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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2405.10590 | Rui Chen | Jianming Chen and Gerui Chen | Emergence of cosmic space and horizon thermodynamics in the context of
the quantum-deformed entropy | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | According to the quantum deformation approach to quantum gravity, the
thermodynamical entropy of a quantum-deformed (q-deformed) black hole with
horizon area $A$ established by Jalalzadeh is expressed as $S_q = \pi\sin
\left( \frac{A}{8G\mathcal N} \right) /\sin\left(\frac{\pi}{2\mathcal
N}\right)$, where $\mathcal N=L_q^2/L_{p}^2$ is the q-deformation parameter,
$L_{p}$ denotes the Planck length, and $L_q$ denotes the quantum-deformed
cosmic apparent horizon distance. In this paper, assuming that the q-deformed
entropy is associated with the apparent horizon of the
Friedmann-Robertson-Walker (FRW) universe, we derive the Friedmann equation
from the unified first law of thermodynamics, ${dE = T_q dS_q + WdV}$. And this
one obtained is in line with the Friedmann equation derived from the law of
emergence proposed by Padmanabhan. It clearly shows the connection between the
law of emergence and the unified first law of thermodynamics. Subsequently, in
the context of the q-deformed horizon entropy, we investigate the constraints
of entropy maximization, and result demonstrates the consistency of the law of
emergence with the maximization of the q-deformed horizon entropy. Hence, the
law of emergence can be understood as a tendency to maximize the q-deformed
horizon entropy.
| [
{
"created": "Fri, 17 May 2024 07:25:29 GMT",
"version": "v1"
}
] | 2024-05-20 | [
[
"Chen",
"Jianming",
""
],
[
"Chen",
"Gerui",
""
]
] | According to the quantum deformation approach to quantum gravity, the thermodynamical entropy of a quantum-deformed (q-deformed) black hole with horizon area $A$ established by Jalalzadeh is expressed as $S_q = \pi\sin \left( \frac{A}{8G\mathcal N} \right) /\sin\left(\frac{\pi}{2\mathcal N}\right)$, where $\mathcal N=L_q^2/L_{p}^2$ is the q-deformation parameter, $L_{p}$ denotes the Planck length, and $L_q$ denotes the quantum-deformed cosmic apparent horizon distance. In this paper, assuming that the q-deformed entropy is associated with the apparent horizon of the Friedmann-Robertson-Walker (FRW) universe, we derive the Friedmann equation from the unified first law of thermodynamics, ${dE = T_q dS_q + WdV}$. And this one obtained is in line with the Friedmann equation derived from the law of emergence proposed by Padmanabhan. It clearly shows the connection between the law of emergence and the unified first law of thermodynamics. Subsequently, in the context of the q-deformed horizon entropy, we investigate the constraints of entropy maximization, and result demonstrates the consistency of the law of emergence with the maximization of the q-deformed horizon entropy. Hence, the law of emergence can be understood as a tendency to maximize the q-deformed horizon entropy. |
1811.02533 | Scott Perkins | Scott Perkins and Nicolas Yunes | Probing Screening and the Graviton Mass with Gravitational Waves | 11 pages, 5 figures | Classical & Quantum Gravity, Volume 36, Number 5, 2018 | 10.1088/1361-6382/aafce6 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves can probe fundamental physics, leading to new constraints
on the mass of the graviton. Previous tests, however, have neglected the effect
of screening, which is typically present in modified theories that predict a
non-zero graviton mass. We here study whether future gravitational wave
observations can constrain the graviton mass when screening effects are taken
into account. We first consider model-independent corrections to the
propagation of gravitational waves due to screened massive graviton effects. We
find that future observation can place constraints on the screening radius and
the graviton mass of ${\cal{O}}(10^{2})$--${\cal{O}}(10^{4})$ Mpc and
${\cal{O}}(10^{-22})$--${\cal{O}}(10^{-26})$ eV respectively. We also consider
screening effects in two specific theories, ghost-free massive gravity and
bigravity, that might not realize these types of propagation modifications, but
that do provide analytic expressions for screening parameters relevant to our
analysis allowing for more concrete results. However, the constraints we are
able to place are small. The reason for this is that second- and
third-generation detectors are sensitive to graviton masses that lead to very
small screening radii in these particular models. The effect of screening,
however, can become important as constraints on the graviton mass are improved
through the stacking of multiple observations in the near future.
| [
{
"created": "Tue, 6 Nov 2018 18:03:36 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Apr 2019 04:23:32 GMT",
"version": "v2"
}
] | 2019-04-12 | [
[
"Perkins",
"Scott",
""
],
[
"Yunes",
"Nicolas",
""
]
] | Gravitational waves can probe fundamental physics, leading to new constraints on the mass of the graviton. Previous tests, however, have neglected the effect of screening, which is typically present in modified theories that predict a non-zero graviton mass. We here study whether future gravitational wave observations can constrain the graviton mass when screening effects are taken into account. We first consider model-independent corrections to the propagation of gravitational waves due to screened massive graviton effects. We find that future observation can place constraints on the screening radius and the graviton mass of ${\cal{O}}(10^{2})$--${\cal{O}}(10^{4})$ Mpc and ${\cal{O}}(10^{-22})$--${\cal{O}}(10^{-26})$ eV respectively. We also consider screening effects in two specific theories, ghost-free massive gravity and bigravity, that might not realize these types of propagation modifications, but that do provide analytic expressions for screening parameters relevant to our analysis allowing for more concrete results. However, the constraints we are able to place are small. The reason for this is that second- and third-generation detectors are sensitive to graviton masses that lead to very small screening radii in these particular models. The effect of screening, however, can become important as constraints on the graviton mass are improved through the stacking of multiple observations in the near future. |
0803.3995 | Shih-Yuin Lin | Shih-Yuin Lin, Chung-Hsien Chou, B. L. Hu | Disentanglement of two harmonic oscillators in relativistic motion | 16 pages, 8 figures; typos added, minor changes in Secs. I and V | Phys.Rev.D78:125025,2008 | 10.1103/PhysRevD.78.125025 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the dynamics of quantum entanglement between two Unruh-DeWitt
detectors, one stationary (Alice), and another uniformly accelerating (Rob),
with no direct interaction but coupled to a common quantum field in (3+1)D
Minkowski space. We find that for all cases studied the initial entanglement
between the detectors disappears in a finite time ("sudden death"). After the
moment of total disentanglement the correlations between the two detectors
remain nonzero until late times. The relation between the disentanglement time
and Rob's proper acceleration is observer dependent. The larger the
acceleration is, the longer the disentanglement time in Alice's coordinate, but
the shorter in Rob's coordinate.
| [
{
"created": "Thu, 27 Mar 2008 18:46:18 GMT",
"version": "v1"
},
{
"created": "Tue, 23 Dec 2008 12:47:56 GMT",
"version": "v2"
}
] | 2009-01-01 | [
[
"Lin",
"Shih-Yuin",
""
],
[
"Chou",
"Chung-Hsien",
""
],
[
"Hu",
"B. L.",
""
]
] | We study the dynamics of quantum entanglement between two Unruh-DeWitt detectors, one stationary (Alice), and another uniformly accelerating (Rob), with no direct interaction but coupled to a common quantum field in (3+1)D Minkowski space. We find that for all cases studied the initial entanglement between the detectors disappears in a finite time ("sudden death"). After the moment of total disentanglement the correlations between the two detectors remain nonzero until late times. The relation between the disentanglement time and Rob's proper acceleration is observer dependent. The larger the acceleration is, the longer the disentanglement time in Alice's coordinate, but the shorter in Rob's coordinate. |
1004.0664 | Lee Smolin | Lee Smolin | Classical paradoxes of locality and their possible quantum resolutions
in deformed special relativity | LaTeX, 28 pages, no figures, substantially revised | null | 10.1007/s10714-011-1235-1 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In deformed or doubly special relativity (DSR) the action of the lorentz
group on momentum eigenstates is deformed to preserve a maximal momenta or
minimal length, supposed equal to the Planck length. The classical and quantum
dynamics of a particle propagating in kappa-Minkowski spacetime is discussed in
order to examine an apparent paradox of locality which arises in the classical
dynamics. This is due to the fact that the Lorentz transformations of spacetime
positions of particles depend on their energies, so whether or not a local
event, defined by the coincidence of two or more particles, takes place appears
to depend on the frame of reference of the observer. Here it is proposed that
the paradox arises only in the classical picture, and may be resolved when the
quantum dynamics is taken into account. If so, the apparent paradoxes arise
because it is inconsistent to study physics in which Planck's constant is zero
but the Planck length is non-vanishing. This may be relevant for phenomenology
such as observations by FERMI, because at leading order there is both a direct
and a stochastic dependence of arrival time on energy, due to an additional
spreading of wavepackets.
