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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1412.6729 | Sunil Maharaj | G. Abebe, K. S. Govinder, S. D. Maharaj | Lie symmetries for a conformally flat radiating star | 12 pages, submitted for publication | Int. J. Theor. Phys. 52: 3244-3254 (2013) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a relativistic radiating spherical star in conformally flat
spacetimes. In particular we study the junction condition relating the radial
pressure to the heat flux at the boundary of the star which is a nonlinear
partial differential equation. The Lie symmetry generators that leave the
equation invariant are identified and we generate an optimal system. Each
element of the optimal system is used to reduce the partial differential
equation to an ordinary differential equation which is further analysed. We
identify new categories of exact solutions to the boundary conditions. Two
classes of solutions are of interest. The first class depends on a self similar
variable. The second class is separable in the spacetime variables.
| [
{
"created": "Sun, 21 Dec 2014 06:13:25 GMT",
"version": "v1"
}
] | 2014-12-23 | [
[
"Abebe",
"G.",
""
],
[
"Govinder",
"K. S.",
""
],
[
"Maharaj",
"S. D.",
""
]
] | We consider a relativistic radiating spherical star in conformally flat spacetimes. In particular we study the junction condition relating the radial pressure to the heat flux at the boundary of the star which is a nonlinear partial differential equation. The Lie symmetry generators that leave the equation invariant are identified and we generate an optimal system. Each element of the optimal system is used to reduce the partial differential equation to an ordinary differential equation which is further analysed. We identify new categories of exact solutions to the boundary conditions. Two classes of solutions are of interest. The first class depends on a self similar variable. The second class is separable in the spacetime variables. |
2201.08305 | Zipeng Wang | Zipeng Wang, Thomas Helfer, Katy Clough, Emanuele Berti | Superradiance in massive vector fields with spatially varying mass | 13 pages, 9 figures, 2 tables | null | 10.1103/PhysRevD.105.104055 | null | gr-qc astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Superradiance is a process by which massive bosonic particles can extract
energy from spinning black holes, leading to the build up of a "cloud" if the
particle has a Compton wavelength comparable to the black hole's Schwarzschild
radius. One interesting possibility is that superradiance may occur for photons
in a diffuse plasma, where they gain a small effective mass. Studies of the
spin-0 case have indicated that such a build up is suppressed by a spatially
varying effective mass, supposed to mimic the photons' interaction with a
physically realistic plasma density profile. We carry out relativistic
simulations of a massive Proca field evolving on a Kerr background, with
modifications to account for the spatially varying effective mass. This allows
us to treat the spin-1 case directly relevant to photons, and to study the
effect of thinner disk profiles in the plasma. We find similar qualitative
results to the scalar case, and so support the conclusions of that work: either
a constant asymptotic mass or a shell-like plasma structure is required for
superradiant growth to occur. We study thin disks and find a leakage of the
superradiant cloud that suppresses its growth, concluding that thick disks are
more likely to support the instability.
| [
{
"created": "Thu, 20 Jan 2022 17:19:17 GMT",
"version": "v1"
},
{
"created": "Wed, 25 May 2022 19:00:35 GMT",
"version": "v2"
}
] | 2022-06-08 | [
[
"Wang",
"Zipeng",
""
],
[
"Helfer",
"Thomas",
""
],
[
"Clough",
"Katy",
""
],
[
"Berti",
"Emanuele",
""
]
] | Superradiance is a process by which massive bosonic particles can extract energy from spinning black holes, leading to the build up of a "cloud" if the particle has a Compton wavelength comparable to the black hole's Schwarzschild radius. One interesting possibility is that superradiance may occur for photons in a diffuse plasma, where they gain a small effective mass. Studies of the spin-0 case have indicated that such a build up is suppressed by a spatially varying effective mass, supposed to mimic the photons' interaction with a physically realistic plasma density profile. We carry out relativistic simulations of a massive Proca field evolving on a Kerr background, with modifications to account for the spatially varying effective mass. This allows us to treat the spin-1 case directly relevant to photons, and to study the effect of thinner disk profiles in the plasma. We find similar qualitative results to the scalar case, and so support the conclusions of that work: either a constant asymptotic mass or a shell-like plasma structure is required for superradiant growth to occur. We study thin disks and find a leakage of the superradiant cloud that suppresses its growth, concluding that thick disks are more likely to support the instability. |
gr-qc/9901006 | George Emanuel Avraam Matsas | Luis C.B. Crispino, Atsushi Higuchi, and George E.A. Matsas | Scalar radiation emitted from a source rotating around a black hole | 19 pages (REVTEX), 5 figures, title slightly changed, extra
demonstration and minor improvements included. To appear in Class. Quant.
Grav | null | 10.1088/0264-9381/17/1/303 | IFT-P.008/99 | gr-qc astro-ph hep-th | null | We analyze the scalar radiation emitted from a source rotating around a
Schwarzschild black hole using the framework of quantum field theory at the
tree level. We show that for relativistic circular orbits the emitted power is
about 20% to 30% smaller than what would be obtained in Minkowski spacetime. We
also show that most of the emitted energy escapes to infinity. Our formalism
can readily be adapted to investigate similar processes.
| [
{
"created": "Tue, 5 Jan 1999 11:22:40 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Apr 1999 18:06:37 GMT",
"version": "v2"
},
{
"created": "Fri, 8 Oct 1999 12:07:40 GMT",
"version": "v3"
}
] | 2009-10-31 | [
[
"Crispino",
"Luis C. B.",
""
],
[
"Higuchi",
"Atsushi",
""
],
[
"Matsas",
"George E. A.",
""
]
] | We analyze the scalar radiation emitted from a source rotating around a Schwarzschild black hole using the framework of quantum field theory at the tree level. We show that for relativistic circular orbits the emitted power is about 20% to 30% smaller than what would be obtained in Minkowski spacetime. We also show that most of the emitted energy escapes to infinity. Our formalism can readily be adapted to investigate similar processes. |
1604.02154 | Marco Sampaio | Fl\'avio S. Coelho and Marco O. P. Sampaio | Radiation from a D-dimensional collision of shock waves: Two dimensional
reduction and Carter-Penrose diagram | 20 pages, 3 figures. To appear in a Special Issue of the IJMPD on
Selected Papers of the III Amazonian Symposium on Physics (Eds. C. Herdeiro,
E. Berti, V. Cardoso, L. C. Crispino, L. Gualtieri and U. Sperhake) | null | 10.1142/S0218271816410108 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyse the causal structure of the two dimensional (2D) reduced
background used in the perturbative treatment of a head-on collision of two
$D$-dimensional Aichelburg-Sexl gravitational shock waves. After defining all
causal boundaries, namely the future light-cone of the collision and the past
light-cone of a future observer, we obtain characteristic coordinates using two
independent methods. The first is a geometrical construction of the null rays
which define the various light cones, using a parametric representation. The
second is a transformation of the 2D reduced wave operator for the problem into
a hyperbolic form. The characteristic coordinates are then compactified
allowing us to represent all causal light rays in a conformal Carter-Penrose
diagram. Our construction holds to all orders in perturbation theory. In
particular, we can easily identify the singularities of the source functions
and of the Green's functions appearing in the perturbative expansion, at each
order, which is crucial for a successful numerical evaluation of any higher
order corrections using this method.
| [
{
"created": "Thu, 7 Apr 2016 20:00:14 GMT",
"version": "v1"
}
] | 2016-08-17 | [
[
"Coelho",
"Flávio S.",
""
],
[
"Sampaio",
"Marco O. P.",
""
]
] | We analyse the causal structure of the two dimensional (2D) reduced background used in the perturbative treatment of a head-on collision of two $D$-dimensional Aichelburg-Sexl gravitational shock waves. After defining all causal boundaries, namely the future light-cone of the collision and the past light-cone of a future observer, we obtain characteristic coordinates using two independent methods. The first is a geometrical construction of the null rays which define the various light cones, using a parametric representation. The second is a transformation of the 2D reduced wave operator for the problem into a hyperbolic form. The characteristic coordinates are then compactified allowing us to represent all causal light rays in a conformal Carter-Penrose diagram. Our construction holds to all orders in perturbation theory. In particular, we can easily identify the singularities of the source functions and of the Green's functions appearing in the perturbative expansion, at each order, which is crucial for a successful numerical evaluation of any higher order corrections using this method. |
gr-qc/9407023 | Paul Henry Casper | Bruce Allen, Paul Casper, and Adrian Ottewill | Closed Form Expression for the Momentum Radiated from Cosmic String
Loops | 17 pages, RevTex 3.0, 3 postscript figures and C-language computer
code available via anonymous ftp from directory pub/pcasper at
alpha1.csd.uwm.edu, WISC-MILW-94-TH-15 | Phys.Rev. D51 (1995) 1546-1552 | 10.1103/PhysRevD.51.1546 | null | gr-qc astro-ph | null | We modify the recent analytic formula given by Allen and Casper for the rate
at which piecewise linear cosmic string loops lose energy to gravitational
radiation to yield the analogous analytic formula for the rate at which loops
radiate momentum. The resulting formula (which is exact when the effects of
gravitational back-reaction are neglected) is a sum of O(N^4) polynomial and
log terms where, N is the total number of segments on the piecewise linear
string loop. As illustration, we write the formula explicitly for a simple
one-parameter family of loops with N=5. For most loops the large number of
terms makes evaluation ``by hand" impractical, but, a computer or symbolic
manipulator may by used to yield accurate results. The formula has been used to
correct numerical results given in the existing literature. To assist future
work in this area, a small catalog of results for a number of simple string
loops is provided.
| [
{
"created": "Tue, 19 Jul 1994 15:17:14 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Allen",
"Bruce",
""
],
[
"Casper",
"Paul",
""
],
[
"Ottewill",
"Adrian",
""
]
] | We modify the recent analytic formula given by Allen and Casper for the rate at which piecewise linear cosmic string loops lose energy to gravitational radiation to yield the analogous analytic formula for the rate at which loops radiate momentum. The resulting formula (which is exact when the effects of gravitational back-reaction are neglected) is a sum of O(N^4) polynomial and log terms where, N is the total number of segments on the piecewise linear string loop. As illustration, we write the formula explicitly for a simple one-parameter family of loops with N=5. For most loops the large number of terms makes evaluation ``by hand" impractical, but, a computer or symbolic manipulator may by used to yield accurate results. The formula has been used to correct numerical results given in the existing literature. To assist future work in this area, a small catalog of results for a number of simple string loops is provided. |
2106.08236 | Felipe Asenjo | Felipe A. Asenjo and Sergio A. Hojman | Light--like propagation of self--interacting Klein--Gordon fields in
cosmology | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is showed that complex scalar fields with a self-interaction potential may
propagate along null geodesics on flat Friedmann--Lema\^itre--Robertson--Walker
universes with different time-dependent scale factors. This occurs provided
they self interact adequately, for different forms of potentials, and
even for the massive case.
| [
{
"created": "Tue, 15 Jun 2021 15:40:59 GMT",
"version": "v1"
}
] | 2021-06-16 | [
[
"Asenjo",
"Felipe A.",
""
],
[
"Hojman",
"Sergio A.",
""
]
] | It is showed that complex scalar fields with a self-interaction potential may propagate along null geodesics on flat Friedmann--Lema\^itre--Robertson--Walker universes with different time-dependent scale factors. This occurs provided they self interact adequately, for different forms of potentials, and even for the massive case. |
0908.1835 | Edward Glass | J.P. Krisch and E.N. Glass | Counter-rotating Kerr manifolds separated by a fluid shell | null | Class. Quantum Grav. vol 26 175010 (2009) | 10.1088/0264-9381/26/17/175010 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe a spheroidal fluid shell between two Kerr vacuum regions which
have opposite rotation parameters. The shell has a stiff equation of state and
a heat flow vector related to the rotational Killing current. The shell
description is useful in exploring the significance of counter-rotation in Kerr
metric matches.
| [
{
"created": "Thu, 13 Aug 2009 05:15:11 GMT",
"version": "v1"
}
] | 2015-05-13 | [
[
"Krisch",
"J. P.",
""
],
[
"Glass",
"E. N.",
""
]
] | We describe a spheroidal fluid shell between two Kerr vacuum regions which have opposite rotation parameters. The shell has a stiff equation of state and a heat flow vector related to the rotational Killing current. The shell description is useful in exploring the significance of counter-rotation in Kerr metric matches. |
gr-qc/0002048 | Georges F. Bressange | C. Barrab\`es, G. F. Bressange and P. A. Hogan | Colliding Plane Impulsive Gravitational Waves | 21 pages, LaTeX2e | Prog.Theor.Phys. 102 (1999) 1085-1101 | 10.1143/PTP.102.1085 | null | gr-qc | null | When two non-interacting plane impulsive gravitational waves undergo a
head-on collision, the vacuum interaction region between the waves after the
collision contains backscattered gravitational radiation from both waves. The
two systems of backscattered waves have each got a family of rays (null
geodesics) associated with them. We demonstrate that if it is assumed that a
parameter exists along each of these families of rays such that the modulus of
the complex shear of each is equal then Einstein's vacuum field equations, with
the appropriate boundary conditions, can be integrated systematically to reveal
the well-known solutions in the interaction region. In so doing the mystery
behind the origin of such solutions is removed. With the use of the field
equations it is suggested that the assumption leading to their integration may
be interpreted physically as implying that the energy densities of the two
backscattered radiation fields are equal. With the use of different boundary
conditions this approach can lead to new collision solutions.
| [
{
"created": "Mon, 14 Feb 2000 15:25:43 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Barrabès",
"C.",
""
],
[
"Bressange",
"G. F.",
""
],
[
"Hogan",
"P. A.",
""
]
] | When two non-interacting plane impulsive gravitational waves undergo a head-on collision, the vacuum interaction region between the waves after the collision contains backscattered gravitational radiation from both waves. The two systems of backscattered waves have each got a family of rays (null geodesics) associated with them. We demonstrate that if it is assumed that a parameter exists along each of these families of rays such that the modulus of the complex shear of each is equal then Einstein's vacuum field equations, with the appropriate boundary conditions, can be integrated systematically to reveal the well-known solutions in the interaction region. In so doing the mystery behind the origin of such solutions is removed. With the use of the field equations it is suggested that the assumption leading to their integration may be interpreted physically as implying that the energy densities of the two backscattered radiation fields are equal. With the use of different boundary conditions this approach can lead to new collision solutions. |
1408.4738 | Yurii Ignatyev | Yu.G. Ignatyev and A.A. Agathonov | Numerical Models of Cosmological Evolution of the Degenerated
Fermi-system of Scalar Charged Particles | 15 pages, 14 figures, 4 references | null | 10.1134/S0202289315020048 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Based on mathematical model of the statistical Fermi system with the
interparticle interaction which was constructed in the previous articles, this
work offers the construction and analysis of the numerical models of
cosmological evolution of the single-component degenerated Fermi system of the
scalar particles. The applied mathematics package Mathematica 9 is used for the
numerical model construction.
| [
{
"created": "Wed, 20 Aug 2014 17:38:47 GMT",
"version": "v1"
}
] | 2023-07-19 | [
[
"Ignatyev",
"Yu. G.",
""
],
[
"Agathonov",
"A. A.",
""
]
] | Based on mathematical model of the statistical Fermi system with the interparticle interaction which was constructed in the previous articles, this work offers the construction and analysis of the numerical models of cosmological evolution of the single-component degenerated Fermi system of the scalar particles. The applied mathematics package Mathematica 9 is used for the numerical model construction. |
1909.07824 | Christian Corda Prof. | F. Feleppa, I. Licata and C. Corda | Hartle-Hawking boundary conditions as Nucleation by de Sitter Vacuum | 23 pages, 2 figures, accepted for publication in Physics of the Dark
Universe | Phys. Dark Un. 26, 100381 (2019) | 10.1016/j.dark.2019.100381 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that, for a de Sitter Universe, the Hartle-Hawking (HH) wave
function can be obtained in a simple way starting from the
Friedmann-Lemaitre-Robertson-Walker (FLRW) line element of cosmological
equations. An oscillator having imaginary time is indeed derived starting from
the Hamiltonian obtaining the HH condition. This proposes again some crucial
matter on the meaning of complex time in cosmology. In order to overcome such
difficulties, we propose an interpretation of the HH framework based on de
Sitter Projective Holography.
| [
{
"created": "Sun, 15 Sep 2019 15:03:26 GMT",
"version": "v1"
}
] | 2019-09-20 | [
[
"Feleppa",
"F.",
""
],
[
"Licata",
"I.",
""
],
[
"Corda",
"C.",
""
]
] | It is shown that, for a de Sitter Universe, the Hartle-Hawking (HH) wave function can be obtained in a simple way starting from the Friedmann-Lemaitre-Robertson-Walker (FLRW) line element of cosmological equations. An oscillator having imaginary time is indeed derived starting from the Hamiltonian obtaining the HH condition. This proposes again some crucial matter on the meaning of complex time in cosmology. In order to overcome such difficulties, we propose an interpretation of the HH framework based on de Sitter Projective Holography. |
0708.3317 | Sunil Maharaj | R. Sharma and S. D. Maharaj | On surface tension for compact stars | 8 pages, To appear in J. Astrophys. Astron | J. Astrophys. Astron. 28 (2007) 133-138 | 10.1007/s12036-007-0010-x | null | gr-qc | null | In an earlier treatment it was demonstrated that general relativity gives
higher values of surface tension in strange stars with quark matter than
neutron stars.We generate the modified Tolman-Oppenheimer-Volkoff equation to
incorporate anisotropic matter and use this to show that pressure anisotropy
provides for a wide range of behaviour in the surface tension than is the case
with isotropic pressures. In particular it is possible that anisotropy
drastically decreases the value of the surface tension.
| [
{
"created": "Fri, 24 Aug 2007 11:40:05 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Sharma",
"R.",
""
],
[
"Maharaj",
"S. D.",
""
]
] | In an earlier treatment it was demonstrated that general relativity gives higher values of surface tension in strange stars with quark matter than neutron stars.We generate the modified Tolman-Oppenheimer-Volkoff equation to incorporate anisotropic matter and use this to show that pressure anisotropy provides for a wide range of behaviour in the surface tension than is the case with isotropic pressures. In particular it is possible that anisotropy drastically decreases the value of the surface tension. |
2307.14156 | Zhuan Ning | Zhuan Ning, Qian Chen, Yu Tian, Xiaoning Wu, Hongbao Zhang | Spontaneous Deformation of an AdS Spherical Black Hole | 16 pages, 9 figures; Eq. (30) and (A7) corrected, figures and details
added, version to appear in PRD | Phys. Rev. D 109 (2024) 6, 064082 | 10.1103/PhysRevD.109.064082 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this study, we investigate the real-time dynamics during the spontaneous
deformation of an unstable spherical black hole in asymptotically anti-de
Sitter (AdS) spacetime. For the initial value, the static solutions with
spherical symmetry are obtained numerically, revealing the presence of a
spinodal region in the phase diagram. From the linear stability analysis, we
find that only the central part of such a thermodynamically unstable spinodal
region leads to the emergence of a type of axial instability. To trigger the
dynamical instability, an axial perturbation is imposed on the scalar field. As
a result, by the fully nonlinear dynamical simulation, the spherical symmetry
of the gravitational system is broken spontaneously, leading to the formation
of an axisymmetric black hole.
| [
{
"created": "Wed, 26 Jul 2023 12:36:23 GMT",
"version": "v1"
},
{
"created": "Sun, 30 Jul 2023 13:15:43 GMT",
"version": "v2"
},
{
"created": "Tue, 5 Mar 2024 12:31:34 GMT",
"version": "v3"
},
{
"created": "Thu, 28 Mar 2024 01:07:36 GMT",
"version": "v4"
}
] | 2024-03-29 | [
[
"Ning",
"Zhuan",
""
],
[
"Chen",
"Qian",
""
],
[
"Tian",
"Yu",
""
],
[
"Wu",
"Xiaoning",
""
],
[
"Zhang",
"Hongbao",
""
]
] | In this study, we investigate the real-time dynamics during the spontaneous deformation of an unstable spherical black hole in asymptotically anti-de Sitter (AdS) spacetime. For the initial value, the static solutions with spherical symmetry are obtained numerically, revealing the presence of a spinodal region in the phase diagram. From the linear stability analysis, we find that only the central part of such a thermodynamically unstable spinodal region leads to the emergence of a type of axial instability. To trigger the dynamical instability, an axial perturbation is imposed on the scalar field. As a result, by the fully nonlinear dynamical simulation, the spherical symmetry of the gravitational system is broken spontaneously, leading to the formation of an axisymmetric black hole. |
1406.0624 | Mohamad Atazadeh | K. Atazadeh, A. Eghbali | Brane cosmology in teleparallel and $f(T)$ gravity | 13 pages, 1 figure, 1 table, published version | Phys. Scr. 90 (2015) 045001 | 10.1088/0031-8949/90/4/045001 | null | gr-qc hep-th | http://creativecommons.org/licenses/by-nc-sa/3.0/ | We consider the cosmology of a brane-world scenario in the framework of
teleparallel and $f(T)$ gravity in a way that matter is localized on the brane.
We show that the cosmology of such branes is different from the standard
cosmology in teleparallelism. In particular, we obtain a class of new solutions
with a constant five-dimensional radius and cosmologically evolving brane in
the context of constant torsion $f(T)$ gravity.
| [
{
"created": "Tue, 3 Jun 2014 08:36:38 GMT",
"version": "v1"
},
{
"created": "Wed, 1 Apr 2015 09:04:03 GMT",
"version": "v2"
}
] | 2015-04-02 | [
[
"Atazadeh",
"K.",
""
],
[
"Eghbali",
"A.",
""
]
] | We consider the cosmology of a brane-world scenario in the framework of teleparallel and $f(T)$ gravity in a way that matter is localized on the brane. We show that the cosmology of such branes is different from the standard cosmology in teleparallelism. In particular, we obtain a class of new solutions with a constant five-dimensional radius and cosmologically evolving brane in the context of constant torsion $f(T)$ gravity. |
1909.13450 | Hamed Pejhan | Hamed Pejhan, Mohammad Enayati, Jean-Pierre Gazeau, and Anzhong Wang | "Massive" Rarita-Schwinger field in de Sitter space | 17 pages, no figure, version accepted for publication in Physical
Review D | Phys. Rev. D 100, 125022 (2019) | 10.1103/PhysRevD.100.125022 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a covariant quantization of the "massive" spin-${\frac{3}{2}}$
Rarita-Schwinger field in de Sitter (dS) spacetime. The dS group representation
theory and its Wigner interpretation combined with the
Wightman-G$\mbox{\"{a}}$rding axiomatic and analyticity requirements in the
complexified pseudo-Riemanian manifold constitute the basis of the quantization
scheme, while the whole procedure is carried out in terms of
coordinate-independent dS plane waves. We make explicit the correspondence
between unitary irreducible representations (UIRs) of the dS group and the
field theory in dS spacetime: by "massive" is meant a field that carries a
particular principal series representation of the dS group. We drive the
plane-wave representation of the dS massive Rarita-Schwinger field in a
manifestly dS-invariant manner. We show that it exactly reduces to its
Minkowskian counterpart when the curvature tends to zero as far as the
analyticity domain conveniently chosen. We then present the Wightman two-point
function fulfilling the minimal requirements of local anticommutativity,
covariance, and normal analyticity. The Hilbert space structure and the
unsmeared field operator are also defined. The analyticity properties of the
waves and the two-point function that we discuss in this paper allow for a
detailed study of the Hilbert space of the theory, and give rise to the thermal
physical interpretation.
| [
{
"created": "Mon, 30 Sep 2019 04:21:15 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Dec 2019 03:41:24 GMT",
"version": "v2"
},
{
"created": "Sun, 22 Dec 2019 01:38:26 GMT",
"version": "v3"
}
] | 2020-01-01 | [
[
"Pejhan",
"Hamed",
""
],
[
"Enayati",
"Mohammad",
""
],
[
"Gazeau",
"Jean-Pierre",
""
],
[
"Wang",
"Anzhong",
""
]
] | We present a covariant quantization of the "massive" spin-${\frac{3}{2}}$ Rarita-Schwinger field in de Sitter (dS) spacetime. The dS group representation theory and its Wigner interpretation combined with the Wightman-G$\mbox{\"{a}}$rding axiomatic and analyticity requirements in the complexified pseudo-Riemanian manifold constitute the basis of the quantization scheme, while the whole procedure is carried out in terms of coordinate-independent dS plane waves. We make explicit the correspondence between unitary irreducible representations (UIRs) of the dS group and the field theory in dS spacetime: by "massive" is meant a field that carries a particular principal series representation of the dS group. We drive the plane-wave representation of the dS massive Rarita-Schwinger field in a manifestly dS-invariant manner. We show that it exactly reduces to its Minkowskian counterpart when the curvature tends to zero as far as the analyticity domain conveniently chosen. We then present the Wightman two-point function fulfilling the minimal requirements of local anticommutativity, covariance, and normal analyticity. The Hilbert space structure and the unsmeared field operator are also defined. The analyticity properties of the waves and the two-point function that we discuss in this paper allow for a detailed study of the Hilbert space of the theory, and give rise to the thermal physical interpretation. |
gr-qc/9801022 | Pasi Tapio Repo | Jarmo Makela | Variation of Area Variables in Regge Calculus | 8 pages, no figures | Class.Quant.Grav. 17 (2000) 4991-4998 | 10.1088/0264-9381/17/24/304 | JYFL preprint 17/97 | gr-qc | null | We consider the possibility to use the areas of two-simplexes, instead of
lengths of edges, as the dynamical variables of Regge calculus. We show that if
the action of Regge calculus is varied with respect to the areas of
two-simplexes, and appropriate constraints are imposed between the variations,
the Einstein-Regge equations are recovered.
| [
{
"created": "Fri, 9 Jan 1998 12:11:21 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Makela",
"Jarmo",
""
]
] | We consider the possibility to use the areas of two-simplexes, instead of lengths of edges, as the dynamical variables of Regge calculus. We show that if the action of Regge calculus is varied with respect to the areas of two-simplexes, and appropriate constraints are imposed between the variations, the Einstein-Regge equations are recovered. |
0705.3933 | Subenoy Chakraborty | Asit Banerjee, Tanwi Bandyopadhyay and Subenoy Chakraborty | Emergent Universe in Brane World Scenario | 4 pages, no figure | Grav.Cosmol.13:290-292,2007 | null | null | gr-qc | null | A model of an emergent universe is obtained in brane world. Here the bulk
energy is in the form of cosmological constant, while the brane consists of the
Chaplygin gas with the modified equation of state such as $p=A\rho-B/\rho$.
