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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/0509104 | Alejandro Cabo | Alejandro Cabo, Alejandro Garcia-Chung and Alejandro Rosabal | Can the cosmological constant undergo abrupt changes? | 10 pages, 1 figure | null | null | CERN-PH-TH/2005-178 | gr-qc | null | The existence of a simple spherically symmetric and static solution of the
Einstein equations in the presence of a cosmological constant vanishing outside
a definite value of the radial distance is investigated. A particular
succession of field configurations, which are solutions of the Einstein
equations in the presence of the considered cosmological term and auxiliary
external sources, is constructed. Then, it is shown that the associated
succession of external sources tend to zero in the sense of the generalized
functions. The type of weak solution that is found becomes the deSitter
homogeneous space-time for the interior region, and the Schwartzschild space in
the outside zone.
| [
{
"created": "Tue, 27 Sep 2005 10:33:23 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Cabo",
"Alejandro",
""
],
[
"Garcia-Chung",
"Alejandro",
""
],
[
"Rosabal",
"Alejandro",
""
]
] | The existence of a simple spherically symmetric and static solution of the Einstein equations in the presence of a cosmological constant vanishing outside a definite value of the radial distance is investigated. A particular succession of field configurations, which are solutions of the Einstein equations in the presence of the considered cosmological term and auxiliary external sources, is constructed. Then, it is shown that the associated succession of external sources tend to zero in the sense of the generalized functions. The type of weak solution that is found becomes the deSitter homogeneous space-time for the interior region, and the Schwartzschild space in the outside zone. |
gr-qc/0611031 | Dr. Anirudh Pradhan | Anirudh Pradhan, Kanti Jotania and Anju Rai | Generation of Bianchi Type V Bulk Viscous Cosmological Models with Time
Dependent $\Lambda$-Term | 22 pages, 3 figures, Some typos corrected | FizikaB15:163-182,2006 | null | null | gr-qc | null | Bianchi type V bulk viscous fluid cosmological models are investigated with
dynamic cosmological term $\Lambda(t)$. Using a generation technique (Camci
{\it et al.}, 2001), it is shown that the Einstein's field equations are
solvable for any arbitrary cosmic scale function. Solutions for particular
forms of cosmic scale functions are also obtained. The cosmological constant is
found to be decreasing function of time, which is supported by results from
recent type Ia supernovae observations. Some physical and geometrical aspects
of the models are also discussed.
| [
{
"created": "Sun, 5 Nov 2006 12:14:55 GMT",
"version": "v1"
},
{
"created": "Fri, 29 Dec 2006 06:35:11 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Pradhan",
"Anirudh",
""
],
[
"Jotania",
"Kanti",
""
],
[
"Rai",
"Anju",
""
]
] | Bianchi type V bulk viscous fluid cosmological models are investigated with dynamic cosmological term $\Lambda(t)$. Using a generation technique (Camci {\it et al.}, 2001), it is shown that the Einstein's field equations are solvable for any arbitrary cosmic scale function. Solutions for particular forms of cosmic scale functions are also obtained. The cosmological constant is found to be decreasing function of time, which is supported by results from recent type Ia supernovae observations. Some physical and geometrical aspects of the models are also discussed. |
2005.06052 | Crist\'obal Corral | Crist\'obal Corral, Norman Cruz, Esteban Gonz\'alez | Diffusion in unimodular gravity: Analytical solutions, late-time
acceleration, and cosmological constraints | v1. 14 pages, 10 figures; v2. Typos corrected, references added, and
more explanations provided. Accepted for publication in Phys. Rev. D | Phys. Rev. D 102, 023508 (2020) | 10.1103/PhysRevD.102.023508 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Unimodular gravity is an appealing approach to address the cosmological
constant problem. In this scenario, the vacuum energy density of quantum fields
does not gravitate and the cosmological constant appears merely as an
integration constant. Recently, it has been shown that energy diffusion that
may arise in quantum gravity and in theories with spontaneous collapse is
compatible with this framework by virtue of its restricted diffeomorphism
invariance. New studies suggest that this phenomenon could lead to higher-order
equations in the context of homogeneous and isotropic Universe, affecting the
well-posedness of their Cauchy initial-value problem. In this work, we show
that this issue can be circumvented by assuming an equation of state that
relates the energy density to the function that characterizes the diffusion. As
an application, we solve the field equations analytically for an isotropic and
homogeneous Universes in a barotropic model and in the mass-proportional
continuous spontaneous localization (CSL) scenario, assuming that only dark
matter develops energy diffusion. Different solutions possessing phase
transition from decelerated to accelerated expansion are found. We use
cosmological data of type Ia Supernovae and observational Hubble data to
constrain the free parameters of both models. It is found that very small but
nontrivial energy nonconservation is compatible with the barotropic model.
However, for the CSL model, we find that the best-fit values are not compatible
with previous laboratory experiments. We comment on this fact and propose
future directions to explore energy diffusion in cosmology.
| [
{
"created": "Tue, 12 May 2020 21:04:20 GMT",
"version": "v1"
},
{
"created": "Mon, 29 Jun 2020 21:36:18 GMT",
"version": "v2"
}
] | 2020-07-03 | [
[
"Corral",
"Cristóbal",
""
],
[
"Cruz",
"Norman",
""
],
[
"González",
"Esteban",
""
]
] | Unimodular gravity is an appealing approach to address the cosmological constant problem. In this scenario, the vacuum energy density of quantum fields does not gravitate and the cosmological constant appears merely as an integration constant. Recently, it has been shown that energy diffusion that may arise in quantum gravity and in theories with spontaneous collapse is compatible with this framework by virtue of its restricted diffeomorphism invariance. New studies suggest that this phenomenon could lead to higher-order equations in the context of homogeneous and isotropic Universe, affecting the well-posedness of their Cauchy initial-value problem. In this work, we show that this issue can be circumvented by assuming an equation of state that relates the energy density to the function that characterizes the diffusion. As an application, we solve the field equations analytically for an isotropic and homogeneous Universes in a barotropic model and in the mass-proportional continuous spontaneous localization (CSL) scenario, assuming that only dark matter develops energy diffusion. Different solutions possessing phase transition from decelerated to accelerated expansion are found. We use cosmological data of type Ia Supernovae and observational Hubble data to constrain the free parameters of both models. It is found that very small but nontrivial energy nonconservation is compatible with the barotropic model. However, for the CSL model, we find that the best-fit values are not compatible with previous laboratory experiments. We comment on this fact and propose future directions to explore energy diffusion in cosmology. |
gr-qc/0606107 | H Mohseni Sadjadi | H. Mohseni Sadjadi | The effect of geometry on charge confinement in three dimensions | 8 pages. To be published in Europhysics Letters | Europhys.Lett.75:371-377,2006 | 10.1209/epl/i2006-10128-3 | null | gr-qc hep-th | null | We show that, in contrast to the flat case, the Maxwell theory is not
confining in the background of the three dimensional BTZ black-hole (covering
space). We also study the effect of the curvature on screening behavior of
Maxwell-Chern-Simons model in this space-time.
| [
{
"created": "Sat, 24 Jun 2006 12:51:51 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Sadjadi",
"H. Mohseni",
""
]
] | We show that, in contrast to the flat case, the Maxwell theory is not confining in the background of the three dimensional BTZ black-hole (covering space). We also study the effect of the curvature on screening behavior of Maxwell-Chern-Simons model in this space-time. |
1909.08620 | Ian Jubb | Christopher Barton, Andrew Counsell, Fay Dowker, Dewi S. W. Gould, Ian
Jubb, Gwylim Taylor | Horizon Molecules in Causal Set Theory | null | Phys. Rev. D 100, 126008 (2019) | 10.1103/PhysRevD.100.126008 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a new definition of "horizon molecules" in Causal Set Theory
following pioneering work by Dou and Sorkin. The new concept applies for any
causal horizon and its intersection with any spacelike hypersurface. In the
continuum limit, as the discreteness scale tends to zero, the leading behaviour
of the expected number of horizon molecules is shown to be the area of the
horizon in discreteness units, up to a dimension dependent factor of order one.
We also determine the first order corrections to the continuum value, and show
how such corrections can be exploited to obtain further geometrical information
about the horizon and the spacelike hypersurface from the causal set.
| [
{
"created": "Wed, 18 Sep 2019 18:00:00 GMT",
"version": "v1"
}
] | 2019-12-11 | [
[
"Barton",
"Christopher",
""
],
[
"Counsell",
"Andrew",
""
],
[
"Dowker",
"Fay",
""
],
[
"Gould",
"Dewi S. W.",
""
],
[
"Jubb",
"Ian",
""
],
[
"Taylor",
"Gwylim",
""
]
] | We propose a new definition of "horizon molecules" in Causal Set Theory following pioneering work by Dou and Sorkin. The new concept applies for any causal horizon and its intersection with any spacelike hypersurface. In the continuum limit, as the discreteness scale tends to zero, the leading behaviour of the expected number of horizon molecules is shown to be the area of the horizon in discreteness units, up to a dimension dependent factor of order one. We also determine the first order corrections to the continuum value, and show how such corrections can be exploited to obtain further geometrical information about the horizon and the spacelike hypersurface from the causal set. |
0907.2637 | Christian Reisswig | C. Reisswig, N. T. Bishop, D. Pollney, and B. Szilagyi | Unambiguous determination of gravitational waveforms from binary black
hole mergers | 4 pages, 3 figures, published version | Phys.Rev.Lett.103:221101,2009 | 10.1103/PhysRevLett.103.221101 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational radiation is properly defined only at future null infinity
($\scri$), but in practice it is estimated from data calculated at a finite
radius. We have used characteristic extraction to calculate gravitational
radiation at $\scri$ for the inspiral and merger of two equal mass non-spinning
black holes. Thus we have determined the first unambiguous merger waveforms for
this problem. The implementation is general purpose, and can be applied to
calculate the gravitational radiation, at $\scri$, given data at a finite
radius calculated in another computation.
| [
{
"created": "Wed, 15 Jul 2009 16:13:00 GMT",
"version": "v1"
},
{
"created": "Thu, 5 Nov 2009 11:57:27 GMT",
"version": "v2"
},
{
"created": "Fri, 8 Jan 2010 10:38:25 GMT",
"version": "v3"
}
] | 2010-01-08 | [
[
"Reisswig",
"C.",
""
],
[
"Bishop",
"N. T.",
""
],
[
"Pollney",
"D.",
""
],
[
"Szilagyi",
"B.",
""
]
] | Gravitational radiation is properly defined only at future null infinity ($\scri$), but in practice it is estimated from data calculated at a finite radius. We have used characteristic extraction to calculate gravitational radiation at $\scri$ for the inspiral and merger of two equal mass non-spinning black holes. Thus we have determined the first unambiguous merger waveforms for this problem. The implementation is general purpose, and can be applied to calculate the gravitational radiation, at $\scri$, given data at a finite radius calculated in another computation. |
1004.5324 | David Campo | David Campo | Problems with models of a fundamental length | null | null | null | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I critically examine various ad hoc models describing a fundamental minimal
length at the level of the propagator. They violate causality and/or unitarity.
| [
{
"created": "Thu, 29 Apr 2010 15:26:53 GMT",
"version": "v1"
}
] | 2015-03-17 | [
[
"Campo",
"David",
""
]
] | I critically examine various ad hoc models describing a fundamental minimal length at the level of the propagator. They violate causality and/or unitarity. |
2305.00711 | Dennis Stock | Dennis Stock, Enea Di Dio, Ruth Durrer | The Hawking Energy in a Perturbed Friedmann-Lema\^{i}tre Universe | matches published version; Mathematica file attached | JCAP08(2023)033 | 10.1088/1475-7516/2023/08/033 | CERN-TH-2023-063 | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | Hawking's quasi-local energy definition quantifies the energy enclosed by a
spacelike 2-sphere in terms of the amount of lightbending on the sphere caused
by the energy distribution inside the sphere. This paper establishes for the
first time a direct connection between the formal mathematical definition of a
quasi-local energy and observations, in the context of cosmological
perturbation theory. This is achieved by studying the Hawking Energy of
spherical sections of the past lightcone of a cosmic observer in a perturbed
Friedmann-Lema\^{i}tre spacetime. We express the Hawking Energy in terms of
gauge-invariant perturbation variables and comment on the cosmic observables
needed to in principle measure it. We then calculate its angular power spectrum
and interpret its contributions.
| [
{
"created": "Mon, 1 May 2023 08:22:33 GMT",
"version": "v1"
},
{
"created": "Tue, 15 Aug 2023 14:06:16 GMT",
"version": "v2"
}
] | 2023-08-16 | [
[
"Stock",
"Dennis",
""
],
[
"Di Dio",
"Enea",
""
],
[
"Durrer",
"Ruth",
""
]
] | Hawking's quasi-local energy definition quantifies the energy enclosed by a spacelike 2-sphere in terms of the amount of lightbending on the sphere caused by the energy distribution inside the sphere. This paper establishes for the first time a direct connection between the formal mathematical definition of a quasi-local energy and observations, in the context of cosmological perturbation theory. This is achieved by studying the Hawking Energy of spherical sections of the past lightcone of a cosmic observer in a perturbed Friedmann-Lema\^{i}tre spacetime. We express the Hawking Energy in terms of gauge-invariant perturbation variables and comment on the cosmic observables needed to in principle measure it. We then calculate its angular power spectrum and interpret its contributions. |
1211.5909 | Mustapha Azreg-A\"inou | Mustapha Azreg-A\"inou and Manuel E. Rodrigues | Thermodynamical, geometrical and Poincar\'e methods for charged black
holes in presence of quintessence | 25 pages, 11 figures. To appear in JHEP | JHEP 09 (2013) 146 | 10.1007/JHEP09(2013)146 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Properties pertaining to thermodynamical local stability of
Reissner-Nordstr\"om black holes surrounded by quintessence as well as
adiabatic invariance, adiabatic charging and a generalized Smarr formula are
discussed. Limits for the entropy, temperature and electric potential ensuring
stability of canonical ensembles are determined by the classical
thermodynamical and Poincar\'e methods. By the latter approach we show that
microcanonical ensembles (isolated black holes) are stable. Two geometrical
approaches lead to determine the same states corresponding to second order
phase transitions.
| [
{
"created": "Mon, 26 Nov 2012 10:59:08 GMT",
"version": "v1"
},
{
"created": "Wed, 4 Sep 2013 13:30:46 GMT",
"version": "v2"
}
] | 2014-01-29 | [
[
"Azreg-Aïnou",
"Mustapha",
""
],
[
"Rodrigues",
"Manuel E.",
""
]
] | Properties pertaining to thermodynamical local stability of Reissner-Nordstr\"om black holes surrounded by quintessence as well as adiabatic invariance, adiabatic charging and a generalized Smarr formula are discussed. Limits for the entropy, temperature and electric potential ensuring stability of canonical ensembles are determined by the classical thermodynamical and Poincar\'e methods. By the latter approach we show that microcanonical ensembles (isolated black holes) are stable. Two geometrical approaches lead to determine the same states corresponding to second order phase transitions. |
1702.01754 | Radouane Gannouji | Miguel Cruz, Apratim Ganguly, Radouane Gannouji, Genly Leon, Emmanuel
N. Saridakis | Global structure of static spherically symmetric solutions surrounded by
quintessence | 37 pages, 5 figures; Accepted for publication in Class. Quantum Grav | Class. Quantum Grav. 34 (2017) 125014 | 10.1088/1361-6382/aa70fc | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate all static spherically symmetric solutions in the context of
general relativity surrounded by a minimally-coupled quintessence field, using
dynamical system analysis. Applying the 1+1+2 formalism and introducing
suitable normalized variables involving the Gaussian curvature, we were able to
reformulate the field equations as first order differential equations. In the
case of a massless canonical scalar field we recovered all known black hole
results, such as the Fisher solution, and we found that apart from the
Schwarzschild solution all other solutions are naked singularities.
Additionally, we identified the symmetric phase space which corresponds to the
white hole part of the solution and in the case of a phantom field, we were
able to extract the conditions for the existence of wormholes and define all
possible class of solutions such as Cold Black holes, singular spacetimes and
wormholes like Ellis wormhole, for example. For an exponential potential, we
found that the black hole solution which is asymptotically flat is unique and
it is the Schwarzschild spacetime, while all other solutions are naked
singularities. Furthermore, we found solutions connecting to a white hole
through a maximum radius, and not a minimum radius (throat) such as wormhole
solutions, therefore violating the flare-out condition. Finally, we have found
a necessary and sufficient condition on the form of the potential to have an
asymptotically AdS spacetime along with a necessary condition for the existence
of asymptotically flat black holes.
| [
{
"created": "Mon, 6 Feb 2017 19:00:02 GMT",
"version": "v1"
},
{
"created": "Fri, 26 May 2017 03:27:49 GMT",
"version": "v2"
}
] | 2017-05-29 | [
[
"Cruz",
"Miguel",
""
],
[
"Ganguly",
"Apratim",
""
],
[
"Gannouji",
"Radouane",
""
],
[
"Leon",
"Genly",
""
],
[
"Saridakis",
"Emmanuel N.",
""
]
] | We investigate all static spherically symmetric solutions in the context of general relativity surrounded by a minimally-coupled quintessence field, using dynamical system analysis. Applying the 1+1+2 formalism and introducing suitable normalized variables involving the Gaussian curvature, we were able to reformulate the field equations as first order differential equations. In the case of a massless canonical scalar field we recovered all known black hole results, such as the Fisher solution, and we found that apart from the Schwarzschild solution all other solutions are naked singularities. Additionally, we identified the symmetric phase space which corresponds to the white hole part of the solution and in the case of a phantom field, we were able to extract the conditions for the existence of wormholes and define all possible class of solutions such as Cold Black holes, singular spacetimes and wormholes like Ellis wormhole, for example. For an exponential potential, we found that the black hole solution which is asymptotically flat is unique and it is the Schwarzschild spacetime, while all other solutions are naked singularities. Furthermore, we found solutions connecting to a white hole through a maximum radius, and not a minimum radius (throat) such as wormhole solutions, therefore violating the flare-out condition. Finally, we have found a necessary and sufficient condition on the form of the potential to have an asymptotically AdS spacetime along with a necessary condition for the existence of asymptotically flat black holes. |
gr-qc/0103015 | Yuri N. Obukhov | Thoralf Chrobok, Yuri N. Obukhov, and Mike Scherfner | On closed rotating worlds | 10 pages, Revtex, to appear in Phys. Rev. D63 | Phys.Rev. D63 (2001) 104014 | 10.1103/PhysRevD.63.104014 | null | gr-qc astro-ph | null | A new solution for the stationary closed world with rigid rotation is
obtained for the spinning fluid source. It is found that the spin and vorticity
are locally balanced. This model qualitatively shows that the local rotation of
the cosmological matter can be indeed related to the global cosmic vorticity,
provided the total angular momentum of the closed world is vanishing.
| [
{
"created": "Tue, 6 Mar 2001 15:12:39 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Chrobok",
"Thoralf",
""
],
[
"Obukhov",
"Yuri N.",
""
],
[
"Scherfner",
"Mike",
""
]
] | A new solution for the stationary closed world with rigid rotation is obtained for the spinning fluid source. It is found that the spin and vorticity are locally balanced. This model qualitatively shows that the local rotation of the cosmological matter can be indeed related to the global cosmic vorticity, provided the total angular momentum of the closed world is vanishing. |
1110.6928 | Tehani Finch | Tehani K. Finch and James Lindesay | Global Causal Structure of a Transient Black Object | 25 pages, 12 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A singularity-free and spherically symmetric transient black object whose
center remains always timelike, yet directly manifests a trapped region, has
been constructed and numerically implemented. The exterior geometry is shown to
be similar to that of a long-lived transient black hole, with a few subtle
differences. The large-scale global structure of the geometry is examined
through the construction of a conformal diagram, which exhibits no event
horizon and bears resemblance to that of a Minkowski spacetime. Since there is
no singularity within the geometry, the evolution of the exchange of
information between timelike observers, including those that fall through the
trapped region, can be directly explored. The dynamics of generic "standard"
communications, as well as entangled communications, is exhibited through both
t-versus-r and conformal spacetime diagrams.
| [
{
"created": "Mon, 31 Oct 2011 19:56:11 GMT",
"version": "v1"
}
] | 2011-11-01 | [
[
"Finch",
"Tehani K.",
""
],
[
"Lindesay",
"James",
""
]
] | A singularity-free and spherically symmetric transient black object whose center remains always timelike, yet directly manifests a trapped region, has been constructed and numerically implemented. The exterior geometry is shown to be similar to that of a long-lived transient black hole, with a few subtle differences. The large-scale global structure of the geometry is examined through the construction of a conformal diagram, which exhibits no event horizon and bears resemblance to that of a Minkowski spacetime. Since there is no singularity within the geometry, the evolution of the exchange of information between timelike observers, including those that fall through the trapped region, can be directly explored. The dynamics of generic "standard" communications, as well as entangled communications, is exhibited through both t-versus-r and conformal spacetime diagrams. |
gr-qc/0207045 | Amos Ori | Amos Ori | Reconstruction of inhomogeneous metric perturbations and electromagnetic
four-potential in Kerr spacetime | 20 pages; few typos corrected and minor modifications made; accepted
to Phys. Rev. D | Phys.Rev. D67 (2003) 124010 | 10.1103/PhysRevD.67.124010 | null | gr-qc | null | We present a procedure that allows the construction of the metric
perturbations and electromagnetic four-potential, for gravitational and
electromagnetic perturbations produced by sources in Kerr spacetime. This may
include, for example, the perturbations produced by a point particle or an
extended object moving in orbit around a Kerr black hole. The construction is
carried out in the frequency domain. Previously, Chrzanowski derived the vacuum
metric perturbations and electromagnetic four-potential by applying a
differential operator to a certain potential $\Psi $. Here we construct $\Psi $
for inhomogeneous perturbations, thereby allowing the application of
Chrzanowski's method. We address this problem in two stages: First, for vacuum
perturbations (i.e. pure gravitational or electromagnetic waves), we construct
the potential from the modes of the Weyl scalars $\psi_{0}$ or $\phi_{0}$.
Second, for perturbations produced by sources, we express $\Psi $ in terms of
the mode functions of the source, i.e. the energy-momentum tensor $T_{\alpha
\beta}$ or the electromagnetic current vector $J_{\alpha}$.
| [
{
"created": "Thu, 11 Jul 2002 09:12:03 GMT",
"version": "v1"
},
{
"created": "Sun, 29 Dec 2002 13:27:21 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Ori",
"Amos",
""
]
] | We present a procedure that allows the construction of the metric perturbations and electromagnetic four-potential, for gravitational and electromagnetic perturbations produced by sources in Kerr spacetime. This may include, for example, the perturbations produced by a point particle or an extended object moving in orbit around a Kerr black hole. The construction is carried out in the frequency domain. Previously, Chrzanowski derived the vacuum metric perturbations and electromagnetic four-potential by applying a differential operator to a certain potential $\Psi $. Here we construct $\Psi $ for inhomogeneous perturbations, thereby allowing the application of Chrzanowski's method. We address this problem in two stages: First, for vacuum perturbations (i.e. pure gravitational or electromagnetic waves), we construct the potential from the modes of the Weyl scalars $\psi_{0}$ or $\phi_{0}$. Second, for perturbations produced by sources, we express $\Psi $ in terms of the mode functions of the source, i.e. the energy-momentum tensor $T_{\alpha \beta}$ or the electromagnetic current vector $J_{\alpha}$. |
gr-qc/9606058 | null | Eva K. Grebel (Sternwarte Bonn, University of Illinois, and Wuerzburg
University) | Be star surveys with CCD photometry. II. NGC 1818 and its neighbouring
cluster in the LMC | LaTeX source with links to 25 postscript figures. Complete postscript
version of the paper with all figures and an ASCII version of Table 2 also
available at http://www.astro.uiuc.edu/~grebel/abs96_aa_n1818be.html Accepted
for publication in A&A | null | null | null | gr-qc | null | As part of an ongoing photometric survey of young Magellanic Cloud clusters
we identified Be stars in NGC 1818 and a nearby smaller cluster in the Large
Magellanic Cloud. The neighbouring cluster does not contain evolved stars, and
its sparsely populated main sequence does not extend to stars as massive as in
NGC 1818. Both clusters are younger than the surrounding field population and
contain a much higher Be star fraction.
