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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1904.09989 | Hiroki Takeda | Hiroki Takeda, Atsushi Nishizawa, Koji Nagano, Yuta Michimura, Kentaro
Komori, Masaki Ando, and Kazuhiro Hayama | Prospects for gravitational-wave polarization test from compact binary
mergers with future ground-based detectors | 12 pages, 4 figures | Phys. Rev. D 100, 042001 (2019) | 10.1103/PhysRevD.100.042001 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There exist six possible polarization modes of gravitational waves in general
metric theory of gravity, while two tensor polarization modes are allowed in
general relativity. The properties and number of polarization modes depend on
gravity theories. The number of the detectors needs to be equal to the number
of the polarization modes of the gravitational waves for separation of
polarizations basically. However, a single detector having great sensitivity at
lower frequency could be effectively regarded as a virtual detector network
including a set of detectors along its trajectory due to a long GW signal from
a compact binary and the Earth's rotation. Thus, time-varying antenna pattern
functions can help testing the polarizations of gravitational waves. We study
the effects of the Earth's rotation on the polarization test and show a
possibility to test the non-tensorial polarization modes from future
observations of compact binary mergers with ground-based gravitational
detectors such as Einstein telescope and Cosmic Explorer.
| [
{
"created": "Mon, 22 Apr 2019 18:00:00 GMT",
"version": "v1"
}
] | 2019-08-28 | [
[
"Takeda",
"Hiroki",
""
],
[
"Nishizawa",
"Atsushi",
""
],
[
"Nagano",
"Koji",
""
],
[
"Michimura",
"Yuta",
""
],
[
"Komori",
"Kentaro",
""
],
[
"Ando",
"Masaki",
""
],
[
"Hayama",
"Kazuhiro",
""
]
] | There exist six possible polarization modes of gravitational waves in general metric theory of gravity, while two tensor polarization modes are allowed in general relativity. The properties and number of polarization modes depend on gravity theories. The number of the detectors needs to be equal to the number of the polarization modes of the gravitational waves for separation of polarizations basically. However, a single detector having great sensitivity at lower frequency could be effectively regarded as a virtual detector network including a set of detectors along its trajectory due to a long GW signal from a compact binary and the Earth's rotation. Thus, time-varying antenna pattern functions can help testing the polarizations of gravitational waves. We study the effects of the Earth's rotation on the polarization test and show a possibility to test the non-tensorial polarization modes from future observations of compact binary mergers with ground-based gravitational detectors such as Einstein telescope and Cosmic Explorer. |
0808.2449 | Richard Woodard | T. M. Janssen (Utrecht), S. P. Miao (Utrecht), T. Prokopec (Utrecht)
and R. P. Woodard (Florida) | Infrared Propagator Corrections for Constant Deceleration | 34 pages, uses LaTeX 2 epsilon | Class.Quant.Grav.25:245013,2008 | 10.1088/0264-9381/25/24/245013 | SPIN-08-38, ITP-UU-08/48, UFIFT-QG-08-06 | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive the propagator for a massless, minimally coupled scalar on a
$D$-dimensional, spatially flat, homogeneous and isotropic background with
arbitrary constant deceleration parameter. Our construction uses the operator
formalism, by integrating the Fourier mode sum. We give special attention to
infrared corrections from the nonzero lower limit associated with working on
finite spatial sections. These corrections eliminate infrared divergences that
would otherwise be incorrectly treated by dimensional regularization, resulting
in off-coincidence divergences for those special values of the deceleration
parameter at which the infrared divergence is logarithmic. As an application we
compute the expectation value of the scalar stress-energy tensor.
| [
{
"created": "Mon, 18 Aug 2008 18:22:34 GMT",
"version": "v1"
}
] | 2008-12-18 | [
[
"Janssen",
"T. M.",
"",
"Utrecht"
],
[
"Miao",
"S. P.",
"",
"Utrecht"
],
[
"Prokopec",
"T.",
"",
"Utrecht"
],
[
"Woodard",
"R. P.",
"",
"Florida"
]
] | We derive the propagator for a massless, minimally coupled scalar on a $D$-dimensional, spatially flat, homogeneous and isotropic background with arbitrary constant deceleration parameter. Our construction uses the operator formalism, by integrating the Fourier mode sum. We give special attention to infrared corrections from the nonzero lower limit associated with working on finite spatial sections. These corrections eliminate infrared divergences that would otherwise be incorrectly treated by dimensional regularization, resulting in off-coincidence divergences for those special values of the deceleration parameter at which the infrared divergence is logarithmic. As an application we compute the expectation value of the scalar stress-energy tensor. |
1506.07579 | Mauricio Cataldo MC | Mauricio Cataldo, Antonella Cid, Pedro Labra\~na and Patricio Mella | Cosmic anisotropic doomsday in Bianchi type I universes | 10 pages, 6 figures, Accepted for publication in Journal of
Mathematical Physics (2016) | J. Math. Phys. 57, 112502 (2016) | 10.1063/1.4967954 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In order to investigate if the anisotropy of the spacetime may induce future
singularities at a finite value of the cosmic time on the evolution of
cosmological models, we study vacuum and non-vacuum Bianchi type I spacetimes
exhibiting such future singularities. We show that in the case of Kasner vacuum
cosmologies the spacetime may rip itself apart in a finite time, and only in
the direction corresponding to the unique scale factor which diverges at this
finite value of the cosmic time. The other two directional scale factors and
the average scale factor do not diverge and tend to zero at this time, while
the directional and average expansion rates also become infinite. Due to the
absence of the matter content this anisotropic future singularity is induced by
the shear scalar, which also blows up at this time. We call such a singularity
"Vacuum Rip". For non-vacuum solutions we discuss fully anisotropic Bianchi
type I spacetimes filled with a stiff fluid and ellipsoidal (axisymmetric)
cosmological models filled with matter with isotropic and anisotropic
barotropic pressure, and characterized by $\sigma/\theta=const$, where $\sigma$
and $\theta$ are the shear scalar and the expansion scalar respectively.
| [
{
"created": "Wed, 24 Jun 2015 22:50:36 GMT",
"version": "v1"
},
{
"created": "Tue, 15 Nov 2016 17:19:12 GMT",
"version": "v2"
}
] | 2016-11-30 | [
[
"Cataldo",
"Mauricio",
""
],
[
"Cid",
"Antonella",
""
],
[
"Labraña",
"Pedro",
""
],
[
"Mella",
"Patricio",
""
]
] | In order to investigate if the anisotropy of the spacetime may induce future singularities at a finite value of the cosmic time on the evolution of cosmological models, we study vacuum and non-vacuum Bianchi type I spacetimes exhibiting such future singularities. We show that in the case of Kasner vacuum cosmologies the spacetime may rip itself apart in a finite time, and only in the direction corresponding to the unique scale factor which diverges at this finite value of the cosmic time. The other two directional scale factors and the average scale factor do not diverge and tend to zero at this time, while the directional and average expansion rates also become infinite. Due to the absence of the matter content this anisotropic future singularity is induced by the shear scalar, which also blows up at this time. We call such a singularity "Vacuum Rip". For non-vacuum solutions we discuss fully anisotropic Bianchi type I spacetimes filled with a stiff fluid and ellipsoidal (axisymmetric) cosmological models filled with matter with isotropic and anisotropic barotropic pressure, and characterized by $\sigma/\theta=const$, where $\sigma$ and $\theta$ are the shear scalar and the expansion scalar respectively. |
2308.00844 | Chad Briddon | Chad Briddon, Clare Burrage, Adam Moss, and Andrius Tamosiunas | Using machine learning to optimise chameleon fifth force experiments | 28 pages, 17 figures, The SELCIE code is available at:
https://github.com/C-Briddon/SELCIE | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | The chameleon is a theorised scalar field that couples to matter and possess
a screening mechanism, which weakens observational constraints from experiments
performed in regions of higher matter density. One consequence of this
screening mechanism is that the force induced by the field is dependent on the
shape of the source mass (a property that distinguishes it from gravity).
Therefore an optimal shape must exist for which the chameleon force is
maximised. Such a shape would allow experiments to improve their sensitivity by
simply changing the shape of the source mass. In this work we use a combination
of genetic algorithms and the chameleon solving software SELCIE to find shapes
that optimise the force at a single point in an idealised experimental
environment. We note that the method we used is easily customised, and so could
be used to optimise a more realistic experiment involving particle trajectories
or the force acting on an extended body. We find the shapes outputted by the
genetic algorithm possess common characteristics, such as a preference for
smaller source masses, and that the largest fifth forces are produced by small
`umbrella'-like shapes with a thickness such that the source is unscreened but
the field reaches its minimum inside the source. This remains the optimal shape
even as we change the chameleon potential, and the distance from the source,
and across a wide range of chameleon parameters. We find that by optimising the
shape in this way the fifth force can be increased by $2.45$ times when
compared to a sphere, centred at the origin, of the same volume and mass.
| [
{
"created": "Tue, 1 Aug 2023 21:18:35 GMT",
"version": "v1"
}
] | 2023-08-03 | [
[
"Briddon",
"Chad",
""
],
[
"Burrage",
"Clare",
""
],
[
"Moss",
"Adam",
""
],
[
"Tamosiunas",
"Andrius",
""
]
] | The chameleon is a theorised scalar field that couples to matter and possess a screening mechanism, which weakens observational constraints from experiments performed in regions of higher matter density. One consequence of this screening mechanism is that the force induced by the field is dependent on the shape of the source mass (a property that distinguishes it from gravity). Therefore an optimal shape must exist for which the chameleon force is maximised. Such a shape would allow experiments to improve their sensitivity by simply changing the shape of the source mass. In this work we use a combination of genetic algorithms and the chameleon solving software SELCIE to find shapes that optimise the force at a single point in an idealised experimental environment. We note that the method we used is easily customised, and so could be used to optimise a more realistic experiment involving particle trajectories or the force acting on an extended body. We find the shapes outputted by the genetic algorithm possess common characteristics, such as a preference for smaller source masses, and that the largest fifth forces are produced by small `umbrella'-like shapes with a thickness such that the source is unscreened but the field reaches its minimum inside the source. This remains the optimal shape even as we change the chameleon potential, and the distance from the source, and across a wide range of chameleon parameters. We find that by optimising the shape in this way the fifth force can be increased by $2.45$ times when compared to a sphere, centred at the origin, of the same volume and mass. |
1509.00148 | J. Ponce de Leon | J. Ponce de Leon | Embeddings for General Relativity | Accepted for publication in Classical and Quantum Gravity | null | 10.1088/0264-9381/32/19/195018 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a systematic approach to embed $n$-dimensional vacuum general
relativity in an $(n + 1)$-dimensional pseudo-Riemannian spacetime whose source
is either a (non)zero cosmological constant or a scalar field minimally-coupled
to Einstein gravity. Our approach allows us to generalize a number of results
discussed in the literature. We construct {\it all} the possible (physically
distinct) embeddings in Einstein spaces, including the Ricci-flat ones widely
discussed in the literature. We examine in detail their generalization, which -
in the framework under consideration - are higher-dimensional spacetimes
sourced by a scalar field with flat (constant $\neq 0$) potential. We use the
Kretschmann curvature scalar to show that many embedding spaces have a physical
singularity at some finite value of the extra coordinate. We develop several
classes of embeddings that are free of singularities, have distinct
non-vanishing self-interacting potentials and are continuously connected (in
various limits) to Einstein embeddings. We point out that the induced metric
possesses scaling symmetry and, as a consequence, the effective physical
parameters (e.g., mass, angular momentum, cosmological constant) can be
interpreted as functions of the extra coordinate.
| [
{
"created": "Tue, 1 Sep 2015 05:29:13 GMT",
"version": "v1"
}
] | 2015-09-30 | [
[
"de Leon",
"J. Ponce",
""
]
] | We present a systematic approach to embed $n$-dimensional vacuum general relativity in an $(n + 1)$-dimensional pseudo-Riemannian spacetime whose source is either a (non)zero cosmological constant or a scalar field minimally-coupled to Einstein gravity. Our approach allows us to generalize a number of results discussed in the literature. We construct {\it all} the possible (physically distinct) embeddings in Einstein spaces, including the Ricci-flat ones widely discussed in the literature. We examine in detail their generalization, which - in the framework under consideration - are higher-dimensional spacetimes sourced by a scalar field with flat (constant $\neq 0$) potential. We use the Kretschmann curvature scalar to show that many embedding spaces have a physical singularity at some finite value of the extra coordinate. We develop several classes of embeddings that are free of singularities, have distinct non-vanishing self-interacting potentials and are continuously connected (in various limits) to Einstein embeddings. We point out that the induced metric possesses scaling symmetry and, as a consequence, the effective physical parameters (e.g., mass, angular momentum, cosmological constant) can be interpreted as functions of the extra coordinate. |
1502.07750 | Adam Stevens | Adam R. H. Stevens | Liberation of specific angular momentum through radiation and scattering
in relativistic black-hole accretion discs | 6 pages, 2 figures. Accepted for publication in PASA | null | null | null | gr-qc astro-ph.CO astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A key component of explaining the array of galaxies observed in the Universe
is the feedback of active galactic nuclei, each powered by a massive black
hole's accretion disc. For accretion to occur, angular momentum must be lost by
that which is accreted. Electromagnetic radiation must offer some respite in
this regard, the contribution for which is quantified in this paper, using
solely general relativity, under the thin-disc regime. Herein, I calculate
extremised situations where photons are entirely responsible for energy removal
in the disc and then extend and relate this to the standard relativistic
accretion disc outlined by Novikov & Thorne, which includes internal
angular-momentum transport. While there is potential for the contribution of
angular-momentum removal from photons to be >~1% out to ~10^4 Schwarzschild
radii if the disc is irradiated and maximally liberated of angular momentum
through inverse Compton scattering, it is more likely of order 10^2
Schwarzschild radii if thermal emission from the disc itself is stronger. The
effect of radiation/scattering is stronger near the horizons of fast-spinning
black holes, but, ultimately, other mechanisms must drive angular-momentum
liberation/transport in accretion discs.
| [
{
"created": "Thu, 26 Feb 2015 21:00:06 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Jul 2015 03:08:33 GMT",
"version": "v2"
}
] | 2015-07-17 | [
[
"Stevens",
"Adam R. H.",
""
]
] | A key component of explaining the array of galaxies observed in the Universe is the feedback of active galactic nuclei, each powered by a massive black hole's accretion disc. For accretion to occur, angular momentum must be lost by that which is accreted. Electromagnetic radiation must offer some respite in this regard, the contribution for which is quantified in this paper, using solely general relativity, under the thin-disc regime. Herein, I calculate extremised situations where photons are entirely responsible for energy removal in the disc and then extend and relate this to the standard relativistic accretion disc outlined by Novikov & Thorne, which includes internal angular-momentum transport. While there is potential for the contribution of angular-momentum removal from photons to be >~1% out to ~10^4 Schwarzschild radii if the disc is irradiated and maximally liberated of angular momentum through inverse Compton scattering, it is more likely of order 10^2 Schwarzschild radii if thermal emission from the disc itself is stronger. The effect of radiation/scattering is stronger near the horizons of fast-spinning black holes, but, ultimately, other mechanisms must drive angular-momentum liberation/transport in accretion discs. |
gr-qc/0606056 | Mizuno Shuntaro | Kazuya Koyama and Shuntaro Mizuno | Inflaton perturbations in brane-world cosmology with induced gravity | 20 pages, 4 figures | JCAP 0607 (2006) 013 | 10.1088/1475-7516/2006/07/013 | ICG 06/30, RESCEU-15/06 | gr-qc astro-ph hep-th | null | We study cosmological perturbations in the brane models with an induced
Einstein-Hilbert term on a brane. We consider an inflaton confined to a de
Sitter brane in a five-dimensional Minkowski spacetime. Inflaton fluctuations
excite Kaluza-Klein modes of bulk metric perturbations with mass $m^2 =
-2(2\ell-1) (\ell +1) H^2$ and $m^2 = -2\ell(2\ell+3) H^2$ where $\ell$ is an
integer. There are two branches ($\pm$ branches) of solutions for the
background spacetime. In the $+$ branch, which includes the self-accelerating
universe, a resonance appears for a mode with $m^2 = 2 H^2$ due to a spin-0
perturbation with $m^2 = 2H^2$. The self-accelerating universe has a distinct
feature because there is also a helicity-0 mode of spin-2 perturbations with
$m^2 = 2H^2$. In the $-$ branch, which can be thought as the Randall-Sundrum
type brane-world with the high energy quantum corrections, there is no
resonance. At high energies, we analytically confirm that four-dimensional
Einstein gravity is recovered, which is related to the disappearance of van
Dam-Veltman-Zakharov discontinuity in de Sitter spacetime.
On sufficiently small scales, we confirm that the lineariaed gravity on the
brane is well described by the Brans-Dicke theory with $\omega=3Hr_c$ in $-$
branch and $\omega = -3H r_c$ in $+$ branch, respectively, which confirms the
existence of the ghost in $+$ branch. We also study large scale perturbations.
In $+$ branch, the resonance induces a non-trivial anisotropic stress on the
brane via the projection of Weyl tensor in the bulk, but no instability is
shown to exist on the brane.
| [
{
"created": "Tue, 13 Jun 2006 02:29:57 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Koyama",
"Kazuya",
""
],
[
"Mizuno",
"Shuntaro",
""
]
] | We study cosmological perturbations in the brane models with an induced Einstein-Hilbert term on a brane. We consider an inflaton confined to a de Sitter brane in a five-dimensional Minkowski spacetime. Inflaton fluctuations excite Kaluza-Klein modes of bulk metric perturbations with mass $m^2 = -2(2\ell-1) (\ell +1) H^2$ and $m^2 = -2\ell(2\ell+3) H^2$ where $\ell$ is an integer. There are two branches ($\pm$ branches) of solutions for the background spacetime. In the $+$ branch, which includes the self-accelerating universe, a resonance appears for a mode with $m^2 = 2 H^2$ due to a spin-0 perturbation with $m^2 = 2H^2$. The self-accelerating universe has a distinct feature because there is also a helicity-0 mode of spin-2 perturbations with $m^2 = 2H^2$. In the $-$ branch, which can be thought as the Randall-Sundrum type brane-world with the high energy quantum corrections, there is no resonance. At high energies, we analytically confirm that four-dimensional Einstein gravity is recovered, which is related to the disappearance of van Dam-Veltman-Zakharov discontinuity in de Sitter spacetime. On sufficiently small scales, we confirm that the lineariaed gravity on the brane is well described by the Brans-Dicke theory with $\omega=3Hr_c$ in $-$ branch and $\omega = -3H r_c$ in $+$ branch, respectively, which confirms the existence of the ghost in $+$ branch. We also study large scale perturbations. In $+$ branch, the resonance induces a non-trivial anisotropic stress on the brane via the projection of Weyl tensor in the bulk, but no instability is shown to exist on the brane. |
gr-qc/9606054 | Yuri Ponomarev | V.Burdyuzha(1), O.Lalakulich(2), Yu.Ponomarev(1), G.Vereshkov(2) ((1)
Astro Space Centre Lebedev Physical Institute of Russian Academy of Sciences,
(2) Scientific Research Institute of Physics of Rostov State University) | The New Scenario of the Initial Evolution of the Universe | 11 pages (RevTex), 5 PostScript figures. Submitted to Physical Review
Letters | Phys.Rev.D55:7340-7344,1997 | 10.1103/PhysRevD.55.7340 | null | gr-qc | null | We propose that the Universe created from "nothing" with relatively small
particles number and quickly relaxed to quasiequilibrium state at the Planck
parameters. The classic cosmological solution for this Universe with
Lambda-term has two branches divided by the gap. The quantum process of
tunneling between the cosmological solution branches and kinetic of the second
order relativistic phase transition in supersymmetric SU(5) model on the GUT
scale are investigated by numerical methods. Einstein equations was solved
together with the equations of relaxation kinetics. Other quantum
geometrodynamics process (the bounce from singularity) and the Wheeler- De Witt
equation are investigated also. For the formation of observable particles
number the model of the slowly swelling Universe in the result of the multiple
reproduction of cosmological cycles is arised naturally.
| [
{
"created": "Tue, 18 Jun 1996 14:01:25 GMT",
"version": "v1"
}
] | 2009-12-30 | [
[
"Burdyuzha",
"V.",
""
],
[
"Lalakulich",
"O.",
""
],
[
"Ponomarev",
"Yu.",
""
],
[
"Vereshkov",
"G.",
""
]
] | We propose that the Universe created from "nothing" with relatively small particles number and quickly relaxed to quasiequilibrium state at the Planck parameters. The classic cosmological solution for this Universe with Lambda-term has two branches divided by the gap. The quantum process of tunneling between the cosmological solution branches and kinetic of the second order relativistic phase transition in supersymmetric SU(5) model on the GUT scale are investigated by numerical methods. Einstein equations was solved together with the equations of relaxation kinetics. Other quantum geometrodynamics process (the bounce from singularity) and the Wheeler- De Witt equation are investigated also. For the formation of observable particles number the model of the slowly swelling Universe in the result of the multiple reproduction of cosmological cycles is arised naturally. |
gr-qc/0505034 | Tiberiu Harko | M. K. Mak, T. Harko | Chaplygin gas dominated anisotropic brane world cosmological models | 13 pages, 6 figures, accepted for publication in PRD | Phys.Rev. D71 (2005) 104022 | 10.1103/PhysRevD.71.104022 | null | gr-qc hep-th | null | We present exact solutions of the gravitational field equations in the
generalized Randall-Sundrum model for an anisotropic brane with Bianchi type I
geometry, with a generalized Chaplygin gas as matter source. The generalized
Chaplygin gas, which interpolates between a high density relativistic era and a
non-relativistic matter phase, is a popular dark energy candidate. For a
Bianchi type I space-time brane filled with a cosmological fluid obeying the
generalized Chaplygin equation of state the general solution of the
gravitational field equations can be expressed in an exact parametric form,
with the comoving volume taken as parameter. In the limiting cases of a stiff
cosmological fluid, with pressure equal to the energy density, and for a
pressureless fluid, the solution of the field equations can be expressed in an
exact analytical form. The evolution of the scalar field associated to the
Chaplygin fluid is also considered and the corresponding potential is obtained.
The behavior of the observationally important parameters like shear, anisotropy
and deceleration parameter is considered in detail.
| [
{
"created": "Mon, 9 May 2005 02:58:40 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Mak",
"M. K.",
""
],
[
"Harko",
"T.",
""
]
] | We present exact solutions of the gravitational field equations in the generalized Randall-Sundrum model for an anisotropic brane with Bianchi type I geometry, with a generalized Chaplygin gas as matter source. The generalized Chaplygin gas, which interpolates between a high density relativistic era and a non-relativistic matter phase, is a popular dark energy candidate. For a Bianchi type I space-time brane filled with a cosmological fluid obeying the generalized Chaplygin equation of state the general solution of the gravitational field equations can be expressed in an exact parametric form, with the comoving volume taken as parameter. In the limiting cases of a stiff cosmological fluid, with pressure equal to the energy density, and for a pressureless fluid, the solution of the field equations can be expressed in an exact analytical form. The evolution of the scalar field associated to the Chaplygin fluid is also considered and the corresponding potential is obtained. The behavior of the observationally important parameters like shear, anisotropy and deceleration parameter is considered in detail. |
2208.02367 | Matthew Duez | Milad Haddadi, Matthew D. Duez, Francois Foucart, Teresita Ramirez,
Rodrigo Fernandez, Alexander L. Knight, Jerred Jesse, Francois Hebert,
Lawrence E. Kidder, Harald P. Pfeiffer, Mark A. Scheel | Late-time post-merger modeling of a compact binary: effects of
relativity, r-process heating, and treatment of transport effects | 23 pages, 7 figures, version accepted to Classical and Quantum
Gravity | null | 10.1088/1361-6382/acc0c6 | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | Detectable electromagnetic counterparts to gravitational waves from compact
binary mergers can be produced by outflows from the black hole-accretion disk
remnant during the first ten seconds after the merger. Two-dimensional
axisymmetric simulations with effective viscosity remain an efficient and
informative way to model this late-time post-merger evolution. In addition to
the inherent approximations of axisymmetry and modeling turbulent angular
momentum transport by a viscosity, previous simulations often make other
simplifications related to the treatment of the equation of state and turbulent
transport effects.
