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/0103009 | Malakhaltsev Mikhail A. | V. I. Bashkov, S. M. Kozyrev | Dark matter an effect of gravitation permeability of material in Jordan,
Brance - Dicke theory | null | null | null | null | gr-qc | null | Analyzing the static spherically symmetric and rotating ellipsoid solutions
in the Newtonian limit of Jordan, Brance - Dicke theory we find the following.
In empty space scalar-tensor theories have trivial solution of field equation
with constant scalar potential (efficient value of gravitation constant). In
this case no celestial-mechanical experiments to reveal a difference between
scalar-tensor theories and Einstein theory is not presented possible. However,
scalar field, inside the matter, has characteristics like gravitation
permeability of material similar electromagnetic permeability of material in
Maxwell theories of electromagnetism. Investigation of obtained exact solutions
for given functions of a matter distributions in the Newtonian limit of Jordan,
Brance - Dicke theory show the efficient value of gravitation constant depends
on density of matter, sizes and form of object, as well as on the value of
theories coupling constant. That for example led to weakening gravitation force
in the central regions of a Galaxies. This assumption constitutes the way to
explain observed rotation curves of Galaxies without using cold dark matter.
| [
{
"created": "Sat, 3 Mar 2001 09:32:08 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Bashkov",
"V. I.",
""
],
[
"Kozyrev",
"S. M.",
""
]
] | Analyzing the static spherically symmetric and rotating ellipsoid solutions in the Newtonian limit of Jordan, Brance - Dicke theory we find the following. In empty space scalar-tensor theories have trivial solution of field equation with constant scalar potential (efficient value of gravitation constant). In this case no celestial-mechanical experiments to reveal a difference between scalar-tensor theories and Einstein theory is not presented possible. However, scalar field, inside the matter, has characteristics like gravitation permeability of material similar electromagnetic permeability of material in Maxwell theories of electromagnetism. Investigation of obtained exact solutions for given functions of a matter distributions in the Newtonian limit of Jordan, Brance - Dicke theory show the efficient value of gravitation constant depends on density of matter, sizes and form of object, as well as on the value of theories coupling constant. That for example led to weakening gravitation force in the central regions of a Galaxies. This assumption constitutes the way to explain observed rotation curves of Galaxies without using cold dark matter. |
1204.3433 | Jean-Philippe Bruneton | Jean-Philippe Bruneton and Julien Larena | Dynamics of a lattice Universe | 14 pages. No figure. Accepted version for Classical and Quantum
Gravity | Class.Quant.Grav. 29 (2012) 155001 | 10.1088/0264-9381/29/15/155001 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We find a solution to Einstein field equations for a regular toroidal lattice
of size L with equal masses M at the centre of each cell; this solution is
exact at order M/L. Such a solution is convenient to study the dynamics of an
assembly of galaxy-like objects. We find that the solution is expanding (or
contracting) in exactly the same way as the solution of a
Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average
density as our model. This points towards the absence of backreaction in a
Universe filled with an infinite number of objects, and this validates the
fluid approximation, as far as dynamics is concerned, and at the level of
approximation considered in this work.
| [
{
"created": "Mon, 16 Apr 2012 10:17:17 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Jun 2012 14:04:06 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Bruneton",
"Jean-Philippe",
""
],
[
"Larena",
"Julien",
""
]
] | We find a solution to Einstein field equations for a regular toroidal lattice of size L with equal masses M at the centre of each cell; this solution is exact at order M/L. Such a solution is convenient to study the dynamics of an assembly of galaxy-like objects. We find that the solution is expanding (or contracting) in exactly the same way as the solution of a Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average density as our model. This points towards the absence of backreaction in a Universe filled with an infinite number of objects, and this validates the fluid approximation, as far as dynamics is concerned, and at the level of approximation considered in this work. |
2005.06640 | Sebasti\'an Bahamonde Dr | Sebastian Bahamonde, Mir Faizal, James Q. Quach, Richard A. Norte | Quantum Weak Equivalence Principle and the Gravitational Casimir Effect
in Superconductors | Essay received an honorable mention in the Gravity Research
Foundation Essay Competition 2020. 9 pages, 3 figures. Matches published
version in IJMPD | Int.J.Mod.Phys.D 29 (2020), 14 | 10.1142/S0218271820430245 | null | gr-qc cond-mat.supr-con hep-ex quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We will use Fisher information to properly analyze the quantum weak
equivalence principle. We argue that gravitational waves will be partially
reflected by superconductors. This will occur as the violation of the weak
equivalence principle in Cooper pairs is larger than the surrounding ionic
lattice. Such reflections of virtual gravitational waves by superconductors can
produce a gravitational Casimir effect, which may be detected using currently
available technology.
| [
{
"created": "Wed, 13 May 2020 22:03:00 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Dec 2020 13:56:02 GMT",
"version": "v2"
}
] | 2020-12-02 | [
[
"Bahamonde",
"Sebastian",
""
],
[
"Faizal",
"Mir",
""
],
[
"Quach",
"James Q.",
""
],
[
"Norte",
"Richard A.",
""
]
] | We will use Fisher information to properly analyze the quantum weak equivalence principle. We argue that gravitational waves will be partially reflected by superconductors. This will occur as the violation of the weak equivalence principle in Cooper pairs is larger than the surrounding ionic lattice. Such reflections of virtual gravitational waves by superconductors can produce a gravitational Casimir effect, which may be detected using currently available technology. |
1308.5954 | Dra\v{z}en Glavan | Drazen Glavan, Tomislav Prokopec, Vasileios Prymidis | Backreaction of a massless minimally coupled scalar field from
inflationary quantum fluctuations | null | Phys. Rev. D 89, 024024 (2014) | 10.1103/PhysRevD.89.024024 | UTP-UU-13/20, SPIN-13/14 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study a massless, minimally coupled scalar field in a FLRW
spacetime with periods of different constant deceleration parameter. We assume
the Bunch-Davies vacuum during inflation and then use a sudden matching
approximation to match it onto radiation era and subsequently onto matter era.
We then proceed to calculate the one-loop energy-momentum tensor from the
inflationary quantum vacuum fluctuations in different eras. The energy-momentum
tensor has the form of an ideal (quantum) fluid, characterized by an equation
of state. When compared with the background, far away from the matching the
quantum energy density in radiation era exhibits a contribution that grows
logarithmically with the scale factor. In matter era the ratio of the quantum
to classical fluid settles eventually to a tiny constant, (rho_q) / (rho) =
10^(-13) for a grand unified scale inflation. Curiously, the late time scaling
of quantum fluctuations suggests that they contribute a little to the dark
matter of the Universe, provided that it clusters as cold dark matter, which
needs to be checked.
| [
{
"created": "Tue, 27 Aug 2013 19:19:22 GMT",
"version": "v1"
}
] | 2014-01-29 | [
[
"Glavan",
"Drazen",
""
],
[
"Prokopec",
"Tomislav",
""
],
[
"Prymidis",
"Vasileios",
""
]
] | In this paper we study a massless, minimally coupled scalar field in a FLRW spacetime with periods of different constant deceleration parameter. We assume the Bunch-Davies vacuum during inflation and then use a sudden matching approximation to match it onto radiation era and subsequently onto matter era. We then proceed to calculate the one-loop energy-momentum tensor from the inflationary quantum vacuum fluctuations in different eras. The energy-momentum tensor has the form of an ideal (quantum) fluid, characterized by an equation of state. When compared with the background, far away from the matching the quantum energy density in radiation era exhibits a contribution that grows logarithmically with the scale factor. In matter era the ratio of the quantum to classical fluid settles eventually to a tiny constant, (rho_q) / (rho) = 10^(-13) for a grand unified scale inflation. Curiously, the late time scaling of quantum fluctuations suggests that they contribute a little to the dark matter of the Universe, provided that it clusters as cold dark matter, which needs to be checked. |
gr-qc/0701096 | Dejan Stojkovic | Tanmay Vachaspati and Dejan Stojkovic | Quantum Radiation from Quantum Gravitational Collapse | accepted for publication in Phys. Lett. B | Phys.Lett.B663:107-110,2008 | 10.1016/j.physletb.2008.04.004 | null | gr-qc astro-ph hep-th | null | We study quantum radiation emitted during the collapse of a quantized,
gravitating, spherical domain wall. The amount of radiation emitted during
collapse now depends on the wavefunction of the collapsing wall and the
background spacetime. If the wavefunction is initially in the form of a sharp
wavepacket, the expectation value of the particle occupation number is
determined as a function of time and frequency. The results are in good
agreement with our earlier semiclassical analysis and show that the quantum
radiation is non-thermal and evaporation accompanies gravitational collapse.
| [
{
"created": "Tue, 16 Jan 2007 21:11:04 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Apr 2008 21:58:41 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Vachaspati",
"Tanmay",
""
],
[
"Stojkovic",
"Dejan",
""
]
] | We study quantum radiation emitted during the collapse of a quantized, gravitating, spherical domain wall. The amount of radiation emitted during collapse now depends on the wavefunction of the collapsing wall and the background spacetime. If the wavefunction is initially in the form of a sharp wavepacket, the expectation value of the particle occupation number is determined as a function of time and frequency. The results are in good agreement with our earlier semiclassical analysis and show that the quantum radiation is non-thermal and evaporation accompanies gravitational collapse. |
gr-qc/0012056 | Jose Martin Garcia | Jose M. Martin-Garcia and Carsten Gundlach | Gauge-invariant and coordinate-independent perturbations of stellar
collapse II: matching to the exterior | 18 pages, RevTex | Phys.Rev.D64:024012,2001 | 10.1103/PhysRevD.64.024012 | null | gr-qc | null | In Paper I in this series we constructed evolution equations for the complete
gauge-invariant linear perturbations of a time-dependent spherically symmetric
perfect fluid spacetime. A key application of this formalism is the interior of
a collapsing star. Here we derive boundary conditions at the surface of the
star, matching the interior perturbations to the well-known perturbations of
the vacuum Schwarzschild spacetime outside the star.
| [
{
"created": "Fri, 15 Dec 2000 15:54:22 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Martin-Garcia",
"Jose M.",
""
],
[
"Gundlach",
"Carsten",
""
]
] | In Paper I in this series we constructed evolution equations for the complete gauge-invariant linear perturbations of a time-dependent spherically symmetric perfect fluid spacetime. A key application of this formalism is the interior of a collapsing star. Here we derive boundary conditions at the surface of the star, matching the interior perturbations to the well-known perturbations of the vacuum Schwarzschild spacetime outside the star. |
2210.06810 | Guilherme Franzmann | The FADE Collaboration: Heliudson Bernardo, Benjamin Bose, Guilherme
Franzmann, Steffen Hagstotz, Yutong He, Aliki Litsa, and Florian Niedermann | Modified gravity approaches to the cosmological constant problem | 54 pages, 2 figures, 1 table. Invited review for Universe, Special
Issue "Cosmological Constant"
(https://www.mdpi.com/journal/universe/special_issues/cosmological_constant_problem) | null | null | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | The cosmological constant and its phenomenology remain among the greatest
puzzles in theoretical physics. We review how modifications of Einstein's
general relativity could alleviate the different problems associated with it
that result from the interplay of classical gravity and quantum field theory.
We introduce a modern and concise language to describe the problems associated
with its phenomenology, and inspect no-go theorems and their loopholes to
motivate the approaches discussed here. Constrained gravity approaches exploit
minimal departures from general relativity; massive gravity introduces mass to
the graviton; Horndeski theories lead to the breaking of translational
invariance of the vacuum; and models with extra dimensions change the
symmetries of the vacuum. We also review screening mechanisms that have to be
present in some of these theories if they aim to recover the success of general
relativity on small scales as well. Finally, we summarise the statuses of these
models in their attempt to solve the different cosmological constant problems
while being able to account for current astrophysical and cosmological
observations.
| [
{
"created": "Thu, 13 Oct 2022 07:46:58 GMT",
"version": "v1"
}
] | 2022-10-14 | [
[
"The FADE Collaboration",
"",
""
],
[
"Bernardo",
"Heliudson",
""
],
[
"Bose",
"Benjamin",
""
],
[
"Franzmann",
"Guilherme",
""
],
[
"Hagstotz",
"Steffen",
""
],
[
"He",
"Yutong",
""
],
[
"Litsa",
"Aliki",
... | The cosmological constant and its phenomenology remain among the greatest puzzles in theoretical physics. We review how modifications of Einstein's general relativity could alleviate the different problems associated with it that result from the interplay of classical gravity and quantum field theory. We introduce a modern and concise language to describe the problems associated with its phenomenology, and inspect no-go theorems and their loopholes to motivate the approaches discussed here. Constrained gravity approaches exploit minimal departures from general relativity; massive gravity introduces mass to the graviton; Horndeski theories lead to the breaking of translational invariance of the vacuum; and models with extra dimensions change the symmetries of the vacuum. We also review screening mechanisms that have to be present in some of these theories if they aim to recover the success of general relativity on small scales as well. Finally, we summarise the statuses of these models in their attempt to solve the different cosmological constant problems while being able to account for current astrophysical and cosmological observations. |
2104.14065 | Jos\'e Antonio N\'ajera | Antonio N\'ajera and Amanda Fajardo | Fitting $f(Q,T)$ gravity models with a $\Lambda$CDM limit using H(z) and
Pantheon data | V3: Accepted version in Physics of the Dark Universe. Minor changes
plus corrections in the results of the sixth model | Physics of the Dark Universe, Volume 34, December 2021, 100889 | 10.1016/j.dark.2021.100889 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We proposed five $f(Q,T)$ models, which are an extension of symmetric
teleparallel gravity, where $Q$ is the non-metricity and $T$ is the trace of
the stress-energy tensor. By taking specific values of their parameters, these
models have a $\Lambda$CDM limit.
Using cosmic chronometers and supernovae Ia data, we found that our models
are consistent with $\Lambda$CDM at a 95\% confidence level. To see whether one
of these models can challenge $\Lambda$CDM at a background perspective, we
computed the Bayesian evidence for them and $\Lambda$CDM. According to it, the
concordance model is preferred over four of them, showing a weak preference
against $f(Q,T) = -Q/G_N + bT$ and $f(Q,T) = -(Q+2\Lambda)/G_N +bT$, a
substantial preference against $f(Q,T) = -(Q+2 H_0^2 c (Q/(6H_0^2))^{n+1})/G_N
+ bT $, and a strong preference against $f(Q,T) = -(Q+2H_0^2c(Q/(6H_0^2))^{n+1}
+ 2\Lambda)/G_N + bT$. Interestingly, a model includying a $T^2$ dependence
($f(Q,T) = -(Q+2\Lambda)/G_N - ((16\pi)^2 G_N b)/(120 H_0^2) T^2$) showed a
{substantial} preference against $\Lambda$CDM. {Therefore, we encourage further
analyses of this model to test its viability outside the background
perspective.}
| [
{
"created": "Thu, 29 Apr 2021 01:00:15 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Jun 2021 14:31:06 GMT",
"version": "v2"
},
{
"created": "Thu, 30 Sep 2021 19:30:16 GMT",
"version": "v3"
}
] | 2021-11-09 | [
[
"Nájera",
"Antonio",
""
],
[
"Fajardo",
"Amanda",
""
]
] | We proposed five $f(Q,T)$ models, which are an extension of symmetric teleparallel gravity, where $Q$ is the non-metricity and $T$ is the trace of the stress-energy tensor. By taking specific values of their parameters, these models have a $\Lambda$CDM limit. Using cosmic chronometers and supernovae Ia data, we found that our models are consistent with $\Lambda$CDM at a 95\% confidence level. To see whether one of these models can challenge $\Lambda$CDM at a background perspective, we computed the Bayesian evidence for them and $\Lambda$CDM. According to it, the concordance model is preferred over four of them, showing a weak preference against $f(Q,T) = -Q/G_N + bT$ and $f(Q,T) = -(Q+2\Lambda)/G_N +bT$, a substantial preference against $f(Q,T) = -(Q+2 H_0^2 c (Q/(6H_0^2))^{n+1})/G_N + bT $, and a strong preference against $f(Q,T) = -(Q+2H_0^2c(Q/(6H_0^2))^{n+1} + 2\Lambda)/G_N + bT$. Interestingly, a model includying a $T^2$ dependence ($f(Q,T) = -(Q+2\Lambda)/G_N - ((16\pi)^2 G_N b)/(120 H_0^2) T^2$) showed a {substantial} preference against $\Lambda$CDM. {Therefore, we encourage further analyses of this model to test its viability outside the background perspective.} |
0905.3243 | Bibekananda Nayak jr | Bibekananda Nayak and Lambodar Prasad Singh | Accretion, Primordial Black Holes and Standard Cosmology | 11 pages, 3 figures | Pramana 76:173-181,2011 | 10.1007/s12043-011-0002-x | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Primordial Black Holes evaporate due to Hawking radiation. We find that the
evaporation time of primordial black holes increase when accretion of radiation
is included.Thus depending on accretion efficiency more and more number of
primordial black holes are existing today, which strengthens the idea that the
primordial black holes are the proper candidate for dark matter.
| [
{
"created": "Wed, 20 May 2009 08:33:42 GMT",
"version": "v1"
},
{
"created": "Tue, 1 Mar 2011 06:57:03 GMT",
"version": "v2"
}
] | 2012-01-20 | [
[
"Nayak",
"Bibekananda",
""
],
[
"Singh",
"Lambodar Prasad",
""
]
] | Primordial Black Holes evaporate due to Hawking radiation. We find that the evaporation time of primordial black holes increase when accretion of radiation is included.Thus depending on accretion efficiency more and more number of primordial black holes are existing today, which strengthens the idea that the primordial black holes are the proper candidate for dark matter. |
1808.00786 | Hans Ringstr\"om | Hans Ringstr\"om | A unified approach to the Klein-Gordon equation on Bianchi backgrounds | 47 pages | Commun. Math. Phys. 372, 599-656 (2019) | 10.1007/s00220-019-03325-7 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we study solutions to the Klein-Gordon equation on Bianchi
backgrounds. In particular, we are interested in the asymptotic behaviour of
solutions in the direction of silent singularities. The main conclusion is
that, for a given solution $u$ to the Klein-Gordon equation, there are smooth
functions $u_{i}$, $i=0,1$, on the Lie group under consideration, such that
$u_{\sigma}(\cdot,\sigma)-u_{1}$ and $u(\cdot,\sigma)-u_{1}\sigma-u_{0}$
asymptotically converge to zero in the direction of the singularity (where
$\sigma$ is a geometrically defined time coordinate such that the singularity
corresponds to $\sigma\rightarrow-\infty$). Here $u_{i}$, $i=0,1$, should be
thought of as data on the singularity. Interestingly, it is possible to prove
that the asymptotics are of this form for a large class of Bianchi spacetimes.
Moreover, the conclusion applies for singularities that are matter dominated;
singularities that are vacuum dominated; and even when the asymptotics of the
underlying Bianchi spacetime are oscillatory. To summarise, there seems to be a
universality as far as the asymptotics in the direction of silent singularities
are concerned. In fact, it is tempting to conjecture that as long as the
singularity of the underlying Bianchi spacetime is silent, then the asymptotics
of solutions are as described above. In order to contrast the above asymptotics
with the non-silent setting, we, by appealing to known results, provide a
complete asymptotic characterisation of solutions to the Klein-Gordon equation
on a flat Kasner background. In that setting, $u_{\sigma}$ does, generically,
not converge.
| [
{
"created": "Thu, 2 Aug 2018 12:51:58 GMT",
"version": "v1"
}
] | 2020-10-15 | [
[
"Ringström",
"Hans",
""
]
] | In this paper, we study solutions to the Klein-Gordon equation on Bianchi backgrounds. In particular, we are interested in the asymptotic behaviour of solutions in the direction of silent singularities. The main conclusion is that, for a given solution $u$ to the Klein-Gordon equation, there are smooth functions $u_{i}$, $i=0,1$, on the Lie group under consideration, such that $u_{\sigma}(\cdot,\sigma)-u_{1}$ and $u(\cdot,\sigma)-u_{1}\sigma-u_{0}$ asymptotically converge to zero in the direction of the singularity (where $\sigma$ is a geometrically defined time coordinate such that the singularity corresponds to $\sigma\rightarrow-\infty$). Here $u_{i}$, $i=0,1$, should be thought of as data on the singularity. Interestingly, it is possible to prove that the asymptotics are of this form for a large class of Bianchi spacetimes. Moreover, the conclusion applies for singularities that are matter dominated; singularities that are vacuum dominated; and even when the asymptotics of the underlying Bianchi spacetime are oscillatory. To summarise, there seems to be a universality as far as the asymptotics in the direction of silent singularities are concerned. In fact, it is tempting to conjecture that as long as the singularity of the underlying Bianchi spacetime is silent, then the asymptotics of solutions are as described above. In order to contrast the above asymptotics with the non-silent setting, we, by appealing to known results, provide a complete asymptotic characterisation of solutions to the Klein-Gordon equation on a flat Kasner background. In that setting, $u_{\sigma}$ does, generically, not converge. |
1212.0729 | Piotr Bizon | Piotr Bizo\'n and Helmut Friedrich | A remark about wave equations on the extreme Reissner-Nordstr\"om black
hole exterior | 9 pages, a sentence added to the abstract, published version | Class. Quantum Grav. 30 (2013) 065001 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a massless scalar field propagating on the exterior of the
extreme Reissner-Nordstr\"om black hole. Using a discrete conformal symmetry of
this spacetime, we draw a one-to-one relationship between the behavior of the
field near the future horizon and near future null infinity. In particular, we
show that the polynomial growth of the second and higher transversal
derivatives along the horizon, recently found by Aretakis, reflects well known
facts about the retarded time asymptotics at null infinity.
| [
{
"created": "Tue, 4 Dec 2012 14:12:13 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Feb 2013 05:35:52 GMT",
"version": "v2"
}
] | 2013-02-20 | [
[
"Bizoń",
"Piotr",
""
],
[
"Friedrich",
"Helmut",
""
]
] | We consider a massless scalar field propagating on the exterior of the extreme Reissner-Nordstr\"om black hole. Using a discrete conformal symmetry of this spacetime, we draw a one-to-one relationship between the behavior of the field near the future horizon and near future null infinity. In particular, we show that the polynomial growth of the second and higher transversal derivatives along the horizon, recently found by Aretakis, reflects well known facts about the retarded time asymptotics at null infinity. |
gr-qc/9411039 | Massar Serge | S. Massar | The Semi-Classical Back Reaction to Black Hole Evaporation | 10 pages, LATEX | Phys.Rev.D52:5857-5864,1995 | 10.1103/PhysRevD.52.5857 | ULB-TH 94/19 | gr-qc | null | The semi-classical back reaction to black hole evaporation (wherein the
renormalized energy momentum tensor is taken as source of Einstein's equations)
is analyzed in detail. It is proven that the mass of a Schwarzshild black hole
decreases according to Hawking's law $dM/dt = - C/ M^2$ where $C$ is a constant
of order one and that the particles are emitted with a thermal spectrum at
temperature $1/8\pi M(t)$.
| [
{
"created": "Tue, 15 Nov 1994 11:41:34 GMT",
"version": "v1"
}
] | 2010-11-01 | [
[
"Massar",
"S.",
""
]
] | The semi-classical back reaction to black hole evaporation (wherein the renormalized energy momentum tensor is taken as source of Einstein's equations) is analyzed in detail. It is proven that the mass of a Schwarzshild black hole decreases according to Hawking's law $dM/dt = - C/ M^2$ where $C$ is a constant of order one and that the particles are emitted with a thermal spectrum at temperature $1/8\pi M(t)$. |
2408.03289 | Kei-Ichiro Kubota | Kei-ichiro Kubota, Shun Arai, Hayato Motohashi, and Shinji Mukohyama | Spin wave optics for gravitational waves lensed by a Kerr black hole | 17 pages, 14 figures. fixed typos | null | null | YITP-24-89, IPMU24-0031 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves exhibit the unique signature of their spin-2 nature in
processes of wave scattering, due to the interaction between spin and a
background spacetime. Since the spin effect is more pronounced for longer
wavelengths and gravitational waves sourced by binaries have a long wavelength,
it may become an important effect in addition to the wave effect. We study the
propagation of gravitational waves lensed by a Kerr black hole by numerically
solving the Teukolsky equation with a source term of the equal-mass circular
binary, taking into account both spin effect and wave effect. We find
helicity-dependent small-period oscillation in the power spectrum of the
amplification factor in the forward direction and the oscillation is enhanced
as spin of a prograde Kerr black hole increases.
