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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/0509013 | Jonathan Halliwell | J.J.Halliwell and P.Wallden | Invariant Class Operators in the Decoherent Histories Analysis of
Timeless Quantum Theories | 45 pages, RevTex. Version 2. Substantial rewriting of Section 9
correcting earlier errors | Phys.Rev. D73 (2006) 024011 | 10.1103/PhysRevD.73.024011 | Imperial-TP | gr-qc | null | The decoherent histories approach to quantum theory is applied to a class of
reparametrization invariant models, which includes systems described by the
Klein-Gordon equation, and by a minisuperspace Wheeler-DeWitt equation. A key
step in this approach is the construction of class operators characterizing the
questions of physical interest, such as the probability of the system entering
a given region of configuration space without regard to time. In
non-relativistic quantum mechanics these class operators are given by
time-ordered products of projection operators. But in reparametrization
invariant models, where there is no time, the construction of the class
operators is more complicated, the main difficulty being to find operators
which commute with the Hamiltonian constraint (and so respect the invariance of
the theory). Here, inspired by classical considerations, we put forward a
proposal for the construction of such class operators for a class of
reparametrization-invariant systems. They consist of continuous infinite
temporal products of Heisenberg picture projection operators. We investigate
the consequences of this proposal in a number of simple models and also compare
with the evolving constants method.
| [
{
"created": "Fri, 2 Sep 2005 12:23:51 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Oct 2005 13:53:13 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Halliwell",
"J. J.",
""
],
[
"Wallden",
"P.",
""
]
] | The decoherent histories approach to quantum theory is applied to a class of reparametrization invariant models, which includes systems described by the Klein-Gordon equation, and by a minisuperspace Wheeler-DeWitt equation. A key step in this approach is the construction of class operators characterizing the questions of physical interest, such as the probability of the system entering a given region of configuration space without regard to time. In non-relativistic quantum mechanics these class operators are given by time-ordered products of projection operators. But in reparametrization invariant models, where there is no time, the construction of the class operators is more complicated, the main difficulty being to find operators which commute with the Hamiltonian constraint (and so respect the invariance of the theory). Here, inspired by classical considerations, we put forward a proposal for the construction of such class operators for a class of reparametrization-invariant systems. They consist of continuous infinite temporal products of Heisenberg picture projection operators. We investigate the consequences of this proposal in a number of simple models and also compare with the evolving constants method. |
2006.15914 | Kazuya Koyama | Kazuya Koyama | Testing Brans-Dicke Gravity with Screening by Scalar Gravitational Wave
Memory | 6 pages, 5 figures, accepted for publication in PRD | null | 10.1103/PhysRevD.102.021502 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Brans-Dicke theory of gravity is one of the oldest ideas to extend
general relativity by introducing a non-minimal coupling between the scalar
field and gravity. The Solar System tests put tight constraints on the theory.
In order to evade these constraints, various screening mechanisms have been
proposed. These screening mechanisms allow the scalar field to couple to matter
as strongly as gravity in low density environments while suppressing it in the
Solar System. The Vainshtein mechanism, which is found in various modified
gravity models such as massive gravity, braneworld models and scalar tensor
theories, suppresses the scalar field efficiently in the vicinity of a massive
object. This makes it difficult to test these theories from gravitational wave
observations. We point out that the recently found scalar gravitational wave
memory effect, which is caused by a permanent change in spacetime geometry due
to the collapse of a star to a back hole can be significantly enhanced in the
Brans-Dicke theory of gravity with the Vainshtein mechanism. This provides a
possibility to detect scalar gravitational waves by a network of three or more
gravitational wave detectors.
| [
{
"created": "Mon, 29 Jun 2020 10:11:51 GMT",
"version": "v1"
}
] | 2020-08-26 | [
[
"Koyama",
"Kazuya",
""
]
] | The Brans-Dicke theory of gravity is one of the oldest ideas to extend general relativity by introducing a non-minimal coupling between the scalar field and gravity. The Solar System tests put tight constraints on the theory. In order to evade these constraints, various screening mechanisms have been proposed. These screening mechanisms allow the scalar field to couple to matter as strongly as gravity in low density environments while suppressing it in the Solar System. The Vainshtein mechanism, which is found in various modified gravity models such as massive gravity, braneworld models and scalar tensor theories, suppresses the scalar field efficiently in the vicinity of a massive object. This makes it difficult to test these theories from gravitational wave observations. We point out that the recently found scalar gravitational wave memory effect, which is caused by a permanent change in spacetime geometry due to the collapse of a star to a back hole can be significantly enhanced in the Brans-Dicke theory of gravity with the Vainshtein mechanism. This provides a possibility to detect scalar gravitational waves by a network of three or more gravitational wave detectors. |
gr-qc/0309100 | Paul S. Wesson | Paul S. Wesson | Is Mass Quantized? | null | Mod.Phys.Lett.A19:1995-2000,2004 | 10.1142/S0217732304015270 | null | gr-qc | null | The cosmological constant combined with Planck's constant and the speed of
light implies a quantum of mass of approximately 2 x 10^{-65}g. This follows
either from a generic dimensional analysis, or from a specific analysis where
the cosmological constant appears in 4D spacetime as the result of a
dimensional reduction from higher dimensional relativity (such as 5D
induced-matter and membrane theory). In the latter type of theory, all the
particles in the universe can be in higher-dimensional contact.
| [
{
"created": "Sat, 20 Sep 2003 14:13:31 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Wesson",
"Paul S.",
""
]
] | The cosmological constant combined with Planck's constant and the speed of light implies a quantum of mass of approximately 2 x 10^{-65}g. This follows either from a generic dimensional analysis, or from a specific analysis where the cosmological constant appears in 4D spacetime as the result of a dimensional reduction from higher dimensional relativity (such as 5D induced-matter and membrane theory). In the latter type of theory, all the particles in the universe can be in higher-dimensional contact. |
2306.13726 | Jiamin Hou | Jiamin Hou and Julian Bautista and Maria Berti and Carolina
Cuesta-Lazaro and C\'esar Hern\'andez-Aguayo and Tilman Tr\"oster and Jinglan
Zheng | Cosmological Probes of Structure Growth and Tests of Gravity | 72 pages, 19 figures, Invited review for Universe, Special Issue
"Cosmological Constant" | null | 10.3390/universe9070302 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The current standard cosmological model is constructed within the framework
of general relativity with a cosmological constant $\Lambda$, which is often
associated with dark energy, and phenomenologically explains the accelerated
cosmic expansion. Understanding the nature of dark energy is one of the most
appealing questions in achieving a self-consistent physical model at
cosmological scales. Modification of general relativity could potentially
provide a more natural and physical solution to the accelerated expansion. The
growth of the cosmic structure is sensitive in constraining gravity models. In
this paper, we aim to provide a concise introductory review of modified gravity
models from an observational point of view. We will discuss various mainstream
cosmological observables, and their potential advantages and limitations as
probes of gravity models.
| [
{
"created": "Fri, 23 Jun 2023 18:21:00 GMT",
"version": "v1"
}
] | 2023-06-27 | [
[
"Hou",
"Jiamin",
""
],
[
"Bautista",
"Julian",
""
],
[
"Berti",
"Maria",
""
],
[
"Cuesta-Lazaro",
"Carolina",
""
],
[
"Hernández-Aguayo",
"César",
""
],
[
"Tröster",
"Tilman",
""
],
[
"Zheng",
"Jinglan",
""
]
] | The current standard cosmological model is constructed within the framework of general relativity with a cosmological constant $\Lambda$, which is often associated with dark energy, and phenomenologically explains the accelerated cosmic expansion. Understanding the nature of dark energy is one of the most appealing questions in achieving a self-consistent physical model at cosmological scales. Modification of general relativity could potentially provide a more natural and physical solution to the accelerated expansion. The growth of the cosmic structure is sensitive in constraining gravity models. In this paper, we aim to provide a concise introductory review of modified gravity models from an observational point of view. We will discuss various mainstream cosmological observables, and their potential advantages and limitations as probes of gravity models. |
1203.0214 | Sean Stotyn | Sean Stotyn and Robert B. Mann | Another Mass Gap in the BTZ Geometry? | 13 pages, 2 appendices, Invited Contribution to an IOP special volume
of Journal of Physics A in honor of Stuart Dowker's 75th birthday, v2:
discussion in section 4 expanded | null | 10.1088/1751-8113/45/37/374025 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We attempt the construction of perturbative rotating hairy black holes and
boson stars, invariant under a single helical Killing field, in 2+1-dimensions
to complete the perturbative analysis in arbitrary odd dimension recently put
forth in \cite{Stotyn:2011ns}. Unlike the higher dimensional cases, we find
evidence for the non-existence of hairy black holes in 2+1-dimensions in the
perturbative regime, which is interpreted as another mass gap, within which the
black holes cannot have hair. The boson star solutions face a similar
impediment in the background of a conical singularity with a sufficiently high
angular deficit, most notably in the zero-mass BTZ background where boson stars
cannot exist at all. We construct such boson stars in the AdS_3 background as
well as in the background of conical singularities of periodicities
\pi,2\pi/3,\pi/2.
| [
{
"created": "Thu, 1 Mar 2012 15:32:08 GMT",
"version": "v1"
},
{
"created": "Sat, 26 May 2012 20:56:58 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Stotyn",
"Sean",
""
],
[
"Mann",
"Robert B.",
""
]
] | We attempt the construction of perturbative rotating hairy black holes and boson stars, invariant under a single helical Killing field, in 2+1-dimensions to complete the perturbative analysis in arbitrary odd dimension recently put forth in \cite{Stotyn:2011ns}. Unlike the higher dimensional cases, we find evidence for the non-existence of hairy black holes in 2+1-dimensions in the perturbative regime, which is interpreted as another mass gap, within which the black holes cannot have hair. The boson star solutions face a similar impediment in the background of a conical singularity with a sufficiently high angular deficit, most notably in the zero-mass BTZ background where boson stars cannot exist at all. We construct such boson stars in the AdS_3 background as well as in the background of conical singularities of periodicities \pi,2\pi/3,\pi/2. |
gr-qc/9808020 | Christian Maulbetsch | Christian Maulbetsch and Sergei V. Shabanov (Institute for Theoretical
Physics, FU-Berlin) | The Inverse Variational Problem for Autoparallels | 13 pages, plain Latex, no figures | J.Phys.A32:5355-5366,1999 | 10.1088/0305-4470/32/28/313 | null | gr-qc hep-th math-ph math.MP quant-ph | null | We study the problem of the existence of a local quantum scalar field theory
in a general affine metric space that in the semiclassical approximation would
lead to the autoparallel motion of wave packets, thus providing a deviation of
the spinless particle trajectory from the geodesics in the presence of torsion.
The problem is shown to be equivalent to the inverse problem of the calculus of
variations for the autoparallel motion with additional conditions that the
action (if it exists) has to be invariant under time reparametrizations and
general coordinate transformations, while depending analytically on the torsion
tensor. The problem is proved to have no solution for a generic torsion in
four-dimensional spacetime. A solution exists only if the contracted torsion
tensor is a gradient of a scalar field. The corresponding field theory
describes coupling of matter to the dilaton field.
| [
{
"created": "Fri, 7 Aug 1998 16:34:09 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Aug 1998 20:00:22 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Maulbetsch",
"Christian",
"",
"Institute for Theoretical\n Physics, FU-Berlin"
],
[
"Shabanov",
"Sergei V.",
"",
"Institute for Theoretical\n Physics, FU-Berlin"
]
] | We study the problem of the existence of a local quantum scalar field theory in a general affine metric space that in the semiclassical approximation would lead to the autoparallel motion of wave packets, thus providing a deviation of the spinless particle trajectory from the geodesics in the presence of torsion. The problem is shown to be equivalent to the inverse problem of the calculus of variations for the autoparallel motion with additional conditions that the action (if it exists) has to be invariant under time reparametrizations and general coordinate transformations, while depending analytically on the torsion tensor. The problem is proved to have no solution for a generic torsion in four-dimensional spacetime. A solution exists only if the contracted torsion tensor is a gradient of a scalar field. The corresponding field theory describes coupling of matter to the dilaton field. |
1204.1714 | Kourosh Nozari | Kourosh Nozari and M. Shoukrani | On the dissipative non-minimal braneworld inflation | 32 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1001.0444 | Astrophys. Space Sci. 339 (2012) 111 | 10.1007/s10509-012-0980-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the effects of the non-minimal coupling on the dissipative dynamics
of the warm inflation in a braneworld setup, where the inflaton field is
non-minimally coupled to induced gravity on the warped DGP brane. We study with
details the effects of the non-minimal coupling and dissipation on the
inflationary dynamics on the normal DGP branch of this scenario in the
high-dissipation and high-energy regime. We show that incorporation of the
non-minimal coupling in this setup decreases the number of e-folds relative to
the minimal case. We also compare our model parameters with recent
observational data.
| [
{
"created": "Sun, 8 Apr 2012 07:29:55 GMT",
"version": "v1"
}
] | 2015-06-04 | [
[
"Nozari",
"Kourosh",
""
],
[
"Shoukrani",
"M.",
""
]
] | We study the effects of the non-minimal coupling on the dissipative dynamics of the warm inflation in a braneworld setup, where the inflaton field is non-minimally coupled to induced gravity on the warped DGP brane. We study with details the effects of the non-minimal coupling and dissipation on the inflationary dynamics on the normal DGP branch of this scenario in the high-dissipation and high-energy regime. We show that incorporation of the non-minimal coupling in this setup decreases the number of e-folds relative to the minimal case. We also compare our model parameters with recent observational data. |
1407.3317 | Edgar Gasperin | Edgar Gasperin, Juan Antonio Valiente Kroon | Spinorial Wave Equations and Stability of the Milne Spacetime | 37 pages, 2 figures | null | 10.1088/0264-9381/32/18/185021 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The spinorial version of the conformal vacuum Einstein field equations are
used to construct a system of quasilinear wave equations for the various
conformal fields. As a part of the analysis we also show how to construct a
subsidiary system of wave equations for the zero quantities associated to the
various conformal field equations. This subsidiary system is used, in turn, to
show that under suitable assumptions on the initial data a solution to the wave
equations for the conformal fields implies a solution to the actual conformal
Einstein field equations. The use of spinors allows for a more unified
deduction of the required wave equations and the analysis of the subsidiary
equations than similar approaches based on the metric conformal field
equations. As an application of our construction we study the non-linear
stability of the Milne Universe. It is shown that sufficiently small
perturbations of initial hyperboloidal data for the Milne Universe gives rise
to a solution to the Einstein field equations which exist towards the future
and has an asymptotic structure similar to that of the Milne Universe.
| [
{
"created": "Fri, 11 Jul 2014 22:28:40 GMT",
"version": "v1"
}
] | 2015-09-23 | [
[
"Gasperin",
"Edgar",
""
],
[
"Kroon",
"Juan Antonio Valiente",
""
]
] | The spinorial version of the conformal vacuum Einstein field equations are used to construct a system of quasilinear wave equations for the various conformal fields. As a part of the analysis we also show how to construct a subsidiary system of wave equations for the zero quantities associated to the various conformal field equations. This subsidiary system is used, in turn, to show that under suitable assumptions on the initial data a solution to the wave equations for the conformal fields implies a solution to the actual conformal Einstein field equations. The use of spinors allows for a more unified deduction of the required wave equations and the analysis of the subsidiary equations than similar approaches based on the metric conformal field equations. As an application of our construction we study the non-linear stability of the Milne Universe. It is shown that sufficiently small perturbations of initial hyperboloidal data for the Milne Universe gives rise to a solution to the Einstein field equations which exist towards the future and has an asymptotic structure similar to that of the Milne Universe. |
1904.04293 | Jun Chen | Jun Chen | Reconstruction of inflation model from tensor-to-scalar ratio | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We reconstruct the potential of minimally coupling inflation model which
produces small value of the tensor-scalar ratio. In these inflation models,
tensor-scalar ratio is proportional to 1/N^2 scalar spectral index is in good
agreement with recent cosmological observations, in which N is the e-folding
number and p is a positive number. We also reconstruct f(R) gravity inflation
from small tensor-tensor ratio.
| [
{
"created": "Mon, 8 Apr 2019 18:42:56 GMT",
"version": "v1"
}
] | 2019-04-10 | [
[
"Chen",
"Jun",
""
]
] | We reconstruct the potential of minimally coupling inflation model which produces small value of the tensor-scalar ratio. In these inflation models, tensor-scalar ratio is proportional to 1/N^2 scalar spectral index is in good agreement with recent cosmological observations, in which N is the e-folding number and p is a positive number. We also reconstruct f(R) gravity inflation from small tensor-tensor ratio. |
gr-qc/0611106 | Ryszard Manka | R. Manka and D. Panchyrz | The Friedman Universe with the stochastic cosmological constant | JHEP3 style, 7 pages, 1 figure | null | null | null | gr-qc | null | The Friedman Universe with the remnant stochastic scalar field in the hybrid
inflation model is examined. It is shown that the small effective cosmological
constant appears which increases the cosmological expansion.
| [
{
"created": "Mon, 20 Nov 2006 14:00:33 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Manka",
"R.",
""
],
[
"Panchyrz",
"D.",
""
]
] | The Friedman Universe with the remnant stochastic scalar field in the hybrid inflation model is examined. It is shown that the small effective cosmological constant appears which increases the cosmological expansion. |
1305.3851 | Li Xiang | Li Xiang, Yi Ling and You Gen Shen | Singularities and the Finale of Black Hole Evaporation | 10 pages | Int. J. Mod. Phys. D22(2013), 1342016 | 10.1142/S0218271813420169 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this essay we argue that once quantum gravitational effects change the
classical geometry of a black hole and remove the curvature singularity, the
black hole would not evaporate entirely but approach a remnant. In a modified
Schwarzschild spacetime characterized by a finite Kretschmann scalar, a minimal
mass of the black hole is naturally bounded by the existence of the horizon
rather than introduced by hand. A thermodynamical analysis discloses that the
temperature, heat capacity and the luminosity are vanishing naturally when the
black hole mass approaches the minimal value. This phenomenon may be attributed
to the existence of the minimal length in quantum gravity. It can also be
understood heuristically by connecting the generalized uncertainty principle
with the running of Newton's gravitational constant.
| [
{
"created": "Thu, 16 May 2013 16:04:11 GMT",
"version": "v1"
}
] | 2015-06-16 | [
[
"Xiang",
"Li",
""
],
[
"Ling",
"Yi",
""
],
[
"Shen",
"You Gen",
""
]
] | In this essay we argue that once quantum gravitational effects change the classical geometry of a black hole and remove the curvature singularity, the black hole would not evaporate entirely but approach a remnant. In a modified Schwarzschild spacetime characterized by a finite Kretschmann scalar, a minimal mass of the black hole is naturally bounded by the existence of the horizon rather than introduced by hand. A thermodynamical analysis discloses that the temperature, heat capacity and the luminosity are vanishing naturally when the black hole mass approaches the minimal value. This phenomenon may be attributed to the existence of the minimal length in quantum gravity. It can also be understood heuristically by connecting the generalized uncertainty principle with the running of Newton's gravitational constant. |
gr-qc/9806117 | Jean-Philippe Uzan | Jean-Philippe Uzan | The No-defect Conjecture: Cosmological Implications | 4 pages, 1 figure, accepted for publication as a brief report in
Phys. Rev. D | Phys.Rev.D58:087301,1998 | 10.1103/PhysRevD.58.087301 | null | gr-qc | null | When the topology of the universe is non trivial, it has been shown that
there are constraints on the network of domain walls, cosmic strings and
monopoles. I generalize these results to textures and study the cosmological
implications of such constraints. I conclude that a large class of
multi-connected universes with topological defects accounting for structure
formation are ruled out by observation of the cosmic microwave background.
| [
{
"created": "Tue, 30 Jun 1998 14:28:48 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Uzan",
"Jean-Philippe",
""
]
] | When the topology of the universe is non trivial, it has been shown that there are constraints on the network of domain walls, cosmic strings and monopoles. I generalize these results to textures and study the cosmological implications of such constraints. I conclude that a large class of multi-connected universes with topological defects accounting for structure formation are ruled out by observation of the cosmic microwave background. |
1107.5987 | Cristina Rugina | G. W. Gibbons and C. Rugina | Goryachev-Chaplygin, Kovalevskaya, and Brdi\v{c}ka-Eardley-Nappi-Witten
pp-waves spacetimes with higher rank St\"ackel-Killing tensors | 11 pages; accepted for publication in JMP | null | 10.1063/1.3664754 | null | gr-qc math-ph math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Hidden symmetries of the Goryachev-Chaplygin and Kovalevskaya gyrostats
spacetimes, as well as the Brdi\v{c}ka-Eardley-Nappi-Witten pp-waves are
studied. We find out that these spacetimes possess higher rank
St\"ackel-Killing tensors and that in the case of the pp-wave spacetimes the
symmetry group of the St\"ackel-Killing tensors is the well-known Newton-Hooke
group.
| [
{
"created": "Fri, 29 Jul 2011 14:55:50 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Nov 2011 10:20:00 GMT",
"version": "v2"
}
] | 2015-05-30 | [
[
"Gibbons",
"G. W.",
""
],
[
"Rugina",
"C.",
""
]
] | Hidden symmetries of the Goryachev-Chaplygin and Kovalevskaya gyrostats spacetimes, as well as the Brdi\v{c}ka-Eardley-Nappi-Witten pp-waves are studied. We find out that these spacetimes possess higher rank St\"ackel-Killing tensors and that in the case of the pp-wave spacetimes the symmetry group of the St\"ackel-Killing tensors is the well-known Newton-Hooke group. |
0711.0188 | Scott A. Hughes | Scott A. Hughes | LISA sources and science | 8 pages, 2 figures. For the Proceedings of the 7th Edoardo Amaldi
Conference on Gravitational Waves (to be published by Classical and Quantum
Gravity) | null | null | null | gr-qc astro-ph | null | LISA is a planned space-based gravitational-wave (GW) detector that would be
sensitive to waves from low-frequency sources, in the band of roughly (0.03 -
0.1) mHz < f < 0.1 Hz. This is expected to be an extremely rich chunk of the GW
spectrum -- observing these waves will provide a unique view of dynamical
processes in astrophysics. Here we give a quick survey of some key LISA sources
and what GWs can uniquely teach us about these sources. Particularly noteworthy
science which is highlighted here is the potential for LISA to track the
moderate to high redshift evolution of black hole masses and spins through the
measurement of GWs generated from massive black hole binaries (which in turn
form by the merger of galaxies and protogalaxies). Measurement of these binary
black hole waves has the potential to determine the masses and spins of the
constituent black holes with percent-level accuracy or better, providing a
unique high-precision probe of an aspect of early structure growth. This
article is based on the "Astrophysics and Relativity using LISA" talk given by
the author at the Seventh Edoardo Amaldi Conference on Gravitational Waves; it
is largely an updating of the author's writeup of a talk given at the Sixth
International LISA Symposium.
| [
{
"created": "Thu, 1 Nov 2007 19:02:54 GMT",
"version": "v1"
}
] | 2007-11-02 | [
[
"Hughes",
"Scott A.",
""
]
] | LISA is a planned space-based gravitational-wave (GW) detector that would be sensitive to waves from low-frequency sources, in the band of roughly (0.03 - 0.1) mHz < f < 0.1 Hz. This is expected to be an extremely rich chunk of the GW spectrum -- observing these waves will provide a unique view of dynamical processes in astrophysics. Here we give a quick survey of some key LISA sources and what GWs can uniquely teach us about these sources. Particularly noteworthy science which is highlighted here is the potential for LISA to track the moderate to high redshift evolution of black hole masses and spins through the measurement of GWs generated from massive black hole binaries (which in turn form by the merger of galaxies and protogalaxies). Measurement of these binary black hole waves has the potential to determine the masses and spins of the constituent black holes with percent-level accuracy or better, providing a unique high-precision probe of an aspect of early structure growth. This article is based on the "Astrophysics and Relativity using LISA" talk given by the author at the Seventh Edoardo Amaldi Conference on Gravitational Waves; it is largely an updating of the author's writeup of a talk given at the Sixth International LISA Symposium. |
2009.07458 | Snehasish Bhattacharjee | Snehasish Bhattacharjee | Configurational entropy in $f(T)$ gravity | Published in EPJ Plus | Eur. Phys. J. Plus 135, 760 (2020) | 10.1140/epjp/s13360-020-00782-1 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | The evolution of the configurational entropy of the universe relies on the
growth rate of density fluctuations and on the Hubble parameter. In this work,
I present the evolution of configurational entropy for the power-law $f(T)$
gravity model of the form $f(T) = \zeta (-T)^ b$, where, $\zeta = (6
H_{0}^{2})^{(1-s)}\frac{\Omega_{P_{0}}}{2 s -1}$ and $b$ a free parameter. From
the analysis, I report that the configurational entropy in $f(T)$ gravity is
negative and decreases with increasing scale factor and therefore consistent
with an accelerating universe. The decrease in configurational entropy is the
highest when $b$ vanishes since the effect of dark energy is maximum when
$b=0$. Additionally, I find that as the parameter $b$ increases, the growth
rate, growing mode, and the matter density parameter evolve slowly whereas the
Hubble parameter evolves rapidly. The rapid evolution of the Hubble parameter
in conjunction with the growth rate for the $b=0$ may provide an explanation
for the large dissipation of configurational entropy.
