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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1106.5000 | Javier Olmedo | Jer\'onimo Cortez, Guillermo A. Mena Marug\'an, Javier Olmedo, Jos\'e
M. Velhinho | A uniqueness criterion for the Fock quantization of scalar fields with
time dependent mass | 11 pages, version accepted for publication in Classical and Quantum
Gravity | Class. Quantum Grav. 28 (2011) 172001 | 10.1088/0264-9381/28/17/172001 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A major problem in the quantization of fields in curved spacetimes is the
ambiguity in the choice of a Fock representation for the canonical commutation
relations. There exists an infinite number of choices leading to different
physical predictions. In stationary scenarios, a common strategy is to select a
vacuum (or a family of unitarily equivalent vacua) by requiring invariance
under the spacetime symmetries. When stationarity is lost, a natural
generalization consists in replacing time invariance by unitarity in the
evolution. We prove that, when the spatial sections are compact, the criterion
of a unitary dynamics, together with the invariance under the spatial
isometries, suffices to select a unique family of Fock quantizations for a
scalar field with time dependent mass.
| [
{
"created": "Fri, 24 Jun 2011 15:35:14 GMT",
"version": "v1"
},
{
"created": "Fri, 19 Aug 2011 09:06:17 GMT",
"version": "v2"
},
{
"created": "Mon, 22 Aug 2011 21:28:17 GMT",
"version": "v3"
}
] | 2011-08-24 | [
[
"Cortez",
"Jerónimo",
""
],
[
"Marugán",
"Guillermo A. Mena",
""
],
[
"Olmedo",
"Javier",
""
],
[
"Velhinho",
"José M.",
""
]
] | A major problem in the quantization of fields in curved spacetimes is the ambiguity in the choice of a Fock representation for the canonical commutation relations. There exists an infinite number of choices leading to different physical predictions. In stationary scenarios, a common strategy is to select a vacuum (or a family of unitarily equivalent vacua) by requiring invariance under the spacetime symmetries. When stationarity is lost, a natural generalization consists in replacing time invariance by unitarity in the evolution. We prove that, when the spatial sections are compact, the criterion of a unitary dynamics, together with the invariance under the spatial isometries, suffices to select a unique family of Fock quantizations for a scalar field with time dependent mass. |
gr-qc/0408010 | Carsten Weber | Claus Kiefer, Carsten Weber | On the interaction of mesoscopic quantum systems with gravity | 27 pages, study for ESA: typos corrected, references and
clarifications added. To appear in Annalen der Physik | Annalen Phys. 14 (2005) 253-278 | 10.1002/andp.200410119 | null | gr-qc cond-mat.mes-hall quant-ph | null | We review the different aspects of the interaction of mesoscopic quantum
systems with gravitational fields. We first discuss briefly the foundations of
general relativity and quantum mechanics. Then, we consider the
non-relativistic expansions of the Klein-Gordon and Dirac equations in the
post-Newtonian approximation. After a short overview of classical gravitational
waves, we discuss two proposed interaction mechanisms: (i) the use of quantum
fluids as generator and/or detector of gravitational waves in the laboratory,
and (ii) the inclusion of gravitomagnetic fields in the study of the properties
of rotating superconductors. The foundations of the proposed experiments are
explained and evaluated.
| [
{
"created": "Tue, 3 Aug 2004 20:43:12 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Sep 2004 13:11:22 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Kiefer",
"Claus",
""
],
[
"Weber",
"Carsten",
""
]
] | We review the different aspects of the interaction of mesoscopic quantum systems with gravitational fields. We first discuss briefly the foundations of general relativity and quantum mechanics. Then, we consider the non-relativistic expansions of the Klein-Gordon and Dirac equations in the post-Newtonian approximation. After a short overview of classical gravitational waves, we discuss two proposed interaction mechanisms: (i) the use of quantum fluids as generator and/or detector of gravitational waves in the laboratory, and (ii) the inclusion of gravitomagnetic fields in the study of the properties of rotating superconductors. The foundations of the proposed experiments are explained and evaluated. |
0804.4224 | Florian Beyer | Florian Beyer | Investigations of solutions of Einstein's field equations close to
lambda-Taub-NUT | 24 pages, 12 figures, uses psfrag and hyperref; replaced with
published version, only minor corrections of typos and references | Class.Quant.Grav.25:235005,2008 | 10.1088/0264-9381/25/23/235005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present investigations of a class of solutions of Einstein's field
equations close to the family of lambda-Taub-NUT spacetimes. The studies are
done using a numerical code introduced by the author elsewhere. One of the main
technical complication is due to the S3-topology of the Cauchy surfaces.
Complementing these numerical results with heuristic arguments, we are able to
yield some first insights into the strong cosmic censorship issue and the
conjectures by Belinskii, Khalatnikov, and Lifschitz in this class of
spacetimes. In particular, the current investigations suggest that strong
cosmic censorship holds in this class. We further identify open issues in our
current approach and point to future research projects.
| [
{
"created": "Sat, 26 Apr 2008 16:36:25 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Nov 2008 09:53:25 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Beyer",
"Florian",
""
]
] | We present investigations of a class of solutions of Einstein's field equations close to the family of lambda-Taub-NUT spacetimes. The studies are done using a numerical code introduced by the author elsewhere. One of the main technical complication is due to the S3-topology of the Cauchy surfaces. Complementing these numerical results with heuristic arguments, we are able to yield some first insights into the strong cosmic censorship issue and the conjectures by Belinskii, Khalatnikov, and Lifschitz in this class of spacetimes. In particular, the current investigations suggest that strong cosmic censorship holds in this class. We further identify open issues in our current approach and point to future research projects. |
gr-qc/0703074 | Chopin Soo | Chopin Soo | Three-geometry and reformulation of the Wheeler-DeWitt equation | 10 pages, LaTeX file | Class.Quant.Grav.24:1547-1555,2007 | 10.1088/0264-9381/24/6/011 | null | gr-qc | null | A reformulation of the Wheeler-DeWitt equation which highlights the role of
gauge-invariant three-geometry elements is presented. It is noted that the
classical super-Hamiltonian of four-dimensional gravity as simplified by
Ashtekar through the use of gauge potential and densitized triad variables can
furthermore be succinctly expressed as a vanishing Poisson bracket involving
three-geometry elements. This is discussed in the general setting of the
Barbero extension of the theory with arbitrary non-vanishing value of the
Immirzi parameter, and when a cosmological constant is also present. A proposed
quantum constraint of density weight two which is polynomial in the basic
conjugate variables is also demonstrated to correspond to a precise simple
ordering of the operators, and may thus help to resolve the factor ordering
ambiguity in the extrapolation from classical to quantum gravity. Alternative
expression of a density weight one quantum constraint which may be more useful
in the spin network context is also discussed, but this constraint is
non-polynomial and is not motivated by factor ordering. The article also
highlights the fact that while the volume operator has become a preeminient
object in the current manifestation of loop quantum gravity, the volume element
and the Chern-Simons functional can be of equal significance, and need not be
mutually exclusive. Both these fundamental objects appear explicitly in the
reformulation of the Wheeler-DeWitt constraint.
| [
{
"created": "Tue, 13 Mar 2007 10:51:23 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Soo",
"Chopin",
""
]
] | A reformulation of the Wheeler-DeWitt equation which highlights the role of gauge-invariant three-geometry elements is presented. It is noted that the classical super-Hamiltonian of four-dimensional gravity as simplified by Ashtekar through the use of gauge potential and densitized triad variables can furthermore be succinctly expressed as a vanishing Poisson bracket involving three-geometry elements. This is discussed in the general setting of the Barbero extension of the theory with arbitrary non-vanishing value of the Immirzi parameter, and when a cosmological constant is also present. A proposed quantum constraint of density weight two which is polynomial in the basic conjugate variables is also demonstrated to correspond to a precise simple ordering of the operators, and may thus help to resolve the factor ordering ambiguity in the extrapolation from classical to quantum gravity. Alternative expression of a density weight one quantum constraint which may be more useful in the spin network context is also discussed, but this constraint is non-polynomial and is not motivated by factor ordering. The article also highlights the fact that while the volume operator has become a preeminient object in the current manifestation of loop quantum gravity, the volume element and the Chern-Simons functional can be of equal significance, and need not be mutually exclusive. Both these fundamental objects appear explicitly in the reformulation of the Wheeler-DeWitt constraint. |
gr-qc/9912037 | Subodha | S. Mishra (CTS and Dept. of Physics, IIT Kharagpur, India), D. N.
Tripathy (Institute of Physics, Bhubaneswar, India) | A quantum mechanical derivation of Gamow's relation for the time and
temperature of the expanding Universe | Tex-file, 13 pages | null | null | CTS-kgp/28/Sept/99 | gr-qc | null | The quantum mechanical approach developed by us recently for the evolution of
the universe is used to derive an alternative derivation connecting the
temperature of the cosmic background radiation and the age of the universe
which is found to be similar to the one obtained by Gamow long back. By
assuming the age of the universe to be $\approx$ 20 billion years, we reproduce
a value of $\approx$ 2.91 K for the cosmic back-ground radiation, agreeing well
with the recently measured experimental value of 2.728 K. Besides, this theory
enables us to calculate the photon density and entropy associated with the
background radiation and the ratio of the number of photons to the number of
nucleons, which quantitatively agree with the results obtained by others.
| [
{
"created": "Fri, 10 Dec 1999 08:15:57 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Mishra",
"S.",
"",
"CTS and Dept. of Physics, IIT Kharagpur, India"
],
[
"Tripathy",
"D. N.",
"",
"Institute of Physics, Bhubaneswar, India"
]
] | The quantum mechanical approach developed by us recently for the evolution of the universe is used to derive an alternative derivation connecting the temperature of the cosmic background radiation and the age of the universe which is found to be similar to the one obtained by Gamow long back. By assuming the age of the universe to be $\approx$ 20 billion years, we reproduce a value of $\approx$ 2.91 K for the cosmic back-ground radiation, agreeing well with the recently measured experimental value of 2.728 K. Besides, this theory enables us to calculate the photon density and entropy associated with the background radiation and the ratio of the number of photons to the number of nucleons, which quantitatively agree with the results obtained by others. |
2001.00615 | Canisius Bernard | Canisius Bernard, Masoud Ghezelbash | Hidden conformal symmetry of the rotating charged AdS black holes in
quadratic $f$($T$) gravity | 21 pages, 8 figures; v2: references added | Phys. Rev. D 101, 024020 (2020) | 10.1103/PhysRevD.101.024020 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The nonextremal Kerr black holes have been considered to be holographically
dual to two-dimensional (2D) conformal field theories (CFTs). In this paper, we
extend the holography to the case of an asymptotically anti--de Sitter (AdS)
rotating charged black holes in $f$($T$) gravity, where $f(T) = T + \alpha
T^2$, where $\alpha$ is a constant. We find that the scalar wave radial
equation at the near-horizon region implies the existence of the 2D conformal
symmetries. We note that the $2\pi$ identification of the azimuthal angle
$\phi$ in the black hole line element, corresponds to a spontaneous breaking of
the conformal symmetry by left and right temperatures $T_{L}$ and $T_{R}$,
respectively. We show that choosing proper central charges for the dual CFT, we
produce exactly the macroscopic Bekenstein-Hawking entropy from the microscopic
Cardy entropy for the dual CFT. These observations suggest that the rotating
charged AdS black hole in $f$($T$) gravity is dual to a 2D CFT at finite
temperatures $T_{L}$ and $T_{R}$ for a specific value of mass $M$, rotational,
charge, and $f$($T$) parameters, $\Omega$, $Q$, and $|\alpha|$, respectively.
| [
{
"created": "Thu, 2 Jan 2020 20:24:23 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Jan 2020 22:36:53 GMT",
"version": "v2"
}
] | 2020-01-17 | [
[
"Bernard",
"Canisius",
""
],
[
"Ghezelbash",
"Masoud",
""
]
] | The nonextremal Kerr black holes have been considered to be holographically dual to two-dimensional (2D) conformal field theories (CFTs). In this paper, we extend the holography to the case of an asymptotically anti--de Sitter (AdS) rotating charged black holes in $f$($T$) gravity, where $f(T) = T + \alpha T^2$, where $\alpha$ is a constant. We find that the scalar wave radial equation at the near-horizon region implies the existence of the 2D conformal symmetries. We note that the $2\pi$ identification of the azimuthal angle $\phi$ in the black hole line element, corresponds to a spontaneous breaking of the conformal symmetry by left and right temperatures $T_{L}$ and $T_{R}$, respectively. We show that choosing proper central charges for the dual CFT, we produce exactly the macroscopic Bekenstein-Hawking entropy from the microscopic Cardy entropy for the dual CFT. These observations suggest that the rotating charged AdS black hole in $f$($T$) gravity is dual to a 2D CFT at finite temperatures $T_{L}$ and $T_{R}$ for a specific value of mass $M$, rotational, charge, and $f$($T$) parameters, $\Omega$, $Q$, and $|\alpha|$, respectively. |
1206.0540 | Lau Loi So | Lau Loi So | Quasilocal energy-momentum for tensors B and V in small regions | 11 pages, a major revision of arXiv:1006.5272 | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The Bel-Robinson tensor $B$ and the tensor $V$ have the same quasilocal
energy-momentum in a small sphere. Using a pseudotensor approach to evaluate
the energy-momentum in a half-cylinder, we find that $B$ and $V$ have different
values, not proportional to the "Bel-Robinson energy-momentum". Furthermore,
even if we arrange things so that we do get the same "Bel-Robinson
energy-momentum" value, the angular momentum gives different values using $B$
and $V$ in a half cylinder. In addition, we find that $B$ and $V$ have a
different number of independent components. The fully trace free property of
$B$ and $V$ implies conservation of pure "Bel-Robinson energy-momentum" in
small regions, and vice versa. In addition, we also demonstrate the tidal
heating, rate of change of momentum and spin angular momentum flux by using
these two tensors.
| [
{
"created": "Mon, 4 Jun 2012 08:11:53 GMT",
"version": "v1"
},
{
"created": "Sun, 29 Sep 2013 14:09:56 GMT",
"version": "v2"
},
{
"created": "Wed, 5 Jan 2022 14:42:48 GMT",
"version": "v3"
}
] | 2022-01-06 | [
[
"So",
"Lau Loi",
""
]
] | The Bel-Robinson tensor $B$ and the tensor $V$ have the same quasilocal energy-momentum in a small sphere. Using a pseudotensor approach to evaluate the energy-momentum in a half-cylinder, we find that $B$ and $V$ have different values, not proportional to the "Bel-Robinson energy-momentum". Furthermore, even if we arrange things so that we do get the same "Bel-Robinson energy-momentum" value, the angular momentum gives different values using $B$ and $V$ in a half cylinder. In addition, we find that $B$ and $V$ have a different number of independent components. The fully trace free property of $B$ and $V$ implies conservation of pure "Bel-Robinson energy-momentum" in small regions, and vice versa. In addition, we also demonstrate the tidal heating, rate of change of momentum and spin angular momentum flux by using these two tensors. |
1803.02620 | Sunny Vagnozzi | Alessandro Casalino, Massimiliano Rinaldi, Lorenzo Sebastiani, Sunny
Vagnozzi | Mimicking dark matter and dark energy in a mimetic model compatible with
GW170817 | 29 pages, 2 figures. Version accepted for publication in Phys. Dark
Univ | Phys. Dark Univ. 22 (2018) 108 | 10.1016/j.dark.2018.10.001 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The recent observation of the the gravitational wave event GW170817 and of
its electromagnetic counterpart GRB170817A, from a binary neutron star merger,
has established that the speed of gravitational waves deviates from the speed
of light by less than one part in $10^{15}$. As a consequence, many extensions
of General Relativity are inevitably ruled out. Among these we find the most
relevant sectors of Horndeski gravity. In its original formulation, mimetic
gravity is able to mimic cosmological dark matter, has tensorial perturbations
that travel exactly at the speed of light but has vanishing scalar
perturbations and this fact persists if we combine mimetic with Horndeski
gravity. In this work, we show that implementing the mimetic gravity action
with higher-order terms that break the Horndeski structure yields a
cosmological model that satisfies the constraint on the speed of gravitational
waves and mimics both dark energy and dark matter with a non-vanishing speed of
sound. In this way, we are able to reproduce the $\Lambda$CDM cosmological
model without introducing particle cold dark matter.
| [
{
"created": "Wed, 7 Mar 2018 12:43:23 GMT",
"version": "v1"
},
{
"created": "Tue, 29 May 2018 15:38:47 GMT",
"version": "v2"
},
{
"created": "Mon, 1 Oct 2018 11:59:40 GMT",
"version": "v3"
}
] | 2018-12-13 | [
[
"Casalino",
"Alessandro",
""
],
[
"Rinaldi",
"Massimiliano",
""
],
[
"Sebastiani",
"Lorenzo",
""
],
[
"Vagnozzi",
"Sunny",
""
]
] | The recent observation of the the gravitational wave event GW170817 and of its electromagnetic counterpart GRB170817A, from a binary neutron star merger, has established that the speed of gravitational waves deviates from the speed of light by less than one part in $10^{15}$. As a consequence, many extensions of General Relativity are inevitably ruled out. Among these we find the most relevant sectors of Horndeski gravity. In its original formulation, mimetic gravity is able to mimic cosmological dark matter, has tensorial perturbations that travel exactly at the speed of light but has vanishing scalar perturbations and this fact persists if we combine mimetic with Horndeski gravity. In this work, we show that implementing the mimetic gravity action with higher-order terms that break the Horndeski structure yields a cosmological model that satisfies the constraint on the speed of gravitational waves and mimics both dark energy and dark matter with a non-vanishing speed of sound. In this way, we are able to reproduce the $\Lambda$CDM cosmological model without introducing particle cold dark matter. |
2301.11665 | Vahideh Memari Rishakani | Vahideh Memari and S. Habib Mazharimousavi | Causal structure and the geodesics in the hairy extension of the
Bertotti-Robinson spacetime | 19 pages and 12 figures | Phys. Scr. 98, 075303 (2023) | 10.1088/1402-4896/acdeb6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A hairy extension of the Bertotti-Robinson regular spacetime has been
recently introduced in the context of the Einstein-Maxwell-Scaler theory that
surprisingly is a singular black hole formed in the $S_{3}$ background spatial
topology [CQG39(2022)167001]. In this research, we first clarify the topology
of the spacetime based on the coordinate transformations as well as the
energy-momentum configuration and the causal structure of the black hole.
Furthermore, we investigate the geodesics of the null and timelike particles in
this spacetime. It is shown that in the radial motion on the equatorial plane,
while photons may collapse to the singularity or escape to the edge of the
universe, a massive particle always collapses to the singularity. The general
geodesics of null and massive particles reveal that all particles except the
outgoing light ray, eventually fall into the black hole.
| [
{
"created": "Fri, 27 Jan 2023 11:49:37 GMT",
"version": "v1"
},
{
"created": "Sat, 1 Jul 2023 16:11:04 GMT",
"version": "v2"
}
] | 2023-07-06 | [
[
"Memari",
"Vahideh",
""
],
[
"Mazharimousavi",
"S. Habib",
""
]
] | A hairy extension of the Bertotti-Robinson regular spacetime has been recently introduced in the context of the Einstein-Maxwell-Scaler theory that surprisingly is a singular black hole formed in the $S_{3}$ background spatial topology [CQG39(2022)167001]. In this research, we first clarify the topology of the spacetime based on the coordinate transformations as well as the energy-momentum configuration and the causal structure of the black hole. Furthermore, we investigate the geodesics of the null and timelike particles in this spacetime. It is shown that in the radial motion on the equatorial plane, while photons may collapse to the singularity or escape to the edge of the universe, a massive particle always collapses to the singularity. The general geodesics of null and massive particles reveal that all particles except the outgoing light ray, eventually fall into the black hole. |
gr-qc/9311029 | null | J.E.Nelson and T.Regge | Quantisation of 2+1 gravity for genus 2 | 11 pages, 2 figures available from authors, DFTT 54/93 | Phys. Rev. D 50, 5125 (1994) | 10.1103/PhysRevD.50.5125 | null | gr-qc hep-th | null | In [1,2] we established and discussed the algebra of observables for $2+1$
gravity at both the classical and quantum level, and gave a systematic
discussion of the reduction of the expected number of independent observables
to $6g - 6 (g > 1)$. In this paper the algebra of observables for the case
$g=2$ is reduced to a very simple form. A Hilbert space of state vectors is
defined and its representations are discussed using a deformation of the
Euler-Gamma function. The deformation parameter $\th$ depends on the
cosmological and Planck's constants.
| [
{
"created": "Wed, 17 Nov 1993 16:45:32 GMT",
"version": "v1"
}
] | 2013-11-13 | [
[
"Nelson",
"J. E.",
""
],
[
"Regge",
"T.",
""
]
] | In [1,2] we established and discussed the algebra of observables for $2+1$ gravity at both the classical and quantum level, and gave a systematic discussion of the reduction of the expected number of independent observables to $6g - 6 (g > 1)$. In this paper the algebra of observables for the case $g=2$ is reduced to a very simple form. A Hilbert space of state vectors is defined and its representations are discussed using a deformation of the Euler-Gamma function. The deformation parameter $\th$ depends on the cosmological and Planck's constants. |
0708.2356 | Elizabeth Winstanley | J. E. Baxter, Marc Helbling and Elizabeth Winstanley | Abundant stable gauge field hair for black holes in anti-de Sitter space | 4 pages, 3 figures, new introduction, additional minor changes,
published in Physical Review Letters | Phys.Rev.Lett.100:011301,2008 | 10.1103/PhysRevLett.100.011301 | null | gr-qc hep-th | null | We present new hairy black hole solutions of su(N) Einstein-Yang-Mills theory
(EYM) in asymptotically anti-de Sitter (adS) space. These black holes are
described by N+1 independent parameters, and have N-1 independent gauge field
degrees of freedom. Solutions in which all gauge field functions have no zeros
exist for all N, and for sufficiently large (and negative) cosmological
constant. At least some of these solutions are shown to be stable under
classical, linear, spherically symmetric perturbations. Therefore there is no
upper bound on the amount of stable gauge field hair with which a black hole in
adS can be endowed.
| [
{
"created": "Fri, 17 Aug 2007 12:40:08 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Jan 2008 16:51:57 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Baxter",
"J. E.",
""
],
[
"Helbling",
"Marc",
""
],
[
"Winstanley",
"Elizabeth",
""
]
] | We present new hairy black hole solutions of su(N) Einstein-Yang-Mills theory (EYM) in asymptotically anti-de Sitter (adS) space. These black holes are described by N+1 independent parameters, and have N-1 independent gauge field degrees of freedom. Solutions in which all gauge field functions have no zeros exist for all N, and for sufficiently large (and negative) cosmological constant. At least some of these solutions are shown to be stable under classical, linear, spherically symmetric perturbations. Therefore there is no upper bound on the amount of stable gauge field hair with which a black hole in adS can be endowed. |
gr-qc/9912048 | Jose Socorro Garcia Diaz | J. Socorro and E. R. Medina | Supersymmetric Quantum Mechanics for Bianchi Class A models | 9 pages, two figures, Revtex, to appear in Phys. Rev. D | Phys.Rev. D61 (2000) 087702 | 10.1103/PhysRevD.61.087702 | IFUG-99-15 | gr-qc | null | In this work we present cosmological quantum solutions for all Bianchi Class
A cosmological models obtained by means of supersymmetric quantum mechanics .
We are able to write one general expression for all bosonic components occuring
in the Grassmann expansion of the wave function of the Universe for this class
of models. These solutions are obtained by means of a more general ansatz for
the so-called master equations.
| [
{
"created": "Mon, 13 Dec 1999 16:53:58 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Socorro",
"J.",
""
],
[
"Medina",
"E. R.",
""
]
] | In this work we present cosmological quantum solutions for all Bianchi Class A cosmological models obtained by means of supersymmetric quantum mechanics . We are able to write one general expression for all bosonic components occuring in the Grassmann expansion of the wave function of the Universe for this class of models. These solutions are obtained by means of a more general ansatz for the so-called master equations. |
2207.05690 | Thomas Helfer | Robin Croft, Thomas Helfer, Bo-Xuan Ge, Miren Radia, Tamara
Evstafyeva, Eugene A. Lim, Ulrich Sperhake, Katy Clough | The Gravitational Afterglow of Boson Stars | Movie: https://youtu.be/JE5FRG7kgvU Data:
https://github.com/ThomasHelfer/BosonStarAfterglow | null | 10.1088/1361-6382/acace4 | KCL-TH-2021-82 | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we study the long-lived post-merger gravitational wave signature
of a boson-star binary coalescence. We use full numerical relativity to
simulate the post-merger and track the gravitational afterglow over an extended
period of time. We implement recent innovations for the binary initial data,
which significantly reduce spurious initial excitations of the scalar field
profiles, as well as a measure for the angular momentum that allows us to track
the total momentum of the spatial volume, including the curvature contribution.
