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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0712.1263 | Kostas Kokkotas D | M. Vavoulidis, K. D. Kokkotas, A. Stavridis | Crustal Oscillations of Slowly Rotating Relativistic Stars | 15 pages | Mon.Not.Roy.Astron.Soc.384:1711,2008. | 10.1111/j.1365-2966.2007.12835.x | null | gr-qc astro-ph | null | We study low-amplitude crustal oscillations of slowly rotating relativistic
stars consisting of a central fluid core and an outer thin solid crust. We
estimate the effect of rotation on the torsional toroidal modes and on the
interfacial and shear spheroidal modes. The results compared against the
Newtonian ones for wide range of neutron star models and equations of state.
| [
{
"created": "Sat, 8 Dec 2007 07:23:14 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Vavoulidis",
"M.",
""
],
[
"Kokkotas",
"K. D.",
""
],
[
"Stavridis",
"A.",
""
]
] | We study low-amplitude crustal oscillations of slowly rotating relativistic stars consisting of a central fluid core and an outer thin solid crust. We estimate the effect of rotation on the torsional toroidal modes and on the interfacial and shear spheroidal modes. The results compared against the Newtonian ones for wide range of neutron star models and equations of state. |
2005.14678 | Mikael Normann | Mikael Normann and Juan Valiente Kroon | Evolution equations for a wide range of Einstein-matter systems | null | null | 10.1007/s10714-020-02759-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use an orthonormal frame approach to provide a general framework for the
first order hyperbolic reduction of the Einstein equations coupled to a fairly
generic class of matter models. Our analysis covers the special cases of dust
and perfect fluid. We also provide a discussion of self-gravitating elastic
matter. The frame is Fermi-Walker propagated and coordinates are chosen such as
to satisfy the Lagrange condition. We show the propagation of the constraints
of the Einstein-matter system.
| [
{
"created": "Fri, 29 May 2020 17:04:46 GMT",
"version": "v1"
}
] | 2020-10-28 | [
[
"Normann",
"Mikael",
""
],
[
"Kroon",
"Juan Valiente",
""
]
] | We use an orthonormal frame approach to provide a general framework for the first order hyperbolic reduction of the Einstein equations coupled to a fairly generic class of matter models. Our analysis covers the special cases of dust and perfect fluid. We also provide a discussion of self-gravitating elastic matter. The frame is Fermi-Walker propagated and coordinates are chosen such as to satisfy the Lagrange condition. We show the propagation of the constraints of the Einstein-matter system. |
0901.2944 | Narit Pidokrajt | Jan E. Aman, Narit Pidokrajt, John Ward | Information geometry of asymptotically AdS black holes | Contribution to proceedings of ERE2008, 4 pages | AIP Conf. Proc.1122:181-184, 2009 | 10.1063/1.3141246 | UVIC-TH-09-02 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate thermodynamic geometries of two families of asymptotically
Anti-de Sitter black holes, i.e. the Reissner-Nordstr\"om Anti-de Sitter in
four dimensions and the BTZ black hole. It is found that the Anti-de Sitter
space renders the geometry nontrivial (c.f. the Reissner-Nordstr\"om black hole
in asymptotically flat background). The BTZ black hole's thermodynamic geometry
is trivial despite the fact that it is characterized by the (negative)
cosmological constant. As a matter of curiosity we compute thermodynamic
geometry of these black holes regarding the cosmological constant as a true
parameter but no physically significant results can be derived.
| [
{
"created": "Mon, 19 Jan 2009 22:14:13 GMT",
"version": "v1"
}
] | 2009-05-15 | [
[
"Aman",
"Jan E.",
""
],
[
"Pidokrajt",
"Narit",
""
],
[
"Ward",
"John",
""
]
] | We investigate thermodynamic geometries of two families of asymptotically Anti-de Sitter black holes, i.e. the Reissner-Nordstr\"om Anti-de Sitter in four dimensions and the BTZ black hole. It is found that the Anti-de Sitter space renders the geometry nontrivial (c.f. the Reissner-Nordstr\"om black hole in asymptotically flat background). The BTZ black hole's thermodynamic geometry is trivial despite the fact that it is characterized by the (negative) cosmological constant. As a matter of curiosity we compute thermodynamic geometry of these black holes regarding the cosmological constant as a true parameter but no physically significant results can be derived. |
gr-qc/0611114 | H Mohseni Sadjadi | H. Mohseni Sadjadi | Schwarzschild black hole and the generalized second law in
phantom-dominated universe | 10 pages, references added, typos corrected, accepted for publication
in Physics Letters B | Phys.Lett.B645:108-112,2007 | 10.1016/j.physletb.2006.12.029 | null | gr-qc astro-ph | null | We study the conditions required for validity of the generalized second law
in phantom dominated universe in the presence of Schwarzschild black hole. Our
study is independent of the origin of the phantom like behavior of the
considered universe. We also discuss the generalized second law in the
neighborhood of transition (from quintessence to phantom regime) time. We show
that even for a constant equation of state parameter the generalized second law
may be satisfied provided the temperature is not taken as de Sitter
temperature. It is shown that in models with (only) a transition from
quintessence to phantom regime the generalized second law does not hold in the
transition epoch.
| [
{
"created": "Wed, 22 Nov 2006 10:04:10 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Dec 2006 14:28:38 GMT",
"version": "v2"
},
{
"created": "Sat, 16 Dec 2006 11:05:04 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Sadjadi",
"H. Mohseni",
""
]
] | We study the conditions required for validity of the generalized second law in phantom dominated universe in the presence of Schwarzschild black hole. Our study is independent of the origin of the phantom like behavior of the considered universe. We also discuss the generalized second law in the neighborhood of transition (from quintessence to phantom regime) time. We show that even for a constant equation of state parameter the generalized second law may be satisfied provided the temperature is not taken as de Sitter temperature. It is shown that in models with (only) a transition from quintessence to phantom regime the generalized second law does not hold in the transition epoch. |
2203.01814 | Yang Liu | Yang Liu | The spectrum of Hawking radiation in Tsallis statistical mechanics | null | null | 10.1140/epjc/s10052-022-10744-9 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Hawking radiation is one of the cores in modern gratitational theory. Several
articles have calculated the spectrum of Hawking radiation in Boltzmann-Gibbs
statistical mechanics. However, based on recent researches, gravitational
systems cannot be studied by the standard statistical mechanics. In this
article, we calculate the modification to the spectrum of Hawking radiation in
Tsallis statistical mechanics. We obtain the modified Stefan-Boltzmann's law
and modified power of Hawking radiation. We confirm the conclusion proposed by
Giddings, namely, the radiation should originate from the effective radius,
which extends well outside the horizon of black-hole. The lifetime of black
hole and the effect of large q are discussed as well.
| [
{
"created": "Wed, 2 Mar 2022 00:42:29 GMT",
"version": "v1"
}
] | 2022-09-14 | [
[
"Liu",
"Yang",
""
]
] | Hawking radiation is one of the cores in modern gratitational theory. Several articles have calculated the spectrum of Hawking radiation in Boltzmann-Gibbs statistical mechanics. However, based on recent researches, gravitational systems cannot be studied by the standard statistical mechanics. In this article, we calculate the modification to the spectrum of Hawking radiation in Tsallis statistical mechanics. We obtain the modified Stefan-Boltzmann's law and modified power of Hawking radiation. We confirm the conclusion proposed by Giddings, namely, the radiation should originate from the effective radius, which extends well outside the horizon of black-hole. The lifetime of black hole and the effect of large q are discussed as well. |
1906.08228 | Marco Astorino | Marco Astorino | Enhanced Ehlers Transformation and the Majumdar-Papapetrou-NUT Spacetime | v1: 28 pages. v2: 32 pages, typos corrected, references added,
extended version, a relation between the gravitomagnetic duality and the
enhanced Ehlers transformation is discussed; v3: 34 pages, final version, to
appear in JHEP | JHEP 01 (2020) 123 | 10.1007/JHEP01(2020)123 | IFUM-1080-FT | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The transformation which adds (or removes) NUT charge when it is applied to
electrovacuum, axisymmetric and stationary space-times is studied. After
analysing the Ehlers and the Reina-Treves transformations we propose a new one,
more precise in the presence of the Maxwell electromagnetic field. The enhanced
Ehlers transformation proposed turns out to act as a gravitomagnetic duality,
analogously to the electromagnetic duality, but for gravity: it rotates the
mass charge into the gravomagnetic (or NUT) charge. As an example the
Kerr-Newman-NUT black hole is obtained with the help of this enhanced
transformation. Moreover a new analytical exact solution is built adding the
NUT charge to a double charged black hole, at equilibrium. It describes the
non-extremal generalisation of the Majumdar-Papapetrou-NUT solution. From the
near-horizon analysis, its microscopic entropy, according to the Kerr/CFT
correspondence, is found and the second law of black hole thermodynamics is
discussed.
| [
{
"created": "Wed, 19 Jun 2019 17:17:16 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Nov 2019 16:34:11 GMT",
"version": "v2"
},
{
"created": "Tue, 14 Jan 2020 19:24:52 GMT",
"version": "v3"
}
] | 2020-01-23 | [
[
"Astorino",
"Marco",
""
]
] | The transformation which adds (or removes) NUT charge when it is applied to electrovacuum, axisymmetric and stationary space-times is studied. After analysing the Ehlers and the Reina-Treves transformations we propose a new one, more precise in the presence of the Maxwell electromagnetic field. The enhanced Ehlers transformation proposed turns out to act as a gravitomagnetic duality, analogously to the electromagnetic duality, but for gravity: it rotates the mass charge into the gravomagnetic (or NUT) charge. As an example the Kerr-Newman-NUT black hole is obtained with the help of this enhanced transformation. Moreover a new analytical exact solution is built adding the NUT charge to a double charged black hole, at equilibrium. It describes the non-extremal generalisation of the Majumdar-Papapetrou-NUT solution. From the near-horizon analysis, its microscopic entropy, according to the Kerr/CFT correspondence, is found and the second law of black hole thermodynamics is discussed. |
0706.1360 | Masoud Alimohammadi | Masoud Alimohammadi | Asymptotic behavior of w in general quintom model | 8 pages, one example is added, accepted for publication in Gen. Rel.
Grav | Gen.Rel.Grav.40:107-115,2008 | 10.1007/s10714-007-0514-3 | null | gr-qc astro-ph hep-th | null | For the quintom models with arbitrary potential $V=V(\phi,\sigma)$, the
asymptotic value of equation of state parameter w is obtained by a new method.
In this method, w of stable attractors are calculated by using the ratio (d ln
V)/(d ln a) in asymptotic region. All the known results, have been obtained by
other methods, are reproduced by this method as specific examples.
| [
{
"created": "Sun, 10 Jun 2007 14:40:33 GMT",
"version": "v1"
},
{
"created": "Sat, 25 Aug 2007 21:56:27 GMT",
"version": "v2"
},
{
"created": "Thu, 11 Oct 2007 09:02:12 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Alimohammadi",
"Masoud",
""
]
] | For the quintom models with arbitrary potential $V=V(\phi,\sigma)$, the asymptotic value of equation of state parameter w is obtained by a new method. In this method, w of stable attractors are calculated by using the ratio (d ln V)/(d ln a) in asymptotic region. All the known results, have been obtained by other methods, are reproduced by this method as specific examples. |
1209.4539 | Frank Hellmann | Bianca Dittrich, Frank Hellmann, Wojciech Kaminski | Holonomy Spin Foam Models: Boundary Hilbert spaces and Time Evolution
Operators | 51 pages, 18 figures | null | 10.1088/0264-9381/30/8/085005 | null | gr-qc hep-lat | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this and the companion paper a novel holonomy formulation of so called
Spin Foam models of lattice gauge gravity are explored. After giving a natural
basis for the space of simplicity constraints we define a universal boundary
Hilbert space, on which the imposition of different forms of the simplicity
constraints can be studied. We detail under which conditions this Hilbert space
can be mapped to a Hilbert space of projected spin networks or an ordinary spin
network space.
These considerations allow to derive the general form of the transfer
operators which generates discrete time evolution. We will describe the
transfer operators for some current models on the different boundary Hilbert
spaces and highlight the role of the simplicity constraints determining the
concrete form of the time evolution operators.
| [
{
"created": "Thu, 20 Sep 2012 14:12:10 GMT",
"version": "v1"
}
] | 2015-06-11 | [
[
"Dittrich",
"Bianca",
""
],
[
"Hellmann",
"Frank",
""
],
[
"Kaminski",
"Wojciech",
""
]
] | In this and the companion paper a novel holonomy formulation of so called Spin Foam models of lattice gauge gravity are explored. After giving a natural basis for the space of simplicity constraints we define a universal boundary Hilbert space, on which the imposition of different forms of the simplicity constraints can be studied. We detail under which conditions this Hilbert space can be mapped to a Hilbert space of projected spin networks or an ordinary spin network space. These considerations allow to derive the general form of the transfer operators which generates discrete time evolution. We will describe the transfer operators for some current models on the different boundary Hilbert spaces and highlight the role of the simplicity constraints determining the concrete form of the time evolution operators. |
1509.05835 | Mauricio Bellini | Mauricio Bellini (IFIMAR - CONICET & UNMdP) | Inflationary back-reaction effects from Relativistic Quantum Geometry | Accepted in Physics of the Dark Universe | null | null | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the dynamics of scalar metric fluctuations in a non-perturbative
variational formalism recently introduced, by which the dynamics of an
geometrical scalar field $\theta$, describes the quantum geometrical effects on
a Weylian-like manifold with respect to a background Riemannian space-time. In
this letter we have examined an example in the framework of inflationary
cosmology. The resulting spectral predictions are in very good agreement with
observations and other models of inflation.
| [
{
"created": "Sat, 19 Sep 2015 00:44:12 GMT",
"version": "v1"
},
{
"created": "Sun, 13 Dec 2015 14:59:49 GMT",
"version": "v2"
}
] | 2015-12-15 | [
[
"Bellini",
"Mauricio",
"",
"IFIMAR - CONICET & UNMdP"
]
] | We study the dynamics of scalar metric fluctuations in a non-perturbative variational formalism recently introduced, by which the dynamics of an geometrical scalar field $\theta$, describes the quantum geometrical effects on a Weylian-like manifold with respect to a background Riemannian space-time. In this letter we have examined an example in the framework of inflationary cosmology. The resulting spectral predictions are in very good agreement with observations and other models of inflation. |
gr-qc/0301028 | Brien C. Nolan | Brien C. Nolan | Dynamical extensions for shell-crossing singularities | 14 pages, 1 figure | Class.Quant.Grav. 20 (2003) 575-586 | 10.1088/0264-9381/20/4/302 | null | gr-qc | null | We derive global weak solutions of Einstein's equations for spherically
symmetric dust-filled space-times which admit shell-crossing singularities. In
the marginally bound case, the solutions are weak solutions of a conservation
law. In the non-marginally bound case, the equations are solved in a
generalized sense involving metric functions of bounded variation. The
solutions are not unique to the future of the shell-crossing singularity, which
is replaced by a shock wave in the present treatment; the metric is bounded but
not continuous.
| [
{
"created": "Wed, 8 Jan 2003 18:02:22 GMT",
"version": "v1"
}
] | 2017-08-23 | [
[
"Nolan",
"Brien C.",
""
]
] | We derive global weak solutions of Einstein's equations for spherically symmetric dust-filled space-times which admit shell-crossing singularities. In the marginally bound case, the solutions are weak solutions of a conservation law. In the non-marginally bound case, the equations are solved in a generalized sense involving metric functions of bounded variation. The solutions are not unique to the future of the shell-crossing singularity, which is replaced by a shock wave in the present treatment; the metric is bounded but not continuous. |
1611.05062 | James Edholm | James Edholm | UV completion of the Starobinsky model, tensor-to-scalar ratio, and
constraints on non-locality | 7 pages, 1 figure | Phys. Rev. D 95, 044004 (2017) | 10.1103/PhysRevD.95.044004 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we build upon the successes of the ultraviolet (UV) completion
of the Starobinsky model of inflation. This involves an extension of the
Einstein-Hilbert term by an infinite covariant derivative theory of gravity,
which is quadratic in curvature. It has been shown that such a theory can
potentially resolve the cosmological singularity for a flat, homogeneous and
isotropic geometry, and now it can also provide a successful cosmological
inflation model, which in the infrared matches all the predictions of the
Starobinsky model of inflation. The aim of this note is to show that the
tensor-to-scalar ratio is modified by the scale of non-locality, and in general
a wider range of tensor-to-scalar ratios can be obtained in this class of
model, which can put a lower bound on the scale of non-locality for the first
time as large as the O$(10^{14})$ GeV.
| [
{
"created": "Tue, 15 Nov 2016 21:20:13 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Aug 2017 11:27:25 GMT",
"version": "v2"
},
{
"created": "Mon, 13 Nov 2017 09:04:50 GMT",
"version": "v3"
}
] | 2017-11-15 | [
[
"Edholm",
"James",
""
]
] | In this paper, we build upon the successes of the ultraviolet (UV) completion of the Starobinsky model of inflation. This involves an extension of the Einstein-Hilbert term by an infinite covariant derivative theory of gravity, which is quadratic in curvature. It has been shown that such a theory can potentially resolve the cosmological singularity for a flat, homogeneous and isotropic geometry, and now it can also provide a successful cosmological inflation model, which in the infrared matches all the predictions of the Starobinsky model of inflation. The aim of this note is to show that the tensor-to-scalar ratio is modified by the scale of non-locality, and in general a wider range of tensor-to-scalar ratios can be obtained in this class of model, which can put a lower bound on the scale of non-locality for the first time as large as the O$(10^{14})$ GeV. |
1407.0319 | Tapobrata Sarkar | Dipanjan Dey, Kaushik Bhattacharya, Tapobrata Sarkar | Galactic space-times in modified theories of gravity | 1 + 29 Pages, LaTeX, 12 .eps figures. Some discussions improved.
Published version | null | 10.1007/s10714-015-1945-x | null | gr-qc astro-ph.GA hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study Bertrand space-times (BSTs), which have been proposed as viable
models of space-times seeded by galactic dark matter, in modified theories of
gravity. We first critically examine the issue of galactic rotation curves in
General Relativity, and establish the usefulness of BSTs to fit experimental
data in this context. We then study BSTs in metric $f(R)$ gravity and in
Brans-Dicke theories. For the former, the nature of the Newtonian potential is
established, and we also compute the effective equation of state and show that
it can provide good fits to some recent experimental results. For the latter,
we calculate the Brans-Dicke scalar analytically in some limits and numerically
in general, and find interesting constraints on the parameters of the theory.
Our results provide evidence for the physical nature of Bertrand space-times in
modified theories of gravity.
| [
{
"created": "Tue, 1 Jul 2014 16:55:32 GMT",
"version": "v1"
},
{
"created": "Sun, 23 Aug 2015 07:47:04 GMT",
"version": "v2"
}
] | 2015-08-25 | [
[
"Dey",
"Dipanjan",
""
],
[
"Bhattacharya",
"Kaushik",
""
],
[
"Sarkar",
"Tapobrata",
""
]
] | We study Bertrand space-times (BSTs), which have been proposed as viable models of space-times seeded by galactic dark matter, in modified theories of gravity. We first critically examine the issue of galactic rotation curves in General Relativity, and establish the usefulness of BSTs to fit experimental data in this context. We then study BSTs in metric $f(R)$ gravity and in Brans-Dicke theories. For the former, the nature of the Newtonian potential is established, and we also compute the effective equation of state and show that it can provide good fits to some recent experimental results. For the latter, we calculate the Brans-Dicke scalar analytically in some limits and numerically in general, and find interesting constraints on the parameters of the theory. Our results provide evidence for the physical nature of Bertrand space-times in modified theories of gravity. |
gr-qc/0607070 | Horst R. Beyer | Horst R. Beyer, Irina Holmes | On a new symmetry of the solutions of the wave equation in the
background of a Kerr black hole | null | Class.Quant.Grav.25:135014,2008 | 10.1088/0264-9381/25/13/135014 | null | gr-qc astro-ph hep-th math-ph math.MP | null | This short paper derives the constant of motion of a scalar field in the
gravitational field of a Kerr black hole which is associated to a Killing
tensor of that space-time. In addition, there is found a related new symmetry
operator S for the solutions of the wave equation in that background. That
operator is a partial differential operator with a leading order time
derivative of the first order that commutes with a normal form of the wave
operator. That form is obtained by multiplication of the wave operator from the
left with the reciprocal of the coefficient function of its second order time
derivative. It is shown that S induces an operator that commutes with the
generator of time evolution in a formulation of the initial value problem for
the wave equation in the setting of strongly continuous semigroups.
| [
{
"created": "Tue, 18 Jul 2006 13:57:38 GMT",
"version": "v1"
}
] | 2012-09-21 | [
[
"Beyer",
"Horst R.",
""
],
[
"Holmes",
"Irina",
""
]
] | This short paper derives the constant of motion of a scalar field in the gravitational field of a Kerr black hole which is associated to a Killing tensor of that space-time. In addition, there is found a related new symmetry operator S for the solutions of the wave equation in that background. That operator is a partial differential operator with a leading order time derivative of the first order that commutes with a normal form of the wave operator. That form is obtained by multiplication of the wave operator from the left with the reciprocal of the coefficient function of its second order time derivative. It is shown that S induces an operator that commutes with the generator of time evolution in a formulation of the initial value problem for the wave equation in the setting of strongly continuous semigroups. |
2404.15450 | Wei-Chen Lin | Pisin Chen, Kuan-Nan Lin, Wei-Chen Lin, Dong-han Yeom | A possible origin of the $\alpha$-vacuum as the initial state of the
Universe | 25 pages, 8 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We investigate the cosmological observables using the Euclidean path integral
approach. Specifically, we study both the no-boundary compact instantons
scenario and the Euclidean wormholes scenario that can induce the creation of
two universes from nothing. It is known that perturbations associated with the
no-boundary scenario can only be consistent with the Bunch-Davies vacuum. Here
we demonstrate that the Euclidean wormholes can allow for a de Sitter invariant
vacuum, the so-called $\alpha$-vacuum state, where the Bunch-Davies vacuum is a
special case. This therefore provides the $\alpha$-vacuum a geometrical origin.
