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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2405.20615
|
James Ripple
|
James Ripple and Anish Agashe
|
The Tolman VII Space-time in the Presence of a Charge and a Cosmological
Constant
|
Comments are welcome
| null | null | null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
The Tolman VII space-time is one of the few physically acceptable exact
solutions in general relativity. In this paper, we derive a generalised Tolman
VII solution which includes a charge and a cosmological constant. We analyse
the spatial geometry of the solution and present conditions for zero and
non-zero spatial curvature. We show that for a particular value of the
boundary, the Tolman VII space-time can be matched to the charged Nariai
space-time. This represents a new class of solutions interior to Nariai.
Matching with the Reissner-Nordstr\"om-de Sitter space-time, we derive analytic
expressions for the metric functions and the pressure. Using this, we show that
the solution allows for trapped null geodesics for a broad range of values for
the charge and the cosmological constant. We investigate a few physical
properties and derive an equation of state for the fluid. Performing numerical
fitting, we show that the fluid can be considered a polytrope with, $\Gamma
\sim 2.4$. Finally, we analyse the energy conditions and conclude that the
solution follows the basic physical acceptability criteria.
|
[
{
"created": "Fri, 31 May 2024 04:07:25 GMT",
"version": "v1"
}
] |
2024-06-03
|
[
[
"Ripple",
"James",
""
],
[
"Agashe",
"Anish",
""
]
] |
The Tolman VII space-time is one of the few physically acceptable exact solutions in general relativity. In this paper, we derive a generalised Tolman VII solution which includes a charge and a cosmological constant. We analyse the spatial geometry of the solution and present conditions for zero and non-zero spatial curvature. We show that for a particular value of the boundary, the Tolman VII space-time can be matched to the charged Nariai space-time. This represents a new class of solutions interior to Nariai. Matching with the Reissner-Nordstr\"om-de Sitter space-time, we derive analytic expressions for the metric functions and the pressure. Using this, we show that the solution allows for trapped null geodesics for a broad range of values for the charge and the cosmological constant. We investigate a few physical properties and derive an equation of state for the fluid. Performing numerical fitting, we show that the fluid can be considered a polytrope with, $\Gamma \sim 2.4$. Finally, we analyse the energy conditions and conclude that the solution follows the basic physical acceptability criteria.
|
0809.3730
|
Slava G. Turyshev
|
Slava G. Turyshev
|
Experimental Tests of General Relativity: Recent Progress and Future
Directions
|
revtex4, 36 pages, 10 figures, 344 refs
|
Usp.Fiz.Nauk 179 (2009) 3-34 [Phys.Usp. 52 (2009) 1-27]
|
10.3367/UFNe.0179.200901a.0003
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Einstein's general theory of relativity is the standard theory of gravity,
especially where the needs of astronomy, astrophysics, cosmology and
fundamental physics are concerned. As such, this theory is used for many
practical purposes involving spacecraft navigation, geodesy and time transfer.
Here I review the foundations of general relativity, discuss recent progress in
the tests of relativistic gravity, and present motivations for the new
generation of high-accuracy tests of new physics beyond general relativity.
Space-based experiments in fundamental physics are capable today to uniquely
address important questions related to the fundamental laws of nature. I
discuss the advances in our understanding of fundamental physics that are
anticipated in the near future and evaluate the discovery potential of a number
of the recently proposed space-based gravitational experiments.
|
[
{
"created": "Mon, 22 Sep 2008 15:50:01 GMT",
"version": "v1"
},
{
"created": "Sun, 18 Jan 2009 08:39:59 GMT",
"version": "v2"
}
] |
2013-01-15
|
[
[
"Turyshev",
"Slava G.",
""
]
] |
Einstein's general theory of relativity is the standard theory of gravity, especially where the needs of astronomy, astrophysics, cosmology and fundamental physics are concerned. As such, this theory is used for many practical purposes involving spacecraft navigation, geodesy and time transfer. Here I review the foundations of general relativity, discuss recent progress in the tests of relativistic gravity, and present motivations for the new generation of high-accuracy tests of new physics beyond general relativity. Space-based experiments in fundamental physics are capable today to uniquely address important questions related to the fundamental laws of nature. I discuss the advances in our understanding of fundamental physics that are anticipated in the near future and evaluate the discovery potential of a number of the recently proposed space-based gravitational experiments.
|
1608.07473
|
Francesco Di Filippo
|
Carlos Barcel\'o, Ra\'ul Carballo-Rubio, Francesco Di Filippo, and
Luis J. Garay
|
From physical symmetries to emergent gauge symmetries
| null |
JHEP 1610 (2016) 084
|
10.1007/JHEP10(2016)084
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Gauge symmetries indicate redundancies in the description of the relevant
degrees of freedom of a given field theory and restrict the nature of
observable quantities. One of the problems faced by emergent theories of
relativistic fields is to understand how gauge symmetries can show up in
systems that contain no trace of these symmetries at a more fundamental level.
In this paper we start a systematic study aimed to establish a satisfactory
mathematical and physical picture of this issue, dealing first with abelian
field theories. We discuss how the trivialization, due to the decoupling and
lack of excitation of some degrees of freedom, of the Noether currents
associated with physical symmetries leads to emergent gauge symmetries in
specific situations. An example of a relativistic field theory of a vector
field is worked out in detail in order to make explicit how this mechanism
works and to clarify the physics behind it. The interplay of these ideas with
well-known results of importance to the emergent gravity program, such as the
Weinberg-Witten theorem, are discussed.
|
[
{
"created": "Fri, 26 Aug 2016 14:32:21 GMT",
"version": "v1"
}
] |
2018-02-08
|
[
[
"Barceló",
"Carlos",
""
],
[
"Carballo-Rubio",
"Raúl",
""
],
[
"Di Filippo",
"Francesco",
""
],
[
"Garay",
"Luis J.",
""
]
] |
Gauge symmetries indicate redundancies in the description of the relevant degrees of freedom of a given field theory and restrict the nature of observable quantities. One of the problems faced by emergent theories of relativistic fields is to understand how gauge symmetries can show up in systems that contain no trace of these symmetries at a more fundamental level. In this paper we start a systematic study aimed to establish a satisfactory mathematical and physical picture of this issue, dealing first with abelian field theories. We discuss how the trivialization, due to the decoupling and lack of excitation of some degrees of freedom, of the Noether currents associated with physical symmetries leads to emergent gauge symmetries in specific situations. An example of a relativistic field theory of a vector field is worked out in detail in order to make explicit how this mechanism works and to clarify the physics behind it. The interplay of these ideas with well-known results of importance to the emergent gravity program, such as the Weinberg-Witten theorem, are discussed.
|
1608.05860
|
Gregory Eskin
|
Gregory Eskin
|
Hawking radiation from acoustic black holes in two space dimensions
|
Final version to be published in the Journal of Math. Physics
|
Journal of Math. Physics, vol. 59, 072502 (2018)
| null | null |
gr-qc math-ph math.AP math.MP
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the Hawking radiation for the acoustic black hole. In the beginning
we follow the outline of T.Jacobson but then we use a different $2+1$ vacuum
state similar to the vacuum state constructed by W.Unruh. We also use a special
form of the wave packets. The focus of the paper is to treat the 2 dimensional
case, in particular, the case when the radial and angular velocity are
variable.
|
[
{
"created": "Sat, 20 Aug 2016 18:32:46 GMT",
"version": "v1"
},
{
"created": "Sun, 25 Sep 2016 06:47:08 GMT",
"version": "v2"
},
{
"created": "Mon, 16 Jan 2017 07:55:05 GMT",
"version": "v3"
},
{
"created": "Mon, 12 Jun 2017 01:09:10 GMT",
"version": "v4"
},
{
"created": "Sun, 15 Jul 2018 19:40:57 GMT",
"version": "v5"
}
] |
2018-07-17
|
[
[
"Eskin",
"Gregory",
""
]
] |
We study the Hawking radiation for the acoustic black hole. In the beginning we follow the outline of T.Jacobson but then we use a different $2+1$ vacuum state similar to the vacuum state constructed by W.Unruh. We also use a special form of the wave packets. The focus of the paper is to treat the 2 dimensional case, in particular, the case when the radial and angular velocity are variable.
|
1909.12773
|
Alireza Talebian Ashkezari
|
Alireza Talebian, Amin Nassiri-Rad, Hassan Firouzjahi
|
Stochastic Effects in Anisotropic Inflation
| null |
Phys. Rev. D 101, 023524 (2020)
|
10.1103/PhysRevD.101.023524
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We revisit the stochastic effects in the model of anisotropic inflation
containing a $U(1)$ gauge field. We obtain the Langevin equations for the
inflaton and gauge fields perturbations and solve them analytically. We show
that if the initial value of the electric field is larger than its classical
attractor value, then the random stochastic forces associated with the gauge
field is balanced by the frictional damping (classical) force and the electric
field falls into an equilibrium (stationary) regime. As a result, the classical
attractor value of the electric field is replaced by its stationary value. We
show that the probability of generating quadrupolar statistical anisotropy
consistent with CMB constraints can be significant.
|
[
{
"created": "Wed, 25 Sep 2019 11:29:01 GMT",
"version": "v1"
}
] |
2020-02-05
|
[
[
"Talebian",
"Alireza",
""
],
[
"Nassiri-Rad",
"Amin",
""
],
[
"Firouzjahi",
"Hassan",
""
]
] |
We revisit the stochastic effects in the model of anisotropic inflation containing a $U(1)$ gauge field. We obtain the Langevin equations for the inflaton and gauge fields perturbations and solve them analytically. We show that if the initial value of the electric field is larger than its classical attractor value, then the random stochastic forces associated with the gauge field is balanced by the frictional damping (classical) force and the electric field falls into an equilibrium (stationary) regime. As a result, the classical attractor value of the electric field is replaced by its stationary value. We show that the probability of generating quadrupolar statistical anisotropy consistent with CMB constraints can be significant.
|
1205.4640
|
Cosimo Bambi
|
Cosimo Bambi
|
A note on the observational evidence for the existence of event horizons
in astrophysical black hole candidates
|
4 pages, no figures. v2: some typos corrected
|
The Scientific World Journal 2013:204315,2013
|
10.1155/2013/204315
|
LMU-ASC-34-12
|
gr-qc astro-ph.HE
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Black holes have the peculiar and intriguing property of having an event
horizon, a one-way membrane causally separating their internal region from the
rest of the Universe. Today astrophysical observations provide some evidence
for the existence of event horizons in astrophysical black hole candidates. In
this short paper, I compare the constraint we can infer from the
non-observation of electromagnetic radiation from the putative surface of these
objects with the bound coming from the ergoregion instability, pointing out the
respective assumptions and limitations.
|
[
{
"created": "Mon, 21 May 2012 15:36:31 GMT",
"version": "v1"
},
{
"created": "Sat, 15 Jun 2013 11:11:33 GMT",
"version": "v2"
}
] |
2013-09-10
|
[
[
"Bambi",
"Cosimo",
""
]
] |
Black holes have the peculiar and intriguing property of having an event horizon, a one-way membrane causally separating their internal region from the rest of the Universe. Today astrophysical observations provide some evidence for the existence of event horizons in astrophysical black hole candidates. In this short paper, I compare the constraint we can infer from the non-observation of electromagnetic radiation from the putative surface of these objects with the bound coming from the ergoregion instability, pointing out the respective assumptions and limitations.
|
1210.2589
|
Maqbool Ahmed
|
Maqbool Ahmed, Rafael Sorkin
|
Everpresent Lambda - II: Structural Stability
|
15 pages, 6 figures, Thoroughly rewritten
| null |
10.1103/PhysRevD.87.063515
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Ideas from causal set theory lead to a fluctuating, time dependent
cosmological-constant of the right order of magnitude to match currently quoted
"dark energy" values. Although such a term was predicted some time ago, a more
detailed analysis of the resulting class of phenomenological models was begun
only recently (based on numerical simulation of the cosmological equations with
such a fluctuating term). In this paper we continue the investigation by
studying the sensitivity of the scheme to some of the ad hoc choices made in
setting it up.
|
[
{
"created": "Tue, 9 Oct 2012 13:12:35 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Nov 2012 10:03:53 GMT",
"version": "v2"
},
{
"created": "Fri, 7 Dec 2012 06:53:30 GMT",
"version": "v3"
}
] |
2013-03-27
|
[
[
"Ahmed",
"Maqbool",
""
],
[
"Sorkin",
"Rafael",
""
]
] |
Ideas from causal set theory lead to a fluctuating, time dependent cosmological-constant of the right order of magnitude to match currently quoted "dark energy" values. Although such a term was predicted some time ago, a more detailed analysis of the resulting class of phenomenological models was begun only recently (based on numerical simulation of the cosmological equations with such a fluctuating term). In this paper we continue the investigation by studying the sensitivity of the scheme to some of the ad hoc choices made in setting it up.
|
1011.3982
|
Simone Calogero
|
Simone Calogero, J. Mark Heinzle
|
Oscillations toward the singularity of LRS Bianchi type IX cosmological
models with Vlasov matter
|
18 pages, 5 figures
|
SIAM J. Appl. Dyn. Syst. 9, 1244-1262 (2010)
| null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We analyze the dynamics of a class of cosmological solutions of the
Einstein-Vlasov equations. These equations describe an ensemble of
collisionless particles (which represent galaxies or clusters of galaxies) that
interact gravitatively through Einstein's equations of general relativity. The
cosmological models we consider are spatially homogeneous, of Bianchi type IX,
and locally rotationally symmetric (LRS). We prove that generic solutions
exhibit an oscillatory approach toward the singularities (the "big bang" in the
past and the "big crunch" in the future); this is in contrast to the behavior
of Einstein-vacuum or Einstein-Euler solutions. To establish this result we
make use of dynamical systems theory; we introduce dimensionless dynamical
variables that are defined on a compact state space; in this formulation the
oscillatory behavior of generic solutions is represented by an approach to
heteroclinic cycles.
|
[
{
"created": "Wed, 17 Nov 2010 15:47:50 GMT",
"version": "v1"
}
] |
2010-11-18
|
[
[
"Calogero",
"Simone",
""
],
[
"Heinzle",
"J. Mark",
""
]
] |
We analyze the dynamics of a class of cosmological solutions of the Einstein-Vlasov equations. These equations describe an ensemble of collisionless particles (which represent galaxies or clusters of galaxies) that interact gravitatively through Einstein's equations of general relativity. The cosmological models we consider are spatially homogeneous, of Bianchi type IX, and locally rotationally symmetric (LRS). We prove that generic solutions exhibit an oscillatory approach toward the singularities (the "big bang" in the past and the "big crunch" in the future); this is in contrast to the behavior of Einstein-vacuum or Einstein-Euler solutions. To establish this result we make use of dynamical systems theory; we introduce dimensionless dynamical variables that are defined on a compact state space; in this formulation the oscillatory behavior of generic solutions is represented by an approach to heteroclinic cycles.
|
1107.3347
|
Rajesh R. Parwani
|
Rajesh R. Parwani and Siti Nursaba Tarih
|
Nonlinear Quantum Cosmology of de Sitter Space
|
Revised version has changed title, abstract and additional review and
clarifying remarks, with typos corrected and references updated. Results
unchanged. 23 pages inclusive of 9 figures
| null | null | null |
gr-qc hep-th quant-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We perform a minisuperspace analysis of an information-theoretic nonlinear
Wheeler-deWitt (WDW) equation for de Sitter universes. The nonlinear WDW
equation, which is in the form of a difference-differential equation, is
transformed into a pure difference equation for the probability density by
using the current conservation constraint. In the present study we observe some
new features not seen in our previous approximate investigation, such as a
nonzero minimum and maximum allowable size to the quantum universe: An
examination of the effective classical dynamics supports the interpretation of
a bouncing universe. The studied model suggests implications for the early
universe, and plausibly also for the future of an ongoing accelerating phase of
the universe.
|
[
{
"created": "Mon, 18 Jul 2011 01:30:51 GMT",
"version": "v1"
},
{
"created": "Fri, 30 Mar 2012 12:47:07 GMT",
"version": "v2"
}
] |
2012-04-02
|
[
[
"Parwani",
"Rajesh R.",
""
],
[
"Tarih",
"Siti Nursaba",
""
]
] |
We perform a minisuperspace analysis of an information-theoretic nonlinear Wheeler-deWitt (WDW) equation for de Sitter universes. The nonlinear WDW equation, which is in the form of a difference-differential equation, is transformed into a pure difference equation for the probability density by using the current conservation constraint. In the present study we observe some new features not seen in our previous approximate investigation, such as a nonzero minimum and maximum allowable size to the quantum universe: An examination of the effective classical dynamics supports the interpretation of a bouncing universe. The studied model suggests implications for the early universe, and plausibly also for the future of an ongoing accelerating phase of the universe.
|
1603.01128
|
Jonathan Engle
|
Christopher Beetle, Jonathan S. Engle, Matthew E. Hogan, Phillip
Mendonca
|
Diffeomorphism invariant cosmological symmetry in full quantum gravity
|
8 pages, invited submission for special issue of Int. J. Mod. Phys.
D; Remark added on use of intertwining condition to reduce quantization
ambiguities, assumptions on matter model made clear, sign convention for
complexification changed to match that of Thiemann, as well as minor
corrections
|
Int. J. Mod. Physics D 25 (2016) 1642012 [issue 8]
|
10.1142/S0218271816420128
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
This paper summarizes a new proposal to define rigorously a sector of loop
quantum gravity at the diffeomorphism invariant level corresponding to
homogeneous and isotropic cosmologies, thereby enabling a detailed comparison
of results in loop quantum gravity and loop quantum cosmology. The key
technical steps we have completed are (a) to formulate conditions for
homogeneity and isotropy in a diffeomorphism covariant way on the classical
phase space of general relativity, and (b) to translate these conditions
consistently using well-understood techniques to loop quantum gravity. Some
additional steps, such as constructing a specific embedding of the Hilbert
space of loop quantum cosmology into a space of (distributional) states in the
full theory, remain incomplete. However, we also describe, as a proof of
concept, a complete analysis of an analogous embedding of homogeneous and
isotropic loop quantum cosmology into the quantum Bianchi I model of Ashtekar
and Wilson-Ewing. Details will appear in a pair of forthcoming papers.
|
[
{
"created": "Thu, 3 Mar 2016 15:25:16 GMT",
"version": "v1"
},
{
"created": "Fri, 9 Sep 2016 15:27:07 GMT",
"version": "v2"
}
] |
2016-09-12
|
[
[
"Beetle",
"Christopher",
""
],
[
"Engle",
"Jonathan S.",
""
],
[
"Hogan",
"Matthew E.",
""
],
[
"Mendonca",
"Phillip",
""
]
] |
This paper summarizes a new proposal to define rigorously a sector of loop quantum gravity at the diffeomorphism invariant level corresponding to homogeneous and isotropic cosmologies, thereby enabling a detailed comparison of results in loop quantum gravity and loop quantum cosmology. The key technical steps we have completed are (a) to formulate conditions for homogeneity and isotropy in a diffeomorphism covariant way on the classical phase space of general relativity, and (b) to translate these conditions consistently using well-understood techniques to loop quantum gravity. Some additional steps, such as constructing a specific embedding of the Hilbert space of loop quantum cosmology into a space of (distributional) states in the full theory, remain incomplete. However, we also describe, as a proof of concept, a complete analysis of an analogous embedding of homogeneous and isotropic loop quantum cosmology into the quantum Bianchi I model of Ashtekar and Wilson-Ewing. Details will appear in a pair of forthcoming papers.
|
0808.1424
|
Yousef Bisabr
|
Yousef Bisabr
|
Holographic Dark Energy Model and Scalar-Tensor Theories
|
11 pages, no figure. To appear in General Relativity and Gravitation
|
Gen.Rel.Grav.41:305-313,2009
|
10.1007/s10714-008-0676-7
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the holographic dark energy model in a generalized scalar tensor
theory. In a universe filled with cold dark matter and dark energy, the effect
of potential of the scalar field is investigated in the equation of state
parameter. We show that for a various types of potentials, the equation of
state parameter is negative and transition from deceleration to acceleration
expansion of the universe is possible.
|
[
{
"created": "Sun, 10 Aug 2008 19:42:00 GMT",
"version": "v1"
}
] |
2009-02-18
|
[
[
"Bisabr",
"Yousef",
""
]
] |
We study the holographic dark energy model in a generalized scalar tensor theory. In a universe filled with cold dark matter and dark energy, the effect of potential of the scalar field is investigated in the equation of state parameter. We show that for a various types of potentials, the equation of state parameter is negative and transition from deceleration to acceleration expansion of the universe is possible.
|
1603.04291
|
Thiago Pereira
|
Thiago S. Pereira and Davincy T. Pabon
|
Extending the LCDM model through shear-free anisotropies
|
12 pages, 2 figures. Proceedings of the 1st Workshop on Inflation and
the Origin of the CMB Anomalies held at Cali -- Colombia, May 2015
| null |
10.1142/S0217732316400095
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
If the spacetime metric has anisotropic spatial curvature, one can afford to
expand the universe isotropically, provided that the energy-momentum tensor
satisfy a certain con- straint. This leads to the so-called shear-free metrics,
which have the interesting property of violating the cosmological principle
while still preserving the isotropy of the cosmic mi- crowave background (CMB)
radiation. In this work we show that shear-free cosmologies correspond to an
attractor solution in the space of models with anisotropic spatial curva- ture.
