id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/0507036 | Kristina Giesel | Kristina Giesel, Thomas Thiemann | Consistency Check on Volume and Triad Operator Quantisation in Loop
Quantum Gravity I | 21 pages, 5 figures | Class.Quant.Grav. 23 (2006) 5667-5692 | 10.1088/0264-9381/23/18/012 | AEI-2005-100 | gr-qc | null | The volume operator plays a pivotal role for the quantum dynamics of Loop
Quantum Gravity (LQG). It is essential in order to construct Triad operators
that enter the Hamiltonian constraint and which become densely defined
operators on the full Hilbert space even though in the classical theory the
triad becomes singular when classical GR breaks down. The expression for the
volume and triad operators derives from the quantisation of the fundamental
electric flux operator of LQG by a complicated regularisation procedure. In
fact, there are two inequivalent volume operators available in the literature
and, moreover, both operators are unique only up to a finite, multiplicative
constant which should be viewed as a regularisation ambiguity. Now on the one
hand, classical volumes and triads can be expressed directly in terms of fluxes
and this fact was used to construct the corresponding volume and triad
operators. On the other hand, fluxes can be expressed in terms of triads and
therefore one can also view the volume operator as fundamental and consider the
flux operator as a derived operator. In this paper we examine whether the
volume, triad and flux quantisations are consistent with each other. The
results of this consistency analysis are rather surprising. Among other
findings we show: 1. The regularisation constant can be uniquely fixed. 2. One
of the volume operators can be ruled out as inconsistent. 3. Factor ordering
ambiguities in the definition of triad operators are immaterial for the
classical limit of the derived flux operator. The results of this paper show
that within full LQG triad operators are consistently quantized. In this paper
we present ideas and results of the consistency check. In a companion paper we
supply detailed proofs.
| [
{
"created": "Fri, 8 Jul 2005 11:32:25 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Jul 2005 15:13:59 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Giesel",
"Kristina",
""
],
[
"Thiemann",
"Thomas",
""
]
] | The volume operator plays a pivotal role for the quantum dynamics of Loop Quantum Gravity (LQG). It is essential in order to construct Triad operators that enter the Hamiltonian constraint and which become densely defined operators on the full Hilbert space even though in the classical theory the triad becomes singular when classical GR breaks down. The expression for the volume and triad operators derives from the quantisation of the fundamental electric flux operator of LQG by a complicated regularisation procedure. In fact, there are two inequivalent volume operators available in the literature and, moreover, both operators are unique only up to a finite, multiplicative constant which should be viewed as a regularisation ambiguity. Now on the one hand, classical volumes and triads can be expressed directly in terms of fluxes and this fact was used to construct the corresponding volume and triad operators. On the other hand, fluxes can be expressed in terms of triads and therefore one can also view the volume operator as fundamental and consider the flux operator as a derived operator. In this paper we examine whether the volume, triad and flux quantisations are consistent with each other. The results of this consistency analysis are rather surprising. Among other findings we show: 1. The regularisation constant can be uniquely fixed. 2. One of the volume operators can be ruled out as inconsistent. 3. Factor ordering ambiguities in the definition of triad operators are immaterial for the classical limit of the derived flux operator. The results of this paper show that within full LQG triad operators are consistently quantized. In this paper we present ideas and results of the consistency check. In a companion paper we supply detailed proofs. |
gr-qc/9207003 | Jim McCarthy | T. Damour (IHES and DARC) S. Deser (Brandeis University) J. McCarthy
(University of Adelaide) | Nonsymmetric Gravity Theories: Inconsistencies and a Cure | 34 pages | Phys.Rev.D47:1541-1556,1993 | 10.1103/PhysRevD.47.1541 | BRX TH-324 | gr-qc | null | Motivated by the apparent dependence of string $\sigma$--models on the sum of
spacetime metric and antisymmetric tensor fields, we reconsider gravity
theories constructed from a nonsymmetric metric. We first show that all such
"geometrical" theories homogeneous in second derivatives violate standard
physical requirements: ghost-freedom, absence of algebraic inconsistencies or
continuity of degree-of-freedom content. This no-go result applies in
particular to the old unified theory of Einstein and its recent avatars.
However, we find that the addition of nonderivative, ``cosmological'' terms
formally restores consistency by giving a mass to the antisymmetric tensor
field, thereby transmuting it into a fifth-force-like massive vector but with
novel possible matter couplings. The resulting macroscopic models also exhibit
``van der Waals''-type gravitational effects, and may provide useful
phenomenological foils to general relativity.
| [
{
"created": "Wed, 22 Jul 1992 22:51:38 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Damour",
"T.",
"",
"IHES and DARC"
],
[
"Deser",
"S.",
"",
"Brandeis University"
],
[
"McCarthy",
"J.",
"",
"University of Adelaide"
]
] | Motivated by the apparent dependence of string $\sigma$--models on the sum of spacetime metric and antisymmetric tensor fields, we reconsider gravity theories constructed from a nonsymmetric metric. We first show that all such "geometrical" theories homogeneous in second derivatives violate standard physical requirements: ghost-freedom, absence of algebraic inconsistencies or continuity of degree-of-freedom content. This no-go result applies in particular to the old unified theory of Einstein and its recent avatars. However, we find that the addition of nonderivative, ``cosmological'' terms formally restores consistency by giving a mass to the antisymmetric tensor field, thereby transmuting it into a fifth-force-like massive vector but with novel possible matter couplings. The resulting macroscopic models also exhibit ``van der Waals''-type gravitational effects, and may provide useful phenomenological foils to general relativity. |
2303.06395 | Rajesh Kumar | Anjali Pandey, Rajesh Kumar and Sudhir Kumar Srivastava | Spherically symmetric gravitational collapse in the background of
Chaplygin gas | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper considers the spherically symmetric gravitational collapse in the
background of Chaplygin gas as dark energy component. The dark energy is
assumed to be generalized and modified Chaplygin gas. The exterior of the star
is considered to be Schwarzschild de-sitter/anti-de sitter metric and discusses
the junction conditions. We have discussed the singularity formation in both
forms of chaplygin gas case and it is obtained that such collapsing fluids
favor the formation of black-hole.
| [
{
"created": "Sat, 11 Mar 2023 12:08:22 GMT",
"version": "v1"
}
] | 2023-03-14 | [
[
"Pandey",
"Anjali",
""
],
[
"Kumar",
"Rajesh",
""
],
[
"Srivastava",
"Sudhir Kumar",
""
]
] | This paper considers the spherically symmetric gravitational collapse in the background of Chaplygin gas as dark energy component. The dark energy is assumed to be generalized and modified Chaplygin gas. The exterior of the star is considered to be Schwarzschild de-sitter/anti-de sitter metric and discusses the junction conditions. We have discussed the singularity formation in both forms of chaplygin gas case and it is obtained that such collapsing fluids favor the formation of black-hole. |
1309.2058 | Takashi Torii | Takashi Torii and Hisa-aki Shinkai | Wormholes in higher dimensional space-time: Exact solutions and their
linear stability analysis | 6 pages, 3 eps figures, LaTeX. Accepted for publication in Phys. Rev.
D | null | 10.1103/PhysRevD.88.064027 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive the simplest traversable wormhole solutions in $n$-dimensional
general relativity, assuming static and spherically symmetric spacetime with a
ghost scalar field. This is the generalization of the Ellis solution (or the
so-called Morris-Thorne's traversable wormhole) into a higher-dimension. We
also study their stability using linear perturbation analysis. We obtain the
master equation for the perturbed gauge-invariant variable and search their
eigenvalues. Our analysis shows that all higher-dimensional wormholes have an
unstable mode against the perturbations with which the throat radius is
changed. The instability is consistent with the earlier numerical analysis in
four-dimensional solution.
| [
{
"created": "Mon, 9 Sep 2013 07:36:03 GMT",
"version": "v1"
}
] | 2015-06-17 | [
[
"Torii",
"Takashi",
""
],
[
"Shinkai",
"Hisa-aki",
""
]
] | We derive the simplest traversable wormhole solutions in $n$-dimensional general relativity, assuming static and spherically symmetric spacetime with a ghost scalar field. This is the generalization of the Ellis solution (or the so-called Morris-Thorne's traversable wormhole) into a higher-dimension. We also study their stability using linear perturbation analysis. We obtain the master equation for the perturbed gauge-invariant variable and search their eigenvalues. Our analysis shows that all higher-dimensional wormholes have an unstable mode against the perturbations with which the throat radius is changed. The instability is consistent with the earlier numerical analysis in four-dimensional solution. |
1806.09259 | Jing-Bo Wang | Jingbo Wang | W-hairs of black holes in three dimensional spacetime | 7 pages, comments are welcomed | null | 10.1088/1674-1137/43/9/095104 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the previous paper (arXiv:1804.09438) we found that the near horizon
symmetry algebra of black holes is a subalgebra of the $W_{1+\infty}$ symmetry
algebra of quantum Hall fluid in three dimensional spacetime. In this paper, we
give a slightly different representation of the former algebra from the latter
one. Similar to the horizon fluff proposal, based on the $W_{1+\infty}$
algebra, we count the number of the microstates of the BTZ black holes and
obtain the Bekenstein-Hawking entropy.
| [
{
"created": "Mon, 25 Jun 2018 02:35:22 GMT",
"version": "v1"
}
] | 2019-09-04 | [
[
"Wang",
"Jingbo",
""
]
] | In the previous paper (arXiv:1804.09438) we found that the near horizon symmetry algebra of black holes is a subalgebra of the $W_{1+\infty}$ symmetry algebra of quantum Hall fluid in three dimensional spacetime. In this paper, we give a slightly different representation of the former algebra from the latter one. Similar to the horizon fluff proposal, based on the $W_{1+\infty}$ algebra, we count the number of the microstates of the BTZ black holes and obtain the Bekenstein-Hawking entropy. |
0712.1258 | Vasileios Paschalidis | Vasileios Paschalidis, Jakob Hansen, and Alexei Khokhlov | Numerical performance of the parabolized ADM (PADM) formulation of
General Relativity | 20 two column pages, 20 figures, submitted to PRD, two typos
corrected | Phys.Rev.D78:064048,2008 | 10.1103/PhysRevD.78.064048 | null | gr-qc | null | In a recent paper the first coauthor presented a new parabolic extension
(PADM) of the standard 3+1 Arnowitt, Deser, Misner formulation of the equations
of general relativity. By parabolizing first-order ADM in a certain way, the
PADM formulation turns it into a mixed hyperbolic - second-order parabolic,
well-posed system. The surface of constraints of PADM becomes a local attractor
for all solutions and all possible well-posed gauge conditions. This paper
describes a numerical implementation of PADM and studies its accuracy and
stability in a series of standard numerical tests. Numerical properties of PADM
are compared with those of standard ADM and its hyperbolic Kidder, Scheel,
Teukolsky (KST) extension. The PADM scheme is numerically stable, convergent
and second-order accurate. The new formulation has better control of the
constraint-violating modes than ADM and KST.
| [
{
"created": "Sat, 8 Dec 2007 04:36:22 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Dec 2007 22:27:25 GMT",
"version": "v2"
}
] | 2009-02-23 | [
[
"Paschalidis",
"Vasileios",
""
],
[
"Hansen",
"Jakob",
""
],
[
"Khokhlov",
"Alexei",
""
]
] | In a recent paper the first coauthor presented a new parabolic extension (PADM) of the standard 3+1 Arnowitt, Deser, Misner formulation of the equations of general relativity. By parabolizing first-order ADM in a certain way, the PADM formulation turns it into a mixed hyperbolic - second-order parabolic, well-posed system. The surface of constraints of PADM becomes a local attractor for all solutions and all possible well-posed gauge conditions. This paper describes a numerical implementation of PADM and studies its accuracy and stability in a series of standard numerical tests. Numerical properties of PADM are compared with those of standard ADM and its hyperbolic Kidder, Scheel, Teukolsky (KST) extension. The PADM scheme is numerically stable, convergent and second-order accurate. The new formulation has better control of the constraint-violating modes than ADM and KST. |
1810.09563 | Aaron Johnson | Aaron D. Johnson, Shasvath J. Kapadia, Andrew Osborne, Alex Hixon, and
Daniel Kennefick | Prospects of detecting the nonlinear gravitational wave memory | 14 pages, 10 figures, 1 tables | Phys. Rev. D 99, 044045 (2019) | 10.1103/PhysRevD.99.044045 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In GW150914, approximately $3M_{\odot}$ were radiated away as gravitational
waves from the binary black hole system as it merged. The stress energy of the
gravitational wave itself causes a nonlinear memory effect in the detectors
here on Earth called the Christodoulou memory. We use an approximation that can
be applied to numerical relativity waveforms to give an estimate of the
displacement magnitude and the profile of the nonlinear memory. We give a
signal to noise ratio for a single GW150914-like detection event, and by
varying the total mass and distance parameters of the event, we find distances
and source masses for which the memory of an optimally oriented GW150914-like
event would be detectable in aLIGO and future detectors.
| [
{
"created": "Mon, 22 Oct 2018 21:23:22 GMT",
"version": "v1"
},
{
"created": "Sat, 23 Feb 2019 16:42:06 GMT",
"version": "v2"
}
] | 2019-02-27 | [
[
"Johnson",
"Aaron D.",
""
],
[
"Kapadia",
"Shasvath J.",
""
],
[
"Osborne",
"Andrew",
""
],
[
"Hixon",
"Alex",
""
],
[
"Kennefick",
"Daniel",
""
]
] | In GW150914, approximately $3M_{\odot}$ were radiated away as gravitational waves from the binary black hole system as it merged. The stress energy of the gravitational wave itself causes a nonlinear memory effect in the detectors here on Earth called the Christodoulou memory. We use an approximation that can be applied to numerical relativity waveforms to give an estimate of the displacement magnitude and the profile of the nonlinear memory. We give a signal to noise ratio for a single GW150914-like detection event, and by varying the total mass and distance parameters of the event, we find distances and source masses for which the memory of an optimally oriented GW150914-like event would be detectable in aLIGO and future detectors. |
2005.03258 | Alessandro Pesci | Alessandro Pesci | Zero-point gravitational field equations | 17 pages; v2: some corrections/editing/clarifications, reference
added, it corresponds to the published version | Class. Quantum Grav. 38 (2021) 145007 | 10.1088/1361-6382/ac0310 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the recently reported qmetric (or zero-point-length) expressions of
the Ricci (bi)scalar $R_{(q)}$ (namely, expressions of the Ricci scalar in a
spacetime with a limit length $L_0$ built in), focusing specifically on the
case of null separated events. A feature of these expressions is that, when
considered in the coincidence limit $p \to P$, they generically exhibit a
dependence on the geodesic along which the varying point $p$ approached $P$,
sort of memory of how $p$ went to $P$. This fact demands a deeper understanding
of the meaning of the quantity $R_{(q)}$, for this latter tells about curvature
of spacetime as a whole at $P$ and would not be supposed to depend on whichever
vector we might happen to consider at $P$. Here, we try to search for a
framework in which these two apparently conflicting aspects might be
consistently reconciled. We find a tentative sense in which this could be
achieved by endowing spacetime of a specific operational meaning. This comes,
however, at the price (or with the benefit) of having a spacetime no longer
arbitrary but, in a specific sense, constrained. The constraint turns out to be
in the form of a relation between spacetime geometry in the large scale (as
compared to $L_0$) and the matter content, namely as sort of field equations.
This comes thanks to something which happens to coincide with the expression of
balance of (matter and spacetime) exchanged heats, i.e. the thermodynamic
variational principle from which the field equations have been reported to be
derivable. This establishes a link between (this specific, operational
understanding of) the meaning of the limit expression of $R_{(q)}$ on one side
and the (large-scale) field equations on the other, this way reconnecting (once
more) the latter to a quantum feature.
| [
{
"created": "Thu, 7 May 2020 05:38:11 GMT",
"version": "v1"
},
{
"created": "Mon, 21 Jun 2021 09:19:42 GMT",
"version": "v2"
}
] | 2021-06-22 | [
[
"Pesci",
"Alessandro",
""
]
] | We study the recently reported qmetric (or zero-point-length) expressions of the Ricci (bi)scalar $R_{(q)}$ (namely, expressions of the Ricci scalar in a spacetime with a limit length $L_0$ built in), focusing specifically on the case of null separated events. A feature of these expressions is that, when considered in the coincidence limit $p \to P$, they generically exhibit a dependence on the geodesic along which the varying point $p$ approached $P$, sort of memory of how $p$ went to $P$. This fact demands a deeper understanding of the meaning of the quantity $R_{(q)}$, for this latter tells about curvature of spacetime as a whole at $P$ and would not be supposed to depend on whichever vector we might happen to consider at $P$. Here, we try to search for a framework in which these two apparently conflicting aspects might be consistently reconciled. We find a tentative sense in which this could be achieved by endowing spacetime of a specific operational meaning. This comes, however, at the price (or with the benefit) of having a spacetime no longer arbitrary but, in a specific sense, constrained. The constraint turns out to be in the form of a relation between spacetime geometry in the large scale (as compared to $L_0$) and the matter content, namely as sort of field equations. This comes thanks to something which happens to coincide with the expression of balance of (matter and spacetime) exchanged heats, i.e. the thermodynamic variational principle from which the field equations have been reported to be derivable. This establishes a link between (this specific, operational understanding of) the meaning of the limit expression of $R_{(q)}$ on one side and the (large-scale) field equations on the other, this way reconnecting (once more) the latter to a quantum feature. |
2004.02602 | Mubasher Jamil | Mustapha Azreg-A\"inou, Zihang Chen, Bojun Deng, Mubasher Jamil, Tao
Zhu, Qiang Wu, Yen-Kheng Lim | Orbital mechanics and quasiperiodic oscillation resonances of black
holes in Einstein-{\AE}ther theory | 21 pages, 17 captioned figures, accepted for publication in
Phys.Rev.D | Phys. Rev. D 102, 044028 (2020) | 10.1103/PhysRevD.102.044028 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we study the motion of test particles around two exact charged
black-hole solutions in Einstein-{\AE}ther theory. Specifically, we first
consider the quasi-periodic oscillations (QPOs) and their resonances generated
by the particle moving in the Einstein-{\AE}ther black hole and then turn to
study the periodic orbits of the massive particles. For QPOs, we drop the
usually adopted assumptions $\nu_U=\nu_\theta$, $\nu_L=\nu_r$, and
$\nu_U/\nu_L=3/2$ with $\nu_U$ ($\nu_L$) and $\nu_r$ ($\nu_\theta$) being the
upper (lower) frequency of QPOs and radial (vertical) epicyclic frequency of
the orbiting particles, respectively. Instead, we put-forward a new working
ansatz for which the Keplerian radius is much closer to that of the innermost
stable circular orbit and explore in detail the effects of the {\ae}ther field
on the frequencies of QPOs. We then realize good curves for the frequencies of
QPOs, which fit to data of three microquasars very well by ignoring any effects
of rotation and magnetic fields. The innermost stable circular orbits (isco) of
timelike particles are also analyzed and we find the isco radius increases with
increasing $c_{13}$ for the first type black hole while decreases with
increasing $c_{14}$ for the second one. We also obtain several periodic orbits
and find that they share similar taxonomy schemes as the periodic equatorial
orbits in the Schwarzschild/Kerr metrics, in addition to exact solutions for
certain choices of the Einstein-\AE ther parameters. The equations for null
geodesics are also briefly considered, where we study circular photon orbits
and bending angles for gravitational lensing.
| [
{
"created": "Thu, 2 Apr 2020 06:56:00 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Aug 2020 01:20:30 GMT",
"version": "v2"
}
] | 2020-08-18 | [
[
"Azreg-Aïnou",
"Mustapha",
""
],
[
"Chen",
"Zihang",
""
],
[
"Deng",
"Bojun",
""
],
[
"Jamil",
"Mubasher",
""
],
[
"Zhu",
"Tao",
""
],
[
"Wu",
"Qiang",
""
],
[
"Lim",
"Yen-Kheng",
""
]
] | In this paper, we study the motion of test particles around two exact charged black-hole solutions in Einstein-{\AE}ther theory. Specifically, we first consider the quasi-periodic oscillations (QPOs) and their resonances generated by the particle moving in the Einstein-{\AE}ther black hole and then turn to study the periodic orbits of the massive particles. For QPOs, we drop the usually adopted assumptions $\nu_U=\nu_\theta$, $\nu_L=\nu_r$, and $\nu_U/\nu_L=3/2$ with $\nu_U$ ($\nu_L$) and $\nu_r$ ($\nu_\theta$) being the upper (lower) frequency of QPOs and radial (vertical) epicyclic frequency of the orbiting particles, respectively. Instead, we put-forward a new working ansatz for which the Keplerian radius is much closer to that of the innermost stable circular orbit and explore in detail the effects of the {\ae}ther field on the frequencies of QPOs. We then realize good curves for the frequencies of QPOs, which fit to data of three microquasars very well by ignoring any effects of rotation and magnetic fields. The innermost stable circular orbits (isco) of timelike particles are also analyzed and we find the isco radius increases with increasing $c_{13}$ for the first type black hole while decreases with increasing $c_{14}$ for the second one. We also obtain several periodic orbits and find that they share similar taxonomy schemes as the periodic equatorial orbits in the Schwarzschild/Kerr metrics, in addition to exact solutions for certain choices of the Einstein-\AE ther parameters. The equations for null geodesics are also briefly considered, where we study circular photon orbits and bending angles for gravitational lensing. |
1511.08160 | Pedro Moraes | P.H.R.S. Moraes and R.A.C. Correa | Braneworld cosmology in $f(R,T)$ gravity | 6 pages, 1 figure | null | 10.1007/s10509-016-2677-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Braneworld scenarios consider our observable universe as a brane embedded in
a 5D space, named bulk. In this work, I derive the field equations of a
braneworld model in a generalized theory of gravitation, namely $f(R,T)$
gravity, with $R$ and $T$, representing the Ricci scalar and the trace of the
energy-momentum tensor, respectively. The cosmological parameters obtained from
this approach are in agreement with recent constraints from Supernovae Ia data
combined with baryon acoustic oscillations and cosmic microwave background
observations, favouring such an alternative description of the universe
dynamics.
| [
{
"created": "Wed, 25 Nov 2015 19:06:32 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Jan 2016 00:14:28 GMT",
"version": "v2"
}
] | 2016-02-17 | [
[
"Moraes",
"P. H. R. S.",
""
],
[
"Correa",
"R. A. C.",
""
]
] | Braneworld scenarios consider our observable universe as a brane embedded in a 5D space, named bulk. In this work, I derive the field equations of a braneworld model in a generalized theory of gravitation, namely $f(R,T)$ gravity, with $R$ and $T$, representing the Ricci scalar and the trace of the energy-momentum tensor, respectively. The cosmological parameters obtained from this approach are in agreement with recent constraints from Supernovae Ia data combined with baryon acoustic oscillations and cosmic microwave background observations, favouring such an alternative description of the universe dynamics. |
1907.13089 | Wei-Can Syu | Wei-Can Syu, Da-Shin Lee and Kin-Wang Ng | Quantum loop effects to the power spectrum of primordial perturbations
during ultra slow-roll inflation | v3: 13 pages, 9 figures | Phys. Rev. D 101, 025013 (2020) | 10.1103/PhysRevD.101.025013 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the quantum loop effects on the single-field inflationary models
in a spatially flat Friedmann-Robertson-Walker (FRW) cosmological space-time
with a general self-interacting scalar field potential, which is modeled in
terms of the Hubble flow parameters in the effective field theory approach. In
particular, we focus on the scenarios in both slow-roll to ultra-slow-roll
(SR-USR) and SR-USR-SR inflation, in which it is shown that density
perturbations originated from quantum vacuum fluctuations can be enhanced at
small-scales, and then potentially collapse into primordial black holes (PBHs).
