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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1903.03836 | Rocco D'Agostino | Rocco D'Agostino | Holographic dark energy from nonadditive entropy: cosmological
perturbations and observational constraints | 10 pages, 4 figures. Accepted for publication in Physical Review D | Phys. Rev. D 99, 103524 (2019) | 10.1103/PhysRevD.99.103524 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We apply the holographic principle in the cosmological context through the
nonadditive Tsallis entropy, used to describe the thermodynamic properties of
nonstandard statistical systems such as the gravitational ones. Assuming the
future event horizon as the infrared cutoff, we build a dark energy model free
from cosmological inconsistencies, which includes standard thermodynamics and
standard holographic dark energy as a limiting case. We thus describe the
dynamics of Tsallis holographic dark energy in a flat FLRW background. Hence,
we investigate cosmological perturbations in the linear regime on sub-horizon
scales. We study the growth of matter fluctuations in the case of clustering
dark matter and a homogeneous dark energy component. Furthermore, we employ the
most recent late-time cosmic data to test the observational viability of our
theoretical scenario. We thus obtain constraints on the free parameters of the
model by means of Monte Carlo numerical method. We also used Bayesian selection
criteria to estimate the statistical preference for Tsallis holographic dark
energy compared to the concordance $\Lambda$CDM paradigm. Our results show
deviations from standard holographic dark energy within the $2\sigma$
confidence level. Finally, the analysis of the dark energy equation of state
indicates a quintessence-like behaviour with no evidence for phantom-divide
crossing at the $1\sigma$ level.
| [
{
"created": "Sat, 9 Mar 2019 17:47:14 GMT",
"version": "v1"
},
{
"created": "Tue, 7 May 2019 14:20:27 GMT",
"version": "v2"
}
] | 2019-05-29 | [
[
"D'Agostino",
"Rocco",
""
]
] | We apply the holographic principle in the cosmological context through the nonadditive Tsallis entropy, used to describe the thermodynamic properties of nonstandard statistical systems such as the gravitational ones. Assuming the future event horizon as the infrared cutoff, we build a dark energy model free from cosmological inconsistencies, which includes standard thermodynamics and standard holographic dark energy as a limiting case. We thus describe the dynamics of Tsallis holographic dark energy in a flat FLRW background. Hence, we investigate cosmological perturbations in the linear regime on sub-horizon scales. We study the growth of matter fluctuations in the case of clustering dark matter and a homogeneous dark energy component. Furthermore, we employ the most recent late-time cosmic data to test the observational viability of our theoretical scenario. We thus obtain constraints on the free parameters of the model by means of Monte Carlo numerical method. We also used Bayesian selection criteria to estimate the statistical preference for Tsallis holographic dark energy compared to the concordance $\Lambda$CDM paradigm. Our results show deviations from standard holographic dark energy within the $2\sigma$ confidence level. Finally, the analysis of the dark energy equation of state indicates a quintessence-like behaviour with no evidence for phantom-divide crossing at the $1\sigma$ level. |
2012.04476 | Saeed Ullah Khan | Saeed Ullah Khan and Jingli Ren | Circular geodesics in Kerr-Newman-Kasuya black hole | 5 pages, 2 figures | AIP Conference Proceedings 2319, 040005 (2021) | 10.1063/5.0039635 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | This article explores the characteristics of ergoregion, horizons and
circular geodesics around a Kerr-Newman-Kasuya black hole. We investigate the
effect of spin and dyonic charge parameters on ergoregion, event horizon and
static limit surface of the said black hole. We observed that both electric, as
well as magnetic charge parameters, results in decreasing the radii of event
horizon and static limit, whereas increasing the area of ergoregion. The
obtained results are compared with that acquired from Kerr and Schwarzschild
black holes. Moreover, we figured out the photons orbit of circular null
geodesics and studied the angular velocity of a particle within ergoregion.
| [
{
"created": "Sat, 5 Dec 2020 18:11:57 GMT",
"version": "v1"
}
] | 2021-02-09 | [
[
"Khan",
"Saeed Ullah",
""
],
[
"Ren",
"Jingli",
""
]
] | This article explores the characteristics of ergoregion, horizons and circular geodesics around a Kerr-Newman-Kasuya black hole. We investigate the effect of spin and dyonic charge parameters on ergoregion, event horizon and static limit surface of the said black hole. We observed that both electric, as well as magnetic charge parameters, results in decreasing the radii of event horizon and static limit, whereas increasing the area of ergoregion. The obtained results are compared with that acquired from Kerr and Schwarzschild black holes. Moreover, we figured out the photons orbit of circular null geodesics and studied the angular velocity of a particle within ergoregion. |
gr-qc/9402002 | Jorge Pullin | Jorge Pullin (Editor) | MATTERS OF GRAVITY, a newsletter for the gravity community, Number 3 | Number 3, Plain Tex, 37 pages | null | null | MOG-3 | gr-qc astro-ph | null | Table of contents
Editorial
Correspondents
Gravity News:
Open Letter to gravitational physicists, Beverly Berger
A Missouri relativist in King Gustav's Court, Clifford Will
Gary Horowitz wins the Xanthopoulos award, Abhay Ashtekar
Research briefs:
Gamma-ray bursts and their possible cosmological implications, Peter Meszaros
Current activity and results in laboratory gravity, Riley Newman
Update on representations of quantum gravity, Donald Marolf
Ligo project report: December 1993, Rochus E. Vogt
Dark matter or new gravity?, Richard Hammond
Conference reports:
Gravitational waves from coalescing compact binaries, Curt Cutler
Mach's principle: from Newton's bucket to quantum gravity, Dieter Brill
Cornelius Lanczos international centenary conference, David Brown
Third Midwest relativity conference, David Garfinkle
| [
{
"created": "Tue, 1 Feb 1994 19:19:52 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Pullin",
"Jorge",
"",
"Editor"
]
] | Table of contents Editorial Correspondents Gravity News: Open Letter to gravitational physicists, Beverly Berger A Missouri relativist in King Gustav's Court, Clifford Will Gary Horowitz wins the Xanthopoulos award, Abhay Ashtekar Research briefs: Gamma-ray bursts and their possible cosmological implications, Peter Meszaros Current activity and results in laboratory gravity, Riley Newman Update on representations of quantum gravity, Donald Marolf Ligo project report: December 1993, Rochus E. Vogt Dark matter or new gravity?, Richard Hammond Conference reports: Gravitational waves from coalescing compact binaries, Curt Cutler Mach's principle: from Newton's bucket to quantum gravity, Dieter Brill Cornelius Lanczos international centenary conference, David Brown Third Midwest relativity conference, David Garfinkle |
2306.09019 | Ronaldas Macas | Ronaldas Macas, Andrew Lundgren | A Sensitive Test of Non-Gaussianity in Gravitational-wave Detector Data | 6 pages, 3 figures. PRD accepted | null | 10.1103/PhysRevD.108.063016 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Methods for parameter estimation of gravitational-wave data assume that
detector noise is stationary and Gaussian. Real data deviates from these
assumptions, which causes bias in the inferred parameters and incorrect
estimates of the errors. We develop a sensitive test of non-Gaussianity for
real gravitational-wave data which measures meaningful parameters that can be
used to characterize these effects. As a test case, we investigate the quality
of data cleaning performed by the LIGO-Virgo-KAGRA collaboration around
GW200129, a binary black hole signal which overlapped with the noise produced
by the radio frequency modulation. We demonstrate that a significant portion of
the non-Gaussian noise is removed below 50 Hz, yet some of the noise still
remains after the cleaning; at frequencies above 85 Hz, there is no excess
noise removed. We also show that this method can quantify the amount of
non-Gaussian noise in continuous data, which is useful for general detector
noise investigations. To do that, we estimate the difference in non-Gaussian
noise in the presence and absence of light scattering noise.
| [
{
"created": "Thu, 15 Jun 2023 10:27:40 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Sep 2023 11:26:56 GMT",
"version": "v2"
}
] | 2023-09-22 | [
[
"Macas",
"Ronaldas",
""
],
[
"Lundgren",
"Andrew",
""
]
] | Methods for parameter estimation of gravitational-wave data assume that detector noise is stationary and Gaussian. Real data deviates from these assumptions, which causes bias in the inferred parameters and incorrect estimates of the errors. We develop a sensitive test of non-Gaussianity for real gravitational-wave data which measures meaningful parameters that can be used to characterize these effects. As a test case, we investigate the quality of data cleaning performed by the LIGO-Virgo-KAGRA collaboration around GW200129, a binary black hole signal which overlapped with the noise produced by the radio frequency modulation. We demonstrate that a significant portion of the non-Gaussian noise is removed below 50 Hz, yet some of the noise still remains after the cleaning; at frequencies above 85 Hz, there is no excess noise removed. We also show that this method can quantify the amount of non-Gaussian noise in continuous data, which is useful for general detector noise investigations. To do that, we estimate the difference in non-Gaussian noise in the presence and absence of light scattering noise. |
2205.04097 | Mudhahir Al-Ajmi | Mudhahir Al Ajmi and Mark Hindmarsh | Thermal suppression of bubble nucleation at first-order phase
transitions in the early Universe | 12 pages, 19 figures | null | null | HIP-2022-3/TH | gr-qc | http://creativecommons.org/licenses/by/4.0/ | One of the key observables in a gravitational wave power spectrum from a
first order phase transition in the early Universe is the mean bubble spacing,
which depends on the rate of nucleation of bubbles of the stable phase, as well
as the bubble wall speed. When the bubbles expand as deflagrations, it is
expected that the heating of the fluid in front of the phase boundary
suppresses the nucleation rate. We quantify the effect, showing that it
increases the mean bubble separation, and acts to enhance the gravitational
wave signal by a factor of up to order 10. The effect is largest for small wall
speeds and strong transitions.
| [
{
"created": "Mon, 9 May 2022 07:59:49 GMT",
"version": "v1"
}
] | 2022-05-10 | [
[
"Ajmi",
"Mudhahir Al",
""
],
[
"Hindmarsh",
"Mark",
""
]
] | One of the key observables in a gravitational wave power spectrum from a first order phase transition in the early Universe is the mean bubble spacing, which depends on the rate of nucleation of bubbles of the stable phase, as well as the bubble wall speed. When the bubbles expand as deflagrations, it is expected that the heating of the fluid in front of the phase boundary suppresses the nucleation rate. We quantify the effect, showing that it increases the mean bubble separation, and acts to enhance the gravitational wave signal by a factor of up to order 10. The effect is largest for small wall speeds and strong transitions. |
gr-qc/9703012 | Matthew S. Piper | W.B.Bonnor, M.S.Piper | Suppression of gravitational radiation | 10 pages LaTex | Class.Quant.Grav. 15 (1998) 955-963 | 10.1088/0264-9381/15/4/016 | null | gr-qc | null | We consider a burst of quadrupole gravitational radiation in the presence of
a large static mass $M$ situated at its source. Some of the radiation is
back-scattered off the static field of the large mass, forming a wave tail.
After the burst, the tail is a pure incoming wave, carrying energy back towards
the source. We calculate this energy, and, in a numerical example, compare it
with the outgoing wave energy. If $M$ is sufficiently large the incoming energy
can equal the outgoing energy, indicating that the primary outgoing wave is
completely suppressed.
| [
{
"created": "Wed, 5 Mar 1997 15:32:32 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Bonnor",
"W. B.",
""
],
[
"Piper",
"M. S.",
""
]
] | We consider a burst of quadrupole gravitational radiation in the presence of a large static mass $M$ situated at its source. Some of the radiation is back-scattered off the static field of the large mass, forming a wave tail. After the burst, the tail is a pure incoming wave, carrying energy back towards the source. We calculate this energy, and, in a numerical example, compare it with the outgoing wave energy. If $M$ is sufficiently large the incoming energy can equal the outgoing energy, indicating that the primary outgoing wave is completely suppressed. |
1210.6736 | Bibhas Majhi Ranjan | Bibhas Ranjan Majhi | Noether current of the surface term of Einstein-Hilbert action, Virasoro
algebra and entropy | V2: 18 pages, no figures, clarifications and references added | Advances in High Energy Physics 2013 (2013) 386342 | 10.1155/2013/386342 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/3.0/ | A derivation of Noether current from the surface term of Einstein-Hilbert
action is given. We show that the corresponding charge, calculated on the
horizon, is related to the Bekenstein-Hawking entropy. Also using the charge,
the same entropy is found based on the Virasoro algebra and Cardy formula
approach. In this approach, the relevant diffeomorphisms are found by imposing
a very simple physical argument: diffeomorphisms keep the horizon structure
invariant. This complements similar earlier results (arXiv:1204.1422) obtained
from York-Gibbons-Hawking surface term. Finally we discuss the technical
simplicities and improvements over the earlier attempts and also various
important physical implications.
| [
{
"created": "Thu, 25 Oct 2012 04:10:29 GMT",
"version": "v1"
},
{
"created": "Sat, 27 Oct 2012 11:06:02 GMT",
"version": "v2"
}
] | 2013-07-24 | [
[
"Majhi",
"Bibhas Ranjan",
""
]
] | A derivation of Noether current from the surface term of Einstein-Hilbert action is given. We show that the corresponding charge, calculated on the horizon, is related to the Bekenstein-Hawking entropy. Also using the charge, the same entropy is found based on the Virasoro algebra and Cardy formula approach. In this approach, the relevant diffeomorphisms are found by imposing a very simple physical argument: diffeomorphisms keep the horizon structure invariant. This complements similar earlier results (arXiv:1204.1422) obtained from York-Gibbons-Hawking surface term. Finally we discuss the technical simplicities and improvements over the earlier attempts and also various important physical implications. |
2208.05730 | Davide Batic | Davide Batic, Suzan Hamad Abdul Karim, Marek Nowakowski | On the eigenvalues of the fermionic angular eigenfunctions in the Kerr
metric | 11 pages | Entropy 2022, 24(8), 1083 | 10.3390/e24081083 | null | gr-qc hep-th math-ph math.MP | http://creativecommons.org/licenses/by-nc-sa/4.0/ | In view of a result recently published in the context of deformation theory
of linear Hamiltonian systems, we reconsider the eigenvalue problem associated
to the angular equation arising after the separation of the Dirac equation in
the Kerr metric and we show how efficiently a quasi-linear first order PDE for
the angular eigenvalues can be derived. We also prove that it is not possible
to obtain an ordinary differential equation for the eigenvalues where the role
of the independent variable is played by the particle energy or the black hole
mass. Finally, we construct new perturbative expansions for the eigenvalues in
the Kerr case and obtain an asymptotic formula for the eigenvalues in the case
of a Kerr naked singularity.
| [
{
"created": "Thu, 11 Aug 2022 09:52:26 GMT",
"version": "v1"
}
] | 2022-08-12 | [
[
"Batic",
"Davide",
""
],
[
"Karim",
"Suzan Hamad Abdul",
""
],
[
"Nowakowski",
"Marek",
""
]
] | In view of a result recently published in the context of deformation theory of linear Hamiltonian systems, we reconsider the eigenvalue problem associated to the angular equation arising after the separation of the Dirac equation in the Kerr metric and we show how efficiently a quasi-linear first order PDE for the angular eigenvalues can be derived. We also prove that it is not possible to obtain an ordinary differential equation for the eigenvalues where the role of the independent variable is played by the particle energy or the black hole mass. Finally, we construct new perturbative expansions for the eigenvalues in the Kerr case and obtain an asymptotic formula for the eigenvalues in the case of a Kerr naked singularity. |
1304.8122 | Slava G. Turyshev | Slava G. Turyshev and Viktor T. Toth | New perturbative method for solving the gravitational N-body problem in
the general theory of relativity | revtex4, 48 pages. arXiv admin note: text overlap with
arXiv:1109.1796 | Int.J.Mod.Phys.D24(6): 1550039 (2015) | 10.1142/S021827181550039X | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a new approach to describe the dynamics of an isolated,
gravitationally bound astronomical $N$-body system in the weak field and
slow-motion approximation of the general theory of relativity. Celestial bodies
are described using an arbitrary energy-momentum tensor and assumed to possess
any number of internal multipole moments. The solution of the gravitational
field equations in any reference frame is presented as a sum of three terms: i)
the inertial flat spacetime in that frame, ii) unperturbed solutions for each
body in the system that is covariantly transformed to the coordinates of this
frame, and iii) the gravitational interaction term. We use the harmonic gauge
conditions that allow reconstruction of a significant part of the structure of
the post-Galilean coordinate transformation functions relating global
coordinates of the inertial reference frame to the local coordinates of the
non-inertial frame associated with a particular body. The remaining parts of
these functions are determined from dynamical conditions, obtained by
constructing the relativistic proper reference frame associated with a
particular body. In this frame, the effect of external forces acting on the
body is balanced by the fictitious frame-reaction force that is needed to keep
the body at rest with respect to the frame, conserving its relativistic
three-momentum. The resulting post-Galilean coordinate transformations have an
approximate group structure that extends the Poincar'e group of global
transformations to the case of accelerating observers in a gravitational field
of $N$-body system. We present and discuss the structure of the metric tensors
corresponding to the reference frames involved, the rules for transforming
relativistic gravitational potentials, the coordinate transformations between
frames and the resulting relativistic equations of motion.
| [
{
"created": "Tue, 30 Apr 2013 19:17:48 GMT",
"version": "v1"
},
{
"created": "Tue, 24 Feb 2015 21:53:49 GMT",
"version": "v2"
},
{
"created": "Thu, 26 Mar 2015 20:33:35 GMT",
"version": "v3"
}
] | 2015-03-30 | [
[
"Turyshev",
"Slava G.",
""
],
[
"Toth",
"Viktor T.",
""
]
] | We present a new approach to describe the dynamics of an isolated, gravitationally bound astronomical $N$-body system in the weak field and slow-motion approximation of the general theory of relativity. Celestial bodies are described using an arbitrary energy-momentum tensor and assumed to possess any number of internal multipole moments. The solution of the gravitational field equations in any reference frame is presented as a sum of three terms: i) the inertial flat spacetime in that frame, ii) unperturbed solutions for each body in the system that is covariantly transformed to the coordinates of this frame, and iii) the gravitational interaction term. We use the harmonic gauge conditions that allow reconstruction of a significant part of the structure of the post-Galilean coordinate transformation functions relating global coordinates of the inertial reference frame to the local coordinates of the non-inertial frame associated with a particular body. The remaining parts of these functions are determined from dynamical conditions, obtained by constructing the relativistic proper reference frame associated with a particular body. In this frame, the effect of external forces acting on the body is balanced by the fictitious frame-reaction force that is needed to keep the body at rest with respect to the frame, conserving its relativistic three-momentum. The resulting post-Galilean coordinate transformations have an approximate group structure that extends the Poincar'e group of global transformations to the case of accelerating observers in a gravitational field of $N$-body system. We present and discuss the structure of the metric tensors corresponding to the reference frames involved, the rules for transforming relativistic gravitational potentials, the coordinate transformations between frames and the resulting relativistic equations of motion. |
gr-qc/0406042 | James E. Lidsey | James E. Lidsey, David J. Mulryne, N. J. Nunes and Reza Tavakol | Oscillatory Universes in Loop Quantum Cosmology and Initial Conditions
for Inflation | 6 pages, 4 figures | Phys.Rev.D70:063521,2004 | 10.1103/PhysRevD.70.063521 | null | gr-qc astro-ph hep-th | null | Positively-curved, oscillatory universes are studied within the context of
Loop Quantum Cosmology subject to a consistent semi-classical treatment. The
semi-classical effects are reformulated in terms of an effective phantom fluid
with a variable equation of state. In cosmologies sourced by a massless scalar
field, these effects lead to a universe that undergoes ever-repeating cycles of
expansion and contraction. The presence of a self-interaction potential for the
field breaks the symmetry of the cycles and can enable the oscillations to
establish the initial conditions for successful slow-roll inflation, even when
the field is initially at the minimum of its potential with a small kinetic
energy. The displacement of the field from its minimum is enhanced for lower
and more natural values of the parameter that sets the effective quantum
gravity scale. For sufficiently small values of this parameter, the universe
can enter a stage of eternal self-reproduction.
| [
{
"created": "Thu, 10 Jun 2004 15:40:42 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Aug 2004 10:33:39 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Lidsey",
"James E.",
""
],
[
"Mulryne",
"David J.",
""
],
[
"Nunes",
"N. J.",
""
],
[
"Tavakol",
"Reza",
""
]
] | Positively-curved, oscillatory universes are studied within the context of Loop Quantum Cosmology subject to a consistent semi-classical treatment. The semi-classical effects are reformulated in terms of an effective phantom fluid with a variable equation of state. In cosmologies sourced by a massless scalar field, these effects lead to a universe that undergoes ever-repeating cycles of expansion and contraction. The presence of a self-interaction potential for the field breaks the symmetry of the cycles and can enable the oscillations to establish the initial conditions for successful slow-roll inflation, even when the field is initially at the minimum of its potential with a small kinetic energy. The displacement of the field from its minimum is enhanced for lower and more natural values of the parameter that sets the effective quantum gravity scale. For sufficiently small values of this parameter, the universe can enter a stage of eternal self-reproduction. |
1807.07941 | Rajibul Shaikh | Rajibul Shaikh (TIFR Mumbai, India) | Wormholes with nonexotic matter in Born-Infeld gravity | 21 pages, no figure, matches published version | Phys. Rev. D 98, 064033 (2018) | 10.1103/PhysRevD.98.064033 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that, in contrast to general relativity, in Eddington-inspired
Born-Infeld gravity (EiBI), a violation of the null convergence condition does
not necessarily lead to a violation of the null energy condition, by
establishing a relationship between them. This serves as a motivation for
finding wormhole solutions which can be supported by nonexotic matter in this
gravity theory. We then obtain exact solutions of the field equations in EiBI
gravity coupled to arbitrary nonlinear electrodynamics and anisotropic fluids.
Depending on the signs and values of different parameters, the general
solutions can represent both black holes and wormholes. In this work, we
analyze the wormhole solutions. These wormholes are supported by nonexotic
matter, i.e., matter satisfying all the energy conditions. As special cases of
our general solutions, we work out several specific examples by considering
Maxwell, power-law, Born-Infeld electrodynamics models and a particular form of
an anisotropic fluid.
| [
{
"created": "Fri, 20 Jul 2018 16:57:29 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Sep 2018 16:58:29 GMT",
"version": "v2"
}
] | 2018-09-18 | [
[
"Shaikh",
"Rajibul",
"",
"TIFR Mumbai, India"
]
] | We show that, in contrast to general relativity, in Eddington-inspired Born-Infeld gravity (EiBI), a violation of the null convergence condition does not necessarily lead to a violation of the null energy condition, by establishing a relationship between them. This serves as a motivation for finding wormhole solutions which can be supported by nonexotic matter in this gravity theory. We then obtain exact solutions of the field equations in EiBI gravity coupled to arbitrary nonlinear electrodynamics and anisotropic fluids. Depending on the signs and values of different parameters, the general solutions can represent both black holes and wormholes. In this work, we analyze the wormhole solutions. These wormholes are supported by nonexotic matter, i.e., matter satisfying all the energy conditions. As special cases of our general solutions, we work out several specific examples by considering Maxwell, power-law, Born-Infeld electrodynamics models and a particular form of an anisotropic fluid. |
gr-qc/0404089 | Ujjal Debnath | Asit Banerjee, Ujjal Debnath, Subenoy Chakraborty | Higher Dimensional Szekeres' Space-time in Brans-Dicke Scalar Tensor
Theory | null | Int.J.Mod.Phys. D13 (2004) 1073-1084 | 10.1142/S0218271804005055 | null | gr-qc | null | The generalized Szekeres family of solution for quasi-spherical space-time of
higher dimensions are obtained in the scalar tensor theory of gravitation.
Brans-Dicke field equations expressed in Dicke's revised units are exhaustively
solved for all the subfamilies of the said family. A particular group of
solutions may also be interpreted as due to the presence of the so-called
C-field of Hoyle and Narlikar and for a chosen sign of the coupling parameter.