In this paper, we test the effect of these modeling choices. By evolving with
the same viscosity the exact post-merger initial configuration previously
evolved in Newtonian viscous hydrodynamics, we find that the Newtonian
treatment provides a good estimate of the disk ejecta mass but underestimates
the outflow velocity. We find that the inclusion of heavy nuclei causes a
notable increase in ejecta mass. An approximate inclusion of r-process effects
has a comparatively smaller effect, except for its designed effect on the
composition. Diffusion of composition and entropy, modeling turbulent transport
effects, has the overall effect of reducing ejecta mass and giving it a speed
with lower average and more tightly-peaked distribution. Also, we find
significant acceleration of outflow even at distances beyond 10,000\,km, so
that thermal wind velocities only asymptote beyond this radius and at somewhat
higher values than previously reported.
| [
{
"created": "Wed, 3 Aug 2022 22:26:42 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Mar 2023 17:56:56 GMT",
"version": "v2"
}
] | 2023-04-05 | [
[
"Haddadi",
"Milad",
""
],
[
"Duez",
"Matthew D.",
""
],
[
"Foucart",
"Francois",
""
],
[
"Ramirez",
"Teresita",
""
],
[
"Fernandez",
"Rodrigo",
""
],
[
"Knight",
"Alexander L.",
""
],
[
"Jesse",
"Jerred",
"... | Detectable electromagnetic counterparts to gravitational waves from compact binary mergers can be produced by outflows from the black hole-accretion disk remnant during the first ten seconds after the merger. Two-dimensional axisymmetric simulations with effective viscosity remain an efficient and informative way to model this late-time post-merger evolution. In addition to the inherent approximations of axisymmetry and modeling turbulent angular momentum transport by a viscosity, previous simulations often make other simplifications related to the treatment of the equation of state and turbulent transport effects. In this paper, we test the effect of these modeling choices. By evolving with the same viscosity the exact post-merger initial configuration previously evolved in Newtonian viscous hydrodynamics, we find that the Newtonian treatment provides a good estimate of the disk ejecta mass but underestimates the outflow velocity. We find that the inclusion of heavy nuclei causes a notable increase in ejecta mass. An approximate inclusion of r-process effects has a comparatively smaller effect, except for its designed effect on the composition. Diffusion of composition and entropy, modeling turbulent transport effects, has the overall effect of reducing ejecta mass and giving it a speed with lower average and more tightly-peaked distribution. Also, we find significant acceleration of outflow even at distances beyond 10,000\,km, so that thermal wind velocities only asymptote beyond this radius and at somewhat higher values than previously reported. |
1302.4411 | Ehoud Pazy | E. Pazy | Quantum statistical modified entropic gravity as a theoretical basis for
MOND | 17 pages, no figures, added references | Phys. Rev. D 87, 084063 (2013) | 10.1103/PhysRevD.87.084063 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Considering the quantum statistics of the degrees of freedom on the
holographic screen it is shown that the ratio of the number of excited bulk
degrees of freedom to the number of excited surface degrees of freedom, is
given by the MOND interpolating function {\mu}. This relationship is shown to
hold also in AQUAL, and in the extension of MOND to de Sitter space. Based on
the relationship between the entropy, and the number of degrees of freedom on
the holographic screen, a simple expression, relating the MOND interpolating
function to the ratio of the two-dimensional entropy to Bekenstein-Hawking
entropy, is obtained. In terms of this expression MOND can be viewed as a
modification of gravity arising due to a bound on the maximum entropy for the
holographic screen.
| [
{
"created": "Mon, 18 Feb 2013 20:22:59 GMT",
"version": "v1"
},
{
"created": "Fri, 10 May 2013 15:39:42 GMT",
"version": "v2"
}
] | 2015-06-15 | [
[
"Pazy",
"E.",
""
]
] | Considering the quantum statistics of the degrees of freedom on the holographic screen it is shown that the ratio of the number of excited bulk degrees of freedom to the number of excited surface degrees of freedom, is given by the MOND interpolating function {\mu}. This relationship is shown to hold also in AQUAL, and in the extension of MOND to de Sitter space. Based on the relationship between the entropy, and the number of degrees of freedom on the holographic screen, a simple expression, relating the MOND interpolating function to the ratio of the two-dimensional entropy to Bekenstein-Hawking entropy, is obtained. In terms of this expression MOND can be viewed as a modification of gravity arising due to a bound on the maximum entropy for the holographic screen. |
gr-qc/0012003 | Gerard Clement | M. Azreg-Ainou, G. Clement, C.P. Constantinidis and J.C. Fabris | Regularity and stability of electrostatic solutions in Kaluza-Klein
theory | 2 pages, "mprocl.sty" with LATEX 2.09, contribution to the 9th Marcel
Grossmann meeting (MG9), Rome, July 2000 | null | null | null | gr-qc hep-th | null | We investigate the family of electrostatic spherically symmetric solutions of
the five-dimensional Kaluza-Klein theory. Besides black holes and wormholes, a
new class of geodesically complete solutions is identified. A monopole
perturbation is carried out, enabling us to prove analytically the stability of
a large class of solutions, including all black holes and neutral solutions.
| [
{
"created": "Fri, 1 Dec 2000 16:08:16 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Azreg-Ainou",
"M.",
""
],
[
"Clement",
"G.",
""
],
[
"Constantinidis",
"C. P.",
""
],
[
"Fabris",
"J. C.",
""
]
] | We investigate the family of electrostatic spherically symmetric solutions of the five-dimensional Kaluza-Klein theory. Besides black holes and wormholes, a new class of geodesically complete solutions is identified. A monopole perturbation is carried out, enabling us to prove analytically the stability of a large class of solutions, including all black holes and neutral solutions. |
1705.03278 | Petarpa Boonserm | Petarpa Boonserm, Tritos Ngampitipan, Pitayuth Wongjun | Greybody factor for black holes in dRGT massive gravity | V1: 21 pages, 8 figures; V2: 7 references added, no physics changes,
now 11 pages (2 columns) | null | 10.1140/epjc/s10052-018-5975-x | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In general relativity, greybody factor is a quantity related to the quantum
nature of a black hole. A high value of greybody factor indicates a high
probability that Hawking radiation can reach infinity. Although general
relativity is correct and has been successful in describing many phenomena,
there are some questions that general relativity cannot answer. Therefore,
general relativity is often modified to attain answers. One of the
modifications is the `massive gravity'. The viable model of the massive gravity
theory belongs to de Rham, Gabadadze and Tolley (dRGT). In this paper, we
calculate the gravitational potential for the de Sitter black hole and for the
dRGT black hole. We also derive the rigorous bound on the greybody factor for
the de Sitter black hole and the dRGT black hole. It is found that the
structure of potentials determines how much the rigorous bound on the greybody
factor should be. That is, the higher the potential, the lesser the bound on
the greybody factor will be. Moreover, we compare the greybody factor derived
from the rigorous bound with the greybody factor derived from the matching
technique. The result shows that the rigorous bound is a true lower bound
because it is less than the greybody factor obtained from the matching
technique.
| [
{
"created": "Tue, 9 May 2017 11:25:20 GMT",
"version": "v1"
},
{
"created": "Mon, 31 Jul 2017 12:26:34 GMT",
"version": "v2"
}
] | 2018-08-01 | [
[
"Boonserm",
"Petarpa",
""
],
[
"Ngampitipan",
"Tritos",
""
],
[
"Wongjun",
"Pitayuth",
""
]
] | In general relativity, greybody factor is a quantity related to the quantum nature of a black hole. A high value of greybody factor indicates a high probability that Hawking radiation can reach infinity. Although general relativity is correct and has been successful in describing many phenomena, there are some questions that general relativity cannot answer. Therefore, general relativity is often modified to attain answers. One of the modifications is the `massive gravity'. The viable model of the massive gravity theory belongs to de Rham, Gabadadze and Tolley (dRGT). In this paper, we calculate the gravitational potential for the de Sitter black hole and for the dRGT black hole. We also derive the rigorous bound on the greybody factor for the de Sitter black hole and the dRGT black hole. It is found that the structure of potentials determines how much the rigorous bound on the greybody factor should be. That is, the higher the potential, the lesser the bound on the greybody factor will be. Moreover, we compare the greybody factor derived from the rigorous bound with the greybody factor derived from the matching technique. The result shows that the rigorous bound is a true lower bound because it is less than the greybody factor obtained from the matching technique. |
2102.05893 | Subenoy Chakraborty | Sanjukta Chakraborty, Akash Bose and Subenoy Chakraborty | Collapse Geometry in Inhomogeneous FRW model | null | International Journal of Geometric Methods in Modern Physics, Vol.
18, No. 02, 2150019 (2021) | 10.1142/S0219887821500195 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Collapsing process is studied in special type of inhomogeneous spherically
symmetric space-time model (known as IFRW model), having no time-like Killing
vector field. The matter field for collapse dynamics is considered to be
perfect fluid with anisotropic pressure. The main issue of the present
investigation is to examine whether the end state of the collapse to be a naked
singularity or a black hole. Finally, null geodesics is studied near the
singularity.
| [
{
"created": "Thu, 11 Feb 2021 08:53:54 GMT",
"version": "v1"
}
] | 2021-02-12 | [
[
"Chakraborty",
"Sanjukta",
""
],
[
"Bose",
"Akash",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | Collapsing process is studied in special type of inhomogeneous spherically symmetric space-time model (known as IFRW model), having no time-like Killing vector field. The matter field for collapse dynamics is considered to be perfect fluid with anisotropic pressure. The main issue of the present investigation is to examine whether the end state of the collapse to be a naked singularity or a black hole. Finally, null geodesics is studied near the singularity. |
1302.0254 | Ivan Agullo | Ivan Agullo, Abhay Ashtekar, and William Nelson | The pre-inflationary dynamics of loop quantum cosmology: Confronting
quantum gravity with observations | 64 pages, 15 figures. Published version | Class. Quant. Grav. 30, 085014 (2013) | 10.1088/0264-9381/30/8/085014 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using techniques from loop quantum gravity, the standard theory of
cosmological perturbations was recently generalized to encompass the Planck
era. We now apply this framework to explore pre-inflationary dynamics. The
framework enables us to isolate and resolve the true trans-Planckian
difficulties, with interesting lessons both for theory and observations.
Specifically, for a large class of initial conditions at the bounce, we are led
to a self consistent extension of the inflationary paradigm over the 11 orders
of magnitude in density and curvature, from the big bounce to the onset of slow
roll. In addition, for a narrow window of initial conditions, there are
departures from the standard paradigm, with novel effects ---such as a
modification of the consistency relation between the ratio of the tensor to
scalar power spectrum and the tensor spectral index, as well as a new source
for non-Gaussianities--- which could extend the reach of cosmological
observations to the deep Planck regime of the early universe.
| [
{
"created": "Fri, 1 Feb 2013 19:12:40 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Apr 2013 08:55:00 GMT",
"version": "v2"
}
] | 2015-03-12 | [
[
"Agullo",
"Ivan",
""
],
[
"Ashtekar",
"Abhay",
""
],
[
"Nelson",
"William",
""
]
] | Using techniques from loop quantum gravity, the standard theory of cosmological perturbations was recently generalized to encompass the Planck era. We now apply this framework to explore pre-inflationary dynamics. The framework enables us to isolate and resolve the true trans-Planckian difficulties, with interesting lessons both for theory and observations. Specifically, for a large class of initial conditions at the bounce, we are led to a self consistent extension of the inflationary paradigm over the 11 orders of magnitude in density and curvature, from the big bounce to the onset of slow roll. In addition, for a narrow window of initial conditions, there are departures from the standard paradigm, with novel effects ---such as a modification of the consistency relation between the ratio of the tensor to scalar power spectrum and the tensor spectral index, as well as a new source for non-Gaussianities--- which could extend the reach of cosmological observations to the deep Planck regime of the early universe. |
gr-qc/0401037 | Wung-Hong Huang | Wung-Hong Huang | Quantum Field Effect on Symmetry Breaking and Restoration in Anisotropic
Spacetimes | null | Phys.Rev.D42:1287,1990 | 10.1103/PhysRevD.42.1287 | null | gr-qc hep-th | null | The one-loop effective potential for $\phi ^4$ theory on a Bianchi type-I
universe is evaluated in the adiabatic approximation. It is used to see the
quantum-field effects on symmetry breaking and restoration in anisotropic
spacetimes. The results show that the fate of symmetry will not be changed in
the cases of conformal coupling or a vanishing scale curvature, and only for
some suitable values of scalar-gravitational coupling could the symmetry be
radiatively broken or restored.
| [
{
"created": "Sat, 10 Jan 2004 15:04:44 GMT",
"version": "v1"
}
] | 2008-12-24 | [
[
"Huang",
"Wung-Hong",
""
]
] | The one-loop effective potential for $\phi ^4$ theory on a Bianchi type-I universe is evaluated in the adiabatic approximation. It is used to see the quantum-field effects on symmetry breaking and restoration in anisotropic spacetimes. The results show that the fate of symmetry will not be changed in the cases of conformal coupling or a vanishing scale curvature, and only for some suitable values of scalar-gravitational coupling could the symmetry be radiatively broken or restored. |
gr-qc/0409052 | Donato Bini | Donato Bini, Luca Lusanna, Bahram Mashhoon | Limitations of Radar Coordinates | 12 pages, revtex and pictex macros, 3 pictex figures, 1 eps figure.
Expanded version | Int.J.Mod.Phys. D14 (2005) 1413-1429 | 10.1142/S0218271805006961 | null | gr-qc astro-ph | null | The construction of a radar coordinate system about the world line of an
observer is discussed. Radar coordinates for a hyperbolic observer as well as a
uniformly rotating observer are described in detail. The utility of the notion
of radar distance and the admissibility of radar coordinates are investigated.
Our results provide a critical assessment of the physical significance of radar
coordinates.
| [
{
"created": "Mon, 13 Sep 2004 07:12:12 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Dec 2004 08:34:53 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Bini",
"Donato",
""
],
[
"Lusanna",
"Luca",
""
],
[
"Mashhoon",
"Bahram",
""
]
] | The construction of a radar coordinate system about the world line of an observer is discussed. Radar coordinates for a hyperbolic observer as well as a uniformly rotating observer are described in detail. The utility of the notion of radar distance and the admissibility of radar coordinates are investigated. Our results provide a critical assessment of the physical significance of radar coordinates. |
2005.11090 | Oleg Zaslavskii | O. B. Zaslavskii | Super-Penrose process for extremal charged white holes | 11 pages. Sec. VII added with brief comparison of mass-inflation and
super-Penrose process | Mod. Phys. Lett. A. 36 (2021) 2150020 | 10.1142/S0217732321500206 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider collision of two particles 1 and 2 near the horizon of the
extremal Reissner-Nordstr\"{o}m (RN) black hole that produce two other
particles 3 and 4. There exists such a scenario that both new particles fall in
a black hole. One of them emerges from the white hole horizon in the
asymptotically flat region, the other one oscillates between turning points.
However, the unbounded energies $E$ at infinity (super-Penrose process - SPP)
turn out to be impossible for any finite angular momenta $L_{3.4}$. In this
sense, the situation for such a white hole scenarios is opposite to the black
hole ones, where the SPP is found earlier to be possible for the RN metric even
for all $L_{i}=0$. However, if $L_{3,4}$ themselves are unbounded, the SPP does
exist for white holes.
| [
{
"created": "Fri, 22 May 2020 10:24:08 GMT",
"version": "v1"
},
{
"created": "Thu, 28 May 2020 19:09:25 GMT",
"version": "v2"
},
{
"created": "Mon, 28 Sep 2020 14:27:40 GMT",
"version": "v3"
}
] | 2021-02-24 | [
[
"Zaslavskii",
"O. B.",
""
]
] | We consider collision of two particles 1 and 2 near the horizon of the extremal Reissner-Nordstr\"{o}m (RN) black hole that produce two other particles 3 and 4. There exists such a scenario that both new particles fall in a black hole. One of them emerges from the white hole horizon in the asymptotically flat region, the other one oscillates between turning points. However, the unbounded energies $E$ at infinity (super-Penrose process - SPP) turn out to be impossible for any finite angular momenta $L_{3.4}$. In this sense, the situation for such a white hole scenarios is opposite to the black hole ones, where the SPP is found earlier to be possible for the RN metric even for all $L_{i}=0$. However, if $L_{3,4}$ themselves are unbounded, the SPP does exist for white holes. |
2111.09307 | Andrew J. S. Hamilton | Andrew J. S. Hamilton | The rules of 4-dimensional perspective: How to implement Lorentz
transformations in relativistic visualization | 13 pages, 2 figures. Invited keynote lecture at the ENGAGE 2021
workshop at the Computer Graphics International CGI 2021 conference, 6-10 Sep
2021 | "Advances in Computer Graphics", 38th Computer Graphics
International Conference CGI 2021, Proceedings, eds. N. Magnenat-Thalmann, V.
Interrante, D. Thalmann, G. Papagiannakis, B. Sheng, J. Kim, M. Gavrilova,
pages 705-717 | 10.1007/978-3-030-89029-2 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | This paper presents a pedagogical introduction to the issue of how to
implement Lorentz transformations in relativistic visualization. The most
efficient approach is to use the even geometric algebra in 3+1 spacetime
dimensions, or equivalently complex quaternions, which are fast, compact, and
robust, and straightforward to compose, interpolate, and spline. The approach
has been incorporated into the Black Hole Flight Simulator, an interactive
general relativistic ray-tracing program developed by the author.
| [
{
"created": "Tue, 16 Nov 2021 23:06:59 GMT",
"version": "v1"
}
] | 2021-11-19 | [
[
"Hamilton",
"Andrew J. S.",
""
]
] | This paper presents a pedagogical introduction to the issue of how to implement Lorentz transformations in relativistic visualization. The most efficient approach is to use the even geometric algebra in 3+1 spacetime dimensions, or equivalently complex quaternions, which are fast, compact, and robust, and straightforward to compose, interpolate, and spline. The approach has been incorporated into the Black Hole Flight Simulator, an interactive general relativistic ray-tracing program developed by the author. |
2102.08717 | Suresh C. Jaryal | Ayan Chatterjee and Suresh C. Jaryal | Gravitationally collapsing stars in $f(R)$ gravity | 23 pages, 35 figures | null | 10.1140/epjc/s10052-021-09079-8 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | The gravitational dynamics of a collapsing matter configuration which is
simultaneously radiating heat flux is studied in $f(R)$ gravity. Three
particular functional forms in $f(R)$ gravity are considered to show that it is
possible to envisage boundary conditions such that the end state of the
collapse has a weak singularity and that the matter configuration radiates away
all of its mass before collapsing to reach the central singularity.
| [
{
"created": "Wed, 17 Feb 2021 12:07:36 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Feb 2021 07:25:07 GMT",
"version": "v2"
},
{
"created": "Fri, 2 Apr 2021 10:05:24 GMT",
"version": "v3"
}
] | 2021-04-05 | [
[
"Chatterjee",
"Ayan",
""
],
[
"Jaryal",
"Suresh C.",
""
]
] | The gravitational dynamics of a collapsing matter configuration which is simultaneously radiating heat flux is studied in $f(R)$ gravity. Three particular functional forms in $f(R)$ gravity are considered to show that it is possible to envisage boundary conditions such that the end state of the collapse has a weak singularity and that the matter configuration radiates away all of its mass before collapsing to reach the central singularity. |
1202.0999 | Pedro J Mora | Pedro J. Mora and Richard P. Woodard | Linearized Weyl-Weyl Correlator in a de Sitter Breaking Gauge | 31 pages, 2 tables, no figures, uses LaTex2e | null | 10.1103/PhysRevD.85.124048 | UFIFT-QG-12-01 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use a de Sitter breaking graviton propagator to compute the tree order
correlator between noncoincident Weyl tensors on a locally de Sitter
background. An explicit, and very simple result is obtained, for any spacetime
dimension D, in terms of a de Sitter invariant length function and the tensor
basis constructed from the metric and derivatives of this length function. Our
answer does not agree with the one derived previously by Kouris, but that
result must be incorrect because it not transverse and lacks some of the
algebraic symmetries of the Weyl tensor. Taking the coincidence limit of our
result (with dimensional regularization) and contracting the indices gives the
expectation value of the square of the Weyl tensor at lowest order. We propose
the next order computation of this as a true test of de Sitter invariance in
quantum gravity.
| [
{
"created": "Sun, 5 Feb 2012 20:17:57 GMT",
"version": "v1"
}
] | 2013-05-30 | [
[
"Mora",
"Pedro J.",
""
],
[
"Woodard",
"Richard P.",
""
]
] | We use a de Sitter breaking graviton propagator to compute the tree order correlator between noncoincident Weyl tensors on a locally de Sitter background. An explicit, and very simple result is obtained, for any spacetime dimension D, in terms of a de Sitter invariant length function and the tensor basis constructed from the metric and derivatives of this length function. Our answer does not agree with the one derived previously by Kouris, but that result must be incorrect because it not transverse and lacks some of the algebraic symmetries of the Weyl tensor. Taking the coincidence limit of our result (with dimensional regularization) and contracting the indices gives the expectation value of the square of the Weyl tensor at lowest order. We propose the next order computation of this as a true test of de Sitter invariance in quantum gravity. |
gr-qc/0507021 | Jerry B. Griffiths | J. B. Griffiths and J. Podolsky | Accelerating and rotating black holes | 14 pages, 1 figure. To appear in Class. Quantum Grav | Class.Quant.Grav. 22 (2005) 3467-3480 | 10.1088/0264-9381/22/17/008 | null | gr-qc | null | An exact solution of Einstein's equations which represents a pair of
accelerating and rotating black holes (a generalised form of the spinning
C-metric) is presented. The starting point is a form of the Plebanski-Demianski
metric which, in addition to the usual parameters, explicitly includes
parameters which describe the acceleration and angular velocity of the sources.
This is transformed to a form which explicitly contains the known special cases
for either rotating or accelerating black holes. Electromagnetic charges and a
NUT parameter are included, the relation between the NUT parameter $l$ and the
Plebanski-Demianski parameter $n$ is given, and the physical meaning of all
parameters is clarified. The possibility of finding an accelerating NUT
solution is also discussed.
| [
{
"created": "Wed, 6 Jul 2005 14:50:49 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Griffiths",
"J. B.",
""
],
[
"Podolsky",
"J.",
""
]
] | An exact solution of Einstein's equations which represents a pair of accelerating and rotating black holes (a generalised form of the spinning C-metric) is presented. The starting point is a form of the Plebanski-Demianski metric which, in addition to the usual parameters, explicitly includes parameters which describe the acceleration and angular velocity of the sources. This is transformed to a form which explicitly contains the known special cases for either rotating or accelerating black holes. Electromagnetic charges and a NUT parameter are included, the relation between the NUT parameter $l$ and the Plebanski-Demianski parameter $n$ is given, and the physical meaning of all parameters is clarified. The possibility of finding an accelerating NUT solution is also discussed. |
1906.10840 | Shao-Wen Wei | Shao-Wen Wei, Yu-Xiao Liu, Robert B. Mann | Repulsive Interactions and Universal Properties of Charged Anti-de
Sitter Black Hole Microstructures | 5 pages, 4 figures | Phys. Rev. Lett. 123, 071103 (2019) | 10.1103/PhysRevLett.123.071103 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Ruppeiner geometry of thermodynamic fluctuations provides a powerful
diagnostic of black hole microstructures. We investigate this for charged AdS
black holes and find that while an attractive microstructure interaction
dominates for most parameter ranges, a weak repulsive interaction dominates for
small black holes of high temperature. This unique property distinguishes the
black hole system from that of a Van der Waals fluid, where only attractive
microstructure interactions are found. We also find two other novel universal
properties for charged black holes. One is that the repulsive interaction is
independent of the black hole charge and temperature. The other is that the
behavior of the Ruppeiner curvature scalar near criticality is characterized by
a dimensionless constant that is identical to that for a Van der Waals fluid,
providing us with new insight into black hole microstructures.
| [
{
"created": "Wed, 26 Jun 2019 04:16:59 GMT",
"version": "v1"
},
{
"created": "Sat, 17 Aug 2019 08:28:38 GMT",
"version": "v2"
}
] | 2019-08-21 | [
[
"Wei",
"Shao-Wen",
""
],
[
"Liu",
"Yu-Xiao",
""
],
[
"Mann",
"Robert B.",
""
]
] | The Ruppeiner geometry of thermodynamic fluctuations provides a powerful diagnostic of black hole microstructures. We investigate this for charged AdS black holes and find that while an attractive microstructure interaction dominates for most parameter ranges, a weak repulsive interaction dominates for small black holes of high temperature. This unique property distinguishes the black hole system from that of a Van der Waals fluid, where only attractive microstructure interactions are found. We also find two other novel universal properties for charged black holes. One is that the repulsive interaction is independent of the black hole charge and temperature. The other is that the behavior of the Ruppeiner curvature scalar near criticality is characterized by a dimensionless constant that is identical to that for a Van der Waals fluid, providing us with new insight into black hole microstructures. |
gr-qc/0002085 | Vladimir Ivashchuk | V. D. Ivashchuk and V. N. Melnikov | P-brane black holes for general intersections | 12 pages, Latex, few typos are eliminated, a correct relation for
parameters of special block-orthogonal solution is added (p. 6) | Grav. Cosmol. 5 (1999) 313-318 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black hole generalized p-brane solutions for a wide class of intersection
rules are presented. The solutions are defined on a manifold that contains a
product of n - 1 Ricci-flat internal spaces. They are defined up to moduli
functions H_s = H_s(R) obeying a non-linear differential equations (equivalent
to Toda-type equations) with certain boundary conditions imposed. Using
conjecture on polynomial structure of H_s for intersections related to Lie
algebras, new A_2-dyon solutions are obtained. Two examples of these A_2-dyon
solutions, i.e. dyon in D = 11 supergravity with M2 and M5 branes intersecting
at a point and dyon in Kaluza-Klein theory, are considered.
| [
{
"created": "Fri, 25 Feb 2000 06:48:24 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Apr 2009 17:39:32 GMT",
"version": "v2"
}
] | 2009-04-17 | [
[
"Ivashchuk",
"V. D.",
""
],
[
"Melnikov",
"V. N.",
""
]
] | Black hole generalized p-brane solutions for a wide class of intersection rules are presented. The solutions are defined on a manifold that contains a product of n - 1 Ricci-flat internal spaces. They are defined up to moduli functions H_s = H_s(R) obeying a non-linear differential equations (equivalent to Toda-type equations) with certain boundary conditions imposed. Using conjecture on polynomial structure of H_s for intersections related to Lie algebras, new A_2-dyon solutions are obtained. Two examples of these A_2-dyon solutions, i.e. dyon in D = 11 supergravity with M2 and M5 branes intersecting at a point and dyon in Kaluza-Klein theory, are considered. |
1203.0205 | Ghulam Abbas | M. Sharif, G. Abbas | Non-Commutative Correction to Thin Shell Collapse in Reissner
Nordstr$\ddot{o}$m Geometry | 18 pages,17 figures | J. Phys. Soc. Jpn 81(2012) 044002 | 10.1143/JPSJ.81.044002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper investigates the polytropic matter shell collapse in the
non-commutative Reissner-Nordstr$\ddot{o}$m geometry. Using the Israel
criteria, equation of motion for the polytropic matter shell is derived. In
order to explore the physical aspects of this equation, the most general
equation of state, $p=k{\rho}^{({1+\frac{1}{n}})}$, has been used for finite
and infinite values of $n$. The effective potentials corresponding to the
equation of motion have been used to explain different states of the matter
shell collapse. The numerical solution of the equation of motion predicts
collapse as well as expansion depending on the choice of initial data. Further,
in order to include the non-commutative correction, we modify the matter
components and re-formulate the equation of motion as well as the corresponding
effective potentials by including non-commutative factor and charge parameter.