| [
{
"created": "Tue, 6 Aug 2024 16:38:09 GMT",
"version": "v1"
},
{
"created": "Wed, 7 Aug 2024 13:22:16 GMT",
"version": "v2"
}
] | 2024-08-08 | [
[
"Kubota",
"Kei-ichiro",
""
],
[
"Arai",
"Shun",
""
],
[
"Motohashi",
"Hayato",
""
],
[
"Mukohyama",
"Shinji",
""
]
] | Gravitational waves exhibit the unique signature of their spin-2 nature in processes of wave scattering, due to the interaction between spin and a background spacetime. Since the spin effect is more pronounced for longer wavelengths and gravitational waves sourced by binaries have a long wavelength, it may become an important effect in addition to the wave effect. We study the propagation of gravitational waves lensed by a Kerr black hole by numerically solving the Teukolsky equation with a source term of the equal-mass circular binary, taking into account both spin effect and wave effect. We find helicity-dependent small-period oscillation in the power spectrum of the amplification factor in the forward direction and the oscillation is enhanced as spin of a prograde Kerr black hole increases. |
gr-qc/9606074 | null | Alpan Raval, B.L. Hu and Don Koks | Near-Thermal Radiation in Detectors, Mirrors and Black Holes: A
Stochastic Approach | 27 pages, Latex | Phys.Rev.D55:4795-4812,1997 | 10.1103/PhysRevD.55.4795 | umdpp 96-53 | gr-qc hep-th | null | In analyzing the nature of thermal radiance experienced by an accelerated
observer (Unruh effect), an eternal black hole (Hawking effect) and in certain
types of cosmological expansion, one of us proposed a unifying viewpoint that
these can be understood as arising from the vacuum fluctuations of the quantum
field being subjected to an exponential scale transformation. This viewpoint,
together with our recently developed stochastic theory of particle-field
interaction understood as quantum open systems described by the influence
functional formalism, can be used to address situations where the spacetime
possesses an event horizon only asymptotically, or none at all. Examples
studied here include detectors moving at uniform acceleration only
asymptotically or for a finite time, a moving mirror, and a collapsing mass. We
show that in such systems radiance indeed is observed, albeit not in a precise
Planckian spectrum. The deviation therefrom is determined by a parameter which
measures the departure from uniform acceleration or from exact exponential
expansion. These results are expected to be useful for the investigation of
non-equilibrium black hole thermodynamics and the linear response regime of
backreaction problems in semiclassical gravity.
| [
{
"created": "Thu, 27 Jun 1996 02:28:37 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Raval",
"Alpan",
""
],
[
"Hu",
"B. L.",
""
],
[
"Koks",
"Don",
""
]
] | In analyzing the nature of thermal radiance experienced by an accelerated observer (Unruh effect), an eternal black hole (Hawking effect) and in certain types of cosmological expansion, one of us proposed a unifying viewpoint that these can be understood as arising from the vacuum fluctuations of the quantum field being subjected to an exponential scale transformation. This viewpoint, together with our recently developed stochastic theory of particle-field interaction understood as quantum open systems described by the influence functional formalism, can be used to address situations where the spacetime possesses an event horizon only asymptotically, or none at all. Examples studied here include detectors moving at uniform acceleration only asymptotically or for a finite time, a moving mirror, and a collapsing mass. We show that in such systems radiance indeed is observed, albeit not in a precise Planckian spectrum. The deviation therefrom is determined by a parameter which measures the departure from uniform acceleration or from exact exponential expansion. These results are expected to be useful for the investigation of non-equilibrium black hole thermodynamics and the linear response regime of backreaction problems in semiclassical gravity. |
1703.06626 | Boris Latosh | A.B. Arbuzov, B.N. Latosh | Fab Four self-interaction in quantum regime | 7 pages, 5 figures; minor corrections added | Arbuzov, A.B. & Latosh, B.N. Eur. Phys. J. C (2017) 77: 702 | 10.1140/epjc/s10052-017-5233-7 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Quantum behavior of the John Lagrangian from the Fab Four class of Covariant
Galileons is stud- ied. We consider one-loop corrections to the John
interaction due to cubic scalar field interactions. Counter Terms are
calculated, one of them belongs to the Fab Four class, the other one to
Covariant Galileons. The role of quantum corrections in context of cosmological
applications is discussed.
| [
{
"created": "Mon, 20 Mar 2017 07:42:59 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Apr 2017 16:22:44 GMT",
"version": "v2"
}
] | 2017-10-25 | [
[
"Arbuzov",
"A. B.",
""
],
[
"Latosh",
"B. N.",
""
]
] | Quantum behavior of the John Lagrangian from the Fab Four class of Covariant Galileons is stud- ied. We consider one-loop corrections to the John interaction due to cubic scalar field interactions. Counter Terms are calculated, one of them belongs to the Fab Four class, the other one to Covariant Galileons. The role of quantum corrections in context of cosmological applications is discussed. |
2307.04151 | Raihaneh Moti | Raihaneh Moti and Ali Shojai | On the Gravitational Precession Memory Effect for an Ensemble of
Gyroscopes | 23 pages, 9 figures, 1 table | null | 10.1088/1361-6382/ad1780 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the thermodynamic properties of a freely falling ensemble of
gyroscopes after the passage of a weak gravitational wave. Due to the
precession memory effect, the thermodynamic quantities will experience a change
because of the space-time perturbation. We discuss that this GravoThermo memory
effect potentially can be used for the detection of the gravitational waves.
| [
{
"created": "Sun, 9 Jul 2023 10:58:36 GMT",
"version": "v1"
},
{
"created": "Mon, 21 Aug 2023 15:35:32 GMT",
"version": "v2"
},
{
"created": "Tue, 21 Nov 2023 06:00:36 GMT",
"version": "v3"
}
] | 2024-01-05 | [
[
"Moti",
"Raihaneh",
""
],
[
"Shojai",
"Ali",
""
]
] | We study the thermodynamic properties of a freely falling ensemble of gyroscopes after the passage of a weak gravitational wave. Due to the precession memory effect, the thermodynamic quantities will experience a change because of the space-time perturbation. We discuss that this GravoThermo memory effect potentially can be used for the detection of the gravitational waves. |
2007.02309 | Vasilis Oikonomou | S.D. Odintsov, V.K. Oikonomou, F.P. Fronimos | Non-Minimally Coupled Einstein Gauss Bonnet Inflation Phenomenology in
View of GW170817 | AoP Accepted | null | 10.1016/j.aop.2020.168250 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the inflationary phenomenology of a non-minimally coupled Einstein
Gauss-Bonnet gravity theory, in the presence of a scalar potential, under the
condition that the gravitational wave speed of the primordial gravitational
waves is equal to unity, that is $c_T^2=1$, in natural units. The equations of
motion, which are derived directly from the gravitational action, form a system
of differential equations with respect to Hubble's parameter and the inflaton
field which are very complicated and cannot be solved analytically, even in the
minimal coupling case. In this paper, we present a variety of different
approximations which could be used, along with the constraint $c_T^2=1$, in
order to produce an inflationary phenomenology compatible with recent
observations. All the different approaches are able to lead to viable results
if the model coupling functions obey simple relations, however, different
approaches contain different approximations which must be obeyed during the
first horizon crossing, in order for the model to be rendered correct. Models
which may lead to a non-viable phenomenology are presented as well in order to
understand better the inner framework of this theory. Furthermore, since the
velocity of the gravitational waves is set equal to $c_T^2=1$, as stated by the
striking event of GW170817 recently, the non-minimal coupling function, the
Gauss-Bonnet scalar coupling and the scalar potential are related to each
other. Here, we shall assume no particular form of the scalar potential and we
choose freely the scalar functions coupled to the Ricci scalar and the
Gauss-Bonnet invariant. Certain models are also studied in order to assess the
phenomenological validity of the theory, but we need to note that all
approximations must hold true in order for a particular model to be valid.
| [
{
"created": "Sun, 5 Jul 2020 12:23:38 GMT",
"version": "v1"
}
] | 2020-08-26 | [
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
],
[
"Fronimos",
"F. P.",
""
]
] | We study the inflationary phenomenology of a non-minimally coupled Einstein Gauss-Bonnet gravity theory, in the presence of a scalar potential, under the condition that the gravitational wave speed of the primordial gravitational waves is equal to unity, that is $c_T^2=1$, in natural units. The equations of motion, which are derived directly from the gravitational action, form a system of differential equations with respect to Hubble's parameter and the inflaton field which are very complicated and cannot be solved analytically, even in the minimal coupling case. In this paper, we present a variety of different approximations which could be used, along with the constraint $c_T^2=1$, in order to produce an inflationary phenomenology compatible with recent observations. All the different approaches are able to lead to viable results if the model coupling functions obey simple relations, however, different approaches contain different approximations which must be obeyed during the first horizon crossing, in order for the model to be rendered correct. Models which may lead to a non-viable phenomenology are presented as well in order to understand better the inner framework of this theory. Furthermore, since the velocity of the gravitational waves is set equal to $c_T^2=1$, as stated by the striking event of GW170817 recently, the non-minimal coupling function, the Gauss-Bonnet scalar coupling and the scalar potential are related to each other. Here, we shall assume no particular form of the scalar potential and we choose freely the scalar functions coupled to the Ricci scalar and the Gauss-Bonnet invariant. Certain models are also studied in order to assess the phenomenological validity of the theory, but we need to note that all approximations must hold true in order for a particular model to be valid. |
1703.01724 | B. S. Ratanpal | S. K. Maurya, B. S. Ratanpal and M. Govender | Anisotropic stars for spherically symmetric spacetimes satisfying the
Karmarkar condition | null | Annals of Physics, 382, (2017), 36-49 | 10.1016/j.aop.2017.04.008 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new class of solution describing an anisotropic stellar configuration
satisfying Karmarkar's condition i.e. spherically symmetric metric of embedding
class 1, is reported. It has been shown that the compact star model is
physically well-behaved and meet all the physical requirements for a stable
configuration in hydrostatic equilibrium. Our model describes compact stars
like Vela X-1 and 4U1608-52 to a very good approximation.
| [
{
"created": "Mon, 6 Mar 2017 04:52:34 GMT",
"version": "v1"
},
{
"created": "Mon, 15 May 2017 16:22:51 GMT",
"version": "v2"
}
] | 2017-05-24 | [
[
"Maurya",
"S. K.",
""
],
[
"Ratanpal",
"B. S.",
""
],
[
"Govender",
"M.",
""
]
] | A new class of solution describing an anisotropic stellar configuration satisfying Karmarkar's condition i.e. spherically symmetric metric of embedding class 1, is reported. It has been shown that the compact star model is physically well-behaved and meet all the physical requirements for a stable configuration in hydrostatic equilibrium. Our model describes compact stars like Vela X-1 and 4U1608-52 to a very good approximation. |
2210.05281 | Fabian L\'aszl\'o Konstantin Wagner | Fabian Wagner | Modified uncertainty relations from classical and quantum gravity | PhD thesis containing an extensive literature on GUPs and EUPs.
110+10+44 pages. Based on publications arXiv:1905.09713, arXiv:2006.02188,
arXiv:2101.05552, arXiv:2110.11067, arXiv:2111.15583 and arXiv:2112.06758 | null | null | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A good hundred years after the necessity for a quantum theory of gravity was
acknowledged by Albert Einstein, the search for it continues to be an ongoing
endeavour. Nevertheless, the field still evolves rapidly as manifested by the
recent rise of quantum gravity phenomenology supported by an enormous surge in
experimental precision. In particular, the minimum length paradigm ingrained in
the program of generalized uncertainty principles (GUPs) is steadily growing in
importance. The present thesis is aimed at establishing a link between modified
uncertainty relations, derived from deformed canonical commutators, and curved
spaces - specifically, GUPs and nontrivial momentum space as well as the
related extended uncertainty principles (EUPs) and curved position space. In
that vein, we derive a new kind of EUP relating the radius of geodesic balls,
assumed to constrain the wave functions in the underlying Hilbert space, with
the standard deviation of the momentum operator. This result is gradually
generalized to relativistic particles in curved spacetime in accordance with
the 3+1 decomposition. In a sense pursuing the inverse route, we find an
explicit correspondence between theories yielding a GUP and quantum dynamics
set on non-Euclidean momentum space. Quantitatively, the coordinate
noncommutativity translates to momentum space curvature in the dual
description, allowing for an analogous transfer of constraints from the
literature. Finally, we find a formulation of quantum mechanics which proves
consistent on the arbitrarily curved cotangent bundle. Along these lines, we
show that the harmonic oscillator can not be used as a means to distinguish
between curvature in position and momentum space, thereby providing an explicit
instantiation of Born reciprocity in the context of curved spaces.
| [
{
"created": "Tue, 11 Oct 2022 09:26:23 GMT",
"version": "v1"
}
] | 2022-10-12 | [
[
"Wagner",
"Fabian",
""
]
] | A good hundred years after the necessity for a quantum theory of gravity was acknowledged by Albert Einstein, the search for it continues to be an ongoing endeavour. Nevertheless, the field still evolves rapidly as manifested by the recent rise of quantum gravity phenomenology supported by an enormous surge in experimental precision. In particular, the minimum length paradigm ingrained in the program of generalized uncertainty principles (GUPs) is steadily growing in importance. The present thesis is aimed at establishing a link between modified uncertainty relations, derived from deformed canonical commutators, and curved spaces - specifically, GUPs and nontrivial momentum space as well as the related extended uncertainty principles (EUPs) and curved position space. In that vein, we derive a new kind of EUP relating the radius of geodesic balls, assumed to constrain the wave functions in the underlying Hilbert space, with the standard deviation of the momentum operator. This result is gradually generalized to relativistic particles in curved spacetime in accordance with the 3+1 decomposition. In a sense pursuing the inverse route, we find an explicit correspondence between theories yielding a GUP and quantum dynamics set on non-Euclidean momentum space. Quantitatively, the coordinate noncommutativity translates to momentum space curvature in the dual description, allowing for an analogous transfer of constraints from the literature. Finally, we find a formulation of quantum mechanics which proves consistent on the arbitrarily curved cotangent bundle. Along these lines, we show that the harmonic oscillator can not be used as a means to distinguish between curvature in position and momentum space, thereby providing an explicit instantiation of Born reciprocity in the context of curved spaces. |
gr-qc/9909059 | Stuart L. Shapiro | Stuart L. Shapiro | Brief Comments on ``The Shapiro Conjecture, Prompt or Delayed Collapse
?'' by Miller, Suen and Tobias | 3 pages | null | null | null | gr-qc astro-ph | null | Recent numerical simulations address a conjecture by Shapiro that when two
neutron stars collide head-on from rest at infinity, sufficient thermal
pressure may be generated to support the hot remnant in quasi-static
equilibrium against collapse prior to neutrino cooling. The conjecture is meant
to apply even when the total remnant mass exceeds the maximum mass of a cold
neutron star. One set of simulations seems to corroborate the conjecture, while
another, involving higher mass progenitors each very close to the maximum mass,
does not. In both cases the total mass of the remnant exceeds the maximum mass.
We point out numerical subtleties in performing such simulations when the
progenitors are near the maximum mass; they can explain why the simulations
might have difficulty assessing the conjecture in such high-mass cases.
| [
{
"created": "Mon, 20 Sep 1999 16:38:31 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Shapiro",
"Stuart L.",
""
]
] | Recent numerical simulations address a conjecture by Shapiro that when two neutron stars collide head-on from rest at infinity, sufficient thermal pressure may be generated to support the hot remnant in quasi-static equilibrium against collapse prior to neutrino cooling. The conjecture is meant to apply even when the total remnant mass exceeds the maximum mass of a cold neutron star. One set of simulations seems to corroborate the conjecture, while another, involving higher mass progenitors each very close to the maximum mass, does not. In both cases the total mass of the remnant exceeds the maximum mass. We point out numerical subtleties in performing such simulations when the progenitors are near the maximum mass; they can explain why the simulations might have difficulty assessing the conjecture in such high-mass cases. |
1601.04395 | Jian-Liang Liu | Jian-Liang Liu and Luen-Fai Tam | Quasilocal Energy in Kerr Spacetime | There are some contents added in section 4 and also some refinement
on abstract and introduction | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we study the quasilocal energy as in [11] for a constant radius
surface in Kerr spacetime in Boyer-Lindquist coordinates. We show that under
suitable conditions for isometric embedding, for a stationary observer the
quasilocal energy defined in [11] for constant radius in a Kerr like spacetime
is exactly equal to the Brown-York quasilocal energy [2]. By some careful
estimations, we show that for a constant radius surface in the Kerr spacetime
which is outside the ergosphere the embedding conditions for the previous
result are satisfied. We discuss extremal solutions as described in [14]. We
prove a uniqueness result. We find all extremal solutions in the Minkowski
spacetime. Finally, we show that near the horizon of the Kerr spacetime for the
small rotation case the extremal solutions are trivial.
| [
{
"created": "Mon, 18 Jan 2016 03:53:59 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Feb 2016 06:01:13 GMT",
"version": "v2"
}
] | 2016-02-08 | [
[
"Liu",
"Jian-Liang",
""
],
[
"Tam",
"Luen-Fai",
""
]
] | In this work we study the quasilocal energy as in [11] for a constant radius surface in Kerr spacetime in Boyer-Lindquist coordinates. We show that under suitable conditions for isometric embedding, for a stationary observer the quasilocal energy defined in [11] for constant radius in a Kerr like spacetime is exactly equal to the Brown-York quasilocal energy [2]. By some careful estimations, we show that for a constant radius surface in the Kerr spacetime which is outside the ergosphere the embedding conditions for the previous result are satisfied. We discuss extremal solutions as described in [14]. We prove a uniqueness result. We find all extremal solutions in the Minkowski spacetime. Finally, we show that near the horizon of the Kerr spacetime for the small rotation case the extremal solutions are trivial. |
1703.10282 | Maxim Eingorn | Ruslan Brilenkov and Maxim Eingorn | Second-order Cosmological Perturbations Engendered by Point-like Masses | v2 = v1 + minor changes + extra discussion + new Refs.; comments
welcome | ApJ 845, 153 (2017) | 10.3847/1538-4357/aa81cd | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the $\Lambda$CDM framework, presenting nonrelativistic matter
inhomogeneities as discrete massive particles, we develop the second-order
cosmological perturbation theory. Our approach relies on the weak gravitational
field limit. The derived equations for the second-order scalar, vector and
tensor metric corrections are suitable at arbitrary distances including regions
with nonlinear contrasts of the matter density. We thoroughly verify fulfilment
of all Einstein equations as well as self-consistency of order assignments. In
addition, we achieve logical positive results in the Minkowski background
limit. Feasible investigations of the cosmological backreaction manifestations
by means of relativistic simulations are also outlined.
| [
{
"created": "Thu, 30 Mar 2017 01:19:37 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Sep 2017 15:05:17 GMT",
"version": "v2"
}
] | 2017-09-11 | [
[
"Brilenkov",
"Ruslan",
""
],
[
"Eingorn",
"Maxim",
""
]
] | In the $\Lambda$CDM framework, presenting nonrelativistic matter inhomogeneities as discrete massive particles, we develop the second-order cosmological perturbation theory. Our approach relies on the weak gravitational field limit. The derived equations for the second-order scalar, vector and tensor metric corrections are suitable at arbitrary distances including regions with nonlinear contrasts of the matter density. We thoroughly verify fulfilment of all Einstein equations as well as self-consistency of order assignments. In addition, we achieve logical positive results in the Minkowski background limit. Feasible investigations of the cosmological backreaction manifestations by means of relativistic simulations are also outlined. |
1402.4291 | Sudipta Das | Sudipta Das, Abdulla Al Mamon | An Interacting model of Dark Energy in Brans-Dicke theory | 12 pages, 15 figures. Accepted for publication in Astrophysics and
Space Science | null | 10.1007/s10509-014-1856-4 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper it is shown that in non-minimally coupled Brans-Dicke theory
containing a self-interacting potential, a suitable conformal transformation
can automatically give rise to an interaction between the normal matter and the
Brans-Dicke scalar field. Considering the scalar field in the Einstein frame as
the quintessence matter, it has been shown that such a non-minimal coupling
between the matter and the scalar field can give rise to a late time
accelerated expansion for the universe preceded by a decelerated expansion for
very high values of the Brans-Dicke parameter $\omega$. We have also studied
the observational constraints on the model parameters considering the Hubble
and Supernova data.
| [
{
"created": "Tue, 18 Feb 2014 11:09:48 GMT",
"version": "v1"
}
] | 2015-06-18 | [
[
"Das",
"Sudipta",
""
],
[
"Mamon",
"Abdulla Al",
""
]
] | In this paper it is shown that in non-minimally coupled Brans-Dicke theory containing a self-interacting potential, a suitable conformal transformation can automatically give rise to an interaction between the normal matter and the Brans-Dicke scalar field. Considering the scalar field in the Einstein frame as the quintessence matter, it has been shown that such a non-minimal coupling between the matter and the scalar field can give rise to a late time accelerated expansion for the universe preceded by a decelerated expansion for very high values of the Brans-Dicke parameter $\omega$. We have also studied the observational constraints on the model parameters considering the Hubble and Supernova data. |
gr-qc/0606119 | Mauricio Bellini | Agustin Membiela (Mar del Plata University), Mauricio Bellini (Mar del
Plata University & CONICET) | Quintessential inflation from a variable cosmological constant in a 5D
vacuum | final version (figure included) | Phys.Lett.B641:125-129,2006 | 10.1016/j.physletb.2006.08.043 | null | gr-qc | null | We explore an effective 4D cosmological model for the universe where the
variable cosmological constant governs its evolution and the pressure remains
negative along all the expansion. This model is introduced from a 5D vacuum
state where the (space-like) extra coordinate is considered as noncompact. The
expansion is produced by the inflaton field, which is considered as
nonminimally coupled to gravity. We conclude from experiental data that the
coupling of the inflaton with gravity should be weak, but variable in different
epochs of the evolution of the universe.
| [
{
"created": "Wed, 28 Jun 2006 15:54:12 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Sep 2006 15:19:05 GMT",
"version": "v2"
},
{
"created": "Wed, 16 May 2007 22:02:19 GMT",
"version": "v3"
}
] | 2010-03-26 | [
[
"Membiela",
"Agustin",
"",
"Mar del Plata University"
],
[
"Bellini",
"Mauricio",
"",
"Mar del\n Plata University & CONICET"
]
] | We explore an effective 4D cosmological model for the universe where the variable cosmological constant governs its evolution and the pressure remains negative along all the expansion. This model is introduced from a 5D vacuum state where the (space-like) extra coordinate is considered as noncompact. The expansion is produced by the inflaton field, which is considered as nonminimally coupled to gravity. We conclude from experiental data that the coupling of the inflaton with gravity should be weak, but variable in different epochs of the evolution of the universe. |
1601.05652 | Pekka Teerikorpi | Pekka Teerikorpi and Yurij Baryshev | Mattig's relation and dynamical distance indicators | 3 pages, 0 figures | null | 10.1002/asna.201512307 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss how the redshift (Mattig) method in Friedmann cosmology relates to
dynamical distance indicators based on Newton's gravity (Teerikorpi 2011). It
belongs to the class of indicators where the relevant length inside the system
is the distance itself (in this case the proper metric distance). As the
Friedmann model has Newtonian analogy, its use to infer distances has
instructive similarities to classical dynamical distance indicators. In view of
the theoretical exact linear distance-velocity law, we emphasize that it is
conceptually correct to derive the cosmological distance via the route:
redshift (primarily observed) --> space expansion velocity (not directly
observed) --> metric distance (physical length in "cm"). Important properties
of the proper metric distance are summarized.
| [
{
"created": "Thu, 21 Jan 2016 14:24:16 GMT",
"version": "v1"
}
] | 2016-03-16 | [
[
"Teerikorpi",
"Pekka",
""
],
[
"Baryshev",
"Yurij",
""
]
] | We discuss how the redshift (Mattig) method in Friedmann cosmology relates to dynamical distance indicators based on Newton's gravity (Teerikorpi 2011). It belongs to the class of indicators where the relevant length inside the system is the distance itself (in this case the proper metric distance). As the Friedmann model has Newtonian analogy, its use to infer distances has instructive similarities to classical dynamical distance indicators. In view of the theoretical exact linear distance-velocity law, we emphasize that it is conceptually correct to derive the cosmological distance via the route: redshift (primarily observed) --> space expansion velocity (not directly observed) --> metric distance (physical length in "cm"). Important properties of the proper metric distance are summarized. |
gr-qc/9506028 | Junichi Iwasaki | Junichi Iwasaki | Woven Geometries: Black Holes | latex 10 pages, 1 epsfig figures, University of Pittsburgh preprint | null | null | null | gr-qc | null | Tangles of loops which approximate an aspect of the Kerr-Newman black hole
metrics at large scales compared to the Planck length are constructed. The
physical aspect the tangles approximate is discussed. This construction may be
useful in the loop representation of canonical quantum gravity. Implications
and applications of the tangles are remarked.
| [
{
"created": "Fri, 16 Jun 1995 00:58:01 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Iwasaki",
"Junichi",
""
]
] | Tangles of loops which approximate an aspect of the Kerr-Newman black hole metrics at large scales compared to the Planck length are constructed. The physical aspect the tangles approximate is discussed. This construction may be useful in the loop representation of canonical quantum gravity. Implications and applications of the tangles are remarked. |
2108.12698 | Daniil Krichevskiy | Valentin Rudenko, Svetlana Andrusenko, Daniil Krichevskiy, Gevorg
Manucharyan | Optimization of the Euro-Asian network of gravitational detectors for
detecting the radiation of collapsing objects | arXiv admin note: substantial text overlap with arXiv:2009.05860 | null | 10.1088/1742-6596/2081/1/012011 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | A Euro-Asian network of four gravitational-wave (GW) interferometers is
considered, taking into account the plan to create such a detector in
Novosibirsk. The efficiency of the network is assessed by typical numerical
criteria, which also depend on the characteristics of the received signal. In
this work, we calculate the optimal orientation of the Novosibirsk detector for
the problem of detecting GW radiation accompanying the collapse of the
progenitor star with an initial angular momentum. The specificity of the
scenario is the presence of the so-called. bar stage deformation, for which the
shape of the emitted GW signal is known.
