, photon orbits,
and ISCO around DDM BHs and emphasize the impact of DDM parameters on them. Our
study reveals that the presence of dark matter (DM) favourably impacts the
radii of photon orbits, the innermost stable circular orbit (ISCO), and the
event horizon. We find the expressions for specific energy and angular momentum
for massive particles in time-like geodesics around DDM BH and investigate
their dependence on DDM parameters. We display BH shadows for various values of
core density and radius that reveal larger shadows cast by a \s BH surrounded
by DDM (SDDM) than a \s BH in vacuum (SV). We then move on to study quasinormal
modes (QNMs) with the help of the $6th$ order WKB method, the greybody factor
using the semi-analytic bounds method, and the Hawking spectrum for scalar and
electromagnetic perturbations. Core density and radius are found to have a
significant impact on QNMs. Since QNMs for scalar and electromagnetic
perturbations differ significantly, we can differentiate the two based on QNM
observation. The greybody factor increases with core density and radius,
whereas, the power emitted as Hawking radiation is adversely impacted by the
presence of DM. We then study the weak gravitational lensing using the
Gauss-Bonnet theorem and obtain the deflection angle with higher-order
correction terms. Here, we see the deflection angle gets enhanced due to DM.
Finally, we use bounds on the deviation from \s, $\delta$, reported by EHT for
$M87^*$, Keck, and VLTI observatories for $Sgr A^*$ to gauge the viability of
our model. Our model is found to be concordant with observations. This leads to
the possibility of our galactic center being surrounded by DDM.
|
[
{
"created": "Fri, 26 Jul 2024 04:33:49 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Aug 2024 06:26:04 GMT",
"version": "v2"
}
] |
2024-08-13
|
[
[
"Jha",
"Sohan Kumar",
""
]
] |
We consider \s black hole (BH) embedded in a Dehnen-$(1,4,0)$ type dark matter halo (DDM) with two additional parameters - core radius $r_s$ and core density $\rs$ apart from mass $M$. We analyze the event horizon, photon orbits, and ISCO around DDM BHs and emphasize the impact of DDM parameters on them. Our study reveals that the presence of dark matter (DM) favourably impacts the radii of photon orbits, the innermost stable circular orbit (ISCO), and the event horizon. We find the expressions for specific energy and angular momentum for massive particles in time-like geodesics around DDM BH and investigate their dependence on DDM parameters. We display BH shadows for various values of core density and radius that reveal larger shadows cast by a \s BH surrounded by DDM (SDDM) than a \s BH in vacuum (SV). We then move on to study quasinormal modes (QNMs) with the help of the $6th$ order WKB method, the greybody factor using the semi-analytic bounds method, and the Hawking spectrum for scalar and electromagnetic perturbations. Core density and radius are found to have a significant impact on QNMs. Since QNMs for scalar and electromagnetic perturbations differ significantly, we can differentiate the two based on QNM observation. The greybody factor increases with core density and radius, whereas, the power emitted as Hawking radiation is adversely impacted by the presence of DM. We then study the weak gravitational lensing using the Gauss-Bonnet theorem and obtain the deflection angle with higher-order correction terms. Here, we see the deflection angle gets enhanced due to DM. Finally, we use bounds on the deviation from \s, $\delta$, reported by EHT for $M87^*$, Keck, and VLTI observatories for $Sgr A^*$ to gauge the viability of our model. Our model is found to be concordant with observations. This leads to the possibility of our galactic center being surrounded by DDM.
|
gr-qc/9304037
| null |
L. Diosi and B. Lukacs
|
Calculation of X-Ray Signals from Karolyhazy Hazy Space-Time
|
7 pages, PlainTeX
|
Phys.Lett. 181A (1993) 366-368
|
10.1016/0375-9601(93)90389-H
| null |
gr-qc
| null |
Karolyhazy's hazy space-time model, invented for breaking down macroscopic
interferences, employs wave-like gravity disturbances. If so, then electric
charges would radiate permanently. Here we discuss the observational
consequences of the radiation. We find that such radiation is excluded by
common experimental situations.
|
[
{
"created": "Sat, 24 Apr 1993 00:09:00 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Diosi",
"L.",
""
],
[
"Lukacs",
"B.",
""
]
] |
Karolyhazy's hazy space-time model, invented for breaking down macroscopic interferences, employs wave-like gravity disturbances. If so, then electric charges would radiate permanently. Here we discuss the observational consequences of the radiation. We find that such radiation is excluded by common experimental situations.
|
gr-qc/0008059
|
Innocenzo M. Pinto
|
R.P. Croce, Th. Demma, V.Pierro, I.M. Pinto, D. Churches, B.S.
Sathyaprakash
|
Gravitational Wave Chirp Search: Economization of PN Matched Filter Bank
via Cardinal Interpolation
|
scheduled for publicatin on Phys. Rev. D 62
|
Phys.Rev.D62:121101,2000
|
10.1103/PhysRevD.62.121101
| null |
gr-qc
| null |
The final inspiral phase in the evolution of a compact binary consisting of
black holes and/or neutron stars is among the most probable events that a
network of ground-based interferometric gravitational wave detectors is likely
to observe. Gravitational radiation emitted during this phase will have to be
dug out of noise by matched-filtering (correlating) the detector output with a
bank of several $10^5$ templates, making the computational resources required
quite demanding, though not formidable. We propose an interpolation method for
evaluating the correlation between template waveforms and the detector output
and show that the method is effective in substantially reducing the number of
templates required. Indeed, the number of templates needed could be a factor
$\sim 4$ smaller than required by the usual approach, when the minimal overlap
between the template bank and an arbitrary signal (the so-called {\it minimal
match}) is 0.97. The method is amenable to easy implementation, and the various
detector projects might benefit by adopting it to reduce the computational
costs of inspiraling neutron star and black hole binary search.
|
[
{
"created": "Thu, 24 Aug 2000 13:28:05 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Sep 2000 11:22:13 GMT",
"version": "v2"
}
] |
2009-12-30
|
[
[
"Croce",
"R. P.",
""
],
[
"Demma",
"Th.",
""
],
[
"Pierro",
"V.",
""
],
[
"Pinto",
"I. M.",
""
],
[
"Churches",
"D.",
""
],
[
"Sathyaprakash",
"B. S.",
""
]
] |
The final inspiral phase in the evolution of a compact binary consisting of black holes and/or neutron stars is among the most probable events that a network of ground-based interferometric gravitational wave detectors is likely to observe. Gravitational radiation emitted during this phase will have to be dug out of noise by matched-filtering (correlating) the detector output with a bank of several $10^5$ templates, making the computational resources required quite demanding, though not formidable. We propose an interpolation method for evaluating the correlation between template waveforms and the detector output and show that the method is effective in substantially reducing the number of templates required. Indeed, the number of templates needed could be a factor $\sim 4$ smaller than required by the usual approach, when the minimal overlap between the template bank and an arbitrary signal (the so-called {\it minimal match}) is 0.97. The method is amenable to easy implementation, and the various detector projects might benefit by adopting it to reduce the computational costs of inspiraling neutron star and black hole binary search.
|
gr-qc/9903084
|
Gerard 't Hooft
|
Gerard 't Hooft
|
Quantum Gravity as a Dissipative Deterministic System
|
20 pages plain TeX, 2 figures PostScript. Added some further
explanations, and the definitions of `beable' and `changeable'. A minor error
corrected
|
Class.Quant.Grav.16:3263-3279,1999
|
10.1088/0264-9381/16/10/316
|
THU-99/07
|
gr-qc hep-th quant-ph
| null |
It is argued that the so-called holographic principle will obstruct attempts
to produce physically realistic models for the unification of general
relativity with quantum mechanics, unless determinism in the latter is
restored. The notion of time in GR is so different from the usual one in
elementary particle physics that we believe that certain versions of hidden
variable theories can -- and must -- be revived. A completely natural procedure
is proposed, in which the dissipation of information plays an essential role.
Unlike earlier attempts, it allows us to use strictly continuous and
differentiable classical field theories as a starting point (although discrete
variables, leading to fermionic degrees of freedom, are also welcome), and we
show how an effective Hilbert space of quantum states naturally emerges when
one attempts to describe the solutions statistically. Our theory removes some
of the mysteries of the holographic principle; apparently non-local features
are to be expected when the quantum degrees of freedom of the world are
projected onto a lower-dimensional black hole horizon. Various examples and
models illustrate the points we wish to make, notably a model showing that
massless, non interacting neutrinos are deterministic.
|
[
{
"created": "Mon, 22 Mar 1999 17:13:30 GMT",
"version": "v1"
},
{
"created": "Tue, 23 Mar 1999 11:53:41 GMT",
"version": "v2"
},
{
"created": "Thu, 1 Apr 1999 15:52:56 GMT",
"version": "v3"
}
] |
2008-11-26
|
[
[
"Hooft",
"Gerard 't",
""
]
] |
It is argued that the so-called holographic principle will obstruct attempts to produce physically realistic models for the unification of general relativity with quantum mechanics, unless determinism in the latter is restored. The notion of time in GR is so different from the usual one in elementary particle physics that we believe that certain versions of hidden variable theories can -- and must -- be revived. A completely natural procedure is proposed, in which the dissipation of information plays an essential role. Unlike earlier attempts, it allows us to use strictly continuous and differentiable classical field theories as a starting point (although discrete variables, leading to fermionic degrees of freedom, are also welcome), and we show how an effective Hilbert space of quantum states naturally emerges when one attempts to describe the solutions statistically. Our theory removes some of the mysteries of the holographic principle; apparently non-local features are to be expected when the quantum degrees of freedom of the world are projected onto a lower-dimensional black hole horizon. Various examples and models illustrate the points we wish to make, notably a model showing that massless, non interacting neutrinos are deterministic.
|
1710.02807
|
Daniele Oriti
|
Daniele Oriti
|
Spacetime as a quantum many-body system
|
15 pages; invited contribution to "Many-body approaches at different
scales: A tribute to Norman H. March on the occasion of his 90th birthday",
edited by G. G. N. Angilella and C. Amovilli (New York, Springer, 2017 - to
appear)
| null | null | null |
gr-qc cond-mat.other hep-th physics.hist-ph physics.pop-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Quantum gravity has become a fertile interface between gravitational physics
and quantum many-body physics, with its double goal of identifying the
microscopic constituents of the universe and their fundamental dynamics, and of
understanding their collective properties and how spacetime and geometry
themselves emerge from them at macroscopic scales. In this brief contribution,
we outline the problem of quantum gravity from this emergent spacetime
perspective, and discuss some examples in which ideas and methods from quantum
many-body systems have found a central role in quantum gravity research.
|
[
{
"created": "Sun, 8 Oct 2017 09:09:32 GMT",
"version": "v1"
}
] |
2017-10-10
|
[
[
"Oriti",
"Daniele",
""
]
] |
Quantum gravity has become a fertile interface between gravitational physics and quantum many-body physics, with its double goal of identifying the microscopic constituents of the universe and their fundamental dynamics, and of understanding their collective properties and how spacetime and geometry themselves emerge from them at macroscopic scales. In this brief contribution, we outline the problem of quantum gravity from this emergent spacetime perspective, and discuss some examples in which ideas and methods from quantum many-body systems have found a central role in quantum gravity research.
|
2002.10659
|
Matt Visser
|
Thomas Berry (Victoria University of Wellington) and Matt Visser
(Victoria University of Wellington)
|
Relativistic combination of non-collinear 3-velocities using quaternions
|
V1: 13 pages. V2: now 17 pages. Four new references, four new pages
of discussion (relativistic combination of three 3-velocities)
| null | null | null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Quaternions have an (over a century-old) extensive and quite complicated
interaction with special relativity. Since quaternions are intrinsically
4-dimensional, and do such a good job of handling 3-dimensional rotations, the
hope has always been that the use of quaternions would simplify some of the
algebra of the Lorentz transformations. Herein we report a relatively nice
result for the relativistic combination of non-collinear 3-velocities. If we
work with the relativistic half-velocities $w$ defined by $v={2w\over1+w^2}$,
and promote them to quaternions using $\mathbf{w} = w \; \mathbf{\hat n}$,
where $\mathbf{\hat n}$ is a unit quaternion, then we shall show \[
\mathbf{w}_{1\oplus2} = \mathbf{w}_1 \oplus \mathbf{w}_2
=(1-\mathbf{w}_1\mathbf{w}_2)^{-1} (\mathbf{w}_1 +\mathbf{w}_2) = (\mathbf{w}_1
+\mathbf{w}_2)(1-\mathbf{w}_2\mathbf{w}_1)^{-1}. \] All of the complicated
angular dependence for relativistic combination of non-collinear 3-velocities
is now encoded in the quaternion multiplication of $\mathbf{w}_1$ with
$\mathbf{w}_2$. This result can furthermore be extended to obtain an elegant
and compact formula for the associated Wigner angle: \[
\mathrm{e}^{\mathbf{\Omega}} = \mathrm{e}^{\Omega \; \mathbf{\hat\Omega} } =
(1-\mathbf{w}_1\mathbf{w}_2)^{-1} (1-\mathbf{w}_2\mathbf{w}_1), \] in terms of
which \[ {\mathbf{\hat{n}}}_{1\oplus2} = \mathrm{e}^{\mathbf{\Omega}/2} \;\;
{\mathbf{w}_1+\mathbf{w}_2\over |\mathbf{w}_1+\mathbf{w}_2|}; \qquad\qquad
{\mathbf{\hat{n}}}_{2\oplus1} = \mathrm{e}^{-\mathbf{\Omega}/2} \;\;
{\mathbf{w}_1+\mathbf{w}_2\over |\mathbf{w}_1+\mathbf{w}_2|}. \] Thus, we would
argue, many key results that are ultimately due to the non-commutativity of
non-collinear boosts can be easily rephrased in terms of the algebra of
quaternions.