We present a table with photometry, astrometric positions, and IAU-conform
identifiers of the Be stars. We compare Be star fractions in Magellanic Cloud
clusters and Galactic open clusters and discuss possible constraints on Be star
theories.
| [
{
"created": "Wed, 19 Jun 1996 02:46:39 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Grebel",
"Eva K.",
"",
"Sternwarte Bonn, University of Illinois, and Wuerzburg\n University"
]
] | As part of an ongoing photometric survey of young Magellanic Cloud clusters we identified Be stars in NGC 1818 and a nearby smaller cluster in the Large Magellanic Cloud. The neighbouring cluster does not contain evolved stars, and its sparsely populated main sequence does not extend to stars as massive as in NGC 1818. Both clusters are younger than the surrounding field population and contain a much higher Be star fraction. We present a table with photometry, astrometric positions, and IAU-conform identifiers of the Be stars. We compare Be star fractions in Magellanic Cloud clusters and Galactic open clusters and discuss possible constraints on Be star theories. |
2102.01555 | Luca Guido Molinari | Carlo Alberto Mantica and Luca Guido Molinari | Doubly Torqued Vectors and a classification of Doubly Twisted and Kundt
spacetimes | 9 pages, 3 tables. Equation in text (3 lines below table 2) has been
corrected | Gen Relativ Gravit 53, 48 (2021) - open access | 10.1007/s10714-021-02819-x | null | gr-qc math.DG | http://creativecommons.org/licenses/by/4.0/ | The simple structure of doubly torqued vectors allows for a natural
characterization of doubly twisted down to warped spacetimes, as well as Kundt
spacetimes down to PP waves. For the first ones the vectors are timelike, for
the others they are null. We also discuss some properties, and their connection
to hypersurface orthogonal conformal Killing vectors, and null Killing vectors.
| [
{
"created": "Mon, 1 Feb 2021 12:30:33 GMT",
"version": "v1"
},
{
"created": "Mon, 8 Feb 2021 19:47:22 GMT",
"version": "v2"
}
] | 2021-05-04 | [
[
"Mantica",
"Carlo Alberto",
""
],
[
"Molinari",
"Luca Guido",
""
]
] | The simple structure of doubly torqued vectors allows for a natural characterization of doubly twisted down to warped spacetimes, as well as Kundt spacetimes down to PP waves. For the first ones the vectors are timelike, for the others they are null. We also discuss some properties, and their connection to hypersurface orthogonal conformal Killing vectors, and null Killing vectors. |
1911.07500 | Colin MacLaurin | Colin MacLaurin | Clarifying spatial distance measurement | 6 pages, 0 figures, submitted to the proceedings of the 2018 Marcel
Grossmann conference, Rome. v2 has minor rewording and typo corrections | p.1372--77 in Battistelli, Jantzen & Ruffini, eds., The Fifteenth
Marcel Grossmann Meeting (World Scientific, 2022, vol. 2) | 10.1142/9789811258251_0198 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine length measurement in curved spacetime, based on the 1+3-splitting
of a local observer frame. This situates extended objects within spacetime, in
terms of a given coordinate which serves as an external reference. The radar
metric is shown to coincide with the spatial projector, but these only give
meaningful results on the observer's 3-space, where they reduce to the metric.
Examples from Schwarzschild spacetime are given.
| [
{
"created": "Mon, 18 Nov 2019 09:39:33 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Nov 2019 03:32:10 GMT",
"version": "v2"
}
] | 2022-09-05 | [
[
"MacLaurin",
"Colin",
""
]
] | We examine length measurement in curved spacetime, based on the 1+3-splitting of a local observer frame. This situates extended objects within spacetime, in terms of a given coordinate which serves as an external reference. The radar metric is shown to coincide with the spatial projector, but these only give meaningful results on the observer's 3-space, where they reduce to the metric. Examples from Schwarzschild spacetime are given. |
gr-qc/0305081 | Saulo Carneiro | Saulo Carneiro | On the vacuum entropy and the cosmological constant | Version to appear in the GRF2003 Special Issue of IJMPD | Int.J.Mod.Phys. D12 (2003) 1669-1674 | 10.1142/S0218271803004158 | null | gr-qc astro-ph hep-th | null | It is generally accepted that the entropy of an asymptotically de Sitter
universe is bounded by the area, in Planck units, of the de Sitter horizon.
Based on an analysis of the entropy associated to the vacuum quantum
fluctuations, we suggest that the existence of such a holographic bound
constitutes a possible explanation for the observed value of the cosmological
constant, theoretically justifying a relation proposed 35 years ago by
Zel'dovich.
| [
{
"created": "Wed, 21 May 2003 17:25:04 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Jul 2003 21:22:37 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Carneiro",
"Saulo",
""
]
] | It is generally accepted that the entropy of an asymptotically de Sitter universe is bounded by the area, in Planck units, of the de Sitter horizon. Based on an analysis of the entropy associated to the vacuum quantum fluctuations, we suggest that the existence of such a holographic bound constitutes a possible explanation for the observed value of the cosmological constant, theoretically justifying a relation proposed 35 years ago by Zel'dovich. |
1712.00738 | Lorenzo Sebastiani | Lorenzo Sebastiani, Shynaray Myrzakul, Ratbay Myrzakulov | Reconstruction of inflation from scalar field non-minimally coupled with
the Gauss-Bonnet term | 11 pages, accepted in EPJ Plus | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we analyze the early-time inflation in a scalar-tensor theory
of gravity where the scalar field is minimally coupled with the Gauss-Bonnet
four dimensional topological invariant. The theory belongs to a class of
Horndeski models where the field equations are at the second order like in
General Relativity. A viable inflationary scenario must correctly reproduce the
last Plank satellite data. By starting from some simple assumptions on the
field and on the coupling function between the field and the Gauss-Bonnet term,
we derive the spectral index and the tensor-to-scalar ratio of the model. Once
the model is viable, it is finally possible to fully reconstruct its
Lagrangian.
| [
{
"created": "Sun, 3 Dec 2017 09:43:10 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Dec 2017 09:35:41 GMT",
"version": "v2"
}
] | 2017-12-11 | [
[
"Sebastiani",
"Lorenzo",
""
],
[
"Myrzakul",
"Shynaray",
""
],
[
"Myrzakulov",
"Ratbay",
""
]
] | In this paper, we analyze the early-time inflation in a scalar-tensor theory of gravity where the scalar field is minimally coupled with the Gauss-Bonnet four dimensional topological invariant. The theory belongs to a class of Horndeski models where the field equations are at the second order like in General Relativity. A viable inflationary scenario must correctly reproduce the last Plank satellite data. By starting from some simple assumptions on the field and on the coupling function between the field and the Gauss-Bonnet term, we derive the spectral index and the tensor-to-scalar ratio of the model. Once the model is viable, it is finally possible to fully reconstruct its Lagrangian. |
gr-qc/9411074 | Luis Octavio Pimentel | Pimentel L O, Camacho A and Macias A | Weyl Equation in G\"Odel Type Universes | 9pages, latex,no figures | Mod.Phys.Lett. A9 (1994) 3703-3706 | null | UAMI-GA-940031 | gr-qc | null | The Weyl equation (massless Dirac equation) is studied in a family of metrics
of the G\"odel type. The field equation is solved exactly for one member of the
family.
| [
{
"created": "Tue, 29 Nov 1994 22:15:57 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"O",
"Pimentel L",
""
],
[
"A",
"Camacho",
""
],
[
"A",
"Macias",
""
]
] | The Weyl equation (massless Dirac equation) is studied in a family of metrics of the G\"odel type. The field equation is solved exactly for one member of the family. |
1001.4384 | S Habib Mazharimousavi | S. Habib Mazharimousavi, M. Halilsoy and Z. Amirabi | Stability of thin-shell wormholes supported by ordinary matter in
Einstein-Maxwell-Gauss-Bonnet gravity | 11 pages, 4 figures | Phys.Rev.D81:104002,2010 | 10.1103/PhysRevD.81.104002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently in (Phys. Rev. D 76, 087502 (2007) and Phys. Rev. D 77, 089903(E)
(2008)) a thin-shell wormhole has been introduced in 5-dimensional
Einstein-Maxwell-Gauss-Bonnet (EMGB) gravity which was supported by normal
matter. We wish to consider this solution and investigate its stability. Our
analysis shows that for the Gauss-Bonnet (GB) parameter $\alpha <0,$ stability
regions form for a narrow band of finely-tuned mass and charge. For the case
$\alpha >0$, we iterate once more that no stable, normal matter thin-shell
wormhole exists.
| [
{
"created": "Mon, 25 Jan 2010 11:02:41 GMT",
"version": "v1"
},
{
"created": "Fri, 29 Jan 2010 09:47:58 GMT",
"version": "v2"
},
{
"created": "Wed, 31 Mar 2010 14:29:41 GMT",
"version": "v3"
}
] | 2015-03-13 | [
[
"Mazharimousavi",
"S. Habib",
""
],
[
"Halilsoy",
"M.",
""
],
[
"Amirabi",
"Z.",
""
]
] | Recently in (Phys. Rev. D 76, 087502 (2007) and Phys. Rev. D 77, 089903(E) (2008)) a thin-shell wormhole has been introduced in 5-dimensional Einstein-Maxwell-Gauss-Bonnet (EMGB) gravity which was supported by normal matter. We wish to consider this solution and investigate its stability. Our analysis shows that for the Gauss-Bonnet (GB) parameter $\alpha <0,$ stability regions form for a narrow band of finely-tuned mass and charge. For the case $\alpha >0$, we iterate once more that no stable, normal matter thin-shell wormhole exists. |
2111.13890 | Hyat Huang | Min-Yan Ou, Meng-Yun Lai and Hyat Huang | Echoes from Asymmetric Wormholes and Black Bounce | 16 pages, 6 figures, Comments welcome | null | 10.1140/epjc/s10052-022-10421-x | null | gr-qc astro-ph.HE hep-th | http://creativecommons.org/licenses/by/4.0/ | The time evolution of the field perturbations in the wormhole and black
bounce backgrounds are investigated. We find that the asymmetry of spacetime
results in the asymmetry of the effective potential of the perturbed equation.
The quasinormal modes are strongly dependent on the shapes of the effective
potentials. Specifically, the signals of echoes arise in some wormhole cases
and reflect the asymmetric properties of wormholes. We examine the features of
echoes within different circumstances. Besides, the negative values of
effective potentials usually imply the instability of the system. By analyzing
some specific metrics, we find that the negative regions of effective
potentials are enclosed by the black hole horizons in these cases. But this
statement could be broken in asymmetric cases.
| [
{
"created": "Sat, 27 Nov 2021 13:14:15 GMT",
"version": "v1"
}
] | 2022-06-01 | [
[
"Ou",
"Min-Yan",
""
],
[
"Lai",
"Meng-Yun",
""
],
[
"Huang",
"Hyat",
""
]
] | The time evolution of the field perturbations in the wormhole and black bounce backgrounds are investigated. We find that the asymmetry of spacetime results in the asymmetry of the effective potential of the perturbed equation. The quasinormal modes are strongly dependent on the shapes of the effective potentials. Specifically, the signals of echoes arise in some wormhole cases and reflect the asymmetric properties of wormholes. We examine the features of echoes within different circumstances. Besides, the negative values of effective potentials usually imply the instability of the system. By analyzing some specific metrics, we find that the negative regions of effective potentials are enclosed by the black hole horizons in these cases. But this statement could be broken in asymmetric cases. |
gr-qc/0311034 | Bryan Kelleher | Bryan Kelleher | Gravity on Conformal Superspace | PhD thesis, 2003 University College Cork, Ireland | null | null | null | gr-qc | null | The configuration space of general relativity is superspace - the space of
all Riemannian 3-metrics modulo diffeomorphisms. However, it has been argued
that the configuration space for gravity should be conformal superspace - the
space of all Riemannian 3-metrics modulo diffeomorphisms and conformal
transformations. Taking this conformal nature seriously leads to a new theory
of gravity which although very similar to general relativity has some very
different features particularly in cosmology and quantisation. It should
reproduce the standard tests of general relativity. The cosmology is studied in
some detail. The theory is incredibly restrictive and as a result admits an
extremely limited number of possible solutions. The problems of the standard
cosmology are addressed and most remarkably the cosmological constant problem
is resolved in a natural way. The theory also has several attractive features
with regard to quantisation particularly regarding the problem of time.
| [
{
"created": "Tue, 11 Nov 2003 00:12:49 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Kelleher",
"Bryan",
""
]
] | The configuration space of general relativity is superspace - the space of all Riemannian 3-metrics modulo diffeomorphisms. However, it has been argued that the configuration space for gravity should be conformal superspace - the space of all Riemannian 3-metrics modulo diffeomorphisms and conformal transformations. Taking this conformal nature seriously leads to a new theory of gravity which although very similar to general relativity has some very different features particularly in cosmology and quantisation. It should reproduce the standard tests of general relativity. The cosmology is studied in some detail. The theory is incredibly restrictive and as a result admits an extremely limited number of possible solutions. The problems of the standard cosmology are addressed and most remarkably the cosmological constant problem is resolved in a natural way. The theory also has several attractive features with regard to quantisation particularly regarding the problem of time. |
1907.10221 | Carlos Albertho Benavides-Gallego | Carlos A. Benavides-Gallego and Ahmadjon Abdujabbarov | Boosted Kerr black hole in the presence of plasma | 14 pages, 8 figures. Talk given at the meeting "Recent Progress in
Relativistic Astrophysics" (6-8 May 2019, Shanghai, China) | null | 10.3390/proceedings2019017006 | proceedings-569645 | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this work, we obtain the deflection angle for a boosted Kerr black hole in
the weak field approximation using the optics in a curved spacetime developed
by J.L. Synge in 1960. We study the behavior of light in the presence of plasma
by considering different distributions: uniform plasma, singular isothermal
sphere, non-singular isothermal gas sphere, and plasma in a galaxy cluster. We
found that the dragging of the inertial system along with the boosted parameter
$\Lambda$ affect the value of the deflection angle. As an application, we
studied the magnification for both uniform and singular isothermal
distributions.
| [
{
"created": "Wed, 24 Jul 2019 03:39:33 GMT",
"version": "v1"
}
] | 2021-11-24 | [
[
"Benavides-Gallego",
"Carlos A.",
""
],
[
"Abdujabbarov",
"Ahmadjon",
""
]
] | In this work, we obtain the deflection angle for a boosted Kerr black hole in the weak field approximation using the optics in a curved spacetime developed by J.L. Synge in 1960. We study the behavior of light in the presence of plasma by considering different distributions: uniform plasma, singular isothermal sphere, non-singular isothermal gas sphere, and plasma in a galaxy cluster. We found that the dragging of the inertial system along with the boosted parameter $\Lambda$ affect the value of the deflection angle. As an application, we studied the magnification for both uniform and singular isothermal distributions. |
gr-qc/0701123 | Pedro Marronetti | Pedro Marronetti, Wolfgang Tichy, Bernd Bruegmann, Jose Gonzalez, Mark
Hannam, Sascha Husa, Ulrich Sperhake | Binary black holes on a budget: Simulations using workstations | 20 pages, 8 figures. Final version, to appear in a special issue of
Class. Quantum Grav. based on the New Frontiers in Numerical Relativity
Conference, Golm, July 2006 | Class.Quant.Grav.24:S43-S58,2007 | 10.1088/0264-9381/24/12/S05 | null | gr-qc | null | Binary black hole simulations have traditionally been computationally very
expensive: current simulations are performed in supercomputers involving dozens
if not hundreds of processors, thus systematic studies of the parameter space
of binary black hole encounters still seem prohibitive with current technology.
Here we show how the multi-layered refinement level code BAM can be used on
dual processor workstations to simulate certain binary black hole systems. BAM,
based on the moving punctures method, provides grid structures composed of
boxes of increasing resolution near the center of the grid. In the case of
binaries, the highest resolution boxes are placed around each black hole and
they track them in their orbits until the final merger when a single set of
levels surrounds the black hole remnant. This is particularly useful when
simulating spinning black holes since the gravitational fields gradients are
larger. We present simulations of binaries with equal mass black holes with
spins parallel to the binary axis and intrinsic magnitude of S/m^2= 0.75. Our
results compare favorably to those of previous simulations of this particular
system. We show that the moving punctures method produces stable simulations at
maximum spatial resolutions up to M/160 and for durations of up to the
equivalent of 20 orbital periods.
| [
{
"created": "Mon, 22 Jan 2007 17:39:46 GMT",
"version": "v1"
},
{
"created": "Sun, 20 May 2007 14:03:15 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Marronetti",
"Pedro",
""
],
[
"Tichy",
"Wolfgang",
""
],
[
"Bruegmann",
"Bernd",
""
],
[
"Gonzalez",
"Jose",
""
],
[
"Hannam",
"Mark",
""
],
[
"Husa",
"Sascha",
""
],
[
"Sperhake",
"Ulrich",
""
]
] | Binary black hole simulations have traditionally been computationally very expensive: current simulations are performed in supercomputers involving dozens if not hundreds of processors, thus systematic studies of the parameter space of binary black hole encounters still seem prohibitive with current technology. Here we show how the multi-layered refinement level code BAM can be used on dual processor workstations to simulate certain binary black hole systems. BAM, based on the moving punctures method, provides grid structures composed of boxes of increasing resolution near the center of the grid. In the case of binaries, the highest resolution boxes are placed around each black hole and they track them in their orbits until the final merger when a single set of levels surrounds the black hole remnant. This is particularly useful when simulating spinning black holes since the gravitational fields gradients are larger. We present simulations of binaries with equal mass black holes with spins parallel to the binary axis and intrinsic magnitude of S/m^2= 0.75. Our results compare favorably to those of previous simulations of this particular system. We show that the moving punctures method produces stable simulations at maximum spatial resolutions up to M/160 and for durations of up to the equivalent of 20 orbital periods. |
1408.1101 | Jos\'e Villanueva | Sergio del Campo, V\'ictor C\'ardenas, Juan Maga\~na and J. R.
Villanueva | Semi-holographic model including the radiation component | 14 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1306.6612 | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this letter we study the semi holographic model which corresponds to the
radiative version of the model proposed by Zhang et al. (Phys. Lett. B 694
(2010), 177) and revisited by C\'ardenas et al. (Mon. Not. Roy. Astron. Soc.
438 (2014), 3603). This inclusion makes the model more realistic, so allows us
to test it with current observational data and then answer if the inconsistency
reported by C\'ardenas et al. is relaxed.
| [
{
"created": "Tue, 5 Aug 2014 20:04:35 GMT",
"version": "v1"
}
] | 2014-08-07 | [
[
"del Campo",
"Sergio",
""
],
[
"Cárdenas",
"Víctor",
""
],
[
"Magaña",
"Juan",
""
],
[
"Villanueva",
"J. R.",
""
]
] | In this letter we study the semi holographic model which corresponds to the radiative version of the model proposed by Zhang et al. (Phys. Lett. B 694 (2010), 177) and revisited by C\'ardenas et al. (Mon. Not. Roy. Astron. Soc. 438 (2014), 3603). This inclusion makes the model more realistic, so allows us to test it with current observational data and then answer if the inconsistency reported by C\'ardenas et al. is relaxed. |
1101.3497 | Eric Gourgoulhon | Eric Gourgoulhon, Charalampos Markakis, Koji Uryu and Yoshiharu
Eriguchi | Magnetohydrodynamics in stationary and axisymmetric spacetimes: a fully
covariant approach | Minor modifications (text only); published version (28 pages) | Phys.Rev.D83:104007,2011 | 10.1103/PhysRevD.83.104007 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A fully geometrical treatment of general relativistic magnetohydrodynamics
(GRMHD) is developed under the hypotheses of perfect conductivity, stationarity
and axisymmetry. The spacetime is not assumed to be circular, which allows for
greater generality than the Kerr-type spacetimes usually considered in GRMHD.
Expressing the electromagnetic field tensor solely in terms of three scalar
fields related to the spacetime symmetries, we generalize previously obtained
results in various directions. In particular, we present the first relativistic
version of the Soloviev transfield equation, subcases of which lead to fully
covariant versions of the Grad-Shafranov equation and of the Stokes equation in
the hydrodynamical limit. We have also derived, as another subcase of the
relativistic Soloviev equation, the equation governing magnetohydrodynamical
equilibria with purely toroidal magnetic fields in stationary and axisymmetric
spacetimes.
| [
{
"created": "Tue, 18 Jan 2011 16:49:36 GMT",
"version": "v1"
},
{
"created": "Wed, 4 May 2011 13:33:20 GMT",
"version": "v2"
}
] | 2011-05-12 | [
[
"Gourgoulhon",
"Eric",
""
],
[
"Markakis",
"Charalampos",
""
],
[
"Uryu",
"Koji",
""
],
[
"Eriguchi",
"Yoshiharu",
""
]
] | A fully geometrical treatment of general relativistic magnetohydrodynamics (GRMHD) is developed under the hypotheses of perfect conductivity, stationarity and axisymmetry. The spacetime is not assumed to be circular, which allows for greater generality than the Kerr-type spacetimes usually considered in GRMHD. Expressing the electromagnetic field tensor solely in terms of three scalar fields related to the spacetime symmetries, we generalize previously obtained results in various directions. In particular, we present the first relativistic version of the Soloviev transfield equation, subcases of which lead to fully covariant versions of the Grad-Shafranov equation and of the Stokes equation in the hydrodynamical limit. We have also derived, as another subcase of the relativistic Soloviev equation, the equation governing magnetohydrodynamical equilibria with purely toroidal magnetic fields in stationary and axisymmetric spacetimes. |
1504.00928 | Eliu Huerta | E. A. Huerta, Sean T. McWilliams, Jonathan R. Gair and Stephen R.