Through a rigorous definition of linear perturbation theory in these
spacetimes, we show that shear-free models represent a viable alternative to
describe the large-scale evo- lution of the universe, leading, in particular,
to a kinematically equivalent Sachs-Wolfe effect. Alternatively, we discuss
some specific signatures that shear-free models would imprint on the
temperature spectrum of CMB.
|
[
{
"created": "Mon, 14 Mar 2016 14:59:11 GMT",
"version": "v1"
}
] |
2016-07-20
|
[
[
"Pereira",
"Thiago S.",
""
],
[
"Pabon",
"Davincy T.",
""
]
] |
If the spacetime metric has anisotropic spatial curvature, one can afford to expand the universe isotropically, provided that the energy-momentum tensor satisfy a certain con- straint. This leads to the so-called shear-free metrics, which have the interesting property of violating the cosmological principle while still preserving the isotropy of the cosmic mi- crowave background (CMB) radiation. In this work we show that shear-free cosmologies correspond to an attractor solution in the space of models with anisotropic spatial curva- ture. Through a rigorous definition of linear perturbation theory in these spacetimes, we show that shear-free models represent a viable alternative to describe the large-scale evo- lution of the universe, leading, in particular, to a kinematically equivalent Sachs-Wolfe effect. Alternatively, we discuss some specific signatures that shear-free models would imprint on the temperature spectrum of CMB.
|
gr-qc/0010018
|
Tatyana P. Shestakova
|
T. P. Shestakova
|
The status of the Lambda term in quantum geometrodynamics in extended
phase space
|
LaTeX, 6 pages, talk presented at the IV International Conference
"Cosmion-99", Moscow, October 1999, to be published in the Conference
Proceedings
|
Grav.Cosmol.Suppl.6:47-50,2000
| null | null |
gr-qc
| null |
S. Weinberg pointed out a way to introduce a cosmological term by modifying
the theory of gravity. This modification would be justified if the Einstein
equations with the cosmological term could be obtained in the classical limit
of some physically satisfied quantum theory of gravity. We propose to consider
quantum geometrodynamics in extended phase space as a candidate for such a
theory. Quantum geometrodynamics in extended phase space aims at giving a
selfconsistent description of the integrated system ``the physical object (the
Universe) + observation means'', observation means being represented by a
reference frame. The Lambda term appears in classical equations under certain
gauge conditions and characterizes the state of gravitational vacuum related to
a chosen reference frame. The eigenvalue spectrum of Lambda depends on a
concrete cosmological model and can be found by solving the Schrodinger
equation for a wave function of the Universe. The proposed version of quantum
geometrodynamics enables one to make predictions concerning probable values of
the Lambda term at various stages of cosmological evolution.
|
[
{
"created": "Thu, 5 Oct 2000 11:47:58 GMT",
"version": "v1"
}
] |
2011-04-15
|
[
[
"Shestakova",
"T. P.",
""
]
] |
S. Weinberg pointed out a way to introduce a cosmological term by modifying the theory of gravity. This modification would be justified if the Einstein equations with the cosmological term could be obtained in the classical limit of some physically satisfied quantum theory of gravity. We propose to consider quantum geometrodynamics in extended phase space as a candidate for such a theory. Quantum geometrodynamics in extended phase space aims at giving a selfconsistent description of the integrated system ``the physical object (the Universe) + observation means'', observation means being represented by a reference frame. The Lambda term appears in classical equations under certain gauge conditions and characterizes the state of gravitational vacuum related to a chosen reference frame. The eigenvalue spectrum of Lambda depends on a concrete cosmological model and can be found by solving the Schrodinger equation for a wave function of the Universe. The proposed version of quantum geometrodynamics enables one to make predictions concerning probable values of the Lambda term at various stages of cosmological evolution.
|
2405.17302
|
Maria Rossell\'o-Sastre
|
Maria Rossell\'o-Sastre, Sascha Husa, Sayantani Bera
|
A waveform model for the missing quadrupole mode from black hole
coalescence: memory effect and ringdown of the $(\ell=2,m=0)$ spherical
harmonic
|
20 pages, 13 figures
| null | null |
LIGO-P2400208
|
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
In this paper we describe a model for the $(\ell=2, m=0)$ spherical harmonic
mode of the gravitational wave signal emitted by the coalescence of binary
black holes, in particular, spin-aligned systems. This mode can be viewed as
consisting of two components, gravitational wave memory and quasi-normal
ringdown, which are both included in our model. Depending on the parameters of
the binary and the sensitivity curve of the detector, but in particular for
high masses, the ringdown part can contribute significantly to the
signal-to-noise ratio. The model is constructed using the methods of the
phenomenological waveforms program, and is calibrated to public numerical
relativity data from the SXS waveforms catalog, with the analytical results
derived from the BMS balance laws. The code has been implemented as an
extension to the computationally efficient IMRPhenomTHM model, it can therefore
be used for computationally expensive applications such as Bayesian parameter
estimation. The region of validity of our model in the parameter space is given
by: $q\leq10$ and $\chi_{1},\chi_{2}\in[-1,1]$, and no restrictions apply in
terms of the length of the waveforms.
|
[
{
"created": "Mon, 27 May 2024 16:03:52 GMT",
"version": "v1"
}
] |
2024-05-28
|
[
[
"Rosselló-Sastre",
"Maria",
""
],
[
"Husa",
"Sascha",
""
],
[
"Bera",
"Sayantani",
""
]
] |
In this paper we describe a model for the $(\ell=2, m=0)$ spherical harmonic mode of the gravitational wave signal emitted by the coalescence of binary black holes, in particular, spin-aligned systems. This mode can be viewed as consisting of two components, gravitational wave memory and quasi-normal ringdown, which are both included in our model. Depending on the parameters of the binary and the sensitivity curve of the detector, but in particular for high masses, the ringdown part can contribute significantly to the signal-to-noise ratio. The model is constructed using the methods of the phenomenological waveforms program, and is calibrated to public numerical relativity data from the SXS waveforms catalog, with the analytical results derived from the BMS balance laws. The code has been implemented as an extension to the computationally efficient IMRPhenomTHM model, it can therefore be used for computationally expensive applications such as Bayesian parameter estimation. The region of validity of our model in the parameter space is given by: $q\leq10$ and $\chi_{1},\chi_{2}\in[-1,1]$, and no restrictions apply in terms of the length of the waveforms.
|
1912.07068
|
Hexu Zhang
|
He-Xu Zhang, Cong Li, Peng-Zhang He, Qi-Qi Fan, Jian-Bo Deng
|
Optical properties of a Brane-World black hole as photons couple to the
Weyl tensor
|
arXiv admin note: text overlap with arXiv:1502.01088,
arXiv:1611.08783, arXiv:1606.04634 by other authors
| null |
10.1140/epjc/s10052-020-8022-7
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this article, we have investigated the equations of motion of the photons
coupled to Weyl tensor by the geometric optics approximation and the
corresponding shadow in a Brane-World black hole spacetime. It is shown that
there exists a double shadow for a black hole since the coupling photons with
different polarization directions propagate along different paths in the
spacetime. Furthermore, we discuss the effects of the metric parameter $\alpha$
related to the cosmological constant, X-cold dark matter parameter $\beta$ and
the coupling parameter $\lambda$ on the umbra (the overlap region of the double
shadow) and the penumbra. We also obtain the finite-distance corrections to the
deflection angle of light in the Brane-World black hole spacetime as the
photons coupled to Weyl tensor by using a recent geometric method.
|
[
{
"created": "Sun, 15 Dec 2019 16:38:25 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Mar 2020 09:06:54 GMT",
"version": "v2"
}
] |
2020-06-24
|
[
[
"Zhang",
"He-Xu",
""
],
[
"Li",
"Cong",
""
],
[
"He",
"Peng-Zhang",
""
],
[
"Fan",
"Qi-Qi",
""
],
[
"Deng",
"Jian-Bo",
""
]
] |
In this article, we have investigated the equations of motion of the photons coupled to Weyl tensor by the geometric optics approximation and the corresponding shadow in a Brane-World black hole spacetime. It is shown that there exists a double shadow for a black hole since the coupling photons with different polarization directions propagate along different paths in the spacetime. Furthermore, we discuss the effects of the metric parameter $\alpha$ related to the cosmological constant, X-cold dark matter parameter $\beta$ and the coupling parameter $\lambda$ on the umbra (the overlap region of the double shadow) and the penumbra. We also obtain the finite-distance corrections to the deflection angle of light in the Brane-World black hole spacetime as the photons coupled to Weyl tensor by using a recent geometric method.
|
1510.00621
|
Jeff Steinhauer
|
Jeff Steinhauer
|
Observation of quantum Hawking radiation and its entanglement in an
analogue black hole
|
The latest version has additional data and explanations
|
Nature Phys. 12, 959 (2016)
|
10.1038/nphys3863
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We observe spontaneous Hawking radiation, stimulated by quantum vacuum
fluctuations, emanating from an analogue black hole in an atomic Bose-Einstein
condensate. Correlations are observed between the Hawking particles outside the
black hole and the partner particles inside. These correlations indicate an
approximately thermal distribution of Hawking radiation. We find that the high
energy pairs are entangled, while the low energy pairs are not, within the
reasonable assumption that excitations with different frequencies are not
correlated. The entanglement verifies the quantum nature of the Hawking
radiation. The results are consistent with a driven oscillation experiment and
a numerical simulation.
|
[
{
"created": "Fri, 2 Oct 2015 15:27:27 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Oct 2015 15:07:32 GMT",
"version": "v2"
},
{
"created": "Tue, 8 Aug 2017 12:22:51 GMT",
"version": "v3"
}
] |
2017-08-09
|
[
[
"Steinhauer",
"Jeff",
""
]
] |
We observe spontaneous Hawking radiation, stimulated by quantum vacuum fluctuations, emanating from an analogue black hole in an atomic Bose-Einstein condensate. Correlations are observed between the Hawking particles outside the black hole and the partner particles inside. These correlations indicate an approximately thermal distribution of Hawking radiation. We find that the high energy pairs are entangled, while the low energy pairs are not, within the reasonable assumption that excitations with different frequencies are not correlated. The entanglement verifies the quantum nature of the Hawking radiation. The results are consistent with a driven oscillation experiment and a numerical simulation.
|
2307.12031
|
Alejandro Perez
|
Alejandro Perez, Salvatore Ribisi
|
Light-cone thermodynamics: purification of the Minkowski vacuum
|
Typos corrected
| null | null | null |
gr-qc hep-th math-ph math.MP
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We explicitly express the Minkowski vacuum of a massless scalar field in
terms of the particle notion associated with suitable spherical conformal
killing fields. These fields are orthogonal to the light wavefronts originating
from a sphere with a radius of $r_{H}$ in flat spacetime: a bifurcate conformal
killing horizon that exhibits semiclassical features similar to those of black
hole horizons and Cauchy horizons of spherically symmetric black holes. Our
result highlights the quantum aspects of this analogy and extends the
well-known decomposition of the Minkowski vacuum in terms of Rindler modes,
which are associated with the boost Killing field normal to a pair of null
planes in Minkowski spacetime (the basis of the Unruh effect). While some
features of our result have been established by Kay and Wald's theorems in the
90s -- on quantum field theory in stationary spacetimes with bifurcate Killing
horizons -- the added value we provide here lies in the explicit expression of
the vacuum.
|
[
{
"created": "Sat, 22 Jul 2023 09:35:58 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Feb 2024 14:39:53 GMT",
"version": "v2"
}
] |
2024-02-20
|
[
[
"Perez",
"Alejandro",
""
],
[
"Ribisi",
"Salvatore",
""
]
] |
We explicitly express the Minkowski vacuum of a massless scalar field in terms of the particle notion associated with suitable spherical conformal killing fields. These fields are orthogonal to the light wavefronts originating from a sphere with a radius of $r_{H}$ in flat spacetime: a bifurcate conformal killing horizon that exhibits semiclassical features similar to those of black hole horizons and Cauchy horizons of spherically symmetric black holes. Our result highlights the quantum aspects of this analogy and extends the well-known decomposition of the Minkowski vacuum in terms of Rindler modes, which are associated with the boost Killing field normal to a pair of null planes in Minkowski spacetime (the basis of the Unruh effect). While some features of our result have been established by Kay and Wald's theorems in the 90s -- on quantum field theory in stationary spacetimes with bifurcate Killing horizons -- the added value we provide here lies in the explicit expression of the vacuum.
|
gr-qc/0701073
|
Luis Herrera
|
L. Herrera
|
The inertia of heat and its role in the dynamics of dissipative collapse
|
Latex file. To appear in Int.J.Mod.Phys.D. Year of reference [1]
corrected
|
Int.J.Mod.Phys.D15:2197-2202,2006
|
10.1142/S0218271806009753
| null |
gr-qc astro-ph physics.space-ph
| null |
The decreasing of the inertial mass density, established in the past for
dissipative fluids, is found to be produced by the ``inertial'' term of the
transport equation. Once the transport equation is coupled to the dynamical
equation one finds that the contribution of the inertial term diminishes the
effective inertial mass and the ``gravitational'' force term, by the same
factor. An intuitive picture, and prospective applications of this result to
astrophysical scenarios are discussed.
|
[
{
"created": "Mon, 15 Jan 2007 18:39:42 GMT",
"version": "v1"
},
{
"created": "Thu, 12 Apr 2007 16:02:03 GMT",
"version": "v2"
}
] |
2008-11-26
|
[
[
"Herrera",
"L.",
""
]
] |
The decreasing of the inertial mass density, established in the past for dissipative fluids, is found to be produced by the ``inertial'' term of the transport equation. Once the transport equation is coupled to the dynamical equation one finds that the contribution of the inertial term diminishes the effective inertial mass and the ``gravitational'' force term, by the same factor. An intuitive picture, and prospective applications of this result to astrophysical scenarios are discussed.
|
gr-qc/9807063
|
Bahram Mashhoon
|
B. Mashhoon (University of Missouri-Columbia) and N. O. Santos (Cidade
Universitaria)
|
Rotating Cylindrical Systems and Gravitomagnetism
|
LaTeX file, 22 pages, no figures, submitted to Phys. Rev. D
|
Annalen Phys. 9 (2000) 49-63
|
10.1002/(SICI)1521-3889(200001)9:1<49::AID-ANDP49>3.0.CO;2-2
| null |
gr-qc
| null |
We discuss gravitomagnetism in connection with rotating cylindrical systems.
In particular, the gravitomagnetic clock effect is investigated for the
exterior vacuum field of an infinite rotating cylinder. The dependence of the
clock effect on the Weyl parameters of the stationary Lewis metric is
determined. We illustrate our results by means of the van Stockum spacetime.
|
[
{
"created": "Thu, 23 Jul 1998 04:35:03 GMT",
"version": "v1"
}
] |
2017-09-27
|
[
[
"Mashhoon",
"B.",
"",
"University of Missouri-Columbia"
],
[
"Santos",
"N. O.",
"",
"Cidade\n Universitaria"
]
] |
We discuss gravitomagnetism in connection with rotating cylindrical systems. In particular, the gravitomagnetic clock effect is investigated for the exterior vacuum field of an infinite rotating cylinder. The dependence of the clock effect on the Weyl parameters of the stationary Lewis metric is determined. We illustrate our results by means of the van Stockum spacetime.
|
1009.1096
|
Swastik Bhattacharya
|
Swastik Bhattacharya, Pankaj S. Joshi
|
Regularity of initial data in dynamical massless scalar field models
|
5 pages, No figures
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We discuss here the issue of regularity of initial data for dynamical
spherically symmetric massless scalar field models in a spacetime. Generalizing
the known solutions of Einstein equations given in this case by Wyman and
Roberts, we examine the issue of regularity on a given spacelike surface,
especially when the gradient of the field is spacelike. In particular, we
isolate the class of models which would have necessarily a singularity at the
center, and therefore these would be unsuitable for studying either
gravitational collapse or dynamical evolutions in cosmology.
|
[
{
"created": "Mon, 6 Sep 2010 17:08:52 GMT",
"version": "v1"
}
] |
2010-09-07
|
[
[
"Bhattacharya",
"Swastik",
""
],
[
"Joshi",
"Pankaj S.",
""
]
] |
We discuss here the issue of regularity of initial data for dynamical spherically symmetric massless scalar field models in a spacetime. Generalizing the known solutions of Einstein equations given in this case by Wyman and Roberts, we examine the issue of regularity on a given spacelike surface, especially when the gradient of the field is spacelike. In particular, we isolate the class of models which would have necessarily a singularity at the center, and therefore these would be unsuitable for studying either gravitational collapse or dynamical evolutions in cosmology.
|
1801.07261
|
Shahar Hod
|
Shahar Hod
|
Strong cosmic censorship in charged black-hole spacetimes: As strong as
ever
|
7 pages
|
Nuclear Physics B 941, 636 (2019)
|
10.1016/j.nuclphysb.2019.03.003
| null |
gr-qc astro-ph.HE hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
It is proved that dynamically formed Reissner-Nordstr\"om-de Sitter (RNdS)
black holes, which have recently been claimed to provide counter-examples to
the Penrose strong cosmic censorship conjecture, are characterized by unstable
(singular) inner Cauchy horizons. The proof is based on analytical techniques
which explicitly reveal the fact that {\it charged} massive scalar fields in
the charged RNdS black-hole spacetime are characterized, in the large-coupling
regime, by quasinormal resonant frequencies with
$\Im\omega^{\text{min}}<{1\over2}\kappa_+$, where $\kappa_+$ is the surface
gravity of the black-hole event horizon. This result implies that the
corresponding relaxation rate $\psi\sim e^{-\Im\omega^{\text{min}}t}$ of the
collapsed charged fields is slow enough to guarantee, through the
mass-inflation mechanism, the instability of the dynamically formed inner
Cauchy horizons. Our results reveal the physically important fact that, taking
into account the unavoidable presence of {\it charged} matter fields in
dynamically formed {\it charged} spacetimes, non-asymptotically flat RNdS black
holes are globally hyperbolic and therefore respect the fundamental strong
cosmic censorship conjecture.
|
[
{
"created": "Mon, 22 Jan 2018 19:00:03 GMT",
"version": "v1"
}
] |
2019-05-01
|
[
[
"Hod",
"Shahar",
""
]
] |
It is proved that dynamically formed Reissner-Nordstr\"om-de Sitter (RNdS) black holes, which have recently been claimed to provide counter-examples to the Penrose strong cosmic censorship conjecture, are characterized by unstable (singular) inner Cauchy horizons. The proof is based on analytical techniques which explicitly reveal the fact that {\it charged} massive scalar fields in the charged RNdS black-hole spacetime are characterized, in the large-coupling regime, by quasinormal resonant frequencies with $\Im\omega^{\text{min}}<{1\over2}\kappa_+$, where $\kappa_+$ is the surface gravity of the black-hole event horizon. This result implies that the corresponding relaxation rate $\psi\sim e^{-\Im\omega^{\text{min}}t}$ of the collapsed charged fields is slow enough to guarantee, through the mass-inflation mechanism, the instability of the dynamically formed inner Cauchy horizons. Our results reveal the physically important fact that, taking into account the unavoidable presence of {\it charged} matter fields in dynamically formed {\it charged} spacetimes, non-asymptotically flat RNdS black holes are globally hyperbolic and therefore respect the fundamental strong cosmic censorship conjecture.
|
1205.0118
|
Yuki Kanai
|
Yuki Kanai and Akio Hosoya
|
Hawking radiation from a collapsing dust sphere and its back reaction at
the event horizon -Weak value approach-
|
13 pages, 1 figure
| null | null | null |
gr-qc quant-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
To see the back reaction of the Hawking radiation in a dynamical spacetime of
the spherical gravitational collapse, we explicitly calculate the weak value of
the energy-momentum tensor of the massless scalar field. The background
geometry of a collapsing dust sphere is specified by using the
Painleve-Gullstrand coordinates, in which the time coordinate coincides with
the proper time of a free-falling observer and the metric tensor is regular at
the event horizon. The result is that in the remote future the weak value
diverges at the event horizon. We argue that since the semi-classical
approximation of the Einstein equation in the sense of the weak value breaks
down there, the future geometry of the spacetime cannot be the Schwarzschild
geometry.
|
[
{
"created": "Tue, 1 May 2012 09:02:21 GMT",
"version": "v1"
},
{
"created": "Sat, 16 Mar 2013 08:59:00 GMT",
"version": "v2"
}
] |
2015-03-20
|
[
[
"Kanai",
"Yuki",
""
],
[
"Hosoya",
"Akio",
""
]
] |
To see the back reaction of the Hawking radiation in a dynamical spacetime of the spherical gravitational collapse, we explicitly calculate the weak value of the energy-momentum tensor of the massless scalar field. The background geometry of a collapsing dust sphere is specified by using the Painleve-Gullstrand coordinates, in which the time coordinate coincides with the proper time of a free-falling observer and the metric tensor is regular at the event horizon. The result is that in the remote future the weak value diverges at the event horizon. We argue that since the semi-classical approximation of the Einstein equation in the sense of the weak value breaks down there, the future geometry of the spacetime cannot be the Schwarzschild geometry.
|
1709.04367
|
Ravindra Saraykar Dr.
|
R V Saraykar and Sujatha Janardhan
|
Role of Topologies in the Study of Dynamical Aspects of Stable and
Generic Properties of Space-times in General Relativity
|
arXiv admin note: substantial text overlap with arXiv:1612.08812,
arXiv:1609.07703
|
Asian Journal of Mathematics and Computer Research, Vol.20, Issue
1 (2017) 22-31
| null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In [1], the authors have studied stability of certain causal properties of
space-times in general relativity. As a continuation of this work, in the
present paper, we review and discuss, some more aspects of stability which
occur in various situations in the dynamics of general relativity. We argue
that not only choice of appropriate topology, but also the nature of
perturbation, like metric, matter or initial data, are key factors in deciding
whether a property is stable or not. We also study certain properties of
space-times which are generic in an appropriate mathematical sense. In
particular we argue that Linearization stability of a space-time is a generic
property.
|
[
{
"created": "Tue, 12 Sep 2017 07:08:23 GMT",
"version": "v1"
}
] |
2017-09-14
|
[
[
"Saraykar",
"R V",
""
],
[
"Janardhan",
"Sujatha",
""
]
] |
In [1], the authors have studied stability of certain causal properties of space-times in general relativity. As a continuation of this work, in the present paper, we review and discuss, some more aspects of stability which occur in various situations in the dynamics of general relativity. We argue that not only choice of appropriate topology, but also the nature of perturbation, like metric, matter or initial data, are key factors in deciding whether a property is stable or not. We also study certain properties of space-times which are generic in an appropriate mathematical sense. In particular we argue that Linearization stability of a space-time is a generic property.
|
1101.4311
|
Mohammad Vahid Takook
|
H. Pejhan, M.R. Tanhayi and M.V. Takook
|
Auxiliary "massless" spin-2 field in de Sitter universe
|
16 pages
|
Int.J.Theor.Phys.49:2263-2277,2010
|
10.1007/s10773-010-0413-3
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
For the tensor field of rank-2 there are two unitary irreducible
representation (UIR) in de Sitter (dS) space denoted by $\Pi^{\pm}_{2,2}$ and
$\Pi^{\pm}_{2,1}$ [1]. In the flat limit only the $\Pi^{\pm}_{2,2}$ coincides
to the UIR of Poincar\'e group, the second one becomes important in the study
of conformal gravity. In the pervious work, Dirac's six-cone formalism has been
utilized to obtain conformally invariant (CI) field equation for the "massless"
spin-2 field in dS space [2]. This equation results in a field which
transformed according to $\Pi^{\pm}_{2,1}$, we name this field the auxiliary
field. In this paper this auxiliary field is considered and also related
two-point function is calculated as a product of a polarization tensor and
"massless" conformally coupled scalar field. This two-point function is de
Sitter invariant.
|
[
{
"created": "Sat, 22 Jan 2011 19:27:43 GMT",
"version": "v1"
}
] |
2011-01-27
|
[
[
"Pejhan",
"H.",
""
],
[
"Tanhayi",
"M. R.",
""
],
[
"Takook",
"M. V.",
""
]
] |
For the tensor field of rank-2 there are two unitary irreducible representation (UIR) in de Sitter (dS) space denoted by $\Pi^{\pm}_{2,2}$ and $\Pi^{\pm}_{2,1}$ [1]. In the flat limit only the $\Pi^{\pm}_{2,2}$ coincides to the UIR of Poincar\'e group, the second one becomes important in the study of conformal gravity. In the pervious work, Dirac's six-cone formalism has been utilized to obtain conformally invariant (CI) field equation for the "massless" spin-2 field in dS space [2]. This equation results in a field which transformed according to $\Pi^{\pm}_{2,1}$, we name this field the auxiliary field. In this paper this auxiliary field is considered and also related two-point function is calculated as a product of a polarization tensor and "massless" conformally coupled scalar field. This two-point function is de Sitter invariant.
|
gr-qc/0702079
|
Valerio Faraoni
|
Valerio Faraoni (Bishop's University)
|
A common misconception about LIGO detectors of gravitational waves
|
9 pages, LaTeX, to appear in Gen. Rel. Grav
|
Gen.Rel.Grav.39:677-684.2007
|
10.1007/s10714-007-0415-5
| null |
gr-qc
| null |
A common misconception about laser interferometric detectors of gravitational
waves purports that, because the wavelength of laser light and the length of an
interferometer's arm are both stretched by a gravitational wave, no effect
should be visible, invoking an analogy with cosmological redshift in an
expanding universe. The issue is clarified with the help of a direct
calculation.
|
[
{
"created": "Wed, 14 Feb 2007 14:29:33 GMT",
"version": "v1"
}
] |
2014-11-17
|
[
[
"Faraoni",
"Valerio",
"",
"Bishop's University"
]
] |
A common misconception about laser interferometric detectors of gravitational waves purports that, because the wavelength of laser light and the length of an interferometer's arm are both stretched by a gravitational wave, no effect should be visible, invoking an analogy with cosmological redshift in an expanding universe. The issue is clarified with the help of a direct calculation.
|
1807.10361
|
Jose Navarro-Salas
|
Antonio Ferreiro, Jose Navarro-Salas and Silvia Pla
|
Role of gravity in the pair creation induced by electric fields
|
Latex file, 7 pages. Misprints corrected. Slight change in title
|
Phys. Rev. D 98, 045015 (2018)
|
10.1103/PhysRevD.98.045015
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We analyze the pair production induced by homogenous, time-dependent electric
fields in an expanding space-time background. We point out that, in obtaining
the semiclassical Maxwell equations, two distinct notions of adiabatic
renormalization are possible. In Minkowski space the two recipes turn out to be
equivalent. However, in the presence of gravity only the recipe requiring an
adiabatic hierarchy between the gravitational and the gauge field is consistent
with the conservation of the energy-momentum tensor.
|
[
{
"created": "Thu, 26 Jul 2018 20:50:42 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Sep 2018 14:54:10 GMT",
"version": "v2"
}
] |
2018-09-20
|
[
[
"Ferreiro",
"Antonio",
""
],
[
"Navarro-Salas",
"Jose",
""
],
[
"Pla",
"Silvia",
""
]
] |
We analyze the pair production induced by homogenous, time-dependent electric fields in an expanding space-time background. We point out that, in obtaining the semiclassical Maxwell equations, two distinct notions of adiabatic renormalization are possible. In Minkowski space the two recipes turn out to be equivalent. However, in the presence of gravity only the recipe requiring an adiabatic hierarchy between the gravitational and the gauge field is consistent with the conservation of the energy-momentum tensor.
|
0810.2209
|
Stefano Viaggiu
|
Stefano Viaggiu
|
Modeling usual and unusual anisotropic spheres
|
Final version published in IJMPD
|
Int.J.Mod.Phys.D18:275-288,2009
|
10.1142/S021827180901442X
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper, we study anisotropic spheres built from known static spherical
solutions. In particular, we are interested in the physical consequences of a
"small" departure from a physically sensible configuration. The obtained
solutions smoothly depend on free parameters. By setting these parameters to
zero, the starting seed solution is regained. We apply our procedure in detail
by taking as seed solutions the Florides metrics, and the Tolman IV solution.