|
[
{
"created": "Tue, 25 Feb 2020 04:09:08 GMT",
"version": "v1"
},
{
"created": "Fri, 13 Mar 2020 09:11:18 GMT",
"version": "v2"
}
] |
2020-03-16
|
[
[
"Berry",
"Thomas",
"",
"Victoria University of Wellington"
],
[
"Visser",
"Matt",
"",
"Victoria University of Wellington"
]
] |
Quaternions have an (over a century-old) extensive and quite complicated interaction with special relativity. Since quaternions are intrinsically 4-dimensional, and do such a good job of handling 3-dimensional rotations, the hope has always been that the use of quaternions would simplify some of the algebra of the Lorentz transformations. Herein we report a relatively nice result for the relativistic combination of non-collinear 3-velocities. If we work with the relativistic half-velocities $w$ defined by $v={2w\over1+w^2}$, and promote them to quaternions using $\mathbf{w} = w \; \mathbf{\hat n}$, where $\mathbf{\hat n}$ is a unit quaternion, then we shall show \[ \mathbf{w}_{1\oplus2} = \mathbf{w}_1 \oplus \mathbf{w}_2 =(1-\mathbf{w}_1\mathbf{w}_2)^{-1} (\mathbf{w}_1 +\mathbf{w}_2) = (\mathbf{w}_1 +\mathbf{w}_2)(1-\mathbf{w}_2\mathbf{w}_1)^{-1}. \] All of the complicated angular dependence for relativistic combination of non-collinear 3-velocities is now encoded in the quaternion multiplication of $\mathbf{w}_1$ with $\mathbf{w}_2$. This result can furthermore be extended to obtain an elegant and compact formula for the associated Wigner angle: \[ \mathrm{e}^{\mathbf{\Omega}} = \mathrm{e}^{\Omega \; \mathbf{\hat\Omega} } = (1-\mathbf{w}_1\mathbf{w}_2)^{-1} (1-\mathbf{w}_2\mathbf{w}_1), \] in terms of which \[ {\mathbf{\hat{n}}}_{1\oplus2} = \mathrm{e}^{\mathbf{\Omega}/2} \;\; {\mathbf{w}_1+\mathbf{w}_2\over |\mathbf{w}_1+\mathbf{w}_2|}; \qquad\qquad {\mathbf{\hat{n}}}_{2\oplus1} = \mathrm{e}^{-\mathbf{\Omega}/2} \;\; {\mathbf{w}_1+\mathbf{w}_2\over |\mathbf{w}_1+\mathbf{w}_2|}. \] Thus, we would argue, many key results that are ultimately due to the non-commutativity of non-collinear boosts can be easily rephrased in terms of the algebra of quaternions.
|
1506.00927
|
Carlo Rovelli
|
Carlo Rovelli
|
The strange equation of quantum gravity
|
Appeared in the Classical and Quantum Gravity Focus issue: Milestones
of general relativity. 7 pages
|
Class. Quantum Grav. 32 (2015) 124005
|
10.1088/0264-9381/32/12/124005
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Disavowed by one its fathers, ill defined, never empirically tested, the
Wheeler-DeWitt equation has nevertheless had a powerful influence on
fundamental physics. A well deserved one.
|
[
{
"created": "Tue, 2 Jun 2015 15:36:51 GMT",
"version": "v1"
}
] |
2015-06-17
|
[
[
"Rovelli",
"Carlo",
""
]
] |
Disavowed by one its fathers, ill defined, never empirically tested, the Wheeler-DeWitt equation has nevertheless had a powerful influence on fundamental physics. A well deserved one.
|
1403.5988
|
Markus Lazar
|
Congrui Jin, Markus Lazar
|
A note on Lorentz-like transformations and superluminal motion
|
9 pages, 1 figure
| null |
10.1002/zamm.201300162
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this extended note a critical discussion of an extension of the Lorentz
transformations for velocities faster than the speed of light given recently by
Hill and Cox is provided. The presented approach reveals the connection between
faster-than-light speeds and the issue of isotropy of space. It is shown if the
relative speed between the two inertial frames $v$ is greater than the speed of
light, the condition of isotropy of space cannot be retained. It further
specifies the respective transformations applying to $-\infty<v<-c$ and
$c<v<+\infty$. It is proved that such Lorentz-like transformations are improper
transformations since the Jacobian is negative. As a consequence, the wave
operator, the light-cone and the volume element are not invariant under such
Lorentz-like transformations. Also it is shown that such Lorentz-like
transformations are not new and already known in the literature.
|
[
{
"created": "Mon, 24 Mar 2014 15:09:35 GMT",
"version": "v1"
},
{
"created": "Mon, 14 Apr 2014 16:56:30 GMT",
"version": "v2"
}
] |
2014-04-15
|
[
[
"Jin",
"Congrui",
""
],
[
"Lazar",
"Markus",
""
]
] |
In this extended note a critical discussion of an extension of the Lorentz transformations for velocities faster than the speed of light given recently by Hill and Cox is provided. The presented approach reveals the connection between faster-than-light speeds and the issue of isotropy of space. It is shown if the relative speed between the two inertial frames $v$ is greater than the speed of light, the condition of isotropy of space cannot be retained. It further specifies the respective transformations applying to $-\infty<v<-c$ and $c<v<+\infty$. It is proved that such Lorentz-like transformations are improper transformations since the Jacobian is negative. As a consequence, the wave operator, the light-cone and the volume element are not invariant under such Lorentz-like transformations. Also it is shown that such Lorentz-like transformations are not new and already known in the literature.
|
gr-qc/0210108
|
I. B. Khriplovich
|
I.B. Khriplovich
|
How Are Black Holes Quantized?
|
Talk at XXXVI Winter School of Petersburg Institute of Nuclear
Physics, Sanct-Petersburg, Februrary 2002
| null | null | null |
gr-qc hep-th
| null |
Some approaches to quantization of the horizon area of black holes are
discussed. The maximum entropy of a quantized surface is demonstrated to be
proportional to the surface area in the classical limit. This result is valid
for a rather general class of approaches to surface quantization. In the case
of rotating black holes no satisfactory solution for the quantization problem
has been found up to now.
|
[
{
"created": "Thu, 31 Oct 2002 06:30:45 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Khriplovich",
"I. B.",
""
]
] |
Some approaches to quantization of the horizon area of black holes are discussed. The maximum entropy of a quantized surface is demonstrated to be proportional to the surface area in the classical limit. This result is valid for a rather general class of approaches to surface quantization. In the case of rotating black holes no satisfactory solution for the quantization problem has been found up to now.
|
1309.3523
|
Adam Kelleher
|
Adam Kelleher
|
Dark Energy and Dark Matter in $f(R)$ Gravity and an Alternative
Chameleon Mechanism
| null | null | null | null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Metric $f(R)$ gravity theories behave like GR with cosmological constant when
$f"(R)$ = 0, and like scalar-tensor theories elsewhere. I investigate the
transition from $f"(R) \neq 0$ to $f"(R) = 0$, and show that this theory may
offer a way to explain Dark Energy and/or Dark Matter without having to make
use of the chameleon mechanism to agree with solar system tests.
|
[
{
"created": "Fri, 13 Sep 2013 17:43:51 GMT",
"version": "v1"
}
] |
2013-09-16
|
[
[
"Kelleher",
"Adam",
""
]
] |
Metric $f(R)$ gravity theories behave like GR with cosmological constant when $f"(R)$ = 0, and like scalar-tensor theories elsewhere. I investigate the transition from $f"(R) \neq 0$ to $f"(R) = 0$, and show that this theory may offer a way to explain Dark Energy and/or Dark Matter without having to make use of the chameleon mechanism to agree with solar system tests.
|
gr-qc/9506077
|
Roberto Gomez
|
Simonetta Frittelli and Oscar Reula
|
On the Newtonian Limit of General Relativity
|
16 pages, uses REVTeX
|
Commun.Math.Phys. 166 (1994) 221
|
10.1007/BF02112314
| null |
gr-qc
| null |
We find a choice of variables for the 3+1 formulation of general relativity
which casts the evolution equations into (flux-conservative)
symmetric-hyperbolic first order form for arbitrary lapse and shift, for the
first time. We redefine the lapse function in terms of the determinant of the
3-metric and a free function U which embodies the lapse freedom. By rescaling
the variables with appropriate factors of 1/c, the system is shown to have a
smooth Newtonian limit when the redefined lapse U and the shift are fixed by
means of elliptic equations to be satisfied on each time slice. We give a
prescription for the choice of appropriate initial data with controlled
extra-radiation content, based on the theory of problems with different
time-scales. Our results are local, in the sense that we are not concerned with
the treatment of asymptotic regions. On the other hand, this local theory is
all what is needed for most problems of practical numerical computation.
|
[
{
"created": "Thu, 29 Jun 1995 19:33:46 GMT",
"version": "v1"
}
] |
2009-10-28
|
[
[
"Frittelli",
"Simonetta",
""
],
[
"Reula",
"Oscar",
""
]
] |
We find a choice of variables for the 3+1 formulation of general relativity which casts the evolution equations into (flux-conservative) symmetric-hyperbolic first order form for arbitrary lapse and shift, for the first time. We redefine the lapse function in terms of the determinant of the 3-metric and a free function U which embodies the lapse freedom. By rescaling the variables with appropriate factors of 1/c, the system is shown to have a smooth Newtonian limit when the redefined lapse U and the shift are fixed by means of elliptic equations to be satisfied on each time slice. We give a prescription for the choice of appropriate initial data with controlled extra-radiation content, based on the theory of problems with different time-scales. Our results are local, in the sense that we are not concerned with the treatment of asymptotic regions. On the other hand, this local theory is all what is needed for most problems of practical numerical computation.
|
1007.2734
|
Miquel Pinyol Ribas
|
Miquel Pinyol Ribas, Ignacio Lopez Aylagas
|
Transition from Established Stationary Vision of Black Holes to
Never-Stationary Gravitational Collapse
|
11 pages, 2 figures
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The established concept of black hole emerged from several results founded on
Einstein's General Theory of Relativity. In this article, the relationship
between these results is analyzed, and it is pointed out how, in spite of being
individually correct, the sum of all them do not actually determine the
existence of black holes. Some logical incompatibilities in the standard Black
Hole model are put into evidence, and the alternative scheme of the
Never-Stationary Gravitational Collapse is defended. To illustrate the essence
of the new paradigm, a simple but conceptually complete toy model is worked out
and a qualitatively suitable metric for Never-Stationary Gravitational Collapse
is presented.
|
[
{
"created": "Fri, 16 Jul 2010 10:27:59 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Jul 2010 15:14:18 GMT",
"version": "v2"
}
] |
2010-07-27
|
[
[
"Ribas",
"Miquel Pinyol",
""
],
[
"Aylagas",
"Ignacio Lopez",
""
]
] |
The established concept of black hole emerged from several results founded on Einstein's General Theory of Relativity. In this article, the relationship between these results is analyzed, and it is pointed out how, in spite of being individually correct, the sum of all them do not actually determine the existence of black holes. Some logical incompatibilities in the standard Black Hole model are put into evidence, and the alternative scheme of the Never-Stationary Gravitational Collapse is defended. To illustrate the essence of the new paradigm, a simple but conceptually complete toy model is worked out and a qualitatively suitable metric for Never-Stationary Gravitational Collapse is presented.
|
gr-qc/9609038
|
65247
|
I-Ching Yang, Ching-Tzung Yeh, Rue-Ron Hsu and Chin-Rong Lee
|
On the energy of a charged dilaton black hole
|
12 pages, 6 figures, LaTeX
|
Int.J.Mod.Phys. D6 (1997) 349-356
|
10.1142/S0218271897000194
|
NCKU-HEP/96-03
|
gr-qc
| null |
Employing energy-momentum pseudotensor of Einstein, we obtian the energy
distribution of a dyonic dilaton black hole. The energy distribution of this
black hole depends on mass $ M $, electric charge $ Q_{e} $, magnetic charge $
Q_{m} $ and asymptotic values of the dilaton $ \phi_{0} $. We also mmake some
comparisons between the results of Virbhadra et. al. and ours.
|
[
{
"created": "Fri, 13 Sep 1996 21:50:42 GMT",
"version": "v1"
}
] |
2009-10-28
|
[
[
"Yang",
"I-Ching",
""
],
[
"Yeh",
"Ching-Tzung",
""
],
[
"Hsu",
"Rue-Ron",
""
],
[
"Lee",
"Chin-Rong",
""
]
] |
Employing energy-momentum pseudotensor of Einstein, we obtian the energy distribution of a dyonic dilaton black hole. The energy distribution of this black hole depends on mass $ M $, electric charge $ Q_{e} $, magnetic charge $ Q_{m} $ and asymptotic values of the dilaton $ \phi_{0} $. We also mmake some comparisons between the results of Virbhadra et. al. and ours.
|
1508.01510
|
Harald Skarke
|
Harald Skarke
|
Cosmic Acceleration as an Optical Illusion
|
34 pages, 7 figures; v2: references added; v3: stronger
modifications, particularly in the discussion section concerning the
reliability of results
| null | null |
TUW-15-14
|
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider light propagation in an inhomogeneous irrotational dust universe
with vanishing cosmological constant, with initial conditions as in standard
linear perturbation theory. A non-perturbative approach to the dynamics of such
a universe is combined with a distance formula based on the Sachs optical
equations. Then a numerical study implies a redshift-distance relation that
roughly agrees with observations. Interpreted in the standard homogeneous
setup, our results would appear to imply the currently accepted values for the
Hubble rate and the deceleration parameter; furthermore there is consistency
with density perturbations at last scattering. The determination of these three
quantities relies only on a single parameter related to a cutoff scale.