It is concluded that charge reduces the velocity of the expanding or collapsing
matter shell but does not bring the shell to static position. While the
non-commutative factor with generic matter favors the formation of black hole.
| [
{
"created": "Wed, 29 Feb 2012 06:54:49 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Mar 2012 08:41:50 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Sharif",
"M.",
""
],
[
"Abbas",
"G.",
""
]
] | This paper investigates the polytropic matter shell collapse in the non-commutative Reissner-Nordstr$\ddot{o}$m geometry. Using the Israel criteria, equation of motion for the polytropic matter shell is derived. In order to explore the physical aspects of this equation, the most general equation of state, $p=k{\rho}^{({1+\frac{1}{n}})}$, has been used for finite and infinite values of $n$. The effective potentials corresponding to the equation of motion have been used to explain different states of the matter shell collapse. The numerical solution of the equation of motion predicts collapse as well as expansion depending on the choice of initial data. Further, in order to include the non-commutative correction, we modify the matter components and re-formulate the equation of motion as well as the corresponding effective potentials by including non-commutative factor and charge parameter. It is concluded that charge reduces the velocity of the expanding or collapsing matter shell but does not bring the shell to static position. While the non-commutative factor with generic matter favors the formation of black hole. |
gr-qc/0508019 | Robert Brout | Robert Brout | From Inflation to Dark Energy | 4 pages, RevTex | null | null | null | gr-qc | null | It is proposed that after the macroscopic fluctuation of energy density that
is responsible for inflation dies away, a class of microscopic fluctuations,
always present, survives to give the present day dark energy. This latter is
simply a reinterpretation of the causet mechanism of Ahmed, Dodelson, Green and
Sorkin, wherein the emergence of space is dropped but only energy
considerations are maintained. At postinflation times, energy is exchanged
between the "cisplanckian" cosmos and an unknown foam-like transplanckian
reservoir. Whereas during inflation, the energy flows only from the latter to
the former after inflation it fluctuates in sign thereby accounting for the
tiny effective cosmological constant that seems to account for dark energy.
| [
{
"created": "Thu, 4 Aug 2005 17:48:26 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Brout",
"Robert",
""
]
] | It is proposed that after the macroscopic fluctuation of energy density that is responsible for inflation dies away, a class of microscopic fluctuations, always present, survives to give the present day dark energy. This latter is simply a reinterpretation of the causet mechanism of Ahmed, Dodelson, Green and Sorkin, wherein the emergence of space is dropped but only energy considerations are maintained. At postinflation times, energy is exchanged between the "cisplanckian" cosmos and an unknown foam-like transplanckian reservoir. Whereas during inflation, the energy flows only from the latter to the former after inflation it fluctuates in sign thereby accounting for the tiny effective cosmological constant that seems to account for dark energy. |
1608.01960 | Emmanuil Saridakis | Rafael C. Nunes, Alexander Bonilla, Supriya Pan, Emmanuel N. Saridakis | Observational Constraints on $f(T)$ gravity from varying fundamental
constants | 9 pages, 6 figures, 3 Tables, version published in Eur.Phys.J. C | Eur.Phys.J. C77 (2017) 230 | 10.1140/epjc/s10052-017-4798-5 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use observations related to the variation of fundamental constants, in
order to impose constraints on the viable and most used $f(T)$ gravity models.
In particular, for the fine-structure constant we use direct measurements
obtained by different spectrographic methods, while for the effective Newton's
constant we use a model-dependent reconstruction, using direct observational
Hubble parameter data, in order to investigate its temporal evolution. We
consider two $f(T)$ models and we quantify their deviation from $\Lambda$CDM
cosmology through a sole parameter. Our analysis reveals that this parameter
can be slightly different from its $\Lambda$CDM value, however the best-fit
value is very close to the $\Lambda$CDM one. Hence, $f(T)$ gravity is
consistent with observations, nevertheless, as every modified gravity, it may
exhibit only small deviations from $\Lambda$CDM cosmology, a feature that must
be taken into account in any $f(T)$ model-building.
| [
{
"created": "Fri, 5 Aug 2016 18:07:27 GMT",
"version": "v1"
},
{
"created": "Fri, 21 Oct 2016 11:25:06 GMT",
"version": "v2"
},
{
"created": "Mon, 17 Apr 2017 15:02:12 GMT",
"version": "v3"
}
] | 2017-04-18 | [
[
"Nunes",
"Rafael C.",
""
],
[
"Bonilla",
"Alexander",
""
],
[
"Pan",
"Supriya",
""
],
[
"Saridakis",
"Emmanuel N.",
""
]
] | We use observations related to the variation of fundamental constants, in order to impose constraints on the viable and most used $f(T)$ gravity models. In particular, for the fine-structure constant we use direct measurements obtained by different spectrographic methods, while for the effective Newton's constant we use a model-dependent reconstruction, using direct observational Hubble parameter data, in order to investigate its temporal evolution. We consider two $f(T)$ models and we quantify their deviation from $\Lambda$CDM cosmology through a sole parameter. Our analysis reveals that this parameter can be slightly different from its $\Lambda$CDM value, however the best-fit value is very close to the $\Lambda$CDM one. Hence, $f(T)$ gravity is consistent with observations, nevertheless, as every modified gravity, it may exhibit only small deviations from $\Lambda$CDM cosmology, a feature that must be taken into account in any $f(T)$ model-building. |
2404.18964 | Bikramarka Samadder Choudhury Mr. | Farook Rahaman, Bikramarka S Choudhury | Evolving wormhole geometry from dark matter energy density | Paper is accepted for publication in 'The European Physical Journal
C' | null | 10.1140/epjc/s10052-024-12859-7 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We analyze traversable wormholes defined by the dynamic line elements that
asymptotically approaches Friedmann-Robertson-Walker (FRW) universe. This
dynamical wormholes is supported by the galactic dark matter as well as perfect
isotropic fluid. We will discuss several evolving Lorentzian wormholes
comprising with different perfect isotropic fluids in addition to various scale
factors. We will speculate the various significance, features and throat energy
conditions for these evolving traversable Lorentzian wormholes.
| [
{
"created": "Mon, 29 Apr 2024 11:20:23 GMT",
"version": "v1"
}
] | 2024-05-24 | [
[
"Rahaman",
"Farook",
""
],
[
"Choudhury",
"Bikramarka S",
""
]
] | We analyze traversable wormholes defined by the dynamic line elements that asymptotically approaches Friedmann-Robertson-Walker (FRW) universe. This dynamical wormholes is supported by the galactic dark matter as well as perfect isotropic fluid. We will discuss several evolving Lorentzian wormholes comprising with different perfect isotropic fluids in addition to various scale factors. We will speculate the various significance, features and throat energy conditions for these evolving traversable Lorentzian wormholes. |
1709.01525 | Vitor Cardoso | Vitor Cardoso, Paolo Pani | Tests for the existence of horizons through gravitational wave echoes | Published in Nature Astronomy, expanded version with further details
available at arXiv:1707.03021 | Nature Astronomy 1: 586-591 (2017) | 10.1038/s41550-017-0225-y | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The existence of black holes and of spacetime singularities is a fundamental
issue in science. Despite this, observations supporting their existence are
scarce, and their interpretation unclear. We overview how strong a case for
black holes has been made in the last few decades, and how well observations
adjust to this paradigm. Unsurprisingly, we conclude that observational proof
for black holes is impossible to come by. However, just like Popper's black
swan, alternatives can be ruled out or confirmed to exist with a single
observation. These observations are within reach. In the next few years and
decades, we will enter the era of precision gravitational-wave physics with
more sensitive detectors. Just as accelerators require larger and larger
energies to probe smaller and smaller scales, more sensitive gravitational-wave
detectors will be probing regions closer and closer to the horizon, potentially
reaching Planck scales and beyond. What may be there, lurking?
| [
{
"created": "Tue, 5 Sep 2017 18:00:26 GMT",
"version": "v1"
}
] | 2017-09-07 | [
[
"Cardoso",
"Vitor",
""
],
[
"Pani",
"Paolo",
""
]
] | The existence of black holes and of spacetime singularities is a fundamental issue in science. Despite this, observations supporting their existence are scarce, and their interpretation unclear. We overview how strong a case for black holes has been made in the last few decades, and how well observations adjust to this paradigm. Unsurprisingly, we conclude that observational proof for black holes is impossible to come by. However, just like Popper's black swan, alternatives can be ruled out or confirmed to exist with a single observation. These observations are within reach. In the next few years and decades, we will enter the era of precision gravitational-wave physics with more sensitive detectors. Just as accelerators require larger and larger energies to probe smaller and smaller scales, more sensitive gravitational-wave detectors will be probing regions closer and closer to the horizon, potentially reaching Planck scales and beyond. What may be there, lurking? |
0903.3368 | Salvatore Capozziello | S. Capozziello and S. Vignolo | A comment on "The Cauchy problem of f(R)- gravity", Class. Quantum
Grav., 24, 5667 (2007), arXiv:0709.4414 | 3 pages | Class.Quant.Grav.24:5667,2007; Class.Quant.Grav.26:168001,2009 | 10.1088/0264-9381/26/16/168001 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A critical comment on [N. Lanahan--Tremblay and V. Faraoni, 2007, {\it Class.
Quantum Grav.}, {\bf 24}, 5667, arXiv:0709.4414] is given discussing the
well-formulation of the Chauchy problem for $f(R)$-gravity in metric-affine
theories.
| [
{
"created": "Thu, 19 Mar 2009 17:02:54 GMT",
"version": "v1"
}
] | 2009-09-17 | [
[
"Capozziello",
"S.",
""
],
[
"Vignolo",
"S.",
""
]
] | A critical comment on [N. Lanahan--Tremblay and V. Faraoni, 2007, {\it Class. Quantum Grav.}, {\bf 24}, 5667, arXiv:0709.4414] is given discussing the well-formulation of the Chauchy problem for $f(R)$-gravity in metric-affine theories. |
0807.0665 | Dah-Wei Chiou | Dah-Wei Chiou | Phenomenological loop quantum geometry of the Schwarzschild black hole | 26 pages, 6 figures, 1 table; version to appear in PRD | Phys.Rev.D78:064040,2008 | 10.1103/PhysRevD.78.064040 | IGC-08/7-1 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The interior of a Schwarzschild black hole is investigated at the level of
phenomenological dynamics with the discreteness corrections of loop quantum
geometry implemented in two different improved quantization schemes. In one
scheme, the classical black hole singularity is resolved by the quantum bounce,
which bridges the black hole interior with a white hole interior. In the other
scheme, the classical singularity is resolved and the event horizon is also
diffused by the quantum bounce. Jumping over the quantum bounce, the black hole
gives birth to a baby black hole with a much smaller mass. This lineage
continues as each classical black hole brings forth its own descendant in the
consecutive classical cycle, giving the whole extended spacetime fractal
structure, until the solution eventually descends into deep Planck regime,
signaling a breakdown of the semiclassical description. The issues of scaling
symmetry and no-hair theorem are also discussed.
| [
{
"created": "Fri, 4 Jul 2008 03:10:40 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Sep 2008 10:04:17 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Chiou",
"Dah-Wei",
""
]
] | The interior of a Schwarzschild black hole is investigated at the level of phenomenological dynamics with the discreteness corrections of loop quantum geometry implemented in two different improved quantization schemes. In one scheme, the classical black hole singularity is resolved by the quantum bounce, which bridges the black hole interior with a white hole interior. In the other scheme, the classical singularity is resolved and the event horizon is also diffused by the quantum bounce. Jumping over the quantum bounce, the black hole gives birth to a baby black hole with a much smaller mass. This lineage continues as each classical black hole brings forth its own descendant in the consecutive classical cycle, giving the whole extended spacetime fractal structure, until the solution eventually descends into deep Planck regime, signaling a breakdown of the semiclassical description. The issues of scaling symmetry and no-hair theorem are also discussed. |
2303.12842 | Emma Albertini | Emma Albertini, Kyle Barnes, Gabriel Herczeg | Dynamical Henneaux-Teitelboim Gravity | 10 pages, 2 figures | null | 10.1103/PhysRevD.108.024031 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider a modified gravity model which we call "dynamical
Henneaux-Teitelboim gravity" because of its close relationship with the
Henneaux-Teitelboim formulation of unimodular gravity. The latter is a fully
diffeomorphism-invariant formulation of unimodular gravity, where full
diffeomorphism invariance is achieved by introducing two additional
non-dynamical fields: a scalar, which plays the role of a cosmological
constant, and a three-form whose exterior derivative is the spacetime volume
element. Dynamical Henneaux-Teitelboim gravity is a generalization of this
model that includes kinetic terms for both the scalar and the three-form with
arbitrary couplings. We study the field equations for the cases of spherically
symmetric and homogeneous, isotropic configurations. In the spherically
symmetric case, we solve the field equations analytically for small values of
the coupling to obtain an approximate black hole solution. In the homogeneous
and isotropic case, we perturb around de Sitter space to find an approximate
cosmological background for our model.
| [
{
"created": "Wed, 22 Mar 2023 18:01:13 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Jun 2023 14:10:12 GMT",
"version": "v2"
}
] | 2023-07-26 | [
[
"Albertini",
"Emma",
""
],
[
"Barnes",
"Kyle",
""
],
[
"Herczeg",
"Gabriel",
""
]
] | We consider a modified gravity model which we call "dynamical Henneaux-Teitelboim gravity" because of its close relationship with the Henneaux-Teitelboim formulation of unimodular gravity. The latter is a fully diffeomorphism-invariant formulation of unimodular gravity, where full diffeomorphism invariance is achieved by introducing two additional non-dynamical fields: a scalar, which plays the role of a cosmological constant, and a three-form whose exterior derivative is the spacetime volume element. Dynamical Henneaux-Teitelboim gravity is a generalization of this model that includes kinetic terms for both the scalar and the three-form with arbitrary couplings. We study the field equations for the cases of spherically symmetric and homogeneous, isotropic configurations. In the spherically symmetric case, we solve the field equations analytically for small values of the coupling to obtain an approximate black hole solution. In the homogeneous and isotropic case, we perturb around de Sitter space to find an approximate cosmological background for our model. |
gr-qc/9902035 | Raul Vera | Jose M M Senovilla and Raul Vera | Segre decomposition of spacetimes | 15 pages, provisionally scheduled for April 1999 in Class. Quantum
Grav | Class.Quant.Grav. 16 (1999) 1185-1196 | 10.1088/0264-9381/16/4/008 | null | gr-qc | null | Following a recent work in which it is shown that a spacetime admitting
Lie-group actions may be disjointly decomposed into a a closed subset with no
interior plus a dense finite union of open sets in each of which the character
and dimension of the group orbits as well as the Petrov type are constant, the
aim of this work is to include the Segre types of the Ricci tensor (and hence
of the Einstein tensor) into the decomposition. We also show how this type of
decomposition can be carried out for any type of property of the spacetime
depending on the existence of a continuous endomorphism.
| [
{
"created": "Thu, 11 Feb 1999 16:39:02 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Senovilla",
"Jose M M",
""
],
[
"Vera",
"Raul",
""
]
] | Following a recent work in which it is shown that a spacetime admitting Lie-group actions may be disjointly decomposed into a a closed subset with no interior plus a dense finite union of open sets in each of which the character and dimension of the group orbits as well as the Petrov type are constant, the aim of this work is to include the Segre types of the Ricci tensor (and hence of the Einstein tensor) into the decomposition. We also show how this type of decomposition can be carried out for any type of property of the spacetime depending on the existence of a continuous endomorphism. |
1706.04288 | V\'ictor Manuel V\'azquez-B\'aez Dr. | V. V\'azquez-B\'aez, C. Ram\'irez | Quantum cosmology of quadratic f(R) theories with a FRW metric | 6 pages, 4 figures | Advances in Mathematical Physics Volume 2017 (2017), Article ID
1056514, 5 pages | 10.1155/2017/1056514 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the quantum cosmology of a quadratic $f(R)$ theory with a FRW
metric, via one of its equivalent Horndeski type actions, where the dynamics of
the scalar field is induced. The classical equations of motion and the
Weeler-deWitt equation, in their exact versions, are solved numerically. From
the choice of a free parameter in the action follow two cases, inflation + exit
and inflation alone. The numerical solution of the Wheeler-DeWitt equation
depends strongly on the boundary conditions, which can be chosen so that the
resulting wave function of the universe seems to be normalizable and consistent
with hermitian operators.
| [
{
"created": "Wed, 14 Jun 2017 00:24:43 GMT",
"version": "v1"
},
{
"created": "Tue, 20 Jun 2017 18:23:40 GMT",
"version": "v2"
}
] | 2017-06-22 | [
[
"Vázquez-Báez",
"V.",
""
],
[
"Ramírez",
"C.",
""
]
] | We study the quantum cosmology of a quadratic $f(R)$ theory with a FRW metric, via one of its equivalent Horndeski type actions, where the dynamics of the scalar field is induced. The classical equations of motion and the Weeler-deWitt equation, in their exact versions, are solved numerically. From the choice of a free parameter in the action follow two cases, inflation + exit and inflation alone. The numerical solution of the Wheeler-DeWitt equation depends strongly on the boundary conditions, which can be chosen so that the resulting wave function of the universe seems to be normalizable and consistent with hermitian operators. |
1109.2928 | Stephane Houndjo Dr | M. Hamani Daouda, Manuel E. Rodrigues, M. J. S. Houndjo | New Black Holes Solutions in a Modified Gravity | 15 pages, accepted for publication in ISRN Astronomy and Astrophysics | ISRN Astronomy and Astrophysics, 2011, ID 341919 (2011) | 10.5402/2011/341919 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a theory of modified gravity, inspired by the gauge theories,
where the commutator algebra of covariant derivative gives us an added term
with respect to the General Relativity, which represents the interaction of
gravity with a substratum. New spherically symmetric solutions of this theory
are obtained and can be view as solutions that reproduce, the mass, the charge,
the cosmological constant and the Rindler acceleration, without coupling with
the matter content, i.e., in the vacuum.
| [
{
"created": "Tue, 13 Sep 2011 21:03:50 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Sep 2011 17:00:32 GMT",
"version": "v2"
},
{
"created": "Wed, 19 Oct 2011 15:32:24 GMT",
"version": "v3"
},
{
"created": "Wed, 14 Dec 2011 01:00:06 GMT",
"version": "v4"
}
] | 2012-01-05 | [
[
"Daouda",
"M. Hamani",
""
],
[
"Rodrigues",
"Manuel E.",
""
],
[
"Houndjo",
"M. J. S.",
""
]
] | We present a theory of modified gravity, inspired by the gauge theories, where the commutator algebra of covariant derivative gives us an added term with respect to the General Relativity, which represents the interaction of gravity with a substratum. New spherically symmetric solutions of this theory are obtained and can be view as solutions that reproduce, the mass, the charge, the cosmological constant and the Rindler acceleration, without coupling with the matter content, i.e., in the vacuum. |
1911.00494 | Timothy Walton | Robin W. Tucker, Timothy J. Walton, Manuel Array\'as and Jos\'e L.
Trueba | A new paradigm for the dynamics of the early Universe | 36 pages, 5 figures | null | 10.1088/1361-6382/ab4ecc | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper invokes a new mechanism for reducing a coupled system of fields
(including Einstein's equations without a cosmological constant) to equations
that possess solutions exhibiting characteristics of immediate relevance to
current observational astronomy. Our approach is formulated as a classical
Einstein-vector-scalar-Maxwell-fluid field theory on a spacetime with
three-sphere spatial sections. Analytic cosmological solutions are found using
local charts familiar from standard LFRW cosmological models. These solutions
can be used to describe different types of evolution for the metric scale
factor, the Hubble, jerk and de-acceleration functions, the scalar spacetime
curvature and the Kretschmann invariant. The cosmological sector of the theory
accommodates a particular single big-bang scenario followed by an eternal
exponential acceleration of the scale factor. Such a solution does not require
an externally prescribed fluid equation of state and leads to a number of new
predictions including a current value of the "jerk" parameter, "Hopfian-like"
source-free Maxwell field configurations with magnetic helicity and
distributional "bi-polar" solutions exhibiting a new charge conjugation
symmetry. An approximate scheme for field perturbations about this particular
cosmology is explored and its consequences for a thermalisation process and a
thermal history are derived, leading to a prediction of the time interval
between the big-bang and the decoupling era. Finally it is shown that field
couplings exist where both vector and scalar localised linearised perturbations
exhibit dispersive wave-packet behaviours. The scalar perturbation may also
give rise to Yukawa solutions associated with a massive Klein-Gordon particle.
It is argued that the vector and scalar fields may offer candidates for
"dark-energy" and "dark-matter" respectively.
| [
{
"created": "Sun, 3 Nov 2019 11:43:14 GMT",
"version": "v1"
}
] | 2019-11-05 | [
[
"Tucker",
"Robin W.",
""
],
[
"Walton",
"Timothy J.",
""
],
[
"Arrayás",
"Manuel",
""
],
[
"Trueba",
"José L.",
""
]
] | This paper invokes a new mechanism for reducing a coupled system of fields (including Einstein's equations without a cosmological constant) to equations that possess solutions exhibiting characteristics of immediate relevance to current observational astronomy. Our approach is formulated as a classical Einstein-vector-scalar-Maxwell-fluid field theory on a spacetime with three-sphere spatial sections. Analytic cosmological solutions are found using local charts familiar from standard LFRW cosmological models. These solutions can be used to describe different types of evolution for the metric scale factor, the Hubble, jerk and de-acceleration functions, the scalar spacetime curvature and the Kretschmann invariant. The cosmological sector of the theory accommodates a particular single big-bang scenario followed by an eternal exponential acceleration of the scale factor. Such a solution does not require an externally prescribed fluid equation of state and leads to a number of new predictions including a current value of the "jerk" parameter, "Hopfian-like" source-free Maxwell field configurations with magnetic helicity and distributional "bi-polar" solutions exhibiting a new charge conjugation symmetry. An approximate scheme for field perturbations about this particular cosmology is explored and its consequences for a thermalisation process and a thermal history are derived, leading to a prediction of the time interval between the big-bang and the decoupling era. Finally it is shown that field couplings exist where both vector and scalar localised linearised perturbations exhibit dispersive wave-packet behaviours. The scalar perturbation may also give rise to Yukawa solutions associated with a massive Klein-Gordon particle. It is argued that the vector and scalar fields may offer candidates for "dark-energy" and "dark-matter" respectively. |
1608.02696 | Amitabha Lahiri | Karan Fernandes, Suman Ghosh, Amitabha Lahiri | Constrained field theories on spherically symmetric spacetimes with
horizons | 23 pp | Phys. Rev. D 95, 045012 (2017) | 10.1103/PhysRevD.95.045012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We apply the Dirac-Bergmann algorithm for the analysis of constraints to
gauge theories defined on spherically symmetric black hole backgrounds. We find
that the constraints for a given theory are modified on such spacetimes through
the presence of additional contributions from the horizon. As a concrete
example, we consider the Maxwell field on a black hole background, and
determine the role of the horizon contributions on the dynamics of the theory.
| [
{
"created": "Tue, 9 Aug 2016 05:52:48 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Dec 2016 15:45:32 GMT",
"version": "v2"
}
] | 2017-03-01 | [
[
"Fernandes",
"Karan",
""
],
[
"Ghosh",
"Suman",
""
],
[
"Lahiri",
"Amitabha",
""
]
] | We apply the Dirac-Bergmann algorithm for the analysis of constraints to gauge theories defined on spherically symmetric black hole backgrounds. We find that the constraints for a given theory are modified on such spacetimes through the presence of additional contributions from the horizon. As a concrete example, we consider the Maxwell field on a black hole background, and determine the role of the horizon contributions on the dynamics of the theory. |
1403.0988 | Gregory J. Galloway | Kenneth L. Baker and Gregory J. Galloway | On the topology of initial data sets with higher genus ends | v2: 13 pages, 1 figure; minor corrections and changes, Lemma 2.2
added. To appear in Commun Math Phys | null | 10.1007/s00220-015-2309-9 | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this note we study the topology of 3-dimensional initial data sets with
horizons of a sort associated with asymptotically locally anti-de Sitter
spacetimes. We show that, within this class, those initial data sets which
contain no (immersed) marginally outer trapped surfaces in their interior must
have simple topology: they are a product of a surface and an interval, or a
mild variation thereof, depending on the connectedness of the horizon and on
its genus relative to that of the end. The results obtained here extend results
in [11] to the case of higher genus ends.
| [
{
"created": "Wed, 5 Mar 2014 02:08:22 GMT",
"version": "v1"
},
{
"created": "Tue, 23 Dec 2014 15:03:55 GMT",
"version": "v2"
}
] | 2015-06-19 | [
[
"Baker",
"Kenneth L.",
""
],
[
"Galloway",
"Gregory J.",
""
]
] | In this note we study the topology of 3-dimensional initial data sets with horizons of a sort associated with asymptotically locally anti-de Sitter spacetimes. We show that, within this class, those initial data sets which contain no (immersed) marginally outer trapped surfaces in their interior must have simple topology: they are a product of a surface and an interval, or a mild variation thereof, depending on the connectedness of the horizon and on its genus relative to that of the end. The results obtained here extend results in [11] to the case of higher genus ends. |
1212.4987 | Remo Garattini | Remo Garattini and Mairi Sakellariadou | Does Gravity's Rainbow induce Inflation without an Inflaton? | Published In Phys. Rev. D. Revised version with major modifications
about Gravity's Rainbow functions. RevTeX, 13 Pages | Phys. Rev. D 90, 043521 (2014) | 10.1103/PhysRevD.90.043521 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study aspects of quantum cosmology in the presence of a modified
space-time geometry. In particular, within the context of Gravity's Rainbow
modified geometry, motivated from quantum gravity corrections at the Planck
energy scale, we show that the distortion of the metric leads to a Wheeler-De
Witt equation whose solution admits outgoing plane waves. Hence, a period of
cosmological inflation may arise without the need for introducing an inflaton
field.
| [
{
"created": "Thu, 20 Dec 2012 11:34:04 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Aug 2014 09:55:12 GMT",
"version": "v2"
}
] | 2014-08-21 | [
[
"Garattini",
"Remo",
""
],
[
"Sakellariadou",
"Mairi",
""
]
] | We study aspects of quantum cosmology in the presence of a modified space-time geometry. In particular, within the context of Gravity's Rainbow modified geometry, motivated from quantum gravity corrections at the Planck energy scale, we show that the distortion of the metric leads to a Wheeler-De Witt equation whose solution admits outgoing plane waves. Hence, a period of cosmological inflation may arise without the need for introducing an inflaton field. |
1702.02800 | Oleksandr Stashko | O. S. Stashko and V. I. Zhdanov | Spherically symmetric configurations of General Relativity in presence
of scalar field: separation of test body circular orbits | 10 pages, 9 figures | null | 10.1007/s10714-018-2425-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study test-body orbits in the gravitational field of a static spherically
symmetric object in presence of a minimally coupled nonlinear scalar field. We
generated a two-parametric family of scalar field potentials, which allow
finding solutions of Einstein's equations in an analytic form. The results are
presented by means of hypergeometric functions; they describe either a naked
singularity (NS) or a black hole (BH). Our numerical investigation shows that
in both cases the stable circular orbits can form separated (non-connected)
regions around the configuration. We found existence conditions for such
separated regions and present examples for some family parameters in case of NS
and BH. The results may be of interest for testing models of the dynamical dark
energy.
