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/9609049 | Mr Blanchet Darc | L. Blanchet | Gravitational radiation reaction and balance equations to post-Newtonian
order | To appear in Phys. Rev. D | Phys.Rev.D55:714-732,1997 | 10.1103/PhysRevD.55.714 | null | gr-qc | null | Gravitational radiation reaction forces and balance equations for energy and
momenta are investigated to 3/2 post-Newtonian (1.5PN) order beyond the
quadrupole approximation, corresponding to the 4PN order in the equations of
motion of an isolated system. By matching a post-Newtonian solution for the
gravitational field inside the system to a post-Minkowskian solution (obtained
in a previous work) for the gravitational field exterior to the system, we
determine the 1PN relativistic corrections to the ``Newtonian" radiation
reaction potential of Burke and Thorne. The 1PN reaction potential involves
both scalar and vectorial components, with the scalar component depending on
the mass-type quadrupole and octupole moments of the system, and the vectorial
component depending in particular on the current-type quadrupole moment. In the
case of binary systems, the 1PN radiation reaction potential has been shown to
yield consistent results for the 3.5PN approximation in the binary's equations
of motion. Adding up the effects of tails, the radiation reaction is then
written to 1.5PN order. In this paper, we establish the validity to 1.5PN
order, for general systems, of the balance equations relating the losses of
energy, linear momentum, and angular momentum in the system to the
corresponding fluxes in the radiation field far from the system.
| [
{
"created": "Fri, 20 Sep 1996 09:20:24 GMT",
"version": "v1"
}
] | 2011-09-09 | [
[
"Blanchet",
"L.",
""
]
] | Gravitational radiation reaction forces and balance equations for energy and momenta are investigated to 3/2 post-Newtonian (1.5PN) order beyond the quadrupole approximation, corresponding to the 4PN order in the equations of motion of an isolated system. By matching a post-Newtonian solution for the gravitational field inside the system to a post-Minkowskian solution (obtained in a previous work) for the gravitational field exterior to the system, we determine the 1PN relativistic corrections to the ``Newtonian" radiation reaction potential of Burke and Thorne. The 1PN reaction potential involves both scalar and vectorial components, with the scalar component depending on the mass-type quadrupole and octupole moments of the system, and the vectorial component depending in particular on the current-type quadrupole moment. In the case of binary systems, the 1PN radiation reaction potential has been shown to yield consistent results for the 3.5PN approximation in the binary's equations of motion. Adding up the effects of tails, the radiation reaction is then written to 1.5PN order. In this paper, we establish the validity to 1.5PN order, for general systems, of the balance equations relating the losses of energy, linear momentum, and angular momentum in the system to the corresponding fluxes in the radiation field far from the system. |
0807.2485 | Giovanni Santostasi | Giovanni Santostasi | Upper and lower limits on the Crab pulsar's astrophysical parameters set
from gravitational wave observations by LIGO: braking index and energy
considerations | 6 pages, 4 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Laser Interferometer Gravitational Observatory (LIGO) has recently
reached the end of its fifth science run (S5), having collected more than a
year worth of data. Analysis of the data is still ongoing but a positive
detection of gravitational waves, while possible, is not realistically expected
for most likely sources. This is particularly true for what concerns
gravitational waves from known pulsars. In fact, even under the most optimistic
(and not very realistic) assumption that all the pulsar's observed spin-down is
due to gravitational waves, the gravitational wave strain at earth from all the
known isolated pulsars (with the only notable exception of the Crab pulsar)
would not be strong enough to be detectable by existing detectors. By August
2006, LIGO had produced enough data for a coherent integration capable to
extract signal from noise that was weaker than the one expected from the Crab
pulsar's spin-down limit. No signal was detected, but beating the spin-down
limit is a considerable achievement for the LIGO Scientific Collaboration
(LSC). It is customary to translate the upper limit on strain from a pulsar
into a more astrophysically significant upper limit on ellipticity. Once the
spin-down limit has been beaten, it is possible to release the constraint that
all the spin-down is due to gravitational wave emission. A more complete model
with diverse braking mechanisms can be used to set limits on several
astrophysical parameters of the pulsar. This paper shows possible values of
such parameters for the Crab pulsar given the current limit on gravitational
waves from this neutron star.
| [
{
"created": "Wed, 16 Jul 2008 00:35:53 GMT",
"version": "v1"
}
] | 2008-07-17 | [
[
"Santostasi",
"Giovanni",
""
]
] | The Laser Interferometer Gravitational Observatory (LIGO) has recently reached the end of its fifth science run (S5), having collected more than a year worth of data. Analysis of the data is still ongoing but a positive detection of gravitational waves, while possible, is not realistically expected for most likely sources. This is particularly true for what concerns gravitational waves from known pulsars. In fact, even under the most optimistic (and not very realistic) assumption that all the pulsar's observed spin-down is due to gravitational waves, the gravitational wave strain at earth from all the known isolated pulsars (with the only notable exception of the Crab pulsar) would not be strong enough to be detectable by existing detectors. By August 2006, LIGO had produced enough data for a coherent integration capable to extract signal from noise that was weaker than the one expected from the Crab pulsar's spin-down limit. No signal was detected, but beating the spin-down limit is a considerable achievement for the LIGO Scientific Collaboration (LSC). It is customary to translate the upper limit on strain from a pulsar into a more astrophysically significant upper limit on ellipticity. Once the spin-down limit has been beaten, it is possible to release the constraint that all the spin-down is due to gravitational wave emission. A more complete model with diverse braking mechanisms can be used to set limits on several astrophysical parameters of the pulsar. This paper shows possible values of such parameters for the Crab pulsar given the current limit on gravitational waves from this neutron star. |
1312.4297 | Alfred Molina | Xavier Ja\'en and Alfred Molina | Homothetic motions and Newtonian cosmology | 14 pages, submitted to GRG | null | 10.1007/s10714-014-1745-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the homothetic motion group. We construct a homothetic covariant
Newtonian gravitation theory which unifies inertial homothetic forces and
gravitational fields. This is achieved through an equivalence principle based
on a local homothetic frame of motion. As a consequence, we can obtain a
coherent Newtonian cosmology which admits a cosmological principle and leads to
the Friedman equations for a dust universe. Finally we prove that this gravity
theory can be obtained as the non-relativistic limit of a class of metrics in
General Relativity. The Friedmann-Lema\^\i tre-Robertson-Walker (FLRW) metric
and its limit are also studied.
| [
{
"created": "Mon, 16 Dec 2013 10:34:35 GMT",
"version": "v1"
}
] | 2015-06-18 | [
[
"Jaén",
"Xavier",
""
],
[
"Molina",
"Alfred",
""
]
] | We consider the homothetic motion group. We construct a homothetic covariant Newtonian gravitation theory which unifies inertial homothetic forces and gravitational fields. This is achieved through an equivalence principle based on a local homothetic frame of motion. As a consequence, we can obtain a coherent Newtonian cosmology which admits a cosmological principle and leads to the Friedman equations for a dust universe. Finally we prove that this gravity theory can be obtained as the non-relativistic limit of a class of metrics in General Relativity. The Friedmann-Lema\^\i tre-Robertson-Walker (FLRW) metric and its limit are also studied. |
1112.3048 | Cormac Breen | Cormac Breen and Adrian C. Ottewill | Hadamard Renormalization of the Stress Energy Tensor in a Spherically
Symmetric Black Hole Space-Time with an Application to Lukewarm Black Holes | 17 pages, 8 figures and 2 tables | null | 10.1103/PhysRevD.85.084029 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a quantum field which is in a Hartle-Hawking state propagating in
a spherically symmetric black hole space-time. We calculate the components of
the stress tensor, renormalized using the Hadamard form of the Green's
function, in the exterior region of this space-time. We then specialize these
results to the case of the `lukewarm' Riessner-Nordstrom-de Sitter black hole.
| [
{
"created": "Tue, 13 Dec 2011 21:29:53 GMT",
"version": "v1"
}
] | 2013-05-30 | [
[
"Breen",
"Cormac",
""
],
[
"Ottewill",
"Adrian C.",
""
]
] | We consider a quantum field which is in a Hartle-Hawking state propagating in a spherically symmetric black hole space-time. We calculate the components of the stress tensor, renormalized using the Hadamard form of the Green's function, in the exterior region of this space-time. We then specialize these results to the case of the `lukewarm' Riessner-Nordstrom-de Sitter black hole. |
2408.03410 | Charlie Hoy | Charlie Hoy, Stephen Fairhurst, Ilya Mandel | Precession and higher order multipoles in binary black holes (and lack
thereof) | 13 pages, 5 figures | null | null | LIGO-P2400332 | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | The latest binary black hole population estimates argue for a subpopulation
of unequal component mass binaries with spins that are likely small but
isotropically distributed. This implies a non-zero probability of detecting
spin-induced orbital precession and higher order multipoles moments in the
observed gravitational-wave signals. In this work we directly calculate the
probability for precession and higher order multipoles in each significant
gravitational-wave candidate observed by the LIGO--Virgo--KAGRA collaborations
(LVK). We find that only one event shows substantial evidence for precession:
GW200129_065458, and two events show substantial evidence for higher order
multipoles: GW190412 and GW190814; any evidence for precession and higher order
multipoles in other gravitational-wave signals is consistent with random
fluctuations caused by noise. We then compare our observations with
expectations from population models, and confirm that current population
estimates from the LVK accurately predict the number of observed events with
significant evidence for precession and higher order multipole moments. In
particular, we find that this population model predicts that a binary with
significant evidence for precession will occur once in every $\sim 50$
detections, and a binary with significant evidence for higher order multipole
moments will occur once in every $\sim 70$ observations. However, we emphasise
that since substantial evidence for precession and higher order multipole
moments have only been observed in three events, any population model that
includes a subpopulation of binaries yielding $\sim 2\%$ of events with
detectable precession and higher order multipole moments will likely be
consistent with the data.
| [
{
"created": "Tue, 6 Aug 2024 19:17:46 GMT",
"version": "v1"
}
] | 2024-08-08 | [
[
"Hoy",
"Charlie",
""
],
[
"Fairhurst",
"Stephen",
""
],
[
"Mandel",
"Ilya",
""
]
] | The latest binary black hole population estimates argue for a subpopulation of unequal component mass binaries with spins that are likely small but isotropically distributed. This implies a non-zero probability of detecting spin-induced orbital precession and higher order multipoles moments in the observed gravitational-wave signals. In this work we directly calculate the probability for precession and higher order multipoles in each significant gravitational-wave candidate observed by the LIGO--Virgo--KAGRA collaborations (LVK). We find that only one event shows substantial evidence for precession: GW200129_065458, and two events show substantial evidence for higher order multipoles: GW190412 and GW190814; any evidence for precession and higher order multipoles in other gravitational-wave signals is consistent with random fluctuations caused by noise. We then compare our observations with expectations from population models, and confirm that current population estimates from the LVK accurately predict the number of observed events with significant evidence for precession and higher order multipole moments. In particular, we find that this population model predicts that a binary with significant evidence for precession will occur once in every $\sim 50$ detections, and a binary with significant evidence for higher order multipole moments will occur once in every $\sim 70$ observations. However, we emphasise that since substantial evidence for precession and higher order multipole moments have only been observed in three events, any population model that includes a subpopulation of binaries yielding $\sim 2\%$ of events with detectable precession and higher order multipole moments will likely be consistent with the data. |
2002.06954 | Gerry McKeon Dr. | D.G.C. McKeon | Derivation of Gauge Symmetries in Supergravity with a Cosmological
Constant in 2 + 1 Dimensions | null | null | 10.1139/cjp-2019-0464 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The canonical structure of supergravity with a cosmological constant is
analyzed in 2 + 1 dimensions using the Dirac constraint formalism. The first
class constraints are used to find two Bosonic and one Fermionic gauge
symmetries that satisfy a superalgebra. Provided the cosmological constant is
negative, this novel algebra closes, without having to invoke the equations of
motion or introducing auxiliary fields.
| [
{
"created": "Mon, 17 Feb 2020 13:43:03 GMT",
"version": "v1"
}
] | 2020-08-26 | [
[
"McKeon",
"D. G. C.",
""
]
] | The canonical structure of supergravity with a cosmological constant is analyzed in 2 + 1 dimensions using the Dirac constraint formalism. The first class constraints are used to find two Bosonic and one Fermionic gauge symmetries that satisfy a superalgebra. Provided the cosmological constant is negative, this novel algebra closes, without having to invoke the equations of motion or introducing auxiliary fields. |
0908.2077 | Alfonso Zerwekh | Fabrizio Canfora, Alex Giacomini, Alfonso R. Zerwekh | Kaluza-Klein theory in the limit of large number of extra dimensions | LaTeX, 18 pages, 4 figures. Final version accepted for publication in
PRD | Phys.Rev.D80:084039,2009 | 10.1103/PhysRevD.80.084039 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Kaluza-Klein compactification in the limit of large number of extra
dimensions is studied. Starting point is the Einstein-Hilbert action plus
cosmological constant in 4+D dimensions. It is shown that in the large D limit
the effective four dimensional cosmological constant is of order 1/D whereas
the size of the extra dimensions remains finite. A 't Hooft like large D
expansion of the effective Lagrangian for the Kaluza-Klein scalar and gauge
fields arising from the dimensional reduction is considered. It is shown that
the propagator of the scalar field associated to the determinant of the metric
of the extra dimensions is strongly suppressed. This is an interesting result
as in standard Kaluza-Klein theory this scalar degree of freedom is responsible
for the constraint on the gauge fields which makes it impossible to recover the
usual Yang-Mills equations. Moreover in the large D limit it turns out that the
ultraviolet divergences due to the interactions between gauge and scalar fields
are softened.
| [
{
"created": "Fri, 14 Aug 2009 15:23:56 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Oct 2009 12:58:51 GMT",
"version": "v2"
}
] | 2009-11-05 | [
[
"Canfora",
"Fabrizio",
""
],
[
"Giacomini",
"Alex",
""
],
[
"Zerwekh",
"Alfonso R.",
""
]
] | The Kaluza-Klein compactification in the limit of large number of extra dimensions is studied. Starting point is the Einstein-Hilbert action plus cosmological constant in 4+D dimensions. It is shown that in the large D limit the effective four dimensional cosmological constant is of order 1/D whereas the size of the extra dimensions remains finite. A 't Hooft like large D expansion of the effective Lagrangian for the Kaluza-Klein scalar and gauge fields arising from the dimensional reduction is considered. It is shown that the propagator of the scalar field associated to the determinant of the metric of the extra dimensions is strongly suppressed. This is an interesting result as in standard Kaluza-Klein theory this scalar degree of freedom is responsible for the constraint on the gauge fields which makes it impossible to recover the usual Yang-Mills equations. Moreover in the large D limit it turns out that the ultraviolet divergences due to the interactions between gauge and scalar fields are softened. |
1403.0129 | Salvatore Vitale | Salvatore Vitale, Ryan Lynch, John Veitch, Vivien Raymond, Riccardo
Sturani | Measuring the spin of black holes in binary systems using gravitational
waves | 4 figures, Version accepted for publication on PRL | Phys. Rev. Lett. 112, 251101 (2014) | 10.1103/PhysRevLett.112.251101 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Compact binary coalescences are the most promising sources of gravitational
waves (GWs) for ground based detectors. Binary systems containing one or two
spinning black holes are particularly interesting due to spin-orbit (and
eventual spin-spin) interactions, and the opportunity of measuring spins
directly through GW observations. In this letter we analyze simulated signals
emitted by spinning binaries with several values of masses, spins, orientation,
and signal-to-noise ratio. We find that spin magnitudes and tilt angles can be
estimated to accuracy of a few percent for neutron star--black hole systems and
$\sim$ 5-30% for black hole binaries. In contrast, the difference in the
azimuth angles of the spins, which may be used to check if spins are locked
into resonant configurations, cannot be constrained. We observe that the best
performances are obtained when the line of sight is perpendicular to the
system's total angular momentum, and that a sudden change of behavior occurs
when a system is observed from angles such that the plane of the orbit can be
seen both from above and below during the time the signal is in band. This
study suggests that the measurement of black hole spin by means of GWs can be
as precise as what can be obtained from X-ray binaries.
| [
{
"created": "Sat, 1 Mar 2014 22:00:47 GMT",
"version": "v1"
},
{
"created": "Sun, 8 Jun 2014 21:54:41 GMT",
"version": "v2"
}
] | 2014-07-02 | [
[
"Vitale",
"Salvatore",
""
],
[
"Lynch",
"Ryan",
""
],
[
"Veitch",
"John",
""
],
[
"Raymond",
"Vivien",
""
],
[
"Sturani",
"Riccardo",
""
]
] | Compact binary coalescences are the most promising sources of gravitational waves (GWs) for ground based detectors. Binary systems containing one or two spinning black holes are particularly interesting due to spin-orbit (and eventual spin-spin) interactions, and the opportunity of measuring spins directly through GW observations. In this letter we analyze simulated signals emitted by spinning binaries with several values of masses, spins, orientation, and signal-to-noise ratio. We find that spin magnitudes and tilt angles can be estimated to accuracy of a few percent for neutron star--black hole systems and $\sim$ 5-30% for black hole binaries. In contrast, the difference in the azimuth angles of the spins, which may be used to check if spins are locked into resonant configurations, cannot be constrained. We observe that the best performances are obtained when the line of sight is perpendicular to the system's total angular momentum, and that a sudden change of behavior occurs when a system is observed from angles such that the plane of the orbit can be seen both from above and below during the time the signal is in band. This study suggests that the measurement of black hole spin by means of GWs can be as precise as what can be obtained from X-ray binaries. |
1212.5064 | Marc Geiller | Marc Geiller, Karim Noui | A note on the Holst action, the time gauge, and the Barbero-Immirzi
parameter | 22 pages. Published version. Choice of gauge at the begining of
section II.B. clarified. Published in Gen. Rel. Grav. (2013) | Gen. Rel. Grav. 45:1733-1760, 2013 | 10.1007/s10714-013-1552-7 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this note, we review the canonical analysis of the Holst action in the
time gauge, with a special emphasis on the Hamiltonian equations of motion and
the fixation of the Lagrange multipliers. This enables us to identify at the
Hamiltonian level the various components of the covariant torsion tensor, which
have to be vanishing in order for the classical theory not to depend upon the
Barbero-Immirzi parameter. We also introduce a formulation of three-dimensional
gravity with an explicit phase space dependency on the Barbero-Immirzi
parameter as a potential way to investigate its fate and relevance in the
quantum theory.
| [
{
"created": "Thu, 20 Dec 2012 14:47:50 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Jun 2013 01:13:50 GMT",
"version": "v2"
}
] | 2014-03-13 | [
[
"Geiller",
"Marc",
""
],
[
"Noui",
"Karim",
""
]
] | In this note, we review the canonical analysis of the Holst action in the time gauge, with a special emphasis on the Hamiltonian equations of motion and the fixation of the Lagrange multipliers. This enables us to identify at the Hamiltonian level the various components of the covariant torsion tensor, which have to be vanishing in order for the classical theory not to depend upon the Barbero-Immirzi parameter. We also introduce a formulation of three-dimensional gravity with an explicit phase space dependency on the Barbero-Immirzi parameter as a potential way to investigate its fate and relevance in the quantum theory. |
2209.06134 | Serban Cicortas | Serban Cicortas | Extensions of Lorentzian Hawking--Page Solutions with Null
Singularities, Spacelike Singularities, and Cauchy horizons of Taub--NUT type | 52 pages, 14 figures | null | null | null | gr-qc math.AP math.DG | http://creativecommons.org/licenses/by/4.0/ | Starting from the Hawking--Page solutions, we consider the corresponding
Lorentzian cone metrics. These represent cone interior scale-invariant vacuum
solutions, defined in the chronological past of the scaling origin. We extend
the Lorentzian Hawking--Page solutions to the cone exterior region in the class
of $(4+1)$-dimensional scale-invariant vacuum solutions with an $SO(3)\times
U(1)$ isometry, using the Kaluza--Klein reduction and the methods of
Christodoulou. We prove that each Lorentzian Hawking--Page solution has
extensions with a null curvature singularity, extensions with a spacelike
curvature singularity, and extensions with a null Cauchy horizon of Taub--NUT
type. These are all the possible extensions within our symmetry class. The
extensions to spacetimes with a null curvature singularity can be used to
construct $(4+1)$-dimensional asymptotically flat vacuum spacetimes with
locally naked singularities, where the null curvature singularity is not
preceded by trapped surfaces. We prove the instability of such locally naked
singularities using the blue-shift effect of Christodoulou.
| [
{
"created": "Tue, 13 Sep 2022 16:26:34 GMT",
"version": "v1"
}
] | 2022-09-14 | [
[
"Cicortas",
"Serban",
""
]
] | Starting from the Hawking--Page solutions, we consider the corresponding Lorentzian cone metrics. These represent cone interior scale-invariant vacuum solutions, defined in the chronological past of the scaling origin. We extend the Lorentzian Hawking--Page solutions to the cone exterior region in the class of $(4+1)$-dimensional scale-invariant vacuum solutions with an $SO(3)\times U(1)$ isometry, using the Kaluza--Klein reduction and the methods of Christodoulou. We prove that each Lorentzian Hawking--Page solution has extensions with a null curvature singularity, extensions with a spacelike curvature singularity, and extensions with a null Cauchy horizon of Taub--NUT type. These are all the possible extensions within our symmetry class. The extensions to spacetimes with a null curvature singularity can be used to construct $(4+1)$-dimensional asymptotically flat vacuum spacetimes with locally naked singularities, where the null curvature singularity is not preceded by trapped surfaces. We prove the instability of such locally naked singularities using the blue-shift effect of Christodoulou. |
1703.08095 | Emmanuele Battista Dr. | Emmanuele Battista, Angelo Tartaglia, Giampiero Esposito, David
Lucchesi, Matteo Luca Ruggiero, Pavol Valko, Simone Dell' Agnello, Luciano Di
Fiore, Jules Simo, Aniello Grado | Quantum time delay in the gravitational field of a rotating mass | 12 pages, 1 figure | null | 10.1088/1361-6382/aa7f11 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine quantum corrections of time delay arising in the gravitational
field of a spinning oblate source. Low-energy quantum effects occurring in Kerr
geometry are derived within a framework where general relativity is fully seen
as an effective field theory. By employing such a pattern, gravitational
radiative modifications of Kerr metric are derived from the energy-momentum
tensor of the source, which at lowest order in the fields is modelled as a
point mass. Therefore, in order to describe a quantum corrected version of time
delay in the case in which the source body has a finite extension, we introduce
a hybrid scheme where quantum fluctuations affect only the monopole term
occurring in the multipole expansion of the Newtonian potential. The predicted
quantum deviation from the corresponding classical value turns out to be too
small to be detected in the next future, showing that new models should be
examined in order to test low-energy quantum gravity within the solar system.
| [
{
"created": "Thu, 23 Mar 2017 14:58:33 GMT",
"version": "v1"
}
] | 2017-07-27 | [
[
"Battista",
"Emmanuele",
""
],
[
"Tartaglia",
"Angelo",
""
],
[
"Esposito",
"Giampiero",
""
],
[
"Lucchesi",
"David",
""
],
[
"Ruggiero",
"Matteo Luca",
""
],
[
"Valko",
"Pavol",
""
],
[
"Agnello",
"Simone Dell'",
""
],
[
"Di Fiore",
"Luciano",
""
],
[
"Simo",
"Jules",
""
],
[
"Grado",
"Aniello",
""
]
] | We examine quantum corrections of time delay arising in the gravitational field of a spinning oblate source. Low-energy quantum effects occurring in Kerr geometry are derived within a framework where general relativity is fully seen as an effective field theory. By employing such a pattern, gravitational radiative modifications of Kerr metric are derived from the energy-momentum tensor of the source, which at lowest order in the fields is modelled as a point mass. Therefore, in order to describe a quantum corrected version of time delay in the case in which the source body has a finite extension, we introduce a hybrid scheme where quantum fluctuations affect only the monopole term occurring in the multipole expansion of the Newtonian potential. The predicted quantum deviation from the corresponding classical value turns out to be too small to be detected in the next future, showing that new models should be examined in order to test low-energy quantum gravity within the solar system. |
1608.08798 | Eliahu Cohen | Yakir Aharonov, Eliahu Cohen, Tomer Shushi | Is the Quilted Multiverse Consistent with a Thermodynamic Arrow of Time? | Revised version, accepted to Front. Phys | null | 10.3389/fphy.2018.00004 | null | gr-qc astro-ph.CO quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Theoretical achievements, as well as much controversy, surround multiverse
theory. Various types of multiverses, with an increasing amount of complexity,
were suggested and thoroughly discussed in literature by now. While these types
are very different, they all share the same basic idea: our physical reality
consists of more than just one universe. Each universe within a possibly huge
multiverse might be slightly or even very different from the others. The
quilted multiverse is one of these types, whose uniqueness arises from the
postulate that every possible event will occur infinitely many times in
infinitely many universes. In this paper we show that the quilted multiverse is
not self-consistent due to the instability of entropy decrease under small
perturbations. We therefore propose a modified version of the quilted
multiverse which might overcome this shortcoming. It includes only those
universes where the minimal entropy occurs at the same instant of
(cosmological) time. Only these universes whose initial conditions are
fine-tuned within a small phase-space region would evolve consistently to form
their "close" states at present. A final boundary condition on the multiverse
may further lower the amount of possible, consistent universes. Finally, some
related observations regarding the many-worlds interpretation of quantum
mechanics and the emergence of classicality are discussed.