The models show either expansion from a big bang type of singularity or a
collapse with the turning point at a lower bound. There is one particular case
which starts from the big bang, reaches a maximum and collapses with the in
course of time to a crunch.
| [
{
"created": "Wed, 21 Apr 2004 11:10:25 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Banerjee",
"Asit",
""
],
[
"Debnath",
"Ujjal",
""
],
[
"Chakraborty",
"Subenoy",
""
]
] | The generalized Szekeres family of solution for quasi-spherical space-time of higher dimensions are obtained in the scalar tensor theory of gravitation. Brans-Dicke field equations expressed in Dicke's revised units are exhaustively solved for all the subfamilies of the said family. A particular group of solutions may also be interpreted as due to the presence of the so-called C-field of Hoyle and Narlikar and for a chosen sign of the coupling parameter. The models show either expansion from a big bang type of singularity or a collapse with the turning point at a lower bound. There is one particular case which starts from the big bang, reaches a maximum and collapses with the in course of time to a crunch. |
1408.5484 | Andrea Geralico | Donato Bini and Andrea Geralico | Extended bodies in a Kerr spacetime: exploring the role of a general
quadrupole tensor | 18 pages, 6 figures; published version. arXiv admin note: text
overlap with arXiv:1311.7512 | Class. Quantum Grav. 31, 075024 (2014) | 10.1088/0264-9381/31/7/075024 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The equatorial motion of extended bodies in a Kerr spacetime is investigated
in the framework of the Mathisson-Papapetrou-Dixon model, including the full
set of effective components of the quadrupole tensor. The numerical integration
of the associated equations shows the specific role of the mass and current
quadrupole moment components. While most of the literature on this topic is
limited to spin-induced (purely electric) quadrupole tensor, the present
analysis highlights the effect of a completely general quadrupole tensor on the
dynamics. The contribution of the magnetic-type components is indeed related to
a number of interesting features, e.g., enhanced inward/outward spiraling
behavior of the orbit and spin-flip-like effects, which may have observational
counterparts. Finally, the validity limit of the Mathisson-Papapetrou-Dixon
model is also discussed through explicit examples.
| [
{
"created": "Sat, 23 Aug 2014 10:32:45 GMT",
"version": "v1"
}
] | 2015-06-22 | [
[
"Bini",
"Donato",
""
],
[
"Geralico",
"Andrea",
""
]
] | The equatorial motion of extended bodies in a Kerr spacetime is investigated in the framework of the Mathisson-Papapetrou-Dixon model, including the full set of effective components of the quadrupole tensor. The numerical integration of the associated equations shows the specific role of the mass and current quadrupole moment components. While most of the literature on this topic is limited to spin-induced (purely electric) quadrupole tensor, the present analysis highlights the effect of a completely general quadrupole tensor on the dynamics. The contribution of the magnetic-type components is indeed related to a number of interesting features, e.g., enhanced inward/outward spiraling behavior of the orbit and spin-flip-like effects, which may have observational counterparts. Finally, the validity limit of the Mathisson-Papapetrou-Dixon model is also discussed through explicit examples. |
2010.15023 | Ali Mostafazadeh | Bahareh Azad, Farhang Loran, and Ali Mostafazadeh | Transmission of low-energy scalar waves through a traversable wormhole | 21 pages, 3 figures, references added, accepted for publication in
European Physical Journal C | null | 10.1140/epjc/s10052-020-08668-3 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the scattering of low-energy massless and massive minimally coupled
scalar fields by an asymptotically flat traversable wormhole. We provide a
comprehensive treatment of this problem offering analytic expressions for the
transmission and reflection amplitudes of the corresponding effective potential
and the absorption cross section of the wormhole. Our results, which are based
on a recently developed dynamical formulation of time-independent scattering
theory, apply to a large class of wormhole spacetimes including a wormhole with
a sharp transition, the Ellis wormhole, and a family of its generalizations.
| [
{
"created": "Wed, 28 Oct 2020 14:55:31 GMT",
"version": "v1"
},
{
"created": "Fri, 30 Oct 2020 06:54:07 GMT",
"version": "v2"
},
{
"created": "Sat, 14 Nov 2020 17:41:59 GMT",
"version": "v3"
}
] | 2020-12-30 | [
[
"Azad",
"Bahareh",
""
],
[
"Loran",
"Farhang",
""
],
[
"Mostafazadeh",
"Ali",
""
]
] | We study the scattering of low-energy massless and massive minimally coupled scalar fields by an asymptotically flat traversable wormhole. We provide a comprehensive treatment of this problem offering analytic expressions for the transmission and reflection amplitudes of the corresponding effective potential and the absorption cross section of the wormhole. Our results, which are based on a recently developed dynamical formulation of time-independent scattering theory, apply to a large class of wormhole spacetimes including a wormhole with a sharp transition, the Ellis wormhole, and a family of its generalizations. |
2311.06932 | Vasilis Oikonomou | Shin'ichi Nojiri, S.D. Odintsov, V.K. Oikonomou | Propagation of Gravitational Waves in Einstein--Gauss-Bonnet Gravity for
Cosmological and Spherically Symmetric Spacetimes | PRD Accepted | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we examine the propagation of gravitational waves in
cosmological and astrophysical spacetimes in the context of
Einstein--Gauss-Bonnet gravity, in view of the GW170817 event. The perspective
we approach the problem is to obtain a theory which can produce a gravitational
wave speed that is equal to that of light in the vacuum, or at least the speed
can be compatible with the constraints imposed by the GW170817 event. As we
show, in the context of Einstein--Gauss-Bonnet gravity, the propagation speed
of gravity waves in cosmological spacetimes can be compatible with the GW170817
event, and we reconstruct some viable models. However, the propagation of
gravity waves in spherically symmetric spacetimes violates the GW170817
constraints, thus it is impossible for the gravitational wave that propagates
in a spherically symmetric spacetime to have a propagating speed which is equal
to that of light in the vacuum. The same conclusion applies to the
Einstein--Gauss-Bonnet theory with two scalars. We discuss the possible
implications of our results on spherically symmetric spacetimes.
| [
{
"created": "Sun, 12 Nov 2023 19:12:05 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Nov 2023 22:13:44 GMT",
"version": "v2"
},
{
"created": "Sat, 27 Jan 2024 16:40:37 GMT",
"version": "v3"
}
] | 2024-01-30 | [
[
"Nojiri",
"Shin'ichi",
""
],
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
]
] | In this work, we examine the propagation of gravitational waves in cosmological and astrophysical spacetimes in the context of Einstein--Gauss-Bonnet gravity, in view of the GW170817 event. The perspective we approach the problem is to obtain a theory which can produce a gravitational wave speed that is equal to that of light in the vacuum, or at least the speed can be compatible with the constraints imposed by the GW170817 event. As we show, in the context of Einstein--Gauss-Bonnet gravity, the propagation speed of gravity waves in cosmological spacetimes can be compatible with the GW170817 event, and we reconstruct some viable models. However, the propagation of gravity waves in spherically symmetric spacetimes violates the GW170817 constraints, thus it is impossible for the gravitational wave that propagates in a spherically symmetric spacetime to have a propagating speed which is equal to that of light in the vacuum. The same conclusion applies to the Einstein--Gauss-Bonnet theory with two scalars. We discuss the possible implications of our results on spherically symmetric spacetimes. |
2302.07283 | Jonathan Oppenheim | Jonathan Oppenheim and Zachary Weller-Davies | Covariant path integrals for quantum fields back-reacting on classical
space-time | 8 pages plus 4 appendices | null | null | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We introduce configuration space path integrals for quantum fields
interacting with classical fields. We show that this can be done consistently
by proving that the dynamics are completely positive directly, without
resorting to master equation methods. These path integrals allow one to readily
impose space-time symmetries, including Lorentz invariance or diffeomorphism
invariance. They generalize and combine the Feynman-Vernon path integral of
open quantum systems and the stochastic path integral of classical stochastic
dynamics while respecting symmetry principles. We introduce a path integral
formulation of general relativity where the space-time metric is treated
classically, as well as a diffeomorphism invariant theory based on the trace of
Einstein's equations. The theory is a candidate for a fundamental theory that
reconciles general relativity with quantum mechanics.
| [
{
"created": "Tue, 14 Feb 2023 19:00:10 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Nov 2023 02:05:48 GMT",
"version": "v2"
}
] | 2023-11-16 | [
[
"Oppenheim",
"Jonathan",
""
],
[
"Weller-Davies",
"Zachary",
""
]
] | We introduce configuration space path integrals for quantum fields interacting with classical fields. We show that this can be done consistently by proving that the dynamics are completely positive directly, without resorting to master equation methods. These path integrals allow one to readily impose space-time symmetries, including Lorentz invariance or diffeomorphism invariance. They generalize and combine the Feynman-Vernon path integral of open quantum systems and the stochastic path integral of classical stochastic dynamics while respecting symmetry principles. We introduce a path integral formulation of general relativity where the space-time metric is treated classically, as well as a diffeomorphism invariant theory based on the trace of Einstein's equations. The theory is a candidate for a fundamental theory that reconciles general relativity with quantum mechanics. |
1101.3569 | Jan Schee | Zdenek Stuchlik and Jan Schee | Appearance of Keplerian discs orbiting Kerr superspinars | accepted in Classical and Quantum Gravity (September 1st, 2010) | Class.Quant.Grav.27:215017,2010 | 10.1088/0264-9381/27/21/215017 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study optical phenomena related to appearance of Keplerian accretion discs
orbiting Kerr superspinars predicted by the string theory. The superspinar
exterior is described by the standard Kerr naked singularity geometry breaking
the black hole limit on the internal angular momentum (spin). We construct
local photon escape cones for a variety of orbiting sources that enable to
determine the superspinars silhouette in the case of distant observers. We show
that the superspinar silhouette depends strongly on the assumed edge where the
external Kerr spacetime is joined to the internal spacetime governed by the
string theory and significantly differs from the black hole silhouette. The
appearance of the accretion disc is strongly dependent on the value of the
superspinar spin in both their shape and frequency shift profile. Apparent
extension of the disc grows significantly with growing spin, while the
frequency shift grows with descending spin. This behavior differs substantially
from appearance of discs orbiting black holes enabling thus, at least in
principle, to distinguish clearly the Kerr superspinars and black holes. In
vicinity of a Kerr superspinar the non-escaped photons have to be separated to
those captured by the superspinar and those being trapped in its strong
gravitational field leading to self-illumination of the disc that could even
influence its structure and causes self-reflection effect of radiation of the
disc. The amount of trapped photons grows with descending of the superspinar
spin. We thus can expect significant self-illumination effects in the field of
Kerr superspinars with near-extreme spin $a \sim 1$.
| [
{
"created": "Wed, 19 Jan 2011 08:57:25 GMT",
"version": "v1"
}
] | 2015-03-17 | [
[
"Stuchlik",
"Zdenek",
""
],
[
"Schee",
"Jan",
""
]
] | We study optical phenomena related to appearance of Keplerian accretion discs orbiting Kerr superspinars predicted by the string theory. The superspinar exterior is described by the standard Kerr naked singularity geometry breaking the black hole limit on the internal angular momentum (spin). We construct local photon escape cones for a variety of orbiting sources that enable to determine the superspinars silhouette in the case of distant observers. We show that the superspinar silhouette depends strongly on the assumed edge where the external Kerr spacetime is joined to the internal spacetime governed by the string theory and significantly differs from the black hole silhouette. The appearance of the accretion disc is strongly dependent on the value of the superspinar spin in both their shape and frequency shift profile. Apparent extension of the disc grows significantly with growing spin, while the frequency shift grows with descending spin. This behavior differs substantially from appearance of discs orbiting black holes enabling thus, at least in principle, to distinguish clearly the Kerr superspinars and black holes. In vicinity of a Kerr superspinar the non-escaped photons have to be separated to those captured by the superspinar and those being trapped in its strong gravitational field leading to self-illumination of the disc that could even influence its structure and causes self-reflection effect of radiation of the disc. The amount of trapped photons grows with descending of the superspinar spin. We thus can expect significant self-illumination effects in the field of Kerr superspinars with near-extreme spin $a \sim 1$. |
2304.10117 | Chaowanzhen Wang | Chao-Wan-Zhen Wang, Jin-Bao Zhu, Guo-Qing Huang, and Fu-Wen Shu | Testing the first law of black hole mechanics with gravitational waves | 8 pages, 4 figures, 4 tables | null | null | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The successful observation of gravitational waves has provided humanity with
an additional method to explore the universe, particularly black holes. In this
study, we utilize data from LIGO and Virgo gravitational wave observations to
test the first law of black hole mechanics, employing two different approaches.
We consider the secondary compact object as a perturbation to the primary black
hole before the merger, and the remnant black hole as a stationary black hole
after the merger. In the pre-merger and post-merger analysis, our results
demonstrate consistency with the first law, with an error level of approximate
25% at a 68% credibility level for GW190403 051519. In the full
inspiral-merger-ringdown analysis, our results show consistency with the first
law of black hole mechanics, with an error level of about 6% at a 68%
credibility level and 10% at a 95% credibility level for GW191219 163120.
Additionally, we observe that the higher the mass ratio of the gravitational
wave source, the more consistent our results are with the first law of black
hole mechanics. Overall, our study sheds light on the nature of compact binary
coalescence and their implications for black hole mechanics.
| [
{
"created": "Thu, 20 Apr 2023 06:43:06 GMT",
"version": "v1"
},
{
"created": "Tue, 25 Jun 2024 08:33:21 GMT",
"version": "v2"
}
] | 2024-06-26 | [
[
"Wang",
"Chao-Wan-Zhen",
""
],
[
"Zhu",
"Jin-Bao",
""
],
[
"Huang",
"Guo-Qing",
""
],
[
"Shu",
"Fu-Wen",
""
]
] | The successful observation of gravitational waves has provided humanity with an additional method to explore the universe, particularly black holes. In this study, we utilize data from LIGO and Virgo gravitational wave observations to test the first law of black hole mechanics, employing two different approaches. We consider the secondary compact object as a perturbation to the primary black hole before the merger, and the remnant black hole as a stationary black hole after the merger. In the pre-merger and post-merger analysis, our results demonstrate consistency with the first law, with an error level of approximate 25% at a 68% credibility level for GW190403 051519. In the full inspiral-merger-ringdown analysis, our results show consistency with the first law of black hole mechanics, with an error level of about 6% at a 68% credibility level and 10% at a 95% credibility level for GW191219 163120. Additionally, we observe that the higher the mass ratio of the gravitational wave source, the more consistent our results are with the first law of black hole mechanics. Overall, our study sheds light on the nature of compact binary coalescence and their implications for black hole mechanics. |
1705.06506 | Amirfarshad Bahrehbakhsh | Amirfarshad Bahrehbakhsh | FLRW Cosmology of Induced Dark Energy Model and Open Universe | Accepted for publication in Canadian Journal of Physics | Canadian Journal of Physics, 2017, 95(12): 1215-1218 | 10.1139/cjp-2016-0827 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the FLRW type cosmology of the Induced Dark Energy model and
illustrate that the extra terms emerging from the fifth dimension can play the
role of dark energy. The model predicts the expansion with deceleration at
early time and acceleration in late time for an open universe.
| [
{
"created": "Thu, 18 May 2017 10:15:55 GMT",
"version": "v1"
}
] | 2017-12-27 | [
[
"Bahrehbakhsh",
"Amirfarshad",
""
]
] | We investigate the FLRW type cosmology of the Induced Dark Energy model and illustrate that the extra terms emerging from the fifth dimension can play the role of dark energy. The model predicts the expansion with deceleration at early time and acceleration in late time for an open universe. |
1110.2408 | \"Ozg\"ur Akarsu | Suresh Kumar, Ozgur Akarsu | Bianchi type II models in the presence of perfect fluid and anisotropic
dark energy | 15 pages; 5 figures; matches the version published in The European
Physical Journal Plus | The European Physical Journal Plus 127 (2012) 64 | 10.1140/epjp/i2012-12064-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Spatially homogeneous but totally anisotropic and non-flat Bianchi type II
cosmological model has been studied in general relativity in the presence of
two minimally interacting fluids; a perfect fluid as the matter fluid and a
hypothetical anisotropic fluid as the dark energy fluid. The Einstein's field
equations have been solved by applying two kinematical ans\"{a}tze: we have
assumed the variation law for the mean Hubble parameter that yields a constant
value of deceleration parameter, and one of the components of the shear tensor
has been considered proportional to the mean Hubble parameter. We have
particularly dwelled on the accelerating models with non-divergent expansion
anisotropy as the Universe evolves. Yielding anisotropic pressure, the fluid we
consider in the context of dark energy, can produce results that can be
produced in the presence of isotropic fluid in accordance with the \Lambda CDM
cosmology. However, the derived model gives additional opportunities by being
able to allow kinematics that cannot be produced in the presence of fluids that
yield only isotropic pressure. We have obtained well behaving cases where the
anisotropy of the expansion and the anisotropy of the fluid converge to finite
values (include zero) in the late Universe. We have also showed that although
the metric we consider is totally anisotropic, the anisotropy of the dark
energy is constrained to be axially symmetric, as long as the overall energy
momentum tensor possesses zero shear stress.
| [
{
"created": "Tue, 11 Oct 2011 15:54:00 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Jun 2012 13:02:57 GMT",
"version": "v2"
}
] | 2012-06-18 | [
[
"Kumar",
"Suresh",
""
],
[
"Akarsu",
"Ozgur",
""
]
] | Spatially homogeneous but totally anisotropic and non-flat Bianchi type II cosmological model has been studied in general relativity in the presence of two minimally interacting fluids; a perfect fluid as the matter fluid and a hypothetical anisotropic fluid as the dark energy fluid. The Einstein's field equations have been solved by applying two kinematical ans\"{a}tze: we have assumed the variation law for the mean Hubble parameter that yields a constant value of deceleration parameter, and one of the components of the shear tensor has been considered proportional to the mean Hubble parameter. We have particularly dwelled on the accelerating models with non-divergent expansion anisotropy as the Universe evolves. Yielding anisotropic pressure, the fluid we consider in the context of dark energy, can produce results that can be produced in the presence of isotropic fluid in accordance with the \Lambda CDM cosmology. However, the derived model gives additional opportunities by being able to allow kinematics that cannot be produced in the presence of fluids that yield only isotropic pressure. We have obtained well behaving cases where the anisotropy of the expansion and the anisotropy of the fluid converge to finite values (include zero) in the late Universe. We have also showed that although the metric we consider is totally anisotropic, the anisotropy of the dark energy is constrained to be axially symmetric, as long as the overall energy momentum tensor possesses zero shear stress. |
1112.2511 | Winston Fairbairn | Winston J. Fairbairn, Catherine Meusburger | q-Deformation of Lorentzian spin foam models | 12 pages, 2 figures, Proceedings of the 3rd Quantum Gravity and
Quantum Geometry School (Zakopane, 2011), to appear in PoS | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct and analyse a quantum deformation of the Lorentzian EPRL model.
The model is based on the representation theory of the quantum Lorentz group
with real deformation parameter. We give a definition of the quantum EPRL
intertwiner, study its convergence and braiding properties and construct an
amplitude for the four-simplexes. We find that the resulting model is finite.
| [
{
"created": "Mon, 12 Dec 2011 11:09:51 GMT",
"version": "v1"
}
] | 2011-12-13 | [
[
"Fairbairn",
"Winston J.",
""
],
[
"Meusburger",
"Catherine",
""
]
] | We construct and analyse a quantum deformation of the Lorentzian EPRL model. The model is based on the representation theory of the quantum Lorentz group with real deformation parameter. We give a definition of the quantum EPRL intertwiner, study its convergence and braiding properties and construct an amplitude for the four-simplexes. We find that the resulting model is finite. |
2111.07731 | David Viennot | David Viennot | Fuzzy Schwarzschild (2+1)-spacetime | null | J. Math. Phys. 63, 082302 (2022) | 10.1063/5.0091364 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a toy model of fuzzy Schwarzschild space slice (as a
noncommutative manifold) which quantum mean values and quantum quasi-coherent
states (states minimizing the quantum uncertainties) have properties close to
the classical slice of the $(r,\theta)$ Schwarzschild coordinates (the
so-called Flamm's paraboloid). This fuzzy Schwarzschild slice is built as a
deformation of the noncommutative plane. Quantum time observables are
introduced to add a time quantization in the model. We study the structure of
the quasi-coherent state of the fuzzy Schwarzschild slice with respect to the
quasi-coherent state and the deformation states of the noncommutative plane .
The quantum dynamics of a fermion interacting with a fuzzy black hole described
by the present model is studied. In particular we study the decoherence effects
appearing in the neighborhood of the fuzzy event horizon. An extension of the
model to describe a quantum wormhole is also proposed, where we show that
fermions cross the wormhole not by traveling by its internal space but by
quantum tunneling, in accordance with the non-traversable character of
classical Einstein-Rosen bridges.
| [
{
"created": "Mon, 15 Nov 2021 13:22:24 GMT",
"version": "v1"
}
] | 2022-08-31 | [
[
"Viennot",
"David",
""
]
] | We present a toy model of fuzzy Schwarzschild space slice (as a noncommutative manifold) which quantum mean values and quantum quasi-coherent states (states minimizing the quantum uncertainties) have properties close to the classical slice of the $(r,\theta)$ Schwarzschild coordinates (the so-called Flamm's paraboloid). This fuzzy Schwarzschild slice is built as a deformation of the noncommutative plane. Quantum time observables are introduced to add a time quantization in the model. We study the structure of the quasi-coherent state of the fuzzy Schwarzschild slice with respect to the quasi-coherent state and the deformation states of the noncommutative plane . The quantum dynamics of a fermion interacting with a fuzzy black hole described by the present model is studied. In particular we study the decoherence effects appearing in the neighborhood of the fuzzy event horizon. An extension of the model to describe a quantum wormhole is also proposed, where we show that fermions cross the wormhole not by traveling by its internal space but by quantum tunneling, in accordance with the non-traversable character of classical Einstein-Rosen bridges. |
gr-qc/0109091 | Bayram Tekin | S. Deser and Bayram Tekin | Newtonian Counterparts of Spin 2 Massless Discontinuities | 6 pages, amplifies the ``Newtonian cosmology'' analysis. To appear as
a Class. Quantum Grav. Letter | Class.Quant.Grav.18:L171,2001 | 10.1088/0264-9381/18/23/103 | BRX-TH-495 | gr-qc hep-th | null | Massive spin 2 theories in flat or cosmological ($\Lambda \ne 0$) backgrounds
are subject to discontinuities as the masses tend to zero. We show and explain
physically why their Newtonian limits do not inherit this behaviour. On the
other hand, conventional ``Newtonian cosmology'', where $\Lambda $ is a
constant source of the potential, displays discontinuities: e.g. for any finite
range, $\Lambda$ can be totally removed.
| [
{
"created": "Thu, 27 Sep 2001 19:58:52 GMT",
"version": "v1"
},
{
"created": "Thu, 27 Sep 2001 21:17:30 GMT",
"version": "v2"
},
{
"created": "Fri, 26 Oct 2001 15:54:57 GMT",
"version": "v3"
}
] | 2010-04-06 | [
[
"Deser",
"S.",
""
],
[
"Tekin",
"Bayram",
""
]
] | Massive spin 2 theories in flat or cosmological ($\Lambda \ne 0$) backgrounds are subject to discontinuities as the masses tend to zero. We show and explain physically why their Newtonian limits do not inherit this behaviour. On the other hand, conventional ``Newtonian cosmology'', where $\Lambda $ is a constant source of the potential, displays discontinuities: e.g. for any finite range, $\Lambda$ can be totally removed. |
2401.17689 | Shao-Wen Wei | Shao-Wen Wei, Yuan-Chuan Zou, Yu-Peng Zhang, Yu-Xiao Liu | Constraining black hole parameters with the precessing jet nozzle of
M87* | 11 pages, 8 figures. Typos are corrected | null | null | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | Recently, Cui et al. [Nature \textbf{621}, 711 (2023)] reported that the jet
nozzle of M87* exhibits a precession with a period of approximately 11 years.
This finding strongly suggests that M87* is a spinning black hole with a tilted
accretion disk. In this paper, our aim is to utilize these observations to
constrain the parameters of the black hole. Firstly, we investigate the
properties of the tilted circular orbits and the innermost stable circular
orbits. The corresponding angular momentum, energy, and Carter constant for
both prograde and retrograde orbits are calculated. We find that, compared to
equatorial circular orbits, these quantities exhibit significant differences
for fixed tilt angles. Moreover, the Carter constant takes positive values for
nonvanishing tilt angles. Notably, the presence of misalignment of the orbit
angular momentum and black hole spin leads to a precession effect in these
tilted circular orbits. We then make use of these circular orbits to model the
warp radius of the tilted accretion disk, which allows us to determine the
corresponding precession period through the motion of massive particles.
