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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/0409109
|
Patricio S. Letelier
|
D. Vogt and P. S. Letelier
|
A General Relativistic Model for the Gravitational Field of Active
Galactic Nuclei Surrounded by a Disk
|
24 pages, LATEX. Phys. Rev. D (in press)
|
Phys.Rev. D71 (2005) 044009
|
10.1103/PhysRevD.71.044009
| null |
gr-qc astro-ph
| null |
An exact but simple general relativistic model for the gravitational field of
active galactic nuclei is constructed, based on the superposition in Weyl
coordinates of a black hole, a Chazy-Curzon disk and two rods, which represent
matter jets. The influence of the rods on the matter properties of the disk and
on its stability is examined. We find that in general they contribute to
destabilize the disk. Also the oscillation frequencies for perturbed circular
geodesics on the disk are computed, and some geodesic orbits for the superposed
metric are numerically calculated.
|
[
{
"created": "Tue, 28 Sep 2004 17:35:03 GMT",
"version": "v1"
}
] |
2009-11-10
|
[
[
"Vogt",
"D.",
""
],
[
"Letelier",
"P. S.",
""
]
] |
An exact but simple general relativistic model for the gravitational field of active galactic nuclei is constructed, based on the superposition in Weyl coordinates of a black hole, a Chazy-Curzon disk and two rods, which represent matter jets. The influence of the rods on the matter properties of the disk and on its stability is examined. We find that in general they contribute to destabilize the disk. Also the oscillation frequencies for perturbed circular geodesics on the disk are computed, and some geodesic orbits for the superposed metric are numerically calculated.
|
2210.15620
|
Ahmad Al-Badawi
|
Ahmad Al-Badawi
|
The Dirac and Klein-Gordon equations and Greybody Radiation for the
Regular Hayward Black Hole
| null |
Canadian Journal of Physics, 2022
|
10.1139/cjp-2022-0075
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We investigate the Dirac and Klein-Gordon equations, as well as greybody
radiation, for the Hayward black hole (BH) spacetime. We first consider the
Dirac equation using a null tetrad in the Newman- Penrose (NP) formalism. The
equations are then separated into angular and radial parts. A pair of
one-dimensional Schr\"odinger like wave equations with effective potentials is
obtained from the radial part. In order to examine the behavior of potentials,
they are plotted with respect to radial distances. Additionally, the
Klein-Gordon equation is considered in the Hayward BH spacetime. At the end, we
compute greybody factors for bosons and fermions and our results are shown
graphically and discussed.
|
[
{
"created": "Sun, 23 Oct 2022 08:33:07 GMT",
"version": "v1"
}
] |
2022-10-28
|
[
[
"Al-Badawi",
"Ahmad",
""
]
] |
We investigate the Dirac and Klein-Gordon equations, as well as greybody radiation, for the Hayward black hole (BH) spacetime. We first consider the Dirac equation using a null tetrad in the Newman- Penrose (NP) formalism. The equations are then separated into angular and radial parts. A pair of one-dimensional Schr\"odinger like wave equations with effective potentials is obtained from the radial part. In order to examine the behavior of potentials, they are plotted with respect to radial distances. Additionally, the Klein-Gordon equation is considered in the Hayward BH spacetime. At the end, we compute greybody factors for bosons and fermions and our results are shown graphically and discussed.
|
1509.04129
|
Valerio Faraoni
|
Valerio Faraoni, Angus Prain, and Andres F. Zambrano Moreno (Bishop's
University)
|
Black holes and wormholes subject to conformal mappings
|
7 pages, 2 figures
|
Phys. Rev. D 93, 024005 (2016)
|
10.1103/PhysRevD.93.024005
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Solutions of the field equations of theories of gravity which admit distinct
conformal frame representations can look very different in these frames. We
show that Brans class IV solutions describe wormholes in the Jordan frame (in a
certain parameter range) but correspond to horizonless geometries in the
Einstein frame. The reasons for such a change of behaviour under conformal
mappings are elucidated in general, using Brans IV solutions as an example.
|
[
{
"created": "Mon, 14 Sep 2015 15:09:05 GMT",
"version": "v1"
}
] |
2016-01-13
|
[
[
"Faraoni",
"Valerio",
"",
"Bishop's\n University"
],
[
"Prain",
"Angus",
"",
"Bishop's\n University"
],
[
"Moreno",
"Andres F. Zambrano",
"",
"Bishop's\n University"
]
] |
Solutions of the field equations of theories of gravity which admit distinct conformal frame representations can look very different in these frames. We show that Brans class IV solutions describe wormholes in the Jordan frame (in a certain parameter range) but correspond to horizonless geometries in the Einstein frame. The reasons for such a change of behaviour under conformal mappings are elucidated in general, using Brans IV solutions as an example.
|
gr-qc/0009030
|
S. Mignemi
|
S.Alexeyev, S.Mignemi
|
Black Holes and Naked Singularities in Low Energy Limit of String
Gravity with Modulus Field
|
more details are added and some misprint are corrected
|
Class.Quant.Grav. 18 (2001) 4165-4178
|
10.1088/0264-9381/18/20/301
|
INFNCA-TH0015
|
gr-qc
| null |
We show that the black hole solutions of the effective string theory action,
where one-loop effects that couple the moduli to gravity via a Gauss-Bonnet
term are taken into account, admit primary scalar hair. The requirement of
absence of naked singularities imposes an upper bound on the scalar charges.
|
[
{
"created": "Mon, 11 Sep 2000 11:27:57 GMT",
"version": "v1"
},
{
"created": "Fri, 16 Mar 2001 12:11:14 GMT",
"version": "v2"
}
] |
2009-10-31
|
[
[
"Alexeyev",
"S.",
""
],
[
"Mignemi",
"S.",
""
]
] |
We show that the black hole solutions of the effective string theory action, where one-loop effects that couple the moduli to gravity via a Gauss-Bonnet term are taken into account, admit primary scalar hair. The requirement of absence of naked singularities imposes an upper bound on the scalar charges.
|
1105.0459
|
Marcelo Salgado
|
Cesar Merlin and Marcelo Salgado
|
The gravitational light shift and the Sachs-Wolfe effect
|
8 pages; accepted for publication in General Relativity and
Gravitation
|
Gen.Rel.Grav.43:2701-2712,2011
|
10.1007/s10714-011-1193-7
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Using a 3+1 decomposition of spacetime, we derive a new formula to compute
the gravitational light shifts as measured by two observers which are normal to
the spacelike hypersurfaces defining the foliation. This formula is quite
general and is also independent of the existence of Killing fields. Known
examples are considered to illustrate the usefulness of the formula. In
particular, we focus on the Sachs-Wolfe effect that arises in a perturbed
Friedman-Robertson-Walker cosmology.
|
[
{
"created": "Tue, 3 May 2011 00:12:15 GMT",
"version": "v1"
}
] |
2011-09-28
|
[
[
"Merlin",
"Cesar",
""
],
[
"Salgado",
"Marcelo",
""
]
] |
Using a 3+1 decomposition of spacetime, we derive a new formula to compute the gravitational light shifts as measured by two observers which are normal to the spacelike hypersurfaces defining the foliation. This formula is quite general and is also independent of the existence of Killing fields. Known examples are considered to illustrate the usefulness of the formula. In particular, we focus on the Sachs-Wolfe effect that arises in a perturbed Friedman-Robertson-Walker cosmology.
|
gr-qc/9509057
|
Robert Manuel Wald
|
Robert M. Wald
|
Quantum Field Theory in Curved Spacetime
|
Write-up of plenary talk given at GR14; 18 pages; plain LaTeX file
| null | null | null |
gr-qc
| null |
We review the mathematically rigorous formulation of the quantum theory of a
linear field propagating in a globally hyperbolic spacetime. This formulation
is accomplished via the algebraic approach, which, in essence, simultaneously
admits all states in all possible (unitarily inequivalent) Hilbert space
constructions. The physically nonsingular states are restricted by the
requirement that their two-point function satisfy the Hadamard condition, which
insures that the ultra-violet behavior of the state be similar to that of the
vacuum state in Minkowski spacetime, and that the expected stress-energy tensor
in the state be finite. We briefly review the Unruh and Hawking effects from
the perspective of the theoretical framework adopted here. A brief discussion
also is given of several open issues and questions in quantum field theory in
curved spacetime regarding the treatment of ``back-reaction", the validity of
some version of the ``averaged null energy condition'', and the formulation and
properties of quantum field theory in causality violating spacetimes.
|
[
{
"created": "Fri, 29 Sep 1995 16:37:47 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Wald",
"Robert M.",
""
]
] |
We review the mathematically rigorous formulation of the quantum theory of a linear field propagating in a globally hyperbolic spacetime. This formulation is accomplished via the algebraic approach, which, in essence, simultaneously admits all states in all possible (unitarily inequivalent) Hilbert space constructions. The physically nonsingular states are restricted by the requirement that their two-point function satisfy the Hadamard condition, which insures that the ultra-violet behavior of the state be similar to that of the vacuum state in Minkowski spacetime, and that the expected stress-energy tensor in the state be finite. We briefly review the Unruh and Hawking effects from the perspective of the theoretical framework adopted here. A brief discussion also is given of several open issues and questions in quantum field theory in curved spacetime regarding the treatment of ``back-reaction", the validity of some version of the ``averaged null energy condition'', and the formulation and properties of quantum field theory in causality violating spacetimes.
|
gr-qc/9706082
|
Bill Walker
|
William D. Walker, J. Dual
|
Propagation Speed of Longitudinally Oscillating Gravitational and
Electrical Fields
|
No changes - better PS, 13 pages, PS
| null | null | null |
gr-qc
| null |
The near-field Lienard-Wiechert potential solution of a longitudinally
oscillating electrical field produced by an oscillating charge is presented,
and the results are compared to the R. P. Feynman multipole far-field solution.
The results indicate that the phase speed of a longitudinally oscillating
electrical field is much faster than the speed of light in the near field. A
similar analysis is presented for a longitudinally oscillating gravitational
field produced by a vibrating mass. The result also indicates that the phase
speed of a longitudinally oscillating gravitational field is also much faster
than the speed of light in the near-field. The possibility of measuring the
group speed of a longitudinally oscillating electrical field and a
longitudinally oscillating gravitational field, which is commonly thought to be
equal to the speed of light, is now being considered. The basic idea is to
amplitude-modulate the longitudinal vibration of a charge or a mass and to
measure the resultant longitudinal vibration of a nearby charge or a mass due
to electrical or gravitational interaction. The modulation signal can then be
extracted using a diode detector and the group speed can then be determined
from the oscillation frequency, the separation distance between the masses, and
the measurement of the phase shift of the modulation signal. If the group speed
is equal to the speed of light, then phase shifts on the order of 1 microdegree
could be generated with a typical experimental set-up. An analysis using the
classical definition of group velocity for a longitudinally oscillating
electrical field is presented, and the results indicate that the group speed is
also much faster that the speed of light in the near field, which should not be
possible due to causality violation.
|
[
{
"created": "Fri, 27 Jun 1997 14:29:59 GMT",
"version": "v1"
},
{
"created": "Mon, 28 Jul 1997 18:37:18 GMT",
"version": "v2"
}
] |
2008-02-03
|
[
[
"Walker",
"William D.",
""
],
[
"Dual",
"J.",
""
]
] |
The near-field Lienard-Wiechert potential solution of a longitudinally oscillating electrical field produced by an oscillating charge is presented, and the results are compared to the R. P. Feynman multipole far-field solution. The results indicate that the phase speed of a longitudinally oscillating electrical field is much faster than the speed of light in the near field. A similar analysis is presented for a longitudinally oscillating gravitational field produced by a vibrating mass. The result also indicates that the phase speed of a longitudinally oscillating gravitational field is also much faster than the speed of light in the near-field. The possibility of measuring the group speed of a longitudinally oscillating electrical field and a longitudinally oscillating gravitational field, which is commonly thought to be equal to the speed of light, is now being considered. The basic idea is to amplitude-modulate the longitudinal vibration of a charge or a mass and to measure the resultant longitudinal vibration of a nearby charge or a mass due to electrical or gravitational interaction. The modulation signal can then be extracted using a diode detector and the group speed can then be determined from the oscillation frequency, the separation distance between the masses, and the measurement of the phase shift of the modulation signal. If the group speed is equal to the speed of light, then phase shifts on the order of 1 microdegree could be generated with a typical experimental set-up. An analysis using the classical definition of group velocity for a longitudinally oscillating electrical field is presented, and the results indicate that the group speed is also much faster that the speed of light in the near field, which should not be possible due to causality violation.
|
gr-qc/9702034
|
Frank Gronwald
|
Frank Gronwald
|
Metric-Affine Gauge Theory of Gravity I. Fundamental Structure and Field
Equations
|
43 pages, LaTeX, six .eps figures included, uses lscape.sty, to
appear in Int. J. Mod. Phys. D
|
Int.J.Mod.Phys. D6 (1997) 263-304
|
10.1142/S0218271897000157
| null |
gr-qc hep-th
| null |
We give a self-contained introduction into the metric-affine gauge theory of
gravity. Starting from the equivalence of reference frames, the prototype of a
gauge theory is presented and illustrated by the example of Yang-Mills theory.
Along the same lines we perform a gauging of the affine group and establish the
geometry of metric-affine gravity. The results are put into the dynamical
framework of a classical field theory. We derive subcases of metric-affine
gravity by restricting the affine group to some of its subgroups. The important
subcase of general relativity as a gauge theory of translations is explained in
detail.
|
[
{
"created": "Tue, 18 Feb 1997 16:56:38 GMT",
"version": "v1"
}
] |
2015-06-25
|
[
[
"Gronwald",
"Frank",
""
]
] |
We give a self-contained introduction into the metric-affine gauge theory of gravity. Starting from the equivalence of reference frames, the prototype of a gauge theory is presented and illustrated by the example of Yang-Mills theory. Along the same lines we perform a gauging of the affine group and establish the geometry of metric-affine gravity. The results are put into the dynamical framework of a classical field theory. We derive subcases of metric-affine gravity by restricting the affine group to some of its subgroups. The important subcase of general relativity as a gauge theory of translations is explained in detail.
|
gr-qc/9701066
|
Marian Fecko
|
Marian Fecko
|
On 3+1 decompositions with respect to an observer field via differential
forms
|
15 pages, AmsTeX, to be published in J.Math.Phys. (sept.'97), minor
changes done
|
J.Math.Phys. 38 (1997) 4542-4560
|
10.1063/1.532142
| null |
gr-qc dg-ga math-ph math.DG math.MP
| null |
3+1 decompositions of differential forms on a Lorentzian manifold (M,g;+ - -
-) with respect to arbitrary observer field and the decomposition of the
standard operations acting on them are studied, making use of the ideas of the
theory of connections on principal bundles. Simple explicit general formulas
are given as well as their application to the Maxwell equations.
|
[
{
"created": "Thu, 30 Jan 1997 15:48:48 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Jun 1997 13:08:37 GMT",
"version": "v2"
}
] |
2009-10-30
|
[
[
"Fecko",
"Marian",
""
]
] |
3+1 decompositions of differential forms on a Lorentzian manifold (M,g;+ - - -) with respect to arbitrary observer field and the decomposition of the standard operations acting on them are studied, making use of the ideas of the theory of connections on principal bundles. Simple explicit general formulas are given as well as their application to the Maxwell equations.
|
0809.0927
|
Matt Visser
|
Matt Visser (Victoria University of Wellington)
|
Traversable wormholes from surgically modified Schwarzschild spacetimes
|
Pre-arXiv article from 1989; 12 pages, no figures. (Uploaded to arXiv
to help researchers with limited library facilities.)
|
Nucl.Phys.B328:203-212,1989
|
10.1016/0550-3213(89)90100-4
|
LA-UR-89-244
|
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this paper I present a new class of traversable wormholes. This is done by
surgically grafting two Schwarzschild spacetimes together in such a way that no
event horizon is permitted to form. This surgery concentrates a non--zero
stress--energy on the boundary layer between the two asymptotically flat
regions. I shall investigate this stress--energy in detail using the "junction
condition" formalism. A feature of the present analysis is that this class of
traversable wormholes is sufficiently simple for a (partial) dynamical
stability analysis to be carried out. The stability analysis places constraints
on the equation of state of the exotic matter that comprises the throat of the
wormhole.
|
[
{
"created": "Thu, 4 Sep 2008 22:35:09 GMT",
"version": "v1"
}
] |
2008-11-26
|
[
[
"Visser",
"Matt",
"",
"Victoria University of Wellington"
]
] |
In this paper I present a new class of traversable wormholes. This is done by surgically grafting two Schwarzschild spacetimes together in such a way that no event horizon is permitted to form. This surgery concentrates a non--zero stress--energy on the boundary layer between the two asymptotically flat regions. I shall investigate this stress--energy in detail using the "junction condition" formalism. A feature of the present analysis is that this class of traversable wormholes is sufficiently simple for a (partial) dynamical stability analysis to be carried out. The stability analysis places constraints on the equation of state of the exotic matter that comprises the throat of the wormhole.
|
gr-qc/0302081
|
Pieter-Jan De Smet
|
Pieter-Jan De Smet
|
Five-dimensional metrics of Petrov type 22
|
13 pages, 1 figure
|
Class.Quant.Grav. 20 (2003) 2541-2552
|
10.1088/0264-9381/20/13/306
|
YITP-SB-03/7
|
gr-qc hep-th
| null |
We classify all five-dimensional Einstein manifolds that are static, have an
SO(3) isometry group and have Petrov type 22. We use this classification to
show that the localized black hole in the Randall-Sundrum scenario necessarily
has Petrov type 4.
|
[
{
"created": "Wed, 19 Feb 2003 20:37:43 GMT",
"version": "v1"
}
] |
2009-11-10
|
[
[
"De Smet",
"Pieter-Jan",
""
]
] |
We classify all five-dimensional Einstein manifolds that are static, have an SO(3) isometry group and have Petrov type 22. We use this classification to show that the localized black hole in the Randall-Sundrum scenario necessarily has Petrov type 4.
|
1101.0319
|
Jun Wu
|
Y.J.Zhang, J. Wu and P.T.Leung
|
High-frequency behavior of w-mode pulsations of compact stars
|
22 pages, 4 figures
|
Phys.Rev.D83:064012,2011
|
10.1103/PhysRevD.83.064012
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the asymptotic behavior of the quasi-normal modes (QNMs) of w-mode
pulsations of compact stars in the high-frequency regime. We observe that both
the axial and polar w-mode QNMs attain similar asymptotic behaviors in spite of
the fact that they are described by two totally different differential equation
systems. We obtain robust asymptotic formulae relating w-mode QNMs of different
polarities and different angular momenta. To explore the physical reason
underlying such similarity, we first derive a high-frequency approximation for
the polar w-mode oscillations to unify the descriptions for both cases. Then,
we develop WKB-type analyses for them and quantitatively explain the observed
asymptotic behaviors for polytropic stars and quark stars. We also point out
that such asymptotic behaviors for realistic stars are strongly dependent on
the equation of state near the stellar surface.
|
[
{
"created": "Sat, 1 Jan 2011 04:58:57 GMT",
"version": "v1"
}
] |
2011-03-22
|
[
[
"Zhang",
"Y. J.",
""
],
[
"Wu",
"J.",
""
],
[
"Leung",
"P. T.",
""
]
] |
We study the asymptotic behavior of the quasi-normal modes (QNMs) of w-mode pulsations of compact stars in the high-frequency regime. We observe that both the axial and polar w-mode QNMs attain similar asymptotic behaviors in spite of the fact that they are described by two totally different differential equation systems. We obtain robust asymptotic formulae relating w-mode QNMs of different polarities and different angular momenta. To explore the physical reason underlying such similarity, we first derive a high-frequency approximation for the polar w-mode oscillations to unify the descriptions for both cases. Then, we develop WKB-type analyses for them and quantitatively explain the observed asymptotic behaviors for polytropic stars and quark stars. We also point out that such asymptotic behaviors for realistic stars are strongly dependent on the equation of state near the stellar surface.
|
gr-qc/9908026
|
David Wands
|
Damien J. Holden and David Wands
|
Self-similar cosmological solutions with a non-minimally coupled scalar
field
|
10 pages, 1 figure, revtex version to appear in Phys Rev D,
references added
|
Phys.Rev.D61:043506,2000
|
10.1103/PhysRevD.61.043506
| null |
gr-qc astro-ph
| null |
We present self-similar cosmological solutions for a barotropic fluid plus
scalar field with Brans-Dicke-type coupling to the spacetime curvature and an
arbitrary power-law potential energy. We identify all the fixed points in the
autonomous phase-plane, including a scaling solution where the fluid density
scales with the scalar field's kinetic and potential energy. This is related by
a conformal transformation to a scaling solution for a scalar field with
exponential potential minimally coupled to the spacetime curvature, but
non-minimally coupled to the barotropic fluid. Radiation is automatically
decoupled from the scalar field, but energy transfer between the field and
non-relativistic dark matter can lead to a change to an accelerated expansion
at late times in the Einstein frame. The scalar field density can mimic a
cosmological constant even for steep potentials in the strong coupling limit.
|
[
{
"created": "Mon, 9 Aug 1999 13:20:06 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Oct 1999 13:32:03 GMT",
"version": "v2"
}
] |
2008-11-26
|
[
[
"Holden",
"Damien J.",
""
],
[
"Wands",
"David",
""
]
] |
We present self-similar cosmological solutions for a barotropic fluid plus scalar field with Brans-Dicke-type coupling to the spacetime curvature and an arbitrary power-law potential energy. We identify all the fixed points in the autonomous phase-plane, including a scaling solution where the fluid density scales with the scalar field's kinetic and potential energy. This is related by a conformal transformation to a scaling solution for a scalar field with exponential potential minimally coupled to the spacetime curvature, but non-minimally coupled to the barotropic fluid. Radiation is automatically decoupled from the scalar field, but energy transfer between the field and non-relativistic dark matter can lead to a change to an accelerated expansion at late times in the Einstein frame. The scalar field density can mimic a cosmological constant even for steep potentials in the strong coupling limit.
|
1611.02013
|
Pantelis Apostolopoulos
|
Pantelis S. Apostolopoulos
|
Vacuum self similar anisotropic cosmologies in $F(R)-$gravity
|
16 pages, no figures, (v2) section 4 is slightly extended (including
the reformulation of the field equations in dimensionless variables) to match
the accepted version in General Relativity and Gravitation
|
Gen.Rel.Grav. 49 (2017) no.4, 59
|
10.1007/s10714-017-2222-y
| null |
gr-qc hep-th math-ph math.MP
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The implications from the existence of a proper Homothetic Vector Field (HVF)
on the dynamics of vacuum anisotropic models in $F(R)$ gravitational theory are
studied. The fact that \emph{every} Spatially Homogeneous vacuum model is
equivalent, formally, with a "flux" -free anisotropic fluid model in standard
gravity and the induced power-law form of the functional $F(R)$ due to
self-similarity enable us to close the system of equations. We found some new
exact anisotropic solutions that arise as fixed points in the associated
dynamical system. The non-existence of Kasner-like (Bianchi type I) solutions
in proper $F(R)-$gravity (i.e. $R\neq 0$) strengthens the belief that curvature
corrections will prevent the shear influence into the past thus permitting an
isotropic singularity. We also discuss certain issues regarding the lack of
vacuum models of type III, IV, VII$_{h}$ in comparison with the corresponding
results in standard gravity.
|
[
{
"created": "Mon, 7 Nov 2016 12:19:10 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Mar 2017 08:09:47 GMT",
"version": "v2"
}
] |
2017-03-28
|
[
[
"Apostolopoulos",
"Pantelis S.",
""
]
] |
The implications from the existence of a proper Homothetic Vector Field (HVF) on the dynamics of vacuum anisotropic models in $F(R)$ gravitational theory are studied. The fact that \emph{every} Spatially Homogeneous vacuum model is equivalent, formally, with a "flux" -free anisotropic fluid model in standard gravity and the induced power-law form of the functional $F(R)$ due to self-similarity enable us to close the system of equations. We found some new exact anisotropic solutions that arise as fixed points in the associated dynamical system. The non-existence of Kasner-like (Bianchi type I) solutions in proper $F(R)-$gravity (i.e. $R\neq 0$) strengthens the belief that curvature corrections will prevent the shear influence into the past thus permitting an isotropic singularity. We also discuss certain issues regarding the lack of vacuum models of type III, IV, VII$_{h}$ in comparison with the corresponding results in standard gravity.
|
1612.01615
|
Zhi-Chao Zhao
|
Zhe Chang, Chao-Guang Huang, Zhi-Chao Zhao
|
Is GW151226 a really signal of gravitational wave?