| [
{
"created": "Mon, 5 Apr 2010 17:14:18 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Jul 2010 22:37:48 GMT",
"version": "v2"
}
] | 2015-05-18 | [
[
"Smolin",
"Lee",
""
]
] | In deformed or doubly special relativity (DSR) the action of the lorentz group on momentum eigenstates is deformed to preserve a maximal momenta or minimal length, supposed equal to the Planck length. The classical and quantum dynamics of a particle propagating in kappa-Minkowski spacetime is discussed in order to examine an apparent paradox of locality which arises in the classical dynamics. This is due to the fact that the Lorentz transformations of spacetime positions of particles depend on their energies, so whether or not a local event, defined by the coincidence of two or more particles, takes place appears to depend on the frame of reference of the observer. Here it is proposed that the paradox arises only in the classical picture, and may be resolved when the quantum dynamics is taken into account. If so, the apparent paradoxes arise because it is inconsistent to study physics in which Planck's constant is zero but the Planck length is non-vanishing. This may be relevant for phenomenology such as observations by FERMI, because at leading order there is both a direct and a stochastic dependence of arrival time on energy, due to an additional spreading of wavepackets. |
gr-qc/0109060 | V. L. Kalashnikov | V. L. Kalashnikov | X-matter induced cosmological scenarios in the relativistic theory of
gravity | 9 pages, 3 figures, LaTeX2e, commented Maple 6 worksheet is
accessible on http://www.geocities.com/optomaplev | Spacetime and Substance 2 (2001) 75-78 | null | null | gr-qc | null | It was shown, that the presence of the so-called X-matter with an equation of
state, which lies between limits of the strong and weak energy conditions,
allows the variety of the cosmological scenarios in the relativistic theory of
gravity. In spite of the fixed negative sign of the cosmological term in the
field equations with massive graviton, it is possible to obtain the solutions
with accelerated and complicated loitering expansion of the universe. The
numerical estimation of the universe's age agrees with the modern observational
data if the upper limit of the graviton's mass is 10^{-71} g
| [
{
"created": "Tue, 18 Sep 2001 18:18:29 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Sep 2001 14:39:48 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Kalashnikov",
"V. L.",
""
]
] | It was shown, that the presence of the so-called X-matter with an equation of state, which lies between limits of the strong and weak energy conditions, allows the variety of the cosmological scenarios in the relativistic theory of gravity. In spite of the fixed negative sign of the cosmological term in the field equations with massive graviton, it is possible to obtain the solutions with accelerated and complicated loitering expansion of the universe. The numerical estimation of the universe's age agrees with the modern observational data if the upper limit of the graviton's mass is 10^{-71} g |
1408.5481 | Andrea Geralico | Donato Bini, Andrea Geralico, Daniele Gregoris, Sauro Succi | Friction forces in cosmological models | 8 pages, 2 figures; published version | Eur. Phys. J. C 73, 2334 (2013) | 10.1140/epjc/s10052-013-2334-9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the dynamics of test particles undergoing friction forces in a
Friedmann-Robertson-Walker (FRW) spacetime. The interaction with the background
fluid is modeled by introducing a Poynting-Robertson-like friction force in the
equations of motion, leading to measurable (at least in principle) deviations
of the particle trajectories from geodesic motion. The effect on the peculiar
velocities of the particles is investigated for various equations of state of
the background fluid and different standard cosmological models. The friction
force is found to have major effects on particle motion in closed FRW
universes, where it turns the time-asymptotic value (approaching the
recollapse) of the peculiar particle velocity from ultra-relativistic (close to
light speed) to a co-moving one, i.e., zero peculiar speed. On the other hand,
for open or flat universes the effect of the friction is not so significant,
because the time-asymptotic peculiar particle speed is largely non-relativistic
also in the geodesic case.
| [
{
"created": "Sat, 23 Aug 2014 10:20:21 GMT",
"version": "v1"
}
] | 2015-06-22 | [
[
"Bini",
"Donato",
""
],
[
"Geralico",
"Andrea",
""
],
[
"Gregoris",
"Daniele",
""
],
[
"Succi",
"Sauro",
""
]
] | We investigate the dynamics of test particles undergoing friction forces in a Friedmann-Robertson-Walker (FRW) spacetime. The interaction with the background fluid is modeled by introducing a Poynting-Robertson-like friction force in the equations of motion, leading to measurable (at least in principle) deviations of the particle trajectories from geodesic motion. The effect on the peculiar velocities of the particles is investigated for various equations of state of the background fluid and different standard cosmological models. The friction force is found to have major effects on particle motion in closed FRW universes, where it turns the time-asymptotic value (approaching the recollapse) of the peculiar particle velocity from ultra-relativistic (close to light speed) to a co-moving one, i.e., zero peculiar speed. On the other hand, for open or flat universes the effect of the friction is not so significant, because the time-asymptotic peculiar particle speed is largely non-relativistic also in the geodesic case. |
1412.2914 | Edward Wilson-Ewing | Yi-Fu Cai, Edward Wilson-Ewing | A $\Lambda$CDM bounce scenario | 14 pages, 8 figures, v2: Discussion extended and references added | JCAP03(2015)006 | 10.1088/1475-7516/2015/03/006 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study a contracting universe composed of cold dark matter and radiation,
and with a positive cosmological constant. As is well known from standard
cosmological perturbation theory, under the assumption of initial quantum
vacuum fluctuations the Fourier modes of the comoving curvature perturbation
that exit the (sound) Hubble radius in such a contracting universe at a time of
matter-domination will be nearly scale-invariant. Furthermore, the modes that
exit the (sound) Hubble radius when the effective equation of state is slightly
negative due to the cosmological constant will have a slight red tilt, in
agreement with observations. We assume that loop quantum cosmology captures the
correct high-curvature dynamics of the space-time, and this ensures that the
big-bang singularity is resolved and is replaced by a bounce. We calculate the
evolution of the perturbations through the bounce and find that they remain
nearly scale-invariant. We also show that the amplitude of the scalar
perturbations in this cosmology depends on a combination of the sound speed of
cold dark matter, the Hubble rate in the contracting branch at the time of
equality of the energy densities of cold dark matter and radiation, and the
curvature scale that the loop quantum cosmology bounce occurs at. Importantly,
as this scenario predicts a positive running of the scalar index, observations
can potentially differentiate between it and inflationary models. Finally, for
a small sound speed of cold dark matter, this scenario predicts a small
tensor-to-scalar ratio.
| [
{
"created": "Tue, 9 Dec 2014 11:10:06 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Jan 2015 15:12:56 GMT",
"version": "v2"
}
] | 2015-06-23 | [
[
"Cai",
"Yi-Fu",
""
],
[
"Wilson-Ewing",
"Edward",
""
]
] | We study a contracting universe composed of cold dark matter and radiation, and with a positive cosmological constant. As is well known from standard cosmological perturbation theory, under the assumption of initial quantum vacuum fluctuations the Fourier modes of the comoving curvature perturbation that exit the (sound) Hubble radius in such a contracting universe at a time of matter-domination will be nearly scale-invariant. Furthermore, the modes that exit the (sound) Hubble radius when the effective equation of state is slightly negative due to the cosmological constant will have a slight red tilt, in agreement with observations. We assume that loop quantum cosmology captures the correct high-curvature dynamics of the space-time, and this ensures that the big-bang singularity is resolved and is replaced by a bounce. We calculate the evolution of the perturbations through the bounce and find that they remain nearly scale-invariant. We also show that the amplitude of the scalar perturbations in this cosmology depends on a combination of the sound speed of cold dark matter, the Hubble rate in the contracting branch at the time of equality of the energy densities of cold dark matter and radiation, and the curvature scale that the loop quantum cosmology bounce occurs at. Importantly, as this scenario predicts a positive running of the scalar index, observations can potentially differentiate between it and inflationary models. Finally, for a small sound speed of cold dark matter, this scenario predicts a small tensor-to-scalar ratio. |
gr-qc/0303043 | Roberto Giambo' | Roberto Giambo', Fabio Giannoni, Giulio Magli and Paolo Piccione | Gravitational collapse of barotropic spherical fluids | 17 pages, LaTeX2e | Gen.Rel.Grav. 36 (2004) 1279-1298 | 10.1023/B:GERG.0000022388.11306.e1 | null | gr-qc astro-ph | null | The gravitational collapse of spherical, barotropic perfect fluids is
analyzed here. For the first time, the final state of these systems is studied
without resorting to simplifying assumptions - such as self-similarity - using
a new approach based on non-linear o.d.e. techniques, and formation of naked
singularities is shown to occur for solutions such that the mass function is
analytic in a neighborhood of the spacetime singularity.
| [
{
"created": "Tue, 11 Mar 2003 16:44:25 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Jul 2003 14:51:00 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Giambo'",
"Roberto",
""
],
[
"Giannoni",
"Fabio",
""
],
[
"Magli",
"Giulio",
""
],
[
"Piccione",
"Paolo",
""
]
] | The gravitational collapse of spherical, barotropic perfect fluids is analyzed here. For the first time, the final state of these systems is studied without resorting to simplifying assumptions - such as self-similarity - using a new approach based on non-linear o.d.e. techniques, and formation of naked singularities is shown to occur for solutions such that the mass function is analytic in a neighborhood of the spacetime singularity. |
1208.3509 | Julio Cesar Fabris | J. C. Fabris, F. T. Falciano, P. Vargas Moniz, J. Marto, N. Pinto-Neto | Dilaton Quantum Cosmology with a Schrodinger-like equation | 14 pages, 3 figures in eps format. Minors corrections, new figures | null | 10.1007/s13538-012-0105-y | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A quantum cosmological model with radiation and a dilaton scalar field is
analysed. The Wheeler-deWitt equation in the mini-superspace induces a
Schr\"odinger equation, which can be solved. An explicit wavepacket is
constructed for a particular choice of the ordering factor. A consistent
solution is possible only when the scalar field is a phantom field. Moreover,
although the wavepacket is time dependent, a Bohmian analysis allows to extract
a bouncing behaviour for the scale factor.