Further comparing with the observation of M87*, the relationship between the
black hole spin and the warp radius is given, through which if one of them is
tested, the other one will be effectively determined. Additionally, our study
establishes an upper bound on the warp radius of the accretion disk. These
findings demonstrate that the precession of the jet nozzle offers a promising
approach for testing the physics of strong gravitational regions near a
supermassive black holes.
| [
{
"created": "Wed, 31 Jan 2024 09:18:22 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Feb 2024 09:22:02 GMT",
"version": "v2"
}
] | 2024-02-02 | [
[
"Wei",
"Shao-Wen",
""
],
[
"Zou",
"Yuan-Chuan",
""
],
[
"Zhang",
"Yu-Peng",
""
],
[
"Liu",
"Yu-Xiao",
""
]
] | Recently, Cui et al. [Nature \textbf{621}, 711 (2023)] reported that the jet nozzle of M87* exhibits a precession with a period of approximately 11 years. This finding strongly suggests that M87* is a spinning black hole with a tilted accretion disk. In this paper, our aim is to utilize these observations to constrain the parameters of the black hole. Firstly, we investigate the properties of the tilted circular orbits and the innermost stable circular orbits. The corresponding angular momentum, energy, and Carter constant for both prograde and retrograde orbits are calculated. We find that, compared to equatorial circular orbits, these quantities exhibit significant differences for fixed tilt angles. Moreover, the Carter constant takes positive values for nonvanishing tilt angles. Notably, the presence of misalignment of the orbit angular momentum and black hole spin leads to a precession effect in these tilted circular orbits. We then make use of these circular orbits to model the warp radius of the tilted accretion disk, which allows us to determine the corresponding precession period through the motion of massive particles. Further comparing with the observation of M87*, the relationship between the black hole spin and the warp radius is given, through which if one of them is tested, the other one will be effectively determined. Additionally, our study establishes an upper bound on the warp radius of the accretion disk. These findings demonstrate that the precession of the jet nozzle offers a promising approach for testing the physics of strong gravitational regions near a supermassive black holes. |
1404.0211 | Sravan Kumar Korumilli | K. Sravan Kumar, J. Marto, Nelson J. Nunes and Paulo Vargas Moniz | Inflation in a two 3-form fields scenario | Version accepted in JCAP. 22 pages, 12 figures, new refs added | JCAP06(2014)064 | 10.1088/1475-7516/2014/06/064 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A setting constituted by $\mathbb{N}$ 3-form fields, without any direct
interaction between them, minimally coupled to gravity, is introduced in this
paper as a framework to study the early evolution of the universe. We focus
particularly on the two 3-forms case. An inflationary scenario is found,
emerging from the coupling to gravity. More concretely, the fields coupled in
this manner exhibit a complex interaction, mediated by the time derivative of
the Hubble parameter. Our investigation is supported by means of a suitable
choice of potentials, employing numerical methods and analytical
approximations. In more detail, the oscillations on the small field limit
become correlated, and one field is intertwined with the other. In this type of
solution, a varying sound speed is present, together with the generation of
isocurvature perturbations. The mentioned features allow to consider an
interesting model, to test against observation. It is subsequently shown how
our results are consistent with current CMB data (viz.Planck and BICEP2).
| [
{
"created": "Tue, 1 Apr 2014 12:15:15 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Jul 2014 11:23:21 GMT",
"version": "v2"
}
] | 2014-07-04 | [
[
"Kumar",
"K. Sravan",
""
],
[
"Marto",
"J.",
""
],
[
"Nunes",
"Nelson J.",
""
],
[
"Moniz",
"Paulo Vargas",
""
]
] | A setting constituted by $\mathbb{N}$ 3-form fields, without any direct interaction between them, minimally coupled to gravity, is introduced in this paper as a framework to study the early evolution of the universe. We focus particularly on the two 3-forms case. An inflationary scenario is found, emerging from the coupling to gravity. More concretely, the fields coupled in this manner exhibit a complex interaction, mediated by the time derivative of the Hubble parameter. Our investigation is supported by means of a suitable choice of potentials, employing numerical methods and analytical approximations. In more detail, the oscillations on the small field limit become correlated, and one field is intertwined with the other. In this type of solution, a varying sound speed is present, together with the generation of isocurvature perturbations. The mentioned features allow to consider an interesting model, to test against observation. It is subsequently shown how our results are consistent with current CMB data (viz.Planck and BICEP2). |
1511.06210 | Axel de la Macorra | Leonardo Quintanar G., Axel de la Macorra | Cosmology and Quantum Field Theory: A study of the Nambu-Jona-Lasinio
Model | 17 pages, 11 figures | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We review the Nambu-Jona-Lasinio model (NJL), proposed long time ago, as a
four-fermion interaction theory with chiral symmetry. The theory is not
renormalizable and presents a symmetry breaking due to quantum corrections
which depends on the strength of the coupling constant. We may associate a
phase transition with this symmetry breaking, leading from a fermion massless
states to fermion condensates. This condensates can be described effectively by
a scalar field. We are interested in this paper in the cosmological dynamics of
the NJL model, and in the possibility that it can be related to dark energy
and/or dark matter, which form up to 95% of the energy content of the universe
at present time. We consider exclusively gravitational interaction between the
NJL and the SM particles.
| [
{
"created": "Thu, 19 Nov 2015 15:35:41 GMT",
"version": "v1"
}
] | 2015-11-20 | [
[
"G.",
"Leonardo Quintanar",
""
],
[
"de la Macorra",
"Axel",
""
]
] | We review the Nambu-Jona-Lasinio model (NJL), proposed long time ago, as a four-fermion interaction theory with chiral symmetry. The theory is not renormalizable and presents a symmetry breaking due to quantum corrections which depends on the strength of the coupling constant. We may associate a phase transition with this symmetry breaking, leading from a fermion massless states to fermion condensates. This condensates can be described effectively by a scalar field. We are interested in this paper in the cosmological dynamics of the NJL model, and in the possibility that it can be related to dark energy and/or dark matter, which form up to 95% of the energy content of the universe at present time. We consider exclusively gravitational interaction between the NJL and the SM particles. |
1706.05900 | Pierre-Henri Chavanis | Pierre-Henri Chavanis | Derivation of a generalized Schr\"odinger equation for dark matter halos
from the theory of scale relativity | null | Phys. Dark Univ. 22, 80 (2018) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using Nottale's theory of scale relativity, we derive a generalized
Schr\"odinger equation applying to dark matter halos. This equation involves a
logarithmic nonlinearity associated with an effective temperature and a source
of dissipation. Fundamentally, this wave equation arises from the
nondifferentiability of the trajectories of the dark matter particles whose
origin may be due to ordinary quantum mechanics, classical ergodic (or almost
ergodic) chaos, or to the fractal nature of spacetime at the cosmic scale. The
generalized Schr\"odinger equation involves a coefficient ${\cal D}$, possibly
different from $\hbar/2m$, whose value for dark matter halos is ${\cal
D}=1.02\times 10^{23}\, {\rm m^2/s}$. We suggest that the cold dark matter
crisis may be solved by the fractal (nondifferentiable) structure of spacetime
at the cosmic scale, or by the chaotic motion of the particles on a very long
timescale, instead of ordinary quantum mechanics. The equilibrium states of the
generalized Schr\"odinger equation correspond to configurations with a
core-halo structure. The quantumlike potential generates a solitonic core that
solves the cusp problem of the classical cold dark matter model. The
logarithmic nonlinearity accounts for the presence of an isothermal halo that
leads to flat rotation curves. The damping term ensures that the system relaxes
towards an equilibrium state. This property is guaranteed by an $H$-theorem
satisfied by a Boltzmann-like free energy functional. In our approach, the
temperature and the friction arise from a single formalism. They correspond to
the real and imaginary parts of the complex friction coefficient present in the
scale covariant equation of dynamics that is at the basis of Nottale's theory
of scale relativity.
| [
{
"created": "Mon, 19 Jun 2017 12:23:08 GMT",
"version": "v1"
},
{
"created": "Thu, 10 May 2018 18:10:04 GMT",
"version": "v2"
}
] | 2019-09-16 | [
[
"Chavanis",
"Pierre-Henri",
""
]
] | Using Nottale's theory of scale relativity, we derive a generalized Schr\"odinger equation applying to dark matter halos. This equation involves a logarithmic nonlinearity associated with an effective temperature and a source of dissipation. Fundamentally, this wave equation arises from the nondifferentiability of the trajectories of the dark matter particles whose origin may be due to ordinary quantum mechanics, classical ergodic (or almost ergodic) chaos, or to the fractal nature of spacetime at the cosmic scale. The generalized Schr\"odinger equation involves a coefficient ${\cal D}$, possibly different from $\hbar/2m$, whose value for dark matter halos is ${\cal D}=1.02\times 10^{23}\, {\rm m^2/s}$. We suggest that the cold dark matter crisis may be solved by the fractal (nondifferentiable) structure of spacetime at the cosmic scale, or by the chaotic motion of the particles on a very long timescale, instead of ordinary quantum mechanics. The equilibrium states of the generalized Schr\"odinger equation correspond to configurations with a core-halo structure. The quantumlike potential generates a solitonic core that solves the cusp problem of the classical cold dark matter model. The logarithmic nonlinearity accounts for the presence of an isothermal halo that leads to flat rotation curves. The damping term ensures that the system relaxes towards an equilibrium state. This property is guaranteed by an $H$-theorem satisfied by a Boltzmann-like free energy functional. In our approach, the temperature and the friction arise from a single formalism. They correspond to the real and imaginary parts of the complex friction coefficient present in the scale covariant equation of dynamics that is at the basis of Nottale's theory of scale relativity. |
gr-qc/9605072 | Michele Maggiore | A. Buonanno, M. Maggiore, and C. Ungarelli | Spectrum of relic gravitational waves in string cosmology | 12 pages, Latex,6 figures | Phys.Rev.D55:3330-3336,1997 | 10.1103/PhysRevD.55.3330 | IFUP-TH 25/96 | gr-qc astro-ph hep-th | null | We compute the spectrum of relic gravitons in a model of string cosmology. In
the low- and in the high-frequency limits we reproduce known results. The full
spectrum, however, also displays a series of oscillations which could give a
characteristic signature at the planned LIGO/VIRGO detectors. For special
values of the parameters of the model the signal reaches its maximum already at
frequencies accessible to LIGO and VIRGO and it is close to the sensitivity of
first generation experiments.
| [
{
"created": "Fri, 31 May 1996 13:04:27 GMT",
"version": "v1"
}
] | 2011-09-09 | [
[
"Buonanno",
"A.",
""
],
[
"Maggiore",
"M.",
""
],
[
"Ungarelli",
"C.",
""
]
] | We compute the spectrum of relic gravitons in a model of string cosmology. In the low- and in the high-frequency limits we reproduce known results. The full spectrum, however, also displays a series of oscillations which could give a characteristic signature at the planned LIGO/VIRGO detectors. For special values of the parameters of the model the signal reaches its maximum already at frequencies accessible to LIGO and VIRGO and it is close to the sensitivity of first generation experiments. |
1005.5730 | Rafael Porto | Rafael A. Porto | Next to leading order spin-orbit effects in the motion of inspiralling
compact binaries | 25 pages, 4 figures, revtex4. v2: minor changes, refs. added. To
appear in Class. Quant. Grav | Class.Quant.Grav.27:205001,2010 | 10.1088/0264-9381/27/20/205001 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using effective field theory (EFT) techniques we calculate the
next-to-leading order (NLO) spin-orbit contributions to the gravitational
potential of inspiralling compact binaries. We use the covariant spin
supplementarity condition (SSC), and explicitly prove the equivalence with
previous results by Faye et al. in arXiv:gr-qc/0605139. We also show that the
direct application of the Newton-Wigner SSC at the level of the action leads to
the correct dynamics using a canonical (Dirac) algebra. This paper then
completes the calculation of the necessary spin dynamics within the EFT
formalism that will be used in a separate paper to compute the spin
contributions to the energy flux and phase evolution to NLO.
| [
{
"created": "Mon, 31 May 2010 19:37:51 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Aug 2010 04:09:41 GMT",
"version": "v2"
}
] | 2014-11-21 | [
[
"Porto",
"Rafael A.",
""
]
] | Using effective field theory (EFT) techniques we calculate the next-to-leading order (NLO) spin-orbit contributions to the gravitational potential of inspiralling compact binaries. We use the covariant spin supplementarity condition (SSC), and explicitly prove the equivalence with previous results by Faye et al. in arXiv:gr-qc/0605139. We also show that the direct application of the Newton-Wigner SSC at the level of the action leads to the correct dynamics using a canonical (Dirac) algebra. This paper then completes the calculation of the necessary spin dynamics within the EFT formalism that will be used in a separate paper to compute the spin contributions to the energy flux and phase evolution to NLO. |
gr-qc/9604048 | Carl Brans | Carl H. Brans (Loyola University) | Exotic Smoothness on Spacetime | To appear in proceedings of Pacific Conference on Gravitation and
Cosmology, Seoul , 1996. LaTeX, 16 pages | null | 10.1007/978-94-011-5812-1_27 | null | gr-qc | null | Recent discoveries in differential topology are reviewed in light of their
possible implications for spacetime models and related subjects in theoretical
physics. Although not often noted, a particular smoothness (differentiability)
structure must be imposed on a topological manifold before geometric or other
structures of physical interest can be discussed. The recent discoveries of
interest here are of various surprising ``exotic'' smoothness structures on
topologically trivial manifolds such as ${S^7}$ and ${\bf R^4}$. Since no two
of these are diffeomorphic to each other, each such manifold represents a
physically distinct model of topologically trivial spacetime. That is, these
are not merely different coordinate representations of a given spacetime. The
path to such structures intertwines many branches of mathematics and
theoretical physics (Yang-Mills and other gauge theories). An overview of these
topics is provided, followed by certain results concerning the geometry and
physics of such manifolds. Although exotic ${\bf R^4}$'s cannot be effectively
exhibited by finite constructions, certain existence and non-existence results
can be stated. For example, it is shown that the ``exoticness'' can be confined
to a time-like world tube, providing a possible model for an exotic source.
Other suggestions and conjectures for future research are made.
| [
{
"created": "Wed, 24 Apr 1996 11:25:20 GMT",
"version": "v1"
}
] | 2016-01-27 | [
[
"Brans",
"Carl H.",
"",
"Loyola University"
]
] | Recent discoveries in differential topology are reviewed in light of their possible implications for spacetime models and related subjects in theoretical physics. Although not often noted, a particular smoothness (differentiability) structure must be imposed on a topological manifold before geometric or other structures of physical interest can be discussed. The recent discoveries of interest here are of various surprising ``exotic'' smoothness structures on topologically trivial manifolds such as ${S^7}$ and ${\bf R^4}$. Since no two of these are diffeomorphic to each other, each such manifold represents a physically distinct model of topologically trivial spacetime. That is, these are not merely different coordinate representations of a given spacetime. The path to such structures intertwines many branches of mathematics and theoretical physics (Yang-Mills and other gauge theories). An overview of these topics is provided, followed by certain results concerning the geometry and physics of such manifolds. Although exotic ${\bf R^4}$'s cannot be effectively exhibited by finite constructions, certain existence and non-existence results can be stated. For example, it is shown that the ``exoticness'' can be confined to a time-like world tube, providing a possible model for an exotic source. Other suggestions and conjectures for future research are made. |
0906.4983 | Yuuiti Sendouda | Nathalie Deruelle, Yuuiti Sendouda, Ahmed Youssef | Various Hamiltonian formulations of f(R) gravity and their canonical
relationships | 15 pages, REVTeX 4 | Phys.Rev.D80:084032,2009 | 10.1103/PhysRevD.80.084032 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Various Hamiltonian formulations of f(R) gravity can be found in the
literature. Some authors follow the Ostrogradsky treatment of higher derivative
theories and introduce as extra variables first order time derivatives of the
metric (typically the extrinsic curvature). Some others take advantage of the
conformal equivalence of f(R) theory with Einstein's gravity coupled to a
scalar field and introduce as an extra variable the scalar curvature R itself,
which includes second time derivatives of the metric. We show that, contrarily
to some claims, these formulations are related by canonical transformations.
| [
{
"created": "Fri, 26 Jun 2009 19:54:30 GMT",
"version": "v1"
}
] | 2009-11-05 | [
[
"Deruelle",
"Nathalie",
""
],
[
"Sendouda",
"Yuuiti",
""
],
[
"Youssef",
"Ahmed",
""
]
] | Various Hamiltonian formulations of f(R) gravity can be found in the literature. Some authors follow the Ostrogradsky treatment of higher derivative theories and introduce as extra variables first order time derivatives of the metric (typically the extrinsic curvature). Some others take advantage of the conformal equivalence of f(R) theory with Einstein's gravity coupled to a scalar field and introduce as an extra variable the scalar curvature R itself, which includes second time derivatives of the metric. We show that, contrarily to some claims, these formulations are related by canonical transformations. |
2112.13403 | Kristo Nugraha Lian | K. N. Lian | Gravity Theories via Algebra Gauging | 42 pages | null | null | null | gr-qc physics.comp-ph | http://creativecommons.org/licenses/by/4.0/ | This work presents instructive, yet comprehensive derivation of quantized
gravity theories in relativistic, classical, and semi-classical spacetime
structure based on the Poincar\'e, Galilean, and Bargmann algebra,
respectively. The technique of algebra gauging to construct the spacetime
dynamics - inspired by the approach of notable previous works - is introduced
to complement the standard vielbein formulation. The key characteristics and
anomalies of Galilean gravity will then be analyzed: the degenerate metric
structure, the additional degree of freedom in metric connection and the
additional necessary conditions of Galilean invariance among others. General
metric connection solution in Galilean spacetime differs fundamentally from
that of general relativity; this will be thoroughly investigated and an
explicit formula for such solution - equivalent to the parameterization by
Hartong and Obers (2015) - shall be derived. Multiple derivations of the
Bargmann algebra will be provided, together with both physical and algebraic
motivation for the extended Bargmann frame bundle. Finally, the physical impact
of constraining temporal torsion in classical spacetime will be discussed with
emphasis on the geometrical interpretation of time foliations.
| [
{
"created": "Sun, 26 Dec 2021 15:49:50 GMT",
"version": "v1"
},
{
"created": "Tue, 28 Dec 2021 07:17:45 GMT",
"version": "v2"
}
] | 2021-12-30 | [
[
"Lian",
"K. N.",
""
]
] | This work presents instructive, yet comprehensive derivation of quantized gravity theories in relativistic, classical, and semi-classical spacetime structure based on the Poincar\'e, Galilean, and Bargmann algebra, respectively. The technique of algebra gauging to construct the spacetime dynamics - inspired by the approach of notable previous works - is introduced to complement the standard vielbein formulation. The key characteristics and anomalies of Galilean gravity will then be analyzed: the degenerate metric structure, the additional degree of freedom in metric connection and the additional necessary conditions of Galilean invariance among others. General metric connection solution in Galilean spacetime differs fundamentally from that of general relativity; this will be thoroughly investigated and an explicit formula for such solution - equivalent to the parameterization by Hartong and Obers (2015) - shall be derived. Multiple derivations of the Bargmann algebra will be provided, together with both physical and algebraic motivation for the extended Bargmann frame bundle. Finally, the physical impact of constraining temporal torsion in classical spacetime will be discussed with emphasis on the geometrical interpretation of time foliations. |
gr-qc/0701009 | Sante Carloni | S Carloni, J A Leach, S Capozziello, P K S Dunsby | Cosmological dynamics of Scalar--Tensor Gravity | 25 pages, 4 figures, 12 tables, submitted to CQG | Class.Quant.Grav.25:035008,2008 | 10.1088/0264-9381/25/3/035008 | null | gr-qc | null | We study the phase--space of FLRW models derived from Scalar--Tensor Gravity
where the non--minimal coupling is $F(\phi)=\xi\phi^2$ and the effective
potential is $V(\phi)=\lambda \phi^n$. Our analysis allows to unfold many
feature of the cosmology of this class of theories. For example, the evolution
mechanism towards states indistinguishable from GR is recovered and proved to
depend critically on the form of the potential $V(\phi)$. Also, transient
almost--Friedmann phases evolving towards accelerated expansion and unstable
inflationary phases evolving towards stable ones are found. Some of our results
are shown to hold also for the String-Dilaton action.
| [
{
"created": "Sun, 31 Dec 2006 13:29:20 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Feb 2007 07:29:05 GMT",
"version": "v2"
},
{
"created": "Mon, 13 Aug 2007 15:30:13 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Carloni",
"S",
""
],
[
"Leach",
"J A",
""
],
[
"Capozziello",
"S",
""
],
[
"Dunsby",
"P K S",
""
]
] | We study the phase--space of FLRW models derived from Scalar--Tensor Gravity where the non--minimal coupling is $F(\phi)=\xi\phi^2$ and the effective potential is $V(\phi)=\lambda \phi^n$. Our analysis allows to unfold many feature of the cosmology of this class of theories. For example, the evolution mechanism towards states indistinguishable from GR is recovered and proved to depend critically on the form of the potential $V(\phi)$. Also, transient almost--Friedmann phases evolving towards accelerated expansion and unstable inflationary phases evolving towards stable ones are found. Some of our results are shown to hold also for the String-Dilaton action. |
1412.0867 | Francisco Lobo | Francisco S. N. Lobo | Beyond Einstein's General Relativity | 16 pages. Proceedings based on a plenary talk delivered at the
Spanish Relativity Meeting 2014 (ERE-2014). V2: references added, typos
corrected. V3: reference added | Journal of Physics: Conference Series 600 (2015) 012006 | 10.1088/1742-6596/600/1/012006 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Modern astrophysical and cosmological models are plagued with two severe
theoretical difficulties, namely, the dark energy and the dark matter problems.
Relative to the former, high-precision observational data have confirmed with
startling evidence that the Universe is undergoing a phase of accelerated
expansion. This phase, one of the most important and challenging current
problems in cosmology, represents a new imbalance in the governing
gravitational equations. Several candidates, responsible for this expansion,
have been proposed in the literature, in particular, dark energy models and
modified gravity, amongst others. Outstanding questions are related to the
nature of this so-called "dark energy" that is driving the acceleration of the
universe, and whether it is due to the vacuum energy or a dynamical field. On
the other hand, the late-time cosmic acceleration may be due to modifications
of General Relativity, which introduce new degrees of freedom to the
gravitational sector itself. We analyze some of the modified theories of
gravity that address these intriguing and exciting problems facing modern
physics, and explore the foundations of gravitation theory, essential for the
construction of modified theories of gravity.
| [
{
"created": "Tue, 2 Dec 2014 11:43:47 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Dec 2014 14:40:04 GMT",
"version": "v2"
},
{
"created": "Tue, 30 Dec 2014 22:25:11 GMT",
"version": "v3"
}
] | 2015-05-05 | [
[
"Lobo",
"Francisco S. N.",
""
]
] | Modern astrophysical and cosmological models are plagued with two severe theoretical difficulties, namely, the dark energy and the dark matter problems. Relative to the former, high-precision observational data have confirmed with startling evidence that the Universe is undergoing a phase of accelerated expansion. This phase, one of the most important and challenging current problems in cosmology, represents a new imbalance in the governing gravitational equations. Several candidates, responsible for this expansion, have been proposed in the literature, in particular, dark energy models and modified gravity, amongst others. Outstanding questions are related to the nature of this so-called "dark energy" that is driving the acceleration of the universe, and whether it is due to the vacuum energy or a dynamical field. On the other hand, the late-time cosmic acceleration may be due to modifications of General Relativity, which introduce new degrees of freedom to the gravitational sector itself. We analyze some of the modified theories of gravity that address these intriguing and exciting problems facing modern physics, and explore the foundations of gravitation theory, essential for the construction of modified theories of gravity. |
1606.02164 | Vasilis Oikonomou | V.K. Oikonomou | Gauss-Bonnet Cosmology Unifying Late and Early-time Acceleration Eras
with Intermediate Eras | null | null | 10.1007/s10509-016-2800-6 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we demonstrate that with vacuum $F(G)$ gravity it is possible
to describe the unification of late and early-time acceleration eras with the
radiation and matter domination era. The Hubble rate of the unified evolution
contains two mild singularities, so called Type IV singularities, and the
evolution itself has some appealing features, such as the existence of a
deceleration-acceleration transition at late times. We also address
quantitatively a fundamental question related to modified gravity models
description of cosmological evolution: Is it possible for all modified gravity
descriptions of our Universe evolution, to produce a nearly scale invariant
spectrum of primordial curvature perturbations? As we demonstrate, the answer
for the $F(G)$ description is no, since the resulting power spectrum is not
scale invariant, in contrast to the $F(R)$ description studied in the
literature. Therefore, although the cosmological evolution can be realized in
the context of vacuum $F(G)$ gravity, the evolution is not compatible with the
observational data, in contrast to the $F(R)$ gravity description of the same
cosmological evolution.
| [
{
"created": "Tue, 7 Jun 2016 14:59:41 GMT",
"version": "v1"
}
] | 2016-06-22 | [
[
"Oikonomou",
"V. K.",
""
]
] | In this paper we demonstrate that with vacuum $F(G)$ gravity it is possible to describe the unification of late and early-time acceleration eras with the radiation and matter domination era. The Hubble rate of the unified evolution contains two mild singularities, so called Type IV singularities, and the evolution itself has some appealing features, such as the existence of a deceleration-acceleration transition at late times. We also address quantitatively a fundamental question related to modified gravity models description of cosmological evolution: Is it possible for all modified gravity descriptions of our Universe evolution, to produce a nearly scale invariant spectrum of primordial curvature perturbations? As we demonstrate, the answer for the $F(G)$ description is no, since the resulting power spectrum is not scale invariant, in contrast to the $F(R)$ description studied in the literature. Therefore, although the cosmological evolution can be realized in the context of vacuum $F(G)$ gravity, the evolution is not compatible with the observational data, in contrast to the $F(R)$ gravity description of the same cosmological evolution. |
2103.15044 | Francesco Di Filippo | Katsuki Aoki, Francesco Di Filippo, Shinji Mukohyama | Non-uniqueness of massless transverse-traceless graviton | 19 pages, 1 figure | null | 10.1088/1475-7516/2021/05/071 | YITP-21-24, IPMU21-0021 | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study a theory of minimally modified gravity called cuscuton/VCDM that
propagates only two gravitational degrees of freedom. Despite being apparently
different from general relativity (GR), it is in principle possible that this
theory might be obtained via a field redefinition starting from the GR action.
This would make the vacuum theory equivalent to GR and the theory would differ
from GR only in the presence of matter. In this paper, studying the dispersion
relation of gravitational waves and the dynamics of the Bianchi-I universe, we
prove that such a field redefinition does not exist and that the theory differs
from GR already in vacuum.
| [
{
"created": "Sun, 28 Mar 2021 04:31:50 GMT",
"version": "v1"
}
] | 2021-06-02 | [
[
"Aoki",
"Katsuki",
""
],
[
"Di Filippo",
"Francesco",
""
],
[
"Mukohyama",
"Shinji",
""
]
] | We study a theory of minimally modified gravity called cuscuton/VCDM that propagates only two gravitational degrees of freedom. Despite being apparently different from general relativity (GR), it is in principle possible that this theory might be obtained via a field redefinition starting from the GR action. This would make the vacuum theory equivalent to GR and the theory would differ from GR only in the presence of matter. In this paper, studying the dispersion relation of gravitational waves and the dynamics of the Bianchi-I universe, we prove that such a field redefinition does not exist and that the theory differs from GR already in vacuum. |
2406.01632 | Muhammad Sharif | M. Sharif and K. Hassan | Compact Objects by Extended Gravitational Decoupling in f(G,T) Gravity | 33 pages, 9 figures | Indian J. Physics 98(2024)2633-2652 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we investigate the anisotropic interior spherically symmetric
solutions by utilizing the extended gravitational decoupling method in the
background of $f(G,T)$ gravity, where $G$ and $T$ signify the Gauss-Bonnet term
and trace of the stress-energy tensor, respectively. The anisotropy in the
interior geometry arises with the inclusion of an additional source in the
isotropic configuration. In this technique, the temporal and radial potentials
are decoupled which split the field equations into two independent sets. Both
sets individually represent the isotropic and anisotropic configurations,
respectively. The solution corresponding to the first set is determined by
using the Krori-Barua metric potentials whereas the second set contains unknown
which are solved with the help of some constraints. The ultimate anisotropic
results are evaluated by combining the solutions of both distributions. The
influence of decoupling parameter is examined on the matter variables as well
as anisotropic factor. We illustrate the viable and stable features of the
constructed solutions by using energy constraints and three stability criteria,
respectively. Finally, we conclude that the obtained solutions are viable as
well as stable for the whole domain of the coupling parameter.
| [
{
"created": "Sat, 1 Jun 2024 12:17:41 GMT",
"version": "v1"
}
] | 2024-06-05 | [
[
"Sharif",
"M.",
""
],
[
"Hassan",
"K.",
""
]
] | In this paper, we investigate the anisotropic interior spherically symmetric solutions by utilizing the extended gravitational decoupling method in the background of $f(G,T)$ gravity, where $G$ and $T$ signify the Gauss-Bonnet term and trace of the stress-energy tensor, respectively. The anisotropy in the interior geometry arises with the inclusion of an additional source in the isotropic configuration. In this technique, the temporal and radial potentials are decoupled which split the field equations into two independent sets. Both sets individually represent the isotropic and anisotropic configurations, respectively. The solution corresponding to the first set is determined by using the Krori-Barua metric potentials whereas the second set contains unknown which are solved with the help of some constraints. The ultimate anisotropic results are evaluated by combining the solutions of both distributions. The influence of decoupling parameter is examined on the matter variables as well as anisotropic factor. We illustrate the viable and stable features of the constructed solutions by using energy constraints and three stability criteria, respectively. Finally, we conclude that the obtained solutions are viable as well as stable for the whole domain of the coupling parameter. |
2112.06056 | Nishanth Abu Gudapati | Nishanth Gudapati | Energy Extraction, or Lack Thereof | a review, intended for a broader and interdisciplinary audience | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The problem of stability of rotating black holes is the subject of a long
standing research program since the 1960s and remains an unresolved problem in
general relativity. A major obstacle in the black hole stability problem is
that the energy of waves propagating through rotating black holes spacetimes is
not necessarily positive-definite, due to the so called ergo-region. This is a
serious complication that limits the efficacy of most mathematical techniques.
