id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/0702067 | Hamid Reza Sepangi | N. Khosravi, S. Jalalzadeh and H. R. Sepangi | Quantum noncommutative multidimensional cosmology | 10 pages, 1 figure, to appear in GRG | Gen.Rel.Grav.39:899-911,2007 | 10.1007/s10714-007-0429-z | null | gr-qc hep-th | null | We present exact quantum solutions for a noncommutative, multidimensional
cosmological model and show that stabilization of extra dimensions sets in with
the introduction of noncommutativity between the scale factors. An
interpretation is offered to accommodate the notion of time, rendering
comparison with the classical solutions possible.
| [
{
"created": "Mon, 12 Feb 2007 10:30:02 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Khosravi",
"N.",
""
],
[
"Jalalzadeh",
"S.",
""
],
[
"Sepangi",
"H. R.",
""
]
] | We present exact quantum solutions for a noncommutative, multidimensional cosmological model and show that stabilization of extra dimensions sets in with the introduction of noncommutativity between the scale factors. An interpretation is offered to accommodate the notion of time, rendering comparison with the classical solutions possible. |
2007.04197 | Xiao-Mei Kuang | Hong Guo, Hang Liu, Xiao-Mei Kuang, Bin Wang | Acoustic black hole in Schwarzschild spacetime: quasi-normal modes,
analogous Hawking radiation and shadows | 19 pages,9 figures;published version | Phys. Rev. D 102, 124019 (2020) | 10.1103/PhysRevD.102.124019 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Various properties of acoustic black holes constructed in Minkowski spacetime
have been widely studied in the past decades. Recently the acoustic black holes
in general spacetime were proposed . In this paper, we first investigate the
basic characteristics of `curved' acoustic black hole in Schwarzschild
spacetime, including the quasi-normal modes, grey-body factor and analogous
Hawking radiation. We find that the signal of quasi-normal mode is weaker than
that of Schwarzschild black hole. Moreover, as the tuning parameter increases,
both the positive real part and negative imaginal part of the quasi-normal
frequency approach to the horizonal axis, but they will not change sign. This
means that all the perturbations could die off and the system is stable under
those perturbations. Since the larger tuning parameter suppresses the effective
potential barrier, so it enhances the grey-body factor. The energy emission
rate of Hawking radiation does not monotonically increase of the tuning
parameter because of the non-monotonicity of the Hawking temperature. Finally,
as a first attempt, we study the acoustic black hole shadow. The radius of
acoustic shadow becomes larger as the tuning parameter increases, because both
the related acoustic horizon and the acoustic sphere become larger. Our studies
could help us to further understand the near horizon geometrical features of
the black hole. We also expect that our observations could be detected
experimentally in the near future.
| [
{
"created": "Wed, 8 Jul 2020 15:38:41 GMT",
"version": "v1"
},
{
"created": "Sat, 12 Dec 2020 08:53:55 GMT",
"version": "v2"
}
] | 2021-01-04 | [
[
"Guo",
"Hong",
""
],
[
"Liu",
"Hang",
""
],
[
"Kuang",
"Xiao-Mei",
""
],
[
"Wang",
"Bin",
""
]
] | Various properties of acoustic black holes constructed in Minkowski spacetime have been widely studied in the past decades. Recently the acoustic black holes in general spacetime were proposed . In this paper, we first investigate the basic characteristics of `curved' acoustic black hole in Schwarzschild spacetime, including the quasi-normal modes, grey-body factor and analogous Hawking radiation. We find that the signal of quasi-normal mode is weaker than that of Schwarzschild black hole. Moreover, as the tuning parameter increases, both the positive real part and negative imaginal part of the quasi-normal frequency approach to the horizonal axis, but they will not change sign. This means that all the perturbations could die off and the system is stable under those perturbations. Since the larger tuning parameter suppresses the effective potential barrier, so it enhances the grey-body factor. The energy emission rate of Hawking radiation does not monotonically increase of the tuning parameter because of the non-monotonicity of the Hawking temperature. Finally, as a first attempt, we study the acoustic black hole shadow. The radius of acoustic shadow becomes larger as the tuning parameter increases, because both the related acoustic horizon and the acoustic sphere become larger. Our studies could help us to further understand the near horizon geometrical features of the black hole. We also expect that our observations could be detected experimentally in the near future. |
1511.01422 | Rafael M. Rubio | Juan A. Aledo, Rafael M. Rubio | Scalar curvature of spacelike hypersurfaces and certain class of
cosmological models for accelerated expanding universes | arXiv admin note: text overlap with arXiv:1503.00120 | null | 10.1016/j.geomphys.2016.02.005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the scalar curvature of spacelike hypersurfaces in the family of
cosmological models known as generalized Robertson-Walker spacetimes, and give
several rigidity results under appropriate mathematical and physical
assumptions. On the other hand, we show that this family of spacetimes provides
suitable models obeying the null convergence condition to explain accelerated
expanding universes.
| [
{
"created": "Wed, 4 Nov 2015 18:22:31 GMT",
"version": "v1"
}
] | 2016-03-23 | [
[
"Aledo",
"Juan A.",
""
],
[
"Rubio",
"Rafael M.",
""
]
] | We study the scalar curvature of spacelike hypersurfaces in the family of cosmological models known as generalized Robertson-Walker spacetimes, and give several rigidity results under appropriate mathematical and physical assumptions. On the other hand, we show that this family of spacetimes provides suitable models obeying the null convergence condition to explain accelerated expanding universes. |
1603.02259 | Alberto S\'anchez | Alberto Sanchez | Geometrothermodynamics of black holes in Lorentz non-invariant massive
gravity | 16 latex pages, 8 figures | Phys. Rev. D 94, 024037 (2016) | 10.1103/PhysRevD.94.024037 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze a static and spherically symmetric hairy black hole solution in
non-invariant massive gravity. The formalism of geometrothermodynamics is used
to describe the thermodynamic characteristics of this black hole in a Legendre
invariant way. For a black hole in massive gravity, the geometry of the space
of equilibrium states is computed showing that it contains information about
the thermodynamic interaction, critical points and phase transitions structure.
| [
{
"created": "Sat, 5 Mar 2016 17:40:41 GMT",
"version": "v1"
}
] | 2016-07-27 | [
[
"Sanchez",
"Alberto",
""
]
] | We analyze a static and spherically symmetric hairy black hole solution in non-invariant massive gravity. The formalism of geometrothermodynamics is used to describe the thermodynamic characteristics of this black hole in a Legendre invariant way. For a black hole in massive gravity, the geometry of the space of equilibrium states is computed showing that it contains information about the thermodynamic interaction, critical points and phase transitions structure. |
gr-qc/9401018 | Neil Cornish | N. J. Cornish and J. W. Moffat | Nonsymmetric Gravity Does Have Acceptable Global Asymptotics | 7 pages, UT-PT-94-01. Our original arguments have been expanded upon
and generalised | null | null | null | gr-qc | null | ``Reports of my death are greatly exaggerated''
- Mark Twain. We consider the claim by Damour, Deser and McCarthy that
nonsymmetric gravity theory has unacceptable global asymptotics. We explain why
this claim is incorrect.
| [
{
"created": "Tue, 18 Jan 1994 23:26:35 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Mar 1994 23:41:28 GMT",
"version": "v2"
}
] | 2008-02-03 | [
[
"Cornish",
"N. J.",
""
],
[
"Moffat",
"J. W.",
""
]
] | ``Reports of my death are greatly exaggerated'' - Mark Twain. We consider the claim by Damour, Deser and McCarthy that nonsymmetric gravity theory has unacceptable global asymptotics. We explain why this claim is incorrect. |
2305.01116 | Jeffrey Hazboun | Jeffrey S. Hazboun and Patrick M. Meyers and Joseph D. Romano and
Xavier Siemens and Anne M. Archibald | Analytic distribution of the optimal cross-correlation statistic for
stochastic gravitational-wave-background searches using pulsar timing arrays | 13 pages, 3 Figures | null | null | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show via both analytical calculation and numerical simulation that the
optimal cross-correlation statistic (OS) for stochastic
gravitational-wave-background (GWB) searches using data from pulsar timing
arrays follows a generalized chi-squared (GX2) distribution-i.e., a linear
combination of chi-squared distributions with coefficients given by the
eigenvalues of the quadratic form defining the statistic. This observation is
particularly important for calculating the frequentist statistical significance
of a possible GWB detection, which depends on the exact form of the
distribution of the OS signal-to-noise ratio (S/N) $\hat\rho \equiv \hat A_{\rm
gw}^2/\sigma_0$ in the absence of GW-induced cross correlations (i.e., the null
distribution). Previous discussions of the OS have incorrectly assumed that the
analytic null distribution of $\hat\rho$ is well-approximated by a zero-mean
unit-variance Gaussian distribution. Empirical calculations show that the null
distribution of $\hat\rho$ has "tails" which differ significantly from those
for a Gaussian distribution, but which follow (exactly) a GX2 distribution. So,
a correct analytical assessment of the statistical significance of a potential
detection requires the use of a GX2 distribution.
| [
{
"created": "Mon, 1 May 2023 23:04:55 GMT",
"version": "v1"
}
] | 2023-05-03 | [
[
"Hazboun",
"Jeffrey S.",
""
],
[
"Meyers",
"Patrick M.",
""
],
[
"Romano",
"Joseph D.",
""
],
[
"Siemens",
"Xavier",
""
],
[
"Archibald",
"Anne M.",
""
]
] | We show via both analytical calculation and numerical simulation that the optimal cross-correlation statistic (OS) for stochastic gravitational-wave-background (GWB) searches using data from pulsar timing arrays follows a generalized chi-squared (GX2) distribution-i.e., a linear combination of chi-squared distributions with coefficients given by the eigenvalues of the quadratic form defining the statistic. This observation is particularly important for calculating the frequentist statistical significance of a possible GWB detection, which depends on the exact form of the distribution of the OS signal-to-noise ratio (S/N) $\hat\rho \equiv \hat A_{\rm gw}^2/\sigma_0$ in the absence of GW-induced cross correlations (i.e., the null distribution). Previous discussions of the OS have incorrectly assumed that the analytic null distribution of $\hat\rho$ is well-approximated by a zero-mean unit-variance Gaussian distribution. Empirical calculations show that the null distribution of $\hat\rho$ has "tails" which differ significantly from those for a Gaussian distribution, but which follow (exactly) a GX2 distribution. So, a correct analytical assessment of the statistical significance of a potential detection requires the use of a GX2 distribution. |
gr-qc/0402064 | Alejandro Corichi | Alejandro Corichi | Comments on area spectra in Loop Quantum Gravity | 4 pages, no figures. Comments and references added | Rev.Mex.Fis. 50 (2005) 549-552 | null | ICN-UNAM-04/01 | gr-qc hep-th | null | We examine and compare different area spectra that have been recently
considered in Loop Quantum Gravity (LQG). In particular we focus our attention
on a Equally Spaced (ES) spectrum operator introduced by Alekseev et. al. that
has gained recent attention. We show that such operator is not well defined
within the LQG framework, and comment on the issue regarding area spectra and
QNM frequencies.
| [
{
"created": "Fri, 13 Feb 2004 18:31:36 GMT",
"version": "v1"
},
{
"created": "Tue, 17 Feb 2004 22:47:29 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Corichi",
"Alejandro",
""
]
] | We examine and compare different area spectra that have been recently considered in Loop Quantum Gravity (LQG). In particular we focus our attention on a Equally Spaced (ES) spectrum operator introduced by Alekseev et. al. that has gained recent attention. We show that such operator is not well defined within the LQG framework, and comment on the issue regarding area spectra and QNM frequencies. |
2207.13435 | S. N Sajadi | S. N. Sajadi, S. H. Hendi | Analytically Approximation Solution to Einstein-Cubic Gravity | 22 pages, 12 Figures, accepted in EPJC | null | 10.1140/epjc/s10052-022-10647-9 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this work, we introduce an analytical approximate black hole solution in
Einstein-Cubic gravity. To obtain complete solutions, we construct the near
horizon and asymptotic solutions as the first step. Then, the approximate
analytic solutions are obtained through continued fraction expansion. We also
compute the thermodynamic quantities and use the first law and Smarr formula to
obtain the analytic solutions for the near horizon quantities. Finally, we
follow the same approach to obtain the new static black hole solutions with
different metric functions.
| [
{
"created": "Wed, 27 Jul 2022 10:26:44 GMT",
"version": "v1"
}
] | 2022-08-24 | [
[
"Sajadi",
"S. N.",
""
],
[
"Hendi",
"S. H.",
""
]
] | In this work, we introduce an analytical approximate black hole solution in Einstein-Cubic gravity. To obtain complete solutions, we construct the near horizon and asymptotic solutions as the first step. Then, the approximate analytic solutions are obtained through continued fraction expansion. We also compute the thermodynamic quantities and use the first law and Smarr formula to obtain the analytic solutions for the near horizon quantities. Finally, we follow the same approach to obtain the new static black hole solutions with different metric functions. |
0807.2159 | Margus Saal | Laur Jarv, Piret Kuusk, Margus Saal | Scalar-tensor cosmologies: fixed points of the Jordan frame scalar field | 21 pages, 4 figures, some comments and references added | Phys.Rev.D78:083530,2008 | 10.1103/PhysRevD.78.083530 | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the evolution of homogeneous and isotropic, flat cosmological models
within the general scalar-tensor theory of gravity with arbitrary coupling
function and potential. After introducing the limit of general relativity we
describe the details of the phase space geometry. Using the methods of
dynamical systems for the decoupled equation of the Jordan frame scalar field
we find the fixed points of flows in two cases: potential domination and matter
domination. We present the conditions on the mathematical form of the coupling
function and potential which determine the nature of the fixed points
(attractor or other). There are two types of fixed points, both are
characterized by cosmological evolution mimicking general relativity, but only
one of the types is compatible with the Solar System PPN constraints. The phase
space structure should also carry over to the Einstein frame as long as the
transformation between the frames is regular which however is not the case for
the latter (PPN compatible) fixed point.
| [
{
"created": "Mon, 14 Jul 2008 13:17:50 GMT",
"version": "v1"
},
{
"created": "Tue, 28 Oct 2008 14:03:42 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Jarv",
"Laur",
""
],
[
"Kuusk",
"Piret",
""
],
[
"Saal",
"Margus",
""
]
] | We study the evolution of homogeneous and isotropic, flat cosmological models within the general scalar-tensor theory of gravity with arbitrary coupling function and potential. After introducing the limit of general relativity we describe the details of the phase space geometry. Using the methods of dynamical systems for the decoupled equation of the Jordan frame scalar field we find the fixed points of flows in two cases: potential domination and matter domination. We present the conditions on the mathematical form of the coupling function and potential which determine the nature of the fixed points (attractor or other). There are two types of fixed points, both are characterized by cosmological evolution mimicking general relativity, but only one of the types is compatible with the Solar System PPN constraints. The phase space structure should also carry over to the Einstein frame as long as the transformation between the frames is regular which however is not the case for the latter (PPN compatible) fixed point. |
2210.15684 | Jacopo Tissino | Jacopo Tissino, Gregorio Carullo, Matteo Breschi, Rossella Gamba,
Stefano Schmidt, Sebastiano Bernuzzi | Combining effective-one-body accuracy and reduced-order-quadrature speed
for binary neutron star merger parameter estimation with machine learning | 20 pages, 11 figures | null | 10.1103/PhysRevD.107.084037 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We present mlgw-bns, a gravitational waveform surrogate that allows for a
significant improvement in the generation speed of frequency-domain waveforms
for binary neutron star mergers, at a negligible cost in accuracy. This
improvement is achieved by training a machine-learning model on a dataset of
waveforms generated with an accurate but comparatively costlier approximant:
the state-of-the-art effective-one-body model TEOBResumSPA. When coupled to a
reduced-order scheme, mlgw-bns can accelerate waveform generation up to a
factor of ~35, outperforming all other approximants of similar accuracy. By
analyzing GW170817 in realistic parameter estimation settings with our scheme,
we showcase an overall speedup against TEOBResumSPA greater than an order of
magnitude. Our methodology will bear a significant impact on the scientific
program of next generation detectors by allowing routine usage of accurate
effective-one-body models.
| [
{
"created": "Thu, 27 Oct 2022 18:00:01 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Nov 2022 17:13:15 GMT",
"version": "v2"
}
] | 2023-05-10 | [
[
"Tissino",
"Jacopo",
""
],
[
"Carullo",
"Gregorio",
""
],
[
"Breschi",
"Matteo",
""
],
[
"Gamba",
"Rossella",
""
],
[
"Schmidt",
"Stefano",
""
],
[
"Bernuzzi",
"Sebastiano",
""
]
] | We present mlgw-bns, a gravitational waveform surrogate that allows for a significant improvement in the generation speed of frequency-domain waveforms for binary neutron star mergers, at a negligible cost in accuracy. This improvement is achieved by training a machine-learning model on a dataset of waveforms generated with an accurate but comparatively costlier approximant: the state-of-the-art effective-one-body model TEOBResumSPA. When coupled to a reduced-order scheme, mlgw-bns can accelerate waveform generation up to a factor of ~35, outperforming all other approximants of similar accuracy. By analyzing GW170817 in realistic parameter estimation settings with our scheme, we showcase an overall speedup against TEOBResumSPA greater than an order of magnitude. Our methodology will bear a significant impact on the scientific program of next generation detectors by allowing routine usage of accurate effective-one-body models. |
2402.02069 | Joshi Ashok B | Divyesh P. Viththani, Ashok B. Joshi, Tapobroto Bhanja and Pankaj S.
Joshi | Particle motion and tidal force in a non-vacuum-charged naked
singularity | 9 pages, 6 figures | null | 10.1140/epjc/s10052-024-12746-1 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this article, we investigate the gravitational field of a charged,
non-vacuum, non-rotating, spherically symmetric body of mass $M$ assuming a
static solution to the Einstein-Maxwell field equations. We demonstrate that
the characteristics of perihelion precession of orbits in Schwarzschild and
Null singularity spacetimes are similar, whereas, in the case of charged naked
singularity (CNS) spacetime, the characteristics are the opposite of those in
Schwarzschild and Null singularity spacetime. Here we discuss some novel
features of the timelike and lightlike geodesics in this spacetime. We also
discuss the comparative study of tidal force in the null singularity spacetime
and charged naked singularity spacetime.
| [
{
"created": "Sat, 3 Feb 2024 07:18:19 GMT",
"version": "v1"
},
{
"created": "Sat, 13 Apr 2024 17:21:32 GMT",
"version": "v2"
}
] | 2024-04-16 | [
[
"Viththani",
"Divyesh P.",
""
],
[
"Joshi",
"Ashok B.",
""
],
[
"Bhanja",
"Tapobroto",
""
],
[
"Joshi",
"Pankaj S.",
""
]
] | In this article, we investigate the gravitational field of a charged, non-vacuum, non-rotating, spherically symmetric body of mass $M$ assuming a static solution to the Einstein-Maxwell field equations. We demonstrate that the characteristics of perihelion precession of orbits in Schwarzschild and Null singularity spacetimes are similar, whereas, in the case of charged naked singularity (CNS) spacetime, the characteristics are the opposite of those in Schwarzschild and Null singularity spacetime. Here we discuss some novel features of the timelike and lightlike geodesics in this spacetime. We also discuss the comparative study of tidal force in the null singularity spacetime and charged naked singularity spacetime. |
gr-qc/0108048 | Shinji Mukohyama | Shinji Mukohyama | Doubly covariant action principle of singular hypersurfaces in general
relativity and scalar-tensor theories | Latex, 8 pages; version to appear in Physical Review D | Phys.Rev. D65 (2002) 024028 | 10.1103/PhysRevD.65.024028 | null | gr-qc hep-th | null | An action principle of singular hypersurfaces in general relativity and
scalar-tensor type theories of gravity in the Einstein frame is presented
without assuming any symmetry. The action principle is manifestly doubly
covariant in the sense that coordinate systems on and off a hypersurface are
disentangled and can be independently specified. It is shown that, including
variation of the metric, the position of the hypersurface and matter fields,
the variational principle gives the correct set of equations of motion: the
Einstein equation off the hypersurface, Israel's junction condition in a doubly
covariant form and equations of motion of matter fields including the scalar
fields. The position of the hypersurface measured from one side of the
hypersurface and that measured from another side can be independently variated
as required by the double covariance.
| [
{
"created": "Sun, 19 Aug 2001 17:12:03 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Aug 2001 00:29:55 GMT",
"version": "v2"
},
{
"created": "Fri, 5 Oct 2001 03:10:49 GMT",
"version": "v3"
}
] | 2009-11-07 | [
[
"Mukohyama",
"Shinji",
""
]
] | An action principle of singular hypersurfaces in general relativity and scalar-tensor type theories of gravity in the Einstein frame is presented without assuming any symmetry. The action principle is manifestly doubly covariant in the sense that coordinate systems on and off a hypersurface are disentangled and can be independently specified. It is shown that, including variation of the metric, the position of the hypersurface and matter fields, the variational principle gives the correct set of equations of motion: the Einstein equation off the hypersurface, Israel's junction condition in a doubly covariant form and equations of motion of matter fields including the scalar fields. The position of the hypersurface measured from one side of the hypersurface and that measured from another side can be independently variated as required by the double covariance. |
gr-qc/9508057 | Erik A. Martinez | Erik A. Martinez | Entropy of eternal black holes | To appear in the proceedings of the Sixth Canadian Conference on
General Relativiy and Relativistic Astrophysics, 7 pages, Latex | null | null | Alberta-Thy-18-95 | gr-qc | null | The entropy of a quantum-statistical system which is classically approximated
by a general stationary eternal black hole is studied by means of a
microcanonical functional integral. This approach opens the possibility of
including explicitly the internal degrees of freedom of a physical black hole
in path integral descriptions of its thermodynamical properties. If the
functional integral is interpreted as the density of states of the system, the
corresponding entropy equals ${cal S} = A_H/4 - A_H/4 =0$ in the semiclassical
approximation, where $A_H$ is the area of the black hole horizon. The
functional integral reflects the properties of a pure state.
| [
{
"created": "Mon, 28 Aug 1995 19:59:57 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Martinez",
"Erik A.",
""
]
] | The entropy of a quantum-statistical system which is classically approximated by a general stationary eternal black hole is studied by means of a microcanonical functional integral. This approach opens the possibility of including explicitly the internal degrees of freedom of a physical black hole in path integral descriptions of its thermodynamical properties. If the functional integral is interpreted as the density of states of the system, the corresponding entropy equals ${cal S} = A_H/4 - A_H/4 =0$ in the semiclassical approximation, where $A_H$ is the area of the black hole horizon. The functional integral reflects the properties of a pure state. |
2208.14308 | Tobias Mistele | Tobias Mistele | A novel Cherenkov radiation constraint for hybrid MOND dark matter
models | 73 pages, 6 figures, minor changes | null | null | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Modified gravity models often contain modes that couple to normal matter and
propagate with slightly less than the speed of light. High-energy cosmic rays
then lose energy due to Cherenkov radiation, which constrains such models. This
is also true for some MOND (Modified Newtonian Dynamics) models. However, these
constraints are difficult to make precise because MOND is inherently non-linear
and because the results may depend on the specific high-acceleration behavior
of these models, i.e. the behavior outside the MOND regime. Recently, various
hybrid MOND dark matter models were proposed, where cold dark matter (CDM)
phenomenology on cosmological scales and MOND phenomenology on galactic scales
share a common origin. Such models typically contain a mode that is directly
coupled to matter (for MOND), but with non-relativistic sound speed (for CDM).
Thus, even non-relativistic objects like stars can emit gravitational Cherenkov
radiation. We calculate a lower bound on the associated energy loss. We use a
controlled approximation that depends only on the MOND regime of these models.
We apply our results to three concrete models: For the original superfluid dark
matter model (SFDM), we rule out a part of the parameter space, including the
most commonly used parameters. For two-field SFDM, we find no constraint since
the matter coupling of the relevant mode is suppressed by mixing. For the
recently-proposed model by Skordis and Z{\l}o\'snik, we find no constraint
since the matter coupling is suppressed in non-static situations.
| [
{
"created": "Tue, 30 Aug 2022 14:47:54 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Sep 2022 09:24:48 GMT",
"version": "v2"
}
] | 2022-09-14 | [
[
"Mistele",
"Tobias",
""
]
] | Modified gravity models often contain modes that couple to normal matter and propagate with slightly less than the speed of light. High-energy cosmic rays then lose energy due to Cherenkov radiation, which constrains such models. This is also true for some MOND (Modified Newtonian Dynamics) models. However, these constraints are difficult to make precise because MOND is inherently non-linear and because the results may depend on the specific high-acceleration behavior of these models, i.e. the behavior outside the MOND regime. Recently, various hybrid MOND dark matter models were proposed, where cold dark matter (CDM) phenomenology on cosmological scales and MOND phenomenology on galactic scales share a common origin. Such models typically contain a mode that is directly coupled to matter (for MOND), but with non-relativistic sound speed (for CDM). Thus, even non-relativistic objects like stars can emit gravitational Cherenkov radiation. We calculate a lower bound on the associated energy loss. We use a controlled approximation that depends only on the MOND regime of these models. We apply our results to three concrete models: For the original superfluid dark matter model (SFDM), we rule out a part of the parameter space, including the most commonly used parameters. For two-field SFDM, we find no constraint since the matter coupling of the relevant mode is suppressed by mixing. For the recently-proposed model by Skordis and Z{\l}o\'snik, we find no constraint since the matter coupling is suppressed in non-static situations. |
2007.12964 | Cesar Alonso Valenzuela Toledo | Alejandro Guarnizo, J. Bayron Orjuela-Quintana, C\'esar A.
