id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1909.02862 | Muhammad Sharif | M. Sharif and Qanitah Ama-Tul-Mughani | Greybody Factor for a Rotating Bardeen Black Hole | 18 pages, 4 figures, to appear in EPJP | Eur. Phys. J. Plus 134(2019)616 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we formulate an analytical expression of greybody factor in
the context of rotating Bardeen black hole which is valid in low energy and low
angular momentum region. Primarily, we analyze the profile of effective
potential which originates the absorption probability. We then derive two
asymptotic solutions by solving the radial part of Klein-Gordon equation in two
different regions, namely, black hole and far-field horizons. We match these
solutions smoothly to an intermediate regime to extend our results over the
whole radial coordinate. In order to elaborate on the significance of the
analytical solution, we compute the energy emission rate and absorption
cross-section for the massless scalar field. It is found that the rotation
parameter increases the emission rate of scalar field particles while the
orbital angular momentum minimizes the emission process.
| [
{
"created": "Thu, 5 Sep 2019 03:44:58 GMT",
"version": "v1"
}
] | 2019-12-09 | [
[
"Sharif",
"M.",
""
],
[
"Ama-Tul-Mughani",
"Qanitah",
""
]
] | In this paper, we formulate an analytical expression of greybody factor in the context of rotating Bardeen black hole which is valid in low energy and low angular momentum region. Primarily, we analyze the profile of effective potential which originates the absorption probability. We then derive two asymptotic solutions by solving the radial part of Klein-Gordon equation in two different regions, namely, black hole and far-field horizons. We match these solutions smoothly to an intermediate regime to extend our results over the whole radial coordinate. In order to elaborate on the significance of the analytical solution, we compute the energy emission rate and absorption cross-section for the massless scalar field. It is found that the rotation parameter increases the emission rate of scalar field particles while the orbital angular momentum minimizes the emission process. |
1706.07657 | Ghulam Abbas | G. Abbas, M.S. Khan, Zahid Ahmad and M. Zubair | Higher Dimensional Inhomogeneous Perfect Fluid Collapse in \emph{f(R)}
Gravity | 17 Pages, to appear in European Physical Journal C | null | 10.1140/epjc/s10052-017-5003-6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper is about the $n+2$-dimensional gravitational contraction of
inhomogeneous fluid without heat flux in the framework of $f(R)$ metric theory
of gravity. Matching conditions for two regions of a star has been derived by
using the Darmois junction conditions. For the analytic solution of equations
of motion in modified $f(R)$ theory of gravity, we have taken scalar curvature
as constant. Hence final result of gravitational collapse in this frame work is
the existence of black hole and cosmological horizons, both of these form
earlier than singularity. It has been shown that constant curvature term
$f(R_{0})$ ($R_0$ is constant scalar curvature) slows down the collapsing
process.
| [
{
"created": "Wed, 21 Jun 2017 05:13:56 GMT",
"version": "v1"
}
] | 2017-08-02 | [
[
"Abbas",
"G.",
""
],
[
"Khan",
"M. S.",
""
],
[
"Ahmad",
"Zahid",
""
],
[
"Zubair",
"M.",
""
]
] | This paper is about the $n+2$-dimensional gravitational contraction of inhomogeneous fluid without heat flux in the framework of $f(R)$ metric theory of gravity. Matching conditions for two regions of a star has been derived by using the Darmois junction conditions. For the analytic solution of equations of motion in modified $f(R)$ theory of gravity, we have taken scalar curvature as constant. Hence final result of gravitational collapse in this frame work is the existence of black hole and cosmological horizons, both of these form earlier than singularity. It has been shown that constant curvature term $f(R_{0})$ ($R_0$ is constant scalar curvature) slows down the collapsing process. |
0901.3926 | Francisco Lobo | Tiberiu Harko, Zolt\'an Kov\'acs, Francisco S. N. Lobo | Thin accretion disks in stationary axisymmetric wormhole spacetimes | 12 pages, 26 figures. V2: minor corrections and references added; to
appear in Physical Review D. V3: typos corrected, matches published version | Phys.Rev.D79:064001,2009 | 10.1103/PhysRevD.79.064001 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we study the physical properties and the equilibrium thermal
radiation emission characteristics of matter forming thin accretion disks in
stationary axially symmetric wormhole spacetimes. The thin disk models are
constructed by taking different values of the wormhole's angular velocity, and
the time averaged energy flux, the disk temperature and the emission spectra of
the accretion disks are obtained. Comparing the mass accretion in a rotating
wormhole geometry with the one of a Kerr black hole, we verify that the
intensity of the flux emerging from the disk surface is greater for wormholes
than for rotating black holes with the same geometrical mass and accretion
rate. We also present the conversion efficiency of the accreting mass into
radiation, and show that the rotating wormholes provide a much more efficient
engine for the transformation of the accreting mass into radiation than the
Kerr black holes. Therefore specific signatures appear in the electromagnetic
spectrum of thin disks around rotating wormholes, thus leading to the
possibility of distinguishing wormhole geometries by using astrophysical
observations of the emission spectra from accretion disks.
| [
{
"created": "Sun, 25 Jan 2009 22:26:45 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Feb 2009 22:07:48 GMT",
"version": "v2"
},
{
"created": "Mon, 2 Mar 2009 21:47:06 GMT",
"version": "v3"
}
] | 2009-03-02 | [
[
"Harko",
"Tiberiu",
""
],
[
"Kovács",
"Zoltán",
""
],
[
"Lobo",
"Francisco S. N.",
""
]
] | In this paper, we study the physical properties and the equilibrium thermal radiation emission characteristics of matter forming thin accretion disks in stationary axially symmetric wormhole spacetimes. The thin disk models are constructed by taking different values of the wormhole's angular velocity, and the time averaged energy flux, the disk temperature and the emission spectra of the accretion disks are obtained. Comparing the mass accretion in a rotating wormhole geometry with the one of a Kerr black hole, we verify that the intensity of the flux emerging from the disk surface is greater for wormholes than for rotating black holes with the same geometrical mass and accretion rate. We also present the conversion efficiency of the accreting mass into radiation, and show that the rotating wormholes provide a much more efficient engine for the transformation of the accreting mass into radiation than the Kerr black holes. Therefore specific signatures appear in the electromagnetic spectrum of thin disks around rotating wormholes, thus leading to the possibility of distinguishing wormhole geometries by using astrophysical observations of the emission spectra from accretion disks. |
2011.04120 | Ren Tsuda | Ren Tsuda, Takanori Fujiwara | Oscillating 4-Polytopal Universe in Regge Calculus | 24 pages, 9 figures. arXiv admin note: text overlap with
arXiv:1612.06536 | Prog. Theor. Exp. Phys. 2021, 083E01 | 10.1093/ptep/ptab079 | null | gr-qc hep-lat hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The discretized closed Friedmann-Lema\^itre-Robertson-Walker (FLRW) universe
with positive cosmological constant is investigated by Regge calculus.
According to the Collins-Williams formalism, a hyperspherical Cauchy surface is
replaced with regular 4-polytopes. Numerical solutions to the Regge equations
approximate well to the continuum solution during the era of small edge length.
Unlike the expanding polyhedral universe in three dimensions, the 4-polytopal
universes repeat expansions and contractions. To go beyond the approximation
using regular 4-polytopes we introduce pseudo-regular 4-polytopes by averaging
the dihedral angles of the tessellated regular 600-cell. The degree of
precision of the tessellation is called the frequency. Regge equations for the
pseudo-regular 4-polytope have simple and unique expressions for any frequency.
In the infinite frequency limit, the pseudo-regular 4-polytope model approaches
the continuum FLRW universe.
| [
{
"created": "Mon, 9 Nov 2020 00:34:21 GMT",
"version": "v1"
},
{
"created": "Sun, 17 Oct 2021 13:33:12 GMT",
"version": "v2"
}
] | 2021-10-25 | [
[
"Tsuda",
"Ren",
""
],
[
"Fujiwara",
"Takanori",
""
]
] | The discretized closed Friedmann-Lema\^itre-Robertson-Walker (FLRW) universe with positive cosmological constant is investigated by Regge calculus. According to the Collins-Williams formalism, a hyperspherical Cauchy surface is replaced with regular 4-polytopes. Numerical solutions to the Regge equations approximate well to the continuum solution during the era of small edge length. Unlike the expanding polyhedral universe in three dimensions, the 4-polytopal universes repeat expansions and contractions. To go beyond the approximation using regular 4-polytopes we introduce pseudo-regular 4-polytopes by averaging the dihedral angles of the tessellated regular 600-cell. The degree of precision of the tessellation is called the frequency. Regge equations for the pseudo-regular 4-polytope have simple and unique expressions for any frequency. In the infinite frequency limit, the pseudo-regular 4-polytope model approaches the continuum FLRW universe. |
gr-qc/0703036 | Mamdouh Wanas | M.I.Wanas | On the Relation between Mass and Charge: A Pure Geometric Approach | 15 pages, LaTeX file | Int.J.Geom.Meth.Mod.Phys.4:373-388,2007 | 10.1142/S0219887807002144 | null | gr-qc | null | A new solution of the field equations of the generalized field theory,
constructed by Mikhail and Wanas in 1977, has been obtained.
The geometric structure used, in the present application, is an absolute
parallelism (AP)-space with spherical symmetry (type FIGI). The solution
obtained represents a generalized field outside a charged massive central body.
Two schemes have been used to get the physical meaning of the solution: The
first is related to the metric of the Riemannian space associated with the
AP-structure. The second is connected to a covariant scheme known as {\it{Type
Analysis}}. It is shown that the dependence on both schemes for interpreting
the results obtained, is more better than the dependence on the metric of the
Riemannian space associated with the AP-structure.
In General, if we consider the solution obtained as representing a geometric
model for an elementary charged particle, then the results of the present work
can be summarized in the following points. (i) It is shown that the mass of the
particle is made of two contributions: The first is the gravitational
contribution, and the second is the contribution due to the existence of
charge. (ii) The model allows for the existence of a charged particle whose
mass is completely electromagnetic in origin. (iii) The model prevents the
existence of a charged massless particle. (iv) The electromagnetic
contribution, to the mass, is independent of the sign of the electric charge.
(v) It is shown that the mass of the electron (or a positron) is purely made of
its charge.
| [
{
"created": "Tue, 6 Mar 2007 13:48:43 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Wanas",
"M. I.",
""
]
] | A new solution of the field equations of the generalized field theory, constructed by Mikhail and Wanas in 1977, has been obtained. The geometric structure used, in the present application, is an absolute parallelism (AP)-space with spherical symmetry (type FIGI). The solution obtained represents a generalized field outside a charged massive central body. Two schemes have been used to get the physical meaning of the solution: The first is related to the metric of the Riemannian space associated with the AP-structure. The second is connected to a covariant scheme known as {\it{Type Analysis}}. It is shown that the dependence on both schemes for interpreting the results obtained, is more better than the dependence on the metric of the Riemannian space associated with the AP-structure. In General, if we consider the solution obtained as representing a geometric model for an elementary charged particle, then the results of the present work can be summarized in the following points. (i) It is shown that the mass of the particle is made of two contributions: The first is the gravitational contribution, and the second is the contribution due to the existence of charge. (ii) The model allows for the existence of a charged particle whose mass is completely electromagnetic in origin. (iii) The model prevents the existence of a charged massless particle. (iv) The electromagnetic contribution, to the mass, is independent of the sign of the electric charge. (v) It is shown that the mass of the electron (or a positron) is purely made of its charge. |
1010.1578 | Manasse R. Mbonye | Manasse R. Mbonye, Nicholas Battista and Benjamin Farr | Time evolution of a non-singular primordial black hole | To appear in Int. J. Mod. Phys. D | null | 10.1142/S0218271812500277 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There is growing notion that black holes may not contain curvature
singularities (and that indeed nature in general may abhor such spacetime
defects). This notion could have implications on our understanding of the
evolution of primordial black holes (PBHs) and possibly on their contribution
to cosmic energy. This paper discusses the evolution of a non-singular black
hole (NSBH) based on a recent model [1]. We begin with a study of the
thermodynamic process of the black hole in this model, and demonstrate the
existence of a maximum horizon temperature T_{max}, corresponding to a unique
mass value. At this mass value the specific heat capacity C changes signs to
positive and the body begins to lose its black hole characteristics. With no
loss of generality, the model is used to discuss the time evolution of a
primordial black hole (PBH), through the early radiation era of the universe to
present, under the assumption that PBHs are non-singular. In particular, we
track the evolution of two benchmark PBHs, namely the one radiating up to the
end of the cosmic radiation domination era, and the one stopping to radiate
currently, and in each case determine some useful features including the
initial mass m_{f} and the corresponding time of formation t_{f}. It is found
that along the evolutionary history of the universe the distribution of PBH
remnant masses (PBH-RM) PBH-RMs follows a power law. We believe such a result
can be a useful step in a study to establish current abundance of PBH-MRs.
| [
{
"created": "Fri, 8 Oct 2010 01:22:07 GMT",
"version": "v1"
}
] | 2015-05-20 | [
[
"Mbonye",
"Manasse R.",
""
],
[
"Battista",
"Nicholas",
""
],
[
"Farr",
"Benjamin",
""
]
] | There is growing notion that black holes may not contain curvature singularities (and that indeed nature in general may abhor such spacetime defects). This notion could have implications on our understanding of the evolution of primordial black holes (PBHs) and possibly on their contribution to cosmic energy. This paper discusses the evolution of a non-singular black hole (NSBH) based on a recent model [1]. We begin with a study of the thermodynamic process of the black hole in this model, and demonstrate the existence of a maximum horizon temperature T_{max}, corresponding to a unique mass value. At this mass value the specific heat capacity C changes signs to positive and the body begins to lose its black hole characteristics. With no loss of generality, the model is used to discuss the time evolution of a primordial black hole (PBH), through the early radiation era of the universe to present, under the assumption that PBHs are non-singular. In particular, we track the evolution of two benchmark PBHs, namely the one radiating up to the end of the cosmic radiation domination era, and the one stopping to radiate currently, and in each case determine some useful features including the initial mass m_{f} and the corresponding time of formation t_{f}. It is found that along the evolutionary history of the universe the distribution of PBH remnant masses (PBH-RM) PBH-RMs follows a power law. We believe such a result can be a useful step in a study to establish current abundance of PBH-MRs. |
1907.07490 | Yen Chin Ong | Yen Chin Ong, Yuan Yao | Charged Particle Production Rate from Cosmic Censorship in Dilaton Black
Hole Spacetimes | 13 pages, 6 figures, Fig.1 improved, typos fixed; published version | JHEP 10 (2019) 129 | 10.1007/JHEP10(2019)129 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Hiscock and Weems showed that under Hawking evaporation, an isolated
asymptotically flat Reissner-Nordstrom (RN) black hole evolves in a surprising
manner: if it starts with a relatively small value of charge-to-mass ratio Q/M,
then said value will temporarily increase along its evolutionary path, before
finally decreases towards zero. This contrasts with highly charged ones that
simply radiate away its charge steadily. The combination of these two effects
is the cosmic censor at work: there exists an attractor that flows towards the
Schwazschild limit, which ensures that extremality -- and hence naked
singularity -- can never be reached under Hawking evaporation. We apply the
scheme of Hiscock and Weems to model the evaporation of an asymptotically flat
dilatonic charge black hole known as the Garfinkle-Horowitz-Strominger (GHS)
black hole. We found that upholding the cosmic censorship requires us to modify
the charged particle production rate, which remarkably agrees with the
expression obtained independently via direct computation of charged particle
production rate on curved spacetime background. This not only strengthens the
case for cosmic censorship, but also provides an example in which cosmic
censorship can be a useful principle to deduce other physics. We also found
that the attractor behavior is not necessarily related to the specific heat,
contrary to the claim by Hiscock and Weems.
| [
{
"created": "Wed, 17 Jul 2019 13:11:05 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Oct 2019 12:47:11 GMT",
"version": "v2"
}
] | 2019-10-24 | [
[
"Ong",
"Yen Chin",
""
],
[
"Yao",
"Yuan",
""
]
] | Hiscock and Weems showed that under Hawking evaporation, an isolated asymptotically flat Reissner-Nordstrom (RN) black hole evolves in a surprising manner: if it starts with a relatively small value of charge-to-mass ratio Q/M, then said value will temporarily increase along its evolutionary path, before finally decreases towards zero. This contrasts with highly charged ones that simply radiate away its charge steadily. The combination of these two effects is the cosmic censor at work: there exists an attractor that flows towards the Schwazschild limit, which ensures that extremality -- and hence naked singularity -- can never be reached under Hawking evaporation. We apply the scheme of Hiscock and Weems to model the evaporation of an asymptotically flat dilatonic charge black hole known as the Garfinkle-Horowitz-Strominger (GHS) black hole. We found that upholding the cosmic censorship requires us to modify the charged particle production rate, which remarkably agrees with the expression obtained independently via direct computation of charged particle production rate on curved spacetime background. This not only strengthens the case for cosmic censorship, but also provides an example in which cosmic censorship can be a useful principle to deduce other physics. We also found that the attractor behavior is not necessarily related to the specific heat, contrary to the claim by Hiscock and Weems. |
gr-qc/9207005 | null | Ted Jacobson and Joseph D. Romano | Degenerate Extensions of General Relativity | 9 pages | Class.Quant.Grav.9:L119-L124,1992 | 10.1088/0264-9381/9/9/003 | UMDGR-92-154 | gr-qc | null | General relativity has previously been extended to incorporate degenerate
metrics using Ashtekar's hamiltonian formulation of the theory. In this letter,
we show that a natural alternative choice for the form of the hamiltonian
constraints leads to a theory which agrees with GR for non-degenerate metrics,
but differs in the degenerate sector from Ashtekar's original degenerate
extension. The Poisson bracket algebra of the alternative constraints closes in
the non-degenerate sector, with structure functions that involve the {\it
inverse} of the spatial triad. Thus, the algebra does {\it not} close in the
degenerate sector. We find that it must be supplemented by an infinite number
ofsecondary constraints, which are shown to be first class (although their
explicit form is not worked out in detail). All of the constraints taken
together are implied by, but do not imply, Ashtekar's original form of
constraints. Thus, the alternative constraints give rise to a different
degenerate extension of GR. In the corresponding quantum theory, the single
loop and intersecting loop holonomy states found in the connection
representation satisfy {\it all} of the constraints. These states are therefore
exact (formal) solutions to this alternative degenerate extension of quantum
gravity, even though they are {\it not} solutions to the usual vector
constraint.
| [
{
"created": "Thu, 23 Jul 1992 15:51:00 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Jacobson",
"Ted",
""
],
[
"Romano",
"Joseph D.",
""
]
] | General relativity has previously been extended to incorporate degenerate metrics using Ashtekar's hamiltonian formulation of the theory. In this letter, we show that a natural alternative choice for the form of the hamiltonian constraints leads to a theory which agrees with GR for non-degenerate metrics, but differs in the degenerate sector from Ashtekar's original degenerate extension. The Poisson bracket algebra of the alternative constraints closes in the non-degenerate sector, with structure functions that involve the {\it inverse} of the spatial triad. Thus, the algebra does {\it not} close in the degenerate sector. We find that it must be supplemented by an infinite number ofsecondary constraints, which are shown to be first class (although their explicit form is not worked out in detail). All of the constraints taken together are implied by, but do not imply, Ashtekar's original form of constraints. Thus, the alternative constraints give rise to a different degenerate extension of GR. In the corresponding quantum theory, the single loop and intersecting loop holonomy states found in the connection representation satisfy {\it all} of the constraints. These states are therefore exact (formal) solutions to this alternative degenerate extension of quantum gravity, even though they are {\it not} solutions to the usual vector constraint. |
1905.06702 | Kubantai Ernazarov | K. K. Ernazarov | Stable exponential cosmological solutions with three factor spaces in
$(1+ 3 + 3 +k)$-dimensional Einstein-Gauss-Bonnet model with a $\Lambda$-term | 17 pages, Latex, no figures | null | 10.1142/S0217732319501116 | IGC-PFUR/2019/03-02 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a $(7 + k)$-dimensional Einstein-Gauss-Bonnet model with the
cosmological $\Lambda$-term. A cosmological model with three factor spaces of
dimensions $3$, $3$ and $k$, $k > 2$ is considered. Exact stable solutions with
three (non-coinciding) Hubble-like parameters in this model are obtained. Some
examples of solutions (e.g. with zero variation of the effective gravitational
constant $G$) are considered in selected dimensions (for $k = 5, 6$).
| [
{
"created": "Thu, 16 May 2019 12:51:12 GMT",
"version": "v1"
}
] | 2019-05-22 | [
[
"Ernazarov",
"K. K.",
""
]
] | We consider a $(7 + k)$-dimensional Einstein-Gauss-Bonnet model with the cosmological $\Lambda$-term. A cosmological model with three factor spaces of dimensions $3$, $3$ and $k$, $k > 2$ is considered. Exact stable solutions with three (non-coinciding) Hubble-like parameters in this model are obtained. Some examples of solutions (e.g. with zero variation of the effective gravitational constant $G$) are considered in selected dimensions (for $k = 5, 6$). |
1209.4501 | Alexander Zhuk | Maxim Eingorn, Seyed Hossein Fakhr and Alexander Zhuk | Kaluza-Klein models with spherical compactification: observational
constraints and possible examples | 18 pages. Combined (with arXiv:1207.4339) version accepted by CQG | Class.Quant.Grav. 30 (2013) 115004 | 10.1088/0264-9381/30/11/115004 | null | gr-qc astro-ph.HE hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider Kaluza-Klein models with background matter in the form of a
multicomponent perfect fluid. This matter provides spherical compactification
of the internal space with an arbitrary number of dimensions. The gravitating
source has the dust-like equation of state in the external/our space and an
arbitrary equation of state (with the parameter $\Omega$) in the internal
space. In the single-component case, tension ($\Omega=-1/2$) is the necessary
condition to satisfy both the gravitational tests in the solar system and the
thermodynamical observations. In the multicomponent case, we propose two models
satisfying both of these observations. One of them also requires tension
$\Omega=-1/2$, but the second one is of special interest because is free of
tension, i.e. $\Omega=0$. To get this result, we need to impose certain
conditions.
| [
{
"created": "Thu, 20 Sep 2012 11:52:27 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Apr 2013 19:44:59 GMT",
"version": "v2"
}
] | 2013-05-08 | [
[
"Eingorn",
"Maxim",
""
],
[
"Fakhr",
"Seyed Hossein",
""
],
[
"Zhuk",
"Alexander",
""
]
] | We consider Kaluza-Klein models with background matter in the form of a multicomponent perfect fluid. This matter provides spherical compactification of the internal space with an arbitrary number of dimensions. The gravitating source has the dust-like equation of state in the external/our space and an arbitrary equation of state (with the parameter $\Omega$) in the internal space. In the single-component case, tension ($\Omega=-1/2$) is the necessary condition to satisfy both the gravitational tests in the solar system and the thermodynamical observations. In the multicomponent case, we propose two models satisfying both of these observations. One of them also requires tension $\Omega=-1/2$, but the second one is of special interest because is free of tension, i.e. $\Omega=0$. To get this result, we need to impose certain conditions. |
2209.09781 | Vasilis Oikonomou | V.K. Oikonomou | Amplification of the Primordial Gravitational Waves Energy Spectrum by a
Kinetic Scalar in $F(R)$ Gravity | Astroparticle Physics in press | null | 10.1016/j.astropartphys.2022.102777 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we consider a combined theoretical framework comprised by $F(R)$
gravity and a kinetic scalar field. The kinetic energy of the scalar field
dominates over its potential for all cosmic times, and the kinetic scalar
potential is chosen to be small and non-trivial. In this case, we show that the
primordial gravitational wave energy spectrum of vacuum $F(R)$ gravity is
significantly enhanced and can be detectable in future interferometers. The
kinetic scalar thus affects significantly the inflationary era, since it
extends its duration, but also has an overall amplifying effect on the energy
spectrum of pure $F(R)$ gravity primordial gravitational waves. The form of the
signal is characteristic for all these theories, since it is basically flat and
should be detectable from all future gravitational wave experiments for a wide
range of frequencies, unless some unknown damping factor occurs due to some
unknown physical process.
| [
{
"created": "Tue, 20 Sep 2022 15:05:58 GMT",
"version": "v1"
}
] | 2022-10-12 | [
[
"Oikonomou",
"V. K.",
""
]
] | In this work we consider a combined theoretical framework comprised by $F(R)$ gravity and a kinetic scalar field. The kinetic energy of the scalar field dominates over its potential for all cosmic times, and the kinetic scalar potential is chosen to be small and non-trivial. In this case, we show that the primordial gravitational wave energy spectrum of vacuum $F(R)$ gravity is significantly enhanced and can be detectable in future interferometers. The kinetic scalar thus affects significantly the inflationary era, since it extends its duration, but also has an overall amplifying effect on the energy spectrum of pure $F(R)$ gravity primordial gravitational waves. The form of the signal is characteristic for all these theories, since it is basically flat and should be detectable from all future gravitational wave experiments for a wide range of frequencies, unless some unknown damping factor occurs due to some unknown physical process. |
gr-qc/9311016 | Jack Gegenberg | H. Zaidi, J. Gegenberg | Quantum Bubble Dynamics in 2+1 Dimensional Gravity I: Geometrodynamic
Approach | 14 pages, Latex (\cite typos corrected) | Phys.Lett.B328:22-27,1994 | 10.1016/0370-2693(94)90422-7 | null | gr-qc hep-th | null | The Dirac quantization of a 2+1 dimensional bubble is performed. The bubble
consists of a string forming a boundary between two regions of space-time with
distinct geometries. The ADM constraints are solved and the coupling to the
string is introduced through the boundary conditions. The wave functional is
obtained and the quantum uncertainty in the radius of the ring is calculated;
this uncertainty becomes large at the Planck scale.