| [
{
"created": "Thu, 16 Aug 2012 22:51:46 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Aug 2012 15:35:17 GMT",
"version": "v2"
}
] | 2015-06-11 | [
[
"Fabris",
"J. C.",
""
],
[
"Falciano",
"F. T.",
""
],
[
"Moniz",
"P. Vargas",
""
],
[
"Marto",
"J.",
""
],
[
"Pinto-Neto",
"N.",
""
]
] | A quantum cosmological model with radiation and a dilaton scalar field is analysed. The Wheeler-deWitt equation in the mini-superspace induces a Schr\"odinger equation, which can be solved. An explicit wavepacket is constructed for a particular choice of the ordering factor. A consistent solution is possible only when the scalar field is a phantom field. Moreover, although the wavepacket is time dependent, a Bohmian analysis allows to extract a bouncing behaviour for the scale factor. |
gr-qc/0012016 | Carlos F. Sopuerta | Francesc Fayos and Carlos F. Sopuerta | Integrability conditions for vacuum spacetimes with a Killing vector
field | 2 pages, ws-p9-75x6-50.cls with LaTeX2e. Contribution to the Ninth
Marcel Grossmann Meeting (Rome, 2-8 July, 2000). Parallel session GT1 | null | null | null | gr-qc | null | We present a new approach to the study of vacuum spacetimes with a Killing
symmetry. The central quantity in this approach is the exterior derivative of
the Killing vector field, which is a test electromagnetic field. Considering
the algebraic structure of this quantity we get a new view of the integrability
conditions, which provides a natural way of studying the connections between
the algebraic structure of the spacetime and properties of the Killing
symmetry.
| [
{
"created": "Tue, 5 Dec 2000 12:24:46 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Fayos",
"Francesc",
""
],
[
"Sopuerta",
"Carlos F.",
""
]
] | We present a new approach to the study of vacuum spacetimes with a Killing symmetry. The central quantity in this approach is the exterior derivative of the Killing vector field, which is a test electromagnetic field. Considering the algebraic structure of this quantity we get a new view of the integrability conditions, which provides a natural way of studying the connections between the algebraic structure of the spacetime and properties of the Killing symmetry. |
2402.18997 | Orlando Luongo | Dario Corona, Roberto Giamb\`o, Orlando Luongo | Motion of test particles in quasi anti-de Sitter regular black holes | 14 pages, 2 figures. Effort prepared for the Special Issue "20th
Anniversary of IJGMMP" | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explore the characteristics of two novel regular spacetimes that exhibit a
non-zero vacuum energy term, under the form of a (quasi) anti-de Sitter phase.
Specifically, the first metric is spherical, while the second, derived by
applying the generalized Newman-Janis algorithm to the first, is axisymmetric.
We show that the equations of state of the effective fluids associated with the
two metrics asymptotically tend to negative values, resembling quintessence. In
addition, we study test particle motions, illustrating the main discrepancies
among our models and more conventional metrics exhibiting non-vanishing anti-de
Sitter phase.
| [
{
"created": "Thu, 29 Feb 2024 09:47:59 GMT",
"version": "v1"
}
] | 2024-03-01 | [
[
"Corona",
"Dario",
""
],
[
"Giambò",
"Roberto",
""
],
[
"Luongo",
"Orlando",
""
]
] | We explore the characteristics of two novel regular spacetimes that exhibit a non-zero vacuum energy term, under the form of a (quasi) anti-de Sitter phase. Specifically, the first metric is spherical, while the second, derived by applying the generalized Newman-Janis algorithm to the first, is axisymmetric. We show that the equations of state of the effective fluids associated with the two metrics asymptotically tend to negative values, resembling quintessence. In addition, we study test particle motions, illustrating the main discrepancies among our models and more conventional metrics exhibiting non-vanishing anti-de Sitter phase. |
2104.04932 | Luis A. Sanchez | Fabi\'an H. Zuluaga (1) and Luis A. S\'anchez (1) ((1) Escuela de
F\'isica, Universidad Nacional de Colombia, Medell\'in, Colombia) | Black holes in asymptotic safety with higher derivatives: accretion and
stability analysis | 20 pages, 11 figures, accepted for publication in Chinese Physics C | null | 10.1088/1674-1137/abf72d | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We review the issue of steady spherically symmetric accretion onto a
renormalization group improved Schwarzschild space-time which is solution to an
asymptotically safe theory (AS) containing high-derivative terms. We use a
Hamiltonian dynamical system approach for the analysis of the accretion of four
types of isothermal test fluids: ultra-stiff fluid, ultra-relativistic fluid,
radiation fluid, and sub-relativistic fluid. An important outcome of our study
is that, contrary to what claimed in a recent work, there exist physical
solutions for the accretion of an ultra-relativistic fluid in AS which include
subsonic, supersonic and transonic regimes. We also study quantum corrections
to the known stability of the accretion in general relativity (GR). To this end
we use a perturbative procedure based on the continuity equation with the mass
accretion rate being the perturbed quantity. Two classes of perturbations are
studied: standing waves and travelling waves. We find that quantum gravity
effects either enhance or diminish the stability of the accretion depending on
the type of test fluid and depending on the radial distance to the central
object.
| [
{
"created": "Sun, 11 Apr 2021 06:32:34 GMT",
"version": "v1"
}
] | 2021-09-01 | [
[
"Zuluaga",
"Fabián H.",
""
],
[
"Sánchez",
"Luis A.",
""
]
] | We review the issue of steady spherically symmetric accretion onto a renormalization group improved Schwarzschild space-time which is solution to an asymptotically safe theory (AS) containing high-derivative terms. We use a Hamiltonian dynamical system approach for the analysis of the accretion of four types of isothermal test fluids: ultra-stiff fluid, ultra-relativistic fluid, radiation fluid, and sub-relativistic fluid. An important outcome of our study is that, contrary to what claimed in a recent work, there exist physical solutions for the accretion of an ultra-relativistic fluid in AS which include subsonic, supersonic and transonic regimes. We also study quantum corrections to the known stability of the accretion in general relativity (GR). To this end we use a perturbative procedure based on the continuity equation with the mass accretion rate being the perturbed quantity. Two classes of perturbations are studied: standing waves and travelling waves. We find that quantum gravity effects either enhance or diminish the stability of the accretion depending on the type of test fluid and depending on the radial distance to the central object. |
1304.2964 | Ernesto Nungesser | Ernesto Nungesser and Woei Chet Lim | The electromagnetic spike solutions | V3: 13 pages and 4 figures. No change in main result. Title and names
of the solutions changed to make their physical interpretation more clear | Class. Quantum Grav. 30 (2013) 235020 | 10.1088/0264-9381/30/23/235020 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The aim of this paper is to use the existing relation between polarized
electromagnetic Gowdy spacetimes and vacuum Gowdy spacetimes to find explicit
solutions for electromagnetic spikes by a procedure which has been developed by
one of the authors for gravitational spikes. We present new inhomogeneous
solutions which we call the EME and MEM electromagnetic spike solutions.
| [
{
"created": "Wed, 10 Apr 2013 13:57:06 GMT",
"version": "v1"
},
{
"created": "Mon, 5 Aug 2013 13:38:46 GMT",
"version": "v2"
},
{
"created": "Sat, 28 Sep 2013 12:54:30 GMT",
"version": "v3"
}
] | 2015-06-15 | [
[
"Nungesser",
"Ernesto",
""
],
[
"Lim",
"Woei Chet",
""
]
] | The aim of this paper is to use the existing relation between polarized electromagnetic Gowdy spacetimes and vacuum Gowdy spacetimes to find explicit solutions for electromagnetic spikes by a procedure which has been developed by one of the authors for gravitational spikes. We present new inhomogeneous solutions which we call the EME and MEM electromagnetic spike solutions. |
1107.5707 | Felipe J. Llanes-Estrada | Antonio Dobado, Felipe J. Llanes-Estrada (U. Complutense Madrid) and
Jose Antonio Oller (U. Murcia) | The existence of a two-solar mass neutron star constrains the
gravitational constant G_N at strong field | 5 pages including 8 figures | null | 10.1103/PhysRevC.85.012801 | null | gr-qc hep-th nucl-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In General Relativity there is a maximum mass allowed for neutron stars that,
if exceeded, entails their collapse into a black hole. Its precise value
depends on details of the nuclear matter equation of state about which we are
much more certain thanks to recent progress in low-energy effective theories.