As an aside, we discuss a subtle phase issue when considering the power
spectrum related to $\alpha$-vacuum in the closed universe framework.
| [
{
"created": "Tue, 23 Apr 2024 18:43:29 GMT",
"version": "v1"
}
] | 2024-04-25 | [
[
"Chen",
"Pisin",
""
],
[
"Lin",
"Kuan-Nan",
""
],
[
"Lin",
"Wei-Chen",
""
],
[
"Yeom",
"Dong-han",
""
]
] | We investigate the cosmological observables using the Euclidean path integral approach. Specifically, we study both the no-boundary compact instantons scenario and the Euclidean wormholes scenario that can induce the creation of two universes from nothing. It is known that perturbations associated with the no-boundary scenario can only be consistent with the Bunch-Davies vacuum. Here we demonstrate that the Euclidean wormholes can allow for a de Sitter invariant vacuum, the so-called $\alpha$-vacuum state, where the Bunch-Davies vacuum is a special case. This therefore provides the $\alpha$-vacuum a geometrical origin. As an aside, we discuss a subtle phase issue when considering the power spectrum related to $\alpha$-vacuum in the closed universe framework. |
2302.04285 | Adri\`a Delhom | Adri\`a Delhom, Gonzalo J. Olmo, and Parampreet Singh | A diffeomorphism invariant family of metric-affine actions for loop
cosmologies | 19 pages, 4 figures and 3 tables | JCAP06(2023)059 | 10.1088/1475-7516/2023/06/059 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In loop quantum cosmology (LQC) the big bang singularity is generically
resolved by a big bounce. This feature holds even when modified quantization
prescriptions of the Hamiltonian constraint are used such as in mLQC-I and
mLQC-II. While the later describes an effective description qualitatively
similar to that of standard LQC, the former describes an asymmetric evolution
with an emergent Planckian de-Sitter pre-bounce phase even in the absence of a
potential. We consider the potential relation of these canonically quantized
non-singular models with effective actions based on a geometric description. We
find a 3-parameter family of metric-affine $f(\mathcal{R})$ theories which
accurately approximate the effective dynamics of LQC and mLQC-II in all regimes
and mLQC-I in the post-bounce phase. Two of the parameters are fixed by
enforcing equivalence at the bounce, and the background evolution of the
relevant observables can be fitted with only one free parameter. It is seen
that the non-perturbative effects of these loop cosmologies are universally
encoded by a logarithmic correction that only depends on the bounce curvature
of the model. In addition, we find that the best fit value of the free
parameter can be very approximately written in terms of fundamental parameters
of the underlying quantum description for the three models. The values of the
best fits can be written in terms of the bounce density in a simple manner, and
the values for each model are related to one another by a proportionality
relation involving only the Barbero-Immirzi parameter.
| [
{
"created": "Wed, 8 Feb 2023 19:01:03 GMT",
"version": "v1"
},
{
"created": "Thu, 29 Jun 2023 13:09:18 GMT",
"version": "v2"
}
] | 2023-06-30 | [
[
"Delhom",
"Adrià",
""
],
[
"Olmo",
"Gonzalo J.",
""
],
[
"Singh",
"Parampreet",
""
]
] | In loop quantum cosmology (LQC) the big bang singularity is generically resolved by a big bounce. This feature holds even when modified quantization prescriptions of the Hamiltonian constraint are used such as in mLQC-I and mLQC-II. While the later describes an effective description qualitatively similar to that of standard LQC, the former describes an asymmetric evolution with an emergent Planckian de-Sitter pre-bounce phase even in the absence of a potential. We consider the potential relation of these canonically quantized non-singular models with effective actions based on a geometric description. We find a 3-parameter family of metric-affine $f(\mathcal{R})$ theories which accurately approximate the effective dynamics of LQC and mLQC-II in all regimes and mLQC-I in the post-bounce phase. Two of the parameters are fixed by enforcing equivalence at the bounce, and the background evolution of the relevant observables can be fitted with only one free parameter. It is seen that the non-perturbative effects of these loop cosmologies are universally encoded by a logarithmic correction that only depends on the bounce curvature of the model. In addition, we find that the best fit value of the free parameter can be very approximately written in terms of fundamental parameters of the underlying quantum description for the three models. The values of the best fits can be written in terms of the bounce density in a simple manner, and the values for each model are related to one another by a proportionality relation involving only the Barbero-Immirzi parameter. |
1712.09966 | Julian Westerweck | Julian Westerweck, Alex B. Nielsen, Ofek Fischer-Birnholtz, Miriam
Cabero, Collin Capano, Thomas Dent, Badri Krishnan, Grant Meadors and
Alexander H. Nitz | Low significance of evidence for black hole echoes in gravitational wave
data | As accepted by Physical Review D | Phys. Rev. D 97, 124037 (2018) | 10.1103/PhysRevD.97.124037 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recent detections of merging black holes allow observational tests of the
nature of these objects. In some proposed models, non-trivial structure at or
near the black hole horizon could lead to echo signals in gravitational wave
data. Recently, Abedi et al. claimed tentative evidence for repeating damped
echo signals following the gravitational-wave signals of the binary black hole
merger events recorded in the first observational period of the Advanced LIGO
interferometers. We reanalyse the same data, addressing some of the
shortcomings of their method using more background data and a modified
procedure. We find a reduced statistical significance for the claims of
evidence for echoes, calculating increased p-values for the null hypothesis of
echo-free noise. The reduced significance is entirely consistent with noise,
and so we conclude that the analysis of Abedi et al. does not provide any
observational evidence for the existence of Planck-scale structure at black
hole horizons.
| [
{
"created": "Thu, 28 Dec 2017 18:22:38 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Feb 2018 17:38:52 GMT",
"version": "v2"
},
{
"created": "Wed, 16 May 2018 16:37:55 GMT",
"version": "v3"
}
] | 2018-06-20 | [
[
"Westerweck",
"Julian",
""
],
[
"Nielsen",
"Alex B.",
""
],
[
"Fischer-Birnholtz",
"Ofek",
""
],
[
"Cabero",
"Miriam",
""
],
[
"Capano",
"Collin",
""
],
[
"Dent",
"Thomas",
""
],
[
"Krishnan",
"Badri",
""
... | Recent detections of merging black holes allow observational tests of the nature of these objects. In some proposed models, non-trivial structure at or near the black hole horizon could lead to echo signals in gravitational wave data. Recently, Abedi et al. claimed tentative evidence for repeating damped echo signals following the gravitational-wave signals of the binary black hole merger events recorded in the first observational period of the Advanced LIGO interferometers. We reanalyse the same data, addressing some of the shortcomings of their method using more background data and a modified procedure. We find a reduced statistical significance for the claims of evidence for echoes, calculating increased p-values for the null hypothesis of echo-free noise. The reduced significance is entirely consistent with noise, and so we conclude that the analysis of Abedi et al. does not provide any observational evidence for the existence of Planck-scale structure at black hole horizons. |
0910.1112 | Kamal Nandi | Amrita Bhattacharya, Ruslan Isaev, Massimo Scalia, Carlo Cattani, and
Kamal K. Nandi | Light bending in the galactic halo by Rindler-Ishak method | 15 pages | JCAP 1009:004,2010 | 10.1088/1475-7516/2010/09/004 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | After the work of Rindler and Ishak, it is now well established that the
bending of light is influenced by the cosmological constant {\Lambda} appearing
in the Schwarzschild-de Sitter spacetime. We show that their method, when
applied to the galactic halo gravity parametrized by a constant {\gamma},
yields exactly the same {\gamma}- correction to Schwarzschild bending as
obtained by standard methods. Different cases are analyzed, which include some
corrections to the special cases considered in the original paper by Rindler
and Ishak.
| [
{
"created": "Tue, 6 Oct 2009 20:57:07 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Jan 2010 17:44:39 GMT",
"version": "v2"
},
{
"created": "Sun, 11 Apr 2010 06:47:32 GMT",
"version": "v3"
},
{
"created": "Sat, 10 Jul 2010 18:40:10 GMT",
"version": "v4"
},
{
"cr... | 2011-03-14 | [
[
"Bhattacharya",
"Amrita",
""
],
[
"Isaev",
"Ruslan",
""
],
[
"Scalia",
"Massimo",
""
],
[
"Cattani",
"Carlo",
""
],
[
"Nandi",
"Kamal K.",
""
]
] | After the work of Rindler and Ishak, it is now well established that the bending of light is influenced by the cosmological constant {\Lambda} appearing in the Schwarzschild-de Sitter spacetime. We show that their method, when applied to the galactic halo gravity parametrized by a constant {\gamma}, yields exactly the same {\gamma}- correction to Schwarzschild bending as obtained by standard methods. Different cases are analyzed, which include some corrections to the special cases considered in the original paper by Rindler and Ishak. |
2011.05109 | Behnam Pourhassan | Jafar Sadeghi, Saeed Noori Gashti, Izzet Sakalli and Behnam Pourhassan | Weak Gravity Conjecture of Charged-Rotating-AdS Black Hole Surrounded by
Quintessence and String Cloud | 22 pages, 4 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A series of corrections to general relativity have recently been applied to
find the relationship between entropy and extremality-bound black holes. This
relationship has been investigated for many black holes, such as charged AdS,
rotating, and massive gravity black holes. We give a minor constant correction
to the action and confirm these universal relations for a charged-rotating-AdS
black hole. We then examine these calculations for the black hole, surrounded
by the quintessence and the cloud of string. In this paper, we evaluate a new
universal relation. It means that we find the relation between the extremal
mass of the black hole and the factor of cloud string and observe that the
corresponding universal relation is well established. We find that the
quintessence terms play a very effective role in calculating the mass-charge
ratio and concept of weak gravity conjecture of black holes. We note here that
the added constant correction is inversely related to the entropy of the black
hole. It leads us to see that the mass-to-charge ratio decreases and fully
confirms the black hole's weak gravity conjecture (WGC).
| [
{
"created": "Tue, 10 Nov 2020 14:15:59 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Feb 2021 01:19:33 GMT",
"version": "v2"
},
{
"created": "Wed, 13 Apr 2022 16:49:19 GMT",
"version": "v3"
},
{
"created": "Thu, 26 May 2022 19:58:24 GMT",
"version": "v4"
},
{
"cr... | 2022-08-03 | [
[
"Sadeghi",
"Jafar",
""
],
[
"Gashti",
"Saeed Noori",
""
],
[
"Sakalli",
"Izzet",
""
],
[
"Pourhassan",
"Behnam",
""
]
] | A series of corrections to general relativity have recently been applied to find the relationship between entropy and extremality-bound black holes. This relationship has been investigated for many black holes, such as charged AdS, rotating, and massive gravity black holes. We give a minor constant correction to the action and confirm these universal relations for a charged-rotating-AdS black hole. We then examine these calculations for the black hole, surrounded by the quintessence and the cloud of string. In this paper, we evaluate a new universal relation. It means that we find the relation between the extremal mass of the black hole and the factor of cloud string and observe that the corresponding universal relation is well established. We find that the quintessence terms play a very effective role in calculating the mass-charge ratio and concept of weak gravity conjecture of black holes. We note here that the added constant correction is inversely related to the entropy of the black hole. It leads us to see that the mass-to-charge ratio decreases and fully confirms the black hole's weak gravity conjecture (WGC). |
1611.01118 | Leszek Soko{\l}owski | Leszek M. Sokolowski | The bizarre anti-de Sitter spacetime | 31 pages, 3 figures | International Journal of Geometric Methods in Modern Physics 13
no.9 (2016) 1630016 | 10.1142/S0219887816300166 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Anti--de Sitter spacetime is important in general relativity and modern field
theory. We review its geometrical features and properties of light signals and
free particles moving in it. Applying only elementary tools of tensor calculus
we derive \textit{ab initio\/} all these properties and show that they are
really weird. One finds superluminal velocities of light and particles,
infinite particle energy necessary to escape at infinite distance and spacetime
regions inaccessible by a free fall, though reachable by an accelerated
spaceship. Radial timelike geodesics are identical to the circular ones and
actually all timelike geodesics are identical to one circle in a fictitious
five--dimensional space. Employing the latter space one is able to explain
these bizarre features of anti--de Sitter spacetime; in this sense the
spacetime is not self--contained. This is not a physical world.
| [
{
"created": "Thu, 3 Nov 2016 18:17:12 GMT",
"version": "v1"
}
] | 2016-11-04 | [
[
"Sokolowski",
"Leszek M.",
""
]
] | Anti--de Sitter spacetime is important in general relativity and modern field theory. We review its geometrical features and properties of light signals and free particles moving in it. Applying only elementary tools of tensor calculus we derive \textit{ab initio\/} all these properties and show that they are really weird. One finds superluminal velocities of light and particles, infinite particle energy necessary to escape at infinite distance and spacetime regions inaccessible by a free fall, though reachable by an accelerated spaceship. Radial timelike geodesics are identical to the circular ones and actually all timelike geodesics are identical to one circle in a fictitious five--dimensional space. Employing the latter space one is able to explain these bizarre features of anti--de Sitter spacetime; in this sense the spacetime is not self--contained. This is not a physical world. |
0705.0235 | Eyo Ita III | Eyo Eyo Ita III | Instanton representation of Plebanski gravity: Application to the
Schwarzchild metric | 22 pages. Background material for revised journal article | The Abraham Zelmanov Journal, 2011, Vol. 4 (pages 72-95) | null | DAMTP-2007-39 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we apply the instanton representation method to the
construction of spherically symmetric blackhole general relativity solutions.
The instanton representation implies the existence of additional Type D
solutions which are axially symmetric. We explicitly construct these solutions,
which are fully consistent with Birkhoff's theorem.
| [
{
"created": "Wed, 2 May 2007 09:33:14 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Apr 2010 18:13:51 GMT",
"version": "v2"
},
{
"created": "Fri, 18 Mar 2011 02:46:14 GMT",
"version": "v3"
}
] | 2012-02-20 | [
[
"Ita",
"Eyo Eyo",
"III"
]
] | In this paper we apply the instanton representation method to the construction of spherically symmetric blackhole general relativity solutions. The instanton representation implies the existence of additional Type D solutions which are axially symmetric. We explicitly construct these solutions, which are fully consistent with Birkhoff's theorem. |
2102.01123 | Vittorio De Falco Dr | Vittorio De Falco, Emmanuele Battista, Salvatore Capozziello,
Mariafelicia De Laurentis | Reconstructing wormhole solutions in curvature based Extended Theories
of Gravity | 9 pages; 2 figures; 1 Table; accepted on EPJ C | Eur. Phys. J. C 81, 157 (2021) | 10.1140/epjc/s10052-021-08958-4 | null | gr-qc astro-ph.HE hep-th | http://creativecommons.org/licenses/by/4.0/ | Static and spherically symmetric wormhole solutions can be reconstructed in
the framework of curvature based Extended Theories of Gravity. In particular,
extensions of the General Relativity, in metric and curvature formalism give
rise to modified gravitational potentials, constituted by the classical
Newtonian potential and Yukawa-like corrections, whose parameters can be, in
turn, gauged by the observations. Such an approach allows to reconstruct the
spacetime out of the wormhole throat considering the asymptotic flatness as a
physical property for the related gravitational field. Such an argument can be
applied for a large class of curvature theories characterising the wormholes
through the parameters of the potentials. According to this procedure, possible
wormhole solutions could be observationally constrained. On the other hand,
stable and traversable wormholes could be a direct probe for this class of
Extended Theories of Gravity.
| [
{
"created": "Mon, 1 Feb 2021 19:36:55 GMT",
"version": "v1"
},
{
"created": "Wed, 3 Feb 2021 13:19:12 GMT",
"version": "v2"
}
] | 2021-02-23 | [
[
"De Falco",
"Vittorio",
""
],
[
"Battista",
"Emmanuele",
""
],
[
"Capozziello",
"Salvatore",
""
],
[
"De Laurentis",
"Mariafelicia",
""
]
] | Static and spherically symmetric wormhole solutions can be reconstructed in the framework of curvature based Extended Theories of Gravity. In particular, extensions of the General Relativity, in metric and curvature formalism give rise to modified gravitational potentials, constituted by the classical Newtonian potential and Yukawa-like corrections, whose parameters can be, in turn, gauged by the observations. Such an approach allows to reconstruct the spacetime out of the wormhole throat considering the asymptotic flatness as a physical property for the related gravitational field. Such an argument can be applied for a large class of curvature theories characterising the wormholes through the parameters of the potentials. According to this procedure, possible wormhole solutions could be observationally constrained. On the other hand, stable and traversable wormholes could be a direct probe for this class of Extended Theories of Gravity. |
1207.3922 | Luca Parisi Ph.D. | Luca Parisi, Ninfa Radicella and Gaetano Vilasi | On the stability of the Einstein Static Universe in Massive Gravity | 7 pages, 7 figures, 1 table, minor changes, references added | Phys. Rev. D 86, 024035 (2012) | 10.1103/PhysRevD.86.024035 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider static cosmological solutions along with their stability
properties in the framework of a recently proposed theory of massive gravity.
We show that the modifcation introduced in the cosmological equations leads to
several new solutions, only sourced by a perfect fluid, generalizing the
Einstein Static Universe found in General Relativity. Using dynamical system
techniques and numerical analysis, we show that the found solutions can be
either neutrally stable or unstable against spatially homogeneous and isotropic
perturbations.
| [
{
"created": "Tue, 17 Jul 2012 09:07:16 GMT",
"version": "v1"
},
{
"created": "Thu, 26 Jul 2012 08:06:09 GMT",
"version": "v2"
}
] | 2012-07-27 | [
[
"Parisi",
"Luca",
""
],
[
"Radicella",
"Ninfa",
""
],
[
"Vilasi",
"Gaetano",
""
]
] | We consider static cosmological solutions along with their stability properties in the framework of a recently proposed theory of massive gravity. We show that the modifcation introduced in the cosmological equations leads to several new solutions, only sourced by a perfect fluid, generalizing the Einstein Static Universe found in General Relativity. Using dynamical system techniques and numerical analysis, we show that the found solutions can be either neutrally stable or unstable against spatially homogeneous and isotropic perturbations. |
2402.07416 | Alfio Bonanno | Alfio Bonanno, Amir-Pouyan Khosravi, Frank Saueressig | Reply to "Comment" on "Regular evaporating black holes with stable
cores" | 3 pages, 1 figure | Phys.Rev.D 108 (2023) 12, 128502 | 10.1103/PhysRevD.108.128502 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We reply to the ``Comment'' on ``Regular evaporating black holes with stable
cores'' by R. Carballo-Rubio, F. Di Filippo, S. Liberati, C. Pacilio, and M.
Visser. As a key result, we show that the regime of mass-inflation identified
in the comment connects smoothly to the late-time attractors discovered in our
works [A. Bonanno et. al., Regular black holes with stable cores, Phys. Rev. D
103, 124027 (2021) and Regular evaporating black holes with stable cores, Phys.
Rev. D 107, 024005 (2023)]. Hence, the late-time stability of regular black
holes is not affected by this intermediate phase.
| [
{
"created": "Mon, 12 Feb 2024 05:38:46 GMT",
"version": "v1"
}
] | 2024-02-13 | [
[
"Bonanno",
"Alfio",
""
],
[
"Khosravi",
"Amir-Pouyan",
""
],
[
"Saueressig",
"Frank",
""
]
] | We reply to the ``Comment'' on ``Regular evaporating black holes with stable cores'' by R. Carballo-Rubio, F. Di Filippo, S. Liberati, C. Pacilio, and M. Visser. As a key result, we show that the regime of mass-inflation identified in the comment connects smoothly to the late-time attractors discovered in our works [A. Bonanno et. al., Regular black holes with stable cores, Phys. Rev. D 103, 124027 (2021) and Regular evaporating black holes with stable cores, Phys. Rev. D 107, 024005 (2023)]. Hence, the late-time stability of regular black holes is not affected by this intermediate phase. |
2310.18962 | Cosimo Bambi | Shuaitongze Zhao, Shafqat Riaz, Cosimo Bambi | About the ability of agnostic X-ray tests of the Kerr Hypothesis to
discover new physics | 12 pages, 5 figures. v2: refereed version | Phys. Rev. D 109, 064059 (2024) | 10.1103/PhysRevD.109.064059 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the past decade, we have seen an unprecedented progress in our ability of
testing general relativity in the strong field regime with black hole
observations. Most studies have focused on the so-called tests of the Kerr
hypothesis: they have tried to verify whether the spacetime geometry around
black holes is described by the Kerr solution as expected in general
relativity. One can follow either a theory-specific analysis or an agnostic
approach. Each strategy has its advantages and disadvantages. In this work, we
study the ability of agnostic X-ray tests of the Kerr hypothesis to discover
new physics. We simulate X-ray observations of bright Galactic black holes of
specific theories of gravity and we analyze the simulated data with a
reflection model employing the correct theory of gravity and another reflection
model for agnostic tests of the Kerr hypothesis. Our results suggest that
agnostic X-ray tests are valid tools to discover new physics, but their
constraining power may be lower than a theory-specific analysis.
| [
{
"created": "Sun, 29 Oct 2023 10:05:08 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Mar 2024 21:42:51 GMT",
"version": "v2"
}
] | 2024-03-21 | [
[
"Zhao",
"Shuaitongze",
""
],
[
"Riaz",
"Shafqat",
""
],
[
"Bambi",
"Cosimo",
""
]
] | In the past decade, we have seen an unprecedented progress in our ability of testing general relativity in the strong field regime with black hole observations. Most studies have focused on the so-called tests of the Kerr hypothesis: they have tried to verify whether the spacetime geometry around black holes is described by the Kerr solution as expected in general relativity. One can follow either a theory-specific analysis or an agnostic approach. Each strategy has its advantages and disadvantages. In this work, we study the ability of agnostic X-ray tests of the Kerr hypothesis to discover new physics. We simulate X-ray observations of bright Galactic black holes of specific theories of gravity and we analyze the simulated data with a reflection model employing the correct theory of gravity and another reflection model for agnostic tests of the Kerr hypothesis. Our results suggest that agnostic X-ray tests are valid tools to discover new physics, but their constraining power may be lower than a theory-specific analysis. |
2111.06442 | Alexandre Pombo | Carlos A. R. Herdeiro, Alexandre M. Pombo and Eugen Radu | Aspects of Gauss-Bonnet scalarisation of charged black holes | 16 pages, 6 figures | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The general relativity vacuum black holes (BHs) can be scalarised in models
where a scalar field non-minimally couples to the Gauss-Bonnet (GB) invariant.
Such GB scalarisation comes in two flavours, depending on the GB sign that
triggers the phenomenon. Hereafter these two cases are termed GB$^\pm$
scalarisation. For vacuum BHs, only GB$^+$ scalarisation is possible in the
static case, while GB$^-$ scalarisation is $spin$ induced. But for
electrovacuum BHs, GB$^-$ is also $charged$ induced. We discuss the GB$^-$
scalarisation of Reissner-Nordstr\"om and Kerr-Newman BHs, discussing zero
modes and constructing fully non-linear solutions. Some comparisons with GB$^+$
scalarisation are given. To assess the generality of the observed features, we
also briefly consider the GB$^\pm$ scalarisation of stringy dilatonic BHs and
coloured BHs which provide qualitative differences with respect to the
electrovacuum case.
| [
{
"created": "Thu, 11 Nov 2021 19:58:20 GMT",
"version": "v1"
}
] | 2021-11-15 | [
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Pombo",
"Alexandre M.",
""
],
[
"Radu",
"Eugen",
""
]
] | The general relativity vacuum black holes (BHs) can be scalarised in models where a scalar field non-minimally couples to the Gauss-Bonnet (GB) invariant. Such GB scalarisation comes in two flavours, depending on the GB sign that triggers the phenomenon. Hereafter these two cases are termed GB$^\pm$ scalarisation. For vacuum BHs, only GB$^+$ scalarisation is possible in the static case, while GB$^-$ scalarisation is $spin$ induced. But for electrovacuum BHs, GB$^-$ is also $charged$ induced. We discuss the GB$^-$ scalarisation of Reissner-Nordstr\"om and Kerr-Newman BHs, discussing zero modes and constructing fully non-linear solutions. Some comparisons with GB$^+$ scalarisation are given. To assess the generality of the observed features, we also briefly consider the GB$^\pm$ scalarisation of stringy dilatonic BHs and coloured BHs which provide qualitative differences with respect to the electrovacuum case. |
gr-qc/9805082 | Jose Navarro Salas | A. Fabbri and J. Navarro-Salas | Critical energy flux and mass in solvable theories of 2d dilaton gravity | LaTeX file, 12 pages, 4 figures | Phys.Rev. D58 (1998) 084011 | 10.1103/PhysRevD.58.084011 | null | gr-qc hep-th | null | In this paper we address the issue of determining the semiclassical threshold
for black hole formation in the context of a one-parameter family of theories
which continuously interpolates between the RST and BPP models. We find that
the results depend significantly on the initial static configuration of the
spacetime geometry before the influx of matter is turned on. In some cases
there is a critical energy density, given by the Hawking rate of evaporation,
as well as a critical mass $m_{cr}$ (eventually vanishing). In others there is
neither $m_{cr}$ nor a critical flux.
| [
{
"created": "Thu, 21 May 1998 08:43:42 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Fabbri",
"A.",
""
],
[
"Navarro-Salas",
"J.",
""
]
] | In this paper we address the issue of determining the semiclassical threshold for black hole formation in the context of a one-parameter family of theories which continuously interpolates between the RST and BPP models. We find that the results depend significantly on the initial static configuration of the spacetime geometry before the influx of matter is turned on. In some cases there is a critical energy density, given by the Hawking rate of evaporation, as well as a critical mass $m_{cr}$ (eventually vanishing). In others there is neither $m_{cr}$ nor a critical flux. |
0901.4818 | Sergei Kopeikin | Sergei Kopeikin (University of Missouri-Columbia) | On the two approaches to the data analysis of the Cassini interplanetary
relativity experiment | 6 pages, no figures. Accepted for publication to Physics Letters A | Physics Letters A, Vol. 373, pp. 2605--2607 (2009) | 10.1016/j.physleta.2009.05.058 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compare two theoretical approaches to the data analysis of the Cassini
relativity experiment based on the Doppler tracking and the time delay
technique that were published correspondingly by Kopeikin et al in Phys. Lett.