Initially the brane matter for the special choice $A=1/3$ may have negative or
positive pressure depending on the relative magnitudes of the parameter $B$ and
the cosmological constant of the bulk, while asymptotically in future the brane
world approaches a $\Lambda$CDM model.
| [
{
"created": "Sun, 27 May 2007 06:36:22 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Banerjee",
"Asit",
""
],
[
"Bandyopadhyay",
"Tanwi",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | A model of an emergent universe is obtained in brane world. Here the bulk energy is in the form of cosmological constant, while the brane consists of the Chaplygin gas with the modified equation of state such as $p=A\rho-B/\rho$. Initially the brane matter for the special choice $A=1/3$ may have negative or positive pressure depending on the relative magnitudes of the parameter $B$ and the cosmological constant of the bulk, while asymptotically in future the brane world approaches a $\Lambda$CDM model. |
gr-qc/0211062 | Pavlov | Yu. V. Pavlov | The Hamilton Operator and Quantum Vacuum for Nonconformal Scalar Fields
in the Homogeneous and Isotropic Space | Talk at S.Kovalevski Symposium (Stockholm University, June 2000).
LaTeX, 10 pages, no figures | Oper.Theor.Advan.Appl.132:323-332,2002 | null | null | gr-qc | null | The diagonalization of the metrical and canonical Hamilton operators of a
scalar field with an arbitrary coupling, with a curvature in N-dimensional
homogeneous isotropic space is considered in this paper. The energy spectrum of
the corresponding quasiparticles is obtained and then the modified
energy-momentum tensor is constructed; the latter coincides with the metrical
energy-momentum tensor for conformal scalar field. Under the diagonalization of
corresponding Hamilton operator the energies of relevant particles of a
nonconformal field are equal to the oscillator frequencies, and the density of
such particles created in a nonstationary metric is finite. It is shown that
the modified Hamilton operator can be constructed as a canonical Hamilton
operator under the special choice of variables.
| [
{
"created": "Mon, 18 Nov 2002 11:34:02 GMT",
"version": "v1"
}
] | 2011-04-20 | [
[
"Pavlov",
"Yu. V.",
""
]
] | The diagonalization of the metrical and canonical Hamilton operators of a scalar field with an arbitrary coupling, with a curvature in N-dimensional homogeneous isotropic space is considered in this paper. The energy spectrum of the corresponding quasiparticles is obtained and then the modified energy-momentum tensor is constructed; the latter coincides with the metrical energy-momentum tensor for conformal scalar field. Under the diagonalization of corresponding Hamilton operator the energies of relevant particles of a nonconformal field are equal to the oscillator frequencies, and the density of such particles created in a nonstationary metric is finite. It is shown that the modified Hamilton operator can be constructed as a canonical Hamilton operator under the special choice of variables. |
2203.05663 | Stefano Bondani | Stefano Bondani, Francesco Haardt, Alberto Sesana, Enrico Barausse,
Massimo Dotti | On the detectability of gravitational waves from primordial black holes
orbiting Sgr A* | 10 pages, 11 figures; Referee reviewed | Phys. Rev. D 106, 043015, 2022 | 10.1103/PhysRevD.106.043015 | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we characterize the expected gravitational wave signal
detectable by the planned space-borne interferometer LISA and the proposed next
generation space-borne interferometer $\mu$Ares arising from a population of
primordial black holes orbiting Sgr A*, the super-massive black hole at the
Galactic center. Assuming that such objects indeed form the entire diffuse mass
allowed by the observed orbit of S2 in the Galactic center, under the
simplified assumption of circular orbits and monochromatic mass function, we
assess the expected signal in gravitational waves, either from resolved and
non-resolved sources. We estimate a small but non negligible chance of $\simeq$
10% of detecting one single 1 M$_{\odot}$ primordial black hole with LISA in a
10-year-long data stream, while the background signal due to unresolved sources
would essentially elude any reasonable chance of detection. On the contrary,
$\mu$Ares, with a $\simeq$ 3 orders-of-magnitude better sensitivity at $\simeq$
10$^{-5}$ Hz, would be able to resolve $\simeq$ 140 solar mass primordial black
holes in the same amount of time, while the unresolved background should be
observable with an integrated signal-to-noise ratio $\gtrsim$ 100. Allowing the
typical PBH mass to be in the range 0.01-10 M$_{\odot}$ would increase LISA
chance of detection to $\simeq$ 40% towards the lower limit of the mass
spectrum. In the case of $\mu$Ares, instead, we find a "sweet spot" just about
1 M$_{\odot}$, a mass for which the number of resolvable events is indeed
maximized.
| [
{
"created": "Thu, 10 Mar 2022 22:18:46 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Aug 2022 13:36:05 GMT",
"version": "v2"
}
] | 2022-08-16 | [
[
"Bondani",
"Stefano",
""
],
[
"Haardt",
"Francesco",
""
],
[
"Sesana",
"Alberto",
""
],
[
"Barausse",
"Enrico",
""
],
[
"Dotti",
"Massimo",
""
]
] | In this work we characterize the expected gravitational wave signal detectable by the planned space-borne interferometer LISA and the proposed next generation space-borne interferometer $\mu$Ares arising from a population of primordial black holes orbiting Sgr A*, the super-massive black hole at the Galactic center. Assuming that such objects indeed form the entire diffuse mass allowed by the observed orbit of S2 in the Galactic center, under the simplified assumption of circular orbits and monochromatic mass function, we assess the expected signal in gravitational waves, either from resolved and non-resolved sources. We estimate a small but non negligible chance of $\simeq$ 10% of detecting one single 1 M$_{\odot}$ primordial black hole with LISA in a 10-year-long data stream, while the background signal due to unresolved sources would essentially elude any reasonable chance of detection. On the contrary, $\mu$Ares, with a $\simeq$ 3 orders-of-magnitude better sensitivity at $\simeq$ 10$^{-5}$ Hz, would be able to resolve $\simeq$ 140 solar mass primordial black holes in the same amount of time, while the unresolved background should be observable with an integrated signal-to-noise ratio $\gtrsim$ 100. Allowing the typical PBH mass to be in the range 0.01-10 M$_{\odot}$ would increase LISA chance of detection to $\simeq$ 40% towards the lower limit of the mass spectrum. In the case of $\mu$Ares, instead, we find a "sweet spot" just about 1 M$_{\odot}$, a mass for which the number of resolvable events is indeed maximized. |
1509.01825 | Edward Malec | Jerzy Knopik, Patryk Mach and Edward Malec | General-relativistic rotation laws in rotating fluid bodies: constant
linear velocity | null | null | 10.5506/APhysPolB.46.2451 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | New rotation laws have been recently found for general-relativistic
self-gravitating stationary fluids. It was not clear whether they apply to
systems rotating with a constant linear velocity. In this paper we fill this
gap. The answer is positive. That means, in particular, that these systems
should exhibit the recently discovered general-relativistic weak-field effects
within rotating tori: the dynamic anti-dragging and the deviation from the
Keplerian motion induced by the fluid selfgravity.
| [
{
"created": "Sun, 6 Sep 2015 16:25:20 GMT",
"version": "v1"
}
] | 2016-01-20 | [
[
"Knopik",
"Jerzy",
""
],
[
"Mach",
"Patryk",
""
],
[
"Malec",
"Edward",
""
]
] | New rotation laws have been recently found for general-relativistic self-gravitating stationary fluids. It was not clear whether they apply to systems rotating with a constant linear velocity. In this paper we fill this gap. The answer is positive. That means, in particular, that these systems should exhibit the recently discovered general-relativistic weak-field effects within rotating tori: the dynamic anti-dragging and the deviation from the Keplerian motion induced by the fluid selfgravity. |
1905.02748 | Sharmila Gunasekaran | Sharmila Gunasekaran, Ivan Booth | Horizons as boundary conditions in spherical symmetry | 14 pages, V3 - published version, small changes to IV B) | Phys. Rev. D 100, 064019 (2019) | 10.1103/PhysRevD.100.064019 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We initiate the development of a horizon-based initial (or rather final)
value formalism to describe the geometry and physics of the near-horizon
spacetime: data specified on the horizon and a future ingoing null boundary
determine the near-horizon geometry. In this initial paper we restrict our
attention to spherically symmetric spacetimes made dynamic by matter fields. We
illustrate the formalism by considering a black hole interacting with a)
inward-falling, null matter (with no outward flux) and b) a massless scalar
field. The inward-falling case can be exactly solved from horizon data. For the
more involved case of the scalar field we analytically investigate the near
slowly evolving horizon regime and propose a numerical integration for the
general case.
| [
{
"created": "Tue, 7 May 2019 18:11:11 GMT",
"version": "v1"
},
{
"created": "Fri, 24 May 2019 11:15:00 GMT",
"version": "v2"
},
{
"created": "Tue, 30 Mar 2021 16:16:49 GMT",
"version": "v3"
}
] | 2021-03-31 | [
[
"Gunasekaran",
"Sharmila",
""
],
[
"Booth",
"Ivan",
""
]
] | We initiate the development of a horizon-based initial (or rather final) value formalism to describe the geometry and physics of the near-horizon spacetime: data specified on the horizon and a future ingoing null boundary determine the near-horizon geometry. In this initial paper we restrict our attention to spherically symmetric spacetimes made dynamic by matter fields. We illustrate the formalism by considering a black hole interacting with a) inward-falling, null matter (with no outward flux) and b) a massless scalar field. The inward-falling case can be exactly solved from horizon data. For the more involved case of the scalar field we analytically investigate the near slowly evolving horizon regime and propose a numerical integration for the general case. |
2210.10295 | Nikolaos Dimakis | N. Dimakis, M. Roumeliotis, A. Paliathanasis, P.S. Apostolopoulos and
T. Christodoulakis | Self-similar Cosmological Solutions in Symmetric Teleparallel theory:
Friedmann-Lema\^itre-Robertson-Walker spacetimes | 25 pages, no figures, Latex2e source file, PRD accepted version | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The existence of self-similar solutions is discussed in symmetric
teleparallel $f(Q)$-theory for a Friedmann-Lema\^itre-Robertson-Walker
background geometry with zero and non-zero spatial curvature. For the four
distinct families of connections which describe the specific cosmology in
symmetric teleparallel gravity, the functional form of $f(Q)$ is reconstructed.
Finally, to see if the analogy with General Relativity holds, we discuss the
relation of the self-similar solutions with the asymptotic behaviour of more
general $f(Q)$ functions.
| [
{
"created": "Wed, 19 Oct 2022 04:44:07 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Nov 2022 03:09:21 GMT",
"version": "v2"
}
] | 2022-12-01 | [
[
"Dimakis",
"N.",
""
],
[
"Roumeliotis",
"M.",
""
],
[
"Paliathanasis",
"A.",
""
],
[
"Apostolopoulos",
"P. S.",
""
],
[
"Christodoulakis",
"T.",
""
]
] | The existence of self-similar solutions is discussed in symmetric teleparallel $f(Q)$-theory for a Friedmann-Lema\^itre-Robertson-Walker background geometry with zero and non-zero spatial curvature. For the four distinct families of connections which describe the specific cosmology in symmetric teleparallel gravity, the functional form of $f(Q)$ is reconstructed. Finally, to see if the analogy with General Relativity holds, we discuss the relation of the self-similar solutions with the asymptotic behaviour of more general $f(Q)$ functions. |
1301.2571 | Tharanath R | R Tharanath and V C Kuriakose | Thermodynamics and Spectroscopy of Schwarzschild black hole surrounded
by Quintessence | 11 pages and 4 figures | Modern Physics Letters A (2013) | 10.1142/S021773231350003X | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The thermodynamic and spectroscopic behaviour of Schwarzschild black hole
surrounded by quintessence are studied. We have derived the thermodynamic
quantities and studied their behaviour for different values of quintessence
parameter. We put the background space-time into the Kruskal-like coordinate to
find the period with respect to Elucidean time. Also assuming that the
adiabatic invariant obeys Bohr-Sommerfeld quantization rule, detailed study of
area spectrum and entropy spectrum have been done for special cases of the
quintessece state parameter. We find that the spectra are equally spaced.
| [
{
"created": "Fri, 11 Jan 2013 18:36:38 GMT",
"version": "v1"
}
] | 2013-01-14 | [
[
"Tharanath",
"R",
""
],
[
"Kuriakose",
"V C",
""
]
] | The thermodynamic and spectroscopic behaviour of Schwarzschild black hole surrounded by quintessence are studied. We have derived the thermodynamic quantities and studied their behaviour for different values of quintessence parameter. We put the background space-time into the Kruskal-like coordinate to find the period with respect to Elucidean time. Also assuming that the adiabatic invariant obeys Bohr-Sommerfeld quantization rule, detailed study of area spectrum and entropy spectrum have been done for special cases of the quintessece state parameter. We find that the spectra are equally spaced. |
gr-qc/9907061 | Lior M. Burko | Lior M. Burko | Strength of the null singularity inside black holes | RevTeX, 6 pages, no figures | Phys.Rev. D60 (1999) 104033 | 10.1103/PhysRevD.60.104033 | null | gr-qc | null | We study analytically the Cauchy horizon singularity inside
spherically-symmetric charged black holes, coupled to a spherical
self-gravitating, minimally-coupled, massless scalar field. We show that all
causal geodesics terminate at the Cauchy horizon at a null singularity, which
is weak according to the Tipler classification. The singularity is also
deformationally-weak in the sense of Ori. Our results are valid at arbitrary
points along the null singularity, in particular at late retarded times, when
non-linear effects are crucial.
| [
{
"created": "Mon, 19 Jul 1999 17:58:07 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Burko",
"Lior M.",
""
]
] | We study analytically the Cauchy horizon singularity inside spherically-symmetric charged black holes, coupled to a spherical self-gravitating, minimally-coupled, massless scalar field. We show that all causal geodesics terminate at the Cauchy horizon at a null singularity, which is weak according to the Tipler classification. The singularity is also deformationally-weak in the sense of Ori. Our results are valid at arbitrary points along the null singularity, in particular at late retarded times, when non-linear effects are crucial. |
2212.01228 | Sergey L Cherkas | Sergey L. Cherkas and Vladimir L. Kalashnikov | AEther as an Inevitable Consequence of Quantum Gravity | 15 pages, 5 figures | Universe 2022, 8(12), 626 | 10.3390/universe8120626 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The fact that quantum gravity does not admit an invariant vacuum state has
far-reaching consequences for all physics. It points out that space could not
be empty, and we return to the notion of an aether. Such a concept requires a
preferred reference frame for describing universe expansion and black holes.
Here, we intend to find a reference system or class of metrics that could be
attributed to ``aether''. We discuss a vacuum and quantum gravity from three
essential viewpoints: universe expansion, black hole existence, and quantum
decoherence.
| [
{
"created": "Tue, 29 Nov 2022 09:55:39 GMT",
"version": "v1"
}
] | 2022-12-05 | [
[
"Cherkas",
"Sergey L.",
""
],
[
"Kalashnikov",
"Vladimir L.",
""
]
] | The fact that quantum gravity does not admit an invariant vacuum state has far-reaching consequences for all physics. It points out that space could not be empty, and we return to the notion of an aether. Such a concept requires a preferred reference frame for describing universe expansion and black holes. Here, we intend to find a reference system or class of metrics that could be attributed to ``aether''. We discuss a vacuum and quantum gravity from three essential viewpoints: universe expansion, black hole existence, and quantum decoherence. |
1105.4145 | Lorenzo Iorio | Lorenzo Iorio | Some considerations on the present-day results for the detection of
frame-dragging after the final outcome of GP-B | LaTex2e, 6 pages, 1 table, 5 figures, 36 references. Minor changes.
Version matching the one at press in Europhysics Letters (EPL) | Europhys.Lett.96:30001,2011 | 10.1209/0295-5075/96/30001 | null | gr-qc astro-ph.EP physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The cancelation of the first even zonal harmonic coefficient J2 of the
multipolar expansion of the Newtonian part of the Earth's gravitational
potential from the linear combination f(2L) of the nodes of LAGEOS and LAGEOS
II used in the latest tests of the general relativistic Lense-Thirring effect
cannot be perfect, as assumed so far. It is so, among other things, because of
the uncertainties in the spatial orientation of the terrestrial spin axis as
well. As a consequence, the coefficient c1 entering f(2L), which is not a
solve-for parameter being theoretically computed from the analytical
expressions of the classical node precessions due to J2, is, on average,
uncertain at a 10-8 level over multi-decadal time spans DT comparable to those
used in the data analyses performed so far. A further \simeq 20% systematic
uncertainty in the theoretically predicted gravitomagnetic signal, thus,
occurs. The shift due to the gravitomagnetic frame-dragging on the
station-spacecraft range is numerically computed over DT = 15 d and DT = 1 yr.
The need of looking at such a directly observable quantity is pointed out,
along with some critical remarks concerning the methodology used so far to
measure the Lense-Thirring effect with the LAGEOS satellites. Suggestions for a
different, more trustable and reliable approach are offered.
| [
{
"created": "Fri, 20 May 2011 18:11:49 GMT",
"version": "v1"
},
{
"created": "Mon, 23 May 2011 19:07:32 GMT",
"version": "v2"
},
{
"created": "Tue, 24 May 2011 14:16:02 GMT",
"version": "v3"
},
{
"created": "Mon, 8 Aug 2011 11:37:30 GMT",
"version": "v4"
},
{
"created": "Tue, 27 Sep 2011 17:20:57 GMT",
"version": "v5"
}
] | 2015-03-19 | [
[
"Iorio",
"Lorenzo",
""
]
] | The cancelation of the first even zonal harmonic coefficient J2 of the multipolar expansion of the Newtonian part of the Earth's gravitational potential from the linear combination f(2L) of the nodes of LAGEOS and LAGEOS II used in the latest tests of the general relativistic Lense-Thirring effect cannot be perfect, as assumed so far. It is so, among other things, because of the uncertainties in the spatial orientation of the terrestrial spin axis as well. As a consequence, the coefficient c1 entering f(2L), which is not a solve-for parameter being theoretically computed from the analytical expressions of the classical node precessions due to J2, is, on average, uncertain at a 10-8 level over multi-decadal time spans DT comparable to those used in the data analyses performed so far. A further \simeq 20% systematic uncertainty in the theoretically predicted gravitomagnetic signal, thus, occurs. The shift due to the gravitomagnetic frame-dragging on the station-spacecraft range is numerically computed over DT = 15 d and DT = 1 yr. The need of looking at such a directly observable quantity is pointed out, along with some critical remarks concerning the methodology used so far to measure the Lense-Thirring effect with the LAGEOS satellites. Suggestions for a different, more trustable and reliable approach are offered. |
1410.0126 | Wei-Tou Ni | Wei-Tou Ni | Dilaton field and cosmic wave propagation | 16 pages, Physics Letters A in press | Physics Letters A 378 (2014) 3413-3418 | 10.1016/j.physleta.2014.09.049 | null | gr-qc astro-ph.CO hep-ph physics.optics | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the electromagnetic wave propagation in the joint dilaton field and
axion field. Dilaton field induces amplification/attenuation in the propagation
while axion field induces polarization rotation. The amplification/attenuation
induced by dilaton is independent of the frequency (energy) and the
polarization of electromagnetic waves (photons). From observations, the
agreement with and the precise calibration of the cosmic microwave background
(CMB) to blackbody radiation constrains the fractional change of dilaton
|{\Delta}{\psi}|/{\psi} to less than about 8 x 10^(-4) since the time of the
last scattering surface of the CMB.
| [
{
"created": "Wed, 1 Oct 2014 07:09:31 GMT",
"version": "v1"
}
] | 2014-11-04 | [
[
"Ni",
"Wei-Tou",
""
]
] | We study the electromagnetic wave propagation in the joint dilaton field and axion field. Dilaton field induces amplification/attenuation in the propagation while axion field induces polarization rotation. The amplification/attenuation induced by dilaton is independent of the frequency (energy) and the polarization of electromagnetic waves (photons). From observations, the agreement with and the precise calibration of the cosmic microwave background (CMB) to blackbody radiation constrains the fractional change of dilaton |{\Delta}{\psi}|/{\psi} to less than about 8 x 10^(-4) since the time of the last scattering surface of the CMB. |
1803.10583 | Izzet Sakalli | \.Izzet Sakall{\i}, Kimet Jusufi, Ali \"Ovg\"un | Analytical Solutions in a Cosmic String Born-Infeld-dilaton Black Hole
Geometry: Quasinormal Modes and Quantization | Accepted for publication in General Relativity and Gravitation | Gen Relativ Gravit (2018) 50: 125 | 10.1007/s10714-018-2455-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Chargeless massive scalar fields are studied in the spacetime of Born-Infeld
dilaton black holes (BIDBHs). We first separate the massive covariant
Klein-Gordon equation into radial and angular parts and obtain the exact
solution of the radial equation in terms of the confluent Heun functions. Using
the obtained radial solution, we show how one gets the exact quasinormal modes
(QNMs) for some particular cases. We also solve the Klein-Gordon equation in
the spacetime of BIDBH with a cosmic string in which we point out the effect of
the conical deficit on the BIDBH. The analytical solutions of the radial and
angular parts are obtained in terms of the confluent Heun functions. Finally,
we study the quantization of the BIDBH. While doing this, we also discuss the
Hawking radiation in terms of the effective temperature.
| [
{
"created": "Wed, 28 Mar 2018 13:19:46 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Sep 2018 20:03:33 GMT",
"version": "v2"
},
{
"created": "Wed, 12 Sep 2018 10:37:54 GMT",
"version": "v3"
}
] | 2018-09-14 | [
[
"Sakallı",
"İzzet",
""
],
[
"Jusufi",
"Kimet",
""
],
[
"Övgün",
"Ali",
""
]
] | Chargeless massive scalar fields are studied in the spacetime of Born-Infeld dilaton black holes (BIDBHs). We first separate the massive covariant Klein-Gordon equation into radial and angular parts and obtain the exact solution of the radial equation in terms of the confluent Heun functions. Using the obtained radial solution, we show how one gets the exact quasinormal modes (QNMs) for some particular cases. We also solve the Klein-Gordon equation in the spacetime of BIDBH with a cosmic string in which we point out the effect of the conical deficit on the BIDBH. The analytical solutions of the radial and angular parts are obtained in terms of the confluent Heun functions. Finally, we study the quantization of the BIDBH. While doing this, we also discuss the Hawking radiation in terms of the effective temperature. |
gr-qc/0507051 | H. D. Zeh | H. D. Zeh | Where has all the information gone? | 10 pages, 1 figure, Latex - Invited paper for a special Einstein
issue of Physics Letters A | Phys.Lett. A347 (2005) 1-7 | 10.1016/j.physleta.2005.05.065 | null | gr-qc hep-th quant-ph | null | The existence of spacetime singularities is irrelevant for the irreversible
appearance of black holes. However, confirmation of the latter's unitary
dynamics would require the preparation of a coherent superposition of a
tremendous number of appropriate ``Everett worlds''.
| [
{
"created": "Tue, 12 Jul 2005 10:15:40 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Zeh",
"H. D.",
""
]
] | The existence of spacetime singularities is irrelevant for the irreversible appearance of black holes. However, confirmation of the latter's unitary dynamics would require the preparation of a coherent superposition of a tremendous number of appropriate ``Everett worlds''. |
2301.10248 | Tiago V. Fernandes | Tiago V. Fernandes, David Hilditch, Jos\'e P. S. Lemos, V\'itor
Cardoso | Normal modes of Proca fields in AdS spacetime | 6 pages | Gen. Relativ. Gravit. 55, 5 (2023) | 10.1007/s10714-022-03052-w | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | A normal mode analysis for Proca fields in the anti-de Sitter (AdS) spacetime
is given. It is found that the equations for the Proca field can be decoupled
analytically. This is performed by changing the basis of the vector spherical
harmonics (VSH) decomposition. The normal modes and the normal mode frequencies
of the Proca equation in the AdS spacetime are then analytically determined. It
is also shown that the Maxwell field can be recovered by taking the massless
limit of the Proca field with care so that the nonphysical gauge modes are
eliminated.