Valenzuela-Toledo | Dynamical analysis of cosmological models with non-Abelian gauge vector
fields | 20 pages, 22 figures. V2: typos corrected and references added.
Published version | Phys. Rev. D 102, 083507 (2020) | 10.1103/PhysRevD.102.083507 | PI/UAN-2020-672FT | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study some models where non-Abelian gauge vector fields
endowed with a SU(2) group representation are the unique source of inflation
and dark energy. These models were first introduced under the name of
gaugeflation and gaugessence, respectively. Although several realizations of
these models have been discussed, not all available parameters and initial
conditions are known. In this work, we use a dynamical system approach to find
the full parameter space of the massive version of each model. In particular,
we found that the inclusion of the mass term increases the length of the
inflationary period. Additionally, the mass term implies new behaviors for the
equation of state of dark energy allowing to distinguish this from other
prototypical models of accelerated expansion. We show that an axially symmetric
gauge field can support an anisotropic accelerated expansion within the
observational bounds.
| [
{
"created": "Sat, 25 Jul 2020 16:06:07 GMT",
"version": "v1"
},
{
"created": "Sat, 10 Oct 2020 16:30:34 GMT",
"version": "v2"
}
] | 2020-10-13 | [
[
"Guarnizo",
"Alejandro",
""
],
[
"Orjuela-Quintana",
"J. Bayron",
""
],
[
"Valenzuela-Toledo",
"César A.",
""
]
] | In this paper we study some models where non-Abelian gauge vector fields endowed with a SU(2) group representation are the unique source of inflation and dark energy. These models were first introduced under the name of gaugeflation and gaugessence, respectively. Although several realizations of these models have been discussed, not all available parameters and initial conditions are known. In this work, we use a dynamical system approach to find the full parameter space of the massive version of each model. In particular, we found that the inclusion of the mass term increases the length of the inflationary period. Additionally, the mass term implies new behaviors for the equation of state of dark energy allowing to distinguish this from other prototypical models of accelerated expansion. We show that an axially symmetric gauge field can support an anisotropic accelerated expansion within the observational bounds. |
1604.06216 | Fatimah Shojai | F. Shojai, M. Kohandel, A. Stepanian | On the Relativistic anisotropic configurations | 4 figures | Eur. Phys. J. C (2016) 76: 347 | 10.1140/epjc/s10052-016-4204-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study anisotropic spherical polytropes within the framework
of general relativity. Using the anisotropic Tolman-Oppenheimer-Volkov (TOV)
equations, we explore the relativistic anisotropic Lane-Emden equations. We
find how the anisotropic pressure affects the boundary conditions of these
equations. Also we argue that the behaviour of physical quantities near the
center of star changes in the presence of anisotropy. For constant density, a
class of exact solution is derived with the aid of a new ansatz and its
physical properties are discussed.
| [
{
"created": "Thu, 21 Apr 2016 08:49:04 GMT",
"version": "v1"
}
] | 2016-07-20 | [
[
"Shojai",
"F.",
""
],
[
"Kohandel",
"M.",
""
],
[
"Stepanian",
"A.",
""
]
] | In this paper we study anisotropic spherical polytropes within the framework of general relativity. Using the anisotropic Tolman-Oppenheimer-Volkov (TOV) equations, we explore the relativistic anisotropic Lane-Emden equations. We find how the anisotropic pressure affects the boundary conditions of these equations. Also we argue that the behaviour of physical quantities near the center of star changes in the presence of anisotropy. For constant density, a class of exact solution is derived with the aid of a new ansatz and its physical properties are discussed. |
2109.09676 | Pujian Mao | Pujian Mao and Weicheng Zhao | Note on the asymptotic structure of Kerr-Schild form | v2: refs added, interpretations about several issues improved v3:
refs added, major revision, published in JHEP | JHEP 01 (2022) 030 | 10.1007/JHEP01(2022)030 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | The Kerr-Schild form provides a natural way of realizing the classical double
copy that relates exact solutions in general relativity to exact solutions in
gauge theory. In this paper, we examine the asymptotic structure of Kerr-Schild
form. In Newman-Unti gauge, we find a generic solution space satisfying the
Kerr-Schild form in series expansion around null infinity. The news function in
the solution space is chiral and can not lead to a mass loss formula. A class
of asymptotically flat complex pp-wave solutions in closed form is obtained
from the solution space.
| [
{
"created": "Mon, 20 Sep 2021 16:45:41 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Oct 2021 07:06:58 GMT",
"version": "v2"
},
{
"created": "Tue, 25 Jan 2022 13:33:45 GMT",
"version": "v3"
}
] | 2022-01-26 | [
[
"Mao",
"Pujian",
""
],
[
"Zhao",
"Weicheng",
""
]
] | The Kerr-Schild form provides a natural way of realizing the classical double copy that relates exact solutions in general relativity to exact solutions in gauge theory. In this paper, we examine the asymptotic structure of Kerr-Schild form. In Newman-Unti gauge, we find a generic solution space satisfying the Kerr-Schild form in series expansion around null infinity. The news function in the solution space is chiral and can not lead to a mass loss formula. A class of asymptotically flat complex pp-wave solutions in closed form is obtained from the solution space. |
1511.01709 | Avirup Ghosh | Ayan Chatterjee, Avirup Ghosh | Quasilocal first law of black hole dynamics from local Lorentz
transformations | 7 pages, revised version | European Physical Journal C 78(7), July 2018 | 10.1140/epjc/s10052-018-6021-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quasilocal formulations of black hole are of immense importance since they
reveal the essential and minimal assumptions required for a consistent
description of black hole horizon, without relying on the asymptotic boundary
conditions on fields. Using the quasilocal formulation of Isolated Horizons, we
construct the Hamiltonian charges corresponding to local Lorentz
transformations on a spacetime admitting isolated horizon as an internal
boundary. From this construction, it arises quite generally that the
\emph{area} of the horizon of an isolated black hole is the Hamiltonian charge
for local Lorentz boost on the horizon. Using this argument further, it is
shown that, observers at a fixed proper distance $l_{0}$, very close to the
horizon, may define a notion of horizon energy given by $E=A/8\pi G l_{0}$, the
surface gravity is given by $\kappa=1/l_{0}$, and consequently, the first law
can be written in the quasilocal setting as $\delta E=(\kappa/8\pi G)\delta
A$..
| [
{
"created": "Thu, 5 Nov 2015 12:02:16 GMT",
"version": "v1"
},
{
"created": "Sat, 7 Jul 2018 14:58:51 GMT",
"version": "v2"
}
] | 2018-07-10 | [
[
"Chatterjee",
"Ayan",
""
],
[
"Ghosh",
"Avirup",
""
]
] | Quasilocal formulations of black hole are of immense importance since they reveal the essential and minimal assumptions required for a consistent description of black hole horizon, without relying on the asymptotic boundary conditions on fields. Using the quasilocal formulation of Isolated Horizons, we construct the Hamiltonian charges corresponding to local Lorentz transformations on a spacetime admitting isolated horizon as an internal boundary. From this construction, it arises quite generally that the \emph{area} of the horizon of an isolated black hole is the Hamiltonian charge for local Lorentz boost on the horizon. Using this argument further, it is shown that, observers at a fixed proper distance $l_{0}$, very close to the horizon, may define a notion of horizon energy given by $E=A/8\pi G l_{0}$, the surface gravity is given by $\kappa=1/l_{0}$, and consequently, the first law can be written in the quasilocal setting as $\delta E=(\kappa/8\pi G)\delta A$.. |
1602.04215 | Alexander Burinskii | Alexander Burinskii | Source of the Kerr-Newman Solution as a Supersymmetric Domain-Wall
Bubble: 50 years of the problem | 5 pages, 3 figures | Physics Letters B 754 (2016) 99 | 10.1016/j.physletb.2016.01.017 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the chiral field model of the source of the Kerr-Newman (KN)
solution and obtain that it represents a supersymmetric spinning soliton,
bounded by the chiral domain wall (DW) of the ellipsoidal form. The known
method for transformation of the planar DW to Bogomolnyi form we generalize to
the curved DW-bubble adapted to the Kerr coordinate system and obtain the
supersymmetric BPS-saturated source of the KN solution, having some remarkable
features, in particular, the quantum angular momentum. The main new result is
that the source forms a breather, i.e. the DW-antiDW combination. Taking into
account that the KN solution describes the spinning particles with gyromagnetic
ratio g = 2, as that of the Dirac electron, we touch the problem of the
compatibility of the spinning particles with gravity.
| [
{
"created": "Fri, 12 Feb 2016 14:39:26 GMT",
"version": "v1"
}
] | 2016-02-16 | [
[
"Burinskii",
"Alexander",
""
]
] | We consider the chiral field model of the source of the Kerr-Newman (KN) solution and obtain that it represents a supersymmetric spinning soliton, bounded by the chiral domain wall (DW) of the ellipsoidal form. The known method for transformation of the planar DW to Bogomolnyi form we generalize to the curved DW-bubble adapted to the Kerr coordinate system and obtain the supersymmetric BPS-saturated source of the KN solution, having some remarkable features, in particular, the quantum angular momentum. The main new result is that the source forms a breather, i.e. the DW-antiDW combination. Taking into account that the KN solution describes the spinning particles with gyromagnetic ratio g = 2, as that of the Dirac electron, we touch the problem of the compatibility of the spinning particles with gravity. |
1002.1066 | Joel Franklin | S. Deser and J. Franklin | De/re-constructing the Kerr Metric | null | Gen Rel Grav 42 2657 (2010) | 10.1007/s10714-010-1002-8 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive the Kerr solution in a pedagogically transparent way, using
physical symmetry and gauge arguments to reduce the candidate metric to just
two unknowns. The resulting field equations are then easy to obtain, and solve.
Separately, we transform the Kerr metric to Schwarzschild frame to exhibit its
limits in that familiar setting.
| [
{
"created": "Thu, 4 Feb 2010 20:02:19 GMT",
"version": "v1"
}
] | 2010-10-21 | [
[
"Deser",
"S.",
""
],
[
"Franklin",
"J.",
""
]
] | We derive the Kerr solution in a pedagogically transparent way, using physical symmetry and gauge arguments to reduce the candidate metric to just two unknowns. The resulting field equations are then easy to obtain, and solve. Separately, we transform the Kerr metric to Schwarzschild frame to exhibit its limits in that familiar setting. |
0809.3284 | Sushil Srivastava | S.K.Srivastava | A Different Approach to $f(R)$-Cosmology | This is an invited article for the anniversary volume on the occasion
of 50th birthday of Prof. Sergie D. Odintsov being published by Tomsk State
Pedagogical University | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Here $f(R)$-cosmology is discussed using a different approach. This model
explains early-inflation, emergence of cosmic background radiation at the exit
from inflation, cosmic deceleration during radiation-dominance followed by
deceleration due to curvature-induced matter and acceleration in the very late
universe due to curvature-induced phantom dark energy. This model predicts
collapse in the future universe. Further, a possible avoidence of collapse as
well as revival of very early universe is suggested.
| [
{
"created": "Fri, 19 Sep 2008 01:35:21 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Oct 2008 10:03:27 GMT",
"version": "v2"
}
] | 2008-10-09 | [
[
"Srivastava",
"S. K.",
""
]
] | Here $f(R)$-cosmology is discussed using a different approach. This model explains early-inflation, emergence of cosmic background radiation at the exit from inflation, cosmic deceleration during radiation-dominance followed by deceleration due to curvature-induced matter and acceleration in the very late universe due to curvature-induced phantom dark energy. This model predicts collapse in the future universe. Further, a possible avoidence of collapse as well as revival of very early universe is suggested. |
2207.02689 | Tatyana P. Shestakova | T. P. Shestakova | The birth of the Universe as a result of the change of the metric
signature | 15 pages, 1 figure; the paper was written for the Special Issue
titled "Light on Dark Worlds - A Themed Issue in Honor of Professor Maxim Yu.
Khlopov on the Occasion of His 70th Birthday" | Physics 4 (2022) 160-171 | 10.3390/physics4010012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, I discuss the idea that the birth of our Universe may be a
result of a quantum transition from a physical continuum with the Euclidean
signature to a Lorentzian spacetime. A similar idea was expressed by Andrei D.
Sakharov. At the classical level, the idea was studied by George F. R. Ellis
and his collaborators, who explored if solutions to the classical Einstein
equation exist which admit a change of metric signature. The present paper aims
at examining possible realizations of this idea at the level of quantum
gravity, in the framework of the Wheeler - DeWitt theory and in the extended
phase space approach to quantization of gravity. I intend to answer the
questions: Does the Hartle - Hawking wave function imply such a realization?
How can this idea be realized in the extended phase space approach to quantum
gravity, where the change of signature is described by imposing special
conditions on $g_{00}$-component of the metric in different regions of the
physical continuum? The conclusion is that the idea can be realized from a
formal mathematical point of view, but it can hardly help in understanding how
spacetime structure and time itself appeared from a timeless continuum.
| [
{
"created": "Wed, 6 Jul 2022 13:52:22 GMT",
"version": "v1"
}
] | 2022-07-07 | [
[
"Shestakova",
"T. P.",
""
]
] | In this paper, I discuss the idea that the birth of our Universe may be a result of a quantum transition from a physical continuum with the Euclidean signature to a Lorentzian spacetime. A similar idea was expressed by Andrei D. Sakharov. At the classical level, the idea was studied by George F. R. Ellis and his collaborators, who explored if solutions to the classical Einstein equation exist which admit a change of metric signature. The present paper aims at examining possible realizations of this idea at the level of quantum gravity, in the framework of the Wheeler - DeWitt theory and in the extended phase space approach to quantization of gravity. I intend to answer the questions: Does the Hartle - Hawking wave function imply such a realization? How can this idea be realized in the extended phase space approach to quantum gravity, where the change of signature is described by imposing special conditions on $g_{00}$-component of the metric in different regions of the physical continuum? The conclusion is that the idea can be realized from a formal mathematical point of view, but it can hardly help in understanding how spacetime structure and time itself appeared from a timeless continuum. |
1712.01101 | Bogdan Dimitrov | Bogdan G. Dimitrov | Two null gravitational cones in the theory of GPS-intersatellite
communications between two moving satellites. I. Physical and mathematical
theory of the space-time interval and the geodesic distance on intersecting
null cones | 162 pages, no figures, one-column style, to be subm. to Phys. Rev.D;
this (third) version is substantially expanded with respect to the second
version, new sections III and IV are added; also within the already existing
sections -(sub)sections II B and VI F are added | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Several space missions such as GRACE, GRAIL, ACES and others rely on
intersatellite communications (ISC) between two satellites at a large distance
one from another. The main goal of the theory is to formulate all the
navigation observables within the General Relativity Theory. The same approach
should be applied also to the intersatellite GPS-communications (in perspective
also between the GPS, GLONASS and Galileo satellite constellations). In this
paper a theoretical approach has been developed for ISC between two satellites
moving on (one-plane) elliptical orbits, based on the introduction of two
gravity null cones with origins at the emitting-signal and receiving-signal
satellites. The two null cones account for the variable distance between the
satellites during their uncorrelated motion.The intersection of the two null
cones defines a distance, which can be found from a differential equation in
full derivatives. This distance is the space-time interval in GRT. Applying
some theorems from higher algebra, it was proved that this space-time distance
can become zero, consequently it can be also negative and positive. But in
order to represent the geodesic distance travelled by the signal, the
space-time interval has to be "compatible" with the Euclidean distance. So this
"compatibility condition", conditionally called "condition for ISC", is the
most important consequence of the theory. The other important consequence is
that the geodesic distance turns out to be the space-time interval, but with
account also of the "condition for ISC". This interpretation enables the strict
mathematical proof that the geodesic distance is greater than the Euclidean
distance - a result, entirely based on the "two null cones approach" and
moreover, without any use of the Shapiro delay formulae. Consistency between
several other newly derived numerical parameters is noted.
| [
{
"created": "Fri, 1 Dec 2017 11:58:01 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Sep 2018 17:19:24 GMT",
"version": "v2"
},
{
"created": "Mon, 23 Sep 2019 18:45:10 GMT",
"version": "v3"
}
] | 2019-09-25 | [
[
"Dimitrov",
"Bogdan G.",
""
]
] | Several space missions such as GRACE, GRAIL, ACES and others rely on intersatellite communications (ISC) between two satellites at a large distance one from another. The main goal of the theory is to formulate all the navigation observables within the General Relativity Theory. The same approach should be applied also to the intersatellite GPS-communications (in perspective also between the GPS, GLONASS and Galileo satellite constellations). In this paper a theoretical approach has been developed for ISC between two satellites moving on (one-plane) elliptical orbits, based on the introduction of two gravity null cones with origins at the emitting-signal and receiving-signal satellites. The two null cones account for the variable distance between the satellites during their uncorrelated motion.The intersection of the two null cones defines a distance, which can be found from a differential equation in full derivatives. This distance is the space-time interval in GRT. Applying some theorems from higher algebra, it was proved that this space-time distance can become zero, consequently it can be also negative and positive. But in order to represent the geodesic distance travelled by the signal, the space-time interval has to be "compatible" with the Euclidean distance. So this "compatibility condition", conditionally called "condition for ISC", is the most important consequence of the theory. The other important consequence is that the geodesic distance turns out to be the space-time interval, but with account also of the "condition for ISC". This interpretation enables the strict mathematical proof that the geodesic distance is greater than the Euclidean distance - a result, entirely based on the "two null cones approach" and moreover, without any use of the Shapiro delay formulae. Consistency between several other newly derived numerical parameters is noted. |
gr-qc/9306017 | Dr. Robert Graham | J. Bene (INSTITUTE for Solid State Physics, E\"otv\"os University,
Muzeum krt. 6-8, H-1088 Budapest, Hungary) and R. Graham (FACHBEREICH Physik,
Universit\"at Gesamthochschule Essen D4300 Essen 1, Germany) | Supersymmetric Homogeneous Quantum Cosmologies Coupled to a Scalar Field | 23 PAGES | Phys.Rev. D49 (1994) 799-815 | 10.1103/PhysRevD.49.799 | null | gr-qc | null | Recent work on $N=2$ supersymmetric Bianchi type IX cosmologies coupled to a
scalar field is extended to a general treatment of homogeneous quantum
cosmologies with explicitely solvable momentum constraints, i.e. Bianchi types
I, II, VII, VIII besides the Bianchi type IX, and special cases, namely the
Friedmann universes, the Kantowski-Sachs space, and Taub-NUT space. Besides the
earlier explicit solution of the Wheeler DeWitt equation for Bianchi type IX,
describing a virtual wormhole fluctuation, an additional explicit solution is
given and identified with the `no-boundary state'.
| [
{
"created": "Mon, 14 Jun 1993 13:26:50 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Bene",
"J.",
"",
"INSTITUTE for Solid State Physics, Eötvös University,\n Muzeum krt. 6-8, H-1088 Budapest, Hungary"
],
[
"Graham",
"R.",
"",
"FACHBEREICH Physik,\n Universität Gesamthochschule Essen D4300 Essen 1, Germany"
]
] | Recent work on $N=2$ supersymmetric Bianchi type IX cosmologies coupled to a scalar field is extended to a general treatment of homogeneous quantum cosmologies with explicitely solvable momentum constraints, i.e. Bianchi types I, II, VII, VIII besides the Bianchi type IX, and special cases, namely the Friedmann universes, the Kantowski-Sachs space, and Taub-NUT space. Besides the earlier explicit solution of the Wheeler DeWitt equation for Bianchi type IX, describing a virtual wormhole fluctuation, an additional explicit solution is given and identified with the `no-boundary state'. |
2405.17212 | Rong-Jia Yang | Tong-Yu He, Jia-Jun Yin, Zhen-Yu Wang, Zhan-Wen Han, Rong-Jia Yang | A new parametrization of Hubble function and Hubble tension | 11 pages, 5 figures | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by-nc-sa/4.0/ | We present a new Hubble parameterization method and employ observational data
from Hubble, Pantheon, and Baryon Acoustic Oscillations to constrain model
parameters. The proposed method is thoroughly validated against these datasets,
demonstrating a robust fit to the observational data. The obtained best-fit
values are $H_0 = 67.5^{+1.3}_{-1.6}$ $\text{km s}^{-1} \text{Mpc}^{-1}$,
$\Omega_{\rm{m0}} = 0.2764\pm{0.0094}$, and $\alpha = 0.33\pm{0.22}$,
consistent with the Planck 2018 results, highlighting the existence of Hubble
tension.
| [
{
"created": "Mon, 27 May 2024 14:33:28 GMT",
"version": "v1"
},
{
"created": "Sun, 16 Jun 2024 07:45:59 GMT",
"version": "v2"
}
] | 2024-06-18 | [
[
"He",
"Tong-Yu",
""
],
[
"Yin",
"Jia-Jun",
""
],
[
"Wang",
"Zhen-Yu",
""
],
[
"Han",
"Zhan-Wen",
""
],
[
"Yang",
"Rong-Jia",
""
]
] | We present a new Hubble parameterization method and employ observational data from Hubble, Pantheon, and Baryon Acoustic Oscillations to constrain model parameters. The proposed method is thoroughly validated against these datasets, demonstrating a robust fit to the observational data. The obtained best-fit values are $H_0 = 67.5^{+1.3}_{-1.6}$ $\text{km s}^{-1} \text{Mpc}^{-1}$, $\Omega_{\rm{m0}} = 0.2764\pm{0.0094}$, and $\alpha = 0.33\pm{0.22}$, consistent with the Planck 2018 results, highlighting the existence of Hubble tension. |
2109.09497 | Marcos Ramiro Alfredo Arcod\'ia | Marcos R. A. Arcod\'ia and Rafael Ferraro | Double-extended Kerr-Schild form for $5D$ electrovacuum solutions | 13 pages | General Relativity and Gravitation 54, 130 (2022) | 10.1007/s10714-022-03013-3 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Five-dimensional Einstein-Maxwell-Chern-Simons equations are investigated in
the framework of an extended Kerr-Schild strategy to search for black holes
solutions. The fulfillment of Einstein equations constrains the Chern-Simons
coupling constant to a value determined by the trace of the energy-momentum
tensor of the electromagnetic configuration.
| [
{
"created": "Thu, 16 Sep 2021 18:02:18 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Mar 2022 14:20:27 GMT",
"version": "v2"
},
{
"created": "Mon, 10 Oct 2022 04:33:05 GMT",
"version": "v3"
},
{
"created": "Sun, 23 Oct 2022 01:18:11 GMT",
"version": "v4"
}
] | 2022-10-25 | [
[
"Arcodía",
"Marcos R. A.",
""
],
[
"Ferraro",
"Rafael",
""
]
] | Five-dimensional Einstein-Maxwell-Chern-Simons equations are investigated in the framework of an extended Kerr-Schild strategy to search for black holes solutions. The fulfillment of Einstein equations constrains the Chern-Simons coupling constant to a value determined by the trace of the energy-momentum tensor of the electromagnetic configuration. |
2210.15895 | Bobby Eka Gunara | Emir Syahreza Fadhilla, Ardian Nata Atmaja, and Bobby Eka Gunara | Global Existence and Singularity Formation of Classical Solutions in
Einstein-Skyrme System | 32 pages, no figures, and comments are welcome. The title slightly
changed, some theorems added, the main theorem revised, and some additional
calculations as the consequences of topology of Skyrmions added | null | null | null | gr-qc hep-th math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | In this paper, we elucidate the problem of gravitating Skyrmion governed by
field equations of the Einstein-Skyrme system with no potential term in the
Bondi coordinate. The spherical symmetry has to be assumed and both the metric
functions and Skyrme ansatz depend on radial and retarded time coordinates
which implies that the system is dynamic. We show that unique smooth solutions
with arbitrary initial data exist for a certain time interval with the extra
condition that the time interval must be finite in order to have a non-zero
topological charge. Then, the strategy to show that global smooth solutions
exist is to restrict the initial data and proceed to find suitable
configurations for extending the time interval to infinity. We also discuss the
possible configurations within The Einstein-Skyrme System which develop
singularities in coordinate origin.
| [
{
"created": "Fri, 28 Oct 2022 05:03:31 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Sep 2023 13:43:47 GMT",
"version": "v2"
}
] | 2023-09-26 | [
[
"Fadhilla",
"Emir Syahreza",
""
],
[
"Atmaja",
"Ardian Nata",
""
],
[
"Gunara",
"Bobby Eka",
""
]
] | In this paper, we elucidate the problem of gravitating Skyrmion governed by field equations of the Einstein-Skyrme system with no potential term in the Bondi coordinate. The spherical symmetry has to be assumed and both the metric functions and Skyrme ansatz depend on radial and retarded time coordinates which implies that the system is dynamic. We show that unique smooth solutions with arbitrary initial data exist for a certain time interval with the extra condition that the time interval must be finite in order to have a non-zero topological charge. Then, the strategy to show that global smooth solutions exist is to restrict the initial data and proceed to find suitable configurations for extending the time interval to infinity. We also discuss the possible configurations within The Einstein-Skyrme System which develop singularities in coordinate origin. |
gr-qc/0205133 | Mohammad Mehrafarin | M. Mehrafarin | A phase transition model for metric fluctuations in vacuum | 4 pages | null | null | null | gr-qc | null | Regarding metric fluctuations as generating {\it roughness} on the fabric of
the otherwise smooth vacuum, it is shown that in its simplest form, the effect
can be described by the scalar $\phi^4$ model. The model exhibits a second
order phase transition between a smooth (low-temperature) phase and a rough
(high-temperature) one, corroborating the absence of metric fluctuations at low
energies. In the rough phase near the critical point, vacuum is characterized
by a power-law behavior for the fluctuating field with critical exponent $\beta
\approx 0.33$.
| [
{
"created": "Thu, 30 May 2002 21:17:48 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Mehrafarin",
"M.",
""
]
] | Regarding metric fluctuations as generating {\it roughness} on the fabric of the otherwise smooth vacuum, it is shown that in its simplest form, the effect can be described by the scalar $\phi^4$ model. The model exhibits a second order phase transition between a smooth (low-temperature) phase and a rough (high-temperature) one, corroborating the absence of metric fluctuations at low energies. In the rough phase near the critical point, vacuum is characterized by a power-law behavior for the fluctuating field with critical exponent $\beta \approx 0.33$. |
2110.10870 | Jobin Thomas Valliyakalayil Mr | Jobin Thomas Valliyakalayil (1), Andrew J. H. Sutton (1), Robert E.