| null | null |
10.1088/1674-1137/41/2/025001
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Recently, the LIGO Scientific Collaboration and Virgo Collaboration published
the second observation on gravitational wave GW151226 [Phys. Rev. Lett. 116,
241103 (2016)] from the binary black hole coalescence with initial masses about
14 M$_\odot$ and 8 M$_\odot$. They claimed that the peak gravitational strain
was reached at about 450 Hz, the inverse of which has been longer than the
average time a photon staying in the Fabry-Perot cavities in two arms. In this
case, the phase-difference of a photon in the two arms due to the propagation
of gravitational wave does not always increase as the photon stays in the
cavities. It might even be cancelled to zero in extreme cases. When the
propagation effect is taken into account, we find that the claimed signal
GW151226 would almost disappear.
|
[
{
"created": "Tue, 6 Dec 2016 01:13:47 GMT",
"version": "v1"
}
] |
2016-12-07
|
[
[
"Chang",
"Zhe",
""
],
[
"Huang",
"Chao-Guang",
""
],
[
"Zhao",
"Zhi-Chao",
""
]
] |
Recently, the LIGO Scientific Collaboration and Virgo Collaboration published the second observation on gravitational wave GW151226 [Phys. Rev. Lett. 116, 241103 (2016)] from the binary black hole coalescence with initial masses about 14 M$_\odot$ and 8 M$_\odot$. They claimed that the peak gravitational strain was reached at about 450 Hz, the inverse of which has been longer than the average time a photon staying in the Fabry-Perot cavities in two arms. In this case, the phase-difference of a photon in the two arms due to the propagation of gravitational wave does not always increase as the photon stays in the cavities. It might even be cancelled to zero in extreme cases. When the propagation effect is taken into account, we find that the claimed signal GW151226 would almost disappear.
|
gr-qc/0604096
|
Katanaev
|
M. O. Katanaev
|
Polynomial Hamiltonian form of General Relativity
|
33 pages, 1 figure, corrected references
|
Theor.Math.Phys. 148 (2006) 1264-1294; Teor.Mat.Fiz. 148 (2006)
459-494
|
10.1007/s11232-006-0116-3
| null |
gr-qc
| null |
Phase space of General Relativity is extended to a Poisson manifold by
inclusion of the determinant of the metric and conjugate momentum as additional
independent variables. As a result, the action and the constraints take a
polynomial form. New expression for the generating functional for the Green
functions is proposed. We show that the Dirac bracket defines degenerate
Poisson structure on a manifold, and a second class constraints are the Casimir
functions with respect to this structure. As an application of the new
variables, we consider the Friedmann universe.
|
[
{
"created": "Fri, 21 Apr 2006 17:18:57 GMT",
"version": "v1"
},
{
"created": "Wed, 6 Sep 2006 18:08:54 GMT",
"version": "v2"
}
] |
2009-11-11
|
[
[
"Katanaev",
"M. O.",
""
]
] |
Phase space of General Relativity is extended to a Poisson manifold by inclusion of the determinant of the metric and conjugate momentum as additional independent variables. As a result, the action and the constraints take a polynomial form. New expression for the generating functional for the Green functions is proposed. We show that the Dirac bracket defines degenerate Poisson structure on a manifold, and a second class constraints are the Casimir functions with respect to this structure. As an application of the new variables, we consider the Friedmann universe.
|
2103.14568
|
Brajesh Gupt
|
Abhay Ashtekar, Brajesh Gupt, and V. Sreenath
|
Cosmic tango between the very small and the very large: Addressing CMB
anomalies through Loop Quantum Cosmology
|
30 pages, 9 figures
|
Frontiers in Astronomy & Space Science, 8, 685288 (2021)
|
10.3389/fspas.2021.685288
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
While the standard, six-parameter, spatially flat $\Lambda$CDM model has been
highly successful, certain anomalies in the cosmic microwave background bring
out a tension between this model and observations. The statistical significance
of any one anomaly is small. However, taken together, the presence of two or
more of them imply that according to standard inflationary theories we live in
quite an exceptional universe. We revisit the analysis of the PLANCK
collaboration using loop quantum cosmology, where an unforeseen interplay
between the ultraviolet and the infrared makes the \emph{primordial} power
spectrum scale dependent at very small $k$. Consequently, we are led to a
somewhat different $\Lambda$CDM universe in which anomalies associated with
large scale power suppression and the lensing amplitude are both alleviated.
The analysis also leads to new predictions for future observations. This
article is addressed both to cosmology and LQG communities, and we have
attempted to make it self-contained.
|
[
{
"created": "Fri, 26 Mar 2021 16:28:46 GMT",
"version": "v1"
}
] |
2021-09-21
|
[
[
"Ashtekar",
"Abhay",
""
],
[
"Gupt",
"Brajesh",
""
],
[
"Sreenath",
"V.",
""
]
] |
While the standard, six-parameter, spatially flat $\Lambda$CDM model has been highly successful, certain anomalies in the cosmic microwave background bring out a tension between this model and observations. The statistical significance of any one anomaly is small. However, taken together, the presence of two or more of them imply that according to standard inflationary theories we live in quite an exceptional universe. We revisit the analysis of the PLANCK collaboration using loop quantum cosmology, where an unforeseen interplay between the ultraviolet and the infrared makes the \emph{primordial} power spectrum scale dependent at very small $k$. Consequently, we are led to a somewhat different $\Lambda$CDM universe in which anomalies associated with large scale power suppression and the lensing amplitude are both alleviated. The analysis also leads to new predictions for future observations. This article is addressed both to cosmology and LQG communities, and we have attempted to make it self-contained.
|
0801.3142
|
Michael Holst
|
Burak Aksoylu, David Bernstein, Stephen Bond, Michael Holst
|
Generating Initial Data in General Relativity using Adaptive Finite
Element Methods
|
54 pages, 15 figures. Published as LSU CCT Technical Report 2008-09
| null | null |
LSU Center for Computation and Technology (CCT) Technical Report
2008-09
|
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The conformal formulation of the Einstein constraint equations is first
reviewed, and we then consider the design, analysis, and implementation of
adaptive multilevel finite element-type numerical methods for the resulting
coupled nonlinear elliptic system. We derive weak formulations of the coupled
constraints, and review some new developments in the solution theory for the
constraints in the cases of constant mean extrinsic curvature (CMC) data,
near-CMC data, and arbitrarily prescribed mean extrinsic curvature data. We
then outline some recent results on a priori and a posteriori error estimates
for a broad class of Galerkin-type approximation methods for this system which
includes techniques such as finite element, wavelet, and spectral methods. We
then use these estimates to construct an adaptive finite element method (AFEM)
for solving this system numerically, and outline some new convergence and
optimality results. We then describe in some detail an implementation of the
methods using the FETK software package, which is an adaptive multilevel finite
element code designed to solve nonlinear elliptic and parabolic systems on
Riemannian manifolds. We finish by describing a simplex mesh generation
algorithm for compact binary objects, and then look at a detailed example
showing the use of FETK for numerical solution of the constraints.
|
[
{
"created": "Mon, 21 Jan 2008 07:23:52 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Feb 2008 22:28:01 GMT",
"version": "v2"
},
{
"created": "Tue, 7 Apr 2009 14:22:04 GMT",
"version": "v3"
}
] |
2009-04-07
|
[
[
"Aksoylu",
"Burak",
""
],
[
"Bernstein",
"David",
""
],
[
"Bond",
"Stephen",
""
],
[
"Holst",
"Michael",
""
]
] |
The conformal formulation of the Einstein constraint equations is first reviewed, and we then consider the design, analysis, and implementation of adaptive multilevel finite element-type numerical methods for the resulting coupled nonlinear elliptic system. We derive weak formulations of the coupled constraints, and review some new developments in the solution theory for the constraints in the cases of constant mean extrinsic curvature (CMC) data, near-CMC data, and arbitrarily prescribed mean extrinsic curvature data. We then outline some recent results on a priori and a posteriori error estimates for a broad class of Galerkin-type approximation methods for this system which includes techniques such as finite element, wavelet, and spectral methods. We then use these estimates to construct an adaptive finite element method (AFEM) for solving this system numerically, and outline some new convergence and optimality results. We then describe in some detail an implementation of the methods using the FETK software package, which is an adaptive multilevel finite element code designed to solve nonlinear elliptic and parabolic systems on Riemannian manifolds. We finish by describing a simplex mesh generation algorithm for compact binary objects, and then look at a detailed example showing the use of FETK for numerical solution of the constraints.
|
1505.06725
|
Matthew Pitkin
|
M. Pitkin
|
Comment on "Measurements of Newton's gravitational constant and the
length of day"
|
To be published in EPL. This is an abridged version of the original
document to conform the the journal's "Comment" page limit, therefore further
figures, tables and explanation of the analysis can be found in v1
arXiv:1505.06725v1. This also contains a response to the comment
arXiv:1508.00532. The analysis code and figures can be found at
https://github.com/mattpitkin/periodicG
| null |
10.1209/0295-5075/111/30002
| null |
gr-qc physics.class-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
There have been recent claims (Anderson et al., EPL, 110, 10002) of a 5.9
year periodicity in measurements of Newton's gravitational constant, $G$, which
show a very strong correlation with observed periodic variations in the length
of the day. I have used Bayesian model comparison to test this claim compared
to other hypotheses that could explain the variation in the $G$ measurements. I
have used the data from the initial claim, and from an updated set of compiled
$G$ measurements that more accurately reflect the experimental dates, and find
that a model containing an additional unknown Gaussian noise component is
hugely favoured, by factors of $\gtrsim e^{30}$, over two models allowing for a
sinusoidal component.
|
[
{
"created": "Mon, 25 May 2015 19:47:12 GMT",
"version": "v1"
},
{
"created": "Wed, 12 Aug 2015 11:18:32 GMT",
"version": "v2"
}
] |
2015-09-02
|
[
[
"Pitkin",
"M.",
""
]
] |
There have been recent claims (Anderson et al., EPL, 110, 10002) of a 5.9 year periodicity in measurements of Newton's gravitational constant, $G$, which show a very strong correlation with observed periodic variations in the length of the day. I have used Bayesian model comparison to test this claim compared to other hypotheses that could explain the variation in the $G$ measurements. I have used the data from the initial claim, and from an updated set of compiled $G$ measurements that more accurately reflect the experimental dates, and find that a model containing an additional unknown Gaussian noise component is hugely favoured, by factors of $\gtrsim e^{30}$, over two models allowing for a sinusoidal component.
|
gr-qc/0103107
|
Hans Ringstrom
|
Hans Ringstrom
|
The future asymptotics of Bianchi VIII vacuum solutions
|
34 pages, no figures
|
Class.Quant.Grav. 18 (2001) 3791-3824
|
10.1088/0264-9381/18/18/302
| null |
gr-qc
| null |
Bianchi VIII vacuum solutions to Einstein's equations are causally
geodesically complete to the future, given an appropriate time orientation, and
the objective of this article is to analyze the asymptotic behaviour of
solutions in this time direction. For the Bianchi class A spacetimes, there is
a formulation of the field equations that was presented in an article by
Wainwright and Hsu, and we analyze the asymptotic behaviour of solutions in
these variables. We also try to give the analytic results a geometric
interpretation by analyzing how a normalized version of the Riemannian metric
on the spatial hypersurfaces of homogeneity evolves.
|
[
{
"created": "Thu, 29 Mar 2001 07:15:25 GMT",
"version": "v1"
}
] |
2009-11-07
|
[
[
"Ringstrom",
"Hans",
""
]
] |
Bianchi VIII vacuum solutions to Einstein's equations are causally geodesically complete to the future, given an appropriate time orientation, and the objective of this article is to analyze the asymptotic behaviour of solutions in this time direction. For the Bianchi class A spacetimes, there is a formulation of the field equations that was presented in an article by Wainwright and Hsu, and we analyze the asymptotic behaviour of solutions in these variables. We also try to give the analytic results a geometric interpretation by analyzing how a normalized version of the Riemannian metric on the spatial hypersurfaces of homogeneity evolves.
|
2007.10080
|
Lijing Shao
|
Rui Xu, Yong Gao, Lijing Shao
|
Strong-field effects in massive scalar-tensor gravity for slowly
spinning neutron stars and application to X-ray pulsar pulse profiles
|
15 pages, 10 figures; accepted by PRD
|
Phys. Rev. D 102, 064057 (2020)
|
10.1103/PhysRevD.102.064057
| null |
gr-qc astro-ph.HE hep-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Neutron stars (NSs) in scalar-tensor (ST) theories of gravitation can acquire
scalar charges and generate distinct spacetimes from those in General
Relativity (GR) through the celebrated phenomenon of spontaneous scalarization.
Taking on an ST theory with the mass term of the scalar field, we determine the
theory parameter space for spontaneous scalarization by investigating the
linearized scalar field equation. Then the full numerical solutions for slowly
rotating NSs are obtained and studied in great detail. The resulted spacetime
is used to calculate test-particle geodesics. The lightlike geodesics are used
to construct the profile of X-ray radiation from a pair of hot spots on the
surface of scalarized NSs, which potentially can be compared with the data from
the Neutron star Interior Composition Explorer (NICER) mission for testing the
ST theory.
|
[
{
"created": "Mon, 20 Jul 2020 13:22:31 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Sep 2020 15:22:30 GMT",
"version": "v2"
}
] |
2020-09-30
|
[
[
"Xu",
"Rui",
""
],
[
"Gao",
"Yong",
""
],
[
"Shao",
"Lijing",
""
]
] |
Neutron stars (NSs) in scalar-tensor (ST) theories of gravitation can acquire scalar charges and generate distinct spacetimes from those in General Relativity (GR) through the celebrated phenomenon of spontaneous scalarization. Taking on an ST theory with the mass term of the scalar field, we determine the theory parameter space for spontaneous scalarization by investigating the linearized scalar field equation. Then the full numerical solutions for slowly rotating NSs are obtained and studied in great detail. The resulted spacetime is used to calculate test-particle geodesics. The lightlike geodesics are used to construct the profile of X-ray radiation from a pair of hot spots on the surface of scalarized NSs, which potentially can be compared with the data from the Neutron star Interior Composition Explorer (NICER) mission for testing the ST theory.
|
2110.10569
|
Jaroslav Vrba
|
Zden\v{e}k Stuchl\'ik and Jaroslav Vrba
|
Epicyclic orbits in the field of Einstein-Dirac-Maxwell traversable
wormholes applied to the quasiperiodic oscillations observed in microquasars
and active galactic nuclei
|
14 pages, 11 figures, 2 tables
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We study the epicyclic oscillatory motion around circular orbits of the
traversable asymptotically flat and reflection-symmetric wormholes obtained in
the Einstein-Dirac-Maxwell theory without applying exotic matter in their
construction. We determine frequencies of the orbital and epicyclic motion in
the Keplerian disks having inner edge at the marginally stable circular
geodesic of the spacetime. The obtained frequencies are applied in the so
called geodesic models of high-frequency quasiperiodic oscillations (HF QPOs)
observed in microquasars and active galactic nuclei containing a supermassive
central object. We show that even the simplest epicyclic resonance variant of
the geodesic models can explain the HF QPOs observed in many active galactic
nuclei for realistic choices of the wormhole parameters, but there are some of
the sources where only wormholes with unrealistically large values of the
parameters can be sufficient for the explanation. On the other hand, in the
case of microquasars, the observed HF QPOs strongly restrict the acceptable
values of the wormhole parameters.
|
[
{
"created": "Wed, 20 Oct 2021 13:58:01 GMT",
"version": "v1"
}
] |
2021-10-22
|
[
[
"Stuchlík",
"Zdeněk",
""
],
[
"Vrba",
"Jaroslav",
""
]
] |
We study the epicyclic oscillatory motion around circular orbits of the traversable asymptotically flat and reflection-symmetric wormholes obtained in the Einstein-Dirac-Maxwell theory without applying exotic matter in their construction. We determine frequencies of the orbital and epicyclic motion in the Keplerian disks having inner edge at the marginally stable circular geodesic of the spacetime. The obtained frequencies are applied in the so called geodesic models of high-frequency quasiperiodic oscillations (HF QPOs) observed in microquasars and active galactic nuclei containing a supermassive central object. We show that even the simplest epicyclic resonance variant of the geodesic models can explain the HF QPOs observed in many active galactic nuclei for realistic choices of the wormhole parameters, but there are some of the sources where only wormholes with unrealistically large values of the parameters can be sufficient for the explanation. On the other hand, in the case of microquasars, the observed HF QPOs strongly restrict the acceptable values of the wormhole parameters.
|
1506.00946
|
John F. Donoghue
|
John F. Donoghue and Barry R. Holstein
|
Low Energy Theorems of Quantum Gravity from Effective Field Theory
|
Invited Topical Review for J. Phys. G, 35 pages
| null |
10.1088/0954-3899/42/10/103102
|
ACFI-T15-05
|
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this survey, we review some of the low energy quantum predictions of
General Relativity which are independent of details of the yet unknown
high-energy completion of the gravitational interaction. Such predictions can
be extracted using the techniques of effective field theory.
|
[
{
"created": "Tue, 2 Jun 2015 16:24:49 GMT",
"version": "v1"
}
] |
2015-09-30
|
[
[
"Donoghue",
"John F.",
""
],
[
"Holstein",
"Barry R.",
""
]
] |
In this survey, we review some of the low energy quantum predictions of General Relativity which are independent of details of the yet unknown high-energy completion of the gravitational interaction. Such predictions can be extracted using the techniques of effective field theory.
|
gr-qc/9710017
|
Hector F. Hernandez G.
|
L. Herrera, H.Hernandez, L. A. Nunez, U. Percoco
|
On the Eccentricity Behaviour of Radiating Slowly Rotating Bodies
|
13 Latex pages, 4 figures, Submitted to Classical and Quantum Gravity
|
Class.Quant.Grav.15:187-196,1998
|
10.1088/0264-9381/15/1/013
| null |
gr-qc
| null |
We study different models of radiating slowly rotating bodies up to the first
order in the angular velocity. It is shown that up to this order the evolution
of the eccentricity is highly model-dependent even for very compact objects.
|
[
{
"created": "Thu, 2 Oct 1997 19:46:30 GMT",
"version": "v1"
}
] |
2011-07-19
|
[
[
"Herrera",
"L.",
""
],
[
"Hernandez",
"H.",
""
],
[
"Nunez",
"L. A.",
""
],
[
"Percoco",
"U.",
""
]
] |
We study different models of radiating slowly rotating bodies up to the first order in the angular velocity. It is shown that up to this order the evolution of the eccentricity is highly model-dependent even for very compact objects.
|
gr-qc/9906009
|
Ms. Amita Shaw
|
S.Biswas, A.Shaw and D.Biswas
|
Schroedinger Wheeler-DeWitt Equation In Multidimensional Cosmology
|
10 Pages, LaTeX, no figure
|
Int.J.Mod.Phys.D10:585-594,2001
|
10.1142/S0218271801001372
| null |
gr-qc
| null |
We study multidimensional cosmology to obtain the wavefunction of the
universe using wormhole dominance proposal. Using a prescription for time we
obtain the Schroedinger-Wheeler-DeWitt equation without any reference to WD
equation and WKB ansatz for WD wavefunction. It is found that the
Hartle-Hawking or wormhole-dominated boundary conditions serve as a seed for
inflation as well as for Gaussian type ansatz to Schroedinger-Wheeler-DeWitt
equation.
|
[
{
"created": "Thu, 3 Jun 1999 09:01:43 GMT",
"version": "v1"
}
] |
2014-11-17
|
[
[
"Biswas",
"S.",
""
],
[
"Shaw",
"A.",
""
],
[
"Biswas",
"D.",
""
]
] |
We study multidimensional cosmology to obtain the wavefunction of the universe using wormhole dominance proposal. Using a prescription for time we obtain the Schroedinger-Wheeler-DeWitt equation without any reference to WD equation and WKB ansatz for WD wavefunction. It is found that the Hartle-Hawking or wormhole-dominated boundary conditions serve as a seed for inflation as well as for Gaussian type ansatz to Schroedinger-Wheeler-DeWitt equation.
|
gr-qc/0307080
|
Daniel A. Shaddock
|
Daniel A. Shaddock, Massimo Tinto, Frank B. Estabrook, J. W. Armstrong
|
Data Combinations Accounting for LISA Spacecraft Motion
|
10 pages, 3 figures
|
Phys.Rev. D68 (2003) 061303
|
10.1103/PhysRevD.68.061303
| null |
gr-qc
| null |
LISA is an array of three spacecraft in an approximately equilateral triangle
configuration which will be used as a low-frequency gravitational wave
detector. We present here new generalizations of the Michelson- and Sagnac-type
time-delay interferometry data combinations. These combinations cancel laser
phase noise in the presence of different up and down propagation delays in each
arm of the array, and slowly varying systematic motion of the spacecraft. The
gravitational wave sensitivities of these generalized combinations are the same
as previously computed for the stationary cases, although the combinations are
now more complicated. We introduce a diagrammatic representation to illustrate
that these combinations are actually synthesized equal-arm interferometers.
|
[
{
"created": "Wed, 16 Jul 2003 21:11:58 GMT",
"version": "v1"
}
] |
2009-11-10
|
[
[
"Shaddock",
"Daniel A.",
""
],
[
"Tinto",
"Massimo",
""
],
[
"Estabrook",
"Frank B.",
""
],
[
"Armstrong",
"J. W.",
""
]
] |
LISA is an array of three spacecraft in an approximately equilateral triangle configuration which will be used as a low-frequency gravitational wave detector. We present here new generalizations of the Michelson- and Sagnac-type time-delay interferometry data combinations. These combinations cancel laser phase noise in the presence of different up and down propagation delays in each arm of the array, and slowly varying systematic motion of the spacecraft. The gravitational wave sensitivities of these generalized combinations are the same as previously computed for the stationary cases, although the combinations are now more complicated. We introduce a diagrammatic representation to illustrate that these combinations are actually synthesized equal-arm interferometers.
|
1403.5319
|
Ahmed Farag Ali
|
Adel Awad and Ahmed Farag Ali
|
Planck-Scale Corrections to Friedmann Equation
|
15 pages, no figure, to appear in Central Eur.J.Phys. arXiv admin
note: text overlap with arXiv:1301.3508
|
Central Eur.J.Phys. 12 (2014) 245-255
|
10.2478/s11534-014-0441-3
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Recently, Verlinde proposed that gravity is an emergent phenomenon which
originates from an entropic force. In this work, we extend Verlinde's proposal
to accommodate generalized uncertainty principles (GUP), which are suggested by
some approaches to \emph{quantum gravity} such as string theory, black hole
physics and doubly special relativity (DSR). Using Verlinde's proposal and two
known models of GUPs, we obtain modifications to Newton's law of gravitation as
well as the Friedmann equation. Our modification to the Friedmann equation
includes higher powers of the Hubble parameter which is used to obtain a
corresponding Raychaudhuri equation. Solving this equation, we obtain a leading
Planck-scale correction to Friedmann-Robertson-Walker (FRW) solutions for the
$p=\omega \rho$ equation of state.
|
[
{
"created": "Thu, 20 Mar 2014 22:35:51 GMT",
"version": "v1"
}
] |
2014-04-24
|
[
[
"Awad",
"Adel",
""
],
[
"Ali",
"Ahmed Farag",
""
]
] |
Recently, Verlinde proposed that gravity is an emergent phenomenon which originates from an entropic force. In this work, we extend Verlinde's proposal to accommodate generalized uncertainty principles (GUP), which are suggested by some approaches to \emph{quantum gravity} such as string theory, black hole physics and doubly special relativity (DSR). Using Verlinde's proposal and two known models of GUPs, we obtain modifications to Newton's law of gravitation as well as the Friedmann equation. Our modification to the Friedmann equation includes higher powers of the Hubble parameter which is used to obtain a corresponding Raychaudhuri equation. Solving this equation, we obtain a leading Planck-scale correction to Friedmann-Robertson-Walker (FRW) solutions for the $p=\omega \rho$ equation of state.
|
2207.05304
|
Zinnat Hassan
|
Zinnat Hassan, G. Mustafa, Joao R.L. Santos, P.K. Sahoo
|
Embedding procedure and wormhole solutions in $f(Q)$ gravity
|
EPL published version
|
Europhysics Letters, 139(3) (2022) 39001
|
10.1209/0295-5075/ac8017
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
An intriguing solution that appears in General Relativity (GR) but has not
been observed so far is the wormhole. This exotic solution describes a
topological bridge connecting two distinct universes or two different points in
the same universe. It is known that the traversable wormhole solutions violate
all the energy conditions in GR, resulting in their instability. In this work,
we are going to unveil new wormhole solutions for $f(Q)$ gravity where $Q$ is
the non-metricity scalar, which is responsible for the gravitational
interaction. The energy conditions to constraint these wormhole solutions were
derived using the embedding procedure. This procedure consists of rewriting the
density and the pressures of the solutions as those presented by General
Relativity. Then, the nontrivial contributions coming from new theories of
gravity are embedded into the effective equations for density and pressures.