| [
{
"created": "Wed, 31 Aug 2016 10:24:46 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Sep 2016 17:54:33 GMT",
"version": "v2"
},
{
"created": "Wed, 15 Mar 2017 19:26:37 GMT",
"version": "v3"
},
{
"created": "Tue, 27 Jun 2017 08:03:51 GMT",
"version": "v4"
},
{
"created": "Mon, 29 Jan 2018 14:53:36 GMT",
"version": "v5"
}
] | 2018-02-08 | [
[
"Aharonov",
"Yakir",
""
],
[
"Cohen",
"Eliahu",
""
],
[
"Shushi",
"Tomer",
""
]
] | Theoretical achievements, as well as much controversy, surround multiverse theory. Various types of multiverses, with an increasing amount of complexity, were suggested and thoroughly discussed in literature by now. While these types are very different, they all share the same basic idea: our physical reality consists of more than just one universe. Each universe within a possibly huge multiverse might be slightly or even very different from the others. The quilted multiverse is one of these types, whose uniqueness arises from the postulate that every possible event will occur infinitely many times in infinitely many universes. In this paper we show that the quilted multiverse is not self-consistent due to the instability of entropy decrease under small perturbations. We therefore propose a modified version of the quilted multiverse which might overcome this shortcoming. It includes only those universes where the minimal entropy occurs at the same instant of (cosmological) time. Only these universes whose initial conditions are fine-tuned within a small phase-space region would evolve consistently to form their "close" states at present. A final boundary condition on the multiverse may further lower the amount of possible, consistent universes. Finally, some related observations regarding the many-worlds interpretation of quantum mechanics and the emergence of classicality are discussed. |
1911.02221 | Puskar Mondal | Puskar Mondal | Attractors of the `n+1' dimensional Einstein-$\Lambda$ flow | null | null | 10.1088/1361-6382/abb9eb | null | gr-qc math-ph math.AP math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Here we prove a global existence theorem for sufficiently small however fully
nonlinear perturbations of a family of background solutions of the $`n+1$'
vacuum Einstein equations in the presence of a positive cosmological constant
$\Lambda$. With the advent of dark energy driven accelerated expansion of the
universe, it is of fundamental importance in mathematical cosmology to include
a positive cosmological constant, the simplest form of the dark energy in the
vacuum Einstein equations. Such Einsteinian evolution is here designated as the
`Einstein-$\Lambda$' flow. We study the background solutions of this
`Einstein-$\Lambda$' flow in $`n+1$' dimensional spacetimes in constant mean
curvature spatial harmonic gauge, $n\geq3$ and establish both linear and
non-linear stability of such solutions. In the cases of number of spatial
dimensions being strictly greater than $3$, the finite dimensional Einstein
muduli spaces form the center manifold of the dynamics. A suitable shadow gauge
condition \cite{andersson2011einstein} is implemented in order to treat these
cases. In addition, the autonomous character of the suitably re-scaled Einstein
flow breaks down as a consequence of including $\Lambda(>0)$. We construct a
Lyapunov function (controlling a suitable norm of the small data) similar to a
wave equation type energy for the non-linear non-autonomous evolution of the
small data and prove its decay in the direction of cosmological expansion. Our
results demonstrate the future stability and geodesic completeness of the
perturbed spacetimes, and show that the scale-free geometry converges to an
element of the Einstein moduli space (a point for $n=3$ and a finite
dimensional space for $n>3$), which has significant consequence for the cosmic
topology while restricting to the case of $n=3$.
| [
{
"created": "Wed, 6 Nov 2019 06:45:30 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Nov 2019 08:18:27 GMT",
"version": "v2"
},
{
"created": "Mon, 25 Nov 2019 05:40:10 GMT",
"version": "v3"
},
{
"created": "Thu, 27 Feb 2020 20:53:36 GMT",
"version": "v4"
},
{
"created": "Sun, 29 Mar 2020 18:24:02 GMT",
"version": "v5"
},
{
"created": "Fri, 15 May 2020 21:29:25 GMT",
"version": "v6"
},
{
"created": "Mon, 10 Aug 2020 22:06:47 GMT",
"version": "v7"
},
{
"created": "Sat, 29 Aug 2020 06:11:36 GMT",
"version": "v8"
}
] | 2020-12-02 | [
[
"Mondal",
"Puskar",
""
]
] | Here we prove a global existence theorem for sufficiently small however fully nonlinear perturbations of a family of background solutions of the $`n+1$' vacuum Einstein equations in the presence of a positive cosmological constant $\Lambda$. With the advent of dark energy driven accelerated expansion of the universe, it is of fundamental importance in mathematical cosmology to include a positive cosmological constant, the simplest form of the dark energy in the vacuum Einstein equations. Such Einsteinian evolution is here designated as the `Einstein-$\Lambda$' flow. We study the background solutions of this `Einstein-$\Lambda$' flow in $`n+1$' dimensional spacetimes in constant mean curvature spatial harmonic gauge, $n\geq3$ and establish both linear and non-linear stability of such solutions. In the cases of number of spatial dimensions being strictly greater than $3$, the finite dimensional Einstein muduli spaces form the center manifold of the dynamics. A suitable shadow gauge condition \cite{andersson2011einstein} is implemented in order to treat these cases. In addition, the autonomous character of the suitably re-scaled Einstein flow breaks down as a consequence of including $\Lambda(>0)$. We construct a Lyapunov function (controlling a suitable norm of the small data) similar to a wave equation type energy for the non-linear non-autonomous evolution of the small data and prove its decay in the direction of cosmological expansion. Our results demonstrate the future stability and geodesic completeness of the perturbed spacetimes, and show that the scale-free geometry converges to an element of the Einstein moduli space (a point for $n=3$ and a finite dimensional space for $n>3$), which has significant consequence for the cosmic topology while restricting to the case of $n=3$. |
gr-qc/0603025 | Iver. H. Brevik | Iver Brevik | Crossing of the w=-1 Barrier in Two-Fluid Viscous Modified Gravity | 16 pages latex, no figures | Gen.Rel.Grav.38:1317-1328,2006 | 10.1007/s10714-006-0309-y | null | gr-qc astro-ph hep-th | null | Singularities in the dark energy late universe are discussed, under the
assumption that the Lagrangian contains the Einstein term R plus a modified
gravity term of the form R^\alpha, where \alpha is a constant. It is found,
similarly as in the case of pure Einstein gravity [I. Brevik and O. Gorbunova,
Gen. Rel. Grav. 37 (2005), 2039], that the fluid can pass from the quintessence
region (w>-1) into the phantom region (w<-1) as a consequence of a bulk
viscosity varying with time. It becomes necessary now, however, to allow for a
two-fluid model, since the viscosities for the two components vary differently
with time. No scalar fields are needed for the description of the passage
through the phantom barrier.
| [
{
"created": "Wed, 8 Mar 2006 11:40:58 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Brevik",
"Iver",
""
]
] | Singularities in the dark energy late universe are discussed, under the assumption that the Lagrangian contains the Einstein term R plus a modified gravity term of the form R^\alpha, where \alpha is a constant. It is found, similarly as in the case of pure Einstein gravity [I. Brevik and O. Gorbunova, Gen. Rel. Grav. 37 (2005), 2039], that the fluid can pass from the quintessence region (w>-1) into the phantom region (w<-1) as a consequence of a bulk viscosity varying with time. It becomes necessary now, however, to allow for a two-fluid model, since the viscosities for the two components vary differently with time. No scalar fields are needed for the description of the passage through the phantom barrier. |
1407.8084 | Stephen Green | Stephen R. Green and Robert M. Wald | How well is our universe described by an FLRW model? | Invited contribution to a Classical and Quantum Gravity focus issue
on "Relativistic Effects in Cosmology", edited by Kazuya Koyama; 18 pages, 2
figures. V2: References added and minor wording changes made | Class. Quantum Grav. 31 (2014) 234003 | 10.1088/0264-9381/31/23/234003 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Extremely well! In the $\Lambda$CDM model, the spacetime metric, $g_{ab}$, of
our universe is approximated by an FLRW metric, $g_{ab}^{(0)}$, to about 1 part
in $10^4$ or better on both large and small scales, except in the immediate
vicinity of very strong field objects, such as black holes. However,
derivatives of $g_{ab}$ are not close to derivatives of $g_{ab}^{(0)}$, so
there can be significant differences in the behavior of geodesics and huge
differences in curvature. Consequently, observable quantities in the actual
universe may differ significantly from the corresponding observables in the
FLRW model. Nevertheless, as we shall review here, we have proven general
results showing that---within the framework of our approach to treating
backreaction---the large matter inhomogeneities that occur on small scales
cannot produce significant effects on large scales, so $g_{ab}^{(0)}$ satisfies
Einstein's equation with the averaged stress-energy tensor of matter as its
source. We discuss the flaws in some other approaches that have suggested that
large backreaction effects may occur. As we also will review here, with a
suitable "dictionary," Newtonian cosmologies provide excellent approximations
to cosmological solutions to Einstein's equation (with dust and a cosmological
constant) on all scales. Our results thereby provide strong justification for
the mathematical consistency and validity of the $\Lambda$CDM model within the
context of general relativistic cosmology.
| [
{
"created": "Wed, 30 Jul 2014 15:22:24 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Oct 2014 21:35:47 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Green",
"Stephen R.",
""
],
[
"Wald",
"Robert M.",
""
]
] | Extremely well! In the $\Lambda$CDM model, the spacetime metric, $g_{ab}$, of our universe is approximated by an FLRW metric, $g_{ab}^{(0)}$, to about 1 part in $10^4$ or better on both large and small scales, except in the immediate vicinity of very strong field objects, such as black holes. However, derivatives of $g_{ab}$ are not close to derivatives of $g_{ab}^{(0)}$, so there can be significant differences in the behavior of geodesics and huge differences in curvature. Consequently, observable quantities in the actual universe may differ significantly from the corresponding observables in the FLRW model. Nevertheless, as we shall review here, we have proven general results showing that---within the framework of our approach to treating backreaction---the large matter inhomogeneities that occur on small scales cannot produce significant effects on large scales, so $g_{ab}^{(0)}$ satisfies Einstein's equation with the averaged stress-energy tensor of matter as its source. We discuss the flaws in some other approaches that have suggested that large backreaction effects may occur. As we also will review here, with a suitable "dictionary," Newtonian cosmologies provide excellent approximations to cosmological solutions to Einstein's equation (with dust and a cosmological constant) on all scales. Our results thereby provide strong justification for the mathematical consistency and validity of the $\Lambda$CDM model within the context of general relativistic cosmology. |
2104.08093 | Valerio Faraoni | Steve Dussault, Valerio Faraoni, and Andrea Giusti | Analogies between logistic equation and relativistic cosmology | 12 pages, no figures. Invited paper to appear in special issue of
Symmetry | null | null | null | gr-qc physics.class-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We develop several formal analogies between the logistic equation and the
spatially homogeneous and isotropic relativistic cosmology described by the
Einstein-Friedmann equations. These analogies produce an effective Lagrangian
and Hamiltonian and new symmetries for the logistic equation.
| [
{
"created": "Fri, 16 Apr 2021 13:04:22 GMT",
"version": "v1"
}
] | 2021-04-19 | [
[
"Dussault",
"Steve",
""
],
[
"Faraoni",
"Valerio",
""
],
[
"Giusti",
"Andrea",
""
]
] | We develop several formal analogies between the logistic equation and the spatially homogeneous and isotropic relativistic cosmology described by the Einstein-Friedmann equations. These analogies produce an effective Lagrangian and Hamiltonian and new symmetries for the logistic equation. |
1207.7097 | David Garrison | David Garrison | Numerical Relativity as a tool for studying the Early Universe | 18 pages, 3 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Numerical simulations are becoming a more effective tool for conducting
detailed investigations into the evolution of our universe. In this article, we
show how the framework of numerical relativity can be used for studying
cosmological models. The author is working to develop a large-scale simulation
of the dynamical processes in the early universe. These take into account
interactions of dark matter, scalar perturbations, gravitational waves,
magnetic fields and a turbulent plasma. The code described in this report is a
GRMHD code based on the Cactus framework and is structured to utilize one of
several different differencing methods chosen at run-time. It is being
developed and tested on the University of Houston's Maxwell cluster.
| [
{
"created": "Mon, 30 Jul 2012 20:52:27 GMT",
"version": "v1"
},
{
"created": "Sat, 15 Dec 2012 19:16:10 GMT",
"version": "v2"
},
{
"created": "Mon, 10 Mar 2014 20:50:59 GMT",
"version": "v3"
},
{
"created": "Wed, 12 Mar 2014 00:28:40 GMT",
"version": "v4"
}
] | 2014-03-13 | [
[
"Garrison",
"David",
""
]
] | Numerical simulations are becoming a more effective tool for conducting detailed investigations into the evolution of our universe. In this article, we show how the framework of numerical relativity can be used for studying cosmological models. The author is working to develop a large-scale simulation of the dynamical processes in the early universe. These take into account interactions of dark matter, scalar perturbations, gravitational waves, magnetic fields and a turbulent plasma. The code described in this report is a GRMHD code based on the Cactus framework and is structured to utilize one of several different differencing methods chosen at run-time. It is being developed and tested on the University of Houston's Maxwell cluster. |
2005.03610 | Neil J. Cornish | Neil J. Cornish and Kevin Shuman | Black Hole Hunting with LISA | 11 pages, 11 figures | Phys. Rev. D 101, 124008 (2020) | 10.1103/PhysRevD.101.124008 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Laser Interferometer Space Antenna (LISA) will be able to detect massive
black hole mergers throughout the visible Universe. These observations will
provide unique information about black hole formation and growth, and the role
black holes play in galaxy evolution. Here we develop several key building
blocks for detecting and characterizing black hole binary mergers with LISA,
including fast heterodyned likelihood evaluations, and efficient stochastic
search techniques.
| [
{
"created": "Thu, 7 May 2020 17:08:47 GMT",
"version": "v1"
}
] | 2020-07-01 | [
[
"Cornish",
"Neil J.",
""
],
[
"Shuman",
"Kevin",
""
]
] | The Laser Interferometer Space Antenna (LISA) will be able to detect massive black hole mergers throughout the visible Universe. These observations will provide unique information about black hole formation and growth, and the role black holes play in galaxy evolution. Here we develop several key building blocks for detecting and characterizing black hole binary mergers with LISA, including fast heterodyned likelihood evaluations, and efficient stochastic search techniques. |
2103.05082 | Atul Kedia | Grant J. Mathews, In-Saeng Suh, N. Q. Lan, Atul Kedia | Conformally flat, quasi-circular numerical simulations of the
gravitational wave chirp from binary neutron star merger GW170817 | 5 pages, 1 figure | J. Phys. Astron., 9, 204 (2021) | null | null | gr-qc astro-ph.HE astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The first detection of gravitational waves from the binary neutron star
merger GW170817 by the LIGO-Virgo Collaboration has provided fundamental new
insights into the astrophysical site for r-process nucleosynthesis and on the
nature of dense neutron-star matter. The detected gravitational wave signal
depends upon the tidal distortion of the neutron stars as they approach merger.
We report on relativistic numerical simulations of the approach to binary
merger in the conformally flat, quasi-circular orbit approximation. We show
that this event serves as a calibration to the quasi-circular approximation and
a confirmation of the validity of the conformally flat approximation to the
three-metric. We then examine how the detected chirp depends upon the adopted
equation of state. This establishes a new efficient means to constrain the
nuclear equation of state in binary neutron star mergers.
| [
{
"created": "Mon, 8 Mar 2021 21:23:14 GMT",
"version": "v1"
}
] | 2021-03-10 | [
[
"Mathews",
"Grant J.",
""
],
[
"Suh",
"In-Saeng",
""
],
[
"Lan",
"N. Q.",
""
],
[
"Kedia",
"Atul",
""
]
] | The first detection of gravitational waves from the binary neutron star merger GW170817 by the LIGO-Virgo Collaboration has provided fundamental new insights into the astrophysical site for r-process nucleosynthesis and on the nature of dense neutron-star matter. The detected gravitational wave signal depends upon the tidal distortion of the neutron stars as they approach merger. We report on relativistic numerical simulations of the approach to binary merger in the conformally flat, quasi-circular orbit approximation. We show that this event serves as a calibration to the quasi-circular approximation and a confirmation of the validity of the conformally flat approximation to the three-metric. We then examine how the detected chirp depends upon the adopted equation of state. This establishes a new efficient means to constrain the nuclear equation of state in binary neutron star mergers. |
1512.07186 | Massimiliano Rinaldi | Massimiliano Rinaldi and Luciano Vanzo | Inflation and reheating in theories with spontaneous scale invariance
symmetry breaking | One appendix added, issues related to scale invariance in the two
frames clarified. References added/updated. Version accepted by PRD | Phys. Rev. D 94, 024009 (2016) | 10.1103/PhysRevD.94.024009 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a scale-invariant model of quadratic gravity with a non-minimally
coupled scalar field. We focus on cosmological solutions and find that scale
invariance is spontaneously broken and a mass scale naturally emerges. Before
the symmetry breaking, the Universe undergoes an inflationary expansion with
nearly the same observational predictions of Starobinsky's model. At the end of
inflation, the Hubble parameter and the scalar field converge to a stable fixed
point through damped oscillations and the usual Einstein-Hilbert action is
recovered. The oscillations around the fixed point can reheat the Universe in
various ways and we study in detail some of these possibilities.
| [
{
"created": "Tue, 22 Dec 2015 18:13:00 GMT",
"version": "v1"
},
{
"created": "Wed, 13 Jan 2016 10:48:32 GMT",
"version": "v2"
},
{
"created": "Thu, 25 Feb 2016 20:36:40 GMT",
"version": "v3"
},
{
"created": "Wed, 22 Jun 2016 06:53:21 GMT",
"version": "v4"
}
] | 2016-07-13 | [
[
"Rinaldi",
"Massimiliano",
""
],
[
"Vanzo",
"Luciano",
""
]
] | We study a scale-invariant model of quadratic gravity with a non-minimally coupled scalar field. We focus on cosmological solutions and find that scale invariance is spontaneously broken and a mass scale naturally emerges. Before the symmetry breaking, the Universe undergoes an inflationary expansion with nearly the same observational predictions of Starobinsky's model. At the end of inflation, the Hubble parameter and the scalar field converge to a stable fixed point through damped oscillations and the usual Einstein-Hilbert action is recovered. The oscillations around the fixed point can reheat the Universe in various ways and we study in detail some of these possibilities. |
1505.01276 | Mustapha Azreg-A\"inou | Mustapha Azreg-A\"inou | Wormhole solutions sourced by fluids, I: Two-fluid charged sources | 12 pages, no figures. Extended version with new title. To appear in
the European Physical Journal C | Eur. Phys. J. C (2016) 76:3 | 10.1140/epjc/s10052-015-3835-5 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We briefly discuss some of the known and new properties of rotating
geometries that are relevant to this work. We generalize the analytical method
of superposition of fields, known for generating nonrotating solutions, and
apply it to construct massless and massive rotating physical wormholes sourced
by a source-free electromagnetic field and an exotic fluid both anisotropic.
Their stress-energy tensors are presented in compact and general forms. For the
massive rotating wormholes there exists a mass-charge constraint yielding
almost no more dragging effects than ordinary stars. There are conical spirals
through the throat along which no local negative energy densities are noticed
for these rotating wormholes. This conclusion extends to nonrotating massive
type I wormholes derived previously by the author that seem to be the first
kind of nonrotating wormholes with this property. Based on the classification
made in J. Cosmol. Astropart. Phys. 07 (2015) 037 [arXiv:1412.8282]: "Type I
wormholes have their radial pressure dying out faster, as one moves away from
the throat, than any other component of the stress-energy and thus violate the
least the local energy conditions. In type II (resp. III) the radial and
transverse pressures are asymptotically proportional and die out faster (resp.
slower) than the energy density".
| [
{
"created": "Wed, 6 May 2015 08:05:30 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Dec 2015 08:42:30 GMT",
"version": "v2"
}
] | 2016-01-07 | [
[
"Azreg-Aïnou",
"Mustapha",
""
]
] | We briefly discuss some of the known and new properties of rotating geometries that are relevant to this work. We generalize the analytical method of superposition of fields, known for generating nonrotating solutions, and apply it to construct massless and massive rotating physical wormholes sourced by a source-free electromagnetic field and an exotic fluid both anisotropic. Their stress-energy tensors are presented in compact and general forms. For the massive rotating wormholes there exists a mass-charge constraint yielding almost no more dragging effects than ordinary stars. There are conical spirals through the throat along which no local negative energy densities are noticed for these rotating wormholes. This conclusion extends to nonrotating massive type I wormholes derived previously by the author that seem to be the first kind of nonrotating wormholes with this property. Based on the classification made in J. Cosmol. Astropart. Phys. 07 (2015) 037 [arXiv:1412.8282]: "Type I wormholes have their radial pressure dying out faster, as one moves away from the throat, than any other component of the stress-energy and thus violate the least the local energy conditions. In type II (resp. III) the radial and transverse pressures are asymptotically proportional and die out faster (resp. slower) than the energy density". |
1304.5795 | Stefano Liberati | Stefano Liberati | Tests of Lorentz invariance: a 2013 update | 62 pages, no figures. Some extra minor typos corrected. Invited
review for CQG | null | 10.1088/0264-9381/30/13/133001 | null | gr-qc astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present an updated review of Lorentz invariance tests in Effective field
theories (EFT) in the matter as well as in the gravity sector. After a general
discussion of the role of Lorentz invariance and a derivation of its
transformations along the so called von Ignatovski theorem, we present the
dynamical frameworks developed within local EFT and the available constraints
on the parameters governing the Lorentz breaking effects. In the end, we
discuss two specific examples, the OPERA "affaire" and the case of
Ho\v{r}ava-Lifshitz gravity. The first case will serve as an example, and a
caveat, of the practical application of the general techniques developed for
constraining Lorentz invariance violation (LIV) to a direct observation
potentially showing these effects. The second case will show how the
application of the same techniques to a specific quantum gravity scenario has
far fetching implications not foreseeable in a purely phenomenological EFT
approach.
| [
{
"created": "Sun, 21 Apr 2013 20:20:09 GMT",
"version": "v1"
},
{
"created": "Thu, 23 May 2013 19:24:26 GMT",
"version": "v2"
},
{
"created": "Thu, 5 Sep 2013 14:30:12 GMT",
"version": "v3"
}
] | 2015-06-15 | [
[
"Liberati",
"Stefano",
""
]
] | We present an updated review of Lorentz invariance tests in Effective field theories (EFT) in the matter as well as in the gravity sector. After a general discussion of the role of Lorentz invariance and a derivation of its transformations along the so called von Ignatovski theorem, we present the dynamical frameworks developed within local EFT and the available constraints on the parameters governing the Lorentz breaking effects. In the end, we discuss two specific examples, the OPERA "affaire" and the case of Ho\v{r}ava-Lifshitz gravity. The first case will serve as an example, and a caveat, of the practical application of the general techniques developed for constraining Lorentz invariance violation (LIV) to a direct observation potentially showing these effects. The second case will show how the application of the same techniques to a specific quantum gravity scenario has far fetching implications not foreseeable in a purely phenomenological EFT approach. |
2407.09576 | Paul Frampton | Paul H. Frampton | Avoidance of Schwinger Mechanism in Electromagnetically Accelerating
Universe | 7 pages LaTeX | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In quantum electrodynamics, Schwinger showed in 1951 that in a uniform
electric field the vacuum may spontaneously produce electron-positron pairs.
For this to occur, the required electric field is exceptionally large, $\sim
10^{18}$ N/C. In the Electromagnetically Accelerating Universe (EAU) model,
such an electric field would be undesirable because it discharges the
Primoridal Extemely Massive Naked Singularities (PEMNSs) whose mutual repulsion
causes the acceleration. This leads to a constraints on the charges and masses
of the PEMNSs which must be satisfied in an EAU model.
| [
{
"created": "Thu, 11 Jul 2024 21:27:14 GMT",
"version": "v1"
}
] | 2024-07-16 | [
[
"Frampton",
"Paul H.",
""
]
] | In quantum electrodynamics, Schwinger showed in 1951 that in a uniform electric field the vacuum may spontaneously produce electron-positron pairs. For this to occur, the required electric field is exceptionally large, $\sim 10^{18}$ N/C. In the Electromagnetically Accelerating Universe (EAU) model, such an electric field would be undesirable because it discharges the Primoridal Extemely Massive Naked Singularities (PEMNSs) whose mutual repulsion causes the acceleration. This leads to a constraints on the charges and masses of the PEMNSs which must be satisfied in an EAU model. |
0708.2720 | Matthew Anderson | Matthew Anderson, Eric W. Hirschmann, Luis Lehner, Steven L. Liebling,
Patrick M. Motl, David Neilsen, Carlos Palenzuela, Joel E. Tohline | Simulating binary neutron stars: dynamics and gravitational waves | 14 pages, 16 figures. Added one figure from previous version;
corrected typos | Phys.Rev.D77:024006,2008 | 10.1103/PhysRevD.77.024006 | null | gr-qc astro-ph | null | We model two mergers of orbiting binary neutron stars, the first forming a
black hole and the second a differentially rotating neutron star. We extract
gravitational waveforms in the wave zone. Comparisons to a post-Newtonian
analysis allow us to compute the orbital kinematics, including trajectories and
orbital eccentricities. We verify our code by evolving single stars and
extracting radial perturbative modes, which compare very well to results from
perturbation theory. The Einstein equations are solved in a first order
reduction of the generalized harmonic formulation, and the fluid equations are
solved using a modified convex essentially non-oscillatory method. All
calculations are done in three spatial dimensions without symmetry assumptions.