Spero (2), Daniel A. Shaddock (1) and Kirk McKenzie (1) ((1) Centre for
Gravitational Astrophysics, Australian National University, (2) Jet
Propulsion Laboratory, California Institute of Technology) | Enhanced Frequency noise suppression for LISA by combining cavity and
arm locking control systems | 17 pages, 15 figures | null | 10.1103/PhysRevD.105.062005 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | This paper presents a novel method for laser frequency stabilisation in the
Laser Interferometer Space Antenna (LISA) mission by locking a laser to two
stable length references - the arms of the interferometer and an on-board
optical cavity. The two references are digitally fused using carefully designed
control systems, attempting minimal or no changes to the baseline LISA mission
hardware. The interferometer arm(s) provides the most stable reference
available in the LISA science band (0.1 mHz - 1 Hz), while the cavity sensor's
wide-band and linear readout enables additional control system gain below and
above the LISA band. The main technical issue with this dual sensor approach is
the undesirable slow laser frequency pulling which couples into the control
system with the imperfect knowledge of the Doppler shift of the light due to
relative spacecraft motion along the LISA arm. This paper outlines requirements
on the Doppler shift knowledge to maintain the cavity well within the resonance
when activating the fused control system. Two Doppler shift estimation methods
are presented that use the already on-board measurements, the inter-spacecraft
interferometer link (the main science measurement), and the absolute
inter-spacecraft laser ranging system. Both methods reach the required
precision after a few thousand seconds of measurement integration. The paper
demonstrates an approach to initialise and engage the proposed laser
stabilization system, starting from free-running laser and ending with the dual
sensor frequency control system. The results show that the technique lowers the
residual laser frequency noise in the LISA science band by over 3 orders of
magnitude, potentially allowing the requirements on Time-Delay-Interferometry
(TDI) to be relaxed - possibly to the point where first-generation TDI may be
sufficient.
| [
{
"created": "Thu, 21 Oct 2021 03:16:56 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Mar 2022 23:12:03 GMT",
"version": "v2"
}
] | 2022-04-06 | [
[
"Valliyakalayil",
"Jobin Thomas",
""
],
[
"Sutton",
"Andrew J. H.",
""
],
[
"Spero",
"Robert E.",
""
],
[
"Shaddock",
"Daniel A.",
""
],
[
"McKenzie",
"Kirk",
""
]
] | This paper presents a novel method for laser frequency stabilisation in the Laser Interferometer Space Antenna (LISA) mission by locking a laser to two stable length references - the arms of the interferometer and an on-board optical cavity. The two references are digitally fused using carefully designed control systems, attempting minimal or no changes to the baseline LISA mission hardware. The interferometer arm(s) provides the most stable reference available in the LISA science band (0.1 mHz - 1 Hz), while the cavity sensor's wide-band and linear readout enables additional control system gain below and above the LISA band. The main technical issue with this dual sensor approach is the undesirable slow laser frequency pulling which couples into the control system with the imperfect knowledge of the Doppler shift of the light due to relative spacecraft motion along the LISA arm. This paper outlines requirements on the Doppler shift knowledge to maintain the cavity well within the resonance when activating the fused control system. Two Doppler shift estimation methods are presented that use the already on-board measurements, the inter-spacecraft interferometer link (the main science measurement), and the absolute inter-spacecraft laser ranging system. Both methods reach the required precision after a few thousand seconds of measurement integration. The paper demonstrates an approach to initialise and engage the proposed laser stabilization system, starting from free-running laser and ending with the dual sensor frequency control system. The results show that the technique lowers the residual laser frequency noise in the LISA science band by over 3 orders of magnitude, potentially allowing the requirements on Time-Delay-Interferometry (TDI) to be relaxed - possibly to the point where first-generation TDI may be sufficient. |
1708.04359 | Torrey Cullen | Torrey Cullen, Ian Harry, Jocelyn Read, Eric Flynn | Matter Effects on LIGO/Virgo Searches for Gravitational Waves from
Merging Neutron Stars | null | null | 10.1088/1361-6382/aa9424 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves from merging neutron stars are expected to be observed in
the next 5 years. We explore the potential impact of matter effects on
gravitational waves from merging double neutron-star binaries. If neutron star
binaries exist with chirp masses less than roughly 1 solar mass and typical
neutron-star radii are larger than roughly 14 km, or if neutron-star radii are
larger than 15-16 km for the chirp masses of galactic neutron-star binaries,
then matter will have a significant impact on the effectiveness of a
point-particle-based search at Advanced LIGO design sensitivity (roughly 5%
additional loss of signals). In a configuration typical of LIGO's first
observing run, extreme matter effects lead to up to 10% potential loss in the
most extreme cases.
| [
{
"created": "Mon, 14 Aug 2017 23:53:07 GMT",
"version": "v1"
}
] | 2017-12-06 | [
[
"Cullen",
"Torrey",
""
],
[
"Harry",
"Ian",
""
],
[
"Read",
"Jocelyn",
""
],
[
"Flynn",
"Eric",
""
]
] | Gravitational waves from merging neutron stars are expected to be observed in the next 5 years. We explore the potential impact of matter effects on gravitational waves from merging double neutron-star binaries. If neutron star binaries exist with chirp masses less than roughly 1 solar mass and typical neutron-star radii are larger than roughly 14 km, or if neutron-star radii are larger than 15-16 km for the chirp masses of galactic neutron-star binaries, then matter will have a significant impact on the effectiveness of a point-particle-based search at Advanced LIGO design sensitivity (roughly 5% additional loss of signals). In a configuration typical of LIGO's first observing run, extreme matter effects lead to up to 10% potential loss in the most extreme cases. |
gr-qc/0610107 | Hamid Reza Sepangi | K. Atazadeh and H. R. Sepangi | Modified gravity inspired DGP brane cosmology | 8 pages, to appear in PLB | Phys.Lett.B643:76-80,2006 | 10.1016/j.physletb.2006.10.029 | null | gr-qc hep-th | null | We consider a DGP brane scenario where a scalar field is present on the brane
through the introduction of a scalar potential, itself motivated by the notion
of modified gravity. This theory predicts that the mass appearing in the
gravitational potential is modified by the addition of the mass of the scalar
field. The cosmological implications that such a scenario entails are examined
and shown to be consistent with a universe expanding with power-law
acceleration.
| [
{
"created": "Sun, 22 Oct 2006 08:01:49 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Dec 2006 14:26:42 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Atazadeh",
"K.",
""
],
[
"Sepangi",
"H. R.",
""
]
] | We consider a DGP brane scenario where a scalar field is present on the brane through the introduction of a scalar potential, itself motivated by the notion of modified gravity. This theory predicts that the mass appearing in the gravitational potential is modified by the addition of the mass of the scalar field. The cosmological implications that such a scenario entails are examined and shown to be consistent with a universe expanding with power-law acceleration. |
2308.03468 | Edward Malec | Edward Malec | The mass density contrast in perturbed
Friedman-Lemaitre-Robertson-Walker cosmologies | 5 pages | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | We analyze the evolution of the mass density contrast in spherical
perturbations of flat Friedman-Lemaitre-Robertson-Walker cosmologies. Both dark
matter and dark energy are included. In the absence of dark energy the
evolution equation coincides with that obtained by Bonnor within the
``Newtonian cosmology''.
| [
{
"created": "Mon, 7 Aug 2023 10:50:16 GMT",
"version": "v1"
}
] | 2023-08-08 | [
[
"Malec",
"Edward",
""
]
] | We analyze the evolution of the mass density contrast in spherical perturbations of flat Friedman-Lemaitre-Robertson-Walker cosmologies. Both dark matter and dark energy are included. In the absence of dark energy the evolution equation coincides with that obtained by Bonnor within the ``Newtonian cosmology''. |
1508.06159 | Pac\^ome Delva Dr. | P. Delva, A. Hees, S. Bertone, E. Richard and P. Wolf | Test of the gravitational redshift with stable clocks in eccentric
orbits: application to Galileo satellites 5 and 6 | 13 pages, 5 figures, accepted in Classical and Quantum Gravity as a
Fast Track Communication | Class. Quantum Grav. 32, 232003, 2015 | 10.1088/0264-9381/32/23/232003 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Einstein Equivalence Principle (EEP) is one of the foundations of the
theory of General Relativity and several alternative theories of gravitation
predict violations of the EEP. Experimental constraints on this fundamental
principle of nature are therefore of paramount importance. The EEP can be split
in three sub-principles: the Universality of Free Fall (UFF), the Local Lorentz
Invariance (LLI) and the Local Position Invariance (LPI). In this paper we
propose to use stable clocks in eccentric orbits to perform a test of the
gravitational redshift, a consequence of the LPI. The best test to date was
performed with the Gravity Probe A (GP-A) experiment in 1976 with an
uncertainty of $1.4\times10^{-4}$. Our proposal considers the opportunity of
using Galileo satellites 5 and 6 to improve on the GP-A test uncertainty. We
show that considering realistic noise and systematic effects, and thanks to a
highly eccentric orbit, it is possible to improve on the GP-A limit to an
uncertainty around $(3-4)\times 10^{-5}$ after one year of integration of
Galileo 5 and 6 data.
| [
{
"created": "Tue, 25 Aug 2015 14:06:47 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Oct 2015 15:53:40 GMT",
"version": "v2"
}
] | 2015-11-19 | [
[
"Delva",
"P.",
""
],
[
"Hees",
"A.",
""
],
[
"Bertone",
"S.",
""
],
[
"Richard",
"E.",
""
],
[
"Wolf",
"P.",
""
]
] | The Einstein Equivalence Principle (EEP) is one of the foundations of the theory of General Relativity and several alternative theories of gravitation predict violations of the EEP. Experimental constraints on this fundamental principle of nature are therefore of paramount importance. The EEP can be split in three sub-principles: the Universality of Free Fall (UFF), the Local Lorentz Invariance (LLI) and the Local Position Invariance (LPI). In this paper we propose to use stable clocks in eccentric orbits to perform a test of the gravitational redshift, a consequence of the LPI. The best test to date was performed with the Gravity Probe A (GP-A) experiment in 1976 with an uncertainty of $1.4\times10^{-4}$. Our proposal considers the opportunity of using Galileo satellites 5 and 6 to improve on the GP-A test uncertainty. We show that considering realistic noise and systematic effects, and thanks to a highly eccentric orbit, it is possible to improve on the GP-A limit to an uncertainty around $(3-4)\times 10^{-5}$ after one year of integration of Galileo 5 and 6 data. |
1610.02211 | Boris Latosh | B.N. Latosh | Horndeski/Galileon in High Energy Collisions | null | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Horndeski/Galileons may be considered as a proper generalization of General
Relativity in high energy regime. Thus one may search for manifestation of
Galileons interaction in collision experiments. In this paper we give arguments
supporting this thesis. Galileon scalar field do not interact with matter via
Standard Model interactions, we discuss a mechanism that allows Galileons to
have influence on particle collisions. We give reasons to narrow the whole
class of Horndeski/Galileons models to one particular term - John term from Fab
Four subclass - for this particular issue. We were able to establish the
constraint on the model coupling constant.
| [
{
"created": "Fri, 7 Oct 2016 10:03:25 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Oct 2016 16:48:19 GMT",
"version": "v2"
}
] | 2016-10-18 | [
[
"Latosh",
"B. N.",
""
]
] | Horndeski/Galileons may be considered as a proper generalization of General Relativity in high energy regime. Thus one may search for manifestation of Galileons interaction in collision experiments. In this paper we give arguments supporting this thesis. Galileon scalar field do not interact with matter via Standard Model interactions, we discuss a mechanism that allows Galileons to have influence on particle collisions. We give reasons to narrow the whole class of Horndeski/Galileons models to one particular term - John term from Fab Four subclass - for this particular issue. We were able to establish the constraint on the model coupling constant. |
2004.01434 | Stefan Grimm | Stefan Grimm, Jan Harms | Multiband Gravitational Wave Parameter Estimation: A Study of Future
Detectors | 20 pages, 18 figures | Phys. Rev. D 102, 022007 (2020) | 10.1103/PhysRevD.102.022007 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The first detection of a gravitational-wave signal of a coalescence of two
black holes marked the beginning of the era of gravitational-wave astronomy,
which opens exciting new possibilities in the fields of astronomy, astrophysics
and cosmology. The currently operating detectors of the LIGO and Virgo
collaborations are sensitive at relatively high frequencies, from 10 Hz up to
about a kHz, and are able to detect gravitational waves emitted in a short time
frame of less than a second (binary black holes) to minutes (binary neutron
stars). Future missions like LISA will be sensitive in lower frequency ranges,
which will make it possible to detect gravitational waves emitted long before
these binaries merge. In this article, we investigate the possibilities for
parameter estimation using the Fisher-matrix formalism with combined
information from present and future detectors in different frequency bands. The
detectors we consider are the LIGO/Virgo detectors, the Einstein Telescope
(ET), the Laser Interferometer Space Antenna (LISA), and the first stage of the
Deci- Hertz Interferometer Gravitational wave Observatory (B-DECIGO). The
underlying models are constructed in time domain, which allows us to accurately
model long-duration signal observations with multiband (or broadband) detector
networks on parameter estimation. We assess the benefit of combining
information from ground-based and space-borne detectors, and how choices of the
orbit of B-DECIGO influence parameter estimates.
| [
{
"created": "Fri, 3 Apr 2020 08:52:54 GMT",
"version": "v1"
}
] | 2020-07-29 | [
[
"Grimm",
"Stefan",
""
],
[
"Harms",
"Jan",
""
]
] | The first detection of a gravitational-wave signal of a coalescence of two black holes marked the beginning of the era of gravitational-wave astronomy, which opens exciting new possibilities in the fields of astronomy, astrophysics and cosmology. The currently operating detectors of the LIGO and Virgo collaborations are sensitive at relatively high frequencies, from 10 Hz up to about a kHz, and are able to detect gravitational waves emitted in a short time frame of less than a second (binary black holes) to minutes (binary neutron stars). Future missions like LISA will be sensitive in lower frequency ranges, which will make it possible to detect gravitational waves emitted long before these binaries merge. In this article, we investigate the possibilities for parameter estimation using the Fisher-matrix formalism with combined information from present and future detectors in different frequency bands. The detectors we consider are the LIGO/Virgo detectors, the Einstein Telescope (ET), the Laser Interferometer Space Antenna (LISA), and the first stage of the Deci- Hertz Interferometer Gravitational wave Observatory (B-DECIGO). The underlying models are constructed in time domain, which allows us to accurately model long-duration signal observations with multiband (or broadband) detector networks on parameter estimation. We assess the benefit of combining information from ground-based and space-borne detectors, and how choices of the orbit of B-DECIGO influence parameter estimates. |
1512.05018 | Matt Visser | Finnian Gray (Victoria University of Wellington) and Matt Visser
(Victoria University of Wellington) | Greybody factors for Schwarzschild black holes: Path-ordered
exponentials and product integrals | 28 pages; 10 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In recent work concerning the sparsity of the Hawking flux
[arXiv:1506.03975v2], we found it necessary to re-examine what is known
regarding the greybody factors of black holes, with a view to extending and
expanding on some old results from the 1970s. Focussing specifically on
Schwarzschild black holes, we re-calculated and re-assessed the greybody
factors using a path-ordered-exponential approach, a technique which has the
virtue of providing a semi-explicit formula for the relevant Bogoliubov
coefficients. These path-ordered-exponentials, (being based on a "transfer
matrix" formalism), are closely related to so-called "product integrals",
leading to quite straightforward and direct numerical evaluation, while
avoiding any need for numerically solving differential equations. Furthermore,
while considerable analytic information is already available regarding both the
high-frequency and low-frequency asymptotics of these greybody factors,
numerical approaches seem better adapted to finding suitable "global models"
for these greybody factors in the intermediate frequency regime, where most of
the Hawking flux is concentrated. Working in a more general context, these
path-ordered-exponential techniques are also likely to be of interest for
generic barrier-penetration problems.
| [
{
"created": "Wed, 16 Dec 2015 01:02:09 GMT",
"version": "v1"
}
] | 2015-12-17 | [
[
"Gray",
"Finnian",
"",
"Victoria University of Wellington"
],
[
"Visser",
"Matt",
"",
"Victoria University of Wellington"
]
] | In recent work concerning the sparsity of the Hawking flux [arXiv:1506.03975v2], we found it necessary to re-examine what is known regarding the greybody factors of black holes, with a view to extending and expanding on some old results from the 1970s. Focussing specifically on Schwarzschild black holes, we re-calculated and re-assessed the greybody factors using a path-ordered-exponential approach, a technique which has the virtue of providing a semi-explicit formula for the relevant Bogoliubov coefficients. These path-ordered-exponentials, (being based on a "transfer matrix" formalism), are closely related to so-called "product integrals", leading to quite straightforward and direct numerical evaluation, while avoiding any need for numerically solving differential equations. Furthermore, while considerable analytic information is already available regarding both the high-frequency and low-frequency asymptotics of these greybody factors, numerical approaches seem better adapted to finding suitable "global models" for these greybody factors in the intermediate frequency regime, where most of the Hawking flux is concentrated. Working in a more general context, these path-ordered-exponential techniques are also likely to be of interest for generic barrier-penetration problems. |
gr-qc/0410139 | George E. A. Matsas | Luis C. B. Crispino, Atsushi Higuchi and George E. A. Matsas | Is the equivalence for the response of static scalar sources in the
Schwarzschild and Rindler spacetimes valid only in four dimensions? | 4 pages, 1 figure | Phys.Rev. D70 (2004) 127504 | 10.1103/PhysRevD.70.127504 | null | gr-qc hep-th | null | It was shown recently that in four dimensions scalar sources with fixed
proper acceleration minimally coupled to a massless Klein-Gordon field lead to
the same responses when they are (i) uniformly accelerated in Minkowski
spacetime (in the inertial vacuum) and (ii) static in the Schwarzschild
spacetime (in the Unruh vacuum). Here we show that this equivalence is broken
if the spacetime dimension is more than four.
| [
{
"created": "Thu, 28 Oct 2004 11:52:45 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Crispino",
"Luis C. B.",
""
],
[
"Higuchi",
"Atsushi",
""
],
[
"Matsas",
"George E. A.",
""
]
] | It was shown recently that in four dimensions scalar sources with fixed proper acceleration minimally coupled to a massless Klein-Gordon field lead to the same responses when they are (i) uniformly accelerated in Minkowski spacetime (in the inertial vacuum) and (ii) static in the Schwarzschild spacetime (in the Unruh vacuum). Here we show that this equivalence is broken if the spacetime dimension is more than four. |
1701.00809 | Khrystyna Gnatenko | Kh. P. Gnatenko, V. M. Tkachuk | Weak equivalence principle in noncommutative phase space and the
parameters of noncommutativity | null | Phys. Lett. A, 381, 2463 (2017) | 10.1016/j.physleta.2017.05.056 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The weak equivalence principle is studied in a space with noncommutativity of
coordinates and noncommutativity of momenta. We find conditions on the
parameters of noncommutativity which give the possibility to recover the
equivalence principle in noncommutative phase space. It is also shown that in
the case when these conditions are satisfied the motion of the center-of-mass
of a composite system in noncommutative phase space and the relative motion are
independent, the kinetic energy of composite system has additivity property and
is independent on the systems composition. So, we propose conditions on the
parameters of noncommutativity which give the possibility to solve the list of
problems in noncommutative phase space.
| [
{
"created": "Wed, 21 Dec 2016 15:15:35 GMT",
"version": "v1"
}
] | 2017-06-27 | [
[
"Gnatenko",
"Kh. P.",
""
],
[
"Tkachuk",
"V. M.",
""
]
] | The weak equivalence principle is studied in a space with noncommutativity of coordinates and noncommutativity of momenta. We find conditions on the parameters of noncommutativity which give the possibility to recover the equivalence principle in noncommutative phase space. It is also shown that in the case when these conditions are satisfied the motion of the center-of-mass of a composite system in noncommutative phase space and the relative motion are independent, the kinetic energy of composite system has additivity property and is independent on the systems composition. So, we propose conditions on the parameters of noncommutativity which give the possibility to solve the list of problems in noncommutative phase space. |
0706.2863 | Chih-Hung Wang | Chih-Hung Wang | Charged Fluid Dynamics in Scalar-Tensor Theories of Gravity with Torsion | 4 pages | null | 10.1142/9789812834300_0129 | null | gr-qc | null | n scalar-tensor theories of gravity with torsion, the gravitational field is
described in terms of a symmetric metric tensor $g$, a metric-compatible
connection $\nabla$ with torsion, and a scalar field $\phi$. The main aim is to
explore an interaction of a charged perfect fluid and a scalar field $\phi$ in
a background electromagnetic and gravitational field described by \{$g$,
$\nabla$, $\phi$\}. The interaction is based on an action functional $S_C$ of a
charged perfect fluid that is invariant under global conformal rescalings.