Here our estimates indicate significant one-loop corrections around the peak of
the density power spectrum in both scenarios. The induced large quantum loop
effects should be confirmed by a more formal quantum field theory, and, if so,
should be treated in a self-consistent manner that will be discussed.
| [
{
"created": "Sat, 27 Jul 2019 01:54:48 GMT",
"version": "v1"
},
{
"created": "Sat, 3 Aug 2019 05:28:43 GMT",
"version": "v2"
},
{
"created": "Thu, 30 Jan 2020 15:40:38 GMT",
"version": "v3"
}
] | 2020-02-05 | [
[
"Syu",
"Wei-Can",
""
],
[
"Lee",
"Da-Shin",
""
],
[
"Ng",
"Kin-Wang",
""
]
] | We examine the quantum loop effects on the single-field inflationary models in a spatially flat Friedmann-Robertson-Walker (FRW) cosmological space-time with a general self-interacting scalar field potential, which is modeled in terms of the Hubble flow parameters in the effective field theory approach. In particular, we focus on the scenarios in both slow-roll to ultra-slow-roll (SR-USR) and SR-USR-SR inflation, in which it is shown that density perturbations originated from quantum vacuum fluctuations can be enhanced at small-scales, and then potentially collapse into primordial black holes (PBHs). Here our estimates indicate significant one-loop corrections around the peak of the density power spectrum in both scenarios. The induced large quantum loop effects should be confirmed by a more formal quantum field theory, and, if so, should be treated in a self-consistent manner that will be discussed. |
2006.05766 | Joao Magueijo | Joao Magueijo, Tom Zlosnik and Simone Speziale | Quantum cosmology of a dynamical Lambda | Version to be published in Phys.Rev.D | Phys. Rev. D 102, 064006 (2020) | 10.1103/PhysRevD.102.064006 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | By allowing torsion into the gravitational dynamics one can promote the
cosmological constant, $\Lambda$, to a dynamical variable in a class of
quasi-topological theories. In this paper we perform a mini-superspace
quantization of these theories in the connection representation. If $\Lambda$
is kept fixed, the solution is a delta-normalizable version of the Chern-Simons
(CS) state, which is the dual of the Hartle and Hawking and Vilenkin
wave-functions. We find that the CS state solves the Wheeler-DeWitt equation
also if $\Lambda$ is rendered dynamical by an Euler quasi-topological
invariant, {\it in the parity-even branch of the theory}. In the absence of an
infra-red (IR) cut-off, the CS state suggests the marginal probability
$P(\Lambda)=\delta(\Lambda)$. Should there be an IR cutoff (for whatever
reason) the probability is sharply peaked at the cut off. In the parity-odd
branch, however, we can still find the CS state as a particular (but not most
general) solution, but further work is needed to sharpen the predictions. For
the theory based on the Pontryagin invariant (which only has a parity-odd
branch) the CS wave function no longer is a solution to the constraints. We
find the most general solution in this case, which again leaves room for a
range of predictions for $\Lambda$.
| [
{
"created": "Wed, 10 Jun 2020 10:47:43 GMT",
"version": "v1"
},
{
"created": "Mon, 31 Aug 2020 11:48:13 GMT",
"version": "v2"
}
] | 2020-09-16 | [
[
"Magueijo",
"Joao",
""
],
[
"Zlosnik",
"Tom",
""
],
[
"Speziale",
"Simone",
""
]
] | By allowing torsion into the gravitational dynamics one can promote the cosmological constant, $\Lambda$, to a dynamical variable in a class of quasi-topological theories. In this paper we perform a mini-superspace quantization of these theories in the connection representation. If $\Lambda$ is kept fixed, the solution is a delta-normalizable version of the Chern-Simons (CS) state, which is the dual of the Hartle and Hawking and Vilenkin wave-functions. We find that the CS state solves the Wheeler-DeWitt equation also if $\Lambda$ is rendered dynamical by an Euler quasi-topological invariant, {\it in the parity-even branch of the theory}. In the absence of an infra-red (IR) cut-off, the CS state suggests the marginal probability $P(\Lambda)=\delta(\Lambda)$. Should there be an IR cutoff (for whatever reason) the probability is sharply peaked at the cut off. In the parity-odd branch, however, we can still find the CS state as a particular (but not most general) solution, but further work is needed to sharpen the predictions. For the theory based on the Pontryagin invariant (which only has a parity-odd branch) the CS wave function no longer is a solution to the constraints. We find the most general solution in this case, which again leaves room for a range of predictions for $\Lambda$. |
1007.3723 | William Nelson | Miguel Campiglia, Adam Henderson and William Nelson | Vertex Expansion for the Bianchi I model | 15 pages, 2 figures | Phys.Rev.D82:064036,2010 | 10.1103/PhysRevD.82.064036 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A perturbative expansion of Loop Quantum Cosmological transitions amplitudes
of Bianchi I models is performed. Following the procedure outlined in [1,2] for
isotropic models, it is shown that the resulting expansion can be written in
the form of a series of amplitudes each with a fixed number of transitions
mimicking a spin foam expansion. This analogy is more complete than in the
isotropic case, since there are now the additional anisotropic degrees of
freedom which play the role of `colouring' of the spin foams. Furthermore, the
isotropic expansion is recovered by integrating out the anisotropies.
| [
{
"created": "Wed, 21 Jul 2010 19:12:01 GMT",
"version": "v1"
}
] | 2010-11-12 | [
[
"Campiglia",
"Miguel",
""
],
[
"Henderson",
"Adam",
""
],
[
"Nelson",
"William",
""
]
] | A perturbative expansion of Loop Quantum Cosmological transitions amplitudes of Bianchi I models is performed. Following the procedure outlined in [1,2] for isotropic models, it is shown that the resulting expansion can be written in the form of a series of amplitudes each with a fixed number of transitions mimicking a spin foam expansion. This analogy is more complete than in the isotropic case, since there are now the additional anisotropic degrees of freedom which play the role of `colouring' of the spin foams. Furthermore, the isotropic expansion is recovered by integrating out the anisotropies. |
gr-qc/0510086 | Sushil Srivastava | S. K. Srivastava | Dual Nature of the Ricci Scalar and its Certain Consequences | 118 pages, suggestions and comments welcome | null | null | null | gr-qc | null | Ricci scalar is the key ingredient of non-Newtonian theory of gravity, where
space-time geometry has a crucial role. Normally, it is supposed to be a
geometrical field, but interestingly it also behaves like a physical field.
Thus it plays dual role in the arena of gravitation. This article is an
overview of the work related to dual roles of the Ricci scalar. A scalar is a
mathematical concept representing a spinless particle.Here, particle concept,
manifesting the physical aspect of the Ricci scalar, is termed as riccion.It is
a scalar particle with (mass)$^2$ inversely proportional to the gravitational
constant. Many intereseting consequences of dual role of the Ricci scalar are
discussed here. It causes inflationary scenario in the early universe without
taking another scalar like ``inflaton''. It is found that a riccion behaves
like an instanton also. This feature inspires``primordial inflation''.It is
interesting to see that a riccion, obtained from higher-dimensional space-time,
decouples into fermion and anti-fermion pair, if parity is violated. One-loop
renormalization of riccion indicates fractal geometry at high
energy.Homogeneous and inhomogeneous models of the early universe are derived
using dual role of the Ricci scalar. Production of spinless and spin-1/2
particles, due to riccion coupling, is discussed here. Contribution of riccion
to the cosmic dark energy is obtained here through one-loop renormalization and
it is shown that dark energy decays to dark matter during expansion of the
universe. It inspires a new cosmological scenario consistent with observational
evidences.
| [
{
"created": "Wed, 19 Oct 2005 07:58:12 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Nov 2005 09:38:31 GMT",
"version": "v2"
}
] | 2019-02-27 | [
[
"Srivastava",
"S. K.",
""
]
] | Ricci scalar is the key ingredient of non-Newtonian theory of gravity, where space-time geometry has a crucial role. Normally, it is supposed to be a geometrical field, but interestingly it also behaves like a physical field. Thus it plays dual role in the arena of gravitation. This article is an overview of the work related to dual roles of the Ricci scalar. A scalar is a mathematical concept representing a spinless particle.Here, particle concept, manifesting the physical aspect of the Ricci scalar, is termed as riccion.It is a scalar particle with (mass)$^2$ inversely proportional to the gravitational constant. Many intereseting consequences of dual role of the Ricci scalar are discussed here. It causes inflationary scenario in the early universe without taking another scalar like ``inflaton''. It is found that a riccion behaves like an instanton also. This feature inspires``primordial inflation''.It is interesting to see that a riccion, obtained from higher-dimensional space-time, decouples into fermion and anti-fermion pair, if parity is violated. One-loop renormalization of riccion indicates fractal geometry at high energy.Homogeneous and inhomogeneous models of the early universe are derived using dual role of the Ricci scalar. Production of spinless and spin-1/2 particles, due to riccion coupling, is discussed here. Contribution of riccion to the cosmic dark energy is obtained here through one-loop renormalization and it is shown that dark energy decays to dark matter during expansion of the universe. It inspires a new cosmological scenario consistent with observational evidences. |
gr-qc/0008030 | Ivan S. N. Booth | Ivan S. Booth | A quasilocal Hamiltonian for gravity with classical and quantum
applications | PhD Thesis from University of Waterloo, 199 pages, 10 figures | null | null | null | gr-qc | null | I modify the quasilocal energy formalism of Brown and York into a purely
Hamiltonian form. As part of the reformulation, I remove their restriction that
the time evolution of the boundary of the spacetime be orthogonal to the leaves
of the time foliation. Thus the new formulation allows an arbitrary evolution
of the boundary which physically corresponds to allowing general motions of the
set of observers making up that boundary. I calculate the rate of change of the
quasilocal energy in such situations, show how it transforms with respect to
boosts of the boundaries, and use the Lanczos-Israel thin shell formalism to
reformulate it from an operational point of view. These steps are performed
both for pure gravity and gravity with attendant matter fields. I then apply
the formalism to characterize naked black holes and study their properties,
investigate gravitational tidal heating, and combine it with the path integral
formulation of quantum gravity to analyze the creation of pairs of charged and
rotating black holes. I show that one must use complex instantons to study this
process though the probabilities of creation remain real and consistent with
the view that the entropy of a black hole is the logarithm of the number of its
quantum states.
| [
{
"created": "Mon, 14 Aug 2000 17:47:41 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Booth",
"Ivan S.",
""
]
] | I modify the quasilocal energy formalism of Brown and York into a purely Hamiltonian form. As part of the reformulation, I remove their restriction that the time evolution of the boundary of the spacetime be orthogonal to the leaves of the time foliation. Thus the new formulation allows an arbitrary evolution of the boundary which physically corresponds to allowing general motions of the set of observers making up that boundary. I calculate the rate of change of the quasilocal energy in such situations, show how it transforms with respect to boosts of the boundaries, and use the Lanczos-Israel thin shell formalism to reformulate it from an operational point of view. These steps are performed both for pure gravity and gravity with attendant matter fields. I then apply the formalism to characterize naked black holes and study their properties, investigate gravitational tidal heating, and combine it with the path integral formulation of quantum gravity to analyze the creation of pairs of charged and rotating black holes. I show that one must use complex instantons to study this process though the probabilities of creation remain real and consistent with the view that the entropy of a black hole is the logarithm of the number of its quantum states. |
1003.4767 | Milton Ruiz | Miguel Alcubierre, Juan C. Degollado, Dario Nunez, Milton Ruiz,
Marcelo Salgado | Dynamic transition to spontaneous scalarization in boson stars | Minor changes to match the final version to appear in PRD | Phys.Rev.D81:124018,2010 | 10.1103/PhysRevD.81.124018 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that the phenomenon of spontaneous scalarization predicted in neutron
stars within the framework of scalar-tensor tensor theories of gravity, also
takes place in boson stars without including a self-interaction term for the
boson field (other than the mass term), contrary to what was claimed before.
The analysis is performed in the physical (Jordan) frame and is based on a 3+1
decomposition of spacetime assuming spherical symmetry.
| [
{
"created": "Wed, 24 Mar 2010 22:32:43 GMT",
"version": "v1"
},
{
"created": "Wed, 19 May 2010 20:17:10 GMT",
"version": "v2"
}
] | 2012-07-30 | [
[
"Alcubierre",
"Miguel",
""
],
[
"Degollado",
"Juan C.",
""
],
[
"Nunez",
"Dario",
""
],
[
"Ruiz",
"Milton",
""
],
[
"Salgado",
"Marcelo",
""
]
] | We show that the phenomenon of spontaneous scalarization predicted in neutron stars within the framework of scalar-tensor tensor theories of gravity, also takes place in boson stars without including a self-interaction term for the boson field (other than the mass term), contrary to what was claimed before. The analysis is performed in the physical (Jordan) frame and is based on a 3+1 decomposition of spacetime assuming spherical symmetry. |
gr-qc/9907075 | Luis A. Nunez | G. Contreras, L.A. N\'u\~nez, and U. Percoco | Ricci Collineations for Non-Degenerate, Diagonal and Spherically
Symmetric Ricci Tensors | null | Gen.Rel.Grav. 32 (2000) 285-294 | 10.1023/A:1001983426767 | null | gr-qc | null | The expression of the vector field generator of a Ricci Collineation for
diagonal, spherically symmetric and non-degenerate Ricci tensors is obtained.
The resulting expressions show that the time and radial first derivatives of
the components of the Ricci tensor can be used to classify the collineation,
leading to 64 families.
Some examples illustrate how to obtain the collineation vector.
| [
{
"created": "Fri, 23 Jul 1999 16:52:56 GMT",
"version": "v1"
}
] | 2016-08-15 | [
[
"Contreras",
"G.",
""
],
[
"Núñez",
"L. A.",
""
],
[
"Percoco",
"U.",
""
]
] | The expression of the vector field generator of a Ricci Collineation for diagonal, spherically symmetric and non-degenerate Ricci tensors is obtained. The resulting expressions show that the time and radial first derivatives of the components of the Ricci tensor can be used to classify the collineation, leading to 64 families. Some examples illustrate how to obtain the collineation vector. |
2106.13607 | Gamal G.L. Nashed | G.G.L. Nashed, S.D. Odintsov and V.K. Oikonomou | Anisotropic compact stars in higher-order curvature theory | 16 pages, 12 figures, 3 tables | Eur. Phys. J. C (2021) 81:528 | 10.1140/epjc/s10052-021-09321-3 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this paper, we shall consider spherically symmetric spacetime solutions
describing the interior of stellar compact objects, in the context of
higher-order curvature theory of the f(R) type. We shall derive the non--vacuum
field equations of the higher-order curvature theory, without assuming any
specific form of the $\mathrm{f(R)}$ theory, specifying the analysis for a
spherically symmetric spacetime with two unknown functions. We obtain a system
of highly non-linear differential equations, which consists of four
differential equations with six unknown functions. To solve such a system, we
assume a specific form of metric potentials, using the Krori-Barua ansatz. We
successfully solve the system of differential equations, and we derive all the
components of the energy-momentum tensor. Moreover, we derive the non-trivial
general form of $\mathrm{f(R)}$ that may generate such solutions and calculate
the dynamic Ricci scalar of the anisotropic star. Accordingly, we calculate the
asymptotic form of the function $\mathrm{f(R)}$, which is a polynomial
function. We match the derived interior solution with the exterior one, which
was derived in \cite{Nashed:2019tuk}, with the latter also resulting in a
non-trivial form of the Ricci scalar. Notably but rather expected, the exterior
solution differs from the Schwarzschild one in the context of general
relativity. The matching procedure will eventually relate two constants with
the mass and radius of the compact stellar object. We list the necessary
conditions that any compact anisotropic star must satisfy and explain in detail
that our model bypasses all of these conditions for a special compact star
$\textit {Her X--1 }$, which has an estimated mass and radius \textit {(mass =
0.85 $\pm 0.15M_{\circledcirc}$\,\, and\, \,radius $= 8.1 \pm 0.41$km)}.
| [
{
"created": "Fri, 25 Jun 2021 12:58:52 GMT",
"version": "v1"
}
] | 2021-06-28 | [
[
"Nashed",
"G. G. L.",
""
],
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
]
] | In this paper, we shall consider spherically symmetric spacetime solutions describing the interior of stellar compact objects, in the context of higher-order curvature theory of the f(R) type. We shall derive the non--vacuum field equations of the higher-order curvature theory, without assuming any specific form of the $\mathrm{f(R)}$ theory, specifying the analysis for a spherically symmetric spacetime with two unknown functions. We obtain a system of highly non-linear differential equations, which consists of four differential equations with six unknown functions. To solve such a system, we assume a specific form of metric potentials, using the Krori-Barua ansatz. We successfully solve the system of differential equations, and we derive all the components of the energy-momentum tensor. Moreover, we derive the non-trivial general form of $\mathrm{f(R)}$ that may generate such solutions and calculate the dynamic Ricci scalar of the anisotropic star. Accordingly, we calculate the asymptotic form of the function $\mathrm{f(R)}$, which is a polynomial function. We match the derived interior solution with the exterior one, which was derived in \cite{Nashed:2019tuk}, with the latter also resulting in a non-trivial form of the Ricci scalar. Notably but rather expected, the exterior solution differs from the Schwarzschild one in the context of general relativity. The matching procedure will eventually relate two constants with the mass and radius of the compact stellar object. We list the necessary conditions that any compact anisotropic star must satisfy and explain in detail that our model bypasses all of these conditions for a special compact star $\textit {Her X--1 }$, which has an estimated mass and radius \textit {(mass = 0.85 $\pm 0.15M_{\circledcirc}$\,\, and\, \,radius $= 8.1 \pm 0.41$km)}. |
1912.04547 | Hideo Iguchi | Tam\'as S. Bir\'o, Viktor G. Czinner, Hideo Iguchi, P\'eter V\'an | Volume dependent extension of Kerr-Newman black hole thermodynamics | 6 pages, 1 figure; accepted for publication in Phys. Lett. B | Phys. Lett. B 803 (2020) 135344 | 10.1016/j.physletb.2020.135344 | null | gr-qc cond-mat.stat-mech hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that the Hawking--Bekenstein entropy formula is modified by a factor
of $8/3$ if one also considers a work term in the 1st law of thermodynamics by
a pressure stemming from the Hawking radiation. We give an intuitive definition
for the corresponding thermodynamical volume by the implicit definition
$\epsilon=Mc^2/V$, which is the average energy density of the Hawking
radiation. This volume scales as $V \sim M^5$, agreeing with other suggestions.
As a result the corresponding Smarr relation describes an extensive entropy and
a stable effective equation of state $S(E,V)\sim E^{3/4}V^{1/4}$. These results
pertain for charged and rotating Kerr-Newman black holes.
| [
{
"created": "Tue, 10 Dec 2019 07:24:58 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Mar 2020 04:38:01 GMT",
"version": "v2"
}
] | 2020-04-22 | [
[
"Biró",
"Tamás S.",
""
],
[
"Czinner",
"Viktor G.",
""
],
[
"Iguchi",
"Hideo",
""
],
[
"Ván",
"Péter",
""
]
] | We show that the Hawking--Bekenstein entropy formula is modified by a factor of $8/3$ if one also considers a work term in the 1st law of thermodynamics by a pressure stemming from the Hawking radiation. We give an intuitive definition for the corresponding thermodynamical volume by the implicit definition $\epsilon=Mc^2/V$, which is the average energy density of the Hawking radiation. This volume scales as $V \sim M^5$, agreeing with other suggestions. As a result the corresponding Smarr relation describes an extensive entropy and a stable effective equation of state $S(E,V)\sim E^{3/4}V^{1/4}$. These results pertain for charged and rotating Kerr-Newman black holes. |
2304.08624 | Kazufumi Takahashi | Kazufumi Takahashi, Masato Minamitsuji, Hayato Motohashi | Effective description of generalized disformal theories | 16 pages | JCAP 07 (2023) 009 | 10.1088/1475-7516/2023/07/009 | YITP-23-46 | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | Generalized disformal transformations enable us to construct the generalized
disformal Horndeski theories, which form the most general class of ghost-free
scalar-tensor theories to this date. We extend the effective field theory (EFT)
of cosmological perturbations to incorporate these generalized disformal
Horndeski theories. The main difference from the conventional EFT is that our
extended EFT involves operators with higher spatial derivatives of the lapse
function. Our EFT also accommodates the generalized disformal transformation of
U-DHOST theories.
| [
{
"created": "Mon, 17 Apr 2023 21:28:47 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Jul 2023 21:51:50 GMT",
"version": "v2"
}
] | 2023-07-06 | [
[
"Takahashi",
"Kazufumi",
""
],
[
"Minamitsuji",
"Masato",
""
],
[
"Motohashi",
"Hayato",
""
]
] | Generalized disformal transformations enable us to construct the generalized disformal Horndeski theories, which form the most general class of ghost-free scalar-tensor theories to this date. We extend the effective field theory (EFT) of cosmological perturbations to incorporate these generalized disformal Horndeski theories. The main difference from the conventional EFT is that our extended EFT involves operators with higher spatial derivatives of the lapse function. Our EFT also accommodates the generalized disformal transformation of U-DHOST theories. |
1405.2215 | Elizabeth Winstanley | Victor E. Ambrus and Elizabeth Winstanley | Dirac fermions on an anti-de Sitter background | 10 pages, 4 figures, submitted to the proceedings of the TIM-13
Physics Conference, 21-24 November 2013, Timisoara, Romania | AIP Conf. Proc. 1634, 40 (2014) | 10.1063/1.4903012 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using an exact expression for the bi-spinor of parallel transport, we
construct the Feynman propagator for Dirac fermions in the vacuum state on
anti-de Sitter space-time. We compute the vacuum expectation value of the
stress-energy tensor by removing coincidence-limit divergences using the
Hadamard method. We then use the vacuum Feynman propagator to compute thermal
expectation values at finite temperature. We end with a discussion of rigidly
rotating thermal states.
| [
{
"created": "Fri, 9 May 2014 12:25:05 GMT",
"version": "v1"
}
] | 2015-01-05 | [
[
"Ambrus",
"Victor E.",
""
],
[
"Winstanley",
"Elizabeth",
""
]
] | Using an exact expression for the bi-spinor of parallel transport, we construct the Feynman propagator for Dirac fermions in the vacuum state on anti-de Sitter space-time. We compute the vacuum expectation value of the stress-energy tensor by removing coincidence-limit divergences using the Hadamard method. We then use the vacuum Feynman propagator to compute thermal expectation values at finite temperature. We end with a discussion of rigidly rotating thermal states. |
2304.05852 | Diego Rubiera-Garcia | Merce Guerrero, Gonzalo J. Olmo, Diego Rubiera-Garcia | Geodesic completeness of effective null geodesics in regular space-times
with non-linear electrodynamics | 7 pages, 4 figures | Eur.Phys.J.C 83 (2023) 9, 785 | 10.1140/epjc/s10052-023-11969-y | IPARCOS-UCM-23-112 | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study the completeness of light trajectories in certain spherically
symmetric regular geometries found in Palatini theories of gravity threaded by
non-linear (electromagnetic) fields, which makes their propagation to happen
along geodesics of an effective metric. Two types of geodesic restoration
mechanisms are employed: by pushing the focal point to infinite affine
distance, thus unreachable in finite time by any sets of geodesics, or by the
presence of a defocusing surface associated to the development of a wormhole
throat. We discuss several examples of such geometries to conclude the
completeness of all such effective paths. Our results are of interest both for
the finding of singularity-free solutions and for the analysis of their optical
appearances e.g. in shadow observations.
| [
{
"created": "Wed, 12 Apr 2023 13:31:49 GMT",
"version": "v1"
}
] | 2023-09-25 | [
[
"Guerrero",
"Merce",
""
],
[
"Olmo",
"Gonzalo J.",
""
],
[
"Rubiera-Garcia",
"Diego",
""
]
] | We study the completeness of light trajectories in certain spherically symmetric regular geometries found in Palatini theories of gravity threaded by non-linear (electromagnetic) fields, which makes their propagation to happen along geodesics of an effective metric. Two types of geodesic restoration mechanisms are employed: by pushing the focal point to infinite affine distance, thus unreachable in finite time by any sets of geodesics, or by the presence of a defocusing surface associated to the development of a wormhole throat. We discuss several examples of such geometries to conclude the completeness of all such effective paths. Our results are of interest both for the finding of singularity-free solutions and for the analysis of their optical appearances e.g. in shadow observations. |
2301.06483 | Guangzhou Guo | Guangzhou Guo, Peng Wang, Houwen Wu and Haitang Yang | Superradiance Instabilities of Charged Black Holes in
Einstein-Maxwell-scalar Theory | 24 pages, 7 figures, references added | null | 10.1007/JHEP07(2023)070 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study time evolutions of charged scalar perturbations on the background of
a charged hairy black hole, in which the perturbations can be governed by a
double-peak effective potential. By extracting quasinormal modes from the
waveform of scalar perturbations, we discover that some quasinormal modes,
which are trapped in a potential well between two potential peaks, can be
superradiantly amplified. These superradiant modes make the hairy black hole
unstable against charged scalar perturbations. Moreover, it is found that the
superradiant modes arise from the competition between the superradiant
amplification caused by tunneling through the outer potential barrier and the
leakage of modes through the inner potential barrier into the black hole.
