id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/9603027 | Robert Paternoga | Robert Graham and Robert Paternoga (Universitaet Essen, Germany) | Physical states of Bianchi type IX quantum cosmologies described by the
Chern-Simons functional | 25 pages, Revtex, 8 figures included, submitted to Phys. Rev. D | Phys.Rev. D54 (1996) 2589-2604 | 10.1103/PhysRevD.54.2589 | null | gr-qc | null | A class of exact solutions of the Wheeler-DeWitt equation for diagonal
Bianchi type IX cosmologies with cosmological constant is derived in the metric
representation. This class consists of all the ``topological solutions'' which
are associated with the Bianchi type IX reduction of the Chern-Simons
functional in Ashtekar variables. The different solutions within the class
arise from the topologically inequivalent choices of the integration contours
in the transformation from the Ashtekarrepresentation to the metric
representation. We show how the saddle-points of the reduced Chern-Simons
functional generate a complete basis of such integration contours and the
associated solutions. Among the solutions we identify two, which,
semi-classically, satisfy the boundary conditions proposed by Vilenkin and by
Hartle and Hawking, respectively. In the limit of vanishing cosmological
constant our solutions reduce to a class found earlier in special fermion
sectors ofsupersymmetric Bianchi type IX models.
| [
{
"created": "Mon, 18 Mar 1996 18:41:07 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Graham",
"Robert",
"",
"Universitaet Essen, Germany"
],
[
"Paternoga",
"Robert",
"",
"Universitaet Essen, Germany"
]
] | A class of exact solutions of the Wheeler-DeWitt equation for diagonal Bianchi type IX cosmologies with cosmological constant is derived in the metric representation. This class consists of all the ``topological solutions'' which are associated with the Bianchi type IX reduction of the Chern-Simons functional in Ashtekar variables. The different solutions within the class arise from the topologically inequivalent choices of the integration contours in the transformation from the Ashtekarrepresentation to the metric representation. We show how the saddle-points of the reduced Chern-Simons functional generate a complete basis of such integration contours and the associated solutions. Among the solutions we identify two, which, semi-classically, satisfy the boundary conditions proposed by Vilenkin and by Hartle and Hawking, respectively. In the limit of vanishing cosmological constant our solutions reduce to a class found earlier in special fermion sectors ofsupersymmetric Bianchi type IX models. |
1703.06729 | Sylvain Carrozza | Sylvain Carrozza, Vincent Lahoche and Daniele Oriti | Renormalizable Group Field Theory beyond melonic diagrams: an example in
rank four | 30 pages, 15 figures, 2 tables; v2: acknowledgements added; v3: minor
modifications (including in the title), matches published version | Phys. Rev. D 96, 066007 (2017) | 10.1103/PhysRevD.96.066007 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We prove the renormalizability of a gauge-invariant, four-dimensional GFT
model on SU(2), whose defining interactions correspond to necklace bubbles
(found also in the context of new large-N expansions of tensor models), rather
than melonic ones, which are not renormalizable in this case. The respective
scaling of different interactions in the vicinity of the Gaussian fixed point
is determined by the renormalization group itself. This is possible because the
appropriate notion of canonical dimension of the GFT coupling constants takes
into account the detailed combinatorial structure of the individual interaction
terms. This is one more instance of the peculiarity (and greater mathematical
richness) of GFTs with respect to ordinary local quantum field theories. We
also explore the renormalization group flow of the model at the
non-perturbative level, using functional renormalization group methods, and
identify a non-trivial fixed point in various truncations. This model is
expected to have a similar structure of divergences as the GFT models of 4d
quantum gravity, thus paving the way to more detailed investigations on them.
| [
{
"created": "Mon, 20 Mar 2017 13:23:56 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Apr 2017 22:19:46 GMT",
"version": "v2"
},
{
"created": "Wed, 13 Sep 2017 16:16:58 GMT",
"version": "v3"
}
] | 2017-09-14 | [
[
"Carrozza",
"Sylvain",
""
],
[
"Lahoche",
"Vincent",
""
],
[
"Oriti",
"Daniele",
""
]
] | We prove the renormalizability of a gauge-invariant, four-dimensional GFT model on SU(2), whose defining interactions correspond to necklace bubbles (found also in the context of new large-N expansions of tensor models), rather than melonic ones, which are not renormalizable in this case. The respective scaling of different interactions in the vicinity of the Gaussian fixed point is determined by the renormalization group itself. This is possible because the appropriate notion of canonical dimension of the GFT coupling constants takes into account the detailed combinatorial structure of the individual interaction terms. This is one more instance of the peculiarity (and greater mathematical richness) of GFTs with respect to ordinary local quantum field theories. We also explore the renormalization group flow of the model at the non-perturbative level, using functional renormalization group methods, and identify a non-trivial fixed point in various truncations. This model is expected to have a similar structure of divergences as the GFT models of 4d quantum gravity, thus paving the way to more detailed investigations on them. |
1701.01027 | Rafael Augusto Couceiro Correa | P.H.R.S. Moraes, R.A.C. Correa, and G. Ribeiro | The Starobinsky model within the $f(R,T)$ formalism as a cosmological
model | null | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we derive a cosmological model from the $f(R,T)$ theory of
gravity, for which $R$ is the Ricci scalar and $T$ is the trace of the
energy-momentum tensor. We consider $f(R,T)=f(R)+f(T)$, with $f(R)$ being the
Starobinksy model $R+\alpha R^{2}$ and $f(T)=\gamma T$, with $\alpha$ and
$\gamma$ constants. We find that from such a functional form, it is possible to
describe the cosmological scenario of a radiation-dominated universe, which has
shown to be a non-trivial feature within the $f(R,T)$ formalism.
| [
{
"created": "Mon, 26 Dec 2016 14:21:22 GMT",
"version": "v1"
}
] | 2017-01-05 | [
[
"Moraes",
"P. H. R. S.",
""
],
[
"Correa",
"R. A. C.",
""
],
[
"Ribeiro",
"G.",
""
]
] | In this paper we derive a cosmological model from the $f(R,T)$ theory of gravity, for which $R$ is the Ricci scalar and $T$ is the trace of the energy-momentum tensor. We consider $f(R,T)=f(R)+f(T)$, with $f(R)$ being the Starobinksy model $R+\alpha R^{2}$ and $f(T)=\gamma T$, with $\alpha$ and $\gamma$ constants. We find that from such a functional form, it is possible to describe the cosmological scenario of a radiation-dominated universe, which has shown to be a non-trivial feature within the $f(R,T)$ formalism. |
1901.05370 | Geoffrey Comp\`ere | Bin Chen, Geoffrey Comp\`ere, Yan Liu, Jiang Long and Xuao Zhang | Spin and Quadrupole Couplings for High Spin Equatorial Intermediate
Mass-ratio Coalescences | 43 pages, 2 ancillary files: data of Appendix A and B, published
version | null | 10.1088/1361-6382/ab4fb0 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Intermediate mass-ratio coalescences are potential signals of ground-based
and space-based gravitational observatories. Accurate modeling of their
waveforms within general relativity can be achieved within black hole
perturbation theory including self-force and finite size effects. In this
paper, we present analytic results to the Teukolsky perturbation of equatorial
orbits in the near-horizon region of an extremely high spin black hole
including spin coupling and finite size effects at leading order in the high
spin limit while neglecting the self-force. We detail the critical behavior
occuring close to the smallest specific angular momentum, and we discuss
features of spin and quadrupole couplings.
| [
{
"created": "Wed, 16 Jan 2019 16:24:04 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Oct 2019 09:05:56 GMT",
"version": "v2"
}
] | 2020-01-08 | [
[
"Chen",
"Bin",
""
],
[
"Compère",
"Geoffrey",
""
],
[
"Liu",
"Yan",
""
],
[
"Long",
"Jiang",
""
],
[
"Zhang",
"Xuao",
""
]
] | Intermediate mass-ratio coalescences are potential signals of ground-based and space-based gravitational observatories. Accurate modeling of their waveforms within general relativity can be achieved within black hole perturbation theory including self-force and finite size effects. In this paper, we present analytic results to the Teukolsky perturbation of equatorial orbits in the near-horizon region of an extremely high spin black hole including spin coupling and finite size effects at leading order in the high spin limit while neglecting the self-force. We detail the critical behavior occuring close to the smallest specific angular momentum, and we discuss features of spin and quadrupole couplings. |
2206.04203 | Haret Rosu | Ivan Perez-Roman, Haret C. Rosu | Relativistic hyperbolic motion and its higher order kinematic quantities | 14 pages, 2 figures, minor corrections, but reference to Born's paper
kept as # 7 to match the published version | Rev. Mex. Fis. 68, 060702 (2022) | 10.31349/RevMexFis.68.060702 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the kinematics of the motion of an observer with constant
proper acceleration (relativistic hyperbolic motion) in 1+1 and 1+3 dimensional
Minkowski spacetimes. We provide explicit formulas for all the kinematic
quantities up to the fourth proper time derivative (the Snap). In the 1+3 case,
following a recent work of Pons and de Palol [Gen. Rel. Grav. 51 (2019) 80], a
vectorial differential equation for the acceleration is obtained which by
considering constant proper acceleration is turned into a nonlinear second
order differential equation in terms of derivatives of the radius vector. If,
furthermore, the velocity is parameterized in terms of hyperbolic functions,
one obtains a differential equation to solve for the argument f(s) of the
velocity. Differently from Pons and de Palol, who employed the particular
solution, linear in the proper time s, we obtain the general solution and use
it to work out more general expressions for the kinematical quantities. As a
byproduct, we obtain a class of modified Rindler hyperbolic worldlines
characterized by supplementary contributions to the components of the
kinematical quantities.
| [
{
"created": "Thu, 9 Jun 2022 00:44:40 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Nov 2022 16:26:01 GMT",
"version": "v2"
}
] | 2022-11-03 | [
[
"Perez-Roman",
"Ivan",
""
],
[
"Rosu",
"Haret C.",
""
]
] | We investigate the kinematics of the motion of an observer with constant proper acceleration (relativistic hyperbolic motion) in 1+1 and 1+3 dimensional Minkowski spacetimes. We provide explicit formulas for all the kinematic quantities up to the fourth proper time derivative (the Snap). In the 1+3 case, following a recent work of Pons and de Palol [Gen. Rel. Grav. 51 (2019) 80], a vectorial differential equation for the acceleration is obtained which by considering constant proper acceleration is turned into a nonlinear second order differential equation in terms of derivatives of the radius vector. If, furthermore, the velocity is parameterized in terms of hyperbolic functions, one obtains a differential equation to solve for the argument f(s) of the velocity. Differently from Pons and de Palol, who employed the particular solution, linear in the proper time s, we obtain the general solution and use it to work out more general expressions for the kinematical quantities. As a byproduct, we obtain a class of modified Rindler hyperbolic worldlines characterized by supplementary contributions to the components of the kinematical quantities. |
2303.06427 | Shubham Narawade Mr. | S.A. Narawade, Shashank P. Singh, B. Mishra | Accelerating cosmological models in $f(Q)$ gravity and the phase space
analysis | 13 pages, 9 figures | Physics of the Dark Universe 42 (2023) 101282 | 10.1016/j.dark.2023.101282 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The dynamical aspect of accelerating cosmological model has been studied in
this paper in the context of modified symmetric teleparallel gravity, the
$f(Q)$ gravity. Initially, we have derived the dynamical parameters for two
well known forms of $f(Q)$ such as: (i) log-square-root form and (ii)
exponential form. The equation of state (EoS) parameter for the dark energy in
the $f(Q)$ gravity in both the models emerges into a dynamical quantity. At
present model-I shows the quintessence behavior and behave like the
$\Lambda$CDM at the late time whereas model-II shows phantom behaviour.
Further, the dynamical system analysis has been performed to determine the
cosmological behaviour of the models along with its stability behaviour. For
both the models the critical points are obtained and analysed the stability at
each critical points with phase portraits. The evolutionary behaviour of
density parameters for the matter-dominated, radiation-dominated, and dark
energy phases are also shown for both the models.
| [
{
"created": "Sat, 11 Mar 2023 15:32:34 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Jul 2023 04:47:25 GMT",
"version": "v2"
}
] | 2023-07-18 | [
[
"Narawade",
"S. A.",
""
],
[
"Singh",
"Shashank P.",
""
],
[
"Mishra",
"B.",
""
]
] | The dynamical aspect of accelerating cosmological model has been studied in this paper in the context of modified symmetric teleparallel gravity, the $f(Q)$ gravity. Initially, we have derived the dynamical parameters for two well known forms of $f(Q)$ such as: (i) log-square-root form and (ii) exponential form. The equation of state (EoS) parameter for the dark energy in the $f(Q)$ gravity in both the models emerges into a dynamical quantity. At present model-I shows the quintessence behavior and behave like the $\Lambda$CDM at the late time whereas model-II shows phantom behaviour. Further, the dynamical system analysis has been performed to determine the cosmological behaviour of the models along with its stability behaviour. For both the models the critical points are obtained and analysed the stability at each critical points with phase portraits. The evolutionary behaviour of density parameters for the matter-dominated, radiation-dominated, and dark energy phases are also shown for both the models. |
2312.03383 | Reginald Christian Bernardo | Reginald Christian Bernardo and Guo-Chin Liu and Kin-Wang Ng | Correlations for an anisotropic polarized stochastic gravitational wave
background in pulsar timing arrays | 29 pages + refs, 6 figures, to appear in JCAP, our codes
https://github.com/reggiebernardo/PTAfast | JCAP 04 (2024) 034 | 10.1088/1475-7516/2024/04/034 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The recent compelling observation of the nanohertz stochastic gravitational
wave background has brought to light a new galactic arena to test gravity. In
this paper, we derive a formula for the most general expression of the
stochastic gravitational wave background correlation that could be tested with
pulsar timing and future square kilometer arrays. Our expressions extends the
harmonic space analysis, also often referred to as the power spectrum approach,
to predict the correlation signatures of an anisotropic polarized stochastic
gravitational wave background with subluminal tensor, vector, and scalar
gravitational degrees of freedom. We present the first few nontrivial
anisotropy and polarization signatures in the correlation and discuss their
dependence on the gravitational wave speed and pulsar distances. Our results
set up tests that could potentially be used to rigorously examine the isotropy
of the stochastic gravitational wave background and strengthen the existing
constraints on possible non-Einsteinian polarizations in the nanohertz
gravitational wave regime.
| [
{
"created": "Wed, 6 Dec 2023 09:50:24 GMT",
"version": "v1"
},
{
"created": "Sun, 25 Feb 2024 12:16:50 GMT",
"version": "v2"
}
] | 2024-04-12 | [
[
"Bernardo",
"Reginald Christian",
""
],
[
"Liu",
"Guo-Chin",
""
],
[
"Ng",
"Kin-Wang",
""
]
] | The recent compelling observation of the nanohertz stochastic gravitational wave background has brought to light a new galactic arena to test gravity. In this paper, we derive a formula for the most general expression of the stochastic gravitational wave background correlation that could be tested with pulsar timing and future square kilometer arrays. Our expressions extends the harmonic space analysis, also often referred to as the power spectrum approach, to predict the correlation signatures of an anisotropic polarized stochastic gravitational wave background with subluminal tensor, vector, and scalar gravitational degrees of freedom. We present the first few nontrivial anisotropy and polarization signatures in the correlation and discuss their dependence on the gravitational wave speed and pulsar distances. Our results set up tests that could potentially be used to rigorously examine the isotropy of the stochastic gravitational wave background and strengthen the existing constraints on possible non-Einsteinian polarizations in the nanohertz gravitational wave regime. |
0909.2773 | Chao-Guang Huang | Chao-Guang Huang, Yu Tian, Xiao-Ning Wu, Zhan Xu and Bin Zhou | New Geometry with All Killing Vectors Spanning the Poincar\'e Algebra | 7 pages. In the new version, the title and text are both revised | CHIN. PHYS. LETT. Vol. 29, (2012) 040303 | 10.1088/0256-307X/29/4/040303 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The new 4D geometry whose Killing vectors span the Poincar\'e algebra is
presented and its structure is analyzed. The new geometry can be regarded as
the Poincar\'e-invariant solution of the degenerate extension of the vacuum
Einstein field equations with a negative cosmological constant and provides a
static cosmological space-time with a Lobachevsky space. The motion of free
particles in the space-time is discussed.
| [
{
"created": "Tue, 15 Sep 2009 11:22:41 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Apr 2012 08:50:59 GMT",
"version": "v2"
}
] | 2012-04-20 | [
[
"Huang",
"Chao-Guang",
""
],
[
"Tian",
"Yu",
""
],
[
"Wu",
"Xiao-Ning",
""
],
[
"Xu",
"Zhan",
""
],
[
"Zhou",
"Bin",
""
]
] | The new 4D geometry whose Killing vectors span the Poincar\'e algebra is presented and its structure is analyzed. The new geometry can be regarded as the Poincar\'e-invariant solution of the degenerate extension of the vacuum Einstein field equations with a negative cosmological constant and provides a static cosmological space-time with a Lobachevsky space. The motion of free particles in the space-time is discussed. |
2308.00203 | Juan M. Z\'arate Pretel | Juan M. Z. Pretel, Sergio E. Jor\'as, Ribamar R. R. Reis, Sergio B.
Duarte and Jos\'e D. V. Arba\~nil | Compact stars in scalar-tensor theories with a single-well potential and
the corresponding $f(R)$ theory | 9 pages, 6 figures. Accepted for publication in Physics of the Dark
Universe | Phys. Dark Universe 43 (2024) 101394 | 10.1016/j.dark.2023.101394 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The macroscopic properties of compact stars in modified gravity theories can
be significantly different from the general relativistic (GR) predictions.
Within the gravitational context of scalar-tensor theories, with a scalar field
$\phi$ and coupling function $\Phi(\phi)= \exp[2\phi/\sqrt{3}]$, we investigate
the hydrostatic equilibrium structure of neutron stars for the simple potential
$V(\phi)= \omega\phi^2/2$ defined in the Einstein frame (EF). From the scalar
field in the EF, we also interpret such theories as $f(R)$ gravity in the
corresponding Jordan frame (JF). The mass-radius relations, proper mass, and
binding energy are obtained for a polytropic equation of state (EoS) in the JF.
Our results reveal that the maximum-mass values increase substantially as
$\omega$ gets smaller, while the radius and mass decrease in the
low-central-density region as we move further away from the pure GR scenario.
Furthermore, a cusp is formed when the binding energy is plotted as a function
of the proper mass, which indicates the appearance of instability.
Specifically, we find that the central-density value where the binding energy
is a minimum corresponds precisely to $dM/d\rho_c^J = 0$ on the
$M(\rho_c^J)$-curve.
| [
{
"created": "Mon, 31 Jul 2023 23:50:09 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Nov 2023 17:05:41 GMT",
"version": "v2"
}
] | 2023-12-05 | [
[
"Pretel",
"Juan M. Z.",
""
],
[
"Jorás",
"Sergio E.",
""
],
[
"Reis",
"Ribamar R. R.",
""
],
[
"Duarte",
"Sergio B.",
""
],
[
"Arbañil",
"José D. V.",
""
]
] | The macroscopic properties of compact stars in modified gravity theories can be significantly different from the general relativistic (GR) predictions. Within the gravitational context of scalar-tensor theories, with a scalar field $\phi$ and coupling function $\Phi(\phi)= \exp[2\phi/\sqrt{3}]$, we investigate the hydrostatic equilibrium structure of neutron stars for the simple potential $V(\phi)= \omega\phi^2/2$ defined in the Einstein frame (EF). From the scalar field in the EF, we also interpret such theories as $f(R)$ gravity in the corresponding Jordan frame (JF). The mass-radius relations, proper mass, and binding energy are obtained for a polytropic equation of state (EoS) in the JF. Our results reveal that the maximum-mass values increase substantially as $\omega$ gets smaller, while the radius and mass decrease in the low-central-density region as we move further away from the pure GR scenario. Furthermore, a cusp is formed when the binding energy is plotted as a function of the proper mass, which indicates the appearance of instability. Specifically, we find that the central-density value where the binding energy is a minimum corresponds precisely to $dM/d\rho_c^J = 0$ on the $M(\rho_c^J)$-curve. |
1810.06522 | David Sloan | David Sloan and George Ellis | Solving the Cosmological Entropy Issue with a Higgs Dilaton | 13 pages, 1 figure | Phys. Rev. D 99, 063518 (2019) | 10.1103/PhysRevD.99.063518 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Current cosmological models require the universe to be in a very smooth
initial state before the onset of inflation, a situation to which Penrose
ascribes a vanishingly small probability, leading to his proposal of a
Conformal Cyclic Cosmology. We present an alternative paradigm, in which the
Higgs plays the role of dilaton and resolves this problem by weakening gravity
at very early times, thus providing a form of inflation that is compatible with
observations and in which the inflaton is solidly related to tested particle
physics.
| [
{
"created": "Mon, 15 Oct 2018 17:15:27 GMT",
"version": "v1"
}
] | 2019-03-27 | [
[
"Sloan",
"David",
""
],
[
"Ellis",
"George",
""
]
] | Current cosmological models require the universe to be in a very smooth initial state before the onset of inflation, a situation to which Penrose ascribes a vanishingly small probability, leading to his proposal of a Conformal Cyclic Cosmology. We present an alternative paradigm, in which the Higgs plays the role of dilaton and resolves this problem by weakening gravity at very early times, thus providing a form of inflation that is compatible with observations and in which the inflaton is solidly related to tested particle physics. |
2407.15947 | Pablo Antonio Cano Molina-Ni\~nirola | Pablo A. Cano, Lodovico Capuano, Nicola Franchini, Simon Maenaut,
Sebastian H. V\"olkel | A parametrized quasi-normal mode framework for modified Teukolsky
equations | 15 pages, 5 figures, comments welcome; v2: references added. Version
sent to the journal | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Modifications to general relativity lead to effects in the spectrum of
quasi-normal modes of black holes. In this paper, we develop a parametrized
formalism to describe deviations from general relativity in the Teukolsky
equation, which governs linear perturbations of spinning black holes. We do
this by introducing a correction to the effective potential of the Teukolsky
equation in the form of a $1/r$ expansion controlled by free parameters. The
method assumes that a small deviation in the effective potential induces a
small modification in the spectrum of modes and in the angular separation
constants. We isolate and compute the universal linear contribution to the
quasi-normal mode frequencies and separation constants in a set of
coefficients, and test them against known examples in the literature (massive
scalar field, Dudley-Finley equation and higher-derivative gravity). We make
the coefficients publicly available for relevant overtone, angular momentum and
azimuthal numbers of modes and different values of the black hole spin.
| [
{
"created": "Mon, 22 Jul 2024 18:01:30 GMT",
"version": "v1"
},
{
"created": "Sun, 28 Jul 2024 15:32:56 GMT",
"version": "v2"
}
] | 2024-07-30 | [
[
"Cano",
"Pablo A.",
""
],
[
"Capuano",
"Lodovico",
""
],
[
"Franchini",
"Nicola",
""
],
[
"Maenaut",
"Simon",
""
],
[
"Völkel",
"Sebastian H.",
""
]
] | Modifications to general relativity lead to effects in the spectrum of quasi-normal modes of black holes. In this paper, we develop a parametrized formalism to describe deviations from general relativity in the Teukolsky equation, which governs linear perturbations of spinning black holes. We do this by introducing a correction to the effective potential of the Teukolsky equation in the form of a $1/r$ expansion controlled by free parameters. The method assumes that a small deviation in the effective potential induces a small modification in the spectrum of modes and in the angular separation constants. We isolate and compute the universal linear contribution to the quasi-normal mode frequencies and separation constants in a set of coefficients, and test them against known examples in the literature (massive scalar field, Dudley-Finley equation and higher-derivative gravity). We make the coefficients publicly available for relevant overtone, angular momentum and azimuthal numbers of modes and different values of the black hole spin. |
gr-qc/9807047 | Luciano Rezzolla | Luciano Rezzolla, Andrew M. Abrahams, Richard A. Matzner, Mark E.