Using a variational principle, we obtain equations of motion for the charged
perfect fluid. Moreover, we verify that these equations of motion are
equivalent to the gauge identities obtained from the invariance of an action
functional under spacetime dffeomorphisms and a local U(1) gauge group.
| [
{
"created": "Tue, 19 Jun 2007 20:00:37 GMT",
"version": "v1"
}
] | 2016-11-15 | [
[
"Wang",
"Chih-Hung",
""
]
] | n scalar-tensor theories of gravity with torsion, the gravitational field is described in terms of a symmetric metric tensor $g$, a metric-compatible connection $\nabla$ with torsion, and a scalar field $\phi$. The main aim is to explore an interaction of a charged perfect fluid and a scalar field $\phi$ in a background electromagnetic and gravitational field described by \{$g$, $\nabla$, $\phi$\}. The interaction is based on an action functional $S_C$ of a charged perfect fluid that is invariant under global conformal rescalings. Using a variational principle, we obtain equations of motion for the charged perfect fluid. Moreover, we verify that these equations of motion are equivalent to the gauge identities obtained from the invariance of an action functional under spacetime dffeomorphisms and a local U(1) gauge group. |
2212.01798 | Chen Wu | Mao-Yuan Wan and Chen Wu | Absorption and scattering of massless scalar wave from Regular Black
Holes | 15 pages, 5 figures | General Relativity and Gravitation (2022)54:148 | 10.1007/s10714-022-03034-y | null | gr-qc | http://creativecommons.org/licenses/by-sa/4.0/ | In this work, we numerically investigate the scattering and absorption cross
section of the massless scalar field from some well-known regular black holes
by using the partial wave approach. Our computational results indicate that the
larger the parameters, the lower the associated total absorption cross section
maxima. When compared to the Schwarzschild black hole, the scattering cross
section is enhanced in some regular black hole spacetimes, meanwhile the
scattering width is narrow in the forward orientation. Moreover, it is found
that the null geodesics of the critical impact parameter and the geometrical
optical value in the high frequency regime have similar changing behavior.
| [
{
"created": "Sun, 4 Dec 2022 11:35:00 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Dec 2022 02:41:36 GMT",
"version": "v2"
}
] | 2022-12-07 | [
[
"Wan",
"Mao-Yuan",
""
],
[
"Wu",
"Chen",
""
]
] | In this work, we numerically investigate the scattering and absorption cross section of the massless scalar field from some well-known regular black holes by using the partial wave approach. Our computational results indicate that the larger the parameters, the lower the associated total absorption cross section maxima. When compared to the Schwarzschild black hole, the scattering cross section is enhanced in some regular black hole spacetimes, meanwhile the scattering width is narrow in the forward orientation. Moreover, it is found that the null geodesics of the critical impact parameter and the geometrical optical value in the high frequency regime have similar changing behavior. |
1307.7045 | Sunandan Gangopadhyay | Sunandan Gangopadhyay, Abhijit Dutta, Anirban Saha | Generalized uncertainty principle and black hole thermodynamics | 9 pages Latex, References added, To appear in Gen.Rel.Grav | Gen. Rel.Grav. 46 (2014) 1661 | 10.1007/s10714-013-1661-3 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the Schwarzschild and Reissner-Nordstr\"{o}m black hole
thermodynamics using the simplest form of the generalized uncertainty principle
(GUP) proposed in the literature. The expressions for the mass-temperature
relation, heat capacity and entropy are obtained in both cases from which the
critical and remnant masses are computed. Our results are exact and reveal that
these masses are identical and larger than the so called singular mass for
which the thermodynamics quantities become ill-defined. The expression for the
entropy reveals the well known area theorem in terms of the horizon area in
both cases upto leading order corrections from GUP. The area theorem written in
terms of a new variable which can be interpreted as the reduced horizon area
arises only when the computation is carried out to the next higher order
correction from GUP.
| [
{
"created": "Fri, 26 Jul 2013 14:32:33 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Jan 2014 09:59:44 GMT",
"version": "v2"
}
] | 2015-06-16 | [
[
"Gangopadhyay",
"Sunandan",
""
],
[
"Dutta",
"Abhijit",
""
],
[
"Saha",
"Anirban",
""
]
] | We study the Schwarzschild and Reissner-Nordstr\"{o}m black hole thermodynamics using the simplest form of the generalized uncertainty principle (GUP) proposed in the literature. The expressions for the mass-temperature relation, heat capacity and entropy are obtained in both cases from which the critical and remnant masses are computed. Our results are exact and reveal that these masses are identical and larger than the so called singular mass for which the thermodynamics quantities become ill-defined. The expression for the entropy reveals the well known area theorem in terms of the horizon area in both cases upto leading order corrections from GUP. The area theorem written in terms of a new variable which can be interpreted as the reduced horizon area arises only when the computation is carried out to the next higher order correction from GUP. |
1401.6062 | Philipp Hoehn | Philipp A. Hoehn | Quantization of systems with temporally varying discretization I:
Evolving Hilbert spaces | 45 pages, 1 appendix, 6 figures (additional explanations, now matches
published version) | J. Math. Phys. 55, 083508 (2014) | 10.1063/1.4890558 | null | gr-qc hep-lat math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A temporally varying discretization often features in discrete gravitational
systems and appears in lattice field theory models subject to a coarse graining
or refining dynamics. To better understand such discretization changing
dynamics in the quantum theory, an according formalism for constrained
variational discrete systems is constructed. While the present manuscript
focuses on global evolution moves and, for simplicity, restricts to Euclidean
configuration spaces, a companion article discusses local evolution moves. In
order to link the covariant and canonical picture, the dynamics of the quantum
states is generated by propagators which satisfy the canonical constraints and
are constructed using the action and group averaging projectors. This projector
formalism offers a systematic method for tracing and regularizing divergences
in the resulting state sums. Non-trivial coarse graining evolution moves lead
to non-unitary, and thus irreversible, projections of physical Hilbert spaces
and Dirac observables such that these concepts become evolution move dependent
on temporally varying discretizations. The formalism is illustrated in a toy
model mimicking a `creation from nothing'. Subtleties arising when applying
such a formalism to quantum gravity models are discussed.
| [
{
"created": "Thu, 23 Jan 2014 17:25:50 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Feb 2014 00:51:02 GMT",
"version": "v2"
},
{
"created": "Thu, 2 Oct 2014 14:41:07 GMT",
"version": "v3"
}
] | 2014-10-03 | [
[
"Hoehn",
"Philipp A.",
""
]
] | A temporally varying discretization often features in discrete gravitational systems and appears in lattice field theory models subject to a coarse graining or refining dynamics. To better understand such discretization changing dynamics in the quantum theory, an according formalism for constrained variational discrete systems is constructed. While the present manuscript focuses on global evolution moves and, for simplicity, restricts to Euclidean configuration spaces, a companion article discusses local evolution moves. In order to link the covariant and canonical picture, the dynamics of the quantum states is generated by propagators which satisfy the canonical constraints and are constructed using the action and group averaging projectors. This projector formalism offers a systematic method for tracing and regularizing divergences in the resulting state sums. Non-trivial coarse graining evolution moves lead to non-unitary, and thus irreversible, projections of physical Hilbert spaces and Dirac observables such that these concepts become evolution move dependent on temporally varying discretizations. The formalism is illustrated in a toy model mimicking a `creation from nothing'. Subtleties arising when applying such a formalism to quantum gravity models are discussed. |
1910.02567 | Marc Casals | Marc Casals, Brien C. Nolan, Adrian C. Ottewill, Barry Wardell | Regularized calculation of the retarded Green function in Schwarzschild
spacetime | 13 pages, 4 figures; 2 Mathematica notebooks as ancillary files | Phys. Rev. D 100, 104037 (2019) | 10.1103/PhysRevD.100.104037 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The retarded Green function for linear field perturbations of black hole
spacetimes is notoriously difficult to calculate. One of the difficulties is
due to a Dirac-$\delta$ divergence that the Green function possesses when the
two spacetime points are connected by a "direct" null geodesic. We present a
procedure which notably aids its calculation in the case of Schwarzschild
spacetime by separating this direct $\delta$-divergence from the remainder of
the retarded Green function. More precisely, the method consists of calculating
the multipolar $\ell$-modes of the direct $\delta$-divergence and subtracting
them from the corresponding modes of the retarded Green function. We illustrate
the usefulness of the method with some specific calculations in the case of the
scalar Green function and self-field for a point scalar charge in Schwarzschild
spacetime.
| [
{
"created": "Mon, 7 Oct 2019 00:55:36 GMT",
"version": "v1"
}
] | 2019-11-27 | [
[
"Casals",
"Marc",
""
],
[
"Nolan",
"Brien C.",
""
],
[
"Ottewill",
"Adrian C.",
""
],
[
"Wardell",
"Barry",
""
]
] | The retarded Green function for linear field perturbations of black hole spacetimes is notoriously difficult to calculate. One of the difficulties is due to a Dirac-$\delta$ divergence that the Green function possesses when the two spacetime points are connected by a "direct" null geodesic. We present a procedure which notably aids its calculation in the case of Schwarzschild spacetime by separating this direct $\delta$-divergence from the remainder of the retarded Green function. More precisely, the method consists of calculating the multipolar $\ell$-modes of the direct $\delta$-divergence and subtracting them from the corresponding modes of the retarded Green function. We illustrate the usefulness of the method with some specific calculations in the case of the scalar Green function and self-field for a point scalar charge in Schwarzschild spacetime. |
0708.1237 | Gaurang Mahajan | Gaurang Mahajan, T. Padmanabhan | Particle creation, classicality and related issues in quantum field
theory: II. Examples from field theory | RevTeX 4; 27 pages; 18 figures; second of a series of two papers, the
first being arXiv:0708.1233 [gr-qc]; high resolution figures available from
the authors on request | Gen.Rel.Grav. 40 (2008) 709-747 | 10.1007/s10714-007-0527-y | null | gr-qc astro-ph hep-th | null | We adopt the general formalism, which was developed in Paper I
(arXiv:0708.1233) to analyze the evolution of a quantized time-dependent
oscillator, to address several questions in the context of quantum field theory
in time dependent external backgrounds. In particular, we study the question of
emergence of classicality in terms of the phase space evolution and its
relation to particle production, and clarify some conceptual issues. We
consider a quantized scalar field evolving in a constant electric field and in
FRW spacetimes which illustrate the two extreme cases of late time adiabatic
and highly non-adiabatic evolution. Using the time-dependent generalizations of
various quantities like particle number density, effective Lagrangian etc.
introduced in Paper I, we contrast the evolution in these two limits bringing
out key differences between the Schwinger effect and evolution in the de Sitter
background. Further, our examples suggest that the notion of classicality is
multifaceted and any one single criterion may not have universal applicability.
For example, the peaking of the phase space Wigner distribution on the
classical trajectory \emph{alone} does not imply transition to classical
behavior. An analysis of the behavior of the \emph{classicality parameter},
which was introduced in Paper I, leads to the conclusion that strong particle
production is necessary for the quantum state to become highly correlated in
phase space at late times.
| [
{
"created": "Thu, 9 Aug 2007 10:23:30 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Mahajan",
"Gaurang",
""
],
[
"Padmanabhan",
"T.",
""
]
] | We adopt the general formalism, which was developed in Paper I (arXiv:0708.1233) to analyze the evolution of a quantized time-dependent oscillator, to address several questions in the context of quantum field theory in time dependent external backgrounds. In particular, we study the question of emergence of classicality in terms of the phase space evolution and its relation to particle production, and clarify some conceptual issues. We consider a quantized scalar field evolving in a constant electric field and in FRW spacetimes which illustrate the two extreme cases of late time adiabatic and highly non-adiabatic evolution. Using the time-dependent generalizations of various quantities like particle number density, effective Lagrangian etc. introduced in Paper I, we contrast the evolution in these two limits bringing out key differences between the Schwinger effect and evolution in the de Sitter background. Further, our examples suggest that the notion of classicality is multifaceted and any one single criterion may not have universal applicability. For example, the peaking of the phase space Wigner distribution on the classical trajectory \emph{alone} does not imply transition to classical behavior. An analysis of the behavior of the \emph{classicality parameter}, which was introduced in Paper I, leads to the conclusion that strong particle production is necessary for the quantum state to become highly correlated in phase space at late times. |
1807.06138 | Claudio Cremaschini | Massimo Tessarotto and Claudio Cremaschini | Generalized Lagrangian Path approach to manifestly-covariant quantum
gravity theory | null | Entropy 20, 205 (2018) | 10.3390/e20030205 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A trajectory-based representation for the quantum theory of the gravitational
field is formulated. This is achieved in terms of a covariant Generalized
Lagrangian-Path (GLP) approach which relies on a suitable statistical
representation of Bohmian Lagrangian trajectories, referred to here as
GLP-representation. The result is established in the framework of the
manifestly-covariant quantum gravity theory (CQG-theory) proposed recently and
the related CQG-wave equation advancing in proper-time the quantum state
associated with massive gravitons. Generally non-stationary analytical
solutions for the CQG-wave equation with non-vanishing cosmological constant
are determined in such a framework, which exhibit Gaussian-like probability
densities that are non-dispersive in proper-time. As a remarkable outcome of
the theory achieved by implementing these analytical solutions, the existence
of an emergent gravity phenomenon is proved to hold. Accordingly, it is shown
that a mean-field background space-time metric tensor can be expressed in terms
of a suitable statistical average of stochastic fluctuations of the quantum
gravitational field whose quantum-wave dynamics is described by GLP
trajectories.
| [
{
"created": "Mon, 16 Jul 2018 22:30:09 GMT",
"version": "v1"
}
] | 2018-07-18 | [
[
"Tessarotto",
"Massimo",
""
],
[
"Cremaschini",
"Claudio",
""
]
] | A trajectory-based representation for the quantum theory of the gravitational field is formulated. This is achieved in terms of a covariant Generalized Lagrangian-Path (GLP) approach which relies on a suitable statistical representation of Bohmian Lagrangian trajectories, referred to here as GLP-representation. The result is established in the framework of the manifestly-covariant quantum gravity theory (CQG-theory) proposed recently and the related CQG-wave equation advancing in proper-time the quantum state associated with massive gravitons. Generally non-stationary analytical solutions for the CQG-wave equation with non-vanishing cosmological constant are determined in such a framework, which exhibit Gaussian-like probability densities that are non-dispersive in proper-time. As a remarkable outcome of the theory achieved by implementing these analytical solutions, the existence of an emergent gravity phenomenon is proved to hold. Accordingly, it is shown that a mean-field background space-time metric tensor can be expressed in terms of a suitable statistical average of stochastic fluctuations of the quantum gravitational field whose quantum-wave dynamics is described by GLP trajectories. |
2202.08150 | Bivudutta Mishra Dr. | L.K. Duchaniya, Santosh V Lohakare, B. Mishra, S.K. Tripathy | Dynamical Stability Analysis of Accelerating f(T) Gravity Models | 13 pages, 12 figures | Eur. Phys. J. C (2022) 82:448 | 10.1140/epjc/s10052-022-10406-w | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we have emphasized the stability analysis of the accelerating
cosmological models obtained in $f(T)$ gravity theory. The behavior of the
models based on the evolution of the equation of state parameter shows
phantom-like behavior at the present epoch. The scalar perturbation technique
is used to create the perturbed evolution equations, and the stability of the
models has been demonstrated. Also, we have performed the dynamical system
analysis for both the models. In the two specific $f(T)$ gravity models, three
critical points are obtained in each model. In each model, at least one
critical point has been observed to be stable.
| [
{
"created": "Tue, 15 Feb 2022 17:09:22 GMT",
"version": "v1"
},
{
"created": "Tue, 24 May 2022 06:39:09 GMT",
"version": "v2"
}
] | 2022-05-25 | [
[
"Duchaniya",
"L. K.",
""
],
[
"Lohakare",
"Santosh V",
""
],
[
"Mishra",
"B.",
""
],
[
"Tripathy",
"S. K.",
""
]
] | In this paper, we have emphasized the stability analysis of the accelerating cosmological models obtained in $f(T)$ gravity theory. The behavior of the models based on the evolution of the equation of state parameter shows phantom-like behavior at the present epoch. The scalar perturbation technique is used to create the perturbed evolution equations, and the stability of the models has been demonstrated. Also, we have performed the dynamical system analysis for both the models. In the two specific $f(T)$ gravity models, three critical points are obtained in each model. In each model, at least one critical point has been observed to be stable. |
1312.1151 | Hossein Mohseni Sadjadi | H. Mohseni Sadjadi | Rapid Oscillatory quintessence with variable equation of state parameter
in non minimal derivative coupling model | 19 pages, 7 figures, major revision | Gen. Relativ Gravit 46 (2014) 1817 | 10.1007/s10714-014-1817-9 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The rapid oscillating scalar field is considered as the quintessence in the
framework of nonminimal kinetic coupling model. The scalar field behaves like a
perfect fluid with a variable equation of state parameter which can be
expressed as a function of the Hubble parameter. This feature enables us to
study its evolution via continuity equation.
The scalar field may behave as dark energy in the present epoch, while it
behaves like dark matter in the future. This characteristic allows the
occurrence of a decelerated expansion after the present acceleration, without
invoking any interaction. The model is also studied in the presence of an
interaction between dark sectors alleviating the coincidence problem. The
stability of the model is investigated and the stable attractor solutions are
studied.
| [
{
"created": "Tue, 3 Dec 2013 14:03:31 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Mar 2014 13:35:46 GMT",
"version": "v2"
},
{
"created": "Tue, 7 Oct 2014 16:58:42 GMT",
"version": "v3"
}
] | 2014-12-24 | [
[
"Sadjadi",
"H. Mohseni",
""
]
] | The rapid oscillating scalar field is considered as the quintessence in the framework of nonminimal kinetic coupling model. The scalar field behaves like a perfect fluid with a variable equation of state parameter which can be expressed as a function of the Hubble parameter. This feature enables us to study its evolution via continuity equation. The scalar field may behave as dark energy in the present epoch, while it behaves like dark matter in the future. This characteristic allows the occurrence of a decelerated expansion after the present acceleration, without invoking any interaction. The model is also studied in the presence of an interaction between dark sectors alleviating the coincidence problem. The stability of the model is investigated and the stable attractor solutions are studied. |
1401.6503 | Gabriele Umberto Varieschi | Gabriele U. Varieschi | Kerr Metric, Geodesic Motion, and Flyby Anomaly in Fourth-Order
Conformal Gravity | Revised version: improved notation, added references, comments, and
one equation. 31 pages, including 2 figures. Accepted for publication in
General Relativity and Gravitation | Gen.Rel.Grav. 46 (2014) 1741 | 10.1007/s10714-014-1741-z | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we analyze the Kerr geometry in the context of Conformal
Gravity, an alternative theory of gravitation, which is a direct extension of
General Relativity. Following previous studies in the literature, we introduce
an explicit expression of the Kerr metric in Conformal Gravity, which naturally
reduces to the standard General Relativity Kerr geometry in the absence of
Conformal Gravity effects. As in the standard case, we show that the
Hamilton-Jacobi equation governing geodesic motion in a space-time based on
this geometry is indeed separable and that a fourth constant of motion-similar
to Carter's constant-can also be introduced in Conformal Gravity. Consequently,
we derive the fundamental equations of geodesic motion and show that the
problem of solving these equations can be reduced to one of quadratures. In
particular, we study the resulting time-like geodesics in Conformal Gravity
Kerr geometry by numerically integrating the equations of motion for Earth
flyby trajectories of spacecraft. We then compare our results with the existing
data of the Flyby Anomaly in order to ascertain whether Conformal Gravity
corrections are possibly the origin of this gravitational anomaly. Although
Conformal Gravity slightly affects the trajectories of geodesic motion around a
rotating spherical object, we show that these corrections are minimal and are
not expected to be the origin of the Flyby Anomaly, unless conformal parameters
are drastically different from current estimates. Therefore, our results
confirm previous analyses, showing that modifications due to Conformal Gravity
are not likely to be detected at the Solar System level, but might affect
gravity at the galactic or cosmological scale.
| [
{
"created": "Sat, 25 Jan 2014 07:57:12 GMT",
"version": "v1"
},
{
"created": "Mon, 21 Apr 2014 16:44:36 GMT",
"version": "v2"
}
] | 2014-05-20 | [
[
"Varieschi",
"Gabriele U.",
""
]
] | In this paper we analyze the Kerr geometry in the context of Conformal Gravity, an alternative theory of gravitation, which is a direct extension of General Relativity. Following previous studies in the literature, we introduce an explicit expression of the Kerr metric in Conformal Gravity, which naturally reduces to the standard General Relativity Kerr geometry in the absence of Conformal Gravity effects. As in the standard case, we show that the Hamilton-Jacobi equation governing geodesic motion in a space-time based on this geometry is indeed separable and that a fourth constant of motion-similar to Carter's constant-can also be introduced in Conformal Gravity. Consequently, we derive the fundamental equations of geodesic motion and show that the problem of solving these equations can be reduced to one of quadratures. In particular, we study the resulting time-like geodesics in Conformal Gravity Kerr geometry by numerically integrating the equations of motion for Earth flyby trajectories of spacecraft. We then compare our results with the existing data of the Flyby Anomaly in order to ascertain whether Conformal Gravity corrections are possibly the origin of this gravitational anomaly. Although Conformal Gravity slightly affects the trajectories of geodesic motion around a rotating spherical object, we show that these corrections are minimal and are not expected to be the origin of the Flyby Anomaly, unless conformal parameters are drastically different from current estimates. Therefore, our results confirm previous analyses, showing that modifications due to Conformal Gravity are not likely to be detected at the Solar System level, but might affect gravity at the galactic or cosmological scale. |
1610.01235 | Carlos Eduardo Gabarrete Fajardo | Luis O. Pimentel and Carlos E. Gabarrete | Some exact solutions in K-essence theory isotropic cosmology | 5 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use a simple form of the K-essence theory and apply it to the classic
isotropic cosmological model and seek exact solutions. The particular form of
the kinetic term that we choose is $K \left(\phi, X \right)= K_0(\phi)X^m
+K_1$. The resulting field equations in the homogeneous and isotropic cosmology
(FRW)is considered. Several exact solutions are obtained.
| [
{
"created": "Tue, 4 Oct 2016 23:57:37 GMT",
"version": "v1"
}
] | 2016-10-06 | [
[
"Pimentel",
"Luis O.",
""
],
[
"Gabarrete",
"Carlos E.",
""
]
] | We use a simple form of the K-essence theory and apply it to the classic isotropic cosmological model and seek exact solutions. The particular form of the kinetic term that we choose is $K \left(\phi, X \right)= K_0(\phi)X^m +K_1$. The resulting field equations in the homogeneous and isotropic cosmology (FRW)is considered. Several exact solutions are obtained. |
2205.04680 | Nikolaos Dimakis | N. Dimakis, A. Paliathanasis, M. Roumeliotis and T. Christodoulakis | FLRW solutions in $f(Q)$ theory: the effect of using different
connections | 19 pages, 5 figures, Latex2e source file, updated version, to appear
in PRD | null | 10.1103/PhysRevD.106.043509 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) space-time in the
theory of $f(Q)$-gravity, where $Q$ denotes the non-metricity scalar. It has
been previously shown in the literature, that there exist four distinct
families of connections, which are compatible with the isometries of the FLRW
metric; three for the spatially flat case and one when the spatial curvature is
present. In the spatially flat case, one connection is dynamically irrelevant
and yields the dynamics of the coincident gauge in the Cartesian coordinates.