| [
{
"created": "Sat, 28 Aug 2021 19:37:04 GMT",
"version": "v1"
}
] | 2021-12-08 | [
[
"Rudenko",
"Valentin",
""
],
[
"Andrusenko",
"Svetlana",
""
],
[
"Krichevskiy",
"Daniil",
""
],
[
"Manucharyan",
"Gevorg",
""
]
] | A Euro-Asian network of four gravitational-wave (GW) interferometers is considered, taking into account the plan to create such a detector in Novosibirsk. The efficiency of the network is assessed by typical numerical criteria, which also depend on the characteristics of the received signal. In this work, we calculate the optimal orientation of the Novosibirsk detector for the problem of detecting GW radiation accompanying the collapse of the progenitor star with an initial angular momentum. The specificity of the scenario is the presence of the so-called. bar stage deformation, for which the shape of the emitted GW signal is known. |
gr-qc/0111075 | Zhang Chengmin | C.M. Zhang and A. Beesham | Rotation intrinsic spin coupling--the parallelism description | 10 pages, no figure | Mod.Phys.Lett.A16:2319-2326,2001 | 10.1142/S0217732301005886 | null | gr-qc | null | For the Dirac particle in the rotational system, the rotation induced inertia
effect is analogously treated as the modification of the "spin connection" on
the Dirac equation in the flat spacetime, which is determined by the equivalent
tetrad. From the point of view of parallelism description of spacetime, the
obtained torsion axial-vector is just the rotational angular velocity, which is
included in the "spin connection". Furthermore the axial-vector spin coupling
induced spin precession is just the rotation-spin(1/2) interaction predicted by
Mashhoon. Our derivation treatment is straightforward and simplified in the
geometrical meaning and physical conception, however the obtained conclusions
are consistent with that of the other previous work.
| [
{
"created": "Thu, 22 Nov 2001 10:23:14 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Zhang",
"C. M.",
""
],
[
"Beesham",
"A.",
""
]
] | For the Dirac particle in the rotational system, the rotation induced inertia effect is analogously treated as the modification of the "spin connection" on the Dirac equation in the flat spacetime, which is determined by the equivalent tetrad. From the point of view of parallelism description of spacetime, the obtained torsion axial-vector is just the rotational angular velocity, which is included in the "spin connection". Furthermore the axial-vector spin coupling induced spin precession is just the rotation-spin(1/2) interaction predicted by Mashhoon. Our derivation treatment is straightforward and simplified in the geometrical meaning and physical conception, however the obtained conclusions are consistent with that of the other previous work. |
gr-qc/9907071 | Jose Luis Jaramillo | V. Aldaya and J.L. Jaramillo | Space-time Structures from Critical Values in 2D Quantum Gravity | 22 pages, latex, no figures. Revised version with an effort in the
development of the underlying classical theory and the clarification of the
classical limit. To appear in Class. Quant. Grav | Class.Quant.Grav. 17 (2000) 1649-1666 | 10.1088/0264-9381/17/7/306 | null | gr-qc | null | A model for 2D Quantum Gravity is constructed out of the Virasoro group. To
this end the quantization of the abstract Virasoro group is revisited. For the
critical values of the conformal anomaly c, some quantum operators (SL(2,R)
generators) lose their dynamical content (they are no longer conjugated
operators). The notion of space-time itself in 2D gravity then arises as
associated with this kinematical SL(2,R) symmetry. An ensemble of different
copies of AdS do co-exist in this model with different weights, depending on
their curvature (which is proportional to \hbar^{2}) and they are connected by
gravity operators. This model suggests that, in general, quantum diffemorphisms
should not be imposed as constraints to the theory, except for the classical
limit.
| [
{
"created": "Thu, 22 Jul 1999 16:00:09 GMT",
"version": "v1"
},
{
"created": "Wed, 12 Jan 2000 17:41:50 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Aldaya",
"V.",
""
],
[
"Jaramillo",
"J. L.",
""
]
] | A model for 2D Quantum Gravity is constructed out of the Virasoro group. To this end the quantization of the abstract Virasoro group is revisited. For the critical values of the conformal anomaly c, some quantum operators (SL(2,R) generators) lose their dynamical content (they are no longer conjugated operators). The notion of space-time itself in 2D gravity then arises as associated with this kinematical SL(2,R) symmetry. An ensemble of different copies of AdS do co-exist in this model with different weights, depending on their curvature (which is proportional to \hbar^{2}) and they are connected by gravity operators. This model suggests that, in general, quantum diffemorphisms should not be imposed as constraints to the theory, except for the classical limit. |
1101.1459 | Ian Harry | Ian Harry, Stephen Fairhurst | A coherent triggered search for single spin compact binary coalescences
in gravitational wave data | 14 pages, 4 figures | Class.Quant.Grav. 28 (2011) 134008 | 10.1088/0264-9381/28/13/134008 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we present a method for conducting a coherent search for single
spin compact binary coalescences in gravitational wave data and compare this
search to the existing coincidence method for single spin searches. We propose
a method to characterize the regions of the parameter space where the single
spin search, both coincident and coherent, will increase detection efficiency
over the existing non-precessing search. We also show example results of the
coherent search on a stretch of data from LIGO's fourth science run but note
that a set of signal based vetoes will be needed before this search can be run
to try to make detections.
| [
{
"created": "Fri, 7 Jan 2011 15:55:55 GMT",
"version": "v1"
}
] | 2014-05-21 | [
[
"Harry",
"Ian",
""
],
[
"Fairhurst",
"Stephen",
""
]
] | In this paper we present a method for conducting a coherent search for single spin compact binary coalescences in gravitational wave data and compare this search to the existing coincidence method for single spin searches. We propose a method to characterize the regions of the parameter space where the single spin search, both coincident and coherent, will increase detection efficiency over the existing non-precessing search. We also show example results of the coherent search on a stretch of data from LIGO's fourth science run but note that a set of signal based vetoes will be needed before this search can be run to try to make detections. |
2402.14893 | Vasiliy P. Neznamov | V.P.Neznamov, S.Yu.Sedov, V.E.Shemarulin | The Quantum Model of Spinning Black Holes | 15 pages, 2 figures, 1 table | Int.J. Mod. Phys. A (2024) 2450012 | 10.1142/S0217751X2450012X | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a quantum model of spinning black holes with the integrable ring
singularities. For the charged Kerr-Newman quantum metric, the complete
regularization takes place at fixing of the maximal (cut-off) energy of
gravitons, $k_{UV}^{reg} = \hbar c/R_{S}^{reg}$.The domains of existence of
one, two and several event horizons $r_{q}$ are shown depending on the
parameters of modified Kerr and Kerr-Newman metrics.
| [
{
"created": "Thu, 22 Feb 2024 15:27:43 GMT",
"version": "v1"
}
] | 2024-02-26 | [
[
"Neznamov",
"V. P.",
""
],
[
"Sedov",
"S. Yu.",
""
],
[
"Shemarulin",
"V. E.",
""
]
] | We propose a quantum model of spinning black holes with the integrable ring singularities. For the charged Kerr-Newman quantum metric, the complete regularization takes place at fixing of the maximal (cut-off) energy of gravitons, $k_{UV}^{reg} = \hbar c/R_{S}^{reg}$.The domains of existence of one, two and several event horizons $r_{q}$ are shown depending on the parameters of modified Kerr and Kerr-Newman metrics. |
0811.2877 | Carlos A. R. Herdeiro | G. W. Gibbons, C. A. R. Herdeiro, C. M. Warnick and M. C. Werner | Stationary Metrics and Optical Zermelo-Randers-Finsler Geometry | 37 pages, 6 figures | Phys.Rev.D79:044022,2009 | 10.1103/PhysRevD.79.044022 | null | gr-qc hep-th math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a triality between the Zermelo navigation problem, the geodesic
flow on a Finslerian geometry of Randers type, and spacetimes in one dimension
higher admitting a timelike conformal Killing vector field. From the latter
viewpoint, the data of the Zermelo problem are encoded in a (conformally)
Painleve-Gullstrand form of the spacetime metric, whereas the data of the
Randers problem are encoded in a stationary generalisation of the usual optical
metric. We discuss how the spacetime viewpoint gives a simple and physical
perspective on various issues, including how Finsler geometries with constant
flag curvature always map to conformally flat spacetimes and that the Finsler
condition maps to either a causality condition or it breaks down at an
ergo-surface in the spacetime picture. The gauge equivalence in this network of
relations is considered as well as the connection to analogue models and the
viewpoint of magnetic flows. We provide a variety of examples.
| [
{
"created": "Tue, 18 Nov 2008 10:32:57 GMT",
"version": "v1"
}
] | 2009-05-05 | [
[
"Gibbons",
"G. W.",
""
],
[
"Herdeiro",
"C. A. R.",
""
],
[
"Warnick",
"C. M.",
""
],
[
"Werner",
"M. C.",
""
]
] | We consider a triality between the Zermelo navigation problem, the geodesic flow on a Finslerian geometry of Randers type, and spacetimes in one dimension higher admitting a timelike conformal Killing vector field. From the latter viewpoint, the data of the Zermelo problem are encoded in a (conformally) Painleve-Gullstrand form of the spacetime metric, whereas the data of the Randers problem are encoded in a stationary generalisation of the usual optical metric. We discuss how the spacetime viewpoint gives a simple and physical perspective on various issues, including how Finsler geometries with constant flag curvature always map to conformally flat spacetimes and that the Finsler condition maps to either a causality condition or it breaks down at an ergo-surface in the spacetime picture. The gauge equivalence in this network of relations is considered as well as the connection to analogue models and the viewpoint of magnetic flows. We provide a variety of examples. |
1703.04579 | Mark D. Roberts | Mark D. Roberts | Quantum Imploding Scalar Fields | 12 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The d'Alembertian $\Box\phi=0$ has solution $\phi=f(v)/r$, where $f$ is a
function of a null coordinate $v$, and this allows creation of a divergent
singularity out of nothing. In scalar-Einstein theory a similar situation
arises both for the scalar field and also for curvature invariants such as the
Ricci scalar. Here what happens in canonical quantum gravity is investigated.
Two minispace Hamiltonian systems are set up: extrapolation and approximation
of these indicates that the quantum mechanical wavefunction can be finite at
the origin.
| [
{
"created": "Wed, 15 Mar 2017 15:00:24 GMT",
"version": "v1"
}
] | 2017-03-16 | [
[
"Roberts",
"Mark D.",
""
]
] | The d'Alembertian $\Box\phi=0$ has solution $\phi=f(v)/r$, where $f$ is a function of a null coordinate $v$, and this allows creation of a divergent singularity out of nothing. In scalar-Einstein theory a similar situation arises both for the scalar field and also for curvature invariants such as the Ricci scalar. Here what happens in canonical quantum gravity is investigated. Two minispace Hamiltonian systems are set up: extrapolation and approximation of these indicates that the quantum mechanical wavefunction can be finite at the origin. |
2012.10213 | Quentin Vigneron | Quentin Vigneron | The 1+3-Newton-Cartan system and Newton-Cartan cosmology | Accepted for publication in Physical Review D; 11 pages; 1 figure | Phys. Rev. D 103, 064064 (2021) | 10.1103/PhysRevD.103.064064 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | We perform a covariant 1+3 split of the Newton-Cartan equations. The
resulting 3-dimensional system of equations, called \textit{the
1+3-Newton-Cartan equations}, is structurally equivalent to the 1+3-Einstein
equations. In particular it features the momentum constraint, and a choice of
adapted coordinates corresponds to a choice of shift vector. We show that these
equations reduce to the classical Newton equations without the need for special
Galilean coordinates. The solutions to the 1+3-Newton-Cartan equations are
equivalent to the solutions of the classical Newton equations if space is
assumed to be compact or if fall-off conditions at infinity are assumed. We
then show that space expansion arises as a fundamental field in Newton-Cartan
theory, and not by construction as in the classical formulation of Newtonian
cosmology. We recover the Buchert-Ehlers theorem for the general expansion law
in Newtonian cosmology.
| [
{
"created": "Fri, 18 Dec 2020 13:16:54 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Mar 2021 12:22:03 GMT",
"version": "v2"
}
] | 2021-03-31 | [
[
"Vigneron",
"Quentin",
""
]
] | We perform a covariant 1+3 split of the Newton-Cartan equations. The resulting 3-dimensional system of equations, called \textit{the 1+3-Newton-Cartan equations}, is structurally equivalent to the 1+3-Einstein equations. In particular it features the momentum constraint, and a choice of adapted coordinates corresponds to a choice of shift vector. We show that these equations reduce to the classical Newton equations without the need for special Galilean coordinates. The solutions to the 1+3-Newton-Cartan equations are equivalent to the solutions of the classical Newton equations if space is assumed to be compact or if fall-off conditions at infinity are assumed. We then show that space expansion arises as a fundamental field in Newton-Cartan theory, and not by construction as in the classical formulation of Newtonian cosmology. We recover the Buchert-Ehlers theorem for the general expansion law in Newtonian cosmology. |
1604.08129 | Javier Olmedo | Javier Olmedo | Evolution in totally constrained models: Schr\"odinger vs. Heisenberg
pictures | 18 pages, minor corrections have been incorporated | International Journal of Modern Physics D, 1642004 (2016) | 10.1142/S0218271816420049 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the relation between two evolution pictures that are currently
considered for totally constrained theories. Both descriptions are based on
Rovelli's evolving constants approach, where one identifies a (possibly local)
degree of freedom of the system as an internal time. This method is well
understood classically in several situations. The purpose of this paper is to
further analyze this approach at the quantum level. Concretely, we will compare
the (Schr\"odinger-like) picture where the physical states evolve in time with
the (Heisenberg-like) picture in which one defines parametrized observables (or
evolving constants of the motion). We will show that in the particular
situations considered in this manuscript (the parametrized relativistic
particle and a spatially flat homogeneous and isotropic spacetime coupled to a
massless scalar field) both descriptions are equivalent. We will finally
comment on possible issues and on the genericness of the equivalence between
both pictures.
| [
{
"created": "Wed, 27 Apr 2016 16:19:10 GMT",
"version": "v1"
},
{
"created": "Tue, 21 Jun 2016 17:09:35 GMT",
"version": "v2"
}
] | 2016-06-22 | [
[
"Olmedo",
"Javier",
""
]
] | We study the relation between two evolution pictures that are currently considered for totally constrained theories. Both descriptions are based on Rovelli's evolving constants approach, where one identifies a (possibly local) degree of freedom of the system as an internal time. This method is well understood classically in several situations. The purpose of this paper is to further analyze this approach at the quantum level. Concretely, we will compare the (Schr\"odinger-like) picture where the physical states evolve in time with the (Heisenberg-like) picture in which one defines parametrized observables (or evolving constants of the motion). We will show that in the particular situations considered in this manuscript (the parametrized relativistic particle and a spatially flat homogeneous and isotropic spacetime coupled to a massless scalar field) both descriptions are equivalent. We will finally comment on possible issues and on the genericness of the equivalence between both pictures. |
1405.2899 | Francisco Frutos-Alfaro Dr. rer. nat. | Paulo Montero-Camacho, Francisco Frutos-Alfaro, Carlos
Gutierrez-Chaves | Slowly rotating Curzon-Chazy Metric | null | Revista de Matem\'atica: Teor\'ia y Aplicaciones, 22 (2): 265-274,
2015 | 10.15517/rmta.v22i2.20833 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new rotation version of the Curzon-Chazy metric is found. This new metric
was obtained by means of a perturbation method, in order to include slow
rotation. The solution is then proved to fulfill the Einstein field equations
using a REDUCE program. Furthermore, the applications of this new solution are
discussed.
| [
{
"created": "Sat, 10 May 2014 01:53:05 GMT",
"version": "v1"
},
{
"created": "Tue, 27 May 2014 02:57:51 GMT",
"version": "v2"
},
{
"created": "Sun, 17 Jul 2016 01:38:41 GMT",
"version": "v3"
}
] | 2016-07-20 | [
[
"Montero-Camacho",
"Paulo",
""
],
[
"Frutos-Alfaro",
"Francisco",
""
],
[
"Gutierrez-Chaves",
"Carlos",
""
]
] | A new rotation version of the Curzon-Chazy metric is found. This new metric was obtained by means of a perturbation method, in order to include slow rotation. The solution is then proved to fulfill the Einstein field equations using a REDUCE program. Furthermore, the applications of this new solution are discussed. |
gr-qc/0302094 | Roy Maartens | John D Barrow (1), George Ellis (2), Roy Maartens (3), Christos Tsagas
(2) ((1) Cambridge, (2) Cape Town, (3) Portsmouth) | On the Stability of the Einstein Static Universe | some additional comments and references; version to appear in Class.
Quant. Grav | Class.Quant.Grav.20:L155-L164,2003 | 10.1088/0264-9381/20/11/102 | null | gr-qc astro-ph | null | We show using covariant techniques that the Einstein static universe
containing a perfect fluid is always neutrally stable against small
inhomogeneous vector and tensor perturbations and neutrally stable against
adiabatic scalar density inhomogeneities so long as c_{s}^2>1/5, and unstable
otherwise. We also show that the stability is not significantly changed by the
presence of a self-interacting scalar field source, but we find that spatially
homogeneous Bianchi type IX modes destabilise an Einstein static universe. The
implications of these results for the initial state of the universe and its
pre-inflationary evolution are also discussed.
| [
{
"created": "Mon, 24 Feb 2003 15:39:23 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Apr 2003 09:36:49 GMT",
"version": "v2"
}
] | 2011-07-19 | [
[
"Barrow",
"John D",
"",
"Cambridge"
],
[
"Ellis",
"George",
"",
"Cape Town"
],
[
"Maartens",
"Roy",
"",
"Portsmouth"
],
[
"Tsagas",
"Christos",
"",
"Cape Town"
]
] | We show using covariant techniques that the Einstein static universe containing a perfect fluid is always neutrally stable against small inhomogeneous vector and tensor perturbations and neutrally stable against adiabatic scalar density inhomogeneities so long as c_{s}^2>1/5, and unstable otherwise. We also show that the stability is not significantly changed by the presence of a self-interacting scalar field source, but we find that spatially homogeneous Bianchi type IX modes destabilise an Einstein static universe. The implications of these results for the initial state of the universe and its pre-inflationary evolution are also discussed. |
2101.11798 | Tousif Islam | Tousif Islam, Vijay Varma, Jackie Lodman, Scott E. Field, Gaurav
Khanna, Mark A. Scheel, Harald P. Pfeiffer, Davide Gerosa, and Lawrence E.
Kidder | Eccentric binary black hole surrogate models for the gravitational
waveform and remnant properties: comparable mass, nonspinning case | 19 pages, 15 figures | Phys. Rev. D 103, 064022 (2021) | 10.1103/PhysRevD.103.064022 | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | We develop new strategies to build numerical relativity surrogate models for
eccentric binary black hole systems, which are expected to play an increasingly
important role in current and future gravitational-wave detectors. We introduce
a new surrogate waveform model, \texttt{NRSur2dq1Ecc}, using 47 nonspinning,
equal-mass waveforms with eccentricities up to $0.2$ when measured at a
reference time of $5500M$ before merger. This is the first waveform model that
is directly trained on eccentric numerical relativity simulations and does not
require that the binary circularizes before merger. The model includes the
$(2,2)$, $(3,2)$, and $(4,4)$ spin-weighted spherical harmonic modes. We also
build a final black hole model, \texttt{NRSur2dq1EccRemnant}, which models the
mass, and spin of the remnant black hole. We show that our waveform model can
accurately predict numerical relativity waveforms with mismatches $\approx
10^{-3}$, while the remnant model can recover the final mass and dimensionless
spin with absolute errors smaller than $\approx 5 \times 10^{-4}M$ and $\approx
2 \times10^{-3}$ respectively. We demonstrate that the waveform model can also
recover subtle effects like mode-mixing in the ringdown signal without any
special ad-hoc modeling steps. Finally, we show that despite being trained only
on equal-mass binaries, \texttt{NRSur2dq1Ecc} can be reasonably extended up to
mass ratio $q\approx3$ with mismatches $\simeq 10^{-2}$ for eccentricities
smaller than $\sim 0.05$ as measured at a reference time of $2000M$ before
merger. The methods developed here should prove useful in the building of
future eccentric surrogate models over larger regions of the parameter space.
| [
{
"created": "Thu, 28 Jan 2021 03:25:19 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Mar 2021 19:23:18 GMT",
"version": "v2"
}
] | 2021-03-26 | [
[
"Islam",
"Tousif",
""
],
[
"Varma",
"Vijay",
""
],
[
"Lodman",
"Jackie",
""
],
[
"Field",
"Scott E.",
""
],
[
"Khanna",
"Gaurav",
""
],
[
"Scheel",
"Mark A.",
""
],
[
"Pfeiffer",
"Harald P.",
""
],
[
... | We develop new strategies to build numerical relativity surrogate models for eccentric binary black hole systems, which are expected to play an increasingly important role in current and future gravitational-wave detectors. We introduce a new surrogate waveform model, \texttt{NRSur2dq1Ecc}, using 47 nonspinning, equal-mass waveforms with eccentricities up to $0.2$ when measured at a reference time of $5500M$ before merger. This is the first waveform model that is directly trained on eccentric numerical relativity simulations and does not require that the binary circularizes before merger. The model includes the $(2,2)$, $(3,2)$, and $(4,4)$ spin-weighted spherical harmonic modes. We also build a final black hole model, \texttt{NRSur2dq1EccRemnant}, which models the mass, and spin of the remnant black hole. We show that our waveform model can accurately predict numerical relativity waveforms with mismatches $\approx 10^{-3}$, while the remnant model can recover the final mass and dimensionless spin with absolute errors smaller than $\approx 5 \times 10^{-4}M$ and $\approx 2 \times10^{-3}$ respectively. We demonstrate that the waveform model can also recover subtle effects like mode-mixing in the ringdown signal without any special ad-hoc modeling steps. Finally, we show that despite being trained only on equal-mass binaries, \texttt{NRSur2dq1Ecc} can be reasonably extended up to mass ratio $q\approx3$ with mismatches $\simeq 10^{-2}$ for eccentricities smaller than $\sim 0.05$ as measured at a reference time of $2000M$ before merger. The methods developed here should prove useful in the building of future eccentric surrogate models over larger regions of the parameter space. |
gr-qc/0410096 | Zuyao Sun | Zu-Yao Sun, You-Gen Shen | Phantom Cosmology with Non-minimally Coupled Real Scalar Field | 12 pages, 2 figures. Accepted for publication in Gen.Rel.Grav | Gen.Rel.Grav.37:243-251,2005 | 10.1007/s10714-005-0014-2 | null | gr-qc | null | We find that the expansion of the universe is accelerating by analyzing the
recent observation data of type $\textsc{I}a$ supernova(SN-Ia) .It indicates
that the equation of state of the dark energy might be smaller than -1,which
leads to the introduction of phantom models featured by its negative kinetic
energy to account for the regime of equation of state parameter $w<-1$.In this
paper the possibility of using a non-minimally coupled real scalar field as
phantom to realize the equation of state parameter $w<-1$ is discussed.The main
equations which govern the evolution of the universe are obtained.Then we
rewrite them with the observable quantities.
| [
{
"created": "Wed, 20 Oct 2004 16:18:05 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Sun",
"Zu-Yao",
""
],
[
"Shen",
"You-Gen",
""
]
] | We find that the expansion of the universe is accelerating by analyzing the recent observation data of type $\textsc{I}a$ supernova(SN-Ia) .It indicates that the equation of state of the dark energy might be smaller than -1,which leads to the introduction of phantom models featured by its negative kinetic energy to account for the regime of equation of state parameter $w<-1$.In this paper the possibility of using a non-minimally coupled real scalar field as phantom to realize the equation of state parameter $w<-1$ is discussed.The main equations which govern the evolution of the universe are obtained.Then we rewrite them with the observable quantities. |
1701.07420 | Patrick Wong | Patrick J. Wong | Shape Dynamical Loop Gravity from a Conformal Immirzi Parameter | 17 pages, published version | Int. J. Mod. Phys. D 26, 1750131 (2017) | 10.1142/S0218271817501310 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Immirzi parameter of loop quantum gravity is a one parameter ambiguity of
the theory whose precise interpretation is not universally agreed upon. It is
an inherent characteristic of the quantum theory as it appears in the spectra
of geometric operators, despite being irrelevant at the classical level. The
parameter's appearance in the area and volume spectra to the same power as the
Planck area suggest that it plays a role in determining the fundamental length
scale of space. In fact, a consistent interpretation is that it represents a
constant rescaling of the kinematical spatial geometry. An interesting
realization is that promoting the Immirzi parameter to be a general conformal
transformation leads to a system which can be identified as analogous to the
linking theory of shape dynamics. A three-dimensional gravitational gauge
connection is then constructed within the linking theory in a manner analogous
to loop quantum gravity, thereby facilitating the application of the
established procedure of loop quantization.