Rupright and Stuart L. Shapiro | Cauchy-perturbative matching and outer boundary conditions:
computational studies | 20 pages, RevTeX | Phys.Rev. D59 (1999) 064001 | 10.1103/PhysRevD.59.064001 | null | gr-qc | null | We present results from a new technique which allows extraction of
gravitational radiation information from a generic three-dimensional numerical
relativity code and provides stable outer boundary conditions. In our approach
we match the solution of a Cauchy evolution of the nonlinear Einstein field
equations to a set of one-dimensional linear equations obtained through
perturbation techniques over a curved background. We discuss the validity of
this approach in the case of linear and mildly nonlinear gravitational waves
and show how a numerical module developed for this purpose is able to provide
an accurate and numerically convergent description of the gravitational wave
propagation and a stable numerical evolution.
| [
{
"created": "Fri, 17 Jul 1998 21:34:43 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Rezzolla",
"Luciano",
""
],
[
"Abrahams",
"Andrew M.",
""
],
[
"Matzner",
"Richard A.",
""
],
[
"Rupright",
"Mark E.",
""
],
[
"Shapiro",
"Stuart L.",
""
]
] | We present results from a new technique which allows extraction of gravitational radiation information from a generic three-dimensional numerical relativity code and provides stable outer boundary conditions. In our approach we match the solution of a Cauchy evolution of the nonlinear Einstein field equations to a set of one-dimensional linear equations obtained through perturbation techniques over a curved background. We discuss the validity of this approach in the case of linear and mildly nonlinear gravitational waves and show how a numerical module developed for this purpose is able to provide an accurate and numerically convergent description of the gravitational wave propagation and a stable numerical evolution. |
2401.15494 | Jaime Manuel Cabrera | Jaime Manuel Cabrera and Jorge Mauricio Paulin Fuentes | Hamiltonian analysis and Faddeev-Jackiw formalism for two-Dimensional
Quadratic Gravity expressed as BF theory | 31 pages | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We examine the model of Two-Dimensional Quadratic Gravity as a consequence of
symmetry breaking within the framework of background field (BF) theory. This
theory is essentially an extension of BF theory, introducing an additional
polynomial term that operates on both the gauge and background fields. We
analyze the theory using the Dirac and Faddeev-Jackiw procedures, determining
the form of the gauge transformation, the full structure of the constraints,
the counting of degrees of freedom, and the generalized Faddeev-Jackiw
brackets. Additionally, we demonstrate the coincidence of the Faddeev-Jackiw
and Dirac's brackets. Finally, we provide some remarks and discuss prospects.
| [
{
"created": "Sat, 27 Jan 2024 20:16:46 GMT",
"version": "v1"
}
] | 2024-01-30 | [
[
"Cabrera",
"Jaime Manuel",
""
],
[
"Fuentes",
"Jorge Mauricio Paulin",
""
]
] | We examine the model of Two-Dimensional Quadratic Gravity as a consequence of symmetry breaking within the framework of background field (BF) theory. This theory is essentially an extension of BF theory, introducing an additional polynomial term that operates on both the gauge and background fields. We analyze the theory using the Dirac and Faddeev-Jackiw procedures, determining the form of the gauge transformation, the full structure of the constraints, the counting of degrees of freedom, and the generalized Faddeev-Jackiw brackets. Additionally, we demonstrate the coincidence of the Faddeev-Jackiw and Dirac's brackets. Finally, we provide some remarks and discuss prospects. |
gr-qc/0208021 | Vladimir Ivashchuk | V.N. Melnikov, V.D. Ivashchuk | Problems of G and multidimensional models | 5 pages, Latex, subm. to Proc. of Int. Workshop in Waseda Univ | null | null | IGC-PFUR-01/2002 | gr-qc | null | The relations for G-dot in multidimensional model with Ricci-flat internal
space and multicomponent perfect fluid are obtained. A two-component example:
dust + 5-brane, is considered.
| [
{
"created": "Thu, 8 Aug 2002 07:51:02 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Melnikov",
"V. N.",
""
],
[
"Ivashchuk",
"V. D.",
""
]
] | The relations for G-dot in multidimensional model with Ricci-flat internal space and multicomponent perfect fluid are obtained. A two-component example: dust + 5-brane, is considered. |
1005.4286 | Rabin Banerjee | Rabin Banerjee | From black holes to emergent gravity | Latex, 6 pages, Gravity Research Foundation essay 2010 (Received
Honorable Mention) | Int.J.Mod.Phys.D19:2365-2369,2010 | 10.1142/S0218271810018475 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Many inequivalent approaches to study black holes yield identical results.
Any meaningful theory of gravity should explain the origin of this property.
Here we show that the basic holomorphic modes characterising the underlying two
dimensional conformal symmetry near the horizon bring about this universality.
Moreover these modes lead to a law of equipartition of energy for black holes
which suggests a statistical origin of gravity. This emergent nature of gravity
is further bolstered by showing the equivalence of entropy with the action
$\left(S=-\frac{i}{\hbar}\,I\right)$ and expressing the generalised Smarr
formula for mass as a thermodynamic relation, $S=\frac{E}{2T}$ where $S$, $E$
and $T$ are the entropy, energy and temperature, respectively, of a black hole.
| [
{
"created": "Mon, 24 May 2010 09:31:13 GMT",
"version": "v1"
}
] | 2011-01-31 | [
[
"Banerjee",
"Rabin",
""
]
] | Many inequivalent approaches to study black holes yield identical results. Any meaningful theory of gravity should explain the origin of this property. Here we show that the basic holomorphic modes characterising the underlying two dimensional conformal symmetry near the horizon bring about this universality. Moreover these modes lead to a law of equipartition of energy for black holes which suggests a statistical origin of gravity. This emergent nature of gravity is further bolstered by showing the equivalence of entropy with the action $\left(S=-\frac{i}{\hbar}\,I\right)$ and expressing the generalised Smarr formula for mass as a thermodynamic relation, $S=\frac{E}{2T}$ where $S$, $E$ and $T$ are the entropy, energy and temperature, respectively, of a black hole. |
gr-qc/0108012 | Robert J. Low | Robert J Low | Stable singularities of wave-fronts in general relativity | 5 pages | J.Math.Phys. 39 (1998) 3332-3335 | 10.1063/1.532257 | null | gr-qc | null | A wave-front in a space-time $\cal M$ is a family of null geodesics
orthogonal to a smooth spacelike two-surface in $\cal M$; it is of some
interest to know how a wave-front can fail to be a smoothly immersed surface in
$\cal M$. In this paper we see that the space of null geodesics $\cal N$ of
$\cal M$, considered as a contact manifold, provides a natural setting for an
efficient study of the stable singularities arising in the time evolution of
wave-fronts.
| [
{
"created": "Fri, 3 Aug 2001 09:01:35 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Low",
"Robert J",
""
]
] | A wave-front in a space-time $\cal M$ is a family of null geodesics orthogonal to a smooth spacelike two-surface in $\cal M$; it is of some interest to know how a wave-front can fail to be a smoothly immersed surface in $\cal M$. In this paper we see that the space of null geodesics $\cal N$ of $\cal M$, considered as a contact manifold, provides a natural setting for an efficient study of the stable singularities arising in the time evolution of wave-fronts. |
gr-qc/0109013 | Roh Suan Tung | Stephen C. Anco, Roh S. Tung | Covariant Hamiltonian boundary conditions in General Relativity for
spatially bounded spacetime regions | 49 pages; published version with minor errata corrected in Eqs.
(3.55) and (3.69) | J.Math.Phys. 43 (2002) 5531-5566 | 10.1063/1.1505984 | null | gr-qc hep-th | null | We investigate the covariant Hamiltonian symplectic structure of General
Relativity for spatially bounded regions of spacetime with a fixed time-flow
vector. For existence of a well-defined Hamiltonian variational principle
taking into account a spatial boundary, it is necessary to modify the standard
Arnowitt-Deser-Misner Hamiltonian by adding a boundary term whose form depends
on the spatial boundary conditions for the gravitational field. The most
general mathematically allowed boundary conditions and corresponding boundary
terms are shown to be determined by solving a certain equation obtained from
the symplectic current pulled back to the hypersurface boundary of the
spacetime region. A main result is that we obtain a covariant derivation of
Dirichlet, Neumann, and mixed type boundary conditions on the gravitational
field at a fixed boundary hypersurface, together with the associated
Hamiltonian boundary terms. As well, we establish uniqueness of these boundary
conditions under certain assumptions motivated by the form of the symplectic
current. Our analysis uses a Noether charge method which extends and unifies
several results developed in recent literature for General Relativity. As an
illustration of the method, we apply it to the Maxwell field equations to
derive allowed boundary conditions and boundary terms for existence of a
well-defined Hamiltonian variational principle for an electromagnetic field in
a fixed spatially bounded region of Minkowski spacetime.
| [
{
"created": "Tue, 4 Sep 2001 18:39:26 GMT",
"version": "v1"
},
{
"created": "Sun, 24 Mar 2002 20:51:23 GMT",
"version": "v2"
},
{
"created": "Tue, 26 Nov 2002 16:22:24 GMT",
"version": "v3"
},
{
"created": "Tue, 24 Feb 2004 14:10:58 GMT",
"version": "v4"
}
] | 2015-06-25 | [
[
"Anco",
"Stephen C.",
""
],
[
"Tung",
"Roh S.",
""
]
] | We investigate the covariant Hamiltonian symplectic structure of General Relativity for spatially bounded regions of spacetime with a fixed time-flow vector. For existence of a well-defined Hamiltonian variational principle taking into account a spatial boundary, it is necessary to modify the standard Arnowitt-Deser-Misner Hamiltonian by adding a boundary term whose form depends on the spatial boundary conditions for the gravitational field. The most general mathematically allowed boundary conditions and corresponding boundary terms are shown to be determined by solving a certain equation obtained from the symplectic current pulled back to the hypersurface boundary of the spacetime region. A main result is that we obtain a covariant derivation of Dirichlet, Neumann, and mixed type boundary conditions on the gravitational field at a fixed boundary hypersurface, together with the associated Hamiltonian boundary terms. As well, we establish uniqueness of these boundary conditions under certain assumptions motivated by the form of the symplectic current. Our analysis uses a Noether charge method which extends and unifies several results developed in recent literature for General Relativity. As an illustration of the method, we apply it to the Maxwell field equations to derive allowed boundary conditions and boundary terms for existence of a well-defined Hamiltonian variational principle for an electromagnetic field in a fixed spatially bounded region of Minkowski spacetime. |
gr-qc/0205044 | Bela Szilagyi | Bela Szilagyi, and Jeffrey Winicour | Well-Posed Initial-Boundary Evolution in General Relativity | 5 pages, 6 figures; added another convergence plot to Fig. 2 + minor
changes | Phys.Rev.D68:041501,2003 | 10.1103/PhysRevD.68.041501 | null | gr-qc | null | Maximally dissipative boundary conditions are applied to the initial-boundary
value problem for Einstein's equations in harmonic coordinates to show that it
is well-posed for homogeneous boundary data and for boundary data that is small
in a linearized sense. The method is implemented as a nonlinear evolution code
which satisfies convergence tests in the nonlinear regime and is robustly
stable in the weak field regime. A linearized version has been stably matched
to a characteristic code to compute the gravitational waveform radiated to
infinity.
| [
{
"created": "Fri, 10 May 2002 21:11:40 GMT",
"version": "v1"
},
{
"created": "Tue, 21 May 2002 00:12:42 GMT",
"version": "v2"
},
{
"created": "Thu, 30 May 2002 20:12:35 GMT",
"version": "v3"
},
{
"created": "Thu, 24 Oct 2002 15:49:29 GMT",
"version": "v4"
},
{
"created": "Thu, 9 Jan 2003 15:41:51 GMT",
"version": "v5"
},
{
"created": "Thu, 20 Feb 2003 17:29:12 GMT",
"version": "v6"
},
{
"created": "Thu, 19 Jun 2003 00:16:08 GMT",
"version": "v7"
}
] | 2011-04-21 | [
[
"Szilagyi",
"Bela",
""
],
[
"Winicour",
"Jeffrey",
""
]
] | Maximally dissipative boundary conditions are applied to the initial-boundary value problem for Einstein's equations in harmonic coordinates to show that it is well-posed for homogeneous boundary data and for boundary data that is small in a linearized sense. The method is implemented as a nonlinear evolution code which satisfies convergence tests in the nonlinear regime and is robustly stable in the weak field regime. A linearized version has been stably matched to a characteristic code to compute the gravitational waveform radiated to infinity. |
1605.01246 | Christine Cordula Dantas | Christine C. Dantas (IAE/DCTA-Brazil) | An Inhomogeneous Space-Time Patching Model Based on a Nonlocal and
Nonlinear Schrodinger Equation | 29 pages, 2 figures, accepted for publication in Foundations of
Physics | null | 10.1007/s10701-016-0019-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider an integrable, nonlocal and nonlinear, Schr\"odinger equation
(NNSE) as a model for building space-time patchings in inhomogeneous loop
quantum cosmology (LQC). We briefly review exact solutions of the NNSE,
specially those obtained through "geometric equivalence" methods. Furthemore,
we argue that the integrability of the NNSE could be linked to consistency
conditions derived from LQC, under the assumption that the patchwork dynamics
behaves as an integrable many-body system.
| [
{
"created": "Wed, 4 May 2016 12:27:19 GMT",
"version": "v1"
}
] | 2016-06-29 | [
[
"Dantas",
"Christine C.",
"",
"IAE/DCTA-Brazil"
]
] | We consider an integrable, nonlocal and nonlinear, Schr\"odinger equation (NNSE) as a model for building space-time patchings in inhomogeneous loop quantum cosmology (LQC). We briefly review exact solutions of the NNSE, specially those obtained through "geometric equivalence" methods. Furthemore, we argue that the integrability of the NNSE could be linked to consistency conditions derived from LQC, under the assumption that the patchwork dynamics behaves as an integrable many-body system. |
2304.01673 | Josu Aurrekoetxea | Josu C. Aurrekoetxea, Katy Clough, Francesco Muia | Oscillon formation during inflationary preheating with general
relativity | 7 pages. 4 figures. Movie: https://youtu.be/vTl9agMfPB0. Matches
version published in PRD | null | 10.1103/PhysRevD.108.023501 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | We study the non-perturbative evolution of inflationary fluctuations during
preheating using fully non-linear general-relativistic field-theory
simulations. We choose a single-field inflationary model that is consistent
with observational constraints and start the simulations at the end of
inflation with fluctuations both in the field and its conjugate momentum.
Gravity enhances the growth of density perturbations, which then collapse and
virialize, forming long-lived stable oscillon-like stars that reach
compactnesses $\mathcal{C}\equiv GM/R \sim 10^{-3}-10^{-2}$. We find that
$\mathcal{C}$ increases for larger field models, until it peaks due to the
interplay between the overdensity growth and Hubble expansion rates. Whilst
gravitational effects can play an important role in the formation of compact
oscillons during preheating, the objects are unlikely to collapse into
primordial black holes without an additional enhancement of the initial
inflationary fluctuations.
| [
{
"created": "Tue, 4 Apr 2023 09:59:21 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Jul 2023 22:11:01 GMT",
"version": "v2"
}
] | 2023-07-19 | [
[
"Aurrekoetxea",
"Josu C.",
""
],
[
"Clough",
"Katy",
""
],
[
"Muia",
"Francesco",
""
]
] | We study the non-perturbative evolution of inflationary fluctuations during preheating using fully non-linear general-relativistic field-theory simulations. We choose a single-field inflationary model that is consistent with observational constraints and start the simulations at the end of inflation with fluctuations both in the field and its conjugate momentum. Gravity enhances the growth of density perturbations, which then collapse and virialize, forming long-lived stable oscillon-like stars that reach compactnesses $\mathcal{C}\equiv GM/R \sim 10^{-3}-10^{-2}$. We find that $\mathcal{C}$ increases for larger field models, until it peaks due to the interplay between the overdensity growth and Hubble expansion rates. Whilst gravitational effects can play an important role in the formation of compact oscillons during preheating, the objects are unlikely to collapse into primordial black holes without an additional enhancement of the initial inflationary fluctuations. |
2203.03295 | Francisco Lobo | Francisco S. N. Lobo, Tiberiu Harko | Curvature-matter couplings in modified gravity: from linear models to
conformally invariant theories | 20 pages, no figures; based on a plenary talk in the 4th PU
International Conference on Gravitation and Cosmology, 22-25 Nov., 2021;
accepted for published in IJMPD (proceedings) | Int.J.Mod.Phys.D 31 (2022) 11, 2240010 | 10.1142/S0218271822400107 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this proceeding, we review modified theories of gravity with a
curvature-matter coupling between an arbitrary function of the scalar curvature
and the Lagrangian density of matter. This explicit nonminimal coupling induces
a non-vanishing covariant derivative of the energy-momentum tensor, that
implies non-geodesic motion and consequently leads to the appearance of an
extra force. Here, we explore the physical and cosmological implications of the
nonconservation of the energy-momentum tensor by using the formalism of
irreversible thermodynamics of open systems in the presence of matter
creation/annihilation. The particle creation rates, pressure, and the
expression of the comoving entropy are obtained in a covariant formulation and
discussed in detail. Applied together with the gravitational field equations,
the thermodynamics of open systems lead to a generalization of the standard
$\Lambda$CDM cosmological paradigm, in which the particle creation rates and
pressures are effectively considered as components of the cosmological fluid
energy-momentum tensor. Furthermore, we also briefly present the coupling of
curvature to geometry in conformal quadratic Weyl gravity, by assuming a
coupling term of the form $L_m\tilde{R}^2$, where $L_m$ is the ordinary matter
Lagrangian, and $\tilde{R}$ is the Weyl scalar. The coupling explicitly
satisfies the requirement of the conformal invariance of the theory. Expressing
$\tilde{R}^2$ with the use of an auxiliary scalar field and of the Weyl scalar,
the gravitational action can be linearized in the Ricci scalar, leading in the
Riemann space to a conformally invariant $f\left(R,L_m\right)$ type theory,
with the matter Lagrangian nonminimally coupled to geometry.
| [
{
"created": "Mon, 7 Mar 2022 11:16:32 GMT",
"version": "v1"
}
] | 2022-09-20 | [
[
"Lobo",
"Francisco S. N.",
""
],
[
"Harko",
"Tiberiu",
""
]
] | In this proceeding, we review modified theories of gravity with a curvature-matter coupling between an arbitrary function of the scalar curvature and the Lagrangian density of matter. This explicit nonminimal coupling induces a non-vanishing covariant derivative of the energy-momentum tensor, that implies non-geodesic motion and consequently leads to the appearance of an extra force. Here, we explore the physical and cosmological implications of the nonconservation of the energy-momentum tensor by using the formalism of irreversible thermodynamics of open systems in the presence of matter creation/annihilation. The particle creation rates, pressure, and the expression of the comoving entropy are obtained in a covariant formulation and discussed in detail. Applied together with the gravitational field equations, the thermodynamics of open systems lead to a generalization of the standard $\Lambda$CDM cosmological paradigm, in which the particle creation rates and pressures are effectively considered as components of the cosmological fluid energy-momentum tensor. Furthermore, we also briefly present the coupling of curvature to geometry in conformal quadratic Weyl gravity, by assuming a coupling term of the form $L_m\tilde{R}^2$, where $L_m$ is the ordinary matter Lagrangian, and $\tilde{R}$ is the Weyl scalar. The coupling explicitly satisfies the requirement of the conformal invariance of the theory. Expressing $\tilde{R}^2$ with the use of an auxiliary scalar field and of the Weyl scalar, the gravitational action can be linearized in the Ricci scalar, leading in the Riemann space to a conformally invariant $f\left(R,L_m\right)$ type theory, with the matter Lagrangian nonminimally coupled to geometry. |
2005.07650 | Burkhard Kleihaus | Burkhard Kleihaus, Jutta Kunz, Panagiota Kanti | Properties of ultra-compact particle-like solutions in
Einstein-scalar-Gauss-Bonnet theories | 29 pages, 15 figures | Phys. Rev. D 102, 024070 (2020) | 10.1103/PhysRevD.102.024070 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Besides scalarized black holes and wormholes, Einstein-scalar-Gauss-Bonnet
theories allow also for particle-like solutions. The scalar field of these
particle-like solutions diverges at the origin, akin to the divergence of the
Coulomb potential at the location of a charged particle. However, these
particle-like solutions possess a globally regular metric, and their effective
stress energy tensor is free from pathologies, as well. We determine the domain
of existence for particle-like solutions in a number of
Einstein-scalar-Gauss-Bonnet theories, considering dilatonic and power-law
coupling functions, and we analyze the physical properties of the solutions.
Interestingly, the solutions may possess pairs of lightrings, and thus
represent ultra-compact objects. We determine the location of these lightrings,
and study the effective potential for the occurrence of echoes in the
gravitational-wave spectrum. We also address the relation of these
particle-like solutions to the respective wormhole and black-hole solutions,
and clarify the limiting procedure to recover the Fisher solution (also known
as Janis-Newman-Winicourt-Wyman solution).
| [
{
"created": "Fri, 15 May 2020 17:10:12 GMT",
"version": "v1"
}
] | 2020-07-29 | [
[
"Kleihaus",
"Burkhard",
""
],
[
"Kunz",
"Jutta",
""
],
[
"Kanti",
"Panagiota",
""
]
] | Besides scalarized black holes and wormholes, Einstein-scalar-Gauss-Bonnet theories allow also for particle-like solutions. The scalar field of these particle-like solutions diverges at the origin, akin to the divergence of the Coulomb potential at the location of a charged particle. However, these particle-like solutions possess a globally regular metric, and their effective stress energy tensor is free from pathologies, as well. We determine the domain of existence for particle-like solutions in a number of Einstein-scalar-Gauss-Bonnet theories, considering dilatonic and power-law coupling functions, and we analyze the physical properties of the solutions. Interestingly, the solutions may possess pairs of lightrings, and thus represent ultra-compact objects. We determine the location of these lightrings, and study the effective potential for the occurrence of echoes in the gravitational-wave spectrum. We also address the relation of these particle-like solutions to the respective wormhole and black-hole solutions, and clarify the limiting procedure to recover the Fisher solution (also known as Janis-Newman-Winicourt-Wyman solution). |
1005.4988 | Subenoy Chakraborty | Nairwita Mazumder, Subenoy Chakraborty | Validity of the Generalized Second Law of Thermodynamics of the Universe
Bounded by the Event Horizon in Brane Scenario | 8 pages, the paper has been accepted in EPJC for publication.
Conclusion has been modified an some references have been added | Eur.Phys.J.C70:329-334,2010 | 10.1140/epjc/s10052-010-1435-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we examine the validity of the generalized second law of
thermodynamics (GSLT) of the universe bounded by the event horizon in
brane-world gravity. Here we consider homogeneous and isotropic model of the
universe filled with perfect fluid in one case and in another case holographic
dark energy model of the universe has been considered. The conclusions are
presented point wise.
| [
{
"created": "Thu, 27 May 2010 05:57:21 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Sep 2010 10:48:18 GMT",
"version": "v2"
}
] | 2011-02-09 | [
[
"Mazumder",
"Nairwita",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | In this paper, we examine the validity of the generalized second law of thermodynamics (GSLT) of the universe bounded by the event horizon in brane-world gravity. Here we consider homogeneous and isotropic model of the universe filled with perfect fluid in one case and in another case holographic dark energy model of the universe has been considered. The conclusions are presented point wise. |
gr-qc/9610030 | Miguel Angel Perez Sebastian | A. Feinstein and M. A. P\'erez Sebasti\'an (Dpto. Fisica Teorica,
Univ. Pais Vasco, Spain) | The Origin of the Entropy in the Universe | 18 pages. LaTeX file. Revised version, some discussions expanded,
several references added. The main results unchanged | Found.Phys.Lett. 13 (2000) 133-145 | null | null | gr-qc hep-th | null | We discuss the entropy generation in quantum tunneling of a relativistic
particle under the influence of a time varying force with the help of squeezing
formalism. It is shown that if one associates classical coarse grained entropy
to the phase space volume, there is an inevitable entropy increase due to the
changes in position and momentum variances. The entropy change can be
quantified by a simple expression $\Delta S=\ln\cosh 2r$, where $r$ is the
squeeze parameter measuring the "height" and "width" of the potential barrier.
We suggest that the universe could have acquired its initial entropy in a
quantum squeeze from "nothing" and briefly discuss the implications of our
proposal.
| [
{
"created": "Tue, 15 Oct 1996 13:21:27 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Oct 1996 10:22:25 GMT",
"version": "v2"
},
{
"created": "Thu, 13 Mar 1997 11:56:49 GMT",
"version": "v3"
}
] | 2008-02-03 | [
[
"Feinstein",
"A.",
"",
"Dpto. Fisica Teorica,\n Univ. Pais Vasco, Spain"
],
[
"Sebastián",
"M. A. Pérez",
"",
"Dpto. Fisica Teorica,\n Univ. Pais Vasco, Spain"
]
] | We discuss the entropy generation in quantum tunneling of a relativistic particle under the influence of a time varying force with the help of squeezing formalism. It is shown that if one associates classical coarse grained entropy to the phase space volume, there is an inevitable entropy increase due to the changes in position and momentum variances. The entropy change can be quantified by a simple expression $\Delta S=\ln\cosh 2r$, where $r$ is the squeeze parameter measuring the "height" and "width" of the potential barrier. We suggest that the universe could have acquired its initial entropy in a quantum squeeze from "nothing" and briefly discuss the implications of our proposal. |
gr-qc/0008037 | A. Puncher | C.G. Hewitt, R. Bridson and J. Wainwright | The asymptotic regimes of tilted Bianchi II cosmologies | null | Gen.Rel.Grav. 33 (2001) 65-94 | 10.1023/A:1002075902953 | null | gr-qc | null | In this paper we give, for the first time, a complete description of the
dynamics of tilted spatially homogeneous cosmologies of Bianchi type II. The
source is assumed to be a perfect fluid with equation of state $p = (\gamma -1)
\mu$, where $\gamma$ is a constant. We show that unless the perfect fluid is
stiff, the tilt destabilizes the Kasner solutions, leading to a Mixmaster-like
initial singularity, with the tilt being dynamically significant. At late times
the tilt becomes dynamically negligible unless the equation of state parameter
satisfies $\gamma > {10/7}$. We also find that the tilt does not destabilize
the flat FL model, with the result that the presence of tilt increases the
likelihood of intermediate isotropization.
| [
{
"created": "Tue, 15 Aug 2000 17:42:44 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Hewitt",
"C. G.",
""
],
[
"Bridson",
"R.",
""
],
[
"Wainwright",
"J.",
""
]
] | In this paper we give, for the first time, a complete description of the dynamics of tilted spatially homogeneous cosmologies of Bianchi type II. The source is assumed to be a perfect fluid with equation of state $p = (\gamma -1) \mu$, where $\gamma$ is a constant. We show that unless the perfect fluid is stiff, the tilt destabilizes the Kasner solutions, leading to a Mixmaster-like initial singularity, with the tilt being dynamically significant. At late times the tilt becomes dynamically negligible unless the equation of state parameter satisfies $\gamma > {10/7}$. We also find that the tilt does not destabilize the flat FL model, with the result that the presence of tilt increases the likelihood of intermediate isotropization. |
gr-qc/0005081 | null | Andrzej Krasinski (N. Copernicus Astronomical Center and College of
Science, Polish Academy of Sciences, Warszawa, Poland) | The newest release of the Ortocartan set of programs for algebraic
calculations in relativity | 16 pages, LaTeX, no figures, accepted for publication in GRG. In the
earlier version, equivalent formulae quoted from different computer printouts
were differently ordered. Now all orderings are the same, and a few typos
have been corrected. Subjects: Algebraic computing, general relativity | Gen.Rel.Grav. 33 (2001) 145-161 | 10.1023/A:1002028019791 | null | gr-qc | null | The program Ortocartan for algebraic calculations in relativity has just been
implemented in the Codemist Standard Lisp and can now be used under the Windows
98 and Linux operating systems. The paper describes the new facilities and
subprograms that have been implemented since the previous release in 1992.