For this, we obtain the general solution of an arbitrary $f(Q)$ theory with a
perfect fluid matter content, and present various examples for specific choices
of the $f(Q)$ function. We proceed by studying the effect of the rest of the
connections, which are dynamical and affect the equations of the motion. We
concentrate in scenarios that depart from the $Q=$const. case, which just
reproduces General Relativity with a cosmological constant, and derive novel
vacuum solutions for a power-law $f(Q)$ function.
| [
{
"created": "Tue, 10 May 2022 05:22:13 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Jul 2022 08:22:16 GMT",
"version": "v2"
}
] | 2022-08-17 | [
[
"Dimakis",
"N.",
""
],
[
"Paliathanasis",
"A.",
""
],
[
"Roumeliotis",
"M.",
""
],
[
"Christodoulakis",
"T.",
""
]
] | We study a Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) space-time in the theory of $f(Q)$-gravity, where $Q$ denotes the non-metricity scalar. It has been previously shown in the literature, that there exist four distinct families of connections, which are compatible with the isometries of the FLRW metric; three for the spatially flat case and one when the spatial curvature is present. In the spatially flat case, one connection is dynamically irrelevant and yields the dynamics of the coincident gauge in the Cartesian coordinates. For this, we obtain the general solution of an arbitrary $f(Q)$ theory with a perfect fluid matter content, and present various examples for specific choices of the $f(Q)$ function. We proceed by studying the effect of the rest of the connections, which are dynamical and affect the equations of the motion. We concentrate in scenarios that depart from the $Q=$const. case, which just reproduces General Relativity with a cosmological constant, and derive novel vacuum solutions for a power-law $f(Q)$ function. |
2104.13611 | Angel Rincon | Grigoris Panotopoulos, Angel Rincon and Ilidio Lopes | Orbits of light rays in scale-dependent gravity: Exact analytical
solutions to the null geodesic equations | 10 pages, 8 figures, accepted in PRD | Phys. Rev. D 103 (2021), 104040 | 10.1103/PhysRevD.103.104040 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study photon orbits in the background of $(1+3)$-dimensional static,
spherically symmetric geometries. In particular, we have obtained exact
analytical solutions to the null geodesic equations for light rays in terms of
the Weierstra{\ss} function for space-times arising in the context of
scale-dependent gravity. The trajectories in the $(x-y)$ plane are shown
graphically, and we make a comparison with similar geometries arising in
different contexts. The light deflection angle is computed as a function of the
running parameter $\xi$, and an upper bound for the latter is obtained.
| [
{
"created": "Wed, 28 Apr 2021 07:45:16 GMT",
"version": "v1"
}
] | 2021-05-20 | [
[
"Panotopoulos",
"Grigoris",
""
],
[
"Rincon",
"Angel",
""
],
[
"Lopes",
"Ilidio",
""
]
] | We study photon orbits in the background of $(1+3)$-dimensional static, spherically symmetric geometries. In particular, we have obtained exact analytical solutions to the null geodesic equations for light rays in terms of the Weierstra{\ss} function for space-times arising in the context of scale-dependent gravity. The trajectories in the $(x-y)$ plane are shown graphically, and we make a comparison with similar geometries arising in different contexts. The light deflection angle is computed as a function of the running parameter $\xi$, and an upper bound for the latter is obtained. |
2401.01541 | Hyeong-Chan Kim | Hyeong-Chan Kim | Temperature of a steady system around a black hole | 18 pages, 1 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the issue of temperature in a steady system around a black hole
event horizon, contrasting it with the appearance of divergence in a thermal
equilibrium system. We focus on a spherically symmetric system governed by
general relativity, particularly examining the steady state with radial heat
conduction. Employing an appropriate approximation, we derive exact solutions
that illuminate the behaviors of number density, local temperature, and heat in
the proximity of a black hole. We demonstrate that a carefully regulated heat
inflow can maintain finite local temperatures at the black hole event horizon,
even without considering the back-reaction of matter. This discovery challenges
conventional expectations that the local temperature near the event horizon
diverges in scenarios of thermal equilibrium. This implications shows that
there's an intricate connection between heat and gravity in the realm of black
hole thermodynamics.
| [
{
"created": "Wed, 3 Jan 2024 04:50:07 GMT",
"version": "v1"
}
] | 2024-01-04 | [
[
"Kim",
"Hyeong-Chan",
""
]
] | We study the issue of temperature in a steady system around a black hole event horizon, contrasting it with the appearance of divergence in a thermal equilibrium system. We focus on a spherically symmetric system governed by general relativity, particularly examining the steady state with radial heat conduction. Employing an appropriate approximation, we derive exact solutions that illuminate the behaviors of number density, local temperature, and heat in the proximity of a black hole. We demonstrate that a carefully regulated heat inflow can maintain finite local temperatures at the black hole event horizon, even without considering the back-reaction of matter. This discovery challenges conventional expectations that the local temperature near the event horizon diverges in scenarios of thermal equilibrium. This implications shows that there's an intricate connection between heat and gravity in the realm of black hole thermodynamics. |
2301.07220 | Tom\'a\v{s} Tint\v{e}ra | Tom\'a\v{s} Tint\v{e}ra | On Weyl alignment preserving Kaluza-Klein reduction of vacuum | 47 pages, 1 figure | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study null alignment properties of Weyl tensors related via
Kaluza$\unicode{x2013}$Klein reduction of vacuum spacetimes by one spatial
Killing direction. Kaluza$\unicode{x2013}$Klein reduction is a method that
relates spacetimes of different dimensionality. Weyl tensor null alignment is
used in a recently proposed generalization of the Petrov algebraic
classification of spacetimes to higher dimensions. Concentrating on the case
where the two considered null directions are parallel in a gauge where they are
perpendicular to the Maxwell potential, we express the relations between
Riemann tensor null frame components of the original and reduced spacetime; we
do the same for the Weyl tensors and also for optical matrices and
non-geodeticities. Based on this, we point out basic consequences regarding
reduction of Kundt spacetimes, and of spacetimes admitting a geodetic null
direction. Finally, we work out the necessary and sufficient conditions for a
Kaluza$\unicode{x2013}$Klein lift to preserve Weyl alignment type with respect
to the related null directions. In the cases of types III and N with
non-vanishing Maxwell field, where both spacetimes turn out to be Kundt, we
show explicit solutions for the scalar potential in six dimensions and greater,
and discuss some qualitative differences from the four-dimensional case.
| [
{
"created": "Tue, 17 Jan 2023 23:01:29 GMT",
"version": "v1"
}
] | 2023-01-19 | [
[
"Tintěra",
"Tomáš",
""
]
] | We study null alignment properties of Weyl tensors related via Kaluza$\unicode{x2013}$Klein reduction of vacuum spacetimes by one spatial Killing direction. Kaluza$\unicode{x2013}$Klein reduction is a method that relates spacetimes of different dimensionality. Weyl tensor null alignment is used in a recently proposed generalization of the Petrov algebraic classification of spacetimes to higher dimensions. Concentrating on the case where the two considered null directions are parallel in a gauge where they are perpendicular to the Maxwell potential, we express the relations between Riemann tensor null frame components of the original and reduced spacetime; we do the same for the Weyl tensors and also for optical matrices and non-geodeticities. Based on this, we point out basic consequences regarding reduction of Kundt spacetimes, and of spacetimes admitting a geodetic null direction. Finally, we work out the necessary and sufficient conditions for a Kaluza$\unicode{x2013}$Klein lift to preserve Weyl alignment type with respect to the related null directions. In the cases of types III and N with non-vanishing Maxwell field, where both spacetimes turn out to be Kundt, we show explicit solutions for the scalar potential in six dimensions and greater, and discuss some qualitative differences from the four-dimensional case. |
1709.01095 | Steffen Gielen | Steffen Gielen, Daniele Oriti | Cosmological perturbations from full quantum gravity | 8 pages, revtex, APS style; v2: included a discussion of density
perturbations (Sec. VI), some statements clarified and shortened; version
accepted for publication; v3: minor spelling and typesetting changes, very
close to published version | Phys. Rev. D 98, 106019 (2018) | 10.1103/PhysRevD.98.106019 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The early universe provides an opportunity for quantum gravity to connect to
observation by explaining the large-scale structure of the Universe. In the
group field theory (GFT) approach, a macroscopic universe is described as a GFT
condensate; this idea has already been shown to reproduce a semiclassical large
universe under generic conditions, and to replace the cosmological singularity
by a quantum bounce. Here we extend the GFT formalism by introducing additional
scalar degrees of freedom that can be used as a physical reference frame for
space and time. This allows, for the first time, the extraction of correlation
functions of inhomogeneities in GFT condensates: in a way conceptually similar
to inflation, but within a quantum field theory of both geometry and matter,
quantum fluctuations of a homogeneous background geometry become the seeds of
cosmological inhomogeneities. We find approximately scale-invariant initial
quantum fluctuations in the local volume, with naturally small amplitude; this
behaviour extends to other quantities such as the matter density. These results
confirm the potential of GFT condensate cosmology to provide a purely quantum
gravitational foundation for the understanding of the early universe.
| [
{
"created": "Mon, 4 Sep 2017 18:01:16 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Nov 2018 16:13:35 GMT",
"version": "v2"
},
{
"created": "Thu, 15 Nov 2018 14:23:47 GMT",
"version": "v3"
}
] | 2018-12-05 | [
[
"Gielen",
"Steffen",
""
],
[
"Oriti",
"Daniele",
""
]
] | The early universe provides an opportunity for quantum gravity to connect to observation by explaining the large-scale structure of the Universe. In the group field theory (GFT) approach, a macroscopic universe is described as a GFT condensate; this idea has already been shown to reproduce a semiclassical large universe under generic conditions, and to replace the cosmological singularity by a quantum bounce. Here we extend the GFT formalism by introducing additional scalar degrees of freedom that can be used as a physical reference frame for space and time. This allows, for the first time, the extraction of correlation functions of inhomogeneities in GFT condensates: in a way conceptually similar to inflation, but within a quantum field theory of both geometry and matter, quantum fluctuations of a homogeneous background geometry become the seeds of cosmological inhomogeneities. We find approximately scale-invariant initial quantum fluctuations in the local volume, with naturally small amplitude; this behaviour extends to other quantities such as the matter density. These results confirm the potential of GFT condensate cosmology to provide a purely quantum gravitational foundation for the understanding of the early universe. |
1711.00087 | Kirill Bronnikov | K. A. Bronnikov | Nonlinear electrodynamics, regular black holes and wormholes | 18 pages, 2 figures | Int. J. Mod. Phys. D 27, 1841005 (2018) | 10.1142/S0218271818410055 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider spherically symmetric configurations in general relativity,
supported by nonlinear electromagnetic fields with gauge-invariant Lagrangians
depending on the single invariant $f = F_{\mu\nu} F^{\mu\nu}$. Static black
hole and solitonic solutions are briefly described, both with only an electric
or magnetic charge and with both nonzero charges (the dyonic ones). It is
stressed that only pure magnetic solutions can be completely nonsingular. For
dyonic systems, apart from a general scheme of obtaining solutions in
quadratures for an arbitrary Lagrangian function $L(f)$, an analytic solution
is found for the truncated Born-Infeld theory (depending on the invariant $f$
only). Furthermore, considering spherically symmetric metrics with two
independent functions of time, we find a natural generalization of the class of
wormholes found previously by Arellano and Lobo with a time-dependent conformal
factor. Such wormholes are shown to be only possible for some particular
choices of the function $L(f)$, having no Maxwell weak-field limit.
| [
{
"created": "Tue, 31 Oct 2017 20:09:03 GMT",
"version": "v1"
}
] | 2020-10-20 | [
[
"Bronnikov",
"K. A.",
""
]
] | We consider spherically symmetric configurations in general relativity, supported by nonlinear electromagnetic fields with gauge-invariant Lagrangians depending on the single invariant $f = F_{\mu\nu} F^{\mu\nu}$. Static black hole and solitonic solutions are briefly described, both with only an electric or magnetic charge and with both nonzero charges (the dyonic ones). It is stressed that only pure magnetic solutions can be completely nonsingular. For dyonic systems, apart from a general scheme of obtaining solutions in quadratures for an arbitrary Lagrangian function $L(f)$, an analytic solution is found for the truncated Born-Infeld theory (depending on the invariant $f$ only). Furthermore, considering spherically symmetric metrics with two independent functions of time, we find a natural generalization of the class of wormholes found previously by Arellano and Lobo with a time-dependent conformal factor. Such wormholes are shown to be only possible for some particular choices of the function $L(f)$, having no Maxwell weak-field limit. |
gr-qc/0703017 | Lorenzo Iorio | Lorenzo Iorio | The impact of the Kuiper Belt Objects and of the asteroid ring on future
high-precision relativistic Solar System tests | Latex2e, Elsevier macros, 5 pages, no figures, 1 table. To appear in
Planetary Space Science. Small change in table's caption | Planet.SpaceSci.55:2045-2048,2007 | 10.1016/j.pss.2007.07.004 | null | gr-qc astro-ph hep-ph physics.space-ph | null | We preliminarily investigate the impact of the Kuiper Belt Objects (KBOs) and
of the asteroid ring on some proposed high-precision tests of Newtonian and
post-Newtonian gravity to be performed in the Solar System by means of
spacecraft in heliocentric \approx 1 AU orbits and accurate orbit determination
of some of the inner planets. It turns out that the Classical KBOSs (CKBOS),
which amount to \approx 70% of the observed population of Trans-Neptunian
bodies, induce a systematic secular error of about 1 m after one year in the
transverse direction T of the orbit of a test particle orbiting at 1 AU from
the Sun. For Mercury the ratios of the secular perihelion precessions induced
by CKBOs to the ones induced by the general relativity and the solar oblateness
J_2 amount to 6 10^-7 and 8 10^-4, respectively. The secular transverse
perturbation induced on a \approx 1 AU orbit by the asteroid ring, which
globally accounts for the action of the minor asteroids whose mass is about 5
10^-10 solar masses, is 10 m yr^-1; the bias on the relativistic and J_2
Mercury perihelion precessions is 6.1 10^-6 and 1 10^-2, respectively. Given
the very ambitious goals of many expensive and complex missions aimed to
testing gravitational theories to unprecedented levels of accuracy, these notes
may suggest further and more accurate investigations of such sources of
potentially insidious systematic bias.
| [
{
"created": "Fri, 2 Mar 2007 15:37:58 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Mar 2007 15:20:08 GMT",
"version": "v2"
},
{
"created": "Wed, 25 Apr 2007 18:15:55 GMT",
"version": "v3"
},
{
"created": "Fri, 1 Jun 2007 16:24:42 GMT",
"version": "v4"
},
{
"created": "Wed, 11 Jul 2007 14:09:57 GMT",
"version": "v5"
},
{
"created": "Mon, 30 Jul 2007 20:52:09 GMT",
"version": "v6"
},
{
"created": "Wed, 8 Aug 2007 22:09:14 GMT",
"version": "v7"
}
] | 2008-11-26 | [
[
"Iorio",
"Lorenzo",
""
]
] | We preliminarily investigate the impact of the Kuiper Belt Objects (KBOs) and of the asteroid ring on some proposed high-precision tests of Newtonian and post-Newtonian gravity to be performed in the Solar System by means of spacecraft in heliocentric \approx 1 AU orbits and accurate orbit determination of some of the inner planets. It turns out that the Classical KBOSs (CKBOS), which amount to \approx 70% of the observed population of Trans-Neptunian bodies, induce a systematic secular error of about 1 m after one year in the transverse direction T of the orbit of a test particle orbiting at 1 AU from the Sun. For Mercury the ratios of the secular perihelion precessions induced by CKBOs to the ones induced by the general relativity and the solar oblateness J_2 amount to 6 10^-7 and 8 10^-4, respectively. The secular transverse perturbation induced on a \approx 1 AU orbit by the asteroid ring, which globally accounts for the action of the minor asteroids whose mass is about 5 10^-10 solar masses, is 10 m yr^-1; the bias on the relativistic and J_2 Mercury perihelion precessions is 6.1 10^-6 and 1 10^-2, respectively. Given the very ambitious goals of many expensive and complex missions aimed to testing gravitational theories to unprecedented levels of accuracy, these notes may suggest further and more accurate investigations of such sources of potentially insidious systematic bias. |
1906.12185 | Sarbari Guha Dr. | Samarjit Chakraborty, Sarbari Guha and D. Panigrahi | Evolution of FRW universe in variable modified Chaplygin gas model | 9 pages, 11 figures, 1 table | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study the evolution of the FRW universe filled with variable
modified Chaplygin gas (VMCG). We begin with a thermodynamical treatment of
VMCG described by the equation of state $P = A\rho-B\rho^{-\alpha}$, and obtain
its temperature as a function of redshift $z$. We show that the results are
consistent with similar works on other types of Chaplygin gas models. In
addition to deriving the exact expression of temperature of the fluid in terms
of the boundary conditions and redshift, we also used observational data to
determine the redshift at the epoch of transition from the decelerated to the
accelerated phase of expansion of the universe. The values of other relevant
parameters like the Hubble parameter, the equation-of-state parameter and the
speed of sound are obtained in terms of the redshift parameter, and these
values are compared with the results obtained from previous works on MCG and
other Chaplygin gas models for the various values of $n$ permitted by
thermodynamic stability. We assume the present value of temperature of the
microwave background radiation to be given by $ T_0 = 2.7 K $, and the
parameter $ A $ in the equation of state is taken as $ 1/3 $ since it
corresponds to the radiation-dominated phase of the universe. The value of the
parameter $\Omega_x$ has been assumed to be $0.7$ in our calculation. Since it
is known that the redshift of photon decoupling is $ z\simeq 1100 $, we used
this value to calculate the temperature of decoupling.
| [
{
"created": "Thu, 27 Jun 2019 12:04:45 GMT",
"version": "v1"
}
] | 2019-07-01 | [
[
"Chakraborty",
"Samarjit",
""
],
[
"Guha",
"Sarbari",
""
],
[
"Panigrahi",
"D.",
""
]
] | In this paper we study the evolution of the FRW universe filled with variable modified Chaplygin gas (VMCG). We begin with a thermodynamical treatment of VMCG described by the equation of state $P = A\rho-B\rho^{-\alpha}$, and obtain its temperature as a function of redshift $z$. We show that the results are consistent with similar works on other types of Chaplygin gas models. In addition to deriving the exact expression of temperature of the fluid in terms of the boundary conditions and redshift, we also used observational data to determine the redshift at the epoch of transition from the decelerated to the accelerated phase of expansion of the universe. The values of other relevant parameters like the Hubble parameter, the equation-of-state parameter and the speed of sound are obtained in terms of the redshift parameter, and these values are compared with the results obtained from previous works on MCG and other Chaplygin gas models for the various values of $n$ permitted by thermodynamic stability. We assume the present value of temperature of the microwave background radiation to be given by $ T_0 = 2.7 K $, and the parameter $ A $ in the equation of state is taken as $ 1/3 $ since it corresponds to the radiation-dominated phase of the universe. The value of the parameter $\Omega_x$ has been assumed to be $0.7$ in our calculation. Since it is known that the redshift of photon decoupling is $ z\simeq 1100 $, we used this value to calculate the temperature of decoupling. |
1301.0821 | Adolfo Toloza Sr. | Adolfo Toloza, Jorge Zanelli | Cosmology with Scalar-Euler form Coupling | null | Class.Quant.Grav. 30 (2013) 135003 | 10.1088/0264-9381/30/13/135003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A coupling between the spacetime geometry and a scalar field involving the
Euler four-form can have important consequences in General Relativity. The
coupling is a four-dimensional version of the Jackiw-Teitelboim action, in
which a scalar couples to the Euler two-form in two dimensions. In this case
the first order formalism, in which the vierbein (or the metric) and the spin
connection (or the afine connection) are varied independently, is not
equivalent to the second order one, in which the geometry is completely
determined by the metric. This is because the torsion postulate (T=0) is not
valid and one cannot algebraically solve the spin connection from its own field
equation. The direct consequence of this obstruction is that the torsion
becomes a new source for the metric curvature, and even if the scalar field is
very slowly varying over cosmic scales as to have no observable astronomical
efects at the galactic scale, it has important dynamical efects that can give
rise to a cosmological evolution radically diferent from the standard FRWL
model.
| [
{
"created": "Fri, 4 Jan 2013 20:46:19 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Jan 2013 02:18:58 GMT",
"version": "v2"
},
{
"created": "Wed, 15 May 2013 01:18:43 GMT",
"version": "v3"
}
] | 2014-09-30 | [
[
"Toloza",
"Adolfo",
""
],
[
"Zanelli",
"Jorge",
""
]
] | A coupling between the spacetime geometry and a scalar field involving the Euler four-form can have important consequences in General Relativity. The coupling is a four-dimensional version of the Jackiw-Teitelboim action, in which a scalar couples to the Euler two-form in two dimensions. In this case the first order formalism, in which the vierbein (or the metric) and the spin connection (or the afine connection) are varied independently, is not equivalent to the second order one, in which the geometry is completely determined by the metric. This is because the torsion postulate (T=0) is not valid and one cannot algebraically solve the spin connection from its own field equation. The direct consequence of this obstruction is that the torsion becomes a new source for the metric curvature, and even if the scalar field is very slowly varying over cosmic scales as to have no observable astronomical efects at the galactic scale, it has important dynamical efects that can give rise to a cosmological evolution radically diferent from the standard FRWL model. |
1005.2953 | S Habib Mazharimousavi | S. Habib Mazharimousavi, M. Halilsoy and Z. Amirabi | d-dimensional non-asymptotically flat thin-shell wormholes in
Einstein-Yang-Mills-Dilaton gravity | 6 pages, 5 figures. Title changed, the first version has been
generalized to d-dimensions. The EYMGB part was removed and was considered in
a more general form separately in arXiv:1007.4627 | Phys.Lett.A375:231-236,2011 | 10.1016/j.physleta.2010.11.012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Thin-shell wormholes in Einstein-Yang-Mills-dilaton (EYMD) gravity are
considered. We show that a non-asymptotically flat (NAF) black hole solution of
the d-dimensional EYMD theory provides stable thin-shell wormholes which are
supported entirely by exotic matter. The presence of dilaton makes the
spacetime naturally NAF, and with our conclusion it remains still open to
construct wormholes supported by normal matter between two such spacetimes.
| [
{
"created": "Mon, 17 May 2010 15:29:06 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Sep 2010 13:19:36 GMT",
"version": "v2"
},
{
"created": "Mon, 3 Jan 2011 15:51:21 GMT",
"version": "v3"
}
] | 2011-01-17 | [
[
"Mazharimousavi",
"S. Habib",
""
],
[
"Halilsoy",
"M.",
""
],
[
"Amirabi",
"Z.",
""
]
] | Thin-shell wormholes in Einstein-Yang-Mills-dilaton (EYMD) gravity are considered. We show that a non-asymptotically flat (NAF) black hole solution of the d-dimensional EYMD theory provides stable thin-shell wormholes which are supported entirely by exotic matter. The presence of dilaton makes the spacetime naturally NAF, and with our conclusion it remains still open to construct wormholes supported by normal matter between two such spacetimes. |
gr-qc/0104012 | Hiroyuki Nakano | Hiroyuki Nakano, Yasushi Mino, Misao Sasaki | Self-Force on a Scalar Charge in Circular Orbit around a Schwarzschild
Black Hole | 16 pages, no figure, Minor typos corrected | Prog.Theor.Phys.106:339-362,2001 | 10.1143/PTP.106.339 | null | gr-qc astro-ph hep-th | null | In an accompanying paper, we have formulated two types of regulariz_ation
methods to calculate the scalar self-force on a particle of charge $q$ moving
around a black hole of mass $M$, one of which is called the ``power expansion
regularization''. In this paper, we analytically evaluate the self-force (which
we also call the reaction force) to the third post-Newtonian (3PN) order on the
scalar particle in circular orbit around a Schwarzschild black hole by using
the power expansion regularization. It is found that the $r$-component of the
self-force arises at the 3PN order, whereas the $t$- and $\phi$-components,
which are due to the radiation reaction, appear at the 2PN and 1.5PN orders,
respectively.
| [
{
"created": "Wed, 4 Apr 2001 05:54:00 GMT",
"version": "v1"
},
{
"created": "Thu, 12 Apr 2001 06:18:03 GMT",
"version": "v2"
}
] | 2009-10-09 | [
[
"Nakano",
"Hiroyuki",
""
],
[
"Mino",
"Yasushi",
""
],
[
"Sasaki",
"Misao",
""
]
] | In an accompanying paper, we have formulated two types of regulariz_ation methods to calculate the scalar self-force on a particle of charge $q$ moving around a black hole of mass $M$, one of which is called the ``power expansion regularization''. In this paper, we analytically evaluate the self-force (which we also call the reaction force) to the third post-Newtonian (3PN) order on the scalar particle in circular orbit around a Schwarzschild black hole by using the power expansion regularization. It is found that the $r$-component of the self-force arises at the 3PN order, whereas the $t$- and $\phi$-components, which are due to the radiation reaction, appear at the 2PN and 1.5PN orders, respectively. |
2408.02895 | Matthew Charles Edwards | Tarin Eccleston and Matthew C. Edwards | A generative adversarial network for stellar core-collapse
gravitational-waves | 12 pages, 7 figures | null | null | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a rapid stellar core-collapse waveform emulator built using a deep
convolutional generative adversarial network (DCGAN). The DCGAN was trained on
the Richers \textit{et al.~}\cite{richers:2017} waveform catalogue to learn the
structure of rotating stellar core-collapse gravitational-wave signals and
generate realistic waveforms. We show that the DCGAN learns the distribution of
the training data reasonably well, and that the waveform emulator produces
signals that appear to have the key features of core-collapse, bounce, early
post-bounce, and ringdown oscillations of the early proto-neutron star. The
pre-trained DCGAN can therefore be used as a phenomenological model for
rotating stellar core-collapse gravitational-waves.
| [
{
"created": "Tue, 6 Aug 2024 02:00:21 GMT",
"version": "v1"
}
] | 2024-08-07 | [
[
"Eccleston",
"Tarin",
""
],
[
"Edwards",
"Matthew C.",
""
]
] | We present a rapid stellar core-collapse waveform emulator built using a deep convolutional generative adversarial network (DCGAN). The DCGAN was trained on the Richers \textit{et al.~}\cite{richers:2017} waveform catalogue to learn the structure of rotating stellar core-collapse gravitational-wave signals and generate realistic waveforms. We show that the DCGAN learns the distribution of the training data reasonably well, and that the waveform emulator produces signals that appear to have the key features of core-collapse, bounce, early post-bounce, and ringdown oscillations of the early proto-neutron star. The pre-trained DCGAN can therefore be used as a phenomenological model for rotating stellar core-collapse gravitational-waves. |
1510.06217 | Chongoh Lee | Chong Oh Lee | The Extended Thermodynamic Properties of a topological Taub-NUT/Bolt-AdS
spaces | 7 pages, 6 figures, typos corrected, version to appear in PLB | null | 10.1016/j.physletb.2015.12.050 | null | gr-qc | http://creativecommons.org/publicdomain/zero/1.0/ | We consider higher dimensional topological Taub-NUT/Bolt-AdS solutions where
a cosmological constant is treated as a pressure. The thermodynamic quantities
of these solutions are explicitly calculated. Furthermore, we find these
thermodynamic quantities satisfy the Clapeyron equation. In particular, a new
thermodynamically stable region for the NUT solution is found by studying the
Gibbs free energy. Intriguingly, we also find that like the AdS black hole
case, the G-T diagram of the Bolt solution has two branches which are joined at
a minimum temperature. The Bolt solution with the large radius, at the lower
branch, becomes stable beyond a certain temperature while the Bolt solution
with the small radius, at the upper branch, is always unstable.