The discovery of a two-solar mass neutron star, near that maximum mass, when
analyzed with modern equations of state, implies that Newton's gravitational
constant in the star cannot exceed its value on Earth by more than 8% at 95%
confidence level. This is a remarkable leap of ten orders of magnitude in the
gravitational field intensity at which the constant has been constrained.
| [
{
"created": "Thu, 28 Jul 2011 13:02:59 GMT",
"version": "v1"
}
] | 2013-05-30 | [
[
"Dobado",
"Antonio",
"",
"U. Complutense Madrid"
],
[
"Llanes-Estrada",
"Felipe J.",
"",
"U. Complutense Madrid"
],
[
"Oller",
"Jose Antonio",
"",
"U. Murcia"
]
] | In General Relativity there is a maximum mass allowed for neutron stars that, if exceeded, entails their collapse into a black hole. Its precise value depends on details of the nuclear matter equation of state about which we are much more certain thanks to recent progress in low-energy effective theories. The discovery of a two-solar mass neutron star, near that maximum mass, when analyzed with modern equations of state, implies that Newton's gravitational constant in the star cannot exceed its value on Earth by more than 8% at 95% confidence level. This is a remarkable leap of ten orders of magnitude in the gravitational field intensity at which the constant has been constrained. |
gr-qc/0506033 | Christian Boehmer | Christian G. Boehmer | On inflation and torsion in cosmology | 5 pages | Acta Phys.Polon. B36 (2005) 2841-2845 | null | Preprint ESI 1661, TUW-05-10 | gr-qc | null | In a recent letter by H. Davoudiasl, R. Kitano, T. Li and H. Murayama ``The
new Minimal Standard Model'' (NMSM) was constructed that incorporates new
physics beyond the Minimal Standard Model (MSM) of particle physics. The
authors follow the principle of minimal particle content and therefore adopt
the viewpoint of particle physicists. It is shown that a generalisation of the
geometric structure of spacetime can also be used to explain physics beyond the
MSM. It is explicitly shown that for example inflation, i.e. an exponentially
expanding universe, can easily be explained within the framework of
Einstein-Cartan theory.
| [
{
"created": "Mon, 6 Jun 2005 11:33:24 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Boehmer",
"Christian G.",
""
]
] | In a recent letter by H. Davoudiasl, R. Kitano, T. Li and H. Murayama ``The new Minimal Standard Model'' (NMSM) was constructed that incorporates new physics beyond the Minimal Standard Model (MSM) of particle physics. The authors follow the principle of minimal particle content and therefore adopt the viewpoint of particle physicists. It is shown that a generalisation of the geometric structure of spacetime can also be used to explain physics beyond the MSM. It is explicitly shown that for example inflation, i.e. an exponentially expanding universe, can easily be explained within the framework of Einstein-Cartan theory. |
1409.2927 | Mercedes Martin-Benito | Beatriz Elizaga Navascu\'es, Mercedes Mart\'in-Benito, and Guillermo
A. Mena Marug\'an | Modeling effective FRW cosmologies with perfect fluids from states of
the hybrid quantum Gowdy model | Version accepted for publication in PRD | Phys. Rev. D 91, 024028, 2015 | 10.1103/PhysRevD.91.024028 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We employ recently developed approximation methods in the hybrid quantization
of the Gowdy $T^3$ model with linear polarization and a massless scalar field
to obtain physically interesting solutions of this inhomogeneous cosmology.
More specifically, we propose approximate solutions of the quantum Gowdy model
constructed in such a way that, for the Hamiltonian constraint, they
effectively behave as those corresponding to a flat homogeneous and isotropic
universe filled with a perfect fluid, even though these quantum states are far
from being homogeneous and isotropic. We analyze how one can get different
perfect fluid effective behaviors, including the cases of dust, radiation, and
cosmological constant.
| [
{
"created": "Wed, 10 Sep 2014 00:41:44 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Jan 2015 13:04:06 GMT",
"version": "v2"
}
] | 2015-06-22 | [
[
"Navascués",
"Beatriz Elizaga",
""
],
[
"Martín-Benito",
"Mercedes",
""
],
[
"Marugán",
"Guillermo A. Mena",
""
]
] | We employ recently developed approximation methods in the hybrid quantization of the Gowdy $T^3$ model with linear polarization and a massless scalar field to obtain physically interesting solutions of this inhomogeneous cosmology. More specifically, we propose approximate solutions of the quantum Gowdy model constructed in such a way that, for the Hamiltonian constraint, they effectively behave as those corresponding to a flat homogeneous and isotropic universe filled with a perfect fluid, even though these quantum states are far from being homogeneous and isotropic. We analyze how one can get different perfect fluid effective behaviors, including the cases of dust, radiation, and cosmological constant. |
2407.04052 | Guilherme Brando | Guilherme Brando, Srashti Goyal, Stefano Savastano, Hector
Villarrubia-Rojo and Miguel Zumalac\'arregui | Signatures of dark and baryonic structures on weakly lensed
gravitational waves | 26 pages, 19 figures, 3 tables | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | Gravitational lensing offers a powerful tool for exploring the matter
distribution in the Universe. Thanks to their low frequencies and phase
coherence, gravitational waves (GWs) allow for the observation of novel
wave-optics features (WOFs) in lensing, inaccessible to electromagnetic
signals. Combined with the existing accurate source models, lensed GWs can be
used to infer the properties of gravitational lenses. The prospect is
particularly compelling for space-borne detectors, where the high
signal-to-noise ratio expected from massive black hole binary mergers allows
WOFs to be distinguished deep into the weak lensing regime, drastically
increasing the detection probability. Here, we investigate in detail the
capacity of the LISA mission to detect WOFs caused by dark matter halos,
galaxies and the supermassive black holes (SMBHs) within them. We estimate the
total optical depth to be $\lambda_{\rm tot} \sim 6 \times 10 ^{-3}$ for the
loudest binaries of total mass $M_{\rm BBH} \sim 10^6 M_{\odot}$, with the
dominant contribution coming from SMBHs. We also find that WOFs in low-mass
binaries $M_{\rm BBH} \sim 10^4 M_{\odot}$ are more likely due to the central
galaxies. Within our model of gravitational lenses, we predict
$\mathcal{O}(0.1)-\mathcal{O}(1)$ weakly-lensed events to be detectable during
the 5 years of LISA mission, depending on the source population models. We show
that WOFs signatures are very sensitive to the properties of dark-matter halos
with $M_{\rm vir}\in (10^6-10^8)M_\odot$: increasing the compactness parameter
by $\sim 3$ in that range raises the detection rate by $\sim 26$. Additionally,
we show that collective effects from the complex inner halo structure can
further enhance detectability. This suggests that lensed GWs in LISA will be an
excellent probe of dark-matter theories, baryonic and halo sub-structures.
| [
{
"created": "Thu, 4 Jul 2024 16:50:19 GMT",
"version": "v1"
}
] | 2024-07-08 | [
[
"Brando",
"Guilherme",
""
],
[
"Goyal",
"Srashti",
""
],
[
"Savastano",
"Stefano",
""
],
[
"Villarrubia-Rojo",
"Hector",
""
],
[
"Zumalacárregui",
"Miguel",
""
]
] | Gravitational lensing offers a powerful tool for exploring the matter distribution in the Universe. Thanks to their low frequencies and phase coherence, gravitational waves (GWs) allow for the observation of novel wave-optics features (WOFs) in lensing, inaccessible to electromagnetic signals. Combined with the existing accurate source models, lensed GWs can be used to infer the properties of gravitational lenses. The prospect is particularly compelling for space-borne detectors, where the high signal-to-noise ratio expected from massive black hole binary mergers allows WOFs to be distinguished deep into the weak lensing regime, drastically increasing the detection probability. Here, we investigate in detail the capacity of the LISA mission to detect WOFs caused by dark matter halos, galaxies and the supermassive black holes (SMBHs) within them. We estimate the total optical depth to be $\lambda_{\rm tot} \sim 6 \times 10 ^{-3}$ for the loudest binaries of total mass $M_{\rm BBH} \sim 10^6 M_{\odot}$, with the dominant contribution coming from SMBHs. We also find that WOFs in low-mass binaries $M_{\rm BBH} \sim 10^4 M_{\odot}$ are more likely due to the central galaxies. Within our model of gravitational lenses, we predict $\mathcal{O}(0.1)-\mathcal{O}(1)$ weakly-lensed events to be detectable during the 5 years of LISA mission, depending on the source population models. We show that WOFs signatures are very sensitive to the properties of dark-matter halos with $M_{\rm vir}\in (10^6-10^8)M_\odot$: increasing the compactness parameter by $\sim 3$ in that range raises the detection rate by $\sim 26$. Additionally, we show that collective effects from the complex inner halo structure can further enhance detectability. This suggests that lensed GWs in LISA will be an excellent probe of dark-matter theories, baryonic and halo sub-structures. |
2303.10339 | Tiberiu Harko | Zahra Haghani, Tiberiu Harko | Compact stellar structures in Weyl geometric gravity | 20 pages, 15 figures, accepted for publication in PRD | null | 10.1103/PhysRevD.107.064068 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the structure and physical properties of specific classes of
neutron, quark, and Bose-Einstein Condensate stars in the conformally invariant
Weyl geometric gravity theory. The basic theory is derived from the simplest
conformally invariant action, constructed, in Weyl geometry, from the square of
the Weyl scalar, the strength of the Weyl vector, and a matter term,
respectively. The action is linearized in the Weyl scalar by introducing an
auxiliary scalar field. To keep the theory conformally invariant the trace
condition is imposed on the matter energy-momentum tensor. The field equations
are derived by varying the action with respect to the metric tensor, Weyl
vector field and scalar field. By adopting a static spherically symmetric
interior geometry, we obtain the field equations, describing the structure and
properties of stellar objects in Weyl geometric gravity. The solutions of the
field equations are obtained numerically, for different equations of state of
the neutron and quark matter. More specifically, constant density stellar
models, and models described by the stiff fluid, radiation fluid, quark bag
model, and Bose-Einstein Condensate equations of state are explicitly
constructed numerically in both general relativity and Weyl geometric gravity,
thus allowing an in depth comparison between the predictions of these two
gravitational theories. As a general result it turns out that for all the
considered equations of state, Weyl geometric gravity stars are more massive
than their general relativistic counterparts. As a possible astrophysical
application of the obtained results we suggest that the recently observed
neutron stars, with masses in the range of 2$M_{\odot}$ and 3$M_{\odot}$,
respectively, could be in fact conformally invariant Weyl geometric neutron or
quark stars.