A 367, 276 (2007) and by Bertotti et al in Class. Quant. Grav. 25, 045013
(2008). Bertotti et al believed that they found a discrepancy with our paper
and claimed that our analysis was erroneous. The present paper elucidates,
however, that the discrepancy is illusory and does not exist. The two
techniques give the same result making it evident that the numerical value of
the PPN parameter 'gamma' measured in the Cassini experiment is indeed affected
by the orbital motion of the Sun around the barycenter of the solar system.
| [
{
"created": "Fri, 30 Jan 2009 02:26:37 GMT",
"version": "v1"
},
{
"created": "Wed, 13 May 2009 00:55:38 GMT",
"version": "v2"
}
] | 2009-07-10 | [
[
"Kopeikin",
"Sergei",
"",
"University of Missouri-Columbia"
]
] | We compare two theoretical approaches to the data analysis of the Cassini relativity experiment based on the Doppler tracking and the time delay technique that were published correspondingly by Kopeikin et al in Phys. Lett. A 367, 276 (2007) and by Bertotti et al in Class. Quant. Grav. 25, 045013 (2008). Bertotti et al believed that they found a discrepancy with our paper and claimed that our analysis was erroneous. The present paper elucidates, however, that the discrepancy is illusory and does not exist. The two techniques give the same result making it evident that the numerical value of the PPN parameter 'gamma' measured in the Cassini experiment is indeed affected by the orbital motion of the Sun around the barycenter of the solar system. |
2309.16379 | Yongqiang Wang | Chen-Hao Hao, Shi-Xian Sun, Long-Xing Huang, Rong Zhang, Xin Su,
Yong-Qiang Wang | Emergency of black holes from wormholes | 32 pages, 23 figures | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we study the spherically symmetric Dirac star model in the
presence of a phantom field, obtaining a traversable wormhole solution in
non-trivial topological spacetime. This solution exhibits asymmetry in both the
field configuration and the metric and possesses a finite ADM mass $M$ and
Noether charge $Q$. Furthermore, we find that due to the presence of a wormhole
at the center, this solution exhibits many differences from the Dirac star
under trivial spacetime. Notably, when the wormhole throat size is small, our
numerical calculations indicate the emergence of an extremely approximate black
hole solution on one side of the wormhole spacetime, a phenomenon unexplored.
At this time, the Kretschmann scalar near the throat tends to infinity,
indicating the wormhole becomes untraversable.
| [
{
"created": "Thu, 28 Sep 2023 12:28:02 GMT",
"version": "v1"
}
] | 2023-09-29 | [
[
"Hao",
"Chen-Hao",
""
],
[
"Sun",
"Shi-Xian",
""
],
[
"Huang",
"Long-Xing",
""
],
[
"Zhang",
"Rong",
""
],
[
"Su",
"Xin",
""
],
[
"Wang",
"Yong-Qiang",
""
]
] | In this paper, we study the spherically symmetric Dirac star model in the presence of a phantom field, obtaining a traversable wormhole solution in non-trivial topological spacetime. This solution exhibits asymmetry in both the field configuration and the metric and possesses a finite ADM mass $M$ and Noether charge $Q$. Furthermore, we find that due to the presence of a wormhole at the center, this solution exhibits many differences from the Dirac star under trivial spacetime. Notably, when the wormhole throat size is small, our numerical calculations indicate the emergence of an extremely approximate black hole solution on one side of the wormhole spacetime, a phenomenon unexplored. At this time, the Kretschmann scalar near the throat tends to infinity, indicating the wormhole becomes untraversable. |
1508.04331 | Xin Li | Xin Li and Sai Wang | Primordial power spectrum of tensor perturbations in Finsler spacetime | 15 pages, 12 fugures. arXiv admin note: text overlap with
arXiv:1502.02256 | null | 10.1140/epjc/s10052-016-3890-6 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We first investigate the gravitational wave in the flat Finsler spacetime. In
the Finslerian universe, we derive the perturbed gravitational field equation
with tensor perturbations. The Finslerian background spacetime breaks
rotational symmetry and induces parity violation. Then we obtain the modified
primordial power spectrum of tensor perturbations. The parity violation feature
requires that the anisotropic effect contributes to $TT,TE,EE,BB$ angular
correlation coefficients with $l'=l+1$ and $TB,EB$ with $l'=l$. The numerical
results show that the anisotropic contributions to angular correlation
coefficients depend on $m$, and $TE$ and $ET$ angular correlation coefficients
are different.
| [
{
"created": "Sun, 16 Aug 2015 16:25:22 GMT",
"version": "v1"
}
] | 2016-03-23 | [
[
"Li",
"Xin",
""
],
[
"Wang",
"Sai",
""
]
] | We first investigate the gravitational wave in the flat Finsler spacetime. In the Finslerian universe, we derive the perturbed gravitational field equation with tensor perturbations. The Finslerian background spacetime breaks rotational symmetry and induces parity violation. Then we obtain the modified primordial power spectrum of tensor perturbations. The parity violation feature requires that the anisotropic effect contributes to $TT,TE,EE,BB$ angular correlation coefficients with $l'=l+1$ and $TB,EB$ with $l'=l$. The numerical results show that the anisotropic contributions to angular correlation coefficients depend on $m$, and $TE$ and $ET$ angular correlation coefficients are different. |
1703.10871 | Lucas Torres Santana | Lucas T. Santana, Maur\'icio O. Calv\~ao, Ribamar R. R. Reis, Beatriz
B. Siffert | How does light move in a generic metric-affine background? | 6 pages, 1 figure | Physical Review D 95, 061501(R) (2017) | 10.1103/PhysRevD.95.061501 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Light is the richest information retriever for most physical systems,
particularly so for astronomy and cosmology, in which gravitation is of
paramount importance, and also for solid state defects and metamaterials, in
which some effects can be mimicked by non-Euclidean or even non-Riemannian
geometries. Thus, it is expedient to probe light motion in geometrical
backgrounds alternative to that of general relativity. Here we investigate this
issue in generic metric-affine theories and derive (i) the expression, in the
geometrical optics (eikonal) limit, for light trajectories, showing that they
still are null (extremal) geodesics and thus, in general, no longer
autoparallels, (ii) a generic {formula} to obtain the relation between source
(galaxy) and reception (observer) angular size (area) distances, generalizing
Etherington's original distance reciprocity relation (DRR), and then applying
it to two particular representative non-Riemannian geometries. First in
metric-compatible, completely antisymmetric torsion geometries, the generalized
DRR is not changed at all, and then in Weyl integrable spacetimes, the
generalized DRR assumes a specially simple expression.
| [
{
"created": "Fri, 31 Mar 2017 12:03:25 GMT",
"version": "v1"
}
] | 2017-04-03 | [
[
"Santana",
"Lucas T.",
""
],
[
"Calvão",
"Maurício O.",
""
],
[
"Reis",
"Ribamar R. R.",
""
],
[
"Siffert",
"Beatriz B.",
""
]
] | Light is the richest information retriever for most physical systems, particularly so for astronomy and cosmology, in which gravitation is of paramount importance, and also for solid state defects and metamaterials, in which some effects can be mimicked by non-Euclidean or even non-Riemannian geometries. Thus, it is expedient to probe light motion in geometrical backgrounds alternative to that of general relativity. Here we investigate this issue in generic metric-affine theories and derive (i) the expression, in the geometrical optics (eikonal) limit, for light trajectories, showing that they still are null (extremal) geodesics and thus, in general, no longer autoparallels, (ii) a generic {formula} to obtain the relation between source (galaxy) and reception (observer) angular size (area) distances, generalizing Etherington's original distance reciprocity relation (DRR), and then applying it to two particular representative non-Riemannian geometries. First in metric-compatible, completely antisymmetric torsion geometries, the generalized DRR is not changed at all, and then in Weyl integrable spacetimes, the generalized DRR assumes a specially simple expression. |
gr-qc/0506026 | Larry Ford | L.H. Ford and Thomas A. Roman | Minkowski Vacuum Stress Tensor Fluctuations | 24 pages, 5 figures; Some additional comments added in Sect. IIB and
a more compact argument given in App. C | Phys.Rev. D72 (2005) 105010 | 10.1103/PhysRevD.72.105010 | null | gr-qc hep-th quant-ph | null | We study the fluctuations of the stress tensor for a massless scalar field in
two and four-dimensional Minkowski spacetime in the vacuum state. Covariant
expressions for the stress tensor correlation function are obtained as sums of
derivatives of a scalar function. These expressions allow one to express
spacetime averages of the correlation function as finite integrals. We also
study the correlation between measurements of the energy density along a
worldline. We find that these measurements may be either positively correlated
or anticorrelated. The anticorrelated measurements can be interpreted as
telling us that if one measurement yields one sign for the averaged energy
density, a successive measurement with a suitable time delay is likely to yield
a result with the opposite sign.
| [
{
"created": "Mon, 6 Jun 2005 00:31:15 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Oct 2005 15:21:56 GMT",
"version": "v2"
},
{
"created": "Fri, 14 Oct 2005 18:31:43 GMT",
"version": "v3"
}
] | 2009-11-11 | [
[
"Ford",
"L. H.",
""
],
[
"Roman",
"Thomas A.",
""
]
] | We study the fluctuations of the stress tensor for a massless scalar field in two and four-dimensional Minkowski spacetime in the vacuum state. Covariant expressions for the stress tensor correlation function are obtained as sums of derivatives of a scalar function. These expressions allow one to express spacetime averages of the correlation function as finite integrals. We also study the correlation between measurements of the energy density along a worldline. We find that these measurements may be either positively correlated or anticorrelated. The anticorrelated measurements can be interpreted as telling us that if one measurement yields one sign for the averaged energy density, a successive measurement with a suitable time delay is likely to yield a result with the opposite sign. |
1811.08538 | Sumanta Chakraborty | Mostafizur Rahman, Sumanta Chakraborty, Soumitra SenGupta and Anjan A.
Sen | Fate of Strong Cosmic Censorship Conjecture in Presence of Higher
Spacetime Dimensions | v3, 35 pages, 7 figures, Accepted in JHEP | JHEP 1903, 178 (2019) | 10.1007/JHEP03(2019)178 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Strong cosmic censorship conjecture has been one of the most important leap
of faith in the context of general relativity, providing assurance in the
deterministic nature of the associated field equations. Though it holds well
for asymptotically flat spacetimes, a potential failure of the strong cosmic
censorship conjecture might arise for spacetimes inheriting Cauchy horizon
along with a positive cosmological constant. We have explicitly demonstrated
that violation of the censorship conjecture holds true in the presence of a
Maxwell field even when higher spacetime dimensions are invoked. In particular,
for a higher dimensional Reissner-Nordstr\"{o}m-de Sitter black hole the
violation of cosmic censorship conjecture is at a larger scale compared to the
four dimensional one, for certain choices of the cosmological constant. On the
other hand, for a brane world black hole, the effect of extra dimension is to
make the violation of cosmic censorship conjecture weaker. For rotating black
holes, intriguingly, the cosmic censorship conjecture is always respected even
in presence of higher dimensions. A similar scenario is also observed for a
rotating black hole on the brane.
| [
{
"created": "Wed, 21 Nov 2018 01:14:01 GMT",
"version": "v1"
},
{
"created": "Sun, 10 Feb 2019 13:25:39 GMT",
"version": "v2"
},
{
"created": "Wed, 20 Mar 2019 01:39:11 GMT",
"version": "v3"
}
] | 2019-03-28 | [
[
"Rahman",
"Mostafizur",
""
],
[
"Chakraborty",
"Sumanta",
""
],
[
"SenGupta",
"Soumitra",
""
],
[
"Sen",
"Anjan A.",
""
]
] | Strong cosmic censorship conjecture has been one of the most important leap of faith in the context of general relativity, providing assurance in the deterministic nature of the associated field equations. Though it holds well for asymptotically flat spacetimes, a potential failure of the strong cosmic censorship conjecture might arise for spacetimes inheriting Cauchy horizon along with a positive cosmological constant. We have explicitly demonstrated that violation of the censorship conjecture holds true in the presence of a Maxwell field even when higher spacetime dimensions are invoked. In particular, for a higher dimensional Reissner-Nordstr\"{o}m-de Sitter black hole the violation of cosmic censorship conjecture is at a larger scale compared to the four dimensional one, for certain choices of the cosmological constant. On the other hand, for a brane world black hole, the effect of extra dimension is to make the violation of cosmic censorship conjecture weaker. For rotating black holes, intriguingly, the cosmic censorship conjecture is always respected even in presence of higher dimensions. A similar scenario is also observed for a rotating black hole on the brane. |
gr-qc/0201008 | Janusz Garecki | Janusz Garecki | A Possible Test for Quadratic Gravity in $d \ge 4$ dimensions | 11 pages, no figures, REVTEX | null | 10.1016/S0034-4877(03)80013-7 | null | gr-qc | null | In this letter we consider the Einsteinian strengths and dynamical degrees of
freedom for quadratic gravity. We show that purely metric quadratic gravity
theories are much stronger in Einsteinian sense than the competitive quadratic
gravity theories which admit torsion.
| [
{
"created": "Thu, 3 Jan 2002 16:54:00 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Garecki",
"Janusz",
""
]
] | In this letter we consider the Einsteinian strengths and dynamical degrees of freedom for quadratic gravity. We show that purely metric quadratic gravity theories are much stronger in Einsteinian sense than the competitive quadratic gravity theories which admit torsion. |
0909.2562 | Lorenzo Iorio | Lorenzo Iorio, Matteo Luca Ruggiero | Phenomenological constraints on the Kehagias-Sfetsos solution in the
Horava-Lifshitz gravity from solar system orbital motions | LaTex2e, 10 pages, no figures, 5 tables, 26 references. References
updated. To appear in International Journal of Modern Physics A (IJMPA) | Int.J.Mod.Phys.A25:5399-5408,2010 | 10.1142/S0217751X10050780 | null | gr-qc astro-ph.EP hep-ph physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We focus on Horava-Lifshitz (HL) theory of gravity, and, in particular, on
the Kehagias and Sfetsos s solution that is the analog of Schwarzschild black
hole of General Relativity. In the weak-field and slow-motion approximation we
analytically work out the secular precession of the longitude of the pericentre
of a test particle induced by this solution. Its analytical form is different
from that of the general relativistic Einstein's pericentre precession. Then,
we compare it to the latest determinations of the corrections to the standard
Newtonian/ Einsteinian planetary perihelion precessions recently estimated by
E.V. Pitjeva with the EPM2008 ephemerides. It turns out that the planets of the
solar system, taken singularly one at a time, allow to put lower bounds on the
adimensional HL parameter \psi_0 of the order of 10^-12 (Mercury) 10^-24
(Pluto). They are not able to account for the Pioneer anomalous acceleration
for r > 20 AU.
| [
{
"created": "Mon, 14 Sep 2009 14:50:42 GMT",
"version": "v1"
},
{
"created": "Fri, 18 Sep 2009 14:57:38 GMT",
"version": "v2"
},
{
"created": "Mon, 15 Mar 2010 15:41:28 GMT",
"version": "v3"
},
{
"created": "Fri, 28 May 2010 07:51:59 GMT",
"version": "v4"
},
{
"c... | 2016-11-25 | [
[
"Iorio",
"Lorenzo",
""
],
[
"Ruggiero",
"Matteo Luca",
""
]
] | We focus on Horava-Lifshitz (HL) theory of gravity, and, in particular, on the Kehagias and Sfetsos s solution that is the analog of Schwarzschild black hole of General Relativity. In the weak-field and slow-motion approximation we analytically work out the secular precession of the longitude of the pericentre of a test particle induced by this solution. Its analytical form is different from that of the general relativistic Einstein's pericentre precession. Then, we compare it to the latest determinations of the corrections to the standard Newtonian/ Einsteinian planetary perihelion precessions recently estimated by E.V. Pitjeva with the EPM2008 ephemerides. It turns out that the planets of the solar system, taken singularly one at a time, allow to put lower bounds on the adimensional HL parameter \psi_0 of the order of 10^-12 (Mercury) 10^-24 (Pluto). They are not able to account for the Pioneer anomalous acceleration for r > 20 AU. |
1102.5423 | James Ira Thorpe | James Ira Thorpe, Peiman Maghami, Jeffrey Livas | Time Domain Simulations of Arm Locking in LISA | Revised to address reviewer comments. Accepted by Phys. Rev. D | Phys.Rev.D83:122002,2011 | 10.1103/PhysRevD.83.122002 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Arm locking is a technique that has been proposed for reducing laser
frequency fluctuations in the Laser Interferometer Space Antenna (LISA), a
gravitational-wave observatory sensitive in the milliHertz frequency band. Arm
locking takes advantage of the geometric stability of the triangular
constellation of three spacecraft that comprise LISA to provide a frequency
reference with a stability in the LISA measurement band that exceeds that
available from a standard reference such as an optical cavity or molecular
absorption line. We have implemented a time-domain simulation of arm locking
including the expected limiting noise sources (shot noise, clock noise,
spacecraft jitter noise, and residual laser frequency noise). The effect of
imperfect a priori knowledge of the LISA heterodyne frequencies and the
associated 'pulling' of an arm locked laser is included. We find that our
implementation meets requirements both on the noise and dynamic range of the
laser frequency.
| [
{
"created": "Sat, 26 Feb 2011 15:07:15 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Apr 2011 14:07:29 GMT",
"version": "v2"
}
] | 2011-06-13 | [
[
"Thorpe",
"James Ira",
""
],
[
"Maghami",
"Peiman",
""
],
[
"Livas",
"Jeffrey",
""
]
] | Arm locking is a technique that has been proposed for reducing laser frequency fluctuations in the Laser Interferometer Space Antenna (LISA), a gravitational-wave observatory sensitive in the milliHertz frequency band. Arm locking takes advantage of the geometric stability of the triangular constellation of three spacecraft that comprise LISA to provide a frequency reference with a stability in the LISA measurement band that exceeds that available from a standard reference such as an optical cavity or molecular absorption line. We have implemented a time-domain simulation of arm locking including the expected limiting noise sources (shot noise, clock noise, spacecraft jitter noise, and residual laser frequency noise). The effect of imperfect a priori knowledge of the LISA heterodyne frequencies and the associated 'pulling' of an arm locked laser is included. We find that our implementation meets requirements both on the noise and dynamic range of the laser frequency. |
gr-qc/0010060 | Julius Vanko | Jozef Sima, Miroslav Sukenik and Julius Vanko | Analysis of quantum evaporation process of black holes in the model of
Expansive Nondecelerative Universe | 6 pages, LaTeX | null | null | SSV-00-05 | gr-qc | null | In the model of Expansive Nondecelerative Universe, black hole cannot totally
evaporate via quantum evaporation process proposed by Hawking. In a limiting
case, an equilibrium of gravitation creation and black hole evaporation can be
reached keeping the surface of its horizon constant. This conclusion is in
accordance with the second law of thermodynamics.
| [
{
"created": "Mon, 16 Oct 2000 08:41:49 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sima",
"Jozef",
""
],
[
"Sukenik",
"Miroslav",
""
],
[
"Vanko",
"Julius",
""
]
] | In the model of Expansive Nondecelerative Universe, black hole cannot totally evaporate via quantum evaporation process proposed by Hawking. In a limiting case, an equilibrium of gravitation creation and black hole evaporation can be reached keeping the surface of its horizon constant. This conclusion is in accordance with the second law of thermodynamics. |
2310.07410 | Himanshu Chaudhary | Himanshu Chaudhary, Niyaz Uddin Molla, Madhur Khurana, Ujjal Debnath,
G.Mustafa | Cosmological Test of Dark Energy Parametrizations in Horava-Lifshitz
Gravity | 24 pages, 20 figures, accepted for publication in European Physical
Journal C (EPJC) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we assume the FRLW Universe which is filled with dark matter
along with dark energy in the framework of Horava-Lifshitz (HL) gravity. The
dark energy is considered as the Linear (Model I) and CPL (Model II)
parametrizations of the equation of state parameter. For both models, we
express the Hubble parameter $H(z)$ in terms of the model parameters and
redshift $z$. To rigorously constrain the model, we have employed a
comprehensive set of recent observational datasets including cosmic
chronometers (CC), Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations
(BAO), Gamma-ray Burst (GRB), Quasar (Q) and Cosmic Microwave Background
Radiation (CMB). Through the joint analysis of this diverse collection of
datasets, we have achieved tighter constraints on the model's parameters. This,
in turn, allows us to delve into both the physical and geometrical aspects of
the model with greater precision. Furthermore, our analysis has enabled us to
determine the present values of crucial cosmological parameters, including
$H_{0}$, $\Omega_{m0}$, $\Omega_{k0}$ and $\Omega_{\Lambda0}$. It's noteworthy
that our results are consistent with recent findings from Planck 2018,
underscoring the reliability and relevance of our models in the current
cosmological context. We also conduct analysis of cosmographic parameters and
apply statefinder and diagnostic tests to explore the evolution of the
Universe. In addition, the AIC and BIC suggest that the $\Lambda$CDM model is
the preferred model among all our considered models. Our investigation into the
models has unveiled intriguing features of the late universe
| [
{
"created": "Wed, 11 Oct 2023 11:56:59 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Feb 2024 17:00:47 GMT",
"version": "v2"
}
] | 2024-02-07 | [
[
"Chaudhary",
"Himanshu",
""
],
[
"Molla",
"Niyaz Uddin",
""
],
[
"Khurana",
"Madhur",
""
],
[
"Debnath",
"Ujjal",
""
],
[
"Mustafa",
"G.",
""
]
] | In this work, we assume the FRLW Universe which is filled with dark matter along with dark energy in the framework of Horava-Lifshitz (HL) gravity. The dark energy is considered as the Linear (Model I) and CPL (Model II) parametrizations of the equation of state parameter. For both models, we express the Hubble parameter $H(z)$ in terms of the model parameters and redshift $z$. To rigorously constrain the model, we have employed a comprehensive set of recent observational datasets including cosmic chronometers (CC), Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), Gamma-ray Burst (GRB), Quasar (Q) and Cosmic Microwave Background Radiation (CMB). Through the joint analysis of this diverse collection of datasets, we have achieved tighter constraints on the model's parameters. This, in turn, allows us to delve into both the physical and geometrical aspects of the model with greater precision. Furthermore, our analysis has enabled us to determine the present values of crucial cosmological parameters, including $H_{0}$, $\Omega_{m0}$, $\Omega_{k0}$ and $\Omega_{\Lambda0}$. It's noteworthy that our results are consistent with recent findings from Planck 2018, underscoring the reliability and relevance of our models in the current cosmological context. We also conduct analysis of cosmographic parameters and apply statefinder and diagnostic tests to explore the evolution of the Universe. In addition, the AIC and BIC suggest that the $\Lambda$CDM model is the preferred model among all our considered models. Our investigation into the models has unveiled intriguing features of the late universe |
2108.09466 | Jaroslav Vrba | Zden\v{e}k Stuchl\'ik and Jaroslav Vrba | Trapping of null geodesics in slowly rotating extremely compact Tolman
VII spacetimes | arXiv admin note: text overlap with arXiv:2011.13616 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Region of trapped null geodesics hidden inside of extremely compact objects
is of astrophysical importance because of trapping of gravitational waves, or
neutrinos. The trapping effect of null geodesics was extensively studied for
spherically symmetric extremely compact objects. Recently, influence of
rotation of the extremely compact objects on the trapping of null geodesics was
treated in the simplest possible model of internal linearised
\mbox{Hartle--Thorne} spacetime with uniform energy density distribution and
uniform emissivity distribution of null geodesics. Here we extend the study of
the rotation influence on the trapping effect in the case of linearized
\mbox{Hartle--Thorne} spacetimes based on the Tolman VII spherically symmetric
solutions, where we assume the emissivity of the null geodesics proportional to
the energy density of the Tolman VII object having quadratic radial profile. We
demonstrate enhancement (suppression) of the trapping effect in the case of
counter-rotating (co-rotating) null geodesics due to the behavior of the
effective potentials and escape cones of the null geodesics in the linearised
Hartle--Thorne--Tolman VII spacetimes. In dependence on the parameters of these
spacetimes we determine the "local" and "global" coefficients of efficiency of
the trapping and compare the results to those related to the rotating
spacetimes based on the internal Schwarzschild spacetimes. We demonstrate that
in the Tolman VII spacetimes the trapping is more efficient, being allowed in
objects with radii larger than those of the trapping internal Schwarzschild
spacetimes, occurring even for $R>3.3M$.
| [
{
"created": "Sat, 21 Aug 2021 09:01:01 GMT",
"version": "v1"
}
] | 2021-08-24 | [
[
"Stuchlík",
"Zdeněk",
""
],
[
"Vrba",
"Jaroslav",
""
]
] | Region of trapped null geodesics hidden inside of extremely compact objects is of astrophysical importance because of trapping of gravitational waves, or neutrinos. The trapping effect of null geodesics was extensively studied for spherically symmetric extremely compact objects. Recently, influence of rotation of the extremely compact objects on the trapping of null geodesics was treated in the simplest possible model of internal linearised \mbox{Hartle--Thorne} spacetime with uniform energy density distribution and uniform emissivity distribution of null geodesics. Here we extend the study of the rotation influence on the trapping effect in the case of linearized \mbox{Hartle--Thorne} spacetimes based on the Tolman VII spherically symmetric solutions, where we assume the emissivity of the null geodesics proportional to the energy density of the Tolman VII object having quadratic radial profile. We demonstrate enhancement (suppression) of the trapping effect in the case of counter-rotating (co-rotating) null geodesics due to the behavior of the effective potentials and escape cones of the null geodesics in the linearised Hartle--Thorne--Tolman VII spacetimes. In dependence on the parameters of these spacetimes we determine the "local" and "global" coefficients of efficiency of the trapping and compare the results to those related to the rotating spacetimes based on the internal Schwarzschild spacetimes. We demonstrate that in the Tolman VII spacetimes the trapping is more efficient, being allowed in objects with radii larger than those of the trapping internal Schwarzschild spacetimes, occurring even for $R>3.3M$. |
gr-qc/9406004 | Melnikov Vitaly Nikolaevich | M. Yu. Konstantinov | Causality Properties of Topologically Nontrivial Space-Time Models | 9 pages., RGA-CSVR-007/94. 3 figures available by request | Int.J.Mod.Phys.D4:247-258,1995 | 10.1142/S0218271895000181 | null | gr-qc | null | The causality properties of space-time models with traversable wormholes are
considered. It is shown that relativity principle cannot be applied to the
motion of the wormhole's mouths in the outer space and the dynamical wormhole
transformation into the time machine is impossible. The examples of both causal
and noncausal space-time models with traversable wormholes are also considered.