We use the \had computational infrastructure for distributed adaptive mesh
refinement.
| [
{
"created": "Mon, 20 Aug 2007 20:11:01 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Jan 2008 18:49:47 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Anderson",
"Matthew",
""
],
[
"Hirschmann",
"Eric W.",
""
],
[
"Lehner",
"Luis",
""
],
[
"Liebling",
"Steven L.",
""
],
[
"Motl",
"Patrick M.",
""
],
[
"Neilsen",
"David",
""
],
[
"Palenzuela",
"Carlos",
""
],
[
"Tohline",
"Joel E.",
""
]
] | We model two mergers of orbiting binary neutron stars, the first forming a black hole and the second a differentially rotating neutron star. We extract gravitational waveforms in the wave zone. Comparisons to a post-Newtonian analysis allow us to compute the orbital kinematics, including trajectories and orbital eccentricities. We verify our code by evolving single stars and extracting radial perturbative modes, which compare very well to results from perturbation theory. The Einstein equations are solved in a first order reduction of the generalized harmonic formulation, and the fluid equations are solved using a modified convex essentially non-oscillatory method. All calculations are done in three spatial dimensions without symmetry assumptions. We use the \had computational infrastructure for distributed adaptive mesh refinement. |
0912.3632 | Muhammad Sharif | M. Sharif and M. Farasat Shamir | Energy Distribution in f(R) Gravity | 15 pages, accepted for publication in Gen. Relativ. & Grav | Gen.Rel.Grav.42:1557-1569,2010 | 10.1007/s10714-009-0927-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The well-known energy problem is discussed in f(R) theory of gravity. We use
the generalized Landau-Lifshitz energy-momentum complex in the framework of
metric f(R) gravity to evaluate the energy density of plane symmetric solutions
for some general f(R) models. In particular, this quantity is found for some
popular choices of f(R) models. The constant scalar curvature condition and the
stability condition for these models are also discussed. Further, we
investigate the energy distribution of cosmic string spacetime.
| [
{
"created": "Fri, 18 Dec 2009 10:31:24 GMT",
"version": "v1"
}
] | 2014-11-20 | [
[
"Sharif",
"M.",
""
],
[
"Shamir",
"M. Farasat",
""
]
] | The well-known energy problem is discussed in f(R) theory of gravity. We use the generalized Landau-Lifshitz energy-momentum complex in the framework of metric f(R) gravity to evaluate the energy density of plane symmetric solutions for some general f(R) models. In particular, this quantity is found for some popular choices of f(R) models. The constant scalar curvature condition and the stability condition for these models are also discussed. Further, we investigate the energy distribution of cosmic string spacetime. |
gr-qc/9212005 | null | Harald H. Soleng | Dark Matter and Non-Newtonian Gravity From General Relativity on a
Stringy Background | 10 pages, LATEX | null | null | UPR-0547-T | gr-qc | null | An exact solution of Einstein's field equations for a static spherically
symmetric medium with a radially boost invariant energy-momentum tensor is
presented. In the limit of an equation of state corresponding to a distribution
of radially directed strings there is a $1/r$ correction to Newton's force law.
At large distances and small accelerations this law coincides with the
phenomenological force law invented by Milgrom in order to explain the flat
rotation curves of galaxies without introducing dark matter. The present model
explaines why the critical acceleration of Milgrom is of the same order of
magnitude as the Hubble parameter.
| [
{
"created": "Wed, 9 Dec 1992 15:41:16 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Soleng",
"Harald H.",
""
]
] | An exact solution of Einstein's field equations for a static spherically symmetric medium with a radially boost invariant energy-momentum tensor is presented. In the limit of an equation of state corresponding to a distribution of radially directed strings there is a $1/r$ correction to Newton's force law. At large distances and small accelerations this law coincides with the phenomenological force law invented by Milgrom in order to explain the flat rotation curves of galaxies without introducing dark matter. The present model explaines why the critical acceleration of Milgrom is of the same order of magnitude as the Hubble parameter. |
0812.4928 | Jiri Podolsky | Jiri Podolsky, Martin Zofka | General Kundt spacetimes in higher dimensions | 15 pages | Class.Quant.Grav.26:105008,2009 | 10.1088/0264-9381/26/10/105008 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate a general metric of the Kundt class of spacetimes in higher
dimensions. Geometrically, it admits a non-twisting, non-shearing and
non-expanding geodesic null congruence. We calculate all components of the
curvature and Ricci tensors, without assuming any specific matter content, and
discuss algebraic types and main geometric constraints imposed by general
Einstein's field equations. We explicitly derive Einstein-Maxwell equations,
including an arbitrary cosmological constant, in the case of vacuum or possibly
an aligned electromagnetic field. Finally, we introduce canonical subclasses of
the Kundt family and we identify the most important special cases, namely
generalised pp-waves, VSI or CSI spacetimes, and gyratons.
| [
{
"created": "Mon, 29 Dec 2008 15:48:14 GMT",
"version": "v1"
}
] | 2009-04-22 | [
[
"Podolsky",
"Jiri",
""
],
[
"Zofka",
"Martin",
""
]
] | We investigate a general metric of the Kundt class of spacetimes in higher dimensions. Geometrically, it admits a non-twisting, non-shearing and non-expanding geodesic null congruence. We calculate all components of the curvature and Ricci tensors, without assuming any specific matter content, and discuss algebraic types and main geometric constraints imposed by general Einstein's field equations. We explicitly derive Einstein-Maxwell equations, including an arbitrary cosmological constant, in the case of vacuum or possibly an aligned electromagnetic field. Finally, we introduce canonical subclasses of the Kundt family and we identify the most important special cases, namely generalised pp-waves, VSI or CSI spacetimes, and gyratons. |
gr-qc/0607025 | Jose M. Martin-Garcia | David Brizuela, Jose M. Martin-Garcia and Guillermo A. Mena Marugan | Second and higher-order perturbations of a spherical spacetime | Accepted for publication in Physical Review D | Phys.Rev. D74 (2006) 044039 | 10.1103/PhysRevD.74.044039 | null | gr-qc | null | The Gerlach and Sengupta (GS) formalism of coordinate-invariant, first-order,
spherical and nonspherical perturbations around an arbitrary spherical
spacetime is generalized to higher orders, focusing on second-order
perturbation theory. The GS harmonics are generalized to an arbitrary number of
indices on the unit sphere and a formula is given for their products. The
formalism is optimized for its implementation in a computer algebra system,
something that becomes essential in practice given the size and complexity of
the equations. All evolution equations for the second-order perturbations, as
well as the conservation equations for the energy-momentum tensor at this
perturbation order, are given in covariant form, in Regge-Wheeler gauge.
| [
{
"created": "Thu, 6 Jul 2006 15:51:15 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Brizuela",
"David",
""
],
[
"Martin-Garcia",
"Jose M.",
""
],
[
"Marugan",
"Guillermo A. Mena",
""
]
] | The Gerlach and Sengupta (GS) formalism of coordinate-invariant, first-order, spherical and nonspherical perturbations around an arbitrary spherical spacetime is generalized to higher orders, focusing on second-order perturbation theory. The GS harmonics are generalized to an arbitrary number of indices on the unit sphere and a formula is given for their products. The formalism is optimized for its implementation in a computer algebra system, something that becomes essential in practice given the size and complexity of the equations. All evolution equations for the second-order perturbations, as well as the conservation equations for the energy-momentum tensor at this perturbation order, are given in covariant form, in Regge-Wheeler gauge. |
gr-qc/9804080 | M. Rainer | U. Kasper, V.R. Gavrilov, V.N. Melnikov, and M. Rainer | Toda chains with type A_m Lie algebra for multidimensional m-component
perfect fluid cosmology | LaTeX, 2 ps figures | Gen.Rel.Grav. 31 (1999) 139-155 | 10.1023/A:1018879807859 | P-Math-98/2 | gr-qc | null | We consider a D-dimensional cosmological model describing an evolution of
Ricci-flat factor spaces, M_1,...M_n (n > 2), in the presence of an m-component
perfect fluid source (n > m > 1). We find characteristic vectors, related to
the matter constants in the barotropic equations of state for fluid components
of all factor spaces.
We show that, in the case where we can interpret these vectors as the root
vectors of a Lie algebra of Cartan type A_m=sl(m+1,C), the model reduces to the
classical open m-body Toda chain.
Using an elegant technique by Anderson (J. Math. Phys. 37 (1996) 1349) for
solving this system, we integrate the Einstein equations for the model and
present the metric in a Kasner-like form.
| [
{
"created": "Wed, 29 Apr 1998 11:25:50 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Kasper",
"U.",
""
],
[
"Gavrilov",
"V. R.",
""
],
[
"Melnikov",
"V. N.",
""
],
[
"Rainer",
"M.",
""
]
] | We consider a D-dimensional cosmological model describing an evolution of Ricci-flat factor spaces, M_1,...M_n (n > 2), in the presence of an m-component perfect fluid source (n > m > 1). We find characteristic vectors, related to the matter constants in the barotropic equations of state for fluid components of all factor spaces. We show that, in the case where we can interpret these vectors as the root vectors of a Lie algebra of Cartan type A_m=sl(m+1,C), the model reduces to the classical open m-body Toda chain. Using an elegant technique by Anderson (J. Math. Phys. 37 (1996) 1349) for solving this system, we integrate the Einstein equations for the model and present the metric in a Kasner-like form. |
gr-qc/0102078 | Sung-Won Kim | Sung-Won Kim | Scattering problem of scalar wave in wormhole geometry | 6 pages, Revtex, 4 figures | null | null | null | gr-qc | null | In this paper, we study the scattering problem of the scalar wave in the
traversable Lorentzian wormhole geometry. The potentials and Schr\"odinger-like
equations are found in cases of the static uncharged and the charged wormholes.
The differential scattering cross sections are determined by the phase shift of
the asymptotic wave function in low frequency limit. It is also found that the
cross section for charged wormhole is smaller than that for uncharged case by
the reduction of the throat size due to the charge effect.
| [
{
"created": "Sat, 17 Feb 2001 06:19:51 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Kim",
"Sung-Won",
""
]
] | In this paper, we study the scattering problem of the scalar wave in the traversable Lorentzian wormhole geometry. The potentials and Schr\"odinger-like equations are found in cases of the static uncharged and the charged wormholes. The differential scattering cross sections are determined by the phase shift of the asymptotic wave function in low frequency limit. It is also found that the cross section for charged wormhole is smaller than that for uncharged case by the reduction of the throat size due to the charge effect. |
1708.07427 | Naoki Tsukamoto | Naoki Tsukamoto | Black hole shadow in an asymptotically-flat, stationary, and
axisymmetric spacetime: The Kerr-Newman and rotating regular black holes | 25 pages, 4 figures, minor changes, the title is changed slightly,
accepted for publication in Physical Review D | Phys. Rev. D 97, 064021 (2018) | 10.1103/PhysRevD.97.064021 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The shadow of a black hole can be one of the strong observational evidences
for stationary black holes. If we see shadows at the center of galaxies, we
would say whether the observed compact objects are black holes. In this paper,
we consider a formula for the contour of a shadow in an asymptotically-flat,
stationary, and axisymmetric black hole spacetime. We show that the formula is
useful for obtaining the contour of the shadow of several black holes such as
the Kerr-Newman black hole and rotating regular black holes. Using the formula,
we can obtain new examples of the contour of the shadow of rotating black holes
if assumptions are satisfied.
| [
{
"created": "Thu, 24 Aug 2017 14:02:37 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Feb 2018 02:33:34 GMT",
"version": "v2"
},
{
"created": "Tue, 13 Mar 2018 07:17:59 GMT",
"version": "v3"
}
] | 2018-03-20 | [
[
"Tsukamoto",
"Naoki",
""
]
] | The shadow of a black hole can be one of the strong observational evidences for stationary black holes. If we see shadows at the center of galaxies, we would say whether the observed compact objects are black holes. In this paper, we consider a formula for the contour of a shadow in an asymptotically-flat, stationary, and axisymmetric black hole spacetime. We show that the formula is useful for obtaining the contour of the shadow of several black holes such as the Kerr-Newman black hole and rotating regular black holes. Using the formula, we can obtain new examples of the contour of the shadow of rotating black holes if assumptions are satisfied. |
1702.00987 | Mohammad Akbar | M. M. Akbar | Embedding FLRW Geometries in Pseudo-Euclidean and Anti-de Sitter Spaces | 17 pages. Minor changes, mostly reflecting journal's editorial style;
one missing reference added | Phys. Rev. D 95, 064058 (2017) | 10.1103/PhysRevD.95.064058 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Contrary to the general consensus in the literature that
Friedmann--Lema\^{i}tre--Robertson--Walker (FLRW) geometries are of embedding
class one (i.e.,\ embeddable in one higher dimensional pseudo-Euclidean
spaces), we show that the most general $k=0$ and $k=-1$ FLRW geometries are of
embedding class two, and their corresponding pseudo-Euclidean spaces have
strictly one and two negative eigenvalues, respectively. These are particular
results that follow from the new perspective on FLRW embedding that we develop
in this paper, namely that these embeddings are equivalent to unit-speed
parametrized curves in two or three dimensions. A careful analysis of
appropriate tensor fields then gives identical results and further explains why
the class-two geometries remained hidden. However, the signatures of the
embedding spaces, as well as the explicit embedding formulae, follow only from
the curve picture. This also streamlines the comparatively difficult $k=0$
class and provides new explicit embedding formulae for it and reproduces known
embedding formulae for the $k=1,-1$ classes. Embedding into anti-de Sitter
space in one higher dimension can likewise be done by constructing associated
curves. In particular, we find that all $k=1$ and mildly restricted subclasses
of $k=0, -1$ geometries are embeddable in anti-de Sitter space in one higher
dimension.
| [
{
"created": "Fri, 3 Feb 2017 12:27:24 GMT",
"version": "v1"
},
{
"created": "Sun, 2 Apr 2017 05:09:20 GMT",
"version": "v2"
}
] | 2017-04-05 | [
[
"Akbar",
"M. M.",
""
]
] | Contrary to the general consensus in the literature that Friedmann--Lema\^{i}tre--Robertson--Walker (FLRW) geometries are of embedding class one (i.e.,\ embeddable in one higher dimensional pseudo-Euclidean spaces), we show that the most general $k=0$ and $k=-1$ FLRW geometries are of embedding class two, and their corresponding pseudo-Euclidean spaces have strictly one and two negative eigenvalues, respectively. These are particular results that follow from the new perspective on FLRW embedding that we develop in this paper, namely that these embeddings are equivalent to unit-speed parametrized curves in two or three dimensions. A careful analysis of appropriate tensor fields then gives identical results and further explains why the class-two geometries remained hidden. However, the signatures of the embedding spaces, as well as the explicit embedding formulae, follow only from the curve picture. This also streamlines the comparatively difficult $k=0$ class and provides new explicit embedding formulae for it and reproduces known embedding formulae for the $k=1,-1$ classes. Embedding into anti-de Sitter space in one higher dimension can likewise be done by constructing associated curves. In particular, we find that all $k=1$ and mildly restricted subclasses of $k=0, -1$ geometries are embeddable in anti-de Sitter space in one higher dimension. |
1602.08019 | Julian Barbour | Julian Barbour | Arrows of time in unconfined systems | 8 pages, to be published in proceedings to the Time in Physics
conference (ETH Zurich 7-11 September 2015) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Entropy and the second law of thermodynamcs were discovered through study of
the behaviour of gases in confined spaces. The related techniques developed in
the kinetic theory of gases have failed to resolve the apparent conflict
between the time-reversal symmetry of all known laws of nature and the
existence of arrows of time that at all times and everywhere in the universe
all point in the same direction. I will argue that the failure may due to
unconscious application to the universe of the conceptual framework developed
for confined systems. If, as seems plausible, the universe is an unconfined
system, new concepts are needed.
| [
{
"created": "Thu, 25 Feb 2016 18:08:39 GMT",
"version": "v1"
}
] | 2016-02-26 | [
[
"Barbour",
"Julian",
""
]
] | Entropy and the second law of thermodynamcs were discovered through study of the behaviour of gases in confined spaces. The related techniques developed in the kinetic theory of gases have failed to resolve the apparent conflict between the time-reversal symmetry of all known laws of nature and the existence of arrows of time that at all times and everywhere in the universe all point in the same direction. I will argue that the failure may due to unconscious application to the universe of the conceptual framework developed for confined systems. If, as seems plausible, the universe is an unconfined system, new concepts are needed. |
gr-qc/0307011 | Hrvoje Nikolic | H. Nikolic | Proper co-ordinates of non-inertial observers and rotation | 9 pages, invited contribution to the book "Relativity in Rotating
Frames", editors G. Rizzi and M. L. Ruggiero, Kluwer Academic Publishers (in
preparation). See also http://digilander.libero.it/solciclos/ | null | null | null | gr-qc | null | By proper co-ordinates of non-inertial observers (shortly - proper
non-inertial co-ordinates) we understand the proper co-ordinates of an
arbitrarily moving local observer. After a brief review of the theory of proper
non-inertial co-ordinates, we apply these co-ordinates to discuss the
relativistic effects seen by observers at different positions on a rotating
ring. Although there is no relative motion among observers at different
positions, they belong to different proper non-inertial frames. The
relativistic length seen by an observer depends only on his instantaneous
velocity, not on his acceleration or rotation. For any observer the velocity of
light is isotropic and equal to $c$, provided that it is measured by
propagating a light beam in a small neighbourhood of the observer.
| [
{
"created": "Thu, 3 Jul 2003 08:04:44 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Nikolic",
"H.",
""
]
] | By proper co-ordinates of non-inertial observers (shortly - proper non-inertial co-ordinates) we understand the proper co-ordinates of an arbitrarily moving local observer. After a brief review of the theory of proper non-inertial co-ordinates, we apply these co-ordinates to discuss the relativistic effects seen by observers at different positions on a rotating ring. Although there is no relative motion among observers at different positions, they belong to different proper non-inertial frames. The relativistic length seen by an observer depends only on his instantaneous velocity, not on his acceleration or rotation. For any observer the velocity of light is isotropic and equal to $c$, provided that it is measured by propagating a light beam in a small neighbourhood of the observer. |
1609.02045 | Zhaoyi Xu | Zhaoyi Xu, Jiancheng Wang | Kerr-Newman-AdS Black Hole In Quintessential Dark Energy | 17 pages, 5 figures | Phys. Rev. D 95, 064015 (2017) | 10.1103/PhysRevD.95.064015 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quintessential dark energy with pressure $p$ and density $\rho$ is related by
equation of state $p=\omega\rho$ with the state parameter $-1<\omega<-1/3$. The
cosmological dark energy influence on black hole spacetime are interesting and
important. In this paper, we study the Kerr-Newman-AdS solutions of the
Einstein-Maxwell equation in quintessence field around a black hole by
Newman-Janis algorithm and complex computations. From the horizon structure
equation, we obtain the expression between quintessence parameter $\alpha$ and
cosmological constant $\Lambda$ if the black hole exists two cosmological
horizon $r_{q}$ and $r_{c}$ when $\omega=-2/3$, the result is different from
rotational black hole in quintessence matter situation. Through analysis we
find that the black hole charge cannot change the value of $\alpha$. But the
black hole spin and cosmological constant are opposite. The black hole spin and
cosmological constant make the maximum value of $\alpha$ to become small. The
existence of four horizon leads seven types of extremal black holes to
constraint the parameter $\alpha$. With the state parameter $\omega$ ranging
from $-1$ to $-1/3$, the maximum value of $\alpha$ changes from $\Lambda$ to
$1$. When $\omega\rightarrow -1$, the quintessential dark energy likes
cosmological constant. The singularity of the black holes is the same with that
of Kerr black hole. We also discuss the rotation velocity of the black holes on
the equatorial plane for $\omega=-2/3,-1/2$ and $-1/3$. For small value of
$\alpha$, the rotation velocity on the equatorial plane is asymptotically flat
and it can explain the rotation curves in spiral galaxies.
| [
{
"created": "Tue, 6 Sep 2016 12:49:52 GMT",
"version": "v1"
},
{
"created": "Sun, 18 Sep 2016 14:10:36 GMT",
"version": "v2"
},
{
"created": "Fri, 10 Mar 2017 09:05:41 GMT",
"version": "v3"
}
] | 2017-03-22 | [
[
"Xu",
"Zhaoyi",
""
],
[
"Wang",
"Jiancheng",
""
]
] | Quintessential dark energy with pressure $p$ and density $\rho$ is related by equation of state $p=\omega\rho$ with the state parameter $-1<\omega<-1/3$. The cosmological dark energy influence on black hole spacetime are interesting and important. In this paper, we study the Kerr-Newman-AdS solutions of the Einstein-Maxwell equation in quintessence field around a black hole by Newman-Janis algorithm and complex computations. From the horizon structure equation, we obtain the expression between quintessence parameter $\alpha$ and cosmological constant $\Lambda$ if the black hole exists two cosmological horizon $r_{q}$ and $r_{c}$ when $\omega=-2/3$, the result is different from rotational black hole in quintessence matter situation. Through analysis we find that the black hole charge cannot change the value of $\alpha$. But the black hole spin and cosmological constant are opposite. The black hole spin and cosmological constant make the maximum value of $\alpha$ to become small. The existence of four horizon leads seven types of extremal black holes to constraint the parameter $\alpha$. With the state parameter $\omega$ ranging from $-1$ to $-1/3$, the maximum value of $\alpha$ changes from $\Lambda$ to $1$. When $\omega\rightarrow -1$, the quintessential dark energy likes cosmological constant. The singularity of the black holes is the same with that of Kerr black hole. We also discuss the rotation velocity of the black holes on the equatorial plane for $\omega=-2/3,-1/2$ and $-1/3$. For small value of $\alpha$, the rotation velocity on the equatorial plane is asymptotically flat and it can explain the rotation curves in spiral galaxies. |
0802.0530 | Jose' P. S. Lemos | Jos\'e P. S. Lemos, Vilson T. Zanchin | Bonnor stars in d spacetime dimensions | 48 pages, 5 figues, references added, minor changes | Phys.Rev.D77:064003,2008 | 10.1103/PhysRevD.77.064003 | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bonnor stars are regular static compact configurations in equilibrium,
composed of an extremal dust fluid, a charged dust fluid where the mass density
is equal to the charge density, joined to an exterior vacuum solution, within
Newtonian gravity and general relativity. In four dimensions, they obey the
corresponding Majumdar-Papapetrou system, where the gravitational potential is
a simple function of the electric potential field and the fluid, when there is
one, is made of extremal dust. The Majumdar-Papapetrou system can be
generalized to d spacetime dimensions. Thus, it is natural to study Bonnor
solutions in higher d dimensions. We analyze Newton-Coulomb theory with an
electrically charged fluid in a Majumdar-Papapetrou context, in d=n+1 spacetime
dimensions, n the number of spatial dimensions. Within the Newtonian theory, in
vacuum, the Majumdar-Papapetrou relation for the gravitational potential in
terms of the electric potential, and its related Weyl relation, are equivalent,
in contrast with general relativity. We study a class of spherically symmetric
Bonnor stars. Under sufficient compactification they form point mass charged
Newtonian singularities. We study the analogue systems in the Einstein-Maxwell
theory with an electrically charged fluid. We restate some properties of this
system and obtain spherically symmetric Bonnor star solutions in d=n+1
spacetime dimensions. These stars, under compactification, form quasi-black
holes. Whereas there are no solutions for Newtonian or relativistic stars
supported by degenerate pressure in higher dimensions, higher dimensional
Bonnor stars, supported by electric repulsion, do indeed have solutions within
Newtonian gravity and general relativity. So the existence of stars depends on
the number of dimensions and on the underlying field content.
| [
{
"created": "Mon, 4 Feb 2008 23:02:01 GMT",
"version": "v1"
},
{
"created": "Thu, 5 Jun 2008 17:18:32 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Lemos",
"José P. S.",
""
],
[
"Zanchin",
"Vilson T.",
""
]
] | Bonnor stars are regular static compact configurations in equilibrium, composed of an extremal dust fluid, a charged dust fluid where the mass density is equal to the charge density, joined to an exterior vacuum solution, within Newtonian gravity and general relativity. In four dimensions, they obey the corresponding Majumdar-Papapetrou system, where the gravitational potential is a simple function of the electric potential field and the fluid, when there is one, is made of extremal dust. The Majumdar-Papapetrou system can be generalized to d spacetime dimensions. Thus, it is natural to study Bonnor solutions in higher d dimensions. We analyze Newton-Coulomb theory with an electrically charged fluid in a Majumdar-Papapetrou context, in d=n+1 spacetime dimensions, n the number of spatial dimensions. Within the Newtonian theory, in vacuum, the Majumdar-Papapetrou relation for the gravitational potential in terms of the electric potential, and its related Weyl relation, are equivalent, in contrast with general relativity. We study a class of spherically symmetric Bonnor stars. Under sufficient compactification they form point mass charged Newtonian singularities. We study the analogue systems in the Einstein-Maxwell theory with an electrically charged fluid. We restate some properties of this system and obtain spherically symmetric Bonnor star solutions in d=n+1 spacetime dimensions. These stars, under compactification, form quasi-black holes. Whereas there are no solutions for Newtonian or relativistic stars supported by degenerate pressure in higher dimensions, higher dimensional Bonnor stars, supported by electric repulsion, do indeed have solutions within Newtonian gravity and general relativity. So the existence of stars depends on the number of dimensions and on the underlying field content. |
2005.03736 | Irene Brito | Irene Brito, J. Carot, E.G.L.R. Vaz | Elastic thick shells in General Relativity | 23 pages, 3 figures | Phys. Rev. D 102, 024081 (2020) | 10.1103/PhysRevD.102.024081 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that exact spherically symmetric solutions to Einstein's Field
Equations exist such that, over an open region of the spacetime, they are
singularity free, satisfy the dominant energy condition, represent elastic
matter with a well defined constitutive function, and are such that elastic
perturbations propagate causally.
Two toy-models are then built up in which a thick elastic, spherically
symmetric shell with the above properties, separates two Robertson-Walker
regions corresponding to different values of the curvature $k$. The junction
conditions (continuity of the first and second fundamental forms) are shown to
be exactly satisfied across the corresponding matching spherical surfaces.
| [
{
"created": "Thu, 7 May 2020 20:27:14 GMT",
"version": "v1"
}
] | 2020-08-05 | [
[
"Brito",
"Irene",
""
],
[
"Carot",
"J.",
""
],
[
"Vaz",
"E. G. L. R.",
""
]
] | It is shown that exact spherically symmetric solutions to Einstein's Field Equations exist such that, over an open region of the spacetime, they are singularity free, satisfy the dominant energy condition, represent elastic matter with a well defined constitutive function, and are such that elastic perturbations propagate causally. Two toy-models are then built up in which a thick elastic, spherically symmetric shell with the above properties, separates two Robertson-Walker regions corresponding to different values of the curvature $k$. The junction conditions (continuity of the first and second fundamental forms) are shown to be exactly satisfied across the corresponding matching spherical surfaces. |
gr-qc/0104085 | Xavier Siemens | Xavier Siemens and Ken D. Olum | Gravitational Radiation and the Small-Scale Structure of Cosmic Strings | Replaced with revised version accepted for publication by Nuclear
Physics B | Nucl.Phys.B611:125-145,2001; Erratum-ibid.B645:367,2002 | 10.1016/S0550-3213(01)00353-4 | null | gr-qc astro-ph hep-ph | null | We calculate the gravitational radiation emitted by an infinite cosmic string
with two oppositely moving wave-trains, in the small amplitude approximation.