| [
{
"created": "Sat, 18 Mar 2023 05:34:52 GMT",
"version": "v1"
}
] | 2023-04-12 | [
[
"Haghani",
"Zahra",
""
],
[
"Harko",
"Tiberiu",
""
]
] | We consider the structure and physical properties of specific classes of neutron, quark, and Bose-Einstein Condensate stars in the conformally invariant Weyl geometric gravity theory. The basic theory is derived from the simplest conformally invariant action, constructed, in Weyl geometry, from the square of the Weyl scalar, the strength of the Weyl vector, and a matter term, respectively. The action is linearized in the Weyl scalar by introducing an auxiliary scalar field. To keep the theory conformally invariant the trace condition is imposed on the matter energy-momentum tensor. The field equations are derived by varying the action with respect to the metric tensor, Weyl vector field and scalar field. By adopting a static spherically symmetric interior geometry, we obtain the field equations, describing the structure and properties of stellar objects in Weyl geometric gravity. The solutions of the field equations are obtained numerically, for different equations of state of the neutron and quark matter. More specifically, constant density stellar models, and models described by the stiff fluid, radiation fluid, quark bag model, and Bose-Einstein Condensate equations of state are explicitly constructed numerically in both general relativity and Weyl geometric gravity, thus allowing an in depth comparison between the predictions of these two gravitational theories. As a general result it turns out that for all the considered equations of state, Weyl geometric gravity stars are more massive than their general relativistic counterparts. As a possible astrophysical application of the obtained results we suggest that the recently observed neutron stars, with masses in the range of 2$M_{\odot}$ and 3$M_{\odot}$, respectively, could be in fact conformally invariant Weyl geometric neutron or quark stars. |
1001.5061 | Eugen Simanek | Eugen Simanek | Gravitational field of twisted Baby Skyrmion strings and loops | 18 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the gravitational field of infinite straight and stationary
twisted Baby Skyrmion cosmic string. Using the approximate solution of Einstein
equations, it is shown that the internal phase rotation (twist) along the
string axis is responsible for a long-range gravitational acceleration
resembling that of massive cylindrical shell. We also study the stability and
gravitational field of circular loops. When the loop radius becomes comparable
with the string width, the rigidity energy tends to stabilize small loops
against radial collapse. The nucleon scale-toroidal knot with Hopf charge Q=1
is found to decay very rapidly on the scale of the age of the universe due to
low energy cost to flux lines crossings. Such knot is therefore excluded from
the dark matter scenario of Spergel and Steinhardt. However, the Q = 0 loop,
stabilized by rigidity, could be a candidate for this scenario. In contrast,
the electroweak strings are prevented from intercommuting due to much larger
energy cost to intersection. This makes them a possible candidate for the solid
dark matter scenario of Bucher and Spergel.
| [
{
"created": "Thu, 28 Jan 2010 20:49:55 GMT",
"version": "v1"
}
] | 2010-01-29 | [
[
"Simanek",
"Eugen",
""
]
] | We consider the gravitational field of infinite straight and stationary twisted Baby Skyrmion cosmic string. Using the approximate solution of Einstein equations, it is shown that the internal phase rotation (twist) along the string axis is responsible for a long-range gravitational acceleration resembling that of massive cylindrical shell. We also study the stability and gravitational field of circular loops. When the loop radius becomes comparable with the string width, the rigidity energy tends to stabilize small loops against radial collapse. The nucleon scale-toroidal knot with Hopf charge Q=1 is found to decay very rapidly on the scale of the age of the universe due to low energy cost to flux lines crossings. Such knot is therefore excluded from the dark matter scenario of Spergel and Steinhardt. However, the Q = 0 loop, stabilized by rigidity, could be a candidate for this scenario. In contrast, the electroweak strings are prevented from intercommuting due to much larger energy cost to intersection. This makes them a possible candidate for the solid dark matter scenario of Bucher and Spergel. |
1009.4665 | Manuel Tiglio | Enrique Pazos, David Brizuela, Jose M. Martin-Garcia, Manuel Tiglio | Mode coupling of Schwarzschild perturbations: Ringdown frequencies | null | Phys.Rev.D82:104028,2010 | 10.1103/PhysRevD.82.104028 | null | gr-qc astro-ph.CO astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Within linearized perturbation theory, black holes decay to their final
stationary state through the well-known spectrum of quasinormal modes. Here we
numerically study whether nonlinearities change this picture. For that purpose
we study the ringdown frequencies of gauge-invariant second-order gravitational
perturbations induced by self-coupling of linearized perturbations of
Schwarzschild black holes. We do so through high-accuracy simulations in the
time domain of first and second-order Regge-Wheeler-Zerilli type equations, for
a variety of initial data sets. We consider first-order even-parity
$(\ell=2,m=\pm 2)$ perturbations and odd-parity $(\ell=2,m=0)$ ones, and all
the multipoles that they generate through self-coupling. For all of them and
all the initial data sets considered we find that ---in contrast to previous
predictions in the literature--- the numerical decay frequencies of
second-order perturbations are the same ones of linearized theory, and we
explain the observed behavior. This would indicate, in particular, that when
modeling or searching for ringdown gravitational waves, appropriately including
the standard quasinormal modes already takes into account nonlinear effects.
| [
{
"created": "Thu, 23 Sep 2010 17:32:32 GMT",
"version": "v1"
}
] | 2010-12-09 | [
[
"Pazos",
"Enrique",
""
],
[
"Brizuela",
"David",
""
],
[
"Martin-Garcia",
"Jose M.",
""
],
[
"Tiglio",
"Manuel",
""
]
] | Within linearized perturbation theory, black holes decay to their final stationary state through the well-known spectrum of quasinormal modes. Here we numerically study whether nonlinearities change this picture. For that purpose we study the ringdown frequencies of gauge-invariant second-order gravitational perturbations induced by self-coupling of linearized perturbations of Schwarzschild black holes. We do so through high-accuracy simulations in the time domain of first and second-order Regge-Wheeler-Zerilli type equations, for a variety of initial data sets. We consider first-order even-parity $(\ell=2,m=\pm 2)$ perturbations and odd-parity $(\ell=2,m=0)$ ones, and all the multipoles that they generate through self-coupling. For all of them and all the initial data sets considered we find that ---in contrast to previous predictions in the literature--- the numerical decay frequencies of second-order perturbations are the same ones of linearized theory, and we explain the observed behavior. This would indicate, in particular, that when modeling or searching for ringdown gravitational waves, appropriately including the standard quasinormal modes already takes into account nonlinear effects. |
1312.3697 | Daisuke Ida | Daisuke Ida and Miyuki Saito | First-Quantized Theory of Expanding Universe from Field Quantization in
Mini-Superspace | 21 pages, 1 figure, published version | null | 10.1007/JHEP08(2014)082 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We propose an improved variant of the third-quantization scheme, for the
spatially homogeneous and isotropic cosmological models in Einstein gravity
coupled with a neutral massless scalar field. Our strategy is to specify a
semi-Riemannian structure on the mini-superspace and to consider the quantum
Klein-Gordon field on the mini-superspace. Then, the Hilbert space of this
quantum system becomes inseparable, which causes the creation of infinite
number of universes. To overcome this issue, we introduce a vector bundle
structure on the Hilbert space and the connection of the vector bundle. Then,
we can define a consistent unitary time evolution of the quantum universe in
terms of the connection field on the vector bundle. By doing this, we are able
to treat the quantum dynamics of a single-universe state. We also find an
appropriate observable set constituting the CCR-algebra, and obtain the
Schr\"odinger equation for the wave function of the single-universe state. We
show that the present quantum theory correctly reproduces the classical
solution to the Einstein equation.
| [
{
"created": "Fri, 13 Dec 2013 03:41:20 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Mar 2014 13:14:31 GMT",
"version": "v2"
},
{
"created": "Tue, 12 Aug 2014 15:55:20 GMT",
"version": "v3"
}
] | 2015-06-18 | [
[
"Ida",
"Daisuke",
""
],
[
"Saito",
"Miyuki",
""
]
] | We propose an improved variant of the third-quantization scheme, for the spatially homogeneous and isotropic cosmological models in Einstein gravity coupled with a neutral massless scalar field. Our strategy is to specify a semi-Riemannian structure on the mini-superspace and to consider the quantum Klein-Gordon field on the mini-superspace. Then, the Hilbert space of this quantum system becomes inseparable, which causes the creation of infinite number of universes. To overcome this issue, we introduce a vector bundle structure on the Hilbert space and the connection of the vector bundle. Then, we can define a consistent unitary time evolution of the quantum universe in terms of the connection field on the vector bundle. By doing this, we are able to treat the quantum dynamics of a single-universe state. We also find an appropriate observable set constituting the CCR-algebra, and obtain the Schr\"odinger equation for the wave function of the single-universe state. We show that the present quantum theory correctly reproduces the classical solution to the Einstein equation. |
gr-qc/0612149 | Manuel Tiglio | Enrique Pazos, Ernst Nils Dorband, Alessandro Nagar, Carlos
Palenzuela, Erik Schnetter, Manuel Tiglio | How far away is far enough for extracting numerical waveforms, and how
much do they depend on the extraction method? | 19 pages | Class.Quant.Grav.24:S341-S368,2007 | 10.1088/0264-9381/24/12/S22 | null | gr-qc | null | We present a method for extracting gravitational waves from numerical
spacetimes which generalizes and refines one of the standard methods based on
the Regge--Wheeler--Zerilli perturbation formalism. [abridged] We then present
fully nonlinear three-dimensional numerical evolutions of a distorted
Schwarzschild black hole in Kerr--Schild coordinates with an odd parity
perturbation and analyze the improvement we gain from our generalized wave
extraction, comparing our new method to the standard one. [abridged]
We find that, even with observers as far out as $R=80 M$--which is larger
than what is commonly used in state-of-the-art simulations--the assumption in
the standard method that the background is close to having Schwarzschild-like
coordinates increases the error in the extracted waveforms considerably. Even
for our coarsest resolutions, our new method decreases the error by between one
and two orders of magnitudes. Furthermore, we explicitly see that the errors in
the extracted waveforms obtained by the standard method do not converge to zero
with increasing resolution. [abridged]
In a general scenario, for example a collision of compact objects, there is
no precise definition of gravitational radiation at a finite distance, and
gravitational wave extraction methods at such distances are thus inherently
approximate. The results of this paper bring up the possibility that different
choices in the wave extraction procedure at a fixed and finite distance may
result in relative differences in the waveforms which are actually larger than
the numerical errors in the solution.