Taylor | Detection of eccentric supermassive black hole binaries with pulsar
timing arrays: Signal-to-noise ratio calculations | 18 pages, 9 figures, 3 Appendices. Submitted to PRD. v2: typos
corrected, references added. Accepted to PRD | Phys. Rev. D 92, 063010 (2015) | 10.1103/PhysRevD.92.063010 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a detailed analysis of the expected signal-to-noise ratios of
supermassive black hole binaries on eccentric orbits observed by pulsar timing
arrays. We derive several analytical relations that extend the results of
Peters and Mathews [Phys. Rev. D 131, 435 (1963)] to quantify the impact of
eccentricity in the detection of single resolvable binaries in the pulsar
timing array band. We present ready-to-use expressions to compute the
increase/loss in signal-to-noise ratio of eccentric single resolvable sources
whose dominant harmonic is located in the low/high frequency sensitivity regime
of pulsar timing arrays. Building upon the work of Phinney
(arXiv:astro-ph/0108028) and Enoki and Nagashima [Prog. Theor. Phys. 117, 241
(2007)], we present an analytical framework that enables the construction of
rapid spectra for a stochastic gravitational-wave background generated by a
cosmological population of eccentric sources. We confirm previous findings
which indicate that, relative to a population of quasicircular binaries, the
strain of a stochastic, isotropic gravitational-wave background generated by a
cosmological population of eccentric binaries will be suppressed in the
frequency band of pulsar timing arrays. We quantify this effect in terms of
signal-to-noise ratios in a pulsar timing array.
| [
{
"created": "Fri, 3 Apr 2015 20:00:51 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Sep 2015 17:16:50 GMT",
"version": "v2"
}
] | 2015-09-11 | [
[
"Huerta",
"E. A.",
""
],
[
"McWilliams",
"Sean T.",
""
],
[
"Gair",
"Jonathan R.",
""
],
[
"Taylor",
"Stephen R.",
""
]
] | We present a detailed analysis of the expected signal-to-noise ratios of supermassive black hole binaries on eccentric orbits observed by pulsar timing arrays. We derive several analytical relations that extend the results of Peters and Mathews [Phys. Rev. D 131, 435 (1963)] to quantify the impact of eccentricity in the detection of single resolvable binaries in the pulsar timing array band. We present ready-to-use expressions to compute the increase/loss in signal-to-noise ratio of eccentric single resolvable sources whose dominant harmonic is located in the low/high frequency sensitivity regime of pulsar timing arrays. Building upon the work of Phinney (arXiv:astro-ph/0108028) and Enoki and Nagashima [Prog. Theor. Phys. 117, 241 (2007)], we present an analytical framework that enables the construction of rapid spectra for a stochastic gravitational-wave background generated by a cosmological population of eccentric sources. We confirm previous findings which indicate that, relative to a population of quasicircular binaries, the strain of a stochastic, isotropic gravitational-wave background generated by a cosmological population of eccentric binaries will be suppressed in the frequency band of pulsar timing arrays. We quantify this effect in terms of signal-to-noise ratios in a pulsar timing array. |
1405.4011 | Saurya Das | Saurya Das | Cosmic coincidence or graviton mass? | This essay received an Honorable Mention in the 2014 Gravity Research
Foundation Essay Competition. 2 pages, revtex4. arXiv admin note: text
overlap with arXiv:1404.3093 | null | 10.1142/S0218271814420176 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using the quantum corrected Friedmann equation, obtained from the quantum
Raychudhuri equation, and assuming a small mass of the graviton (but consistent
with observations and theory), we propose a resolution of the smallness
problem(why is observed vacuum energy so small?) and the coincidence
problem(why does it constitute most of the universe, about 70%, in the current
epoch?).
| [
{
"created": "Thu, 15 May 2014 20:53:47 GMT",
"version": "v1"
}
] | 2015-06-19 | [
[
"Das",
"Saurya",
""
]
] | Using the quantum corrected Friedmann equation, obtained from the quantum Raychudhuri equation, and assuming a small mass of the graviton (but consistent with observations and theory), we propose a resolution of the smallness problem(why is observed vacuum energy so small?) and the coincidence problem(why does it constitute most of the universe, about 70%, in the current epoch?). |
0902.1238 | Luis Manuel Gonzalez-Romero | L. M. Gonz\'alez-Romero and F. Navarro-L\'erida | Neutron Stars Properties and Crust Movements in Post-glitch Epoch | Latex, 4 pages, 3 eps figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Using a new numerical code with non-uniform adapted mesh, we study the
changes produced in the global properties of neutron stars by the motion of
matter in crust region during post-glitch epoch. Our numerical analysis shows
that these changes may contribute to explain the observed spin-down of
rotational frequency.
| [
{
"created": "Sat, 7 Feb 2009 13:25:34 GMT",
"version": "v1"
}
] | 2009-02-10 | [
[
"González-Romero",
"L. M.",
""
],
[
"Navarro-Lérida",
"F.",
""
]
] | Using a new numerical code with non-uniform adapted mesh, we study the changes produced in the global properties of neutron stars by the motion of matter in crust region during post-glitch epoch. Our numerical analysis shows that these changes may contribute to explain the observed spin-down of rotational frequency. |
gr-qc/9806089 | Yasunori Fujii | Yasunori Fujii | Nonzero $\Omega_{\Lambda}$ and a new type of the dissipative structure | LaTex, 6 pages, 2 figures | null | null | NFU-98-11 | gr-qc astro-ph | null | We revisit the proposed theoretical model for a small but nonzero
cosmological constant which seems supported increasingly better by recent
observations. The model features two scalar fields which interact with each
other through a specifically chosen nonlinear potential. We find a very
sensitive dependence of the solutions of the scalar field equations on the
initial values. We discuss how the behavior is similar to and different from
those in well-known chaotic systems, coming to suggest an interesting new type
of the dissipative structure.
| [
{
"created": "Tue, 23 Jun 1998 11:40:47 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Fujii",
"Yasunori",
""
]
] | We revisit the proposed theoretical model for a small but nonzero cosmological constant which seems supported increasingly better by recent observations. The model features two scalar fields which interact with each other through a specifically chosen nonlinear potential. We find a very sensitive dependence of the solutions of the scalar field equations on the initial values. We discuss how the behavior is similar to and different from those in well-known chaotic systems, coming to suggest an interesting new type of the dissipative structure. |
1108.4421 | Yosef Zlochower | Hiroyuki Nakano, Yosef Zlochower, Carlos O. Lousto, Manuela Campanelli | Intermediate-mass-ratio black hole binaries II: Modeling Trajectories
and Gravitational Waveforms | 23 pages, 35 figures, revtex4 | Phys. Rev. D 84, 124006 (2011) | 10.1103/PhysRevD.84.124006 | null | gr-qc astro-ph.CO astro-ph.GA astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We revisit the scenario of small-mass-ratio (q) black-hole binaries;
performing new, more accurate, simulations of mass ratios 10:1 and 100:1 for
initially nonspinning black holes. We propose fitting functions for the
trajectories of the two black holes as a function of time and mass ratio (in
the range 1/100 < q < 1/10$) that combine aspects of post-Newtonian
trajectories at smaller orbital frequencies and plunging geodesics at larger
frequencies. We then use these trajectories to compute waveforms via black hole
perturbation theory. Using the advanced LIGO noise curve, we see a match of
~99.5% for the leading (l,m)=(2,2) mode between the numerical relativity and
perturbative waveforms. Nonleading modes have similarly high matches. We thus
prove the feasibility of efficiently generating a bank of gravitational
waveforms in the intermediate-mass-ratio regime using only a sparse set of full
numerical simulations.
| [
{
"created": "Mon, 22 Aug 2011 20:01:09 GMT",
"version": "v1"
}
] | 2011-12-13 | [
[
"Nakano",
"Hiroyuki",
""
],
[
"Zlochower",
"Yosef",
""
],
[
"Lousto",
"Carlos O.",
""
],
[
"Campanelli",
"Manuela",
""
]
] | We revisit the scenario of small-mass-ratio (q) black-hole binaries; performing new, more accurate, simulations of mass ratios 10:1 and 100:1 for initially nonspinning black holes. We propose fitting functions for the trajectories of the two black holes as a function of time and mass ratio (in the range 1/100 < q < 1/10$) that combine aspects of post-Newtonian trajectories at smaller orbital frequencies and plunging geodesics at larger frequencies. We then use these trajectories to compute waveforms via black hole perturbation theory. Using the advanced LIGO noise curve, we see a match of ~99.5% for the leading (l,m)=(2,2) mode between the numerical relativity and perturbative waveforms. Nonleading modes have similarly high matches. We thus prove the feasibility of efficiently generating a bank of gravitational waveforms in the intermediate-mass-ratio regime using only a sparse set of full numerical simulations. |
1506.08650 | Hooman Moradpour Hooman | H. Moradpour and S. Nasirimoghadam | Thermodynamic motivations of spherically symmetric static metrics | Accepted by Rom. J. Phys | Rom. Journ. Phys. Vol. 61, Nos. 9-10, P. 1453--1464 (2016) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bearing the thermodynamic arguments together with the two definitions of mass
in mind, we try to find metrics with spherical symmetry. We consider the
adiabatic condition along with the Gong-Wang mass, and evaluate the $g_{rr}$
element which points to a null hypersurface. In addition, we generalize the
thermodynamics laws to this hypersurface to find its temperature and thus the
corresponding surface gravity which enables us to get a relation for the
$g_{tt}$ element. Moreover, we investigate the mathematical and physical
properties of the discovered metric in the Einstein relativity framework which
shows that the primary mentioned null hypersurface is an event horizon. The
obtained energy-momentum tensor equals the energy-momentum tensor of a
polytropic black hole embedded into an anti-de Sitter background. We also show
that if one considers the Misner-Sharp mass in the calculations, the
Schwarzschild metric will be got. The relationship between the two mass
definitions in each metric is studied. The results of considering the
geometrical surface gravity are also addressed. Our investigation shows that
the geometrical surface gravity's definition is not always compatible with the
validity of the first law of thermodynamics on the horizons of spherically
symmetric static metrics.
| [
{
"created": "Sun, 14 Jun 2015 04:03:41 GMT",
"version": "v1"
},
{
"created": "Wed, 18 Nov 2015 09:01:22 GMT",
"version": "v2"
},
{
"created": "Mon, 4 Apr 2016 07:51:01 GMT",
"version": "v3"
}
] | 2016-12-23 | [
[
"Moradpour",
"H.",
""
],
[
"Nasirimoghadam",
"S.",
""
]
] | Bearing the thermodynamic arguments together with the two definitions of mass in mind, we try to find metrics with spherical symmetry. We consider the adiabatic condition along with the Gong-Wang mass, and evaluate the $g_{rr}$ element which points to a null hypersurface. In addition, we generalize the thermodynamics laws to this hypersurface to find its temperature and thus the corresponding surface gravity which enables us to get a relation for the $g_{tt}$ element. Moreover, we investigate the mathematical and physical properties of the discovered metric in the Einstein relativity framework which shows that the primary mentioned null hypersurface is an event horizon. The obtained energy-momentum tensor equals the energy-momentum tensor of a polytropic black hole embedded into an anti-de Sitter background. We also show that if one considers the Misner-Sharp mass in the calculations, the Schwarzschild metric will be got. The relationship between the two mass definitions in each metric is studied. The results of considering the geometrical surface gravity are also addressed. Our investigation shows that the geometrical surface gravity's definition is not always compatible with the validity of the first law of thermodynamics on the horizons of spherically symmetric static metrics. |
1908.08784 | Recai Erdem | Recai Erdem and Kemal G\"ultekin | A mechanism for formation of Bose-Einstein condensation in cosmology | Some technical details in the main text are moved to two appendices.
Typos are fixed, and the presentation of the manuscript is improved | null | 10.1088/1475-7516/2019/10/061 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We introduce a toy model of scalar particles with a trilinear scalar coupling
in cosmology. The trilinear coupling $\phi^2\chi$ causes production of
non-relativistic $\phi$ particles through the process
$\chi\chi\,\rightarrow\,\phi\phi$ where, initially, only relativistic $\chi$
particles are present. We consider the initial times of
$\chi\chi\,\rightarrow\,\phi\phi$ and observe that the curved space effects
promote formation of Bose-Einstein condensate of $\phi$ particles.
| [
{
"created": "Fri, 23 Aug 2019 15:50:32 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Oct 2019 06:29:51 GMT",
"version": "v2"
}
] | 2019-11-06 | [
[
"Erdem",
"Recai",
""
],
[
"Gültekin",
"Kemal",
""
]
] | We introduce a toy model of scalar particles with a trilinear scalar coupling in cosmology. The trilinear coupling $\phi^2\chi$ causes production of non-relativistic $\phi$ particles through the process $\chi\chi\,\rightarrow\,\phi\phi$ where, initially, only relativistic $\chi$ particles are present. We consider the initial times of $\chi\chi\,\rightarrow\,\phi\phi$ and observe that the curved space effects promote formation of Bose-Einstein condensate of $\phi$ particles. |
1007.0067 | Shun-Zhi Wang | Shun-Zhi Wang | Hexad Preons and Emergent Gravity in 3-dimensional Complex Spacetime | 5 pages, no figure | null | null | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We suggest that at high energy each space dimension has their own time
dimension, forming a 3-dimensional complex spacetime. Based on this hypothesis,
we propose that the primordial universe is made of six fundamental
anticommutative fields and their complex conjugate states. These fields are
called Hexad Preons which carry hypercolor degree of freedom transforming under
U(3,3) gauge group. Upon the breakdown of the gauge group from U(3,3) to its
maximal compact subgroup $U(3)\otimes U(3)$, the metric emerges. Leptons,
quarks, as well as other matter states may be formed from the subsequent
condensate of Hexad Preons. Strong and electroweak forces are manifestations of
the hypercolor interaction in the corresponding cases. Our framework may shed
light on many problems in cosmology and particle physics.
| [
{
"created": "Thu, 1 Jul 2010 05:06:55 GMT",
"version": "v1"
},
{
"created": "Tue, 27 Mar 2012 08:20:49 GMT",
"version": "v2"
},
{
"created": "Tue, 3 Apr 2012 08:08:38 GMT",
"version": "v3"
}
] | 2012-04-04 | [
[
"Wang",
"Shun-Zhi",
""
]
] | We suggest that at high energy each space dimension has their own time dimension, forming a 3-dimensional complex spacetime. Based on this hypothesis, we propose that the primordial universe is made of six fundamental anticommutative fields and their complex conjugate states. These fields are called Hexad Preons which carry hypercolor degree of freedom transforming under U(3,3) gauge group. Upon the breakdown of the gauge group from U(3,3) to its maximal compact subgroup $U(3)\otimes U(3)$, the metric emerges. Leptons, quarks, as well as other matter states may be formed from the subsequent condensate of Hexad Preons. Strong and electroweak forces are manifestations of the hypercolor interaction in the corresponding cases. Our framework may shed light on many problems in cosmology and particle physics. |
1902.01422 | Vasilis Oikonomou | S.D Odintsov, V.K. Oikonomou | Effects of Spatial Curvature on the $f(R)$ Gravity Phase Space: no
Inflationary Attractor? | CQG Accepted | null | 10.1088/1361-6382/ab0505 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study the effects of spatial curvature of the metric on the
phase space of vacuum $f(R)$ gravity. Particularly, we appropriately choose the
variables of the dynamical system, in order for this to be autonomous, and we
study the phase space of the resulting theory, focusing on de Sitter, matter
and radiation domination fixed points. Our analysis indicates that the effect
of spatial curvature on the phase space is radical, since it destabilizes all
the stable de Sitter vacua of the flat spacetime vacuum $f(R)$ gravity phase
space, making the phase space having non-trivial unstable submanifolds. This
instability occurs regardless if the spacetime has elliptic or hyperbolic
spatial sections, and it is also robust towards the choice of initial
conditions. We investigate the source of the instability in the system, and
also we discuss the stability of the matter and radiation domination vacua,
which, as we demonstrate, are also highly unstable. Our results for de Sitter
attractors indicate that the stable de Sitter attractors of the vacuum $f(R)$
gravity theory for a flat Universe, are destabilized by the presence of
curvature, and this shows that inflation for vacuum $f(R)$ gravity in non-flat
spacetime is problematic, at least at the phase space level. This result holds
true for both elliptic and hyperbolic spacetimes.
| [
{
"created": "Mon, 4 Feb 2019 19:02:21 GMT",
"version": "v1"
}
] | 2019-05-22 | [
[
"Odintsov",
"S. D",
""
],
[
"Oikonomou",
"V. K.",
""
]
] | In this paper we study the effects of spatial curvature of the metric on the phase space of vacuum $f(R)$ gravity. Particularly, we appropriately choose the variables of the dynamical system, in order for this to be autonomous, and we study the phase space of the resulting theory, focusing on de Sitter, matter and radiation domination fixed points. Our analysis indicates that the effect of spatial curvature on the phase space is radical, since it destabilizes all the stable de Sitter vacua of the flat spacetime vacuum $f(R)$ gravity phase space, making the phase space having non-trivial unstable submanifolds. This instability occurs regardless if the spacetime has elliptic or hyperbolic spatial sections, and it is also robust towards the choice of initial conditions. We investigate the source of the instability in the system, and also we discuss the stability of the matter and radiation domination vacua, which, as we demonstrate, are also highly unstable. Our results for de Sitter attractors indicate that the stable de Sitter attractors of the vacuum $f(R)$ gravity theory for a flat Universe, are destabilized by the presence of curvature, and this shows that inflation for vacuum $f(R)$ gravity in non-flat spacetime is problematic, at least at the phase space level. This result holds true for both elliptic and hyperbolic spacetimes. |
1510.01377 | John W. Barrett | John W. Barrett, Lisa Glaser | Monte Carlo simulations of random non-commutative geometries | 35 pages, author manuscript accepted by journal | null | 10.1088/1751-8113/49/24/245001 | null | gr-qc hep-lat hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Random non-commutative geometries are introduced by integrating over the
space of Dirac operators that form a spectral triple with a fixed algebra and
Hilbert space. The cases with the simplest types of Clifford algebra are
investigated using Monte Carlo simulations to compute the integrals. Various
qualitatively different types of behaviour of these random Dirac operators are
exhibited. Some features are explained in terms of the theory of random
matrices but other phenomena remain mysterious. Some of the models with a
quartic action of symmetry-breaking type display a phase transition. Close to
the phase transition the spectrum of a typical Dirac operator shows
manifold-like behaviour for the eigenvalues below a cut-off scale.
| [
{
"created": "Mon, 5 Oct 2015 21:45:14 GMT",
"version": "v1"
},
{
"created": "Wed, 11 May 2016 14:39:08 GMT",
"version": "v2"
}
] | 2016-06-22 | [
[
"Barrett",
"John W.",
""
],
[
"Glaser",
"Lisa",
""
]
] | Random non-commutative geometries are introduced by integrating over the space of Dirac operators that form a spectral triple with a fixed algebra and Hilbert space. The cases with the simplest types of Clifford algebra are investigated using Monte Carlo simulations to compute the integrals. Various qualitatively different types of behaviour of these random Dirac operators are exhibited. Some features are explained in terms of the theory of random matrices but other phenomena remain mysterious. Some of the models with a quartic action of symmetry-breaking type display a phase transition. Close to the phase transition the spectrum of a typical Dirac operator shows manifold-like behaviour for the eigenvalues below a cut-off scale. |
1107.5183 | Santiago Esteban Perez Bergliaffa | Santiago Esteban Perez Bergliaffa | An overview of f(R) theories | Talk given at the XIV Brazilian School of Cosmology and Gravitation
(2010), included in the proceedings to be published by Cambridge U. Press,
references added | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A brief introduction to theories of the gravitational field with a Lagrangian
that is a function of the scalar curvature is given. The emphasis will be
placed in formal developments, while comparison to observation will be
discussed in the chapter by S. Jor\'as in this volume.
| [
{
"created": "Tue, 26 Jul 2011 11:50:57 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Nov 2011 21:07:25 GMT",
"version": "v2"
}
] | 2011-11-14 | [
[
"Bergliaffa",
"Santiago Esteban Perez",
""
]
] | A brief introduction to theories of the gravitational field with a Lagrangian that is a function of the scalar curvature is given. The emphasis will be placed in formal developments, while comparison to observation will be discussed in the chapter by S. Jor\'as in this volume. |
2111.15583 | Fabian L\'aszl\'o Konstantin Wagner | Fabian Wagner | Relativistic Extended Uncertainty Principle from Spacetime Curvature | 22 pages, 5 figures | Phys. Rev. D 105, 025005 (2022) | 10.1103/PhysRevD.105.025005 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The investigations presented in this study are directed at relativistic
modifications of the uncertainty relation derived from the curvature of the
background spacetime. These findings generalize previous work which is
recovered in the nonrelativistic limit. Applying the 3+1-splitting in
accordance with the ADM-formalism, we find the relativistic physical momentum
operator and compute its standard deviation for wave functions confined to a
geodesic ball on a spacelike hypersurface. Its radius can then be understood as
a measure of position uncertainty. Under the assumtion of small position
uncertainties in comparison to background curvature length scales, we obtain
the corresponding corrections to the uncertainty relation in flat space. Those
depend on the Ricci scalar of the effective spatial metric, the particle is
moving on, and, if there are nonvanishing time-space components of the
spacetime metric, gradients of the shift vector and the lapse function.
Interestingly, this result is applicable not only to massive but also to
massless particles. Over all, this is not a covariant, yet a consistently
general relativistic approach. We further speculate on a possible covariant
extension.
| [
{
"created": "Tue, 30 Nov 2021 17:21:49 GMT",
"version": "v1"
}
] | 2022-10-12 | [
[
"Wagner",
"Fabian",
""
]
] | The investigations presented in this study are directed at relativistic modifications of the uncertainty relation derived from the curvature of the background spacetime. These findings generalize previous work which is recovered in the nonrelativistic limit. Applying the 3+1-splitting in accordance with the ADM-formalism, we find the relativistic physical momentum operator and compute its standard deviation for wave functions confined to a geodesic ball on a spacelike hypersurface. Its radius can then be understood as a measure of position uncertainty. Under the assumtion of small position uncertainties in comparison to background curvature length scales, we obtain the corresponding corrections to the uncertainty relation in flat space. Those depend on the Ricci scalar of the effective spatial metric, the particle is moving on, and, if there are nonvanishing time-space components of the spacetime metric, gradients of the shift vector and the lapse function. Interestingly, this result is applicable not only to massive but also to massless particles. Over all, this is not a covariant, yet a consistently general relativistic approach. We further speculate on a possible covariant extension. |
1203.1580 | Hossein Mohseni Sadjadi | H. Mohseni Sadjadi and Parviz Goodarzi | Reheating in nonminimal derivative coupling model | 16 pages, 5 figures; discussions added; accepted by JCAP | JCAP02(2013)038 | 10.1088/1475-7516/2013/02/038 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a model with nonminimal derivative coupling of inflaton to
gravity. The reheating process during rapid oscillation of the inflaton is
studied and the reheating temperature is obtained. Behaviors of the inflaton
and produced radiation in this era are discussed.
| [
{
"created": "Wed, 7 Mar 2012 19:40:17 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Jul 2012 13:17:12 GMT",
"version": "v2"
},
{
"created": "Sun, 3 Feb 2013 10:07:03 GMT",
"version": "v3"
}
] | 2015-06-04 | [
[
"Sadjadi",
"H. Mohseni",
""
],
[
"Goodarzi",
"Parviz",
""
]
] | We consider a model with nonminimal derivative coupling of inflaton to gravity. The reheating process during rapid oscillation of the inflaton is studied and the reheating temperature is obtained. Behaviors of the inflaton and produced radiation in this era are discussed. |
gr-qc/9408019 | Rainer Mueller | Juergen Audretsch and Rainer Mueller | Spontaneous excitation of an accelerated atom: The contributions of
vacuum fluctuations and radiation reaction | 13 pages, KONS-RGKU-94-09, to appear in Phys. Rev. A | Phys.Rev. A50 (1994) 1755-1763 | 10.1103/PhysRevA.50.1755 | null | gr-qc hep-th | null | We consider an atom in interaction with a massless scalar quantum field. We
discuss the structure of the rate of variation of the atomic energy for an
arbitrary stationary motion of the atom through the quantum vacuum. Our main
intention is to identify and to analyze quantitatively the distinct
contributions of vacuum fluctuations and radiation reaction to the spontaneous
excitation of a uniformly accelerated atom in its ground state. This gives an
understanding of the role of the different physical processes underlying the
Unruh effect. The atom's evolution into equilibrium and the Einstein
coefficients for spontaneous excitation and spontaneous emission are
calculated.
| [
{
"created": "Tue, 16 Aug 1994 20:24:57 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Audretsch",
"Juergen",
""
],
[
"Mueller",
"Rainer",
""
]
] | We consider an atom in interaction with a massless scalar quantum field. We discuss the structure of the rate of variation of the atomic energy for an arbitrary stationary motion of the atom through the quantum vacuum. Our main intention is to identify and to analyze quantitatively the distinct contributions of vacuum fluctuations and radiation reaction to the spontaneous excitation of a uniformly accelerated atom in its ground state. This gives an understanding of the role of the different physical processes underlying the Unruh effect. The atom's evolution into equilibrium and the Einstein coefficients for spontaneous excitation and spontaneous emission are calculated. |
gr-qc/9901040 | Kazuhiro Tominaga | Kazuhiro Tominaga, Motoyuki Saijo, and Kei-ichi Maeda | Gravitational waves from a test particle scattered by a neutron star:
Axial mode case | 21 pages, revtex, 11 figures are attached with eps files Accepted to
Phys. Rev. D | Phys.Rev. D60 (1999) 024004 | 10.1103/PhysRevD.60.024004 | WU-AP/76/99 (Waseda Univ. Astrophysics) | gr-qc | null | Using a metric perturbation method, we study gravitational waves from a test
particle scattered by a spherically symmetric relativistic star. We calculate
the energy spectrum and the waveform of gravitational waves for axial modes.