| [
{
"created": "Tue, 9 Nov 1993 18:49:37 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Nov 1993 13:53:58 GMT",
"version": "v2"
}
] | 2010-11-01 | [
[
"Zaidi",
"H.",
""
],
[
"Gegenberg",
"J.",
""
]
] | The Dirac quantization of a 2+1 dimensional bubble is performed. The bubble consists of a string forming a boundary between two regions of space-time with distinct geometries. The ADM constraints are solved and the coupling to the string is introduced through the boundary conditions. The wave functional is obtained and the quantum uncertainty in the radius of the ring is calculated; this uncertainty becomes large at the Planck scale. |
1712.05149 | Soumya Chakrabarti | Soumya Chakrabarti | Collapsing spherical star in Scalar-Einstein-Gauss-Bonnet gravity with a
quadratic coupling | To Appear in EPJC | null | 10.1140/epjc/s10052-018-5798-9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the evolution of a self interacting scalar field in
Einstein-Gauss-Bonnet theory in four dimension where the scalar field couples
non minimally with the Gauss-Bonnet term. Considering a polynomial coupling of
the scalar field with the Gauss-Bonnet term, a self-interaction potential and
an additional perfect fluid distribution alongwith the scalar field, we
investigate different possibilities regarding the outcome of the collapsing
scalar field. The strength of the coupling and choice of the self-interaction
potential serves as the pivotal initial conditions of the models presented. The
high degree of non-linearity in the equation system is taken care off by using
a method of invertibe point transformation of anharmonic oscillator equation,
which has proven itself very useful in recent past while investigating dynamics
of minimally coupled scalar fields.
| [
{
"created": "Thu, 14 Dec 2017 10:19:15 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Apr 2018 17:36:11 GMT",
"version": "v2"
}
] | 2018-05-09 | [
[
"Chakrabarti",
"Soumya",
""
]
] | We study the evolution of a self interacting scalar field in Einstein-Gauss-Bonnet theory in four dimension where the scalar field couples non minimally with the Gauss-Bonnet term. Considering a polynomial coupling of the scalar field with the Gauss-Bonnet term, a self-interaction potential and an additional perfect fluid distribution alongwith the scalar field, we investigate different possibilities regarding the outcome of the collapsing scalar field. The strength of the coupling and choice of the self-interaction potential serves as the pivotal initial conditions of the models presented. The high degree of non-linearity in the equation system is taken care off by using a method of invertibe point transformation of anharmonic oscillator equation, which has proven itself very useful in recent past while investigating dynamics of minimally coupled scalar fields. |
gr-qc/0304013 | Ralf Lehnert | Ralf Lehnert | Threshold analyses and Lorentz violation | 9 pages | Phys.Rev.D68:085003,2003 | 10.1103/PhysRevD.68.085003 | null | gr-qc | null | In the context of threshold investigations of Lorentz violation, we discuss
the fundamental principle of coordinate invariance, the role of an effective
dynamical framework, and the conditions of positivity and causality. Our
analysis excludes a variety of previously considered Lorentz-breaking
parameters and opens an avenue for viable dispersion-relation investigations of
Lorentz violation.
| [
{
"created": "Wed, 2 Apr 2003 14:52:55 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Lehnert",
"Ralf",
""
]
] | In the context of threshold investigations of Lorentz violation, we discuss the fundamental principle of coordinate invariance, the role of an effective dynamical framework, and the conditions of positivity and causality. Our analysis excludes a variety of previously considered Lorentz-breaking parameters and opens an avenue for viable dispersion-relation investigations of Lorentz violation. |
1307.0594 | Sergey Kozyrev | Sergey N. Andrianov, Rinat A. Daishev, Sergey M. Kozyrev | Klein-Gordon equation for a particles in brane model | 8 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Brane model of universe is considered for a free particle. Conservation laws
on the brane are obtained using the symmetry properties of the brane. Equation
of motion is derived for a particle using variation principle from these
conservation laws. This equation has a form of Klein-Gordon equation.
Comparison of squared Dirac-Fok-Ivanenko equation for a spin particle with
Klein-Gordon equation in curved space has given an expression for chiral spin
current variation through the derivative of spin connectivity. This chiral spin
current is anomalous spin current corresponding to spontaneous chiral symmetry
breaking of massive particle in the space of KG equation solutions.
| [
{
"created": "Tue, 2 Jul 2013 06:13:11 GMT",
"version": "v1"
}
] | 2013-07-03 | [
[
"Andrianov",
"Sergey N.",
""
],
[
"Daishev",
"Rinat A.",
""
],
[
"Kozyrev",
"Sergey M.",
""
]
] | Brane model of universe is considered for a free particle. Conservation laws on the brane are obtained using the symmetry properties of the brane. Equation of motion is derived for a particle using variation principle from these conservation laws. This equation has a form of Klein-Gordon equation. Comparison of squared Dirac-Fok-Ivanenko equation for a spin particle with Klein-Gordon equation in curved space has given an expression for chiral spin current variation through the derivative of spin connectivity. This chiral spin current is anomalous spin current corresponding to spontaneous chiral symmetry breaking of massive particle in the space of KG equation solutions. |
2204.13161 | Alberto Escalante | Alberto Escalante and J. Aldair Pantoja-Gonzalez (Puebla U., Inst.
Fis.) | Canonical analysis for Chern-Simons modification of general relativity | null | null | 10.1016/j.aop.2023.169246 | null | gr-qc math-ph math.MP | http://creativecommons.org/publicdomain/zero/1.0/ | By using the Gitman-Lyakhovich-Tyutin canonical analysis for higher-order
theories a four-dimensional Chern-Simons modification of general relativity is
analyzed. The counting of physical degrees of freedom, the symmetries, and the
fundamental Dirac brackets are reported. Additionally, we report the complete
structure of the constraints and its Dirac algebra is developed.
| [
{
"created": "Wed, 27 Apr 2022 19:53:53 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Oct 2022 00:50:09 GMT",
"version": "v2"
},
{
"created": "Thu, 26 Jan 2023 00:44:04 GMT",
"version": "v3"
}
] | 2023-03-22 | [
[
"Escalante",
"Alberto",
"",
"Puebla U., Inst.\n Fis."
],
[
"Pantoja-Gonzalez",
"J. Aldair",
"",
"Puebla U., Inst.\n Fis."
]
] | By using the Gitman-Lyakhovich-Tyutin canonical analysis for higher-order theories a four-dimensional Chern-Simons modification of general relativity is analyzed. The counting of physical degrees of freedom, the symmetries, and the fundamental Dirac brackets are reported. Additionally, we report the complete structure of the constraints and its Dirac algebra is developed. |
1404.3144 | Everton Murilo Carvalho Abreu | Everton M. C. Abreu and N\'elio Sasaki | Rotating traversable wormholes in a noncommutative space and the energy
conditions | 10 pages. Pre-print format. arXiv admin note: substantial text
overlap with arXiv:1207.7130 | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is a very well known fact that the energy conditions concerning
traversable wormhole (WH) solutions of Einstein equations are violated.
Consequently, attempts to avoid the violation of the energy conditions
constitutes one of the main areas of research in WH physics. On the other hand,
the current literature shows us that noncommutativity is one of the most
promising candidates to help us to understand the physics of the early
Universe. However, since noncommutativity does not change the commutative
results, we also can expect that energy conditions violation near the throat
must occur. We will show here that the violation of the energy conditions,
described in a noncommutative space-time, has fixed conditions on the angular
momentum of a rotating WH with constant angular velocity. Also, we have
established a new theoretical bound on the NC constant, $\theta$, as a function
of some WH parameters.
| [
{
"created": "Wed, 9 Apr 2014 20:29:09 GMT",
"version": "v1"
}
] | 2014-04-14 | [
[
"Abreu",
"Everton M. C.",
""
],
[
"Sasaki",
"Nélio",
""
]
] | It is a very well known fact that the energy conditions concerning traversable wormhole (WH) solutions of Einstein equations are violated. Consequently, attempts to avoid the violation of the energy conditions constitutes one of the main areas of research in WH physics. On the other hand, the current literature shows us that noncommutativity is one of the most promising candidates to help us to understand the physics of the early Universe. However, since noncommutativity does not change the commutative results, we also can expect that energy conditions violation near the throat must occur. We will show here that the violation of the energy conditions, described in a noncommutative space-time, has fixed conditions on the angular momentum of a rotating WH with constant angular velocity. Also, we have established a new theoretical bound on the NC constant, $\theta$, as a function of some WH parameters. |
gr-qc/0006015 | Garcia | L.C.Garcia de Andrade | Extended Thermodynamics to Einstein-Cartan Cosmology | Latex file | null | null | null | gr-qc | null | The thermodynamics is extented to spacetimes with spin-torsion
density.Impplications to Einstein-Cartan-de Sitter inflationary phases are
discussed.A relation between the spin-torsion density,entropy and temperature
is presented.A lower limit for the radius of the Universe may be obtained from
the spin-torsion density and the Planck lenght.
| [
{
"created": "Sun, 4 Jun 2000 01:02:18 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"de Andrade",
"L. C. Garcia",
""
]
] | The thermodynamics is extented to spacetimes with spin-torsion density.Impplications to Einstein-Cartan-de Sitter inflationary phases are discussed.A relation between the spin-torsion density,entropy and temperature is presented.A lower limit for the radius of the Universe may be obtained from the spin-torsion density and the Planck lenght. |
gr-qc/0304067 | Roy Maartens | Burin Gumjudpai, Roy Maartens (Portsmouth), Christopher Gordon
(Cambridge) | Density perturbations in a brane-world universe with dark radiation | 10 pages, 4 figures | Class.Quant.Grav. 20 (2003) 3295 | 10.1088/0264-9381/20/15/302 | null | gr-qc astro-ph hep-th | null | We investigate the effects on cosmological density perturbations of dark
radiation in a Randall-Sundrum 2 type brane-world. Dark radiation in the
background is limited by observational constraints to be a small fraction of
the radiation energy density, but it has an interesting qualitative effect in
the radiation era. On large scales, it serves to slightly suppress the
radiation density perturbations at late times, while boosting the perturbations
in dark radiation. In a kinetic (stiff) era, the suppression is much stronger,
and drives the density perturbations to zero.
| [
{
"created": "Sat, 19 Apr 2003 11:23:52 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Gumjudpai",
"Burin",
"",
"Portsmouth"
],
[
"Maartens",
"Roy",
"",
"Portsmouth"
],
[
"Gordon",
"Christopher",
"",
"Cambridge"
]
] | We investigate the effects on cosmological density perturbations of dark radiation in a Randall-Sundrum 2 type brane-world. Dark radiation in the background is limited by observational constraints to be a small fraction of the radiation energy density, but it has an interesting qualitative effect in the radiation era. On large scales, it serves to slightly suppress the radiation density perturbations at late times, while boosting the perturbations in dark radiation. In a kinetic (stiff) era, the suppression is much stronger, and drives the density perturbations to zero. |
2111.13882 | Zhi-Chao Zhao | Zhi-Chao Zhao, Xiaolin Liu, Zhoujian Cao, and Xiaokai He | Gravitational wave memory of the binary black hole events in GWTC-2 | 10 pages, 11 figures | null | 10.1103/PhysRevD.104.064056 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Gravitational wave (GW) memory is an important prediction of general
relativity. Existing works on the GW memory detection focus on the waveform
analysis. It is hard for waveform analysis method to detect the GW memory due
to its quasi-direct current behavior and weakness. We implement a completely
different scheme in this work to estimate the GW memory. In this scheme, we
firstly apply the Bondi-Metzner-Sachs method to calculate the GW memory of
binary black hole based on numerical relativity simulation. Then we construct a
surrogate model to relate binary black hole's parameters and the GW memory.
Afterwards we apply this surrogate model together with Bayesian techniques to
estimate the GW memory of the 48 binary black hole events recorded in GWTC-2.
The GW memory corresponding to the all 48 events has been estimated. The most
interesting results are for GW190814. The corresponding GW memory is about
$-1\times10^{-23}$ and $1\times10^{-23}$ for Hanford detector and Livingston
detector respectively. At the same time we find with 3$\sigma$ C.L. that the
memory strain of GW190814 is negative on Hanford detector while positive on
Livingston detector.
| [
{
"created": "Sat, 27 Nov 2021 12:38:51 GMT",
"version": "v1"
}
] | 2021-11-30 | [
[
"Zhao",
"Zhi-Chao",
""
],
[
"Liu",
"Xiaolin",
""
],
[
"Cao",
"Zhoujian",
""
],
[
"He",
"Xiaokai",
""
]
] | Gravitational wave (GW) memory is an important prediction of general relativity. Existing works on the GW memory detection focus on the waveform analysis. It is hard for waveform analysis method to detect the GW memory due to its quasi-direct current behavior and weakness. We implement a completely different scheme in this work to estimate the GW memory. In this scheme, we firstly apply the Bondi-Metzner-Sachs method to calculate the GW memory of binary black hole based on numerical relativity simulation. Then we construct a surrogate model to relate binary black hole's parameters and the GW memory. Afterwards we apply this surrogate model together with Bayesian techniques to estimate the GW memory of the 48 binary black hole events recorded in GWTC-2. The GW memory corresponding to the all 48 events has been estimated. The most interesting results are for GW190814. The corresponding GW memory is about $-1\times10^{-23}$ and $1\times10^{-23}$ for Hanford detector and Livingston detector respectively. At the same time we find with 3$\sigma$ C.L. that the memory strain of GW190814 is negative on Hanford detector while positive on Livingston detector. |
2005.02225 | Alexander Zhidenko | R. A. Konoplya and A. Zhidenko | 4D Einstein-Lovelock black holes: Hierarchy of orders in curvature | 8 pages, 1 ancillary Mathematica(R) notebook | Phys. Lett. B807 (2020) 135607 | 10.1016/j.physletb.2020.135607 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Einstein-Lovelock theory contains an infinite series of corrections to
the Einstein term with an increasing power of the curvature. It is well-known
that for large black holes the lowest (Gauss-Bonnet) term is the dominant one,
while for smaller black holes higher curvature corrections become important. We
will show that if one is limited by positive values of the coupling constants,
then the dynamical instability of black holes serves as an effective cut-off of
influence of higher curvature corrections in the 4D Einstein-Lovelock approach:
the higher is the order of the Lovelock term, the smaller is the maximal value
of the coupling constant allowing for stability, so that effectively only a
first few orders can deform the observable values seemingly. For negative
values of coupling constants this is not so, and, despite some suppression of
higher order terms also occurs due to the decreasing threshold values of the
coupling constant, this does not lead to an noticeable opportunity to neglect
higher order corrections. In the case a lot of orders of Lovelock theory are
taken into account, so that the black-hole solution depends on a great number
of coupling constants, we propose a compact description of it in terms of only
two or three parameters encoding all the observable values.
| [
{
"created": "Sun, 3 May 2020 14:34:11 GMT",
"version": "v1"
},
{
"created": "Fri, 10 Jul 2020 15:45:26 GMT",
"version": "v2"
}
] | 2020-07-13 | [
[
"Konoplya",
"R. A.",
""
],
[
"Zhidenko",
"A.",
""
]
] | The Einstein-Lovelock theory contains an infinite series of corrections to the Einstein term with an increasing power of the curvature. It is well-known that for large black holes the lowest (Gauss-Bonnet) term is the dominant one, while for smaller black holes higher curvature corrections become important. We will show that if one is limited by positive values of the coupling constants, then the dynamical instability of black holes serves as an effective cut-off of influence of higher curvature corrections in the 4D Einstein-Lovelock approach: the higher is the order of the Lovelock term, the smaller is the maximal value of the coupling constant allowing for stability, so that effectively only a first few orders can deform the observable values seemingly. For negative values of coupling constants this is not so, and, despite some suppression of higher order terms also occurs due to the decreasing threshold values of the coupling constant, this does not lead to an noticeable opportunity to neglect higher order corrections. In the case a lot of orders of Lovelock theory are taken into account, so that the black-hole solution depends on a great number of coupling constants, we propose a compact description of it in terms of only two or three parameters encoding all the observable values. |
2310.09464 | Emanuel Costa | Emanuel Wallison de Oliveira Costa, Raheleh Jalalzadeh, Pedro Felix da
Silva J\'unior, Seyed Meraj Mousavi Rasouli, and Shahram Jalalzadeh | Estimated Age of the Universe in Fractional Cosmology | 24 pages, 9 figures | Fractal Fract. 7 (2023) 854 | 10.3390/fractalfract7120854 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Our proposed cosmological framework, which is based on fractional quantum
cosmology, aims to address the issue of synchronicity in the age of the
universe. To achieve this, we have developed a new fractional $\Lambda$CDM
cosmological model. We obtained the necessary formalism by obtaining the
fractional Hamiltonian constraint in a general minisuperspace. This formalism
has allowed us to derive the fractional Friedmann and Raychaudhuri equations
for a homogeneous and isotropic cosmology. Unlike the traditional de Sitter
phase, our model exhibits a power-law accelerated expansion in the late-time
universe, when vacuum energy becomes dominant. By fitting the model's
parameters to cosmological observations, we determined that the fractional
parameter of L\'{e}vy equals $\alpha=1.986$. Additionally, we have calculated
the age of the universe to be 13.8196 Gyr. Furthermore, we have found that the
ratio of the age to Hubble time from the present epoch to the distant future is
finite and confined within the interval $0.9858\leq Ht<95.238$.
| [
{
"created": "Sat, 14 Oct 2023 01:30:15 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Nov 2023 16:58:07 GMT",
"version": "v2"
},
{
"created": "Mon, 5 Aug 2024 18:05:01 GMT",
"version": "v3"
}
] | 2024-08-07 | [
[
"Costa",
"Emanuel Wallison de Oliveira",
""
],
[
"Jalalzadeh",
"Raheleh",
""
],
[
"Júnior",
"Pedro Felix da Silva",
""
],
[
"Rasouli",
"Seyed Meraj Mousavi",
""
],
[
"Jalalzadeh",
"Shahram",
""
]
] | Our proposed cosmological framework, which is based on fractional quantum cosmology, aims to address the issue of synchronicity in the age of the universe. To achieve this, we have developed a new fractional $\Lambda$CDM cosmological model. We obtained the necessary formalism by obtaining the fractional Hamiltonian constraint in a general minisuperspace. This formalism has allowed us to derive the fractional Friedmann and Raychaudhuri equations for a homogeneous and isotropic cosmology. Unlike the traditional de Sitter phase, our model exhibits a power-law accelerated expansion in the late-time universe, when vacuum energy becomes dominant. By fitting the model's parameters to cosmological observations, we determined that the fractional parameter of L\'{e}vy equals $\alpha=1.986$. Additionally, we have calculated the age of the universe to be 13.8196 Gyr. Furthermore, we have found that the ratio of the age to Hubble time from the present epoch to the distant future is finite and confined within the interval $0.9858\leq Ht<95.238$. |
1911.05311 | Mandar Patil | Harsha Miriam Reji, Mandar Patil | Gravitational lensing signature of matter distribution around
Schwarzschild black hole | 42 pages, 7 figures, published in PRD | Phys. Rev. D 101, 064051 (2020) | 10.1103/PhysRevD.101.064051 | null | gr-qc astro-ph.GA hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we focus on the situation where a significant amount of matter
could be located close to the event horizon of the central black hole and how
it affects the gravitational lensing signal. We consider a simple toy model
where the matter is concentrated in the rather small region between the inner
photon sphere associated with the mass of central black hole and outer photon
sphere associated with the total mass outside. If no photon sphere is present
inside the matter distribution, then effective potential displays an
interesting trend with maxima at inner and outer photon sphere, with a peak at
inner photon sphere higher than that at outer photon sphere. In such a case we
get three distinct set of infinitely many relativistic images and Einstein
rings that occur due to the light rays that approach the black hole from a
distant source and get reflected just outside the outer photon sphere, due to
light rays that enter the outer photon sphere slightly above the outer peak and
get reflected off the potential barrier inside the matter distribution and due
to the light rays that get reflected just outside the inner photon sphere. This
kind of pattern of images is quite unprecedented. We show that since
relativistic images are highly demagnified, only three images are prominently
visible from the point of observations in the presence of matter as opposed to
only one prominent image in case of a single isolated black hole and also
compute the time delay between them. This provides a smoking gun signature of
the presence of matter lump around the black hole. We further argue that if the
mass of the black hole inferred from the observation of the size of its shadow
is less than the mass inferred from the motion of objects around it, it signals
the presence of matter in the vicinity of the black hole.
| [
{
"created": "Wed, 13 Nov 2019 06:11:00 GMT",
"version": "v1"
},
{
"created": "Sat, 16 Nov 2019 05:01:39 GMT",
"version": "v2"
},
{
"created": "Wed, 26 Feb 2020 09:06:45 GMT",
"version": "v3"
},
{
"created": "Mon, 27 Apr 2020 15:21:43 GMT",
"version": "v4"
}
] | 2020-04-28 | [
[
"Reji",
"Harsha Miriam",
""
],
[
"Patil",
"Mandar",
""
]
] | In this work, we focus on the situation where a significant amount of matter could be located close to the event horizon of the central black hole and how it affects the gravitational lensing signal. We consider a simple toy model where the matter is concentrated in the rather small region between the inner photon sphere associated with the mass of central black hole and outer photon sphere associated with the total mass outside. If no photon sphere is present inside the matter distribution, then effective potential displays an interesting trend with maxima at inner and outer photon sphere, with a peak at inner photon sphere higher than that at outer photon sphere. In such a case we get three distinct set of infinitely many relativistic images and Einstein rings that occur due to the light rays that approach the black hole from a distant source and get reflected just outside the outer photon sphere, due to light rays that enter the outer photon sphere slightly above the outer peak and get reflected off the potential barrier inside the matter distribution and due to the light rays that get reflected just outside the inner photon sphere. This kind of pattern of images is quite unprecedented. We show that since relativistic images are highly demagnified, only three images are prominently visible from the point of observations in the presence of matter as opposed to only one prominent image in case of a single isolated black hole and also compute the time delay between them. This provides a smoking gun signature of the presence of matter lump around the black hole. We further argue that if the mass of the black hole inferred from the observation of the size of its shadow is less than the mass inferred from the motion of objects around it, it signals the presence of matter in the vicinity of the black hole. |
2006.10614 | Gabriele Barca | Eleonora Giovannetti, Gabriele Barca, Federico Mandini, Giovanni
Montani | Polymer dynamics of isotropic universe in Ashtekar and in volume
variables | 16 pages, 6 figures | null | 10.3390/universe8060302 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We analyze the semiclassical and quantum polymer dynamics of the isotropic
Universe in terms of both the standard Ashtekar-Barbero-Immirzi connection and
its conjugate momentum and also of the new generalized coordinate conjugate to
the Universe volume. We study the properties of the resulting bouncing
cosmology that emerges in both the representations and we show that the Big
Bounce is an intrinsic cut-off on the cosmological dynamics only when the
volume variable is implemented, while in terms of the standard connection the
Universe Bounce energy density is fixed by the initial conditions on the
prepared wavepacket. As a phenomenological implication, we introduce particle
creation as a dissipative term and study the production of entropy in the two
formulations. Then, we compare the obtained dynamics with what emerges in Loop
Quantum Cosmology, where the same difference in the nature of the Big Bounce is
associated to fixing a minimum area eigenvalue in a comoving or in a physical
representation. We conclude that the privileged character of the
Ashtekar-Barbero-Immirzi connection suggests that the natural scenario in the
polymer framework is a Big Bounce that is not a Universal cut-off. However, by
a parallelism between the polymer and Loop Quantum Cosmology properties of the
basic operators, we also develop some considerations in favour of the viability
of the $\bar{\mu}$ scheme of Loop Quantum Cosmology on a semiclassical level.
| [
{
"created": "Thu, 18 Jun 2020 15:35:20 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Aug 2020 12:16:10 GMT",
"version": "v2"
},
{
"created": "Tue, 16 Mar 2021 13:03:01 GMT",
"version": "v3"
},
{
"created": "Tue, 22 Jun 2021 13:14:11 GMT",
"version": "v4"
},
{
"created": "Wed, 30 Jun 2021 12:50:18 GMT",
"version": "v5"
},
{
"created": "Wed, 7 Jul 2021 10:34:53 GMT",
"version": "v6"
},
{
"created": "Tue, 31 May 2022 13:49:57 GMT",
"version": "v7"
}
] | 2022-06-01 | [
[
"Giovannetti",
"Eleonora",
""
],
[
"Barca",
"Gabriele",
""
],
[
"Mandini",
"Federico",
""
],
[
"Montani",
"Giovanni",
""
]
] | We analyze the semiclassical and quantum polymer dynamics of the isotropic Universe in terms of both the standard Ashtekar-Barbero-Immirzi connection and its conjugate momentum and also of the new generalized coordinate conjugate to the Universe volume. We study the properties of the resulting bouncing cosmology that emerges in both the representations and we show that the Big Bounce is an intrinsic cut-off on the cosmological dynamics only when the volume variable is implemented, while in terms of the standard connection the Universe Bounce energy density is fixed by the initial conditions on the prepared wavepacket. As a phenomenological implication, we introduce particle creation as a dissipative term and study the production of entropy in the two formulations. Then, we compare the obtained dynamics with what emerges in Loop Quantum Cosmology, where the same difference in the nature of the Big Bounce is associated to fixing a minimum area eigenvalue in a comoving or in a physical representation. We conclude that the privileged character of the Ashtekar-Barbero-Immirzi connection suggests that the natural scenario in the polymer framework is a Big Bounce that is not a Universal cut-off. However, by a parallelism between the polymer and Loop Quantum Cosmology properties of the basic operators, we also develop some considerations in favour of the viability of the $\bar{\mu}$ scheme of Loop Quantum Cosmology on a semiclassical level. |
gr-qc/0504087 | Elizabeth Winstanley | Anne-Marie Barlow, Daniel Doherty and Elizabeth Winstanley | Thermodynamics of de Sitter black holes with a conformally coupled
scalar field | 9 pages, 2 figures, REVTEX. Minor changes, accepted for publication
in Phys. Rev. D | Phys.Rev.D72:024008,2005 | 10.1103/PhysRevD.72.024008 | null | gr-qc hep-th | null | We study the thermodynamics of de Sitter black holes with a conformally
coupled scalar field. The geometry is that of the ``lukewarm''
Reissner-Nordstrom-de Sitter black holes, with the event and cosmological
horizons at the same temperature. This means that the region between the event
and cosmological horizons can form a regular Euclidean instanton. The entropy
is modified by the non-minimal coupling of the scalar field to the geometry,
but can still be derived from the Euclidean action, provided suitable
modifications are made to deal with the electrically charged case. We use the
first law as derived from the isolated horizons formalism to compute the local
horizon energies for the event and cosmological horizons.