We show that the chosen Tolman IV, and also Heint IIa Durg IV,V perfect fluid
solutions, can be used to generate a class of parametric solutions where the
anisotropic factor has features recalling boson stars. This is an indication
that boson stars could emerge by "perturbing" appropriately a perfect fluid
solution (at least for the seed metrics considered). Finally, starting with
Tolman IV, Heint IIa and Durg IV,V solutions, we build anisotropic
gravastar-like sources with the appropriate boundary conditions.
|
[
{
"created": "Mon, 13 Oct 2008 11:24:12 GMT",
"version": "v1"
},
{
"created": "Mon, 6 Apr 2009 11:16:09 GMT",
"version": "v2"
}
] |
2009-04-17
|
[
[
"Viaggiu",
"Stefano",
""
]
] |
In this paper, we study anisotropic spheres built from known static spherical solutions. In particular, we are interested in the physical consequences of a "small" departure from a physically sensible configuration. The obtained solutions smoothly depend on free parameters. By setting these parameters to zero, the starting seed solution is regained. We apply our procedure in detail by taking as seed solutions the Florides metrics, and the Tolman IV solution. We show that the chosen Tolman IV, and also Heint IIa Durg IV,V perfect fluid solutions, can be used to generate a class of parametric solutions where the anisotropic factor has features recalling boson stars. This is an indication that boson stars could emerge by "perturbing" appropriately a perfect fluid solution (at least for the seed metrics considered). Finally, starting with Tolman IV, Heint IIa and Durg IV,V solutions, we build anisotropic gravastar-like sources with the appropriate boundary conditions.
|
gr-qc/0511116
|
Jared Maruskin
|
Jared M. Maruskin
|
Considerations of a $k=+1$ Varluminopic Cosmology
|
24 pages
| null | null | null |
gr-qc astro-ph
| null |
Every relativistic particle has 4-speed equal to $c$, since $g_{\mu \nu}
\frac{dx^\mu}{d\tau} \frac{dx^\nu}{d\tau} = c^2$. With the choice of $k = +1$
in the FRW metric, the cosmological scale factor $a(t)$ has the natural
interpretation of the radius of the sphere $S^3_a = \{x \in \mathbb{R}^4 : (x,
x) = a^2\}$. Thus, a particle at rest in the cosmological frame has 4-speed
equal to $\frac{da}{dt}$. This leads us to infer that $\dot a = c$, which
respresents a simple kinematic constraint linking the speed of light to the
cosmological scale factor. This drastically changes the $k=+1$ picture from a
closed deaccelerating universe to an open accelerating universe, settles the
horizon problem, and provides for a new cosmological model more appealing to
our natural intuition. In this paper we shall consider ramifications of this
model.
|
[
{
"created": "Mon, 21 Nov 2005 19:21:24 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Maruskin",
"Jared M.",
""
]
] |
Every relativistic particle has 4-speed equal to $c$, since $g_{\mu \nu} \frac{dx^\mu}{d\tau} \frac{dx^\nu}{d\tau} = c^2$. With the choice of $k = +1$ in the FRW metric, the cosmological scale factor $a(t)$ has the natural interpretation of the radius of the sphere $S^3_a = \{x \in \mathbb{R}^4 : (x, x) = a^2\}$. Thus, a particle at rest in the cosmological frame has 4-speed equal to $\frac{da}{dt}$. This leads us to infer that $\dot a = c$, which respresents a simple kinematic constraint linking the speed of light to the cosmological scale factor. This drastically changes the $k=+1$ picture from a closed deaccelerating universe to an open accelerating universe, settles the horizon problem, and provides for a new cosmological model more appealing to our natural intuition. In this paper we shall consider ramifications of this model.
|
gr-qc/9504021
|
Bill Hiscock
|
Tsunefumi Tanaka and William A. Hiscock (Montana State University)
|
Massive scalar field in multiply connected flat spacetimes
|
19 pages, REVTeX, 5 figures in separate uuencoded compressed file
|
Phys.Rev.D52:4503-4511,1995
|
10.1103/PhysRevD.52.4503
| null |
gr-qc
| null |
The vacuum expectation value of the stress-energy tensor $\left\langle
0\left| T_{\mu\nu} \right|0\right\rangle$ is calculated in several multiply
connected flat spacetimes for a massive scalar field with arbitrary curvature
coupling. We find that a nonzero field mass always decreases the magnitude of
the energy density in chronology-respecting manifolds such as $R^3 \times S^1$,
$R^2 \times T^2$, $R^1 \times T^3$, the M\"{o}bius strip, and the Klein bottle.
In Grant space, which contains nonchronal regions, whether $\left\langle
0\left| T_{\mu\nu} \right|0\right\rangle$ diverges on a chronology horizon or
not depends on the field mass. For a sufficiently large mass $\left\langle
0\left| T_{\mu\nu} \right|0\right\rangle$ remains finite, and the metric
backreaction caused by a massive quantized field may not be large enough to
significantly change the Grant space geometry.
|
[
{
"created": "Fri, 14 Apr 1995 17:17:49 GMT",
"version": "v1"
}
] |
2010-11-01
|
[
[
"Tanaka",
"Tsunefumi",
"",
"Montana State University"
],
[
"Hiscock",
"William A.",
"",
"Montana State University"
]
] |
The vacuum expectation value of the stress-energy tensor $\left\langle 0\left| T_{\mu\nu} \right|0\right\rangle$ is calculated in several multiply connected flat spacetimes for a massive scalar field with arbitrary curvature coupling. We find that a nonzero field mass always decreases the magnitude of the energy density in chronology-respecting manifolds such as $R^3 \times S^1$, $R^2 \times T^2$, $R^1 \times T^3$, the M\"{o}bius strip, and the Klein bottle. In Grant space, which contains nonchronal regions, whether $\left\langle 0\left| T_{\mu\nu} \right|0\right\rangle$ diverges on a chronology horizon or not depends on the field mass. For a sufficiently large mass $\left\langle 0\left| T_{\mu\nu} \right|0\right\rangle$ remains finite, and the metric backreaction caused by a massive quantized field may not be large enough to significantly change the Grant space geometry.
|
1905.12428
|
Mohammad Ghanaatian
|
A. Bazrafshan, F. Naeimipour, M. Ghanaatian, A. Khajeh
|
Physical and thermodynamic properties of quartic quasitopological black
holes and rotating black branes with nonlinear source
|
14 pages, 7 figures
|
Phys. Rev. D 100, 064062 (2019)
|
10.1103/PhysRevD.100.064062
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper, we find the solutions of quartic quasitopological black holes
and branes coupled to logarithmic and exponential forms of nonlinear
electrodynamics. These solutions have an essential singularity at $r=0$.
Depending on the value of charge parameter $q$, we have an extreme black
hole/brane, a black hole/brane with two horizons or a naked singularity. For
small values of parameter $q$, the solutions lead to a black hole/brane with
two horizons. The values of the horizons are independent of the values of
quasitopological parameters and depend only on the values of $q$, dimensions
$n$, nonlinear parameter $\beta$ and mass parameter. Also, the solutions are
not thermally stable for dS and flat spacetimes. However, AdS solutions are
stable for $r_{+}>{r_{+}}_{\rm{ext}}$ which the temperature is zero for
$r_{+}={r_{+}}_{\rm{ext}}$. The value of ${r_{+}}_{\rm{ext}}$ also depends on
the values of parameters $q$, $\beta$, $n$ and $m$. As the value of
${r_{+}}_{\rm{ext}}$ decreases, the region of stability becomes larger. We also
use HPEM metric to probe GTD formalism for our solutions. This metric is
successful to predict the divergences of the scalar curvature exactly at the
phase transition points. For large values of parameter $\Xi$, the black
hole/brane has a transition to a stable state and stays stable.
|
[
{
"created": "Mon, 27 May 2019 22:12:57 GMT",
"version": "v1"
}
] |
2019-10-02
|
[
[
"Bazrafshan",
"A.",
""
],
[
"Naeimipour",
"F.",
""
],
[
"Ghanaatian",
"M.",
""
],
[
"Khajeh",
"A.",
""
]
] |
In this paper, we find the solutions of quartic quasitopological black holes and branes coupled to logarithmic and exponential forms of nonlinear electrodynamics. These solutions have an essential singularity at $r=0$. Depending on the value of charge parameter $q$, we have an extreme black hole/brane, a black hole/brane with two horizons or a naked singularity. For small values of parameter $q$, the solutions lead to a black hole/brane with two horizons. The values of the horizons are independent of the values of quasitopological parameters and depend only on the values of $q$, dimensions $n$, nonlinear parameter $\beta$ and mass parameter. Also, the solutions are not thermally stable for dS and flat spacetimes. However, AdS solutions are stable for $r_{+}>{r_{+}}_{\rm{ext}}$ which the temperature is zero for $r_{+}={r_{+}}_{\rm{ext}}$. The value of ${r_{+}}_{\rm{ext}}$ also depends on the values of parameters $q$, $\beta$, $n$ and $m$. As the value of ${r_{+}}_{\rm{ext}}$ decreases, the region of stability becomes larger. We also use HPEM metric to probe GTD formalism for our solutions. This metric is successful to predict the divergences of the scalar curvature exactly at the phase transition points. For large values of parameter $\Xi$, the black hole/brane has a transition to a stable state and stays stable.
|
0704.2670
|
Adrian Sabin Popescu
|
Adrian Sabin Popescu
|
D.E.U.S. (Dimension Embedded in Unified Symmetry)
|
247 pages, 113 figures; We merged all the DEUS model papers in a
single volume
| null | null | null |
gr-qc
| null |
An unified model of the Universe, Black Holes, particles .... and beyond.
|
[
{
"created": "Fri, 20 Apr 2007 08:41:41 GMT",
"version": "v1"
},
{
"created": "Mon, 7 May 2007 12:51:50 GMT",
"version": "v2"
}
] |
2009-09-29
|
[
[
"Popescu",
"Adrian Sabin",
""
]
] |
An unified model of the Universe, Black Holes, particles .... and beyond.
|
2407.07156
|
Valerio De Luca
|
Valerio De Luca, Alice Garoffolo, Justin Khoury, Mark Trodden
|
Tidal Love numbers and Green's functions in black hole space-times
|
18 pages, 3 figures
| null | null | null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Tidal interactions play a crucial role in deciphering gravitational wave
signals emitted by the coalescence of binary systems. They are usually
quantified by a set of complex coefficients which include tidal Love numbers,
describing the conservative response to an external perturbation. In the static
case, these are found to vanish exactly for asymptotically flat black holes in
general relativity in four space-time dimensions, and recently they have been
generalized to dynamical interactions. In the context of response theory, the
retarded Green's function provides the complete description of the behavior of
dynamical systems. In this work we investigate the relation between Love
numbers and Green's functions, and highlight the relevance of radiation
reaction effects to their connection. As a special case, we discuss BTZ black
holes, where the absence of radiative modes allows us to make a direct link
between them.
|
[
{
"created": "Tue, 9 Jul 2024 18:00:09 GMT",
"version": "v1"
}
] |
2024-07-11
|
[
[
"De Luca",
"Valerio",
""
],
[
"Garoffolo",
"Alice",
""
],
[
"Khoury",
"Justin",
""
],
[
"Trodden",
"Mark",
""
]
] |
Tidal interactions play a crucial role in deciphering gravitational wave signals emitted by the coalescence of binary systems. They are usually quantified by a set of complex coefficients which include tidal Love numbers, describing the conservative response to an external perturbation. In the static case, these are found to vanish exactly for asymptotically flat black holes in general relativity in four space-time dimensions, and recently they have been generalized to dynamical interactions. In the context of response theory, the retarded Green's function provides the complete description of the behavior of dynamical systems. In this work we investigate the relation between Love numbers and Green's functions, and highlight the relevance of radiation reaction effects to their connection. As a special case, we discuss BTZ black holes, where the absence of radiative modes allows us to make a direct link between them.
|
1101.1391
|
Walter Del Pozzo
|
Walter Del Pozzo, John Veitch and Alberto Vecchio
|
Testing General Relativity using Bayesian model selection: Applications
to observations of gravitational waves from compact binary systems
|
Submitted to PRD
|
Phys.Rev.D83:082002,2011
|
10.1103/PhysRevD.83.082002
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Second generation interferometric gravitational wave detectors, such as
Advanced LIGO and Advanced Virgo, are expected to begin operation by 2015. Such
instruments plan to reach sensitivities that will offer the unique possibility
to test General Relativity in the dynamical, strong field regime and
investigate departures from its predictions, in particular using the signal
from coalescing binary systems. We introduce a statistical framework based on
Bayesian model selection in which the Bayes factor between two competing
hypotheses measures which theory is favored by the data. Probability density
functions of the model parameters are then used to quantify the inference on
individual parameters. We also develop a method to combine the information
coming from multiple independent observations of gravitational waves, and show
how much stronger inference could be. As an introduction and illustration of
this framework - and a practical numerical implementation through the Monte
Carlo integration technique of nested sampling - we apply it to gravitational
waves from the inspiral phase of coalescing binary systems as predicted by
General Relativity and a very simple alternative theory in which the graviton
has a non-zero mass. This method can trivially (and should) be extended to more
realistic and physically motivated theories.
|
[
{
"created": "Fri, 7 Jan 2011 09:44:53 GMT",
"version": "v1"
}
] |
2015-03-17
|
[
[
"Del Pozzo",
"Walter",
""
],
[
"Veitch",
"John",
""
],
[
"Vecchio",
"Alberto",
""
]
] |
Second generation interferometric gravitational wave detectors, such as Advanced LIGO and Advanced Virgo, are expected to begin operation by 2015. Such instruments plan to reach sensitivities that will offer the unique possibility to test General Relativity in the dynamical, strong field regime and investigate departures from its predictions, in particular using the signal from coalescing binary systems. We introduce a statistical framework based on Bayesian model selection in which the Bayes factor between two competing hypotheses measures which theory is favored by the data. Probability density functions of the model parameters are then used to quantify the inference on individual parameters. We also develop a method to combine the information coming from multiple independent observations of gravitational waves, and show how much stronger inference could be. As an introduction and illustration of this framework - and a practical numerical implementation through the Monte Carlo integration technique of nested sampling - we apply it to gravitational waves from the inspiral phase of coalescing binary systems as predicted by General Relativity and a very simple alternative theory in which the graviton has a non-zero mass. This method can trivially (and should) be extended to more realistic and physically motivated theories.
|
gr-qc/0201016
|
Ian G. Moss
|
Ian G Moss and James P Norman
|
Gravitational quasinormal modes for Anti-de Sitter black holes
|
12 pages, 6 figures in ReVTeX
|
Class.Quant.Grav. 19 (2002) 2323-2332
|
10.1088/0264-9381/19/8/319
| null |
gr-qc
| null |
Quasinormal mode spectra for gravitational perturbations of black holes in
four dimensional de Sitter and anti-de Sitter space are investigated. The
anti-de Sitter case is relevant to the ADS-CFT correspondence in superstring
theory. The ADS-CFT correspondence suggests a prefered set of boundary
conditions.
|
[
{
"created": "Sun, 6 Jan 2002 12:18:24 GMT",
"version": "v1"
},
{
"created": "Sat, 19 Jan 2002 11:01:56 GMT",
"version": "v2"
}
] |
2009-11-07
|
[
[
"Moss",
"Ian G",
""
],
[
"Norman",
"James P",
""
]
] |
Quasinormal mode spectra for gravitational perturbations of black holes in four dimensional de Sitter and anti-de Sitter space are investigated. The anti-de Sitter case is relevant to the ADS-CFT correspondence in superstring theory. The ADS-CFT correspondence suggests a prefered set of boundary conditions.
|
2305.12037
|
Hoang Nguyen
|
Hoang Ky Nguyen
|
Non-triviality of asymptotically flat Buchdahl-inspired metrics in pure
$R^2$ gravity
|
7 pages, 1 figure
|
Mod. Phys. Lett. A (2023) 2450100
|
10.1142/S0217732324501001
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In Phys. Rev. D $\textbf{107}$, 104008 (2023) we reported a novel exact
closed-form solution which describes asymptotically flat spacetimes in pure
$R^2$ gravity. The solution is Ricci scalar flat, viz. $R\equiv0$ everywhere.
Whereas any metric with a null Ricci scalar would $\textit{trivially}$ satisfy
the $R^2$ vacuo field equation,
$R\left(R_{\mu\nu}-\frac{1}{4}g_{\mu\nu}\,R\right)+g_{\mu\nu}\,\square\,R-\nabla_{\mu}\nabla_{\nu}R=0$,
in this article, we shall show that our solution satisfies a "stronger" version
of the $R^2$ vacuo field equation, viz.
$R_{\mu\nu}-\frac{1}{4}g_{\mu\nu}\,R+R^{-1}\left(g_{\mu\nu}\,\square\,R-\nabla_{\mu}\nabla_{\nu}R\right)=0$,
despite the term $R^{-1}$ being $\textit{singular}$. Even though $R$
identically vanishes, for our solution, the combinations
$\,R^{-1}\,\nabla_{\mu}\nabla_{\nu}R\,$ and $\,R^{-1}\,\square\,R\,$ are
$\textit{free of singularity}$. This exceptional property sets our solution
apart from the set of null-Ricci-scalar metrics and makes it a genuinely
$\textit{non-trivial}$ solution. We further demonstrate that, as a member of a
larger class of asymptotically de Sitter metrics, our solution is resilient
against perturbations in the scalar curvature at largest distances, making it
relevant for physical situations where the background deviates from asymptotic
flatness.
|
[
{
"created": "Fri, 19 May 2023 23:36:37 GMT",
"version": "v1"
},
{
"created": "Thu, 5 Oct 2023 16:19:45 GMT",
"version": "v2"
},
{
"created": "Tue, 28 May 2024 17:58:04 GMT",
"version": "v3"
}
] |
2024-07-09
|
[
[
"Nguyen",
"Hoang Ky",
""
]
] |
In Phys. Rev. D $\textbf{107}$, 104008 (2023) we reported a novel exact closed-form solution which describes asymptotically flat spacetimes in pure $R^2$ gravity. The solution is Ricci scalar flat, viz. $R\equiv0$ everywhere. Whereas any metric with a null Ricci scalar would $\textit{trivially}$ satisfy the $R^2$ vacuo field equation, $R\left(R_{\mu\nu}-\frac{1}{4}g_{\mu\nu}\,R\right)+g_{\mu\nu}\,\square\,R-\nabla_{\mu}\nabla_{\nu}R=0$, in this article, we shall show that our solution satisfies a "stronger" version of the $R^2$ vacuo field equation, viz. $R_{\mu\nu}-\frac{1}{4}g_{\mu\nu}\,R+R^{-1}\left(g_{\mu\nu}\,\square\,R-\nabla_{\mu}\nabla_{\nu}R\right)=0$, despite the term $R^{-1}$ being $\textit{singular}$. Even though $R$ identically vanishes, for our solution, the combinations $\,R^{-1}\,\nabla_{\mu}\nabla_{\nu}R\,$ and $\,R^{-1}\,\square\,R\,$ are $\textit{free of singularity}$. This exceptional property sets our solution apart from the set of null-Ricci-scalar metrics and makes it a genuinely $\textit{non-trivial}$ solution. We further demonstrate that, as a member of a larger class of asymptotically de Sitter metrics, our solution is resilient against perturbations in the scalar curvature at largest distances, making it relevant for physical situations where the background deviates from asymptotic flatness.
|
gr-qc/0608130
|
Jose Ademir Sales Lima
|
R. C. Santos, J. Santos, J. A. S. Lima
|
Hamilton-Jacobi Approach for Power-Law Potentials
|
12 pages, Latex
|
Braz.J.Phys. 36 (2006) 1257-1261
|
10.1590/S0103-97332006000700024
| null |
gr-qc
| null |
The classical and relativistic Hamilton-Jacobi approach is applied to the
one-dimensional homogeneous potential, $V(q)=\alpha q^n$, where $\alpha$ and
$n$ are continuously varying parameters. In the non-relativistic case, the
exact analytical solution is determined in terms of $\alpha$, $n$ and the total
energy $E$. It is also shown that the non-linear equation of motion can be
linearized by constructing a hypergeometric differential equation for the
inverse problem $t(q)$. A variable transformation reducing the general problem
to that one of a particle subjected to a linear force is also established. For
any value of $n$, it leads to a simple harmonic oscillator if $E>0$, an
"anti-oscillator" if $E<0$, or a free particle if E=0. However, such a
reduction is not possible in the relativistic case. For a bounded relativistic
motion, the first order correction to the period is determined for any value of
$n$. For $n >> 1$, it is found that the correction is just twice that one
deduced for the simple harmonic oscillator ($n=2$), and does not depend on the
specific value of $n$.
|
[
{
"created": "Wed, 30 Aug 2006 02:06:10 GMT",
"version": "v1"
}
] |
2015-06-25
|
[
[
"Santos",
"R. C.",
""
],
[
"Santos",
"J.",
""
],
[
"Lima",
"J. A. S.",
""
]
] |
The classical and relativistic Hamilton-Jacobi approach is applied to the one-dimensional homogeneous potential, $V(q)=\alpha q^n$, where $\alpha$ and $n$ are continuously varying parameters. In the non-relativistic case, the exact analytical solution is determined in terms of $\alpha$, $n$ and the total energy $E$. It is also shown that the non-linear equation of motion can be linearized by constructing a hypergeometric differential equation for the inverse problem $t(q)$. A variable transformation reducing the general problem to that one of a particle subjected to a linear force is also established. For any value of $n$, it leads to a simple harmonic oscillator if $E>0$, an "anti-oscillator" if $E<0$, or a free particle if E=0. However, such a reduction is not possible in the relativistic case. For a bounded relativistic motion, the first order correction to the period is determined for any value of $n$. For $n >> 1$, it is found that the correction is just twice that one deduced for the simple harmonic oscillator ($n=2$), and does not depend on the specific value of $n$.
|
1409.3046
|
Rafael Ribeiro
|
Rafael Ribeiro and Jorge P\'aramos
|
Dynamical analysis of nonminimal coupled theories
|
13 pages, 10 figures, 7 tables. Published version
|
Phys. Rev. D 90, 124065, 2014
|
10.1103/PhysRevD.90.124065
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this work a dynamical system approach to nonminimal coupled f(R) theories
is made. The solutions of three distinct models are obtained and their
stability and physical interpretation are studied to ascertain their viability
as candidates for dark energy. Comparison is drawn with previous works in the
context of f(R) and nonminimally coupled models.
|
[
{
"created": "Wed, 10 Sep 2014 12:46:40 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Jan 2015 01:53:57 GMT",
"version": "v2"
}
] |
2015-01-06
|
[
[
"Ribeiro",
"Rafael",
""
],
[
"Páramos",
"Jorge",
""
]
] |
In this work a dynamical system approach to nonminimal coupled f(R) theories is made. The solutions of three distinct models are obtained and their stability and physical interpretation are studied to ascertain their viability as candidates for dark energy. Comparison is drawn with previous works in the context of f(R) and nonminimally coupled models.
|
gr-qc/0403020
|
Valerio Faraoni
|
Valerio Faraoni (University of Northern British Columbia)
|
Singularities in scalar-tensor gravity
|
6 pages, LaTeX
|
Phys.Rev. D70 (2004) 047301
|
10.1103/PhysRevD.70.047301
| null |
gr-qc
| null |
The analysis of certain singularities in scalar-tensor gravity contained in a
recent paper is completed, and situations are pointed out in which these
singularities cannot occur.
|
[
{
"created": "Wed, 3 Mar 2004 22:15:26 GMT",
"version": "v1"
}
] |
2009-11-10
|
[
[
"Faraoni",
"Valerio",
"",
"University of Northern British Columbia"
]
] |
The analysis of certain singularities in scalar-tensor gravity contained in a recent paper is completed, and situations are pointed out in which these singularities cannot occur.
|
2006.14928
|
Shankar Dayal Pathak
|
A Kundu, S D Pathak, and V K Ojha
|
Interacting tachyonic scalar field
|
V1
|
Commun. Theor. Phys. 73 025402(2021)
|
10.1088/1572-9494/abcfb1
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We discuss the coupling between dark energy and matter by considering a
homogeneous tachyonic scalar field as a candidate for dark energy. We obtained
the functional form of scale factor by assuming that the coupling strength
depends linearly on the Hubble parameter and energy density. We also estimated
the cosmic age of the universe for different values of coupling constant.
|
[
{
"created": "Thu, 25 Jun 2020 02:57:58 GMT",
"version": "v1"
},
{
"created": "Sun, 3 Jan 2021 19:18:13 GMT",
"version": "v2"
}
] |
2021-01-27
|
[
[
"Kundu",
"A",
""
],
[
"Pathak",
"S D",
""
],
[
"Ojha",
"V K",
""
]
] |
We discuss the coupling between dark energy and matter by considering a homogeneous tachyonic scalar field as a candidate for dark energy. We obtained the functional form of scale factor by assuming that the coupling strength depends linearly on the Hubble parameter and energy density. We also estimated the cosmic age of the universe for different values of coupling constant.
|
gr-qc/9607074
|
Maurice van Putten
|
Maurice H.P.M. van Putten
|
Approximate Black Holes for Numerical Relativity
|
Postscript, 2 figures
|
Phys.Rev.D54:5931-5934,1996
|
10.1103/PhysRevD.54.R5931
| null |
gr-qc
| null |
Spherically symmetric solutions in Brans-Dicke theory of relativity with zero
coupling constant, $\omega=0$, are derived in the Schwarzschild line-element.