| [
{
"created": "Wed, 21 Oct 2015 11:36:52 GMT",
"version": "v1"
},
{
"created": "Mon, 28 Dec 2015 05:05:36 GMT",
"version": "v2"
}
] | 2015-12-29 | [
[
"Lee",
"Chong Oh",
""
]
] | We consider higher dimensional topological Taub-NUT/Bolt-AdS solutions where a cosmological constant is treated as a pressure. The thermodynamic quantities of these solutions are explicitly calculated. Furthermore, we find these thermodynamic quantities satisfy the Clapeyron equation. In particular, a new thermodynamically stable region for the NUT solution is found by studying the Gibbs free energy. Intriguingly, we also find that like the AdS black hole case, the G-T diagram of the Bolt solution has two branches which are joined at a minimum temperature. The Bolt solution with the large radius, at the lower branch, becomes stable beyond a certain temperature while the Bolt solution with the small radius, at the upper branch, is always unstable. |
2206.03146 | Prashant Kocherlakota | Prashant Kocherlakota and Luciano Rezzolla | Comment on the Analytical Bounds in the Rezzolla-Zhidenko
Parametrization | 2 pages | null | null | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | In this short note, we briefly comment on the analytical bounds that must be
imposed on the parameter space of the Rezzolla-Zhidenko (RZ)
metric-parametrization approach introduced in Ref. [1]. We hope this will
clarify some of the confusion recently emerged on this issue [2].
| [
{
"created": "Tue, 7 Jun 2022 09:40:09 GMT",
"version": "v1"
}
] | 2022-06-08 | [
[
"Kocherlakota",
"Prashant",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | In this short note, we briefly comment on the analytical bounds that must be imposed on the parameter space of the Rezzolla-Zhidenko (RZ) metric-parametrization approach introduced in Ref. [1]. We hope this will clarify some of the confusion recently emerged on this issue [2]. |
gr-qc/9807028 | Tevian Dray | Jim Fischer and Tevian Dray | A New Look at the Ashtekar-Magnon Energy Condition | REVTeX, 10 pages | Gen.Rel.Grav. 31 (1999) 511-526 | 10.1023/A:1026694106351 | null | gr-qc | null | In 1975, Ashtekar and Magnon showed that an energy condition selects a unique
quantization procedure for certain observers in general, curved spacetimes. We
generalize this result in two important ways, by eliminating the need to assume
a particular form for the (quantum) Hamiltonian, and by considering the
surprisingly nontrivial extension to nonminimal coupling.
| [
{
"created": "Tue, 14 Jul 1998 18:08:34 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Fischer",
"Jim",
""
],
[
"Dray",
"Tevian",
""
]
] | In 1975, Ashtekar and Magnon showed that an energy condition selects a unique quantization procedure for certain observers in general, curved spacetimes. We generalize this result in two important ways, by eliminating the need to assume a particular form for the (quantum) Hamiltonian, and by considering the surprisingly nontrivial extension to nonminimal coupling. |
2403.07045 | Lidia J. Gomes Da Silva Miss | Juan A. Valiente Kroon, Lidia J. Gomes Da Silva | The \v{d}Alembert solution in hyperboloidal foliations | 15 pages, 7 figures. Submitted to Springer's topical collection:
"Hyperboloidal foliations in the era of gravitational-wave astronomy: from
mathematical relativity to astrophysics". Comments welcomed | null | null | null | gr-qc astro-ph.IM math-ph math.MP physics.comp-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explicitly construct the analogue of the \v{d}Alembert solution to the 1+1
wave equation in an hyperboloidal setting. This hyperboloidal \v{d}Alembert
solution is used, in turn, to gain intuition into the behaviour of solutions to
the wave equation in a hyperboloidal foliation and to explain some apparently
anomalous behaviour observed in numerically constructed solutions discussed in
the literature.
| [
{
"created": "Mon, 11 Mar 2024 18:00:00 GMT",
"version": "v1"
}
] | 2024-03-13 | [
[
"Kroon",
"Juan A. Valiente",
""
],
[
"Da Silva",
"Lidia J. Gomes",
""
]
] | We explicitly construct the analogue of the \v{d}Alembert solution to the 1+1 wave equation in an hyperboloidal setting. This hyperboloidal \v{d}Alembert solution is used, in turn, to gain intuition into the behaviour of solutions to the wave equation in a hyperboloidal foliation and to explain some apparently anomalous behaviour observed in numerically constructed solutions discussed in the literature. |
1212.1769 | H.-J. Schmidt | H.-J. Schmidt and D. Singleton | Isotropic universe with almost scale-invariant fourth-order gravity | several revisions included, 28 pages, J. Math. Phys. accepted | J.Math.Phys. 54 (2013) 062502 | 10.1063/1.4808255 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a broad class of isotropic vacuum cosmologies in fourth-order
gravity under the condition that the gravitational Lagrangian be
scale-invariant or almost scale-invariant. The gravitational Lagrangians
considered will be of the form L = f(R) + k(G) where R and G are the Ricci and
Gauss-Bonnet scalars respectively. Specifically we take f(R) = R^2n and k(G) =
G^n or k(G) = G ln G. We find solutions in closed form for a spatially flat
Friedmann space-time and interpret their asymptotic early-time and late-time
behaviour as well as their inflationary stages. One unique example which we
discuss is the case of a very small negative value of the parameter b in the
Lagrangian L = R^2 + b G ln G which leads to the replacement of the exact de
Sitter solution from L = R^2 (being a local attractor) to a power-law inflation
exact solution also representing a local attractor. This shows how one can
modify the dynamics from de Sitter to power-law inflation by the addition of
the G ln G-term.
| [
{
"created": "Sat, 8 Dec 2012 08:52:35 GMT",
"version": "v1"
},
{
"created": "Thu, 16 May 2013 19:55:21 GMT",
"version": "v2"
}
] | 2013-06-12 | [
[
"Schmidt",
"H. -J.",
""
],
[
"Singleton",
"D.",
""
]
] | We study a broad class of isotropic vacuum cosmologies in fourth-order gravity under the condition that the gravitational Lagrangian be scale-invariant or almost scale-invariant. The gravitational Lagrangians considered will be of the form L = f(R) + k(G) where R and G are the Ricci and Gauss-Bonnet scalars respectively. Specifically we take f(R) = R^2n and k(G) = G^n or k(G) = G ln G. We find solutions in closed form for a spatially flat Friedmann space-time and interpret their asymptotic early-time and late-time behaviour as well as their inflationary stages. One unique example which we discuss is the case of a very small negative value of the parameter b in the Lagrangian L = R^2 + b G ln G which leads to the replacement of the exact de Sitter solution from L = R^2 (being a local attractor) to a power-law inflation exact solution also representing a local attractor. This shows how one can modify the dynamics from de Sitter to power-law inflation by the addition of the G ln G-term. |
0711.1004 | J. Ponce de Leon | J. Ponce de Leon | The principle of least action for test particles in a four-dimensional
spacetime embedded in 5D | null | Mod.Phys.Lett.A23:249-259,2008 | 10.1142/S0217732308026376 | null | gr-qc | null | It is well known that, in the five-dimensional scenario of braneworld and
space-time-mass theories, geodesic motion in 5D is observed to be non-geodesic
in 4D. Usually, the discussion is purely geometric and based on the dimensional
reduction of the geodesic equation in 5D, without any reference to the test
particle whatsoever. In this work we obtain the equation of motion in 4D
directly from the principle of least action. So our main thrust is not the
geometry but the particle observed in 4D. A clear physical picture emerges from
our work. Specifically, that the deviation from the geodesic motion in 4D is
due to the variation of the rest mass of a particle, which is induced by the
scalar field in the 5D metric and the explicit dependence of the spacetime
metric on the extra coordinate. Thus, the principle of least action not only
leads to the correct equations of motion, but also provides a concrete physical
meaning for a number of algebraic quantities appearing in the geometrical
reduction of the geodesic equation.
| [
{
"created": "Wed, 7 Nov 2007 03:58:06 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"de Leon",
"J. Ponce",
""
]
] | It is well known that, in the five-dimensional scenario of braneworld and space-time-mass theories, geodesic motion in 5D is observed to be non-geodesic in 4D. Usually, the discussion is purely geometric and based on the dimensional reduction of the geodesic equation in 5D, without any reference to the test particle whatsoever. In this work we obtain the equation of motion in 4D directly from the principle of least action. So our main thrust is not the geometry but the particle observed in 4D. A clear physical picture emerges from our work. Specifically, that the deviation from the geodesic motion in 4D is due to the variation of the rest mass of a particle, which is induced by the scalar field in the 5D metric and the explicit dependence of the spacetime metric on the extra coordinate. Thus, the principle of least action not only leads to the correct equations of motion, but also provides a concrete physical meaning for a number of algebraic quantities appearing in the geometrical reduction of the geodesic equation. |
0812.0702 | Jakob Hansen | Andrey Doroshkevich, Jakob Hansen, Igor Novikov, Alexander Shatskiy | Passage of radiation through wormholes | 18 Pages, 13 figures, minor typos corrected, updated references | Int.J.Mass Spectr.Ion Process.18:1665-1691,2009 | 10.1142/S0218271809015230 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate numerically the process of the passage of a radiation pulse
through a wormhole and the subsequent evolution of the wormhole that is caused
by the gravitational action of this pulse. The initial static wormhole is
modeled by the spherically symmetrical Armendariz-Picon solution with zero
mass. The radiation pulses are modeled by spherically symmetrical shells of
self-gravitating massless scalar fields. We demonstrate that the compact signal
propagates through the wormhole and investigate the dynamics of the fields in
this process for both cases: collapse of the wormhole into the black hole and
for the expanding wormhole.
| [
{
"created": "Wed, 3 Dec 2008 12:11:21 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Jan 2009 11:19:35 GMT",
"version": "v2"
}
] | 2014-11-18 | [
[
"Doroshkevich",
"Andrey",
""
],
[
"Hansen",
"Jakob",
""
],
[
"Novikov",
"Igor",
""
],
[
"Shatskiy",
"Alexander",
""
]
] | We investigate numerically the process of the passage of a radiation pulse through a wormhole and the subsequent evolution of the wormhole that is caused by the gravitational action of this pulse. The initial static wormhole is modeled by the spherically symmetrical Armendariz-Picon solution with zero mass. The radiation pulses are modeled by spherically symmetrical shells of self-gravitating massless scalar fields. We demonstrate that the compact signal propagates through the wormhole and investigate the dynamics of the fields in this process for both cases: collapse of the wormhole into the black hole and for the expanding wormhole. |
1310.5029 | Fernando Oscar Minotti | F. O. Minotti and T. E. Raptis | Transient force effects, as predicted by Mbelek and Lachi\`{e}ze-Rey
scalar tensor theory of gravitation | 8 pages, 1 figure (minor corrections made) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The scalar-tensor theory of gravitation proposed by Mbelek and
Lachi\`{e}ze-Rey have been recently shown to lead to some remarkable effects
beyond those initially explored by its authors. These new effects include a
possible explanation of the forces measured in asymmetric resonant microwave
cavities, and the variation of the amplitude of electromagnetic waves as they
propagate in static electric or magnetic fields. These rather unique effects
are excelent candidates for laboratory tests of this particular type of
scalar-tensor theory. In the present work we introduce an additional remarkable
effect of the theory: the generation of pulsed gravitational forces by
transient, quasi-stationary electromagnetic fields. In particular, we explore
the possible measurable effects of the simple experiment of turning on and off
the current in a coil. We show that with the proposed values of the constant in
the theory, this effect could resonantly excite a pendulum oscillation up to an
easily measurable magnitude.
| [
{
"created": "Fri, 18 Oct 2013 14:17:47 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Dec 2013 19:55:16 GMT",
"version": "v2"
}
] | 2013-12-12 | [
[
"Minotti",
"F. O.",
""
],
[
"Raptis",
"T. E.",
""
]
] | The scalar-tensor theory of gravitation proposed by Mbelek and Lachi\`{e}ze-Rey have been recently shown to lead to some remarkable effects beyond those initially explored by its authors. These new effects include a possible explanation of the forces measured in asymmetric resonant microwave cavities, and the variation of the amplitude of electromagnetic waves as they propagate in static electric or magnetic fields. These rather unique effects are excelent candidates for laboratory tests of this particular type of scalar-tensor theory. In the present work we introduce an additional remarkable effect of the theory: the generation of pulsed gravitational forces by transient, quasi-stationary electromagnetic fields. In particular, we explore the possible measurable effects of the simple experiment of turning on and off the current in a coil. We show that with the proposed values of the constant in the theory, this effect could resonantly excite a pendulum oscillation up to an easily measurable magnitude. |
0807.0824 | Jose M. Martin-Garcia | David Brizuela, Jose M. Martin-Garcia, Guillermo A. Mena Marugan | xPert: Computer algebra for metric perturbation theory | 11 pages, 4 figures. Package can be downloaded from
http://metric.iem.csic.es/Martin-Garcia/xAct/xPert/ | Gen.Rel.Grav.41:2415-2431,2009 | 10.1007/s10714-009-0773-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the tensor computer algebra package xPert for fast construction
and manipulation of the equations of metric perturbation theory, around
arbitrary backgrounds. It is based on the combination of explicit combinatorial
formulas for the n-th order perturbation of curvature tensors and their gauge
changes, and the use of highly efficient techniques of index canonicalization,
provided by the underlying tensor system xAct, for Mathematica. We give
examples of use and show the efficiency of the system with timings plots: it is
possible to handle orders n=4 or n=5 within seconds, or reach n=10 with timings
below 1 hour.
| [
{
"created": "Sun, 6 Jul 2008 18:04:09 GMT",
"version": "v1"
}
] | 2009-09-28 | [
[
"Brizuela",
"David",
""
],
[
"Martin-Garcia",
"Jose M.",
""
],
[
"Marugan",
"Guillermo A. Mena",
""
]
] | We present the tensor computer algebra package xPert for fast construction and manipulation of the equations of metric perturbation theory, around arbitrary backgrounds. It is based on the combination of explicit combinatorial formulas for the n-th order perturbation of curvature tensors and their gauge changes, and the use of highly efficient techniques of index canonicalization, provided by the underlying tensor system xAct, for Mathematica. We give examples of use and show the efficiency of the system with timings plots: it is possible to handle orders n=4 or n=5 within seconds, or reach n=10 with timings below 1 hour. |
2011.07079 | Carlos Molina Mendes | F. Ruiz, C. Molina, J. A. S. Lima | Dynamical model for primordial black holes | 14 pages, 8 figures | Physical Review D 102, 123516 (2020) | 10.1103/PhysRevD.102.123516 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | Primordial black holes are analytically and numerically discussed based on
the extended McVittie spacetime solution. By assuming that dark matter and
radiation are the only sources of energy accreted by the forming central
object, it is found that the black-hole mass evolution depends on the initial
mass of the seed, the time in which the black hole emerges, and also on the
average peculiar velocity of dark matter particles. Constraints on the initial
conditions of the primordial black holes are derived from profiles of the
black-hole accretion mechanism and cosmological environment. A large range of
masses is compatible with our approach. In particular, masses of the order of
$10^{10}M_{\odot}$ today may also be generated from small seeds. An incubation
time for the emerging horizons is observed when the initial masses of the seeds
are close to the particle-horizon mass. It is also argued that the
McVittie-type description is consistent with the Schwarzschild solution as long
as other astrophysical processes near the central object are neglected.
| [
{
"created": "Fri, 13 Nov 2020 19:00:08 GMT",
"version": "v1"
},
{
"created": "Mon, 7 Dec 2020 19:00:06 GMT",
"version": "v2"
}
] | 2020-12-09 | [
[
"Ruiz",
"F.",
""
],
[
"Molina",
"C.",
""
],
[
"Lima",
"J. A. S.",
""
]
] | Primordial black holes are analytically and numerically discussed based on the extended McVittie spacetime solution. By assuming that dark matter and radiation are the only sources of energy accreted by the forming central object, it is found that the black-hole mass evolution depends on the initial mass of the seed, the time in which the black hole emerges, and also on the average peculiar velocity of dark matter particles. Constraints on the initial conditions of the primordial black holes are derived from profiles of the black-hole accretion mechanism and cosmological environment. A large range of masses is compatible with our approach. In particular, masses of the order of $10^{10}M_{\odot}$ today may also be generated from small seeds. An incubation time for the emerging horizons is observed when the initial masses of the seeds are close to the particle-horizon mass. It is also argued that the McVittie-type description is consistent with the Schwarzschild solution as long as other astrophysical processes near the central object are neglected. |
1208.3927 | Frederic H. Vincent | Frederic H. Vincent, Eric Gourgoulhon, J\'er\^ome Novak | 3+1 geodesic equation and images in numerical spacetimes | 20 pages, 4 figures, accepted by CQG, with substantial improvements
from referees remarks | Class. Quantum Grav., 29, 245005 (2012) | 10.1088/0264-9381/29/24/245005 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The equations governing null and timelike geodesics are derived within the
3+1 formalism of general relativity. In addition to the particle's position,
they encompass an evolution equation for the particle's energy leading to a 3+1
expression of the redshift factor for photons. An important application is the
computation of images and spectra in spacetimes arising from numerical
relativity, via the ray-tracing technique. This is illustrated here by images
of numerically computed stationary neutron stars and dynamical neutron stars
collapsing to a black hole.
| [
{
"created": "Mon, 20 Aug 2012 07:18:10 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Oct 2012 16:28:51 GMT",
"version": "v2"
}
] | 2012-12-18 | [
[
"Vincent",
"Frederic H.",
""
],
[
"Gourgoulhon",
"Eric",
""
],
[
"Novak",
"Jérôme",
""
]
] | The equations governing null and timelike geodesics are derived within the 3+1 formalism of general relativity. In addition to the particle's position, they encompass an evolution equation for the particle's energy leading to a 3+1 expression of the redshift factor for photons. An important application is the computation of images and spectra in spacetimes arising from numerical relativity, via the ray-tracing technique. This is illustrated here by images of numerically computed stationary neutron stars and dynamical neutron stars collapsing to a black hole. |
2106.08954 | Grigory Volovik | G.E. Volovik | Type-II Weyl semimetal vs gravastar | 7 pages, 3 figures, version accepted in JETP Letters | null | 10.1134/S0021364021160013 | null | gr-qc cond-mat.str-el hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The boundary between the type I and type II Weyl semimetals serves as the
event horizon for the "relativistic" fermions. The interior of the black hole
is represented by the type II Weyl semimetal, where the Fermi surface is
formed. The process of the filling of the Fermi surface by electrons results in
the relaxation inside the horizon. This leads to the Hawking radiation and to
the reconstruction of the interior vacuum state. After the Fermi surface is
fully occupied, the interior region reaches the equilibrium state, for which
the Hawking radiation is absent. If this scenario is applicable to the real
black hole, then the final state of the black hole will be the dark energy star
with the event horizon. Inside the event horizon one would have de Sitter space
time, which is separated from the event horizon by the shell of the Planck
length width. Both the de Sitter part and the shell are made of the vacuum
fields without matter. This is distinct from the gravastar, in which the matter
shell is outside the "horizon", and which we call the type I gravastar. But
this is similar to the other type of the vacuum black hole, where the shell is
inside the event horizon, and which we call the type II gravastar. We suggest
to study the vacuum structure of the type II gravastar using the $q$-theory,
where the vacuum variable is the 4-form field introduced for the
phenomenological description of the quantum vacuum.
| [
{
"created": "Tue, 15 Jun 2021 15:44:54 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Jun 2021 10:11:43 GMT",
"version": "v2"
},
{
"created": "Mon, 5 Jul 2021 08:26:56 GMT",
"version": "v3"
},
{
"created": "Fri, 16 Jul 2021 09:16:06 GMT",
"version": "v4"
}
] | 2021-09-01 | [
[
"Volovik",
"G. E.",
""
]
] | The boundary between the type I and type II Weyl semimetals serves as the event horizon for the "relativistic" fermions. The interior of the black hole is represented by the type II Weyl semimetal, where the Fermi surface is formed. The process of the filling of the Fermi surface by electrons results in the relaxation inside the horizon. This leads to the Hawking radiation and to the reconstruction of the interior vacuum state. After the Fermi surface is fully occupied, the interior region reaches the equilibrium state, for which the Hawking radiation is absent. If this scenario is applicable to the real black hole, then the final state of the black hole will be the dark energy star with the event horizon. Inside the event horizon one would have de Sitter space time, which is separated from the event horizon by the shell of the Planck length width. Both the de Sitter part and the shell are made of the vacuum fields without matter. This is distinct from the gravastar, in which the matter shell is outside the "horizon", and which we call the type I gravastar. But this is similar to the other type of the vacuum black hole, where the shell is inside the event horizon, and which we call the type II gravastar. We suggest to study the vacuum structure of the type II gravastar using the $q$-theory, where the vacuum variable is the 4-form field introduced for the phenomenological description of the quantum vacuum. |
1205.3893 | Shin'ichirou Yoshida | Shin'ichirou Yoshida | Non-axisymmetric oscillations of rapidly rotating relativistic stars by
conformal flatness approximation | 3 figures. To appear in Phys.Rev.D | null | 10.1103/PhysRevD.86.104055 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a new numerical code to compute non-axisymmetric eigenmodes of
rapidly rotating relativistic stars by adopting spatially conformally flat
approximation of general relativity. The approximation suppresses the radiative
degree of freedom of relativistic gravity and the field equations are cast into
a set of elliptic equations. The code is tested against the low-order f- and
p-modes of slowly rotating stars for which a good agreement is observed in
frequencies computed by our new code and those computed by the full theory.