| [
{
"created": "Tue, 19 Apr 2005 18:31:41 GMT",
"version": "v1"
},
{
"created": "Wed, 29 Jun 2005 09:43:36 GMT",
"version": "v2"
}
] | 2011-07-19 | [
[
"Barlow",
"Anne-Marie",
""
],
[
"Doherty",
"Daniel",
""
],
[
"Winstanley",
"Elizabeth",
""
]
] | We study the thermodynamics of de Sitter black holes with a conformally coupled scalar field. The geometry is that of the ``lukewarm'' Reissner-Nordstrom-de Sitter black holes, with the event and cosmological horizons at the same temperature. This means that the region between the event and cosmological horizons can form a regular Euclidean instanton. The entropy is modified by the non-minimal coupling of the scalar field to the geometry, but can still be derived from the Euclidean action, provided suitable modifications are made to deal with the electrically charged case. We use the first law as derived from the isolated horizons formalism to compute the local horizon energies for the event and cosmological horizons. |
2302.03846 | Xi-Long Fan | Yang Jiang, Xi-Long Fan and Qing-Guo Huang | Search for stochastic gravitational-wave background from string
cosmology with Advanced LIGO and Virgo's O1$\sim$O3 data | Accepted by Journal of Cosmology and Astroparticle Physics | null | 10.1088/1475-7516/2023/04/024 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | String cosmology models predict a relic background of gravitational-wave (GW)
radiation in the early universe. The GW energy spectrum of radiated power
increases rapidly with the frequency, and therefore it becomes a potential and
meaningful observation object for high-frequency GW detector. We focus on the
stochastic background generated by superinflation in string theory and search
for such signal in the observing data of Advanced LIGO and Virgo O1$\sim$O3
runs in a Bayesian framework. We do not find the existence of the signal, and
thus put constraints on the GW energy density. Our results indicate that at
$f=100\,\text{Hz}$, the fractional energy density of GW background is less than
$1.7\times10^{-8}$ and $2.1\times10^{-8}$ for dilaton-string and dilaton only
cases respectively, and further rule out the parameter space restricted by the
model itself due to the non-decreasing dilaton and stable cosmology background
($\beta$ bound).
| [
{
"created": "Wed, 8 Feb 2023 02:41:31 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Apr 2023 05:39:34 GMT",
"version": "v2"
}
] | 2023-04-19 | [
[
"Jiang",
"Yang",
""
],
[
"Fan",
"Xi-Long",
""
],
[
"Huang",
"Qing-Guo",
""
]
] | String cosmology models predict a relic background of gravitational-wave (GW) radiation in the early universe. The GW energy spectrum of radiated power increases rapidly with the frequency, and therefore it becomes a potential and meaningful observation object for high-frequency GW detector. We focus on the stochastic background generated by superinflation in string theory and search for such signal in the observing data of Advanced LIGO and Virgo O1$\sim$O3 runs in a Bayesian framework. We do not find the existence of the signal, and thus put constraints on the GW energy density. Our results indicate that at $f=100\,\text{Hz}$, the fractional energy density of GW background is less than $1.7\times10^{-8}$ and $2.1\times10^{-8}$ for dilaton-string and dilaton only cases respectively, and further rule out the parameter space restricted by the model itself due to the non-decreasing dilaton and stable cosmology background ($\beta$ bound). |
gr-qc/0605041 | James Lindesay | James Lindesay | Thermal Evolution of a Dual Scale Cosmology | 8 pages | null | null | null | gr-qc | null | Previous work developed a space-time metric with two cosmological scales; one
that conveniently describes the classical evolution of the dynamics, and the
other describing a scale associated with macroscopic quantum aspects like
vacuum energy. The present work expands upon the dynamics of these scales to
demonstrate the usefulness of these coordinates for describing early and late
time behaviors of our universe. A convenient parameter, the fraction of
classical energy density, is introduced as a means to parameterize the various
early time models for the microscopic input.
| [
{
"created": "Sun, 7 May 2006 20:33:41 GMT",
"version": "v1"
},
{
"created": "Tue, 9 May 2006 02:31:30 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Lindesay",
"James",
""
]
] | Previous work developed a space-time metric with two cosmological scales; one that conveniently describes the classical evolution of the dynamics, and the other describing a scale associated with macroscopic quantum aspects like vacuum energy. The present work expands upon the dynamics of these scales to demonstrate the usefulness of these coordinates for describing early and late time behaviors of our universe. A convenient parameter, the fraction of classical energy density, is introduced as a means to parameterize the various early time models for the microscopic input. |
2408.00832 | James Alvey | James Alvey, Uddipta Bhardwaj, Valerie Domcke, Mauro Pieroni and
Christoph Weniger | Leveraging Time-Dependent Instrumental Noise for LISA SGWB Analysis | 12 pages, 5 figures. saqqara available at
https://github.com/peregrine-gw/saqqara, GW_response available at
https://github.com/Mauropieroni/GW_response | null | null | CERN-TH-2024-127 | gr-qc astro-ph.CO astro-ph.IM hep-ph | http://creativecommons.org/licenses/by/4.0/ | Variations in the instrumental noise of the Laser Interferometer Space
Antenna (LISA) over time are expected as a result of e.g. scheduled satellite
operations or unscheduled glitches. We demonstrate that these fluctuations can
be leveraged to improve the sensitivity to stochastic gravitational wave
backgrounds (SGWBs) compared to the stationary noise scenario. This requires
optimal use of data segments with downward noise fluctuations, and thus a data
analysis pipeline capable of analysing and combining shorter time segments of
mission data. We propose that simulation based inference is well suited for
this challenge. In an approximate, but state-of-the-art, modeling setup, we
show by comparison with Fisher Information Matrix estimates that the optimal
information gain can be achieved in practice.
| [
{
"created": "Thu, 1 Aug 2024 18:00:01 GMT",
"version": "v1"
}
] | 2024-08-05 | [
[
"Alvey",
"James",
""
],
[
"Bhardwaj",
"Uddipta",
""
],
[
"Domcke",
"Valerie",
""
],
[
"Pieroni",
"Mauro",
""
],
[
"Weniger",
"Christoph",
""
]
] | Variations in the instrumental noise of the Laser Interferometer Space Antenna (LISA) over time are expected as a result of e.g. scheduled satellite operations or unscheduled glitches. We demonstrate that these fluctuations can be leveraged to improve the sensitivity to stochastic gravitational wave backgrounds (SGWBs) compared to the stationary noise scenario. This requires optimal use of data segments with downward noise fluctuations, and thus a data analysis pipeline capable of analysing and combining shorter time segments of mission data. We propose that simulation based inference is well suited for this challenge. In an approximate, but state-of-the-art, modeling setup, we show by comparison with Fisher Information Matrix estimates that the optimal information gain can be achieved in practice. |
1109.5837 | Naiereh Elyasi | Naiereh Elyasi and Nasser Boroojerdian | Application of Lie algebroid structures to unification of Einstein and
yang-mills field equations | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Yang-mills field equations describe new forces in the context of Lie groups
and principle bundles. It is of interest to know if the new forces and
gravitation can be described in the context of algebroids. This work was
intended as an attempt to answer last question. The basic idea is to construct
Einstein field equation in an algebroid bundle associated to space-time
manifold. This equation contains Einstein and yang-mills field equations
simultaneously. Also this equation yields a new equation that can have
interesting experimental results.
| [
{
"created": "Tue, 27 Sep 2011 11:10:42 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Oct 2011 07:00:04 GMT",
"version": "v2"
}
] | 2011-10-05 | [
[
"Elyasi",
"Naiereh",
""
],
[
"Boroojerdian",
"Nasser",
""
]
] | Yang-mills field equations describe new forces in the context of Lie groups and principle bundles. It is of interest to know if the new forces and gravitation can be described in the context of algebroids. This work was intended as an attempt to answer last question. The basic idea is to construct Einstein field equation in an algebroid bundle associated to space-time manifold. This equation contains Einstein and yang-mills field equations simultaneously. Also this equation yields a new equation that can have interesting experimental results. |
1208.3731 | Valerio Faraoni | Valerio Faraoni and Andres F. Zambrano Moreno (Bishop's University) | Interpreting the conformal cousin of the Husain-Martinez-Nunez solution | 7 pages, 2 figures. Removed a subsection which referred to an empty
subclass of solutions, added discussion, a special (static) case, and
references | null | 10.1103/PhysRevD.86.084044 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A 2-parameter inhomogeneous cosmology in Brans-Dicke theory, obtained by
conformally transforming the Husain-Martinez-Nunez (HMN) scalar field solution
of the Einstein equations is studied and interpreted physically. According to
the values of the parameters it describes a wormhole, a naked singularity, or
else a spacetime containing apparent black hole horizons which appear/disappear
in pairs (as well as a cosmological horizon) as in the original HMN metric. The
reasons why there isn't a one-to-one correspondence between conformal copies of
this metric are discussed.
| [
{
"created": "Sat, 18 Aug 2012 08:49:48 GMT",
"version": "v1"
},
{
"created": "Wed, 3 Oct 2012 22:51:47 GMT",
"version": "v2"
}
] | 2013-05-30 | [
[
"Faraoni",
"Valerio",
"",
"Bishop's University"
],
[
"Moreno",
"Andres F. Zambrano",
"",
"Bishop's University"
]
] | A 2-parameter inhomogeneous cosmology in Brans-Dicke theory, obtained by conformally transforming the Husain-Martinez-Nunez (HMN) scalar field solution of the Einstein equations is studied and interpreted physically. According to the values of the parameters it describes a wormhole, a naked singularity, or else a spacetime containing apparent black hole horizons which appear/disappear in pairs (as well as a cosmological horizon) as in the original HMN metric. The reasons why there isn't a one-to-one correspondence between conformal copies of this metric are discussed. |
1305.5512 | Farkhat Zaripov Shaukatovich | Farkhat Zaripov | Modified equations in the theory of induced gravity. Solution to the
cosmological constant problem | 21 pages, 13 Postscript figures | Astrophysics and Space Science : Volume 352, Issue 1 (2014), Page
289-305 | 10.1007/s10509-014-1909-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This research is an extension of the author's article \cite{zar}, in which
conformally invariant generalization of string theory was suggested to
higher-dimensional objects. Special cases of the proposed theory are Einstein's
theory of gravity and string theory. This work is devoted to the formation of
self-consistent equations of the theory of induced gravity \cite{zar},
\cite{zari} in the presence of matter in the form of a perfect fluid that
interacts with scalar fields. The study is done to solve these equations for
the case of the cosmological model. In this model time-evolving gravitational
and cosmological "constants" take place which are determined by the square of
scalar fields. The values of which can be matched with the observational data.
The equations that describe the theory have solutions that can both match with
the solutions of the standard theory of gravity as well as it can differ from
it. This is due to the fact that the fundamental "constants" of the theory,
such as gravitational and cosmological, can evolve over time and also depend of
the coordinates. Thus, in a rather general case the theory describes the two
systems (stages): Einstein and "evolving" or "restructuring" (the name
suggested by the author). This process is similar to the phenomenon of phase
transition, where the different phases (Einstein gravity system, but with
different constants) transit into each other.
| [
{
"created": "Thu, 23 May 2013 18:36:58 GMT",
"version": "v1"
},
{
"created": "Fri, 10 Oct 2014 15:30:00 GMT",
"version": "v2"
}
] | 2014-10-13 | [
[
"Zaripov",
"Farkhat",
""
]
] | This research is an extension of the author's article \cite{zar}, in which conformally invariant generalization of string theory was suggested to higher-dimensional objects. Special cases of the proposed theory are Einstein's theory of gravity and string theory. This work is devoted to the formation of self-consistent equations of the theory of induced gravity \cite{zar}, \cite{zari} in the presence of matter in the form of a perfect fluid that interacts with scalar fields. The study is done to solve these equations for the case of the cosmological model. In this model time-evolving gravitational and cosmological "constants" take place which are determined by the square of scalar fields. The values of which can be matched with the observational data. The equations that describe the theory have solutions that can both match with the solutions of the standard theory of gravity as well as it can differ from it. This is due to the fact that the fundamental "constants" of the theory, such as gravitational and cosmological, can evolve over time and also depend of the coordinates. Thus, in a rather general case the theory describes the two systems (stages): Einstein and "evolving" or "restructuring" (the name suggested by the author). This process is similar to the phenomenon of phase transition, where the different phases (Einstein gravity system, but with different constants) transit into each other. |
2401.09818 | Lang Liu | Zu-Cheng Chen, Jun Li, Lang Liu and Zhu Yi | Probing the speed of scalar-induced gravitational waves with pulsar
timing arrays | 8 pages, 2 figures | Phys. Rev. D 109, L101302 (2024) | 10.1103/PhysRevD.109.L101302 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, several regional pulsar timing array collaborations, including
CPTA, EPTA, PPTA, and NANOGrav, have individually reported compelling evidence
for a stochastic signal at nanohertz frequencies. This signal originates
potentially from scalar-induced gravitational waves associated with significant
primordial curvature perturbations on small scales. In this letter, we employ
data from the EPTA DR2, PPTA DR3, and NANOGrav 15-year data set, to explore the
speed of scalar-induced gravitational waves using a comprehensive Bayesian
analysis. Our results suggest that, to be consistent with pulsar timing array
observations, the speed of scalar-induced gravitational waves should be $c_g
\gtrsim 0.61$ at a $95\%$ credible interval for a lognormal power spectrum of
curvature perturbations. Additionally, this constraint aligns with the
prediction of general relativity that $c_g=1$ within a $90\%$ credible
interval. Our findings underscore the capacity of pulsar timing arrays as a
powerful tool for probing the speed of scalar-induced gravitational waves.
| [
{
"created": "Thu, 18 Jan 2024 09:19:53 GMT",
"version": "v1"
},
{
"created": "Fri, 10 May 2024 15:14:41 GMT",
"version": "v2"
}
] | 2024-05-13 | [
[
"Chen",
"Zu-Cheng",
""
],
[
"Li",
"Jun",
""
],
[
"Liu",
"Lang",
""
],
[
"Yi",
"Zhu",
""
]
] | Recently, several regional pulsar timing array collaborations, including CPTA, EPTA, PPTA, and NANOGrav, have individually reported compelling evidence for a stochastic signal at nanohertz frequencies. This signal originates potentially from scalar-induced gravitational waves associated with significant primordial curvature perturbations on small scales. In this letter, we employ data from the EPTA DR2, PPTA DR3, and NANOGrav 15-year data set, to explore the speed of scalar-induced gravitational waves using a comprehensive Bayesian analysis. Our results suggest that, to be consistent with pulsar timing array observations, the speed of scalar-induced gravitational waves should be $c_g \gtrsim 0.61$ at a $95\%$ credible interval for a lognormal power spectrum of curvature perturbations. Additionally, this constraint aligns with the prediction of general relativity that $c_g=1$ within a $90\%$ credible interval. Our findings underscore the capacity of pulsar timing arrays as a powerful tool for probing the speed of scalar-induced gravitational waves. |
gr-qc/9404010 | Lee Smolin | Lee Smolin | Fermions and Topology | LATEX, 17 pages, no figures, CGPG-93/9-4 | null | null | null | gr-qc | null | The canonical theory of quantum gravity in the loop representation can be
extended to incorporate topology change, in the simple case that this refers to
the creation or annihilation of "minimalist wormholes" in which two points of
the spatial manifold are identified. Furthermore, if the states of the
wormholes threaded by loop states are taken to be antisymmetrized under the
permutation of wormhole mouths, as required by the relation between spin and
statistics, then the quantum theory of pure general relativity, without matter
but with minimalist wormholes, is shown to be equivalent to the quantum theory
of general relativity coupled to a single Weyl fermion field, at both the
kinematical and diffeomorphism invariant levels. The correspondence is also
shown to extend to the action of the dynamics generated by the Hamiltonian
constraint, on a large subspace of the physical state space, and is thus
conjectured to be completely general.
| [
{
"created": "Thu, 7 Apr 1994 22:23:40 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Smolin",
"Lee",
""
]
] | The canonical theory of quantum gravity in the loop representation can be extended to incorporate topology change, in the simple case that this refers to the creation or annihilation of "minimalist wormholes" in which two points of the spatial manifold are identified. Furthermore, if the states of the wormholes threaded by loop states are taken to be antisymmetrized under the permutation of wormhole mouths, as required by the relation between spin and statistics, then the quantum theory of pure general relativity, without matter but with minimalist wormholes, is shown to be equivalent to the quantum theory of general relativity coupled to a single Weyl fermion field, at both the kinematical and diffeomorphism invariant levels. The correspondence is also shown to extend to the action of the dynamics generated by the Hamiltonian constraint, on a large subspace of the physical state space, and is thus conjectured to be completely general. |
2011.06792 | Jun-Qi Guo | Jun-Qi Guo, Lin Zhang, Yuewen Chen, Pankaj S. Joshi, Hongsheng Zhang | Strength of the naked singularity in critical collapse | 5 pages, 3 figures | Eur. Phys. J. C 80, 924 (2020) | 10.1140/epjc/s10052-020-08486-7 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The critical collapse of a scalar field is a threshold solution of black hole
formation, in which a naked singularity arises. We study here the curvature
strength of this singularity using a numerical ansatz. The behavior of the
Jacobi volume forms is examined along a non-spacelike geodesic in the limit of
approach to the singularity. These are seen to be vanishing, thus showing that
all physical objects will be crushed to zero size near the singularity.
Consequently, although the critical collapse is considered to be a fine-tuning
problem, the naked singularity forming is gravitationally strong. This implies
that the spacetime cannot be extended beyond the singularity, thus making the
singularity genuine and physically interesting. These results imply that the
nature of critical collapse may need to be examined and explored further.
| [
{
"created": "Fri, 13 Nov 2020 07:17:02 GMT",
"version": "v1"
}
] | 2020-11-16 | [
[
"Guo",
"Jun-Qi",
""
],
[
"Zhang",
"Lin",
""
],
[
"Chen",
"Yuewen",
""
],
[
"Joshi",
"Pankaj S.",
""
],
[
"Zhang",
"Hongsheng",
""
]
] | The critical collapse of a scalar field is a threshold solution of black hole formation, in which a naked singularity arises. We study here the curvature strength of this singularity using a numerical ansatz. The behavior of the Jacobi volume forms is examined along a non-spacelike geodesic in the limit of approach to the singularity. These are seen to be vanishing, thus showing that all physical objects will be crushed to zero size near the singularity. Consequently, although the critical collapse is considered to be a fine-tuning problem, the naked singularity forming is gravitationally strong. This implies that the spacetime cannot be extended beyond the singularity, thus making the singularity genuine and physically interesting. These results imply that the nature of critical collapse may need to be examined and explored further. |
0807.4874 | Martin Bojowald | Martin Bojowald | Canonical Relativity and the Dimensionality of the World | 17 pages, 2 figures; Chapter in: Relativity and the Dimensionality of
the World, Ed. V. Petkov (Springer, 2007), pp. 137-152 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Different aspects of relativity, mainly in a canonical formulation, relevant
for the question "Is spacetime nothing more than a mathematical space (which
describes the evolution in time of the ordinary three-dimensional world) or is
it a mathematical model of a real four-dimensional world with time entirely
given as the fourth dimension?" are presented. The availability as well as
clarity of the arguments depend on which framework is being used, for which
currently special relativity, general relativity and some schemes of quantum
gravity are available. Canonical gravity provides means to analyze the field
equations as well as observable quantities, the latter even in coordinate
independent form. This allows a unique perspective on the question of
dimensionality since the space-time manifold does not play a prominent role.
After re-introducing a Minkowski background into the formalism, one can see how
distinguished coordinates of special relativity arise, where also the nature of
time is different from that in the general perspective. Just as it is of
advantage to extend special to general relativity, general relativity itself
has to be extended to some theory of quantum gravity. This suggests that a
final answer has to await a thorough formulation and understanding of a
fundamental theory of space-time. Nevertheless, we argue that current insights
into quantum gravity do not change the picture of the role of time obtained
from general relativity.
| [
{
"created": "Wed, 30 Jul 2008 14:44:19 GMT",
"version": "v1"
}
] | 2008-07-31 | [
[
"Bojowald",
"Martin",
""
]
] | Different aspects of relativity, mainly in a canonical formulation, relevant for the question "Is spacetime nothing more than a mathematical space (which describes the evolution in time of the ordinary three-dimensional world) or is it a mathematical model of a real four-dimensional world with time entirely given as the fourth dimension?" are presented. The availability as well as clarity of the arguments depend on which framework is being used, for which currently special relativity, general relativity and some schemes of quantum gravity are available. Canonical gravity provides means to analyze the field equations as well as observable quantities, the latter even in coordinate independent form. This allows a unique perspective on the question of dimensionality since the space-time manifold does not play a prominent role. After re-introducing a Minkowski background into the formalism, one can see how distinguished coordinates of special relativity arise, where also the nature of time is different from that in the general perspective. Just as it is of advantage to extend special to general relativity, general relativity itself has to be extended to some theory of quantum gravity. This suggests that a final answer has to await a thorough formulation and understanding of a fundamental theory of space-time. Nevertheless, we argue that current insights into quantum gravity do not change the picture of the role of time obtained from general relativity. |
1902.06748 | Nuno M. Santos | Carlos A. R. Herdeiro, Nuno M. Santos | Exotic compact object behavior in black hole analogues | 12 pages, 6 figures. Accepted for publication as a Regular Article in
Physical Review D | Phys. Rev. D 99, 084029 (2019) | 10.1103/PhysRevD.99.084029 | null | gr-qc astro-ph.HE hep-ph hep-th physics.flu-dyn | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Classical phenomenological aspects of acoustic perturbations on a draining
bathtub geometry where a surface with reflectivity $\mathcal{R}$ is set at a
small distance from the would-be acoustic horizon, which is excised, are
addressed. Like most exotic compact objects featuring an ergoregion but not a
horizon, this model is prone to instabilities when $|\mathcal{R}|^2\approx 1$.