Discrepancies with the existing literature are related to subtleties of higher
order perturbation theory which make both the reliability of the present
approach and the magnitude of perturbative effects beyond second order hard to
assess.
|
[
{
"created": "Thu, 6 Aug 2015 12:19:45 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Aug 2015 11:13:49 GMT",
"version": "v2"
},
{
"created": "Thu, 29 Sep 2016 12:45:07 GMT",
"version": "v3"
}
] |
2016-09-30
|
[
[
"Skarke",
"Harald",
""
]
] |
We consider light propagation in an inhomogeneous irrotational dust universe with vanishing cosmological constant, with initial conditions as in standard linear perturbation theory. A non-perturbative approach to the dynamics of such a universe is combined with a distance formula based on the Sachs optical equations. Then a numerical study implies a redshift-distance relation that roughly agrees with observations. Interpreted in the standard homogeneous setup, our results would appear to imply the currently accepted values for the Hubble rate and the deceleration parameter; furthermore there is consistency with density perturbations at last scattering. The determination of these three quantities relies only on a single parameter related to a cutoff scale. Discrepancies with the existing literature are related to subtleties of higher order perturbation theory which make both the reliability of the present approach and the magnitude of perturbative effects beyond second order hard to assess.
|
1011.2036
|
Li Zhengxiang
|
Zhengxiang Li, Puxun Wu, Hongwei Yu
|
Probing the course of cosmic expansion with a combination of
observational data
|
19 pages, 6 figures, accepted for publication in JCAP
|
JCAP 1011:031,2010
|
10.1088/1475-7516/2010/11/031
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the cosmic expansion history by reconstructing the deceleration
parameter $q(z)$ from the SDSS-II type Ia supernova sample (SNIa) with two
different light curve fits (MLCS2k2 and SALT-II), the baryon acoustic
oscillation (BAO) distance ratio, the cosmic microwave background (CMB) shift
parameter, and the lookback time-redshift (LT) from the age of old passive
galaxies. Three parametrization forms for the equation of state of dark energy
(CPL, JBP, and UIS) are considered. Our results show that, for the CPL and the
UIS forms, MLCS2k2 SDSS-II SNIa+BAO+CMB and MLCS2k2 SDSS-II SNIa+BAO+CMB+LT
favor a currently slowing-down cosmic acceleration, but this does not occur for
all other cases, where an increasing cosmic acceleration is still favored.
Thus, the reconstructed evolutionary behaviors of dark energy and the course of
the cosmic acceleration are highly dependent both on the light curve fitting
method for the SNIa and the parametrization form for the equation of state of
dark energy.
|
[
{
"created": "Tue, 9 Nov 2010 10:49:21 GMT",
"version": "v1"
}
] |
2011-05-10
|
[
[
"Li",
"Zhengxiang",
""
],
[
"Wu",
"Puxun",
""
],
[
"Yu",
"Hongwei",
""
]
] |
We study the cosmic expansion history by reconstructing the deceleration parameter $q(z)$ from the SDSS-II type Ia supernova sample (SNIa) with two different light curve fits (MLCS2k2 and SALT-II), the baryon acoustic oscillation (BAO) distance ratio, the cosmic microwave background (CMB) shift parameter, and the lookback time-redshift (LT) from the age of old passive galaxies. Three parametrization forms for the equation of state of dark energy (CPL, JBP, and UIS) are considered. Our results show that, for the CPL and the UIS forms, MLCS2k2 SDSS-II SNIa+BAO+CMB and MLCS2k2 SDSS-II SNIa+BAO+CMB+LT favor a currently slowing-down cosmic acceleration, but this does not occur for all other cases, where an increasing cosmic acceleration is still favored. Thus, the reconstructed evolutionary behaviors of dark energy and the course of the cosmic acceleration are highly dependent both on the light curve fitting method for the SNIa and the parametrization form for the equation of state of dark energy.
|
1803.10066
|
Jian-Yang Zhu
|
Yang-Yang Wang, Jian-Yang Zhu and Xiao-Min Zhang
|
Two-field Warm Inflation and Its Scalar Perturbations on Large Scales
|
10 pages, 4 figures
|
Phys. Rev. D 97, 063510 (2018)
|
10.1103/PhysRevD.97.063510
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We explore the homogeneous background dynamics and the evolution of generated
perturbations of cosmological inflation that is driven by multiple scalar
fields interacting with a perfect fluid.Then we apply the method to warm
inflation driven by two scalar fields and a radiation fluid, and present
general results about the evolution of the inflaton and radiation. After
decomposing the perturbations into adiabatic and entropy modes, we give the
equation of motion of adiabatic and entropy perturbations on large scales.
Then, we give numerical results of background and perturbation equations in a
concrete model (the dissipative coefficient $\Gamma \propto H$). At last, we
use the most recent observational data to constrain our models and give the
observationally allowed regions of parameters. This work is a natural extension
of warm inflation to multi-field cases.
|
[
{
"created": "Tue, 27 Mar 2018 13:31:08 GMT",
"version": "v1"
}
] |
2018-04-04
|
[
[
"Wang",
"Yang-Yang",
""
],
[
"Zhu",
"Jian-Yang",
""
],
[
"Zhang",
"Xiao-Min",
""
]
] |
We explore the homogeneous background dynamics and the evolution of generated perturbations of cosmological inflation that is driven by multiple scalar fields interacting with a perfect fluid.Then we apply the method to warm inflation driven by two scalar fields and a radiation fluid, and present general results about the evolution of the inflaton and radiation. After decomposing the perturbations into adiabatic and entropy modes, we give the equation of motion of adiabatic and entropy perturbations on large scales. Then, we give numerical results of background and perturbation equations in a concrete model (the dissipative coefficient $\Gamma \propto H$). At last, we use the most recent observational data to constrain our models and give the observationally allowed regions of parameters. This work is a natural extension of warm inflation to multi-field cases.
|
gr-qc/0403108
|
Mehmet Cem Calik
|
M. Arik and M. C. Calik
|
Primordial and asymptotic inflation in Brans-Dicke cosmology
|
7 pages, no figures
|
JCAP 0501 (2005) 013
|
10.1088/1475-7516/2005/01/013
| null |
gr-qc
| null |
The basic motivation of this work is to attempt to explain the rapid
primordial inflation and the observed slow late-time inflation by using the
Brans-Dicke theory of gravity. We show that the ratio of these two inflation
parameters is proportional to the square root of the Brans-Dicke parameter $%
\omega$ $(\omega\gg1) $. We also calculate the Hubble parameter $% H$ and the
time variation of the time dependent Newtonian gravitational constant $G$ for
both regimes. The variation of the Hubble parameter predicted by Brans-Dicke
cosmology is shown to be consistent with recent measurements: The value of $H$
in the late-time future is predicted as 0.86 times the present value of $H$.
|
[
{
"created": "Fri, 26 Mar 2004 16:06:57 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Dec 2005 20:36:35 GMT",
"version": "v2"
}
] |
2009-11-10
|
[
[
"Arik",
"M.",
""
],
[
"Calik",
"M. C.",
""
]
] |
The basic motivation of this work is to attempt to explain the rapid primordial inflation and the observed slow late-time inflation by using the Brans-Dicke theory of gravity. We show that the ratio of these two inflation parameters is proportional to the square root of the Brans-Dicke parameter $% \omega$ $(\omega\gg1) $. We also calculate the Hubble parameter $% H$ and the time variation of the time dependent Newtonian gravitational constant $G$ for both regimes. The variation of the Hubble parameter predicted by Brans-Dicke cosmology is shown to be consistent with recent measurements: The value of $H$ in the late-time future is predicted as 0.86 times the present value of $H$.
|
1903.00287
|
Haruka Suzuki
|
Haruka Suzuki, Priti Gupta, Hirotada Okawa and Kei-ichi Maeda
|
Cumulative Shift of Periastron Time of Binary Pulsar with Kozai-Lidov
Oscillation
|
6 pages, 3 figures, accepted by MNRAS letters
| null |
10.1093/mnrasl/slz058
| null |
gr-qc astro-ph.SR
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study a hierarchical triple system with the Kozai-Lidov mechanism, and
analyse the cumulative shift of periastron time of a binary pulsar by the
emission of gravitational waves. Time evolution of the osculating orbital
elements of the triple system is calculated by directly integrating the
first-order post-Newtonian equations of motion. The Kozai-Lidov mechanism will
bend the evolution curve of the cumulative shift when the eccentricity becomes
large. We also investigate the parameter range of mass and semi-major axis of
the third companion with which the bending of the cumulative-shift curve could
occur within 100 years.
|
[
{
"created": "Fri, 1 Mar 2019 13:28:16 GMT",
"version": "v1"
},
{
"created": "Fri, 26 Apr 2019 14:44:26 GMT",
"version": "v2"
}
] |
2019-05-08
|
[
[
"Suzuki",
"Haruka",
""
],
[
"Gupta",
"Priti",
""
],
[
"Okawa",
"Hirotada",
""
],
[
"Maeda",
"Kei-ichi",
""
]
] |
We study a hierarchical triple system with the Kozai-Lidov mechanism, and analyse the cumulative shift of periastron time of a binary pulsar by the emission of gravitational waves. Time evolution of the osculating orbital elements of the triple system is calculated by directly integrating the first-order post-Newtonian equations of motion. The Kozai-Lidov mechanism will bend the evolution curve of the cumulative shift when the eccentricity becomes large. We also investigate the parameter range of mass and semi-major axis of the third companion with which the bending of the cumulative-shift curve could occur within 100 years.
|
2303.08183
|
Andrea Maselli
|
Enzo Figueiredo, Andrea Maselli, Vitor Cardoso
|
Black holes surrounded by generic dark matter profiles: appearance and
gravitational-wave emission
|
8 pages, 5 figures
| null |
10.1103/PhysRevD.107.104033
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We develop a numerical approach to find asymptotically flat black hole
solutions coupled to anisotropic fluids, described by generic density profiles.