Entire sequences of the low order counter-rotating f-modes are computed, which
are susceptible to an instability driven by gravitational radiation.
| [
{
"created": "Thu, 17 May 2012 10:00:34 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Nov 2012 05:45:23 GMT",
"version": "v2"
}
] | 2013-05-30 | [
[
"Yoshida",
"Shin'ichirou",
""
]
] | We present a new numerical code to compute non-axisymmetric eigenmodes of rapidly rotating relativistic stars by adopting spatially conformally flat approximation of general relativity. The approximation suppresses the radiative degree of freedom of relativistic gravity and the field equations are cast into a set of elliptic equations. The code is tested against the low-order f- and p-modes of slowly rotating stars for which a good agreement is observed in frequencies computed by our new code and those computed by the full theory. Entire sequences of the low order counter-rotating f-modes are computed, which are susceptible to an instability driven by gravitational radiation. |
gr-qc/0407033 | Pawe{\l} O. Mazur | George Chapline and Pawel O. Mazur (Lawrence Livermore National
Laboratory, University of South Carolina) | Superfluid Picture for Rotating Space-Times | 12 pages, LaTeX, Acta Physica Polonica B45, 2014; Dedicated to
Professor Andrzej Staruszkiewicz on the occasion of His birthday | null | null | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new prescription, in the framework of condensate models for space-times,
for physical stationary gravitational fields is presented. We show that the
spinning cosmic string metric describes the gravitational field associated with
the single vortex in a superfluid condensate model for space-time outside the
vortex core. This metric differs significantly from the usual acoustic metric
for the Onsager-Feynman vortex. We also consider the question of what happens
when many vortices are present, and show that on large scales a G\"odel-like
metric emerges. In both the single and multiple vortex cases the failure of
general relativity exemplified by the presence of closed time-like curves is
attributed to the breakdown of superfluid rigidity.
| [
{
"created": "Thu, 8 Jul 2004 03:46:18 GMT",
"version": "v1"
},
{
"created": "Thu, 5 May 2005 17:51:04 GMT",
"version": "v2"
},
{
"created": "Fri, 28 Mar 2014 22:48:42 GMT",
"version": "v3"
}
] | 2014-04-01 | [
[
"Chapline",
"George",
"",
"Lawrence Livermore National\n Laboratory, University of South Carolina"
],
[
"Mazur",
"Pawel O.",
"",
"Lawrence Livermore National\n Laboratory, University of South Carolina"
]
] | A new prescription, in the framework of condensate models for space-times, for physical stationary gravitational fields is presented. We show that the spinning cosmic string metric describes the gravitational field associated with the single vortex in a superfluid condensate model for space-time outside the vortex core. This metric differs significantly from the usual acoustic metric for the Onsager-Feynman vortex. We also consider the question of what happens when many vortices are present, and show that on large scales a G\"odel-like metric emerges. In both the single and multiple vortex cases the failure of general relativity exemplified by the presence of closed time-like curves is attributed to the breakdown of superfluid rigidity. |
2307.14042 | Tomoya Kinugawa | Tomoya Kinugawa, Takashi Nakamura, and Hiroyuki Nakano | Mass Ratio of Binary Black Holes Determined from LIGO/Virgo Data
Restricted to Small False Alarm Rate | Comment welcome. accepted by MNRAS | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We focus on gravitational-wave events of binary black-hole mergers up to the
third observing run with the minimum false alarm rate smaller than
$10^{-5}\,{\rm yr}^{-1}$. These events tell us that the mass ratio of two black
holes follows $m_2/m_1=0.723$ with the chance probability of 0.00301% for the
chirp mass $M_{\rm chirp} > 18\,M_{\odot}$. We show that the relation of
$m_2/m_1=0.723$ is consistent with the binaries originated from population III
stars which are the first stars in the universe. On the other hand, it is found
for ${\rm chirp} < 18 M_{\odot}$ that the mass ratio follows $m_2/m_1=0.601$
with the chance probability of 0.117% if we ignore GW190412 with $m_2/m_1\sim
0.32$. This suggests a different origin from that for $M_{\rm chirp} > 18
M_{\odot}$.
| [
{
"created": "Wed, 26 Jul 2023 08:48:35 GMT",
"version": "v1"
},
{
"created": "Thu, 27 Jun 2024 09:44:32 GMT",
"version": "v2"
}
] | 2024-06-28 | [
[
"Kinugawa",
"Tomoya",
""
],
[
"Nakamura",
"Takashi",
""
],
[
"Nakano",
"Hiroyuki",
""
]
] | We focus on gravitational-wave events of binary black-hole mergers up to the third observing run with the minimum false alarm rate smaller than $10^{-5}\,{\rm yr}^{-1}$. These events tell us that the mass ratio of two black holes follows $m_2/m_1=0.723$ with the chance probability of 0.00301% for the chirp mass $M_{\rm chirp} > 18\,M_{\odot}$. We show that the relation of $m_2/m_1=0.723$ is consistent with the binaries originated from population III stars which are the first stars in the universe. On the other hand, it is found for ${\rm chirp} < 18 M_{\odot}$ that the mass ratio follows $m_2/m_1=0.601$ with the chance probability of 0.117% if we ignore GW190412 with $m_2/m_1\sim 0.32$. This suggests a different origin from that for $M_{\rm chirp} > 18 M_{\odot}$. |
2201.05287 | Valerio Faraoni | Valerio Faraoni, Genevi\`eve Vachon, Robert Vanderwee, Sonia Jose | Friedmann-Lema\^itre-Robertson-Walker cosmology through the lens of
gravitoelectromagnetism | Introduction expanded and explanation added. Matches version in press
in Phys. Rev. D | null | 10.1103/PhysRevD.105.083530 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Friedmann-Lema\^itre-Robertson-Walker cosmology is examined from the point of
view of gravitoelectromagnetism, in the approximation of spacetime regions
small in comparison with the Hubble radius. The usual Lorentz gauge is not
appropriate for this situation, while the Painlev\'e-Gullstrand gauge is rather
natural. Several non-trivial features and differences with respect to
"standard" asymptotically flat gravitoelectromagnetism are discussed.
| [
{
"created": "Fri, 14 Jan 2022 03:16:40 GMT",
"version": "v1"
},
{
"created": "Wed, 13 Apr 2022 01:16:36 GMT",
"version": "v2"
}
] | 2022-05-11 | [
[
"Faraoni",
"Valerio",
""
],
[
"Vachon",
"Geneviève",
""
],
[
"Vanderwee",
"Robert",
""
],
[
"Jose",
"Sonia",
""
]
] | Friedmann-Lema\^itre-Robertson-Walker cosmology is examined from the point of view of gravitoelectromagnetism, in the approximation of spacetime regions small in comparison with the Hubble radius. The usual Lorentz gauge is not appropriate for this situation, while the Painlev\'e-Gullstrand gauge is rather natural. Several non-trivial features and differences with respect to "standard" asymptotically flat gravitoelectromagnetism are discussed. |
1807.01100 | Federico Urban | Tom Z{\l}o\'snik, Federico Urban, Luca Marzola, Tomi Koivisto | Spacetime and dark matter from spontaneous breaking of Lorentz symmetry | v2 with minor edits, as published | null | 10.1088/1361-6382/aaea96 | NORDITA 2018-048 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that a spontaneously-broken gauge theory of the Lorentz group
contains Ashtekar's chiral formulation of General Relativity accompanied by
dust. From this perspective, gravity is described entirely by a connection
$\omega$ valued in the Lie algebra of the complexified Lorentz group and a
Lorentz-charged scalar field $\tau$. The model is "pre-geometric" in the sense
that the spacetime metric may be constructed only in the symmetry-broken
regime. We speculate on the extent to which this dust may account for dark
matter and on the behaviour of the theory in regimes where the symmetry is not
broken.
| [
{
"created": "Tue, 3 Jul 2018 11:56:36 GMT",
"version": "v1"
},
{
"created": "Mon, 29 Oct 2018 13:17:32 GMT",
"version": "v2"
}
] | 2018-10-30 | [
[
"Złośnik",
"Tom",
""
],
[
"Urban",
"Federico",
""
],
[
"Marzola",
"Luca",
""
],
[
"Koivisto",
"Tomi",
""
]
] | It is shown that a spontaneously-broken gauge theory of the Lorentz group contains Ashtekar's chiral formulation of General Relativity accompanied by dust. From this perspective, gravity is described entirely by a connection $\omega$ valued in the Lie algebra of the complexified Lorentz group and a Lorentz-charged scalar field $\tau$. The model is "pre-geometric" in the sense that the spacetime metric may be constructed only in the symmetry-broken regime. We speculate on the extent to which this dust may account for dark matter and on the behaviour of the theory in regimes where the symmetry is not broken. |
1412.2567 | Sunandan Gangopadhyay | Sunandan Gangopadhyay, Anirban Saha, S. Mukherjee | Emergent Universe with particle production | Addition made in the Acknowledgement | Int. J. Theo. Phys. 55 (2016) 4445 | 10.1007/s10773-016-3067-y | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The possibility of an emergent universe solution to Einstein's field
equations allowing for an irreversible creation of matter at the expense of the
gravitational field is shown. With the universe being chosen as spatially flat
FRW spacetime together with equation of state proposed in [17], the solution
exists when the ratio of the phenomenological matter creation rate to the
number density times the Hubble parameter is a number $\beta$ of the order of
unity and independent of time. The thermodynamic behaviour is also determined
for this solution. Interestingly, we also find that an emergent universe
scenario is present with usual equation of state in cosmology when the matter
creation rate is chosen to be a constant. More general class of emergent
universe solutions are also discussed.
| [
{
"created": "Mon, 8 Dec 2014 14:02:14 GMT",
"version": "v1"
},
{
"created": "Sat, 24 Sep 2016 13:23:22 GMT",
"version": "v2"
}
] | 2016-09-27 | [
[
"Gangopadhyay",
"Sunandan",
""
],
[
"Saha",
"Anirban",
""
],
[
"Mukherjee",
"S.",
""
]
] | The possibility of an emergent universe solution to Einstein's field equations allowing for an irreversible creation of matter at the expense of the gravitational field is shown. With the universe being chosen as spatially flat FRW spacetime together with equation of state proposed in [17], the solution exists when the ratio of the phenomenological matter creation rate to the number density times the Hubble parameter is a number $\beta$ of the order of unity and independent of time. The thermodynamic behaviour is also determined for this solution. Interestingly, we also find that an emergent universe scenario is present with usual equation of state in cosmology when the matter creation rate is chosen to be a constant. More general class of emergent universe solutions are also discussed. |
gr-qc/9908069 | Leonard Parker | Leonard Parker and Alpan Raval | Vacuum-driven Metamorphosis | 4 pages, 1 figure, revtex | null | null | WISC-MILW-99-TH-11 | gr-qc astro-ph hep-th quant-ph | null | We show that nonperturbative vacuum effects can produce a vacuum-driven
transition from a matter-dominated universe to one in which the effective
equation of state is that of radiation plus cosmological constant. The actual
material content of the universe after the transition remains that of
non-relativistic matter. This metamorphosis of the equation of state can be
traced to nonperturbative vacuum effects that cause the scalar curvature to
remain nearly constant at a well-defined value after the transition, and is
responsible for the observed acceleration of the recent expansion of the
universe.
| [
{
"created": "Thu, 26 Aug 1999 17:29:27 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Parker",
"Leonard",
""
],
[
"Raval",
"Alpan",
""
]
] | We show that nonperturbative vacuum effects can produce a vacuum-driven transition from a matter-dominated universe to one in which the effective equation of state is that of radiation plus cosmological constant. The actual material content of the universe after the transition remains that of non-relativistic matter. This metamorphosis of the equation of state can be traced to nonperturbative vacuum effects that cause the scalar curvature to remain nearly constant at a well-defined value after the transition, and is responsible for the observed acceleration of the recent expansion of the universe. |
1207.2733 | Alfredo Sandoval-Villalbazo | A. Sandoval-Villalbazo, A. L. Garcia-Perciante and D.Brun-Battistini | Tolman's law in linear irreversible thermodynamics: a kinetic theory
approach | 9 pages, one figure | Phys. Rev. D 86, 084015 (2012) | 10.1103/PhysRevD.86.084015 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper it is shown that Tolman's law can be derived from relativistic
kinetic theory applied to a simple fluid in a BGK-like approximation. Using
this framework, it becomes clear that the contribution of the gravitational
field can be viewed as a cross effect that resembles the so-called
\emph{Thomson effect} in irreversible thermodynamics. A proper generalization
of Tolman's law in an inhomogeneous medium is formally established based on
these grounds.
| [
{
"created": "Tue, 10 Jul 2012 18:31:15 GMT",
"version": "v1"
}
] | 2012-10-08 | [
[
"Sandoval-Villalbazo",
"A.",
""
],
[
"Garcia-Perciante",
"A. L.",
""
],
[
"Brun-Battistini",
"D.",
""
]
] | In this paper it is shown that Tolman's law can be derived from relativistic kinetic theory applied to a simple fluid in a BGK-like approximation. Using this framework, it becomes clear that the contribution of the gravitational field can be viewed as a cross effect that resembles the so-called \emph{Thomson effect} in irreversible thermodynamics. A proper generalization of Tolman's law in an inhomogeneous medium is formally established based on these grounds. |
gr-qc/0612130 | Angela Di Virgilio dr | A. Di Virgilio, S. Bigotta, L. Barsotti, S. Braccini, C. Bradaschia,
G. Cella, V. Dattilo, M. Del Prete, I. Ferrante, F. Fidecaro, I. Fiori, F.
Frasconi, A. Gennai, A. Giazotto, P. La Penna, G.Losurdo, E. Majorana, M.
Mantovani, F. Paoletti, R. Passaquieti, D. Passuello, F. Piergiovanni, A.
Porzio, P. Puppo, F. Raffaelli, P. Rapagnani, F. Ricci, S. Solimeno, G.
Vajente, F. Vetrano | Displacement power spectrum measurement of a macroscopic optomechanical
system at thermal equilibrium | 11 pages, 9 figures, 2 tables, to be submitted | null | 10.1103/PhysRevD.76.122004 | null | gr-qc | null | The mirror relative motion of a suspended Fabry-Perot cavity is studied in
the frequency range 3-10 Hz. The experimental measurements presented in this
paper, have been performed at the Low Frequency Facility, a high finesse
optical cavity 1 cm long suspended to a mechanical seismic isolation system
identical to that one used in the VIRGO experiment. The measured relative
displacement power spectrum is compatible with a system at thermal equilibrium
within its environmental. In the frequency region above 3 Hz, where seismic
noise contamination is negligible, the measurement distribution is stationary
and Gaussian, as expected for a system at thermal equilibrium. Through a simple
mechanical model it is shown that: applying the fluctuation dissipation theorem
the measured power spectrum is reproduced below 90 Hz and noise induced by
external sources are below the measurement.
| [
{
"created": "Wed, 20 Dec 2006 18:12:49 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Dec 2006 08:10:43 GMT",
"version": "v2"
}
] | 2013-05-29 | [
[
"Di Virgilio",
"A.",
""
],
[
"Bigotta",
"S.",
""
],
[
"Barsotti",
"L.",
""
],
[
"Braccini",
"S.",
""
],
[
"Bradaschia",
"C.",
""
],
[
"Cella",
"G.",
""
],
[
"Dattilo",
"V.",
""
],
[
"Del Prete",
"M.",
""
],
[
"Ferrante",
"I.",
""
],
[
"Fidecaro",
"F.",
""
],
[
"Fiori",
"I.",
""
],
[
"Frasconi",
"F.",
""
],
[
"Gennai",
"A.",
""
],
[
"Giazotto",
"A.",
""
],
[
"La Penna",
"P.",
""
],
[
"Losurdo",
"G.",
""
],
[
"Majorana",
"E.",
""
],
[
"Mantovani",
"M.",
""
],
[
"Paoletti",
"F.",
""
],
[
"Passaquieti",
"R.",
""
],
[
"Passuello",
"D.",
""
],
[
"Piergiovanni",
"F.",
""
],
[
"Porzio",
"A.",
""
],
[
"Puppo",
"P.",
""
],
[
"Raffaelli",
"F.",
""
],
[
"Rapagnani",
"P.",
""
],
[
"Ricci",
"F.",
""
],
[
"Solimeno",
"S.",
""
],
[
"Vajente",
"G.",
""
],
[
"Vetrano",
"F.",
""
]
] | The mirror relative motion of a suspended Fabry-Perot cavity is studied in the frequency range 3-10 Hz. The experimental measurements presented in this paper, have been performed at the Low Frequency Facility, a high finesse optical cavity 1 cm long suspended to a mechanical seismic isolation system identical to that one used in the VIRGO experiment. The measured relative displacement power spectrum is compatible with a system at thermal equilibrium within its environmental. In the frequency region above 3 Hz, where seismic noise contamination is negligible, the measurement distribution is stationary and Gaussian, as expected for a system at thermal equilibrium. Through a simple mechanical model it is shown that: applying the fluctuation dissipation theorem the measured power spectrum is reproduced below 90 Hz and noise induced by external sources are below the measurement. |
gr-qc/9807038 | Tomohiro Harada | Tomohiro Harada | Final fate of the spherically symmetric collapse of a perfect fluid | 17 pages, including 21 ps figures. Accepted for publication in
Physical Review D, Typos corrected, References updated | Phys.Rev. D58 (1998) 104015 | 10.1103/PhysRevD.58.104015 | KUNS-1518 | gr-qc astro-ph | null | The final fate of the spherically symmetric collapse of a perfect fluid which
follows the $\gamma$-law equation of state and adiabatic condition is
investigated. Full general relativistic hydrodynamics is solved numerically
using a retarded time coordinate, the so-called observer time coordinate.
Thanks to this coordinate, the causal structure of the resultant space-time is
automatically constructed. Then, it is found that a globally naked,
shell-focusing singularity can occur at the center from relativistically
high-density, isentropic and time symmetric initial data if $\gamma \alt 1.01$
within the numerical accuracy. The result is free from the assumption of
self-similarity. The upper limit of $\gamma$ with which a naked singularity can
occur from generic initial data is consistent with the result of Ori and Piran
based on the assumption of self-similarity.
| [
{
"created": "Thu, 16 Jul 1998 05:29:48 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Sep 1998 07:53:40 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Harada",
"Tomohiro",
""
]
] | The final fate of the spherically symmetric collapse of a perfect fluid which follows the $\gamma$-law equation of state and adiabatic condition is investigated. Full general relativistic hydrodynamics is solved numerically using a retarded time coordinate, the so-called observer time coordinate. Thanks to this coordinate, the causal structure of the resultant space-time is automatically constructed. Then, it is found that a globally naked, shell-focusing singularity can occur at the center from relativistically high-density, isentropic and time symmetric initial data if $\gamma \alt 1.01$ within the numerical accuracy. The result is free from the assumption of self-similarity. The upper limit of $\gamma$ with which a naked singularity can occur from generic initial data is consistent with the result of Ori and Piran based on the assumption of self-similarity. |
1412.5045 | Roberto Chan | O. Goldoni, M.F.A. da Silva, R. Chan and G. Pinheiro | Vaidya Solution in General Covariant Ho\v{r}ava-Lifshitz Gravity with
the Minimum Coupling and without Projectability: Infrared Limit | 11 pages. Accepted for publication in IJMPD | International Journal Modern Physics D 245, 21 (2015) | 10.1142/S0218271815500212 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we have studied nonstationary radiative spherically symmetric
spacetime, in general covariant theory ($U(1)$ extension) of {the}
Ho\v{r}ava-Lifshitz gravity with the minimum coupling, in the post-newtonian
approximation (PPN), without the projectability condition and in the infrared
limit. The Newtonian prepotential $\varphi$ was assumed null. We have shown
that there is not the analogue of the Vaidya's solution in the
Ho\v{r}ava-Lifshitz Theory (HLT) with the minimum coupling, as we know in the
General Relativity Theory (GRT).
| [
{
"created": "Tue, 16 Dec 2014 15:30:37 GMT",
"version": "v1"
}
] | 2016-02-09 | [
[
"Goldoni",
"O.",
""
],
[
"da Silva",
"M. F. A.",
""
],
[
"Chan",
"R.",
""
],
[
"Pinheiro",
"G.",
""
]
] | In this paper, we have studied nonstationary radiative spherically symmetric spacetime, in general covariant theory ($U(1)$ extension) of {the} Ho\v{r}ava-Lifshitz gravity with the minimum coupling, in the post-newtonian approximation (PPN), without the projectability condition and in the infrared limit. The Newtonian prepotential $\varphi$ was assumed null. We have shown that there is not the analogue of the Vaidya's solution in the Ho\v{r}ava-Lifshitz Theory (HLT) with the minimum coupling, as we know in the General Relativity Theory (GRT). |
1803.10770 | Antonio Candido de Siqueira V. V. | A.C.V.V. de Siqueira | Topics in Non-Riemannian Geometry | 11 pages, no figures, last version | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we present some new results on non-Riemannian geometry, more
specifically, asymmetric connections and Weyl's geometry. For asymmetric
connections, we show that a projective change in the symmetric part generates a
vector field that its not arbitrary, as usually presented, but rather, the
gradient of a non-arbitrary scalar function. We use normal coordinates for the
symmetric part of asymmetric connections as well as for the Weyl's geometry.
This has a direct impact on asymmetric conections, although normal frames are
usual in antisymmetic connections, unlike normal coordinates. In this symmetric
part of asymmetric connections, the vector fields obeys a well-known partial
differential equantion, whereas in Weyl's geometry, gauge vector fields obey an
equation that we believe is presented for the first time in this paper. We
deduce the exact solution of each of these vector fields as the gradient of a
scalar function. For both asymmetric and Weyl's symmetric connections, the
respective scalar functions obey respective scalar partial differential
equations. As a consequence, Weyl's geometry is a conformal differential
geometry and is associated with asymmetric geometry by a projective change. We
also show that a metric tensor naturally appears in asymmetric geometry and is
not introduced via a postulate, as is usually done. In Weyl's geometry, the
eletromagnetic gauge is the gradient of a non-arbitrary scalar function and
eletromagnetic fields are null. Despide the origin in Weyl's differential
geometry, the use of the eletromagnetic gauge is correct in Lagrangean and
Hamiltonian formulations of field theories.
| [
{
"created": "Wed, 28 Mar 2018 15:02:04 GMT",
"version": "v1"
},
{
"created": "Sat, 31 Mar 2018 14:06:56 GMT",
"version": "v2"
}
] | 2018-04-03 | [
[
"de Siqueira",
"A. C. V. V.",
""
]
] | In this paper, we present some new results on non-Riemannian geometry, more specifically, asymmetric connections and Weyl's geometry. For asymmetric connections, we show that a projective change in the symmetric part generates a vector field that its not arbitrary, as usually presented, but rather, the gradient of a non-arbitrary scalar function. We use normal coordinates for the symmetric part of asymmetric connections as well as for the Weyl's geometry. This has a direct impact on asymmetric conections, although normal frames are usual in antisymmetic connections, unlike normal coordinates. In this symmetric part of asymmetric connections, the vector fields obeys a well-known partial differential equantion, whereas in Weyl's geometry, gauge vector fields obey an equation that we believe is presented for the first time in this paper. We deduce the exact solution of each of these vector fields as the gradient of a scalar function. For both asymmetric and Weyl's symmetric connections, the respective scalar functions obey respective scalar partial differential equations. As a consequence, Weyl's geometry is a conformal differential geometry and is associated with asymmetric geometry by a projective change. We also show that a metric tensor naturally appears in asymmetric geometry and is not introduced via a postulate, as is usually done. In Weyl's geometry, the eletromagnetic gauge is the gradient of a non-arbitrary scalar function and eletromagnetic fields are null. Despide the origin in Weyl's differential geometry, the use of the eletromagnetic gauge is correct in Lagrangean and Hamiltonian formulations of field theories. |
1303.2436 | \"Ozcan Sert | \"Ozcan Sert | Electromagnetic Duality and New Solutions of the Non-minimally Coupled
Y(R)-Maxwell Gravity | 10 pages, accepted for publication in MPLA | Mod. Phys. Lett. A 2013 | 10.1142/S0217732313500491 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Non-minimally coupled Y(R)-Maxwell gravity which have some interesting
solutions may be used to understand dark matter, dark energy, the origin of
cosmic magnetic field and the evaluation of the universe. We give some new
solutions to the model such as spherically symmetric electric, magnetic and
dyon solutions. We point out an existence of an electromagnetic duality
transformation for the model.
| [
{
"created": "Mon, 11 Mar 2013 06:29:53 GMT",
"version": "v1"
}
] | 2013-04-09 | [
[
"Sert",
"Özcan",
""
]
] | Non-minimally coupled Y(R)-Maxwell gravity which have some interesting solutions may be used to understand dark matter, dark energy, the origin of cosmic magnetic field and the evaluation of the universe. We give some new solutions to the model such as spherically symmetric electric, magnetic and dyon solutions. We point out an existence of an electromagnetic duality transformation for the model. |
1909.03055 | Sergio Servidio | C. Meringolo, S. Servidio, P. Veltri | A spectral approach to numerical simulations of the ADM equations | arXiv admin note: text overlap with arXiv:gr-qc/0305023 by other
authors | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a numerical study of the Einstein equations, according to the
Arnowitt-Deser-Misner (ADM) formalism, in order to simulate the dynamics of
gravitational fields. We took in consideration the original $3+1$ decomposition
of the ADM equations, in vacuum conditions, in simplified geometries. The
numerical code is based on spectral methods, making use of filtering
(de-aliasing) techniques. The algorithm has been stabilized via an adaptive
time-refinement, based on a procedure that checks self-consistently the
regularity of the solutions. The accuracy of our numerical model has been
validated through a series of standard tests. Finally, we present also a new
kind of initial data that can be used for testing numerical codes.
| [
{
"created": "Fri, 6 Sep 2019 11:43:33 GMT",
"version": "v1"
}
] | 2019-09-10 | [
[
"Meringolo",
"C.",
""
],
[
"Servidio",
"S.",
""
],
[
"Veltri",
"P.",
""
]
] | We present a numerical study of the Einstein equations, according to the Arnowitt-Deser-Misner (ADM) formalism, in order to simulate the dynamics of gravitational fields. We took in consideration the original $3+1$ decomposition of the ADM equations, in vacuum conditions, in simplified geometries. The numerical code is based on spectral methods, making use of filtering (de-aliasing) techniques. The algorithm has been stabilized via an adaptive time-refinement, based on a procedure that checks self-consistently the regularity of the solutions. The accuracy of our numerical model has been validated through a series of standard tests. Finally, we present also a new kind of initial data that can be used for testing numerical codes. |
1809.00844 | Daniela Doneva | Daniela D. Doneva, Stella Kiorpelidi, Petya G. Nedkova, Eleftherios
Papantonopoulos, Stoytcho S. Yazadjiev | Charged Gauss-Bonnet black holes with curvature induced scalarization in
the extended scalar-tensor theories | 20 pages, 7 figures | Phys. Rev. D 98, 104056 (2018) | 10.1103/PhysRevD.98.104056 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently new scalarized black hole solutions were constructed in the extended
scalar-tensor-Gauss-Bonnet gravity, where the scalar field is sourced by the
curvature of the spacetime via the Gauss-Bonnet invariant. A natural extension
of these results is to consider the case of nonzero black hole charge. In
addition we have explored a large set of coupling functions between the
Gauss-Bonnet invariant and the scalar field, that was not done until now even
in the uncharged case, in order to understand better the behavior of the
solutions and the deviations from pure general relativity. The results show
that in the case of nonzero black hole charge two bifurcation points can exist
- one at larger masses where the scalarized solutions bifurcated from the
Reissner-Nordstrom one, and one at smaller masses where the scalar charge of
the solutions decreases again to zero and the branch merges again with the GR
one. All of the constructed scalarized branches do not reach an extremal limit.