However, stability can be attained for sufficiently slow drains when
$|\mathcal{R}|^2\lesssim70\%$. It is shown that the superradiant scattering of
acoustic waves is more effective when their frequency approaches one of the
system's quasi-normal mode frequencies.
| [
{
"created": "Mon, 18 Feb 2019 19:00:01 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Apr 2019 21:42:09 GMT",
"version": "v2"
}
] | 2019-04-17 | [
[
"Herdeiro",
"Carlos A. R.",
""
],
[
"Santos",
"Nuno M.",
""
]
] | Classical phenomenological aspects of acoustic perturbations on a draining bathtub geometry where a surface with reflectivity $\mathcal{R}$ is set at a small distance from the would-be acoustic horizon, which is excised, are addressed. Like most exotic compact objects featuring an ergoregion but not a horizon, this model is prone to instabilities when $|\mathcal{R}|^2\approx 1$. However, stability can be attained for sufficiently slow drains when $|\mathcal{R}|^2\lesssim70\%$. It is shown that the superradiant scattering of acoustic waves is more effective when their frequency approaches one of the system's quasi-normal mode frequencies. |
gr-qc/0011088 | Victor K. Shchigolev | V.K.Shchigolev, M.V.Shchigolev | Cosmological Models with Nonlinearity of Scalar Field Induced by
Yang-Mills Field | 9 pages, LaTeX | Grav.Cosmol. 7 (2001) 219-222 | null | null | gr-qc | null | The exact solutions of Einstein - Yang - Mills and interacting with SO (3) -
Yang-Mills field nonlinear scalar field equations in a class of spatially
homogeneous cosmological Friedmann models are obtained.
| [
{
"created": "Fri, 24 Nov 2000 14:58:31 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Shchigolev",
"V. K.",
""
],
[
"Shchigolev",
"M. V.",
""
]
] | The exact solutions of Einstein - Yang - Mills and interacting with SO (3) - Yang-Mills field nonlinear scalar field equations in a class of spatially homogeneous cosmological Friedmann models are obtained. |
1801.07195 | Alexander Zhidenko | R. A. Konoplya, Z. Stuchl\'ik, A. Zhidenko | Axisymmetric black holes allowing for separation of variables in the
Klein-Gordon and Hamilton-Jacobi equation | 14 pages | Phys. Rev. D 97, 084044 (2018) | 10.1103/PhysRevD.97.084044 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We determine the class of axisymmetric and asymptotically flat black-hole
spacetimes for which the test Klein-Gordon and Hamilton-Jacobi equations allow
for the separation of variables. The known Kerr, Kerr-Newman, Kerr-Sen and some
other black-hole metrics in various theories of gravity are within the class of
spacetimes described here. It is shown that although the black-hole metric in
the Einstein-dilaton-Gauss-Bonnet theory does not allow for the separation of
variables (at least in the considered coordinates), for a number of
applications it can be effectively approximated by a metric within the above
class. This gives us some hope that the class of spacetimes described here may
be not only generic for the known solutions allowing for the separation of
variables, but also a good approximation for a broader class of metrics, which
does not admit such separation. Finally, the generic form of the axisymmetric
metric is expanded in the radial direction in terms of the continued fractions
and the connection with other black-hole parametrizations is discussed.
| [
{
"created": "Mon, 22 Jan 2018 17:05:34 GMT",
"version": "v1"
},
{
"created": "Tue, 23 Jan 2018 20:54:30 GMT",
"version": "v2"
},
{
"created": "Mon, 16 Apr 2018 23:59:07 GMT",
"version": "v3"
}
] | 2018-04-27 | [
[
"Konoplya",
"R. A.",
""
],
[
"Stuchlík",
"Z.",
""
],
[
"Zhidenko",
"A.",
""
]
] | We determine the class of axisymmetric and asymptotically flat black-hole spacetimes for which the test Klein-Gordon and Hamilton-Jacobi equations allow for the separation of variables. The known Kerr, Kerr-Newman, Kerr-Sen and some other black-hole metrics in various theories of gravity are within the class of spacetimes described here. It is shown that although the black-hole metric in the Einstein-dilaton-Gauss-Bonnet theory does not allow for the separation of variables (at least in the considered coordinates), for a number of applications it can be effectively approximated by a metric within the above class. This gives us some hope that the class of spacetimes described here may be not only generic for the known solutions allowing for the separation of variables, but also a good approximation for a broader class of metrics, which does not admit such separation. Finally, the generic form of the axisymmetric metric is expanded in the radial direction in terms of the continued fractions and the connection with other black-hole parametrizations is discussed. |
2210.02669 | Tomohiro Ishikawa | Tomohiro Ishikawa, Shoki Iwaguchi, Bin Wu, Izumi Watanabe, Yuki
Kawasaki, Ryuma Shimizu, Yutaro Enomoto, Yuta Michimura, Akira Furusawa,
Seiji Kawamura | Can the phase of radiation pressure fluctuations be flipped in a single
path for laser interferometric gravitational wave detectors? | 14 pages, 8 figures | null | 10.1016/j.physleta.2022.128485 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Radiation pressure (RP) noise, one component of quantum noise, can limit the
sensitivity of laser interferometric gravitational wave (GW) detectors at lower
frequencies. We conceived a possible RP noise cancellation method, using phase
flipped ponderomotive-squeezed light (FPSL) incident on free-mass mirrors in
interferometers' arms. This possibility is investigated under the constraint
that the method is for space-based GW detectors in a broad frequency band lower
than 1 Hz without using a long optical cavity. Considering various patterns in
a single path small-scale case to generate the FPSL, we proved that no
configuration exists in the single path case.
| [
{
"created": "Thu, 6 Oct 2022 04:17:06 GMT",
"version": "v1"
}
] | 2022-10-19 | [
[
"Ishikawa",
"Tomohiro",
""
],
[
"Iwaguchi",
"Shoki",
""
],
[
"Wu",
"Bin",
""
],
[
"Watanabe",
"Izumi",
""
],
[
"Kawasaki",
"Yuki",
""
],
[
"Shimizu",
"Ryuma",
""
],
[
"Enomoto",
"Yutaro",
""
],
[
"Michimura",
"Yuta",
""
],
[
"Furusawa",
"Akira",
""
],
[
"Kawamura",
"Seiji",
""
]
] | Radiation pressure (RP) noise, one component of quantum noise, can limit the sensitivity of laser interferometric gravitational wave (GW) detectors at lower frequencies. We conceived a possible RP noise cancellation method, using phase flipped ponderomotive-squeezed light (FPSL) incident on free-mass mirrors in interferometers' arms. This possibility is investigated under the constraint that the method is for space-based GW detectors in a broad frequency band lower than 1 Hz without using a long optical cavity. Considering various patterns in a single path small-scale case to generate the FPSL, we proved that no configuration exists in the single path case. |
1604.06217 | Pavel Bushev | Pavel Bushev, Jared H. Cole, Dmitry Sholokhov, Nadezhda Kukharchyk and
Magdalena Zych | Single electron relativistic clock interferometer | 9 pages, 4 figures | New J. Phys. 18, 093050 (2016) | 10.1088/1367-2630/18/9/093050 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Although time is one of the fundamental notions in physics, it does not have
a unique description. In quantum theory time is a parameter ordering the
succession of the probability amplitudes of a quantum system, while according
to relativity theory each system experiences in general a different proper
time, depending on the system's world line, due to time to time dilation. It is
therefore of fundamental interest to test the notion of time in the regime
where both quantum and relativistic effects play a role, for example, when
different amplitudes of a single quantum clock experience different magnitudes
of time dilation. Here we propose a realization of such an experiment with a
single electron in a Penning trap. The clock can be implemented in the
electronic spin precession and its time dilation then depends on the radial
(cyclotron) state of the electron. We show that coherent manipulation and
detection of the electron can be achieved already with present day technology.
A single electron in a Penning trap is a technologically ready platform where
the notion of time can be probed in a hitherto untested regime, where it
requires a relativistic as well as quantum description.
| [
{
"created": "Thu, 21 Apr 2016 08:58:14 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Oct 2016 17:20:55 GMT",
"version": "v2"
}
] | 2016-10-04 | [
[
"Bushev",
"Pavel",
""
],
[
"Cole",
"Jared H.",
""
],
[
"Sholokhov",
"Dmitry",
""
],
[
"Kukharchyk",
"Nadezhda",
""
],
[
"Zych",
"Magdalena",
""
]
] | Although time is one of the fundamental notions in physics, it does not have a unique description. In quantum theory time is a parameter ordering the succession of the probability amplitudes of a quantum system, while according to relativity theory each system experiences in general a different proper time, depending on the system's world line, due to time to time dilation. It is therefore of fundamental interest to test the notion of time in the regime where both quantum and relativistic effects play a role, for example, when different amplitudes of a single quantum clock experience different magnitudes of time dilation. Here we propose a realization of such an experiment with a single electron in a Penning trap. The clock can be implemented in the electronic spin precession and its time dilation then depends on the radial (cyclotron) state of the electron. We show that coherent manipulation and detection of the electron can be achieved already with present day technology. A single electron in a Penning trap is a technologically ready platform where the notion of time can be probed in a hitherto untested regime, where it requires a relativistic as well as quantum description. |
1310.7632 | Roberto A. Sussman | Roberto A Sussman and Julien Larena | Gravitational entropies in LTB dust models | Version accepted for publication in Classical and Quantum Gravity. 39
pages, 6 figures | Classical and Quantum Gravity, vol 31, page 075021, (2014) | 10.1088/0264-9381/31/7/075021 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider generic Lemaitre-Tolman-Bondi (LTB) dust models to probe the
gravitational entropy proposals of Clifton, Ellis and Tavakol (CET) and of
Hosoya and Buchert (HB). We also consider a variant of the HB proposal based on
a suitable quasi-local scalar weighted average. We show that the conditions for
entropy growth for all proposals are directly related to a negative correlation
of similar fluctuations of the energy density and Hubble scalar. While this
correlation is evaluated locally for the CET proposal, it must be evaluated in
a non--local domain dependent manner for the two HB proposals. By looking at
the fulfillment of these conditions at the relevant asymptotic limits we are
able to provide a well grounded qualitative description of the full time
evolution and radial asymptotic scaling of the three entropies in generic
models. The following rigorous analytic results are obtained for the three
proposals: (i) entropy grows when the density growing mode is dominant, (ii)
all ever-expanding hyperbolic models reach a stable terminal equilibrium
characterized by an inhomogeneous entropy maximum in their late time evolution;
(iii) regions with decaying modes and collapsing elliptic models exhibit
unstable equilibria associated with an entropy minimum (iv) near singularities
the CET entropy diverges while the HB entropies converge; (v) the CET entropy
converges for all models in the radial asymptotic range, whereas the HB
entropies only converge for models asymptotic to an FLRW background. The fact
that different independent proposals yield fairly similar conditions for
entropy production, time evolution and radial scaling in generic LTB models
seems to suggest that their common notion of a "gravitational entropy" may be a
theoretically robust concept applicable to more general spacetimes.
| [
{
"created": "Mon, 28 Oct 2013 21:53:28 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Mar 2014 04:51:15 GMT",
"version": "v2"
}
] | 2015-06-17 | [
[
"Sussman",
"Roberto A",
""
],
[
"Larena",
"Julien",
""
]
] | We consider generic Lemaitre-Tolman-Bondi (LTB) dust models to probe the gravitational entropy proposals of Clifton, Ellis and Tavakol (CET) and of Hosoya and Buchert (HB). We also consider a variant of the HB proposal based on a suitable quasi-local scalar weighted average. We show that the conditions for entropy growth for all proposals are directly related to a negative correlation of similar fluctuations of the energy density and Hubble scalar. While this correlation is evaluated locally for the CET proposal, it must be evaluated in a non--local domain dependent manner for the two HB proposals. By looking at the fulfillment of these conditions at the relevant asymptotic limits we are able to provide a well grounded qualitative description of the full time evolution and radial asymptotic scaling of the three entropies in generic models. The following rigorous analytic results are obtained for the three proposals: (i) entropy grows when the density growing mode is dominant, (ii) all ever-expanding hyperbolic models reach a stable terminal equilibrium characterized by an inhomogeneous entropy maximum in their late time evolution; (iii) regions with decaying modes and collapsing elliptic models exhibit unstable equilibria associated with an entropy minimum (iv) near singularities the CET entropy diverges while the HB entropies converge; (v) the CET entropy converges for all models in the radial asymptotic range, whereas the HB entropies only converge for models asymptotic to an FLRW background. The fact that different independent proposals yield fairly similar conditions for entropy production, time evolution and radial scaling in generic LTB models seems to suggest that their common notion of a "gravitational entropy" may be a theoretically robust concept applicable to more general spacetimes. |
gr-qc/9307020 | David Garfinkle | David Garfinkle and G. Comer Duncan | Collapse of a Circular Loop of Cosmic String | 15 pages | Phys.Rev. D49 (1994) 2752-2758 | 10.1103/PhysRevD.49.2752 | null | gr-qc | null | We study the collapse of a circular loop of cosmic string. The gravitational
field of the string is treated using the weak field approximation. The
gravitational radiation from the loop is evaluated numerically. The memtric of
the loop near the point of collapse is found analytically.
| [
{
"created": "Wed, 14 Jul 1993 23:23:55 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Garfinkle",
"David",
""
],
[
"Duncan",
"G. Comer",
""
]
] | We study the collapse of a circular loop of cosmic string. The gravitational field of the string is treated using the weak field approximation. The gravitational radiation from the loop is evaluated numerically. The memtric of the loop near the point of collapse is found analytically. |
2206.15145 | Yi Zhong | Yi Zhong, Ke Yang, and Yu-Xiao Liu | Thick brane in Rastall gravity | 13 pages, 7 figures | JHEP 09 (2022) 128 | 10.1007/JHEP09(2022)128 | null | gr-qc | http://creativecommons.org/publicdomain/zero/1.0/ | In this work, thick branes in Rastall gravity are investigated. Three types
of maximally symmetric thick brane models are constructed and the linear tensor
perturbation is analyzed. In the flat brane model, the tensor modes of the
perturbation are either unstable or nonlocalizable for a nonvanishing Rastall
parameter. In the de Sitter brane model, only the ground state of the tensor
mode is localized. In the anti-de Sitter brane model, the number of the bound
tensor states is infinity. For both the de Sitter and anti-de Sitter brane
models, the condition of stability for the Rastall parameter is obtained.
| [
{
"created": "Thu, 30 Jun 2022 09:26:37 GMT",
"version": "v1"
},
{
"created": "Sat, 2 Jul 2022 05:11:11 GMT",
"version": "v2"
}
] | 2022-09-27 | [
[
"Zhong",
"Yi",
""
],
[
"Yang",
"Ke",
""
],
[
"Liu",
"Yu-Xiao",
""
]
] | In this work, thick branes in Rastall gravity are investigated. Three types of maximally symmetric thick brane models are constructed and the linear tensor perturbation is analyzed. In the flat brane model, the tensor modes of the perturbation are either unstable or nonlocalizable for a nonvanishing Rastall parameter. In the de Sitter brane model, only the ground state of the tensor mode is localized. In the anti-de Sitter brane model, the number of the bound tensor states is infinity. For both the de Sitter and anti-de Sitter brane models, the condition of stability for the Rastall parameter is obtained. |
2106.00392 | Suvodip Mukherjee | Suvodip Mukherjee, Tom Broadhurst, Jose M. Diego, Joseph Silk, George
F. Smoot | Impact of astrophysical binary coalescence timescales on the rate of
lensed gravitational wave events | 10 pages, 6 figures. Accepted for publication in MNRAS | null | 10.1093/mnras/stab1980 | null | gr-qc astro-ph.CO astro-ph.GA astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The expected event rate of lensed gravitational wave sources scales with the
merger rate at redshift $z\geq 1$, where the optical depth for lensing is high.
It is commonly assumed that the merger rate of the astrophysical compact
objects is closely connected with the star formation rate, which peaks around
redshift $z\sim 2$. However, a major source of uncertainty is the delay time
between the formation and merger of compact objects. We explore the impact of
delay time on the lensing event rate. We show that as the delay time increases,
the peak of the merger rate of gravitational wave sources gets deferred to a
lower redshift. This leads to a reduction in the event rate of the lensed
events which are detectable by the gravitational wave detectors. We show that
for a delay time of around $10$ Gyr or larger, the lensed event rate can be
less than one per year for the design sensitivity of LIGO/Virgo. We also
estimate the merger rate for lensed sub-threshold for different delay time
scenarios, finding that for larger delay times the number of lensed
sub-threshold events is reduced, whereas for small-delay time models they are
significantly more frequent. This analysis shows for the first time that
lensing is a complementary probe to explore different formation channels of
binary systems by exploiting the lensing event rate from the well-detected
events and sub-threshold events which are measurable using the network of
gravitational wave detectors.
| [
{
"created": "Tue, 1 Jun 2021 11:02:09 GMT",
"version": "v1"
},
{
"created": "Thu, 8 Jul 2021 11:51:00 GMT",
"version": "v2"
}
] | 2021-07-21 | [
[
"Mukherjee",
"Suvodip",
""
],
[
"Broadhurst",
"Tom",
""
],
[
"Diego",
"Jose M.",
""
],
[
"Silk",
"Joseph",
""
],
[
"Smoot",
"George F.",
""
]
] | The expected event rate of lensed gravitational wave sources scales with the merger rate at redshift $z\geq 1$, where the optical depth for lensing is high. It is commonly assumed that the merger rate of the astrophysical compact objects is closely connected with the star formation rate, which peaks around redshift $z\sim 2$. However, a major source of uncertainty is the delay time between the formation and merger of compact objects. We explore the impact of delay time on the lensing event rate. We show that as the delay time increases, the peak of the merger rate of gravitational wave sources gets deferred to a lower redshift. This leads to a reduction in the event rate of the lensed events which are detectable by the gravitational wave detectors. We show that for a delay time of around $10$ Gyr or larger, the lensed event rate can be less than one per year for the design sensitivity of LIGO/Virgo. We also estimate the merger rate for lensed sub-threshold for different delay time scenarios, finding that for larger delay times the number of lensed sub-threshold events is reduced, whereas for small-delay time models they are significantly more frequent. This analysis shows for the first time that lensing is a complementary probe to explore different formation channels of binary systems by exploiting the lensing event rate from the well-detected events and sub-threshold events which are measurable using the network of gravitational wave detectors. |
2205.14742 | Maria Babiuc | Dillon Buskirk and Maria C. Babiuc Hamilton | Merging Black Holes: Assessing the Performance of Two Analytic
Gravitational Waves Models | 28 pages, 8 figures | Journal of Cosmology and Astroparticle Physics (2023) 005 | 10.1088/1475-7516/2023/03/005 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Merging black holes produce the loudest signal in the detectors. However,
this is the most difficult signal to accurately predict with analytical
techniques. Only computer simulations can account for the nonlinear physics
during the collision, but they are inherently complex, costly, and affected by
numerical errors. In order to bypass this problem, two analytical models for
the merger have been developed: the Implicit Rotating Source (IRS) and the
newer Backwards one Body (BoB). In this work, we assess the performance of the
BoB model by comparing it with the older IRS model and with the numerical data,
identifying its strengths and weaknesses. Our main finding reveals
discrepancies in amplitude, but overall excellent accord in frequency. The BoB
model is comparable with the IRS and NR simulations, having the added advantage
that it depends only indirectly on numerical data, it accounts for spin, and it
offers a seamless fit with the analytical formalisms for the inspiral. By
independently evaluating and testing those models, we bring evidence of their
reproducibility, thus upholding high scientific standards, and make available
our implementation, enabling readers to evaluate our results themselves.
| [
{
"created": "Sun, 29 May 2022 19:29:52 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Sep 2022 14:37:13 GMT",
"version": "v2"
},
{
"created": "Thu, 22 Dec 2022 21:01:32 GMT",
"version": "v3"
},
{
"created": "Wed, 1 Mar 2023 22:20:29 GMT",
"version": "v4"
}
] | 2023-03-08 | [
[
"Buskirk",
"Dillon",
""
],
[
"Hamilton",
"Maria C. Babiuc",
""
]
] | Merging black holes produce the loudest signal in the detectors. However, this is the most difficult signal to accurately predict with analytical techniques. Only computer simulations can account for the nonlinear physics during the collision, but they are inherently complex, costly, and affected by numerical errors. In order to bypass this problem, two analytical models for the merger have been developed: the Implicit Rotating Source (IRS) and the newer Backwards one Body (BoB). In this work, we assess the performance of the BoB model by comparing it with the older IRS model and with the numerical data, identifying its strengths and weaknesses. Our main finding reveals discrepancies in amplitude, but overall excellent accord in frequency. The BoB model is comparable with the IRS and NR simulations, having the added advantage that it depends only indirectly on numerical data, it accounts for spin, and it offers a seamless fit with the analytical formalisms for the inspiral. By independently evaluating and testing those models, we bring evidence of their reproducibility, thus upholding high scientific standards, and make available our implementation, enabling readers to evaluate our results themselves. |
gr-qc/0407051 | Jerzy Lewandowski | Marcin Domagala and Jerzy Lewandowski (Uniwersytet Warszawski) | Black hole entropy from Quantum Geometry | a new section ``The spin probability distribution'' added | Class.Quant.Grav. 21 (2004) 5233-5244 | 10.1088/0264-9381/21/22/014 | null | gr-qc hep-th | null | Quantum Geometry (the modern Loop Quantum Gravity using graphs and
spin-networks instead of the loops) provides microscopic degrees of freedom
that account for the black-hole entropy. However, the procedure for state
counting used in the literature contains an error and the number of the
relevant horizon states is underestimated. In our paper a correct method of
counting is presented. Our results lead to a revision of the literature of the
subject. It turns out that the contribution of spins greater then 1/2 to the
entropy is not negligible. Hence, the value of the Barbero-Immirzi parameter
involved in the spectra of all the geometric and physical operators in this
theory is different than previously derived. Also, the conjectured relation
between Quantum Geometry and the black hole quasi-normal modes should be
understood again.
| [
{
"created": "Wed, 14 Jul 2004 18:52:16 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Aug 2004 08:08:23 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Domagala",
"Marcin",
"",
"Uniwersytet Warszawski"
],
[
"Lewandowski",
"Jerzy",
"",
"Uniwersytet Warszawski"
]
] | Quantum Geometry (the modern Loop Quantum Gravity using graphs and spin-networks instead of the loops) provides microscopic degrees of freedom that account for the black-hole entropy. However, the procedure for state counting used in the literature contains an error and the number of the relevant horizon states is underestimated. In our paper a correct method of counting is presented. Our results lead to a revision of the literature of the subject. It turns out that the contribution of spins greater then 1/2 to the entropy is not negligible. Hence, the value of the Barbero-Immirzi parameter involved in the spectra of all the geometric and physical operators in this theory is different than previously derived. Also, the conjectured relation between Quantum Geometry and the black hole quasi-normal modes should be understood again. |
gr-qc/0506137 | Herbert Hamber | Herbert W. Hamber and Ruth M. Williams | Nonlocal Effective Field Equations for Quantum Cosmology | 9 pages | Mod.Phys.Lett. A21 (2006) 735-742 | 10.1142/S0217732306019979 | DAMTP-2005-58 | gr-qc | null | The possibility that the strength of gravitational interactions might slowly
increase with distance, is explored by formulating a set of effective field
equations, which incorporate the gravitational, vacuum-polarization induced,
running of Newton's constant $G$. The resulting long distance (or large time)
behaviour depends on only one adjustable parameter $\xi$, and the implications
for the Robertson-Walker universe are calculated, predicting an accelerated
power-law expansion at later times $t \sim \xi \sim 1/H$.
| [
{
"created": "Wed, 29 Jun 2005 18:33:36 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Hamber",
"Herbert W.",
""
],
[
"Williams",
"Ruth M.",
""
]
] | The possibility that the strength of gravitational interactions might slowly increase with distance, is explored by formulating a set of effective field equations, which incorporate the gravitational, vacuum-polarization induced, running of Newton's constant $G$. The resulting long distance (or large time) behaviour depends on only one adjustable parameter $\xi$, and the implications for the Robertson-Walker universe are calculated, predicting an accelerated power-law expansion at later times $t \sim \xi \sim 1/H$. |
2302.08900 | Marco Brito MSc | Marco Brito, Carlos Herdeiro, Eugen Radu, Nicolas Sanchis-Gual and
Miguel Zilh\~ao | Stability and physical properties of spherical excited scalar boson
stars | 16 pages, 16 figures, updated with an appendix to match published
version | Phys. Rev. D 107, 084022 (2023) | 10.1103/PhysRevD.107.084022 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the time evolution of spherical, excited -- with $n$ radial nodes --
scalar boson stars in General Relativity minimally coupled to a complex massive
scalar field with quartic self-interactions. We report that these stars, with
up to $n=10$, can be made dynamically stable, up to timescales of
$t\sim\frac{10^{4}}{c\mu}$, where $\mu$ is the inverse Compton wavelength of
the scalar particle, for sufficiently large values of the self-interactions
coupling constant $\lambda$, which depend on $n$. We observe that the
compactness of these solutions is rather insensitive to $n$, for large
$\lambda$ and fixed frequency. Generically, along the branches where stability
was studied, these excited boson stars are not compact enough to allow for
innermost stable circular orbits or light rings. Finally, we discuss the
angular velocity of particles along timelike circular orbits, suggesting an
application, for solutions in the Newtonian limit, to galactic rotation curves.
| [
{
"created": "Fri, 17 Feb 2023 14:28:36 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Apr 2023 13:47:19 GMT",
"version": "v2"
}
] | 2023-04-17 | [
[
"Brito",
"Marco",
""
],
[
"Herdeiro",
"Carlos",
""
],
[
"Radu",
"Eugen",
""
],
[
"Sanchis-Gual",
"Nicolas",
""
],
[
"Zilhão",
"Miguel",
""
]
] | We study the time evolution of spherical, excited -- with $n$ radial nodes -- scalar boson stars in General Relativity minimally coupled to a complex massive scalar field with quartic self-interactions. We report that these stars, with up to $n=10$, can be made dynamically stable, up to timescales of $t\sim\frac{10^{4}}{c\mu}$, where $\mu$ is the inverse Compton wavelength of the scalar particle, for sufficiently large values of the self-interactions coupling constant $\lambda$, which depend on $n$. We observe that the compactness of these solutions is rather insensitive to $n$, for large $\lambda$ and fixed frequency. Generically, along the branches where stability was studied, these excited boson stars are not compact enough to allow for innermost stable circular orbits or light rings. Finally, we discuss the angular velocity of particles along timelike circular orbits, suggesting an application, for solutions in the Newtonian limit, to galactic rotation curves. |
1902.09531 | Wenbin Lin | Bo Yang and Chunhua Jiang and Wenbin Lin | Post-Minkowskian solution for the small-deflection motion of test
particles in Kerr-Newman spacetime | Submitted to Class. Quantum Grav | null | 10.1088/1361-6382/ab0ec9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive the second-order post-Minkowskian solution for the small-deflection
motion of test particles in the external field of the Kerr-Newman black hole
via an iterative method. The analytical results are exhibited in the coordinate
system constituted by the particles' initial velocity unit vector, impact
vector, and their cross-product. The achieved formulas explicitly give the
dependences of the particles' trajectory and velocity on the time once their
initial position and velocity are specified, and can be applied not only to a
massive particle, but also to a photon as well.
| [
{
"created": "Sun, 24 Feb 2019 14:02:43 GMT",
"version": "v1"
}
] | 2019-05-22 | [
[
"Yang",
"Bo",
""
],
[
"Jiang",
"Chunhua",
""
],
[
"Lin",
"Wenbin",
""
]
] | We derive the second-order post-Minkowskian solution for the small-deflection motion of test particles in the external field of the Kerr-Newman black hole via an iterative method. The analytical results are exhibited in the coordinate system constituted by the particles' initial velocity unit vector, impact vector, and their cross-product. The achieved formulas explicitly give the dependences of the particles' trajectory and velocity on the time once their initial position and velocity are specified, and can be applied not only to a massive particle, but also to a photon as well. |
gr-qc/9709044 | Carlo Baccigalupi | Carlo Baccigalupi, Luca Amendola, Pierluigi Fortini, Franco Occhionero | Stochastic gravitational background from inflationary phase transitions | 12 pages, 3 figures. Phys.Rev.D in press | Phys.Rev.D56:4610-4617,1997 | 10.1103/PhysRevD.56.4610 | null | gr-qc | null | We consider true vacuum bubbles generated in a first order phase transition
occurring during the slow rolling era of a two field inflation: it is known
that gravitational waves are produced by the collision of such bubbles. We find
that the epoch of the phase transition strongly affects the characteristic peak
frequency of the gravitational waves, causing an observationally interesting
redshift in addition to the post-inflationary expansion. In particular it is
found that a phase transition occurring typically 10$\div$20 $e-$foldings
before the reheating at $kT\simeq 10^{15}$ GeV may be detected by the next Ligo
gravity waves interferometers. Moreover, for recently proposed models capable
of generating the observed large scale voids as remnants of the primordial
bubbles (for which the characteristic wave lengths are several tens of Mpc), it
is found that the level of anisotropy of the cosmic microwave background
provides a deep insight upon the physical parameters of the effective
Lagrangian.