| [
{
"created": "Tue, 24 Jan 2023 19:00:00 GMT",
"version": "v1"
}
] | 2023-01-26 | [
[
"Fernandes",
"Tiago V.",
""
],
[
"Hilditch",
"David",
""
],
[
"Lemos",
"José P. S.",
""
],
[
"Cardoso",
"Vítor",
""
]
] | A normal mode analysis for Proca fields in the anti-de Sitter (AdS) spacetime is given. It is found that the equations for the Proca field can be decoupled analytically. This is performed by changing the basis of the vector spherical harmonics (VSH) decomposition. The normal modes and the normal mode frequencies of the Proca equation in the AdS spacetime are then analytically determined. It is also shown that the Maxwell field can be recovered by taking the massless limit of the Proca field with care so that the nonphysical gauge modes are eliminated. |
1708.05576 | D\'aniel Barta | D\'aniel Barta, M\'aty\'as Vas\'uth | Dispersion of gravitational waves in cold spherical interstellar medium | null | Int. J. Mod. Phys. D 27 1850040 (2018) | 10.1142/S0218271818500402 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the propagation of locally plane, small-amplitude,
monochromatic gravitational waves through cold compressible interstellar gas in
order to provide a more accurate picture of expected waveforms for direct
detection. The quasi-isothermal gas is concentrated in a spherical symmetric
cloud held together by self-gravitation. Gravitational waves can be treated as
linearized perturbations on the background inner Schwarzschild spacetime. The
perturbed quantities lead to the field equations governing the gas dynamics and
describe the interaction of gravitational waves with matter. The resulted field
equations decouple asymptotically for slowly varying short waves to a set of
three PDEs of different orders of magnitude. A second-order WKB method provides
transport equations for the wave amplitudes. The influence of background
curvature already appears in the first-order amplitudes, which gives rise to
diffraction. We have shown that the transport equation of these amplitudes
provides numerical solutions for the frequency-alteration. The energy
dissipating process is responsible for decreasing frequency. The decrease is
significantly smaller than the magnitude of the original frequency and exhibits
a power-law relationship between original and decreased frequencies. The
frequency deviation was examined particularly for the transient signal
GW150914. Considering AGNs as larger background structures and high-frequency
signals emitted by BNS mergers, the frequency-deviation grows large enough to
be relevant in future GW-observations with increased sensitivity.
| [
{
"created": "Fri, 18 Aug 2017 12:22:53 GMT",
"version": "v1"
}
] | 2018-06-11 | [
[
"Barta",
"Dániel",
""
],
[
"Vasúth",
"Mátyás",
""
]
] | We investigate the propagation of locally plane, small-amplitude, monochromatic gravitational waves through cold compressible interstellar gas in order to provide a more accurate picture of expected waveforms for direct detection. The quasi-isothermal gas is concentrated in a spherical symmetric cloud held together by self-gravitation. Gravitational waves can be treated as linearized perturbations on the background inner Schwarzschild spacetime. The perturbed quantities lead to the field equations governing the gas dynamics and describe the interaction of gravitational waves with matter. The resulted field equations decouple asymptotically for slowly varying short waves to a set of three PDEs of different orders of magnitude. A second-order WKB method provides transport equations for the wave amplitudes. The influence of background curvature already appears in the first-order amplitudes, which gives rise to diffraction. We have shown that the transport equation of these amplitudes provides numerical solutions for the frequency-alteration. The energy dissipating process is responsible for decreasing frequency. The decrease is significantly smaller than the magnitude of the original frequency and exhibits a power-law relationship between original and decreased frequencies. The frequency deviation was examined particularly for the transient signal GW150914. Considering AGNs as larger background structures and high-frequency signals emitted by BNS mergers, the frequency-deviation grows large enough to be relevant in future GW-observations with increased sensitivity. |
gr-qc/0211086 | Miguel Sanchez | J.L. Flores and M. S\'anchez | Causality and Conjugate Points in General Plane Waves | Version improved with further discussions and a new section; 21
pages, Latex | Class.Quant.Grav. 20 (2003) 2275-2292 | null | null | gr-qc hep-th | null | Let $M = M_0 \times \R^2$ be a pp--wave type spacetime endowed with the
metric $<\cdot,\cdot>_z = <\cdot,\cdot>_x + 2 du dv + H(x,u) du^2$, where
$(M_0, <\cdot,\cdot>_x) $ is any Riemannian manifold and $H(x,u)$ an arbitrary
function. We show that the behaviour of $H(x,u)$ at spatial infinity determines
the causality of $M$, say: (a) if $-H(x,u)$ behaves subquadratically (i.e,
essentially $-H(x,u) \leq R_1(u) |x|^{2-\epsilon} $ for some $\epsilon >0$ and
large distance $|x|$ to a fixed point) and the spatial part $(M_0,
<\cdot,\cdot>_x) $ is complete, then the spacetime $M$ is globally hyperbolic,
(b) if $-H(x,u)$ grows at most quadratically (i.e, $-H(x,u) \leq R_1(u)
|x|^{2}$ for large $|x|$) then it is strongly causal and (c) $M$ is always
causal, but there are non-distinguishing examples (and thus, non-strongly
causal), even when $-H(x,u) \leq R_1(u) |x|^{2+\epsilon} $, for small $\epsilon
>0$.
Therefore, the classical model $M_0 = \R^2$, $H(x,u) = \sum_{i,j} h_{ij}(u)
x_i x_j (\not\equiv 0)$, which is known to be strongly causal but not globally
hyperbolic, lies in the critical quadratic situation with complete $M_0$. This
must be taken into account for realistic applications. In fact, we argue that
$-H$ will be subquadratic (and the spacetime globally hyperbolic) if $M$ is
asymptotically flat. The relation of these results with the notion of
astigmatic conjugacy and the existence of conjugate points is also discussed.
| [
{
"created": "Tue, 26 Nov 2002 17:47:42 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Jun 2003 19:03:25 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Flores",
"J. L.",
""
],
[
"Sánchez",
"M.",
""
]
] | Let $M = M_0 \times \R^2$ be a pp--wave type spacetime endowed with the metric $<\cdot,\cdot>_z = <\cdot,\cdot>_x + 2 du dv + H(x,u) du^2$, where $(M_0, <\cdot,\cdot>_x) $ is any Riemannian manifold and $H(x,u)$ an arbitrary function. We show that the behaviour of $H(x,u)$ at spatial infinity determines the causality of $M$, say: (a) if $-H(x,u)$ behaves subquadratically (i.e, essentially $-H(x,u) \leq R_1(u) |x|^{2-\epsilon} $ for some $\epsilon >0$ and large distance $|x|$ to a fixed point) and the spatial part $(M_0, <\cdot,\cdot>_x) $ is complete, then the spacetime $M$ is globally hyperbolic, (b) if $-H(x,u)$ grows at most quadratically (i.e, $-H(x,u) \leq R_1(u) |x|^{2}$ for large $|x|$) then it is strongly causal and (c) $M$ is always causal, but there are non-distinguishing examples (and thus, non-strongly causal), even when $-H(x,u) \leq R_1(u) |x|^{2+\epsilon} $, for small $\epsilon >0$. Therefore, the classical model $M_0 = \R^2$, $H(x,u) = \sum_{i,j} h_{ij}(u) x_i x_j (\not\equiv 0)$, which is known to be strongly causal but not globally hyperbolic, lies in the critical quadratic situation with complete $M_0$. This must be taken into account for realistic applications. In fact, we argue that $-H$ will be subquadratic (and the spacetime globally hyperbolic) if $M$ is asymptotically flat. The relation of these results with the notion of astigmatic conjugacy and the existence of conjugate points is also discussed. |
2210.16166 | Qihong Huang | Qihong Huang, Kaituo Zhang, He Huang, Bing Xu and Feiquan Tu | CMB power spectrum in the emergent universe with k-essence | null | Universe 2023, 9(5), 221 | 10.3390/universe9050221 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The emergent universe provides a possible method to avoid the big bang
singularity by considering that the universe stems from an stable Einstein
static universe rather than the singularity. Since the Einstein static universe
exists before inflation, it may leave some relics in the CMB power spectrum. In
this paper, we analyze the stability condition for the Einstein static universe
in general relativity with k-essence against both the scalar and tensor
perturbations. And we find the emergent universe can be successfully realized
by constructing a scalar potential and an equation of state parameter. Solving
the curved Mukhanov-Sasaki equation, we obtain the analytical approximation for
the primordial power spectrum, and then depict the TT-spectrum of the emergent
universe. The results show that both the primordial power spectrum and CMB
TT-spectrum are suppressed on large scales.
| [
{
"created": "Fri, 28 Oct 2022 14:40:45 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Jan 2023 04:17:15 GMT",
"version": "v2"
},
{
"created": "Wed, 10 May 2023 12:24:14 GMT",
"version": "v3"
}
] | 2023-05-11 | [
[
"Huang",
"Qihong",
""
],
[
"Zhang",
"Kaituo",
""
],
[
"Huang",
"He",
""
],
[
"Xu",
"Bing",
""
],
[
"Tu",
"Feiquan",
""
]
] | The emergent universe provides a possible method to avoid the big bang singularity by considering that the universe stems from an stable Einstein static universe rather than the singularity. Since the Einstein static universe exists before inflation, it may leave some relics in the CMB power spectrum. In this paper, we analyze the stability condition for the Einstein static universe in general relativity with k-essence against both the scalar and tensor perturbations. And we find the emergent universe can be successfully realized by constructing a scalar potential and an equation of state parameter. Solving the curved Mukhanov-Sasaki equation, we obtain the analytical approximation for the primordial power spectrum, and then depict the TT-spectrum of the emergent universe. The results show that both the primordial power spectrum and CMB TT-spectrum are suppressed on large scales. |
1606.03886 | Ebrahim Yusofi Ramneti | M. Mohsenzadeh and E. Yusofi | Higher Order Corrections to Asymptotic-de Sitter Inflation | 7 pages, 3 figures, Accepted for publication in Chinese Physics C | Chin.Phys. C41 (2017) no.8 | 10.1088/1674-1137/41/8/085101 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Since trans-Planckian considerations can be associated with the re-definition
of the initial vacuum, we investigate further the influence of trans-Planckian
physics on the spectra produced by the initial quasi-de Sitter (dS) state
during inflation. We use the asymptotic-dS mode to study the trans-Planckian
correction of the power spectrum to the quasi-dS inflation. The obtained
spectra consist of higher order corrections associated with the type of
geometry and harmonic terms sensitive to the fluctuations of space-time (or
gravitational waves) during inflation. As an important result, the amplitude of
the power spectrum is dependent on the choice of $c$, i.e. the type of
space-time in the period of inflation. Also, the results are always valid for
any asymptotic dS space-time and particularly coincide with the conventional
results for dS and flat space-time.
| [
{
"created": "Mon, 13 Jun 2016 10:30:33 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Jun 2016 08:32:05 GMT",
"version": "v2"
},
{
"created": "Sat, 3 Jun 2017 09:44:45 GMT",
"version": "v3"
}
] | 2018-04-06 | [
[
"Mohsenzadeh",
"M.",
""
],
[
"Yusofi",
"E.",
""
]
] | Since trans-Planckian considerations can be associated with the re-definition of the initial vacuum, we investigate further the influence of trans-Planckian physics on the spectra produced by the initial quasi-de Sitter (dS) state during inflation. We use the asymptotic-dS mode to study the trans-Planckian correction of the power spectrum to the quasi-dS inflation. The obtained spectra consist of higher order corrections associated with the type of geometry and harmonic terms sensitive to the fluctuations of space-time (or gravitational waves) during inflation. As an important result, the amplitude of the power spectrum is dependent on the choice of $c$, i.e. the type of space-time in the period of inflation. Also, the results are always valid for any asymptotic dS space-time and particularly coincide with the conventional results for dS and flat space-time. |
1907.07336 | Yasutaka Koga | Yasutaka Koga, Tomohiro Harada | Stability of null orbits on photon spheres and photon surfaces | 9 pages | Phys. Rev. D 100, 064040 (2019) | 10.1103/PhysRevD.100.064040 | RUP-19-21 | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Stability of a photon sphere, or stability of circular null geodesics on the
sphere, plays a key role in its applications to astrophysics. For instance, an
unstable photon sphere is responsible for determining the size of a black hole
shadow, while a stable photon sphere is inferred to cause the instability of
spacetime due to the trapping of gravitational waves on the radius. A photon
surface is a geometrical structure first introduced by Claudel, Virbhadra and
Ellis as the generalization of a photon sphere. The surface does not require
any symmetry of spacetime and has its second fundamental form pure-trace. In
this paper, we define the stability of null geodesics on a photon surface. It
represents whether null geodesics perturbed from the photon surface are
attracted to or repelled from the photon surface. Then, we define a strictly
(un)stable photon surface as a photon surface on which all null geodesics are
(un)stable. We find that the stability is determined by Riemann curvature.
Furthermore, it is characterized by the normal derivative of the second
fundamental form. As a consequence, for example, a strictly unstable photon
surface requires nonvanishing Weyl curvature on it if the null energy condition
is satisfied.
| [
{
"created": "Wed, 17 Jul 2019 05:14:34 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Sep 2019 03:03:50 GMT",
"version": "v2"
}
] | 2019-10-02 | [
[
"Koga",
"Yasutaka",
""
],
[
"Harada",
"Tomohiro",
""
]
] | Stability of a photon sphere, or stability of circular null geodesics on the sphere, plays a key role in its applications to astrophysics. For instance, an unstable photon sphere is responsible for determining the size of a black hole shadow, while a stable photon sphere is inferred to cause the instability of spacetime due to the trapping of gravitational waves on the radius. A photon surface is a geometrical structure first introduced by Claudel, Virbhadra and Ellis as the generalization of a photon sphere. The surface does not require any symmetry of spacetime and has its second fundamental form pure-trace. In this paper, we define the stability of null geodesics on a photon surface. It represents whether null geodesics perturbed from the photon surface are attracted to or repelled from the photon surface. Then, we define a strictly (un)stable photon surface as a photon surface on which all null geodesics are (un)stable. We find that the stability is determined by Riemann curvature. Furthermore, it is characterized by the normal derivative of the second fundamental form. As a consequence, for example, a strictly unstable photon surface requires nonvanishing Weyl curvature on it if the null energy condition is satisfied. |
0810.1903 | Jeffrey Winicour | Jeffrey Winicour | Characteristic Evolution and Matching | New version to appear in Living Reviews 2012. arXiv admin note:
updated version of arXiv:gr-qc/0508097 | null | 10.12942/lrr-2009-3 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I review the development of numerical evolution codes for general relativity
based upon the characteristic initial value problem. Progress in characteristic
evolution is traced from the early stage of 1D feasibility studies to 2D
axisymmetric codes that accurately simulate the oscillations and gravitational
collapse of relativistic stars and to current 3D codes that provide pieces of a
binary black hole spacetime. Cauchy codes have now been successful at
simulating all aspects of the binary black hole problem inside an artificially
constructed outer boundary. A prime application of characteristic evolution is
to extend such simulations to null infinity where the waveform from the binary
inspiral and merger can be unambiguously computed. This has now been
accomplished by Cauchy-characteristic extraction, where data for the
characteristic evolution is supplied by Cauchy data on an extraction worldtube
inside the artificial outer boundary. The ultimate application of
characteristic evolution is to eliminate the role of this outer boundary by
constructing a global solution via Cauchy-characteristic matching. Progress in
this direction is discussed.
| [
{
"created": "Fri, 10 Oct 2008 15:19:34 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Oct 2008 15:04:42 GMT",
"version": "v2"
},
{
"created": "Wed, 24 Aug 2011 14:05:10 GMT",
"version": "v3"
},
{
"created": "Thu, 12 Jan 2012 16:31:49 GMT",
"version": "v4"
}
] | 2017-01-04 | [
[
"Winicour",
"Jeffrey",
""
]
] | I review the development of numerical evolution codes for general relativity based upon the characteristic initial value problem. Progress in characteristic evolution is traced from the early stage of 1D feasibility studies to 2D axisymmetric codes that accurately simulate the oscillations and gravitational collapse of relativistic stars and to current 3D codes that provide pieces of a binary black hole spacetime. Cauchy codes have now been successful at simulating all aspects of the binary black hole problem inside an artificially constructed outer boundary. A prime application of characteristic evolution is to extend such simulations to null infinity where the waveform from the binary inspiral and merger can be unambiguously computed. This has now been accomplished by Cauchy-characteristic extraction, where data for the characteristic evolution is supplied by Cauchy data on an extraction worldtube inside the artificial outer boundary. The ultimate application of characteristic evolution is to eliminate the role of this outer boundary by constructing a global solution via Cauchy-characteristic matching. Progress in this direction is discussed. |
1212.4049 | Sunandan Gangopadhyay | Sunandan Gangopadhyay | Noncommutative inspired Schwarzschild black hole, Voros product and
Komar energy | Presented at International Conference, COSGRAV12, Indian Statistical
Institute, Kolkata, India, Appeared in Journal of Physics: Conference Series | Journal of Physics : Conference Series 405 (2012) 012014 | 10.1088/1742-6596/405/1/012014 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The importance of the Voros product in defining a noncommutative
Schwarzschild black hole is shown. The entropy is then computed and the area
law is shown to hold upto order $\frac{1}{\sqrt{\theta}}e^{-M^2/\theta}$. The
leading correction to the entropy (computed in the tunneling formalism) is
shown to be logarithmic. The Komar energy $E$ for these black holes is then
obtained and a deformation from the conventional identity $E=2ST_H$ is found at
the order $\sqrt{\theta}e^{-M^2/\theta}$. This deformation leads to a
nonvanishing Komar energy at the extremal point $T_{H}=0$ of these black holes.
Finally, the Smarr formula is worked out. Similar features also exist for a
deSitter-Schwarzschild geometry. This presentation is based on the work in
references [1,2].
| [
{
"created": "Mon, 17 Dec 2012 16:14:12 GMT",
"version": "v1"
}
] | 2015-06-12 | [
[
"Gangopadhyay",
"Sunandan",
""
]
] | The importance of the Voros product in defining a noncommutative Schwarzschild black hole is shown. The entropy is then computed and the area law is shown to hold upto order $\frac{1}{\sqrt{\theta}}e^{-M^2/\theta}$. The leading correction to the entropy (computed in the tunneling formalism) is shown to be logarithmic. The Komar energy $E$ for these black holes is then obtained and a deformation from the conventional identity $E=2ST_H$ is found at the order $\sqrt{\theta}e^{-M^2/\theta}$. This deformation leads to a nonvanishing Komar energy at the extremal point $T_{H}=0$ of these black holes. Finally, the Smarr formula is worked out. Similar features also exist for a deSitter-Schwarzschild geometry. This presentation is based on the work in references [1,2]. |
1906.01735 | Paul R. Anderson | Paul R. Anderson, Raymond D. Clark, Alessandro Fabbri, and Michael R.
R. Good | Late time approach to Hawking radiation: terms beyond leading order | Improved version, significant changes in the presentation, minor
errors corrected, main conclusions unchanged | Phys. Rev. D 100, 061703 (2019) | 10.1103/PhysRevD.100.061703 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black hole evaporation is studied using wave packets for the modes. These
allow for approximate frequency and time resolution. The leading order late
time behavior gives the well known Hawking radiation that is independent of how
the black hole formed. The focus here is on the higher order terms and the rate
at which they damp at late times. Some of these terms carry information about
how the black hole formed. A general argument is given which shows that the
damping is significantly slower (power law) than what might be naively expected
from a stationary phase approximation (exponential). This result is verified by
numerical calculations in the cases of 2D and 4D black holes that form from the
collapse of a null shell.
| [
{
"created": "Tue, 4 Jun 2019 21:47:33 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Jun 2019 14:26:39 GMT",
"version": "v2"
}
] | 2019-09-26 | [
[
"Anderson",
"Paul R.",
""
],
[
"Clark",
"Raymond D.",
""
],
[
"Fabbri",
"Alessandro",
""
],
[
"Good",
"Michael R. R.",
""
]
] | Black hole evaporation is studied using wave packets for the modes. These allow for approximate frequency and time resolution. The leading order late time behavior gives the well known Hawking radiation that is independent of how the black hole formed. The focus here is on the higher order terms and the rate at which they damp at late times. Some of these terms carry information about how the black hole formed. A general argument is given which shows that the damping is significantly slower (power law) than what might be naively expected from a stationary phase approximation (exponential). This result is verified by numerical calculations in the cases of 2D and 4D black holes that form from the collapse of a null shell. |
1910.04437 | Xiao-Mei Kuang | Shi-Qian Hu, Bo Liu, Xiao-Mei Kuang, Rui-Hong Yue | Revisiting black hole thermodynamics in massive gravity: charged
particle absorption and shell of dust falling | 26 pages, 5 figures | Chinese Physics C Vol. 44, No. 10 (2020) 105107 | 10.1088/1674-1137/abab8a | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the variation of the massive black hole in both normal and extended
thermodynamic phase spaces via two methods. The first method includes a charged
particle absorbed by the black hole, while the second method includes a shell
of dust falling into the black hole. Using the former method, the first and
second laws of thermodynamics are always satisfied in the normal phase space,
while in the extended phase space, the first law of thermodynamics is also
satisfied, but the validity of the second law of thermodynamics depends on the
model parameters. Applying the latter method, the first and second laws of
thermodynamics are both valid. We argue that the possible reason for the
violation of the second law of thermodynamics via the former method may be
attributed to the assumption that the change of internal energy of the black
hole is equal to the energy of the particle. Finally, we show that the event
horizon always exists to guarantee the validity of the weak cosmic censorship
in both phase spaces, which means that the violation of the second law of
thermodynamics under the assumption does not affect the weak cosmic censorship
conjecture. This further supports our argument that the assumption in the first
method may be the reason for the violation of the law and it requires deeper
treatment.
| [
{
"created": "Thu, 10 Oct 2019 08:51:33 GMT",
"version": "v1"
}
] | 2020-10-02 | [
[
"Hu",
"Shi-Qian",
""
],
[
"Liu",
"Bo",
""
],
[
"Kuang",
"Xiao-Mei",
""
],
[
"Yue",
"Rui-Hong",
""
]
] | We study the variation of the massive black hole in both normal and extended thermodynamic phase spaces via two methods. The first method includes a charged particle absorbed by the black hole, while the second method includes a shell of dust falling into the black hole. Using the former method, the first and second laws of thermodynamics are always satisfied in the normal phase space, while in the extended phase space, the first law of thermodynamics is also satisfied, but the validity of the second law of thermodynamics depends on the model parameters. Applying the latter method, the first and second laws of thermodynamics are both valid. We argue that the possible reason for the violation of the second law of thermodynamics via the former method may be attributed to the assumption that the change of internal energy of the black hole is equal to the energy of the particle. Finally, we show that the event horizon always exists to guarantee the validity of the weak cosmic censorship in both phase spaces, which means that the violation of the second law of thermodynamics under the assumption does not affect the weak cosmic censorship conjecture. This further supports our argument that the assumption in the first method may be the reason for the violation of the law and it requires deeper treatment. |
1212.2155 | Ratbay Myrzakulov | Ratbay Myrzakulov | Cosmology of F(T) gravity and k-essence | 21 pages | Entropy, v.14, N9, 1627-1651 (2012) | 10.3390/e14091627 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This a brief review on $F(T)$ gravity and its relation with k-essence.
Modified teleparallel gravity theory with the torsion scalar has recently
gained a lot of attention as a possible explanation of dark energy. We perform
a thorough reconstruction analysis on the so-called $F(T)$ models, where $F(T)$
is some general function of the torsion term, and deduce the required
conditions for the equivalence between of $F(T)$ models with pure kinetic
k-essence models. We present a new class of models of $F(T)$-gravity and
k-essence.
| [
{
"created": "Sat, 24 Nov 2012 10:25:01 GMT",
"version": "v1"
}
] | 2012-12-11 | [
[
"Myrzakulov",
"Ratbay",
""
]
] | This a brief review on $F(T)$ gravity and its relation with k-essence. Modified teleparallel gravity theory with the torsion scalar has recently gained a lot of attention as a possible explanation of dark energy. We perform a thorough reconstruction analysis on the so-called $F(T)$ models, where $F(T)$ is some general function of the torsion term, and deduce the required conditions for the equivalence between of $F(T)$ models with pure kinetic k-essence models. We present a new class of models of $F(T)$-gravity and k-essence. |
gr-qc/0109040 | Don N. Page | Don N. Page | Black Holes with Less Entropy Than A/4 | 26 pages, LaTeX, no figures, accepted 2001 Sept. 25 for Phys. Rev. D.