| [
{
"created": "Thu, 9 Feb 2017 12:09:35 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Jul 2017 22:32:56 GMT",
"version": "v2"
}
] | 2018-08-22 | [
[
"Stashko",
"O. S.",
""
],
[
"Zhdanov",
"V. I.",
""
]
] | We study test-body orbits in the gravitational field of a static spherically symmetric object in presence of a minimally coupled nonlinear scalar field. We generated a two-parametric family of scalar field potentials, which allow finding solutions of Einstein's equations in an analytic form. The results are presented by means of hypergeometric functions; they describe either a naked singularity (NS) or a black hole (BH). Our numerical investigation shows that in both cases the stable circular orbits can form separated (non-connected) regions around the configuration. We found existence conditions for such separated regions and present examples for some family parameters in case of NS and BH. The results may be of interest for testing models of the dynamical dark energy. |
gr-qc/0112063 | Wu Ning | Ning Wu, Germano Resconi, Zhan Xu, Zhi-Peng Zheng, Da-Hua Zhang,
Tu-Nan Ruan | Determination of Cosmological Constant from Gauge Theory of Gravity | 6 pages, no fugures, Latex File | null | null | null | gr-qc | null | Combining general relativity and gravitational gauge theory, the cosmological
constant is determined theoretically. The cosmological constant is related to
the average vacuum energy of gravitational gauge field. Because the vacuum
energy of gravitational gauge field is negative, the cosmological constant is
positive, which generates repulsive force on stars to make the expansion rate
of the Universe accelerated. A rough estimation of it gives out its magnitude
of the order of $10^{-52} m^{-2}$, which is well constant with experimental
results.
| [
{
"created": "Mon, 24 Dec 2001 03:29:59 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Wu",
"Ning",
""
],
[
"Resconi",
"Germano",
""
],
[
"Xu",
"Zhan",
""
],
[
"Zheng",
"Zhi-Peng",
""
],
[
"Zhang",
"Da-Hua",
""
],
[
"Ruan",
"Tu-Nan",
""
]
] | Combining general relativity and gravitational gauge theory, the cosmological constant is determined theoretically. The cosmological constant is related to the average vacuum energy of gravitational gauge field. Because the vacuum energy of gravitational gauge field is negative, the cosmological constant is positive, which generates repulsive force on stars to make the expansion rate of the Universe accelerated. A rough estimation of it gives out its magnitude of the order of $10^{-52} m^{-2}$, which is well constant with experimental results. |
1406.7514 | Rong-Jia Yang | Jun Li, Rong-Jia Yang, Bohai Chen | Discriminating dark energy models by using the statefinder hierarchy and
the growth rate of matter perturbations | 12 pages, 9 figures | JCAP12(2014)043 | 10.1088/1475-7516/2014/12/043 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We apply the Statefinder hierarchy and the growth rate of matter
perturbations to discriminate modified Chaplygin gas (MCG), generalized
Chaplygin gas (GCG), superfluid Chaplygin gas (SCG), purely kinetic k-essence
(PKK), and $\Lambda$CDM model. We plot the evolutional trajectories of these
models in the statefinder plane and in the composite diagnostic plane. We find
that GCG, MCG, SCG, PKK, and $\Lambda$CDM can be distinguished well from each
other at the present epoch by using the composite diagnostic $\{\epsilon(z),
S^{(1)}_{5}\}$. Using other combinations, such as $\{S^{(1)}_{3}, S^{(1)}_4\}$,
$\{S^{(1)}_{3}, S_{5}\}$, $\{\epsilon(z), S^{(1)}_{3}\}$, and $\{\epsilon(z),
S_4 \}$, some of these five dark energy models cannot be distinguished.
| [
{
"created": "Sun, 29 Jun 2014 14:44:14 GMT",
"version": "v1"
},
{
"created": "Sun, 28 Dec 2014 14:27:34 GMT",
"version": "v2"
}
] | 2014-12-30 | [
[
"Li",
"Jun",
""
],
[
"Yang",
"Rong-Jia",
""
],
[
"Chen",
"Bohai",
""
]
] | We apply the Statefinder hierarchy and the growth rate of matter perturbations to discriminate modified Chaplygin gas (MCG), generalized Chaplygin gas (GCG), superfluid Chaplygin gas (SCG), purely kinetic k-essence (PKK), and $\Lambda$CDM model. We plot the evolutional trajectories of these models in the statefinder plane and in the composite diagnostic plane. We find that GCG, MCG, SCG, PKK, and $\Lambda$CDM can be distinguished well from each other at the present epoch by using the composite diagnostic $\{\epsilon(z), S^{(1)}_{5}\}$. Using other combinations, such as $\{S^{(1)}_{3}, S^{(1)}_4\}$, $\{S^{(1)}_{3}, S_{5}\}$, $\{\epsilon(z), S^{(1)}_{3}\}$, and $\{\epsilon(z), S_4 \}$, some of these five dark energy models cannot be distinguished. |
1312.2906 | Ranjan Sharma | Megan Govender, Robert Bogadi, Ranjan Sharma and Shyam Das | Gravitational collapse in spatially isotropic coordinates | Submitted for publication | Gen. Relativ. Gravit (2015) 47:25 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the dynamical nature of the collapse process of a spherically
symmetric star in quasi-static hydrodynamical equilibrium. The star collapses
from an initial static configuration by dissipating energy in the form of a
radial heat flux. The dissipation ensures that the singularity is never formed
and the stellar mass completely evaporates over a finite time.
| [
{
"created": "Mon, 9 Dec 2013 06:24:40 GMT",
"version": "v1"
}
] | 2017-11-20 | [
[
"Govender",
"Megan",
""
],
[
"Bogadi",
"Robert",
""
],
[
"Sharma",
"Ranjan",
""
],
[
"Das",
"Shyam",
""
]
] | We investigate the dynamical nature of the collapse process of a spherically symmetric star in quasi-static hydrodynamical equilibrium. The star collapses from an initial static configuration by dissipating energy in the form of a radial heat flux. The dissipation ensures that the singularity is never formed and the stellar mass completely evaporates over a finite time. |
1409.5069 | Douglas A. Singleton | Piero Nicolini and Douglas Singleton | Connecting horizon pixels and interior voxels of a black hole | 10 pages, 0 figures, published version with note added | Phys.Lett. B738 (2014) 213-217 | 10.1016/j.physletb.2014.09.038 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we discuss to what extent one can infer details of the interior
structure of a black hole based on its horizon. Recalling that black hole
thermal properties are connected to the non-classical nature of gravity, we
circumvent the restrictions of the no hair theorem by postulating that the
black hole interior is singularity free due to violations of the usual energy
conditions. Further these conditions allow one to establish a one-to-one,
holographic projection between Planckian areal "bits" on the horizon and
"voxels", representing the gravitational degrees of freedom in the black hole
interior. We illustrate the repercussions of this idea by discussing an example
of the black hole interior consisting of a de Sitter core postulated to arise
from the local graviton quantum vacuum energy. It is shown that the black hole
entropy can emerge as the statistical entropy of a gas of voxels.
| [
{
"created": "Wed, 17 Sep 2014 17:02:23 GMT",
"version": "v1"
},
{
"created": "Fri, 3 Oct 2014 19:13:20 GMT",
"version": "v2"
}
] | 2014-10-06 | [
[
"Nicolini",
"Piero",
""
],
[
"Singleton",
"Douglas",
""
]
] | In this paper we discuss to what extent one can infer details of the interior structure of a black hole based on its horizon. Recalling that black hole thermal properties are connected to the non-classical nature of gravity, we circumvent the restrictions of the no hair theorem by postulating that the black hole interior is singularity free due to violations of the usual energy conditions. Further these conditions allow one to establish a one-to-one, holographic projection between Planckian areal "bits" on the horizon and "voxels", representing the gravitational degrees of freedom in the black hole interior. We illustrate the repercussions of this idea by discussing an example of the black hole interior consisting of a de Sitter core postulated to arise from the local graviton quantum vacuum energy. It is shown that the black hole entropy can emerge as the statistical entropy of a gas of voxels. |
2110.02489 | Panagiotis Mavrogiannis | Panagiotis Mavrogiannis and Christos G. Tsagas | How the magnetic field behaves during the motion of a highly conducting
fluid under its own gravity--A new theoretical, relativistic approach | 34 pages, minor comments added | Phys. Rev. D 104, 124053 (2021) | 10.1103/PhysRevD.104.124053 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Within the context of general relativity we study in a fully covariant way
the so-called Euler-Maxwell system of equations. In particular, on decomposing
the aforementioned system into its 1 temporal and 1 + 2 spatial components at
the ideal magnetohydrodynamic limit, we bring it in a simplified form that
favors physical insight to the problem of a self-gravitating, magnetized fluid.
Of central interest is the decomposition of Faraday's equation which leads to a
new general solution governing the evolution of the magnetic field during the
motion of the highly conducting fluid. According to the latter relation, the
magnetic field generally grows or decays in proportion to the inverse cube law
of the scale factor--associated with the continuous contraction or expansion of
the fluid's volume respectively. The magnetic field's law of variation, which
has remarkable implications for the motion of the whole fluid, is subsequently
applied to homogeneous (anisotropic-magnetized) cosmological models--especially
to the Bianchi I case--as well as to the study of homogeneous and anisotropic
gravitational collapse in a magnetized environment. Concerning the cosmological
application, we derive the evolution equations of Bianchi I spacetime permeated
by large-scale magnetic fields (these equations reduce to their FRW
counterparts at the small/large--scale limit). Also, the compatibility of the
new evolution formula for the magnetic field with the standard cosmic
nucleosynthesis constraint is examined. As for the application in astrophysics,
our results predict that homogeneous gravitational implosion is impeded when
the electric Weyl tensor (associated with tidal forces) along the magnetic
forcelines overwhelms the magnetic energy density. Lastly, our model denotes
that the satisfaction of the aforementioned criterion is ultimately driven into
a problem of initial conditions.
| [
{
"created": "Wed, 6 Oct 2021 03:54:12 GMT",
"version": "v1"
},
{
"created": "Sat, 18 Dec 2021 11:25:53 GMT",
"version": "v2"
},
{
"created": "Fri, 1 Apr 2022 15:35:35 GMT",
"version": "v3"
}
] | 2022-04-04 | [
[
"Mavrogiannis",
"Panagiotis",
""
],
[
"Tsagas",
"Christos G.",
""
]
] | Within the context of general relativity we study in a fully covariant way the so-called Euler-Maxwell system of equations. In particular, on decomposing the aforementioned system into its 1 temporal and 1 + 2 spatial components at the ideal magnetohydrodynamic limit, we bring it in a simplified form that favors physical insight to the problem of a self-gravitating, magnetized fluid. Of central interest is the decomposition of Faraday's equation which leads to a new general solution governing the evolution of the magnetic field during the motion of the highly conducting fluid. According to the latter relation, the magnetic field generally grows or decays in proportion to the inverse cube law of the scale factor--associated with the continuous contraction or expansion of the fluid's volume respectively. The magnetic field's law of variation, which has remarkable implications for the motion of the whole fluid, is subsequently applied to homogeneous (anisotropic-magnetized) cosmological models--especially to the Bianchi I case--as well as to the study of homogeneous and anisotropic gravitational collapse in a magnetized environment. Concerning the cosmological application, we derive the evolution equations of Bianchi I spacetime permeated by large-scale magnetic fields (these equations reduce to their FRW counterparts at the small/large--scale limit). Also, the compatibility of the new evolution formula for the magnetic field with the standard cosmic nucleosynthesis constraint is examined. As for the application in astrophysics, our results predict that homogeneous gravitational implosion is impeded when the electric Weyl tensor (associated with tidal forces) along the magnetic forcelines overwhelms the magnetic energy density. Lastly, our model denotes that the satisfaction of the aforementioned criterion is ultimately driven into a problem of initial conditions. |
gr-qc/0011054 | Leo Brewin | Leo Brewin | Stable evolution of a maximally sliced Schwarzschild spacetime using a
smooth lattice | 3 pages, 4 eps figures, talk given at MG9, Rome, July 2000 | null | null | null | gr-qc | null | We will present results of a long term stable evolution, to $t=1000m$, of a
maximally sliced Schwarzschild blackhole using a smooth lattice method.
| [
{
"created": "Wed, 15 Nov 2000 14:12:02 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Brewin",
"Leo",
""
]
] | We will present results of a long term stable evolution, to $t=1000m$, of a maximally sliced Schwarzschild blackhole using a smooth lattice method. |
1001.5380 | Antoine Petiteau | Antoine Petiteau, Yu Shang, Stanislav Babak and Farhan Feroz | The search for spinning black hole binaries in mock LISA data using a
genetic algorithm | 25 pages, 9 figures | Phys.Rev.D81:104016,2010 | 10.1103/PhysRevD.81.104016 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Coalescing massive Black Hole binaries are the strongest and probably the
most important gravitational wave sources in the LISA band. The spin and
orbital precessions bring complexity in the waveform and make the likelihood
surface richer in structure as compared to the non-spinning case. We introduce
an extended multimodal genetic algorithm which utilizes the properties of the
signal and the detector response function to analyze the data from the third
round of mock LISA data challenge (MLDC 3.2). The performance of this method is
comparable, if not better, to already existing algorithms. We have found all
five sources present in MLDC 3.2 and recovered the coalescence time, chirp
mass, mass ratio and sky location with reasonable accuracy. As for the orbital
angular momentum and two spins of the Black Holes, we have found a large number
of widely separated modes in the parameter space with similar maximum
likelihood values.
| [
{
"created": "Fri, 29 Jan 2010 11:05:03 GMT",
"version": "v1"
}
] | 2010-05-25 | [
[
"Petiteau",
"Antoine",
""
],
[
"Shang",
"Yu",
""
],
[
"Babak",
"Stanislav",
""
],
[
"Feroz",
"Farhan",
""
]
] | Coalescing massive Black Hole binaries are the strongest and probably the most important gravitational wave sources in the LISA band. The spin and orbital precessions bring complexity in the waveform and make the likelihood surface richer in structure as compared to the non-spinning case. We introduce an extended multimodal genetic algorithm which utilizes the properties of the signal and the detector response function to analyze the data from the third round of mock LISA data challenge (MLDC 3.2). The performance of this method is comparable, if not better, to already existing algorithms. We have found all five sources present in MLDC 3.2 and recovered the coalescence time, chirp mass, mass ratio and sky location with reasonable accuracy. As for the orbital angular momentum and two spins of the Black Holes, we have found a large number of widely separated modes in the parameter space with similar maximum likelihood values. |
2006.08027 | Sergey Yu. Vernov | Ekaterina O. Pozdeeva, Mayukh Raj Gangopadhyay, Mohammad Sami, Alexey
V. Toporensky, Sergey Yu. Vernov | Inflation with a quartic potential in the framework of
Einstein-Gauss-Bonnet gravity | 17 pages, 5 figures, references and comments are added, revised
version to appear in Phys. Rev. D | Phys. Rev. D 102, 043525 (2020) | 10.1103/PhysRevD.102.043525 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate inflationary dynamics in the framework of the
Einstein-Gauss-Bonnet gravity. In the model under consideration, the inflaton
field is non-minimally coupled to the Gauss-Bonnet curvature invariant, so that
the latter appears to be dynamically important. We consider a quartic potential
for the inflaton field, in particular the one asymptotically connected to the
Higgs inflation, and a wider class of coupling functions not considered in the
earlier work. Keeping in mind the observational bounds on the parameters - the
amplitude of scalar perturbations $A_s$, spectral index $n_s$ and
tensor-to-scalar ratio $r$, we demonstrate that the model a quartic potential
and the proposed coupling function is in agreement with observation.
| [
{
"created": "Sun, 14 Jun 2020 21:27:50 GMT",
"version": "v1"
},
{
"created": "Sat, 15 Aug 2020 19:27:24 GMT",
"version": "v2"
}
] | 2020-09-02 | [
[
"Pozdeeva",
"Ekaterina O.",
""
],
[
"Gangopadhyay",
"Mayukh Raj",
""
],
[
"Sami",
"Mohammad",
""
],
[
"Toporensky",
"Alexey V.",
""
],
[
"Vernov",
"Sergey Yu.",
""
]
] | We investigate inflationary dynamics in the framework of the Einstein-Gauss-Bonnet gravity. In the model under consideration, the inflaton field is non-minimally coupled to the Gauss-Bonnet curvature invariant, so that the latter appears to be dynamically important. We consider a quartic potential for the inflaton field, in particular the one asymptotically connected to the Higgs inflation, and a wider class of coupling functions not considered in the earlier work. Keeping in mind the observational bounds on the parameters - the amplitude of scalar perturbations $A_s$, spectral index $n_s$ and tensor-to-scalar ratio $r$, we demonstrate that the model a quartic potential and the proposed coupling function is in agreement with observation. |
2101.11467 | Marcelo Byrro Ribeiro | Osvaldo L. Santos-Pereira (1), Everton M. C. Abreu (2,3,4), Marcelo B.
Ribeiro (1,4,5) ((1) Physics Institute, Universidade Federal do Rio de
Janeiro, (2) Physics Department, Universidade Federal Rural do Rio de
Janeiro, (3) Physics Department, Universidade Federal de Juiz de Fora, (4)
Applied Physics Graduate Program, Physics Institute, Universidade Federal do
Rio de Janeiro, (5) Valongo Observatory, Universidade Federal do Rio de
Janeiro) | Fluid dynamics in the warp drive spacetime geometry | 39 pages, 3 tables. LaTeX. Minor changes to match proofs. Accepted
for publication in the European Physical Journal C | Eur. Phys. J. C 81(2021)133 | 10.1140/epjc/s10052-021-08921-3 | null | gr-qc physics.flu-dyn | http://creativecommons.org/licenses/by/4.0/ | The Alcubierre warp drive metric is a spacetime geometry featuring a
spacetime distortion, called warp bubble, where a massive particle inside it
acquires global superluminal velocities, or warp speeds. This work presents
solutions of the Einstein equations for the Alcubierre metric having fluid
matter as gravity source. The energy-momentum tensor considered two fluid
contents, the perfect fluid and the parametrized perfect fluid (PPF), a
tentative more flexible model whose aim is to explore the possibilities of warp
drive solutions with positive matter density content. Santos-Pereira et al.
(2020; arXiv:2008.06560) have already showed that the Alcubierre metric having
dust as source connects this geometry to the Burgers equation, which describes
shock waves moving through an inviscid fluid, but led the solutions back to
vacuum. The same happened for two out of four solutions subcases for the
perfect fluid. Other solutions for the perfect fluid indicate the possibility
of warp drive with positive matter density, but at the cost of a complex
solution for the warp drive regulating function. Regarding the PPF, solutions
were also obtained indicating that warp speeds could be created with positive
matter density. Weak, dominant, strong and null energy conditions were
calculated for all studied subcases, being satisfied for the perfect fluid and
creating constraints in the PPF quantities such that positive matter density is
also possible for creating a warp bubble. Summing up all
results,energy-momentum tensors describing more complex forms of matter, or
field, distributions generate solutions for the Einstein equations with the
warp drive metric where negative matter density might not be a strict
precondition for attaining warp speeds.
| [
{
"created": "Wed, 27 Jan 2021 14:55:53 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Feb 2021 03:13:36 GMT",
"version": "v2"
}
] | 2021-02-10 | [
[
"Santos-Pereira",
"Osvaldo L.",
""
],
[
"Abreu",
"Everton M. C.",
""
],
[
"Ribeiro",
"Marcelo B.",
""
]
] | The Alcubierre warp drive metric is a spacetime geometry featuring a spacetime distortion, called warp bubble, where a massive particle inside it acquires global superluminal velocities, or warp speeds. This work presents solutions of the Einstein equations for the Alcubierre metric having fluid matter as gravity source. The energy-momentum tensor considered two fluid contents, the perfect fluid and the parametrized perfect fluid (PPF), a tentative more flexible model whose aim is to explore the possibilities of warp drive solutions with positive matter density content. Santos-Pereira et al. (2020; arXiv:2008.06560) have already showed that the Alcubierre metric having dust as source connects this geometry to the Burgers equation, which describes shock waves moving through an inviscid fluid, but led the solutions back to vacuum. The same happened for two out of four solutions subcases for the perfect fluid. Other solutions for the perfect fluid indicate the possibility of warp drive with positive matter density, but at the cost of a complex solution for the warp drive regulating function. Regarding the PPF, solutions were also obtained indicating that warp speeds could be created with positive matter density. Weak, dominant, strong and null energy conditions were calculated for all studied subcases, being satisfied for the perfect fluid and creating constraints in the PPF quantities such that positive matter density is also possible for creating a warp bubble. Summing up all results,energy-momentum tensors describing more complex forms of matter, or field, distributions generate solutions for the Einstein equations with the warp drive metric where negative matter density might not be a strict precondition for attaining warp speeds. |
gr-qc/0604035 | Carsten Gundlach | Carsten Gundlach, Jose M. Martin-Garcia | Well-posedness of formulations of the Einstein equations with dynamical
lapse and shift conditions | null | Phys.Rev.D74:024016,2006 | 10.1103/PhysRevD.74.024016 | null | gr-qc | null | We prove that when the equations are restricted to the principal part the
standard version of the BSSN formulation of the Einstein equations is
equivalent to the NOR formulation for any gauge, and that the KST formulation
is equivalent to NOR for a variety of gauges. We review a family of elliptic
gauge conditions and the implicit parabolic and hyperbolic drivers that can be
derived from them, and show how to make them symmetry-seeking. We investigate
the hyperbolicity of ADM, NOR and BSSN with implicit hyperbolic lapse and shift
drivers. We show that BSSN with the coordinate drivers used in recent "moving
puncture" binary black hole evolutions is ill-posed at large shifts, and
suggest how to make it strongly hyperbolic for arbitrary shifts. For ADM, NOR
and BSSN with elliptic and parabolic gauge conditions, which cannot be
hyperbolic, we investigate a necessary condition for well-posedness of the
initial-value problem.
| [
{
"created": "Sat, 8 Apr 2006 14:47:21 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Jun 2006 18:35:47 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Gundlach",
"Carsten",
""
],
[
"Martin-Garcia",
"Jose M.",
""
]
] | We prove that when the equations are restricted to the principal part the standard version of the BSSN formulation of the Einstein equations is equivalent to the NOR formulation for any gauge, and that the KST formulation is equivalent to NOR for a variety of gauges. We review a family of elliptic gauge conditions and the implicit parabolic and hyperbolic drivers that can be derived from them, and show how to make them symmetry-seeking. We investigate the hyperbolicity of ADM, NOR and BSSN with implicit hyperbolic lapse and shift drivers. We show that BSSN with the coordinate drivers used in recent "moving puncture" binary black hole evolutions is ill-posed at large shifts, and suggest how to make it strongly hyperbolic for arbitrary shifts. For ADM, NOR and BSSN with elliptic and parabolic gauge conditions, which cannot be hyperbolic, we investigate a necessary condition for well-posedness of the initial-value problem. |
0806.2423 | Vojt\v{e}ch Pravda | Alena Pravdova, Vojtech Pravda | Newman-Penrose formalism in higher dimensions: vacuum spacetimes with a
non-twisting geodetic multiple Weyl aligned null direction | 25 pages, version to be published in Class. Quantum Grav. (expanded
-background material included, 3 references added, small change in notation) | Class.Quant.Grav.25:235008,2008 | 10.1088/0264-9381/25/23/235008 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Vacuum spacetimes admitting a non-twisting geodetic multiple Weyl aligned
null direction (WAND) are analyzed in arbitrary dimension using recently
developed higher-dimensional Newman-Penrose (NP) formalism. We determine
dependence of the metric and of the Weyl tensor on the affine parameter r along
null geodesics generated by the WAND for type III and N spacetimes and for a
special class of type II and D spacetimes, containing e.g.
Schwarzschild-Tangherlini black holes and black strings and branes.
For types III and N, all metric components are at most quadratic polynomials
in r while for types II and D the r-dependence of the metric as well as of the
Weyl tensor is determined by an integer m corresponding to the rank of the
expansion matrix S_{ij}. It is shown that for non-vanishing expansion, all
these spacetimes contain a curvature singularity.