Since metric perturbations in axial modes do not couple to the matter fluid of
the star, emitted waves for a normal neutron star show only one peak in the
spectrum, which corresponds to the orbital frequency at the turning point,
where the gravitational field is strongest. However, for an ultracompact star
(the radius $R \lesssim 3M$), another type of resonant periodic peak appears in
the spectrum. This is just because of an excitation by a scattered particle of
axial quasinormal modes, which were found by Chandrasekhar and Ferrari. This
excitation comes from the existence of the potential minimum inside of a star.
We also find for an ultracompact star many small periodic peaks at the
frequency region beyond the maximum of the potential, which would be due to a
resonance of two waves reflected by two potential barriers (Regge-Wheeler type
and one at the center of the star). Such resonant peaks appear neither for a
normal neutron star nor for a Schwarzschild black hole. Consequently, even if
we analyze the energy spectrum of gravitational waves only for axial modes, it
would be possible to distinguish between an ultracompact star and a normal
neutron star (or a Schwarzschild black hole).
| [
{
"created": "Thu, 14 Jan 1999 14:34:51 GMT",
"version": "v1"
},
{
"created": "Mon, 20 Sep 1999 14:19:59 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Tominaga",
"Kazuhiro",
""
],
[
"Saijo",
"Motoyuki",
""
],
[
"Maeda",
"Kei-ichi",
""
]
] | Using a metric perturbation method, we study gravitational waves from a test particle scattered by a spherically symmetric relativistic star. We calculate the energy spectrum and the waveform of gravitational waves for axial modes. Since metric perturbations in axial modes do not couple to the matter fluid of the star, emitted waves for a normal neutron star show only one peak in the spectrum, which corresponds to the orbital frequency at the turning point, where the gravitational field is strongest. However, for an ultracompact star (the radius $R \lesssim 3M$), another type of resonant periodic peak appears in the spectrum. This is just because of an excitation by a scattered particle of axial quasinormal modes, which were found by Chandrasekhar and Ferrari. This excitation comes from the existence of the potential minimum inside of a star. We also find for an ultracompact star many small periodic peaks at the frequency region beyond the maximum of the potential, which would be due to a resonance of two waves reflected by two potential barriers (Regge-Wheeler type and one at the center of the star). Such resonant peaks appear neither for a normal neutron star nor for a Schwarzschild black hole. Consequently, even if we analyze the energy spectrum of gravitational waves only for axial modes, it would be possible to distinguish between an ultracompact star and a normal neutron star (or a Schwarzschild black hole). |
2108.02841 | Philip Beltracchi | Philip Beltracchi, Paolo Gondolo | Physical interpretation of Newman-Janis rotating systems. II. General
systems | Replaced with updated version, published at Phys. Rev. D 104, 124067
(2021) | null | 10.1103/PhysRevD.104.124067 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Drake and Szekeres have extended the Newman-Janis algorithm to produce
stationary axisymmetric spacetimes from general static spherically symmetric
solutions of the Einstein equations. The algorithm mathematically generates an
energy-momentum tensor for the rotating solution, but the rotating and
nonrotating system may or may not represent the same physical system, in the
sense of both being a perfect fluid, or an electromagnetic field, or a
$\Lambda$-term, and so on. In Part I (arxiv:2104.02255), we compared the
structure of the eigenvalues and eigenvectors of the rotating and nonrotating
energy-momentum tensors (their Segre types) and looked for the existence of
equations of state relating the rotating energy density and principal pressures
for Kerr-Schild systems. Here we extend our analysis to general static
spherically symmetric systems obtained according to the Drake-Szekeres
generalization of the Newman-Janis algorithm. We find that these rotating
systems can have almost all Segre types except [31] and [(31)]. Moreover, the
Segre type of the spacetime can change severely in passing from the nonrotating
to the rotating configurations, for example to $[11Z\bar{Z}]$ from seed systems
which were initially [(111,1)]. We also find conditions dictating how many
equations of state may exist in a Drake-Szekeres system.
| [
{
"created": "Thu, 5 Aug 2021 20:47:46 GMT",
"version": "v1"
},
{
"created": "Thu, 23 Dec 2021 21:28:44 GMT",
"version": "v2"
}
] | 2022-01-05 | [
[
"Beltracchi",
"Philip",
""
],
[
"Gondolo",
"Paolo",
""
]
] | Drake and Szekeres have extended the Newman-Janis algorithm to produce stationary axisymmetric spacetimes from general static spherically symmetric solutions of the Einstein equations. The algorithm mathematically generates an energy-momentum tensor for the rotating solution, but the rotating and nonrotating system may or may not represent the same physical system, in the sense of both being a perfect fluid, or an electromagnetic field, or a $\Lambda$-term, and so on. In Part I (arxiv:2104.02255), we compared the structure of the eigenvalues and eigenvectors of the rotating and nonrotating energy-momentum tensors (their Segre types) and looked for the existence of equations of state relating the rotating energy density and principal pressures for Kerr-Schild systems. Here we extend our analysis to general static spherically symmetric systems obtained according to the Drake-Szekeres generalization of the Newman-Janis algorithm. We find that these rotating systems can have almost all Segre types except [31] and [(31)]. Moreover, the Segre type of the spacetime can change severely in passing from the nonrotating to the rotating configurations, for example to $[11Z\bar{Z}]$ from seed systems which were initially [(111,1)]. We also find conditions dictating how many equations of state may exist in a Drake-Szekeres system. |
0711.0040 | Alexandru Ionescu | Alexandru D. Ionescu and Sergiu Klainerman | On the uniqueness of smooth, stationary black holes in vacuum | Various corrections | null | 10.1007/s00222-008-0146-6 | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We prove a conditional "no hair" theorem for smooth manifolds: if $E$ is the
domain of outer communication of a smooth, regular, stationary Einstein vacuum,
and if a technical condition relating the Ernst potential and Killing scalar is
satisfied on the bifurcate sphere, then $E$ is locally isometric to the domain
of outer communication of a Kerr space-time.
| [
{
"created": "Thu, 1 Nov 2007 00:03:04 GMT",
"version": "v1"
},
{
"created": "Sat, 26 Jul 2008 21:20:11 GMT",
"version": "v2"
}
] | 2009-11-13 | [
[
"Ionescu",
"Alexandru D.",
""
],
[
"Klainerman",
"Sergiu",
""
]
] | We prove a conditional "no hair" theorem for smooth manifolds: if $E$ is the domain of outer communication of a smooth, regular, stationary Einstein vacuum, and if a technical condition relating the Ernst potential and Killing scalar is satisfied on the bifurcate sphere, then $E$ is locally isometric to the domain of outer communication of a Kerr space-time. |
1910.08166 | Philip Beltracchi | Philip Beltracchi, Paolo Gondolo | A curious general relativistic sphere | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a particular solution to the Einstein field equations that could
arise as a magnetic monopole in the strong field limit of the Born-Infeld
electrodynamics. We solve its geodesics exactly and show that they can mimic
the gravitational lensing of a singular isothermal sphere, but with matter and
radiation following the same trajectories. This solution has previously been
called "cloud of strings" or "string hedgehog," and has appeared as the limit
of a global O(3) monopole.
| [
{
"created": "Thu, 17 Oct 2019 21:05:44 GMT",
"version": "v1"
},
{
"created": "Thu, 23 Jul 2020 18:18:30 GMT",
"version": "v2"
}
] | 2020-07-27 | [
[
"Beltracchi",
"Philip",
""
],
[
"Gondolo",
"Paolo",
""
]
] | We present a particular solution to the Einstein field equations that could arise as a magnetic monopole in the strong field limit of the Born-Infeld electrodynamics. We solve its geodesics exactly and show that they can mimic the gravitational lensing of a singular isothermal sphere, but with matter and radiation following the same trajectories. This solution has previously been called "cloud of strings" or "string hedgehog," and has appeared as the limit of a global O(3) monopole. |
1309.4529 | Israel Quiros | Israel Quiros | Matter Couplings which are Compatible with a Fundamental Theory of
Physics | 13 pages, no figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A criterion to seek for compatibility of any given matter coupling with a
fundamental theory of physics - assumed here to be the string theory - is
developed. We call this criterion as"`compatibility check", and apply it to
test different kinds of matter coupling which are familiar in cosmological
scenarios. The so called "chameleon effect" - useful to overcome the stringent
constraints on additional non gravitational interactions - is reviewed by
relaxing several assumptions which are commonly found in the bibliography in
order to explore the chameleon behavior of self-interacting scalar fields.
Although the results of this study are far from being conclusive, these (i)
suggest that matter couplings other than the exponential (dilaton) are very
unlikely to arise in a cosmological setup, and (ii) pose reasonable doubts on
the validity of the chameleon picture as we know it.
| [
{
"created": "Wed, 18 Sep 2013 03:09:10 GMT",
"version": "v1"
}
] | 2013-09-19 | [
[
"Quiros",
"Israel",
""
]
] | A criterion to seek for compatibility of any given matter coupling with a fundamental theory of physics - assumed here to be the string theory - is developed. We call this criterion as"`compatibility check", and apply it to test different kinds of matter coupling which are familiar in cosmological scenarios. The so called "chameleon effect" - useful to overcome the stringent constraints on additional non gravitational interactions - is reviewed by relaxing several assumptions which are commonly found in the bibliography in order to explore the chameleon behavior of self-interacting scalar fields. Although the results of this study are far from being conclusive, these (i) suggest that matter couplings other than the exponential (dilaton) are very unlikely to arise in a cosmological setup, and (ii) pose reasonable doubts on the validity of the chameleon picture as we know it. |
2407.04862 | Sergei Kopeikin | Sergei M. Kopeikin and George H. Kaplan | Lunar Time in General Relativity | 34 pages, 7 figures, 2 tables, appendix | null | null | null | gr-qc astro-ph.IM physics.space-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We introduce the general-relativistic definition of Lunar Coordinate Time
(TCL) based on the IAU 2000 resolutions that provide a framework of
relativistic reference systems. From this foundation, we derive a
transformation equation that describes the relative rate of TCL with respect to
Geocentric Coordinate Time (TCG). This equation serves as the cornerstone for
constructing a relativistic TCL--TCG time conversion algorithm. Using this
algorithm, we can compute both secular and periodic variations in the rate of
an atomic clock placed on the Moon, relative to an identical clock on Earth.
The algorithm accounts for various effects, including time dilation caused by
the Moon's orbital motion around Earth, gravitational potentials of both Earth
and Moon, and direct and indirect time dilation effects due to tidal
perturbations caused by the Sun. Our approach provides exquisite details of the
TCL--TCG transformation, accurate to a precision of 1 nanosecond. To validate
our methodology for lunar coordinate time, we compare it with the formalism of
local inertial frames applied to the Earth-Moon system and confirm their
equivalence.
| [
{
"created": "Fri, 5 Jul 2024 20:54:48 GMT",
"version": "v1"
}
] | 2024-07-09 | [
[
"Kopeikin",
"Sergei M.",
""
],
[
"Kaplan",
"George H.",
""
]
] | We introduce the general-relativistic definition of Lunar Coordinate Time (TCL) based on the IAU 2000 resolutions that provide a framework of relativistic reference systems. From this foundation, we derive a transformation equation that describes the relative rate of TCL with respect to Geocentric Coordinate Time (TCG). This equation serves as the cornerstone for constructing a relativistic TCL--TCG time conversion algorithm. Using this algorithm, we can compute both secular and periodic variations in the rate of an atomic clock placed on the Moon, relative to an identical clock on Earth. The algorithm accounts for various effects, including time dilation caused by the Moon's orbital motion around Earth, gravitational potentials of both Earth and Moon, and direct and indirect time dilation effects due to tidal perturbations caused by the Sun. Our approach provides exquisite details of the TCL--TCG transformation, accurate to a precision of 1 nanosecond. To validate our methodology for lunar coordinate time, we compare it with the formalism of local inertial frames applied to the Earth-Moon system and confirm their equivalence. |
gr-qc/0308029 | Ali Mostafazadeh | Ali Mostafazadeh | Wave Function of the Universe and Its Meaning | 9 pages, contributed to the First International Workshop on
Pseudo-Hermitian Hamiltonians in Quantum Physics, held in Prag June 2003 | Czech.J.Phys. 54 (2004) 93-99 | 10.1023/B:CJOP.0000014373.58075.95 | null | gr-qc hep-th quant-ph | null | For a FRW-spacetime coupled to an arbitrary real scalar field, we endow the
solution space of the associated Wheeler-DeWitt equation with a Hilbert-space
structure, construct the observables, and introduce the physical wave functions
of the universe that admit a genuine probabilistic interpretation. We also
discuss a proposal for the formulation of the dynamics. The approach to quantum
cosmology outlined in this article is based on the results obtained within the
theory of pseudo-Hermitian operators.
| [
{
"created": "Mon, 11 Aug 2003 12:07:28 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Mostafazadeh",
"Ali",
""
]
] | For a FRW-spacetime coupled to an arbitrary real scalar field, we endow the solution space of the associated Wheeler-DeWitt equation with a Hilbert-space structure, construct the observables, and introduce the physical wave functions of the universe that admit a genuine probabilistic interpretation. We also discuss a proposal for the formulation of the dynamics. The approach to quantum cosmology outlined in this article is based on the results obtained within the theory of pseudo-Hermitian operators. |
1703.08160 | Lisa Glaser | L. Glaser and R. Loll | CDT and Cosmology | 14 pages, invited review for a special issue of Compte Rendus
Physique | null | 10.1016/j.crhy.2017.04.002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the approach of Causal Dynamical Triangulations (CDT), quantum gravity is
obtained as a scaling limit of a non-perturbative path integral over
space-times whose causal structure plays a crucial role in the construction.
After some general considerations about the relation between quantum gravity
and cosmology, we examine which aspects of CDT are potentially interesting from
a cosmological point of view, focussing on the emergence of a de Sitter
universe in CDT quantum gravity.
| [
{
"created": "Thu, 23 Mar 2017 17:44:06 GMT",
"version": "v1"
},
{
"created": "Thu, 29 Nov 2018 15:28:13 GMT",
"version": "v2"
}
] | 2018-11-30 | [
[
"Glaser",
"L.",
""
],
[
"Loll",
"R.",
""
]
] | In the approach of Causal Dynamical Triangulations (CDT), quantum gravity is obtained as a scaling limit of a non-perturbative path integral over space-times whose causal structure plays a crucial role in the construction. After some general considerations about the relation between quantum gravity and cosmology, we examine which aspects of CDT are potentially interesting from a cosmological point of view, focussing on the emergence of a de Sitter universe in CDT quantum gravity. |
1610.08548 | Michael Heyl | H.J. Fahr and M. Heyl | Cosmic vacuum energy decay and creation of cosmic matter | 16 pages | Naturwissenschaften 94, 2007, 709 | 10.1007/s00114-007-0235-1 | null | gr-qc | http://creativecommons.org/publicdomain/zero/1.0/ | In the more recent literature on cosmological evolutions of the universe the
cosmic vacuum energy has become a non-renouncable ingredient. The cosmological
constant $\Lambda$, first invented by Einstein, but later also rejected by him,
presently experiences an astonishing revival. Interestingly enough it acts,
like a constant vacuum energy density would also do. Namely, it has an
accelerating action on cosmic dynamics without which, as it appears, presently
obtained cosmological data cannot be conciliated with theory. As we are going
to show in this review, however, the concept of a constant vacuum energy
density is unsatisfactory for very basic reasons, since it would claim for a
physical reality that acts upon spacetime and matter dynamics without itself
being acted upon by spacetime or matter.
| [
{
"created": "Thu, 20 Oct 2016 14:45:18 GMT",
"version": "v1"
}
] | 2016-10-28 | [
[
"Fahr",
"H. J.",
""
],
[
"Heyl",
"M.",
""
]
] | In the more recent literature on cosmological evolutions of the universe the cosmic vacuum energy has become a non-renouncable ingredient. The cosmological constant $\Lambda$, first invented by Einstein, but later also rejected by him, presently experiences an astonishing revival. Interestingly enough it acts, like a constant vacuum energy density would also do. Namely, it has an accelerating action on cosmic dynamics without which, as it appears, presently obtained cosmological data cannot be conciliated with theory. As we are going to show in this review, however, the concept of a constant vacuum energy density is unsatisfactory for very basic reasons, since it would claim for a physical reality that acts upon spacetime and matter dynamics without itself being acted upon by spacetime or matter. |
0708.1236 | Carlo Rovelli | Jonathan Engle, Roberto Pereira, Carlo Rovelli | Flipped spinfoam vertex and loop gravity | 37 pages, 4 figures | Nucl.Phys.B798:251-290,2008 | 10.1016/j.nuclphysb.2008.02.002 | null | gr-qc | null | We introduce a vertex amplitude for 4d loop quantum gravity. We derive it
from a conventional quantization of a Regge discretization of euclidean general
relativity. This yields a spinfoam sum that corrects some difficulties of the
Barrett-Crane theory. The second class simplicity constraints are imposed
weakly, and not strongly as in Barrett-Crane theory. Thanks to a flip in the
quantum algebra, the boundary states turn out to match those of SO(3) loop
quantum gravity -- the two can be identified as eigenstates of the same
physical quantities -- providing a solution to the problem of connecting the
covariant SO(4) spinfoam formalism with the canonical SO(3) spin-network one.
The vertex amplitude is SO(3) and SO(4)-covariant. It rectifies the triviality
of the intertwiner dependence of the Barrett-Crane vertex, which is responsible
for its failure to yield the correct propagator tensorial structure. The
construction provides also an independent derivation of the kinematics of loop
quantum gravity and of the result that geometry is quantized.
| [
{
"created": "Thu, 9 Aug 2007 09:35:40 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Engle",
"Jonathan",
""
],
[
"Pereira",
"Roberto",
""
],
[
"Rovelli",
"Carlo",
""
]
] | We introduce a vertex amplitude for 4d loop quantum gravity. We derive it from a conventional quantization of a Regge discretization of euclidean general relativity. This yields a spinfoam sum that corrects some difficulties of the Barrett-Crane theory. The second class simplicity constraints are imposed weakly, and not strongly as in Barrett-Crane theory. Thanks to a flip in the quantum algebra, the boundary states turn out to match those of SO(3) loop quantum gravity -- the two can be identified as eigenstates of the same physical quantities -- providing a solution to the problem of connecting the covariant SO(4) spinfoam formalism with the canonical SO(3) spin-network one. The vertex amplitude is SO(3) and SO(4)-covariant. It rectifies the triviality of the intertwiner dependence of the Barrett-Crane vertex, which is responsible for its failure to yield the correct propagator tensorial structure. The construction provides also an independent derivation of the kinematics of loop quantum gravity and of the result that geometry is quantized. |
1511.07731 | Cemsinan Deliduman | Cemsinan Deliduman, Oguzhan Kasikci, and Baris Yapiskan | Flat Galactic Rotation Curves from Geometry in Weyl Gravity | 8 pages, latex; v2: typos corrected, v3: discussion shortened, v4:
new section added, v5: discussion extended, v6: published version | Astrophys.Space Sci. 365 (2020) 3, 51 | 10.1007/s10509-020-03764-y | null | gr-qc astro-ph.GA hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We searched for a resolution of the flat galactic rotation curve problem from
geometry instead of assuming the existence of dark matter. We observed that the
scale independence of the rotational velocity in the outer region of galaxies
could point out to a possible existence of local scale symmetry and therefore
the gravitational phenomena inside such regions should be described by the
unique local scale symmetric theory, namely Weyl's theory of gravity. We solved
field equations of Weyl gravity and determined the special geometry in the
outer region of galaxies. In order to understand the effective description of
gravitational phenomena, we compared individual terms of so called
Einstein-Weyl theory and concluded that while the outer region of galaxies are
described by the Weyl term, the inner region of galaxies are described by the
Einstein-Hilbert term.
| [
{
"created": "Tue, 24 Nov 2015 14:36:47 GMT",
"version": "v1"
},
{
"created": "Sun, 6 Dec 2015 10:55:22 GMT",
"version": "v2"
},
{
"created": "Wed, 30 Aug 2017 18:52:37 GMT",
"version": "v3"
},
{
"created": "Sun, 30 Sep 2018 14:38:35 GMT",
"version": "v4"
},
{
"created": "Thu, 17 Oct 2019 15:20:22 GMT",
"version": "v5"
},
{
"created": "Sun, 5 Apr 2020 12:05:59 GMT",
"version": "v6"
}
] | 2020-04-15 | [
[
"Deliduman",
"Cemsinan",
""
],
[
"Kasikci",
"Oguzhan",
""
],
[
"Yapiskan",
"Baris",
""
]
] | We searched for a resolution of the flat galactic rotation curve problem from geometry instead of assuming the existence of dark matter. We observed that the scale independence of the rotational velocity in the outer region of galaxies could point out to a possible existence of local scale symmetry and therefore the gravitational phenomena inside such regions should be described by the unique local scale symmetric theory, namely Weyl's theory of gravity. We solved field equations of Weyl gravity and determined the special geometry in the outer region of galaxies. In order to understand the effective description of gravitational phenomena, we compared individual terms of so called Einstein-Weyl theory and concluded that while the outer region of galaxies are described by the Weyl term, the inner region of galaxies are described by the Einstein-Hilbert term. |
2105.01594 | Masoud Ghezelbash | Masoud Ghezelbash | Fubini-Study geometries in the higher-dimensional gravity | 21 pages, 9 figures, typos corrected, references added, some revision | Int. J. of Mod. Phys. A38 (2023) 2350084 | 10.1142/S0217751X23500847 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct approximate solutions to the Einstein-Maxwell theory with
uplifting the four dimensional Fubini-Study Kahler manifold. We find the
solutions can be expressed as the integrals of two special functions. The
solutions are regular almost everywhere except a bolt structure on a single
point in any dimensionality. We also show that in the context of considered
ansatzes for the metric function and the Maxwell field, the solutions are
unique and can not be non-trivially extended to include the cosmological
constant in any dimensions.