The solutions are obtained from a cubic transition equation with one small
parameter. The exterior space-time of one family of solutions is arbitrarily
close to the exterior Schwarzschild space-time. These nontopological solitons
have some similarity with soliton stars, and are proposed as candidates for
{\em approximate black holes} for the use in numerical relativity, in
particular for treatment of horizon boundary conditions.
|
[
{
"created": "Tue, 30 Jul 1996 19:12:21 GMT",
"version": "v1"
}
] |
2009-12-30
|
[
[
"van Putten",
"Maurice H. P. M.",
""
]
] |
Spherically symmetric solutions in Brans-Dicke theory of relativity with zero coupling constant, $\omega=0$, are derived in the Schwarzschild line-element. The solutions are obtained from a cubic transition equation with one small parameter. The exterior space-time of one family of solutions is arbitrarily close to the exterior Schwarzschild space-time. These nontopological solitons have some similarity with soliton stars, and are proposed as candidates for {\em approximate black holes} for the use in numerical relativity, in particular for treatment of horizon boundary conditions.
|
1705.09662
|
Lavinia Heisenberg
|
Lavinia Heisenberg, Ryotaro Kase, Masato Minamitsuji and Shinji
Tsujikawa
|
Hairy black-hole solutions in generalized Proca theories
|
5 pages, 1 figure, published version
|
Phys. Rev. D 96, 084049 (2017)
|
10.1103/PhysRevD.96.084049
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We present a family of exact black-hole solutions on a static spherically
symmetric background in second-order generalized Proca theories with derivative
vector-field interactions coupled to gravity. We also derive non-exact
solutions in power-law coupling models including vector Galileons and
numerically show the existence of regular black holes with a primary hair
associated with the longitudinal propagation. The intrinsic vector-field
derivative interactions generally give rise to a secondary hair induced by
non-trivial field profiles. The deviation from General Relativity is most
significant around the horizon and hence there is a golden opportunity for
probing the Proca hair by the measurements of gravitational waves (GWs) in the
regime of strong gravity.
|
[
{
"created": "Fri, 26 May 2017 18:00:01 GMT",
"version": "v1"
},
{
"created": "Thu, 26 Oct 2017 15:27:08 GMT",
"version": "v2"
}
] |
2017-11-01
|
[
[
"Heisenberg",
"Lavinia",
""
],
[
"Kase",
"Ryotaro",
""
],
[
"Minamitsuji",
"Masato",
""
],
[
"Tsujikawa",
"Shinji",
""
]
] |
We present a family of exact black-hole solutions on a static spherically symmetric background in second-order generalized Proca theories with derivative vector-field interactions coupled to gravity. We also derive non-exact solutions in power-law coupling models including vector Galileons and numerically show the existence of regular black holes with a primary hair associated with the longitudinal propagation. The intrinsic vector-field derivative interactions generally give rise to a secondary hair induced by non-trivial field profiles. The deviation from General Relativity is most significant around the horizon and hence there is a golden opportunity for probing the Proca hair by the measurements of gravitational waves (GWs) in the regime of strong gravity.
|
gr-qc/9608027
|
Manuela Campanelli
|
Manuela Campanelli (U. Bern) and Carlos O. Lousto (U. Utah)
|
Semiclassical models for uniform-density Cosmic Strings and Relativistic
Stars
|
19 pages, REVTEX, no figures
|
Int.J.Mod.Phys. D6 (1997) 771-784
|
10.1142/S0218271897000455
| null |
gr-qc hep-th
| null |
In this paper we show how quantum corrections, although perturbatively small,
may play an important role in the analysis of the existence of some classical
models. This, in fact, appears to be the case of static, uniform--density
models of the interior metric of cosmic strings and neutron stars. We consider
the fourth order semiclassical equations and first look for perturbative
solutions in the coupling constants $\alpha$ and $\beta$ of the quadratic
curvature terms in the effective gravitational Lagrangian. We find that there
is not a consistent solution; neither for strings nor for spherical stars. We
then look for non--perturbative solutions and find an explicit approximate
metric for the case of straight cosmic strings. We finally analyse the
contribution of the non--local terms to the renormalized energy--momentum
tensor and the possibility of this terms to allow for a perturbative solution.
We explicitly build up a particular renormalized energy--momentum tensor to
fulfill that end. These state--dependent corrections are found by simple
considerations of symmetry, conservation law and trace anomaly, and are chosen
to compensate for the local terms. However, they are not only ad hoc, but have
to depend on $\alpha$ and $\beta$, what is not expected to first perturbative
order. We then conclude that non--perturbative solutions are valuable for
describing certain physical situations.
|
[
{
"created": "Sat, 10 Aug 1996 22:50:06 GMT",
"version": "v1"
}
] |
2009-10-28
|
[
[
"Campanelli",
"Manuela",
"",
"U. Bern"
],
[
"Lousto",
"Carlos O.",
"",
"U. Utah"
]
] |
In this paper we show how quantum corrections, although perturbatively small, may play an important role in the analysis of the existence of some classical models. This, in fact, appears to be the case of static, uniform--density models of the interior metric of cosmic strings and neutron stars. We consider the fourth order semiclassical equations and first look for perturbative solutions in the coupling constants $\alpha$ and $\beta$ of the quadratic curvature terms in the effective gravitational Lagrangian. We find that there is not a consistent solution; neither for strings nor for spherical stars. We then look for non--perturbative solutions and find an explicit approximate metric for the case of straight cosmic strings. We finally analyse the contribution of the non--local terms to the renormalized energy--momentum tensor and the possibility of this terms to allow for a perturbative solution. We explicitly build up a particular renormalized energy--momentum tensor to fulfill that end. These state--dependent corrections are found by simple considerations of symmetry, conservation law and trace anomaly, and are chosen to compensate for the local terms. However, they are not only ad hoc, but have to depend on $\alpha$ and $\beta$, what is not expected to first perturbative order. We then conclude that non--perturbative solutions are valuable for describing certain physical situations.
|
1506.05207
|
Supratik Sarkar
|
Supratik Sarkar and Arijit Bhattacharyay
|
Effects of the Quantum Potential on lower dimensional models of analogue
gravity
|
9 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:1405.1865
|
Phys. Rev. D 93, 024050 (2016)
|
10.1103/PhysRevD.93.024050
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We address the issues related to the presence of the quantum potential term
in a BEC on the observable Analogue Gravity systems. We show that the quantum
potential term apparently gives rise to massive scalar excitations of length
scales of the order $\mathcal{O}(1/\xi)$ in the lower dimensional space. Since,
in 'analogue models', there is a window for experimental observations generally
in (2 + 1) or even lower dimensional space, one has to take proper account of
the presence of these massive excitations to interpret the results.
|
[
{
"created": "Wed, 17 Jun 2015 05:10:45 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Dec 2015 19:53:49 GMT",
"version": "v2"
},
{
"created": "Mon, 7 Dec 2015 21:51:43 GMT",
"version": "v3"
},
{
"created": "Tue, 8 Aug 2017 11:28:37 GMT",
"version": "v4"
}
] |
2017-08-09
|
[
[
"Sarkar",
"Supratik",
""
],
[
"Bhattacharyay",
"Arijit",
""
]
] |
We address the issues related to the presence of the quantum potential term in a BEC on the observable Analogue Gravity systems. We show that the quantum potential term apparently gives rise to massive scalar excitations of length scales of the order $\mathcal{O}(1/\xi)$ in the lower dimensional space. Since, in 'analogue models', there is a window for experimental observations generally in (2 + 1) or even lower dimensional space, one has to take proper account of the presence of these massive excitations to interpret the results.
|
1911.09520
|
Subenoy Chakraborty
|
Santu Mondal, Sourav Dutta and Subenoy Chakraborty
|
Variable $G$ and $\Lambda$ gravity theory and analytical Cosmological
Solutions using Noether symmetry approach
|
10 pages, 6 figures
|
Gen.Rel.Grav. 51 (2019) no.9, 105
|
10.1007/s10714-019-2595-1
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The present work deals with scalar field cosmology in the framework of a
quantum gravity modified Einstein-Hilbert Lagrangian with variable $G$ and
$\Lambda$. Using Renormalization group, variable $G$ behaves as a minimally
coupled filed (not the scalar-tensor theory) and variable $\Lambda$ can be
interpreted as a potential function. The point Lagrangian for this model in the
background of homogeneous and isotropic flat FLRW space-time model experiences
point-like Noether symmetry and equivalent potential function $\Lambda(G)$ is
determined. Using a point transformation in the $3D$ augmented space is found
that one of the variable become cyclic and as a consequence there is
considerable simplification to the physical system. Lastly, the constants of
motion can be written in compact form and it is possible to have analytic
cosmological solutions in the present context.
|
[
{
"created": "Wed, 20 Nov 2019 11:18:03 GMT",
"version": "v1"
}
] |
2019-11-22
|
[
[
"Mondal",
"Santu",
""
],
[
"Dutta",
"Sourav",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] |
The present work deals with scalar field cosmology in the framework of a quantum gravity modified Einstein-Hilbert Lagrangian with variable $G$ and $\Lambda$. Using Renormalization group, variable $G$ behaves as a minimally coupled filed (not the scalar-tensor theory) and variable $\Lambda$ can be interpreted as a potential function. The point Lagrangian for this model in the background of homogeneous and isotropic flat FLRW space-time model experiences point-like Noether symmetry and equivalent potential function $\Lambda(G)$ is determined. Using a point transformation in the $3D$ augmented space is found that one of the variable become cyclic and as a consequence there is considerable simplification to the physical system. Lastly, the constants of motion can be written in compact form and it is possible to have analytic cosmological solutions in the present context.
|
gr-qc/0604122
|
Bojan Losic
|
B. Losic and W.G. Unruh
|
On leading order gravitational backreactions in de Sitter spacetime
|
12 pages, no figures, typos corrected and some clarifying comments
added, version accepted by Phys. Rev. D
|
Phys.Rev. D74 (2006) 023511
|
10.1103/PhysRevD.74.023511
| null |
gr-qc
| null |
Backreactions are considered in a de Sitter spacetime whose cosmological
constant is generated by the potential of scalar field. The leading order
gravitational effect of nonlinear matter fluctuations is analyzed and it is
found that the initial value problem for the perturbed Einstein equations
possesses linearization instabilities. We show that these linearization
instabilities can be avoided by assuming strict de Sitter invariance of the
quantum states of the linearized fluctuations. We furthermore show that quantum
anomalies do not block the invariance requirement. This invariance constraint
applies to the entire spectrum of states, from the vacuum to the excited states
(should they exist), and is in that sense much stronger than the usual Poincare
invariance requirement of the Minkowski vacuum alone. Thus to leading order in
their effect on the gravitational field, the quantum states of the matter and
metric fluctuations must be de Sitter invariant.
|
[
{
"created": "Fri, 28 Apr 2006 03:05:01 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Jun 2006 17:56:35 GMT",
"version": "v2"
}
] |
2009-11-11
|
[
[
"Losic",
"B.",
""
],
[
"Unruh",
"W. G.",
""
]
] |
Backreactions are considered in a de Sitter spacetime whose cosmological constant is generated by the potential of scalar field. The leading order gravitational effect of nonlinear matter fluctuations is analyzed and it is found that the initial value problem for the perturbed Einstein equations possesses linearization instabilities. We show that these linearization instabilities can be avoided by assuming strict de Sitter invariance of the quantum states of the linearized fluctuations. We furthermore show that quantum anomalies do not block the invariance requirement. This invariance constraint applies to the entire spectrum of states, from the vacuum to the excited states (should they exist), and is in that sense much stronger than the usual Poincare invariance requirement of the Minkowski vacuum alone. Thus to leading order in their effect on the gravitational field, the quantum states of the matter and metric fluctuations must be de Sitter invariant.
|
2406.08363
|
Oliver Long
|
Oliver Long, Christopher Whittall, Leor Barack
|
Black hole scattering near the transition to plunge: Self-force and
resummation of post-Minkowskian theory
|
15 pages, 9 figures; v2 minor typographic changes; v3 minor edits to
match published version
| null | null | null |
gr-qc astro-ph.HE hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Geodesic scattering of a test particle off a Schwarzschild black hole can be
parameterized by the speed-at-infinity $v$ and the impact parameter $b$, with a
"separatrix", $b=b_c(v)$, marking the threshold between scattering and plunge.
Near the separatrix, the scattering angle diverges as $\sim\log(b-b_c)$. The
self-force correction to the scattering angle (at fixed $v,b$) diverges even
faster, like $\sim A_1(v)b_c/(b-b_c)$. Here we numerically calculate the
divergence coefficient $A_1(v)$ in a scalar-charge toy model. We then use our
knowledge of $A_1(v)$ to inform a resummation of the post-Minkowskian expansion
for the scattering angle, and demonstrate that the resummed series agrees
remarkably well with numerical self-force results even in the strong-field
regime. We propose that a similar resummation technique, applied to a mass
particle subject to a gravitational self-force, can significantly enhance the
utility and regime of validity of post-Minkowskian calculations for black-hole
scattering.
|
[
{
"created": "Wed, 12 Jun 2024 16:13:13 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Jun 2024 11:46:17 GMT",
"version": "v2"
},
{
"created": "Fri, 26 Jul 2024 15:15:50 GMT",
"version": "v3"
}
] |
2024-07-29
|
[
[
"Long",
"Oliver",
""
],
[
"Whittall",
"Christopher",
""
],
[
"Barack",
"Leor",
""
]
] |
Geodesic scattering of a test particle off a Schwarzschild black hole can be parameterized by the speed-at-infinity $v$ and the impact parameter $b$, with a "separatrix", $b=b_c(v)$, marking the threshold between scattering and plunge. Near the separatrix, the scattering angle diverges as $\sim\log(b-b_c)$. The self-force correction to the scattering angle (at fixed $v,b$) diverges even faster, like $\sim A_1(v)b_c/(b-b_c)$. Here we numerically calculate the divergence coefficient $A_1(v)$ in a scalar-charge toy model. We then use our knowledge of $A_1(v)$ to inform a resummation of the post-Minkowskian expansion for the scattering angle, and demonstrate that the resummed series agrees remarkably well with numerical self-force results even in the strong-field regime. We propose that a similar resummation technique, applied to a mass particle subject to a gravitational self-force, can significantly enhance the utility and regime of validity of post-Minkowskian calculations for black-hole scattering.
|
gr-qc/0508100
|
Daniel Sudarsky
|
Alejandro Perez, Hanno Sahlmann, and Daniel Sudarsky
|
On the quantum origin of the seeds of cosmic structure
|
replacement with final version to appear in Classical and Quantum
Gravity
|
Class.Quant.Grav. 23 (2006) 2317-2354
|
10.1088/0264-9381/23/7/008
| null |
gr-qc astro-ph hep-th quant-ph
| null |
The current understanding of the quantum origin of cosmic structure is
discussed critically. We point out that in the existing treatments a transition
from a symmetric quantum state to an (essentially classical) non-symmetric
state is implicitly assumed, but not specified or analyzed in any detail. In
facing the issue we are led to conclude that new physics is required to explain
the apparent predictive power of the usual schemes. Furthermore we show that
the novel way of looking at the relevant issues opens new windows from where
relevant information might be extracted regarding cosmological issues and
perhaps even clues about aspects of quantum gravity.
|
[
{
"created": "Wed, 24 Aug 2005 13:54:34 GMT",
"version": "v1"
},
{
"created": "Thu, 25 Aug 2005 00:15:43 GMT",
"version": "v2"
},
{
"created": "Sat, 25 Feb 2006 19:55:57 GMT",
"version": "v3"
}
] |
2015-06-25
|
[
[
"Perez",
"Alejandro",
""
],
[
"Sahlmann",
"Hanno",
""
],
[
"Sudarsky",
"Daniel",
""
]
] |
The current understanding of the quantum origin of cosmic structure is discussed critically. We point out that in the existing treatments a transition from a symmetric quantum state to an (essentially classical) non-symmetric state is implicitly assumed, but not specified or analyzed in any detail. In facing the issue we are led to conclude that new physics is required to explain the apparent predictive power of the usual schemes. Furthermore we show that the novel way of looking at the relevant issues opens new windows from where relevant information might be extracted regarding cosmological issues and perhaps even clues about aspects of quantum gravity.
|
1501.04181
|
Ward Struyve
|
Felipe Tovar Falciano, Nelson Pinto-Neto, Ward Struyve
|
Wheeler-DeWitt quantization and singularities
|
10 pages, 3 figures, PDFLaTeX, revtex4
|
Phys. Rev. D 91, 043524 (2015)
|
10.1103/PhysRevD.91.043524
| null |
gr-qc hep-th quant-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider a Bohmian approach to the Wheeler-DeWitt quantization of the
Friedmann-Lemaitre-Robertson-Walker model and investigate the question whether
or not there are singularities, in the sense that the universe reaches zero
volume. We find that for generic wave functions (i.e., non-classical wave
functions), there is a non-zero probability for a trajectory to be
non-singular. This should be contrasted to the consistent histories approach
for which it was recently shown by Craig and Singh that there is always a
singularity. This result illustrates that the question of singularities depends
much on which version of quantum theory one adopts. This was already pointed
out by Pinto-Neto et al., albeit with a different Bohmian approach. Our current
Bohmian approach agrees with the consistent histories approach by Craig and
Singh for single-time histories, unlike the one studied earlier by Pinto-Neto
et al. Although the trajectories are usually different in the two Bohmian
approach, their qualitative behavior is the same for generic wave functions.
|
[
{
"created": "Sat, 17 Jan 2015 09:32:54 GMT",
"version": "v1"
}
] |
2015-02-24
|
[
[
"Falciano",
"Felipe Tovar",
""
],
[
"Pinto-Neto",
"Nelson",
""
],
[
"Struyve",
"Ward",
""
]
] |
We consider a Bohmian approach to the Wheeler-DeWitt quantization of the Friedmann-Lemaitre-Robertson-Walker model and investigate the question whether or not there are singularities, in the sense that the universe reaches zero volume. We find that for generic wave functions (i.e., non-classical wave functions), there is a non-zero probability for a trajectory to be non-singular. This should be contrasted to the consistent histories approach for which it was recently shown by Craig and Singh that there is always a singularity. This result illustrates that the question of singularities depends much on which version of quantum theory one adopts. This was already pointed out by Pinto-Neto et al., albeit with a different Bohmian approach. Our current Bohmian approach agrees with the consistent histories approach by Craig and Singh for single-time histories, unlike the one studied earlier by Pinto-Neto et al. Although the trajectories are usually different in the two Bohmian approach, their qualitative behavior is the same for generic wave functions.
|
gr-qc/9509054
|
James Hartle
|
Murray Gell-Mann (Santa Fe Institute, Los Alamos, University of New
Mexico) and James B. Hartle (University of California, Santa Barbara)
|
Strong Decoherence
|
27pages, uses REVTEX 3.0, minor corrections
|
in Proceedings of the 4th Drexel Conference on Quantum
Non-Integrability: The Quantum-Classical Correspondence, ed by D.-H. Feng and
B.-L. Hu, International Press of Boston, Hong Kong (1998)
| null |
UCSBTH-95-28
|
gr-qc hep-th quant-ph
| null |
We introduce a condition for the strong decoherence of a set of alternative
histories of a closed quantum-mechanical system such as the universe. The
condition applies, for a pure initial state, to sets of homogeneous histories
that are chains of projections, generally branch-dependent. Strong decoherence
implies the consistency of probability sum rules but not every set of
consistent or even medium decoherent histories is strongly decoherent. Two
conditions characterize a strongly decoherent set of histories: (1) At any time
the operators that effectively commute with generalized records of history up
to that moment provide the pool from which -- with suitable adjustment for
elapsed time -- the chains of projections extending history to the future may
be drawn. (2) Under the adjustment process, generalized record operators acting
on the initial state of the universe are approximately unchanged. This
expresses the permanence of generalized records. The strong decoherence
conditions (1) and (2) guarantee what we call ``permanence of the past'' -- in
particular the continued decoherence of past alternatives as the chains of
projections are extended into the future. Strong decoherence is an idealization
capturing in a general way this and other aspects of realistic physical
mechanisms that destroy interference, as we illustrate in a simple model. We
discuss the connection between the reduced density matrices that have often
been used to characterize mechanisms of decoherence and the more general notion
of strong decoherence. The relation between strong decoherence and a measure of
classicality is briefly described.
|
[
{
"created": "Thu, 28 Sep 1995 00:27:21 GMT",
"version": "v1"
},
{
"created": "Thu, 28 Sep 1995 17:47:35 GMT",
"version": "v2"
},
{
"created": "Sun, 29 Oct 1995 21:48:18 GMT",
"version": "v3"
},
{
"created": "Thu, 23 Nov 1995 19:46:38 GMT",
"version": "v4"
}
] |
2008-02-03
|
[
[
"Gell-Mann",
"Murray",
"",
"Santa Fe Institute, Los Alamos, University of New\n Mexico"
],
[
"Hartle",
"James B.",
"",
"University of California, Santa Barbara"
]
] |
We introduce a condition for the strong decoherence of a set of alternative histories of a closed quantum-mechanical system such as the universe. The condition applies, for a pure initial state, to sets of homogeneous histories that are chains of projections, generally branch-dependent. Strong decoherence implies the consistency of probability sum rules but not every set of consistent or even medium decoherent histories is strongly decoherent. Two conditions characterize a strongly decoherent set of histories: (1) At any time the operators that effectively commute with generalized records of history up to that moment provide the pool from which -- with suitable adjustment for elapsed time -- the chains of projections extending history to the future may be drawn. (2) Under the adjustment process, generalized record operators acting on the initial state of the universe are approximately unchanged. This expresses the permanence of generalized records. The strong decoherence conditions (1) and (2) guarantee what we call ``permanence of the past'' -- in particular the continued decoherence of past alternatives as the chains of projections are extended into the future. Strong decoherence is an idealization capturing in a general way this and other aspects of realistic physical mechanisms that destroy interference, as we illustrate in a simple model. We discuss the connection between the reduced density matrices that have often been used to characterize mechanisms of decoherence and the more general notion of strong decoherence. The relation between strong decoherence and a measure of classicality is briefly described.
|
2206.06516
|
Jeferson de Oliveira
|
B. Cuadros-Melgar, R. D. B. Fontana, Jeferson de Oliveira
|
Gauss-Bonnet black holes in (2+1) dimensions: Perturbative aspects and
entropy features
|
27 pages, 4 figures
|
Phys, Rev. D 106, 124007 (2022)
|
10.1103/PhysRevD.106.124007
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We investigate some aspects of the $(2+1)$-dimensional Gauss-Bonnet black
hole proposed in [1][2]. The perturbations of scalar and massless spinorial
fields are studied suggesting the dynamical stability of the geometry. The
field evolution is analyzed calculating the quasinormal modes for different
parameters and exploring the influence of the coupling constant of the theory.
The hydrodynamical modes are also obtained in the small coupling limit.