As an illustrative example, a shearing expanding type N five-dimensional
vacuum solution is also re-derived using higher-dimensional NP formalism. This
solution can be, however, identified with a direct product of a known
four-dimensional type N metric with an extra dimension.
| [
{
"created": "Sun, 15 Jun 2008 07:37:11 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Nov 2008 20:10:23 GMT",
"version": "v2"
}
] | 2008-12-18 | [
[
"Pravdova",
"Alena",
""
],
[
"Pravda",
"Vojtech",
""
]
] | Vacuum spacetimes admitting a non-twisting geodetic multiple Weyl aligned null direction (WAND) are analyzed in arbitrary dimension using recently developed higher-dimensional Newman-Penrose (NP) formalism. We determine dependence of the metric and of the Weyl tensor on the affine parameter r along null geodesics generated by the WAND for type III and N spacetimes and for a special class of type II and D spacetimes, containing e.g. Schwarzschild-Tangherlini black holes and black strings and branes. For types III and N, all metric components are at most quadratic polynomials in r while for types II and D the r-dependence of the metric as well as of the Weyl tensor is determined by an integer m corresponding to the rank of the expansion matrix S_{ij}. It is shown that for non-vanishing expansion, all these spacetimes contain a curvature singularity. As an illustrative example, a shearing expanding type N five-dimensional vacuum solution is also re-derived using higher-dimensional NP formalism. This solution can be, however, identified with a direct product of a known four-dimensional type N metric with an extra dimension. |
gr-qc/9310036 | Dr. Norman J. LaFave | Norman J. LaFave | A Step Toward Pregeometry I.: Ponzano-Regge Spin Networks and the Origin
of Spacetime Structure in Four Dimensions | 57 pages + 20 shar'ed, uuencoded, compressed eps figures, no local
preprint number | null | null | null | gr-qc hep-lat hep-th | null | In this paper, a candidate for pregeometry, Ponzano-Regge spin networks, will
be examined in the context of the pregeometric philosophy of Wheeler. Ponzano
and Regge were able to construct a theory for 3-dimensional quantum gravity
based on 3nj-symbols, obtaining the path integral over the metric in the
semiclassical limit. However, extension of this model to 4-dimensions has
proven to be difficult. It will be shown that the building blocks for
4-dimensional spacetime are already present in the Ponzano-Regge formalism
using a reinterpretation of the theory based on the pregeometric hypotheses of
Wheeler.
| [
{
"created": "Tue, 26 Oct 1993 19:38:00 GMT",
"version": "v1"
},
{
"created": "Tue, 26 Oct 1993 20:16:00 GMT",
"version": "v2"
},
{
"created": "Tue, 26 Oct 1993 20:27:00 GMT",
"version": "v3"
}
] | 2009-09-25 | [
[
"LaFave",
"Norman J.",
""
]
] | In this paper, a candidate for pregeometry, Ponzano-Regge spin networks, will be examined in the context of the pregeometric philosophy of Wheeler. Ponzano and Regge were able to construct a theory for 3-dimensional quantum gravity based on 3nj-symbols, obtaining the path integral over the metric in the semiclassical limit. However, extension of this model to 4-dimensions has proven to be difficult. It will be shown that the building blocks for 4-dimensional spacetime are already present in the Ponzano-Regge formalism using a reinterpretation of the theory based on the pregeometric hypotheses of Wheeler. |
2312.09640 | Venkatesha Venkatesha | Chaitra Chooda Chalavadi, V. Venkatesha, N. S. Kavya, and S. V. Divya
Rashmi | Conformally symmetric wormhole solutions supported by non-commutative
geometry in $f(Q,T)$ gravity | Accepted version in Communications in Theoretical Physics | null | 10.1088/1572-9494/ad15fa | null | gr-qc | http://creativecommons.org/licenses/by-nc-nd/4.0/ | This manuscript investigates wormhole solutions within the framework of
extended symmetric teleparallel gravity, incorporating non-commutative
geometry, and conformal symmetries. To achieve this, we examine the linear
wormhole model with anisotropic fluid under Gaussian and Lorentzian
distributions. The primary objective is to derive wormhole solutions while
considering the influence of the shape function on model parameters under
Gaussian and Lorentzian distributions. The resulting shape function satisfies
all the necessary conditions for a traversable wormhole. Furthermore, we
analyze the characteristics of the energy conditions and provide a detailed
graphical discussion of the matter contents via energy conditions.
Additionally, we explore the effect of anisotropy under Gaussian and Lorentzian
distributions. Finally, we present our conclusions based on the obtained
results.
| [
{
"created": "Fri, 15 Dec 2023 09:29:30 GMT",
"version": "v1"
}
] | 2023-12-18 | [
[
"Chalavadi",
"Chaitra Chooda",
""
],
[
"Venkatesha",
"V.",
""
],
[
"Kavya",
"N. S.",
""
],
[
"Rashmi",
"S. V. Divya",
""
]
] | This manuscript investigates wormhole solutions within the framework of extended symmetric teleparallel gravity, incorporating non-commutative geometry, and conformal symmetries. To achieve this, we examine the linear wormhole model with anisotropic fluid under Gaussian and Lorentzian distributions. The primary objective is to derive wormhole solutions while considering the influence of the shape function on model parameters under Gaussian and Lorentzian distributions. The resulting shape function satisfies all the necessary conditions for a traversable wormhole. Furthermore, we analyze the characteristics of the energy conditions and provide a detailed graphical discussion of the matter contents via energy conditions. Additionally, we explore the effect of anisotropy under Gaussian and Lorentzian distributions. Finally, we present our conclusions based on the obtained results. |
1501.01619 | Matt Visser | Matt Visser | Energy conditions in the epoch of galaxy formation | Old article from 1997; somewhat tricky to access online; 5 pages in
preprint form. arXiv admin note: text overlap with arXiv:gr-qc/9705070 | Science 276 (1997) 88-90 | 10.1126/science.276.5309.88 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The energy conditions of Einstein gravity (classical general relativity) do
not require one to fix a specific equation of state. In a
Friedmann-Robertson-Walker universe where the equation of state for the
cosmological fluid is uncertain, the energy conditions provide simple,
model-independent, and robust bounds on the behaviour of the density and
look-back time as a function of red-shift. Current observations suggest that
the "strong energy condition" is violated sometime between the epoch of galaxy
formation and the present. This implies that no possible combination of
"normal" matter is capable of fitting the observational data.
| [
{
"created": "Wed, 7 Jan 2015 20:48:01 GMT",
"version": "v1"
}
] | 2015-01-08 | [
[
"Visser",
"Matt",
""
]
] | The energy conditions of Einstein gravity (classical general relativity) do not require one to fix a specific equation of state. In a Friedmann-Robertson-Walker universe where the equation of state for the cosmological fluid is uncertain, the energy conditions provide simple, model-independent, and robust bounds on the behaviour of the density and look-back time as a function of red-shift. Current observations suggest that the "strong energy condition" is violated sometime between the epoch of galaxy formation and the present. This implies that no possible combination of "normal" matter is capable of fitting the observational data. |
gr-qc/9706075 | Nils Andersson | Nils Andersson | A new class of unstable modes of rotating relativistic stars | 14 pages, latex | Astrophys.J.502:708-713,1998 | 10.1086/305919 | null | gr-qc astro-ph | null | The first numerical study of axial (toroidal) pulsation modes of a slowly
rotating relativistic star is presented. The calculation includes terms of
first order in $\epsilon \equiv \Omega \sqrt{R^3/M}<<1$ ($R$ is the radius, $M$
is the mass and $\Omega$ is the rotation frequency of the star), and accounts
for effects due to the coriolis force. Effects due to the centrifugal
flattening of the star enter at order $\epsilon^2$ and are not included in the
analysis. It is shown that increased rotation tends to decrease the damping
times for prograde modes, while retrograde become longer lived. Specifically,
we show that rotation affects the axial gravitational-wave $w$-modes in this
way. We also present the first relativistic calculation of the so-called
$r$-modes (analogous to Rossby waves in the Earth's oceans). These have
frequencies of the same order of magnitude as the rotation frequency of the
star. The presented results indicate that the $r$-modes are unstable due to the
emission of gravitational radiation for \underline{all} rotating perfect fluid
stars. This is interesting since the previously considered gravitational-wave
instability associated with (for example) the $f$-mode of the star sets in at a
critical rotation rate. Because they are unstable also for the slowest rotating
stars the $r$-modes may well be of considerable astrophysical importance.
| [
{
"created": "Tue, 24 Jun 1997 13:52:12 GMT",
"version": "v1"
}
] | 2009-07-09 | [
[
"Andersson",
"Nils",
""
]
] | The first numerical study of axial (toroidal) pulsation modes of a slowly rotating relativistic star is presented. The calculation includes terms of first order in $\epsilon \equiv \Omega \sqrt{R^3/M}<<1$ ($R$ is the radius, $M$ is the mass and $\Omega$ is the rotation frequency of the star), and accounts for effects due to the coriolis force. Effects due to the centrifugal flattening of the star enter at order $\epsilon^2$ and are not included in the analysis. It is shown that increased rotation tends to decrease the damping times for prograde modes, while retrograde become longer lived. Specifically, we show that rotation affects the axial gravitational-wave $w$-modes in this way. We also present the first relativistic calculation of the so-called $r$-modes (analogous to Rossby waves in the Earth's oceans). These have frequencies of the same order of magnitude as the rotation frequency of the star. The presented results indicate that the $r$-modes are unstable due to the emission of gravitational radiation for \underline{all} rotating perfect fluid stars. This is interesting since the previously considered gravitational-wave instability associated with (for example) the $f$-mode of the star sets in at a critical rotation rate. Because they are unstable also for the slowest rotating stars the $r$-modes may well be of considerable astrophysical importance. |
1304.5995 | Jorge Ovalle | J Ovalle, F Linares, A Pasqua and A Sotomayor | The role of exterior Weyl fluids on compact stellar structures in
Randall-Sundrum gravity | 14 pages, 1 figure. References added. Final version to appear in CQG | Class. Quantum Grav. 30 (2013) 175019, | 10.1088/0264-9381/30/17/175019 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the context of the Randall-Sundrum braneworld, the minimal geometric
deformation approach (MGD) is used to generate a new physically acceptable
interior solution to Einstein's field equations for a spherically symmetric
compact distribution. This new solution is used to elucidate the role of
exterior Weyl stresses from bulk gravitons on compact stellar distributions. We
found strong evidences showing that the exterior dark radiation ${\cal U}^+$
always increases both the pressure and the compactness of stellar structures,
and that the exterior "dark pressure" ${\cal P}^+$ always reduces them.
| [
{
"created": "Mon, 22 Apr 2013 15:54:52 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Jul 2013 16:47:13 GMT",
"version": "v2"
}
] | 2013-11-21 | [
[
"Ovalle",
"J",
""
],
[
"Linares",
"F",
""
],
[
"Pasqua",
"A",
""
],
[
"Sotomayor",
"A",
""
]
] | In the context of the Randall-Sundrum braneworld, the minimal geometric deformation approach (MGD) is used to generate a new physically acceptable interior solution to Einstein's field equations for a spherically symmetric compact distribution. This new solution is used to elucidate the role of exterior Weyl stresses from bulk gravitons on compact stellar distributions. We found strong evidences showing that the exterior dark radiation ${\cal U}^+$ always increases both the pressure and the compactness of stellar structures, and that the exterior "dark pressure" ${\cal P}^+$ always reduces them. |
2208.09737 | Yisong Yang Professor | Yisong Yang | Dyonic Matter Equations, Exact Point-Source Solutions, and Charged Black
Holes in Generalized Born--Infeld Theory | 38 pages, 1 figure | Physical Review D 107 (2023) 085007 | 10.1103/PhysRevD.107.085007 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive the equations of motion governing static dyonic matters, described
in terms of two real scalar fields, in nonlinear electrodynamics of the
Born--Infeld theory type. We then obtain exact finite-energy solutions of these
equations in the quadratic and logarithmic nonlinearity cases subject to dyonic
point-charge sources and construct dyonically charged black holes with
relegated curvature singularities. In the case of quadratic nonlinearity, which
is the core model of this work, we show that dyonic solutions enable us to
restore electromagnetic symmetry, which is known to be broken in non-dyonic
situations by exclusion of monopoles. We further demonstrate that in the
context of k-essence cosmology the nonlinear electrodynamics models possess
their own distinctive signatures in light of the underlying equations of state
of the cosmic fluids they represent. In this context, the quadratic and
logarithmic models are shown to resolve a density-pressure inconsistency issue
exhibited by the original Born--Infeld model k-essence action function as well
as by all of its fractional-powered extensions. Moreover, it is shown that the
quadratic model is uniquely positioned to give rise to a radiation-dominated
era in the early universe among all the polynomial models and other examples
considered.
| [
{
"created": "Sat, 20 Aug 2022 19:50:33 GMT",
"version": "v1"
},
{
"created": "Tue, 27 Sep 2022 13:18:16 GMT",
"version": "v2"
},
{
"created": "Tue, 11 Oct 2022 15:04:11 GMT",
"version": "v3"
},
{
"created": "Wed, 7 Dec 2022 19:36:03 GMT",
"version": "v4"
},
{
"cr... | 2023-04-19 | [
[
"Yang",
"Yisong",
""
]
] | We derive the equations of motion governing static dyonic matters, described in terms of two real scalar fields, in nonlinear electrodynamics of the Born--Infeld theory type. We then obtain exact finite-energy solutions of these equations in the quadratic and logarithmic nonlinearity cases subject to dyonic point-charge sources and construct dyonically charged black holes with relegated curvature singularities. In the case of quadratic nonlinearity, which is the core model of this work, we show that dyonic solutions enable us to restore electromagnetic symmetry, which is known to be broken in non-dyonic situations by exclusion of monopoles. We further demonstrate that in the context of k-essence cosmology the nonlinear electrodynamics models possess their own distinctive signatures in light of the underlying equations of state of the cosmic fluids they represent. In this context, the quadratic and logarithmic models are shown to resolve a density-pressure inconsistency issue exhibited by the original Born--Infeld model k-essence action function as well as by all of its fractional-powered extensions. Moreover, it is shown that the quadratic model is uniquely positioned to give rise to a radiation-dominated era in the early universe among all the polynomial models and other examples considered. |
1109.3996 | Paolo Pani | Paolo Pani, Caio F. B. Macedo, Luis C. B. Crispino, Vitor Cardoso | Slowly rotating black holes in alternative theories of gravity | 5 pages, no figures. v2: references added and one minor correction in
the discussion. Published in PRD as Brief Report | null | 10.1103/PhysRevD.84.087501 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present, in closed analytic form, a general stationary, slowly rotating
black hole, which is solution to a large class of alternative theories of
gravity in four dimensions. In these theories, the Einstein-Hilbert action is
supplemented by all possible quadratic, algebraic curvature invariants coupled
to a scalar field. The solution is found as a deformation of the Schwarzschild
metric in General Relativity. We explicitly derive the changes to the orbital
frequency at the innermost stable circular orbit and at the light ring in
closed form. These results could be useful when comparing General Relativity
against alternative theories by (say) measurements of X-ray emission in
accretion disks, or by stellar motion around supermassive black holes. When
gravitational-wave astronomy comes into force, strong constraints on the
coupling parameters can in principle be made.
| [
{
"created": "Mon, 19 Sep 2011 11:10:49 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Oct 2011 08:39:47 GMT",
"version": "v2"
}
] | 2011-10-27 | [
[
"Pani",
"Paolo",
""
],
[
"Macedo",
"Caio F. B.",
""
],
[
"Crispino",
"Luis C. B.",
""
],
[
"Cardoso",
"Vitor",
""
]
] | We present, in closed analytic form, a general stationary, slowly rotating black hole, which is solution to a large class of alternative theories of gravity in four dimensions. In these theories, the Einstein-Hilbert action is supplemented by all possible quadratic, algebraic curvature invariants coupled to a scalar field. The solution is found as a deformation of the Schwarzschild metric in General Relativity. We explicitly derive the changes to the orbital frequency at the innermost stable circular orbit and at the light ring in closed form. These results could be useful when comparing General Relativity against alternative theories by (say) measurements of X-ray emission in accretion disks, or by stellar motion around supermassive black holes. When gravitational-wave astronomy comes into force, strong constraints on the coupling parameters can in principle be made. |
1506.04749 | Sebastian Steinhaus | Sebastian Steinhaus | Coupled intertwiner dynamics: A toy model for coupling matter to spin
foam models | 31 + 6 pages, 8 figures, 7 tables, v2: minor mistakes corrected,
references and acknowledgements updated. Matches accepted version in Phys.
Rev. D, v3: Title matching published version and added PACS numbers | Phys. Rev. D 92, 064007 (2015) | 10.1103/PhysRevD.92.064007 | null | gr-qc cond-mat.str-el hep-lat | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The universal coupling of matter and gravity is one of the most important
features of general relativity. In quantum gravity, in particular spin foams,
matter couplings have been defined in the past, yet the mutual dynamics, in
particular if matter and gravity are strongly coupled, are hardly explored,
which is related to the definition of both matter and gravitational degrees of
freedom on the discretisation. However extracting this mutual dynamics is
crucial in testing the viability of the spin foam approach and also
establishing connections to other discrete approaches such as lattice gauge
theories.
Therefore, we introduce a simple 2D toy model for Yang--Mills coupled to spin
foams, namely an Ising model coupled to so--called intertwiner models defined
for $\text{SU}(2)_k$. The two systems are coupled by choosing the Ising
coupling constant to depend on spin labels of the background, as these are
interpreted as the edge lengths of the discretisation. We coarse grain this toy
model via tensor network renormalization and uncover an interesting dynamics:
the Ising phase transition temperature turns out to be sensitive to the
background configurations and conversely, the Ising model can induce phase
transitions in the background. Moreover, we observe a strong coupling of both
systems if close to both phase transitions.
| [
{
"created": "Mon, 15 Jun 2015 20:00:42 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Sep 2015 12:04:42 GMT",
"version": "v2"
},
{
"created": "Thu, 17 Sep 2015 08:24:01 GMT",
"version": "v3"
}
] | 2015-09-18 | [
[
"Steinhaus",
"Sebastian",
""
]
] | The universal coupling of matter and gravity is one of the most important features of general relativity. In quantum gravity, in particular spin foams, matter couplings have been defined in the past, yet the mutual dynamics, in particular if matter and gravity are strongly coupled, are hardly explored, which is related to the definition of both matter and gravitational degrees of freedom on the discretisation. However extracting this mutual dynamics is crucial in testing the viability of the spin foam approach and also establishing connections to other discrete approaches such as lattice gauge theories. Therefore, we introduce a simple 2D toy model for Yang--Mills coupled to spin foams, namely an Ising model coupled to so--called intertwiner models defined for $\text{SU}(2)_k$. The two systems are coupled by choosing the Ising coupling constant to depend on spin labels of the background, as these are interpreted as the edge lengths of the discretisation. We coarse grain this toy model via tensor network renormalization and uncover an interesting dynamics: the Ising phase transition temperature turns out to be sensitive to the background configurations and conversely, the Ising model can induce phase transitions in the background. Moreover, we observe a strong coupling of both systems if close to both phase transitions. |
0901.0814 | Eugenio R. Bezerra de Mello | T. R. P. Caram\^es and E. R. Bezerra de Mello | Spherically symmetric vacuum solutions of modified gravity theory in
higher dimensions | 14 pages, no figure. New version accepted for publication in EPJC | Eur.Phys.J.C64:113-121,2009 | 10.1140/epjc/s10052-009-1115-y | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we investigate spherically symmetric vacuum solutions of $f(R)$
gravity in a higher dimensional spacetime. With this objective we construct a
system of non-linear differential equations, whose solutions depend on the
explicit form assumed for the function $F(R)=\frac{df(R)}{dR}$. We explicit
show that for specific classes of this function exact solutions from the field
equations are obtained; also we find approximated results for the metric tensor
for more general cases admitting $F(R)$ close to the unity.
| [
{
"created": "Wed, 7 Jan 2009 12:26:10 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Aug 2009 11:35:31 GMT",
"version": "v2"
}
] | 2014-11-18 | [
[
"Caramês",
"T. R. P.",
""
],
[
"de Mello",
"E. R. Bezerra",
""
]
] | In this paper we investigate spherically symmetric vacuum solutions of $f(R)$ gravity in a higher dimensional spacetime. With this objective we construct a system of non-linear differential equations, whose solutions depend on the explicit form assumed for the function $F(R)=\frac{df(R)}{dR}$. We explicit show that for specific classes of this function exact solutions from the field equations are obtained; also we find approximated results for the metric tensor for more general cases admitting $F(R)$ close to the unity. |
gr-qc/0601115 | Yun-Song Piao | Yun-Song Piao | Gravitational Wave Background from Phantom Superinflation | 3 pages, 2 eps figures, to be published in PRD, revised with
published version, refs. added | Phys.Rev. D73 (2006) 047302 | 10.1103/PhysRevD.73.047302 | null | gr-qc | null | Recently, the early superinflation driven by phantom field has been proposed
and studied. The detection of primordial gravitational wave is an important
means to know the state of very early universe. In this brief report we discuss
in detail the gravitational wave background excited during the phantom
superinflation.
| [
{
"created": "Fri, 27 Jan 2006 03:35:34 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Feb 2006 05:10:43 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Piao",
"Yun-Song",
""
]
] | Recently, the early superinflation driven by phantom field has been proposed and studied. The detection of primordial gravitational wave is an important means to know the state of very early universe. In this brief report we discuss in detail the gravitational wave background excited during the phantom superinflation. |
1704.02593 | Fatemeh Oboudiat | Behrouz Mirza, Fatemeh Oboudiat | Constraining f(T) gravity by dynamical system analysis | 11 pages | JCAP11(2017)011 | 10.1088/1475-7516/2017/11/011 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the cosmological solutions of the $f(T)$ gravity theory using
the method of dynamical systems. For this purpose a general form of the $f(T)$
function is considered and four conditions are defined that they have to
satisfy in order to describe the standard cosmological history. We examine the
power law, and another form of $f(T)$ against these conditions. For a power law
function $f(T)= B(-T)^\beta$, $\beta$ must be less than one and unequal to
$\frac{1}{2}$ to obtain a consistent cosmological model. We also investigate a
model of inflation in this theory.
| [
{
"created": "Sun, 9 Apr 2017 12:38:06 GMT",
"version": "v1"
},
{
"created": "Sat, 9 Dec 2017 09:04:33 GMT",
"version": "v2"
}
] | 2017-12-12 | [
[
"Mirza",
"Behrouz",
""
],
[
"Oboudiat",
"Fatemeh",
""
]
] | We investigate the cosmological solutions of the $f(T)$ gravity theory using the method of dynamical systems. For this purpose a general form of the $f(T)$ function is considered and four conditions are defined that they have to satisfy in order to describe the standard cosmological history. We examine the power law, and another form of $f(T)$ against these conditions. For a power law function $f(T)= B(-T)^\beta$, $\beta$ must be less than one and unequal to $\frac{1}{2}$ to obtain a consistent cosmological model. We also investigate a model of inflation in this theory. |
2309.06093 | Titus K Mathew | Vishnu A Pai and Titus K Mathew | Bulk viscous late acceleration under near equilibrium conditions in f(R,
T) gravity with mixed matter | 26 pages, 14 figures | null | null | null | gr-qc | http://creativecommons.org/publicdomain/zero/1.0/ | Various studies have shown that the late acceleration of the universe can be
caused by the bulk viscosity associated with dark matter. But recently, it was
indicated that a cosmological constant is essential for maintaining Near
Equilibrium Conditions (NEC) for the bulk viscous matter during the accelerated
expansion of the universe. In the present study, we investigate a model of the
universe composed of mixed dark matter components, with viscous dark matter
(vDM), and inviscid cold dark matter (CDM) as it's constituents, in the context
of $f(R,T)$ gravity and showed that the model predicts late acceleration by
satisfying NEC throughout the evolution, without cosmological constant. We have
also compared the model predictions with combined Type Ia Supernovae and
observational Hubble data sets and thereby determined the estimated values of
different cosmological parameters.
| [
{
"created": "Tue, 12 Sep 2023 09:52:13 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Nov 2023 18:14:36 GMT",
"version": "v2"
}
] | 2023-11-10 | [
[
"Pai",
"Vishnu A",
""
],
[
"Mathew",
"Titus K",
""
]
] | Various studies have shown that the late acceleration of the universe can be caused by the bulk viscosity associated with dark matter. But recently, it was indicated that a cosmological constant is essential for maintaining Near Equilibrium Conditions (NEC) for the bulk viscous matter during the accelerated expansion of the universe. In the present study, we investigate a model of the universe composed of mixed dark matter components, with viscous dark matter (vDM), and inviscid cold dark matter (CDM) as it's constituents, in the context of $f(R,T)$ gravity and showed that the model predicts late acceleration by satisfying NEC throughout the evolution, without cosmological constant. We have also compared the model predictions with combined Type Ia Supernovae and observational Hubble data sets and thereby determined the estimated values of different cosmological parameters. |
1202.3558 | Takashi Uchiyama | Takashi Uchiyama, Shinji Miyoki, Souichi Telada, Kazuhiro Yamamoto,
Masatake Ohashi, Kazuhiro Agatsuma, Koji Arai, Masa-Katsu Fujimoto, Tomiyoshi
Haruyama, Seiji Kawamura, Osamu Miyakawa, Naoko Ohishi, Takanori Saito,
Takakazu Shintomi, Toshikazu Suzuki, Ryutaro Takahashi, Daisuke Tatsumi | Reduction of thermal fluctuations in a cryogenic laser interferometric
gravitational wave detector | Accepted for publication in Physical Review Letters, 5 pages, 2
figures | null | 10.1103/PhysRevLett.108.141101 | null | gr-qc physics.ins-det | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The thermal fluctuation of mirror surfaces is the fundamental limitation for
interferometric gravitational wave (GW) detectors. Here, we experimentally
demonstrate for the first time a reduction in a mirror's thermal fluctuation in
a GW detector with sapphire mirrors from the Cryogenic Laser Interferometer
Observatory at 17\,K and 18\,K. The detector sensitivity, which was limited by
the mirror's thermal fluctuation at room temperature, was improved in the
frequency range of 90\,Hz to 240\,Hz by cooling the mirrors. The improved
sensitivity reached a maximum of $2.2 \times
10^{-19}\,\textrm{m}/\sqrt{\textrm{Hz}}$ at 165\,Hz.
| [
{
"created": "Thu, 16 Feb 2012 10:50:16 GMT",
"version": "v1"
}
] | 2015-06-04 | [
[
"Uchiyama",
"Takashi",
""
],
[
"Miyoki",
"Shinji",
""
],
[
"Telada",
"Souichi",
""
],
[
"Yamamoto",
"Kazuhiro",
""
],
[
"Ohashi",
"Masatake",
""
],
[
"Agatsuma",
"Kazuhiro",
""
],
[
"Arai",
"Koji",
""
],
... | The thermal fluctuation of mirror surfaces is the fundamental limitation for interferometric gravitational wave (GW) detectors. Here, we experimentally demonstrate for the first time a reduction in a mirror's thermal fluctuation in a GW detector with sapphire mirrors from the Cryogenic Laser Interferometer Observatory at 17\,K and 18\,K. The detector sensitivity, which was limited by the mirror's thermal fluctuation at room temperature, was improved in the frequency range of 90\,Hz to 240\,Hz by cooling the mirrors. The improved sensitivity reached a maximum of $2.2 \times 10^{-19}\,\textrm{m}/\sqrt{\textrm{Hz}}$ at 165\,Hz. |
2305.01331 | Albert Munyeshyaka Mr | Albert Munyeshyaka, Joseph Ntahompagaze, Tom Mutabazi and Manasse.R
Mbonye | On 1 + 3 covariant perturbations of the quasi-Newtonian space-time in
modified Gauss-Bonnet gravity | This manuscript is accepted for publication in the International
Journal of Modern Physics D(IJMPD). 28 pages, 9 figures | null | 10.1142/S0218271823500530 | null | gr-qc | http://creativecommons.org/licenses/by-sa/4.0/ | The consideration of a 1 + 3 covariant approach to cold dark matter universe
with no shear cosmological dust model with irrotational flows is developed in
the context of f (G) gravity theory in the present study. This approach reveals
the existence of integrability conditions which do not appear in non-covariant
treatments. We constructed the integrability conditions in modified
Gauss-Bonnet f (G) gravity basing on the constraints and propagation equations.