| [
{
"created": "Tue, 16 Sep 1997 15:17:07 GMT",
"version": "v1"
}
] | 2011-09-09 | [
[
"Baccigalupi",
"Carlo",
""
],
[
"Amendola",
"Luca",
""
],
[
"Fortini",
"Pierluigi",
""
],
[
"Occhionero",
"Franco",
""
]
] | We consider true vacuum bubbles generated in a first order phase transition occurring during the slow rolling era of a two field inflation: it is known that gravitational waves are produced by the collision of such bubbles. We find that the epoch of the phase transition strongly affects the characteristic peak frequency of the gravitational waves, causing an observationally interesting redshift in addition to the post-inflationary expansion. In particular it is found that a phase transition occurring typically 10$\div$20 $e-$foldings before the reheating at $kT\simeq 10^{15}$ GeV may be detected by the next Ligo gravity waves interferometers. Moreover, for recently proposed models capable of generating the observed large scale voids as remnants of the primordial bubbles (for which the characteristic wave lengths are several tens of Mpc), it is found that the level of anisotropy of the cosmic microwave background provides a deep insight upon the physical parameters of the effective Lagrangian. |
gr-qc/0312109 | Masato Minamitsuji | Masato Minamitsuji and Misao Sasaki | Local conservation law and dark radiation in cosmological braneworld | 21 pages, discussions on naked singularity formation and references
added | Phys.Rev.D70:044021,2004 | 10.1103/PhysRevD.70.044021 | YITP-03-81 | gr-qc astro-ph hep-th | null | In the context of the Randall-Sundrum (RS) single-brane scenario, we discuss
the bulk geometry and dynamics of a cosmological brane in terms of the local
energy conservation law which exists for the bulk that allows slicing with a
maximally symmetric 3-space. This conservation law enables us to define a local
mass in the bulk. We show that there is a unique generalization of the dark
radiation on the brane, which is given by the local mass. We find there also
exists a conserved current associated with the Weyl tensor, and the
corresponding local charge, which we call the Weyl charge, is given by the sum
of the local mass and a certain linear combination of the components of the
bulk energy-momentum tensor. This expression of the Weyl charge relates the
local mass with the projected Weyl tensor, $E_{\mu\nu}$, which plays a central
role in the geometrical formalism of the RS braneworld. On the brane, in
particular, this gives a decomposition of the projected Weyl tensor into the
local mass and the bulk energy-momentum tensor. Then, as an application of
these results, we consider a null dust model for the bulk energy-momentum
tensor and discuss the black hole formation in the bulk. We investigate the
causal structure by identifying the locus of the apparent horizon and clarify
possible brane trajectories in the bulk. We find that the brane stays always
outside the black hole as long as it is expanding. We also find an upper bound
on the value of the Hubble parameter in terms of the matter energy density on
the brane, irrespective of the energy flux emitted from the brane.
| [
{
"created": "Thu, 25 Dec 2003 05:05:32 GMT",
"version": "v1"
},
{
"created": "Sun, 11 Jan 2004 11:25:29 GMT",
"version": "v2"
},
{
"created": "Mon, 26 Jan 2004 09:24:50 GMT",
"version": "v3"
}
] | 2009-10-09 | [
[
"Minamitsuji",
"Masato",
""
],
[
"Sasaki",
"Misao",
""
]
] | In the context of the Randall-Sundrum (RS) single-brane scenario, we discuss the bulk geometry and dynamics of a cosmological brane in terms of the local energy conservation law which exists for the bulk that allows slicing with a maximally symmetric 3-space. This conservation law enables us to define a local mass in the bulk. We show that there is a unique generalization of the dark radiation on the brane, which is given by the local mass. We find there also exists a conserved current associated with the Weyl tensor, and the corresponding local charge, which we call the Weyl charge, is given by the sum of the local mass and a certain linear combination of the components of the bulk energy-momentum tensor. This expression of the Weyl charge relates the local mass with the projected Weyl tensor, $E_{\mu\nu}$, which plays a central role in the geometrical formalism of the RS braneworld. On the brane, in particular, this gives a decomposition of the projected Weyl tensor into the local mass and the bulk energy-momentum tensor. Then, as an application of these results, we consider a null dust model for the bulk energy-momentum tensor and discuss the black hole formation in the bulk. We investigate the causal structure by identifying the locus of the apparent horizon and clarify possible brane trajectories in the bulk. We find that the brane stays always outside the black hole as long as it is expanding. We also find an upper bound on the value of the Hubble parameter in terms of the matter energy density on the brane, irrespective of the energy flux emitted from the brane. |
gr-qc/0409022 | Spiros Cotsakis | Spiros Cotsakis and Ifigeneia Klaoudatou | Future Singularities of Isotropic Cosmologies | v2: 16 pages, references added, clarrifications throughout, version
to appear in the J.Geom.Phys | J.Geom.Phys. 55 (2005) 306-315 | 10.1016/j.geomphys.2004.12.012 | null | gr-qc | null | We show that globally and regularly hyperbolic future geodesically incomplete
isotropic universes, except for the standard all-encompassing `big crunch', can
accommodate singularities of only one kind, namely, those having a
non-integrable Hubble parameter, $H$. We analyze several examples from recent
literature which illustrate this result and show that such behaviour may arise
in a number of different ways. We also discuss the existence of new types of
lapse singularities in inhomogeneous models, impossible to meet in the
isotropic ones.
| [
{
"created": "Sun, 5 Sep 2004 17:52:00 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Dec 2004 09:59:16 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Cotsakis",
"Spiros",
""
],
[
"Klaoudatou",
"Ifigeneia",
""
]
] | We show that globally and regularly hyperbolic future geodesically incomplete isotropic universes, except for the standard all-encompassing `big crunch', can accommodate singularities of only one kind, namely, those having a non-integrable Hubble parameter, $H$. We analyze several examples from recent literature which illustrate this result and show that such behaviour may arise in a number of different ways. We also discuss the existence of new types of lapse singularities in inhomogeneous models, impossible to meet in the isotropic ones. |
1511.03655 | Abdul Jawad | Abdul Jawad, Davood Momeni, Shamaila Rani and Ratbay Myrzakulov | Dynamical Instability of Cylindrically Symmetric Collapsing Star in
Generalized Teleparallel Gravity | 20 pages; Accepted for publication in Astrophysics and Space Sceince | Astrophys. Space Sci. 361 (2016) | 10.1007/s10509-016-2721-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper is devoted to analyze the dynamical instability of a
self-gravitating object undergoes to collapse process. We take the framework of
generalized teleparallel gravity with cylindrically symmetric gravitating
object. The matter distribution is represented by locally anisotropic
energy-momentum tensor. We develop basic equations such as dynamical equations
along with matching conditions and Harrison-Wheeler equation of state. By
applying linear perturbation strategy, we construct collapse equation which is
used to accomplish the instability ranges in Newtonian and post-Newtonian
regimes. We find these ranges for isotropic pressure as well as reduce the
results in general relativity. The unstable behavior depends on matter, metric,
mass and torsion based terms.
| [
{
"created": "Wed, 11 Nov 2015 11:00:16 GMT",
"version": "v1"
},
{
"created": "Tue, 15 Mar 2016 09:46:46 GMT",
"version": "v2"
}
] | 2016-10-31 | [
[
"Jawad",
"Abdul",
""
],
[
"Momeni",
"Davood",
""
],
[
"Rani",
"Shamaila",
""
],
[
"Myrzakulov",
"Ratbay",
""
]
] | This paper is devoted to analyze the dynamical instability of a self-gravitating object undergoes to collapse process. We take the framework of generalized teleparallel gravity with cylindrically symmetric gravitating object. The matter distribution is represented by locally anisotropic energy-momentum tensor. We develop basic equations such as dynamical equations along with matching conditions and Harrison-Wheeler equation of state. By applying linear perturbation strategy, we construct collapse equation which is used to accomplish the instability ranges in Newtonian and post-Newtonian regimes. We find these ranges for isotropic pressure as well as reduce the results in general relativity. The unstable behavior depends on matter, metric, mass and torsion based terms. |
1501.07161 | Ayan Banerjee | Piyali Bhar and Ayan Banerjee | Stability of Thin-Shell Wormholes from Noncommutative BTZ Black Hole | 13 pages, 16 figures, accepted in Int.J.Mod.Phys. D. arXiv admin
note: text overlap with arXiv:0806.4459, arXiv:0909.1071 by other authors | International Journal of Modern Physics D, Vol. 24, No. 5 (2015)
1550034 | 10.1142/S0218271815500340 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we construct thin-shell wormholes in (2+1)-dimensions from
noncommutative BTZ black hole by applying the cut-and-paste procedure
implemented by Visser. We calculate the surface stresses localized at the
wormhole throat by using the Darmois-Israel formalism, and we find that the
wormholes are supported by matter violating the energy conditions. In order to
explore the dynamical analysis of the wormhole throat, we consider that the
matter at the shell is supported by dark energy equation of state P = w\rho
with w < 0. The stability analysis is carried out of these wormholes to
linearized spherically symmetric perturbations around static solutions.
Preserving the symmetry we also consider the linearized radial perturbation
around static solution to investigate the stability of wormholes which explored
by the parameter \beta (speed of sound).
| [
{
"created": "Tue, 27 Jan 2015 18:02:39 GMT",
"version": "v1"
}
] | 2016-10-31 | [
[
"Bhar",
"Piyali",
""
],
[
"Banerjee",
"Ayan",
""
]
] | In this paper, we construct thin-shell wormholes in (2+1)-dimensions from noncommutative BTZ black hole by applying the cut-and-paste procedure implemented by Visser. We calculate the surface stresses localized at the wormhole throat by using the Darmois-Israel formalism, and we find that the wormholes are supported by matter violating the energy conditions. In order to explore the dynamical analysis of the wormhole throat, we consider that the matter at the shell is supported by dark energy equation of state P = w\rho with w < 0. The stability analysis is carried out of these wormholes to linearized spherically symmetric perturbations around static solutions. Preserving the symmetry we also consider the linearized radial perturbation around static solution to investigate the stability of wormholes which explored by the parameter \beta (speed of sound). |
1611.06935 | Guido Pizzella | R. de Sangro, G. Finocchiaro, P. Patteri, M. Piccolo, G. Pizzella | Why the interpretation of "Measuring propagation speed of Coulomb
fields" stands | 3 pages | null | 10.1140/epjc/s10052-017-4650-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The experimental findings reported in our original paper [1]
(arXiv:1211.2913) have been criticized in ref.[2] (arXiv:1606.00710). We
believe that the arguments brought in ref. [2] are not correct and we show
evidence for this.
| [
{
"created": "Fri, 18 Nov 2016 10:25:59 GMT",
"version": "v1"
}
] | 2017-03-08 | [
[
"de Sangro",
"R.",
""
],
[
"Finocchiaro",
"G.",
""
],
[
"Patteri",
"P.",
""
],
[
"Piccolo",
"M.",
""
],
[
"Pizzella",
"G.",
""
]
] | The experimental findings reported in our original paper [1] (arXiv:1211.2913) have been criticized in ref.[2] (arXiv:1606.00710). We believe that the arguments brought in ref. [2] are not correct and we show evidence for this. |
0704.3102 | Hernando Quevedo | Hernando Quevedo | Geometrothermodynamics of black holes | Revised version, to be published in Gen.Rel.Grav.(Mashhoon's
Festschrift) | Gen.Rel.Grav.40:971-984,2008 | 10.1007/s10714-007-0586-0 | null | gr-qc | null | The thermodynamics of black holes is reformulated within the context of the
recently developed formalism of geometrothermodynamics. This reformulation is
shown to be invariant with respect to Legendre transformations, and to allow
several equivalent representations. Legendre invariance allows us to explain a
series of contradictory results known in the literature from the use of
Weinhold's and Ruppeiner's thermodynamic metrics for black holes. For the
Reissner-Nordstr\"om black hole the geometry of the space of equilibrium states
is curved, showing a non trivial thermodynamic interaction, and the curvature
contains information about critical points and phase transitions. On the
contrary, for the Kerr black hole the geometry is flat and does not explain its
phase transition structure.
| [
{
"created": "Tue, 24 Apr 2007 01:37:35 GMT",
"version": "v1"
},
{
"created": "Mon, 2 Jul 2007 18:33:21 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Quevedo",
"Hernando",
""
]
] | The thermodynamics of black holes is reformulated within the context of the recently developed formalism of geometrothermodynamics. This reformulation is shown to be invariant with respect to Legendre transformations, and to allow several equivalent representations. Legendre invariance allows us to explain a series of contradictory results known in the literature from the use of Weinhold's and Ruppeiner's thermodynamic metrics for black holes. For the Reissner-Nordstr\"om black hole the geometry of the space of equilibrium states is curved, showing a non trivial thermodynamic interaction, and the curvature contains information about critical points and phase transitions. On the contrary, for the Kerr black hole the geometry is flat and does not explain its phase transition structure. |
1111.2647 | Peter Komorowski | N. Kiriushcheva, P. G. Komorowski and S. V. Kuzmin | Comment on "Arnowitt--Deser--Misner representation and Hamiltonian
analysis of covariant renormalizable gravity" by M. Chaichian, M. Oksanen, A.
Tureanu | 10 Pages. We found a mistake in our first version -- the Horava-type
models of EPJC 71, 1657 (2011) do have a spatial diffeomorphism gauge
symmetry, but the partial Hamiltonian analysis of the action presented in the
EPJC paper has been confirmed to be incorrect. The true algebra of
constraints is different from what is reported in the EPJC paper | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The partial Hamiltonian analysis of the actions presented in the paper by M.
Chaichian, M. Oksanen, A. Tureanu (Eur. Phys. J. C 71, 1657 (2011)) is
incorrect; the true algebra of constraints differs from what they claim for
their choice of momentum constraint. Our blind acceptance of the correctness of
their constraint algebra led us to conclude, wrongly, that a few of the models
presented by the authors (sharing the same constraint algebra) are not
invariant under spatial diffeomorphism. We "proved" this by using Noether's
second theorem (see first version of the paper), but we then found a mistake in
our calculations. The differential identity of spatial diffeomorphism is
intact, therefore, their actions are invariant; but in this case, the spatial
diffeomorphism gauge symmetry cannot be compatible with their algebra. We now
explicitly demonstrate that the actual algebra of constraints is different, and
briefly describe how it affects the generator and gauge transformations of the
fields.
| [
{
"created": "Fri, 11 Nov 2011 02:36:50 GMT",
"version": "v1"
},
{
"created": "Tue, 15 Nov 2011 23:41:06 GMT",
"version": "v2"
},
{
"created": "Sun, 20 Nov 2011 21:55:10 GMT",
"version": "v3"
}
] | 2011-11-22 | [
[
"Kiriushcheva",
"N.",
""
],
[
"Komorowski",
"P. G.",
""
],
[
"Kuzmin",
"S. V.",
""
]
] | The partial Hamiltonian analysis of the actions presented in the paper by M. Chaichian, M. Oksanen, A. Tureanu (Eur. Phys. J. C 71, 1657 (2011)) is incorrect; the true algebra of constraints differs from what they claim for their choice of momentum constraint. Our blind acceptance of the correctness of their constraint algebra led us to conclude, wrongly, that a few of the models presented by the authors (sharing the same constraint algebra) are not invariant under spatial diffeomorphism. We "proved" this by using Noether's second theorem (see first version of the paper), but we then found a mistake in our calculations. The differential identity of spatial diffeomorphism is intact, therefore, their actions are invariant; but in this case, the spatial diffeomorphism gauge symmetry cannot be compatible with their algebra. We now explicitly demonstrate that the actual algebra of constraints is different, and briefly describe how it affects the generator and gauge transformations of the fields. |
gr-qc/9905106 | Martin Rainer | Martin Rainer | Cones and causal structures on topological and differentiable manifolds | v3: 12 pages, latex+amssymb; compatibility conditions (2.5) and (3.2)
with misprints corrected and improved argument | J.Math.Phys. 40 (1999) 6589-6597; Erratum-ibid. 41 (2000) 3303 | 10.1063/1.533108 | null | gr-qc | null | General definitions for causal structures on manifolds of dimension d+1>2 are
presented for the topological category and for any differentiable one.
Locally, these are given as cone structures via local (pointwise)
homeomorphic or diffeomorphic abstraction from the standard null cone variety
in R^{d+1}. Weak and strong local cone (LC) structures refer to the cone itself
or a manifold thickening of the cone respectively.
After introducing cone (C-)causality, a causal complement with reasonable
duality properties can be defined. The most common causal concepts of
space-times are generalized to the present topological setting. A new notion of
precausality precludes inner boundaries within future/past cones.
LC-structures, C-causality, a topological causal complement, and precausality
may be useful tools in conformal and background independent formulations of
(algebraic) quantum field theory and quantum gravity.
| [
{
"created": "Mon, 31 May 1999 21:43:01 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Oct 1999 10:43:45 GMT",
"version": "v2"
},
{
"created": "Wed, 5 Jan 2000 17:30:17 GMT",
"version": "v3"
}
] | 2015-06-25 | [
[
"Rainer",
"Martin",
""
]
] | General definitions for causal structures on manifolds of dimension d+1>2 are presented for the topological category and for any differentiable one. Locally, these are given as cone structures via local (pointwise) homeomorphic or diffeomorphic abstraction from the standard null cone variety in R^{d+1}. Weak and strong local cone (LC) structures refer to the cone itself or a manifold thickening of the cone respectively. After introducing cone (C-)causality, a causal complement with reasonable duality properties can be defined. The most common causal concepts of space-times are generalized to the present topological setting. A new notion of precausality precludes inner boundaries within future/past cones. LC-structures, C-causality, a topological causal complement, and precausality may be useful tools in conformal and background independent formulations of (algebraic) quantum field theory and quantum gravity. |
2307.04678 | Frans Klinkhamer | Frans R. Klinkhamer | New Type of Traversable Wormhole | Invited paper at Bahamas Advanced Study Institute & Conferences
(BASIC), February 8-14, 2023, Stella Maris, Long Island, Bahamas. v2: final
version to appear in Bulg. J. Phys | null | null | KA-TP-13-2023 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We review a new traversable-wormhole solution of the gravitational field
equation of general relativity without exotic matter. Instead of having exotic
matter to keep the wormhole throat open, the solution relies on a 3-dimensional
"spacetime defect," which is characterized by a locally vanishing metric
determinant. We also discuss the corresponding multiple-vacuum-defect-wormhole
solution and possible experimental signatures from a "gas" of vacuum-defect
wormholes. Multiple vacuum-defect wormholes appear to allow for backward time
travel.
| [
{
"created": "Thu, 6 Jul 2023 17:40:22 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Jul 2023 13:00:49 GMT",
"version": "v2"
}
] | 2023-07-25 | [
[
"Klinkhamer",
"Frans R.",
""
]
] | We review a new traversable-wormhole solution of the gravitational field equation of general relativity without exotic matter. Instead of having exotic matter to keep the wormhole throat open, the solution relies on a 3-dimensional "spacetime defect," which is characterized by a locally vanishing metric determinant. We also discuss the corresponding multiple-vacuum-defect-wormhole solution and possible experimental signatures from a "gas" of vacuum-defect wormholes. Multiple vacuum-defect wormholes appear to allow for backward time travel. |
2107.05171 | Xiao-Mei Kuang | Ru Ling, Hong Guo, Hang Liu, Xiao-Mei Kuang, Bin Wang | Shadow and near-horizon characteristics of the acoustic charged black
hole in curved spacetime | Published version | Physical Review D 104, 104003 (2021) | 10.1103/PhysRevD.104.104003 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this paper, we first analyze the horizon structure of the acoustic charged
black hole in curved spacetime, and then study its acoustic shadow as well as
the near-horizon characteristics including the quasinormal modes (QNM)
frequencies and analogue Hawking radiation. We find that the radius of the
acoustic shadow for acoustic charged black hole is larger than that for
Reissner-Nordstr\"{o}m (RN) black hole, and both of them are suppressed by
increasing the black hole charge because their related outer horizons become
smaller. Then the QNM frequencies under scalar field perturbation and its
eikonal limit are computed via numeric method and acoustic shadow,
respectively. We find that the acoustic charged black hole is stable under the
perturbation and the QNM frequencies are much weaker than that for the
astrophysical black hole. Moreover, as the tuning parameter increases, the
perturbation oscillates more mildly and its damping time becomes longer, while
as the charge increases, the oscillation is enhanced slightly and the
perturbation decays a little faster which is different from that in RN black
hole. Finally, we numerically study the analogue Hawking radiation. We find
that the grey-body factor and energy emission rate are suppressed by the
angular number and the charge, but they do not monotonically depend on the
tuning parameter in the acoustic charged black hole. The behavior of the energy
emission rate affected by the parameters could be explained by the dependent
behavior of the Hawking temperature. We expect that our results could shed
light to the study of black holes in both theoretical and experimental
perspectives.
| [
{
"created": "Mon, 12 Jul 2021 03:05:23 GMT",
"version": "v1"
},
{
"created": "Tue, 2 Nov 2021 04:49:25 GMT",
"version": "v2"
}
] | 2021-11-03 | [
[
"Ling",
"Ru",
""
],
[
"Guo",
"Hong",
""
],
[
"Liu",
"Hang",
""
],
[
"Kuang",
"Xiao-Mei",
""
],
[
"Wang",
"Bin",
""
]
] | In this paper, we first analyze the horizon structure of the acoustic charged black hole in curved spacetime, and then study its acoustic shadow as well as the near-horizon characteristics including the quasinormal modes (QNM) frequencies and analogue Hawking radiation. We find that the radius of the acoustic shadow for acoustic charged black hole is larger than that for Reissner-Nordstr\"{o}m (RN) black hole, and both of them are suppressed by increasing the black hole charge because their related outer horizons become smaller. Then the QNM frequencies under scalar field perturbation and its eikonal limit are computed via numeric method and acoustic shadow, respectively. We find that the acoustic charged black hole is stable under the perturbation and the QNM frequencies are much weaker than that for the astrophysical black hole. Moreover, as the tuning parameter increases, the perturbation oscillates more mildly and its damping time becomes longer, while as the charge increases, the oscillation is enhanced slightly and the perturbation decays a little faster which is different from that in RN black hole. Finally, we numerically study the analogue Hawking radiation. We find that the grey-body factor and energy emission rate are suppressed by the angular number and the charge, but they do not monotonically depend on the tuning parameter in the acoustic charged black hole. The behavior of the energy emission rate affected by the parameters could be explained by the dependent behavior of the Hawking temperature. We expect that our results could shed light to the study of black holes in both theoretical and experimental perspectives. |
gr-qc/9407009 | Othmar Brodbeck | Othmar Brodbeck and Norbert Straumann | Instability Proof for Einstein-Yang-Mills Solitons with Arbitrary Gauge
Groups | 18 pages, Latex, ZU-TH 19/94 | null | null | null | gr-qc | null | We prove that static, spherically symmetric, asymptotically flat, regular
solutions of the Einstein-Yang-Mills equations are unstable for arbitrary gauge
groups, at least for the ``generic" case. This conclusion is derived without
explicit knowledge of the possible equilibrium solutions.
| [
{
"created": "Tue, 12 Jul 1994 11:45:59 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Brodbeck",
"Othmar",
""
],
[
"Straumann",
"Norbert",
""
]
] | We prove that static, spherically symmetric, asymptotically flat, regular solutions of the Einstein-Yang-Mills equations are unstable for arbitrary gauge groups, at least for the ``generic" case. This conclusion is derived without explicit knowledge of the possible equilibrium solutions. |
gr-qc/0502015 | Valerio Faraoni | Valerio Faraoni (Bishop's University) | Phase space geometry in scalar-tensor cosmology | 18 pages, 9 figures, latex, to appear in Ann. Phys. (NY) | Ann.Phys.317:366-382,2005 | 10.1016/j.aop.2004.11.009 | null | gr-qc astro-ph | null | We study the phase space of spatially homogeneous and isotropic cosmology in
general scalar-tensor theories. A reduction to a two-dimensional phase space is
performed when possible-in these situations the phase space is usually a
two-dimensional curved surface embedded in a three-dimensional space and
composed of two sheets attached to each other, possibly with complicated
topology. The results obtained are independent of the choice of the coupling
function of the theory and, in certain situations, also of the potential.
| [
{
"created": "Thu, 3 Feb 2005 20:54:04 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Faraoni",
"Valerio",
"",
"Bishop's University"
]
] | We study the phase space of spatially homogeneous and isotropic cosmology in general scalar-tensor theories. A reduction to a two-dimensional phase space is performed when possible-in these situations the phase space is usually a two-dimensional curved surface embedded in a three-dimensional space and composed of two sheets attached to each other, possibly with complicated topology. The results obtained are independent of the choice of the coupling function of the theory and, in certain situations, also of the potential. |
0803.0416 | Jesus Martin-Martin | J. Martin and A. Tiemblo | The role of translational invariance in non linear gauge theories of
gravity | 17 pages, LaTeX | Int.J.Geom.Meth.Mod.Phys.05:253-264,2008 | 10.1142/S0219887808002734 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The internal structure of the tetrads in a Poincar\'e non linear gauge theory
of gravity is considered. Minkowskian coordinates becomes dynamical degrees of
freedom playing the role of Goldstone bosons of the translations. A critical
length allowing a covariant expansion similar to the weak field approach is
deduced, the zeroth order metric being maximally symmetric (Minkowskian in some
cases).