Crucially, we find the afterglow to last much longer than the spin-down
timescale. This prolonged gravitational wave afterglow provides a
characteristic signal that may distinguish it from other astrophysical sources.
| [
{
"created": "Tue, 12 Jul 2022 17:10:24 GMT",
"version": "v1"
}
] | 2023-03-01 | [
[
"Croft",
"Robin",
""
],
[
"Helfer",
"Thomas",
""
],
[
"Ge",
"Bo-Xuan",
""
],
[
"Radia",
"Miren",
""
],
[
"Evstafyeva",
"Tamara",
""
],
[
"Lim",
"Eugene A.",
""
],
[
"Sperhake",
"Ulrich",
""
],
[
"Clough",
"Katy",
""
]
] | In this work we study the long-lived post-merger gravitational wave signature of a boson-star binary coalescence. We use full numerical relativity to simulate the post-merger and track the gravitational afterglow over an extended period of time. We implement recent innovations for the binary initial data, which significantly reduce spurious initial excitations of the scalar field profiles, as well as a measure for the angular momentum that allows us to track the total momentum of the spatial volume, including the curvature contribution. Crucially, we find the afterglow to last much longer than the spin-down timescale. This prolonged gravitational wave afterglow provides a characteristic signal that may distinguish it from other astrophysical sources. |
1909.10295 | Pawan Joshi | Pawan Joshi, Utkarsh Kumar, Sukanta Panda | Hamiltonian Formalism for Nonlocal Gravity Models | 19 pages | International Journal of Geometric Methods in Modern Physics 2
(2022) | 10.1142/S0219887822500360 | 2250036 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Nonlocal gravity models are constructed to explain the current acceleration
of the universe. These models are inspired by the infrared correction appearing
in Einstein Hilbert action. Here we develop the Hamiltonian formalism of a
nonlocal model by considering only terms to quadratic order in Ricci tensor and
Ricci scalar. We also show how to count the degree of freedom using Hamiltonian
formalism in this model.
| [
{
"created": "Mon, 23 Sep 2019 11:23:53 GMT",
"version": "v1"
}
] | 2021-12-28 | [
[
"Joshi",
"Pawan",
""
],
[
"Kumar",
"Utkarsh",
""
],
[
"Panda",
"Sukanta",
""
]
] | Nonlocal gravity models are constructed to explain the current acceleration of the universe. These models are inspired by the infrared correction appearing in Einstein Hilbert action. Here we develop the Hamiltonian formalism of a nonlocal model by considering only terms to quadratic order in Ricci tensor and Ricci scalar. We also show how to count the degree of freedom using Hamiltonian formalism in this model. |
1005.0627 | Michael Kesden | Michael Kesden, Guglielmo Lockhart, and E. Sterl Phinney | Maximum black-hole spin from quasi-circular binary mergers | final version accepted in PRD, new Fig.4 and discussion | Phys.Rev.D82:124045,2010 | 10.1103/PhysRevD.82.124045 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black holes of mass M must have a spin angular momentum S below the Kerr
limit chi = S/M^2 < 1, but whether astrophysical black holes can attain this
limiting spin depends on their accretion history. Gas accretion from a thin
disk limits the black-hole spin to chi_gas < 0.9980 +- 0.0002, as
electromagnetic radiation from this disk with retrograde angular momentum is
preferentially absorbed by the black hole. Extrapolation of
numerical-relativity simulations of equal-mass binary black-hole mergers to
maximum initial spins suggests these mergers yield a maximum spin chi_eq <
0.95. Here we show that for smaller mass ratios q = m/M << 1, the superradiant
extraction of angular momentum from the larger black hole imposes a fundamental
limit chi_lim < 0.9979 +- 0.0001 on the final black-hole spin even in the
test-particle limit q -> 0 of binary black-hole mergers. The nearly equal
values of chi_gas and chi_lim imply that measurement of supermassive black-hole
spins cannot distinguish a black hole built by gas accretion from one assembled
by the gravitational inspiral of a disk of compact stellar remnants. We also
show how superradiant scattering alters the mass and spin predicted by models
derived from extrapolating test-particle mergers to finite mass ratios.
| [
{
"created": "Tue, 4 May 2010 20:07:43 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Dec 2010 16:11:09 GMT",
"version": "v2"
}
] | 2010-12-21 | [
[
"Kesden",
"Michael",
""
],
[
"Lockhart",
"Guglielmo",
""
],
[
"Phinney",
"E. Sterl",
""
]
] | Black holes of mass M must have a spin angular momentum S below the Kerr limit chi = S/M^2 < 1, but whether astrophysical black holes can attain this limiting spin depends on their accretion history. Gas accretion from a thin disk limits the black-hole spin to chi_gas < 0.9980 +- 0.0002, as electromagnetic radiation from this disk with retrograde angular momentum is preferentially absorbed by the black hole. Extrapolation of numerical-relativity simulations of equal-mass binary black-hole mergers to maximum initial spins suggests these mergers yield a maximum spin chi_eq < 0.95. Here we show that for smaller mass ratios q = m/M << 1, the superradiant extraction of angular momentum from the larger black hole imposes a fundamental limit chi_lim < 0.9979 +- 0.0001 on the final black-hole spin even in the test-particle limit q -> 0 of binary black-hole mergers. The nearly equal values of chi_gas and chi_lim imply that measurement of supermassive black-hole spins cannot distinguish a black hole built by gas accretion from one assembled by the gravitational inspiral of a disk of compact stellar remnants. We also show how superradiant scattering alters the mass and spin predicted by models derived from extrapolating test-particle mergers to finite mass ratios. |
gr-qc/0703148 | Patricio S. Letelier | V. M. Rosa and P. S. Letelier | Stability of Closed Timelike Geodesics | 5 pages, REvTex, discussion added. PLA, in press | Phys.Lett.A370:99-103,2007 | 10.1016/j.physleta.2007.05.041 | null | gr-qc | null | The existence and stability under linear perturbations of closed timelike
geodesics (CTGs) in Bonnor-Ward spacetime is studied in some detail. Regions
where the CTG exist and are linearly stable are exhibited.
| [
{
"created": "Thu, 29 Mar 2007 15:37:32 GMT",
"version": "v1"
},
{
"created": "Mon, 28 May 2007 18:07:02 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Rosa",
"V. M.",
""
],
[
"Letelier",
"P. S.",
""
]
] | The existence and stability under linear perturbations of closed timelike geodesics (CTGs) in Bonnor-Ward spacetime is studied in some detail. Regions where the CTG exist and are linearly stable are exhibited. |
1902.09170 | Gary Gibbons | G. W. Gibbons | The Ashtekar-Hansen universal structure at spatial infinity is weakly
pseudo-Carrollian | Appendix deleted and typos corrected | null | null | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that Ashtekar and Hansens's Universal Structure at Spatial
Infinity (SPI), which has recently be used to establish the conservation of
supercharges from past null infity to future null infinity, is an example of a
(pseudo-) Carollian structure. The relation to Kinematic Algebras is clarified.
| [
{
"created": "Mon, 25 Feb 2019 09:57:44 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Jun 2019 11:11:45 GMT",
"version": "v2"
}
] | 2019-06-14 | [
[
"Gibbons",
"G. W.",
""
]
] | It is shown that Ashtekar and Hansens's Universal Structure at Spatial Infinity (SPI), which has recently be used to establish the conservation of supercharges from past null infity to future null infinity, is an example of a (pseudo-) Carollian structure. The relation to Kinematic Algebras is clarified. |
gr-qc/0505046 | Jaime Fernando Villas da Rocha | R. Chan, M. F. A. da Silva, Jaime F. Villas da Rocha | Perturbed Self-Similar Massless Scalar Field in the Spacetimes with
Circular Symmetry in 2+1 Gravity | no figures | Int.J.Mod.Phys.D14:1725-1738,2005 | 10.1142/S0218271805007309 | null | gr-qc | null | We present in this work the study of the linear perturbations of the
2+1-dimensional circularly symmetric solution, obtained in a previous work,
with kinematic self-similarity of the second kind. We have obtained an exact
solution for the perturbation equations and the possible perturbation modes. We
have shown that the background solution is a stable solution.
| [
{
"created": "Tue, 10 May 2005 20:39:22 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Chan",
"R.",
""
],
[
"da Silva",
"M. F. A.",
""
],
[
"da Rocha",
"Jaime F. Villas",
""
]
] | We present in this work the study of the linear perturbations of the 2+1-dimensional circularly symmetric solution, obtained in a previous work, with kinematic self-similarity of the second kind. We have obtained an exact solution for the perturbation equations and the possible perturbation modes. We have shown that the background solution is a stable solution. |
1702.06459 | Aaron Johnson | Kostas Glampedakis, Aaron D. Johnson, Daniel Kennefick | The Darboux transformation in black hole perturbation theory | Accepted for publication in PRD, minor changes have been made to
update to the journal version, 13 pages, 1 table | Phys. Rev. D 96, 024036 (2017) | 10.1103/PhysRevD.96.024036 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Darboux transformation between ordinary differential equations is a 19th
century technique that has seen wide use in quantum theory for producing
exactly solvable potentials for the Schr\"odinger equation with specific
spectral properties. In this paper we show that the same transformation appears
in black hole theory, relating, for instance, the Zerilli and Regge-Wheeler
equations for axial and polar Schwarzschild perturbations. The transformation
reveals these two equations to be isospectral, a well known result whose method
has been repeatedly reintroduced under different names. We highlight the key
role that the so-called algebraically special solutions play in the black hole
Darboux theory and show that a similar relation exists between the
Chandrasekhar-Detweiler equations for Kerr perturbations. Finally, we discuss
the limitations of the method when dealing with long-range potentials and
explore the possibilities offered by a generalised Darboux transformation.
| [
{
"created": "Tue, 21 Feb 2017 16:10:58 GMT",
"version": "v1"
},
{
"created": "Sat, 15 Jul 2017 23:34:33 GMT",
"version": "v2"
},
{
"created": "Tue, 18 Jul 2017 17:22:41 GMT",
"version": "v3"
}
] | 2017-08-02 | [
[
"Glampedakis",
"Kostas",
""
],
[
"Johnson",
"Aaron D.",
""
],
[
"Kennefick",
"Daniel",
""
]
] | The Darboux transformation between ordinary differential equations is a 19th century technique that has seen wide use in quantum theory for producing exactly solvable potentials for the Schr\"odinger equation with specific spectral properties. In this paper we show that the same transformation appears in black hole theory, relating, for instance, the Zerilli and Regge-Wheeler equations for axial and polar Schwarzschild perturbations. The transformation reveals these two equations to be isospectral, a well known result whose method has been repeatedly reintroduced under different names. We highlight the key role that the so-called algebraically special solutions play in the black hole Darboux theory and show that a similar relation exists between the Chandrasekhar-Detweiler equations for Kerr perturbations. Finally, we discuss the limitations of the method when dealing with long-range potentials and explore the possibilities offered by a generalised Darboux transformation. |
0902.2490 | Jakub Mielczarek | Jakub Mielczarek | Tensor power spectrum with holonomy corrections in LQC | 13 pages, 12 figures. Numerical computations improved. Major revision | Phys.Rev.D79:123520,2009 | 10.1103/PhysRevD.79.123520 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we consider tensor perturbations produced at a bounce phase in
presence of the holonomy corrections. Here bounce phase and holonomy
corrections originate from Loop Quantum Cosmology. We re-derive formulas for
the corrections for the model with a scalar field content. Background dynamics
with a free scalar field and multi-fluid potential are considered. Since the
considerations are semi-classical effects of quantum fluctuations of the
background dynamics are not taken into account. Quantum and classical
back-reaction effects are also neglected. To find spectrum of the gravitational
waves both analytical approximations as well as numerical investigations were
performed. We have found analytical solutions on super-horizontal and
sub-horizontal regimes and derived corresponding tensor power spectra. Also
occupation number $n_{\bf k}$ and parameter $\Omega_{\text{gw}}$ were derived
in sub-horizontal limit, leading to its extremely low present value. Final
results are numerical power spectra of the gravitational waves produced in
presence of quantum holonomy corrections. The obtained spectrum has two UV and
IR branches where $\mathcal{P}_T \propto k^2$, however with the different
prefactors. Spectrum connecting these regions is in the form of oscillations.
We have found good agreement between numerical spectrum and this obtained from
the analytical model. Obtained spectrum can be directly applied as initial
conditions for the inflationary modes. We mention possible resulting
observational features of the CMB in particular B-type polarization.
| [
{
"created": "Sat, 14 Feb 2009 19:14:15 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Apr 2009 21:50:17 GMT",
"version": "v2"
}
] | 2009-07-09 | [
[
"Mielczarek",
"Jakub",
""
]
] | In this paper we consider tensor perturbations produced at a bounce phase in presence of the holonomy corrections. Here bounce phase and holonomy corrections originate from Loop Quantum Cosmology. We re-derive formulas for the corrections for the model with a scalar field content. Background dynamics with a free scalar field and multi-fluid potential are considered. Since the considerations are semi-classical effects of quantum fluctuations of the background dynamics are not taken into account. Quantum and classical back-reaction effects are also neglected. To find spectrum of the gravitational waves both analytical approximations as well as numerical investigations were performed. We have found analytical solutions on super-horizontal and sub-horizontal regimes and derived corresponding tensor power spectra. Also occupation number $n_{\bf k}$ and parameter $\Omega_{\text{gw}}$ were derived in sub-horizontal limit, leading to its extremely low present value. Final results are numerical power spectra of the gravitational waves produced in presence of quantum holonomy corrections. The obtained spectrum has two UV and IR branches where $\mathcal{P}_T \propto k^2$, however with the different prefactors. Spectrum connecting these regions is in the form of oscillations. We have found good agreement between numerical spectrum and this obtained from the analytical model. Obtained spectrum can be directly applied as initial conditions for the inflationary modes. We mention possible resulting observational features of the CMB in particular B-type polarization. |
2003.00044 | Astrid Eichhorn | Astrid Eichhorn | Asymptotically safe gravity | 14 pages plus references, prepared for the proceedings of the 57th
Course of the Erice International School of Subnuclear Physics, "In search
for the unexpected", June 2019 | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is an introduction to asymptotically safe quantum gravity, explaining
the main idea of asymptotic safety and how it could solve the problem of
predictivity in quantum gravity. In the first part, the concept of an
asymptotically safe fixed point is discussed within the functional
Renormalization Group framework for gravity, which is also briefly reviewed. A
concise overview of key results on asymptotically safe gravity is followed by a
short discussion of important open questions. The second part highlights how
the interplay with matter provides observational consistency tests for all
quantum-gravity models, followed by an overview of the state of results on
asymptotic safety and its implications in gravity-matter models. Finally,
effective asymptotic safety is briefly discussed as a scenario in which
asymptotically safe gravity could be connected to other approaches to quantum
gravity.
| [
{
"created": "Fri, 28 Feb 2020 20:02:32 GMT",
"version": "v1"
}
] | 2020-03-03 | [
[
"Eichhorn",
"Astrid",
""
]
] | This is an introduction to asymptotically safe quantum gravity, explaining the main idea of asymptotic safety and how it could solve the problem of predictivity in quantum gravity. In the first part, the concept of an asymptotically safe fixed point is discussed within the functional Renormalization Group framework for gravity, which is also briefly reviewed. A concise overview of key results on asymptotically safe gravity is followed by a short discussion of important open questions. The second part highlights how the interplay with matter provides observational consistency tests for all quantum-gravity models, followed by an overview of the state of results on asymptotic safety and its implications in gravity-matter models. Finally, effective asymptotic safety is briefly discussed as a scenario in which asymptotically safe gravity could be connected to other approaches to quantum gravity. |
2202.05643 | Alessandro Nagar | Alessandro Nagar, James Healy, Carlos O. Lousto, Sebastiano Bernuzzi,
and Angelica Albertini | Numerical-relativity validation of effective-one-body waveforms in the
intermediate-mass-ratio regime | 15 pages, 14 figures, submitted to Phys. Rev. D | null | 10.1103/PhysRevD.105.124061 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | One of the open problems in developing binary black hole (BBH) waveforms for
gravitational wave astronomy is to model the intermediate mass ratio regime and
connect it to the extreme mass ratio regime. A natural approach is to employ
the effective one body (EOB) approach to the two-body dynamics that, by design,
can cover the entire mass ratio range and naturally incorporates the extreme
mass ratio limit. Here we use recently obtained numerical relativity (NR) data
with mass ratios $m_1/m_2=(7,15,\,32,\,64,\,128)$ to test the accuracy of the
state-of-the-art EOB model TEOBResumS in the intermediate mass ratio regime. We
generally find an excellent EOB/NR consistency around merger and ringdown for
all mass ratios and for all available subdominant multipoles, except for the
$\ell=m=5$ one. This mode can be crucially improved using the new large-mass
ratio NR data of this paper. The EOB/NR inspirals are also consistent with the
estimated NR uncertainties. We also use several NR datasets taken by different
public catalogs to probe the universal behavior of the multipolar hierarchy of
waveform amplitudes at merger, that smoothly connects the equal-mass BBH to the
test-mass result. Interestingly, the universal behavior is strengthened if the
nonoscillatory memory contribution is included in the NR waveform. Future NR
simulations with improved accuracy will be necessary to further probe, and
possibly quantitatively refine, the TEOBResumS transition from late inspiral to
plunge in the intermediate mass ratio regime.
| [
{
"created": "Fri, 11 Feb 2022 14:32:24 GMT",
"version": "v1"
}
] | 2022-07-13 | [
[
"Nagar",
"Alessandro",
""
],
[
"Healy",
"James",
""
],
[
"Lousto",
"Carlos O.",
""
],
[
"Bernuzzi",
"Sebastiano",
""
],
[
"Albertini",
"Angelica",
""
]
] | One of the open problems in developing binary black hole (BBH) waveforms for gravitational wave astronomy is to model the intermediate mass ratio regime and connect it to the extreme mass ratio regime. A natural approach is to employ the effective one body (EOB) approach to the two-body dynamics that, by design, can cover the entire mass ratio range and naturally incorporates the extreme mass ratio limit. Here we use recently obtained numerical relativity (NR) data with mass ratios $m_1/m_2=(7,15,\,32,\,64,\,128)$ to test the accuracy of the state-of-the-art EOB model TEOBResumS in the intermediate mass ratio regime. We generally find an excellent EOB/NR consistency around merger and ringdown for all mass ratios and for all available subdominant multipoles, except for the $\ell=m=5$ one. This mode can be crucially improved using the new large-mass ratio NR data of this paper. The EOB/NR inspirals are also consistent with the estimated NR uncertainties. We also use several NR datasets taken by different public catalogs to probe the universal behavior of the multipolar hierarchy of waveform amplitudes at merger, that smoothly connects the equal-mass BBH to the test-mass result. Interestingly, the universal behavior is strengthened if the nonoscillatory memory contribution is included in the NR waveform. Future NR simulations with improved accuracy will be necessary to further probe, and possibly quantitatively refine, the TEOBResumS transition from late inspiral to plunge in the intermediate mass ratio regime. |
1205.6877 | Mohamad Shalaby | Mohamad Shalaby | Dynamics and Light Propagation in a Universe with Discrete Matter
Content | submitted as AIIMS diploma essay at http://archive.aims.ac.za/2010 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss a model for a universe with discrete matter content instead of the
continuous perfect fluid taken in FRW models. We show how the redshift in such
a universe deviates from the corresponding one in an FRW cosmology. This
illustrates the fact that averaging the matter content in a universe and then
evolving it in time, is not the same as evolving a universe with discrete
matter content. The main reason for such deviation is the fact that the photons
in such a universe mainly travel in an empty space rather than the continuous
perfect fluid in FRW geometry.
| [
{
"created": "Thu, 31 May 2012 03:41:08 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Jun 2012 22:40:11 GMT",
"version": "v2"
},
{
"created": "Wed, 6 Jun 2012 16:08:46 GMT",
"version": "v3"
}
] | 2012-06-07 | [
[
"Shalaby",
"Mohamad",
""
]
] | We discuss a model for a universe with discrete matter content instead of the continuous perfect fluid taken in FRW models. We show how the redshift in such a universe deviates from the corresponding one in an FRW cosmology. This illustrates the fact that averaging the matter content in a universe and then evolving it in time, is not the same as evolving a universe with discrete matter content. The main reason for such deviation is the fact that the photons in such a universe mainly travel in an empty space rather than the continuous perfect fluid in FRW geometry. |
1009.5595 | Mattias N. R. Wohlfarth | Felix Tennie, Mattias N.R. Wohlfarth | Consistent matter couplings for Plebanski gravity | 20 pages | Phys.Rev.D82:104052,2010 | 10.1103/PhysRevD.82.104052 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We develop a scheme for the minimal coupling of all standard types of tensor
and spinor field matter to Plebanski gravity. This theory is a geometric
reformulation of vacuum general relativity in terms of two-form frames and
connection one-forms, and provides a covariant basis for various quantization
approaches. Using the spinor formalism we prove the consistency of the newly
proposed matter coupling by demonstrating the full equivalence of Plebanski
gravity plus matter to Einstein--Cartan gravity. As a byproduct we also show
the consistency of some previous suggestions for matter actions.
| [
{
"created": "Tue, 28 Sep 2010 15:10:43 GMT",
"version": "v1"
}
] | 2010-12-23 | [
[
"Tennie",
"Felix",
""
],
[
"Wohlfarth",
"Mattias N. R.",
""
]
] | We develop a scheme for the minimal coupling of all standard types of tensor and spinor field matter to Plebanski gravity. This theory is a geometric reformulation of vacuum general relativity in terms of two-form frames and connection one-forms, and provides a covariant basis for various quantization approaches. Using the spinor formalism we prove the consistency of the newly proposed matter coupling by demonstrating the full equivalence of Plebanski gravity plus matter to Einstein--Cartan gravity. As a byproduct we also show the consistency of some previous suggestions for matter actions. |
2203.06767 | Emilio Elizalde | Emilio Elizalde, Martiros Khurshudyan, K. Myrzakulov and S. Bekov | Reconstruction of the quintessence dark energy potential from a Gaussian
process | 15 pages, 10 figures | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | The quintessence dark energy potential is reconstructed in a
model-independent way. Reconstruction relies on a Gaussian process and on
available expansion-rate data. Specifically, 40-point values of $H(z)$ are
used, consisting of a 30-point sample deduced from a differential age method
and an additional 10-point sample obtained from the radial BAO method. Results
are obtained for two kernel functions and for three different values of
$H_{0}$. They shed light on the $H_{0}$ tension problem for a universe
described with quintessence dark energy. They are also a clear indication that
the tension has to do with the physical understanding of the issue, rather than
being just a numerical problem with statistics. Moreover, the model-independent
reconstruction of the potential here obtained can serve as a reference to
constraint available models and it can be also used as a reference frame to
construct new ones. Various possibilities, including $V(\phi) \sim e^{-\lambda
\phi}$, are compared with the reconstructions here obtained, which is notably
the first truly model independent reconstruction of the quintessence dark
energy potential. This allows to select new models that can be interesting for
cosmology. The method can be extended to reconstruct the potential of related
dark energy models, to be considered in future work.
| [
{
"created": "Sun, 13 Mar 2022 21:36:50 GMT",
"version": "v1"
}
] | 2022-03-15 | [
[
"Elizalde",
"Emilio",
""
],
[
"Khurshudyan",
"Martiros",
""
],
[
"Myrzakulov",
"K.",
""
],
[
"Bekov",
"S.",
""
]
] | The quintessence dark energy potential is reconstructed in a model-independent way. Reconstruction relies on a Gaussian process and on available expansion-rate data. Specifically, 40-point values of $H(z)$ are used, consisting of a 30-point sample deduced from a differential age method and an additional 10-point sample obtained from the radial BAO method. Results are obtained for two kernel functions and for three different values of $H_{0}$. They shed light on the $H_{0}$ tension problem for a universe described with quintessence dark energy. They are also a clear indication that the tension has to do with the physical understanding of the issue, rather than being just a numerical problem with statistics. Moreover, the model-independent reconstruction of the potential here obtained can serve as a reference to constraint available models and it can be also used as a reference frame to construct new ones. Various possibilities, including $V(\phi) \sim e^{-\lambda \phi}$, are compared with the reconstructions here obtained, which is notably the first truly model independent reconstruction of the quintessence dark energy potential. This allows to select new models that can be interesting for cosmology. The method can be extended to reconstruct the potential of related dark energy models, to be considered in future work. |
0707.0128 | John T. Whelan | Reinhard Prix and John T. Whelan | F-statistic search for white-dwarf binaries in the first Mock LISA Data
Challenge | submitted to CQG for proceedings of 11th GW Data Analysis workshop | Class.Quant.Grav.24:S565-S574,2007 | 10.1088/0264-9381/24/19/S19 | LIGO-P070029-01-Z | gr-qc | null | The F-statistic is an optimal detection statistic for continuous
gravitational waves, i.e., long-duration (quasi-)monochromatic signals with
slowly-varying intrinsic frequency. This method was originally developed in the
context of ground-based detectors, but it is equally applicable to LISA where
many signals fall into this class of signals. We report on the application of a
LIGO/GEO F-statistic code to LISA data-analysis using the long-wavelength limit
(LWL), and we present results of our search for white-dwarf binary signals in
the first Mock LISA Data Challenge. Somewhat surprisingly, the LWL is found to
be sufficient -- even at high frequencies -- for detection of signals and their
accurate localization on the sky and in frequency, while a more accurate
modelling of the TDI response only seems necessary to correctly estimate the
four amplitude parameters.
| [
{
"created": "Sun, 1 Jul 2007 21:37:34 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Prix",
"Reinhard",
""
],
[
"Whelan",
"John T.",
""
]
] | The F-statistic is an optimal detection statistic for continuous gravitational waves, i.e., long-duration (quasi-)monochromatic signals with slowly-varying intrinsic frequency. This method was originally developed in the context of ground-based detectors, but it is equally applicable to LISA where many signals fall into this class of signals. We report on the application of a LIGO/GEO F-statistic code to LISA data-analysis using the long-wavelength limit (LWL), and we present results of our search for white-dwarf binary signals in the first Mock LISA Data Challenge. Somewhat surprisingly, the LWL is found to be sufficient -- even at high frequencies -- for detection of signals and their accurate localization on the sky and in frequency, while a more accurate modelling of the TDI response only seems necessary to correctly estimate the four amplitude parameters. |
1005.0935 | Giovanni Venturi | A. Cerioni, F. Finelli, A. Tronconi, G. Venturi | Inflation and Reheating in Spontaneously Generated Gravity | 15 pages, 10 figures, to be published in Phys. Rev. D | Phys.Rev.D81:123505,2010 | 10.1103/PhysRevD.81.123505 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Inflation is studied in the context of induced gravity (IG) $\gamma \sigma^2
R$, where $R$ is the Ricci scalar, $\sigma$ a scalar field and $\gamma$ a
dimensionless constant, and diverse symmetry-breaking potentials $V(\sigma)$
are considered. In particular we compared the predictions for Landau-Ginzburg
(LG) and Coleman-Weinberg (CW) type potentials and their possible
generalizations with the most recent data. We find that large field inflation
generally leads to fewer constraints on the parameters and the shape of the
potential whereas small field inflation is more problematic and, if viable,
implies more constraints, in particular on the parameter $\gamma$. We also
examined the reheating phase and obtained an accurate analytical solution for
the dynamics of inflaton and the Hubble parameter by using a multiple scale
analysis (MSA). The solutions were then used to study the average expansion of
the Universe, the average equation of state for the scalar field and both the
perturbative and resonant decays of the inflaton field.
| [
{
"created": "Thu, 6 May 2010 09:03:32 GMT",
"version": "v1"
}
] | 2014-11-21 | [
[
"Cerioni",
"A.",
""
],
[
"Finelli",
"F.",
""
],
[
"Tronconi",
"A.",
""
],
[
"Venturi",
"G.",
""
]
] | Inflation is studied in the context of induced gravity (IG) $\gamma \sigma^2 R$, where $R$ is the Ricci scalar, $\sigma$ a scalar field and $\gamma$ a dimensionless constant, and diverse symmetry-breaking potentials $V(\sigma)$ are considered. In particular we compared the predictions for Landau-Ginzburg (LG) and Coleman-Weinberg (CW) type potentials and their possible generalizations with the most recent data. We find that large field inflation generally leads to fewer constraints on the parameters and the shape of the potential whereas small field inflation is more problematic and, if viable, implies more constraints, in particular on the parameter $\gamma$. We also examined the reheating phase and obtained an accurate analytical solution for the dynamics of inflaton and the Hubble parameter by using a multiple scale analysis (MSA). The solutions were then used to study the average expansion of the Universe, the average equation of state for the scalar field and both the perturbative and resonant decays of the inflaton field. |
2309.12087 | Pierre Vanhove | Philippe Brax, Pierre Vanhove | Scalaron dynamics from UV to IR | v2: expanded version with new appendices and references. 35 pages.