We have examined the entropy of the black holes with nontrivial scalar field
and it turns out, that similar to the uncharged case, the fundamental branch
which possesses scalar field with no nodes is thermodynamically favorable over
the Reissner-Nordstrom one for the considered coupling functions, while the
rest of the branches possessing scalar field with one or more zeros have lower
entropy compared to the GR case and they are supposed to be unstable.
| [
{
"created": "Tue, 4 Sep 2018 08:57:54 GMT",
"version": "v1"
}
] | 2018-12-05 | [
[
"Doneva",
"Daniela D.",
""
],
[
"Kiorpelidi",
"Stella",
""
],
[
"Nedkova",
"Petya G.",
""
],
[
"Papantonopoulos",
"Eleftherios",
""
],
[
"Yazadjiev",
"Stoytcho S.",
""
]
] | Recently new scalarized black hole solutions were constructed in the extended scalar-tensor-Gauss-Bonnet gravity, where the scalar field is sourced by the curvature of the spacetime via the Gauss-Bonnet invariant. A natural extension of these results is to consider the case of nonzero black hole charge. In addition we have explored a large set of coupling functions between the Gauss-Bonnet invariant and the scalar field, that was not done until now even in the uncharged case, in order to understand better the behavior of the solutions and the deviations from pure general relativity. The results show that in the case of nonzero black hole charge two bifurcation points can exist - one at larger masses where the scalarized solutions bifurcated from the Reissner-Nordstrom one, and one at smaller masses where the scalar charge of the solutions decreases again to zero and the branch merges again with the GR one. All of the constructed scalarized branches do not reach an extremal limit. We have examined the entropy of the black holes with nontrivial scalar field and it turns out, that similar to the uncharged case, the fundamental branch which possesses scalar field with no nodes is thermodynamically favorable over the Reissner-Nordstrom one for the considered coupling functions, while the rest of the branches possessing scalar field with one or more zeros have lower entropy compared to the GR case and they are supposed to be unstable. |
2408.04004 | Anna Tokareva | Andrea Addazi, Alexey S. Koshelev, Shi Pi, Anna Tokareva | Secondary Gravitational Waves in Non-local Starobinsky inflation | 17 pages, 3 figures | null | null | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/publicdomain/zero/1.0/ | We show how infinite derivative modifications of gravity impact on the
stochastic background of Gravitational Waves from early Universe. The generic
property of the ghost-free theory fixed on Minkowski space-time is the
emergence of an infinite number of complex mass states when other classical
backgrounds are considered. These additional states are shown to enhance the
power spectrum of scalar perturbations generated during inflation. Current and
future space-based and terrestrial interferometers offer indirect testing
methods for the infinite derivative gravity action, enabling the exploration of
new parameter spaces. In particular, we identify unconventional blue-tilted
Gravitational Wave spectra, presenting a novel approach for testing infinite
derivative quantum gravity in the future.
| [
{
"created": "Wed, 7 Aug 2024 18:00:06 GMT",
"version": "v1"
}
] | 2024-08-09 | [
[
"Addazi",
"Andrea",
""
],
[
"Koshelev",
"Alexey S.",
""
],
[
"Pi",
"Shi",
""
],
[
"Tokareva",
"Anna",
""
]
] | We show how infinite derivative modifications of gravity impact on the stochastic background of Gravitational Waves from early Universe. The generic property of the ghost-free theory fixed on Minkowski space-time is the emergence of an infinite number of complex mass states when other classical backgrounds are considered. These additional states are shown to enhance the power spectrum of scalar perturbations generated during inflation. Current and future space-based and terrestrial interferometers offer indirect testing methods for the infinite derivative gravity action, enabling the exploration of new parameter spaces. In particular, we identify unconventional blue-tilted Gravitational Wave spectra, presenting a novel approach for testing infinite derivative quantum gravity in the future. |
0811.0012 | David Kubiznak | David Kubiznak, Valeri P. Frolov, Pavel Krtous, Patrick Connell | Parallel-propagated frame along null geodesics in higher-dimensional
black hole spacetimes | 17 pages, no figures | Phys.Rev.D79:024018,2009 | 10.1103/PhysRevD.79.024018 | Alberta-Thy-08-08, DAMTP-2008-97 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In [arXiv:0803.3259] the equations describing the parallel transport of
orthonormal frames along timelike (spacelike) geodesics in a spacetime
admitting a non-degenerate principal conformal Killing-Yano 2-form h were
solved. The construction employed is based on studying the Darboux subspaces of
the 2-form F obtained as a projection of h along the geodesic trajectory. In
this paper we demonstrate that, although slightly modified, a similar
construction is possible also in the case of null geodesics. In particular, we
explicitly construct the parallel-transported frames along null geodesics in
D=4,5,6 Kerr-NUT-(A)dS spacetimes. We further discuss the parallel transport
along principal null directions in these spacetimes. Such directions coincide
with the eigenvectors of the principal conformal Killing-Yano tensor. Finally,
we show how to obtain a parallel-transported frame along null geodesics in the
background of the 4D Plebanski-Demianski metric which admits only a conformal
generalization of the Killing-Yano tensor.
| [
{
"created": "Fri, 31 Oct 2008 20:46:04 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Kubiznak",
"David",
""
],
[
"Frolov",
"Valeri P.",
""
],
[
"Krtous",
"Pavel",
""
],
[
"Connell",
"Patrick",
""
]
] | In [arXiv:0803.3259] the equations describing the parallel transport of orthonormal frames along timelike (spacelike) geodesics in a spacetime admitting a non-degenerate principal conformal Killing-Yano 2-form h were solved. The construction employed is based on studying the Darboux subspaces of the 2-form F obtained as a projection of h along the geodesic trajectory. In this paper we demonstrate that, although slightly modified, a similar construction is possible also in the case of null geodesics. In particular, we explicitly construct the parallel-transported frames along null geodesics in D=4,5,6 Kerr-NUT-(A)dS spacetimes. We further discuss the parallel transport along principal null directions in these spacetimes. Such directions coincide with the eigenvectors of the principal conformal Killing-Yano tensor. Finally, we show how to obtain a parallel-transported frame along null geodesics in the background of the 4D Plebanski-Demianski metric which admits only a conformal generalization of the Killing-Yano tensor. |
2106.02057 | Merced Montesinos | Merced Montesinos, Ricardo Escobedo, Mariano Celada | Straightforward Hamiltonian analysis of $BF$ gravity in $n$ dimensions | It matches published version. arXiv admin note: text overlap with
arXiv:2010.14526 | Gen. Relativ. Gravit. 53, 52 (2021) | 10.1007/s10714-021-02821-3 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We perform, in a manifestly $SO(n-1,1)$ [$SO(n)$] covariant fashion, the
Hamiltonian analysis of general relativity in $n$ dimensions written as a
constrained $BF$ theory. We solve the constraint on the $B$ field in a way
naturally adapted to the foliation of the spacetime that avoids explicitly the
introduction of the vielbein. This leads to a form of the action involving a
presymplectic structure, which is reduced by doing a suitable parametrization
of the connection and then, after integrating out some auxiliary fields, the
Hamiltonian form involving only first-class constraints is obtained.
| [
{
"created": "Thu, 3 Jun 2021 18:00:22 GMT",
"version": "v1"
}
] | 2021-06-07 | [
[
"Montesinos",
"Merced",
""
],
[
"Escobedo",
"Ricardo",
""
],
[
"Celada",
"Mariano",
""
]
] | We perform, in a manifestly $SO(n-1,1)$ [$SO(n)$] covariant fashion, the Hamiltonian analysis of general relativity in $n$ dimensions written as a constrained $BF$ theory. We solve the constraint on the $B$ field in a way naturally adapted to the foliation of the spacetime that avoids explicitly the introduction of the vielbein. This leads to a form of the action involving a presymplectic structure, which is reduced by doing a suitable parametrization of the connection and then, after integrating out some auxiliary fields, the Hamiltonian form involving only first-class constraints is obtained. |
2108.08206 | Farhad Darabi | F. Gholami, F. Darabi, and A. Haji Badali | On Einstein equations with cosmological constant in braneworld models | 7 pages | Indian. J. Phys (2021) | 10.1007/s12648-020-01995-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we investigate the Einstein equations with cosmological
constant for Randall-Sundrum (RS) and Dvali-Gabadadze-Porrati (DGP) models to
determine the warp functions in the context of warp product spacetimes. In RS
model, it is shown that Einstein's equation in the bulk is reduced into the
brane as a vacuum equation, having vacuum solution, which is not affected by
the cosmological constant in the bulk. In DGP model, it is shown that the
Einstein's equation in the bulk is reduced into the brane and along the extra
dimension, where both equations are affected by the cosmological constant in
the bulk. We have solved these equations in DGP model, subject to vanishing
cosmological constants on the brane and along extra dimension, and obtained
exact solutions for the warp functions. The solutions depend on the typical
values of cosmological constant in the bulk as well as the dimension of the
brane. So, corresponding to the typical values, some solutions have exponential
behaviours which may be set to represent warp inflation on the brane, and some
other solutions have oscillating behaviours which may be set to represent warp
waves or branes waves along the extra dimension.
| [
{
"created": "Tue, 17 Aug 2021 12:16:30 GMT",
"version": "v1"
}
] | 2021-08-19 | [
[
"Gholami",
"F.",
""
],
[
"Darabi",
"F.",
""
],
[
"Badali",
"A. Haji",
""
]
] | In this paper, we investigate the Einstein equations with cosmological constant for Randall-Sundrum (RS) and Dvali-Gabadadze-Porrati (DGP) models to determine the warp functions in the context of warp product spacetimes. In RS model, it is shown that Einstein's equation in the bulk is reduced into the brane as a vacuum equation, having vacuum solution, which is not affected by the cosmological constant in the bulk. In DGP model, it is shown that the Einstein's equation in the bulk is reduced into the brane and along the extra dimension, where both equations are affected by the cosmological constant in the bulk. We have solved these equations in DGP model, subject to vanishing cosmological constants on the brane and along extra dimension, and obtained exact solutions for the warp functions. The solutions depend on the typical values of cosmological constant in the bulk as well as the dimension of the brane. So, corresponding to the typical values, some solutions have exponential behaviours which may be set to represent warp inflation on the brane, and some other solutions have oscillating behaviours which may be set to represent warp waves or branes waves along the extra dimension. |
gr-qc/0203033 | Martin Tajmar | M. Tajmar, C.J. de Matos | Gravitomagnetic Field of a Rotating Superconductor and of a Rotating
Superfluid | null | Physica C385:551-554,2003 | 10.1016/S0921-4534(02)02305-5 | null | gr-qc | null | The quantization of the extended canonical momentum in quantum materials
including the effects of gravitational drag is applied successively to the case
of a multiply connected rotating superconductor and superfluid. Experiments
carried out on rotating superconductors, based on the quantization of the
magnetic flux in rotating superconductors, lead to a disagreement with the
theoretical predictions derived from the quantization of a canonical momentum
without any gravitomagnetic term. To what extent can these discrepancies be
attributed to the additional gravitomagnetic term of the extended canonical
momentum? This is an open and important question. For the case of multiply
connected rotating neutral superfluids, gravitational drag effects derived from
rotating superconductor data appear to be hidden in the noise of present
experiments according to a first rough analysis.
| [
{
"created": "Mon, 11 Mar 2002 13:36:20 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Tajmar",
"M.",
""
],
[
"de Matos",
"C. J.",
""
]
] | The quantization of the extended canonical momentum in quantum materials including the effects of gravitational drag is applied successively to the case of a multiply connected rotating superconductor and superfluid. Experiments carried out on rotating superconductors, based on the quantization of the magnetic flux in rotating superconductors, lead to a disagreement with the theoretical predictions derived from the quantization of a canonical momentum without any gravitomagnetic term. To what extent can these discrepancies be attributed to the additional gravitomagnetic term of the extended canonical momentum? This is an open and important question. For the case of multiply connected rotating neutral superfluids, gravitational drag effects derived from rotating superconductor data appear to be hidden in the noise of present experiments according to a first rough analysis. |
1408.0516 | Fatemeh Bagheri | Fatemeh Bagheri, Reza Mansouri | The symmetry of the energy momentum tensor does not necessarily reflect
the space-time symmetry: a viscous axially symmetric cosmological solution | 9 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Applying the method of conformal metric to a given static axially symmetric
vacuum solution of the Einstein equations, we have shown that there is no
solution representing a cosmic ideal fluid which is asymtotically FLRW. Letting
the cosmic fluid to be imperfect there are axially symmetric solutions tending
to FLRW at space infinity. The solution we have found represents an axially
symmetric spacetime leading to a spherically symmetric Einstein tensor.
Therefore, we have found a solution of Einstein equations representing a
spherically symmetric matter distribution corresponding to a spacetime which
does not reflect the same symmetry. We have also found another solution of
Einstein equation corresponding to the same energy tensor with spherical
symmetry.
| [
{
"created": "Sun, 3 Aug 2014 17:21:18 GMT",
"version": "v1"
},
{
"created": "Thu, 5 Sep 2019 18:02:47 GMT",
"version": "v2"
}
] | 2019-09-09 | [
[
"Bagheri",
"Fatemeh",
""
],
[
"Mansouri",
"Reza",
""
]
] | Applying the method of conformal metric to a given static axially symmetric vacuum solution of the Einstein equations, we have shown that there is no solution representing a cosmic ideal fluid which is asymtotically FLRW. Letting the cosmic fluid to be imperfect there are axially symmetric solutions tending to FLRW at space infinity. The solution we have found represents an axially symmetric spacetime leading to a spherically symmetric Einstein tensor. Therefore, we have found a solution of Einstein equations representing a spherically symmetric matter distribution corresponding to a spacetime which does not reflect the same symmetry. We have also found another solution of Einstein equation corresponding to the same energy tensor with spherical symmetry. |
gr-qc/0412083 | Tatyana P. Shestakova | T. P. Shestakova | The prospects for extended phase space approach to quantization of
gravity | 11 pages, talk presented at the VI International Conference on
cosmoparticle physics "Cosmion-2004", September 2004 | Grav.Cosmol. 11 (2005) 183-188 | null | null | gr-qc | null | A brief review of main features of the new approach named ``quantum
geometrodynamics in extended phase space'' is given and its possible prospects
are discussed. Gauge degrees of freedom are treated as a subsystem of the
Universe which affects the evolution of the physical subsystem. Three points
can be singled out when the gauge subsystem shows itself as a real constituent
of the Universe: a chosen gauge condition determines the form of equation for
the physical part of wave function, the form of density matrix and the measure
in physical subspace. An example is considered when a physically relevant
choice of gauge condition leads to almost diagonal density matrix. The analogy
between a transition to another reference frame (another basis in physical
subspace) and a transition to accelerating reference frame in Rindler space is
suggested.
| [
{
"created": "Fri, 17 Dec 2004 12:26:31 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Shestakova",
"T. P.",
""
]
] | A brief review of main features of the new approach named ``quantum geometrodynamics in extended phase space'' is given and its possible prospects are discussed. Gauge degrees of freedom are treated as a subsystem of the Universe which affects the evolution of the physical subsystem. Three points can be singled out when the gauge subsystem shows itself as a real constituent of the Universe: a chosen gauge condition determines the form of equation for the physical part of wave function, the form of density matrix and the measure in physical subspace. An example is considered when a physically relevant choice of gauge condition leads to almost diagonal density matrix. The analogy between a transition to another reference frame (another basis in physical subspace) and a transition to accelerating reference frame in Rindler space is suggested. |
1303.2243 | Roldao da Rocha | D. Bazeia, J. M. Hoff da SIlva, Roldao da Rocha | Black holes in realistic branes: black string-like objects? | 7 pages, 6 figures, to appear in Phys. Lett. B | Phys. Lett. B 721 (2013) 306 | 10.1016/j.physletb.2013.03.010 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A realistic model describing a black string-like object in an expanding
Universe is analyzed in the context of the McVittie's solution of the Einstein
field equations. The bulk metric near the brane is provided analogously to
previous solutions for black strings. In particular, we show that at least when
the Hubble parameter on the brane is positive, a black string-like object seems
to play a fundamental role in the braneworld scenario, generalizing the
standard black strings in the context of a dynamical brane.
| [
{
"created": "Sat, 9 Mar 2013 17:54:54 GMT",
"version": "v1"
}
] | 2013-04-12 | [
[
"Bazeia",
"D.",
""
],
[
"da SIlva",
"J. M. Hoff",
""
],
[
"da Rocha",
"Roldao",
""
]
] | A realistic model describing a black string-like object in an expanding Universe is analyzed in the context of the McVittie's solution of the Einstein field equations. The bulk metric near the brane is provided analogously to previous solutions for black strings. In particular, we show that at least when the Hubble parameter on the brane is positive, a black string-like object seems to play a fundamental role in the braneworld scenario, generalizing the standard black strings in the context of a dynamical brane. |
gr-qc/9402024 | null | Edward Malec (Physics Department, UCC, Cork, Ireland and Institute of
Physics, UJ 30-059 Cracow, Reymonta) | Event horizons and apparent horizons in spherically symmetric geometries | 4, Poland July 1993, 24 pages, latex | Phys.Rev.D49:6475-6483,1994 | 10.1103/PhysRevD.49.6475 | null | gr-qc | null | Spherical configurations that are very massive must be surrounded by apparent
horizons. These in turn, when placed outside a collapsing body, have a fixed
area and must propagate outward with a velocity equal to the velocity of
radially outgoing photons. That proves, within the framework of the (1+3)
formalism and without resorting to the Birkhoff theorem, that apparent horizons
coincide with event horizons in electrovacuum.
| [
{
"created": "Fri, 11 Feb 1994 11:30:43 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Malec",
"Edward",
"",
"Physics Department, UCC, Cork, Ireland and Institute of\n Physics, UJ 30-059 Cracow, Reymonta"
]
] | Spherical configurations that are very massive must be surrounded by apparent horizons. These in turn, when placed outside a collapsing body, have a fixed area and must propagate outward with a velocity equal to the velocity of radially outgoing photons. That proves, within the framework of the (1+3) formalism and without resorting to the Birkhoff theorem, that apparent horizons coincide with event horizons in electrovacuum. |
1803.06640 | Dheeraj Kumar Mishra | Dheeraj Kumar Mishra and Nitin Chandra | Invariant ultraviolet scale corrections to the thermodynamics of
degenerate Fermi gas and its implications | 35 pages, 7 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the invariant Planck scale correction to the thermodynamics of the
ideal Fermi gas. We have considered the modified dispersion relation and the
cut-off to the maximum possible momentum/energy (Planck energy) of the
non-interacting ideal degenerate Fermi gas particles. With such a modification
the expression for the degenerate pressure and the total energy gets modified
accordingly. We discuss the number density and mass dependence of the
degenerate pressure. We found that the degenerate pressure is perturbative in
the SR limit. We then take the example of white dwarfs to explore the possible
implications. Using this modified degenerate pressure, we calculate the
possible modification to the Chandrashekhar limit for white dwarfs using the
Magueijo-Smolin (MS) modified dispersion relation. The mass-radius M-R plot
shows that the modified/corrected radius of the white dwarf can be greater
than, equal to and smaller than the usual special relativity (SR) value for
particular masses. We found that the Chandrasekhar mass limit gets a positive
correction. We note that the presence of observed white dwarfs having radius
smaller than the SR Chandrasekhar limit may find an explanation if they are
modeled using a modified dispersion relation. As the correction is perturbative
in the SR limit, therefore this correction is solely because of the modified
dispersion relation. The value of the obtained degenerate pressure for a given
mass is found to be greater than, equal to and smaller than the usual special
relativity (SR) value for particular masses as expected. We have also
calculated the luminosity of the white dwarf by taking the model of partially
degenerate gas and considering the modified radiative envelope equation. The
luminosity also gets a negative correction. The correction to luminosity is
nonperturbative as expected for such a theory.
| [
{
"created": "Sun, 18 Mar 2018 10:52:36 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Jul 2019 11:43:25 GMT",
"version": "v2"
}
] | 2019-07-10 | [
[
"Mishra",
"Dheeraj Kumar",
""
],
[
"Chandra",
"Nitin",
""
]
] | We study the invariant Planck scale correction to the thermodynamics of the ideal Fermi gas. We have considered the modified dispersion relation and the cut-off to the maximum possible momentum/energy (Planck energy) of the non-interacting ideal degenerate Fermi gas particles. With such a modification the expression for the degenerate pressure and the total energy gets modified accordingly. We discuss the number density and mass dependence of the degenerate pressure. We found that the degenerate pressure is perturbative in the SR limit. We then take the example of white dwarfs to explore the possible implications. Using this modified degenerate pressure, we calculate the possible modification to the Chandrashekhar limit for white dwarfs using the Magueijo-Smolin (MS) modified dispersion relation. The mass-radius M-R plot shows that the modified/corrected radius of the white dwarf can be greater than, equal to and smaller than the usual special relativity (SR) value for particular masses. We found that the Chandrasekhar mass limit gets a positive correction. We note that the presence of observed white dwarfs having radius smaller than the SR Chandrasekhar limit may find an explanation if they are modeled using a modified dispersion relation. As the correction is perturbative in the SR limit, therefore this correction is solely because of the modified dispersion relation. The value of the obtained degenerate pressure for a given mass is found to be greater than, equal to and smaller than the usual special relativity (SR) value for particular masses as expected. We have also calculated the luminosity of the white dwarf by taking the model of partially degenerate gas and considering the modified radiative envelope equation. The luminosity also gets a negative correction. The correction to luminosity is nonperturbative as expected for such a theory. |
2110.00648 | James Read | Niels Linnemann and James Read | Comment on `Do electromagnetic waves always propagate along null
geodesics?' | Forthcoming in Classical and Quantum Gravity. Title different but
otherwise unaltered from previous version | null | 10.1088/1361-6382/ac2c19 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study the propagation of Maxwellian electromagnetic waves in curved
spacetimes in terms of the appropriate geometrical optics limit, notions of
signal speed, and minimal coupling prescription from Maxwellian theory in flat
spacetime. In the course of this, we counter a recent major claim by Asenjo and
Hojman (2017) to the effect that the geometrical optics limit is partly
ill-defined in G\"odel spacetime; we thereby dissolve the present tension
concerning established results on wave propagation and the optical limit.
| [
{
"created": "Fri, 1 Oct 2021 20:54:27 GMT",
"version": "v1"
},
{
"created": "Sat, 11 Dec 2021 07:47:40 GMT",
"version": "v2"
}
] | 2021-12-22 | [
[
"Linnemann",
"Niels",
""
],
[
"Read",
"James",
""
]
] | We study the propagation of Maxwellian electromagnetic waves in curved spacetimes in terms of the appropriate geometrical optics limit, notions of signal speed, and minimal coupling prescription from Maxwellian theory in flat spacetime. In the course of this, we counter a recent major claim by Asenjo and Hojman (2017) to the effect that the geometrical optics limit is partly ill-defined in G\"odel spacetime; we thereby dissolve the present tension concerning established results on wave propagation and the optical limit. |
gr-qc/9906003 | Yee J. Ng | Y. Jack Ng and H. van Dam (University of North Carolina) | Measuring the foaminess of space-time with gravity-wave interferometers | 15 pages, TeX, A simple connection to the holographic principle is
added, minor changes in the text and abstract, and some changes in the
References; this new version will appear in the third "Haller" issue in
Foundations of Physics | Found.Phys.30:795-805,2000 | 10.1023/A:1003745212871 | null | gr-qc astro-ph hep-ph hep-th quant-ph | null | By analyzing a gedanken experiment designed to measure the distance $l$
between two spatially separated points, we find that this distance cannot be
measured with uncertainty less than $(ll_P^2)^{1/3}$, considerably larger than
the Planck scale $l_P$ (or the string scale in string theories), the
conventional wisdom uncertainty in distance measurements. This limitation to
space-time measurements is interpreted as resulting from quantum fluctuations
of space-time itself. Thus, at very short distance scales, space-time is
"foamy." This intrinsic foaminess of space-time provides another source of
noise in the interferometers. The LIGO/VIRGO and LISA generations of
gravity-wave interferometers, through future refinements, are expected to reach
displacement noise levels low enough to test our proposed degree of foaminess
in the structure of space-time. We also point out a simple connection to the
holographic principle which asserts that the number of degrees of freedom of a
region of space is bounded by the area of the region in Planck units.
| [
{
"created": "Tue, 1 Jun 1999 18:57:20 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Mar 2000 19:07:12 GMT",
"version": "v2"
}
] | 2011-07-19 | [
[
"Ng",
"Y. Jack",
"",
"University of North Carolina"
],
[
"van Dam",
"H.",
"",
"University of North Carolina"
]
] | By analyzing a gedanken experiment designed to measure the distance $l$ between two spatially separated points, we find that this distance cannot be measured with uncertainty less than $(ll_P^2)^{1/3}$, considerably larger than the Planck scale $l_P$ (or the string scale in string theories), the conventional wisdom uncertainty in distance measurements. This limitation to space-time measurements is interpreted as resulting from quantum fluctuations of space-time itself. Thus, at very short distance scales, space-time is "foamy." This intrinsic foaminess of space-time provides another source of noise in the interferometers. The LIGO/VIRGO and LISA generations of gravity-wave interferometers, through future refinements, are expected to reach displacement noise levels low enough to test our proposed degree of foaminess in the structure of space-time. We also point out a simple connection to the holographic principle which asserts that the number of degrees of freedom of a region of space is bounded by the area of the region in Planck units. |
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