| [
{
"created": "Wed, 16 Sep 2020 04:15:44 GMT",
"version": "v1"
}
] | 2020-09-28 | [
[
"Bhattacharjee",
"Snehasish",
""
]
] | The evolution of the configurational entropy of the universe relies on the growth rate of density fluctuations and on the Hubble parameter. In this work, I present the evolution of configurational entropy for the power-law $f(T)$ gravity model of the form $f(T) = \zeta (-T)^ b$, where, $\zeta = (6 H_{0}^{2})^{(1-s)}\frac{\Omega_{P_{0}}}{2 s -1}$ and $b$ a free parameter. From the analysis, I report that the configurational entropy in $f(T)$ gravity is negative and decreases with increasing scale factor and therefore consistent with an accelerating universe. The decrease in configurational entropy is the highest when $b$ vanishes since the effect of dark energy is maximum when $b=0$. Additionally, I find that as the parameter $b$ increases, the growth rate, growing mode, and the matter density parameter evolve slowly whereas the Hubble parameter evolves rapidly. The rapid evolution of the Hubble parameter in conjunction with the growth rate for the $b=0$ may provide an explanation for the large dissipation of configurational entropy. |
gr-qc/9901074 | Larry Ford | L.H. Ford and Thomas A. Roman | The Quantum Interest Conjecture | 17 pages, Latex, 3 figures, uses epsf | Phys. Rev. D 60, 104018 (1999) | 10.1103/PhysRevD.60.104018 | null | gr-qc hep-th quant-ph | null | Although quantum field theory allows local negative energy densities and
fluxes, it also places severe restrictions upon the magnitude and extent of the
negative energy. The restrictions take the form of quantum inequalities. These
inequalities imply that a pulse of negative energy must not only be followed by
a compensating pulse of positive energy, but that the temporal separation
between the pulses is inversely proportional to their amplitude. In an earlier
paper we conjectured that there is a further constraint upon a negative and
positive energy delta-function pulse pair. This conjecture (the quantum
interest conjecture) states that a positive energy pulse must overcompensate
the negative energy pulse by an amount which is a monotonically increasing
function of the pulse separation. In the present paper we prove the conjecture
for massless quantized scalar fields in two and four-dimensional flat
spacetime, and show that it is implied by the quantum inequalities.
| [
{
"created": "Tue, 26 Jan 1999 17:10:21 GMT",
"version": "v1"
}
] | 2016-08-25 | [
[
"Ford",
"L. H.",
""
],
[
"Roman",
"Thomas A.",
""
]
] | Although quantum field theory allows local negative energy densities and fluxes, it also places severe restrictions upon the magnitude and extent of the negative energy. The restrictions take the form of quantum inequalities. These inequalities imply that a pulse of negative energy must not only be followed by a compensating pulse of positive energy, but that the temporal separation between the pulses is inversely proportional to their amplitude. In an earlier paper we conjectured that there is a further constraint upon a negative and positive energy delta-function pulse pair. This conjecture (the quantum interest conjecture) states that a positive energy pulse must overcompensate the negative energy pulse by an amount which is a monotonically increasing function of the pulse separation. In the present paper we prove the conjecture for massless quantized scalar fields in two and four-dimensional flat spacetime, and show that it is implied by the quantum inequalities. |
2008.03879 | Alexandru Lupsasca | Samuel E. Gralla, Alexandru Lupsasca, Daniel P. Marrone | The Shape of the Black Hole Photon Ring: A Precise Test of Strong-Field
General Relativity | 20 pages, 9 figures. v2: minor changes | null | 10.1103/PhysRevD.102.124004 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a new test of strong-field general relativity (GR) based on the
universal interferometric signature of the black hole photon ring. The photon
ring is a narrow ring-shaped feature, predicted by GR but not yet observed,
that appears on images of sources near a black hole. It is caused by extreme
bending of light within a few Schwarzschild radii of the event horizon and
provides a direct probe of the unstable bound photon orbits of the Kerr
geometry. We show that the precise shape of the observable photon ring is
remarkably insensitive to the astronomical source profile and can therefore be
used as a stringent test of GR. We forecast that a tailored space-based
interferometry experiment targeting M87* could test the Kerr nature of the
source to the sub-sub-percent level.
| [
{
"created": "Mon, 10 Aug 2020 03:16:42 GMT",
"version": "v1"
},
{
"created": "Mon, 14 Sep 2020 03:00:53 GMT",
"version": "v2"
}
] | 2020-12-09 | [
[
"Gralla",
"Samuel E.",
""
],
[
"Lupsasca",
"Alexandru",
""
],
[
"Marrone",
"Daniel P.",
""
]
] | We propose a new test of strong-field general relativity (GR) based on the universal interferometric signature of the black hole photon ring. The photon ring is a narrow ring-shaped feature, predicted by GR but not yet observed, that appears on images of sources near a black hole. It is caused by extreme bending of light within a few Schwarzschild radii of the event horizon and provides a direct probe of the unstable bound photon orbits of the Kerr geometry. We show that the precise shape of the observable photon ring is remarkably insensitive to the astronomical source profile and can therefore be used as a stringent test of GR. We forecast that a tailored space-based interferometry experiment targeting M87* could test the Kerr nature of the source to the sub-sub-percent level. |
0903.0774 | Wlodzimierz Piechocki | Przemyslaw Malkiewicz and Wlodzimierz Piechocki | Classical membrane in a time dependent orbifold | 10 pages, no figures, revtex4; version submitted for publication | null | null | null | gr-qc | http://creativecommons.org/licenses/by/3.0/ | We analyze classical theory of a membrane propagating in a singular
background spacetime. The algebra of the first-class constraints of the system
defines the membrane dynamics. A membrane winding uniformly around compact
dimension of embedding spacetime is described by two constraints, which are
interpreted in terms of world-sheet diffeomorhisms. The system is equivalent to
a closed bosonic string propagating in a curved spacetime. Our results may be
used for finding a quantum theory of a membrane in the compactified Milne
space.
| [
{
"created": "Wed, 4 Mar 2009 14:37:02 GMT",
"version": "v1"
},
{
"created": "Sun, 10 May 2009 14:03:42 GMT",
"version": "v2"
}
] | 2009-05-10 | [
[
"Malkiewicz",
"Przemyslaw",
""
],
[
"Piechocki",
"Wlodzimierz",
""
]
] | We analyze classical theory of a membrane propagating in a singular background spacetime. The algebra of the first-class constraints of the system defines the membrane dynamics. A membrane winding uniformly around compact dimension of embedding spacetime is described by two constraints, which are interpreted in terms of world-sheet diffeomorhisms. The system is equivalent to a closed bosonic string propagating in a curved spacetime. Our results may be used for finding a quantum theory of a membrane in the compactified Milne space. |
1104.1925 | Isha Pahwa | Isha Pahwa, Debajyoti Choudhury and T.R. Seshadri | Late-time acceleration in Higher Dimensional Cosmology | 10 pages, 5 figures | JCAP 1109 (2011) 015 | 10.1088/1475-7516/2011/09/015 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate late time acceleration of the universe in higher dimensional
cosmology. The content in the universe is assumed to exert pressure which is
different in the normal and extra dimensions. Cosmologically viable solutions
are found to exist for simple forms of the equation of state. The parameters of
the model are fixed by comparing the predictions with supernovae data. While
observations stipulate that the matter exerts almost vanishing pressure in the
normal dimensions, we assume that, in the extra dimensions, the equation of
state is of the form $P \propto \, \rho^{1 - \gamma}$. For appropriate choice
of parameters, a late time acceleration in the universe occurs with $q_0$ and
$z_{tr}$ being approximately -0.46 and 0.76 respectively.
| [
{
"created": "Mon, 11 Apr 2011 12:13:59 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Sep 2011 10:33:01 GMT",
"version": "v2"
}
] | 2011-09-29 | [
[
"Pahwa",
"Isha",
""
],
[
"Choudhury",
"Debajyoti",
""
],
[
"Seshadri",
"T. R.",
""
]
] | We investigate late time acceleration of the universe in higher dimensional cosmology. The content in the universe is assumed to exert pressure which is different in the normal and extra dimensions. Cosmologically viable solutions are found to exist for simple forms of the equation of state. The parameters of the model are fixed by comparing the predictions with supernovae data. While observations stipulate that the matter exerts almost vanishing pressure in the normal dimensions, we assume that, in the extra dimensions, the equation of state is of the form $P \propto \, \rho^{1 - \gamma}$. For appropriate choice of parameters, a late time acceleration in the universe occurs with $q_0$ and $z_{tr}$ being approximately -0.46 and 0.76 respectively. |
2401.07495 | Yong-Zhuang Li | Yong-Zhuang Li and Xiao-Mei Kuang | Trajectories of photons around a rotating black hole with unusual
asymptotics | 12 pages, 7 figures | Eur. Phys. J. C (2024) 84:271 | 10.1140/epjc/s10052-024-12627-7 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Most black hole solutions are characterized with asymptotically flat, or
asymptotically (anti) de-Sitter behaviors, but some black holes with unusual
asymptotics have also been constructed, which is believed to provide remarkable
insights into our understanding of the nature of gravity. In this paper,
focusing on a rotating black hole with unusual asymptotics in
Einstein-Maxwell-dilaton (EMD) theory, we innovatively analyze the photons'
trajectories around this black hole background, showing that the unusual
asymptotics has significant influences on the photons' trajectories. We expect
that our analysis could give more insights in the scenario of black holes'
shadow and image.
| [
{
"created": "Mon, 15 Jan 2024 06:27:25 GMT",
"version": "v1"
}
] | 2024-07-03 | [
[
"Li",
"Yong-Zhuang",
""
],
[
"Kuang",
"Xiao-Mei",
""
]
] | Most black hole solutions are characterized with asymptotically flat, or asymptotically (anti) de-Sitter behaviors, but some black holes with unusual asymptotics have also been constructed, which is believed to provide remarkable insights into our understanding of the nature of gravity. In this paper, focusing on a rotating black hole with unusual asymptotics in Einstein-Maxwell-dilaton (EMD) theory, we innovatively analyze the photons' trajectories around this black hole background, showing that the unusual asymptotics has significant influences on the photons' trajectories. We expect that our analysis could give more insights in the scenario of black holes' shadow and image. |
2309.04114 | Morifumi Mizuno | Morifumi Mizuno, Teruaki Suyama, Ryuichi Takahashi | New Consistency Relations between Averages and Variances of Weakly
Lensed Signals of Gravitational Waves | 11 pages, 1 figure, accepted version | Phys. Rev. D 109, 083505 (2024) | 10.1103/PhysRevD.109.083505 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | The lensing of gravitational waves (GWs) occurs when GWs experience local
gravitational potential. In the weak lensing regime, it has been reported that
a simple consistency relation holds between the variances of the magnification
and phase modulation. In this paper, we present two additional consistency
relations between the averages and variances of the weakly lensed GW signals in
wave optics. We demonstrate that these consistency relations are derived as the
weak lensing limit of the full-order relations for the averages of the
amplification factor and its absolute square. These full-order relations appear
to originate from energy conservation and the Shapiro time delay, and they are
demonstrated to hold irrespective of the matter distribution.
| [
{
"created": "Fri, 8 Sep 2023 04:27:10 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Apr 2024 21:41:23 GMT",
"version": "v2"
}
] | 2024-04-10 | [
[
"Mizuno",
"Morifumi",
""
],
[
"Suyama",
"Teruaki",
""
],
[
"Takahashi",
"Ryuichi",
""
]
] | The lensing of gravitational waves (GWs) occurs when GWs experience local gravitational potential. In the weak lensing regime, it has been reported that a simple consistency relation holds between the variances of the magnification and phase modulation. In this paper, we present two additional consistency relations between the averages and variances of the weakly lensed GW signals in wave optics. We demonstrate that these consistency relations are derived as the weak lensing limit of the full-order relations for the averages of the amplification factor and its absolute square. These full-order relations appear to originate from energy conservation and the Shapiro time delay, and they are demonstrated to hold irrespective of the matter distribution. |
2008.09430 | Maximilian Becker | Maximilian Becker and Martin Reuter | Background Independent Field Quantization with Sequences of
Gravity-Coupled Approximants | 53 pages, 3 figures | null | 10.1103/PhysRevD.102.125001 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We outline, test, and apply a new scheme for nonpertubative analyses of
quantized field systems in contact with dynamical gravity. While gravity is
treated classically in the present paper, the approach lends itself for a
generalization to full Quantum Gravity. We advocate the point of view that
quantum field theories should be regularized by sequences of quasi-physical
systems comprising a well defined number of the field's degrees of freedom. In
dependence on this number, each system backreacts autonomously and
self-consistently on the gravitational field. In this approach, the limit which
removes the regularization automatically generates the physically correct
spacetime geometry, i.e., the metric the quantum states of the field prefer to
"live" in. We apply the scheme to a Gaussian scalar field on maximally
symmetric spacetimes, thereby confronting it with the standard approaches. As
an application, the results are used to elucidate the cosmological constant
problem allegedly arising from the vacuum fluctuations of quantum matter
fields. An explicit calculation shows that the problem disappears if the
pertinent continuum limit is performed in the improved way advocated here. A
further application concerns the thermodynamics of de Sitter space where the
approach offers a natural interpretation of the micro-states that are counted
by the Bekenstein-Hawking entropy.
| [
{
"created": "Fri, 21 Aug 2020 11:49:36 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Nov 2020 14:41:38 GMT",
"version": "v2"
}
] | 2020-12-30 | [
[
"Becker",
"Maximilian",
""
],
[
"Reuter",
"Martin",
""
]
] | We outline, test, and apply a new scheme for nonpertubative analyses of quantized field systems in contact with dynamical gravity. While gravity is treated classically in the present paper, the approach lends itself for a generalization to full Quantum Gravity. We advocate the point of view that quantum field theories should be regularized by sequences of quasi-physical systems comprising a well defined number of the field's degrees of freedom. In dependence on this number, each system backreacts autonomously and self-consistently on the gravitational field. In this approach, the limit which removes the regularization automatically generates the physically correct spacetime geometry, i.e., the metric the quantum states of the field prefer to "live" in. We apply the scheme to a Gaussian scalar field on maximally symmetric spacetimes, thereby confronting it with the standard approaches. As an application, the results are used to elucidate the cosmological constant problem allegedly arising from the vacuum fluctuations of quantum matter fields. An explicit calculation shows that the problem disappears if the pertinent continuum limit is performed in the improved way advocated here. A further application concerns the thermodynamics of de Sitter space where the approach offers a natural interpretation of the micro-states that are counted by the Bekenstein-Hawking entropy. |
1007.3150 | Adrian Tanasa | Thomas Krajewski, Jacques Magnen, Vincent Rivasseau, Adrian Tanasa and
Patrizia Vitale | Quantum Corrections in the Group Field Theory Formulation of the EPRL/FK
Models | 36 pages, 5 figures; an appendix giving a more precise behaviour of
the degenerate configuration case has been added; further comments on
geometrogenesis as a group field theory phase transition are given; version
accepted for publication in Phys Rev D | Phys.Rev.D82:124069,2010 | 10.1103/PhysRevD.82.124069 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the group field theory formulation of the EPRL/FK spin foam
models. These models aim at a dynamical, i.e. non-topological formulation of 4D
quantum gravity. We introduce a saddle point method for general group field
theory amplitudes and compare it with existing results, in particular for a
second order correction to the EPRL/FK propagator.
| [
{
"created": "Mon, 19 Jul 2010 13:52:40 GMT",
"version": "v1"
},
{
"created": "Mon, 15 Nov 2010 16:41:39 GMT",
"version": "v2"
}
] | 2011-03-07 | [
[
"Krajewski",
"Thomas",
""
],
[
"Magnen",
"Jacques",
""
],
[
"Rivasseau",
"Vincent",
""
],
[
"Tanasa",
"Adrian",
""
],
[
"Vitale",
"Patrizia",
""
]
] | We investigate the group field theory formulation of the EPRL/FK spin foam models. These models aim at a dynamical, i.e. non-topological formulation of 4D quantum gravity. We introduce a saddle point method for general group field theory amplitudes and compare it with existing results, in particular for a second order correction to the EPRL/FK propagator. |
2308.05130 | Alireza Amani | Alireza Amani, A. S. Kubeka, and E. Mahichi | Bouncing cosmology and dynamical analysis of stability with non-minimal
kinetic coupled gravity | 20 pages, 9 figures | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by-nc-sa/4.0/ | In this paper, we model the bounce phase, stability and the reconstruction of
the universe by non-minimal kinetic coupling. In the process, we obtained
importance information about the energy density and the matter pressure of the
universe in relation to the previous universe through the bounce quantum phase.
The novelty of the work is that the scale factor is obtained directly from the
model and is fitted with an exponential function, with this view we explore the
process of the early universe even the bounce phase. After that, we plot the
cosmological parameters in terms of time evolution. In what follows, we
investigate the stability of the model by the dynamical system analysis in a
phase plane. Finally, we examine the stability of the universe, especially in
the inflationary period, by using the phase space trajectories.
| [
{
"created": "Wed, 9 Aug 2023 10:56:52 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Jul 2024 22:43:42 GMT",
"version": "v2"
}
] | 2024-07-08 | [
[
"Amani",
"Alireza",
""
],
[
"Kubeka",
"A. S.",
""
],
[
"Mahichi",
"E.",
""
]
] | In this paper, we model the bounce phase, stability and the reconstruction of the universe by non-minimal kinetic coupling. In the process, we obtained importance information about the energy density and the matter pressure of the universe in relation to the previous universe through the bounce quantum phase. The novelty of the work is that the scale factor is obtained directly from the model and is fitted with an exponential function, with this view we explore the process of the early universe even the bounce phase. After that, we plot the cosmological parameters in terms of time evolution. In what follows, we investigate the stability of the model by the dynamical system analysis in a phase plane. Finally, we examine the stability of the universe, especially in the inflationary period, by using the phase space trajectories. |
1801.10594 | Debabrata Deb | M.K. Jasim, Debabrata Deb, Saibal Ray, Y.K. Gupta, and Sourav Roy
Chowdhury | Anisotropic strange stars in Tolman-Kuchowicz spacetime | 18 pages, 10 figures | Eur. Phys. J. C (2018) 78:603 | 10.1140/epjc/s10052-018-6072-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We attempt to study a singularity-free model for the spherically symmetric
anisotropic strange stars under Einstein's general theory of relativity by
exploiting the Tolman-Kuchowicz metric. Further, we have assumed that the
cosmological constant $\Lambda$ is a scalar variable dependent on the spatial
coordinate $r$. To describe the strange star candidates we have considered that
they are made of strange quark matter (SQM) distribution, which is assumed to
be governed by the MIT bag equation of state. To obtain unknown constants of
the stellar system we match the interior Tolman-Kuchowicz metric to the
exterior modified Schwarzschild metric with the cosmological constant, at the
surface of the system. Following Deb et al. we have predicted the exact values
of the radii for different strange star candidates based on the observed values
of the masses of the stellar objects and the chosen parametric values of the
$\Lambda$ as well as the bag constant $\mathcal{B}$. The set of solutions
satisfies all the physical requirements to represent strange stars.
Interestingly, our study reveals that as the values of the $\Lambda$ and
$\mathcal{B}$ increase the anisotropic system becomes gradually smaller in size
turning the whole system into a more compact ultra-dense stellar object.
| [
{
"created": "Wed, 31 Jan 2018 18:31:52 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Oct 2018 07:55:50 GMT",
"version": "v2"
}
] | 2018-10-03 | [
[
"Jasim",
"M. K.",
""
],
[
"Deb",
"Debabrata",
""
],
[
"Ray",
"Saibal",
""
],
[
"Gupta",
"Y. K.",
""
],
[
"Chowdhury",
"Sourav Roy",
""
]
] | We attempt to study a singularity-free model for the spherically symmetric anisotropic strange stars under Einstein's general theory of relativity by exploiting the Tolman-Kuchowicz metric. Further, we have assumed that the cosmological constant $\Lambda$ is a scalar variable dependent on the spatial coordinate $r$. To describe the strange star candidates we have considered that they are made of strange quark matter (SQM) distribution, which is assumed to be governed by the MIT bag equation of state. To obtain unknown constants of the stellar system we match the interior Tolman-Kuchowicz metric to the exterior modified Schwarzschild metric with the cosmological constant, at the surface of the system. Following Deb et al. we have predicted the exact values of the radii for different strange star candidates based on the observed values of the masses of the stellar objects and the chosen parametric values of the $\Lambda$ as well as the bag constant $\mathcal{B}$. The set of solutions satisfies all the physical requirements to represent strange stars. Interestingly, our study reveals that as the values of the $\Lambda$ and $\mathcal{B}$ increase the anisotropic system becomes gradually smaller in size turning the whole system into a more compact ultra-dense stellar object. |
0808.2830 | Joel Saavedra | Sergio del Campo, Ramon Herrera, Pedro Labrana, Carlos Leiva and Joel
Saavedra | Tachyonic Universes in Patch Cosmologies with $\Omega>1$ | 15 pages, 2 figures. Accepted by Modern Physics Letters A | null | 10.1142/S0217732309030849 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we study closed inflationary universe models by means of a
tachyonic field. We described a general treatment for created a universe with
$\Omega>1$ in patch cosmology, which is able to represent General Relativity,
Gauss-Bonnet or Randall-Sundrum patches. We use recent data from astronomical
observations to constrain the parameters appearing in our model.
| [
{
"created": "Wed, 20 Aug 2008 22:28:58 GMT",
"version": "v1"
},
{
"created": "Thu, 26 Mar 2009 21:34:36 GMT",
"version": "v2"
}
] | 2015-05-13 | [
[
"del Campo",
"Sergio",
""
],
[
"Herrera",
"Ramon",
""
],
[
"Labrana",
"Pedro",
""
],
[
"Leiva",
"Carlos",
""
],
[
"Saavedra",
"Joel",
""
]
] | In this article we study closed inflationary universe models by means of a tachyonic field. We described a general treatment for created a universe with $\Omega>1$ in patch cosmology, which is able to represent General Relativity, Gauss-Bonnet or Randall-Sundrum patches. We use recent data from astronomical observations to constrain the parameters appearing in our model. |
0811.1916 | Francesco Cianfrani dr | Francesco Cianfrani, Giovanni Montani | Towards Loop Quantum Gravity without the time gauge | 5 pages, accepted for publication in Phys. Rev. Lett | Phys.Rev.Lett.102:091301,2009 | 10.1103/PhysRevLett.102.091301 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Hamiltonian formulation of the Holst action is reviewed and it is
provided a solution of second-class constraints corresponding to a generic
local Lorentz frame. Within this scheme the form of rotation constraints can be
reduced to a Gauss-like one by a proper generalization of
Ashtekar-Barbero-Immirzi connections. This result emphasizes that the Loop
Quantum Gravity quantization procedure can be applied when the time-gauge
condition does not stand.
| [
{
"created": "Wed, 12 Nov 2008 15:13:46 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Jan 2009 17:35:44 GMT",
"version": "v2"
}
] | 2009-04-08 | [
[
"Cianfrani",
"Francesco",
""
],
[
"Montani",
"Giovanni",
""
]
] | The Hamiltonian formulation of the Holst action is reviewed and it is provided a solution of second-class constraints corresponding to a generic local Lorentz frame. Within this scheme the form of rotation constraints can be reduced to a Gauss-like one by a proper generalization of Ashtekar-Barbero-Immirzi connections. This result emphasizes that the Loop Quantum Gravity quantization procedure can be applied when the time-gauge condition does not stand. |
1201.4853 | Edison Montoya | Alejandro Corichi, Edison Montoya | Effective Dynamics in Bianchi Type II Loop Quantum Cosmology | 24 pages, 26 figures | Phys. Rev. D 85, 104052 (2012) | 10.1103/PhysRevD.85.104052 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We numerically investigate the solutions to the effective equations of the
Bianchi II model within the "improved" Loop Quantum Cosmology (LQC) dynamics.