These integrability conditions reveal the linearized silent nature of
quasi-Newtonian models in f (G) gravity. Finally, the linear equations for the
overdensity and velocity perturbations of the quasi-Newtonian space-time were
constructed in the context of modified f (G) gravity. The application of
harmonic decomposition and redshift transformation techniques to explore the
behaviour of the overdensity and velocity perturbations using f (G) model were
made. On the other hand we applied the quasi-static approximation to study the
approximated solutions on small scales which helps to get both analytical and
numerical results of the perturbation equations. The analysis of the energy
overdensity and velocity perturbations for both short and long wavelength modes
in a dust-Gauss-Bonnet fluids were done and we see that both energy overdensity
and velocity perturbations decay with redshift for both modes. In the limits to
{\Lambda}CDM , it means f (G) = G the considered f (G) model results coincide
with {\Lambda}CDM .
| [
{
"created": "Tue, 2 May 2023 11:27:05 GMT",
"version": "v1"
}
] | 2023-05-19 | [
[
"Munyeshyaka",
"Albert",
""
],
[
"Ntahompagaze",
"Joseph",
""
],
[
"Mutabazi",
"Tom",
""
],
[
"Mbonye",
"Manasse. R",
""
]
] | The consideration of a 1 + 3 covariant approach to cold dark matter universe with no shear cosmological dust model with irrotational flows is developed in the context of f (G) gravity theory in the present study. This approach reveals the existence of integrability conditions which do not appear in non-covariant treatments. We constructed the integrability conditions in modified Gauss-Bonnet f (G) gravity basing on the constraints and propagation equations. These integrability conditions reveal the linearized silent nature of quasi-Newtonian models in f (G) gravity. Finally, the linear equations for the overdensity and velocity perturbations of the quasi-Newtonian space-time were constructed in the context of modified f (G) gravity. The application of harmonic decomposition and redshift transformation techniques to explore the behaviour of the overdensity and velocity perturbations using f (G) model were made. On the other hand we applied the quasi-static approximation to study the approximated solutions on small scales which helps to get both analytical and numerical results of the perturbation equations. The analysis of the energy overdensity and velocity perturbations for both short and long wavelength modes in a dust-Gauss-Bonnet fluids were done and we see that both energy overdensity and velocity perturbations decay with redshift for both modes. In the limits to {\Lambda}CDM , it means f (G) = G the considered f (G) model results coincide with {\Lambda}CDM . |
1805.09810 | Joan Sola | Joan Sola | Brans-Dicke gravity: from Higgs physics to (dynamical) dark energy | Version accepted for publication in Int. J. of Mod. Phys. D. This
essay received an Honorable Mention from the Gravity Research Foundation
Awards Essays on Gravitation (2018). Extended presentation, references added,
typos corrected | Int.J.Mod.Phys. D27 (2018) no.14, 1847029 | 10.1142/S0218271818470296 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Higgs mechanism is one of the central pieces of the Standard Model of
electroweak interactions and thanks to it we can generate the masses of the
elementary particles. Its fundamental origin is nonetheless unknown.
Furthermore, in order to preserve renormalizability we have to break the gauge
symmetry spontaneously, what leads to a huge induced cosmological constant
incompatible with observations. It turns out that in the context of generalized
Brans-Dicke theories of gravity the Higgs potential structure can be motivated
from solutions of the field equations which carry harmless cosmological vacuum
energy. In addition, the late time cosmic evolution effectively appears like an
universe filled with mildly evolving dynamical dark energy mimicking
quintessence or phantom dark energy.
| [
{
"created": "Thu, 24 May 2018 17:53:34 GMT",
"version": "v1"
},
{
"created": "Tue, 29 May 2018 17:16:11 GMT",
"version": "v2"
},
{
"created": "Thu, 31 May 2018 17:58:45 GMT",
"version": "v3"
},
{
"created": "Wed, 31 Oct 2018 19:14:14 GMT",
"version": "v4"
}
] | 2018-12-04 | [
[
"Sola",
"Joan",
""
]
] | The Higgs mechanism is one of the central pieces of the Standard Model of electroweak interactions and thanks to it we can generate the masses of the elementary particles. Its fundamental origin is nonetheless unknown. Furthermore, in order to preserve renormalizability we have to break the gauge symmetry spontaneously, what leads to a huge induced cosmological constant incompatible with observations. It turns out that in the context of generalized Brans-Dicke theories of gravity the Higgs potential structure can be motivated from solutions of the field equations which carry harmless cosmological vacuum energy. In addition, the late time cosmic evolution effectively appears like an universe filled with mildly evolving dynamical dark energy mimicking quintessence or phantom dark energy. |
2105.07150 | Saurya Das | Saurya Das, Sourav Sur | Emergent gravity and the quantum | This essay received an Honorable Mention in the 2021 Gravity Research
Foundation Essay Competition | null | 10.1142/S021827182142030X | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that if one starts with a Universe with some matter and a
cosmological constant, then quantum mechanics naturally induces an attractive
gravitational potential and an effective Newton's coupling. Thus gravity is an
emergent phenomenon and what should be quantized are the fundamental degrees of
freedom from which it emerges.
| [
{
"created": "Sat, 15 May 2021 06:19:22 GMT",
"version": "v1"
}
] | 2022-01-26 | [
[
"Das",
"Saurya",
""
],
[
"Sur",
"Sourav",
""
]
] | We show that if one starts with a Universe with some matter and a cosmological constant, then quantum mechanics naturally induces an attractive gravitational potential and an effective Newton's coupling. Thus gravity is an emergent phenomenon and what should be quantized are the fundamental degrees of freedom from which it emerges. |
gr-qc/0309029 | Sergio M. C. V. Goncalves | Sergio M. C. V. Goncalves | Global symmetries: matter from geometry, hoop conjecture, and cosmic
censorship | 6 pages, revtex4; slightly modified version of an essay submitted to
the Gravity Research Foundation Competition; references updated | null | null | null | gr-qc | null | We show that four-dimensional Lorentzian metrics admitting a global spacelike
Lie group of isometries, $G_{1}={\mathbb R}$, which obey the Einstein equations
for vacuum and certain types of matter, cannot contain apparent horizons. The
assumed global isometry allows for the dimensional reduction of the (3+1)
system to a (2+1) picture, wherein the four-dimensional metric fields act
formally as matter fields. A theorem by Ida allows one to check for the absence
of apparent horizons in the dimensionally reduced spacetime, with the
four-dimensional results following from the topological product nature of the
corresponding manifold. We argue that the absence of apparent horizons in
spacetimes with translational symmetry constitutes strong evidence for the
validity of the hoop conjecture, and also hints at possible (albeit arguably
unlikely) generic violations of strong cosmic censorship.
| [
{
"created": "Thu, 4 Sep 2003 19:51:26 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Dec 2003 20:05:12 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Goncalves",
"Sergio M. C. V.",
""
]
] | We show that four-dimensional Lorentzian metrics admitting a global spacelike Lie group of isometries, $G_{1}={\mathbb R}$, which obey the Einstein equations for vacuum and certain types of matter, cannot contain apparent horizons. The assumed global isometry allows for the dimensional reduction of the (3+1) system to a (2+1) picture, wherein the four-dimensional metric fields act formally as matter fields. A theorem by Ida allows one to check for the absence of apparent horizons in the dimensionally reduced spacetime, with the four-dimensional results following from the topological product nature of the corresponding manifold. We argue that the absence of apparent horizons in spacetimes with translational symmetry constitutes strong evidence for the validity of the hoop conjecture, and also hints at possible (albeit arguably unlikely) generic violations of strong cosmic censorship. |
1904.09997 | Carlos A. R. Herdeiro | Pedro V. P. Cunha, Carlos A. R. Herdeiro, Eugen Radu | Spontaneously scalarised Kerr black holes | 6 pages, 6 figures | Phys. Rev. Lett. 123, 011101 (2019) | 10.1103/PhysRevLett.123.011101 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct asymptotically flat, spinning, regular on and outside an event
horizon, scalarised black holes (SBHs) in extended scalar-tensor-Gauss-Bonnet
models. They reduce to Kerr BHs when the scalar field vanishes. For an
illustrative choice of non-minimal coupling, we scan the domain of existence.
For each value of spin, SBHs exist in an interval between two critical masses,
with the lowest one vanishing in the static limit. Non-uniqueness with Kerr BHs
of equal global charges is observed; the SBHs are entropically favoured. This
suggests SBHs form dynamically from the spontaneous scalarisation of Kerr BHs,
which are prone to a scalar-triggered tachyonic instability, below the largest
critical mass. Phenomenologically, the introduction of BH spin damps the
maximal observable difference between comparable scalarised and vacuum BHs. In
the static limit, (perturbatively stable) SBHs can store over 20% of the
spacetime energy outside the event horizon; in comparison with Schwarzschild
BHs, their geodesic frequency at the ISCO can differ by a factor of 2.5 and
deviations in the shadow areal radius may top 40%. As the BH spin grows, low
mass SBHs are excluded, and the maximal relative differences decrease, becoming
of order $\sim$ few % for dimensionless spin $j\gtrsim 0.5$. This reveals a
spin selection effect: non-GR effects are only significant for low spin. We
discuss if and how the recently measured shadow size of the M87 supermassive
BH, constrains the length scale of the Gauss-Bonnet coupling.
| [
{
"created": "Mon, 22 Apr 2019 18:00:03 GMT",
"version": "v1"
}
] | 2019-07-10 | [
[
"Cunha",
"Pedro V. P.",
""
],
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Radu",
"Eugen",
""
]
] | We construct asymptotically flat, spinning, regular on and outside an event horizon, scalarised black holes (SBHs) in extended scalar-tensor-Gauss-Bonnet models. They reduce to Kerr BHs when the scalar field vanishes. For an illustrative choice of non-minimal coupling, we scan the domain of existence. For each value of spin, SBHs exist in an interval between two critical masses, with the lowest one vanishing in the static limit. Non-uniqueness with Kerr BHs of equal global charges is observed; the SBHs are entropically favoured. This suggests SBHs form dynamically from the spontaneous scalarisation of Kerr BHs, which are prone to a scalar-triggered tachyonic instability, below the largest critical mass. Phenomenologically, the introduction of BH spin damps the maximal observable difference between comparable scalarised and vacuum BHs. In the static limit, (perturbatively stable) SBHs can store over 20% of the spacetime energy outside the event horizon; in comparison with Schwarzschild BHs, their geodesic frequency at the ISCO can differ by a factor of 2.5 and deviations in the shadow areal radius may top 40%. As the BH spin grows, low mass SBHs are excluded, and the maximal relative differences decrease, becoming of order $\sim$ few % for dimensionless spin $j\gtrsim 0.5$. This reveals a spin selection effect: non-GR effects are only significant for low spin. We discuss if and how the recently measured shadow size of the M87 supermassive BH, constrains the length scale of the Gauss-Bonnet coupling. |
gr-qc/0407047 | Lorenzo Iorio | Lorenzo Iorio | Is it possible to measure the Lense-Thirring effect on the orbits of the
planets in the gravitational field of the Sun? | LaTex2e, A&A macros, 6 pages, no figure, 3 tables. Substantial
revision. More realistic conclusions. Estimations of the impact of
BepiColombo presented | Astron.Astrophys.431:385-389,2005 | 10.1051/0004-6361:20041646 | null | gr-qc astro-ph | null | Here we explore a novel approach in order to try to measure the
post-Newtonian 1/c^2 Lense-Thirring secular effect induced by the
gravitomagnetic field of the Sun on the planetary orbital motion. Due to the
relative smallness of the solar angular momentum J and the large values of the
planetary semimajor axes a, the gravitomagnetic precessions, which affect the
nodes Omega and the perihelia omega and are proportional to J/a^3, are of the
order of 10^-3 arcseconds per century only for, e.g., Mercury. This value lies
just at the edge of the present-day observational sensitivity in reconstructing
the planetary orbits, although future missions to Mercury like Messenger and
BepiColombo could allow to increase it. The major problems come from the main
sources of systematic errors. They are the aliasing classical precessions
induced by the multipolar expansion of the Sun's gravitational potential and
the classical secular N-body precessions which are of the same order of
magnitude or much larger than the Lense-Thirring precessions of interest. This
definitely rules out the possibility of analyzing only one orbital element of,
e.g., Mercury. In order to circumvent these problems, we propose a suitable
linear combination of the orbital residuals of the nodes of Mercury, Venus and
Mars which is, by construction, independent of such classical secular
precessions. A 1-sigma reasonable estimate of the obtainable accuracy yields a
36% error. Since the major role in the proposed combination is played by the
Mercury's node, it could happen that the new, more accurate ephemerides
available in future thanks to the Messenger and BepiColombo missions will offer
an opportunity to improve the present unfavorable situation.
| [
{
"created": "Tue, 13 Jul 2004 13:20:25 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Jul 2004 20:17:03 GMT",
"version": "v2"
},
{
"created": "Tue, 17 Aug 2004 14:36:53 GMT",
"version": "v3"
},
{
"created": "Sat, 21 Aug 2004 09:39:35 GMT",
"version": "v4"
},
{
"c... | 2011-05-23 | [
[
"Iorio",
"Lorenzo",
""
]
] | Here we explore a novel approach in order to try to measure the post-Newtonian 1/c^2 Lense-Thirring secular effect induced by the gravitomagnetic field of the Sun on the planetary orbital motion. Due to the relative smallness of the solar angular momentum J and the large values of the planetary semimajor axes a, the gravitomagnetic precessions, which affect the nodes Omega and the perihelia omega and are proportional to J/a^3, are of the order of 10^-3 arcseconds per century only for, e.g., Mercury. This value lies just at the edge of the present-day observational sensitivity in reconstructing the planetary orbits, although future missions to Mercury like Messenger and BepiColombo could allow to increase it. The major problems come from the main sources of systematic errors. They are the aliasing classical precessions induced by the multipolar expansion of the Sun's gravitational potential and the classical secular N-body precessions which are of the same order of magnitude or much larger than the Lense-Thirring precessions of interest. This definitely rules out the possibility of analyzing only one orbital element of, e.g., Mercury. In order to circumvent these problems, we propose a suitable linear combination of the orbital residuals of the nodes of Mercury, Venus and Mars which is, by construction, independent of such classical secular precessions. A 1-sigma reasonable estimate of the obtainable accuracy yields a 36% error. Since the major role in the proposed combination is played by the Mercury's node, it could happen that the new, more accurate ephemerides available in future thanks to the Messenger and BepiColombo missions will offer an opportunity to improve the present unfavorable situation. |
0902.1863 | Farhad Darabi | F. Darabi | Classical and Quantum Cosmology of an Accelerating Model Universe with
Compactification of Extra Dimensions | 20 pages, "Trends in General Relativity and Quantum Cosmology"
Editor: Charles V. Benton, Nova Science Publishers, New York (2006) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a $(4+D)$-dimensional Kaluza-Klein cosmology with a Robertson-Walker
type metric having two scale factors $a$ and $R$, corresponding to
$D$-dimensional internal space and 4-dimensional universe, respectively. By
introducing an exotic matter in the form of perfect fluid with an special
equation of state, as the space-time part of the higher dimensional
energy-momentum tensor, a four dimensional effective decaying cosmological term
appears as $\lambda \sim R^{-m}$ with $0 \leq m\leq 2$, playing the role of an
evolving dark energy in the universe. By taking $m=2$, which has some
interesting implications in reconciling observations with inflationary models
and is consistent with quantum tunneling, the resulting Einstein's field
equations yield the exponential solutions for the scale factors $a$ and $R$.
These exponential behaviors may account for the dynamical compactification of
extra dimensions and the accelerating expansion of the 4-dimensional universe
in terms of Hubble parameter, $H$. The acceleration of the universe may be
explained by the negative pressure of the exotic matter. It is shown that the
rate of compactification of higher dimensions as well as expansion of
4-dimensional universe depends on the dimension, $D$. We then obtain the
corresponding Wheeler-DeWitt equation and find the general exact solutions in
$D$-dimensions. A good correspondence between the solutions of classical
Einstein's equations and the solutions of quantum Wheeler-DeWitt equation in
any dimension, $D$, is obtained based on Hartle's point of view concerning the
classical limits of quantum cosmology.
| [
{
"created": "Wed, 11 Feb 2009 12:31:22 GMT",
"version": "v1"
}
] | 2009-02-12 | [
[
"Darabi",
"F.",
""
]
] | We study a $(4+D)$-dimensional Kaluza-Klein cosmology with a Robertson-Walker type metric having two scale factors $a$ and $R$, corresponding to $D$-dimensional internal space and 4-dimensional universe, respectively. By introducing an exotic matter in the form of perfect fluid with an special equation of state, as the space-time part of the higher dimensional energy-momentum tensor, a four dimensional effective decaying cosmological term appears as $\lambda \sim R^{-m}$ with $0 \leq m\leq 2$, playing the role of an evolving dark energy in the universe. By taking $m=2$, which has some interesting implications in reconciling observations with inflationary models and is consistent with quantum tunneling, the resulting Einstein's field equations yield the exponential solutions for the scale factors $a$ and $R$. These exponential behaviors may account for the dynamical compactification of extra dimensions and the accelerating expansion of the 4-dimensional universe in terms of Hubble parameter, $H$. The acceleration of the universe may be explained by the negative pressure of the exotic matter. It is shown that the rate of compactification of higher dimensions as well as expansion of 4-dimensional universe depends on the dimension, $D$. We then obtain the corresponding Wheeler-DeWitt equation and find the general exact solutions in $D$-dimensions. A good correspondence between the solutions of classical Einstein's equations and the solutions of quantum Wheeler-DeWitt equation in any dimension, $D$, is obtained based on Hartle's point of view concerning the classical limits of quantum cosmology. |
gr-qc/9505049 | Christian Wiesendanger | C. Wiesendanger | Poincare gauge invariance and gravitation in Minkowski spacetime | 36 pages, latex-file | Class.Quant.Grav. 13 (1996) 681-700 | 10.1088/0264-9381/13/4/008 | DIAS-STP-95-18 | gr-qc | null | A formulation of Poincare symmetry as an inner symmetry of field theories
defined on a fixed Minkowski spacetime is given. Local P gauge transformations
and the corresponding covariant derivative with P gauge fields are introduced.
The renormalization properties of scalar, spinor and vector fields in P gauge
field backgrounds are determined. A minimal gauge field dynamics consistent
with the renormalization constraints is given.
| [
{
"created": "Tue, 30 May 1995 12:30:49 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Wiesendanger",
"C.",
""
]
] | A formulation of Poincare symmetry as an inner symmetry of field theories defined on a fixed Minkowski spacetime is given. Local P gauge transformations and the corresponding covariant derivative with P gauge fields are introduced. The renormalization properties of scalar, spinor and vector fields in P gauge field backgrounds are determined. A minimal gauge field dynamics consistent with the renormalization constraints is given. |
1609.06803 | J\"org Hennig | J\"org Frauendiener and J\"org Hennig | Fully pseudospectral solution of the conformally invariant wave equation
near the cylinder at spacelike infinity. II: Schwarzschild background | 25 pages, 7 figures | Class. Quantum Grav. 34, 045005 (2017) | 10.1088/1361-6382/aa54c4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has recently been demonstrated (Class. Quantum Grav. 31, 085010, 2014)
that the conformally invariant wave equation on a Minkowski background can be
solved with a fully pseudospectral numerical method. In particular, it is
possible to include spacelike infinity into the numerical domain, which is
appropriately represented as a cylinder, and highly accurate numerical
solutions can be obtained with a moderate number of gridpoints. In this paper,
we generalise these considerations to the spherically-symmetric wave equation
on a Schwarzschild background. In the Minkowski case, a logarithmic singularity
at the future boundary is present at leading order, which can easily be removed
to obtain completely regular solutions. An important new feature of the
Schwarzschild background is that the corresponding solutions develop
logarithmic singularities at infinitely many orders. This behaviour seems to be
characteristic for massive space-times. In this sense this work is indicative
of properties of the solutions of the Einstein equations near spatial infinity.
The use of fully pseudospectral methods allows us to still obtain very accurate
numerical solutions, and the convergence properties of the spectral
approximations reveal details about the singular nature of the solutions on
spacelike and null infinity. These results seem to be impossible to achieve
with other current numerical methods. Moreover, we describe how to impose
conditions on the asymptotic behaviour of initial data so that the
leading-order logarithmic terms are avoided, which further improves the
numerical accuracy.
| [
{
"created": "Thu, 22 Sep 2016 02:48:03 GMT",
"version": "v1"
},
{
"created": "Tue, 24 Jan 2017 19:58:14 GMT",
"version": "v2"
}
] | 2017-01-26 | [
[
"Frauendiener",
"Jörg",
""
],
[
"Hennig",
"Jörg",
""
]
] | It has recently been demonstrated (Class. Quantum Grav. 31, 085010, 2014) that the conformally invariant wave equation on a Minkowski background can be solved with a fully pseudospectral numerical method. In particular, it is possible to include spacelike infinity into the numerical domain, which is appropriately represented as a cylinder, and highly accurate numerical solutions can be obtained with a moderate number of gridpoints. In this paper, we generalise these considerations to the spherically-symmetric wave equation on a Schwarzschild background. In the Minkowski case, a logarithmic singularity at the future boundary is present at leading order, which can easily be removed to obtain completely regular solutions. An important new feature of the Schwarzschild background is that the corresponding solutions develop logarithmic singularities at infinitely many orders. This behaviour seems to be characteristic for massive space-times. In this sense this work is indicative of properties of the solutions of the Einstein equations near spatial infinity. The use of fully pseudospectral methods allows us to still obtain very accurate numerical solutions, and the convergence properties of the spectral approximations reveal details about the singular nature of the solutions on spacelike and null infinity. These results seem to be impossible to achieve with other current numerical methods. Moreover, we describe how to impose conditions on the asymptotic behaviour of initial data so that the leading-order logarithmic terms are avoided, which further improves the numerical accuracy. |
gr-qc/0105071 | Robert D. Klauber | Robert D. Klauber | Physical Components, Coordinate Components, and the Speed of Light | 10 pages including 4 figures, references | null | null | null | gr-qc | null | For generalized coordinate systems, the numerical values of vector and tensor
components do not generally equal the physical values, i.e., the values one
would measure with standard physical instruments. Hence, calculating physical
components from coordinate components is important for comparing experiment
with theory. Surprisingly, however, this calculational method is not widely
known among physicists, and is rarely taught in relativity courses, though it
is commonly employed in at least one other field (applied mechanics.) Different
derivations of this method, ranging from elementary to advanced level, are
presented. The result is then applied to clarify the oftentimes confusing issue
of whether or not the speed of light in non-inertial frames is equal to c.
| [
{
"created": "Fri, 18 May 2001 22:23:29 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Klauber",
"Robert D.",
""
]
] | For generalized coordinate systems, the numerical values of vector and tensor components do not generally equal the physical values, i.e., the values one would measure with standard physical instruments. Hence, calculating physical components from coordinate components is important for comparing experiment with theory. Surprisingly, however, this calculational method is not widely known among physicists, and is rarely taught in relativity courses, though it is commonly employed in at least one other field (applied mechanics.) Different derivations of this method, ranging from elementary to advanced level, are presented. The result is then applied to clarify the oftentimes confusing issue of whether or not the speed of light in non-inertial frames is equal to c. |
1903.09704 | Ulrich Sperhake | Roxana Rosca-Mead, Christopher J Moore, Michalis Agathos, Ulrich
Sperhake | Inverse-chirp signals and spontaneous scalarisation with
self-interacting potentials in stellar collapse | 15 pages, 5 figures; submitted to CQG | null | 10.1088/1361-6382/ab256f | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study how the gravitational wave signal from stellar collapse in
scalar-tensor gravity varies under the influence of scalar self-interaction. To
this end, we extract the gravitational radiation from numerical simulations of
stellar collapse for a range of potentials with higher-order terms in addition
to the quadratic mass term. Our study includes collapse to neutron stars and
black holes and we find the strong inverse-chirp signals obtained for the
purely quadratic potential to be exceptionally robust under changes in the
potential at higher orders; quartic and sextic terms in the potential lead to
noticeable differences in the wave signal only if their contribution is
amplified, implying a relative fine-tuning to within 5 or more orders of
magnitude between the mass and self-interaction parameters.
| [
{
"created": "Fri, 22 Mar 2019 20:39:51 GMT",
"version": "v1"
}
] | 2019-09-04 | [
[
"Rosca-Mead",
"Roxana",
""
],
[
"Moore",
"Christopher J",
""
],
[
"Agathos",
"Michalis",
""
],
[
"Sperhake",
"Ulrich",
""
]
] | We study how the gravitational wave signal from stellar collapse in scalar-tensor gravity varies under the influence of scalar self-interaction. To this end, we extract the gravitational radiation from numerical simulations of stellar collapse for a range of potentials with higher-order terms in addition to the quadratic mass term. Our study includes collapse to neutron stars and black holes and we find the strong inverse-chirp signals obtained for the purely quadratic potential to be exceptionally robust under changes in the potential at higher orders; quartic and sextic terms in the potential lead to noticeable differences in the wave signal only if their contribution is amplified, implying a relative fine-tuning to within 5 or more orders of magnitude between the mass and self-interaction parameters. |
2110.06667 | Arash Hajibarat | Arash Hajibarat, Behrouz Mirza, and Alireza Azizallahi | $\gamma$-Metrics in Higher Dimensions | 9 pages, 1 figure | Nuclear Physics B 978 (2022) 115739 | 10.1016/j.nuclphysb.2022.115739 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We introduce five and higher dimensional $\gamma$-metrics. The higher
dimensional metrics are exact solutions of the vacuum field equations and
represent new types of singularities. For dimensions $d>5$ we have obtained
$\gamma$-metrics in flat coordinates. We obtain singularities of metrics and
for a better understanding of geometrical and physical properties of the five
dimensional metric, stable circular orbits are determined by means of the
effective potential. Effect of the deformed parameter ($\gamma$) on redshift of
the $\gamma$-metric are calculated. Interior solution for the five-dimensional
$\gamma$-metric is also obtained.