| [
{
"created": "Tue, 4 May 2021 16:06:07 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Jul 2021 15:11:00 GMT",
"version": "v2"
},
{
"created": "Mon, 19 Jun 2023 16:23:06 GMT",
"version": "v3"
}
] | 2024-02-09 | [
[
"Ghezelbash",
"Masoud",
""
]
] | We construct approximate solutions to the Einstein-Maxwell theory with uplifting the four dimensional Fubini-Study Kahler manifold. We find the solutions can be expressed as the integrals of two special functions. The solutions are regular almost everywhere except a bolt structure on a single point in any dimensionality. We also show that in the context of considered ansatzes for the metric function and the Maxwell field, the solutions are unique and can not be non-trivially extended to include the cosmological constant in any dimensions. |
1011.1024 | Miguel Campiglia | Abhay Ashtekar, Miguel Campiglia, Adam Henderson | Path Integrals and the WKB approximation in Loop Quantum Cosmology | 21 pages, 4 figures | Phys.Rev.D82:124043,2010 | 10.1103/PhysRevD.82.124043 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We follow the Feynman procedure to obtain a path integral formulation of loop
quantum cosmology starting from the Hilbert space framework. Quantum geometry
effects modify the weight associated with each path so that the effective
measure on the space of paths is different from that used in the Wheeler-DeWitt
theory. These differences introduce some conceptual subtleties in arriving at
the WKB approximation. But the approximation is well defined and provides
intuition for the differences between loop quantum cosmology and the
Wheeler-DeWitt theory from a path integral perspective.
| [
{
"created": "Wed, 3 Nov 2010 22:22:23 GMT",
"version": "v1"
}
] | 2011-01-25 | [
[
"Ashtekar",
"Abhay",
""
],
[
"Campiglia",
"Miguel",
""
],
[
"Henderson",
"Adam",
""
]
] | We follow the Feynman procedure to obtain a path integral formulation of loop quantum cosmology starting from the Hilbert space framework. Quantum geometry effects modify the weight associated with each path so that the effective measure on the space of paths is different from that used in the Wheeler-DeWitt theory. These differences introduce some conceptual subtleties in arriving at the WKB approximation. But the approximation is well defined and provides intuition for the differences between loop quantum cosmology and the Wheeler-DeWitt theory from a path integral perspective. |
1506.06713 | Dong-han Yeom | Pisin Chen, Dong-han Yeom | Cusp singularities in f(R) gravity: pros and cons | 19 pages, 11 figures | JCAP 10(2015)022 | 10.1088/1475-7516/2015/10/022 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate cusp singularities in f(R) gravity, especially for Starobinsky
and Hu-Sawicki dark energy models. We illustrate that, by using double-null
numerical simulations, a cusp singularity can be triggered by gravitational
collapses. This singularity can be cured by adding a quadratic term, but this
causes a Ricci scalar bump that can be observed by an observer outside the
event horizon. Comparing with cosmological parameters, it seems that it would
be difficult to see super-Planckian effects by astrophysical experiments. On
the other hand, at once there exists a cusp singularity, it can be a mechanism
to realize a horizon scale curvature singularity that can be interpreted by a
firewall.
| [
{
"created": "Mon, 22 Jun 2015 18:28:03 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Oct 2015 05:27:14 GMT",
"version": "v2"
}
] | 2015-10-14 | [
[
"Chen",
"Pisin",
""
],
[
"Yeom",
"Dong-han",
""
]
] | We investigate cusp singularities in f(R) gravity, especially for Starobinsky and Hu-Sawicki dark energy models. We illustrate that, by using double-null numerical simulations, a cusp singularity can be triggered by gravitational collapses. This singularity can be cured by adding a quadratic term, but this causes a Ricci scalar bump that can be observed by an observer outside the event horizon. Comparing with cosmological parameters, it seems that it would be difficult to see super-Planckian effects by astrophysical experiments. On the other hand, at once there exists a cusp singularity, it can be a mechanism to realize a horizon scale curvature singularity that can be interpreted by a firewall. |
gr-qc/0511099 | Gilberto Medeiros Kremer | M. O. Ribas, F. P. Devecchi, G. M. Kremer | Fermions as sources of accelerated regimes in cosmology | 4 figures, accepted in PRD | Phys.Rev. D72 (2005) 123502 | 10.1103/PhysRevD.72.123502 | null | gr-qc | null | In this work it is investigated if fermionic sources could be responsible for
accelerated periods during the evolution of a universe where a matter field
would answer for the decelerated period. The self-interaction potential of the
fermionic field is considered as a function of the scalar and pseudo-scalar
invariants. Irreversible processes of energy transfer between the matter and
gravitational fields are also considered. It is shown that the fermionic field
could behave like an inflaton field in the early universe and as dark energy
for an old universe.
| [
{
"created": "Thu, 17 Nov 2005 10:24:36 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Ribas",
"M. O.",
""
],
[
"Devecchi",
"F. P.",
""
],
[
"Kremer",
"G. M.",
""
]
] | In this work it is investigated if fermionic sources could be responsible for accelerated periods during the evolution of a universe where a matter field would answer for the decelerated period. The self-interaction potential of the fermionic field is considered as a function of the scalar and pseudo-scalar invariants. Irreversible processes of energy transfer between the matter and gravitational fields are also considered. It is shown that the fermionic field could behave like an inflaton field in the early universe and as dark energy for an old universe. |
gr-qc/0610035 | Yurii V. Dumin | Yurii V. Dumin (Theoretical Department, IZMIRAN, Russian Academy of
Sciences, Troitsk, Moscow reg.) | Can (dG/dt)/G Bound the Local Cosmological Dynamics? | REVTeX4, 1 page | Phys.Rev.Lett. 98 (2007) 059001 | 10.1103/PhysRevLett.98.059001 | null | gr-qc astro-ph hep-ph | null | It is argued that constraints on time variation of the gravitational constant
(dG/dt)/G, e.g. derived from the lunar laser ranging, cannot be immediately
applied to restrict the cosmological expansion at planetary scales, as it was
done by Williams, Turyshev, and Boggs [PRL, 93, 261101 (2004),
arXiv:gr-qc/0411113].
| [
{
"created": "Mon, 9 Oct 2006 15:05:52 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Dumin",
"Yurii V.",
"",
"Theoretical Department, IZMIRAN, Russian Academy of\n Sciences, Troitsk, Moscow reg."
]
] | It is argued that constraints on time variation of the gravitational constant (dG/dt)/G, e.g. derived from the lunar laser ranging, cannot be immediately applied to restrict the cosmological expansion at planetary scales, as it was done by Williams, Turyshev, and Boggs [PRL, 93, 261101 (2004), arXiv:gr-qc/0411113]. |
1111.1325 | Stefano Bertone | Stefano Bertone and Christophe Le Poncin-Lafitte | Light Deflection for relativistic space astrometry in closed form | proceedings of Great-ESF workshop, June 2011, Porto, Portugal | Memorie della Societa Astronomica Italiana, v.83, p.1020 (2012) | null | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Given the extreme accuracy reached by future global space astrometry, one
needs a global relativistic modeling of observations. A relativistic definition
of astrometric observables is then essential to find uniquely coordinates,
parallax and proper motion of a stellar object. The standard procedure is to
explicitly solve the null geodesic equations to describe the trajectory of a
photon emitted by a celestial object and received by a moving observing
satellite. However, this task can be avoided if one builds an astrometric set
up using the recent formalism of time transfer functions.
| [
{
"created": "Sat, 5 Nov 2011 16:20:23 GMT",
"version": "v1"
},
{
"created": "Fri, 10 May 2013 08:16:59 GMT",
"version": "v2"
}
] | 2013-05-13 | [
[
"Bertone",
"Stefano",
""
],
[
"Poncin-Lafitte",
"Christophe Le",
""
]
] | Given the extreme accuracy reached by future global space astrometry, one needs a global relativistic modeling of observations. A relativistic definition of astrometric observables is then essential to find uniquely coordinates, parallax and proper motion of a stellar object. The standard procedure is to explicitly solve the null geodesic equations to describe the trajectory of a photon emitted by a celestial object and received by a moving observing satellite. However, this task can be avoided if one builds an astrometric set up using the recent formalism of time transfer functions. |
2204.14222 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | Periodic signature change in spacetimes of embedding class one | 10 pages, no figures | Int. J. Astron. Astrophys. (IJAA), vol. 12, pp. 167-176, 2022 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The idea of an oscillating Universe has remained a topic of interest even
after the discovery of dark energy. This paper confirms this idea by means of
another well-established theory in general relativity, the embedding of curved
spacetimes in higher-dimensional flat spacetimes: an $n$-dimensional Riemannian
space is said to be of embedding class $m$ if $m+n$ is the lowest dimension $d$
of the flat space in which the given space can be embedded; here
$d=\frac{1}{2}n(n-1)$. So a four-dimensional Riemannian space is of class two
since it can be embedded in a six-dimensional flat space. A line element of
class two can be reduced to a line element of class one by a suitable
coordinate transformation. The extra dimension can be either spacelike or
timelike, leading to accelerating and decelerating expansions, respectively.
Accordingly, it is proposed in this paper that the free parameter occurring in
the transformation be a periodic function of time. The result is a mathematical
model that can be interpreted as a periodic change in the signature of the
embedding space. This signature change may be the best model for an oscillating
Universe and complements various models proposed in the literature.
| [
{
"created": "Fri, 29 Apr 2022 16:55:46 GMT",
"version": "v1"
},
{
"created": "Sun, 3 Mar 2024 17:55:40 GMT",
"version": "v2"
},
{
"created": "Wed, 6 Mar 2024 16:11:18 GMT",
"version": "v3"
}
] | 2024-03-07 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | The idea of an oscillating Universe has remained a topic of interest even after the discovery of dark energy. This paper confirms this idea by means of another well-established theory in general relativity, the embedding of curved spacetimes in higher-dimensional flat spacetimes: an $n$-dimensional Riemannian space is said to be of embedding class $m$ if $m+n$ is the lowest dimension $d$ of the flat space in which the given space can be embedded; here $d=\frac{1}{2}n(n-1)$. So a four-dimensional Riemannian space is of class two since it can be embedded in a six-dimensional flat space. A line element of class two can be reduced to a line element of class one by a suitable coordinate transformation. The extra dimension can be either spacelike or timelike, leading to accelerating and decelerating expansions, respectively. Accordingly, it is proposed in this paper that the free parameter occurring in the transformation be a periodic function of time. The result is a mathematical model that can be interpreted as a periodic change in the signature of the embedding space. This signature change may be the best model for an oscillating Universe and complements various models proposed in the literature. |
1811.08797 | Nelson Christensen | Nelson Christensen | Stochastic Gravitational Wave Backgrounds | null | Reports on Progress in Physics, Vol. 82, 016903 (2019) | 10.1088/1361-6633/aae6b5 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A stochastic background of gravitational waves can be created by the
superposition of a large number of independent sources. The physical processes
occurring at the earliest moments of the universe certainly created a
stochastic background that exists, at some level, today. This is analogous to
the cosmic microwave background, which is an electromagnetic record of the
early universe. The recent observations of gravitational waves by the Advanced
LIGO and Advanced Virgo detectors imply that there is also a stochastic
background that has been created by binary black hole and binary neutron star
mergers over the history of the universe. Whether the stochastic background is
observed directly, or upper limits placed on it in specific frequency bands,
important astrophysical and cosmological statements about it can be made. This
review will summarize the current state of research of the stochastic
background, from the sources of these gravitational waves, to the current
methods used to observe them.
| [
{
"created": "Wed, 21 Nov 2018 15:50:01 GMT",
"version": "v1"
}
] | 2018-11-22 | [
[
"Christensen",
"Nelson",
""
]
] | A stochastic background of gravitational waves can be created by the superposition of a large number of independent sources. The physical processes occurring at the earliest moments of the universe certainly created a stochastic background that exists, at some level, today. This is analogous to the cosmic microwave background, which is an electromagnetic record of the early universe. The recent observations of gravitational waves by the Advanced LIGO and Advanced Virgo detectors imply that there is also a stochastic background that has been created by binary black hole and binary neutron star mergers over the history of the universe. Whether the stochastic background is observed directly, or upper limits placed on it in specific frequency bands, important astrophysical and cosmological statements about it can be made. This review will summarize the current state of research of the stochastic background, from the sources of these gravitational waves, to the current methods used to observe them. |
gr-qc/9608008 | Raphael Bousso | Raphael Bousso and Stephen W. Hawking (DAMTP, Cambridge) | Pair Creation and Evolution of Black Holes During Inflation | 8 pages, LaTeX, 3 figures; contribution to the proceedings of the
Journees Relativistes 96, contains extra figures | Helv.Phys.Acta 69:261-264,1996 | null | DAMTP/R-96/35 | gr-qc astro-ph hep-th | null | We summarise recent work on the quantum production of black holes in the
inflationary era. We describe, in simple terms, the Euclidean approach used,
and the results obtained both for the pair creation rate and for the evolution
of the black holes.
| [
{
"created": "Fri, 2 Aug 1996 18:41:31 GMT",
"version": "v1"
}
] | 2011-04-15 | [
[
"Bousso",
"Raphael",
"",
"DAMTP, Cambridge"
],
[
"Hawking",
"Stephen W.",
"",
"DAMTP, Cambridge"
]
] | We summarise recent work on the quantum production of black holes in the inflationary era. We describe, in simple terms, the Euclidean approach used, and the results obtained both for the pair creation rate and for the evolution of the black holes. |
gr-qc/0212034 | Jose Geraldo Pereira | R. Aldrovandi, P. B. Barros and J. G. Pereira | The Equivalence Principle Revisited | RevTeX, 18 pages, no figures, to appear in Foundations of Physics | Found.Phys. 33 (2003) 545-575 | null | null | gr-qc | null | A precise formulation of the strong Equivalence Principle is essential to the
understanding of the relationship between gravitation and quantum mechanics.
The relevant aspects are reviewed in a context including General Relativity,
but allowing for the presence of torsion. For the sake of brevity, a concise
statement is proposed for the Principle: "An ideal observer immersed in a
gravitational field can choose a reference frame in which gravitation goes
unnoticed". This statement is given a clear mathematical meaning through an
accurate discussion of its terms. It holds for ideal observers (time-like
smooth non-intersecting curves), but not for real, spatially extended
observers. Analogous results hold for gauge fields. The difference between
gravitation and the other fundamental interactions comes from their distinct
roles in the equation of force.
| [
{
"created": "Sat, 7 Dec 2002 18:00:02 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Aldrovandi",
"R.",
""
],
[
"Barros",
"P. B.",
""
],
[
"Pereira",
"J. G.",
""
]
] | A precise formulation of the strong Equivalence Principle is essential to the understanding of the relationship between gravitation and quantum mechanics. The relevant aspects are reviewed in a context including General Relativity, but allowing for the presence of torsion. For the sake of brevity, a concise statement is proposed for the Principle: "An ideal observer immersed in a gravitational field can choose a reference frame in which gravitation goes unnoticed". This statement is given a clear mathematical meaning through an accurate discussion of its terms. It holds for ideal observers (time-like smooth non-intersecting curves), but not for real, spatially extended observers. Analogous results hold for gauge fields. The difference between gravitation and the other fundamental interactions comes from their distinct roles in the equation of force. |
2205.13560 | Rebecca Briffa Ms | Rebecca Briffa, Celia Escamilla-Rivera, Jackson Levi Said and Jurgen
Mifsud | $f(T,B)$ Gravity in the late Universe in the context of local
measurements | null | null | 10.1016/j.dark.2022.101153 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We explore the viability of three models in $f(T,B)$ gravity using data from
recent surveys based on cosmic chronometers, the Pantheon data set, and
baryonic acoustic oscillation data. We also assess the consistency of these
models and data set combinations with two important priors on the Hubble
constant coming from the SH0ES Team and measurements using the tip of the red
giant branch respectively. These give the highest and lowest values of the
Hubble constant coming from cosmology independent studies. In general, our
analysis does provide a more consistent fit for the late time data being
analyzed. However, each model does include an additional model parameter in
comparison with the concordance model. We close the analysis with a comparative
analysis in which each model, data set and Hubble constant prior combination
are cross-analyzed against each other.
| [
{
"created": "Thu, 26 May 2022 18:01:47 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Dec 2022 14:25:58 GMT",
"version": "v2"
}
] | 2022-12-23 | [
[
"Briffa",
"Rebecca",
""
],
[
"Escamilla-Rivera",
"Celia",
""
],
[
"Said",
"Jackson Levi",
""
],
[
"Mifsud",
"Jurgen",
""
]
] | We explore the viability of three models in $f(T,B)$ gravity using data from recent surveys based on cosmic chronometers, the Pantheon data set, and baryonic acoustic oscillation data. We also assess the consistency of these models and data set combinations with two important priors on the Hubble constant coming from the SH0ES Team and measurements using the tip of the red giant branch respectively. These give the highest and lowest values of the Hubble constant coming from cosmology independent studies. In general, our analysis does provide a more consistent fit for the late time data being analyzed. However, each model does include an additional model parameter in comparison with the concordance model. We close the analysis with a comparative analysis in which each model, data set and Hubble constant prior combination are cross-analyzed against each other. |
1410.6636 | Luis Herrera | L. Herrera, A. Di Prisco, W. Barreto, J. Ospino | Conformally flat polytropes for anisotropic matter | 9 pages Revtex-4, 6 figures. To appear in Gen. Rel. Grav. Some typos
corrected | Gen. Rel. Grav. 46,1827, (2014) | 10.1007/s10714-014-1827-7 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze in detail conformally flat spherically symmetric fluid
distributions, satisfying a polytropic equation of state. Among the two
possible families of relativistic polytropes, only one contains models which
satisfy all the required physical conditions. The ensuing configurations are
necessarily anisotropic and show interesting physical properties. Prospective
applications of the presented models to the study of super-Chandrasekhar white
dwarfs, are discussed.
| [
{
"created": "Fri, 24 Oct 2014 10:09:54 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Nov 2014 12:26:28 GMT",
"version": "v2"
}
] | 2014-11-06 | [
[
"Herrera",
"L.",
""
],
[
"Di Prisco",
"A.",
""
],
[
"Barreto",
"W.",
""
],
[
"Ospino",
"J.",
""
]
] | We analyze in detail conformally flat spherically symmetric fluid distributions, satisfying a polytropic equation of state. Among the two possible families of relativistic polytropes, only one contains models which satisfy all the required physical conditions. The ensuing configurations are necessarily anisotropic and show interesting physical properties. Prospective applications of the presented models to the study of super-Chandrasekhar white dwarfs, are discussed. |
1107.0802 | Jose Natario | Joao L. Costa, Artur Alho and Jose Natario | Spherical linear waves in de Sitter spacetime | 9 pages, 1 figure; v2: minor changes, references added, matches final
published version | J. Math. Phys. 53 (2012) 052501 | 10.1063/1.4721644 | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We apply Christodoulou's framework, developed to study the Einstein-scalar
field equations in spherical symmetry, to the linear wave equation in de Sitter
spacetime, as a first step towards the Einstein-scalar field equations with
positive cosmological constant. We obtain an integro-differential evolution
equation which we solve by taking initial data on a null cone. As a corollary
we obtain elementary derivations of expected properties of linear waves in de
Sitter spacetime: boundedness in terms of (characteristic) initial data, and a
Price law establishing uniform exponential decay, in Bondi time, to a constant.
| [
{
"created": "Tue, 5 Jul 2011 07:34:26 GMT",
"version": "v1"
},
{
"created": "Fri, 25 May 2012 17:05:56 GMT",
"version": "v2"
}
] | 2015-05-28 | [
[
"Costa",
"Joao L.",
""
],
[
"Alho",
"Artur",
""
],
[
"Natario",
"Jose",
""
]
] | We apply Christodoulou's framework, developed to study the Einstein-scalar field equations in spherical symmetry, to the linear wave equation in de Sitter spacetime, as a first step towards the Einstein-scalar field equations with positive cosmological constant. We obtain an integro-differential evolution equation which we solve by taking initial data on a null cone. As a corollary we obtain elementary derivations of expected properties of linear waves in de Sitter spacetime: boundedness in terms of (characteristic) initial data, and a Price law establishing uniform exponential decay, in Bondi time, to a constant. |
gr-qc/0701002 | T. Padmanabhan | Dawood Kothawala, Sudipta Sarkar, T. Padmanabhan | Einstein's equations as a thermodynamic identity: The cases of
stationary axisymmetric horizons and evolving spherically symmetric horizons | revtex; 6 pages; no figures | Phys.Lett.B652:338-342,2007 | 10.1016/j.physletb.2007.07.021 | null | gr-qc astro-ph hep-th | null | There is an intriguing analogy between the gravitational dynamics of the
horizons and thermodynamics. In case of general relativity, as well as for a
wider class of Lanczos-Lovelock theories of gravity, it is possible to
interpret the field equations near any spherically symmetric horizon as a
thermodynamic identity TdS = dE + PdV. We study this approach further and
generalize the results to two more generic cases within the context of general
relativity: (i) stationary axis-symmetric horizons and (ii) time dependent
evolving horizons. In both the cases, the near horizon structure of Einstein
equations can be expressed as a thermodynamic identity under the virtual
displacement of the horizon. This result demonstrates the fact that the
thermodynamic interpretation of gravitational dynamics is not restricted to
spherically symmetric or static horizons but is quite generic in nature and
indicates a deeper connection between gravity and thermodynamics.
| [
{
"created": "Sat, 30 Dec 2006 08:20:11 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Kothawala",
"Dawood",
""
],
[
"Sarkar",
"Sudipta",
""
],
[
"Padmanabhan",
"T.",
""
]
] | There is an intriguing analogy between the gravitational dynamics of the horizons and thermodynamics. In case of general relativity, as well as for a wider class of Lanczos-Lovelock theories of gravity, it is possible to interpret the field equations near any spherically symmetric horizon as a thermodynamic identity TdS = dE + PdV. We study this approach further and generalize the results to two more generic cases within the context of general relativity: (i) stationary axis-symmetric horizons and (ii) time dependent evolving horizons. In both the cases, the near horizon structure of Einstein equations can be expressed as a thermodynamic identity under the virtual displacement of the horizon. This result demonstrates the fact that the thermodynamic interpretation of gravitational dynamics is not restricted to spherically symmetric or static horizons but is quite generic in nature and indicates a deeper connection between gravity and thermodynamics. |
1910.02990 | Herbert Hamber | Herbert W. Hamber and Lu Heng Sunny Yu | Gravitational Fluctuations as an Alternative to Inflation II. CMB
Angular Power Spectrum | 43 pages, 8 figures (typos fixed, references added) | Universe 2019, 5(11), 216 | 10.3390/universe5110216 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Power spectra always play an important role in the theory of inflation. In
particular, the ability to reproduce the galaxy matter power spectrum and the
CMB temperature angular power spectrum coefficients to high accuracy is often
considered a triumph of inflation. In our previous work, we presented an
alternative explanation for the matter power spectrum based on nonperturbative
quantum field-theoretical methods applied to Einstein's gravity, instead of
inflation models based on scalar fields. In this work, we review the basic
concepts and provide further in-depth investigations. We first update the
analysis with more recent data sets and error analysis, and then extend our
predictions to the CMB angular spectrum coefficients, which we did not consider
previously. Then we investigate further the potential freedoms and
uncertainties associated with the fundamental parameters that are part of this
picture, and show how recent cosmological data provides significant constraints
on these quantities. Overall, we find good general consistency between theory
and data, even potentially favoring the gravitationally-motivated picture at
the largest scales. We summarize our results by outlining how this picture can
be tested in the near future with increasingly accurate astrophysical
measurements.
| [
{
"created": "Mon, 7 Oct 2019 18:14:41 GMT",
"version": "v1"
},
{
"created": "Thu, 31 Oct 2019 17:00:20 GMT",
"version": "v2"
}
] | 2019-11-01 | [
[
"Hamber",
"Herbert W.",
""
],
[
"Yu",
"Lu Heng Sunny",
""
]
] | Power spectra always play an important role in the theory of inflation. In particular, the ability to reproduce the galaxy matter power spectrum and the CMB temperature angular power spectrum coefficients to high accuracy is often considered a triumph of inflation. In our previous work, we presented an alternative explanation for the matter power spectrum based on nonperturbative quantum field-theoretical methods applied to Einstein's gravity, instead of inflation models based on scalar fields. In this work, we review the basic concepts and provide further in-depth investigations. We first update the analysis with more recent data sets and error analysis, and then extend our predictions to the CMB angular spectrum coefficients, which we did not consider previously. Then we investigate further the potential freedoms and uncertainties associated with the fundamental parameters that are part of this picture, and show how recent cosmological data provides significant constraints on these quantities. Overall, we find good general consistency between theory and data, even potentially favoring the gravitationally-motivated picture at the largest scales. We summarize our results by outlining how this picture can be tested in the near future with increasingly accurate astrophysical measurements. |
2010.12360 | Diego S\'aez-Chill\'on G\'omez | Sabit Bekov, Kairat Myrzakulov, Ratbay Myrzakulov, Diego
S\'aez-Chill\'on G\'omez | General slow-roll inflation in $f(R)$ gravity under the Palatini
approach | 11 pages, version published | Symmetry 2020, 12(12), 1958 | 10.3390/sym12121958 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Slow-roll inflation is analyzed in the context of modified gravity within the
Palatini formalism. As shown in the literature, inflation in this framework
requires the presence of non-traceless matter, otherwise it does not occur just
as a consequence of the non-linear gravitational terms of the action.