Some properties of space-time models with causality violation are briefly
discussed.
| [
{
"created": "Fri, 3 Jun 1994 00:44:59 GMT",
"version": "v1"
}
] | 2011-04-20 | [
[
"Konstantinov",
"M. Yu.",
""
]
] | The causality properties of space-time models with traversable wormholes are considered. It is shown that relativity principle cannot be applied to the motion of the wormhole's mouths in the outer space and the dynamical wormhole transformation into the time machine is impossible. The examples of both causal and noncausal space-time models with traversable wormholes are also considered. Some properties of space-time models with causality violation are briefly discussed. |
1910.05277 | Cliff Burgess | Ivana Babic, C.P. Burgess and Ghazal Geshnizjani | Keeping an Eye on DBI: Power-counting for small-$c_s$ Cosmology | 24 pages, 1 figure | null | 10.1088/1475-7516/2020/05/023 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Inflationary mechanisms for generating primordial fluctuations ultimately
compute them as the leading contributions in a derivative expansion, with
corrections controlled by powers of derivatives like the Hubble scale over
Planck mass: $H/M_p$. At face value this derivative expansion breaks down for
models with a small sound speed, $c_s$, to the extent that $c_s \ll 1$ is
obtained by having higher-derivative interactions like $\mathfrak{L}_{\rm eff}
\sim (\partial \Phi)^4$ compete with lower-derivative propagation. This concern
arises more generally for models whose lagrangian is given as a function $P(X)$
for $X = -\partial_\mu \Phi \partial^\mu \Phi$ --- including in particular DBI
models for which $P(X) \propto \sqrt{1-kX}$ --- since these keep all orders in
$\partial \Phi$ while dropping $\partial^n \Phi$ for $n > 1$. We here find a
sensible power-counting scheme for DBI models that gives a controlled expansion
in powers of three types of small parameters: $H/M_p$, slow-roll parameters
(possibly) and $c_s \ll 1$. We do not find a similar expansion framework for
generic small-$c_s$ or $P(X)$ models. Our power-counting result quantifies the
theoretical error for any prediction (such as for inflationary correlation
functions) by fixing the leading power of these small parameters that is
dropped when not computing all graphs (such as by restricting to the classical
approximation); a prerequisite for meaningful comparisons with observations.
The new power-counting regime arises because small $c_s$ alters the kinematics
of free fluctuations in a way that changes how interactions scale at low
energies, in particular allowing $1-c_s$ to be larger than derivative-measuring
quantities like $(H/M_p)^2$.
| [
{
"created": "Fri, 11 Oct 2019 16:13:13 GMT",
"version": "v1"
}
] | 2020-05-20 | [
[
"Babic",
"Ivana",
""
],
[
"Burgess",
"C. P.",
""
],
[
"Geshnizjani",
"Ghazal",
""
]
] | Inflationary mechanisms for generating primordial fluctuations ultimately compute them as the leading contributions in a derivative expansion, with corrections controlled by powers of derivatives like the Hubble scale over Planck mass: $H/M_p$. At face value this derivative expansion breaks down for models with a small sound speed, $c_s$, to the extent that $c_s \ll 1$ is obtained by having higher-derivative interactions like $\mathfrak{L}_{\rm eff} \sim (\partial \Phi)^4$ compete with lower-derivative propagation. This concern arises more generally for models whose lagrangian is given as a function $P(X)$ for $X = -\partial_\mu \Phi \partial^\mu \Phi$ --- including in particular DBI models for which $P(X) \propto \sqrt{1-kX}$ --- since these keep all orders in $\partial \Phi$ while dropping $\partial^n \Phi$ for $n > 1$. We here find a sensible power-counting scheme for DBI models that gives a controlled expansion in powers of three types of small parameters: $H/M_p$, slow-roll parameters (possibly) and $c_s \ll 1$. We do not find a similar expansion framework for generic small-$c_s$ or $P(X)$ models. Our power-counting result quantifies the theoretical error for any prediction (such as for inflationary correlation functions) by fixing the leading power of these small parameters that is dropped when not computing all graphs (such as by restricting to the classical approximation); a prerequisite for meaningful comparisons with observations. The new power-counting regime arises because small $c_s$ alters the kinematics of free fluctuations in a way that changes how interactions scale at low energies, in particular allowing $1-c_s$ to be larger than derivative-measuring quantities like $(H/M_p)^2$. |
1405.2465 | Genly Le\'on | Carlos R. Fadragas (Havana, Central de Las Villas U.) and Genly Leon
(Valparaiso U., Catolica) | Some remarks about non-minimally coupled scalar field models | 32 pages, 6 figures. Matches the published version in CQG | Class. Quantum Grav. 31, 195011 (2014) | 10.1088/0264-9381/31/19/195011 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Several results related to flat Friedmann-Lema\^{\i}tre-Robertson-Walker
models in the conformal (Einstein) frame of scalar-tensor gravity theories are
extended. Scalar fields with arbitrary (positive) potentials and arbitrary
coupling functions are considered. Mild assumptions under such functions
(differentiable class, number of singular points, asymptotes, etc) are
introduced in a straightforward manner in order to characterize the asymptotic
structure on a phase space. We pay special attention to the possible scaling
solutions. Numerical evidence confirming our results is presented.
| [
{
"created": "Sat, 10 May 2014 19:43:44 GMT",
"version": "v1"
},
{
"created": "Sun, 12 Oct 2014 21:46:09 GMT",
"version": "v2"
}
] | 2014-10-14 | [
[
"Fadragas",
"Carlos R.",
"",
"Havana, Central de Las Villas U."
],
[
"Leon",
"Genly",
"",
"Valparaiso U., Catolica"
]
] | Several results related to flat Friedmann-Lema\^{\i}tre-Robertson-Walker models in the conformal (Einstein) frame of scalar-tensor gravity theories are extended. Scalar fields with arbitrary (positive) potentials and arbitrary coupling functions are considered. Mild assumptions under such functions (differentiable class, number of singular points, asymptotes, etc) are introduced in a straightforward manner in order to characterize the asymptotic structure on a phase space. We pay special attention to the possible scaling solutions. Numerical evidence confirming our results is presented. |
gr-qc/0105012 | Papakostas Taksiarhis | T.Papakostas | Anisotropic fluids in the case of stationary and axisymmetric spaces of
General Relativity | 14 pages,submitted to Int J Mod Phys D | Int.J.Mod.Phys. D10 (2001) 869-880 | 10.1142/S0218271801001268 | null | gr-qc | null | We present a stationary axisymmetric solution belonging to Carter's family
[A] of spaces and representing an anisotropic fluid configuration.
| [
{
"created": "Thu, 3 May 2001 08:23:00 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Papakostas",
"T.",
""
]
] | We present a stationary axisymmetric solution belonging to Carter's family [A] of spaces and representing an anisotropic fluid configuration. |
2209.01050 | Vladimir Kassandrov | Vladimir V. Kassandrov and Nina V. Markova | Extended geometry and kinematics induced by biquaternionic and twistor
structures | 9 pages. Report on the conference PIRT-21 | Journal of Physics: Conference Series (2021), 2081 012023, 012023 | 10.1088/1742-6596/2081/1/2023 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The algebra of biquaternions possess a manifestly Lorentz invariant form and
induces an extended space-time geometry. We consider the links between this
complex pre-geometry and real geometry of the Minkowski space-time. Twistor
structures naturally arise in the framework of biquaternionic analysis. Both
together, algebraic and twistor structures impose rigid restriction on the
transport of singular points of biquaternion-valued fields identified with
particle-like formations.
| [
{
"created": "Wed, 31 Aug 2022 13:05:07 GMT",
"version": "v1"
}
] | 2022-09-05 | [
[
"Kassandrov",
"Vladimir V.",
""
],
[
"Markova",
"Nina V.",
""
]
] | The algebra of biquaternions possess a manifestly Lorentz invariant form and induces an extended space-time geometry. We consider the links between this complex pre-geometry and real geometry of the Minkowski space-time. Twistor structures naturally arise in the framework of biquaternionic analysis. Both together, algebraic and twistor structures impose rigid restriction on the transport of singular points of biquaternion-valued fields identified with particle-like formations. |
1508.05745 | Arunava Bhadra Dr. | Samrat Ghosh and Arunava Bhadra | Influences of Dark Energy and dark matter on Gravitational Time
Advancement | 7 pages, no figure | Eur. Phys. J. C (2015) 75:494 | 10.1140/epjc/s10052-015-3719-8 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The effect of dark matter/energy on gravitational time advancement (negative
effective time delay) has been investigated considering few dark energy/matter
models including cosmological constant. It is found that dark energy gives only
(positive) gravitational time delay irrespective of the position of the
observer whereas pure Schwarzschild geometry leads to gravitational time
advancement when the observer is situated at relatively stronger gravitational
field point in the light trajectory. Consequently, there will be no time
advancement effect at all at radial distances where gravitational field due to
dark energy is stronger than the gravitational field of Schwarzschild geometry.
| [
{
"created": "Mon, 24 Aug 2015 10:14:08 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Nov 2015 09:03:33 GMT",
"version": "v2"
}
] | 2015-11-09 | [
[
"Ghosh",
"Samrat",
""
],
[
"Bhadra",
"Arunava",
""
]
] | The effect of dark matter/energy on gravitational time advancement (negative effective time delay) has been investigated considering few dark energy/matter models including cosmological constant. It is found that dark energy gives only (positive) gravitational time delay irrespective of the position of the observer whereas pure Schwarzschild geometry leads to gravitational time advancement when the observer is situated at relatively stronger gravitational field point in the light trajectory. Consequently, there will be no time advancement effect at all at radial distances where gravitational field due to dark energy is stronger than the gravitational field of Schwarzschild geometry. |
1102.3803 | Remo Garattini | Remo Garattini and Gianluca Mandanici | Modified Dispersion Relations lead to a finite Zero Point Gravitational
Energy | LaTex 16 pages, 6 figures | Phys.Rev.D83:084021,2011 | 10.1103/PhysRevD.83.084021 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compute the Zero Point Energy in a spherically symmetric background
distorted at high energy as predicted by \textit{Gravity's Rainbow}. In this
context we setup a Sturm-Liouville problem with the cosmological constant
considered as the associated eigenvalue. The eigenvalue equation is a
reformulation of the Wheeler-DeWitt equation. With the help of a canonical
decomposition, we find that the relevant contribution to one loop is given by
the graviton quantum fluctuations around the given background. By means of a
variational approach based on gaussian trial functionals, we find that the
ordinary divergences can here be handled by an appropriate choice of the
rainbow's functions, in contrast to what happens in other conventional
approaches. A final discussion on the connection of our result with the
observed cosmological constant is also reported.
| [
{
"created": "Fri, 18 Feb 2011 10:44:17 GMT",
"version": "v1"
}
] | 2011-04-22 | [
[
"Garattini",
"Remo",
""
],
[
"Mandanici",
"Gianluca",
""
]
] | We compute the Zero Point Energy in a spherically symmetric background distorted at high energy as predicted by \textit{Gravity's Rainbow}. In this context we setup a Sturm-Liouville problem with the cosmological constant considered as the associated eigenvalue. The eigenvalue equation is a reformulation of the Wheeler-DeWitt equation. With the help of a canonical decomposition, we find that the relevant contribution to one loop is given by the graviton quantum fluctuations around the given background. By means of a variational approach based on gaussian trial functionals, we find that the ordinary divergences can here be handled by an appropriate choice of the rainbow's functions, in contrast to what happens in other conventional approaches. A final discussion on the connection of our result with the observed cosmological constant is also reported. |
1812.07836 | Jibitesh Dutta | Jibitesh Dutta, Wompherdeiki Khyllep, Hmar Zonunmawia | Cosmological dynamics of the general non-canonical scalar field models | Revised to match EPJC version; 12 pages, 6 figures; Accepted in EPJC | The European Physical Journal C, (2019) 79: 359 | 10.1140/epjc/s10052-019-6885-2 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We extend the investigation of cosmological dynamics of the general
non-canonical scalar field models by dynamical system techniques for a broad
class of potentials and coupling functions. In other words, we do not restrict
the analysis to exponential or power-law potentials and coupling functions.
This type of investigation helps in understanding the general properties of a
class of cosmological models. In order to better understand the phase space of
the models, we investigate the various special cases and discuss the stability
and viability issues. Performing a detailed stability analysis, we show that it
is possible to describe the cosmic history of the universe at the background
level namely the early radiation dominated era, intermediate matter dominated
era and the late time dark energy domination. Moreover, we find that we can
identify a broad class of coupling functions for which it is possible to get an
appealing unified description of dark matter and dark energy. The results
obtained here, therefore, enlarge the previous analyses wherein only a specific
potential and coupling functions describes the unification of dark sectors.
Further, we also observe that a specific scenario can also possibly explain the
phenomenon of slow-roll inflationary exit.
| [
{
"created": "Wed, 19 Dec 2018 09:32:04 GMT",
"version": "v1"
},
{
"created": "Tue, 23 Apr 2019 12:49:24 GMT",
"version": "v2"
}
] | 2019-04-30 | [
[
"Dutta",
"Jibitesh",
""
],
[
"Khyllep",
"Wompherdeiki",
""
],
[
"Zonunmawia",
"Hmar",
""
]
] | We extend the investigation of cosmological dynamics of the general non-canonical scalar field models by dynamical system techniques for a broad class of potentials and coupling functions. In other words, we do not restrict the analysis to exponential or power-law potentials and coupling functions. This type of investigation helps in understanding the general properties of a class of cosmological models. In order to better understand the phase space of the models, we investigate the various special cases and discuss the stability and viability issues. Performing a detailed stability analysis, we show that it is possible to describe the cosmic history of the universe at the background level namely the early radiation dominated era, intermediate matter dominated era and the late time dark energy domination. Moreover, we find that we can identify a broad class of coupling functions for which it is possible to get an appealing unified description of dark matter and dark energy. The results obtained here, therefore, enlarge the previous analyses wherein only a specific potential and coupling functions describes the unification of dark sectors. Further, we also observe that a specific scenario can also possibly explain the phenomenon of slow-roll inflationary exit. |
gr-qc/9401004 | Roh-Suan Tung | James M. Nester, Roh-Suan Tung and Yuan Zhong Zhang | Ashtekar's New Variables and Positive Energy | 12 pages Plain TeX | Class.Quant.Grav.11:757-766,1994 | 10.1088/0264-9381/11/3/024 | null | gr-qc | null | We discuss earlier unsuccessful attempts to formulate a positive
gravitational energy proof in terms of the New Variables of Ashtekar. We also
point out the difficulties of a Witten spinor type proof. We then use the
special orthonormal frame gauge conditions to obtain a locally positive
expression for the New Variables Hamiltonian and thereby a ``localization'' of
gravitational energy as well as a positive energy proof.
| [
{
"created": "Fri, 7 Jan 1994 16:51:47 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Nester",
"James M.",
""
],
[
"Tung",
"Roh-Suan",
""
],
[
"Zhang",
"Yuan Zhong",
""
]
] | We discuss earlier unsuccessful attempts to formulate a positive gravitational energy proof in terms of the New Variables of Ashtekar. We also point out the difficulties of a Witten spinor type proof. We then use the special orthonormal frame gauge conditions to obtain a locally positive expression for the New Variables Hamiltonian and thereby a ``localization'' of gravitational energy as well as a positive energy proof. |
gr-qc/9212007 | Desmond Mc Manus | Des J. Mc Manus and Michel A. Vandyck | Weak-Field Gravity of Revolving Circular Cosmic Strings | 13 pages, LaTeX | Phys.Rev. D47 (1993) 1491-1496 | 10.1103/PhysRevD.47.1491 | null | gr-qc | null | A weak-field solution of Einstein's equations is constructed. It is generated
by a circular cosmic string revolving in its plane about the centre of the
circle. (The revolution is introduced to prevent the string from collapsing.)
This solution exhibits a conical singularity, and the corresponding deficit
angle is the same as for a straight string of the same linear energy density,
irrespective of the angular velocity of the string.
| [
{
"created": "Thu, 10 Dec 1992 15:33:40 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Manus",
"Des J. Mc",
""
],
[
"Vandyck",
"Michel A.",
""
]
] | A weak-field solution of Einstein's equations is constructed. It is generated by a circular cosmic string revolving in its plane about the centre of the circle. (The revolution is introduced to prevent the string from collapsing.) This solution exhibits a conical singularity, and the corresponding deficit angle is the same as for a straight string of the same linear energy density, irrespective of the angular velocity of the string. |
2006.08663 | Baoyi Chen | Baoyi Chen, Feng-Li Lin, Bo Ning and Yanbei Chen | Constraints on low-energy effective theories from weak cosmic censorship | 22 pages, 2 figures | Phys. Rev. Lett. 126 (2021) 031102 | 10.1103/PhysRevLett.126.031102 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the weak cosmic censorship conjecture (WCCC) for the extremal
charged black hole in possible generalizations of Einstein-Maxwell theory due
to the higher order corrections, up to fourth-derivative terms. Our derivation
is based on Wald's gedanken experiment to destroy an extremal black hole. We
find that, provided the null energy condition for the falling matter, the WCCC
is preserved for all possible generalizations. Thus, the WCCC cannot serve as a
constraint to the higher order effective theories. We also show that up to
first order variations of black hole mass and charge, WCCC is preserved for
non-rotating extremal black holes in all $n$-dimensional
diffeomorphism-covariant theories of gravity and $U(1)$ gauge field.
| [
{
"created": "Mon, 15 Jun 2020 18:12:34 GMT",
"version": "v1"
},
{
"created": "Sun, 7 Mar 2021 19:28:43 GMT",
"version": "v2"
}
] | 2021-03-09 | [
[
"Chen",
"Baoyi",
""
],
[
"Lin",
"Feng-Li",
""
],
[
"Ning",
"Bo",
""
],
[
"Chen",
"Yanbei",
""
]
] | We examine the weak cosmic censorship conjecture (WCCC) for the extremal charged black hole in possible generalizations of Einstein-Maxwell theory due to the higher order corrections, up to fourth-derivative terms. Our derivation is based on Wald's gedanken experiment to destroy an extremal black hole. We find that, provided the null energy condition for the falling matter, the WCCC is preserved for all possible generalizations. Thus, the WCCC cannot serve as a constraint to the higher order effective theories. We also show that up to first order variations of black hole mass and charge, WCCC is preserved for non-rotating extremal black holes in all $n$-dimensional diffeomorphism-covariant theories of gravity and $U(1)$ gauge field. |
gr-qc/0201093 | George E. A. Matsas | Jorge Castineiras, Luis C. B. Crispino, George E. A. Matsas and Daniel
A. T. Vanzella | Free massive particles with total energy E < mc^2 in curved spacetimes | 12 pages (REVTEX), 12 figures | Phys.Rev. D65 (2002) 104019 | 10.1103/PhysRevD.65.104019 | null | gr-qc | null | We analyze free elementary particles with rest mass $m$ and total energy $E <
m c^2$ in the Rindler wedge, outside Reissner-Nordstrom black holes and in the
spacetime of relativistic (and non-relativistic) stars, and use
Unruh-DeWitt-like detectors to calculate the associated particle detection rate
in each case. The (mean) particle position is identified with the spatial
average of the excitation probability of the detectors, which are supposed to
cover the whole space. Our results are shown to be in harmony with General
Relativity classical predictions. Eventually we reconcile our conclusions with
Earth-based experiments which are in good agreement with $E \geq m c^2$.
| [
{
"created": "Wed, 30 Jan 2002 11:46:45 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Castineiras",
"Jorge",
""
],
[
"Crispino",
"Luis C. B.",
""
],
[
"Matsas",
"George E. A.",
""
],
[
"Vanzella",
"Daniel A. T.",
""
]
] | We analyze free elementary particles with rest mass $m$ and total energy $E < m c^2$ in the Rindler wedge, outside Reissner-Nordstrom black holes and in the spacetime of relativistic (and non-relativistic) stars, and use Unruh-DeWitt-like detectors to calculate the associated particle detection rate in each case. The (mean) particle position is identified with the spatial average of the excitation probability of the detectors, which are supposed to cover the whole space. Our results are shown to be in harmony with General Relativity classical predictions. Eventually we reconcile our conclusions with Earth-based experiments which are in good agreement with $E \geq m c^2$. |
2401.09482 | Dr. Sudhaker Upadhyay | Behnam Pourhassan, Seyed Hossein Hendi, Sudhaker Upadhyay, Izzet
Sakalli, Emmanuel N. Saridakis | Thermal fluctuations of (non)linearly charged BTZ black hole in massive
gravity | 25 pages, 25 captioned figures, to appear in IJMPD | null | 10.1142/S0218271823501109 | null | gr-qc astro-ph.HE hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider a charged BTZ black hole in asymptotically AdS space-time of
massive gravity to study the effect of the thermal fluctuations on the black
hole thermodynamics. We consider the Einstein-Born-Infeld solution and
investigate critical points and stability. We also compare the results with the
case of Einstein-Maxwell solutions. Besides, we find that thermal fluctuations,
which appear as a logarithmic term in the entropy, affect the stability of the
black hole and change the phase transition point. Moreover, we study the
geometrical thermodynamics and find that the behaviour of the linear Maxwell
solution is the same as the nonlinear one.
| [
{
"created": "Mon, 15 Jan 2024 18:12:00 GMT",
"version": "v1"
}
] | 2024-01-19 | [
[
"Pourhassan",
"Behnam",
""
],
[
"Hendi",
"Seyed Hossein",
""
],
[
"Upadhyay",
"Sudhaker",
""
],
[
"Sakalli",
"Izzet",
""
],
[
"Saridakis",
"Emmanuel N.",
""
]
] | We consider a charged BTZ black hole in asymptotically AdS space-time of massive gravity to study the effect of the thermal fluctuations on the black hole thermodynamics. We consider the Einstein-Born-Infeld solution and investigate critical points and stability. We also compare the results with the case of Einstein-Maxwell solutions. Besides, we find that thermal fluctuations, which appear as a logarithmic term in the entropy, affect the stability of the black hole and change the phase transition point. Moreover, we study the geometrical thermodynamics and find that the behaviour of the linear Maxwell solution is the same as the nonlinear one. |
gr-qc/0701140 | Bayram Tekin | S. Deser and Bayram Tekin | New Energy Definition for Higher Curvature Gravities | 3 pages, Typos fixed | Phys.Rev.D75:084032,2007 | 10.1103/PhysRevD.75.084032 | BRX-TH-585 | gr-qc hep-th | null | We propose a novel but natural definition of conserved quantities for gravity
models quadratic and higher in curvature. Based on the spatial asymptotics of
curvature rather than of metric, it avoids the GR energy machinery's more
egregious problems--such as zero energy "theorems" and failure in flat
backgrounds -- in this fourth-derivative realm. In D>4, the present expression
indeed correctly discriminates between second derivative Gauss-Bonnet and
generic, fourth derivative, actions.
| [
{
"created": "Thu, 25 Jan 2007 20:49:27 GMT",
"version": "v1"
},
{
"created": "Thu, 3 May 2007 13:46:17 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Deser",
"S.",
""
],
[
"Tekin",
"Bayram",
""
]
] | We propose a novel but natural definition of conserved quantities for gravity models quadratic and higher in curvature. Based on the spatial asymptotics of curvature rather than of metric, it avoids the GR energy machinery's more egregious problems--such as zero energy "theorems" and failure in flat backgrounds -- in this fourth-derivative realm. In D>4, the present expression indeed correctly discriminates between second derivative Gauss-Bonnet and generic, fourth derivative, actions. |
gr-qc/0605124 | Charles Wang | Charles H.-T. Wang | New 'phase' of quantum gravity | 17 pages, 6 figures, To appear in the 2006 Christmas Issue of Phil.