Along with our approach, we carefully analyze two families of $f(Q)$ models and
we used two different shape functions to build the wormholes solutions for each
of these $f(Q)$ models. We are going to present new scenarios with the
possibility of traversable wormholes satisfying SEC or DEC energy conditions in
the presence of exotic matter.
|
[
{
"created": "Tue, 12 Jul 2022 04:29:40 GMT",
"version": "v1"
}
] |
2022-08-08
|
[
[
"Hassan",
"Zinnat",
""
],
[
"Mustafa",
"G.",
""
],
[
"Santos",
"Joao R. L.",
""
],
[
"Sahoo",
"P. K.",
""
]
] |
An intriguing solution that appears in General Relativity (GR) but has not been observed so far is the wormhole. This exotic solution describes a topological bridge connecting two distinct universes or two different points in the same universe. It is known that the traversable wormhole solutions violate all the energy conditions in GR, resulting in their instability. In this work, we are going to unveil new wormhole solutions for $f(Q)$ gravity where $Q$ is the non-metricity scalar, which is responsible for the gravitational interaction. The energy conditions to constraint these wormhole solutions were derived using the embedding procedure. This procedure consists of rewriting the density and the pressures of the solutions as those presented by General Relativity. Then, the nontrivial contributions coming from new theories of gravity are embedded into the effective equations for density and pressures. Along with our approach, we carefully analyze two families of $f(Q)$ models and we used two different shape functions to build the wormholes solutions for each of these $f(Q)$ models. We are going to present new scenarios with the possibility of traversable wormholes satisfying SEC or DEC energy conditions in the presence of exotic matter.
|
1601.05518
|
Suman Ghosh
|
Suman Ghosh
|
Spin 1/2 field and regularization in de Sitter and radiation dominated
universe
|
12 pages, 10 figures, version accepted for publication in Physical
Review D. arXiv admin note: substantial text overlap with arXiv:1506.06909
| null |
10.1103/PhysRevD.93.044032
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We construct a simple algorithm to derive number density of spin 1/2
particles created in spatially flat FLRW spacetimes and resulting renormalized
energy-momentum tensor within the framework of adiabatic regularization.
Physical quantities thus found are in agreement with the known results. This
formalism can be considered as an appropriate extension of the techniques
originally introduced for scalar fields, applicable to fermions in curved
space. We apply this formalism to compute the particle number density and the
renormalized energy density and pressure analytically (wherever possible) and
numerically, in two interesting cosmological scenarios: a de Sitter spacetime
and a radiation dominated universe. Results prove the efficiency of the
methodology presented here.
|
[
{
"created": "Thu, 21 Jan 2016 05:48:10 GMT",
"version": "v1"
}
] |
2016-03-23
|
[
[
"Ghosh",
"Suman",
""
]
] |
We construct a simple algorithm to derive number density of spin 1/2 particles created in spatially flat FLRW spacetimes and resulting renormalized energy-momentum tensor within the framework of adiabatic regularization. Physical quantities thus found are in agreement with the known results. This formalism can be considered as an appropriate extension of the techniques originally introduced for scalar fields, applicable to fermions in curved space. We apply this formalism to compute the particle number density and the renormalized energy density and pressure analytically (wherever possible) and numerically, in two interesting cosmological scenarios: a de Sitter spacetime and a radiation dominated universe. Results prove the efficiency of the methodology presented here.
|
1403.0896
|
Richard Woodard
|
Katie E. Leonard (Applied Mathematics), Sohyun Park (Penn State
University), Tomislav Prokopec (Utrecht University) and R. P. Woodard
(University of Florida)
|
Representing the Graviton Self-Energy on de Sitter Background
|
38 pages, no figures, uses LaTeX2e, version 2 (39 pages) revised for
publication with many errors corrected
|
Phys. Rev. D 90, 024032 (2014)
|
10.1103/PhysRevD.90.024032
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We derive a noncovariant but simple representation for the self-energy of a
conformally transformed graviton field on the cosmological patch of de Sitter.
Our representation involves four structure functions, as opposed to the two
that would be necessary for a manifestly de Sitter invariant representation. We
work out what the four structure functions are for the one loop correction due
to a massless, minimally coupled scalar. And we employ the result to work out
what happens to dynamical gravitons.
|
[
{
"created": "Tue, 4 Mar 2014 18:43:12 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Jul 2014 05:53:30 GMT",
"version": "v2"
}
] |
2014-07-18
|
[
[
"Leonard",
"Katie E.",
"",
"Applied Mathematics"
],
[
"Park",
"Sohyun",
"",
"Penn State\n University"
],
[
"Prokopec",
"Tomislav",
"",
"Utrecht University"
],
[
"Woodard",
"R. P.",
"",
"University of Florida"
]
] |
We derive a noncovariant but simple representation for the self-energy of a conformally transformed graviton field on the cosmological patch of de Sitter. Our representation involves four structure functions, as opposed to the two that would be necessary for a manifestly de Sitter invariant representation. We work out what the four structure functions are for the one loop correction due to a massless, minimally coupled scalar. And we employ the result to work out what happens to dynamical gravitons.
|
2309.08203
|
Jia-Hui Huang
|
Wenbin Li, Kai-Peng Lu, W. LiMing and Jia-Hui Huang
|
Stability of five-dimensional Myers-Perry black holes under massive
scalar perturbation: bound states and quasinormal modes
|
references added
| null | null | null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
The stability of five-dimensional singly rotating Myers-Perry Black Holes
against massive scalar perturbations is studied. Both the quasibound states and
quasinormal modes of the massive scalar field are considered. For the
quasibound states, we use an analytical method to discuss the effective
potential felt by the scalar field, and found that there is no potential well
outside the event horizon. Thus, singly rotating Myers-Perry Black Holes are
stable against the perturbation of quasibound states of massive scalar fields.
Then, We use continued fraction method based on solving a seven-term recurrence
relations to compute the spectra of the quasinormal modes. For different values
of the black hole rotation parameter $a$, scalar mass parameter $\mu$ and
angular quantum numbers, all found quasinormal modes are damped. So singly
rotating Myers-Perry Black Holes are also stable against the perturbation of
quasinormal modes of massive scalar fields. Besides, when the scalar mass $\mu$
becomes relatively large, the long-living quasiresonances are also found as in
other rotating black hole models. Our results complement previous arguments on
the stability of five-dimensional singly rotating Myers-Perry black holes
against massive scalar perturbations.
|
[
{
"created": "Fri, 15 Sep 2023 07:12:18 GMT",
"version": "v1"
},
{
"created": "Sat, 23 Sep 2023 12:21:40 GMT",
"version": "v2"
}
] |
2023-09-26
|
[
[
"Li",
"Wenbin",
""
],
[
"Lu",
"Kai-Peng",
""
],
[
"LiMing",
"W.",
""
],
[
"Huang",
"Jia-Hui",
""
]
] |
The stability of five-dimensional singly rotating Myers-Perry Black Holes against massive scalar perturbations is studied. Both the quasibound states and quasinormal modes of the massive scalar field are considered. For the quasibound states, we use an analytical method to discuss the effective potential felt by the scalar field, and found that there is no potential well outside the event horizon. Thus, singly rotating Myers-Perry Black Holes are stable against the perturbation of quasibound states of massive scalar fields. Then, We use continued fraction method based on solving a seven-term recurrence relations to compute the spectra of the quasinormal modes. For different values of the black hole rotation parameter $a$, scalar mass parameter $\mu$ and angular quantum numbers, all found quasinormal modes are damped. So singly rotating Myers-Perry Black Holes are also stable against the perturbation of quasinormal modes of massive scalar fields. Besides, when the scalar mass $\mu$ becomes relatively large, the long-living quasiresonances are also found as in other rotating black hole models. Our results complement previous arguments on the stability of five-dimensional singly rotating Myers-Perry black holes against massive scalar perturbations.
|
0710.1351
|
Jacques Smulevici
|
Jacques Smulevici
|
Strong cosmic censorship for T^2-symmetric spacetimes with cosmological
constant and matter
|
29 pages, 6 figures, v2 is the version published in Annales Henri
Poincare
|
AnnalesHenriPoincare9:1425-1453,2008
|
10.1007/s00023-008-0391-7
| null |
gr-qc math.AP math.DG
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We address the issue of strong cosmic censorship for T^2-symmetric spacetimes
with positive cosmological constant. In the case of collisionless matter, we
complete the proof of the C^2 formulation of the conjecture for this class of
spacetimes. In the vacuum case, we prove that the conjecture holds for the
special cases where the area element of the group orbits does not vanish on the
past boundary of the maximal Cauchy development.
|
[
{
"created": "Sat, 6 Oct 2007 14:38:08 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Apr 2009 09:53:06 GMT",
"version": "v2"
}
] |
2009-04-07
|
[
[
"Smulevici",
"Jacques",
""
]
] |
We address the issue of strong cosmic censorship for T^2-symmetric spacetimes with positive cosmological constant. In the case of collisionless matter, we complete the proof of the C^2 formulation of the conjecture for this class of spacetimes. In the vacuum case, we prove that the conjecture holds for the special cases where the area element of the group orbits does not vanish on the past boundary of the maximal Cauchy development.
|
0902.0559
|
Francisco Lobo
|
Orfeu Bertolami, Francisco S. N. Lobo
|
Time and Causation
|
12 pages. To appear in a special issue of NeuroQuantology
|
NeuroQuantol.7:1-15,2009
| null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this review paper, we consider the fundamental nature of time and
causality, most particularly, in the context of the theories of special and
general relativity. We also discuss the issue of closed timelike curves in the
context of general relativity, and the associated paradoxes, the question of
directionality of the time flow and, rather briefly, the problem of time in
quantum gravity.
|
[
{
"created": "Tue, 3 Feb 2009 17:24:18 GMT",
"version": "v1"
}
] |
2009-04-15
|
[
[
"Bertolami",
"Orfeu",
""
],
[
"Lobo",
"Francisco S. N.",
""
]
] |
In this review paper, we consider the fundamental nature of time and causality, most particularly, in the context of the theories of special and general relativity. We also discuss the issue of closed timelike curves in the context of general relativity, and the associated paradoxes, the question of directionality of the time flow and, rather briefly, the problem of time in quantum gravity.
|
2202.04118
|
Bita Farsi
|
Bita Farsi, Ahmad Sheykhi
|
Structure formation in mimetic gravity
|
13 pages, 13 figures
|
Phys. Rev. D 106, 024053 (2022)
|
10.1103/PhysRevD.106.024053
| null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
We disclose the effects of an extra longitudinal degree of freedom on the
evolution of perturbations in the framework of mimetic gravity. We consider a
flat Friedmann-Robertson-Walker (FRW) background and explore the linear
perturbations by adopting the spherically symmetric collapse formalism. By
suitably choosing the potential of the mimetic field, we are able to solve the
perturbed field equations in the linear regime and derive the matter density
contrast {\delta}m in terms of the redshift parameter z. We observe that
{\delta}m starts growing at the early stages and as the universe expands, it
grows faster compared to the standard cosmology. This may due to the extra
degree of freedom of the gravitational field which affects the growth of
perturbations. We observe that in the presence of a mimetic potential, the
growth rate function is smaller than {\Lambda}CDM model in small redshifts. We
then consider the effects of this potential on the density abundance, the
deceleration parameter and jerk parameter. We find out that mimetic potential
can play the role of dark energy (DE) and affects the dynamics of matter
perturbations and cosmological parameters. We also investigate the mass
function and the number count for the collapsed objects in the mimetic
scenario. We find that the mass function of models with potential is smaller
than model without potential. With decreasing the role of DE, the mass function
start to grow in smaller redshifts i.e., halo abundance is formed later. It is
found that the more massive structures are less abundant and form at later
times, as it should be in the hierarchical model of structure formation.
|
[
{
"created": "Tue, 8 Feb 2022 19:45:04 GMT",
"version": "v1"
},
{
"created": "Mon, 11 Jul 2022 06:50:13 GMT",
"version": "v2"
}
] |
2022-08-02
|
[
[
"Farsi",
"Bita",
""
],
[
"Sheykhi",
"Ahmad",
""
]
] |
We disclose the effects of an extra longitudinal degree of freedom on the evolution of perturbations in the framework of mimetic gravity. We consider a flat Friedmann-Robertson-Walker (FRW) background and explore the linear perturbations by adopting the spherically symmetric collapse formalism. By suitably choosing the potential of the mimetic field, we are able to solve the perturbed field equations in the linear regime and derive the matter density contrast {\delta}m in terms of the redshift parameter z. We observe that {\delta}m starts growing at the early stages and as the universe expands, it grows faster compared to the standard cosmology. This may due to the extra degree of freedom of the gravitational field which affects the growth of perturbations. We observe that in the presence of a mimetic potential, the growth rate function is smaller than {\Lambda}CDM model in small redshifts. We then consider the effects of this potential on the density abundance, the deceleration parameter and jerk parameter. We find out that mimetic potential can play the role of dark energy (DE) and affects the dynamics of matter perturbations and cosmological parameters. We also investigate the mass function and the number count for the collapsed objects in the mimetic scenario. We find that the mass function of models with potential is smaller than model without potential. With decreasing the role of DE, the mass function start to grow in smaller redshifts i.e., halo abundance is formed later. It is found that the more massive structures are less abundant and form at later times, as it should be in the hierarchical model of structure formation.
|
gr-qc/0307064
|
Tiberiu Harko
|
T. Harko
|
Gravitational collapse of a Hagedorn fluid in Vaidya geometry
|
14 pages, 2 figures, to appear in Phys. Rev. D
|
Phys.Rev. D68 (2003) 064005
|
10.1103/PhysRevD.68.064005
| null |
gr-qc hep-th
| null |
The gravitational collapse of a high-density null charged matter fluid,
satisfying the Hagedorn equation of state, is considered in the framework of
the Vaidya geometry. The general solution of the gravitational field equations
can be obtained in an exact parametric form. The conditions for the formation
of a naked singularity, as a result of the collapse of the compact object, are
also investigated. For an appropriate choice of the arbitrary integration
functions the null radial outgoing geodesic, originating from the shell
focussing central singularity, admits one or more positive roots. Hence a
collapsing Hagedorn fluid could end either as a black hole, or as a naked
singularity. A possible astrophysical application of the model, to describe the
energy source of gamma-ray bursts, is also considered.
|
[
{
"created": "Mon, 14 Jul 2003 01:37:47 GMT",
"version": "v1"
}
] |
2009-11-10
|
[
[
"Harko",
"T.",
""
]
] |
The gravitational collapse of a high-density null charged matter fluid, satisfying the Hagedorn equation of state, is considered in the framework of the Vaidya geometry. The general solution of the gravitational field equations can be obtained in an exact parametric form. The conditions for the formation of a naked singularity, as a result of the collapse of the compact object, are also investigated. For an appropriate choice of the arbitrary integration functions the null radial outgoing geodesic, originating from the shell focussing central singularity, admits one or more positive roots. Hence a collapsing Hagedorn fluid could end either as a black hole, or as a naked singularity. A possible astrophysical application of the model, to describe the energy source of gamma-ray bursts, is also considered.
|
1008.4639
|
Matt Visser
|
Bethan Cropp (Victoria University of Wellington) and Matt Visser
(Victoria University of Wellington)
|
Any spacetime has a Bianchi type I spacetime as a limit
|
19 pages; no figures
|
Class.Quant.Grav.28:055007,2011
|
10.1088/0264-9381/28/5/055007
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Pick an arbitrary timelike geodesic in an arbitrary spacetime. We demonstrate
that there is a particular limiting process, an "ultra-local limit", in which
the immediate neighborhood of the timelike geodesic can be "blown up" to yield
a general (typically non-diagonal) Bianchi type I spacetime. This process
shares some (but definitely not all) of the features of the Penrose limit,
whereby the immediate neighborhood of an arbitrary null geodesic is "blown up"
to yield a pp-wave as a limit.
|
[
{
"created": "Fri, 27 Aug 2010 04:36:42 GMT",
"version": "v1"
}
] |
2011-02-18
|
[
[
"Cropp",
"Bethan",
"",
"Victoria University of Wellington"
],
[
"Visser",
"Matt",
"",
"Victoria University of Wellington"
]
] |
Pick an arbitrary timelike geodesic in an arbitrary spacetime. We demonstrate that there is a particular limiting process, an "ultra-local limit", in which the immediate neighborhood of the timelike geodesic can be "blown up" to yield a general (typically non-diagonal) Bianchi type I spacetime. This process shares some (but definitely not all) of the features of the Penrose limit, whereby the immediate neighborhood of an arbitrary null geodesic is "blown up" to yield a pp-wave as a limit.
|
1411.0941
|
Supriya Pan
|
Subenoy Chakraborty, Supriya Pan, and Subhajit Saha
|
A third alternative to explain recent observations: Future deceleration
|
9 pages, 3 figures
|
Physics Letters B 738, 424 (2014)
|
10.1016/j.physletb.2014.10.009
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In the present work we discuss a third alternative to explain the latest
observational data concerning the accelerating Universe and its different
stages. The particle creation mechanism in the framework of non-equilibrium
thermodynamics is considered as a basic cosmic mechanism acting on the flat FRW
geometry. By assuming that the gravitationally induced particle production
occurs under "adiabatic" conditions, the deceleration parameter is expressed in
terms of the particle creation rate which is chosen as a truncated power series
of the Hubble parameter. The model shows the evolution of the Universe starting
from inflation to the present late time acceleration and it also predicts
future decelerating stage.
|
[
{
"created": "Thu, 30 Oct 2014 07:37:19 GMT",
"version": "v1"
}
] |
2016-05-17
|
[
[
"Chakraborty",
"Subenoy",
""
],
[
"Pan",
"Supriya",
""
],
[
"Saha",
"Subhajit",
""
]
] |
In the present work we discuss a third alternative to explain the latest observational data concerning the accelerating Universe and its different stages. The particle creation mechanism in the framework of non-equilibrium thermodynamics is considered as a basic cosmic mechanism acting on the flat FRW geometry. By assuming that the gravitationally induced particle production occurs under "adiabatic" conditions, the deceleration parameter is expressed in terms of the particle creation rate which is chosen as a truncated power series of the Hubble parameter. The model shows the evolution of the Universe starting from inflation to the present late time acceleration and it also predicts future decelerating stage.
|
gr-qc/0207068
|
Alexander E. Margolin
|
A.E.Shalyt-Margolin (NC PHEP, Belarus), A.Ya.Tregubovich (IP NAS
Belarus)
|
Generalized Uncertainty Relations,Fundamental Length and Density Matrix
|
11 pages, no figures,some corrections of abstract,introduction and
section 2
| null | null | null |
gr-qc
| null |
It was shown that if in Quantum Theory a fundamental length exists and a
well-known measurement procedure is used, then the density matrix at the Planck
scale cannot be defined in the usual way, because in this case density matrix
trace is strongly less than one.
Density matrix must be changed by a progenitrix or as we call it throughout
this paper, density pro-matrix. This pro-matrix is a deformed density matrix,
which at low energy limit turns to usual one.
Below the explicit form of the deformation is described. Implications of
obtained results are summarized as well as their application to the
interpretation of Information Paradox on the Black Holes.
|
[
{
"created": "Thu, 18 Jul 2002 15:29:37 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Oct 2002 10:25:00 GMT",
"version": "v2"
},
{
"created": "Wed, 20 Aug 2003 06:16:20 GMT",
"version": "v3"
}
] |
2016-08-31
|
[
[
"Shalyt-Margolin",
"A. E.",
"",
"NC PHEP, Belarus"
],
[
"Tregubovich",
"A. Ya.",
"",
"IP NAS\n Belarus"
]
] |
It was shown that if in Quantum Theory a fundamental length exists and a well-known measurement procedure is used, then the density matrix at the Planck scale cannot be defined in the usual way, because in this case density matrix trace is strongly less than one. Density matrix must be changed by a progenitrix or as we call it throughout this paper, density pro-matrix. This pro-matrix is a deformed density matrix, which at low energy limit turns to usual one. Below the explicit form of the deformation is described. Implications of obtained results are summarized as well as their application to the interpretation of Information Paradox on the Black Holes.
|
1604.05301
|
Sumanta Chakraborty
|
Sumanta Chakraborty and Soumitra SenGupta
|
Solving higher curvature gravity theories
|
Revised, 23 pages, no figures
|
Eur. Phys. J. C 76, 552 (2016)
|
10.1140/epjc/s10052-016-4394-0
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Solving field equations in the context of higher curvature gravity theories
is a formidable task. However in many situations, e.g., in the context of
$f(R)$ theories the higher curvature gravity action can be written as
Einstein-Hilbert action plus a scalar field action. We show that not only the
action but the field equations derived from the action are also equivalent
provided the spacetime is regular. We also demonstrate that such equivalence
continues to hold even when gravitational field equations are projected on a
lower dimensional hypersurface. We have further depicted explicit examples in
which the solutions for Einstein-Hilbert and a scalar field system lead to
solutions of the equivalent higher curvature theory. The same, but on the lower
dimensional hypersurface, has been illustrated in the reverse order as well. We
conclude with a brief discussion on this technique of solving higher curvature
field equations.
|
[
{
"created": "Mon, 18 Apr 2016 03:43:52 GMT",
"version": "v1"
},
{
"created": "Sun, 9 Oct 2016 02:19:17 GMT",
"version": "v2"
}
] |
2016-10-11
|
[
[
"Chakraborty",
"Sumanta",
""
],
[
"SenGupta",
"Soumitra",
""
]
] |
Solving field equations in the context of higher curvature gravity theories is a formidable task. However in many situations, e.g., in the context of $f(R)$ theories the higher curvature gravity action can be written as Einstein-Hilbert action plus a scalar field action. We show that not only the action but the field equations derived from the action are also equivalent provided the spacetime is regular. We also demonstrate that such equivalence continues to hold even when gravitational field equations are projected on a lower dimensional hypersurface. We have further depicted explicit examples in which the solutions for Einstein-Hilbert and a scalar field system lead to solutions of the equivalent higher curvature theory. The same, but on the lower dimensional hypersurface, has been illustrated in the reverse order as well. We conclude with a brief discussion on this technique of solving higher curvature field equations.
|
gr-qc/0410064
|
Jian Qi Shen
|
Guoyou Huang
|
On Structure and History of Space-time with Variable Speed of Light
|
11 pages, Latex
| null | null | null |
gr-qc
| null |
We apply the variable speed of light into general relativity in order to
solve the problems we met in the standard cosmology. We're surprised to find
that, the results from the general relativity in cosmology are exactly the same
as those we got from Newtonian dynamics. The relation between the Newtonian
dynamics and the relativistic dynamics can be demonstrated with the variable
speed of light. With this approach, some problems in the standard cosmology
such as the flatness problem and the horizon problem doesn't arise any more.
All the cosmological results and the physical results are reasonable and
natural. There are no any difficulties in the standard cosmology.
|
[
{
"created": "Fri, 15 Oct 2004 04:51:01 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Huang",
"Guoyou",
""
]
] |
We apply the variable speed of light into general relativity in order to solve the problems we met in the standard cosmology. We're surprised to find that, the results from the general relativity in cosmology are exactly the same as those we got from Newtonian dynamics. The relation between the Newtonian dynamics and the relativistic dynamics can be demonstrated with the variable speed of light. With this approach, some problems in the standard cosmology such as the flatness problem and the horizon problem doesn't arise any more. All the cosmological results and the physical results are reasonable and natural. There are no any difficulties in the standard cosmology.
|
gr-qc/0203050
|
Lorenzo Iorio
|
Lorenzo Iorio
|
The impact of the static part of the Earth's gravity field on some tests
of General Relativity with Satellite Laser Ranging
|
LaTex2e, 18 pages, 5 tables. Preliminary estimates of the error in
the Lense-Thirring measurement due to geopotential according to EIGEN-1S
model added. To appear in Celestial Mechanics and Dynamical Astronomy
|
Celest.Mech.Dyn.Astron. 86 (2003) 277-294
|
10.1023/A:1024223200686
| null |
gr-qc astro-ph physics.geo-ph physics.space-ph
| null |
In this paper we calculate explicitly the secular classical precessions of
the node \Omega and the perigee \omega of an Earth artificial satellite induced
by the static, even zonal harmonics of the geopotential up to degree l=20.