In this Letter, we report that, despite the ergo-region, there exists a
positive-definite \emph{total energy} for axisymmetric Maxwell, gravitational
and electrovacuum perturbations of Kerr and Kerr-Newman black hole spacetimes.
| [
{
"created": "Sat, 11 Dec 2021 19:42:50 GMT",
"version": "v1"
}
] | 2021-12-14 | [
[
"Gudapati",
"Nishanth",
""
]
] | The problem of stability of rotating black holes is the subject of a long standing research program since the 1960s and remains an unresolved problem in general relativity. A major obstacle in the black hole stability problem is that the energy of waves propagating through rotating black holes spacetimes is not necessarily positive-definite, due to the so called ergo-region. This is a serious complication that limits the efficacy of most mathematical techniques. In this Letter, we report that, despite the ergo-region, there exists a positive-definite \emph{total energy} for axisymmetric Maxwell, gravitational and electrovacuum perturbations of Kerr and Kerr-Newman black hole spacetimes. |
0908.4233 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | Theoretical construction of Morris-Thorne wormholes compatible with
quantum field theory | This paper is based on a talk given at the Center for Gravitation and
Cosmology (University of Wisconsin-Milwaukee), September, 2007. (Expanded
version with updated quantum inequalities) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper completes and extends some earlier studies by the author to show
that Morris-Thorne wormholes are compatible with quantum field theory. The
strategy is to strike a balance between reducing the size of the unavoidable
exotic region and the degree of fine-tuning of the metric coefficients required
to achieve this reduction, while simultaneously satisfying the constraints from
quantum field theory. The fine-tuning also serves to satisfy various
traversabilty criteria such as tidal constraints and proper distances through
the wormhole. The degree of fine-tuning turns out to be a generic feature of
the type of wormhole discussed.
| [
{
"created": "Fri, 28 Aug 2009 16:10:36 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Nov 2009 21:05:41 GMT",
"version": "v2"
},
{
"created": "Mon, 8 Nov 2010 01:06:58 GMT",
"version": "v3"
}
] | 2010-11-09 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | This paper completes and extends some earlier studies by the author to show that Morris-Thorne wormholes are compatible with quantum field theory. The strategy is to strike a balance between reducing the size of the unavoidable exotic region and the degree of fine-tuning of the metric coefficients required to achieve this reduction, while simultaneously satisfying the constraints from quantum field theory. The fine-tuning also serves to satisfy various traversabilty criteria such as tidal constraints and proper distances through the wormhole. The degree of fine-tuning turns out to be a generic feature of the type of wormhole discussed. |
1008.3244 | Jude Prezens Mr | Jude Prezens | The Double Kerr Solution as a Possible Mechanism for Controlled Global
Causality Violation | 10 pages, 2 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | For over 25 years, a solution has existed to Einstein's vacuum equation that
describes a space-time with two Kerr black holes. First formulated by Kramer
and Neugebauer (KN) in 1980 [1], this solution has been extensively researched
by many, with many and varied implications. One of which is causality
violation.
| [
{
"created": "Thu, 19 Aug 2010 09:04:35 GMT",
"version": "v1"
}
] | 2010-08-20 | [
[
"Prezens",
"Jude",
""
]
] | For over 25 years, a solution has existed to Einstein's vacuum equation that describes a space-time with two Kerr black holes. First formulated by Kramer and Neugebauer (KN) in 1980 [1], this solution has been extensively researched by many, with many and varied implications. One of which is causality violation. |
2004.06884 | Snehasish Bhattacharjee | Snehasish Bhattacharjee | Growth of matter fluctuations in $f(R,T)$ Gravity | Published in Chinese Journal of Physics | Chinese Journal of Physics, 68, 633-640 (2020) | 10.1016/j.cjph.2020.09.033 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | In this work, I present for the first time the analysis concerning the growth
of matter fluctuations in the framework of $f(R,T)$ modified gravity where I
presume $f(R,T) = R + \lambda T$, where $R$ denote the Ricci scalar, $T$ the
trace of the energy-momentum tensor and $\lambda$ a constant. I first solve the
Friedman equations assuming a dust universe ($\omega =0$) for the Hubble
parameter $H(z)$ and then employ it in the equation of matter density
fluctuations $\delta(z)$ to solve for $\delta(z)$ and the growth rate $f(z)$.
Next, I proceed to show the behavior of $f(z)$ and $\delta(z)$ with redshift
for some values of $\lambda$ with observational constraints. Finally, following
the prescription of \cite{growft41}, I present an analytical expression for the
growth index $\gamma$ which is redshift dependent and the expression reduces to
$3/5$ for $\lambda=0$, which is the growth index for a dust universe.
| [
{
"created": "Wed, 15 Apr 2020 05:15:06 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Sep 2020 13:57:18 GMT",
"version": "v2"
}
] | 2020-11-06 | [
[
"Bhattacharjee",
"Snehasish",
""
]
] | In this work, I present for the first time the analysis concerning the growth of matter fluctuations in the framework of $f(R,T)$ modified gravity where I presume $f(R,T) = R + \lambda T$, where $R$ denote the Ricci scalar, $T$ the trace of the energy-momentum tensor and $\lambda$ a constant. I first solve the Friedman equations assuming a dust universe ($\omega =0$) for the Hubble parameter $H(z)$ and then employ it in the equation of matter density fluctuations $\delta(z)$ to solve for $\delta(z)$ and the growth rate $f(z)$. Next, I proceed to show the behavior of $f(z)$ and $\delta(z)$ with redshift for some values of $\lambda$ with observational constraints. Finally, following the prescription of \cite{growft41}, I present an analytical expression for the growth index $\gamma$ which is redshift dependent and the expression reduces to $3/5$ for $\lambda=0$, which is the growth index for a dust universe. |
2102.00840 | Merce Guerrero | Merce Guerrero, Gonzalo J. Olmo, Diego Rubiera-Garcia | Double shadows of reflection-asymmetric wormholes supported by positive
energy thin-shells | 14 pages, 15 figures, revtex4-1 style | null | 10.1088/1475-7516/2021/04/066 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We consider reflection-asymmetric thin-shell wormholes within Palatini
$f(\mathcal{R})$ gravity using a matching procedure of two patches of
electrovacuum space-times at a hypersurface (the shell) via suitable junction
conditions. The conditions for having (linearly) stable wormholes supported by
positive-energy matter sources are determined. We also identify some subsets of
parameters able to locate the shell radius above the event horizon (when
present) but below the photon sphere (on both sides). We illustrate with an
specific example that such two photon spheres allow an observer on one of the
sides of the wormhole to see another (circular) shadow in addition to the one
generated by its own photon sphere, which is due to the photons passing above
the maximum of the effective potential on its side and bouncing back across the
throat due to a higher effective potential on the other side. We finally
comment on the capability of these double shadows to seek for traces of new
gravitational physics beyond that described by General Relativity.
| [
{
"created": "Mon, 1 Feb 2021 13:54:16 GMT",
"version": "v1"
}
] | 2021-05-05 | [
[
"Guerrero",
"Merce",
""
],
[
"Olmo",
"Gonzalo J.",
""
],
[
"Rubiera-Garcia",
"Diego",
""
]
] | We consider reflection-asymmetric thin-shell wormholes within Palatini $f(\mathcal{R})$ gravity using a matching procedure of two patches of electrovacuum space-times at a hypersurface (the shell) via suitable junction conditions. The conditions for having (linearly) stable wormholes supported by positive-energy matter sources are determined. We also identify some subsets of parameters able to locate the shell radius above the event horizon (when present) but below the photon sphere (on both sides). We illustrate with an specific example that such two photon spheres allow an observer on one of the sides of the wormhole to see another (circular) shadow in addition to the one generated by its own photon sphere, which is due to the photons passing above the maximum of the effective potential on its side and bouncing back across the throat due to a higher effective potential on the other side. We finally comment on the capability of these double shadows to seek for traces of new gravitational physics beyond that described by General Relativity. |
gr-qc/9506026 | James E. Lidsey | James E. Lidsey | Wavefunctions for Highly Anisotropic Homogeneous Cosmologies | 11 pages, latex | Phys.Lett. B352 (1995) 207-213 | 10.1016/0370-2693(95)00494-6 | null | gr-qc | null | The canonical quantization of homogeneous cosmologies is considered in the
high anisotropic limit. Exact wavefunctions are found in this limit when the
momentum constraints are reduced at the classical level. Lorentzian solutions
that represent tunnelling from classically forbidden regimes are identified.
Solutions to the modified Wheeler-DeWitt equation are also found for the vacuum
Bianchi IX model when a quantum reduction of the momentum constraints is
considered.
| [
{
"created": "Thu, 15 Jun 1995 13:05:09 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Lidsey",
"James E.",
""
]
] | The canonical quantization of homogeneous cosmologies is considered in the high anisotropic limit. Exact wavefunctions are found in this limit when the momentum constraints are reduced at the classical level. Lorentzian solutions that represent tunnelling from classically forbidden regimes are identified. Solutions to the modified Wheeler-DeWitt equation are also found for the vacuum Bianchi IX model when a quantum reduction of the momentum constraints is considered. |
2107.12953 | Salah Nasri | Hemza Azri and Salah Nasri | Dynamical aspects of asymmetric Eddington gravity with scalar fields | null | Phys. Rev. D 104, 064028 (2021) | 10.1103/PhysRevD.104.064028 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In Eddington gravity, the action principle involves only the symmetric parts
of the connection and the Ricci tensor, with a metric that emerges
proportionally to the latter. Here, we relax this symmetric character, prolong
the action with the antisymmetric parts of the Ricci term, and allow for
various couplings with scalar fields. We propose two possible invariant actions
formed by distinct combinations of the independent Ricci tensors and show that
the generated metric must involve an additional antisymmetric part due to the
relaxation of the symmetrization property. The comprehensive study shows that
the second curvature influences the dynamics of the connection, hence its
solution in terms of the metric, and the evolution of the scalar fields. These
new dynamical features are expected to stand viable and to have interesting
implications in domains where scalar fields are indispensable.
| [
{
"created": "Tue, 27 Jul 2021 17:15:08 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Sep 2021 17:20:36 GMT",
"version": "v2"
}
] | 2021-09-10 | [
[
"Azri",
"Hemza",
""
],
[
"Nasri",
"Salah",
""
]
] | In Eddington gravity, the action principle involves only the symmetric parts of the connection and the Ricci tensor, with a metric that emerges proportionally to the latter. Here, we relax this symmetric character, prolong the action with the antisymmetric parts of the Ricci term, and allow for various couplings with scalar fields. We propose two possible invariant actions formed by distinct combinations of the independent Ricci tensors and show that the generated metric must involve an additional antisymmetric part due to the relaxation of the symmetrization property. The comprehensive study shows that the second curvature influences the dynamics of the connection, hence its solution in terms of the metric, and the evolution of the scalar fields. These new dynamical features are expected to stand viable and to have interesting implications in domains where scalar fields are indispensable. |
1011.4772 | Jaume Haro | Jaume Haro | Topics in Quantum Field Theory in Curved Space | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In these lectures we consider some topics of Quantum Field Theory in Curved
Space. In the first one particle creation in curved space is studied from a
mathematical point of view, especially, particle production at a given time
using the so called "instantaneous diagonalization method". Particle production
by strong electromagnetic fields (Schwinger's effect) and particle production
by moving mirrors simulating black hole collapse are also studied. In the
second lecture we calculate the re-normalized two-point function using the
adiabatic regularization. The conformally and minimally coupled cases are
considered for a scalar massive and massless field. We reproduce previous
results in a rigorous mathematical form and clarify some empirical
approximations and bounds. The re-normalized stress tensor is also calculated
in several situations. Finally, in last lecture quantum correction due to a
massless fields conformally coupled with gravity are considered in order to
study the avoidance of singularities that appear in the flat
Friedmann-Robertson-Walker (FRW) model.
| [
{
"created": "Mon, 22 Nov 2010 11:10:31 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Feb 2011 15:54:14 GMT",
"version": "v2"
}
] | 2011-02-07 | [
[
"Haro",
"Jaume",
""
]
] | In these lectures we consider some topics of Quantum Field Theory in Curved Space. In the first one particle creation in curved space is studied from a mathematical point of view, especially, particle production at a given time using the so called "instantaneous diagonalization method". Particle production by strong electromagnetic fields (Schwinger's effect) and particle production by moving mirrors simulating black hole collapse are also studied. In the second lecture we calculate the re-normalized two-point function using the adiabatic regularization. The conformally and minimally coupled cases are considered for a scalar massive and massless field. We reproduce previous results in a rigorous mathematical form and clarify some empirical approximations and bounds. The re-normalized stress tensor is also calculated in several situations. Finally, in last lecture quantum correction due to a massless fields conformally coupled with gravity are considered in order to study the avoidance of singularities that appear in the flat Friedmann-Robertson-Walker (FRW) model. |
1412.8282 | Mustapha Azreg-A\"inou | Mustapha Azreg-A\"inou | Confined-exotic-matter wormholes with no gluing effects -- Imaging
supermassive wormholes and black holes | 14 pages, 7 figures. Extended version. To appear in JCAP | JCAP07(2015)037 | 10.1088/1475-7516/2015/07/037 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We classify wormholes endowed with redshift effects and finite mass into
three types. Type I wormholes have their radial pressure dying out faster, as
one moves away from the throat, than any other component of the stress-energy
and thus violate the least the local energy conditions. In type II (resp. III)
wormholes the radial and transverse pressures are asymptotically proportional
and die out faster (resp. slower) than the energy density. We introduce a novel
and generalizable method for deriving, with no cutoff in the stress-energy or
gluing, a class of each of the three wormhole types. We focus on type I
wormholes and construct different asymptotically flat solutions with finite,
upper- and lower-bounded, mass $M$. It is observed that the radial pressure is
negative, and the null energy condition is violated, only inside a narrow
layer, adjacent to the throat, of relative spacial extent $\epsilon$. Reducing
the relative size of the layer, without harming the condition of
traversability, yields an inverse square law of $\epsilon$ versus $M$ for
supermassive wormholes. We show that the diameter of the shadow of this type I
supermassive wormhole overlaps with that of the black hole candidate at the
center of the Milky Way and that the recent derivation, using the up-to-date
millimeter-wavelength very long baseline interferometry made in Astrophys. J.
\textbf{795} 134 (2014) [arXiv:1409.4690], remains inconclusive.
We show that redshift-free wormholes, with positive energy density, have one
of their barotropic equations of state in the phantom regime (at least in the
region adjacent to the throat), have their stress energy tensor traceless, and
are anisotropic. They are all type III wormholes having their variable
equations of state approaching 1 and $-1$ at spatial infinity. We also
introduce a new approach for deriving new redshift-free wormholes.
| [
{
"created": "Mon, 29 Dec 2014 08:52:02 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Jul 2015 11:56:44 GMT",
"version": "v2"
}
] | 2015-07-27 | [
[
"Azreg-Aïnou",
"Mustapha",
""
]
] | We classify wormholes endowed with redshift effects and finite mass into three types. Type I wormholes have their radial pressure dying out faster, as one moves away from the throat, than any other component of the stress-energy and thus violate the least the local energy conditions. In type II (resp. III) wormholes the radial and transverse pressures are asymptotically proportional and die out faster (resp. slower) than the energy density. We introduce a novel and generalizable method for deriving, with no cutoff in the stress-energy or gluing, a class of each of the three wormhole types. We focus on type I wormholes and construct different asymptotically flat solutions with finite, upper- and lower-bounded, mass $M$. It is observed that the radial pressure is negative, and the null energy condition is violated, only inside a narrow layer, adjacent to the throat, of relative spacial extent $\epsilon$. Reducing the relative size of the layer, without harming the condition of traversability, yields an inverse square law of $\epsilon$ versus $M$ for supermassive wormholes. We show that the diameter of the shadow of this type I supermassive wormhole overlaps with that of the black hole candidate at the center of the Milky Way and that the recent derivation, using the up-to-date millimeter-wavelength very long baseline interferometry made in Astrophys. J. \textbf{795} 134 (2014) [arXiv:1409.4690], remains inconclusive. We show that redshift-free wormholes, with positive energy density, have one of their barotropic equations of state in the phantom regime (at least in the region adjacent to the throat), have their stress energy tensor traceless, and are anisotropic. They are all type III wormholes having their variable equations of state approaching 1 and $-1$ at spatial infinity. We also introduce a new approach for deriving new redshift-free wormholes. |
2303.16590 | Parth Bambhaniya | Kauntey Acharya, Kshitij Pandey, Parth Bambhaniya, Pankaj S. Joshi and
Vishva Patel | Naked Singularity as a Possible Source of Ultra-High Energy Cosmic Rays | Calculation errors | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The source of Ultra-High Energy Cosmic Rays (UHECRs) remains one of the
greatest mysteries in astrophysics. Their possible source can be the galactic
nuclei, where the ultra-high gravity region plays a crucial role. Cosmic rays
are extremely energetic particles that travel through space with energies
exceeding $10^{20}eV$, but their origin is still a mystery despite years of
studies and observations. In view of this, in this work, we studied the
Joshi-Malafarina-Narayan (JMN-1) naked singularity as a natural particle
accelerator. We derived the necessary expressions to find center of mass energy
when two particles collide. We have obtained results showing that center of
mass energy of the two particles will reach to Planck energy scale. This will
form a microscopic black hole which will decay in Hawking radiation, having
energy on the order of $10^{26} eV$ from the ultra-high gravity region of Sgr
A*. These outgoing highly energetic particles from the naked singularity could
be the possible sources of UHECRs.
| [
{
"created": "Wed, 29 Mar 2023 10:53:26 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Jul 2024 11:30:32 GMT",
"version": "v2"
}
] | 2024-07-18 | [
[
"Acharya",
"Kauntey",
""
],
[
"Pandey",
"Kshitij",
""
],
[
"Bambhaniya",
"Parth",
""
],
[
"Joshi",
"Pankaj S.",
""
],
[
"Patel",
"Vishva",
""
]
] | The source of Ultra-High Energy Cosmic Rays (UHECRs) remains one of the greatest mysteries in astrophysics. Their possible source can be the galactic nuclei, where the ultra-high gravity region plays a crucial role. Cosmic rays are extremely energetic particles that travel through space with energies exceeding $10^{20}eV$, but their origin is still a mystery despite years of studies and observations. In view of this, in this work, we studied the Joshi-Malafarina-Narayan (JMN-1) naked singularity as a natural particle accelerator. We derived the necessary expressions to find center of mass energy when two particles collide. We have obtained results showing that center of mass energy of the two particles will reach to Planck energy scale. This will form a microscopic black hole which will decay in Hawking radiation, having energy on the order of $10^{26} eV$ from the ultra-high gravity region of Sgr A*. These outgoing highly energetic particles from the naked singularity could be the possible sources of UHECRs. |
gr-qc/0604033 | Carlos Mendes | E. Abdalla, B. Cuadros-Melgar, A. B. Pavan, C. Molina | Stability and thermodynamics of brane black holes | 13 pages, 8 figures, published version | Nucl.Phys. B752 (2006) 40-59 | 10.1016/j.nuclphysb.2006.06.017 | null | gr-qc astro-ph hep-th | null | We consider scalar and axial gravitational perturbations of black hole
solutions in brane world scenarios. We show that perturbation dynamics is
surprisingly similar to the Schwarzschild case with strong indications that the
models are stable. Quasinormal modes and late-time tails are discussed. We also
study the thermodynamics of these scenarios verifying the universality of
Bekenstein's entropy bound as well as the applicability of 't Hooft's brickwall
method.
| [
{
"created": "Fri, 7 Apr 2006 18:28:48 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Aug 2006 21:47:08 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Abdalla",
"E.",
""
],
[
"Cuadros-Melgar",
"B.",
""
],
[
"Pavan",
"A. B.",
""
],
[
"Molina",
"C.",
""
]
] | We consider scalar and axial gravitational perturbations of black hole solutions in brane world scenarios. We show that perturbation dynamics is surprisingly similar to the Schwarzschild case with strong indications that the models are stable. Quasinormal modes and late-time tails are discussed. We also study the thermodynamics of these scenarios verifying the universality of Bekenstein's entropy bound as well as the applicability of 't Hooft's brickwall method. |
gr-qc/0701035 | Pouria Pedram | S. S. Gousheh, H. R. Sepangi, P. Pedram, M. Mirzaei | Canonical wave packets in quantum cosmology | 19 pages, 8 figures | Class.Quant.Grav.24:4377-4390,2007 | 10.1088/0264-9381/24/17/007 | null | gr-qc | null | We discuss the construction of wave packets resulting from the solutions of a
class of Wheeler-DeWitt equations in Robertson-Walker type cosmologies, for
arbitrary curvature. We show that there always exists a ``canonical initial
slope" for a given initial wave function, which optimizes some desirable
properties of the resulting wave packet, most importantly good
classical-quantum correspondence. This can be properly denoted as a canonical
wave packet. We introduce a general method for finding these canonical initial
slopes which is generalization of our earlier work.
| [
{
"created": "Fri, 5 Jan 2007 17:41:01 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Jan 2007 14:24:40 GMT",
"version": "v2"
},
{
"created": "Fri, 6 Apr 2007 16:33:19 GMT",
"version": "v3"
},
{
"created": "Mon, 20 Aug 2007 14:22:19 GMT",
"version": "v4"
}
] | 2008-11-26 | [
[
"Gousheh",
"S. S.",
""
],
[
"Sepangi",
"H. R.",
""
],
[
"Pedram",
"P.",
""
],
[
"Mirzaei",
"M.",
""
]
] | We discuss the construction of wave packets resulting from the solutions of a class of Wheeler-DeWitt equations in Robertson-Walker type cosmologies, for arbitrary curvature. We show that there always exists a ``canonical initial slope" for a given initial wave function, which optimizes some desirable properties of the resulting wave packet, most importantly good classical-quantum correspondence. This can be properly denoted as a canonical wave packet. We introduce a general method for finding these canonical initial slopes which is generalization of our earlier work. |
1501.02471 | Andronikos Paliathanasis | Michael Tsamparlis, Andronikos Paliathanasis, Leonidas Karpathopoulos | Exact solutions of Bianchi I spacetimes which admit Conformal Killing
vectors | 17 pages; 3 tables; accepted for publication by Gen. Relativ. Gravit | Gen.Rel.Grav. 47 (2015) 2, 15 | 10.1007/s10714-015-1856-x | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We develop a new method in order to classify the Bianchi I spacetimes which
admit conformal Killing vectors (CKV). The method is based on two propositions
which relate the CKVs of 1+(n-1) decomposable Riemannian spaces with the CKVs
of the (n-1) subspace and show that if 1+(n-1) space is conformally flat then
the (n-1) spacetime is maximally symmetric. The method is used to study the
conformal algebra of the Kasner spacetime and other less known Bianchi type I
matter solutions of General Relativity.
| [
{
"created": "Sun, 11 Jan 2015 16:51:35 GMT",
"version": "v1"
}
] | 2015-02-13 | [
[
"Tsamparlis",
"Michael",
""
],
[
"Paliathanasis",
"Andronikos",
""
],
[
"Karpathopoulos",
"Leonidas",
""
]
] | We develop a new method in order to classify the Bianchi I spacetimes which admit conformal Killing vectors (CKV). The method is based on two propositions which relate the CKVs of 1+(n-1) decomposable Riemannian spaces with the CKVs of the (n-1) subspace and show that if 1+(n-1) space is conformally flat then the (n-1) spacetime is maximally symmetric. The method is used to study the conformal algebra of the Kasner spacetime and other less known Bianchi type I matter solutions of General Relativity. |
1612.01462 | Juan D Reyes | Alejandro Corichi, Juan D. Reyes, and Tatjana Vuka\v{s}inac | Weakly Isolated Horizons: First order actions and gauge symmetries | 42 pages, 5 figures, 1 table | null | 10.1088/1361-6382/aa631c | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Isolated Horizons have played an important role in gravitational physics,
from characterization of the endpoint of black hole mergers to black hole
entropy. With an eye towards a canonical formulation we consider general
relativity in first order form. We focus on two issues: i) The role of the
internal gauge freedom in consistent formulations of the action principle, and
ii) the role a 3+1 decomposition has in the allowed internal gauge. We clarify
how the requirement of well posed variational principles compatible with
general weakly isolated horizons (WIHs) does lead to a partial gauge fixing in
the first order descriptions used previously in the literature. We consider the
Palatini action together with the Holst extension, with and without boundary
terms at the horizon. We show that, for the complete configuration space --with
no gauge fixing--, the Palatini action is differentiable without additional
surface terms at the WIH boundary, but the more general Holst action is not. A
surface term at the horizon --that renders the action for asymptotically flat
configurations differentiable-- makes the Holst action differentiable, but only
if one restricts configuration space and partially reduces the internal Lorentz
gauge. For the second issue, we show that upon performing a 3+1 decomposition
and imposing the time gauge, there is a further gauge reduction of the
Hamiltonian theory in terms of Ashtekar-Barbero variables to a $U(1)$-gauge
theory on the horizon. We show that even when the Holst action is
differentiable without additional surface terms or any gauge fixing for Type I
spherically symmetric (strongly) isolated horizons --and a preferred
foliation--, this result does not go through for more general isolated or
weakly isolated horizons. Our results represent the first comprehensive study
of these issues and clarify some contradictory statements found in the
literature.