| [
{
"created": "Wed, 13 Oct 2021 12:05:49 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Apr 2022 08:26:38 GMT",
"version": "v2"
}
] | 2022-04-12 | [
[
"Hajibarat",
"Arash",
""
],
[
"Mirza",
"Behrouz",
""
],
[
"Azizallahi",
"Alireza",
""
]
] | We introduce five and higher dimensional $\gamma$-metrics. The higher dimensional metrics are exact solutions of the vacuum field equations and represent new types of singularities. For dimensions $d>5$ we have obtained $\gamma$-metrics in flat coordinates. We obtain singularities of metrics and for a better understanding of geometrical and physical properties of the five dimensional metric, stable circular orbits are determined by means of the effective potential. Effect of the deformed parameter ($\gamma$) on redshift of the $\gamma$-metric are calculated. Interior solution for the five-dimensional $\gamma$-metric is also obtained. |
2011.12714 | Andrew Farley | Andrew Farley | The Hyperbolic Bloch Equations of General Relativity | 23 pages, no figures. This version 2 includes corrections,
clarifications and additional non-Hermitian Hamiltonian and underlying Lie
group discussions | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | New equations are derived which describe the evolution in curved spacetime of
null geodesics with non-zero (complex) shear $\sigma$ and twist $\omega$ rates
resembling Grishchuk's squeezed states evolution equations from inflationary
cosmology. A ``squeeze" angle $\phi$ (obtained from the direction of the major
axis of the elliptical cross section of the congruence and the direction of the
shear rate), an ellipse axis ratio parameter $w$ and a rotation angle $v$ are
the primary variables. Interpreting $\phi$ as a polar angle and $w$ as a radial
distance, we obtain a mapping to points on the upper sheet, $H_{2}^{+}\,,$ of a
two-sheet hyperboloid, establishing the connection between gravitational optics
and hyperbolic geometry. Points on $H_{2}^{+}$ trace out paths evolving
according to hyperbolic Bloch equations, similar to the optical Bloch
equations, which can also be represented as a Schr\"{o}dinger-like equation
with a non-Hermitian Hamiltonian. A single vector equation on $H_{2}^{+}$
describes the precession of hyperbolic Bloch vectors about a rotation or
birefringence vector on $H_{2}^{+}\,,$ analogous to the precession of Bloch
vectors on the Bloch sphere or Stokes vectors on the Poincar\'{e} sphere. Tidal
gravitational effects and a non-zero twist $\omega$ contribute to the
precession of hyperbolic Bloch vectors.
| [
{
"created": "Mon, 23 Nov 2020 20:52:32 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Apr 2021 16:39:04 GMT",
"version": "v2"
}
] | 2021-04-20 | [
[
"Farley",
"Andrew",
""
]
] | New equations are derived which describe the evolution in curved spacetime of null geodesics with non-zero (complex) shear $\sigma$ and twist $\omega$ rates resembling Grishchuk's squeezed states evolution equations from inflationary cosmology. A ``squeeze" angle $\phi$ (obtained from the direction of the major axis of the elliptical cross section of the congruence and the direction of the shear rate), an ellipse axis ratio parameter $w$ and a rotation angle $v$ are the primary variables. Interpreting $\phi$ as a polar angle and $w$ as a radial distance, we obtain a mapping to points on the upper sheet, $H_{2}^{+}\,,$ of a two-sheet hyperboloid, establishing the connection between gravitational optics and hyperbolic geometry. Points on $H_{2}^{+}$ trace out paths evolving according to hyperbolic Bloch equations, similar to the optical Bloch equations, which can also be represented as a Schr\"{o}dinger-like equation with a non-Hermitian Hamiltonian. A single vector equation on $H_{2}^{+}$ describes the precession of hyperbolic Bloch vectors about a rotation or birefringence vector on $H_{2}^{+}\,,$ analogous to the precession of Bloch vectors on the Bloch sphere or Stokes vectors on the Poincar\'{e} sphere. Tidal gravitational effects and a non-zero twist $\omega$ contribute to the precession of hyperbolic Bloch vectors. |
1808.07490 | Vijay Varma | Vijay Varma and Mark A. Scheel | Constructing a boosted, spinning black hole in the damped harmonic gauge | Matches PRD version. 8 pages, 3 figures | Phys. Rev. D 98, 084032 (2018) | 10.1103/PhysRevD.98.084032 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The damped harmonic gauge is important for numerical relativity computations
based on the generalized harmonic formulation of Einstein's equations, and is
used to reduce coordinate distortions near binary black hole mergers. However,
currently there is no prescription to construct quasiequilibrium binary black
hole initial data in this gauge. Instead, initial data are typically
constructed using a superposition of two boosted analytic single black hole
solutions as free data in the solution of the constraint equations. Then, a
smooth time-dependent gauge transformation is done early in the evolution to
move into the damped harmonic gauge. Using this strategy to produce initial
data in damped harmonic gauge would require the solution of a single black hole
in this gauge, which is not known analytically. In this work we construct a
single boosted, spinning, equilibrium BH in damped harmonic coordinates as a
regular time-independent coordinate transformation from Kerr-Schild
coordinates. To do this, we derive and solve a set of 4 coupled, nonlinear,
elliptic equations for this transformation, with appropriate boundary
conditions. This solution can now be used in the construction of damped
harmonic initial data for binary black holes.
| [
{
"created": "Wed, 22 Aug 2018 18:00:02 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Aug 2018 04:13:33 GMT",
"version": "v2"
},
{
"created": "Tue, 13 Nov 2018 22:53:24 GMT",
"version": "v3"
}
] | 2018-11-15 | [
[
"Varma",
"Vijay",
""
],
[
"Scheel",
"Mark A.",
""
]
] | The damped harmonic gauge is important for numerical relativity computations based on the generalized harmonic formulation of Einstein's equations, and is used to reduce coordinate distortions near binary black hole mergers. However, currently there is no prescription to construct quasiequilibrium binary black hole initial data in this gauge. Instead, initial data are typically constructed using a superposition of two boosted analytic single black hole solutions as free data in the solution of the constraint equations. Then, a smooth time-dependent gauge transformation is done early in the evolution to move into the damped harmonic gauge. Using this strategy to produce initial data in damped harmonic gauge would require the solution of a single black hole in this gauge, which is not known analytically. In this work we construct a single boosted, spinning, equilibrium BH in damped harmonic coordinates as a regular time-independent coordinate transformation from Kerr-Schild coordinates. To do this, we derive and solve a set of 4 coupled, nonlinear, elliptic equations for this transformation, with appropriate boundary conditions. This solution can now be used in the construction of damped harmonic initial data for binary black holes. |
1403.6177 | Anna Heffernan | Anna Heffernan | The Self-Force Problem: Local Behaviour of the Detweiler-Whiting
Singular Field | PhD Thesis | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The growing reality of gravitational wave astronomy is giving age-old
problems a new lease of life; one such problem is that of the self-force. A
charged or massive particle moving in a curved background space-time produces a
field that affects its motion, pushing it off its expected geodesic. This
self-field gives rise to a so-called self-force acting on the particle. In
modelling this motion, the self-force approach uses a perturbative expansion in
the mass ratio. One of the most interesting sources of gravitational waves are
extreme mass ratio inspirals - systems perfectly suited to self-force
modelling. One of the key problems within the self-force model is the
divergence of the field at the particle. To resolve this, the field is split
into a singular component and a smooth regular field. This regular-singular
split, introduced by Detweiler and Whiting, is used in most modern self-force
calculations. In this thesis, we derive high-order expansions of the
Detweiler-Whiting singular field, and use these to push the boundaries on
current precision limits of self-force calculations. Within the mode-sum
scheme, we give over 14 previously unknown regularisation parameters, almost
doubling the current regularisation parameter database. We also produce smooth
effective sources to high order, and propose an application of the higher terms
to improve accuracy in the m-mode scheme. Finally, we investigate the status of
the cosmic censorship conjecture and the role that the self-force plays. To
this end, we give regularisation parameters for non-geodesic motion. We also
show the necessity of our results in the exciting area of second order
self-force calculations, which benefit significantly from high-order coordinate
expansions of the singular field. We calculate several parameters that these
schemes require, and highlight the further advancements possible from the
results of this thesis.
| [
{
"created": "Mon, 24 Mar 2014 22:51:19 GMT",
"version": "v1"
}
] | 2014-03-26 | [
[
"Heffernan",
"Anna",
""
]
] | The growing reality of gravitational wave astronomy is giving age-old problems a new lease of life; one such problem is that of the self-force. A charged or massive particle moving in a curved background space-time produces a field that affects its motion, pushing it off its expected geodesic. This self-field gives rise to a so-called self-force acting on the particle. In modelling this motion, the self-force approach uses a perturbative expansion in the mass ratio. One of the most interesting sources of gravitational waves are extreme mass ratio inspirals - systems perfectly suited to self-force modelling. One of the key problems within the self-force model is the divergence of the field at the particle. To resolve this, the field is split into a singular component and a smooth regular field. This regular-singular split, introduced by Detweiler and Whiting, is used in most modern self-force calculations. In this thesis, we derive high-order expansions of the Detweiler-Whiting singular field, and use these to push the boundaries on current precision limits of self-force calculations. Within the mode-sum scheme, we give over 14 previously unknown regularisation parameters, almost doubling the current regularisation parameter database. We also produce smooth effective sources to high order, and propose an application of the higher terms to improve accuracy in the m-mode scheme. Finally, we investigate the status of the cosmic censorship conjecture and the role that the self-force plays. To this end, we give regularisation parameters for non-geodesic motion. We also show the necessity of our results in the exciting area of second order self-force calculations, which benefit significantly from high-order coordinate expansions of the singular field. We calculate several parameters that these schemes require, and highlight the further advancements possible from the results of this thesis. |
1101.4520 | Rituparno Goswami | Rituparno Goswami, George F R Ellis | Almost Birkhoff Theorem in General Relativity | 7 pages, revtex4 | null | 10.1007/s10714-011-1172-z | null | gr-qc astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We extend Birkhoff's theorem for almost LRS-II vacuum spacetimes to show that
the rigidity of spherical vacuum solutions of Einstein's field equations
continues even in the perturbed scenario.
| [
{
"created": "Mon, 24 Jan 2011 13:21:22 GMT",
"version": "v1"
}
] | 2015-05-27 | [
[
"Goswami",
"Rituparno",
""
],
[
"Ellis",
"George F R",
""
]
] | We extend Birkhoff's theorem for almost LRS-II vacuum spacetimes to show that the rigidity of spherical vacuum solutions of Einstein's field equations continues even in the perturbed scenario. |
2401.05311 | Khalil El Bourakadi | K. El Bourakadi, H.Chakir, M.Yu. Khlopov | Leptogenesis Effects on the Gravitational Waves Background: Interpreting
the NANOGrav Measurements and JWST Constraints on Primordial Black Holes | 21 pages, 10 figures, 1 table | null | null | null | gr-qc hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | We demonstrate that the leptogenesis mechanisms, which are associated with
B-L symmetry breaking mechanism has notable effects on the production of
gravitational waves. These gravitational waves align well with the recent
observations of a stochastic gravitational wave background by NANOGrav and
pulsar-timing arrays (PTAs). For these gravitational waves to match the recent
measurements, the critical value of the B-L breaking should be around the GUT
scale. Moreover, we consider the generation of primordial gravitational waves
from binary systems of Primordial Black Holes (PBHs) which could be predicted
by the recent detection of gravitational waves. PBHs with specific masses can
be responsible for massive galaxy formation observed at high redshifts reported
by the James Webb Space Telescope (JWST). We contemplate the potential for a
shared source between the NANOGrav and JWST observations, namely primordial
black holes. These black holes could serve as seeds of rapid galaxy formation,
offering an explanation for the galaxies observed by JWST.
| [
{
"created": "Wed, 10 Jan 2024 18:29:01 GMT",
"version": "v1"
},
{
"created": "Mon, 20 May 2024 02:03:03 GMT",
"version": "v2"
}
] | 2024-05-21 | [
[
"Bourakadi",
"K. El",
""
],
[
"Chakir",
"H.",
""
],
[
"Khlopov",
"M. Yu.",
""
]
] | We demonstrate that the leptogenesis mechanisms, which are associated with B-L symmetry breaking mechanism has notable effects on the production of gravitational waves. These gravitational waves align well with the recent observations of a stochastic gravitational wave background by NANOGrav and pulsar-timing arrays (PTAs). For these gravitational waves to match the recent measurements, the critical value of the B-L breaking should be around the GUT scale. Moreover, we consider the generation of primordial gravitational waves from binary systems of Primordial Black Holes (PBHs) which could be predicted by the recent detection of gravitational waves. PBHs with specific masses can be responsible for massive galaxy formation observed at high redshifts reported by the James Webb Space Telescope (JWST). We contemplate the potential for a shared source between the NANOGrav and JWST observations, namely primordial black holes. These black holes could serve as seeds of rapid galaxy formation, offering an explanation for the galaxies observed by JWST. |
1409.6867 | Leonardo Campanelli | Leonardo Campanelli | Electromagnetism with dimension-five operators | 7 pages, no figures, typos corrected, version matching the published
one in Physical Review D | Phys. Rev. D 90, 105014 (2014) | 10.1103/PhysRevD.90.105014 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive, in curved spacetime, the most general Lorentz-violating
electromagnetic Lagrangian containing dimension-five operators with one more
derivative than the Maxwell term in the hypothesis that Lorentz symmetry is
broken by a background four-vector $n_\mu$. We then study, for the case of
isotropic $n_\mu$, the generation of cosmic magnetic fields at inflation and
cosmic birefringence. In the limiting case of Minkowski spacetime, we find that
other than the CPT-odd Myers-Pospelov term, there exists another CPT-odd term
that gives rise to nontrivial dispersion and constitutive relations.
| [
{
"created": "Wed, 24 Sep 2014 09:23:33 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Oct 2014 08:45:01 GMT",
"version": "v2"
},
{
"created": "Thu, 13 Nov 2014 08:19:44 GMT",
"version": "v3"
}
] | 2014-11-19 | [
[
"Campanelli",
"Leonardo",
""
]
] | We derive, in curved spacetime, the most general Lorentz-violating electromagnetic Lagrangian containing dimension-five operators with one more derivative than the Maxwell term in the hypothesis that Lorentz symmetry is broken by a background four-vector $n_\mu$. We then study, for the case of isotropic $n_\mu$, the generation of cosmic magnetic fields at inflation and cosmic birefringence. In the limiting case of Minkowski spacetime, we find that other than the CPT-odd Myers-Pospelov term, there exists another CPT-odd term that gives rise to nontrivial dispersion and constitutive relations. |
1603.08719 | Andrea Addazi AndAdd | Andrea Addazi | Quantum chaos inside space-temporal Sinai billiards | Version accepted in Int. J. of Geometric Methods in Modern Physics.
arXiv admin note: substantial text overlap with arXiv:1508.04054,
arXiv:1510.09128 | null | 10.1142/S0219887816500821 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss general aspects of non-relativistic quantum chaos theory of
scattering of a quantum particle on a system of a large number of naked
singularities. We define such a system space-temporal Sinai billiard We dis-
cuss the problem in semiclassical approach. We show that in semiclassical
regime the formation of trapped periodic semiclassical orbits inside the sys-
tem is unavoidable. This leads to general expression of survival probabilities
and scattering time delays, expanded to the chaotic Pollicott-Ruelle reso-
nances. Finally, we comment on possible generalizations of these aspects to
relativistic quantum field theory.
| [
{
"created": "Tue, 29 Mar 2016 10:51:06 GMT",
"version": "v1"
}
] | 2016-06-29 | [
[
"Addazi",
"Andrea",
""
]
] | We discuss general aspects of non-relativistic quantum chaos theory of scattering of a quantum particle on a system of a large number of naked singularities. We define such a system space-temporal Sinai billiard We dis- cuss the problem in semiclassical approach. We show that in semiclassical regime the formation of trapped periodic semiclassical orbits inside the sys- tem is unavoidable. This leads to general expression of survival probabilities and scattering time delays, expanded to the chaotic Pollicott-Ruelle reso- nances. Finally, we comment on possible generalizations of these aspects to relativistic quantum field theory. |
1310.2790 | Alexey Golovnev | Alexey Golovnev | On the recently proposed Mimetic Dark Matter | 3 pages; minor corrections | Physics Letters B 728 (2014) 39 | 10.1016/j.physletb.2013.11.026 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, an interesting gravitational model was proposed in order to mimic
the effect of Dark Matter. Chamseddine and Mukhanov in the arXiv preprint
1308.5410 have separated the conformal mode of a physical metric in the form of
a squared gradient of an auxiliary scalar field. Notably, the variational
principle has given a more general equation of motion than that of purely
Einsteinian relativity theory, with a possibility of reproducing an effective
Dark Matter. In this short paper, we explain the nature of this phenomenon in
terms of the class of functions on which the variation takes place. Then we
give a more transparent equivalent formulation of the model without an
auxiliary metric. Finally, we speculate a bit about possible extensions.
| [
{
"created": "Thu, 10 Oct 2013 12:29:52 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Oct 2013 12:25:05 GMT",
"version": "v2"
}
] | 2013-12-02 | [
[
"Golovnev",
"Alexey",
""
]
] | Recently, an interesting gravitational model was proposed in order to mimic the effect of Dark Matter. Chamseddine and Mukhanov in the arXiv preprint 1308.5410 have separated the conformal mode of a physical metric in the form of a squared gradient of an auxiliary scalar field. Notably, the variational principle has given a more general equation of motion than that of purely Einsteinian relativity theory, with a possibility of reproducing an effective Dark Matter. In this short paper, we explain the nature of this phenomenon in terms of the class of functions on which the variation takes place. Then we give a more transparent equivalent formulation of the model without an auxiliary metric. Finally, we speculate a bit about possible extensions. |
0711.0873 | Anil Zengino\u{g}lu C | An{\i}l Zengino\u{g}lu | A conformal approach to numerical calculations of asymptotically flat
spacetimes | PhD thesis, Max-Planck Institute for Gravitational Physics (AEI) and
University of Potsdam, June 2007, 116 pages, 47 figures. Not the official
version. Corrected two typos (p22 and p97) | null | null | AEI-2007-154 | gr-qc | null | This thesis is concerned with the development and application of conformal
techniques to numerical calculations of asymptotically flat spacetimes. The
conformal compactification technique enables us to calculate spatially
unbounded domains, thereby avoiding the introduction of an artificial timelike
outer boundary. We construct in spherical symmetry an explicit scri-fixing
gauge, i.e. a conformal and a coordinate gauge in which the spatial coordinate
location of null infinity is independent of time so that no resolution loss in
the physical part of the conformal extension appears. Going beyond spherical
symmetry, we develop a method to include null infinity in the computational
domain. With this method, hyperboloidal initial value problems for the Einstein
equations can be solved in a scri-fixing general wave gauge. To study spatial
infinity, we discuss the conformal Gauss gauge and the reduced general
conformal field equations from a numerical point of view. This leads us to the
first numerical calculation of the entire Schwarzschild-Kruskal solution
including spatial, null and timelike infinity and the domain close to the
singularity. After developing a three dimensional, frame based evolution code
with smooth inner and outer boundaries we calculate a radiative axisymmetric
vacuum solution in a neighbourhood of spatial infinity represented as a
cylinder including a piece of null infinity. In this context, a certain
component of the rescaled Weyl tensor representing the radiation field is
calculated unambiguously with respect to an adapted tetrad at null infinity.
| [
{
"created": "Tue, 6 Nov 2007 14:13:50 GMT",
"version": "v1"
},
{
"created": "Sun, 11 Nov 2007 19:21:04 GMT",
"version": "v2"
}
] | 2012-05-08 | [
[
"Zenginoğlu",
"Anıl",
""
]
] | This thesis is concerned with the development and application of conformal techniques to numerical calculations of asymptotically flat spacetimes. The conformal compactification technique enables us to calculate spatially unbounded domains, thereby avoiding the introduction of an artificial timelike outer boundary. We construct in spherical symmetry an explicit scri-fixing gauge, i.e. a conformal and a coordinate gauge in which the spatial coordinate location of null infinity is independent of time so that no resolution loss in the physical part of the conformal extension appears. Going beyond spherical symmetry, we develop a method to include null infinity in the computational domain. With this method, hyperboloidal initial value problems for the Einstein equations can be solved in a scri-fixing general wave gauge. To study spatial infinity, we discuss the conformal Gauss gauge and the reduced general conformal field equations from a numerical point of view. This leads us to the first numerical calculation of the entire Schwarzschild-Kruskal solution including spatial, null and timelike infinity and the domain close to the singularity. After developing a three dimensional, frame based evolution code with smooth inner and outer boundaries we calculate a radiative axisymmetric vacuum solution in a neighbourhood of spatial infinity represented as a cylinder including a piece of null infinity. In this context, a certain component of the rescaled Weyl tensor representing the radiation field is calculated unambiguously with respect to an adapted tetrad at null infinity. |
1712.02296 | Felipe Falciano | M. L. Pe\~nafiel, F. T. Falciano | Bekenstein Inequalities and Nonlinear Electrodynamics | Accepted for publication Phys. Rev. D | null | 10.1103/PhysRevD.96.125011 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bekenstein and Mayo proposed a generalised bound for the entropy, which
implies some inequalities between the charge, energy, angular momentum, and the
size of the macroscopic system. Dain has shown that Maxwell's electrodynamics
satisfies all three inequalities. We investigate the validity of these
relations in the context of nonlinear electrodynamics and show that Born-Infeld
electrodynamics satisfies all of them. However, contrary to the linear theory,
there is no rigidity statement in Born-Infeld. We study the physical meaning
and the relationship between these inequalities and, in particular, we analyse
the connection between the energy-angular momentum inequality and causality.
| [
{
"created": "Wed, 6 Dec 2017 17:23:21 GMT",
"version": "v1"
}
] | 2018-01-17 | [
[
"Peñafiel",
"M. L.",
""
],
[
"Falciano",
"F. T.",
""
]
] | Bekenstein and Mayo proposed a generalised bound for the entropy, which implies some inequalities between the charge, energy, angular momentum, and the size of the macroscopic system. Dain has shown that Maxwell's electrodynamics satisfies all three inequalities. We investigate the validity of these relations in the context of nonlinear electrodynamics and show that Born-Infeld electrodynamics satisfies all of them. However, contrary to the linear theory, there is no rigidity statement in Born-Infeld. We study the physical meaning and the relationship between these inequalities and, in particular, we analyse the connection between the energy-angular momentum inequality and causality. |
gr-qc/9712037 | Luciano Rezzolla | L. Rezzolla(1), A. M. Abrahams(1), T. W. Baumgarte(1), G. B. Cook(2),
M. A. Scheel(2), S. L. Shapiro(1) and S. A. Teukolsky(2) ((1) University of
Illinois at Urbana-Champaign, (2) Cornell University) | Waveform propagation in black hole spacetimes: evaluating the quality of
numerical solutions | 13 pages, RevTeX, to appear in Phys. Rev. D | Phys.Rev. D57 (1998) 1084-1091 | 10.1103/PhysRevD.57.1084 | null | gr-qc | null | We compute the propagation and scattering of linear gravitational waves off a
Schwarzschild black hole using a numerical code which solves a generalization
of the Zerilli equation to a three dimensional cartesian coordinate system.