Version to appear in Physical Review D | null | null | IPHT-t23/049, LAPTH-033/23 | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider a scenario where the scalaron of $f({\cal R})$ models is related
to the volume modulus of string compactifications leaving only one scalar
degree of freedom at low energy. The coefficient of the leading curvature
squared contribution to the low energy effective action of gravity determines
the mass of the scalaron. We impose that this mass is small enough to allow for
the scalaron to drive Starobinski's inflation. After inflation, the
renormalisation group evolution of the couplings of the $f({\cal R})$ theory,
viewed as a scalar-tensor theory, provides the link with the Infra-Red regime.
We consider a scenario where the corrections to the mass of the scalaron are
large and reduce it below the electron mass in the Infra-Red, so that the
scalaron plays a central role in the low energy dynamics of the Universe. In
particular this leads to a connection between the scalaron mass and the
measured vacuum energy provided its renormalisation group running at energies
higher than the electron mass never drops below the present day value of the
dark energy.
| [
{
"created": "Thu, 21 Sep 2023 13:58:03 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Mar 2024 08:29:59 GMT",
"version": "v2"
}
] | 2024-03-20 | [
[
"Brax",
"Philippe",
""
],
[
"Vanhove",
"Pierre",
""
]
] | We consider a scenario where the scalaron of $f({\cal R})$ models is related to the volume modulus of string compactifications leaving only one scalar degree of freedom at low energy. The coefficient of the leading curvature squared contribution to the low energy effective action of gravity determines the mass of the scalaron. We impose that this mass is small enough to allow for the scalaron to drive Starobinski's inflation. After inflation, the renormalisation group evolution of the couplings of the $f({\cal R})$ theory, viewed as a scalar-tensor theory, provides the link with the Infra-Red regime. We consider a scenario where the corrections to the mass of the scalaron are large and reduce it below the electron mass in the Infra-Red, so that the scalaron plays a central role in the low energy dynamics of the Universe. In particular this leads to a connection between the scalaron mass and the measured vacuum energy provided its renormalisation group running at energies higher than the electron mass never drops below the present day value of the dark energy. |
2112.03869 | Victor Danchev Mr. | Victor I. Danchev, Daniela D. Doneva and Stoytcho S. Yazadjiev | Constraining scalarization in scalar-Gauss-Bonnet gravity through binary
pulsars | 17 pages, 6 figures v2: Improvements made, additional references
added, v3: Improvements of data analysis methods and text, v4: Improvements
of data analysis, matches the published version | null | 10.1103/PhysRevD.106.124001 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present paper we derive strong constrains on scalarization in
scalar-Gauss-Bonnet (sGB) gravity using observations of pulsars in close binary
systems. Since scalarized neutron stars carry a nonzero scalar change, they
emit scalar dipole radiation while inspiraling which speeds up the orbital
decay. The observations support the conjecture that such radiation is either
absent or very small for the observed binary pulsars. Using this, we determine
the allowed range of parameters for sGB gravity. We also transfer the derived
constraints to black holes in sGB gravity. It turns out that the maximum mass
of a scalarized static black hole can not exceed roughly ten to twenty solar
masses, depending on the initial assumptions we make for the nuclear matter
equations of state. The black hole scalar charge on the other hand can reach
relatively large values that are potentially observable.
| [
{
"created": "Tue, 7 Dec 2021 18:02:38 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Jan 2022 18:23:52 GMT",
"version": "v2"
},
{
"created": "Sat, 28 May 2022 14:30:04 GMT",
"version": "v3"
},
{
"created": "Thu, 17 Nov 2022 21:30:53 GMT",
"version": "v4"
}
] | 2022-12-14 | [
[
"Danchev",
"Victor I.",
""
],
[
"Doneva",
"Daniela D.",
""
],
[
"Yazadjiev",
"Stoytcho S.",
""
]
] | In the present paper we derive strong constrains on scalarization in scalar-Gauss-Bonnet (sGB) gravity using observations of pulsars in close binary systems. Since scalarized neutron stars carry a nonzero scalar change, they emit scalar dipole radiation while inspiraling which speeds up the orbital decay. The observations support the conjecture that such radiation is either absent or very small for the observed binary pulsars. Using this, we determine the allowed range of parameters for sGB gravity. We also transfer the derived constraints to black holes in sGB gravity. It turns out that the maximum mass of a scalarized static black hole can not exceed roughly ten to twenty solar masses, depending on the initial assumptions we make for the nuclear matter equations of state. The black hole scalar charge on the other hand can reach relatively large values that are potentially observable. |
2308.12140 | Harsh Narola | Harsh Narola, Justin Janquart, Quirijn Meijer, K. Haris, and Chris Van
Den Broeck | Relative binning for complete gravitational-wave parameter estimation
with higher-order modes and precession, and applications to lensing and
third-generation detectors | Minor changes before journal submission, attempt 2 | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Once a gravitational wave signal is detected, the measurement of its source
parameters is important to achieve various scientific goals. This is done
through Bayesian inference, where the analysis cost increases with the model
complexity and the signal duration. For typical binary black hole signals with
precession and higher-order modes, one has 15 model parameters. With standard
methods, such analyses require at least a few days. For strong gravitational
wave lensing, where multiple images of the same signal are produced, the joint
analysis of two data streams requires 19 parameters, further increasing the
complexity and run time. Moreover, for third generation detectors, due to the
lowered minimum sensitive frequency, the signal duration increases, leading to
even longer analysis times. With the increased detection rate, such analyses
can then become intractable. In this work, we present a fast and precise
parameter estimation method relying on relative binning and capable of
including higher-order modes and precession. We also extend the method to
perform joint Bayesian inference for lensed gravitational wave signals. Then,
we compare its accuracy and speed to those of state-of-the-art parameter
estimation routines by analyzing a set of simulated signals for the current and
third generation of interferometers. Additionally, for the first time, we
analyze some real events known to contain higher-order modes with relative
binning. For binary black hole systems with a total mass larger than $50\,
M_{\odot}$, our method is about 2.5 times faster than current techniques. This
speed-up increases for lower masses, with the analysis time being reduced by a
factor of 10 on average. In all cases, the recovered posterior probability
distributions for the parameters match those found with traditional techniques.
| [
{
"created": "Wed, 23 Aug 2023 13:55:26 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Aug 2023 17:52:54 GMT",
"version": "v2"
}
] | 2023-08-29 | [
[
"Narola",
"Harsh",
""
],
[
"Janquart",
"Justin",
""
],
[
"Meijer",
"Quirijn",
""
],
[
"Haris",
"K.",
""
],
[
"Broeck",
"Chris Van Den",
""
]
] | Once a gravitational wave signal is detected, the measurement of its source parameters is important to achieve various scientific goals. This is done through Bayesian inference, where the analysis cost increases with the model complexity and the signal duration. For typical binary black hole signals with precession and higher-order modes, one has 15 model parameters. With standard methods, such analyses require at least a few days. For strong gravitational wave lensing, where multiple images of the same signal are produced, the joint analysis of two data streams requires 19 parameters, further increasing the complexity and run time. Moreover, for third generation detectors, due to the lowered minimum sensitive frequency, the signal duration increases, leading to even longer analysis times. With the increased detection rate, such analyses can then become intractable. In this work, we present a fast and precise parameter estimation method relying on relative binning and capable of including higher-order modes and precession. We also extend the method to perform joint Bayesian inference for lensed gravitational wave signals. Then, we compare its accuracy and speed to those of state-of-the-art parameter estimation routines by analyzing a set of simulated signals for the current and third generation of interferometers. Additionally, for the first time, we analyze some real events known to contain higher-order modes with relative binning. For binary black hole systems with a total mass larger than $50\, M_{\odot}$, our method is about 2.5 times faster than current techniques. This speed-up increases for lower masses, with the analysis time being reduced by a factor of 10 on average. In all cases, the recovered posterior probability distributions for the parameters match those found with traditional techniques. |
1309.5519 | Pankaj Sheoran | Sushant G. Ghosh, Pankaj Sheoran | Higher dimensional non-Kerr black hole and energy extraction | 14 pages, 6 figures, 6 tables, analysis extended upto 10 dimensions,
published in PRD | Phys. Rev. D 89, 024023 (2014) | 10.1103/PhysRevD.89.024023 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the properties of the horizons and ergosphere in a rotating
higher dimensional (HD) deformed Kerr-like black hole. We also explicitly bring
out the effect of deformation parameter $\epsilon$ and the extra dimension on
the efficiency of the Penrose process of energy extraction from a black hole.
It is interesting to see that the ergosphere size is sensitive to the
deformation parameter $\epsilon$ as well as spacetime dimensions $D$. This
gives rise to a much richer structure of the ergosphere in a HD non-Kerr black
hole, thereby making the Penrose process more efficient compared with that of
the four-dimensional Kerr black hole.
| [
{
"created": "Sat, 21 Sep 2013 19:19:20 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Feb 2014 16:42:51 GMT",
"version": "v2"
}
] | 2014-02-17 | [
[
"Ghosh",
"Sushant G.",
""
],
[
"Sheoran",
"Pankaj",
""
]
] | We investigate the properties of the horizons and ergosphere in a rotating higher dimensional (HD) deformed Kerr-like black hole. We also explicitly bring out the effect of deformation parameter $\epsilon$ and the extra dimension on the efficiency of the Penrose process of energy extraction from a black hole. It is interesting to see that the ergosphere size is sensitive to the deformation parameter $\epsilon$ as well as spacetime dimensions $D$. This gives rise to a much richer structure of the ergosphere in a HD non-Kerr black hole, thereby making the Penrose process more efficient compared with that of the four-dimensional Kerr black hole. |
1512.02291 | Arthur Suvorov Mr. | Arthur George Suvorov and Andrew Melatos | Testing modified gravity and no-hair relations for the Kerr-Newman
metric through quasi-periodic oscillations of galactic microquasars | 14 pages, 5 figures; Accepted for publication in PRD | Phys. Rev. D 93, 024004 (2016) | 10.1103/PhysRevD.93.024004 | null | gr-qc astro-ph.HE math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct multipole moments for stationary, asymptotically flat, spacetime
solutions to higher-order curvature theories of gravity. The moments are
defined using $3+1$ techniques involving timelike Killing vector constructions
as in the classic papers by Geroch and Hansen. Using the fact that the
Kerr-Newman metric is a vacuum solution to a particular class of $f(R)$
theories of gravity, we compute all its moments, and find that they admit
recurrence relations similar to those for the Kerr solution in general
relativity. It has been proposed previously that modelling the measured
frequencies of quasi-periodic oscillations from galactic microquasars enables
experimental tests of the no-hair theorem. We explore the possibility that,
even if the no-hair relation is found to break down in the context of general
relativity, there may be an $f(R)$ counterpart that is preserved. We apply the
results to the microquasars GRS $1915$+$105$ and GRO J$1655$-$40$ using the
diskoseismology and kinematic resonance models, and constrain the spins and
`charges' [which are not really electric charges in the $f(R)$ context] of
their black holes.
| [
{
"created": "Tue, 8 Dec 2015 00:27:03 GMT",
"version": "v1"
}
] | 2016-01-13 | [
[
"Suvorov",
"Arthur George",
""
],
[
"Melatos",
"Andrew",
""
]
] | We construct multipole moments for stationary, asymptotically flat, spacetime solutions to higher-order curvature theories of gravity. The moments are defined using $3+1$ techniques involving timelike Killing vector constructions as in the classic papers by Geroch and Hansen. Using the fact that the Kerr-Newman metric is a vacuum solution to a particular class of $f(R)$ theories of gravity, we compute all its moments, and find that they admit recurrence relations similar to those for the Kerr solution in general relativity. It has been proposed previously that modelling the measured frequencies of quasi-periodic oscillations from galactic microquasars enables experimental tests of the no-hair theorem. We explore the possibility that, even if the no-hair relation is found to break down in the context of general relativity, there may be an $f(R)$ counterpart that is preserved. We apply the results to the microquasars GRS $1915$+$105$ and GRO J$1655$-$40$ using the diskoseismology and kinematic resonance models, and constrain the spins and `charges' [which are not really electric charges in the $f(R)$ context] of their black holes. |
gr-qc/9808062 | Mattias Marklund | M. Marklund (U. of Umea), M. Bradley (U. of Umea) | Invariant construction of solutions to Einstein's field equations - LRS
perfect fluids II | 24 pages, 1 figure | Class.Quant.Grav. 16 (1999) 1577-1597 | 10.1088/0264-9381/16/5/308 | mth.uct.ac.za-9808 | gr-qc | null | The properties of LRS class II perfect fluid space-times are analyzed using
the description of geometries in terms of the Riemann tensor and a finite
number of its covariant derivatives. In this manner it is straightforward to
obtain the plane and hyperbolic analogues to the spherical symmetric case. For
spherically symmetric static models the set of equations is reduced to the
Tolman-Oppenheimer-Volkoff equation only. Some new non-stationary and
inhomogeneous solutions with shear, expansion, and acceleration of the fluid
are presented. Among these are a class of temporally self-similar solutions
with equation of state given by $p=(\gamma-1)\mu, 1<\gamma<2$, and a class of
solutions characterized by $\sigma=-\Theta/6$. We give an example of geometry
where the Riemann tensor and the Ricci rotation coefficients are not sufficient
to give a complete description of the geometry. Using an extension of the
method, we find the full metric in terms of curvature quantities.
| [
{
"created": "Mon, 24 Aug 1998 13:03:41 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Marklund",
"M.",
"",
"U. of Umea"
],
[
"Bradley",
"M.",
"",
"U. of Umea"
]
] | The properties of LRS class II perfect fluid space-times are analyzed using the description of geometries in terms of the Riemann tensor and a finite number of its covariant derivatives. In this manner it is straightforward to obtain the plane and hyperbolic analogues to the spherical symmetric case. For spherically symmetric static models the set of equations is reduced to the Tolman-Oppenheimer-Volkoff equation only. Some new non-stationary and inhomogeneous solutions with shear, expansion, and acceleration of the fluid are presented. Among these are a class of temporally self-similar solutions with equation of state given by $p=(\gamma-1)\mu, 1<\gamma<2$, and a class of solutions characterized by $\sigma=-\Theta/6$. We give an example of geometry where the Riemann tensor and the Ricci rotation coefficients are not sufficient to give a complete description of the geometry. Using an extension of the method, we find the full metric in terms of curvature quantities. |
1602.05764 | Matthew Wright | Matthew Wright | Conformal transformations in modified teleparallel theories of gravity
revisited | 13 pages, 1 figure | Phys. Rev. D 93, 103002 (2016) | 10.1103/PhysRevD.93.103002 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is well known that one cannot apply a conformal transformation to $f(T)$
gravity to obtain a minimally coupled scalar field model, and thus no Einstein
frame exists for $f(T)$ gravity. Furthermore nonminimally coupled "teleparallel
dark energy models" are not conformally equivalent to $f(T)$ gravity. However,
it can be shown that $f(T)$ gravity is conformally equivalent to a teleparallel
phantom scalar field model with a nonminimal coupling to a boundary term only.
In this work, we extend this analysis by considering a recently studied
extended class of models, known as $f(T,B)$ gravity, where $B$ is a boundary
term related to the divergence of a contraction of the torsion tensor. We find
that nonminimally coupled "teleparallel dark energy models" are conformally
equivalent to either an $f(T,B)$ or $f(B)$ gravity model. Finally conditions on
the functional form of $f(T,B)$ gravity are derived to allow it to be
transformed to particular nonminimally coupled scalar field models.
| [
{
"created": "Thu, 18 Feb 2016 11:34:44 GMT",
"version": "v1"
},
{
"created": "Wed, 4 May 2016 13:15:49 GMT",
"version": "v2"
}
] | 2016-05-05 | [
[
"Wright",
"Matthew",
""
]
] | It is well known that one cannot apply a conformal transformation to $f(T)$ gravity to obtain a minimally coupled scalar field model, and thus no Einstein frame exists for $f(T)$ gravity. Furthermore nonminimally coupled "teleparallel dark energy models" are not conformally equivalent to $f(T)$ gravity. However, it can be shown that $f(T)$ gravity is conformally equivalent to a teleparallel phantom scalar field model with a nonminimal coupling to a boundary term only. In this work, we extend this analysis by considering a recently studied extended class of models, known as $f(T,B)$ gravity, where $B$ is a boundary term related to the divergence of a contraction of the torsion tensor. We find that nonminimally coupled "teleparallel dark energy models" are conformally equivalent to either an $f(T,B)$ or $f(B)$ gravity model. Finally conditions on the functional form of $f(T,B)$ gravity are derived to allow it to be transformed to particular nonminimally coupled scalar field models. |
2211.06880 | Marcello Seri | Martijn Kluitenberg, Diederik Roest, Marcello Seri | Chaotic light scattering around extremal black holes | Refereed version | Bollettino dell'Unione Matematica Italiana 16.2 (2023): 381-396 | 10.1007/s40574-022-00345-5 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that the scattering of light in the field of $N\geq 3$ static
extremal black holes is chaotic in the planar case. The relativistic dynamics
of such extremal objects reduce to that of a classical Hamiltonian system.
Certain values of the dilaton coupling then allow one to apply techniques from
symbolic dynamics and classical potential scattering. This results in a lower
bound on the topological entropy of order $\log(N-1)$, thus proving the
emergence of chaotic scattering for $N \geq 3$ black holes.
| [
{
"created": "Sun, 13 Nov 2022 11:23:55 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Dec 2022 10:55:07 GMT",
"version": "v2"
}
] | 2023-12-21 | [
[
"Kluitenberg",
"Martijn",
""
],
[
"Roest",
"Diederik",
""
],
[
"Seri",
"Marcello",
""
]
] | We show that the scattering of light in the field of $N\geq 3$ static extremal black holes is chaotic in the planar case. The relativistic dynamics of such extremal objects reduce to that of a classical Hamiltonian system. Certain values of the dilaton coupling then allow one to apply techniques from symbolic dynamics and classical potential scattering. This results in a lower bound on the topological entropy of order $\log(N-1)$, thus proving the emergence of chaotic scattering for $N \geq 3$ black holes. |
gr-qc/0505140 | Yuri Pavlov | A. A. Grib and Yu. V. Pavlov | Some effects of the quantum field theory in the early Universe | LATEX, 21 pages, no figure | In: "Focus on Quantum Field Theory", ed. O. Kovras, Nova Science
Publishers, Inc., New York, 2005, pp. 1-21. | null | null | gr-qc hep-th | null | Effects of the vacuum polarization leading to change of the effective
gravitational constant and particle creation in the early Universe are
discussed. Gauss-Bonnet type coupling to the curvature is considered.
Renormalization methods are generalized for such coupling and the N-dimensional
space-time. Calculations of creation of entropy and visible matter of the
Universe by the gravity of dark matter are made.
| [
{
"created": "Fri, 27 May 2005 12:31:11 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Grib",
"A. A.",
""
],
[
"Pavlov",
"Yu. V.",
""
]
] | Effects of the vacuum polarization leading to change of the effective gravitational constant and particle creation in the early Universe are discussed. Gauss-Bonnet type coupling to the curvature is considered. Renormalization methods are generalized for such coupling and the N-dimensional space-time. Calculations of creation of entropy and visible matter of the Universe by the gravity of dark matter are made. |
2205.13677 | David Quispe Aruquipa | David Q. Aruquipa and Marc Casals | Hadamard Tail from Initial Data on the Light Cone | 15 pages, 5 figures | null | 10.1103/PhysRevD.107.084008 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Field perturbations of a curved background spacetime generally propagate not
only at the speed of light but also at all smaller velocities. This so-called
$Hadamard\,tail$ contribution to wave propagation is relevant in various
settings, from classical self-force calculations to communication between
quantum particle detectors. One method for calculating this tail contribution
is by integrating the homogeneous wave equation using Characteristic Initial
Data on the light cone. However, to the best of our knowledge, this method has
never been implemented before except in flat or conformally-flat spacetimes,
where null geodesics emanating from a point do not cross. In this work, we
implement this method on the black hole toy model Pleba\'nski-Hacyan spacetime,
$\mathbb{M}_2\times\mathbb{S}^2$. We obtain new results in this spacetime by
calculating the Hadamard tail of a scalar field everywhere where it is defined
(namely, in the maximal normal neighbourhood of an arbitrary point) and
investigate how it varies for various values of the coupling constant. This
serves as a proof-of-concept for the Characteristic Initial Data method on
spacetimes where null geodesics emanating from a point $do$ cross.
| [
{
"created": "Thu, 26 May 2022 23:43:51 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Mar 2023 17:35:22 GMT",
"version": "v2"
}
] | 2023-04-11 | [
[
"Aruquipa",
"David Q.",
""
],
[
"Casals",
"Marc",
""
]
] | Field perturbations of a curved background spacetime generally propagate not only at the speed of light but also at all smaller velocities. This so-called $Hadamard\,tail$ contribution to wave propagation is relevant in various settings, from classical self-force calculations to communication between quantum particle detectors. One method for calculating this tail contribution is by integrating the homogeneous wave equation using Characteristic Initial Data on the light cone. However, to the best of our knowledge, this method has never been implemented before except in flat or conformally-flat spacetimes, where null geodesics emanating from a point do not cross. In this work, we implement this method on the black hole toy model Pleba\'nski-Hacyan spacetime, $\mathbb{M}_2\times\mathbb{S}^2$. We obtain new results in this spacetime by calculating the Hadamard tail of a scalar field everywhere where it is defined (namely, in the maximal normal neighbourhood of an arbitrary point) and investigate how it varies for various values of the coupling constant. This serves as a proof-of-concept for the Characteristic Initial Data method on spacetimes where null geodesics emanating from a point $do$ cross. |
1511.01625 | Sunil Maurya DR. | S.K. Maurya, Y.K. Gupta, Baiju Dayanandan, M. K. Jasim, Ahmed Al-Jamel | Generalized relativistic anisotropic models for compact stars | 18 pages, 13 figures (Submitted in Eur. Phys. J. C) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present new anisotropic generalization of Buchdahl [1] type perfect fluid
solution by using the method of earlier work [2]. In similar approach we have
constructed the new pressure anisotropy factor ${\Delta}$ by the help both the
metric potential $e^{\lambda}$ and $e^{\nu}$. The metric potential
$e^{\lambda}$ same as Buchdahl [1] and $e^{\nu}$ is monotonic increasing
function as suggested by Lake [3]. After that we obtain new well behaved
general solution for anisotropic fluid distribution. We calculated the physical
quantities like energy density, radial and tangential pressures, velocity of
sound and red-shift etc. We observe that these quantities are positive and
finite inside the compact star. Also note that mass and radius of our models
can represent the structure of realistic astrophysical objects such as like Her
X-1 and RXJ1856-37.