| [
{
"created": "Mon, 5 Dec 2016 18:27:54 GMT",
"version": "v1"
}
] | 2017-03-29 | [
[
"Corichi",
"Alejandro",
""
],
[
"Reyes",
"Juan D.",
""
],
[
"Vukašinac",
"Tatjana",
""
]
] | Isolated Horizons have played an important role in gravitational physics, from characterization of the endpoint of black hole mergers to black hole entropy. With an eye towards a canonical formulation we consider general relativity in first order form. We focus on two issues: i) The role of the internal gauge freedom in consistent formulations of the action principle, and ii) the role a 3+1 decomposition has in the allowed internal gauge. We clarify how the requirement of well posed variational principles compatible with general weakly isolated horizons (WIHs) does lead to a partial gauge fixing in the first order descriptions used previously in the literature. We consider the Palatini action together with the Holst extension, with and without boundary terms at the horizon. We show that, for the complete configuration space --with no gauge fixing--, the Palatini action is differentiable without additional surface terms at the WIH boundary, but the more general Holst action is not. A surface term at the horizon --that renders the action for asymptotically flat configurations differentiable-- makes the Holst action differentiable, but only if one restricts configuration space and partially reduces the internal Lorentz gauge. For the second issue, we show that upon performing a 3+1 decomposition and imposing the time gauge, there is a further gauge reduction of the Hamiltonian theory in terms of Ashtekar-Barbero variables to a $U(1)$-gauge theory on the horizon. We show that even when the Holst action is differentiable without additional surface terms or any gauge fixing for Type I spherically symmetric (strongly) isolated horizons --and a preferred foliation--, this result does not go through for more general isolated or weakly isolated horizons. Our results represent the first comprehensive study of these issues and clarify some contradictory statements found in the literature. |
2207.02146 | Muhammad Sharif | M. Sharif and Shazmeena Iltaf | Anisotropic Tolman V Solutions by Decoupling Approach in $f(R,T^{2})$
Gravity | 29 pages, 9 figures | Physica Scripta 97(2022)075002 | 10.1088/1402-4896/ac74f2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper investigates the behavior of anisotropic static spheres that are
constructed by employing a minimal geometric deformation in the framework of
$f(R,T^{2})$ gravity ($T^{2}=T_{\zeta\nu}T^{\zeta\nu}$, $R$ is the Ricci scalar
and $T_{\zeta\nu}$ is the energy-momentum tensor). We consider a spherical
setup with two sources: seed and additional. It is assumed that the seed source
is isotropic whereas the new source is responsible for inducing anisotropy. We
deform the $g_{rr}$ component to split the field equations into two sets. The
first array corresponds to the isotropic solution whereas the second set
contains the effect of the anisotropic source. The system related to isotropic
source is determined by the metric potentials of Tolman V solution while three
solutions of the second set are constructed corresponding to three different
constraints. The physical acceptability of all solutions is checked through
energy conditions by employing the radius and mass of PSR J1614-2230 star. We
also examine the stability, mass, compactness and redshift of the obtained
solutions. We conclude that first two solutions satisfy the viability and
stability criteria only for small values of the decoupling parameter while
third solution is stable for its all possible values.
| [
{
"created": "Mon, 4 Jul 2022 03:15:20 GMT",
"version": "v1"
}
] | 2022-07-13 | [
[
"Sharif",
"M.",
""
],
[
"Iltaf",
"Shazmeena",
""
]
] | This paper investigates the behavior of anisotropic static spheres that are constructed by employing a minimal geometric deformation in the framework of $f(R,T^{2})$ gravity ($T^{2}=T_{\zeta\nu}T^{\zeta\nu}$, $R$ is the Ricci scalar and $T_{\zeta\nu}$ is the energy-momentum tensor). We consider a spherical setup with two sources: seed and additional. It is assumed that the seed source is isotropic whereas the new source is responsible for inducing anisotropy. We deform the $g_{rr}$ component to split the field equations into two sets. The first array corresponds to the isotropic solution whereas the second set contains the effect of the anisotropic source. The system related to isotropic source is determined by the metric potentials of Tolman V solution while three solutions of the second set are constructed corresponding to three different constraints. The physical acceptability of all solutions is checked through energy conditions by employing the radius and mass of PSR J1614-2230 star. We also examine the stability, mass, compactness and redshift of the obtained solutions. We conclude that first two solutions satisfy the viability and stability criteria only for small values of the decoupling parameter while third solution is stable for its all possible values. |
2002.08787 | Aritra Ghosh | Aditya Singh, Aritra Ghosh and Chandrasekhar Bhamidipati | Thermodynamic curvature of AdS black holes with dark energy | v3: revised version to appear in Front. Phys | null | 10.3389/fphy.2021.631471 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we study the effect of dark energy on the extended
thermodynamic structure and interacting microstructures of black holes in AdS,
through an analysis of thermodynamic geometry. Considering various limiting
cases of the novel equation of state obtained in charged rotating black holes
with quintessence, and taking enthalpy $H$ as the key potential in the extended
phase space, we scrutinize the behavior of the Ruppeiner curvature scalar $R$
in the entropy-pressure $(S,P)$-plane (or equivalently in the
temperature-volume ($T,V$)-plane). Analysis of $R$ empirically reveals that
dark energy parameterized by $\alpha$, significantly alters the dominant
interactions of neutral, charged and slowly rotating black hole
microstructures. In the Schwarzschild-AdS case: black holes smaller than a
certain size continue to have attractive interactions whereas larger black
holes are completely dominated by repulsive interactions which arise to due
dark energy. For charged or rotating AdS black holes with quintessence, $R$ can
change sign at multiple points depending upon the relation between $\alpha$ and
charge $q$ or angular momentum $J$. In particular, above a threshold value of
$\alpha$, $R$ is never negative at all, suggesting heuristically that the
repulsive interactions due to quintessence are long ranged as opposed to the
previously known short ranged repulsion in charged AdS black holes. A mean
field interaction potential is proposed whose extrema effectively capture the
points where the curvature $R$ changes sign.
| [
{
"created": "Thu, 20 Feb 2020 15:09:15 GMT",
"version": "v1"
},
{
"created": "Sat, 25 Apr 2020 11:22:01 GMT",
"version": "v2"
},
{
"created": "Thu, 4 Feb 2021 07:23:41 GMT",
"version": "v3"
}
] | 2021-02-05 | [
[
"Singh",
"Aditya",
""
],
[
"Ghosh",
"Aritra",
""
],
[
"Bhamidipati",
"Chandrasekhar",
""
]
] | In this paper, we study the effect of dark energy on the extended thermodynamic structure and interacting microstructures of black holes in AdS, through an analysis of thermodynamic geometry. Considering various limiting cases of the novel equation of state obtained in charged rotating black holes with quintessence, and taking enthalpy $H$ as the key potential in the extended phase space, we scrutinize the behavior of the Ruppeiner curvature scalar $R$ in the entropy-pressure $(S,P)$-plane (or equivalently in the temperature-volume ($T,V$)-plane). Analysis of $R$ empirically reveals that dark energy parameterized by $\alpha$, significantly alters the dominant interactions of neutral, charged and slowly rotating black hole microstructures. In the Schwarzschild-AdS case: black holes smaller than a certain size continue to have attractive interactions whereas larger black holes are completely dominated by repulsive interactions which arise to due dark energy. For charged or rotating AdS black holes with quintessence, $R$ can change sign at multiple points depending upon the relation between $\alpha$ and charge $q$ or angular momentum $J$. In particular, above a threshold value of $\alpha$, $R$ is never negative at all, suggesting heuristically that the repulsive interactions due to quintessence are long ranged as opposed to the previously known short ranged repulsion in charged AdS black holes. A mean field interaction potential is proposed whose extrema effectively capture the points where the curvature $R$ changes sign. |
0912.4907 | John W. Barrett | John W. Barrett, Winston J. Fairbairn, Frank Hellmann | Quantum gravity asymptotics from the SU(2) 15j symbol | approx 17 pages | null | 10.1142/S0217751X10049281 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The asymptotics of the SU(2) 15j symbol are obtained using coherent states
for the boundary data. The geometry of all non-suppressed boundary data is
given. For some boundary data, the resulting formula is interpreted in terms of
the Regge action of the geometry of a 4-simplex in 4-dimensional Euclidean
space. This asymptotic formula can be used to derive and extend the asymptotics
of the spin foam amplitudes for quantum gravity models. The relation of the
SU(2) Ooguri model to these quantum gravity models and their continuum
Lagrangians is discussed.
| [
{
"created": "Thu, 24 Dec 2009 20:08:41 GMT",
"version": "v1"
}
] | 2015-05-14 | [
[
"Barrett",
"John W.",
""
],
[
"Fairbairn",
"Winston J.",
""
],
[
"Hellmann",
"Frank",
""
]
] | The asymptotics of the SU(2) 15j symbol are obtained using coherent states for the boundary data. The geometry of all non-suppressed boundary data is given. For some boundary data, the resulting formula is interpreted in terms of the Regge action of the geometry of a 4-simplex in 4-dimensional Euclidean space. This asymptotic formula can be used to derive and extend the asymptotics of the spin foam amplitudes for quantum gravity models. The relation of the SU(2) Ooguri model to these quantum gravity models and their continuum Lagrangians is discussed. |
gr-qc/9609047 | null | M. Sawaguchi and C.-B. Kim | Reality conditions for (2+1)-dimensional gravity coupled with the Dirac
field | 13 pages, latex | Class.Quant.Grav. 14 (1997) 905-913 | 10.1088/0264-9381/14/4/008 | STUPP-96-148 | gr-qc | null | The canonical formalism of three dimensional gravity coupled with the Dirac
field is considered. We introduce complex variables to simplify the Dirac
brackets of canonical variables and examine the canonical structure of the
theory. We discuss the reality conditions which guarantee the equivalence
between the complex and real theory.
| [
{
"created": "Thu, 19 Sep 1996 09:55:36 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Sawaguchi",
"M.",
""
],
[
"Kim",
"C. -B.",
""
]
] | The canonical formalism of three dimensional gravity coupled with the Dirac field is considered. We introduce complex variables to simplify the Dirac brackets of canonical variables and examine the canonical structure of the theory. We discuss the reality conditions which guarantee the equivalence between the complex and real theory. |
1612.05263 | Davide Gerosa | Davide Gerosa, Ulrich Sperhake, Jakub Vo\v{s}mera | On the equal-mass limit of precessing black-hole binaries | 13 pages, 1 figure, accepted for publication in CQG | Class. Quantum Grav. 34, 6, 064004 (2017) | 10.1088/1361-6382/aa5e58 | null | gr-qc astro-ph.GA astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the inspiral dynamics of equal-mass precessing black-hole binaries
using multi-timescale techniques. The orbit-averaged post-Newtonian
evolutionary equations admit two constants of motion in the equal-mass limit,
namely the magnitude of the total spin $S$ and the effective spin $\xi$. This
feature makes the entire dynamics qualitatively different compared to the
generic unequal-mass case, where only $\xi$ is constant while the variable $S$
parametrizes the precession dynamics. For fixed individual masses and spin
magnitudes, an equal-mass black-hole inspiral is uniquely characterized by the
two parameters $(S,\xi)$: these two numbers completely determine the entire
evolution under the effect of radiation reaction. In particular, for equal-mass
binaries we find that (i) the black-hole binary spin morphology is constant
throughout the inspiral, and that (ii) the precessional motion of the two
black-hole spins about the total spin takes place on a longer timescale than
the precession of the total spin and the orbital plane about the total angular
momentum.
| [
{
"created": "Thu, 15 Dec 2016 21:00:03 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Mar 2017 20:03:44 GMT",
"version": "v2"
}
] | 2017-03-06 | [
[
"Gerosa",
"Davide",
""
],
[
"Sperhake",
"Ulrich",
""
],
[
"Vošmera",
"Jakub",
""
]
] | We analyze the inspiral dynamics of equal-mass precessing black-hole binaries using multi-timescale techniques. The orbit-averaged post-Newtonian evolutionary equations admit two constants of motion in the equal-mass limit, namely the magnitude of the total spin $S$ and the effective spin $\xi$. This feature makes the entire dynamics qualitatively different compared to the generic unequal-mass case, where only $\xi$ is constant while the variable $S$ parametrizes the precession dynamics. For fixed individual masses and spin magnitudes, an equal-mass black-hole inspiral is uniquely characterized by the two parameters $(S,\xi)$: these two numbers completely determine the entire evolution under the effect of radiation reaction. In particular, for equal-mass binaries we find that (i) the black-hole binary spin morphology is constant throughout the inspiral, and that (ii) the precessional motion of the two black-hole spins about the total spin takes place on a longer timescale than the precession of the total spin and the orbital plane about the total angular momentum. |
0710.2667 | Volker Perlick | Volker Perlick | On the generalized Jacobi equation | Contribution to Mashhoon Festschrift (Special Issue of Gen. Rel.
Grav.). 17 pages, 2 figures | Gen.Rel.Grav.40:1029-1045,2008 | 10.1007/s10714-007-0589-x | null | gr-qc | null | The standard text-book Jacobi equation (equation of geodesic deviation)
arises by linearizing the geodesic equation around some chosen geodesic, where
the linearization is done with respect to the coordinates and the velocities.
The generalized Jacobi equation, introduced by Hodgkinson in 1972 and further
developed by Mashhoon and others, arises if the linearization is done only with
respect to the coordinates, but not with respect to the velocities. The
resulting equation has been studied by several authors in some detail for
timelike geodesics in a Lorentzian manifold. Here we begin by briefly
considering the generalized Jacobi equation on affine manifolds, without a
metric; then we specify to lightlike geodesics in a Lorentzian manifold. We
illustrate the latter case by considering particular lightlike geodesics (a) in
Schwarzschild spacetime and (b) in a plane-wave spacetime.
| [
{
"created": "Sun, 14 Oct 2007 14:18:45 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Perlick",
"Volker",
""
]
] | The standard text-book Jacobi equation (equation of geodesic deviation) arises by linearizing the geodesic equation around some chosen geodesic, where the linearization is done with respect to the coordinates and the velocities. The generalized Jacobi equation, introduced by Hodgkinson in 1972 and further developed by Mashhoon and others, arises if the linearization is done only with respect to the coordinates, but not with respect to the velocities. The resulting equation has been studied by several authors in some detail for timelike geodesics in a Lorentzian manifold. Here we begin by briefly considering the generalized Jacobi equation on affine manifolds, without a metric; then we specify to lightlike geodesics in a Lorentzian manifold. We illustrate the latter case by considering particular lightlike geodesics (a) in Schwarzschild spacetime and (b) in a plane-wave spacetime. |
gr-qc/0304055 | Guillermo A. Mena Marugan | Luis J. Garay and Guillermo A. Mena Marugan | Immirzi Ambiguity, Boosts and Conformal Frames for Black Holes | 8 pages, accepted for publication in Classical and Quantum Gravity | null | 10.1088/0264-9381/20/8/103 | null | gr-qc | null | We analyze changes of the Immirzi parameter in loop quantum gravity and
compare their consequences with those of Lorentz boosts and constant conformal
transformations in black hole physics. We show that the effective value deduced
for the Planck length in local measurements of vacuum black holes by an
asymptotic observer may depend on its conformal or Lorentz frame. This
introduces an apparent ambiguity in the expression of the black hole entropy
which is analogous to that produced by the Immirzi parameter. For quantities
involving a notion of energy, the similarity between the implications of the
Immirzi ambiguity and a conformal scaling disappears, but the parallelism with
boosts is maintained.
| [
{
"created": "Tue, 15 Apr 2003 09:36:03 GMT",
"version": "v1"
}
] | 2017-08-23 | [
[
"Garay",
"Luis J.",
""
],
[
"Marugan",
"Guillermo A. Mena",
""
]
] | We analyze changes of the Immirzi parameter in loop quantum gravity and compare their consequences with those of Lorentz boosts and constant conformal transformations in black hole physics. We show that the effective value deduced for the Planck length in local measurements of vacuum black holes by an asymptotic observer may depend on its conformal or Lorentz frame. This introduces an apparent ambiguity in the expression of the black hole entropy which is analogous to that produced by the Immirzi parameter. For quantities involving a notion of energy, the similarity between the implications of the Immirzi ambiguity and a conformal scaling disappears, but the parallelism with boosts is maintained. |
2301.03504 | Juan M. Z\'arate Pretel | Juan M. Z. Pretel | Radial pulsations, moment of inertia and tidal deformability of dark
energy stars | 15 pages, 9 figures and 2 tables. Accepted for publication in
European Physical Journal C | Eur. Phys. J. C 83 (2023) 26 | 10.1140/epjc/s10052-023-11198-3 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct dark energy stars with Chaplygin-type equation of state (EoS) in
the presence of anisotropic pressure within the framework of Einstein gravity.
From the classification established by Iyer et al. [Class. Quantum Grav. 2, 219
(1985)], we discuss the possible existence of isotropic dark energy stars as
compact objects. However, there is the possibility of constructing
ultra-compact stars for sufficiently large anisotropies. We investigate the
stellar stability against radial oscillations, and we also determine the moment
of inertia and tidal deformability of these stars. We find that the usual
static criterion for radial stability $dM/d\rho_c >0$ still holds for dark
energy stars since the squared frequency of the fundamental pulsation mode
vanishes at the critical central density corresponding to the maximum-mass
configuration. The dependence of the tidal Love number on the anisotropy
parameter $\alpha$ is also examined. We show that the surface gravitational
redshift, moment of inertia and dimensionless tidal deformability undergo
significant changes due to anisotropic pressure, primarily in the high-mass
region. Furthermore, in light of the detection of gravitational waves GW190814,
we explore the possibility of describing the secondary component of such event
as a stable dark energy star in the presence of anisotropy.
| [
{
"created": "Mon, 9 Jan 2023 16:54:41 GMT",
"version": "v1"
}
] | 2023-01-18 | [
[
"Pretel",
"Juan M. Z.",
""
]
] | We construct dark energy stars with Chaplygin-type equation of state (EoS) in the presence of anisotropic pressure within the framework of Einstein gravity. From the classification established by Iyer et al. [Class. Quantum Grav. 2, 219 (1985)], we discuss the possible existence of isotropic dark energy stars as compact objects. However, there is the possibility of constructing ultra-compact stars for sufficiently large anisotropies. We investigate the stellar stability against radial oscillations, and we also determine the moment of inertia and tidal deformability of these stars. We find that the usual static criterion for radial stability $dM/d\rho_c >0$ still holds for dark energy stars since the squared frequency of the fundamental pulsation mode vanishes at the critical central density corresponding to the maximum-mass configuration. The dependence of the tidal Love number on the anisotropy parameter $\alpha$ is also examined. We show that the surface gravitational redshift, moment of inertia and dimensionless tidal deformability undergo significant changes due to anisotropic pressure, primarily in the high-mass region. Furthermore, in light of the detection of gravitational waves GW190814, we explore the possibility of describing the secondary component of such event as a stable dark energy star in the presence of anisotropy. |
1111.2795 | Jack Gegenberg | Jack Gegenberg, Gabor Kunstatter and Timothy Taves | Quantum Mechanics of the Interior of Radiating 2-D Black Holes | null | null | 10.1103/PhysRevD.85.024025 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the homogeneous sector of the RST model describing the gravitational
dynamics, including back-reaction, of radiating 2-d black holes. We find the
exact solutions both in conformal gauge and in time-parametrized form, isolate
the black hole sector of the classical phase space and quantize the near
singularity dynamics in conformal gauge. We show that different choices of
measure and different self-adjoint extensions can lead to inequivalent quantum
theories, all of which resolve the singularity. For a specific range of
extension parameters, the Hamiltonian spectrum admits bound states that
correspond physically to stable remnants. Finally, we argue that our work
provides a good starting point for quantization of the full homogeneous theory
using both reduced and Dirac quantization.
| [
{
"created": "Fri, 11 Nov 2011 16:41:51 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Mar 2012 22:36:36 GMT",
"version": "v2"
}
] | 2015-06-03 | [
[
"Gegenberg",
"Jack",
""
],
[
"Kunstatter",
"Gabor",
""
],
[
"Taves",
"Timothy",
""
]
] | We study the homogeneous sector of the RST model describing the gravitational dynamics, including back-reaction, of radiating 2-d black holes. We find the exact solutions both in conformal gauge and in time-parametrized form, isolate the black hole sector of the classical phase space and quantize the near singularity dynamics in conformal gauge. We show that different choices of measure and different self-adjoint extensions can lead to inequivalent quantum theories, all of which resolve the singularity. For a specific range of extension parameters, the Hamiltonian spectrum admits bound states that correspond physically to stable remnants. Finally, we argue that our work provides a good starting point for quantization of the full homogeneous theory using both reduced and Dirac quantization. |
0710.3435 | Andrew Moylan | Andrew Moylan | Numerical experimentation within GRworkbench | Honours thesis (ANU, 2003) | null | null | null | gr-qc | null | The software tool GRworkbench is an ongoing project in visual, numerical
General Relativity at The Australian National University. This year,
GRworkbench has been significantly extended to facilitate numerical
experimentation. The numerical differential geometric engine has been rewritten
using functional programming techniques, enabling fundamental concepts to be
directly represented as variables in the C++ code of GRworkbench. Sophisticated
general numerical methods have replaced simpler specialised algorithms. Various
tools for numerical experimentation have been implemented, allowing for the
simulation of complex physical situations.
A recent claim, that the mass of the Milky Way can be measured using a small
interferometer located on the surface of the Earth, has been investigated, and
found to be an artifact of the approximations employed in the analysis. This
difficulty is symptomatic of the limitations of traditional pen-and-paper
analysis in General Relativity, which was the motivation behind the original
development of GRworkbench. The physical situation pertaining to the claim has
been modelled in a numerical experiment in GRworkbench, without the necessity
of making any simplifying assumptions, and an accurate estimate of the effect
has been obtained.
| [
{
"created": "Thu, 18 Oct 2007 04:33:30 GMT",
"version": "v1"
}
] | 2007-10-19 | [
[
"Moylan",
"Andrew",
""
]
] | The software tool GRworkbench is an ongoing project in visual, numerical General Relativity at The Australian National University. This year, GRworkbench has been significantly extended to facilitate numerical experimentation. The numerical differential geometric engine has been rewritten using functional programming techniques, enabling fundamental concepts to be directly represented as variables in the C++ code of GRworkbench. Sophisticated general numerical methods have replaced simpler specialised algorithms. Various tools for numerical experimentation have been implemented, allowing for the simulation of complex physical situations. A recent claim, that the mass of the Milky Way can be measured using a small interferometer located on the surface of the Earth, has been investigated, and found to be an artifact of the approximations employed in the analysis. This difficulty is symptomatic of the limitations of traditional pen-and-paper analysis in General Relativity, which was the motivation behind the original development of GRworkbench. The physical situation pertaining to the claim has been modelled in a numerical experiment in GRworkbench, without the necessity of making any simplifying assumptions, and an accurate estimate of the effect has been obtained. |
1911.02484 | Geanderson Carvalho Dr. | G.A. Carvalho, S.I. dos Santos, Jr., P.H.R.S. Moraes, M. Malheiro | Strange stars in energy-momentum-conserved $f(R,T)$ gravity | preprint version with 14 pages and 3 figures. arXiv admin note: text
overlap with arXiv:1803.07719 | null | null | null | gr-qc astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | For the accurate understanding of compact objects such as neutron stars and
strange stars, the Tolmann-Openheimer-Volkof (TOV) equation has proved to be of
great use. Hence, in this work, we obtain the TOV equation for the
energy-momentum-conserved $f(R,T)$ theory of gravity to study strange quark
stars. The $f(R,T)$ theory is important, especially in cosmology, because it
solves certain incompleteness of the standard model. In general, there is no
intrinsic conservation of the energy-momentum tensor in the $f(R,T)$ gravity.
Since this conservation is important in the astrophysical context, we impose
the condition $\nabla T_{\mu\nu}=0$, so that we obtain a function $f(R,T)$ that
implies conservation. This choice of a function $f(R,T)$ that conserves the
momentum-energy tensor gives rise to a strong link between gravity and the
microphysics of the compact object. We obtain the TOV by taking into account a
linear equation of state to describe the matter inside strange stars, such as
$p=\omega\rho$ and the MIT bag model $p=\omega(\rho-4B)$. With these
assumptions it was possible to derive macroscopic properties of these objects.
| [
{
"created": "Tue, 5 Nov 2019 17:32:26 GMT",
"version": "v1"
}
] | 2019-11-07 | [
[
"Carvalho",
"G. A.",
""
],
[
"Santos,",
"S. I. dos",
"Jr."