| [
{
"created": "Wed, 25 Jan 2017 18:45:21 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Jun 2017 07:28:34 GMT",
"version": "v2"
}
] | 2017-06-07 | [
[
"Wong",
"Patrick J.",
""
]
] | The Immirzi parameter of loop quantum gravity is a one parameter ambiguity of the theory whose precise interpretation is not universally agreed upon. It is an inherent characteristic of the quantum theory as it appears in the spectra of geometric operators, despite being irrelevant at the classical level. The parameter's appearance in the area and volume spectra to the same power as the Planck area suggest that it plays a role in determining the fundamental length scale of space. In fact, a consistent interpretation is that it represents a constant rescaling of the kinematical spatial geometry. An interesting realization is that promoting the Immirzi parameter to be a general conformal transformation leads to a system which can be identified as analogous to the linking theory of shape dynamics. A three-dimensional gravitational gauge connection is then constructed within the linking theory in a manner analogous to loop quantum gravity, thereby facilitating the application of the established procedure of loop quantization. |
2002.01148 | Zhie Liu | Zhi-E Liu, Xia Tan, Yu-Zhen Liu, Bei Sha, Jie Zhang, Shu-Zheng Yang | Lorentz symmetry violation and the tunneling radiation of fermions with
spin $1/2$ for Kerr Anti-de-Sitter black hole | 12 pages | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We studied the correction of the quantum tunneling radiation of fermions with
spin $1/2$ in Kerr Anti-de-Sitter black hole. First, the dynamic equation of
spin $1/2$ fermions was corrected using Lorentz's violation theory. Second, the
new expressions of the fermions quantum tunneling rate, the Hawking temperature
of the black hole and the entropy of the black hole were obtained according to
the corrected fermions dynamic equation. At last, some comments are made on the
results of our work.
| [
{
"created": "Tue, 4 Feb 2020 06:38:02 GMT",
"version": "v1"
}
] | 2020-02-05 | [
[
"Liu",
"Zhi-E",
""
],
[
"Tan",
"Xia",
""
],
[
"Liu",
"Yu-Zhen",
""
],
[
"Sha",
"Bei",
""
],
[
"Zhang",
"Jie",
""
],
[
"Yang",
"Shu-Zheng",
""
]
] | We studied the correction of the quantum tunneling radiation of fermions with spin $1/2$ in Kerr Anti-de-Sitter black hole. First, the dynamic equation of spin $1/2$ fermions was corrected using Lorentz's violation theory. Second, the new expressions of the fermions quantum tunneling rate, the Hawking temperature of the black hole and the entropy of the black hole were obtained according to the corrected fermions dynamic equation. At last, some comments are made on the results of our work. |
0810.0468 | Alexander Shatskiy Dr. | Alexander Shatskiy, I.D. Novikov, N.S. Kardashev | New analytic models of traversable wormholes | 15 pages, 2 figures | Phys.Usp.51:457-464,2008 | 10.1070/PU2008v051n05ABEH006581 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The analytic solution of the general relativity equations for spherically
symmetric wormholes are given. We investigate the special case of a
"traversable" wormhole i.e., one allowing the signal to pass through it. The
energy-momentum tensor of wormhole matter is represented as a superposition of
a spherically symmetric magnetic field and dust matter with negative matter
density. The dynamics of the model are investigated. We discuss both the
solution of the equation with a Lambda-term and without it. Superposing enough
dust matter, a magnetic field, and a Lambda-term can produce a static solution,
which turns out to be a spherical Multiverse model with an infinite number of
wormholes connected spherical universes. Corresponding solution can be static
and dynamic.
| [
{
"created": "Thu, 2 Oct 2008 16:23:50 GMT",
"version": "v1"
}
] | 2009-11-13 | [
[
"Shatskiy",
"Alexander",
""
],
[
"Novikov",
"I. D.",
""
],
[
"Kardashev",
"N. S.",
""
]
] | The analytic solution of the general relativity equations for spherically symmetric wormholes are given. We investigate the special case of a "traversable" wormhole i.e., one allowing the signal to pass through it. The energy-momentum tensor of wormhole matter is represented as a superposition of a spherically symmetric magnetic field and dust matter with negative matter density. The dynamics of the model are investigated. We discuss both the solution of the equation with a Lambda-term and without it. Superposing enough dust matter, a magnetic field, and a Lambda-term can produce a static solution, which turns out to be a spherical Multiverse model with an infinite number of wormholes connected spherical universes. Corresponding solution can be static and dynamic. |
1511.03530 | Christof Wetterich | C. Wetterich | Primordial cosmic fluctuations for variable gravity | new reference, small changes in text | null | 10.1088/1475-7516/2016/05/041 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The observability of primordial cosmic fluctuations does not require a
geometric horizon $H^{-1}$, which is exceeded temporarily by the wavelength of
fluctuations. The primordial information can be protected against later thermal
washout even if all relevant wavelengths remain smaller than $H^{-1}$. This is
demonstrated by formulating the equations governing the cosmic fluctuations in
a form that is manifestly invariant under conformal field transformations of
the metric. Beyond the field equations this holds for the defining equation for
the correlation function, as expressed by the inverse of the second functional
derivative of the quantum effective action. An observable almost scale
invariant spectrum does not need an expanding geometry. For a variable Planck
mass it can even arise in flat Minkowski space.
| [
{
"created": "Wed, 11 Nov 2015 15:23:39 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Dec 2015 13:01:28 GMT",
"version": "v2"
}
] | 2016-05-25 | [
[
"Wetterich",
"C.",
""
]
] | The observability of primordial cosmic fluctuations does not require a geometric horizon $H^{-1}$, which is exceeded temporarily by the wavelength of fluctuations. The primordial information can be protected against later thermal washout even if all relevant wavelengths remain smaller than $H^{-1}$. This is demonstrated by formulating the equations governing the cosmic fluctuations in a form that is manifestly invariant under conformal field transformations of the metric. Beyond the field equations this holds for the defining equation for the correlation function, as expressed by the inverse of the second functional derivative of the quantum effective action. An observable almost scale invariant spectrum does not need an expanding geometry. For a variable Planck mass it can even arise in flat Minkowski space. |
gr-qc/0508090 | Hamid Reza Sepangi | B. Vakili and H. R. Sepangi | Bianchi-I classical and quantum spinor cosmology with signature change | 11 pages, 1 figure | JCAP 0509 (2005) 008 | 10.1088/1475-7516/2005/09/008 | null | gr-qc hep-th | null | We study the classical and quantum evolution of a universe in which the
matter source is a massive Dirac spinor field and the universe is described by
a Bianchi type I metric. We focus attention on those classical solutions that
admit a degenerate metric in which the scale factors have smooth behavior in
transition from a Euclidean to a Lorentzian domain and show that this
transition happens when the cosmological constant, $\Lambda$, is negative. The
resulting quantum cosmology and the corresponding Wheeler-DeWitt equation are
also studied and closed form expressions for the wave functions of the universe
is presented. We have shown that there is a close relationship between the
quantum states and signature changing classical solutions, suggesting a
mechanism for creation of a Lorentzian universe from a Euclidean region by a
continuous change of signature. The quantum solutions also represent a
quantization rule for the mass of the spinor field.
| [
{
"created": "Sun, 21 Aug 2005 11:01:10 GMT",
"version": "v1"
},
{
"created": "Sat, 10 Sep 2005 04:13:22 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Vakili",
"B.",
""
],
[
"Sepangi",
"H. R.",
""
]
] | We study the classical and quantum evolution of a universe in which the matter source is a massive Dirac spinor field and the universe is described by a Bianchi type I metric. We focus attention on those classical solutions that admit a degenerate metric in which the scale factors have smooth behavior in transition from a Euclidean to a Lorentzian domain and show that this transition happens when the cosmological constant, $\Lambda$, is negative. The resulting quantum cosmology and the corresponding Wheeler-DeWitt equation are also studied and closed form expressions for the wave functions of the universe is presented. We have shown that there is a close relationship between the quantum states and signature changing classical solutions, suggesting a mechanism for creation of a Lorentzian universe from a Euclidean region by a continuous change of signature. The quantum solutions also represent a quantization rule for the mass of the spinor field. |
2011.15070 | Emmanuil Saridakis | W. El Hanafy and Emmanuel N. Saridakis | $f(T)$ cosmology: From Pseudo-Bang to Pseudo-Rip | 32 pages, 8 figures, 1 table, version published in JCAP | JCAP 09 (2021) 019 | 10.1088/1475-7516/2021/09/019 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the complete universe evolution in the framework of $f(T)$
cosmology. We first study the requirements at the kinematic level and we
introduce a simple scale factor with the necessary features. Performing a
detailed analysis of the phase portrait we show that the universe begins in the
infinite past from a phase where the scale factor goes to zero but the Hubble
parameter goes to a constant, and its derivative to zero. Since these features
resemble those of the Pseudo-Rip fate but in a reverted way, we call this
initial phase as Pseudo-Bang. Then the universe evolves in a first inflationary
phase, a cosmological turnaround and a bounce, after which we have a second
inflationary regime with a successful exit. Subsequently we obtain the standard
thermal history and the sequence of radiation, matter and late-time
acceleration epochs, showing that the universe will result in an everlasting
Pseudo-Rip phase. Finally, taking advantage of the fact that the field
equations of $f(T)$ gravity are of second order, and therefore the
corresponding autonomous dynamical system is one dimensional, we incorporate
the aforementioned kinematic features and we reconstruct the specific $f(T)$
form that can dynamically generate the Pseudo-Bang cosmological scenario.
Lastly, we examine the evolution of the primordial fluctuations showing that
they are initially sub-horizon, and we show that the total fluid does not
exhibit any singular behaviour at the phantom crossing points, while the
torsional fluid experiences them as Type II singular phases.
| [
{
"created": "Mon, 30 Nov 2020 18:08:26 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Sep 2021 17:51:49 GMT",
"version": "v2"
}
] | 2021-09-16 | [
[
"Hanafy",
"W. El",
""
],
[
"Saridakis",
"Emmanuel N.",
""
]
] | We investigate the complete universe evolution in the framework of $f(T)$ cosmology. We first study the requirements at the kinematic level and we introduce a simple scale factor with the necessary features. Performing a detailed analysis of the phase portrait we show that the universe begins in the infinite past from a phase where the scale factor goes to zero but the Hubble parameter goes to a constant, and its derivative to zero. Since these features resemble those of the Pseudo-Rip fate but in a reverted way, we call this initial phase as Pseudo-Bang. Then the universe evolves in a first inflationary phase, a cosmological turnaround and a bounce, after which we have a second inflationary regime with a successful exit. Subsequently we obtain the standard thermal history and the sequence of radiation, matter and late-time acceleration epochs, showing that the universe will result in an everlasting Pseudo-Rip phase. Finally, taking advantage of the fact that the field equations of $f(T)$ gravity are of second order, and therefore the corresponding autonomous dynamical system is one dimensional, we incorporate the aforementioned kinematic features and we reconstruct the specific $f(T)$ form that can dynamically generate the Pseudo-Bang cosmological scenario. Lastly, we examine the evolution of the primordial fluctuations showing that they are initially sub-horizon, and we show that the total fluid does not exhibit any singular behaviour at the phantom crossing points, while the torsional fluid experiences them as Type II singular phases. |
gr-qc/9411072 | Luis Octavio Pimentel | Pimentel L O and Obregon O | Quantum Cosmology for a Quadratic Theory of Gravity | 13 pages, latex,no figures | Class.Quant.Grav.11:2219-2223,1994; ERRATUM-ibid.11:2833,1994 | 10.1088/0264-9381/11/9/007 | UAMI-AG-940021 | gr-qc | null | For pure fourth order (${\cal{L}} \propto R^2$) quantum cosmology the
Wheeler-DeWitt equation is solved exactly for the closed homogeneous and
isotropic model. It is shown that by imposing as boundary condition that $\Psi
= 0$ at the origin of the universe the wave functions behave as suggested by
Vilenkin.
| [
{
"created": "Tue, 29 Nov 1994 21:46:23 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"O",
"Pimentel L",
""
],
[
"O",
"Obregon",
""
]
] | For pure fourth order (${\cal{L}} \propto R^2$) quantum cosmology the Wheeler-DeWitt equation is solved exactly for the closed homogeneous and isotropic model. It is shown that by imposing as boundary condition that $\Psi = 0$ at the origin of the universe the wave functions behave as suggested by Vilenkin. |
2208.11906 | Chi-Yong Lin | Chen-Yu Wang, Da-Shin Lee, and Chi-Yong Lin | Null and time-like geodesics in Kerr-Newman black hole exterior | 50 pages, 18 figures | null | 10.1103/PhysRevD.106.084048 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the null and time-like geodesics of the light and the neutral
particles respectively in the exterior of Kerr-Newman black holes. The geodesic
equations are known to be written as a set of first-order differential
equations in Mino time from which the angular and radial potentials can be
defined. We classify the roots for both potentials, and mainly focus on those
of the radial potential with an emphasis on the effect from the charge of the
black holes. We then obtain the solutions of the trajectories in terms of the
elliptical integrals and the Jacobian elliptic functions for both null and
time-like geodesics, which are manifestly real functions of the Mino time that
the initial conditions can be explicitly specified. We also describe the
details of how to reduce those solutions into the cases of the spherical
orbits. The effect of the black hole's charge decreases the radii of the
spherical motion of the light and the particle for both direct and retrograde
motions. In particular, we focus on the light/particle boomerang of the
spherical orbits due to the frame dragging from the back hole's spin with the
effect from the charge of the black hole. To sustain the change of the
azimuthal angle of the light rays, say for example $\Delta \phi=\pi$ during the
whole trip, the presence of the black hole's charge decreases the radius of the
orbit and consequently reduces the needed values of the black hole's spin. As
for the particle boomerang, the particle's inertia renders smaller change of
the angle $\Delta \phi$ as compared with the light boomerang. Moreover, the
black hole's charge also results in the smaller angle change $\Delta \phi$ of
the particle than that in the Kerr case. The implications of the obtained
results to observations are discussed.
| [
{
"created": "Thu, 25 Aug 2022 07:41:06 GMT",
"version": "v1"
}
] | 2022-11-09 | [
[
"Wang",
"Chen-Yu",
""
],
[
"Lee",
"Da-Shin",
""
],
[
"Lin",
"Chi-Yong",
""
]
] | We study the null and time-like geodesics of the light and the neutral particles respectively in the exterior of Kerr-Newman black holes. The geodesic equations are known to be written as a set of first-order differential equations in Mino time from which the angular and radial potentials can be defined. We classify the roots for both potentials, and mainly focus on those of the radial potential with an emphasis on the effect from the charge of the black holes. We then obtain the solutions of the trajectories in terms of the elliptical integrals and the Jacobian elliptic functions for both null and time-like geodesics, which are manifestly real functions of the Mino time that the initial conditions can be explicitly specified. We also describe the details of how to reduce those solutions into the cases of the spherical orbits. The effect of the black hole's charge decreases the radii of the spherical motion of the light and the particle for both direct and retrograde motions. In particular, we focus on the light/particle boomerang of the spherical orbits due to the frame dragging from the back hole's spin with the effect from the charge of the black hole. To sustain the change of the azimuthal angle of the light rays, say for example $\Delta \phi=\pi$ during the whole trip, the presence of the black hole's charge decreases the radius of the orbit and consequently reduces the needed values of the black hole's spin. As for the particle boomerang, the particle's inertia renders smaller change of the angle $\Delta \phi$ as compared with the light boomerang. Moreover, the black hole's charge also results in the smaller angle change $\Delta \phi$ of the particle than that in the Kerr case. The implications of the obtained results to observations are discussed. |
1803.03271 | Christopher Moore | Vitor Cardoso, Taishi Ikeda, Christopher J. Moore, and Chul-Moon Yoo | Remarks on the maximum luminosity | 10 pages (including appendices), 4 figures, 1 table, submitted to
Phys. Rev. D | Phys. Rev. D 97, 084013 (2018) | 10.1103/PhysRevD.97.084013 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The quest for fundamental limitations on physical processes is old and
venerable. Here, we investigate the maximum possible power, or luminosity, that
any event can produce. We show, via full nonlinear simulations of Einstein's
equations, that there exist initial conditions which give rise to arbitrarily
large luminosities. However, the requirement that there is no past horizon in
the spacetime seems to limit the luminosity to below the Planck value, ${{\cal
L}_\textrm{P}\!=\!c^5/G}$. Numerical relativity simulations of critical
collapse yield the largest luminosities observed to date, ${\approx \! 0.2
{\cal L}_\textrm{P}}$. We also present an analytic solution to the Einstein
equations which seems to give an unboundedly large luminosity; this will guide
future numerical efforts to investigate super-Planckian luminosities.
| [
{
"created": "Thu, 8 Mar 2018 19:00:08 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Apr 2018 13:56:11 GMT",
"version": "v2"
}
] | 2018-04-12 | [
[
"Cardoso",
"Vitor",
""
],
[
"Ikeda",
"Taishi",
""
],
[
"Moore",
"Christopher J.",
""
],
[
"Yoo",
"Chul-Moon",
""
]
] | The quest for fundamental limitations on physical processes is old and venerable. Here, we investigate the maximum possible power, or luminosity, that any event can produce. We show, via full nonlinear simulations of Einstein's equations, that there exist initial conditions which give rise to arbitrarily large luminosities. However, the requirement that there is no past horizon in the spacetime seems to limit the luminosity to below the Planck value, ${{\cal L}_\textrm{P}\!=\!c^5/G}$. Numerical relativity simulations of critical collapse yield the largest luminosities observed to date, ${\approx \! 0.2 {\cal L}_\textrm{P}}$. We also present an analytic solution to the Einstein equations which seems to give an unboundedly large luminosity; this will guide future numerical efforts to investigate super-Planckian luminosities. |
0709.3465 | Tim Koslowski A | Tim A. Koslowski | Dynamical Quantum Geometry (DQG Programme) | 19 pages, LaTeX, 3 figures | null | null | null | gr-qc | null | In this brief note (written as a lengthy letter), we describe the
construction of a representation for the Weyl-algebra underlying Loop Quantum
Geometry constructed from a diffeomorphism variant state, which corresponds to
a ''condensate'' of Loop Quantum Geometry, resembling a static spatial
geometry. We present the kinematical GNS-representation and the gauge- and
diffeomorphism invariant Hilbert space representation and show that the
expectation values of the geometric operators take essentialy classical values
plus quantum corrections, which is similar to a ''local condensate'' of quantum
geometry. We describe the idea for the construction of a scale dependent
asymptotic map into a family of scale dependent lattice gauge theories, where
scale separates the essential geometry and a low energy effective theory, which
is described as degrees of freedom in the lattice gauge theory. If this idea
can be implemented then it is likely to turn out that this Hilbert space
contains in addition to gravity also gauge coupled ''extra degrees of
freedom'', which may not be dynamically irrelevant.
| [
{
"created": "Fri, 21 Sep 2007 15:59:06 GMT",
"version": "v1"
}
] | 2007-09-24 | [
[
"Koslowski",
"Tim A.",
""
]
] | In this brief note (written as a lengthy letter), we describe the construction of a representation for the Weyl-algebra underlying Loop Quantum Geometry constructed from a diffeomorphism variant state, which corresponds to a ''condensate'' of Loop Quantum Geometry, resembling a static spatial geometry. We present the kinematical GNS-representation and the gauge- and diffeomorphism invariant Hilbert space representation and show that the expectation values of the geometric operators take essentialy classical values plus quantum corrections, which is similar to a ''local condensate'' of quantum geometry. We describe the idea for the construction of a scale dependent asymptotic map into a family of scale dependent lattice gauge theories, where scale separates the essential geometry and a low energy effective theory, which is described as degrees of freedom in the lattice gauge theory. If this idea can be implemented then it is likely to turn out that this Hilbert space contains in addition to gravity also gauge coupled ''extra degrees of freedom'', which may not be dynamically irrelevant. |
gr-qc/0207087 | Dr Henk van Elst | Henk van Elst and Reza Tavakol | BritGravII - The Second British Gravity Meeting | 13 pages, LaTeX2e (11pt), uses packages times, mathptm, hyperref | null | null | null | gr-qc | null | The second of the annual BritGrav meetings on current research in
Gravitational Physics in Britain took place at the School of Mathematical
Sciences of Queen Mary, University of London on June 10/11, 2002. 47 plenary
talks of 12min duration were given. We make available the abstracts of the
talks and the references to the electronic preprints at arXiv.org where they
exist.
| [
{
"created": "Tue, 23 Jul 2002 16:34:51 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"van Elst",
"Henk",
""
],
[
"Tavakol",
"Reza",
""
]
] | The second of the annual BritGrav meetings on current research in Gravitational Physics in Britain took place at the School of Mathematical Sciences of Queen Mary, University of London on June 10/11, 2002. 47 plenary talks of 12min duration were given. We make available the abstracts of the talks and the references to the electronic preprints at arXiv.org where they exist. |
gr-qc/0207110 | Alfonso Garcia-Parrado | Alfonso Garc\'ia-Parrado and Jos\'e M M Senovilla | Causal Relationship: a new tool for the causal characterization of
Lorentzian manifolds | 47 pages, 10 figures. Version to appear in Classical and Quantum
Gravity | Class.Quant.Grav.20:625-664,2003 | 10.1088/0264-9381/20/4/305 | null | gr-qc math-ph math.DG math.MP | null | We define and study a new kind of relation between two diffeomorphic
Lorentzian manifolds called {\em causal relation}, which is any diffeomorphism
characterized by mapping every causal vector of the first manifold onto a
causal vector of the second. We perform a thorough study of the mathematical
properties of causal relations and prove in particular that two given
Lorentzian manifolds (say $V$ and $W$) may be causally related only in one
direction (say from $V$ to $W$, but not from $W$ to $V$). This leads us to the
concept of causally equivalent (or {\em isocausal} in short) Lorentzian
manifolds as those mutually causally related. This concept is more general and
of a more basic nature than the conformal relationship, because we prove the
remarkable result that a conformal relation $\f$ is characterized by the fact
of being a causal relation of the {\em particular} kind in which both $\f$ and
$\f^{-1}$ are causal relations. For isocausal Lorentzian manifolds there are
one-to-one correspondences, which sometimes are non-trivial, between several
classes of their respective future (and past) objects. A more important feature
of isocausal Lorentzian manifolds is that they satisfy the same causality
constraints. This indicates that the causal equivalence provides a possible
characterization of the {\it basic causal structure}, in the sense of mutual
causal compatibility, for Lorentzian manifolds. Thus, we introduce a partial
order for the equivalence classes of isocausal Lorentzian manifolds providing a
classification of spacetimes in terms of their causal properties, and a
classification of all the causal structures that a given fixed manifold can
have. A full abstract inside the paper.
| [
{
"created": "Sat, 27 Jul 2002 13:02:07 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Nov 2002 17:22:13 GMT",
"version": "v2"
},
{
"created": "Wed, 15 Jan 2003 09:57:22 GMT",
"version": "v3"
}
] | 2016-08-16 | [
[
"García-Parrado",
"Alfonso",
""
],
[
"Senovilla",
"José M M",
""
]
] | We define and study a new kind of relation between two diffeomorphic Lorentzian manifolds called {\em causal relation}, which is any diffeomorphism characterized by mapping every causal vector of the first manifold onto a causal vector of the second. We perform a thorough study of the mathematical properties of causal relations and prove in particular that two given Lorentzian manifolds (say $V$ and $W$) may be causally related only in one direction (say from $V$ to $W$, but not from $W$ to $V$). This leads us to the concept of causally equivalent (or {\em isocausal} in short) Lorentzian manifolds as those mutually causally related. This concept is more general and of a more basic nature than the conformal relationship, because we prove the remarkable result that a conformal relation $\f$ is characterized by the fact of being a causal relation of the {\em particular} kind in which both $\f$ and $\f^{-1}$ are causal relations. For isocausal Lorentzian manifolds there are one-to-one correspondences, which sometimes are non-trivial, between several classes of their respective future (and past) objects. A more important feature of isocausal Lorentzian manifolds is that they satisfy the same causality constraints. This indicates that the causal equivalence provides a possible characterization of the {\it basic causal structure}, in the sense of mutual causal compatibility, for Lorentzian manifolds. Thus, we introduce a partial order for the equivalence classes of isocausal Lorentzian manifolds providing a classification of spacetimes in terms of their causal properties, and a classification of all the causal structures that a given fixed manifold can have. A full abstract inside the paper. |
1407.3980 | Petr Tretyakov | Petr V. Tretyakov | Dynamical stability of Minkowski space in higher order gravity | 15 pages; version accepted for publication in IJGMMP | Int. J. Geom. Methods Mod. Phys., 12, 1550094 (2015) | 10.1142/S0219887815500942 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the Minkowski stability problem in modified gravity by using
dynamical system approach. The method to investigate dynamical stability of
Minkowski space was proposed. This method was applied for some modified gravity
theories, such as $f(R)$ gravity, $f(R)+\alpha R\Box R$ gravity and
scalar-tensor gravity models with non-minimal kinetic coupling. It was shown
that in the case of $f(R)$ gravity Minkowski solution asymptotically stable in
ghost-free ($f'>0$) and tachyon-free ($f">0$) theories in expanding Universe
with respect to isotropic and basic anisotropic perturbations. In the case of
higher order gravity with $\alpha R\Box R$ correction conditions of Minkowski
stability with respect to isotropic perturbations significantly different:
$f'(0)<0$, $f"(0)<0$ and $3f'(0)+f"(0)^2/\alpha>0$. And in the case of
scalar-tensor gravity with non-minimal kinetic coupling Minkowski solution
asymptotically stable in expanding Universe with respect to isotropic
perturbations of metric. Moreover the developed method may be used for finding
additional restrictions on parameters of different modified gravity theories.