| [
{
"created": "Thu, 5 Nov 2015 06:33:30 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Nov 2015 15:21:55 GMT",
"version": "v2"
}
] | 2015-11-26 | [
[
"Maurya",
"S. K.",
""
],
[
"Gupta",
"Y. K.",
""
],
[
"Dayanandan",
"Baiju",
""
],
[
"Jasim",
"M. K.",
""
],
[
"Al-Jamel",
"Ahmed",
""
]
] | We present new anisotropic generalization of Buchdahl [1] type perfect fluid solution by using the method of earlier work [2]. In similar approach we have constructed the new pressure anisotropy factor ${\Delta}$ by the help both the metric potential $e^{\lambda}$ and $e^{\nu}$. The metric potential $e^{\lambda}$ same as Buchdahl [1] and $e^{\nu}$ is monotonic increasing function as suggested by Lake [3]. After that we obtain new well behaved general solution for anisotropic fluid distribution. We calculated the physical quantities like energy density, radial and tangential pressures, velocity of sound and red-shift etc. We observe that these quantities are positive and finite inside the compact star. Also note that mass and radius of our models can represent the structure of realistic astrophysical objects such as like Her X-1 and RXJ1856-37. |
gr-qc/0701122 | Andrea Passamonti | Adamantios Stavridis, Andrea Passamonti, Kostas Kokkotas | Nonradial oscillations of slowly and differentially rotating compact
stars | 18 pages, 5 figures, ReVTeX 4.0, submitted to Phys. Rev. D | Phys.Rev.D75:064019,2007 | 10.1103/PhysRevD.75.064019 | null | gr-qc astro-ph | null | The equations describing nonradial adiabatic oscillations of differentially
rotating relativistic stars are derived in relativistic slow rotation
approximation. The differentially rotating configuration is described by a
perturbative version of the relativistic j-constant rotation law. Focusing on
the oscillation properties of the stellar fluid, the adiabatic nonradial
perturbations are studied in the Cowling approximation with a system of five
partial differential equations. In these equations, differential rotation
introduces new coupling terms between the perturbative quantites with respect
to the uniformly rotating stars. In particular, we investigate the axisymmetric
and barotropic oscillations and compare their spectral properties with those
obtained in nonlinear hydrodynamical studies. The perturbative description of
the differentially rotating background and the oscillation spectrum agree
within a few percent with those of the nonlinear studies.
| [
{
"created": "Mon, 22 Jan 2007 16:38:23 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Stavridis",
"Adamantios",
""
],
[
"Passamonti",
"Andrea",
""
],
[
"Kokkotas",
"Kostas",
""
]
] | The equations describing nonradial adiabatic oscillations of differentially rotating relativistic stars are derived in relativistic slow rotation approximation. The differentially rotating configuration is described by a perturbative version of the relativistic j-constant rotation law. Focusing on the oscillation properties of the stellar fluid, the adiabatic nonradial perturbations are studied in the Cowling approximation with a system of five partial differential equations. In these equations, differential rotation introduces new coupling terms between the perturbative quantites with respect to the uniformly rotating stars. In particular, we investigate the axisymmetric and barotropic oscillations and compare their spectral properties with those obtained in nonlinear hydrodynamical studies. The perturbative description of the differentially rotating background and the oscillation spectrum agree within a few percent with those of the nonlinear studies. |
1408.6041 | Juhua Chen | Sheng Zhou, Ruanjing Zhang, Juhua Chen and Yongjiu Wang | Geodesic structure of Janis-Newman-Winicour space-time | 19 pages,39 figs | null | 10.1007/s10773-015-2526-1 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the present paper we study the geodesic structure of the
Janis-Newman-Winicour(JNW) space-time which contains a strong curvature naked
singularity. This metric is an extension of the Schwarzschild geometry when a
massless scalar field is included. We find that the strength parameter $\mu$ of
the scalar field effects on the geodesic structure of the JNW space-time. By
solving the geodesic equation and analyzing the behavior of effective
potential, we investigate all geodesic types of the test particle and the
photon in the JNW space-time. At the same time we simulate all the geodesic
orbits corresponding to the energy levels of the effective potential in the JNW
space-time.
| [
{
"created": "Tue, 26 Aug 2014 07:51:13 GMT",
"version": "v1"
}
] | 2015-06-22 | [
[
"Zhou",
"Sheng",
""
],
[
"Zhang",
"Ruanjing",
""
],
[
"Chen",
"Juhua",
""
],
[
"Wang",
"Yongjiu",
""
]
] | In the present paper we study the geodesic structure of the Janis-Newman-Winicour(JNW) space-time which contains a strong curvature naked singularity. This metric is an extension of the Schwarzschild geometry when a massless scalar field is included. We find that the strength parameter $\mu$ of the scalar field effects on the geodesic structure of the JNW space-time. By solving the geodesic equation and analyzing the behavior of effective potential, we investigate all geodesic types of the test particle and the photon in the JNW space-time. At the same time we simulate all the geodesic orbits corresponding to the energy levels of the effective potential in the JNW space-time. |
gr-qc/9604047 | Friedrich Wilhelm Hehl | Yuval Ne'eman (Tel-Aviv Univ. and Univ. of Texas at Austin) and
Friedrich W. Hehl (Univ. of Cologne) | Test Matter in a Spacetime with Nonmetricity | 14 pages, file in latex | Class.Quant.Grav.14:A251-A260,1997 | 10.1088/0264-9381/14/1A/020 | TAUP N-253-96 | gr-qc hep-th | null | Examples in which spacetime might become non-Riemannian appear above Planck
energies in string theory or, in the very early universe, in the inflationary
model. The simplest such geometry is metric-affine geometry, in which {\it
nonmetricity} appears as a field strength, side by side with curvature and
torsion. In matter, the shear and dilation currents couple to nonmetricity, and
they are its sources. After reviewing the equations of motion and the Noether
identities, we study two recent vacuum solutions of the metric-affine gauge
theory of gravity. We then use the values of the nonmetricity in these
solutions to study the motion of the appropriate test-matter. As a
Regge-trajectory like hadronic excitation band, the test matter is endowed with
shear degrees of freedom and described by a world spinor.
| [
{
"created": "Wed, 24 Apr 1996 16:02:56 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Ne'eman",
"Yuval",
"",
"Tel-Aviv Univ. and Univ. of Texas at Austin"
],
[
"Hehl",
"Friedrich W.",
"",
"Univ. of Cologne"
]
] | Examples in which spacetime might become non-Riemannian appear above Planck energies in string theory or, in the very early universe, in the inflationary model. The simplest such geometry is metric-affine geometry, in which {\it nonmetricity} appears as a field strength, side by side with curvature and torsion. In matter, the shear and dilation currents couple to nonmetricity, and they are its sources. After reviewing the equations of motion and the Noether identities, we study two recent vacuum solutions of the metric-affine gauge theory of gravity. We then use the values of the nonmetricity in these solutions to study the motion of the appropriate test-matter. As a Regge-trajectory like hadronic excitation band, the test matter is endowed with shear degrees of freedom and described by a world spinor. |
1910.10388 | Anjali Ramesh | Anjali Ramesh | Generalized uncertainty principle for a Dirac fermion in a torsion field | 16 pages, 14 figures | null | 10.1088/1361-6382/ab7c00 | null | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | We derive the uncertainty principle for a Dirac fermion in a torsion field
obeying the Hehl-Datta (HD) equation. We first discuss that there should be a
correction factor to the Heisenberg uncertainty principle (HUP) when torsional
effects are taken into consideration. We then derive the uncertainty relation
from a solitary wave solution of the HD equation in 1+1 dimensions. We find
that the results agree with the generalized uncertainty principle (GUP). We
then introduce the unified length scale $L_{CS}$ (which unifies Compton
wavelength and Schwarzschild radius) into the HD equation and see how the
probability density of the solution transforms for particles of different
masses.
| [
{
"created": "Wed, 23 Oct 2019 07:12:05 GMT",
"version": "v1"
}
] | 2020-06-17 | [
[
"Ramesh",
"Anjali",
""
]
] | We derive the uncertainty principle for a Dirac fermion in a torsion field obeying the Hehl-Datta (HD) equation. We first discuss that there should be a correction factor to the Heisenberg uncertainty principle (HUP) when torsional effects are taken into consideration. We then derive the uncertainty relation from a solitary wave solution of the HD equation in 1+1 dimensions. We find that the results agree with the generalized uncertainty principle (GUP). We then introduce the unified length scale $L_{CS}$ (which unifies Compton wavelength and Schwarzschild radius) into the HD equation and see how the probability density of the solution transforms for particles of different masses. |
2212.04482 | Gabriele Montefalcone | Gabriele Montefalcone, Vikas Aragam, Luca Visinelli and Katherine
Freese | Observational Constraints on Warm Natural Inflation | 23 pages, 3 figures, 1 table, Replacement due to typo on DOE
acknowledgement number | JCAP 2303, 002 (2023) | 10.1088/1475-7516/2023/03/002 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Warm natural inflation is studied for the case of the original cosine
potential. The radiation bath during inflation induces a dissipation (friction)
rate in the equation of motion for the inflaton field, which can potentially
reduce the field excursion needed for an observationally viable period of
inflation. We examine if the dissipation thus provides a mechanism to avoid the
large decay constant $f \gtrsim M_{\mathrm{pl}}$ of cold cosine natural
inflation. Whereas temperature independent dissipation has previously been
shown to alleviate the need for a trans-Planckian decay constant $f$, we
illustrate here the difficulties of accommodating a significantly sub-Planckian
decay constant ($f<10^{-1}M_{\mathrm{pl}}$) in the case of the following
temperature dependent dissipation rates, $\Gamma \propto T^c$, with
$c=\{1,3\}$. Such dissipation rates represent physically well-motivated
constructions in the literature. For each model, we map its location in the
$r$-$n_s$ plane and compare with Cosmic Microwave Background data. For $c=1 \,
(c=3)$, we find that agreement with CMB data requires that dissipation be in
the weak (moderate) regime and that the minimum allowed value of the decay
constant in the potential is $f_{\rm min} = 0.3 \, (0.8)\,M_{\mathrm{pl}}$
respectively.
| [
{
"created": "Thu, 8 Dec 2022 18:54:44 GMT",
"version": "v1"
},
{
"created": "Wed, 18 Jan 2023 02:56:54 GMT",
"version": "v2"
}
] | 2023-03-08 | [
[
"Montefalcone",
"Gabriele",
""
],
[
"Aragam",
"Vikas",
""
],
[
"Visinelli",
"Luca",
""
],
[
"Freese",
"Katherine",
""
]
] | Warm natural inflation is studied for the case of the original cosine potential. The radiation bath during inflation induces a dissipation (friction) rate in the equation of motion for the inflaton field, which can potentially reduce the field excursion needed for an observationally viable period of inflation. We examine if the dissipation thus provides a mechanism to avoid the large decay constant $f \gtrsim M_{\mathrm{pl}}$ of cold cosine natural inflation. Whereas temperature independent dissipation has previously been shown to alleviate the need for a trans-Planckian decay constant $f$, we illustrate here the difficulties of accommodating a significantly sub-Planckian decay constant ($f<10^{-1}M_{\mathrm{pl}}$) in the case of the following temperature dependent dissipation rates, $\Gamma \propto T^c$, with $c=\{1,3\}$. Such dissipation rates represent physically well-motivated constructions in the literature. For each model, we map its location in the $r$-$n_s$ plane and compare with Cosmic Microwave Background data. For $c=1 \, (c=3)$, we find that agreement with CMB data requires that dissipation be in the weak (moderate) regime and that the minimum allowed value of the decay constant in the potential is $f_{\rm min} = 0.3 \, (0.8)\,M_{\mathrm{pl}}$ respectively. |
1603.07830 | Maciej Wielgus | M. A. Abramowicz, T. Bulik, G. F. R. Ellis, K. A. Meissner, M. Wielgus | The electromagnetic afterglows of gravitational waves as a test for
Quantum Gravity | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We argue that if particularly powerful electromagnetic afterglows of the
gravitational waves bursts will be observed in the future, this could be used
as a strong observational support for some suggested quantum alternatives for
black holes (e.g., firewalls and gravastars). A universal absence of powerful
afterglows should be taken as a suggestive argument against such hypothetical
quantum-gravity objects.
| [
{
"created": "Fri, 25 Mar 2016 06:44:00 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Apr 2016 23:13:24 GMT",
"version": "v2"
}
] | 2016-04-14 | [
[
"Abramowicz",
"M. A.",
""
],
[
"Bulik",
"T.",
""
],
[
"Ellis",
"G. F. R.",
""
],
[
"Meissner",
"K. A.",
""
],
[
"Wielgus",
"M.",
""
]
] | We argue that if particularly powerful electromagnetic afterglows of the gravitational waves bursts will be observed in the future, this could be used as a strong observational support for some suggested quantum alternatives for black holes (e.g., firewalls and gravastars). A universal absence of powerful afterglows should be taken as a suggestive argument against such hypothetical quantum-gravity objects. |
gr-qc/0007036 | Joao Magueijo | Joao Magueijo (Imperial College) | Covariant and locally Lorentz-invariant varying speed of light theories | To be published in Physical Review D | Phys.Rev. D62 (2000) 103521 | 10.1103/PhysRevD.62.103521 | null | gr-qc astro-ph hep-th | null | We propose definitions for covariance and local Lorentz invariance applicable
when the speed of light $c$ is allowed to vary. They have the merit of
retaining only those aspects of the usual definitions which are invariant under
unit transformations, and which can therefore legitimately represent the
outcome of an experiment. We then discuss some possibilities for invariant
actions governing the dynamics of such theories. We consider first the
classical action for matter fields and the effects of a changing $c$ upon
quantization. We discover a peculiar form of quantum particle creation due to a
varying $c$. We then study actions governing the dynamics of gravitation and
the speed of light. We find the free, empty-space, no-gravity solution, to be
interpreted as the counterpart of Minkowksi space-time, and highlight its
similarities with Fock-Lorentz space-time. We also find flat-space string-type
solutions, in which near the string core $c$ is much higher. We label them
fast-tracks and compare them with gravitational wormholes. We finally discuss
general features of cosmological and black hole solutions, and digress on the
meaning of singularities in these theories.
| [
{
"created": "Mon, 17 Jul 2000 15:31:14 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Magueijo",
"Joao",
"",
"Imperial College"
]
] | We propose definitions for covariance and local Lorentz invariance applicable when the speed of light $c$ is allowed to vary. They have the merit of retaining only those aspects of the usual definitions which are invariant under unit transformations, and which can therefore legitimately represent the outcome of an experiment. We then discuss some possibilities for invariant actions governing the dynamics of such theories. We consider first the classical action for matter fields and the effects of a changing $c$ upon quantization. We discover a peculiar form of quantum particle creation due to a varying $c$. We then study actions governing the dynamics of gravitation and the speed of light. We find the free, empty-space, no-gravity solution, to be interpreted as the counterpart of Minkowksi space-time, and highlight its similarities with Fock-Lorentz space-time. We also find flat-space string-type solutions, in which near the string core $c$ is much higher. We label them fast-tracks and compare them with gravitational wormholes. We finally discuss general features of cosmological and black hole solutions, and digress on the meaning of singularities in these theories. |
2001.06990 | Junpei Harada | Junpei Harada | Connection independent formulation of general relativity | 4 pages, to appear in PRD, a reference added | Phys. Rev. D 101, 024053 (2020) | 10.1103/PhysRevD.101.024053 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A connection-independent formulation of general relativity is presented, in
which the dynamics does not depend on the choice of connection. The gravity
action in this formulation includes one additional scalar term in addition to
the Einstein-Hilbert action. No conditions on the connection are imposed.
Nevertheless, this formulation yields the Einstein equations, without adding
the Gibbons-Hawking-York term even when a manifold has a boundary. Furthermore,
this formulation yields a unified description of general relativity,
teleparallel gravity, and symmetric teleparallel gravity.
| [
{
"created": "Mon, 20 Jan 2020 06:12:17 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Feb 2020 06:54:55 GMT",
"version": "v2"
}
] | 2021-05-20 | [
[
"Harada",
"Junpei",
""
]
] | A connection-independent formulation of general relativity is presented, in which the dynamics does not depend on the choice of connection. The gravity action in this formulation includes one additional scalar term in addition to the Einstein-Hilbert action. No conditions on the connection are imposed. Nevertheless, this formulation yields the Einstein equations, without adding the Gibbons-Hawking-York term even when a manifold has a boundary. Furthermore, this formulation yields a unified description of general relativity, teleparallel gravity, and symmetric teleparallel gravity. |
1812.02961 | Guido Magnano | Guido Magnano, Krzysztof A. Meissner, Leszek M. Soko{\L}Owski | Test-field limit of metric nonlinear gravity theories | Title and abstract modified to make the content of the paper more
clear and readable | null | 10.1140/epjc/s10052-019-7124-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the framework of alternative metric gravity theories, it has been shown by
several authors that a generic Lagrangian depending on the Riemann tensor
describes a theory with 8 degrees of freedom (which reduce to 3 for f(R)
Lagrangians depending only on the curvature scalar). This result is often
related to a reformulation of the fourth-order equations for the metric into a
set of second-order equations for a multiplet of fields, including a massive
scalar field and a massive spin-2 field. In this article we investigate an
issue which does not seem to have been addressed so far: in ordinary
general-relativistic field theories, all fundamental fields (i.e. fields with
definite spin and mass) reduce to test fields in some appropriate limit of the
model, where they cease to act as sources for the metric curvature. In this
limit, each of the fundamental fields can be excited from its ground state
independently from the others. The question is: does higher-derivative gravity
admit a test-field limit for its fundamental fields? It is easy to show that
for a f(R) theory the test-field limit does exist; then, we consider the case
of Lagrangians quadratically depending on the full Ricci tensor. We show that
the constraint binding together the scalar field and the massive spin-2 field
does not disappear in the limit where they should be expected to act as test
fields, except for a particular choice of the Lagrangian, which cause the
scalar field to disappear (reducing to 7 DOF). We finally consider the addition
of an arbitrary function of the quadratic invariant of the Weyl tensor and show
that the resulting model still lacks a proper test-field limit. We argue that
the lack of a test-field limit for the fundamental fields may constitute a
serious drawback of the full 8 DOF higher-order gravity models, which is not
encountered in the restricted 7 DOF or 3 DOF cases.
| [
{
"created": "Fri, 7 Dec 2018 09:49:14 GMT",
"version": "v1"
},
{
"created": "Tue, 14 May 2019 14:26:52 GMT",
"version": "v2"
}
] | 2019-09-04 | [
[
"Magnano",
"Guido",
""
],
[
"Meissner",
"Krzysztof A.",
""
],
[
"SokoŁOwski",
"Leszek M.",
""
]
] | In the framework of alternative metric gravity theories, it has been shown by several authors that a generic Lagrangian depending on the Riemann tensor describes a theory with 8 degrees of freedom (which reduce to 3 for f(R) Lagrangians depending only on the curvature scalar). This result is often related to a reformulation of the fourth-order equations for the metric into a set of second-order equations for a multiplet of fields, including a massive scalar field and a massive spin-2 field. In this article we investigate an issue which does not seem to have been addressed so far: in ordinary general-relativistic field theories, all fundamental fields (i.e. fields with definite spin and mass) reduce to test fields in some appropriate limit of the model, where they cease to act as sources for the metric curvature. In this limit, each of the fundamental fields can be excited from its ground state independently from the others. The question is: does higher-derivative gravity admit a test-field limit for its fundamental fields? It is easy to show that for a f(R) theory the test-field limit does exist; then, we consider the case of Lagrangians quadratically depending on the full Ricci tensor. We show that the constraint binding together the scalar field and the massive spin-2 field does not disappear in the limit where they should be expected to act as test fields, except for a particular choice of the Lagrangian, which cause the scalar field to disappear (reducing to 7 DOF). We finally consider the addition of an arbitrary function of the quadratic invariant of the Weyl tensor and show that the resulting model still lacks a proper test-field limit. We argue that the lack of a test-field limit for the fundamental fields may constitute a serious drawback of the full 8 DOF higher-order gravity models, which is not encountered in the restricted 7 DOF or 3 DOF cases. |
1011.3153 | Vojtech Pravda | Marcello Ortaggio, Vojtech Pravda, Alena Pravdova | On higher dimensional Einstein spacetimes with a warped extra dimension | 14 pages, minor changes in the text, mainly in Section 2.1 | Class. Quant. Grav. 28:105006, 2011 | 10.1088/0264-9381/28/10/105006 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a class of higher dimensional warped Einstein spacetimes with one
extra dimension. These were originally identified by Brinkmann as those
Einstein spacetimes that can be mapped conformally on other Einstein
spacetimes, and have subsequently appeared in various contexts to describe,
e.g., different braneworld models or warped black strings. After clarifying the
relation between the general Brinkmann metric and other more specific
coordinate systems, we analyze the algebraic type of the Weyl tensor of the
solutions. In particular, we describe the relation between Weyl aligned null
directions (WANDs) of the lower dimensional Einstein slices and of the full
spacetime, which in some cases can be algebraically more special. Possible
spacetime singularities introduced by the warp factor are determined via a
study of scalar curvature invariants and of Weyl components measured by
geodetic observers. Finally, we illustrate how Brinkmann's metric can be
employed to generate new solutions by presenting the metric of spinning and
accelerating black strings in five dimensional anti-de Sitter space.
| [
{
"created": "Sat, 13 Nov 2010 18:55:07 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Mar 2011 18:24:52 GMT",
"version": "v2"
}
] | 2011-04-08 | [
[
"Ortaggio",
"Marcello",
""
],
[
"Pravda",
"Vojtech",
""
],
[
"Pravdova",
"Alena",
""
]
] | We study a class of higher dimensional warped Einstein spacetimes with one extra dimension. These were originally identified by Brinkmann as those Einstein spacetimes that can be mapped conformally on other Einstein spacetimes, and have subsequently appeared in various contexts to describe, e.g., different braneworld models or warped black strings. After clarifying the relation between the general Brinkmann metric and other more specific coordinate systems, we analyze the algebraic type of the Weyl tensor of the solutions. In particular, we describe the relation between Weyl aligned null directions (WANDs) of the lower dimensional Einstein slices and of the full spacetime, which in some cases can be algebraically more special. Possible spacetime singularities introduced by the warp factor are determined via a study of scalar curvature invariants and of Weyl components measured by geodetic observers. Finally, we illustrate how Brinkmann's metric can be employed to generate new solutions by presenting the metric of spinning and accelerating black strings in five dimensional anti-de Sitter space. |
1105.2346 | Edward Glass | J.P. Krisch and E.N. Glass | Levi-Civita cylinders with fractional angular deficit | 5 figures | J.Math.Phys.52:052503,2011 | 10.1063/1.3579130 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The angular deficit factor in the Levi-Civita vacuum metric has been
parametrized using a Riemann-Liouville fractional integral. This introduces a
new parameter into the general relativistic cylinder description, the
fractional index {\alpha}. When the fractional index is continued into the
negative {\alpha} region, new behavior is found in the Gott-Hiscock cylinder
and in an Israel shell.
| [
{
"created": "Thu, 12 May 2011 00:49:00 GMT",
"version": "v1"
}
] | 2011-07-26 | [
[
"Krisch",
"J. P.",
""
],
[
"Glass",
"E. N.",
""
]
] | The angular deficit factor in the Levi-Civita vacuum metric has been parametrized using a Riemann-Liouville fractional integral. This introduces a new parameter into the general relativistic cylinder description, the fractional index {\alpha}. When the fractional index is continued into the negative {\alpha} region, new behavior is found in the Gott-Hiscock cylinder and in an Israel shell. |
1707.05680 | Shahar Hod | Shahar Hod | Marginally bound (critical) geodesics of rapidly rotating black holes | 10 pages. arXiv admin note: substantial text overlap with
arXiv:1210.2486 | Physical Review D 88, 087502 (2013) | null | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | One of the most important geodesics in a black-hole spacetime is the
marginally bound spherical orbit. This critical geodesic represents the
innermost spherical orbit which is bound to the central black hole. The radii
$r_{\text{mb}}({\bar a})$ of the marginally bound {\it equatorial} circular
geodesics of rotating Kerr black holes were found analytically by Bardeen {\it
et. al.} more than four decades ago (here $\bar a\equiv J/M^2$ is the
dimensionless angular-momentum of the black hole). On the other hand, no
closed-form formula exists in the literature for the radii of generic ({\it
non}-equatorial) marginally bound geodesics of the rotating Kerr spacetime. In
the present study we analyze the critical (marginally bound) orbits of rapidly
rotating Kerr black holes. In particular, we derive a simple {\it analytical}
formula for the radii $r_{\text{mb}}(\bar a\simeq 1;\cos i)$ of the marginally
bound spherical orbits, where $\cos i$ is an effective inclination angle (with
respect to the black-hole equatorial plane) of the geodesic. We find that the
marginally bound spherical orbits of rapidly-rotating black holes are
characterized by a critical inclination angle, $\cos i=\sqrt{{2/3}}$, above
which the coordinate radii of the geodesics approach the black-hole radius in
the extremal $\bar a\to1$ limit. It is shown that this critical inclination
angle signals a transition in the physical properties of the orbits: in
particular, it separates marginally bound spherical geodesics which lie a
finite proper distance from the black-hole horizon from marginally bound
geodesics which lie an infinite proper distance from the horizon.