Since the solution to this problem is well understood it represents a very good
testbed for evaluating our ability to perform three dimensional computations of
gravitational waves in spacetimes in which a black hole event horizon is
present.
| [
{
"created": "Mon, 8 Dec 1997 16:20:27 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Rezzolla",
"L.",
""
],
[
"Abrahams",
"A. M.",
""
],
[
"Baumgarte",
"T. W.",
""
],
[
"Cook",
"G. B.",
""
],
[
"Scheel",
"M. A.",
""
],
[
"Shapiro",
"S. L.",
""
],
[
"Teukolsky",
"S. A.",
""
]
] | We compute the propagation and scattering of linear gravitational waves off a Schwarzschild black hole using a numerical code which solves a generalization of the Zerilli equation to a three dimensional cartesian coordinate system. Since the solution to this problem is well understood it represents a very good testbed for evaluating our ability to perform three dimensional computations of gravitational waves in spacetimes in which a black hole event horizon is present. |
1203.4305 | Ivan Arraut | Ivan Arraut | About the propagation of the Gravitational Waves in an asymptotically
de-Sitter space: Comparing two points of view | Accepted for publication in MPLA | Mod. Phys. Lett. A 28 1350019 (2013) | 10.1142/S0217732313500193 | MPLA-D-12-00344R1 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the propagation of gravitational waves (GWs) in an asymptotically
de-Sitter space by expanding the perturbation around Minkowski and introducing
the effects of the Cosmological Constant ($\Lambda$), first as an additional
source (de-Donder gauge) and after as a gauge effect ($\Lambda$-gauge). In both
cases the inclusion of the Cosmological Constant $\Lambda$ impedes the
detection of a gravitational wave at a distance larger than
$L_{crit}=(6\sqrt{2}\pi f \hat{h}/\sqrt{5})r_\Lambda^2$, where
$r_\Lambda=\frac{1}{\sqrt{\Lambda}}$ and f and $\hat{h}$ are the frequency and
strain of the wave respectively. We demonstrate that $L_{crit}$ is just a
confirmation of the Cosmic No hair Conjecture (CNC) already explained in the
literature.
| [
{
"created": "Tue, 20 Mar 2012 01:36:15 GMT",
"version": "v1"
},
{
"created": "Wed, 9 May 2012 16:25:34 GMT",
"version": "v2"
},
{
"created": "Thu, 12 Jul 2012 12:57:25 GMT",
"version": "v3"
},
{
"created": "Sat, 26 Jan 2013 09:08:03 GMT",
"version": "v4"
}
] | 2013-04-09 | [
[
"Arraut",
"Ivan",
""
]
] | We analyze the propagation of gravitational waves (GWs) in an asymptotically de-Sitter space by expanding the perturbation around Minkowski and introducing the effects of the Cosmological Constant ($\Lambda$), first as an additional source (de-Donder gauge) and after as a gauge effect ($\Lambda$-gauge). In both cases the inclusion of the Cosmological Constant $\Lambda$ impedes the detection of a gravitational wave at a distance larger than $L_{crit}=(6\sqrt{2}\pi f \hat{h}/\sqrt{5})r_\Lambda^2$, where $r_\Lambda=\frac{1}{\sqrt{\Lambda}}$ and f and $\hat{h}$ are the frequency and strain of the wave respectively. We demonstrate that $L_{crit}$ is just a confirmation of the Cosmic No hair Conjecture (CNC) already explained in the literature. |
gr-qc/0505072 | Shinya Tomizawa | Shinya Tomizawa and Masaru Siino | Limit structure of Future Null Infinity tangent -topology of the event
horizon and gravitational wave tail- | 20 pages, 3 figures, accepted for publication in Class. Quant. Grav | Class.Quant.Grav. 23 (2006) 683-700 | 10.1088/0264-9381/23/3/009 | null | gr-qc | null | We investigated the relation between the behavior of gravitational wave at
late time and the limit structure of future null infinity tangent which will
determine the topology of the event horizon far in the future. In the present
article, we mainly consider a spacetime with two black holes. Although in most
of cases, the black holes coalesce and its event horizon is topologically a
single sphere far in the future, there are several possibilities that the black
holes never coalesce and such exact solutions as examples. In our formulation,
the tangent vector of future null infinity is, under conformal embedding,
related to the number of black holes far in the future through the
Poincar\'e-Hopf's theorem. Under the conformal embedding, the topology of event
horizon far in the future will be affected by the geometrical structure of the
future null infinity. In this article, we related the behavior of Weyl
curvature to this limit behavior of the generator vector of the future null
infinity. We show if Weyl curvature decays sufficiently slowly at late time in
the neighborhood of future null infinity, two black holes never coalesce.
| [
{
"created": "Sat, 14 May 2005 10:50:05 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Dec 2005 02:02:37 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Tomizawa",
"Shinya",
""
],
[
"Siino",
"Masaru",
""
]
] | We investigated the relation between the behavior of gravitational wave at late time and the limit structure of future null infinity tangent which will determine the topology of the event horizon far in the future. In the present article, we mainly consider a spacetime with two black holes. Although in most of cases, the black holes coalesce and its event horizon is topologically a single sphere far in the future, there are several possibilities that the black holes never coalesce and such exact solutions as examples. In our formulation, the tangent vector of future null infinity is, under conformal embedding, related to the number of black holes far in the future through the Poincar\'e-Hopf's theorem. Under the conformal embedding, the topology of event horizon far in the future will be affected by the geometrical structure of the future null infinity. In this article, we related the behavior of Weyl curvature to this limit behavior of the generator vector of the future null infinity. We show if Weyl curvature decays sufficiently slowly at late time in the neighborhood of future null infinity, two black holes never coalesce. |
1304.0462 | Priscilla Canizares | Priscilla Canizares (1), Scott E. Field (2), Jonathan R. Gair (1),
Manuel Tiglio (2,3) ((1) Institute of Astronomy, Cambridge (UK), (2)
University of Maryland, College Park (USA), (3) California Institute of
Technology, Pasadena (USA)) | Gravitational wave parameter estimation with compressed likelihood
evaluations | 18 pages, 12 figures (2 updated) and 2 tables. Minor edits based on
referee report | Phys. Rev. D 87, 124005 (2013) | 10.1103/PhysRevD.87.124005 | null | gr-qc astro-ph.IM stat.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | One of the main bottlenecks in gravitational wave (GW) astronomy is the high
cost of performing parameter estimation and GW searches on the fly. We propose
a novel technique based on Reduced Order Quadratures (ROQs), an application and
data-specific quadrature rule, to perform fast and accurate likelihood
evaluations. These are the dominant cost in Markov chain Monte Carlo (MCMC)
algorithms, which are widely employed in parameter estimation studies, and so
ROQs offer a new way to accelerate GW parameter estimation. We illustrate our
approach using a four dimensional GW burst model embedded in noise. We build an
ROQ for this model, and perform four dimensional MCMC searches with both the
standard and ROQs quadrature rules, showing that, for this model, the ROQ
approach is around 25 times faster than the standard approach with essentially
no loss of accuracy. The speed-up from using ROQs is expected to increase for
more complex GW signal models and therefore has significant potential to
accelerate parameter estimation of GW sources such as compact binary
coalescences.
| [
{
"created": "Mon, 1 Apr 2013 20:02:21 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Sep 2013 11:35:49 GMT",
"version": "v2"
}
] | 2013-09-26 | [
[
"Canizares",
"Priscilla",
""
],
[
"Field",
"Scott E.",
""
],
[
"Gair",
"Jonathan R.",
""
],
[
"Tiglio",
"Manuel",
""
]
] | One of the main bottlenecks in gravitational wave (GW) astronomy is the high cost of performing parameter estimation and GW searches on the fly. We propose a novel technique based on Reduced Order Quadratures (ROQs), an application and data-specific quadrature rule, to perform fast and accurate likelihood evaluations. These are the dominant cost in Markov chain Monte Carlo (MCMC) algorithms, which are widely employed in parameter estimation studies, and so ROQs offer a new way to accelerate GW parameter estimation. We illustrate our approach using a four dimensional GW burst model embedded in noise. We build an ROQ for this model, and perform four dimensional MCMC searches with both the standard and ROQs quadrature rules, showing that, for this model, the ROQ approach is around 25 times faster than the standard approach with essentially no loss of accuracy. The speed-up from using ROQs is expected to increase for more complex GW signal models and therefore has significant potential to accelerate parameter estimation of GW sources such as compact binary coalescences. |
1403.7054 | Ettore Minguzzi | E. Minguzzi | Spacetime metrics from gauge potentials | 8 pages. Contribution to the special "Symmetry" volume: Physics based
on two-by-two matrices | Symmetry 6 (2014) 164-170 | 10.3390/sym6020164 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I present an approach to gravity in which the spacetime metric is constructed
from a non-Abelian gauge potential with values in the Lie algebra of the group
U(2) (or the Lie algebra of quaternions). If the curvature of this potential
vanishes, the metric reduces to a canonical curved background form reminiscent
of the Friedmann S^3 cosmological metric.
| [
{
"created": "Thu, 27 Mar 2014 14:32:26 GMT",
"version": "v1"
}
] | 2014-03-28 | [
[
"Minguzzi",
"E.",
""
]
] | I present an approach to gravity in which the spacetime metric is constructed from a non-Abelian gauge potential with values in the Lie algebra of the group U(2) (or the Lie algebra of quaternions). If the curvature of this potential vanishes, the metric reduces to a canonical curved background form reminiscent of the Friedmann S^3 cosmological metric. |
1307.4116 | Neil J. Cornish | Matthew R. Adams and Neil J. Cornish | Detecting a Stochastic Gravitational Wave Background in the presence of
a Galactic Foreground and Instrument Noise | 10 pages, 13 figures. Error in 6 link results corrected | Phys. Rev. D 89, 022001 (2014) | 10.1103/PhysRevD.89.022001 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Detecting a stochastic gravitational wave background requires that we first
understand and model any astrophysical foregrounds. In the millihertz frequency
band, the predominate foreground signal will be from unresolved white dwarf
binaries in the galaxy. We build on our previous work to show that a stochastic
gravitational wave background can be detected in the presence of both
instrument noise and a galactic confusion foreground. The key to our approach
is accurately modeling the spectra for each of the various signal components.
We simulate data for a gigameter Laser Interferometer Space Antenna (LISA)
operating in the mHz frequency band detector operating with both 6- and
4-links. We obtain posterior distribution functions for the instrument noise
parameters, the galaxy level and modulation parameters, and the stochastic
background energy density. We find that we are able to detect a scale-invariant
stochastic background with energy density as low as Omega_gw = 2e-13 for a
6-link interferometer and Omega_gw = 5e-13 for a 4-link interferometer with one
year of data.
| [
{
"created": "Mon, 15 Jul 2013 22:03:30 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Oct 2013 15:37:16 GMT",
"version": "v2"
}
] | 2014-01-23 | [
[
"Adams",
"Matthew R.",
""
],
[
"Cornish",
"Neil J.",
""
]
] | Detecting a stochastic gravitational wave background requires that we first understand and model any astrophysical foregrounds. In the millihertz frequency band, the predominate foreground signal will be from unresolved white dwarf binaries in the galaxy. We build on our previous work to show that a stochastic gravitational wave background can be detected in the presence of both instrument noise and a galactic confusion foreground. The key to our approach is accurately modeling the spectra for each of the various signal components. We simulate data for a gigameter Laser Interferometer Space Antenna (LISA) operating in the mHz frequency band detector operating with both 6- and 4-links. We obtain posterior distribution functions for the instrument noise parameters, the galaxy level and modulation parameters, and the stochastic background energy density. We find that we are able to detect a scale-invariant stochastic background with energy density as low as Omega_gw = 2e-13 for a 6-link interferometer and Omega_gw = 5e-13 for a 4-link interferometer with one year of data. |
gr-qc/9509024 | Steve Carlip | S. Carlip | Statistical Mechanics and Black Hole Entropy | 10 pages, one figure in separate (uuencoded, compressed) tar file;
factor of 2 corrected in eqn. (2.8) | null | null | UCD-95-30 | gr-qc hep-th | null | I review a new (and still tentative) approach to black hole thermodynamics
that seeks to explain black hole entropy in terms of microscopic quantum
gravitational boundary states induced on the black hole horizon.
| [
{
"created": "Wed, 13 Sep 1995 17:45:20 GMT",
"version": "v1"
},
{
"created": "Fri, 20 Oct 1995 18:35:46 GMT",
"version": "v2"
}
] | 2008-02-03 | [
[
"Carlip",
"S.",
""
]
] | I review a new (and still tentative) approach to black hole thermodynamics that seeks to explain black hole entropy in terms of microscopic quantum gravitational boundary states induced on the black hole horizon. |
2204.02419 | Jorge Delgado B.S. | Jorge F. M. Delgado | Spinning Black Holes with Scalar Hair and Horizonless Compact Objects
within and beyond General Relativity | Ph.D. thesis defended at the University of Aveiro in March 2022.
Based on the papers arXiv:1804.04910, arXiv:1903.01488, arXiv:2002.05012,
arXiv:2005.05982, arXiv:2012.03952 and arXiv:2107.03404 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The last years have brought upon us a golden age of observational
gravitational physics. The several observations by the LIGO/Virgo/KAGRA
collaboration about gravitational waves and by the EHT collaboration about the
shadow and lensing of light around the supermassive black hole in the centre of
M87 will point the scientific community in the correct direction to find an
answer to the Kerr hypothesis. In order to follow that direction, the
systematic construction and analysis of the physical properties of solutions
within General Relativity with additional fields or within modified theories of
gravity is necessary. In this thesis, we shall provide such construction and
analysis for compact objects within (complex-)Einstein-Klein-Gordon theory with
various scalar potentials and within a particular scalar-tensor theory -- the
shift-symmetric Horndesky theory. After a brief introduction to some key topics
that shall be useful throughout this thesis, we present a discussion about the
horizon geometry of Kerr black holes with and without scalar hair. We follow up
with the construction and study of the same hairy solutions discussed in the
previous chapter but with higher azimuthal harmonic indexes. In the following
two chapters, we introduce a different scalar potential based on the Quantum
Chromodynamic axion potential and obtain and study both horizonless compact
objects and black holes. We then go to the shift-symmetric Horndeski theory,
where we perform similar constructions and analyses to the ones already
mentioned. Lastly, we derive a relation between the radial stability of
light-rings and timelike circular orbits around them. We follow up with a study
on how efficient it is the conversion of gravitational energy in radiation as a
timelike particle falls towards all compact objects studied throughout this
thesis. We end with some conclusions and remarks.
| [
{
"created": "Tue, 5 Apr 2022 18:00:19 GMT",
"version": "v1"
}
] | 2022-04-07 | [
[
"Delgado",
"Jorge F. M.",
""
]
] | The last years have brought upon us a golden age of observational gravitational physics. The several observations by the LIGO/Virgo/KAGRA collaboration about gravitational waves and by the EHT collaboration about the shadow and lensing of light around the supermassive black hole in the centre of M87 will point the scientific community in the correct direction to find an answer to the Kerr hypothesis. In order to follow that direction, the systematic construction and analysis of the physical properties of solutions within General Relativity with additional fields or within modified theories of gravity is necessary. In this thesis, we shall provide such construction and analysis for compact objects within (complex-)Einstein-Klein-Gordon theory with various scalar potentials and within a particular scalar-tensor theory -- the shift-symmetric Horndesky theory. After a brief introduction to some key topics that shall be useful throughout this thesis, we present a discussion about the horizon geometry of Kerr black holes with and without scalar hair. We follow up with the construction and study of the same hairy solutions discussed in the previous chapter but with higher azimuthal harmonic indexes. In the following two chapters, we introduce a different scalar potential based on the Quantum Chromodynamic axion potential and obtain and study both horizonless compact objects and black holes. We then go to the shift-symmetric Horndeski theory, where we perform similar constructions and analyses to the ones already mentioned. Lastly, we derive a relation between the radial stability of light-rings and timelike circular orbits around them. We follow up with a study on how efficient it is the conversion of gravitational energy in radiation as a timelike particle falls towards all compact objects studied throughout this thesis. We end with some conclusions and remarks. |
0911.1020 | Flavio Mercati | Giovanni Amelino-Camelia, Claus Laemmerzahl, Flavio Mercati, Guglielmo
M. Tino | Constraining the energy-momentum dispersion relation with Planck-scale
sensitivity using cold atoms | LaTex, 4 pages, preprint version of Physical Review Letters 103
(2009) 171302 | Phys.Rev.Lett.103:171302,2009 | 10.1103/PhysRevLett.103.171302 | null | gr-qc physics.atom-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use the results of ultra-precise cold-atom-recoil experiments to constrain
the form of the energy-momentum dispersion relation, a structure that is
expected to be modified in several quantum-gravity approaches. Our strategy of
analysis applies to the nonrelativistic (small speeds) limit of the dispersion
relation, and is therefore complementary to an analogous ongoing effort of
investigation of the dispersion relation in the ultrarelativistic regime using
observations in astrophysics. For the leading correction in the nonrelativistic
limit the exceptional sensitivity of cold-atom-recoil experiments remarkably
allows us to set a limit within a single order of magnitude of the desired
Planck-scale level, thereby providing the first example of Planck-scale
sensitivity in the study of the dispersion relation in controlled laboratory
experiments. For the next-to-leading term we obtain a limit which is a few
orders of magnitude away from the Planck scale, but still amounts to the best
limit on a class of Lorentz-symmetry test theories that has been extensively
used to investigate the hypothesis of "deformation" (rather than breakdown) of
spacetime symmetries.
| [
{
"created": "Thu, 5 Nov 2009 12:57:04 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Amelino-Camelia",
"Giovanni",
""
],
[
"Laemmerzahl",
"Claus",
""
],
[
"Mercati",
"Flavio",
""
],
[
"Tino",
"Guglielmo M.",
""
]
] | We use the results of ultra-precise cold-atom-recoil experiments to constrain the form of the energy-momentum dispersion relation, a structure that is expected to be modified in several quantum-gravity approaches. Our strategy of analysis applies to the nonrelativistic (small speeds) limit of the dispersion relation, and is therefore complementary to an analogous ongoing effort of investigation of the dispersion relation in the ultrarelativistic regime using observations in astrophysics. For the leading correction in the nonrelativistic limit the exceptional sensitivity of cold-atom-recoil experiments remarkably allows us to set a limit within a single order of magnitude of the desired Planck-scale level, thereby providing the first example of Planck-scale sensitivity in the study of the dispersion relation in controlled laboratory experiments. For the next-to-leading term we obtain a limit which is a few orders of magnitude away from the Planck scale, but still amounts to the best limit on a class of Lorentz-symmetry test theories that has been extensively used to investigate the hypothesis of "deformation" (rather than breakdown) of spacetime symmetries. |
1406.0634 | Jose Natario | Jose Natario | Relativistic elasticity of rigid rods and strings | 20 pages, 8 figures; v2: typos corrected, figure added, some points
clarified, matches final published version; v3: typos in the references fixed | Gen. Rel. Grav. 46 (2014) 1816 | 10.1007/s10714-014-1816-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that the equation of motion for a rigid one-dimensional elastic body
(i.e. a rod or string whose speed of sound is equal to the speed of light) in a
two-dimensional spacetime is simply the wave equation. We then solve this
equation in a few simple examples: a rigid rod colliding with an unmovable
wall, a rigid rod being pushed by a constant force, a rigid string whose
endpoints are simultaneously set in motion (seen as a special case of Bell's
spaceships paradox), and a radial rigid string that has partially crossed the
event horizon of a Schwarzschild black hole while still being held from the
outside.
| [
{
"created": "Tue, 3 Jun 2014 09:07:30 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Sep 2014 09:36:19 GMT",
"version": "v2"
},
{
"created": "Mon, 14 Oct 2019 10:04:11 GMT",
"version": "v3"
}
] | 2019-10-15 | [
[
"Natario",
"Jose",
""
]
] | We show that the equation of motion for a rigid one-dimensional elastic body (i.e. a rod or string whose speed of sound is equal to the speed of light) in a two-dimensional spacetime is simply the wave equation. We then solve this equation in a few simple examples: a rigid rod colliding with an unmovable wall, a rigid rod being pushed by a constant force, a rigid string whose endpoints are simultaneously set in motion (seen as a special case of Bell's spaceships paradox), and a radial rigid string that has partially crossed the event horizon of a Schwarzschild black hole while still being held from the outside. |
1806.03894 | Amare Abebe | Alnadhief H. A. Alfedeel, Amare Abebe and Hussam M. Gubara | A Generalized Solution of Bianchi Type-V Models with Time-dependent $G$
and $\Lambda$ | 21 pages, 12 figures. Published version | Universe 2018, 4(8), 83 | 10.3390/universe4080083 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the homogeneous but anisotropic Bianchi type-V cosmological model
with time-dependent gravitational and cosmological "constants". Exact solutions
of the Einstein field equations (EFEs) are presented in terms of adjustable
parameters of quantum field theory in a spatially curved and expanding
background. It has been found that the general solution of the average scale
factor R as a function of time involved the hypergeometric function. Two
cosmological models are obtained from the general solution of the
hypergeometric function and the Emden-Fowler equation. The analysis of the
models shows that for a particular choice of parameters in our first model, the
cosmological "constant" decreases whereas the Newtonian gravitational
"constant" increases with time, and for another choice of parameters, the
opposite behaviour is observed. The models become isotropic at late times for
all parameter choices of the first model. In the second model of the general
solution, both the cosmological and gravitational "constants" decrease while
the model becomes more anisotropic over time. The exact dynamical and
kinematical quantities have been calculated analytically for each model.
| [
{
"created": "Mon, 11 Jun 2018 10:30:30 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Jul 2018 15:17:11 GMT",
"version": "v2"
}
] | 2018-07-30 | [
[
"Alfedeel",
"Alnadhief H. A.",
""
],
[
"Abebe",
"Amare",
""
],
[
"Gubara",
"Hussam M.",
""
]
] | We study the homogeneous but anisotropic Bianchi type-V cosmological model with time-dependent gravitational and cosmological "constants". Exact solutions of the Einstein field equations (EFEs) are presented in terms of adjustable parameters of quantum field theory in a spatially curved and expanding background. It has been found that the general solution of the average scale factor R as a function of time involved the hypergeometric function. Two cosmological models are obtained from the general solution of the hypergeometric function and the Emden-Fowler equation. The analysis of the models shows that for a particular choice of parameters in our first model, the cosmological "constant" decreases whereas the Newtonian gravitational "constant" increases with time, and for another choice of parameters, the opposite behaviour is observed. The models become isotropic at late times for all parameter choices of the first model. In the second model of the general solution, both the cosmological and gravitational "constants" decrease while the model becomes more anisotropic over time. The exact dynamical and kinematical quantities have been calculated analytically for each model. |
1204.2683 | Mordehai Milgrom | Mordehai Milgrom (Weizmann Institute) | Practically linear analogs of the Born-Infeld and other nonlinear
theories | 20 pages, Version published in Phys. Rev. D | Phys. Rev. D 85 105018 (2012) | 10.1103/PhysRevD.85.105018 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I discuss theories that describe fully nonlinear physics, while being
practically linear (PL), in that they require solving only linear differential
equations. These theories may be interesting in themselves as manageable
nonlinear theories. But, they can also be chosen to emulate genuinely nonlinear
theories of special interest, for which they can serve as approximations. The
idea can be applied to a large class of nonlinear theories, exemplified here
with a PL analogs of scalar theories, and of Born-Infeld (BI) electrodynamics.
The general class of such PL theories of electromagnetism are governed by a
Lagrangian L=-(1/2)F_mnQ^mn+ S(Q_mn), where the electromagnetic field couples
to currents in the standard way, while Qmn is an auxiliary field, derived from
a vector potential that does not couple directly to currents. By picking a
special form of S(Q_mn), we can make such a theory similar in some regards to a
given fully nonlinear theory, governed by the Lagrangian -U(F_mn). A
particularly felicitous choice is to take S as the Legendre transform of U. For
the BI theory, this Legendre transform has the same form as the BI Lagrangian
itself. Various matter-of-principle questions remain to be answered regarding
such theories. As a specific example, I discuss BI electrostatics in more
detail. As an aside, for BI, I derive an exact expression for the
short-distance force between two arbitrary point charges of the same sign, in
any dimension.
| [
{
"created": "Thu, 12 Apr 2012 10:55:56 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Jun 2012 13:00:12 GMT",
"version": "v2"
}
] | 2012-06-11 | [
[
"Milgrom",
"Mordehai",
"",
"Weizmann Institute"
]
] | I discuss theories that describe fully nonlinear physics, while being practically linear (PL), in that they require solving only linear differential equations. These theories may be interesting in themselves as manageable nonlinear theories. But, they can also be chosen to emulate genuinely nonlinear theories of special interest, for which they can serve as approximations. The idea can be applied to a large class of nonlinear theories, exemplified here with a PL analogs of scalar theories, and of Born-Infeld (BI) electrodynamics. The general class of such PL theories of electromagnetism are governed by a Lagrangian L=-(1/2)F_mnQ^mn+ S(Q_mn), where the electromagnetic field couples to currents in the standard way, while Qmn is an auxiliary field, derived from a vector potential that does not couple directly to currents. By picking a special form of S(Q_mn), we can make such a theory similar in some regards to a given fully nonlinear theory, governed by the Lagrangian -U(F_mn). A particularly felicitous choice is to take S as the Legendre transform of U. For the BI theory, this Legendre transform has the same form as the BI Lagrangian itself. Various matter-of-principle questions remain to be answered regarding such theories. As a specific example, I discuss BI electrostatics in more detail. As an aside, for BI, I derive an exact expression for the short-distance force between two arbitrary point charges of the same sign, in any dimension. |
2207.06994 | Anish Das | Anish Das, Ashis Saha, Sunandan Gangopadhyay | Shadow of Kottler black hole in the presence of plasma for a co-moving
observer | V1, 21 Pages, 12 Figures; V2, 23 Pages, 18 Figures; Accepted in
Classical and Quantum Gravity | Class. Quantum Grav. 40 015008 (2023) 1 | 10.1088/1361-6382/aca5e4 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider a spherically symmetric black hole metric in (3+1)-dimensions in
presence of a positive cosmological constant $\Lambda$. We use a general
approach as proposed in \cite{1} to transform the metric in co-moving
coordinates. Then for a general metric we have evaluated the angular shadow
size both in absence and presence of plasma. By using the aberration relation,
we then find the corresponding shadow radius as viewed by a co-moving observer
for Schwarzschild de-Sitter or Kottler spacetime. The effect of cosmological
constant $\Lambda$ and plasma parameter $k$ on the angular size of black hole
shadow has been observed in detail. Finally, by using the observed angular size
of M87$^*$ and Sgr A$^*$ black hole, we constrain the value of the plasma
parameter $k$ with a specific observational value of the cosmological constant
$\Lambda$ (or the Hubble constant $H_0$).
| [
{
"created": "Thu, 14 Jul 2022 15:22:34 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Nov 2022 14:30:22 GMT",
"version": "v2"
}
] | 2022-12-12 | [
[
"Das",
"Anish",
""
],
[
"Saha",
"Ashis",
""
],
[
"Gangopadhyay",
"Sunandan",
""
]
] | We consider a spherically symmetric black hole metric in (3+1)-dimensions in presence of a positive cosmological constant $\Lambda$. We use a general approach as proposed in \cite{1} to transform the metric in co-moving coordinates. Then for a general metric we have evaluated the angular shadow size both in absence and presence of plasma. By using the aberration relation, we then find the corresponding shadow radius as viewed by a co-moving observer for Schwarzschild de-Sitter or Kottler spacetime. The effect of cosmological constant $\Lambda$ and plasma parameter $k$ on the angular size of black hole shadow has been observed in detail. Finally, by using the observed angular size of M87$^*$ and Sgr A$^*$ black hole, we constrain the value of the plasma parameter $k$ with a specific observational value of the cosmological constant $\Lambda$ (or the Hubble constant $H_0$). |
2301.00669 | Lucrezia Ravera | Damianos Iosifidis, Ratbay Myrzakulov, Lucrezia Ravera | Cosmology of Metric-Affine $R + \beta R^2$ Gravity with Pure Shear
Hypermomentum | 26 pages | Fortsch.Phys. 72 (2024) 1, 2300003 | 10.1002/prop.202300003 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study the cosmological aspects of metric-affine $f(R)$
gravity with hyperfluid. The equations of motion of the theory are obtained by
varying the action with respect to the metric and the independent connection.
Subsequently, considering a Friedmann-Lema\^itre-Robertson-Walker background,
we derive the modified Friedmann equations in the presence of a perfect
cosmological hyperfluid. Especially, we focus on the particular case in which
$f(R)=R+\beta R^2$, considering purely shear hypermomentum and finding exact
solutions in the weak coupling limit.
| [
{
"created": "Thu, 29 Dec 2022 18:52:40 GMT",
"version": "v1"
}
] | 2024-04-29 | [
[
"Iosifidis",
"Damianos",
""
],
[
"Myrzakulov",
"Ratbay",
""
],
[
"Ravera",
"Lucrezia",
""
]
] | In this paper we study the cosmological aspects of metric-affine $f(R)$ gravity with hyperfluid. The equations of motion of the theory are obtained by varying the action with respect to the metric and the independent connection. Subsequently, considering a Friedmann-Lema\^itre-Robertson-Walker background, we derive the modified Friedmann equations in the presence of a perfect cosmological hyperfluid. Especially, we focus on the particular case in which $f(R)=R+\beta R^2$, considering purely shear hypermomentum and finding exact solutions in the weak coupling limit. |
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