The matter source is a massless scalar field. We perform a systematic study of
the space of solutions, and focus on the behavior of several geometrical
observables. We show that the big-bang singularity is replaced by a bounce and
the point-like singularities do not saturate the energy density bound. There
are up to three directional bounces in the scale factors, one global bounce in
the expansion, the shear presents up to four local maxima and can be zero at
the bounce. This allows for solutions with density larger than the maximal
density for the isotropic and Bianchi I cases. The asymptotic behavior is shown
to behave like that of a Bianchi I model, and the effective solutions connect
anisotropic solutions even when the shear is zero at the bounce. All known
facts of Bianchi I are reproduced. In the "vacuum limit", solutions are such
that almost all the dynamics is due to the anisotropies. Since Bianchi II plays
an important role in the Bianchi IX model and the Belinskii, Khalatnikov,
Lifshitz (BKL) conjecture, our results can provide an intuitive understanding
of the behavior in the vicinity of general space-like singularities, when
loop-geometric corrections are present.
| [
{
"created": "Mon, 23 Jan 2012 20:52:54 GMT",
"version": "v1"
},
{
"created": "Thu, 8 Mar 2012 05:24:36 GMT",
"version": "v2"
}
] | 2012-10-08 | [
[
"Corichi",
"Alejandro",
""
],
[
"Montoya",
"Edison",
""
]
] | We numerically investigate the solutions to the effective equations of the Bianchi II model within the "improved" Loop Quantum Cosmology (LQC) dynamics. The matter source is a massless scalar field. We perform a systematic study of the space of solutions, and focus on the behavior of several geometrical observables. We show that the big-bang singularity is replaced by a bounce and the point-like singularities do not saturate the energy density bound. There are up to three directional bounces in the scale factors, one global bounce in the expansion, the shear presents up to four local maxima and can be zero at the bounce. This allows for solutions with density larger than the maximal density for the isotropic and Bianchi I cases. The asymptotic behavior is shown to behave like that of a Bianchi I model, and the effective solutions connect anisotropic solutions even when the shear is zero at the bounce. All known facts of Bianchi I are reproduced. In the "vacuum limit", solutions are such that almost all the dynamics is due to the anisotropies. Since Bianchi II plays an important role in the Bianchi IX model and the Belinskii, Khalatnikov, Lifshitz (BKL) conjecture, our results can provide an intuitive understanding of the behavior in the vicinity of general space-like singularities, when loop-geometric corrections are present. |
0812.4149 | Riccardo Sturani | S. Foffa and R. Sturani | Coherent detection method of gravitational wave bursts for spherical
antennas | 31 pages, 15 figures | Class.Quant.Grav.26:105013,2009 | 10.1088/0264-9381/26/10/105013 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We provide a comprehensive theoretical framework and a quantitative test of
the method we recently proposed for processing data from a spherical detector
with five or six transducers. Our algorithm is a trigger event generator
performing a coherent analysis of the sphere channels. In order to test our
pipeline we first built a detailed numerical model of the detector, including
deviations from the ideal case such as quadrupole modes splitting, and
non-identical transducer readout chains. This model, coupled with a Gaussian
noise generator, has then been used to produce six time series, corresponding
to the outputs of the six transducers attached to the sphere. We finally
injected gravitational wave burst signals into the data stream, as well as
bursts of non-gravitational origin in order to mimic the presence of
non-Gaussian noise, and then processed the mock data. We report quantitative
results for the detection efficiency versus false alarm rate and for the
affordability of the reconstruction of the direction of arrival. In particular,
the combination of the two direction reconstruction methods can reduce by a
factor of 10 the number false alarms due to the non-Gaussian noise.
| [
{
"created": "Mon, 22 Dec 2008 10:47:19 GMT",
"version": "v1"
}
] | 2014-11-18 | [
[
"Foffa",
"S.",
""
],
[
"Sturani",
"R.",
""
]
] | We provide a comprehensive theoretical framework and a quantitative test of the method we recently proposed for processing data from a spherical detector with five or six transducers. Our algorithm is a trigger event generator performing a coherent analysis of the sphere channels. In order to test our pipeline we first built a detailed numerical model of the detector, including deviations from the ideal case such as quadrupole modes splitting, and non-identical transducer readout chains. This model, coupled with a Gaussian noise generator, has then been used to produce six time series, corresponding to the outputs of the six transducers attached to the sphere. We finally injected gravitational wave burst signals into the data stream, as well as bursts of non-gravitational origin in order to mimic the presence of non-Gaussian noise, and then processed the mock data. We report quantitative results for the detection efficiency versus false alarm rate and for the affordability of the reconstruction of the direction of arrival. In particular, the combination of the two direction reconstruction methods can reduce by a factor of 10 the number false alarms due to the non-Gaussian noise. |
gr-qc/0003076 | Garcia | L.C.Garcia de Andrade | Criteria for de Sitter inflation in Einstein-Cartan cosmology and COBE
data | Latex file | null | null | null | gr-qc | null | Criteria for the existence of de Sitter inflation with dilaton fields in
four-dimensional space-times with torsion is discussed.The relation between
matter density perturbation and the spin-density perturbation is stablished
based on this criteria.From COBE data it is shown that there is a linear
relationship between the spin-torsion density and temperature of the Universe
for the case where matter density dominates the kinetic part of dilaton fields.
| [
{
"created": "Sat, 18 Mar 2000 08:55:21 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"de Andrade",
"L. C. Garcia",
""
]
] | Criteria for the existence of de Sitter inflation with dilaton fields in four-dimensional space-times with torsion is discussed.The relation between matter density perturbation and the spin-density perturbation is stablished based on this criteria.From COBE data it is shown that there is a linear relationship between the spin-torsion density and temperature of the Universe for the case where matter density dominates the kinetic part of dilaton fields. |
1109.3287 | Ninfa Radicella | Ninfa Radicella and Diego Pav\'on | Thermodynamical analysis on a braneworld scenario with curvature
corrections | 7 pages, 2 figures. Accepted for publication on PLB | null | 10.1016/j.physletb.2011.09.031 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the thermodynamics of some cosmological models based on modified
gravity, a braneworld with induced gravity and curvature effect. Dark energy
component seems necessary if the models are to approach thermal equilibrium in
the long run.
| [
{
"created": "Thu, 15 Sep 2011 08:25:54 GMT",
"version": "v1"
}
] | 2011-09-16 | [
[
"Radicella",
"Ninfa",
""
],
[
"Pavón",
"Diego",
""
]
] | We study the thermodynamics of some cosmological models based on modified gravity, a braneworld with induced gravity and curvature effect. Dark energy component seems necessary if the models are to approach thermal equilibrium in the long run. |
2306.01480 | Piero Nicolini | Piero Nicolini | How strings can explain regular black holes | 23 pages, 1 figure, invited contribution to "Regular Black Holes:
Towards a New Paradigm of Gravitational Collapse'', C. Bambi (ed), Springer,
Singapore | In: Bambi, C. (eds) Regular Black Holes. Springer Series in
Astrophysics and Cosmology. Springer, Singapore (2023) | 10.1007/978-981-99-1596-5_3 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper reviews the role of black holes in the context of fundamental
physics. After recalling some basic results stemming from Planckian string
calculations, I present three examples of how stringy effects can improve the
curvature singularity of classical black hole geometries.
| [
{
"created": "Fri, 2 Jun 2023 12:07:33 GMT",
"version": "v1"
}
] | 2024-02-27 | [
[
"Nicolini",
"Piero",
""
]
] | This paper reviews the role of black holes in the context of fundamental physics. After recalling some basic results stemming from Planckian string calculations, I present three examples of how stringy effects can improve the curvature singularity of classical black hole geometries. |
1211.4107 | Oldrich Semerak | O. Semer\'ak and P. Sukov\'a | Free motion around black holes with discs or rings: between
integrability and chaos - II | 22 pages, 14 figures | MNRAS 425 (2012) 2455-2476 | 10.1111/j.1365-2966.2012.21630.x | null | gr-qc nlin.CD | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We continue the study of time-like geodesic dynamics in exact static, axially
and reflection symmetric space-times describing the fields of a Schwarzschild
black hole surrounded by thin discs or rings. In the previous paper, the rise
(and decline) of geodesic chaos with ring/disc mass and position and with test
particle energy was revealed on Poincar\'e sections, on time series of position
or velocity and their power spectra, and on time evolution of the orbital
`latitudinal action'. In agreement with the KAM theory of nearly integrable
dynamical systems and with the results observed in similar gravitational
systems in the literature, we found orbits of very different degrees of
chaoticity in the phase space of perturbed fields. Here we compare selected
orbits in more detail and try to classify them according to the characteristics
of the corresponding phase-variable time series, mainly according to the shape
of the time-series power spectra, and also applying two recurrence methods: the
method of `average directional vectors', which traces the directions in which
the trajectory (recurrently) passes through a chosen phase-space cell, and the
`recurrence-matrix' method, which consists of statistics over the recurrences
themselves. All the methods proved simple and powerful, while it is interesting
to observe how they differ in sensitivity to certain types of behaviour.
| [
{
"created": "Sat, 17 Nov 2012 10:05:06 GMT",
"version": "v1"
}
] | 2012-11-20 | [
[
"Semerák",
"O.",
""
],
[
"Suková",
"P.",
""
]
] | We continue the study of time-like geodesic dynamics in exact static, axially and reflection symmetric space-times describing the fields of a Schwarzschild black hole surrounded by thin discs or rings. In the previous paper, the rise (and decline) of geodesic chaos with ring/disc mass and position and with test particle energy was revealed on Poincar\'e sections, on time series of position or velocity and their power spectra, and on time evolution of the orbital `latitudinal action'. In agreement with the KAM theory of nearly integrable dynamical systems and with the results observed in similar gravitational systems in the literature, we found orbits of very different degrees of chaoticity in the phase space of perturbed fields. Here we compare selected orbits in more detail and try to classify them according to the characteristics of the corresponding phase-variable time series, mainly according to the shape of the time-series power spectra, and also applying two recurrence methods: the method of `average directional vectors', which traces the directions in which the trajectory (recurrently) passes through a chosen phase-space cell, and the `recurrence-matrix' method, which consists of statistics over the recurrences themselves. All the methods proved simple and powerful, while it is interesting to observe how they differ in sensitivity to certain types of behaviour. |
1708.00918 | Mandar Patil | Andrzej Kr\'olak and Mandar Patil | The First Detection of Gravitational Waves | 20 pages, 9 figures, Published in a special issue of Universe
"Varying Constants and Fundamental Cosmology" | Universe, 3(3), 59 (2017) | 10.3390/universe3030059 | null | gr-qc astro-ph.HE hep-ph hep-th physics.pop-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This article deals with the first detection of gravitational waves by the
advanced Laser Interferometer Gravitational Wave Observatory (LIGO) detectors
on 14 September 2015, where the signal was generated by two stellar mass black
holes with masses 36 $ M_{\odot}$ and 29 $ M_{\odot}$ that merged to form a 62
$ M_{\odot}$ black hole, releasing 3 $M_{\odot}$ energy in gravitational waves,
almost 1.3 billion years ago. We begin by providing a brief overview of
gravitational waves, their sources and the gravitational wave detectors. We
then describe in detail the first detection of gravitational waves from a
binary black hole merger. We then comment on the electromagnetic follow up of
the detection event with various telescopes. Finally, we conclude with the
discussion on the tests of gravity and fundamental physics with the first
gravitational wave detection event.
| [
{
"created": "Wed, 2 Aug 2017 20:16:24 GMT",
"version": "v1"
}
] | 2017-08-04 | [
[
"Królak",
"Andrzej",
""
],
[
"Patil",
"Mandar",
""
]
] | This article deals with the first detection of gravitational waves by the advanced Laser Interferometer Gravitational Wave Observatory (LIGO) detectors on 14 September 2015, where the signal was generated by two stellar mass black holes with masses 36 $ M_{\odot}$ and 29 $ M_{\odot}$ that merged to form a 62 $ M_{\odot}$ black hole, releasing 3 $M_{\odot}$ energy in gravitational waves, almost 1.3 billion years ago. We begin by providing a brief overview of gravitational waves, their sources and the gravitational wave detectors. We then describe in detail the first detection of gravitational waves from a binary black hole merger. We then comment on the electromagnetic follow up of the detection event with various telescopes. Finally, we conclude with the discussion on the tests of gravity and fundamental physics with the first gravitational wave detection event. |
gr-qc/0103095 | B. V. Ivanov | B.V.Ivanov | Pure-radiation gravitational fields with a simple twist and a Killing
vector | revtex, 9 pages | Phys.Rev.D61:064011,2000 | 10.1103/PhysRevD.61.064011 | null | gr-qc | null | Pure-radiation solutions are found, exploiting the analogy with the Euler-
Darboux equation for aligned colliding plane waves and the Euler-Tricomi
equation in hydrodynamics of two-dimensional flow. They do not depend on one of
the spacelike coordinates and comprise the Hauser solution as a special
subcase.
| [
{
"created": "Tue, 27 Mar 2001 08:42:56 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Ivanov",
"B. V.",
""
]
] | Pure-radiation solutions are found, exploiting the analogy with the Euler- Darboux equation for aligned colliding plane waves and the Euler-Tricomi equation in hydrodynamics of two-dimensional flow. They do not depend on one of the spacelike coordinates and comprise the Hauser solution as a special subcase. |
2407.02017 | Marina David | Pablo A. Cano, Marina David | Teukolsky equation for near-extremal black holes beyond general
relativity: near-horizon analysis | 44 pages, 2 figures, ancillary Mathematica notebook included;
v2:references added, version sent to journal | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We study gravitational perturbations on the near-horizon region of extremal
and near-extremal rotating black holes in a general higher-derivative extension
of Einstein gravity. We find a decoupled modified Teukolsky equation that rules
the gravitational perturbations and that separates into an angular and a radial
equation. The angular equation leads to a deformation of the spin-weighted
spheroidal harmonics, while the radial equation takes the same form as in Kerr
except for a modification of the angular separation constants. We provide a
detailed analysis of the corrections to these angular separation constants and
find analytic results for axisymmetric modes as well as in the eikonal limit.
As an application, we reproduce recent results that show that extremal Kerr
black holes in higher-derivative gravity become singular under certain
deformations and extend them by including parity-breaking corrections, which we
show lead to the same effect. Finally, we obtain constraints on the form of the
full modified Teukolsky radial equation by demanding that it has the right
near-horizon limit. These results serve as an stepping stone towards the study
of quasinormal modes of near-extremal black holes in higher-derivative
extensions of GR.
| [
{
"created": "Tue, 2 Jul 2024 07:39:08 GMT",
"version": "v1"
},
{
"created": "Sun, 14 Jul 2024 13:45:27 GMT",
"version": "v2"
}
] | 2024-07-16 | [
[
"Cano",
"Pablo A.",
""
],
[
"David",
"Marina",
""
]
] | We study gravitational perturbations on the near-horizon region of extremal and near-extremal rotating black holes in a general higher-derivative extension of Einstein gravity. We find a decoupled modified Teukolsky equation that rules the gravitational perturbations and that separates into an angular and a radial equation. The angular equation leads to a deformation of the spin-weighted spheroidal harmonics, while the radial equation takes the same form as in Kerr except for a modification of the angular separation constants. We provide a detailed analysis of the corrections to these angular separation constants and find analytic results for axisymmetric modes as well as in the eikonal limit. As an application, we reproduce recent results that show that extremal Kerr black holes in higher-derivative gravity become singular under certain deformations and extend them by including parity-breaking corrections, which we show lead to the same effect. Finally, we obtain constraints on the form of the full modified Teukolsky radial equation by demanding that it has the right near-horizon limit. These results serve as an stepping stone towards the study of quasinormal modes of near-extremal black holes in higher-derivative extensions of GR. |
1201.1627 | Behnaz Fazlpour | A. Banijamali and B. Fazlpour | Phantom Behavior Bounce with Tachyon and Non-minimal Derivative Coupling | 15 pages, 8 figures, Accepted for publication in JCAP. arXiv admin
note: substantial text overlap with arXiv:1105.4967 | null | 10.1088/1475-7516/2012/01/039 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The bouncing cosmology provides a successful solution of the cosmological
singularity problem. In this paper, we study the bouncing behavior of a single
scalar field model with tachyon field non-minimally coupled to itself, its
derivative and to the curvature. By utilizing the numerical calculations we
will show that the bouncing solution can appear in the universe dominated by
such a quintom matter with equation of state crossing the phantom divide line.
We also investigate the classical stability of our model using the phase
velocity of the homogeneous perturbations of the tachyon scalar field.
| [
{
"created": "Sun, 8 Jan 2012 12:26:19 GMT",
"version": "v1"
}
] | 2015-06-03 | [
[
"Banijamali",
"A.",
""
],
[
"Fazlpour",
"B.",
""
]
] | The bouncing cosmology provides a successful solution of the cosmological singularity problem. In this paper, we study the bouncing behavior of a single scalar field model with tachyon field non-minimally coupled to itself, its derivative and to the curvature. By utilizing the numerical calculations we will show that the bouncing solution can appear in the universe dominated by such a quintom matter with equation of state crossing the phantom divide line. We also investigate the classical stability of our model using the phase velocity of the homogeneous perturbations of the tachyon scalar field. |
2406.12088 | Jos\'e Arturo B\'aez Mr. | A. Baez, Nora Breton and I. Cabrera-Munguia | Energy extraction from the Reissner-Nordstr\"om de Sitter black hole | 17 pages, 17 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The energy extraction from an electrostatic black hole by the decay or
splitting of electrically charged particles is analyzed. We determine the
energetic conditions that make the extraction process viable and present a
general expression for the efficiency in terms of the parameters of the
electrostatic black hole and the decaying particles. We also examine the
conditions that optimize the efficiency of the extraction process. We analyze
two particular cases, the first one is the extraction process from a Reissner
Nordstr\"om black hole, for charged test particles with nonvanishing angular
momentum; the second one and more interesting corresponds to the energy
extraction from a Reissner Nordstr\"om de Sitter black hole. For the latter
there are two regions where the energy extraction is possible, the generalized
ergosphere and a cosmological ergosphere induced by the cosmological horizon.
Under certain conditions the two ergospheres get connected and cover the whole
region between the event horizon and the cosmological horizon, and therefore
the energy extraction is possible at any point in the vicinity of the black
hole. Moreover, the efficiency of the energy extraction can be the same for
different break up points and also there is the possibility of a different
efficiency for the same break up point. The conditions that maximize the
efficiency are determined as well.
| [
{
"created": "Mon, 17 Jun 2024 21:00:22 GMT",
"version": "v1"
}
] | 2024-06-19 | [
[
"Baez",
"A.",
""
],
[
"Breton",
"Nora",
""
],
[
"Cabrera-Munguia",
"I.",
""
]
] | The energy extraction from an electrostatic black hole by the decay or splitting of electrically charged particles is analyzed. We determine the energetic conditions that make the extraction process viable and present a general expression for the efficiency in terms of the parameters of the electrostatic black hole and the decaying particles. We also examine the conditions that optimize the efficiency of the extraction process. We analyze two particular cases, the first one is the extraction process from a Reissner Nordstr\"om black hole, for charged test particles with nonvanishing angular momentum; the second one and more interesting corresponds to the energy extraction from a Reissner Nordstr\"om de Sitter black hole. For the latter there are two regions where the energy extraction is possible, the generalized ergosphere and a cosmological ergosphere induced by the cosmological horizon. Under certain conditions the two ergospheres get connected and cover the whole region between the event horizon and the cosmological horizon, and therefore the energy extraction is possible at any point in the vicinity of the black hole. Moreover, the efficiency of the energy extraction can be the same for different break up points and also there is the possibility of a different efficiency for the same break up point. The conditions that maximize the efficiency are determined as well. |
gr-qc/0411056 | Amjad Ashoorioon | A. Ashoorioon, R.B. Mann | On the Tensor/Scalar Ratio in Inflation with UV Cutoff | 19 pages, 14 figures, to appear in Nucl. Phys. B; v4: typos
corrected, matched with the published version | Nucl.Phys. B716 (2005) 261-279 | 10.1016/j.nuclphysb.2005.03.033 | null | gr-qc astro-ph hep-th | null | Anisotropy of the cosmic microwave background radiation (CMB) originates from
both tensor and scalar perturbations. To study the characteristics of each of
these two kinds of perturbations, one has to determine the contribution of each
to the anisotropy of CMB. For example, the ratio of the power spectra of
tensor/scalar perturbations can be used to tighten bounds on the scalar
spectral index. We investigate here the implications for the tensor/scalar
ratio of the recent discovery (noted in astro-ph/0410139) that the introduction
of a minimal length cutoff in the structure of spacetime does not leave
boundary terms invariant. Such a cutoff introduces an ambiguity in the choice
of action for tensor and scalar perturbations, which in turn can affect this
ratio. We numerically solve for both tensor and scalar mode equations in a
near-de-sitter background and explicitly find the cutoff dependence of the
tensor/scalar ratio during inflation.
| [
{
"created": "Wed, 10 Nov 2004 22:33:58 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Nov 2004 20:50:07 GMT",
"version": "v2"
},
{
"created": "Fri, 11 Mar 2005 17:49:17 GMT",
"version": "v3"
},
{
"created": "Fri, 20 May 2005 21:10:48 GMT",
"version": "v4"
}
] | 2007-05-23 | [
[
"Ashoorioon",
"A.",
""
],
[
"Mann",
"R. B.",
""
]
] | Anisotropy of the cosmic microwave background radiation (CMB) originates from both tensor and scalar perturbations. To study the characteristics of each of these two kinds of perturbations, one has to determine the contribution of each to the anisotropy of CMB. For example, the ratio of the power spectra of tensor/scalar perturbations can be used to tighten bounds on the scalar spectral index. We investigate here the implications for the tensor/scalar ratio of the recent discovery (noted in astro-ph/0410139) that the introduction of a minimal length cutoff in the structure of spacetime does not leave boundary terms invariant. Such a cutoff introduces an ambiguity in the choice of action for tensor and scalar perturbations, which in turn can affect this ratio. We numerically solve for both tensor and scalar mode equations in a near-de-sitter background and explicitly find the cutoff dependence of the tensor/scalar ratio during inflation. |
0907.4280 | M. B. Altaie | M.B. Altaie | The Friedmann Paradigm: A critical review | Revtex4, 19 pages, 2 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Friedmann paradigm for a dynamical universe emanating from a spacetime
singularity is critically reviwed. Quantum effects, playing the essential role
at the very early stages, suggests that the universe may follow different
course to that presented by the standard Friedmann solutions. The investigation
of the back-reaction effect of the vacuum energy of quantized massless matter
fields at finite temperatures shows that the original spatial singularity is
avoided and that the universe is maintained all times at a critical density.
Instead of having a universe that was created at once we have an emergent
universe with energy being created continuously so as to maintain the overall
density at its critical value. The calculations presented here provide a basis
to construct a dynamical model for the universe where all the known problems of
the standard big bang can be avioded from start without the need to assume the
occurence of an inflation phase.
| [
{
"created": "Fri, 24 Jul 2009 13:19:59 GMT",
"version": "v1"
}
] | 2009-07-27 | [
[
"Altaie",
"M. B.",
""
]
] | The Friedmann paradigm for a dynamical universe emanating from a spacetime singularity is critically reviwed. Quantum effects, playing the essential role at the very early stages, suggests that the universe may follow different course to that presented by the standard Friedmann solutions. The investigation of the back-reaction effect of the vacuum energy of quantized massless matter fields at finite temperatures shows that the original spatial singularity is avoided and that the universe is maintained all times at a critical density. Instead of having a universe that was created at once we have an emergent universe with energy being created continuously so as to maintain the overall density at its critical value. The calculations presented here provide a basis to construct a dynamical model for the universe where all the known problems of the standard big bang can be avioded from start without the need to assume the occurence of an inflation phase. |
2010.01682 | Graham Cox | Liam Bussey, Graham Cox and Hari Kunduri | Eigenvalues of the MOTS stability operator for slowly rotating Kerr
black holes | 12 pages; comments welcome! Main results have been generalized in v2 | General Relativity and Gravitation 53 (2021) | 10.1007/s10714-021-02786-3 | null | gr-qc math-ph math.MP math.SP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the eigenvalues of the MOTS stability operator for the Kerr black
hole with angular momentum per unit mass $|a| \ll M$. We prove that each
eigenvalue depends analytically on $a$ (in a neighbourhood of $a=0$), and
compute its first nonvanishing derivative. Recalling that $a=0$ corresponds to
the Schwarzschild solution, where each eigenvalue has multiplicity $2\ell+1$,
we find that this degeneracy is completely broken for nonzero $a$. In
particular, for $0 < |a| \ll M$ we obtain a cluster consisting of $\ell$
distinct complex conjugate pairs and one real eigenvalue. As a special case of
our results, we get a simple formula for the variation of the principal
eigenvalue. For perturbations that preserve the total area or mass of the black
hole, we find that the principal eigenvalue has a local maximum at $a=0$.