Our model allows for a variety of applications in realistic astrophysical
scenarios, and is potentially able to describe the geometry of galaxies hosting
supermassive black holes, dark matter environments and accretion phenomena. We
apply our framework to a black hole surrounded by different families of dark
matter profiles, namely the Hernquist, the Navarro-Frenk White and the Einasto
models. We study the geodesic motion of light and of massive particles in such
spacetimes. Moreover we compute gravitational axial perturbations induced by a
small secondary on the numerical background, and determine the changes in the
emitted gravitational wave fluxes compared to the vacuum case. Our analysis
confirms and extend previous studies showing that modifications of orbital
frequencies and axial fluxes can be described in terms of
gravitational-redshift, regardless of the halo model.
|
[
{
"created": "Tue, 14 Mar 2023 19:00:02 GMT",
"version": "v1"
}
] |
2023-05-24
|
[
[
"Figueiredo",
"Enzo",
""
],
[
"Maselli",
"Andrea",
""
],
[
"Cardoso",
"Vitor",
""
]
] |
We develop a numerical approach to find asymptotically flat black hole solutions coupled to anisotropic fluids, described by generic density profiles. Our model allows for a variety of applications in realistic astrophysical scenarios, and is potentially able to describe the geometry of galaxies hosting supermassive black holes, dark matter environments and accretion phenomena. We apply our framework to a black hole surrounded by different families of dark matter profiles, namely the Hernquist, the Navarro-Frenk White and the Einasto models. We study the geodesic motion of light and of massive particles in such spacetimes. Moreover we compute gravitational axial perturbations induced by a small secondary on the numerical background, and determine the changes in the emitted gravitational wave fluxes compared to the vacuum case. Our analysis confirms and extend previous studies showing that modifications of orbital frequencies and axial fluxes can be described in terms of gravitational-redshift, regardless of the halo model.
|
2112.14777
|
Giovanni Maria Tomaselli
|
Daniel Baumann, Gianfranco Bertone, John Stout, and Giovanni Maria
Tomaselli
|
Ionization of Gravitational Atoms
|
34+21 pages, 16 figures
| null |
10.1103/PhysRevD.105.115036
| null |
gr-qc hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Superradiant instabilities may create clouds of ultralight bosons around
rotating black holes, forming so-called "gravitational atoms." It was recently
shown that the presence of a binary companion can induce resonant transitions
between bound states of these clouds, whose backreaction on the binary's orbit
leads to characteristic signatures in the emitted gravitational waves. In this
work, we show that the interaction with the companion can also trigger
transitions from bound to unbound states of the cloud -- a process that we
refer to as "ionization" in analogy with the photoelectric effect in atomic
physics. The orbital energy lost in the process overwhelms the losses due to
gravitational wave emission and contains sharp features carrying information
about the energy spectrum of the cloud. Moreover, we also show that if the
companion is a black hole, then the part of the cloud impinging on the event
horizon will be absorbed. This "accretion" leads to a significant increase of
the companion's mass, which alters the dynamical evolution and ensuing waveform
of the binary. We argue that a combined treatment of resonances, ionization,
and accretion is crucial to discover and characterize gravitational atoms with
upcoming gravitational wave detectors.
|
[
{
"created": "Wed, 29 Dec 2021 19:00:00 GMT",
"version": "v1"
},
{
"created": "Mon, 6 Jun 2022 09:29:40 GMT",
"version": "v2"
}
] |
2022-07-13
|
[
[
"Baumann",
"Daniel",
""
],
[
"Bertone",
"Gianfranco",
""
],
[
"Stout",
"John",
""
],
[
"Tomaselli",
"Giovanni Maria",
""
]
] |
Superradiant instabilities may create clouds of ultralight bosons around rotating black holes, forming so-called "gravitational atoms." It was recently shown that the presence of a binary companion can induce resonant transitions between bound states of these clouds, whose backreaction on the binary's orbit leads to characteristic signatures in the emitted gravitational waves. In this work, we show that the interaction with the companion can also trigger transitions from bound to unbound states of the cloud -- a process that we refer to as "ionization" in analogy with the photoelectric effect in atomic physics. The orbital energy lost in the process overwhelms the losses due to gravitational wave emission and contains sharp features carrying information about the energy spectrum of the cloud. Moreover, we also show that if the companion is a black hole, then the part of the cloud impinging on the event horizon will be absorbed. This "accretion" leads to a significant increase of the companion's mass, which alters the dynamical evolution and ensuing waveform of the binary. We argue that a combined treatment of resonances, ionization, and accretion is crucial to discover and characterize gravitational atoms with upcoming gravitational wave detectors.
|
2109.00247
|
Abolhassan Mohammadi
|
Abolhassan Mohammadi
|
Holographic warm inflation
|
9 pages, 5 figures
| null |
10.1103/PhysRevD.104.123538
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The increasing interest in studying the role of holographic dark energy in
the evolution of the very early universe motivates us to study it for the
scenario of warm inflation. Due to this scenario, the holographic dark energy,
which now drives inflation, has an interaction with the radiation. The case of
interacting dark energy also has received increasing interest in studying the
late time cosmology. The Infrared cutoff is taken as the Hubble length and all
corrections are assumed to be exhibited by the parameter $c$, which appears in
the holographic dark energy. By comparing the predictions of the model with
observational data, the free constants of the model could be determined. Then,
by using these values of the constants, the energy density of inflation is
estimated. Next, we consider the validity of the fundamental assumptions of the
warm inflation, e.g. $T/H > 1$, which is necessary to be held during inflation,
for the obtained values of the constant. Gathering all outcomes, the model
could be count as a suitable candidate for warm inflation.
|
[
{
"created": "Wed, 1 Sep 2021 08:36:21 GMT",
"version": "v1"
}
] |
2022-01-05
|
[
[
"Mohammadi",
"Abolhassan",
""
]
] |
The increasing interest in studying the role of holographic dark energy in the evolution of the very early universe motivates us to study it for the scenario of warm inflation. Due to this scenario, the holographic dark energy, which now drives inflation, has an interaction with the radiation. The case of interacting dark energy also has received increasing interest in studying the late time cosmology. The Infrared cutoff is taken as the Hubble length and all corrections are assumed to be exhibited by the parameter $c$, which appears in the holographic dark energy. By comparing the predictions of the model with observational data, the free constants of the model could be determined. Then, by using these values of the constants, the energy density of inflation is estimated. Next, we consider the validity of the fundamental assumptions of the warm inflation, e.g. $T/H > 1$, which is necessary to be held during inflation, for the obtained values of the constant. Gathering all outcomes, the model could be count as a suitable candidate for warm inflation.
|
gr-qc/0202098
|
D. V. Ahluwalia
|
D. V. Ahluwalia (Zacatecas)
|
At the interface of quantum and gravitational realms
|
Invited talk presented at "Mexican meeting on mathematical and
experimental physics (Colegio Nacional, 10-14 IX 2001)." 8 pages, 37
references
| null | null | null |
gr-qc astro-ph hep-ph hep-th
| null |
In this talk I review a series of recent conceptual developments at the
interface of the quantum and gravitational realms. Wherever possible, I comment
on the possibility to probe the interface experimentally. It is concluded that
the underlying spacetime for a quantum theory of gravity must be
non-commutative, that wave-particle duality suffers significant modification at
the Planck scale, and that the latter forbids probing spacetime below Planck
length. Furthermore, study of quantum test particles in classical and quantum
sources of gravity puts forward theoretical challenges and new experimental
possibilities. It is suggested that existing technology may allow to probe
gravitationally-modified wave particle duality in the laboratory.
|
[
{
"created": "Wed, 27 Feb 2002 23:34:01 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Ahluwalia",
"D. V.",
"",
"Zacatecas"
]
] |
In this talk I review a series of recent conceptual developments at the interface of the quantum and gravitational realms. Wherever possible, I comment on the possibility to probe the interface experimentally. It is concluded that the underlying spacetime for a quantum theory of gravity must be non-commutative, that wave-particle duality suffers significant modification at the Planck scale, and that the latter forbids probing spacetime below Planck length. Furthermore, study of quantum test particles in classical and quantum sources of gravity puts forward theoretical challenges and new experimental possibilities. It is suggested that existing technology may allow to probe gravitationally-modified wave particle duality in the laboratory.
|
gr-qc/9605014
|
Andrew M. Abrahams
|
A. Abrahams, A. Anderson, Y. Choquet-Bruhat and J.W. York Jr
|
Geometrical Hyperbolic Systems for General Relativity and Gauge Theories
|
24 pages, latex, no figures
|
Class.Quant.Grav.14:A9-A22,1997
|
10.1088/0264-9381/14/1A/002
|
IFP-UNC-516, TAR-UNC-053
|
gr-qc
| null |
The evolution equations of Einstein's theory and of Maxwell's theory---the
latter used as a simple model to illustrate the former--- are written in gauge
covariant first order symmetric hyperbolic form with only physically natural
characteristic directions and speeds for the dynamical variables. Quantities
representing gauge degrees of freedom [the spatial shift vector
$\beta^{i}(t,x^{j})$ and the spatial scalar potential $\phi(t,x^{j})$,
respectively] are not among the dynamical variables: the gauge and the physical
quantities in the evolution equations are effectively decoupled. For example,
the gauge quantities could be obtained as functions of $(t,x^{j})$ from
subsidiary equations that are not part of the evolution equations. Propagation
of certain (``radiative'') dynamical variables along the physical light cone is
gauge invariant while the remaining dynamical variables are dragged along the
axes orthogonal to the spacelike time slices by the propagating variables. We
obtain these results by $(1)$ taking a further time derivative of the equation
of motion of the canonical momentum, and $(2)$ adding a covariant spatial
derivative of the momentum constraints of general relativity (Lagrange
multiplier $\beta^{i}$) or of the Gauss's law constraint of electromagnetism
(Lagrange multiplier $\phi$). General relativity also requires a harmonic time
slicing condition or a specific generalization of it that brings in the
Hamiltonian constraint when we pass to first order symmetric form. The
dynamically propagating gravity fields straightforwardly determine the
``electric'' or ``tidal'' parts of the Riemann tensor.
|
[
{
"created": "Wed, 8 May 1996 20:14:27 GMT",
"version": "v1"
}
] |
2010-04-06
|
[
[
"Abrahams",
"A.",
""
],
[
"Anderson",
"A.",
""
],
[
"Choquet-Bruhat",
"Y.",
""
],
[
"York",
"J. W.",
"Jr"
]
] |
The evolution equations of Einstein's theory and of Maxwell's theory---the latter used as a simple model to illustrate the former--- are written in gauge covariant first order symmetric hyperbolic form with only physically natural characteristic directions and speeds for the dynamical variables. Quantities representing gauge degrees of freedom [the spatial shift vector $\beta^{i}(t,x^{j})$ and the spatial scalar potential $\phi(t,x^{j})$, respectively] are not among the dynamical variables: the gauge and the physical quantities in the evolution equations are effectively decoupled. For example, the gauge quantities could be obtained as functions of $(t,x^{j})$ from subsidiary equations that are not part of the evolution equations. Propagation of certain (``radiative'') dynamical variables along the physical light cone is gauge invariant while the remaining dynamical variables are dragged along the axes orthogonal to the spacelike time slices by the propagating variables. We obtain these results by $(1)$ taking a further time derivative of the equation of motion of the canonical momentum, and $(2)$ adding a covariant spatial derivative of the momentum constraints of general relativity (Lagrange multiplier $\beta^{i}$) or of the Gauss's law constraint of electromagnetism (Lagrange multiplier $\phi$). General relativity also requires a harmonic time slicing condition or a specific generalization of it that brings in the Hamiltonian constraint when we pass to first order symmetric form. The dynamically propagating gravity fields straightforwardly determine the ``electric'' or ``tidal'' parts of the Riemann tensor.
|
1606.00910
|
Mohammad Ali Gorji
|
M. A. Gorji, K. Nozari, B. Vakili
|
Gravity's rainbow: a bridge between LQC and DSR
|
10 pages, 4 figures, Refs. added
|
Phys. Lett. B 765 (2017) 113
|
10.1016/j.physletb.2016.12.023
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The doubly special relativity (DSR) theories are investigated in order to
take into account an observer-independent length scale in special relativity
framework. It is widely believed that any quantum theory of gravity would
reduce to a DSR model at the flat limit when purely gravitational and quantum
mechanical effects are negligible. Gravity's rainbow is a simple generalization
of DSR theories to incorporate gravity. In this paper, we show that the
effective Friedmann equations that are suggested by loop quantum cosmology
(LQC) can be exactly reobtained in rainbow cosmology setup. The deformed
geometry of LQC then completely fixes the modified dispersion relation and
results in unique DSR model. In comparison with standard LQC scenario where
only the geometry is modified, both of the geometry and matter parts get
modifications in our setup. In this respect, we find that the total number of
microstates for the universe is finite which suggests the statistical origin
for the energy and entropy density bounds. These results explicitly show that
the DSR theories are appropriate candidates for the flat limit of loop quantum
gravity.
|
[
{
"created": "Thu, 2 Jun 2016 21:47:50 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Aug 2016 11:30:53 GMT",
"version": "v2"
}
] |
2016-12-20
|
[
[
"Gorji",
"M. A.",
""
],
[
"Nozari",
"K.",
""
],
[
"Vakili",
"B.",
""
]
] |
The doubly special relativity (DSR) theories are investigated in order to take into account an observer-independent length scale in special relativity framework. It is widely believed that any quantum theory of gravity would reduce to a DSR model at the flat limit when purely gravitational and quantum mechanical effects are negligible. Gravity's rainbow is a simple generalization of DSR theories to incorporate gravity. In this paper, we show that the effective Friedmann equations that are suggested by loop quantum cosmology (LQC) can be exactly reobtained in rainbow cosmology setup. The deformed geometry of LQC then completely fixes the modified dispersion relation and results in unique DSR model. In comparison with standard LQC scenario where only the geometry is modified, both of the geometry and matter parts get modifications in our setup. In this respect, we find that the total number of microstates for the universe is finite which suggests the statistical origin for the energy and entropy density bounds. These results explicitly show that the DSR theories are appropriate candidates for the flat limit of loop quantum gravity.