Comments added on ineffective reflection of gravitational radiation | Phys.Rev. D65 (2002) 024017 | 10.1103/PhysRevD.65.024017 | Alberta-Thy-14-01 | gr-qc | null | One can increase one-quarter the area of a black hole, A/4, to exceed the
total thermodynamic entropy, S, by surrounding the hole with a perfectly
reflecting shell and adiabatically squeezing it inward. A/4 can be made to
exceed S by a factor of order unity before the shell enters the Planck regime,
though practical limitations are much more restrictive. One interpretation is
that the black hole entropy resides in its thermal atmosphere, and the shell
restricts the atmosphere so that its entropy is less than A/4.
| [
{
"created": "Tue, 11 Sep 2001 18:12:43 GMT",
"version": "v1"
},
{
"created": "Thu, 27 Sep 2001 20:38:23 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Page",
"Don N.",
""
]
] | One can increase one-quarter the area of a black hole, A/4, to exceed the total thermodynamic entropy, S, by surrounding the hole with a perfectly reflecting shell and adiabatically squeezing it inward. A/4 can be made to exceed S by a factor of order unity before the shell enters the Planck regime, though practical limitations are much more restrictive. One interpretation is that the black hole entropy resides in its thermal atmosphere, and the shell restricts the atmosphere so that its entropy is less than A/4. |
2305.07684 | Muhammad Sharif | M. Sharif and Sana Manzoor | Compact Objects admitting Finch-Skea Symmetry in $f(\mathcal{R},T^2)$
Gravity | 26 pages, 11 figures | Annals Phys. 454(2023)169337 | 10.1016/j.aop.2023.169337 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper investigates the viability and stability of anisotropic compact
stars in the framework of $f(\mathcal{R},\mathrm{T}^{2})$ theory ($\mathcal{R}$
is the Ricci scalar and
$\mathrm{T}^{2}=\mathrm{T}_{\tau\upsilon}\mathrm{T}^{\tau\upsilon}$). In this
perspective, we use Finch-Skea symmetry and consider different
$f(\mathcal{R},\mathrm{T}^{2})$ models to examine physical characteristics of
compact stars. We match interior spacetime with the exterior region to find the
values of unknown constants. Further, we analyze the behavior of several
physical quantities such as effective matter variables, energy bounds,
anisotropic factor and equation of state parameters in the interior of Vela
X-1, SAX J 1808.4-3658, Her X-1 and PSR J0348+0432 stars. The equilibrium state
of these compact stars is examined through the Tolman-Oppenheimer-Volkoff
equation and their stability is checked by causality condition, Herrera
cracking approach and adiabatic index. It is found that all the required
conditions are fulfilled for the considered models. We can conclude that more
viable and stable compact stars are obtained in this modified theory.
| [
{
"created": "Fri, 12 May 2023 13:06:16 GMT",
"version": "v1"
}
] | 2023-05-31 | [
[
"Sharif",
"M.",
""
],
[
"Manzoor",
"Sana",
""
]
] | This paper investigates the viability and stability of anisotropic compact stars in the framework of $f(\mathcal{R},\mathrm{T}^{2})$ theory ($\mathcal{R}$ is the Ricci scalar and $\mathrm{T}^{2}=\mathrm{T}_{\tau\upsilon}\mathrm{T}^{\tau\upsilon}$). In this perspective, we use Finch-Skea symmetry and consider different $f(\mathcal{R},\mathrm{T}^{2})$ models to examine physical characteristics of compact stars. We match interior spacetime with the exterior region to find the values of unknown constants. Further, we analyze the behavior of several physical quantities such as effective matter variables, energy bounds, anisotropic factor and equation of state parameters in the interior of Vela X-1, SAX J 1808.4-3658, Her X-1 and PSR J0348+0432 stars. The equilibrium state of these compact stars is examined through the Tolman-Oppenheimer-Volkoff equation and their stability is checked by causality condition, Herrera cracking approach and adiabatic index. It is found that all the required conditions are fulfilled for the considered models. We can conclude that more viable and stable compact stars are obtained in this modified theory. |
1907.04946 | Benjamin J. Owen | Santiago Caride, Ra Inta, Benjamin J. Owen and Binod Rajbhandari
(Texas Tech University) | How to search for gravitational waves from $r$-modes of known pulsars | 10 pages, 2 figures | Phys. Rev. D 100, 064013 (2019) | 10.1103/PhysRevD.100.064013 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Searches for continuous gravitational waves from known pulsars so far have
been targeted at or near the spin frequency or double the spin frequency of
each pulsar, appropriate for mass quadrupole emission. But some neutron stars
might radiate strongly through current quadrupoles via $r$-modes, which
oscillate at about four thirds the spin frequency. We show for the first time
how to construct searches over appropriate ranges of frequencies and spin-down
parameters to target $r$-modes from known pulsars. We estimate computational
costs and sensitivities of realistic $r$-mode searches using the coherent
$\mathcal{F}$-statistic, and find that feasible searches for known pulsars can
beat spin-down limits on gravitational wave emission even with existing LIGO
and Virgo data.
| [
{
"created": "Wed, 10 Jul 2019 22:35:06 GMT",
"version": "v1"
}
] | 2019-09-18 | [
[
"Caride",
"Santiago",
"",
"Texas Tech University"
],
[
"Inta",
"Ra",
"",
"Texas Tech University"
],
[
"Owen",
"Benjamin J.",
"",
"Texas Tech University"
],
[
"Rajbhandari",
"Binod",
"",
"Texas Tech University"
]
] | Searches for continuous gravitational waves from known pulsars so far have been targeted at or near the spin frequency or double the spin frequency of each pulsar, appropriate for mass quadrupole emission. But some neutron stars might radiate strongly through current quadrupoles via $r$-modes, which oscillate at about four thirds the spin frequency. We show for the first time how to construct searches over appropriate ranges of frequencies and spin-down parameters to target $r$-modes from known pulsars. We estimate computational costs and sensitivities of realistic $r$-mode searches using the coherent $\mathcal{F}$-statistic, and find that feasible searches for known pulsars can beat spin-down limits on gravitational wave emission even with existing LIGO and Virgo data. |
1709.02650 | Bibhas Majhi Ranjan | Krishnakanta Bhattacharya, Bibhas Ranjan Majhi, Saurav Samanta | Van der Waals criticality in AdS black holes: a phenomenological study | Refs. and comments added, to appear in Phys. Rev. D | Phys. Rev. D 96, 084037 (2017) | 10.1103/PhysRevD.96.084037 | null | gr-qc cond-mat.stat-mech hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | AdS black holes exhibit van der Waals type phase transition. In the {\it
extended} phase-space formalism, the critical exponents for any spacetime
metric are identical to the standard ones. Motivated by this fact, we give a
general expression for the Helmholtz free energy near the critical point which
correctly reproduces these exponents. The idea is similar to the Landau model
which gives a phenomenological description of the usual second order phase
transition. Here two main inputs are taken into account for the analysis: (a)
black holes should have van der Waals like isotherms and (b) free energy can be
expressed solely as a function of thermodynamic volume and horizon temperature.
Resulting analysis shows that the form of Helmholtz free energy correctly
encapsulates the features of Landau function. We also discuss the {\it isolated
critical point} accompanied by nonstandard values of critical exponents. The
whole formalism is then extended to other two criticalities, namely $Y-X$ and
$T-S$ (based on the standard; i.e. non-extended phase-space), where $X$ and $Y$
are generalized force and displacement, whereas $T$ and $S$ are horizon
temperature and entropy. We observe that in the former case Gibbs free energy
plays the role of Landau function, whereas in the later case that role is
played by the internal energy (here it is black hole mass). Our analysis shows
that, although the existence of van der Waals phase transition depends on the
explicit form of the black hole metric, the values of the critical exponents
are universal in nature.
| [
{
"created": "Fri, 8 Sep 2017 11:14:19 GMT",
"version": "v1"
},
{
"created": "Thu, 28 Sep 2017 12:52:38 GMT",
"version": "v2"
}
] | 2017-10-19 | [
[
"Bhattacharya",
"Krishnakanta",
""
],
[
"Majhi",
"Bibhas Ranjan",
""
],
[
"Samanta",
"Saurav",
""
]
] | AdS black holes exhibit van der Waals type phase transition. In the {\it extended} phase-space formalism, the critical exponents for any spacetime metric are identical to the standard ones. Motivated by this fact, we give a general expression for the Helmholtz free energy near the critical point which correctly reproduces these exponents. The idea is similar to the Landau model which gives a phenomenological description of the usual second order phase transition. Here two main inputs are taken into account for the analysis: (a) black holes should have van der Waals like isotherms and (b) free energy can be expressed solely as a function of thermodynamic volume and horizon temperature. Resulting analysis shows that the form of Helmholtz free energy correctly encapsulates the features of Landau function. We also discuss the {\it isolated critical point} accompanied by nonstandard values of critical exponents. The whole formalism is then extended to other two criticalities, namely $Y-X$ and $T-S$ (based on the standard; i.e. non-extended phase-space), where $X$ and $Y$ are generalized force and displacement, whereas $T$ and $S$ are horizon temperature and entropy. We observe that in the former case Gibbs free energy plays the role of Landau function, whereas in the later case that role is played by the internal energy (here it is black hole mass). Our analysis shows that, although the existence of van der Waals phase transition depends on the explicit form of the black hole metric, the values of the critical exponents are universal in nature. |
1202.5699 | Salvatore Capozziello | S. Capozziello, M. De Laurentis, L. Fatibene, M. Francaviglia | The physical foundations for the geometric structure of relativistic
theories of gravitation. From General Relativity to Extended Theories of
Gravity through Ehlers-Pirani-Schild approach | 11 pages, 2 figures | International Journal of Geometric Methods in Modern Physics Vol.
9, No. 8 (2012) 1250072 (18 pages) | 10.1142/S0219887812500727 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss in a critical way the physical foundations of geometric structure
of relativistic theories of gravity by the so-called Ehlers-Pirani-Schild
formalism. This approach provides a natural interpretation of the observables
showing how relate them to General Relativity and to a large class of Extended
Theories of Gravity. In particular we show that, in such a formalism, geodesic
and causal structures of space-time can be safely disentangled allowing a
correct analysis in view of observations and experiment. As specific case, we
take into account the case of f(R) gravity.
| [
{
"created": "Sat, 25 Feb 2012 21:24:57 GMT",
"version": "v1"
}
] | 2012-07-26 | [
[
"Capozziello",
"S.",
""
],
[
"De Laurentis",
"M.",
""
],
[
"Fatibene",
"L.",
""
],
[
"Francaviglia",
"M.",
""
]
] | We discuss in a critical way the physical foundations of geometric structure of relativistic theories of gravity by the so-called Ehlers-Pirani-Schild formalism. This approach provides a natural interpretation of the observables showing how relate them to General Relativity and to a large class of Extended Theories of Gravity. In particular we show that, in such a formalism, geodesic and causal structures of space-time can be safely disentangled allowing a correct analysis in view of observations and experiment. As specific case, we take into account the case of f(R) gravity. |
2005.11572 | Martin Bojowald | Garrett Wendel, Luis Martinez, Martin Bojowald | Physical implications of a fundamental period of time | 5 pages, 3 figures | Phys. Rev. Lett. 124 (2020) 241301 | 10.1103/PhysRevLett.124.241301 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | If time is described by a fundamental process rather than a coordinate, it
interacts with any physical system that evolves in time. The resulting dynamics
is shown here to be consistent provided the fundamental period of the time
system is sufficiently small. A strong upper bound T_C < 10^{-33}s of the
fundamental period of time, several orders of magnitude below any direct time
measurement, is obtained from bounds on dynamical variations of the period of a
system evolving in time.
| [
{
"created": "Sat, 23 May 2020 17:13:03 GMT",
"version": "v1"
}
] | 2020-07-07 | [
[
"Wendel",
"Garrett",
""
],
[
"Martinez",
"Luis",
""
],
[
"Bojowald",
"Martin",
""
]
] | If time is described by a fundamental process rather than a coordinate, it interacts with any physical system that evolves in time. The resulting dynamics is shown here to be consistent provided the fundamental period of the time system is sufficiently small. A strong upper bound T_C < 10^{-33}s of the fundamental period of time, several orders of magnitude below any direct time measurement, is obtained from bounds on dynamical variations of the period of a system evolving in time. |
1210.1146 | Luca Fabbri | Luca Fabbri | On a purely geometric approach to the Dirac matter field and its quantum
properties | 14 pages | Int.J.Theor.Phys.53, 1896-1909 (2014) | 10.1007/s10773-013-1992-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the most general axial torsion completion of gravity with
electrodynamics for $\frac{1}{2}$-spin spinors in an $8$-dimensional
representation of the Dirac matter field: this theory will allow to define
antimatter as matter with all quantum numbers reversed, where also the sign of
the mass beside that of the charge is inverted: we shall see that matter and
antimatter solutions of the Dirac field equations coincide with the known ones
with respect to all observables, that despite the inversion of the sign of the
mass term only positive-mass states are present and only positive-energy
densities are given; the present and the common approach will be compared, and
some experimental implications will be discussed.
| [
{
"created": "Wed, 3 Oct 2012 15:28:13 GMT",
"version": "v1"
},
{
"created": "Sun, 12 Jan 2014 17:23:12 GMT",
"version": "v2"
},
{
"created": "Thu, 8 May 2014 10:53:31 GMT",
"version": "v3"
}
] | 2014-05-13 | [
[
"Fabbri",
"Luca",
""
]
] | We consider the most general axial torsion completion of gravity with electrodynamics for $\frac{1}{2}$-spin spinors in an $8$-dimensional representation of the Dirac matter field: this theory will allow to define antimatter as matter with all quantum numbers reversed, where also the sign of the mass beside that of the charge is inverted: we shall see that matter and antimatter solutions of the Dirac field equations coincide with the known ones with respect to all observables, that despite the inversion of the sign of the mass term only positive-mass states are present and only positive-energy densities are given; the present and the common approach will be compared, and some experimental implications will be discussed. |
1602.08512 | Sergiu I. Vacaru | Tamara Gheorghiu, Vyacheslav Ruchin, Olivia Vacaru, Sergiu I. Vacaru | Geometric Flows and Perelman's Thermodynamics for Black Ellipsoids in
$R^2$ and Einstein Gravity Theories | latex2e, 12pt, 46 pages; accepted: Annals Phys. NY | Annals of Physics NY 369 (2016) 1-35 | 10.1016/j.aop.2016.02.008 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study geometric relativistic flow and Ricci soliton equations which (for
respective nonholonomic constraints and self-similarity conditions) are
equivalent to the gravitational field equations of $R^2$ gravity and/or to the
Einstein equations with scalar field in general relativity, GR. Perelman's
functionals are generalized for modified gravity theories, MGTs, which allows
to formulate an analogous statistical thermodynamics for geometric flows and
Ricci solitons. There are constructed and analyzed generic off-diagonal black
ellipsoid, black hole and solitonic exact solutions in MGTs and GR encoding
geometric flow evolution scenarios and nonlinear parametric interactions. Such
new classes of solutions in MGTs can be with polarized and/or running
constants, nonholonomically deformed horizons and/or imbedded self-consistently
into solitonic backgrounds. They exist also in GR as generic off-diagonal
vacuum configurations with effective cosmological constant and/or mimicking
effective scalar field interactions. Finally, we compute Perelman's energy and
entropy for black ellipsoids and evolution solitons in $R^2$ gravity.
| [
{
"created": "Fri, 19 Feb 2016 13:30:54 GMT",
"version": "v1"
}
] | 2016-03-25 | [
[
"Gheorghiu",
"Tamara",
""
],
[
"Ruchin",
"Vyacheslav",
""
],
[
"Vacaru",
"Olivia",
""
],
[
"Vacaru",
"Sergiu I.",
""
]
] | We study geometric relativistic flow and Ricci soliton equations which (for respective nonholonomic constraints and self-similarity conditions) are equivalent to the gravitational field equations of $R^2$ gravity and/or to the Einstein equations with scalar field in general relativity, GR. Perelman's functionals are generalized for modified gravity theories, MGTs, which allows to formulate an analogous statistical thermodynamics for geometric flows and Ricci solitons. There are constructed and analyzed generic off-diagonal black ellipsoid, black hole and solitonic exact solutions in MGTs and GR encoding geometric flow evolution scenarios and nonlinear parametric interactions. Such new classes of solutions in MGTs can be with polarized and/or running constants, nonholonomically deformed horizons and/or imbedded self-consistently into solitonic backgrounds. They exist also in GR as generic off-diagonal vacuum configurations with effective cosmological constant and/or mimicking effective scalar field interactions. Finally, we compute Perelman's energy and entropy for black ellipsoids and evolution solitons in $R^2$ gravity. |
1305.2177 | Sebastian Szybka | Christa R. \"Olz, Sebastian J. Szybka | Conformal and projection diagrams in LaTeX | 18 pages, tutorial | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In general relativity, the causal structure of space-time may sometimes be
depicted by conformal Carter-Penrose diagrams or a recent extension of these -
the projection diagrams. The introduction of conformal diagrams in the sixties
was one of the progenitors of the golden age of relativity. They are the key
ingredient of many scientific papers. Unfortunately, drawing them in the form
suitable for LaTeX documents is time-consuming and not easy. We present below a
library that allows one to draw an arbitrary conformal diagram in a few simple
steps.
| [
{
"created": "Thu, 9 May 2013 18:56:35 GMT",
"version": "v1"
}
] | 2013-05-10 | [
[
"Ölz",
"Christa R.",
""
],
[
"Szybka",
"Sebastian J.",
""
]
] | In general relativity, the causal structure of space-time may sometimes be depicted by conformal Carter-Penrose diagrams or a recent extension of these - the projection diagrams. The introduction of conformal diagrams in the sixties was one of the progenitors of the golden age of relativity. They are the key ingredient of many scientific papers. Unfortunately, drawing them in the form suitable for LaTeX documents is time-consuming and not easy. We present below a library that allows one to draw an arbitrary conformal diagram in a few simple steps. |
2309.13594 | Gaetano Lambiase | G. Lambiase, L. Mastrototaro, Reggie C. Pantig, Ali Ovgun | Probing Schwarzschild-like Black Holes in Metric-Affine Bumblebee
Gravity with Accretion Disk, Deflection Angle, Greybody Bounds, and Neutrino
Propagation | 14 pages, 7 figures | JCAP 12 (2023) 026 | 10.1088/1475-7516/2023/12/026 | null | gr-qc astro-ph.GA astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | In this paper, we investigate Schwarzschild-like black holes within the
framework of metric-affine bumblebee gravity. We explore the implications of
such a gravitational setup on various astrophysical phenomena, including the
presence of an accretion disk, the deflection angle of light rays, the
establishment of greybody bounds, and the propagation of neutrinos. The
metric-affine bumblebee gravity theory offers a unique perspective on
gravitational interactions by introducing a vector field that couples to
spacetime curvature. We analyze the behavior of accretion disks around
Schwarzschild-like black holes in this modified gravity scenario, considering
the effects of the bumblebee field on the accretion process. Furthermore, we
scrutinize the deflection angle of light rays as they traverse the
gravitational field, highlighting potential deviations from standard
predictions due to the underlying metric-affine structure. Investigating
greybody bounds in this context sheds light on the thermal radiation emitted by
black holes and how the modified gravity framework influences this phenomenon.
Moreover, we explore neutrino propagation around Schwarzschild-like black holes
within metric-affine bumblebee gravity, examining alterations in neutrino
trajectories and interactions compared to conventional general relativity. By
comprehensively probing these aspects, we aim to unravel the distinctive
features and consequences of Schwarzschild-like black holes in the context of
metric-affine bumblebee gravity, offering new insights into the nature of
gravitational interactions and their observable signatures.
| [
{
"created": "Sun, 24 Sep 2023 09:38:27 GMT",
"version": "v1"
}
] | 2024-01-09 | [
[
"Lambiase",
"G.",
""
],
[
"Mastrototaro",
"L.",
""
],
[
"Pantig",
"Reggie C.",
""
],
[
"Ovgun",
"Ali",
""
]
] | In this paper, we investigate Schwarzschild-like black holes within the framework of metric-affine bumblebee gravity. We explore the implications of such a gravitational setup on various astrophysical phenomena, including the presence of an accretion disk, the deflection angle of light rays, the establishment of greybody bounds, and the propagation of neutrinos. The metric-affine bumblebee gravity theory offers a unique perspective on gravitational interactions by introducing a vector field that couples to spacetime curvature. We analyze the behavior of accretion disks around Schwarzschild-like black holes in this modified gravity scenario, considering the effects of the bumblebee field on the accretion process. Furthermore, we scrutinize the deflection angle of light rays as they traverse the gravitational field, highlighting potential deviations from standard predictions due to the underlying metric-affine structure. Investigating greybody bounds in this context sheds light on the thermal radiation emitted by black holes and how the modified gravity framework influences this phenomenon. Moreover, we explore neutrino propagation around Schwarzschild-like black holes within metric-affine bumblebee gravity, examining alterations in neutrino trajectories and interactions compared to conventional general relativity. By comprehensively probing these aspects, we aim to unravel the distinctive features and consequences of Schwarzschild-like black holes in the context of metric-affine bumblebee gravity, offering new insights into the nature of gravitational interactions and their observable signatures. |
2305.11118 | Juliano Neves | R. R. Cuzinatto, C. A. M. de Melo, Juliano C. S. Neves | Shadows of black holes at cosmological distances in the co-varying
physical couplings framework | 10 pages, 2 figures. Published in Monthly Notices of the Royal
Astronomical Society | MNRAS 526 (3), 3987-3993 (2023) | 10.1093/mnras/stad2954 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The co-varying physical couplings (CPC) framework states that physical
parameters like the speed of light in vacuum $c$, the Newtonian constant $G$,
and the cosmological constant $\Lambda$ could indeed vary with the spacetime
coordinates $x^{\mu}$. Here, we assume a temporal variation, that is,
$c(t),G(t)$ and $\Lambda(t)$. We show that the McVittie spacetime, a black hole
in an expanding universe, is a solution of the CPC framework providing
naturally an important parameter of the model. Then, we calculate the shadow
angular radius of this black hole at cosmological distances. A black hole
shadow in the CPC context could be either larger or smaller than the same
shadow in the standard cosmology. It depends on how the set $\{ c,G,\Lambda \}$
varies with time or with the cosmic expansion.
| [
{
"created": "Thu, 18 May 2023 16:59:01 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Oct 2023 22:15:40 GMT",
"version": "v2"
}
] | 2023-10-18 | [
[
"Cuzinatto",
"R. R.",
""
],
[
"de Melo",
"C. A. M.",
""
],
[
"Neves",
"Juliano C. S.",
""
]
] | The co-varying physical couplings (CPC) framework states that physical parameters like the speed of light in vacuum $c$, the Newtonian constant $G$, and the cosmological constant $\Lambda$ could indeed vary with the spacetime coordinates $x^{\mu}$. Here, we assume a temporal variation, that is, $c(t),G(t)$ and $\Lambda(t)$. We show that the McVittie spacetime, a black hole in an expanding universe, is a solution of the CPC framework providing naturally an important parameter of the model. Then, we calculate the shadow angular radius of this black hole at cosmological distances. A black hole shadow in the CPC context could be either larger or smaller than the same shadow in the standard cosmology. It depends on how the set $\{ c,G,\Lambda \}$ varies with time or with the cosmic expansion. |
1910.00784 | Zhoujian Cao Dr | Xiaolin Liu and Zhoujian Cao and Lijing Shao | Validating the Effective-One-Body Numerical-Relativity Waveform Models
for Spin-aligned Binary Black Holes along Eccentric Orbits | 13 pages, 8 figures and 2 tables | Phys. Rev. D 101, 044049 (2020) | 10.1103/PhysRevD.101.044049 | null | gr-qc astro-ph.GA astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Effective-one-body (EOB) numerical-relativity (NR) waveform models for
spin-aligned binary black holes (BBHs), known as the SEOBNR waveform models,
are based on the EOB theoretical framework and NR simulations. SEOBNR models
have played an important role in the LIGO scientific collaboration (LSC)
gravitational wave (GW) data analysis for both signal search and parameter
estimation. SEOBNR models for quasi-circular orbits have evolved through
version 1 to version 4 by extending their validity domain and including more NR
results. Along another direction, we recently extended SEOBNRv1 model to
SEOBNRE model which is valid for spin-aligned BBH coalescence along eccentric
orbits. In this paper we validate this theoretical waveform model by comparing
them against the numerical relativity simulation bank, Simulating eXtreme
Spacetimes (SXS) catalog. In total, 278 NR waveforms are investigated which
include binaries with large eccentricity; large spin and large mass ratio. Our
SEOBNRE can model the NR waveforms quite well. The fitting factor for most of
the 278 waveforms is larger than 99\%. It indicates that the SEOBNRE model
could be used as template waveforms for eccentric spin-aligned BBH coalescence.
| [
{
"created": "Wed, 2 Oct 2019 05:46:44 GMT",
"version": "v1"
}
] | 2020-03-04 | [
[
"Liu",
"Xiaolin",
""
],
[
"Cao",
"Zhoujian",
""
],
[
"Shao",
"Lijing",
""
]
] | Effective-one-body (EOB) numerical-relativity (NR) waveform models for spin-aligned binary black holes (BBHs), known as the SEOBNR waveform models, are based on the EOB theoretical framework and NR simulations. SEOBNR models have played an important role in the LIGO scientific collaboration (LSC) gravitational wave (GW) data analysis for both signal search and parameter estimation. SEOBNR models for quasi-circular orbits have evolved through version 1 to version 4 by extending their validity domain and including more NR results. Along another direction, we recently extended SEOBNRv1 model to SEOBNRE model which is valid for spin-aligned BBH coalescence along eccentric orbits. In this paper we validate this theoretical waveform model by comparing them against the numerical relativity simulation bank, Simulating eXtreme Spacetimes (SXS) catalog. In total, 278 NR waveforms are investigated which include binaries with large eccentricity; large spin and large mass ratio. Our SEOBNRE can model the NR waveforms quite well. The fitting factor for most of the 278 waveforms is larger than 99\%. It indicates that the SEOBNRE model could be used as template waveforms for eccentric spin-aligned BBH coalescence. |
1611.07501 | Ali \"Ovg\"un Dr. | Ali \"Ovg\"un and Kimet Jusufi | Stable Dyonic Thin-Shell Wormholes in Low-Energy String Theory | 10 pages, 3 figures, will appear in Advances in High Energy Physics | Advances in High Energy Physics Volume 2017, 1215254 (2017) | 10.1155/2017/1215254 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Considerable attention has been devoted to the wormhole physics in the past
30 years by exploring the possibilities of finding traversable wormholes
without the need of exotic matter. In particular the thin-shell wormhole
formalism has been widely investigated by exploiting the cut-and-paste
technique to merge two space-time regions and, to research the stability of
these wormholes developed by Visser. This method helps us to minimize the
amount of the exotic matter. In this paper we construct a four dimensional,
spherically symmetric, dyonic thin-shell wormhole with electric charge $Q$,
magnetic charge $P$, and dilaton charge $\Sigma$, in the context of
Einstein-Maxwell-dilaton theory. We have applied Darmois-Israel formalism and
the cut-and-paste method by joining together two identical spacetime solutions.