Furthermore, the entropy bound and the dominant semiclassical correction to the
black hole entropy are calculated.
|
[
{
"created": "Mon, 13 Jun 2022 23:02:18 GMT",
"version": "v1"
}
] |
2024-01-31
|
[
[
"Cuadros-Melgar",
"B.",
""
],
[
"Fontana",
"R. D. B.",
""
],
[
"de Oliveira",
"Jeferson",
""
]
] |
We investigate some aspects of the $(2+1)$-dimensional Gauss-Bonnet black hole proposed in [1][2]. The perturbations of scalar and massless spinorial fields are studied suggesting the dynamical stability of the geometry. The field evolution is analyzed calculating the quasinormal modes for different parameters and exploring the influence of the coupling constant of the theory. The hydrodynamical modes are also obtained in the small coupling limit. Furthermore, the entropy bound and the dominant semiclassical correction to the black hole entropy are calculated.
|
0804.1410
|
Tomohiro Harada
|
Masanori Kyo, Tomohiro Harada, Hideki Maeda
|
Asymptotically Friedmann self-similar scalar field solutions with
potential
|
accepted for publication in Physical Review D, minor correction,
typos corrected
|
Phys.Rev.D77:124036,2008
|
10.1103/PhysRevD.77.124036
|
CECS-PHY-08/04
|
gr-qc astro-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We investigate self-similar solutions which are asymptotic to the Friedmann
universe at spatial infinity and contain a scalar field with potential. The
potential is required to be exponential by self-similarity. It is found that
there are two distinct one-parameter families of asymptotic solutions,one is
asymptotic to the proper Friedmann universe, while the other is asymptotic to
the quasi-Friedmann universe, i.e., the Friedmann universe with anomalous solid
angle. The asymptotically proper Friedmann solution is possible only if the
universe is accelerated or the potential is negative. If the potential is
positive, the density perturbation in the asymptotically proper Friedmann
solution rapidly falls off at spatial infinity, while the mass perturbation is
compensated. In the asymptotically quasi-Friedmann solution, the density
perturbation falls off only in proportion to the inverse square of the areal
radius and the relative mass perturbation approaches a nonzero constant at
spatial infinity. The present result shows that a necessary condition holds in
order that a self-gravitating body grows self-similarly due to the constant
accretion of quintessence in an accelerating universe.
|
[
{
"created": "Wed, 9 Apr 2008 05:52:05 GMT",
"version": "v1"
},
{
"created": "Fri, 9 May 2008 02:29:55 GMT",
"version": "v2"
},
{
"created": "Mon, 16 Jun 2008 05:07:46 GMT",
"version": "v3"
}
] |
2008-11-26
|
[
[
"Kyo",
"Masanori",
""
],
[
"Harada",
"Tomohiro",
""
],
[
"Maeda",
"Hideki",
""
]
] |
We investigate self-similar solutions which are asymptotic to the Friedmann universe at spatial infinity and contain a scalar field with potential. The potential is required to be exponential by self-similarity. It is found that there are two distinct one-parameter families of asymptotic solutions,one is asymptotic to the proper Friedmann universe, while the other is asymptotic to the quasi-Friedmann universe, i.e., the Friedmann universe with anomalous solid angle. The asymptotically proper Friedmann solution is possible only if the universe is accelerated or the potential is negative. If the potential is positive, the density perturbation in the asymptotically proper Friedmann solution rapidly falls off at spatial infinity, while the mass perturbation is compensated. In the asymptotically quasi-Friedmann solution, the density perturbation falls off only in proportion to the inverse square of the areal radius and the relative mass perturbation approaches a nonzero constant at spatial infinity. The present result shows that a necessary condition holds in order that a self-gravitating body grows self-similarly due to the constant accretion of quintessence in an accelerating universe.
|
2101.08289
|
Boris Daszuta
|
Boris Daszuta, Francesco Zappa, William Cook, David Radice, Sebastiano
Bernuzzi, Viktoriya Morozova
|
GRAthena++: puncture evolutions on vertex-centered oct-tree AMR
| null | null |
10.3847/1538-4365/ac157b
| null |
gr-qc astro-ph.HE
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Numerical relativity is central to the investigation of astrophysical sources
in the dynamical and strong-field gravity regime, such as binary black hole and
neutron star coalescences. Current challenges set by gravitational-wave and
multi-messenger astronomy call for highly performant and scalable codes on
modern massively-parallel architectures. We present GR-Athena++, a
general-relativistic, high-order, vertex-centered solver that extends the
oct-tree, adaptive mesh refinement capabilities of the astrophysical
(radiation) magnetohydrodynamics code Athena++. To simulate dynamical
space-times GR-Athena++ uses the Z4c evolution scheme of numerical relativity
coupled to the moving puncture gauge. We demonstrate stable and accurate binary
black hole merger evolutions via extensive convergence testing, cross-code
validation, and verification against state-of-the-art effective-one-body
waveforms. GR-Athena++ leverages the task-based parallelism paradigm of
Athena++ to achieve excellent scalability. We measure strong scaling
efficiencies above $95\%$ for up to $\sim 1.2\times10^4$ CPUs and excellent
weak scaling is shown up to $\sim 10^5$ CPUs in a production binary black hole
setup with adaptive mesh refinement. GR-Athena++ thus allows for the robust
simulation of compact binary coalescences and offers a viable path towards
numerical relativity at exascale.
|
[
{
"created": "Wed, 20 Jan 2021 19:08:08 GMT",
"version": "v1"
}
] |
2022-11-04
|
[
[
"Daszuta",
"Boris",
""
],
[
"Zappa",
"Francesco",
""
],
[
"Cook",
"William",
""
],
[
"Radice",
"David",
""
],
[
"Bernuzzi",
"Sebastiano",
""
],
[
"Morozova",
"Viktoriya",
""
]
] |
Numerical relativity is central to the investigation of astrophysical sources in the dynamical and strong-field gravity regime, such as binary black hole and neutron star coalescences. Current challenges set by gravitational-wave and multi-messenger astronomy call for highly performant and scalable codes on modern massively-parallel architectures. We present GR-Athena++, a general-relativistic, high-order, vertex-centered solver that extends the oct-tree, adaptive mesh refinement capabilities of the astrophysical (radiation) magnetohydrodynamics code Athena++. To simulate dynamical space-times GR-Athena++ uses the Z4c evolution scheme of numerical relativity coupled to the moving puncture gauge. We demonstrate stable and accurate binary black hole merger evolutions via extensive convergence testing, cross-code validation, and verification against state-of-the-art effective-one-body waveforms. GR-Athena++ leverages the task-based parallelism paradigm of Athena++ to achieve excellent scalability. We measure strong scaling efficiencies above $95\%$ for up to $\sim 1.2\times10^4$ CPUs and excellent weak scaling is shown up to $\sim 10^5$ CPUs in a production binary black hole setup with adaptive mesh refinement. GR-Athena++ thus allows for the robust simulation of compact binary coalescences and offers a viable path towards numerical relativity at exascale.
|
0708.0593
|
Alain Ulacia Rey A.Ulacia Rey
|
A. Ulacia Rey, A. Perez Martinez and Roberto A. Sussman
|
Local dynamics and gravitational collapse of a self-gravitating
magnetized Fermi gas
|
6 pages, 3 figures (accepted in General Relativity and Gravitation)
|
Gen.Rel.Grav.40:1499-1510,2008
|
10.1007/s10714-007-0542-z
| null |
gr-qc astro-ph hep-th
| null |
We use the Bianchi-I spacetime to study the local dynamics of a magnetized
self-gravitating Fermi gas. The set of Einstein-Maxwell field equations for
this gas becomes a dynamical system in a 4-dimensional phase space. We consider
a qualitative study and examine numeric solutions for the degenerate zero
temperature case. All dynamic quantities exhibit similar qualitative behavior
in the 3-dimensional sections of the phase space, with all trajectories
reaching a stable attractor whenever the initial expansion scalar H_{0} is
negative. If H_{0} is positive, and depending on initial conditions, the
trajectories end up in a curvature singularity that could be isotropic(singular
"point") or anisotropic (singular "line"). In particular, for a sufficiently
large initial value of the magnetic field it is always possible to obtain an
anisotropic type of singularity in which the "line" points in the same
direction of the field.
|
[
{
"created": "Fri, 3 Aug 2007 23:15:42 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Nov 2007 00:03:22 GMT",
"version": "v2"
}
] |
2008-12-16
|
[
[
"Rey",
"A. Ulacia",
""
],
[
"Martinez",
"A. Perez",
""
],
[
"Sussman",
"Roberto A.",
""
]
] |
We use the Bianchi-I spacetime to study the local dynamics of a magnetized self-gravitating Fermi gas. The set of Einstein-Maxwell field equations for this gas becomes a dynamical system in a 4-dimensional phase space. We consider a qualitative study and examine numeric solutions for the degenerate zero temperature case. All dynamic quantities exhibit similar qualitative behavior in the 3-dimensional sections of the phase space, with all trajectories reaching a stable attractor whenever the initial expansion scalar H_{0} is negative. If H_{0} is positive, and depending on initial conditions, the trajectories end up in a curvature singularity that could be isotropic(singular "point") or anisotropic (singular "line"). In particular, for a sufficiently large initial value of the magnetic field it is always possible to obtain an anisotropic type of singularity in which the "line" points in the same direction of the field.
|
1506.02479
|
Philip D. Mannheim
|
Philip D. Mannheim
|
Comment on "Problems with Mannheim's conformal gravity program"
|
4 pages, revtex4. Final version, to appear as a Comment in Phys. Rev.
D. Note change in title
| null |
10.1103/PhysRevD.93.068501
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Recently in Phys. Rev. D 88, 027504 (2013) Yoon has suggested that there may
be problems for the non-relativistic limit of the conformal gravity theory.
Here we show that Yoon's results only hold because of the assumption that
gravitational sources can be treated the same way that they are treated in
standard Newton-Einstein gravity. Since such an assumption violates the
theory's underlying conformal invariance,Yoon's conclusions are invalidated.
|
[
{
"created": "Mon, 8 Jun 2015 13:17:48 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Mar 2016 20:32:39 GMT",
"version": "v2"
}
] |
2016-04-20
|
[
[
"Mannheim",
"Philip D.",
""
]
] |
Recently in Phys. Rev. D 88, 027504 (2013) Yoon has suggested that there may be problems for the non-relativistic limit of the conformal gravity theory. Here we show that Yoon's results only hold because of the assumption that gravitational sources can be treated the same way that they are treated in standard Newton-Einstein gravity. Since such an assumption violates the theory's underlying conformal invariance,Yoon's conclusions are invalidated.
|
2001.11484
|
Alexandru Dima
|
Alexandru Dima and Enrico Barausse
|
Numerical investigation of plasma-driven superradiant instabilities
|
30 pages, 7 figures. Minor changes to match version accepted by CQG
|
Class. Quantum Grav. 37 175006 (2020)
|
10.1088/1361-6382/ab9ce0
| null |
gr-qc astro-ph.HE
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Photons propagating in a plasma acquire an effective mass $\mu$, which is
given by the plasma frequency and which scales with the square root of the
plasma density. As noted previously by Conlon and Herdeiro, for electron number
densities $n_e\sim 10^{-3}$ cm$^{-3}$ (such as those measured in the
interstellar medium) the effective mass induced by the plasma is $\mu \sim
10^{-12}$ eV. This would cause superradiant instabilities for spinning black
holes of a few tens of solar masses. An obvious problem with this picture is
that densities in the vicinity of black holes are much higher than in the
interstellar medium because of accretion. We have conducted numerical
simulations of the superradiant instability in spinning black holes surrounded
by a plasma with density increasing closer to the black hole, in order to mimic
the effect of accretion. While we confirm that superradiant instabilities
appear for plasma densities that are sufficiently low near the black hole, we
find that astrophysically realistic accretion disks are unlikely to trigger
such instabilities.
|
[
{
"created": "Thu, 30 Jan 2020 18:07:33 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Jul 2020 12:04:11 GMT",
"version": "v2"
}
] |
2020-08-07
|
[
[
"Dima",
"Alexandru",
""
],
[
"Barausse",
"Enrico",
""
]
] |
Photons propagating in a plasma acquire an effective mass $\mu$, which is given by the plasma frequency and which scales with the square root of the plasma density. As noted previously by Conlon and Herdeiro, for electron number densities $n_e\sim 10^{-3}$ cm$^{-3}$ (such as those measured in the interstellar medium) the effective mass induced by the plasma is $\mu \sim 10^{-12}$ eV. This would cause superradiant instabilities for spinning black holes of a few tens of solar masses. An obvious problem with this picture is that densities in the vicinity of black holes are much higher than in the interstellar medium because of accretion. We have conducted numerical simulations of the superradiant instability in spinning black holes surrounded by a plasma with density increasing closer to the black hole, in order to mimic the effect of accretion. While we confirm that superradiant instabilities appear for plasma densities that are sufficiently low near the black hole, we find that astrophysically realistic accretion disks are unlikely to trigger such instabilities.
|
1001.2578
|
Stephen R. Lau
|
Scott E. Field (1), Jan S. Hesthaven (1), Stephen R. Lau (2) ((1)
Brown, (2) New Mexico)
|
Persistent junk solutions in time-domain modeling of extreme mass ratio
binaries
|
Uses revtex4, 16 pages, 9 figures, 3 tables. Document reformatted and
modified based on referee's report. Commentary added which addresses the
possible presence of persistent junk solutions in other approaches for
solving master wave equations
|
Phys.Rev.D81:124030,2010
|
10.1103/PhysRevD.81.124030
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In the context of metric perturbation theory for non-spinning black holes,
extreme mass ratio binary (EMRB) systems are described by distributionally
forced master wave equations. Numerical solution of a master wave equation as
an initial boundary value problem requires initial data. However, because the
correct initial data for generic-orbit systems is unknown, specification of
trivial initial data is a common choice, despite being inconsistent and
resulting in a solution which is initially discontinuous in time. As is well
known, this choice leads to a "burst" of junk radiation which eventually
propagates off the computational domain. We observe another unintended
consequence of trivial initial data: development of a persistent spurious
solution, here referred to as the Jost junk solution, which contaminates the
physical solution for long times. This work studies the influence of both types
of junk on metric perturbations, waveforms, and self-force measurements, and it
demonstrates that smooth modified source terms mollify the Jost solution and
reduce junk radiation. Our concluding section discusses the applicability of
these observations to other numerical schemes and techniques used to solve
distributionally forced master wave equations.
|
[
{
"created": "Thu, 14 Jan 2010 22:59:29 GMT",
"version": "v1"
},
{
"created": "Fri, 28 May 2010 16:44:22 GMT",
"version": "v2"
}
] |
2014-11-20
|
[
[
"Field",
"Scott E.",
""
],
[
"Hesthaven",
"Jan S.",
""
],
[
"Lau",
"Stephen R.",
""
]
] |
In the context of metric perturbation theory for non-spinning black holes, extreme mass ratio binary (EMRB) systems are described by distributionally forced master wave equations. Numerical solution of a master wave equation as an initial boundary value problem requires initial data. However, because the correct initial data for generic-orbit systems is unknown, specification of trivial initial data is a common choice, despite being inconsistent and resulting in a solution which is initially discontinuous in time. As is well known, this choice leads to a "burst" of junk radiation which eventually propagates off the computational domain. We observe another unintended consequence of trivial initial data: development of a persistent spurious solution, here referred to as the Jost junk solution, which contaminates the physical solution for long times. This work studies the influence of both types of junk on metric perturbations, waveforms, and self-force measurements, and it demonstrates that smooth modified source terms mollify the Jost solution and reduce junk radiation. Our concluding section discusses the applicability of these observations to other numerical schemes and techniques used to solve distributionally forced master wave equations.
|
gr-qc/9604015
|
Int. Lab. HTSC and Sse
|
Sergiu I. Vacaru
|
Spinors in Higher Dimensional and Locally Anisotropic Spaces
|
54 pages, Revtex, an extension of the paper published in J. Math.
Phys. 37 (1996), 508--523
| null |
10.1063/1.531406
| null |
gr-qc dg-ga hep-th math.DG
| null |
The theory of spinors is developed for locally anisotropic (la) spaces, in
brief la-spaces, which in general are modeled as vector bundles provided with
nonlinear and distinguished connections and metric structures (such la-spaces
contain as particular cases the Lagrange, Finsler and, for trivial nonlinear
connections, Kaluza-Klein spaces). The la-spinor differential geometry is
constructed. The distinguished spinor connections are studied and compared with
similar ones on la-spaces. We derive the la-spinor expressions of curvatures
and torsions and analyze the conditions when the distinguished torsion and
nonmetricity tensors can be generated from distinguished spinor connections.
The dynamical equations for gravitational and matter field la-interactions are
formulated.
|
[
{
"created": "Fri, 5 Apr 1996 14:28:00 GMT",
"version": "v1"
}
] |
2009-10-28
|
[
[
"Vacaru",
"Sergiu I.",
""
]
] |
The theory of spinors is developed for locally anisotropic (la) spaces, in brief la-spaces, which in general are modeled as vector bundles provided with nonlinear and distinguished connections and metric structures (such la-spaces contain as particular cases the Lagrange, Finsler and, for trivial nonlinear connections, Kaluza-Klein spaces). The la-spinor differential geometry is constructed. The distinguished spinor connections are studied and compared with similar ones on la-spaces. We derive the la-spinor expressions of curvatures and torsions and analyze the conditions when the distinguished torsion and nonmetricity tensors can be generated from distinguished spinor connections. The dynamical equations for gravitational and matter field la-interactions are formulated.
|
1806.04086
|
Sudan Hansraj
|
Sudan Hansraj
|
Spherically symmetric isothermal fluids in $f(R,T)$ gravity
| null | null |
10.1140/epjc/s10052-018-6194-1
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We analyze the isothermal property in static fluid spheres within the
framework of the modified $f(R, T)$ theory of gravitation. The equation of
pressure isotropy of the standard Einstein theory is preserved however, the
energy density and pressure are expressed in terms of both gravitational
potentials. Invoking the isothermal prescription requires that the isotropy
condition assumes the role of a consistency condition and an exact model
generalizing that of general relativity is found. Moreover it is found that the
Einstein model is unstable and acausal while the $f(R, T)$ counterpart is well
behaved on account of the freedom available through an additional coupling
constant. The case of a constant spatial gravitational potential is considered
and the complete model is determined. This model is markedly different from its
Einstein counterpart which is known to be isothermal. Dropping the restriction
on the density and imposing a linear barotropic equation of state generates an
exact solution and consequently a stellar distribution as the vanishing of the
pressure is possible and a boundary hypersurface exists. Finally we comment on
the case of relaxing the equation of state but demanding an inverse square
fall-off of the density - this case proves intractable.
|
[
{
"created": "Mon, 11 Jun 2018 16:15:37 GMT",
"version": "v1"
}
] |
2018-09-26
|
[
[
"Hansraj",
"Sudan",
""
]
] |
We analyze the isothermal property in static fluid spheres within the framework of the modified $f(R, T)$ theory of gravitation. The equation of pressure isotropy of the standard Einstein theory is preserved however, the energy density and pressure are expressed in terms of both gravitational potentials. Invoking the isothermal prescription requires that the isotropy condition assumes the role of a consistency condition and an exact model generalizing that of general relativity is found. Moreover it is found that the Einstein model is unstable and acausal while the $f(R, T)$ counterpart is well behaved on account of the freedom available through an additional coupling constant. The case of a constant spatial gravitational potential is considered and the complete model is determined. This model is markedly different from its Einstein counterpart which is known to be isothermal. Dropping the restriction on the density and imposing a linear barotropic equation of state generates an exact solution and consequently a stellar distribution as the vanishing of the pressure is possible and a boundary hypersurface exists. Finally we comment on the case of relaxing the equation of state but demanding an inverse square fall-off of the density - this case proves intractable.
|
2101.06094
|
Daniel Coumbe
|
Daniel Coumbe
|
Is Asymptotically Weyl-Invariant Gravity Viable?
|
14 pages, 6 figures, 3 tables. References added. Conforms with
version published in PRD
|
Phys. Rev. D 103, 084050 (2021)
|
10.1103/PhysRevD.103.084050
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
We explore the cosmological viability of a theory of gravity defined by the
Lagrangian $f(\mathcal{R})=\mathcal{R}^{n\left(\mathcal{R}\right)}$ in the
Palatini formalism, where $n\left(\mathcal{R}\right)$ is a dimensionless
function of the Palatini scalar curvature $\mathcal{R}$ that interpolates
between general relativity when $n\left(\mathcal{R}\right)=1$ and a locally
scale-invariant and superficially renormalizable theory when
$n\left(\mathcal{R}\right)=2$. We refer to this model as asymptotically
Weyl-invariant gravity (AWIG).
We analyse perhaps the simplest possible implementation of AWIG. A phase
space analysis yields three fixed points with effective equation of states
corresponding to de Sitter, radiation and matter-dominated phases. An analysis
of the deceleration parameter suggests our model is consistent with an early
and late period of accelerated cosmic expansion, with an intermediate period of
decelerated expansion. We show that the model contains no obvious curvature
singularities. Therefore, AWIG appears to be cosmologically viable, at least
for the simple implementation explored.
|
[
{
"created": "Fri, 15 Jan 2021 13:31:04 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Mar 2021 11:27:18 GMT",
"version": "v2"
},
{
"created": "Tue, 27 Apr 2021 18:10:43 GMT",
"version": "v3"
}
] |
2021-05-05
|
[
[
"Coumbe",
"Daniel",
""
]
] |
We explore the cosmological viability of a theory of gravity defined by the Lagrangian $f(\mathcal{R})=\mathcal{R}^{n\left(\mathcal{R}\right)}$ in the Palatini formalism, where $n\left(\mathcal{R}\right)$ is a dimensionless function of the Palatini scalar curvature $\mathcal{R}$ that interpolates between general relativity when $n\left(\mathcal{R}\right)=1$ and a locally scale-invariant and superficially renormalizable theory when $n\left(\mathcal{R}\right)=2$. We refer to this model as asymptotically Weyl-invariant gravity (AWIG). We analyse perhaps the simplest possible implementation of AWIG. A phase space analysis yields three fixed points with effective equation of states corresponding to de Sitter, radiation and matter-dominated phases. An analysis of the deceleration parameter suggests our model is consistent with an early and late period of accelerated cosmic expansion, with an intermediate period of decelerated expansion. We show that the model contains no obvious curvature singularities. Therefore, AWIG appears to be cosmologically viable, at least for the simple implementation explored.
|
2306.13218
|
Mouhssine Koussour
|
N. Myrzakulov, M. Koussour, and Dhruba Jyoti Gogoi
|
A new $f(Q)$ cosmological model with $H(z)$ quadratic expansion
|
Physics of the Dark Universe published version
| null |
10.1016/j.dark.2023.101268
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We present a new $f(Q)$ cosmological model capable of reproducing late-time
acceleration, i.e. $f\left( Q\right) = \lambda_{0}\left( \lambda +Q\right)
^{n}$ by supporting certain parametrization of the Hubble parameter. By using
observational data from Hubble, Pantheon, and Baryonic Acoustic Oscillations
(BAO) dataset, we investigate the constraints on the proposed quadratic Hubble
parameter $H(z)$. This proposal caused the Universe to transition from its
decelerated phase to its accelerated phase. Further, the current constrained
value of the deceleration parameter from the combined Hubble+Pantheon+BAO
dataset is $q_{0}=-0.285\pm 0.021$, which indicates that the Universe is
accelerating. We also analyze the evolution of energy density, pressure, and
EoS parameters to infer the Universe's accelerating behavior. Finally, we use a
stability analysis with linear perturbations to assure the model's stability.
|
[
{
"created": "Thu, 22 Jun 2023 21:39:51 GMT",
"version": "v1"
}
] |
2023-06-26
|
[
[
"Myrzakulov",
"N.",
""
],
[
"Koussour",
"M.",
""
],
[
"Gogoi",
"Dhruba Jyoti",
""
]
] |
We present a new $f(Q)$ cosmological model capable of reproducing late-time acceleration, i.e. $f\left( Q\right) = \lambda_{0}\left( \lambda +Q\right) ^{n}$ by supporting certain parametrization of the Hubble parameter. By using observational data from Hubble, Pantheon, and Baryonic Acoustic Oscillations (BAO) dataset, we investigate the constraints on the proposed quadratic Hubble parameter $H(z)$. This proposal caused the Universe to transition from its decelerated phase to its accelerated phase. Further, the current constrained value of the deceleration parameter from the combined Hubble+Pantheon+BAO dataset is $q_{0}=-0.285\pm 0.021$, which indicates that the Universe is accelerating. We also analyze the evolution of energy density, pressure, and EoS parameters to infer the Universe's accelerating behavior. Finally, we use a stability analysis with linear perturbations to assure the model's stability.
|
1308.5402
|
Shabbir Ghulam
|
Ghulam Shabbir, M. Ramzan and Suhail Khan
|
Classification of non conformally flat cylindrically symmetric non
static space-times according to their proper conformal motions
|
9 pages
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper we considered the most general form of non conformally flat
cylindrically symmetric non-static space-times to study proper conformal
motions using direct integration technique. We have shown that very special
classes for cylindrically symmetric space-times admit proper conformal motions.