| [
{
"created": "Mon, 16 Jan 2023 15:41:56 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Feb 2023 08:30:33 GMT",
"version": "v2"
}
] | 2023-07-26 | [
[
"Guo",
"Guangzhou",
""
],
[
"Wang",
"Peng",
""
],
[
"Wu",
"Houwen",
""
],
[
"Yang",
"Haitang",
""
]
] | We study time evolutions of charged scalar perturbations on the background of a charged hairy black hole, in which the perturbations can be governed by a double-peak effective potential. By extracting quasinormal modes from the waveform of scalar perturbations, we discover that some quasinormal modes, which are trapped in a potential well between two potential peaks, can be superradiantly amplified. These superradiant modes make the hairy black hole unstable against charged scalar perturbations. Moreover, it is found that the superradiant modes arise from the competition between the superradiant amplification caused by tunneling through the outer potential barrier and the leakage of modes through the inner potential barrier into the black hole. |
gr-qc/0211043 | Felix Finster | Felix Finster, Joel Smoller, and Shing-Tung Yau | Non-Existence of Black Hole Solutions to Static, Spherically Symmetric
Einstein-Dirac Systems - a Critical Discussion | 4 pages, 2 figures | null | null | null | gr-qc | null | This short note compares different methods to prove that Einstein-Dirac
systems have no static, spherically symmetric solutions.
| [
{
"created": "Tue, 12 Nov 2002 17:08:09 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Finster",
"Felix",
""
],
[
"Smoller",
"Joel",
""
],
[
"Yau",
"Shing-Tung",
""
]
] | This short note compares different methods to prove that Einstein-Dirac systems have no static, spherically symmetric solutions. |
1512.06397 | Sebastiano Bernuzzi | Sebastiano Bernuzzi, David Radice, Christian D. Ott, Luke F. Roberts,
Philipp Moesta, Filippo Galeazzi | How loud are neutron star mergers? | 6 pages, 3 figures. Waveforms available at
https://zenodo.org/record/57844 | Phys. Rev. D 94, 024023 (2016) | 10.1103/PhysRevD.94.024023 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present results from the first large parameter study of neutron star
mergers using fully general relativistic simulations with finite-temperature
microphysical equations of state and neutrino cooling. We consider equal and
unequal-mass binaries drawn from the galactic population and simulate each
binary with three different equations of state. Our focus is on the emission of
energy and angular momentum in gravitational waves in the postmerger phase. We
find that the emitted gravitational-wave energy in the first
$\sim$$10\,\mathrm{ms}$ of the life of the resulting hypermassive neutron star
(HMNS) is about twice the energy emitted over the entire inspiral history of
the binary. The total radiated energy per binary mass is comparable to or
larger than that of nonspinning black hole inspiral-mergers. About $0.8-2.5\%$
of the binary mass-energy is emitted at kHz frequencies in the early HMNS
evolution. We find a clear dependence of the postmerger GW emission on binary
configuration and equation of state and show that it can be encoded as a broad
function of the binary tidal coupling constant $\kappa^T_2$. Our results also
demonstrate that the dimensionless spin of black holes resulting from
subsequent HMNS collapse are limited to $\lesssim0.7-0.8$. This may
significantly impact the neutrino pair annihilation mechanism for powering
short gamma-ray bursts (sGRB).
| [
{
"created": "Sun, 20 Dec 2015 16:47:28 GMT",
"version": "v1"
},
{
"created": "Wed, 13 Jul 2016 21:36:49 GMT",
"version": "v2"
}
] | 2016-07-20 | [
[
"Bernuzzi",
"Sebastiano",
""
],
[
"Radice",
"David",
""
],
[
"Ott",
"Christian D.",
""
],
[
"Roberts",
"Luke F.",
""
],
[
"Moesta",
"Philipp",
""
],
[
"Galeazzi",
"Filippo",
""
]
] | We present results from the first large parameter study of neutron star mergers using fully general relativistic simulations with finite-temperature microphysical equations of state and neutrino cooling. We consider equal and unequal-mass binaries drawn from the galactic population and simulate each binary with three different equations of state. Our focus is on the emission of energy and angular momentum in gravitational waves in the postmerger phase. We find that the emitted gravitational-wave energy in the first $\sim$$10\,\mathrm{ms}$ of the life of the resulting hypermassive neutron star (HMNS) is about twice the energy emitted over the entire inspiral history of the binary. The total radiated energy per binary mass is comparable to or larger than that of nonspinning black hole inspiral-mergers. About $0.8-2.5\%$ of the binary mass-energy is emitted at kHz frequencies in the early HMNS evolution. We find a clear dependence of the postmerger GW emission on binary configuration and equation of state and show that it can be encoded as a broad function of the binary tidal coupling constant $\kappa^T_2$. Our results also demonstrate that the dimensionless spin of black holes resulting from subsequent HMNS collapse are limited to $\lesssim0.7-0.8$. This may significantly impact the neutrino pair annihilation mechanism for powering short gamma-ray bursts (sGRB). |
gr-qc/0102020 | Garcia | L.C.Garcia de Andrade | Spin-Polarised Cylinders and Torsion Balances to test Einstein-Cartan
Gravity? | latex file | null | null | null | gr-qc | null | Spin-Polarised cylinders with and without axial magnetic fields are obtained
as particular families of solutions of Einstein-Cartan gravity (EC).The first
solution represents a spin-polarised cylinder in teleparallel gravity.The
second solution is a magnetized solution representing a spin-polarised cylinder
where the magnetic fields and spins are distributed along the infinite axis of
the cylinder.Altough it seems that the first solution is less realist than the
second it could be obtained by shielding the magnetic fields with a
superconductor.The second solution is computed by taking into account the
Ritter et al. experiment with the test spin-polarized mass to test spin
dependent forces.Ritter experiment deals with a test mass with $>10^{23}$ spin
polarized electrons which leads to a spin density of $10^{-4}gcm^{-1}s^{-1}$.
| [
{
"created": "Tue, 6 Feb 2001 04:15:35 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"de Andrade",
"L. C. Garcia",
""
]
] | Spin-Polarised cylinders with and without axial magnetic fields are obtained as particular families of solutions of Einstein-Cartan gravity (EC).The first solution represents a spin-polarised cylinder in teleparallel gravity.The second solution is a magnetized solution representing a spin-polarised cylinder where the magnetic fields and spins are distributed along the infinite axis of the cylinder.Altough it seems that the first solution is less realist than the second it could be obtained by shielding the magnetic fields with a superconductor.The second solution is computed by taking into account the Ritter et al. experiment with the test spin-polarized mass to test spin dependent forces.Ritter experiment deals with a test mass with $>10^{23}$ spin polarized electrons which leads to a spin density of $10^{-4}gcm^{-1}s^{-1}$. |
1402.3155 | Francesco Cianfrani dr | Emanuele Alesci, Francesco Cianfrani | Quantum Reduced Loop Gravity: Semiclassical limit | 23 pages | null | 10.1103/PhysRevD.90.024006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the semiclassical limit of Quantum Reduced Loop Gravity, a
recently proposed model to address the quantum dynamics of the early Universe.
We apply the techniques developed in full Loop Quantum Gravity to define the
semiclassical states in the kinematical Hilbert space and evaluating the
expectation value of the euclidean scalar constraint we demonstrate that it
coincides with the classical expression, {\it i.e.} the one of a local Bianchi
I dynamics. The result holds as a leading order expansion in the scale factors
of the Universe and opens the way to study the subleading corrections to the
semiclassical dynamics. We outline how by retaining a suitable finite
coordinate length for holonomies our effective Hamiltonian at the leading order
coincides with the one expected from LQC. This result is an important step in
fixing the correspondence between LQG and LQC.
| [
{
"created": "Thu, 13 Feb 2014 14:47:43 GMT",
"version": "v1"
}
] | 2015-06-18 | [
[
"Alesci",
"Emanuele",
""
],
[
"Cianfrani",
"Francesco",
""
]
] | We discuss the semiclassical limit of Quantum Reduced Loop Gravity, a recently proposed model to address the quantum dynamics of the early Universe. We apply the techniques developed in full Loop Quantum Gravity to define the semiclassical states in the kinematical Hilbert space and evaluating the expectation value of the euclidean scalar constraint we demonstrate that it coincides with the classical expression, {\it i.e.} the one of a local Bianchi I dynamics. The result holds as a leading order expansion in the scale factors of the Universe and opens the way to study the subleading corrections to the semiclassical dynamics. We outline how by retaining a suitable finite coordinate length for holonomies our effective Hamiltonian at the leading order coincides with the one expected from LQC. This result is an important step in fixing the correspondence between LQG and LQC. |
1003.1889 | Olivier Minazzoli | Olivier Minazzoli and Bertrand Chauvineau | Explicit form of the Scalar-Tensor metric to be used for propagation of
light in the Solar system in continuity of the GR IAU2000 metric | 10 pages, 1 figure | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The metric recommanded by the IAU2000 resolutions allows propagation of light
calculations at the c-3 level in the general relativity framework. In a recent
paper [1], motivated by forthcoming space experiments involving propagation of
light in the Solar System (ASTROD, GAIA, LATOR, ODYSSEY, SAGAS, SIM, TIPO,
...), we have proposed an extention of the IAU metric equations at the c-4
level. This has been made in the general relativity framework. However,
scalar-tensor theories may induce corrections numerically comparable to the c-4
general relativistic terms. Accordingly, one proposes in this paper an
extension of [1] to the scalar-tensor case. The case of a strongly hierarchized
system (such as the Solar system) is emphasized. In this case, an explicit
metric solution is proposed.
| [
{
"created": "Tue, 9 Mar 2010 14:54:10 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Mar 2010 07:59:12 GMT",
"version": "v2"
}
] | 2010-03-15 | [
[
"Minazzoli",
"Olivier",
""
],
[
"Chauvineau",
"Bertrand",
""
]
] | The metric recommanded by the IAU2000 resolutions allows propagation of light calculations at the c-3 level in the general relativity framework. In a recent paper [1], motivated by forthcoming space experiments involving propagation of light in the Solar System (ASTROD, GAIA, LATOR, ODYSSEY, SAGAS, SIM, TIPO, ...), we have proposed an extention of the IAU metric equations at the c-4 level. This has been made in the general relativity framework. However, scalar-tensor theories may induce corrections numerically comparable to the c-4 general relativistic terms. Accordingly, one proposes in this paper an extension of [1] to the scalar-tensor case. The case of a strongly hierarchized system (such as the Solar system) is emphasized. In this case, an explicit metric solution is proposed. |
gr-qc/0307044 | Sergio E. Jor\'as | S.E. Jor\'as and T.J. Stuchi | Chaos in a closed Friedmann-Robertson-Walker universe: An imaginary
approach | 11 pages, 27 figures. Corrected some references and typos | Phys.Rev. D68 (2003) 123525 | 10.1103/PhysRevD.68.123525 | null | gr-qc nlin.CD | null | In this work we study the existence of mechanisms of transition to global
chaos in a closed Friedmann-Robertson-Walker universe with a massive
conformally coupled scalar field. We propose a complexification of the radius
of the universe so that the global dynamics can be understood. We show
numerically the existence of heteroclinic connections of the unstable and
stable manifolds to periodic orbits associated to the saddle-center equilibrium
points. We find two bifurcations which are crucial in creating non-collapsing
universes both in the real and imaginary version of the models. The techniques
presented here can be employed in any cosmological model.
| [
{
"created": "Wed, 9 Jul 2003 23:36:29 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Feb 2004 23:40:10 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Jorás",
"S. E.",
""
],
[
"Stuchi",
"T. J.",
""
]
] | In this work we study the existence of mechanisms of transition to global chaos in a closed Friedmann-Robertson-Walker universe with a massive conformally coupled scalar field. We propose a complexification of the radius of the universe so that the global dynamics can be understood. We show numerically the existence of heteroclinic connections of the unstable and stable manifolds to periodic orbits associated to the saddle-center equilibrium points. We find two bifurcations which are crucial in creating non-collapsing universes both in the real and imaginary version of the models. The techniques presented here can be employed in any cosmological model. |
1210.7466 | Junichi Iwasaki | Junichi Iwasaki | Time evolution of Hamiltonian constraint system: an idea applicable to
quantum gravity | 10 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Hamiltonian constraint system is the canonical formulation of a physical
system with a Hamiltonian constrained to vanish. In terms of the canonical
variables, we define what we call reference observable, with respect to which
other observables evolve. We study if it plays the role of time. As simple
examples, we study the theories of non-relativistic and relativistic particles.
We outline an application of the idea to general relativity.
| [
{
"created": "Sun, 28 Oct 2012 14:59:51 GMT",
"version": "v1"
}
] | 2012-10-30 | [
[
"Iwasaki",
"Junichi",
""
]
] | The Hamiltonian constraint system is the canonical formulation of a physical system with a Hamiltonian constrained to vanish. In terms of the canonical variables, we define what we call reference observable, with respect to which other observables evolve. We study if it plays the role of time. As simple examples, we study the theories of non-relativistic and relativistic particles. We outline an application of the idea to general relativity. |
1511.03785 | Babak Vakili | B. Vakili and M. A. Gorji | Nonsingular universe from generalized thermostatistics | 6 pages, no figures | Int. J. Mod. Phys. D 25 (2016) 1650028 | 10.1142/S0218271816500280 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the statistical mechanics of the early radiation dominated universe
in the context of a generalized uncertainty principle which supports the
existence of a minimal length scale. Utilizing the resultant modified
thermodynamical quantities, we obtain a deformed Friedmann equation which is
very similar to that arises from loop quantum cosmology scenarios. The energy
and entropy densities get maximum bounds about Planck temperature and a
nonsingular universe then emerges in this setup.
| [
{
"created": "Thu, 12 Nov 2015 05:50:48 GMT",
"version": "v1"
}
] | 2016-01-22 | [
[
"Vakili",
"B.",
""
],
[
"Gorji",
"M. A.",
""
]
] | We study the statistical mechanics of the early radiation dominated universe in the context of a generalized uncertainty principle which supports the existence of a minimal length scale. Utilizing the resultant modified thermodynamical quantities, we obtain a deformed Friedmann equation which is very similar to that arises from loop quantum cosmology scenarios. The energy and entropy densities get maximum bounds about Planck temperature and a nonsingular universe then emerges in this setup. |
1111.4356 | Stefano Finazzi | Antonin Coutant, Stefano Finazzi, Stefano Liberati, and Renaud
Parentani | Impossibility of superluminal travel in Lorentz violating theories | 5 pages, 3 figures | Phys. Rev. D 85, 064020 (2012) | 10.1103/PhysRevD.85.064020 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Warp drives are space-times allowing for superluminal travel. However, they
are quantum mechanically unstable because they produce a Hawking-like radiation
which is blue shifted at their front wall without any bound. We reexamine this
instability when local Lorentz invariance is violated at ultrahigh energy by
dispersion, as in some theories of quantum gravity. Interestingly, even though
the ultraviolet divergence is now regulated, warp drives are still unstable.
Moreover the type of instability is different whether one uses a subluminal or
a superluminal dispersion relation. In the first case, a black-hole laser
yields an exponential amplification of the emitted flux whereas, in the second,
infrared effects produce a linear growth of that flux. These results suggest
that chronology could still be protected when violating Lorentz invariance.
| [
{
"created": "Fri, 18 Nov 2011 13:28:33 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Apr 2012 10:05:58 GMT",
"version": "v2"
}
] | 2012-04-12 | [
[
"Coutant",
"Antonin",
""
],
[
"Finazzi",
"Stefano",
""
],
[
"Liberati",
"Stefano",
""
],
[
"Parentani",
"Renaud",
""
]
] | Warp drives are space-times allowing for superluminal travel. However, they are quantum mechanically unstable because they produce a Hawking-like radiation which is blue shifted at their front wall without any bound. We reexamine this instability when local Lorentz invariance is violated at ultrahigh energy by dispersion, as in some theories of quantum gravity. Interestingly, even though the ultraviolet divergence is now regulated, warp drives are still unstable. Moreover the type of instability is different whether one uses a subluminal or a superluminal dispersion relation. In the first case, a black-hole laser yields an exponential amplification of the emitted flux whereas, in the second, infrared effects produce a linear growth of that flux. These results suggest that chronology could still be protected when violating Lorentz invariance. |
2404.11931 | Shagun Kaushal | Sourav Bhattacharya and Shagun Kaushal | Entanglement generation between two comoving Unruh-DeWitt detectors in
the cosmological de Sitter spacetime | 23 pages, 5 figs | null | null | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the entanglement generation or harvesting between two
identical Unruh-DeWitt detectors in the cosmological de Sitter spacetime. We
consider two comoving two-level detectors at a coincident spatial position. The
detectors are assumed to be unentangled initially. The detectors are
individually coupled to a scalar field, which eventually leads to coupling
between the two detectors. We consider two kinds of scalar fields --
conformally symmetric and massless minimally coupled, for both real and complex
cases. By tracing out the degrees of freedom corresponding to the scalar field,
we construct the reduced density matrix for the two detectors, whose
eigenvalues characterise transitions between the energy levels of the
detectors. By using the existing results for the detector response functions
per unit proper time for these fields, we next compute the logarithmic
negativity, quantifying the degree of entanglement generated at late times
between the two detectors. The similarities and differences of these results
for different kind of scalar fields have been discussed.
| [
{
"created": "Thu, 18 Apr 2024 06:20:07 GMT",
"version": "v1"
},
{
"created": "Sat, 20 Apr 2024 17:39:59 GMT",
"version": "v2"
}
] | 2024-04-23 | [
[
"Bhattacharya",
"Sourav",
""
],
[
"Kaushal",
"Shagun",
""
]
] | We investigate the entanglement generation or harvesting between two identical Unruh-DeWitt detectors in the cosmological de Sitter spacetime. We consider two comoving two-level detectors at a coincident spatial position. The detectors are assumed to be unentangled initially. The detectors are individually coupled to a scalar field, which eventually leads to coupling between the two detectors. We consider two kinds of scalar fields -- conformally symmetric and massless minimally coupled, for both real and complex cases. By tracing out the degrees of freedom corresponding to the scalar field, we construct the reduced density matrix for the two detectors, whose eigenvalues characterise transitions between the energy levels of the detectors. By using the existing results for the detector response functions per unit proper time for these fields, we next compute the logarithmic negativity, quantifying the degree of entanglement generated at late times between the two detectors. The similarities and differences of these results for different kind of scalar fields have been discussed. |
0908.3431 | Valerio Faraoni | Valerio Faraoni (Bishop's University) | Harrison's interpretation of the cosmological redshift revisited | 12 pages, LaTeX, to appear in Gen. Rel. Gravit | null | 10.1007/s10714-009-0885-8 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Harrison's argument against the interpretation of the cosmological redshift
as a Doppler effect is revisited, exaggerated, and discussed. The context,
purpose, and limitations of the interpretations of this phenomenon are
clarified.
| [
{
"created": "Mon, 24 Aug 2009 13:05:12 GMT",
"version": "v1"
}
] | 2015-05-14 | [
[
"Faraoni",
"Valerio",
"",
"Bishop's University"
]
] | Harrison's argument against the interpretation of the cosmological redshift as a Doppler effect is revisited, exaggerated, and discussed. The context, purpose, and limitations of the interpretations of this phenomenon are clarified. |
2208.04218 | Patryk Mach | Adam Cie\'slik, Patryk Mach, Andrzej Odrzywolek | Accretion of the relativistic Vlasov gas in the equatorial plane of the
Kerr black hole | 24 pages, 17 figures | null | 10.1103/PhysRevD.106.104056 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate stationary accretion of the collisionless Vlasov gas onto the
Kerr black hole, occurring in the equatorial plane. The solution is specified
by imposing asymptotic boundary conditions: at infinity the gas obeys the
Maxwell-J\"{u}ttner distribution, restricted to the equatorial plane (both in
positions and momenta). In the vicinity of the black hole, the motion of the
gas is governed by the spacetime geometry. We compute accretion rates of the
rest-mass, the energy, and the angular momentum, as well as the particle number
surface density, focusing on the dependence of these quantities on the
asymptotic temperature of the gas and the black hole spin. The rest-mass and
energy accretion rates, normalized by the black hole mass and appropriate
asymptotic surface densities of the gas, increase with increasing asymptotic
temperature. The accretion slows down the rotation of the black hole.
| [
{
"created": "Mon, 8 Aug 2022 15:41:46 GMT",
"version": "v1"
}
] | 2022-12-07 | [
[
"Cieślik",
"Adam",
""
],
[
"Mach",
"Patryk",
""
],
[
"Odrzywolek",
"Andrzej",
""
]
] | We investigate stationary accretion of the collisionless Vlasov gas onto the Kerr black hole, occurring in the equatorial plane. The solution is specified by imposing asymptotic boundary conditions: at infinity the gas obeys the Maxwell-J\"{u}ttner distribution, restricted to the equatorial plane (both in positions and momenta). In the vicinity of the black hole, the motion of the gas is governed by the spacetime geometry. We compute accretion rates of the rest-mass, the energy, and the angular momentum, as well as the particle number surface density, focusing on the dependence of these quantities on the asymptotic temperature of the gas and the black hole spin. The rest-mass and energy accretion rates, normalized by the black hole mass and appropriate asymptotic surface densities of the gas, increase with increasing asymptotic temperature. The accretion slows down the rotation of the black hole. |
0805.4179 | Raul Vera | Marc Mars, Filipe C. Mena and Ra\"ul Vera | First order perturbations of the Einstein-Straus and Oppenheimer-Snyder
models | LaTeX; 29 pages | Phys.Rev.D78:084022,2008 | 10.1103/PhysRevD.78.084022 | null | gr-qc astro-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive the linearly perturbed matching conditions between a Schwarzschild
spacetime region with stationary and axially symmetric perturbations and a FLRW
spacetime with arbitrary perturbations. The matching hypersurface is also
perturbed arbitrarily and, in all cases, the perturbations are decomposed into
scalars using the Hodge operator on the sphere. This allows us to write down
the matching conditions in a compact way. In particular, we find that the
existence of a perturbed (rotating, stationary and vacuum) Schwarzschild cavity
in a perturbed FLRW universe forces the cosmological perturbations to satisfy
constraints that link rotational and gravitational wave perturbations. We also
prove that if the perturbation on the FLRW side vanishes identically, then the
vacuole must be perturbatively static and hence Schwarzschild. By the dual
nature of the problem, the first result translates into links between
rotational and gravitational wave perturbations on a perturbed
Oppenheimer-Snyder model, where the perturbed FLRW dust collapses in a
perturbed Schwarzschild environment which rotates in equilibrium. The second
result implies in particular that no region described by FLRW can be a source
of the Kerr metric.
| [
{
"created": "Tue, 27 May 2008 19:44:26 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Mars",
"Marc",
""
],
[
"Mena",
"Filipe C.",
""
],
[
"Vera",
"Raül",
""
]
] | We derive the linearly perturbed matching conditions between a Schwarzschild spacetime region with stationary and axially symmetric perturbations and a FLRW spacetime with arbitrary perturbations. The matching hypersurface is also perturbed arbitrarily and, in all cases, the perturbations are decomposed into scalars using the Hodge operator on the sphere. This allows us to write down the matching conditions in a compact way. In particular, we find that the existence of a perturbed (rotating, stationary and vacuum) Schwarzschild cavity in a perturbed FLRW universe forces the cosmological perturbations to satisfy constraints that link rotational and gravitational wave perturbations. We also prove that if the perturbation on the FLRW side vanishes identically, then the vacuole must be perturbatively static and hence Schwarzschild. By the dual nature of the problem, the first result translates into links between rotational and gravitational wave perturbations on a perturbed Oppenheimer-Snyder model, where the perturbed FLRW dust collapses in a perturbed Schwarzschild environment which rotates in equilibrium. The second result implies in particular that no region described by FLRW can be a source of the Kerr metric. |
1410.3895 | Ravindra Saraykar Dr. | R. V. Saraykar and Sujatha Janardhan | Zeeman-like topologies in Special and General theory of Relativity | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is a short review article in which we discuss and summarize the works of
various researchers over past four decades on Zeeman topology and Zeeman-like
topologies, which occur in special and general theory of relativity. We also
discuss various properties and inter-relationship of these topologies.
| [
{
"created": "Tue, 14 Oct 2014 23:45:33 GMT",
"version": "v1"
}
] | 2014-10-16 | [
[
"Saraykar",
"R. V.",
""
],
[
"Janardhan",
"Sujatha",
""
]
] | This is a short review article in which we discuss and summarize the works of various researchers over past four decades on Zeeman topology and Zeeman-like topologies, which occur in special and general theory of relativity. We also discuss various properties and inter-relationship of these topologies. |
0904.1263 | Morteza Mohseni | M. Mortazavimanesh and Morteza Mohseni | Spinning particles in Schwarzschild-de Sitter space-time | 8 pages, 5 eps figures, submitted to Gen.Rel.Grav | Gen.Rel.Grav.41:2697-2706,2009 | 10.1007/s10714-009-0798-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | After considering the reference case of the motion of spinning test bodies in
the equatorial plane of the Schwarzschild space-time, we generalize the results
to the case of the motion of a spinning particle in the equatorial plane of the
Schwarzschild-de Sitter space-time. Specifically, we obtain the loci of turning
points of the particle in this plane. We show that the cosmological constant
affect the particle motion when the particle distance from the black hole is of
the order of the inverse square root of the cosmological constant.
| [
{
"created": "Wed, 8 Apr 2009 05:42:23 GMT",
"version": "v1"
}
] | 2014-11-18 | [
[
"Mortazavimanesh",
"M.",
""
],
[
"Mohseni",
"Morteza",
""
]
] | After considering the reference case of the motion of spinning test bodies in the equatorial plane of the Schwarzschild space-time, we generalize the results to the case of the motion of a spinning particle in the equatorial plane of the Schwarzschild-de Sitter space-time. Specifically, we obtain the loci of turning points of the particle in this plane. We show that the cosmological constant affect the particle motion when the particle distance from the black hole is of the order of the inverse square root of the cosmological constant. |
1704.00599 | Zachariah Etienne | Zachariah B. Etienne, Mew-Bing Wan, Maria C. Babiuc, Sean T.