Trans. Roy. Soc. A | Phil.Trans.Roy.Soc.Lond. A364 (2006) 3375-3388 | 10.1098/rsta.2006.1904 | null | gr-qc hep-th physics.pop-ph quant-ph | null | The emergence of loop quantum gravity over the past two decades has
stimulated a great resurgence of interest in unifying general relativity and
quantum mechanics. Amongst a number of appealing features of this approach are
the intuitive picture of quantum geometry using spin networks and powerful
mathematical tools from gauge field theory. However, the present form of loop
quantum gravity suffers from a quantum ambiguity, due to the presence of a free
(Barbero-Immirzi) parameter. Following recent progress on the conformal
decomposition of gravitational fields, we present a new phase space for general
relativity. In addition to spin-gauge symmetry, the new phase space also
incorporates conformal symmetry making the description parameter free. The
Barbero-Immirzi ambiguity is shown to occur only if the conformal symmetry is
gauge-fixed prior to quantization. By withholding its full symmetries, the new
phase space offers a promising platform for the future development of loop
quantum gravity. This paper aims to provide an exposition, at a reduced
technical level, of the above theoretical advances and their background
developments. Further details are referred to cited references.
| [
{
"created": "Wed, 24 May 2006 00:51:44 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Sep 2006 20:59:32 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Wang",
"Charles H. -T.",
""
]
] | The emergence of loop quantum gravity over the past two decades has stimulated a great resurgence of interest in unifying general relativity and quantum mechanics. Amongst a number of appealing features of this approach are the intuitive picture of quantum geometry using spin networks and powerful mathematical tools from gauge field theory. However, the present form of loop quantum gravity suffers from a quantum ambiguity, due to the presence of a free (Barbero-Immirzi) parameter. Following recent progress on the conformal decomposition of gravitational fields, we present a new phase space for general relativity. In addition to spin-gauge symmetry, the new phase space also incorporates conformal symmetry making the description parameter free. The Barbero-Immirzi ambiguity is shown to occur only if the conformal symmetry is gauge-fixed prior to quantization. By withholding its full symmetries, the new phase space offers a promising platform for the future development of loop quantum gravity. This paper aims to provide an exposition, at a reduced technical level, of the above theoretical advances and their background developments. Further details are referred to cited references. |
gr-qc/9310016 | null | J.W. Barrett and T.J. Foxon | Semi-Classical Limits of Simplicial Quantum Gravity | 14 pages in Plain TeX, (figures available on request), DAMTP-R93/26 | Class.Quant.Grav.11:543-556,1994 | 10.1088/0264-9381/11/3/009 | null | gr-qc hep-th | null | We consider the simplicial state-sum model of Ponzano and Regge as a path
integral for quantum gravity in three dimensions.
We examine the Lorentzian geometry of a single 3-simplex and of a simplicial
manifold, and interpret an asymptotic formula for $6j$-symbols in terms of this
geometry. This extends Ponzano and Regge's similar interpretation for Euclidean
geometry.
We give a geometric interpretation of the stationary points of this
state-sum, by showing that, at these points, the simplicial manifold may be
mapped locally into flat Lorentzian or Euclidean space. This lends weight to
the interpretation of the state-sum as a path integral, which has solutions
corresponding to both Lorentzian and Euclidean gravity in three dimensions.
| [
{
"created": "Fri, 8 Oct 1993 12:11:36 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Barrett",
"J. W.",
""
],
[
"Foxon",
"T. J.",
""
]
] | We consider the simplicial state-sum model of Ponzano and Regge as a path integral for quantum gravity in three dimensions. We examine the Lorentzian geometry of a single 3-simplex and of a simplicial manifold, and interpret an asymptotic formula for $6j$-symbols in terms of this geometry. This extends Ponzano and Regge's similar interpretation for Euclidean geometry. We give a geometric interpretation of the stationary points of this state-sum, by showing that, at these points, the simplicial manifold may be mapped locally into flat Lorentzian or Euclidean space. This lends weight to the interpretation of the state-sum as a path integral, which has solutions corresponding to both Lorentzian and Euclidean gravity in three dimensions. |
1706.01112 | Maur\'icio Richartz | Maur\'icio Richartz, Carlos A. R. Herdeiro, Emanuele Berti | Synchronous frequencies of extremal Kerr black holes: resonances,
scattering and stability | v2: 10 pages, 2 figures, 1 table. Matches published version | Phys. Rev. D 96, 044034 (2017) | 10.1103/PhysRevD.96.044034 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The characteristic damping times of the natural oscillations of a Kerr black
hole become arbitrarily large as the extremal limit is approached. This
behavior is associated with the so-called zero damped modes (ZDMs), and
suggests that extremal black holes are characterized by quasinormal modes whose
frequencies are purely real. Since these frequencies correspond to oscillations
whose angular phase velocity matches the horizon angular velocity of the black
hole, they are sometimes called "synchronous frequencies". Several authors have
studied the ZDMs for near-extremal black holes. Recently, their correspondence
to branch points of the Green's function of the wave equation was linked to the
Aretakis instability of extremal black holes. Here we investigate the existence
of ZDMs for extremal black holes, showing that these real-axis resonances of
the field are unphysical as natural black hole oscillations: the corresponding
frequency is always associated with a scattering mode. By analyzing the
behavior of these modes near the event horizon we obtain new insight into the
transition to extremality, including a simple way to understand the Aretakis
instability.
| [
{
"created": "Sun, 4 Jun 2017 17:19:53 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Aug 2017 03:06:22 GMT",
"version": "v2"
}
] | 2017-08-28 | [
[
"Richartz",
"Maurício",
""
],
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Berti",
"Emanuele",
""
]
] | The characteristic damping times of the natural oscillations of a Kerr black hole become arbitrarily large as the extremal limit is approached. This behavior is associated with the so-called zero damped modes (ZDMs), and suggests that extremal black holes are characterized by quasinormal modes whose frequencies are purely real. Since these frequencies correspond to oscillations whose angular phase velocity matches the horizon angular velocity of the black hole, they are sometimes called "synchronous frequencies". Several authors have studied the ZDMs for near-extremal black holes. Recently, their correspondence to branch points of the Green's function of the wave equation was linked to the Aretakis instability of extremal black holes. Here we investigate the existence of ZDMs for extremal black holes, showing that these real-axis resonances of the field are unphysical as natural black hole oscillations: the corresponding frequency is always associated with a scattering mode. By analyzing the behavior of these modes near the event horizon we obtain new insight into the transition to extremality, including a simple way to understand the Aretakis instability. |
2011.06711 | Ai-Chen Li | Ai-chen Li, Xin-Fei Li | Morris-Thorne Wormhole in the Vector-Tensor theories with Abelian gauge
symmetry breaking | null | Phys. Rev. D 104, 044006 (2021) | 10.1103/PhysRevD.104.044006 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct an asymptotically flat Morris-Thorne wormhole solution supported
by anisotropic matter fluid and a vector field which is coupled to gravity in a
non-minimal way with broken Abelian gauge symmetry. In this paper, a specific
shape function is considered. We find that the ansatz of vector field plays a
significant role in determining the spacetime geometry of the wormhole. If
there exists the electrostatic potential only, the redshift function could be
considered as a constant value, implying the vanishing tidal force. However,
when the vector potential in radial-direction is involved, the r-component of
extended Maxwell equations at the wormhole's throat is invalid. To solve this
issue, a thin shell is introduced near the throat, dividing the spacetime into
two parts. Furthermore, it is proved that the spacetime geometry of wormhole
could be smooth at junction position if the expressions of redshift function
and vector potential are given appropriately. Finally, the energy conditions
and the volume integral quantifer are explored.
| [
{
"created": "Fri, 13 Nov 2020 01:05:14 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Aug 2021 19:55:34 GMT",
"version": "v2"
}
] | 2021-08-06 | [
[
"Li",
"Ai-chen",
""
],
[
"Li",
"Xin-Fei",
""
]
] | We construct an asymptotically flat Morris-Thorne wormhole solution supported by anisotropic matter fluid and a vector field which is coupled to gravity in a non-minimal way with broken Abelian gauge symmetry. In this paper, a specific shape function is considered. We find that the ansatz of vector field plays a significant role in determining the spacetime geometry of the wormhole. If there exists the electrostatic potential only, the redshift function could be considered as a constant value, implying the vanishing tidal force. However, when the vector potential in radial-direction is involved, the r-component of extended Maxwell equations at the wormhole's throat is invalid. To solve this issue, a thin shell is introduced near the throat, dividing the spacetime into two parts. Furthermore, it is proved that the spacetime geometry of wormhole could be smooth at junction position if the expressions of redshift function and vector potential are given appropriately. Finally, the energy conditions and the volume integral quantifer are explored. |
2303.08399 | Chao Zhang | Chao Zhang, Anzhong Wang and Tao Zhu | Odd-parity perturbations of the wormhole-like geometries and
quasi-normal modes in Einstein-\AE{}ther theory | 15 pages, 14 figures. arXiv admin note: substantial text overlap with
arXiv:2209.04735 | JCAP05(2023)059 | 10.1088/1475-7516/2023/05/059 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The Einstein-$\AE$ther theory has drawn a lot of attentions in recent years.
As a representative case of gravitational theories that break the Lorentz
symmetry, it plays an important role in testing the Lorentz-violating effects
and shedding light on the attempts to construct quantum gravity. Since the
first detection to the gravitational wave, the event GW150914, a brand new
window has been opened to testing the theory of gravity with gravitational wave
observations. At the same time, the study of gravitational waves itself also
provides us a serendipity of accessing the nature of a theory. In this paper,
we focus on the odd-parity gravitational perturbations to a background that
describes a wormhole-like geometry under the Einstein-$\AE$ther theory. Taking
advantage of this set of analytic background solutions, we are able to simplify
the Lagrangian and construct a set of coupled single-parameter dependent master
equations, from which we solve for the quasi-normal modes that carry the
physical information of the emitted gravitational waves. Basically, the results
reflect a consistency between Einstein-$\AE$ther theory and general relativity.
More importantly, as long as the no-ghost condition and the latest
observational constraints are concerned, we notice that the resultant
quasi-normal mode solutions intimate a kind of dynamical instability. Thus, the
solutions are ruled out based on their stability against small linear
perturbations.
| [
{
"created": "Wed, 15 Mar 2023 07:03:05 GMT",
"version": "v1"
},
{
"created": "Fri, 2 Jun 2023 05:54:01 GMT",
"version": "v2"
}
] | 2023-06-05 | [
[
"Zhang",
"Chao",
""
],
[
"Wang",
"Anzhong",
""
],
[
"Zhu",
"Tao",
""
]
] | The Einstein-$\AE$ther theory has drawn a lot of attentions in recent years. As a representative case of gravitational theories that break the Lorentz symmetry, it plays an important role in testing the Lorentz-violating effects and shedding light on the attempts to construct quantum gravity. Since the first detection to the gravitational wave, the event GW150914, a brand new window has been opened to testing the theory of gravity with gravitational wave observations. At the same time, the study of gravitational waves itself also provides us a serendipity of accessing the nature of a theory. In this paper, we focus on the odd-parity gravitational perturbations to a background that describes a wormhole-like geometry under the Einstein-$\AE$ther theory. Taking advantage of this set of analytic background solutions, we are able to simplify the Lagrangian and construct a set of coupled single-parameter dependent master equations, from which we solve for the quasi-normal modes that carry the physical information of the emitted gravitational waves. Basically, the results reflect a consistency between Einstein-$\AE$ther theory and general relativity. More importantly, as long as the no-ghost condition and the latest observational constraints are concerned, we notice that the resultant quasi-normal mode solutions intimate a kind of dynamical instability. Thus, the solutions are ruled out based on their stability against small linear perturbations. |
gr-qc/0106021 | Vishwakarma R. G. | R. G. Vishwakarma | Study of the Magnitude-Redshift Relation for type Ia Supernovae in a
Model resulting from a Ricci-Symmetry | 14 pages including 1 figure, accepted for publication in Gen.
Relativ. Grav | Gen.Rel.Grav. 33 (2001) 1973-1984 | 10.1023/A:1013051026760 | null | gr-qc astro-ph | null | Models with a dynamic cosmological term \Lambda (t) are becoming popular as
they solve the cosmological constant problem in a natural way. Instead of
considering any ad-hoc assumption for the variation of \Lambda, we consider a
particular symmetry, the contracted Ricci-collineation along the fluid flow, in
Einstein's theory. We show that apart from having interesting properties, this
symmetry does require \Lambda to be a function of the scale factor of the
Robertson-Walker metric. In order to test the consistency of the resulting
model with observations, we study the magnitude-redshift relation for the type
Ia supernovae data from Perlmutter et al. The data fit the model very well and
require a positive non-zero \Lambda and a negative deceleration parameter. The
best-fitting flat model is obtained as \Omega_0 \approx 0.5 with q_0 \approx
-0.2.
| [
{
"created": "Wed, 6 Jun 2001 12:35:28 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Vishwakarma",
"R. G.",
""
]
] | Models with a dynamic cosmological term \Lambda (t) are becoming popular as they solve the cosmological constant problem in a natural way. Instead of considering any ad-hoc assumption for the variation of \Lambda, we consider a particular symmetry, the contracted Ricci-collineation along the fluid flow, in Einstein's theory. We show that apart from having interesting properties, this symmetry does require \Lambda to be a function of the scale factor of the Robertson-Walker metric. In order to test the consistency of the resulting model with observations, we study the magnitude-redshift relation for the type Ia supernovae data from Perlmutter et al. The data fit the model very well and require a positive non-zero \Lambda and a negative deceleration parameter. The best-fitting flat model is obtained as \Omega_0 \approx 0.5 with q_0 \approx -0.2. |
gr-qc/0612123 | Enrico Barausse | Enrico Barausse, Luciano Rezzolla, David Petroff, Marcus Ansorg | Gravitational waves from Extreme Mass Ratio Inspirals in non-pure Kerr
spacetimes | 21 pages, 12 figures. Short discussion on the accuracy of the
spacetimes added, typos corrected. Accepted for publication in PRD | Phys.Rev.D75:064026,2007 | 10.1103/PhysRevD.75.064026 | null | gr-qc astro-ph | null | To investigate the imprint on the gravitational-wave emission from extreme
mass-ratio inspirals in non-pure Kerr spacetimes, we have studied the
``kludge'' waveforms generated in highly-accurate, numerically-generated
spacetimes containing a black hole and a self-gravitating, homogeneous torus
with comparable mass and spin. In order to maximize their impact on the
produced waveforms, we have considered tori that are compact, massive and close
to the central black hole, investigating under what conditions the LISA
experiment could detect their presence. Our results show that for a large
portion of the space of parameters the waveforms produced by EMRIs in these
black hole-torus systems are indistinguishable from pure-Kerr waveforms. Hence,
a ``confusion problem'' will be present for observations carried out over a
timescale below or comparable to the dephasing time.
| [
{
"created": "Wed, 20 Dec 2006 19:43:32 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Feb 2007 13:47:47 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Barausse",
"Enrico",
""
],
[
"Rezzolla",
"Luciano",
""
],
[
"Petroff",
"David",
""
],
[
"Ansorg",
"Marcus",
""
]
] | To investigate the imprint on the gravitational-wave emission from extreme mass-ratio inspirals in non-pure Kerr spacetimes, we have studied the ``kludge'' waveforms generated in highly-accurate, numerically-generated spacetimes containing a black hole and a self-gravitating, homogeneous torus with comparable mass and spin. In order to maximize their impact on the produced waveforms, we have considered tori that are compact, massive and close to the central black hole, investigating under what conditions the LISA experiment could detect their presence. Our results show that for a large portion of the space of parameters the waveforms produced by EMRIs in these black hole-torus systems are indistinguishable from pure-Kerr waveforms. Hence, a ``confusion problem'' will be present for observations carried out over a timescale below or comparable to the dephasing time. |
1205.0884 | Vicente Jos\'e Bol\'os | Vicente J. Bol\'os | Kinematic relative velocity with respect to stationary observers in
Schwarzschild spacetime | 8 pages, 2 figures | J. Geom. Phys. 66 (2013), 18-23 | 10.1016/j.geomphys.2012.12.005 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the kinematic relative velocity of general test particles with
respect to stationary observers (using spherical coordinates) in Schwarzschild
spacetime, obtaining that its modulus does not depend on the observer, unlike
Fermi, spectroscopic and astrometric relative velocities. We study some
fundamental particular cases, generalizing some results given in other work
about stationary and radial free-falling test particles. Moreover, we give a
new result about test particles with circular geodesic orbits: the modulus of
their kinematic relative velocity with respect to any stationary observer
depends only on the radius of the circular orbit, and so, it remains constant.
| [
{
"created": "Fri, 4 May 2012 08:48:01 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Dec 2012 09:04:34 GMT",
"version": "v2"
}
] | 2013-01-24 | [
[
"Bolós",
"Vicente J.",
""
]
] | We study the kinematic relative velocity of general test particles with respect to stationary observers (using spherical coordinates) in Schwarzschild spacetime, obtaining that its modulus does not depend on the observer, unlike Fermi, spectroscopic and astrometric relative velocities. We study some fundamental particular cases, generalizing some results given in other work about stationary and radial free-falling test particles. Moreover, we give a new result about test particles with circular geodesic orbits: the modulus of their kinematic relative velocity with respect to any stationary observer depends only on the radius of the circular orbit, and so, it remains constant. |
1607.02759 | Lars Andersson | Lars Andersson, Siyuan Ma, Claudio Paganini, Bernard F. Whiting | Mode stability on the real axis | 20 pages, 4 figures. Reference added, revtex4-1 format | null | 10.1063/1.4991656 | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A generalization of the mode stability result of Whiting (1989) for the
Teukolsky equation is proved for the case of real frequencies. The main result
of the paper states that a separated solution of the Teukolsky equation
governing massless test fields on the Kerr spacetime, which is purely outgoing
at infinity, and purely ingoing at the horizon, must vanish. This has the
consequence, that for real frequencies, there are linearly independent
fundamental solutions of the radial Teukolsky equation which are purely ingoing
at the horizon, and purely outgoing at infinity, respectively. This fact yields
a representation formula for solutions of the inhomogenous Teukolsky equation.
| [
{
"created": "Sun, 10 Jul 2016 15:52:18 GMT",
"version": "v1"
},
{
"created": "Fri, 16 Sep 2016 10:22:48 GMT",
"version": "v2"
}
] | 2017-08-02 | [
[
"Andersson",
"Lars",
""
],
[
"Ma",
"Siyuan",
""
],
[
"Paganini",
"Claudio",
""
],
[
"Whiting",
"Bernard F.",
""
]
] | A generalization of the mode stability result of Whiting (1989) for the Teukolsky equation is proved for the case of real frequencies. The main result of the paper states that a separated solution of the Teukolsky equation governing massless test fields on the Kerr spacetime, which is purely outgoing at infinity, and purely ingoing at the horizon, must vanish. This has the consequence, that for real frequencies, there are linearly independent fundamental solutions of the radial Teukolsky equation which are purely ingoing at the horizon, and purely outgoing at infinity, respectively. This fact yields a representation formula for solutions of the inhomogenous Teukolsky equation. |
2303.09392 | Jorge Pullin | Rodolfo Gambini and Jorge Pullin | Loop quantum gravity of a spherically symmetric scalar field coupled to
gravity with a clock | 10 pages, RevTex, no figures, to appear in Classical and Quantum
Gravity | Class. Quantum Grav. 40 085016 (2023) | 10.1088/1361-6382/acc510 | LSU-REL-031623 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The inclusion of matter fields in spherically symmetric loop quantum gravity
has proved problematic at the level of implementing the constraint algebra
including the Hamiltonian constraint. Here we consider the system with the
introduction of a clock. Using the Abelianizaton technique we introduced in
previous papers in the case of gravity coupled to matter, the system can be
gauge fixed and rewritten in terms of a restricted set of dynamical variables
that satisfy simple Poisson bracket relations. This creates a true Hamiltonian
and therefore one bypasses the issue of the constraint algebra. We show how
loop quantum gravity techniques may be applied for the vacuum case and show
that the Hamiltonian system reproduces previous results for the physical space
of states and the observables of a Schwarzchild black hole.
| [
{
"created": "Thu, 16 Mar 2023 15:32:37 GMT",
"version": "v1"
}
] | 2023-08-08 | [
[
"Gambini",
"Rodolfo",
""
],
[
"Pullin",
"Jorge",
""
]
] | The inclusion of matter fields in spherically symmetric loop quantum gravity has proved problematic at the level of implementing the constraint algebra including the Hamiltonian constraint. Here we consider the system with the introduction of a clock. Using the Abelianizaton technique we introduced in previous papers in the case of gravity coupled to matter, the system can be gauge fixed and rewritten in terms of a restricted set of dynamical variables that satisfy simple Poisson bracket relations. This creates a true Hamiltonian and therefore one bypasses the issue of the constraint algebra. We show how loop quantum gravity techniques may be applied for the vacuum case and show that the Hamiltonian system reproduces previous results for the physical space of states and the observables of a Schwarzchild black hole. |
2407.18644 | Anna Chrysostomou | Chun-Hung Chen, Hing-Tong Cho, Anna Chrysostomou and Alan S. Cornell | A semi-analytic treatment of quasinormal excitation factors in the
eikonal regime | 32 pages, 4 figures, 3 tables, and 2 appendices | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this paper, we present an enhanced semi-analytic method for calculating
quasinormal excitation factors in the eikonal regime, specifically for
Schwarzschild black holes. To achieve improved accuracy in our quasinormal mode
computations, we extend the Dolan and Ottewill inverse multipolar expansion
technique and incorporate higher-order corrections from the WKB method of Iyer
and Will. Our approach is carried out to a higher order than previous methods,
thereby reducing the relative error, particularly for lower multipolar numbers.