Subsequently, their systematic errors induced by the mismodelling in the even
zonal geopotential coefficients J_l are compared to the general relativistic
secular gravitomagnetic and gravitoelectric precessions of the node and the
perigee of the existing laser-ranged geodetic satellites and of the proposed
LARES.
|
[
{
"created": "Thu, 14 Mar 2002 16:38:34 GMT",
"version": "v1"
},
{
"created": "Sat, 16 Mar 2002 14:15:14 GMT",
"version": "v2"
},
{
"created": "Fri, 22 Mar 2002 16:28:18 GMT",
"version": "v3"
},
{
"created": "Tue, 23 Apr 2002 14:22:45 GMT",
"version": "v4"
},
{
"created": "Wed, 24 Apr 2002 14:53:45 GMT",
"version": "v5"
},
{
"created": "Sat, 18 May 2002 08:50:54 GMT",
"version": "v6"
},
{
"created": "Thu, 24 Oct 2002 15:25:49 GMT",
"version": "v7"
}
] |
2007-11-12
|
[
[
"Iorio",
"Lorenzo",
""
]
] |
In this paper we calculate explicitly the secular classical precessions of the node \Omega and the perigee \omega of an Earth artificial satellite induced by the static, even zonal harmonics of the geopotential up to degree l=20. Subsequently, their systematic errors induced by the mismodelling in the even zonal geopotential coefficients J_l are compared to the general relativistic secular gravitomagnetic and gravitoelectric precessions of the node and the perigee of the existing laser-ranged geodetic satellites and of the proposed LARES.
|
gr-qc/0701101
|
Lior M. Burko
|
Lior M. Burko
|
Towards a wave-extraction method for numerical relativity. V. Extracting
the Weyl scalars in the quasi-Kinnersley tetrad from spatial data
|
13 pages
|
Phys.Rev.D75:084039,2007
|
10.1103/PhysRevD.75.084039
| null |
gr-qc
| null |
We extract the Weyl scalars $\Psi_0$ and $\Psi_4$ in the quasi-Kinnersley
tetrad by finding initially the (gauge--, tetrad--, and
background--independent) transverse quasi-Kinnersley frame. This step still
leaves two undetermined degrees of freedom: the ratio $|\Psi_0|/|\Psi_4|$, and
one of the phases (the product $|\Psi_0|\cdot |\Psi_4|$ and the {\em sum} of
the phases are determined by the so-called BB radiation scalar). The residual
symmetry ("spin/boost") can be removed by gauge fixing of spin coefficients in
two steps: First, we break the boost symmetry by requiring that $\rho$
corresponds to a global constant mass parameter that equals the ADM mass (or,
equivalently in perturbation theory, that $\rho$ or $\mu$ equal their values in
the no-radiation limits), thus determining the two moduli of the Weyl scalars
$|\Psi_0|, |\Psi_4|$, while leaving their phases as yet undetermined. Second,
we break the spin symmetry by requiring that the ratio $\pi/\tau$ gives the
expected polarization state for the gravitational waves, thus determining the
phases. Our method of gauge fixing--specifically its second step--is
appropriate for cases for which the Weyl curvature is purely electric. Applying
this method to Misner and Brill--Lindquist data, we explicitly find the Weyl
scalars $\Psi_0$ and $\Psi_4$ perturbatively in the quasi-Kinnersley tetrad.
|
[
{
"created": "Thu, 18 Jan 2007 03:06:34 GMT",
"version": "v1"
}
] |
2008-11-26
|
[
[
"Burko",
"Lior M.",
""
]
] |
We extract the Weyl scalars $\Psi_0$ and $\Psi_4$ in the quasi-Kinnersley tetrad by finding initially the (gauge--, tetrad--, and background--independent) transverse quasi-Kinnersley frame. This step still leaves two undetermined degrees of freedom: the ratio $|\Psi_0|/|\Psi_4|$, and one of the phases (the product $|\Psi_0|\cdot |\Psi_4|$ and the {\em sum} of the phases are determined by the so-called BB radiation scalar). The residual symmetry ("spin/boost") can be removed by gauge fixing of spin coefficients in two steps: First, we break the boost symmetry by requiring that $\rho$ corresponds to a global constant mass parameter that equals the ADM mass (or, equivalently in perturbation theory, that $\rho$ or $\mu$ equal their values in the no-radiation limits), thus determining the two moduli of the Weyl scalars $|\Psi_0|, |\Psi_4|$, while leaving their phases as yet undetermined. Second, we break the spin symmetry by requiring that the ratio $\pi/\tau$ gives the expected polarization state for the gravitational waves, thus determining the phases. Our method of gauge fixing--specifically its second step--is appropriate for cases for which the Weyl curvature is purely electric. Applying this method to Misner and Brill--Lindquist data, we explicitly find the Weyl scalars $\Psi_0$ and $\Psi_4$ perturbatively in the quasi-Kinnersley tetrad.
|
1705.09674
|
Yakov Shlapentokh-Rothman
|
Igor Rodnianski and Yakov Shlapentokh-Rothman
|
The Asymptotically Self-Similar Regime for the Einstein Vacuum Equations
|
final version
| null | null | null |
gr-qc math-ph math.AP math.DG math.MP
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We develop a local theory for the construction of singular spacetimes in all
spacetime dimensions which become asymptotically self-similar as the
singularity is approached. The techniques developed also allow us to construct
and classify exact self-similar solutions which correspond to the formal
asymptotic expansions of Fefferman and Graham's ambient metric.
|
[
{
"created": "Fri, 26 May 2017 18:11:47 GMT",
"version": "v1"
},
{
"created": "Sat, 10 Jun 2017 17:29:53 GMT",
"version": "v2"
},
{
"created": "Mon, 26 Feb 2018 03:32:51 GMT",
"version": "v3"
}
] |
2018-02-27
|
[
[
"Rodnianski",
"Igor",
""
],
[
"Shlapentokh-Rothman",
"Yakov",
""
]
] |
We develop a local theory for the construction of singular spacetimes in all spacetime dimensions which become asymptotically self-similar as the singularity is approached. The techniques developed also allow us to construct and classify exact self-similar solutions which correspond to the formal asymptotic expansions of Fefferman and Graham's ambient metric.
|
1605.07614
|
Gabriel Farrugia
|
Gabriel Farrugia, Jackson Levi Said, Matteo Luca Ruggiero
|
Solar System tests in $f(T)$ gravity
|
16 pages, 1 figure
|
Phys. Rev. D 93, 104034 (2016)
|
10.1103/PhysRevD.93.104034
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We investigate the four solar system tests of gravity - perihelion
precession, light bending, Shapiro time delay, gravitational redshift - in
$f(T)$ gravity. In particular, we investigate the solution derived by Ruggiero
and Radicella, Phys. Rev. D 91, 104014 (2015), for a nondiagonal vierbein field
for a polynomial $f(T) = T + \alpha T^n$, where $\alpha$ is a constant and $|n|
\neq 1$. In this paper, we derive the solutions for each test, in which
Weinberg's, Bodenner and Will's, Cattani et al. and Rindler and Ishak's methods
are applied, Gravitation and Cosmology: Principles and Applications of the
General Theory of Relativity (Wiley, New York, 1972); Am. J. Phys. 71 (2003);
Phys. Rev. D 87, 047503 (2013); Phys. Rev. D 76, 043006 (2007). We set a
constraint on alpha for $n$ = 2, 3 by using data available from literature.
|
[
{
"created": "Tue, 24 May 2016 17:51:52 GMT",
"version": "v1"
}
] |
2016-05-26
|
[
[
"Farrugia",
"Gabriel",
""
],
[
"Said",
"Jackson Levi",
""
],
[
"Ruggiero",
"Matteo Luca",
""
]
] |
We investigate the four solar system tests of gravity - perihelion precession, light bending, Shapiro time delay, gravitational redshift - in $f(T)$ gravity. In particular, we investigate the solution derived by Ruggiero and Radicella, Phys. Rev. D 91, 104014 (2015), for a nondiagonal vierbein field for a polynomial $f(T) = T + \alpha T^n$, where $\alpha$ is a constant and $|n| \neq 1$. In this paper, we derive the solutions for each test, in which Weinberg's, Bodenner and Will's, Cattani et al. and Rindler and Ishak's methods are applied, Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity (Wiley, New York, 1972); Am. J. Phys. 71 (2003); Phys. Rev. D 87, 047503 (2013); Phys. Rev. D 76, 043006 (2007). We set a constraint on alpha for $n$ = 2, 3 by using data available from literature.
|
gr-qc/0304101
|
Charles Wang
|
Charles Wang
|
A nonlinear quantum model of the Friedmann universe
|
11 pages of text + 4 pages for 8 figures
|
Class.Quant.Grav. 20 (2003) 3151-3164
|
10.1088/0264-9381/20/14/316
| null |
gr-qc
| null |
A discussion is given of the quantisation of a physical system with finite
degrees of freedom subject to a Hamiltonian constraint by treating time as a
constrained classical variable interacting with an unconstrained quantum state.
This leads to a quantisation scheme that yields a Schrodinger-type equation
which is in general nonlinear in evolution. Nevertheless it is compatible with
a probabilistic interpretation of quantum mechanics and in particular the
construction of a Hilbert space with a Euclidean norm is possible. The new
scheme is applied to the quantisation of a Friedmann Universe with a massive
scalar field whose dynamical behaviour is investigated numerically.
|
[
{
"created": "Tue, 29 Apr 2003 13:01:13 GMT",
"version": "v1"
},
{
"created": "Thu, 1 May 2003 09:06:10 GMT",
"version": "v2"
},
{
"created": "Mon, 12 May 2003 11:28:29 GMT",
"version": "v3"
},
{
"created": "Mon, 19 May 2003 23:13:21 GMT",
"version": "v4"
},
{
"created": "Fri, 13 Jun 2003 12:54:53 GMT",
"version": "v5"
},
{
"created": "Mon, 16 Jun 2003 22:05:29 GMT",
"version": "v6"
},
{
"created": "Tue, 1 Jul 2003 16:13:04 GMT",
"version": "v7"
},
{
"created": "Fri, 4 Jul 2003 12:44:22 GMT",
"version": "v8"
}
] |
2009-11-10
|
[
[
"Wang",
"Charles",
""
]
] |
A discussion is given of the quantisation of a physical system with finite degrees of freedom subject to a Hamiltonian constraint by treating time as a constrained classical variable interacting with an unconstrained quantum state. This leads to a quantisation scheme that yields a Schrodinger-type equation which is in general nonlinear in evolution. Nevertheless it is compatible with a probabilistic interpretation of quantum mechanics and in particular the construction of a Hilbert space with a Euclidean norm is possible. The new scheme is applied to the quantisation of a Friedmann Universe with a massive scalar field whose dynamical behaviour is investigated numerically.
|
gr-qc/0201006
|
Helmut Friedrich
|
Helmut Friedrich
|
Conformal geodesics on vacuum space-times
| null |
Commun.Math.Phys. 235 (2003) 513-543
|
10.1007/s00220-003-0794-8
| null |
gr-qc
| null |
We discuss properties of conformal geodesics on general, vacuum, and warped
product space-times and derive a system of conformal deviation equations. The
results are used to show how to construct on the Schwarzschild-Kruskal
space-time global conformal Gauss coordinates which extends smoothly and
without degeneracy to future and past null infinity.
|
[
{
"created": "Thu, 3 Jan 2002 10:08:50 GMT",
"version": "v1"
}
] |
2009-11-07
|
[
[
"Friedrich",
"Helmut",
""
]
] |
We discuss properties of conformal geodesics on general, vacuum, and warped product space-times and derive a system of conformal deviation equations. The results are used to show how to construct on the Schwarzschild-Kruskal space-time global conformal Gauss coordinates which extends smoothly and without degeneracy to future and past null infinity.
|
1408.5257
|
Andrea Geralico
|
Donato Bini, Andrea Geralico, Sauro Succi
|
Particle scattering by a test fluid on a Schwarzschild spacetime: the
equation of state matters
|
4 pages, 2 figures; published version
|
Eur. Phys. J. C 72, 1913 (2012)
|
10.1140/epjc/s10052-012-1913-5
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The motion of a massive test particle in a Schwarzschild spacetime surrounded
by a perfect fluid with equation of state $p_0= w \rho_0$ is investigated.
Deviations from geodesic motion are analyzed as a function of the parameter
$w$, ranging from $w=1$ which corresponds to the case of massive free scalar
fields, down into the so-called "phantom" energy, with $w<-1$. It is found that
the interaction with the fluid distribution leads to capture (escape) of the
particle trajectory in the case $1+w>0$ ($<0$), respectively. Based on this
result, it is argued that inspection of the trajectories of test particles in
the vicinity of a Schwarzschild black hole may offer a new means of gaining
insights into the nature of cosmic matter.
|
[
{
"created": "Fri, 22 Aug 2014 10:47:44 GMT",
"version": "v1"
}
] |
2015-06-22
|
[
[
"Bini",
"Donato",
""
],
[
"Geralico",
"Andrea",
""
],
[
"Succi",
"Sauro",
""
]
] |
The motion of a massive test particle in a Schwarzschild spacetime surrounded by a perfect fluid with equation of state $p_0= w \rho_0$ is investigated. Deviations from geodesic motion are analyzed as a function of the parameter $w$, ranging from $w=1$ which corresponds to the case of massive free scalar fields, down into the so-called "phantom" energy, with $w<-1$. It is found that the interaction with the fluid distribution leads to capture (escape) of the particle trajectory in the case $1+w>0$ ($<0$), respectively. Based on this result, it is argued that inspection of the trajectories of test particles in the vicinity of a Schwarzschild black hole may offer a new means of gaining insights into the nature of cosmic matter.
|
gr-qc/9606081
|
Ayon Juan Eloy
|
Eloy Ay\'on-Beato
|
Staticity Theorem for Non-Rotating Black Holes with Non-Minimally
Coupled Self-Interacting Scalar Fields
|
8 pages, LaTeX; new version to appear in ``Exact Solutions and Scalar
Fields in Gravity: Recent Developments,'' eds. A. Macias, J. Cervantes-Cota,
and C. Laemmerzahl (Kluwer Academic Publishing)
|
``Exact Solutions and Scalar Fields in Gravity: Recent
Developments,'' edited by A. Macias, J.L. Cervantes-Cota, and C. Laemmerzahl
(Kluwer Academic/Plenum Publishers, New York 2001), p. 263.
| null | null |
gr-qc
| null |
Self-interacting scalar field configurations which are non-minimally coupled
($\zeta\neq0$) to the gravity of a strictly stationary black hole with
non-rotating horizon are studied. It is concluded that for analytical
configurations the corresponding domain of outer communications is static.
|
[
{
"created": "Fri, 28 Jun 1996 03:03:21 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Jan 2001 18:11:14 GMT",
"version": "v2"
}
] |
2008-02-03
|
[
[
"Ayón-Beato",
"Eloy",
""
]
] |
Self-interacting scalar field configurations which are non-minimally coupled ($\zeta\neq0$) to the gravity of a strictly stationary black hole with non-rotating horizon are studied. It is concluded that for analytical configurations the corresponding domain of outer communications is static.
|
0812.0921
|
Dah-Wei Chiou
|
Dah-Wei Chiou
|
Effective equations of motion for constrained quantum systems: A study
of the Bianchi I loop quantum cosmology
|
30 pages
| null | null |
IGC-08/11-7
|
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
A new mathematical framework is formulated to derive the effective equations
of motion for the constrained quantum system which possesses an internal clock.
In the realm close to classical behavior, the quantum evolution is approximated
by a finite system of coupled but ordinary differential equations adhered to
the weakly imposed Hamiltonian constraint. For the simplified version of loop
quantum cosmology in the Bianchi I model with a free massless scalar filed, the
resulting effective equations of motion affirm the bouncing scenario predicted
by the previous studies: The big bang singularity is resolved and replaced by
the big bounces, which take place up to three times, once in each diagonal
direction, whenever the directional density approaches the critical value in
the regime of Planckian density. It is also revealed that back-reaction arises
from the quantum corrections and modifies the precise value of the directional
density at the bouncing epoch. Additionally, as an example of symmetry
reduction, we study isotropy emerging from the anisotropic Bianchi I model in
the context of effective equations of motion.
|
[
{
"created": "Thu, 4 Dec 2008 12:28:26 GMT",
"version": "v1"
}
] |
2008-12-05
|
[
[
"Chiou",
"Dah-Wei",
""
]
] |
A new mathematical framework is formulated to derive the effective equations of motion for the constrained quantum system which possesses an internal clock. In the realm close to classical behavior, the quantum evolution is approximated by a finite system of coupled but ordinary differential equations adhered to the weakly imposed Hamiltonian constraint. For the simplified version of loop quantum cosmology in the Bianchi I model with a free massless scalar filed, the resulting effective equations of motion affirm the bouncing scenario predicted by the previous studies: The big bang singularity is resolved and replaced by the big bounces, which take place up to three times, once in each diagonal direction, whenever the directional density approaches the critical value in the regime of Planckian density. It is also revealed that back-reaction arises from the quantum corrections and modifies the precise value of the directional density at the bouncing epoch. Additionally, as an example of symmetry reduction, we study isotropy emerging from the anisotropic Bianchi I model in the context of effective equations of motion.
|
1001.3237
|
Yungui Gong
|
Fu-Wen Shu, Yungui Gong
|
Equipartition of energy and the first law of thermodynamics at the
apparent horizon
|
v2: 7 pages, 1 figure, add discussion on consistency check, Int. J.
Mod. Phys. D in press
|
Int. J. Mod. Phys. D 20 (2011) 553
|
10.1142/S0218271811018883
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We apply the holographic principle and the equipartition law of energy to the
apparent horizon of a Friedmann-Robertson-Walker universe and derive the
Friedmann equation describing the dynamics of the universe. We also show that
the equipartition law of energy can be interpreted as the first law of
thermodynamics at the apparent horizon.
|
[
{
"created": "Tue, 19 Jan 2010 09:41:02 GMT",
"version": "v1"
},
{
"created": "Fri, 18 Mar 2011 02:26:07 GMT",
"version": "v2"
}
] |
2011-05-05
|
[
[
"Shu",
"Fu-Wen",
""
],
[
"Gong",
"Yungui",
""
]
] |
We apply the holographic principle and the equipartition law of energy to the apparent horizon of a Friedmann-Robertson-Walker universe and derive the Friedmann equation describing the dynamics of the universe. We also show that the equipartition law of energy can be interpreted as the first law of thermodynamics at the apparent horizon.
|
2309.04130
|
Soumya Bhattacharya
|
Soumya Bhattacharya, Shramana Ghosh
|
Gravitational wave memory for a class of static and spherically
symmetric spacetimes
|
21 pages, 14 figures
| null | null | null |
gr-qc astro-ph.CO hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
This article aims at comparing gravitational wave memory effect in a
Schwarzschild spacetime with that of other compact objects with static and
spherically symmetric spacetime, with the purpose of proposing a procedure for
differentiating between various compact object geometries. We do this by
considering the relative evolution of two nearby test geodesics with in
different backgrounds in the presence and absence of a gravitational wave pulse
and comparing them. Memory effect due to a gravitational wave would ensure that
there is a permanent effect on each spacetime and the corresponding geodesic
evolution, being metric dependent, would display distinct results in each case.
For a complete picture, we have considered both displacement and velocity
memory effect in each geometry.
|
[
{
"created": "Fri, 8 Sep 2023 05:08:52 GMT",
"version": "v1"
}
] |
2023-09-12
|
[
[
"Bhattacharya",
"Soumya",
""
],
[
"Ghosh",
"Shramana",
""
]
] |
This article aims at comparing gravitational wave memory effect in a Schwarzschild spacetime with that of other compact objects with static and spherically symmetric spacetime, with the purpose of proposing a procedure for differentiating between various compact object geometries. We do this by considering the relative evolution of two nearby test geodesics with in different backgrounds in the presence and absence of a gravitational wave pulse and comparing them. Memory effect due to a gravitational wave would ensure that there is a permanent effect on each spacetime and the corresponding geodesic evolution, being metric dependent, would display distinct results in each case. For a complete picture, we have considered both displacement and velocity memory effect in each geometry.
|
1610.04396
|
Andrea Addazi AndAdd
|
Andrea Addazi
|
Brane Bounce from logarithmic entropic corrections in the bulk
| null | null |
10.1142/S0217751X17501743
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We calculate new corrections to the Brane-world dynamics, lying in a 5D
Schwarzschild-De Sitter black hole, generalizing the result of Nojiri, Odintsov
and Ogushi (NOO) in Ref.\cite{Nojiri:2002vu}, The NOO entropy effect is based
on the Logharitmic correction to the bulk entropy firstly calculated by
Mukherji and Pal in Ref.\cite{Mukherji:2002de}. We calculate higher order
contributions to the brane worldsheet. The extra terms obtained lead to
interesting implications in brane-cosmology. In particular, new entropic terms
rapidly disappear in the late Universe while exploding in the very Early
Universe. In particular, we show that they may trigger a cosmological bounce in
the very early Universe. On the other hand, they contribute to the cosmological
expansion in the Late Universe. We also discuss a scenario in which the BLK
anisotropies are washed-out, toward a new Ekpyrotic Brane Cosmology.
|
[
{
"created": "Fri, 14 Oct 2016 10:23:37 GMT",
"version": "v1"
}
] |
2017-11-22
|
[
[
"Addazi",
"Andrea",
""
]
] |
We calculate new corrections to the Brane-world dynamics, lying in a 5D Schwarzschild-De Sitter black hole, generalizing the result of Nojiri, Odintsov and Ogushi (NOO) in Ref.\cite{Nojiri:2002vu}, The NOO entropy effect is based on the Logharitmic correction to the bulk entropy firstly calculated by Mukherji and Pal in Ref.\cite{Mukherji:2002de}. We calculate higher order contributions to the brane worldsheet. The extra terms obtained lead to interesting implications in brane-cosmology. In particular, new entropic terms rapidly disappear in the late Universe while exploding in the very Early Universe. In particular, we show that they may trigger a cosmological bounce in the very early Universe. On the other hand, they contribute to the cosmological expansion in the Late Universe. We also discuss a scenario in which the BLK anisotropies are washed-out, toward a new Ekpyrotic Brane Cosmology.
|
2308.01709
|
Harsh Narola
|
Harsh Narola, Justin Janquart, Le\"ila Haegel, K. Haris, Otto A.