We carry out the dyonic thin-shell wormhole stability analyses by using a
linear barotropic gas, Chaplygin gas, and logarithmic gas for the exotic
matter. It is shown that by choosing suitable parameter values as well as
equation of state parameter, under specific conditions we obtain a stable
dyonic thin-shell wormhole solution. Finally we argue that, the stability
domain of the dyonic thin-shell wormhole can be increased in terms of electric
charge, magnetic charge, and dilaton charge.
| [
{
"created": "Tue, 22 Nov 2016 20:28:45 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Jun 2017 15:15:53 GMT",
"version": "v2"
},
{
"created": "Tue, 3 Oct 2017 16:53:10 GMT",
"version": "v3"
}
] | 2017-11-03 | [
[
"Övgün",
"Ali",
""
],
[
"Jusufi",
"Kimet",
""
]
] | Considerable attention has been devoted to the wormhole physics in the past 30 years by exploring the possibilities of finding traversable wormholes without the need of exotic matter. In particular the thin-shell wormhole formalism has been widely investigated by exploiting the cut-and-paste technique to merge two space-time regions and, to research the stability of these wormholes developed by Visser. This method helps us to minimize the amount of the exotic matter. In this paper we construct a four dimensional, spherically symmetric, dyonic thin-shell wormhole with electric charge $Q$, magnetic charge $P$, and dilaton charge $\Sigma$, in the context of Einstein-Maxwell-dilaton theory. We have applied Darmois-Israel formalism and the cut-and-paste method by joining together two identical spacetime solutions. We carry out the dyonic thin-shell wormhole stability analyses by using a linear barotropic gas, Chaplygin gas, and logarithmic gas for the exotic matter. It is shown that by choosing suitable parameter values as well as equation of state parameter, under specific conditions we obtain a stable dyonic thin-shell wormhole solution. Finally we argue that, the stability domain of the dyonic thin-shell wormhole can be increased in terms of electric charge, magnetic charge, and dilaton charge. |
0710.0022 | Lorenzo Iorio | Lorenzo Iorio | Astronomical constraints on some long-range models of modified gravity | Latex, 13 pages, no figures, 1 table. Other references added. Minor
stylistic changes. To appear in AHEP (Advances in High Energy Physics). Typo
corrected in eq. 6: thanks to G.E. Melki | Adv.High Energy Phys.2009:90731,2009 | 10.1155/2007/90731 | null | gr-qc astro-ph hep-ph physics.space-ph | null | In this paper we use the corrections to the usual Newton-Einstein secular
precessions of the perihelia of the inner planets of the Solar System,
phenomenologically estimated as solve-for parameters by the Russian astronomer
E.V. Pitjeva by fitting almost one century of data with the EPM2004
ephemerides, in order to constrain some long-range models of modified gravity
recently put forth to address the dark energy and dark matter problems. The
models examined here are the four-dimensional ones obtained with the addition
of inverse powers and logarithm of some curvature invariants, and the
multidimensional braneworld model by Dvali, Gabadadze and Porrati (DGP). After
working out the analytical expressions of the secular perihelion precessions
induced by the corrections to the Newtonian potential of such models, we
compare them to the estimated corrections to the rates of perihelia by taking
their ratio for different pairs of planets instead of using one perihelion at a
time for each planet separately, as done so far in literature. As a result, the
curvature invariants-based models are ruled out, even by re-scaling by a factor
10 the errors in the planetary orbital parameters estimated by Pitjeva. Less
neat is the situation for the DGP model. Only the general relativistic
Lense-Thirring effect, not included, as the other exotic models considered
here, by Pitjeva in the dynamical force models used in the estimation process,
passes such a test. It would be important to repeat the present analysis by
using corrections to the precessions of perihelia independently estimated by
other teams of astronomers as well, but, at present, such rates are not yet
available.
| [
{
"created": "Fri, 28 Sep 2007 22:26:27 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Oct 2007 12:41:30 GMT",
"version": "v2"
},
{
"created": "Wed, 3 Oct 2007 13:26:52 GMT",
"version": "v3"
},
{
"created": "Sat, 6 Oct 2007 15:32:26 GMT",
"version": "v4"
},
{
"created": "Sun, 21 Oct 2007 23:51:17 GMT",
"version": "v5"
}
] | 2009-12-17 | [
[
"Iorio",
"Lorenzo",
""
]
] | In this paper we use the corrections to the usual Newton-Einstein secular precessions of the perihelia of the inner planets of the Solar System, phenomenologically estimated as solve-for parameters by the Russian astronomer E.V. Pitjeva by fitting almost one century of data with the EPM2004 ephemerides, in order to constrain some long-range models of modified gravity recently put forth to address the dark energy and dark matter problems. The models examined here are the four-dimensional ones obtained with the addition of inverse powers and logarithm of some curvature invariants, and the multidimensional braneworld model by Dvali, Gabadadze and Porrati (DGP). After working out the analytical expressions of the secular perihelion precessions induced by the corrections to the Newtonian potential of such models, we compare them to the estimated corrections to the rates of perihelia by taking their ratio for different pairs of planets instead of using one perihelion at a time for each planet separately, as done so far in literature. As a result, the curvature invariants-based models are ruled out, even by re-scaling by a factor 10 the errors in the planetary orbital parameters estimated by Pitjeva. Less neat is the situation for the DGP model. Only the general relativistic Lense-Thirring effect, not included, as the other exotic models considered here, by Pitjeva in the dynamical force models used in the estimation process, passes such a test. It would be important to repeat the present analysis by using corrections to the precessions of perihelia independently estimated by other teams of astronomers as well, but, at present, such rates are not yet available. |
1502.02593 | Pedro Moraes | Pedro H.R.S. Moraes | Cosmological solutions from Induced Matter Model applied to 5D f(R,T)
gravity and the shrinking of the extra coordinate | 8 pages, 4 figures. Accepted for publication in European Physical
Journal C | null | 10.1140/epjc/s10052-015-3393-x | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, I present exact cosmological solutions from Wesson's Induced
Matter Model application to a general 5D metric in f(R,T) theory of gravity.
The non-conservation of the energy-momentum tensor, predicted by f(R,T) theory,
allows the derivation of a relation that describes the time evolution of the
extra coordinate, revealing its compactification. It is showed that such a
compactification could induce the effects of an accelerated expansion in the
observable universe.
| [
{
"created": "Mon, 9 Feb 2015 18:27:30 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Apr 2015 19:15:19 GMT",
"version": "v2"
}
] | 2015-04-23 | [
[
"Moraes",
"Pedro H. R. S.",
""
]
] | In this work, I present exact cosmological solutions from Wesson's Induced Matter Model application to a general 5D metric in f(R,T) theory of gravity. The non-conservation of the energy-momentum tensor, predicted by f(R,T) theory, allows the derivation of a relation that describes the time evolution of the extra coordinate, revealing its compactification. It is showed that such a compactification could induce the effects of an accelerated expansion in the observable universe. |
2111.09163 | Atsuhisa Ota | Atsuhisa Ota, Hayley J. Macpherson, William R. Coulton | Covariant transverse-traceless projection for secondary gravitational
waves | 14 pages, 2 figure, major revision | null | 10.1103/PhysRevD.106.063521 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Second-order tensor modes induced by nonlinear gravity are a key component of
the cosmological background of gravitational waves. A detection of this
background would allow us to probe the primordial power spectrum at otherwise
inaccessible scales. Usually, the energy density of these gravitational waves
is studied within perturbation theory in a particular gauge -- a connection
between our physical spacetime and a fictitious background. It is a widely
recognized issue that the second-order, scalar-induced gravitational waves are
gauge dependent. This issue arises because they are not well-defined as tensors
in the physical spacetime at second-order and are thus unphysical. In this
paper, we propose the covariant transverse-traceless projection of the
extrinsic curvature to study cosmological gravitational waves on a spatial
hypersurface. We define a new energy density which is based purely on spacetime
tensors, independent of perturbation theory, and thus is gauge invariant by
definition. We show that, in the context of second-order perturbation theory,
this new energy density contains only propagating modes in the constant-time
hypersurface in the Newtonian gauge. We further show that we can recover the
same gravitational waves after a transformation to the synchronous gauge, so
long as we correctly identify the Newtonian hypersurface.
| [
{
"created": "Wed, 17 Nov 2021 14:54:12 GMT",
"version": "v1"
},
{
"created": "Fri, 1 Jul 2022 11:43:32 GMT",
"version": "v2"
}
] | 2022-10-05 | [
[
"Ota",
"Atsuhisa",
""
],
[
"Macpherson",
"Hayley J.",
""
],
[
"Coulton",
"William R.",
""
]
] | Second-order tensor modes induced by nonlinear gravity are a key component of the cosmological background of gravitational waves. A detection of this background would allow us to probe the primordial power spectrum at otherwise inaccessible scales. Usually, the energy density of these gravitational waves is studied within perturbation theory in a particular gauge -- a connection between our physical spacetime and a fictitious background. It is a widely recognized issue that the second-order, scalar-induced gravitational waves are gauge dependent. This issue arises because they are not well-defined as tensors in the physical spacetime at second-order and are thus unphysical. In this paper, we propose the covariant transverse-traceless projection of the extrinsic curvature to study cosmological gravitational waves on a spatial hypersurface. We define a new energy density which is based purely on spacetime tensors, independent of perturbation theory, and thus is gauge invariant by definition. We show that, in the context of second-order perturbation theory, this new energy density contains only propagating modes in the constant-time hypersurface in the Newtonian gauge. We further show that we can recover the same gravitational waves after a transformation to the synchronous gauge, so long as we correctly identify the Newtonian hypersurface. |
1312.4357 | Olivier Minazzoli | Olivier Minazzoli | On the cosmic convergence mechanism of the massless dilaton | 4 pages -- accepted for publication in Physics Letters B | Physics Letters B, Volume 735, 30 July 2014 | 10.1016/j.physletb.2014.06.027 | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The converging mechanism discussed in [Damour & Nordtvedt, Physical Review
Letters,70,15] for scalar-tensor theories has been applied to dilaton-like
theories in several subsequent papers. In the present communication, we show
that an unfortunate assumption in those studies led to a scalar-field equation
unsuitable for the study of the dilaton field. The corrected scalar-field
equation turns to change the numerical outcome of those studies in general, but
even sometimes their qualitative aftermath. Therefore, the present result call
for new investigations of the subject. On the other hand, our result shows that
the string-inspired theory presented in [Minazzoli & Hees, Physical Review
D,88,4] is naturally solution to the problem of the effective constancy of the
fundamental coupling constants at late cosmic times, while it requires less
fine-tuning than other massless dilaton or usual stalar-tensor theories.
| [
{
"created": "Mon, 16 Dec 2013 13:43:02 GMT",
"version": "v1"
},
{
"created": "Sun, 15 Jun 2014 09:49:38 GMT",
"version": "v2"
}
] | 2014-06-24 | [
[
"Minazzoli",
"Olivier",
""
]
] | The converging mechanism discussed in [Damour & Nordtvedt, Physical Review Letters,70,15] for scalar-tensor theories has been applied to dilaton-like theories in several subsequent papers. In the present communication, we show that an unfortunate assumption in those studies led to a scalar-field equation unsuitable for the study of the dilaton field. The corrected scalar-field equation turns to change the numerical outcome of those studies in general, but even sometimes their qualitative aftermath. Therefore, the present result call for new investigations of the subject. On the other hand, our result shows that the string-inspired theory presented in [Minazzoli & Hees, Physical Review D,88,4] is naturally solution to the problem of the effective constancy of the fundamental coupling constants at late cosmic times, while it requires less fine-tuning than other massless dilaton or usual stalar-tensor theories. |
gr-qc/9507015 | null | Giampiero Esposito and Giuseppe Pollifrone | Twistors in Conformally Flat Einstein Four-Manifolds | 22 pages, plain-tex | Int.J.Mod.Phys. D5 (1996) 481-494 | 10.1142/S0218271896000291 | DSF 95/24 | gr-qc | null | This paper studies the two-component spinor form of massive spin-3/2
potentials in conformally flat Einstein four-manifolds. Following earlier work
in the literature, a non-vanishing cosmological constant makes it necessary to
introduce a supercovariant derivative operator. The analysis of supergauge
transformations of primary and secondary potentials for spin 3/2 shows that the
gauge freedom for massive spin-3/2 potentials is generated by solutions of the
supertwistor equations. The supercovariant form of a partial connection on a
non-linear bundle is then obtained, and the basic equation of massive secondary
potentials is shown to be the integrability condition on super beta-surfaces of
a differential operator on a vector bundle of rank three. Moreover, in the
presence of boundaries, a simple algebraic relation among some spinor fields is
found to ensure the gauge invariance of locally supersymmetric boundary
conditions relevant for quantum cosmology and supergravity.
| [
{
"created": "Thu, 6 Jul 1995 15:48:39 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Esposito",
"Giampiero",
""
],
[
"Pollifrone",
"Giuseppe",
""
]
] | This paper studies the two-component spinor form of massive spin-3/2 potentials in conformally flat Einstein four-manifolds. Following earlier work in the literature, a non-vanishing cosmological constant makes it necessary to introduce a supercovariant derivative operator. The analysis of supergauge transformations of primary and secondary potentials for spin 3/2 shows that the gauge freedom for massive spin-3/2 potentials is generated by solutions of the supertwistor equations. The supercovariant form of a partial connection on a non-linear bundle is then obtained, and the basic equation of massive secondary potentials is shown to be the integrability condition on super beta-surfaces of a differential operator on a vector bundle of rank three. Moreover, in the presence of boundaries, a simple algebraic relation among some spinor fields is found to ensure the gauge invariance of locally supersymmetric boundary conditions relevant for quantum cosmology and supergravity. |
gr-qc/0608098 | Marek Szydlowski | Marek Szydlowski, Aleksandra Kurek | Towards classification of simple dark energy cosmological models | 10 pages, 2 figures, the paper presented at 42nd Karpacz Winter
School of Theoretical Physics: Ladek, Poland, 6-11 Feb 2006 | ECONFC0602061:18,2006; Int.J.Geom.Meth.Mod.Phys.4:313,2007 | 10.1142/S0219887807002016 | null | gr-qc | null | We characterize a class of simple FRW models filled by both dark energy and
dark matter in notion of a single potential function of the scale factor
$a(t)$; $t$ is the cosmological time. It is representing potential of
fictitious particle - Universe moving in 1-dimensional well $V(a)$ which the
positional variable mimics the evolution of the Universe. Then the class of all
dark energy models (called a multiverse) can be regarded as a Banach space
naturally equipment in the structure of the Sobolev metric. In this paper we
explore notion of $C^{1}$ metric introduced in the multiverse which measure
distance between any two dark energy models. If we choose cold dark matter as a
reference one then we can find how so far apart are different models offering
explanation of present accelerating expansion phase of the Universe. We
consider both models with dark energy (models with the generalized Chaplygin
gas, models with variable coefficient equation of state
$w_{X}=\frac{p_{X}}{\rho_{X}}$ parameterized by redshift $z$, models with
phantom matter) as well as models basing on some modification of the Friedmann
equation (Cardassian models, Dvali-Gabadadze-Porati brane models). We argue
that because observational data still favor the $\Lambda$CDM model all
reasonable dark energy models should belong to the nearby neighborhood of this
model.
| [
{
"created": "Sun, 20 Aug 2006 19:57:38 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Szydlowski",
"Marek",
""
],
[
"Kurek",
"Aleksandra",
""
]
] | We characterize a class of simple FRW models filled by both dark energy and dark matter in notion of a single potential function of the scale factor $a(t)$; $t$ is the cosmological time. It is representing potential of fictitious particle - Universe moving in 1-dimensional well $V(a)$ which the positional variable mimics the evolution of the Universe. Then the class of all dark energy models (called a multiverse) can be regarded as a Banach space naturally equipment in the structure of the Sobolev metric. In this paper we explore notion of $C^{1}$ metric introduced in the multiverse which measure distance between any two dark energy models. If we choose cold dark matter as a reference one then we can find how so far apart are different models offering explanation of present accelerating expansion phase of the Universe. We consider both models with dark energy (models with the generalized Chaplygin gas, models with variable coefficient equation of state $w_{X}=\frac{p_{X}}{\rho_{X}}$ parameterized by redshift $z$, models with phantom matter) as well as models basing on some modification of the Friedmann equation (Cardassian models, Dvali-Gabadadze-Porati brane models). We argue that because observational data still favor the $\Lambda$CDM model all reasonable dark energy models should belong to the nearby neighborhood of this model. |
1607.08052 | Mohammad Ali Gorji | Mohammad Ali Gorji | Late time cosmic acceleration from natural infrared cutoff? | 11 pages, 2 figures, accepted for publication in PLB | Phys. Lett. B 760 (2016) 769 | 10.1016/j.physletb.2016.07.064 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, inspired by the ultraviolet deformation of the
Friedmann-Lema\^{\i}tre-Robertson-Walker geometry in loop quantum cosmology, we
formulate an infrared-modified cosmological model. We obtain the associated
deformed Friedmann and Raychaudhuri equations and we show that the late time
cosmic acceleration can be addressed by the infrared corrections. As a
particular example, we applied the setup to the case of matter dominated
universe. This model has the same number of parameters as $\Lambda$CDM, but a
dynamical dark energy generates in the matter dominated era at the late time.
According to our model, as the universe expands, the energy density of the cold
dark matter dilutes and when the Hubble parameter approaches to its minimum,
the infrared effects dominate such that the effective equation of state
parameter smoothly changes from $w_{_{\rm eff}}=0$ to $w_{_{\rm eff}}=-2$.
Interestingly and nontrivially, the unstable de Sitter phase with $w_{_{\rm
eff}}=-1$ is corresponding to $\Omega_m=\Omega_d =0.5$ and the universe crosses
the phantom divide from the quintessence phase with $w_{_{\rm eff}}>-1$ and
$\Omega_m> \Omega_d$ to the phantom phase with $w_{_{\rm eff}}<-1$ and $
\Omega_m<\Omega_d$ which shows that the model is observationally viable. The
results show that the universe finally ends up in a big rip singularity for a
finite time proportional to the inverse of the minimum of the Hubble parameter.
Moreover, we consider the dynamical stability of the model and we show that the
universe starts from the matter dominated era at the past attractor with
$w_{_{\rm eff}}=0$ and ends up in a future attractor at the big rip with
$w_{_{\rm eff}}=-2$.
| [
{
"created": "Wed, 27 Jul 2016 11:52:41 GMT",
"version": "v1"
}
] | 2016-08-12 | [
[
"Gorji",
"Mohammad Ali",
""
]
] | In this paper, inspired by the ultraviolet deformation of the Friedmann-Lema\^{\i}tre-Robertson-Walker geometry in loop quantum cosmology, we formulate an infrared-modified cosmological model. We obtain the associated deformed Friedmann and Raychaudhuri equations and we show that the late time cosmic acceleration can be addressed by the infrared corrections. As a particular example, we applied the setup to the case of matter dominated universe. This model has the same number of parameters as $\Lambda$CDM, but a dynamical dark energy generates in the matter dominated era at the late time. According to our model, as the universe expands, the energy density of the cold dark matter dilutes and when the Hubble parameter approaches to its minimum, the infrared effects dominate such that the effective equation of state parameter smoothly changes from $w_{_{\rm eff}}=0$ to $w_{_{\rm eff}}=-2$. Interestingly and nontrivially, the unstable de Sitter phase with $w_{_{\rm eff}}=-1$ is corresponding to $\Omega_m=\Omega_d =0.5$ and the universe crosses the phantom divide from the quintessence phase with $w_{_{\rm eff}}>-1$ and $\Omega_m> \Omega_d$ to the phantom phase with $w_{_{\rm eff}}<-1$ and $ \Omega_m<\Omega_d$ which shows that the model is observationally viable. The results show that the universe finally ends up in a big rip singularity for a finite time proportional to the inverse of the minimum of the Hubble parameter. Moreover, we consider the dynamical stability of the model and we show that the universe starts from the matter dominated era at the past attractor with $w_{_{\rm eff}}=0$ and ends up in a future attractor at the big rip with $w_{_{\rm eff}}=-2$. |
gr-qc/0701004 | Dmitri Gal'tsov | Dmitri Gal'tsov, Pavel Spirin and Simona Staub | Radiation reaction in curved space-time: local method | 10 pages, ws-procs9x6, published in "Gravitation and Astrophysics",
Proceedings of the VII Asia-Pacific International Conference National Central
University, Taiwan 23 - 26 November 2005, ed. J.M. Nester, C.-M. Chen, J.-P.
Hsu. World Scientific, 2006, pp. 345-354 | null | 10.1142/9789812772923_0041 | null | gr-qc | null | Although consensus seems to exist about the validity of equations accounting
for radiation reaction in curved space-time, their previous derivations were
criticized recently as not fully satisfactory: some ambiguities were noticed in
the procedure of integration of the field momentum over the tube surrounding
the world-line. To avoid these problems we suggest a purely local derivation
dealing with the field quantities defined only {\em on the world-line}. We
consider point particle interacting with scalar, vector (electromagnetic) and
linearized gravitational fields in the (generally non-vacuum) curved
space-time. To properly renormalize the self-action in the gravitational case,
we use a manifestly reparameterization-invariant formulation of the theory.
Scalar and vector divergences are shown to cancel for a certain ratio of the
corresponding charges. We also report on a modest progress in extending the
results for the gravitational radiation reaction to the case of non-vacuum
background.
| [
{
"created": "Sat, 30 Dec 2006 12:03:02 GMT",
"version": "v1"
}
] | 2016-11-09 | [
[
"Gal'tsov",
"Dmitri",
""
],
[
"Spirin",
"Pavel",
""
],
[
"Staub",
"Simona",
""
]
] | Although consensus seems to exist about the validity of equations accounting for radiation reaction in curved space-time, their previous derivations were criticized recently as not fully satisfactory: some ambiguities were noticed in the procedure of integration of the field momentum over the tube surrounding the world-line. To avoid these problems we suggest a purely local derivation dealing with the field quantities defined only {\em on the world-line}. We consider point particle interacting with scalar, vector (electromagnetic) and linearized gravitational fields in the (generally non-vacuum) curved space-time. To properly renormalize the self-action in the gravitational case, we use a manifestly reparameterization-invariant formulation of the theory. Scalar and vector divergences are shown to cancel for a certain ratio of the corresponding charges. We also report on a modest progress in extending the results for the gravitational radiation reaction to the case of non-vacuum background. |
1912.01304 | Xavier Ja\'en | Xavier Ja\'en and Pere Talavera | New design of gravitational wave detectors | pdfLaTeX, 24 pages, 7 figures | 2021 Classical and Quantum Gravity, Volume 38, Number 9 | 10.1088/1361-6382/abf1c2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a novel approach to detect gravitational waves based on a
semi-rigid detector. The approach relies upon the time delay that the light
takes to travel from a fixed mirror at the end of a rigid bar to a nearby free
mirror. We show that the dimensions of the experimental device can be shortened
in comparison to the conventional ones based on two free mirrors.
| [
{
"created": "Tue, 3 Dec 2019 11:21:26 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Dec 2020 15:56:46 GMT",
"version": "v2"
},
{
"created": "Tue, 2 Mar 2021 18:20:25 GMT",
"version": "v3"
},
{
"created": "Thu, 22 Apr 2021 07:30:12 GMT",
"version": "v4"
}
] | 2021-04-23 | [
[
"Jaén",
"Xavier",
""
],
[
"Talavera",
"Pere",
""
]
] | We propose a novel approach to detect gravitational waves based on a semi-rigid detector. The approach relies upon the time delay that the light takes to travel from a fixed mirror at the end of a rigid bar to a nearby free mirror. We show that the dimensions of the experimental device can be shortened in comparison to the conventional ones based on two free mirrors. |
1611.09016 | Li Xiang | Xiang Li, Yi Ling, You-Gen Shen, Cheng-Zhou Liu, Hong-Sheng He,
Lan-Fang Xu | Generalized uncertainty principles, effective Newton constant and
regular black holes | 22 pages | null | null | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we explore the quantum spacetimes that are potentially
connected with the generalized uncertainty principles. By analyzing the
gravity-induced quantum interference pattern and the Gedanken for weighting
photon, we find that the generalized uncertainty principles inspire the
effective Newton constant as same as our previous proposal. A characteristic
momentum associated with the tidal effect is suggested, which incorporates the
quantum effect with the geometric nature of gravity. When the simplest
generalized uncertainty principle is considered, the minimal model of the
regular black holes is reproduced by the effective Newton constant. The black
hole's tunneling probability, accurate to the second order correction, is
carefully analyzed. We find that the tunneling probability is regularized by
the size of the black hole remnant. Moreover, the black hole remnant is the
final state of a tunneling process that the probability is minimized. A theory
of modified gravity is suggested, by substituting the effective Newton constant
into the Hilbert-Einstein action.
| [
{
"created": "Mon, 28 Nov 2016 08:14:14 GMT",
"version": "v1"
}
] | 2016-11-29 | [
[
"Li",
"Xiang",
""
],
[
"Ling",
"Yi",
""
],
[
"Shen",
"You-Gen",
""
],
[
"Liu",
"Cheng-Zhou",
""
],
[
"He",
"Hong-Sheng",
""
],
[
"Xu",
"Lan-Fang",
""
]
] | In this paper, we explore the quantum spacetimes that are potentially connected with the generalized uncertainty principles. By analyzing the gravity-induced quantum interference pattern and the Gedanken for weighting photon, we find that the generalized uncertainty principles inspire the effective Newton constant as same as our previous proposal. A characteristic momentum associated with the tidal effect is suggested, which incorporates the quantum effect with the geometric nature of gravity. When the simplest generalized uncertainty principle is considered, the minimal model of the regular black holes is reproduced by the effective Newton constant. The black hole's tunneling probability, accurate to the second order correction, is carefully analyzed. We find that the tunneling probability is regularized by the size of the black hole remnant. Moreover, the black hole remnant is the final state of a tunneling process that the probability is minimized. A theory of modified gravity is suggested, by substituting the effective Newton constant into the Hilbert-Einstein action. |
1506.08579 | Francesco Cianfrani dr | Jakub Bilski, Emanuele Alesci, Francesco Cianfrani | Quantum reduced loop gravity: extension to scalar field | 14 pages, typos corrected | Phys. Rev. D 92, 124029 (2015) | 10.1103/PhysRevD.92.124029 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The quantization of the Hamiltonian for a scalar field is performed in the
framework of Quantum Reduced Loop Gravity. We outline how the regularization
can be performed by using the analogous tools adopted in full Loop Quantum
Gravity and the matrix elements of the resulting operator between basis states
are analytic coefficients. These achievements open the way for a consistent
analysis of the Quantum Gravity corrections to the classical dynamics of
gravity in the presence of a scalar field in a cosmological setting.
| [
{
"created": "Mon, 29 Jun 2015 11:03:15 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Jul 2015 16:10:57 GMT",
"version": "v2"
}
] | 2015-12-23 | [
[
"Bilski",
"Jakub",
""
],
[
"Alesci",
"Emanuele",
""
],
[
"Cianfrani",
"Francesco",
""
]
] | The quantization of the Hamiltonian for a scalar field is performed in the framework of Quantum Reduced Loop Gravity. We outline how the regularization can be performed by using the analogous tools adopted in full Loop Quantum Gravity and the matrix elements of the resulting operator between basis states are analytic coefficients. These achievements open the way for a consistent analysis of the Quantum Gravity corrections to the classical dynamics of gravity in the presence of a scalar field in a cosmological setting. |
2006.12604 | Francesco Salemi | M. Drago, V.Gayathri, S. Klimenko, C. Lazzaro, E. Milotti, G.