| [
{
"created": "Tue, 15 Jul 2014 13:15:56 GMT",
"version": "v1"
},
{
"created": "Tue, 19 May 2015 16:26:42 GMT",
"version": "v2"
}
] | 2015-10-21 | [
[
"Tretyakov",
"Petr V.",
""
]
] | We discuss the Minkowski stability problem in modified gravity by using dynamical system approach. The method to investigate dynamical stability of Minkowski space was proposed. This method was applied for some modified gravity theories, such as $f(R)$ gravity, $f(R)+\alpha R\Box R$ gravity and scalar-tensor gravity models with non-minimal kinetic coupling. It was shown that in the case of $f(R)$ gravity Minkowski solution asymptotically stable in ghost-free ($f'>0$) and tachyon-free ($f">0$) theories in expanding Universe with respect to isotropic and basic anisotropic perturbations. In the case of higher order gravity with $\alpha R\Box R$ correction conditions of Minkowski stability with respect to isotropic perturbations significantly different: $f'(0)<0$, $f"(0)<0$ and $3f'(0)+f"(0)^2/\alpha>0$. And in the case of scalar-tensor gravity with non-minimal kinetic coupling Minkowski solution asymptotically stable in expanding Universe with respect to isotropic perturbations of metric. Moreover the developed method may be used for finding additional restrictions on parameters of different modified gravity theories. |
gr-qc/9912054 | Philippos Papadopoulos | Philippos Papadopoulos (Portsmouth) and Jose A. Font (MPI, Garching) | Analysis of relativistic hydrodynamics in conservation form | 13 pages, uses iopart | null | null | null | gr-qc astro-ph | null | Formulations of Eulerian general relativistic ideal hydrodynamics in
conservation form are analyzed in some detail, with particular emphasis to
geometric source terms. Simple linear transformations of the equations are
introduced and the associated equivalence class is exploited for the
optimization of such sources. A significant reduction of their complexity is
readily possible in generic spacetimes. The local characteristic structure of
the standard member of the equivalence class is analyzed for a general equation
of state (EOS). This extends previous results restricted to the polytropic
case. The properties of all other members of the class, in particular
specialized forms employing Killing symmetries, are derivable from the standard
form. Special classes of EOS are identified for both spacelike and null
foliations, which lead to explicit inversion of the state vector and
computational savings. The entire approach is equally applicable to spacelike
or lightlike foliations and presents a complete proposal for numerical
relativistic hydrodynamics on stationary or dynamic geometries.
| [
{
"created": "Tue, 14 Dec 1999 15:37:39 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Papadopoulos",
"Philippos",
"",
"Portsmouth"
],
[
"Font",
"Jose A.",
"",
"MPI, Garching"
]
] | Formulations of Eulerian general relativistic ideal hydrodynamics in conservation form are analyzed in some detail, with particular emphasis to geometric source terms. Simple linear transformations of the equations are introduced and the associated equivalence class is exploited for the optimization of such sources. A significant reduction of their complexity is readily possible in generic spacetimes. The local characteristic structure of the standard member of the equivalence class is analyzed for a general equation of state (EOS). This extends previous results restricted to the polytropic case. The properties of all other members of the class, in particular specialized forms employing Killing symmetries, are derivable from the standard form. Special classes of EOS are identified for both spacelike and null foliations, which lead to explicit inversion of the state vector and computational savings. The entire approach is equally applicable to spacelike or lightlike foliations and presents a complete proposal for numerical relativistic hydrodynamics on stationary or dynamic geometries. |
2104.00536 | Manuel Hohmann | Manuel Hohmann | Variational Principles in Teleparallel Gravity Theories | 23 pages, no figures, journal version; invited contribution to the
Universe Special Issue "Teleparallel Gravity: Foundations and Observational
Constraints" | Universe 7 (2021) 114 | 10.3390/universe7050114 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the variational principle and derivation of the field equations for
different classes of teleparallel gravity theories, using both their
metric-affine and covariant tetrad formulations. These theories have in common
that in addition to the tetrad or metric, they employ a flat connection as
additional field variable, but differ by the presence of absence of torsion and
nonmetricity for this independent connection. Besides the different underlying
geometric formulation using a tetrad or metric as fundamental field variable,
one has different choices to introduce the conditions of vanishing curvature,
torsion and nonmetricity, either by imposing them a priori and correspondingly
restricting the variation of the action when the field equations are derived,
or by using Lagrange multipliers. Special care must be taken, since these
conditions form non-holonomic constraints. Here we show explicitly that all of
the aforementioned approaches are equivalent, and that the same set of field
equations is obtained, independently of the choice of the geometric formulation
and variation procedure. We further discuss consequences arising from the
diffeomorphism invariance of the gravitational action, and show how they
establish relations between the gravitational field equations.
| [
{
"created": "Tue, 30 Mar 2021 22:19:42 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Apr 2021 17:27:05 GMT",
"version": "v2"
}
] | 2021-04-22 | [
[
"Hohmann",
"Manuel",
""
]
] | We study the variational principle and derivation of the field equations for different classes of teleparallel gravity theories, using both their metric-affine and covariant tetrad formulations. These theories have in common that in addition to the tetrad or metric, they employ a flat connection as additional field variable, but differ by the presence of absence of torsion and nonmetricity for this independent connection. Besides the different underlying geometric formulation using a tetrad or metric as fundamental field variable, one has different choices to introduce the conditions of vanishing curvature, torsion and nonmetricity, either by imposing them a priori and correspondingly restricting the variation of the action when the field equations are derived, or by using Lagrange multipliers. Special care must be taken, since these conditions form non-holonomic constraints. Here we show explicitly that all of the aforementioned approaches are equivalent, and that the same set of field equations is obtained, independently of the choice of the geometric formulation and variation procedure. We further discuss consequences arising from the diffeomorphism invariance of the gravitational action, and show how they establish relations between the gravitational field equations. |
2001.08485 | Jinzhao Wang | Jinzhao Wang | The small sphere limit of quasilocal energy in higher dimensions along
lightcone cuts | 21 pages. Extended version of arXiv:1909.11973 | null | 10.1088/1361-6382/ab719d | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The problem of quasilocal energy has been extensively studied mainly in four
dimensions. Here we report results regarding the quasilocal energy in spacetime
dimension $n\geq 4$. After generalising three distinct quasilocal energy
definitions to higher dimensions under appropriate assumptions, we evaluate
their small sphere limits along lightcone cuts shrinking towards the lightcone
vertex. The results in vacuum are conveniently represented in terms of the
electromagnetic decompositions of the Weyl tensor. We find that the limits at
presence of matter yield the stress tensor as expected, but the vacuum limits
are in general not proportional to the Bel-Robinson superenergy $Q$ in
dimensions $n>4$. The result defies the role of the Bel-Robinson superenergy as
characterising the gravitational energy in higher dimensions, albeit the fact
that it uniquely generalises. Surprisingly, the Hawking energy and the
Brown-York energy exactly agree upon the small sphere limits across all
dimensions. The new vacuum limit $\mathcal{Q}$, however, cannot be interpreted
as a gravitational energy because of its non-positivity. Furthermore, we also
give the small sphere limits of the Kijowski-Epp-Liu-Yau type energy in higher
dimensions, and again we see $\mathcal{Q}$ in place of $Q$. Our work extends
earlier investigations of the small sphere limits [1, 2, 3, 4], and also
complements [5].
| [
{
"created": "Thu, 23 Jan 2020 13:10:12 GMT",
"version": "v1"
}
] | 2020-02-05 | [
[
"Wang",
"Jinzhao",
""
]
] | The problem of quasilocal energy has been extensively studied mainly in four dimensions. Here we report results regarding the quasilocal energy in spacetime dimension $n\geq 4$. After generalising three distinct quasilocal energy definitions to higher dimensions under appropriate assumptions, we evaluate their small sphere limits along lightcone cuts shrinking towards the lightcone vertex. The results in vacuum are conveniently represented in terms of the electromagnetic decompositions of the Weyl tensor. We find that the limits at presence of matter yield the stress tensor as expected, but the vacuum limits are in general not proportional to the Bel-Robinson superenergy $Q$ in dimensions $n>4$. The result defies the role of the Bel-Robinson superenergy as characterising the gravitational energy in higher dimensions, albeit the fact that it uniquely generalises. Surprisingly, the Hawking energy and the Brown-York energy exactly agree upon the small sphere limits across all dimensions. The new vacuum limit $\mathcal{Q}$, however, cannot be interpreted as a gravitational energy because of its non-positivity. Furthermore, we also give the small sphere limits of the Kijowski-Epp-Liu-Yau type energy in higher dimensions, and again we see $\mathcal{Q}$ in place of $Q$. Our work extends earlier investigations of the small sphere limits [1, 2, 3, 4], and also complements [5]. |
2010.03973 | Mohammad Ali Gorji | Katsuki Aoki, Mohammad Ali Gorji, Shuntaro Mizuno, Shinji Mukohyama | Inflationary gravitational waves in consistent $D\to 4$
Einstein-Gauss-Bonnet gravity | 30 pages, 4 figures, observational bound is corrected | null | 10.1088/1475-7516/2021/01/054 | YITP-20-124, IPMU20-0104 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the slow-roll single field inflation in the context of the
consistent $D\to4$ Einstein-Gauss-Bonnet gravity that was recently proposed in
\cite{Aoki:2020lig}. In addition to the standard attractor regime, we find a
new attractor regime which we call the Gauss-Bonnet attractor as the dominant
contribution comes from the Gauss-Bonnet term. Around this attractor solution,
we find power spectra and spectral tilts for the curvature perturbations and
gravitational waves (GWs) and also a model-independent consistency relation
among observable quantities. The Gauss-Bonnet term provides a nonlinear $k^4$
term to the GWs dispersion relation which has the same order as the standard
linear $k^2$ term at the time of horizon crossing around the Gauss-Bonnet
attractor. The Gauss-Bonnet attractor regime thus provides a new scenario for
the primordial GWs which can be tested by observations. Finally, we study
non-Gaussianity of GWs in this model and estimate the nonlinear parameters
$f^{s_1s_2s_3}_{\rm NL,\;sq}$ and $f^{s_1s_2s_3}_{\rm NL,\;eq}$ by fitting the
computed GWs bispectra with the local-type and equilateral-type templates
respectively at the squeezed limit and at the equilateral shape. For helicities
$(+++)$ and $( -- )$, $f^{s_1s_2s_3}_{\rm NL,\;sq}$ is larger while
$f^{s_1s_2s_3}_{\rm NL,\;eq}$ is larger for helicities $(++-)$ and $(--+)$.
| [
{
"created": "Wed, 7 Oct 2020 13:14:20 GMT",
"version": "v1"
},
{
"created": "Fri, 30 Apr 2021 10:11:43 GMT",
"version": "v2"
}
] | 2021-05-03 | [
[
"Aoki",
"Katsuki",
""
],
[
"Gorji",
"Mohammad Ali",
""
],
[
"Mizuno",
"Shuntaro",
""
],
[
"Mukohyama",
"Shinji",
""
]
] | We study the slow-roll single field inflation in the context of the consistent $D\to4$ Einstein-Gauss-Bonnet gravity that was recently proposed in \cite{Aoki:2020lig}. In addition to the standard attractor regime, we find a new attractor regime which we call the Gauss-Bonnet attractor as the dominant contribution comes from the Gauss-Bonnet term. Around this attractor solution, we find power spectra and spectral tilts for the curvature perturbations and gravitational waves (GWs) and also a model-independent consistency relation among observable quantities. The Gauss-Bonnet term provides a nonlinear $k^4$ term to the GWs dispersion relation which has the same order as the standard linear $k^2$ term at the time of horizon crossing around the Gauss-Bonnet attractor. The Gauss-Bonnet attractor regime thus provides a new scenario for the primordial GWs which can be tested by observations. Finally, we study non-Gaussianity of GWs in this model and estimate the nonlinear parameters $f^{s_1s_2s_3}_{\rm NL,\;sq}$ and $f^{s_1s_2s_3}_{\rm NL,\;eq}$ by fitting the computed GWs bispectra with the local-type and equilateral-type templates respectively at the squeezed limit and at the equilateral shape. For helicities $(+++)$ and $( -- )$, $f^{s_1s_2s_3}_{\rm NL,\;sq}$ is larger while $f^{s_1s_2s_3}_{\rm NL,\;eq}$ is larger for helicities $(++-)$ and $(--+)$. |
2107.06726 | Jose Luis Bl\'azquez-Salcedo | Jose Luis Bl\'azquez-Salcedo, Fech Scen Khoo, Jutta Kunz and Vincent
Preut | Polar Quasinormal Modes of Neutron Stars in Massive Scalar-Tensor
Theories | 24 pages, 10 figures; Invited contribution to the volume "Quasinormal
Modes in Relativistic Stars and Black Holes", published in Frontiers in
Physics | Front. Phys. 9:741427 (2021) | 10.3389/fphy.2021.741427 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study polar quasinormal modes of relativistic stars in scalar-tensor
theories, where we include a massive gravitational scalar field and employ the
standard Brans-Dicke coupling function. For the potential of the scalar field
we consider a simple mass term as well as a potential associated with $R^2$
gravity. The presence of the scalar field makes the spectrum of quasinormal
modes much richer than the spectrum in General Relativity. We here investigate
radial modes ($l=0$) and quadrupole modes ($l=2$). The general relativistic
$l=0$ normal modes turn into quasinormal modes in scalar-tensor theories, that
are able to propagate outside of the stars. In addition to the pressure-led
modes new scalar-led $\phi$-modes arise. We analyze the dependence of the
quasinormal mode frequencies and decay times on the scalar field mass.
| [
{
"created": "Wed, 14 Jul 2021 14:17:02 GMT",
"version": "v1"
}
] | 2021-09-15 | [
[
"Blázquez-Salcedo",
"Jose Luis",
""
],
[
"Khoo",
"Fech Scen",
""
],
[
"Kunz",
"Jutta",
""
],
[
"Preut",
"Vincent",
""
]
] | We study polar quasinormal modes of relativistic stars in scalar-tensor theories, where we include a massive gravitational scalar field and employ the standard Brans-Dicke coupling function. For the potential of the scalar field we consider a simple mass term as well as a potential associated with $R^2$ gravity. The presence of the scalar field makes the spectrum of quasinormal modes much richer than the spectrum in General Relativity. We here investigate radial modes ($l=0$) and quadrupole modes ($l=2$). The general relativistic $l=0$ normal modes turn into quasinormal modes in scalar-tensor theories, that are able to propagate outside of the stars. In addition to the pressure-led modes new scalar-led $\phi$-modes arise. We analyze the dependence of the quasinormal mode frequencies and decay times on the scalar field mass. |
1404.6639 | Yuxuan Peng | Li-Ming Cao, Yuxuan Peng, Jianfei Xu | Lichnerowicz-Type Theorems for Self-gravitating Systems with Nonlinear
Electromagnetic Fields | revtex4, 7 pages, no figure, one conclusion and an explanation for
the derivation added | Phys. Rev. D 90, 024046 (2014) | 10.1103/PhysRevD.90.024046 | ICTS-USTC-14-13 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a self-gravitating system containing a globally timelike Killing
vector and a nonlinear Born-Infeld electromagnetic field and scalar fields. We
prove that under certain boundary conditions (asymptotically flat/AdS) there
can't be any nontrivial field configurations in the spacetime. To explore
nontrivial solutions one should break any of the conditions we imposed. The
case with another type of nonlinear electromagnetic field is also analyzed, and
similar conclusions have been obtained under certain conditions.
| [
{
"created": "Sat, 26 Apr 2014 13:15:03 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Jul 2014 08:19:13 GMT",
"version": "v2"
}
] | 2014-07-22 | [
[
"Cao",
"Li-Ming",
""
],
[
"Peng",
"Yuxuan",
""
],
[
"Xu",
"Jianfei",
""
]
] | We consider a self-gravitating system containing a globally timelike Killing vector and a nonlinear Born-Infeld electromagnetic field and scalar fields. We prove that under certain boundary conditions (asymptotically flat/AdS) there can't be any nontrivial field configurations in the spacetime. To explore nontrivial solutions one should break any of the conditions we imposed. The case with another type of nonlinear electromagnetic field is also analyzed, and similar conclusions have been obtained under certain conditions. |
gr-qc/0508086 | Eduardo V. Correa Silva | G. A. Monerat, E. V. Correa Silva, G. Oliveira-Neto, L. G. Ferreira
Filho and N. A. Lemos | Quantization of Friedmann-Robertson-Walker spacetimes in the presence of
a negative cosmological constant and radiation | 34 pages, 3 figures | Phys.Rev. D73 (2006) 044022 | 10.1103/PhysRevD.73.044022 | null | gr-qc | null | We quantize three Friedmann-Robertson-Walker models in the presence of a
negative cosmological constant and radiation. The models differ from each other
by the constant curvature of the spatial sections, which may be positive,
negative or zero. They give rise to Wheeler-DeWitt equations for the scale
factor which have the form of the Schroedinger equation for the quartic
anharmonic oscillator. We find their eigenvalues and eigenfunctions by using a
method first developed by Chhajlany and Malnev, and use the eigenfunctions in
order to construct wave packets for each case and evaluate the time-dependent
expected value of the scale factors. We find for all of them that the expected
values of the scale factors oscillate between maximum and minimum values. Since
the expectation values of the scale factors never vanish, we conclude that
these models do not have singularities.
| [
{
"created": "Sat, 20 Aug 2005 15:29:37 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Monerat",
"G. A.",
""
],
[
"Silva",
"E. V. Correa",
""
],
[
"Oliveira-Neto",
"G.",
""
],
[
"Filho",
"L. G. Ferreira",
""
],
[
"Lemos",
"N. A.",
""
]
] | We quantize three Friedmann-Robertson-Walker models in the presence of a negative cosmological constant and radiation. The models differ from each other by the constant curvature of the spatial sections, which may be positive, negative or zero. They give rise to Wheeler-DeWitt equations for the scale factor which have the form of the Schroedinger equation for the quartic anharmonic oscillator. We find their eigenvalues and eigenfunctions by using a method first developed by Chhajlany and Malnev, and use the eigenfunctions in order to construct wave packets for each case and evaluate the time-dependent expected value of the scale factors. We find for all of them that the expected values of the scale factors oscillate between maximum and minimum values. Since the expectation values of the scale factors never vanish, we conclude that these models do not have singularities. |
1806.07742 | Prabir Rudra | Prabir Rudra (Asutosh College), Sayani Maity (Techno India Salt Lake) | Vaidya Spacetime in Brans-Dicke Gravity's Rainbow | 19 pages, 15 figures | null | 10.1140/epjc/s10052-018-6304-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this note we study an energy dependent deformation of a time dependent
geometry in the background of Brans-Dicke gravity theory. The study is
performed using the gravity's rainbow formalism. We compute the field equations
in Brans-Dicke gravity's rainbow using Vaidya metric which is a time dependent
geometry. We study a star collapsing under such conditions. Our prime objective
is to determine the nature of singularity formed as a result of gravitational
collapse and its strength. The idea is to test the validity of the cosmic
censorship hypothesis for our model. We have also studied the effect of such a
deformation on the thermalization process. In this regard we have calculated
the important thermodynamical quantities such as thermalization temperature,
Helmholtz free energy, specific heat and analyzed the behavior of such
quantities.
| [
{
"created": "Mon, 18 Jun 2018 19:05:13 GMT",
"version": "v1"
}
] | 2018-11-14 | [
[
"Rudra",
"Prabir",
"",
"Asutosh College"
],
[
"Maity",
"Sayani",
"",
"Techno India Salt Lake"
]
] | In this note we study an energy dependent deformation of a time dependent geometry in the background of Brans-Dicke gravity theory. The study is performed using the gravity's rainbow formalism. We compute the field equations in Brans-Dicke gravity's rainbow using Vaidya metric which is a time dependent geometry. We study a star collapsing under such conditions. Our prime objective is to determine the nature of singularity formed as a result of gravitational collapse and its strength. The idea is to test the validity of the cosmic censorship hypothesis for our model. We have also studied the effect of such a deformation on the thermalization process. In this regard we have calculated the important thermodynamical quantities such as thermalization temperature, Helmholtz free energy, specific heat and analyzed the behavior of such quantities. |
1512.05663 | Nigel Bishop | Nigel T. Bishop | Gravitational waves in a de Sitter universe | 9 pages | Phys. Rev. D 93, 044025 (2016) | 10.1103/PhysRevD.93.044025 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The construction of exact linearized solutions to the Einstein equations
within the Bondi-Sachs formalism is extended to the case of linearization about
de Sitter spacetime. The gravitational wave field measured by distant observers
is constructed, leading to a determination of the energy measured by such
observers. It is found that gravitational wave energy conservation does not
normally apply to inertial observers, but that it can be formulated for a class
of accelerated observers, i.e. with worldlines that are timelike but not
geodesic.
| [
{
"created": "Thu, 17 Dec 2015 16:43:42 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Mar 2016 11:39:24 GMT",
"version": "v2"
}
] | 2016-03-03 | [
[
"Bishop",
"Nigel T.",
""
]
] | The construction of exact linearized solutions to the Einstein equations within the Bondi-Sachs formalism is extended to the case of linearization about de Sitter spacetime. The gravitational wave field measured by distant observers is constructed, leading to a determination of the energy measured by such observers. It is found that gravitational wave energy conservation does not normally apply to inertial observers, but that it can be formulated for a class of accelerated observers, i.e. with worldlines that are timelike but not geodesic. |
2310.06018 | Tajron Juri\'c Dr. sc. | Nikola Herceg, Tajron Juri\'c, Andjelo Samsarov, Ivica Smoli\'c, Kumar
S. Gupta | Gravitational probe of quantum spacetime | 7 pages, 2 figures, improved version | Phys.Lett.B 854 (2024) 138716 | 10.1016/j.physletb.2024.138716 | RBI-ThPhys-2023-39; ZTF-EP-23-05 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A quest for phenomenological footprints of quantum gravity is among the
central scientific tasks in the rising era of gravitational wave astronomy. We
study gravitational wave dynamics within the noncommutative geometry framework,
based on a Drinfeld twist and newly proposed noncommutative Einstein equation,
and obtain the leading quantum correction to Regge-Wheeler potential up to
first order in the noncommutativity parameter. By calculating the quasinormal
mode frequencies we show that the noncommutative Schwarzschild black hole
remains stable under axial gravitational perturbations.
| [
{
"created": "Mon, 9 Oct 2023 18:00:01 GMT",
"version": "v1"
},
{
"created": "Mon, 22 Apr 2024 12:20:26 GMT",
"version": "v2"
}
] | 2024-05-24 | [
[
"Herceg",
"Nikola",
""
],
[
"Jurić",
"Tajron",
""
],
[
"Samsarov",
"Andjelo",
""
],
[
"Smolić",
"Ivica",
""
],
[
"Gupta",
"Kumar S.",
""
]
] | A quest for phenomenological footprints of quantum gravity is among the central scientific tasks in the rising era of gravitational wave astronomy. We study gravitational wave dynamics within the noncommutative geometry framework, based on a Drinfeld twist and newly proposed noncommutative Einstein equation, and obtain the leading quantum correction to Regge-Wheeler potential up to first order in the noncommutativity parameter. By calculating the quasinormal mode frequencies we show that the noncommutative Schwarzschild black hole remains stable under axial gravitational perturbations. |
1712.08724 | Wilson Rojas warojasc | W. A. Rojas C, J. R. Arenas S | Black Shells, Dirac's Field and the species problem | 31 pages, 11 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe a thermal atmosphere around a black hole as vacuum excitations
near to gravitational radius of a contracting thin black shell, i.e., in terms
of properties of the physical vacuum of fields around a thin shell of mass $M$
collapsing from infinity to the Schwarzschild radius according to an external
stationary observer. A natural explanation is introduced for the necessary
cutoff using the equations of motion of the shells. We make a thermodynamic
description of a fermionic field near the gravitational radius. Then a solution
to the species problem for two fields, scalar one and spinor one, is proposed.