After comparing our result to the previously studied cases we extend the
results to a new regime where the wavelengths of the opposing wave-trains are
very different. We show that in this case the amount of power radiated vanishes
exponentially. This means that small excitations moving in only one direction
may be very long lived, and so the size of the smallest scales in a string
network might be much smaller than what one would expect from gravitational
back reaction. This result allows for a potential host of interesting
cosmological possibilities involving ultra-high energy cosmic rays, gamma ray
bursts and gravitational wave bursts.
| [
{
"created": "Wed, 25 Apr 2001 19:09:01 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Aug 2001 15:30:41 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Siemens",
"Xavier",
""
],
[
"Olum",
"Ken D.",
""
]
] | We calculate the gravitational radiation emitted by an infinite cosmic string with two oppositely moving wave-trains, in the small amplitude approximation. After comparing our result to the previously studied cases we extend the results to a new regime where the wavelengths of the opposing wave-trains are very different. We show that in this case the amount of power radiated vanishes exponentially. This means that small excitations moving in only one direction may be very long lived, and so the size of the smallest scales in a string network might be much smaller than what one would expect from gravitational back reaction. This result allows for a potential host of interesting cosmological possibilities involving ultra-high energy cosmic rays, gamma ray bursts and gravitational wave bursts. |
0803.2913 | Yun Soo Myung | Yun Soo Myung, Min-Gyun Seo | Origin of holographic dark energy models | 14 pages, version to appear in PLB | Phys.Lett.B671:435-439,2009 | 10.1016/j.physletb.2009.01.001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the origin of holographic dark energy models which were
recently proposed to explain the dark energy-dominated universe. For this
purpose, we introduce the spacetime foam uncertainty of $\delta l \ge l_{\rm
p}^{\alpha}l^{\alpha-1}$. It was argued that the case of $\alpha=2/3$ could
describe the dark energy with infinite statistics, while the case of
$\alpha=1/2$ can describe the ordinary matter with Bose-Fermi statistics.
However, two cases may lead to the holographic energy density if the latter
recovers from the geometric mean of UV and IR scales. Hence the dark energy
with infinite statistics based on the entropy bound is not an ingredient for
deriving the holographic dark energy model. Furthermore, it is shown that the
agegraphic dark energy models are the holographic dark energy model with
different IR length scales.
| [
{
"created": "Thu, 20 Mar 2008 00:14:20 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Jan 2009 22:59:54 GMT",
"version": "v2"
}
] | 2009-02-02 | [
[
"Myung",
"Yun Soo",
""
],
[
"Seo",
"Min-Gyun",
""
]
] | We investigate the origin of holographic dark energy models which were recently proposed to explain the dark energy-dominated universe. For this purpose, we introduce the spacetime foam uncertainty of $\delta l \ge l_{\rm p}^{\alpha}l^{\alpha-1}$. It was argued that the case of $\alpha=2/3$ could describe the dark energy with infinite statistics, while the case of $\alpha=1/2$ can describe the ordinary matter with Bose-Fermi statistics. However, two cases may lead to the holographic energy density if the latter recovers from the geometric mean of UV and IR scales. Hence the dark energy with infinite statistics based on the entropy bound is not an ingredient for deriving the holographic dark energy model. Furthermore, it is shown that the agegraphic dark energy models are the holographic dark energy model with different IR length scales. |
gr-qc/9907076 | Unanyan | A. M. Gevorkian, R. A. Gevorkian | Inertia in the Structure of Space-Time | 8 pages | null | null | null | gr-qc | null | In Einstein's equation we suggest a geometrical object substituting the
tensor of energy of impulse and tension. The obtained equation, together with
the equation for external field, makes up the complete problem of mathematical
equations of gravitation, as well as those of inertia. Based on the example of
centrally symmetrical field those problems and their consequences are
discussed.
| [
{
"created": "Fri, 23 Jul 1999 19:29:05 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Gevorkian",
"A. M.",
""
],
[
"Gevorkian",
"R. A.",
""
]
] | In Einstein's equation we suggest a geometrical object substituting the tensor of energy of impulse and tension. The obtained equation, together with the equation for external field, makes up the complete problem of mathematical equations of gravitation, as well as those of inertia. Based on the example of centrally symmetrical field those problems and their consequences are discussed. |
2104.09504 | Ui Ri Mun | Ui Ri Mun | Constant-roll warm inflation and the $\beta$-function approach | 10 pages, 5 figures | null | 10.1103/PhysRevD.103.083527 | null | gr-qc astro-ph.CO hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | We propose a new approach to constant-roll warm inflation as a generalization
of constant-roll inflation. Based on the $\beta$-function formalism, it is
shown that constant-roll warm inflation models with a natural end fall into
universality classes defined by three different types of $\beta$-functions,
under the assumption that radiation energy density is quasi-stable. Given that
warm inflation is completely specified by the $\beta$-function and dissipation
coefficient ratio, we investigate whether or not the inflation can physically
be realized for enough number of e-foldings at the background level for some
combinations of the $\beta$-functions and non-trivial dissipation coefficient
ratios.
| [
{
"created": "Mon, 19 Apr 2021 02:38:13 GMT",
"version": "v1"
}
] | 2021-05-12 | [
[
"Mun",
"Ui Ri",
""
]
] | We propose a new approach to constant-roll warm inflation as a generalization of constant-roll inflation. Based on the $\beta$-function formalism, it is shown that constant-roll warm inflation models with a natural end fall into universality classes defined by three different types of $\beta$-functions, under the assumption that radiation energy density is quasi-stable. Given that warm inflation is completely specified by the $\beta$-function and dissipation coefficient ratio, we investigate whether or not the inflation can physically be realized for enough number of e-foldings at the background level for some combinations of the $\beta$-functions and non-trivial dissipation coefficient ratios. |
1508.06022 | Hamid Reza Sepangi | M. Honardoost, H. Mohseni Sadjadi and H. R. Sepangi | Thawing in a coupled quintessence model | 11 pages, 2 figures | Gen. Rel. Grav. 48 (2016) no.10, 125 | 10.1007/s10714-016-2125-3 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the thawing model in the framework of coupled quintessence model.
The effective potential has $Z_2$ symmetry which is broken spontaneously when
the dark matter density becomes less than a critical value leading the
quintessence equation of state parameter to deviate from -1. Conditions
required for this procedure are obtained and analytical solution for the
equation of state parameter is derived.
| [
{
"created": "Tue, 25 Aug 2015 03:49:26 GMT",
"version": "v1"
},
{
"created": "Sat, 3 Sep 2016 02:46:12 GMT",
"version": "v2"
}
] | 2016-09-21 | [
[
"Honardoost",
"M.",
""
],
[
"Sadjadi",
"H. Mohseni",
""
],
[
"Sepangi",
"H. R.",
""
]
] | We consider the thawing model in the framework of coupled quintessence model. The effective potential has $Z_2$ symmetry which is broken spontaneously when the dark matter density becomes less than a critical value leading the quintessence equation of state parameter to deviate from -1. Conditions required for this procedure are obtained and analytical solution for the equation of state parameter is derived. |
2102.06051 | Peter M\'esz\'aros | Peter M\'esz\'aros | Solid matter with zero shear modulus in flat universe | 20 pages | Class. Quantum Grav. 38 (2021) 165008 | 10.1088/1361-6382/ac11aa | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | For a perfect fluid, the quantity defined through mixed components of the
stress-energy tensor
$\widetilde{w}=(T_{i}^{\phantom{i}i}/3)/(-T_{0}^{\phantom{0}0})$ is independent
on the choice of coordinates only for two values of the pressure to energy
density ratio $w=p/\rho$: for radiation with $w=1/3$, and for dark energy with
$w=-1$. With other choices of $w$, the quantity $\widetilde{w}$ is coordinate
dependent, and $\widetilde{w}=w$ only in the local rest frame of the fluid. We
show that the same is true also for solid matter with shear stress Lam\'e
coefficient set to zero in a flat Friedmann--Lema\^itre--Robertson--Walker
universe with perturbed metric as well as stress-energy tensor. We call the two
different solids with coordinate independent $\widetilde{w}$ radiation-like
solid and dark energy-like solid, and we restrict ourselves to these two
special cases. By analysing second order perturbations we discover two one
parametric sets of such solid matter models containing special cases of
radiation and dark energy as perfect fluids. We also study equations for
perturbations up to the second order for both sets of models.
| [
{
"created": "Thu, 11 Feb 2021 14:55:50 GMT",
"version": "v1"
},
{
"created": "Mon, 29 Mar 2021 13:22:34 GMT",
"version": "v2"
},
{
"created": "Thu, 22 Jul 2021 10:42:33 GMT",
"version": "v3"
}
] | 2021-07-23 | [
[
"Mészáros",
"Peter",
""
]
] | For a perfect fluid, the quantity defined through mixed components of the stress-energy tensor $\widetilde{w}=(T_{i}^{\phantom{i}i}/3)/(-T_{0}^{\phantom{0}0})$ is independent on the choice of coordinates only for two values of the pressure to energy density ratio $w=p/\rho$: for radiation with $w=1/3$, and for dark energy with $w=-1$. With other choices of $w$, the quantity $\widetilde{w}$ is coordinate dependent, and $\widetilde{w}=w$ only in the local rest frame of the fluid. We show that the same is true also for solid matter with shear stress Lam\'e coefficient set to zero in a flat Friedmann--Lema\^itre--Robertson--Walker universe with perturbed metric as well as stress-energy tensor. We call the two different solids with coordinate independent $\widetilde{w}$ radiation-like solid and dark energy-like solid, and we restrict ourselves to these two special cases. By analysing second order perturbations we discover two one parametric sets of such solid matter models containing special cases of radiation and dark energy as perfect fluids. We also study equations for perturbations up to the second order for both sets of models. |
1503.07750 | Saugata Mitra | Saugata Mitra, Subhajit Saha, and Subenoy Chakraborty | A Study of Universal Thermodynamics in Brane World Scenario | null | Advances in High Energy Physics 2015, 430764 (2015) | 10.1155/2015/430764 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A study of Universal thermodynamics is done in the frame work of RSII brane
model and DGP brane scenario. The Universe is chosen as FRW model bounded by
apparent or event horizon. Assuming extended Hawking temperature on the
horizon, the unified first law is examined for perfect fluid (with constant
equation of state) and modified Chaplygin gas model. As a result there is a
modification of Bekenstein entropy on the horizons. Further the validity of the
generalized second law of thermodynamics and thermodynamical equilibrium are
also investigated.
| [
{
"created": "Wed, 25 Mar 2015 04:51:13 GMT",
"version": "v1"
}
] | 2016-05-17 | [
[
"Mitra",
"Saugata",
""
],
[
"Saha",
"Subhajit",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | A study of Universal thermodynamics is done in the frame work of RSII brane model and DGP brane scenario. The Universe is chosen as FRW model bounded by apparent or event horizon. Assuming extended Hawking temperature on the horizon, the unified first law is examined for perfect fluid (with constant equation of state) and modified Chaplygin gas model. As a result there is a modification of Bekenstein entropy on the horizons. Further the validity of the generalized second law of thermodynamics and thermodynamical equilibrium are also investigated. |
2302.09085 | Oscar J. C. Dias | Oscar J.C. Dias, Takaaki Ishii, Keiju Murata, Jorge E. Santos and
Benson Way | Superradiance and black resonator strings encounter helical black
strings | 57 pages, 9 figures. v2: Matches published version (minor
improvements) | null | 10.1007/JHEP05(2023)041 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We construct a cohomogeneity-1 helical black string in six-dimensional
Einstein gravity. The helical solution branches from the onset of the
gravitational superradiant instability of the equal-spinning Myers-Perry black
string. The isometry group of the helical black string is $\mathbb{R}_T \times
U(1)_Z \times SU(2)$, where the first two are helical isometries generated by
linear combinations of time translation, shifts along the string, and rotation,
each of which is individually broken by the superradiant instability. The
helical black string is stationary, non-axisymmetric, and has nonzero horizon
velocity despite the absence of momentum in the string direction. The entropy
of the helical black string is higher than that of the Myers-Perry black
string, but lower than cohomogeneity-2 ``black resonator strings'' (recently
found) when the solutions overlap in the microcanonical ensemble. The entropy
of the helical black string approaches zero when the horizon velocity along the
string reaches its maximum given by the speed of light. Nevertheless, we find
no evidence for the existence of regular horizonless solutions in this limit.
| [
{
"created": "Fri, 17 Feb 2023 19:00:01 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Aug 2023 18:31:15 GMT",
"version": "v2"
}
] | 2023-08-07 | [
[
"Dias",
"Oscar J. C.",
""
],
[
"Ishii",
"Takaaki",
""
],
[
"Murata",
"Keiju",
""
],
[
"Santos",
"Jorge E.",
""
],
[
"Way",
"Benson",
""
]
] | We construct a cohomogeneity-1 helical black string in six-dimensional Einstein gravity. The helical solution branches from the onset of the gravitational superradiant instability of the equal-spinning Myers-Perry black string. The isometry group of the helical black string is $\mathbb{R}_T \times U(1)_Z \times SU(2)$, where the first two are helical isometries generated by linear combinations of time translation, shifts along the string, and rotation, each of which is individually broken by the superradiant instability. The helical black string is stationary, non-axisymmetric, and has nonzero horizon velocity despite the absence of momentum in the string direction. The entropy of the helical black string is higher than that of the Myers-Perry black string, but lower than cohomogeneity-2 ``black resonator strings'' (recently found) when the solutions overlap in the microcanonical ensemble. The entropy of the helical black string approaches zero when the horizon velocity along the string reaches its maximum given by the speed of light. Nevertheless, we find no evidence for the existence of regular horizonless solutions in this limit. |
2001.07920 | Kazem Rezazadeh | K. Rezazadeh, S. Asadzadeh, K. Fahimi, K. Karami, A. Mehrabi | The growth of DM and DE perturbations in DBI non-canonical scalar field
scenario | 33 pages, 13 figures | Annals of Physics 422 (2020) 168299 | 10.1016/j.aop.2020.168299 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the effect of varying sound speed on clustering dark energy in the
Dirac-Born-Infeld (DBI) scenario. The DBI action is included in the class of
$k$-essence models, and it has an important role in describing the effective
degrees of freedom of D-branes in the string theory. In the DBI setup, we take
the anti-de Sitter (AdS) warp factor $f(\phi)=f_0\, \phi^{-4}$, and investigate
the self-interacting quartic potential $V(\phi)=\lambda\phi^{4}/4$. We
calculate the full expression of the effective sound speed for our model, and
show that it can evolve with time during the cosmological evolution. Besides,
the adiabatic sound speed evolves with time here, and this influences the
background dynamics to some extent. We show that the effective sound speed is
very close to the adiabatic sound speed. We examine the effect of the variable
sound speed on growth of the perturbations in both the linear and non-linear
regimes. In the linear regime, we apply the Pseudo-Newtonian formalism, and
show that dark energy suppresses the growth of perturbations at low redshifts.
From study the Integrated Sachs-Wolf (ISW) effect in our setup, we see that the
model manifests some deviation from the concordance $\Lambda$CDM model. In the
non-linear regime, we follow the approach of spherical collapse model, and
calculate the linear overdensity, the virial overdensity, overdensity at the
turn around and the rate of expansion of collapsed region. We further compute
relative number density of halo objects above a given mass in our setting, and
show that the number of structures with respect to the $\Lambda$CDM model is
reduced more in the high mass tail at high redshifts.
| [
{
"created": "Wed, 22 Jan 2020 09:08:06 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Sep 2020 16:36:50 GMT",
"version": "v2"
}
] | 2020-09-08 | [
[
"Rezazadeh",
"K.",
""
],
[
"Asadzadeh",
"S.",
""
],
[
"Fahimi",
"K.",
""
],
[
"Karami",
"K.",
""
],
[
"Mehrabi",
"A.",
""
]
] | We study the effect of varying sound speed on clustering dark energy in the Dirac-Born-Infeld (DBI) scenario. The DBI action is included in the class of $k$-essence models, and it has an important role in describing the effective degrees of freedom of D-branes in the string theory. In the DBI setup, we take the anti-de Sitter (AdS) warp factor $f(\phi)=f_0\, \phi^{-4}$, and investigate the self-interacting quartic potential $V(\phi)=\lambda\phi^{4}/4$. We calculate the full expression of the effective sound speed for our model, and show that it can evolve with time during the cosmological evolution. Besides, the adiabatic sound speed evolves with time here, and this influences the background dynamics to some extent. We show that the effective sound speed is very close to the adiabatic sound speed. We examine the effect of the variable sound speed on growth of the perturbations in both the linear and non-linear regimes. In the linear regime, we apply the Pseudo-Newtonian formalism, and show that dark energy suppresses the growth of perturbations at low redshifts. From study the Integrated Sachs-Wolf (ISW) effect in our setup, we see that the model manifests some deviation from the concordance $\Lambda$CDM model. In the non-linear regime, we follow the approach of spherical collapse model, and calculate the linear overdensity, the virial overdensity, overdensity at the turn around and the rate of expansion of collapsed region. We further compute relative number density of halo objects above a given mass in our setting, and show that the number of structures with respect to the $\Lambda$CDM model is reduced more in the high mass tail at high redshifts. |
gr-qc/9904019 | Mamdouh Wanas | M.I.Wanas | Motion of Spinning Particles in Gravitational Fields | 20 pages Tex file, published in Astrophysics and Space Science,
vol.258, 237, (1998) | Astrophys.Space Sci. 258 (1998) 237 | 10.1023/A:1001747710135 | null | gr-qc quant-ph | null | A new path equation in absolute parallelism (AP) geometry is derived. The
equation is a generalization of three path equations derived in a previous
work. It can be considered as a geodesic equation modified by a torsion term,
whose numerical coefficient jumps by steps of one half. The torsion term is
parametrized using the fine structure constant. It is suggested that the new
equation may describe the trajectories of spinning particles under the
influence of a gravitational field, and the torsion term represents a type of
interaction between the quantum spin of the moving particle and the background
field.
Weak field limits of the new path equation show that the gravitational
potential felt by a spinning particle is different from that felt by a spinless
particle (or a macroscopic body).
As a byproduct, and in order to derive the new path equation, the AP-space is
reconstructed using a new affine connexion preserving metricity. The new
AP-structure has non-vanishing curvature. In certain limits, the new
AP-structure can be reduced either to the ordinary Riemannian space, or to the
conventional AP-space.
| [
{
"created": "Wed, 7 Apr 1999 12:16:25 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Wanas",
"M. I.",
""
]
] | A new path equation in absolute parallelism (AP) geometry is derived. The equation is a generalization of three path equations derived in a previous work. It can be considered as a geodesic equation modified by a torsion term, whose numerical coefficient jumps by steps of one half. The torsion term is parametrized using the fine structure constant. It is suggested that the new equation may describe the trajectories of spinning particles under the influence of a gravitational field, and the torsion term represents a type of interaction between the quantum spin of the moving particle and the background field. Weak field limits of the new path equation show that the gravitational potential felt by a spinning particle is different from that felt by a spinless particle (or a macroscopic body). As a byproduct, and in order to derive the new path equation, the AP-space is reconstructed using a new affine connexion preserving metricity. The new AP-structure has non-vanishing curvature. In certain limits, the new AP-structure can be reduced either to the ordinary Riemannian space, or to the conventional AP-space. |
2404.07757 | Leandro Gomes G | Leandro G. Gomes | Spacetimes with homogeneous and isotropic expansion | null | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this short note, we define and characterize all the spacetimes admitting
observers to whom the cosmic expansion is homogeneous and isotropic and
interpret their Einstein's equations.
| [
{
"created": "Thu, 11 Apr 2024 14:02:23 GMT",
"version": "v1"
}
] | 2024-04-12 | [
[
"Gomes",
"Leandro G.",
""
]
] | In this short note, we define and characterize all the spacetimes admitting observers to whom the cosmic expansion is homogeneous and isotropic and interpret their Einstein's equations. |
gr-qc/9606092 | Thomas Thiemann | T. Thiemann | A length operator for canonical quantum gravity | 23 pages, Latex | J.Math.Phys. 39 (1998) 3372-3392 | 10.1063/1.532445 | HUTMP-96/B-354 | gr-qc | null | We construct an operator that measures the length of a curve in
four-dimensional Lorentzian vacuum quantum gravity. We work in a representation
in which a $SU(2)$ connection is diagonal and it is therefore surprising that
the operator obtained after regularization is densely defined, does not suffer
from factor ordering singularities and does not require any renormalization. We
show that the length operator admits self-adjoint extensions and compute part
of its spectrum which like its companions, the volume and area operators
already constructed in the literature, is purely discrete and roughly is
quantized in units of the Planck length. The length operator contains full and
direct information about all the components of the metric tensor which
faciliates the construction of a new type of weave states which approximate a
given classical 3-geometry.
| [
{
"created": "Sat, 29 Jun 1996 23:40:26 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Thiemann",
"T.",
""
]
] | We construct an operator that measures the length of a curve in four-dimensional Lorentzian vacuum quantum gravity. We work in a representation in which a $SU(2)$ connection is diagonal and it is therefore surprising that the operator obtained after regularization is densely defined, does not suffer from factor ordering singularities and does not require any renormalization. We show that the length operator admits self-adjoint extensions and compute part of its spectrum which like its companions, the volume and area operators already constructed in the literature, is purely discrete and roughly is quantized in units of the Planck length. The length operator contains full and direct information about all the components of the metric tensor which faciliates the construction of a new type of weave states which approximate a given classical 3-geometry. |
1107.2224 | Sergey Cherkas L | S. L. Cherkas and V. L. Kalashnikov | An inhomogeneous toy-model of the quantum gravity with explicitly
evolvable observables | 18 pages | Gen. Rel. Grav. 44 (2012) 3081 | 10.1007/s10714-012-1441-5 | null | gr-qc hep-ph hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An inhomogeneous (1+1)-dimensional model of the quantum gravity is
considered. It is found, that this model corresponds to a string propagating
against some curved background space. The quantization scheme including the
Wheeler-DeWitt equation and the "particle on a sphere" type of the gauge
condition is suggested. In the quantization scheme considered, the "problem of
time" is solved by building of the quasi-Heisenberg operators acting in a space
of solutions of the Wheeler-DeWitt equation and the normalization of the wave
function corresponds to the Klein-Gordon type. To analyze the physical
consequences of the scheme, a (1+1)-dimensional background space is considered
for which a classical solution is found and quantized. The obtained estimations
show the way to solution of the cosmological constant problem, which consists
in compensation of the zero-point oscillations of the matter fields by the
quantum oscillations of the scale factor. Along with such a compensation, a
slow global evolution of a background corresponding to an universe expansion
exists.
| [
{
"created": "Tue, 12 Jul 2011 09:39:00 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Jan 2012 09:39:16 GMT",
"version": "v2"
}
] | 2015-05-28 | [
[
"Cherkas",
"S. L.",
""
],
[
"Kalashnikov",
"V. L.",
""
]
] | An inhomogeneous (1+1)-dimensional model of the quantum gravity is considered. It is found, that this model corresponds to a string propagating against some curved background space. The quantization scheme including the Wheeler-DeWitt equation and the "particle on a sphere" type of the gauge condition is suggested. In the quantization scheme considered, the "problem of time" is solved by building of the quasi-Heisenberg operators acting in a space of solutions of the Wheeler-DeWitt equation and the normalization of the wave function corresponds to the Klein-Gordon type. To analyze the physical consequences of the scheme, a (1+1)-dimensional background space is considered for which a classical solution is found and quantized. The obtained estimations show the way to solution of the cosmological constant problem, which consists in compensation of the zero-point oscillations of the matter fields by the quantum oscillations of the scale factor. Along with such a compensation, a slow global evolution of a background corresponding to an universe expansion exists. |
1508.01940 | Arundhati Dasgupta | Arundhati Dasgupta | Quantum Field Theory in Accelerated Frames | 28 pages, two figures, clarification and references added | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we re-investigate the Bogoliubov transformations which relate
the Minkowski inertial vacuum to the vacuum of an accelerated observer. We
implement the transformation using a non-unitary operator used in formulations
of irreversible systems by Prigogine. We derive a Lyapunov function which
signifies an irreversible time flow. We extend the formalism to the black hole
space-time which has similar near-horizon geometry of an accelerated observer,
and in addition show that thermalization is due to presence of black hole and
white hole regions. Finally we discuss an attempt to generalize quantum field
theory for accelerated frames using this new connection to Prigogine
transformations.
| [
{
"created": "Sat, 8 Aug 2015 18:29:45 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Jan 2016 20:03:28 GMT",
"version": "v2"
}
] | 2016-01-08 | [
[
"Dasgupta",
"Arundhati",
""
]
] | In this paper we re-investigate the Bogoliubov transformations which relate the Minkowski inertial vacuum to the vacuum of an accelerated observer. We implement the transformation using a non-unitary operator used in formulations of irreversible systems by Prigogine. We derive a Lyapunov function which signifies an irreversible time flow. We extend the formalism to the black hole space-time which has similar near-horizon geometry of an accelerated observer, and in addition show that thermalization is due to presence of black hole and white hole regions. Finally we discuss an attempt to generalize quantum field theory for accelerated frames using this new connection to Prigogine transformations. |
1401.0588 | Michael Devin | Michael Devin | Musings on Firewalls and the Information Paradox | 4 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The past year has seen an explosion of new and old ideas about black hole
physics. Prior to the firewall paper, the dominant picture was the thermofield
model apparently implied by ADS/CFT duality\cite{mal2}. While some seek a
narrow responce to Almheiri, Marolf, Polchinski, and Sully,(AMPS)\cite{amps},
there are a number of competing models. One problem in the field is the
ambiguity of the competing proposals. Some are equivalent while others
incompatible. This paper will attempt to define and classify a few models
representative of the current discussions.