Mitselmakher, V. Necula, B. O'Brian, G. A. Prodi, F. Salemi, M. Szczepanczyk,
S. Tiwari, V. Tiwari, G. Vedovato and I. Yakushin | Coherent WaveBurst, a pipeline for unmodeled gravitational-wave data
analysis | 15 pages, 3 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | coherent WaveBurst (cWB) is a highly configurable pipeline designed to detect
a broad range of gravitational-wave (GW) transients in the data of the
worldwide network of GW detectors. The algorithmic core of cWB is a
time-frequency analysis with the Wilson-Daubechies-Meyer wavelets aimed at the
identification of GW events without prior knowledge of the signal waveform. cWB
has been in active development since 2003 and it has been used to analyze all
scientific data collected by the LIGO-Virgo detectors ever since. On September
14, 2015, the cWB low-latency search detected the first gravitational-wave
event, GW150914, a merger of two black holes. In 2019, a public open-source
version of cWB has been released with GPLv3 license.
| [
{
"created": "Mon, 22 Jun 2020 20:42:50 GMT",
"version": "v1"
},
{
"created": "Wed, 13 Jan 2021 14:46:33 GMT",
"version": "v2"
}
] | 2021-01-14 | [
[
"Drago",
"M.",
""
],
[
"Gayathri",
"V.",
""
],
[
"Klimenko",
"S.",
""
],
[
"Lazzaro",
"C.",
""
],
[
"Milotti",
"E.",
""
],
[
"Mitselmakher",
"G.",
""
],
[
"Necula",
"V.",
""
],
[
"O'Brian",
"B.",
""
],
[
"Prodi",
"G. A.",
""
],
[
"Salemi",
"F.",
""
],
[
"Szczepanczyk",
"M.",
""
],
[
"Tiwari",
"S.",
""
],
[
"Tiwari",
"V.",
""
],
[
"Vedovato",
"G.",
""
],
[
"Yakushin",
"I.",
""
]
] | coherent WaveBurst (cWB) is a highly configurable pipeline designed to detect a broad range of gravitational-wave (GW) transients in the data of the worldwide network of GW detectors. The algorithmic core of cWB is a time-frequency analysis with the Wilson-Daubechies-Meyer wavelets aimed at the identification of GW events without prior knowledge of the signal waveform. cWB has been in active development since 2003 and it has been used to analyze all scientific data collected by the LIGO-Virgo detectors ever since. On September 14, 2015, the cWB low-latency search detected the first gravitational-wave event, GW150914, a merger of two black holes. In 2019, a public open-source version of cWB has been released with GPLv3 license. |
1811.12494 | Che-Yu Chen | Che-Yu Chen, Mariam Bouhmadi-L\'opez, Pisin Chen | Probing Palatini-type gravity theories through gravitational wave
detections via quasinormal modes | 18 pages, 5 figures | Eur. Phys. J. C (2019) 79:63 | 10.1140/epjc/s10052-019-6585-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The possibility of testing gravity theories with the help of gravitational
wave detections has become an interesting arena of recent research. In this
paper, we follow this direction by investigating the quasinormal modes (QNMs)
of the axial perturbations for charged black holes in the Palatini-type
theories of gravity, specifically ($i$) the Palatini $f(R)$ gravity coupled
with Born-Infeld nonlinear electrodynamics and ($ii$) the
Eddington-inspired-Born-Infeld gravity (EiBI) coupled with Maxwell
electromagnetic fields. The coupled master equations describing perturbations
of charged black holes in these theories are obtained with the tetrad
formalism. By using the Wentzel-Kramers- Brillouin (WKB) method up to 6th
order, we calculate the QNM frequencies of the EiBI charged black holes, the
Einstein-Born-Infeld black holes, and the Born-Infeld charged black holes
within the Palatini $R+\alpha R^2$ gravity. The QNM spectra of these black
holes would deviate from those of the Reissner-Nordstr\"om black hole. In
addition, we study the QNMs in the eikonal limit and find that for the axial
perturbations of the EiBI charged black holes, the link between the eikonal
QNMs and the unstable null circular orbit around the black hole is violated.
| [
{
"created": "Thu, 29 Nov 2018 21:28:15 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Jan 2019 07:10:48 GMT",
"version": "v2"
}
] | 2019-01-30 | [
[
"Chen",
"Che-Yu",
""
],
[
"Bouhmadi-López",
"Mariam",
""
],
[
"Chen",
"Pisin",
""
]
] | The possibility of testing gravity theories with the help of gravitational wave detections has become an interesting arena of recent research. In this paper, we follow this direction by investigating the quasinormal modes (QNMs) of the axial perturbations for charged black holes in the Palatini-type theories of gravity, specifically ($i$) the Palatini $f(R)$ gravity coupled with Born-Infeld nonlinear electrodynamics and ($ii$) the Eddington-inspired-Born-Infeld gravity (EiBI) coupled with Maxwell electromagnetic fields. The coupled master equations describing perturbations of charged black holes in these theories are obtained with the tetrad formalism. By using the Wentzel-Kramers- Brillouin (WKB) method up to 6th order, we calculate the QNM frequencies of the EiBI charged black holes, the Einstein-Born-Infeld black holes, and the Born-Infeld charged black holes within the Palatini $R+\alpha R^2$ gravity. The QNM spectra of these black holes would deviate from those of the Reissner-Nordstr\"om black hole. In addition, we study the QNMs in the eikonal limit and find that for the axial perturbations of the EiBI charged black holes, the link between the eikonal QNMs and the unstable null circular orbit around the black hole is violated. |
2107.13547 | Marzieh Faraji | Marzieh Faraji, Narges Rashidi, Kourosh Nozari | Inflation in Energy-Momentum Squared Gravity in Light of Planck2018 | 16 Pages, 9 Figures | null | null | null | gr-qc astro-ph.CO hep-ph hep-th | http://creativecommons.org/publicdomain/zero/1.0/ | We study cosmological dynamics of the energy-momentum squared gravity. By
adding the squared of the matter field's energy-momentum tensor ($\zeta\,
\textbf{T}^{2}$) to the Einstein Hilbert action, we obtain the Einstein's field
equations and study the conservation law. We show that the presence of $\zeta\,
\textbf{T}^{2}$ term, breaks the conservation of the energy-momentum tensor of
the matter fields. However, an effective energy-momentum tensor in this model
is conserved in time. By considering the FRW metric as the background, we find
the Friedmann equations and by which we explore the cosmological inflation in
$\zeta\,\textbf{T}^{2}$ model. We perform numerical analysis on the
perturbation parameters and compare the results with Planck2018 different data
sets at $68\%$ and $95\%$ CL, to obtain some constraints on the coupling
parameter $\zeta$. We show that \textbf{ for $0< \zeta \leq 2.1\times 10^{-5}$,
the $\zeta\, \textbf{T}^{2}$ gravity is an observationally viable model of
inflation.
| [
{
"created": "Thu, 29 Jul 2021 07:31:13 GMT",
"version": "v1"
}
] | 2021-07-30 | [
[
"Faraji",
"Marzieh",
""
],
[
"Rashidi",
"Narges",
""
],
[
"Nozari",
"Kourosh",
""
]
] | We study cosmological dynamics of the energy-momentum squared gravity. By adding the squared of the matter field's energy-momentum tensor ($\zeta\, \textbf{T}^{2}$) to the Einstein Hilbert action, we obtain the Einstein's field equations and study the conservation law. We show that the presence of $\zeta\, \textbf{T}^{2}$ term, breaks the conservation of the energy-momentum tensor of the matter fields. However, an effective energy-momentum tensor in this model is conserved in time. By considering the FRW metric as the background, we find the Friedmann equations and by which we explore the cosmological inflation in $\zeta\,\textbf{T}^{2}$ model. We perform numerical analysis on the perturbation parameters and compare the results with Planck2018 different data sets at $68\%$ and $95\%$ CL, to obtain some constraints on the coupling parameter $\zeta$. We show that \textbf{ for $0< \zeta \leq 2.1\times 10^{-5}$, the $\zeta\, \textbf{T}^{2}$ gravity is an observationally viable model of inflation. |
gr-qc/0207084 | Etera R. Livine | Etera R Livine | Projected Spin Networks for Lorentz connection: Linking Spin Foams and
Loop Gravity | Latex, 15 pages | Class.Quant.Grav. 19 (2002) 5525-5542 | 10.1088/0264-9381/19/21/316 | null | gr-qc | null | In the search for a covariant formulation for Loop Quantum Gravity, spin
foams have arised as the corresponding discrete space-time structure and, among
the different models, the Barrett-Crane model seems the most promising. Here,
we study its boundary states and introduce cylindrical functions on both the
Lorentz connection and the time normal to the studied hypersurface. We call
them projected cylindrical functions and we explain how they would naturally
arise in a covariant formulation of Loop Quantum Gravity.
| [
{
"created": "Mon, 22 Jul 2002 09:58:53 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Livine",
"Etera R",
""
]
] | In the search for a covariant formulation for Loop Quantum Gravity, spin foams have arised as the corresponding discrete space-time structure and, among the different models, the Barrett-Crane model seems the most promising. Here, we study its boundary states and introduce cylindrical functions on both the Lorentz connection and the time normal to the studied hypersurface. We call them projected cylindrical functions and we explain how they would naturally arise in a covariant formulation of Loop Quantum Gravity. |
gr-qc/9811017 | Garcia | L.C.Garcia de Andrade | Distributional torsion of charged domain walls with spin | 8 pages,Latex | null | null | null | gr-qc | null | An exact solution of Einstein-Cartan-Maxwell (ECM) field equations
representing a charged domain wall given by the jump on the electric charge and
spin density across the wall is obtained from the Riemannian theory of
distributions. The Gauss-Coddazzi equations are used to show that spin, charge
and Cartan torsion increases the repulsive character of the domain wall. Taub
and Vilenkin walls are discussed as well as their relations to wormhole
geometry. The electric and torsion fields are constants at the wall.
| [
{
"created": "Thu, 5 Nov 1998 12:01:18 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"de Andrade",
"L. C. Garcia",
""
]
] | An exact solution of Einstein-Cartan-Maxwell (ECM) field equations representing a charged domain wall given by the jump on the electric charge and spin density across the wall is obtained from the Riemannian theory of distributions. The Gauss-Coddazzi equations are used to show that spin, charge and Cartan torsion increases the repulsive character of the domain wall. Taub and Vilenkin walls are discussed as well as their relations to wormhole geometry. The electric and torsion fields are constants at the wall. |
0804.0973 | Kirill Bronnikov | K.A. Bronnikov, S.A. Kononogov, V.N. Melnikov, S.G. Rubin | Cosmologies from nonlinear multidimensional gravity with acceleration
and slowly varying G | 5 pages, to be published in Grav. Cosmol | Grav.Cosmol.14:230-234,2008 | 10.1134/S0202289308030043 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider multidimensional gravity with a Lagrangian containing the Ricci
tensor squared and the Kretschmann invariant. In a Kaluza-Klein approach with a
single compact extra space of arbitrary dimension, with the aid of a
slow-change approximation (as compared with the Planck scale), we build a class
of spatially flat cosmological models in which both the observed scale factor
$a(\tau)$ and the extra-dimensional one, $b(\tau)$, grow exponentially at large
times, but $b(\tau)$ grows slowly enough to admit variations of the effective
gravitational constant $G$ within observational limits. Such models predict a
drastic change in the physical laws of our Universe in the remote future due to
further growth of the extra dimensions.
| [
{
"created": "Mon, 7 Apr 2008 07:04:39 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Bronnikov",
"K. A.",
""
],
[
"Kononogov",
"S. A.",
""
],
[
"Melnikov",
"V. N.",
""
],
[
"Rubin",
"S. G.",
""
]
] | We consider multidimensional gravity with a Lagrangian containing the Ricci tensor squared and the Kretschmann invariant. In a Kaluza-Klein approach with a single compact extra space of arbitrary dimension, with the aid of a slow-change approximation (as compared with the Planck scale), we build a class of spatially flat cosmological models in which both the observed scale factor $a(\tau)$ and the extra-dimensional one, $b(\tau)$, grow exponentially at large times, but $b(\tau)$ grows slowly enough to admit variations of the effective gravitational constant $G$ within observational limits. Such models predict a drastic change in the physical laws of our Universe in the remote future due to further growth of the extra dimensions. |
gr-qc/9504033 | Steve Carlip | Steven Carlip | A Phase Space Path Integral for (2+1)-Dimensional Gravity | 9 pages, LaTeX, no figures. (Minor changes, in particular to clarify
exceptional features of torus topology; final version to appear in Class.
Quant. Grav.) | Class.Quant.Grav.12:2201-2208,1995 | 10.1088/0264-9381/12/9/007 | UCD-95-10 | gr-qc hep-th | null | I investigate the relationship between the phase space path integral in
(2+1)-dimensional gravity and the canonical quantization of the corresponding
reduced phase space in the York time slicing. I demonstrate the equivalence of
these two approaches, and discuss some subtleties in the definition of the path
integral necessary to prove this equivalence.
| [
{
"created": "Fri, 21 Apr 1995 00:28:59 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Jul 1995 19:06:30 GMT",
"version": "v2"
}
] | 2010-04-28 | [
[
"Carlip",
"Steven",
""
]
] | I investigate the relationship between the phase space path integral in (2+1)-dimensional gravity and the canonical quantization of the corresponding reduced phase space in the York time slicing. I demonstrate the equivalence of these two approaches, and discuss some subtleties in the definition of the path integral necessary to prove this equivalence. |
gr-qc/9704003 | Gentil O. Pires | Carlos Pinheiro, Gentil O. Pires and Claudio Sasaki | On a Three-Dimensional Gravity Model with Higher Derivatives | 9 pages, Latex, no figures; to be published in Gen. Rel. Grav | Gen.Rel.Grav. 29 (1997) 409-416 | 10.1023/A:1018849730067 | null | gr-qc hep-th | null | The purpose of this work is to present a model for 3D massive gravity with
topological and higher-derivative terms. Causality and unitarity are discussed
at tree-level. Power-counting renormalizability is also contemplated.
| [
{
"created": "Tue, 1 Apr 1997 17:58:36 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Pinheiro",
"Carlos",
""
],
[
"Pires",
"Gentil O.",
""
],
[
"Sasaki",
"Claudio",
""
]
] | The purpose of this work is to present a model for 3D massive gravity with topological and higher-derivative terms. Causality and unitarity are discussed at tree-level. Power-counting renormalizability is also contemplated. |
gr-qc/0307078 | M. Blagojevic | M. Blagojevic and M. Vasilic | 3D gravity with torsion as a Chern-Simons gauge theory | 12 pages, RevTeX | Phys.Rev. D68 (2003) 104023 | 10.1103/PhysRevD.68.104023 | null | gr-qc hep-th | null | We show that topological 3D gravity with torsion can be formulated as a
Chern-Simons gauge theory, provided a specific parameter, known as the
effective cosmological constant, is negative. In that case, the boundary
dynamics of the theory corresponding to anti-de Sitter boundary conditions is
described by a conformal field theory with two different central charges.
| [
{
"created": "Wed, 16 Jul 2003 10:49:59 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Blagojevic",
"M.",
""
],
[
"Vasilic",
"M.",
""
]
] | We show that topological 3D gravity with torsion can be formulated as a Chern-Simons gauge theory, provided a specific parameter, known as the effective cosmological constant, is negative. In that case, the boundary dynamics of the theory corresponding to anti-de Sitter boundary conditions is described by a conformal field theory with two different central charges. |
1908.07089 | Sizheng Ma | Sizheng Ma and Nicolas Yunes | Improved Constraints on Modified Gravity with Eccentric Gravitational
Waves | 23 pages, 9 figures | Phys. Rev. D 100, 124032 (2019) | 10.1103/PhysRevD.100.124032 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recent gravitational wave observations have allowed stringent new constraints
on modifications to General Relativity (GR) in the extreme gravity regime.
Although these observations were consistent with compact binaries with no
orbital eccentricity, gravitational waves emitted in mildly eccentric binaries
may be observed once detectors reach their design sensitivity. In this paper,
we study the effect of eccentricity in gravitational wave constraints of
modified gravity, focusing on Jordan-Brans- Dicke-Fierz theory as an example.
Using the stationary phase approximation and the post-circular approximation
(an expansion in small eccentricity), we first construct an analytical
expression for frequency-domain gravitational waveforms produced by inspiraling
compact binaries with small eccentricity in this theory. We then calculate the
overlap between our approximate analytical waveforms and an eccentric numerical
model (TaylorT4) to determine the regime of validity (in eccentricity) of the
former. With this at hand, we carry out a Fisher analysis to determine the
accuracy to which Jordan-Brans-Dicke-Fierz theory could be constrained given
future eccentric detections consistent with General Relativity. We find that
the constraint on the theory initially deteriorates (due to covariances between
the eccentricity and the Brans-Dicke coupling parameter), but then it begins to
recover, once the eccentricity is larger than approximately 0.03. We also find
that third-generation ground-based detectors and space-based detectors could
allow for constraints that are up to an order of magnitude more stringent than
current Solar System bounds. Our results suggest that waveforms in modified
gravity for systems with moderate eccentricity should be developed to maximize
the theoretical physics that can be extracted in the future.
| [
{
"created": "Mon, 19 Aug 2019 22:37:13 GMT",
"version": "v1"
}
] | 2019-12-12 | [
[
"Ma",
"Sizheng",
""
],
[
"Yunes",
"Nicolas",
""
]
] | Recent gravitational wave observations have allowed stringent new constraints on modifications to General Relativity (GR) in the extreme gravity regime. Although these observations were consistent with compact binaries with no orbital eccentricity, gravitational waves emitted in mildly eccentric binaries may be observed once detectors reach their design sensitivity. In this paper, we study the effect of eccentricity in gravitational wave constraints of modified gravity, focusing on Jordan-Brans- Dicke-Fierz theory as an example. Using the stationary phase approximation and the post-circular approximation (an expansion in small eccentricity), we first construct an analytical expression for frequency-domain gravitational waveforms produced by inspiraling compact binaries with small eccentricity in this theory. We then calculate the overlap between our approximate analytical waveforms and an eccentric numerical model (TaylorT4) to determine the regime of validity (in eccentricity) of the former. With this at hand, we carry out a Fisher analysis to determine the accuracy to which Jordan-Brans-Dicke-Fierz theory could be constrained given future eccentric detections consistent with General Relativity. We find that the constraint on the theory initially deteriorates (due to covariances between the eccentricity and the Brans-Dicke coupling parameter), but then it begins to recover, once the eccentricity is larger than approximately 0.03. We also find that third-generation ground-based detectors and space-based detectors could allow for constraints that are up to an order of magnitude more stringent than current Solar System bounds. Our results suggest that waveforms in modified gravity for systems with moderate eccentricity should be developed to maximize the theoretical physics that can be extracted in the future. |
2110.00766 | N V Krishnendu | N V Krishnendu and Frank Ohme | Interplay of spin-precession and higher harmonics in the parameter
estimation of binary black holes | 12 pages, 8 figures Data release URL:
https://zenodo.org/record/6337692#.YieS5BDMKLp | Phys. Rev. D 105, 064012, Published 7 March 2022 | 10.1103/PhysRevD.105.064012 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational-wave (GW) signals from coalescing compact binaries carry
enormous information about the source dynamics and are an excellent tool to
probe unknown astrophysics and fundamental physics. Though the updated catalog
of compact binary signals reports evidence for slowly spinning systems and
unequal mass binaries, the data so far cannot provide convincing proof of
strongly precessing binaries. Here, we use the GW inference library parallel
Bilby to compare the performance of two waveform models for measuring
spin-induced orbital precession. One of the waveform models incorporates both
spin-precession effects and sub-dominant harmonics. The other model accounts
for precession but only includes the leading harmonic. By simulating signals
with varying mass ratios and spins, we find that the waveform model with
sub-dominant harmonics enables us to infer the presence of precession in most
cases accurately. In contrast, the dominant model often fails to extract enough
information to measure precession. In particular, it cannot distinguish a
face-on highly precessing binary from a slowly precessing binary system
irrespective of the binary's mass ratio. As expected, we see a significant
improvement in measuring precession for edge-on binaries. Other intrinsic
parameters also become better constrained, indicating that precession effects
help break the correlations between mass and spin parameters. However, the
precession measurements are prior dominated for equal-mass binaries with
face-on orientation, even if we employ waveform model including subdominant
harmonics. In this case, doubling the signal-to-noise ratio does not help to
reduce these prior induced biases. As we expect detections of highly spinning
binary signals with misaligned spin orientations in the future, simulation
studies like ours are crucial for understanding the prospects and limitations
of GW parameter inferences.
| [
{
"created": "Sat, 2 Oct 2021 09:47:38 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Mar 2022 09:45:55 GMT",
"version": "v2"
}
] | 2022-03-10 | [
[
"Krishnendu",
"N V",
""
],
[
"Ohme",
"Frank",
""
]
] | Gravitational-wave (GW) signals from coalescing compact binaries carry enormous information about the source dynamics and are an excellent tool to probe unknown astrophysics and fundamental physics. Though the updated catalog of compact binary signals reports evidence for slowly spinning systems and unequal mass binaries, the data so far cannot provide convincing proof of strongly precessing binaries. Here, we use the GW inference library parallel Bilby to compare the performance of two waveform models for measuring spin-induced orbital precession. One of the waveform models incorporates both spin-precession effects and sub-dominant harmonics. The other model accounts for precession but only includes the leading harmonic. By simulating signals with varying mass ratios and spins, we find that the waveform model with sub-dominant harmonics enables us to infer the presence of precession in most cases accurately. In contrast, the dominant model often fails to extract enough information to measure precession. In particular, it cannot distinguish a face-on highly precessing binary from a slowly precessing binary system irrespective of the binary's mass ratio. As expected, we see a significant improvement in measuring precession for edge-on binaries. Other intrinsic parameters also become better constrained, indicating that precession effects help break the correlations between mass and spin parameters. However, the precession measurements are prior dominated for equal-mass binaries with face-on orientation, even if we employ waveform model including subdominant harmonics. In this case, doubling the signal-to-noise ratio does not help to reduce these prior induced biases. As we expect detections of highly spinning binary signals with misaligned spin orientations in the future, simulation studies like ours are crucial for understanding the prospects and limitations of GW parameter inferences. |
1305.3509 | Johan Noldus | Johan Noldus | Interpretation of quantal manifolds | 16 pages. arXiv admin note: substantial text overlap with
arXiv:1101.5113 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In quantum gravity, one looks for alternative structures to spacetime physics
than ordinary real manifolds. Here, we propose an alternative universal
construction containing the latter as an equilibrium state under the action of
the universal diffeomorphism group. Our theory contains many other previous
proposals in the literature as special cases. However, the crucial point we
make is that those have to be appreciated in the universal context developed
here.
| [
{
"created": "Sat, 11 May 2013 17:28:23 GMT",
"version": "v1"
}
] | 2013-05-16 | [
[
"Noldus",
"Johan",
""
]
] | In quantum gravity, one looks for alternative structures to spacetime physics than ordinary real manifolds. Here, we propose an alternative universal construction containing the latter as an equilibrium state under the action of the universal diffeomorphism group. Our theory contains many other previous proposals in the literature as special cases. However, the crucial point we make is that those have to be appreciated in the universal context developed here. |
gr-qc/0408037 | Jonathan Eakins | J. S. Eakins | Classical and Quantum Causality in Quantum Field Theory. Or, "The
Quantum Universe" | 398 pages, 9 figures. Thesis submitted to the University of
Nottingham for the degree of Doctor of Philosophy, April 2004 | null | null | null | gr-qc quant-ph | null | Based on a number of experimentally verified physical observations, it is
argued that the standard principles of quantum mechanics should be applied to
the Universe as a whole. Thus, a paradigm is proposed in which the entire
Universe is represented by a pure state wavefunction contained in a
factorisable Hilbert space of enormous dimension, and where this statevector is
developed by successive applications of operators that correspond to unitary
rotations and Hermitian tests. Moreover, because by definition the Universe
contains everything, it is argued that these operators must be chosen
self-referentially; the overall dynamics of the system is envisaged to be
analogous to a gigantic, self-governing, quantum computation. The issue of how
the Universe could choose these operators without requiring or referring to a
fictitious external observer is addressed.