Finally we get the Bekenstein-Hawking entropy as entanglement entropy of a
thermal atmosphere, independent from number of fields.
| [
{
"created": "Sat, 23 Dec 2017 06:52:15 GMT",
"version": "v1"
}
] | 2017-12-27 | [
[
"C",
"W. A. Rojas",
""
],
[
"S",
"J. R. Arenas",
""
]
] | We describe a thermal atmosphere around a black hole as vacuum excitations near to gravitational radius of a contracting thin black shell, i.e., in terms of properties of the physical vacuum of fields around a thin shell of mass $M$ collapsing from infinity to the Schwarzschild radius according to an external stationary observer. A natural explanation is introduced for the necessary cutoff using the equations of motion of the shells. We make a thermodynamic description of a fermionic field near the gravitational radius. Then a solution to the species problem for two fields, scalar one and spinor one, is proposed. Finally we get the Bekenstein-Hawking entropy as entanglement entropy of a thermal atmosphere, independent from number of fields. |
2010.12910 | Alexander B. Balakin | Alexander B. Balakin and Amir F. Shakirzyanov | Is the axionic dark matter an equilibrium system? | Based on the talk presented on the 17th Russian Conference on
Gravitation, Cosmology and Astrophysics (RUSGRAV-17) | Universe 2020, 6(11), 192 | 10.3390/universe6110192 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider an axionic dark matter model with a modified periodic potential
for the pseudoscalar field in the framework of the axionic extension of the
Einstein-aether theory. The modified potential is assumed to be equipped by the
guiding function, which depends on the expansion scalar constructed as the
trace of the covariant derivative of the aether velocity four-vector. The
equilibrium state of the axion field is defined as the state, for which the
modified potential itself and its first derivative with respect to the
pseudoscalar field are equal to zero. We apply the developed formalism to the
homogeneous isotropic cosmological model, and find the basic function, which
describes the equilibrium state of the axionic dark matter in the expanding
Universe.
| [
{
"created": "Sat, 24 Oct 2020 14:43:44 GMT",
"version": "v1"
}
] | 2020-10-27 | [
[
"Balakin",
"Alexander B.",
""
],
[
"Shakirzyanov",
"Amir F.",
""
]
] | We consider an axionic dark matter model with a modified periodic potential for the pseudoscalar field in the framework of the axionic extension of the Einstein-aether theory. The modified potential is assumed to be equipped by the guiding function, which depends on the expansion scalar constructed as the trace of the covariant derivative of the aether velocity four-vector. The equilibrium state of the axion field is defined as the state, for which the modified potential itself and its first derivative with respect to the pseudoscalar field are equal to zero. We apply the developed formalism to the homogeneous isotropic cosmological model, and find the basic function, which describes the equilibrium state of the axionic dark matter in the expanding Universe. |
2212.10893 | Yong Cai | Yong Cai | Generating enhanced parity-violating gravitational waves during
inflation with violation of the null energy condition | 24 pages, 16 figures; new references added, updated to match the
published version | Phys. Rev. D 107, 063512 (2023) | 10.1103/PhysRevD.107.063512 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | A violation of the null energy condition (NEC) during inflation in a
single-field inflation model will naturally enhance the amplitude of the parity
violation effect (defined by $\Delta\chi$) of inflationary primordial
gravitational waves (GWs), provided the inflaton is non-minimally coupled to a
gravitational Chern-Simons term. After going through the NEC-violating phase,
the Universe enters subsequent slow-roll inflation with a higher energy scale
(i.e., a greater Hubble parameter $H$), which results in an enhanced nearly
scale-invariant power spectrum (i.e., $P_{\rm T}$) of inflationary primordial
GWs in the high-frequency band, while $P_{\rm T}$ remains consistent with
observations in the frequency band of the cosmic microwave background.
Therefore, the violation of NEC during inflation will amplify the observability
(i.e., $P_{\rm T}\cdot\Delta\chi$) of the parity violation effect on small
scales. Intriguingly, our model has particular oscillatory features on
$\Delta\chi$ that may not be mimicked by others.
| [
{
"created": "Wed, 21 Dec 2022 10:03:49 GMT",
"version": "v1"
},
{
"created": "Sat, 11 Mar 2023 08:08:58 GMT",
"version": "v2"
}
] | 2023-03-14 | [
[
"Cai",
"Yong",
""
]
] | A violation of the null energy condition (NEC) during inflation in a single-field inflation model will naturally enhance the amplitude of the parity violation effect (defined by $\Delta\chi$) of inflationary primordial gravitational waves (GWs), provided the inflaton is non-minimally coupled to a gravitational Chern-Simons term. After going through the NEC-violating phase, the Universe enters subsequent slow-roll inflation with a higher energy scale (i.e., a greater Hubble parameter $H$), which results in an enhanced nearly scale-invariant power spectrum (i.e., $P_{\rm T}$) of inflationary primordial GWs in the high-frequency band, while $P_{\rm T}$ remains consistent with observations in the frequency band of the cosmic microwave background. Therefore, the violation of NEC during inflation will amplify the observability (i.e., $P_{\rm T}\cdot\Delta\chi$) of the parity violation effect on small scales. Intriguingly, our model has particular oscillatory features on $\Delta\chi$ that may not be mimicked by others. |
gr-qc/0410071 | Surhud More | Surhud Shrikant More | Higher Order Corrections to Black Hole Entropy | 9 pages, Revised version to appear in Classical and Quantum Gravity | Class.Quant.Grav. 22 (2005) 4129-4140 | 10.1088/0264-9381/22/19/021 | null | gr-qc hep-th | null | A scheme for calculating corrections to all orders to the entropy of any
thermodynamic system due to statistical fluctuations around equilibrium has
been developed. It is then applied to the BTZ black hole, AdS-Schwarzschild
black Hole and Schwarzschild black Hole in a cavity. The scheme that we present
is a model-independent scheme and hence universally applicable to all classical
black holes with positive specific heat. It has been seen earlier that the
microcanonical entropy of a system can be more accurately reproduced by
considering a logarithmic correction to the canonical entropy function. The
higher order corrections will be a step further in calculating the
microcanonical entropy of a black hole.
| [
{
"created": "Fri, 15 Oct 2004 16:53:55 GMT",
"version": "v1"
},
{
"created": "Wed, 31 Aug 2005 04:39:41 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"More",
"Surhud Shrikant",
""
]
] | A scheme for calculating corrections to all orders to the entropy of any thermodynamic system due to statistical fluctuations around equilibrium has been developed. It is then applied to the BTZ black hole, AdS-Schwarzschild black Hole and Schwarzschild black Hole in a cavity. The scheme that we present is a model-independent scheme and hence universally applicable to all classical black holes with positive specific heat. It has been seen earlier that the microcanonical entropy of a system can be more accurately reproduced by considering a logarithmic correction to the canonical entropy function. The higher order corrections will be a step further in calculating the microcanonical entropy of a black hole. |
gr-qc/0503085 | Luis Nunez A. | F. Aguirre, L. A. Nunez and T. Soldovieri | Variable Eddington Factor and Radiating Slowly Rotating Bodies in
General Relativity | 37 pages, 11 figures. Same results, we hope better presented. Two
last sections re-written | null | null | null | gr-qc astro-ph | null | We present an extension to a previous work to study the collapse of a
radiating, slow-rotating self-gravitating relativistic configuration. In order
to simulate dissipation effects due to the transfer of photons and/or neutrinos
within the matter configuration, we introduce the flux factor, the variable
Eddington factor and a closure relation between them. Rotation in General
Relativity is considered in the slow rotation approximation, i.e. tangential
velocity of every fluid element is much less than the speed of light and the
centrifugal forces are little compared with the gravitational ones. Solutions
are properly matched, up to the first order in the Kerr parameter, to the
exterior Kerr-Vaidya metric and the evolution of the physical variables are
obtained inside the matter configuration. To illustrate the method we work out
three models with different equations of state and several closure relations.
We have found that, for the closure relations considered, the matching
conditions implies that a total diffusion regime can not be attained at the
surface of the configuration. It has also been obtained that the eccentricity
at the surface of radiating configurations is greater for models near the
diffusion approximation than for those in the free streaming out limit. At
least for the static ``seed'' equations of state considered, the simulation we
performed show that these models have differential rotation and that the more
diffusive the model is, the slower it rotates.
| [
{
"created": "Sun, 20 Mar 2005 04:34:06 GMT",
"version": "v1"
},
{
"created": "Sat, 5 Aug 2006 19:12:28 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Aguirre",
"F.",
""
],
[
"Nunez",
"L. A.",
""
],
[
"Soldovieri",
"T.",
""
]
] | We present an extension to a previous work to study the collapse of a radiating, slow-rotating self-gravitating relativistic configuration. In order to simulate dissipation effects due to the transfer of photons and/or neutrinos within the matter configuration, we introduce the flux factor, the variable Eddington factor and a closure relation between them. Rotation in General Relativity is considered in the slow rotation approximation, i.e. tangential velocity of every fluid element is much less than the speed of light and the centrifugal forces are little compared with the gravitational ones. Solutions are properly matched, up to the first order in the Kerr parameter, to the exterior Kerr-Vaidya metric and the evolution of the physical variables are obtained inside the matter configuration. To illustrate the method we work out three models with different equations of state and several closure relations. We have found that, for the closure relations considered, the matching conditions implies that a total diffusion regime can not be attained at the surface of the configuration. It has also been obtained that the eccentricity at the surface of radiating configurations is greater for models near the diffusion approximation than for those in the free streaming out limit. At least for the static ``seed'' equations of state considered, the simulation we performed show that these models have differential rotation and that the more diffusive the model is, the slower it rotates. |
gr-qc/9212012 | Ctirad Klimcik | C. Klim\v{c}\'ik and P. Koln\'ik | Collisions of Einstein-Conformal Scalar Waves | 17 pages, LaTeX | null | 10.1103/PhysRevD.48.616 | PRA-HEP-92/19 | gr-qc | null | A large class of solutions of the Einstein-conformal scalar equations in
D=2+1 and D=3+1 is identified. They describe the collisions of asymptotic
conformal scalar waves and are generated from Einstein-minimally coupled scalar
spacetimes via a (generalized) Bekenstein transformation. Particular emphasis
is given to the study of the global properties and the singularity structure of
the obtained solutions. It is shown, that in the case of the absence of pure
gravitational radiation in the initial data, the formation of the final
singularity is not only generic, but is even inevitable.
| [
{
"created": "Fri, 18 Dec 1992 13:58:14 GMT",
"version": "v1"
}
] | 2016-08-17 | [
[
"Klimčík",
"C.",
""
],
[
"Kolník",
"P.",
""
]
] | A large class of solutions of the Einstein-conformal scalar equations in D=2+1 and D=3+1 is identified. They describe the collisions of asymptotic conformal scalar waves and are generated from Einstein-minimally coupled scalar spacetimes via a (generalized) Bekenstein transformation. Particular emphasis is given to the study of the global properties and the singularity structure of the obtained solutions. It is shown, that in the case of the absence of pure gravitational radiation in the initial data, the formation of the final singularity is not only generic, but is even inevitable. |
2011.09818 | Emmanuele Battista Dr. | Emmanuele Battista | Nonsingular bouncing cosmology in general relativity: physical analysis
of the spacetime defect | v4: 34 pages, 12 figures; Sec. 2 has been expanded and new references
have been added. Accepted for publication in Classical and Quantum Gravity | null | 10.1088/1361-6382/ac1900 | KA-TP-20-2020 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we describe physical effects occurring in the regularized
Robertson-Walker spacetime which can reveal the presence of the defect. Our
analysis is based on two main physical quantities: the compressive forces
acting on (human) observers and the energy possessed by massive particles and
photons during their dynamical evolution. In Sec. 3, we claim that with a
characteristic length scale of the order of the Planck length compressive
forces become so intense near the defect that no (human) observer is able to
cross it. In Sec. 4, we show that the energy exhibits an unusual character over
a small time interval around the bounce contrasting with the behaviour in the
standard cosmology picture. We conclude the paper with some considerations and
open problems related to our results.
| [
{
"created": "Thu, 19 Nov 2020 13:41:03 GMT",
"version": "v1"
},
{
"created": "Wed, 17 Mar 2021 12:28:41 GMT",
"version": "v2"
},
{
"created": "Wed, 12 May 2021 21:26:42 GMT",
"version": "v3"
},
{
"created": "Thu, 29 Jul 2021 11:32:59 GMT",
"version": "v4"
}
] | 2021-08-02 | [
[
"Battista",
"Emmanuele",
""
]
] | In this paper, we describe physical effects occurring in the regularized Robertson-Walker spacetime which can reveal the presence of the defect. Our analysis is based on two main physical quantities: the compressive forces acting on (human) observers and the energy possessed by massive particles and photons during their dynamical evolution. In Sec. 3, we claim that with a characteristic length scale of the order of the Planck length compressive forces become so intense near the defect that no (human) observer is able to cross it. In Sec. 4, we show that the energy exhibits an unusual character over a small time interval around the bounce contrasting with the behaviour in the standard cosmology picture. We conclude the paper with some considerations and open problems related to our results. |
0904.2774 | Thomas Sotiriou | Thomas P. Sotiriou | f(R) gravity, torsion and non-metricity | v2: slightly shortened version published in CQG as a Fast Track
Communication | Class.Quant.Grav.26:152001,2009 | 10.1088/0264-9381/26/15/152001 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | For both f(R) theories of gravity with an independent symmetric connection
(no torsion), usually referred to as Palatini f(R) gravity theories, and for
f(R) theories of gravity with torsion but no non-metricity, called U4 theories,
it has been shown that the independent connection can actually be eliminated
algebraically, as long as this connection does not couple to matter.
Remarkably, the outcome in both case is the same theory, which is dynamically
equivalent with an \omega_0=-3/2 Brans--Dicke theory. It is shown here that
even for the most general case of an independent connection with both
non-metricity and torsion one arrives at exactly the same theory as in the more
restricted cases. This generalizes the previous results and explains why
assuming that either the torsion or the the non-metricity vanishes ultimately
leads to the same theory. It also demonstrates that f(R) actions cannot support
an independent connection which carries dynamical degrees of freedom,
irrespectively of how general this connection is, at least as long as there is
no connection-matter coupling.
| [
{
"created": "Fri, 17 Apr 2009 20:05:06 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Jul 2009 16:45:32 GMT",
"version": "v2"
}
] | 2010-04-30 | [
[
"Sotiriou",
"Thomas P.",
""
]
] | For both f(R) theories of gravity with an independent symmetric connection (no torsion), usually referred to as Palatini f(R) gravity theories, and for f(R) theories of gravity with torsion but no non-metricity, called U4 theories, it has been shown that the independent connection can actually be eliminated algebraically, as long as this connection does not couple to matter. Remarkably, the outcome in both case is the same theory, which is dynamically equivalent with an \omega_0=-3/2 Brans--Dicke theory. It is shown here that even for the most general case of an independent connection with both non-metricity and torsion one arrives at exactly the same theory as in the more restricted cases. This generalizes the previous results and explains why assuming that either the torsion or the the non-metricity vanishes ultimately leads to the same theory. It also demonstrates that f(R) actions cannot support an independent connection which carries dynamical degrees of freedom, irrespectively of how general this connection is, at least as long as there is no connection-matter coupling. |
1102.2451 | Anil Zenginoglu C | An{\i}l Zengino\u{g}lu | A geometric framework for black hole perturbations | 4 pages, 1 figure | Phys.Rev.D83:127502,2011 | 10.1103/PhysRevD.83.127502 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Black hole perturbation theory is typically studied on time surfaces that
extend between the bifurcation sphere and spatial infinity. From a physical
point of view, however, it may be favorable to employ time surfaces that extend
between the future event horizon and future null infinity. This framework
resolves problems regarding the representation of quasinormal mode
eigenfunctions and the construction of short-ranged potentials for the
perturbation equations in frequency domain.
| [
{
"created": "Fri, 11 Feb 2011 22:21:41 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Jun 2011 04:04:30 GMT",
"version": "v2"
}
] | 2011-07-04 | [
[
"Zenginoğlu",
"Anıl",
""
]
] | Black hole perturbation theory is typically studied on time surfaces that extend between the bifurcation sphere and spatial infinity. From a physical point of view, however, it may be favorable to employ time surfaces that extend between the future event horizon and future null infinity. This framework resolves problems regarding the representation of quasinormal mode eigenfunctions and the construction of short-ranged potentials for the perturbation equations in frequency domain. |
gr-qc/9409035 | P. R. Brady | Patrick R Brady | Self-Similar Scalar Field Collapse: Naked Singularities and Critical
Behaviour | 27 pages including 5 encapsulated postcript figures in separate
compressed file, report NCL94-TP12 | Phys.Rev. D51 (1995) 4168-4176 | 10.1103/PhysRevD.51.4168 | null | gr-qc | null | Homothetic scalar field collapse is considered in this article. By making a
suitable choice of variables the equations are reduced to an autonomous system.
Then using a combination of numerical and analytic techniques it is shown that
there are two classes of solutions. The first consists of solutions with a
non-singular origin in which the scalar field collapses and disperses again.
There is a singularity at one point of these solutions, however it is not
visible to observers at finite radius. The second class of solutions includes
both black holes and naked singularities with a critical evolution (which is
neither) interpolating between these two extremes. The properties of these
solutions are discussed in detail. The paper also contains some speculation
about the significance of self-similarity in recent numerical studies.
| [
{
"created": "Fri, 16 Sep 1994 15:16:06 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Brady",
"Patrick R",
""
]
] | Homothetic scalar field collapse is considered in this article. By making a suitable choice of variables the equations are reduced to an autonomous system. Then using a combination of numerical and analytic techniques it is shown that there are two classes of solutions. The first consists of solutions with a non-singular origin in which the scalar field collapses and disperses again. There is a singularity at one point of these solutions, however it is not visible to observers at finite radius. The second class of solutions includes both black holes and naked singularities with a critical evolution (which is neither) interpolating between these two extremes. The properties of these solutions are discussed in detail. The paper also contains some speculation about the significance of self-similarity in recent numerical studies. |
2107.04359 | Alexandru Dima | Alexandru Dima, Miguel Bezares, Enrico Barausse | Dynamical Chameleon Neutron Stars: stability, radial oscillations and
scalar radiation in spherical symmetry | 21 pages, 17 figures | Phys. Rev. D 104, 084017 (2021) | 10.1103/PhysRevD.104.084017 | null | gr-qc astro-ph.CO astro-ph.HE hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Scalar-tensor theories whose phenomenology differs significantly from general
relativity on large (e.g. cosmological) scales do not typically pass local
experimental tests (e.g. in the solar system) unless they present a suitable
"screening mechanism". An example is provided by chameleon screening, whereby
the local general relativistic behavior is recovered in high density
environments, at least in weak-field and quasi-static configurations. Here, we
test the validity of chameleon screening in strong-field and highly
relativistic/dynamical conditions, by performing fully non-linear simulations
of neutron stars subjected to initial perturbations that cause them to
oscillate or even collapse to a black hole. We confirm that screened chameleon
stars are stable to sufficiently small radial oscillations, but that the
frequency spectrum of the latter shows deviations from the general relativistic
predictions. We also calculate the scalar fluxes produced during collapse to a
black hole, and comment on their detectability with future gravitational-wave
interferometers.
| [
{
"created": "Fri, 9 Jul 2021 10:51:34 GMT",
"version": "v1"
}
] | 2021-10-13 | [
[
"Dima",
"Alexandru",
""
],
[
"Bezares",
"Miguel",
""
],
[
"Barausse",
"Enrico",
""
]
] | Scalar-tensor theories whose phenomenology differs significantly from general relativity on large (e.g. cosmological) scales do not typically pass local experimental tests (e.g. in the solar system) unless they present a suitable "screening mechanism". An example is provided by chameleon screening, whereby the local general relativistic behavior is recovered in high density environments, at least in weak-field and quasi-static configurations. Here, we test the validity of chameleon screening in strong-field and highly relativistic/dynamical conditions, by performing fully non-linear simulations of neutron stars subjected to initial perturbations that cause them to oscillate or even collapse to a black hole. We confirm that screened chameleon stars are stable to sufficiently small radial oscillations, but that the frequency spectrum of the latter shows deviations from the general relativistic predictions. We also calculate the scalar fluxes produced during collapse to a black hole, and comment on their detectability with future gravitational-wave interferometers. |
1011.5399 | Valeria Kagramanova | Saskia Grunau and Valeria Kagramanova | Geodesics of electrically and magnetically charged test particles in the
Reissner-Nordstr\"om space-time: analytical solutions | null | Phys.Rev.D83:044009,2011 | 10.1103/PhysRevD.83.044009 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the full set of analytical solutions of the geodesic equations of
charged test particles in the Reissner-Nordstr\"om space-time in terms of the
Weierstra{\ss} $\wp$, $\sigma$ and $\zeta$ elliptic functions. Based on the
study of the polynomials in the $\vartheta$ and $r$ equations we characterize
the motion of test particles and discuss their properties. The motion of
charged test particles in the Reissner-Nordstr\"om space-time is compared with
the motion of neutral test particles in the field of a gravitomagnetic
monopole. Electrically or magnetically charged particles in the
Reissner-Nordstr\"om space-time with magnetic or electric charges,
respectively, move on cones similar to neutral test particles in the Taub-NUT
space-times.
| [
{
"created": "Wed, 24 Nov 2010 15:36:03 GMT",
"version": "v1"
}
] | 2011-02-18 | [
[
"Grunau",
"Saskia",
""
],
[
"Kagramanova",
"Valeria",
""
]
] | We present the full set of analytical solutions of the geodesic equations of charged test particles in the Reissner-Nordstr\"om space-time in terms of the Weierstra{\ss} $\wp$, $\sigma$ and $\zeta$ elliptic functions. Based on the study of the polynomials in the $\vartheta$ and $r$ equations we characterize the motion of test particles and discuss their properties. The motion of charged test particles in the Reissner-Nordstr\"om space-time is compared with the motion of neutral test particles in the field of a gravitomagnetic monopole. Electrically or magnetically charged particles in the Reissner-Nordstr\"om space-time with magnetic or electric charges, respectively, move on cones similar to neutral test particles in the Taub-NUT space-times. |
1910.12083 | Ben David Normann Mr. | Ben David Normann and Sigbj{\o}rn Hervik | Collins in Wonderland | 27 pages, 4 figures | 2020 Class. Quantum Grav. 37 145002 | 10.1088/1361-6382/ab8be7 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | What is the asymptotic future of a scalar-field model if the assumption of
isotropy is relaxed in generic, homogeneous space-times with general
relativity? This paper is a continuation of our previous work on Bianchi
cosmologies with a $p$-form field (where $p\,\in\,\{1,3\}$)---or equivalently:
an inhomogeneous, mass-less scalar gauge field with a homogeneous gradient. In
this work we investigate such matter sector in General Relativity, and restrict
to space-times of the particular Bianchi types VI$_0$ and VI$_{\tilde{h}}$,
where $\tilde{h}=h<0\,\cap\,\neq\,-1/9\,\cup\,-1$. We show that the previously
found fabric of exact solutions named Wonderland are future attractors in
$\mathcal{B}$(VI$_0$) and $\mathcal{B}$(VI$_{\tilde{h}}$), extending the
Collins perfect-fluid equilibrium set to include a $p$-form (with
$p\,\in\,\{1,3\}$). We also write down the line-element corresponding to
Wonderland in VI$_{\tilde{h}}$ and give explicit expressions for the underling
gauge-potential $\phi(t,\mathbf{x})$ corresponding to this solution. Simulation
of a path approaching Wonderland in Bianchi type I is also given.
| [
{
"created": "Sat, 26 Oct 2019 15:12:26 GMT",
"version": "v1"
},
{
"created": "Tue, 31 Mar 2020 10:48:47 GMT",
"version": "v2"
}
] | 2020-07-08 | [
[
"Normann",
"Ben David",
""
],
[
"Hervik",
"Sigbjørn",
""
]
] | What is the asymptotic future of a scalar-field model if the assumption of isotropy is relaxed in generic, homogeneous space-times with general relativity? This paper is a continuation of our previous work on Bianchi cosmologies with a $p$-form field (where $p\,\in\,\{1,3\}$)---or equivalently: an inhomogeneous, mass-less scalar gauge field with a homogeneous gradient. In this work we investigate such matter sector in General Relativity, and restrict to space-times of the particular Bianchi types VI$_0$ and VI$_{\tilde{h}}$, where $\tilde{h}=h<0\,\cap\,\neq\,-1/9\,\cup\,-1$. We show that the previously found fabric of exact solutions named Wonderland are future attractors in $\mathcal{B}$(VI$_0$) and $\mathcal{B}$(VI$_{\tilde{h}}$), extending the Collins perfect-fluid equilibrium set to include a $p$-form (with $p\,\in\,\{1,3\}$). We also write down the line-element corresponding to Wonderland in VI$_{\tilde{h}}$ and give explicit expressions for the underling gauge-potential $\phi(t,\mathbf{x})$ corresponding to this solution. Simulation of a path approaching Wonderland in Bianchi type I is also given. |
gr-qc/0002023 | Merced Montesinos | Merced Montesinos | Relational evolution of the degrees of freedom of generally covariant
quantum theories | 25 pages, no figures, Latex file. Revised version | Gen.Rel.Grav. 33 (2001) 1-28 | 10.1023/A:1002067601136 | null | gr-qc hep-th quant-ph | null | We study the classical and quantum dynamics of generally covariant theories
with vanishing a Hamiltonian and with a finite number of degrees of freedom. In
particular, the geometric meaning of the full solution of the relational
evolution of the degrees of freedom is displayed, which means the determination
of the total number of evolving constants of motion required. Also a method to
find evolving constants is proposed. The generalized Heinsenberg picture needs
M time variables, as opposed to the Heisenberg picture of standard quantum
mechanics where one time variable t is enough. As an application, we study the
parameterized harmonic oscillator and the SL(2,R) model with one physical
degree of freedom that mimics the constraint structure of general relativity
where a Schrodinger equation emerges in its quantum dynamics.
| [
{
"created": "Fri, 4 Feb 2000 17:13:26 GMT",
"version": "v1"
},
{
"created": "Tue, 16 Jan 2001 18:51:52 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Montesinos",
"Merced",
""
]
] | We study the classical and quantum dynamics of generally covariant theories with vanishing a Hamiltonian and with a finite number of degrees of freedom. In particular, the geometric meaning of the full solution of the relational evolution of the degrees of freedom is displayed, which means the determination of the total number of evolving constants of motion required. Also a method to find evolving constants is proposed. The generalized Heinsenberg picture needs M time variables, as opposed to the Heisenberg picture of standard quantum mechanics where one time variable t is enough. As an application, we study the parameterized harmonic oscillator and the SL(2,R) model with one physical degree of freedom that mimics the constraint structure of general relativity where a Schrodinger equation emerges in its quantum dynamics. |
0906.5430 | Salvatore Capozziello | S. Capozziello, E. Piedipalumbo, C. Rubano, P. Scudellaro | Testing an exact $f(R)$-gravity model at Galactic and local scales | 8 pages, 2 figures, accepted in Astron. & Astroph | Astron.Astrophys.505:21-28,2009 | 10.1051/0004-6361/200911992 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The weak field limit for a pointlike source of a $f(R) \propto
R^{3/2}$-gravity model is studied. We aim to show the viability of such a model
as a valid alternative to GR + dark matter at Galactic and local scales.