This classification also covers non-static and static plane symmetric
space-times. In [9] it was claimed that non conformally flat plane symmetric
static space-times do not admit proper conformal motion. Here it is also shown
that static and non static plane symmetric space-times admit proper conformal
motions. We also discuss the Lie algebra in each case.
|
[
{
"created": "Sun, 25 Aug 2013 12:49:19 GMT",
"version": "v1"
}
] |
2013-08-27
|
[
[
"Shabbir",
"Ghulam",
""
],
[
"Ramzan",
"M.",
""
],
[
"Khan",
"Suhail",
""
]
] |
In this paper we considered the most general form of non conformally flat cylindrically symmetric non-static space-times to study proper conformal motions using direct integration technique. We have shown that very special classes for cylindrically symmetric space-times admit proper conformal motions. This classification also covers non-static and static plane symmetric space-times. In [9] it was claimed that non conformally flat plane symmetric static space-times do not admit proper conformal motion. Here it is also shown that static and non static plane symmetric space-times admit proper conformal motions. We also discuss the Lie algebra in each case.
|
1105.6328
|
Alexandre Baranov
|
A.M.Baranov and R.V.Bikmurzin
|
Exact static solutions for fluid gravitating balls in homogeneous
coordinates
|
3 pages, 2 figures. Proceedings of the International Conference on
Gravitation, Cosmology, Astrophysics and Nonstationary Gas Dynamics,
Delicated to Prof. K.P.Staniukovich's 90th birthday, Moscow, 2-6 March 2006
|
Gravition & Cosmology, Vol.12 (2006), No.2-3 (46-47), pp.103-105
| null | null |
gr-qc math-ph math.MP
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Two new classes of exact interior static solutions of the Einstein equations
in homogeneous coordinates for a gravitating ball filled by a Pascal perfect
fluid are obtained. Schwarzschild's interior solution of is a special case of
these solutions.
|
[
{
"created": "Tue, 31 May 2011 16:05:14 GMT",
"version": "v1"
}
] |
2011-06-01
|
[
[
"Baranov",
"A. M.",
""
],
[
"Bikmurzin",
"R. V.",
""
]
] |
Two new classes of exact interior static solutions of the Einstein equations in homogeneous coordinates for a gravitating ball filled by a Pascal perfect fluid are obtained. Schwarzschild's interior solution of is a special case of these solutions.
|
2201.00226
|
James B. Hartle
|
James B. Hartle
|
Simplicial Quantum Gravity
|
14 pages, revtex4, content unchanged from ist version but typos and
other small mistakes fixed
| null | null | null |
gr-qc hep-th physics.hist-ph quant-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Simplicial approximation and the ideas associated with the Regge
calculus.provide a concrete way of implementing a sum over histories
formulation ofquantum gravity. A four-dimensional simplicial geometry is made
up of flat four-simplices joined together.A sum over simplicial geometries is a
sum over thedifferent ways the simplices can be joined together with an
integral over their edge lengths.Theconstruction of the simplicial Euclidean
action for this approach to quantum general relativity is illustrated. The
recovery of the diffeomorphism group in the continuum limit is discussed. Some
possible classes of simplicial complexes with which to define a sum over
topologies are described.
|
[
{
"created": "Sat, 1 Jan 2022 18:20:07 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Jan 2022 22:07:04 GMT",
"version": "v2"
}
] |
2022-01-27
|
[
[
"Hartle",
"James B.",
""
]
] |
Simplicial approximation and the ideas associated with the Regge calculus.provide a concrete way of implementing a sum over histories formulation ofquantum gravity. A four-dimensional simplicial geometry is made up of flat four-simplices joined together.A sum over simplicial geometries is a sum over thedifferent ways the simplices can be joined together with an integral over their edge lengths.Theconstruction of the simplicial Euclidean action for this approach to quantum general relativity is illustrated. The recovery of the diffeomorphism group in the continuum limit is discussed. Some possible classes of simplicial complexes with which to define a sum over topologies are described.
|
2207.10410
|
Harsh Narola
|
Harsh Narola, Soumen Roy, Anand S. Sengupta
|
Beyond general relativity: designing a template-based search for exotic
gravitational wave signals
| null | null |
10.1103/PhysRevD.107.024017
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Accurate waveform models describing the complete evolution of compact
binaries are crucial for the maximum likelihood detection framework, testing
the predictions of General Relativity (GR) and investigating the possibility of
an alternative theory of gravity. Deviations from GR could manifest in subtle
variations of the numerical value of the GW signal's post-Newtonian (PN)
phasing coefficients. Once the search pipelines confirm an unambiguous signal
detection, deviations of the signal phasing coefficients at various PN orders
are routinely measured and reported. As the search templates themselves do not
incorporate any deviations from GR, they may miss astrophysical signals
carrying a significant departure from general relativity. We present a
parametrized template-based search for exotic gravitational-wave signals beyond
General Relativity by incorporating deviations to the signal's phasing
coefficients at different post-Newtonian orders in the search templates. We
present critical aspects of the new search, such as improvements in search
volume and its effect on various parts of the parameter space. In particular,
we demonstrate a factor x2 increase in search sensitivity (at a fixed
false-alarm rate) to beyond-GR exotic signals by using search templates that
admit a range of departures from general relativity. We also present the
results from a re-analysis of the 10-days long duration of LIGO's O1 data,
including the epoch of the GW150914 event, highlighting the differences from a
standard search. We indicate several directions for future research, including
ways of making the proposed new search computationally more efficient.
|
[
{
"created": "Thu, 21 Jul 2022 11:01:20 GMT",
"version": "v1"
}
] |
2023-02-01
|
[
[
"Narola",
"Harsh",
""
],
[
"Roy",
"Soumen",
""
],
[
"Sengupta",
"Anand S.",
""
]
] |
Accurate waveform models describing the complete evolution of compact binaries are crucial for the maximum likelihood detection framework, testing the predictions of General Relativity (GR) and investigating the possibility of an alternative theory of gravity. Deviations from GR could manifest in subtle variations of the numerical value of the GW signal's post-Newtonian (PN) phasing coefficients. Once the search pipelines confirm an unambiguous signal detection, deviations of the signal phasing coefficients at various PN orders are routinely measured and reported. As the search templates themselves do not incorporate any deviations from GR, they may miss astrophysical signals carrying a significant departure from general relativity. We present a parametrized template-based search for exotic gravitational-wave signals beyond General Relativity by incorporating deviations to the signal's phasing coefficients at different post-Newtonian orders in the search templates. We present critical aspects of the new search, such as improvements in search volume and its effect on various parts of the parameter space. In particular, we demonstrate a factor x2 increase in search sensitivity (at a fixed false-alarm rate) to beyond-GR exotic signals by using search templates that admit a range of departures from general relativity. We also present the results from a re-analysis of the 10-days long duration of LIGO's O1 data, including the epoch of the GW150914 event, highlighting the differences from a standard search. We indicate several directions for future research, including ways of making the proposed new search computationally more efficient.
|
1509.01452
|
Chayan Ranjit
|
Chayan Ranjit, Prabir Rudra
|
Study of Some Cosmological Parameters for Interacting New Holographic
Dark Energy Model in f(T) Gravity
|
12 pages, 12 figures, Accepted in International Journal of Modern
Physics D
| null |
10.1142/S0218271816500085
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The present work is based on the idea of an interacting framework of new
holographic dark energy with cold dark matter in the background of $f(T)$
gravity. Here, we have considered the flat modified Friedmann universe for
$f(T)$ gravity which is filled with new Holographic dark energy and dark
matter. We have derived some cosmological parameters like Deceleration
parameter, EoS parameter, State-finder parameters, Cosmographic parameters,
{\it Om} parameter and graphically investigated the nature of these parameters
for the above mentioned interacting scenario. The results are found to be
consistent with the accelerating universe. Also we have graphically
investigated the trajectories in $\omega $--$ \omega'$ plane for different
values of the interacting parameter and explored the freezing region and
thawing region in $\omega $--$ \omega'$ plane. Finally, we have analyzed the
stability of this model.
|
[
{
"created": "Thu, 3 Sep 2015 15:39:44 GMT",
"version": "v1"
}
] |
2016-02-17
|
[
[
"Ranjit",
"Chayan",
""
],
[
"Rudra",
"Prabir",
""
]
] |
The present work is based on the idea of an interacting framework of new holographic dark energy with cold dark matter in the background of $f(T)$ gravity. Here, we have considered the flat modified Friedmann universe for $f(T)$ gravity which is filled with new Holographic dark energy and dark matter. We have derived some cosmological parameters like Deceleration parameter, EoS parameter, State-finder parameters, Cosmographic parameters, {\it Om} parameter and graphically investigated the nature of these parameters for the above mentioned interacting scenario. The results are found to be consistent with the accelerating universe. Also we have graphically investigated the trajectories in $\omega $--$ \omega'$ plane for different values of the interacting parameter and explored the freezing region and thawing region in $\omega $--$ \omega'$ plane. Finally, we have analyzed the stability of this model.
|
1609.00700
|
Mariam Bouhmadi-Lopez
|
Mariam Bouhmadi-L\'opez, Che-Yu Chen
|
Towards the Quantization of Eddington-inspired-Born-Infeld Theory
|
26 pages, 1 figure. Discussion expanded and further mathematical and
physical details provided. Version accepted in JCAP
|
JCAP 11 (2016) 023
|
10.1088/1475-7516/2016/11/023
| null |
gr-qc hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The quantum effects close to the classical big rip singularity within the
Eddington-inspired-Born-Infeld theory (EiBI) are investigated through quantum
geometrodynamics. It is the first time that this approach is applied to a
modified theory constructed upon Palatini formalism. The Wheeler-DeWitt (WDW)
equation is obtained and solved based on an alternative action proposed in
Ref.[1], under two different factor ordering choices. This action is
dynamically equivalent to the original EiBI action while it is free of square
root of the spacetime curvature. We consider a homogeneous, isotropic and
spatially flat universe, which is assumed to be dominated by a phantom perfect
fluid whose equation of state is a constant. We obtain exact solutions of the
WDW equation based on some specific conditions. In more general cases, we
propose a qualitative argument with the help of a Wentzel-Kramers-Brillouin
(WKB) approximation to get further solutions. Besides, we also construct an
effective WDW equation by simply promoting the classical Friedmann equations.
We find that for all the approaches considered, the DeWitt condition hinting
singularity avoidance is satisfied. Therefore the big rip singularity can be
avoided through the quantum approach within the EiBI theory.
|
[
{
"created": "Fri, 2 Sep 2016 19:05:48 GMT",
"version": "v1"
},
{
"created": "Sat, 10 Sep 2016 13:54:35 GMT",
"version": "v2"
},
{
"created": "Fri, 21 Oct 2016 12:56:30 GMT",
"version": "v3"
}
] |
2016-11-10
|
[
[
"Bouhmadi-López",
"Mariam",
""
],
[
"Chen",
"Che-Yu",
""
]
] |
The quantum effects close to the classical big rip singularity within the Eddington-inspired-Born-Infeld theory (EiBI) are investigated through quantum geometrodynamics. It is the first time that this approach is applied to a modified theory constructed upon Palatini formalism. The Wheeler-DeWitt (WDW) equation is obtained and solved based on an alternative action proposed in Ref.[1], under two different factor ordering choices. This action is dynamically equivalent to the original EiBI action while it is free of square root of the spacetime curvature. We consider a homogeneous, isotropic and spatially flat universe, which is assumed to be dominated by a phantom perfect fluid whose equation of state is a constant. We obtain exact solutions of the WDW equation based on some specific conditions. In more general cases, we propose a qualitative argument with the help of a Wentzel-Kramers-Brillouin (WKB) approximation to get further solutions. Besides, we also construct an effective WDW equation by simply promoting the classical Friedmann equations. We find that for all the approaches considered, the DeWitt condition hinting singularity avoidance is satisfied. Therefore the big rip singularity can be avoided through the quantum approach within the EiBI theory.
|
2312.01636
|
Tousif Islam
|
Tousif Islam, Scott E. Field, Gaurav Khanna
|
Comparing numerical relativity and perturbation theory waveforms for a
non-spinning equal-mass binary
|
Published in a themed issue in honor of Prof. Jorge Pullin on his
60th anniversary; Universe 2024, 10(1), 25
| null |
10.3390/universe10010025
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Past studies have empirically demonstrated a surprising agreement between
gravitational waveforms computed using adiabatic-driven-inspiral point-particle
black hole perturbation theory (ppBHPT) and numerical relativity (NR) following
a straightforward calibration step, sometimes referred to as $\alpha$-$\beta$
scaling. Specifically focusing on the quadrupole mode, this calibration
technique necessitates only two time-independent parameters to scale the
overall amplitude and time coordinate. In this article, part of a special
issue, we investigate this scaling for non-spinning binaries at the equal mass
limit. Even without calibration, NR and ppBHPT waveforms exhibit an unexpected
degree of similarity after accounting for different mass scale definitions.
Post-calibration, good agreement between ppBHPT and NR waveforms extends nearly
up to the point of the merger. We also assess the breakdown of the
time-independent assumption of the scaling parameters, shedding light on
current limitations and suggesting potential generalizations for the
$\alpha$-$\beta$ scaling technique.
|
[
{
"created": "Mon, 4 Dec 2023 05:37:04 GMT",
"version": "v1"
},
{
"created": "Sun, 4 Feb 2024 00:17:36 GMT",
"version": "v2"
}
] |
2024-02-06
|
[
[
"Islam",
"Tousif",
""
],
[
"Field",
"Scott E.",
""
],
[
"Khanna",
"Gaurav",
""
]
] |
Past studies have empirically demonstrated a surprising agreement between gravitational waveforms computed using adiabatic-driven-inspiral point-particle black hole perturbation theory (ppBHPT) and numerical relativity (NR) following a straightforward calibration step, sometimes referred to as $\alpha$-$\beta$ scaling. Specifically focusing on the quadrupole mode, this calibration technique necessitates only two time-independent parameters to scale the overall amplitude and time coordinate. In this article, part of a special issue, we investigate this scaling for non-spinning binaries at the equal mass limit. Even without calibration, NR and ppBHPT waveforms exhibit an unexpected degree of similarity after accounting for different mass scale definitions. Post-calibration, good agreement between ppBHPT and NR waveforms extends nearly up to the point of the merger. We also assess the breakdown of the time-independent assumption of the scaling parameters, shedding light on current limitations and suggesting potential generalizations for the $\alpha$-$\beta$ scaling technique.
|
1612.09077
|
Shoichiro Miyashita
|
Yosuke Misonoh, Mitsuhiro Fukushima, Shoichiro Miyashita
|
Stability of Singularity-free Cosmological Solutions in
Ho\v{r}ava-Lifshitz Gravity
|
22 pages, 8 figures ; v3 : some results modified
|
Phys. Rev. D 95, 044044 (2017)
|
10.1103/PhysRevD.95.044044
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study stability of singularity-free cosmological solutions with positive
cosmological constant based on projectable Ho\v{r}ava-Lifshitz (HL) theory. In
HL theory, the isotropic and homogeneous cosmological solutions with bounce can
be realized if spacial curvature is non-zero. By performing perturbation
analysis around non-flat Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime,
we derive a quadratic action and discuss the stability, i.e, ghost and
tachyon-free conditions. Although the squared effective mass of scalar
perturbation must be negative in infrared regime, we can avoid tachyon
instability by considering strong Hubble friction. Additionally, we estimate
the backreaction from the perturbations on background geometry, especially,
against anisotropic perturbation in closed FLRW spacetime. It turns out that
certain types of bouncing solution may be spoiled even if all perturbation
modes are stable.
|
[
{
"created": "Thu, 29 Dec 2016 08:54:12 GMT",
"version": "v1"
},
{
"created": "Sun, 8 Jan 2017 09:17:39 GMT",
"version": "v2"
},
{
"created": "Sun, 22 Jan 2017 10:33:56 GMT",
"version": "v3"
}
] |
2017-03-08
|
[
[
"Misonoh",
"Yosuke",
""
],
[
"Fukushima",
"Mitsuhiro",
""
],
[
"Miyashita",
"Shoichiro",
""
]
] |
We study stability of singularity-free cosmological solutions with positive cosmological constant based on projectable Ho\v{r}ava-Lifshitz (HL) theory. In HL theory, the isotropic and homogeneous cosmological solutions with bounce can be realized if spacial curvature is non-zero. By performing perturbation analysis around non-flat Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime, we derive a quadratic action and discuss the stability, i.e, ghost and tachyon-free conditions. Although the squared effective mass of scalar perturbation must be negative in infrared regime, we can avoid tachyon instability by considering strong Hubble friction. Additionally, we estimate the backreaction from the perturbations on background geometry, especially, against anisotropic perturbation in closed FLRW spacetime. It turns out that certain types of bouncing solution may be spoiled even if all perturbation modes are stable.
|
2201.10875
|
Jaros{\l}aw Kopi\'nski
|
Jaros{\l}aw Kopi\'nski, Juan A. Valiente Kroon
|
Bach equation and the matching of spacetimes in conformal cyclic
cosmology models
|
10 pages; updated to match the published version
|
Phys. Rev. D 106, 084034 2022
|
10.1103/PhysRevD.106.084034
| null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
We consider the problem of matching two spacetimes, the previous and present
aeons, in the Conformal Cyclic Cosmology model. The common boundary between
them inherits two sets of constraints -- one for each solution of the Einstein
field equations extended to the conformal boundaries. The previous aeon is
assumed to be an asymptotically de Sitter spacetime, so the standard conformal
formulation of the Einstein field equations suffice to derive the constraints
on the future null infinity. For the future aeon, which is supposed to evolve
from an initial singularity, they are obtained with the use of the Bach
equation. This equation is regular at the past conformal infinity for
conformally flat and conformally Einstein spacetimes, so we will mostly focus
on them here. An example of the electrovacuum spacetime which does not fall
into this class and has regular conformal Bach tensor will be discussed in the
appendix.
|
[
{
"created": "Wed, 26 Jan 2022 11:21:38 GMT",
"version": "v1"
},
{
"created": "Thu, 27 Oct 2022 15:14:04 GMT",
"version": "v2"
}
] |
2023-02-28
|
[
[
"Kopiński",
"Jarosław",
""
],
[
"Kroon",
"Juan A. Valiente",
""
]
] |
We consider the problem of matching two spacetimes, the previous and present aeons, in the Conformal Cyclic Cosmology model. The common boundary between them inherits two sets of constraints -- one for each solution of the Einstein field equations extended to the conformal boundaries. The previous aeon is assumed to be an asymptotically de Sitter spacetime, so the standard conformal formulation of the Einstein field equations suffice to derive the constraints on the future null infinity. For the future aeon, which is supposed to evolve from an initial singularity, they are obtained with the use of the Bach equation. This equation is regular at the past conformal infinity for conformally flat and conformally Einstein spacetimes, so we will mostly focus on them here. An example of the electrovacuum spacetime which does not fall into this class and has regular conformal Bach tensor will be discussed in the appendix.
|
1607.05318
|
Farhad Darabi
|
M. R. Setare, F. Felegary, F. Darabi
|
Evolution of spherical over-densities in tachyon scalar field model
|
14 pages, 15 figures, revision
|
Physics Letters B, 772, 70 (2017)
|
10.1016/j.physletb.2017.06.039
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the tachyon scalar field model in flat FRW cosmology with the
particular potential $\phi^{-2}$ and the scale factor behavior $a(t)=t^n$. We
consider the spherical collapse model and investigate the effects of the
tachyon scalar field on the structure formation in flat FRW universe. We
calculate $\delta_{c}(z_{c})$, $\lambda(z_{c})$, $\xi(z_{c})$,
$\Delta_{V}(z_{c})$, $\log [\nu f(\nu)]$ and $\log [n(k)]$ for the tachyon
scalar field model and compare the results with the results of EdS model and
$\Lambda CDM$ model. It is shown that in the tachyon scalar field model the
structure formation may occur earlier, in comparison to the other models.
|
[
{
"created": "Mon, 18 Jul 2016 20:41:54 GMT",
"version": "v1"
},
{
"created": "Sat, 8 Oct 2016 18:33:26 GMT",
"version": "v2"
},
{
"created": "Wed, 28 Jun 2017 21:41:03 GMT",
"version": "v3"
}
] |
2017-08-23
|
[
[
"Setare",
"M. R.",
""
],
[
"Felegary",
"F.",
""
],
[
"Darabi",
"F.",
""
]
] |
We study the tachyon scalar field model in flat FRW cosmology with the particular potential $\phi^{-2}$ and the scale factor behavior $a(t)=t^n$. We consider the spherical collapse model and investigate the effects of the tachyon scalar field on the structure formation in flat FRW universe. We calculate $\delta_{c}(z_{c})$, $\lambda(z_{c})$, $\xi(z_{c})$, $\Delta_{V}(z_{c})$, $\log [\nu f(\nu)]$ and $\log [n(k)]$ for the tachyon scalar field model and compare the results with the results of EdS model and $\Lambda CDM$ model. It is shown that in the tachyon scalar field model the structure formation may occur earlier, in comparison to the other models.
|
1811.08551
|
P. A. Gonzalez
|
P. A. Gonz\'alez, Marco Olivares, Yerko V\'asquez, Joel Saavedra and
Ali \"Ovg\"un
|
Motion and collision of particles near DST Black holes
|
21 pages and 10 figures. New version
|
Eur. Phys. J. C (2019) 79: 528
|
10.1140/epjc/s10052-019-7043-6
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider Deser-Sarioglu-Tekin (DST) black holes as background and we study
such the motion of massive particles as the collision of two spinning particles
in the vicinity of its horizon. New kinds of orbits are allowed for small
deviations of General Relativity, but the behavior of the collision is similar
to the one observed for General Relativity. Some observables like bending of
light and the perihelion precession are analyzed.
|
[
{
"created": "Wed, 21 Nov 2018 02:14:47 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Mar 2019 21:57:59 GMT",
"version": "v2"
}
] |
2019-06-24
|
[
[
"González",
"P. A.",
""
],
[
"Olivares",
"Marco",
""
],
[
"Vásquez",
"Yerko",
""
],
[
"Saavedra",
"Joel",
""
],
[
"Övgün",
"Ali",
""
]
] |
We consider Deser-Sarioglu-Tekin (DST) black holes as background and we study such the motion of massive particles as the collision of two spinning particles in the vicinity of its horizon. New kinds of orbits are allowed for small deviations of General Relativity, but the behavior of the collision is similar to the one observed for General Relativity. Some observables like bending of light and the perihelion precession are analyzed.
|
gr-qc/0607012
|
Robert Brout
|
Robert Brout
|
The Causet Mechanism for the Creation of Energy
|
Dedicated to Rafael Sorkin, to appear in his 60th birthday
Festschrift
| null | null | null |
gr-qc
| null |
Sorkin's causet mechanism is generalized to include energy exchange between
causet elements and conventional vacuum fluctuations to the inflationary epoch.
In this, the dark energy of the adiabatic era is the fluctuating remnant of
inflation. The mechanism is also applicable to black hole evaporation.
|
[
{
"created": "Tue, 4 Jul 2006 19:48:06 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Aug 2006 16:11:29 GMT",
"version": "v2"
},
{
"created": "Thu, 3 Aug 2006 18:55:21 GMT",
"version": "v3"
}
] |
2007-05-23
|
[
[
"Brout",
"Robert",
""
]
] |
Sorkin's causet mechanism is generalized to include energy exchange between causet elements and conventional vacuum fluctuations to the inflationary epoch. In this, the dark energy of the adiabatic era is the fluctuating remnant of inflation. The mechanism is also applicable to black hole evaporation.
|
1506.07119
|
Lunchakorn Tannukij
|
Sushant G. Ghosh, Lunchakorn Tannukij, Pitayuth Wongjun
|
A class of black holes in dRGT massive gravity and their thermodynamical
properties
|
29 pages, 20 figures, typos fixed
|
Eur. Phys. J. C 76, no. 3, 119 (2016)
|
10.1140/epjc/s10052-016-3943-x
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We present exact spherical black hole solutions in de Rham, Gabadadze and
Tolley (dRGT) massive gravity for a generic choice of the parameters in the
theory, and also discuss the thermodynamical and phase structure of the black
hole in both the grand canonical and canonical ensembles (for charged case). It
turns out that the dGRT black hole solutions includes the known solutions to
the Einstein field equations, such as, the monopole-de Sitter-Schwarzschild
ones with the coefficients for the third and fourth terms in the potential and
the graviton mass in massive gravity naturally generates the cosmological
constant and the global monopole term. Furthermore, we compute the mass,
temperature, and entropy of dGRT black hole solutions and also perform
thermodynamical stability. It turns out that the presence of the graviton mass
completely changes the black hole thermodynamics, and it can provide the
Hawking-Page phase transition which is also true for the obtained charged black
holes. Interestingly, the entropy of a black hole is unaffected and still obeys
area law. In particular, our results, in the limit $m_g \rightarrow 0$, reduced
exactly to \emph{vis-$\grave{a}$-vis} the general relativity results.
|
[
{
"created": "Thu, 18 Jun 2015 11:26:51 GMT",
"version": "v1"
},
{
"created": "Fri, 20 Nov 2015 06:43:39 GMT",
"version": "v2"
},
{
"created": "Tue, 15 Mar 2016 07:46:14 GMT",
"version": "v3"
}
] |
2016-03-16
|
[
[
"Ghosh",
"Sushant G.",
""
],
[
"Tannukij",
"Lunchakorn",
""
],
[
"Wongjun",
"Pitayuth",
""
]
] |
We present exact spherical black hole solutions in de Rham, Gabadadze and Tolley (dRGT) massive gravity for a generic choice of the parameters in the theory, and also discuss the thermodynamical and phase structure of the black hole in both the grand canonical and canonical ensembles (for charged case). It turns out that the dGRT black hole solutions includes the known solutions to the Einstein field equations, such as, the monopole-de Sitter-Schwarzschild ones with the coefficients for the third and fourth terms in the potential and the graviton mass in massive gravity naturally generates the cosmological constant and the global monopole term. Furthermore, we compute the mass, temperature, and entropy of dGRT black hole solutions and also perform thermodynamical stability. It turns out that the presence of the graviton mass completely changes the black hole thermodynamics, and it can provide the Hawking-Page phase transition which is also true for the obtained charged black holes. Interestingly, the entropy of a black hole is unaffected and still obeys area law. In particular, our results, in the limit $m_g \rightarrow 0$, reduced exactly to \emph{vis-$\grave{a}$-vis} the general relativity results.
|
1405.7023
|
Sam Young
|
Sam Young, Christian T. Byrnes, Misao Sasaki
|
Calculating the mass spectrum of primordial black holes
|
16 pages, 7 figures. Version 2: updated to match published version
and include journal reference. Version 3 and 4: minor corrections,
conclusions unchanged
|
JCAP 1407 (2014) 045
|
10.1088/1475-7516/2014/07/045
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We reinspect the calculation for the mass fraction of primordial black holes
(PBHs) which are formed from primordial perturbations, finding that performing
the calculation using the comoving curvature perturbation $\mathcal{R}_{c}$ in
the standard way vastly overestimates the number of PBHs, by many orders of
magnitude. This is because PBHs form shortly after horizon entry, meaning modes
significantly larger than the PBH are unobservable and should not affect
whether a PBH forms or not - this important effect is not taken into account by
smoothing the distribution in the standard fashion. We discuss alternative
methods and argue that the density contrast, $\Delta$, should be used instead
as super-horizon modes are damped by a factor $k^{2}$. We make a comparison
between using a Press-Schechter approach and peaks theory, finding that the two
are in close agreement in the region of interest. We also investigate the
effect of varying the spectral index, and the running of the spectral index, on
the abundance of primordial black holes.