Hannuksela, Chris Van Den Broeck
|
How well can modified gravitational wave propagation be constrained with
strong lensing?
|
Arxiv submission
| null | null | null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
Strong gravitational lensing produces multiple images of a gravitational wave
(GW) signal, which can be observed by detectors as time-separated copies of the
same event. It has been shown that under favourable circumstances, by combining
information from a quadruply lensed GW with electromagnetic observations of
lensed galaxies, it is possible to identify the host galaxy of a binary black
hole coalescence. Comparing the luminosity distance obtained through
electromagnetic means with the effective luminosity distance inferred from the
lensed GW signal would then enable us to constrain alternative theories of
gravity that allow for modified GW propagation. Here we analyze models
including large extra spatial dimensions, a running Planck mass, and a model
that captures propagation effects occurring in a variety of alternative
theories to general relativity. We consider a plausible population of lenses
and binary black holes and use Bayesian inference on simulated GW signals as
seen in current detectors at design sensitivity, to arrive at a realistic
assessment of the bounds that could be placed. We find that, due to the fact
that the sources of lensed events will typically be at much larger redshifts,
this method can improve over bounds from GW170817 and its electromagnetic
counterpart by a factor of $\sim 5$ to $\mathcal{O}(10^2)$, depending on the
alternative gravity model.
|
[
{
"created": "Thu, 3 Aug 2023 12:08:02 GMT",
"version": "v1"
}
] |
2023-08-04
|
[
[
"Narola",
"Harsh",
""
],
[
"Janquart",
"Justin",
""
],
[
"Haegel",
"Leïla",
""
],
[
"Haris",
"K.",
""
],
[
"Hannuksela",
"Otto A.",
""
],
[
"Broeck",
"Chris Van Den",
""
]
] |
Strong gravitational lensing produces multiple images of a gravitational wave (GW) signal, which can be observed by detectors as time-separated copies of the same event. It has been shown that under favourable circumstances, by combining information from a quadruply lensed GW with electromagnetic observations of lensed galaxies, it is possible to identify the host galaxy of a binary black hole coalescence. Comparing the luminosity distance obtained through electromagnetic means with the effective luminosity distance inferred from the lensed GW signal would then enable us to constrain alternative theories of gravity that allow for modified GW propagation. Here we analyze models including large extra spatial dimensions, a running Planck mass, and a model that captures propagation effects occurring in a variety of alternative theories to general relativity. We consider a plausible population of lenses and binary black holes and use Bayesian inference on simulated GW signals as seen in current detectors at design sensitivity, to arrive at a realistic assessment of the bounds that could be placed. We find that, due to the fact that the sources of lensed events will typically be at much larger redshifts, this method can improve over bounds from GW170817 and its electromagnetic counterpart by a factor of $\sim 5$ to $\mathcal{O}(10^2)$, depending on the alternative gravity model.
|
gr-qc/9704068
|
N. K. Dadhich
|
Naresh Dadhich
|
On the Schwarzschild field
|
19 pages, TeX version
| null | null |
IUCAA-33/97
|
gr-qc
| null |
General relativity is a non-linear theory with the distinguishing feature
that gravitational field energy also acts as gravitational charge density. In
the well-known Schwarzschild solution describing field of an isolated massive
body at rest, the scalar function $\phi$ characterising the field acts as a
gravitational potential as well as it curves space part of spacetime. We
demonstrate explicitly that it is the latter property that accounts for the
non-linear (gravity as its own source) aspect which is not explicit in usual
derivations. It is worth noting that the Einstein vacuum equations ultimately
reduce to the Laplace equation and its first integral which fixes zero of
$\phi$ at infinity. Thus the Schwarzschild field alongwith its asymptotic flat
character is completely determined without application of any boundary
condition by the field equations themselves. That means non-zero constant value
of $\phi$ will have non-vacuous effect. It in fact produces stresses exactly of
the form required to represent a global monopole. By retaining freedom of
choosing zero of $\phi$, which will break asymptotic flatness, we can obtain
the Schwarzschild black hole with global monopole charge. It is the non-linear
aspect responsible for ``curving'' space, which has no Newtonian analogue,
survives even when $\phi$ is constant but not zero.
|
[
{
"created": "Thu, 24 Apr 1997 12:05:00 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Dadhich",
"Naresh",
""
]
] |
General relativity is a non-linear theory with the distinguishing feature that gravitational field energy also acts as gravitational charge density. In the well-known Schwarzschild solution describing field of an isolated massive body at rest, the scalar function $\phi$ characterising the field acts as a gravitational potential as well as it curves space part of spacetime. We demonstrate explicitly that it is the latter property that accounts for the non-linear (gravity as its own source) aspect which is not explicit in usual derivations. It is worth noting that the Einstein vacuum equations ultimately reduce to the Laplace equation and its first integral which fixes zero of $\phi$ at infinity. Thus the Schwarzschild field alongwith its asymptotic flat character is completely determined without application of any boundary condition by the field equations themselves. That means non-zero constant value of $\phi$ will have non-vacuous effect. It in fact produces stresses exactly of the form required to represent a global monopole. By retaining freedom of choosing zero of $\phi$, which will break asymptotic flatness, we can obtain the Schwarzschild black hole with global monopole charge. It is the non-linear aspect responsible for ``curving'' space, which has no Newtonian analogue, survives even when $\phi$ is constant but not zero.
|
2005.11609
|
Jorge Ananias Neto
|
Everton M. C. Abreu, Jorge Ananias Neto and Ed\'esio M. Barboza Jr
|
Barrow's black hole entropy and the equipartition theorem
|
minor adjustments
| null |
10.1209/0295-5075/130/40005
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The Barrow entropy appears from the fact that the black hole surface can be
modified due to quantum gravitational outcome. The measure of this perturbation
is given by a new exponent $\Delta$. In this letter we have shown that, from
the standard mathematical form of the equipartition theorem, we can relate it
with Barrow entropy. From this equivalence, we have calculated precisely the
value of the exponent for the equipartition law. After that, we tested the
thermodynamical coherence of the system by calculating the heat capacity which
established an interval of the possible thermodynamical coherent values of
Barrow entropic exponent and corroborated our first result.
|
[
{
"created": "Sat, 23 May 2020 22:05:37 GMT",
"version": "v1"
},
{
"created": "Tue, 26 May 2020 16:34:14 GMT",
"version": "v2"
},
{
"created": "Mon, 1 Jun 2020 19:58:16 GMT",
"version": "v3"
}
] |
2020-08-26
|
[
[
"Abreu",
"Everton M. C.",
""
],
[
"Neto",
"Jorge Ananias",
""
],
[
"Barboza",
"Edésio M.",
"Jr"
]
] |
The Barrow entropy appears from the fact that the black hole surface can be modified due to quantum gravitational outcome. The measure of this perturbation is given by a new exponent $\Delta$. In this letter we have shown that, from the standard mathematical form of the equipartition theorem, we can relate it with Barrow entropy. From this equivalence, we have calculated precisely the value of the exponent for the equipartition law. After that, we tested the thermodynamical coherence of the system by calculating the heat capacity which established an interval of the possible thermodynamical coherent values of Barrow entropic exponent and corroborated our first result.
|
gr-qc/9804003
|
Hideki Asada
|
Hideki Asada
|
Formulation for the internal motion of quasi-equilibrium configurations
in general relativity
|
11 pages (RevTeX); accepted for publication in Phys. Rev. D
|
Phys.Rev. D57 (1998) 7292-7298
|
10.1103/PhysRevD.57.7292
| null |
gr-qc
| null |
We present a formulation for the internal motion of equilibrium
configurations with a rotational Killing vector in general relativity. As an
approximation, this formulation is applicable to investigation of the internal
motion of quasi-equilibrium configurations such as binary neutron stars. Based
on this simple formulation, a condition for the general relativistic counter
rotation has been obtained, though in the recent work by Bonazzola, Gourgoulhon
and Marck, their condition for the counter rotation is not enough to specify
the internal velocity field. Under the condition given in this paper, the
internal velocity field can be determined completely. Indeed, in the
counter-rotating case, we have also derived Poisson equations for the internal
velocity, which take tractable forms in numerical implementation.
|
[
{
"created": "Thu, 2 Apr 1998 06:05:52 GMT",
"version": "v1"
}
] |
2009-10-31
|
[
[
"Asada",
"Hideki",
""
]
] |
We present a formulation for the internal motion of equilibrium configurations with a rotational Killing vector in general relativity. As an approximation, this formulation is applicable to investigation of the internal motion of quasi-equilibrium configurations such as binary neutron stars. Based on this simple formulation, a condition for the general relativistic counter rotation has been obtained, though in the recent work by Bonazzola, Gourgoulhon and Marck, their condition for the counter rotation is not enough to specify the internal velocity field. Under the condition given in this paper, the internal velocity field can be determined completely. Indeed, in the counter-rotating case, we have also derived Poisson equations for the internal velocity, which take tractable forms in numerical implementation.
|
2108.09524
|
Pedro Labra\~na
|
Pedro Labra\~na and Juan Ortiz
|
Classically and Quantum Stable Emergent Universe in a Jordan-Brans-Dicke
Theory
|
22 pages, 4 figures, changes in abstract and introduction,
improvements in the text and comments added in conclusions. References added
| null | null | null |
gr-qc astro-ph.CO hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
The study of Emergent Universe models is based on the assumption that the
universe emerged from a past eternal Einstein Static (ES) state towards an
inflationary phase and then evolves into a hot big bang era. These models are
appealing since they provide specific examples of nonsingular (geodesically
complete) inflationary universes. However, it has been pointed out by
Mithani-Vilenkin that certain Emergent Universe scenarios which have a
classically stable ES state could experience a semiclassical instability and
collapse. In this paper, we investigate the classical and quantum stability of
the ES regime of Emergent Universes within the framework of Jordan-Brans-Dicke
theory. We demonstrate that when considering these models, it is possible to
have both, classical and semiclassical stability of the ES state without
addressing the instability highlighted by Mithani-Vilenkin.
|
[
{
"created": "Sat, 21 Aug 2021 15:01:47 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Mar 2024 23:32:03 GMT",
"version": "v2"
}
] |
2024-03-18
|
[
[
"Labraña",
"Pedro",
""
],
[
"Ortiz",
"Juan",
""
]
] |
The study of Emergent Universe models is based on the assumption that the universe emerged from a past eternal Einstein Static (ES) state towards an inflationary phase and then evolves into a hot big bang era. These models are appealing since they provide specific examples of nonsingular (geodesically complete) inflationary universes. However, it has been pointed out by Mithani-Vilenkin that certain Emergent Universe scenarios which have a classically stable ES state could experience a semiclassical instability and collapse. In this paper, we investigate the classical and quantum stability of the ES regime of Emergent Universes within the framework of Jordan-Brans-Dicke theory. We demonstrate that when considering these models, it is possible to have both, classical and semiclassical stability of the ES state without addressing the instability highlighted by Mithani-Vilenkin.
|
gr-qc/9709007
|
Carlo Del Noce
|
Carlo Del Noce, Giovanni Preti and Fernando de Felice (University of
Padova, Italy, and INFN, Sezione di Padova)
|
Coalescing binary systems of compact objects: Dynamics of angular
momenta
|
22 pages, AASTeX and 13 figures in PostScript
|
The Astrophysical Journal, 507:287-299, 1998 November 1
|
10.1086/306295
| null |
gr-qc astro-ph
| null |
The end state of a coalescing binary of compact objects depends strongly on
the final total mass M and angular momentum J. Since gravitational radiation
emission causes a slow evolution of the binary system through quasi-circular
orbits down to the innermost stable one, in this paper we examine the
corresponding behavior of the ratio J/M^2 which must be less than 1(G/c) or
about 0.7(G/c) for the formation of a black hole or a neutron star
respectively. The results show cases for which, at the end of the inspiral
phase, the conditions for black hole or neutron star formation are not
satisfied. The inclusion of spin effects leads us to a study of precession
equations valid also for the calculation of gravitational waveforms.
|
[
{
"created": "Wed, 3 Sep 1997 18:34:30 GMT",
"version": "v1"
},
{
"created": "Tue, 15 Dec 1998 12:26:02 GMT",
"version": "v2"
}
] |
2009-10-30
|
[
[
"Del Noce",
"Carlo",
"",
"University of\n Padova, Italy, and INFN, Sezione di Padova"
],
[
"Preti",
"Giovanni",
"",
"University of\n Padova, Italy, and INFN, Sezione di Padova"
],
[
"de Felice",
"Fernando",
"",
"University of\n Padova, Italy, and INFN, Sezione di Padova"
]
] |
The end state of a coalescing binary of compact objects depends strongly on the final total mass M and angular momentum J. Since gravitational radiation emission causes a slow evolution of the binary system through quasi-circular orbits down to the innermost stable one, in this paper we examine the corresponding behavior of the ratio J/M^2 which must be less than 1(G/c) or about 0.7(G/c) for the formation of a black hole or a neutron star respectively. The results show cases for which, at the end of the inspiral phase, the conditions for black hole or neutron star formation are not satisfied. The inclusion of spin effects leads us to a study of precession equations valid also for the calculation of gravitational waveforms.
|
1501.03538
|
Merced Montesinos
|
Diego Gonz\'alez, Merced Montesinos
|
Gauge connection formulations for general relativity
|
No figures
|
Phys.Rev.D91:024021,2015
|
10.1103/PhysRevD.91.024021
| null |
gr-qc hep-th math-ph math.MP
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We report a new class of $SO(3,\mathbb{C})$ and diffeomorphism invariant
formulations for general relativity with either a vanishing or a nonvanishing
cosmological constant, which depends functionally on a $SO(3,\mathbb{C})$ gauge
connection and a complex-valued 4-form via a holomorphic function of the trace
of a symmetric $3\times3$ matrix that is constructed from these variables. We
present two members of this class, one of which results from the implementation
of a method for obtaining action principles belonging to the class. For the
case of a nonvanishing cosmological constant, we solve for the complex-valued
4-form and get pure connection action principles. We perform the canonical
analysis of the class. The analysis shows that only the Hamiltonian constraint
is modified with respect to the Ashtekar formulation and that the members of
the class have two physical degrees of freedom per space point.
|
[
{
"created": "Wed, 14 Jan 2015 23:50:17 GMT",
"version": "v1"
}
] |
2015-01-16
|
[
[
"González",
"Diego",
""
],
[
"Montesinos",
"Merced",
""
]
] |
We report a new class of $SO(3,\mathbb{C})$ and diffeomorphism invariant formulations for general relativity with either a vanishing or a nonvanishing cosmological constant, which depends functionally on a $SO(3,\mathbb{C})$ gauge connection and a complex-valued 4-form via a holomorphic function of the trace of a symmetric $3\times3$ matrix that is constructed from these variables. We present two members of this class, one of which results from the implementation of a method for obtaining action principles belonging to the class. For the case of a nonvanishing cosmological constant, we solve for the complex-valued 4-form and get pure connection action principles. We perform the canonical analysis of the class. The analysis shows that only the Hamiltonian constraint is modified with respect to the Ashtekar formulation and that the members of the class have two physical degrees of freedom per space point.
|
2301.09021
|
Valerio Faraoni
|
Valerio Faraoni and Robert Vanderwee (Bishop's University)
|
Tolman-Ehrenfest's criterion of thermal equilibrium extended to
conformally static spacetimes
|
Section on cosmological black holes added, bibliography expanded.
Matches the version accepted in Phys. Rev. D
| null |
10.1103/PhysRevD.107.064072
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
With insight from examples and physical arguments, the Tolman-Ehrenfest
criterion of thermal equilibrium for test fluids in static spacetimes is
extended to local thermal equilibrium in conformally static geometries. The
temperature of the conformally rescaled fluid scales with the inverse of the
conformal factor, reproducing the evolution of the cosmic microwave background
in Friedmann universes, the Hawking temperature of the Sultana-Dyer
cosmological black hole, and a heuristic argument by Dicke.
|
[
{
"created": "Sat, 21 Jan 2023 22:29:10 GMT",
"version": "v1"
},
{
"created": "Sat, 18 Mar 2023 00:57:23 GMT",
"version": "v2"
}
] |
2023-04-12
|
[
[
"Faraoni",
"Valerio",
"",
"Bishop's University"
],
[
"Vanderwee",
"Robert",
"",
"Bishop's University"
]
] |
With insight from examples and physical arguments, the Tolman-Ehrenfest criterion of thermal equilibrium for test fluids in static spacetimes is extended to local thermal equilibrium in conformally static geometries. The temperature of the conformally rescaled fluid scales with the inverse of the conformal factor, reproducing the evolution of the cosmic microwave background in Friedmann universes, the Hawking temperature of the Sultana-Dyer cosmological black hole, and a heuristic argument by Dicke.
|
1310.5976
|
Peter Van
|
P. V\'an and T.S. Bir\'o
|
Thermodynamics and flow-frames for dissipative relativistic fluids
|
9 pages
|
Proceedings of the V Leopoldo Garc\'ia-Col\'in Mexican Meeting on
Mathematical and Experimental Physics, 2014, V1578 AIP Conf. Proc., p114-121
|
10.1063/1.4862456
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
A general thermodynamic treatment of dissipative relativistic fluids is
introduced, where the temperature four vector is not parallel to the velocity
field of the fluid. Generic stability and kinetic equilibrium points out a
particular thermodynamics, where the temperature vector is parallel to the
enthalpy flow vector and the choice of the flow fixes the constitutive
functions for viscous stress and heat. The linear stability of the homogeneous
equilibrium is proved in a mixed particle-energy flow-frame.
|
[
{
"created": "Tue, 22 Oct 2013 16:23:26 GMT",
"version": "v1"
}
] |
2014-05-27
|
[
[
"Ván",
"P.",
""
],
[
"Biró",
"T. S.",
""
]
] |
A general thermodynamic treatment of dissipative relativistic fluids is introduced, where the temperature four vector is not parallel to the velocity field of the fluid. Generic stability and kinetic equilibrium points out a particular thermodynamics, where the temperature vector is parallel to the enthalpy flow vector and the choice of the flow fixes the constitutive functions for viscous stress and heat. The linear stability of the homogeneous equilibrium is proved in a mixed particle-energy flow-frame.
|
1608.02882
|
Jean-Pierre Lasota
|
M.A. Abramowicz and J.-P. Lasota
|
No repulsive force in General Relativity
|
2 pages, submitted to MNRAS Letters
| null | null | null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We show that a recent assertion [arXiv:1608.01541] that gravitational wave
emission can lead to a repulsive force explaining the accelerated expansion of
the Universe is totally unfounded.
|
[
{
"created": "Mon, 8 Aug 2016 16:06:10 GMT",
"version": "v1"
}
] |
2016-08-11
|
[
[
"Abramowicz",
"M. A.",
""
],
[
"Lasota",
"J. -P.",
""
]
] |
We show that a recent assertion [arXiv:1608.01541] that gravitational wave emission can lead to a repulsive force explaining the accelerated expansion of the Universe is totally unfounded.
|
2302.11229
|
Khalil El Bourakadi
|
K. El Bourakadi, Z. Sakhi, M. Bennai
|
Observational constraints on Tachyon inflation and reheating in f(Q)
gravity
| null | null | null | null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
In this work we study one of the most appealing string theory-motivated
models, we present a tachyonic inflationary model in the recently proposed
symmetric teleparallel framework, and examine constraints on tachyon inflation
with the exponential potential along with the reheating for a chosen $f(Q)$
gravity model. Considering a reheating phase parametrized by a number of
e-folds $N_{re},$ a temperature $T_{re}$, and an equation of state $\omega
_{re}$, we relate the reheating parameters as functions of the exponential
tachyon potential, $f(Q)$ model, and\ the spectral index $n_{s}$ parameters. We
argue that our model predicts inflationary e-folds bounded as $50\leq N\leq
64$. While for the reheating phase, wide ranges of reheating e-folds numbers
and temperatures can be obtained as we increase $\omega_{re} $ towards the
value $1/4$ according to recent Planck Data.
|
[
{
"created": "Wed, 22 Feb 2023 09:18:57 GMT",
"version": "v1"
},
{
"created": "Thu, 23 Feb 2023 19:04:34 GMT",
"version": "v2"
}
] |
2023-02-27
|
[
[
"Bourakadi",
"K. El",
""
],
[
"Sakhi",
"Z.",
""
],
[
"Bennai",
"M.",
""
]
] |
In this work we study one of the most appealing string theory-motivated models, we present a tachyonic inflationary model in the recently proposed symmetric teleparallel framework, and examine constraints on tachyon inflation with the exponential potential along with the reheating for a chosen $f(Q)$ gravity model. Considering a reheating phase parametrized by a number of e-folds $N_{re},$ a temperature $T_{re}$, and an equation of state $\omega _{re}$, we relate the reheating parameters as functions of the exponential tachyon potential, $f(Q)$ model, and\ the spectral index $n_{s}$ parameters. We argue that our model predicts inflationary e-folds bounded as $50\leq N\leq 64$. While for the reheating phase, wide ranges of reheating e-folds numbers and temperatures can be obtained as we increase $\omega_{re} $ towards the value $1/4$ according to recent Planck Data.
|
1711.10721
|
Debabrata Deb
|
Debabrata Deb, Farook Rahaman, Saibal Ray and B.K. Guha
|
Strange stars in $f(R,\mathcal{T})$ gravity
|
20 pages, 9 figures, 2 tables, Major revisions
|
JCAP03(2018)044
|
10.1088/1475-7516/2018/03/044
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this article we try to present spherically symmetric isotropic strange
star model under the framework of $f(R,\mathcal{T})$ theory of gravity. To this
end, we consider that the Lagrangian density is an arbitrary linear function of
the Ricci scalar $R$ and the trace of the energy momentum tensor~$\mathcal{T}$
given as $f\left(R,\mathcal{T}\right)=R+2\chi T$. We also assume that the quark
matter distribution is governed by the simplest form of the MIT bag model
equation of state (EOS) as $p=\frac{1}{3}\left(\rho-4B\right)$, where $B$ is
the bag constant. We have obtained an exact solution of the modified form of
the the Tolman-Oppenheimer-Volkoff (TOV) equation in the framework of
$f(R,\mathcal{T})$ gravity theory and studied the dependence of different
physical properties, viz., total mass, radius, energy density and pressure on
the chosen values of $\chi$. Further, to examine physical acceptability of the
proposed stellar model in detail, we conducted different tests, viz. energy
conditions, modified TOV equation, mass-radius relation, causality condition
etc. We have precisely explained the effects arising due to the coupling of the
matter and geometry on the compact stellar system. For a chosen value of the
Bag constant we have predicted numerical values of different physical
parameters in tabular format for the different strange stars. It is found that
as the factor $\chi$ increases the strange stars shrink gradually and become
less massive to turn into a more compact stellar system. The maximum mass point
is well within the observational limits and hence our proposed model is
suitable to explain the ultra dense compact stars. For $\chi=0$ we retrieve as
usual the standard results of general relativity (GR).
|
[
{
"created": "Wed, 29 Nov 2017 08:23:22 GMT",
"version": "v1"
},
{
"created": "Fri, 20 Apr 2018 17:56:13 GMT",
"version": "v2"
}
] |
2018-04-23
|
[
[
"Deb",
"Debabrata",
""
],
[
"Rahaman",
"Farook",
""
],
[
"Ray",
"Saibal",
""
],
[
"Guha",
"B. K.",
""
]
] |
In this article we try to present spherically symmetric isotropic strange star model under the framework of $f(R,\mathcal{T})$ theory of gravity. To this end, we consider that the Lagrangian density is an arbitrary linear function of the Ricci scalar $R$ and the trace of the energy momentum tensor~$\mathcal{T}$ given as $f\left(R,\mathcal{T}\right)=R+2\chi T$. We also assume that the quark matter distribution is governed by the simplest form of the MIT bag model equation of state (EOS) as $p=\frac{1}{3}\left(\rho-4B\right)$, where $B$ is the bag constant. We have obtained an exact solution of the modified form of the the Tolman-Oppenheimer-Volkoff (TOV) equation in the framework of $f(R,\mathcal{T})$ gravity theory and studied the dependence of different physical properties, viz., total mass, radius, energy density and pressure on the chosen values of $\chi$. Further, to examine physical acceptability of the proposed stellar model in detail, we conducted different tests, viz. energy conditions, modified TOV equation, mass-radius relation, causality condition etc. We have precisely explained the effects arising due to the coupling of the matter and geometry on the compact stellar system. For a chosen value of the Bag constant we have predicted numerical values of different physical parameters in tabular format for the different strange stars. It is found that as the factor $\chi$ increases the strange stars shrink gradually and become less massive to turn into a more compact stellar system. The maximum mass point is well within the observational limits and hence our proposed model is suitable to explain the ultra dense compact stars. For $\chi=0$ we retrieve as usual the standard results of general relativity (GR).
|
gr-qc/0002071
|
Israel Quiroz
|
Israel Quiros, Rolando Cardenas and Rolando Bonal (Departamento de
Fisica. Universidad Central de Las Villas. Santa Clara. Cuba)
|
Open universes and avoidance of the cosmological singularity
|
11 pages, latex, no figures, submitted to PRD. New important
arguments have been added. Correspondingly the abstract has been enlarged.