Nevertheless, by including a single scalar field that plays the role of the
inflaton, slow-roll inflation can be performed in these theories, where the
equations lead to an effective potential that modifies the dynamics. We obtain
the general slow-roll parameters and analyze a simple model to illustrate the
differences introduced by the gravitational terms under the Palatini approach,
and the modifications on the spectral index and the tensor to scalar ratio
predicted by the model.
| [
{
"created": "Thu, 22 Oct 2020 17:00:13 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Nov 2020 16:53:58 GMT",
"version": "v2"
}
] | 2020-11-30 | [
[
"Bekov",
"Sabit",
""
],
[
"Myrzakulov",
"Kairat",
""
],
[
"Myrzakulov",
"Ratbay",
""
],
[
"Gómez",
"Diego Sáez-Chillón",
""
]
] | Slow-roll inflation is analyzed in the context of modified gravity within the Palatini formalism. As shown in the literature, inflation in this framework requires the presence of non-traceless matter, otherwise it does not occur just as a consequence of the non-linear gravitational terms of the action. Nevertheless, by including a single scalar field that plays the role of the inflaton, slow-roll inflation can be performed in these theories, where the equations lead to an effective potential that modifies the dynamics. We obtain the general slow-roll parameters and analyze a simple model to illustrate the differences introduced by the gravitational terms under the Palatini approach, and the modifications on the spectral index and the tensor to scalar ratio predicted by the model. |
gr-qc/0409017 | Bahram Mashhoon | C. Chicone and B. Mashhoon | Ultrarelativistic Motion: Inertial and Tidal Effects in Fermi
Coordinates | 13 pages, 3 figures, slightly expanded version accepted for
publication in Class. Quantum Grav | Class.Quant.Grav. 22 (2005) 195-206 | 10.1088/0264-9381/22/1/013 | null | gr-qc astro-ph | null | Fermi coordinates are the natural generalization of inertial Cartesian
coordinates to accelerated systems and gravitational fields. We study the
motion of ultrarelativistic particles and light rays in Fermi coordinates and
investigate inertial and tidal effects beyond the critical speed c/sqrt(2). In
particular, we discuss the black-hole tidal acceleration mechanism for
ultrarelativistic particles in connection with a possible origin for
high-energy cosmic rays.
| [
{
"created": "Sat, 4 Sep 2004 02:22:13 GMT",
"version": "v1"
},
{
"created": "Fri, 12 Nov 2004 19:43:16 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Chicone",
"C.",
""
],
[
"Mashhoon",
"B.",
""
]
] | Fermi coordinates are the natural generalization of inertial Cartesian coordinates to accelerated systems and gravitational fields. We study the motion of ultrarelativistic particles and light rays in Fermi coordinates and investigate inertial and tidal effects beyond the critical speed c/sqrt(2). In particular, we discuss the black-hole tidal acceleration mechanism for ultrarelativistic particles in connection with a possible origin for high-energy cosmic rays. |
2006.12266 | Ranjan Sharma | S. Thirukkanesh, Ranjan Sharma and Sunil D. Maharaj | Anisotropic generalization of Vaidya-Tikekar superdense star | null | Eur. Phys. J. Plus (2019) 134:378 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study superdense relativistic stars with anisotropic matter distributions
with spheroidal spatial hypersurfaces. We propose a methodology to make an
anisotropic generalization of the Vaidya-Tikekar superdense star model. The
anisotropic Einstein field equations can be solved in terms of hypergeometric
functions for our choice of gravitational potential and anisotropy. Particular
parameter choices allow us to generate models of anisotropic stars in terms of
elementary functions. Also, isotropic stars can be generated in the limit of
vanishing anisotropy. In particular, we obtain the well known superdense models
of Tikekar which are isotropic and have specific spheroidal geometries. The
impact of anisotropy on the gross physical behaviour of a compact star is
studied.
| [
{
"created": "Fri, 19 Jun 2020 05:53:44 GMT",
"version": "v1"
}
] | 2020-06-23 | [
[
"Thirukkanesh",
"S.",
""
],
[
"Sharma",
"Ranjan",
""
],
[
"Maharaj",
"Sunil D.",
""
]
] | We study superdense relativistic stars with anisotropic matter distributions with spheroidal spatial hypersurfaces. We propose a methodology to make an anisotropic generalization of the Vaidya-Tikekar superdense star model. The anisotropic Einstein field equations can be solved in terms of hypergeometric functions for our choice of gravitational potential and anisotropy. Particular parameter choices allow us to generate models of anisotropic stars in terms of elementary functions. Also, isotropic stars can be generated in the limit of vanishing anisotropy. In particular, we obtain the well known superdense models of Tikekar which are isotropic and have specific spheroidal geometries. The impact of anisotropy on the gross physical behaviour of a compact star is studied. |
1401.6940 | Giampiero Esposito Dr. | Enrico Calloni, Martina De Laurentis, Rosario De Rosa, Luciano Di
Fiore, Giampiero Esposito, Fabio Garufi, Luigi Rosa, Carlo Rovelli, Paolo
Ruggi, Francesco Tafuri | Towards weighing the condensation energy to ascertain the Archimedes
force of vacuum | Revtex, 33 pages, 8 figures. In the final version, the title has been
changed, and all sections have been improved, while 2 appendices have been
added | null | 10.1103/PhysRevD.90.022002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The force exerted by the gravitational field on a Casimir cavity in terms of
Archimedes force of vacuum is discussed, the force that can be tested against
observation is identified, and it is shown that the present technology makes it
possible to perform the first experimental tests. The use of suitable high-Tc
superconductors as modulators of Archimedes force is motivated. The possibility
is analyzed of using gravitational wave interferometers as detectors of the
force, transported through an optical spring from the Archimedes vacuum force
apparatus to the gravitational interferometer test masses to maintain the two
systems well separated. The use of balances to actuate and detect the force is
also analyzed, the different solutions are compared, and the most important
experimental issues are discussed.
| [
{
"created": "Mon, 27 Jan 2014 17:30:03 GMT",
"version": "v1"
},
{
"created": "Sun, 22 Jun 2014 20:47:15 GMT",
"version": "v2"
}
] | 2015-06-18 | [
[
"Calloni",
"Enrico",
""
],
[
"De Laurentis",
"Martina",
""
],
[
"De Rosa",
"Rosario",
""
],
[
"Di Fiore",
"Luciano",
""
],
[
"Esposito",
"Giampiero",
""
],
[
"Garufi",
"Fabio",
""
],
[
"Rosa",
"Luigi",
""
],
[
"Rovelli",
"Carlo",
""
],
[
"Ruggi",
"Paolo",
""
],
[
"Tafuri",
"Francesco",
""
]
] | The force exerted by the gravitational field on a Casimir cavity in terms of Archimedes force of vacuum is discussed, the force that can be tested against observation is identified, and it is shown that the present technology makes it possible to perform the first experimental tests. The use of suitable high-Tc superconductors as modulators of Archimedes force is motivated. The possibility is analyzed of using gravitational wave interferometers as detectors of the force, transported through an optical spring from the Archimedes vacuum force apparatus to the gravitational interferometer test masses to maintain the two systems well separated. The use of balances to actuate and detect the force is also analyzed, the different solutions are compared, and the most important experimental issues are discussed. |
1709.09514 | Bertrand Berche | Frankbelson dos S. Azevedo, Fernando Moraes, Francisco Mireles,
Bertrand Berche, S\'ebastien Fumeron | The wiggly cosmic string as a waveguide for massless and massive fields | null | null | 10.1103/PhysRevD.96.084047 | null | gr-qc cond-mat.mes-hall | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine the effect of a wiggly cosmic string for both massless and massive
particle propagation along the string axis. We show that the wave equation that
governs the propagation of a scalar field in the neighborhood of a wiggly
string is formally equivalent to the quantum wave equation describing the
hydrogen atom in two dimensions. We further show that the wiggly string
spacetime behaves as a gravitational waveguide in which the quantized wave
modes propagate with frequencies that depend on the mass, string energy
density, and string tension. We propose an analogy with an optical fiber,
defining an effective refractive index likely to mimic the cosmic string effect
in the laboratory.
| [
{
"created": "Wed, 27 Sep 2017 13:46:30 GMT",
"version": "v1"
}
] | 2017-11-22 | [
[
"Azevedo",
"Frankbelson dos S.",
""
],
[
"Moraes",
"Fernando",
""
],
[
"Mireles",
"Francisco",
""
],
[
"Berche",
"Bertrand",
""
],
[
"Fumeron",
"Sébastien",
""
]
] | We examine the effect of a wiggly cosmic string for both massless and massive particle propagation along the string axis. We show that the wave equation that governs the propagation of a scalar field in the neighborhood of a wiggly string is formally equivalent to the quantum wave equation describing the hydrogen atom in two dimensions. We further show that the wiggly string spacetime behaves as a gravitational waveguide in which the quantized wave modes propagate with frequencies that depend on the mass, string energy density, and string tension. We propose an analogy with an optical fiber, defining an effective refractive index likely to mimic the cosmic string effect in the laboratory. |
1012.0077 | Fethi M. Ramazanoglu | Abhay Ashtekar, Frans Pretorius, Fethi M. Ramazano\u{g}lu | Evaporation of 2-Dimensional Black Holes | Two citations added | Phys.Rev.D83:044040,2011 | 10.1103/PhysRevD.83.044040 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a detailed analysis of results from a new study of the quantum
evaporation of Callan-Giddings-Harvey-Strominger (CGHS) black holes within the
mean-field approximation. This semi-classical theory incorporates back
reaction. Our analytical and numerical calculations show that, while some of
the assumptions underlying the standard evaporation paradigm are borne out,
several are not. One of the anticipated properties we confirm is that the
semi-classical space-time is asymptotically flat at right future null infinity,
$\spr$, yet incomplete in the sense that null observers reach a future Cauchy
horizon in finite affine time. Unexpected behavior includes that the Bondi mass
traditionally used in the literature can become negative even when the area of
the horizon is macroscopic; an improved Bondi mass remains positive until the
end of semi-classical evaporation, yet the final value can be arbitrarily large
relative to the Planck mass; and the flux of the quantum radiation at $\spr$ is
non-thermal even when the horizon area is large compared to the Planck scale.
Furthermore, if the black hole is initially macroscopic, the evaporation
process exhibits remarkable universal properties. Although the literature on
CGHS black holes is quite rich, these features had escaped previous analyses,
in part because of lack of required numerical precision, and in part due to
misinterpretation of certain properties and symmetries of the model. Finally,
our results provide support for the full quantum scenario recently developed by
Ashtekar, Taveras and Varadarajan, and also offer a number of interesting
problems to the mathematical relativity and geometric analysis communities.
| [
{
"created": "Wed, 1 Dec 2010 01:24:26 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Mar 2011 00:08:09 GMT",
"version": "v2"
}
] | 2011-03-23 | [
[
"Ashtekar",
"Abhay",
""
],
[
"Pretorius",
"Frans",
""
],
[
"Ramazanoğlu",
"Fethi M.",
""
]
] | We present a detailed analysis of results from a new study of the quantum evaporation of Callan-Giddings-Harvey-Strominger (CGHS) black holes within the mean-field approximation. This semi-classical theory incorporates back reaction. Our analytical and numerical calculations show that, while some of the assumptions underlying the standard evaporation paradigm are borne out, several are not. One of the anticipated properties we confirm is that the semi-classical space-time is asymptotically flat at right future null infinity, $\spr$, yet incomplete in the sense that null observers reach a future Cauchy horizon in finite affine time. Unexpected behavior includes that the Bondi mass traditionally used in the literature can become negative even when the area of the horizon is macroscopic; an improved Bondi mass remains positive until the end of semi-classical evaporation, yet the final value can be arbitrarily large relative to the Planck mass; and the flux of the quantum radiation at $\spr$ is non-thermal even when the horizon area is large compared to the Planck scale. Furthermore, if the black hole is initially macroscopic, the evaporation process exhibits remarkable universal properties. Although the literature on CGHS black holes is quite rich, these features had escaped previous analyses, in part because of lack of required numerical precision, and in part due to misinterpretation of certain properties and symmetries of the model. Finally, our results provide support for the full quantum scenario recently developed by Ashtekar, Taveras and Varadarajan, and also offer a number of interesting problems to the mathematical relativity and geometric analysis communities. |
1201.1069 | Vladimir Dzhunushaliev | Vladimir Dzhunushaliev | Dynamical $F(R)$ gravities | discussion on quantum corrections is added | null | 10.1142/S0218271812500423 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is offered that $F(R)-$modified gravities can be considered as
nonperturbative quantum effects arising from Einstein gravity. It is assumed
that nonperturbative quantum effects gives rise to the fact that the connection
becomes incompatible with the metric, the metric factors and the square of the
connection in Einstein - Hilbert Lagrangian have nonperturbative additions. In
the simplest approximation both additions can be considered as functions of one
scalar field. The scalar field can be excluded from the Lagrangian obtaining
$F(R)-$gravity. The essence of quantum correction to the affine connection as a
torsion is discussed.
| [
{
"created": "Thu, 5 Jan 2012 06:45:05 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Mar 2012 07:48:17 GMT",
"version": "v2"
}
] | 2015-06-03 | [
[
"Dzhunushaliev",
"Vladimir",
""
]
] | It is offered that $F(R)-$modified gravities can be considered as nonperturbative quantum effects arising from Einstein gravity. It is assumed that nonperturbative quantum effects gives rise to the fact that the connection becomes incompatible with the metric, the metric factors and the square of the connection in Einstein - Hilbert Lagrangian have nonperturbative additions. In the simplest approximation both additions can be considered as functions of one scalar field. The scalar field can be excluded from the Lagrangian obtaining $F(R)-$gravity. The essence of quantum correction to the affine connection as a torsion is discussed. |
2103.13714 | Hiroki Asami | Hiroki Asami and Chul-Moon Yoo | Thermal equilibrium states and instability of self-gravitating particles
in an asymptotically AdS spacetime | 12 pages | null | 10.1088/1361-6382/ac129e | null | gr-qc hep-th | http://creativecommons.org/publicdomain/zero/1.0/ | We investigate the existence and the stability of spherically symmetric
thermal equilibrium states of the self-gravitating many-particle system which
satisfies the Einstein-Vlasov equations with a negative cosmological constant.
While a thermal equilibrium state of the self-gravitating particle system
cannot have a finite mass without an artificial wall in the asymptotically flat
case, in the asymptotically AdS case, the total mass can be finite without any
artificial wall due to the AdS potential barrier. In this case, the typical
size of the system is characterized by the AdS radius. The equilibrium states
can be parametrized by two independent parameters. Taking the total rest mass
as the unit and fixing the AdS radius, we obtain the one-parameter family of
equilibria which describes a curve in the parameter space spanned by the
gravothermal energy and the temperature. Then we investigate the instability of
the system based on the turning point method for each value of the AdS radius.
We find that the curve typically has a double spiral structure as in the
asymptotically flat case with an artificial wall. The possible value of the
gravothermal energy is restricted to the finite region between the first
turning points on the two respective spirals.
| [
{
"created": "Thu, 25 Mar 2021 09:42:46 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Apr 2021 07:36:49 GMT",
"version": "v2"
},
{
"created": "Thu, 10 Jun 2021 05:10:41 GMT",
"version": "v3"
},
{
"created": "Tue, 29 Jun 2021 12:19:01 GMT",
"version": "v4"
}
] | 2021-08-17 | [
[
"Asami",
"Hiroki",
""
],
[
"Yoo",
"Chul-Moon",
""
]
] | We investigate the existence and the stability of spherically symmetric thermal equilibrium states of the self-gravitating many-particle system which satisfies the Einstein-Vlasov equations with a negative cosmological constant. While a thermal equilibrium state of the self-gravitating particle system cannot have a finite mass without an artificial wall in the asymptotically flat case, in the asymptotically AdS case, the total mass can be finite without any artificial wall due to the AdS potential barrier. In this case, the typical size of the system is characterized by the AdS radius. The equilibrium states can be parametrized by two independent parameters. Taking the total rest mass as the unit and fixing the AdS radius, we obtain the one-parameter family of equilibria which describes a curve in the parameter space spanned by the gravothermal energy and the temperature. Then we investigate the instability of the system based on the turning point method for each value of the AdS radius. We find that the curve typically has a double spiral structure as in the asymptotically flat case with an artificial wall. The possible value of the gravothermal energy is restricted to the finite region between the first turning points on the two respective spirals. |
gr-qc/0009018 | Luca Bombelli | Brett Bolen, Luca Bombelli, and Raymond Puzio | Expansion-induced contribution to the precession of binary orbits | revtex, 7 pages, no figures; revised for publication in Classical and
Quantum Gravity, with minor changes in response to referees' comments | Class.Quant.Grav.18:1173-1178,2001 | 10.1088/0264-9381/18/7/302 | null | gr-qc astro-ph | null | We point out the existence of new effects of global spacetime expansion on
local binary systems. In addition to a possible change of orbital size, there
is a contribution to the precession of elliptic orbits, to be added to the
well-known general relativistic effect in static spacetimes, and the
eccentricity can change. Our model calculations are done using geodesics in a
McVittie metric, representing a localized system in an asymptotically
Robertson-Walker spacetime; we give a few numerical estimates for that case,
and indicate ways in which the model should be improved.
| [
{
"created": "Thu, 7 Sep 2000 01:57:56 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Mar 2001 21:27:37 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Bolen",
"Brett",
""
],
[
"Bombelli",
"Luca",
""
],
[
"Puzio",
"Raymond",
""
]
] | We point out the existence of new effects of global spacetime expansion on local binary systems. In addition to a possible change of orbital size, there is a contribution to the precession of elliptic orbits, to be added to the well-known general relativistic effect in static spacetimes, and the eccentricity can change. Our model calculations are done using geodesics in a McVittie metric, representing a localized system in an asymptotically Robertson-Walker spacetime; we give a few numerical estimates for that case, and indicate ways in which the model should be improved. |
gr-qc/0404003 | Hernando Quevedo | Octavio Obregon, Hernando Quevedo and Michael P. Ryan | Time and "angular" dependent backgrounds from stationary axisymmetric
solutions | 24 pages, 5 figures, corrected typos, references added | Phys.Rev. D70 (2004) 064035 | 10.1103/PhysRevD.70.064035 | null | gr-qc hep-th | null | Backgrounds depending on time and on "angular" variable, namely polarized and
unpolarized $S^1 \times S^2$ Gowdy models, are generated as the sector inside
the horizons of the manifold corresponding to axisymmetric solutions. As is
known, an analytical continuation of ordinary $D$-branes, $iD$-branes allows
one to find $S$-brane solutions. Simple models have been constructed by means
of analytic continuation of the Schwarzchild and the Kerr metrics. The
possibility of studying the $i$-Gowdy models obtained here is outlined with an
eye toward seeing if they could represent some kind of generalized $S$-branes
depending not only on time but also on an ``angular'' variable.
| [
{
"created": "Thu, 1 Apr 2004 07:14:36 GMT",
"version": "v1"
},
{
"created": "Thu, 20 May 2004 02:31:59 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Obregon",
"Octavio",
""
],
[
"Quevedo",
"Hernando",
""
],
[
"Ryan",
"Michael P.",
""
]
] | Backgrounds depending on time and on "angular" variable, namely polarized and unpolarized $S^1 \times S^2$ Gowdy models, are generated as the sector inside the horizons of the manifold corresponding to axisymmetric solutions. As is known, an analytical continuation of ordinary $D$-branes, $iD$-branes allows one to find $S$-brane solutions. Simple models have been constructed by means of analytic continuation of the Schwarzchild and the Kerr metrics. The possibility of studying the $i$-Gowdy models obtained here is outlined with an eye toward seeing if they could represent some kind of generalized $S$-branes depending not only on time but also on an ``angular'' variable. |
1403.4549 | Michael Holst | Michael Holst and Caleb Meier | Non-CMC Solutions to the Einstein Constraint Equations on Asymptotically
Euclidean Manifolds with Apparent Horizon Boundaries | 25 pages, no figures | null | 10.1088/0264-9381/32/2/025006 | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article we further develop the solution theory for the Einstein
constraint equations on an n-dimensional, asymptotically Euclidean manifold M
with interior boundary S. Building on recent results for both the
asymptotically Euclidean and compact with boundary settings, we show existence
of far-from-CMC and near-CMC solutions to the conformal formulation of the
Einstein constraints when nonlinear Robin boundary conditions are imposed on S,
similar to those analyzed previously by Dain (2004), by Maxwell (2004, 2005),
and by Holst and Tsogtgerel (2013) as a model of black holes in various CMC
settings, and by Holst, Meier, and Tsogtgerel (2013) in the setting of
far-from-CMC solutions on compact manifolds with boundary. These "marginally
trapped surface" Robin conditions ensure that the expansion scalars along null
geodesics perpendicular to the boundary region S are non-positive, which is
considered the correct mathematical model for black holes in the context of the
Einstein constraint equations. Assuming a suitable form of weak cosmic
censorship, the results presented in this article guarantee the existence of
initial data that will evolve into a space-time containing an arbitrary number
of black holes. A particularly important feature of our results are the minimal
restrictions we place on the mean curvature, giving both near- and far-from-CMC
results that are new.
| [
{
"created": "Tue, 18 Mar 2014 17:42:43 GMT",
"version": "v1"
}
] | 2015-06-19 | [
[
"Holst",
"Michael",
""
],
[
"Meier",
"Caleb",
""
]
] | In this article we further develop the solution theory for the Einstein constraint equations on an n-dimensional, asymptotically Euclidean manifold M with interior boundary S. Building on recent results for both the asymptotically Euclidean and compact with boundary settings, we show existence of far-from-CMC and near-CMC solutions to the conformal formulation of the Einstein constraints when nonlinear Robin boundary conditions are imposed on S, similar to those analyzed previously by Dain (2004), by Maxwell (2004, 2005), and by Holst and Tsogtgerel (2013) as a model of black holes in various CMC settings, and by Holst, Meier, and Tsogtgerel (2013) in the setting of far-from-CMC solutions on compact manifolds with boundary. These "marginally trapped surface" Robin conditions ensure that the expansion scalars along null geodesics perpendicular to the boundary region S are non-positive, which is considered the correct mathematical model for black holes in the context of the Einstein constraint equations. Assuming a suitable form of weak cosmic censorship, the results presented in this article guarantee the existence of initial data that will evolve into a space-time containing an arbitrary number of black holes. A particularly important feature of our results are the minimal restrictions we place on the mean curvature, giving both near- and far-from-CMC results that are new. |
2111.07873 | Maciej Kolanowski | Abhay Ashtekar, Neev Khera, Maciej Kolanowski and Jerzy Lewandowski | Non-Expanding horizons: Multipoles and the Symmetry Group | 31 pages, 2 figures. Some clarifications and references added.