| [
{
"created": "Fri, 3 Jan 2014 05:49:54 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Mar 2014 19:12:30 GMT",
"version": "v2"
}
] | 2014-03-14 | [
[
"Devin",
"Michael",
""
]
] | The past year has seen an explosion of new and old ideas about black hole physics. Prior to the firewall paper, the dominant picture was the thermofield model apparently implied by ADS/CFT duality\cite{mal2}. While some seek a narrow responce to Almheiri, Marolf, Polchinski, and Sully,(AMPS)\cite{amps}, there are a number of competing models. One problem in the field is the ambiguity of the competing proposals. Some are equivalent while others incompatible. This paper will attempt to define and classify a few models representative of the current discussions. |
gr-qc/9909082 | Herbert Balasin | Herbert Balasin (TU-Wien) | Generalized Kerr Schild metrics and the gravitational field of a
massless particle on the horizon | uses AMS macros | Class.Quant.Grav. 17 (2000) 1913-1920 | 10.1088/0264-9381/17/9/303 | UWThPh 1999-58, TUW 99/20 | gr-qc | null | We investigate the structure of the gravitational field generated by a
massless particle moving on the horizon of an arbitrary (stationary) black
hole. This is done by employing the generalized Kerr-Schild class where we take
the null generators of the horizon as the geodetic null vector-field and a
scalar function which is concentrated on the horizon.
| [
{
"created": "Mon, 27 Sep 1999 09:58:53 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Balasin",
"Herbert",
"",
"TU-Wien"
]
] | We investigate the structure of the gravitational field generated by a massless particle moving on the horizon of an arbitrary (stationary) black hole. This is done by employing the generalized Kerr-Schild class where we take the null generators of the horizon as the geodetic null vector-field and a scalar function which is concentrated on the horizon. |
1904.09963 | Marius Adrian Oancea | Marius A. Oancea, Claudio F. Paganini, J\'er\'emie Joudioux, Lars
Andersson | An overview of the gravitational spin Hall effect | 49 pages, 2 figures. First version. Comments and suggestions are
welcomed | null | null | null | gr-qc physics.optics | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In General Relativity, the propagation of electromagnetic waves is usually
described by the vacuum Maxwell's equations on a fixed curved background. In
the limit of infinitely high frequencies, electromagnetic waves can be
localized as point particles, following null geodesics. However, at finite
frequencies, electromagnetic waves can no longer be treated as point particles
following null geodesics, and the spin angular momentum of light comes into
play, via the spin-curvature coupling. We will refer to this effect as the
gravitational spin Hall effect of light. Here, we review a series of
theoretical results related to the gravitational spin Hall effect of light, and
we compare the predictions of different models. The analogy with the spin Hall
effect in Optics is also explored, since in this field the effect is well
understood, both theoretically and experimentally.
| [
{
"created": "Mon, 22 Apr 2019 17:32:01 GMT",
"version": "v1"
}
] | 2019-04-23 | [
[
"Oancea",
"Marius A.",
""
],
[
"Paganini",
"Claudio F.",
""
],
[
"Joudioux",
"Jérémie",
""
],
[
"Andersson",
"Lars",
""
]
] | In General Relativity, the propagation of electromagnetic waves is usually described by the vacuum Maxwell's equations on a fixed curved background. In the limit of infinitely high frequencies, electromagnetic waves can be localized as point particles, following null geodesics. However, at finite frequencies, electromagnetic waves can no longer be treated as point particles following null geodesics, and the spin angular momentum of light comes into play, via the spin-curvature coupling. We will refer to this effect as the gravitational spin Hall effect of light. Here, we review a series of theoretical results related to the gravitational spin Hall effect of light, and we compare the predictions of different models. The analogy with the spin Hall effect in Optics is also explored, since in this field the effect is well understood, both theoretically and experimentally. |
0705.2048 | Tanmay Vachaspati | Tanmay Vachaspati | On Constructing Baby Universes and Black Holes | Not an "Honorable Mention" in the Gravity Research Foundation Essay
Competition | null | null | null | gr-qc astro-ph hep-th | null | The creation of spacetimes with horizons is discussed, focussing on baby
universes and black holes as examples. There is a complex interplay of quantum
theory and General Relativity in both cases, leading to consequences for the
future of the universe and the information loss paradox, and to a deeper
understanding of quantum gravity.
| [
{
"created": "Tue, 15 May 2007 17:15:07 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Vachaspati",
"Tanmay",
""
]
] | The creation of spacetimes with horizons is discussed, focussing on baby universes and black holes as examples. There is a complex interplay of quantum theory and General Relativity in both cases, leading to consequences for the future of the universe and the information loss paradox, and to a deeper understanding of quantum gravity. |
gr-qc/9508060 | Remo Garattini | Remo Garattini | Vacuum Energy in Ultralocal metrics for TT tensors with Gaussian Wave
Functionals | Revtex 3.0, preprint, 20 pages, new references included. Some
Comments on the reparametrisation invariance added in the introduction and in
the conclusion | null | null | null | gr-qc hep-th | null | We calculate, in a class of Gauge invariant functionals, by variational
methods, the difference of vacuum energy between two different backgrounds:
Schwarzschild and Flat Space. We perform this evaluation in an Hamiltonian
formulation of Quantum Gravity by standard ''$3+1$'' decomposition. After the
decomposition the scalar curvature is expanded to second order with respect to
the Schwarzschild metric. We evaluate this energy difference in momentum space,
in the lowest possible state (regardless of any negative mode). We find a
singular behaviour in the UV-limit, due to the presence of the horizon when
$r=2m.$ When $r>2m$ this singular behaviour disappears, which is in agreement
with various other models presented in the literature.
| [
{
"created": "Tue, 29 Aug 1995 21:16:41 GMT",
"version": "v1"
},
{
"created": "Sun, 21 Apr 1996 15:54:43 GMT",
"version": "v2"
}
] | 2008-02-03 | [
[
"Garattini",
"Remo",
""
]
] | We calculate, in a class of Gauge invariant functionals, by variational methods, the difference of vacuum energy between two different backgrounds: Schwarzschild and Flat Space. We perform this evaluation in an Hamiltonian formulation of Quantum Gravity by standard ''$3+1$'' decomposition. After the decomposition the scalar curvature is expanded to second order with respect to the Schwarzschild metric. We evaluate this energy difference in momentum space, in the lowest possible state (regardless of any negative mode). We find a singular behaviour in the UV-limit, due to the presence of the horizon when $r=2m.$ When $r>2m$ this singular behaviour disappears, which is in agreement with various other models presented in the literature. |
1705.11091 | Lorenzo Iorio | Lorenzo Iorio | Analytically calculated post-Keplerian range and range-rate
perturbations: the solar Lense-Thirring effect and BepiColombo | LaTex2e, 29 pages, 8 figures, no tables. Matching the version at
press in Monthly Notices of the Royal Astronomical Society (MNRAS) | Mon.Not.Roy.Astron.Soc.476:1811-1825,2018 | 10.1093/mnras/sty351 | null | gr-qc physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analytically calculate the time series for the perturbations
$\Delta\rho(t),~\Delta\dot\rho(t)$ induced by a general disturbing acceleration
$\boldsymbol{A}$ on the mutual range $\rho$ and range-rate $\dot\rho$ of two
test particles $\textrm{A},~\textrm{B}$ orbiting the same spinning body. We
apply it to the general relativistic Lense-Thirring effect, due to the
primary's spin $\boldsymbol{S}$, and the classical perturbation arising from
its quadrupole mass moment $J_2$ for arbitrary orbital geometries and
orientation of the source's symmetry axis $\boldsymbol{\hat{S}}$. The
Earth-Mercury range and range-rate are nominally affected by the Sun's
gravitomagnetic field to the $10~\textrm{m},~10^{-3}~\textrm{cm s}^{-1}$ level,
respectively, during the extended phase (2026-2028) of the forthcoming
BepiColombo mission to Mercury whose expected tracking accuracy is of the order
of $\simeq 0.1~\textrm{m},~2\times 10^{-4}~\textrm{cm s}^{-1}$. The competing
signatures due to the solar quadrupole $J_2^\odot$, if modelled at the
$\sigma_{J_2^\odot}\simeq 10^{-9}$ level of the latest planetary ephemerides
INPOP17a, are nearly 10 times smaller than the relativistic gravitomagnetic
effects. The position and velocity vectors $\mathbf{r},~\mathbf{v}$ of Mercury
and Earth are changed by the solar Lense-Thirring effect by about
$10~\textrm{m},~1.5~\textrm{m}$ and $10^{-3}~\textrm{cm
s}^{-1},~10^{-5}~\textrm{cm s}^{-1}$, respectively, over 2 yr; neglecting such
shifts may have an impact on long-term integrations of the inner solar system
dynamics over $\sim\textrm{Gyr}$ timescales.
| [
{
"created": "Tue, 30 May 2017 10:11:08 GMT",
"version": "v1"
},
{
"created": "Sun, 17 Dec 2017 21:07:52 GMT",
"version": "v2"
},
{
"created": "Fri, 12 Jan 2018 16:40:37 GMT",
"version": "v3"
},
{
"created": "Tue, 23 Jan 2018 15:17:13 GMT",
"version": "v4"
},
{
"created": "Mon, 26 Feb 2018 19:15:58 GMT",
"version": "v5"
}
] | 2018-03-19 | [
[
"Iorio",
"Lorenzo",
""
]
] | We analytically calculate the time series for the perturbations $\Delta\rho(t),~\Delta\dot\rho(t)$ induced by a general disturbing acceleration $\boldsymbol{A}$ on the mutual range $\rho$ and range-rate $\dot\rho$ of two test particles $\textrm{A},~\textrm{B}$ orbiting the same spinning body. We apply it to the general relativistic Lense-Thirring effect, due to the primary's spin $\boldsymbol{S}$, and the classical perturbation arising from its quadrupole mass moment $J_2$ for arbitrary orbital geometries and orientation of the source's symmetry axis $\boldsymbol{\hat{S}}$. The Earth-Mercury range and range-rate are nominally affected by the Sun's gravitomagnetic field to the $10~\textrm{m},~10^{-3}~\textrm{cm s}^{-1}$ level, respectively, during the extended phase (2026-2028) of the forthcoming BepiColombo mission to Mercury whose expected tracking accuracy is of the order of $\simeq 0.1~\textrm{m},~2\times 10^{-4}~\textrm{cm s}^{-1}$. The competing signatures due to the solar quadrupole $J_2^\odot$, if modelled at the $\sigma_{J_2^\odot}\simeq 10^{-9}$ level of the latest planetary ephemerides INPOP17a, are nearly 10 times smaller than the relativistic gravitomagnetic effects. The position and velocity vectors $\mathbf{r},~\mathbf{v}$ of Mercury and Earth are changed by the solar Lense-Thirring effect by about $10~\textrm{m},~1.5~\textrm{m}$ and $10^{-3}~\textrm{cm s}^{-1},~10^{-5}~\textrm{cm s}^{-1}$, respectively, over 2 yr; neglecting such shifts may have an impact on long-term integrations of the inner solar system dynamics over $\sim\textrm{Gyr}$ timescales. |
gr-qc/0202074 | Plamen petkov Fiziev | Plamen P. Fiziev | Basic Principles of 4D Dilatonic Gravity and Some of Their Consequences
for Cosmology, Astrophysics and Cosmological Constant Problem | 34 pages, 5 figures, LaTeX file, added references, corrected typos | null | null | UTTG-02-02 | gr-qc astro-ph hep-ph hep-th | null | We present a class of simple scalar-tensor models of gravity with one scalar
field (dilaton $\Phi$) and only one unknown function (cosmological potential
$U(\Phi)$). These models might be considered as a stringy inspired ones with
broken SUSY. They have the following basic properties: 1) Positive dilaton
mass, $m_\Phi$, and positive cosmological constant $\Lambda$, define two
extremely different scales. The models under consideration are consistent with
the known experimental facts if $m_\Phi > 10^{-3} eV$ and
$\Lambda=\Lambda^{obs}\sim 10^{-56} cm^{-2}$. 2) Einstein week equivalence
principle is strictly satisfied and extended to scalar-tensor theories of
gravity using a novel form of principle of "constancy of fundamental
constants". 3) The dilaton plays simultaneously role of inflation field and
quintessence field and yields a sequential hyper-inflation with graceful exit
to asymptotic de Sitter space-time which is an attractor, and is approached as
$\exp(-\sqrt{3\Lambda^{obs}} ct/2)$. The time duration of inflation is $\Delta
t_{infl} \sim m_\Phi^{-1}$. 4) Ultra-high frequency ($\omega_\Phi \sim m_\Phi$)
dilatonic oscillations take place in asymptotic regime. 5) No fine tuning. (The
Robertson-Walker solutions of general type have the above properties.) 6) A
novel adjustment mechanism for cosmological constant problem seems to be
possible: the huge value of cosmological constant in the stringy frame is
re-scaled to its observed value by dilaton after transition to phenomenological
frame.
| [
{
"created": "Thu, 21 Feb 2002 00:50:06 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Feb 2002 23:07:05 GMT",
"version": "v2"
},
{
"created": "Wed, 27 Feb 2002 04:05:47 GMT",
"version": "v3"
},
{
"created": "Tue, 2 Jul 2002 18:02:39 GMT",
"version": "v4"
}
] | 2007-05-23 | [
[
"Fiziev",
"Plamen P.",
""
]
] | We present a class of simple scalar-tensor models of gravity with one scalar field (dilaton $\Phi$) and only one unknown function (cosmological potential $U(\Phi)$). These models might be considered as a stringy inspired ones with broken SUSY. They have the following basic properties: 1) Positive dilaton mass, $m_\Phi$, and positive cosmological constant $\Lambda$, define two extremely different scales. The models under consideration are consistent with the known experimental facts if $m_\Phi > 10^{-3} eV$ and $\Lambda=\Lambda^{obs}\sim 10^{-56} cm^{-2}$. 2) Einstein week equivalence principle is strictly satisfied and extended to scalar-tensor theories of gravity using a novel form of principle of "constancy of fundamental constants". 3) The dilaton plays simultaneously role of inflation field and quintessence field and yields a sequential hyper-inflation with graceful exit to asymptotic de Sitter space-time which is an attractor, and is approached as $\exp(-\sqrt{3\Lambda^{obs}} ct/2)$. The time duration of inflation is $\Delta t_{infl} \sim m_\Phi^{-1}$. 4) Ultra-high frequency ($\omega_\Phi \sim m_\Phi$) dilatonic oscillations take place in asymptotic regime. 5) No fine tuning. (The Robertson-Walker solutions of general type have the above properties.) 6) A novel adjustment mechanism for cosmological constant problem seems to be possible: the huge value of cosmological constant in the stringy frame is re-scaled to its observed value by dilaton after transition to phenomenological frame. |
2207.03690 | Rakshit Vyas | Rakshit P. Vyas and Mihir J. Joshi | New Quantum Spin Perspective and Geometrical Operators of Quantum
Geometry | 5 pages, 1 figure, 1 table | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we propose a new perspective of quantum spin (angular
momentum) in which the Boltzmann constant \(k_{\beta}\), Planck temperature
\(T_{P}\), Planck mass \(m_{P}\) and Planck area \(l_{P}^{2}\) are the integral
part of the total angular momentum \(J\). With the aid of this new perspective,
we modify the equation of the area and volume operator. In the quantum
geometry, for \(SO(3)\) group, the angular momentum operators \(J^{k}\) is the
\(k\)th Lie group generator \(T^{k}\); hence, \(T^{k} \equiv J^{k}\).
Therefore, new perspective of quantum spin can be directly applicable to
quantum geometry. From data, the value of the area operator \(\hat{A}_{S}\)
increases with \(n^{2}\) in discrete way that suggests discrete spectrum of the
area operator similar to the actual formula of the area operator. This
perspective provides an auto-correct or auto-balance mechanism within the
equation of these geometrical operators. At the quantum gravity scale, it means
that the mutual small change in \(T_{P}\), \(m_{P}\), and \(l_{P}^{2}\) occur
in such a way that \(\hbar\), \(l_{P}\) and \(\hat{A}_{S}\) and \(
\hat{V}_{S}\) remain invariant for a value of \(j_{i}\). The constancy of the
reduced Planck constant \(\hbar\) in the geometrical operators can provide a
way through which smooth transition of the Planck scale to the nuclear or the
atomic scale can be understood.
| [
{
"created": "Fri, 8 Jul 2022 05:02:51 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Sep 2022 09:58:00 GMT",
"version": "v2"
}
] | 2022-09-07 | [
[
"Vyas",
"Rakshit P.",
""
],
[
"Joshi",
"Mihir J.",
""
]
] | In this paper, we propose a new perspective of quantum spin (angular momentum) in which the Boltzmann constant \(k_{\beta}\), Planck temperature \(T_{P}\), Planck mass \(m_{P}\) and Planck area \(l_{P}^{2}\) are the integral part of the total angular momentum \(J\). With the aid of this new perspective, we modify the equation of the area and volume operator. In the quantum geometry, for \(SO(3)\) group, the angular momentum operators \(J^{k}\) is the \(k\)th Lie group generator \(T^{k}\); hence, \(T^{k} \equiv J^{k}\). Therefore, new perspective of quantum spin can be directly applicable to quantum geometry. From data, the value of the area operator \(\hat{A}_{S}\) increases with \(n^{2}\) in discrete way that suggests discrete spectrum of the area operator similar to the actual formula of the area operator. This perspective provides an auto-correct or auto-balance mechanism within the equation of these geometrical operators. At the quantum gravity scale, it means that the mutual small change in \(T_{P}\), \(m_{P}\), and \(l_{P}^{2}\) occur in such a way that \(\hbar\), \(l_{P}\) and \(\hat{A}_{S}\) and \( \hat{V}_{S}\) remain invariant for a value of \(j_{i}\). The constancy of the reduced Planck constant \(\hbar\) in the geometrical operators can provide a way through which smooth transition of the Planck scale to the nuclear or the atomic scale can be understood. |
2405.09703 | Mateo Casariego | Mateo Casariego | Diffeomorphism invariance and general covariance: a pedagogical
introduction | 6 pages, 3 figures, informal style | null | null | null | gr-qc physics.hist-ph | http://creativecommons.org/licenses/by/4.0/ | Diffeomorphism invariance is a feature that gets sometimes highlighted as
something with profound implications in the physics of spacetime. Moreover, it
is often wrongly associated exclusively with General Relativity. The fact that
diffeomorphism invariance and general covariance are used interchangeably does
not help. Here, we attempt at clarifying these concepts.
| [
{
"created": "Wed, 15 May 2024 21:05:42 GMT",
"version": "v1"
}
] | 2024-05-17 | [
[
"Casariego",
"Mateo",
""
]
] | Diffeomorphism invariance is a feature that gets sometimes highlighted as something with profound implications in the physics of spacetime. Moreover, it is often wrongly associated exclusively with General Relativity. The fact that diffeomorphism invariance and general covariance are used interchangeably does not help. Here, we attempt at clarifying these concepts. |
2305.09849 | Tatsuya Yamaoka | Sinya Aoki, Tetsuya Onogi, Tatsuya Yamaoka | Energies and a gravitational charge for massive particles in general
relativity | 17 pages, Reference added, typo corrected | null | null | YITP-23-66, OU-HET-1188 | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this paper, we investigate relations or differences among various
conserved quantities which involve the matter Energy Momentum Tensor (EMT) in
general relativity. These charges include the energy with Einstein's pseudo
EMT, the generalized Komar integral, or the ADM energy, all of which can be
derived from Noether's second theorem, as well as an extra conserved charge
recently proposed in general relativity. For detailed analyses, we apply
definitions of these charges to a system of free massive particles. We employ
the post-Newtonian (PN) expansion to make physical interpretations. We find
that the generalized Komar integral is not conserved at the first non-trivial
order in the PN expansion due to non-zero contributions at spatial boundaries,
while the energy with Einstein's pseudo EMT at this order agrees with a total
energy of massive particles with gravitational interactions through the
Newtonian potential, and thus is conserved. In addition, this total energy is
shown to be identical to the ADM energy not only at this order but also all
orders in the PN expansion. We next calculate an extra conserved charge for the
system of massive particles, at all orders in the PN expansion, which turns out
to be a total number of particles. We call it a gravitational charge, since it
is clearly different from the total energy. We finally discuss an implication
from a fact that there exist two conserved quantities, energy and gravitational
charge, in general relativity.
| [
{
"created": "Tue, 16 May 2023 23:37:34 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Jul 2023 02:47:38 GMT",
"version": "v2"
}
] | 2023-07-06 | [
[
"Aoki",
"Sinya",
""
],
[
"Onogi",
"Tetsuya",
""
],
[
"Yamaoka",
"Tatsuya",
""
]
] | In this paper, we investigate relations or differences among various conserved quantities which involve the matter Energy Momentum Tensor (EMT) in general relativity. These charges include the energy with Einstein's pseudo EMT, the generalized Komar integral, or the ADM energy, all of which can be derived from Noether's second theorem, as well as an extra conserved charge recently proposed in general relativity. For detailed analyses, we apply definitions of these charges to a system of free massive particles. We employ the post-Newtonian (PN) expansion to make physical interpretations. We find that the generalized Komar integral is not conserved at the first non-trivial order in the PN expansion due to non-zero contributions at spatial boundaries, while the energy with Einstein's pseudo EMT at this order agrees with a total energy of massive particles with gravitational interactions through the Newtonian potential, and thus is conserved. In addition, this total energy is shown to be identical to the ADM energy not only at this order but also all orders in the PN expansion. We next calculate an extra conserved charge for the system of massive particles, at all orders in the PN expansion, which turns out to be a total number of particles. We call it a gravitational charge, since it is clearly different from the total energy. We finally discuss an implication from a fact that there exist two conserved quantities, energy and gravitational charge, in general relativity. |
0809.5098 | Gabor Kunstatter | G. Kunstatter (1), J. Louko (2) and J. Ziprick (3) ((1) University of
Winnipeg, (2) University of Nottingham,(3) University of Manitoba) | Polymer quantization, singularity resolution and the 1/r^2 potential | 21 pages, LaTeX including 7 figures. v2: analytic bounds improved;
references added | Phys.Rev.A79:032104,2009 | 10.1103/PhysRevA.79.032104 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a polymer quantization of the -lambda/r^2 potential on the
positive real line and compute numerically the bound state eigenenergies in
terms of the dimensionless coupling constant lambda. The singularity at the
origin is handled in two ways: first, by regularizing the potential and
adopting either symmetric or antisymmetric boundary conditions; second, by
keeping the potential unregularized but allowing the singularity to be balanced
by an antisymmetric boundary condition. The results are compared to the
semiclassical limit of the polymer theory and to the conventional Schrodinger
quantization on L_2(R_+). The various quantization schemes are in excellent
agreement for the highly excited states but differ for the low-lying states,
and the polymer spectrum is bounded below even when the Schrodinger spectrum is
not. We find as expected that for the antisymmetric boundary condition the
regularization of the potential is redundant: the polymer quantum theory is
well defined even with the unregularized potential and the regularization of
the potential does not significantly affect the spectrum.
| [
{
"created": "Tue, 30 Sep 2008 00:45:29 GMT",
"version": "v1"
},
{
"created": "Fri, 13 Mar 2009 17:07:33 GMT",
"version": "v2"
}
] | 2009-05-26 | [
[
"Kunstatter",
"G.",
""
],
[
"Louko",
"J.",
""
],
[
"Ziprick",
"J.",
""
]
] | We present a polymer quantization of the -lambda/r^2 potential on the positive real line and compute numerically the bound state eigenenergies in terms of the dimensionless coupling constant lambda. The singularity at the origin is handled in two ways: first, by regularizing the potential and adopting either symmetric or antisymmetric boundary conditions; second, by keeping the potential unregularized but allowing the singularity to be balanced by an antisymmetric boundary condition. The results are compared to the semiclassical limit of the polymer theory and to the conventional Schrodinger quantization on L_2(R_+). The various quantization schemes are in excellent agreement for the highly excited states but differ for the low-lying states, and the polymer spectrum is bounded below even when the Schrodinger spectrum is not. We find as expected that for the antisymmetric boundary condition the regularization of the potential is redundant: the polymer quantum theory is well defined even with the unregularized potential and the regularization of the potential does not significantly affect the spectrum. |
1212.2290 | Eleni-Alexandra Kontou | Eleni-Alexandra Kontou and Ken D. Olum | Averaged null energy condition in a classical curved background | null | null | 10.1103/PhysRevD.87.064009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Averaged Null Energy Condition (ANEC) states that the integral along a
complete null geodesic of the projection of the stress-energy tensor onto the
tangent vector to the geodesic cannot be negative. Exotic spacetimes, such as
those allow wormholes or the construction of time machines are possible in
general relativity only if ANEC is violated along achronal geodesics. Starting
from a conjecture that flat-space quantum inequalities apply with small
corrections in spacetimes with small curvature, we prove that ANEC is obeyed by
a minimally-coupled, free quantum scalar field on any achronal null geodesic
surrounded by a tubular neighborhood whose curvature is produced by a classical
source.
| [
{
"created": "Tue, 11 Dec 2012 03:30:34 GMT",
"version": "v1"
}
] | 2013-03-14 | [
[
"Kontou",
"Eleni-Alexandra",
""
],
[
"Olum",
"Ken D.",
""
]
] | The Averaged Null Energy Condition (ANEC) states that the integral along a complete null geodesic of the projection of the stress-energy tensor onto the tangent vector to the geodesic cannot be negative. Exotic spacetimes, such as those allow wormholes or the construction of time machines are possible in general relativity only if ANEC is violated along achronal geodesics. Starting from a conjecture that flat-space quantum inequalities apply with small corrections in spacetimes with small curvature, we prove that ANEC is obeyed by a minimally-coupled, free quantum scalar field on any achronal null geodesic surrounded by a tubular neighborhood whose curvature is produced by a classical source. |
1203.1803 | Mandar Patil | Mandar Patil, Pankaj S. Joshi | Ultra-high energy particle collisions in a regular spacetime without
blackholes or naked singularities | 10 pages, 1 figure, Revised version accepted for publication in Phys.