|
0910.5128
|
Yu Zhang
|
Wang Chun-Yan, Zhang Yu, Gui Yuan-Xing, Lu Jian-Bo
|
Quasinormal modes of Dirac field perturbation in Reissner-Nordstr\"{o}m
black hole surrounded by quintessence
|
12pages, 11 figures
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The dirac quasinormal modes of the Reissner-Nordstr\"om black hole surrounded
by quintessence are investigated using the third WKB approximation. We find
that the magnitude of the imaginary part of the quasinormal mode frequencies
increases firstly and then decreases as the charge $Q$ increases, but it
decreases as the absolute value of $w_{q}$ increases. The magnitude of the
imaginary part of quasinormal complex frequencies is smaller than those with no
quintessence. That is to say, the dirac field damps more slowly due to the
presence of quintessence.
|
[
{
"created": "Tue, 27 Oct 2009 14:07:30 GMT",
"version": "v1"
},
{
"created": "Fri, 30 Oct 2009 12:18:07 GMT",
"version": "v2"
}
] |
2009-10-31
|
[
[
"Chun-Yan",
"Wang",
""
],
[
"Yu",
"Zhang",
""
],
[
"Yuan-Xing",
"Gui",
""
],
[
"Jian-Bo",
"Lu",
""
]
] |
The dirac quasinormal modes of the Reissner-Nordstr\"om black hole surrounded by quintessence are investigated using the third WKB approximation. We find that the magnitude of the imaginary part of the quasinormal mode frequencies increases firstly and then decreases as the charge $Q$ increases, but it decreases as the absolute value of $w_{q}$ increases. The magnitude of the imaginary part of quasinormal complex frequencies is smaller than those with no quintessence. That is to say, the dirac field damps more slowly due to the presence of quintessence.
|
gr-qc/0612006
|
George Sparling
|
George Sparling
|
The Xi-transform for conformally flat space-time
|
51 pages
| null | null | null |
gr-qc
| null |
The Xi-transform is a new spinor transform arising naturally in Einstein's
general relativity. Here the example of conformally flat space-time is
discussed in detail. In particular it is shown that for this case, the
transform coincides with two other naturally defined transforms: one a
two-variable transform on the Lie group SU(2, C), the other a transform on the
space of null split octaves. The key properties of the transform are developed.
|
[
{
"created": "Fri, 1 Dec 2006 03:22:29 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Sparling",
"George",
""
]
] |
The Xi-transform is a new spinor transform arising naturally in Einstein's general relativity. Here the example of conformally flat space-time is discussed in detail. In particular it is shown that for this case, the transform coincides with two other naturally defined transforms: one a two-variable transform on the Lie group SU(2, C), the other a transform on the space of null split octaves. The key properties of the transform are developed.
|
gr-qc/0209103
|
Daniel Muller
|
D. Muller, H. V. Fagundes, R. Opher
|
Casimir energy in multiply connected static hyperbolic Universes
|
accepted for publication
|
Phys.Rev. D66 (2002) 083507
|
10.1103/PhysRevD.66.083507
| null |
gr-qc
| null |
We generalize a previously obtained result, for the case of a few other
static hyperbolic universes with manifolds of nontrivial topology as spatial
sections.
|
[
{
"created": "Thu, 26 Sep 2002 21:30:07 GMT",
"version": "v1"
}
] |
2009-11-07
|
[
[
"Muller",
"D.",
""
],
[
"Fagundes",
"H. V.",
""
],
[
"Opher",
"R.",
""
]
] |
We generalize a previously obtained result, for the case of a few other static hyperbolic universes with manifolds of nontrivial topology as spatial sections.
|
0906.2367
|
Gary T. Horowitz
|
Aaron J. Amsel, Gary T. Horowitz, Donald Marolf, and Matthew M.
Roberts
|
Uniqueness of Extremal Kerr and Kerr-Newman Black Holes
|
12 pages, v2: important references to earlier work added, v3: minor
clarifications
|
Phys.Rev.D81:024033,2010
|
10.1103/PhysRevD.81.024033
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We prove that the only four dimensional, stationary, rotating, asymptotically
flat (analytic) vacuum black hole with a single degenerate horizon is given by
the extremal Kerr solution. We also prove a similar uniqueness theorem for the
extremal Kerr-Newman solution. This closes a longstanding gap in the black hole
uniqueness theorems.
|
[
{
"created": "Fri, 12 Jun 2009 18:07:52 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Jun 2009 21:19:27 GMT",
"version": "v2"
},
{
"created": "Wed, 25 Nov 2009 19:42:07 GMT",
"version": "v3"
}
] |
2010-04-06
|
[
[
"Amsel",
"Aaron J.",
""
],
[
"Horowitz",
"Gary T.",
""
],
[
"Marolf",
"Donald",
""
],
[
"Roberts",
"Matthew M.",
""
]
] |
We prove that the only four dimensional, stationary, rotating, asymptotically flat (analytic) vacuum black hole with a single degenerate horizon is given by the extremal Kerr solution. We also prove a similar uniqueness theorem for the extremal Kerr-Newman solution. This closes a longstanding gap in the black hole uniqueness theorems.
|
1712.03054
|
S\'ergio Mittmann dos Santos
|
S. Mittmann dos Santos, J. M. Hoff da Silva, M. E. X. Guimar\~aes, J.
L. Neto
|
A nearly cylindrically symmetric source in the Brans-Dicke gravity as
the generator of the rotational curves of the galaxies
|
24 pages, 4 figures, accepted for publication in Eur. Phys. J. C
|
Eur. Phys. J. C 77, 848 (2017)
|
10.1140/epjc/s10052-017-5397-1
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Observation shows that the velocities of stars grow by approximately 2 to 3
orders of magnitude when the distances from the centers of the galaxies are in
the range of $0.5$ kpc to $82.3$ kpc, before they begin to tend to a constant
value. Up to know, the reason for this behavior is still a matter for debate.
In this work, we propose a model which adequately describes this unusual
behavior using a (nearly) cylindrical symmetrical solution in the framework of
a scalar-tensor-like (the Brans-Dicke model) theory of gravity.
|
[
{
"created": "Fri, 8 Dec 2017 13:32:18 GMT",
"version": "v1"
}
] |
2022-09-07
|
[
[
"Santos",
"S. Mittmann dos",
""
],
[
"da Silva",
"J. M. Hoff",
""
],
[
"Guimarães",
"M. E. X.",
""
],
[
"Neto",
"J. L.",
""
]
] |
Observation shows that the velocities of stars grow by approximately 2 to 3 orders of magnitude when the distances from the centers of the galaxies are in the range of $0.5$ kpc to $82.3$ kpc, before they begin to tend to a constant value. Up to know, the reason for this behavior is still a matter for debate. In this work, we propose a model which adequately describes this unusual behavior using a (nearly) cylindrical symmetrical solution in the framework of a scalar-tensor-like (the Brans-Dicke model) theory of gravity.
|
0906.5219
|
Boris Kosyakov
|
Andrew E. Chubykalo, Augusto Espinoza, B. P. Kosyakov
|
Inertial frames of reference, space and time measurements, and physical
principles of special relativity revisited
|
LaTeX, 17 pages, 2 figures
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We give a critical analysis of the conceptual foundations of special
relativity. We formulate a simple operational criterion for distinguishing
between noninertial and inertial frames which is introduced prior to geometry.
We associate the concept of maximal velocity with the existence of an upper
bound for a set of rates of movers which travel in the same direction. We
define the standard scale for reading the time flow. We refine the treatment of
both Einstein's postulates, the principle of relativity and constancy of the
velocity of light. The proposed ``reconstruction'' of the geometry of Minkowski
space will hopefully be useful for the ongoing examination of possible Lorentz
violations.
|
[
{
"created": "Mon, 29 Jun 2009 08:22:35 GMT",
"version": "v1"
}
] |
2009-06-30
|
[
[
"Chubykalo",
"Andrew E.",
""
],
[
"Espinoza",
"Augusto",
""
],
[
"Kosyakov",
"B. P.",
""
]
] |
We give a critical analysis of the conceptual foundations of special relativity. We formulate a simple operational criterion for distinguishing between noninertial and inertial frames which is introduced prior to geometry. We associate the concept of maximal velocity with the existence of an upper bound for a set of rates of movers which travel in the same direction. We define the standard scale for reading the time flow. We refine the treatment of both Einstein's postulates, the principle of relativity and constancy of the velocity of light. The proposed ``reconstruction'' of the geometry of Minkowski space will hopefully be useful for the ongoing examination of possible Lorentz violations.
|
1301.6650
|
Ion I. Cotaescu
|
Ion I. Cotaescu
|
How to kill the Unruh effect
|
13 pages no figures
| null | null | null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
How to kill the Unruh effect? Very simple, by requiring the Rindler
transformation to behave continuously for vanishing acceleration. Then the
Unruh effect disappears as we show in the case of the massive scalar quantum
field. The main point is that the continuity condition restricts the integral
of the mode expansion to the positive energy spectrum, suppressing thus the
$\beta$ - terms of the Bogoliubov transformation.
|
[
{
"created": "Mon, 28 Jan 2013 19:24:21 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Jan 2013 07:30:34 GMT",
"version": "v2"
},
{
"created": "Thu, 31 Jan 2013 16:32:02 GMT",
"version": "v3"
},
{
"created": "Wed, 6 Feb 2013 14:50:58 GMT",
"version": "v4"
}
] |
2013-02-07
|
[
[
"Cotaescu",
"Ion I.",
""
]
] |
How to kill the Unruh effect? Very simple, by requiring the Rindler transformation to behave continuously for vanishing acceleration. Then the Unruh effect disappears as we show in the case of the massive scalar quantum field. The main point is that the continuity condition restricts the integral of the mode expansion to the positive energy spectrum, suppressing thus the $\beta$ - terms of the Bogoliubov transformation.
|
gr-qc/0307006
|
Peter Dimitris Rippis
|
Oyvind Gron, Peter D. Rippis
|
Singular shell embedded into a cosmological model
|
25 pages, 2 figures
|
Gen.Rel.Grav.35:2189-2215,2003
|
10.1023/A:1027353707603
| null |
gr-qc astro-ph
| null |
We generalize Israel's formalism to cover singular shells embedded in a
non-vacuum Universe. That is, we deduce the relativistic equation of motion for
a thin shell embedded in a Schwarzschild/Friedmann-Lemaitre-Robertson-Walker
spacetime. Also, we review the embedding of a Schwarzschild mass into a
cosmological model using "curvature" coordinates and give solutions with
(Sch/FLRW) and without the embedded mass (FLRW).
|
[
{
"created": "Tue, 1 Jul 2003 15:40:55 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Jul 2003 15:10:31 GMT",
"version": "v2"
},
{
"created": "Fri, 7 Nov 2003 10:36:16 GMT",
"version": "v3"
}
] |
2011-07-19
|
[
[
"Gron",
"Oyvind",
""
],
[
"Rippis",
"Peter D.",
""
]
] |
We generalize Israel's formalism to cover singular shells embedded in a non-vacuum Universe. That is, we deduce the relativistic equation of motion for a thin shell embedded in a Schwarzschild/Friedmann-Lemaitre-Robertson-Walker spacetime. Also, we review the embedding of a Schwarzschild mass into a cosmological model using "curvature" coordinates and give solutions with (Sch/FLRW) and without the embedded mass (FLRW).
|
0711.1048
|
Piotr Jaranowski
|
Thibault Damour, Piotr Jaranowski, Gerhard Sch\"afer
|
Hamiltonian of two spinning compact bodies with next-to-leading order
gravitational spin-orbit coupling
|
Few minor corrections made, 2 references added, some misprints
removed
|
Phys.Rev.D77:064032,2008
|
10.1103/PhysRevD.77.064032
| null |
gr-qc
| null |
A Hamiltonian formulation is given for the gravitational dynamics of two
spinning compact bodies to next-to-leading order ($G/c^4$ and $G^2/c^4$) in the
spin-orbit interaction. We use a novel approach (valid to linear order in the
spins), which starts from the second-post-Newtonian metric (in ADM coordinates)
generated by two spinless bodies, and computes the next-to-leading order
precession, in this metric, of suitably redefined ``constant-magnitude''
3-dimensional spin vectors ${\bf S}_1$, ${\bf S}_2$. We prove the Poincar\'e
invariance of our Hamiltonian by explicitly constructing ten phase-space
generators realizing the Poincar\'e algebra. A remarkable feature of our
approach is that it allows one to derive the {\it orbital} equations of motion
of spinning binaries to next-to-leading order in spin-orbit coupling without
having to solve Einstein's field equations with a spin-dependent stress tensor.