These are: the possibility to write the output as Latex input code and as
Ortocartan's input code, the calculation of the Ellis evolution equations for
the kinematic tensors of flow, the calculation of the curvature tensors from
given (torsion-free) connection coefficients in a manifold of arbitrary
dimension, the calculation of the lagrangian from a given metric by the
Landau-Lifshitz method, the calculation of the Euler-Lagrange equations from a
given lagrangian (only for sets of ordinary differential equations) and the
calculation of first integrals of sets of ordinary differential equations of
second order (the first integrals are assumed to be polynomials of second
degree in the first derivatives of the functions).
| [
{
"created": "Thu, 18 May 2000 10:47:38 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Jul 2000 15:13:16 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Krasinski",
"Andrzej",
"",
"N. Copernicus Astronomical Center and College of\n Science, Polish Academy of Sciences, Warszawa, Poland"
]
] | The program Ortocartan for algebraic calculations in relativity has just been implemented in the Codemist Standard Lisp and can now be used under the Windows 98 and Linux operating systems. The paper describes the new facilities and subprograms that have been implemented since the previous release in 1992. These are: the possibility to write the output as Latex input code and as Ortocartan's input code, the calculation of the Ellis evolution equations for the kinematic tensors of flow, the calculation of the curvature tensors from given (torsion-free) connection coefficients in a manifold of arbitrary dimension, the calculation of the lagrangian from a given metric by the Landau-Lifshitz method, the calculation of the Euler-Lagrange equations from a given lagrangian (only for sets of ordinary differential equations) and the calculation of first integrals of sets of ordinary differential equations of second order (the first integrals are assumed to be polynomials of second degree in the first derivatives of the functions). |
2103.11613 | Bibhas Majhi Ranjan | Surojit Dalui, Bibhas Ranjan Majhi | Horizon thermalization of Kerr black hole through local instability | Minor changes, to appear in Phys. Lett. B | null | 10.1016/j.physletb.2022.136899 | null | gr-qc hep-th nlin.CD quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The validity of our already proposed conjecture -- {\it horizon creates a
local instability which acts as the source of the quantum temperature of black
hole} -- is being tested here for Kerr black hole. Earlier this has been
explicitly shown for spherically symmetric static black hole (SSS BH). The more
realistic situation like Kerr spacetime, being stationary and axisymmetric, is
a non-trivial example to analyze. We show that for a chargeless massless
particle, the near horizon radial motion in Kerr spacetime, like SSS BH, can be
locally unstable. The radial contribution in the corresponding Hamiltonian is
$\sim xp$ kind, where $p$ is the canonical momentum and $x$ is its conjugate
position of particle. Finally we show that the horizon thermalization can be
explained through this Hamiltonian when one dose a semi-classical analysis. It
again confirms that near horizon instability is liable for its own temperature
and moreover generalizes the validity of our conjectured mechanism for the
black hole horizon thermalization.
| [
{
"created": "Mon, 22 Mar 2021 06:50:58 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Jan 2022 11:42:30 GMT",
"version": "v2"
}
] | 2022-01-19 | [
[
"Dalui",
"Surojit",
""
],
[
"Majhi",
"Bibhas Ranjan",
""
]
] | The validity of our already proposed conjecture -- {\it horizon creates a local instability which acts as the source of the quantum temperature of black hole} -- is being tested here for Kerr black hole. Earlier this has been explicitly shown for spherically symmetric static black hole (SSS BH). The more realistic situation like Kerr spacetime, being stationary and axisymmetric, is a non-trivial example to analyze. We show that for a chargeless massless particle, the near horizon radial motion in Kerr spacetime, like SSS BH, can be locally unstable. The radial contribution in the corresponding Hamiltonian is $\sim xp$ kind, where $p$ is the canonical momentum and $x$ is its conjugate position of particle. Finally we show that the horizon thermalization can be explained through this Hamiltonian when one dose a semi-classical analysis. It again confirms that near horizon instability is liable for its own temperature and moreover generalizes the validity of our conjectured mechanism for the black hole horizon thermalization. |
1601.04558 | Shuang Nan Zhang | Shuang-Nan Zhang | Testing Einstein's Equivalence Principle with Cosmological Fast Radio
Bursts behind Clusters of Galaxies | 2 pages; submitted to A&A research note on Jan. 13th, 2016 | null | null | null | gr-qc astro-ph.CO astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Aims: Recently, cosmological fast radio bursts (FRBs) have been used to
provide the most stringent limit up to date on Einstein's Equivalence Principle
(EEP). We study how to further test EEP with FRBs. Methods: Future systematic
radio surveys will certainly find abundant FRBs at cosmological distances and
some of them will inevitably be located behind clusters of galaxies. Here we
suggest to use those FRBs to further test EEP. Results: We find that the
robustness and accuracy of testing EEP can be improved further by orders of
magnitude with these FRBs. The same methodology can also be applied to any
other types of fast and bright transients at cosmological distances.
| [
{
"created": "Fri, 15 Jan 2016 02:49:11 GMT",
"version": "v1"
}
] | 2016-01-19 | [
[
"Zhang",
"Shuang-Nan",
""
]
] | Aims: Recently, cosmological fast radio bursts (FRBs) have been used to provide the most stringent limit up to date on Einstein's Equivalence Principle (EEP). We study how to further test EEP with FRBs. Methods: Future systematic radio surveys will certainly find abundant FRBs at cosmological distances and some of them will inevitably be located behind clusters of galaxies. Here we suggest to use those FRBs to further test EEP. Results: We find that the robustness and accuracy of testing EEP can be improved further by orders of magnitude with these FRBs. The same methodology can also be applied to any other types of fast and bright transients at cosmological distances. |
1601.02838 | Rudolf A. Frick | Rudolf Frick | A model of the two-dimensional quantum harmonic oscillator in an $AdS_3$
background | 9 pages | Eur. Phys. C (2016) 76:551 | 10.1140/epjc/s10052-016-4381-5 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study a model of the two-dimensional quantum harmonic
oscillator in a 3-dimensional anti-de Sitter background. We use a generalized
Schr\"odinger picture in which the analogs of the Schr\"odinger operators of
the particle are independent of both the time and the space coordinates in
different representations. The spacetime independent operators of the particle
induce the Lie algebra of Killing vector fields of the $AdS_3$ spacetime. In
this picture, we have a metamorphosis of the Heisenberg's uncertainty
relations.
| [
{
"created": "Tue, 12 Jan 2016 12:56:04 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Jun 2016 13:14:05 GMT",
"version": "v2"
}
] | 2016-10-28 | [
[
"Frick",
"Rudolf",
""
]
] | In this paper we study a model of the two-dimensional quantum harmonic oscillator in a 3-dimensional anti-de Sitter background. We use a generalized Schr\"odinger picture in which the analogs of the Schr\"odinger operators of the particle are independent of both the time and the space coordinates in different representations. The spacetime independent operators of the particle induce the Lie algebra of Killing vector fields of the $AdS_3$ spacetime. In this picture, we have a metamorphosis of the Heisenberg's uncertainty relations. |
1811.05041 | Che-Yu Chen | Imanol Albarran, Mariam Bouhmadi-L\'opez, Che-Yu Chen, Pisin Chen | Quantum cosmology of Eddington-Born-Infeld gravity fed by a scalar
field: the big rip case | 12 pages | null | null | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the quantum avoidance of the big rip singularity in the
Eddington-inspired-Born-Infeld (EiBI) phantom model. Instead of considering a
simple phantom dark energy component, which is described by a perfect fluid, we
consider a more fundamental degree of freedom corresponding to a phantom scalar
field with its corresponding potential, which would lead the classical universe
to a big rip singularity. We apply a quantum geometrodynamical approach by
performing an appropriate Hamiltonian study including an analysis of the
constraints of the system. We then derive the Wheeler-DeWitt (WDW) equation and
see whether the solutions to the WDW equation satisfy the DeWitt boundary
condition. We find that by using a suitable Born-Oppenheimer (BO)
approximation, whose validity is proven, the DeWitt condition is satisfied.
Therefore, the big rip singularity is expected to be avoided in the quantum
realm.
| [
{
"created": "Mon, 12 Nov 2018 23:20:33 GMT",
"version": "v1"
}
] | 2018-11-14 | [
[
"Albarran",
"Imanol",
""
],
[
"Bouhmadi-López",
"Mariam",
""
],
[
"Chen",
"Che-Yu",
""
],
[
"Chen",
"Pisin",
""
]
] | We study the quantum avoidance of the big rip singularity in the Eddington-inspired-Born-Infeld (EiBI) phantom model. Instead of considering a simple phantom dark energy component, which is described by a perfect fluid, we consider a more fundamental degree of freedom corresponding to a phantom scalar field with its corresponding potential, which would lead the classical universe to a big rip singularity. We apply a quantum geometrodynamical approach by performing an appropriate Hamiltonian study including an analysis of the constraints of the system. We then derive the Wheeler-DeWitt (WDW) equation and see whether the solutions to the WDW equation satisfy the DeWitt boundary condition. We find that by using a suitable Born-Oppenheimer (BO) approximation, whose validity is proven, the DeWitt condition is satisfied. Therefore, the big rip singularity is expected to be avoided in the quantum realm. |
0910.5439 | Ricardo E. Gamboa Saravi | Ricardo E. Gamboa Saravi, Marcela Sanmartino and Philippe Tchamitchian | An alternative well-posedness property and static spacetimes with naked
singularities | 34 pages, 3 figures. Accepted for publication in Class. Quantum Grav | Class.Quant.Grav.27:215016,2010 | 10.1088/0264-9381/27/21/215016 | null | gr-qc math-ph math.MP math.SP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the first part of this paper, we show that the Cauchy problem for wave
propagation in some static spacetimes presenting a singular time-like boundary
is well posed, if we only demand the waves to have finite energy, although no
boundary condition is required. This feature does not come from essential
self-adjointness, which is false in these cases, but from a different
phenomenon that we call the alternative well-posedness property, whose origin
is due to the degeneracy of the metric components near the boundary.
Beyond these examples, in the second part, we characterize the type of
degeneracy which leads to this phenomenon.
| [
{
"created": "Wed, 28 Oct 2009 17:14:22 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Sep 2010 20:13:21 GMT",
"version": "v2"
}
] | 2014-11-20 | [
[
"Saravi",
"Ricardo E. Gamboa",
""
],
[
"Sanmartino",
"Marcela",
""
],
[
"Tchamitchian",
"Philippe",
""
]
] | In the first part of this paper, we show that the Cauchy problem for wave propagation in some static spacetimes presenting a singular time-like boundary is well posed, if we only demand the waves to have finite energy, although no boundary condition is required. This feature does not come from essential self-adjointness, which is false in these cases, but from a different phenomenon that we call the alternative well-posedness property, whose origin is due to the degeneracy of the metric components near the boundary. Beyond these examples, in the second part, we characterize the type of degeneracy which leads to this phenomenon. |
0802.3232 | Sergey G. Klimenko | S.Klimenko, I.Yakushin, A.Mercer, G.Mitselmakher | Coherent method for detection of gravitational wave bursts | 11 pages, 3 figures, proceedings of Amaldi conference in Sydney,
Australia | Class.Quant.Grav.25:114029,2008 | 10.1088/0264-9381/25/11/114029 | LIGO-P070093-00-Z | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe a coherent network algorithm for detection and reconstruction of
gravitational wave bursts. The algorithm works for two and more arbitrarily
aligned detectors and can be used for both all-sky and triggered burst
searches. We describe the main components of the algorithm, including the
time-frequency analysis in wavelet domain, construction of the likelihood
time-frequency maps, the identification and selection of burst events.
| [
{
"created": "Thu, 21 Feb 2008 23:03:50 GMT",
"version": "v1"
},
{
"created": "Thu, 28 Feb 2008 16:35:33 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Klimenko",
"S.",
""
],
[
"Yakushin",
"I.",
""
],
[
"Mercer",
"A.",
""
],
[
"Mitselmakher",
"G.",
""
]
] | We describe a coherent network algorithm for detection and reconstruction of gravitational wave bursts. The algorithm works for two and more arbitrarily aligned detectors and can be used for both all-sky and triggered burst searches. We describe the main components of the algorithm, including the time-frequency analysis in wavelet domain, construction of the likelihood time-frequency maps, the identification and selection of burst events. |
1101.0202 | Changhong Li | Changhong Li, Lingfei Wang and Yeuk-Kwan E. Cheung (Nanjing U.,
Physics) | Bound to bounce: a coupled scalar-tachyon model for a smooth
bouncing/cyclic universe | Extensive revision with comprehensive analytic and numerical studies
of the locked inflation, the tachyon matter dominated process--rolling
expansion, turnaround and contraction--as well as subsequent deflation and
bounce process carefully presented. 31 pages and 21 figures | null | null | NITS-PHY-2010001 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We introduce a string-inspired model for a bouncing/cyclic universe,
utilizing the scalar-tachyon coupling as well as contribution from curvature in
a closed universe. The universe undergoes the locked inflation, tachyon matter
dominated rolling expansion, turnaround and contraction, as well as the
subsequent deflation and "bounce" in each cycle of the cosmological evolution.
We perform extensive analytic and numerical studies of the above evolution
process. The minimum size of the universe is nonzero for generic initial
values. The smooth bounce are made possible because of the negative
contribution to effective energy density by the curvature term. No ghosts are
ever generated at any point in the entire evolution of the universe, with the
Null, Weak, and Dominant Energy Conditions preserved even at the bounce points,
contrary to many bounce models previously proposed. And the Strong Energy
Condition is satisfied in periods with tachyon matter domination.
| [
{
"created": "Fri, 31 Dec 2010 05:10:15 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Jan 2014 11:37:45 GMT",
"version": "v2"
}
] | 2014-01-22 | [
[
"Li",
"Changhong",
"",
"Nanjing U.,\n Physics"
],
[
"Wang",
"Lingfei",
"",
"Nanjing U.,\n Physics"
],
[
"Cheung",
"Yeuk-Kwan E.",
"",
"Nanjing U.,\n Physics"
]
] | We introduce a string-inspired model for a bouncing/cyclic universe, utilizing the scalar-tachyon coupling as well as contribution from curvature in a closed universe. The universe undergoes the locked inflation, tachyon matter dominated rolling expansion, turnaround and contraction, as well as the subsequent deflation and "bounce" in each cycle of the cosmological evolution. We perform extensive analytic and numerical studies of the above evolution process. The minimum size of the universe is nonzero for generic initial values. The smooth bounce are made possible because of the negative contribution to effective energy density by the curvature term. No ghosts are ever generated at any point in the entire evolution of the universe, with the Null, Weak, and Dominant Energy Conditions preserved even at the bounce points, contrary to many bounce models previously proposed. And the Strong Energy Condition is satisfied in periods with tachyon matter domination. |
1005.1404 | Deyou Chen | Deyou Chen, Peng Wang, Houwen Wu and Haitang Yang | Hidden conformal symmetry of rotating charged black holes | minor changes, accepted version | Gen.Rel.Grav.43:181-190,2011 | 10.1007/s10714-010-1080-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Motivated by the recent work of the hidden conformal symmetry of the Kerr
black hole, we investigate the hidden conformal symmetry of a Kerr-Sen black
hole and a Kerr-Newman-Kasuya black hole. Our result shows the conformal
symmetry is spontaneously broken due to the periodicity of the azimuthal angle.
The absorption across section is in consistence with the finite temperature
absorption cross section for a 2D CFT. The entropies of the black holes are
reproduced by the Cardy formula.
| [
{
"created": "Sun, 9 May 2010 14:52:39 GMT",
"version": "v1"
},
{
"created": "Sat, 22 May 2010 16:53:56 GMT",
"version": "v2"
},
{
"created": "Fri, 13 Aug 2010 13:13:10 GMT",
"version": "v3"
},
{
"created": "Tue, 17 Aug 2010 03:30:14 GMT",
"version": "v4"
}
] | 2011-03-04 | [
[
"Chen",
"Deyou",
""
],
[
"Wang",
"Peng",
""
],
[
"Wu",
"Houwen",
""
],
[
"Yang",
"Haitang",
""
]
] | Motivated by the recent work of the hidden conformal symmetry of the Kerr black hole, we investigate the hidden conformal symmetry of a Kerr-Sen black hole and a Kerr-Newman-Kasuya black hole. Our result shows the conformal symmetry is spontaneously broken due to the periodicity of the azimuthal angle. The absorption across section is in consistence with the finite temperature absorption cross section for a 2D CFT. The entropies of the black holes are reproduced by the Cardy formula. |
1103.4660 | Ahmad Borzou | Ahmad Borzou | A Five Dimensional Space Without Local Lorentz Invariance | 9 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A five dimensional space without invariance under local Lorentz
transformations is studied, and the transformations under which the theory is
invariant are introduced. We show that the Lorentz force is included in the
ensuing equations of motion. The four dimensional Einstein and Maxwell
equations emerge from the field equations while the homogeneous Maxwell
equations naturally appear in the work. A corresponding quantum theory is
introduced. The spectrum of a free particle and the hydrogen atom are
recovered. Quantum structure of Schwarzschild spaces are also studied.
| [
{
"created": "Thu, 24 Mar 2011 01:29:44 GMT",
"version": "v1"
}
] | 2011-03-25 | [
[
"Borzou",
"Ahmad",
""
]
] | A five dimensional space without invariance under local Lorentz transformations is studied, and the transformations under which the theory is invariant are introduced. We show that the Lorentz force is included in the ensuing equations of motion. The four dimensional Einstein and Maxwell equations emerge from the field equations while the homogeneous Maxwell equations naturally appear in the work. A corresponding quantum theory is introduced. The spectrum of a free particle and the hydrogen atom are recovered. Quantum structure of Schwarzschild spaces are also studied. |
2007.09797 | Zacharias Roupas | Zacharias Roupas, Gamal G. L. Nashed | Anisotropic Neutron Stars Modelling: Constraints in Krori-Barua
Spacetime | Revised version includes more data | The European Physical Journal C, 80, 905 (2020) | 10.1140/epjc/s10052-020-08462-1 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Dense nuclear matter is expected to be anisotropic due to effects such as
solidification, superfluidity, strong magnetic fields, hyperons,
pion-condesation. Therefore an anisotropic neutron star core seems more
realistic than an ideally isotropic one. We model anisotropic neutron stars
working in the Krori-Barua (KB) ansatz without preassuming an equation of
state. We show that the physics of general KB solutions is encapsulated in the
compactness. Imposing physical and stability requirements yields a maximum
allowed compactness $2GM/Rc^2 < 0.71$ for a KB-spacetime. We further input
observational data from numerous pulsars and calculate the boundary density. We
focus especially on data from the LIGO/Virgo collaboration as well as recent
independent measurements of mass and radius of miilisecond pulsars with white
dwarf companions by the Neutron Star Interior Composition Explorer (NICER). For
these data the KB-spacetime gives the same boundary density which surprisingly
equals the nuclear saturation density within the data precision. Since this
value designates the boundary of a neutron core, the KB-spacetime applies
naturally to neutron stars. For this boundary condition we calculate a maximum
mass of 4.1 solar masses.
| [
{
"created": "Sun, 19 Jul 2020 22:08:17 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Oct 2020 14:27:49 GMT",
"version": "v2"
}
] | 2020-10-02 | [
[
"Roupas",
"Zacharias",
""
],
[
"Nashed",
"Gamal G. L.",
""
]
] | Dense nuclear matter is expected to be anisotropic due to effects such as solidification, superfluidity, strong magnetic fields, hyperons, pion-condesation. Therefore an anisotropic neutron star core seems more realistic than an ideally isotropic one. We model anisotropic neutron stars working in the Krori-Barua (KB) ansatz without preassuming an equation of state. We show that the physics of general KB solutions is encapsulated in the compactness. Imposing physical and stability requirements yields a maximum allowed compactness $2GM/Rc^2 < 0.71$ for a KB-spacetime. We further input observational data from numerous pulsars and calculate the boundary density. We focus especially on data from the LIGO/Virgo collaboration as well as recent independent measurements of mass and radius of miilisecond pulsars with white dwarf companions by the Neutron Star Interior Composition Explorer (NICER). For these data the KB-spacetime gives the same boundary density which surprisingly equals the nuclear saturation density within the data precision. Since this value designates the boundary of a neutron core, the KB-spacetime applies naturally to neutron stars. For this boundary condition we calculate a maximum mass of 4.1 solar masses. |
1805.09672 | Arif Shaikh Md | Md Arif Shaikh | Nonlinear variations in spherically symmetric accretion in the
Schwarzschild metric | 9 pages, 1 figure, comments are welcome | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we study the implications of nonlinearity in general
relativistic spherically symmetric inviscid irrotational accretion flow in a
stationary non-rotating spacetime. It has been found that the perturbation
scheme leads to a differential equation of the form of general Li{\'e}nard's
equation. We discuss the equilibrium conditions of this system and its
implications for globally subsonic accretion flows in the spherically symmetric
stationary background. It is found that the stable solution predicted by linear
stability analysis may become unstable under inclusion of lowest order
nonlinearity.
| [
{
"created": "Tue, 22 May 2018 15:39:36 GMT",
"version": "v1"
}
] | 2018-05-25 | [
[
"Shaikh",
"Md Arif",
""
]
] | In this work, we study the implications of nonlinearity in general relativistic spherically symmetric inviscid irrotational accretion flow in a stationary non-rotating spacetime. It has been found that the perturbation scheme leads to a differential equation of the form of general Li{\'e}nard's equation. We discuss the equilibrium conditions of this system and its implications for globally subsonic accretion flows in the spherically symmetric stationary background. It is found that the stable solution predicted by linear stability analysis may become unstable under inclusion of lowest order nonlinearity. |
2206.09404 | Daisuke Yoshida | Kimihiro Nomura, Daisuke Yoshida | Implications of the singularity theorem for the size of a nonsingular
universe | 11 pages, 3 figures, published version | Phys.Rev.D 106 (2022) 12, 124016 | 10.1103/PhysRevD.106.124016 | KOBE-COSMO-22-06 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A general property of universes without initial singularity is investigated
based on the singularity theorem, assuming the null convergence condition and
the global hyperbolicity. As a direct consequence of the singularity theorem,
the universal covering of a Cauchy surface of a nonsingular universe with a
past trapped surface must have the topology of $S^3$. In addition, we find that
the affine size of a nonsingular universe, defined through the affine length of
null geodesics, is bounded above. In the case where a part of the nonsingular
spacetime is described by Friedmann-Lema\^itre-Robertson-Walker spacetime, we
find that this upper bound can be understood as the affine size of the
corresponding closed de Sitter universe. We also evaluate the upper bound of
the affine size of our Universe based on the trapped surface confirmed by
recent observations of baryon acoustic oscillations, assuming that our Universe
has no initial singularity.