Rev. D | Phys. Rev. D 86, 044040 (2012) | 10.1103/PhysRevD.86.044040 | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate here the particle acceleration and collisions with extremely
large center of mass energies in a perfectly regular spacetime containing
neither singularity nor an event horizon. The ultra-high energy collisions of
particles near the event horizon of extremal Kerr blackhole, and also in many
other examples of extremal blackholes have been investigated and reported
recently. We studied an analogous particle acceleration process in the Kerr and
Reissner-Nordstrom spacetimes without horizon, containing naked singularities.
Further to this, we show here that the particle acceleration and collision
process is in fact independent of blackholes and naked singularities, and can
happen in a fully regular spacetime containing neither of these. We derive the
conditions on the general static spherically symmetric metric for such a
phenomena to happen. We show that in order to have ultra-high energy collisions
it is necessary for the norm of the timelike Killing vector to admit a maximum
with a vanishingly small but a negative value. This is also a condition
implying the presence of a surface with extremely large but nevertheless finite
value of the redshift or blueshift. Conditions to have ultrahigh energy
collisions and regular center imply the violation of strong energy condition
near the center while the weak energy condition is respected in the region
around the center. Thus the central region is surrounded by a dark energy
fluid. Both the energy conditions are respected at the location where the high
energy collisions take place. As a concrete example we then investigate the
acceleration process in the spacetime geometry derived by Bardeen which is
sourced by a non-liner self-gravitating magnetic monopole.
| [
{
"created": "Thu, 8 Mar 2012 14:11:40 GMT",
"version": "v1"
},
{
"created": "Wed, 1 Aug 2012 13:46:19 GMT",
"version": "v2"
}
] | 2012-08-27 | [
[
"Patil",
"Mandar",
""
],
[
"Joshi",
"Pankaj S.",
""
]
] | We investigate here the particle acceleration and collisions with extremely large center of mass energies in a perfectly regular spacetime containing neither singularity nor an event horizon. The ultra-high energy collisions of particles near the event horizon of extremal Kerr blackhole, and also in many other examples of extremal blackholes have been investigated and reported recently. We studied an analogous particle acceleration process in the Kerr and Reissner-Nordstrom spacetimes without horizon, containing naked singularities. Further to this, we show here that the particle acceleration and collision process is in fact independent of blackholes and naked singularities, and can happen in a fully regular spacetime containing neither of these. We derive the conditions on the general static spherically symmetric metric for such a phenomena to happen. We show that in order to have ultra-high energy collisions it is necessary for the norm of the timelike Killing vector to admit a maximum with a vanishingly small but a negative value. This is also a condition implying the presence of a surface with extremely large but nevertheless finite value of the redshift or blueshift. Conditions to have ultrahigh energy collisions and regular center imply the violation of strong energy condition near the center while the weak energy condition is respected in the region around the center. Thus the central region is surrounded by a dark energy fluid. Both the energy conditions are respected at the location where the high energy collisions take place. As a concrete example we then investigate the acceleration process in the spacetime geometry derived by Bardeen which is sourced by a non-liner self-gravitating magnetic monopole. |
1402.2385 | Behnam Pourhassan | M. Khurshudyan, E. Chubaryan and B. Pourhassan | Interacting Quintessence Models of Dark Energy | 8 pages, accepted in Int. J. Theor. Phys | Int. J. Theor. Phys. 53 (2014) 2370 | 10.1007/s10773-014-2036-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we consider two models of quintessence scalar fields with
different potentials. Interaction with generalized cosmic Chaplygin gas is also
investigated. Cosmological parameters are studied and graphical behavior is
analyzed. We find that our model is agree with observational data specially
$\Lambda$CDM model.
| [
{
"created": "Tue, 11 Feb 2014 07:07:07 GMT",
"version": "v1"
}
] | 2014-07-08 | [
[
"Khurshudyan",
"M.",
""
],
[
"Chubaryan",
"E.",
""
],
[
"Pourhassan",
"B.",
""
]
] | In this paper we consider two models of quintessence scalar fields with different potentials. Interaction with generalized cosmic Chaplygin gas is also investigated. Cosmological parameters are studied and graphical behavior is analyzed. We find that our model is agree with observational data specially $\Lambda$CDM model. |
gr-qc/9710124 | Jose Wadih Maluf | J. W. Maluf (Universidade de Brasilia) | Sparling two-forms, the conformal factor and the gravitational energy
density of the teleparallel equivalent of general relativity | 12 pages, Latex file, no figures, to be published in Gen. Rel. Grav | Gen.Rel.Grav. 30 (1998) 413-423 | 10.1023/A:1018806825254 | null | gr-qc | null | It has been shown recently that within the framework of the teleparallel
equivalent of general relativity (TEGR) it is possible to define the energy
density of the gravitational field. The TEGR amounts to an alternative
formulation of Einstein's general relativity, not to an alternative gravity
theory. The localizability of the gravitational energy has been investigated in
a number of space-times with distinct topologies, and the outcome of these
analises agree with previously known results regarding the exact expression of
the gravitational energy, and/or with the specific properties of the space-time
manifold. In this article we establish a relationship between the expression
for the gravitational energy density of the TEGR and the Sparling two-forms,
which are known to be closely connected with the gravitational energy. We also
show that our expression of energy yields the correct value of gravitational
mass contained in the conformal factor of the metric field.
| [
{
"created": "Tue, 28 Oct 1997 17:16:07 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Maluf",
"J. W.",
"",
"Universidade de Brasilia"
]
] | It has been shown recently that within the framework of the teleparallel equivalent of general relativity (TEGR) it is possible to define the energy density of the gravitational field. The TEGR amounts to an alternative formulation of Einstein's general relativity, not to an alternative gravity theory. The localizability of the gravitational energy has been investigated in a number of space-times with distinct topologies, and the outcome of these analises agree with previously known results regarding the exact expression of the gravitational energy, and/or with the specific properties of the space-time manifold. In this article we establish a relationship between the expression for the gravitational energy density of the TEGR and the Sparling two-forms, which are known to be closely connected with the gravitational energy. We also show that our expression of energy yields the correct value of gravitational mass contained in the conformal factor of the metric field. |
1712.03730 | Stefano Chinaglia | Aimeric Coll\'eaux, Stefano Chinaglia, Sergio Zerbini | Non-polynomial Lagrangian approach to Regular Black Holes | 39 pages; submitted and accepted for publication in Int. J. Mod.
Phys. D; references added | null | 10.1142/S0218271818300021 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a review on Lagrangian models admitting spherically symmetric
regular black holes, and cosmological bounce solutions. Non-linear
electrodynamics, non-polynomial gravity, and fluid approaches are explained in
details. They consist respectively in a gauge invariant generalization of the
Maxwell Lagrangian, in modifications of the Einstein-Hilbert action via
non-polynomial curvature invariants, and finally in the reconstruction of
density profiles able to cure the central singularity of black holes. The
non-polynomial gravity curvature invariants have the special property to be
second order and polynomial in the metric field, in spherically symmetric
spacetimes. Along the way, other models and results are discussed, and some
general properties that regular black holes should satisfy are mentioned. A
covariant Sakharov criterion for the absence of singularities in dynamical
spherically symmetric spacetimes is also proposed and checked for some examples
of such regular metric fields.
| [
{
"created": "Mon, 11 Dec 2017 11:50:41 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Dec 2017 14:43:54 GMT",
"version": "v2"
}
] | 2018-02-28 | [
[
"Colléaux",
"Aimeric",
""
],
[
"Chinaglia",
"Stefano",
""
],
[
"Zerbini",
"Sergio",
""
]
] | We present a review on Lagrangian models admitting spherically symmetric regular black holes, and cosmological bounce solutions. Non-linear electrodynamics, non-polynomial gravity, and fluid approaches are explained in details. They consist respectively in a gauge invariant generalization of the Maxwell Lagrangian, in modifications of the Einstein-Hilbert action via non-polynomial curvature invariants, and finally in the reconstruction of density profiles able to cure the central singularity of black holes. The non-polynomial gravity curvature invariants have the special property to be second order and polynomial in the metric field, in spherically symmetric spacetimes. Along the way, other models and results are discussed, and some general properties that regular black holes should satisfy are mentioned. A covariant Sakharov criterion for the absence of singularities in dynamical spherically symmetric spacetimes is also proposed and checked for some examples of such regular metric fields. |
1910.13718 | Yan Peng | Yan Peng | Scalarization of compact stars in the scalar-Gauss-Bonnet gravity | 9 pages, 2 figures | JHEP 12(2019)064 | 10.1007/JHEP12(2019)064 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study scalarization of horizonless neutral compact reflecting stars. In
our model, the scalar hair can be induced by the coupling of static scalar
fields to the Gauss-Bonnet invariant. We analytically obtain lower bounds on
the coupling parameter. Below the bound, the static scalar hair cannot form.
And above the bound, we numerically get the discrete coupling parameter that
can support scalar hairs outside stars. We also disclose effects of model
parameters on the discrete coupling parameter.
| [
{
"created": "Wed, 30 Oct 2019 08:39:09 GMT",
"version": "v1"
},
{
"created": "Sun, 24 Nov 2019 08:29:00 GMT",
"version": "v2"
},
{
"created": "Wed, 11 Dec 2019 11:08:09 GMT",
"version": "v3"
}
] | 2019-12-12 | [
[
"Peng",
"Yan",
""
]
] | We study scalarization of horizonless neutral compact reflecting stars. In our model, the scalar hair can be induced by the coupling of static scalar fields to the Gauss-Bonnet invariant. We analytically obtain lower bounds on the coupling parameter. Below the bound, the static scalar hair cannot form. And above the bound, we numerically get the discrete coupling parameter that can support scalar hairs outside stars. We also disclose effects of model parameters on the discrete coupling parameter. |
2109.03174 | Lavinia Heisenberg | Fabio D'Ambrosio, Shaun D.B. Fell, Lavinia Heisenberg and Simon Kuhn | Black holes in $f(\mathbb Q)$ Gravity | 39 pages, 1 figure | null | 10.1103/PhysRevD.105.024042 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We systematically study the field equations of $f(\mathbb Q)$ gravity for
spherically symmetric and stationary metric-affine spacetimes. Such spacetimes
are described by a metric as well as a flat and torsionless affine connection.
In the Symmetric Teleparallel Equivalent of GR (STEGR), the connection is pure
gauge and hence unphysical. However, in the non-linear extension $f(\Q)$, it is
promoted to a dynamical field which changes the physics. Starting from a
general metric-affine geometry, we construct the most general static and
spherically symmetric forms of the metric and the affine connection. We then
use these symmetry reduced geometric objects to prove that the field equations
of $f(\Q)$ gravity admit GR solutions as well as beyond-GR solutions, contrary
to what has been claimed in the literature. We formulate precise criteria,
under which conditions it is possible to obtain GR solutions and under which
conditions it is possible to obtain beyond-GR solutions. We subsequently
construct several perturbative corrections to the Schwarzschild solution for
different choices of $f(\Q)$, which in particular include a hair stemming from
the now dynamical affine connection. We also present an exact beyond-GR vacuum
solution. Lastly, we apply this method of constructing spherically symmetric
and stationary solutions to $f(\T)$ gravity, which reproduces similar solutions
but without a dynamical connection.
| [
{
"created": "Tue, 7 Sep 2021 16:12:15 GMT",
"version": "v1"
}
] | 2022-02-02 | [
[
"D'Ambrosio",
"Fabio",
""
],
[
"Fell",
"Shaun D. B.",
""
],
[
"Heisenberg",
"Lavinia",
""
],
[
"Kuhn",
"Simon",
""
]
] | We systematically study the field equations of $f(\mathbb Q)$ gravity for spherically symmetric and stationary metric-affine spacetimes. Such spacetimes are described by a metric as well as a flat and torsionless affine connection. In the Symmetric Teleparallel Equivalent of GR (STEGR), the connection is pure gauge and hence unphysical. However, in the non-linear extension $f(\Q)$, it is promoted to a dynamical field which changes the physics. Starting from a general metric-affine geometry, we construct the most general static and spherically symmetric forms of the metric and the affine connection. We then use these symmetry reduced geometric objects to prove that the field equations of $f(\Q)$ gravity admit GR solutions as well as beyond-GR solutions, contrary to what has been claimed in the literature. We formulate precise criteria, under which conditions it is possible to obtain GR solutions and under which conditions it is possible to obtain beyond-GR solutions. We subsequently construct several perturbative corrections to the Schwarzschild solution for different choices of $f(\Q)$, which in particular include a hair stemming from the now dynamical affine connection. We also present an exact beyond-GR vacuum solution. Lastly, we apply this method of constructing spherically symmetric and stationary solutions to $f(\T)$ gravity, which reproduces similar solutions but without a dynamical connection. |
1506.08575 | Frederico Arroja Dr. | Frederico Arroja, Nicola Bartolo, Purnendu Karmakar and Sabino
Matarrese | The two faces of mimetic Horndeski gravity: disformal transformations
and Lagrange multiplier | v1: 14 pages, 1 figure; v2: minor changes and references added,
replaced to match published version | JCAP 1509 (2015) 051 | 10.1088/1475-7516/2015/09/051 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that very general scalar-tensor theories of gravity (including, e.g.,
Horndeski models) are generically invariant under disformal transformations.
However there is a special subset, when the transformation is not invertible,
that yields new equations of motion which are a generalization of the so-called
"mimetic" dark matter theory recently introduced by Chamsedinne and Mukhanov.
These conclusions hold true irrespective of whether the scalar field in the
action of the assumed scalar-tensor theory of gravity is the same or different
than the scalar field involved in the transformation. The new equations of
motion for our general mimetic theory can also be derived from an action
containing an additional Lagrange multiplier field. The general mimetic
scalar-tensor theory has the same number of derivatives in the equations of
motion as the original scalar-tensor theory. As an application we show that the
simplest mimetic scalar-tensor model is able to mimic the cosmological
background of a flat FLRW model with a barotropic perfect fluid with any
constant equation of state.
| [
{
"created": "Mon, 29 Jun 2015 10:41:37 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Dec 2015 16:56:12 GMT",
"version": "v2"
}
] | 2015-12-31 | [
[
"Arroja",
"Frederico",
""
],
[
"Bartolo",
"Nicola",
""
],
[
"Karmakar",
"Purnendu",
""
],
[
"Matarrese",
"Sabino",
""
]
] | We show that very general scalar-tensor theories of gravity (including, e.g., Horndeski models) are generically invariant under disformal transformations. However there is a special subset, when the transformation is not invertible, that yields new equations of motion which are a generalization of the so-called "mimetic" dark matter theory recently introduced by Chamsedinne and Mukhanov. These conclusions hold true irrespective of whether the scalar field in the action of the assumed scalar-tensor theory of gravity is the same or different than the scalar field involved in the transformation. The new equations of motion for our general mimetic theory can also be derived from an action containing an additional Lagrange multiplier field. The general mimetic scalar-tensor theory has the same number of derivatives in the equations of motion as the original scalar-tensor theory. As an application we show that the simplest mimetic scalar-tensor model is able to mimic the cosmological background of a flat FLRW model with a barotropic perfect fluid with any constant equation of state. |
gr-qc/9410029 | null | D. Giulini, C. Kiefer, and H. D. Zeh | Symmetries, superselection rules, and decoherence | 12 pages, LATEX, Report Freiburg THEP-94/30 | Phys.Lett.A199:291-298,1995 | 10.1016/0375-9601(95)00128-P | null | gr-qc hep-th | null | We discuss the applicability of the programme of decoherence -- emergence of
approximate classical behaviour through interaction with the environment -- to
cases where it was suggested that the presence of symmetries would lead to
exact superselection rules. For this discussion it is useful to make a
distinction between pure symmetries and redundancies, which results from an
investigation into the constraint equations of the corresponding theories. We
discuss, in particular, superpositions of states with different charges, as
well as with different masses, and suggest how the corresponding interference
terms, although they exist in principle, become inaccessible through
decoherence.
| [
{
"created": "Fri, 21 Oct 1994 08:43:12 GMT",
"version": "v1"
}
] | 2010-11-01 | [
[
"Giulini",
"D.",
""
],
[
"Kiefer",
"C.",
""
],
[
"Zeh",
"H. D.",
""
]
] | We discuss the applicability of the programme of decoherence -- emergence of approximate classical behaviour through interaction with the environment -- to cases where it was suggested that the presence of symmetries would lead to exact superselection rules. For this discussion it is useful to make a distinction between pure symmetries and redundancies, which results from an investigation into the constraint equations of the corresponding theories. We discuss, in particular, superpositions of states with different charges, as well as with different masses, and suggest how the corresponding interference terms, although they exist in principle, become inaccessible through decoherence. |
1908.11701 | Ettore Minguzzi | R. A. Hounnonkpe and E. Minguzzi | Globally hyperbolic spacetimes can be defined without the 'causal'
condition | Latex2e, 12 pages. v2: fixed a few typos | Class. Quantum. Grav. 36 (2019) 197001 | 10.1088/1361-6382/ab3f11 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Reasonable spacetimes are non-compact and of dimension larger than two. We
show that these spacetimes are globally hyperbolic if and only if the causal
diamonds are compact. That is, there is no need to impose the causality
condition, as it can be deduced. We also improve the definition of global
hyperbolicity for the non-regular theory (non $C^{1,1}$ metric) and for general
cone structures by proving the following convenient characterization for upper
semi-continuous cone distributions: causality and the causally convex hull of
compact sets is compact. In this case the causality condition cannot be
dropped, independently of the spacetime dimension. Similar results are obtained
for causal simplicity.
| [
{
"created": "Fri, 30 Aug 2019 12:48:29 GMT",
"version": "v1"
},
{
"created": "Tue, 3 Sep 2019 08:50:27 GMT",
"version": "v2"
}
] | 2019-09-17 | [
[
"Hounnonkpe",
"R. A.",
""
],
[
"Minguzzi",
"E.",
""
]
] | Reasonable spacetimes are non-compact and of dimension larger than two. We show that these spacetimes are globally hyperbolic if and only if the causal diamonds are compact. That is, there is no need to impose the causality condition, as it can be deduced. We also improve the definition of global hyperbolicity for the non-regular theory (non $C^{1,1}$ metric) and for general cone structures by proving the following convenient characterization for upper semi-continuous cone distributions: causality and the causally convex hull of compact sets is compact. In this case the causality condition cannot be dropped, independently of the spacetime dimension. Similar results are obtained for causal simplicity. |
2012.14016 | Guillem Dom\`enech | Guillem Dom\`enech and Misao Sasaki | Approximate gauge independence of the induced gravitational wave
spectrum | Typos corrected, matches published version | Phys. Rev. D 103, 063531 (2021) | 10.1103/PhysRevD.103.063531 | YITP-20-163 | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves (GWs) induced by scalar curvature fluctuations are an
important source of the cosmological GW background and a crucial counterpart of
the primordial black hole scenario. However, doubts have been cast on the
theoretically predicted induced GW spectrum due to its seeming gauge
dependence. In this paper, we shed light on the gauge dependence issue of the
induced GW spectrum in general cosmological backgrounds. First, inspired by the
Hamiltonian formalism we provide very simple formulas for the tensor modes at
second order in cosmological perturbation theory. We also emphasize the
difference between observable and gauge invariant variables. Second, we argue
that the Newton (or shear-free) gauge is suitable for both the calculation of
induced GWs and the physical interpretation. We then show that, most notably,
the induced GW spectrum is invariant under a set of reasonable gauge
transformations, i.e. physically well behaved on small scales, once the source
term has become inactive. This includes the commonly used flat, constant Hubble
and synchronous gauges but excludes the comoving slicing gauge. We also show
that a particular solution of the GW equation in a dust dominated universe
while the source term is active can be gauged away by a small change of gauge.
| [
{
"created": "Sun, 27 Dec 2020 21:29:06 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Apr 2021 09:11:20 GMT",
"version": "v2"
}
] | 2021-04-14 | [
[
"Domènech",
"Guillem",
""
],
[
"Sasaki",
"Misao",
""
]
] | Gravitational waves (GWs) induced by scalar curvature fluctuations are an important source of the cosmological GW background and a crucial counterpart of the primordial black hole scenario. However, doubts have been cast on the theoretically predicted induced GW spectrum due to its seeming gauge dependence. In this paper, we shed light on the gauge dependence issue of the induced GW spectrum in general cosmological backgrounds. First, inspired by the Hamiltonian formalism we provide very simple formulas for the tensor modes at second order in cosmological perturbation theory. We also emphasize the difference between observable and gauge invariant variables. Second, we argue that the Newton (or shear-free) gauge is suitable for both the calculation of induced GWs and the physical interpretation. We then show that, most notably, the induced GW spectrum is invariant under a set of reasonable gauge transformations, i.e. physically well behaved on small scales, once the source term has become inactive. This includes the commonly used flat, constant Hubble and synchronous gauges but excludes the comoving slicing gauge. We also show that a particular solution of the GW equation in a dust dominated universe while the source term is active can be gauged away by a small change of gauge. |
2110.10127 | Ernesto Contreras | J. Andrade, E. Contreras | Stellar models with like--Tolman IV complexity factor | References updated. Some new references added. arXiv admin note: text
overlap with arXiv:2108.10311 | Eur. Phys. J. C 81, 889 (2021) | 10.1140/epjc/s10052-021-09695-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we construct stellar models ba-\break sed on the complexity
factor as a supplementary condition which allows to close the system of
differential equations arising from the Gravitational Decoupling. The assumed
complexity is a generalization of the one obtained from the well known Tolman
IV solution. We use Tolman IV, Wyman IIa, Durgapal IV and Heintzmann IIa as
seeds solutions. Reported compactness parameters of SMC X-1 and Cen X-3 are
used to study the physical acceptability of the models. Some aspects related to
the density ratio are also discussed.
| [
{
"created": "Tue, 19 Oct 2021 17:41:35 GMT",
"version": "v1"
}
] | 2021-10-20 | [
[
"Andrade",
"J.",
""
],
[
"Contreras",
"E.",
""
]
] | In this work, we construct stellar models ba-\break sed on the complexity factor as a supplementary condition which allows to close the system of differential equations arising from the Gravitational Decoupling. The assumed complexity is a generalization of the one obtained from the well known Tolman IV solution. We use Tolman IV, Wyman IIa, Durgapal IV and Heintzmann IIa as seeds solutions. Reported compactness parameters of SMC X-1 and Cen X-3 are used to study the physical acceptability of the models. Some aspects related to the density ratio are also discussed. |
gr-qc/0011078 | Uchida GENUrsity | Uchida Gen and Misao Sasaki | Radion on the de Sitter brane | 10 pages with no figures, typos corrected, references added, minor
changes in the text | Prog.Theor.Phys.105:591-606,2001 | 10.1143/PTP.105.591 | OU-TAP-150 UTAP-379 | gr-qc astro-ph hep-th | null | The radion on the de Sitter brane is investigated at the linear perturbation
level, using the covariant curvature tensor formalism developed by Shiromizu,
Maeda and Sasaki. It is found that if there is only one de Sitter brane with
positive tension, there is no radion and thus the ordinary Einstein gravity is
recoverd on the brane other than corrections due to the massive Kaluza-Klein
modes. As a by-product of using the covariant curvature tensor formalism, it is
immediately seen that the cosmological scalar, vector and tensor type
perturbations all have the same Kaluza-Klein spectrum. On the other hand, if
there are two branes with positive and negative tensions, the gravity on each
brane takes corrections from the radion mode in addition to the Kaluza-Klein
modes and the radion is found to have a negative mass-squared proportional to
the curvature of the de Sitter brane, in contrast to the flat brane case in
which the radion mass vanishes and degenerates with the 4-dimensional graviton
modes. To relate our result with the metric perturbation approach, we derive
the second order action for the brane displacement. We find that the radion
identified in our approach indeed corresponds to the relative displacement of
the branes in the Randall-Sundrum gauge and describes the scalar curvature
perturbations of the branes in the gaussian normal coordinates around the
branes. Implications to the inflationary brane universe are briefly discussed.
| [
{
"created": "Wed, 22 Nov 2000 12:01:07 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Dec 2000 13:51:46 GMT",
"version": "v2"
}
] | 2009-10-09 | [
[
"Gen",
"Uchida",
""
],
[
"Sasaki",
"Misao",
""
]
] | The radion on the de Sitter brane is investigated at the linear perturbation level, using the covariant curvature tensor formalism developed by Shiromizu, Maeda and Sasaki. It is found that if there is only one de Sitter brane with positive tension, there is no radion and thus the ordinary Einstein gravity is recoverd on the brane other than corrections due to the massive Kaluza-Klein modes. As a by-product of using the covariant curvature tensor formalism, it is immediately seen that the cosmological scalar, vector and tensor type perturbations all have the same Kaluza-Klein spectrum. On the other hand, if there are two branes with positive and negative tensions, the gravity on each brane takes corrections from the radion mode in addition to the Kaluza-Klein modes and the radion is found to have a negative mass-squared proportional to the curvature of the de Sitter brane, in contrast to the flat brane case in which the radion mass vanishes and degenerates with the 4-dimensional graviton modes. To relate our result with the metric perturbation approach, we derive the second order action for the brane displacement. We find that the radion identified in our approach indeed corresponds to the relative displacement of the branes in the Randall-Sundrum gauge and describes the scalar curvature perturbations of the branes in the gaussian normal coordinates around the branes. Implications to the inflationary brane universe are briefly discussed. |
2011.02860 | Grigoris Panotopoulos | Grigoris Panotopoulos and Angel Rincon | Quasinormal spectra of scale-dependent Schwarzschild-de Sitter black
holes | 10 pages, 3 tables, 3 figures, accepted for publication in Phys. Dark
Univ. arXiv admin note: substantial text overlap with arXiv:2006.11889 | Phys. Dark Univ. 31 (2021) 100743 | 10.1016/j.dark.2020.100743 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compute the quasinormal spectra for scalar, Dirac and electromagnetic
perturbations of the Schwarzschild-de Sitter geometry in the framework of
scale-dependent gravity, which is one of the current approaches to quantum
gravity. Adopting the widely used WKB semi-classical approximation, we
investigate the impact on the spectrum of the angular degree, the overtone
number as well as the scale-dependent parameter for fixed black hole mass and
cosmological constant. We summarize our numerical results in tables, and for
better visualization, we show them graphically as well. All modes are found to
be stable. Our findings show that both the real part and the absolute value of
the imaginary part of the frequencies increase with the parameter $\epsilon$
that measures the deviation from the classical geometry. Therefore, in the
framework of scale-dependent gravity the modes oscillate and decay faster in
comparison with their classical counterparts.