We validate our results by comparing them with those obtained using the Mano,
Suzuki, and Takasugi method, demonstrating excellent agreement. A key advantage
of our method is its ability to extract quasinormal excitation factors, which
are crucial for accurately modeling gravitational wave signals from binary
black hole mergers. This advancement provides a useful tool for future
gravitational wave studies, enabling better quantification of quasinormal mode
excitations and more precise identification of individual modes during black
hole ringdowns.
| [
{
"created": "Fri, 26 Jul 2024 10:22:44 GMT",
"version": "v1"
}
] | 2024-07-29 | [
[
"Chen",
"Chun-Hung",
""
],
[
"Cho",
"Hing-Tong",
""
],
[
"Chrysostomou",
"Anna",
""
],
[
"Cornell",
"Alan S.",
""
]
] | In this paper, we present an enhanced semi-analytic method for calculating quasinormal excitation factors in the eikonal regime, specifically for Schwarzschild black holes. To achieve improved accuracy in our quasinormal mode computations, we extend the Dolan and Ottewill inverse multipolar expansion technique and incorporate higher-order corrections from the WKB method of Iyer and Will. Our approach is carried out to a higher order than previous methods, thereby reducing the relative error, particularly for lower multipolar numbers. We validate our results by comparing them with those obtained using the Mano, Suzuki, and Takasugi method, demonstrating excellent agreement. A key advantage of our method is its ability to extract quasinormal excitation factors, which are crucial for accurately modeling gravitational wave signals from binary black hole mergers. This advancement provides a useful tool for future gravitational wave studies, enabling better quantification of quasinormal mode excitations and more precise identification of individual modes during black hole ringdowns. |
1103.3204 | Giampiero Esposito Dr. | Donato Bini, Giampiero Esposito, Andrea Geralico | de Sitter spacetime: effects of metric perturbations on geodesic motion | IOP macros, 10 figures | null | 10.1007/s10714-011-1287-2 | DSF preprint 2011/2 | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational perturbations of the de Sitter spacetime are investigated using
the Regge--Wheeler formalism. The set of perturbation equations is reduced to a
single second order differential equation of the Heun-type for both electric
and magnetic multipoles. The solution so obtained is used to study the
deviation from an initially radial geodesic due to the perturbation. The
spectral properties of the perturbed metric are also analyzed. Finally, gauge-
and tetrad-invariant first-order massless perturbations of any spin are
explored following the approach of Teukolsky. The existence of closed-form,
i.e. Liouvillian, solutions to the radial part of the Teukolsky master equation
is discussed.
| [
{
"created": "Wed, 16 Mar 2011 15:40:37 GMT",
"version": "v1"
}
] | 2015-05-27 | [
[
"Bini",
"Donato",
""
],
[
"Esposito",
"Giampiero",
""
],
[
"Geralico",
"Andrea",
""
]
] | Gravitational perturbations of the de Sitter spacetime are investigated using the Regge--Wheeler formalism. The set of perturbation equations is reduced to a single second order differential equation of the Heun-type for both electric and magnetic multipoles. The solution so obtained is used to study the deviation from an initially radial geodesic due to the perturbation. The spectral properties of the perturbed metric are also analyzed. Finally, gauge- and tetrad-invariant first-order massless perturbations of any spin are explored following the approach of Teukolsky. The existence of closed-form, i.e. Liouvillian, solutions to the radial part of the Teukolsky master equation is discussed. |
gr-qc/0310042 | Erik Schnetter | Erik Schnetter, Scott H. Hawley, and Ian Hawke | Evolutions in 3D numerical relativity using fixed mesh refinement | 20 pages, 15 figures; published version, but with colour figures | Class.Quant.Grav.21:1465-1488,2004 | 10.1088/0264-9381/21/6/014 | AEI-2003-078 | gr-qc | null | We present results of 3D numerical simulations using a finite difference code
featuring fixed mesh refinement (FMR), in which a subset of the computational
domain is refined in space and time. We apply this code to a series of test
cases including a robust stability test, a nonlinear gauge wave and an excised
Schwarzschild black hole in an evolving gauge. We find that the mesh refinement
results are comparable in accuracy, stability and convergence to unigrid
simulations with the same effective resolution. At the same time, the use of
FMR reduces the computational resources needed to obtain a given accuracy.
Particular care must be taken at the interfaces between coarse and fine grids
to avoid a loss of convergence at higher resolutions, and we introduce the use
of "buffer zones" as one resolution of this issue. We also introduce a new
method for initial data generation, which enables higher-order interpolation in
time even from the initial time slice. This FMR system, "Carpet", is a driver
module in the freely available Cactus computational infrastructure, and is able
to endow generic existing Cactus simulation modules ("thorns") with FMR with
little or no extra effort.
| [
{
"created": "Tue, 7 Oct 2003 16:46:32 GMT",
"version": "v1"
},
{
"created": "Fri, 9 Jan 2004 11:56:18 GMT",
"version": "v2"
},
{
"created": "Tue, 2 Mar 2004 14:04:24 GMT",
"version": "v3"
}
] | 2010-04-06 | [
[
"Schnetter",
"Erik",
""
],
[
"Hawley",
"Scott H.",
""
],
[
"Hawke",
"Ian",
""
]
] | We present results of 3D numerical simulations using a finite difference code featuring fixed mesh refinement (FMR), in which a subset of the computational domain is refined in space and time. We apply this code to a series of test cases including a robust stability test, a nonlinear gauge wave and an excised Schwarzschild black hole in an evolving gauge. We find that the mesh refinement results are comparable in accuracy, stability and convergence to unigrid simulations with the same effective resolution. At the same time, the use of FMR reduces the computational resources needed to obtain a given accuracy. Particular care must be taken at the interfaces between coarse and fine grids to avoid a loss of convergence at higher resolutions, and we introduce the use of "buffer zones" as one resolution of this issue. We also introduce a new method for initial data generation, which enables higher-order interpolation in time even from the initial time slice. This FMR system, "Carpet", is a driver module in the freely available Cactus computational infrastructure, and is able to endow generic existing Cactus simulation modules ("thorns") with FMR with little or no extra effort. |
1104.2140 | Emilio Santos Corchero | Emilio Santos | Neutron stars in generalized f(R) gravity | Keywords: stars, neutron stars; gravity; modified gravity Accepted in
Astrophysics and Space Science | Astrophysics and Space Science (2012) 341,411-416 | 10.1007/s10509-012-1049-y | null | gr-qc astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quartic gravity theory is considered with the Einstein-Hilbert Lagrangean
$R+aR^{2}+bR_{\mu \nu}R^{\mu \nu},$ $R_{\mu \nu}$ being Ricci\'s tensor and R
the curvature scalar. The parameters $a$ and $b$ are taken of order 1 km$^{2}.$
Arguments are given which suggest that the effective theory so obtained may be
a plausible approximation of a viable theory. A numerical integration is
performed of the field equations for a free neutron gas. As in the standard
Oppenheimer-Volkoff calculation the star mass increases with increasing central
density until about 1 solar mass and then decreases. However a dramatic
difference exists in the behaviour of the baryon number, which increases
monotonically. The calculation suggests that the theory allows stars in
equilibrium with arbitrary baryon number, no matter how large.
| [
{
"created": "Tue, 12 Apr 2011 08:47:48 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Apr 2011 09:33:04 GMT",
"version": "v2"
},
{
"created": "Tue, 22 Nov 2011 12:28:51 GMT",
"version": "v3"
},
{
"created": "Sat, 3 Mar 2012 10:41:19 GMT",
"version": "v4"
}
] | 2021-06-16 | [
[
"Santos",
"Emilio",
""
]
] | Quartic gravity theory is considered with the Einstein-Hilbert Lagrangean $R+aR^{2}+bR_{\mu \nu}R^{\mu \nu},$ $R_{\mu \nu}$ being Ricci\'s tensor and R the curvature scalar. The parameters $a$ and $b$ are taken of order 1 km$^{2}.$ Arguments are given which suggest that the effective theory so obtained may be a plausible approximation of a viable theory. A numerical integration is performed of the field equations for a free neutron gas. As in the standard Oppenheimer-Volkoff calculation the star mass increases with increasing central density until about 1 solar mass and then decreases. However a dramatic difference exists in the behaviour of the baryon number, which increases monotonically. The calculation suggests that the theory allows stars in equilibrium with arbitrary baryon number, no matter how large. |
gr-qc/0101047 | Sascha Husa | Sascha Husa, Roberto Gomez and Jeffrey Winicour | Complete null data for a black hole collision | 2 pages, uses World Scientific style file ws-p9-75x6-50.cls
(enclosed), contribution to the 9th Marcel Grossmann meeting (MG9), Rome,
July 2000 | null | 10.1142/9789812777386_0316 | AEI-2001-004 | gr-qc | null | We discuss a sequence of numerically constructed geometries describing binary
black hole event horizons -- providing the necessary input for characteristic
evolution of the exterior spacetime. Our sequence approaches a single
Schwarzschild horizon as one limiting case and also includes cases where the
horizon's crossover surface is not hidden by a marginally anti-trapped surface
(MATS).
| [
{
"created": "Fri, 12 Jan 2001 16:10:39 GMT",
"version": "v1"
}
] | 2017-08-23 | [
[
"Husa",
"Sascha",
""
],
[
"Gomez",
"Roberto",
""
],
[
"Winicour",
"Jeffrey",
""
]
] | We discuss a sequence of numerically constructed geometries describing binary black hole event horizons -- providing the necessary input for characteristic evolution of the exterior spacetime. Our sequence approaches a single Schwarzschild horizon as one limiting case and also includes cases where the horizon's crossover surface is not hidden by a marginally anti-trapped surface (MATS). |
0710.5282 | Emre Kahya Mr. | E. O. Kahya and R. P. Woodard | Scalar Field Equations from Quantum Gravity during Inflation | 19 pages, 5 tables | Phys.Rev.D77:084012,2008 | 10.1103/PhysRevD.77.084012 | UFIFT-QG-07-05 | gr-qc astro-ph hep-th | null | We exploit a previous computation of the self-mass-squared from quantum
gravity to include quantum corrections to the scalar evolution equation. The
plane wave mode functions are shown to receive no significant one loop
corrections at late times. This result probably applies as well to the inflaton
of scalar-driven inflation. If so, there is no significant correction to the
$\phi \phi$ correlator that plays a crucial role in computations of the power
spectrum.
| [
{
"created": "Sun, 28 Oct 2007 18:20:12 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Kahya",
"E. O.",
""
],
[
"Woodard",
"R. P.",
""
]
] | We exploit a previous computation of the self-mass-squared from quantum gravity to include quantum corrections to the scalar evolution equation. The plane wave mode functions are shown to receive no significant one loop corrections at late times. This result probably applies as well to the inflaton of scalar-driven inflation. If so, there is no significant correction to the $\phi \phi$ correlator that plays a crucial role in computations of the power spectrum. |
gr-qc/0602078 | Ruxandra Bondarescu | Jayashree Balakrishna, Ruxandra Bondarescu, Gregory Daues, F.
Siddhartha Guzman and Edward Seidel | Evolution of 3D Boson Stars with Waveform Extraction | 26 pages, 12 figures | Class.Quant.Grav. 23 (2006) 2631-2652 | 10.1088/0264-9381/23/7/024 | null | gr-qc | null | Numerical results from a study of boson stars under nonspherical
perturbations using a fully general relativistic 3D code are presented together
with the analysis of emitted gravitational radiation. We have constructed a
simulation code suitable for the study of scalar fields in space-times of
general symmetry by bringing together components for addressing the initial
value problem, the full evolution system and the detection and analysis of
gravitational waves. Within a series of numerical simulations, we explicitly
extract the Zerilli and Newman-Penrose scalar $\Psi_4$ gravitational waveforms
when the stars are subjected to different types of perturbations. Boson star
systems have rapidly decaying nonradial quasinormal modes and thus the complete
gravitational waveform could be extracted for all configurations studied. The
gravitational waves emitted from stable, critical, and unstable boson star
configurations are analyzed and the numerically observed quasinormal mode
frequencies are compared with known linear perturbation results. The
superposition of the high frequency nonspherical modes on the lower frequency
spherical modes was observed in the metric oscillations when perturbations with
radial and nonradial components were applied. The collapse of unstable boson
stars to black holes was simulated. The apparent horizons were observed to be
slightly nonspherical when initially detected and became spherical as the
system evolved. The application of nonradial perturbations proportional to
spherical harmonics is observed not to affect the collapse time. An unstable
star subjected to a large perturbation was observed to migrate to a stable
configuration.
| [
{
"created": "Mon, 20 Feb 2006 20:48:11 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Mar 2006 22:04:37 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Balakrishna",
"Jayashree",
""
],
[
"Bondarescu",
"Ruxandra",
""
],
[
"Daues",
"Gregory",
""
],
[
"Guzman",
"F. Siddhartha",
""
],
[
"Seidel",
"Edward",
""
]
] | Numerical results from a study of boson stars under nonspherical perturbations using a fully general relativistic 3D code are presented together with the analysis of emitted gravitational radiation. We have constructed a simulation code suitable for the study of scalar fields in space-times of general symmetry by bringing together components for addressing the initial value problem, the full evolution system and the detection and analysis of gravitational waves. Within a series of numerical simulations, we explicitly extract the Zerilli and Newman-Penrose scalar $\Psi_4$ gravitational waveforms when the stars are subjected to different types of perturbations. Boson star systems have rapidly decaying nonradial quasinormal modes and thus the complete gravitational waveform could be extracted for all configurations studied. The gravitational waves emitted from stable, critical, and unstable boson star configurations are analyzed and the numerically observed quasinormal mode frequencies are compared with known linear perturbation results. The superposition of the high frequency nonspherical modes on the lower frequency spherical modes was observed in the metric oscillations when perturbations with radial and nonradial components were applied. The collapse of unstable boson stars to black holes was simulated. The apparent horizons were observed to be slightly nonspherical when initially detected and became spherical as the system evolved. The application of nonradial perturbations proportional to spherical harmonics is observed not to affect the collapse time. An unstable star subjected to a large perturbation was observed to migrate to a stable configuration. |
0908.2605 | Roman Sverdlov | Thomas Scanlon, Roman Sverdlov | A use of geometric calculus to reduce Berezin integral to the limit of a
Riemann sum | 34 pages, no figures | Journal of Mathematical Physics 61, 063505 (2020) | 10.1063/1.5144877 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Berezin integration of functions of anticommuting Grassmann variables is
usually seen as a formal operation, sometimes even defined via differentiation.
Using the formalism of geometric algebra and geometric calculus in which the
Grassmann numbers are endowed with a second associative product coming from a
Clifford algebra structure, we show how Berezin integrals can be realized in
the high dimensional limit as integrals in the sense of geometric calculus. We
then show how the concepts of spinors and superspace transform into this
framework.
| [
{
"created": "Tue, 18 Aug 2009 19:26:35 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Aug 2009 14:03:29 GMT",
"version": "v2"
},
{
"created": "Thu, 20 Aug 2009 07:42:11 GMT",
"version": "v3"
},
{
"created": "Wed, 2 Sep 2015 19:56:17 GMT",
"version": "v4"
},
{
"cr... | 2020-06-19 | [
[
"Scanlon",
"Thomas",
""
],
[
"Sverdlov",
"Roman",
""
]
] | Berezin integration of functions of anticommuting Grassmann variables is usually seen as a formal operation, sometimes even defined via differentiation. Using the formalism of geometric algebra and geometric calculus in which the Grassmann numbers are endowed with a second associative product coming from a Clifford algebra structure, we show how Berezin integrals can be realized in the high dimensional limit as integrals in the sense of geometric calculus. We then show how the concepts of spinors and superspace transform into this framework. |
0903.4723 | Pin Yu | Pin Yu | On Hawking's Local Rigidity Theorems for Charged Black Holes | 20 pages | Annales Henri Poincare 11:1-21,2010 | 10.1007/s00023-010-0033-8 | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show the existence of a Hawking vector field in a full neighborhood of a
local, regular, bifurcate, non-expanding horizon embedded in a smooth
Einstein-Maxwell space-time without assuming the underlying space-time is
analytic. It extends one result of Friedrich, R\'{a}cz and Wald, which was
limited to the interior of the black hole region. Moreover, we also show, in
the presence of an additional Killing vector field $T$ which tangent to the
horizon and not vanishing on the bifurcate sphere, then space-time must be
locally axially symmetric without the analyticity assumption. This axial
symmetry plays a fundamental role in the classification theory of stationary
black holes.
| [
{
"created": "Fri, 27 Mar 2009 01:35:58 GMT",
"version": "v1"
}
] | 2014-11-18 | [
[
"Yu",
"Pin",
""
]
] | We show the existence of a Hawking vector field in a full neighborhood of a local, regular, bifurcate, non-expanding horizon embedded in a smooth Einstein-Maxwell space-time without assuming the underlying space-time is analytic. It extends one result of Friedrich, R\'{a}cz and Wald, which was limited to the interior of the black hole region. Moreover, we also show, in the presence of an additional Killing vector field $T$ which tangent to the horizon and not vanishing on the bifurcate sphere, then space-time must be locally axially symmetric without the analyticity assumption. This axial symmetry plays a fundamental role in the classification theory of stationary black holes. |
1107.0718 | Juan Antonio Nieto | J. A. Nieto | Canonical gravity in two time and two space dimensions | 13 pages, Latex, improved version | Int. J. Geom. Meth. Mod. Phys. 09 (2012) 1250069 | 10.1142/S0219887812500697 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe a program for developing a canonical gravity in 2+2 dimensions
(two time and two space dimensions). Our procedure is similar to the usual
canonical gravity but with two times rather than just one time. Our work may be
of particular interest as an alternative approach to loop quantum gravity in
2+2 dimensions.
| [
{
"created": "Thu, 23 Jun 2011 17:26:13 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Sep 2011 16:46:49 GMT",
"version": "v2"
},
{
"created": "Fri, 25 Nov 2011 16:51:37 GMT",
"version": "v3"
}
] | 2014-08-28 | [
[
"Nieto",
"J. A.",
""
]
] | We describe a program for developing a canonical gravity in 2+2 dimensions (two time and two space dimensions). Our procedure is similar to the usual canonical gravity but with two times rather than just one time. Our work may be of particular interest as an alternative approach to loop quantum gravity in 2+2 dimensions. |
1001.1255 | Hossein Farajollahi | Hossein Farajollahi, Narges Mohamadi | Generalized Brans-Dicke cosmology in the presence of matter and dark
energy | 9 pages | Int.J.Theor.Phys.49:72-78,2010 | 10.1007/s10773-009-0179-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the Generalized Brans-Dicke cosmology in the presence of matter and
dark energy. Of particular interest for a constant Brans-Dicke parameter, the
de Sitter space has also been investigated.
| [
{
"created": "Fri, 8 Jan 2010 12:31:19 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Jun 2011 07:20:04 GMT",
"version": "v2"
}
] | 2011-06-09 | [
[
"Farajollahi",
"Hossein",
""
],
[
"Mohamadi",
"Narges",
""
]
] | We study the Generalized Brans-Dicke cosmology in the presence of matter and dark energy. Of particular interest for a constant Brans-Dicke parameter, the de Sitter space has also been investigated. |
gr-qc/0105018 | Diego F. Torres | M. E. Pessah, and Diego F. Torres | Statistical mechanics and the description of the early universe II.
Principle of detailed balance and primordial 4He formation | 24 pages, to appear in Physica A (2001) | Physica A297 (2001) 201-228 | 10.1016/S0378-4371(01)00236-9 | null | gr-qc astro-ph cond-mat.stat-mech | null | If the universe is slightly non-extensive, and the distribution functions are
not exactly given by those of Boltzmann-Gibbs, the primordial production of
light elements will be non-trivially modified. In particular, the principle of
detailed balance (PDB), of fundamental importance in the standard analytical
analysis, is no longer valid, and a non-extensive correction appears. This
correction is computed and its influence is studied and compared with previous
works, where, even when the universe was considered as an slightly
non-extensive system, the PDB was assumed valid. We analytically track the
formation of Helium and Deuterium, and study the kind of deviation one could
expect from the standard regime. The correction to the capture time, the moment
in which Deuterium can no longer be substantially photo-disintegrated, is also
presented. This allows us to take into account the process of the free decay of
neutrons, which was absent in all previous treatments of the topic. We show
that even when considering a first (linear) order correction in the quantum
distribution functions, the final output on the primordial nucleosynthesis
yields cannot be reduced to a linear correction in the abundances. We finally
obtain new bounds upon the non-extensive parameter, both comparing the range of
physical viability of the theory, and using the latest observational data.
| [
{
"created": "Fri, 4 May 2001 15:28:55 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Pessah",
"M. E.",
""
],
[
"Torres",
"Diego F.",
""
]
] | If the universe is slightly non-extensive, and the distribution functions are not exactly given by those of Boltzmann-Gibbs, the primordial production of light elements will be non-trivially modified. In particular, the principle of detailed balance (PDB), of fundamental importance in the standard analytical analysis, is no longer valid, and a non-extensive correction appears. This correction is computed and its influence is studied and compared with previous works, where, even when the universe was considered as an slightly non-extensive system, the PDB was assumed valid. We analytically track the formation of Helium and Deuterium, and study the kind of deviation one could expect from the standard regime. The correction to the capture time, the moment in which Deuterium can no longer be substantially photo-disintegrated, is also presented. This allows us to take into account the process of the free decay of neutrons, which was absent in all previous treatments of the topic. We show that even when considering a first (linear) order correction in the quantum distribution functions, the final output on the primordial nucleosynthesis yields cannot be reduced to a linear correction in the abundances. We finally obtain new bounds upon the non-extensive parameter, both comparing the range of physical viability of the theory, and using the latest observational data. |
2202.04249 | Norichika Sago | Norichika Sago, Takahiro Tanaka | Efficient search method of anomalous reflection by the central object in
an EMRI system by future space gravitational wave detectors | 10 pages, 9 figures. v2: 11 pages, 9 figures, accepted version | null | 10.1103/PhysRevD.106.024032 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In our previous work we investigated the effect of the hypothetical
reflecting boundary near the black hole event horizon on the waveform from
extreme mass-ratio inspirals (EMRIs). Even if the reflection efficiency is not
extremely high, we found that a significant modification of the waveform can be
expected. Then, the question is how to implement the search for this signature
in the actual data analysis of future space gravitational wave antennas, such
as LISA. In this paper we propose a simple but efficient method to detect the
signature of the reflecting boundary. The interesting feature of the effect of
the reflecting boundary on the orbital evolution of EMRIs is that the energy
and angular momentum loss rates periodically oscillate in the frequency domain.
The oscillation period is corresponding to the inverse time scale for the round
trip of gravitational waves between the hypothetical boundary and the angular
momentum barrier. We will show that this peculiar feature allows to detect the
signature of the reflecting boundary without much additional computational
cost.
| [
{
"created": "Wed, 9 Feb 2022 03:14:15 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Jul 2022 01:12:43 GMT",
"version": "v2"
}
] | 2022-08-31 | [
[
"Sago",
"Norichika",
""
],
[
"Tanaka",
"Takahiro",
""
]
] | In our previous work we investigated the effect of the hypothetical reflecting boundary near the black hole event horizon on the waveform from extreme mass-ratio inspirals (EMRIs). Even if the reflection efficiency is not extremely high, we found that a significant modification of the waveform can be expected. Then, the question is how to implement the search for this signature in the actual data analysis of future space gravitational wave antennas, such as LISA. In this paper we propose a simple but efficient method to detect the signature of the reflecting boundary. The interesting feature of the effect of the reflecting boundary on the orbital evolution of EMRIs is that the energy and angular momentum loss rates periodically oscillate in the frequency domain. The oscillation period is corresponding to the inverse time scale for the round trip of gravitational waves between the hypothetical boundary and the angular momentum barrier. We will show that this peculiar feature allows to detect the signature of the reflecting boundary without much additional computational cost. |
gr-qc/0604118 | Robert D. Klauber | Robert D. Klauber | Relativistic Rotation: A Comparison of Theories | 45 pages including 11 figures and one table. Revision includes
suggestions by reviewers | Found.Phys.37:198-252,2007 | 10.1007/s10701-006-9099-z | null | gr-qc | null | Alternative theories of relativistic rotation considered viable as of 2004
are compared in the light of experiments reported in 2005. En route, the
contentious issue of simultaneity choice in rotation is resolved by showing
that only one simultaneity choice, the one possessing continuous time, gives
rise, via the general relativistic equation of motion, to the correct Newtonian
limit Coriolis acceleration. In addition, the widely dispersed argument
purporting Lorentz contraction in rotation and the concomitant curved surface
of a rotating disk is analyzed and argued to be lacking for more than one
reason. It is posited that not by theoretical arguments, but only via
experiment can we know whether such effect exists in rotation or not.