The content of the paper is now split into sections
| null | null | null |
gr-qc
| null |
In the present paper we give conclusive arguments pointing at physical
equivalence among conformally related metrics. Based on the argument that any
consistent effective theory of spacetime must be invariant under the
one-parameter group of transformations of the units of length, time and
reciprocal mass, it is shown, also, that canonical general relativity is not
such a consistent theory. Conformal general relativity provides a consistent
formulation of the laws of gravity instead. We further extend the results of
papers gr-qc/9908075 and gr-qc/9905071 to open universes by studying the
Raychaudhuri equation.
|
[
{
"created": "Mon, 21 Feb 2000 20:09:53 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Mar 2000 17:55:33 GMT",
"version": "v2"
},
{
"created": "Fri, 28 Apr 2000 19:36:10 GMT",
"version": "v3"
}
] |
2007-05-23
|
[
[
"Quiros",
"Israel",
"",
"Departamento de\n Fisica. Universidad Central de Las Villas. Santa Clara. Cuba"
],
[
"Cardenas",
"Rolando",
"",
"Departamento de\n Fisica. Universidad Central de Las Villas. Santa Clara. Cuba"
],
[
"Bonal",
"Rolando",
"",
"Departamento de\n Fisica. Universidad Central de Las Villas. Santa Clara. Cuba"
]
] |
In the present paper we give conclusive arguments pointing at physical equivalence among conformally related metrics. Based on the argument that any consistent effective theory of spacetime must be invariant under the one-parameter group of transformations of the units of length, time and reciprocal mass, it is shown, also, that canonical general relativity is not such a consistent theory. Conformal general relativity provides a consistent formulation of the laws of gravity instead. We further extend the results of papers gr-qc/9908075 and gr-qc/9905071 to open universes by studying the Raychaudhuri equation.
|
gr-qc/0312051
|
Andreas K\"allberg
|
A. K\"allberg, G. Brodin, M. Bradley
|
Nonlinear coupled Alfv\'{e}n and gravitational waves
|
20 pages, revtex4, accepted in PRD
|
Phys.Rev. D70 (2004) 044014
|
10.1103/PhysRevD.70.044014
| null |
gr-qc astro-ph
| null |
In this paper we consider nonlinear interaction between gravitational and
electromagnetic waves in a strongly magnetized plasma. More specifically, we
investigate the propagation of gravitational waves with the direction of
propagation perpendicular to a background magnetic field, and the coupling to
compressional Alfv\'{e}n waves. The gravitational waves are considered in the
high frequency limit and the plasma is modelled by a multifluid description. We
make a self-consistent, weakly nonlinear analysis of the Einstein-Maxwell
system and derive a wave equation for the coupled gravitational and
electromagnetic wave modes. A WKB-approximation is then applied and as a result
we obtain the nonlinear Schr\"{o}dinger equation for the slowly varying wave
amplitudes. The analysis is extended to 3D wave pulses, and we discuss the
applications to radiation generated from pulsar binary mergers. It turns out
that the electromagnetic radiation from a binary merger should experience a
focusing effect, that in principle could be detected.
|
[
{
"created": "Tue, 9 Dec 2003 13:02:46 GMT",
"version": "v1"
},
{
"created": "Mon, 24 May 2004 08:22:34 GMT",
"version": "v2"
}
] |
2016-08-16
|
[
[
"Källberg",
"A.",
""
],
[
"Brodin",
"G.",
""
],
[
"Bradley",
"M.",
""
]
] |
In this paper we consider nonlinear interaction between gravitational and electromagnetic waves in a strongly magnetized plasma. More specifically, we investigate the propagation of gravitational waves with the direction of propagation perpendicular to a background magnetic field, and the coupling to compressional Alfv\'{e}n waves. The gravitational waves are considered in the high frequency limit and the plasma is modelled by a multifluid description. We make a self-consistent, weakly nonlinear analysis of the Einstein-Maxwell system and derive a wave equation for the coupled gravitational and electromagnetic wave modes. A WKB-approximation is then applied and as a result we obtain the nonlinear Schr\"{o}dinger equation for the slowly varying wave amplitudes. The analysis is extended to 3D wave pulses, and we discuss the applications to radiation generated from pulsar binary mergers. It turns out that the electromagnetic radiation from a binary merger should experience a focusing effect, that in principle could be detected.
|
gr-qc/0701006
|
Ralf Lehnert
|
Ralf Lehnert
|
Quantum gravity and spacetime symmetries
|
3 pages; Presented at 11th Marcel Grossmann Meeting on Recent
Developments in Theoretical and Experimental General Relativity, Gravitation,
and Relativistic Field Theories, Berlin, Germany, 23-29 Jul 2006
| null | null |
MIT-CTP-3801
|
gr-qc
| null |
Small violations of spacetime symmetries have recently been identified as
promising Planck-scale signals. This talk reviews how such violations can arise
in various approaches to quantum gravity, how the emergent low-energy effects
can be described within the framework of relativistic effective field theories,
how suitable tests can be identified, and what sensitivities can be expected in
current and near-future experiments.
|
[
{
"created": "Sat, 30 Dec 2006 19:49:00 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Lehnert",
"Ralf",
""
]
] |
Small violations of spacetime symmetries have recently been identified as promising Planck-scale signals. This talk reviews how such violations can arise in various approaches to quantum gravity, how the emergent low-energy effects can be described within the framework of relativistic effective field theories, how suitable tests can be identified, and what sensitivities can be expected in current and near-future experiments.
|
gr-qc/0612179
|
Alikram Aliev
|
Alikram N. Aliev and Cihan Saclioglu
|
Self-Dual Fields on the space of a Kerr-Taub-bolt Instanton
|
3 pages, to appear in the Proceedings of the Eleventh Marcel
Grossmann Meeting, Berlin, Germany, 23-29 Jule 2006, World Scientific,
Singapore (2007)
| null | null | null |
gr-qc
| null |
We discuss a new exact solution for self-dual Abelian gauge fields living on
the space of the Kerr-Taub-bolt instanton, which is a generalized example of
asymptotically flat instantons with non-self-dual curvature.
|
[
{
"created": "Thu, 28 Dec 2006 10:22:39 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Aliev",
"Alikram N.",
""
],
[
"Saclioglu",
"Cihan",
""
]
] |
We discuss a new exact solution for self-dual Abelian gauge fields living on the space of the Kerr-Taub-bolt instanton, which is a generalized example of asymptotically flat instantons with non-self-dual curvature.
|
0711.1996
|
Shahram Jalalzadeh
|
P. Pedram and S. Jalalzadeh
|
Quantum FRW cosmological solutions in the presence of Chaplygin gas and
perfect fluid
|
18 pages, 2 figures, to appear in PLB
|
Phys.Lett.B659:6-13,2008
|
10.1016/j.physletb.2007.11.013
| null |
gr-qc
| null |
We present a Friedmann-Robertson-Walker quantum cosmological model in the
presence of Chaplygin gas and perfect fluid for early and late time epoches. In
this work, we consider perfect fluid as an effective potential and apply
Schutz's variational formalism to the Chaplygin gas which recovers the notion
of time. These give rise to Schr\"odinger-Wheeler-DeWitt equation for the scale
factor. We use the eigenfunctions in order to construct wave packets and study
the time dependent behavior of the expectation value of the scale factor using
the many-worlds interpretation of quantum mechanics. We show that contrary to
the classical case, the expectation value of the scale factor avoids
singularity at quantum level. Moreover, this model predicts that the expansion
of Universe is accelerating for the late times.
|
[
{
"created": "Tue, 13 Nov 2007 14:51:21 GMT",
"version": "v1"
}
] |
2008-11-26
|
[
[
"Pedram",
"P.",
""
],
[
"Jalalzadeh",
"S.",
""
]
] |
We present a Friedmann-Robertson-Walker quantum cosmological model in the presence of Chaplygin gas and perfect fluid for early and late time epoches. In this work, we consider perfect fluid as an effective potential and apply Schutz's variational formalism to the Chaplygin gas which recovers the notion of time. These give rise to Schr\"odinger-Wheeler-DeWitt equation for the scale factor. We use the eigenfunctions in order to construct wave packets and study the time dependent behavior of the expectation value of the scale factor using the many-worlds interpretation of quantum mechanics. We show that contrary to the classical case, the expectation value of the scale factor avoids singularity at quantum level. Moreover, this model predicts that the expansion of Universe is accelerating for the late times.
|
1801.02661
|
Juliano Neves
|
R. V. Maluf, Juliano C. S. Neves
|
Thermodynamics of a class of regular black holes with a generalized
uncertainty principle
|
8 pages, 1 figure. Version with corrected typos. Accepted in Physical
Review D
|
Phys. Rev. D 97, 104015 (2018)
|
10.1103/PhysRevD.97.104015
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this article, we present a study on thermodynamics of a class of regular
black holes. Such a class includes Bardeen and Hayward regular black holes. We
obtained thermodynamic quantities like the Hawking temperature, entropy, and
heat capacity for the entire class. As part of an effort to indicate some
physical observable to distinguish regular black holes from singular black
holes, we suggest that regular black holes are colder than singular black
holes. Besides, contrary to the Schwarzschild black hole, that class of regular
black holes may be thermodynamically stable. From a generalized uncertainty
principle, we also obtained the quantum-corrected thermodynamics for the
studied class. Such quantum corrections provide a logarithmic term for the
quantum-corrected entropy.
|
[
{
"created": "Mon, 8 Jan 2018 19:54:05 GMT",
"version": "v1"
},
{
"created": "Mon, 14 May 2018 14:52:59 GMT",
"version": "v2"
}
] |
2018-05-15
|
[
[
"Maluf",
"R. V.",
""
],
[
"Neves",
"Juliano C. S.",
""
]
] |
In this article, we present a study on thermodynamics of a class of regular black holes. Such a class includes Bardeen and Hayward regular black holes. We obtained thermodynamic quantities like the Hawking temperature, entropy, and heat capacity for the entire class. As part of an effort to indicate some physical observable to distinguish regular black holes from singular black holes, we suggest that regular black holes are colder than singular black holes. Besides, contrary to the Schwarzschild black hole, that class of regular black holes may be thermodynamically stable. From a generalized uncertainty principle, we also obtained the quantum-corrected thermodynamics for the studied class. Such quantum corrections provide a logarithmic term for the quantum-corrected entropy.
|
gr-qc/0607138
|
Muhammad Sharif
|
M. Sharif and M. Jamil Amir
|
Teleparallel Versions of Friedmann and Lewis-Papapetrou Spacetimes
|
13 pages, accepted for publication in GRG
|
Gen.Rel.Grav. 38 (2006) 1735-1745
|
10.1007/s10714-006-0354-6
| null |
gr-qc
| null |
This paper is devoted to investigate the teleparallel versions of the
Friedmann models as well as the Lewis-Papapetrou solution. We obtain the tetrad
and the torsion fields for both the spacetimes. It is shown that the
axial-vector vanishes for the Friedmann models. We discuss the different
possibilities of the axial-vector depending on the arbitrary functions $\omega$
and $\psi$ in the Lewis-Papapetrou metric. The vector related with spin has
also been evaluated.
|
[
{
"created": "Mon, 31 Jul 2006 13:01:28 GMT",
"version": "v1"
}
] |
2009-11-11
|
[
[
"Sharif",
"M.",
""
],
[
"Amir",
"M. Jamil",
""
]
] |
This paper is devoted to investigate the teleparallel versions of the Friedmann models as well as the Lewis-Papapetrou solution. We obtain the tetrad and the torsion fields for both the spacetimes. It is shown that the axial-vector vanishes for the Friedmann models. We discuss the different possibilities of the axial-vector depending on the arbitrary functions $\omega$ and $\psi$ in the Lewis-Papapetrou metric. The vector related with spin has also been evaluated.
|
2011.03548
|
Barry Wardell
|
Barry Wardell, Chris Kavanagh
|
Separable electromagnetic perturbations of rotating black holes
|
Minor typos corrected
|
Phys. Rev. D 103, 104049 (2021)
|
10.1103/PhysRevD.103.104049
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We identify a set of Hertz potentials for solutions to the vector wave
equation on black hole spacetimes. The Hertz potentials yield Lorenz gauge
electromagnetic vector potentials that represent physical solutions to the
Maxwell equations, satisfy the Teukolsky equation, and are related to the
Maxwell scalars by straightforward and separable inversion relations. Our
construction, based on the GHP formalism, avoids the need for a mode ansatz and
leads to potentials that represent both static and non-static solutions. As an
explicit example, we specialise the procedure to mode-decomposed perturbations
of Kerr spacetime and in the process make connections with previous results.
|
[
{
"created": "Fri, 6 Nov 2020 19:00:01 GMT",
"version": "v1"
},
{
"created": "Thu, 26 Nov 2020 11:25:10 GMT",
"version": "v2"
},
{
"created": "Wed, 15 May 2024 16:48:48 GMT",
"version": "v3"
}
] |
2024-05-16
|
[
[
"Wardell",
"Barry",
""
],
[
"Kavanagh",
"Chris",
""
]
] |
We identify a set of Hertz potentials for solutions to the vector wave equation on black hole spacetimes. The Hertz potentials yield Lorenz gauge electromagnetic vector potentials that represent physical solutions to the Maxwell equations, satisfy the Teukolsky equation, and are related to the Maxwell scalars by straightforward and separable inversion relations. Our construction, based on the GHP formalism, avoids the need for a mode ansatz and leads to potentials that represent both static and non-static solutions. As an explicit example, we specialise the procedure to mode-decomposed perturbations of Kerr spacetime and in the process make connections with previous results.
|
0810.3558
|
Lucy MacNay
|
Lucy Macnay
|
Dynamics of Solutions of $f(R)$ Theory
|
34 pages
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We use the correspondence between the $f(R)$ theory and an Einstein-scalar
field system to study late-time dynamics of solutions of $f(R)$ theory. We
discuss how reasonable assumptions on the potential of the scalar field lead to
restrictions on the function $f(R)$ and use known results for the scalar field
system to gain results on solutions of the $f(R)$ theory. In particular, we
prove accelerated expansion at late times for several different categories of
functions $f(R)$ that satisfy certain restrictions.
|
[
{
"created": "Mon, 20 Oct 2008 14:00:10 GMT",
"version": "v1"
}
] |
2008-10-21
|
[
[
"Macnay",
"Lucy",
""
]
] |
We use the correspondence between the $f(R)$ theory and an Einstein-scalar field system to study late-time dynamics of solutions of $f(R)$ theory. We discuss how reasonable assumptions on the potential of the scalar field lead to restrictions on the function $f(R)$ and use known results for the scalar field system to gain results on solutions of the $f(R)$ theory. In particular, we prove accelerated expansion at late times for several different categories of functions $f(R)$ that satisfy certain restrictions.
|
gr-qc/0309036
|
Gregory V. Vereshchagin
|
G.V. Vereshchagin
|
On the problem of cosmological singularity within gauge theories of
gravitation
|
3 pages
| null | null | null |
gr-qc
| null |
In this note I discuss the problem of cosmological singularities within gauge
theories of gravitation. Solutions of cosmological equations with the scalar
field are considered.
|
[
{
"created": "Sat, 6 Sep 2003 13:04:31 GMT",
"version": "v1"
},
{
"created": "Fri, 19 Dec 2003 09:20:39 GMT",
"version": "v2"
},
{
"created": "Thu, 17 Jun 2004 16:51:44 GMT",
"version": "v3"
}
] |
2007-05-23
|
[
[
"Vereshchagin",
"G. V.",
""
]
] |
In this note I discuss the problem of cosmological singularities within gauge theories of gravitation. Solutions of cosmological equations with the scalar field are considered.
|
1901.05762
|
Ramil Izmailov N
|
R.Kh. Karimov, R.N. Izmailov and K.K. Nandi
|
Accretion disk around the rotating Damour-Solodukhin wormhole
|
9 pages, 3 tables, 13 figures
|
Eur. Phys. J. C 79, 952 (2019)
|
10.1140/epjc/s10052-019-7488-7
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
A new rotating generalization of the Damour-Solodukhin wormhole (RDSWH),
called Kerr-like wormhole, has recently been proposed and investigated by Bueno
\textit{et al} for echoes in the gravitational wave signal. We show a novel
feature of the RDSWH, viz., that the kinematic properties such as the ISCO\ or
marginally stable radius $r_{\text{ms}}$, efficiency $\epsilon$ and the disk
potential $V_{\text{eff}}$ are \textit{independent} of $\lambda$ (which means
they are identical to their KBH counterparts for any given spin). Differences
however appear in the emissivity properties for higher values $0.1<\lambda\leq
1$ (say) and for the extreme spin $a_{\star}=0.998$. The kinematic and
emissivity are generic properties as variations of the wormhole mass and the
rate of accretion within the model preserve these properties. Specifically, the
behavior of the luminosity peak is quite opposite to each other for the two
objects, which could be useful from the viewpoint of observations. Apart from
this, an estimate of the difference $\Delta_{\lambda}$ in the maxima of flux of
radiation $F(r)$ shows non-zero values but is too tiny to be observable at
present for $\lambda < 10^{-3}$ permitted by the strong lensing bound. The
broad conclusion is that RDSWH\ are experimentally indistinguishable from KBH
by accretion characteristics.
|
[
{
"created": "Thu, 17 Jan 2019 12:39:20 GMT",
"version": "v1"
},
{
"created": "Thu, 16 May 2019 12:43:09 GMT",
"version": "v2"
},
{
"created": "Tue, 13 Aug 2019 13:01:26 GMT",
"version": "v3"
},
{
"created": "Tue, 4 Feb 2020 06:36:22 GMT",
"version": "v4"
}
] |
2020-02-05
|
[
[
"Karimov",
"R. Kh.",
""
],
[
"Izmailov",
"R. N.",
""
],
[
"Nandi",
"K. K.",
""
]
] |
A new rotating generalization of the Damour-Solodukhin wormhole (RDSWH), called Kerr-like wormhole, has recently been proposed and investigated by Bueno \textit{et al} for echoes in the gravitational wave signal. We show a novel feature of the RDSWH, viz., that the kinematic properties such as the ISCO\ or marginally stable radius $r_{\text{ms}}$, efficiency $\epsilon$ and the disk potential $V_{\text{eff}}$ are \textit{independent} of $\lambda$ (which means they are identical to their KBH counterparts for any given spin). Differences however appear in the emissivity properties for higher values $0.1<\lambda\leq 1$ (say) and for the extreme spin $a_{\star}=0.998$. The kinematic and emissivity are generic properties as variations of the wormhole mass and the rate of accretion within the model preserve these properties. Specifically, the behavior of the luminosity peak is quite opposite to each other for the two objects, which could be useful from the viewpoint of observations. Apart from this, an estimate of the difference $\Delta_{\lambda}$ in the maxima of flux of radiation $F(r)$ shows non-zero values but is too tiny to be observable at present for $\lambda < 10^{-3}$ permitted by the strong lensing bound. The broad conclusion is that RDSWH\ are experimentally indistinguishable from KBH by accretion characteristics.
|
2407.01385
|
Richard Henriksen
|
R N Henriksen, A G Emslie
|
An Event Horizon 'Firewall' Undergoing Cosmological Expansion
|
25 pages, eight figures
| null | null | null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
We embed an object with a singular horizon structure, reminiscent of (but
fundamentally different from, except in a limiting case) a black-hole event
horizon, in an expanding, spherically symmetric, homogeneous, Universe that has
a positive cosmological constant. Conformal representation is discussed. There
is a temperature/pressure singularity and a corresponding scalar curvature
singularity at the horizon. The expanding singular horizon ultimately bounds
the entire space-time manifold. It is is preceded by an expanding light front,
which separates the space-time affected by the singularity from that which is
not yet affected. An appropriately located observer in front of the light front
can have a Hubble-Lema\^itre constant that is consistent with that currently
observed.
|
[
{
"created": "Mon, 1 Jul 2024 15:35:25 GMT",
"version": "v1"
}
] |
2024-07-02
|
[
[
"Henriksen",
"R N",
""
],
[
"Emslie",
"A G",
""
]
] |
We embed an object with a singular horizon structure, reminiscent of (but fundamentally different from, except in a limiting case) a black-hole event horizon, in an expanding, spherically symmetric, homogeneous, Universe that has a positive cosmological constant. Conformal representation is discussed. There is a temperature/pressure singularity and a corresponding scalar curvature singularity at the horizon. The expanding singular horizon ultimately bounds the entire space-time manifold. It is is preceded by an expanding light front, which separates the space-time affected by the singularity from that which is not yet affected. An appropriately located observer in front of the light front can have a Hubble-Lema\^itre constant that is consistent with that currently observed.
|
2001.00031
|
Klaus Liegener Dr
|
Klaus Liegener, Stefan Andreas Weigl
|
Effective LQC model for k=+1 isotropic cosmologies from spatial
discretisations
|
19 pages, 4 figures
|
Phys. Rev. D 102, (2020) no. 106014
|
10.1103/PhysRevD.102.106014
| null |
gr-qc hep-lat
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The closed, spatially isotropic FLRW universe (k=+1) is endowed with
modifications due to a discrete underlying space-structure. Motivated from Loop
Quantum Gravity techniques, a full Thiemann regularisation is performed. The
impact of these modifications of the single-graph-sector appearing in the
scalar constraint are interpreted as physical quantum gravity effects. We
investigate the form of the modified scalar constraint and its analytical
approximations for k=+1 spacetimes and assume this effective constraint as the
generator of dynamics on the reduced isotropic phase space. It transpires that
the system still features a classical recollapse with only marginal
discreteness corrections. Moreover, the initial and final singularities are
resolved and we present an effective model mirroring the qualitative features
of system.
|
[
{
"created": "Tue, 31 Dec 2019 19:00:13 GMT",
"version": "v1"
},
{
"created": "Fri, 19 Mar 2021 05:54:06 GMT",
"version": "v2"
}
] |
2021-03-22
|
[
[
"Liegener",
"Klaus",
""
],
[
"Weigl",
"Stefan Andreas",
""
]
] |
The closed, spatially isotropic FLRW universe (k=+1) is endowed with modifications due to a discrete underlying space-structure. Motivated from Loop Quantum Gravity techniques, a full Thiemann regularisation is performed. The impact of these modifications of the single-graph-sector appearing in the scalar constraint are interpreted as physical quantum gravity effects. We investigate the form of the modified scalar constraint and its analytical approximations for k=+1 spacetimes and assume this effective constraint as the generator of dynamics on the reduced isotropic phase space. It transpires that the system still features a classical recollapse with only marginal discreteness corrections. Moreover, the initial and final singularities are resolved and we present an effective model mirroring the qualitative features of system.
|
2102.13551
|
Matt Visser
|
Prado Martin-Moruno (Complutense de Madrid) and Matt Visser (Victoria
University of Wellington)
|
Hawking-Ellis classification of stress-energy: test-fields versus
back-reaction
|
V1: 30 pages; V2: minor typos fixed; no physics changes
|
Phys. Rev. D 103, 124003 (2021)
|
10.1103/PhysRevD.103.124003
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We consider the Hawking-Ellis (Segre-Plebanski) classification of
stress-energy tensors, both in the test-field limit, and in the presence of
back-reaction governed by the usual Einstein equations. For test fields it is
not too difficult to get a type~IV stress-energy via quantum vacuum
polarization effects. (For example, consider the Unruh quantum vacuum state for
a massless scalar field in the Schwarzschild background.) However, in the
presence of back-reaction driven by the ordinary Einstein equations the
situation is often much more constrained. For instance: (1) in any static
spacetime the stress-energy is always type I in the domain of outer
communication, and on any horizon that might be present; (2) in any stationary
axisymmetric spacetime the stress-energy is always type I on any horizon that
might be present; (3) on any Killing horizon that is extendable to a
bifurcation 2-surface the stress-energy is always type I; (4) in any stationary
axisymmetric spacetime the stress-energy is always type I on the axis of
symmetry; (5) some of the homogeneous Bianchi cosmologies are guaranteed to be
Hawking-Ellis type I (for example, all the Bianchi type I cosmologies, all the
FLRW cosmologies, and all the "single mode" Bianchi cosmologies). That is, in
very many physically interesting situations once one includes back-reaction the
more unusual stress-energy types are automatically excluded.
|
[
{
"created": "Fri, 26 Feb 2021 15:42:49 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Mar 2021 05:35:37 GMT",
"version": "v2"
}
] |
2021-06-09
|
[
[
"Martin-Moruno",
"Prado",
"",
"Complutense de Madrid"
],
[
"Visser",
"Matt",
"",
"Victoria\n University of Wellington"
]
] |
We consider the Hawking-Ellis (Segre-Plebanski) classification of stress-energy tensors, both in the test-field limit, and in the presence of back-reaction governed by the usual Einstein equations. For test fields it is not too difficult to get a type~IV stress-energy via quantum vacuum polarization effects. (For example, consider the Unruh quantum vacuum state for a massless scalar field in the Schwarzschild background.) However, in the presence of back-reaction driven by the ordinary Einstein equations the situation is often much more constrained. For instance: (1) in any static spacetime the stress-energy is always type I in the domain of outer communication, and on any horizon that might be present; (2) in any stationary axisymmetric spacetime the stress-energy is always type I on any horizon that might be present; (3) on any Killing horizon that is extendable to a bifurcation 2-surface the stress-energy is always type I; (4) in any stationary axisymmetric spacetime the stress-energy is always type I on the axis of symmetry; (5) some of the homogeneous Bianchi cosmologies are guaranteed to be Hawking-Ellis type I (for example, all the Bianchi type I cosmologies, all the FLRW cosmologies, and all the "single mode" Bianchi cosmologies). That is, in very many physically interesting situations once one includes back-reaction the more unusual stress-energy types are automatically excluded.
|
2407.01961
|
Sara Saghafi
|
Kourosh Nozari, Sara Saghafi and Milad Hajebrahimi
|
Extended Uncertainty Principle: A Deeper Insight into the Hubble
Tension?
|
13 pages, 2 figures, 4 tables Accepted for Publication in Physics of
the Dark Universe
|
Physics of the Dark Universe (2024)
|
10.1016/j.dark.2024.101571
| null |
gr-qc astro-ph.CO hep-ph hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
The standard cosmological model, known as the LambdaCDM model, has been
successful in many respects, but it has some significant discrepancies, some of
which have not been resolved yet. In measuring the Hubble-Lematre parameter,
there is an apparent discrepancy which is known as the Hubble tension, defined
as differences in values of this parameter measured by the Type Ia Supernovae
(SNeIa) data (a model-independent method) and by the Cosmic Microwave
Background (CMB) radiation maps (a model-dependent method). Although many
potential solutions have been proposed, the issue still remains unresolved.