| [
{
"created": "Sun, 19 Jun 2022 13:50:24 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Jan 2023 12:28:26 GMT",
"version": "v2"
}
] | 2023-01-09 | [
[
"Nomura",
"Kimihiro",
""
],
[
"Yoshida",
"Daisuke",
""
]
] | A general property of universes without initial singularity is investigated based on the singularity theorem, assuming the null convergence condition and the global hyperbolicity. As a direct consequence of the singularity theorem, the universal covering of a Cauchy surface of a nonsingular universe with a past trapped surface must have the topology of $S^3$. In addition, we find that the affine size of a nonsingular universe, defined through the affine length of null geodesics, is bounded above. In the case where a part of the nonsingular spacetime is described by Friedmann-Lema\^itre-Robertson-Walker spacetime, we find that this upper bound can be understood as the affine size of the corresponding closed de Sitter universe. We also evaluate the upper bound of the affine size of our Universe based on the trapped surface confirmed by recent observations of baryon acoustic oscillations, assuming that our Universe has no initial singularity. |
2201.02971 | Yan-Gang Miao | Yang Guo, Chen Lan and Yan-Gang Miao | Bounce corrections to gravitational lensing, quasinormal spectral
stability and gray-body factors of Reissner-Nordstr\"om black holes | v1: 8 pages, 2 figures, 2 tables; v2: references added; v3: 16 pages,
four tables, one author, two appendixes, clarifications, and references
added, final version to appear in Physical Review D | Phys. Rev. D 106, 124052 (2022) | 10.1103/PhysRevD.106.124052 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational lensing in the weak field limit, quasinormal spectra, and
gray-body factors are investigated in the Reissner-Nordstr\"om spacetime
corrected by bounce parameters. Using the Gauss-Bonnet theorem, we analyze the
effects of bounce corrections to the weak gravitational deflection angle and
find that the divergence of the deflection angle can be suppressed by a bounce
correction in the Reissner-Nordstr\"om spacetime. We also notice that the
bounce correction plays the same role as the Morse potential in the deflection
angle. Moreover, we derive the perturbation equations with the spin-dependent
Regge-Wheeler potential and discuss the quasinormal spectral stability. We
observe that the quasinormal spectra decrease for both the massless scalar and
electromagnetic field perturbations. We further study the transmission
probability of particles scattered by the Regge-Wheeler potential and reveal
that the bounce correction introduced into the Reissner-Nordstr\"om spacetime
increases the gray-body factors of perturbation fields.
| [
{
"created": "Sun, 9 Jan 2022 09:38:35 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Jan 2022 05:40:17 GMT",
"version": "v2"
},
{
"created": "Sun, 1 Jan 2023 09:20:07 GMT",
"version": "v3"
}
] | 2023-01-03 | [
[
"Guo",
"Yang",
""
],
[
"Lan",
"Chen",
""
],
[
"Miao",
"Yan-Gang",
""
]
] | Gravitational lensing in the weak field limit, quasinormal spectra, and gray-body factors are investigated in the Reissner-Nordstr\"om spacetime corrected by bounce parameters. Using the Gauss-Bonnet theorem, we analyze the effects of bounce corrections to the weak gravitational deflection angle and find that the divergence of the deflection angle can be suppressed by a bounce correction in the Reissner-Nordstr\"om spacetime. We also notice that the bounce correction plays the same role as the Morse potential in the deflection angle. Moreover, we derive the perturbation equations with the spin-dependent Regge-Wheeler potential and discuss the quasinormal spectral stability. We observe that the quasinormal spectra decrease for both the massless scalar and electromagnetic field perturbations. We further study the transmission probability of particles scattered by the Regge-Wheeler potential and reveal that the bounce correction introduced into the Reissner-Nordstr\"om spacetime increases the gray-body factors of perturbation fields. |
1011.6286 | Mayeul Arminjon | Mayeul Arminjon and Frank Reifler | Representations of the Dirac wave function in a curved spacetime | 14 pages (standard 12pt article). Text of a talk given at DICE2010:
"Space-Time-Matter - current issues in quantum mechanics and beyond"
(Castiglioncello, Italy, September 13-17, 2010) | J.Phys.Conf.Ser.306:012061,2011 | 10.1088/1742-6596/306/1/012061 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Dirac wave function in a curved spacetime is usually defined as a
quadruplet of scalar fields. It can alternatively be defined as a four-vector
field. We describe these two representations in a common geometrical framework
and we prove theorems that relate together the different representations and
the different choices of connections. In particular, the standard Dirac
equation in a curved spacetime, with any choice of the tetrad field, is
equivalent to a particular realization of the Dirac equation for a vector wave
function, in the same spacetime.
| [
{
"created": "Mon, 29 Nov 2010 16:45:56 GMT",
"version": "v1"
}
] | 2011-10-05 | [
[
"Arminjon",
"Mayeul",
""
],
[
"Reifler",
"Frank",
""
]
] | The Dirac wave function in a curved spacetime is usually defined as a quadruplet of scalar fields. It can alternatively be defined as a four-vector field. We describe these two representations in a common geometrical framework and we prove theorems that relate together the different representations and the different choices of connections. In particular, the standard Dirac equation in a curved spacetime, with any choice of the tetrad field, is equivalent to a particular realization of the Dirac equation for a vector wave function, in the same spacetime. |
1306.6554 | Jiri Podolsky | Jiri Podolsky, Robert Svarc | Physical interpretation of Kundt spacetimes using geodesic deviation | 24 pages, 5 figures | Class.Quant.Grav.30:205016,2013 | 10.1088/0264-9381/30/20/205016 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the fully general class of non-expanding, non-twisting and
shear-free D-dimensional geometries using the invariant form of geodesic
deviation equation which describes the relative motion of free test particles.
We show that the local effect of such gravitational fields on the particles
basically consists of isotropic motion caused by the cosmological constant
Lambda, Newtonian-type tidal deformations typical for spacetimes of algebraic
type D or II, longitudinal motion characteristic for spacetimes of type III,
and type N purely transverse effects of exact gravitational waves with D(D-3)/2
polarizations. We explicitly discuss the canonical forms of the geodesic
deviation motion in all algebraically special subtypes of the Kundt family for
which the optically privileged direction is a multiple Weyl aligned null
direction (WAND), namely D(a), D(b), D(c), D(d), III(a), III(b), IIIi, IIi,
II(a), II(b), II(c) and II(d). We demonstrate that the key invariant quantities
determining these algebraic types and subtypes also directly determine the
specific local motion of test particles, and are thus measurable by
gravitational detectors. As an example, we analyze an interesting class of type
N or II gravitational waves which propagate on backgrounds of type O or D,
including Minkowski, Bertotti-Robinson, Nariai and Plebanski-Hacyan universes.
| [
{
"created": "Thu, 27 Jun 2013 15:57:49 GMT",
"version": "v1"
}
] | 2014-06-04 | [
[
"Podolsky",
"Jiri",
""
],
[
"Svarc",
"Robert",
""
]
] | We investigate the fully general class of non-expanding, non-twisting and shear-free D-dimensional geometries using the invariant form of geodesic deviation equation which describes the relative motion of free test particles. We show that the local effect of such gravitational fields on the particles basically consists of isotropic motion caused by the cosmological constant Lambda, Newtonian-type tidal deformations typical for spacetimes of algebraic type D or II, longitudinal motion characteristic for spacetimes of type III, and type N purely transverse effects of exact gravitational waves with D(D-3)/2 polarizations. We explicitly discuss the canonical forms of the geodesic deviation motion in all algebraically special subtypes of the Kundt family for which the optically privileged direction is a multiple Weyl aligned null direction (WAND), namely D(a), D(b), D(c), D(d), III(a), III(b), IIIi, IIi, II(a), II(b), II(c) and II(d). We demonstrate that the key invariant quantities determining these algebraic types and subtypes also directly determine the specific local motion of test particles, and are thus measurable by gravitational detectors. As an example, we analyze an interesting class of type N or II gravitational waves which propagate on backgrounds of type O or D, including Minkowski, Bertotti-Robinson, Nariai and Plebanski-Hacyan universes. |
2302.07997 | Alberto Escalante | Alberto Escalante (Puebla U., Inst. Fis.), Victor Alberto Zavala-Perez
(Puebla U., Inst. Fis.) | Analysis of linearized Weyl gravity via the Hamilton-Jacobi method | null | null | null | null | gr-qc math-ph math.MP | http://creativecommons.org/publicdomain/zero/1.0/ | The Hamilton-Jacobi formalism is used to analyze the Weyl theory in the
weak-field limit. The complete set of involutive Hamiltonians is obtained,
which are classified into involutive and non-involutive. The counting of
degrees of freedom is performed. Additionally, the generalized brackets and
gauge symmetries are reported.
| [
{
"created": "Thu, 16 Feb 2023 00:07:17 GMT",
"version": "v1"
}
] | 2023-02-17 | [
[
"Escalante",
"Alberto",
"",
"Puebla U., Inst. Fis."
],
[
"Zavala-Perez",
"Victor Alberto",
"",
"Puebla U., Inst. Fis."
]
] | The Hamilton-Jacobi formalism is used to analyze the Weyl theory in the weak-field limit. The complete set of involutive Hamiltonians is obtained, which are classified into involutive and non-involutive. The counting of degrees of freedom is performed. Additionally, the generalized brackets and gauge symmetries are reported. |
1509.05782 | Kevin Barkett | Kevin Barkett, Mark A. Scheel, Roland Haas, Christian D. Ott,
Sebastiano Bernuzzi, Duncan A. Brown, B\'ela Szil\'agyi, Jeffrey D. Kaplan,
Jonas Lippuner, Curran D. Muhlberger, Francois Foucart, and Matthew D. Duez | Gravitational waveforms for neutron star binaries from binary black hole
simulations | 7 pages, 3 figures; updated acknowledgements; published PRD version | Phys. Rev. D 93, 044064 (2016) | 10.1103/PhysRevD.93.044064 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves from binary neutron star (BNS) and black hole/neutron
star (BHNS) inspirals are primary sources for detection by the Advanced Laser
Interferometer Gravitational-Wave Observatory. The tidal forces acting on the
neutron stars induce changes in the phase evolution of the gravitational
waveform, and these changes can be used to constrain the nuclear equation of
state. Current methods of generating BNS and BHNS waveforms rely on either
computationally challenging full 3D hydrodynamical simulations or approximate
analytic solutions. We introduce a new method for computing inspiral waveforms
for BNS/BHNS systems by adding the post-Newtonian (PN) tidal effects to full
numerical simulations of binary black holes (BBHs), effectively replacing the
nontidal terms in the PN expansion with BBH results. Comparing a waveform
generated with this method against a full hydrodynamical simulation of a BNS
inspiral yields a phase difference of $<1$ radian over $\sim 15$ orbits. The
numerical phase accuracy required of BNS simulations to measure the accuracy of
the method we present here is estimated as a function of the tidal
deformability parameter ${\lambda}$.
| [
{
"created": "Fri, 18 Sep 2015 20:05:46 GMT",
"version": "v1"
},
{
"created": "Tue, 22 Sep 2015 20:21:30 GMT",
"version": "v2"
},
{
"created": "Thu, 25 Feb 2016 21:47:57 GMT",
"version": "v3"
}
] | 2016-02-29 | [
[
"Barkett",
"Kevin",
""
],
[
"Scheel",
"Mark A.",
""
],
[
"Haas",
"Roland",
""
],
[
"Ott",
"Christian D.",
""
],
[
"Bernuzzi",
"Sebastiano",
""
],
[
"Brown",
"Duncan A.",
""
],
[
"Szilágyi",
"Béla",
""
],
[
"Kaplan",
"Jeffrey D.",
""
],
[
"Lippuner",
"Jonas",
""
],
[
"Muhlberger",
"Curran D.",
""
],
[
"Foucart",
"Francois",
""
],
[
"Duez",
"Matthew D.",
""
]
] | Gravitational waves from binary neutron star (BNS) and black hole/neutron star (BHNS) inspirals are primary sources for detection by the Advanced Laser Interferometer Gravitational-Wave Observatory. The tidal forces acting on the neutron stars induce changes in the phase evolution of the gravitational waveform, and these changes can be used to constrain the nuclear equation of state. Current methods of generating BNS and BHNS waveforms rely on either computationally challenging full 3D hydrodynamical simulations or approximate analytic solutions. We introduce a new method for computing inspiral waveforms for BNS/BHNS systems by adding the post-Newtonian (PN) tidal effects to full numerical simulations of binary black holes (BBHs), effectively replacing the nontidal terms in the PN expansion with BBH results. Comparing a waveform generated with this method against a full hydrodynamical simulation of a BNS inspiral yields a phase difference of $<1$ radian over $\sim 15$ orbits. The numerical phase accuracy required of BNS simulations to measure the accuracy of the method we present here is estimated as a function of the tidal deformability parameter ${\lambda}$. |
1808.03619 | Chris Pankow | Chris Pankow, Katerina Chatziioannou, Eve A. Chase, Tyson B.
Littenberg, Matthew Evans, Jessica McIver, Neil J. Cornish, Carl-Johan
Haster, Jonah Kanner, Vivien Raymond, Salvatore Vitale, Aaron Zimmerman | Mitigation of the instrumental noise transient in gravitational-wave
data surrounding GW170817 | 11 pages, 3 figures, accepted in PRD | Phys. Rev. D 98, 084016 (2018) | 10.1103/PhysRevD.98.084016 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the coming years gravitational-wave detectors will undergo a series of
improvements, with an increase in their detection rate by about an order of
magnitude. Routine detections of gravitational-wave signals promote novel
astrophysical and fundamental theory studies, while simultaneously leading to
an increase in the number of detections temporally overlapping with
instrumentally- or environmentally-induced transients in the detectors
(glitches), often of unknown origin. Indeed, this was the case for the very
first detection by the LIGO and Virgo detectors of a gravitational-wave signal
consistent with a binary neutron star coalescence, GW170817. A loud glitch in
the LIGO-Livingston detector, about one second before the merger, hampered
coincident detection (which was initially achieved solely with LIGO-Hanford
data). Moreover, accurate source characterization depends on specific
assumptions about the behavior of the detector noise that are rendered invalid
by the presence of glitches. In this paper, we present the various techniques
employed for the initial mitigation of the glitch to perform source
characterization of GW170817 and study advantages and disadvantages of each
mitigation method. We show that, despite the presence of instrumental noise
transients louder than the one affecting GW170817, we are still able to produce
unbiased measurements of the intrinsic parameters from simulated injections
with properties similar to GW170817.
| [
{
"created": "Fri, 10 Aug 2018 16:54:58 GMT",
"version": "v1"
},
{
"created": "Sat, 20 Oct 2018 18:50:04 GMT",
"version": "v2"
}
] | 2018-10-23 | [
[
"Pankow",
"Chris",
""
],
[
"Chatziioannou",
"Katerina",
""
],
[
"Chase",
"Eve A.",
""
],
[
"Littenberg",
"Tyson B.",
""
],
[
"Evans",
"Matthew",
""
],
[
"McIver",
"Jessica",
""
],
[
"Cornish",
"Neil J.",
""
],
[
"Haster",
"Carl-Johan",
""
],
[
"Kanner",
"Jonah",
""
],
[
"Raymond",
"Vivien",
""
],
[
"Vitale",
"Salvatore",
""
],
[
"Zimmerman",
"Aaron",
""
]
] | In the coming years gravitational-wave detectors will undergo a series of improvements, with an increase in their detection rate by about an order of magnitude. Routine detections of gravitational-wave signals promote novel astrophysical and fundamental theory studies, while simultaneously leading to an increase in the number of detections temporally overlapping with instrumentally- or environmentally-induced transients in the detectors (glitches), often of unknown origin. Indeed, this was the case for the very first detection by the LIGO and Virgo detectors of a gravitational-wave signal consistent with a binary neutron star coalescence, GW170817. A loud glitch in the LIGO-Livingston detector, about one second before the merger, hampered coincident detection (which was initially achieved solely with LIGO-Hanford data). Moreover, accurate source characterization depends on specific assumptions about the behavior of the detector noise that are rendered invalid by the presence of glitches. In this paper, we present the various techniques employed for the initial mitigation of the glitch to perform source characterization of GW170817 and study advantages and disadvantages of each mitigation method. We show that, despite the presence of instrumental noise transients louder than the one affecting GW170817, we are still able to produce unbiased measurements of the intrinsic parameters from simulated injections with properties similar to GW170817. |
1807.11420 | Seramika Ariwahjoedi | Seramika Ariwahjoedi, Freddy P. Zen | Contracted Bianchi Identity and Angle Relation on n-dimensional
Simplicial Complex of Regge Calculus | 16 pages | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article, we prove the theorems concerning the trace relation of
SO(3), SU(2), and SO(n) which are representation of SO(3) and SU(2). An
interesting fact we found is the trace relation of SU(2) gives the spherical
law of cosine which in turns is a dihedral angle relation, a constraint that
must be satisfied by closed Euclidean simplices. Moreover, we applied our
results on general group elements to holonomies on the simplicial complex of
Regge Calculus, which is the main motivation of this article. Here, we found
that: (1) in 4-dimensional Euclidean Regge Gravity, all the holonomy circling a
single hinge are simple rotations, and (2) the dihedral angle relation
represents the 'contracted' Bianchi identity for a simplicial complex.
| [
{
"created": "Mon, 30 Jul 2018 16:19:24 GMT",
"version": "v1"
}
] | 2018-08-07 | [
[
"Ariwahjoedi",
"Seramika",
""
],
[
"Zen",
"Freddy P.",
""
]
] | In this article, we prove the theorems concerning the trace relation of SO(3), SU(2), and SO(n) which are representation of SO(3) and SU(2). An interesting fact we found is the trace relation of SU(2) gives the spherical law of cosine which in turns is a dihedral angle relation, a constraint that must be satisfied by closed Euclidean simplices. Moreover, we applied our results on general group elements to holonomies on the simplicial complex of Regge Calculus, which is the main motivation of this article. Here, we found that: (1) in 4-dimensional Euclidean Regge Gravity, all the holonomy circling a single hinge are simple rotations, and (2) the dihedral angle relation represents the 'contracted' Bianchi identity for a simplicial complex. |
0912.1609 | Vladimir Popov | V. A. Popov | Dark Energy and Dark Matter unification via superfluid Chaplygin gas | 13 pages, 3 figures | Phys.Lett.B686:211-215, 2010 | 10.1016/j.physletb.2010.02.035 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new model describing the dark sector of the universe is established. The
model involves Bose-Einstein condensate (BEC) as dark energy (DE) and an
excited state above it as dark matter (DM). The condensate is assumed to have a
negative pressure and is embodied as an exotic fluid with Chaplygin equation of
state. Excitations are described as a quasiparticle gas. It is shown that the
model is not in disagreement with the current observations of the cosmic
acceleration. The model predicts increase of the effective cosmological
constant and a complete disappearance of the matter at the far future.
| [
{
"created": "Tue, 8 Dec 2009 21:11:28 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Mar 2010 05:47:13 GMT",
"version": "v2"
},
{
"created": "Sun, 22 May 2011 10:48:36 GMT",
"version": "v3"
}
] | 2011-05-24 | [
[
"Popov",
"V. A.",
""
]
] | A new model describing the dark sector of the universe is established. The model involves Bose-Einstein condensate (BEC) as dark energy (DE) and an excited state above it as dark matter (DM). The condensate is assumed to have a negative pressure and is embodied as an exotic fluid with Chaplygin equation of state. Excitations are described as a quasiparticle gas. It is shown that the model is not in disagreement with the current observations of the cosmic acceleration. The model predicts increase of the effective cosmological constant and a complete disappearance of the matter at the far future. |
1911.06628 | Yiqian Chen | Yiqian Chen, Qingyu Gan, Guangzhou Guo | Strong Cosmic Censorship for a Scalar Field in a Logarithmic-de Sitter
Black Hole | 21 pages, 5 figures, 1 table | null | 10.1088/1572-9494/ab6912 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been shown that the quasinormal modes of perturebated fields can be
used to investigate the validity of strong cosmic censorship (SCC). Relevant
issues for Reissner-Nordstrom-de Sitter (RNdS) black holes and Born-Infeld-de
Sitter (BI-dS) black holes have been discussed. In this paper, we investigate
SCC in an asymptotic RN-dS black hole with logarithmic nonlinear
electromagnetic field perturbed by massless scalar fields. It has been argued
that SCC can be violated in a near-extremal RN-dS black hole. However, we find
that the NLED effect can rescue SCC for a near-extremal logarithmic-de Sitter
black hole. Compared with Born-Infeld model, we find that the NLED effect have
similar behavior.
| [
{
"created": "Fri, 15 Nov 2019 13:40:46 GMT",
"version": "v1"
}
] | 2020-04-22 | [
[
"Chen",
"Yiqian",
""
],
[
"Gan",
"Qingyu",
""
],
[
"Guo",
"Guangzhou",
""
]
] | It has been shown that the quasinormal modes of perturebated fields can be used to investigate the validity of strong cosmic censorship (SCC). Relevant issues for Reissner-Nordstrom-de Sitter (RNdS) black holes and Born-Infeld-de Sitter (BI-dS) black holes have been discussed. In this paper, we investigate SCC in an asymptotic RN-dS black hole with logarithmic nonlinear electromagnetic field perturbed by massless scalar fields. It has been argued that SCC can be violated in a near-extremal RN-dS black hole. However, we find that the NLED effect can rescue SCC for a near-extremal logarithmic-de Sitter black hole. Compared with Born-Infeld model, we find that the NLED effect have similar behavior. |
1109.1043 | Muhammad Sharif | M. Sharif and G. Abbas | Phantom Accretion onto the Schwarzschild de-Sitter Black Hole | 9 pages, no figure | Chin. Phys. Lett. 28(2011)090402 | 10.1088/0256-307X/28/9/090402 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We deal with phantom energy accretion onto the Schwarzschild de-Sitter black
hole. The energy flux conservation, relativistic Bernoulli equation and mass
flux conservation equation are formulated to discuss the phantom accretion. We
discuss the conditions for critical accretion. It is found that mass of the
black hole decreases due to phantom accretion. There exist two critical points
which lie in the exterior of horizons (black hole and cosmological horizons).
The results for the phantom energy accretion onto the Schwarzschild black hole
can be recovered by taking $\Lambda\rightarrow0$.
| [
{
"created": "Tue, 6 Sep 2011 02:18:20 GMT",
"version": "v1"
}
] | 2017-08-23 | [
[
"Sharif",
"M.",
""
],
[
"Abbas",
"G.",
""
]
] | We deal with phantom energy accretion onto the Schwarzschild de-Sitter black hole. The energy flux conservation, relativistic Bernoulli equation and mass flux conservation equation are formulated to discuss the phantom accretion. We discuss the conditions for critical accretion. It is found that mass of the black hole decreases due to phantom accretion. There exist two critical points which lie in the exterior of horizons (black hole and cosmological horizons). The results for the phantom energy accretion onto the Schwarzschild black hole can be recovered by taking $\Lambda\rightarrow0$. |
1708.08766 | Yuri Obukhov | Milutin Blagojevi\'c, Branislav Cvetkovi\'c, Yuri N. Obukhov | Generalized plane waves in Poincar\'e gauge theory of gravity | 13 pages, Rextex, Paper is dedicated to Friedrich Hehl on the
occasion of his 80th birthday, in appreciation of his contribution to the
development of gauge theories of gravity. arXiv admin note: text overlap with
arXiv:1702.05185 | null | 10.1103/PhysRevD.96.064031 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A family of exact vacuum solutions, representing generalized plane waves
propagating on the (anti-)de Sitter background, is constructed in the framework
of Poincar\'e gauge theory. The wave dynamics is defined by the general
Lagrangian that includes all parity even and parity odd invariants up to the
second order in the gauge field strength. The structure of the solution shows
that the wave metric significantly depends on the spacetime torsion.
| [
{
"created": "Sat, 26 Aug 2017 08:12:29 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Sep 2017 15:52:12 GMT",
"version": "v2"
}
] | 2017-09-21 | [
[
"Blagojević",
"Milutin",
""
],
[
"Cvetković",
"Branislav",
""
],
[
"Obukhov",
"Yuri N.",
""
]
] | A family of exact vacuum solutions, representing generalized plane waves propagating on the (anti-)de Sitter background, is constructed in the framework of Poincar\'e gauge theory. The wave dynamics is defined by the general Lagrangian that includes all parity even and parity odd invariants up to the second order in the gauge field strength. The structure of the solution shows that the wave metric significantly depends on the spacetime torsion. |
1304.6688 | David Sloan | Julian Rennert and David Sloan | A Homogeneous Model of Spinfoam Cosmology | 22 pages, 4 figures | Class. Quantum Grav. 30 (2013) 235019 | 10.1088/0264-9381/30/23/235019 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine spinfoam cosmology by use of a simple graph adapted to homogeneous
cosmological models. We calculate dynamics in the isotropic limit, and provide
the framework for the aniostropic case. The dynamical behaviour is calculating
transition amplitudes between holomorphic coherent states on a single node
graph. The resultant dynamics is peaked on solutions which have no support on
the zero volume state, indicating that big bang type singularities are avoided
within such models.
| [
{
"created": "Wed, 24 Apr 2013 18:21:52 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Oct 2013 19:25:58 GMT",
"version": "v2"
}
] | 2013-11-21 | [
[
"Rennert",
"Julian",
""
],
[
"Sloan",
"David",
""
]
] | We examine spinfoam cosmology by use of a simple graph adapted to homogeneous cosmological models. We calculate dynamics in the isotropic limit, and provide the framework for the aniostropic case. The dynamical behaviour is calculating transition amplitudes between holomorphic coherent states on a single node graph. The resultant dynamics is peaked on solutions which have no support on the zero volume state, indicating that big bang type singularities are avoided within such models. |
1003.3845 | Claude Warnick | G. W. Gibbons and C. M. Warnick | Dark Energy and Projective Symmetry | null | Phys.Lett.B688:337-340,2010 | 10.1016/j.physletb.2010.04.016 | DAMTP-2010-19 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Nurowski [arXiv:1003.1503] has recently suggested a link between the
observation of Dark Energy in cosmology and the projective equivalence of
certain Friedman-Lemaitre-Robertson-Walker (FLRW) metrics. Specifically, he
points out that two FLRW metrics with the same unparameterized geodesics have
their energy densities differing by a constant. From this he queries whether
the existence of dark energy is meaningful. We point out that physical
observables in cosmology are not projectively invariant and we relate the
projective symmetry uncovered by Nurowski to some previous work on projective
equivalence in cosmology.