The Coriolis/simultaneity correlation, and the results of the 2005
experiments, support the Selleri theory as being closest to the truth, though
it is incomplete in a more general applicability sense, because it does not
provide a global metric. Two alternatives, a modified Klauber approach and a
Selleri-Klauber hybrid, are presented which are consistent with recent
experiment and have a global metric, thereby making them applicable to rotation
problems of all types.
| [
{
"created": "Thu, 27 Apr 2006 15:22:42 GMT",
"version": "v1"
},
{
"created": "Sat, 16 Dec 2006 21:58:39 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Klauber",
"Robert D.",
""
]
] | Alternative theories of relativistic rotation considered viable as of 2004 are compared in the light of experiments reported in 2005. En route, the contentious issue of simultaneity choice in rotation is resolved by showing that only one simultaneity choice, the one possessing continuous time, gives rise, via the general relativistic equation of motion, to the correct Newtonian limit Coriolis acceleration. In addition, the widely dispersed argument purporting Lorentz contraction in rotation and the concomitant curved surface of a rotating disk is analyzed and argued to be lacking for more than one reason. It is posited that not by theoretical arguments, but only via experiment can we know whether such effect exists in rotation or not. The Coriolis/simultaneity correlation, and the results of the 2005 experiments, support the Selleri theory as being closest to the truth, though it is incomplete in a more general applicability sense, because it does not provide a global metric. Two alternatives, a modified Klauber approach and a Selleri-Klauber hybrid, are presented which are consistent with recent experiment and have a global metric, thereby making them applicable to rotation problems of all types. |
0905.2983 | Francesca Vidotto | Carlo Rovelli and Francesca Vidotto | Single particle in quantum gravity and Braunstein-Ghosh-Severini entropy
of a spin network | 8 pages | Phys.Rev.D81:044038,2010 | 10.1103/PhysRevD.81.044038 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Passerini and Severini have recently shown that the Braunstein-Ghosh-Severini
(BGS) entropy S(Gamma) = -Tr[rho(Gamma) log rho(Gamma)] of a certain density
matrix rho(Gamma) naturally associated to a graph Gamma, is maximized, among
all graphs with a fixed number of links and nodes, by regular graphs. We ask if
this result can play a role in quantum gravity, and be related to the apparent
regularity of the physical geometry of space. We show that in Loop Quantum
Gravity the matrix rho(Gamma) is precisely the Hamiltonian operator (suitably
normalized) of a non-relativistic quantum particle interacting with the quantum
gravitational field, if we restrict elementary area and volume eigenvalues to a
fixed value. This operator provides a spectral characterization of the physical
geometry, and can be interpreted as a state describing the spectral information
about the geometry available when geometry is measured by its physical
interaction with matter. It is then tempting to interpret its BGS entropy
S(Gamma) as a genuine physical entropy: we discuss the appeal and the
difficulties of this interpretation.
| [
{
"created": "Mon, 18 May 2009 20:59:39 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Feb 2010 18:11:19 GMT",
"version": "v2"
}
] | 2010-04-06 | [
[
"Rovelli",
"Carlo",
""
],
[
"Vidotto",
"Francesca",
""
]
] | Passerini and Severini have recently shown that the Braunstein-Ghosh-Severini (BGS) entropy S(Gamma) = -Tr[rho(Gamma) log rho(Gamma)] of a certain density matrix rho(Gamma) naturally associated to a graph Gamma, is maximized, among all graphs with a fixed number of links and nodes, by regular graphs. We ask if this result can play a role in quantum gravity, and be related to the apparent regularity of the physical geometry of space. We show that in Loop Quantum Gravity the matrix rho(Gamma) is precisely the Hamiltonian operator (suitably normalized) of a non-relativistic quantum particle interacting with the quantum gravitational field, if we restrict elementary area and volume eigenvalues to a fixed value. This operator provides a spectral characterization of the physical geometry, and can be interpreted as a state describing the spectral information about the geometry available when geometry is measured by its physical interaction with matter. It is then tempting to interpret its BGS entropy S(Gamma) as a genuine physical entropy: we discuss the appeal and the difficulties of this interpretation. |
1009.5998 | Miquel Trias | T. Damour, A. Nagar and M. Trias | Accuracy and effectualness of closed-form, frequency-domain waveforms
for non-spinning black hole binaries | 29 pages, 8 figures, 1 table. Accepted for publication in Phys. Rev.
D | Phys.Rev.D83:024006,2011 | 10.1103/PhysRevD.83.024006 | LIGO-P1000099-v3 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The coalescences of binary black hole (BBH) systems, here taken to be
non-spinning, are among the most promising sources for gravitational wave (GW)
ground-based detectors, such as LIGO and Virgo. To detect the GW signals
emitted by BBHs, and measure the parameters of the source, one needs to have in
hand a bank of GW templates that are both effectual (for detection), and
accurate (for measurement). We study the effectualness and the accuracy of the
two types of parametrized banks of templates that are directly defined in the
frequency-domain by means of closed-form expressions, namely 'post-Newtonian'
(PN) and 'phenomenological' models. In absence of knowledge of the exact
waveforms, our study assumes as fiducial, target waveforms the ones generated
by the most accurate version of the effective one body (EOB) formalism. We find
that, for initial GW detectors the use, at each point of parameter space, of
the best closed-form template (among PN and phenomenological models) leads to
an effectualness >97% over the entire mass range and >99% in an important
fraction of parameter space; however, when considering advanced detectors, both
of the closed-form frequency-domain models fail to be effectual enough in
significant domains of the two-dimensional [total mass and mass ratio]
parameter space. Moreover, we find that, both for initial and advanced
detectors, the two closed-form frequency-domain models fail to satisfy the
minimal required accuracy standard in a very large domain of the
two-dimensional parameter space. In addition, a side result of our study is the
determination, as a function of the mass ratio, of the maximum frequency at
which a frequency-domain PN waveform can be 'joined' onto a NR-calibrated EOB
waveform without undue loss of accuracy.
| [
{
"created": "Wed, 29 Sep 2010 20:18:13 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Dec 2010 22:51:21 GMT",
"version": "v2"
}
] | 2011-02-25 | [
[
"Damour",
"T.",
""
],
[
"Nagar",
"A.",
""
],
[
"Trias",
"M.",
""
]
] | The coalescences of binary black hole (BBH) systems, here taken to be non-spinning, are among the most promising sources for gravitational wave (GW) ground-based detectors, such as LIGO and Virgo. To detect the GW signals emitted by BBHs, and measure the parameters of the source, one needs to have in hand a bank of GW templates that are both effectual (for detection), and accurate (for measurement). We study the effectualness and the accuracy of the two types of parametrized banks of templates that are directly defined in the frequency-domain by means of closed-form expressions, namely 'post-Newtonian' (PN) and 'phenomenological' models. In absence of knowledge of the exact waveforms, our study assumes as fiducial, target waveforms the ones generated by the most accurate version of the effective one body (EOB) formalism. We find that, for initial GW detectors the use, at each point of parameter space, of the best closed-form template (among PN and phenomenological models) leads to an effectualness >97% over the entire mass range and >99% in an important fraction of parameter space; however, when considering advanced detectors, both of the closed-form frequency-domain models fail to be effectual enough in significant domains of the two-dimensional [total mass and mass ratio] parameter space. Moreover, we find that, both for initial and advanced detectors, the two closed-form frequency-domain models fail to satisfy the minimal required accuracy standard in a very large domain of the two-dimensional parameter space. In addition, a side result of our study is the determination, as a function of the mass ratio, of the maximum frequency at which a frequency-domain PN waveform can be 'joined' onto a NR-calibrated EOB waveform without undue loss of accuracy. |
2110.01104 | Bei Lok Hu | Bei-Lok Hu | Weyl Curvature Hypothesis in light of Quantum Backreaction at
Cosmological Singularities or Bounces | This v2 (57 pages) contains a footnote on how WCH fares with
inflationary cosmology, and expanded descriptions of ekpyrotic cosmology in
the contraction phase and quantum BLK-mixmaster models. To appear in the
journal "Universe": Special Issue on Quantum Cosmology | Universe 7, 424 (2021) | 10.3390/universe7110424 | null | gr-qc hep-th quant-ph | http://creativecommons.org/licenses/by/4.0/ | Penrose's 1979 Weyl curvature hypothesis (WCH) \cite{WCH} assumes that the
universe began at a very low gravitational entropy state, corresponding to zero
Weyl curvature, namely, the FLRW universe. This is a simple assumption with
far-reaching implications. In classical general relativity the most general
cosmological solutions of the Einstein equation are that of the BKL-Misner
inhomogeneous mixmaster types. How could WCH and BKL-M co-exist? An answer was
provided in the 80s with the consideration of quantum field processes such as
vacuum particle creation, which was copious at the Planck time ($10^{-43}
sec$), and their backreaction effects were shown to be so powerful as to
rapidly damp away the irregularities in the geometry. It was proposed that the
vacuum viscosity due to particle creation can act as an efficient transducer of
gravitational entropy (large for BKL-M) to matter entropy, keeping the universe
at that very early time in a state commensurate with the WCH. In this essay I
expand the scope of that inquiry to a broader range, asking how the WCH would
fare with various cosmological theories, from classical to semiclassical to
quantum, focusing on their predictions near the cosmological singularities
(past and future) or avoidance thereof, allowing the Universe to encounter
different scenarios, such as undergoing a phase transition or a bounce. We
point out that regardless of what other processes may be present near the
beginning and the end states of the universe, the backreaction effects of
quantum field processes probably serve as the best guarantor of WCH because
these vacuum processes are ubiquitous, powerful and efficient in dissipating
the irregularities to effectively nudge the Universe to a near-zero Weyl
curvature condition.
| [
{
"created": "Sun, 3 Oct 2021 21:22:08 GMT",
"version": "v1"
},
{
"created": "Sat, 30 Oct 2021 21:05:42 GMT",
"version": "v2"
}
] | 2021-11-09 | [
[
"Hu",
"Bei-Lok",
""
]
] | Penrose's 1979 Weyl curvature hypothesis (WCH) \cite{WCH} assumes that the universe began at a very low gravitational entropy state, corresponding to zero Weyl curvature, namely, the FLRW universe. This is a simple assumption with far-reaching implications. In classical general relativity the most general cosmological solutions of the Einstein equation are that of the BKL-Misner inhomogeneous mixmaster types. How could WCH and BKL-M co-exist? An answer was provided in the 80s with the consideration of quantum field processes such as vacuum particle creation, which was copious at the Planck time ($10^{-43} sec$), and their backreaction effects were shown to be so powerful as to rapidly damp away the irregularities in the geometry. It was proposed that the vacuum viscosity due to particle creation can act as an efficient transducer of gravitational entropy (large for BKL-M) to matter entropy, keeping the universe at that very early time in a state commensurate with the WCH. In this essay I expand the scope of that inquiry to a broader range, asking how the WCH would fare with various cosmological theories, from classical to semiclassical to quantum, focusing on their predictions near the cosmological singularities (past and future) or avoidance thereof, allowing the Universe to encounter different scenarios, such as undergoing a phase transition or a bounce. We point out that regardless of what other processes may be present near the beginning and the end states of the universe, the backreaction effects of quantum field processes probably serve as the best guarantor of WCH because these vacuum processes are ubiquitous, powerful and efficient in dissipating the irregularities to effectively nudge the Universe to a near-zero Weyl curvature condition. |
gr-qc/9411013 | Sardanashvily Gennadi | G.Sardanashvily | Gravity as a Higgs Field. III. Nongravitional Deviations of
Gravitational Fields | 17 pp., compuscript LaTeX | null | null | TP\94\219 | gr-qc | null | In Parts I and II of the work (gr-qc/9405013, 9407032), we have shown that
gravity is {\it sui generis} a Higgs field corresponding to spontaneous
symmetry breaking when the fermion matter admits only the Lorentz subgroup of
world symmetries of the geometric arena. From the mathematical viewpoint, the
Higgs nature of gravity issues from the fact that different gravitational
fields are responsible for nonequivalent representations of cotangent vectors
to a world manifold by $\gamma$-matrices on spinor bundles. It follows that
gravitational fields fail to form an affine space modelled on a linear space of
deviations of some background field. In other words, even weak gravitational
fields do not satisfy the superposition principle and, in particular, can not
be quantized by usual methods. At the same time, one can examine superposable
deviations $\sigma$ of a gravitational field $h$ so that $h+\sigma$ fails to be
a gravitational field. These deviations are provided with the adequate
mathematical description in the framework of the affine group gauge theory in
dislocated manifolds, and their Lagrangian densities differ from the familiar
gravitational ones. They make contribution to the standard gravitational
effects, e.g., modify Newton's gravitational potential.
| [
{
"created": "Sun, 6 Nov 1994 00:17:48 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sardanashvily",
"G.",
""
]
] | In Parts I and II of the work (gr-qc/9405013, 9407032), we have shown that gravity is {\it sui generis} a Higgs field corresponding to spontaneous symmetry breaking when the fermion matter admits only the Lorentz subgroup of world symmetries of the geometric arena. From the mathematical viewpoint, the Higgs nature of gravity issues from the fact that different gravitational fields are responsible for nonequivalent representations of cotangent vectors to a world manifold by $\gamma$-matrices on spinor bundles. It follows that gravitational fields fail to form an affine space modelled on a linear space of deviations of some background field. In other words, even weak gravitational fields do not satisfy the superposition principle and, in particular, can not be quantized by usual methods. At the same time, one can examine superposable deviations $\sigma$ of a gravitational field $h$ so that $h+\sigma$ fails to be a gravitational field. These deviations are provided with the adequate mathematical description in the framework of the affine group gauge theory in dislocated manifolds, and their Lagrangian densities differ from the familiar gravitational ones. They make contribution to the standard gravitational effects, e.g., modify Newton's gravitational potential. |
0901.4106 | Benjamin Koch | Benjamin Koch | A geometrical dual to relativistic Bohmian mechanics - the multi
particle case | 7 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article it is shown that the fundamental equations of relativistic
Bohmian mechanics for multiple bosonic particles have a dual description in
terms of a classical theory of curved space-time. We further generalize the
results to interactions with an external electromagnetic field, which
corresponds to the minimally coupled Klein-Gordon equation.
| [
{
"created": "Tue, 27 Jan 2009 13:35:10 GMT",
"version": "v1"
}
] | 2009-01-28 | [
[
"Koch",
"Benjamin",
""
]
] | In this article it is shown that the fundamental equations of relativistic Bohmian mechanics for multiple bosonic particles have a dual description in terms of a classical theory of curved space-time. We further generalize the results to interactions with an external electromagnetic field, which corresponds to the minimally coupled Klein-Gordon equation. |
2206.07715 | Ben Kain | Joseph E. Nyhan, Ben Kain | Dynamical evolution of fermion-boson stars with realistic equations of
state | 12 pages, 6 figures. arXiv admin note: text overlap with
arXiv:2201.02274 | Phys. Rev. D 105, 123016 (2022) | 10.1103/PhysRevD.105.123016 | null | gr-qc astro-ph.HE hep-ph nucl-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Fermion-boson stars are mixtures of the ordinary nuclear matter of a neutron
star and bosonic dark matter. We dynamically evolve fermion-boson stars for the
first time using a realistic equation of state for nuclear matter. We use our
dynamical solutions to make a detailed study of the evolution of weakly and
strongly perturbed static solutions. As examples of our findings, we identify a
region of parameter space where weakly perturbed unstable static solutions
migrate to a stable configuration and we determine the criteria under which
strongly perturbed stable static solutions will always move to a stable
configuration instead of collapsing to a black hole.
| [
{
"created": "Wed, 15 Jun 2022 18:00:00 GMT",
"version": "v1"
}
] | 2022-06-29 | [
[
"Nyhan",
"Joseph E.",
""
],
[
"Kain",
"Ben",
""
]
] | Fermion-boson stars are mixtures of the ordinary nuclear matter of a neutron star and bosonic dark matter. We dynamically evolve fermion-boson stars for the first time using a realistic equation of state for nuclear matter. We use our dynamical solutions to make a detailed study of the evolution of weakly and strongly perturbed static solutions. As examples of our findings, we identify a region of parameter space where weakly perturbed unstable static solutions migrate to a stable configuration and we determine the criteria under which strongly perturbed stable static solutions will always move to a stable configuration instead of collapsing to a black hole. |
2403.10463 | Haidar Sheikhahmadi | Hassan Firouzjahi, Haidar Sheikhahmadi | Vacuum zero point energy of self-interacting quantum fields in dS
background | 21 Pages, 4 figures | Phys. Rev. D 109, 125005, 2024 | 10.1103/PhysRevD.109.125005 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider self-interacting scalar fields with a conformal coupling in the
dS background and study the quantum corrections from bubble loop diagrams.
Incorporating the perturbative in-in formalism, we calculate the quantum
corrections in the vacuum zero point energy and pressure of self-interacting
fields with the potential $V \propto \Phi^n $ for even values of $n$. We
calculate the equation of state corresponding to these quantum corrections and
examine the scaling of the divergent terms in the vacuum zero point energy and
pressure associated to the dimensional regularization scheme. In particular, we
show that for quartic self-interacting scalar field the conformal invariance is
respected at two-loop order at the conformal point.
| [
{
"created": "Fri, 15 Mar 2024 16:54:24 GMT",
"version": "v1"
}
] | 2024-06-06 | [
[
"Firouzjahi",
"Hassan",
""
],
[
"Sheikhahmadi",
"Haidar",
""
]
] | We consider self-interacting scalar fields with a conformal coupling in the dS background and study the quantum corrections from bubble loop diagrams. Incorporating the perturbative in-in formalism, we calculate the quantum corrections in the vacuum zero point energy and pressure of self-interacting fields with the potential $V \propto \Phi^n $ for even values of $n$. We calculate the equation of state corresponding to these quantum corrections and examine the scaling of the divergent terms in the vacuum zero point energy and pressure associated to the dimensional regularization scheme. In particular, we show that for quartic self-interacting scalar field the conformal invariance is respected at two-loop order at the conformal point. |
1806.10539 | Maximilian Thaller | Tomohiro Harada, Maximilian Thaller | Uniqueness of static, isotropic low-pressure solutions of the
Einstein-Vlasov system | 18 pages, 4 figures | null | null | RUP-18-17 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Due to R. Beig and W. Simon (1990) there is a uniqueness theorem for static
solutions of the Einstein-Euler system which applies to fluid models whose
equation of state fulfills certain conditions. In this article it is shown that
this uniqueness theorem can be applied to isotropic Vlasov matter, if the
gravitational potential well is shallow. To this end we first show how
isotropic Vlasov matter can be described as a perfect fluid giving rise to a
barotropic equation of state. This 'Vlasov' equation of state is investigated
and it is shown analytically that the requirements of the uniqueness theorem
are met for shallow potential wells. Finally the regime of shallow
gravitational potential is investigated by numerical means. An example for a
unique static solution is constructed and it is compared to astrophysical
objects like globular clusters. Finally we find numerical indications that
solutions with deep potential wells are not unique.
| [
{
"created": "Wed, 27 Jun 2018 15:48:39 GMT",
"version": "v1"
},
{
"created": "Tue, 3 Jul 2018 17:34:46 GMT",
"version": "v2"
},
{
"created": "Fri, 6 Jul 2018 08:29:10 GMT",
"version": "v3"
}
] | 2018-07-09 | [
[
"Harada",
"Tomohiro",
""
],
[
"Thaller",
"Maximilian",
""
]
] | Due to R. Beig and W. Simon (1990) there is a uniqueness theorem for static solutions of the Einstein-Euler system which applies to fluid models whose equation of state fulfills certain conditions. In this article it is shown that this uniqueness theorem can be applied to isotropic Vlasov matter, if the gravitational potential well is shallow. To this end we first show how isotropic Vlasov matter can be described as a perfect fluid giving rise to a barotropic equation of state. This 'Vlasov' equation of state is investigated and it is shown analytically that the requirements of the uniqueness theorem are met for shallow potential wells. Finally the regime of shallow gravitational potential is investigated by numerical means. An example for a unique static solution is constructed and it is compared to astrophysical objects like globular clusters. Finally we find numerical indications that solutions with deep potential wells are not unique. |
1805.09620 | Juho Lankinen | Juho Lankinen and Iiro Vilja | Particle decay in expanding Friedmann-Robertson-Walker universes | 9 pages, 5 figures | Phys. Rev. D 98, 045010 (2018) | 10.1103/PhysRevD.98.045010 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The lack of energy conservation introduces new particle processes in curved
spacetime that are forbidden in flat space. Therefore one has to be very
cautious about using the results calculated in Minkowskian space in early
universe applications. This is true for particle decay rates in particular,
which need to be calculated using quantum field theory in curved spacetime.
Previous studies are usually restricted to using minimal or conformal coupling
for the decaying particle, while using a more general coupling would give
deeper insight into particle decay. This paper presents the results we obtained
for a massive particle decaying in a general power-law universe with arbitrary
coupling to gravity. We find that depending on the value of the gravitational
coupling, the effect of gravitation may either strengthen or weaken the decay.
The analysis further reveals that, apart from radiation dominated universe,
there are values of the coupling constant for which the decay rate is exactly
Minkowskian for all universe types. Because the decay rate may be considerably
modified in curved space, these issues need to be considered when doing precise
cosmological calculations.
| [
{
"created": "Thu, 24 May 2018 12:01:16 GMT",
"version": "v1"
}
] | 2018-08-22 | [
[
"Lankinen",
"Juho",
""
],
[
"Vilja",
"Iiro",
""
]
] | The lack of energy conservation introduces new particle processes in curved spacetime that are forbidden in flat space. Therefore one has to be very cautious about using the results calculated in Minkowskian space in early universe applications. This is true for particle decay rates in particular, which need to be calculated using quantum field theory in curved spacetime. Previous studies are usually restricted to using minimal or conformal coupling for the decaying particle, while using a more general coupling would give deeper insight into particle decay. This paper presents the results we obtained for a massive particle decaying in a general power-law universe with arbitrary coupling to gravity. We find that depending on the value of the gravitational coupling, the effect of gravitation may either strengthen or weaken the decay. The analysis further reveals that, apart from radiation dominated universe, there are values of the coupling constant for which the decay rate is exactly Minkowskian for all universe types. Because the decay rate may be considerably modified in curved space, these issues need to be considered when doing precise cosmological calculations. |
2108.05111 | Roberto Casadio | Andrea Giusti, Silvia Buffa, Lavinia Heisenberg, and Roberto Casadio | A quantum state for the late Universe | LaTeX, 12 pages, no figures | null | 10.1016/j.physletb.2022.136900 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider the quantum description of a toy model universe in which the
Schwarzschild-de Sitter geometry emerges from the coherent state of a massless
scalar field. Although highly idealised, this simple model allows us to find
clear hints supporting the conclusion that the reaction of the de Sitter
background to the presence of matter sources induces i) a modified Newtonian
dynamics at galactic scales and ii) different values measured for the present
Hubble parameter. Both effects stem from the conditions required to have a
normalisable quantum state.
| [
{
"created": "Wed, 11 Aug 2021 09:31:24 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Jan 2022 10:47:46 GMT",
"version": "v2"
}
] | 2022-01-19 | [
[
"Giusti",
"Andrea",
""
],
[
"Buffa",
"Silvia",
""
],
[
"Heisenberg",
"Lavinia",
""
],
[
"Casadio",
"Roberto",
""
]
] | We consider the quantum description of a toy model universe in which the Schwarzschild-de Sitter geometry emerges from the coherent state of a massless scalar field. Although highly idealised, this simple model allows us to find clear hints supporting the conclusion that the reaction of the de Sitter background to the presence of matter sources induces i) a modified Newtonian dynamics at galactic scales and ii) different values measured for the present Hubble parameter. Both effects stem from the conditions required to have a normalisable quantum state. |
gr-qc/0611018 | Dr. Anirudh Pradhan | Raj Bali and Anirudh Pradhan | Bianchi Type III String Cosmological Models with Time Dependent Bulk
Viscosity | 11 pages, no figure | Chin. Phys. Lett.24:585-588,2007 | 10.1088/0256-307X/24/2/079 | null | gr-qc | null | Bianchi type III string cosmological models with bulk viscous fluid for
massive string are investigated. To get the determinate model of the universe,
we have assumed that the coefficient of bulk viscosity ($\xi$) is inversely
proportional to the expansion ($\theta$) in the model and expansion ($\theta$)
in the model is proportional to the shear ($\sigma$). This leads to $B = \ell
C^{n}$, $\ell$ and $n$ are constants. The behaviour of the model in presence
and absence of bulk viscosity, is discussed. The physical implications of the
models are also discussed in detail.
| [
{
"created": "Fri, 3 Nov 2006 07:17:40 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Jan 2007 07:28:24 GMT",
"version": "v2"
}
] | 2009-03-19 | [
[
"Bali",
"Raj",
""
],
[
"Pradhan",
"Anirudh",
""
]
] | Bianchi type III string cosmological models with bulk viscous fluid for massive string are investigated. To get the determinate model of the universe, we have assumed that the coefficient of bulk viscosity ($\xi$) is inversely proportional to the expansion ($\theta$) in the model and expansion ($\theta$) in the model is proportional to the shear ($\sigma$). This leads to $B = \ell C^{n}$, $\ell$ and $n$ are constants. The behaviour of the model in presence and absence of bulk viscosity, is discussed. The physical implications of the models are also discussed in detail. |
2207.00888 | Anirban Chatterjee | Anirban Chatterjee, Biswajit Jana and Abhijit Bandyopadhyay | Modified scaling in $k$-essence model in interacting dark energy - dark
matter scenario | 21 pages and 6 figures. This version has been accepted for
publication in European Physical Journal Plus | Eur. Phys. J. Plus (2022) 137, 1271 | 10.1140/epjp/s13360-022-03476-y | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | It has been shown by \textit{Scherrer and Putter et.al} that, when dynamics
of dark energy is driven by a homogeneous $k-$essence scalar field $\phi$, with
a Lagrangian of the form $L = V_0F(X)$ with a constant potential $V_0$ and $X =
\frac{1}{2}\nabla^\mu\phi \nabla_\mu\phi = \frac{1}{2}\dot{\phi}^2$, one
obtains a scaling relation $X(dF/dX)^2 = Ca^{-6}$ , where $C$ is a constant and
$a$ is the FRW scale factor of the universe. The separate energy conservation
in the dark energy sector and the constancy of $k-$essence potential are
instrumental in obtaining such a scaling. In this paper, we have shown that
even when considering time-dependent interactions between dark energy and dark
matter, the constancy of $k-$essence potential may lead to a modified form of
scaling. We have obtained such a scaling relation for a particular class of
parametrisation of the source term occurring in the continuity equation of dark
energy and dark matter in the interacting scenario. We used inputs from the JLA
analysis of luminosity distance and redshift data from Supernova Ia
observations, to obtain the modified form of the scaling.