| [
{
"created": "Tue, 4 Mar 2008 11:34:48 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Martin",
"J.",
""
],
[
"Tiemblo",
"A.",
""
]
] | The internal structure of the tetrads in a Poincar\'e non linear gauge theory of gravity is considered. Minkowskian coordinates becomes dynamical degrees of freedom playing the role of Goldstone bosons of the translations. A critical length allowing a covariant expansion similar to the weak field approach is deduced, the zeroth order metric being maximally symmetric (Minkowskian in some cases). |
1409.0527 | Hooman Moradpour Hooman | Hooman Moradpour and Nematollah Riazi | Dynamic conformal spherically symmetric solutions in an accelerated
background | Accepted by Rom. Rep. Phys | Romanian Reports in Physics, Vol. 68, No. 4, P. 1382--1396 (2016) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider dynamical spherically symmetric spacetimes, which are conformal
to the static spherically symmetric metrics, and find new solutions of Einstein
equations by symmetry considerations. Our study help us classify various
conformal Black Holes that are embedded within a dynamic background into the
one class of solutions with the same conformal symmetry. In addition,
Thermodynamics, mathematical and gravitational properties are addressed. These
solutions point to have a better resolution of the meaning of the Black Holes
in the dynamic background.
| [
{
"created": "Sun, 31 Aug 2014 14:27:22 GMT",
"version": "v1"
},
{
"created": "Wed, 18 Feb 2015 08:04:27 GMT",
"version": "v2"
},
{
"created": "Tue, 23 Jun 2015 10:26:30 GMT",
"version": "v3"
},
{
"created": "Mon, 3 Aug 2015 12:48:44 GMT",
"version": "v4"
}
] | 2016-12-23 | [
[
"Moradpour",
"Hooman",
""
],
[
"Riazi",
"Nematollah",
""
]
] | We consider dynamical spherically symmetric spacetimes, which are conformal to the static spherically symmetric metrics, and find new solutions of Einstein equations by symmetry considerations. Our study help us classify various conformal Black Holes that are embedded within a dynamic background into the one class of solutions with the same conformal symmetry. In addition, Thermodynamics, mathematical and gravitational properties are addressed. These solutions point to have a better resolution of the meaning of the Black Holes in the dynamic background. |
gr-qc/9912083 | Gaetano Lambiase | S. Capozziello, G. Lambiase | Selection Rules in Minisuperspace Quantum Cosmology | LaTex file, 22 pag., no figures, to appear in Gen. Rel. Grav | Gen.Rel.Grav. 32 (2000) 673-696 | 10.1023/A:1001967102409 | null | gr-qc | null | The existence of a Noether symmetry for a given minisuperspace cosmological
model is a sort of selection rule to recover classical behaviours in cosmic
evolution since oscillatory regimes for the wave function of the universe come
out. The so called Hartle criterion to select correlated regions in the
configuration space of dynamical variables can be directly connected to the
presence of a Noether symmetry and we show that such a statement works for
generic extended theories of gravity in the framework of minisuperspace
approximation. Examples and exact cosmological solutions are given for
nonminimally coupled and higher--order theories.
| [
{
"created": "Mon, 20 Dec 1999 18:22:40 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Capozziello",
"S.",
""
],
[
"Lambiase",
"G.",
""
]
] | The existence of a Noether symmetry for a given minisuperspace cosmological model is a sort of selection rule to recover classical behaviours in cosmic evolution since oscillatory regimes for the wave function of the universe come out. The so called Hartle criterion to select correlated regions in the configuration space of dynamical variables can be directly connected to the presence of a Noether symmetry and we show that such a statement works for generic extended theories of gravity in the framework of minisuperspace approximation. Examples and exact cosmological solutions are given for nonminimally coupled and higher--order theories. |
gr-qc/0502037 | Oliver Rinne | Oliver Rinne and John M. Stewart | A strongly hyperbolic and regular reduction of Einstein's equations for
axisymmetric spacetimes | 22 pages, to appear in Class. Quantum Grav. 22 | Class. Quantum Grav. 22, 1143-1166 (2005) | 10.1088/0264-9381/22/6/015 | DAMTP-2005-17 | gr-qc | null | This paper is concerned exclusively with axisymmetric spacetimes. We want to
develop reductions of Einstein's equations which are suitable for numerical
evolutions. We first make a Kaluza-Klein type dimensional reduction followed by
an ADM reduction on the Lorentzian 3-space, the (2+1)+1 formalism. We include
also the Z4 extension of Einstein's equations adapted to this formalism. Our
gauge choice is based on a generalized harmonic gauge condition. We consider
vacuum and perfect fluid sources.
We use these ingredients to construct a strongly hyperbolic first-order
evolution system and exhibit its characteristic structure. This enables us to
construct constraint-preserving stable outer boundary conditions. We use
cylindrical polar coordinates and so we provide a careful discussion of the
coordinate singularity on axis. By choosing our dependent variables
appropriately we are able to produce an evolution system in which each and
every term is manifestly regular on axis.
| [
{
"created": "Wed, 9 Feb 2005 15:16:38 GMT",
"version": "v1"
}
] | 2008-11-22 | [
[
"Rinne",
"Oliver",
""
],
[
"Stewart",
"John M.",
""
]
] | This paper is concerned exclusively with axisymmetric spacetimes. We want to develop reductions of Einstein's equations which are suitable for numerical evolutions. We first make a Kaluza-Klein type dimensional reduction followed by an ADM reduction on the Lorentzian 3-space, the (2+1)+1 formalism. We include also the Z4 extension of Einstein's equations adapted to this formalism. Our gauge choice is based on a generalized harmonic gauge condition. We consider vacuum and perfect fluid sources. We use these ingredients to construct a strongly hyperbolic first-order evolution system and exhibit its characteristic structure. This enables us to construct constraint-preserving stable outer boundary conditions. We use cylindrical polar coordinates and so we provide a careful discussion of the coordinate singularity on axis. By choosing our dependent variables appropriately we are able to produce an evolution system in which each and every term is manifestly regular on axis. |
1503.05552 | Subenoy Chakraborty | Subenoy Chakraborty, Supriya Pan, and Subhajit Saha | A unified cosmic evolution: Inflation to late time acceleration | 21 pages, 17 figures, some typos corrected, references updated | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The present work deals with a cosmological model having particle creation
mechanism in the framework of irreversible thermodynamics. In the second order
non-equilibrium thermodynamical prescription, the particle creation rate is
treated as the dissipative effect. The non-equilibrium thermodynamical process
is assumed to be isentropic, and, as a consequence, the entropy per particle is
constant, and, hence, the dissipative pressure can be expressed linearly in
terms of the particle creation rate in the background of the homogeneous and
isotropic flat FLRW model. By proper choice of the particle creation rate as a
function of the Hubble parameter, the model shows the evolution of the universe
starting from the inflationary scenario to the present accelerating phase,
considering the cosmic matter as normal perfect fluid with barotropic equation
of state.
| [
{
"created": "Wed, 18 Mar 2015 18:54:20 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Apr 2015 12:36:50 GMT",
"version": "v2"
}
] | 2015-05-01 | [
[
"Chakraborty",
"Subenoy",
""
],
[
"Pan",
"Supriya",
""
],
[
"Saha",
"Subhajit",
""
]
] | The present work deals with a cosmological model having particle creation mechanism in the framework of irreversible thermodynamics. In the second order non-equilibrium thermodynamical prescription, the particle creation rate is treated as the dissipative effect. The non-equilibrium thermodynamical process is assumed to be isentropic, and, as a consequence, the entropy per particle is constant, and, hence, the dissipative pressure can be expressed linearly in terms of the particle creation rate in the background of the homogeneous and isotropic flat FLRW model. By proper choice of the particle creation rate as a function of the Hubble parameter, the model shows the evolution of the universe starting from the inflationary scenario to the present accelerating phase, considering the cosmic matter as normal perfect fluid with barotropic equation of state. |
1103.6140 | Vyacheslav Ivanovich Dokuchaev | Vyacheslav I. Dokuchaev | Is there life inside black holes? | 11 pages, 5 figures; references added | Class. Quantum Grav. 28 (2011) 235015 | 10.1088/0264-9381/28/23/235015 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bound inside rotating or charged black holes, there are stable periodic
planetary orbits, which neither come out nor terminate at the central
singularity. Stable periodic orbits inside black holes exist even for photons.
These bound orbits may be defined as orbits of the third kind, following the
Chandrasekhar classification of particle orbits in the black hole gravitational
field. The existence domain for the third kind orbits is rather spacious, and
thus there is place for life inside supermassive black holes in the galactic
nuclei. Interiors of the supermassive black holes may be inhabited by
civilizations, being invisible from the outside. In principle, one can get
information from the interiors of black holes by observing their white hole
counterparts.
| [
{
"created": "Thu, 31 Mar 2011 10:50:03 GMT",
"version": "v1"
},
{
"created": "Sat, 9 Apr 2011 17:04:02 GMT",
"version": "v2"
},
{
"created": "Fri, 13 May 2011 12:34:09 GMT",
"version": "v3"
},
{
"created": "Fri, 18 Nov 2011 17:50:52 GMT",
"version": "v4"
}
] | 2015-03-19 | [
[
"Dokuchaev",
"Vyacheslav I.",
""
]
] | Bound inside rotating or charged black holes, there are stable periodic planetary orbits, which neither come out nor terminate at the central singularity. Stable periodic orbits inside black holes exist even for photons. These bound orbits may be defined as orbits of the third kind, following the Chandrasekhar classification of particle orbits in the black hole gravitational field. The existence domain for the third kind orbits is rather spacious, and thus there is place for life inside supermassive black holes in the galactic nuclei. Interiors of the supermassive black holes may be inhabited by civilizations, being invisible from the outside. In principle, one can get information from the interiors of black holes by observing their white hole counterparts. |
gr-qc/0009085 | Rafael A. Vera | Rafael A. Vera | Conflict between the Gravitational Field Energy and the Experiments | Standard Latex, 24 pages. Submitted to Physical Reviews D Minor but
important changes are made up to prevent any arguments based in
non-experimental facts | null | null | null | gr-qc | null | From the equivalence principle and true gravitational (G) time dilation
experiments it is concluded that ``matter is not invariable after a change of
relative position with respect to other bodies''. As a general principle (GP),
such variations cannot be locally detected because the basic parameters of all
of the 'well-defined parts' of the instruments change, lineally, in the same
proportion with respect to their original values''. Only observers that don't
change of position can detect them. Thus, to relate quantities measured by
observers in different G potentials they must be previously transformed after
Lorenz and G transformations derived from experiments. They are account for all
of the ``G tests''. However ``they are not consistent with the presumed energy
exchange between the field and the bodies''. The lack of energy of the G field
is justified from the GP, according to which particles models made up of
photons in stationary state obey same inertial and G laws as particle. Such
model has been previously tested with relativistic quantum-mechanics and all of
the G tests.
PACS: 04.80.cc, 04.20.Cv, 04.80.-y, 98.80.Cq
| [
{
"created": "Mon, 25 Sep 2000 14:37:47 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Feb 2001 08:25:54 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Vera",
"Rafael A.",
""
]
] | From the equivalence principle and true gravitational (G) time dilation experiments it is concluded that ``matter is not invariable after a change of relative position with respect to other bodies''. As a general principle (GP), such variations cannot be locally detected because the basic parameters of all of the 'well-defined parts' of the instruments change, lineally, in the same proportion with respect to their original values''. Only observers that don't change of position can detect them. Thus, to relate quantities measured by observers in different G potentials they must be previously transformed after Lorenz and G transformations derived from experiments. They are account for all of the ``G tests''. However ``they are not consistent with the presumed energy exchange between the field and the bodies''. The lack of energy of the G field is justified from the GP, according to which particles models made up of photons in stationary state obey same inertial and G laws as particle. Such model has been previously tested with relativistic quantum-mechanics and all of the G tests. PACS: 04.80.cc, 04.20.Cv, 04.80.-y, 98.80.Cq |
2004.12523 | Osvaldo Pablo Santillan | J. Osorio Morales and O. Santill\'an | About apparent superluminal drives in generic gravity theories | Some typos corrected | null | null | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | As is well known, there exists warp drives in GR, such as the Alcubierre
bubbles, which achieve an apparent faster than light travel \cite{alcubierre}.
A result due to Gao and Wald \cite{gaowald} suggests that such a travel is
unlikely for GR with matter satisfying both the Null Energy and the Null
Generic Conditions. There exists a generalization of this statement due to
Galloway, that ensures that the Gao-Wald result is true regardless the
underlying gravity model, unless there exists at least one inextendible null
geodesic with achronal image in the space time (a null line). The proof of this
proposition is based on techniques of causal theories, and has never been
released. In the present work an independent proof of this result is presented
by use of the Raychaudhuri equation, and avoiding several technical
complications described along the text. Some consequences of these affirmations
are discussed at last section, in particular their potential use in problems of
causality.
| [
{
"created": "Mon, 27 Apr 2020 00:55:03 GMT",
"version": "v1"
},
{
"created": "Sun, 8 Aug 2021 22:54:07 GMT",
"version": "v2"
},
{
"created": "Tue, 16 Nov 2021 00:37:13 GMT",
"version": "v3"
},
{
"created": "Thu, 14 Apr 2022 23:52:31 GMT",
"version": "v4"
}
] | 2022-04-18 | [
[
"Morales",
"J. Osorio",
""
],
[
"Santillán",
"O.",
""
]
] | As is well known, there exists warp drives in GR, such as the Alcubierre bubbles, which achieve an apparent faster than light travel \cite{alcubierre}. A result due to Gao and Wald \cite{gaowald} suggests that such a travel is unlikely for GR with matter satisfying both the Null Energy and the Null Generic Conditions. There exists a generalization of this statement due to Galloway, that ensures that the Gao-Wald result is true regardless the underlying gravity model, unless there exists at least one inextendible null geodesic with achronal image in the space time (a null line). The proof of this proposition is based on techniques of causal theories, and has never been released. In the present work an independent proof of this result is presented by use of the Raychaudhuri equation, and avoiding several technical complications described along the text. Some consequences of these affirmations are discussed at last section, in particular their potential use in problems of causality. |
gr-qc/0410076 | Michael A. Ivanov | Michael A. Ivanov | May gravitons be super-strong interacting particles? | 6 pages without figures, LaTeX. Contribution to The 14th Workshop on
General Relativity and Gravitation (JGRG14), which will be held in Nov 29 -
Dec 3 2004, Kyoto, Japan | null | null | null | gr-qc | null | A scheme, in which gravitons are super-strong interacting, is described. The
graviton background with the Planckian spectrum and a small effective
temperature is considered as a reservoir of gravitons. A cross-section of
interaction of a graviton with any particle is assumed to be a bilinear
function of its energies. Any pair of bodies are attracting not due to an
exchange with its own gravitons, but due to a pressure of external gravitons of
this background. A graviton pairing is necessary to obtain classical gravity.
Any divergencies are not possible in such the model because of natural smooth
cut-offs of the graviton spectrum from both sides. Some cosmological
consequences of this scheme are discussed, too. Also it is shown here that the
main conjecture of this approach may be verified at present on the Earth.
| [
{
"created": "Mon, 18 Oct 2004 06:34:41 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Ivanov",
"Michael A.",
""
]
] | A scheme, in which gravitons are super-strong interacting, is described. The graviton background with the Planckian spectrum and a small effective temperature is considered as a reservoir of gravitons. A cross-section of interaction of a graviton with any particle is assumed to be a bilinear function of its energies. Any pair of bodies are attracting not due to an exchange with its own gravitons, but due to a pressure of external gravitons of this background. A graviton pairing is necessary to obtain classical gravity. Any divergencies are not possible in such the model because of natural smooth cut-offs of the graviton spectrum from both sides. Some cosmological consequences of this scheme are discussed, too. Also it is shown here that the main conjecture of this approach may be verified at present on the Earth. |
gr-qc/9808028 | Jacob D. Bekenstein | Jacob D. Bekenstein (Hebrew University, Jerusalem) | Black Holes: Classical Properties, Thermodynamics and Heuristic
Quantization | LaTeX, 44 pages, 4 eps figs. and conf_cg.sty included. Lectures
delivered at the IX Brazilian School on Cosmology and Gravitation, Rio de
Janeiro 7-8/98. Updated references and positioning on page corrected | in Cosmology and Gravitation, M. Novello, ed. (Atlantisciences,
France 2000), pp. 1-85 | null | null | gr-qc | null | I discuss the no hair principle, the recently found hairy solutions, generic
properties of nonvacuum spherical static black holes, and the new no scalar
hair theorems. I go into the generic phenomenon of superradiance, first uniform
linear motion superradiance, then Kerr black hole superradiance, and finally
general rotational superradiance and its possible applications in the
laboratory. I show that the horizon area of a nearly stationary black hole can
be regarded as an adiabatic invariant. This invariance suggests that quantum
horizon area is quantized in multiples of a basic unit. Consideration of the
quantum version of the Christodoulou reversible processes provides support for
this idea. Horizon area quantization dictates a definite discrete black hole
mass spectrum, so that Hawking's semiclassical spectrum is predicted to be
replaced by a spectrum of nearly uniformly spaced lines whose envelope is
roughly Planckian. Line natural broadening seems not enough to wash out the
lines. To check on the possibility of line splitting, I present a simple
algebra involving, among other operators, the black hole observables. Under
simple assumptions it also leads to the uniformly spaced area spectrum.
| [
{
"created": "Tue, 11 Aug 1998 08:12:01 GMT",
"version": "v1"
},
{
"created": "Fri, 30 Oct 1998 07:40:51 GMT",
"version": "v2"
},
{
"created": "Mon, 2 Nov 1998 10:33:31 GMT",
"version": "v3"
}
] | 2007-05-23 | [
[
"Bekenstein",
"Jacob D.",
"",
"Hebrew University, Jerusalem"
]
] | I discuss the no hair principle, the recently found hairy solutions, generic properties of nonvacuum spherical static black holes, and the new no scalar hair theorems. I go into the generic phenomenon of superradiance, first uniform linear motion superradiance, then Kerr black hole superradiance, and finally general rotational superradiance and its possible applications in the laboratory. I show that the horizon area of a nearly stationary black hole can be regarded as an adiabatic invariant. This invariance suggests that quantum horizon area is quantized in multiples of a basic unit. Consideration of the quantum version of the Christodoulou reversible processes provides support for this idea. Horizon area quantization dictates a definite discrete black hole mass spectrum, so that Hawking's semiclassical spectrum is predicted to be replaced by a spectrum of nearly uniformly spaced lines whose envelope is roughly Planckian. Line natural broadening seems not enough to wash out the lines. To check on the possibility of line splitting, I present a simple algebra involving, among other operators, the black hole observables. Under simple assumptions it also leads to the uniformly spaced area spectrum. |
1901.02785 | Dmitri Gal'tsov | D.V. Gal'tsov and K.V. Kobialko | Completing characterization of photon orbits in Kerr and Kerr-Newman
metrics | Minor corrections, editing, Appendix added. 33 pages, 52 figures | Phys. Rev. D 99, 084043 (2019) | 10.1103/PhysRevD.99.084043 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, several new characteristics have been introduced to describe null
geodesic structure of stationary spacetimes, such as photon regions (PR) and
transversely trapping surfaces (TTS). The former are three-dimensional domains
confining the spherical photon orbits, while the latter are closed two-surface
of spherical topology which fill other regions called TTR. It is argued that in
generic stationary axisymmetric spacetime it is natural to consider also the
non-closed TTSs of the geometry of spherical cups, satisfying the same
conditions ("partial" TTS or PTTS), which fill the three-dimensional regions,
PTTR. We then show that PR, TTR and PTTR together with the corresponding
anti-trapping regions constitute the complete set of regions filling the entire
three-space (where timelike surfaces are defined) of Kerr-like spacetimes. This
construction provides a novel optical description of such spacetimes without
recurring to explicit solution of the geodesic equations. Applying this
analysis to Kerr-Newman metrics (including the overspinning ones) we reveal
four different optical types for different sets of the rotation and charge
parameters. To illustrate their properties we extend Synge analysis of photon
escape in the Schwarzschild metric to stationary spacetimes and construct
density graphs describing escape of photons from all the above regions.
| [
{
"created": "Wed, 9 Jan 2019 15:43:57 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Jan 2019 16:07:57 GMT",
"version": "v2"
}
] | 2019-05-01 | [
[
"Gal'tsov",
"D. V.",
""
],
[
"Kobialko",
"K. V.",
""
]
] | Recently, several new characteristics have been introduced to describe null geodesic structure of stationary spacetimes, such as photon regions (PR) and transversely trapping surfaces (TTS). The former are three-dimensional domains confining the spherical photon orbits, while the latter are closed two-surface of spherical topology which fill other regions called TTR. It is argued that in generic stationary axisymmetric spacetime it is natural to consider also the non-closed TTSs of the geometry of spherical cups, satisfying the same conditions ("partial" TTS or PTTS), which fill the three-dimensional regions, PTTR. We then show that PR, TTR and PTTR together with the corresponding anti-trapping regions constitute the complete set of regions filling the entire three-space (where timelike surfaces are defined) of Kerr-like spacetimes. This construction provides a novel optical description of such spacetimes without recurring to explicit solution of the geodesic equations. Applying this analysis to Kerr-Newman metrics (including the overspinning ones) we reveal four different optical types for different sets of the rotation and charge parameters. To illustrate their properties we extend Synge analysis of photon escape in the Schwarzschild metric to stationary spacetimes and construct density graphs describing escape of photons from all the above regions. |
1005.3110 | Morteza Mohseni | Morteza Mohseni | Stability of circular orbits of spinning particles in Schwarzschild-like
space-times | eps figures, submitted to General Relativity and Gravitation | Gen.Rel.Grav.42:2477-2490,2010 | 10.1007/s10714-010-0995-3 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Circular orbits of spinning test particles and their stability in
Schwarzschild-like backgrounds are investigated. For these space-times the
equations of motion admit solutions representing circular orbits with particles
spins being constant and normal to the plane of orbits. For the de Sitter
background the orbits are always stable with particle velocity and momentum
being co-linear along them. The world-line deviation equations for particles of
the same spin-to-mass ratios are solved and the resulting deviation vectors are
used to study the stability of orbits. It is shown that the orbits are stable
against radial perturbations. The general criterion for stability against
normal perturbations is obtained. Explicit calculations are performed in the
case of the Schwarzschild space-time leading to the conclusion that the orbits
are stable.
| [
{
"created": "Tue, 18 May 2010 06:32:12 GMT",
"version": "v1"
}
] | 2014-11-21 | [
[
"Mohseni",
"Morteza",
""
]
] | Circular orbits of spinning test particles and their stability in Schwarzschild-like backgrounds are investigated. For these space-times the equations of motion admit solutions representing circular orbits with particles spins being constant and normal to the plane of orbits. For the de Sitter background the orbits are always stable with particle velocity and momentum being co-linear along them. The world-line deviation equations for particles of the same spin-to-mass ratios are solved and the resulting deviation vectors are used to study the stability of orbits. It is shown that the orbits are stable against radial perturbations. The general criterion for stability against normal perturbations is obtained. Explicit calculations are performed in the case of the Schwarzschild space-time leading to the conclusion that the orbits are stable. |
2009.05459 | Christian Pfeifer | Manuel Hohmann, Christian Pfeifer, Nicoleta Voicu | Canonical variational completion and 4D Gauss-Bonnet gravity | 16 pages | The European Physical Journal Plus volume 136, Article number: 180
(2021) | 10.1140/epjp/s13360-021-01153-0 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, a proposal to obtain a finite contribution of second derivative
order to the gravitational field equations in \(D = 4\) dimensions from a
renormalized Gauss-Bonnet term in the action has received a wave of attention.
It triggered a discussion whether the employed renormalization procedure yields
a well-defined theory. One of the main criticisms is based on the fact that the
resulting field equations cannot be obtained as the Euler-Lagrange equations
from a diffeomorphism invariant action. In this work, we use techniques from
the inverse calculus of variations to point out that the renormalized truncated
Gauss-Bonnet equations cannot be obtained from any action at all (either
diffeomorphism invariant or not), in any dimension. Then, we employ canonical
variational completion, based on the notion of Vainberg-Tonti Lagrangian -
which consists in adding a canonically defined correction term to a given
system of equations, so as to make them derivable from an action. To apply this
technique to the suggested $4$D renormalized Gauss-Bonnet equations, we extend
the variational completion algorithm to some classes of PDE systems for which
the usual integral providing the Vainberg-Tonti Lagrangian diverges. We
discover that in $D>4$ the suggested field equations can be variationally
completed, choosing either the metric or its inverse as field variables; both
approaches yield consistently the same Lagrangian, whose variation leads to
fourth order field equations. In $D=4$, the Lagrangian of the variationally
completed theory diverges in both cases.
| [
{
"created": "Fri, 11 Sep 2020 14:12:29 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Dec 2020 11:22:54 GMT",
"version": "v2"
},
{
"created": "Tue, 9 Feb 2021 10:50:30 GMT",
"version": "v3"
}
] | 2021-02-10 | [
[
"Hohmann",
"Manuel",
""
],
[
"Pfeifer",
"Christian",
""
],
[
"Voicu",
"Nicoleta",
""
]
] | Recently, a proposal to obtain a finite contribution of second derivative order to the gravitational field equations in \(D = 4\) dimensions from a renormalized Gauss-Bonnet term in the action has received a wave of attention. It triggered a discussion whether the employed renormalization procedure yields a well-defined theory. One of the main criticisms is based on the fact that the resulting field equations cannot be obtained as the Euler-Lagrange equations from a diffeomorphism invariant action. In this work, we use techniques from the inverse calculus of variations to point out that the renormalized truncated Gauss-Bonnet equations cannot be obtained from any action at all (either diffeomorphism invariant or not), in any dimension. Then, we employ canonical variational completion, based on the notion of Vainberg-Tonti Lagrangian - which consists in adding a canonically defined correction term to a given system of equations, so as to make them derivable from an action. To apply this technique to the suggested $4$D renormalized Gauss-Bonnet equations, we extend the variational completion algorithm to some classes of PDE systems for which the usual integral providing the Vainberg-Tonti Lagrangian diverges. We discover that in $D>4$ the suggested field equations can be variationally completed, choosing either the metric or its inverse as field variables; both approaches yield consistently the same Lagrangian, whose variation leads to fourth order field equations. In $D=4$, the Lagrangian of the variationally completed theory diverges in both cases. |
2005.12384 | Davi Rodrigues | Davi C. Rodrigues, Valerio Marra | The radial acceleration relation and its emergent nature | 2 pages, 1 figure. To appear in the Proceedings IAU Symposium No.