However, there are other perturbations for which the principal eigenvalue has a
local minimum at $a=0$.
| [
{
"created": "Sun, 4 Oct 2020 20:59:23 GMT",
"version": "v1"
},
{
"created": "Tue, 5 Jan 2021 16:41:18 GMT",
"version": "v2"
}
] | 2021-02-01 | [
[
"Bussey",
"Liam",
""
],
[
"Cox",
"Graham",
""
],
[
"Kunduri",
"Hari",
""
]
] | We study the eigenvalues of the MOTS stability operator for the Kerr black hole with angular momentum per unit mass $|a| \ll M$. We prove that each eigenvalue depends analytically on $a$ (in a neighbourhood of $a=0$), and compute its first nonvanishing derivative. Recalling that $a=0$ corresponds to the Schwarzschild solution, where each eigenvalue has multiplicity $2\ell+1$, we find that this degeneracy is completely broken for nonzero $a$. In particular, for $0 < |a| \ll M$ we obtain a cluster consisting of $\ell$ distinct complex conjugate pairs and one real eigenvalue. As a special case of our results, we get a simple formula for the variation of the principal eigenvalue. For perturbations that preserve the total area or mass of the black hole, we find that the principal eigenvalue has a local maximum at $a=0$. However, there are other perturbations for which the principal eigenvalue has a local minimum at $a=0$. |
2302.08941 | Osmin Lacombe | Osmin Lacombe, Shinji Mukohyama | Multi-scalar theories of gravity with direct matter couplings and their
parametrized post-Newtonian parameters | 28 pages v2: published version, small modification of the abstract,
subsection 3.4 added | null | 10.1088/1475-7516/2023/08/054 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study theories of gravity including, in addition to the metric, several
scalar fields in the gravitational sector. The particularity of this work is
that we allow for direct couplings between these gravitating scalars and the
matter sector, which can generally be different for the source and the probe of
gravity, in addition to the universal interactions generated by the Jordan
frame metric. The weak gravity regime of this theory, which would describe
solar-system experiments, is studied using the parametrized post-Newtonian
(PPN) formalism. We derive the expression of the ten parameters of this
formalism. Among them, $\zeta_3$ and $\zeta_4$ are modified with respect to
their values in the theories without direct couplings. This fact holds even
after eliminating the direct couplings between the gravitating scalars and the
energy density of the source, by redefinition of the Jordan frame. All other
PPN parameters are insensitive to the direct couplings once in the correctly
identified Jordan frame. When direct couplings are different for the source and
the probe of gravity, they make non-relativistic probes deviate from the
geodesics of the PPN metric in this frame, already at Newtonian order. Such
couplings would thus be directly detectable and would have excluded by
experiments. This shows that, contrary to the claims in the recent literature,
it is impossible to screen the presence of gravitating scalars relying only on
a curved target space and direct couplings to matter.
| [
{
"created": "Fri, 17 Feb 2023 15:25:21 GMT",
"version": "v1"
},
{
"created": "Fri, 18 Aug 2023 17:15:11 GMT",
"version": "v2"
}
] | 2023-08-28 | [
[
"Lacombe",
"Osmin",
""
],
[
"Mukohyama",
"Shinji",
""
]
] | We study theories of gravity including, in addition to the metric, several scalar fields in the gravitational sector. The particularity of this work is that we allow for direct couplings between these gravitating scalars and the matter sector, which can generally be different for the source and the probe of gravity, in addition to the universal interactions generated by the Jordan frame metric. The weak gravity regime of this theory, which would describe solar-system experiments, is studied using the parametrized post-Newtonian (PPN) formalism. We derive the expression of the ten parameters of this formalism. Among them, $\zeta_3$ and $\zeta_4$ are modified with respect to their values in the theories without direct couplings. This fact holds even after eliminating the direct couplings between the gravitating scalars and the energy density of the source, by redefinition of the Jordan frame. All other PPN parameters are insensitive to the direct couplings once in the correctly identified Jordan frame. When direct couplings are different for the source and the probe of gravity, they make non-relativistic probes deviate from the geodesics of the PPN metric in this frame, already at Newtonian order. Such couplings would thus be directly detectable and would have excluded by experiments. This shows that, contrary to the claims in the recent literature, it is impossible to screen the presence of gravitating scalars relying only on a curved target space and direct couplings to matter. |
2203.07745 | Hugo Roussille | Hugo Roussille | A new look on black hole perturbations in modified gravity | Contribution to the 2022 Gravitation session of the 56th Rencontres
de Moriond | null | null | null | gr-qc hep-th | http://creativecommons.org/publicdomain/zero/1.0/ | We study the linear perturbations about a nonrotating black hole solution of
Horndeski's theory, using a systematic approach that extracts the asymptotic
behaviour of perturbations (at spatial infinity and near the horizon) directly
from the first-order radial differential system governing these perturbations
instead of finding Schr\"odinger-like equations for their dynamics. We
illustrate this method in the case of a specific black hole solution. The
knowledge of the asymptotic behaviours of the perturbations paves the way for a
numerical computation of the quasinormal modes. Finally, the asymptotic form of
the modes also signals some pathologies in the scalar sector of the solution
considered here.
| [
{
"created": "Tue, 15 Mar 2022 09:35:04 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Mar 2022 17:04:02 GMT",
"version": "v2"
}
] | 2022-03-17 | [
[
"Roussille",
"Hugo",
""
]
] | We study the linear perturbations about a nonrotating black hole solution of Horndeski's theory, using a systematic approach that extracts the asymptotic behaviour of perturbations (at spatial infinity and near the horizon) directly from the first-order radial differential system governing these perturbations instead of finding Schr\"odinger-like equations for their dynamics. We illustrate this method in the case of a specific black hole solution. The knowledge of the asymptotic behaviours of the perturbations paves the way for a numerical computation of the quasinormal modes. Finally, the asymptotic form of the modes also signals some pathologies in the scalar sector of the solution considered here. |
1301.0221 | Remo Garattini | Remo Garattini and Francisco S. N. Lobo | Self-sustained traversable wormholes in modified gravity theories | 3 pages; contribution to the proceedings of the Thirteenth Marcel
Grossmann Meeting, Stockholm University, Sweden, 1-7 July, 2012; based on a
talk in the AT3 "Gravitational Fields with Sources, Regular Black Holes,
Quasiblack Holes, and Analog Black Holes" parallel session | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the possibility that wormhole geometries are sustained by their
own quantum fluctuations, in the context of noncommutative geometry and
Gravity's Rainbow models. More specifically, the energy density of the graviton
one-loop contribution to a classical energy in a wormhole background is
considered as a self-consistent source for wormholes. In this semi-classical
context, we consider the effects of a smeared particle-like source in
noncommutative geometry and of the Rainbow's functions in sustaining wormhole
geometries.
| [
{
"created": "Wed, 2 Jan 2013 12:47:39 GMT",
"version": "v1"
}
] | 2013-01-03 | [
[
"Garattini",
"Remo",
""
],
[
"Lobo",
"Francisco S. N.",
""
]
] | We consider the possibility that wormhole geometries are sustained by their own quantum fluctuations, in the context of noncommutative geometry and Gravity's Rainbow models. More specifically, the energy density of the graviton one-loop contribution to a classical energy in a wormhole background is considered as a self-consistent source for wormholes. In this semi-classical context, we consider the effects of a smeared particle-like source in noncommutative geometry and of the Rainbow's functions in sustaining wormhole geometries. |
gr-qc/9911075 | Robert van den Hoogen | A.A. Coley and R.J. van den Hoogen | The Dynamics of Multi-Scalar Field Cosmological Models and Assisted
Inflation | 27 pages, uses REVTeX Added an appendix illustrating some of the
details needed to compute the stability of the assisted inflationary solution | Phys.Rev. D62 (2000) 023517 | 10.1103/PhysRevD.62.023517 | null | gr-qc astro-ph | null | We investigate the dynamical properties of a class of spatially homogeneous
and isotropic cosmological models containing a barotropic perfect fluid and
multiple scalar fields with independent exponential potentials. We show that
the assisted inflationary scaling solution is the global late-time attractor
for the parameter values for which the model is inflationary, even when
curvature and barotropic matter are included. For all other parameter values
the multi-field curvature scaling solution is the global late-time attractor
(in these solutions asymptotically the curvature is not dynamically
negligible). Consequently, we find that in general all of the scalar fields in
multi-field models with exponential potentials are non-negligible in late-time
behaviour, contrary to what is commonly believed. The early-time and
intermediate behaviour of the models is also studied. In particular, n-scalar
field models are investigated and the structure of the saddle equilibrium
points corresponding to inflationary m-field scaling solutions and
non-inflationary m-field matter scaling solutions are also studied (where m<n),
leading to interesting transient dynamical behaviour with new physical
scenarios of potential importance.
| [
{
"created": "Fri, 19 Nov 1999 18:22:39 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Jan 2000 21:06:21 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Coley",
"A. A.",
""
],
[
"Hoogen",
"R. J. van den",
""
]
] | We investigate the dynamical properties of a class of spatially homogeneous and isotropic cosmological models containing a barotropic perfect fluid and multiple scalar fields with independent exponential potentials. We show that the assisted inflationary scaling solution is the global late-time attractor for the parameter values for which the model is inflationary, even when curvature and barotropic matter are included. For all other parameter values the multi-field curvature scaling solution is the global late-time attractor (in these solutions asymptotically the curvature is not dynamically negligible). Consequently, we find that in general all of the scalar fields in multi-field models with exponential potentials are non-negligible in late-time behaviour, contrary to what is commonly believed. The early-time and intermediate behaviour of the models is also studied. In particular, n-scalar field models are investigated and the structure of the saddle equilibrium points corresponding to inflationary m-field scaling solutions and non-inflationary m-field matter scaling solutions are also studied (where m<n), leading to interesting transient dynamical behaviour with new physical scenarios of potential importance. |
2309.11280 | Felipe Agurto Sep\'ulveda | F. Agurto-Sepulveda, J. H Lagunas, J. Pedreros, B. Bandyopadhyay,
D.R.G Schleicher | Exploring how deviations from the Kerr metric can affect SMBH images | 3 pages, 2 figures,Accepted for publication in Bolet\'in de la
Asociaci\'on Argentina de Astronom\'ia | 2023BAAA...64..283A | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black holes (BH) are objects described by General Relativity (GR),
particularly by the Kerr solution. However, this solution is based on
simplifying assumptions. To achieve a more realistic approach, we investigate
the impact of deviations from the Kerr solution on the imaging of supermassive
black holes (SMBH). We conduct General Relativistic Radiation Transport
simulations using a Kerr-Like metric, which includes four nonlinear free
deviation functions and is stationary, axis-symmetric, and asymptotically flat.
The RAPTOR I code, an open-source ray-tracing code capable of handling
arbitrary spacetimes, is employed to generate the images. We analyze the
asymmetry, diameter, and shadow displacement of the BH to compare them with
those of a Kerr BH. Our findings confirm that these deviations significantly
affect the shape of the shadow. However, we acknowledge the importance of
considering the matter distribution and emissivities surrounding the BH, as the
results cannot be solely inferred from the shape of the photon ring.
| [
{
"created": "Wed, 20 Sep 2023 13:04:53 GMT",
"version": "v1"
}
] | 2023-09-22 | [
[
"Agurto-Sepulveda",
"F.",
""
],
[
"Lagunas",
"J. H",
""
],
[
"Pedreros",
"J.",
""
],
[
"Bandyopadhyay",
"B.",
""
],
[
"Schleicher",
"D. R. G",
""
]
] | Black holes (BH) are objects described by General Relativity (GR), particularly by the Kerr solution. However, this solution is based on simplifying assumptions. To achieve a more realistic approach, we investigate the impact of deviations from the Kerr solution on the imaging of supermassive black holes (SMBH). We conduct General Relativistic Radiation Transport simulations using a Kerr-Like metric, which includes four nonlinear free deviation functions and is stationary, axis-symmetric, and asymptotically flat. The RAPTOR I code, an open-source ray-tracing code capable of handling arbitrary spacetimes, is employed to generate the images. We analyze the asymmetry, diameter, and shadow displacement of the BH to compare them with those of a Kerr BH. Our findings confirm that these deviations significantly affect the shape of the shadow. However, we acknowledge the importance of considering the matter distribution and emissivities surrounding the BH, as the results cannot be solely inferred from the shape of the photon ring. |
gr-qc/0405130 | Bjorn Einarsson | Bjorn Einarsson | Conditions for negative specific heat in systems of attracting classical
particles | 11 pages, 1 figure, Published version (including correlation between
positive specific heat and singular points) | Phys.Lett. A332 (2004) 335-344 | 10.1016/j.physleta.2004.09.066 | null | gr-qc astro-ph cond-mat.stat-mech | null | We identify conditions for the presence of negative specific heat in
non-relativistic self-gravitating systems and similar systems of attracting
particles.
The method used, is to analyse the Virial theorem and two soluble models of
systems of attracting particles, and to map the sign of the specific heat for
different combinations of the number of spatial dimensions of the system,
$D$($\geq 2$), and the exponent, $\nu$($\neq 0$), in the force potential,
$\phi=Cr^\nu$. Negative specific heat in such systems is found to be present
exactly for $\nu=-1$, at least for $D \geq 3$. For many combinations of $D$ and
$\nu$ representing long-range forces, the specific heat is positive or zero,
for both models and the Virial theorem. Hence negative specific heat is not
caused by long-range forces as such. We also find that negative specific heat
appears when $\nu$ is negative, and there is no singular point in a certain
density distribution. A possible mechanism behind this is suggested.
| [
{
"created": "Wed, 26 May 2004 10:26:15 GMT",
"version": "v1"
},
{
"created": "Sun, 20 Jun 2004 18:31:46 GMT",
"version": "v2"
},
{
"created": "Tue, 8 Feb 2005 10:54:49 GMT",
"version": "v3"
}
] | 2009-11-10 | [
[
"Einarsson",
"Bjorn",
""
]
] | We identify conditions for the presence of negative specific heat in non-relativistic self-gravitating systems and similar systems of attracting particles. The method used, is to analyse the Virial theorem and two soluble models of systems of attracting particles, and to map the sign of the specific heat for different combinations of the number of spatial dimensions of the system, $D$($\geq 2$), and the exponent, $\nu$($\neq 0$), in the force potential, $\phi=Cr^\nu$. Negative specific heat in such systems is found to be present exactly for $\nu=-1$, at least for $D \geq 3$. For many combinations of $D$ and $\nu$ representing long-range forces, the specific heat is positive or zero, for both models and the Virial theorem. Hence negative specific heat is not caused by long-range forces as such. We also find that negative specific heat appears when $\nu$ is negative, and there is no singular point in a certain density distribution. A possible mechanism behind this is suggested. |
gr-qc/0201059 | Jose Geraldo Pereira | M. Calcada and J. G. Pereira | Gravitation and the Local Symmetry Group of Spacetime | 8 pages, no figures. Some signs and references corrected; version to
appear in Int. J. Theor. Phys | Int.J.Theor.Phys. 41 (2002) 729-736 | null | null | gr-qc | null | According to general relativity, the interaction of a matter field with
gravitation requires the simultaneous introduction of a tetrad field, which is
a field related to translations, and a spin connection, which is a field
assuming values in the Lie algebra of the Lorentz group. These two fields,
however, are not independent. By analyzing the constraint between them, it is
concluded that the relevant local symmetry group behind general relativity is
provided by the Lorentz group. Furthermore, it is shown that the minimal
coupling prescription obtained from the Lorentz covariant derivative coincides
exactly with the usual coupling prescription of general relativity. Instead of
the tetrad, therefore, the spin connection is to be considered as the
fundamental field representing gravitation.
| [
{
"created": "Thu, 17 Jan 2002 17:09:37 GMT",
"version": "v1"
},
{
"created": "Thu, 28 Feb 2002 13:15:01 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Calcada",
"M.",
""
],
[
"Pereira",
"J. G.",
""
]
] | According to general relativity, the interaction of a matter field with gravitation requires the simultaneous introduction of a tetrad field, which is a field related to translations, and a spin connection, which is a field assuming values in the Lie algebra of the Lorentz group. These two fields, however, are not independent. By analyzing the constraint between them, it is concluded that the relevant local symmetry group behind general relativity is provided by the Lorentz group. Furthermore, it is shown that the minimal coupling prescription obtained from the Lorentz covariant derivative coincides exactly with the usual coupling prescription of general relativity. Instead of the tetrad, therefore, the spin connection is to be considered as the fundamental field representing gravitation. |
0908.3041 | Hiromi Saida | Hiromi Saida | de Sitter thermodynamics in the canonical ensemble | 28 pages, 2 figures, Accepted for publication in Prog.Theor.Phys,
Typos are corrected | Prog. Theor. Phys. 122 (2009), 1239-1266 | 10.1143/PTP.122.1239 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The existing thermodynamics of the cosmological horizon in de-Sitter
spacetime is established in the micro-canonical ensemble, while thermodynamics
of black hole horizons are established in the canonical ensemble. Generally in
the ordinary thermodynamics and statistical mechanics, both of the
micro-canonical and canonical ensembles yield the same equation of state for
any thermodynamic system. This implies the existence of a formulation of
de-Sitter thermodynamics based on the canonical ensemble. This paper reproduces
the de-Sitter thermodynamics in the canonical ensemble. The procedure is as
follows: We put a spherical wall at the center of de-Sitter spacetime, whose
mass is negligible and perfectly reflects the Hawking radiation coming from the
cosmological horizon. Then the region enclosed by the wall and horizon settles
down to a thermal equilibrium state, for which the Euclidean action is
evaluated and the partition function is obtained. The integration constant
(subtraction term) of Euclidean action is determined to reproduce the equation
of state (e.g. entropy-area law) verified already in the micro-canonical
ensemble. Our de-Sitter canonical ensemble is well-defined to preserve the
"thermodynamic consistency", which means that the state variables satisfy not
only the four laws of thermodynamics but also the appropriate differential
relations with thermodynamic functions; e.g. partial derivatives of the free
energy give the entropy, pressure, and so on. The special role of cosmological
constant in de-Sitter thermodynamics is also revealed.
| [
{
"created": "Fri, 21 Aug 2009 02:27:47 GMT",
"version": "v1"
},
{
"created": "Mon, 31 Aug 2009 02:59:41 GMT",
"version": "v2"
},
{
"created": "Mon, 4 Nov 2013 01:31:15 GMT",
"version": "v3"
}
] | 2013-11-05 | [
[
"Saida",
"Hiromi",
""
]
] | The existing thermodynamics of the cosmological horizon in de-Sitter spacetime is established in the micro-canonical ensemble, while thermodynamics of black hole horizons are established in the canonical ensemble. Generally in the ordinary thermodynamics and statistical mechanics, both of the micro-canonical and canonical ensembles yield the same equation of state for any thermodynamic system. This implies the existence of a formulation of de-Sitter thermodynamics based on the canonical ensemble. This paper reproduces the de-Sitter thermodynamics in the canonical ensemble. The procedure is as follows: We put a spherical wall at the center of de-Sitter spacetime, whose mass is negligible and perfectly reflects the Hawking radiation coming from the cosmological horizon. Then the region enclosed by the wall and horizon settles down to a thermal equilibrium state, for which the Euclidean action is evaluated and the partition function is obtained. The integration constant (subtraction term) of Euclidean action is determined to reproduce the equation of state (e.g. entropy-area law) verified already in the micro-canonical ensemble. Our de-Sitter canonical ensemble is well-defined to preserve the "thermodynamic consistency", which means that the state variables satisfy not only the four laws of thermodynamics but also the appropriate differential relations with thermodynamic functions; e.g. partial derivatives of the free energy give the entropy, pressure, and so on. The special role of cosmological constant in de-Sitter thermodynamics is also revealed. |
2006.08780 | Theodore Pailas | T. Pailas | "Time"-covariant Schr\"odinger equation and the canonical quantization
of the Reissner-Nordstr\"om black hole | 4 figures | null | 10.3390/quantum2030029 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A "time"-covariant Schr\"{o}dinger equation is defined for the minisuperspace
model of the Reissner-Nordstr\"{o}m (RN) black hole, as a "hybrid" between the
"intrinsic time" Schr\"{o}dinger and Wheeler-DeWitt(WDW) equations. To do so, a
reduced, regular and "time(r)"-dependent Hamiltonian density was constructed,
without "breaking" the re-parametrization covariance $r\rightarrow
f(\tilde{r})$. As a result, evolution of states with respect to the parameter
$r$ and probabilistic interpretation of the resulting quantum description is
possible, while quantum schemes for different gauge choices are equivalent by
construction. The solutions are found for a Dirac's delta and a Gaussian
initial states. A geometrical interpretation of the wavefunctions is presented
via Bohm analysis. Alongside, a criterion is presented to adjudicate which,
between two singular spacetimes is "more" or "less" singular. Two ways to
adjudicate about the existence of singularities are compared (vanishing of the
probability density at the classical singularity and semi-classical spacetime
singularity). Finally, an equivalence of the reduced equations with these of a
3D electromagnetic pp-wave spacetime is revealed.
| [
{
"created": "Mon, 15 Jun 2020 21:31:42 GMT",
"version": "v1"
},
{
"created": "Tue, 24 Nov 2020 23:17:10 GMT",
"version": "v2"
}
] | 2020-11-26 | [
[
"Pailas",
"T.",
""
]
] | A "time"-covariant Schr\"{o}dinger equation is defined for the minisuperspace model of the Reissner-Nordstr\"{o}m (RN) black hole, as a "hybrid" between the "intrinsic time" Schr\"{o}dinger and Wheeler-DeWitt(WDW) equations. To do so, a reduced, regular and "time(r)"-dependent Hamiltonian density was constructed, without "breaking" the re-parametrization covariance $r\rightarrow f(\tilde{r})$. As a result, evolution of states with respect to the parameter $r$ and probabilistic interpretation of the resulting quantum description is possible, while quantum schemes for different gauge choices are equivalent by construction. The solutions are found for a Dirac's delta and a Gaussian initial states. A geometrical interpretation of the wavefunctions is presented via Bohm analysis. Alongside, a criterion is presented to adjudicate which, between two singular spacetimes is "more" or "less" singular. Two ways to adjudicate about the existence of singularities are compared (vanishing of the probability density at the classical singularity and semi-classical spacetime singularity). Finally, an equivalence of the reduced equations with these of a 3D electromagnetic pp-wave spacetime is revealed. |
gr-qc/0101103 | Christodoulakis Theodosios | T. Christodoulakis, G. Kofinas, G.O. Papadopoulos | Conditional Symmetries and Phase Space Reduction towards G.C.T.