| [
{
"created": "Fri, 22 Dec 2006 20:20:35 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Pazos",
"Enrique",
""
],
[
"Dorband",
"Ernst Nils",
""
],
[
"Nagar",
"Alessandro",
""
],
[
"Palenzuela",
"Carlos",
""
],
[
"Schnetter",
"Erik",
""
],
[
"Tiglio",
"Manuel",
""
]
] | We present a method for extracting gravitational waves from numerical spacetimes which generalizes and refines one of the standard methods based on the Regge--Wheeler--Zerilli perturbation formalism. [abridged] We then present fully nonlinear three-dimensional numerical evolutions of a distorted Schwarzschild black hole in Kerr--Schild coordinates with an odd parity perturbation and analyze the improvement we gain from our generalized wave extraction, comparing our new method to the standard one. [abridged] We find that, even with observers as far out as $R=80 M$--which is larger than what is commonly used in state-of-the-art simulations--the assumption in the standard method that the background is close to having Schwarzschild-like coordinates increases the error in the extracted waveforms considerably. Even for our coarsest resolutions, our new method decreases the error by between one and two orders of magnitudes. Furthermore, we explicitly see that the errors in the extracted waveforms obtained by the standard method do not converge to zero with increasing resolution. [abridged] In a general scenario, for example a collision of compact objects, there is no precise definition of gravitational radiation at a finite distance, and gravitational wave extraction methods at such distances are thus inherently approximate. The results of this paper bring up the possibility that different choices in the wave extraction procedure at a fixed and finite distance may result in relative differences in the waveforms which are actually larger than the numerical errors in the solution. |
gr-qc/0406021 | Pierre Noundjeu | Pierre Noundjeu | On a Regularity Theorem for Solutions of the Spherically Symmetric
Einstein-Vlasov-Maxwell System | 15 pages | null | null | null | gr-qc | null | Using an estimate, we prove that if solution of the spherically symmetric
Einstein-Vlasov-Maxwell system develops a singularity at all time, then the
first one has to appear at the center of symmetry.
| [
{
"created": "Mon, 7 Jun 2004 14:33:46 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Noundjeu",
"Pierre",
""
]
] | Using an estimate, we prove that if solution of the spherically symmetric Einstein-Vlasov-Maxwell system develops a singularity at all time, then the first one has to appear at the center of symmetry. |
gr-qc/0603017 | Philip Tillman Mr. | Philip Tillman, George Sparling | Fedosov Observables on Constant Curvature Manifolds and the Klein-Gordon
Equation | null | null | null | null | gr-qc | null | In this paper we construct the set of quantum mechanical observables in the
Fedosov *-formalism (a coordinate invariant way to do quantum mechanics on any
manifold M) of a single free particle that lives on a constant curvature
manifold with metric signature (p,q). This was done for most but not all
constant curvature manifolds. We show that the algebra of all observables in
n=p+q dimensions is SO(p+1,q+1) in a nonperturbative calculation. A subgroup of
this group is identified as the analogue of the Poincare group in Minkowski
space i.e. it is the space of symmetries on the manifolds considered. We then
write down a Klein-Gordon (KG) equation given by the the equation
p^2|phi>=m^2|phi> for the set of allowed physical states. This result is
consistent with previous results on AdS. Furthermore we lay out the standard
scheme for the free KG field from the single particle theory. Furthermore we
argue that this scheme will work on a general space-time.
| [
{
"created": "Tue, 7 Mar 2006 22:03:55 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Feb 2007 19:13:34 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Tillman",
"Philip",
""
],
[
"Sparling",
"George",
""
]
] | In this paper we construct the set of quantum mechanical observables in the Fedosov *-formalism (a coordinate invariant way to do quantum mechanics on any manifold M) of a single free particle that lives on a constant curvature manifold with metric signature (p,q). This was done for most but not all constant curvature manifolds. We show that the algebra of all observables in n=p+q dimensions is SO(p+1,q+1) in a nonperturbative calculation. A subgroup of this group is identified as the analogue of the Poincare group in Minkowski space i.e. it is the space of symmetries on the manifolds considered. We then write down a Klein-Gordon (KG) equation given by the the equation p^2|phi>=m^2|phi> for the set of allowed physical states. This result is consistent with previous results on AdS. Furthermore we lay out the standard scheme for the free KG field from the single particle theory. Furthermore we argue that this scheme will work on a general space-time. |
gr-qc/9701012 | Thomas Kloesch | Thomas Kloesch | Solutions of arbitrary topology in 1+1 gravity | 4 pages, LaTex, 5 eps-figures; contribution to the 2nd Conference on
Constrained Dynamics and Quantum Gravity, Santa Margherita Ligure, September
1996 | Nucl.Phys.Proc.Suppl. 57 (1997) 326-329 | 10.1016/S0920-5632(97)00384-8 | TUW-97-01 | gr-qc | null | We present a classification of all global solutions for generalized 2D
dilaton gravity models (with Lorentzian signature). While for some of the
popular choices of potential-like terms in the Lagrangian, describing, e.g.,
string inspired dilaton gravity or spherically reduced gravity, the possible
topologies of the resulting spacetimes are restricted severely, we find that
for generic choices of these `potentials' there exist maximally extended
solutions to the field equations on all non-compact two-surfaces.
| [
{
"created": "Thu, 9 Jan 1997 10:48:26 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Kloesch",
"Thomas",
""
]
] | We present a classification of all global solutions for generalized 2D dilaton gravity models (with Lorentzian signature). While for some of the popular choices of potential-like terms in the Lagrangian, describing, e.g., string inspired dilaton gravity or spherically reduced gravity, the possible topologies of the resulting spacetimes are restricted severely, we find that for generic choices of these `potentials' there exist maximally extended solutions to the field equations on all non-compact two-surfaces. |
2208.01668 | Brian Seymour | Brian C. Seymour, Hang Yu, and Yanbei Chen | Multiband Gravitational Wave Cosmography with Dark Sirens | 13 pages, 6 figures. Minor edits | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | Gravitational waves might help resolve the tension between early and late
Universe measurements of the Hubble constant, and this possibility can be
enhanced with a gravitational wave detector in the decihertz band as we will
demonstrate in this study. Such a detector is particularly suitable for the
multiband observation of stellar-mass black hole binaries between space and
ground, which would significantly improve the source localization accuracy
thanks to a long baseline for timing triangulation, hence promoting the "dark
siren" cosmology. Proposed decihertz concepts include DECIGO/B-DECIGO, TianGO,
and others. We consider here the prospects of multiband observation of dark
siren binaries with a variety of network configurations. We find that a
multiband observation can uniquely identify a black hole binary to a single
galaxy to a cosmological distance, and thus a dark siren behaves as if it had
an electromagnetic counterpart. Considering only fully localized dark sirens,
we use a Fisher matrix approach to estimate the error in the Hubble constant
and matter density parameter. We find that a decihertz detector substantially
improves our ability to measure cosmological parameters because it enables host
galaxies to be identified out to a larger distance without the systematics from
statistical techniques based on comparing the population distribution.
| [
{
"created": "Tue, 2 Aug 2022 18:00:36 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Feb 2023 00:51:54 GMT",
"version": "v2"
},
{
"created": "Fri, 9 Jun 2023 22:00:55 GMT",
"version": "v3"
}
] | 2023-06-13 | [
[
"Seymour",
"Brian C.",
""
],
[
"Yu",
"Hang",
""
],
[
"Chen",
"Yanbei",
""
]
] | Gravitational waves might help resolve the tension between early and late Universe measurements of the Hubble constant, and this possibility can be enhanced with a gravitational wave detector in the decihertz band as we will demonstrate in this study. Such a detector is particularly suitable for the multiband observation of stellar-mass black hole binaries between space and ground, which would significantly improve the source localization accuracy thanks to a long baseline for timing triangulation, hence promoting the "dark siren" cosmology. Proposed decihertz concepts include DECIGO/B-DECIGO, TianGO, and others. We consider here the prospects of multiband observation of dark siren binaries with a variety of network configurations. We find that a multiband observation can uniquely identify a black hole binary to a single galaxy to a cosmological distance, and thus a dark siren behaves as if it had an electromagnetic counterpart. Considering only fully localized dark sirens, we use a Fisher matrix approach to estimate the error in the Hubble constant and matter density parameter. We find that a decihertz detector substantially improves our ability to measure cosmological parameters because it enables host galaxies to be identified out to a larger distance without the systematics from statistical techniques based on comparing the population distribution. |
2402.17190 | Kumar Shwetketu Virbhadra | K. S. Virbhadra | Conservation of distortion of gravitationally lensed images | The title has been changed and typos have been corrected | Physical Review D 109, 124004 (2024) | 10.1103/PhysRevD.109.124004 | null | gr-qc astro-ph.GA | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We recently hypothesized that a distortion parameter exists such that its
signed sum for all images of singular gravitational lensing of a source
vanishes identically [K. S. Virbhadra, Phys. Rev. D {\bf 106}, 064038 (2022)].