Without considering dark matter, within the weak field approximation, we find
general exact solutions for gravity with standard matter, and apply them to
some astrophysical scales, recovering the consistency of the same
$f(R)$-gravity model with cosmological results.}{In particular, we show that it
is possible to obtain flat rotation curves for galaxies, [and consistency with]
Solar System tests, as in the so-called "Chameleon Approach". In fact, the
peripheral velocity $ v_\infty $ is shown to be expressed as $ v_\infty =
\lambda \sqrt{M}$, so that the Tully-Fisher relation is recovered. The results
point out the possibility of achieving alternative theories of gravity in which
exotic ingredients like dark matter and dark energy are not necessary, while
their coarse-grained astrophysical and cosmological effects can be related to a
geometric origin.
| [
{
"created": "Tue, 30 Jun 2009 07:53:40 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Jul 2009 14:54:06 GMT",
"version": "v2"
}
] | 2011-05-09 | [
[
"Capozziello",
"S.",
""
],
[
"Piedipalumbo",
"E.",
""
],
[
"Rubano",
"C.",
""
],
[
"Scudellaro",
"P.",
""
]
] | The weak field limit for a pointlike source of a $f(R) \propto R^{3/2}$-gravity model is studied. We aim to show the viability of such a model as a valid alternative to GR + dark matter at Galactic and local scales. Without considering dark matter, within the weak field approximation, we find general exact solutions for gravity with standard matter, and apply them to some astrophysical scales, recovering the consistency of the same $f(R)$-gravity model with cosmological results.}{In particular, we show that it is possible to obtain flat rotation curves for galaxies, [and consistency with] Solar System tests, as in the so-called "Chameleon Approach". In fact, the peripheral velocity $ v_\infty $ is shown to be expressed as $ v_\infty = \lambda \sqrt{M}$, so that the Tully-Fisher relation is recovered. The results point out the possibility of achieving alternative theories of gravity in which exotic ingredients like dark matter and dark energy are not necessary, while their coarse-grained astrophysical and cosmological effects can be related to a geometric origin. |
gr-qc/0212069 | Clifford M. Will | Clifford M. Will | Covariant Calculation of General Relativistic Effects in an Orbiting
Gyroscope Experiment | 7 pages, 1 figure, to be submitted to Phys. Rev. D | Phys.Rev. D67 (2003) 062003 | 10.1103/PhysRevD.67.062003 | null | gr-qc | null | We carry out a covariant calculation of the measurable relativistic effects
in an orbiting gyroscope experiment. The experiment, currently known as Gravity
Probe B, compares the spin directions of an array of spinning gyroscopes with
the optical axis of a telescope, all housed in a spacecraft that rolls about
the optical axis. The spacecraft is steered so that the telescope always points
toward a known guide star. We calculate the variation in the spin directions
relative to readout loops rigidly fixed in the spacecraft, and express the
variations in terms of quantities that can be measured, to sufficient accuracy,
using an Earth-centered coordinate system. The measurable effects include the
aberration of starlight, the geodetic precession caused by space curvature, the
frame-dragging effect caused by the rotation of the Earth and the deflection of
light by the Sun.
| [
{
"created": "Mon, 16 Dec 2002 15:39:18 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Will",
"Clifford M.",
""
]
] | We carry out a covariant calculation of the measurable relativistic effects in an orbiting gyroscope experiment. The experiment, currently known as Gravity Probe B, compares the spin directions of an array of spinning gyroscopes with the optical axis of a telescope, all housed in a spacecraft that rolls about the optical axis. The spacecraft is steered so that the telescope always points toward a known guide star. We calculate the variation in the spin directions relative to readout loops rigidly fixed in the spacecraft, and express the variations in terms of quantities that can be measured, to sufficient accuracy, using an Earth-centered coordinate system. The measurable effects include the aberration of starlight, the geodetic precession caused by space curvature, the frame-dragging effect caused by the rotation of the Earth and the deflection of light by the Sun. |
2202.11458 | Hans Ringstr\"om | Hans Ringstr\"om | Initial data on big bang singularities in symmetric settings | 20 pages, 1 figure | null | null | null | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | In a recent article, we propose a general geometric notion of initial data on
big bang singularities. This notion is of interest in its own right. However,
it also serves the purpose of giving a unified perspective on many of the
results in the literature. In the present article, we give a partial
justification of this statement by rephrasing the results concerning Bianchi
class A orthogonal stiff solutions and solutions in the $\mathbb{T}^{3}$-Gowdy
symmetric vacuum setting in terms of our general geometric notion of initial
data on the big bang singularity.
| [
{
"created": "Wed, 23 Feb 2022 12:20:37 GMT",
"version": "v1"
}
] | 2022-02-24 | [
[
"Ringström",
"Hans",
""
]
] | In a recent article, we propose a general geometric notion of initial data on big bang singularities. This notion is of interest in its own right. However, it also serves the purpose of giving a unified perspective on many of the results in the literature. In the present article, we give a partial justification of this statement by rephrasing the results concerning Bianchi class A orthogonal stiff solutions and solutions in the $\mathbb{T}^{3}$-Gowdy symmetric vacuum setting in terms of our general geometric notion of initial data on the big bang singularity. |
1105.3971 | Luciano Rezzolla | Riccardo Ciolfi, Samuel K. Lander, Gian Mario Manca, Luciano Rezzolla | Instability-driven evolution of poloidal magnetic fields in relativistic
stars | 5 pages, 4 figures; small changes; accepted for publication in ApJL | Astrophys. J. Lett. 736, L6 (2011) | 10.1088/2041-8205/736/1/L6 | null | gr-qc astro-ph.HE astro-ph.SR | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The problem of the stability of magnetic fields in stars has a long history
and has been investigated in detail in perturbation theory. Here we consider
the nonlinear evolution of a non-rotating neutron star with a purely poloidal
magnetic field, in general relativity. We find that an instability develops in
the region of the closed magnetic field lines and over an Alfven timescale, as
predicted by perturbation theory. After the initial unstable growth, our
evolutions show that a toroidal magnetic field component is generated, which
increases until it is locally comparable in strength with the poloidal one. On
longer timescales the system relaxes to a new non-axisymmetric configuration
with a reorganization of the stellar structure and large-amplitude
oscillations, mostly in the fundamental mode. We discuss the energies involved
in the instability and the impact they may have on the phenomenology of
magnetar flares and on their detectability through gravitational-wave emission.
| [
{
"created": "Thu, 19 May 2011 19:43:16 GMT",
"version": "v1"
},
{
"created": "Sun, 12 Jun 2011 05:19:41 GMT",
"version": "v2"
}
] | 2015-03-19 | [
[
"Ciolfi",
"Riccardo",
""
],
[
"Lander",
"Samuel K.",
""
],
[
"Manca",
"Gian Mario",
""
],
[
"Rezzolla",
"Luciano",
""
]
] | The problem of the stability of magnetic fields in stars has a long history and has been investigated in detail in perturbation theory. Here we consider the nonlinear evolution of a non-rotating neutron star with a purely poloidal magnetic field, in general relativity. We find that an instability develops in the region of the closed magnetic field lines and over an Alfven timescale, as predicted by perturbation theory. After the initial unstable growth, our evolutions show that a toroidal magnetic field component is generated, which increases until it is locally comparable in strength with the poloidal one. On longer timescales the system relaxes to a new non-axisymmetric configuration with a reorganization of the stellar structure and large-amplitude oscillations, mostly in the fundamental mode. We discuss the energies involved in the instability and the impact they may have on the phenomenology of magnetar flares and on their detectability through gravitational-wave emission. |
2201.13335 | Lisa Valerie Drummond | Lisa V. Drummond and Scott A. Hughes | Precisely computing bound orbits of spinning bodies around black holes
II: Generic orbits | 24 pages, 8 figures, submitted to Physical Review D; typos in
supplementary Mathematica notebook corrected | null | 10.1103/PhysRevD.105.124041 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we continue our study of the motion of spinning test bodies
orbiting Kerr black holes. Non-spinning test bodies follow geodesics of the
spacetime in which they move. A test body's spin couples to the curvature of
that spacetime, introducing a "spin-curvature force" which pushes the body's
worldline away from a geodesic trajectory. The spin-curvature force is an
important example of a post-geodesic effect which must be modeled carefully in
order to accurately characterize the motion of bodies orbiting black holes. One
motivation for this work is to understand how to include such effects in models
of gravitational waves produced from the inspiral of stellar mass bodies into
massive black holes. In this paper's predecessor, we describe a technique for
computing bound orbits of spinning bodies around black holes with a
frequency-domain description which can be solved very precisely. In that paper,
we present an overview of our methods, as well as present results for orbits
which are eccentric and nearly equatorial (i.e., the orbit's motion is no more
than $\mathcal{O}(S)$ out of the equatorial plane). In this paper, we apply
this formulation to the fully generic case -- orbits which are inclined and
eccentric, with the small body's spin arbitrarily oriented. We compute the
trajectories which such orbits follow, and compute how the small body's spin
affects important quantities such as the observable orbital frequencies
$\Omega_r$, $\Omega_\theta$ and $\Omega_\phi$.
| [
{
"created": "Mon, 31 Jan 2022 16:31:16 GMT",
"version": "v1"
},
{
"created": "Tue, 22 Mar 2022 17:48:15 GMT",
"version": "v2"
}
] | 2022-07-13 | [
[
"Drummond",
"Lisa V.",
""
],
[
"Hughes",
"Scott A.",
""
]
] | In this paper, we continue our study of the motion of spinning test bodies orbiting Kerr black holes. Non-spinning test bodies follow geodesics of the spacetime in which they move. A test body's spin couples to the curvature of that spacetime, introducing a "spin-curvature force" which pushes the body's worldline away from a geodesic trajectory. The spin-curvature force is an important example of a post-geodesic effect which must be modeled carefully in order to accurately characterize the motion of bodies orbiting black holes. One motivation for this work is to understand how to include such effects in models of gravitational waves produced from the inspiral of stellar mass bodies into massive black holes. In this paper's predecessor, we describe a technique for computing bound orbits of spinning bodies around black holes with a frequency-domain description which can be solved very precisely. In that paper, we present an overview of our methods, as well as present results for orbits which are eccentric and nearly equatorial (i.e., the orbit's motion is no more than $\mathcal{O}(S)$ out of the equatorial plane). In this paper, we apply this formulation to the fully generic case -- orbits which are inclined and eccentric, with the small body's spin arbitrarily oriented. We compute the trajectories which such orbits follow, and compute how the small body's spin affects important quantities such as the observable orbital frequencies $\Omega_r$, $\Omega_\theta$ and $\Omega_\phi$. |
1401.0800 | Abdelmoumene Belabbas moumene | Abdelmoumene Belabbas | Les Interactions Fondamentales et la Structure de l'Espace-temps | PhD Thesis (2011), 193 pages, 3 figures, text in french, University
of Bejaia (Algeria) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the light of intriguing results of C.C.Barros, we investigate in this
thesis the possibilities of geometrical interpretation of all the fundamental
interactions in order to unify them. More exactly we try to supply a unified
geometrical description for gravitation and electromagnetism.
The analysis of Huei's standard approach of Linear Gravity, in which the
Einstein equations can be written in the same form of the Maxwell ones,
revealed the existence of some imperfections. In fact, the relation between the
scalar potential and the electric-type field is not valid except in the
harmonic gauge, the Lorentz-type force is obtained with a time independence
restriction and an undesired factor 4 appears in the magnetic-type part. A
subtle gauge conditions allows us to eliminate these imperfections and to
revisit the Linear Gravity in a way to get a strong similarity with
electromagnetism. In the linear case, we showed that Maxwell's equations could
be derived from an electromagnetic version of the Einstein ones, and that the
higher order terms are negligible in the current domain of application of
electromagnetism.
| [
{
"created": "Sat, 4 Jan 2014 11:45:36 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Mar 2014 15:45:06 GMT",
"version": "v2"
}
] | 2014-03-20 | [
[
"Belabbas",
"Abdelmoumene",
""
]
] | In the light of intriguing results of C.C.Barros, we investigate in this thesis the possibilities of geometrical interpretation of all the fundamental interactions in order to unify them. More exactly we try to supply a unified geometrical description for gravitation and electromagnetism. The analysis of Huei's standard approach of Linear Gravity, in which the Einstein equations can be written in the same form of the Maxwell ones, revealed the existence of some imperfections. In fact, the relation between the scalar potential and the electric-type field is not valid except in the harmonic gauge, the Lorentz-type force is obtained with a time independence restriction and an undesired factor 4 appears in the magnetic-type part. A subtle gauge conditions allows us to eliminate these imperfections and to revisit the Linear Gravity in a way to get a strong similarity with electromagnetism. In the linear case, we showed that Maxwell's equations could be derived from an electromagnetic version of the Einstein ones, and that the higher order terms are negligible in the current domain of application of electromagnetism. |
gr-qc/9212001 | Sean Hayward | Sean A. Hayward | Cosmic Censorship in 2-Dimensional Dilaton Gravity | 10 pages | Class.Quant.Grav.10:985-994,1993 | 10.1088/0264-9381/10/5/015 | null | gr-qc | null | The global structure of 2-dimensional dilaton gravity is studied, attending
in particular to black holes and singularities. A gravitational energy is
defined and shown to be positive at spatial singularities and negative at
temporal singularities. Trapped points are defined, and it is shown that
spatial singularities are trapped and temporal singularities are not. Thus a
local form of cosmic censorship holds for positive energy. In an analogue of
gravitational collapse to a black hole, matter falling into an initially flat
space creates a spatial curvature singularity which is cloaked in a spatial or
null apparent horizon with non-decreasing energy and area.
| [
{
"created": "Wed, 2 Dec 1992 13:28:05 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Hayward",
"Sean A.",
""
]
] | The global structure of 2-dimensional dilaton gravity is studied, attending in particular to black holes and singularities. A gravitational energy is defined and shown to be positive at spatial singularities and negative at temporal singularities. Trapped points are defined, and it is shown that spatial singularities are trapped and temporal singularities are not. Thus a local form of cosmic censorship holds for positive energy. In an analogue of gravitational collapse to a black hole, matter falling into an initially flat space creates a spatial curvature singularity which is cloaked in a spatial or null apparent horizon with non-decreasing energy and area. |
gr-qc/9704029 | Andrew Liddle | Franz E Schunck and Andrew R Liddle | The gravitational redshift of boson stars | 7 pages RevTeX file with five figures incorporated (uses RevTeX and
psfig) | Phys.Lett.B404:25-32,1997 | 10.1016/S0370-2693(97)00559-5 | SUSSEX-AST 97/4-1 | gr-qc astro-ph | null | We investigate the possible gravitational redshift values for boson stars
with a self-interaction, studying a wide range of possible masses. We find a
limiting value of $z_{lim} \simeq 0.687$ for stable boson star configurations.
We compare theoretical expectation with the observational capabilities in
several different wavebands, concluding that direct observation of boson stars
by this means will be extremely challenging. X-ray spectroscopy is perhaps the
most interesting possibility.
| [
{
"created": "Thu, 10 Apr 1997 08:25:32 GMT",
"version": "v1"
}
] | 2010-11-19 | [
[
"Schunck",
"Franz E",
""
],
[
"Liddle",
"Andrew R",
""
]
] | We investigate the possible gravitational redshift values for boson stars with a self-interaction, studying a wide range of possible masses. We find a limiting value of $z_{lim} \simeq 0.687$ for stable boson star configurations. We compare theoretical expectation with the observational capabilities in several different wavebands, concluding that direct observation of boson stars by this means will be extremely challenging. X-ray spectroscopy is perhaps the most interesting possibility. |
1608.01002 | Jorma Louko | Jorma Louko, Vladimir Toussaint | Unruh-DeWitt detector's response to fermions in flat spacetimes | 30 pages, low resolution figures. v2: typos corrected | Phys. Rev. D 94, 064027 (2016) | 10.1103/PhysRevD.94.064027 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We examine an Unruh-DeWitt particle detector that is coupled linearly to the
scalar density of a massless Dirac field in Minkowski spacetimes of dimension
$d\ge2$ and on the static Minkowski cylinder in spacetime dimension two,
allowing the detector's motion to remain arbitrary and working to leading order
in perturbation theory. In $d$-dimensional Minkowski, with the field in the
usual Fock vacuum, we show that the detector's response is identical to that of
a detector coupled linearly to a massless scalar field in $2d$-dimensional
Minkowski. In the special case of uniform linear acceleration, the detector's
response hence exhibits the Unruh effect with a Planckian factor in both even
and odd dimensions, in contrast to the Rindler power spectrum of the Dirac
field, which has a Planckian factor for odd $d$ but a Fermi-Dirac factor for
even~$d$. On the two-dimensional cylinder, we set the oscillator modes in the
usual Fock vacuum but allow an arbitrary state for the zero mode of the
periodic spinor. We show that the detector's response distinguishes the
periodic and antiperiodic spin structures, and the zero mode of the periodic
spinor contributes to the response by a state-dependent but well defined
amount. Explicit analytic and numerical results on the cylinder are obtained
for inertial and uniformly accelerated trajectories, recovering the $d=2$
Minkowski results in the limit of large circumference. The detector's response
has no infrared ambiguity for $d=2$, neither in Minkowski nor on the cylinder.
| [
{
"created": "Tue, 2 Aug 2016 20:54:54 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Sep 2016 16:39:39 GMT",
"version": "v2"
}
] | 2016-09-20 | [
[
"Louko",
"Jorma",
""
],
[
"Toussaint",
"Vladimir",
""
]
] | We examine an Unruh-DeWitt particle detector that is coupled linearly to the scalar density of a massless Dirac field in Minkowski spacetimes of dimension $d\ge2$ and on the static Minkowski cylinder in spacetime dimension two, allowing the detector's motion to remain arbitrary and working to leading order in perturbation theory. In $d$-dimensional Minkowski, with the field in the usual Fock vacuum, we show that the detector's response is identical to that of a detector coupled linearly to a massless scalar field in $2d$-dimensional Minkowski. In the special case of uniform linear acceleration, the detector's response hence exhibits the Unruh effect with a Planckian factor in both even and odd dimensions, in contrast to the Rindler power spectrum of the Dirac field, which has a Planckian factor for odd $d$ but a Fermi-Dirac factor for even~$d$. On the two-dimensional cylinder, we set the oscillator modes in the usual Fock vacuum but allow an arbitrary state for the zero mode of the periodic spinor. We show that the detector's response distinguishes the periodic and antiperiodic spin structures, and the zero mode of the periodic spinor contributes to the response by a state-dependent but well defined amount. Explicit analytic and numerical results on the cylinder are obtained for inertial and uniformly accelerated trajectories, recovering the $d=2$ Minkowski results in the limit of large circumference. The detector's response has no infrared ambiguity for $d=2$, neither in Minkowski nor on the cylinder. |
1805.03751 | Igor Khavkine | Igor Khavkine | Compatibility complexes of overdetermined PDEs of finite type, with
applications to the Killing equation | v2: 40 pages, added background and notation overview appendices,
close to published version; v1: 29 pages, no figures | Class. Quantum Grav. 36 (2019) 185012 | 10.1088/1361-6382/ab329a | null | gr-qc math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | In linearized gravity, two linearized metrics are considered
gauge-equivalent, $h_{ab} \sim h_{ab} + K_{ab}[v]$, when they differ by the
image of the Killing operator, $K_{ab}[v] = \nabla_a v_b + \nabla_b v_a$. A
universal (or complete) compatibility operator for $K$ is a differential
operator $K_1$ such that $K_1 \circ K = 0$ and any other operator annihilating
$K$ must factor through $K_1$. The components of $K_1$ can be interpreted as a
complete (or generating) set of local gauge-invariant observables in linearized
gravity. By appealing to known results in the formal theory of overdetermined
PDEs and basic notions from homological algebra, we solve the problem of
constructing the Killing compatibility operator $K_1$ on an arbitrary
background geometry, as well as of extending it to a full compatibility complex
$K_i$ ($i\ge 1$), meaning that for each $K_i$ the operator $K_{i+1}$ is its
universal compatibility operator. Our solution is practical enough that we
apply it explicitly in two examples, giving the first construction of full
compatibility complexes for the Killing operator on these geometries. The first
example consists of the cosmological FLRW spacetimes, in any dimension. The
second consists of a generalization of the Schwarzschild-Tangherlini black hole
spacetimes, also in any dimension. The generalization allows an arbitrary
cosmological constant and the replacement of spherical symmetry by planar or
pseudo-spherical symmetry.
| [
{
"created": "Wed, 9 May 2018 22:48:34 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Sep 2019 07:49:29 GMT",
"version": "v2"
}
] | 2019-09-20 | [
[
"Khavkine",
"Igor",
""
]
] | In linearized gravity, two linearized metrics are considered gauge-equivalent, $h_{ab} \sim h_{ab} + K_{ab}[v]$, when they differ by the image of the Killing operator, $K_{ab}[v] = \nabla_a v_b + \nabla_b v_a$. A universal (or complete) compatibility operator for $K$ is a differential operator $K_1$ such that $K_1 \circ K = 0$ and any other operator annihilating $K$ must factor through $K_1$. The components of $K_1$ can be interpreted as a complete (or generating) set of local gauge-invariant observables in linearized gravity. By appealing to known results in the formal theory of overdetermined PDEs and basic notions from homological algebra, we solve the problem of constructing the Killing compatibility operator $K_1$ on an arbitrary background geometry, as well as of extending it to a full compatibility complex $K_i$ ($i\ge 1$), meaning that for each $K_i$ the operator $K_{i+1}$ is its universal compatibility operator. Our solution is practical enough that we apply it explicitly in two examples, giving the first construction of full compatibility complexes for the Killing operator on these geometries. The first example consists of the cosmological FLRW spacetimes, in any dimension. The second consists of a generalization of the Schwarzschild-Tangherlini black hole spacetimes, also in any dimension. The generalization allows an arbitrary cosmological constant and the replacement of spherical symmetry by planar or pseudo-spherical symmetry. |
1110.3181 | Valentin Gladush | Valentin D. Gladush, Dmitry A. Kulikov | Naked Reissner-Nordstr\"om singularity and quasiclassical bound states | 3 pages | null | null | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The bound-state problem for an uncharged massive scalar particle in the field
of a naked Reissner-Nordstr\"om singularity is approached by means of the
quasiclassical Bohr-Sommerfeld quantization. An approximate analytical
expression for the energy levels of the system is derived. It is shown that in
order to obtain non-vanishing binding energies the masses of both the central
object and the particle should be comparable with the Planck mass.
| [
{
"created": "Fri, 14 Oct 2011 12:07:01 GMT",
"version": "v1"
}
] | 2011-10-17 | [
[
"Gladush",
"Valentin D.",
""
],
[
"Kulikov",
"Dmitry A.",
""
]
] | The bound-state problem for an uncharged massive scalar particle in the field of a naked Reissner-Nordstr\"om singularity is approached by means of the quasiclassical Bohr-Sommerfeld quantization. An approximate analytical expression for the energy levels of the system is derived. It is shown that in order to obtain non-vanishing binding energies the masses of both the central object and the particle should be comparable with the Planck mass. |
1603.02851 | Daniel M\"uller | A. Toporensky and D. M\"uller | On stability of the Kasner solution in quadratic gravity | null | null | 10.1007/s10714-016-2172-9 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider dynamics of a flat anisotropic Universe filled by a perfect fluid
near a cosmological singularity in quadratic gravity. Two possible regimes are
described -- the Kasner anisotropic solution and an isotropic "vacuum
radiation" solution which has three sub cases depending on whether the equation
of state parameter $w$ is bigger, smaller or equals to $1/3$. Initial
conditions for numerical integrations have been chosen near General Relativity
anisotropic solution with matter (Jacobs solution). We have found that for such
initial conditions there is a range of values of coupling constants so that the
resulting cosmological singularity is isotropic.