We show that our Hamiltonian (orbital and spin) dynamics is equivalent to the
dynamics recently obtained by Faye, Blanchet, and Buonanno, by solving
Einstein's equations in harmonic coordinates.
|
[
{
"created": "Wed, 7 Nov 2007 10:01:22 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Apr 2008 15:37:45 GMT",
"version": "v2"
}
] |
2008-11-26
|
[
[
"Damour",
"Thibault",
""
],
[
"Jaranowski",
"Piotr",
""
],
[
"Schäfer",
"Gerhard",
""
]
] |
A Hamiltonian formulation is given for the gravitational dynamics of two spinning compact bodies to next-to-leading order ($G/c^4$ and $G^2/c^4$) in the spin-orbit interaction. We use a novel approach (valid to linear order in the spins), which starts from the second-post-Newtonian metric (in ADM coordinates) generated by two spinless bodies, and computes the next-to-leading order precession, in this metric, of suitably redefined ``constant-magnitude'' 3-dimensional spin vectors ${\bf S}_1$, ${\bf S}_2$. We prove the Poincar\'e invariance of our Hamiltonian by explicitly constructing ten phase-space generators realizing the Poincar\'e algebra. A remarkable feature of our approach is that it allows one to derive the {\it orbital} equations of motion of spinning binaries to next-to-leading order in spin-orbit coupling without having to solve Einstein's field equations with a spin-dependent stress tensor. We show that our Hamiltonian (orbital and spin) dynamics is equivalent to the dynamics recently obtained by Faye, Blanchet, and Buonanno, by solving Einstein's equations in harmonic coordinates.
|
0806.4459
|
Francisco Lobo
|
Jos\'e P. S. Lemos, Francisco S. N. Lobo
|
Plane symmetric thin-shell wormholes: solutions and stability
|
10 pages, 4 figures. V2: typo corrections and minor modifications
|
Phys.Rev.D78:044030,2008
|
10.1103/PhysRevD.78.044030
| null |
gr-qc astro-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Using the cut-and-paste procedure, we construct static and dynamic plane
symmetric wormholes by surgically grafting together two spacetimes of plane
symmetric vacuum solutions with a negative cosmological constant. These plane
symmetric wormholes may be viewed as domain walls connecting different
universes, having planar topology, and upon compactification of one or two
coordinates, cylindrical topology or toroidal topology, respectively. A
stability analysis is carried out for the dynamic case by taking into account
specific equations of state, and a linearized stability analysis around static
solutions is also explored. It is found that thin shell wormholes made of a
dark energy fluid or of a cosmological constant fluid are stable, while thin
shell wormholes made of phantom energy are unstable.
|
[
{
"created": "Fri, 27 Jun 2008 08:45:51 GMT",
"version": "v1"
},
{
"created": "Wed, 13 Aug 2008 17:13:24 GMT",
"version": "v2"
}
] |
2008-11-26
|
[
[
"Lemos",
"José P. S.",
""
],
[
"Lobo",
"Francisco S. N.",
""
]
] |
Using the cut-and-paste procedure, we construct static and dynamic plane symmetric wormholes by surgically grafting together two spacetimes of plane symmetric vacuum solutions with a negative cosmological constant. These plane symmetric wormholes may be viewed as domain walls connecting different universes, having planar topology, and upon compactification of one or two coordinates, cylindrical topology or toroidal topology, respectively. A stability analysis is carried out for the dynamic case by taking into account specific equations of state, and a linearized stability analysis around static solutions is also explored. It is found that thin shell wormholes made of a dark energy fluid or of a cosmological constant fluid are stable, while thin shell wormholes made of phantom energy are unstable.
|
1302.6075
|
Cosimo Bambi
|
Cosimo Bambi, Leonardo Modesto
|
Rotating regular black holes
|
8 pages, 3 figures. v2: refereed version
|
Phys.Lett.B721:329-334,2013
|
10.1016/j.physletb.2013.03.025
| null |
gr-qc astro-ph.HE
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The formation of spacetime singularities is a quite common phenomenon in
General Relativity and it is regulated by specific theorems. It is widely
believed that spacetime singularities do not exist in Nature, but that they
represent a limitation of the classical theory. While we do not yet have any
solid theory of quantum gravity, toy models of black hole solutions without
singularities have been proposed. So far, there are only non-rotating regular
black holes in the literature. These metrics can be hardly tested by
astrophysical observations, as the black hole spin plays a fundamental role in
any astrophysical process. In this letter, we apply the Newman-Janis algorithm
to the Hayward and to the Bardeen black hole metrics. In both cases, we obtain
a family of rotating solutions. Every solution corresponds to a different
matter configuration. Each family has one solution with special properties,
which can be written in Kerr-like form in Boyer-Lindquist coordinates. These
special solutions are of Petrov type D, they are singularity free, but they
violate the weak energy condition for a non-vanishing spin and their curvature
invariants have different values at $r=0$ depending on the way one approaches
the origin. We propose a natural prescription to have rotating solutions with a
minimal violation of the weak energy condition and without the questionable
property of the curvature invariants at the origin.
|
[
{
"created": "Mon, 25 Feb 2013 12:29:05 GMT",
"version": "v1"
},
{
"created": "Tue, 26 Mar 2013 14:31:07 GMT",
"version": "v2"
}
] |
2013-04-08
|
[
[
"Bambi",
"Cosimo",
""
],
[
"Modesto",
"Leonardo",
""
]
] |
The formation of spacetime singularities is a quite common phenomenon in General Relativity and it is regulated by specific theorems. It is widely believed that spacetime singularities do not exist in Nature, but that they represent a limitation of the classical theory. While we do not yet have any solid theory of quantum gravity, toy models of black hole solutions without singularities have been proposed. So far, there are only non-rotating regular black holes in the literature. These metrics can be hardly tested by astrophysical observations, as the black hole spin plays a fundamental role in any astrophysical process. In this letter, we apply the Newman-Janis algorithm to the Hayward and to the Bardeen black hole metrics. In both cases, we obtain a family of rotating solutions. Every solution corresponds to a different matter configuration. Each family has one solution with special properties, which can be written in Kerr-like form in Boyer-Lindquist coordinates. These special solutions are of Petrov type D, they are singularity free, but they violate the weak energy condition for a non-vanishing spin and their curvature invariants have different values at $r=0$ depending on the way one approaches the origin. We propose a natural prescription to have rotating solutions with a minimal violation of the weak energy condition and without the questionable property of the curvature invariants at the origin.
|
2112.00938
|
Krishnakanta Bhattacharya
|
Krishnakanta Bhattacharya
|
Extended phase space thermodynamics of black holes: A study in
Einstein's gravity and beyond
|
Modified version, To appear in NPB
|
Nuclear Physics B 989 (2023) 116130
|
10.1016/j.nuclphysb.2023.116130
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In the extended phase space approach, one can define thermodynamic pressure
and volume that gives rise to the van der Waals type phase transition for black
holes. For Einstein's GR, the expressions of these quantities are unanimously
accepted. Of late, the van der Waals phase transition in black holes has been
found in modified theories of gravity as well, such as the $f(R)$ gravity and
the scalar-tensor gravity. However, in the case of these modified theories of
gravity, the expression of pressure (and, hence, volume) is not uniquely
determined. In addition, for these modified theories, the extended phase space
thermodynamics has not been studied extensively, especially in a covariant way.
Since both the scalar-tensor and the $f(R)$ gravity can be discussed in the two
conformally connected frames (the Jordan and the Einstein frame respectively),
the arbitrariness in the expression of pressure, will act upon the equivalence
of the thermodynamic parameters in the two frames. We highlight these issues in
the paper. Before that, in Einstein's gravity (GR), we obtain a general
expression of the equilibrium state version of first law and the Smarr-like
formula from the Einstein's equation for a general static and spherically
symmetric (SSS) metric. Here we directly obtain the first law as well as the
Smarr-like formula in GR in terms of the parameters present in the metric (such
as mass, charge \textit{etc.}). This study also shows how the extended phase
space is formulated (by considering the cosmological constant as variable) and,
also shows why the cosmological constant plays the role of thermodynamic
pressure in GR in extended phase space. Moreover, obtaining the Smarr formula
from the Einstein's equation for the SSS metric suggests that this dynamical
equation encodes more information on BH thermodynamics than what has been
anticipated before.
|
[
{
"created": "Thu, 2 Dec 2021 02:24:28 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Feb 2023 10:38:05 GMT",
"version": "v2"
}
] |
2023-03-01
|
[
[
"Bhattacharya",
"Krishnakanta",
""
]
] |
In the extended phase space approach, one can define thermodynamic pressure and volume that gives rise to the van der Waals type phase transition for black holes. For Einstein's GR, the expressions of these quantities are unanimously accepted. Of late, the van der Waals phase transition in black holes has been found in modified theories of gravity as well, such as the $f(R)$ gravity and the scalar-tensor gravity. However, in the case of these modified theories of gravity, the expression of pressure (and, hence, volume) is not uniquely determined. In addition, for these modified theories, the extended phase space thermodynamics has not been studied extensively, especially in a covariant way. Since both the scalar-tensor and the $f(R)$ gravity can be discussed in the two conformally connected frames (the Jordan and the Einstein frame respectively), the arbitrariness in the expression of pressure, will act upon the equivalence of the thermodynamic parameters in the two frames. We highlight these issues in the paper. Before that, in Einstein's gravity (GR), we obtain a general expression of the equilibrium state version of first law and the Smarr-like formula from the Einstein's equation for a general static and spherically symmetric (SSS) metric. Here we directly obtain the first law as well as the Smarr-like formula in GR in terms of the parameters present in the metric (such as mass, charge \textit{etc.}). This study also shows how the extended phase space is formulated (by considering the cosmological constant as variable) and, also shows why the cosmological constant plays the role of thermodynamic pressure in GR in extended phase space. Moreover, obtaining the Smarr formula from the Einstein's equation for the SSS metric suggests that this dynamical equation encodes more information on BH thermodynamics than what has been anticipated before.
|
2004.09598
|
Robie Hennigar
|
Connor Adair, Pablo Bueno, Pablo A. Cano, Robie A. Hennigar, Robert B.
Mann
|
Slowly rotating black holes in Einsteinian cubic gravity
|
39 pages, 14 figures
|
Phys. Rev. D 102, 084001 (2020)
|
10.1103/PhysRevD.102.084001
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We construct slowly rotating black-hole solutions of Einsteinian cubic
gravity (ECG) in four dimensions with flat and AdS asymptotes. At leading order
in the rotation parameter, the only modification with respect to the static
case is the appearance of a non-vanishing $g_{t\phi}$ component. Similarly to
the static case, the order of the equation determining such component can be
reduced twice, giving rise to a second-order differential equation which can be
easily solved numerically as a function of the ECG coupling. We study how
various physical properties of the solutions are modified with respect to the
Einstein gravity case, including its angular velocity, photon sphere, photon
rings, shadow, and innermost stable circular orbits (in the case of timelike
geodesics).
|
[
{
"created": "Mon, 20 Apr 2020 19:45:29 GMT",
"version": "v1"
}
] |
2020-10-07
|
[
[
"Adair",
"Connor",
""
],
[
"Bueno",
"Pablo",
""
],
[
"Cano",
"Pablo A.",
""
],
[
"Hennigar",
"Robie A.",
""
],
[
"Mann",
"Robert B.",
""
]
] |
We construct slowly rotating black-hole solutions of Einsteinian cubic gravity (ECG) in four dimensions with flat and AdS asymptotes. At leading order in the rotation parameter, the only modification with respect to the static case is the appearance of a non-vanishing $g_{t\phi}$ component. Similarly to the static case, the order of the equation determining such component can be reduced twice, giving rise to a second-order differential equation which can be easily solved numerically as a function of the ECG coupling. We study how various physical properties of the solutions are modified with respect to the Einstein gravity case, including its angular velocity, photon sphere, photon rings, shadow, and innermost stable circular orbits (in the case of timelike geodesics).
|
2112.02835
|
Motohiko Yoshimura
|
M. Yoshimura
|
Bifurcated symmetry breaking in scalar-tensor gravity
|
14 pages and 3 figures
| null |
10.1103/PhysRevD.105.083522
| null |
gr-qc astro-ph.CO hep-ph hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
We present models that simultaneously predict presence of dark energy and
cold dark matter along with slow-roll inflation. The dark energy density is
found to be of order $({\rm a \;few \;meV})^4$, and the mass of dark matter
constituent is $\approx 1\,$ meV. These numbers are given in terms of the
present value of Hubble constant $H_0$ and the Plank energy $1/\sqrt{16 \pi
G_N}$: they are $(H_0 M_{\rm P})^2$ for the energy density and $(H_0 M_{\rm
P})^{1/2}$ for the dark matter constituent mass. The basic framework is a
multi-scalar tensor gravity with non-trivial conformal coupling to the Ricci
scalar curvature in the lagrangian density. The key for a right amount of dark
energy is to incorporate in a novel way the spatially homogeneous kinetic
contribution of Nambu-Goldstone modes in a spontaneously broken multi-scalar
field sector. Proposed theories are made consistent with general relativity
tests at small cosmological distances, yet are different from general
relativity at cosmological scales. Dark matter is generated as spatially
inhomogeneous component of the scalar system, with roughly comparable amount to
the dark energy. In some presented models a cosmological bifurcation of
symmetry breaking of scalar sector is triggered by the spontaneous breaking of
electroweak SU(2) $\times $ U(1) gauge symmetry, hence the separation occurring
simultaneously at the electroweak phase transition. The best experimental
method to test presented models is to search for the fifth-force type of scalar
exchange interaction with a force range, $O(10^{-2})$ cm, whose coupling to
matter is basically of gravitational strength.