],
[
"Moraes",
"P. H. R. S.",
""
],
[
"Malheiro",
"M.",
""
]
] | For the accurate understanding of compact objects such as neutron stars and strange stars, the Tolmann-Openheimer-Volkof (TOV) equation has proved to be of great use. Hence, in this work, we obtain the TOV equation for the energy-momentum-conserved $f(R,T)$ theory of gravity to study strange quark stars. The $f(R,T)$ theory is important, especially in cosmology, because it solves certain incompleteness of the standard model. In general, there is no intrinsic conservation of the energy-momentum tensor in the $f(R,T)$ gravity. Since this conservation is important in the astrophysical context, we impose the condition $\nabla T_{\mu\nu}=0$, so that we obtain a function $f(R,T)$ that implies conservation. This choice of a function $f(R,T)$ that conserves the momentum-energy tensor gives rise to a strong link between gravity and the microphysics of the compact object. We obtain the TOV by taking into account a linear equation of state to describe the matter inside strange stars, such as $p=\omega\rho$ and the MIT bag model $p=\omega(\rho-4B)$. With these assumptions it was possible to derive macroscopic properties of these objects. |
1003.0561 | Tomas Ledvinka | Tomas Ledvinka, Gerhard Schaefer, Jiri Bicak | Post-Minkowskian closed-form Hamiltonian for gravitating N-body systems | 3 pages, to appear in the proceedings of the 12th Marcel Grossmann
Meeting, Paris, July 2009 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Hamiltonian for a system of relativistic bodies interacting by their
gravitational field is found in the post-Minkowskian approximation, including
all terms linear in the gravitational constant. It is given in a surprisingly
simple closed form as a function of canonical variables describing the bodies
only. The field is eliminated by solving inhomogeneous wave equations, applying
transverse-traceless projections, and using the Routh functional. By including
all special relativistic effects our Hamiltonian extends the results described
in classical textbooks of theoretical physics. As an application, the
scattering of relativistic objects is considered.
| [
{
"created": "Tue, 2 Mar 2010 11:28:19 GMT",
"version": "v1"
}
] | 2010-03-03 | [
[
"Ledvinka",
"Tomas",
""
],
[
"Schaefer",
"Gerhard",
""
],
[
"Bicak",
"Jiri",
""
]
] | The Hamiltonian for a system of relativistic bodies interacting by their gravitational field is found in the post-Minkowskian approximation, including all terms linear in the gravitational constant. It is given in a surprisingly simple closed form as a function of canonical variables describing the bodies only. The field is eliminated by solving inhomogeneous wave equations, applying transverse-traceless projections, and using the Routh functional. By including all special relativistic effects our Hamiltonian extends the results described in classical textbooks of theoretical physics. As an application, the scattering of relativistic objects is considered. |
gr-qc/9406027 | Peter Schaller | P.Schaller and T.Strobl | Quantization of Field Theories Generalizing Gravity-Yang-Mills Systems
on the Cylinder | 26, pages, TUW-94-2 | Lect.Notes Phys. 436 (1994) 98-122 | 10.1007/3-540-58453-6_6 | null | gr-qc | null | Pure gravity and gauge theories in two dimensions are shown to be special
cases of a much more general class of field theories each of which is
characterized by a Poisson structure on a finite dimensional target space. A
general scheme for the quantization of these theories is formulated. Explicit
examples are studied in some detail. In particular gravity and gauge theories
with equivalent actions are compared. Big gauge transformations as well as the
condition of metric nondegeneracy in gravity turn out to cause significant
differences in the structure of the corresponding reduced phase spaces and the
quantum spectra of Dirac observables. For $R^2$ gravity coupled to SU(2) Yang
Mills the question of quantum dynamics (`problem of time') is addressed. [This
article is a contribution to the proceedings (to appear in LNP) of the 3rd
Baltic RIM Student Seminar (1993). Importance is attached to concrete examples.
A more abstract presentation of the ideas underlying this article (including
new developments) is found in hep-th/9405110.]
| [
{
"created": "Thu, 16 Jun 1994 17:55:16 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Schaller",
"P.",
""
],
[
"Strobl",
"T.",
""
]
] | Pure gravity and gauge theories in two dimensions are shown to be special cases of a much more general class of field theories each of which is characterized by a Poisson structure on a finite dimensional target space. A general scheme for the quantization of these theories is formulated. Explicit examples are studied in some detail. In particular gravity and gauge theories with equivalent actions are compared. Big gauge transformations as well as the condition of metric nondegeneracy in gravity turn out to cause significant differences in the structure of the corresponding reduced phase spaces and the quantum spectra of Dirac observables. For $R^2$ gravity coupled to SU(2) Yang Mills the question of quantum dynamics (`problem of time') is addressed. [This article is a contribution to the proceedings (to appear in LNP) of the 3rd Baltic RIM Student Seminar (1993). Importance is attached to concrete examples. A more abstract presentation of the ideas underlying this article (including new developments) is found in hep-th/9405110.] |
gr-qc/9406046 | Ahmed Hindawi | F. I. Mikhail, M. I. Wanas, Ahmed Hindawi, and E. I. Lashin | Energy-Momentum Complex in M\o ller's Tetrad Theory of Gravitation | LaTeX2e with AMS-LaTeX 1.2, 13 pages | Int.J.Theor.Phys.32:1627-1642,1993 | 10.1007/BF00672861 | IC/91/209 | gr-qc | null | M\o ller's Tetrad Theory of Gravitation is examined with regard to the
energy-momentum complex. The energy-momentum complex as well as the
superpotential associated with M\o ller's theory are derived. M\o ller's field
equations are solved in the case of spherical symmetry. Two different
solutions, giving rise to the same metric, are obtained. The energy associated
with one solution is found to be twice the energy associated with the other.
Some suggestions to get out of this inconsistency are discussed at the end of
the paper.
| [
{
"created": "Tue, 28 Jun 1994 08:48:53 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Nov 1995 20:54:16 GMT",
"version": "v2"
},
{
"created": "Mon, 19 Feb 1996 03:26:04 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Mikhail",
"F. I.",
""
],
[
"Wanas",
"M. I.",
""
],
[
"Hindawi",
"Ahmed",
""
],
[
"Lashin",
"E. I.",
""
]
] | M\o ller's Tetrad Theory of Gravitation is examined with regard to the energy-momentum complex. The energy-momentum complex as well as the superpotential associated with M\o ller's theory are derived. M\o ller's field equations are solved in the case of spherical symmetry. Two different solutions, giving rise to the same metric, are obtained. The energy associated with one solution is found to be twice the energy associated with the other. Some suggestions to get out of this inconsistency are discussed at the end of the paper. |
2407.01228 | Marcos Leopoldo Wayhs Basso | Marcos L. W. Basso and Vilson T. Zanchin | Kerr-Newman outside a rotating de Sitter-type core: A rotating version
of the Lemos-Zanchin electrically charged solution | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A rotating version of the electrically charged solution of the
Einstein-Maxwell system of equations modeling static regular black holes by
Lemos and Zanchin [Phys. Rev. D 83, 124005 (2011)] is obtained in the present
work. The full rotating geometry consists of the Kerr-Newman exterior geometry
outside a rotating de Sitter-type core with an electrically charged spheroidal
shell at the boundary. To achieve this interior geometry, we utilize the
G\"urses-G\"ursey metric and employ the Newman-Janis algorithm to generate the
rotating version of the static solution. The metrics of the two spacetime
regions are smoothly matched together at the rotating electrically charged
shell, while the electromagnetic field satisfies the usual boundary conditions
at a charged surface. Interestingly, we note that, although the Newman-Janis
procedure preserves the overall electric charge of the static solution, the
arbitrariness of the algorithm allows us to propose different electromagnetic
fields and charge (current) distributions for the same geometry of the interior
region, together with different charge (current) densities on the rotating
boundary shell. For a particular choice of the interior electromagnetic field,
we show that it is possible to interpret the rotating de Sitter fluid as being
electrically polarized due to its rotation, despite the absence of net electric
charge within the interior region, which is instead concentrated solely on the
charged shell. The properties of the entire rotating solution, such as
curvature regularity, energy-momentum tensor and energy conditions, are
thoroughly examined in the text, revealing various types of charged rotating
objects.
| [
{
"created": "Mon, 1 Jul 2024 12:18:59 GMT",
"version": "v1"
}
] | 2024-07-02 | [
[
"Basso",
"Marcos L. W.",
""
],
[
"Zanchin",
"Vilson T.",
""
]
] | A rotating version of the electrically charged solution of the Einstein-Maxwell system of equations modeling static regular black holes by Lemos and Zanchin [Phys. Rev. D 83, 124005 (2011)] is obtained in the present work. The full rotating geometry consists of the Kerr-Newman exterior geometry outside a rotating de Sitter-type core with an electrically charged spheroidal shell at the boundary. To achieve this interior geometry, we utilize the G\"urses-G\"ursey metric and employ the Newman-Janis algorithm to generate the rotating version of the static solution. The metrics of the two spacetime regions are smoothly matched together at the rotating electrically charged shell, while the electromagnetic field satisfies the usual boundary conditions at a charged surface. Interestingly, we note that, although the Newman-Janis procedure preserves the overall electric charge of the static solution, the arbitrariness of the algorithm allows us to propose different electromagnetic fields and charge (current) distributions for the same geometry of the interior region, together with different charge (current) densities on the rotating boundary shell. For a particular choice of the interior electromagnetic field, we show that it is possible to interpret the rotating de Sitter fluid as being electrically polarized due to its rotation, despite the absence of net electric charge within the interior region, which is instead concentrated solely on the charged shell. The properties of the entire rotating solution, such as curvature regularity, energy-momentum tensor and energy conditions, are thoroughly examined in the text, revealing various types of charged rotating objects. |
1402.3290 | Ronald Adler | Ronald J. Adler | On a digital quantum description of physical space versus the continuum
description | 17 pages, 3 figures | null | null | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The continuum of real numbers has served well as a model for physical space
in mechanics and field theories. However it is a well-motivated and popular
idea that at the fundamental Planck scale the combination of gravitational and
quantum effects forces us to re-evaluate the concept of space (and time), and
some sort of discreteness or granularity is expected. Here we study a cubic
grid of points representing fundamental volumes of space and derive the spectra
of momenta and wave number, which are not generally proportional to each other.
The momentum is bounded and discrete for a finite grid. The uncertainty
principle must be modified to reflect small scale spatial non-locality but it
is consistent with the standard uncertainty principle in the continuum limit.
We only consider kinematics in this work, and do not discuss time or energy or
dynamical evolution.
| [
{
"created": "Thu, 13 Feb 2014 00:31:35 GMT",
"version": "v1"
}
] | 2014-02-17 | [
[
"Adler",
"Ronald J.",
""
]
] | The continuum of real numbers has served well as a model for physical space in mechanics and field theories. However it is a well-motivated and popular idea that at the fundamental Planck scale the combination of gravitational and quantum effects forces us to re-evaluate the concept of space (and time), and some sort of discreteness or granularity is expected. Here we study a cubic grid of points representing fundamental volumes of space and derive the spectra of momenta and wave number, which are not generally proportional to each other. The momentum is bounded and discrete for a finite grid. The uncertainty principle must be modified to reflect small scale spatial non-locality but it is consistent with the standard uncertainty principle in the continuum limit. We only consider kinematics in this work, and do not discuss time or energy or dynamical evolution. |
gr-qc/9909065 | Doc. Ing. Jozef Sima DRSc. | Miroslav Sukenik and Jozef Sima | An alternative method for calculating the energy of gravitational waves | 4 pages, LaTex | null | null | SS-99-02 | gr-qc | null | In the expansive nondecelerative universe model, creation of matter occurs
due to which the Vaidya metrics is applied. This fact allows for localizing
gravitational energy and calculating the energy of gravitational waves using an
approach alternative to the well established procedure based on quadrupole
formula. Rationalization of the gradual increase in entropy of the Universe
using relation describing the total curvature of space-time is given too.
| [
{
"created": "Tue, 21 Sep 1999 14:39:28 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Sukenik",
"Miroslav",
""
],
[
"Sima",
"Jozef",
""
]
] | In the expansive nondecelerative universe model, creation of matter occurs due to which the Vaidya metrics is applied. This fact allows for localizing gravitational energy and calculating the energy of gravitational waves using an approach alternative to the well established procedure based on quadrupole formula. Rationalization of the gradual increase in entropy of the Universe using relation describing the total curvature of space-time is given too. |
gr-qc/9604012 | Adrian Kent | Adrian Kent (DAMTP, University of Cambridge) | Consistent Sets Yield Contrary Inferences in Quantum Theory | 10 pages, TeX with harvmac. Revised version, with extended discussion
and references added. To appear in Phys. Rev. Lett | Phys.Rev.Lett.78:2874-2877,1997 | 10.1103/PhysRevLett.78.2874 | DAMTP/96-18 (revised) | gr-qc cond-mat hep-th quant-ph | null | In the consistent histories formulation of quantum theory, the probabilistic
predictions and retrodictions made from observed data depend on the choice of a
consistent set. We show that this freedom allows the formalism to retrodict
contrary propositions which correspond to orthogonal commuting projections and
which each have probability one. We also show that the formalism makes contrary
probability one predictions when applied to Gell-Mann and Hartle's generalised
time-neutral quantum mechanics.
| [
{
"created": "Thu, 4 Apr 1996 21:12:37 GMT",
"version": "v1"
},
{
"created": "Fri, 21 Mar 1997 18:04:56 GMT",
"version": "v2"
}
] | 2010-11-19 | [
[
"Kent",
"Adrian",
"",
"DAMTP, University of Cambridge"
]
] | In the consistent histories formulation of quantum theory, the probabilistic predictions and retrodictions made from observed data depend on the choice of a consistent set. We show that this freedom allows the formalism to retrodict contrary propositions which correspond to orthogonal commuting projections and which each have probability one. We also show that the formalism makes contrary probability one predictions when applied to Gell-Mann and Hartle's generalised time-neutral quantum mechanics. |
2406.07691 | Poulami Dutta Roy | Poulami Dutta Roy, Sayantani Datta, K. G. Arun | Tests of general relativity at the fourth post-Newtonian order | 11 pages, 2 figures, 2 tables | null | null | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | The recently computed post-Newtonian (PN) gravitational-wave phasing up to
4.5PN order accounts for several novel physical effects in compact binary
dynamics such as the {\it tail of the memory, tails of tails of tails and tails
of mass hexadecupole and current octupole moments}. Therefore, it is
instructive to assess the ability of current-generation (2G) detectors such as
LIGO/Virgo, next-generation (XG) ground-based gravitational wave detectors such
as Cosmic Explorer/Einstein Telescope and space-based detectors like LISA to
test the predictions of PN theory at these orders. Employing Fisher information
matrix, we find that the projected bounds on the deviations from the
logarithmic PN phasing coefficient at 4PN is ${\cal O}(10^{-2})$ and ${\cal
O}(10^{-1})$ for XG and 2G detectors, respectively. Similarly, the projected
bounds on other three PN coefficients that appear at 4PN and 4.5PN are ${\cal
O}(10^{-1}-10^{-2})$ for XG and ${\cal O}(1)$ for 2G detectors. LISA
observations of supermassive BHs could provide the tightest constraints on
these four parameters ranging from ${\cal O}(10^{-4}-10^{-2})$. The variation
in these bounds are studied as a function of total mass and the mass ratio of
the binaries in quasi-circular orbits. These new tests are unique probes of
higher order nonlinear interactions in compact binary dynamics and their
consistency with the predictions of general relativity.
| [
{
"created": "Tue, 11 Jun 2024 20:11:35 GMT",
"version": "v1"
}
] | 2024-06-13 | [
[
"Roy",
"Poulami Dutta",
""
],
[
"Datta",
"Sayantani",
""
],
[
"Arun",
"K. G.",
""
]
] | The recently computed post-Newtonian (PN) gravitational-wave phasing up to 4.5PN order accounts for several novel physical effects in compact binary dynamics such as the {\it tail of the memory, tails of tails of tails and tails of mass hexadecupole and current octupole moments}. Therefore, it is instructive to assess the ability of current-generation (2G) detectors such as LIGO/Virgo, next-generation (XG) ground-based gravitational wave detectors such as Cosmic Explorer/Einstein Telescope and space-based detectors like LISA to test the predictions of PN theory at these orders. Employing Fisher information matrix, we find that the projected bounds on the deviations from the logarithmic PN phasing coefficient at 4PN is ${\cal O}(10^{-2})$ and ${\cal O}(10^{-1})$ for XG and 2G detectors, respectively. Similarly, the projected bounds on other three PN coefficients that appear at 4PN and 4.5PN are ${\cal O}(10^{-1}-10^{-2})$ for XG and ${\cal O}(1)$ for 2G detectors. LISA observations of supermassive BHs could provide the tightest constraints on these four parameters ranging from ${\cal O}(10^{-4}-10^{-2})$. The variation in these bounds are studied as a function of total mass and the mass ratio of the binaries in quasi-circular orbits. These new tests are unique probes of higher order nonlinear interactions in compact binary dynamics and their consistency with the predictions of general relativity. |
2104.08703 | Qingyu Gan | Qingyu Gan, Peng Wang, Houwen Wu, Haitang Yang | Photon Spheres and Spherical Accretion Image of a Hairy Black Hole | v1: 13 pages, 6 figures; v2: 13 pages, 6 figures, references added | Phys. Rev. D 104, 024003 (2021) | 10.1103/PhysRevD.104.024003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we first consider null geodesics of a class of charged,
spherical and asymptotically flat hairy black holes in an
Einstein-Maxwell-scalar theory with a non-minimal coupling for the scalar and
electromagnetic fields. Remarkably, we show that there are two unstable
circular orbits for a photon in a certain parameter regime, corresponding to
two unstable photon spheres of different sizes outside the event horizon. To
illustrate the optical appearance of photon spheres, we then consider a simple
spherical model of optically thin accretion on the hairy black hole, and obtain
the accretion image seen by a distant observer. In the single photon sphere
case, only one bright ring appears in the image, and is identified as the edge
of the black hole shadow. Whereas in the case with two photon spheres, there
can be two concentric bright rings of different radii in the image, and the
smaller one serves as the boundary of the shadow, whose radius goes to zero at
the critical charge.
| [
{
"created": "Sun, 18 Apr 2021 04:02:16 GMT",
"version": "v1"
},
{
"created": "Mon, 3 May 2021 14:38:52 GMT",
"version": "v2"
}
] | 2021-07-07 | [
[
"Gan",
"Qingyu",
""
],
[
"Wang",
"Peng",
""
],
[
"Wu",
"Houwen",
""
],
[
"Yang",
"Haitang",
""
]
] | In this paper, we first consider null geodesics of a class of charged, spherical and asymptotically flat hairy black holes in an Einstein-Maxwell-scalar theory with a non-minimal coupling for the scalar and electromagnetic fields. Remarkably, we show that there are two unstable circular orbits for a photon in a certain parameter regime, corresponding to two unstable photon spheres of different sizes outside the event horizon. To illustrate the optical appearance of photon spheres, we then consider a simple spherical model of optically thin accretion on the hairy black hole, and obtain the accretion image seen by a distant observer. In the single photon sphere case, only one bright ring appears in the image, and is identified as the edge of the black hole shadow. Whereas in the case with two photon spheres, there can be two concentric bright rings of different radii in the image, and the smaller one serves as the boundary of the shadow, whose radius goes to zero at the critical charge. |
1811.12923 | Yury F. Pirogov | Yury F. Pirogov | Quartet-metric/multi-component gravity: scalar graviton as emergent dark
substance | 16 pages, 2 figures. Minor revision, references added | JCAP01(2019)055 | 10.1088/1475-7516/2019/01/055 | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the general frameworks of an earlier introduced
quartet-metric/multi-component gravity, a theory of a massive scalar graviton
supplementing the massless tensor one is consistently deduced. The
peculiarities of the scalar-graviton field compared to the canonical scalar one
are demonstrated. The light scalar graviton is treated as an emergent dark
substance of the Universe: dark matter and/or dark energy depending on the
solution. The case with scalar graviton as dark energy responsible for the
late-time accelerated expansion of the Universe is studied in more detail. In
particular, it is shown that due to an attractor solution for the light scalar
graviton there naturally emerges at the classical level a tiny nonzero
effective cosmological constant, even in the absence of the Lagrangian one. The
prospects of going beyond LCDM model per scalar graviton are shortly indicated.
| [
{
"created": "Fri, 30 Nov 2018 18:15:37 GMT",
"version": "v1"
},
{
"created": "Thu, 31 Jan 2019 17:55:26 GMT",
"version": "v2"
}
] | 2019-02-13 | [
[
"Pirogov",
"Yury F.",
""
]
] | In the general frameworks of an earlier introduced quartet-metric/multi-component gravity, a theory of a massive scalar graviton supplementing the massless tensor one is consistently deduced. The peculiarities of the scalar-graviton field compared to the canonical scalar one are demonstrated. The light scalar graviton is treated as an emergent dark substance of the Universe: dark matter and/or dark energy depending on the solution. The case with scalar graviton as dark energy responsible for the late-time accelerated expansion of the Universe is studied in more detail. In particular, it is shown that due to an attractor solution for the light scalar graviton there naturally emerges at the classical level a tiny nonzero effective cosmological constant, even in the absence of the Lagrangian one. The prospects of going beyond LCDM model per scalar graviton are shortly indicated. |
2306.17577 | Hai-Long Huang | Hai-Long Huang, Yong Cai, Jun-Qian Jiang, Jun Zhang and Yun-Song Piao | Supermassive primordial black holes in multiverse: for nano-Hertz
gravitational wave and high-redshift JWST galaxies | 15 pages, 4 figures | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, observational hints for supermassive black holes have been
accumulating, which has inspired ones to wonder: Can primordial black holes
(PBHs) be supermassive, in particular with the mass $M\gtrsim 10^{9}M_\odot$? A
supercritical bubble (with an inflating baby universe inside it) that nucleated
during inflation can develop into a PBH in our observable Universe. Here, we
find that when the inflaton slowly passes by a neighboring vacuum, the
nucleating rate of supercritical bubbles would inevitably attain a peak, so the
mass distribution of multiverse PBHs, and the mass of peak can be up to
$M\gtrsim 10^{11}M_\odot$. Thus our mechanism naturally provides a primordial
origin of supermassive BHs.
| [
{
"created": "Fri, 30 Jun 2023 11:54:50 GMT",
"version": "v1"
}
] | 2023-07-03 | [
[
"Huang",
"Hai-Long",
""
],
[
"Cai",
"Yong",
""
],
[
"Jiang",
"Jun-Qian",
""
],
[
"Zhang",
"Jun",
""
],
[
"Piao",
"Yun-Song",
""
]
] | Recently, observational hints for supermassive black holes have been accumulating, which has inspired ones to wonder: Can primordial black holes (PBHs) be supermassive, in particular with the mass $M\gtrsim 10^{9}M_\odot$? A supercritical bubble (with an inflating baby universe inside it) that nucleated during inflation can develop into a PBH in our observable Universe. Here, we find that when the inflaton slowly passes by a neighboring vacuum, the nucleating rate of supercritical bubbles would inevitably attain a peak, so the mass distribution of multiverse PBHs, and the mass of peak can be up to $M\gtrsim 10^{11}M_\odot$. Thus our mechanism naturally provides a primordial origin of supermassive BHs. |
1108.0061 | Rodrigo P. Macedo | Jos\'e Luis Jaramillo and Rodrigo P. Macedo and Philipp Moesta and
Luciano Rezzolla | Black-hole horizons as probes of black-hole dynamics II: geometrical
insights | Final version published on PRD | Phys. Rev. D 85, 084031 (2012) | 10.1103/PhysRevD.85.084031 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In a companion paper [1], we have presented a cross-correlation approach to
near-horizon physics in which bulk dynamics is probed through the correlation
of quantities defined at inner and outer spacetime hypersurfaces acting as test
screens. More specifically, dynamical horizons provide appropriate inner
screens in a 3+1 setting and, in this context, we have shown that an
effective-curvature vector measured at the common horizon produced in a head-on
collision merger can be correlated with the flux of linear Bondi-momentum at
null infinity. In this paper we provide a more sound geometric basis to this
picture. First, we show that a rigidity property of dynamical horizons, namely
foliation uniqueness, leads to a preferred class of null tetrads and Weyl
scalars on these hypersurfaces. Second, we identify a heuristic horizon
news-like function, depending only on the geometry of spatial sections of the
horizon. Fluxes constructed from this function offer refined geometric
quantities to be correlated with Bondi fluxes at infinity, as well as a contact
with the discussion of quasi-local 4-momentum on dynamical horizons. Third, we
highlight the importance of tracking the internal horizon dual to the apparent
horizon in spatial 3-slices when integrating fluxes along the horizon. Finally,
we discuss the link between the dissipation of the non-stationary part of the
horizon's geometry with the viscous-fluid analogy for black holes, introducing
a geometric prescription for a "slowness parameter" in black-hole recoil
dynamics.
| [
{
"created": "Sat, 30 Jul 2011 11:28:38 GMT",
"version": "v1"
},
{
"created": "Sat, 5 May 2012 13:44:43 GMT",
"version": "v2"
}
] | 2012-05-08 | [
[
"Jaramillo",
"José Luis",
""
],
[
"Macedo",
"Rodrigo P.",
""
],
[
"Moesta",
"Philipp",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | In a companion paper [1], we have presented a cross-correlation approach to near-horizon physics in which bulk dynamics is probed through the correlation of quantities defined at inner and outer spacetime hypersurfaces acting as test screens. More specifically, dynamical horizons provide appropriate inner screens in a 3+1 setting and, in this context, we have shown that an effective-curvature vector measured at the common horizon produced in a head-on collision merger can be correlated with the flux of linear Bondi-momentum at null infinity. In this paper we provide a more sound geometric basis to this picture. First, we show that a rigidity property of dynamical horizons, namely foliation uniqueness, leads to a preferred class of null tetrads and Weyl scalars on these hypersurfaces. Second, we identify a heuristic horizon news-like function, depending only on the geometry of spatial sections of the horizon. Fluxes constructed from this function offer refined geometric quantities to be correlated with Bondi fluxes at infinity, as well as a contact with the discussion of quasi-local 4-momentum on dynamical horizons. Third, we highlight the importance of tracking the internal horizon dual to the apparent horizon in spatial 3-slices when integrating fluxes along the horizon. Finally, we discuss the link between the dissipation of the non-stationary part of the horizon's geometry with the viscous-fluid analogy for black holes, introducing a geometric prescription for a "slowness parameter" in black-hole recoil dynamics. |
gr-qc/0512056 | Alfred Scharff Goldhaber | Alfred Scharff Goldhaber | Magnetic Monopoles and Cosmic Inflation | 10 pages | null | null | YITP-SB-05-45 | gr-qc | null | It is possible that the expansion of the universe began with an inflationary
phase, in which the inflaton driving the process also was a Higgs field capable
of stabilizing magnetic monopoles in a grand-unified gauge theory. If so, then
the smallness of intensity fluctuations observed in the cosmic microwave
background radiation implies that the self-coupling of the inflaton-Higgs field
was exceedingly weak. It is argued here that the resulting broad, flat maximum
in the Higgs potential makes the presence or absence of a topological zero in
the field insignificant for inflation. There may be monopoles present in the
universe, but the universe itself is not in the inflating core of a giant
magnetic monopole.