| [
{
"created": "Mon, 17 Jul 2017 16:53:34 GMT",
"version": "v1"
}
] | 2017-07-19 | [
[
"Hod",
"Shahar",
""
]
] | One of the most important geodesics in a black-hole spacetime is the marginally bound spherical orbit. This critical geodesic represents the innermost spherical orbit which is bound to the central black hole. The radii $r_{\text{mb}}({\bar a})$ of the marginally bound {\it equatorial} circular geodesics of rotating Kerr black holes were found analytically by Bardeen {\it et. al.} more than four decades ago (here $\bar a\equiv J/M^2$ is the dimensionless angular-momentum of the black hole). On the other hand, no closed-form formula exists in the literature for the radii of generic ({\it non}-equatorial) marginally bound geodesics of the rotating Kerr spacetime. In the present study we analyze the critical (marginally bound) orbits of rapidly rotating Kerr black holes. In particular, we derive a simple {\it analytical} formula for the radii $r_{\text{mb}}(\bar a\simeq 1;\cos i)$ of the marginally bound spherical orbits, where $\cos i$ is an effective inclination angle (with respect to the black-hole equatorial plane) of the geodesic. We find that the marginally bound spherical orbits of rapidly-rotating black holes are characterized by a critical inclination angle, $\cos i=\sqrt{{2/3}}$, above which the coordinate radii of the geodesics approach the black-hole radius in the extremal $\bar a\to1$ limit. It is shown that this critical inclination angle signals a transition in the physical properties of the orbits: in particular, it separates marginally bound spherical geodesics which lie a finite proper distance from the black-hole horizon from marginally bound geodesics which lie an infinite proper distance from the horizon. |
2010.15445 | Isha Kotecha | Isha Kotecha | On Generalised Statistical Equilibrium and Discrete Quantum Gravity | PhD thesis, Humboldt University of Berlin, Albert Einstein Institute
- Potsdam; v2 few minor changes and updated references, to be published in
Springer Theses book series | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Statistical equilibrium configurations are important in the physics of
macroscopic systems with a large number of constituent degrees of freedom. They
are expected to be crucial also in discrete quantum gravity, where dynamical
spacetime should emerge from the collective physics of the underlying quantum
gravitational degrees of freedom. However, defining statistical equilibrium in
a background independent system is a challenging open issue, mainly due to the
absence of absolute notions of time and energy. This is especially so in
non-perturbative quantum gravity frameworks that are devoid of usual space and
time structures. In this thesis, we investigate aspects of a generalisation of
statistical equilibrium, specifically Gibbs states, suitable for background
independent systems. We emphasise on an information theoretic characterisation
based on the maximum entropy principle. Subsequently, we explore the resultant
generalised Gibbs states in a discrete quantum gravitational system composed of
many candidate quanta of geometry, utilising their field theoretic formulation
of group field theory and various many-body techniques. We construct several
concrete examples of quantum gravitational generalised Gibbs states. We further
develop inequivalent thermal representations based on entangled, two-mode
squeezed, thermofield double vacua, induced by a class of generalised Gibbs
states. In these representations, we define a class of thermal condensates
which encode statistical fluctuations in a given observable, e.g. volume of the
quantum geometry. We apply these states in the condensate cosmology programme
of group field theory to study a relational effective cosmological dynamics
extracted from a class of free models, for homogeneous and isotropic
spacetimes. We find the correct classical limit of Friedmann equations at late
times, with a bounce and accelerated expansion at early times.
| [
{
"created": "Thu, 29 Oct 2020 09:36:52 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Sep 2021 10:02:55 GMT",
"version": "v2"
}
] | 2021-09-14 | [
[
"Kotecha",
"Isha",
""
]
] | Statistical equilibrium configurations are important in the physics of macroscopic systems with a large number of constituent degrees of freedom. They are expected to be crucial also in discrete quantum gravity, where dynamical spacetime should emerge from the collective physics of the underlying quantum gravitational degrees of freedom. However, defining statistical equilibrium in a background independent system is a challenging open issue, mainly due to the absence of absolute notions of time and energy. This is especially so in non-perturbative quantum gravity frameworks that are devoid of usual space and time structures. In this thesis, we investigate aspects of a generalisation of statistical equilibrium, specifically Gibbs states, suitable for background independent systems. We emphasise on an information theoretic characterisation based on the maximum entropy principle. Subsequently, we explore the resultant generalised Gibbs states in a discrete quantum gravitational system composed of many candidate quanta of geometry, utilising their field theoretic formulation of group field theory and various many-body techniques. We construct several concrete examples of quantum gravitational generalised Gibbs states. We further develop inequivalent thermal representations based on entangled, two-mode squeezed, thermofield double vacua, induced by a class of generalised Gibbs states. In these representations, we define a class of thermal condensates which encode statistical fluctuations in a given observable, e.g. volume of the quantum geometry. We apply these states in the condensate cosmology programme of group field theory to study a relational effective cosmological dynamics extracted from a class of free models, for homogeneous and isotropic spacetimes. We find the correct classical limit of Friedmann equations at late times, with a bounce and accelerated expansion at early times. |
2106.14672 | Francesco Gozzini | Pietro Dona, Francesco Gozzini, Alessandro Nicotra | A Wick rotation for EPRL spin foam models | 25 pages, 1 figure | Phys.Rev.D 104 (2021) 12, 126008 | 10.1103/PhysRevD.104.126008 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We show that the Euclidean and Lorentzian EPRL vertex amplitudes of covariant
Loop Quantum Gravity are related through a ``Wick rotation'' of the real
Immirzi parameter to purely imaginary values. Our result follows from the
simultaneous analytic continuation of the algebras, group elements and unitary
irreducible representations of the gauge groups $Spin(4)$ and
$SL(2,\mathbb{C})$, applied to the decomposition of the two models in terms of
$SU(2)$ invariants and booster functions.
| [
{
"created": "Mon, 28 Jun 2021 12:52:03 GMT",
"version": "v1"
}
] | 2024-02-27 | [
[
"Dona",
"Pietro",
""
],
[
"Gozzini",
"Francesco",
""
],
[
"Nicotra",
"Alessandro",
""
]
] | We show that the Euclidean and Lorentzian EPRL vertex amplitudes of covariant Loop Quantum Gravity are related through a ``Wick rotation'' of the real Immirzi parameter to purely imaginary values. Our result follows from the simultaneous analytic continuation of the algebras, group elements and unitary irreducible representations of the gauge groups $Spin(4)$ and $SL(2,\mathbb{C})$, applied to the decomposition of the two models in terms of $SU(2)$ invariants and booster functions. |
1110.1175 | Salvatore Capozziello | S. Capozziello, G. Cristofano, M. De Laurentis | Primordial black holes, astrophysical systems and the Eddington-Weinberg
relation | 5 pages | null | 10.1142/S0217732311036966 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Starting from a quantization relation for primordial black holes, it is shown
that quantum fluctuations can play a fundamental role in determining the
effective scales of self-gravitating astrophysical systems. Furthermore the
Eddington-Weinberg relation between the current scale of the observed universe
to the Planck constant (the standard action unit) is naturally derived.
Finally, such an approach allows to recover the current value of the
cosmological constant.
| [
{
"created": "Thu, 6 Oct 2011 08:08:35 GMT",
"version": "v1"
}
] | 2015-05-30 | [
[
"Capozziello",
"S.",
""
],
[
"Cristofano",
"G.",
""
],
[
"De Laurentis",
"M.",
""
]
] | Starting from a quantization relation for primordial black holes, it is shown that quantum fluctuations can play a fundamental role in determining the effective scales of self-gravitating astrophysical systems. Furthermore the Eddington-Weinberg relation between the current scale of the observed universe to the Planck constant (the standard action unit) is naturally derived. Finally, such an approach allows to recover the current value of the cosmological constant. |
2009.10997 | Diego Rubiera-Garcia | Francisco S. N. Lobo, Gonzalo J. Olmo, Emanuele Orazi, Diego
Rubiera-Garcia, Azmat Rustam | Structure and stability of traversable thin-shell wormholes in Palatini
$f(\mathcal{R})$ gravity | 10 pages, revtex4-1 style. v2: some minor corrections, version
accepted for publication in Phys. Rev. D | Phys. Rev. D 102, 104012 (2020) | 10.1103/PhysRevD.102.104012 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the structure and stability of traversable wormholes built as
(spherically symmetric) thin shells in the context of Palatini $f(\mathcal{R})$
gravity. Using a suitable junction formalism for these theories we find that
the effective number of degrees of freedom on the shell is reduced to a single
one, which fixes the equation of state to be that of massless stress-energy
fields, contrary to the general relativistic and metric $f(R)$ cases. Another
major difference is that the surface energy density threading the thin-shell,
needed in order to sustain the wormhole, can take any sign, and may even
vanish, depending on the desired features of the corresponding solutions. We
illustrate our results by constructing thin-shell wormholes by surgically
grafting Schwarzschild space-times, and show that these configurations are
always linearly unstable. However, surgically joined Reissner-Nordstr\"om
space-times allow for linearly stable, traversable thin-shell wormholes
supported by a positive energy density provided that the (squared)
mass-to-charge ratio, given by $y=Q^2/M^2$, satisfies the constraint $1<y<9/8$
(corresponding to overcharged Reissner-Nordstr\"om configurations having a
photon sphere) and lies in a region bounded by specific curves defined in terms
of the (dimensionless) radius of the shell $x_0=R/M$.
| [
{
"created": "Wed, 23 Sep 2020 08:27:08 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Oct 2020 09:50:40 GMT",
"version": "v2"
}
] | 2020-11-11 | [
[
"Lobo",
"Francisco S. N.",
""
],
[
"Olmo",
"Gonzalo J.",
""
],
[
"Orazi",
"Emanuele",
""
],
[
"Rubiera-Garcia",
"Diego",
""
],
[
"Rustam",
"Azmat",
""
]
] | We study the structure and stability of traversable wormholes built as (spherically symmetric) thin shells in the context of Palatini $f(\mathcal{R})$ gravity. Using a suitable junction formalism for these theories we find that the effective number of degrees of freedom on the shell is reduced to a single one, which fixes the equation of state to be that of massless stress-energy fields, contrary to the general relativistic and metric $f(R)$ cases. Another major difference is that the surface energy density threading the thin-shell, needed in order to sustain the wormhole, can take any sign, and may even vanish, depending on the desired features of the corresponding solutions. We illustrate our results by constructing thin-shell wormholes by surgically grafting Schwarzschild space-times, and show that these configurations are always linearly unstable. However, surgically joined Reissner-Nordstr\"om space-times allow for linearly stable, traversable thin-shell wormholes supported by a positive energy density provided that the (squared) mass-to-charge ratio, given by $y=Q^2/M^2$, satisfies the constraint $1<y<9/8$ (corresponding to overcharged Reissner-Nordstr\"om configurations having a photon sphere) and lies in a region bounded by specific curves defined in terms of the (dimensionless) radius of the shell $x_0=R/M$. |
0910.5145 | Bogus{\l}aw Broda | Bogus{\l}aw Broda, Micha{\l} Szanecki | Dark energy from quantum fluctuations | 4 pages (in AdP style), 2 references added, prepared for the
proceedings of the Grassmannian Conference in Fundamental Cosmology
(Grasscosmofun'09), 14-19 September 2009, Szczecin, Poland | Annalen Phys.19:312-315,2010 | 10.1002/andp.201010435 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We have derived the quantum vacuum pressure P_vac as a primary entity,
removing a trivial and a gauge terms from the cosmological constant-like part
(the zeroth term) of the effective action for a free matter field. The quantum
vacuum energy density G_vac appears a secondary entity, but both are of
expected order. Moreover P_vac and G_vac are dynamical, and therefore they can
be used in the Einstein equations. In particular, they could dynamically
support holographic dark energy model as well as the `thermodynamic' one.
| [
{
"created": "Tue, 27 Oct 2009 15:33:48 GMT",
"version": "v1"
},
{
"created": "Thu, 12 Nov 2009 12:08:59 GMT",
"version": "v2"
}
] | 2014-11-20 | [
[
"Broda",
"Bogusław",
""
],
[
"Szanecki",
"Michał",
""
]
] | We have derived the quantum vacuum pressure P_vac as a primary entity, removing a trivial and a gauge terms from the cosmological constant-like part (the zeroth term) of the effective action for a free matter field. The quantum vacuum energy density G_vac appears a secondary entity, but both are of expected order. Moreover P_vac and G_vac are dynamical, and therefore they can be used in the Einstein equations. In particular, they could dynamically support holographic dark energy model as well as the `thermodynamic' one. |
1704.03691 | Giovanni Rabuffo | Benjamin Bahr, Sebastian Kloser, Giovanni Rabuffo | Towards a Cosmological subsector of Spin Foam Quantum Gravity | 38 pages, 10 figures | Phys. Rev. D 96, 086009 (2017) | 10.1103/PhysRevD.96.086009 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the four dimensional path integral for Euclidean quantum gravity
in the context of the EPRL-FK spin foam model. The state sum is restricted to
certain symmetric configurations which resembles the geometry of a flat
homogeneous and isotropic universe. The vertex structure is specially chosen so
that a basic concept of expansion and contraction of the lattice universe is
allowed.
We compute the asymptotic form of the spin foam state sum in the symmetry
restricted setting, and recover a Regge-type action, as well as an explicit
form of the Hessian matrix, which captures quantum corrections. We investigate
the action in the three cases of vacuum, a cosmological constant, and coupled
to dust, and find that in all cases, the corresponding FRW dynamics is
recovered in the limit of large lattices. While this work demonstrates a large
intersection with computations done in the context of cosmological modelling
with Regge Calculus, it is ultimately a setup for treating curved geometries in
the renormalization of the EPRL-FK spin foam model.
| [
{
"created": "Wed, 12 Apr 2017 10:37:20 GMT",
"version": "v1"
}
] | 2017-10-25 | [
[
"Bahr",
"Benjamin",
""
],
[
"Kloser",
"Sebastian",
""
],
[
"Rabuffo",
"Giovanni",
""
]
] | We examine the four dimensional path integral for Euclidean quantum gravity in the context of the EPRL-FK spin foam model. The state sum is restricted to certain symmetric configurations which resembles the geometry of a flat homogeneous and isotropic universe. The vertex structure is specially chosen so that a basic concept of expansion and contraction of the lattice universe is allowed. We compute the asymptotic form of the spin foam state sum in the symmetry restricted setting, and recover a Regge-type action, as well as an explicit form of the Hessian matrix, which captures quantum corrections. We investigate the action in the three cases of vacuum, a cosmological constant, and coupled to dust, and find that in all cases, the corresponding FRW dynamics is recovered in the limit of large lattices. While this work demonstrates a large intersection with computations done in the context of cosmological modelling with Regge Calculus, it is ultimately a setup for treating curved geometries in the renormalization of the EPRL-FK spin foam model. |
gr-qc/9905108 | Alessandro D.A.M. Spallicci | Alessandro D.A.M. Spallicci | Analytic solution of the Regge-Wheeler differential equation for black
hole pertubations in radial coordinate and time domains | Conference paper of 6 pages. Keywords: Partial differential equations
(35Q75), Equations of motion (83C10), Black holes (83C57) | XIII Convegno Nazionale di Relativita' Generale e Fisica della
Gravitazione, 21-25 September 1998 | null | null | gr-qc | null | An analytic solution of the Regge-Wheeler (RW) equation has been found via
the Frobenius method at the regular singularity of the horizon 2M, in the form
of a time and radial coordinate dependent series. The RW partial differential
equation, derived from the Einstein field equations, represents the first order
perturbations of the Schwarzschild metric. The known solutions are numerical in
time domain or approximate and asymptotic for low or high frequencies in
Fourier domain. The former is of scarce relevance for comprehension of the
geodesic equations for a body in the black hole field, while the latter is
mainly useful for the description of the emitted gravitational radiation.
Instead a time domain solution is essential for the determination of radiation
reaction of the falling particle into the black hole, i.e. the influence of the
emitted radiation on the motion of the perturbing mass in the black hole field.
To this end, a semi-analytic solution of the inhomogeneous RW equation with the
source term (Regge-Wheeler-Zerilli equation) shall be the next development.
| [
{
"created": "Mon, 31 May 1999 10:24:18 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Spallicci",
"Alessandro D. A. M.",
""
]
] | An analytic solution of the Regge-Wheeler (RW) equation has been found via the Frobenius method at the regular singularity of the horizon 2M, in the form of a time and radial coordinate dependent series. The RW partial differential equation, derived from the Einstein field equations, represents the first order perturbations of the Schwarzschild metric. The known solutions are numerical in time domain or approximate and asymptotic for low or high frequencies in Fourier domain. The former is of scarce relevance for comprehension of the geodesic equations for a body in the black hole field, while the latter is mainly useful for the description of the emitted gravitational radiation. Instead a time domain solution is essential for the determination of radiation reaction of the falling particle into the black hole, i.e. the influence of the emitted radiation on the motion of the perturbing mass in the black hole field. To this end, a semi-analytic solution of the inhomogeneous RW equation with the source term (Regge-Wheeler-Zerilli equation) shall be the next development. |
0704.3606 | John Ward Mr | Tapan Naskar and John Ward | Type I singularities and the Phantom Menace | More references added. Final PRD version | Phys.Rev.D76:063514,2007 | 10.1103/PhysRevD.76.063514 | null | gr-qc hep-ph | null | We consider the future dynamics of a transient phantom dominated phase of the
universe in LQC and in the RS braneworld, which both have a non-standard
Friedmann equation. We find that for a certain class of potentials, the Hubble
parameter oscillates with simple harmonic motion in the LQC case and therefore
avoids any future singularity. For more general potentials we find that damping
effects eventually lead to the Hubble parameter becoming constant. On the other
hand in the braneworld case we find that although the type I singularity can be
avoided, the scale factor still diverges at late times.
| [
{
"created": "Thu, 26 Apr 2007 19:07:10 GMT",
"version": "v1"
},
{
"created": "Wed, 2 May 2007 12:20:26 GMT",
"version": "v2"
},
{
"created": "Tue, 22 May 2007 10:22:39 GMT",
"version": "v3"
},
{
"created": "Thu, 11 Oct 2007 21:15:08 GMT",
"version": "v4"
}
] | 2008-11-26 | [
[
"Naskar",
"Tapan",
""
],
[
"Ward",
"John",
""
]
] | We consider the future dynamics of a transient phantom dominated phase of the universe in LQC and in the RS braneworld, which both have a non-standard Friedmann equation. We find that for a certain class of potentials, the Hubble parameter oscillates with simple harmonic motion in the LQC case and therefore avoids any future singularity. For more general potentials we find that damping effects eventually lead to the Hubble parameter becoming constant. On the other hand in the braneworld case we find that although the type I singularity can be avoided, the scale factor still diverges at late times. |
2011.12368 | Indranil Chakraborty | Siddhant Siddhant, Indranil Chakraborty, Sayan Kar (IIT Kharagpur,
India) | Kundt geometries and memory effects in the Brans-Dicke theory of gravity | Some minor typos corrected, matches with the published version in
EPJC | null | 10.1140/epjc/s10052-021-09118-4 | null | gr-qc hep-th | http://creativecommons.org/publicdomain/zero/1.0/ | Memory effects are studied in the simplest scalar-tensor theory, the
Brans--Dicke (BD) theory. To this end, we introduce, in BD theory, novel Kundt
spacetimes (without and with gyratonic terms), which serve as backgrounds for
the ensuing analysis on memory. The BD parameter $\omega$ and the scalar field
($\phi$) profile, expectedly, distinguishes between different solutions.
Choosing specific localised forms for the free metric functions $H'(u)$
(related to the wave profile) and $J(u)$ (the gyraton) we obtain displacement
memory effects using both geodesics and geodesic deviation. An interesting and
easy-to-understand exactly solvable case arises when $\omega=-2$ (with $J(u)$
absent) which we discuss in detail. For other $\omega$ (in the presence of $J$
or without), numerically obtained geodesics lead to results on displacement
memory which appear to match qualitatively with those found from a deviation
analysis. Thus, the issue of how memory effects in BD theory may arise and also
differ from their GR counterparts, is now partially addressed, at least
theoretically, within the context of this new class of Kundt geometries.
| [
{
"created": "Tue, 24 Nov 2020 20:42:29 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Mar 2021 07:27:31 GMT",
"version": "v2"
},
{
"created": "Tue, 27 Apr 2021 11:47:40 GMT",
"version": "v3"
}
] | 2021-05-12 | [
[
"Siddhant",
"Siddhant",
"",
"IIT Kharagpur,\n India"
],
[
"Chakraborty",
"Indranil",
"",
"IIT Kharagpur,\n India"
],
[
"Kar",
"Sayan",
"",
"IIT Kharagpur,\n India"
]
] | Memory effects are studied in the simplest scalar-tensor theory, the Brans--Dicke (BD) theory. To this end, we introduce, in BD theory, novel Kundt spacetimes (without and with gyratonic terms), which serve as backgrounds for the ensuing analysis on memory. The BD parameter $\omega$ and the scalar field ($\phi$) profile, expectedly, distinguishes between different solutions. Choosing specific localised forms for the free metric functions $H'(u)$ (related to the wave profile) and $J(u)$ (the gyraton) we obtain displacement memory effects using both geodesics and geodesic deviation. An interesting and easy-to-understand exactly solvable case arises when $\omega=-2$ (with $J(u)$ absent) which we discuss in detail. For other $\omega$ (in the presence of $J$ or without), numerically obtained geodesics lead to results on displacement memory which appear to match qualitatively with those found from a deviation analysis. Thus, the issue of how memory effects in BD theory may arise and also differ from their GR counterparts, is now partially addressed, at least theoretically, within the context of this new class of Kundt geometries. |
1704.03536 | Yusuf Sucu | Ganim Gecim and Yusuf Sucu | The GUP effect on Hawking Radiation of the 2+1 dimensional Black Hole | 9 pages | Phys. Lett. B 773 (2017) 391-394 | 10.1016/j.physletb.2017.08.053 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the Generalized Uncertainty Principle (GUP) effect on the
Hawking radiation of the 2+1 dimensional Martinez-Zanelli black hole by using
the Hamilton-Jacobi method. In this connection, we discuss the tunnelling
probabilities and Hawking temperature of the spin-1/2 and spin-0 particles for
the black hole. Therefore, we use the modified Klein-Gordon and Dirac equations
based on the GUP. Then, we observe that the Hawking temperature of the scalar
and Dirac particles depend on not only the black hole properties, but also the
properties of the tunnelling particle, such as angular momentum, energy and
mass. And, in this situation, we see that the tunnellig probability and the
Hawking radiation of the Dirac particle is different from that of the scalar
particle.
| [
{
"created": "Mon, 10 Apr 2017 15:29:27 GMT",
"version": "v1"
}
] | 2017-10-09 | [
[
"Gecim",
"Ganim",
""
],
[
"Sucu",
"Yusuf",
""
]
] | We investigate the Generalized Uncertainty Principle (GUP) effect on the Hawking radiation of the 2+1 dimensional Martinez-Zanelli black hole by using the Hamilton-Jacobi method. In this connection, we discuss the tunnelling probabilities and Hawking temperature of the spin-1/2 and spin-0 particles for the black hole. Therefore, we use the modified Klein-Gordon and Dirac equations based on the GUP. Then, we observe that the Hawking temperature of the scalar and Dirac particles depend on not only the black hole properties, but also the properties of the tunnelling particle, such as angular momentum, energy and mass. And, in this situation, we see that the tunnellig probability and the Hawking radiation of the Dirac particle is different from that of the scalar particle. |
gr-qc/0207091 | Toporenskij A. V. | A.V. Toporensky, P.V. Tretyakov and V.O.Ustiansky | New properties of scalar field dynamics in brane isotropic cosmological
models | 13 pages with 2 eps figures, submitted to Astronomy Letters | Astron.Lett.29:1-5,2003 | 10.1134/1.1537370 | null | gr-qc | null | Several aspects of scalar field dynamics on a brane which differs from
corresponding regimes in the standard cosmology are investigated. We consider
asymptotic solution near a singularity, condition for inflation and bounces and
some detail of chaotic behavior in the brane model. Each results are compared
with those known in the standard cosmology.