Invariant Wave Functions, for the Class A Bianchi Type VI & VII Vacuum
Cosmologies | 12 pages, LaTeX2e, no figures | Phys.Lett.B514:149-154,2001 | 10.1016/S0370-2693(01)00793-6 | UA/NPPS-02-2001 | gr-qc | null | The quantization of Class A Bianchi Type VI and VII geometries -with all six
scale factors, as well as the lapse function and the shift vector present- is
considered. A first reduction of the initial 6-dimensional configuration space
is achieved by the usage of the information furnished by the quantum form of
the linear constraints. Further reduction of the space in which the wave
function -obeying the Wheeler-DeWitt equation- lives, is accomplished by
revealing a classical integral of motion, tantamount to an extra symmetry of
the corresponding classical Hamiltonian. This symmetry generator -member of a
larger group- is linear in momenta and corresponds to G.C.T.s through the
action of the automorphism group -especially through the action of the outer
automorphism subgroup. Thus, a G.C.T. invariant wave function is found, which
depends on one combination of the two curvature invariants --which uniquely and
irreducibly characterizes the hypersurfaces t=const.
| [
{
"created": "Fri, 26 Jan 2001 15:39:33 GMT",
"version": "v1"
},
{
"created": "Tue, 22 May 2001 10:57:40 GMT",
"version": "v2"
}
] | 2009-10-09 | [
[
"Christodoulakis",
"T.",
""
],
[
"Kofinas",
"G.",
""
],
[
"Papadopoulos",
"G. O.",
""
]
] | The quantization of Class A Bianchi Type VI and VII geometries -with all six scale factors, as well as the lapse function and the shift vector present- is considered. A first reduction of the initial 6-dimensional configuration space is achieved by the usage of the information furnished by the quantum form of the linear constraints. Further reduction of the space in which the wave function -obeying the Wheeler-DeWitt equation- lives, is accomplished by revealing a classical integral of motion, tantamount to an extra symmetry of the corresponding classical Hamiltonian. This symmetry generator -member of a larger group- is linear in momenta and corresponds to G.C.T.s through the action of the automorphism group -especially through the action of the outer automorphism subgroup. Thus, a G.C.T. invariant wave function is found, which depends on one combination of the two curvature invariants --which uniquely and irreducibly characterizes the hypersurfaces t=const. |
0807.2652 | Nicolas Yunes | Victor Taveras and Nicolas Yunes | The Barbero-Immirzi Parameter as a Scalar Field: K-Inflation from Loop
Quantum Gravity? | Phys. Rev. D78, 064070 (2008) | Phys.Rev.D78:064070,2008 | 10.1103/PhysRevD.78.064070 | IGC-08/7-1 | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a loop-quantum gravity inspired modification of general
relativity, where the Holst action is generalized by making the Barbero-Immirzi
(BI) parameter a scalar field, whose value could be dynamically determined. The
modified theory leads to a non-zero torsion tensor that corrects the field
equations through quadratic first-derivatives of the BI field. Such a
correction is equivalent to general relativity in the presence of a scalar
field with non-trivial kinetic energy. This stress-energy of this field is
automatically covariantly conserved by its own dynamical equations of motion,
thus satisfying the strong equivalence principle. Every general relativistic
solution remains a solution to the modified theory for any constant value of
the BI field. For arbitrary time-varying BI fields, a study of cosmological
solutions reduces the scalar field stress-energy to that of a pressureless
perfect fluid in a comoving reference frame, forcing the scale factor dynamics
to be equivalent to those of a stiff equation of state. Upon ultraviolet
completion, this model could provide a natural mechanism for k-inflation, where
the role of the inflaton is played by the BI field and inflation is driven by
its non-trivial kinetic energy instead of a potential.
| [
{
"created": "Wed, 16 Jul 2008 20:17:33 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Nov 2008 20:11:29 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Taveras",
"Victor",
""
],
[
"Yunes",
"Nicolas",
""
]
] | We consider a loop-quantum gravity inspired modification of general relativity, where the Holst action is generalized by making the Barbero-Immirzi (BI) parameter a scalar field, whose value could be dynamically determined. The modified theory leads to a non-zero torsion tensor that corrects the field equations through quadratic first-derivatives of the BI field. Such a correction is equivalent to general relativity in the presence of a scalar field with non-trivial kinetic energy. This stress-energy of this field is automatically covariantly conserved by its own dynamical equations of motion, thus satisfying the strong equivalence principle. Every general relativistic solution remains a solution to the modified theory for any constant value of the BI field. For arbitrary time-varying BI fields, a study of cosmological solutions reduces the scalar field stress-energy to that of a pressureless perfect fluid in a comoving reference frame, forcing the scale factor dynamics to be equivalent to those of a stiff equation of state. Upon ultraviolet completion, this model could provide a natural mechanism for k-inflation, where the role of the inflaton is played by the BI field and inflation is driven by its non-trivial kinetic energy instead of a potential. |
0812.3552 | Jian-Yang Zhu | Li-Fang Li and Jian-Yang Zhu | Tachyon field in loop quantum cosmology: An example of traversable
singularity | 7 pages, 3 figures. Accepted for publication in Physical Review D | Phys.Rev.D79:124011,2009 | 10.1103/PhysRevD.79.124011 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Loop quantum cosmology (LQC) predicts a nonsingular evolution of the universe
through a bounce in the high energy region. But LQC has an ambiguity about the
quantization scheme. Recently, the authors in [Phys. Rev. D 77, 124008 (2008)]
proposed a new quantization scheme. Similar to others, this new quantization
scheme also replaces the big bang singularity with the quantum bounce. More
interestingly, it introduces a quantum singularity, which is traversable. We
investigate this novel dynamics quantitatively with a tachyon scalar field,
which gives us a concrete example. Our result shows that our universe can
evolve through the quantum singularity regularly, which is different from the
classical big bang singularity. So this singularity is only a week singularity.
| [
{
"created": "Thu, 18 Dec 2008 15:26:27 GMT",
"version": "v1"
},
{
"created": "Sat, 23 May 2009 00:34:06 GMT",
"version": "v2"
}
] | 2014-11-18 | [
[
"Li",
"Li-Fang",
""
],
[
"Zhu",
"Jian-Yang",
""
]
] | Loop quantum cosmology (LQC) predicts a nonsingular evolution of the universe through a bounce in the high energy region. But LQC has an ambiguity about the quantization scheme. Recently, the authors in [Phys. Rev. D 77, 124008 (2008)] proposed a new quantization scheme. Similar to others, this new quantization scheme also replaces the big bang singularity with the quantum bounce. More interestingly, it introduces a quantum singularity, which is traversable. We investigate this novel dynamics quantitatively with a tachyon scalar field, which gives us a concrete example. Our result shows that our universe can evolve through the quantum singularity regularly, which is different from the classical big bang singularity. So this singularity is only a week singularity. |
gr-qc/0511096 | Jorge Pullin | Rodolfo Gambini, Jorge Pullin | Consistent discretization and canonical classical and quantum Regge
calculus | 8 pages, Dedicated to Rafael Sorkin on his 60th birthday, to appear
in Proceedings of the Puri Conference, special issue of IJMPD | Int.J.Mod.Phys. D15 (2006) 1699-1706 | 10.1142/S0218271806009042 | LSU-REL-111605 | gr-qc hep-th | null | We apply the ``consistent discretization'' technique to the Regge action for
(Euclidean and Lorentzian) general relativity in arbitrary number of
dimensions. The result is a well defined canonical theory that is free of
constraints and where the dynamics is implemented as a canonical
transformation. This provides a framework for the discussion of topology change
in canonical quantum gravity. In the Lorentzian case, the framework appears to
be naturally free of the ``spikes'' that plague traditional formulations. It
also provides a well defined recipe for determining the measure of the path
integral.
| [
{
"created": "Wed, 16 Nov 2005 22:14:06 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Jun 2006 17:31:43 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Gambini",
"Rodolfo",
""
],
[
"Pullin",
"Jorge",
""
]
] | We apply the ``consistent discretization'' technique to the Regge action for (Euclidean and Lorentzian) general relativity in arbitrary number of dimensions. The result is a well defined canonical theory that is free of constraints and where the dynamics is implemented as a canonical transformation. This provides a framework for the discussion of topology change in canonical quantum gravity. In the Lorentzian case, the framework appears to be naturally free of the ``spikes'' that plague traditional formulations. It also provides a well defined recipe for determining the measure of the path integral. |
2306.13782 | R Loll | R. Loll | Quantum Curvature as Key to the Quantum Universe | 38 pages, 17 figures, contribution to Handbook of Quantum Gravity
(eds. C. Bambi, L. Modesto and I.L. Shapiro, Springer Singapore, expected in
2023) | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Curvature is a key notion in General Relativity, characterizing the local
physical properties of spacetime. By contrast, the concept of curvature has
received scant attention in nonperturbative quantum gravity. One may even
wonder whether in a Planckian regime meaningful notions of (quantum) curvature
exist at all. Remarkably, recent work in quantum gravity using Causal Dynamical
Triangulations (CDT) has demonstrated both the existence and usefulness of a
new notion of quantum Ricci curvature (QRC), which relies neither on smooth
structures nor on tensor calculus. This overview article recalls some classical
notions related to curvature and parallel transport, as well as previous
unsuccessful attempts to construct quantum curvature observables based on
deficit angles and Wilson loops. It introduces the quasi-local QRC on piecewise
flat triangulations, and describes its behaviour in a purely classical setting,
its use in quantum observables, and currently known results in (C)DT quantum
gravity in two and four dimensions. The QRC opens the door to a range of
interesting physical observables that were previously out of reach, and will
help to bridge the gap between the nonperturbative quantum theory and
gravitational phenomena at lower energies.
| [
{
"created": "Fri, 23 Jun 2023 20:52:03 GMT",
"version": "v1"
}
] | 2023-06-27 | [
[
"Loll",
"R.",
""
]
] | Curvature is a key notion in General Relativity, characterizing the local physical properties of spacetime. By contrast, the concept of curvature has received scant attention in nonperturbative quantum gravity. One may even wonder whether in a Planckian regime meaningful notions of (quantum) curvature exist at all. Remarkably, recent work in quantum gravity using Causal Dynamical Triangulations (CDT) has demonstrated both the existence and usefulness of a new notion of quantum Ricci curvature (QRC), which relies neither on smooth structures nor on tensor calculus. This overview article recalls some classical notions related to curvature and parallel transport, as well as previous unsuccessful attempts to construct quantum curvature observables based on deficit angles and Wilson loops. It introduces the quasi-local QRC on piecewise flat triangulations, and describes its behaviour in a purely classical setting, its use in quantum observables, and currently known results in (C)DT quantum gravity in two and four dimensions. The QRC opens the door to a range of interesting physical observables that were previously out of reach, and will help to bridge the gap between the nonperturbative quantum theory and gravitational phenomena at lower energies. |
1202.2677 | Alexander Zhuk | Alexey Chopovsky, Maxim Eingorn and Alexander Zhuk | Exact and asymptotic black branes with spherical compactification | 6 pages, no figures | Physical Review, D86 (2012) 024025 | 10.1103/PhysRevD.86.024025 | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the six-dimensional Kaluza-Klein model with the multidimensional
cosmological constant $\Lambda_6$, we obtain the black brane with spherical
compactification of the internal space. The matter source for this exact
solution consists of two parts. First, it is a fine-tuned homogeneous perfect
fluid which provides spherical compactification of the internal space. Second,
it is a gravitating massive body with the dustlike equation of state in the
external space and tension $\hat p_1=-(1/2)\hat\varepsilon$ in the internal
space. This solution exists both in the presence and absence of $\Lambda_6$. In
the weak-field approximation, we also get solutions of the linearized Einstein
equations for the model with spherical compactification. Here, the gravitating
matter source has the dustlike equation of state in the external space and an
arbitrary equation of state $\hat p_1=\Omega \hat\varepsilon$ in the internal
space. In the case $\Lambda_6>0$ and $\Omega\neq -1/2$, these approximate
solutions tend asymptotically to the weak-field limit of the exact black brane
solution. Both the exact and asymptotic black branes satisfy the gravitational
experiments at the same level of accuracy as general relativity.
| [
{
"created": "Mon, 13 Feb 2012 09:53:52 GMT",
"version": "v1"
}
] | 2012-08-08 | [
[
"Chopovsky",
"Alexey",
""
],
[
"Eingorn",
"Maxim",
""
],
[
"Zhuk",
"Alexander",
""
]
] | In the six-dimensional Kaluza-Klein model with the multidimensional cosmological constant $\Lambda_6$, we obtain the black brane with spherical compactification of the internal space. The matter source for this exact solution consists of two parts. First, it is a fine-tuned homogeneous perfect fluid which provides spherical compactification of the internal space. Second, it is a gravitating massive body with the dustlike equation of state in the external space and tension $\hat p_1=-(1/2)\hat\varepsilon$ in the internal space. This solution exists both in the presence and absence of $\Lambda_6$. In the weak-field approximation, we also get solutions of the linearized Einstein equations for the model with spherical compactification. Here, the gravitating matter source has the dustlike equation of state in the external space and an arbitrary equation of state $\hat p_1=\Omega \hat\varepsilon$ in the internal space. In the case $\Lambda_6>0$ and $\Omega\neq -1/2$, these approximate solutions tend asymptotically to the weak-field limit of the exact black brane solution. Both the exact and asymptotic black branes satisfy the gravitational experiments at the same level of accuracy as general relativity. |
2001.05968 | Olga Babourova Valer'evna | Olga V. Babourova, Boris N. Frolov | Harrison-Zel'dovich scale invariance and the exponential decrease of the
"cosmological constant" in the super-early Universe | 6 pages, 4 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cosmological consequences of the Poincare-Weyl gauge theory of gravity are
considered. A generalized cosmological constant depending from the Dirac scalar
field is introduced. The stage of a super-early (Harrison-Zel'dovich) scale
invariant Universe is considered. It is shown that while the scale factor
sharply increases and demonstrates inflationary behavior, the generalized
cosmological constant decreases sharply from a huge value at the beginning of
the Big Bang to an extremely small value in the modern era, which solves the
well-known "cosmological constant problem".
| [
{
"created": "Thu, 16 Jan 2020 18:02:34 GMT",
"version": "v1"
}
] | 2020-01-17 | [
[
"Babourova",
"Olga V.",
""
],
[
"Frolov",
"Boris N.",
""
]
] | Cosmological consequences of the Poincare-Weyl gauge theory of gravity are considered. A generalized cosmological constant depending from the Dirac scalar field is introduced. The stage of a super-early (Harrison-Zel'dovich) scale invariant Universe is considered. It is shown that while the scale factor sharply increases and demonstrates inflationary behavior, the generalized cosmological constant decreases sharply from a huge value at the beginning of the Big Bang to an extremely small value in the modern era, which solves the well-known "cosmological constant problem". |
1102.4266 | Sergey Vyatchanin | Andrey Rakhubovsky, Stefan Hild and Sergey Vyatchanin | Stable double-resonance optical spring in laser gravitational-wave
detectors | 9 pafes, 8 figures | null | 10.1103/PhysRevD.84.062002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the optical spring characteristics of a double pumped Fabry-Perot
cavity. A double-resonance optical spring occurs when the optical spring
frequency and the detuning frequency of the cavity coincide. We formulate a
simple criterion for the stability of an optical spring and apply it to the
double resonance regime. Double resonance configurations are very promising for
future gravitational wave detectors as they allow us to surpass the Standard
Quantum Limit. We show that stable double resonance can be demonstrated in
middle scale prototype interferometers such as the Glasgow 10m-Prototype,
Gingin High Optical Power Test Facility or the AEI 10m Prototype Interferometer
before being implemented in future gravitational wave detectors.
| [
{
"created": "Mon, 21 Feb 2011 16:08:15 GMT",
"version": "v1"
}
] | 2013-05-29 | [
[
"Rakhubovsky",
"Andrey",
""
],
[
"Hild",
"Stefan",
""
],
[
"Vyatchanin",
"Sergey",
""
]
] | We analyze the optical spring characteristics of a double pumped Fabry-Perot cavity. A double-resonance optical spring occurs when the optical spring frequency and the detuning frequency of the cavity coincide. We formulate a simple criterion for the stability of an optical spring and apply it to the double resonance regime. Double resonance configurations are very promising for future gravitational wave detectors as they allow us to surpass the Standard Quantum Limit. We show that stable double resonance can be demonstrated in middle scale prototype interferometers such as the Glasgow 10m-Prototype, Gingin High Optical Power Test Facility or the AEI 10m Prototype Interferometer before being implemented in future gravitational wave detectors. |
gr-qc/9907066 | Gilad Gour | Gilad Gour | Schwarzschild black hole as a grand canonical ensemble | RevTex, 10 pages, Accepted for publication in Physical Review D | Phys.Rev.D61:021501,2000 | 10.1103/PhysRevD.61.021501 | null | gr-qc hep-th quant-ph | null | For long black holes have been considered as endowed with a definite
temperature. Yet when the Schwarzschild black hole is treated as a canonical
ensemble three problems arise: incompatibility with the Hawking radiation,
divergence of the partition function, and a formally negative mean-square
fluctuation of the energy. We solve all three problems by considering the
Schwarzschild black hole as a grand canonical ensemble, with the Hamiltonian
(the ADM mass) and the horizon surface area, separately, as observable
parameters. The horizon area simulates the number of particles in statistical
mechanics since its spectrum is assumed to be discrete and equally spaced. We
obtain a logarithmic correction to the Bekenstein-Hawking entropy and a
Gaussian type distribution for the energy levels.
| [
{
"created": "Wed, 21 Jul 1999 07:38:33 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Oct 1999 09:36:39 GMT",
"version": "v2"
}
] | 2009-12-30 | [
[
"Gour",
"Gilad",
""
]
] | For long black holes have been considered as endowed with a definite temperature. Yet when the Schwarzschild black hole is treated as a canonical ensemble three problems arise: incompatibility with the Hawking radiation, divergence of the partition function, and a formally negative mean-square fluctuation of the energy. We solve all three problems by considering the Schwarzschild black hole as a grand canonical ensemble, with the Hamiltonian (the ADM mass) and the horizon surface area, separately, as observable parameters. The horizon area simulates the number of particles in statistical mechanics since its spectrum is assumed to be discrete and equally spaced. We obtain a logarithmic correction to the Bekenstein-Hawking entropy and a Gaussian type distribution for the energy levels. |
1901.05592 | Carolina Benone | Carolina L. Benone and Lu\'is C. B. Crispino | Massive and charged scalar field in Kerr-Newman spacetime: Absorption
and superradiance | 8 pages, 7 figures | null | 10.1103/PhysRevD.99.044009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the propagation of a generic scalar field around a rotating and
charged black hole. Using the partial wave method, we find, numerically, the
total and partial absorption cross sections for different incidence angles. We
investigate the low- and high-frequency limits, finding semi-analytical
approximations for the absorption cross section, which we compare with our
numerical results. Finally, we consider the superradiant regime, showing that,
for charged fields, planar waves can be superradiantly scattered.
| [
{
"created": "Thu, 17 Jan 2019 02:35:14 GMT",
"version": "v1"
}
] | 2019-02-27 | [
[
"Benone",
"Carolina L.",
""
],
[
"Crispino",
"Luís C. B.",
""
]
] | We consider the propagation of a generic scalar field around a rotating and charged black hole. Using the partial wave method, we find, numerically, the total and partial absorption cross sections for different incidence angles. We investigate the low- and high-frequency limits, finding semi-analytical approximations for the absorption cross section, which we compare with our numerical results. Finally, we consider the superradiant regime, showing that, for charged fields, planar waves can be superradiantly scattered. |
1305.1723 | Semyon Dyatlov | Semyon Dyatlov | Asymptotics of linear waves and resonances with applications to black
holes | 45 pages, 4 figures | null | 10.1007/s00220-014-2255-y | null | gr-qc math.AP math.SP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We apply the results of arXiv:1301.5633 to describe asymptotic behavior of
linear waves on stationary Lorentzian metrics with r-normally hyperbolic
trapped sets, in particular Kerr and Kerr-de Sitter metrics with |a|<M and
M\Lambda a << 1. We prove that if the initial data is localized at frequencies
\lambda >> 1, then the energy norm of the solution is bounded by
O(\lambda^{1/2} exp(-(\nu_min - \epsilon)t/2) + \lambda^(-\infty)), for t < C
log\lambda, where \nu_min is a natural dynamical quantity. The key tool is a
microlocal projector splitting the solution into a component with controlled
rate of exponential decay and an O(\lambda exp(-(\nu_min -\epsilon)t) +
\lambda^(-\infty)) remainder; this splitting can be viewed as an analog of
resonance expansion. Moreover, for the Kerr-de Sitter case we study
quasi-normal modes; under a dynamical pinching condition, a Weyl law in a band
holds.
| [
{
"created": "Wed, 8 May 2013 06:17:39 GMT",
"version": "v1"
}
] | 2015-02-02 | [
[
"Dyatlov",
"Semyon",
""
]
] | We apply the results of arXiv:1301.5633 to describe asymptotic behavior of linear waves on stationary Lorentzian metrics with r-normally hyperbolic trapped sets, in particular Kerr and Kerr-de Sitter metrics with |a|<M and M\Lambda a << 1. We prove that if the initial data is localized at frequencies \lambda >> 1, then the energy norm of the solution is bounded by O(\lambda^{1/2} exp(-(\nu_min - \epsilon)t/2) + \lambda^(-\infty)), for t < C log\lambda, where \nu_min is a natural dynamical quantity. The key tool is a microlocal projector splitting the solution into a component with controlled rate of exponential decay and an O(\lambda exp(-(\nu_min -\epsilon)t) + \lambda^(-\infty)) remainder; this splitting can be viewed as an analog of resonance expansion. Moreover, for the Kerr-de Sitter case we study quasi-normal modes; under a dynamical pinching condition, a Weyl law in a band holds. |
1012.3083 | Thomas Buchert | Thomas Buchert, Nathaniel Obadia and Xavier Roy | Effective Inhomogeneous Cosmologies and Emerging Scalar Fields | 4 pages, 4 figures, contribution to the Workshop: New Directions in
Modern Cosmology, Leiden, The Netherlands, 27.9.-1.10. (2010) | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this contribution we summarize two recent applications of a correspondence
between backreaction terms in averaged inhomogeneous cosmologies and an
effective scalar field (the `morphon'). Backreaction terms that add to the
standard sources of Friedmannian kinematical laws and that emerge from
geometrical curvature invariants built from inhomogeneities, can be interpreted
in terms of a minimally coupled scalar field in the case of a dust matter
source. We consider closure conditions of the averaged equations that lead to
different evolution scenarii: a) the standard Chaplygin equation of state
imposed as an effective relation between kinematical fluctuations and intrinsic
curvature of space sections, and b) an inflationary scenario that emerges out
of inhomogeneities of the Einstein vacuum, where averaged curvature
inhomogeneities model the potential of an effective classical inflaton.
| [
{
"created": "Tue, 14 Dec 2010 16:26:59 GMT",
"version": "v1"
}
] | 2010-12-15 | [
[
"Buchert",
"Thomas",
""
],
[
"Obadia",
"Nathaniel",
""
],
[
"Roy",
"Xavier",
""
]
] | In this contribution we summarize two recent applications of a correspondence between backreaction terms in averaged inhomogeneous cosmologies and an effective scalar field (the `morphon'). Backreaction terms that add to the standard sources of Friedmannian kinematical laws and that emerge from geometrical curvature invariants built from inhomogeneities, can be interpreted in terms of a minimally coupled scalar field in the case of a dust matter source. We consider closure conditions of the averaged equations that lead to different evolution scenarii: a) the standard Chaplygin equation of state imposed as an effective relation between kinematical fluctuations and intrinsic curvature of space sections, and b) an inflationary scenario that emerges out of inhomogeneities of the Einstein vacuum, where averaged curvature inhomogeneities model the potential of an effective classical inflaton. |
gr-qc/0107021 | Alessandra Buonanno | Alessandra Buonanno and Yanbei Chen | Signal recycled laser-interferometer gravitational-wave detectors as
optical springs | 42 pages, 13 figures | Phys.Rev. D65 (2002) 042001 | 10.1103/PhysRevD.65.042001 | GRP/00/555 | gr-qc | null | Using the force-susceptibility formalism of linear quantum measurements, we
study the dynamics of signal recycled interferometers, such as LIGO-II. We show
that, although the antisymmetric mode of motion of the four arm-cavity mirrors
is originally described by a free mass, when the signal-recycling mirror is
added to the interferometer, the radiation-pressure force not only disturbs the
motion of that ``free mass'' randomly due to quantum fluctuations, but also and
more fundamentally, makes it respond to forces as though it were connected to a
spring with a specific optical-mechanical rigidity. This oscillatory response
gives rise to a much richer dynamics than previously known for SR
interferometers, which enhances the possibilities for reshaping the noise
curves and, if thermal noise can be pushed low enough, enables the standard
quantum limit to be beaten. We also show the possibility of using servo systems
to suppress the instability associated with the optical-mechanical interaction
without compromising the sensitivity of the interferometer.
| [
{
"created": "Thu, 5 Jul 2001 19:15:14 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Buonanno",
"Alessandra",
""
],
[
"Chen",
"Yanbei",
""
]
] | Using the force-susceptibility formalism of linear quantum measurements, we study the dynamics of signal recycled interferometers, such as LIGO-II. We show that, although the antisymmetric mode of motion of the four arm-cavity mirrors is originally described by a free mass, when the signal-recycling mirror is added to the interferometer, the radiation-pressure force not only disturbs the motion of that ``free mass'' randomly due to quantum fluctuations, but also and more fundamentally, makes it respond to forces as though it were connected to a spring with a specific optical-mechanical rigidity. This oscillatory response gives rise to a much richer dynamics than previously known for SR interferometers, which enhances the possibilities for reshaping the noise curves and, if thermal noise can be pushed low enough, enables the standard quantum limit to be beaten. We also show the possibility of using servo systems to suppress the instability associated with the optical-mechanical interaction without compromising the sensitivity of the interferometer. |
2108.09051 | Minyong Guo | Haopeng Yan, Zezhou Hu, Minyong Guo and Bin Chen | Photon emissions from near-horizon extremal and near-extremal Kerr
equatorial emitters | Slight change in title, matched the published version in PRD | null | 10.1103/PhysRevD.104.124005 | null | gr-qc | http://creativecommons.org/publicdomain/zero/1.0/ | We consider isotropic and monochromatic photon emissions from equatorial
emitters moving along future-directed timelike geodesics in the near-horizon
extremal Kerr (NHEK) and near-horizon near-extremal Kerr (near-NHEK) regions,
to asymptotic infinity. We obtain numerical results for the photon escaping
probability (PEP) and derive analytical expressions for the maximum observable
blueshift (MOB) of the escaping photons, both depending on the emission radius
and the emitter's proper motion. In particular, we find that for all
anti-plunging or deflecting emitters that can eventually reach to asymptotic
infinity, the PEP is greater than $50\%$ while for all plunging emitters the
PEP is less than $55\%$, and for the bounded emitters in the (near-)NHEK
region, the PEP is always less than $59\%$. In addition, for the emitters on
unstable circular orbits in the near-NHEK region, the PEP decreases from $55\%$
to $50\%$ as the orbital radius decreases from the one of the innermost stable
circular orbit to the one of the horizon. Furthermore, we show how the
orientation of the emitter's motion along the radial or azimuthal direction
affects the PEP and the MOB of the emitted photons.