| [
{
"created": "Fri, 9 Dec 2005 18:37:21 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Goldhaber",
"Alfred Scharff",
""
]
] | It is possible that the expansion of the universe began with an inflationary phase, in which the inflaton driving the process also was a Higgs field capable of stabilizing magnetic monopoles in a grand-unified gauge theory. If so, then the smallness of intensity fluctuations observed in the cosmic microwave background radiation implies that the self-coupling of the inflaton-Higgs field was exceedingly weak. It is argued here that the resulting broad, flat maximum in the Higgs potential makes the presence or absence of a topological zero in the field insignificant for inflation. There may be monopoles present in the universe, but the universe itself is not in the inflating core of a giant magnetic monopole. |
1709.07236 | Juho Lankinen | Juho Lankinen and Iiro Vilja | Decay of a Massive Particle in a Stiff Matter Dominated Universe | 6 pages, 1 figure | Phys. Rev. D 96, 105026 (2017) | 10.1103/PhysRevD.96.105026 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the presence of a gravitational field decay rates may significantly differ
from flat space equivalent. By studying mutually interacting quantum fields the
decay rates can be calculated on a given spacetime. This paper presents the
calculation of the transition probability for the decay of a massive scalar
particle in a stiff matter dominated universe. We find that due to the precence
of a gravitational field a finite correction to the transition probability is
added which depends inversely on the mass. Moreover the decay rate is smaller
and lifetime of the particles is longer compared to flat space. The mass
dependence is such that the lifetime of lighter particles is prolonged more
compared to heavier particles. This result may be of significance when studying
cosmological situations involving stiff matter.
| [
{
"created": "Thu, 21 Sep 2017 09:48:26 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Nov 2017 08:23:19 GMT",
"version": "v2"
}
] | 2017-12-06 | [
[
"Lankinen",
"Juho",
""
],
[
"Vilja",
"Iiro",
""
]
] | In the presence of a gravitational field decay rates may significantly differ from flat space equivalent. By studying mutually interacting quantum fields the decay rates can be calculated on a given spacetime. This paper presents the calculation of the transition probability for the decay of a massive scalar particle in a stiff matter dominated universe. We find that due to the precence of a gravitational field a finite correction to the transition probability is added which depends inversely on the mass. Moreover the decay rate is smaller and lifetime of the particles is longer compared to flat space. The mass dependence is such that the lifetime of lighter particles is prolonged more compared to heavier particles. This result may be of significance when studying cosmological situations involving stiff matter. |
0905.0450 | Frank Ohme | Frank Ohme, Mark Hannam, Sascha Husa and Niall \'O Murchadha | Stationary hyperboloidal slicings with evolved gauge conditions | 18 pages, 11 figures, LaTeX; minor changes for the published version | 2009 Class. Quantum Grav. 26 175014 | 10.1088/0264-9381/26/17/175014 | AEI-2009-043 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze stationary slicings of the Schwarzschild spacetime defined by
members of the Bona-Masso family of slicing conditions. Our main focus is on
the influence of a non-vanishing offset to the extrinsic curvature, which
forbids the existence of standard Cauchy foliations but at the same time allows
gauge choices that are adapted to include null infinity (scri) in the
evolution. These hyperboloidal slicings are especially interesting for
observing outgoing gravitational waves. We show that the standard 1+log slicing
condition admits no overall regular hyperboloidal slicing, but by appropriately
combining with harmonic slicing, we construct a gauge condition that leads to a
strongly singularity-avoiding hyperboloidal foliation that connects the black
hole to scri.
| [
{
"created": "Mon, 4 May 2009 19:58:18 GMT",
"version": "v1"
},
{
"created": "Thu, 20 Aug 2009 08:01:01 GMT",
"version": "v2"
}
] | 2009-08-20 | [
[
"Ohme",
"Frank",
""
],
[
"Hannam",
"Mark",
""
],
[
"Husa",
"Sascha",
""
],
[
"Murchadha",
"Niall Ó",
""
]
] | We analyze stationary slicings of the Schwarzschild spacetime defined by members of the Bona-Masso family of slicing conditions. Our main focus is on the influence of a non-vanishing offset to the extrinsic curvature, which forbids the existence of standard Cauchy foliations but at the same time allows gauge choices that are adapted to include null infinity (scri) in the evolution. These hyperboloidal slicings are especially interesting for observing outgoing gravitational waves. We show that the standard 1+log slicing condition admits no overall regular hyperboloidal slicing, but by appropriately combining with harmonic slicing, we construct a gauge condition that leads to a strongly singularity-avoiding hyperboloidal foliation that connects the black hole to scri. |
1606.08073 | Saeed Rastgoo | Saeed Rastgoo, Manfred Requardt | Emergent Space-Time via a Geometric Renormalization Method | 29 pages, v2 matching the published PRD version | Phys. Rev. D 94, 124019 (2016) | 10.1103/PhysRevD.94.124019 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a purely geometric renormalization scheme for metric spaces
(including uncolored graphs), which consists of a coarse graining and a
rescaling operation on such spaces. The coarse graining is based on the concept
of quasi-isometry, which yields a sequence of discrete coarse grained spaces
each having a continuum limit under the rescaling operation. We provide
criteria under which such sequences do converge within a superspace of metric
spaces, or may constitute the basin of attraction of a common continuum limit,
which hopefully, may represent our space-time continuum.
We discuss some of the properties of these coarse grained spaces as well as
their continuum limits, such as scale invariance and metric similarity, and
show that different layers of spacetime can carry different distance functions
while being homeomorphic.
Important tools in this analysis are the Gromov-Hausdorff distance functional
for general metric spaces and the growth degree of graphs or networks. The
whole construction is in the spirit of the Wilsonian renormalization group.
Furthermore we introduce a physically relevant notion of dimension on the
spaces of interest in our analysis, which e.g. for regular lattices reduces to
the ordinary lattice dimension. We show that this dimension is stable under the
proposed coarse graining procedure as long as the latter is sufficiently local,
i.e. quasi-isometric, and discuss the conditions under which this dimension is
an integer. We comment on the possibility that the limit space may turn out to
be fractal in case the dimension is non-integer. At the end of the paper we
briefly mention the possibility that our network carries a translocal far-order
which leads to the concept of wormhole spaces and a scale dependent dimension
if the coarse graining procedure is no longer local.
| [
{
"created": "Sun, 26 Jun 2016 19:14:42 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Dec 2016 23:28:36 GMT",
"version": "v2"
}
] | 2016-12-21 | [
[
"Rastgoo",
"Saeed",
""
],
[
"Requardt",
"Manfred",
""
]
] | We present a purely geometric renormalization scheme for metric spaces (including uncolored graphs), which consists of a coarse graining and a rescaling operation on such spaces. The coarse graining is based on the concept of quasi-isometry, which yields a sequence of discrete coarse grained spaces each having a continuum limit under the rescaling operation. We provide criteria under which such sequences do converge within a superspace of metric spaces, or may constitute the basin of attraction of a common continuum limit, which hopefully, may represent our space-time continuum. We discuss some of the properties of these coarse grained spaces as well as their continuum limits, such as scale invariance and metric similarity, and show that different layers of spacetime can carry different distance functions while being homeomorphic. Important tools in this analysis are the Gromov-Hausdorff distance functional for general metric spaces and the growth degree of graphs or networks. The whole construction is in the spirit of the Wilsonian renormalization group. Furthermore we introduce a physically relevant notion of dimension on the spaces of interest in our analysis, which e.g. for regular lattices reduces to the ordinary lattice dimension. We show that this dimension is stable under the proposed coarse graining procedure as long as the latter is sufficiently local, i.e. quasi-isometric, and discuss the conditions under which this dimension is an integer. We comment on the possibility that the limit space may turn out to be fractal in case the dimension is non-integer. At the end of the paper we briefly mention the possibility that our network carries a translocal far-order which leads to the concept of wormhole spaces and a scale dependent dimension if the coarse graining procedure is no longer local. |
gr-qc/0412082 | Pankaj S. Joshi | Pankaj S Joshi | Gravitational Collapse End States | 6 pages, Invited talk at `International workshop on dynamics and
thermodynamics of black holes and naked singularities', 13-15 May, Milano | null | null | null | gr-qc | null | Recent developments on the final state of a gravitationally collapsing
massive matter cloud are summarized and reviewed here. After a brief background
on the problem, we point out how the black hole and naked singularity end
states arise naturally in spherical collapse. We see that it is the geometry of
trapped surfaces that governs this phenomena.
| [
{
"created": "Fri, 17 Dec 2004 11:21:20 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Joshi",
"Pankaj S",
""
]
] | Recent developments on the final state of a gravitationally collapsing massive matter cloud are summarized and reviewed here. After a brief background on the problem, we point out how the black hole and naked singularity end states arise naturally in spherical collapse. We see that it is the geometry of trapped surfaces that governs this phenomena. |
1202.2755 | Norman G\"urlebeck | D. Lynden-Bell, J. Bi\v{c}\'ak, J. Katz | On Fast Linear Gravitational Dragging | 4 pages, 1 figure | Class. Quantum Grav. 29 (2012) 017001 | 10.1088/0264-9381/29/1/017001 | null | gr-qc astro-ph.CO astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new formula is given for the fast linear gravitational dragging of the
inertial frame within a rapidly accelerated spherical shell of deep potential.
The shell is charged and is electrically accelerated by an electric field whose
sources are included in the solution.
| [
{
"created": "Mon, 13 Feb 2012 14:51:40 GMT",
"version": "v1"
}
] | 2012-02-14 | [
[
"Lynden-Bell",
"D.",
""
],
[
"Bičák",
"J.",
""
],
[
"Katz",
"J.",
""
]
] | A new formula is given for the fast linear gravitational dragging of the inertial frame within a rapidly accelerated spherical shell of deep potential. The shell is charged and is electrically accelerated by an electric field whose sources are included in the solution. |
1701.06636 | Tao Wang | Yun-Chao Wang, Tower Wang | Primordial perturbations generated by Higgs field and $R^2$ operator | 14 pages, 5 figures, $\rho$-field redefined, Sect V and appendices
enlarged | Phys. Rev. D 96, 123506 (2017) | 10.1103/PhysRevD.96.123506 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | If the very early Universe is dominated by the non-minimally coupled Higgs
field and Starobinsky's curvature-squared term together, the potential diagram
would mimic the landscape of a valley, serving as a cosmological attractor. The
inflationary dynamics along this valley is studied, model parameters are
constrained against observational data, and the isocurvature perturbation is
evaluated.
| [
{
"created": "Mon, 23 Jan 2017 21:18:35 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Jun 2017 04:30:00 GMT",
"version": "v2"
},
{
"created": "Tue, 5 Dec 2017 01:51:28 GMT",
"version": "v3"
}
] | 2017-12-13 | [
[
"Wang",
"Yun-Chao",
""
],
[
"Wang",
"Tower",
""
]
] | If the very early Universe is dominated by the non-minimally coupled Higgs field and Starobinsky's curvature-squared term together, the potential diagram would mimic the landscape of a valley, serving as a cosmological attractor. The inflationary dynamics along this valley is studied, model parameters are constrained against observational data, and the isocurvature perturbation is evaluated. |
2309.04368 | Gabriele Bozzola | Gabriele Bozzola and Vasileios Paschalidis | Can quasi-circular mergers of charged black holes produce extremal black
holes? | 7 pages, 2 figures, code available | Phys. Rev. D 108, 064010 (2023) | 10.1103/PhysRevD.108.064010 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In contrast to energy and angular momentum, electric charge is conserved in
mergers of charged black holes. This opens up the possibility for the remnant
to have Kerr-Newman parameter $\chi^{2} + \lambda^{2}$ greater than 1 (with
$\chi$ and $\lambda$ being the black hole dimensionless spin and dimensionless
charge, respectively), which is forbidden by the cosmic censorship conjecture.
In this paper, we investigate whether a naked singularity can form in
quasi-circular mergers of charged binary black holes. We extend a theoretical
model to estimate the final properties of the remnant left by quasicircular
mergers of binary black holes to the charged case. We validate the model with
numerical-relativity simulations, finding agreement at the percent level. We
then use our theoretical model to argue that while naked singularities cannot
form following quasi-circular mergers of non-spinning charged binary black
holes, it is possible to produce remnants that are arbitrarily close to the
extremal limit.
| [
{
"created": "Fri, 8 Sep 2023 14:58:16 GMT",
"version": "v1"
}
] | 2023-09-11 | [
[
"Bozzola",
"Gabriele",
""
],
[
"Paschalidis",
"Vasileios",
""
]
] | In contrast to energy and angular momentum, electric charge is conserved in mergers of charged black holes. This opens up the possibility for the remnant to have Kerr-Newman parameter $\chi^{2} + \lambda^{2}$ greater than 1 (with $\chi$ and $\lambda$ being the black hole dimensionless spin and dimensionless charge, respectively), which is forbidden by the cosmic censorship conjecture. In this paper, we investigate whether a naked singularity can form in quasi-circular mergers of charged binary black holes. We extend a theoretical model to estimate the final properties of the remnant left by quasicircular mergers of binary black holes to the charged case. We validate the model with numerical-relativity simulations, finding agreement at the percent level. We then use our theoretical model to argue that while naked singularities cannot form following quasi-circular mergers of non-spinning charged binary black holes, it is possible to produce remnants that are arbitrarily close to the extremal limit. |
2204.02979 | Hossein Ghaffarnejad | Elham Ghasemi and Hossein Ghaffarnejad | Magnetic charge effects on thermodynamic phase transition of modified
Anti de Sitter Ay\'{o}n-Beato-Garc\'{i}a Black Holes with five parameters | 10 pages, 3 figures, virtually presented as invited speaker at the
1th International conference of Holography and its Applications, 9-10 March
2022, School of Physics, Damghan University, Damghan, IRAN | Journal of Holography Applications in Physics(2022) | 10.22128/jhap.2022.524.1022 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this letter we choose generalized Ayon Beato Gracia (ABG) magnetic charged
black hole with five parameters to investigate possibility of thermodynamic
phase transition and coexistence of different gass/liquid/solid phases of this
black hole. In fact this work is an extension of our recently work where ABG
black hole with three parameters was used to seek the phase transition. In this
work we obtain other physical values on the parameters with respect to our
previous work where the phase transition is happened together with coexistence
point of different phases in the phase space.
| [
{
"created": "Wed, 6 Apr 2022 22:23:51 GMT",
"version": "v1"
}
] | 2022-05-10 | [
[
"Ghasemi",
"Elham",
""
],
[
"Ghaffarnejad",
"Hossein",
""
]
] | In this letter we choose generalized Ayon Beato Gracia (ABG) magnetic charged black hole with five parameters to investigate possibility of thermodynamic phase transition and coexistence of different gass/liquid/solid phases of this black hole. In fact this work is an extension of our recently work where ABG black hole with three parameters was used to seek the phase transition. In this work we obtain other physical values on the parameters with respect to our previous work where the phase transition is happened together with coexistence point of different phases in the phase space. |
1306.3246 | Marc Geiller | Jibril Ben Achour, Marc Geiller, Karim Noui, Chao Yu | Spectra of geometric operators in three-dimensional LQG: From discrete
to continuous | 13 pages. 2 figures | Phys. Rev. D 89, 064064 (2014) | 10.1103/PhysRevD.89.064064 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study and compare the spectra of geometric operators (length and area) in
the quantum kinematics of two formulations of three-dimensional Lorentzian loop
quantum gravity. In the SU(2) Ashtekar-Barbero framework, the spectra are
discrete and depend on the Barbero-Immirzi parameter $\gamma$ exactly like in
the four-dimensional case. However, we show that when working with the
self-dual variables and imposing the reality conditions the spectra become
continuous and $\gamma$-independent.
| [
{
"created": "Thu, 13 Jun 2013 20:10:43 GMT",
"version": "v1"
}
] | 2014-05-07 | [
[
"Achour",
"Jibril Ben",
""
],
[
"Geiller",
"Marc",
""
],
[
"Noui",
"Karim",
""
],
[
"Yu",
"Chao",
""
]
] | We study and compare the spectra of geometric operators (length and area) in the quantum kinematics of two formulations of three-dimensional Lorentzian loop quantum gravity. In the SU(2) Ashtekar-Barbero framework, the spectra are discrete and depend on the Barbero-Immirzi parameter $\gamma$ exactly like in the four-dimensional case. However, we show that when working with the self-dual variables and imposing the reality conditions the spectra become continuous and $\gamma$-independent. |
0907.0760 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig, Farook Rahaman, Ashis Ghosh | Quintom wormholes | 8 pages, 3 figures | Int.J.Theor.Phys.49:1222-1231,2010 | 10.1007/s10773-010-0302-9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The combination of quintessence and phantom energy in a joint model is
referred to as quintom dark energy. This paper discusses traversable wormholes
supported by such quintom matter. Two particular solutions are explored, a
constant redshift function and a specific shape function. Both isotropic and
anisotropic pressures are considered.
| [
{
"created": "Sat, 4 Jul 2009 14:02:23 GMT",
"version": "v1"
},
{
"created": "Sat, 12 Jun 2010 21:29:22 GMT",
"version": "v2"
}
] | 2010-06-15 | [
[
"Kuhfittig",
"Peter K. F.",
""
],
[
"Rahaman",
"Farook",
""
],
[
"Ghosh",
"Ashis",
""
]
] | The combination of quintessence and phantom energy in a joint model is referred to as quintom dark energy. This paper discusses traversable wormholes supported by such quintom matter. Two particular solutions are explored, a constant redshift function and a specific shape function. Both isotropic and anisotropic pressures are considered. |
0807.2051 | Sa\v{s}a Iliji\'c | Dubravko Horvat, Sasa Ilijic, Anja Marunovic | Electrically charged gravastar configurations | LaTeX, 14 pages, 3 figs, changes wrt v1: discussion of emergent
equation of state included and references updated (to appear in CQG) | Class.Quant.Grav.26:025003,2009 | 10.1088/0264-9381/26/2/025003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The notion of a compact object immune to the horizon problem and comprising
an anisotropic inhomogeneous fluid with a specific radial pressure behavior,
i.e. the gravastar, is extended by introducing an electrically charged
component. Einstein-Maxwell field equations are solved in the asymptotically de
Sitter interior where a source of the electric field is coupled to the fluid
energy density. Two different solutions which satisfy the dominant energy
condition are given: one is the delta-shell model for which the analysis is
carried out within Israel's thin shell formalism, the other approach - the
continuous profile model - is solved numerically and the interior solutions
have been (smoothly) joined with the Reissner-Nordstrom exterior. The effect of
electric charge is considered, and the equation of state, the speed of sound
and the surface redshift are calculated for both models.
| [
{
"created": "Sun, 13 Jul 2008 18:38:06 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Dec 2008 08:49:45 GMT",
"version": "v2"
}
] | 2009-01-16 | [
[
"Horvat",
"Dubravko",
""
],
[
"Ilijic",
"Sasa",
""
],
[
"Marunovic",
"Anja",
""
]
] | The notion of a compact object immune to the horizon problem and comprising an anisotropic inhomogeneous fluid with a specific radial pressure behavior, i.e. the gravastar, is extended by introducing an electrically charged component. Einstein-Maxwell field equations are solved in the asymptotically de Sitter interior where a source of the electric field is coupled to the fluid energy density. Two different solutions which satisfy the dominant energy condition are given: one is the delta-shell model for which the analysis is carried out within Israel's thin shell formalism, the other approach - the continuous profile model - is solved numerically and the interior solutions have been (smoothly) joined with the Reissner-Nordstrom exterior. The effect of electric charge is considered, and the equation of state, the speed of sound and the surface redshift are calculated for both models. |
0712.2268 | Shinji Tsujikawa | Salvatore Capozziello, Shinji Tsujikawa | Solar system and equivalence principle constraints on f(R) gravity by
chameleon approach | 5 pages, no figures, version to appear in Physical Review D | Phys.Rev.D77:107501,2008 | 10.1103/PhysRevD.77.107501 | null | gr-qc astro-ph hep-ph hep-th | null | We study constraints on f(R) dark energy models from solar system experiments
combined with experiments on the violation of equivalence principle. When the
mass of an equivalent scalar field degree of freedom is heavy in a region with
high density, a spherically symmetric body has a thin-shell so that an
effective coupling of the fifth force is suppressed through a chameleon
mechanism. We place experimental bounds on the cosmologically viable models
recently proposed in literature which have an asymptotic form f(R)=R-lambda R_c
[1-(R_c/R)^{2n}] in the regime R >> R_c. From the solar-system constraints on
the post-Newtonian parameter gamma, we derive the bound n>0.5, whereas the
constraints from the violations of weak and strong equivalence principles give
the bound n>0.9. This allows a possibility to find the deviation from the
LambdaCDM cosmological model. For the model f(R)=R-lambda R_c(R/R_c)^p with
0<p<1 the severest constraint is found to be p<10^{-10}, which shows that this
model is hardly distinguishable from the LambdaCDM cosmology.
| [
{
"created": "Fri, 14 Dec 2007 00:51:42 GMT",
"version": "v1"
},
{
"created": "Sun, 30 Mar 2008 07:49:04 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Capozziello",
"Salvatore",
""
],
[
"Tsujikawa",
"Shinji",
""
]
] | We study constraints on f(R) dark energy models from solar system experiments combined with experiments on the violation of equivalence principle. When the mass of an equivalent scalar field degree of freedom is heavy in a region with high density, a spherically symmetric body has a thin-shell so that an effective coupling of the fifth force is suppressed through a chameleon mechanism. We place experimental bounds on the cosmologically viable models recently proposed in literature which have an asymptotic form f(R)=R-lambda R_c [1-(R_c/R)^{2n}] in the regime R >> R_c. From the solar-system constraints on the post-Newtonian parameter gamma, we derive the bound n>0.5, whereas the constraints from the violations of weak and strong equivalence principles give the bound n>0.9. This allows a possibility to find the deviation from the LambdaCDM cosmological model. For the model f(R)=R-lambda R_c(R/R_c)^p with 0<p<1 the severest constraint is found to be p<10^{-10}, which shows that this model is hardly distinguishable from the LambdaCDM cosmology. |
gr-qc/9312022 | null | Arvind Borde and Alexander Vilenkin | Eternal inflation and the initial singularity | 11 pages, Tufts University cosmology preprint | Phys.Rev.Lett.72:3305-3309,1994 | 10.1103/PhysRevLett.72.3305 | null | gr-qc | null | It is shown that a physically reasonable spacetime that is eternally
inflating to the future must possess an initial singularity.
| [
{
"created": "Wed, 15 Dec 1993 16:41:23 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Borde",
"Arvind",
""
],
[
"Vilenkin",
"Alexander",
""
]
] | It is shown that a physically reasonable spacetime that is eternally inflating to the future must possess an initial singularity. |
2303.18039 | Lorenzo Pompili | Lorenzo Pompili, Alessandra Buonanno, H\'ector Estell\'es, Mohammed
Khalil, Maarten van de Meent, Deyan P. Mihaylov, Serguei Ossokine, Michael
P\"urrer, Antoni Ramos-Buades, Ajit Kumar Mehta, Roberto Cotesta, Sylvain
Marsat, Michael Boyle, Lawrence E. Kidder, Harald P. Pfeiffer, Mark A.