We found a distortion parameter (the ratio of the tangential to radial
magnifications) that satisfied the hypothesis for the images of Schwarzschild
lensing with flying colors. We now show that another distortion parameter (the
difference of tangential and radial magnifications) also magnificently supports
our hypothesis when we perform computations with the primary-secondary and
relativistic images. The distortion parameters, which satisfy the aesthetically
appealing hypothesis, will likely aid in developing gravitational lensing
theory. Finally, we discuss the conservation of distortion of images in
gravitational lensing.
| [
{
"created": "Tue, 27 Feb 2024 04:11:58 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Jun 2024 01:48:16 GMT",
"version": "v2"
}
] | 2024-06-05 | [
[
"Virbhadra",
"K. S.",
""
]
] | We recently hypothesized that a distortion parameter exists such that its signed sum for all images of singular gravitational lensing of a source vanishes identically [K. S. Virbhadra, Phys. Rev. D {\bf 106}, 064038 (2022)]. We found a distortion parameter (the ratio of the tangential to radial magnifications) that satisfied the hypothesis for the images of Schwarzschild lensing with flying colors. We now show that another distortion parameter (the difference of tangential and radial magnifications) also magnificently supports our hypothesis when we perform computations with the primary-secondary and relativistic images. The distortion parameters, which satisfy the aesthetically appealing hypothesis, will likely aid in developing gravitational lensing theory. Finally, we discuss the conservation of distortion of images in gravitational lensing. |
1809.08238 | Ra\'ul Carballo-Rubio | Ra\'ul Carballo-Rubio, Francesco Di Filippo, Stefano Liberati and Matt
Visser | Phenomenological aspects of black holes beyond general relativity | 21 double-column pages + references, 4 figures; V2: 21 double-column
pages + updated references, some minor changes, 4 figures; V3: references
added, matches published version | Phys. Rev. D 98, 124009 (2018) | 10.1103/PhysRevD.98.124009 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | While singularities are inevitable in the classical theory of general
relativity, it is commonly believed that they will not be present when quantum
gravity effects are taken into account in a consistent framework. In
particular, the structure of black holes should be modified in frameworks
beyond general relativity that aim at regularizing singularities. Being
agnostic on the nature of such theory, in this paper we classify the possible
alternatives to classical black holes and provide a minimal set of
phenomenological parameters that describe their characteristic features. The
introduction of these parameters allows us to study, in a largely
model-independent manner and taking into account all the relevant physics, the
phenomenology associated with these quantum-modified black holes. We perform an
extensive analysis of different observational channels and obtain the most
accurate characterization of the viable constraints that can be placed using
current data. Aside from facilitating a critical revision of previous work,
this analysis also allows us to highlight how different channels are capable of
probing certain features but are oblivious to others, and pinpoint the
theoretical aspects that should be addressed in order to strengthen these
tests.
| [
{
"created": "Fri, 21 Sep 2018 18:00:00 GMT",
"version": "v1"
},
{
"created": "Wed, 3 Oct 2018 15:13:03 GMT",
"version": "v2"
},
{
"created": "Tue, 11 Dec 2018 18:09:13 GMT",
"version": "v3"
}
] | 2018-12-12 | [
[
"Carballo-Rubio",
"Raúl",
""
],
[
"Di Filippo",
"Francesco",
""
],
[
"Liberati",
"Stefano",
""
],
[
"Visser",
"Matt",
""
]
] | While singularities are inevitable in the classical theory of general relativity, it is commonly believed that they will not be present when quantum gravity effects are taken into account in a consistent framework. In particular, the structure of black holes should be modified in frameworks beyond general relativity that aim at regularizing singularities. Being agnostic on the nature of such theory, in this paper we classify the possible alternatives to classical black holes and provide a minimal set of phenomenological parameters that describe their characteristic features. The introduction of these parameters allows us to study, in a largely model-independent manner and taking into account all the relevant physics, the phenomenology associated with these quantum-modified black holes. We perform an extensive analysis of different observational channels and obtain the most accurate characterization of the viable constraints that can be placed using current data. Aside from facilitating a critical revision of previous work, this analysis also allows us to highlight how different channels are capable of probing certain features but are oblivious to others, and pinpoint the theoretical aspects that should be addressed in order to strengthen these tests. |
2403.11604 | Dinesh Chandra Maurya | Dinesh Chandra Maurya, K. Yesmakhanova, R. Myrzakulov, G. Nugmanova | FLRW Cosmology in Metric-Affine $F(R,Q)$ Gravity | 22 pages, 10 figures | Chinese Phys. C, (2024) | 10.1088/1674-1137/ad6e62 | null | gr-qc | http://creativecommons.org/publicdomain/zero/1.0/ | We investigate some FLRW cosmological models in the context of Metric-Affine
$F(R,Q)$ gravity, as proposed in [arXiv:1205.52666]. Here, $R$ and $Q$ are the
curvature and nonmetricity scalars using non-special connections, respectively.
We get the modified field equations using a flat
Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) metric. We then find a
connection between the Hubble constant $H_{0}$, the density parameter
$\Omega_{m0}$, and the other model parameters in two different situations
involving scalars $u$ and $w$. Next, we used new observational datasets, such
as the cosmic chronometer (CC) Hubble datasets and the Pantheon SNe Ia
datasets, to determine the optimal model parameter values through MCMC
analysis. Using these best-fit values of model parameters, we have discussed
the results and behavior of the derived models. We have also discussed the AIC
and BIC criteria for the derived models in the context of $\Lambda$CDM. We have
found that the geometrical sector dark equation of state parameter
$\omega_{de}$ behaves just like a dark energy candidate. We have found that
both models are transit phase models and Model-I approaches to the Lambda CDM
model in the late-time universe and Model-II approaches to quintessence
scenarios.
| [
{
"created": "Mon, 18 Mar 2024 09:28:45 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Aug 2024 08:27:16 GMT",
"version": "v2"
}
] | 2024-08-16 | [
[
"Maurya",
"Dinesh Chandra",
""
],
[
"Yesmakhanova",
"K.",
""
],
[
"Myrzakulov",
"R.",
""
],
[
"Nugmanova",
"G.",
""
]
] | We investigate some FLRW cosmological models in the context of Metric-Affine $F(R,Q)$ gravity, as proposed in [arXiv:1205.52666]. Here, $R$ and $Q$ are the curvature and nonmetricity scalars using non-special connections, respectively. We get the modified field equations using a flat Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) metric. We then find a connection between the Hubble constant $H_{0}$, the density parameter $\Omega_{m0}$, and the other model parameters in two different situations involving scalars $u$ and $w$. Next, we used new observational datasets, such as the cosmic chronometer (CC) Hubble datasets and the Pantheon SNe Ia datasets, to determine the optimal model parameter values through MCMC analysis. Using these best-fit values of model parameters, we have discussed the results and behavior of the derived models. We have also discussed the AIC and BIC criteria for the derived models in the context of $\Lambda$CDM. We have found that the geometrical sector dark equation of state parameter $\omega_{de}$ behaves just like a dark energy candidate. We have found that both models are transit phase models and Model-I approaches to the Lambda CDM model in the late-time universe and Model-II approaches to quintessence scenarios. |
2112.10863 | Emmanuil Saridakis | Petros Asimakis, Spyros Basilakos, Nick E. Mavromatos, Emmanuel N.