McWilliams, Ashok Choudhary | GiRaFFE: An Open-Source General Relativistic Force-Free Electrodynamics
Code | 23 pages, 4 figures. Consistent with published version | Class. Quantum Grav. 34 (2017) 215001 | 10.1088/1361-6382/aa8ab3 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present GiRaFFE, the first open-source general relativistic force-free
electrodynamics (GRFFE) code for dynamical, numerical-relativity generated
spacetimes. GiRaFFE adopts the strategy pioneered by McKinney and modified by
Paschalidis and Shapiro to convert a GR magnetohydrodynamic (GRMHD) code into a
GRFFE code. In short, GiRaFFE exists as a modification of IllinoisGRMHD, a
user-friendly, open-source, dynamical-spacetime GRMHD code. Both GiRaFFE and
IllinoisGRMHD leverage the Einstein Toolkit's highly-scalable infrastructure to
make possible large-scale simulations of magnetized plasmas in strong,
dynamical spacetimes on adaptive-mesh refinement (AMR) grids. We demonstrate
that GiRaFFE passes a large suite of both flat and curved-spacetime code tests
passed by a number of other state-of-the-art GRFFE codes, and is thus ready for
production-scale simulations of GRFFE phenomena of key interest to relativistic
astrophysics.
| [
{
"created": "Thu, 30 Mar 2017 18:00:00 GMT",
"version": "v1"
},
{
"created": "Sun, 1 Oct 2017 21:44:01 GMT",
"version": "v2"
}
] | 2017-10-25 | [
[
"Etienne",
"Zachariah B.",
""
],
[
"Wan",
"Mew-Bing",
""
],
[
"Babiuc",
"Maria C.",
""
],
[
"McWilliams",
"Sean T.",
""
],
[
"Choudhary",
"Ashok",
""
]
] | We present GiRaFFE, the first open-source general relativistic force-free electrodynamics (GRFFE) code for dynamical, numerical-relativity generated spacetimes. GiRaFFE adopts the strategy pioneered by McKinney and modified by Paschalidis and Shapiro to convert a GR magnetohydrodynamic (GRMHD) code into a GRFFE code. In short, GiRaFFE exists as a modification of IllinoisGRMHD, a user-friendly, open-source, dynamical-spacetime GRMHD code. Both GiRaFFE and IllinoisGRMHD leverage the Einstein Toolkit's highly-scalable infrastructure to make possible large-scale simulations of magnetized plasmas in strong, dynamical spacetimes on adaptive-mesh refinement (AMR) grids. We demonstrate that GiRaFFE passes a large suite of both flat and curved-spacetime code tests passed by a number of other state-of-the-art GRFFE codes, and is thus ready for production-scale simulations of GRFFE phenomena of key interest to relativistic astrophysics. |
2306.16168 | Sagarika Tripathy | Sagarika Tripathy, Rathul Nath Raveendran, Krishnamohan Parattu, and
L. Sriramkumar | Amplifying quantum discord during inflationary magnetogenesis through
violation of parity | 24 pages, 5 figures | Phys. Rev. D 108, 123512 (2023) | 10.1103/PhysRevD.108.123512 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is well known that, during inflation, the conformal invariance of the
electromagnetic action has to be broken in order to produce magnetic fields of
observed strengths today. Often, to further enhance the strengths of the
magnetic fields, parity is also assumed to be violated when the fields are
being generated. In this work, we examine the evolution of the quantum state of
the Fourier modes of the non-conformally coupled and parity violating
electromagnetic field during inflation. We utilize tools such as the Wigner
ellipse, squeezing parameters and quantum discord to understand the evolution
of the field. We show that the violation of parity leads to an enhancement of
the squeezing amplitude and the quantum discord (or, equivalently, in this
context, the entanglement entropy) associated with a pair of opposite wave
vectors for one of the two states of polarization (and a suppression for the
other state of polarization), when compared to the case wherein parity is
conserved. We highlight the similarities between the evolution of the Fourier
modes of the electromagnetic field when parity is violated during inflation and
the behavior of the modes of a charged, quantum, scalar field in the presence
of a constant electric field in a de Sitter universe. We briefly discuss the
implications of the results we obtain.
| [
{
"created": "Wed, 28 Jun 2023 12:44:57 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Nov 2023 09:54:58 GMT",
"version": "v2"
}
] | 2023-12-19 | [
[
"Tripathy",
"Sagarika",
""
],
[
"Raveendran",
"Rathul Nath",
""
],
[
"Parattu",
"Krishnamohan",
""
],
[
"Sriramkumar",
"L.",
""
]
] | It is well known that, during inflation, the conformal invariance of the electromagnetic action has to be broken in order to produce magnetic fields of observed strengths today. Often, to further enhance the strengths of the magnetic fields, parity is also assumed to be violated when the fields are being generated. In this work, we examine the evolution of the quantum state of the Fourier modes of the non-conformally coupled and parity violating electromagnetic field during inflation. We utilize tools such as the Wigner ellipse, squeezing parameters and quantum discord to understand the evolution of the field. We show that the violation of parity leads to an enhancement of the squeezing amplitude and the quantum discord (or, equivalently, in this context, the entanglement entropy) associated with a pair of opposite wave vectors for one of the two states of polarization (and a suppression for the other state of polarization), when compared to the case wherein parity is conserved. We highlight the similarities between the evolution of the Fourier modes of the electromagnetic field when parity is violated during inflation and the behavior of the modes of a charged, quantum, scalar field in the presence of a constant electric field in a de Sitter universe. We briefly discuss the implications of the results we obtain. |
0904.0219 | Lorenzo Iorio | Lorenzo Iorio | Galactic orbital motions in the Dark Matter, MOdified Newtonian Dynamics
and MOdified Gravity scenarios | LaTex2e, 11 pages, 2 tables, 8 figures. Issues concerning the masses
of MCs clarified. Integration time changed to -1 Gyr <= t <= +1 Gyr. To
appear in Monthly Notices of the Royal Astronomical Society (MNRAS) | Mon.Not.Roy.Astron.Soc.401:2012-2020,2010 | 10.1111/j.1365-2966.2009.15811.x | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We simultaneously integrate in a numerical way the equations of motion of
both the Magellanic Clouds (MCs) in MOND, MOG and CDM for -1 <= t <= +1 Gyr to
see if, at least in principle, it is possible to discriminate between them
(Abridged version).
| [
{
"created": "Wed, 1 Apr 2009 17:03:26 GMT",
"version": "v1"
},
{
"created": "Sun, 9 Aug 2009 11:44:24 GMT",
"version": "v2"
},
{
"created": "Wed, 16 Sep 2009 08:04:40 GMT",
"version": "v3"
},
{
"created": "Thu, 1 Oct 2009 15:45:54 GMT",
"version": "v4"
}
] | 2010-01-12 | [
[
"Iorio",
"Lorenzo",
""
]
] | We simultaneously integrate in a numerical way the equations of motion of both the Magellanic Clouds (MCs) in MOND, MOG and CDM for -1 <= t <= +1 Gyr to see if, at least in principle, it is possible to discriminate between them (Abridged version). |
1907.04341 | Jeffrey Hazboun | Jeffrey S. Hazboun and Joseph D. Romano and Tristan L. Smith | Realistic sensitivity curves for pulsar timing arrays | 21 pages, 18 figues | Phys. Rev. D 100, 104028 (2019) | 10.1103/PhysRevD.100.104028 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct realistic sensitivity curves for pulsar timing array searches
for gravitational waves, incorporating both red and white noise contributions
to individual pulsar noise spectra, as well as the effect of fitting to a
pulsar timing model. We demonstrate the method on both simulated pulsars and a
realistic array consisting of a subset of NANOGrav pulsars used in recent
analyses. A comparison between the results presented here and exact sensitivity
curves shows agreement to tens of percent. The resulting sensitivity curves can
be used to assess the detectability of predicted gravitational-wave signals in
the nanohertz frequency band in a fraction of the time that it would take to
compute the exact sensitivity curves.
| [
{
"created": "Tue, 9 Jul 2019 18:01:12 GMT",
"version": "v1"
}
] | 2019-11-20 | [
[
"Hazboun",
"Jeffrey S.",
""
],
[
"Romano",
"Joseph D.",
""
],
[
"Smith",
"Tristan L.",
""
]
] | We construct realistic sensitivity curves for pulsar timing array searches for gravitational waves, incorporating both red and white noise contributions to individual pulsar noise spectra, as well as the effect of fitting to a pulsar timing model. We demonstrate the method on both simulated pulsars and a realistic array consisting of a subset of NANOGrav pulsars used in recent analyses. A comparison between the results presented here and exact sensitivity curves shows agreement to tens of percent. The resulting sensitivity curves can be used to assess the detectability of predicted gravitational-wave signals in the nanohertz frequency band in a fraction of the time that it would take to compute the exact sensitivity curves. |
1408.4592 | Andrea Geralico | Donato Bini, Fernando de Felice, Andrea Geralico | Strains and axial outflows in the field of a rotating black hole | 8 pages, 1 figure; published version | Phys. Rev. D 76, 047502 (2007) | 10.1103/PhysRevD.76.047502 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the behaviour of an initially spherical bunch of accelerated
particles emitted along trajectories parallel to the symmetry axis of a
rotating black hole. We find that, under suitable conditions, curvature and
inertial strains compete to model the shape of axial outflows of matter
contributing to generate jet-like structures. This is of course a purely
kinematical effect which does not account by itself for physical processes
underlying the formation of jets. In our analysis a crucial role is played by a
property of the electric and magnetic part of the Weyl tensor to be
Lorentz-invariant boosting along the axis of symmetry in Kerr spacetime.
| [
{
"created": "Wed, 20 Aug 2014 10:18:31 GMT",
"version": "v1"
}
] | 2015-06-22 | [
[
"Bini",
"Donato",
""
],
[
"de Felice",
"Fernando",
""
],
[
"Geralico",
"Andrea",
""
]
] | We study the behaviour of an initially spherical bunch of accelerated particles emitted along trajectories parallel to the symmetry axis of a rotating black hole. We find that, under suitable conditions, curvature and inertial strains compete to model the shape of axial outflows of matter contributing to generate jet-like structures. This is of course a purely kinematical effect which does not account by itself for physical processes underlying the formation of jets. In our analysis a crucial role is played by a property of the electric and magnetic part of the Weyl tensor to be Lorentz-invariant boosting along the axis of symmetry in Kerr spacetime. |
0807.0060 | David Hestenes | David Hestenes | Gauge Gravity and Electroweak Theory | 19 pages, no figures, from the Eleventh Marcel Grossmann Meeting on
General Relativity | null | 10.1142/9789812834300_0026 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Reformulation of the Dirac equation in terms of the real Spacetime Algebra
(STA) reveals hidden geometric structure, including a geometric role for the
unit imaginary as generator of rotations in a spacelike plane. The STA and the
real Dirac equation play essential roles in a new Gauge Theory Gravity (GTG)
version of General Relativity (GR). Besides clarifying the conceptual
foundations of GR and facilitating complex computations, GTG opens up new
possibilities for a unified gauge theory of gravity and quantum mechanics,
including spacetime geometry of electroweak interactions. The Weinberg-Salam
model fits perfectly into this geometric framework, and a promising variant
that replaces chiral states with Majorana states is formulated to incorporate
zitterbewegung in electron states.
| [
{
"created": "Tue, 1 Jul 2008 03:45:40 GMT",
"version": "v1"
}
] | 2016-11-15 | [
[
"Hestenes",
"David",
""
]
] | Reformulation of the Dirac equation in terms of the real Spacetime Algebra (STA) reveals hidden geometric structure, including a geometric role for the unit imaginary as generator of rotations in a spacelike plane. The STA and the real Dirac equation play essential roles in a new Gauge Theory Gravity (GTG) version of General Relativity (GR). Besides clarifying the conceptual foundations of GR and facilitating complex computations, GTG opens up new possibilities for a unified gauge theory of gravity and quantum mechanics, including spacetime geometry of electroweak interactions. The Weinberg-Salam model fits perfectly into this geometric framework, and a promising variant that replaces chiral states with Majorana states is formulated to incorporate zitterbewegung in electron states. |
gr-qc/0002087 | Alexei Zakharov | A. V. Zakharov | Macroscopic Einstein equations for a system of interacting particles and
their cosmological applications | 10 pages LATEX 2.09 | null | null | KSU-GRG-00-az02 | gr-qc | null | One of the possible applications of macroscopic Einstein equations has been
considered. So, the nonsingular isotropic and uniform cosmological model is
built. The cosmological consequences of this model are agree with conclusions
of standard hot model of the Universe.
| [
{
"created": "Fri, 25 Feb 2000 07:16:40 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Zakharov",
"A. V.",
""
]
] | One of the possible applications of macroscopic Einstein equations has been considered. So, the nonsingular isotropic and uniform cosmological model is built. The cosmological consequences of this model are agree with conclusions of standard hot model of the Universe. |
gr-qc/0605002 | Patrick Sutton | Shourov Chatterji, Albert Lazzarini, Leo Stein, Patrick Sutton, Antony
Searle, Massimo Tinto | Coherent network analysis technique for discriminating
gravitational-wave bursts from instrumental noise | 18 pages, 11 figures; corrected corrupted figure | Phys.Rev.D74:082005,2006 | 10.1103/PhysRevD.74.082005 | LIGO-P060009-01-E | gr-qc | null | Existing coherent network analysis techniques for detecting
gravitational-wave bursts simultaneously test data from multiple observatories
for consistency with the expected properties of the signals. These techniques
assume the output of the detector network to be the sum of a stationary
Gaussian noise process and a gravitational-wave signal, and they may fail in
the presence of transient non-stationarities, which are common in real
detectors. In order to address this problem we introduce a consistency test
that is robust against noise non-stationarities and allows one to distinguish
between gravitational-wave bursts and noise transients. This technique does not
require any a priori knowledge of the putative burst waveform.
| [
{
"created": "Sat, 29 Apr 2006 03:54:04 GMT",
"version": "v1"
},
{
"created": "Mon, 1 May 2006 21:08:52 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Chatterji",
"Shourov",
""
],
[
"Lazzarini",
"Albert",
""
],
[
"Stein",
"Leo",
""
],
[
"Sutton",
"Patrick",
""
],
[
"Searle",
"Antony",
""
],
[
"Tinto",
"Massimo",
""
]
] | Existing coherent network analysis techniques for detecting gravitational-wave bursts simultaneously test data from multiple observatories for consistency with the expected properties of the signals. These techniques assume the output of the detector network to be the sum of a stationary Gaussian noise process and a gravitational-wave signal, and they may fail in the presence of transient non-stationarities, which are common in real detectors. In order to address this problem we introduce a consistency test that is robust against noise non-stationarities and allows one to distinguish between gravitational-wave bursts and noise transients. This technique does not require any a priori knowledge of the putative burst waveform. |
1101.2084 | Daniele Malafarina | Pankaj S. Joshi and Daniele Malafarina | Instability of black hole formation in gravitational collapse | 5 pages | Phys.Rev.D83:024009,2011 | 10.1103/PhysRevD.83.024009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider here the classic scenario given by Oppenheimer, Snyder, and Datt,
for the gravitational collapse of a massive matter cloud, and examine its
stability under the introduction of small tangential stresses. We show, by
offering an explicit class of physically valid tangential stress perturbations,
that an introduction of tangential pressure, however small, can qualitatively
change the final fate of collapse from a black hole final state to a naked
singularity. This shows instability of black hole formation in collapse and
sheds important light on the nature of cosmic censorship hypothesis and its
possible formulations. The key effect of these perturbations is to alter the
trapped surface formation pattern within the collapsing cloud and the apparent
horizon structure. This allows the singularity to be visible, and implications
are discussed.
| [
{
"created": "Tue, 11 Jan 2011 10:17:33 GMT",
"version": "v1"
}
] | 2011-02-02 | [
[
"Joshi",
"Pankaj S.",
""
],
[
"Malafarina",
"Daniele",
""
]
] | We consider here the classic scenario given by Oppenheimer, Snyder, and Datt, for the gravitational collapse of a massive matter cloud, and examine its stability under the introduction of small tangential stresses. We show, by offering an explicit class of physically valid tangential stress perturbations, that an introduction of tangential pressure, however small, can qualitatively change the final fate of collapse from a black hole final state to a naked singularity. This shows instability of black hole formation in collapse and sheds important light on the nature of cosmic censorship hypothesis and its possible formulations. The key effect of these perturbations is to alter the trapped surface formation pattern within the collapsing cloud and the apparent horizon structure. This allows the singularity to be visible, and implications are discussed. |
1701.06724 | Miguel Cruz | Miguel Cruz, Norman Cruz and Samuel Lepe | Phantom solution in a non-linear Israel-Stewart theory | 18 pages and 6 figures. Published version in PLB | Phys. Lett. B 769, 159 (2017) | 10.1016/j.physletb.2017.03.065 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we present a phantom solution with a big rip singularity in a
non-linear regime of the Israel-Stewart formalism. In this framework it is
possible to extend this causal formalism in order to describe accelerated
expansion, where assumption of near equilibrium is no longer valid. We assume a
flat universe filled with a single viscous fluid ruled by a barotropic EoS,
$p=\omega \rho$, which can represent a late time accelerated phase of the
cosmic evolution. The solution allows to cross the phantom divide without
evoking an exotic matter fluid and the effective EoS parameter is always lesser
than $-1$ and constant in time.
| [
{
"created": "Tue, 24 Jan 2017 03:57:20 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Apr 2017 16:04:08 GMT",
"version": "v2"
}
] | 2017-04-06 | [
[
"Cruz",
"Miguel",
""
],
[
"Cruz",
"Norman",
""
],
[
"Lepe",
"Samuel",
""
]
] | In this paper we present a phantom solution with a big rip singularity in a non-linear regime of the Israel-Stewart formalism. In this framework it is possible to extend this causal formalism in order to describe accelerated expansion, where assumption of near equilibrium is no longer valid. We assume a flat universe filled with a single viscous fluid ruled by a barotropic EoS, $p=\omega \rho$, which can represent a late time accelerated phase of the cosmic evolution. The solution allows to cross the phantom divide without evoking an exotic matter fluid and the effective EoS parameter is always lesser than $-1$ and constant in time. |
0810.0671 | Mayeul Arminjon | Mayeul Arminjon and Frank Reifler | Quantum mechanics for three versions of the Dirac equation in a curved
spacetime | 8 pages in standard LaTeX. Text of a talk given at the 11th Conf.
"Physical Interpretations of Relativity Theory", London, 12-15 Sept. 2008 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a recent work on the Dirac equation in a curved spacetime. In
addition to the standard equation, two alternative versions are considered,
derived from wave mechanics, and based on the tensor representation of the
Dirac field. The latter considers the Dirac wave function as a spacetime vector
and the set of the Dirac matrices as a third-order tensor. Having the
probability current conserved for any solution of the Dirac equation gives an
equation to be satisfied by the coefficient fields. A positive definite scalar
product is defined and a hermiticity condition for the Dirac Hamiltonian is
derived for a general coordinate system in a general curved spacetime. For the
standard equation, the hermiticity of the Dirac Hamiltonian is not preserved
under all admissible changes of the coefficient fields.
| [
{
"created": "Fri, 3 Oct 2008 15:49:05 GMT",
"version": "v1"
}
] | 2008-10-06 | [
[
"Arminjon",
"Mayeul",
""
],
[
"Reifler",
"Frank",
""
]
] | We present a recent work on the Dirac equation in a curved spacetime. In addition to the standard equation, two alternative versions are considered, derived from wave mechanics, and based on the tensor representation of the Dirac field. The latter considers the Dirac wave function as a spacetime vector and the set of the Dirac matrices as a third-order tensor. Having the probability current conserved for any solution of the Dirac equation gives an equation to be satisfied by the coefficient fields. A positive definite scalar product is defined and a hermiticity condition for the Dirac Hamiltonian is derived for a general coordinate system in a general curved spacetime. For the standard equation, the hermiticity of the Dirac Hamiltonian is not preserved under all admissible changes of the coefficient fields. |
1010.0672 | Suresh Kumar | Suresh Kumar | Some FRW Models of Accelerating Universe with Dark Energy | 10 pages, 5 figures | Astrophysics & Space Science 332 (2011) 449-454 | 10.1007/s10509-010-0540-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The paper deals with a spatially homogeneous and isotropic FRW space-time
filled with perfect fluid and dark energy components. The two sources are
assumed to interact minimally, and therefore their energy momentum tensors are
conserved separately. A special law of variation for the Hubble parameter
proposed by Berman (1983) has been utilized to solve the field equations. The
Berman's law yields two explicit forms of the scale factor governing the FRW
space-time and constant values of deceleration parameter. The role of dark
energy with variable equation of state parameter has been studied in detail in
the evolution of FRW universe. It has been found that dark energy dominates the
universe at the present epoch, which is consistent with the observations. The
physical behavior of the universe is discussed in detail.
| [
{
"created": "Fri, 1 Oct 2010 03:42:20 GMT",
"version": "v1"
}
] | 2014-08-21 | [
[
"Kumar",
"Suresh",
""
]
] | The paper deals with a spatially homogeneous and isotropic FRW space-time filled with perfect fluid and dark energy components. The two sources are assumed to interact minimally, and therefore their energy momentum tensors are conserved separately. A special law of variation for the Hubble parameter proposed by Berman (1983) has been utilized to solve the field equations. The Berman's law yields two explicit forms of the scale factor governing the FRW space-time and constant values of deceleration parameter. The role of dark energy with variable equation of state parameter has been studied in detail in the evolution of FRW universe. It has been found that dark energy dominates the universe at the present epoch, which is consistent with the observations. The physical behavior of the universe is discussed in detail. |
0710.0428 | Francisco Lobo | Francisco S. N. Lobo | Nature of time and causality in Physics | 14 pages, 11 figures. Book chapter to appear in 'Psychology of Time',
Elsevier Publishers, editor Simon Grondin. V2: comments, one figure and a
reference added; typos corrected | Psychology of Time, 395-422, (2008) | null | null | gr-qc | null | The conceptual definition and understanding of the nature of time, both
qualitatively and quantitatively is of the utmost difficulty and importance,
and plays a fundamental role in physics. Physical systems seem to evolve in
paths of increasing entropy and of complexity, and thus, the arrow of time
shall be explored in the context of thermodynamic irreversibility and quantum
physics. In Newtonian physics, time flows at a constant rate, the same for all
observers; however, it necessarily flows at different rates for different
observers in special and general relativity. Special relativity provides
important quantitative elucidations of the fundamental processes related to
time dilation effects, and general relativity provides a deep analysis to
effects of time flow, such as in the presence of gravitational fields. Through
the special theory of relativity, time became intimately related with space,
giving rise to the notion of spacetime, in which both parameters cannot be
considered as separate entities. As time is incorporated into the proper
structure of the fabric of spacetime, it is interesting to note that general
relativity is contaminated with non-trivial geometries that generate closed
timelike curves, and thus apparently violates causality. The notion of
causality is fundamental in the construction of physical theories; therefore
time travel and its associated paradoxes have to be treated with great caution.