|
[
{
"created": "Tue, 27 May 2014 19:23:15 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Sep 2014 13:54:09 GMT",
"version": "v2"
},
{
"created": "Tue, 16 Dec 2014 15:08:15 GMT",
"version": "v3"
},
{
"created": "Wed, 4 Mar 2015 12:15:39 GMT",
"version": "v4"
}
] |
2015-03-05
|
[
[
"Young",
"Sam",
""
],
[
"Byrnes",
"Christian T.",
""
],
[
"Sasaki",
"Misao",
""
]
] |
We reinspect the calculation for the mass fraction of primordial black holes (PBHs) which are formed from primordial perturbations, finding that performing the calculation using the comoving curvature perturbation $\mathcal{R}_{c}$ in the standard way vastly overestimates the number of PBHs, by many orders of magnitude. This is because PBHs form shortly after horizon entry, meaning modes significantly larger than the PBH are unobservable and should not affect whether a PBH forms or not - this important effect is not taken into account by smoothing the distribution in the standard fashion. We discuss alternative methods and argue that the density contrast, $\Delta$, should be used instead as super-horizon modes are damped by a factor $k^{2}$. We make a comparison between using a Press-Schechter approach and peaks theory, finding that the two are in close agreement in the region of interest. We also investigate the effect of varying the spectral index, and the running of the spectral index, on the abundance of primordial black holes.
|
1011.4444
|
Ian D. Lawrie
|
Ian D. Lawrie
|
Time evolution in quantum cosmology
|
21 pages, no figures; minor revisions and added references; matches
version in Phys Rev D
|
Phys.Rev.D83:043503,2011
|
10.1103/PhysRevD.83.043503
| null |
gr-qc hep-ph hep-th quant-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
A commonly adopted relational account of time evolution in
generally-covariant systems, and more specifically in quantum cosmology, is
argued to be unsatisfactory, insofar as it describes evolution relative to
observed readings of a clock that does not exist as a bona fide observable
object. A modified strategy is proposed, in which evolution relative to the
proper time that elapses along the worldline of a specific observer can be
described through the introduction of a `test clock', regarded as internal to,
and hence unobservable by, that observer. This strategy is worked out in detail
in the case of a homogeneous cosmology, in the context of both a conventional
Schrodinger quantization scheme, and a `polymer' quantization scheme of the
kind inspired by loop quantum gravity. Particular attention is given to
limitations placed on the observability of time evolution by the requirement
that a test clock should contribute only a negligible energy to the Hamiltonian
constraint. It is found that suitable compromises are available, in which the
clock energy is reasonably small, while Dirac observables are reasonably
sharply defined.
|
[
{
"created": "Fri, 19 Nov 2010 15:07:32 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Mar 2011 11:56:54 GMT",
"version": "v2"
}
] |
2011-03-10
|
[
[
"Lawrie",
"Ian D.",
""
]
] |
A commonly adopted relational account of time evolution in generally-covariant systems, and more specifically in quantum cosmology, is argued to be unsatisfactory, insofar as it describes evolution relative to observed readings of a clock that does not exist as a bona fide observable object. A modified strategy is proposed, in which evolution relative to the proper time that elapses along the worldline of a specific observer can be described through the introduction of a `test clock', regarded as internal to, and hence unobservable by, that observer. This strategy is worked out in detail in the case of a homogeneous cosmology, in the context of both a conventional Schrodinger quantization scheme, and a `polymer' quantization scheme of the kind inspired by loop quantum gravity. Particular attention is given to limitations placed on the observability of time evolution by the requirement that a test clock should contribute only a negligible energy to the Hamiltonian constraint. It is found that suitable compromises are available, in which the clock energy is reasonably small, while Dirac observables are reasonably sharply defined.
|
1503.01221
|
Jia-Hui Huang
|
Jia-Hui Huang, Zhan-Feng Mai
|
Superradiantly stable non-extremal Reissner-Nordstrom black holes
| null | null |
10.1140/epjc/s10052-016-4157-y
| null |
gr-qc
|
http://creativecommons.org/licenses/by/3.0/
|
The superradiant stability is investigated for non-extremal
Reissner-Nordstrom black hole. We use an algebraic method to demonstrate that
all non-extremal Reissner-Nordstrom black holes are superradiantly stable
against a charged massive scalar perturbation. This improves the results
obtained before for non-extremal Reissner-Nordstrom black holes.
|
[
{
"created": "Wed, 4 Mar 2015 05:05:40 GMT",
"version": "v1"
}
] |
2016-06-14
|
[
[
"Huang",
"Jia-Hui",
""
],
[
"Mai",
"Zhan-Feng",
""
]
] |
The superradiant stability is investigated for non-extremal Reissner-Nordstrom black hole. We use an algebraic method to demonstrate that all non-extremal Reissner-Nordstrom black holes are superradiantly stable against a charged massive scalar perturbation. This improves the results obtained before for non-extremal Reissner-Nordstrom black holes.
|
gr-qc/0311070
|
Sivasubramanian Somu
|
S. Sivasubramanian, A. Widom, Y.N. Srivastava
|
Gravitational Waves and the Sagnac Effect
|
LaTeX format 1 *.eps figure
| null | null | null |
gr-qc
| null |
We consider light waves propagating clockwise and other light waves
propagating counterclockwise around a closed path in a plane (theoretically
with the help of stationary mirrors). The time difference between the two light
propagating path orientations constitutes the Sagnac effect. The general
relativistic expression for the Sagnac effect is discussed. It is shown that a
gravitational wave incident to the light beams at an arbitrary angle will not
induce a Sagnac effect so long as the wave length of the weak gravitational
wave is long on the length scale of the closed light beam paths. The
gravitational wave induced Sagnac effect is thereby null.
|
[
{
"created": "Fri, 21 Nov 2003 03:15:37 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Sivasubramanian",
"S.",
""
],
[
"Widom",
"A.",
""
],
[
"Srivastava",
"Y. N.",
""
]
] |
We consider light waves propagating clockwise and other light waves propagating counterclockwise around a closed path in a plane (theoretically with the help of stationary mirrors). The time difference between the two light propagating path orientations constitutes the Sagnac effect. The general relativistic expression for the Sagnac effect is discussed. It is shown that a gravitational wave incident to the light beams at an arbitrary angle will not induce a Sagnac effect so long as the wave length of the weak gravitational wave is long on the length scale of the closed light beam paths. The gravitational wave induced Sagnac effect is thereby null.
|
2310.13150
|
Pablo Pais
|
Nick E. Mavromatos, Pablo Pais, Alfredo Iorio
|
Torsion at different scales: from materials to the Universe
|
48 pages, 9 figures incorporated. Invited review, the version matches
the published version in the journal Universe
|
Universe 2023, 9(12), 516
|
10.3390/universe9120516
|
KCL-PH-TH/2023-54
|
gr-qc cond-mat.mtrl-sci hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The concept of torsion in geometry, although known for a long time, has not
gained considerable attention by the physics community until relatively
recently, due to its diverse and potentially important applications to a
plethora of contexts of physical interest. These range from novel materials,
such as graphene and graphene-like materials, to advanced theoretical ideas,
such as string theory and supersymmetry/supergravity and applications thereof
in understanding the dark sector of our Universe. This work reviews such
applications of torsion at different physical scales.
|
[
{
"created": "Thu, 19 Oct 2023 20:47:11 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Dec 2023 18:29:12 GMT",
"version": "v2"
},
{
"created": "Sun, 31 Dec 2023 19:00:44 GMT",
"version": "v3"
}
] |
2024-01-02
|
[
[
"Mavromatos",
"Nick E.",
""
],
[
"Pais",
"Pablo",
""
],
[
"Iorio",
"Alfredo",
""
]
] |
The concept of torsion in geometry, although known for a long time, has not gained considerable attention by the physics community until relatively recently, due to its diverse and potentially important applications to a plethora of contexts of physical interest. These range from novel materials, such as graphene and graphene-like materials, to advanced theoretical ideas, such as string theory and supersymmetry/supergravity and applications thereof in understanding the dark sector of our Universe. This work reviews such applications of torsion at different physical scales.
|
gr-qc/0204022
|
Matt Visser
|
Matt Visser (Washington University in Saint Louis)
|
The quantum physics of chronology protection
|
CUP style: uses cmmp.cls; 18 pages; contribution to "The future of
theoretical physics and cosmology", conference in honour of Professor Stephen
Hawking on the occasion of his 60'th birthday. V2: Some references added
| null | null | null |
gr-qc hep-th
| null |
This is a brief survey of the current status of Stephen Hawking's
``chronology protection conjecture''. That is: ``Why does nature abhor a time
machine?'' I'll discuss a few examples of spacetimes containing ``time
machines'' (closed causal curves), the sorts of peculiarities that arise, and
the reactions of the physics community. While pointing out other possibilities,
this article concentrates on the possibility of ``chronology protection''. As
Stephen puts it:
``It seems that there is a Chronology Protection Agency which prevents the
appearance of closed timelike curves and so makes the universe safe for
historians.''
|
[
{
"created": "Fri, 5 Apr 2002 02:20:47 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Apr 2002 19:49:54 GMT",
"version": "v2"
}
] |
2016-08-31
|
[
[
"Visser",
"Matt",
"",
"Washington University in Saint Louis"
]
] |
This is a brief survey of the current status of Stephen Hawking's ``chronology protection conjecture''. That is: ``Why does nature abhor a time machine?'' I'll discuss a few examples of spacetimes containing ``time machines'' (closed causal curves), the sorts of peculiarities that arise, and the reactions of the physics community. While pointing out other possibilities, this article concentrates on the possibility of ``chronology protection''. As Stephen puts it: ``It seems that there is a Chronology Protection Agency which prevents the appearance of closed timelike curves and so makes the universe safe for historians.''
|
2104.00754
|
Daniel Flores
|
D. Flores-Alfonso, C. S. Lopez-Monsalvo, M. Maceda
|
Thurston Geometries in Three-Dimensional New Massive Gravity
| null |
Phys. Rev. Lett. 127, 061102 (2021)
|
10.1103/PhysRevLett.127.061102
| null |
gr-qc hep-th math-ph math.MP
|
http://creativecommons.org/licenses/by/4.0/
|
We show that the three-dimensional Thurston geometries are vacuum solutions
to the 3D new massive gravity equations of motion. We analyze their Lorentzian
counterparts as well.
|
[
{
"created": "Thu, 1 Apr 2021 20:25:25 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Jun 2021 01:23:34 GMT",
"version": "v2"
},
{
"created": "Mon, 9 Aug 2021 01:58:37 GMT",
"version": "v3"
}
] |
2021-08-10
|
[
[
"Flores-Alfonso",
"D.",
""
],
[
"Lopez-Monsalvo",
"C. S.",
""
],
[
"Maceda",
"M.",
""
]
] |
We show that the three-dimensional Thurston geometries are vacuum solutions to the 3D new massive gravity equations of motion. We analyze their Lorentzian counterparts as well.
|
2401.08885
|
Messias De Brito Cruz
|
M. B. Cruz, R. M. P. Neves and Celio R. Muniz
|
Traversable Wormholes from Loop Quantum Gravity
|
20 pages and 19 figures
| null | null | null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
This study introduces and investigates Lorentzian traversable wormhole
solutions rooted in Loop Quantum Gravity (LQG). The static and spherically
symmetric solutions to be examined stem from the energy density sourcing
self-dual regular black holes discovered by L. Modesto, relying on the
parameters associated with LQG, which account for the quantum nature of
spacetime. We specifically focus on macroscopic wormholes characterized by
small values of these parameters. Our analysis encompasses zero-tidal solutions
and those with non-constant redshift functions, exploring immersion diagrams,
curvatures, energy conditions, equilibrium requirements, and the requisite
quantity of exotic matter to sustain these wormholes. The investigation
underscores the influence of LQG parameters on these features, highlighting the
pivotal role of spacetime's quantum properties in shaping these wormholes and
governing their behavior.
|
[
{
"created": "Tue, 16 Jan 2024 23:44:17 GMT",
"version": "v1"
}
] |
2024-01-18
|
[
[
"Cruz",
"M. B.",
""
],
[
"Neves",
"R. M. P.",
""
],
[
"Muniz",
"Celio R.",
""
]
] |
This study introduces and investigates Lorentzian traversable wormhole solutions rooted in Loop Quantum Gravity (LQG). The static and spherically symmetric solutions to be examined stem from the energy density sourcing self-dual regular black holes discovered by L. Modesto, relying on the parameters associated with LQG, which account for the quantum nature of spacetime. We specifically focus on macroscopic wormholes characterized by small values of these parameters. Our analysis encompasses zero-tidal solutions and those with non-constant redshift functions, exploring immersion diagrams, curvatures, energy conditions, equilibrium requirements, and the requisite quantity of exotic matter to sustain these wormholes. The investigation underscores the influence of LQG parameters on these features, highlighting the pivotal role of spacetime's quantum properties in shaping these wormholes and governing their behavior.
|
gr-qc/9404046
|
Robert Mann
|
M.S. Delgaty and R.B. Mann
|
Traversable Wormholes in (2+1) and (3+1) Dimensions with a Cosmological
Constant
|
19 pgs. WATPHYS TH-93/06
|
Int.J.Mod.Phys. D4 (1995) 231-246
|
10.1142/S021827189500017X
| null |
gr-qc
| null |
Macroscopic traversable wormhole solutions to Einstein's field equations in
$(2+1)$ and $(3+1)$ dimensions with a cosmological constant are investigated.
Ensuring traversability severely constrains the material used to generate the
wormhole's spacetime curvature. Although the presence of a cosmological
constant modifies to some extent the type of matter permitted (for example it
is possible to have a positive energy density for the material threading the
throat of the wormhole in $(2+1)$ dimensions), the material must still be
``exotic'', that is matter with a larger radial tension than total mass-energy
density multiplied by $c^2$. Two specific solutions are applied to the general
cases and a partial stability analysis of a $(2+1)$ dimensional solution is
explored.
|
[
{
"created": "Mon, 25 Apr 1994 19:22:30 GMT",
"version": "v1"
}
] |
2009-10-22
|
[
[
"Delgaty",
"M. S.",
""
],
[
"Mann",
"R. B.",
""
]
] |
Macroscopic traversable wormhole solutions to Einstein's field equations in $(2+1)$ and $(3+1)$ dimensions with a cosmological constant are investigated. Ensuring traversability severely constrains the material used to generate the wormhole's spacetime curvature. Although the presence of a cosmological constant modifies to some extent the type of matter permitted (for example it is possible to have a positive energy density for the material threading the throat of the wormhole in $(2+1)$ dimensions), the material must still be ``exotic'', that is matter with a larger radial tension than total mass-energy density multiplied by $c^2$. Two specific solutions are applied to the general cases and a partial stability analysis of a $(2+1)$ dimensional solution is explored.
|
1805.05684
|
Rituparno Goswami
|
Abbas Sherif, Rituparno Goswami, Sunil D Maharaj
|
Geometrical properties of trapped surfaces and apparent horizons
|
16 pages, Revtex4
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper, we perform a detailed investigation on the various geometrical
properties of trapped surfaces and the boundaries of trapped region in general
relativity. This treatment extends earlier work on LRS II spacetimes to a
general 4 dimensional spacetime manifold. Using a semi-tetrad covariant
formalism, that provides a set of geometrical and matter variables, we
transparently demonstrate the evolution of the trapped region and also extend
Hawking's topology theorem to a wider class of spacetimes. In addition, we
perform a stability analysis for the apparent horizons in this formalism,
encompassing earlier works on this subject. As examples, we consider the
stability of MOTS of the Schwarzschild geometry and Oppenheimer-Snyder
collapse.
|
[
{
"created": "Tue, 15 May 2018 10:15:43 GMT",
"version": "v1"
}
] |
2018-05-16
|
[
[
"Sherif",
"Abbas",
""
],
[
"Goswami",
"Rituparno",
""
],
[
"Maharaj",
"Sunil D",
""
]
] |
In this paper, we perform a detailed investigation on the various geometrical properties of trapped surfaces and the boundaries of trapped region in general relativity. This treatment extends earlier work on LRS II spacetimes to a general 4 dimensional spacetime manifold. Using a semi-tetrad covariant formalism, that provides a set of geometrical and matter variables, we transparently demonstrate the evolution of the trapped region and also extend Hawking's topology theorem to a wider class of spacetimes. In addition, we perform a stability analysis for the apparent horizons in this formalism, encompassing earlier works on this subject. As examples, we consider the stability of MOTS of the Schwarzschild geometry and Oppenheimer-Snyder collapse.
|
0707.2390
|
Mariam Bouhmadi-Lopez
|
Mariam Bouhmadi-Lopez, Pedro F. Gonzalez-Diaz, Prado Martin-Moruno
|
On the generalised Chaplygin gas: worse than a big rip or quieter than a
sudden singularity?
|
19 pages, 6 figures. Discussion expanded and references added.
Version to appear in the International Journal of Modern Physics D
|
Int.J.Mod.Phys.D17:2269-2290,2008
|
10.1142/S0218271808013856
| null |
gr-qc
| null |
Although it has been believed that the models with generalised Chaplygin gas
do not contain singularities, in a previous work we have studied how a big
freeze could take place in some kinds of phantom generalised Chaplygin gas. In
the present work, we study some types of generalised Chaplygin gas in order to
show how different sorts of singularities could appears in such models, in the
future or in the past. We point out that: (i) singularities may not be
originated from the phantom nature of the fluid, and (ii) if initially the
tension of the brane in a brane-world Chaplygin model is large enough then an
infrared cut off appears in the past.
|
[
{
"created": "Mon, 16 Jul 2007 20:28:21 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Mar 2008 15:51:10 GMT",
"version": "v2"
}
] |
2009-02-11
|
[
[
"Bouhmadi-Lopez",
"Mariam",
""
],
[
"Gonzalez-Diaz",
"Pedro F.",
""
],
[
"Martin-Moruno",
"Prado",
""
]
] |
Although it has been believed that the models with generalised Chaplygin gas do not contain singularities, in a previous work we have studied how a big freeze could take place in some kinds of phantom generalised Chaplygin gas. In the present work, we study some types of generalised Chaplygin gas in order to show how different sorts of singularities could appears in such models, in the future or in the past. We point out that: (i) singularities may not be originated from the phantom nature of the fluid, and (ii) if initially the tension of the brane in a brane-world Chaplygin model is large enough then an infrared cut off appears in the past.
|
1803.06431
|
Christopher Pilot
|
Christopher Pilot
|
Is Quintessence an Indication of a Time-Varying Gravitational Constant?
| null |
JHEPGC (Journal of High Energy Physics, Gravitation and Cosmology)
Vol 5 No 1 (2019)
|
10.4236/jhepgc.2019.51003
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
A model is presented where the quintessence parameter, w, is related to a
time-varying gravitational constant. Assuming a present value of w equals -.98,
we predict a current variation of G dot/G = -.06 H0. H0 is Hubbles parameter, G
is Newtons constant and G dot is the derivative of G with respect to time.
Thus, G has a cosmic origin, is decreasing with respect to cosmological time,
and is proportional to H0, as originally proposed by the Dirac-Jordan
hypothesis. Within our model, we can explain the cosmological constant
fine-tuning problem, the discrepancy between the present very weak value of the
cosmological constant, and the much greater vacuum energy found in earlier
epochs. To formalize and solidify our model, we give two distinct functions of
G(a), the cosmic scale parameter. We treat inverse G as an order parameter,
which vanishes at high energies; at low temperatures, it reaches a saturation
value, a value we are close to today. Our first function for inverse G is
motivated by a charging capacitor; the second treats inverse G by analogy to a
magnetic response. Both functions, even though very distinct, give a remarkably
similar tracking behavior for w(a). Interestingly, both functions indicate the
onset of G formation at a temperature of approximately 7 *1021 degrees Kelvin,
in contrast to the concordance model. At the temperature of formation, we find
that G has increased to roughly 4*1020 times its present value. For most of
cosmic evolution, however, our variable G model gives results similar to the
predictions of the concordance model, except in the very early universe, as we
shall demonstrate. Within our framework, the weakening of G to its current
value G0 is speculated as the true cause for the observed unanticipated
acceleration of the universe.
|
[
{
"created": "Sat, 17 Mar 2018 00:19:41 GMT",
"version": "v1"
}
] |
2020-08-03
|
[
[
"Pilot",
"Christopher",
""
]
] |
A model is presented where the quintessence parameter, w, is related to a time-varying gravitational constant. Assuming a present value of w equals -.98, we predict a current variation of G dot/G = -.06 H0. H0 is Hubbles parameter, G is Newtons constant and G dot is the derivative of G with respect to time. Thus, G has a cosmic origin, is decreasing with respect to cosmological time, and is proportional to H0, as originally proposed by the Dirac-Jordan hypothesis. Within our model, we can explain the cosmological constant fine-tuning problem, the discrepancy between the present very weak value of the cosmological constant, and the much greater vacuum energy found in earlier epochs. To formalize and solidify our model, we give two distinct functions of G(a), the cosmic scale parameter. We treat inverse G as an order parameter, which vanishes at high energies; at low temperatures, it reaches a saturation value, a value we are close to today. Our first function for inverse G is motivated by a charging capacitor; the second treats inverse G by analogy to a magnetic response. Both functions, even though very distinct, give a remarkably similar tracking behavior for w(a). Interestingly, both functions indicate the onset of G formation at a temperature of approximately 7 *1021 degrees Kelvin, in contrast to the concordance model. At the temperature of formation, we find that G has increased to roughly 4*1020 times its present value. For most of cosmic evolution, however, our variable G model gives results similar to the predictions of the concordance model, except in the very early universe, as we shall demonstrate. Within our framework, the weakening of G to its current value G0 is speculated as the true cause for the observed unanticipated acceleration of the universe.
|
1101.4797
|
Rong-Jia Yang
|
Rong-Jia Yang, Zong-Hong Zhu, and Fengquan Wu
|
Spatial Ricci scalar dark energy model
|
9 pages, 7 figures
|
Int.J.Mod.Phys.A 26 (2011) 317-329
|
10.1142/S0217751X11051263
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Inspired by holographic principle, we suggest that the density of dark energy
is proportional to the spatial Ricci scalar curvature (SRDE). Such model is
phenomenologically viable. The best fit values of its parameters at 68%
confidence level are found to be: $\Omega_{\rm m0}=0.259\pm0.016$ and
$\alpha=0.261\pm0.0122$, constrained from the Union+CFA3 sample of 397 SNIa and
the BAO measurement. We find the equation of state of SRDE crosses -1 at
$z\simeq-0.14$. The present values of the deceleration parameter $q(z)$ for
SRDE is found to be $q_{z=0}\sim -0.85$. The phase transition from deceleration
to acceleration of the Universe for SRDE occurs at the redshift $z_{q=0}\sim
0.4$. After studying on the perturbation of each component of the Universe, we
show that the matter power spectra and cosmic microwave background temperature
anisotropy is slightly affected by SRDE, compared with $\Lambda$CDM.
|
[
{
"created": "Tue, 25 Jan 2011 12:54:38 GMT",
"version": "v1"
},
{
"created": "Tue, 27 May 2014 14:03:32 GMT",
"version": "v2"
}
] |
2014-05-28
|
[
[
"Yang",
"Rong-Jia",
""
],
[
"Zhu",
"Zong-Hong",
""
],
[
"Wu",
"Fengquan",
""
]
] |
Inspired by holographic principle, we suggest that the density of dark energy is proportional to the spatial Ricci scalar curvature (SRDE). Such model is phenomenologically viable. The best fit values of its parameters at 68% confidence level are found to be: $\Omega_{\rm m0}=0.259\pm0.016$ and $\alpha=0.261\pm0.0122$, constrained from the Union+CFA3 sample of 397 SNIa and the BAO measurement. We find the equation of state of SRDE crosses -1 at $z\simeq-0.14$. The present values of the deceleration parameter $q(z)$ for SRDE is found to be $q_{z=0}\sim -0.85$. The phase transition from deceleration to acceleration of the Universe for SRDE occurs at the redshift $z_{q=0}\sim 0.4$. After studying on the perturbation of each component of the Universe, we show that the matter power spectra and cosmic microwave background temperature anisotropy is slightly affected by SRDE, compared with $\Lambda$CDM.
|
1907.12866
|
Bibekananda Nayak Dr.