| [
{
"created": "Wed, 9 Mar 2016 11:30:16 GMT",
"version": "v1"
},
{
"created": "Tue, 31 May 2016 08:10:15 GMT",
"version": "v2"
}
] | 2017-01-04 | [
[
"Toporensky",
"A.",
""
],
[
"Müller",
"D.",
""
]
] | We consider dynamics of a flat anisotropic Universe filled by a perfect fluid near a cosmological singularity in quadratic gravity. Two possible regimes are described -- the Kasner anisotropic solution and an isotropic "vacuum radiation" solution which has three sub cases depending on whether the equation of state parameter $w$ is bigger, smaller or equals to $1/3$. Initial conditions for numerical integrations have been chosen near General Relativity anisotropic solution with matter (Jacobs solution). We have found that for such initial conditions there is a range of values of coupling constants so that the resulting cosmological singularity is isotropic. |
2104.15123 | Emmanuil Saridakis | Fotios K. Anagnostopoulos, Spyros Basilakos, Emmanuel N. Saridakis | First evidence that non-metricity f(Q) gravity could challenge
$\Lambda$CDM | 4 pages, 2 figures, 2 Tables, version to appear in Phys.Lett.B | null | 10.1016/j.physletb.2021.136634 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose a novel model in the framework of $f(Q)$ gravity, which is a
gravitational modification class arising from the incorporation of
non-metricity. The model has General Relativity as a particular limit, it has
the same number of free parameters to those of $\Lambda$CDM, however at a
cosmological framework it gives rise to a scenario that does not have
$\Lambda$CDM as a limit. Nevertheless, confrontation with observations at both
background and perturbation levels, namely with Supernovae type Ia (SNIa),
Baryonic Acoustic Oscillations (BAO), cosmic chronometers (CC), and Redshift
Space Distortion (RSD) data, reveals that the scenario, according to AIC, BIC
and DIC information criteria, is in some datasets slightly preferred comparing
to $\Lambda$CDM cosmology, although in all cases the two models are
statistically indiscriminate. Finally, the model does not exhibit early dark
energy features, and thus it immediately passes BBN constraints, while the
variation of the effective Newton's constant lies well inside the observational
bounds.
| [
{
"created": "Fri, 30 Apr 2021 17:26:52 GMT",
"version": "v1"
},
{
"created": "Tue, 7 Sep 2021 16:33:37 GMT",
"version": "v2"
}
] | 2021-09-15 | [
[
"Anagnostopoulos",
"Fotios K.",
""
],
[
"Basilakos",
"Spyros",
""
],
[
"Saridakis",
"Emmanuel N.",
""
]
] | We propose a novel model in the framework of $f(Q)$ gravity, which is a gravitational modification class arising from the incorporation of non-metricity. The model has General Relativity as a particular limit, it has the same number of free parameters to those of $\Lambda$CDM, however at a cosmological framework it gives rise to a scenario that does not have $\Lambda$CDM as a limit. Nevertheless, confrontation with observations at both background and perturbation levels, namely with Supernovae type Ia (SNIa), Baryonic Acoustic Oscillations (BAO), cosmic chronometers (CC), and Redshift Space Distortion (RSD) data, reveals that the scenario, according to AIC, BIC and DIC information criteria, is in some datasets slightly preferred comparing to $\Lambda$CDM cosmology, although in all cases the two models are statistically indiscriminate. Finally, the model does not exhibit early dark energy features, and thus it immediately passes BBN constraints, while the variation of the effective Newton's constant lies well inside the observational bounds. |
1208.3729 | Jungjai Lee | Hyeong-Chan Kim, Jae-Weon Lee and Jungjai Lee | Causality Problem in a Holographic Dark Energy Model | 5 pages | Europhysics Letters 102, 29001 (2013) | 10.1209/0295-5075/102/29001 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the model of holographic dark energy, there is a notorious problem of
circular reasoning between the introduction of future event horizon and the
accelerating expansion of the universe. We examine the problem after dividing
into two parts, the causality problem of the equation of motion and the
circular logic on the use of the future event horizon. We specify and isolate
the root of the problem from causal equation of motion as a boundary condition,
which can be determined from the initial data of the universe. We show that
there is no violation of causality if it is defined appropriately and the
circular logic problem can be reduced to an initial value problem.
| [
{
"created": "Sat, 18 Aug 2012 07:12:24 GMT",
"version": "v1"
}
] | 2017-08-22 | [
[
"Kim",
"Hyeong-Chan",
""
],
[
"Lee",
"Jae-Weon",
""
],
[
"Lee",
"Jungjai",
""
]
] | In the model of holographic dark energy, there is a notorious problem of circular reasoning between the introduction of future event horizon and the accelerating expansion of the universe. We examine the problem after dividing into two parts, the causality problem of the equation of motion and the circular logic on the use of the future event horizon. We specify and isolate the root of the problem from causal equation of motion as a boundary condition, which can be determined from the initial data of the universe. We show that there is no violation of causality if it is defined appropriately and the circular logic problem can be reduced to an initial value problem. |
2301.01163 | Tummala Vinutha | T. Vinutha, K. Niharika and K. Sri Kavya | The study of Kantowski-Sachs perfect fluid cosmological model in
modified gravity | null | null | 10.1007/s10511-023-09771-5 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | Kantowski-Sachs perfect fluid cosmological model is explored in modified
gravity with functional form $f(R, T)$=$f_1(R)$+$f_2(T)$ where $R$ is Ricci
scalar, and $T$ is the trace of the energy-momentum tensor. With this
functional form, three different cases have been formulated, namely negative
and positive powers of curvature, logarithmic curvature, and exponential
curvature given by $f_1(R)=R+\gamma R^2-\frac{\mu^4}{R}$, $f_1(R)=R+\nu ln(\tau
R)$ and $f_1(R)=R+\kappa e^{-\iota R}$ respectively. For all these three cases,
$f_2(T)=\lambda T$, here $\gamma$, $\lambda$, $\mu$, $\nu$, $\tau$, $\kappa$
and $\iota$ are constants. While solving the field equations, two constraints
i) the Expansion scalar is proportional to shear scalar ii) the Hyperbolic
scale factor is used. By using these conditions, the required optimum solutions
are obtained. The physical parameters are calculated, and the geometrical
parameters of three cases are analyzed against redshift($z$) with the help of
pictorial representation. In the context of $f(R, T)$ gravity, energy
conditions are discussed with the help of pressure and energy density. If a
strong energy condition is positive, gravity should be attractive but in our
model, it shows negative, which means that cosmic acceleration is due to
antigravity, whereas NEC and DEC are fulfilled. The perturbation technique is
used to test the stability of the background solutions of the obtained models.
The inferences obtained from this paper are persistent with the present
cosmological observations, and the model represents an accelerating universe.
| [
{
"created": "Tue, 3 Jan 2023 15:48:05 GMT",
"version": "v1"
},
{
"created": "Thu, 5 Jan 2023 04:17:03 GMT",
"version": "v2"
},
{
"created": "Mon, 6 Feb 2023 07:26:35 GMT",
"version": "v3"
}
] | 2023-04-26 | [
[
"Vinutha",
"T.",
""
],
[
"Niharika",
"K.",
""
],
[
"Kavya",
"K. Sri",
""
]
] | Kantowski-Sachs perfect fluid cosmological model is explored in modified gravity with functional form $f(R, T)$=$f_1(R)$+$f_2(T)$ where $R$ is Ricci scalar, and $T$ is the trace of the energy-momentum tensor. With this functional form, three different cases have been formulated, namely negative and positive powers of curvature, logarithmic curvature, and exponential curvature given by $f_1(R)=R+\gamma R^2-\frac{\mu^4}{R}$, $f_1(R)=R+\nu ln(\tau R)$ and $f_1(R)=R+\kappa e^{-\iota R}$ respectively. For all these three cases, $f_2(T)=\lambda T$, here $\gamma$, $\lambda$, $\mu$, $\nu$, $\tau$, $\kappa$ and $\iota$ are constants. While solving the field equations, two constraints i) the Expansion scalar is proportional to shear scalar ii) the Hyperbolic scale factor is used. By using these conditions, the required optimum solutions are obtained. The physical parameters are calculated, and the geometrical parameters of three cases are analyzed against redshift($z$) with the help of pictorial representation. In the context of $f(R, T)$ gravity, energy conditions are discussed with the help of pressure and energy density. If a strong energy condition is positive, gravity should be attractive but in our model, it shows negative, which means that cosmic acceleration is due to antigravity, whereas NEC and DEC are fulfilled. The perturbation technique is used to test the stability of the background solutions of the obtained models. The inferences obtained from this paper are persistent with the present cosmological observations, and the model represents an accelerating universe. |
2405.12534 | Alejandro Perez | Gabriel R. Bengochea, Gabriel Leon, Alejandro Perez | Is Planckian discreteness observable in cosmology? | null | null | null | null | gr-qc astro-ph.HE hep-ph hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A Planck scale inflationary era -- in a quantum gravity theory predicting
discreteness of quantum geometry at the fundamental scale -- produces the scale
invariant spectrum of inhomogeneities with very small tensor-to-scalar ratio of
perturbations and a hot big bang leading to a natural dark matter genesis
scenario. Here we evoke the possibility that some of the major puzzles in
cosmology would have an explanation rooted in quantum gravity.
| [
{
"created": "Tue, 21 May 2024 06:53:37 GMT",
"version": "v1"
}
] | 2024-05-24 | [
[
"Bengochea",
"Gabriel R.",
""
],
[
"Leon",
"Gabriel",
""
],
[
"Perez",
"Alejandro",
""
]
] | A Planck scale inflationary era -- in a quantum gravity theory predicting discreteness of quantum geometry at the fundamental scale -- produces the scale invariant spectrum of inhomogeneities with very small tensor-to-scalar ratio of perturbations and a hot big bang leading to a natural dark matter genesis scenario. Here we evoke the possibility that some of the major puzzles in cosmology would have an explanation rooted in quantum gravity. |
gr-qc/9610025 | Vivek Iyer | Vivek Iyer | Lagrangian perfect fluids and black hole mechanics | 26 pages LaTeX-2e | Phys.Rev. D55 (1997) 3411-3426 | 10.1103/PhysRevD.55.3411 | null | gr-qc | null | The first law of black hole mechanics (in the form derived by Wald), is
expressed in terms of integrals over surfaces, at the horizon and spatial
infinity, of a stationary, axisymmetric black hole, in a diffeomorphism
invariant Lagrangian theory of gravity. The original statement of the first law
given by Bardeen, Carter and Hawking for an Einstein-perfect fluid system
contained, in addition, volume integrals of the fluid fields, over a spacelike
slice stretching between these two surfaces. When applied to the
Einstein-perfect fluid system, however, Wald's methods yield restricted
results. The reason is that the fluid fields in the Lagrangian of a gravitating
perfect fluid are typically nonstationary. We therefore first derive a first
law-like relation for an arbitrary Lagrangian metric theory of gravity coupled
to arbitrary Lagrangian matter fields, requiring only that the metric field be
stationary. This relation includes a volume integral of matter fields over a
spacelike slice between the black hole horizon and spatial infinity, and
reduces to the first law originally derived by Bardeen, Carter and Hawking when
the theory is general relativity coupled to a perfect fluid. We also consider a
specific Lagrangian formulation for an isentropic perfect fluid given by
Carter, and directly apply Wald's analysis. The resulting first law contains
only surface integrals at the black hole horizon and spatial infinity, but this
relation is much more restrictive in its allowed fluid configurations and
perturbations than that given by Bardeen, Carter and Hawking. In the Appendix,
we use the symplectic structure of the Einstein-perfect fluid system to derive
a conserved current for perturbations of this system: this current reduces to
one derived ab initio for this system by Chandrasekhar and Ferrari.
| [
{
"created": "Tue, 15 Oct 1996 03:26:47 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Iyer",
"Vivek",
""
]
] | The first law of black hole mechanics (in the form derived by Wald), is expressed in terms of integrals over surfaces, at the horizon and spatial infinity, of a stationary, axisymmetric black hole, in a diffeomorphism invariant Lagrangian theory of gravity. The original statement of the first law given by Bardeen, Carter and Hawking for an Einstein-perfect fluid system contained, in addition, volume integrals of the fluid fields, over a spacelike slice stretching between these two surfaces. When applied to the Einstein-perfect fluid system, however, Wald's methods yield restricted results. The reason is that the fluid fields in the Lagrangian of a gravitating perfect fluid are typically nonstationary. We therefore first derive a first law-like relation for an arbitrary Lagrangian metric theory of gravity coupled to arbitrary Lagrangian matter fields, requiring only that the metric field be stationary. This relation includes a volume integral of matter fields over a spacelike slice between the black hole horizon and spatial infinity, and reduces to the first law originally derived by Bardeen, Carter and Hawking when the theory is general relativity coupled to a perfect fluid. We also consider a specific Lagrangian formulation for an isentropic perfect fluid given by Carter, and directly apply Wald's analysis. The resulting first law contains only surface integrals at the black hole horizon and spatial infinity, but this relation is much more restrictive in its allowed fluid configurations and perturbations than that given by Bardeen, Carter and Hawking. In the Appendix, we use the symplectic structure of the Einstein-perfect fluid system to derive a conserved current for perturbations of this system: this current reduces to one derived ab initio for this system by Chandrasekhar and Ferrari. |
gr-qc/9602007 | Miroslav Pardy | Miroslav Pardy (Department of Theoretical Physics and Astrophysics,
Masaryk University, Czech Republic) | The String Model of Gravity | 7 pages, revtex, 0 figures | null | null | null | gr-qc | null | The string model of gravitational force is proposed where the string forms
the mediation of the gravitational interaction between two gravitating bodies.
It reproduces the Newtonian results in the first-order approximation and it
predicts in the higher-oder approximations the existence of oscillations of the
gravitational field between two massive bodies. It can be easily generalized to
the two-body interaction in particle physics.
| [
{
"created": "Mon, 5 Feb 1996 08:16:46 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Pardy",
"Miroslav",
"",
"Department of Theoretical Physics and Astrophysics,\n Masaryk University, Czech Republic"
]
] | The string model of gravitational force is proposed where the string forms the mediation of the gravitational interaction between two gravitating bodies. It reproduces the Newtonian results in the first-order approximation and it predicts in the higher-oder approximations the existence of oscillations of the gravitational field between two massive bodies. It can be easily generalized to the two-body interaction in particle physics. |
gr-qc/0310107 | David Wiltshire | Matt Visser (Victoria University of Wellington), David L. Wiltshire
(University of Canterbury) | Stable gravastars - an alternative to black holes? | 20 pages, 5 figures; uses iopart.cls, setstack.sty; v2 - note and one
reference added | Class.Quant.Grav. 21 (2004) 1135-1152 | 10.1088/0264-9381/21/4/027 | null | gr-qc astro-ph hep-th | null | The "gravastar" picture developed by Mazur and Mottola is one of a very small
number of serious challenges to our usual conception of a "black hole". In the
gravastar picture there is effectively a phase transition at/ near where the
event horizon would have been expected to form, and the interior of what would
have been the black hole is replaced by a segment of de Sitter space. While
Mazur and Mottola were able to argue for the thermodynamic stability of their
configuration, the question of dynamic stability against spherically symmetric
perturbations of the matter or gravity fields remains somewhat obscure. In this
article we construct a model that shares the key features of the Mazur-Mottola
scenario, and which is sufficiently simple for a full dynamical analysis. We
find that there are some physically reasonable equations of state for the
transition layer that lead to stability.
| [
{
"created": "Thu, 23 Oct 2003 03:50:24 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Dec 2003 03:57:00 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Visser",
"Matt",
"",
"Victoria University of Wellington"
],
[
"Wiltshire",
"David L.",
"",
"University of Canterbury"
]
] | The "gravastar" picture developed by Mazur and Mottola is one of a very small number of serious challenges to our usual conception of a "black hole". In the gravastar picture there is effectively a phase transition at/ near where the event horizon would have been expected to form, and the interior of what would have been the black hole is replaced by a segment of de Sitter space. While Mazur and Mottola were able to argue for the thermodynamic stability of their configuration, the question of dynamic stability against spherically symmetric perturbations of the matter or gravity fields remains somewhat obscure. In this article we construct a model that shares the key features of the Mazur-Mottola scenario, and which is sufficiently simple for a full dynamical analysis. We find that there are some physically reasonable equations of state for the transition layer that lead to stability. |
2312.04301 | Long-Yue Li | Li-Ming Cao, Long-Yue Li, Xia-Yuan Liu, Yu-Sen Zhou | The appearance of the regular black hole with a stable inner horizon | 12 pages, 15 figures, tiltle is changed, references and discussion
are added, accepted by Phys. Rev. D | null | null | ICTS-USTC/PCFT-23-39 | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The strong cosmic censorship conjecture, which states that the evolution of
generic initial data will always produce a globally hyperbolic spacetime, is
hard to be tested by astronomical observations. In this paper, we study the
appearance of the regular black hole without mass inflation, which violates the
strong cosmic censorship conjecture. Since the inner horizon is stable, the
photons entering the two horizons of the regular black hole in the preceding
companion universe can come out from the white hole in our universe. These rays
create a novel multi-ring structure, which is significantly different from the
image of the Schwarzschild black hole. This serves a potential method to test
the strong cosmic censorship conjecture.
| [
{
"created": "Thu, 7 Dec 2023 13:53:19 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Feb 2024 10:15:46 GMT",
"version": "v2"
}
] | 2024-02-26 | [
[
"Cao",
"Li-Ming",
""
],
[
"Li",
"Long-Yue",
""
],
[
"Liu",
"Xia-Yuan",
""
],
[
"Zhou",
"Yu-Sen",
""
]
] | The strong cosmic censorship conjecture, which states that the evolution of generic initial data will always produce a globally hyperbolic spacetime, is hard to be tested by astronomical observations. In this paper, we study the appearance of the regular black hole without mass inflation, which violates the strong cosmic censorship conjecture. Since the inner horizon is stable, the photons entering the two horizons of the regular black hole in the preceding companion universe can come out from the white hole in our universe. These rays create a novel multi-ring structure, which is significantly different from the image of the Schwarzschild black hole. This serves a potential method to test the strong cosmic censorship conjecture. |
1907.04892 | Francisco X. Linares Cede\~no | Francisco X. Linares Cede\~no and Ernesto Contreras | Gravitational Decoupling in Cosmology | 10 pages. Two new figures included. Accepted for publication in
Physics of the Dark Universe | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Whereas the nature of dark components in the Universe remains unknown,
alternative models of gravity have been developed to offer a geometric
explanation to the origin of such components. In this work we use the Minimal
Geometric Deformation approach to study extensions of the theory of General
Relativity in a cosmological context. This is possible since such approach
allows the decoupling of gravitational sources, and the Einstein field
equations can be analytically solved with the presence of a new gravitational
sector once a known GR solution is considered. In particular, we implement such
approach in Friedmann-Robertson-Walker and Kantowski-Sachs universes. We
demonstrate that the gravitational decoupling leads to modifications of well
known cosmological solutions. For instance, we show that an effective spatial
curvature in the Friedmann-Robertson-Walker metric, as well as several kind of
matter components in the Kantowski-Sachs case, are obtained. Thus, we found
that it is possible to obtain spatial curvature and new matter terms from
geometry, which in cosmology they could be useful in addressing problems such
as the spatial flatness of the Universe, dark matter and dark energy.
| [
{
"created": "Wed, 10 Jul 2019 19:11:55 GMT",
"version": "v1"
},
{
"created": "Sat, 26 Oct 2019 21:00:47 GMT",
"version": "v2"
},
{
"created": "Thu, 2 Apr 2020 01:44:20 GMT",
"version": "v3"
}
] | 2020-04-03 | [
[
"Cedeño",
"Francisco X. Linares",
""
],
[
"Contreras",
"Ernesto",
""
]
] | Whereas the nature of dark components in the Universe remains unknown, alternative models of gravity have been developed to offer a geometric explanation to the origin of such components. In this work we use the Minimal Geometric Deformation approach to study extensions of the theory of General Relativity in a cosmological context. This is possible since such approach allows the decoupling of gravitational sources, and the Einstein field equations can be analytically solved with the presence of a new gravitational sector once a known GR solution is considered. In particular, we implement such approach in Friedmann-Robertson-Walker and Kantowski-Sachs universes. We demonstrate that the gravitational decoupling leads to modifications of well known cosmological solutions. For instance, we show that an effective spatial curvature in the Friedmann-Robertson-Walker metric, as well as several kind of matter components in the Kantowski-Sachs case, are obtained. Thus, we found that it is possible to obtain spatial curvature and new matter terms from geometry, which in cosmology they could be useful in addressing problems such as the spatial flatness of the Universe, dark matter and dark energy. |
gr-qc/9710082 | Georges Bressange | G.F. Bressange | Plane Light-Like Shells and Impulsive Gravitational Waves in
Scalar-Tensor Theories of Gravity | 19 pages, latex, 1 figure, accepted for publication in Class. Quant.
Grav | Class.Quant.Grav. 15 (1998) 225-238 | 10.1088/0264-9381/15/1/017 | null | gr-qc | null | We study gravitational plane impulsive waves and electromagnetic shock waves
in a scalar-tensor theory of gravity of the Brans-Dicke type. In vacuum, we
present an exact solution of Brans-Dicke's field equations and give an example
in which a plane impulsive gravitational wave and a null shell of matter
coexist on the same hypersurface. In the homogenous case, we characterize them
by their surface energy density and wave amplitude and discuss the inhomogenous
case. We also give an exact solution of the Brans-Dicke's field equations in
the electrovacuum case which admits a true curvature singularity and use it to
built an example where a plane impulsive gravitational wave and an
electromagnetic shock wave have the same null hypersurface as history of their
wave fronts and propagate independently and decoupled from a null shell of
matter. This last solution is shown to correspond to the space-time describing
the interaction region resulting from the collision of two electromagnetic
shock waves leading to the formation of two gravitational impulsive waves. The
properties of this solution are discussed and compared to those of the
Bell-Szekeres solution of general relativity.
| [
{
"created": "Thu, 16 Oct 1997 09:48:21 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Bressange",
"G. F.",
""
]
] | We study gravitational plane impulsive waves and electromagnetic shock waves in a scalar-tensor theory of gravity of the Brans-Dicke type. In vacuum, we present an exact solution of Brans-Dicke's field equations and give an example in which a plane impulsive gravitational wave and a null shell of matter coexist on the same hypersurface. In the homogenous case, we characterize them by their surface energy density and wave amplitude and discuss the inhomogenous case. We also give an exact solution of the Brans-Dicke's field equations in the electrovacuum case which admits a true curvature singularity and use it to built an example where a plane impulsive gravitational wave and an electromagnetic shock wave have the same null hypersurface as history of their wave fronts and propagate independently and decoupled from a null shell of matter. This last solution is shown to correspond to the space-time describing the interaction region resulting from the collision of two electromagnetic shock waves leading to the formation of two gravitational impulsive waves. The properties of this solution are discussed and compared to those of the Bell-Szekeres solution of general relativity. |
0704.1728 | S. Mignemi | S. Mignemi | Doubly Special Relativity and Finsler geometry | 8 pages, plain TeX | Phys.Rev.D76:047702,2007 | 10.1103/PhysRevD.76.047702 | null | gr-qc | null | We discuss the recent proposal of implementing Doubly Special Relativity in
configuration space by means of Finsler geometry. Although this formalism leads
to a consistent description of the dynamics of a particle, it does not seem to
give a complete description of the physics. In particular, the Finsler line
element is not invariant under the deformed Lorentz transformations of Doubly
Special Relativity. We study in detail some simple applications of the
formalism.
| [
{
"created": "Fri, 13 Apr 2007 09:51:02 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Mignemi",
"S.",
""
]
] | We discuss the recent proposal of implementing Doubly Special Relativity in configuration space by means of Finsler geometry. Although this formalism leads to a consistent description of the dynamics of a particle, it does not seem to give a complete description of the physics. In particular, the Finsler line element is not invariant under the deformed Lorentz transformations of Doubly Special Relativity. We study in detail some simple applications of the formalism. |
gr-qc/0611038 | Julio Cesar Fabris | K.A. Bronnikov, J.C. Fabris, S.V.B. Gon\c{c}alves | Different faces of the phantom | 6 pages, presented at IRGAC 2006, Barcelona, 11-15 July 2006 | J.Phys.A40:6835-6840,2007 | 10.1088/1751-8113/40/25/S27 | null | gr-qc | null | The SNe type Ia data admit that the Universe today may be dominated by some
exotic matter with negative pressure violating all energy conditions. Such
exotic matter is called {\it phantom matter} due to the anomalies connected
with violation of the energy conditions. If a phantom matter dominates the
matter content of the universe, it can develop a singularity in a finite future
proper time. Here we show that, under certain conditions, the evolution of
perturbations of this matter may lead to avoidance of this future singularity
(the Big Rip). At the same time, we show that local concentrations of a phantom
field may form, among other regular configurations, black holes with
asymptotically flat static regions, separated by an event horizon from an
expanding, singularity-free, asymptotically de Sitter universe.
| [
{
"created": "Mon, 6 Nov 2006 14:35:40 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Bronnikov",
"K. A.",
""
],
[
"Fabris",
"J. C.",
""
],
[
"Gonçalves",
"S. V. B.",
""
]
] | The SNe type Ia data admit that the Universe today may be dominated by some exotic matter with negative pressure violating all energy conditions. Such exotic matter is called {\it phantom matter} due to the anomalies connected with violation of the energy conditions. If a phantom matter dominates the matter content of the universe, it can develop a singularity in a finite future proper time. Here we show that, under certain conditions, the evolution of perturbations of this matter may lead to avoidance of this future singularity (the Big Rip). At the same time, we show that local concentrations of a phantom field may form, among other regular configurations, black holes with asymptotically flat static regions, separated by an event horizon from an expanding, singularity-free, asymptotically de Sitter universe. |
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