These issues are briefly analyzed in this review paper.
| [
{
"created": "Tue, 2 Oct 2007 02:46:57 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Feb 2008 14:40:15 GMT",
"version": "v2"
}
] | 2015-01-14 | [
[
"Lobo",
"Francisco S. N.",
""
]
] | The conceptual definition and understanding of the nature of time, both qualitatively and quantitatively is of the utmost difficulty and importance, and plays a fundamental role in physics. Physical systems seem to evolve in paths of increasing entropy and of complexity, and thus, the arrow of time shall be explored in the context of thermodynamic irreversibility and quantum physics. In Newtonian physics, time flows at a constant rate, the same for all observers; however, it necessarily flows at different rates for different observers in special and general relativity. Special relativity provides important quantitative elucidations of the fundamental processes related to time dilation effects, and general relativity provides a deep analysis to effects of time flow, such as in the presence of gravitational fields. Through the special theory of relativity, time became intimately related with space, giving rise to the notion of spacetime, in which both parameters cannot be considered as separate entities. As time is incorporated into the proper structure of the fabric of spacetime, it is interesting to note that general relativity is contaminated with non-trivial geometries that generate closed timelike curves, and thus apparently violates causality. The notion of causality is fundamental in the construction of physical theories; therefore time travel and its associated paradoxes have to be treated with great caution. These issues are briefly analyzed in this review paper. |
2401.04179 | Leonhard Kehrberger | Leonhard Kehrberger, Hamed Masaood | The Case Against Smooth Null Infinity V: Early-Time Asymptotics of
Linearised Gravity Around Schwarzschild for Fixed Spherical Harmonic Modes | 170 pages, 9 figures, arXiv abstract differs from the paper's
abstract. Comments and questions welcome! v2: Fixed a few typos | null | null | null | gr-qc math-ph math.AP math.MP | http://creativecommons.org/licenses/by-sa/4.0/ | Starting from Post-Newtonian predictions for a system of $N$ infalling masses
from the infinite past, we formulate and solve a scattering problem for the
system of linearised gravity around Schwarzschild as introduced in [DHR19]. The
scattering data are posed on a null hypersurface $\mathcal C$ emanating from a
section of past null infinity $\mathcal I^-$, and on the part of $\mathcal I^-$
that lies to the future of this section: Along $\mathcal C$, we implement the
Post-Newtonian theory-inspired hypothesis that the gauge-invariant components
of the Weyl tensor $\alpha$ and $\underline{\alpha}$ (a.k.a. $\Psi_0$ and
$\Psi_4$) decay like $r^{-3}$, $r^{-4}$, respectively, and we exclude incoming
radiation from $\mathcal I^-$ by demanding the News function to vanish along
$\mathcal I^-$.
We also show that compactly supported gravitational perturbations along
$\mathcal I^-$ induce very similar data, with $\alpha$, $\underline{\alpha}$
decaying like $r^{-3}$, $r^{-5}$ along $\mathcal C$.
After constructing the unique solution to this scattering problem, we provide
a complete analysis of the asymptotic behaviour of projections onto fixed
spherical harmonic number $\ell$ near spacelike $i^0$ and future null infinity
$\mathcal I^+$. Using our results, we also give constructive corrections to
popular historical notions of asymptotic flatness such as Bondi coordinates or
asymptotic simplicity. In particular, confirming earlier heuristics due to
Damour and Christodoulou, we find that the peeling property is violated both
near $\mathcal I^-$ and near $\mathcal I^+$, with e.g. $\alpha$ near $\mathcal
I^+$ only decaying like $r^{-4}$ instead of $r^{-5}$. We also find that the
resulting solution decays slower towards $i^0$ than often assumed, with
$\alpha$ decaying like $r^{-3}$ towards $i^0$.
The issue of summing up the fixed angular mode estimates in $\ell$ is dealt
with in forthcoming work.
| [
{
"created": "Mon, 8 Jan 2024 19:00:11 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Apr 2024 07:26:35 GMT",
"version": "v2"
}
] | 2024-05-01 | [
[
"Kehrberger",
"Leonhard",
""
],
[
"Masaood",
"Hamed",
""
]
] | Starting from Post-Newtonian predictions for a system of $N$ infalling masses from the infinite past, we formulate and solve a scattering problem for the system of linearised gravity around Schwarzschild as introduced in [DHR19]. The scattering data are posed on a null hypersurface $\mathcal C$ emanating from a section of past null infinity $\mathcal I^-$, and on the part of $\mathcal I^-$ that lies to the future of this section: Along $\mathcal C$, we implement the Post-Newtonian theory-inspired hypothesis that the gauge-invariant components of the Weyl tensor $\alpha$ and $\underline{\alpha}$ (a.k.a. $\Psi_0$ and $\Psi_4$) decay like $r^{-3}$, $r^{-4}$, respectively, and we exclude incoming radiation from $\mathcal I^-$ by demanding the News function to vanish along $\mathcal I^-$. We also show that compactly supported gravitational perturbations along $\mathcal I^-$ induce very similar data, with $\alpha$, $\underline{\alpha}$ decaying like $r^{-3}$, $r^{-5}$ along $\mathcal C$. After constructing the unique solution to this scattering problem, we provide a complete analysis of the asymptotic behaviour of projections onto fixed spherical harmonic number $\ell$ near spacelike $i^0$ and future null infinity $\mathcal I^+$. Using our results, we also give constructive corrections to popular historical notions of asymptotic flatness such as Bondi coordinates or asymptotic simplicity. In particular, confirming earlier heuristics due to Damour and Christodoulou, we find that the peeling property is violated both near $\mathcal I^-$ and near $\mathcal I^+$, with e.g. $\alpha$ near $\mathcal I^+$ only decaying like $r^{-4}$ instead of $r^{-5}$. We also find that the resulting solution decays slower towards $i^0$ than often assumed, with $\alpha$ decaying like $r^{-3}$ towards $i^0$. The issue of summing up the fixed angular mode estimates in $\ell$ is dealt with in forthcoming work. |
0909.0912 | Antonio F. Ranada | Antonio F. Ranada and Alfredo Tiemblo | On the compatibility of a proposed explanation of the Pioneer anomaly
with the cartography of the solar system | 8 pages, no figures, corrected typos | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze here the reasons why an explanation of the Pioneer anomaly
proposed by the authors is fully compatible with the cartography of the solar
system. First, this proposal posits that the phenomenon is an apparent
acceleration, not a real one, caused by a progressive desynchronization of the
astronomical and the atomic clock-times, after they had been synchronized at a
previous instant. The desynchronization could be caused by a coupling between
the background gravitation and the quantum vacuum. Therefore, the standard
argument for the incompatibility of the Pioneer acceleration and the values of
the planets' orbits radii cannot be applied. Second, this proposal gives
exactly the same results for radar ranging observations as standard physics.
Hence, it cannot be in conflict with the very precise cartography of the solar
system determined by NASA's Viking mission. Otherwise stated, while this
proposal predicts apparent changes in the velocities of the spaceships and in
the frequencies of Doppler observations, as really observed, it does not affect
the values of the distances in any way whatsoever. Note that an acceleration
between the astronomical and the atomic clock-times ({\it i. e.} a progressive
desynchronization) can not be discarded a priori as long as we will lack a
theory of quantum gravity.
| [
{
"created": "Fri, 4 Sep 2009 16:10:08 GMT",
"version": "v1"
}
] | 2009-09-07 | [
[
"Ranada",
"Antonio F.",
""
],
[
"Tiemblo",
"Alfredo",
""
]
] | We analyze here the reasons why an explanation of the Pioneer anomaly proposed by the authors is fully compatible with the cartography of the solar system. First, this proposal posits that the phenomenon is an apparent acceleration, not a real one, caused by a progressive desynchronization of the astronomical and the atomic clock-times, after they had been synchronized at a previous instant. The desynchronization could be caused by a coupling between the background gravitation and the quantum vacuum. Therefore, the standard argument for the incompatibility of the Pioneer acceleration and the values of the planets' orbits radii cannot be applied. Second, this proposal gives exactly the same results for radar ranging observations as standard physics. Hence, it cannot be in conflict with the very precise cartography of the solar system determined by NASA's Viking mission. Otherwise stated, while this proposal predicts apparent changes in the velocities of the spaceships and in the frequencies of Doppler observations, as really observed, it does not affect the values of the distances in any way whatsoever. Note that an acceleration between the astronomical and the atomic clock-times ({\it i. e.} a progressive desynchronization) can not be discarded a priori as long as we will lack a theory of quantum gravity. |
0811.0138 | Ilya Mandel | Ilya Mandel, Jonathan R. Gair | Can we Detect Intermediate Mass Ratio Inspirals? | Updated to match published version | Class.Quant.Grav.26:094036,2009 | 10.1088/0264-9381/26/9/094036 | null | gr-qc astro-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves emitted during intermediate-mass-ratio inspirals (IMRIs)
of intermediate-mass black holes (IMBHs) into supermassive black holes could
represent a very interesting source for LISA. Similarly, IMRIs of stellar-mass
compact objects into IMBHs could be detectable by Advanced LIGO. At present,
however, it is not clear what waveforms could be used for IMRI detection, since
the post-Newtonian approximation breaks down as an IMRI approaches the
innermost stable circular orbit, and perturbative solutions are only known to
the lowest order in the mass ratio. We discuss the expected mismatches between
approximate and true waveforms, and the choice of the best available waveform
as a function of the mass ratio and the total mass of the system. We also
comment on the significance of the spin of the smaller body and the need for
its inclusion in the waveforms.
| [
{
"created": "Sun, 2 Nov 2008 07:51:19 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Feb 2009 13:30:00 GMT",
"version": "v2"
},
{
"created": "Mon, 20 Apr 2009 16:06:40 GMT",
"version": "v3"
}
] | 2009-11-13 | [
[
"Mandel",
"Ilya",
""
],
[
"Gair",
"Jonathan R.",
""
]
] | Gravitational waves emitted during intermediate-mass-ratio inspirals (IMRIs) of intermediate-mass black holes (IMBHs) into supermassive black holes could represent a very interesting source for LISA. Similarly, IMRIs of stellar-mass compact objects into IMBHs could be detectable by Advanced LIGO. At present, however, it is not clear what waveforms could be used for IMRI detection, since the post-Newtonian approximation breaks down as an IMRI approaches the innermost stable circular orbit, and perturbative solutions are only known to the lowest order in the mass ratio. We discuss the expected mismatches between approximate and true waveforms, and the choice of the best available waveform as a function of the mass ratio and the total mass of the system. We also comment on the significance of the spin of the smaller body and the need for its inclusion in the waveforms. |
1907.01561 | Vitor Cardoso | Vitor Cardoso, Adrian del Rio, Masashi Kimura | Distinguishing black holes from horizonless objects through the
excitation of resonances during inspiral | 3+11 pages. v4: corrects one typo (in Eq. A39 and in Eq. 3 for the
scalar flux formula) in the published version | Phys. Rev. D 100, 084046 (2019) | 10.1103/PhysRevD.100.084046 | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | How well is the vacuum Kerr geometry a good description of the dark, compact
objects in our universe? Precision measurements of accreting matter in the deep
infrared and gravitational-wave measurements of coalescing objects are finally
providing answers to this question. Here, we study the possibility of resonant
excitation of the modes of the central object -- taken to be very compact but
horizonless -- during an extreme-mass-ratio inspiral. We show that for very
compact objects resonances are indeed excited. However, the impact of such
excitation on the phase of the gravitational-wave signal is negligible, since
resonances are crossed very quickly during inspiral.
| [
{
"created": "Tue, 2 Jul 2019 18:00:05 GMT",
"version": "v1"
},
{
"created": "Sat, 6 Jul 2019 07:53:43 GMT",
"version": "v2"
},
{
"created": "Wed, 9 Oct 2019 18:33:51 GMT",
"version": "v3"
},
{
"created": "Mon, 9 Mar 2020 00:11:03 GMT",
"version": "v4"
}
] | 2020-03-10 | [
[
"Cardoso",
"Vitor",
""
],
[
"del Rio",
"Adrian",
""
],
[
"Kimura",
"Masashi",
""
]
] | How well is the vacuum Kerr geometry a good description of the dark, compact objects in our universe? Precision measurements of accreting matter in the deep infrared and gravitational-wave measurements of coalescing objects are finally providing answers to this question. Here, we study the possibility of resonant excitation of the modes of the central object -- taken to be very compact but horizonless -- during an extreme-mass-ratio inspiral. We show that for very compact objects resonances are indeed excited. However, the impact of such excitation on the phase of the gravitational-wave signal is negligible, since resonances are crossed very quickly during inspiral. |
gr-qc/0205025 | Sawa Manoff | Sawa Manoff | Lagrangian fluid mechanics | 10 pages LaTeX | Published in: "Perspectives in Complex Analysis, Differential
Geometry and Mathematical Physics". World Scientific, Singapore, 2001,
190-200 | null | null | gr-qc | null | The method of Lagrangians with covariant derivative (MLCD) is applied to a
special type of Lagrangian density depending on scalar and vector fields as
well as on their first covariant derivatives. The corresponding
Euler-Lagrange's equations and energy-momentum tensors are found on the basis
of the covariant Noether's identities.
| [
{
"created": "Tue, 7 May 2002 11:09:27 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Manoff",
"Sawa",
""
]
] | The method of Lagrangians with covariant derivative (MLCD) is applied to a special type of Lagrangian density depending on scalar and vector fields as well as on their first covariant derivatives. The corresponding Euler-Lagrange's equations and energy-momentum tensors are found on the basis of the covariant Noether's identities. |
gr-qc/9902028 | Andrey Neronov | V. A. Berezin, A. M. Boyarsky, A. Yu. Neronov | On the spectrum of relativistic Schroedinger equation in finite
differences | 16 pages, 1 figure | null | null | INR 0115/99 | gr-qc | null | We develop a method for constructing asymptotic solutions of
finite-difference equations and implement it to a relativistic Schroedinger
equation which describes motion of a selfgravitating spherically symmetric dust
shell. Exact mass spectrum of black hole formed due to the collapse of the
shell is determined from the analysis of asymptotic solutions of the equation.
| [
{
"created": "Wed, 10 Feb 1999 21:08:09 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Feb 1999 15:09:29 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Berezin",
"V. A.",
""
],
[
"Boyarsky",
"A. M.",
""
],
[
"Neronov",
"A. Yu.",
""
]
] | We develop a method for constructing asymptotic solutions of finite-difference equations and implement it to a relativistic Schroedinger equation which describes motion of a selfgravitating spherically symmetric dust shell. Exact mass spectrum of black hole formed due to the collapse of the shell is determined from the analysis of asymptotic solutions of the equation. |
gr-qc/0605095 | Farook Rahaman | F.Rahaman, M. Kalam and A. Ghosh | Existence of Wormholes in Einstein-Kalb-Ramond space time | 5 pages, to appear in Nuovo Cimento B | Nuovo Cim.B121:303-307,2006 | 10.1393/ncb/i2006-10026-9 | null | gr-qc | null | In recent, Kar.S et.al [ Phys Rev D 67,044005 (2003) ] have obtained static
spherically symmetric solutions of the Einstein-Kalb-Ramond field equations. We
have shown that their solutions, indeed, represent Wormholes.
| [
{
"created": "Wed, 17 May 2006 07:08:05 GMT",
"version": "v1"
}
] | 2010-11-11 | [
[
"Rahaman",
"F.",
""
],
[
"Kalam",
"M.",
""
],
[
"Ghosh",
"A.",
""
]
] | In recent, Kar.S et.al [ Phys Rev D 67,044005 (2003) ] have obtained static spherically symmetric solutions of the Einstein-Kalb-Ramond field equations. We have shown that their solutions, indeed, represent Wormholes. |
1907.00955 | Maciej Kolanowski | Maciej Kolanowski, Jerzy Lewandowski and Adam Szereszewski | Extremal horizons stationary to the second order: new constraints | 20 pages, a typo in Eq. (22) corrected | Phys. Rev. D 100, 104057 (2019) | 10.1103/PhysRevD.100.104057 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider non-expanding shear free (NE-SF) null surface geometries
embeddable as extremal Killing horizons to the second order in Einstein vacuum
spacetimes. A NE-SF null surface geometry consists of a degenerate metric
tensor and a consistent torsion free covariant derivative. We derive the
constraints implied by the existence of an embedding. The first constraint is
well known as the near horizon geometry equation. The second constraint we find
is new. The constraints lead to a complete characterization of those NE-SF null
geometries that are embeddable in the extremal Kerr spacetime. Our results are
also valid for spacetimes with a cosmological constant.
| [
{
"created": "Mon, 1 Jul 2019 17:49:09 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Jan 2022 22:35:35 GMT",
"version": "v2"
}
] | 2022-01-20 | [
[
"Kolanowski",
"Maciej",
""
],
[
"Lewandowski",
"Jerzy",
""
],
[
"Szereszewski",
"Adam",
""
]
] | We consider non-expanding shear free (NE-SF) null surface geometries embeddable as extremal Killing horizons to the second order in Einstein vacuum spacetimes. A NE-SF null surface geometry consists of a degenerate metric tensor and a consistent torsion free covariant derivative. We derive the constraints implied by the existence of an embedding. The first constraint is well known as the near horizon geometry equation. The second constraint we find is new. The constraints lead to a complete characterization of those NE-SF null geometries that are embeddable in the extremal Kerr spacetime. Our results are also valid for spacetimes with a cosmological constant. |
gr-qc/0511011 | Ingemar Eriksson | Ingemar Eriksson | Conserved Matter Superenergy Currents for Hypersurface Orthogonal
Killing Vectors | 13 pages | Class.Quant.Grav. 23 (2006) 2279-2290 | 10.1088/0264-9381/23/7/005 | null | gr-qc | null | We show that for hypersurface orthogonal Killing vectors, the corresponding
Chevreton superenergy currents will be conserved and proportional to the
Killing vectors. This holds for four-dimensional Einstein-Maxwell spacetimes
with an electromagnetic field that is sourcefree and inherits the symmetry of
the spacetime. A similar result also holds for the trace of the Chevreton
tensor. The corresponding Bel currents have previously been proven to be
conserved and our result can be seen as giving further support to the concept
of conserved mixed superenergy currents. The analogous case for a scalar field
has also previously been proven to give conserved currents and we show, for
completeness, that these currents also are proportional to the Killing vectors.
| [
{
"created": "Wed, 2 Nov 2005 15:29:34 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Eriksson",
"Ingemar",
""
]
] | We show that for hypersurface orthogonal Killing vectors, the corresponding Chevreton superenergy currents will be conserved and proportional to the Killing vectors. This holds for four-dimensional Einstein-Maxwell spacetimes with an electromagnetic field that is sourcefree and inherits the symmetry of the spacetime. A similar result also holds for the trace of the Chevreton tensor. The corresponding Bel currents have previously been proven to be conserved and our result can be seen as giving further support to the concept of conserved mixed superenergy currents. The analogous case for a scalar field has also previously been proven to give conserved currents and we show, for completeness, that these currents also are proportional to the Killing vectors. |
1010.2086 | Christian Corda cordac | Christian Corda | Gravitational wave astronomy: the definitive test for the "Einstein
frame versus Jordan frame" controversy | Corrected latest typos. This definitive version matches the version
to be published in Astroparticle Physics 34 (2011) 412-419, 22 pages | Astropart.Phys.34:412-419,2011 | 10.1016/j.astropartphys.2010.10.006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The potential realization of a gravitational wave (GW) astronomy in next
years is a great challenge for the scientific community. By giving a
significant amount of new information, GWs will be a cornerstone for a better
understanding of the universe and of the gravitational physics. In this paper
the author shows that the GW astronomy will permit to solve a captivating issue
of gravitation as it will be the definitive test for the famous "Einstein frame
versus Jordan frame" controversy. In fact, we show that the motion of the test
masses, i.e. the beam splitter and the mirror in the case of an interferometer,
which is due to the scalar component of a GW, is different in the two frames.