Published in JHEP. Typos corrected in Section 2.2 and 2.3.1 | JHEP 01 028 (2022) | 10.1007/JHEP01(2022)028 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is well-known that blackhole and cosmological horizons in equilibrium
situations are well-modeled by non-expanding horizons (NEHs). In the first part
of the paper we introduce multipole moments to characterize their geometry,
removing the restriction to axisymmetric situations made in the existing
literature. We then show that the symmetry group $\mathfrak{G}$ of NEHs is a
1-dimensional extension of the BMS group $\mathfrak{B}$. These symmetries are
used in a companion paper to define charges and fluxes on NHEs, as well as
perturbed NEHs. They have physically attractive properties. Finally, it is
generally not appreciated that $\mathcal{I}^\pm$ of asymptotically flat
space-times are NEHs in the conformally completed space-time. Forthcoming
papers will (i) show that $\mathcal{I}^\pm$ have a small additional structure
that reduces $\mathfrak{G}$ to the BMS group $\mathfrak{B}$, and the BMS
charges and fluxes can be recovered from the NEH framework; and, (ii) develop
gravitational wave tomography for the late stage of compact binary
coalescences: reading-off the dynamics of perturbed NEHs in the strong field
regime (via evolution of their multipoles), from the waveform at
$\mathcal{I}^+$.
| [
{
"created": "Mon, 15 Nov 2021 16:23:32 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Dec 2021 20:06:04 GMT",
"version": "v2"
},
{
"created": "Mon, 4 Jul 2022 17:45:32 GMT",
"version": "v3"
}
] | 2022-07-05 | [
[
"Ashtekar",
"Abhay",
""
],
[
"Khera",
"Neev",
""
],
[
"Kolanowski",
"Maciej",
""
],
[
"Lewandowski",
"Jerzy",
""
]
] | It is well-known that blackhole and cosmological horizons in equilibrium situations are well-modeled by non-expanding horizons (NEHs). In the first part of the paper we introduce multipole moments to characterize their geometry, removing the restriction to axisymmetric situations made in the existing literature. We then show that the symmetry group $\mathfrak{G}$ of NEHs is a 1-dimensional extension of the BMS group $\mathfrak{B}$. These symmetries are used in a companion paper to define charges and fluxes on NHEs, as well as perturbed NEHs. They have physically attractive properties. Finally, it is generally not appreciated that $\mathcal{I}^\pm$ of asymptotically flat space-times are NEHs in the conformally completed space-time. Forthcoming papers will (i) show that $\mathcal{I}^\pm$ have a small additional structure that reduces $\mathfrak{G}$ to the BMS group $\mathfrak{B}$, and the BMS charges and fluxes can be recovered from the NEH framework; and, (ii) develop gravitational wave tomography for the late stage of compact binary coalescences: reading-off the dynamics of perturbed NEHs in the strong field regime (via evolution of their multipoles), from the waveform at $\mathcal{I}^+$. |
2007.05182 | B. S. Ratanpal | B. S. Ratanpal, V. O Thomas and Rinkal Patel | Compact Relativistic Stars under Karmarkar Condition | 9 Figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A class of new solutions for Einstein's field equations, by choosing the
ansatz $e^{\lambda(r)}=\frac{1+ar^{2}}{1+br^{2}}$ for metric potential, are
obtained under Karmarkar condition. It is found that a number of pulsars like
4U 1820-30, PSR J1903+327, 4U 1608-52, Vela X-1, PSR J1614-2230, Cen X-3 can be
accomodated in this model. We have displayed the nature of physical parameters
and energy conditions throughout the distribution using numerical and graphical
methods for a particular pulsar 4U 1820-30 and found that the solution
satisfies all physical requirements.
| [
{
"created": "Fri, 10 Jul 2020 06:02:19 GMT",
"version": "v1"
}
] | 2020-07-13 | [
[
"Ratanpal",
"B. S.",
""
],
[
"Thomas",
"V. O",
""
],
[
"Patel",
"Rinkal",
""
]
] | A class of new solutions for Einstein's field equations, by choosing the ansatz $e^{\lambda(r)}=\frac{1+ar^{2}}{1+br^{2}}$ for metric potential, are obtained under Karmarkar condition. It is found that a number of pulsars like 4U 1820-30, PSR J1903+327, 4U 1608-52, Vela X-1, PSR J1614-2230, Cen X-3 can be accomodated in this model. We have displayed the nature of physical parameters and energy conditions throughout the distribution using numerical and graphical methods for a particular pulsar 4U 1820-30 and found that the solution satisfies all physical requirements. |
1812.03000 | Jorge Ovalle | J Ovalle | Decoupling gravitational sources in general relativity: the extended
case | 7 pages | Phys.Lett. B788 (2019) 213-218 | 10.1016/j.physletb.2018.11.029 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show how to decoupling two spherically symmetric and static gravitational
sources through the most general possible extension of the so-called Minimal
Geometric Deformation-decoupling. As a test, we decouple the Einstein-Maxwell
system and reproduce the Reissner-Nordstrom black hole solution. We show the
potential of this method to study i) the consequences of modified gravity on
general relativity, ii) to investigate the conjectured dark matter, and iii) to
study hairy black holes.
| [
{
"created": "Fri, 7 Dec 2018 12:25:51 GMT",
"version": "v1"
}
] | 2018-12-10 | [
[
"Ovalle",
"J",
""
]
] | We show how to decoupling two spherically symmetric and static gravitational sources through the most general possible extension of the so-called Minimal Geometric Deformation-decoupling. As a test, we decouple the Einstein-Maxwell system and reproduce the Reissner-Nordstrom black hole solution. We show the potential of this method to study i) the consequences of modified gravity on general relativity, ii) to investigate the conjectured dark matter, and iii) to study hairy black holes. |
gr-qc/9801014 | B. S. Sathyaprakash | T. Damour(Institut des Hautes Etudes Scientifiques), B.R. Iyer (Raman
Research Institute) and B.S. Sathyaprakash (Cardiff University of Wales) | Modelling Gravitational Waves from Inspiralling Compact Binaries | Needs sprocl.sty which is bundled together with the tex file. To
appear in the proceedings "Second Edoardo Amaldi Conference on Gravitational
Waves", CERN, 1 - 4 July 1997 | null | null | null | gr-qc | null | Gravitational waves from inspiralling compact binaries can be reliably
extracted from a noisy detector output only if the template used in the
detection is a faithful representation of the true signal. In this article we
suggest a new approach to constructing faithful signal models.
| [
{
"created": "Wed, 7 Jan 1998 17:08:51 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Damour",
"T.",
"",
"Institut des Hautes Etudes Scientifiques"
],
[
"Iyer",
"B. R.",
"",
"Raman\n Research Institute"
],
[
"Sathyaprakash",
"B. S.",
"",
"Cardiff University of Wales"
]
] | Gravitational waves from inspiralling compact binaries can be reliably extracted from a noisy detector output only if the template used in the detection is a faithful representation of the true signal. In this article we suggest a new approach to constructing faithful signal models. |
1308.0010 | Robert Schneider | Stefan Hofmann, Florian Niedermann, Robert Schneider | Interpretation of the Weyl tensor | 12 pages, 2 figures; v2: matches version published in Physical Review
D | Phys. Rev. D 88, 064047 (2013) | 10.1103/PhysRevD.88.064047 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | According to folklore in general relativity, the Weyl tensor can be
decomposed into parts corresponding to Newton-like, incoming and outgoing
wavelike field components. It is shown here that this one-to-one correspondence
does not hold for space-time geometries with cylindrical isometries. This is
done by investigating some well-known exact solutions of Einstein's field
equations with whole-cylindrical symmetry, for which the physical
interpretation is very clear, but for which the standard Weyl interpretation
would give contradictory results. For planar or spherical geometries, however,
the standard interpretation works for both, static and dynamical space-times.
It is argued that one reason for the failure in the cylindrical case is that
for waves spreading in two spatial dimensions there is no local criterion to
distinguish incoming and outgoing waves already at the linear level. It turns
out that Thorne's local energy notion, subject to certain qualifications,
provides an efficient diagnostic tool to extract the proper physical
interpretation of the space-time geometry in the case of cylindrical
configurations.
| [
{
"created": "Wed, 31 Jul 2013 20:00:01 GMT",
"version": "v1"
},
{
"created": "Thu, 24 Oct 2013 12:25:49 GMT",
"version": "v2"
}
] | 2013-10-25 | [
[
"Hofmann",
"Stefan",
""
],
[
"Niedermann",
"Florian",
""
],
[
"Schneider",
"Robert",
""
]
] | According to folklore in general relativity, the Weyl tensor can be decomposed into parts corresponding to Newton-like, incoming and outgoing wavelike field components. It is shown here that this one-to-one correspondence does not hold for space-time geometries with cylindrical isometries. This is done by investigating some well-known exact solutions of Einstein's field equations with whole-cylindrical symmetry, for which the physical interpretation is very clear, but for which the standard Weyl interpretation would give contradictory results. For planar or spherical geometries, however, the standard interpretation works for both, static and dynamical space-times. It is argued that one reason for the failure in the cylindrical case is that for waves spreading in two spatial dimensions there is no local criterion to distinguish incoming and outgoing waves already at the linear level. It turns out that Thorne's local energy notion, subject to certain qualifications, provides an efficient diagnostic tool to extract the proper physical interpretation of the space-time geometry in the case of cylindrical configurations. |
1311.0537 | Oleg Zaslavskii | O. B. Zaslavskii | High-energy collisions inside black holes and their counterpart in flat
space-time | 15 pages, 2 figures. Presentation improved. To appear in IJMP D | Int. Journal of Mod. Physics D 23 (2014) 1450045 | 10.1142/S021827181450045X | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Two particles can collide inside a nonextremal black hole in such a way that
the energy E_{c.m.} in their centre of mass frame becomes as large as one
likes. We show that this effect can be understood with the help of a simple
analogy with particle collisions in flat space-time. As the two-dimensional
part of near-horizon geometry inside a black hole is described by the flat
Milne metric, the results have a general character. Full classification of
scenarios with unbound E_{c.m.} is suggested. Some scenarios of this kind
require proximity of collision to the bifurcation point, but for some other
ones this is not necessary.
| [
{
"created": "Sun, 3 Nov 2013 22:19:23 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Mar 2014 11:59:23 GMT",
"version": "v2"
}
] | 2014-04-01 | [
[
"Zaslavskii",
"O. B.",
""
]
] | Two particles can collide inside a nonextremal black hole in such a way that the energy E_{c.m.} in their centre of mass frame becomes as large as one likes. We show that this effect can be understood with the help of a simple analogy with particle collisions in flat space-time. As the two-dimensional part of near-horizon geometry inside a black hole is described by the flat Milne metric, the results have a general character. Full classification of scenarios with unbound E_{c.m.} is suggested. Some scenarios of this kind require proximity of collision to the bifurcation point, but for some other ones this is not necessary. |
1411.2317 | Miguel Angel Garcia Aspeitia | Aldrin Cervantes and Miguel A. Garc\'ia-Aspeitia | Numerical Prediction of cusps or kinks in the Nambu-Goto dynamics | 17 pages, 4 figures. Accepted for Publication in Mod. Phys. Lett. A | null | 10.1142/S0217732315502107 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is known that Nambu-Goto extended objects present some pathological
structures, such as cusps and kinks, during their evolution. In this paper, we
propose a model through the generalized Raychaudhuri equation [Rh] for
membranes to determine if there are cusps and kinks in the world-sheet. We
extend the generalized Rh equation for membranes to allow the study of the
effect of higher order curvature terms in the action on the issue of cusps and
kinks, using it as a tool for determining when a Nambu-Goto string generates
cusps or kinks in its evolution. Furthermore, we present three examples where
we test graphically this approach.
| [
{
"created": "Mon, 10 Nov 2014 03:54:04 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Sep 2015 13:45:38 GMT",
"version": "v2"
}
] | 2015-12-16 | [
[
"Cervantes",
"Aldrin",
""
],
[
"García-Aspeitia",
"Miguel A.",
""
]
] | It is known that Nambu-Goto extended objects present some pathological structures, such as cusps and kinks, during their evolution. In this paper, we propose a model through the generalized Raychaudhuri equation [Rh] for membranes to determine if there are cusps and kinks in the world-sheet. We extend the generalized Rh equation for membranes to allow the study of the effect of higher order curvature terms in the action on the issue of cusps and kinks, using it as a tool for determining when a Nambu-Goto string generates cusps or kinks in its evolution. Furthermore, we present three examples where we test graphically this approach. |
0707.3969 | Nelson Christensen | Christian R\"over, Alexander Stroeer, Ed Bloomer, Nelson Christensen,
James Clark, Martin Hendry, Chris Messenger, Renate Meyer, Matt Pitkin,
Jennifer Toher, Richard Umst\"atter, Alberto Vecchio, John Veitch, Graham
Woan | Inference on inspiral signals using LISA MLDC data | Accepted for publication in Classical and Quantum Gravity, GWDAW-11
special issue | Class.Quant.Grav.24:S521-S528,2007 | 10.1088/0264-9381/24/19/S15 | null | gr-qc | null | In this paper we describe a Bayesian inference framework for analysis of data
obtained by LISA. We set up a model for binary inspiral signals as defined for
the Mock LISA Data Challenge 1.2 (MLDC), and implemented a Markov chain Monte
Carlo (MCMC) algorithm to facilitate exploration and integration of the
posterior distribution over the 9-dimensional parameter space. Here we present
intermediate results showing how, using this method, information about the 9
parameters can be extracted from the data.
| [
{
"created": "Thu, 26 Jul 2007 17:30:21 GMT",
"version": "v1"
},
{
"created": "Sun, 5 Aug 2007 14:17:08 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Röver",
"Christian",
""
],
[
"Stroeer",
"Alexander",
""
],
[
"Bloomer",
"Ed",
""
],
[
"Christensen",
"Nelson",
""
],
[
"Clark",
"James",
""
],
[
"Hendry",
"Martin",
""
],
[
"Messenger",
"Chris",
""
],
[
"Meyer",
"Renate",
""
],
[
"Pitkin",
"Matt",
""
],
[
"Toher",
"Jennifer",
""
],
[
"Umstätter",
"Richard",
""
],
[
"Vecchio",
"Alberto",
""
],
[
"Veitch",
"John",
""
],
[
"Woan",
"Graham",
""
]
] | In this paper we describe a Bayesian inference framework for analysis of data obtained by LISA. We set up a model for binary inspiral signals as defined for the Mock LISA Data Challenge 1.2 (MLDC), and implemented a Markov chain Monte Carlo (MCMC) algorithm to facilitate exploration and integration of the posterior distribution over the 9-dimensional parameter space. Here we present intermediate results showing how, using this method, information about the 9 parameters can be extracted from the data. |
2105.10696 | Abhik Kumar Sanyal Dr. | A. Banerjee, Abhik Kumar Sanyal and S. Chakraborty | Bianchi II, VIII, and IX viscous fluid cosmology | 7 pages, 0 figures | Astrophysics and Space Science 166: 259-268, 1990 | 10.1007/BF01094897 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study the exact solutions for a viscous fluid distribution
in Bianchi II, VIII, and IX models. The metric is simplified by assuming a
relationship between the coefficients and the metric tensor. Solutions are
obtained in two special cases: in one, an additional assumption is made where
the matter density and the expansion scalar have a definite relation and in the
other a barotropic equation of state between the matter density and the
thermodynamic pressure is assumed. While the Bianchi II solutions are already
found in the literature the other two classes of solutions are apparently new.
| [
{
"created": "Sat, 22 May 2021 11:31:23 GMT",
"version": "v1"
}
] | 2021-05-25 | [
[
"Banerjee",
"A.",
""
],
[
"Sanyal",
"Abhik Kumar",
""
],
[
"Chakraborty",
"S.",
""
]
] | In this paper we study the exact solutions for a viscous fluid distribution in Bianchi II, VIII, and IX models. The metric is simplified by assuming a relationship between the coefficients and the metric tensor. Solutions are obtained in two special cases: in one, an additional assumption is made where the matter density and the expansion scalar have a definite relation and in the other a barotropic equation of state between the matter density and the thermodynamic pressure is assumed. While the Bianchi II solutions are already found in the literature the other two classes of solutions are apparently new. |
2402.05316 | Macarena Lagos | Macarena Lagos, Leah Jenks, Maximiliano Isi, Kenta Hotokezaka, Brian
D. Metzger, Eric Burns, Will M. Farr, Scott Perkins, Kaze W. K. Wong, Nicolas
Yunes | Birefringence tests of gravity with multi-messenger binaries | null | null | null | null | gr-qc astro-ph.CO hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Extensions to General Relativity (GR) allow the polarization of gravitational
waves (GW) from astrophysical sources to suffer from amplitude and velocity
birefringence, which respectively induce changes in the ellipticity and
orientation of the polarization tensor. We introduce a multi-messenger approach
to test this polarization behavior of GWs during their cosmological propagation
using binary sources, for which the initial polarization is determined by the
inclination and orientation angles of the orbital angular momentum vector with
respect to the line of sight. In particular, we use spatially-resolved radio
imaging of the jet from a binary neutron star (BNS) merger to constrain the
orientation angle and hence the emitted polarization orientation of the GW
signal at the site of the merger, and compare to that observed on Earth by GW
detectors. For GW170817 we constrain the deviation from GR due to amplitude
birefringence to $\kappa_A = -0.12^{+0.60}_{-0.61}$, while the velocity
birefringence parameter $\kappa_V$ remains unconstrained. The inability to
constrain $\kappa_V$ is due to the fact that Virgo did not detect GW170817, and
measurements of the polarization orientation require information from a
combination of multiple detectors with different alignments. For this reason,
we also mock future BNS mergers with resolved afterglow proper motion and
project that $\kappa_V$ could be constrained to a precision of $5\,$rad
(corresponding to an angular shift of the GW polarization of
$\delta\phi_V\approx 0.2\,$rad for a BNS at $100\,$Mpc) by a future network of
third-generation ground-based GW detectors such as Cosmic Explorer and the
radio High Sensitivity Array. Crucially, this velocity birefringence effect
cannot be constrained with dark binary mergers as it requires polarization
information at the emission time, which can be provided only by electromagnetic
emission.
| [
{
"created": "Wed, 7 Feb 2024 23:38:27 GMT",
"version": "v1"
}
] | 2024-02-09 | [
[
"Lagos",
"Macarena",
""
],
[
"Jenks",
"Leah",
""
],
[
"Isi",
"Maximiliano",
""
],
[
"Hotokezaka",
"Kenta",
""
],
[
"Metzger",
"Brian D.",
""
],
[
"Burns",
"Eric",
""
],
[
"Farr",
"Will M.",
""
],
[
"Perkins",
"Scott",
""
],
[
"Wong",
"Kaze W. K.",
""
],
[
"Yunes",
"Nicolas",
""
]
] | Extensions to General Relativity (GR) allow the polarization of gravitational waves (GW) from astrophysical sources to suffer from amplitude and velocity birefringence, which respectively induce changes in the ellipticity and orientation of the polarization tensor. We introduce a multi-messenger approach to test this polarization behavior of GWs during their cosmological propagation using binary sources, for which the initial polarization is determined by the inclination and orientation angles of the orbital angular momentum vector with respect to the line of sight. In particular, we use spatially-resolved radio imaging of the jet from a binary neutron star (BNS) merger to constrain the orientation angle and hence the emitted polarization orientation of the GW signal at the site of the merger, and compare to that observed on Earth by GW detectors. For GW170817 we constrain the deviation from GR due to amplitude birefringence to $\kappa_A = -0.12^{+0.60}_{-0.61}$, while the velocity birefringence parameter $\kappa_V$ remains unconstrained. The inability to constrain $\kappa_V$ is due to the fact that Virgo did not detect GW170817, and measurements of the polarization orientation require information from a combination of multiple detectors with different alignments. For this reason, we also mock future BNS mergers with resolved afterglow proper motion and project that $\kappa_V$ could be constrained to a precision of $5\,$rad (corresponding to an angular shift of the GW polarization of $\delta\phi_V\approx 0.2\,$rad for a BNS at $100\,$Mpc) by a future network of third-generation ground-based GW detectors such as Cosmic Explorer and the radio High Sensitivity Array. Crucially, this velocity birefringence effect cannot be constrained with dark binary mergers as it requires polarization information at the emission time, which can be provided only by electromagnetic emission. |
gr-qc/0211004 | Allan Joseph Medved | A.J.M. Medved (University of Alberta) | Horizon Dynamics of a BTZ Black Hole | 13 pages and now in Revtex; some discussion and references added | Class.Quant.Grav. 20 (2003) 3165-3174 | 10.1088/0264-9381/20/14/317 | null | gr-qc hep-th | null | It has been suggested in the literature that, given a black hole spacetime, a
relativistic membrane can provide an effective description of the horizon
dynamics. In this paper, we explore such a framework in the context of a
2+1-dimensional BTZ black hole. Following this membrane prescription, we are
able to translate the horizon dynamics (now described by a string) into the
convenient form of a 1+1-dimensional Klein-Gordon equation. We proceed to
quantize the solutions and construct a thermodynamic partition function.