| [
{
"created": "Wed, 4 Nov 2020 16:24:40 GMT",
"version": "v1"
}
] | 2020-11-12 | [
[
"Panotopoulos",
"Grigoris",
""
],
[
"Rincon",
"Angel",
""
]
] | We compute the quasinormal spectra for scalar, Dirac and electromagnetic perturbations of the Schwarzschild-de Sitter geometry in the framework of scale-dependent gravity, which is one of the current approaches to quantum gravity. Adopting the widely used WKB semi-classical approximation, we investigate the impact on the spectrum of the angular degree, the overtone number as well as the scale-dependent parameter for fixed black hole mass and cosmological constant. We summarize our numerical results in tables, and for better visualization, we show them graphically as well. All modes are found to be stable. Our findings show that both the real part and the absolute value of the imaginary part of the frequencies increase with the parameter $\epsilon$ that measures the deviation from the classical geometry. Therefore, in the framework of scale-dependent gravity the modes oscillate and decay faster in comparison with their classical counterparts. |
2212.02039 | Abhishek Hegade K R | Abhishek Hegade K R, Elias R. Most, Jorge Noronha, Helvi Witek and
Nicol\'as Yunes | How Do Axisymmetric Black Holes Grow Monopole and Dipole Hair? | v2-matches published version in PRD | null | 10.1103/PhysRevD.107.104047 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the dynamical formation of scalar monopole and dipole hair in scalar
Gauss-Bonnet theory and dynamical Chern-Simons theory. We prove that the
spherically-symmetric mode of the dipole hair is completely determined by the
product of the mass of the spacetime and the value of the monopole hair. We
then show that the dynamics of the $\ell=1$ mode of the dipole hair is
intimately tied to the appearance of the event horizon during axisymmetric
collapse, which results in the radiation of certain modes that could have been
divergent in the future of the collapse. We confirm these analytical
predictions by simulating the gravitational collapse of a rapidly rotating
neutron star in the decoupling limit, both in scalar Gauss-Bonnet and dynamical
Chern-Simons theory. Our results, combined with those of Ref.~\cite{R:2022cwe},
provide a clear physical picture of the dynamics of scalar monopole and dipole
radiation in axisymmetric and spherical gravitational collapse in these
theories.
| [
{
"created": "Mon, 5 Dec 2022 05:25:16 GMT",
"version": "v1"
},
{
"created": "Tue, 27 Jun 2023 23:22:57 GMT",
"version": "v2"
}
] | 2023-07-05 | [
[
"R",
"Abhishek Hegade K",
""
],
[
"Most",
"Elias R.",
""
],
[
"Noronha",
"Jorge",
""
],
[
"Witek",
"Helvi",
""
],
[
"Yunes",
"Nicolás",
""
]
] | We study the dynamical formation of scalar monopole and dipole hair in scalar Gauss-Bonnet theory and dynamical Chern-Simons theory. We prove that the spherically-symmetric mode of the dipole hair is completely determined by the product of the mass of the spacetime and the value of the monopole hair. We then show that the dynamics of the $\ell=1$ mode of the dipole hair is intimately tied to the appearance of the event horizon during axisymmetric collapse, which results in the radiation of certain modes that could have been divergent in the future of the collapse. We confirm these analytical predictions by simulating the gravitational collapse of a rapidly rotating neutron star in the decoupling limit, both in scalar Gauss-Bonnet and dynamical Chern-Simons theory. Our results, combined with those of Ref.~\cite{R:2022cwe}, provide a clear physical picture of the dynamics of scalar monopole and dipole radiation in axisymmetric and spherical gravitational collapse in these theories. |
1910.12494 | Cosimo Bambi | Menglei Zhou, Dimitry Ayzenberg, Cosimo Bambi, Sourabh Nampalliwar | Modeling uncertainties in X-ray reflection spectroscopy measurements I:
Impact of higher order disk images | 9 pages, 5 figures. v2: refereed version | Phys. Rev. D 101, 043010 (2020) | 10.1103/PhysRevD.101.043010 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There are many simplifications in current relativistic reflection models and
this introduces systematic uncertainties in the measurement of the properties
of the source. In this paper, we study the impact of the radiation crossing the
equatorial plane between the black hole and the inner edge of the accretion
disk; that is, the radiation produced by the other side of the disk or circling
the black hole one or more times (higher order disk images). For slow-rotating
black holes with a larger plunging region, the effect is not very sensitive to
the exact inclination angle of the disk. For fast-rotating black holes with a
smaller plunging region, the effect is very weak for low inclination angles and
becomes more important as the angle increases. We simulate some observations
without and with higher order disk images and fit the data with the reflection
model RELXILL_NK to check its capability of recovering the correct input
parameters. Our results suggest that the effect of higher order disk images can
be safely ignored for observations with present and near future X-ray missions,
even for tests of the Kerr hypothesis.
| [
{
"created": "Mon, 28 Oct 2019 08:19:47 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Feb 2020 15:19:23 GMT",
"version": "v2"
}
] | 2020-02-17 | [
[
"Zhou",
"Menglei",
""
],
[
"Ayzenberg",
"Dimitry",
""
],
[
"Bambi",
"Cosimo",
""
],
[
"Nampalliwar",
"Sourabh",
""
]
] | There are many simplifications in current relativistic reflection models and this introduces systematic uncertainties in the measurement of the properties of the source. In this paper, we study the impact of the radiation crossing the equatorial plane between the black hole and the inner edge of the accretion disk; that is, the radiation produced by the other side of the disk or circling the black hole one or more times (higher order disk images). For slow-rotating black holes with a larger plunging region, the effect is not very sensitive to the exact inclination angle of the disk. For fast-rotating black holes with a smaller plunging region, the effect is very weak for low inclination angles and becomes more important as the angle increases. We simulate some observations without and with higher order disk images and fit the data with the reflection model RELXILL_NK to check its capability of recovering the correct input parameters. Our results suggest that the effect of higher order disk images can be safely ignored for observations with present and near future X-ray missions, even for tests of the Kerr hypothesis. |
2309.15246 | Giuseppe Lingetti | Giuseppe Lingetti | Numerical aspects of black hole superradiance | PhD thesis, 134 pages | null | null | null | gr-qc astro-ph.HE math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | In this work we explore a numerical technique, based on the spherical
harmonic decomposition and the discretization of the radial coordinate through
\v{C}eby\v{s}\"ev polynomial interpolation, for the computation of quasi-bound
states of linear massive scalar and vector perturbations in spinning black hole
spacetimes in General Relativity. The aim is studying black hole superradiant
instabilities, an energy-extraction mechanism triggered by the presence of
massive bosonic fields near black holes, which finds wide applications in
constraining scenarios beyond Standard Model and General Relativity. This
method does not rely on any separation ans\"atze, thus it can have wide
applications. Consequently we extend the technique so that it can be applied
also to the computation of massive tensor quasi-bound states in spinning black
holes in General Relativity, whose separability ansatz is currently unknown. We
also apply it to spinning black holes in scalar-tensor theory non-linearly
interacting with plasma, wherein the massless scalar perturbations acquires an
effective mass, finding a novel way for constraining scalar-tensor theories.
| [
{
"created": "Tue, 26 Sep 2023 20:19:20 GMT",
"version": "v1"
}
] | 2023-09-28 | [
[
"Lingetti",
"Giuseppe",
""
]
] | In this work we explore a numerical technique, based on the spherical harmonic decomposition and the discretization of the radial coordinate through \v{C}eby\v{s}\"ev polynomial interpolation, for the computation of quasi-bound states of linear massive scalar and vector perturbations in spinning black hole spacetimes in General Relativity. The aim is studying black hole superradiant instabilities, an energy-extraction mechanism triggered by the presence of massive bosonic fields near black holes, which finds wide applications in constraining scenarios beyond Standard Model and General Relativity. This method does not rely on any separation ans\"atze, thus it can have wide applications. Consequently we extend the technique so that it can be applied also to the computation of massive tensor quasi-bound states in spinning black holes in General Relativity, whose separability ansatz is currently unknown. We also apply it to spinning black holes in scalar-tensor theory non-linearly interacting with plasma, wherein the massless scalar perturbations acquires an effective mass, finding a novel way for constraining scalar-tensor theories. |
2107.09806 | Jose Wadih Maluf Dr. | F. L. Carneiro, S. C. Ulhoa and J. W. Maluf | On the Black Hole Acceleration in the C-metric Space-time | 24 pages, 4 figures. The article has been revised and simplified; two
paragraphs were added in section 5 regarding the notion and definition of
gravitational energy | Gravit. Cosmol. 28 (2022) 352-361 | 10.1134/S0202289322040077 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We consider the C-metric as a gravitational field configuration that
describes an accelerating black hole in the presence of a semi-infinite cosmic
string, along the accelerating direction. We adopt the expression for the
gravitational energy-momentum developed in the teleparallel equivalent of
general relativity (TEGR) and obtain a possible explanation for the
acceleration of the black hole. The gravitational energy enclosed by surfaces
of constant radius around the black hole is evaluated, and in particular the
energy contained within the gravitational horizon is obtained. This energy
turns out to be proportional to the square root of the area of the horizon. We
find that the gravitational energy of the semi-infinite cosmic string is
negative and dominant for large values of the radius of integration. This
negative energy may explain the acceleration of the black hole, that moves
towards regions of lower gravitational energy along the string.
| [
{
"created": "Tue, 20 Jul 2021 23:25:33 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Mar 2022 12:07:56 GMT",
"version": "v2"
},
{
"created": "Tue, 29 Nov 2022 17:52:32 GMT",
"version": "v3"
}
] | 2022-11-30 | [
[
"Carneiro",
"F. L.",
""
],
[
"Ulhoa",
"S. C.",
""
],
[
"Maluf",
"J. W.",
""
]
] | We consider the C-metric as a gravitational field configuration that describes an accelerating black hole in the presence of a semi-infinite cosmic string, along the accelerating direction. We adopt the expression for the gravitational energy-momentum developed in the teleparallel equivalent of general relativity (TEGR) and obtain a possible explanation for the acceleration of the black hole. The gravitational energy enclosed by surfaces of constant radius around the black hole is evaluated, and in particular the energy contained within the gravitational horizon is obtained. This energy turns out to be proportional to the square root of the area of the horizon. We find that the gravitational energy of the semi-infinite cosmic string is negative and dominant for large values of the radius of integration. This negative energy may explain the acceleration of the black hole, that moves towards regions of lower gravitational energy along the string. |
gr-qc/0101006 | Etesi Gabor | Gabor Etesi (YITP, Japan) | A rigidity theorem for nonvacuum initial data | This is an extended and published version: LaTex, 10 pages, no
figures | Journ. Math. Phys. 43(2) 554-562 (2002) | 10.1063/1.1421422 | null | gr-qc | null | In this note we prove a theorem on non-vacuum initial data for general
relativity. The result presents a ``rigidity phenomenon'' for the extrinsic
curvature, caused by the non-positive scalar curvature.
More precisely, we state that in the case of asymptotically flat non-vacuum
initial data if the metric has everywhere non-positive scalar curvature then
the extrinsic curvature cannot be compactly supported.
| [
{
"created": "Sun, 31 Dec 2000 07:39:23 GMT",
"version": "v1"
},
{
"created": "Sun, 14 Jan 2001 04:31:24 GMT",
"version": "v2"
},
{
"created": "Mon, 21 Jan 2002 15:39:28 GMT",
"version": "v3"
}
] | 2016-08-31 | [
[
"Etesi",
"Gabor",
"",
"YITP, Japan"
]
] | In this note we prove a theorem on non-vacuum initial data for general relativity. The result presents a ``rigidity phenomenon'' for the extrinsic curvature, caused by the non-positive scalar curvature. More precisely, we state that in the case of asymptotically flat non-vacuum initial data if the metric has everywhere non-positive scalar curvature then the extrinsic curvature cannot be compactly supported. |
2101.11764 | Yasusada Nambu | Yasusada Nambu and Yuki Osawa | Tripartite Entanglement of Hawking Radiation in Dispersive Model | 24 pages, 18 figures, version to appear in Physical Review D | Phys. Rev. D 103, 125007 (2021) | 10.1103/PhysRevD.103.125007 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate entanglement of the Hawking radiation in a dispersive model
with subluminal dispersion. In this model, feature of the Hawking radiation is
represented by three mode Bogoliubov transformation connecting the in-vacuum
state and the out-state. We obtain the exact form of the tripartite in-vacuum
state which encodes structure of multipartite entanglement. Bogoliubov
coefficients are computed by numerical calculation of the wave equation with
subluminal dispersion and it is found that genuine tripartite entanglement
persists in whole frequency range up to the cutoff arisen from the subluminal
dispersion. In the low frequency region, amount of genuine tripartite
entanglement is small compared to bipartite entanglement between the Hawking
particle and its partner mode, and the deviation from the thermal spectrum is
negligible. On the other hand, in the high frequency region near the cutoff,
entanglement is equally shared by two pairs of three modes and the partner
picture of the Hawking radiation does not hold.
| [
{
"created": "Thu, 28 Jan 2021 01:21:12 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Jun 2021 04:57:47 GMT",
"version": "v2"
}
] | 2021-06-16 | [
[
"Nambu",
"Yasusada",
""
],
[
"Osawa",
"Yuki",
""
]
] | We investigate entanglement of the Hawking radiation in a dispersive model with subluminal dispersion. In this model, feature of the Hawking radiation is represented by three mode Bogoliubov transformation connecting the in-vacuum state and the out-state. We obtain the exact form of the tripartite in-vacuum state which encodes structure of multipartite entanglement. Bogoliubov coefficients are computed by numerical calculation of the wave equation with subluminal dispersion and it is found that genuine tripartite entanglement persists in whole frequency range up to the cutoff arisen from the subluminal dispersion. In the low frequency region, amount of genuine tripartite entanglement is small compared to bipartite entanglement between the Hawking particle and its partner mode, and the deviation from the thermal spectrum is negligible. On the other hand, in the high frequency region near the cutoff, entanglement is equally shared by two pairs of three modes and the partner picture of the Hawking radiation does not hold. |
1501.03054 | Paul Frampton | Paul Howard Frampton | Cyclic Entropy: An Alternative to Inflationary Cosmology | 14 pages LaTeX. arXiv admin note: text overlap with arXiv:1411.7887 | null | 10.1142/S0217751X15501298 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We address how to construct an infinitely cyclic universe model. A major
consideration is to make the entropy cyclic which requires the entropy to be
reset to zero in each cycle expansion to turnaround, to contraction, to bounce,
etc. Here we reset entropy at the turnaround by selecting the introverse
(visible universe) from the extroverse which is generated by the accelerated
expansion. In the model, the observed homogeneity is explained by the low
entropy at the bounce, The observed flatness arises from the contraction
together with the reduction in size between the expanding and contracting
universe. The present flatness is predicted to be very precise.
| [
{
"created": "Fri, 9 Jan 2015 22:14:04 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Mar 2015 08:54:18 GMT",
"version": "v2"
}
] | 2015-08-06 | [
[
"Frampton",
"Paul Howard",
""
]
] | We address how to construct an infinitely cyclic universe model. A major consideration is to make the entropy cyclic which requires the entropy to be reset to zero in each cycle expansion to turnaround, to contraction, to bounce, etc. Here we reset entropy at the turnaround by selecting the introverse (visible universe) from the extroverse which is generated by the accelerated expansion. In the model, the observed homogeneity is explained by the low entropy at the bounce, The observed flatness arises from the contraction together with the reduction in size between the expanding and contracting universe. The present flatness is predicted to be very precise. |
2011.12058 | Sudipta Das | Manisha Banerjee, Sudipta Das, Abdulla Al Mamon, Subhajit Saha,
Kazuharu Bamba | Growth of Perturbations using Lambert$W$ Equation of State | 6 pages, 8 figures | International Journal of Geometric Methods in Modern Physics,
2150139 (2021) | 10.1142/S0219887821501395 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, a novel equation of state (EoS) parameter for dark energy has been
introduced which deals with a special mathematical function, known as the
Lambert$W$ function. In this paper, we study the effect on the growth of
perturbations for the Lambert$W$ dark energy model. We perform the analysis for
two different approaches. In the first case we consider the universe to be
filled with two different fluid components, namely, the baryonic matter
component and the Lambert$W$ dark energy component, while in the second case we
consider that there is a single fluid component in the universe whose equation
of state parameter is described by the Lambert$W$ function. We then compare the
growth rates of Lambert$W$ model with that for a standard $\Lambda$CDM model as
well as the CPL model. Our results indicate that the presence of Lambert$W$
dynamical dark energy sector changes the growth rate and affects the matter
fluctuations in the universe to a great extent.
| [
{
"created": "Tue, 24 Nov 2020 12:21:07 GMT",
"version": "v1"
}
] | 2021-06-11 | [
[
"Banerjee",
"Manisha",
""
],
[
"Das",
"Sudipta",
""
],
[
"Mamon",
"Abdulla Al",
""
],
[
"Saha",
"Subhajit",
""
],
[
"Bamba",
"Kazuharu",
""
]
] | Recently, a novel equation of state (EoS) parameter for dark energy has been introduced which deals with a special mathematical function, known as the Lambert$W$ function. In this paper, we study the effect on the growth of perturbations for the Lambert$W$ dark energy model. We perform the analysis for two different approaches. In the first case we consider the universe to be filled with two different fluid components, namely, the baryonic matter component and the Lambert$W$ dark energy component, while in the second case we consider that there is a single fluid component in the universe whose equation of state parameter is described by the Lambert$W$ function. We then compare the growth rates of Lambert$W$ model with that for a standard $\Lambda$CDM model as well as the CPL model. Our results indicate that the presence of Lambert$W$ dynamical dark energy sector changes the growth rate and affects the matter fluctuations in the universe to a great extent. |
2203.03861 | Dr. Sudhaker Upadhyay | Dharm Veer Singh, Benoy Kumar Singh and Sudhaker Upadhyay | $4D$ AdS Einstein-Gauss-Bonnet black hole with Yang-Mills field and its
thermodynamics | 13 pages, 12 captioned figures, published in Annals of Physics | Annals of Physics 434 (2021) 168642 | 10.1016/j.aop.2021.168642 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We derive an exact black hole solution for the Einstein-Gauss-Bonnet gravity
with Yang-Mills field in $4D$ AdS spacetime and investigate its thermodynamic
properties to calculate exact expressions for the black hole mass, temperature,
entropy and heat capacity. The thermodynamic quantities get modification in the
presence of Yang-Mills field, however, entropy remains unaffected by the
Yang-Mills charge. The solution exhibits $P-v$ criticality and belongs to the
universality class of Van der Waals fluid. We study the effect of Gauss-Bonnet
coupling and Yang-Mills charge on the critical behaviour and black hole phase
transition. We observe that the values of critical exponents increase with the
Yang-Mills charge and decrease with the Gauss-Bonnet coupling constant.
| [
{
"created": "Tue, 8 Mar 2022 05:38:21 GMT",
"version": "v1"
}
] | 2022-03-09 | [
[
"Singh",
"Dharm Veer",
""
],
[
"Singh",
"Benoy Kumar",
""
],
[
"Upadhyay",
"Sudhaker",
""
]
] | We derive an exact black hole solution for the Einstein-Gauss-Bonnet gravity with Yang-Mills field in $4D$ AdS spacetime and investigate its thermodynamic properties to calculate exact expressions for the black hole mass, temperature, entropy and heat capacity. The thermodynamic quantities get modification in the presence of Yang-Mills field, however, entropy remains unaffected by the Yang-Mills charge. The solution exhibits $P-v$ criticality and belongs to the universality class of Van der Waals fluid. We study the effect of Gauss-Bonnet coupling and Yang-Mills charge on the critical behaviour and black hole phase transition. We observe that the values of critical exponents increase with the Yang-Mills charge and decrease with the Gauss-Bonnet coupling constant. |
gr-qc/0012106 | A. K. Guts | Alexander K. Guts, Marina S. Shapovalova | Large fluctuations of time and change of space-time signature | 5 pages, 3 figures, LaTeX, talk given at the International
School-Seminar "Problems of Theoretical Cosmology", Ulyanovsk, 2000 | Grav.Cosmol. 7 (2001) 193-196 | null | null | gr-qc | null | We consider five-dimensional cylindric spacetime $V^5$ with foliation of
codimension ~1. The leaves of this foliation are four-dimensional
"parallel" universes. The metric of five-dimensional spacetime and induced
metrics of four-dimensional universes are flat. The "large" fluctuations of the
5-metric are studied. These fluctuations depend only on the coordinate $x^0$,
and under these fluctuations the curvature of $V^5$ is not zero. The
contribution of the fluctuations in the Feynman path integral over
five-dimensional trajectories doesn't change the amplitude of the probability
of the real physical four-dimensional universe. Moreover the large fluctuations
of 5-metric $G_{AB}$ are large fluctuations for physical four-dimensional
universe $V^4$ and change signature of $V^4$. The change of the signature from
$<+--->$ to $<---->$ and inversely occurs in the all 3-dimensional space
simultaneously (in absolute time) and can take arbitrarily large period of
time.
| [
{
"created": "Thu, 28 Dec 2000 19:31:11 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Guts",
"Alexander K.",
""
],
[
"Shapovalova",
"Marina S.",
""
]
] | We consider five-dimensional cylindric spacetime $V^5$ with foliation of codimension ~1. The leaves of this foliation are four-dimensional "parallel" universes. The metric of five-dimensional spacetime and induced metrics of four-dimensional universes are flat. The "large" fluctuations of the 5-metric are studied. These fluctuations depend only on the coordinate $x^0$, and under these fluctuations the curvature of $V^5$ is not zero. The contribution of the fluctuations in the Feynman path integral over five-dimensional trajectories doesn't change the amplitude of the probability of the real physical four-dimensional universe. Moreover the large fluctuations of 5-metric $G_{AB}$ are large fluctuations for physical four-dimensional universe $V^4$ and change signature of $V^4$. The change of the signature from $<+--->$ to $<---->$ and inversely occurs in the all 3-dimensional space simultaneously (in absolute time) and can take arbitrarily large period of time. |
2007.09714 | Leah Jenks | Leah Jenks, Kent Yagi, Stephon Alexander | Probing Noncommutative Gravity with Gravitational Wave and Binary Pulsar
Observations | 9 pages, 5 figures | Phys. Rev. D 102, 084022 (2020) | 10.1103/PhysRevD.102.084022 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Noncommutative gravity is a natural method of quantizing spacetime by
promoting the spacetime coordinates themselves to operators which do not
commute. This approach is motivated, for example, from a quantum gravity
perspective, among others. Noncommutative gravity has been tested against the
binary black hole merger event GW150914. Here, we extend and improve upon such
a previous analysis by (i) relaxing an assumption made on the preferred
direction due to noncommutativity, (ii) using posterior samples produced by the
LIGO/Virgo Collaborations, (iii) consider other gravitational wave events,
namely GW151226, GW170608, GW170814 and GW170817, and (iv) consider binary
pulsar observations. Using Kepler's law that contains the noncommutative effect
at second post-Newtonian order, we derive corrections to the gravitational
waveform phase and the pericenter precession. Using the gravitational wave and
double pulsar binary observations, we find bounds on a space-time
noncommutative tensor $\theta^{0i}$ in terms of the preferred frame direction
with respect to the orientation of each binary. We find that the gravitational
wave bounds are stronger than the binary pulsar one by an order of magnitude
and the noncommutative tensor normalized by the Planck length and time is
constrained to be of order unity.
| [
{
"created": "Sun, 19 Jul 2020 16:51:45 GMT",
"version": "v1"
}
] | 2020-10-14 | [
[
"Jenks",
"Leah",
""
],
[
"Yagi",
"Kent",
""
],
[
"Alexander",
"Stephon",
""
]
] | Noncommutative gravity is a natural method of quantizing spacetime by promoting the spacetime coordinates themselves to operators which do not commute. This approach is motivated, for example, from a quantum gravity perspective, among others. Noncommutative gravity has been tested against the binary black hole merger event GW150914. Here, we extend and improve upon such a previous analysis by (i) relaxing an assumption made on the preferred direction due to noncommutativity, (ii) using posterior samples produced by the LIGO/Virgo Collaborations, (iii) consider other gravitational wave events, namely GW151226, GW170608, GW170814 and GW170817, and (iv) consider binary pulsar observations. Using Kepler's law that contains the noncommutative effect at second post-Newtonian order, we derive corrections to the gravitational waveform phase and the pericenter precession. Using the gravitational wave and double pulsar binary observations, we find bounds on a space-time noncommutative tensor $\theta^{0i}$ in terms of the preferred frame direction with respect to the orientation of each binary. We find that the gravitational wave bounds are stronger than the binary pulsar one by an order of magnitude and the noncommutative tensor normalized by the Planck length and time is constrained to be of order unity. |
2101.07673 | Saeed Ullah Khan | Muhammad Zahid, Saeed Ullah Khan, Jingli Ren | Shadow cast and center of mass energy in a charged Gauss-Bonnet-AdS
black hole | 13 Pages, 9 Figures | null | 10.1016/j.cjph.2021.05.003 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This work is devoted to the exploration of shadow cast and center of mass
energy in the background of a 4-dimensional charged Gauss-Bonnet AdS black
hole. On investigating particle dynamics, we have examined BH's metric
function. Whereas, with the help of null geodesics, we pursue to calculate the
celestial coordinates and the shadow radius of the black hole. We have made use
of the hawking temperature to study the energy emission rate. Moreover, we have
explored the center of mass energy and discussed its characteristics under the
influence of spacetime parameters. For a better understanding, we graphically
represent all of our main findings. The acquired result shows that both charge
and AdS radius ($l$) decrease the shadow radius, while the Gauss-Bonnet
coupling parameter $\alpha$ increases the shadow radius in AdS spacetime. On
the other hand, both $Q$ and $\alpha$ result in diminishing the shadow radius
in asymptotically flat spacetime. Finally, we investigate the energy emission
rate and center of mass energy under the influence of $Q$ and $\alpha$.