Thus, if a consistent GW astronomy will be realized, an eventual detection of
signals of scalar GWs will permit to discriminate among the two frames. In this
way, a direct evidence from observations will solve in an ultimate way the
famous and long history of the "Einstein frame versus Jordan frame"
controversy.
| [
{
"created": "Mon, 11 Oct 2010 12:37:52 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Nov 2010 15:29:12 GMT",
"version": "v2"
},
{
"created": "Mon, 29 Nov 2010 08:35:46 GMT",
"version": "v3"
},
{
"created": "Tue, 21 Dec 2010 10:05:08 GMT",
"version": "v4"
}
] | 2011-02-01 | [
[
"Corda",
"Christian",
""
]
] | The potential realization of a gravitational wave (GW) astronomy in next years is a great challenge for the scientific community. By giving a significant amount of new information, GWs will be a cornerstone for a better understanding of the universe and of the gravitational physics. In this paper the author shows that the GW astronomy will permit to solve a captivating issue of gravitation as it will be the definitive test for the famous "Einstein frame versus Jordan frame" controversy. In fact, we show that the motion of the test masses, i.e. the beam splitter and the mirror in the case of an interferometer, which is due to the scalar component of a GW, is different in the two frames. Thus, if a consistent GW astronomy will be realized, an eventual detection of signals of scalar GWs will permit to discriminate among the two frames. In this way, a direct evidence from observations will solve in an ultimate way the famous and long history of the "Einstein frame versus Jordan frame" controversy. |
gr-qc/0203084 | Irina Radinschi | I. Radinschi (Department of Physics, ``Gh. Asachi'' Technical
University, Iasi, Romania) | M{\o}ller Energy-Momentum Complex for an Axially Symmetric Scalar Field | LaTex | null | null | null | gr-qc | null | We calculate the energy-distribution for an axially symmetric scalar field in
the M{\o}ller prescription. The total energy is given by the parameter m of the
space-time.
| [
{
"created": "Mon, 25 Mar 2002 09:56:26 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Radinschi",
"I.",
"",
"Department of Physics, ``Gh. Asachi'' Technical\n University, Iasi, Romania"
]
] | We calculate the energy-distribution for an axially symmetric scalar field in the M{\o}ller prescription. The total energy is given by the parameter m of the space-time. |
1101.5061 | Etera R. Livine | Etera R. Livine | A Short and Subjective Introduction to the Spinfoam Framework for
Quantum Gravity | 90 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is my Th\`ese d'Habilitation (HDR) on the topic of spinfoam models for
quantum gravity, which I presented in l'Ecole Normale Sup\'erieure de Lyon on
december 16 2010. The spinfoam framework is a proposal for a regularized path
integral for quantum gravity, inspired from Topological Quantum Field Theory
(TQFT) and state-sum models. It can also be seen as defining transition
amplitudes for the quantum states of geometry for Loop Quantum Gravity (LQG).
| [
{
"created": "Wed, 26 Jan 2011 13:51:14 GMT",
"version": "v1"
}
] | 2015-03-18 | [
[
"Livine",
"Etera R.",
""
]
] | This is my Th\`ese d'Habilitation (HDR) on the topic of spinfoam models for quantum gravity, which I presented in l'Ecole Normale Sup\'erieure de Lyon on december 16 2010. The spinfoam framework is a proposal for a regularized path integral for quantum gravity, inspired from Topological Quantum Field Theory (TQFT) and state-sum models. It can also be seen as defining transition amplitudes for the quantum states of geometry for Loop Quantum Gravity (LQG). |
0708.1811 | Raymond Burston | R. B. Burston and A. W. C. Lun | 1+1+2 Electromagnetic perturbations on general LRS space-times:
Regge-Wheeler and Bardeen-Press equations | null | Class.Quant.Grav.25:075003,2008 | 10.1088/0264-9381/25/7/075003 | null | gr-qc | null | We use the, covariant and gauge-invariant, 1+1+2 formalism developed by
Clarkson and Barrett, and develop new techniques, to decouple electromagnetic
(EM) perturbations on arbitrary locally rotationally symmetric (LRS)
space-times. Ultimately, we derive 3 decoupled complex equations governing 3
complex scalars. One of these is a new Regge-Wheeler (RW) equation generalized
for LRS space-times, whereas the remaining two are new generalizations of the
Bardeen-Press (BP) equations. This is achieved by first using linear algebra
techniques to rewrite the first-order Maxwell equations in a new complex 1+1+2
form which is conducive to decoupling. This new complex system immediately
yields the generalized RW equation, and furthermore, we also derive a decoupled
equation governing a newly defined complex EM 2-vector. Subsequently, a further
decomposition of the 1+1+2 formalism into a 1+1+1+1 formalism is developed,
allowing us to decompose the complex EM 2-vector, and its governing equations,
into spin-weighted scalars, giving rise to the generalized BP equations.
| [
{
"created": "Tue, 14 Aug 2007 09:44:42 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Burston",
"R. B.",
""
],
[
"Lun",
"A. W. C.",
""
]
] | We use the, covariant and gauge-invariant, 1+1+2 formalism developed by Clarkson and Barrett, and develop new techniques, to decouple electromagnetic (EM) perturbations on arbitrary locally rotationally symmetric (LRS) space-times. Ultimately, we derive 3 decoupled complex equations governing 3 complex scalars. One of these is a new Regge-Wheeler (RW) equation generalized for LRS space-times, whereas the remaining two are new generalizations of the Bardeen-Press (BP) equations. This is achieved by first using linear algebra techniques to rewrite the first-order Maxwell equations in a new complex 1+1+2 form which is conducive to decoupling. This new complex system immediately yields the generalized RW equation, and furthermore, we also derive a decoupled equation governing a newly defined complex EM 2-vector. Subsequently, a further decomposition of the 1+1+2 formalism into a 1+1+1+1 formalism is developed, allowing us to decompose the complex EM 2-vector, and its governing equations, into spin-weighted scalars, giving rise to the generalized BP equations. |
gr-qc/0209042 | Christodoulakis Theodosios | T. Christodoulakis, G.O. Papadopoulos, A. Dimakis | Automorphisms of Real 4 Dimensional Lie Algebras and the Invariant
Characterization of Homogeneous 4-Spaces | LaTeX2e, 23 pages, 2 Tables. To appear in Journal of Physics A:
Mathematical & General | J.Phys.A36:427-442,2003 | 10.1088/0305-4470/36/2/310 | null | gr-qc math-ph math.MP | null | The automorphisms of all 4-dimensional, real Lie Algebras are presented in a
comprehensive way. Their action on the space of $4\times 4$, real, symmetric
and positive definite, matrices, defines equivalence classes which are used for
the invariant characterization of the 4-dimensional homogeneous spaces which
possess an invariant basis.
| [
{
"created": "Thu, 12 Sep 2002 09:47:37 GMT",
"version": "v1"
},
{
"created": "Wed, 13 Nov 2002 12:05:55 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Christodoulakis",
"T.",
""
],
[
"Papadopoulos",
"G. O.",
""
],
[
"Dimakis",
"A.",
""
]
] | The automorphisms of all 4-dimensional, real Lie Algebras are presented in a comprehensive way. Their action on the space of $4\times 4$, real, symmetric and positive definite, matrices, defines equivalence classes which are used for the invariant characterization of the 4-dimensional homogeneous spaces which possess an invariant basis. |
2211.01103 | Hugo Roussille | Hugo Roussille | Black hole perturbations in modified gravity theories | PhD thesis (defended 17/06/2022, Universit\'e Paris Cit\'e), 267
pages, 17 figures, 1 appendix, short introduction in French. Based on
arXiv:2012.10218, arXiv:2103.14744, arXiv:2103.14750, arXiv:2204.04107,
arXiv:2205.07746 | null | null | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by-nc-sa/4.0/ | The recent first detection of gravitational waves (GWs) from binary black
hole mergers has spurred a renewed interest in possible deviations from General
Relativity (GR), since they could be detected in the GWs emitted by such
systems. Of particular interest is the ringdown phase of a binary black hole
merger, which can be described by linear perturbations about a background
stationary black hole solution. These perturbations mainly correspond to a
superposition of 'quasi-normal modes' (QNMs), whose frequencies form a discrete
set. One expects that modified gravity models could predict QNMs that differ
from their GR counterpart: the detailed analysis of the GW signal represents an
invaluable window to test GR and to look for specific signatures of modified
gravity.
The work done in this thesis takes place in the context of scalar-tensor
theories of gravity, and more particularly the Degenerate Higher-Order
Scalar-Tensor theories. We start by a review of these theories and their
properties, and describe a way to reformulate them in a framework with a clear
geometrical interpretation. We then study linear perturbations about several
existing nonrotating black hole solutions of such theories, and show why the
perturbation equations obtained are very hard to decouple in general. When it
is possible, in the case of odd parity perturbations, we describe the
propagation of waves and relate it to the stability of the underlying
spacetime. When it is not, we circumvent the difficulty by making use of an
algorithm proposed recently in the mathematical literature that allows us to
decouple the equations both at the black hole horizon and at infinity. This
allows us to get the asymptotic behaviour of waves on such spacetimes, yielding
valuable information that can allow us to rule some of them out. Finally, we
use the asymptotic behaviours obtained to compute QNMs numerically.
| [
{
"created": "Wed, 2 Nov 2022 13:25:22 GMT",
"version": "v1"
}
] | 2022-11-03 | [
[
"Roussille",
"Hugo",
""
]
] | The recent first detection of gravitational waves (GWs) from binary black hole mergers has spurred a renewed interest in possible deviations from General Relativity (GR), since they could be detected in the GWs emitted by such systems. Of particular interest is the ringdown phase of a binary black hole merger, which can be described by linear perturbations about a background stationary black hole solution. These perturbations mainly correspond to a superposition of 'quasi-normal modes' (QNMs), whose frequencies form a discrete set. One expects that modified gravity models could predict QNMs that differ from their GR counterpart: the detailed analysis of the GW signal represents an invaluable window to test GR and to look for specific signatures of modified gravity. The work done in this thesis takes place in the context of scalar-tensor theories of gravity, and more particularly the Degenerate Higher-Order Scalar-Tensor theories. We start by a review of these theories and their properties, and describe a way to reformulate them in a framework with a clear geometrical interpretation. We then study linear perturbations about several existing nonrotating black hole solutions of such theories, and show why the perturbation equations obtained are very hard to decouple in general. When it is possible, in the case of odd parity perturbations, we describe the propagation of waves and relate it to the stability of the underlying spacetime. When it is not, we circumvent the difficulty by making use of an algorithm proposed recently in the mathematical literature that allows us to decouple the equations both at the black hole horizon and at infinity. This allows us to get the asymptotic behaviour of waves on such spacetimes, yielding valuable information that can allow us to rule some of them out. Finally, we use the asymptotic behaviours obtained to compute QNMs numerically. |
1912.03868 | Cosimo Bambi | Ashutosh Tripathi, Biao Zhou, Askar B. Abdikamalov, Dimitry Ayzenberg,
Cosimo Bambi | Search for traversable wormholes in active galactic nuclei using X-ray
data | 10 pages, 7 figures. v2: refereed version | Phys. Rev. D 101, 064030 (2020) | 10.1103/PhysRevD.101.064030 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a previous paper, one of us calculated iron K$\alpha$ line profiles
emitted from possible accretion disks around traversable wormholes as a first
step to use X-ray reflection spectroscopy to search for astrophysical wormholes
in active galactic nuclei. In the present paper, we extend that work and
construct an XSPEC model for the whole relativistic reflection spectrum. We
apply our model to XMM-Newton and NuSTAR observations of the supermassive
object in MCG-6-30-15 and we check whether these observations prefer the
hypothesis that the central body is a Kerr black hole or a traversable
wormhole. We find that the two models provide equally good fits, so with the
available data we cannot distinguish the black hole and wormhole scenarios.
| [
{
"created": "Mon, 9 Dec 2019 06:16:52 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Mar 2020 16:28:33 GMT",
"version": "v2"
}
] | 2020-03-17 | [
[
"Tripathi",
"Ashutosh",
""
],
[
"Zhou",
"Biao",
""
],
[
"Abdikamalov",
"Askar B.",
""
],
[
"Ayzenberg",
"Dimitry",
""
],
[
"Bambi",
"Cosimo",
""
]
] | In a previous paper, one of us calculated iron K$\alpha$ line profiles emitted from possible accretion disks around traversable wormholes as a first step to use X-ray reflection spectroscopy to search for astrophysical wormholes in active galactic nuclei. In the present paper, we extend that work and construct an XSPEC model for the whole relativistic reflection spectrum. We apply our model to XMM-Newton and NuSTAR observations of the supermassive object in MCG-6-30-15 and we check whether these observations prefer the hypothesis that the central body is a Kerr black hole or a traversable wormhole. We find that the two models provide equally good fits, so with the available data we cannot distinguish the black hole and wormhole scenarios. |
2111.07352 | Yu-Xiao Liu | Yu-Qi Dong, Yu-Xiao Liu | Polarization Modes of Gravitational Waves in Palatini Horndeski theory | 23 pages, 1 figure, 1 table | Phys.Rev.D 105 (2022) 6, 064035 | 10.1103/PhysRevD.105.064035 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, the polarization modes of gravitational waves in Horndeski
gravity are studied under the Palatini formalism. After obtaining the
linearized equation of perturbations in Minkowski background, we find that the
polarization modes of gravitational waves depend on the selection of the
theoretical parameters. The polarization modes can be divided into quite rich
cases by parameters. In all cases of parameter selection, there are $+$ and
$\times$ modes propagating at the speed of light but no vector modes. The only
difference from general relativity is scalar modes, especially the scalar
degrees of freedom can be 0, 1 or 2 in different cases. The appropriate
parameter cases can be expected to be selected in the detection of
gravitational wave polarization modes by Lisa, Taiji and TianQin in the future.
| [
{
"created": "Sun, 14 Nov 2021 14:12:50 GMT",
"version": "v1"
},
{
"created": "Sat, 20 Nov 2021 15:11:25 GMT",
"version": "v2"
},
{
"created": "Wed, 23 Mar 2022 09:21:32 GMT",
"version": "v3"
}
] | 2022-03-24 | [
[
"Dong",
"Yu-Qi",
""
],
[
"Liu",
"Yu-Xiao",
""
]
] | In this paper, the polarization modes of gravitational waves in Horndeski gravity are studied under the Palatini formalism. After obtaining the linearized equation of perturbations in Minkowski background, we find that the polarization modes of gravitational waves depend on the selection of the theoretical parameters. The polarization modes can be divided into quite rich cases by parameters. In all cases of parameter selection, there are $+$ and $\times$ modes propagating at the speed of light but no vector modes. The only difference from general relativity is scalar modes, especially the scalar degrees of freedom can be 0, 1 or 2 in different cases. The appropriate parameter cases can be expected to be selected in the detection of gravitational wave polarization modes by Lisa, Taiji and TianQin in the future. |
1511.04284 | Pierre Teyssandier | Bernard Linet and Pierre Teyssandier | Time transfer functions in Schwarzschild-like metrics in the weak-field
limit: A unified description of Shapiro and lensing effects | 12 pages, added one figure in section 3; a paragraph in Introduction
rewritten without changing the argument; corrected typos; one reference added
for section 2; Eq. (84) rewritten in a more elegant form; slightly revised
argument in section 9, results unchanged | Phys. Rev. D 93, 044028 (2016) | 10.1103/PhysRevD.93.044028 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a complete analysis of the light rays within the linearized,
weak-field approximation of a Schwarzschild-like metric describing the
gravitational field of an isolated, spherically symmetric body. We prove in
this context the existence of two time transfer functions and we obtain these
functions in an exact closed-form. We are led to distinguish two regimes. In
the first regime, the two time transfer functions correspond to rays which are
confined in regions of spacetime where the weak-field approximation is valid.
Such a regime occurs in gravitational lensing configurations with double images
of a given source. We find the general expressions of the angular separation
and the difference in light travel time between the two images. In the second
regime, there exists only one time transfer function corresponding to a light
ray remaining in a region of weak field. Performing a Taylor expansion of this
function with respect to the gravitational constant, we obtain the Shapiro time
delay completed by a series of so-called "enhanced terms". The enhanced terms
beyond the third order are new.
| [
{
"created": "Fri, 13 Nov 2015 14:11:31 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Feb 2016 15:29:56 GMT",
"version": "v2"
}
] | 2016-02-17 | [
[
"Linet",
"Bernard",
""
],
[
"Teyssandier",
"Pierre",
""
]
] | We present a complete analysis of the light rays within the linearized, weak-field approximation of a Schwarzschild-like metric describing the gravitational field of an isolated, spherically symmetric body. We prove in this context the existence of two time transfer functions and we obtain these functions in an exact closed-form. We are led to distinguish two regimes. In the first regime, the two time transfer functions correspond to rays which are confined in regions of spacetime where the weak-field approximation is valid. Such a regime occurs in gravitational lensing configurations with double images of a given source. We find the general expressions of the angular separation and the difference in light travel time between the two images. In the second regime, there exists only one time transfer function corresponding to a light ray remaining in a region of weak field. Performing a Taylor expansion of this function with respect to the gravitational constant, we obtain the Shapiro time delay completed by a series of so-called "enhanced terms". The enhanced terms beyond the third order are new. |
0810.3542 | Felipe Falciano | F. T. Falciano, N. Pinto-Neto | Scalar Perturbations in Scalar Field Quantum Cosmology | 10 pages, 2 figures, accepted version to Physical Review D 79 | Phys.Rev.D79:023507,2009 | 10.1103/PhysRevD.79.023507 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper it is shown how to obtain the simplest equations for the
Mukhanov-Sasaki variables describing quantum linear scalar perturbations in the
case of scalar fields without potential term. This was done through the
implementation of canonical transformations at the classical level, and unitary
transformations at the quantum level, without ever using any classical
background equation, and it completes the simplification initiated in
investigations by Langlois \cite{langlois}, and Pinho and Pinto-Neto
\cite{emanuel2} for this case. These equations were then used to calculate the
spectrum index $n_s$ of quantum scalar perturbations of a non-singular
inflationary quantum background model, which starts at infinity past from flat
space-time with Planckian size spacelike hypersurfaces, and inflates due to a
quantum cosmological effect, until it makes an analytical graceful exit from
this inflationary epoch to a decelerated classical stiff matter expansion
phase. The result is $n_s=3$, incompatible with observations.
| [
{
"created": "Mon, 20 Oct 2008 12:14:10 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Jan 2009 16:19:28 GMT",
"version": "v2"
}
] | 2009-01-21 | [
[
"Falciano",
"F. T.",
""
],
[
"Pinto-Neto",
"N.",
""
]
] | In this paper it is shown how to obtain the simplest equations for the Mukhanov-Sasaki variables describing quantum linear scalar perturbations in the case of scalar fields without potential term. This was done through the implementation of canonical transformations at the classical level, and unitary transformations at the quantum level, without ever using any classical background equation, and it completes the simplification initiated in investigations by Langlois \cite{langlois}, and Pinho and Pinto-Neto \cite{emanuel2} for this case. These equations were then used to calculate the spectrum index $n_s$ of quantum scalar perturbations of a non-singular inflationary quantum background model, which starts at infinity past from flat space-time with Planckian size spacelike hypersurfaces, and inflates due to a quantum cosmological effect, until it makes an analytical graceful exit from this inflationary epoch to a decelerated classical stiff matter expansion phase. The result is $n_s=3$, incompatible with observations. |
0806.2716 | Molin Liu | Molin Liu, Hongya Liu, Yuanxing Gui | Quasi-Normal Modes of Massless Scalar Field around the 5D Ricci-flat
Black String | revtex4 source file, 11 pages, 5 figures | Class.Quant.Grav.25:105001,2008 | 10.1088/0264-9381/25/10/105001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | As one candidate of the higher dimensional black holes, the 5D Ricci-flat
black string is considered in this paper. By means of a non-trivial potential
$V_{n}$, the quasi-normal modes of a massless scalar field around this black
string space is studied. By using the classical third order WKB approximation,
we analyse carefully the evolution of frequencies in two aspects, one is the
induced cosmological constant $\Lambda$ and the other is the quantum number
$n$. The massless scalar field decays more slowly because of the existences of
the fifth dimension and the induced cosmological constant. If extra dimension
has in fact existed near black hole, those quasi-normal frequencies may have
some indication on it.
| [
{
"created": "Tue, 17 Jun 2008 07:15:24 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Liu",
"Molin",
""
],
[
"Liu",
"Hongya",
""
],
[
"Gui",
"Yuanxing",
""
]
] | As one candidate of the higher dimensional black holes, the 5D Ricci-flat black string is considered in this paper. By means of a non-trivial potential $V_{n}$, the quasi-normal modes of a massless scalar field around this black string space is studied. By using the classical third order WKB approximation, we analyse carefully the evolution of frequencies in two aspects, one is the induced cosmological constant $\Lambda$ and the other is the quantum number $n$. The massless scalar field decays more slowly because of the existences of the fifth dimension and the induced cosmological constant. If extra dimension has in fact existed near black hole, those quasi-normal frequencies may have some indication on it. |
gr-qc/0508015 | Richard Woodard | E. O. Kahya and R. P. Woodard (University of Florida) | Charged Scalar Self-Mass during Inflation | 41 pages, LaTeX 2epsilon, 3 figures, uses axodraw | Phys.Rev. D72 (2005) 104001 | 10.1103/PhysRevD.72.104001 | UFIFT-QG-05-07 | gr-qc astro-ph hep-ph | null | We compute the one loop self-mass of a charged massless, minimally coupled
scalar in a locally de Sitter background geometry. The computation is done in
two different gauges: the noninvariant generalization of Feynman gauge which
gives the simplest expression for the photon propagator and the de Sitter
invariant gauge of Allen and Jacobson. In each case dimensional regularization
is employed and fully renormalized results are obtained. By using our result in
the linearized, effective field equations one can infer how the scalar responds
to the dielectric medium produced by inflationary particle production. We also
work out the result for a conformally coupled scalar. Although the conformally
coupled case is of no great physical interest the fact that we obtain a
manifestly de Sitter invariant form for its self-mass-squared establishes that
our noninvariant gauge introduces no physical breaking of de Sitter invariance
at one loop order.
| [
{
"created": "Wed, 3 Aug 2005 08:26:07 GMT",
"version": "v1"
}
] | 2013-05-29 | [
[
"Kahya",
"E. O.",
"",
"University of Florida"
],
[
"Woodard",
"R. P.",
"",
"University of Florida"
]
] | We compute the one loop self-mass of a charged massless, minimally coupled scalar in a locally de Sitter background geometry. The computation is done in two different gauges: the noninvariant generalization of Feynman gauge which gives the simplest expression for the photon propagator and the de Sitter invariant gauge of Allen and Jacobson. In each case dimensional regularization is employed and fully renormalized results are obtained. By using our result in the linearized, effective field equations one can infer how the scalar responds to the dielectric medium produced by inflationary particle production. We also work out the result for a conformally coupled scalar. Although the conformally coupled case is of no great physical interest the fact that we obtain a manifestly de Sitter invariant form for its self-mass-squared establishes that our noninvariant gauge introduces no physical breaking of de Sitter invariance at one loop order. |
1510.02035 | Kuantay Boshkayev | Kuantay Boshkayev, Hernando Quevedo, Saken Toktarbay, Bakytzhan Zhami
and Medeu Abishev | On the equivalence of approximate stationary axially symmetric solutions
of Einstein field equations | 8 pages | null | 10.1134/S0202289316040046 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study stationary axially symmetric solutions of the Einstein vacuum field
equations that can be used to describe the gravitational field of astrophysical
compact objects in the limiting case of slow rotation and slight deformation.
We derive explicitly the exterior Sedrakyan-Chubaryan approximate solution, and
express it in analytical form, which makes it practical in the context of
astrophysical applications. In the limiting case of vanishing angular momentum,
the solution reduces to the well-known Schwarzschild solution in vacuum. We
demonstrate that the new solution is equivalent to the exterior Hartle-Thorne
solution. We establish the mathematical equivalence between the
Sedrakyan-Chubaryan, Fock-Abdildin and Hartle-Thorne formalisms.
| [
{
"created": "Wed, 7 Oct 2015 17:28:51 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Oct 2016 00:21:44 GMT",
"version": "v2"
}
] | 2016-12-07 | [
[
"Boshkayev",
"Kuantay",
""
],
[
"Quevedo",
"Hernando",
""
],
[
"Toktarbay",
"Saken",
""
],
[
"Zhami",
"Bakytzhan",
""
],
[
"Abishev",
"Medeu",
""
]
] | We study stationary axially symmetric solutions of the Einstein vacuum field equations that can be used to describe the gravitational field of astrophysical compact objects in the limiting case of slow rotation and slight deformation. We derive explicitly the exterior Sedrakyan-Chubaryan approximate solution, and express it in analytical form, which makes it practical in the context of astrophysical applications. In the limiting case of vanishing angular momentum, the solution reduces to the well-known Schwarzschild solution in vacuum. We demonstrate that the new solution is equivalent to the exterior Hartle-Thorne solution. We establish the mathematical equivalence between the Sedrakyan-Chubaryan, Fock-Abdildin and Hartle-Thorne formalisms. |
1009.3559 | Niall \'O Murchadha | Julian Barbour and Niall \'O Murchadha | Conformal Superspace: the configuration space of general relativity | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has long been considered that conformal superspace is the natural
configuration space for canonical general relativity. However, this was never
definitively demonstrated. We have found that the standard conformal method of
solving the Einstein constraints has an unexpected extra symmetry. This allows
us to complete the project. We show that given a point and a velocity in
conformal superspace, the Einstein equations generate a unique curve in
conformal superspace.
| [
{
"created": "Sat, 18 Sep 2010 15:00:12 GMT",
"version": "v1"
}
] | 2010-09-21 | [
[
"Barbour",
"Julian",
""
],
[
"Murchadha",
"Niall Ó",
""
]
] | It has long been considered that conformal superspace is the natural configuration space for canonical general relativity. However, this was never definitively demonstrated. We have found that the standard conformal method of solving the Einstein constraints has an unexpected extra symmetry. This allows us to complete the project. We show that given a point and a velocity in conformal superspace, the Einstein equations generate a unique curve in conformal superspace. |
0907.1553 | Natalia Kiriushcheva | N. Kiriushcheva and S.V. Kuzmin | The Hamiltonian formulation of N-bein, Einstein-Cartan, gravity in any
dimension: the Progress Report (Extended version of a talk given on
CAIMS-2009, June 11-14, London, Canada) | 48 pages | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Hamiltonian formulation of N-bein, Einstein-Cartan, gravity, using its
first order form in any dimension higher than two, is analyzed. This
Hamiltonian formulation allows to explicitly show where peculiarities of three
dimensional case (\textit{A.M.Frolov et al, 0902.0856 [gr-qc]}) occur and make
a conjecture, based on presented in this report results, that there is one
general for \textit{all} dimensions characteristic of N-bein formulation of
gravity: after elimination of second class constraints the algebra of Poisson
brackets among remaining first class secondary constraints is the Poincare
algebra and in all dimensions N-bein, Cartan-Einstein, gravity \textit{is the
Poincare gauge theory}. The gauge symmetry corresponding to the algebra of
first class constraints has two parameters - rotational (Lorentz) and
translational. Translational invariance is common to all dimensions but some
terms in general expressions for gauge transformations of N-beins and
connections are zero in a particular, three dimensional, case.