|
[
{
"created": "Mon, 6 Dec 2021 07:47:31 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Dec 2021 09:02:49 GMT",
"version": "v2"
}
] |
2022-05-04
|
[
[
"Yoshimura",
"M.",
""
]
] |
We present models that simultaneously predict presence of dark energy and cold dark matter along with slow-roll inflation. The dark energy density is found to be of order $({\rm a \;few \;meV})^4$, and the mass of dark matter constituent is $\approx 1\,$ meV. These numbers are given in terms of the present value of Hubble constant $H_0$ and the Plank energy $1/\sqrt{16 \pi G_N}$: they are $(H_0 M_{\rm P})^2$ for the energy density and $(H_0 M_{\rm P})^{1/2}$ for the dark matter constituent mass. The basic framework is a multi-scalar tensor gravity with non-trivial conformal coupling to the Ricci scalar curvature in the lagrangian density. The key for a right amount of dark energy is to incorporate in a novel way the spatially homogeneous kinetic contribution of Nambu-Goldstone modes in a spontaneously broken multi-scalar field sector. Proposed theories are made consistent with general relativity tests at small cosmological distances, yet are different from general relativity at cosmological scales. Dark matter is generated as spatially inhomogeneous component of the scalar system, with roughly comparable amount to the dark energy. In some presented models a cosmological bifurcation of symmetry breaking of scalar sector is triggered by the spontaneous breaking of electroweak SU(2) $\times $ U(1) gauge symmetry, hence the separation occurring simultaneously at the electroweak phase transition. The best experimental method to test presented models is to search for the fifth-force type of scalar exchange interaction with a force range, $O(10^{-2})$ cm, whose coupling to matter is basically of gravitational strength.
|
2009.06113
|
Vasilis Oikonomou
|
S.D. Odintsov, V.K. Oikonomou, F.P. Fronimos, S.A. Venikoudis
|
GW170817-compatible Constant-roll Einstein-Gauss-Bonnet Inflation and
Non-Gaussianities
|
PDU Accepted
| null | null | null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper we investigate the inflationary phenomenology of an
Einstein-Gauss-Bonnet theory compatible with the GW170817 event, by imposing
the constant-roll evolution on the scalar field. We develop the constant-roll
GW170817-compatible Einstein-Gauss-Bonnet formalism, and we calculate the
slow-roll indices and the observational indices of inflation, for several
models of interest. As we demonstrate, the phenomenological viability of the
models we study is achieved for a wide range of the free parameters. In
addition, for the same values of the free parameters that guarantee the
inflationary phenomenological viability of the models, we also make predictions
for the non-Gaussianities of the models, since the constant-roll evolution is
known to enhance non-Gaussianities. As we show the non-Gaussianities are of the
same order for the slow-roll and constant-roll case, and in fact in some cases,
the amount of the non-Gaussianities is smaller in the constant-roll case.
|
[
{
"created": "Sun, 13 Sep 2020 23:29:54 GMT",
"version": "v1"
}
] |
2020-09-15
|
[
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
],
[
"Fronimos",
"F. P.",
""
],
[
"Venikoudis",
"S. A.",
""
]
] |
In this paper we investigate the inflationary phenomenology of an Einstein-Gauss-Bonnet theory compatible with the GW170817 event, by imposing the constant-roll evolution on the scalar field. We develop the constant-roll GW170817-compatible Einstein-Gauss-Bonnet formalism, and we calculate the slow-roll indices and the observational indices of inflation, for several models of interest. As we demonstrate, the phenomenological viability of the models we study is achieved for a wide range of the free parameters. In addition, for the same values of the free parameters that guarantee the inflationary phenomenological viability of the models, we also make predictions for the non-Gaussianities of the models, since the constant-roll evolution is known to enhance non-Gaussianities. As we show the non-Gaussianities are of the same order for the slow-roll and constant-roll case, and in fact in some cases, the amount of the non-Gaussianities is smaller in the constant-roll case.
|
2009.03866
|
Vesselin G. Gueorguiev
|
Vesselin G. Gueorguiev and Andre Maeder
|
Revisiting the Cosmological Constant Problem within Quantum Cosmology
|
16 pages, no figures
|
Universe 2020, Volume 6, Issue 8, Article 108
|
10.3390/universe6080108
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
A new perspective on the Cosmological Constant Problem (CCP) is proposed and
discussed within the multiverse approach of Quantum Cosmology. It is assumed
that each member of the ensemble of universes has a characteristic scale $a$
that can be used as integration variable in the partition function. An averaged
characteristic scale of the ensemble is estimated by using only members that
satisfy the Einstein field equations. The averaged characteristic scale is
compatible with the Planck length when considering an ensemble of solutions to
the Einstein field equations with an effective cosmological constant. The
multiverse ensemble is split in Planck-seed universes with vacuum energy
density of order one; thus, $ \tilde{\Lambda}\approx 8\pi$ in Planck units and
$a$-derivable universes. For~$a$-derivable universe with a characteristic scale
of the order of the observed Universe $a\approx 8\times10^{60}$, the
cosmological constant $\Lambda=\tilde{\Lambda}/a^{2}$ is in the range
$10^{-121}$--$10^{-122}$, which is close in magnitude to the observed value
$10^{-123}$. We point out that the smallness of $\Lambda$ can be viewed to be
natural if its value is associated with the entropy of the Universe. This
approach to the CCP reconciles the Planck-scale huge vacuum energy--density
predicted by QFT considerations, as valid for Planck-seed universes, with the
observed small value of the cosmological constant as relevant to an
$a$-derivable universe as~observed.
|
[
{
"created": "Tue, 8 Sep 2020 17:06:27 GMT",
"version": "v1"
}
] |
2020-09-09
|
[
[
"Gueorguiev",
"Vesselin G.",
""
],
[
"Maeder",
"Andre",
""
]
] |
A new perspective on the Cosmological Constant Problem (CCP) is proposed and discussed within the multiverse approach of Quantum Cosmology. It is assumed that each member of the ensemble of universes has a characteristic scale $a$ that can be used as integration variable in the partition function. An averaged characteristic scale of the ensemble is estimated by using only members that satisfy the Einstein field equations. The averaged characteristic scale is compatible with the Planck length when considering an ensemble of solutions to the Einstein field equations with an effective cosmological constant. The multiverse ensemble is split in Planck-seed universes with vacuum energy density of order one; thus, $ \tilde{\Lambda}\approx 8\pi$ in Planck units and $a$-derivable universes. For~$a$-derivable universe with a characteristic scale of the order of the observed Universe $a\approx 8\times10^{60}$, the cosmological constant $\Lambda=\tilde{\Lambda}/a^{2}$ is in the range $10^{-121}$--$10^{-122}$, which is close in magnitude to the observed value $10^{-123}$. We point out that the smallness of $\Lambda$ can be viewed to be natural if its value is associated with the entropy of the Universe. This approach to the CCP reconciles the Planck-scale huge vacuum energy--density predicted by QFT considerations, as valid for Planck-seed universes, with the observed small value of the cosmological constant as relevant to an $a$-derivable universe as~observed.
|
2312.13858
|
Alexey Golovnev
|
Alexey Golovnev
|
Geometry of teleparallel theories
|
8 pages; a remark added; prepared for proceedings of the
International Conference on Particle Physics and Cosmology dedicated to
memory of Valery Rubakov, Yerevan, Armenia, October 2023
|
Proceedings of Science, PoS ICPPCRubakov2023 (2024) 031
|
10.22323/1.455.0031
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
I give a brief introduction to and explain the geometry of teleparallel
models of modified gravity. In particular I explain why, in my opinion, the
covariantised approaches are not needed and the Weitzenb\"ock connection is the
most natural representation of the parallel transport structure. An interesting
point is that it also applies to the symmetric teleparallel case. I also share
my thoughts on why the teleparallel framework does not seem to be a next rung
in the ladder of understanding the real worlds' gravity. At the same time,
these theories do have a clear and justified academic interest to them.
|
[
{
"created": "Thu, 21 Dec 2023 13:53:48 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Dec 2023 19:16:36 GMT",
"version": "v2"
},
{
"created": "Wed, 17 Jan 2024 11:06:15 GMT",
"version": "v3"
}
] |
2024-06-12
|
[
[
"Golovnev",
"Alexey",
""
]
] |
I give a brief introduction to and explain the geometry of teleparallel models of modified gravity. In particular I explain why, in my opinion, the covariantised approaches are not needed and the Weitzenb\"ock connection is the most natural representation of the parallel transport structure. An interesting point is that it also applies to the symmetric teleparallel case. I also share my thoughts on why the teleparallel framework does not seem to be a next rung in the ladder of understanding the real worlds' gravity. At the same time, these theories do have a clear and justified academic interest to them.
|
2211.12188
|
Zhao Li
|
Zhao Li, Jin Qiao, Tan Liu, Tao Zhu, Wen Zhao
|
Gravitational Waveform and Polarization from Binary Black Hole Inspiral
in Dynamical Chern-Simons Gravity: From Generation to Propagation
|
30 pages
|
https://iopscience.iop.org/article/10.1088/1475-7516/2023/04/006
|
10.1088/1475-7516/2023/04/006
| null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
We calculate the gravitational waveform radiated from spinning black holes
(BHs) binary in dynamical Chern-Simons (dCS) gravity. The equation of motion
(EOM) of the spinining binary BHs is derived based on the modified
Mathisson-Papapetrou-Dixon equation for the spin-aligned circular orbits. The
leading-order effects induced by the dCS theory contains spin-spin interaction
and monopole-quadrupole interaction, which influence both the EOM of the binary
system and corresponding gravitational waveform at the second post-Newtonian
(PN) order (i.e., 2PN order). After reporting the waveforms, we investigate the
polarization modes of gravitational waves (GWs) in dCS theory. None of the
extra modes appears in this theory up to the considered PN order. Moreover,
since the time scale of the binary merger is much smaller than that of the
cosmological expansion, the parity-violating effect of the dCS theory does not
appear in the process of GW generation. However, during the process of GW
propagation, amplitude birefringence, a typical parity-violating effect, makes
plus and cross modes convert to each other, which modifies the gravitational
waveform at 1.5PN order.
|
[
{
"created": "Tue, 22 Nov 2022 11:28:02 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Apr 2023 06:50:12 GMT",
"version": "v2"
}
] |
2023-04-07
|
[
[
"Li",
"Zhao",
""
],
[
"Qiao",
"Jin",
""
],
[
"Liu",
"Tan",
""
],
[
"Zhu",
"Tao",
""
],
[
"Zhao",
"Wen",
""
]
] |
We calculate the gravitational waveform radiated from spinning black holes (BHs) binary in dynamical Chern-Simons (dCS) gravity. The equation of motion (EOM) of the spinining binary BHs is derived based on the modified Mathisson-Papapetrou-Dixon equation for the spin-aligned circular orbits. The leading-order effects induced by the dCS theory contains spin-spin interaction and monopole-quadrupole interaction, which influence both the EOM of the binary system and corresponding gravitational waveform at the second post-Newtonian (PN) order (i.e., 2PN order). After reporting the waveforms, we investigate the polarization modes of gravitational waves (GWs) in dCS theory. None of the extra modes appears in this theory up to the considered PN order. Moreover, since the time scale of the binary merger is much smaller than that of the cosmological expansion, the parity-violating effect of the dCS theory does not appear in the process of GW generation. However, during the process of GW propagation, amplitude birefringence, a typical parity-violating effect, makes plus and cross modes convert to each other, which modifies the gravitational waveform at 1.5PN order.
|
1710.01172
|
Orfeu Bertolami
|
P. Leal, A. E. Bernardini, O. Bertolami
|
Collapsing Shells and Black Holes: a quantum analysis
|
26 pages, 5 figs
| null |
10.1088/1361-6382/aac083
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The quantization of a spherically symmetric null shells is performed and
extended to the framework of phase-space noncommutative (NC) quantum mechanics.