The processes by which conventional physics might be recovered from this
fundamental, mathematical and global description of reality are particularly
investigated. Specifically, it is demonstrated that by considering the changing
properties, separabilities and factorisations of both the state and the
operators as the Universe proceeds though a sequence of discrete computations,
familiar notions such as classical distinguishability, particle physics, space,
time, special relativity and endo-physical experiments can all begin to emerge
from the proposed picture. A pregeometric vision of cosmology is therefore
discussed, with all of physics ultimately arising from the relationships
occurring between the elements of the underlying mathematical structure.
| [
{
"created": "Thu, 12 Aug 2004 16:23:41 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Eakins",
"J. S.",
""
]
] | Based on a number of experimentally verified physical observations, it is argued that the standard principles of quantum mechanics should be applied to the Universe as a whole. Thus, a paradigm is proposed in which the entire Universe is represented by a pure state wavefunction contained in a factorisable Hilbert space of enormous dimension, and where this statevector is developed by successive applications of operators that correspond to unitary rotations and Hermitian tests. Moreover, because by definition the Universe contains everything, it is argued that these operators must be chosen self-referentially; the overall dynamics of the system is envisaged to be analogous to a gigantic, self-governing, quantum computation. The issue of how the Universe could choose these operators without requiring or referring to a fictitious external observer is addressed. The processes by which conventional physics might be recovered from this fundamental, mathematical and global description of reality are particularly investigated. Specifically, it is demonstrated that by considering the changing properties, separabilities and factorisations of both the state and the operators as the Universe proceeds though a sequence of discrete computations, familiar notions such as classical distinguishability, particle physics, space, time, special relativity and endo-physical experiments can all begin to emerge from the proposed picture. A pregeometric vision of cosmology is therefore discussed, with all of physics ultimately arising from the relationships occurring between the elements of the underlying mathematical structure. |
0907.2749 | Hao Wei | Hao Wei | Varying Alpha Driven by the Dirac-Born-Infeld Scalar Field | 12 pages, 1 table, 8 figures, revtex4; v2: discussions added, Phys.
Lett. B in press; v3: published version | Phys.Lett.B682:98-104,2009 | 10.1016/j.physletb.2009.10.086 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Since about ten years ago, varying $\alpha$ theories attracted many
attentions, mainly due to the first observational evidence from the quasar
absorption spectra that the fine structure ``constant'' might change with
cosmological time. In this work, we investigate the cosmic evolution of
$\alpha$ driven by the Dirac-Born-Infeld (DBI) scalar field. To be general, we
consider various couplings between the DBI scalar field and the electromagnetic
field. We also confront the resulting $\Delta\alpha/\alpha$ with the
observational constraints, and find that various cosmological evolution
histories of $\Delta\alpha/\alpha$ are allowed. Comparing with the case of
varying $\alpha$ driven by quintessence, the corresponding constraints on the
parameters of coupling have been relaxed, thanks to the relativistic correction
of the DBI scalar field.
| [
{
"created": "Thu, 16 Jul 2009 12:30:00 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Oct 2009 04:45:00 GMT",
"version": "v2"
},
{
"created": "Sun, 15 Nov 2009 09:00:00 GMT",
"version": "v3"
}
] | 2009-11-15 | [
[
"Wei",
"Hao",
""
]
] | Since about ten years ago, varying $\alpha$ theories attracted many attentions, mainly due to the first observational evidence from the quasar absorption spectra that the fine structure ``constant'' might change with cosmological time. In this work, we investigate the cosmic evolution of $\alpha$ driven by the Dirac-Born-Infeld (DBI) scalar field. To be general, we consider various couplings between the DBI scalar field and the electromagnetic field. We also confront the resulting $\Delta\alpha/\alpha$ with the observational constraints, and find that various cosmological evolution histories of $\Delta\alpha/\alpha$ are allowed. Comparing with the case of varying $\alpha$ driven by quintessence, the corresponding constraints on the parameters of coupling have been relaxed, thanks to the relativistic correction of the DBI scalar field. |
2401.05514 | Andrea Russo | Jonathan Oppenheim, Andrea Russo, Zachary Weller-Davies | Diffeomorphism invariant classical-quantum path integrals for Nordstrom
gravity | null | null | null | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | When classical degrees of freedom and quantum degrees of freedom are
consistently coupled, the former diffuse, while the latter undergo decoherence.
Here, we construct a theory of quantum matter fields and Nordstrom gravity in
which the space-time metric is treated classically. The dynamics is constructed
via the classical-quantum path integral and is completely positive, trace
preserving (CPTP), and respects the classical-quantum split. The weak field
limit of the model matches the Newtonian limit of the full covariant path
integral but it is easier to show that the theory is both diffeomorphism
invariant, CPTP, and has the appropriate classical limit.
| [
{
"created": "Wed, 10 Jan 2024 19:23:00 GMT",
"version": "v1"
}
] | 2024-01-12 | [
[
"Oppenheim",
"Jonathan",
""
],
[
"Russo",
"Andrea",
""
],
[
"Weller-Davies",
"Zachary",
""
]
] | When classical degrees of freedom and quantum degrees of freedom are consistently coupled, the former diffuse, while the latter undergo decoherence. Here, we construct a theory of quantum matter fields and Nordstrom gravity in which the space-time metric is treated classically. The dynamics is constructed via the classical-quantum path integral and is completely positive, trace preserving (CPTP), and respects the classical-quantum split. The weak field limit of the model matches the Newtonian limit of the full covariant path integral but it is easier to show that the theory is both diffeomorphism invariant, CPTP, and has the appropriate classical limit. |
gr-qc/9511055 | Luis Anchordoqui | Luis A. Anchordoqui, Diego F. Torres, H\'ector Vucetich | Primordial Nucleosynthesis as a test of variable rest masses
5-dimensional cosmology | Corrected version with referee's remarks. Unchanged global results.
Some references added; to be published in Phys. Lett. A. | Phys.Lett. A222 (1996) 43-46 | 10.1016/0375-9601(96)00621-4 | null | gr-qc | null | The deviation of primordial Helium production due to a variation on the
difference between the rest masses of the nucleons is presented. It is found an
upper bound $\delta (M_{_n} - M_{_p}) \alt 0.129$ MeV, between the present and
nucleosynthesis epochs. This bound is used to analyze Wesson's theory of
gravitation; as a result, it is ruled out by observation.
| [
{
"created": "Mon, 20 Nov 1995 19:04:56 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Aug 1996 20:57:04 GMT",
"version": "v2"
}
] | 2009-10-28 | [
[
"Anchordoqui",
"Luis A.",
""
],
[
"Torres",
"Diego F.",
""
],
[
"Vucetich",
"Héctor",
""
]
] | The deviation of primordial Helium production due to a variation on the difference between the rest masses of the nucleons is presented. It is found an upper bound $\delta (M_{_n} - M_{_p}) \alt 0.129$ MeV, between the present and nucleosynthesis epochs. This bound is used to analyze Wesson's theory of gravitation; as a result, it is ruled out by observation. |
2303.17666 | S\'ergio Vinicius Monteiro Castelo Branco Xavier | S\'ergio V. M. C. B. Xavier, Haroldo C. D. Lima Junior, Lu\'is C. B.
Crispino | Shadows of black holes with dark matter halo | 8 pages, 6 figures | Phys. Rev. D 107, 064040 (2023) | 10.1103/PhysRevD.107.064040 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We investigate the shadow of an exact black hole solution of Einstein's
equations recently proposed by Cardoso et al., to describe a supermassive black
hole immersed in a dark matter halo. We analyze and discuss the light rings and
the gravitational lensing of this spacetime comparing them with an isolated
Schwarzschild black hole. Using backward ray-tracing techniques, we study the
shadows cast by such black hole when illuminated by a celestial sphere that
emits radiation isotropically. We find that when the dark matter distribution
concentrates near the event horizon of the black hole, multiple light rings
emerge. In this high compactness regime, the shadows and gravitational lensing
are significantly different from the Schwarzschild one. We also use the M87*
and SgrA* shadow data, obtained by the Event Horizon Telescope collaboration,
to constrain the parameters of the dark matter halo.
| [
{
"created": "Thu, 30 Mar 2023 19:06:05 GMT",
"version": "v1"
}
] | 2023-04-03 | [
[
"Xavier",
"Sérgio V. M. C. B.",
""
],
[
"Junior",
"Haroldo C. D. Lima",
""
],
[
"Crispino",
"Luís C. B.",
""
]
] | We investigate the shadow of an exact black hole solution of Einstein's equations recently proposed by Cardoso et al., to describe a supermassive black hole immersed in a dark matter halo. We analyze and discuss the light rings and the gravitational lensing of this spacetime comparing them with an isolated Schwarzschild black hole. Using backward ray-tracing techniques, we study the shadows cast by such black hole when illuminated by a celestial sphere that emits radiation isotropically. We find that when the dark matter distribution concentrates near the event horizon of the black hole, multiple light rings emerge. In this high compactness regime, the shadows and gravitational lensing are significantly different from the Schwarzschild one. We also use the M87* and SgrA* shadow data, obtained by the Event Horizon Telescope collaboration, to constrain the parameters of the dark matter halo. |
1003.1609 | Stoytcho Yazadjiev | Ivan Zh. Stefanov, Stoytcho S. Yazadjiev, Galin G. Gyulchev | Connection between black-hole quasinormal modes and lensing in the
strong deflection limit | 7 pages, v2 minor changes, references added, v3 title changed,
comments and references added, typos corrected | Phys.Rev.Lett.104:251103,2010 | 10.1103/PhysRevLett.104.251103 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The purpose of the current Letter is to give some relations between
gravitational lensing in the strong-deflection limit and the frequencies of the
quasinormal modes of spherically symmetric, asymptotically flat black holes. On
the one side, the obtained relations can give a physical interpretation of the
strong-deflection limit parameters. On the other side, they also give an
alternative method for the measurement of the frequencies of the quasinormal
modes of spherically symmetric, asymptotically flat black holes. They could be
applied to the localization of the sources of gravitational waves and could
tell us what frequencies of the gravitational waves we could expect from a
black hole acting simultaneously as a gravitational lens and a source of
gravitational waves.
| [
{
"created": "Mon, 8 Mar 2010 12:00:39 GMT",
"version": "v1"
},
{
"created": "Wed, 31 Mar 2010 14:37:19 GMT",
"version": "v2"
},
{
"created": "Thu, 23 Sep 2010 11:32:51 GMT",
"version": "v3"
}
] | 2010-09-24 | [
[
"Stefanov",
"Ivan Zh.",
""
],
[
"Yazadjiev",
"Stoytcho S.",
""
],
[
"Gyulchev",
"Galin G.",
""
]
] | The purpose of the current Letter is to give some relations between gravitational lensing in the strong-deflection limit and the frequencies of the quasinormal modes of spherically symmetric, asymptotically flat black holes. On the one side, the obtained relations can give a physical interpretation of the strong-deflection limit parameters. On the other side, they also give an alternative method for the measurement of the frequencies of the quasinormal modes of spherically symmetric, asymptotically flat black holes. They could be applied to the localization of the sources of gravitational waves and could tell us what frequencies of the gravitational waves we could expect from a black hole acting simultaneously as a gravitational lens and a source of gravitational waves. |
gr-qc/0309042 | Wung-Hong Huang | Wung-Hong Huang and I-Chin Wang | Quantum Perfect-Fluid Kaluza-Klein Cosmology | Latex 18 pages, add section 2 to introduce the quantization of
perfect fluid | Int.J.Mod.Phys. A21 (2006) 4463-4478 | 10.1142/S0217751X06031442 | null | gr-qc hep-th | null | The perfect fluid cosmology in the 1+d+D dimensional Kaluza-Klein spacetimes
for an arbitrary barotropic equation of state $p= n \rho$ is quantized by using
the Schutz's variational formalism. We make efforts in the mathematics to solve
the problems in two cases. For the first case of the stiff fluid $n=1$ we
exactly solve the Wheeler-DeWitt equation when the $d$ space is flat. After the
superposition of the solutions we analyze the Bohmian trajectories of the
final-stage wave-packet functions and show that the flat $d$ spaces and the
compact $D$ spaces will eventually evolve into finite scale functions. For the
second case of $n \approx 1$, we use the approximated wavefunction in the
Wheeler-DeWitt equation to find the analytic forms of the final-stage
wave-packet functions. After analyzing the Bohmian trajectories we show that
the flat $d$ spaces will be expanding forever while the scale function of the
contracting $D$ spaces would not become zero within finite time. Our
investigations indicate that the quantum effect in the quantum perfect-fluid
cosmology could prevent the extra compact $D$ spaces in the Kaluza-Klein theory
from collapsing into a singularity or that the "crack-of-doom" singularity of
the extra compact dimensions is made to occur at $t=\infty$.
| [
{
"created": "Mon, 8 Sep 2003 06:07:35 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Sep 2007 09:07:06 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Huang",
"Wung-Hong",
""
],
[
"Wang",
"I-Chin",
""
]
] | The perfect fluid cosmology in the 1+d+D dimensional Kaluza-Klein spacetimes for an arbitrary barotropic equation of state $p= n \rho$ is quantized by using the Schutz's variational formalism. We make efforts in the mathematics to solve the problems in two cases. For the first case of the stiff fluid $n=1$ we exactly solve the Wheeler-DeWitt equation when the $d$ space is flat. After the superposition of the solutions we analyze the Bohmian trajectories of the final-stage wave-packet functions and show that the flat $d$ spaces and the compact $D$ spaces will eventually evolve into finite scale functions. For the second case of $n \approx 1$, we use the approximated wavefunction in the Wheeler-DeWitt equation to find the analytic forms of the final-stage wave-packet functions. After analyzing the Bohmian trajectories we show that the flat $d$ spaces will be expanding forever while the scale function of the contracting $D$ spaces would not become zero within finite time. Our investigations indicate that the quantum effect in the quantum perfect-fluid cosmology could prevent the extra compact $D$ spaces in the Kaluza-Klein theory from collapsing into a singularity or that the "crack-of-doom" singularity of the extra compact dimensions is made to occur at $t=\infty$. |
2103.12845 | Jean-Pierre Petit | J.P.Petit and G.D'Agostini | Cancellation of the central singularity of the Schwarzschild solution
with natural mass inversion process | 11 pages , 12 figures | Modern Physics Letters A, Vol. 30, No. 9 (2015) 1550051 | 10.1142/S0217732315500510 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We reconsider the classical Schwarzschild solution in the context of a Janus
cosmological model. We show that the central singularity can be eliminated
through a simple coordinate change and that the subsequent transit from one
fold to the other is accompanied by mass inversion. In such scenario matter
swallowed by black holes could be ejected as invisible negative mass and
dispersed in space.
| [
{
"created": "Tue, 23 Mar 2021 21:12:50 GMT",
"version": "v1"
}
] | 2021-11-22 | [
[
"Petit",
"J. P.",
""
],
[
"D'Agostini",
"G.",
""
]
] | We reconsider the classical Schwarzschild solution in the context of a Janus cosmological model. We show that the central singularity can be eliminated through a simple coordinate change and that the subsequent transit from one fold to the other is accompanied by mass inversion. In such scenario matter swallowed by black holes could be ejected as invisible negative mass and dispersed in space. |
gr-qc/9811004 | Carsten Gundlach | D. Garfinkle, C. Gundlach, and J. M. Martin-Garcia | Angular momentum near the black hole threshold in scalar field collapse | 7 pages, RevTex | Phys.Rev.D59:104012,1999 | 10.1103/PhysRevD.59.104012 | null | gr-qc | null | For the formation of a black hole in the gravitational collapse of a massless
scalar field, we calculate a critical exponent that governs the black hole
angular momentum for slightly non-spherical initial data near the black hole
threshold. We calculate the scaling law by second-order perturbation theory. We
then use the numerical results of a previous first-order perturbative analysis
to obtain the numerical value mu ~ 0.76 for the angular momentum critical
exponent. A quasi-periodic fine structure is superimposed on the overall power
law.
| [
{
"created": "Mon, 2 Nov 1998 23:32:18 GMT",
"version": "v1"
}
] | 2011-04-20 | [
[
"Garfinkle",
"D.",
""
],
[
"Gundlach",
"C.",
""
],
[
"Martin-Garcia",
"J. M.",
""
]
] | For the formation of a black hole in the gravitational collapse of a massless scalar field, we calculate a critical exponent that governs the black hole angular momentum for slightly non-spherical initial data near the black hole threshold. We calculate the scaling law by second-order perturbation theory. We then use the numerical results of a previous first-order perturbative analysis to obtain the numerical value mu ~ 0.76 for the angular momentum critical exponent. A quasi-periodic fine structure is superimposed on the overall power law. |
1503.00033 | Nilza Pires Prof | M. R. G. Maia, N. Pires and H. S. Gimenes | Equivalence between generalized phenomenological schemes for the
interaction of cosmological fluids: applications to arbitrary linear
barotropic fluids and vacuum decay | One more reference and two figures has been added | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Interactions between cosmic fluids may appear in many cosmological scenarios
that go far beyond the usually studied energy exchange in the dark sector. In
the absence of known microscopic interaction mechanisms, phenomenological
ansatzes are usually proposed in order to describe such models. In this paper,
we derive a generalization of one of the most frequently used of such
ansatzes:the one based on a initial proposal of Shapiro, Sol\`a, Espa\~na-Bonet
and Ruiz-Lapuente who described a time-dependent cosmological "constant" whose
variation arises from quantum effects near the Planck scale [I. L. Shapiro, J.
Sol\`a, C. Espa\~na-Bonet, and P. Ruiz-Lapuente, (2003). This physically
motivated model was based on a single free parameter $\nu$, and was
subsequently studied by Wang and Meng (2005), under the pure phenomenological
reasoning that the vacuum decay would slightly modify the exponent describing
how the energy density of dark matter decreases with the scale factor. This
modification is described by a single parameter $\varepsilon$ (= 3 $\nu$ of the
former paper). The generalization derived in the present article requires two
free parameters ($\varepsilon_{1}$, $\varepsilon_{2}$). We show that this
extension is dynamically equivalent to the ansatz proposed by Barrow and
Clifton (2006) which deals with the transfer of energy between any two fluids
using a two-parameter scheme ($\alpha_{1}$, $\alpha_{2}$) and that has the
advantage of exhibiting explicitly the form of the interaction factor appearing
in the continuity equation of each fluid.
| [
{
"created": "Fri, 27 Feb 2015 23:23:54 GMT",
"version": "v1"
},
{
"created": "Sun, 29 Mar 2015 21:00:31 GMT",
"version": "v2"
},
{
"created": "Sun, 26 Jul 2015 20:19:04 GMT",
"version": "v3"
}
] | 2015-07-28 | [
[
"Maia",
"M. R. G.",
""
],
[
"Pires",
"N.",
""
],
[
"Gimenes",
"H. S.",
""
]
] | Interactions between cosmic fluids may appear in many cosmological scenarios that go far beyond the usually studied energy exchange in the dark sector. In the absence of known microscopic interaction mechanisms, phenomenological ansatzes are usually proposed in order to describe such models. In this paper, we derive a generalization of one of the most frequently used of such ansatzes:the one based on a initial proposal of Shapiro, Sol\`a, Espa\~na-Bonet and Ruiz-Lapuente who described a time-dependent cosmological "constant" whose variation arises from quantum effects near the Planck scale [I. L. Shapiro, J. Sol\`a, C. Espa\~na-Bonet, and P. Ruiz-Lapuente, (2003). This physically motivated model was based on a single free parameter $\nu$, and was subsequently studied by Wang and Meng (2005), under the pure phenomenological reasoning that the vacuum decay would slightly modify the exponent describing how the energy density of dark matter decreases with the scale factor. This modification is described by a single parameter $\varepsilon$ (= 3 $\nu$ of the former paper). The generalization derived in the present article requires two free parameters ($\varepsilon_{1}$, $\varepsilon_{2}$). We show that this extension is dynamically equivalent to the ansatz proposed by Barrow and Clifton (2006) which deals with the transfer of energy between any two fluids using a two-parameter scheme ($\alpha_{1}$, $\alpha_{2}$) and that has the advantage of exhibiting explicitly the form of the interaction factor appearing in the continuity equation of each fluid. |
1305.5668 | Lorenzo Reverberi | E.V. Arbuzova, A.D. Dolgov, L. Reverberi | Particle Production in f(R) Gravity during Structure Formation | 16 pages, 3 figures | Phys. Rev. D 88, 024035 (2013) | 10.1103/PhysRevD.88.024035 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study particle production in infrared-modified gravitational theories in
the contemporary universe. It is shown that in astronomical systems with rising
mass density, the curvature scalar may oscillate with very high frequency.
These oscillations lead to efficient particle production and in an interesting
range of model parameters could be a source of energetic cosmic rays. This
effect either excludes some models of modified gravity or suggests a new
mechanism of cosmic ray production.
| [
{
"created": "Fri, 24 May 2013 09:50:47 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Jul 2013 12:08:50 GMT",
"version": "v2"
}
] | 2015-06-16 | [
[
"Arbuzova",
"E. V.",
""
],
[
"Dolgov",
"A. D.",
""
],
[
"Reverberi",
"L.",
""
]
] | We study particle production in infrared-modified gravitational theories in the contemporary universe. It is shown that in astronomical systems with rising mass density, the curvature scalar may oscillate with very high frequency. These oscillations lead to efficient particle production and in an interesting range of model parameters could be a source of energetic cosmic rays. This effect either excludes some models of modified gravity or suggests a new mechanism of cosmic ray production. |
2301.06886 | Alexander Zhuk | Maxim Eingorn, Brianna O'Briant, Adjaratou Diouf and Alexander Zhuk | Backreaction in cosmic screening approach | 11 pages, 2 figures | Physics Letters B 839 (2023) 137797 | 10.1016/j.physletb.2023.137797 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the backreaction of nonlinear perturbations on the global
evolution of the Universe within the cosmic screening approach. To this end, we
have considered the second-order scalar perturbations. An analytical study of
these perturbations followed by a numerical evaluation shows that, first, the
corresponding average values have a negligible backreaction effect on the
Friedmann equations and, second, the second-order correction to the
gravitational potential is much less than the first-order quantity.