359, 2020. Galaxy evolution and feedback across different environments
(Galfeed) | Proc. IAU 15 (2020) 457-459 | 10.1017/S1743921320001684 | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We review some of our recent results about the Radial Acceleration Relation
(RAR) and its interpretation as either a fundamental or an emergent law. The
former interpretation is in agreement with a class of modified gravity theories
that dismiss the need for dark matter in galaxies (MOND in particular). Our
most recent analysis, which includes refinements on the priors and the Bayesian
test for compatibility between the posteriors, confirms that the hypothesis of
a fundamental RAR is rejected at more than 5$\sigma$ from the very same data
that was used to infer the RAR.
| [
{
"created": "Mon, 25 May 2020 20:30:08 GMT",
"version": "v1"
}
] | 2021-07-01 | [
[
"Rodrigues",
"Davi C.",
""
],
[
"Marra",
"Valerio",
""
]
] | We review some of our recent results about the Radial Acceleration Relation (RAR) and its interpretation as either a fundamental or an emergent law. The former interpretation is in agreement with a class of modified gravity theories that dismiss the need for dark matter in galaxies (MOND in particular). Our most recent analysis, which includes refinements on the priors and the Bayesian test for compatibility between the posteriors, confirms that the hypothesis of a fundamental RAR is rejected at more than 5$\sigma$ from the very same data that was used to infer the RAR. |
0706.3538 | Fabrizio Canfora | F. Canfora | Some solutions with torsion in Chern-Simons gravity and observable
effects | 17 pages, no figures; test polished; references added; physical
interpretation clarified; | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that in all odd dimensional Chern-Simons theories states in which
the torsion is non zero (but it can approach smoothly to zero outside suitable
regions) do exist. Some possible observational effects related to neutrino
oscillations are pointed out. In the theory of continuum media (in which
suitable defects can be described by localized non vanishing torsion) "the
gravitational intuition" is a rather useful tool to describe the physical
effects of such defects. A possible astrophysical application is shortly
described.
| [
{
"created": "Sun, 24 Jun 2007 22:31:19 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Jul 2008 15:41:53 GMT",
"version": "v2"
}
] | 2008-07-02 | [
[
"Canfora",
"F.",
""
]
] | It is shown that in all odd dimensional Chern-Simons theories states in which the torsion is non zero (but it can approach smoothly to zero outside suitable regions) do exist. Some possible observational effects related to neutrino oscillations are pointed out. In the theory of continuum media (in which suitable defects can be described by localized non vanishing torsion) "the gravitational intuition" is a rather useful tool to describe the physical effects of such defects. A possible astrophysical application is shortly described. |
1910.09245 | Manuel Hohmann | Manuel Hohmann | Gauge-invariant approach to the parametrized post-Newtonian formalism | LaTeX, 21 pages, no figures; published version | Phys. Rev. D 101, 024061 (2020) | 10.1103/PhysRevD.101.024061 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present an approach to the parametrized post-Newtonian (PPN) formalism
which is based on gauge-invariant higher order perturbation theory. This
approach divides the components of the metric perturbations into
gauge-invariant quantities, which carry information about the physical system
under consideration, and pure gauge quantities, which describe the choice of
the coordinate system. This separation generally leads to a simplification of
the PPN procedure, since only the gauge-invariant quantities appear in the
field equations and must be determined by solving them. Another simplification
arises from the fact that the gauge-invariant approach supersedes the necessity
to first choose a gauge for solving the gravitational field equations and later
transforming the obtained solution into the standard PPN gauge, as it is
conventionally done in the PPN formalism, whose standard PPN gauge is
determined only after the full solution is known. In addition to the usual
metric formulation, we also present a tetrad formulation of the gauge-invariant
PPN formalism. To illustrate their practical application, we demonstrate the
calculation of the PPN parameters of a well-known scalar-tensor class of
theories.
| [
{
"created": "Mon, 21 Oct 2019 10:02:09 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Feb 2020 06:27:44 GMT",
"version": "v2"
}
] | 2020-02-05 | [
[
"Hohmann",
"Manuel",
""
]
] | We present an approach to the parametrized post-Newtonian (PPN) formalism which is based on gauge-invariant higher order perturbation theory. This approach divides the components of the metric perturbations into gauge-invariant quantities, which carry information about the physical system under consideration, and pure gauge quantities, which describe the choice of the coordinate system. This separation generally leads to a simplification of the PPN procedure, since only the gauge-invariant quantities appear in the field equations and must be determined by solving them. Another simplification arises from the fact that the gauge-invariant approach supersedes the necessity to first choose a gauge for solving the gravitational field equations and later transforming the obtained solution into the standard PPN gauge, as it is conventionally done in the PPN formalism, whose standard PPN gauge is determined only after the full solution is known. In addition to the usual metric formulation, we also present a tetrad formulation of the gauge-invariant PPN formalism. To illustrate their practical application, we demonstrate the calculation of the PPN parameters of a well-known scalar-tensor class of theories. |
1309.4685 | Andrzej Okolow | Andrzej Okolow | ADM-like Hamiltonian formulation of gravity in the teleparallel
geometry: derivation of constraint algebra | 50 pages, LaTeX2e. The original 73 page paper arXiv:1111.5498v1 was
revised and divided into two parts. The present paper is the second part of
the original one (the first part is available as arXiv:1111.5498v2) | Gen. Rel. Grav. 46, 1636 (2014) | 10.1007/s10714-013-1636-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive a new constraint algebra for a Hamiltonian formulation of the
Teleparallel Equivalent of General Relativity treated as a theory of cotetrad
fields on a spacetime. The algebra turns out to be closed.
| [
{
"created": "Wed, 18 Sep 2013 15:46:24 GMT",
"version": "v1"
}
] | 2021-06-22 | [
[
"Okolow",
"Andrzej",
""
]
] | We derive a new constraint algebra for a Hamiltonian formulation of the Teleparallel Equivalent of General Relativity treated as a theory of cotetrad fields on a spacetime. The algebra turns out to be closed. |
gr-qc/0504090 | Kourosh Nozari | Kourosh Nozari and Tahereh Azizi | Coherent States of Harmonic Oscillator and Generalized Uncertainty
Principle | 12 pages, no figure | Int.J.Quant.Inf. 3 (2005) 623-632 | 10.1142/S0219749905001468 | null | gr-qc | null | In this paper dynamics and quantum mechanical coherent states of a simple
harmonic oscillator are considered in the framework of Generalized Uncertainty
Principle(GUP). Equations of motion for simple harmonic oscillator are derived
and some of their new implications are discussed. Then coherent states of
harmonic oscillator in the case of GUP are compared with relative situation in
ordinary quantum mechanics. It is shown that in the framework of GUP there is
no considerable difference in definition of coherent states relative to
ordinary quantum mechanics. But, considering expectation values and variances
of some operators, based on quantum gravitational arguments one concludes that
although it is possible to have complete coherency and vanishing broadening in
usual quantum mechanics, gravitational induced uncertainty destroys complete
coherency in quantum gravity and it is not possible to have a monochromatic ray
in principle.
| [
{
"created": "Wed, 20 Apr 2005 11:12:37 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Nozari",
"Kourosh",
""
],
[
"Azizi",
"Tahereh",
""
]
] | In this paper dynamics and quantum mechanical coherent states of a simple harmonic oscillator are considered in the framework of Generalized Uncertainty Principle(GUP). Equations of motion for simple harmonic oscillator are derived and some of their new implications are discussed. Then coherent states of harmonic oscillator in the case of GUP are compared with relative situation in ordinary quantum mechanics. It is shown that in the framework of GUP there is no considerable difference in definition of coherent states relative to ordinary quantum mechanics. But, considering expectation values and variances of some operators, based on quantum gravitational arguments one concludes that although it is possible to have complete coherency and vanishing broadening in usual quantum mechanics, gravitational induced uncertainty destroys complete coherency in quantum gravity and it is not possible to have a monochromatic ray in principle. |
gr-qc/0601134 | Alfredo Henriques Barbosa | Alfredo B. Henriques | Loop quantum cosmology and the Wheeler-De Witt equation | 17 pages; 5 figures | Gen.Rel.Grav. 38 (2006) 1645-1659 | 10.1007/s10714-006-0330-1 | null | gr-qc | null | We present some results concerning the large volume limit of loop quantum
cosmology in the flat homogeneous and isotropic case. We derive the Wheeler-De
Witt equation in this limit. Looking for the action from which this equation
can also be obtained, we then address the problem of the modifications to be
brought to the Friedman's equation of motion and to the equation of motion of
the scalar field, in the classical limit.
| [
{
"created": "Mon, 30 Jan 2006 15:33:33 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Henriques",
"Alfredo B.",
""
]
] | We present some results concerning the large volume limit of loop quantum cosmology in the flat homogeneous and isotropic case. We derive the Wheeler-De Witt equation in this limit. Looking for the action from which this equation can also be obtained, we then address the problem of the modifications to be brought to the Friedman's equation of motion and to the equation of motion of the scalar field, in the classical limit. |
1910.13448 | Matteo Braglia | M. Ballardini, M. Braglia, F. Finelli, G. Marozzi, A. A. Starobinsky | Energy-momentum tensor and helicity for gauge fields coupled to a
pseudo-scalar inflaton | 18 pages, 9 figures. Corrected some typos and removed Appendix B. The
results are unchanged | Phys. Rev. D 100, 123542 (2019) | 10.1103/PhysRevD.100.123542 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the energy-momentum tensor and helicity of gauge fields coupled
through $g \phi F \tilde{F}/4$ to a pseudo-scalar field $\phi$ driving
inflation. Under the assumption of a constant time derivative of the background
inflaton, we compute analitically divergent and finite terms of the energy
density and helicity of gauge fields for any value of the coupling $g$. We
introduce a suitable adiabatic expansion for mode functions of physical states
of the gauge fields which correctly reproduces ultraviolet divergences in
average quantities and identify corresponding counterterms. Our calculations
shed light on the accuracy and the range of validity of approximated analytic
estimates of the energy density and helicity terms previously existed in the
literature in the strongly coupled regime only, i.e. for $g \dot \phi/(2H) \gg
1$. We discuss the implications of our analytic calculations for the
backreaction of quantum fluctuations onto the inflaton evolution.
| [
{
"created": "Tue, 29 Oct 2019 15:38:58 GMT",
"version": "v1"
},
{
"created": "Wed, 25 Dec 2019 11:04:30 GMT",
"version": "v2"
},
{
"created": "Sat, 15 Jan 2022 09:44:32 GMT",
"version": "v3"
}
] | 2022-01-19 | [
[
"Ballardini",
"M.",
""
],
[
"Braglia",
"M.",
""
],
[
"Finelli",
"F.",
""
],
[
"Marozzi",
"G.",
""
],
[
"Starobinsky",
"A. A.",
""
]
] | We study the energy-momentum tensor and helicity of gauge fields coupled through $g \phi F \tilde{F}/4$ to a pseudo-scalar field $\phi$ driving inflation. Under the assumption of a constant time derivative of the background inflaton, we compute analitically divergent and finite terms of the energy density and helicity of gauge fields for any value of the coupling $g$. We introduce a suitable adiabatic expansion for mode functions of physical states of the gauge fields which correctly reproduces ultraviolet divergences in average quantities and identify corresponding counterterms. Our calculations shed light on the accuracy and the range of validity of approximated analytic estimates of the energy density and helicity terms previously existed in the literature in the strongly coupled regime only, i.e. for $g \dot \phi/(2H) \gg 1$. We discuss the implications of our analytic calculations for the backreaction of quantum fluctuations onto the inflaton evolution. |
1210.7499 | Naonori Sugiyama | Naonori S. Sugiyama and Toshifumi Futamase | Toward an accurate Dark Matter power spectrum beyond BAO scales | 4 pages, 1 figure | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a new approximated expression for non-linear Dark Matter power
spectrum much beyond BAO scales. The proposed expression agrees with the result
of N-body simulation with the accuracy better than 2 % up to k=1.0 [h/Mpc] and
k=0.7 [h/Mpc] at z=3.0 and z=1.0, respectively. Even at z=0.35, the accuracy
remains within 10 % up to k=0.8 [h/Mpc]. In doing so, we used an approximation
for the kernel functions used in the Standard Perturbation Theory (SPT) which
is also used to prove the Reg PT proposed by Bernardeau et al. (2011).
| [
{
"created": "Sun, 28 Oct 2012 19:53:30 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Nov 2012 11:29:25 GMT",
"version": "v2"
},
{
"created": "Fri, 30 Nov 2012 19:25:03 GMT",
"version": "v3"
}
] | 2012-12-03 | [
[
"Sugiyama",
"Naonori S.",
""
],
[
"Futamase",
"Toshifumi",
""
]
] | We propose a new approximated expression for non-linear Dark Matter power spectrum much beyond BAO scales. The proposed expression agrees with the result of N-body simulation with the accuracy better than 2 % up to k=1.0 [h/Mpc] and k=0.7 [h/Mpc] at z=3.0 and z=1.0, respectively. Even at z=0.35, the accuracy remains within 10 % up to k=0.8 [h/Mpc]. In doing so, we used an approximation for the kernel functions used in the Standard Perturbation Theory (SPT) which is also used to prove the Reg PT proposed by Bernardeau et al. (2011). |
2303.02877 | Jose Miguel Ladino | Jose Miguel Ladino and Eduard Larra\~naga | Eikonal quasinormal modes, photon sphere and shadow of a charged black
hole in the 4D Einstein-Gauss-Bonnet gravity | 16 pages, 5 figures, 5 tables | Int J Theor Phys 62, 209 (2023) | 10.1007/s10773-023-05440-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we investigate the relationship between the geometrical
properties, the photon sphere, the shadow, and the eikonal quasinormal modes of
electrically charged black holes in 4D Einstein-Gauss-Bonnet gravity.
Quasinormal modes are complex frequency oscillations that are dependent on the
geometry of spacetime and have significant applications in studying black hole
properties and testing alternative theories of gravity. Here, we focus on the
eikonal limit for high frequency quasinormal modes and their connection to the
black holes geometric characteristics. To study the photon sphere, quasinormal
modes, and black hole shadow, we employ various techniques such as the WKB
method in various orders of approximation, the Poschl-Teller potential method,
and Churilova's analytical formulas. Our results indicate that the real part of
the eikonal quasinormal mode frequencies of test fields are linked to the
unstable circular null geodesic and are correlated with the shadow radius for
an Charged Einstein-Gauss-Bonnet 4D black hole. Furthermore, we found that the
real part of quasinormal modes, the photon sphere and shadow radius have a
lower value for charged black holes in 4D Einstein-Gauss-Bonnet gravity
compared to black holes without electric charge and those of static black holes
in general relativity. Additionally, we explore various analytical formulas for
the photon spheres and shadows, deducing an Churilova's approximate formula for
the black hole shadow radius of the Charged Einstein-Gauss-Bonnet 4D black
hole, which arises from its connection with the eikonal quasinormal modes.
| [
{
"created": "Mon, 6 Mar 2023 04:09:49 GMT",
"version": "v1"
},
{
"created": "Sun, 12 Mar 2023 05:59:03 GMT",
"version": "v2"
}
] | 2023-10-03 | [
[
"Ladino",
"Jose Miguel",
""
],
[
"Larrañaga",
"Eduard",
""
]
] | In this work, we investigate the relationship between the geometrical properties, the photon sphere, the shadow, and the eikonal quasinormal modes of electrically charged black holes in 4D Einstein-Gauss-Bonnet gravity. Quasinormal modes are complex frequency oscillations that are dependent on the geometry of spacetime and have significant applications in studying black hole properties and testing alternative theories of gravity. Here, we focus on the eikonal limit for high frequency quasinormal modes and their connection to the black holes geometric characteristics. To study the photon sphere, quasinormal modes, and black hole shadow, we employ various techniques such as the WKB method in various orders of approximation, the Poschl-Teller potential method, and Churilova's analytical formulas. Our results indicate that the real part of the eikonal quasinormal mode frequencies of test fields are linked to the unstable circular null geodesic and are correlated with the shadow radius for an Charged Einstein-Gauss-Bonnet 4D black hole. Furthermore, we found that the real part of quasinormal modes, the photon sphere and shadow radius have a lower value for charged black holes in 4D Einstein-Gauss-Bonnet gravity compared to black holes without electric charge and those of static black holes in general relativity. Additionally, we explore various analytical formulas for the photon spheres and shadows, deducing an Churilova's approximate formula for the black hole shadow radius of the Charged Einstein-Gauss-Bonnet 4D black hole, which arises from its connection with the eikonal quasinormal modes. |
0709.1680 | Madhavan Varadarajan | Madhavan Varadarajan | Towards new background independent representations for Loop Quantum
Gravity | 22 pages, minor changes | Class.Quant.Grav.25:105011,2008 | 10.1088/0264-9381/25/10/105011 | null | gr-qc | null | Recently, uniqueness theorems were constructed for the representation used in
Loop Quantum Gravity. We explore the existence of alternate representations by
weakening the assumptions of the so called LOST uniqueness theorem. The
weakened assumptions seem physically reasonable and retain the key requirement
of explicit background independence. For simplicity, we restrict attention to
the case of gauge group U(1).
| [
{
"created": "Tue, 11 Sep 2007 17:21:48 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Sep 2007 23:55:13 GMT",
"version": "v2"
}
] | 2015-01-30 | [
[
"Varadarajan",
"Madhavan",
""
]
] | Recently, uniqueness theorems were constructed for the representation used in Loop Quantum Gravity. We explore the existence of alternate representations by weakening the assumptions of the so called LOST uniqueness theorem. The weakened assumptions seem physically reasonable and retain the key requirement of explicit background independence. For simplicity, we restrict attention to the case of gauge group U(1). |
gr-qc/9710119 | Roland Steinbauer | Roland Steinbauer | Geodesics and geodesic deviation for impulsive gravitational waves | final version, minor grammatical changes | J.Math.Phys. 39 (1998) 2201-2212 | 10.1063/1.532283 | null | gr-qc math-ph math.MP | null | The geometry of impulsive pp-waves is explored via the analysis of the
geodesic and geodesic deviation equation using the distributional form of the
metric. The geodesic equation involves formally ill-defined products of
distributions due to the nonlinearity of the equations and the presence of the
Dirac $\de$-distribution in the space time metric. Thus, strictly speaking, it
cannot be treated within Schwartz's linear theory of distributions. To cope
with this difficulty we proceed by first regularizing the
$\de$-singularity,then solving the regularized equation within classical smooth
functions and, finally, obtaining a distributional limit as solution to the
original problem. Furthermore it is shown that this limit is independent of the
regularization without requiring any additional condition, thereby confirming
earlier results in a mathematical rigorous fashion. We also treat the Jacobi
equation which, despite being linear in the deviation vector field, involves
even more delicate singular expressions, like the ``square'' of the Dirac
$\de$-distribution. Again the same regularization procedure provides us with a
perfectly well behaved smooth regularization and a regularization-independent
distributional limit. Hence it is concluded that the geometry of impulsive
pp-waves can be described consistently using distributions as long as careful
regularization procedures are used to handle the ill-defined products.
| [
{
"created": "Tue, 28 Oct 1997 16:14:15 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Mar 1998 12:09:29 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Steinbauer",
"Roland",
""
]
] | The geometry of impulsive pp-waves is explored via the analysis of the geodesic and geodesic deviation equation using the distributional form of the metric. The geodesic equation involves formally ill-defined products of distributions due to the nonlinearity of the equations and the presence of the Dirac $\de$-distribution in the space time metric. Thus, strictly speaking, it cannot be treated within Schwartz's linear theory of distributions. To cope with this difficulty we proceed by first regularizing the $\de$-singularity,then solving the regularized equation within classical smooth functions and, finally, obtaining a distributional limit as solution to the original problem. Furthermore it is shown that this limit is independent of the regularization without requiring any additional condition, thereby confirming earlier results in a mathematical rigorous fashion. We also treat the Jacobi equation which, despite being linear in the deviation vector field, involves even more delicate singular expressions, like the ``square'' of the Dirac $\de$-distribution. Again the same regularization procedure provides us with a perfectly well behaved smooth regularization and a regularization-independent distributional limit. Hence it is concluded that the geometry of impulsive pp-waves can be described consistently using distributions as long as careful regularization procedures are used to handle the ill-defined products. |
1003.3324 | Bernard J. Carr | B. J. Carr, Tomohiro Harada and Hideki Maeda | Can a primordial black hole or wormhole grow as fast as the universe? | 17 pages, 9 figures | null | 10.1088/0264-9381/27/18/183101 | RESCEU-8/10, CECS-PH-10/02 | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This review addresses the issue of whether there are physically realistic
self-similar solutions in which a primordial black hole is attached to an exact
or asymptotically Friedmann model for an equation of state of the form
$p=(\gamma-1)\rho c^2$. In the positive pressure case ($1 < \gamma < 2$), there
is no such solution when the black hole is attached to an exact Friedmann
background via a sonic point. However, it has been claimed that there is a
one-parameter family of asymptotically Friedmann black hole solutions providing
the ratio of the black hole size to the cosmological horizon size is in a
narrow range above some critical value. There are also "universal" black holes
in which the black hole has an apparent horizon but no event horizon. It turns
out that both these types of solution are only asymptotically {\it
quasi}-Friedmann, because they contain a solid angle deficit at large
distances, but they are not necessarily excluded observationally.
We also consider the possibility of self-similar black hole solutions in a
universe dominated by a scalar field. If the field is massless, the situation
resembles the stiff fluid case, so any black hole solution is again contrived,
although there may still be universal black hole solutions. The situation is
less clear if the scalar field is rolling down a potential and therefore
massive, as in the quintessence scenario. Although no explicit asymptotically
Friedmann black hole solutions of this kind are known, they are not excluded
and comparison with the $0 < \gamma < 2/3$ perfect fluid case suggests that
they should exist if the black hole is not too large. This implies that a black
hole might grow as fast as the cosmological horizon in a quintessence-dominated
universe in some circumstances, supporting the proposal that accretion onto
primordial black holes may have played a role in the production of the
supermassive black holes in galactic nuclei.
| [
{
"created": "Wed, 17 Mar 2010 08:47:00 GMT",
"version": "v1"
}
] | 2015-05-18 | [
[
"Carr",
"B. J.",
""
],
[
"Harada",
"Tomohiro",
""
],
[
"Maeda",
"Hideki",
""
]
] | This review addresses the issue of whether there are physically realistic self-similar solutions in which a primordial black hole is attached to an exact or asymptotically Friedmann model for an equation of state of the form $p=(\gamma-1)\rho c^2$. In the positive pressure case ($1 < \gamma < 2$), there is no such solution when the black hole is attached to an exact Friedmann background via a sonic point. However, it has been claimed that there is a one-parameter family of asymptotically Friedmann black hole solutions providing the ratio of the black hole size to the cosmological horizon size is in a narrow range above some critical value. There are also "universal" black holes in which the black hole has an apparent horizon but no event horizon. It turns out that both these types of solution are only asymptotically {\it quasi}-Friedmann, because they contain a solid angle deficit at large distances, but they are not necessarily excluded observationally. We also consider the possibility of self-similar black hole solutions in a universe dominated by a scalar field. If the field is massless, the situation resembles the stiff fluid case, so any black hole solution is again contrived, although there may still be universal black hole solutions. The situation is less clear if the scalar field is rolling down a potential and therefore massive, as in the quintessence scenario. Although no explicit asymptotically Friedmann black hole solutions of this kind are known, they are not excluded and comparison with the $0 < \gamma < 2/3$ perfect fluid case suggests that they should exist if the black hole is not too large. This implies that a black hole might grow as fast as the cosmological horizon in a quintessence-dominated universe in some circumstances, supporting the proposal that accretion onto primordial black holes may have played a role in the production of the supermassive black holes in galactic nuclei. |
gr-qc/0403116 | Christos G. Tsagas | N.K. Spyrou (Thessaloniki), C.G. Tsagas (UCT/DAMTP) | Covariant approach to the conformal dynamical equivalence in
astrophysics | 10 pages, to appear in Class. Quantum Grav | Class.Quant.Grav. 21 (2004) 2435-2444 | 10.1088/0264-9381/21/9/017 | null | gr-qc astro-ph | null | We use covariant techniques to examine the implications of the dynamical
equivalence between geodesic motions and adiabatic hydrodynamic flows. Assuming
that the metrics of a geodesically and a non-geodesically moving fluid are
conformally related, we calculate and compare their mass densities. The density
difference is then expressed in terms of the fundamental physical quantities of
the fluid, such as its energy and isotropic pressure. Both the relativistic and
the non-relativistic case are examined and their differences identified. Our
analysis suggests that observational determinations of astrophysical masses
based on purely Keplerian motions could underestimate the available amount of
matter.
| [
{
"created": "Tue, 30 Mar 2004 19:33:24 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Spyrou",
"N. K.",
"",
"Thessaloniki"
],
[
"Tsagas",
"C. G.",
"",
"UCT/DAMTP"
]
] | We use covariant techniques to examine the implications of the dynamical equivalence between geodesic motions and adiabatic hydrodynamic flows. Assuming that the metrics of a geodesically and a non-geodesically moving fluid are conformally related, we calculate and compare their mass densities. The density difference is then expressed in terms of the fundamental physical quantities of the fluid, such as its energy and isotropic pressure. Both the relativistic and the non-relativistic case are examined and their differences identified. Our analysis suggests that observational determinations of astrophysical masses based on purely Keplerian motions could underestimate the available amount of matter. |
1407.7038 | Laura Sampson | Laura Sampson, Nicolas Yunes, Neil Cornish, Marcelo Ponce, Enrico
Barausse, Antoine Klein, Carlos Palenzuela, and Luis Lehner | Projected Constraints on Scalarization with Gravitational Waves from
Neutron Star Binaries | 26 pages, 15 figures, 2 tables. Version resubmitted to PRD after
referee report. Discussion added to the conclusions addressing questions
raised in arXiv:1410.0738 | Phys. Rev. D 90, 124091 (2014) | 10.1103/PhysRevD.90.124091 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Certain scalar-tensor theories have the property of endowing stars with
scalar hair, sourced either by the star's own compactness (spontaneous
scalarization) or, for binary systems, by the companion's scalar hair (induced
scalarization) or by the orbital binding energy (dynamical scalarization).