The proof of our conjecture is outlined in detail. Some straightforward but
tedious calculations remain to be completed to call our conjecture - a theorem
and will be reported later.
| [
{
"created": "Thu, 9 Jul 2009 14:01:45 GMT",
"version": "v1"
}
] | 2009-07-11 | [
[
"Kiriushcheva",
"N.",
""
],
[
"Kuzmin",
"S. V.",
""
]
] | The Hamiltonian formulation of N-bein, Einstein-Cartan, gravity, using its first order form in any dimension higher than two, is analyzed. This Hamiltonian formulation allows to explicitly show where peculiarities of three dimensional case (\textit{A.M.Frolov et al, 0902.0856 [gr-qc]}) occur and make a conjecture, based on presented in this report results, that there is one general for \textit{all} dimensions characteristic of N-bein formulation of gravity: after elimination of second class constraints the algebra of Poisson brackets among remaining first class secondary constraints is the Poincare algebra and in all dimensions N-bein, Cartan-Einstein, gravity \textit{is the Poincare gauge theory}. The gauge symmetry corresponding to the algebra of first class constraints has two parameters - rotational (Lorentz) and translational. Translational invariance is common to all dimensions but some terms in general expressions for gauge transformations of N-beins and connections are zero in a particular, three dimensional, case. The proof of our conjecture is outlined in detail. Some straightforward but tedious calculations remain to be completed to call our conjecture - a theorem and will be reported later. |
gr-qc/0502087 | Mark A. Miller | Mark Miller | Accuracy requirements for the calculation of gravitational waveforms
from coalescing compact binaries in numerical relativity | One figure added, various clarifications and references added;
accepted to Phys. Rev. D | Phys.Rev.D71:104016,2005 | 10.1103/PhysRevD.71.104016 | null | gr-qc astro-ph | null | I discuss the accuracy requirements on numerical relativity calculations of
inspiraling compact object binaries whose extracted gravitational waveforms are
to be used as templates for matched filtering signal extraction and physical
parameter estimation in modern interferometric gravitational wave detectors.
Using a post-Newtonian point particle model for the pre-merger phase of the
binary inspiral, I calculate the maximum allowable errors for the mass and
relative velocity and positions of the binary during numerical simulations of
the binary inspiral. These maximum allowable errors are compared to the errors
of state-of-the-art numerical simulations of multiple-orbit binary neutron star
calculations in full general relativity, and are found to be smaller by several
orders of magnitude. A post-Newtonian model for the error of these numerical
simulations suggests that adaptive mesh refinement coupled with second order
accurate finite difference codes will {\it not} be able to robustly obtain the
accuracy required for reliable gravitational wave extraction on Terabyte-scale
computers. I conclude that higher order methods (higher order finite difference
methods and/or spectral methods) combined with adaptive mesh refinement and/or
multipatch technology will be needed for robustly accurate gravitational wave
extraction from numerical relativity calculations of binary coalescence
scenarios.
| [
{
"created": "Mon, 21 Feb 2005 21:21:17 GMT",
"version": "v1"
},
{
"created": "Mon, 11 Apr 2005 15:59:42 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Miller",
"Mark",
""
]
] | I discuss the accuracy requirements on numerical relativity calculations of inspiraling compact object binaries whose extracted gravitational waveforms are to be used as templates for matched filtering signal extraction and physical parameter estimation in modern interferometric gravitational wave detectors. Using a post-Newtonian point particle model for the pre-merger phase of the binary inspiral, I calculate the maximum allowable errors for the mass and relative velocity and positions of the binary during numerical simulations of the binary inspiral. These maximum allowable errors are compared to the errors of state-of-the-art numerical simulations of multiple-orbit binary neutron star calculations in full general relativity, and are found to be smaller by several orders of magnitude. A post-Newtonian model for the error of these numerical simulations suggests that adaptive mesh refinement coupled with second order accurate finite difference codes will {\it not} be able to robustly obtain the accuracy required for reliable gravitational wave extraction on Terabyte-scale computers. I conclude that higher order methods (higher order finite difference methods and/or spectral methods) combined with adaptive mesh refinement and/or multipatch technology will be needed for robustly accurate gravitational wave extraction from numerical relativity calculations of binary coalescence scenarios. |
0810.5356 | Mairi Sakellariadou | Mairi Sakellariadou | Lattice refinement in loop quantum cosmology | 17 pages, 1 figure, to appear in the Proceedings of "Recent
Developments in Gravity-NEB XIII"; Thessaloniki (Greece), June 2008 | J.Phys.Conf.Ser.189:012035,2009 | 10.1088/1742-6596/189/1/012035 | null | gr-qc astro-ph hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Lattice refinement in LQC, its meaning and its necessity are discussed. The
r\^ole of lattice refinement for the realisation of a successful inflationary
model is explicitly shown. A simple and effective numerical technique to solve
the constraint equation for any choice of lattice refinement model is briefly
illustrated. Phenomenological and consistency requirements leading to a
particular choice of lattice refinement model are presented, while it is
subsequently proved that only this choice of lattice refinement leads to a
unique factor ordering in the Wheeler-De Witt equation, which is the continuum
limit of LQC.
| [
{
"created": "Wed, 29 Oct 2008 20:58:46 GMT",
"version": "v1"
}
] | 2009-11-05 | [
[
"Sakellariadou",
"Mairi",
""
]
] | Lattice refinement in LQC, its meaning and its necessity are discussed. The r\^ole of lattice refinement for the realisation of a successful inflationary model is explicitly shown. A simple and effective numerical technique to solve the constraint equation for any choice of lattice refinement model is briefly illustrated. Phenomenological and consistency requirements leading to a particular choice of lattice refinement model are presented, while it is subsequently proved that only this choice of lattice refinement leads to a unique factor ordering in the Wheeler-De Witt equation, which is the continuum limit of LQC. |
0705.0787 | Parvin Moyassari | Hadi Salehi, Parvin Moyassari, Reza Rashidi | On the gravitational coupling of Hadamard states | 10 pages | null | null | null | gr-qc | null | We study the constraints imposed by the Hadamard condition on the two-point
function of local states of a scalar quantum field conformally coupled to a
gravitational background. We propose a method to assign a stress tensor to the
state-dependent part of the two point function which arises as a conserved
tensor with an anomalous trace. To characterize the local Hadamard states of
physical interest we apply a super-selection rule relating this quantum stress
tensor to the matter stress tensor of a conformal invariant gravitational model
subject to a conformal symmetry breaking term. This implies that the
determination of a Hadamard state may be considered as an integral part of its
gravitational coupling via the back-reaction effect.
| [
{
"created": "Sun, 6 May 2007 09:10:33 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Salehi",
"Hadi",
""
],
[
"Moyassari",
"Parvin",
""
],
[
"Rashidi",
"Reza",
""
]
] | We study the constraints imposed by the Hadamard condition on the two-point function of local states of a scalar quantum field conformally coupled to a gravitational background. We propose a method to assign a stress tensor to the state-dependent part of the two point function which arises as a conserved tensor with an anomalous trace. To characterize the local Hadamard states of physical interest we apply a super-selection rule relating this quantum stress tensor to the matter stress tensor of a conformal invariant gravitational model subject to a conformal symmetry breaking term. This implies that the determination of a Hadamard state may be considered as an integral part of its gravitational coupling via the back-reaction effect. |
1909.00438 | Charis Anastopoulos | Charis Anastopoulos and Ntina Savvidou | Multi-Time Measurements in Hawking Radiation: Information at
Higher-Order Correlations | 35 pages, 3 figures. Minor changes, some references added, version to
appear in Class. Quant. Grav | null | 10.1088/1361-6382/ab5eb2 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is believed that no information can be stored in Hawking radiation,
because correlations between quanta of different field modes vanish. However,
such correlations have been defined only with reference to a single moment of
time. In this article, we develop a method for the evaluation of {\em
multi-time} correlations. We find that these correlations are highly
non-trivial: for a scalar field in the Schwarzschild black hole, multi-time
correlations have an explicit dependence on angular variables and on the
scattering history of Hawking quanta. This result leads us to the conjecture
that some pre-collapse information can be stored in multi-time correlations
after backreaction effects have been incorporated in the physical description.
| [
{
"created": "Sun, 1 Sep 2019 17:36:19 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Dec 2019 17:39:07 GMT",
"version": "v2"
}
] | 2020-01-29 | [
[
"Anastopoulos",
"Charis",
""
],
[
"Savvidou",
"Ntina",
""
]
] | It is believed that no information can be stored in Hawking radiation, because correlations between quanta of different field modes vanish. However, such correlations have been defined only with reference to a single moment of time. In this article, we develop a method for the evaluation of {\em multi-time} correlations. We find that these correlations are highly non-trivial: for a scalar field in the Schwarzschild black hole, multi-time correlations have an explicit dependence on angular variables and on the scattering history of Hawking quanta. This result leads us to the conjecture that some pre-collapse information can be stored in multi-time correlations after backreaction effects have been incorporated in the physical description. |
2203.14631 | Sayan Kar | Sayan Kar (IIT Kharagpur, India) | Wormholes with a warped extra dimension? | 20 pages, 3 figures. Article prepared for the special issue of
General Relativity and Gravitation, dedicated to the memory of Professor
Thanu Padmanabhan. References added | null | 10.1007/s10714-022-02951-2 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We investigate the role of a specifically warped extra dimension in
constructing examples of higher dimensional spacetimes representing Lorentzian
wormholes. The warping chosen is largely inspired by the well-known non-static
Witten bubble of nothing, though our spacetimes are static and geometrically
different. Vacuum solutions in $D\geq 5$ dimensions and others
(non-asymptotically flat) with `perfectly normal' matter stress energy are
interpreted as possible Lorentzian wormholes. Asymptotically flat wormholes in
$D\geq 5$ with `exotic matter' and within this class of spacetimes also appear
to exist in all dimensions. A wormhole-black hole correspondence via double
Wick rotation is revisited and discussed. Finally, geodesic motion as well as
the behaviour of geodesic congruences, in the sub-class of five dimensional,
warped, vacuum wormhole spacetimes is also briefly analysed, with the aim of
obtaining characteristic properties and specific signatures which may help
improve our understanding of these geometries.
| [
{
"created": "Mon, 28 Mar 2022 10:35:16 GMT",
"version": "v1"
},
{
"created": "Thu, 19 May 2022 05:20:06 GMT",
"version": "v2"
}
] | 2022-07-20 | [
[
"Kar",
"Sayan",
"",
"IIT Kharagpur, India"
]
] | We investigate the role of a specifically warped extra dimension in constructing examples of higher dimensional spacetimes representing Lorentzian wormholes. The warping chosen is largely inspired by the well-known non-static Witten bubble of nothing, though our spacetimes are static and geometrically different. Vacuum solutions in $D\geq 5$ dimensions and others (non-asymptotically flat) with `perfectly normal' matter stress energy are interpreted as possible Lorentzian wormholes. Asymptotically flat wormholes in $D\geq 5$ with `exotic matter' and within this class of spacetimes also appear to exist in all dimensions. A wormhole-black hole correspondence via double Wick rotation is revisited and discussed. Finally, geodesic motion as well as the behaviour of geodesic congruences, in the sub-class of five dimensional, warped, vacuum wormhole spacetimes is also briefly analysed, with the aim of obtaining characteristic properties and specific signatures which may help improve our understanding of these geometries. |
1707.01092 | Paul Frampton | Paul H. Frampton | Holographic Entanglement Entropy in Cyclic Cosmology | 10 pages LaTeX. Rewritten to increase transparency | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss a cyclic cosmology in which the visible universe, or introverse,
is all that is accessible to an observer while the extroverse represents the
total spacetime originating from the time when the dark energy began to
dominate. It is argued that entanglement entropy of the introverse is the more
appropriate quantity to render infinitely cyclic, rather than the entropy of
the total universe. Since vanishing entanglement entropy implies disconnected
spacetimes, at the turnaround when the introverse entropy is zero the
disconnected extroverse can be jettisoned with impunity.
| [
{
"created": "Tue, 4 Jul 2017 11:51:45 GMT",
"version": "v1"
},
{
"created": "Fri, 1 Sep 2017 14:15:10 GMT",
"version": "v2"
}
] | 2017-09-04 | [
[
"Frampton",
"Paul H.",
""
]
] | We discuss a cyclic cosmology in which the visible universe, or introverse, is all that is accessible to an observer while the extroverse represents the total spacetime originating from the time when the dark energy began to dominate. It is argued that entanglement entropy of the introverse is the more appropriate quantity to render infinitely cyclic, rather than the entropy of the total universe. Since vanishing entanglement entropy implies disconnected spacetimes, at the turnaround when the introverse entropy is zero the disconnected extroverse can be jettisoned with impunity. |
gr-qc/0106029 | G. Sudhakaran | G.Sudhakaran, C.Sivaram | Cosmic repulsion in presence of matter | 11 pages | null | null | null | gr-qc | null | A basic problem that confronts the standard cosmological models is the
problem of initial singularity characterised by infinite material density,
infinite temperature and infinite spacetime curvature. The inevitable existence
of such a phase of the universe may be considered to be one of the major
drawbacks of Einstein's field equations. To some extent inflation models
ameliorate this. In the present work we postulate that whenever matter
(radiation) arises in flat spacetime, it introduces curvature and causes a
repulsive interaction to develop. A modified energy momentum tensor is
introduced towards this end, which invokes the temperature, entropy and a
cosmic scalar field. This redefinition of the energy momentum distribution when
applied to the early universe dynamics has the effect of producing a
non-singular initial behaviour. the repulsive interaction introduces some
features of an accelarating universe. In this model all cosmological parameters
are mathematically well behaved. There is no flatness problem. Temperature at
the beginning of this universe is 10^32 kelvin.
| [
{
"created": "Thu, 7 Jun 2001 18:48:43 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sudhakaran",
"G.",
""
],
[
"Sivaram",
"C.",
""
]
] | A basic problem that confronts the standard cosmological models is the problem of initial singularity characterised by infinite material density, infinite temperature and infinite spacetime curvature. The inevitable existence of such a phase of the universe may be considered to be one of the major drawbacks of Einstein's field equations. To some extent inflation models ameliorate this. In the present work we postulate that whenever matter (radiation) arises in flat spacetime, it introduces curvature and causes a repulsive interaction to develop. A modified energy momentum tensor is introduced towards this end, which invokes the temperature, entropy and a cosmic scalar field. This redefinition of the energy momentum distribution when applied to the early universe dynamics has the effect of producing a non-singular initial behaviour. the repulsive interaction introduces some features of an accelarating universe. In this model all cosmological parameters are mathematically well behaved. There is no flatness problem. Temperature at the beginning of this universe is 10^32 kelvin. |
gr-qc/0610129 | Darragh Walsh Mr | D. M. Walsh | Non-uniqueness in conformal formulations of the Einstein constraints | Arguments clarified and typos corrected. Matches published version | Class.Quant.Grav.24:1911-1926,2007 | 10.1088/0264-9381/24/8/002 | null | gr-qc | null | Standard methods in non-linear analysis are used to show that there exists a
parabolic branching of solutions of the Lichnerowicz-York equation with an
unscaled source. We also apply these methods to the extended conformal thin
sandwich formulation and show that if the linearised system develops a kernel
solution for sufficiently large initial data then we obtain parabolic solution
curves for the conformal factor, lapse and shift identical to those found
numerically by Pfeiffer and York. The implications of these results for
constrained evolutions are discussed.
| [
{
"created": "Thu, 26 Oct 2006 19:53:32 GMT",
"version": "v1"
},
{
"created": "Sat, 28 Apr 2007 23:51:16 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Walsh",
"D. M.",
""
]
] | Standard methods in non-linear analysis are used to show that there exists a parabolic branching of solutions of the Lichnerowicz-York equation with an unscaled source. We also apply these methods to the extended conformal thin sandwich formulation and show that if the linearised system develops a kernel solution for sufficiently large initial data then we obtain parabolic solution curves for the conformal factor, lapse and shift identical to those found numerically by Pfeiffer and York. The implications of these results for constrained evolutions are discussed. |
1307.1378 | Ehsan Hatefi | Luis Alvarez-Gaume, Ehsan Hatefi | More On Critical Collapse of Axion-Dilaton System in Dimension Four | 13 pages, Latex file, no figure,v2: to appear in JCAP | JCAP 1310 (2013) 037 | 10.1088/1475-7516/2013/10/037 | CERN-PH-TH/2013-249 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We complete our previous study of critical gravitational collapse in the
axion-dilaton system by analysing the hyperbolic and parabolic ans\"atze. As
could be expected, the corresponding Choptuik exponents in four-dimensions
differ from the elliptic case.
| [
{
"created": "Thu, 4 Jul 2013 15:38:37 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Oct 2013 18:00:29 GMT",
"version": "v2"
}
] | 2013-10-23 | [
[
"Alvarez-Gaume",
"Luis",
""
],
[
"Hatefi",
"Ehsan",
""
]
] | We complete our previous study of critical gravitational collapse in the axion-dilaton system by analysing the hyperbolic and parabolic ans\"atze. As could be expected, the corresponding Choptuik exponents in four-dimensions differ from the elliptic case. |
1809.07620 | Lorenzo Iorio | Lorenzo Iorio | On testing frame-dragging with LAGEOS and a recently announced geodetic
satellite | LaTex2e, 27 pages, 3 tables, 7 figures. Accepted for publication | Universe 2018, 4(11), 113 | 10.3390/universe4110113 | null | gr-qc physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, Ciufolini and coworkers announced the forthcoming launch of a new
cannonball geodetic satellite in 2019. It should be injected in an essentially
circular path with the same semimajor axis $a$ of LAGEOS, in orbit since 1976,
and an inclination $I$ of its orbital plane supplementary with respect to that
of its existing cousin. According to their proponents, the sum of the
satellites' precessions of the longitudes of the ascending nodes $\Omega$
should allow one to test the general relativistic Lense-Thirring effect to a
$\simeq 0.2\%$ accuracy level, with a contribution of the mismodeling in the
even zonal harmonics $J_\ell,~\ell=2,4,6,\ldots$ of the geopotential to the
total error budget as little as $0.1\%$. Actually, such an ambitious goal seems
to be hardly attainable because of the direct and indirect impact of, at least,
the first even zonal $J_2$. On the one hand, the lingering scatter of the
estimated values of such a key geophysical parameter from different recent
GRACE/GOCE-based global gravity field solutions is representative of an
uncertainty which may directly impact the summed Lense-Thirring node
precessions at a $\simeq 70-80\%$ in the worst scenarios, and to a $\simeq
3-10\%$ level in other, more favorable cases. On the other hand, the
phenomenologically measured secular decay $\dot a$ of the semimajor axis of
LAGEOS (and, presumably, of the other satellite as well), currently known at a
$\sigma_{\dot a}\simeq 0.03~\textrm{m~yr}^{-1}$ level after more than 30 yr,
will couple with the sum of the $J_2$-induced node precessions yielding an
overall bias as large as $\simeq 20-40\%$ after $5-10$ yr. A further systematic
error of the order of $\simeq 2-14\%$ may arise from an analogous interplay of
the secular decay of the inclination $\dot I$ with the oblateness-driven node
precessions.
| [
{
"created": "Tue, 18 Sep 2018 20:19:41 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Oct 2018 14:01:21 GMT",
"version": "v2"
}
] | 2018-10-30 | [
[
"Iorio",
"Lorenzo",
""
]
] | Recently, Ciufolini and coworkers announced the forthcoming launch of a new cannonball geodetic satellite in 2019. It should be injected in an essentially circular path with the same semimajor axis $a$ of LAGEOS, in orbit since 1976, and an inclination $I$ of its orbital plane supplementary with respect to that of its existing cousin. According to their proponents, the sum of the satellites' precessions of the longitudes of the ascending nodes $\Omega$ should allow one to test the general relativistic Lense-Thirring effect to a $\simeq 0.2\%$ accuracy level, with a contribution of the mismodeling in the even zonal harmonics $J_\ell,~\ell=2,4,6,\ldots$ of the geopotential to the total error budget as little as $0.1\%$. Actually, such an ambitious goal seems to be hardly attainable because of the direct and indirect impact of, at least, the first even zonal $J_2$. On the one hand, the lingering scatter of the estimated values of such a key geophysical parameter from different recent GRACE/GOCE-based global gravity field solutions is representative of an uncertainty which may directly impact the summed Lense-Thirring node precessions at a $\simeq 70-80\%$ in the worst scenarios, and to a $\simeq 3-10\%$ level in other, more favorable cases. On the other hand, the phenomenologically measured secular decay $\dot a$ of the semimajor axis of LAGEOS (and, presumably, of the other satellite as well), currently known at a $\sigma_{\dot a}\simeq 0.03~\textrm{m~yr}^{-1}$ level after more than 30 yr, will couple with the sum of the $J_2$-induced node precessions yielding an overall bias as large as $\simeq 20-40\%$ after $5-10$ yr. A further systematic error of the order of $\simeq 2-14\%$ may arise from an analogous interplay of the secular decay of the inclination $\dot I$ with the oblateness-driven node precessions. |
2009.02311 | Pedro Alvarez | Pedro D. Alvarez, Benjamin Koch, Cristobal Laporte and Angel Rincon | Can scale-dependent cosmology alleviate the $H_0$ tension? | revised version, accepted for publication in JCAP | null | 10.1088/1475-7516/2021/06/019 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Scale-dependence is a common feature to all effective models of quantum
gravity. In this paper, a cosmological model based on the scale-dependent
scenario of gravity is presented. It is argued that such models, where the
scale-dependence appears as a correction to the classical $\Lambda$CDM
evolution, have the potential of addressing the tensions between early and late
time measurements of $H_0$. After defining criteria to parametrize this
tension, we perform a numerical scan over the parameter space of the
scale-dependent model, subject to these criteria. In this analysis, it is found
that, indeed, the tension can be released.
| [
{
"created": "Fri, 4 Sep 2020 17:27:46 GMT",
"version": "v1"
},
{
"created": "Thu, 27 May 2021 20:33:14 GMT",
"version": "v2"
}
] | 2021-06-23 | [
[
"Alvarez",
"Pedro D.",
""
],
[
"Koch",
"Benjamin",
""
],
[
"Laporte",
"Cristobal",
""
],
[
"Rincon",
"Angel",
""
]
] | Scale-dependence is a common feature to all effective models of quantum gravity. In this paper, a cosmological model based on the scale-dependent scenario of gravity is presented. It is argued that such models, where the scale-dependence appears as a correction to the classical $\Lambda$CDM evolution, have the potential of addressing the tensions between early and late time measurements of $H_0$. After defining criteria to parametrize this tension, we perform a numerical scan over the parameter space of the scale-dependent model, subject to these criteria. In this analysis, it is found that, indeed, the tension can be released. |
gr-qc/9705081 | Shijun Yoshida | Shijun Yoshida and Yasufumi Kojima | Accuracy of the relativistic Cowling approximation in slowly rotating
stars | 5 pages, LaTeX, 3 figures, to appear in Mon. Not. R. Astron. Soc | null | 10.1093/mnras/289.1.117 | null | gr-qc astro-ph | null | We have calculated the non-radial oscillation in slowly rotating relativistic
stars with the Cowling approximation. The frequencies are compared with those
based on the complete linearized equations of general relativity. It is found
that the results with the approximation differ by less than about $20 %$ for
typical relativistic stellar models. The approximation is more accurate for
higher-order modes as in the Newtonian case.