Consequently, the expansion of perturbations into orders of smallness in the
cosmic screening approach is correct.
| [
{
"created": "Tue, 17 Jan 2023 13:46:01 GMT",
"version": "v1"
}
] | 2023-07-04 | [
[
"Eingorn",
"Maxim",
""
],
[
"O'Briant",
"Brianna",
""
],
[
"Diouf",
"Adjaratou",
""
],
[
"Zhuk",
"Alexander",
""
]
] | We investigate the backreaction of nonlinear perturbations on the global evolution of the Universe within the cosmic screening approach. To this end, we have considered the second-order scalar perturbations. An analytical study of these perturbations followed by a numerical evaluation shows that, first, the corresponding average values have a negligible backreaction effect on the Friedmann equations and, second, the second-order correction to the gravitational potential is much less than the first-order quantity. Consequently, the expansion of perturbations into orders of smallness in the cosmic screening approach is correct. |
gr-qc/0604097 | Oleg Zaslavskii | O. B. Zaslavskii | Extrinsically flat static spacetimes | 25 pages. To appear in Class. Quant. Grav | Class.Quant.Grav. 23 (2006) 4083-4100 | null | null | gr-qc hep-th math.DG | null | We consider static spacetimes whose spatial part admits foliations with the
extrinsic curvature tensor K_{ab}=0. There are two complementary cases when the
gradient of the lapse function points 1) to the direction of foliation or 2)
orthogonally to it. Case 1) gives generalization of metrics like
Bertotti-Robinson or Nariai. In case 2) the matter source violates the null
energy condition at least on the part of the manifold, having in this sense
phantom nature. We also demonstrate that for the manifolds under discussion the
horizon can be naked in the sense that certain Weyl components diverge in the
free-falling frame although the Kretschmann scalar is finite. The Petrov type
is D or O. Explicit solutions for (i) the linear anisotropic equation of state,
(ii) Chaplygin gas and (iii) uniform energy density are found.
| [
{
"created": "Fri, 21 Apr 2006 17:29:13 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Zaslavskii",
"O. B.",
""
]
] | We consider static spacetimes whose spatial part admits foliations with the extrinsic curvature tensor K_{ab}=0. There are two complementary cases when the gradient of the lapse function points 1) to the direction of foliation or 2) orthogonally to it. Case 1) gives generalization of metrics like Bertotti-Robinson or Nariai. In case 2) the matter source violates the null energy condition at least on the part of the manifold, having in this sense phantom nature. We also demonstrate that for the manifolds under discussion the horizon can be naked in the sense that certain Weyl components diverge in the free-falling frame although the Kretschmann scalar is finite. The Petrov type is D or O. Explicit solutions for (i) the linear anisotropic equation of state, (ii) Chaplygin gas and (iii) uniform energy density are found. |
1210.3261 | Jiri Podolsky | Robert Svarc, Jiri Podolsky | Geodesic deviation in Kundt spacetimes of any dimension | 8 pages, 2 figures, to appear in the Proceedings of the conference
"Relativity and Gravitation, 100 Years after Einstein in Prague", Prague,
June 25-29, 2012 | Springer Proceedings in Physics, Vol. 157, 2014, pages 229-237 | 10.1007/978-3-319-06761-2_29 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using the invariant form of the equation of geodesic deviation, which
describes relative motion of free test particles, we investigate a general
family of D-dimensional Kundt spacetimes. We demonstrate that local influence
of the gravitational field can be naturally decomposed into Newton-type tidal
effects typical for type II spacetimes, longitudinal deformations mainly
present in spacetimes of algebraic type III, and type N purely transverse
effects corresponding to gravitational waves with D(D-3)/2 independent
polarization states. We explicitly study the most important examples, namely
exact pp-waves, gyratons, and VSI spacetimes. This analysis helps us to clarify
the geometrical and physical interpretation of the Kundt class of nonexpanding,
nontwisting and shearfree geometries.
| [
{
"created": "Thu, 11 Oct 2012 14:45:34 GMT",
"version": "v1"
}
] | 2016-04-07 | [
[
"Svarc",
"Robert",
""
],
[
"Podolsky",
"Jiri",
""
]
] | Using the invariant form of the equation of geodesic deviation, which describes relative motion of free test particles, we investigate a general family of D-dimensional Kundt spacetimes. We demonstrate that local influence of the gravitational field can be naturally decomposed into Newton-type tidal effects typical for type II spacetimes, longitudinal deformations mainly present in spacetimes of algebraic type III, and type N purely transverse effects corresponding to gravitational waves with D(D-3)/2 independent polarization states. We explicitly study the most important examples, namely exact pp-waves, gyratons, and VSI spacetimes. This analysis helps us to clarify the geometrical and physical interpretation of the Kundt class of nonexpanding, nontwisting and shearfree geometries. |
1111.6738 | Luis Herrera | L. Herrera | On the Meaning of General Covariance and the Relevance of Observers in
General Relativity | 9 pages Latex. Published in Int. J. Mod. Phys. D. Some typos
corrected | Int. J. Mod. Phys. D 20, 2773, (2011) | 10.1142/S0218271811020676. | null | gr-qc physics.hist-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Since the appearance of General Relativity, its intrinsec general covariance
has been very often misinterpreted as implying that physically meaningful
quantitities (and conclusions extracted from the theory) have to be absolutely
independent on observers. This incorrect point of view is sometimes expressed
by discarding the very concept of observer in the structure and applications of
the theory. As we shall stress in this essay, through some examples, the
concept of observer is as essential to General Relativity as it is to any
physical theory.
| [
{
"created": "Tue, 29 Nov 2011 09:22:32 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Dec 2011 11:55:22 GMT",
"version": "v2"
},
{
"created": "Fri, 17 Feb 2012 11:18:22 GMT",
"version": "v3"
}
] | 2012-02-20 | [
[
"Herrera",
"L.",
""
]
] | Since the appearance of General Relativity, its intrinsec general covariance has been very often misinterpreted as implying that physically meaningful quantitities (and conclusions extracted from the theory) have to be absolutely independent on observers. This incorrect point of view is sometimes expressed by discarding the very concept of observer in the structure and applications of the theory. As we shall stress in this essay, through some examples, the concept of observer is as essential to General Relativity as it is to any physical theory. |
gr-qc/9802065 | Eric W. Hirschmann | Eric W. Hirschmann and Anzhong Wang | Spherical Self-Similar Solutions in Einstein-Multi-Scalar Gravity | 11 pages, 1 figure | Phys.Lett.A249:383-388,1998 | 10.1016/S0375-9601(98)00686-0 | UTCR-98-01 | gr-qc | null | We consider a general non-linear sigma model coupled to Einstein gravity and
show that in spherical symmetry and for a simple realization of
self-similarity, the spacetime can be completely determined. We also examine
some more specific matter models and discuss their relation to critical
collapse.
| [
{
"created": "Thu, 26 Feb 1998 17:40:36 GMT",
"version": "v1"
}
] | 2009-07-07 | [
[
"Hirschmann",
"Eric W.",
""
],
[
"Wang",
"Anzhong",
""
]
] | We consider a general non-linear sigma model coupled to Einstein gravity and show that in spherical symmetry and for a simple realization of self-similarity, the spacetime can be completely determined. We also examine some more specific matter models and discuss their relation to critical collapse. |
2402.08868 | Shinji Tsujikawa | Antonio De Felice, Shinji Tsujikawa | Probing the signature of axions through the quasinormal modes of black
holes | 8 pages, 3 figures | Phys. Lett. B 855 (2024) 138808 | 10.1016/j.physletb.2024.138808 | YITP-24-19, WUCG-24-01 | gr-qc astro-ph.CO hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | The axion-photon coupling allows the existence of a magnetically and
electrically charged black hole (BH) solution endowed with a pseudo-scalar
hair. For the Reissner-Nordstrom BH with a given total charge and mass, it is
known that the quasinormal modes (QNMs) are independent of the mixture between
the magnetic and electric charges due to the presence of electric-magnetic
duality. We show that the BH with an axion hair breaks this degeneracy by
realizing nontrivial QNMs that depend on the ratio between the magnetic and
total charges. Thus, the upcoming observations of BH QNMs through gravitational
waves offer an exciting possibility for probing the existence of both magnetic
monopoles and the axion coupled to photons.
| [
{
"created": "Wed, 14 Feb 2024 00:30:17 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Jun 2024 23:47:11 GMT",
"version": "v2"
}
] | 2024-06-24 | [
[
"De Felice",
"Antonio",
""
],
[
"Tsujikawa",
"Shinji",
""
]
] | The axion-photon coupling allows the existence of a magnetically and electrically charged black hole (BH) solution endowed with a pseudo-scalar hair. For the Reissner-Nordstrom BH with a given total charge and mass, it is known that the quasinormal modes (QNMs) are independent of the mixture between the magnetic and electric charges due to the presence of electric-magnetic duality. We show that the BH with an axion hair breaks this degeneracy by realizing nontrivial QNMs that depend on the ratio between the magnetic and total charges. Thus, the upcoming observations of BH QNMs through gravitational waves offer an exciting possibility for probing the existence of both magnetic monopoles and the axion coupled to photons. |
gr-qc/0104043 | Daniele Oriti | Richard E. Livine and Daniele Oriti | Barrett-Crane spin foam model from generalized BF-type action for
gravity | 15 pages, revtex; a sign corrected (area spectrum); some of these
results were presented in a preliminary form in gr-qc/0103081; v2: improved
presentation of the results, some changes in the text; to appear in Phys.
Rev. D | Phys.Rev.D65:044025,2002 | 10.1103/PhysRevD.65.044025 | DAMTP-2001-85 | gr-qc hep-th | null | We study a generalized action for gravity as a constrained BF theory, and its
relationship with the Plebanski action. We analyse the discretization of the
constraints and the spin foam quantization of the theory, showing that it leads
naturally to the Barrett-Crane spin foam model for quantum gravity. Our
analysis holds true in both the Euclidean and Lorentzian formulation.
| [
{
"created": "Sun, 15 Apr 2001 13:55:28 GMT",
"version": "v1"
},
{
"created": "Wed, 18 Apr 2001 19:06:52 GMT",
"version": "v2"
},
{
"created": "Wed, 17 Oct 2001 16:59:38 GMT",
"version": "v3"
}
] | 2014-11-17 | [
[
"Livine",
"Richard E.",
""
],
[
"Oriti",
"Daniele",
""
]
] | We study a generalized action for gravity as a constrained BF theory, and its relationship with the Plebanski action. We analyse the discretization of the constraints and the spin foam quantization of the theory, showing that it leads naturally to the Barrett-Crane spin foam model for quantum gravity. Our analysis holds true in both the Euclidean and Lorentzian formulation. |
1902.06900 | Chandramouli Chowdhury | Chandramouli Chowdhury, Susmita Das, Surojit Dalui and Bibhas Ranjan
Majhi | How robust is the indistinguishability between quantum fluctuation seen
from non-inertial frame and real thermal bath | Latex, 18 pages, 5 figures, to appear in Phys. Rev. D | Phys. Rev. D 99, 045021 (2019) | 10.1103/PhysRevD.99.045021 | null | gr-qc cond-mat.stat-mech hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We re-advocated the conjecture of indistinguishability between the quantum
fluctuation observed from a Rindler frame and a real thermal bath, for the case
of a free massless scalar field. To clarify the robustness and how far such is
admissible, in this paper, we investigate the issue from two different
non-inertial observers' perspective. A detailed analysis is being done to find
the observable quantities as measured by two non-inertial observers (one is
Rindler and another is uniformly rotating) on the real thermal bath and Rindler
frame in Minkowski spacetime. More precisely, we compare Thermal-Rindler with
Rindler-Rindler and Thermal-rotating with Rindler-rotating situations. In the
first model it is observed that although some of the observables are
equivalent, all the components of renormalised stress-tensor are not the same.
In the later model, we again find that this equivalence is not totally
guaranteed. Therefore we argue that the indistinguishability between the real
thermal bath and the Rindler frame may not be totally true.
| [
{
"created": "Tue, 19 Feb 2019 05:25:18 GMT",
"version": "v1"
}
] | 2019-03-06 | [
[
"Chowdhury",
"Chandramouli",
""
],
[
"Das",
"Susmita",
""
],
[
"Dalui",
"Surojit",
""
],
[
"Majhi",
"Bibhas Ranjan",
""
]
] | We re-advocated the conjecture of indistinguishability between the quantum fluctuation observed from a Rindler frame and a real thermal bath, for the case of a free massless scalar field. To clarify the robustness and how far such is admissible, in this paper, we investigate the issue from two different non-inertial observers' perspective. A detailed analysis is being done to find the observable quantities as measured by two non-inertial observers (one is Rindler and another is uniformly rotating) on the real thermal bath and Rindler frame in Minkowski spacetime. More precisely, we compare Thermal-Rindler with Rindler-Rindler and Thermal-rotating with Rindler-rotating situations. In the first model it is observed that although some of the observables are equivalent, all the components of renormalised stress-tensor are not the same. In the later model, we again find that this equivalence is not totally guaranteed. Therefore we argue that the indistinguishability between the real thermal bath and the Rindler frame may not be totally true. |
gr-qc/9910078 | Iver H. Brevik | I. Brevik and H. B. Sandvik | Magnetohydrodynamics in the Inflationary Universe | 19 pages, LaTeX, no figures. Minor additions to the Summary section
and Acknowledgments section. Two new references. Version to appear in Phys.
Rev. D | Phys.Rev.D61:083505,2000 | 10.1103/PhysRevD.61.083505 | null | gr-qc | null | Magnetohydrodynamic (MHD) waves are analysed in the early Universe, in the
inflationary era, assuming the Universe to be filled with a nonviscous fluid of
the Zel'dovich type ($p=\rho$) in a metric of the de Sitter form. A spatially
uniform, time dependent, magnetic field ${\bf B_0}$ is assumed to be present.
The Einstein equations are first solved to give the time dependence of the
scale factor, assuming that the matter density, but not the magnetic field,
contribute as source terms. The various modes are thereafter analysed; they
turn out to be essentially of the same kind as those encountered in
conventional nongravitational MHD, although the longitudinal magnetosonic wave
is not interpretable as a physical energy-transporting wave as the group
velocity becomes superluminal. We determine the phase speed of the various
modes; they turn out to be scale factor independent. The Alfv\'{e}n velocity of
the transverse magnetohydrodynamic wave becomes extremely small in the
inflationary era, showing that the wave is in practice 'frozen in'.
| [
{
"created": "Fri, 22 Oct 1999 15:23:55 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Dec 1999 09:17:10 GMT",
"version": "v2"
}
] | 2009-01-14 | [
[
"Brevik",
"I.",
""
],
[
"Sandvik",
"H. B.",
""
]
] | Magnetohydrodynamic (MHD) waves are analysed in the early Universe, in the inflationary era, assuming the Universe to be filled with a nonviscous fluid of the Zel'dovich type ($p=\rho$) in a metric of the de Sitter form. A spatially uniform, time dependent, magnetic field ${\bf B_0}$ is assumed to be present. The Einstein equations are first solved to give the time dependence of the scale factor, assuming that the matter density, but not the magnetic field, contribute as source terms. The various modes are thereafter analysed; they turn out to be essentially of the same kind as those encountered in conventional nongravitational MHD, although the longitudinal magnetosonic wave is not interpretable as a physical energy-transporting wave as the group velocity becomes superluminal. We determine the phase speed of the various modes; they turn out to be scale factor independent. The Alfv\'{e}n velocity of the transverse magnetohydrodynamic wave becomes extremely small in the inflationary era, showing that the wave is in practice 'frozen in'. |
1807.06260 | Mahdi Godazgar | Mahdi Godazgar, Andre Kaderli | Penrose quasi-local energy and Kerr-Schild metrics | 18 pages, appendix added | null | 10.1088/1361-6382/aae444 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Specialising to the case of Kerr-Schild spacetimes, which include the Kerr
black hole and gravitational wave solutions, we propose a modification of the
Penrose quasi-local energy. The modification relies on the existence of a
natural Minkowski background for Kerr-Schild spacetimes. We find that the
modified surface integral reduces to a volume integral of the Einstein tensor,
which has been proposed previously as an appropriate definition for quasi-local
energy for Kerr-Schild backgrounds. Furthermore, in the special case that the
Kerr-Schild null vector is normal to the surface of interest, we construct a
1-1 map between the 2-surface twistors in the Kerr-Schild background and
Minkowski twistors projected onto the surface.
| [
{
"created": "Tue, 17 Jul 2018 07:23:10 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Sep 2018 13:22:36 GMT",
"version": "v2"
}
] | 2018-11-14 | [
[
"Godazgar",
"Mahdi",
""
],
[
"Kaderli",
"Andre",
""
]
] | Specialising to the case of Kerr-Schild spacetimes, which include the Kerr black hole and gravitational wave solutions, we propose a modification of the Penrose quasi-local energy. The modification relies on the existence of a natural Minkowski background for Kerr-Schild spacetimes. We find that the modified surface integral reduces to a volume integral of the Einstein tensor, which has been proposed previously as an appropriate definition for quasi-local energy for Kerr-Schild backgrounds. Furthermore, in the special case that the Kerr-Schild null vector is normal to the surface of interest, we construct a 1-1 map between the 2-surface twistors in the Kerr-Schild background and Minkowski twistors projected onto the surface. |
2004.09536 | Nuno M. Santos | Nuno M. Santos, Carolina L. Benone, Lu\'is C. B. Crispino, Carlos A.
R. Herdeiro, Eugen Radu | Black holes with synchronised Proca hair: linear clouds and fundamental
non-linear solutions | 36 pages, 13 figures | null | 10.1007/JHEP07(2020)010 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recent studies have made key progress on the black hole/solitonic solutions
of the Einstein-Proca system. Firstly, fully non-linear dynamical evolutions of
the Kerr black hole superradiant instability, triggered by a Proca field, have
shown the formation of a new equilibrium state, a spinning black hole with
synchronised Proca hair. Secondly, non-linear evolutions of spinning Proca
stars have established that they are dynamically stable, unlike their scalar
cousins. Thirdy, separability of the Proca equation on the Kerr background has
been achieved. Motivated by these results, in this paper we reconsider Kerr
black holes with synchronised Proca hair. The separability of the Proca
equation on the Kerr background allows us to examine the stationary Proca
clouds in greater detail, in particular their dependence on the different
quantum numbers. These stationary clouds occur at a set of existence lines in
the Kerr parameter space, from which the black holes with synchronised Proca
hair bifurcate. We construct the domain of existence of these black holes,
comparing the fundamental states missed in the original study with the first
excited states and with the cousin scalar model, giving illustrative examples
of Kerr-like and non-Kerr-like BHs. In the vanishing event horizon limit, these
hairy black holes connect to the fundamental states of spinning Proca stars,
which include the dynamically stable solutions.
| [
{
"created": "Mon, 20 Apr 2020 18:00:10 GMT",
"version": "v1"
}
] | 2020-07-15 | [
[
"Santos",
"Nuno M.",
""
],
[
"Benone",
"Carolina L.",
""
],
[
"Crispino",
"Luís C. B.",
""
],
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Radu",
"Eugen",
""
]
] | Recent studies have made key progress on the black hole/solitonic solutions of the Einstein-Proca system. Firstly, fully non-linear dynamical evolutions of the Kerr black hole superradiant instability, triggered by a Proca field, have shown the formation of a new equilibrium state, a spinning black hole with synchronised Proca hair. Secondly, non-linear evolutions of spinning Proca stars have established that they are dynamically stable, unlike their scalar cousins. Thirdy, separability of the Proca equation on the Kerr background has been achieved. Motivated by these results, in this paper we reconsider Kerr black holes with synchronised Proca hair. The separability of the Proca equation on the Kerr background allows us to examine the stationary Proca clouds in greater detail, in particular their dependence on the different quantum numbers. These stationary clouds occur at a set of existence lines in the Kerr parameter space, from which the black holes with synchronised Proca hair bifurcate. We construct the domain of existence of these black holes, comparing the fundamental states missed in the original study with the first excited states and with the cousin scalar model, giving illustrative examples of Kerr-like and non-Kerr-like BHs. In the vanishing event horizon limit, these hairy black holes connect to the fundamental states of spinning Proca stars, which include the dynamically stable solutions. |
gr-qc/9911063 | Hideo Iguchi | Hideo Iguchi, Tomohiro Harada, and Ken-ichi Nakao | Gravitational Radiation from a Naked Singularity. II - Even-Parity
Perturbation - | 16 pages, 5 figures, errors and typos corrected, final version | Prog.Theor.Phys. 103 (2000) 53-72 | 10.1143/PTP.103.53 | KUNS 1614 | gr-qc | null | A naked singularity occurs in the generic collapse of an inhomogeneous dust
ball. We study the even-parity mode of gravitational waves from a naked
singularity of the Lema\^{\i}tre-Tolman-Bondi spacetime. The wave equations for
gravitational waves are solved by numerical integration using the single null
coordinate. The result implies that the metric perturbation grows when it
approaches the Cauchy horizon and diverges there, although the naked
singularity is not a strong source of even-parity gravitational radiation.
Therefore, the Cauchy horizon in this spacetime should be unstable with respect
to linear even-parity perturbations.
| [
{
"created": "Thu, 18 Nov 1999 01:46:40 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Feb 2000 03:25:57 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Iguchi",
"Hideo",
""
],
[
"Harada",
"Tomohiro",
""
],
[
"Nakao",
"Ken-ichi",
""
]
] | A naked singularity occurs in the generic collapse of an inhomogeneous dust ball. We study the even-parity mode of gravitational waves from a naked singularity of the Lema\^{\i}tre-Tolman-Bondi spacetime. The wave equations for gravitational waves are solved by numerical integration using the single null coordinate. The result implies that the metric perturbation grows when it approaches the Cauchy horizon and diverges there, although the naked singularity is not a strong source of even-parity gravitational radiation. Therefore, the Cauchy horizon in this spacetime should be unstable with respect to linear even-parity perturbations. |
2311.14040 | Georgios Lukes-Gerakopoulos | Georgios Lukes-Gerakopoulos and Sajal Mukherjee | Can extended bodies follow geodesic trajectories? | 8 pages, Proceedings of RAGtime 23-25, Edited by Z. Stuchl\'{i}k, G.
T\"{o}r\"{o}k , V. Karas and D. Lan\v{c}ov\'{a}, Silesian University in Opava | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We provide an extension of the analysis on whether an extended test body can
follow a geodesic trajectory given by Mukherjee, S., Lukes-Gerakopoulos, G. and
Nayak, R. K. (2022), Extended bodies moving on geodesic trajectories, General
Relativity and Gravitation, 54(9), 113, arXiv: 1907.05659. In particular, we
consider a test body in a pole-dipole-quadrupole approximation under the
Ohashi-Kyrian-Semer\'{a}k spin supplementary condition moving in the
Schwarzschild and Kerr background. Using orbital setups under which a
pole-dipole body can follow geodesic motion, we explore under which conditions
this can take place also in the pole-dipole-quadrupole approximation, when only
the mass quadrupole is taken into account. For our analysis we employ the
assumption that the dipole contribution and the quadrupole contribution vanish
independently.
| [
{
"created": "Thu, 23 Nov 2023 14:48:25 GMT",
"version": "v1"
}
] | 2023-11-27 | [
[
"Lukes-Gerakopoulos",
"Georgios",
""
],
[
"Mukherjee",
"Sajal",
""
]
] | We provide an extension of the analysis on whether an extended test body can follow a geodesic trajectory given by Mukherjee, S., Lukes-Gerakopoulos, G. and Nayak, R. K. (2022), Extended bodies moving on geodesic trajectories, General Relativity and Gravitation, 54(9), 113, arXiv: 1907.05659. In particular, we consider a test body in a pole-dipole-quadrupole approximation under the Ohashi-Kyrian-Semer\'{a}k spin supplementary condition moving in the Schwarzschild and Kerr background. Using orbital setups under which a pole-dipole body can follow geodesic motion, we explore under which conditions this can take place also in the pole-dipole-quadrupole approximation, when only the mass quadrupole is taken into account. For our analysis we employ the assumption that the dipole contribution and the quadrupole contribution vanish independently. |
1609.06915 | Emil Nissimov | Eduardo Guendelman, Emil Nissimov, Svetlana Pacheva | Quintessential Inflation, Unified Dark Energy and Dark Matter, and Higgs
Mechanism | 15 pages, to appear in the Proc. of 3rd Bulgarian National Congress
on Physical Sciences (Sept-Oct 2016), Bulgarian Journal of Physics, vol.43
(2016) | Bulgarian Journal of Physics 44 (2017) 15-30 | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe a new type of gravity-matter models where gravity couples in a
non-conventional way to two distinct scalar fields providing a unified
Lagrangian action principle description of: (a) the evolution of both "early"
and "late" Universe - by the "inflaton" scalar field; (b) dark energy and dark
matter as a unified manifestation of a single material entity - the "darkon"
scalar field. The essential non-standard feature of our models is employing the
formalism of non-Riemannian space-time volume forms - alternative generally
covariant integration measure densities (volume elements) defined in terms of
auxiliary antisymmetric tensor gauge fields. Although being (almost) pure-gauge
degrees of freedom, the non-Riemannian space-time volume forms trigger a series
of important features unavailable in ordinary gravity-matter models. When
including in addition interactions with the electro-weak model bosonic sector
we obtain a gravity-assisted generation of electro-weak spontaneous gauge
symmetry breaking in the post-inflationary "late" Universe, while the
Higgs-like scalar remains massless in the "early" Universe.
| [
{
"created": "Thu, 22 Sep 2016 11:19:41 GMT",
"version": "v1"
}
] | 2017-07-25 | [
[
"Guendelman",
"Eduardo",
""
],
[
"Nissimov",
"Emil",
""
],
[
"Pacheva",
"Svetlana",
""
]
] | We describe a new type of gravity-matter models where gravity couples in a non-conventional way to two distinct scalar fields providing a unified Lagrangian action principle description of: (a) the evolution of both "early" and "late" Universe - by the "inflaton" scalar field; (b) dark energy and dark matter as a unified manifestation of a single material entity - the "darkon" scalar field. The essential non-standard feature of our models is employing the formalism of non-Riemannian space-time volume forms - alternative generally covariant integration measure densities (volume elements) defined in terms of auxiliary antisymmetric tensor gauge fields. Although being (almost) pure-gauge degrees of freedom, the non-Riemannian space-time volume forms trigger a series of important features unavailable in ordinary gravity-matter models. When including in addition interactions with the electro-weak model bosonic sector we obtain a gravity-assisted generation of electro-weak spontaneous gauge symmetry breaking in the post-inflationary "late" Universe, while the Higgs-like scalar remains massless in the "early" Universe. |
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