| [
{
"created": "Wed, 24 Jul 2002 12:04:07 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Toporensky",
"A. V.",
""
],
[
"Tretyakov",
"P. V.",
""
],
[
"Ustiansky",
"V. O.",
""
]
] | Several aspects of scalar field dynamics on a brane which differs from corresponding regimes in the standard cosmology are investigated. We consider asymptotic solution near a singularity, condition for inflation and bounces and some detail of chaotic behavior in the brane model. Each results are compared with those known in the standard cosmology. |
0710.5692 | Sophie de Buyl | Thibault Damour and Sophie de Buyl | Describing general cosmological singularities in Iwasawa variables | 50 pages, 4 figures | Phys.Rev.D77:043520,2008 | 10.1103/PhysRevD.77.043520 | IHES/P/07/36 | gr-qc hep-th | null | Belinskii, Khalatnikov, and Lifshitz (BKL) conjectured that the description
of the asymptotic behavior of a generic solution of Einstein equations near a
spacelike singularity could be drastically simplified by considering that the
time derivatives of the metric asymptotically dominate (except at a sequence of
instants, in the `chaotic case') over the spatial derivatives. We present a
precise formulation of the BKL conjecture (in the chaotic case) that consists
of basically three elements: (i) we parametrize the spatial metric $g_{ij}$ by
means of \it{Iwasawa variables} $\beta^a, {\cal N}^a{}_i$); (ii) we define, at
each spatial point, a (chaotic) \it{asymptotic evolution system} made of
ordinary differential equations for the Iwasawa variables; and (iii) we
characterize the exact Einstein solutions $\beta, {\cal{N}}$ whose asymptotic
behavior is described by a solution $\beta_{[0]}, {\cal N}_{[0]}$ of the
previous evolution system by means of a `\it{generalized Fuchsian system}' for
the differenced variables $\bar \beta = \beta - \beta_{[0]}$, $\bar {\cal N} =
{\cal N} - {\cal N}_{[0]}$, and by requiring that $\bar \beta$ and $\bar {\cal
N}$ tend to zero on the singularity. We also show that, in spite of the
apparently chaotic infinite succession of `Kasner epochs' near the singularity,
there exists a well-defined \it{asymptotic geometrical structure} on the
singularity : it is described by a \it{partially framed flag}. Our treatment
encompasses Einstein-matter systems (comprising scalar and p-forms), and also
shows how the use of Iwasawa variables can simplify the usual (`asymptotically
velocity term dominated') description of non-chaotic systems.
| [
{
"created": "Tue, 30 Oct 2007 17:16:02 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Damour",
"Thibault",
""
],
[
"de Buyl",
"Sophie",
""
]
] | Belinskii, Khalatnikov, and Lifshitz (BKL) conjectured that the description of the asymptotic behavior of a generic solution of Einstein equations near a spacelike singularity could be drastically simplified by considering that the time derivatives of the metric asymptotically dominate (except at a sequence of instants, in the `chaotic case') over the spatial derivatives. We present a precise formulation of the BKL conjecture (in the chaotic case) that consists of basically three elements: (i) we parametrize the spatial metric $g_{ij}$ by means of \it{Iwasawa variables} $\beta^a, {\cal N}^a{}_i$); (ii) we define, at each spatial point, a (chaotic) \it{asymptotic evolution system} made of ordinary differential equations for the Iwasawa variables; and (iii) we characterize the exact Einstein solutions $\beta, {\cal{N}}$ whose asymptotic behavior is described by a solution $\beta_{[0]}, {\cal N}_{[0]}$ of the previous evolution system by means of a `\it{generalized Fuchsian system}' for the differenced variables $\bar \beta = \beta - \beta_{[0]}$, $\bar {\cal N} = {\cal N} - {\cal N}_{[0]}$, and by requiring that $\bar \beta$ and $\bar {\cal N}$ tend to zero on the singularity. We also show that, in spite of the apparently chaotic infinite succession of `Kasner epochs' near the singularity, there exists a well-defined \it{asymptotic geometrical structure} on the singularity : it is described by a \it{partially framed flag}. Our treatment encompasses Einstein-matter systems (comprising scalar and p-forms), and also shows how the use of Iwasawa variables can simplify the usual (`asymptotically velocity term dominated') description of non-chaotic systems. |
1802.05290 | Zhongmin Qian | Zhongmin Qian | Spacetime orientation and the meaning of Lorentz invariance in general
relativity | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The parity violation at the level of weak interactions and other similar
discrete symmetries breaking show that the invariance of laws under the full
group of Lorentz transformations can not be taken granted. We examine the
principle of Lorentz invariance under the general theory of relativity, and
demonstrate the importance of a concept of the spacetime orientation as part of
the causal structure of spacetime.
| [
{
"created": "Wed, 14 Feb 2018 19:10:25 GMT",
"version": "v1"
}
] | 2018-02-16 | [
[
"Qian",
"Zhongmin",
""
]
] | The parity violation at the level of weak interactions and other similar discrete symmetries breaking show that the invariance of laws under the full group of Lorentz transformations can not be taken granted. We examine the principle of Lorentz invariance under the general theory of relativity, and demonstrate the importance of a concept of the spacetime orientation as part of the causal structure of spacetime. |
1501.06591 | Vasilis Oikonomou | S.D. Odintsov, V.K. Oikonomou, Emmanuel N. Saridakis | Superbounce and Loop Quantum Ekpyrotic Cosmologies from Modified
Gravity: $F(R)$, $F(G)$ and $F(T)$ Theories | Revised version, to appear in AOP | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the realization of two bouncing paradigms, namely of the
superbounce and the loop quantum cosmological ekpyrosis, in the framework of
various modified gravities. In particular, we focus on the $F(R)$, $F(G)$ and
$F(T)$ gravities, and we reconstruct their specific subclasses which lead to
such universe evolutions. These subclasses constitute from power laws,
polynomials, or hypergeometric ansatzes, which can be approximated by power
laws. The qualitative similarity of different effective gravities which realize
the above two bouncing cosmologies, indicates to some universality lying behind
such a bounce. Finally, performing a linear perturbation analysis, we show that
the obtained solutions are conditionally or fully stable.
| [
{
"created": "Mon, 26 Jan 2015 21:17:32 GMT",
"version": "v1"
},
{
"created": "Sun, 23 Aug 2015 18:37:25 GMT",
"version": "v2"
}
] | 2015-08-25 | [
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
],
[
"Saridakis",
"Emmanuel N.",
""
]
] | We investigate the realization of two bouncing paradigms, namely of the superbounce and the loop quantum cosmological ekpyrosis, in the framework of various modified gravities. In particular, we focus on the $F(R)$, $F(G)$ and $F(T)$ gravities, and we reconstruct their specific subclasses which lead to such universe evolutions. These subclasses constitute from power laws, polynomials, or hypergeometric ansatzes, which can be approximated by power laws. The qualitative similarity of different effective gravities which realize the above two bouncing cosmologies, indicates to some universality lying behind such a bounce. Finally, performing a linear perturbation analysis, we show that the obtained solutions are conditionally or fully stable. |
2005.13464 | Pedro Pina Avelino | P. P. Avelino | Reply to note on "Boltzmann's H-theorem, entropy and the strength of
gravity in theories with a nonminimal coupling between matter and geometry" | 2 pages, no figures | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this brief reply we respond to the note of Bertolami and Gomes
(arXiv:2005.03968) on our recent paper (arXiv:2003.10154).
| [
{
"created": "Wed, 27 May 2020 16:21:39 GMT",
"version": "v1"
}
] | 2020-05-28 | [
[
"Avelino",
"P. P.",
""
]
] | In this brief reply we respond to the note of Bertolami and Gomes (arXiv:2005.03968) on our recent paper (arXiv:2003.10154). |
gr-qc/0406070 | Jose A. Gonzalez | Miguel Alcubierre, Jose A. Gonzalez, Marcelo Salgado and Daniel
Sudarsky | On a debate about cosmic censor violation | 3 pages. We add a comment and a reference | null | null | null | gr-qc | null | We review the arguments and counter arguments about the recent proposal for
generic censorship violation. In particular the argument made in gr-qc/0405050
against our proposal for a possible expanding domain wall that could encompass
a large black hole, is shown to have a serious flaw. Other problems of the
original idea are also discussed.
| [
{
"created": "Fri, 18 Jun 2004 02:42:54 GMT",
"version": "v1"
},
{
"created": "Fri, 18 Jun 2004 23:43:37 GMT",
"version": "v2"
},
{
"created": "Wed, 30 Jun 2004 17:33:20 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Alcubierre",
"Miguel",
""
],
[
"Gonzalez",
"Jose A.",
""
],
[
"Salgado",
"Marcelo",
""
],
[
"Sudarsky",
"Daniel",
""
]
] | We review the arguments and counter arguments about the recent proposal for generic censorship violation. In particular the argument made in gr-qc/0405050 against our proposal for a possible expanding domain wall that could encompass a large black hole, is shown to have a serious flaw. Other problems of the original idea are also discussed. |
2105.11785 | Rikpratik Sengupta | Rikpratik Sengupta, Shounak Ghosh, Mehedi Kalam, Saibal Ray | Wormhole on the Brane with Ordinary Matter: The Broader View | 27 Pages, 5 figures | Classical and Quantum Gravity, Vol 39, 2022 | 10.1088/1361-6382/ac61ae | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this paper we attempt to examine the possibility of construction of a
traversable wormhole on the Randall-Sundrum braneworld with ordinary matter
employing the Kuchowicz potential as one of the metric potentials. In this
scenario, the wormhole shape function is obtained and studied, along with
validity of Null Energy Condition (NEC) and the junction conditions at the
surface of the wormhole are used to obtain a few of the model parameters. The
investigation, besides giving an estimate for the bulk equation of state
parameter, draws important constraints on the brane tension which is a novel
attempt in this aspect and very interestingly the constraints imposed by a
physically plausible traversable wormhole is in high confirmity with those
drawn from more general space-times or space-time independent situations
involved in fundamental physics. Also, we go on to claim that the possible
existence of a wormhole may very well indicate that we live on a three-brane
universe.
| [
{
"created": "Tue, 25 May 2021 09:27:48 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Mar 2022 17:53:55 GMT",
"version": "v2"
}
] | 2022-03-31 | [
[
"Sengupta",
"Rikpratik",
""
],
[
"Ghosh",
"Shounak",
""
],
[
"Kalam",
"Mehedi",
""
],
[
"Ray",
"Saibal",
""
]
] | In this paper we attempt to examine the possibility of construction of a traversable wormhole on the Randall-Sundrum braneworld with ordinary matter employing the Kuchowicz potential as one of the metric potentials. In this scenario, the wormhole shape function is obtained and studied, along with validity of Null Energy Condition (NEC) and the junction conditions at the surface of the wormhole are used to obtain a few of the model parameters. The investigation, besides giving an estimate for the bulk equation of state parameter, draws important constraints on the brane tension which is a novel attempt in this aspect and very interestingly the constraints imposed by a physically plausible traversable wormhole is in high confirmity with those drawn from more general space-times or space-time independent situations involved in fundamental physics. Also, we go on to claim that the possible existence of a wormhole may very well indicate that we live on a three-brane universe. |
2405.04653 | Shu Yan Lau | Shu Yan Lau, Siddarth Ajith, Victor Guedes, Kent Yagi | Nonradial instabilities in anisotropic neutron stars | 7+7 pages, 2+1 figures, submitted to PRL | null | null | null | gr-qc astro-ph.HE hep-ph | http://creativecommons.org/licenses/by/4.0/ | Non-radial oscillation modes of a neutron star possess valuable information
about its internal structure and nuclear physics. Starting from the quadrupolar
order, such modes under general relativity are known as quasi-normal modes
since they dissipate energy through gravitational radiation and their
frequencies are complex. The stability of these modes is governed by the sign
of the imaginary part of the frequency, which determines whether the mode would
decay or grow over time. In this Letter, we develop a fully consistent
framework in general relativity to study quasi-normal modes of neutron stars
with anisotropic pressure, whose motivation includes strong internal magnetic
fields and non-vanishing shear or viscosity. We employ parametrized models for
the anisotropy and solve the perturbed Einstein field equations numerically. We
find that, unlike the case for isotropic neutron stars, the imaginary parts of
some of the pressure ($p$-)modes flip signs as the degree of anisotropy
deviates from zero, depicting a transition from stable modes to unstable modes.
This finding indicates that some anisotropic neutron star models are unstable,
potentially restricting the form of sustained anisotropy.
| [
{
"created": "Tue, 7 May 2024 20:25:37 GMT",
"version": "v1"
}
] | 2024-05-09 | [
[
"Lau",
"Shu Yan",
""
],
[
"Ajith",
"Siddarth",
""
],
[
"Guedes",
"Victor",
""
],
[
"Yagi",
"Kent",
""
]
] | Non-radial oscillation modes of a neutron star possess valuable information about its internal structure and nuclear physics. Starting from the quadrupolar order, such modes under general relativity are known as quasi-normal modes since they dissipate energy through gravitational radiation and their frequencies are complex. The stability of these modes is governed by the sign of the imaginary part of the frequency, which determines whether the mode would decay or grow over time. In this Letter, we develop a fully consistent framework in general relativity to study quasi-normal modes of neutron stars with anisotropic pressure, whose motivation includes strong internal magnetic fields and non-vanishing shear or viscosity. We employ parametrized models for the anisotropy and solve the perturbed Einstein field equations numerically. We find that, unlike the case for isotropic neutron stars, the imaginary parts of some of the pressure ($p$-)modes flip signs as the degree of anisotropy deviates from zero, depicting a transition from stable modes to unstable modes. This finding indicates that some anisotropic neutron star models are unstable, potentially restricting the form of sustained anisotropy. |
2006.08693 | Jorge Bellor\'in | Jorge Bellorin, Claudio Borquez and Byron Droguett | Curvature vs degrees of freedom: The case of the critical 2+1 Horava
theory | We have included the results of this paper in another work with a
different focusing | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the interesting case of the 2+1 nonprojectable Horava theory
formulated at the critical point, where it does not posses local degrees of
freedom. The critical point is defined by the value of a coupling constant of
the theory. We discuss how, in spite of the absence of degrees of freedom, the
theory admits solutions with nonflat or nonconstant curvature. We consider the
theory without cosmological constant and without terms of higher order
derivatives, hence this is an effect that can be seen at the same order of 2+1
general relativity. We present an exact nonflat solution that is not
asymptotically flat. The presence of solutions with nontrivial curvature seems
to be related to the relaxing of the asymptotically flat condition. We discuss
that there is no analogue of Newtonian potential in this theory, and a broad
class of asymptotically flat geometries leads to the restriction that the only
solutions that can be found among them are the flat ones.
| [
{
"created": "Mon, 15 Jun 2020 19:04:55 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Aug 2020 21:53:10 GMT",
"version": "v2"
}
] | 2020-09-01 | [
[
"Bellorin",
"Jorge",
""
],
[
"Borquez",
"Claudio",
""
],
[
"Droguett",
"Byron",
""
]
] | We present the interesting case of the 2+1 nonprojectable Horava theory formulated at the critical point, where it does not posses local degrees of freedom. The critical point is defined by the value of a coupling constant of the theory. We discuss how, in spite of the absence of degrees of freedom, the theory admits solutions with nonflat or nonconstant curvature. We consider the theory without cosmological constant and without terms of higher order derivatives, hence this is an effect that can be seen at the same order of 2+1 general relativity. We present an exact nonflat solution that is not asymptotically flat. The presence of solutions with nontrivial curvature seems to be related to the relaxing of the asymptotically flat condition. We discuss that there is no analogue of Newtonian potential in this theory, and a broad class of asymptotically flat geometries leads to the restriction that the only solutions that can be found among them are the flat ones. |
2105.08543 | Hao-Jui Kuan | Hao-Jui Kuan, Jasbir Singh, Daniela D. Doneva, Stoytcho S. Yazadjiev,
Kostas D. Kokkotas | Nonlinear evolution and non-uniqueness of scalarized neutron stars | 10 pages, 5 figures, 1 table | null | 10.1103/PhysRevD.104.124013 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It was recently shown, that in a class of tensor-multi-scalar theories of
gravity with a nontrivial target space metric, there exist scalarized neutron
star solutions. An important property of these compact objects is that the
scalar charge is zero and therefore, the binary pulsar experiments can not
impose constraints based on the absence of scalar dipole radiation. Moreover,
the structure of the solutions is very complicated. For a fixed central energy
density up to three neutron star solutions can exist -- one general
relativistic and two scalarized, that is quite different from the scalarization
in other alternative theories of gravity. In the present paper we address the
stability of these solutions using two independent approaches -- solving the
linearized radial perturbation equations and performing nonlinear simulations
in spherical symmetry. The results show that the change of stability occurs at
the maximum mass models and all solutions before that point are stable. This
leads to the interesting consequence that there exists a stable part of the
scalarized branch close to the bifurcation point where the mass of the star
increases with the decrease of the central energy density.
| [
{
"created": "Tue, 18 May 2021 14:22:50 GMT",
"version": "v1"
}
] | 2021-12-15 | [
[
"Kuan",
"Hao-Jui",
""
],
[
"Singh",
"Jasbir",
""
],
[
"Doneva",
"Daniela D.",
""
],
[
"Yazadjiev",
"Stoytcho S.",
""
],
[
"Kokkotas",
"Kostas D.",
""
]
] | It was recently shown, that in a class of tensor-multi-scalar theories of gravity with a nontrivial target space metric, there exist scalarized neutron star solutions. An important property of these compact objects is that the scalar charge is zero and therefore, the binary pulsar experiments can not impose constraints based on the absence of scalar dipole radiation. Moreover, the structure of the solutions is very complicated. For a fixed central energy density up to three neutron star solutions can exist -- one general relativistic and two scalarized, that is quite different from the scalarization in other alternative theories of gravity. In the present paper we address the stability of these solutions using two independent approaches -- solving the linearized radial perturbation equations and performing nonlinear simulations in spherical symmetry. The results show that the change of stability occurs at the maximum mass models and all solutions before that point are stable. This leads to the interesting consequence that there exists a stable part of the scalarized branch close to the bifurcation point where the mass of the star increases with the decrease of the central energy density. |
gr-qc/0703134 | Michael Reisenberger | Michael P. Reisenberger | The symplectic 2-form and Poisson bracket of null canonical gravity | 132 pages, 4 figures | null | null | null | gr-qc | null | It is well known that free (unconstrained) initial data for the gravitational
field in general relativity can be identified on an initial hypersurface
consisting of two intersecting null hypersurfaces. Here the phase space of
vacuum general relativity associated with such an initial data hypersurface is
defined; a Poisson bracket is defined, via Peierls' prescription, on
sufficiently regular functions on this phase space, called ``observables''; and
a bracket on initial data is defined so that it reproduces the Peierls bracket
between observables when these are expressed in terms of the initial data. The
brackets between all elements of a free initial data set are calculated
explicitly. The bracket on initial data presented here has all the
characteristics of a Poisson bracket except that it does not satisfy the Jacobi
relations (even though the brackets between the observables do).
The initial data set used is closely related to that of Sachs. However, one
significant difference is that it includes a ``new'' pair of degrees of freedom
on the intersection of the two null hypersurfaces which are present but quite
hidden in Sachs' formalism. As a step in the calculation an explicit expression
for the symplectic 2-form in terms of these free initial data is obtained.
| [
{
"created": "Tue, 27 Mar 2007 19:47:49 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Reisenberger",
"Michael P.",
""
]
] | It is well known that free (unconstrained) initial data for the gravitational field in general relativity can be identified on an initial hypersurface consisting of two intersecting null hypersurfaces. Here the phase space of vacuum general relativity associated with such an initial data hypersurface is defined; a Poisson bracket is defined, via Peierls' prescription, on sufficiently regular functions on this phase space, called ``observables''; and a bracket on initial data is defined so that it reproduces the Peierls bracket between observables when these are expressed in terms of the initial data. The brackets between all elements of a free initial data set are calculated explicitly. The bracket on initial data presented here has all the characteristics of a Poisson bracket except that it does not satisfy the Jacobi relations (even though the brackets between the observables do). The initial data set used is closely related to that of Sachs. However, one significant difference is that it includes a ``new'' pair of degrees of freedom on the intersection of the two null hypersurfaces which are present but quite hidden in Sachs' formalism. As a step in the calculation an explicit expression for the symplectic 2-form in terms of these free initial data is obtained. |
0902.4767 | Kohkichi Konno | Kohkichi Konno, Toyoki Matsuyama, Satoshi Tanda | Rotating black hole in extended Chern-Simons modified gravity | 9 pages, 1 figure, to appear in Progress of Theoretical Physics,
typos corrected | Prog.Theor.Phys.122:561-568,2009 | 10.1143/PTP.122.561 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate a slowly rotating black hole in four-dimensional extended
Chern-Simons modified gravity. We obtain an approximate solution that reduces
to the Kerr solution when a coupling constant vanishes. The Chern-Simons
correction effectively reduces the frame-dragging effect around a black hole in
comparison with that of the Kerr solution.
| [
{
"created": "Fri, 27 Feb 2009 08:36:09 GMT",
"version": "v1"
},
{
"created": "Mon, 11 May 2009 03:59:58 GMT",
"version": "v2"
},
{
"created": "Mon, 13 Jul 2009 04:44:09 GMT",
"version": "v3"
}
] | 2009-11-19 | [
[
"Konno",
"Kohkichi",
""
],
[
"Matsuyama",
"Toyoki",
""
],
[
"Tanda",
"Satoshi",
""
]
] | We investigate a slowly rotating black hole in four-dimensional extended Chern-Simons modified gravity. We obtain an approximate solution that reduces to the Kerr solution when a coupling constant vanishes. The Chern-Simons correction effectively reduces the frame-dragging effect around a black hole in comparison with that of the Kerr solution. |
gr-qc/0210044 | Ozay Gurtug | Ozay Gurtug and Izzet Sakalli | Cosmic Strings Coupled With a Massless Scalar Field | 14 pages, Introduction is revised. To be published in Int. Jour. of
Ther. Phys | Int.J.Theor.Phys. 42 (2003) 1875-1888 | null | null | gr-qc | null | A scalar field generalization of Xanthopoulos's cylindrically symmetric
solutions of the vacuum Einstein equation is obtained. The obtained solution
preserves the properties of the Xanthopoulos solution, which are regular on the
axis, asymptotically flat and free from the curvature singularities. The
solution describes stable, infinite length of rotating cosmic string
interacting with gravitational and scalar waves.
| [
{
"created": "Tue, 15 Oct 2002 06:46:40 GMT",
"version": "v1"
},
{
"created": "Sat, 5 Jul 2003 07:43:12 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Gurtug",
"Ozay",
""
],
[
"Sakalli",
"Izzet",
""
]
] | A scalar field generalization of Xanthopoulos's cylindrically symmetric solutions of the vacuum Einstein equation is obtained. The obtained solution preserves the properties of the Xanthopoulos solution, which are regular on the axis, asymptotically flat and free from the curvature singularities. The solution describes stable, infinite length of rotating cosmic string interacting with gravitational and scalar waves. |
2101.10854 | \"Onder D\"unya | Onder Dunya, Levent Akant, Metin Arik, Yelda Kardas, Selale Sahin and
Tarik Tok | The Higgs Field and the Jordan Brans Dicke Cosmology | 18 pages | Eur. Phys. J. C 81, 66 (2021) | 10.1140/epjc/s10052-021-08880-9 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We investigate a field theoretical approach to the Jordan-Brans- Dicke (JBD)
theory extended with a particular potential term on a cosmological background
by starting with the motivation that the Higgs field and the scale factor of
the universe are related. Based on this relation, it is possible to come up
with mathematically equivalent but two different interpretations. From one
point of view while the universe is static, the masses of the elementary
particles change with time. The other one, which we stick with throughout the
manuscript, is that while the universe is expanding, particle masses are
constant. Thus, a coupled Lagrangian density of the JBD field and the scale
factor (the Higgs field), which exhibit a massive particle and a linearly
expanding space in zeroth order respectively, is obtained. By performing a
coordinate transformation in the field space for the reduced JBD action whose
kinetic part is nonlinear sigma model, the Lagrangian of two scalar fields can
be written as uncoupled for the Higgs mechanism. After this transformation, as
a result of spontaneous symmetry breaking, the time dependent vacuum
expectation value (vev) of the Higgs field and the Higgs bosons which are the
particles corresponding to quantized oscillation modes about the vacuum, are
found.
| [
{
"created": "Sun, 24 Jan 2021 10:25:32 GMT",
"version": "v1"
}
] | 2021-01-27 | [
[
"Dunya",
"Onder",
""
],
[
"Akant",
"Levent",
""
],
[
"Arik",
"Metin",
""
],
[
"Kardas",
"Yelda",
""
],
[
"Sahin",
"Selale",
""
],
[
"Tok",
"Tarik",
""
]
] | We investigate a field theoretical approach to the Jordan-Brans- Dicke (JBD) theory extended with a particular potential term on a cosmological background by starting with the motivation that the Higgs field and the scale factor of the universe are related. Based on this relation, it is possible to come up with mathematically equivalent but two different interpretations. From one point of view while the universe is static, the masses of the elementary particles change with time. The other one, which we stick with throughout the manuscript, is that while the universe is expanding, particle masses are constant. Thus, a coupled Lagrangian density of the JBD field and the scale factor (the Higgs field), which exhibit a massive particle and a linearly expanding space in zeroth order respectively, is obtained. By performing a coordinate transformation in the field space for the reduced JBD action whose kinetic part is nonlinear sigma model, the Lagrangian of two scalar fields can be written as uncoupled for the Higgs mechanism. After this transformation, as a result of spontaneous symmetry breaking, the time dependent vacuum expectation value (vev) of the Higgs field and the Higgs bosons which are the particles corresponding to quantized oscillation modes about the vacuum, are found. |
1202.4888 | Simone Calogero | Simone Calogero | Cosmological models with fluid matter undergoing velocity diffusion | 11 Pages, 4 Figures. Version in press | null | 10.1016/j.geomphys.2012.06.004 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new type of fluid matter model in general relativity is introduced, in
which the fluid particles are subject to velocity diffusion without friction.