| [
{
"created": "Fri, 19 Mar 2010 17:25:35 GMT",
"version": "v1"
}
] | 2014-11-20 | [
[
"Gibbons",
"G. W.",
""
],
[
"Warnick",
"C. M.",
""
]
] | Nurowski [arXiv:1003.1503] has recently suggested a link between the observation of Dark Energy in cosmology and the projective equivalence of certain Friedman-Lemaitre-Robertson-Walker (FLRW) metrics. Specifically, he points out that two FLRW metrics with the same unparameterized geodesics have their energy densities differing by a constant. From this he queries whether the existence of dark energy is meaningful. We point out that physical observables in cosmology are not projectively invariant and we relate the projective symmetry uncovered by Nurowski to some previous work on projective equivalence in cosmology. |
1008.0448 | Edward Glass | E.N. Glass | Gravothermal Catastrophe, an Example | To appear in Phys. Rev. D | Phys.Rev.D82:044039,2010 | 10.1103/PhysRevD.82.044039 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This work discusses gravothermal catastrophe in astrophysical systems and
provides an analytic collapse solution which exhibits many of the catastrophe
properties. The system collapses into a trapped surface with outgoing energy
radiated to a future boundary, and provides an example of catastrophic
collapse.
| [
{
"created": "Tue, 3 Aug 2010 03:13:51 GMT",
"version": "v1"
}
] | 2011-02-24 | [
[
"Glass",
"E. N.",
""
]
] | This work discusses gravothermal catastrophe in astrophysical systems and provides an analytic collapse solution which exhibits many of the catastrophe properties. The system collapses into a trapped surface with outgoing energy radiated to a future boundary, and provides an example of catastrophic collapse. |
gr-qc/0511136 | Koji Uryu | Koji Uryu, Francois Limousin, John L. Friedman, Eric Gourgoulhon,
Masaru Shibata | Binary neutron stars: Equilibrium models beyond spatial conformal
flatness | 4 pages, 6 figures, revised version, PRL in press | Phys.Rev.Lett. 97 (2006) 171101 | 10.1103/PhysRevLett.97.171101 | null | gr-qc astro-ph | null | Equilibria of binary neutron stars in close circular orbits are computed
numerically in a waveless formulation: The full Einstein-relativistic-Euler
system is solved on an initial hypersurface to obtain an asymptotically flat
form of the 4-metric and an extrinsic curvature whose time derivative vanishes
in a comoving frame. Two independent numerical codes are developed, and
solution sequences that model inspiraling binary neutron stars during the final
several orbits are successfully computed. The binding energy of the system near
its final orbit deviates from earlier results of third post-Newtonian and of
spatially conformally flat calculations. The new solutions may serve as initial
data for merger simulations and as members of quasiequilibrium sequences to
generate gravitational wave templates, and may improve estimates of the
gravitational-wave cutoff frequency set by the last inspiral orbit.
| [
{
"created": "Fri, 25 Nov 2005 13:32:24 GMT",
"version": "v1"
},
{
"created": "Sat, 21 Oct 2006 16:13:04 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Uryu",
"Koji",
""
],
[
"Limousin",
"Francois",
""
],
[
"Friedman",
"John L.",
""
],
[
"Gourgoulhon",
"Eric",
""
],
[
"Shibata",
"Masaru",
""
]
] | Equilibria of binary neutron stars in close circular orbits are computed numerically in a waveless formulation: The full Einstein-relativistic-Euler system is solved on an initial hypersurface to obtain an asymptotically flat form of the 4-metric and an extrinsic curvature whose time derivative vanishes in a comoving frame. Two independent numerical codes are developed, and solution sequences that model inspiraling binary neutron stars during the final several orbits are successfully computed. The binding energy of the system near its final orbit deviates from earlier results of third post-Newtonian and of spatially conformally flat calculations. The new solutions may serve as initial data for merger simulations and as members of quasiequilibrium sequences to generate gravitational wave templates, and may improve estimates of the gravitational-wave cutoff frequency set by the last inspiral orbit. |
1906.04847 | J\"org Hennig | J\"org Hennig | On the balance problem for two rotating and charged black holes | 17 pages, 1 figure | Class. Quantum Grav. 36, 235001 (2019) | 10.1088/1361-6382/ab4f41 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is an interesting open problem whether two non-extremal rotating and
electrically charged black holes can be in physical equilibrium, which might be
possible due to a balance between the gravitational attraction and the
spin-spin and electrical repulsions. Exact candidate solutions were
constructed, but it is unclear whether they are physically acceptable. These
solutions were obtained by assuming a particular behaviour on the symmetry
axis. However, it was not known whether the assumed form of the axis data
covers the general case or whether data of some other type need to be
considered as well. By studying a boundary value problem for the axisymmetric
and stationary Einstein-Maxwell equations, we address this question and derive
the most general form of permissible axis potentials for possible equilibrium
configurations.
| [
{
"created": "Tue, 11 Jun 2019 22:32:57 GMT",
"version": "v1"
},
{
"created": "Sun, 3 Nov 2019 21:18:35 GMT",
"version": "v2"
}
] | 2019-11-05 | [
[
"Hennig",
"Jörg",
""
]
] | It is an interesting open problem whether two non-extremal rotating and electrically charged black holes can be in physical equilibrium, which might be possible due to a balance between the gravitational attraction and the spin-spin and electrical repulsions. Exact candidate solutions were constructed, but it is unclear whether they are physically acceptable. These solutions were obtained by assuming a particular behaviour on the symmetry axis. However, it was not known whether the assumed form of the axis data covers the general case or whether data of some other type need to be considered as well. By studying a boundary value problem for the axisymmetric and stationary Einstein-Maxwell equations, we address this question and derive the most general form of permissible axis potentials for possible equilibrium configurations. |
gr-qc/9606027 | BS Kay | Claes R Cramer (York), Bernard S. Kay (York) | Stress-Energy Must be Singular on the Misner Space Horizon even for
Automorphic Fields | 10 pages, LaTeX, 2 postscript figures | Class.Quant.Grav.13:L143-L149,1996 | 10.1088/0264-9381/13/12/002 | null | gr-qc | null | We use the image sum method to reproduce Sushkov's result that for a massless
automorphic field on the initial globally hyperbolic region $IGH$ of Misner
space, one can always find a special value of the automorphic parameter
$\alpha$ such that the renormalized expectation value
$\langle\alpha|T_{ab}|\alpha\rangle$ in the {\it Sushkov state}
``$\langle\alpha|\cdot|\alpha\rangle$'' (i.e. the automorphic generalization of
the Hiscock-Konkowski state) vanishes. However, we shall prove by elementary
methods that the conclusions of a recent general theorem of
Kay-Radzikowski-Wald apply in this case. I.e. for any value of $\alpha$ and any
neighbourhood $N$ of any point $b$ on the chronology horizon there exists at
least one pair of non-null related points $(x,x') \in (N\cap IGH)\times (N\cap
IGH)$ such that the renormalized two-point function of an automorphic field
$G^\alpha_{\rm ren}(x,x')$ in the Sushkov state is singular. In consequence
$\langle\alpha|T_{ab}|\alpha\rangle$ (as well as other renormalized expectation
values such as $\langle\alpha|\phi^2|\alpha\rangle$) is necessarily singular
{\it on} the chronology horizon. We point out that a similar situation (i.e.
singularity {\it on} the chronology horizon) holds for states on Gott space and
Grant space.
| [
{
"created": "Thu, 13 Jun 1996 11:46:51 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Cramer",
"Claes R",
"",
"York"
],
[
"Kay",
"Bernard S.",
"",
"York"
]
] | We use the image sum method to reproduce Sushkov's result that for a massless automorphic field on the initial globally hyperbolic region $IGH$ of Misner space, one can always find a special value of the automorphic parameter $\alpha$ such that the renormalized expectation value $\langle\alpha|T_{ab}|\alpha\rangle$ in the {\it Sushkov state} ``$\langle\alpha|\cdot|\alpha\rangle$'' (i.e. the automorphic generalization of the Hiscock-Konkowski state) vanishes. However, we shall prove by elementary methods that the conclusions of a recent general theorem of Kay-Radzikowski-Wald apply in this case. I.e. for any value of $\alpha$ and any neighbourhood $N$ of any point $b$ on the chronology horizon there exists at least one pair of non-null related points $(x,x') \in (N\cap IGH)\times (N\cap IGH)$ such that the renormalized two-point function of an automorphic field $G^\alpha_{\rm ren}(x,x')$ in the Sushkov state is singular. In consequence $\langle\alpha|T_{ab}|\alpha\rangle$ (as well as other renormalized expectation values such as $\langle\alpha|\phi^2|\alpha\rangle$) is necessarily singular {\it on} the chronology horizon. We point out that a similar situation (i.e. singularity {\it on} the chronology horizon) holds for states on Gott space and Grant space. |
gr-qc/9805053 | Dan Baleanu | Dumitru Baleanu (Bogoliubov LTPH, Dubna,Russia) | Symmetries of the dual metrics | 10 pages,LATEX, content revised | null | null | null | gr-qc | null | In this paper the symmetries of the dual manifold were investigated. We found
the conditions when the manifold and its dual admit the same Killing vectors
and Killing-Yano tensors. In the case of an Einstein's metric $g_{\mu\nu}$ the
corresponding equations for its dual were found. The examples of Kerr-Newman
geometry and the separable coordinates in 1+1 dimensions were analyzed in
details.
| [
{
"created": "Thu, 14 May 1998 00:38:46 GMT",
"version": "v1"
},
{
"created": "Sun, 31 May 1998 23:50:34 GMT",
"version": "v2"
},
{
"created": "Sun, 27 Feb 2000 15:17:11 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Baleanu",
"Dumitru",
"",
"Bogoliubov LTPH, Dubna,Russia"
]
] | In this paper the symmetries of the dual manifold were investigated. We found the conditions when the manifold and its dual admit the same Killing vectors and Killing-Yano tensors. In the case of an Einstein's metric $g_{\mu\nu}$ the corresponding equations for its dual were found. The examples of Kerr-Newman geometry and the separable coordinates in 1+1 dimensions were analyzed in details. |
1101.1641 | Yurii Ignatyev | Yu.G. Ignatyev | Gravimagnetic shock waves and gravitational-wave experiments | 31 pages, 16 figures, 3 tables, 24 references | Grav.Cosmol.2:345-360,1996 | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Causes of the unsatisfactory condition of the gravitational-wave experiments
are discussed and a new outlook at the detection of gravitational waves of
astrophysical origin is proposed. It is shown that there are strong grounds for
identifying the so-called giant pulses in the pulsar NP 0532 radiation with
gravimagnetic shock waves (GMSW) excited in the neutron star magnetosphere by
sporadic gravitational radiation of this pulsar.
| [
{
"created": "Sun, 9 Jan 2011 14:44:26 GMT",
"version": "v1"
}
] | 2015-03-17 | [
[
"Ignatyev",
"Yu. G.",
""
]
] | Causes of the unsatisfactory condition of the gravitational-wave experiments are discussed and a new outlook at the detection of gravitational waves of astrophysical origin is proposed. It is shown that there are strong grounds for identifying the so-called giant pulses in the pulsar NP 0532 radiation with gravimagnetic shock waves (GMSW) excited in the neutron star magnetosphere by sporadic gravitational radiation of this pulsar. |
1704.07825 | Saulo Carneiro | S. Carneiro and H. A. Borges | Dynamical system analysis of interacting models | 6 pages, 3 figures. A section was added with an analysis of
structures growth rate and peculiar velocities. To appear in General
Relativity and Gravitation | Gen Relativ Gravit (2018) 50:1; Erratum: Gen Relativ Gravit (2018)
50: 129 | 10.1007/s10714-017-2322-8 10.1007/s10714-018-2458-1 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We perform a dynamical system analysis of a cosmological model with linear
dependence between the vacuum density and the Hubble parameter, with
constant-rate creation of dark matter. We show that the de Sitter spacetime is
an asymptotically stable critical point, future limit of any expanding
solution. Our analysis also shows that the Minkowski spacetime is an unstable
critical point, which eventually collapses to a singularity. In this way, such
a prescription for the vacuum decay not only predicts the correct future de
Sitter limit, but also forbids the existence of a stable Minkowski universe. We
also study the effect of matter creation on the growth of structures and their
peculiar velocities, showing that it is inside the current errors of redshift
space distortions observations.
| [
{
"created": "Tue, 25 Apr 2017 13:13:29 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Nov 2017 15:08:25 GMT",
"version": "v2"
}
] | 2018-09-25 | [
[
"Carneiro",
"S.",
""
],
[
"Borges",
"H. A.",
""
]
] | We perform a dynamical system analysis of a cosmological model with linear dependence between the vacuum density and the Hubble parameter, with constant-rate creation of dark matter. We show that the de Sitter spacetime is an asymptotically stable critical point, future limit of any expanding solution. Our analysis also shows that the Minkowski spacetime is an unstable critical point, which eventually collapses to a singularity. In this way, such a prescription for the vacuum decay not only predicts the correct future de Sitter limit, but also forbids the existence of a stable Minkowski universe. We also study the effect of matter creation on the growth of structures and their peculiar velocities, showing that it is inside the current errors of redshift space distortions observations. |
2312.17198 | Athanasios Bakopoulos | Athanasios Bakopoulos, Nikos Chatzifotis, Theodoros Nakas | Compact objects with primary hair in shift and parity symmetric beyond
Horndeski gravities | 14 pages, 2 figures, typos corrected, matches published version | Phys. Rev. D 110, (2024) 024044 | 10.1103/PhysRevD.110.024044 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we delve into the model of the shift symmetric and
parity-preserving Beyond Horndeski theory in all its generality. We present an
explicit algorithm to extract static and spherically symmetric black holes with
primary scalar charge adhering to the conservation of the Noether current
emanating from the shift symmetry. We show that when the functionals $G_2$ and
$G_4$ of the theory are linearly dependent, analytic homogeneous black-hole
solutions exist, which can become regular by virtue of the primary charge
contribution. Such geometries can easily enjoy the preservation of the Weak
Energy Conditions, elevating them into healthier compact objects than most
hairy black holes in modified theories of gravity. Finally, we revisit the
concept of disformal transformations as a solution-generating mechanism and
discuss the case of generic $G_2$ and $G_4$ functionals.
| [
{
"created": "Thu, 28 Dec 2023 18:31:03 GMT",
"version": "v1"
},
{
"created": "Fri, 19 Jul 2024 16:19:33 GMT",
"version": "v2"
}
] | 2024-07-22 | [
[
"Bakopoulos",
"Athanasios",
""
],
[
"Chatzifotis",
"Nikos",
""
],
[
"Nakas",
"Theodoros",
""
]
] | In this work, we delve into the model of the shift symmetric and parity-preserving Beyond Horndeski theory in all its generality. We present an explicit algorithm to extract static and spherically symmetric black holes with primary scalar charge adhering to the conservation of the Noether current emanating from the shift symmetry. We show that when the functionals $G_2$ and $G_4$ of the theory are linearly dependent, analytic homogeneous black-hole solutions exist, which can become regular by virtue of the primary charge contribution. Such geometries can easily enjoy the preservation of the Weak Energy Conditions, elevating them into healthier compact objects than most hairy black holes in modified theories of gravity. Finally, we revisit the concept of disformal transformations as a solution-generating mechanism and discuss the case of generic $G_2$ and $G_4$ functionals. |
2005.12804 | Vasilis Oikonomou | S.D. Odintsov, V.K. Oikonomou | Inflationary Attractors in $F(R)$ Gravity | PLB Accepted | null | 10.1016/j.physletb.2020.135576 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this letter we shall demonstrate that the viable $F(R)$ gravities can be
classified mainly into two classes of inflationary attractors, either the $R^2$
attractors or the $\alpha$-attractors. To show this, we shall derive the most
general relation between the tensor-to-scalar ratio $r$ and the spectral index
of primordial curvature perturbations $n_s$, namely the $r-n_s$ relation, by
assuming that the slow-roll condition constrains the values of the slow-roll
indices. As we show, the relation between the tensor-to-scalar ratio and the
spectral index of the primordial curvature perturbations has the form $r\simeq
\frac{48 (1-n_s)^2}{(4-x)^2}$, where the dimensionless parameter $x$ contains
higher derivatives of the $F(R)$ gravity function with respect to the Ricci
scalar, and it is a function of the $e$-foldings number $N$ and may also be a
function of the free parameters of the various $F(R)$ gravity models. For
$F(R)$ gravities which have a spectral index compatible with the observational
data and also yield $x\ll 1$, these belong to the $R^2$-type of attractors,
with $r\sim 3 (1-n_s)^2$, and these are viable theories. Moreover, in the case
that $x$ takes larger values in specific ranges and is constant for a given
$F(R)$ gravity, the resulting $r-n_s$ relation has the form $r\sim 3 \alpha
(1-n_s)^2$, where $\alpha$ is a constant. Thus we conclude that the viable
$F(R)$ gravities may be classified into two limiting types of $r-n_s$
relations, one identical to the $R^2$ model at leading order in $x$, and one
similar to the $\alpha$-attractors $r-n_s$ relation, for the $F(R)$ gravity
models that yield $x$ constant. Finally, we also discuss the case that $x$ is
not constant.
| [
{
"created": "Tue, 26 May 2020 15:38:42 GMT",
"version": "v1"
}
] | 2020-08-26 | [
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
]
] | In this letter we shall demonstrate that the viable $F(R)$ gravities can be classified mainly into two classes of inflationary attractors, either the $R^2$ attractors or the $\alpha$-attractors. To show this, we shall derive the most general relation between the tensor-to-scalar ratio $r$ and the spectral index of primordial curvature perturbations $n_s$, namely the $r-n_s$ relation, by assuming that the slow-roll condition constrains the values of the slow-roll indices. As we show, the relation between the tensor-to-scalar ratio and the spectral index of the primordial curvature perturbations has the form $r\simeq \frac{48 (1-n_s)^2}{(4-x)^2}$, where the dimensionless parameter $x$ contains higher derivatives of the $F(R)$ gravity function with respect to the Ricci scalar, and it is a function of the $e$-foldings number $N$ and may also be a function of the free parameters of the various $F(R)$ gravity models. For $F(R)$ gravities which have a spectral index compatible with the observational data and also yield $x\ll 1$, these belong to the $R^2$-type of attractors, with $r\sim 3 (1-n_s)^2$, and these are viable theories. Moreover, in the case that $x$ takes larger values in specific ranges and is constant for a given $F(R)$ gravity, the resulting $r-n_s$ relation has the form $r\sim 3 \alpha (1-n_s)^2$, where $\alpha$ is a constant. Thus we conclude that the viable $F(R)$ gravities may be classified into two limiting types of $r-n_s$ relations, one identical to the $R^2$ model at leading order in $x$, and one similar to the $\alpha$-attractors $r-n_s$ relation, for the $F(R)$ gravity models that yield $x$ constant. Finally, we also discuss the case that $x$ is not constant. |
gr-qc/0310023 | Dr. Anirudh Pradhan | Anirudh Pradhan, Purnima Pandey, G.P. Singh and R.V. Deshpandey | Causal Bulk Viscous LRS Bianchi I Models With Variable Gravitational and
Cosmological "Constant" | 9 pages, LaTex, typos added | SpacetimeandSubstance6:116-120,2005 | null | null | gr-qc | null | In this paper we have investigated an LRS Bianchi I anisotropic cosmological
model of the universe by taking time varying $G$ and $\Lambda$ in the presence
of bulk viscous fluid source described by full causal non-equilibrium
thermodynamics. We obtain a cosmological constant as a decreasing function of
time and for $m, n > 0$, the value of cosmological ``constant'' for this model
is found to be small and positive which is supported by the results from recent
supernovae observations.
| [
{
"created": "Sat, 4 Oct 2003 06:13:35 GMT",
"version": "v1"
},
{
"created": "Sat, 23 Jul 2005 04:57:11 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Pradhan",
"Anirudh",
""
],
[
"Pandey",
"Purnima",
""
],
[
"Singh",
"G. P.",
""
],
[
"Deshpandey",
"R. V.",
""
]
] | In this paper we have investigated an LRS Bianchi I anisotropic cosmological model of the universe by taking time varying $G$ and $\Lambda$ in the presence of bulk viscous fluid source described by full causal non-equilibrium thermodynamics. We obtain a cosmological constant as a decreasing function of time and for $m, n > 0$, the value of cosmological ``constant'' for this model is found to be small and positive which is supported by the results from recent supernovae observations. |
1606.03282 | Ryan McManus | Ryan McManus, Lucas Lombriser, Jorge Pe\~narrubia | Finding Horndeski theories with Einstein gravity limits | 33 pages | JCAP11(2016)006 | 10.1088/1475-7516/2016/11/006 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Horndeski action is the most general scalar-tensor theory with at most
second-order derivatives in the equations of motion, thus evading Ostrogradsky
instabilities and making it of interest when modifying gravity at large scales.
To pass local tests of gravity, these modifications predominantly rely on
nonlinear screening mechanisms that recover Einstein's Theory of General
Relativity in regions of high density. We derive a set of conditions on the
four free functions of the Horndeski action that examine whether a specific
model embedded in the action possesses an Einstein gravity limit or not. For
this purpose, we develop a new and surprisingly simple scaling method that
identifies dominant terms in the equations of motion by considering formal
limits of the couplings that enter through the new terms in the modified
action. This enables us to find regimes where nonlinear terms dominate and
Einstein's field equations are recovered to leading order. Together with an
efficient approximation of the scalar field profile, one can then further
evaluate whether these limits can be attributed to a genuine screening effect.
For illustration, we apply the analysis to both a cubic galileon and a
chameleon model as well as to Brans-Dicke theory. Finally, we emphasise that
the scaling method also provides a natural approach for performing
post-Newtonian expansions in screened regimes.
| [
{
"created": "Fri, 10 Jun 2016 14:26:58 GMT",
"version": "v1"
}
] | 2016-12-07 | [
[
"McManus",
"Ryan",
""
],
[
"Lombriser",
"Lucas",
""
],
[
"Peñarrubia",
"Jorge",
""
]
] | The Horndeski action is the most general scalar-tensor theory with at most second-order derivatives in the equations of motion, thus evading Ostrogradsky instabilities and making it of interest when modifying gravity at large scales. To pass local tests of gravity, these modifications predominantly rely on nonlinear screening mechanisms that recover Einstein's Theory of General Relativity in regions of high density. We derive a set of conditions on the four free functions of the Horndeski action that examine whether a specific model embedded in the action possesses an Einstein gravity limit or not. For this purpose, we develop a new and surprisingly simple scaling method that identifies dominant terms in the equations of motion by considering formal limits of the couplings that enter through the new terms in the modified action. This enables us to find regimes where nonlinear terms dominate and Einstein's field equations are recovered to leading order. Together with an efficient approximation of the scalar field profile, one can then further evaluate whether these limits can be attributed to a genuine screening effect. For illustration, we apply the analysis to both a cubic galileon and a chameleon model as well as to Brans-Dicke theory. Finally, we emphasise that the scaling method also provides a natural approach for performing post-Newtonian expansions in screened regimes. |
2102.12747 | Geoffrey Comp\`ere | Geoffrey Comp\`ere and Lorenzo K\"uchler | Self-consistent adiabatic inspiral and transition motion | Matches the Erratum version in Physical Review Letters, 6 pages | Phys. Rev. Lett. 126, 241106 (2021) | 10.1103/PhysRevLett.126.241106 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The transition motion of a point particle around the last stable orbit of
Kerr is described at leading order in the transition-timescale expansion.