The encountered properties are investigated making use of the Israel junction
conditions on the shell, considering that it is the boundary between two
spherically symmetric spacetimes. Using this method, and considering two
different Kantowski-Sachs spacetimes as a representation for the Schwarzschild
spacetime, the relevant quantities on the shell are computed, such as its
stress-energy tensor and the action for the whole spacetime. From the obtained
action, the Wheeler-deWitt equation is deduced in order to provide the quantum
framework for the system. Solutions for the wavefunction of the system are
found on both the commutative and NC scenarios. It is shown that, on the
commutative version, the wave function has a purely oscillatory behavior in the
interior of the shell. In the NC setting, it is shown that the wavefunction
vanishes at the singularity, as well as, at the event horizon of the black
hole.
|
[
{
"created": "Tue, 3 Oct 2017 14:05:08 GMT",
"version": "v1"
}
] |
2018-06-13
|
[
[
"Leal",
"P.",
""
],
[
"Bernardini",
"A. E.",
""
],
[
"Bertolami",
"O.",
""
]
] |
The quantization of a spherically symmetric null shells is performed and extended to the framework of phase-space noncommutative (NC) quantum mechanics. The encountered properties are investigated making use of the Israel junction conditions on the shell, considering that it is the boundary between two spherically symmetric spacetimes. Using this method, and considering two different Kantowski-Sachs spacetimes as a representation for the Schwarzschild spacetime, the relevant quantities on the shell are computed, such as its stress-energy tensor and the action for the whole spacetime. From the obtained action, the Wheeler-deWitt equation is deduced in order to provide the quantum framework for the system. Solutions for the wavefunction of the system are found on both the commutative and NC scenarios. It is shown that, on the commutative version, the wave function has a purely oscillatory behavior in the interior of the shell. In the NC setting, it is shown that the wavefunction vanishes at the singularity, as well as, at the event horizon of the black hole.
|
1706.06519
|
Puttarak Jai-akson
|
Puttarak Jai-akson, Auttakit Chatrabhuti, Oleg Evnin, Luis Lehner
|
Black hole merger estimates in Einstein-Maxwell and
Einstein-Maxwell-dilaton gravity
|
23 pages, 23 figures, v2: minor improvements, accepted to PRD
|
Phys. Rev. D 96, 044031 (2017)
|
10.1103/PhysRevD.96.044031
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The recent birth of gravitational wave astronomy invites a new generation of
precision tests of general relativity. Signatures of black hole (BH) mergers
must be systematically explored in a wide spectrum of modified gravity
theories. Here, we turn to one such theory in which the initial value problem
for BH mergers is well posed, the Einstein-Maxwell-dilaton system. We present
conservative estimates for the merger parameters (final spins, quasinormal
modes) based on techniques that have worked well for ordinary gravity mergers
and utilize information extracted from test particle motion in the final BH
metric. The computation is developed in parallel for the modified gravity BHs
(we specifically focus on the Kaluza-Klein value of the dilaton coupling, for
which analytic BH solutions are known) and ordinary Kerr-Newman BHs. We comment
on the possibility of obtaining final BHs with spins consistent with current
observations.
|
[
{
"created": "Tue, 20 Jun 2017 15:29:38 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Aug 2017 15:43:12 GMT",
"version": "v2"
}
] |
2017-09-01
|
[
[
"Jai-akson",
"Puttarak",
""
],
[
"Chatrabhuti",
"Auttakit",
""
],
[
"Evnin",
"Oleg",
""
],
[
"Lehner",
"Luis",
""
]
] |
The recent birth of gravitational wave astronomy invites a new generation of precision tests of general relativity. Signatures of black hole (BH) mergers must be systematically explored in a wide spectrum of modified gravity theories. Here, we turn to one such theory in which the initial value problem for BH mergers is well posed, the Einstein-Maxwell-dilaton system. We present conservative estimates for the merger parameters (final spins, quasinormal modes) based on techniques that have worked well for ordinary gravity mergers and utilize information extracted from test particle motion in the final BH metric. The computation is developed in parallel for the modified gravity BHs (we specifically focus on the Kaluza-Klein value of the dilaton coupling, for which analytic BH solutions are known) and ordinary Kerr-Newman BHs. We comment on the possibility of obtaining final BHs with spins consistent with current observations.
|
gr-qc/9506032
|
Kouji Nakamura
|
K.Nakamura, Y.Oshiro and A.Tomimatsu
|
Quantum Formation of Black Hole and Wormhole in Gravitational Collapse
of a Dust Shell
|
10 pages in twocolumn, 8 figures, RevTeX 3.0
|
Phys.Rev.D53:4356-4365,1996
|
10.1103/PhysRevD.53.4356
| null |
gr-qc
| null |
Quantum-mechanical model of self-gravitating dust shell is considered. To
clarify the relation between classical and quantum spacetime which the shell
collapse form, we consider various time slicing on which quantum mechanics is
developed. By considering the static time slicing which corresponds to an
observer at a constant circumference radius, we obtain the wave functions of
the shell motion and the discrete mass spectra which specify the global
structures of spherically symmetric spacetime formed by the shell collapse. It
is found that wormhole states are forbidden when the rest mass is comparable
with Plank mass scale due to the zero-point quantum fluctuations.
|
[
{
"created": "Sat, 17 Jun 1995 09:11:00 GMT",
"version": "v1"
}
] |
2011-09-09
|
[
[
"Nakamura",
"K.",
""
],
[
"Oshiro",
"Y.",
""
],
[
"Tomimatsu",
"A.",
""
]
] |
Quantum-mechanical model of self-gravitating dust shell is considered. To clarify the relation between classical and quantum spacetime which the shell collapse form, we consider various time slicing on which quantum mechanics is developed. By considering the static time slicing which corresponds to an observer at a constant circumference radius, we obtain the wave functions of the shell motion and the discrete mass spectra which specify the global structures of spherically symmetric spacetime formed by the shell collapse. It is found that wormhole states are forbidden when the rest mass is comparable with Plank mass scale due to the zero-point quantum fluctuations.
|
0704.3140
|
Farook Rahaman
|
Farook Rahaman
|
Non static cosmic strings in Lyra geometry
|
8 pages, Published in Nuovo Cim.118B:99-105,2003
| null | null | null |
gr-qc
| null |
The gravitational field of both local and global non static cosmic strings in
the context of Lyra geometry are investigated. Local strings are characterized
by having an energy momentum tensor whose only non null components are $T_{tt}
= T_{zz}$ . As linearized Einstein equations are formally analogous to the
Maxwell equations, the exterior solution does not depend on the radial
distribution of the source and hence a Dirac d function was used to approximate
the radial distribution of the energy momentum tensor for a local cosmic string
along the z-axis: $T_{ab} = \delta(x) \delta(y)diag (\sigma, 0, 0, \sigma) $,
$\sigma $being the energy density of the string [A.Vilenkin.
Phys.Rep.(1985)121,263]. For a global string, the energy momentum tensor
components are calculated from the action density for a complex scalar field y
along with a Maxican hat potential. The gravitational field of the global
string is shown to be attractive in nature.
|
[
{
"created": "Tue, 24 Apr 2007 08:09:22 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Rahaman",
"Farook",
""
]
] |
The gravitational field of both local and global non static cosmic strings in the context of Lyra geometry are investigated. Local strings are characterized by having an energy momentum tensor whose only non null components are $T_{tt} = T_{zz}$ . As linearized Einstein equations are formally analogous to the Maxwell equations, the exterior solution does not depend on the radial distribution of the source and hence a Dirac d function was used to approximate the radial distribution of the energy momentum tensor for a local cosmic string along the z-axis: $T_{ab} = \delta(x) \delta(y)diag (\sigma, 0, 0, \sigma) $, $\sigma $being the energy density of the string [A.Vilenkin. Phys.Rep.(1985)121,263]. For a global string, the energy momentum tensor components are calculated from the action density for a complex scalar field y along with a Maxican hat potential. The gravitational field of the global string is shown to be attractive in nature.
|
gr-qc/0303006
|
Mu-Lin Yan
|
Hua Bai, Mu-Lin Yan
|
Remarks on 't Hooft's Brick Wall Model
|
RevTeX, 5 pages, no figures
|
JHEP0307:058,2003
|
10.1088/1126-6708/2003/07/058
|
USTC-ICTS-03-6
|
gr-qc hep-th
| null |
A semi-classical reasoning leads to the non-commutativity of the space and
time coordinates near the horizon of Schwarzschild black hole. This
non-commutativity in turn provides a mechanism to interpret the brick wall
thickness hypothesis in 't Hooft's brick wall model as well as the boundary
condition imposed for the field considered. For concreteness, we consider a
noncommutative scalar field model near the horizon and derive the effective
metric via the equation of motion of noncommutative scalar field. This metric
displays a new horizon in addition to the original one associated with the
Schwarzschild black hole. The infinite red-shifting of the scalar field on the
new horizon determines the range of the noncommutativ space and explains the
relevant boundary condition for the field. This range enables us to calculate
the entropy of black hole as proportional to the area of its original horizon
along the same line as in 't Hooft's model, and the thickness of the brick wall
is found to be proportional to the thermal average of the noncommutative
space-time range. The Hawking temperature has been derived in this formalism.
The study here represents an attempt to reveal some physics beyond the brick
wall model.
|
[
{
"created": "Mon, 3 Mar 2003 02:51:33 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Apr 2003 02:53:22 GMT",
"version": "v2"
},
{
"created": "Fri, 25 Jul 2003 02:42:15 GMT",
"version": "v3"
}
] |
2009-11-10
|
[
[
"Bai",
"Hua",
""
],
[
"Yan",
"Mu-Lin",
""
]
] |
A semi-classical reasoning leads to the non-commutativity of the space and time coordinates near the horizon of Schwarzschild black hole. This non-commutativity in turn provides a mechanism to interpret the brick wall thickness hypothesis in 't Hooft's brick wall model as well as the boundary condition imposed for the field considered. For concreteness, we consider a noncommutative scalar field model near the horizon and derive the effective metric via the equation of motion of noncommutative scalar field. This metric displays a new horizon in addition to the original one associated with the Schwarzschild black hole. The infinite red-shifting of the scalar field on the new horizon determines the range of the noncommutativ space and explains the relevant boundary condition for the field. This range enables us to calculate the entropy of black hole as proportional to the area of its original horizon along the same line as in 't Hooft's model, and the thickness of the brick wall is found to be proportional to the thermal average of the noncommutative space-time range. The Hawking temperature has been derived in this formalism. The study here represents an attempt to reveal some physics beyond the brick wall model.
|
1512.07109
|
Kirill Krasnov
|
Joel Fine, Yannick Herfray, Kirill Krasnov and Carlos Scarinci
|
Asymptotically hyperbolic connections
|
25 pages, no figures
|
Classical and Quantum Gravity 33 (2016), no 18, 25pp
|
10.1088/0264-9381/33/18/185011
| null |
gr-qc hep-th math.DG
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
General Relativity in 4 dimensions can be equivalently described as a
dynamical theory of SO(3)-connections rather than metrics. We introduce the
notion of asymptotically hyperbolic connections, and work out an analog of the
Fefferman-Graham expansion in the language of connections. As in the metric
setup, one can solve the arising "evolution" equations order by order in the
expansion in powers of the radial coordinate. The solution in the connection
setting is arguably simpler, and very straightforward algebraic manipulations
allow one to see how the obstruction appears at third order in the expansion.
Another interesting feature of the connection formulation is that the "counter
terms" required in the computation of the renormalised volume all combine into
the Chern-Simons functional of the restriction of the connection to the
boundary. As the Chern-Simons invariant is only defined modulo large gauge
transformations, the requirement that the path integral over asymptotically
hyperbolic connections is well-defined requires the cosmological constant to be
quantised. Finally, in the connection setting one can deform the 4D Einstein
condition in an interesting way, and we show that asymptotically hyperbolic
connection expansion is universal and valid for any of the deformed theories.
|
[
{
"created": "Tue, 22 Dec 2015 14:57:49 GMT",
"version": "v1"
}
] |
2017-03-24
|
[
[
"Fine",
"Joel",
""
],
[
"Herfray",
"Yannick",
""
],
[
"Krasnov",
"Kirill",
""
],
[
"Scarinci",
"Carlos",
""
]
] |
General Relativity in 4 dimensions can be equivalently described as a dynamical theory of SO(3)-connections rather than metrics. We introduce the notion of asymptotically hyperbolic connections, and work out an analog of the Fefferman-Graham expansion in the language of connections. As in the metric setup, one can solve the arising "evolution" equations order by order in the expansion in powers of the radial coordinate. The solution in the connection setting is arguably simpler, and very straightforward algebraic manipulations allow one to see how the obstruction appears at third order in the expansion. Another interesting feature of the connection formulation is that the "counter terms" required in the computation of the renormalised volume all combine into the Chern-Simons functional of the restriction of the connection to the boundary. As the Chern-Simons invariant is only defined modulo large gauge transformations, the requirement that the path integral over asymptotically hyperbolic connections is well-defined requires the cosmological constant to be quantised. Finally, in the connection setting one can deform the 4D Einstein condition in an interesting way, and we show that asymptotically hyperbolic connection expansion is universal and valid for any of the deformed theories.
|
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