In order to compensate for the energy gained by the fluid particles due to
diffusion, a cosmological scalar field term is added to the left hand side of
the Einstein equations. This hypothesis promotes diffusion to a new mechanism
for accelerated expansion in cosmology. It is shown that diffusion alters not
only quantitatively, but also qualitatively the global dynamical properties of
the standard cosmological models.
| [
{
"created": "Wed, 22 Feb 2012 11:45:50 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Jun 2012 16:41:11 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Calogero",
"Simone",
""
]
] | A new type of fluid matter model in general relativity is introduced, in which the fluid particles are subject to velocity diffusion without friction. In order to compensate for the energy gained by the fluid particles due to diffusion, a cosmological scalar field term is added to the left hand side of the Einstein equations. This hypothesis promotes diffusion to a new mechanism for accelerated expansion in cosmology. It is shown that diffusion alters not only quantitatively, but also qualitatively the global dynamical properties of the standard cosmological models. |
2307.04405 | Jinhua Wang | Jinhua Wang and Wei Yuan | Global stability of the open Milne spacetime | More references are added | null | null | null | gr-qc math.AP math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The open Milne cosmological spacetime has a 3-dimensional Cauchy surface
isometric to the (non-compact) hyperbolic space. We prove the globally
nonlinear stability of the open Milne spacetime for both massive and massless
Einstein-scalar field equations and show that as time goes to infinity, the
spatial metric tends to the hyperbolic metric. The proof is based on the
Gaussian normal coordinates, in which the decay rates of gravity are determined
by the expanding geometry of Milne spacetime.
| [
{
"created": "Mon, 10 Jul 2023 08:11:59 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Jul 2023 00:37:57 GMT",
"version": "v2"
}
] | 2023-07-26 | [
[
"Wang",
"Jinhua",
""
],
[
"Yuan",
"Wei",
""
]
] | The open Milne cosmological spacetime has a 3-dimensional Cauchy surface isometric to the (non-compact) hyperbolic space. We prove the globally nonlinear stability of the open Milne spacetime for both massive and massless Einstein-scalar field equations and show that as time goes to infinity, the spatial metric tends to the hyperbolic metric. The proof is based on the Gaussian normal coordinates, in which the decay rates of gravity are determined by the expanding geometry of Milne spacetime. |
1210.4412 | Iver Brevik | I. Brevik, V. V. Obukhov, K. E. Osetrin, and A. V. Timoshkin | Little Rip cosmological models with time-dependent equation of state | 11 pages, latex, to appear in Mod. Phys. Lett. A. Abstract
reformulated | Modern Physics Letters A, Vol. 27, No. 36 (2012) 1250210 | 10.1142/S0217732312502100 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Specific dark energy models, leading to the Little Rip (LR) cosmology in the
far future, are investigated. Conditions for the occurrence of LR in terms of
the parameters present in the proposed equation of state for the dark energy
cosmic fluid are studied. Estimates about the time needed before the occurrence
of the rip singularity in the standard LR model and the model in which the
universe approaches the de Sitter space-time asymptotically, are given.
| [
{
"created": "Tue, 16 Oct 2012 13:55:47 GMT",
"version": "v1"
},
{
"created": "Thu, 18 Oct 2012 15:05:15 GMT",
"version": "v2"
}
] | 2012-11-08 | [
[
"Brevik",
"I.",
""
],
[
"Obukhov",
"V. V.",
""
],
[
"Osetrin",
"K. E.",
""
],
[
"Timoshkin",
"A. V.",
""
]
] | Specific dark energy models, leading to the Little Rip (LR) cosmology in the far future, are investigated. Conditions for the occurrence of LR in terms of the parameters present in the proposed equation of state for the dark energy cosmic fluid are studied. Estimates about the time needed before the occurrence of the rip singularity in the standard LR model and the model in which the universe approaches the de Sitter space-time asymptotically, are given. |
gr-qc/0701135 | Alejandro Cabo | Owen Pavel Fernandez Piedra and Alejandro Cabo Montes de Oca | Quantization of massive scalar fields over axis symmetric space-time
backgrounds | 13 pages | null | null | null | gr-qc | null | The renormalized mean value of the quantum Lagrangian and the Energy-Momentum
tensor for scalar fields coupled to an arbitrary gravitational field
configuration are analytically evaluated in the Schwinger-DeWitt approximation,
up to second order in the inverse mass value. The cylindrical symmetry
situation is considered. The results furnish the starting point for
investigating iterative solutions of the back-reaction problem related with the
quantization of cylindrical scalar field configurations. Due to the homogeneity
of the equations of motion of the Klein-Gordon field, the general results are
also valid for performing the quantization over either vanishing or
non-vanishing mean field configurations. As an application, compact analytical
expressions are derived here for the quantum mean Lagrangian and
Energy-Momentum tensor in the particular background given by the Black-String
space-time.
| [
{
"created": "Wed, 24 Jan 2007 23:20:40 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Piedra",
"Owen Pavel Fernandez",
""
],
[
"de Oca",
"Alejandro Cabo Montes",
""
]
] | The renormalized mean value of the quantum Lagrangian and the Energy-Momentum tensor for scalar fields coupled to an arbitrary gravitational field configuration are analytically evaluated in the Schwinger-DeWitt approximation, up to second order in the inverse mass value. The cylindrical symmetry situation is considered. The results furnish the starting point for investigating iterative solutions of the back-reaction problem related with the quantization of cylindrical scalar field configurations. Due to the homogeneity of the equations of motion of the Klein-Gordon field, the general results are also valid for performing the quantization over either vanishing or non-vanishing mean field configurations. As an application, compact analytical expressions are derived here for the quantum mean Lagrangian and Energy-Momentum tensor in the particular background given by the Black-String space-time. |
1412.3865 | Miko{\l}aj Korzy\'nski | Miko{\l}aj Korzy\'nski | Nonlinear effects of general relativity from multiscale structure | 30 pages, 10 figures | Class. Quantum Grav. 32 (2015) 215013 | 10.1088/0264-9381/32/21/215013 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | When do the nonlinear effects of general relativity matter in astrophysical
situations? They are obviously relevant for very compact sources of the
gravitational field, such as neutron stars or black holes. In this paper I
discuss another, less obvious situation, in which large relativistic effects
may arise due to a complicated, multiscale structure of the matter
distribution. I present an exact solution with an inhomogeneous energy density
distribution in the form of a hierarchy of nested voids and overdensities of
various sizes, extending from the homogeneity scale down to arbitrary small
scales. I show that although each of the voids and overdensities seems to be
very weakly relativistic, and thus easy to describe using the linearized
general relativity, the solution taken as a whole lies in fact in the nonlinear
regime. Its nonlinear properties are most easily seen when we compare the ADM
mass of the solution and the integral of the local mass density: the difference
between them, i.e. the relativistic mass deficit, can be significant provided
that the inhomogeneities extend to sufficiently small scales. The
non-additivity of masses implies a large backreaction effect, i.e. significant
discrepancy between the averaged, large-scale effective stress-energy tensor
and the naive average of the local energy density. I show that this is a
general relativistic effect arising due to the inhomogeneous, multiscale
structure. I also discuss the relevance of the results in cosmology and
relativistic astrophysics.
| [
{
"created": "Fri, 12 Dec 2014 01:00:40 GMT",
"version": "v1"
}
] | 2015-10-13 | [
[
"Korzyński",
"Mikołaj",
""
]
] | When do the nonlinear effects of general relativity matter in astrophysical situations? They are obviously relevant for very compact sources of the gravitational field, such as neutron stars or black holes. In this paper I discuss another, less obvious situation, in which large relativistic effects may arise due to a complicated, multiscale structure of the matter distribution. I present an exact solution with an inhomogeneous energy density distribution in the form of a hierarchy of nested voids and overdensities of various sizes, extending from the homogeneity scale down to arbitrary small scales. I show that although each of the voids and overdensities seems to be very weakly relativistic, and thus easy to describe using the linearized general relativity, the solution taken as a whole lies in fact in the nonlinear regime. Its nonlinear properties are most easily seen when we compare the ADM mass of the solution and the integral of the local mass density: the difference between them, i.e. the relativistic mass deficit, can be significant provided that the inhomogeneities extend to sufficiently small scales. The non-additivity of masses implies a large backreaction effect, i.e. significant discrepancy between the averaged, large-scale effective stress-energy tensor and the naive average of the local energy density. I show that this is a general relativistic effect arising due to the inhomogeneous, multiscale structure. I also discuss the relevance of the results in cosmology and relativistic astrophysics. |
2205.14973 | Nikolaos Dimakis | N. Dimakis | Hidden symmetries from distortions of the conformal structure | 37 pages, 1 figure, Latex2e source file, minor changes to match
published version | Phys. Rev. D 106 (2022) 024043 | 10.1103/PhysRevD.106.024043 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is well established that the mass parameter breaks the conformal
symmetries in the case of geodesic motion. The proper conformal Killing vectors
cease to generate conserved charges when non-null geodesics are considered. We
examine how the introduction of the mass is actually related to the appearance
of appropriate distortions in the conformal sector, which lead to new
conservation laws. As a prominent example we use a general pp-wave metric,
which exploits this property to the maximum. We study the necessary geometric
conditions, so that such types of distortions are applicable. We show that the
relative vectors are generators of disformal transformations and prove their
connection to higher order (hidden) symmetries. Except from the pp-wave
geometry, we also provide an additional example in the form of the de Sitter
metric. Again, the proper conformal Killing vectors can be appropriately
distorted to generate conserved quantities for massive geodesics. Subsequently,
we proceed by introducing an additional symmetry breaking effect. The latter is
realized by considering a Bogoslovsky type of line-element, which involves a
Lorentz violating parameter. We utilize once more the pp-wave case as a guide
to study how the broken symmetries - this time also related to Killing vectors
- are substituted by distortions of the original generators. We further analyze
and discuss the necessary geometric conditions that lead to the emergence of
these distortions.
| [
{
"created": "Mon, 30 May 2022 10:21:48 GMT",
"version": "v1"
},
{
"created": "Wed, 13 Jul 2022 02:57:29 GMT",
"version": "v2"
},
{
"created": "Wed, 27 Jul 2022 03:36:36 GMT",
"version": "v3"
}
] | 2022-07-28 | [
[
"Dimakis",
"N.",
""
]
] | It is well established that the mass parameter breaks the conformal symmetries in the case of geodesic motion. The proper conformal Killing vectors cease to generate conserved charges when non-null geodesics are considered. We examine how the introduction of the mass is actually related to the appearance of appropriate distortions in the conformal sector, which lead to new conservation laws. As a prominent example we use a general pp-wave metric, which exploits this property to the maximum. We study the necessary geometric conditions, so that such types of distortions are applicable. We show that the relative vectors are generators of disformal transformations and prove their connection to higher order (hidden) symmetries. Except from the pp-wave geometry, we also provide an additional example in the form of the de Sitter metric. Again, the proper conformal Killing vectors can be appropriately distorted to generate conserved quantities for massive geodesics. Subsequently, we proceed by introducing an additional symmetry breaking effect. The latter is realized by considering a Bogoslovsky type of line-element, which involves a Lorentz violating parameter. We utilize once more the pp-wave case as a guide to study how the broken symmetries - this time also related to Killing vectors - are substituted by distortions of the original generators. We further analyze and discuss the necessary geometric conditions that lead to the emergence of these distortions. |
gr-qc/9601009 | Jorge Pullin | Richard H. Price, Jorge Pullin | Analytic approximations to the spacetime of a critical gravitational
collapse | 12 pages, Revtex, 9 figures included with epsf | Phys.Rev.D54:3792-3799,1996 | 10.1103/PhysRevD.54.3792 | CGPG-96/1-1 | gr-qc | null | We present analytic expressions that approximate the behavior of the
spacetime of a collapsing spherically symmetric scalar field in the critical
regime first discovered by Choptuik. We find that the critical region of
spacetime can usefully be divided into a ``quiescent'' region and an
``oscillatory'' region, and a moving ``transition edge'' that separates the two
regions. We find that in each region the critical solution can be well
approximated by a flat spacetime scalar field solution. A qualitative nonlinear
matching of the solutions across the edge yields the right order of magnitude
for the oscillations of the discretely self-similar critical solution found by
Choptuik.
| [
{
"created": "Tue, 9 Jan 1996 17:02:08 GMT",
"version": "v1"
}
] | 2011-09-09 | [
[
"Price",
"Richard H.",
""
],
[
"Pullin",
"Jorge",
""
]
] | We present analytic expressions that approximate the behavior of the spacetime of a collapsing spherically symmetric scalar field in the critical regime first discovered by Choptuik. We find that the critical region of spacetime can usefully be divided into a ``quiescent'' region and an ``oscillatory'' region, and a moving ``transition edge'' that separates the two regions. We find that in each region the critical solution can be well approximated by a flat spacetime scalar field solution. A qualitative nonlinear matching of the solutions across the edge yields the right order of magnitude for the oscillations of the discretely self-similar critical solution found by Choptuik. |
gr-qc/9605073 | Roberto Longo | Roberto Longo (Universita' di Roma ``Tor Vergata'') | An Analogue of the Kac-Wakimoto Formula and Black Hole Conditional
Entropy | AMS-TeX v1.1c, minor grammatical corrections | Commun.Math.Phys.186:451-479,1997 | 10.1007/s002200050116 | null | gr-qc funct-an hep-th math.FA | null | A local formula for the dimension of a superselection sector in Quantum Field
Theory is obtained as vacuum expectation value of the exponential of the proper
Hamiltonian. In the particular case of a chiral conformal theory, this provides
a local analogue of a global formula obtained by Kac and Wakimoto within the
context of representations of certain affine Lie algebras. Our formula is model
independent and its version in general Quantum Field Theory applies to black
hole thermodynamics. The relative free energy between two thermal equilibrium
states associated with a black hole turns out to be proportional to the
variation of the conditional entropy in different superselection sectors, where
the conditional entropy is defined as the Connes-Stoermer entropy associated
with the DHR localized endomorphism representing the sector. The constant of
proportionality is half of the Hawking temperature. As a consequence the
relative free energy is quantized proportionally to the logarithm of a rational
number, in particular it is equal to a linear function the logarithm of an
integer once the initial state or the final state is taken fixed.
| [
{
"created": "Fri, 31 May 1996 14:57:15 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Jul 1997 15:59:18 GMT",
"version": "v2"
}
] | 2011-04-06 | [
[
"Longo",
"Roberto",
"",
"Universita' di Roma ``Tor Vergata''"
]
] | A local formula for the dimension of a superselection sector in Quantum Field Theory is obtained as vacuum expectation value of the exponential of the proper Hamiltonian. In the particular case of a chiral conformal theory, this provides a local analogue of a global formula obtained by Kac and Wakimoto within the context of representations of certain affine Lie algebras. Our formula is model independent and its version in general Quantum Field Theory applies to black hole thermodynamics. The relative free energy between two thermal equilibrium states associated with a black hole turns out to be proportional to the variation of the conditional entropy in different superselection sectors, where the conditional entropy is defined as the Connes-Stoermer entropy associated with the DHR localized endomorphism representing the sector. The constant of proportionality is half of the Hawking temperature. As a consequence the relative free energy is quantized proportionally to the logarithm of a rational number, in particular it is equal to a linear function the logarithm of an integer once the initial state or the final state is taken fixed. |
1710.00919 | Hector O. Silva | Hector O. Silva, Nicolas Yunes | I-Love-Q to the extreme | 18 pages, 7 figures | null | 10.1088/1361-6382/aa995a | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Certain bulk properties of neutron stars, in particular their moment of
inertia, rotational quadrupole moment and tidal Love number, when properly
normalized, are related to one another in a nearly equation of state
independent way. The goal of this paper is to test these relations with extreme
equations of state at supranuclear densities constrained to satisfy only a
handful of generic, physically sensible conditions. By requiring that the
equation of state be (i) barotropic and (ii) its associated speed of sound be
real, we construct a piecewise function that matches a tabulated equation of
state at low densities, while matching a stiff equation of state parametrized
by its sound speed in the high-density region. We show that the I-Love-Q
relations hold to 1 percent with this class of equations of state, even in the
extreme case where the speed of sound becomes superluminal and independently of
the transition density. We also find further support for the interpretation of
the I-Love-Q relations as an emergent symmetry due to the nearly constant
eccentricity of isodensity contours inside the star. These results reinforce
the robustness of the I-Love-Q relations against our current incomplete picture
of physics at supranuclear densities, while strengthening our confidence in the
applicability of these relations in neutron star astrophysics.
| [
{
"created": "Mon, 2 Oct 2017 21:33:48 GMT",
"version": "v1"
}
] | 2017-12-20 | [
[
"Silva",
"Hector O.",
""
],
[
"Yunes",
"Nicolas",
""
]
] | Certain bulk properties of neutron stars, in particular their moment of inertia, rotational quadrupole moment and tidal Love number, when properly normalized, are related to one another in a nearly equation of state independent way. The goal of this paper is to test these relations with extreme equations of state at supranuclear densities constrained to satisfy only a handful of generic, physically sensible conditions. By requiring that the equation of state be (i) barotropic and (ii) its associated speed of sound be real, we construct a piecewise function that matches a tabulated equation of state at low densities, while matching a stiff equation of state parametrized by its sound speed in the high-density region. We show that the I-Love-Q relations hold to 1 percent with this class of equations of state, even in the extreme case where the speed of sound becomes superluminal and independently of the transition density. We also find further support for the interpretation of the I-Love-Q relations as an emergent symmetry due to the nearly constant eccentricity of isodensity contours inside the star. These results reinforce the robustness of the I-Love-Q relations against our current incomplete picture of physics at supranuclear densities, while strengthening our confidence in the applicability of these relations in neutron star astrophysics. |
2109.01640 | Roman Konoplya | R. A. Konoplya | Black holes in galactic centers: quasinormal ringing, grey-body factors
and Unruh temperature | 7 pages, revtex, the version accepted for publication in Physics
Letters B | Physics Letters B 823 (2021) 136734 | 10.1016/j.physletb.2021.136734 | null | gr-qc astro-ph.HE hep-th | http://creativecommons.org/licenses/by/4.0/ | Recently, Cardoso et al. [arXiv:2109.00005] found an exact solution
describing the black hole immersed in a galactic-like distribution of matter.
There, the properties of gravitational radiation were studied. Here we continue
analysis of properties of this geometry via consideration of the
electromagnetic radiation. We calculate quasinormal modes, asymptotic tails and
grey-body factors for electromagnetic radiation. In addition, we discuss the
Unruh temperature for this spacetime. Estimations made in the regime which is
best fitting the galaxies behavior show that influence of the environment on
classical and quantum radiation around such black holes must be relatively
small.
| [
{
"created": "Fri, 3 Sep 2021 17:36:35 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Sep 2021 21:24:21 GMT",
"version": "v2"
},
{
"created": "Mon, 25 Oct 2021 11:24:27 GMT",
"version": "v3"
}
] | 2021-10-26 | [
[
"Konoplya",
"R. A.",
""
]
] | Recently, Cardoso et al. [arXiv:2109.00005] found an exact solution describing the black hole immersed in a galactic-like distribution of matter. There, the properties of gravitational radiation were studied. Here we continue analysis of properties of this geometry via consideration of the electromagnetic radiation. We calculate quasinormal modes, asymptotic tails and grey-body factors for electromagnetic radiation. In addition, we discuss the Unruh temperature for this spacetime. Estimations made in the regime which is best fitting the galaxies behavior show that influence of the environment on classical and quantum radiation around such black holes must be relatively small. |
2304.08348 | Haximjan Abdusattar | Haximjan Abdusattar | Insight into the Microstructure of FRW Universe from a $P$-$V$ Phase
Transition | 9 pages,3 figures | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The $P$-$V$ phase transition of the FRW (Friedmann-Robertson-Walker) universe
with a perfect fluid has recently been investigated, revealing that the four
critical exponents near the critical point are consistent with the values
predicted by mean field theory. Notably, the coexistence phase of the $P$-$V$
phase transition in the FRW universe above the critical temperature, which
distinguishes it from van der Waals system and most of AdS black holes system.
This unique property allows us to investigate the microstructure of the FRW
universe as a thermodynamic system. Our analysis of the Ruppeiner geometry for
the FRW universe reveals that the behavior of the thermodynamic scalar
curvature near criticality is characterized by a dimensionless constant
identical to that of the van der Waals fluid. Additionally, we observe that
while repulsive interactions dominate for the coexistence samll phase with
higher temperature, the scalar curvature for the coexistence large phase is
always negative, indicating attractive interactions, providing new insights
into the nature of interactions among the perfect fluid matter constituents in
the expanding FRW universe.
| [
{
"created": "Mon, 17 Apr 2023 15:10:12 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Sep 2023 11:27:41 GMT",
"version": "v2"
}
] | 2023-09-20 | [
[
"Abdusattar",
"Haximjan",
""
]
] | The $P$-$V$ phase transition of the FRW (Friedmann-Robertson-Walker) universe with a perfect fluid has recently been investigated, revealing that the four critical exponents near the critical point are consistent with the values predicted by mean field theory. Notably, the coexistence phase of the $P$-$V$ phase transition in the FRW universe above the critical temperature, which distinguishes it from van der Waals system and most of AdS black holes system. This unique property allows us to investigate the microstructure of the FRW universe as a thermodynamic system. Our analysis of the Ruppeiner geometry for the FRW universe reveals that the behavior of the thermodynamic scalar curvature near criticality is characterized by a dimensionless constant identical to that of the van der Waals fluid. Additionally, we observe that while repulsive interactions dominate for the coexistence samll phase with higher temperature, the scalar curvature for the coexistence large phase is always negative, indicating attractive interactions, providing new insights into the nature of interactions among the perfect fluid matter constituents in the expanding FRW universe. |
gr-qc/0512037 | Bahtiyar Ozgur Sarioglu | Reinaldo J. Gleiser, Metin Gurses, Atalay Karasu, Ozgur Sarioglu | Closed timelike curves and geodesics of Godel-type metrics | REVTeX 4, 12 pages, no figures; the Introduction has been rewritten,
some minor mistakes corrected, many references added | Class.Quant.Grav. 23 (2006) 2653-2664 | 10.1088/0264-9381/23/7/025 | null | gr-qc hep-th | null | It is shown explicitly that when the characteristic vector field that defines
a Godel-type metric is also a Killing vector, there always exist closed
timelike or null curves in spacetimes described by such a metric. For these
geometries, the geodesic curves are also shown to be characterized by a lower
dimensional Lorentz force equation for a charged point particle in the relevant
Riemannian background. Moreover, two explicit examples are given for which
timelike and null geodesics can never be closed.
| [
{
"created": "Tue, 6 Dec 2005 07:40:07 GMT",
"version": "v1"
},
{
"created": "Sat, 28 Jan 2006 13:17:13 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Gleiser",
"Reinaldo J.",
""
],
[
"Gurses",
"Metin",
""
],
[
"Karasu",
"Atalay",
""
],
[
"Sarioglu",
"Ozgur",
""
]
] | It is shown explicitly that when the characteristic vector field that defines a Godel-type metric is also a Killing vector, there always exist closed timelike or null curves in spacetimes described by such a metric. For these geometries, the geodesic curves are also shown to be characterized by a lower dimensional Lorentz force equation for a charged point particle in the relevant Riemannian background. Moreover, two explicit examples are given for which timelike and null geodesics can never be closed. |
gr-qc/0301053 | Salvatore Capozziello | Salvatore Capozziello and Gaetano Lambiase | Newtonian limit of String-Dilaton Gravity | 11 pages, LATEX file, to appear in IJMPD | Int.J.Mod.Phys. D12 (2003) 843-852 | 10.1142/S0218271803003347 | null | gr-qc | null | We study the weak-field limit of string-dilaton gravity and derive
corrections to the Newtonian potential which strength directly depends on the
self interaction potential and the nonminimal coupling of the dilaton scalar
field. We discuss also possible astrophysical applications of the results, in
particular the flat rotation curves of spiral galaxies.
| [
{
"created": "Wed, 15 Jan 2003 17:06:07 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Capozziello",
"Salvatore",
""
],
[
"Lambiase",
"Gaetano",
""
]
] | We study the weak-field limit of string-dilaton gravity and derive corrections to the Newtonian potential which strength directly depends on the self interaction potential and the nonminimal coupling of the dilaton scalar field. We discuss also possible astrophysical applications of the results, in particular the flat rotation curves of spiral galaxies. |
1710.01722 | Jonathan Luk | Mihalis Dafermos and Jonathan Luk | The interior of dynamical vacuum black holes I: The $C^0$-stability of
the Kerr Cauchy horizon | null | null | null | null | gr-qc math-ph math.AP math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We initiate a series of works where we study the interior of dynamical
rotating vacuum black holes without symmetry. In the present paper, we take up
the problem starting from appropriate Cauchy data for the Einstein vacuum
equations defined on a hypersurface already within the black hole interior,
representing the expected geometry just inside the event horizon. We prove that
for all such data, the maximal Cauchy evolution can be extended across a
non-trivial piece of Cauchy horizon as a Lorentzian manifold with continuous
metric. In subsequent work, we will retrieve our assumptions on data assuming
only that the black hole event horizon geometry suitably asymptotes to a
rotating Kerr solution. In particular, if the exterior region of the Kerr
family is proven to be dynamically stable---as is widely expected---then it
will follow that the $C^0$-inextendibility formulation of Penrose's celebrated
strong cosmic censorship conjecture is in fact false. The proof suggests,
however, that the $C^0$-metric Cauchy horizons thus arising are generically
singular in an essential way, representing so-called "weak null singularities",
and thus that a revised version of strong cosmic censorship holds.