| [
{
"created": "Sat, 2 Jul 2022 17:52:23 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Nov 2022 13:34:32 GMT",
"version": "v2"
},
{
"created": "Wed, 23 Nov 2022 10:45:43 GMT",
"version": "v3"
}
] | 2022-11-24 | [
[
"Chatterjee",
"Anirban",
""
],
[
"Jana",
"Biswajit",
""
],
[
"Bandyopadhyay",
"Abhijit",
""
]
] | It has been shown by \textit{Scherrer and Putter et.al} that, when dynamics of dark energy is driven by a homogeneous $k-$essence scalar field $\phi$, with a Lagrangian of the form $L = V_0F(X)$ with a constant potential $V_0$ and $X = \frac{1}{2}\nabla^\mu\phi \nabla_\mu\phi = \frac{1}{2}\dot{\phi}^2$, one obtains a scaling relation $X(dF/dX)^2 = Ca^{-6}$ , where $C$ is a constant and $a$ is the FRW scale factor of the universe. The separate energy conservation in the dark energy sector and the constancy of $k-$essence potential are instrumental in obtaining such a scaling. In this paper, we have shown that even when considering time-dependent interactions between dark energy and dark matter, the constancy of $k-$essence potential may lead to a modified form of scaling. We have obtained such a scaling relation for a particular class of parametrisation of the source term occurring in the continuity equation of dark energy and dark matter in the interacting scenario. We used inputs from the JLA analysis of luminosity distance and redshift data from Supernova Ia observations, to obtain the modified form of the scaling. |
gr-qc/9309019 | null | Victor M. Villalba | Dirac spinor in a nonstationary Godel-type cosmological Universe | 6pp, IVIC-CFLE 93/04 | Mod. Phys. Lett. A8 (1993) 3011-3018 | 10.1142/S0217732393001963 | null | gr-qc | null | In the present article we solve, via separation of variables, the massless
Dirac equation in a nonstationary rotating, causal G\"odel-type cosmological
universe, having a constant rotational speed in all the points of the space. We
compute the frequency spectrum. We show that the spectrum of massless Dirac
particles is discrete and unbounded.
| [
{
"created": "Thu, 16 Sep 1993 17:48:03 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Villalba",
"Victor M.",
""
]
] | In the present article we solve, via separation of variables, the massless Dirac equation in a nonstationary rotating, causal G\"odel-type cosmological universe, having a constant rotational speed in all the points of the space. We compute the frequency spectrum. We show that the spectrum of massless Dirac particles is discrete and unbounded. |
gr-qc/0505107 | Lorenzo Iorio | Lorenzo Iorio | Are we far from testing general relativity with the transiting
extrasolar planet HD 209458b `Osiris'? | LaTex2e, 11 pages, 18 references, no figures, no tables. Section 5
improved. Small corrections. To appear in New Astronomy | New Astron. 11 (2006) 490-494 | 10.1016/j.newast.2005.12.001 | null | gr-qc astro-ph | null | In this paper we investigate the possibility of measuring the general
relativistic gravitoelectric contribution P^(GE) to the orbital period P of the
transiting exoplanet HD 209458b 'Osiris'. It turns out that the predicted
magnitude of such an effect is \sim 0.1 s, while the most recent determinations
of the orbital period of HD 209458b with the photometric transit method are
accurate to \sim 0.01 s. The present analysis shows that the major limiting
factor is the \sim 1 m s^-1 sensitivity in the measurement of the projected
semiamplitude of the star's radial velocity K. Indeed, it affects the
determination of the mass m of the planet which, in turn, induces a systematic
error in the Keplerian period P^(0) of \sim 8 s. It is of crucial importance
because P^(0) should be subtracted from the measured period in order to extract
the relativistic correction. The present-day uncertainty in $m$ does not yet
make necessary the inclusion of relativistic corrections in the data-reduction
process of the determination of the system's parameters. The present situation
could change only if improvements of one-two orders of magnitude in the
ground-based Doppler spectroscopy technique occurred.
| [
{
"created": "Fri, 20 May 2005 10:33:36 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Jun 2005 20:22:11 GMT",
"version": "v2"
},
{
"created": "Tue, 23 Aug 2005 16:42:07 GMT",
"version": "v3"
},
{
"created": "Mon, 7 Nov 2005 21:08:55 GMT",
"version": "v4"
},
{
"cr... | 2007-05-23 | [
[
"Iorio",
"Lorenzo",
""
]
] | In this paper we investigate the possibility of measuring the general relativistic gravitoelectric contribution P^(GE) to the orbital period P of the transiting exoplanet HD 209458b 'Osiris'. It turns out that the predicted magnitude of such an effect is \sim 0.1 s, while the most recent determinations of the orbital period of HD 209458b with the photometric transit method are accurate to \sim 0.01 s. The present analysis shows that the major limiting factor is the \sim 1 m s^-1 sensitivity in the measurement of the projected semiamplitude of the star's radial velocity K. Indeed, it affects the determination of the mass m of the planet which, in turn, induces a systematic error in the Keplerian period P^(0) of \sim 8 s. It is of crucial importance because P^(0) should be subtracted from the measured period in order to extract the relativistic correction. The present-day uncertainty in $m$ does not yet make necessary the inclusion of relativistic corrections in the data-reduction process of the determination of the system's parameters. The present situation could change only if improvements of one-two orders of magnitude in the ground-based Doppler spectroscopy technique occurred. |
0804.0833 | Peter Hogan | C. Barrabes and P. A. Hogan | On Generating Gravity Waves with Matter and Electromagnetic Waves | Latex file, 15 pages, accepted for publication in Physical Review D | Phys.Rev.D77:104014,2008 | 10.1103/PhysRevD.77.104014 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | If a homogeneous plane light-like shell collides head-on with a homogeneous
plane electromagnetic shock wave having a step-function profile then no
backscattered gravitational waves are produced. We demonstrate, by explicit
calculation, that if the matter is accompanied by a homogeneous plane
electromagnetic shock wave with a step-function profile then backscattered
gravitational waves appear after the collision.
| [
{
"created": "Sat, 5 Apr 2008 02:19:58 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Barrabes",
"C.",
""
],
[
"Hogan",
"P. A.",
""
]
] | If a homogeneous plane light-like shell collides head-on with a homogeneous plane electromagnetic shock wave having a step-function profile then no backscattered gravitational waves are produced. We demonstrate, by explicit calculation, that if the matter is accompanied by a homogeneous plane electromagnetic shock wave with a step-function profile then backscattered gravitational waves appear after the collision. |
2005.10631 | Fay\c{c}al Hammad | F. Hammad, A. Landry and K. Mathieu | A fresh look at the influence of gravity on the quantum Hall effect | 35 pages, 3 figures, references updated | Eur. Phys. J. Plus 135, 449 (2020) | 10.1140/epjp/s13360-020-00481-x | null | gr-qc cond-mat.other | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the quantum Hall effect inside a gravitational field. First, we
review the influence of the gravitational field of the Earth on the quantum
Hall effect. Taking the gravitational field of the Earth to be uniform along
the vertical direction, we compute the affected quantized Hall resistivity.
Then, we investigate how the gravitational field modifies the Landau levels of
a particle moving between two massive hemispheres in the presence of a constant
and uniform magnetic field perpendicular to the plane of motion. We find that
the familiar degeneracy of the Landau levels is removed and the spacing between
the latter becomes dependent on the mass density of the hemispheres and on the
gravitational constant $G$. We use this result to show that the quantum Hall
effect in a thin conductor, sandwiched between two massive hemispheres, should
yield a slightly different variation of the Hall resistivity with the applied
magnetic field. We then argue that the well-known problem of the
gravitationally induced electric field, that might a priori be thought to
hinder the effect of gravity, has actually a beneficial role as it amplifies
the latter. We finally discuss whether there is a possibility of using the
quantum Hall effect to probe the inverse-square law of gravity.
| [
{
"created": "Thu, 21 May 2020 13:33:43 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Jun 2020 22:26:14 GMT",
"version": "v2"
}
] | 2020-07-02 | [
[
"Hammad",
"F.",
""
],
[
"Landry",
"A.",
""
],
[
"Mathieu",
"K.",
""
]
] | We study the quantum Hall effect inside a gravitational field. First, we review the influence of the gravitational field of the Earth on the quantum Hall effect. Taking the gravitational field of the Earth to be uniform along the vertical direction, we compute the affected quantized Hall resistivity. Then, we investigate how the gravitational field modifies the Landau levels of a particle moving between two massive hemispheres in the presence of a constant and uniform magnetic field perpendicular to the plane of motion. We find that the familiar degeneracy of the Landau levels is removed and the spacing between the latter becomes dependent on the mass density of the hemispheres and on the gravitational constant $G$. We use this result to show that the quantum Hall effect in a thin conductor, sandwiched between two massive hemispheres, should yield a slightly different variation of the Hall resistivity with the applied magnetic field. We then argue that the well-known problem of the gravitationally induced electric field, that might a priori be thought to hinder the effect of gravity, has actually a beneficial role as it amplifies the latter. We finally discuss whether there is a possibility of using the quantum Hall effect to probe the inverse-square law of gravity. |
0805.1403 | Ernesto F. Eiroa | Ernesto F. Eiroa | Stability of thin-shell wormholes with spherical symmetry | 14 pages, 3 figures | Phys.Rev.D78:024018,2008 | 10.1103/PhysRevD.78.024018 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article, the stability of a general class of spherically symmetric
thin-shell wormholes is studied under perturbations preserving the symmetry.
For this purpose, the equation of state at the throat is linearized around the
static solutions. The formalism presented here is applied to dilaton wormholes
and it is found that there is a smaller range of possible stable configurations
for them than in the case of Reissner-Nordstrom wormholes with the same charge.
| [
{
"created": "Fri, 9 May 2008 19:48:40 GMT",
"version": "v1"
}
] | 2010-05-12 | [
[
"Eiroa",
"Ernesto F.",
""
]
] | In this article, the stability of a general class of spherically symmetric thin-shell wormholes is studied under perturbations preserving the symmetry. For this purpose, the equation of state at the throat is linearized around the static solutions. The formalism presented here is applied to dilaton wormholes and it is found that there is a smaller range of possible stable configurations for them than in the case of Reissner-Nordstrom wormholes with the same charge. |
gr-qc/9307019 | Kristin Schleich | Kristin Schleich and Donald M. Witt | Generalized Sums over Histories for Quantum Gravity II. Simplicial
Conifolds | 82pp., plain TeX, To appear in Nucl. Phys. B,FF-92-2 | Nucl.Phys. B402 (1993) 469-530 | 10.1016/0550-3213(93)90650-E | null | gr-qc hep-th | null | This paper examines the issues involved with concretely implementing a sum
over conifolds in the formulation of Euclidean sums over histories for gravity.
The first step in precisely formulating any sum over topological spaces is that
one must have an algorithmically implementable method of generating a list of
all spaces in the set to be summed over. This requirement causes well known
problems in the formulation of sums over manifolds in four or more dimensions;
there is no algorithmic method of determining whether or not a topological
space is an n-manifold in five or more dimensions and the issue of whether or
not such an algorithm exists is open in four. However, as this paper shows,
conifolds are algorithmically decidable in four dimensions. Thus the set of
4-conifolds provides a starting point for a concrete implementation of
Euclidean sums over histories in four dimensions. Explicit algorithms for
summing over various sets of 4-conifolds are presented in the context of Regge
calculus. Postscript figures available via anonymous ftp at
black-hole.physics.ubc.ca (137.82.43.40) in file gen2.ps.
| [
{
"created": "Wed, 14 Jul 1993 20:57:00 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Schleich",
"Kristin",
""
],
[
"Witt",
"Donald M.",
""
]
] | This paper examines the issues involved with concretely implementing a sum over conifolds in the formulation of Euclidean sums over histories for gravity. The first step in precisely formulating any sum over topological spaces is that one must have an algorithmically implementable method of generating a list of all spaces in the set to be summed over. This requirement causes well known problems in the formulation of sums over manifolds in four or more dimensions; there is no algorithmic method of determining whether or not a topological space is an n-manifold in five or more dimensions and the issue of whether or not such an algorithm exists is open in four. However, as this paper shows, conifolds are algorithmically decidable in four dimensions. Thus the set of 4-conifolds provides a starting point for a concrete implementation of Euclidean sums over histories in four dimensions. Explicit algorithms for summing over various sets of 4-conifolds are presented in the context of Regge calculus. Postscript figures available via anonymous ftp at black-hole.physics.ubc.ca (137.82.43.40) in file gen2.ps. |
1401.2626 | Hossein Shojaie | Amir Pouyan Khosravi Karchi and Hossein Shojaie | An FLRW Cosmology with a Chameleon Field | 13 pages, 7 figures, to appear in IJMPD | Int. J. Mod. Phys. D 25, No. 3, 1650045 (2016) | 10.1142/S0218271816500450 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this manuscript, the field equations of a chameleon field in which the
matter Lagrangian term is a general function of the scalar field as well as
matter field, are derived. The equations are then expressed in
Friedmann--Lema\^itre--Robertson--Walker~(FLRW) framework and the associated
phase portraits and a power law solution are discussed in details. It is shown
that why non-minimal coupling between the chameleon and matter fields leads to
an energy transfer between the fields which consequently, affects the expansion
rate of the universe. The transfer direction is determined by the second law of
thermodynamics. The solution indicates that an accelerating expansion of the
universe can be described as a result of the energy flow from the chameleon
field to matter field.
| [
{
"created": "Sun, 12 Jan 2014 13:30:52 GMT",
"version": "v1"
},
{
"created": "Tue, 15 Mar 2016 14:01:35 GMT",
"version": "v2"
}
] | 2016-03-16 | [
[
"Karchi",
"Amir Pouyan Khosravi",
""
],
[
"Shojaie",
"Hossein",
""
]
] | In this manuscript, the field equations of a chameleon field in which the matter Lagrangian term is a general function of the scalar field as well as matter field, are derived. The equations are then expressed in Friedmann--Lema\^itre--Robertson--Walker~(FLRW) framework and the associated phase portraits and a power law solution are discussed in details. It is shown that why non-minimal coupling between the chameleon and matter fields leads to an energy transfer between the fields which consequently, affects the expansion rate of the universe. The transfer direction is determined by the second law of thermodynamics. The solution indicates that an accelerating expansion of the universe can be described as a result of the energy flow from the chameleon field to matter field. |
1407.4309 | Rituparno Goswami | Maombi D. Mkenyeleye, Rituparno Goswami, Sunil D. Maharaj | Gravitational collapse of generalised Vaidya spacetime | 8 pages, 2 figures, Changes in the text, Matches the accepted version
in Physical Review D | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the gravitational collapse of a generalised Vaidya spacetime in the
context of the Cosmic Censorship hypothesis. We develop a general mathematical
framework to study the conditions on the mass function so that future directed
non-spacelike geodesics can terminate at the singularity in the past. Thus our
result generalises earlier works on gravitational collapse of the combinations
of Type-I and Type-II matter fields. Our analysis shows transparently that
there exist classes of generalised Vaidya mass functions for which the collapse
terminates with a locally naked central singularity. We calculate the strength
of the these singularities to show that they are strong curvature singularities
and there can be no extension of spacetime through them.
| [
{
"created": "Wed, 16 Jul 2014 13:49:38 GMT",
"version": "v1"
},
{
"created": "Mon, 29 Sep 2014 13:59:35 GMT",
"version": "v2"
}
] | 2014-09-30 | [
[
"Mkenyeleye",
"Maombi D.",
""
],
[
"Goswami",
"Rituparno",
""
],
[
"Maharaj",
"Sunil D.",
""
]
] | We study the gravitational collapse of a generalised Vaidya spacetime in the context of the Cosmic Censorship hypothesis. We develop a general mathematical framework to study the conditions on the mass function so that future directed non-spacelike geodesics can terminate at the singularity in the past. Thus our result generalises earlier works on gravitational collapse of the combinations of Type-I and Type-II matter fields. Our analysis shows transparently that there exist classes of generalised Vaidya mass functions for which the collapse terminates with a locally naked central singularity. We calculate the strength of the these singularities to show that they are strong curvature singularities and there can be no extension of spacetime through them. |
2212.03890 | Don N. Page | Don N. Page | Can Two Ultrarelativistic Objects Lose Almost All Their Energy to
Gravitational Radiation? | 29 pages, LaTeX | null | 10.1103/PhysRevD.107.064057 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In 2007 Pretorius and Khurana did "speculate that at threshold [at a critical
impact parameter], all of the kinetic energy of the system [two
ultrarelativistic black holes] is converted to gravitational waves, which can
be an arbitrarily large fraction of the total energy." However, in 2012
Sperhake, Berti, Cardoso, and Pretorius performed numerical calculations that
led them to the contrary conclusion: "An extrapolation of our results to the
limit $\gamma \rightarrow \infty$ suggests that about half of the
center-of-mass energy of the system can be emitted in gravitational radiation,
while the rest must be converted into rest-mass and spin energy." Here I
present arguments against this latter conclusion and in support of the earlier
speculation that for sufficiently large $\gamma$, all but an arbitrarily small
fraction of the total energy can be radiated away.
| [
{
"created": "Wed, 7 Dec 2022 19:00:03 GMT",
"version": "v1"
}
] | 2023-04-05 | [
[
"Page",
"Don N.",
""
]
] | In 2007 Pretorius and Khurana did "speculate that at threshold [at a critical impact parameter], all of the kinetic energy of the system [two ultrarelativistic black holes] is converted to gravitational waves, which can be an arbitrarily large fraction of the total energy." However, in 2012 Sperhake, Berti, Cardoso, and Pretorius performed numerical calculations that led them to the contrary conclusion: "An extrapolation of our results to the limit $\gamma \rightarrow \infty$ suggests that about half of the center-of-mass energy of the system can be emitted in gravitational radiation, while the rest must be converted into rest-mass and spin energy." Here I present arguments against this latter conclusion and in support of the earlier speculation that for sufficiently large $\gamma$, all but an arbitrarily small fraction of the total energy can be radiated away. |
2012.04795 | Saeed Rastgoo | Pasquale Bosso, Octavio Obreg\'on, Saeed Rastgoo, Wilfredo Yupanqui | Deformed algebra and the effective dynamics of the interior of black
holes | 24 pages, 2 figures. arXiv admin note: text overlap with
arXiv:2011.11815, v2: analysis extended, a new prescription to deal with
fiducial elements introduced, figures are slightly modified and are now in
color | Class. Quantum Grav. 38 (2021) 14, 145006 | 10.1088/1361-6382/ac025f | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the classical Hamiltonian of the interior of the Schwarzschild
black hole in Ashtekar-Barbero connection formalism. Then, inspired by
generalized uncertainty principle models, we deform the classical canonical
algebra and derive the effective dynamics of the model under this modification.
We show that such a deformation leads to the resolution of the singularity of
the black hole and a minimum nonzero radius for the infalling 2-spheres,
provided that the deformation parameters are chosen to be negative.
| [
{
"created": "Wed, 9 Dec 2020 00:09:49 GMT",
"version": "v1"
},
{
"created": "Tue, 15 Jun 2021 15:18:35 GMT",
"version": "v2"
}
] | 2021-06-16 | [
[
"Bosso",
"Pasquale",
""
],
[
"Obregón",
"Octavio",
""
],
[
"Rastgoo",
"Saeed",
""
],
[
"Yupanqui",
"Wilfredo",
""
]
] | We consider the classical Hamiltonian of the interior of the Schwarzschild black hole in Ashtekar-Barbero connection formalism. Then, inspired by generalized uncertainty principle models, we deform the classical canonical algebra and derive the effective dynamics of the model under this modification. We show that such a deformation leads to the resolution of the singularity of the black hole and a minimum nonzero radius for the infalling 2-spheres, provided that the deformation parameters are chosen to be negative. |
2110.05434 | Celia Escamilla-Rivera | Celia Escamilla-Rivera, Geovanny A. Rave-Franco and Jackson Levi Said | $f(T,B)$ cosmography for high redshifts | 16 pages, 3 figures. Version accepted in Universe | Universe 2021, 7(11) | 10.3390/universe7110441 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | In light of the statistical performance of cosmological observations, in this
work we present the cosmography in $f(T,B)$ gravity. In this scenario we found
a cosmological viable standard case that allows to reduce the degeneracy
between several $f(T,B)$ models already proposed in the literature.
Furthermore, we constrain this model using Pantheon SNeIa compilation, Cosmic
Chronometers and a newly GRB calibrated data sample. We found that with an
appropriate strategy for including the cosmographic parameter, we do produce a
viable cosmology with our model within $f(T,B)$ gravity.
| [
{
"created": "Mon, 11 Oct 2021 17:25:24 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Nov 2021 18:24:15 GMT",
"version": "v2"
}
] | 2021-11-17 | [
[
"Escamilla-Rivera",
"Celia",
""
],
[
"Rave-Franco",
"Geovanny A.",
""
],
[
"Said",
"Jackson Levi",
""
]
] | In light of the statistical performance of cosmological observations, in this work we present the cosmography in $f(T,B)$ gravity. In this scenario we found a cosmological viable standard case that allows to reduce the degeneracy between several $f(T,B)$ models already proposed in the literature. Furthermore, we constrain this model using Pantheon SNeIa compilation, Cosmic Chronometers and a newly GRB calibrated data sample. We found that with an appropriate strategy for including the cosmographic parameter, we do produce a viable cosmology with our model within $f(T,B)$ gravity. |
gr-qc/0208047 | Yuri Shtanov | Yuri Shtanov, Varun Sahni | Bouncing Braneworlds | 9 pages, 1 figure, revtex, accepted for publication in Phys. Lett. B | Phys.Lett.B557:1-6,2003 | 10.1016/S0370-2693(03)00179-5 | null | gr-qc astro-ph hep-ph hep-th | null | We study cosmological braneworld models with a single timelike extra
dimension. Such models admit the intriguing possibility that a contracting
braneworld experiences a natural bounce without ever reaching a singular state.
This feature persists in the case of anisotropic braneworlds under some
additional and not very restrictive assumptions. Generalizing our study to
braneworld models containing an induced brane curvature term, we find that a
FRW-type singularity is once again absent if the bulk extra dimension is
timelike. In this case, the universe either has a non-singular origin or
commences its expansion from a quasi-singular state during which both the
Hubble parameter and the energy density and pressure remain finite while the
curvature tensor diverges. The non-singular and quasi-singular behaviour which
we have discovered differs both qualitatively and quantitatively from what is
usually observed in braneworld models with spacelike extra dimensions and could
have interesting cosmological implications.
| [
{
"created": "Sat, 17 Aug 2002 11:28:14 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Feb 2003 02:42:46 GMT",
"version": "v2"
},
{
"created": "Sun, 9 Feb 2003 18:41:38 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Shtanov",
"Yuri",
""
],
[
"Sahni",
"Varun",
""
]
] | We study cosmological braneworld models with a single timelike extra dimension. Such models admit the intriguing possibility that a contracting braneworld experiences a natural bounce without ever reaching a singular state. This feature persists in the case of anisotropic braneworlds under some additional and not very restrictive assumptions. Generalizing our study to braneworld models containing an induced brane curvature term, we find that a FRW-type singularity is once again absent if the bulk extra dimension is timelike. In this case, the universe either has a non-singular origin or commences its expansion from a quasi-singular state during which both the Hubble parameter and the energy density and pressure remain finite while the curvature tensor diverges. The non-singular and quasi-singular behaviour which we have discovered differs both qualitatively and quantitatively from what is usually observed in braneworld models with spacelike extra dimensions and could have interesting cosmological implications. |
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