|
Bibekananda Nayak
|
Interacting Holographic Dark Energy, the Present Accelerated Expansion
and Black Holes
|
11 pages, 6 figures
|
Gravitation and Cosmology 26 (2020) 273-280
|
10.1134/S020228932003010X
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the evolution of the universe by assuming an integrated model, which
involves interacting dark energy and holographic principle with Hubble scale as
IR cutoff. First we determined the interaction rate at which matter is
converting to dark energy. In the next step, we evaluated the equation of state
parameter which describes the nature of dark energy. Our result predicts that
the present state of the universe is dominated by quintessence type dark energy
and it will become phantom dominated in near future. Again our analysis
successfully addresses the problem of present accelerated expansion of the
universe and softens the coincidence problem. We also found that the universe
was previously undergoing a decelerated phase of expansion and transition from
deceleration to acceleration would occur at a time $t_{q=0}=0.732 t_0$, where
$t_0$ is the present age of the universe. Finally, we discuss the evolution of
Black Holes in this environment.
|
[
{
"created": "Tue, 30 Jul 2019 12:51:32 GMT",
"version": "v1"
},
{
"created": "Tue, 26 Nov 2019 12:37:15 GMT",
"version": "v2"
},
{
"created": "Mon, 30 Mar 2020 10:04:33 GMT",
"version": "v3"
},
{
"created": "Sun, 6 Sep 2020 10:56:18 GMT",
"version": "v4"
}
] |
2020-10-14
|
[
[
"Nayak",
"Bibekananda",
""
]
] |
We study the evolution of the universe by assuming an integrated model, which involves interacting dark energy and holographic principle with Hubble scale as IR cutoff. First we determined the interaction rate at which matter is converting to dark energy. In the next step, we evaluated the equation of state parameter which describes the nature of dark energy. Our result predicts that the present state of the universe is dominated by quintessence type dark energy and it will become phantom dominated in near future. Again our analysis successfully addresses the problem of present accelerated expansion of the universe and softens the coincidence problem. We also found that the universe was previously undergoing a decelerated phase of expansion and transition from deceleration to acceleration would occur at a time $t_{q=0}=0.732 t_0$, where $t_0$ is the present age of the universe. Finally, we discuss the evolution of Black Holes in this environment.
|
2010.09966
|
Giovanni Tricella
|
Stefano Liberati, Giovanni Tricella, Andrea Trombettoni
|
Back-reaction in canonical analogue black holes
|
This article belongs to the Special Issue Analogue Gravitational
Dynamics
|
Applied Sciences 2020, 10(24), 8868
|
10.3390/app10248868
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the back-reaction associated with Hawking evaporation of an acoustic
canonical analogue black hole in a Bose-Einstein condensate. We show that the
emission of Hawking radiation induces a local back-reaction on the condensate,
perturbing it in the near-horizon region, and a global back-reaction in the
density distribution of the atoms. We discuss how these results produce useful
insights into the process of black hole evaporation and its compatibility with
a unitary evolution.
|
[
{
"created": "Tue, 20 Oct 2020 02:29:09 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Dec 2020 16:07:23 GMT",
"version": "v2"
}
] |
2020-12-14
|
[
[
"Liberati",
"Stefano",
""
],
[
"Tricella",
"Giovanni",
""
],
[
"Trombettoni",
"Andrea",
""
]
] |
We study the back-reaction associated with Hawking evaporation of an acoustic canonical analogue black hole in a Bose-Einstein condensate. We show that the emission of Hawking radiation induces a local back-reaction on the condensate, perturbing it in the near-horizon region, and a global back-reaction in the density distribution of the atoms. We discuss how these results produce useful insights into the process of black hole evaporation and its compatibility with a unitary evolution.
|
1804.07440
|
Hwa-Tung Nieh
|
H.T. Nieh
|
Torsional Topological Invariants
| null |
Phys. Rev. D 98, 104045 (2018)
|
10.1103/PhysRevD.98.104045
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Making use of the SO(3,1) Lorentz algebra, we derive in this paper two series
of Gauss-Bonnet type identities involving torsion, one being of the Pontryagin
type and the other of the Euler type. Two of the six identities involve only
torsional tensorial entities and are purely torsional topological invariants.
|
[
{
"created": "Fri, 20 Apr 2018 03:25:36 GMT",
"version": "v1"
},
{
"created": "Tue, 20 Nov 2018 09:40:01 GMT",
"version": "v2"
}
] |
2018-12-05
|
[
[
"Nieh",
"H. T.",
""
]
] |
Making use of the SO(3,1) Lorentz algebra, we derive in this paper two series of Gauss-Bonnet type identities involving torsion, one being of the Pontryagin type and the other of the Euler type. Two of the six identities involve only torsional tensorial entities and are purely torsional topological invariants.
|
1811.09571
|
Xavier Lachaume
|
Xavier Lachaume
|
On the number of terms in the Lovelock products
|
5 pages
|
Eur. Phys. J. C (2019) 79: 266
|
10.1140/epjc/s10052-019-6776-6
| null |
gr-qc math-ph math.MP math.RT
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this short note we wonder about the explicit expression of the expanding
of the $p$-th Lovelock product. We use the 1990's works of S. A. Fulling et al.
on the symmetries of the Riemann tensor, and we show that the number of
independent scalars appearing in this expanding is equal to the number of Young
diagrams with all row lengths even in the decomposition of the $p$-th plethysm
of the Young diagram representing the symmetries of the Riemann tensor.
|
[
{
"created": "Fri, 23 Nov 2018 17:27:51 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Mar 2019 14:58:18 GMT",
"version": "v2"
}
] |
2019-03-25
|
[
[
"Lachaume",
"Xavier",
""
]
] |
In this short note we wonder about the explicit expression of the expanding of the $p$-th Lovelock product. We use the 1990's works of S. A. Fulling et al. on the symmetries of the Riemann tensor, and we show that the number of independent scalars appearing in this expanding is equal to the number of Young diagrams with all row lengths even in the decomposition of the $p$-th plethysm of the Young diagram representing the symmetries of the Riemann tensor.
|
1305.2599
|
Donald Neville
|
Donald E. Neville
|
Plane wave holonomies in loop quantum gravity II: sine wave solution
|
56 pages, LaTeX Much improved presentation. Material on
coarse-graining and U(N) SHO formalism added
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
This paper constructs an approximate sinusoidal wave packet solution to the
equations of loop quantum gravity (LQG). There is an SU(2) holonomy on each
edge of the LQG simplex, and the goal is to study the behavior of these
holonomies under the influence of a passing gravitational wave. The equations
are solved in a small sine approximation: holonomies are expanded in powers of
sines, and terms beyond $\sin^2$ are dropped; also, fields vary slowly from
vertex to vertex. The wave is unidirectional and linearly polarized. The
Hilbert space is spanned by a set of coherent states tailored to the symmetry
of the plane wave case. Fixing the spatial diffeomorphisms is equivalent to
fixing the spatial interval between vertices of the loop quantum gravity
lattice. This spacing can be chosen such that the eigenvalues of the triad
operators are large, as required in the small sine limit, even though the
holonomies are not large. Appendices compute the energy of the wave, estimate
the lifetime of the coherent state packet, discuss coarse-graining, and
determine the behavior of the spinors used in the U(N) SHO realization of LQG.
|
[
{
"created": "Sun, 12 May 2013 16:21:36 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Nov 2014 23:01:12 GMT",
"version": "v2"
}
] |
2014-11-12
|
[
[
"Neville",
"Donald E.",
""
]
] |
This paper constructs an approximate sinusoidal wave packet solution to the equations of loop quantum gravity (LQG). There is an SU(2) holonomy on each edge of the LQG simplex, and the goal is to study the behavior of these holonomies under the influence of a passing gravitational wave. The equations are solved in a small sine approximation: holonomies are expanded in powers of sines, and terms beyond $\sin^2$ are dropped; also, fields vary slowly from vertex to vertex. The wave is unidirectional and linearly polarized. The Hilbert space is spanned by a set of coherent states tailored to the symmetry of the plane wave case. Fixing the spatial diffeomorphisms is equivalent to fixing the spatial interval between vertices of the loop quantum gravity lattice. This spacing can be chosen such that the eigenvalues of the triad operators are large, as required in the small sine limit, even though the holonomies are not large. Appendices compute the energy of the wave, estimate the lifetime of the coherent state packet, discuss coarse-graining, and determine the behavior of the spinors used in the U(N) SHO realization of LQG.
|
2307.11809
|
Sneha Pradhan
|
Piyali Bhar, Sneha Pradhan, Adnan Malik, P.K. Sahoo
|
Physical Characteristics and Maximum Allowable Mass of Hybrid Star in
the Context of $f(Q)$ Gravity
|
EPJ C published version
|
Eur. Phys. J. C 83(7), 646 (2023)
|
10.1140/epjc/s10052-023-11745-y
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
In this study, we explore several new characteristics of a static anisotropic
hybrid star with strange quark matter (SQM) and ordinary baryonic matter (OBM)
distribution. Here, we use the MIT bag model equation of state to connect the
density and pressure of SQM inside stars, whereas the linear equation of state
$p_r =\alpha \rho-\beta$ connects the radial pressure and matter density caused
by baryonic matter. The stellar model was developed under a background of
$f(Q)$ gravity using the quadratic form of $f(Q)$. We utilized the
Tolman-Kuchowicz ansatz to find the solutions to the field equations under
modified gravity. We have matched the interior solution to the external
Schwarzschild spacetime in order to acquire the numerical values of the model
parameters. We have selected the star Her X-1 to develop various profiles of
the model parameters. Several significant physical characteristics have been
examined analytically and graphically, including matter densities, tangential
and radial pressures, energy conditions, anisotropy factor, redshirt,
compactness, etc. The main finding is that there is no core singularity present
in the formations of the star under investigation. The nature of mass and the
bag constant $B_g$ have been studied in details through equi-mass and
equi-$B_g$ contour. The maximum allowable mass and the corresponding radius
have been obtained via $M-R$ plots.
|
[
{
"created": "Fri, 21 Jul 2023 17:42:57 GMT",
"version": "v1"
}
] |
2023-07-25
|
[
[
"Bhar",
"Piyali",
""
],
[
"Pradhan",
"Sneha",
""
],
[
"Malik",
"Adnan",
""
],
[
"Sahoo",
"P. K.",
""
]
] |
In this study, we explore several new characteristics of a static anisotropic hybrid star with strange quark matter (SQM) and ordinary baryonic matter (OBM) distribution. Here, we use the MIT bag model equation of state to connect the density and pressure of SQM inside stars, whereas the linear equation of state $p_r =\alpha \rho-\beta$ connects the radial pressure and matter density caused by baryonic matter. The stellar model was developed under a background of $f(Q)$ gravity using the quadratic form of $f(Q)$. We utilized the Tolman-Kuchowicz ansatz to find the solutions to the field equations under modified gravity. We have matched the interior solution to the external Schwarzschild spacetime in order to acquire the numerical values of the model parameters. We have selected the star Her X-1 to develop various profiles of the model parameters. Several significant physical characteristics have been examined analytically and graphically, including matter densities, tangential and radial pressures, energy conditions, anisotropy factor, redshirt, compactness, etc. The main finding is that there is no core singularity present in the formations of the star under investigation. The nature of mass and the bag constant $B_g$ have been studied in details through equi-mass and equi-$B_g$ contour. The maximum allowable mass and the corresponding radius have been obtained via $M-R$ plots.
|
gr-qc/0306026
|
Pieter-Jan De Smet
|
Pieter-Jan De Smet
|
On stationary metrics in five dimensions
|
8 pages
| null | null |
YITP-SB-03-25
|
gr-qc
| null |
It is well-known that the Kerr-metric (rotating black hole in four
dimensions) has Petrov type D. We prove a similar property in five dimensions.
The Myers-Perry metric (rotating black hole in five dimensions) with one
non-zero angular momentum has Petrov type \underline{22}. Conversely, we show
that the Myers-Perry solution is unique within a certain restricted class of
metrics of Petrov type \underline{22}.
|
[
{
"created": "Fri, 6 Jun 2003 17:03:41 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"De Smet",
"Pieter-Jan",
""
]
] |
It is well-known that the Kerr-metric (rotating black hole in four dimensions) has Petrov type D. We prove a similar property in five dimensions. The Myers-Perry metric (rotating black hole in five dimensions) with one non-zero angular momentum has Petrov type \underline{22}. Conversely, we show that the Myers-Perry solution is unique within a certain restricted class of metrics of Petrov type \underline{22}.
|
1805.01066
|
Shinji Tsujikawa
|
Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa
|
Cosmology in scalar-vector-tensor theories
|
17pages, 4 figures
|
Phys. Rev. D 98, 024038 (2018)
|
10.1103/PhysRevD.98.024038
| null |
gr-qc astro-ph.CO hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the cosmology on the Friedmann-Lemaitre-Robertson-Walker background
in scalar-vector-tensor theories with a broken $U(1)$ gauge symmetry. For
parity-invariant interactions arising in scalar-vector-tensor theories with
second-order equations of motion, we derive conditions for the absence of
ghosts and Laplacian instabilities associated with tensor, vector, and scalar
perturbations at linear order. This general result is applied to the
computation of the primordial tensor power spectrum generated during inflation
as well as to the speed of gravity relevant to dark energy. We also construct a
concrete inflationary model in which a temporal vector component $A_0$
contributes to the dynamics of cosmic acceleration besides a scalar field
$\phi$ through their kinetic mixings. In this model, we show that all the
stability conditions of perturbations can be consistently satisfied during
inflation and subsequent reheating.
|
[
{
"created": "Thu, 3 May 2018 00:41:53 GMT",
"version": "v1"
},
{
"created": "Thu, 26 Jul 2018 12:53:35 GMT",
"version": "v2"
}
] |
2018-07-27
|
[
[
"Heisenberg",
"Lavinia",
""
],
[
"Kase",
"Ryotaro",
""
],
[
"Tsujikawa",
"Shinji",
""
]
] |
We study the cosmology on the Friedmann-Lemaitre-Robertson-Walker background in scalar-vector-tensor theories with a broken $U(1)$ gauge symmetry. For parity-invariant interactions arising in scalar-vector-tensor theories with second-order equations of motion, we derive conditions for the absence of ghosts and Laplacian instabilities associated with tensor, vector, and scalar perturbations at linear order. This general result is applied to the computation of the primordial tensor power spectrum generated during inflation as well as to the speed of gravity relevant to dark energy. We also construct a concrete inflationary model in which a temporal vector component $A_0$ contributes to the dynamics of cosmic acceleration besides a scalar field $\phi$ through their kinetic mixings. In this model, we show that all the stability conditions of perturbations can be consistently satisfied during inflation and subsequent reheating.
|
1710.05990
|
Anna Ijjas
|
Anna Ijjas
|
Space-time slicing in Horndeski theories and its implications for
non-singular bouncing solutions
|
33 pages, 3 figures; accepted for publication in JCAP; v2: updated to
match journal version
|
JCAP 02 (2018) 007
|
10.1088/1475-7516/2018/02/007
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper, we show how the proper choice of gauge is critical in
analyzing the stability of non-singular cosmological bounce solutions based on
Horndeski theories. We show that it is possible to construct non-singular
cosmological bounce solutions with classically stable behavior for all modes
with wavelengths above the Planck scale where: (a) the solution involves a
stage of null-energy condition violation during which gravity is described by a
modification of Einstein's general relativity; and (b) the solution reduces to
Einstein gravity both before and after the null-energy condition violating
stage. Similar considerations apply to galilean genesis scenarios.
|
[
{
"created": "Mon, 16 Oct 2017 20:20:57 GMT",
"version": "v1"
},
{
"created": "Sat, 27 Jan 2018 16:35:41 GMT",
"version": "v2"
}
] |
2018-02-07
|
[
[
"Ijjas",
"Anna",
""
]
] |
In this paper, we show how the proper choice of gauge is critical in analyzing the stability of non-singular cosmological bounce solutions based on Horndeski theories. We show that it is possible to construct non-singular cosmological bounce solutions with classically stable behavior for all modes with wavelengths above the Planck scale where: (a) the solution involves a stage of null-energy condition violation during which gravity is described by a modification of Einstein's general relativity; and (b) the solution reduces to Einstein gravity both before and after the null-energy condition violating stage. Similar considerations apply to galilean genesis scenarios.
|
1303.2469
|
Mikjel Thorsrud
|
Mikjel Thorsrud
|
Quintessence with Kaluza-Klein type couplings to matter and an
isotropy-violating vector field
|
3 pages, 1 figure. Contribution to the proceedings of the 13th Marcel
Grossmann Meeting (MG13), Stockholm, 1-7 July 2012
| null | null | null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the dynamics of a scalar field with Kaluza-Klein type couplings to
cold dark matter and an isotropy-violating vector field. The vector coupling,
$f^2(\phi)F^2$, has been studied thoroughly in the context of inflation
recently. We generalize the model to a dark energy context and study the
cosmological consequences. We find a rich set of exact anisotropic power-law
solutions and identify a strong vector coupling regime where the anisotropy is
controllable and all solutions are close to the LCDM limit.
|
[
{
"created": "Mon, 11 Mar 2013 10:07:02 GMT",
"version": "v1"
}
] |
2013-03-12
|
[
[
"Thorsrud",
"Mikjel",
""
]
] |
We study the dynamics of a scalar field with Kaluza-Klein type couplings to cold dark matter and an isotropy-violating vector field. The vector coupling, $f^2(\phi)F^2$, has been studied thoroughly in the context of inflation recently. We generalize the model to a dark energy context and study the cosmological consequences. We find a rich set of exact anisotropic power-law solutions and identify a strong vector coupling regime where the anisotropy is controllable and all solutions are close to the LCDM limit.
|
1611.06680
|
Andronikos Paliathanasis
|
John D. Barrow and Andronikos Paliathanasis
|
Reconstructions of the dark-energy equation of state and the
inflationary potential
|
17 pages, 7 figures, discussion improved, references added, to appear
in GRG
| null | null | null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We use a mathematical approach based on the constraints systems in order to
reconstruct the equation of state and the inflationary potential for the
inflaton field from the observed spectral indices for the density perturbations
$n_{s}$ and the tensor to scalar ratio $r$. From the astronomical data, we can
observe that the measured values of these two indices lie on a two-dimensional
surface. We express these indices in terms of the Hubble slow-roll parameters
and we assume that $n_{s}-1=h\left( r\right) $. For the function $h\left(
r\right) $, we consider three cases, where $h\left( r\right) $ is constant,
linear and quadratic, respectively. From this, we derive second-order equations
whose solutions provide us with the explicit forms for the expansion
scale-factor, the scalar-field potential, and the effective equation of state
for the scalar field. Finally, we show that for there exist mappings which
transform one cosmological solution to another and allow new solutions to be
generated from existing ones.
|
[
{
"created": "Mon, 21 Nov 2016 08:36:06 GMT",
"version": "v1"
},
{
"created": "Fri, 2 Jun 2017 16:05:02 GMT",
"version": "v2"
},
{
"created": "Sat, 9 Jun 2018 13:57:37 GMT",
"version": "v3"
}
] |
2018-06-12
|
[
[
"Barrow",
"John D.",
""
],
[
"Paliathanasis",
"Andronikos",
""
]
] |
We use a mathematical approach based on the constraints systems in order to reconstruct the equation of state and the inflationary potential for the inflaton field from the observed spectral indices for the density perturbations $n_{s}$ and the tensor to scalar ratio $r$. From the astronomical data, we can observe that the measured values of these two indices lie on a two-dimensional surface. We express these indices in terms of the Hubble slow-roll parameters and we assume that $n_{s}-1=h\left( r\right) $. For the function $h\left( r\right) $, we consider three cases, where $h\left( r\right) $ is constant, linear and quadratic, respectively. From this, we derive second-order equations whose solutions provide us with the explicit forms for the expansion scale-factor, the scalar-field potential, and the effective equation of state for the scalar field. Finally, we show that for there exist mappings which transform one cosmological solution to another and allow new solutions to be generated from existing ones.
|
1507.04683
|
Federico Lopez Armengol
|
Gustavo E. Romero, Daniela P\'erez and Federico G. Lopez Armengol
|
Cosmological black holes and the direction of time
|
13 pages, 2 figures in Foundations of Science (2017)
| null |
10.1007/s10699-017-9527-x
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Macroscopic irreversible processes emerge from fundamental physical laws of
reversible character. The source of the local irreversibility seems to be not
in the laws themselves but in the initial and boundary conditions of the
equations that represent the laws. In this work we propose that the screening
of currents by black hole event horizons determines, locally, a preferred
direction for the flux of electromagnetic energy. We study the growth of black
hole event horizons due to the cosmological expansion and accretion of cosmic
microwave background radiation, for different cosmological models. We propose
generalized McVittie co-moving metrics and integrate the rate of accretion of
cosmic microwave background radiation onto a supermassive black hole over
cosmic time. We find that for flat, open, and closed Friedmann cosmological
models, the ratio of the total area of the black hole event horizons with
respect to the area of a radial co-moving space-like hypersurface always
increases. Since accretion of cosmic radiation sets an absolute lower limit to
the total matter accreted by black holes, this implies that the causal past and
future are not mirror symmetric for any spacetime event. The asymmetry causes a
net Poynting flux in the global future direction; the latter is in turn related
to the ever increasing thermodynamic entropy. Thus, we expose a connection
between four different "time arrows": cosmological, electromagnetic,
gravitational, and thermodynamic.
|
[
{
"created": "Mon, 13 Jul 2015 18:27:55 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Mar 2017 18:49:31 GMT",
"version": "v2"
}
] |
2017-03-20
|
[
[
"Romero",
"Gustavo E.",
""
],
[
"Pérez",
"Daniela",
""
],
[
"Armengol",
"Federico G. Lopez",
""
]
] |
Macroscopic irreversible processes emerge from fundamental physical laws of reversible character. The source of the local irreversibility seems to be not in the laws themselves but in the initial and boundary conditions of the equations that represent the laws. In this work we propose that the screening of currents by black hole event horizons determines, locally, a preferred direction for the flux of electromagnetic energy. We study the growth of black hole event horizons due to the cosmological expansion and accretion of cosmic microwave background radiation, for different cosmological models. We propose generalized McVittie co-moving metrics and integrate the rate of accretion of cosmic microwave background radiation onto a supermassive black hole over cosmic time. We find that for flat, open, and closed Friedmann cosmological models, the ratio of the total area of the black hole event horizons with respect to the area of a radial co-moving space-like hypersurface always increases. Since accretion of cosmic radiation sets an absolute lower limit to the total matter accreted by black holes, this implies that the causal past and future are not mirror symmetric for any spacetime event. The asymmetry causes a net Poynting flux in the global future direction; the latter is in turn related to the ever increasing thermodynamic entropy. Thus, we expose a connection between four different "time arrows": cosmological, electromagnetic, gravitational, and thermodynamic.
|
0707.3830
|
Neven Bilic
|
Neven Bilic, Branko Guberina, Raul Horvat, Hrvoje Nikolic and Hrvoje
Stefancic
|
On Cosmological Implications of Gravitational Trace Anomaly
|
11 pages, equation (4) corrected, discussions expanded, references
added, results unchanged, to appear in PLB
|
Phys.Lett.B657:232-237,2007
|
10.1016/j.physletb.2007.09.067
| null |
gr-qc astro-ph hep-th
| null |
We study the infrared effective theory of gravity that stems from the quantum
trace anomaly. Quantum fluctuations of the metric induce running of the
cosmological constant and the Newton constant at cosmological scales. By
imposing the generalized Bianchi identity we obtain a prediction for the scale
dependence of the dark matter and dark energy densities in terms of the
parameters of the underlying conformal theory. For certain values of the model
parameters the dark energy equation of state and the observed spectral index of
the primordial density fluctuations can be simultaneously reproduced.
|
[
{
"created": "Thu, 26 Jul 2007 14:43:32 GMT",
"version": "v1"
},
{
"created": "Tue, 31 Jul 2007 13:25:49 GMT",
"version": "v2"
},
{
"created": "Mon, 15 Oct 2007 13:11:36 GMT",
"version": "v3"
}
] |
2008-11-26
|
[
[
"Bilic",
"Neven",
""
],
[
"Guberina",
"Branko",
""
],
[
"Horvat",
"Raul",
""
],
[
"Nikolic",
"Hrvoje",
""
],
[
"Stefancic",
"Hrvoje",
""
]
] |
We study the infrared effective theory of gravity that stems from the quantum trace anomaly. Quantum fluctuations of the metric induce running of the cosmological constant and the Newton constant at cosmological scales. By imposing the generalized Bianchi identity we obtain a prediction for the scale dependence of the dark matter and dark energy densities in terms of the parameters of the underlying conformal theory. For certain values of the model parameters the dark energy equation of state and the observed spectral index of the primordial density fluctuations can be simultaneously reproduced.
|
0708.4388
|
Bjoern S. Schmekel
|
Bjoern S. Schmekel
|
Quasi-local definitions of energy in general relativity
|
4 pages, very brief review article about quasi-local energy
|
Matters of Gravity, 30, 13 (2007), arXiv:0709.0942
| null | null |
gr-qc
| null |
The problem of defining energy in general relativity is reviewed very
briefly, and the properties of Brown-York-like expressions are discussed.
|
[
{
"created": "Fri, 31 Aug 2007 16:55:44 GMT",
"version": "v1"
}
] |
2007-09-08
|
[
[
"Schmekel",
"Bjoern S.",
""
]
] |
The problem of defining energy in general relativity is reviewed very briefly, and the properties of Brown-York-like expressions are discussed.
|
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