| [
{
"created": "Wed, 4 Oct 2017 17:54:05 GMT",
"version": "v1"
}
] | 2017-10-05 | [
[
"Dafermos",
"Mihalis",
""
],
[
"Luk",
"Jonathan",
""
]
] | We initiate a series of works where we study the interior of dynamical rotating vacuum black holes without symmetry. In the present paper, we take up the problem starting from appropriate Cauchy data for the Einstein vacuum equations defined on a hypersurface already within the black hole interior, representing the expected geometry just inside the event horizon. We prove that for all such data, the maximal Cauchy evolution can be extended across a non-trivial piece of Cauchy horizon as a Lorentzian manifold with continuous metric. In subsequent work, we will retrieve our assumptions on data assuming only that the black hole event horizon geometry suitably asymptotes to a rotating Kerr solution. In particular, if the exterior region of the Kerr family is proven to be dynamically stable---as is widely expected---then it will follow that the $C^0$-inextendibility formulation of Penrose's celebrated strong cosmic censorship conjecture is in fact false. The proof suggests, however, that the $C^0$-metric Cauchy horizons thus arising are generically singular in an essential way, representing so-called "weak null singularities", and thus that a revised version of strong cosmic censorship holds. |
gr-qc/9912017 | Carlos Lousto | C. O. Lousto (AEI-Golm) | Pragmatic approach to gravitational radiation reaction in binary black
holes | 5 pages, 2 figures, improved text and figures. To appear in PRL | Phys.Rev.Lett. 84 (2000) 5251-5254 | 10.1103/PhysRevLett.84.5251 | AEI-1999-25 | gr-qc | null | We study the relativistic orbit of binary black holes in systems with small
mass ratio. The trajectory of the smaller object (another black hole or a
neutron star), represented as a particle, is determined by the geodesic
equation on the perturbed massive black hole spacetime. The particle itself
generates the gravitational perturbations leading to a problem that needs
regularization. Here we study perturbations around a Schwarzschild black hole
using Moncrief's gauge invariant formalism. We decompose the perturbations into
$\ell-$multipoles to show that all $\ell-$metric coefficients are $C^0$ at the
location of the particle. Summing over $\ell$, to reconstruct the full metric,
gives a formally divergent result. We succeed in bringing this sum to a
generalized Riemann's $\zeta-$function regularization scheme and show that this
is tantamount to subtract the $\ell\to\infty$ piece to each multipole. We
explicitly carry out this regularization and numerically compute the first
order geodesics. Application of this method to general orbits around rotating
black holes would generate accurate templates for gravitational wave laser
interferometric detectors.
| [
{
"created": "Fri, 3 Dec 1999 16:00:06 GMT",
"version": "v1"
},
{
"created": "Tue, 9 May 2000 18:32:50 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Lousto",
"C. O.",
"",
"AEI-Golm"
]
] | We study the relativistic orbit of binary black holes in systems with small mass ratio. The trajectory of the smaller object (another black hole or a neutron star), represented as a particle, is determined by the geodesic equation on the perturbed massive black hole spacetime. The particle itself generates the gravitational perturbations leading to a problem that needs regularization. Here we study perturbations around a Schwarzschild black hole using Moncrief's gauge invariant formalism. We decompose the perturbations into $\ell-$multipoles to show that all $\ell-$metric coefficients are $C^0$ at the location of the particle. Summing over $\ell$, to reconstruct the full metric, gives a formally divergent result. We succeed in bringing this sum to a generalized Riemann's $\zeta-$function regularization scheme and show that this is tantamount to subtract the $\ell\to\infty$ piece to each multipole. We explicitly carry out this regularization and numerically compute the first order geodesics. Application of this method to general orbits around rotating black holes would generate accurate templates for gravitational wave laser interferometric detectors. |
1606.01830 | Chun-Yen Lin | Jerzy Lewandowski, Chun-Yen Lin | Exploring the Tomlin-Varadarajan quantum constraints in $U(1)^3$ loop
quantum gravity: solutions and the Minkowski theorem | 17 pages, this version with improved descriptions and clarifications | Phys. Rev. D 95, 064032 (2017) | 10.1103/PhysRevD.95.064032 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explicitly solved the anomaly-free quantum constraints proposed by Tomlin
and Varadarajan for the weak Euclidean model of canonical loop quantum gravity,
in a large subspace of the model's kinematic Hilbert space which is the space
of the charge network states. In doing so, we first identified the subspace on
which each of the constraints acts convergingly, and then by explicitly
evaluating such actions we found the complete set of the solutions in the
identified subspace. We showed that the space of solutions consists of two
classes of states, with the first class having a property that involves the
condition known from the Minkowski theorem on polyhedra, and the second class
satisfying a weaker form of the spatial diffeomorphism invariance.
| [
{
"created": "Mon, 6 Jun 2016 17:09:40 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Jun 2016 14:54:18 GMT",
"version": "v2"
},
{
"created": "Wed, 22 Feb 2017 14:57:39 GMT",
"version": "v3"
}
] | 2018-07-24 | [
[
"Lewandowski",
"Jerzy",
""
],
[
"Lin",
"Chun-Yen",
""
]
] | We explicitly solved the anomaly-free quantum constraints proposed by Tomlin and Varadarajan for the weak Euclidean model of canonical loop quantum gravity, in a large subspace of the model's kinematic Hilbert space which is the space of the charge network states. In doing so, we first identified the subspace on which each of the constraints acts convergingly, and then by explicitly evaluating such actions we found the complete set of the solutions in the identified subspace. We showed that the space of solutions consists of two classes of states, with the first class having a property that involves the condition known from the Minkowski theorem on polyhedra, and the second class satisfying a weaker form of the spatial diffeomorphism invariance. |
2306.16743 | Simone D'Onofrio Dr. | Simone D'Onofrio | Holographic description of $F(R)$ gravity coupled with Axion Dark Matter | "International Journal of Geometric Methods in Modern Physics"
Accepted | null | 10.1142/S0219887823502249 | null | gr-qc hep-th | http://creativecommons.org/licenses/by-nc-nd/4.0/ | In this work we study the autonomous dynamical system of different $F(R)$
models in the formalism of holographic dark energy using the generalized
Nojiri-Odintsov cut-off. We explicitly give the expression of the fixed points
as functions of the infrared cut-off for vacuum $F(R)$ gravity in flat and
non-flat FRW background and for $F(R)$ coupling axion dark matter. Each fixed
point component can be taken as a condition on the cut-off and on the
expression of $F(R)$, leading to physically interesting constraints on these
functions.
| [
{
"created": "Thu, 29 Jun 2023 07:34:55 GMT",
"version": "v1"
}
] | 2023-09-18 | [
[
"D'Onofrio",
"Simone",
""
]
] | In this work we study the autonomous dynamical system of different $F(R)$ models in the formalism of holographic dark energy using the generalized Nojiri-Odintsov cut-off. We explicitly give the expression of the fixed points as functions of the infrared cut-off for vacuum $F(R)$ gravity in flat and non-flat FRW background and for $F(R)$ coupling axion dark matter. Each fixed point component can be taken as a condition on the cut-off and on the expression of $F(R)$, leading to physically interesting constraints on these functions. |
1707.09702 | Yasusada Nambu | Marcello Rotondo and Yasusada Nambu | Quantum Cramer-Rao bound for a Massless Scalar Field in de Sitter Space | 16 pages, published version | Universe 2017,3,71 | 10.3390/universe3040071 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | How precisely can we estimate cosmological parameters by performing a quantum
measurement on a cosmological quantum state? In quantum estimation theory the
variance of an unbiased parameter estimator is bounded from below by the
inverse of measurement-dependent Fisher information and ultimately by quantum
Fisher information, which is the maximization of the former over all positive
operator valued measurements. Such bound is known as the quantum Cramer-Rao
bound. We consider the evolution of a massless scalar field with Bunch-Davies
vacuum in a spatially flat FLRW spacetime, which results in a two-mode squeezed
vacuum out-state for each field wave number mode. We obtain the expressions of
the quantum Fisher information as well as the Fisher informations associated to
occupation number measurement and power spectrum measurement, and show the
specific results of their evoluation for pure de Sitter expansion and de Sitter
expansion followed by a radiation-dominated phase as examples. We will discuss
these results from the point of view of the quantum-to-classical transition of
cosmological perturbations and show quantitatively how this transition and the
residual quantum correlations affect the bound on the precision.
| [
{
"created": "Mon, 31 Jul 2017 02:55:36 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Oct 2017 02:00:16 GMT",
"version": "v2"
}
] | 2017-10-17 | [
[
"Rotondo",
"Marcello",
""
],
[
"Nambu",
"Yasusada",
""
]
] | How precisely can we estimate cosmological parameters by performing a quantum measurement on a cosmological quantum state? In quantum estimation theory the variance of an unbiased parameter estimator is bounded from below by the inverse of measurement-dependent Fisher information and ultimately by quantum Fisher information, which is the maximization of the former over all positive operator valued measurements. Such bound is known as the quantum Cramer-Rao bound. We consider the evolution of a massless scalar field with Bunch-Davies vacuum in a spatially flat FLRW spacetime, which results in a two-mode squeezed vacuum out-state for each field wave number mode. We obtain the expressions of the quantum Fisher information as well as the Fisher informations associated to occupation number measurement and power spectrum measurement, and show the specific results of their evoluation for pure de Sitter expansion and de Sitter expansion followed by a radiation-dominated phase as examples. We will discuss these results from the point of view of the quantum-to-classical transition of cosmological perturbations and show quantitatively how this transition and the residual quantum correlations affect the bound on the precision. |
gr-qc/0701079 | Francesco Cianfrani dr | Francesco Cianfrani, Giovanni Montani | The Electro-Weak model as low-energy sector of 8-dimensional General
Relativity | 5 pages, to appear in the Proceedings of the 1st Stueckelberg
Workshop | Nuovo Cim.B122:213-218,2007 | 10.1393/ncb/i2007-10356-0 | null | gr-qc | null | In a Kaluza-Klein background $V^4\otimes S^3$, we provide a way to reproduce,
by the dimensional reduction, a 4-spinor with a SU(2) gauge coupling. Since
additional gauge violating terms cannot be avoided, we compute their order of
magnitude by virtue of the application to the Electro-Weak model.
| [
{
"created": "Mon, 15 Jan 2007 14:16:30 GMT",
"version": "v1"
}
] | 2010-11-11 | [
[
"Cianfrani",
"Francesco",
""
],
[
"Montani",
"Giovanni",
""
]
] | In a Kaluza-Klein background $V^4\otimes S^3$, we provide a way to reproduce, by the dimensional reduction, a 4-spinor with a SU(2) gauge coupling. Since additional gauge violating terms cannot be avoided, we compute their order of magnitude by virtue of the application to the Electro-Weak model. |
2205.00575 | Rafael Hern\'andez-Jim\'enez | Clara Rojas, Rafael Hern\'andez-Jim\'enez | Inflation from a chaotic potential with a step | 21 pages, 16 figures | Phys. Dark Univ. 40 (2023) 101188 | 10.1016/j.dark.2023.101188 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we study the effects on the relevant observational parameters
of an inflationary universe from a chaotic potential with a step. We
numerically evolve the perturbation equations within both cold inflation and
warm inflation. On the one hand, in a cold inflation scenario we analyse the
scalar power spectrum $P_{\mathcal{R}}$ in terms of the number of e-folds
$N_{e}$, and in terms of the ratio $k/k_{0}$, where $k_{0}$ is our pivot scale.
We show how $P_{\mathcal{R}}$ oscillates around $0.2< k/k_{0} < 20$.
Additionally, we present the evolution of two relevant parameters: the scalar
spectral index $n_\mathrm{s}$ and the tensor-to-scalar ratio $r$. In fact, more
than one region of $(n_\mathrm{s},r)$ lies within the observable window (Planck
2018). On the other hand, in the warm inflationary case, we also examine the
evolution of $P_{\mathcal{R}}$ in terms of $N_{e}$ and $k/k_{0}$. Perturbations
are amplified in WI; in fact, $P_{\mathcal{R}}$ can be much larger than the CMB
value $P_{\mathcal{R}}> 2.22\times 10^{-9}$. This time, the spectral index
$n_\mathrm{s}$ is clearly blue-tilted, at smaller scales, and the
tensor-to-scalar ratio $r$ becomes too low. However, $n_\mathrm{s}$ can change
from blue-tilted towards red-tilted, since $P_{\mathcal{R}}$ starts oscillating
around $k/k_{0}\sim 40$. Indeed, the result from the step potential skims the
Planck contours. Finally, one key aspect of this research was to contrast the
features of an inflationary potential between both paradigms, and, in fact,
they show similarities and differences. Due to a featured background and a
combined effect of entropy fluctuations (only in warm inflation), in both
scenarios certain fluctuation scales are not longer ``freeze in'' on
super-horizon scales.
| [
{
"created": "Sun, 1 May 2022 22:50:23 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Jun 2022 19:21:19 GMT",
"version": "v2"
},
{
"created": "Tue, 7 Mar 2023 16:56:23 GMT",
"version": "v3"
}
] | 2023-03-09 | [
[
"Rojas",
"Clara",
""
],
[
"Hernández-Jiménez",
"Rafael",
""
]
] | In this work, we study the effects on the relevant observational parameters of an inflationary universe from a chaotic potential with a step. We numerically evolve the perturbation equations within both cold inflation and warm inflation. On the one hand, in a cold inflation scenario we analyse the scalar power spectrum $P_{\mathcal{R}}$ in terms of the number of e-folds $N_{e}$, and in terms of the ratio $k/k_{0}$, where $k_{0}$ is our pivot scale. We show how $P_{\mathcal{R}}$ oscillates around $0.2< k/k_{0} < 20$. Additionally, we present the evolution of two relevant parameters: the scalar spectral index $n_\mathrm{s}$ and the tensor-to-scalar ratio $r$. In fact, more than one region of $(n_\mathrm{s},r)$ lies within the observable window (Planck 2018). On the other hand, in the warm inflationary case, we also examine the evolution of $P_{\mathcal{R}}$ in terms of $N_{e}$ and $k/k_{0}$. Perturbations are amplified in WI; in fact, $P_{\mathcal{R}}$ can be much larger than the CMB value $P_{\mathcal{R}}> 2.22\times 10^{-9}$. This time, the spectral index $n_\mathrm{s}$ is clearly blue-tilted, at smaller scales, and the tensor-to-scalar ratio $r$ becomes too low. However, $n_\mathrm{s}$ can change from blue-tilted towards red-tilted, since $P_{\mathcal{R}}$ starts oscillating around $k/k_{0}\sim 40$. Indeed, the result from the step potential skims the Planck contours. Finally, one key aspect of this research was to contrast the features of an inflationary potential between both paradigms, and, in fact, they show similarities and differences. Due to a featured background and a combined effect of entropy fluctuations (only in warm inflation), in both scenarios certain fluctuation scales are not longer ``freeze in'' on super-horizon scales. |
1712.09534 | Alexey Golovnev | Alexey Golovnev, Fedor Smirnov | Algebraic aspects of massive gravity | 9 pages, 1 figure; some typos corrected | International Journal of Geometric Methods in Modern Physics 15
(2018) 1840003 | 10.1142/S0219887818400030 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe the freedom of choosing a square root in massive gravity from
algebraic point of view. This contribution is based on the talk given by one of
us (AG) at the Geometric Foundations of Gravity conference in Tartu in August
2017.
| [
{
"created": "Wed, 27 Dec 2017 09:50:27 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Jan 2018 06:43:57 GMT",
"version": "v2"
}
] | 2018-05-08 | [
[
"Golovnev",
"Alexey",
""
],
[
"Smirnov",
"Fedor",
""
]
] | We describe the freedom of choosing a square root in massive gravity from algebraic point of view. This contribution is based on the talk given by one of us (AG) at the Geometric Foundations of Gravity conference in Tartu in August 2017. |
2004.10795 | Victor I. Afonso | Victor I. Afonso | Compact scalar field solutions in EiBI gravity | 27 onecolumn pages, 4 figures, Contribution to Selected Papers of the
Fifth Amazonian Symposium on Physics, Accepted in IJMPD | null | 10.1142/S0218271820410114 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss exact scalar field solutions describing gravitating compact
objects in the Eddington-inspired Born-Infeld gravity (EiBI), a member of the
class of (metric-affine formulated) Ricci-based gravity theories (RBGs). We
include a detailed account of the RBGs/GR correspondence exploited to
analytically solve the field equations. The single parameter $\e$ of the EiBI
model defines two branches for the solution. The $\e>0$ branch may be described
as a `shell with no interior', and constitutes an ill-defined, geodesically
incomplete spacetime. The more interesting $\e<0$ branch admits the
interpretation of a `wormhole membrane', an exotic horizonless compact object
with the ability to transfer particles and light from any point on its surface
(located slightly below the would-be Schwarzschild radius) to its antipodal
point, in a vanishing fraction of proper time. This is a single example
illustrating how the structural modifications introduced by the metric-affine
formulation may lead to significant departures from GR even at astrophysically
relevant scales, giving rise to physically plausible objects radically
different from those we are used to think of in the metric approach, and that
could act as a black hole mimickers whose shadows might present distinguishable
signals.
| [
{
"created": "Wed, 22 Apr 2020 19:01:38 GMT",
"version": "v1"
}
] | 2020-07-21 | [
[
"Afonso",
"Victor I.",
""
]
] | We discuss exact scalar field solutions describing gravitating compact objects in the Eddington-inspired Born-Infeld gravity (EiBI), a member of the class of (metric-affine formulated) Ricci-based gravity theories (RBGs). We include a detailed account of the RBGs/GR correspondence exploited to analytically solve the field equations. The single parameter $\e$ of the EiBI model defines two branches for the solution. The $\e>0$ branch may be described as a `shell with no interior', and constitutes an ill-defined, geodesically incomplete spacetime. The more interesting $\e<0$ branch admits the interpretation of a `wormhole membrane', an exotic horizonless compact object with the ability to transfer particles and light from any point on its surface (located slightly below the would-be Schwarzschild radius) to its antipodal point, in a vanishing fraction of proper time. This is a single example illustrating how the structural modifications introduced by the metric-affine formulation may lead to significant departures from GR even at astrophysically relevant scales, giving rise to physically plausible objects radically different from those we are used to think of in the metric approach, and that could act as a black hole mimickers whose shadows might present distinguishable signals. |
2008.13744 | Pedro Pessoa | Pedro Pessoa, Bruno Arderucio Costa | Comment on "Black Hole Entropy: A Closer Look" | null | Entropy 2020, 22(10), 1110 | 10.3390/e22101110 | null | gr-qc cond-mat.stat-mech physics.data-an | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a recent paper [Entropy 2020, 22(1), 17] C. Tsallis states that entropy --
as in Shannon's or Kullback-Leiber's definitions -- is inadequate to interpret
black hole entropy and suggests that a new non-additive functional should take
the role of entropy. Here we counter argue by explaining the important
distinction between the properties of extensivity and additivity, the latter is
fundamental for entropy while the former is a property of particular
thermodynamical systems that is not expected on black holes. We also point out
other debatable statements in his analysis of black hole entropy.
| [
{
"created": "Mon, 31 Aug 2020 17:08:15 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Sep 2020 20:21:45 GMT",
"version": "v2"
}
] | 2021-03-23 | [
[
"Pessoa",
"Pedro",
""
],
[
"Costa",
"Bruno Arderucio",
""
]
] | In a recent paper [Entropy 2020, 22(1), 17] C. Tsallis states that entropy -- as in Shannon's or Kullback-Leiber's definitions -- is inadequate to interpret black hole entropy and suggests that a new non-additive functional should take the role of entropy. Here we counter argue by explaining the important distinction between the properties of extensivity and additivity, the latter is fundamental for entropy while the former is a property of particular thermodynamical systems that is not expected on black holes. We also point out other debatable statements in his analysis of black hole entropy. |
gr-qc/0002009 | Eric Chassande-Mottin | E. Chassande-Mottin (1) and S. Dhurandhar (1 and 2) ((1)
Albert-Einstein-Institut, (2) IUCAA) | Adaptive filtering techniques for interferometric data preparation:
removal of long-term sinusoidal signals and oscillatory transients | 4 pages, 2 figures. Proceedings of GWDAW99 (Roma, Dec. 1999), to
appear in Int. J. Mod. Phys. D | Int.J.Mod.Phys. D9 (2000) 275-279 | 10.1142/S021827180000027X | AEI-2000-010 | gr-qc | null | We propose an adaptive denoising scheme for poorly modeled non-Gaussian
features in the gravitational wave interferometric data. Preliminary tests on
real data show encouraging results.
| [
{
"created": "Wed, 2 Feb 2000 16:51:47 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Chassande-Mottin",
"E.",
"",
"1 and 2"
],
[
"Dhurandhar",
"S.",
"",
"1 and 2"
]
] | We propose an adaptive denoising scheme for poorly modeled non-Gaussian features in the gravitational wave interferometric data. Preliminary tests on real data show encouraging results. |
2209.08202 | Zhaoyi Xu | Meirong Tang and Zhaoyi Xu | The no-hair theorem and black hole shadows | 19 pages, 11 figures | null | 10.1007/JHEP12(2022)125 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The successful observation of M87 supermassive black hole by the Black Hole
Event Horizon Telescope(EHT) provides a very good opportunity to study the
theory of gravity. In this work, we obtain the exact solution for the short
hair black hole (BH) in the rotation situation, and calculate in detail how
hairs affect the BH shadow. For the exact solution part, using the Newman-Janis
algorithm, we generalize the spherically symmetric short-hair black hole metric
to the rotation case (space-time lie element (2.25)). For the BH shadow part,
we study two hairy BH models. In model 1, the properties of scalar hair are
determined by the parameters $\alpha_{0}$ and $L$. In model 2, the scalar hair
of the BH is short hair. In this model, the shape of the BH shadow is
determined by scalar charge $Q_{m}$ and $k$. In general, various BH hairs have
different effects on the shadows, such as non-monotonic properties and
intersection phenomena mentioned in this work. Using these characteristics, it
is possible to test the no-hair theorem in future EHT observations, so as to
have a deeper understanding of the quantum effect of BHs. In future work, we
will use numerical simulations to study the effects of various hairs on BHs and
their observed properties.
| [
{
"created": "Sat, 17 Sep 2022 00:25:46 GMT",
"version": "v1"
}
] | 2023-01-04 | [
[
"Tang",
"Meirong",
""
],
[
"Xu",
"Zhaoyi",
""
]
] | The successful observation of M87 supermassive black hole by the Black Hole Event Horizon Telescope(EHT) provides a very good opportunity to study the theory of gravity. In this work, we obtain the exact solution for the short hair black hole (BH) in the rotation situation, and calculate in detail how hairs affect the BH shadow. For the exact solution part, using the Newman-Janis algorithm, we generalize the spherically symmetric short-hair black hole metric to the rotation case (space-time lie element (2.25)). For the BH shadow part, we study two hairy BH models. In model 1, the properties of scalar hair are determined by the parameters $\alpha_{0}$ and $L$. In model 2, the scalar hair of the BH is short hair. In this model, the shape of the BH shadow is determined by scalar charge $Q_{m}$ and $k$. In general, various BH hairs have different effects on the shadows, such as non-monotonic properties and intersection phenomena mentioned in this work. Using these characteristics, it is possible to test the no-hair theorem in future EHT observations, so as to have a deeper understanding of the quantum effect of BHs. In future work, we will use numerical simulations to study the effects of various hairs on BHs and their observed properties. |
gr-qc/0306076 | Thomas B. Bahder | Thomas B. Bahder | Relativity of GPS Measurement | 18 pages, 5 figures, ReVTeX4 | Phys.Rev. D68 (2003) 063005 | 10.1103/PhysRevD.68.063005 | null | gr-qc | null | The relativity of Global Positioning System (GPS) pseudorange measurements is
explored within the geometrical optics approximation in the curved space-time
near Earth. A space-time grid for navigation is created by the discontinuities
introduced in the electromagnetic field amplitude by the P-code broadcast by
the GPS satellites. We compute the world function of space-time near Earth, and
we use it to define a scalar phase function that describes the space-time grid.
We use this scalar phase function to define the measured pseudorange, which
turns out to be a two-point space-time scalar under generalized coordinate
transformations. Though the measured pseudorange is an invariant, it depends on
the world lines of the receiver and satellite. While two colocated receivers
measure two different pseudoranges to the same satellite, they obtain correct
position and time, independent of their velocity. We relate the measured
pseudorange to the geometry of space-time and find corrections to the
conventional model of pseudorange that are on the order of the gravitational
radius of the Earth.
| [
{
"created": "Tue, 17 Jun 2003 04:29:46 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Jul 2003 19:12:28 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Bahder",
"Thomas B.",
""
]
] | The relativity of Global Positioning System (GPS) pseudorange measurements is explored within the geometrical optics approximation in the curved space-time near Earth. A space-time grid for navigation is created by the discontinuities introduced in the electromagnetic field amplitude by the P-code broadcast by the GPS satellites. We compute the world function of space-time near Earth, and we use it to define a scalar phase function that describes the space-time grid. We use this scalar phase function to define the measured pseudorange, which turns out to be a two-point space-time scalar under generalized coordinate transformations. Though the measured pseudorange is an invariant, it depends on the world lines of the receiver and satellite. While two colocated receivers measure two different pseudoranges to the same satellite, they obtain correct position and time, independent of their velocity. We relate the measured pseudorange to the geometry of space-time and find corrections to the conventional model of pseudorange that are on the order of the gravitational radius of the Earth. |
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