Taking systematically into account all self-force effects, we prove that the
transition motion is still described by the Painlev\'e transcendent equation of
the first kind. Using an asymptotically matched expansions scheme, we
consistently match the quasi-circular adiabatic inspiral with the transition
motion. The matching requires us to take into account the secular change of
angular velocity due to radiation reaction during the adiabatic inspiral.
| [
{
"created": "Thu, 25 Feb 2021 09:17:45 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Jun 2021 09:43:53 GMT",
"version": "v2"
},
{
"created": "Thu, 16 Dec 2021 14:48:01 GMT",
"version": "v3"
}
] | 2021-12-17 | [
[
"Compère",
"Geoffrey",
""
],
[
"Küchler",
"Lorenzo",
""
]
] | The transition motion of a point particle around the last stable orbit of Kerr is described at leading order in the transition-timescale expansion. Taking systematically into account all self-force effects, we prove that the transition motion is still described by the Painlev\'e transcendent equation of the first kind. Using an asymptotically matched expansions scheme, we consistently match the quasi-circular adiabatic inspiral with the transition motion. The matching requires us to take into account the secular change of angular velocity due to radiation reaction during the adiabatic inspiral. |
2311.03209 | Ernesto Nungesser | Ho Lee and Ernesto Nungesser | Future global existence of homogeneous solutions to the
Einstein-Boltzmann system with soft potentials | 40 pages, accepted in JDE version | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the Cauchy problem for the Einstein-Boltzmann system with soft
potentials in a cosmological setting. We assume the Bianchi I symmetry to
describe a spatially homogeneous, but anisotropic universe and consider a
cosmological constant $ \Lambda > 0 $ to describe an accelerated expansion of
the universe. For the Boltzmann equation we introduce a new weight function and
apply the method of Illner and Shinbrot to obtain the future global existence
of spatially homogeneous, small solutions. For the Einstein equations we assume
that the initial value of the Hubble variable is close to $ ( \Lambda / 3 )^{ 1
/ 2 } $. We obtain the future global existence and asymptotic behavior of
spatially homogeneous solutions to the Einstein-Boltzmann system with soft
potentials.
| [
{
"created": "Mon, 6 Nov 2023 15:52:16 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Jul 2024 13:31:16 GMT",
"version": "v2"
}
] | 2024-07-11 | [
[
"Lee",
"Ho",
""
],
[
"Nungesser",
"Ernesto",
""
]
] | We study the Cauchy problem for the Einstein-Boltzmann system with soft potentials in a cosmological setting. We assume the Bianchi I symmetry to describe a spatially homogeneous, but anisotropic universe and consider a cosmological constant $ \Lambda > 0 $ to describe an accelerated expansion of the universe. For the Boltzmann equation we introduce a new weight function and apply the method of Illner and Shinbrot to obtain the future global existence of spatially homogeneous, small solutions. For the Einstein equations we assume that the initial value of the Hubble variable is close to $ ( \Lambda / 3 )^{ 1 / 2 } $. We obtain the future global existence and asymptotic behavior of spatially homogeneous solutions to the Einstein-Boltzmann system with soft potentials. |
gr-qc/9308030 | Yasusada Nambu | Yasusada Nambu | Fate of Inhomogeneity in Schwarzschild-deSitter Space-time | 6pages | Phys.Lett.B323:13-17,1994 | 10.1016/0370-2693(94)00034-4 | DNPU-93-32 | gr-qc astro-ph | null | We investigate the global structure of the space time with a spherically
symmetric inhomogeneity using a metric junction, and classify all possible
types. We found that a motion with a negative gravitational mass is possible
although the energy condition of the matter is not violated. Using the result,
formation of black hole and worm hole during the inflationary era is discussed.
| [
{
"created": "Fri, 27 Aug 1993 10:30:18 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Nambu",
"Yasusada",
""
]
] | We investigate the global structure of the space time with a spherically symmetric inhomogeneity using a metric junction, and classify all possible types. We found that a motion with a negative gravitational mass is possible although the energy condition of the matter is not violated. Using the result, formation of black hole and worm hole during the inflationary era is discussed. |
2208.07710 | Alireza Amani | S. Ganjizadeh, Alireza Amani, and M. A. Ramzanpour | Observational Hubble parameter data constraints on the interactive model
of $f(T)$ gravity with particle creation | 19 pages, 7 figures, Accepted in Chinese Physics C | null | 10.1088/1674-1137/ac8c22 | CPC-2022-0297.R2 | gr-qc | http://creativecommons.org/licenses/by-nc-sa/4.0/ | In this paper, we consider an open system from the thermodynamic perspective
for an adiabatic FRW universe model in which particle creation occurs within
the system. In that case, the modified continuity equation is obtained and then
we correspond it to the continuity equation of $f(T)$ gravity. So, we take
$f(T)$ gravity with the viscous fluid in flat-FRW metric, in which $T$ is the
torsion scalar. We consider the contents of the universe to be dark matter and
dark energy and consider an interaction term between them. The interesting
point of this study is that we make equivalent the modified continuity equation
resulting from the particle creation with the matter continuity equation
resulting from $f(T)$ gravity. The result of this evaluation creates a
relationship between the number of particles and the scale factor. In what
follows, we write the corresponding cosmological parameters in terms of the
number of particles and also reconstruct the number of particles in terms of
the redshift parameter, then We parameterize the Hubble parameter derived from
power-law cosmology with 51 data from the Hubble observational parameter. Next,
we plot the corresponding cosmological parameters for the dark energy in terms
of the redshift to investigate the accelerated expansion of the universe. In
addition, by using the sound speed parameter, we discuss the stability analysis
and instability analysis of the present model in different eras of the
universe. Finally, we plot the density parameter values for dark energy and
dark matter in terms of the redshift parameter.
| [
{
"created": "Sat, 13 Aug 2022 20:35:15 GMT",
"version": "v1"
}
] | 2022-12-14 | [
[
"Ganjizadeh",
"S.",
""
],
[
"Amani",
"Alireza",
""
],
[
"Ramzanpour",
"M. A.",
""
]
] | In this paper, we consider an open system from the thermodynamic perspective for an adiabatic FRW universe model in which particle creation occurs within the system. In that case, the modified continuity equation is obtained and then we correspond it to the continuity equation of $f(T)$ gravity. So, we take $f(T)$ gravity with the viscous fluid in flat-FRW metric, in which $T$ is the torsion scalar. We consider the contents of the universe to be dark matter and dark energy and consider an interaction term between them. The interesting point of this study is that we make equivalent the modified continuity equation resulting from the particle creation with the matter continuity equation resulting from $f(T)$ gravity. The result of this evaluation creates a relationship between the number of particles and the scale factor. In what follows, we write the corresponding cosmological parameters in terms of the number of particles and also reconstruct the number of particles in terms of the redshift parameter, then We parameterize the Hubble parameter derived from power-law cosmology with 51 data from the Hubble observational parameter. Next, we plot the corresponding cosmological parameters for the dark energy in terms of the redshift to investigate the accelerated expansion of the universe. In addition, by using the sound speed parameter, we discuss the stability analysis and instability analysis of the present model in different eras of the universe. Finally, we plot the density parameter values for dark energy and dark matter in terms of the redshift parameter. |
2304.12831 | Anna Puecher | Maria Concetta Tringali, Anna Puecher, Claudia Lazzaro, Riccardo
Ciolfi, Marco Drago, Bruno Giacomazzo, Gabriele Vedovato and Giovanni Andrea
Prodi | Minimally modeled characterization method of postmerger gravitational
wave emission from binary neutron star coalescences | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves emitted during the coalescence of binary neutron star
systems carry information about the equation of state describing the extremely
dense matter inside neutron stars. In particular, the equation of state
determines the fate of the binary after the merger: a prompt collapse to black
hole, or the formation of a neutron star remnant that is either stable or
survives up to a few seconds before collapsing to a black hole. Determining the
evolution of a binary neutron star system will therefore place strong
constraints on the equation of state. We present a morphology-independent
method, developed in the framework of the coherentWaveBurst analysis of signals
from ground-based interferometric detectors of gravitational waves. The method
characterizes the time-frequency postmerger gravitational-wave emission from a
binary neutron star system, and determines whether, after the merger, it formed
a remnant neutron star or promptly collapsed to a black hole. We measure the
following quantities to characterize the postmerger emission: ratio of signal
energies and match of luminosity profile in different frequency bands, weighted
central frequency and bandwidth. From these quantities, based on the study of
signals simulated through injections of numerical relativity waveforms, we
build a statistics to discriminate between the different scenarios after the
merger. Finally, we test our method on a set of signals simulated with new
models, to estimate its efficiency as a function of the source distance.
| [
{
"created": "Tue, 25 Apr 2023 14:02:15 GMT",
"version": "v1"
}
] | 2023-04-26 | [
[
"Tringali",
"Maria Concetta",
""
],
[
"Puecher",
"Anna",
""
],
[
"Lazzaro",
"Claudia",
""
],
[
"Ciolfi",
"Riccardo",
""
],
[
"Drago",
"Marco",
""
],
[
"Giacomazzo",
"Bruno",
""
],
[
"Vedovato",
"Gabriele",
""
],
[
"Prodi",
"Giovanni Andrea",
""
]
] | Gravitational waves emitted during the coalescence of binary neutron star systems carry information about the equation of state describing the extremely dense matter inside neutron stars. In particular, the equation of state determines the fate of the binary after the merger: a prompt collapse to black hole, or the formation of a neutron star remnant that is either stable or survives up to a few seconds before collapsing to a black hole. Determining the evolution of a binary neutron star system will therefore place strong constraints on the equation of state. We present a morphology-independent method, developed in the framework of the coherentWaveBurst analysis of signals from ground-based interferometric detectors of gravitational waves. The method characterizes the time-frequency postmerger gravitational-wave emission from a binary neutron star system, and determines whether, after the merger, it formed a remnant neutron star or promptly collapsed to a black hole. We measure the following quantities to characterize the postmerger emission: ratio of signal energies and match of luminosity profile in different frequency bands, weighted central frequency and bandwidth. From these quantities, based on the study of signals simulated through injections of numerical relativity waveforms, we build a statistics to discriminate between the different scenarios after the merger. Finally, we test our method on a set of signals simulated with new models, to estimate its efficiency as a function of the source distance. |
2212.06745 | Naresh Dadhich | Naresh Dadhich | On the equilibrium of the Buchdahl star | 6 pages, Title changed, abstract modified. Overall arguements and
analysis revamped and sharpened. New references added. Main result remains
unaltered | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Buchdahl star is the limiting compactness (which is indicated by
sturation of the Buchdahl bound) object without horizon. It is in general
defined by the potential felt by radially falling timelike particle, $\Phi(R) =
4/9$, in the field of a static object. On the other hand black hole is
similarly characterized by $\Phi(R)=1/2$ which defines the horizon. Further it
is remarkable that in terms of gravitational and non-gravitational energy, the
Buchdahl star is alternatively defined when gravitational energy is half of
non-gravitational energy while the black hole when the two are equal. When an
infinitely dispersed system of bare mass $M$ collapses under its own gravity to
radius $R$, total energy encompassed inside $R$ would be
$E_{tot}(R)=M-E_{grav}(R)$. That is, energy inside the object is increased by
the amount equivalent to gravitational energy lying outside and which manifests
as internal energy in the interior. If the interior consists of free particles
in motion interacting only through gravity as is the case for the Vlasov
kinetic matter, internal (gravitational) energy could be thought of as kinetic
energy and the defining condition for the Buchdahl star would then be kinetic
(gravitational) energy equal to half of non-gravitational (potential) energy.
Consequently it could be envisaged that equilibrium of the Buchdahl star
interior is governed by the celebrated Virial theorem like relation (average
kinetic energy equal to half of average potential energy). On the same count
the black hole equilibrium is governed by equality of gravitational and
non-gravitational energy !
| [
{
"created": "Sun, 11 Dec 2022 12:20:55 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Dec 2022 07:04:48 GMT",
"version": "v2"
},
{
"created": "Sat, 4 Mar 2023 15:49:31 GMT",
"version": "v3"
},
{
"created": "Thu, 9 Nov 2023 06:25:55 GMT",
"version": "v4"
}
] | 2023-11-10 | [
[
"Dadhich",
"Naresh",
""
]
] | The Buchdahl star is the limiting compactness (which is indicated by sturation of the Buchdahl bound) object without horizon. It is in general defined by the potential felt by radially falling timelike particle, $\Phi(R) = 4/9$, in the field of a static object. On the other hand black hole is similarly characterized by $\Phi(R)=1/2$ which defines the horizon. Further it is remarkable that in terms of gravitational and non-gravitational energy, the Buchdahl star is alternatively defined when gravitational energy is half of non-gravitational energy while the black hole when the two are equal. When an infinitely dispersed system of bare mass $M$ collapses under its own gravity to radius $R$, total energy encompassed inside $R$ would be $E_{tot}(R)=M-E_{grav}(R)$. That is, energy inside the object is increased by the amount equivalent to gravitational energy lying outside and which manifests as internal energy in the interior. If the interior consists of free particles in motion interacting only through gravity as is the case for the Vlasov kinetic matter, internal (gravitational) energy could be thought of as kinetic energy and the defining condition for the Buchdahl star would then be kinetic (gravitational) energy equal to half of non-gravitational (potential) energy. Consequently it could be envisaged that equilibrium of the Buchdahl star interior is governed by the celebrated Virial theorem like relation (average kinetic energy equal to half of average potential energy). On the same count the black hole equilibrium is governed by equality of gravitational and non-gravitational energy ! |
1711.09963 | Nikolaos Kalogeropoulos | Nikolaos Kalogeropoulos | Systolic aspects of black hole entropy | 20 pages. No figures. LaTeX2e. This version: change of the author's
affiliation. Other minor changes. To be published in a Special Issue of
"Axioms" on "Theory and Mathematical Aspects of Black Holes" | Axioms 9(1), 30 (2020) | null | null | gr-qc cond-mat.stat-mech hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We attempt to provide a mesoscopic treatment of the origin of black hole
entropy in (3+1)-dimensional spacetimes. We ascribe this entropy to the
non-trivial topology of the space-like sections $\Sigma$ of the horizon. This
is not forbidden by topological censorship, since all the known energy
inequalities needed to prove the spherical topology of $\Sigma$ are violated in
quantum theory. We choose the systoles of $\Sigma$ to encode its complexity,
which gives rise to the black hole entropy. We present hand-waving reasons why
the entropy of the black hole can be considered as a function of the volume
entropy of $\Sigma$. We focus on the limiting case of $\Sigma$ having a large
genus.
| [
{
"created": "Mon, 27 Nov 2017 20:13:16 GMT",
"version": "v1"
},
{
"created": "Fri, 20 Apr 2018 07:23:14 GMT",
"version": "v2"
},
{
"created": "Wed, 11 Mar 2020 13:13:10 GMT",
"version": "v3"
}
] | 2020-03-18 | [
[
"Kalogeropoulos",
"Nikolaos",
""
]
] | We attempt to provide a mesoscopic treatment of the origin of black hole entropy in (3+1)-dimensional spacetimes. We ascribe this entropy to the non-trivial topology of the space-like sections $\Sigma$ of the horizon. This is not forbidden by topological censorship, since all the known energy inequalities needed to prove the spherical topology of $\Sigma$ are violated in quantum theory. We choose the systoles of $\Sigma$ to encode its complexity, which gives rise to the black hole entropy. We present hand-waving reasons why the entropy of the black hole can be considered as a function of the volume entropy of $\Sigma$. We focus on the limiting case of $\Sigma$ having a large genus. |
1311.6841 | Florian Girelli | Ma\"it\'e Dupuis, Florian Girelli | Observables in Loop Quantum Gravity with a cosmological constant | 29 pages, 2 figures | Phys. Rev. D 90, 104037 (2014) | 10.1103/PhysRevD.90.104037 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An open issue in loop quantum gravity (LQG) is the introduction of a
non-vanishing cosmological constant $\Lambda$. In 3d, Chern-Simons theory
provides some guiding lines: $\Lambda$ appears in the quantum deformation of
the gauge group. The Turaev-Viro model, which is an example of spin foam model
is also defined in terms of a quantum group. By extension, it is believed that
in 4d, a quantum group structure could encode the presence of $\Lambda\neq0$.
In this article, we introduce by hand the quantum group
$\mathcal{U}_{q}(\mathfrak{su}(2))$ into the LQG framework, that is we deal
with $\mathcal{U}_{q}(\mathfrak{su}(2))$-spin networks. We explore some of the
consequences, focusing in particular on the structure of the observables. Our
fundamental tools are tensor operators for $\mathcal{U}_{q}(\mathfrak{su}(2))$.
We review their properties and give an explicit realization of the spinorial
and vectorial ones. We construct the generalization of the U($n$) formalism in
this deformed case, which is given by the quantum group
$\mathcal{U}_{q}(\mathfrak{u}(n))$. We are then able to build geometrical
observables, such as the length, area or angle operators ... We show that these
operators characterize a quantum discrete hyperbolic geometry in the 3d LQG
case. Our results confirm that the use of quantum group in LQG can be a tool to
introduce a non-zero cosmological constant into the theory.
| [
{
"created": "Tue, 26 Nov 2013 23:05:27 GMT",
"version": "v1"
}
] | 2014-12-03 | [
[
"Dupuis",
"Maïté",
""
],
[
"Girelli",
"Florian",
""
]
] | An open issue in loop quantum gravity (LQG) is the introduction of a non-vanishing cosmological constant $\Lambda$. In 3d, Chern-Simons theory provides some guiding lines: $\Lambda$ appears in the quantum deformation of the gauge group. The Turaev-Viro model, which is an example of spin foam model is also defined in terms of a quantum group. By extension, it is believed that in 4d, a quantum group structure could encode the presence of $\Lambda\neq0$. In this article, we introduce by hand the quantum group $\mathcal{U}_{q}(\mathfrak{su}(2))$ into the LQG framework, that is we deal with $\mathcal{U}_{q}(\mathfrak{su}(2))$-spin networks. We explore some of the consequences, focusing in particular on the structure of the observables. Our fundamental tools are tensor operators for $\mathcal{U}_{q}(\mathfrak{su}(2))$. We review their properties and give an explicit realization of the spinorial and vectorial ones. We construct the generalization of the U($n$) formalism in this deformed case, which is given by the quantum group $\mathcal{U}_{q}(\mathfrak{u}(n))$. We are then able to build geometrical observables, such as the length, area or angle operators ... We show that these operators characterize a quantum discrete hyperbolic geometry in the 3d LQG case. Our results confirm that the use of quantum group in LQG can be a tool to introduce a non-zero cosmological constant into the theory. |
1608.08359 | Aloke Sinha | Aloke Kumar Sinha | Thermal Fluctuations Of Stable Quantum ADS Kerr-Newman Black Hole | arXiv admin note: substantial text overlap with arXiv:1512.04181 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We have already derived the Criteria for thermal stability of charged
rotating black holes in any dimension , for horizon areas that are large
relative to the Planck area (in these dimensions). The derivation is done by
using results of loop quantum gravity and equilibrium statistical mechanics of
the Grand Canonical ensemble. It is also shown there [1] that in four
dimensional spacetime, ADS Kerr-Newman Black hole is thermally stable. In this
paper, the expectation values of fluctuations of horizon area,charge and
angular momentum of stable ADS black hole are calculated. Interestingly, it is
found that leading order fluctuations of charge and angular momentum , in large
horizon area limit , are independent of the values of charge and angular
momentum at equilibrium.
| [
{
"created": "Tue, 30 Aug 2016 08:18:40 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Sinha",
"Aloke Kumar",
""
]
] | We have already derived the Criteria for thermal stability of charged rotating black holes in any dimension , for horizon areas that are large relative to the Planck area (in these dimensions). The derivation is done by using results of loop quantum gravity and equilibrium statistical mechanics of the Grand Canonical ensemble. It is also shown there [1] that in four dimensional spacetime, ADS Kerr-Newman Black hole is thermally stable. In this paper, the expectation values of fluctuations of horizon area,charge and angular momentum of stable ADS black hole are calculated. Interestingly, it is found that leading order fluctuations of charge and angular momentum , in large horizon area limit , are independent of the values of charge and angular momentum at equilibrium. |
1608.05963 | Jose Luis Jaramillo | Jos\'e Luis Jaramillo | A perspective on Black Hole Horizons from the Quantum Charged Particle | 6 pages, no figures, contribution to the proceedings volume of the
Spanish Relativity Meeting ERE2014: "Almost 100 years after Einstein
Revolution", Valencia, Spain, 1-5 September 2014 | J.Phys.Conf.Ser. 600 (2015) no.1, 012037 | 10.1088/1742-6596/600/1/012037 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black hole apparent horizons possess a natural notion of stability, whose
spectral characterization can be related to the problem of the stationary
quantum charged particle. Such mathematical relation leads to an "analyticity
conjecture" on the dependence of the spectral properties on a complex
"fine-structure-constant" parameter, that can reduce the study of the spectrum
of the (non-selfadjoint) MOTS-stability operator to that of the (selfadjoint)
Hamiltonian of the quantum charged particle. Moreover, this perspective might
open an avenue to the spinorial treatment of apparent horizon (MOTS-)stability
and to the introduction of semiclassical tools to explore some of the
qualitative aspects of this black hole spectral problem.
| [
{
"created": "Sun, 21 Aug 2016 16:38:55 GMT",
"version": "v1"
}
] | 2016-08-23 | [
[
"Jaramillo",
"José Luis",
""
]
] | Black hole apparent horizons possess a natural notion of stability, whose spectral characterization can be related to the problem of the stationary quantum charged particle. Such mathematical relation leads to an "analyticity conjecture" on the dependence of the spectral properties on a complex "fine-structure-constant" parameter, that can reduce the study of the spectrum of the (non-selfadjoint) MOTS-stability operator to that of the (selfadjoint) Hamiltonian of the quantum charged particle. Moreover, this perspective might open an avenue to the spinorial treatment of apparent horizon (MOTS-)stability and to the introduction of semiclassical tools to explore some of the qualitative aspects of this black hole spectral problem. |
2110.13508 | Kouji Nakamura | Kouji Nakamura | Gauge-invariant perturbation theory on the Schwarzschild background
spacetime Part I : -- Formulation and odd-mode perturbations | 61 pages, 4 figures, The Part I paper of the full paper version of
arXiv:2102.00830v3[gr-qc], minor revision (v8) | null | null | null | gr-qc astro-ph.HE hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is the Part I paper of our series of full papers on a gauge-invariant
{\it linear} perturbation theory on the Schwarzschild background spacetime
which was briefly reported in our short papers [K.~Nakamura, Class. Quantum
Grav. {\bf 38} (2021), 145010; K.~Nakamura, Letters in High Energy Physics {\bf
2021} (2021), 215.]. We first review our general framework of the
gauge-invariant perturbation theory, which can be easily extended to the {\it
higher-order} perturbation theory. When we apply this general framework to
perturbations on the Schwarzschild background spacetime, a gauge-invariant
treatments of $l=0,1$ mode perturbations are required. On the other hand, in
the current consensus on the perturbations of the Schwarzschild spacetime,
gauge-invariant treatments for $l=0,1$ modes are difficult if we keep the
reconstruction of the original metric perturbations in our mind. Based on this
situation, we propose a strategy of a gauge-invariant treatments of $l=0,1$
mode perturbations through the decomposition of the metric perturbations by
singular harmonic functions at once and the regularization of this singularity
through the imposition of the boundary conditions to the Einstein equations.
Following this proposal, we derive the linearized Einstein equations for any
modes of $l\geq 0$ in a gauge-invariant manner. We discuss the solutions to the
odd-mode perturbation equations in the linearized Einstein equations and show
that these perturbations include the Kerr parameter perturbation in these
odd-mode perturbation, which is physically reasonable.
| [
{
"created": "Tue, 26 Oct 2021 09:04:39 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Oct 2021 07:07:47 GMT",
"version": "v2"
},
{
"created": "Fri, 17 Dec 2021 09:57:39 GMT",
"version": "v3"
},
{
"created": "Mon, 17 Jan 2022 06:07:59 GMT",
"version": "v4"
},
{
"created": "Sun, 27 Mar 2022 17:12:22 GMT",
"version": "v5"
},
{
"created": "Fri, 27 May 2022 13:18:04 GMT",
"version": "v6"
},
{
"created": "Mon, 13 Mar 2023 06:53:50 GMT",
"version": "v7"
},
{
"created": "Fri, 22 Sep 2023 10:19:22 GMT",
"version": "v8"
}
] | 2023-09-25 | [
[
"Nakamura",
"Kouji",
""
]
] | This is the Part I paper of our series of full papers on a gauge-invariant {\it linear} perturbation theory on the Schwarzschild background spacetime which was briefly reported in our short papers [K.~Nakamura, Class. Quantum Grav. {\bf 38} (2021), 145010; K.~Nakamura, Letters in High Energy Physics {\bf 2021} (2021), 215.]. We first review our general framework of the gauge-invariant perturbation theory, which can be easily extended to the {\it higher-order} perturbation theory. When we apply this general framework to perturbations on the Schwarzschild background spacetime, a gauge-invariant treatments of $l=0,1$ mode perturbations are required. On the other hand, in the current consensus on the perturbations of the Schwarzschild spacetime, gauge-invariant treatments for $l=0,1$ modes are difficult if we keep the reconstruction of the original metric perturbations in our mind. Based on this situation, we propose a strategy of a gauge-invariant treatments of $l=0,1$ mode perturbations through the decomposition of the metric perturbations by singular harmonic functions at once and the regularization of this singularity through the imposition of the boundary conditions to the Einstein equations. Following this proposal, we derive the linearized Einstein equations for any modes of $l\geq 0$ in a gauge-invariant manner. We discuss the solutions to the odd-mode perturbation equations in the linearized Einstein equations and show that these perturbations include the Kerr parameter perturbation in these odd-mode perturbation, which is physically reasonable. |
1503.02172 | Christian Heinicke | Christian Heinicke (1) and Friedrich W. Hehl (1 and 2). ((1) Inst.