| [
{
"created": "Fri, 20 Aug 2021 08:27:45 GMT",
"version": "v1"
},
{
"created": "Sat, 4 Dec 2021 08:43:10 GMT",
"version": "v2"
}
] | 2021-12-07 | [
[
"Yan",
"Haopeng",
""
],
[
"Hu",
"Zezhou",
""
],
[
"Guo",
"Minyong",
""
],
[
"Chen",
"Bin",
""
]
] | We consider isotropic and monochromatic photon emissions from equatorial emitters moving along future-directed timelike geodesics in the near-horizon extremal Kerr (NHEK) and near-horizon near-extremal Kerr (near-NHEK) regions, to asymptotic infinity. We obtain numerical results for the photon escaping probability (PEP) and derive analytical expressions for the maximum observable blueshift (MOB) of the escaping photons, both depending on the emission radius and the emitter's proper motion. In particular, we find that for all anti-plunging or deflecting emitters that can eventually reach to asymptotic infinity, the PEP is greater than $50\%$ while for all plunging emitters the PEP is less than $55\%$, and for the bounded emitters in the (near-)NHEK region, the PEP is always less than $59\%$. In addition, for the emitters on unstable circular orbits in the near-NHEK region, the PEP decreases from $55\%$ to $50\%$ as the orbital radius decreases from the one of the innermost stable circular orbit to the one of the horizon. Furthermore, we show how the orientation of the emitter's motion along the radial or azimuthal direction affects the PEP and the MOB of the emitted photons. |
gr-qc/9307033 | Centro De Estudios Cientificos De Santia | Maximo Banados, Claudio Teitelboim and Jorge Zanelli | Dimensionally Continued Black Holes | RevTex (3.0), 33 pages | Phys.Rev. D49 (1994) 975-986 | 10.1103/PhysRevD.49.975 | null | gr-qc | null | Static, spherically symmetric solutions of the field equations for a
particular dimensional continuation of general relativity with negative
cosmological constant are studied. The action is, in odd dimensions, the
Chern-Simons form for the anti-de Sitter group and, in even dimensions, the
Euler density constructed with the Lorentz part of the anti-de Sitter curvature
tensor. Both actions are special cases of the Lovelock action, and they reduce
to the Hilbert action (with negative cosmological constant) in the lower
dimensional cases $\mbox{$\cal D$}=3$ and $\mbox{$\cal D$}=4$. Exact black hole
solutions characterized by mass ($M$) and electric charge ($Q$) are found. In
odd dimensions a negative cosmological constant is necessary to obtain a black
hole, while in even dimensions, both asymptotically flat and asymptotically
anti-de Sitter black holes exist. The causal structure is analyzed and the
Penrose diagrams are exhibited.
| [
{
"created": "Fri, 23 Jul 1993 02:22:50 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Sep 1993 02:57:32 GMT",
"version": "v2"
}
] | 2009-10-22 | [
[
"Banados",
"Maximo",
""
],
[
"Teitelboim",
"Claudio",
""
],
[
"Zanelli",
"Jorge",
""
]
] | Static, spherically symmetric solutions of the field equations for a particular dimensional continuation of general relativity with negative cosmological constant are studied. The action is, in odd dimensions, the Chern-Simons form for the anti-de Sitter group and, in even dimensions, the Euler density constructed with the Lorentz part of the anti-de Sitter curvature tensor. Both actions are special cases of the Lovelock action, and they reduce to the Hilbert action (with negative cosmological constant) in the lower dimensional cases $\mbox{$\cal D$}=3$ and $\mbox{$\cal D$}=4$. Exact black hole solutions characterized by mass ($M$) and electric charge ($Q$) are found. In odd dimensions a negative cosmological constant is necessary to obtain a black hole, while in even dimensions, both asymptotically flat and asymptotically anti-de Sitter black holes exist. The causal structure is analyzed and the Penrose diagrams are exhibited. |
gr-qc/9806097 | Robert M. Wald | Robert M. Wald | Gravitational Lensing in Inhomogeneous Universes | 9 pages, latex 2e. To appear in proceedings of XLIXth Yamada
Conference on Black Holes and High Energy Astrophysics | null | null | null | gr-qc | null | I describe a new approach (developed in collaboration with D.E. Holz) to
calculating the statistical distributions for magnification, shear, and
rotation of images of cosmological sources due to gravitational lensing by mass
inhomogeneities on galactic and smaller scales. Our approach is somewhat
similar to that used in ``Swiss cheese'' models, but the ``cheese'' has been
completely eliminated, the matter distribution in the ``voids'' need not be
spherically symmetric, the total mass in each void need equal the corresponding
Robertson-Walker mass only on average, and we do not impose an ``opaque
radius'' cutoff. In our approach, we integrate the geodesic deviation equation
backwards in time until the desired redshift is reached, using a Monte Carlo
procedure wherein each photon beam in effect ``creates its own universe'' as it
propagates. Our approach fully takes into account effects of multiple
encounters with gravitational lenses and is much easier to apply than ``ray
shooting'' methods.
| [
{
"created": "Wed, 24 Jun 1998 23:35:34 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Wald",
"Robert M.",
""
]
] | I describe a new approach (developed in collaboration with D.E. Holz) to calculating the statistical distributions for magnification, shear, and rotation of images of cosmological sources due to gravitational lensing by mass inhomogeneities on galactic and smaller scales. Our approach is somewhat similar to that used in ``Swiss cheese'' models, but the ``cheese'' has been completely eliminated, the matter distribution in the ``voids'' need not be spherically symmetric, the total mass in each void need equal the corresponding Robertson-Walker mass only on average, and we do not impose an ``opaque radius'' cutoff. In our approach, we integrate the geodesic deviation equation backwards in time until the desired redshift is reached, using a Monte Carlo procedure wherein each photon beam in effect ``creates its own universe'' as it propagates. Our approach fully takes into account effects of multiple encounters with gravitational lenses and is much easier to apply than ``ray shooting'' methods. |
2210.17379 | Konstantin Osetrin | Konstantin Osetrin and Altair Filippov and Ilya Kirnos and Evgeny
Osetrin | Type I Shapovalov wave spacetimes in the Brans-Dicke scalar-tensor
theory of gravity | 12 pages | Symmetry, 2022, 14(12), 2636 | 10.3390/sym14122636 | null | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by-nc-nd/4.0/ | Exact solutions for Shapovalov wave spacetimes of type I in the scalar-tensor
theory of gravity of Brans-Dicke are constructed. Shapovalov's wave spacetimes
describe gravitational-wave models that allow the separation of wave variables
in privileged coordinate systems. In contrast to the general theory of
relativity, the vacuum field equations of the Brans-Dicke scalar-tensor theory
of gravity lead to exact solutions for type I Shapovalov spaces, which makes it
possible to construct observational checks for detecting such wave
disturbances. For the models under consideration, equations for the
trajectories of test particles are obtained.
| [
{
"created": "Mon, 31 Oct 2022 15:04:23 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Nov 2022 05:16:57 GMT",
"version": "v2"
}
] | 2022-12-20 | [
[
"Osetrin",
"Konstantin",
""
],
[
"Filippov",
"Altair",
""
],
[
"Kirnos",
"Ilya",
""
],
[
"Osetrin",
"Evgeny",
""
]
] | Exact solutions for Shapovalov wave spacetimes of type I in the scalar-tensor theory of gravity of Brans-Dicke are constructed. Shapovalov's wave spacetimes describe gravitational-wave models that allow the separation of wave variables in privileged coordinate systems. In contrast to the general theory of relativity, the vacuum field equations of the Brans-Dicke scalar-tensor theory of gravity lead to exact solutions for type I Shapovalov spaces, which makes it possible to construct observational checks for detecting such wave disturbances. For the models under consideration, equations for the trajectories of test particles are obtained. |
2208.07752 | Jan Sbierski | Jan Sbierski | Uniqueness and non-uniqueness results for spacetime extensions | 36 pages | null | null | null | gr-qc math-ph math.CA math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Given a function $f : A \to \mathbb{R}^n$ of a certain regularity defined on
some open subset $A \subseteq \mathbb{R}^m$, it is a classical problem of
analysis to investigate whether the function can be extended to all of
$\mathbb{R}^m$ in a certain regularity class. If an extension exists and is
continuous, then certainly it is uniquely determined on the closure of $A$. A
similar problem arises in general relativity for Lorentzian manifolds instead
of functions on $\mathbb{R}^m$. It is well-known, however, that even if the
extension of a Lorentzian manifold $(M,g)$ is analytic, various choices are in
general possible at the boundary. This paper establishes a uniqueness condition
for extensions of globally hyperbolic Lorentzian manifolds $(M,g)$ with a focus
on low regularities: any two extensions which are anchored by an inextendible
causal curve $\gamma : [-1,0) \to M$ in the sense that $\gamma$ has limit
points in both extensions, must agree locally around those limit points on the
boundary as long as the extensions are at least locally Lipschitz continuous.
We also show that this is sharp: anchored extensions which are only H\"older
continuous do in general not enjoy this local uniqueness result.
| [
{
"created": "Tue, 16 Aug 2022 13:49:34 GMT",
"version": "v1"
}
] | 2022-08-17 | [
[
"Sbierski",
"Jan",
""
]
] | Given a function $f : A \to \mathbb{R}^n$ of a certain regularity defined on some open subset $A \subseteq \mathbb{R}^m$, it is a classical problem of analysis to investigate whether the function can be extended to all of $\mathbb{R}^m$ in a certain regularity class. If an extension exists and is continuous, then certainly it is uniquely determined on the closure of $A$. A similar problem arises in general relativity for Lorentzian manifolds instead of functions on $\mathbb{R}^m$. It is well-known, however, that even if the extension of a Lorentzian manifold $(M,g)$ is analytic, various choices are in general possible at the boundary. This paper establishes a uniqueness condition for extensions of globally hyperbolic Lorentzian manifolds $(M,g)$ with a focus on low regularities: any two extensions which are anchored by an inextendible causal curve $\gamma : [-1,0) \to M$ in the sense that $\gamma$ has limit points in both extensions, must agree locally around those limit points on the boundary as long as the extensions are at least locally Lipschitz continuous. We also show that this is sharp: anchored extensions which are only H\"older continuous do in general not enjoy this local uniqueness result. |
1102.1452 | Stefano Finazzi | Stefano Finazzi and Renaud Parentani | On the robustness of acoustic black hole spectra | 4 pages, 2 figure, jpconf.cls; to appear in the proceedings of the
Spanish Relativity Meeting ERE2010 | J.Phys.Conf.Ser.314:012030,2011 | 10.1088/1742-6596/314/1/012030 | null | gr-qc cond-mat.other | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the robustness of the spectrum emitted by an acoustic black hole by
considering series of stationary flows that become either subsonic or
supersonic, i.e. when the horizon disappears. We work with the superluminal
Bogoliubov dispersion of Bose--Einstein condensates. We find that the spectrum
remains remarkably Planckian until the horizon disappears. When the flow is
everywhere supersonic, new pair creation channels open. This will be the
subject of a forthcoming work.
| [
{
"created": "Mon, 7 Feb 2011 22:03:19 GMT",
"version": "v1"
}
] | 2015-03-18 | [
[
"Finazzi",
"Stefano",
""
],
[
"Parentani",
"Renaud",
""
]
] | We study the robustness of the spectrum emitted by an acoustic black hole by considering series of stationary flows that become either subsonic or supersonic, i.e. when the horizon disappears. We work with the superluminal Bogoliubov dispersion of Bose--Einstein condensates. We find that the spectrum remains remarkably Planckian until the horizon disappears. When the flow is everywhere supersonic, new pair creation channels open. This will be the subject of a forthcoming work. |
gr-qc/0506123 | Allemandi Gianluca | Gianluca Allemandi, Mauro Francaviglia, Matteo Luca Ruggiero, Angelo
Tartaglia | Post-Newtonian Parameters from Alternative Theories of Gravity | 17 pages, no figures | Gen.Rel.Grav.37:1891-1904,2005 | 10.1007/s10714-005-0195-8 | null | gr-qc | null | Alternative theories of gravity have been recently studied in connection with
their cosmological applications, both in the Palatini and in the metric
formalism. The aim of this paper is to propose a theoretical framework (in the
Palatini formalism) to test these theories at the solar system level and
possibly at the galactic scales. We exactly solve field equations in vacuum and
find the corresponding corrections to the standard general relativistic
gravitational field. On the other hand, approximate solutions are found in
matter cases starting from a Lagrangian which depends on a phenomenological
parameter. Both in the vacuum case and in the matter case the deviations from
General Relativity are controlled by parameters that provide the Post-Newtonian
corrections which prove to be in good agreement with solar system experiments.
| [
{
"created": "Mon, 27 Jun 2005 07:52:31 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Allemandi",
"Gianluca",
""
],
[
"Francaviglia",
"Mauro",
""
],
[
"Ruggiero",
"Matteo Luca",
""
],
[
"Tartaglia",
"Angelo",
""
]
] | Alternative theories of gravity have been recently studied in connection with their cosmological applications, both in the Palatini and in the metric formalism. The aim of this paper is to propose a theoretical framework (in the Palatini formalism) to test these theories at the solar system level and possibly at the galactic scales. We exactly solve field equations in vacuum and find the corresponding corrections to the standard general relativistic gravitational field. On the other hand, approximate solutions are found in matter cases starting from a Lagrangian which depends on a phenomenological parameter. Both in the vacuum case and in the matter case the deviations from General Relativity are controlled by parameters that provide the Post-Newtonian corrections which prove to be in good agreement with solar system experiments. |
gr-qc/0012109 | Vladimir Kassandrov | Vladimir V. Kassandrov, Joseph A. Rizcallah | Twistor and "weak" gauge structures in the framework of quaternionic
analysis | 20 pages, 2 figures | null | null | null | gr-qc hep-th math-ph math.MP | null | The earlier proposed conditions of (bi)quaternionic differentiability are
nonlinear, give rize to the 2-spinor and the self-dual gauge structures and may
be considered as the it generating system of equations (GSE) with respect to
the source-free Maxwell, Yang-Mills and eikonal equations. We present the
general solution of the GSE in terms of twistor variables, analize its rather
specific gauge symmetry and demonstrate the relation of GSE to the equations of
shear-free null congruences and, consequently, - to effective metrics of Kerr-
Shild type. The concept of particles as singularities of physical fields
associated with the solutions of GSE is developed
| [
{
"created": "Fri, 29 Dec 2000 15:35:26 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Kassandrov",
"Vladimir V.",
""
],
[
"Rizcallah",
"Joseph A.",
""
]
] | The earlier proposed conditions of (bi)quaternionic differentiability are nonlinear, give rize to the 2-spinor and the self-dual gauge structures and may be considered as the it generating system of equations (GSE) with respect to the source-free Maxwell, Yang-Mills and eikonal equations. We present the general solution of the GSE in terms of twistor variables, analize its rather specific gauge symmetry and demonstrate the relation of GSE to the equations of shear-free null congruences and, consequently, - to effective metrics of Kerr- Shild type. The concept of particles as singularities of physical fields associated with the solutions of GSE is developed |
1409.4117 | Edward Anderson | Edward Anderson | Problem of Time and Background Independence: the Individual Facets | 40 pages including 13 Figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I lay out the problem of time facets as arising piecemeal from a number of
aspects of background independence. Almost all of these already have simpler
classical counterparts. This approach can be viewed as a facet by facet
completion of the observation that Barbour-type relationalism is a background
independent precursor to 2 of the 9 facets. That completion proceeds in an
order dictated by the additional layers of mathematical structure required to
support each. Moreover, the `nonlinear nature' of the interactions between the
Problem of Time facets renders a joint study of them mandatory. The current
article is none the less a useful prequel via gaining a conceptual
understanding of each facet, prior to embarking on rendering some combinations
of facets consistent and what further obstructions arise in attempting such
joint considerations. See [20, 21, 26] for up to date studies of this more
complicated joint version. I also identify new facets (threading based),
subfacets (of observables and of reconstructions) and further source of variety
from how far down the levels of mathematical structure these facets extend.
| [
{
"created": "Sun, 14 Sep 2014 23:23:05 GMT",
"version": "v1"
}
] | 2014-09-16 | [
[
"Anderson",
"Edward",
""
]
] | I lay out the problem of time facets as arising piecemeal from a number of aspects of background independence. Almost all of these already have simpler classical counterparts. This approach can be viewed as a facet by facet completion of the observation that Barbour-type relationalism is a background independent precursor to 2 of the 9 facets. That completion proceeds in an order dictated by the additional layers of mathematical structure required to support each. Moreover, the `nonlinear nature' of the interactions between the Problem of Time facets renders a joint study of them mandatory. The current article is none the less a useful prequel via gaining a conceptual understanding of each facet, prior to embarking on rendering some combinations of facets consistent and what further obstructions arise in attempting such joint considerations. See [20, 21, 26] for up to date studies of this more complicated joint version. I also identify new facets (threading based), subfacets (of observables and of reconstructions) and further source of variety from how far down the levels of mathematical structure these facets extend. |
gr-qc/0210006 | Dumitru Vulcanov | D.N. Vulcanov (Max-Planck-Institut fur Gravitationsphysik,
Albert-Einstein-Institut, Golm, Germany) | Doing numerical cosmology with the Cactus code | 18 pages, 8 figures, Latex | null | null | null | gr-qc astro-ph physics.comp-ph | null | The article presents some aspects concerning the construction of a new thorn
for the Cactus code, a complete 3-dimensional machinery for numerical
relativity. This thorn is completely dedicated to numerical simulations in
cosmology, that means it can provide evolutions of different cosmological
models, mainly based on Friedman-Robertson-Walker metric. Some numerical
results are presented, testing the convergence, stability and the applicability
of the code.
| [
{
"created": "Wed, 2 Oct 2002 14:42:03 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Vulcanov",
"D. N.",
"",
"Max-Planck-Institut fur Gravitationsphysik,\n Albert-Einstein-Institut, Golm, Germany"
]
] | The article presents some aspects concerning the construction of a new thorn for the Cactus code, a complete 3-dimensional machinery for numerical relativity. This thorn is completely dedicated to numerical simulations in cosmology, that means it can provide evolutions of different cosmological models, mainly based on Friedman-Robertson-Walker metric. Some numerical results are presented, testing the convergence, stability and the applicability of the code. |
1405.2611 | Yen-Kheng Lim | Yen-Kheng Lim | Geodesic motion in the vacuum C-metric | 24 pages, 10 figures | Phys. Rev. D 89, 104016 (2014) | 10.1103/PhysRevD.89.104016 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Geodesic equations of the vacuum C-metric are derived and solved for various
cases. The solutions describe the motion of timelike or null particles with
conserved energy and angular momentum. Polar, nearly-circular orbits around
weakly accelerated black holes may be regarded as a perturbation of circular
Schwarzschild geodesics. Results indicate that circular Schwarzschild geodesics
of radius $r_0>6m$ are stable under small uniform accelerations along the
orbital plane. These stable orbits undergo small oscillations around $r_0$,
behaving like a harmonic oscillator driven by a periodic force plus another
constant force. Circular orbits with axis parallel to the direction of black
hole acceleration are also considered. In this case an algebraic relation
expressing the condition of stability is obtained. This refines the stability
analysis done in previous literature. We also present an analysis of radial
geodesics along the poles. There exist a solution where a particle remains at
unstable equilibrium at a fixed distance directly behind the accelerating black
hole. Examples of numerical solutions are presented for other more general
cases.
| [
{
"created": "Mon, 12 May 2014 01:41:59 GMT",
"version": "v1"
}
] | 2014-05-13 | [
[
"Lim",
"Yen-Kheng",
""
]
] | Geodesic equations of the vacuum C-metric are derived and solved for various cases. The solutions describe the motion of timelike or null particles with conserved energy and angular momentum. Polar, nearly-circular orbits around weakly accelerated black holes may be regarded as a perturbation of circular Schwarzschild geodesics. Results indicate that circular Schwarzschild geodesics of radius $r_0>6m$ are stable under small uniform accelerations along the orbital plane. These stable orbits undergo small oscillations around $r_0$, behaving like a harmonic oscillator driven by a periodic force plus another constant force. Circular orbits with axis parallel to the direction of black hole acceleration are also considered. In this case an algebraic relation expressing the condition of stability is obtained. This refines the stability analysis done in previous literature. We also present an analysis of radial geodesics along the poles. There exist a solution where a particle remains at unstable equilibrium at a fixed distance directly behind the accelerating black hole. Examples of numerical solutions are presented for other more general cases. |
1010.1664 | Kentaro Tanabe | Kentaro Tanabe, Norihiro Tanahashi, Tetsuya Shiromizu | Angular momentum at null infinity in five dimensions | 15 pages, published version in JMP | J.Math.Phys.52:032501,2011 | 10.1063/1.3559917 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, using the Bondi coordinates, we discuss the angular momentum
at null infinity in five dimensions and address the Poincare covariance of the
Bondi mass and angular momentum. We also show the angular momentum loss/gain
law due to gravitational waves. In four dimensions, the angular momentum at
null infinity has the supertranslational ambiguity and then it is known that we
cannot construct well-defined angular momentum there. On the other hand, we
would stress that we can define angular momentum at null infinity without any
ambiguity in higher dimensions. This is because of the non-existence of
supertranslations in higher dimensions.
| [
{
"created": "Fri, 8 Oct 2010 11:31:07 GMT",
"version": "v1"
},
{
"created": "Sun, 6 Mar 2011 14:45:24 GMT",
"version": "v2"
}
] | 2011-03-08 | [
[
"Tanabe",
"Kentaro",
""
],
[
"Tanahashi",
"Norihiro",
""
],
[
"Shiromizu",
"Tetsuya",
""
]
] | In this paper, using the Bondi coordinates, we discuss the angular momentum at null infinity in five dimensions and address the Poincare covariance of the Bondi mass and angular momentum. We also show the angular momentum loss/gain law due to gravitational waves. In four dimensions, the angular momentum at null infinity has the supertranslational ambiguity and then it is known that we cannot construct well-defined angular momentum there. On the other hand, we would stress that we can define angular momentum at null infinity without any ambiguity in higher dimensions. This is because of the non-existence of supertranslations in higher dimensions. |
gr-qc/0405139 | Ettore Minguzzi | E. Minguzzi | A globally well-behaved simultaneity connection for stationary frames in
the weak field limit | 19 pages, Revtex4. Some misprints removed. Final version | Class.Quant.Grav. 21 (2004) 4123-4146 | 10.1088/0264-9381/21/17/007 | null | gr-qc | null | Local simultaneity conventions are mathematically represented by connections
on the bundle of timelike curves that defines the frame. Those simultaneity
conventions having an holonomy proportional to the Riemann tensor have a
special interest since they exhibit a good global behavior in the weak field
limit. By requiring that the simultaneity convention depends on the the
acceleration, vorticity vector and the angle between them we are able to
restrict considerably the allowed simultaneity conventions. In particular, we
focus our study on the simplest among the allowed conventions. It should be
preferred over Einstein's in flat spacetime and in general if the tidal force
between neighboring particles is weaker than the centrifugal force. It reduces
to the Einstein convention if the vectorial product between the acceleration
and the vorticity vector vanishes. We finally show how to use this convention
in practice.
| [
{
"created": "Fri, 28 May 2004 15:47:07 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Aug 2004 14:15:09 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Minguzzi",
"E.",
""
]
] | Local simultaneity conventions are mathematically represented by connections on the bundle of timelike curves that defines the frame. Those simultaneity conventions having an holonomy proportional to the Riemann tensor have a special interest since they exhibit a good global behavior in the weak field limit. By requiring that the simultaneity convention depends on the the acceleration, vorticity vector and the angle between them we are able to restrict considerably the allowed simultaneity conventions. In particular, we focus our study on the simplest among the allowed conventions. It should be preferred over Einstein's in flat spacetime and in general if the tidal force between neighboring particles is weaker than the centrifugal force. It reduces to the Einstein convention if the vectorial product between the acceleration and the vorticity vector vanishes. We finally show how to use this convention in practice. |
1003.0476 | Barry Wardell | Barry Wardell and Adrian C. Ottewill | A Transport Equation Approach to Green Functions and Self-force
Calculations | 3 pages, 1 figure; to appear in the proceedings of the 12th Marcel
Grossmann meeting on general relativity | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a recent work, we presented the first application of the
Poisson-Wiseman-Anderson method of `matched expansions' to compute the
self-force acting on a point particle moving in a curved spacetime. The method
employs two expansions for the Green function which are respectively valid in
the `quasilocal' and `distant past' regimes, and which may be matched together
within the normal neighbourhood. In this article, we introduce the method of
matched expansions and discuss transport equation methods for the calculation
of the Green function in the quasilocal region. These methods allow the Green
function to be evaluated throughout the normal neighborhood and are also
relevant to a broad range of problems from radiation reaction to quantum field
theory in curved spacetime and quantum gravity.
| [
{
"created": "Mon, 1 Mar 2010 23:06:09 GMT",
"version": "v1"
}
] | 2010-03-03 | [
[
"Wardell",
"Barry",
""
],
[
"Ottewill",
"Adrian C.",
""
]
] | In a recent work, we presented the first application of the Poisson-Wiseman-Anderson method of `matched expansions' to compute the self-force acting on a point particle moving in a curved spacetime. The method employs two expansions for the Green function which are respectively valid in the `quasilocal' and `distant past' regimes, and which may be matched together within the normal neighbourhood. In this article, we introduce the method of matched expansions and discuss transport equation methods for the calculation of the Green function in the quasilocal region. These methods allow the Green function to be evaluated throughout the normal neighborhood and are also relevant to a broad range of problems from radiation reaction to quantum field theory in curved spacetime and quantum gravity. |
2203.03449 | Connor McIsaac | Connor McIsaac, Ian Harry | Using machine learning to auto-tune chi-squared tests for gravitational
wave searches | 10 pages, 5 figures. Supplementary data:
https://icg-gravwaves.github.io/chisqnet/ . Version accepted for publication
in PRD. Various updates made during review process. Typos corrected | Phys. Rev. D 105, 104056 (2022) | 10.1103/PhysRevD.105.104056 | LIGO-P2100244 | gr-qc astro-ph.HE astro-ph.IM | http://creativecommons.org/licenses/by/4.0/ | The sensitivity of gravitational wave searches is reduced by the presence of
non-Gaussian noise in the detector data. These non-Gaussianities often match
well with the template waveforms used in matched filter searches, and require
signal-consistency tests to distinguish them from astrophysical signals.