Scalarized stars in binaries present different conservative dynamics than in
General Relativity, and can also excite a scalar mode in the metric
perturbation that carries away dipolar radiation. As a result, the binary orbit
shrinks faster than predicted in General Relativity, modifying the rate of
decay of the orbital period. In spite of this, scalar-tensor theories can pass
existing binary pulsar tests, because observed pulsars may not be compact
enough or sufficiently orbitally bound to activate scalarization. Gravitational
waves emitted during the last stages of compact binary inspirals are thus ideal
probes of scalarization effects. For the standard projected sensitivity of
advanced LIGO, we here show that, if neutron stars are sufficiently compact to
enter the detector's sensitivity band already scalarized, then gravitational
waves could place constraints at least comparable to binary pulsars. If the
stars dynamically scalarize while inspiraling in band, then constraints are
still possible provided the scalarization occurs sufficiently early in the
inspiral, roughly below an orbital frequency of 50Hz. In performing these
studies, we derive an easy-to-calculate data analysis measure, an integrated
phase difference between a General Relativistic and a modified signal, that
maps directly to the Bayes factor so as to determine whether a modified gravity
effect is detectable. Finally, we find that custom-made templates are equally
effective as model-independent, parameterized post-Einsteinian waveforms at
detecting such modified gravity effects at realistic signal-to-noise ratios.
| [
{
"created": "Fri, 25 Jul 2014 20:00:08 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Nov 2014 20:44:43 GMT",
"version": "v2"
}
] | 2015-01-07 | [
[
"Sampson",
"Laura",
""
],
[
"Yunes",
"Nicolas",
""
],
[
"Cornish",
"Neil",
""
],
[
"Ponce",
"Marcelo",
""
],
[
"Barausse",
"Enrico",
""
],
[
"Klein",
"Antoine",
""
],
[
"Palenzuela",
"Carlos",
""
],
[
"Lehner",
"Luis",
""
]
] | Certain scalar-tensor theories have the property of endowing stars with scalar hair, sourced either by the star's own compactness (spontaneous scalarization) or, for binary systems, by the companion's scalar hair (induced scalarization) or by the orbital binding energy (dynamical scalarization). Scalarized stars in binaries present different conservative dynamics than in General Relativity, and can also excite a scalar mode in the metric perturbation that carries away dipolar radiation. As a result, the binary orbit shrinks faster than predicted in General Relativity, modifying the rate of decay of the orbital period. In spite of this, scalar-tensor theories can pass existing binary pulsar tests, because observed pulsars may not be compact enough or sufficiently orbitally bound to activate scalarization. Gravitational waves emitted during the last stages of compact binary inspirals are thus ideal probes of scalarization effects. For the standard projected sensitivity of advanced LIGO, we here show that, if neutron stars are sufficiently compact to enter the detector's sensitivity band already scalarized, then gravitational waves could place constraints at least comparable to binary pulsars. If the stars dynamically scalarize while inspiraling in band, then constraints are still possible provided the scalarization occurs sufficiently early in the inspiral, roughly below an orbital frequency of 50Hz. In performing these studies, we derive an easy-to-calculate data analysis measure, an integrated phase difference between a General Relativistic and a modified signal, that maps directly to the Bayes factor so as to determine whether a modified gravity effect is detectable. Finally, we find that custom-made templates are equally effective as model-independent, parameterized post-Einsteinian waveforms at detecting such modified gravity effects at realistic signal-to-noise ratios. |
gr-qc/0001018 | Michael T. Anderson | Michael T. Anderson (SUNY Stony Brook) | On the structure of solutions to the static vacuum Einstein equations | 34 pages, Final version - contains corrections and improvements to
initial version. Annales Henri Poincare, (to appear) | Annales Henri Poincare 1 (2000) 995 | 10.1007/PL00001026 | null | gr-qc math.DG | null | A complete characterization is obtained of the asymptotic behavior of
solutions of the static vacuum Einstein equations which have a (pseudo)-compact
horizon or boundary and are complete away from the boundary. It is proved that
the time-symmetric space-like hypersurface has only finitely many ends, each of
which is either asymptotically flat (AF) or parabolic, as in the (static)
Kasner metric. Examples are given with both types of behavior, together with an
extensive discussion and new characterization of Weyl metrics. The asymptotics
result allows one in most circumstances to drop the AF assumption from the
static black hole uniqueness theorems and replace it with just a completeness
assumption.
| [
{
"created": "Fri, 7 Jan 2000 16:25:05 GMT",
"version": "v1"
},
{
"created": "Sun, 29 Oct 2000 19:40:37 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Anderson",
"Michael T.",
"",
"SUNY Stony Brook"
]
] | A complete characterization is obtained of the asymptotic behavior of solutions of the static vacuum Einstein equations which have a (pseudo)-compact horizon or boundary and are complete away from the boundary. It is proved that the time-symmetric space-like hypersurface has only finitely many ends, each of which is either asymptotically flat (AF) or parabolic, as in the (static) Kasner metric. Examples are given with both types of behavior, together with an extensive discussion and new characterization of Weyl metrics. The asymptotics result allows one in most circumstances to drop the AF assumption from the static black hole uniqueness theorems and replace it with just a completeness assumption. |
gr-qc/9510063 | Chris Isham | Chris Isham | Structural Issues in Quantum Gravity | 42 pages, latex, no figures. Writeup of GR14 plenary lecture | null | null | IMPERIAL/TP/95-96/07 | gr-qc hep-th quant-ph | null | A discursive, non-technical, analysis is made of some of the basic issues
that arise in almost any approach to quantum gravity, and of how these issues
stand in relation to recent developments in the field. Specific topics include
the applicability of the conceptual and mathematical structures of both
classical general relativity and standard quantum theory. This discussion is
preceded by a short history of the last twenty-five years of research in
quantum gravity, and concludes with speculations on what a future theory might
look like.
| [
{
"created": "Tue, 31 Oct 1995 22:45:43 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Isham",
"Chris",
""
]
] | A discursive, non-technical, analysis is made of some of the basic issues that arise in almost any approach to quantum gravity, and of how these issues stand in relation to recent developments in the field. Specific topics include the applicability of the conceptual and mathematical structures of both classical general relativity and standard quantum theory. This discussion is preceded by a short history of the last twenty-five years of research in quantum gravity, and concludes with speculations on what a future theory might look like. |
1408.0306 | Elias C. Vagenas | Leonardo Balart and Elias C. Vagenas | Regular black holes with a nonlinear electrodynamics source | v1: 19 pages, LaTeX, no figures; v2: typos corrected and one
reference removed to match published version in Phys. Rev. D | Phys. Rev. D 90, 124045 (2014) | 10.1103/PhysRevD.90.124045 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct several charged regular black hole metrics employing mass
distribution functions which are inspired by continuous probability
distributions. Some of these metrics satisfy the weak energy condition and
asymptotically behave as the Reissner--Nordstrom black hole. In each case, the
source to the Einstein equations corresponds to a nonlinear electrodynamics
model, which in the weak field limit becomes the Maxwell theory (compatible
with the Maxwell weak field limit or approximation). Furthermore, we include
other regular black hole solutions that satisfy the weak energy condition and
some of them correspond to the Maxwell theory in the weak field limit.
| [
{
"created": "Fri, 1 Aug 2014 21:08:40 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Dec 2014 18:59:50 GMT",
"version": "v2"
}
] | 2014-12-24 | [
[
"Balart",
"Leonardo",
""
],
[
"Vagenas",
"Elias C.",
""
]
] | We construct several charged regular black hole metrics employing mass distribution functions which are inspired by continuous probability distributions. Some of these metrics satisfy the weak energy condition and asymptotically behave as the Reissner--Nordstrom black hole. In each case, the source to the Einstein equations corresponds to a nonlinear electrodynamics model, which in the weak field limit becomes the Maxwell theory (compatible with the Maxwell weak field limit or approximation). Furthermore, we include other regular black hole solutions that satisfy the weak energy condition and some of them correspond to the Maxwell theory in the weak field limit. |
gr-qc/0608110 | Burkhard Kleihaus | Theodora Ioannidou, Burkhard Kleihaus and Jutta Kunz | Spinning Gravitating Skyrmions | 13 pages, 6 figures | Phys.Lett.B643:213-220,2006 | 10.1016/j.physletb.2006.10.055 | null | gr-qc hep-th | null | We investigate self-gravitating rotating solutions in the Einstein-Skyrme
theory. These solutions are globally regular and asymptotically flat. We
present a new kind of solutions with zero baryon number, which possess neither
a flat limit nor a static limit.
| [
{
"created": "Fri, 25 Aug 2006 15:24:50 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Ioannidou",
"Theodora",
""
],
[
"Kleihaus",
"Burkhard",
""
],
[
"Kunz",
"Jutta",
""
]
] | We investigate self-gravitating rotating solutions in the Einstein-Skyrme theory. These solutions are globally regular and asymptotically flat. We present a new kind of solutions with zero baryon number, which possess neither a flat limit nor a static limit. |
gr-qc/0309088 | Stephane Fay | Stephane Fay | Noether Symmetry of the Hyperextended Scalar Tensor theory for the FLRW
models | 11 pages | Class.Quant.Grav. 18 (2001) 4863-4870 | 10.1088/0264-9381/18/22/311 | null | gr-qc | null | We study in which conditions the Hyperextended Scalar Tensor theory in an
FLRW background admits a Noether symmetry and derive the vectors field
generating it.
| [
{
"created": "Thu, 18 Sep 2003 12:25:49 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Fay",
"Stephane",
""
]
] | We study in which conditions the Hyperextended Scalar Tensor theory in an FLRW background admits a Noether symmetry and derive the vectors field generating it. |
2003.01070 | Shahram Jalalzadeh | P.V. Moniz and S. Jalalzadeh | From Fractional Quantum Mechanics to Quantum Cosmology: An Overture | 21 pages, 1 figure | Mathematics 8(3), 313 (2020) | 10.3390/math8030313 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Fractional calculus is a couple of centuries old, but its development has
been less embraced and it was only within the last century that a program of
applications for physics started. Regarding quantum physics, it has been only
in the previous decade or so that the corresponding literature resulted in a
set of defying papers. In such a context, this manuscript constitutes a cordial
invitation, whose purpose is simply to suggest, mostly through a heuristic and
unpretentious presentation, the extension of fractional quantum mechanics to
cosmological settings. Being more specific, we start by outlining a historical
summary of fractional calculus. Then, following this motivation, a (very) brief
appraisal of fractional quantum mechanics is presented, but where details
(namely those of a mathematical nature) are left for literature perusing.
Subsequently, the application of fractional calculus in quantum cosmology is
introduced, advocating it as worthy to consider: if the progress of fractional
calculus serves as an argument, indeed useful consequences will also be drawn
(to cite from Leibnitz). In particular, we discuss different difficulties that
may affect the operational framework to employ, namely the issues of
minisuperspace covariance and fractional derivatives, for instance. An example
of investigation is provided by means of a very simple model. Concretely, we
restrict ourselves to speculate that with minimal fractional calculus elements,
we may have a peculiar tool to inspect the flatness problem of standard
cosmology. In summary, the subject of fractional quantum cosmology is herewith
proposed, merely realized in terms of an open program constituted by several
challenges.
| [
{
"created": "Mon, 2 Mar 2020 18:01:34 GMT",
"version": "v1"
}
] | 2020-03-03 | [
[
"Moniz",
"P. V.",
""
],
[
"Jalalzadeh",
"S.",
""
]
] | Fractional calculus is a couple of centuries old, but its development has been less embraced and it was only within the last century that a program of applications for physics started. Regarding quantum physics, it has been only in the previous decade or so that the corresponding literature resulted in a set of defying papers. In such a context, this manuscript constitutes a cordial invitation, whose purpose is simply to suggest, mostly through a heuristic and unpretentious presentation, the extension of fractional quantum mechanics to cosmological settings. Being more specific, we start by outlining a historical summary of fractional calculus. Then, following this motivation, a (very) brief appraisal of fractional quantum mechanics is presented, but where details (namely those of a mathematical nature) are left for literature perusing. Subsequently, the application of fractional calculus in quantum cosmology is introduced, advocating it as worthy to consider: if the progress of fractional calculus serves as an argument, indeed useful consequences will also be drawn (to cite from Leibnitz). In particular, we discuss different difficulties that may affect the operational framework to employ, namely the issues of minisuperspace covariance and fractional derivatives, for instance. An example of investigation is provided by means of a very simple model. Concretely, we restrict ourselves to speculate that with minimal fractional calculus elements, we may have a peculiar tool to inspect the flatness problem of standard cosmology. In summary, the subject of fractional quantum cosmology is herewith proposed, merely realized in terms of an open program constituted by several challenges. |
2304.08659 | Alfredo D. Millano | Alfredo D. Millano (Catolica del Norte U.), Genly Leon (Catolica del
Norte U. and DUT, Durban), Andronikos Paliathanasis (Catolica del Norte U.
and DUT, Durban) | Global dynamics in Einstein-Gauss-Bonnet scalar field cosmology with
matter | 33 pages, 11 compound figures | null | 10.1103/PhysRevD.108.023519 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the dynamics of the field equations in a four-dimensional isotropic
and homogeneous spatially flat Friedmann--Lema\^{\i}tre--Robertson--Walker
geometry in the context of Einstein-Gauss-Bonnet theory with a matter source
and a scalar field coupled to the Gauss-Bonnet scalar. In this theory, the
Gauss-Bonnet term contributes to the field equations. The mass of the scalar
field depends on the potential function and the Gauss-Bonnet term. For the
scalar field potential, we consider the exponential function and the coupling
function between the scalar field and the Gauss-Bonnet scalar is considered to
be the linear function. Moreover, the scalar field can have a phantom
behaviour. We consider a set of dimensionless variables and write the field
equations into a system or algebraic-differential equations. For the latter, we
investigate the equilibrium points and their stability properties. In order to
perform a global analysis of the asymptotic dynamics, we use compactified
variables. This gravitational theory can explain the Universe's recent and past
acceleration phases. Therefore, it can be used as a toy model for studying
inflation or as a dark energy candidate.
| [
{
"created": "Mon, 17 Apr 2023 23:20:03 GMT",
"version": "v1"
}
] | 2023-08-02 | [
[
"Millano",
"Alfredo D.",
"",
"Catolica del Norte U."
],
[
"Leon",
"Genly",
"",
"Catolica del\n Norte U. and DUT, Durban"
],
[
"Paliathanasis",
"Andronikos",
"",
"Catolica del Norte U.\n and DUT, Durban"
]
] | We study the dynamics of the field equations in a four-dimensional isotropic and homogeneous spatially flat Friedmann--Lema\^{\i}tre--Robertson--Walker geometry in the context of Einstein-Gauss-Bonnet theory with a matter source and a scalar field coupled to the Gauss-Bonnet scalar. In this theory, the Gauss-Bonnet term contributes to the field equations. The mass of the scalar field depends on the potential function and the Gauss-Bonnet term. For the scalar field potential, we consider the exponential function and the coupling function between the scalar field and the Gauss-Bonnet scalar is considered to be the linear function. Moreover, the scalar field can have a phantom behaviour. We consider a set of dimensionless variables and write the field equations into a system or algebraic-differential equations. For the latter, we investigate the equilibrium points and their stability properties. In order to perform a global analysis of the asymptotic dynamics, we use compactified variables. This gravitational theory can explain the Universe's recent and past acceleration phases. Therefore, it can be used as a toy model for studying inflation or as a dark energy candidate. |
gr-qc/0512166 | Aleksandr Zheltukhin | A.A. Zheltukhin | Supersymmetric Lorentz invariant deformations of superspaces | Latex, 13 pages, no figures; Talk at the Conference ``Cosmology 2005:
a reality check'', December 14-17, 2005, Copenhagen, Denmark; To appear at
http://www.astro.ku.dk/dark/workshops/dark05/presentations.html | Mod.Phys.Lett.A21:2117-2132,2006 | 10.1142/S0217732306021517 | null | gr-qc | null | Lorentz invariant supersymmetric deformations of superspaces based on Moyal
star product parametrized by Majorana spinor $\lambda_{a}$ and Ramond
grassmannian vector $\psi_{m}=-{1\over 2}(\bar\theta\gamma_{m}\lambda)$ in the
spinor realization \cite{VZ} are proposed. The map of supergravity background
into composite supercoordinates: $(B^{-1}_{mn}, \Psi^{a}_{m}, C_{ab})
\leftrightarrow (i\psi_{m}\psi_{n}, \psi_{m}\lambda^{a},
\lambda_{a}\lambda_{b})$ valid up to the second order corrections in
deformation parameter $h$ and transforming the background dependent Lorentz
noninvariant (anti)commutators of supercoordinates into their invariant Moyal
brackets is revealed. We found one of the deformations to depend on the axial
vector $\psi_{1m}={1/2}(\bar\theta\gamma_{m}\gamma_{5}\lambda)$ and to vanish
for the $\theta$ components with the same chiralities. The deformations in the
(super)twistor picture are discussed.
| [
{
"created": "Fri, 30 Dec 2005 17:04:34 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Zheltukhin",
"A. A.",
""
]
] | Lorentz invariant supersymmetric deformations of superspaces based on Moyal star product parametrized by Majorana spinor $\lambda_{a}$ and Ramond grassmannian vector $\psi_{m}=-{1\over 2}(\bar\theta\gamma_{m}\lambda)$ in the spinor realization \cite{VZ} are proposed. The map of supergravity background into composite supercoordinates: $(B^{-1}_{mn}, \Psi^{a}_{m}, C_{ab}) \leftrightarrow (i\psi_{m}\psi_{n}, \psi_{m}\lambda^{a}, \lambda_{a}\lambda_{b})$ valid up to the second order corrections in deformation parameter $h$ and transforming the background dependent Lorentz noninvariant (anti)commutators of supercoordinates into their invariant Moyal brackets is revealed. We found one of the deformations to depend on the axial vector $\psi_{1m}={1/2}(\bar\theta\gamma_{m}\gamma_{5}\lambda)$ and to vanish for the $\theta$ components with the same chiralities. The deformations in the (super)twistor picture are discussed. |
gr-qc/0408095 | Spiros Cotsakis | Spiros Cotsakis | Slice Energy in Higher Order Gravity Theories and Conformal
Transformations | 18 pages, references added, remark added in last Section related to
the choice of physical frame, various other improvements, final version to
appear in Gravitation and Cosmology | Grav.Cosmol.14:176-183,2008 | 10.1134/S0202289308020096 | null | gr-qc | null | We study the generic transport of slice energy between the scalar field
generated by the conformal transformation of higher-order gravity theories and
the matter component. We give precise relations for this exchange in the cases
of dust and perfect fluids. We show that, unless we are in a stationary
spacetime where slice energy is always conserved, in non-stationary situations
contributions to the total slice energy depend on whether or not test matter
follows geodesics in both frame representations of the dynamics, that is on
whether or not the two conformally related frames are physically
indistinguishable.
| [
{
"created": "Mon, 30 Aug 2004 13:29:57 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Dec 2004 10:05:56 GMT",
"version": "v2"
},
{
"created": "Wed, 30 Jan 2008 15:08:49 GMT",
"version": "v3"
}
] | 2009-11-10 | [
[
"Cotsakis",
"Spiros",
""
]
] | We study the generic transport of slice energy between the scalar field generated by the conformal transformation of higher-order gravity theories and the matter component. We give precise relations for this exchange in the cases of dust and perfect fluids. We show that, unless we are in a stationary spacetime where slice energy is always conserved, in non-stationary situations contributions to the total slice energy depend on whether or not test matter follows geodesics in both frame representations of the dynamics, that is on whether or not the two conformally related frames are physically indistinguishable. |
1407.6294 | Chandrachur Chakraborty | Chandrachur Chakraborty | Anomalous Lense-Thirring precession in Kerr-Taub-NUT spacetimes | LaTex; 12 pages including 16 figures, modified version, accepted for
publication in Eur. Phys. J. C | Eur. Phys. J. C (2015) 75:572 | 10.1140/epjc/s10052-015-3785-y | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Exact Lense-Thirring (LT) precession in Kerr-Taub-NUT spacetime is reviewed.
It is shown that the LT precession does not obey the general inverse cube law
of distance at strong gravity regime in Kerr-Taub-NUT spacetime. Rather, it
becomes maximum just near the horizon, falls sharply and becomes zero near the
horizon. The precession rate increases again and after that it falls obeying
the general inverse cube law of distance. This anomaly is maximum at the polar
region of this spacetime and it vanishes after crossing a certain `critical'
angle towards equator from pole. We highlight that this particular `anomaly'
also arises in the LT effect at the interior spacetime of the pulsars and such
a signature could be used to identify a role of Taub-NUT solutions in the
astrophysical observations or equivalently, a signature of the existence of NUT
charge in the pulsars. In addition, we show that if the Kerr-Taub-NUT spacetime
rotates with the angular momentum $J=Mn$ (Mass$\times$Dual Mass), inner horizon
goes to at $r=0$ and only {\it event horizon} exists at the distance $r=2M$.
| [
{
"created": "Wed, 23 Jul 2014 17:00:53 GMT",
"version": "v1"
},
{
"created": "Sun, 27 Jul 2014 08:57:03 GMT",
"version": "v2"
},
{
"created": "Mon, 11 May 2015 15:23:08 GMT",
"version": "v3"
},
{
"created": "Sat, 7 Nov 2015 08:34:39 GMT",
"version": "v4"
}
] | 2015-12-02 | [
[
"Chakraborty",
"Chandrachur",
""
]
] | Exact Lense-Thirring (LT) precession in Kerr-Taub-NUT spacetime is reviewed. It is shown that the LT precession does not obey the general inverse cube law of distance at strong gravity regime in Kerr-Taub-NUT spacetime. Rather, it becomes maximum just near the horizon, falls sharply and becomes zero near the horizon. The precession rate increases again and after that it falls obeying the general inverse cube law of distance. This anomaly is maximum at the polar region of this spacetime and it vanishes after crossing a certain `critical' angle towards equator from pole. We highlight that this particular `anomaly' also arises in the LT effect at the interior spacetime of the pulsars and such a signature could be used to identify a role of Taub-NUT solutions in the astrophysical observations or equivalently, a signature of the existence of NUT charge in the pulsars. In addition, we show that if the Kerr-Taub-NUT spacetime rotates with the angular momentum $J=Mn$ (Mass$\times$Dual Mass), inner horizon goes to at $r=0$ and only {\it event horizon} exists at the distance $r=2M$. |
1112.3629 | Neelima Kelkar Dr | D. Batic, N. G. Kelkar, M. Nowakowski | On Born approximation in black hole scattering | null | Eur. Phys. J. C 71, 1831 (2011) | 10.1140/epjc/s10052-011-1831-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A massless field propagating on spherically symmetric black hole metrics such
as the Schwarzschild, Reissner-Nordstr\"{o}m and Reissner-Nordstr\"{o}m-de
Sitter backgrounds is considered. In particular, explicit formulae in terms of
transcendental functions for the scattering of massless scalar particles off
black holes are derived within a Born approximation. It is shown that the
conditions on the existence of the Born integral forbid a straightforward
extraction of the quasi normal modes using the Born approximation for the
scattering amplitude. Such a method has been used in literature. We suggest a
novel, well defined method, to extract the large imaginary part of quasinormal
modes via the Coulomb-like phase shift. Furthermore, we compare the numerically
evaluated exact scattering amplitude with the Born one to find that the
approximation is not very useful for the scattering of massless scalar,
electromagnetic as well as gravitational waves from black holes.
| [
{
"created": "Thu, 15 Dec 2011 20:11:51 GMT",
"version": "v1"
}
] | 2011-12-16 | [
[
"Batic",
"D.",
""
],
[
"Kelkar",
"N. G.",
""
],
[
"Nowakowski",
"M.",
""
]
] | A massless field propagating on spherically symmetric black hole metrics such as the Schwarzschild, Reissner-Nordstr\"{o}m and Reissner-Nordstr\"{o}m-de Sitter backgrounds is considered. In particular, explicit formulae in terms of transcendental functions for the scattering of massless scalar particles off black holes are derived within a Born approximation. It is shown that the conditions on the existence of the Born integral forbid a straightforward extraction of the quasi normal modes using the Born approximation for the scattering amplitude. Such a method has been used in literature. We suggest a novel, well defined method, to extract the large imaginary part of quasinormal modes via the Coulomb-like phase shift. Furthermore, we compare the numerically evaluated exact scattering amplitude with the Born one to find that the approximation is not very useful for the scattering of massless scalar, electromagnetic as well as gravitational waves from black holes. |
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