Theor. Physics, Univ. of Cologne, Germany, (2) Dept. Physics & Astron., Univ.
of Missouri, Columbia, USA) | Schwarzschild and Kerr Solutions of Einstein's Field Equation -- an
introduction | 96 pages, 17 figures, pdflatex. Invited review article. To appear in
Wei-Tou Ni (editor) "One Hundred Years of General Relativity: Cosmology and
Gravity," World Scientific, Singapore (2015) | Int. J. Mod. Phys. D 24 (2015) 1530006 (78 pages) | 10.1142/S0218271815300062 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Starting from Newton's gravitational theory, we give a general introduction
into the spherically symmetric solution of Einstein's vacuum field equation,
the Schwarzschild(-Droste) solution, and into one specific stationary axially
symmetric solution, the Kerr solution. The Schwarzschild solution is unique and
its metric can be interpreted as the exterior gravitational field of a
spherically symmetric mass. The Kerr solution is only unique if the multipole
moments of its mass and its angular momentum take on prescribed values. Its
metric can be interpreted as the exterior gravitational field of a suitably
rotating mass distribution. Both solutions describe objects exhibiting an event
horizon, a frontier of no return. The corresponding notion of a black hole is
explained to some extent. Eventually, we present some generalizations of the
Kerr solution.
| [
{
"created": "Sat, 7 Mar 2015 13:48:44 GMT",
"version": "v1"
}
] | 2015-03-10 | [
[
"Heinicke",
"Christian",
"",
"1 and 2"
],
[
"Hehl",
"Friedrich W.",
"",
"1 and 2"
],
[
".",
"",
""
]
] | Starting from Newton's gravitational theory, we give a general introduction into the spherically symmetric solution of Einstein's vacuum field equation, the Schwarzschild(-Droste) solution, and into one specific stationary axially symmetric solution, the Kerr solution. The Schwarzschild solution is unique and its metric can be interpreted as the exterior gravitational field of a spherically symmetric mass. The Kerr solution is only unique if the multipole moments of its mass and its angular momentum take on prescribed values. Its metric can be interpreted as the exterior gravitational field of a suitably rotating mass distribution. Both solutions describe objects exhibiting an event horizon, a frontier of no return. The corresponding notion of a black hole is explained to some extent. Eventually, we present some generalizations of the Kerr solution. |
1604.06947 | Viktor G. Czinner | Viktor G. Czinner and Filipe C. Mena | Relative information entropy in cosmology: The problem of information
entanglement | 6 pages, 3 figures, to appear in Phys. Lett. B | Phys. Lett. B 758 (2016) 9-13 | 10.1016/j.physletb.2016.04.043 | null | gr-qc astro-ph.CO cond-mat.stat-mech | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The necessary information to distinguish a local inhomogeneous mass density
field from its spatial average on a compact domain of the universe can be
measured by relative information entropy. The Kullback-Leibler (KL) formula
arises very naturally in this context, however, it provides a very complicated
way to compute the mutual information between spatially separated but causally
connected regions of the universe in a realistic, inhomogeneous model. To
circumvent this issue, by considering a parametric extension of the KL measure,
we develop a simple model to describe the mutual information which is entangled
via the gravitational field equations. We show that the Tsallis relative
entropy can be a good approximation in the case of small inhomogeneities, and
for measuring the independent relative information inside the domain, we
propose the R\'enyi relative entropy formula.
| [
{
"created": "Sat, 23 Apr 2016 20:18:53 GMT",
"version": "v1"
}
] | 2016-04-28 | [
[
"Czinner",
"Viktor G.",
""
],
[
"Mena",
"Filipe C.",
""
]
] | The necessary information to distinguish a local inhomogeneous mass density field from its spatial average on a compact domain of the universe can be measured by relative information entropy. The Kullback-Leibler (KL) formula arises very naturally in this context, however, it provides a very complicated way to compute the mutual information between spatially separated but causally connected regions of the universe in a realistic, inhomogeneous model. To circumvent this issue, by considering a parametric extension of the KL measure, we develop a simple model to describe the mutual information which is entangled via the gravitational field equations. We show that the Tsallis relative entropy can be a good approximation in the case of small inhomogeneities, and for measuring the independent relative information inside the domain, we propose the R\'enyi relative entropy formula. |
gr-qc/0101032 | Seth A. Major | Seth A. Major | New Operators for Spin Net Gravity: Definitions and Consequences | 7 pages, 2 figures, a talk at the MG9 Meeting, Rome, July 2-8, 2000 | null | 10.1142/9789812777386_0287 | null | gr-qc | null | Two operators for quantum gravity, angle and quasilocal energy, are briefly
reviewed. The requirements to model semi-classical angles are discussed. To
model semi-classical angles it is shown that the internal spins of the vertex
must be very large, ~10^20.
| [
{
"created": "Tue, 9 Jan 2001 18:31:01 GMT",
"version": "v1"
}
] | 2017-08-23 | [
[
"Major",
"Seth A.",
""
]
] | Two operators for quantum gravity, angle and quasilocal energy, are briefly reviewed. The requirements to model semi-classical angles are discussed. To model semi-classical angles it is shown that the internal spins of the vertex must be very large, ~10^20. |
gr-qc/0607031 | Lorenzo Iorio | Lorenzo Iorio | Constraining the relative inclinations of the planets B and C of the
millisecond pulsar PSR B1257+12 | LaTex2e, 10 pages, 1 table, 3 figures, 17 references. Small stylistic
changes. Version to appear in Journal of Astrophysics and Astronomy (JAA) | J.Astrophys.Astron.31:147-153,2010 | 10.1007/s12036-010-0015-8 | null | gr-qc astro-ph physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate on the relative inclination of the planets B and C orbiting
the pulsar PSR B1257+12 in connection with potential violations of the
equivalence principle (Abridged).
| [
{
"created": "Fri, 7 Jul 2006 18:22:08 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Oct 2009 08:00:42 GMT",
"version": "v2"
},
{
"created": "Wed, 28 Jul 2010 13:16:48 GMT",
"version": "v3"
},
{
"created": "Thu, 19 Aug 2010 14:25:02 GMT",
"version": "v4"
}
] | 2010-11-16 | [
[
"Iorio",
"Lorenzo",
""
]
] | We investigate on the relative inclination of the planets B and C orbiting the pulsar PSR B1257+12 in connection with potential violations of the equivalence principle (Abridged). |
1005.4990 | Mihai Visinescu | Bijan Saha, Mihai Visinescu | Bianchi type-VI model with cosmic strings in the presence of a magnetic
field | 13 pages, revised version, to appear in Rom. J. Phys | Rom. J. Phys. 55 (2010) 1064-1074 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A Bianchi type-VI cosmological model in the presence of a magnetic flux
together with a cloud of cosmic strings is considered. In general, the presence
of a magnetic field imposes severe restrictions regarding the consistency of
the field equations. These difficulties could be overtaken working either in a
Bianchi type-VI$_0$ spacetime or assuming a particular coordinate-dependence of
the magnetic field. Using a few plausible assumptions regarding the
parametrization of the cosmic strings, some exact analytical solutions are
presented. Their asymptotic behavior for large time is exhibited.
| [
{
"created": "Thu, 27 May 2010 06:03:06 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Jul 2010 10:46:54 GMT",
"version": "v2"
}
] | 2012-06-01 | [
[
"Saha",
"Bijan",
""
],
[
"Visinescu",
"Mihai",
""
]
] | A Bianchi type-VI cosmological model in the presence of a magnetic flux together with a cloud of cosmic strings is considered. In general, the presence of a magnetic field imposes severe restrictions regarding the consistency of the field equations. These difficulties could be overtaken working either in a Bianchi type-VI$_0$ spacetime or assuming a particular coordinate-dependence of the magnetic field. Using a few plausible assumptions regarding the parametrization of the cosmic strings, some exact analytical solutions are presented. Their asymptotic behavior for large time is exhibited. |
1801.08630 | Breno Giacchini | Breno L. Giacchini, Ilya L. Shapiro | Light bending in $F\left[g(\square)R\right]$ extended gravity theories | 17 pages, 1 figure | Phys. Lett. B 780, 54-60 (2018) | 10.1016/j.physletb.2018.02.055 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that in the weak field limit the light deflection alone cannot
distinguish between different $R + F[g(\square)R]$ models of gravity, where $F$
and $g$ are arbitrary functions. This does not imply, however, that in all
these theories an observer will see the same deflection angle. Owed to the need
to calibrate the Newton constant, the deflection angle may be model-dependent
after all necessary types of measurements are taken into account.
| [
{
"created": "Thu, 25 Jan 2018 23:26:48 GMT",
"version": "v1"
},
{
"created": "Thu, 8 Mar 2018 18:22:56 GMT",
"version": "v2"
}
] | 2018-03-09 | [
[
"Giacchini",
"Breno L.",
""
],
[
"Shapiro",
"Ilya L.",
""
]
] | We show that in the weak field limit the light deflection alone cannot distinguish between different $R + F[g(\square)R]$ models of gravity, where $F$ and $g$ are arbitrary functions. This does not imply, however, that in all these theories an observer will see the same deflection angle. Owed to the need to calibrate the Newton constant, the deflection angle may be model-dependent after all necessary types of measurements are taken into account. |
gr-qc/0411144 | Alexey Boyarsky | A. Boyarsky, A. Neronov, I. Tkachev | Quantum cosmology of the brane universe | 4 pages, revtex | Phys.Rev.Lett. 95 (2005) 091301 | 10.1103/PhysRevLett.95.091301 | null | gr-qc hep-th | null | We canonically quantize the dynamics of the brane universe embedded into the
five-dimensional Schwarzschild-anti-deSitter bulk space-time. We show that in
the brane-world settings the formulation of the quantum cosmology, including
the problem of initial conditions, is conceptually more simple than in the
3+1-dimensional case. The Wheeler-deWitt equation is a finite-difference
equation. It is exactly solvable in the case of a flat universe and we find the
ground state of the system. The closed brane universe can be created as a
result of decay of the bulk black hole.
| [
{
"created": "Mon, 29 Nov 2004 20:42:44 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Boyarsky",
"A.",
""
],
[
"Neronov",
"A.",
""
],
[
"Tkachev",
"I.",
""
]
] | We canonically quantize the dynamics of the brane universe embedded into the five-dimensional Schwarzschild-anti-deSitter bulk space-time. We show that in the brane-world settings the formulation of the quantum cosmology, including the problem of initial conditions, is conceptually more simple than in the 3+1-dimensional case. The Wheeler-deWitt equation is a finite-difference equation. It is exactly solvable in the case of a flat universe and we find the ground state of the system. The closed brane universe can be created as a result of decay of the bulk black hole. |
1404.3765 | Andrei Lebed G | Andrei G. Lebed | Does the Equivalence between Gravitational Mass and Energy Survive for a
Composite Quantum Body? | 10 pages, no figures. arXiv admin note: substantial text overlap with
arXiv:1304.6106, arXiv:1311.2627, arXiv:1205.3134 | Advances in High Energy Physics, vol. 2014, Article ID 678087
(2014) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We define passive and active gravitational mass operators of the simplest
composite quantum body - a hydrogen atom. Although they do not commute with its
energy operator, the equivalence between the expectation values of passive and
active gravitational masses and energy is shown to survive for stationary
quantum states. In our calculations of passive gravitational mass operator, we
take into account not only kinetic and Coulomb potential energies but also the
so-called relativistic corrections to electron motion in a hydrogen atom.
Inequivalence between passive and active gravitational masses and energy at a
macroscopic level is demonstrated to reveal itself as time dependent
oscillations of the expectation values of the gravitational masses for
superpositions of stationary quantum states. Breakdown of the equivalence
between passive gravitational mass and energy at a microscopic level reveals
itself as unusual electromagnetic radiation, emitted by macroscopic ensemble of
hydrogen atoms, moved by small spacecraft with constant velocity in the Earth's
gravitational field. We suggest the corresponding experiment on the Earth's
orbit to detect this radiation, which would be the first direct experiment
where quantum effects in general relativity are observed.
| [
{
"created": "Mon, 14 Apr 2014 22:00:17 GMT",
"version": "v1"
}
] | 2014-04-16 | [
[
"Lebed",
"Andrei G.",
""
]
] | We define passive and active gravitational mass operators of the simplest composite quantum body - a hydrogen atom. Although they do not commute with its energy operator, the equivalence between the expectation values of passive and active gravitational masses and energy is shown to survive for stationary quantum states. In our calculations of passive gravitational mass operator, we take into account not only kinetic and Coulomb potential energies but also the so-called relativistic corrections to electron motion in a hydrogen atom. Inequivalence between passive and active gravitational masses and energy at a macroscopic level is demonstrated to reveal itself as time dependent oscillations of the expectation values of the gravitational masses for superpositions of stationary quantum states. Breakdown of the equivalence between passive gravitational mass and energy at a microscopic level reveals itself as unusual electromagnetic radiation, emitted by macroscopic ensemble of hydrogen atoms, moved by small spacecraft with constant velocity in the Earth's gravitational field. We suggest the corresponding experiment on the Earth's orbit to detect this radiation, which would be the first direct experiment where quantum effects in general relativity are observed. |
1001.1202 | Olivier Sarbach | Olivier Sarbach and Thomas Zannias | Nonlinear instability of wormholes supported by exotic dust and a
magnetic field | 5 pages, no figures. A small paragraph added in Sec. III. An appendix
added explaining the derivation of the main equations | Phys.Rev.D81:047502,2010 | 10.1103/PhysRevD.81.047502 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, spherically symmetric, static wormholes supported by exotic dust
and a radial magnetic field have been derived and argued to be stable with
respect to linear radial fluctuations. In this report we point out that these
wormholes are unstable due to the formation of shell-crossing singularities
when the nonlinearities of the theory are taken into account.
| [
{
"created": "Fri, 8 Jan 2010 06:30:11 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Feb 2010 15:29:34 GMT",
"version": "v2"
}
] | 2010-04-06 | [
[
"Sarbach",
"Olivier",
""
],
[
"Zannias",
"Thomas",
""
]
] | Recently, spherically symmetric, static wormholes supported by exotic dust and a radial magnetic field have been derived and argued to be stable with respect to linear radial fluctuations. In this report we point out that these wormholes are unstable due to the formation of shell-crossing singularities when the nonlinearities of the theory are taken into account. |
0712.2555 | Ujjal Debnath | Subenoy Chakraborty and Ujjal Debnath | Shell Crossing Singularities in Quasi-Spherical Szekeres Models | 10 latex pages, RevTex style, no figures | Grav.Cosmol.14:184-189,2008 | 10.1134/S0202289308020102 | null | gr-qc | null | We investigate the occurrence of shell crossing singularities in
quasi-spherical Szekeres dust models with or without a cosmological constant.
We study the conditions for shell crossing singularity both from physical and
geometrical point of view and they are in agreement.
| [
{
"created": "Sun, 16 Dec 2007 02:45:15 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Chakraborty",
"Subenoy",
""
],
[
"Debnath",
"Ujjal",
""
]
] | We investigate the occurrence of shell crossing singularities in quasi-spherical Szekeres dust models with or without a cosmological constant. We study the conditions for shell crossing singularity both from physical and geometrical point of view and they are in agreement. |
1903.09020 | Ahmad Sheykhi | H. Yazdikarimi, A. Sheykhi and Z. Dayyani | Critical behavior of Gauss-Bonnet black holes via an alternative phase
space | 15 pages | Phys. Rev. D 99, 124017 (2019) | 10.1103/PhysRevD.99.124017 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Recently, it was argued that charged Anti-de Sitter (AdS) black holes admit
critical behavior, without extending phase space, similar to the Van der Waals
fluid system in the $Q^2-\Psi$ plans where $\Psi=1/v$ (the conjugate of $Q^2$)
is the inverse of the specific volume \cite{Dehy}. In this picture, the square
of the charge of the black hole, $Q^2$, is treated as a thermodynamic variable
and the cosmological constant $\Lambda$ is fixed. In this paper, we would like
to examine whether this new approach toward critical behaviour of AdS black
holes can work in other gravity such as Gauss-Bonnet (GB) gravity as well as in
higher dimensional spacetime. We obtain the equation of state, $Q^2=Q^2(\Psi,
T)$, Gibbs free energy and the critical quantities of the system, and study the
effects of the GB coupling $\tilde{\alpha}$ on their behaviour. We find out
that the critical quantities have reasonable values, provided the GB coupling
constant, $\tilde{\alpha}$, is taken small and the horizon topology is assumed
to be $(d-2)$-sphere. Finally, we calculate the critical exponents and show
that they are independent of the model parameters and have the same values as
the Van der Waals system which is predicted by the mean field theory.
| [
{
"created": "Wed, 20 Mar 2019 15:44:55 GMT",
"version": "v1"
}
] | 2019-06-19 | [
[
"Yazdikarimi",
"H.",
""
],
[
"Sheykhi",
"A.",
""
],
[
"Dayyani",
"Z.",
""
]
] | Recently, it was argued that charged Anti-de Sitter (AdS) black holes admit critical behavior, without extending phase space, similar to the Van der Waals fluid system in the $Q^2-\Psi$ plans where $\Psi=1/v$ (the conjugate of $Q^2$) is the inverse of the specific volume \cite{Dehy}. In this picture, the square of the charge of the black hole, $Q^2$, is treated as a thermodynamic variable and the cosmological constant $\Lambda$ is fixed. In this paper, we would like to examine whether this new approach toward critical behaviour of AdS black holes can work in other gravity such as Gauss-Bonnet (GB) gravity as well as in higher dimensional spacetime. We obtain the equation of state, $Q^2=Q^2(\Psi, T)$, Gibbs free energy and the critical quantities of the system, and study the effects of the GB coupling $\tilde{\alpha}$ on their behaviour. We find out that the critical quantities have reasonable values, provided the GB coupling constant, $\tilde{\alpha}$, is taken small and the horizon topology is assumed to be $(d-2)$-sphere. Finally, we calculate the critical exponents and show that they are independent of the model parameters and have the same values as the Van der Waals system which is predicted by the mean field theory. |
1112.3222 | Edward Porter | J\'er\^ome Carr\'e and Edward K. Porter | Calculating the continued fraction coefficients of a sub-diagonal Pad\'e
approximant at arbitrary order | 7 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The inspiral of two compact objects in gravitational wave astronomy is
described by a post-Newtonian expansion in powers of $(v/c)$. In most cases, it
is believed that the post-Newtonian expansion is asymptotically divergent. A
standard technique for accelerating the convergence of a power series is to
re-sum the series by means of a rational polynomial called a Pad\'e
approximation. If we liken this approximation to a matrix, the best convergence
is achieved by staying close to a diagonal Pad\'e approximation. This broadly
presents two subsets of the approximation : a super-diagonal approximation
$P^M_N$ and a sub-diagonal approximation $P_M^N$, where $M = N+\epsilon$, and
$\epsilon$ takes the values of 0 or 1. Left as rational polynomials, the
coefficients in both the numerator and denominator need to be re-calculated as
the order of the initial power series approximation is increased. However, the
sub-diagonal Pad\'e approximant is computationally advantageous as it can be
expressed in terms of a Gauss-like continued fraction. Once in this form, each
coefficient in the continued fraction is uniquely determined at each order.
This means that as we increase the order of approximation of the original power
series, we now have only one new additional coefficient to calculate in the
continued fraction. While it is possible to provide explicit expressions for
the continued fraction coefficients, they rapidly become unwieldy at high
orders of approximation. It is also possible to numerically calculate the
coefficients by means of ratios of Hankel determinants. However, these
determinants can be ill-conditioned and lead to numerical instabilities. In
this article, we present a method for calculating the continued fraction
coefficients at arbitrary orders of approximation.
| [
{
"created": "Wed, 14 Dec 2011 14:08:34 GMT",
"version": "v1"
}
] | 2011-12-15 | [
[
"Carré",
"Jérôme",
""
],
[
"Porter",
"Edward K.",
""
]
] | The inspiral of two compact objects in gravitational wave astronomy is described by a post-Newtonian expansion in powers of $(v/c)$. In most cases, it is believed that the post-Newtonian expansion is asymptotically divergent. A standard technique for accelerating the convergence of a power series is to re-sum the series by means of a rational polynomial called a Pad\'e approximation. If we liken this approximation to a matrix, the best convergence is achieved by staying close to a diagonal Pad\'e approximation. This broadly presents two subsets of the approximation : a super-diagonal approximation $P^M_N$ and a sub-diagonal approximation $P_M^N$, where $M = N+\epsilon$, and $\epsilon$ takes the values of 0 or 1. Left as rational polynomials, the coefficients in both the numerator and denominator need to be re-calculated as the order of the initial power series approximation is increased. However, the sub-diagonal Pad\'e approximant is computationally advantageous as it can be expressed in terms of a Gauss-like continued fraction. Once in this form, each coefficient in the continued fraction is uniquely determined at each order. This means that as we increase the order of approximation of the original power series, we now have only one new additional coefficient to calculate in the continued fraction. While it is possible to provide explicit expressions for the continued fraction coefficients, they rapidly become unwieldy at high orders of approximation. It is also possible to numerically calculate the coefficients by means of ratios of Hankel determinants. However, these determinants can be ill-conditioned and lead to numerical instabilities. In this article, we present a method for calculating the continued fraction coefficients at arbitrary orders of approximation. |
1309.0352 | Jaume Haro | Jaime Haro | Cosmological perturbations in teleparallel Loop Quantum Cosmology | version accepted for publication in JCAP | JCAP(11)068 (2013) | 10.1088/1475-7516/2013/11/068 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Cosmological perturbations in Loop Quantum Cosmology (LQC) are usually
studied incorporating either holonomy corrections, where the Ashtekar
connection is replaced by a suitable sinus function in order to have a
well-defined quantum analogue, or inverse-volume corrections coming from the
eigenvalues of the inverse-volume operator.
In this paper we will develop an alternative approach to calculate
cosmological perturbations in LQC based on the fact that, holonomy corrected
LQC in the flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) geometry could be
also obtained as a particular case of teleparallel $F(T)$ gravity (teleparallel
LQC). The main idea of our approach is to mix the simple bounce provided by
holonomy corrections in LQC with the non-singular perturbation equations given
by $F(T)$ gravity, in order to obtain a matter bounce scenario as a viable
alternative to slow-roll inflation.
In our study, we have obtained an scale invariant power spectrum of
cosmological perturbations. However, the ratio of tensor to scalar
perturbations is of order $1$, which does not agree with the current
observations. For this reason, we suggest a model where a transition from the
matter domination to a quasi de Sitter phase is produced in order to enhance
the scalar power spectrum.
| [
{
"created": "Mon, 2 Sep 2013 10:13:57 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Sep 2013 10:28:13 GMT",
"version": "v2"
},
{
"created": "Mon, 18 Nov 2013 10:03:31 GMT",
"version": "v3"
}
] | 2015-06-17 | [
[
"Haro",
"Jaime",
""
]
] | Cosmological perturbations in Loop Quantum Cosmology (LQC) are usually studied incorporating either holonomy corrections, where the Ashtekar connection is replaced by a suitable sinus function in order to have a well-defined quantum analogue, or inverse-volume corrections coming from the eigenvalues of the inverse-volume operator. In this paper we will develop an alternative approach to calculate cosmological perturbations in LQC based on the fact that, holonomy corrected LQC in the flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) geometry could be also obtained as a particular case of teleparallel $F(T)$ gravity (teleparallel LQC). The main idea of our approach is to mix the simple bounce provided by holonomy corrections in LQC with the non-singular perturbation equations given by $F(T)$ gravity, in order to obtain a matter bounce scenario as a viable alternative to slow-roll inflation. In our study, we have obtained an scale invariant power spectrum of cosmological perturbations. However, the ratio of tensor to scalar perturbations is of order $1$, which does not agree with the current observations. For this reason, we suggest a model where a transition from the matter domination to a quasi de Sitter phase is produced in order to enhance the scalar power spectrum. |
1901.00388 | Andrzej Woszczyna | Zdzislaw A. Golda, Andrzej Woszczyna, Lukasz Bratek | First integrals in the Brans-Dicke cosmology | 8 pages, 3 figures, 2 tables | null | null | null | gr-qc nlin.SI | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The work presents the frst and the second degree Darboux polynomials,
Jacobi's last multipliers as well as the set of frst integrals for Brans-Dicke
cosmology. Algebraic invariant sets are constructed. First integrals are
visualized for some particular values of the $\omega$ parameter.
| [
{
"created": "Mon, 31 Dec 2018 18:41:34 GMT",
"version": "v1"
}
] | 2019-01-03 | [
[
"Golda",
"Zdzislaw A.",
""
],
[
"Woszczyna",
"Andrzej",
""
],
[
"Bratek",
"Lukasz",
""
]
] | The work presents the frst and the second degree Darboux polynomials, Jacobi's last multipliers as well as the set of frst integrals for Brans-Dicke cosmology. Algebraic invariant sets are constructed. First integrals are visualized for some particular values of the $\omega$ parameter. |
1504.01302 | Tapobrata Sarkar | Akash Goel, Reevu Maity, Pratim Roy, Tapobrata Sarkar | Tidal Forces in Naked Singularity Backgrounds | 1 + 18 Pages, 9 figures | null | 10.1103/PhysRevD.91.104029 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The end stage of a gravitational collapse process can generically result in a
black hole or a naked singularity. Here we undertake a comparative analysis of
the nature of tidal forces in these backgrounds. The effect of such forces is
generically exemplified by the Roche limit, which predicts the distance within
which a celestial object disintegrates due to the tidal effects of a second
more massive object. In this paper, using Fermi normal coordinates, we
numerically compute the Roche limit for a class of non-rotating naked
singularity backgrounds, and compare them with known results for Schwarzschild
black holes. Our analysis indicates that there might be substantially large
deviations in the magnitudes of tidal forces in naked singularity backgrounds,
compared to the black hole cases. If observationally established, these can
prove to be an effective indicator of the nature of the singularity at a
galactic centre.
| [
{
"created": "Mon, 6 Apr 2015 15:15:07 GMT",
"version": "v1"
}
] | 2015-06-11 | [
[
"Goel",
"Akash",
""
],
[
"Maity",
"Reevu",
""
],
[
"Roy",
"Pratim",
""
],
[
"Sarkar",
"Tapobrata",
""
]
] | The end stage of a gravitational collapse process can generically result in a black hole or a naked singularity. Here we undertake a comparative analysis of the nature of tidal forces in these backgrounds. The effect of such forces is generically exemplified by the Roche limit, which predicts the distance within which a celestial object disintegrates due to the tidal effects of a second more massive object. In this paper, using Fermi normal coordinates, we numerically compute the Roche limit for a class of non-rotating naked singularity backgrounds, and compare them with known results for Schwarzschild black holes. Our analysis indicates that there might be substantially large deviations in the magnitudes of tidal forces in naked singularity backgrounds, compared to the black hole cases. If observationally established, these can prove to be an effective indicator of the nature of the singularity at a galactic centre. |
gr-qc/0401036 | Sung Won Kim | Sung-Won Kim | Rotating wormhole and scalar perturbation | 6 pages, 4 figures, Revtex4 | Nuovo Cim.B120:1235-1242,2005 | 10.1393/ncb/i2005-10151-y | null | gr-qc | null | In this paper, we study the rotational wormhole and scalar perturbation under
the spacetime. We found the Schr\"odinger like equation and consider the
asymptotic solutions for the special cases.
| [
{
"created": "Sat, 10 Jan 2004 07:01:41 GMT",
"version": "v1"
}
] | 2010-11-11 | [
[
"Kim",
"Sung-Won",
""
]
] | In this paper, we study the rotational wormhole and scalar perturbation under the spacetime. We found the Schr\"odinger like equation and consider the asymptotic solutions for the special cases. |
gr-qc/0211019 | Sushant G. Ghosh | S. G. Ghosh (Science College, Nagpur) and Naresh Dadhich (IUCAA, Pune) | Gravitational collapse of null strange quark fluid and cosmic censorship | 8 pages, RevTeX 4, no figures, Accepted in GRG | Gen.Rel.Grav. 35 (2003) 359-370 | 10.1023/A:1022361631003 | null | gr-qc | null | We study gravitational collapse of the general spherically symmetric null
strange quark fluid having the equation of state, $p = (\rho - 4B)/n$, where
$B$ is the bag constant. An interesting feature that emerges is that the
initial data set giving rise to naked singularity in the Vaidya collapse of
null fluid gets covered due to the presence of strange quark matter component.