Scheel, Hannes R. R\"uter, Nils Vu, Reetika Dudi, Sizheng Ma, Keefe Mitman,
Denyz Melchor, Sierra Thomas and Jennifer Sanchez | Laying the foundation of the effective-one-body waveform models
SEOBNRv5: improved accuracy and efficiency for spinning non-precessing binary
black holes | null | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We present SEOBNRv5HM, a more accurate and faster inspiral-merger-ringdown
gravitational waveform model for quasi-circular, spinning, nonprecessing binary
black holes within the effective-one-body (EOB) formalism. Compared to its
predecessor, SEOBNRv4HM, the waveform model i) incorporates recent high-order
post- Newtonian results in the inspiral, with improved resummations, ii)
includes the gravitational modes (l, |m|) = (3, 2), (4, 3), in addition to the
(2, 2), (3, 3), (2, 1), (4, 4), (5, 5) modes already implemented in SEOBNRv4HM,
iii) is calibrated to larger mass-ratios and spins using a catalog of 442
numerical-relativity (NR) simulations and 13 additional waveforms from
black-hole perturbation theory, iv) incorporates information from second-order
gravitational self-force (2GSF) in the nonspinning modes and radiation-reaction
force. Computing the unfaithfulness against NR simulations, we find that for
the dominant (2, 2) mode the maximum unfaithfulness in the total mass range
$10-300 M_{\odot}$ is below $10^{-3}$ for 90% of the cases (38% for
SEOBNRv4HM). When including all modes up to l = 5 we find 98% (49%) of the
cases with unfaithfulness below $10^{-2} (10^{-3})$, while these numbers reduce
to 88% (5%) when using SEOBNRv4HM. Furthermore, the model shows improved
agreement with NR in other dynamical quantities (e.g., the angular momentum
flux and binding energy), providing a powerful check of its physical
robustness. We implemented the waveform model in a high-performance Python
package (pySEOBNR), which leads to evaluation times faster than SEOBNRv4HM by a
factor 10 to 50, depending on the configuration, and provides the flexibility
to easily include spin-precession and eccentric effects, thus making it the
starting point for a new generation of EOBNR waveform models (SEOBNRv5) to be
employed for upcoming observing runs of the LIGO-Virgo-KAGRA detectors.
| [
{
"created": "Fri, 31 Mar 2023 13:20:10 GMT",
"version": "v1"
}
] | 2023-04-03 | [
[
"Pompili",
"Lorenzo",
""
],
[
"Buonanno",
"Alessandra",
""
],
[
"Estellés",
"Héctor",
""
],
[
"Khalil",
"Mohammed",
""
],
[
"van de Meent",
"Maarten",
""
],
[
"Mihaylov",
"Deyan P.",
""
],
[
"Ossokine",
"Serguei",
""
],
[
"Pürrer",
"Michael",
""
],
[
"Ramos-Buades",
"Antoni",
""
],
[
"Mehta",
"Ajit Kumar",
""
],
[
"Cotesta",
"Roberto",
""
],
[
"Marsat",
"Sylvain",
""
],
[
"Boyle",
"Michael",
""
],
[
"Kidder",
"Lawrence E.",
""
],
[
"Pfeiffer",
"Harald P.",
""
],
[
"Scheel",
"Mark A.",
""
],
[
"Rüter",
"Hannes R.",
""
],
[
"Vu",
"Nils",
""
],
[
"Dudi",
"Reetika",
""
],
[
"Ma",
"Sizheng",
""
],
[
"Mitman",
"Keefe",
""
],
[
"Melchor",
"Denyz",
""
],
[
"Thomas",
"Sierra",
""
],
[
"Sanchez",
"Jennifer",
""
]
] | We present SEOBNRv5HM, a more accurate and faster inspiral-merger-ringdown gravitational waveform model for quasi-circular, spinning, nonprecessing binary black holes within the effective-one-body (EOB) formalism. Compared to its predecessor, SEOBNRv4HM, the waveform model i) incorporates recent high-order post- Newtonian results in the inspiral, with improved resummations, ii) includes the gravitational modes (l, |m|) = (3, 2), (4, 3), in addition to the (2, 2), (3, 3), (2, 1), (4, 4), (5, 5) modes already implemented in SEOBNRv4HM, iii) is calibrated to larger mass-ratios and spins using a catalog of 442 numerical-relativity (NR) simulations and 13 additional waveforms from black-hole perturbation theory, iv) incorporates information from second-order gravitational self-force (2GSF) in the nonspinning modes and radiation-reaction force. Computing the unfaithfulness against NR simulations, we find that for the dominant (2, 2) mode the maximum unfaithfulness in the total mass range $10-300 M_{\odot}$ is below $10^{-3}$ for 90% of the cases (38% for SEOBNRv4HM). When including all modes up to l = 5 we find 98% (49%) of the cases with unfaithfulness below $10^{-2} (10^{-3})$, while these numbers reduce to 88% (5%) when using SEOBNRv4HM. Furthermore, the model shows improved agreement with NR in other dynamical quantities (e.g., the angular momentum flux and binding energy), providing a powerful check of its physical robustness. We implemented the waveform model in a high-performance Python package (pySEOBNR), which leads to evaluation times faster than SEOBNRv4HM by a factor 10 to 50, depending on the configuration, and provides the flexibility to easily include spin-precession and eccentric effects, thus making it the starting point for a new generation of EOBNR waveform models (SEOBNRv5) to be employed for upcoming observing runs of the LIGO-Virgo-KAGRA detectors. |
1301.1895 | Eliu Huerta | E. A. Huerta and Duncan A. Brown | Effect of eccentricity on binary neutron star searches in Advanced LIGO | 5 pages, 2 figures. Submitted to Phys. Rev. D. v2: Typos corrected,
various edits in light of referee's comments. Accepted to Phys. Rev. D | Phys. Rev. D.87:127501, 2013 | 10.1103/PhysRevD.87.127501 | LIGO DCC 1200187; KITP number NSF-KITP-12-194 | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Binary neutron stars (BNSs) are the primary source of gravitational waves for
the Laser Interferometer Gravitational-Wave Observatory (LIGO) and its
international partners Virgo and KAGRA. Current BNS searches target field
binaries whose orbits will have circularized by radiation reaction before their
gravitational waves enter the Advanced LIGO sensitive band at 15 Hz. It has
been suggested that a population of BNSs may form by n-body interactions near
supermassive black holes or in globular clusters and that these systems may
have non-negligible eccentricity in the Advanced LIGO band. We show that for
BNS systems with total mass of 2.4 (6.0) solar masses, the effect of
eccentricity e < 0.02 (0.05) is negligible and a circular search is effectual
for these binaries. For eccentricities up to e = 0.4, we investigate the
selection bias caused by neglecting eccentricity in BNS searches. If such high
eccentricity systems exist, searches that specifically target eccentric
binaries will be needed in Advanced LIGO and Virgo.
| [
{
"created": "Wed, 9 Jan 2013 17:39:50 GMT",
"version": "v1"
},
{
"created": "Fri, 7 Jun 2013 21:33:29 GMT",
"version": "v2"
}
] | 2013-06-11 | [
[
"Huerta",
"E. A.",
""
],
[
"Brown",
"Duncan A.",
""
]
] | Binary neutron stars (BNSs) are the primary source of gravitational waves for the Laser Interferometer Gravitational-Wave Observatory (LIGO) and its international partners Virgo and KAGRA. Current BNS searches target field binaries whose orbits will have circularized by radiation reaction before their gravitational waves enter the Advanced LIGO sensitive band at 15 Hz. It has been suggested that a population of BNSs may form by n-body interactions near supermassive black holes or in globular clusters and that these systems may have non-negligible eccentricity in the Advanced LIGO band. We show that for BNS systems with total mass of 2.4 (6.0) solar masses, the effect of eccentricity e < 0.02 (0.05) is negligible and a circular search is effectual for these binaries. For eccentricities up to e = 0.4, we investigate the selection bias caused by neglecting eccentricity in BNS searches. If such high eccentricity systems exist, searches that specifically target eccentric binaries will be needed in Advanced LIGO and Virgo. |
1810.03902 | Pradip Mukherjee | Rabin Banerjee and Pradip Mukherjee | Galilean gauge theory from Poincare gauge theory | 20 pages, Latex; title changed, the review part is shortened and text
revised accompanying a change of emphasis. Published version | Phys. Rev. D 98, 124021 (2018) | 10.1103/PhysRevD.98.124021 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We provide an exact mapping between the Galilian gauge theory, recently
advocated by us \cite{BMM1, BMM2, BM}, and the Poincare gauge theory. Applying
this correspondence we provide a vielbein approach to the geometric formulation
of Newton's gravity where no ansatze or additional conditions are required.
| [
{
"created": "Tue, 9 Oct 2018 10:46:37 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Jan 2019 14:35:08 GMT",
"version": "v2"
}
] | 2019-01-03 | [
[
"Banerjee",
"Rabin",
""
],
[
"Mukherjee",
"Pradip",
""
]
] | We provide an exact mapping between the Galilian gauge theory, recently advocated by us \cite{BMM1, BMM2, BM}, and the Poincare gauge theory. Applying this correspondence we provide a vielbein approach to the geometric formulation of Newton's gravity where no ansatze or additional conditions are required. |
gr-qc/0001088 | Chiang-Mei Chen | Chiang-Mei Chen and James M. Nester | A Symplectic Hamiltonian Derivation of Quasilocal Energy-Momentum for GR | 24 pages, REVTEX, no figures | Grav.Cosmol. 6 (2000) 257-270 | null | null | gr-qc | null | The various roles of boundary terms in the gravitational Lagrangian and
Hamiltonian are explored. A symplectic Hamiltonian-boundary-term approach is
ideally suited for a large class of quasilocal energy-momentum expressions for
general relativity. This approach provides a physical interpretation for many
of the well-known gravitational energy-momentum expressions including all of
the pseudotensors, associating each with unique boundary conditions. From this
perspective we find that the pseudotensors of Einstein and M{\o}ller (which is
closely related to Komar's superpotential) are especially natural, but the
latter has certain shortcomings. Among the infinite possibilities, we found
that there are really only two Hamiltonian-boundary-term quasilocal expressions
which correspond to {\em covariant} boundary conditions; they are respectively
of the Dirichlet or Neumann type. Our Dirichlet expression coincides with the
expression recently obtained by Katz and coworkers using Noether arguments and
a fixed background. A modification of their argument yields our Neumann
expression.
| [
{
"created": "Thu, 27 Jan 2000 05:16:56 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Chen",
"Chiang-Mei",
""
],
[
"Nester",
"James M.",
""
]
] | The various roles of boundary terms in the gravitational Lagrangian and Hamiltonian are explored. A symplectic Hamiltonian-boundary-term approach is ideally suited for a large class of quasilocal energy-momentum expressions for general relativity. This approach provides a physical interpretation for many of the well-known gravitational energy-momentum expressions including all of the pseudotensors, associating each with unique boundary conditions. From this perspective we find that the pseudotensors of Einstein and M{\o}ller (which is closely related to Komar's superpotential) are especially natural, but the latter has certain shortcomings. Among the infinite possibilities, we found that there are really only two Hamiltonian-boundary-term quasilocal expressions which correspond to {\em covariant} boundary conditions; they are respectively of the Dirichlet or Neumann type. Our Dirichlet expression coincides with the expression recently obtained by Katz and coworkers using Noether arguments and a fixed background. A modification of their argument yields our Neumann expression. |
0705.4066 | Andrzej Krasi\'nski | Andrzej Krasi\'nski and Krzysztof Bolejko | Can a charged dust ball be sent through the Reissner--Nordstr\"{o}m
wormhole? | 30 pages, 21 figures; several corrections after referee's comments, 4
figures modified | Phys.Rev.D76:124013,2007 | 10.1103/PhysRevD.76.124013 | null | gr-qc | null | In a previous paper we formulated a set of necessary conditions for the
spherically symmetric weakly charged dust to avoid Big Bang/Big Crunch, shell
crossing and permanent central singularities. However, we did not discuss the
properties of the energy density, some of which are surprising and seem not to
have been known up to now. A singularity of infinite energy density does exist
-- it is a point singularity situated on the world line of the center of
symmetry. The condition that no mass shell collapses to $R = 0$ if it had $R >
0$ initially thus turns out to be still insufficient for avoiding a
singularity. Moreover, at the singularity the energy density $\epsilon$ is
direction-dependent: $\epsilon \to - \infty$ when we approach the singular
point along a $t =$ const hypersurface and $\epsilon \to + \infty$ when we
approach that point along the center of symmetry. The appearance of
negative-energy-density regions turns out to be inevitable. We discuss various
aspects of this property of our configuration. We also show that a permanently
pulsating configuration, with the period of pulsation independent of mass, is
possible only if there exists a permanent central singularity.
| [
{
"created": "Mon, 28 May 2007 16:55:39 GMT",
"version": "v1"
},
{
"created": "Tue, 29 May 2007 11:37:36 GMT",
"version": "v2"
},
{
"created": "Wed, 31 Oct 2007 12:58:43 GMT",
"version": "v3"
}
] | 2009-09-29 | [
[
"Krasiński",
"Andrzej",
""
],
[
"Bolejko",
"Krzysztof",
""
]
] | In a previous paper we formulated a set of necessary conditions for the spherically symmetric weakly charged dust to avoid Big Bang/Big Crunch, shell crossing and permanent central singularities. However, we did not discuss the properties of the energy density, some of which are surprising and seem not to have been known up to now. A singularity of infinite energy density does exist -- it is a point singularity situated on the world line of the center of symmetry. The condition that no mass shell collapses to $R = 0$ if it had $R > 0$ initially thus turns out to be still insufficient for avoiding a singularity. Moreover, at the singularity the energy density $\epsilon$ is direction-dependent: $\epsilon \to - \infty$ when we approach the singular point along a $t =$ const hypersurface and $\epsilon \to + \infty$ when we approach that point along the center of symmetry. The appearance of negative-energy-density regions turns out to be inevitable. We discuss various aspects of this property of our configuration. We also show that a permanently pulsating configuration, with the period of pulsation independent of mass, is possible only if there exists a permanent central singularity. |
1206.2509 | Edward Porter | J\'er\^ome Carr\'e and Edward K. Porter | Modeling a circular equatorial test-particle in a Kerr spacetime | 18 pages, 11 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Extreme Mass Ratio Inspirals (EMRIs) are one of the main gravitational wave
(GW) sources for a future space detector, such as eLISA/NGO, and third
generation ground-based detectors, like the Einstein Telescope. These systems
present an interest both in astrophysics and fundamental physics. In order to
make a high precision determination of their physical parameters, we need very
accurate theoretical waveform models or templates. In the case of a circular
equatorial orbit, the key stumbling block to the creation of these templates is
the flux function of the GW. This function can be modeled either via very
expensive numerical simulations, which then make the templates unusable for GW
astronomy, or via some analytic approximation method such as a post-Newtonian
approximation. This approximation is known to be asymptotically divergent and
is only known up to 5.5PN order for the Schwarzschild case and to 4PN order for
the Kerr case. A way to improve the convergence of the flux is to use
re-summation methods. In this work we extend previous results using the Pad\'e
and Chebyshev approximations, first by taking into account the absorption of
the GWs by the central black hole which was neglected in previous studies, and
secondly by using the information from the Schwarzschild and absorption terms
to create a Kerr flux up to 5.5PN order. We found that these two additions both
improve the convergence. We also demonstrate that the best re-summation method
for improving the flux model is based on a flux function which we call the
"inverted Chebyshev approximation".
| [
{
"created": "Tue, 12 Jun 2012 12:38:40 GMT",
"version": "v1"
}
] | 2012-06-13 | [
[
"Carré",
"Jérôme",
""
],
[
"Porter",
"Edward K.",
""
]
] | Extreme Mass Ratio Inspirals (EMRIs) are one of the main gravitational wave (GW) sources for a future space detector, such as eLISA/NGO, and third generation ground-based detectors, like the Einstein Telescope. These systems present an interest both in astrophysics and fundamental physics. In order to make a high precision determination of their physical parameters, we need very accurate theoretical waveform models or templates. In the case of a circular equatorial orbit, the key stumbling block to the creation of these templates is the flux function of the GW. This function can be modeled either via very expensive numerical simulations, which then make the templates unusable for GW astronomy, or via some analytic approximation method such as a post-Newtonian approximation. This approximation is known to be asymptotically divergent and is only known up to 5.5PN order for the Schwarzschild case and to 4PN order for the Kerr case. A way to improve the convergence of the flux is to use re-summation methods. In this work we extend previous results using the Pad\'e and Chebyshev approximations, first by taking into account the absorption of the GWs by the central black hole which was neglected in previous studies, and secondly by using the information from the Schwarzschild and absorption terms to create a Kerr flux up to 5.5PN order. We found that these two additions both improve the convergence. We also demonstrate that the best re-summation method for improving the flux model is based on a flux function which we call the "inverted Chebyshev approximation". |
2207.08749 | Kristina Giesel | Kristina Giesel and Michael Kobler | An open scattering model in polymerized quantum mechanics | 37 pages, 2 figures, corrected some typos and updated references | Mathematics 2022, 10(22), 4248 | 10.3390/math10224248 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive a quantum master equation in the context of a polymerized open
quantum mechanical system for the scattering of a Brownian particle in an ideal
gas environment. The model is formulated in a top-down approach by choosing a
Hamiltonian with a coupling between the system and environment that is
generally associated with spatial decoherence. We extend the existing work on
such models by using a non-standard representation of the canonical commutation
relations, inspired by the quantization procedure applied in loop quantum
gravity, which yields a model in which position operators are replaced by
holonomies. The derivation of the master equation in a top-down approach opens
up the possibility to investigate in detail whether the assumptions, usually
used in such models in order to obtain a tractable form of the dissipator, hold
also in the polymerized case or whether they need to be dropped or modified.
Furthermore, we discuss some physical properties of the master equation
associated to effective equations for the expectation values of the fundamental
operators and compare our results to the already existing models of collisional
decoherence.
| [
{
"created": "Mon, 18 Jul 2022 16:52:18 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Feb 2023 21:20:34 GMT",
"version": "v2"
}
] | 2023-02-17 | [
[
"Giesel",
"Kristina",
""
],
[
"Kobler",
"Michael",
""
]
] | We derive a quantum master equation in the context of a polymerized open quantum mechanical system for the scattering of a Brownian particle in an ideal gas environment. The model is formulated in a top-down approach by choosing a Hamiltonian with a coupling between the system and environment that is generally associated with spatial decoherence. We extend the existing work on such models by using a non-standard representation of the canonical commutation relations, inspired by the quantization procedure applied in loop quantum gravity, which yields a model in which position operators are replaced by holonomies. The derivation of the master equation in a top-down approach opens up the possibility to investigate in detail whether the assumptions, usually used in such models in order to obtain a tractable form of the dissipator, hold also in the polymerized case or whether they need to be dropped or modified. Furthermore, we discuss some physical properties of the master equation associated to effective equations for the expectation values of the fundamental operators and compare our results to the already existing models of collisional decoherence. |
gr-qc/9807052 | Francesco Fucito | E. Coccia and F. Fucito | Detection of Scalar Particles in Gravitational Waves from Resonant-Mass
Detectors of Spherical Shape | 4 pages, contribution to PASCOS 98 | null | null | null | gr-qc astro-ph hep-th | null | We report on some recent work, which points out the relevance of future
measurements of gravitational waves by resonant-mass detectors of spherical
shape for theories of gravity of non-Einstein type.
| [
{
"created": "Mon, 20 Jul 1998 13:06:43 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Coccia",
"E.",
""
],
[
"Fucito",
"F.",
""
]
] | We report on some recent work, which points out the relevance of future measurements of gravitational waves by resonant-mass detectors of spherical shape for theories of gravity of non-Einstein type. |
2004.04521 | Naveena Kumara A | A. Naveena Kumara, C.L. Ahmed Rizwan, Kartheek Hegde, Md Sabir Ali,
Ajith K.M | Rotating 4D Gauss-Bonnet black hole as particle accelerator | 17 pages, 4 figures | Annals of Physics 434 (2021) 168599 | 10.1016/j.aop.2021.168599 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We demonstrate that the four-dimensional Gauss-Bonnet black hole can act as a
particle accelerator with arbitrarily high centre-of-mass energy, during the
collision of two general particles near the event horizon. The Gauss-Bonnet
coupling constant $\alpha$, provides a deviation in the results from that of
Kerr black hole. Our results show that the horizon structure, the range of
allowed angular momentum and the critical angular momentum depend on the value
of $\alpha$. For extremal cases, the centre-of-mass energy diverges near the
horizon, suggesting that Gauss-Bonnet black hole can also act as a particle
accelerator like a Kerr black hole. This is interesting in the context of
probing the Planck scale physics. For the non-extremal case there exists a
finite upper bound on the centre-of-mass energy, the maximal value of which
depends on the parameter $\alpha$.
| [
{
"created": "Thu, 9 Apr 2020 12:56:52 GMT",
"version": "v1"
}
] | 2021-09-28 | [
[
"Kumara",
"A. Naveena",
""
],
[
"Rizwan",
"C. L. Ahmed",
""
],
[
"Hegde",
"Kartheek",
""
],
[
"Ali",
"Md Sabir",
""
],
[
"M",
"Ajith K.",
""
]
] | We demonstrate that the four-dimensional Gauss-Bonnet black hole can act as a particle accelerator with arbitrarily high centre-of-mass energy, during the collision of two general particles near the event horizon. The Gauss-Bonnet coupling constant $\alpha$, provides a deviation in the results from that of Kerr black hole. Our results show that the horizon structure, the range of allowed angular momentum and the critical angular momentum depend on the value of $\alpha$. For extremal cases, the centre-of-mass energy diverges near the horizon, suggesting that Gauss-Bonnet black hole can also act as a particle accelerator like a Kerr black hole. This is interesting in the context of probing the Planck scale physics. For the non-extremal case there exists a finite upper bound on the centre-of-mass energy, the maximal value of which depends on the parameter $\alpha$. |
2303.18172 | Kristina Giesel | Thomas Thiemann and Kristina Giesel | Hamiltonian Theory: Dynamics | 52 pages. This is a preprint of a chapter to appear in the "Handbook
of Quantum Gravity", edited by Cosimo Bambi, Leonardo Modesto and Ilya
Shapiro, 2023, Springer, reproduced with permission of Springer | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This chapter focuses on the status of the implementation of the dynamics in
the canonical version of Loop Quantum Gravity (LQG). Concretely this means to
provide a mathematical meaning of the quantum Einstein equations, sometimes
called Wheeler-DeWitt equations, to give a physical interpretation and Hilbert
space structure to its solutions and to construct a representation of the
algebra of observables including a physical Hamiltonian. This is a structural
overview intentionally skipping technical details.
| [
{
"created": "Fri, 31 Mar 2023 16:11:31 GMT",
"version": "v1"
}
] | 2023-04-03 | [
[
"Thiemann",
"Thomas",
""
],
[
"Giesel",
"Kristina",
""
]
] | This chapter focuses on the status of the implementation of the dynamics in the canonical version of Loop Quantum Gravity (LQG). Concretely this means to provide a mathematical meaning of the quantum Einstein equations, sometimes called Wheeler-DeWitt equations, to give a physical interpretation and Hilbert space structure to its solutions and to construct a representation of the algebra of observables including a physical Hamiltonian. This is a structural overview intentionally skipping technical details. |
1612.04205 | Kirill Bronnikov | K.A. Bronnikov, P.A. Korolyov, A. Makhmudov, M.V. Skvortsova | Wormholes and black universes communicated with extra dimensions | 6 pages, 2 figures, 1 table. Submitted to Proceedings of the
International conference on particle physics and astrophysics (10-14.10.2016,
Moscow, Russia) | J. Phys. Conf. Series 798, 012090 (2017) | 10.1088/1742-6596/798/1/012090 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In 6D general relativity with a phantom scalar field as a source of gravity,
we present solutions that implement a transition from an effective 4D geometry
times small extra dimensions to an effectively 6D space-time where the physical
laws are different from ours. We consider manifolds with the structure M0 x M1
x M2, where M0 is 2D Lorentzian space-time while each of M1 and M2 can be a
2-sphere or a 2-torus. Some solutions describe wormholes with spherical
symmetry in our space-time and toroidal extra dimensions. Others are of black
universe type: at one end there is a 6D asymptotically anti-de Sitter black
hole while beyond the horizon the geometry tends to a 4D de Sitter cosmology
times a small 2D spherical extra space.
| [
{
"created": "Tue, 13 Dec 2016 14:36:07 GMT",
"version": "v1"
}
] | 2017-09-19 | [
[
"Bronnikov",
"K. A.",
""
],
[
"Korolyov",
"P. A.",
""
],
[
"Makhmudov",
"A.",
""
],
[
"Skvortsova",
"M. V.",
""
]
] | In 6D general relativity with a phantom scalar field as a source of gravity, we present solutions that implement a transition from an effective 4D geometry times small extra dimensions to an effectively 6D space-time where the physical laws are different from ours. We consider manifolds with the structure M0 x M1 x M2, where M0 is 2D Lorentzian space-time while each of M1 and M2 can be a 2-sphere or a 2-torus. Some solutions describe wormholes with spherical symmetry in our space-time and toroidal extra dimensions. Others are of black universe type: at one end there is a 6D asymptotically anti-de Sitter black hole while beyond the horizon the geometry tends to a 4D de Sitter cosmology times a small 2D spherical extra space. |
2110.01874 | Qian Hu | Qian Hu, Cong Zhou, Jhao-Hong Peng, Linqing Wen, Qi Chu, and Manoj
Kovalam | Semianalytical Approach for Sky Localization of Gravitational Waves | 15 pages, 8 figures | Phys. Rev. D 104, 104008 (2021) | 10.1103/PhysRevD.104.104008 | null | gr-qc astro-ph.HE astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Rapid sky localization of gravitational wave sources is crucial to enable
prompt electromagnetic follow-ups. In this article, we present a novel
semianalytical approach for sky localization of gravitational waves from
compact binary coalescences. We use the Bayesian framework with an analytical
approximation to the prior distributions for a given astrophysical model. We
derive a semianalytical solution to the posterior distribution of source
directions. This method only requires one-fold numerical integral that
marginalizes over the merger time, compared to the five-fold numerical
integration otherwise needed in the Bayesian localization method. The
performance of the method is demonstrated using a set of binary neutron stars
(BNS) injections on Gaussian noise using LIGO-Virgo's design and O2
sensitivity. We find the median of 90% confidence area in O2 sensitivity to be
$\mathcal{O}(10^2) ~\mathrm{deg}^2$, comparable to that of the existing
LIGO-Virgo online localization method Bayestar and parameter estimation toolkit
LALInference. In the end, we apply this method to localize the BNS event
GW170817 and find the 50% (90%) confidence region of 11 $\mathrm{deg}^2$ (50
$\mathrm{deg}^2$). The detected optical counterpart of GW170817 resides within
our 50% confidence area.
| [
{
"created": "Tue, 5 Oct 2021 08:26:07 GMT",
"version": "v1"
},
{
"created": "Wed, 3 Nov 2021 14:43:33 GMT",
"version": "v2"
}
] | 2021-11-04 | [
[
"Hu",
"Qian",
""
],
[
"Zhou",
"Cong",
""
],
[
"Peng",
"Jhao-Hong",
""
],
[
"Wen",
"Linqing",
""
],
[
"Chu",
"Qi",
""
],
[
"Kovalam",
"Manoj",
""
]
] | Rapid sky localization of gravitational wave sources is crucial to enable prompt electromagnetic follow-ups. In this article, we present a novel semianalytical approach for sky localization of gravitational waves from compact binary coalescences. We use the Bayesian framework with an analytical approximation to the prior distributions for a given astrophysical model. We derive a semianalytical solution to the posterior distribution of source directions. This method only requires one-fold numerical integral that marginalizes over the merger time, compared to the five-fold numerical integration otherwise needed in the Bayesian localization method. The performance of the method is demonstrated using a set of binary neutron stars (BNS) injections on Gaussian noise using LIGO-Virgo's design and O2 sensitivity. We find the median of 90% confidence area in O2 sensitivity to be $\mathcal{O}(10^2) ~\mathrm{deg}^2$, comparable to that of the existing LIGO-Virgo online localization method Bayestar and parameter estimation toolkit LALInference. In the end, we apply this method to localize the BNS event GW170817 and find the 50% (90%) confidence region of 11 $\mathrm{deg}^2$ (50 $\mathrm{deg}^2$). The detected optical counterpart of GW170817 resides within our 50% confidence area. |
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