| [
{
"created": "Mon, 18 Jan 2021 17:17:56 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Jan 2021 16:48:57 GMT",
"version": "v2"
}
] | 2021-07-07 | [
[
"Zahid",
"Muhammad",
""
],
[
"Khan",
"Saeed Ullah",
""
],
[
"Ren",
"Jingli",
""
]
] | This work is devoted to the exploration of shadow cast and center of mass energy in the background of a 4-dimensional charged Gauss-Bonnet AdS black hole. On investigating particle dynamics, we have examined BH's metric function. Whereas, with the help of null geodesics, we pursue to calculate the celestial coordinates and the shadow radius of the black hole. We have made use of the hawking temperature to study the energy emission rate. Moreover, we have explored the center of mass energy and discussed its characteristics under the influence of spacetime parameters. For a better understanding, we graphically represent all of our main findings. The acquired result shows that both charge and AdS radius ($l$) decrease the shadow radius, while the Gauss-Bonnet coupling parameter $\alpha$ increases the shadow radius in AdS spacetime. On the other hand, both $Q$ and $\alpha$ result in diminishing the shadow radius in asymptotically flat spacetime. Finally, we investigate the energy emission rate and center of mass energy under the influence of $Q$ and $\alpha$. |
gr-qc/0310069 | Yuri Obukhov | Yuri N. Obukhov | New solutions in 3D gravity | Revtex, 21 pages, no figures | Phys.Rev. D68 (2003) 124015 | 10.1103/PhysRevD.68.124015 | null | gr-qc hep-th | null | We study gravitational theory in 1+2 spacetime dimensions which is determined
by the Lagrangian constructed as a sum of the Einstein-Hilbert term plus the
two (translational and rotational) gravitational Chern-Simons terms. When the
corresponding coupling constants vanish, we are left with the purely Einstein
theory of gravity. We obtain new exact solutions for the gravitational field
equations with the nontrivial material sources. Special attention is paid to
plane-fronted gravitational waves (in case of the Maxwell field source) and to
the circularly symmetric as well as the anisotropic cosmological solutions
which arise for the ideal fluid matter source.
| [
{
"created": "Tue, 14 Oct 2003 10:30:40 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Obukhov",
"Yuri N.",
""
]
] | We study gravitational theory in 1+2 spacetime dimensions which is determined by the Lagrangian constructed as a sum of the Einstein-Hilbert term plus the two (translational and rotational) gravitational Chern-Simons terms. When the corresponding coupling constants vanish, we are left with the purely Einstein theory of gravity. We obtain new exact solutions for the gravitational field equations with the nontrivial material sources. Special attention is paid to plane-fronted gravitational waves (in case of the Maxwell field source) and to the circularly symmetric as well as the anisotropic cosmological solutions which arise for the ideal fluid matter source. |
2303.14574 | Jean-Philippe Nicolas | Jack Borthwick, Eric Gourgoulhon, Jean-Philippe Nicolas | Peeling at extreme black hole horizons | 33 pages, 3 figures | null | null | null | gr-qc math-ph math.AP math.MP | http://creativecommons.org/licenses/by/4.0/ | The starting point of this work was an intriguing similarity between the
behaviour of fields near a degenerate horizon and near the infinity of an
asymptotically flat spacetime, as revealed by the scattering theory for Dirac
fields in the ``exterior'' region of the extreme Kerr - de Sitter black hole,
developed by one of the authors (JB). However, in that situation, the
comparison was somewhat clouded by some of the analytical techniques used in
intermediate steps of the proof. The aim of the present work is to clarify the
comparison further by studying instead the peeling behaviour of solutions to
the wave equation at an extremal horizon. We focus first on the extreme
Reissner-Nordstr\"om black hole, for which the Couch-Torrence inversion (a
global conformal isometry that exchanges the horizon and infinity) makes the
analogy explicit. Then, we explore more general spherically symmetric
situations using the Couch-Torrence inversion outside of its natural context.
| [
{
"created": "Sat, 25 Mar 2023 22:09:36 GMT",
"version": "v1"
}
] | 2023-03-28 | [
[
"Borthwick",
"Jack",
""
],
[
"Gourgoulhon",
"Eric",
""
],
[
"Nicolas",
"Jean-Philippe",
""
]
] | The starting point of this work was an intriguing similarity between the behaviour of fields near a degenerate horizon and near the infinity of an asymptotically flat spacetime, as revealed by the scattering theory for Dirac fields in the ``exterior'' region of the extreme Kerr - de Sitter black hole, developed by one of the authors (JB). However, in that situation, the comparison was somewhat clouded by some of the analytical techniques used in intermediate steps of the proof. The aim of the present work is to clarify the comparison further by studying instead the peeling behaviour of solutions to the wave equation at an extremal horizon. We focus first on the extreme Reissner-Nordstr\"om black hole, for which the Couch-Torrence inversion (a global conformal isometry that exchanges the horizon and infinity) makes the analogy explicit. Then, we explore more general spherically symmetric situations using the Couch-Torrence inversion outside of its natural context. |
gr-qc/0211071 | Joshua T. Horwood | C. G. Hewitt, J. T. Horwood, J. Wainwright | Asymptotic dynamics of the exceptional Bianchi cosmologies | 15 pages, 6 figures, submitted to Class. Quantum Grav | Class.Quant.Grav. 20 (2003) 1743-1756 | 10.1088/0264-9381/20/9/311 | null | gr-qc | null | In this paper we give, for the first time, a qualitative description of the
asymptotic dynamics of a class of non-tilted spatially homogeneous (SH)
cosmologies, the so-called exceptional Bianchi cosmologies, which are of
Bianchi type VI$_{-1/9}$. This class is of interest for two reasons. Firstly,
it is generic within the class of non-tilted SH cosmologies, being of the same
generality as the models of Bianchi types VIII and IX. Secondly, it is the SH
limit of a generic class of spatially inhomogeneous $G_{2}$ cosmologies.
Using the orthonormal frame formalism and Hubble-normalized variables, we
show that the exceptional Bianchi cosmologies differ from the non-exceptional
Bianchi cosmologies of type VI$_{h}$ in two significant ways. Firstly, the
models exhibit an oscillatory approach to the initial singularity and hence are
not asymptotically self-similar. Secondly, at late times, although the models
are asymptotically self-similar, the future attractor for the vacuum-dominated
models is the so-called Robinson-Trautman SH model instead of the vacuum SH
plane wave models.
| [
{
"created": "Thu, 21 Nov 2002 18:53:49 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Hewitt",
"C. G.",
""
],
[
"Horwood",
"J. T.",
""
],
[
"Wainwright",
"J.",
""
]
] | In this paper we give, for the first time, a qualitative description of the asymptotic dynamics of a class of non-tilted spatially homogeneous (SH) cosmologies, the so-called exceptional Bianchi cosmologies, which are of Bianchi type VI$_{-1/9}$. This class is of interest for two reasons. Firstly, it is generic within the class of non-tilted SH cosmologies, being of the same generality as the models of Bianchi types VIII and IX. Secondly, it is the SH limit of a generic class of spatially inhomogeneous $G_{2}$ cosmologies. Using the orthonormal frame formalism and Hubble-normalized variables, we show that the exceptional Bianchi cosmologies differ from the non-exceptional Bianchi cosmologies of type VI$_{h}$ in two significant ways. Firstly, the models exhibit an oscillatory approach to the initial singularity and hence are not asymptotically self-similar. Secondly, at late times, although the models are asymptotically self-similar, the future attractor for the vacuum-dominated models is the so-called Robinson-Trautman SH model instead of the vacuum SH plane wave models. |
gr-qc/0012072 | Julio Cesar Fabris | A.B. Batista, J.C. Fabris, S.V.B. Goncalves and J. Tossa | Qualitative analysis of a scalar-tensor theory with exponential
potential | Latex file, 9 pages, 1 figure | Int.J.Mod.Phys. A16 (2001) 4527-4542 | 10.1142/S0217751X0100533X | null | gr-qc | null | A qualitative analysis of a scalar-tensor cosmological model, with an
exponential potential for the scalar field, is performed. The phase diagram for
the flat case is constructed. It is shown that solutions with an initial and
final inflationary behaviour appear. The conditions for which the scenario
favored by supernova type Ia observations becomes an attractor in the space of
the solutions are established.
| [
{
"created": "Tue, 19 Dec 2000 20:17:54 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Batista",
"A. B.",
""
],
[
"Fabris",
"J. C.",
""
],
[
"Goncalves",
"S. V. B.",
""
],
[
"Tossa",
"J.",
""
]
] | A qualitative analysis of a scalar-tensor cosmological model, with an exponential potential for the scalar field, is performed. The phase diagram for the flat case is constructed. It is shown that solutions with an initial and final inflationary behaviour appear. The conditions for which the scenario favored by supernova type Ia observations becomes an attractor in the space of the solutions are established. |
1605.00862 | Ugur Camci | U. Camci, A. Yildirim | Noether gauge symmetry classes for pp-wave spacetimes | 30 pages, 5 tables | Int. J. Geo. Meth. Mod. Phys., vol.12, pp.1550120 (2015) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Noether gauge symmetries of geodesic Lagrangian for the pp-wave
spacetimes are determined in each of the Noether gauge symmetry classes of the
pp-wave spacetimes. It is shown that a type N pp-wave spacetime can admit at
most three Noether gauge symmetry, and furthermore the number of Noether gauge
symmetries turn out to be four, five, six, seven and eight. We found that all
conformally flat plane wave spacetimes admit the maximal, i.e. ten, Noether
gauge symmetry. Also it is found that if the pp-wave spacetime is
non-conformally flat plane wave, then the number of Noether gauge symmetry is
nine or ten. By means of the obtained Noether constants the search of the exact
solutions of the geodesic equations for the pp-wave spacetimes is considered
and we found new exact solutions of the geodesic equations in some special
Noether gauge symmetry classes.
| [
{
"created": "Tue, 3 May 2016 12:20:45 GMT",
"version": "v1"
}
] | 2016-05-04 | [
[
"Camci",
"U.",
""
],
[
"Yildirim",
"A.",
""
]
] | The Noether gauge symmetries of geodesic Lagrangian for the pp-wave spacetimes are determined in each of the Noether gauge symmetry classes of the pp-wave spacetimes. It is shown that a type N pp-wave spacetime can admit at most three Noether gauge symmetry, and furthermore the number of Noether gauge symmetries turn out to be four, five, six, seven and eight. We found that all conformally flat plane wave spacetimes admit the maximal, i.e. ten, Noether gauge symmetry. Also it is found that if the pp-wave spacetime is non-conformally flat plane wave, then the number of Noether gauge symmetry is nine or ten. By means of the obtained Noether constants the search of the exact solutions of the geodesic equations for the pp-wave spacetimes is considered and we found new exact solutions of the geodesic equations in some special Noether gauge symmetry classes. |
gr-qc/0302101 | Raul Vera | Ruth Lazkoz, Jos\'e M.M. Senovilla, Ra\"ul Vera | Conserved superenergy currents | LaTeX, 19 pages; improved version adding new content to the second
section and some minor corrections | Class.Quant.Grav. 20 (2003) 4135-4152 | 10.1088/0264-9381/20/19/301 | null | gr-qc | null | We exploit once again the analogy between the energy-momentum tensor and the
so-called ``superenergy'' tensors in order to build conserved currents in the
presence of Killing vectors. First of all, we derive the divergence-free
property of the gravitational superenergy currents under very general
circumstances, even if the superenergy tensor is not divergence-free itself.
The associated conserved quantities are explicitly computed for the
Reissner-Nordstrom and Schwarzschild solutions. The remaining cases, when the
above currents are not conserved, lead to the possibility of an interchange of
some superenergy quantities between the gravitational and other physical fields
in such a manner that the total, mixed, current may be conserved. Actually,
this possibility has been recently proved to hold for the Einstein-Klein-Gordon
system of field equations. By using an adequate family of known exact
solutions, we present explicit and completely non-obvious examples of such
mixed conserved currents.
| [
{
"created": "Tue, 25 Feb 2003 19:05:22 GMT",
"version": "v1"
},
{
"created": "Tue, 15 Apr 2003 10:17:52 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Lazkoz",
"Ruth",
""
],
[
"Senovilla",
"José M. M.",
""
],
[
"Vera",
"Raül",
""
]
] | We exploit once again the analogy between the energy-momentum tensor and the so-called ``superenergy'' tensors in order to build conserved currents in the presence of Killing vectors. First of all, we derive the divergence-free property of the gravitational superenergy currents under very general circumstances, even if the superenergy tensor is not divergence-free itself. The associated conserved quantities are explicitly computed for the Reissner-Nordstrom and Schwarzschild solutions. The remaining cases, when the above currents are not conserved, lead to the possibility of an interchange of some superenergy quantities between the gravitational and other physical fields in such a manner that the total, mixed, current may be conserved. Actually, this possibility has been recently proved to hold for the Einstein-Klein-Gordon system of field equations. By using an adequate family of known exact solutions, we present explicit and completely non-obvious examples of such mixed conserved currents. |
gr-qc/0601060 | Muhammad Sharif | M. Sharif and Tasnim Fatima | Energy Distribution associated with Static Axisymmetric Solutions | 18 pages, accepted for publication in Astrophysics and SpaceScience | Astrophys.Space Sci. 302 (2006) 217-224 | 10.1007/s10509-006-9037-8 | null | gr-qc | null | This paper has been addressed to a very old but burning problem of energy in
General Relativity. We evaluate energy and momentum densities for the static
and axisymmetric solutions. This specializes to two metrics, i.e., Erez-Rosen
and the gamma metrics, belonging to the Weyl class. We apply four well-known
prescriptions of Einstein, Landau-Lifshitz, Papaterou and M$\ddot{o}$ller to
compute energy-momentum density components. We obtain that these prescriptions
do not provide similar energy density, however momentum becomes constant in
each case. The results can be matched under particular boundary conditions.
| [
{
"created": "Mon, 16 Jan 2006 11:55:16 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Sharif",
"M.",
""
],
[
"Fatima",
"Tasnim",
""
]
] | This paper has been addressed to a very old but burning problem of energy in General Relativity. We evaluate energy and momentum densities for the static and axisymmetric solutions. This specializes to two metrics, i.e., Erez-Rosen and the gamma metrics, belonging to the Weyl class. We apply four well-known prescriptions of Einstein, Landau-Lifshitz, Papaterou and M$\ddot{o}$ller to compute energy-momentum density components. We obtain that these prescriptions do not provide similar energy density, however momentum becomes constant in each case. The results can be matched under particular boundary conditions. |
gr-qc/0006020 | Edward N. Glass | E.N. Glass and J.P. Krisch (Department of Physics, University of
Michigan, Ann Arbor, Michgan) | Fractal Scales in a Schwarzschild Atmosphere | to appear in Class. Quantum Grav | Class.Quant.Grav. 17 (2000) 2611-2620 | 10.1088/0264-9381/17/14/301 | null | gr-qc | null | Recently, Glass and Krisch have extended the Vaidya radiating metric to
include both a radiation fluid and a string fluid [1999 Class. Quantum Grav.
vol 16, 1175]. Mass diffusion in the extended Schwarzschild atmosphere was
studied. The continuous solutions of classical diffusive transport are believed
to describe the envelope of underlying fractal behavior. In this work we
examine the classical picture at scales on which fractal behavior might be
evident.
| [
{
"created": "Tue, 6 Jun 2000 16:39:18 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Glass",
"E. N.",
"",
"Department of Physics, University of\n Michigan, Ann Arbor, Michgan"
],
[
"Krisch",
"J. P.",
"",
"Department of Physics, University of\n Michigan, Ann Arbor, Michgan"
]
] | Recently, Glass and Krisch have extended the Vaidya radiating metric to include both a radiation fluid and a string fluid [1999 Class. Quantum Grav. vol 16, 1175]. Mass diffusion in the extended Schwarzschild atmosphere was studied. The continuous solutions of classical diffusive transport are believed to describe the envelope of underlying fractal behavior. In this work we examine the classical picture at scales on which fractal behavior might be evident. |
1006.3759 | Neil J. Cornish | Joey Shapiro Key and Neil J. Cornish | Characterizing Spinning Black Hole Binaries in Eccentric Orbits with
LISA | 11 pages, 13 figures, references, text and figures updated | Phys.Rev.D83:083001,2011 | 10.1103/PhysRevD.83.083001 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Laser Interferometer Space Antenna (LISA) is designed to detect
gravitational wave signals from astrophysical sources, including those from
coalescing binary systems of compact objects such as black holes. Colliding
galaxies have central black holes that sink to the center of the merged galaxy
and begin to orbit one another and emit gravitational waves. Some galaxy
evolution models predict that the binary black hole system will enter the LISA
band with significant orbital eccentricity, while other models suggest that the
orbits will already have circularized. Using a full seventeen parameter
waveform model that includes the effects of orbital eccentricity, spin
precession and higher harmonics, we investigate how well the source parameters
can be inferred from simulated LISA data. Defining the reference eccentricity
as the value one year before merger, we find that for typical LISA sources, it
will be possible to measure the eccentricity to an accuracy of parts in a
thousand. The accuracy with which the eccentricity can be measured depends only
very weakly on the eccentricity, making it possible to distinguish circular
orbits from those with very small eccentricities. LISA measurements of the
orbital eccentricity can help constraints theories of galaxy mergers in the
early universe. Failing to account for the eccentricity in the waveform
modeling can lead to a loss of signal power and bias the estimation of
parameters such as the black hole masses and spins.
| [
{
"created": "Fri, 18 Jun 2010 17:45:43 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Aug 2010 20:56:16 GMT",
"version": "v2"
},
{
"created": "Sat, 12 Feb 2011 14:35:45 GMT",
"version": "v3"
}
] | 2011-04-22 | [
[
"Key",
"Joey Shapiro",
""
],
[
"Cornish",
"Neil J.",
""
]
] | The Laser Interferometer Space Antenna (LISA) is designed to detect gravitational wave signals from astrophysical sources, including those from coalescing binary systems of compact objects such as black holes. Colliding galaxies have central black holes that sink to the center of the merged galaxy and begin to orbit one another and emit gravitational waves. Some galaxy evolution models predict that the binary black hole system will enter the LISA band with significant orbital eccentricity, while other models suggest that the orbits will already have circularized. Using a full seventeen parameter waveform model that includes the effects of orbital eccentricity, spin precession and higher harmonics, we investigate how well the source parameters can be inferred from simulated LISA data. Defining the reference eccentricity as the value one year before merger, we find that for typical LISA sources, it will be possible to measure the eccentricity to an accuracy of parts in a thousand. The accuracy with which the eccentricity can be measured depends only very weakly on the eccentricity, making it possible to distinguish circular orbits from those with very small eccentricities. LISA measurements of the orbital eccentricity can help constraints theories of galaxy mergers in the early universe. Failing to account for the eccentricity in the waveform modeling can lead to a loss of signal power and bias the estimation of parameters such as the black hole masses and spins. |
1803.06346 | Tyler Knowles | Tyler D. Knowles, Caleb Devine, David A. Buch, Serdar A. Bilgili,
Thomas R. Adams, Zachariah B. Etienne, Sean T. McWilliams | Improving performance of SEOBNRv3 by $\sim$300x | 16 pages, 1 figure, 9 tables; updated to clarify science background
and fix typos | Knowles et al 2018 Class. Quantum Grav.
https://doi.org/10.1088/1361-6382/aacb8c | 10.1088/1361-6382/aacb8c | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | When a gravitational wave is detected by Advanced LIGO/Virgo, sophisticated
parameter estimation (PE) pipelines spring into action. These pipelines
leverage approximants to generate large numbers of theoretical gravitational
waveform predictions to characterize the detected signal. One of the most
accurate and physically comprehensive classes of approximants in wide use is
the "Spinning Effective One Body--Numerical Relativity" (SEOBNR) family.
Waveform generation with these approximants can be computationally expensive,
which has limited their usefulness in multiple data analysis contexts. In prior
work we improved the performance of the aligned-spin approximant SEOBNR version
2 (v2) by nearly 300x. In this work we focus on optimizing the full
eight-dimensional, precessing approximant SEOBNR version 3 (v3). While several
v2 optimizations were implemented during its development, v3 is far too slow
for use in state-of-the-art source characterization efforts for long-inspiral
detections. Completion of a PE run after such a detection could take centuries
to complete using v3. Here we develop and implement a host of optimizations for
v3, calling the optimized approximant v3_Opt. Our optimized approximant is
about 340x faster than v3, and generates waveforms that are numerically
indistinguishable.
| [
{
"created": "Fri, 16 Mar 2018 18:00:00 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Jul 2018 14:10:40 GMT",
"version": "v2"
}
] | 2018-07-03 | [
[
"Knowles",
"Tyler D.",
""
],
[
"Devine",
"Caleb",
""
],
[
"Buch",
"David A.",
""
],
[
"Bilgili",
"Serdar A.",
""
],
[
"Adams",
"Thomas R.",
""
],
[
"Etienne",
"Zachariah B.",
""
],
[
"McWilliams",
"Sean T.",
""
]
] | When a gravitational wave is detected by Advanced LIGO/Virgo, sophisticated parameter estimation (PE) pipelines spring into action. These pipelines leverage approximants to generate large numbers of theoretical gravitational waveform predictions to characterize the detected signal. One of the most accurate and physically comprehensive classes of approximants in wide use is the "Spinning Effective One Body--Numerical Relativity" (SEOBNR) family. Waveform generation with these approximants can be computationally expensive, which has limited their usefulness in multiple data analysis contexts. In prior work we improved the performance of the aligned-spin approximant SEOBNR version 2 (v2) by nearly 300x. In this work we focus on optimizing the full eight-dimensional, precessing approximant SEOBNR version 3 (v3). While several v2 optimizations were implemented during its development, v3 is far too slow for use in state-of-the-art source characterization efforts for long-inspiral detections. Completion of a PE run after such a detection could take centuries to complete using v3. Here we develop and implement a host of optimizations for v3, calling the optimized approximant v3_Opt. Our optimized approximant is about 340x faster than v3, and generates waveforms that are numerically indistinguishable. |
1007.4612 | Ujjal Debnath | Ujjal Debnath | Thermodynamics in Quasi-Spherical Szekeres Space-Time | 8 pages | Europhys.Lett.94:29001,2011 | 10.1209/0295-5075/94/29001 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We have considered that the universe is the inhomogeneous $(n+2)$ dimensional
quasi-spherical Szekeres space-time model. We consider the universe as a
thermodynamical system with the horizon surface as a boundary of the system. To
study the generalized second law (GSL) of thermodynamics through the universe,
we have assumed the trapped surface is the apparent horizon. Next we have
examined the validity of the generalized second law of thermodynamics (GSL) on
the apparent horizon by two approaches: (i) using first law of thermodynamics
on the apparent horizon and (ii) without using the first law. In the first
approach, the horizon entropy have been calculated by the first law. In the
second approach, first we have calculated the surface gravity and temperature
on the apparent horizon and then horizon entropy have found from area formula.
The variation of internal entropy have been found by Gibb's law. Using these
two approaches separately, we find the conditions for validity of GSL in
$(n+2)$ dimensional quasi-spherical Szekeres model.
| [
{
"created": "Tue, 27 Jul 2010 03:49:08 GMT",
"version": "v1"
}
] | 2011-04-20 | [
[
"Debnath",
"Ujjal",
""
]
] | We have considered that the universe is the inhomogeneous $(n+2)$ dimensional quasi-spherical Szekeres space-time model. We consider the universe as a thermodynamical system with the horizon surface as a boundary of the system. To study the generalized second law (GSL) of thermodynamics through the universe, we have assumed the trapped surface is the apparent horizon. Next we have examined the validity of the generalized second law of thermodynamics (GSL) on the apparent horizon by two approaches: (i) using first law of thermodynamics on the apparent horizon and (ii) without using the first law. In the first approach, the horizon entropy have been calculated by the first law. In the second approach, first we have calculated the surface gravity and temperature on the apparent horizon and then horizon entropy have found from area formula. The variation of internal entropy have been found by Gibb's law. Using these two approaches separately, we find the conditions for validity of GSL in $(n+2)$ dimensional quasi-spherical Szekeres model. |
gr-qc/0112030 | Hwei-Jang Yo | H.J. Yo and J.M. Nester | Hamiltonian Analysis of Poincar\'e Gauge Theory: Higher Spin Modes | 30 pages, submitted to Int. J. Mod. Phys. D | Int.J.Mod.Phys. D11 (2002) 747-780 | 10.1142/S0218271802001998 | null | gr-qc | null | We examine several higher spin modes of the Poincar\'e gauge theory (PGT) of
gravity using the Hamiltonian analysis. The appearance of certain undesirable
effects due to non-linear constraints in the Hamiltonian analysis are used as a
test. We find that the phenomena of field activation and constraint bifurcation
both exist in the pure spin 1 and the pure spin 2 modes. The coupled spin-$0^-$
and spin-$2^-$ modes also fail our test due to the appearance of constraint
bifurcation. The ``promising'' case in the linearized theory of PGT given by
Kuhfuss and Nitsch (KRNJ86) likewise does not pass. From this analysis of these
specific PGT modes we conclude that an examination of such nonlinear constraint
effects shows great promise as a strong test for this and other alternate
theories of gravity.
| [
{
"created": "Fri, 14 Dec 2001 07:13:31 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Yo",
"H. J.",
""
],
[
"Nester",
"J. M.",
""
]
] | We examine several higher spin modes of the Poincar\'e gauge theory (PGT) of gravity using the Hamiltonian analysis. The appearance of certain undesirable effects due to non-linear constraints in the Hamiltonian analysis are used as a test. We find that the phenomena of field activation and constraint bifurcation both exist in the pure spin 1 and the pure spin 2 modes. The coupled spin-$0^-$ and spin-$2^-$ modes also fail our test due to the appearance of constraint bifurcation. The ``promising'' case in the linearized theory of PGT given by Kuhfuss and Nitsch (KRNJ86) likewise does not pass. From this analysis of these specific PGT modes we conclude that an examination of such nonlinear constraint effects shows great promise as a strong test for this and other alternate theories of gravity. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.