| [
{
"created": "Thu, 29 May 1997 11:14:44 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Yoshida",
"Shijun",
""
],
[
"Kojima",
"Yasufumi",
""
]
] | We have calculated the non-radial oscillation in slowly rotating relativistic stars with the Cowling approximation. The frequencies are compared with those based on the complete linearized equations of general relativity. It is found that the results with the approximation differ by less than about $20 %$ for typical relativistic stellar models. The approximation is more accurate for higher-order modes as in the Newtonian case. |
gr-qc/0512124 | Zelnikov Andrei | Valeri P. Frolov and Andrei Zelnikov | Gravitational field of charged gyratons | 11 pages, some new comments and new references added. To appear in
Classical and Quantum Gravity | Class.Quant.Grav. 23 (2006) 2119-2128 | 10.1088/0264-9381/23/6/014 | Alberta-Thy-15-05 | gr-qc | null | We study relativistic gyratons which carry an electric charge. The
Einstein-Maxwell equations in arbitrary dimensions are solved exactly in the
case of a charged gyraton propagating in an asymptotically flat metric.
| [
{
"created": "Thu, 22 Dec 2005 00:03:20 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Feb 2006 00:03:12 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Frolov",
"Valeri P.",
""
],
[
"Zelnikov",
"Andrei",
""
]
] | We study relativistic gyratons which carry an electric charge. The Einstein-Maxwell equations in arbitrary dimensions are solved exactly in the case of a charged gyraton propagating in an asymptotically flat metric. |
2406.01412 | Tomi Koivisto | Damianos Iosifidis, Erik Jensko, Tomi S. Koivisto | Relativistic interacting fluids in cosmology | 15 pages, 1 figure | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Motivated by cosmological applications for interacting matters, an extension
of the action functional for relativistic fluids is proposed to incorporate the
physics of non-adiabatic processes and chemical reactions. The former are
characterised by entropy growth, while the latter violate particle number
conservation. The relevance of these physics is demonstrated in the contexts of
self-interacting fluids, fluids interacting with scalar fields, and
hyperhydrodynamical interactions with geometry. The possible cosmological
applications range from early-universe phase transitions to astrophysical
phenomena, and from matter creation inflationary alternatives to interacting
dark sector alternatives to the $\Lambda$CDM model that aim to address its
tensions. As an example of the latter, a single fluid model of a unified dark
sector is presented. The simple action of the model features one field and one
parameter, yet it can both reproduce the $\Lambda$CDM cosmology and predict new
phenomenology.
| [
{
"created": "Mon, 3 Jun 2024 15:12:42 GMT",
"version": "v1"
}
] | 2024-06-04 | [
[
"Iosifidis",
"Damianos",
""
],
[
"Jensko",
"Erik",
""
],
[
"Koivisto",
"Tomi S.",
""
]
] | Motivated by cosmological applications for interacting matters, an extension of the action functional for relativistic fluids is proposed to incorporate the physics of non-adiabatic processes and chemical reactions. The former are characterised by entropy growth, while the latter violate particle number conservation. The relevance of these physics is demonstrated in the contexts of self-interacting fluids, fluids interacting with scalar fields, and hyperhydrodynamical interactions with geometry. The possible cosmological applications range from early-universe phase transitions to astrophysical phenomena, and from matter creation inflationary alternatives to interacting dark sector alternatives to the $\Lambda$CDM model that aim to address its tensions. As an example of the latter, a single fluid model of a unified dark sector is presented. The simple action of the model features one field and one parameter, yet it can both reproduce the $\Lambda$CDM cosmology and predict new phenomenology. |
2012.05424 | Ran Li | Ran Li, Jin Wang | Energy and entropy compensation, phase transition and kinetics of four
dimensional charged Gauss-Bonnet Anti-de Sitter black holes on the underlying
free energy landscape | References added | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the phase transition and the kinetics of the four dimensional
charged AdS black hole in GB gravity based on the free energy landscape. Below
the critical temperature, the free energy landscape topography has the shape of
double basins with each representing one stable/unstable black hole phase. The
thermodynamic small/large black hole phase transition is determined by the
equal depths of the basins. We also demonstrate the underlying kinetics of the
phase transition by studying the time evolution of the probability distribution
of the state in the ensemble as well as the MFPT and the kinetic fluctuation of
the state switching process caused by the thermal fluctuations. The final
distribution is determined by the Boltzmann law and the MFPT and its
fluctuation are closely related to the free energy landscape topography through
barrier heights and ensemble temperature. Furthermore, we provide a complete
description of the kinetics of phase transition with different physical
parameters. The free energy is the result of the delicate balance and
competition between the two relatively large numbers, the energy and entropy
multiplied by temperature. Low energy and low entropy can give rise to a stable
thermodynamic state in terms of free energy minimum (energy/mass preferred)
while the high energy and high entropy can also give rise to a stable state in
terms of free energy minimum. When the GB coupling constant increases, or the
electric charge (potential) increases, or the pressure (absolute value of
cosmological constant) decreases, it is easier for the small black hole state
to escape to the large black hole state. Meanwhile, the inverse process becomes
harder, i.e. the small (large) black hole state becomes less (more) stable.
| [
{
"created": "Thu, 10 Dec 2020 02:50:41 GMT",
"version": "v1"
},
{
"created": "Sat, 12 Dec 2020 02:46:24 GMT",
"version": "v2"
}
] | 2020-12-15 | [
[
"Li",
"Ran",
""
],
[
"Wang",
"Jin",
""
]
] | We study the phase transition and the kinetics of the four dimensional charged AdS black hole in GB gravity based on the free energy landscape. Below the critical temperature, the free energy landscape topography has the shape of double basins with each representing one stable/unstable black hole phase. The thermodynamic small/large black hole phase transition is determined by the equal depths of the basins. We also demonstrate the underlying kinetics of the phase transition by studying the time evolution of the probability distribution of the state in the ensemble as well as the MFPT and the kinetic fluctuation of the state switching process caused by the thermal fluctuations. The final distribution is determined by the Boltzmann law and the MFPT and its fluctuation are closely related to the free energy landscape topography through barrier heights and ensemble temperature. Furthermore, we provide a complete description of the kinetics of phase transition with different physical parameters. The free energy is the result of the delicate balance and competition between the two relatively large numbers, the energy and entropy multiplied by temperature. Low energy and low entropy can give rise to a stable thermodynamic state in terms of free energy minimum (energy/mass preferred) while the high energy and high entropy can also give rise to a stable state in terms of free energy minimum. When the GB coupling constant increases, or the electric charge (potential) increases, or the pressure (absolute value of cosmological constant) decreases, it is easier for the small black hole state to escape to the large black hole state. Meanwhile, the inverse process becomes harder, i.e. the small (large) black hole state becomes less (more) stable. |
1205.0911 | Alejandro Perez | Alejandro Perez | The new spin foam models and quantum gravity | To appear in Papers in Physics | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we give a systematic definition of the recently introduced
spin foam models for four dimensional quantum gravity reviewing the main
results on their semiclassical limit on fixed discretizations.
| [
{
"created": "Fri, 4 May 2012 10:42:37 GMT",
"version": "v1"
}
] | 2012-05-07 | [
[
"Perez",
"Alejandro",
""
]
] | In this article we give a systematic definition of the recently introduced spin foam models for four dimensional quantum gravity reviewing the main results on their semiclassical limit on fixed discretizations. |
gr-qc/0010036 | Hiroyuki Nakano | Hiroyuki Nakano, Misao Sasaki | Gravitational reaction force on a particle in the Schwarzschild
background | 15 pages, no figure, submitted to Prog. Theor. Phys | Prog.Theor.Phys.105:197-218,2001 | 10.1143/PTP.105.197 | OU-TAP-145 | gr-qc astro-ph | null | We formulate a new method to calculate the gravitational reaction force on a
particle of mass $\mu$ orbiting a massive black hole of mass $M$. In this
formalism, the tail part of the retarded Green function, which is responsible
for the reaction force, is calculated at the level of the Teukolsky equation.
Our method naturally allows a systematic post-Minkowskian (PM) expansion of the
tail part at short distances. As a first step, we consider the case of a
Schwarzschild black hole and explicitly calculate the first post-Newtonian
(1PN) tail part of the Green function. There are, however, a couple of issues
to be resolved before explicitly evaluating the reaction force by applying the
present method. We discuss possible resolutions of these issues.
| [
{
"created": "Tue, 10 Oct 2000 08:56:38 GMT",
"version": "v1"
},
{
"created": "Tue, 17 Oct 2000 06:45:13 GMT",
"version": "v2"
},
{
"created": "Wed, 17 Jan 2001 03:50:08 GMT",
"version": "v3"
}
] | 2009-10-09 | [
[
"Nakano",
"Hiroyuki",
""
],
[
"Sasaki",
"Misao",
""
]
] | We formulate a new method to calculate the gravitational reaction force on a particle of mass $\mu$ orbiting a massive black hole of mass $M$. In this formalism, the tail part of the retarded Green function, which is responsible for the reaction force, is calculated at the level of the Teukolsky equation. Our method naturally allows a systematic post-Minkowskian (PM) expansion of the tail part at short distances. As a first step, we consider the case of a Schwarzschild black hole and explicitly calculate the first post-Newtonian (1PN) tail part of the Green function. There are, however, a couple of issues to be resolved before explicitly evaluating the reaction force by applying the present method. We discuss possible resolutions of these issues. |
gr-qc/0506031 | Hermann Nicolai | H. Nicolai | Gravitational Billiards, Dualities and Hidden Symmetries | 37 pages, invited contribution to the volume "100 years of relativity
spacetime structure: Einstein and beyond", ed. A. Ashtekar | null | null | AEI-2005-024 | gr-qc | null | The purpose of this article is to highlight the fascinating, but only very
incompletely understood relation between Einstein's theory and its
generalizations on the one hand, and the theory of indefinite, and in
particular hyperbolic, Kac Moody algebras on the other. The elucidation of this
link could lead to yet another revolution in our understanding of Einstein's
theory and attempts to quantize it.
| [
{
"created": "Mon, 6 Jun 2005 08:10:07 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Nicolai",
"H.",
""
]
] | The purpose of this article is to highlight the fascinating, but only very incompletely understood relation between Einstein's theory and its generalizations on the one hand, and the theory of indefinite, and in particular hyperbolic, Kac Moody algebras on the other. The elucidation of this link could lead to yet another revolution in our understanding of Einstein's theory and attempts to quantize it. |
0905.2730 | Ahmadjon Abdujabbarov | Ahmadjon Abdujabbarov, Bobomurat Ahmedov | Charged Particle Motion Around Rotating Black Hole in Braneworld
Immersed in Magnetic Field | 9 pages, 8 figures, revised version to be resubmitted to Phys. Rev. D | Phys.Rev.D81:044022,2010 | 10.1103/PhysRevD.81.044022 | null | gr-qc astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Analytical solutions of Maxwell equations in background spacetime of black
hole in braneworld immersed in external uniform magnetic field have been found.
Influence of both magnetic and brane parameters on effective potential of the
radial motion of charged test particle around slowly rotating black hole in
braneworld immersed in uniform magnetic field has been investigated by using
Hamilton-Jacobi method. Exact analytical solution for dependence of the radius
of the innermost stable circular orbits (ISCO) $r_{\rm ISCO}$ from brane
parameter for motion of test particle around nonrotating isolated black hole in
braneworld has been derived. It has been shown that radius $r_{\rm ISCO}$ is
monotonically growing with the increase of module of brane tidal charge.
Comparison of the predictions on $r_{\rm ISCO}$ of the brane world model and of
the observational results of ISCO from relativistic accretion disks around
black holes provided upper limit for brane tidal charge $\lesssim 10^9 {\rm
cm}^2$.
| [
{
"created": "Sun, 17 May 2009 11:47:04 GMT",
"version": "v1"
}
] | 2010-05-12 | [
[
"Abdujabbarov",
"Ahmadjon",
""
],
[
"Ahmedov",
"Bobomurat",
""
]
] | Analytical solutions of Maxwell equations in background spacetime of black hole in braneworld immersed in external uniform magnetic field have been found. Influence of both magnetic and brane parameters on effective potential of the radial motion of charged test particle around slowly rotating black hole in braneworld immersed in uniform magnetic field has been investigated by using Hamilton-Jacobi method. Exact analytical solution for dependence of the radius of the innermost stable circular orbits (ISCO) $r_{\rm ISCO}$ from brane parameter for motion of test particle around nonrotating isolated black hole in braneworld has been derived. It has been shown that radius $r_{\rm ISCO}$ is monotonically growing with the increase of module of brane tidal charge. Comparison of the predictions on $r_{\rm ISCO}$ of the brane world model and of the observational results of ISCO from relativistic accretion disks around black holes provided upper limit for brane tidal charge $\lesssim 10^9 {\rm cm}^2$. |
1609.03613 | Davi Rodrigues | Davi C. Rodrigues, Sebasti\~ao Mauro, \'Alefe O. F. de Almeida | Solar System constraints on Renormalization Group extended General
Relativity: The PPN and Laplace-Runge-Lenz analyses with the external
potential effect | 13 pages, 4 figures. Added references and minor corrections in text.
Version to appear in PRD | Phys. Rev. D 94, 084036 (2016) | 10.1103/PhysRevD.94.084036 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | General Relativity extensions based on Renormalization Group effects are
motivated by a known physical principle and constitute a class of extended
gravity theories that have some unexplored unique aspects. In this work we
develop in detail the Newtonian and post Newtonian limits of a realisation
called Renormalization Group extended General Relativity (RGGR). Special
attention is taken to the external potential effect, which constitutes a type
of screening mechanism typical of RGGR. In the Solar System, RGGR depends on a
single dimensionless parameter $\bar \nu_\odot$, and this parameter is such
that for $\bar \nu_\odot = 0$ one fully recovers GR in the Solar System.
Previously this parameter was constrained to be $|\bar \nu_\odot| \lesssim
10^{-21}$, without considering the external potential effect. Here we show that
under a certain approximation RGGR can be cast in a form compatible with the
Parametrised Post-Newtonian (PPN) formalism, and we use both the PPN formalism
and the Laplace-Runge-Lenz technique to put new bounds on $\bar \nu_\odot$,
either considering or not the external potential effect. With the external
potential effect the new bound reads $|\bar \nu_\odot| \lesssim 10^{-16}$. We
discuss the possible consequences of this bound to the dark matter abundance in
galaxies.
| [
{
"created": "Mon, 12 Sep 2016 21:59:34 GMT",
"version": "v1"
},
{
"created": "Sun, 9 Oct 2016 21:19:23 GMT",
"version": "v2"
}
] | 2016-10-27 | [
[
"Rodrigues",
"Davi C.",
""
],
[
"Mauro",
"Sebastião",
""
],
[
"de Almeida",
"Álefe O. F.",
""
]
] | General Relativity extensions based on Renormalization Group effects are motivated by a known physical principle and constitute a class of extended gravity theories that have some unexplored unique aspects. In this work we develop in detail the Newtonian and post Newtonian limits of a realisation called Renormalization Group extended General Relativity (RGGR). Special attention is taken to the external potential effect, which constitutes a type of screening mechanism typical of RGGR. In the Solar System, RGGR depends on a single dimensionless parameter $\bar \nu_\odot$, and this parameter is such that for $\bar \nu_\odot = 0$ one fully recovers GR in the Solar System. Previously this parameter was constrained to be $|\bar \nu_\odot| \lesssim 10^{-21}$, without considering the external potential effect. Here we show that under a certain approximation RGGR can be cast in a form compatible with the Parametrised Post-Newtonian (PPN) formalism, and we use both the PPN formalism and the Laplace-Runge-Lenz technique to put new bounds on $\bar \nu_\odot$, either considering or not the external potential effect. With the external potential effect the new bound reads $|\bar \nu_\odot| \lesssim 10^{-16}$. We discuss the possible consequences of this bound to the dark matter abundance in galaxies. |
1401.1400 | Mohammad Reza Setare | M. R. Setare and V. Kamali | Some aspects of non-abelian gauge field inflation model | 12 pages, 4 figures. arXiv admin note: substantial text overlap with
arXiv:1308.5674 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study non-abelian gauge field inflation (gauge-flation)
model in the context of intermediate and logamediate scenario. Important
parameters of this model are presented for these two cases. Numerical study
shows that the intermediate and logamediate gauge-flation are compatible with
WMAP9 observational data. For intermediate inflation, where the cosmological
scale factor expands as: $a(t)=a_0\exp(At^f)$ ($A>0, 0<f<1$), $N\geq 100$ cases
lead to $0.02<r<0.11$ ($r$ is tensor-scalar ratio) and $N\simeq50 $ case leads
to $n_s\simeq 0.96$ ($n_s$ is spectral index). These constraints of
perturbation parameters are agree with Planck and WMAP9 data. For logamediate
model, where the scale factor expands as: $a(t)=a_0 \exp(a[\ln t]^{\lambda})$
($\lambda >1, A>0$), $N\geq 200$ and $\lambda=2$ cases lead to interesting
agreement with observational data.
| [
{
"created": "Mon, 6 Jan 2014 06:12:09 GMT",
"version": "v1"
}
] | 2014-01-08 | [
[
"Setare",
"M. R.",
""
],
[
"Kamali",
"V.",
""
]
] | In this paper we study non-abelian gauge field inflation (gauge-flation) model in the context of intermediate and logamediate scenario. Important parameters of this model are presented for these two cases. Numerical study shows that the intermediate and logamediate gauge-flation are compatible with WMAP9 observational data. For intermediate inflation, where the cosmological scale factor expands as: $a(t)=a_0\exp(At^f)$ ($A>0, 0<f<1$), $N\geq 100$ cases lead to $0.02<r<0.11$ ($r$ is tensor-scalar ratio) and $N\simeq50 $ case leads to $n_s\simeq 0.96$ ($n_s$ is spectral index). These constraints of perturbation parameters are agree with Planck and WMAP9 data. For logamediate model, where the scale factor expands as: $a(t)=a_0 \exp(a[\ln t]^{\lambda})$ ($\lambda >1, A>0$), $N\geq 200$ and $\lambda=2$ cases lead to interesting agreement with observational data. |
gr-qc/0405091 | John W. Moffat | J. W. Moffat | Modified Gravitational Theory and the Gravity Probe-B Gyroscope
Experiment | 8 pages, LeTex file, no figures | null | null | null | gr-qc | null | A possible deviation from the precession of the Gravity Probe-B gyroscope
predicted by general relativity is obtained in the nonsymmetric gravity theory.
The time delay of radio signals emitted by spacecraft at planetary distances
from the Sun, in nonsymmetric gravity theory is the same as in general
relativity. A correction to the precession of the gyroscope would provide a
possible experimental signature for the Gravity Probe-B gyroscope experiment.
The Lense-Thirring frame-dragging effect is predicted to be the same as in GR.
| [
{
"created": "Mon, 17 May 2004 23:08:51 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Moffat",
"J. W.",
""
]
] | A possible deviation from the precession of the Gravity Probe-B gyroscope predicted by general relativity is obtained in the nonsymmetric gravity theory. The time delay of radio signals emitted by spacecraft at planetary distances from the Sun, in nonsymmetric gravity theory is the same as in general relativity. A correction to the precession of the gyroscope would provide a possible experimental signature for the Gravity Probe-B gyroscope experiment. The Lense-Thirring frame-dragging effect is predicted to be the same as in GR. |
1511.00226 | Alexander Pavlov E | Alexander E. Pavlov | Exact solutions of Friedmann equation for supernovae data | 7 pages, 2 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An intrinsic time of homogeneous models is global. The Friedmann equation by
its sense ties time intervals. Exact solutions of the Friedmann equation in
Standard cosmology and Conformal cosmology are presented. Theoretical curves
interpolated the Hubble diagram on latest supernovae are expressed in
analytical form. The class of functions in which the concordance model is
described is Weierstrass meromorphic functions. The Standard cosmological model
and Conformal one fit the modern Hubble diagram equivalently. However, the
physical interpretation of the modern data from concepts of the Conformal
cosmology is simpler, so is preferable.
| [
{
"created": "Sun, 1 Nov 2015 10:45:24 GMT",
"version": "v1"
}
] | 2015-11-03 | [
[
"Pavlov",
"Alexander E.",
""
]
] | An intrinsic time of homogeneous models is global. The Friedmann equation by its sense ties time intervals. Exact solutions of the Friedmann equation in Standard cosmology and Conformal cosmology are presented. Theoretical curves interpolated the Hubble diagram on latest supernovae are expressed in analytical form. The class of functions in which the concordance model is described is Weierstrass meromorphic functions. The Standard cosmological model and Conformal one fit the modern Hubble diagram equivalently. However, the physical interpretation of the modern data from concepts of the Conformal cosmology is simpler, so is preferable. |
1001.2220 | Narit Pidokrajt | Jan E. Aman, Narit Pidokrajt | Critical phenomena and information geometry in black hole physics | Contribution to ERE2009, 5 pages | J.Phys.Conf.Ser.229:012060,2010 | 10.1088/1742-6596/229/1/012060 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the use of information geometry in black hole physics and present
the outcomes. The type of information geometry we utilize in this approach is
the thermodynamic (Ruppeiner) geometry defined on the state space of a given
thermodynamic system in equilibrium. The Ruppeiner geometry can be used to
analyze stability and critical phenomena in black hole physics with results
consistent with those from the Poincare stability analysis for black holes and
black rings. Furthermore other physical phenomena are well encoded in the
Ruppeiner metric such as the sign of specific heat and the extremality of the
solutions. The black hole families we discuss in particular in this manuscript
are the Myers-Perry black holes.
| [
{
"created": "Wed, 13 Jan 2010 16:19:40 GMT",
"version": "v1"
}
] | 2011-02-18 | [
[
"Aman",
"Jan E.",
""
],
[
"Pidokrajt",
"Narit",
""
]
] | We discuss the use of information geometry in black hole physics and present the outcomes. The type of information geometry we utilize in this approach is the thermodynamic (Ruppeiner) geometry defined on the state space of a given thermodynamic system in equilibrium. The Ruppeiner geometry can be used to analyze stability and critical phenomena in black hole physics with results consistent with those from the Poincare stability analysis for black holes and black rings. Furthermore other physical phenomena are well encoded in the Ruppeiner metric such as the sign of specific heat and the extremality of the solutions. The black hole families we discuss in particular in this manuscript are the Myers-Perry black holes. |
1811.05640 | Chiang-Mei Chen | Chiang-Mei Chen, Jian-Liang Liu, James M. Nester | Quasi-local energy from a Minkowski reference | 14 pages, accepted by Gen Rel Grav, selected as an Editor's Choice | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The specification of energy for gravitating systems has been an unsettled
issue since Einstein proposed his pseudotensor. It is now understood that
energy-momentum is \emph{quasi-local} (associated with a closed 2-surface).
Here we consider quasi-local proposals (including pseudotensors) in the
Lagrangian-Noether-Hamiltonian formulations. There are two ambiguities: (i)
there are many possible expressions, (ii) they depend on some non-dynamical
structure, e.g., a reference frame. The Hamiltonian approach gives a handle on
both problems. The Hamiltonian perspective helped us to make a remarkable
discovery: with an isometric Minkowski reference a large class of
expressions---namely all those that agree with the Einstein pseudotensor's
Freud superpotential to linear order---give a common quasi-local energy value.
Moreover, with a best-matched reference on the boundary this is the Wang-Yau
mass value.
| [
{
"created": "Wed, 14 Nov 2018 04:59:38 GMT",
"version": "v1"
}
] | 2018-11-15 | [
[
"Chen",
"Chiang-Mei",
""
],
[
"Liu",
"Jian-Liang",
""
],
[
"Nester",
"James M.",
""
]
] | The specification of energy for gravitating systems has been an unsettled issue since Einstein proposed his pseudotensor. It is now understood that energy-momentum is \emph{quasi-local} (associated with a closed 2-surface). Here we consider quasi-local proposals (including pseudotensors) in the Lagrangian-Noether-Hamiltonian formulations. There are two ambiguities: (i) there are many possible expressions, (ii) they depend on some non-dynamical structure, e.g., a reference frame. The Hamiltonian approach gives a handle on both problems. The Hamiltonian perspective helped us to make a remarkable discovery: with an isometric Minkowski reference a large class of expressions---namely all those that agree with the Einstein pseudotensor's Freud superpotential to linear order---give a common quasi-local energy value. Moreover, with a best-matched reference on the boundary this is the Wang-Yau mass value. |
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