Its implication to the Cosmic Censorship Conjecture is discussed.
| [
{
"created": "Wed, 6 Nov 2002 10:55:01 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Ghosh",
"S. G.",
"",
"Science College, Nagpur"
],
[
"Dadhich",
"Naresh",
"",
"IUCAA, Pune"
]
] | We study gravitational collapse of the general spherically symmetric null strange quark fluid having the equation of state, $p = (\rho - 4B)/n$, where $B$ is the bag constant. An interesting feature that emerges is that the initial data set giving rise to naked singularity in the Vaidya collapse of null fluid gets covered due to the presence of strange quark matter component. Its implication to the Cosmic Censorship Conjecture is discussed. |
1502.03236 | Prado Martin-Moruno | Prado Martin-Moruno, Nelson J. Nunes, and Francisco S. N. Lobo | Horndeski theories self-tuning to a de Sitter vacuum | V1: 5 pages. V2: 8 pages; 5 references added; 2 new appendixes;
clarifications in the discussion; no physics changes. This version accepted
for publication in Physical Review D | Phys.Rev.D91:084029,2015 | 10.1103/PhysRevD.91.084029 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider Horndeski cosmological models able to screen the vacuum energy
coming from any field theory assuming that after this screening the space
should be in a de Sitter vacuum with a particular value of the cosmological
constant specified by the theory of gravity itself. The most general
scalar-tensor cosmological models without higher than second order derivatives
in the field equations that have a spatially flat de Sitter critical point for
any kind of material content or vacuum energy are, therefore, presented. These
models could allow us to understand the current accelerated expansion of the
universe as the result of a dynamical evolution towards a de Sitter attractor.
| [
{
"created": "Wed, 11 Feb 2015 09:54:46 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Mar 2015 17:58:57 GMT",
"version": "v2"
}
] | 2015-04-15 | [
[
"Martin-Moruno",
"Prado",
""
],
[
"Nunes",
"Nelson J.",
""
],
[
"Lobo",
"Francisco S. N.",
""
]
] | We consider Horndeski cosmological models able to screen the vacuum energy coming from any field theory assuming that after this screening the space should be in a de Sitter vacuum with a particular value of the cosmological constant specified by the theory of gravity itself. The most general scalar-tensor cosmological models without higher than second order derivatives in the field equations that have a spatially flat de Sitter critical point for any kind of material content or vacuum energy are, therefore, presented. These models could allow us to understand the current accelerated expansion of the universe as the result of a dynamical evolution towards a de Sitter attractor. |
2201.01015 | Oem Trivedi | Oem Trivedi, Maxim Khlopov | On finite time singularities in scalar field dark energy models based in
the RS-II Braneworld | v2, 17 pages with no figures, matches the published version in EPJC | Eur. Phys. J. C 82, 800 (2022) | 10.1140/epjc/s10052-022-10767-2 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | The quest of deciphering the true nature of dark energy has proven to be one
of the most exciting in recent times in cosmology. Various ideas have been put
forward in this regard besides the usual cosmological constant approach,
ranging from scalar field based models like Quintessence and Phantom dark
energy to various modified gravity approaches as well. A very interesting idea
then is to consider scalar field dark energy models in quantum gravitationally
corrected cosmologies with the RS-II Braneworld being one of the most well
known in this regard. So in this work, we consider RS-II Braneworld based
scalar field dark energy models and try to look out for the existence of finite
time singularities in these regimes both through a dynamical system
perspective, for which we employ the Goriely-Hyde singularity analysis method,
and a physical perspective. Our approach is general in the sense that it is not
limited to any particular class of potentials or for any constrained parameter
region for the brane tension and is valid for both Quintessence and phantom
dark energy regimes. We firstly show through Goriely-Hyde procedure that finite
time singularities can exist in these models for a limited set of initial
conditions and that this result would hold irrespective of any consideration
given to the swampland dS conjecture. We then discuss the physical nature of
the singularities that can occur in this regime, where we use a well motivated
ansatz for the Hubble parameter and show that these models of dark energy can
allow for weak singularities like those of Type III and Type IV and can also
allow for strong singularities like the Big Rip (Type I).
| [
{
"created": "Tue, 4 Jan 2022 07:22:32 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Sep 2022 16:54:47 GMT",
"version": "v2"
}
] | 2022-09-08 | [
[
"Trivedi",
"Oem",
""
],
[
"Khlopov",
"Maxim",
""
]
] | The quest of deciphering the true nature of dark energy has proven to be one of the most exciting in recent times in cosmology. Various ideas have been put forward in this regard besides the usual cosmological constant approach, ranging from scalar field based models like Quintessence and Phantom dark energy to various modified gravity approaches as well. A very interesting idea then is to consider scalar field dark energy models in quantum gravitationally corrected cosmologies with the RS-II Braneworld being one of the most well known in this regard. So in this work, we consider RS-II Braneworld based scalar field dark energy models and try to look out for the existence of finite time singularities in these regimes both through a dynamical system perspective, for which we employ the Goriely-Hyde singularity analysis method, and a physical perspective. Our approach is general in the sense that it is not limited to any particular class of potentials or for any constrained parameter region for the brane tension and is valid for both Quintessence and phantom dark energy regimes. We firstly show through Goriely-Hyde procedure that finite time singularities can exist in these models for a limited set of initial conditions and that this result would hold irrespective of any consideration given to the swampland dS conjecture. We then discuss the physical nature of the singularities that can occur in this regime, where we use a well motivated ansatz for the Hubble parameter and show that these models of dark energy can allow for weak singularities like those of Type III and Type IV and can also allow for strong singularities like the Big Rip (Type I). |
gr-qc/9801016 | Mark Trodden | Andrew A. de Laix, Mark Trodden and Tanmay Vachaspati (Case Western
Reserve University) | Topological Inflation with Multiple Winding | 13 pages, 4 figures, RevTeX | Phys. Rev. D 57, 7186 (1998) | 10.1103/PhysRevD.57.7186 | CWRU-P23-97 | gr-qc astro-ph hep-ph | null | We analyze the core dynamics of critically coupled, superheavy gauge vortices
in the (2+1) dimensional Einstein-Abelian-Higgs system. By numerically solving
the Eistein and field equations for various values of the symmetry breaking
scale, we identify the regime in which static solutions cease to exist and
topological inflation begins. We explicitly include the topological winding of
the vortices into the calculation and extract the dependence on the winding of
the critical scale separating the static and inflating regimes. Extrapolation
of our results suggests that topological inflation might occur within high
winding strings formed at the Grand Unified scale.
| [
{
"created": "Wed, 7 Jan 1998 20:58:04 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Mar 1998 17:01:12 GMT",
"version": "v2"
}
] | 2016-08-25 | [
[
"de Laix",
"Andrew A.",
"",
"Case Western\n Reserve University"
],
[
"Trodden",
"Mark",
"",
"Case Western\n Reserve University"
],
[
"Vachaspati",
"Tanmay",
"",
"Case Western\n Reserve University"
]
] | We analyze the core dynamics of critically coupled, superheavy gauge vortices in the (2+1) dimensional Einstein-Abelian-Higgs system. By numerically solving the Eistein and field equations for various values of the symmetry breaking scale, we identify the regime in which static solutions cease to exist and topological inflation begins. We explicitly include the topological winding of the vortices into the calculation and extract the dependence on the winding of the critical scale separating the static and inflating regimes. Extrapolation of our results suggests that topological inflation might occur within high winding strings formed at the Grand Unified scale. |
1909.08039 | Pedro V. P. Cunha | Pedro V.P. Cunha, Carlos A. R. Herdeiro, Eugen Radu | EHT constraint on the ultralight scalar hair of the M87 supermassive
black hole | 16 pages, 4 figures; v2: small modifications accounting for the
referee's feedback; references added | Universe 2019, 5(12), 220 | 10.3390/universe5120220 | null | gr-qc astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Hypothetical ultralight bosonic fields will spontaneously form macroscopic
bosonic halos around Kerr black holes, via superradiance, transferring part of
the mass and angular momentum of the black hole into the halo. Such process,
however, is only efficient if resonant: when the Compton wavelength of the
field approximately matches the gravitational scale of the black hole. For a
complex-valued field, the process can form a stationary, bosonic field-black
hole equilibrium state - a black hole with synchronised hair. For sufficiently
massive black holes, such as the one at the centre of the M87 supergiant
elliptic galaxy, the hairy black hole can be robust against its own
superradiant instabilities, within a Hubble time. Studying the shadows of such
scalar hairy black holes, we constrain the amount of hair which is compatible
with the Event Horizon Telescope (EHT) observations of the M87 supermassive
black hole, assuming the hair is a condensate of ultralight scalar particles of
mass $\mu\sim 10^{-20}$ eV, as to be dynamically viable. We show the EHT
observations set a weak constraint, in the sense that typical hairy black holes
that could develop their hair dynamically, are compatible with the
observations, when taking into account the EHT error bars and the black hole
mass/distance uncertainty.
| [
{
"created": "Tue, 17 Sep 2019 19:14:36 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Jan 2020 11:55:05 GMT",
"version": "v2"
}
] | 2020-01-08 | [
[
"Cunha",
"Pedro V. P.",
""
],
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Radu",
"Eugen",
""
]
] | Hypothetical ultralight bosonic fields will spontaneously form macroscopic bosonic halos around Kerr black holes, via superradiance, transferring part of the mass and angular momentum of the black hole into the halo. Such process, however, is only efficient if resonant: when the Compton wavelength of the field approximately matches the gravitational scale of the black hole. For a complex-valued field, the process can form a stationary, bosonic field-black hole equilibrium state - a black hole with synchronised hair. For sufficiently massive black holes, such as the one at the centre of the M87 supergiant elliptic galaxy, the hairy black hole can be robust against its own superradiant instabilities, within a Hubble time. Studying the shadows of such scalar hairy black holes, we constrain the amount of hair which is compatible with the Event Horizon Telescope (EHT) observations of the M87 supermassive black hole, assuming the hair is a condensate of ultralight scalar particles of mass $\mu\sim 10^{-20}$ eV, as to be dynamically viable. We show the EHT observations set a weak constraint, in the sense that typical hairy black holes that could develop their hair dynamically, are compatible with the observations, when taking into account the EHT error bars and the black hole mass/distance uncertainty. |
1508.00971 | Muhammad Raza | Muhammad Raza, Kairat Myrzakulov, Davood Momeni, and Ratbay Myrzakulov | Mimetic Attractors | null | Int.J.Theor.Phys. 55 (2016) no.5, 2558-2572 | 10.1007/s10773-015-2891-9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we investigate the mathematical modeling for the cosmological
attractors propagated in mimetic gravity upon which an interacting dark
energy-dark matter is supposed to be existed. The average value of the
interaction of these percentages, namely $\Gamma_i$ say, may be used to
investigate generally the modeling of an attractor; the actual value could only
be determined by data in any particular case. We have seen, for example, that
it was led to investigate the subject of initially invariant submanifolds.
| [
{
"created": "Wed, 5 Aug 2015 04:33:04 GMT",
"version": "v1"
}
] | 2017-10-17 | [
[
"Raza",
"Muhammad",
""
],
[
"Myrzakulov",
"Kairat",
""
],
[
"Momeni",
"Davood",
""
],
[
"Myrzakulov",
"Ratbay",
""
]
] | In this paper, we investigate the mathematical modeling for the cosmological attractors propagated in mimetic gravity upon which an interacting dark energy-dark matter is supposed to be existed. The average value of the interaction of these percentages, namely $\Gamma_i$ say, may be used to investigate generally the modeling of an attractor; the actual value could only be determined by data in any particular case. We have seen, for example, that it was led to investigate the subject of initially invariant submanifolds. |
2302.08289 | Tiberiu Harko | Piyabut Burikham, Tiberiu Harko, Kulapant Pimsamarn, Shahab Shahidi | Dark matter as a Weyl geometric effect | 20 pages, 2 figures, accepted for publication in PRD | null | 10.1103/PhysRevD.107.064008 | null | gr-qc astro-ph.GA hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the possibility that the observed behavior of test particles
outside galaxies, which is usually explained by assuming the existence of dark
matter, is the result of the dynamical evolution of particles in a Weyl type
geometry, and its associated conformally invariant Weyl geometric quadratic
gravity. As a first step in our investigations we write down the simplest
possible conformally invariant gravitational action, constructed in Weyl
geometry, and containing the Weyl scalar, and the strength of the Weyl vector
only. By introducing an auxiliary scalar field, the theoretical model can be
reformulated in the Riemann geometry as scalar-vector-tensor theory, containing
a scalar field, and the Weyl vector, respectively. The field equations of the
theory are derived in the metric formalism, in the absence of matter. A
specific static, spherically symmetric model, in which the Weyl vector has only
a radial component, is considered. In this case, an exact analytic solution of
the gravitational field equations can be obtained. The behavior of the galactic
rotation curves is also considered in detail, and it is shown that an effective
geometric mass term, with an associated density profile, can also be
introduced. Three particular cases, corresponding to some specific functional
forms of the Weyl vector, are also investigated. A comparison of the model with
a selected sample of galactic rotation curves is also performed when an
explicit breaking of conformal invariance is introduced, which allows the fix
of the numerical values of the free parameters of the model. Our results show
that Weyl geometric models can be considered as a viable theoretical
alternative to the dark matter paradigm.
| [
{
"created": "Thu, 16 Feb 2023 13:38:25 GMT",
"version": "v1"
}
] | 2023-03-29 | [
[
"Burikham",
"Piyabut",
""
],
[
"Harko",
"Tiberiu",
""
],
[
"Pimsamarn",
"Kulapant",
""
],
[
"Shahidi",
"Shahab",
""
]
] | We investigate the possibility that the observed behavior of test particles outside galaxies, which is usually explained by assuming the existence of dark matter, is the result of the dynamical evolution of particles in a Weyl type geometry, and its associated conformally invariant Weyl geometric quadratic gravity. As a first step in our investigations we write down the simplest possible conformally invariant gravitational action, constructed in Weyl geometry, and containing the Weyl scalar, and the strength of the Weyl vector only. By introducing an auxiliary scalar field, the theoretical model can be reformulated in the Riemann geometry as scalar-vector-tensor theory, containing a scalar field, and the Weyl vector, respectively. The field equations of the theory are derived in the metric formalism, in the absence of matter. A specific static, spherically symmetric model, in which the Weyl vector has only a radial component, is considered. In this case, an exact analytic solution of the gravitational field equations can be obtained. The behavior of the galactic rotation curves is also considered in detail, and it is shown that an effective geometric mass term, with an associated density profile, can also be introduced. Three particular cases, corresponding to some specific functional forms of the Weyl vector, are also investigated. A comparison of the model with a selected sample of galactic rotation curves is also performed when an explicit breaking of conformal invariance is introduced, which allows the fix of the numerical values of the free parameters of the model. Our results show that Weyl geometric models can be considered as a viable theoretical alternative to the dark matter paradigm. |
gr-qc/9307032 | Bev Berger | B.K. Berger, V. Moncrief | Numerical Investigation of Cosmological Singularities | 37 pp +14 figures (not included, available on request), plain TeX | Phys.Rev. D48 (1993) 4676-4687 | 10.1103/PhysRevD.48.4676 | null | gr-qc | null | Although cosmological solutions to Einstein's equations are known to be
generically singular, little is known about the nature of singularities in
typical spacetimes. It is shown here how the operator splitting used in a
particular symplectic numerical integration scheme fits naturally into the
Einstein equations for a large class of cosmological models and thus allows
study of their approach to the singularity. The numerical method also naturally
singles out the asymptotically velocity term dominated (AVTD) behavior known to
be characteristic of some of these models, conjectured to describe others, and
probably characteristic of a subclass of the rest. The method is first applied
to the unpolarized Gowdy T$^3$ cosmology. Exact pseudo-unpolarized solutions
are used as a code test and demonstrate that a 4th order accurate
implementation of the numerical method yields acceptable agreement. For generic
initial data, support for the conjecture that the singularity is AVTD with
geodesic velocity (in the harmonic map target space) < 1 is found. A new
phenomenon of the development of small scale spatial structure is also
observed. Finally, it is shown that the numerical method straightforwardly
generalizes to an arbitrary cosmological spacetime on $T^3 \times R$ with one
spacelike U(1) symmetry.
| [
{
"created": "Thu, 22 Jul 1993 21:06:02 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Berger",
"B. K.",
""
],
[
"Moncrief",
"V.",
""
]
] | Although cosmological solutions to Einstein's equations are known to be generically singular, little is known about the nature of singularities in typical spacetimes. It is shown here how the operator splitting used in a particular symplectic numerical integration scheme fits naturally into the Einstein equations for a large class of cosmological models and thus allows study of their approach to the singularity. The numerical method also naturally singles out the asymptotically velocity term dominated (AVTD) behavior known to be characteristic of some of these models, conjectured to describe others, and probably characteristic of a subclass of the rest. The method is first applied to the unpolarized Gowdy T$^3$ cosmology. Exact pseudo-unpolarized solutions are used as a code test and demonstrate that a 4th order accurate implementation of the numerical method yields acceptable agreement. For generic initial data, support for the conjecture that the singularity is AVTD with geodesic velocity (in the harmonic map target space) < 1 is found. A new phenomenon of the development of small scale spatial structure is also observed. Finally, it is shown that the numerical method straightforwardly generalizes to an arbitrary cosmological spacetime on $T^3 \times R$ with one spacelike U(1) symmetry. |
1404.4586 | Yury F. Pirogov | Yu. F. Pirogov | Emergent gravity, violated relativity and dark matter | 10 pages, minor improvements | Journal of Modern Physics, 5, 1418-1426 (2014) | 10.4236/jmp.2014.515143 | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The nonlinear affine Goldstone model of the emergent gravity, built on the
nonlinearly realized/hidden affine symmetry, is concisely revisited. Beyond
General Relativity, the explicit violation of general invariance/relativity,
under preserving general covariance, is exposed. Dependent on a nondynamical
affine connection, a generally covariant second-order effective Lagrangian for
metric gravity is worked out, with the general relativity violation and the
gravitational dark matter serving as the signatures of emergence.
| [
{
"created": "Thu, 17 Apr 2014 17:15:50 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Apr 2014 14:42:00 GMT",
"version": "v2"
}
] | 2015-06-19 | [
[
"Pirogov",
"Yu. F.",
""
]
] | The nonlinear affine Goldstone model of the emergent gravity, built on the nonlinearly realized/hidden affine symmetry, is concisely revisited. Beyond General Relativity, the explicit violation of general invariance/relativity, under preserving general covariance, is exposed. Dependent on a nondynamical affine connection, a generally covariant second-order effective Lagrangian for metric gravity is worked out, with the general relativity violation and the gravitational dark matter serving as the signatures of emergence. |
1106.4932 | Michael Bradley | Michael Bradley, Peter K. S. Dunsby, Mats Forsberg and Zolt\'an
Keresztes | Density growth in Kantowski-Sachs cosmologies with cosmological constant | 33 pages, 17 pictures | Class. Quantum Grav. 29 (2012) 095023 | 10.1088/0264-9381/29/9/095023 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work the growth of density perturbations in Kantowski-Sachs
cosmologies with a positive cosmological constant is studied, using the 1+3 and
1+1+2 covariant formalisms. For each wave number we obtain a closed system for
scalars formed from quantities that are zero on the background and hence are
gauge-invariant. The solutions to this system are then analyzed both
analytically and numerically. In particular the effects of anisotropy and the
behaviour close to a bounce in the cosmic scale factor are considered. We find
that typically the density gradient in the bouncing directions experiences a
local maximum at or slightly after the bounce.
| [
{
"created": "Fri, 24 Jun 2011 10:13:18 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Jul 2011 14:40:39 GMT",
"version": "v2"
},
{
"created": "Tue, 10 Jan 2012 19:58:06 GMT",
"version": "v3"
},
{
"created": "Mon, 30 Apr 2012 15:14:43 GMT",
"version": "v4"
}
] | 2012-05-01 | [
[
"Bradley",
"Michael",
""
],
[
"Dunsby",
"Peter K. S.",
""
],
[
"Forsberg",
"Mats",
""
],
[
"Keresztes",
"Zoltán",
""
]
] | In this work the growth of density perturbations in Kantowski-Sachs cosmologies with a positive cosmological constant is studied, using the 1+3 and 1+1+2 covariant formalisms. For each wave number we obtain a closed system for scalars formed from quantities that are zero on the background and hence are gauge-invariant. The solutions to this system are then analyzed both analytically and numerically. In particular the effects of anisotropy and the behaviour close to a bounce in the cosmic scale factor are considered. We find that typically the density gradient in the bouncing directions experiences a local maximum at or slightly after the bounce. |
0709.0942 | David Garfinkle | David Garfinkle and Greg Comer | Matters of Gravity, The Newsletter of the Topical Group in Gravitation
of the American Physical Society, Volume 30, Fall 2007 | 37 pages, latex, 3 figures | null | null | null | gr-qc | null | GGR News:
-we hear that..., by David Garfinkle
-News from the GRG Society, by Abhay Ashtekar
-LIGO/GEO/Virgo work together, by Peter Saulson
-GWIC Ten Years on, by Stan Whitcomb
Research Briefs:
-Quasi-local energy, by Bjoern S. Schmekel
-The current status of cosmic strings, by Patrick Peter
-Gravitational waves from `mountains' on neutron stars, by Ian Jones
Conference reports:
-GR18/Amaldi 2007 in Sydney, by Jorge Pullin
-Synergy in Singularities? by Don Marolf
-Gravitation and the Cosmos, by Derek Fox and Parampreet Singh
-NumRel meets PN, by Buonanno et al
-SaulFest, by Greg Cook
-3rd Gulf Coast Gravity Conference, by Vitor Cardoso
| [
{
"created": "Thu, 6 Sep 2007 19:17:52 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Sep 2007 22:33:04 GMT",
"version": "v2"
}
] | 2007-10-10 | [
[
"Garfinkle",
"David",
""
],
[
"Comer",
"Greg",
""
]
] | GGR News: -we hear that..., by David Garfinkle -News from the GRG Society, by Abhay Ashtekar -LIGO/GEO/Virgo work together, by Peter Saulson -GWIC Ten Years on, by Stan Whitcomb Research Briefs: -Quasi-local energy, by Bjoern S. Schmekel -The current status of cosmic strings, by Patrick Peter -Gravitational waves from `mountains' on neutron stars, by Ian Jones Conference reports: -GR18/Amaldi 2007 in Sydney, by Jorge Pullin -Synergy in Singularities? by Don Marolf -Gravitation and the Cosmos, by Derek Fox and Parampreet Singh -NumRel meets PN, by Buonanno et al -SaulFest, by Greg Cook -3rd Gulf Coast Gravity Conference, by Vitor Cardoso |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.