Recently, it was observed that the Hubble tension can be due to the concept of
uncertainty in measuring cosmological parameters at large distance scales
through applying the Heisenberg Uncertainty Principle (HUP) in cosmological
setups. Extending this pioneering idea, in the present study we plan to
incorporate the Extended Uncertainty Principle (EUP) containing a minimal
fundamental measurable momentum (or equivalently, a maximal fundamental
measurable length) as a candidate setup for describing large-scale effects of
Quantum Gravity (QG) to address the Hubble tension and constrain the EUP length
scale. In this regard, by finding a relevant formula for the effective photon
rest mass in terms of the present-time value of the Hubble-Lematre parameter,
we see that discrepancies in the value of photon rest mass associated with the
Hubble-Lematre parameter values estimated from model-independent and
model-dependent methods perhaps is the cause of Hubble tension.
|
[
{
"created": "Tue, 2 Jul 2024 05:33:08 GMT",
"version": "v1"
}
] |
2024-07-10
|
[
[
"Nozari",
"Kourosh",
""
],
[
"Saghafi",
"Sara",
""
],
[
"Hajebrahimi",
"Milad",
""
]
] |
The standard cosmological model, known as the LambdaCDM model, has been successful in many respects, but it has some significant discrepancies, some of which have not been resolved yet. In measuring the Hubble-Lematre parameter, there is an apparent discrepancy which is known as the Hubble tension, defined as differences in values of this parameter measured by the Type Ia Supernovae (SNeIa) data (a model-independent method) and by the Cosmic Microwave Background (CMB) radiation maps (a model-dependent method). Although many potential solutions have been proposed, the issue still remains unresolved. Recently, it was observed that the Hubble tension can be due to the concept of uncertainty in measuring cosmological parameters at large distance scales through applying the Heisenberg Uncertainty Principle (HUP) in cosmological setups. Extending this pioneering idea, in the present study we plan to incorporate the Extended Uncertainty Principle (EUP) containing a minimal fundamental measurable momentum (or equivalently, a maximal fundamental measurable length) as a candidate setup for describing large-scale effects of Quantum Gravity (QG) to address the Hubble tension and constrain the EUP length scale. In this regard, by finding a relevant formula for the effective photon rest mass in terms of the present-time value of the Hubble-Lematre parameter, we see that discrepancies in the value of photon rest mass associated with the Hubble-Lematre parameter values estimated from model-independent and model-dependent methods perhaps is the cause of Hubble tension.
|
2209.10612
|
Amir-Pouyan Khosravi
|
Alfio Bonanno, Amir-Pouyan Khosravi, Frank Saueressig
|
Regular evaporating black holes with stable cores
|
17 pages, 9 figures
| null |
10.1103/PhysRevD.107.024005
| null |
gr-qc hep-th
|
http://creativecommons.org/licenses/by/4.0/
|
A feature shared by many regular black hole spacetimes is the occurrence of a
Cauchy horizon. It is then commonly believed that this renders the geometry
unstable against perturbations through the mass-inflation effect. In this work,
we perform the first dynamical study of this effect taking into account the
mass-loss of the black hole due to Hawking radiation. It is shown that the
time-dependence of the background leads to two novel types of late-time
behavior whose properties are entirely determined by the Hawking flux. The
first class of attractor-behavior is operative for regular black holes of the
Hayward and renormalization group improved type and characterized by the square
of the Weyl curvature growing as $v^6$ at asymptotically late times. This
singularity is inaccessible to a radially free-falling observer though. The
second class is realized by Reissner-Nordstr{\"o}m black holes and regular
black holes of the Bardeen type. In this case the curvature scalars remain
finite as $v\rightarrow\infty$. Thus the Hawking flux has a profound effect on
the mass-inflation instability, either weakening the effect significantly or
even expelling it entirely.
|
[
{
"created": "Wed, 21 Sep 2022 19:15:46 GMT",
"version": "v1"
}
] |
2023-01-18
|
[
[
"Bonanno",
"Alfio",
""
],
[
"Khosravi",
"Amir-Pouyan",
""
],
[
"Saueressig",
"Frank",
""
]
] |
A feature shared by many regular black hole spacetimes is the occurrence of a Cauchy horizon. It is then commonly believed that this renders the geometry unstable against perturbations through the mass-inflation effect. In this work, we perform the first dynamical study of this effect taking into account the mass-loss of the black hole due to Hawking radiation. It is shown that the time-dependence of the background leads to two novel types of late-time behavior whose properties are entirely determined by the Hawking flux. The first class of attractor-behavior is operative for regular black holes of the Hayward and renormalization group improved type and characterized by the square of the Weyl curvature growing as $v^6$ at asymptotically late times. This singularity is inaccessible to a radially free-falling observer though. The second class is realized by Reissner-Nordstr{\"o}m black holes and regular black holes of the Bardeen type. In this case the curvature scalars remain finite as $v\rightarrow\infty$. Thus the Hawking flux has a profound effect on the mass-inflation instability, either weakening the effect significantly or even expelling it entirely.
|
2109.08146
|
Kevin Croker
|
Kevin S. Croker, Michael J. Zevin, Duncan Farrah, Kurtis A. Nishimura,
Gregory Tarle
|
Cosmologically coupled compact objects: a single parameter model for
LIGO--Virgo mass and redshift distributions
|
8 pages, 2 figures. Submitted to ApJL
| null |
10.3847/2041-8213/ac2fad
| null |
gr-qc astro-ph.CO
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We demonstrate a single-parameter route for reproducing higher mass objects
as observed in the LIGO--Virgo mass distribution, using only the isolated
binary stellar evolution channel. This single parameter encodes the
cosmological mass growth of compact stellar remnants that exceed the
Tolman-Oppenheimer-Volkoff limit. Cosmological mass growth appears in known
solutions to General Relativity with cosmological boundary conditions. We
consider the possibility of solutions with cosmological boundary conditions,
which reduce to Kerr on timescales short compared to the Hubble time. We
discuss complementary observational signatures of these solutions that can
confirm or invalidate their astrophysical relevance.
|
[
{
"created": "Wed, 15 Sep 2021 18:00:03 GMT",
"version": "v1"
}
] |
2021-11-17
|
[
[
"Croker",
"Kevin S.",
""
],
[
"Zevin",
"Michael J.",
""
],
[
"Farrah",
"Duncan",
""
],
[
"Nishimura",
"Kurtis A.",
""
],
[
"Tarle",
"Gregory",
""
]
] |
We demonstrate a single-parameter route for reproducing higher mass objects as observed in the LIGO--Virgo mass distribution, using only the isolated binary stellar evolution channel. This single parameter encodes the cosmological mass growth of compact stellar remnants that exceed the Tolman-Oppenheimer-Volkoff limit. Cosmological mass growth appears in known solutions to General Relativity with cosmological boundary conditions. We consider the possibility of solutions with cosmological boundary conditions, which reduce to Kerr on timescales short compared to the Hubble time. We discuss complementary observational signatures of these solutions that can confirm or invalidate their astrophysical relevance.
|
gr-qc/0211075
|
Philippe Grandclement
|
P. Grandclement and V. Kalogera
|
Searching for Gravitational Waves from the Inspiral of Precessing Binary
Systems: New Hierarchical Scheme using "Spiky" Templates
|
17 pages, 22 figures, version accepted by PRD. Minor revisions
|
Phys.Rev. D67 (2003) 082002
|
10.1103/PhysRevD.67.082002
| null |
gr-qc astro-ph
| null |
In a recent investigation of the effects of precession on the anticipated
detection of gravitational-wave inspiral signals from compact object binaries
with moderate total masses, we found that (i) if precession is ignored, the
inspiral detection rate can decrease by almost a factor of 10, and (ii)
previously proposed ``mimic'' templates cannot improve the detection rate
significantly (by more than a factor of 2). In this paper we propose a new
family of templates that can improve the detection rate by factors of 5--6 in
cases where precession is most important. Our proposed method for these new
``mimic'' templates involves a hierarchical scheme of efficient, two-parameter
template searches that can account for a sequence of spikes that appear in the
residual inspiral phase, after one corrects for the any oscillatory
modification in the phase. We present our results for two cases of compact
object masses (10 and 1.4 solar masses and 7 and 3 solar masses) as a function
of spin properties. Although further work is needed to fully assess the
computational efficiency of this newly proposed template family, we conclude
that these ``spiky templates'' are good candidates for a family of precession
templates used in realistic searches, that can improve detection rates of
inspiral events.
|
[
{
"created": "Fri, 22 Nov 2002 22:30:14 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Jan 2003 17:08:25 GMT",
"version": "v2"
}
] |
2009-11-07
|
[
[
"Grandclement",
"P.",
""
],
[
"Kalogera",
"V.",
""
]
] |
In a recent investigation of the effects of precession on the anticipated detection of gravitational-wave inspiral signals from compact object binaries with moderate total masses, we found that (i) if precession is ignored, the inspiral detection rate can decrease by almost a factor of 10, and (ii) previously proposed ``mimic'' templates cannot improve the detection rate significantly (by more than a factor of 2). In this paper we propose a new family of templates that can improve the detection rate by factors of 5--6 in cases where precession is most important. Our proposed method for these new ``mimic'' templates involves a hierarchical scheme of efficient, two-parameter template searches that can account for a sequence of spikes that appear in the residual inspiral phase, after one corrects for the any oscillatory modification in the phase. We present our results for two cases of compact object masses (10 and 1.4 solar masses and 7 and 3 solar masses) as a function of spin properties. Although further work is needed to fully assess the computational efficiency of this newly proposed template family, we conclude that these ``spiky templates'' are good candidates for a family of precession templates used in realistic searches, that can improve detection rates of inspiral events.
|
2107.05614
|
Kouji Nakamura
|
Kouji Nakamura
|
Quantum noise and vacuum fluctuations in balanced homodyne detections
through ideal multi-mode detectors
|
39 pages, 5 figures, This is the full paper version of
[arXiv:2101.11838 [gr-qc]] (v1); Acknowledgements is added (v2); Minor
changes in Sec.1, Sec.6, Fig.3, and Fig.A2. Some typos are corrected (v3)
|
Prog. Theor. Exp. Phys. 2021, 103A01 (38 pages)
|
10.1093/ptep/ptab113
| null |
gr-qc astro-ph.IM quant-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The balanced homodyne detection as a readout scheme of gravitational-wave
detectors is carefully examined from the quantum field theoretical point of
view. The readout scheme in gravitational-wave detectors specifies the directly
measured quantum operator in the detection. This specification is necessary
when we apply the recently developed quantum measurement theory to
gravitational-wave detections. We examine the two models of measurement. One is
the model in which the directly measured quantum operator at the photodetector
is Glauber's photon number operator, and the other is the model in which the
power operator of the optical field is directly measured. These two are
regarded as ideal models of photodetectors. We first show these two models
yield the same expectation value of the measurement. Since it is consensus in
the gravitational-wave community that vacuum fluctuations contribute to the
noises in the detectors, we also clarify the contributions of vacuum
fluctuations to the quantum noise spectral density without using the two-photon
formulation which is used in the gravitational-wave community. We found that
the conventional noise spectral density in the two-photon formulation includes
vacuum fluctuations from the main interferometer but does not include those
from the local oscillator. Although the contribution of vacuum fluctuations
from the local oscillator theoretically yields the difference between the above
two models in the noise spectral densities, this difference is negligible in
realistic situations.
|
[
{
"created": "Mon, 12 Jul 2021 17:48:58 GMT",
"version": "v1"
},
{
"created": "Sun, 18 Jul 2021 13:17:04 GMT",
"version": "v2"
},
{
"created": "Fri, 20 Aug 2021 10:29:19 GMT",
"version": "v3"
}
] |
2021-10-27
|
[
[
"Nakamura",
"Kouji",
""
]
] |
The balanced homodyne detection as a readout scheme of gravitational-wave detectors is carefully examined from the quantum field theoretical point of view. The readout scheme in gravitational-wave detectors specifies the directly measured quantum operator in the detection. This specification is necessary when we apply the recently developed quantum measurement theory to gravitational-wave detections. We examine the two models of measurement. One is the model in which the directly measured quantum operator at the photodetector is Glauber's photon number operator, and the other is the model in which the power operator of the optical field is directly measured. These two are regarded as ideal models of photodetectors. We first show these two models yield the same expectation value of the measurement. Since it is consensus in the gravitational-wave community that vacuum fluctuations contribute to the noises in the detectors, we also clarify the contributions of vacuum fluctuations to the quantum noise spectral density without using the two-photon formulation which is used in the gravitational-wave community. We found that the conventional noise spectral density in the two-photon formulation includes vacuum fluctuations from the main interferometer but does not include those from the local oscillator. Although the contribution of vacuum fluctuations from the local oscillator theoretically yields the difference between the above two models in the noise spectral densities, this difference is negligible in realistic situations.
|
1808.02798
|
Thiago R.P. Caram\^es
|
Thiago R. P. Caram\^es, H. Velten, J. C. Fabris and Matheus J. Lazo
|
Dark energy with zero pressure: Accelerated expansion and large scale
structure in action-dependent Lagrangian theories
|
8 pages, 7 figures. Revised version: Title slightly changed, typos
corrected, more discussion added. Matches the published version in PRD
|
Phys. Rev. D 98, 103501 (2018)
|
10.1103/PhysRevD.98.103501
| null |
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We develop a cosmological model based on action-dependent Lagrangian
theories. The main feature here is the nonconservation of the energy momentum
tensor due to the nontrivial geometrical construction of the theory. We provide
the basic set of equations necessary to study both the cosmological background
expansion as well as the linear matter perturbation growth. We show that the
simplest realization of the Universe as described by only one component is not
viable as expected from the existing correspondence between this model and the
case of viscous cosmological fluids. However, modeling the energy content of
the Universe as composed by two pressureless fluids, i.e., one a typical cold
dark matter fluid and the other a pressureless dark energy fluid which is
responsible for driving the late-time acceleration expansion, is qualitatively
compatible with observational data.
|
[
{
"created": "Wed, 8 Aug 2018 14:37:12 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Nov 2018 19:36:52 GMT",
"version": "v2"
}
] |
2018-11-05
|
[
[
"Caramês",
"Thiago R. P.",
""
],
[
"Velten",
"H.",
""
],
[
"Fabris",
"J. C.",
""
],
[
"Lazo",
"Matheus J.",
""
]
] |
We develop a cosmological model based on action-dependent Lagrangian theories. The main feature here is the nonconservation of the energy momentum tensor due to the nontrivial geometrical construction of the theory. We provide the basic set of equations necessary to study both the cosmological background expansion as well as the linear matter perturbation growth. We show that the simplest realization of the Universe as described by only one component is not viable as expected from the existing correspondence between this model and the case of viscous cosmological fluids. However, modeling the energy content of the Universe as composed by two pressureless fluids, i.e., one a typical cold dark matter fluid and the other a pressureless dark energy fluid which is responsible for driving the late-time acceleration expansion, is qualitatively compatible with observational data.
|
1807.04580
|
Manuel Hohmann
|
Manuel Hohmann, Martin Kr\v{s}\v{s}\'ak, Christian Pfeifer, Ulbossyn
Ualikhanova
|
Propagation of gravitational waves in teleparallel gravity theories
|
11 pages, 1 figure; updated references to match published version.
arXiv admin note: substantial text overlap with arXiv:1808.02894
|
Phys. Rev. D 98, 124004 (2018)
|
10.1103/PhysRevD.98.124004
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We investigate propagation of gravitational waves in the most general
teleparallel gravity model with second order field equations around the
Minkowski background. We argue that in this case the most general Lagrangian at
the first order of perturbations is given by the linear combination of
quadratic invariants and hence coincides with the well-known new general
relativity model. We derive the linearized field equations and analyze them
using the principal polynomial and the Newman-Penrose formalism. We demonstrate
that all gravitational wave modes propagate at the speed of light and there are
up to six possible polarizations. We show that two tensorial modes of general
relativity are always present and the number of extra polarizations depends on
the free parameters of the new general relativity model.
|
[
{
"created": "Thu, 12 Jul 2018 12:46:36 GMT",
"version": "v1"
},
{
"created": "Fri, 3 Jul 2020 20:36:08 GMT",
"version": "v2"
}
] |
2020-07-08
|
[
[
"Hohmann",
"Manuel",
""
],
[
"Krššák",
"Martin",
""
],
[
"Pfeifer",
"Christian",
""
],
[
"Ualikhanova",
"Ulbossyn",
""
]
] |
We investigate propagation of gravitational waves in the most general teleparallel gravity model with second order field equations around the Minkowski background. We argue that in this case the most general Lagrangian at the first order of perturbations is given by the linear combination of quadratic invariants and hence coincides with the well-known new general relativity model. We derive the linearized field equations and analyze them using the principal polynomial and the Newman-Penrose formalism. We demonstrate that all gravitational wave modes propagate at the speed of light and there are up to six possible polarizations. We show that two tensorial modes of general relativity are always present and the number of extra polarizations depends on the free parameters of the new general relativity model.
|
gr-qc/0308030
|
Piechocki Wlodzimierz
|
Wlodzimierz Piechocki
|
Quantum particle on hyperboloid
|
7 pages, no figures, revtex4
|
Class.Quant.Grav. 21 (2004) 331-336
|
10.1088/0264-9381/21/1/024
| null |
gr-qc hep-th math-ph math.MP quant-ph
| null |
We present quantization of particle dynamics on one-sheet hyperboloid
embedded in three dimensional Minkowski space. Taking account of all global
symmetries enables unique quantization. Making use of topology of canonical
variables not only simplifies calculations but also gives proper framework for
analysis.
|
[
{
"created": "Mon, 11 Aug 2003 12:39:05 GMT",
"version": "v1"
}
] |
2009-11-10
|
[
[
"Piechocki",
"Wlodzimierz",
""
]
] |
We present quantization of particle dynamics on one-sheet hyperboloid embedded in three dimensional Minkowski space. Taking account of all global symmetries enables unique quantization. Making use of topology of canonical variables not only simplifies calculations but also gives proper framework for analysis.
|
2305.19485
|
Jos\'e Villanueva
|
Mohsen Fathi, Mart\'in Molina, J.R. Villanueva
|
Carath\'eodory's thermodynamics of the Schwarzschild black hole
surrounded by quintessence
|
9 pages, 7 figures
| null |
10.1088/1402-4896/acd886
| null |
gr-qc
|
http://creativecommons.org/licenses/by/4.0/
|
In this paper, we apply the Carath\'eodory's method of geometrothermodynamics
to investigate the behavior of the main thermodynamic parameters associated
with a Schwarzschild black hole surrounded by quintessence. The corresponding
Pfaffian form is constructed by means of the Schwarzschild radius $r_s$, and
the quintessential radius $r_{\gamma}$ as independent variables. This form is
then used to characterize the thermodynamic manifold. The homogeneity of the
system allows for the recognition of the empirical temperature and entropy, and
thus, connects with the usual laws of thermodynamics. In particular, we show
that the Helmholtz and Gibbs free energies lead to the same value for the
Schwarzschild black hole, in the case of the vanishing cosmological term.
|
[
{
"created": "Wed, 31 May 2023 01:43:37 GMT",
"version": "v1"
}
] |
2023-06-01
|
[
[
"Fathi",
"Mohsen",
""
],
[
"Molina",
"Martín",
""
],
[
"Villanueva",
"J. R.",
""
]
] |
In this paper, we apply the Carath\'eodory's method of geometrothermodynamics to investigate the behavior of the main thermodynamic parameters associated with a Schwarzschild black hole surrounded by quintessence. The corresponding Pfaffian form is constructed by means of the Schwarzschild radius $r_s$, and the quintessential radius $r_{\gamma}$ as independent variables. This form is then used to characterize the thermodynamic manifold. The homogeneity of the system allows for the recognition of the empirical temperature and entropy, and thus, connects with the usual laws of thermodynamics. In particular, we show that the Helmholtz and Gibbs free energies lead to the same value for the Schwarzschild black hole, in the case of the vanishing cosmological term.
|
gr-qc/9707034
| null |
M. Gasperini
|
Testing string cosmology with gravity wave detectors
|
13 pages, LATEX, three figures included using EPSFIG. Talk given at
the "Second Edoardo Amaldi Conference on Gravitational Wawes" (CERN, 1-4 July
1997). To be published in the Proceedings (World Scientific, Singapore), eds
E. Coccia et al. An updated collection of papers on the pre-big bang scenario
is available at http://www.to.infn.it/teorici/gasperini
| null | null |
DFTT-43/97
|
gr-qc astro-ph hep-ph hep-th
| null |
The general properties of the gravity wave backgrounds of cosmological origin
are reviewed and briefly discussed, with emphasis on the relic background
expected from an early pre-big bang phase typical of string cosmology models.
|
[
{
"created": "Tue, 15 Jul 1997 15:11:13 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Gasperini",
"M.",
""
]
] |
The general properties of the gravity wave backgrounds of cosmological origin are reviewed and briefly discussed, with emphasis on the relic background expected from an early pre-big bang phase typical of string cosmology models.
|
gr-qc/0312113
|
George Izmailov Nickolaevich
|
A.I. Golovashkin, G.N. Izmailov, G.V. Kuleshova, A.M. Tzhovrebov, Tran
Quoc Khanh
|
Detection of Weak Gravitational Waves by Interferometric Methods and
Problem of Invertible Calculations
|
12 pages, 5 figures, presented at Moscow Satellite PIRT Meeting (30
June - 03 July 2003)
| null | null | null |
gr-qc
| null |
The fundamental features of the detection of non-stationary undulatory
perturbations of metrics based on the interference effects are considered. The
advantage of the Aharonov-Bohm effect in superconductors for these purposes in
comparison with the ordinary optical interference is demonstrated. Some
circuitries of the interferometric detectors in order to be used with SQUID are
suggested. The possibilities of lowering the noise temperature of the ultraweak
signals detectors based on the analogy between the processes of high-sensitive
measurements and the reversible calculations are discussed.
|
[
{
"created": "Fri, 26 Dec 2003 18:16:25 GMT",
"version": "v1"
}
] |
2007-05-23
|
[
[
"Golovashkin",
"A. I.",
""
],
[
"Izmailov",
"G. N.",
""
],
[
"Kuleshova",
"G. V.",
""
],
[
"Tzhovrebov",
"A. M.",
""
],
[
"Khanh",
"Tran Quoc",
""
]
] |
The fundamental features of the detection of non-stationary undulatory perturbations of metrics based on the interference effects are considered. The advantage of the Aharonov-Bohm effect in superconductors for these purposes in comparison with the ordinary optical interference is demonstrated. Some circuitries of the interferometric detectors in order to be used with SQUID are suggested. The possibilities of lowering the noise temperature of the ultraweak signals detectors based on the analogy between the processes of high-sensitive measurements and the reversible calculations are discussed.
|
1703.06898
|
Tommi Markkanen
|
Tommi Markkanen
|
De Sitter Stability and Coarse Graining
|
v6: added an appendix giving details on mode normalization
|
Eur. Phys. J. C (2018) 78: 97
|
10.1140/epjc/s10052-018-5575-9
|
KCL-PH-TH/2017-14, IMPERIAL/TP/2018/TM/01
|
gr-qc astro-ph.CO hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We present a 4-dimensional back reaction analysis of de Sitter space for a
conformally coupled scalar field in the presence of vacuum energy initialized
in the Bunch-Davies vacuum. In contrast to the usual semi-classical
prescription, as the source term in the Friedmann equations we use expectation
values where the unobservable information hidden by the cosmological event
horizon has been neglected i.e. coarse grained over. It is shown that in this
approach the energy-momentum is precisely thermal with constant temperature
despite the dilution from the expansion of space due to a flux of energy
radiated from the horizon. This leads to a self-consistent solution for the
Hubble rate, which is gradually evolving and at late times deviates
significantly from de Sitter. Our results hence imply de Sitter space to be
unstable in this prescription. The solution also suggests dynamical vacuum
energy: the continuous flux of energy is balanced by the generation of negative
vacuum energy, which accumulatively decreases the overall contribution.