However, empirically tuning these tests for maximum efficacy is time consuming
and limits the complexity of these tests. In this work we demonstrate a
framework to use machine-learning techniques to automatically tune
signal-consistency tests. We implement a new $\chi^2$ signal-consistency test
targeting the large population of noise found in searches for intermediate mass
black hole binaries, training the new test using the framework set out in this
paper. We find that this method effectively trains a complex model to
down-weight the noise, while leaving the signal population relatively
unaffected. This improves the sensitivity of the search by $\sim 11\%$ for
signals with masses $> 300 M_\odot$. In the future this framework could be used
to implement new tests in any of the commonly used matched-filter search
algorithms, further improving the sensitivity of our searches.
| [
{
"created": "Mon, 7 Mar 2022 15:07:54 GMT",
"version": "v1"
},
{
"created": "Wed, 25 May 2022 14:30:30 GMT",
"version": "v2"
}
] | 2022-05-26 | [
[
"McIsaac",
"Connor",
""
],
[
"Harry",
"Ian",
""
]
] | The sensitivity of gravitational wave searches is reduced by the presence of non-Gaussian noise in the detector data. These non-Gaussianities often match well with the template waveforms used in matched filter searches, and require signal-consistency tests to distinguish them from astrophysical signals. However, empirically tuning these tests for maximum efficacy is time consuming and limits the complexity of these tests. In this work we demonstrate a framework to use machine-learning techniques to automatically tune signal-consistency tests. We implement a new $\chi^2$ signal-consistency test targeting the large population of noise found in searches for intermediate mass black hole binaries, training the new test using the framework set out in this paper. We find that this method effectively trains a complex model to down-weight the noise, while leaving the signal population relatively unaffected. This improves the sensitivity of the search by $\sim 11\%$ for signals with masses $> 300 M_\odot$. In the future this framework could be used to implement new tests in any of the commonly used matched-filter search algorithms, further improving the sensitivity of our searches. |
1304.2240 | Mubasher Jamil | Mubasher Jamil, Farook Rahaman, Ratbay Myrzakulov, P.K.F. Kuhfittig,
Nasr Ahmed and Umar F Mondal | Nonommutative wormholes in $f(R)$ gravity | 9 pages, 17 figures, Accepted for publication in the Journal of
Korean Physical Society (Proceedings of 13th Italian-Korean Symposium on
Relativistic Astrophysics) | Journal of the Korean Physical Society Vol. 65 (2014) pp 917-925 | 10.3938/jkps.65.917 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper discusses several new exact solutions of static wormholes in
$f(R)$ gravity with a noncommutative-geometry background, which replaces
point-like structures by smeared objects. In the first part of the paper we
assume the power-law form $f(R)=aR^n$ and discuss several solutions
corresponding to different values of the exponent. The second part of the paper
assumes a particular form of the shape function that also yields a viable
solution. This investigation generalizes some of our previous work in $f(R)$
gravity, as well as in noncommutative geometry.
| [
{
"created": "Sat, 23 Mar 2013 09:09:18 GMT",
"version": "v1"
},
{
"created": "Thu, 8 May 2014 16:19:47 GMT",
"version": "v2"
}
] | 2014-10-21 | [
[
"Jamil",
"Mubasher",
""
],
[
"Rahaman",
"Farook",
""
],
[
"Myrzakulov",
"Ratbay",
""
],
[
"Kuhfittig",
"P. K. F.",
""
],
[
"Ahmed",
"Nasr",
""
],
[
"Mondal",
"Umar F",
""
]
] | This paper discusses several new exact solutions of static wormholes in $f(R)$ gravity with a noncommutative-geometry background, which replaces point-like structures by smeared objects. In the first part of the paper we assume the power-law form $f(R)=aR^n$ and discuss several solutions corresponding to different values of the exponent. The second part of the paper assumes a particular form of the shape function that also yields a viable solution. This investigation generalizes some of our previous work in $f(R)$ gravity, as well as in noncommutative geometry. |
gr-qc/0304073 | Shijun Yoshida | Shijun Yoshida, Umin Lee | r-modes in Relativistic Superfluid Stars | 14 pages, 4 figures. To appear in Physical Review D | Phys.Rev. D67 (2003) 124019 | 10.1103/PhysRevD.67.124019 | null | gr-qc astro-ph | null | We discuss the modal properties of the $r$-modes of relativistic superfluid
neutron stars, taking account of the entrainment effects between superfluids.
In this paper, the neutron stars are assumed to be filled with neutron and
proton superfluids and the strength of the entrainment effects between the
superfluids are represented by a single parameter $\eta$. We find that the
basic properties of the $r$-modes in a relativistic superfluid star are very
similar to those found for a Newtonian superfluid star. The $r$-modes of a
relativistic superfluid star are split into two families, ordinary fluid-like
$r$-modes ($r^o$-mode) and superfluid-like $r$-modes ($r^s$-mode). The two
superfluids counter-move for the $r^s$-modes, while they co-move for the
$r^o$-modes. For the $r^o$-modes, the quantity $\kappa\equiv\sigma/\Omega+m$ is
almost independent of the entrainment parameter $\eta$, where $m$ and $\sigma$
are the azimuthal wave number and the oscillation frequency observed by an
inertial observer at spatial infinity, respectively. For the $r^s$-modes, on
the other hand, $\kappa$ almost linearly increases with increasing $\eta$. It
is also found that the radiation driven instability due to the $r^s$-modes is
much weaker than that of the $r^o$-modes because the matter current associated
with the axial parity perturbations almost completely vanishes.
| [
{
"created": "Mon, 21 Apr 2003 15:55:47 GMT",
"version": "v1"
},
{
"created": "Mon, 5 May 2003 14:04:42 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Yoshida",
"Shijun",
""
],
[
"Lee",
"Umin",
""
]
] | We discuss the modal properties of the $r$-modes of relativistic superfluid neutron stars, taking account of the entrainment effects between superfluids. In this paper, the neutron stars are assumed to be filled with neutron and proton superfluids and the strength of the entrainment effects between the superfluids are represented by a single parameter $\eta$. We find that the basic properties of the $r$-modes in a relativistic superfluid star are very similar to those found for a Newtonian superfluid star. The $r$-modes of a relativistic superfluid star are split into two families, ordinary fluid-like $r$-modes ($r^o$-mode) and superfluid-like $r$-modes ($r^s$-mode). The two superfluids counter-move for the $r^s$-modes, while they co-move for the $r^o$-modes. For the $r^o$-modes, the quantity $\kappa\equiv\sigma/\Omega+m$ is almost independent of the entrainment parameter $\eta$, where $m$ and $\sigma$ are the azimuthal wave number and the oscillation frequency observed by an inertial observer at spatial infinity, respectively. For the $r^s$-modes, on the other hand, $\kappa$ almost linearly increases with increasing $\eta$. It is also found that the radiation driven instability due to the $r^s$-modes is much weaker than that of the $r^o$-modes because the matter current associated with the axial parity perturbations almost completely vanishes. |
1802.04665 | Mohammad Reza Setare | M. R. Setare and H. Adami | Near Horizon Symmetry and Entropy Formula for Kerr-Newman (A)dS Black
Holes | 16 pages. Version published in JHEP | JHEP 04 (2018) 133 | 10.1007/JHEP04(2018)133 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we provide the first non-trivial evidence for universality of
the entropy formula $4\pi J_{0}^{+}J_{0}^{-}$ beyond pure Einstein gravity in
4-dimensions. We consider the Einstein-Maxwell theory in the presence of
cosmological constant, then write near horizon metric of the Kerr-Newman (A)dS
black hole in the Gaussian null coordinate system. We consider near horizon
fall-off conditions for metric and $U(1)$ gauge field. We find asymptotic
combined symmetry generator, consists of diffeomorphism and $U(1)$ gauge
transformation, so that it preserves fall-off conditions. Consequently, we find
supertranslation, supperrotation and multiple-charge modes and then we show
that the entropy formula is held for the Kerr-Newman (A)dS black hole.
Supperrotation modes suffer from a problem. By introducing new combined
symmetry generator, we cure that problem.
| [
{
"created": "Mon, 12 Feb 2018 05:29:24 GMT",
"version": "v1"
},
{
"created": "Wed, 2 May 2018 06:53:28 GMT",
"version": "v2"
}
] | 2018-05-23 | [
[
"Setare",
"M. R.",
""
],
[
"Adami",
"H.",
""
]
] | In this paper we provide the first non-trivial evidence for universality of the entropy formula $4\pi J_{0}^{+}J_{0}^{-}$ beyond pure Einstein gravity in 4-dimensions. We consider the Einstein-Maxwell theory in the presence of cosmological constant, then write near horizon metric of the Kerr-Newman (A)dS black hole in the Gaussian null coordinate system. We consider near horizon fall-off conditions for metric and $U(1)$ gauge field. We find asymptotic combined symmetry generator, consists of diffeomorphism and $U(1)$ gauge transformation, so that it preserves fall-off conditions. Consequently, we find supertranslation, supperrotation and multiple-charge modes and then we show that the entropy formula is held for the Kerr-Newman (A)dS black hole. Supperrotation modes suffer from a problem. By introducing new combined symmetry generator, we cure that problem. |
1003.1847 | Richard Dowdall Mr | Richard J. Dowdall, Winston J. Fairbairn | Observables in 3d spinfoam quantum gravity with fermions | 32 pages, many diagrams, uses psfrag. | null | 10.1007/s10714-010-1107-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study expectation values of observables in three-dimensional spinfoam
quantum gravity coupled to Dirac fermions. We revisit the model introduced by
one of the authors and extend it to the case of massless fermionic fields. We
introduce observables, analyse their symmetries and the corresponding proper
gauge fixing. The Berezin integral over the fermionic fields is performed and
the fermionic observables are expanded in open paths and closed loops
associated to pure quantum gravity observables. We obtain the vertex amplitudes
for gauge-invariant observables, while the expectation values of gauge-variant
observables, such as the fermion propagator, are given by the evaluation of
particular spin networks.
| [
{
"created": "Tue, 9 Mar 2010 11:18:21 GMT",
"version": "v1"
}
] | 2015-05-18 | [
[
"Dowdall",
"Richard J.",
""
],
[
"Fairbairn",
"Winston J.",
""
]
] | We study expectation values of observables in three-dimensional spinfoam quantum gravity coupled to Dirac fermions. We revisit the model introduced by one of the authors and extend it to the case of massless fermionic fields. We introduce observables, analyse their symmetries and the corresponding proper gauge fixing. The Berezin integral over the fermionic fields is performed and the fermionic observables are expanded in open paths and closed loops associated to pure quantum gravity observables. We obtain the vertex amplitudes for gauge-invariant observables, while the expectation values of gauge-variant observables, such as the fermion propagator, are given by the evaluation of particular spin networks. |
gr-qc/0611107 | Thomas Sotiriou | Thomas P. Sotiriou | Curvature scalar instability in f(R) gravity | typos corrected, replaced to match published version | Phys.Lett.B645:389-392,2007 | 10.1016/j.physletb.2007.01.003 | null | gr-qc astro-ph hep-th | null | An instability in the presence of matter in theories of gravity which include
a 1/R correction in the gravitational action has been found by Dolgov and
Kawasaki. In the present paper this instability is discussed for f(R) gravity
in general. We focus on the Palatini formalism of the theory and it is shown
that no such instability occurs in this version of f(R) gravity. The reasons
for the appearance of the instability in the metric but not in the Palatini
formalism are fully investigated.
| [
{
"created": "Mon, 20 Nov 2006 15:07:05 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Feb 2007 19:18:16 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Sotiriou",
"Thomas P.",
""
]
] | An instability in the presence of matter in theories of gravity which include a 1/R correction in the gravitational action has been found by Dolgov and Kawasaki. In the present paper this instability is discussed for f(R) gravity in general. We focus on the Palatini formalism of the theory and it is shown that no such instability occurs in this version of f(R) gravity. The reasons for the appearance of the instability in the metric but not in the Palatini formalism are fully investigated. |
1611.04618 | Miftachul Hadi | Miftachul Hadi, Malcolm Anderson, Andri Husein | The Gravitational Field Equations of a Twisted Skyrmion String:
Numerical Solution | 8 pages, 5 figures, submitted to ICSAS 2016 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study nonlinear sigma model, especially Skyrme model with twist: twisted
Skyrmion string where twist term, $mkz$, is indicated in vortex solution. To
add gravity, we replace $\eta^{\mu\nu}$ in Lagrangian system with a space-time
metric tensor, $g^{\mu\nu}$, which in view of the time-independence and
cylindrical symmetry of the assumed vortex solution is taken to be a function
of $r$ alone. We use ode45 for numerical calculation, i.e. a tool box in Matlab
to solve coupled Einstein field equations which have ordinary differential
equations (ODE) form.
| [
{
"created": "Wed, 9 Nov 2016 02:38:18 GMT",
"version": "v1"
}
] | 2016-11-16 | [
[
"Hadi",
"Miftachul",
""
],
[
"Anderson",
"Malcolm",
""
],
[
"Husein",
"Andri",
""
]
] | We study nonlinear sigma model, especially Skyrme model with twist: twisted Skyrmion string where twist term, $mkz$, is indicated in vortex solution. To add gravity, we replace $\eta^{\mu\nu}$ in Lagrangian system with a space-time metric tensor, $g^{\mu\nu}$, which in view of the time-independence and cylindrical symmetry of the assumed vortex solution is taken to be a function of $r$ alone. We use ode45 for numerical calculation, i.e. a tool box in Matlab to solve coupled Einstein field equations which have ordinary differential equations (ODE) form. |
1510.04745 | Hongwei Yu | Huabing Cai, Hongwei Yu, Wenting Zhou | Spontaneous excitation of a static atom in a thermal bath in cosmic
string spacetime | 20 pages, 4 figures, to appear in PRD | Phys. Rev. D92, 084062(2015) | 10.1103/PhysRevD.92.084062 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the average rate of change of energy for a static atom immersed in a
thermal bath of electromagnetic radiation in the cosmic string spacetime and
separately calculate the contributions of thermal fluctuations and radiation
reaction. We find that the transition rates are crucially dependent on the
atom-string distance and polarization of the atom and they in general oscillate
as the atom-string distance varies. Moreover, the atomic transition rates in
the cosmic string spacetime can be larger or smaller than those in Minkowski
spacetime contingent upon the atomic polarization and position. In particular,
when located on the string, ground-state atoms can make a transition to excited
states only if they are polarizable parallel to the string, whereas ground
state atoms polarizable only perpendicular to the string are stable as if they
were in a vacuum, even if they are immersed in a thermal bath. Our results
suggest that the influence of a cosmic string is very similar to that of a
reflecting boundary in Minkowski spacetime.
| [
{
"created": "Thu, 15 Oct 2015 23:31:59 GMT",
"version": "v1"
}
] | 2017-02-02 | [
[
"Cai",
"Huabing",
""
],
[
"Yu",
"Hongwei",
""
],
[
"Zhou",
"Wenting",
""
]
] | We study the average rate of change of energy for a static atom immersed in a thermal bath of electromagnetic radiation in the cosmic string spacetime and separately calculate the contributions of thermal fluctuations and radiation reaction. We find that the transition rates are crucially dependent on the atom-string distance and polarization of the atom and they in general oscillate as the atom-string distance varies. Moreover, the atomic transition rates in the cosmic string spacetime can be larger or smaller than those in Minkowski spacetime contingent upon the atomic polarization and position. In particular, when located on the string, ground-state atoms can make a transition to excited states only if they are polarizable parallel to the string, whereas ground state atoms polarizable only perpendicular to the string are stable as if they were in a vacuum, even if they are immersed in a thermal bath. Our results suggest that the influence of a cosmic string is very similar to that of a reflecting boundary in Minkowski spacetime. |
gr-qc/9512019 | Mihail Tentyukov | M.N.Tentyukov (Joint Institute for Nuclear Research,Dubna) | Spherically symmetric solutions of gravitation equations on the
background with spatial sections of constant curvature | 16 pages, LaTeX file, no macros required, 11 figures in separate
Postscript file | null | null | null | gr-qc | null | We investigate the vacuum and charged spherically symmetric static solutions
of the Einstein equations on cosmological background. The background metric is
not flat, but curved, with constant - curvature spatial sections. Both vacuum
and charged cases contain two branches. The first branches transform into the
Schwarzschild and Reissner-Nordstr\"om solutions if the background metric goes
to the Minkovski one. The second branches describe wormholes and have no
Einstein limit.
| [
{
"created": "Sat, 9 Dec 1995 20:51:55 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Tentyukov",
"M. N.",
"",
"Joint Institute for Nuclear Research,Dubna"
]
] | We investigate the vacuum and charged spherically symmetric static solutions of the Einstein equations on cosmological background. The background metric is not flat, but curved, with constant - curvature spatial sections. Both vacuum and charged cases contain two branches. The first branches transform into the Schwarzschild and Reissner-Nordstr\"om solutions if the background metric goes to the Minkovski one. The second branches describe wormholes and have no Einstein limit. |
1804.05485 | Tomohiro Nakamura | Tomohiro Nakamura, Taishi Ikeda, Ryo Saito and Chul-Moon Yoo | Chameleon Field in a Spherical Shell System | 20 pages, 10 figures | Phys. Rev. D 99, 044024 (2019) | 10.1103/PhysRevD.99.044024 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the validity of screening mechanism of the fifth force for
chameleon field in highly inhomogeneous density profile. For simplicity, we
consider a static and spherically symmetric system which is composed of
concentric infinitely thin shells. We calculate the fifth force profile by
using a numerical method for a relatively large Compton wavelength of the
chameleon field. An approximate solution is also derived for the small Compton
wavelength limit. Our results show that, if the thin-shell condition for the
corresponding smoothed density profile is satisfied, the fifth force is safely
screened outside the system irrespective of the configuration of the shells
inside the system. In contrast to the screening outside the system, we find
that the fifth force can be comparable to the Newtonian gravitational force
inside the system. If the system is highly inhomogeneous, the chameleon field
cannot trace the potential minimum varying with the density and repeats being
kicked, climbing up and rolling down the potential even when the effective mass
of the chameleon field is sufficiently large in the system on average. One
should not feel complacent about the wellbehavedness of the fifth force field
with an averaged density distribution when we consider inhomogeneous objects.
| [
{
"created": "Mon, 16 Apr 2018 02:53:06 GMT",
"version": "v1"
},
{
"created": "Sun, 21 Oct 2018 13:43:24 GMT",
"version": "v2"
}
] | 2019-02-20 | [
[
"Nakamura",
"Tomohiro",
""
],
[
"Ikeda",
"Taishi",
""
],
[
"Saito",
"Ryo",
""
],
[
"Yoo",
"Chul-Moon",
""
]
] | We investigate the validity of screening mechanism of the fifth force for chameleon field in highly inhomogeneous density profile. For simplicity, we consider a static and spherically symmetric system which is composed of concentric infinitely thin shells. We calculate the fifth force profile by using a numerical method for a relatively large Compton wavelength of the chameleon field. An approximate solution is also derived for the small Compton wavelength limit. Our results show that, if the thin-shell condition for the corresponding smoothed density profile is satisfied, the fifth force is safely screened outside the system irrespective of the configuration of the shells inside the system. In contrast to the screening outside the system, we find that the fifth force can be comparable to the Newtonian gravitational force inside the system. If the system is highly inhomogeneous, the chameleon field cannot trace the potential minimum varying with the density and repeats being kicked, climbing up and rolling down the potential even when the effective mass of the chameleon field is sufficiently large in the system on average. One should not feel complacent about the wellbehavedness of the fifth force field with an averaged density distribution when we consider inhomogeneous objects. |
1802.10396 | Ingemar Bengtsson | Ingemar Bengtsson and Irina Galstyan | Black Hole Lattices Under the Microscope | 17 pages, 6 figures | Class. Quantum Grav. 35 (2018) 145004 | 10.1088/1361-6382/aac7e0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is known how to choose initial data for Einstein's equations describing an
arbitrary number of black holes at a moment of time symmetry. This idea has
been used to give insight into the cosmological averaging problem. We study the
local curvature of the initial data space, for configurations of 8, 120, or 600
black holes obtained by choosing points either regularly or randomly on the
3-sphere. We conclude that the asymptotic regions are remarkably close to that
of Schwarzschild, while the region in between shows interesting behaviour. The
cosmological back reaction as defined in the recent literature is actually a
bit smaller for the random configurations.
| [
{
"created": "Wed, 28 Feb 2018 13:16:07 GMT",
"version": "v1"
}
] | 2018-07-11 | [
[
"Bengtsson",
"Ingemar",
""
],
[
"Galstyan",
"Irina",
""
]
] | It is known how to choose initial data for Einstein's equations describing an arbitrary number of black holes at a moment of time symmetry. This idea has been used to give insight into the cosmological averaging problem. We study the local curvature of the initial data space, for configurations of 8, 120, or 600 black holes obtained by choosing points either regularly or randomly on the 3-sphere. We conclude that the asymptotic regions are remarkably close to that of Schwarzschild, while the region in between shows interesting behaviour. The cosmological back reaction as defined in the recent literature is actually a bit smaller for the random configurations. |
1408.1448 | Changlong Wang | C. L. Wang, R. P. Woodard | Excitation of Photons by Inflationary Gravitons | Version 2 revised for publication in Physical Review D contains
substantial discussion of the eventual breakdown of perturbation implied by
our result | Phys. Rev. D 91, 124054 (2015) | 10.1103/PhysRevD.91.124054 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use a recent result for the graviton contribution to the one loop vacuum
polarization to solve the effective field equations for dynamical photons on de
Sitter background. Our results show that the electric field experiences a
secular enhancement proportional to the number of inflationary e-foldings. We
discuss the minimum this establishes for primordial inflation to seed cosmic
magnetic fields.