Ultimately, we are able to extract the quantum-corrected entropy, which is
shown to comply with the BTZ form of the Bekenstein-Hawking area law. We also
substantiate that the leading-order correction is proportional to the logarithm
of the area.
| [
{
"created": "Fri, 1 Nov 2002 16:14:24 GMT",
"version": "v1"
},
{
"created": "Mon, 12 May 2003 15:22:25 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Medved",
"A. J. M.",
"",
"University of Alberta"
]
] | It has been suggested in the literature that, given a black hole spacetime, a relativistic membrane can provide an effective description of the horizon dynamics. In this paper, we explore such a framework in the context of a 2+1-dimensional BTZ black hole. Following this membrane prescription, we are able to translate the horizon dynamics (now described by a string) into the convenient form of a 1+1-dimensional Klein-Gordon equation. We proceed to quantize the solutions and construct a thermodynamic partition function. Ultimately, we are able to extract the quantum-corrected entropy, which is shown to comply with the BTZ form of the Bekenstein-Hawking area law. We also substantiate that the leading-order correction is proportional to the logarithm of the area. |
2009.11823 | Ryotaku Suzuki | Ryotaku Suzuki | Black hole interactions at large $D$: brane blobology | 41 pages, 13 figures; v2: minor modifications; v3: published version,
title changed, figures added, 43 pages, 17 figures | JHEP 02 (2021) 131 | 10.1007/JHEP02(2021)131 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the large dimension ($D$) limit, Einstein's equation reduces to an
effective theory on the horizon surface, drastically simplifying the black hole
analysis. Especially, the effective theory on the black brane has been
successful in describing the non-linear dynamics not only of black branes, but
also of compact black objects which are encoded as solitary Gaussian-shaped
lumps, {\it blobs}. For a rigidly rotating ansatz, in addition to axisymmetric
deformed branches, various non-axisymmetric solutions have been found, such as
black bars, which only stay stationary in the large $D$ limit.
In this article, we demonstrate the blob approximation has a wider range of
applicability by formulating the interaction between blobs and subsequent
dynamics. We identify that this interaction occurs via thin necks connecting
blobs. Especially, black strings are well captured in this approximation
sufficiently away from the perturbative regime. Highly deformed black dumbbells
and ripples are also found to be tractable in the approximation. By defining
the local quantities, the effective force acting on distant blobs are evaluated
as well. These results reveal that the large $D$ effective theory is capable of
describing not only individual black holes but also the gravitational
interactions between them, as a full dynamical theory of interactive blobs,
which we call {\it brane blobology}.
| [
{
"created": "Thu, 24 Sep 2020 17:02:45 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Oct 2020 16:37:07 GMT",
"version": "v2"
},
{
"created": "Tue, 16 Feb 2021 11:17:08 GMT",
"version": "v3"
}
] | 2021-02-17 | [
[
"Suzuki",
"Ryotaku",
""
]
] | In the large dimension ($D$) limit, Einstein's equation reduces to an effective theory on the horizon surface, drastically simplifying the black hole analysis. Especially, the effective theory on the black brane has been successful in describing the non-linear dynamics not only of black branes, but also of compact black objects which are encoded as solitary Gaussian-shaped lumps, {\it blobs}. For a rigidly rotating ansatz, in addition to axisymmetric deformed branches, various non-axisymmetric solutions have been found, such as black bars, which only stay stationary in the large $D$ limit. In this article, we demonstrate the blob approximation has a wider range of applicability by formulating the interaction between blobs and subsequent dynamics. We identify that this interaction occurs via thin necks connecting blobs. Especially, black strings are well captured in this approximation sufficiently away from the perturbative regime. Highly deformed black dumbbells and ripples are also found to be tractable in the approximation. By defining the local quantities, the effective force acting on distant blobs are evaluated as well. These results reveal that the large $D$ effective theory is capable of describing not only individual black holes but also the gravitational interactions between them, as a full dynamical theory of interactive blobs, which we call {\it brane blobology}. |
2207.08397 | Shao-Wen Wei | Shao-Wen Wei, Yu-Xiao Liu | Topology of equatorial timelike circular orbits around stationary black
holes | 20 pages, 10 figures | Phys. Rev. D 107, 064006 (2023) | 10.1103/PhysRevD.107.064006 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | A topological approach has been successfully used to study the properties of
the light ring and the null circular orbit, in a generic black hole background.
However, for the equatorial timelike circular orbit, quite different from the
light ring case, its radius is closely dependent of the energy and angular
momentum of a test particle. This fact seems to restrict the extension of the
topological treatment to the timelike circular orbit. In this paper, we confirm
that the angular momentum does not affect the asymptotic behavior of the
constructed vector with its zero points denoting the equatorial timelike
circular orbits. As a result, a well-behaved topology to characterize the
equatorial timelike circular orbits can be constructed. Our study shows that
the total topological number of the timelike circular orbits vanishes for a
generic black hole, which is dependent of the energy of the particle.
Significantly, it reveals that if there the timelike circular orbits exist,
they always come in pairs for fixed angular momentum. Meanwhile, the stable and
unstable timelike circular orbits have positive or negative winding number. Of
particular interest is that the marginally stable circular orbit corresponds to
the bifurcation point of the zero point of the constructed vector. Moreover, we
also examine the case when the particle energy acts as the control parameter.
It is shown that there will be topological phase transition when the value of
the particle energy is one. Below this value, the timelike circular orbits
always come in pairs for fixed energy. Otherwise, we will have one more
unstable timelike circular orbit. We further apply the treatment to the Kerr
black hole. All the results given in a generic black hole background are
exactly reproduced. These strongly indicate that our topological approach can
be generalized to the equatorial timelike circular orbits.
| [
{
"created": "Mon, 18 Jul 2022 06:14:36 GMT",
"version": "v1"
},
{
"created": "Sat, 11 Mar 2023 09:13:23 GMT",
"version": "v2"
}
] | 2023-03-14 | [
[
"Wei",
"Shao-Wen",
""
],
[
"Liu",
"Yu-Xiao",
""
]
] | A topological approach has been successfully used to study the properties of the light ring and the null circular orbit, in a generic black hole background. However, for the equatorial timelike circular orbit, quite different from the light ring case, its radius is closely dependent of the energy and angular momentum of a test particle. This fact seems to restrict the extension of the topological treatment to the timelike circular orbit. In this paper, we confirm that the angular momentum does not affect the asymptotic behavior of the constructed vector with its zero points denoting the equatorial timelike circular orbits. As a result, a well-behaved topology to characterize the equatorial timelike circular orbits can be constructed. Our study shows that the total topological number of the timelike circular orbits vanishes for a generic black hole, which is dependent of the energy of the particle. Significantly, it reveals that if there the timelike circular orbits exist, they always come in pairs for fixed angular momentum. Meanwhile, the stable and unstable timelike circular orbits have positive or negative winding number. Of particular interest is that the marginally stable circular orbit corresponds to the bifurcation point of the zero point of the constructed vector. Moreover, we also examine the case when the particle energy acts as the control parameter. It is shown that there will be topological phase transition when the value of the particle energy is one. Below this value, the timelike circular orbits always come in pairs for fixed energy. Otherwise, we will have one more unstable timelike circular orbit. We further apply the treatment to the Kerr black hole. All the results given in a generic black hole background are exactly reproduced. These strongly indicate that our topological approach can be generalized to the equatorial timelike circular orbits. |
1204.2778 | John Morris | John D. Anderson and J.R. Morris | Chameleon effect and the Pioneer anomaly | 16 pages; to appear in Phys.Rev.D | Phys.Rev.D 85, 084017 (2012) | 10.1103/PhysRevD.85.084017 | null | gr-qc astro-ph.EP hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The possibility that the apparent anomalous acceleration of the Pioneer 10
and 11 spacecraft may be due, at least in part, to a chameleon field effect is
examined. A small spacecraft, with no thin shell, can have a more pronounced
anomalous acceleration than a large compact body, such as a planet, having a
thin shell. The chameleon effect seems to present a natural way to explain the
differences seen in deviations from pure Newtonian gravity for a spacecraft and
for a planet, and appears to be compatible with the basic features of the
Pioneer anomaly, including the appearance of a jerk term. However, estimates of
the size of the chameleon effect indicate that its contribution to the
anomalous acceleration is negligible. We conclude that any inverse-square
component in the anomalous acceleration is more likely caused by an unmodelled
reaction force from solar-radiation pressure, rather than a chameleon field
effect.
| [
{
"created": "Thu, 12 Apr 2012 17:28:43 GMT",
"version": "v1"
}
] | 2012-07-24 | [
[
"Anderson",
"John D.",
""
],
[
"Morris",
"J. R.",
""
]
] | The possibility that the apparent anomalous acceleration of the Pioneer 10 and 11 spacecraft may be due, at least in part, to a chameleon field effect is examined. A small spacecraft, with no thin shell, can have a more pronounced anomalous acceleration than a large compact body, such as a planet, having a thin shell. The chameleon effect seems to present a natural way to explain the differences seen in deviations from pure Newtonian gravity for a spacecraft and for a planet, and appears to be compatible with the basic features of the Pioneer anomaly, including the appearance of a jerk term. However, estimates of the size of the chameleon effect indicate that its contribution to the anomalous acceleration is negligible. We conclude that any inverse-square component in the anomalous acceleration is more likely caused by an unmodelled reaction force from solar-radiation pressure, rather than a chameleon field effect. |
gr-qc/9506043 | Kiyoshi Ezawa | Kiyoshi Ezawa | Combinatorial solutions to the Hamiltonian constraint in
(2+1)-dimensional Ashtekar gravity | 41 pages Latex (2 figures available as a postscript file) | Nucl.Phys. B459 (1996) 355-392 | 10.1016/0550-3213(95)00557-9 | OU-HET/217 | gr-qc | null | Dirac's quantization of the (2+1)-dimensional analog of Ashtekar's approach
to quantum gravity is investigated. After providing a diffeomorphism-invariant
regularization of the Hamiltonian constraint, we find a set of solutions to
this Hamiltonian constraint which is a generalization of the solution
discovered by Jacobson and Smolin. These solutions are given by particular
linear combinations of the spin network states. While the classical
counterparts of these solutions have degenerate metric, due to a \lq quantum
effect' the area operator has nonvanishing action on these states. We also
discuss how to extend our results to (3+1)-dimensions.
| [
{
"created": "Thu, 22 Jun 1995 07:56:08 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Jun 1995 13:19:10 GMT",
"version": "v2"
}
] | 2009-10-28 | [
[
"Ezawa",
"Kiyoshi",
""
]
] | Dirac's quantization of the (2+1)-dimensional analog of Ashtekar's approach to quantum gravity is investigated. After providing a diffeomorphism-invariant regularization of the Hamiltonian constraint, we find a set of solutions to this Hamiltonian constraint which is a generalization of the solution discovered by Jacobson and Smolin. These solutions are given by particular linear combinations of the spin network states. While the classical counterparts of these solutions have degenerate metric, due to a \lq quantum effect' the area operator has nonvanishing action on these states. We also discuss how to extend our results to (3+1)-dimensions. |
gr-qc/9802047 | Aroon Beesham | Aroonkumar Beesham (University of Zululand, S. Africa) | Physical interpretation of constants in the solutions to the Brans-Dicke
equations | 10 pages, RevTex | Mod.Phys.Lett.A13:805-810,1998 | 10.1142/S0217732398000863 | null | gr-qc | null | Using an energy-momentum complex we give a physical interpretation to the
constants in the well-known static spherically symmetric asymptotically flat
vacuum solution to the Brans-Dicke equations. The positivity of the tensor mass
puts a bound on parameters in the solution.
| [
{
"created": "Wed, 18 Feb 1998 08:49:58 GMT",
"version": "v1"
}
] | 2010-03-03 | [
[
"Beesham",
"Aroonkumar",
"",
"University of Zululand, S. Africa"
]
] | Using an energy-momentum complex we give a physical interpretation to the constants in the well-known static spherically symmetric asymptotically flat vacuum solution to the Brans-Dicke equations. The positivity of the tensor mass puts a bound on parameters in the solution. |
0801.4401 | Francisco Lobo | Francisco S. N. Lobo | General class of wormhole geometries in conformal Weyl gravity | 7 pages, Revtex4. V2: typos corrected. V3: 8 pages, section on the
energy conditions added, version to appear in Class. Quant. Gravity | Class.Quant.Grav.25:175006,2008 | 10.1088/0264-9381/25/17/175006 | null | gr-qc astro-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, a general class of wormhole geometries in conformal Weyl
gravity is analyzed. A wide variety of exact solutions of asymptotically flat
spacetimes is found, in which the stress energy tensor profile differs
radically from its general relativistic counterpart. In particular, a class of
geometries is constructed that satisfies the energy conditions in the throat
neighborhood, which is in clear contrast to the general relativistic solutions.
| [
{
"created": "Tue, 29 Jan 2008 12:43:51 GMT",
"version": "v1"
},
{
"created": "Thu, 14 Feb 2008 14:25:59 GMT",
"version": "v2"
},
{
"created": "Fri, 4 Jul 2008 16:00:40 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Lobo",
"Francisco S. N.",
""
]
] | In this work, a general class of wormhole geometries in conformal Weyl gravity is analyzed. A wide variety of exact solutions of asymptotically flat spacetimes is found, in which the stress energy tensor profile differs radically from its general relativistic counterpart. In particular, a class of geometries is constructed that satisfies the energy conditions in the throat neighborhood, which is in clear contrast to the general relativistic solutions. |
gr-qc/9908014 | Parthasarathi Mitra | P. Mitra | A note on the entropy of charged multi - black - holes | LaTeX, 8 pages | Phys.Rev. D61 (2000) 024028 | 10.1103/PhysRevD.61.024028 | SINP/TNP/99-26 | gr-qc hep-th | null | Majumdar--Papapetrou multi--black-hole solutions of the Einstein--Maxwell
equations are considered in four and higher dimensions. The Euclidean action
with boundary conditions appropriate to the canonical ensemble is shown to lead
to zero entropy.
| [
{
"created": "Thu, 5 Aug 1999 10:26:05 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Mitra",
"P.",
""
]
] | Majumdar--Papapetrou multi--black-hole solutions of the Einstein--Maxwell equations are considered in four and higher dimensions. The Euclidean action with boundary conditions appropriate to the canonical ensemble is shown to lead to zero entropy. |
1307.6525 | Neil Ashby | Neil Ashby, Marc Weiss | Why there is no noon-midnight red shift in the GPS | null | null | null | null | gr-qc | http://creativecommons.org/licenses/publicdomain/ | Although the effects of solar (and lunar) gravitational potentials on the
frequencies of orbiting Global Positioning System (GPS) clocks are actually no
more than a few parts in 10^(15), a na\"ive calculation appears to show that
such effects are much larger, and depend on whether the orbiting clock is
between the earth and the sun, or on the side of the earth opposite to the sun.
Consequently questions about whether such effects have been properly accounted
for in the GPS continue to arise. This issue has been discussed in a misleading
way in terms of cancellations arising from a second-order Doppler shift in the
literature for almost 50 years. The purpose of this article is to provide a
correct argument, based on fundamental relativity principles, so that one may
understand in a simple way why the effects of external solar system bodies on
orbiting or earth-bound clocks in the GPS are so small. The relativity of
simultaneity plays a crucial role in these arguments.
| [
{
"created": "Wed, 24 Jul 2013 18:42:10 GMT",
"version": "v1"
}
] | 2013-07-25 | [
[
"Ashby",
"Neil",
""
],
[
"Weiss",
"Marc",
""
]
] | Although the effects of solar (and lunar) gravitational potentials on the frequencies of orbiting Global Positioning System (GPS) clocks are actually no more than a few parts in 10^(15), a na\"ive calculation appears to show that such effects are much larger, and depend on whether the orbiting clock is between the earth and the sun, or on the side of the earth opposite to the sun. Consequently questions about whether such effects have been properly accounted for in the GPS continue to arise. This issue has been discussed in a misleading way in terms of cancellations arising from a second-order Doppler shift in the literature for almost 50 years. The purpose of this article is to provide a correct argument, based on fundamental relativity principles, so that one may understand in a simple way why the effects of external solar system bodies on orbiting or earth-bound clocks in the GPS are so small. The relativity of simultaneity plays a crucial role in these arguments. |
1301.1538 | Sean Gryb B | Sean Gryb and Flavio Mercati | Right about time? | 12 pages, 2 figures. Only author affiliations and emails added. This
essay received fourth prize in the juried FQXi essay competition of 2012 | Questioning the Foundations of Physics. The Frontiers Collection.
pp 87-102. Springer, 2015 | 10.1007/978-3-319-13045-3_6 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Have our fundamental theories got time right? Does size really matter? Or is
physics all in the eyes of the beholder? In this essay, we question the origin
of time and scale by reevaluating the nature of measurement. We then argue for
a radical scenario, supported by a suggestive calculation, where the flow of
time is inseparable from the measurement process. Our scenario breaks the bond
of time and space and builds a new one: the marriage of time and scale.
| [
{
"created": "Tue, 8 Jan 2013 14:07:24 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Jan 2013 16:54:12 GMT",
"version": "v2"
}
] | 2015-02-06 | [
[
"Gryb",
"Sean",
""
],
[
"Mercati",
"Flavio",
""
]
] | Have our fundamental theories got time right? Does size really matter? Or is physics all in the eyes of the beholder? In this essay, we question the origin of time and scale by reevaluating the nature of measurement. We then argue for a radical scenario, supported by a suggestive calculation, where the flow of time is inseparable from the measurement process. Our scenario breaks the bond of time and space and builds a new one: the marriage of time and scale. |
2301.09332 | Vladimir S. Manko | H. Garc\'ia-Compe\'an, V. S. Manko, C. J. Ram\'irez-Valdez | Dyonic black holes: The theory of two electromagnetic potentials. II | 14 pages, no figures | null | 10.1103/PhysRevD.107.064017 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The results obtained in our previous paper are now extended to the case of
stationary axially symmetric dyonic black boles within the theory of two
electromagnetic potentials. We slightly enlarge the classical Ernst formalism
by introducing, with the aid of the $t$- and $\varphi$-components of the dual
potential $B_\mu$, the magnetic potential $\Phi_m$ which, similar to the known
electric potential $\Phi_e$, also takes constant value on the black hole
horizon. We analyze in detail the case of the dyonic Kerr-Newman black hole and
show how the Komar mass must be evaluated correctly in this stationary dyonic
model. In particular, we rigorously prove the validity of the standard
Tomimatsu mass formula and point out that attempts to "improve" it made in
recent years are explained by misunderstanding of the auxiliary role that
singular potentials play in the description of magnetic charges. Our approach
is symmetrical with respect to electric and magnetic charges and, like in the
static case considered earlier, Dirac strings of all kind are excluded from the
physical picture of the stationary black hole dyonic spacetimes.
| [
{
"created": "Mon, 23 Jan 2023 09:19:56 GMT",
"version": "v1"
}
] | 2023-03-29 | [
[
"García-Compeán",
"H.",
""
],
[
"Manko",
"V. S.",
""
],
[
"Ramírez-Valdez",
"C. J.",
""
]
] | The results obtained in our previous paper are now extended to the case of stationary axially symmetric dyonic black boles within the theory of two electromagnetic potentials. We slightly enlarge the classical Ernst formalism by introducing, with the aid of the $t$- and $\varphi$-components of the dual potential $B_\mu$, the magnetic potential $\Phi_m$ which, similar to the known electric potential $\Phi_e$, also takes constant value on the black hole horizon. We analyze in detail the case of the dyonic Kerr-Newman black hole and show how the Komar mass must be evaluated correctly in this stationary dyonic model. In particular, we rigorously prove the validity of the standard Tomimatsu mass formula and point out that attempts to "improve" it made in recent years are explained by misunderstanding of the auxiliary role that singular potentials play in the description of magnetic charges. Our approach is symmetrical with respect to electric and magnetic charges and, like in the static case considered earlier, Dirac strings of all kind are excluded from the physical picture of the stationary black hole dyonic spacetimes. |
1608.05958 | Seyed Meraj Mousavi Rasouli | S. M. M. Rasouli, A. H. Ziaie, S. Jalalzadeh and P. V. Moniz | Non-singular Brans-Dicke collapse in deformed phase space | 23 pages, 10 figures | Annals of Physics 375(2016)154 | 10.1016/j.aop.2016.09.007 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the collapse process of a homogeneous perfect fluid (in FLRW
background) with a barotropic equation of state in Brans-Dicke (BD) theory in
the presence of phase space deformation effects. Such a deformation is
introduced as a particular type of non-commutativity between phase space
coordinates. For the commutative case, it has been shown in the literature [1],
that the dust collapse in BD theory leads to the formation of a spacetime
singularity which is covered by an event horizon. In comparison to general
relativity (GR), the authors concluded that the final state of black holes in
BD theory is identical to the GR case but differs from GR during the dynamical
evolution of the collapse process. However, the presence of non-commutative
effects influences the dynamics of the collapse scenario and consequently a
non-singular evolution is developed in the sense that a bounce emerges at a
minimum radius, after which an expanding phase begins. Such a behavior is
observed for positive values of the BD coupling parameter. For large positive
values of the BD coupling parameter, when non-commutative effects are present,
the dynamics of collapse process differs from the GR case. Finally, we show
that for negative values of the BD coupling parameter, the singularity is
replaced by an oscillatory bounce occurring at a finite time, with the
frequency of oscillation and amplitude being damped at late times.
| [
{
"created": "Sun, 21 Aug 2016 15:47:13 GMT",
"version": "v1"
},
{
"created": "Sun, 23 Oct 2016 23:31:04 GMT",
"version": "v2"
}
] | 2016-10-25 | [
[
"Rasouli",
"S. M. M.",
""
],
[
"Ziaie",
"A. H.",
""
],
[
"Jalalzadeh",
"S.",
""
],
[
"Moniz",
"P. V.",
""
]
] | We study the collapse process of a homogeneous perfect fluid (in FLRW background) with a barotropic equation of state in Brans-Dicke (BD) theory in the presence of phase space deformation effects. Such a deformation is introduced as a particular type of non-commutativity between phase space coordinates. For the commutative case, it has been shown in the literature [1], that the dust collapse in BD theory leads to the formation of a spacetime singularity which is covered by an event horizon. In comparison to general relativity (GR), the authors concluded that the final state of black holes in BD theory is identical to the GR case but differs from GR during the dynamical evolution of the collapse process. However, the presence of non-commutative effects influences the dynamics of the collapse scenario and consequently a non-singular evolution is developed in the sense that a bounce emerges at a minimum radius, after which an expanding phase begins. Such a behavior is observed for positive values of the BD coupling parameter. For large positive values of the BD coupling parameter, when non-commutative effects are present, the dynamics of collapse process differs from the GR case. Finally, we show that for negative values of the BD coupling parameter, the singularity is replaced by an oscillatory bounce occurring at a finite time, with the frequency of oscillation and amplitude being damped at late times. |
gr-qc/9411030 | Jim Wheeler | James T. Wheeler | Scale-invariant phase space and the conformal group | 7 pages, plain tex, no figures | null | null | USU-FTG-123 | gr-qc | null | The gauge bundle of the 4-dim conformal group over an 8-dim base space,
called biconformal space, is shown have a consistent interpretation as a
scale-invariant phase space. Specifically, we show that a classical Hamiltonian
system generates a differential geometry which is necessarily biconformal, and
that the classical Hamiltonian dynamics of a point particle is equivalent to
the specification of a 7-dim hypersurface in flat biconformal space together
with the consequent necessary existence of a set of preferred curves. The
result is centrally important for establishing the physical interpretation of
conformal gauging.
| [
{
"created": "Fri, 11 Nov 1994 19:18:20 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Wheeler",
"James T.",
""
]
] | The gauge bundle of the 4-dim conformal group over an 8-dim base space, called biconformal space, is shown have a consistent interpretation as a scale-invariant phase space. Specifically, we show that a classical Hamiltonian system generates a differential geometry which is necessarily biconformal, and that the classical Hamiltonian dynamics of a point particle is equivalent to the specification of a 7-dim hypersurface in flat biconformal space together with the consequent necessary existence of a set of preferred curves. The result is centrally important for establishing the physical interpretation of conformal gauging. |
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