Finally, we show that our results admit a thermodynamic interpretation which
provides a simple alternate derivation of the mechanism. For very long times
the solutions coincide with flat space.
|
[
{
"created": "Mon, 20 Mar 2017 18:10:08 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Mar 2017 23:53:35 GMT",
"version": "v2"
},
{
"created": "Wed, 19 Apr 2017 21:33:12 GMT",
"version": "v3"
},
{
"created": "Fri, 25 Aug 2017 18:27:04 GMT",
"version": "v4"
},
{
"created": "Mon, 22 Jan 2018 19:00:06 GMT",
"version": "v5"
},
{
"created": "Mon, 24 Sep 2018 13:01:29 GMT",
"version": "v6"
}
] |
2018-09-25
|
[
[
"Markkanen",
"Tommi",
""
]
] |
We present a 4-dimensional back reaction analysis of de Sitter space for a conformally coupled scalar field in the presence of vacuum energy initialized in the Bunch-Davies vacuum. In contrast to the usual semi-classical prescription, as the source term in the Friedmann equations we use expectation values where the unobservable information hidden by the cosmological event horizon has been neglected i.e. coarse grained over. It is shown that in this approach the energy-momentum is precisely thermal with constant temperature despite the dilution from the expansion of space due to a flux of energy radiated from the horizon. This leads to a self-consistent solution for the Hubble rate, which is gradually evolving and at late times deviates significantly from de Sitter. Our results hence imply de Sitter space to be unstable in this prescription. The solution also suggests dynamical vacuum energy: the continuous flux of energy is balanced by the generation of negative vacuum energy, which accumulatively decreases the overall contribution. Finally, we show that our results admit a thermodynamic interpretation which provides a simple alternate derivation of the mechanism. For very long times the solutions coincide with flat space.
|
1710.10615
|
Robert Bluhm
|
Robert Bluhm
|
Gravity Theories with Background Fields and Spacetime Symmetry Breaking
| null |
Symmetry 9, 230 (2017)
|
10.3390/sym9100230
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
An overview is given of effective gravitational field theories with fixed
background fields that break spacetime symmetry. The behavior of the background
fields and the types of excitations that can occur depend on whether the
symmetry breaking is explicit or spontaneous. For example, when the breaking is
spontaneous, the background field is dynamical and massless Nambu--Goldstone
and massive Higgs excitations can appear. However, if the breaking is explicit,
the background is nondynamical, and in this case additional metric or vierbein
excitations occur due to the loss of local symmetry, or these excitations can
be replaced by dynamical scalar fields using a Stuckelberg approach. The
interpretation of Noether identities that must hold in each case differs,
depending on the type of symmetry breaking, and this affects the nature of the
consistency conditions that must hold. The Noether identities also shed light
on why the Stuckelberg approach works, and how it is able to restore the broken
spacetime symmetry in a theory with explicit breaking.
|
[
{
"created": "Sun, 29 Oct 2017 13:44:09 GMT",
"version": "v1"
}
] |
2017-10-31
|
[
[
"Bluhm",
"Robert",
""
]
] |
An overview is given of effective gravitational field theories with fixed background fields that break spacetime symmetry. The behavior of the background fields and the types of excitations that can occur depend on whether the symmetry breaking is explicit or spontaneous. For example, when the breaking is spontaneous, the background field is dynamical and massless Nambu--Goldstone and massive Higgs excitations can appear. However, if the breaking is explicit, the background is nondynamical, and in this case additional metric or vierbein excitations occur due to the loss of local symmetry, or these excitations can be replaced by dynamical scalar fields using a Stuckelberg approach. The interpretation of Noether identities that must hold in each case differs, depending on the type of symmetry breaking, and this affects the nature of the consistency conditions that must hold. The Noether identities also shed light on why the Stuckelberg approach works, and how it is able to restore the broken spacetime symmetry in a theory with explicit breaking.
|
1410.5763
|
Steven Carlip
|
S. Carlip
|
A Note on Black Hole Entropy in Loop Quantum Gravity
|
v2: added references; v3: slight addition to discussion of 3d
gravity; v4: more references, typos fixed
| null |
10.1088/0264-9381/32/15/155009
| null |
gr-qc hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Several recent results have hinted that black hole thermodynamics in loop
quantum gravity simplifies if one chooses an imaginary Barbero-Immirzi
parameter $\gamma=i$. This suggests a connection with
$\mathrm{SL}(2,\mathbb{C})$ or $\mathrm{SL}(2,\mathbb{R})$ conformal field
theories at the "boundaries" formed by spin network edges intersecting the
horizon. I present a bit of background regarding the relevant conformal field
theories, along with some speculations about how they might be used to count
black hole states. I show, in particular, that a set of unproven but plausible
assumptions can lead to a boundary conformal field theory whose density of
states matches the Bekenstein-Hawking entropy.
|
[
{
"created": "Tue, 21 Oct 2014 17:59:38 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Dec 2014 20:24:18 GMT",
"version": "v2"
},
{
"created": "Thu, 26 Mar 2015 21:29:57 GMT",
"version": "v3"
},
{
"created": "Fri, 29 May 2015 20:42:32 GMT",
"version": "v4"
}
] |
2015-08-06
|
[
[
"Carlip",
"S.",
""
]
] |
Several recent results have hinted that black hole thermodynamics in loop quantum gravity simplifies if one chooses an imaginary Barbero-Immirzi parameter $\gamma=i$. This suggests a connection with $\mathrm{SL}(2,\mathbb{C})$ or $\mathrm{SL}(2,\mathbb{R})$ conformal field theories at the "boundaries" formed by spin network edges intersecting the horizon. I present a bit of background regarding the relevant conformal field theories, along with some speculations about how they might be used to count black hole states. I show, in particular, that a set of unproven but plausible assumptions can lead to a boundary conformal field theory whose density of states matches the Bekenstein-Hawking entropy.
|
1310.1171
|
Md. Farid Ahmed
|
Md. Farid Ahmed, Brendan M. Quine, Spiros Pagiatakis and A. D.
Stauffer (York University, Toronto, Canada)
|
Results of a one-way experiment to test the isotropy of the speed of
light
|
13 pages, 9 figures. arXiv admin note: text overlap with
arXiv:1103.6086
| null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
This paper presents the outcome of an experiment based on an improved version
of Fizeau's coupled-slotted-discs that tests the fundamental postulates of
Special Relativity for the one-way speed of light propagation. According to our
methodology, important phenomena - a limit on and the diurnal regularity of the
variation of the speed of light due to the movements of the Earth (assuming
that the speed of light follows a Galilean transformation) - can be tested by
the present experiment. However, these measurements do not indicate any
significant diurnal variation. Consequently, the limit of the present outcome
on the variation of the speed of light is insignificant. Assuming that the
speed of light is not invariant and performing a rigorous statistical analysis,
the limit established is approximately 1/50 of the previous Fizeau-type
experiment with 95% confidence level. These outcomes are consistent with the
assumptions of Einstein's Special Relativity.
|
[
{
"created": "Fri, 4 Oct 2013 05:27:17 GMT",
"version": "v1"
}
] |
2013-10-07
|
[
[
"Ahmed",
"Md. Farid",
"",
"York University, Toronto, Canada"
],
[
"Quine",
"Brendan M.",
"",
"York University, Toronto, Canada"
],
[
"Pagiatakis",
"Spiros",
"",
"York University, Toronto, Canada"
],
[
"Stauffer",
"A. D.",
"",
"York University, Toronto, Canada"
]
] |
This paper presents the outcome of an experiment based on an improved version of Fizeau's coupled-slotted-discs that tests the fundamental postulates of Special Relativity for the one-way speed of light propagation. According to our methodology, important phenomena - a limit on and the diurnal regularity of the variation of the speed of light due to the movements of the Earth (assuming that the speed of light follows a Galilean transformation) - can be tested by the present experiment. However, these measurements do not indicate any significant diurnal variation. Consequently, the limit of the present outcome on the variation of the speed of light is insignificant. Assuming that the speed of light is not invariant and performing a rigorous statistical analysis, the limit established is approximately 1/50 of the previous Fizeau-type experiment with 95% confidence level. These outcomes are consistent with the assumptions of Einstein's Special Relativity.
|
1110.3668
|
Hossein Farajollahi
|
H. Farajollahi, F. Tayebi, F. Milani, M. Enayati
|
Cosmological observations in non-local $F(R)$ cosmology
|
12 pages, 7 figures, will be published in Astrophysics and space
science
|
Astrophysics and Space Science, 337, 2 773-778 (2012)
|
10.1007/s10509-011-0889-1
| null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
In this article in a generalization of our previous work, we investigate the
dynamics of the non-local $F(R)$ gravity after casting it into local form. The
non-singular bouncing behavior and quintom model of dark energy are achieved
without involving negative kinetic energy fields. Two cosmological tests are
performed to constrain the model parameters. In case of phantom crossing the
distance modulus predicted by the model best-fits the observational data. In
comparison with the CPL parametrization for drift velocity, the model in some
redshift intervals is in good agreement with the data.
|
[
{
"created": "Mon, 17 Oct 2011 13:55:47 GMT",
"version": "v1"
}
] |
2015-05-30
|
[
[
"Farajollahi",
"H.",
""
],
[
"Tayebi",
"F.",
""
],
[
"Milani",
"F.",
""
],
[
"Enayati",
"M.",
""
]
] |
In this article in a generalization of our previous work, we investigate the dynamics of the non-local $F(R)$ gravity after casting it into local form. The non-singular bouncing behavior and quintom model of dark energy are achieved without involving negative kinetic energy fields. Two cosmological tests are performed to constrain the model parameters. In case of phantom crossing the distance modulus predicted by the model best-fits the observational data. In comparison with the CPL parametrization for drift velocity, the model in some redshift intervals is in good agreement with the data.
|
2207.10459
|
Peter K.F. Kuhfittig
|
Peter K.F. Kuhfittig
|
Noncommutative geometry and MOND
|
5 pages, no figures
|
Journal of High Energy Physics, Gravitation and Cosmology, vol. 8,
pp. 642-646, 2022
| null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Modified Newtonian dynamics (MOND) is a hypothesized modification of Newton's
law of universal gravitation to account for the flat rotation curves in the
outer regions of galaxies, thereby eliminating the need for dark matter.
Although a highly successful model, it is not a self-contained physical theory
since it is based entirely on observations. It is proposed in this paper that
noncommutative geometry, an offshoot of string theory, can account for the flat
rotation curves and thereby provide a justification for MOND. This paper
extends an earlier heuristic argument by the author.
|
[
{
"created": "Thu, 21 Jul 2022 12:56:34 GMT",
"version": "v1"
},
{
"created": "Sun, 26 May 2024 18:22:53 GMT",
"version": "v2"
}
] |
2024-05-28
|
[
[
"Kuhfittig",
"Peter K. F.",
""
]
] |
Modified Newtonian dynamics (MOND) is a hypothesized modification of Newton's law of universal gravitation to account for the flat rotation curves in the outer regions of galaxies, thereby eliminating the need for dark matter. Although a highly successful model, it is not a self-contained physical theory since it is based entirely on observations. It is proposed in this paper that noncommutative geometry, an offshoot of string theory, can account for the flat rotation curves and thereby provide a justification for MOND. This paper extends an earlier heuristic argument by the author.
|
2005.01837
|
Ra\'ul Carballo-Rubio
|
Anna Zulianello, Ra\'ul Carballo-Rubio, Stefano Liberati and Stefano
Ansoldi
|
Electromagnetic tests of horizonless rotating black hole mimickers
|
V2: 25 pages, 14 figures, 8 tables. Additional discussions included
following suggestions by referees, no physics changes. This version accepted
for publication. V1: 23 pages, 13 figures, 8 tables
|
Phys. Rev. D 103, 064071 (2021)
|
10.1103/PhysRevD.103.064071
| null |
gr-qc astro-ph.HE
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The interest in the implications that astrophysical observations have for the
understanding of the structure of black holes has grown since the first
detection of gravitational waves. Many arguments that are put forward in order
to constraint alternative black hole models rely on substantial assumptions
such as perfect spherical symmetry, which implies absence of rotation. However,
given that astrophysical black holes will generally exhibit nonzero angular
momentum, realistic constraints must take into account the effects of rotation.
In this work we analyze the gravitational effect that rotation has on the
emission from the surface of ultracompact objects, by studying how angular
momentum affects the propagation of light rays. This allows us to evaluate the
reliability of the constraints derived for supermassive black holes (more
specifically, Sagittarius A* and M87*) assuming lack of rotation, as presented
in [Astrophys. J. 701, 1357 (2009); Astrophys. J. 805, 179 (2015)]. We find
that for rapidly spinning objects rotation can significantly affect the
escaping probability of photon emitted from the surface of the object, with a
significant increase at the equatorial regions and a decrease at the poles with
respect to the non-rotating case. For not so rapidly spinning black hole
candidates like Sagittarius A*, such modifications do not affect significantly
the present constraints, which are nevertheless weaker than originally supposed
due to the relativistic lensing here considered and additional phenomenological
parameters that describe basic processes such as absorption. However, taking
into account the angular dependence of the superficial emission of rapidly
spinning black hole mimickers will be necessary for future studies of objects
like e.g. M87*.
|
[
{
"created": "Mon, 4 May 2020 20:43:36 GMT",
"version": "v1"
},
{
"created": "Fri, 29 Jan 2021 15:51:36 GMT",
"version": "v2"
}
] |
2021-03-31
|
[
[
"Zulianello",
"Anna",
""
],
[
"Carballo-Rubio",
"Raúl",
""
],
[
"Liberati",
"Stefano",
""
],
[
"Ansoldi",
"Stefano",
""
]
] |
The interest in the implications that astrophysical observations have for the understanding of the structure of black holes has grown since the first detection of gravitational waves. Many arguments that are put forward in order to constraint alternative black hole models rely on substantial assumptions such as perfect spherical symmetry, which implies absence of rotation. However, given that astrophysical black holes will generally exhibit nonzero angular momentum, realistic constraints must take into account the effects of rotation. In this work we analyze the gravitational effect that rotation has on the emission from the surface of ultracompact objects, by studying how angular momentum affects the propagation of light rays. This allows us to evaluate the reliability of the constraints derived for supermassive black holes (more specifically, Sagittarius A* and M87*) assuming lack of rotation, as presented in [Astrophys. J. 701, 1357 (2009); Astrophys. J. 805, 179 (2015)]. We find that for rapidly spinning objects rotation can significantly affect the escaping probability of photon emitted from the surface of the object, with a significant increase at the equatorial regions and a decrease at the poles with respect to the non-rotating case. For not so rapidly spinning black hole candidates like Sagittarius A*, such modifications do not affect significantly the present constraints, which are nevertheless weaker than originally supposed due to the relativistic lensing here considered and additional phenomenological parameters that describe basic processes such as absorption. However, taking into account the angular dependence of the superficial emission of rapidly spinning black hole mimickers will be necessary for future studies of objects like e.g. M87*.
|
gr-qc/9802014
|
Roy Maartens
|
Roy Maartens, William Lesame and George Ellis
|
Newtonian-like and anti-Newtonian universes
|
16 pages Latex (IOP style); to appear Class. Quantum Grav
|
Class.Quant.Grav. 15 (1998) 1005-1017
|
10.1088/0264-9381/15/4/021
| null |
gr-qc
| null |
In an irrotational dust universe, the locally free gravitational field is
covariantly described by the gravito-electric and gravito-magnetic tensors
$E_{ab}$ and $H_{ab}$. In Newtonian theory, $H_{ab}=0$ and $E_{ab}$ is the
tidal tensor. Newtonian-like dust universes in general relativity (i.e. with
$H_{ab}=0$, often called `silent') have been shown to be inconsistent in
general and unlikely to extend beyond the known spatially homogeneous or
Szekeres examples. Furthermore, they are subject to a linearization
instability. Here we show that `anti-Newtonian' universes, i.e. with purely
gravito-magnetic field, so that $E_{ab} = 0\neq H_{ab}$, are also subject to
severe integrability conditions. Thus these models are inconsistent in general.
We show also that there are no anti-Newtonian spacetimes that are linearized
perturbations of Robertson-Walker universes. The only $E_{ab}=0\neq H_{ab}$
solution known to us is not a dust solution, and we show that it is
kinematically G\"{o}del-like but dynamically unphysical.
|
[
{
"created": "Fri, 6 Feb 1998 10:37:38 GMT",
"version": "v1"
}
] |
2009-10-31
|
[
[
"Maartens",
"Roy",
""
],
[
"Lesame",
"William",
""
],
[
"Ellis",
"George",
""
]
] |
In an irrotational dust universe, the locally free gravitational field is covariantly described by the gravito-electric and gravito-magnetic tensors $E_{ab}$ and $H_{ab}$. In Newtonian theory, $H_{ab}=0$ and $E_{ab}$ is the tidal tensor. Newtonian-like dust universes in general relativity (i.e. with $H_{ab}=0$, often called `silent') have been shown to be inconsistent in general and unlikely to extend beyond the known spatially homogeneous or Szekeres examples. Furthermore, they are subject to a linearization instability. Here we show that `anti-Newtonian' universes, i.e. with purely gravito-magnetic field, so that $E_{ab} = 0\neq H_{ab}$, are also subject to severe integrability conditions. Thus these models are inconsistent in general. We show also that there are no anti-Newtonian spacetimes that are linearized perturbations of Robertson-Walker universes. The only $E_{ab}=0\neq H_{ab}$ solution known to us is not a dust solution, and we show that it is kinematically G\"{o}del-like but dynamically unphysical.
|
1410.4555
|
Pedro Pina Avelino
|
P. P. Avelino
|
Vacuum energy sequestering and cosmic dynamics
|
6 pages, 6 figures
|
Phys.Rev.D 90:103523,2014
|
10.1103/PhysRevD.90.103523
| null |
gr-qc astro-ph.CO hep-ph hep-th
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
We explicitly compute the dynamics of closed homogeneous and isotropic
universes permeated by a single perfect fluid with a constant equation of state
parameter $w$ in the context of a recent reformulation of general relativity,
proposed in [1], which prevents the vacuum energy from acting as a
gravitational source. This is done using an iterative algorithm, taking as an
initial guess the background cosmological evolution obtained using standard
general relativity in the absence of a cosmological constant. We show that, in
general, the impact of the vacuum energy sequestering mechanism on the dynamics
of the universe is significant, except for the $w=1/3$ case where the results
are identical to those obtained in the context of general relativity with a
null cosmological constant. We also show that there are well behaved models in
general relativity that do not have a well behaved counterpart in the vacuum
energy sequestering paradigm studied in this paper, highlighting the specific
case of a quintessence scalar field with a linear potential.
|
[
{
"created": "Thu, 16 Oct 2014 19:28:37 GMT",
"version": "v1"
}
] |
2015-05-06
|
[
[
"Avelino",
"P. P.",
""
]
] |
We explicitly compute the dynamics of closed homogeneous and isotropic universes permeated by a single perfect fluid with a constant equation of state parameter $w$ in the context of a recent reformulation of general relativity, proposed in [1], which prevents the vacuum energy from acting as a gravitational source. This is done using an iterative algorithm, taking as an initial guess the background cosmological evolution obtained using standard general relativity in the absence of a cosmological constant. We show that, in general, the impact of the vacuum energy sequestering mechanism on the dynamics of the universe is significant, except for the $w=1/3$ case where the results are identical to those obtained in the context of general relativity with a null cosmological constant. We also show that there are well behaved models in general relativity that do not have a well behaved counterpart in the vacuum energy sequestering paradigm studied in this paper, highlighting the specific case of a quintessence scalar field with a linear potential.
|
2307.11665
|
Enrico Cannizzaro
|
Enrico Cannizzaro, Gabriele Franciolini and Paolo Pani
|
Novel tests of gravity using nano-Hertz stochastic gravitational-wave
background signals
|
7 pages, 4 figures. Matches the published version
| null | null | null |
gr-qc astro-ph.CO astro-ph.HE hep-ph
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
Gravity theories that modify General Relativity in the slow-motion regime can
introduce nonperturbative corrections to the stochastic gravitational-wave
background~(SGWB) from supermassive black-hole binaries in the nano-Hertz band,
while remaining perturbative in the highly-relativistic regime and satisfying
current post-Newtonian~(PN) constraints. We present a model-agnostic formalism
to map such theories into a modified tilt for the SGWB spectrum, showing that
negative PN corrections (in particular -2PN) can alleviate the tension in the
recent pulsar-timing-array data if the detected SGWB is interpreted as arising
from supermassive binaries. Despite being preliminary, current data have
already strong constraining power, for example they set a novel (conservative)
upper bound on theories with time-varying Newton's constant at least at the
level of $\dot{G}/G \lesssim 10^{-5} \text{yr}^{-1}$ for redshift
$z=[0.1\div1]$. We also show that NANOGrav data are best fitted by a broken
power-law interpolating between a dominant -2PN or -3PN modification at low
frequency, and the standard general-relativity scaling at high frequency.
Nonetheless, a modified gravity explanation should be confronted with binary
eccentricity, environmental effects, nonastrophysical origins of the signal,
and scrutinized against statistical uncertainties. These novel tests of gravity
will soon become more stringent when combining all pulsar-timing-array
facilities and when collecting more data.
|
[
{
"created": "Fri, 21 Jul 2023 16:07:51 GMT",
"version": "v1"
},
{
"created": "Tue, 7 May 2024 14:41:44 GMT",
"version": "v2"
}
] |
2024-05-08
|
[
[
"Cannizzaro",
"Enrico",
""
],
[
"Franciolini",
"Gabriele",
""
],
[
"Pani",
"Paolo",
""
]
] |
Gravity theories that modify General Relativity in the slow-motion regime can introduce nonperturbative corrections to the stochastic gravitational-wave background~(SGWB) from supermassive black-hole binaries in the nano-Hertz band, while remaining perturbative in the highly-relativistic regime and satisfying current post-Newtonian~(PN) constraints. We present a model-agnostic formalism to map such theories into a modified tilt for the SGWB spectrum, showing that negative PN corrections (in particular -2PN) can alleviate the tension in the recent pulsar-timing-array data if the detected SGWB is interpreted as arising from supermassive binaries. Despite being preliminary, current data have already strong constraining power, for example they set a novel (conservative) upper bound on theories with time-varying Newton's constant at least at the level of $\dot{G}/G \lesssim 10^{-5} \text{yr}^{-1}$ for redshift $z=[0.1\div1]$. We also show that NANOGrav data are best fitted by a broken power-law interpolating between a dominant -2PN or -3PN modification at low frequency, and the standard general-relativity scaling at high frequency. Nonetheless, a modified gravity explanation should be confronted with binary eccentricity, environmental effects, nonastrophysical origins of the signal, and scrutinized against statistical uncertainties. These novel tests of gravity will soon become more stringent when combining all pulsar-timing-array facilities and when collecting more data.
|
2001.03773
|
Leonid Perlov
|
Leonid Perlov
|
Hamiltonian and Diffeomorphism Constraints Generalized for Timelike and
Spacelike 3+1 Foliation
| null | null | null | null |
gr-qc
|
http://arxiv.org/licenses/nonexclusive-distrib/1.0/
|
The form of Hamiltonian and Diffeomorphism constraints in
Sen-Ashtekar-Barbero-Immirzi variables is well known for the spacelike 3+1 ADM
foliation. It is also known that Sen-Ashtekar-Barbero-Immirzi connection can be
introduced only in 3 dimensional space and does not work for $D > 3$. The
reason it works in $D = 3$ is due to existence of isomorphism between $so(3)$
algebra and $R^3$ space with vector product. It turns out that similar
isomorphism exists between $so(2,1)$ algebra and $R^3_{2,1}$ space algebra with
respect to its vector product. By using this isomorphism we find both analog of
Sen-Ashtekar-Barbero-Immirzi connection for timelike 3+1 foliation and
corresponding forms of Gauss, Diffeomorphism and Hamiltonian constraints. We
then combine spacelike and timelike foliation constraints into the generalized
form of the Hamiltonian and Diffeomorphism constrains using generalized
Sen-Ashtekar-Barbero-Immirzi connection variables. We prove that Immirzi
parameter is covariant with respect to timelike-spacelike ADM foliation change
as in both cases in self-dual Ashtekar case it disappears in Hamiltionian
constraint keeping it polynomial.
|
[
{
"created": "Sat, 11 Jan 2020 16:51:46 GMT",
"version": "v1"
},
{
"created": "Thu, 2 Apr 2020 15:05:49 GMT",
"version": "v2"
},
{
"created": "Tue, 7 Apr 2020 19:40:32 GMT",
"version": "v3"
},
{
"created": "Fri, 8 May 2020 14:38:22 GMT",
"version": "v4"
},
{
"created": "Mon, 26 Apr 2021 21:06:29 GMT",
"version": "v5"
}
] |
2021-04-28
|
[
[
"Perlov",
"Leonid",
""
]
] |
The form of Hamiltonian and Diffeomorphism constraints in Sen-Ashtekar-Barbero-Immirzi variables is well known for the spacelike 3+1 ADM foliation. It is also known that Sen-Ashtekar-Barbero-Immirzi connection can be introduced only in 3 dimensional space and does not work for $D > 3$. The reason it works in $D = 3$ is due to existence of isomorphism between $so(3)$ algebra and $R^3$ space with vector product. It turns out that similar isomorphism exists between $so(2,1)$ algebra and $R^3_{2,1}$ space algebra with respect to its vector product. By using this isomorphism we find both analog of Sen-Ashtekar-Barbero-Immirzi connection for timelike 3+1 foliation and corresponding forms of Gauss, Diffeomorphism and Hamiltonian constraints. We then combine spacelike and timelike foliation constraints into the generalized form of the Hamiltonian and Diffeomorphism constrains using generalized Sen-Ashtekar-Barbero-Immirzi connection variables. We prove that Immirzi parameter is covariant with respect to timelike-spacelike ADM foliation change as in both cases in self-dual Ashtekar case it disappears in Hamiltionian constraint keeping it polynomial.
|
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