| [
{
"created": "Thu, 7 Aug 2014 00:52:12 GMT",
"version": "v1"
},
{
"created": "Fri, 19 Jun 2015 14:11:10 GMT",
"version": "v2"
}
] | 2015-06-22 | [
[
"Wang",
"C. L.",
""
],
[
"Woodard",
"R. P.",
""
]
] | We use a recent result for the graviton contribution to the one loop vacuum polarization to solve the effective field equations for dynamical photons on de Sitter background. Our results show that the electric field experiences a secular enhancement proportional to the number of inflationary e-foldings. We discuss the minimum this establishes for primordial inflation to seed cosmic magnetic fields. |
1711.02685 | Joshua Cooperman | Joshua H. Cooperman | Scaling analyses of the spectral dimension in 3-dimensional causal
dynamical triangulations | 16+3 pages, 19 figures | null | 10.1088/1361-6382/aab86e | null | gr-qc hep-lat hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The spectral dimension measures the dimensionality of a space as witnessed by
a diffusing random walker. Within the causal dynamical triangulations approach
to the quantization of gravity, the spectral dimension exhibits novel
scale-dependent dynamics: reducing towards a value near 2 on sufficiently small
scales, matching closely the topological dimension on intermediate scales, and
decaying in the presence of positive curvature on sufficiently large scales. I
report the first comprehensive scaling analysis of the small-to-intermediate
scale spectral dimension for the test case of the causal dynamical
triangulations of 3-dimensional Einstein gravity. I find that the spectral
dimension scales trivially with the diffusion constant. I find that the
spectral dimension is completely finite in the infinite volume limit, and I
argue that its maximal value is exactly consistent with the topological
dimension of 3 in this limit. I find that the spectral dimension reduces
further towards a value near 2 as this case's bare coupling approaches its
phase transition, and I present evidence against the conjecture that the bare
coupling simply sets the overall scale of the quantum geometry. On the basis of
these findings, I advance a tentative physical explanation for the dynamical
reduction of the spectral dimension observed within causal dynamical
triangulations: branched polymeric quantum geometry on sufficiently small
scales. My analyses should facilitate attempts to employ the spectral dimension
as a physical observable with which to delineate renormalization group
trajectories in the hope of taking a continuum limit of causal dynamical
triangulations at a nontrivial ultraviolet fixed point.
| [
{
"created": "Tue, 7 Nov 2017 19:01:34 GMT",
"version": "v1"
}
] | 2018-05-02 | [
[
"Cooperman",
"Joshua H.",
""
]
] | The spectral dimension measures the dimensionality of a space as witnessed by a diffusing random walker. Within the causal dynamical triangulations approach to the quantization of gravity, the spectral dimension exhibits novel scale-dependent dynamics: reducing towards a value near 2 on sufficiently small scales, matching closely the topological dimension on intermediate scales, and decaying in the presence of positive curvature on sufficiently large scales. I report the first comprehensive scaling analysis of the small-to-intermediate scale spectral dimension for the test case of the causal dynamical triangulations of 3-dimensional Einstein gravity. I find that the spectral dimension scales trivially with the diffusion constant. I find that the spectral dimension is completely finite in the infinite volume limit, and I argue that its maximal value is exactly consistent with the topological dimension of 3 in this limit. I find that the spectral dimension reduces further towards a value near 2 as this case's bare coupling approaches its phase transition, and I present evidence against the conjecture that the bare coupling simply sets the overall scale of the quantum geometry. On the basis of these findings, I advance a tentative physical explanation for the dynamical reduction of the spectral dimension observed within causal dynamical triangulations: branched polymeric quantum geometry on sufficiently small scales. My analyses should facilitate attempts to employ the spectral dimension as a physical observable with which to delineate renormalization group trajectories in the hope of taking a continuum limit of causal dynamical triangulations at a nontrivial ultraviolet fixed point. |
2205.06953 | Yoshimasa Kurihara | Yoshimasa Kurihara | Topological indices of general relativity and Yang-Mills theory in
four-dimensional space-time | 65 pages, 7 figures | null | null | null | gr-qc hep-ph | http://creativecommons.org/licenses/by/4.0/ | This report investigates general relativity and the Yang-Mills theory in
four-dimensional space-time using a common mathematical framework, the
Chern--Weil theory for principal bundles. The whole theory is described owing
to the fibre bundle with the $GL(4)$ symmetry by twisting several principal
bundles with the gauge symmetry.
In addition to the principal connection, we introduce the Hodge-dual
connection into the Lagrangian to make gauge fields have dynamics independent
from the Bianchi identity. We show that the duplex superstructure appears in
the bundle when a $\mathbb{Z}_2$-grading operator exists in the total space of
the bundle in general. The Dirac operator appears in the secondary superspace
using the one-dimensional Clifford algebra, and it provides topological indices
from the Atiyah--Singer index theorem.
Though the topological index is usually discussed in the elliptic-type
manifold, this report treats it in the hyperbolic type space-time manifold
using a novel method, namely the $\theta$-metric space. The $\theta$-metric
treats the Euclidean and Minkowski spaces simultaneously and defines the
topological index in the Minkowski space-time.
| [
{
"created": "Sat, 14 May 2022 02:38:45 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Jun 2022 00:51:27 GMT",
"version": "v2"
},
{
"created": "Wed, 30 Nov 2022 07:00:06 GMT",
"version": "v3"
},
{
"created": "Thu, 10 Aug 2023 09:37:52 GMT",
"version": "v4"
}
] | 2023-08-14 | [
[
"Kurihara",
"Yoshimasa",
""
]
] | This report investigates general relativity and the Yang-Mills theory in four-dimensional space-time using a common mathematical framework, the Chern--Weil theory for principal bundles. The whole theory is described owing to the fibre bundle with the $GL(4)$ symmetry by twisting several principal bundles with the gauge symmetry. In addition to the principal connection, we introduce the Hodge-dual connection into the Lagrangian to make gauge fields have dynamics independent from the Bianchi identity. We show that the duplex superstructure appears in the bundle when a $\mathbb{Z}_2$-grading operator exists in the total space of the bundle in general. The Dirac operator appears in the secondary superspace using the one-dimensional Clifford algebra, and it provides topological indices from the Atiyah--Singer index theorem. Though the topological index is usually discussed in the elliptic-type manifold, this report treats it in the hyperbolic type space-time manifold using a novel method, namely the $\theta$-metric space. The $\theta$-metric treats the Euclidean and Minkowski spaces simultaneously and defines the topological index in the Minkowski space-time. |
gr-qc/9709001 | Nese Ozdemir | M.Hortacsu and N. Ozdemir | An Extension of Multiple Cosmic String Solution | latex,no figure | Mod.Phys.Lett. A13 (1998) 3081-3090 | 10.1142/S0217732398003284 | null | gr-qc | null | We extend the work done for cosmic strings on the perturbative calculation of
vacuum polarization of a massless field in the space-time of multiple cosmic
strings and show that for a more general class of locally flat metrics the one
loop calculation do not introduce any new divergences to the VEV of the energy
of a scalar particle or a spinor particle. We explicitly perform the
calculation for the configuration where we have one cosmic string in the
presence of a dipole made out of cosmic strings both for the scalar and the
spinor cases.
| [
{
"created": "Mon, 1 Sep 1997 09:29:06 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Hortacsu",
"M.",
""
],
[
"Ozdemir",
"N.",
""
]
] | We extend the work done for cosmic strings on the perturbative calculation of vacuum polarization of a massless field in the space-time of multiple cosmic strings and show that for a more general class of locally flat metrics the one loop calculation do not introduce any new divergences to the VEV of the energy of a scalar particle or a spinor particle. We explicitly perform the calculation for the configuration where we have one cosmic string in the presence of a dipole made out of cosmic strings both for the scalar and the spinor cases. |
gr-qc/0303013 | Massimo Tinto | Massimo Tinto, Daniel A. Shaddock, Julien Sylvestre, J.W. Armstrong | Implementation of Time-Delay Interferometry for LISA | 39 pages, 6 figures, 2 tables | Phys.Rev. D67 (2003) 122003 | 10.1103/PhysRevD.67.122003 | null | gr-qc | null | We discuss the baseline optical configuration for the Laser Interferometer
Space Antenna (LISA) mission, in which the lasers are not free-running, but
rather one of them is used as the main frequency reference generator (the {\it
master}) and the remaining five as {\it slaves}, these being phase-locked to
the master (the {\it master-slave configuration}). Under the condition that the
frequency fluctuations due to the optical transponders can be made negligible
with respect to the secondary LISA noise sources (mainly proof-mass and shot
noises), we show that the entire space of interferometric combinations LISA can
generate when operated with six independent lasers (the {\it one-way method})
can also be constructed with the {\it master-slave} system design. The
corresponding hardware trade-off analysis for these two optical designs is
presented, which indicates that the two sets of systems needed for implementing
the {\it one-way method}, and the {\it master-slave configuration}, are
essentially identical. Either operational mode could therefore be implemented
without major implications on the hardware configuration. We then.......
| [
{
"created": "Mon, 3 Mar 2003 19:33:35 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Tinto",
"Massimo",
""
],
[
"Shaddock",
"Daniel A.",
""
],
[
"Sylvestre",
"Julien",
""
],
[
"Armstrong",
"J. W.",
""
]
] | We discuss the baseline optical configuration for the Laser Interferometer Space Antenna (LISA) mission, in which the lasers are not free-running, but rather one of them is used as the main frequency reference generator (the {\it master}) and the remaining five as {\it slaves}, these being phase-locked to the master (the {\it master-slave configuration}). Under the condition that the frequency fluctuations due to the optical transponders can be made negligible with respect to the secondary LISA noise sources (mainly proof-mass and shot noises), we show that the entire space of interferometric combinations LISA can generate when operated with six independent lasers (the {\it one-way method}) can also be constructed with the {\it master-slave} system design. The corresponding hardware trade-off analysis for these two optical designs is presented, which indicates that the two sets of systems needed for implementing the {\it one-way method}, and the {\it master-slave configuration}, are essentially identical. Either operational mode could therefore be implemented without major implications on the hardware configuration. We then....... |
2303.17969 | Hiroshi Kozaki | Hiroshi Kozaki, Tatsuhiko Koike, Yoshiyuki Morisawa and Hideki
Ishihara | Nambu-Goto Strings with a null symmetry and contact structure | 33 pages, 4 figures, version accepted for publication | null | null | OCU-PHYS-577, AP-GR-188, NITEP-154 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the classical dynamics of the Nambu-Goto strings with a null
symmetry in curved spacetimes admitting a null Killing vector field. The
Nambu-Goto equation is reduced to first order ordinary differential equations
and is always integrable in contrast to the case of non-null symmetries where
integrability requires additional spacetime symmetries. It is found that in the
case of null symmetry, an almost contact structure associated with the metric
dual 1-form $\eta$ of the null Killing vector field emerges naturally. This
structure determines the allowed class of string worldsheets in such a way that
the tangent vector fields of the worldsheet lie in $\ker \mathrm{d}\eta$. In
the special case that the almost contact structure becomes a contact structure,
its Reeb vector field completely characterizes the worldsheet. We apply our
formulation to the strings in the pp-waves, the Einstein static universe and
the G\"odel universe. We also study their worldsheet geometry in detail.
| [
{
"created": "Fri, 31 Mar 2023 11:13:43 GMT",
"version": "v1"
},
{
"created": "Fri, 29 Sep 2023 04:03:43 GMT",
"version": "v2"
}
] | 2023-10-02 | [
[
"Kozaki",
"Hiroshi",
""
],
[
"Koike",
"Tatsuhiko",
""
],
[
"Morisawa",
"Yoshiyuki",
""
],
[
"Ishihara",
"Hideki",
""
]
] | We study the classical dynamics of the Nambu-Goto strings with a null symmetry in curved spacetimes admitting a null Killing vector field. The Nambu-Goto equation is reduced to first order ordinary differential equations and is always integrable in contrast to the case of non-null symmetries where integrability requires additional spacetime symmetries. It is found that in the case of null symmetry, an almost contact structure associated with the metric dual 1-form $\eta$ of the null Killing vector field emerges naturally. This structure determines the allowed class of string worldsheets in such a way that the tangent vector fields of the worldsheet lie in $\ker \mathrm{d}\eta$. In the special case that the almost contact structure becomes a contact structure, its Reeb vector field completely characterizes the worldsheet. We apply our formulation to the strings in the pp-waves, the Einstein static universe and the G\"odel universe. We also study their worldsheet geometry in detail. |
1511.03644 | Atousa Chaharsough Shirazi | Atousa Chaharsough Shirazi, Jonathan Engle and Ilya Vilensky | Hessian and graviton propagator of the proper vertex | 20 pages | null | 10.1088/0264-9381/33/20/205010 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The proper spin-foam vertex amplitude is obtained from the EPRL vertex by
projecting out all but a single gravitational sector, in order to achieve
correct semi-classical behavior. In this paper we calculate the gravitational
two-point function predicted by the proper spin-foam vertex to lowest order in
the vertex expansion. We find the same answer as in the EPRL case in the
`continuum spectrum' limit, so that the theory is consistent with the
predictions of linearized gravity in the regime of small curvature. The method
for calculating the two-point function is similar to that used in prior works:
we cast it in terms of an action integral and to use stationary phase methods.
Thus, the calculation of the Hessian matrix plays a key role. Once the Hessian
is calculated, it is used not only to calculate the two-point function, but
also to calculate the coefficient appearing in the semi-classical limit of the
proper vertex amplitude itself. This coefficient is the effective discrete
"measure factor" encoded in the spin-foam model. Through a non-trivial
cancellation of different factors, we find that this coefficient is the same as
the coefficient in front of the term in the asymptotics of the EPRL vertex
corresponding to the selected gravitational sector.
| [
{
"created": "Wed, 11 Nov 2015 20:29:18 GMT",
"version": "v1"
}
] | 2016-10-19 | [
[
"Shirazi",
"Atousa Chaharsough",
""
],
[
"Engle",
"Jonathan",
""
],
[
"Vilensky",
"Ilya",
""
]
] | The proper spin-foam vertex amplitude is obtained from the EPRL vertex by projecting out all but a single gravitational sector, in order to achieve correct semi-classical behavior. In this paper we calculate the gravitational two-point function predicted by the proper spin-foam vertex to lowest order in the vertex expansion. We find the same answer as in the EPRL case in the `continuum spectrum' limit, so that the theory is consistent with the predictions of linearized gravity in the regime of small curvature. The method for calculating the two-point function is similar to that used in prior works: we cast it in terms of an action integral and to use stationary phase methods. Thus, the calculation of the Hessian matrix plays a key role. Once the Hessian is calculated, it is used not only to calculate the two-point function, but also to calculate the coefficient appearing in the semi-classical limit of the proper vertex amplitude itself. This coefficient is the effective discrete "measure factor" encoded in the spin-foam model. Through a non-trivial cancellation of different factors, we find that this coefficient is the same as the coefficient in front of the term in the asymptotics of the EPRL vertex corresponding to the selected gravitational sector. |
1411.3997 | Ulrich Sperhake | Ulrich Sperhake | The numerical relativity breakthrough for binary black holes | 34 pages, 5 figures; Invited article for Classical and Quantum
Gravity's "Milestones of General Relativity" series; to match published
version | null | 10.1088/0264-9381/32/12/124011 | null | gr-qc physics.hist-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The evolution of black-hole binaries in vacuum spacetimes constitutes the
two-body problem in general relativity. The solution of this problem in the
framework of the Einstein field equations is a substantially more complex
exercise than that of the dynamics of two point masses in Newtonian gravity,
but it also presents us with a wealth of new exciting physics. Numerical
methods are likely the only method to compute the dynamics of black-hole
systems in the fully non-linear regime and have been pursued since the 1960s,
culminating in dramatic breakthroughs in 2005. Here we review the methodology
and the developments that finally gave us a solution of this fundamental
problem of Einstein's theory and discuss the breakthrough's implication for the
wide range of contemporary black-hole physics.
| [
{
"created": "Fri, 14 Nov 2014 18:13:45 GMT",
"version": "v1"
}
] | 2015-06-17 | [
[
"Sperhake",
"Ulrich",
""
]
] | The evolution of black-hole binaries in vacuum spacetimes constitutes the two-body problem in general relativity. The solution of this problem in the framework of the Einstein field equations is a substantially more complex exercise than that of the dynamics of two point masses in Newtonian gravity, but it also presents us with a wealth of new exciting physics. Numerical methods are likely the only method to compute the dynamics of black-hole systems in the fully non-linear regime and have been pursued since the 1960s, culminating in dramatic breakthroughs in 2005. Here we review the methodology and the developments that finally gave us a solution of this fundamental problem of Einstein's theory and discuss the breakthrough's implication for the wide range of contemporary black-hole physics. |
2005.13644 | Gustav Holzegel | Gustav Holzegel, Christopher Kauffman | A note on the wave equation on black hole spacetimes with small
non-decaying first order terms | 7 pages | null | null | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present an elementary physical space argument to establish local
integrated decay estimates for the perturbed wave equation $\Box_g \phi =
\epsilon \beta^a \partial_a \phi$ on the exterior of the Schwarzschild geometry
$(\mathcal{M},g)$. Here $\beta$ is a regular vectorfield on $\mathcal{M}$
decaying suitably in space but not necessarily in time. The proof is formulated
to cover also perturbations of the Regge--Wheeler equation.
| [
{
"created": "Wed, 27 May 2020 20:50:06 GMT",
"version": "v1"
}
] | 2020-05-29 | [
[
"Holzegel",
"Gustav",
""
],
[
"Kauffman",
"Christopher",
""
]
] | We present an elementary physical space argument to establish local integrated decay estimates for the perturbed wave equation $\Box_g \phi = \epsilon \beta^a \partial_a \phi$ on the exterior of the Schwarzschild geometry $(\mathcal{M},g)$. Here $\beta$ is a regular vectorfield on $\mathcal{M}$ decaying suitably in space but not necessarily in time. The proof is formulated to cover also perturbations of the Regge--Wheeler equation. |
1805.04470 | Jiliang Jing | Xiaobao Liu, Zehua Tian, Jieci Wang, Jiliang Jing | Radiative process of two entanglement atoms in de Sitter spacetime | 9 pages, 4 figures. Accepted by PRD for publication. arXiv admin
note: text overlap with arXiv:1512.02886 by other authors | Phys. Rev. D 97, (2018) 105030 | 10.1103/PhysRevD.97.105030 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the radiative processes of a quantum system composed by two
identical two-level atoms in the de Sitter spacetime, interacting with a
conformally coupled massless scalar field prepared in the de Sitter-invariant
vacuum. We discuss the structure of the rate of variations of the atomic energy
for two static atoms. Following a procedure developed by Dalibard, Dupont-Roc
and Cohen-Tannoudji, our intention is to identify in a quantitative way the
contributions of vacuum fluctuations and the radiation reaction to the
generation of quantum entanglement and to the degradation of entangled states.
We find that when the distance between two atoms larger than the characteristic
length scale, the rate of variation of atomic energy in the de Sitter-invariant
vacuum behaves differently compared with that in the thermal Minkowski
spacetime. In particular, the generation and degradation of quantum
entanglement can be enhanced or inhibited, which are dependent not only on the
specific entangled state but also on the distance between the atoms.
| [
{
"created": "Thu, 10 May 2018 00:49:51 GMT",
"version": "v1"
}
] | 2018-06-05 | [
[
"Liu",
"Xiaobao",
""
],
[
"Tian",
"Zehua",
""
],
[
"Wang",
"Jieci",
""
],
[
"Jing",
"Jiliang",
""
]
] | We investigate the radiative processes of a quantum system composed by two identical two-level atoms in the de Sitter spacetime, interacting with a conformally coupled massless scalar field prepared in the de Sitter-invariant vacuum. We discuss the structure of the rate of variations of the atomic energy for two static atoms. Following a procedure developed by Dalibard, Dupont-Roc and Cohen-Tannoudji, our intention is to identify in a quantitative way the contributions of vacuum fluctuations and the radiation reaction to the generation of quantum entanglement and to the degradation of entangled states. We find that when the distance between two atoms larger than the characteristic length scale, the rate of variation of atomic energy in the de Sitter-invariant vacuum behaves differently compared with that in the thermal Minkowski spacetime. In particular, the generation and degradation of quantum entanglement can be enhanced or inhibited, which are dependent not only on the specific entangled state but also on the distance between the atoms. |
2301.13685 | Joris van Heijningen | Joris van Heijningen, Marcel ter Brake, Oliver Gerberding, Shreevathsa
Chalathadka Subrahmanya, Jan Harms, Xing Bian, Alberto Gatti, Morgane Zeoli,
Alessandro Bertolini, Christophe Collette, Andrea Perali, Nicola Pinto,
Meenakshi Sharma, Filip Tavernier and Javad Rezvani | The payload of the Lunar Gravitational-wave Antenna | null | null | 10.1063/5.0144687 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The toolbox to study the Universe grew on 14 September 2015 when the
LIGO-Virgo collaboration heard a signal from two colliding black holes between
30-250 Hz. Since then, many more gravitational waves have been detected as
detectors increased sensitivity. However, the current detector design
sensitivity curves still have a lower cut-off of 10 Hz. To detect even
lower-frequency gravitational-wave signals, the Lunar Gravitational-wave
Antenna will use an array of seismic stations in a permanently shadowed crater.
It aims to detect the differential between the elastic response of the Moon and
the suspended inertial sensor proof mass motion induced by gravitational waves.
A cryogenic superconducting inertial sensor is under development that aims for
fm/rtHz sensitivity or better down to 1 Hz and is planned to be deployed in
seismic stations. Here, we describe the current state of research towards the
inertial sensor, its applications and additional auxiliary technologies in the
payload of the lunar gravitational-wave detection mission.
| [
{
"created": "Tue, 31 Jan 2023 15:03:00 GMT",
"version": "v1"
},
{
"created": "Wed, 1 Feb 2023 10:52:52 GMT",
"version": "v2"
}
] | 2023-07-05 | [
[
"van Heijningen",
"Joris",
""
],
[
"ter Brake",
"Marcel",
""
],
[
"Gerberding",
"Oliver",
""
],
[
"Subrahmanya",
"Shreevathsa Chalathadka",
""
],
[
"Harms",
"Jan",
""
],
[
"Bian",
"Xing",
""
],
[
"Gatti",
"Alberto",
""
],
[
"Zeoli",
"Morgane",
""
],
[
"Bertolini",
"Alessandro",
""
],
[
"Collette",
"Christophe",
""
],
[
"Perali",
"Andrea",
""
],
[
"Pinto",
"Nicola",
""
],
[
"Sharma",
"Meenakshi",
""
],
[
"Tavernier",
"Filip",
""
],
[
"Rezvani",
"Javad",
""
]
] | The toolbox to study the Universe grew on 14 September 2015 when the LIGO-Virgo collaboration heard a signal from two colliding black holes between 30-250 Hz. Since then, many more gravitational waves have been detected as detectors increased sensitivity. However, the current detector design sensitivity curves still have a lower cut-off of 10 Hz. To detect even lower-frequency gravitational-wave signals, the Lunar Gravitational-wave Antenna will use an array of seismic stations in a permanently shadowed crater. It aims to detect the differential between the elastic response of the Moon and the suspended inertial sensor proof mass motion induced by gravitational waves. A cryogenic superconducting inertial sensor is under development that aims for fm/rtHz sensitivity or better down to 1 Hz and is planned to be deployed in seismic stations. Here, we describe the current state of research towards the inertial sensor, its applications and additional auxiliary technologies in the payload of the lunar gravitational-wave detection mission. |
1102.3553 | Jackson Levi Said | Jackson Levi Said, Kristian Zarb Adami | The Generalized Uncertainty Principle in f(R) Gravity for a Charged
Black Hole | 10 pages, 3 figures, Physical Review D (Accepted) | Phys.Rev.D83:043008,2011 | 10.1103/PhysRevD.83.043008 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using f (R) gravity in the Palatini formularism, the metric for a charged
spherically symmetric black hole is derived, taking the Ricci scalar curvature
to be constant. The generalized uncertainty principle is then used to calculate
the temperature of the resulting black hole, through this the entropy is found
correcting the Bekenstein-Hawking entropy in this case. Using the entropy the
tunneling probability and heat capacity are calculated up to the order of the
Planck length, which produces an extra factor that becomes important as black
holes become small, such as in the case of mini black holes.
| [
{
"created": "Thu, 17 Feb 2011 10:29:36 GMT",
"version": "v1"
},
{
"created": "Sun, 20 Mar 2011 13:53:54 GMT",
"version": "v2"
}
] | 2015-03-19 | [
[
"Said",
"Jackson Levi",
""
],
[
"Adami",
"Kristian Zarb",
""
]
] | Using f (R) gravity in the Palatini formularism, the metric for a charged spherically symmetric black hole is derived, taking the Ricci scalar curvature to be constant. The generalized uncertainty principle is then used to calculate the temperature of the resulting black hole, through this the entropy is found correcting the Bekenstein-Hawking entropy in this case. Using the entropy the tunneling probability and heat capacity are calculated up to the order of the Planck length, which produces an extra factor that becomes important as black holes become small, such as in the case of mini black holes. |
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