Saridakis | Big Bang Nucleosynthesis constraints on higher-order modified gravities | 16 pages, 3 figures, version to appear in Phys.Rev.D | Phys.Rev.D 105 (2022) 8, 084010 | 10.1103/PhysRevD.105.084010 | KCL-PH-TH/2021-48 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We use Big Bang Nucleosynthesis (BBN) data in order to impose constraints on
higher-order modified gravity, and in particular on: (i) $f(G)$ Gauss-Bonnet
gravity, and $f(P)$ cubic gravities, arising respectively through the use of
the quadratic-curvature Gauss-Bonnet $G$ term, and the cubic-curvature
combination, (ii) string-inspired quadratic Gauss-Bonnet gravity coupled to the
dilaton field, (iii) models with string-inspired quartic curvature corrections,
and (iv) running vacuum models. We perform a detailed investigation of the BBN
epoch and we calculate the deviations of the freeze-out temperature $T_f$ in
comparison to $\Lambda$CDM paradigm. We then use the observational bound on $
\left|\frac{\delta {T}_f}{{T}_f}\right|$ in order to extract constraints on the
involved parameters of various models. We find that all models can satisfy the
BBN constraints and thus they constitute viable cosmological scenarios, since
they can additionally account for the dark energy sector and the late-time
acceleration, in a quantitative manner, without spoiling the formation of light
elements during the BBN epoch. Nevertheless, the obtained constraints on the
relevant model parameters are quite strong.
| [
{
"created": "Mon, 20 Dec 2021 21:17:08 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Dec 2021 15:23:48 GMT",
"version": "v2"
},
{
"created": "Thu, 24 Mar 2022 17:25:53 GMT",
"version": "v3"
}
] | 2022-04-11 | [
[
"Asimakis",
"Petros",
""
],
[
"Basilakos",
"Spyros",
""
],
[
"Mavromatos",
"Nick E.",
""
],
[
"Saridakis",
"Emmanuel N.",
""
]
] | We use Big Bang Nucleosynthesis (BBN) data in order to impose constraints on higher-order modified gravity, and in particular on: (i) $f(G)$ Gauss-Bonnet gravity, and $f(P)$ cubic gravities, arising respectively through the use of the quadratic-curvature Gauss-Bonnet $G$ term, and the cubic-curvature combination, (ii) string-inspired quadratic Gauss-Bonnet gravity coupled to the dilaton field, (iii) models with string-inspired quartic curvature corrections, and (iv) running vacuum models. We perform a detailed investigation of the BBN epoch and we calculate the deviations of the freeze-out temperature $T_f$ in comparison to $\Lambda$CDM paradigm. We then use the observational bound on $ \left|\frac{\delta {T}_f}{{T}_f}\right|$ in order to extract constraints on the involved parameters of various models. We find that all models can satisfy the BBN constraints and thus they constitute viable cosmological scenarios, since they can additionally account for the dark energy sector and the late-time acceleration, in a quantitative manner, without spoiling the formation of light elements during the BBN epoch. Nevertheless, the obtained constraints on the relevant model parameters are quite strong. |
1607.04524 | Neven Bili\'c | Neven Bilic, Dragoljub Dimitrijevic, Goran Djordjevic, and Milan
Milosevic | Tachyon inflation in an AdS braneworld with back-reaction | 19 pages, 11 figures, typos corrected, results unchanged, published
in Int. J. Mod. Phys. A | Int. J. Mod. Phys. A 32, 1750039 (2017) | 10.1142/S0217751X17500397 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the inflationary scenario based on the tachyon field coupled with
the radion of the second Randall-Sundrum model (RSII). The tachyon Lagrangian
is derived from the dynamics of a 3-brane moving in the five dimensional bulk.
The AdS$_5$ geometry of the bulk is extended to include the radion. Using the
Hamiltonian formalism we find four nonlinear field equations supplemented by
the modified Friedmann equations of the RSII braneworld cosmology. After a
suitable rescaling we reduce the parameters of our model to only one free
parameter related to the brane tension and the AdS$_5$ curvature. We solve the
equations numerically assuming a reasonably wide range of initial conditions
determined by physical considerations. Varying the free parameter and initial
conditions we confront our results with the Planck 2015 data.
| [
{
"created": "Fri, 15 Jul 2016 14:30:10 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Oct 2016 16:18:31 GMT",
"version": "v2"
},
{
"created": "Mon, 20 Feb 2017 15:18:03 GMT",
"version": "v3"
}
] | 2017-02-21 | [
[
"Bilic",
"Neven",
""
],
[
"Dimitrijevic",
"Dragoljub",
""
],
[
"Djordjevic",
"Goran",
""
],
[
"Milosevic",
"Milan",
""
]
] | We analyze the inflationary scenario based on the tachyon field coupled with the radion of the second Randall-Sundrum model (RSII). The tachyon Lagrangian is derived from the dynamics of a 3-brane moving in the five dimensional bulk. The AdS$_5$ geometry of the bulk is extended to include the radion. Using the Hamiltonian formalism we find four nonlinear field equations supplemented by the modified Friedmann equations of the RSII braneworld cosmology. After a suitable rescaling we reduce the parameters of our model to only one free parameter related to the brane tension and the AdS$_5$ curvature. We solve the equations numerically assuming a reasonably wide range of initial conditions determined by physical considerations. Varying the free parameter and initial conditions we confront our results with the Planck 2015 data. |
1011.4920 | Stephen Green | Stephen R. Green and Robert M. Wald | A new framework for analyzing the effects of small scale inhomogeneities
in cosmology | 56 pages, minor corrections | Phys.Rev.D83:084020,2011 | 10.1103/PhysRevD.83.084020 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We develop a new, mathematically precise framework for treating the effects
of nonlinear phenomena occurring on small scales in general relativity. Our
approach is an adaptation of Burnett's formulation of the "shortwave
approximation", which we generalize to analyze the effects of matter
inhomogeneities as well as gravitational radiation. Our framework requires the
metric to be close to a "background metric", but allows arbitrarily large
stress-energy fluctuations on small scales. We prove that, within our
framework, if the matter stress-energy tensor satisfies the weak energy
condition (i.e., positivity of energy density in all frames), then the only
effect that small scale inhomogeneities can have on the dynamics of the
background metric is to provide an "effective stress-energy tensor" that is
traceless and has positive energy density---corresponding to the presence of
gravitational radiation. In particular, nonlinear effects produced by small
scale inhomogeneities cannot mimic the effects of dark energy. We also develop
"perturbation theory" off of the background metric. We derive an equation for
the "long-wavelength part" of the leading order deviation of the metric from
the background metric, which contains the usual terms occurring in linearized
perturbation theory plus additional contributions from the small-scale
inhomogeneities. Under various assumptions concerning the absence of
gravitational radiation and the non-relativistic behavior of the matter, we
argue that the "short wavelength" deviations of the metric from the background
metric near a point $x$ should be accurately described by Newtonian gravity,
taking into account only the matter lying within a "homogeneity lengthscale" of
$x$. Finally, we argue that our framework should provide an accurate
description of the actual universe.
| [
{
"created": "Mon, 22 Nov 2010 19:56:42 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Apr 2011 03:54:11 GMT",
"version": "v2"
}
] | 2011-04-14 | [
[
"Green",
"Stephen R.",
""
],
[
"Wald",
"Robert M.",
""
]
] | We develop a new, mathematically precise framework for treating the effects of nonlinear phenomena occurring on small scales in general relativity. Our approach is an adaptation of Burnett's formulation of the "shortwave approximation", which we generalize to analyze the effects of matter inhomogeneities as well as gravitational radiation. Our framework requires the metric to be close to a "background metric", but allows arbitrarily large stress-energy fluctuations on small scales. We prove that, within our framework, if the matter stress-energy tensor satisfies the weak energy condition (i.e., positivity of energy density in all frames), then the only effect that small scale inhomogeneities can have on the dynamics of the background metric is to provide an "effective stress-energy tensor" that is traceless and has positive energy density---corresponding to the presence of gravitational radiation. In particular, nonlinear effects produced by small scale inhomogeneities cannot mimic the effects of dark energy. We also develop "perturbation theory" off of the background metric. We derive an equation for the "long-wavelength part" of the leading order deviation of the metric from the background metric, which contains the usual terms occurring in linearized perturbation theory plus additional contributions from the small-scale inhomogeneities. Under various assumptions concerning the absence of gravitational radiation and the non-relativistic behavior of the matter, we argue that the "short wavelength" deviations of the metric from the background metric near a point $x$ should be accurately described by Newtonian gravity, taking into account only the matter lying within a "homogeneity lengthscale" of $x$. Finally, we argue that our framework should provide an accurate description of the actual universe. |
gr-qc/0607105 | Emmanuel Serie | Antonio Troisi, Emmanuel S\'eri\'e (LPT, LPTMC), Richard Kerner
(LPTMC) | Cosmological model with Born-Infeld type scalar field | 27 pages | ECONF C0602061:13,2006; Int.J.Geom.Meth.Mod.Phys.4:249,2007 | 10.1142/S0219887807001989 | 06-54 | gr-qc hep-th | null | The non-abelian generalization of the Born-Infeld non-linear lagrangian is
extended to the non-commutative geometry of matrices on a manifold. In this
case not only the usual SU(n) gauge fields appear, but also a natural
generalization of the multiplet of scalar Higgs fields, with the double-well
potential as a first approximation. The matrix realization of non-commutative
geometry provides a natural framework in which the notion of a determinant can
be easily generalized and used as the lowest-order term in a gravitational
lagrangian of a new kind. As a result, we obtain a Born-Infeld-like lagrangian
as a root of sufficiently high order of a combination of metric, gauge
potentials and the scalar field interactions. We then analyze the behavior of
cosmological models based on this lagrangian. It leads to primordial inflation
with varying speed, with possibility of early deceleration ruled by the
relative strength of the Higgs field.
| [
{
"created": "Mon, 24 Jul 2006 11:50:22 GMT",
"version": "v1"
},
{
"created": "Sun, 24 Sep 2006 20:15:59 GMT",
"version": "v2"
}
] | 2016-08-16 | [
[
"Troisi",
"Antonio",
"",
"LPT, LPTMC"
],
[
"Sérié",
"Emmanuel",
"",
"LPT, LPTMC"
],
[
"Kerner",
"Richard",
"",
"LPTMC"
]
] | The non-abelian generalization of the Born-Infeld non-linear lagrangian is extended to the non-commutative geometry of matrices on a manifold. In this case not only the usual SU(n) gauge fields appear, but also a natural generalization of the multiplet of scalar Higgs fields, with the double-well potential as a first approximation. The matrix realization of non-commutative geometry provides a natural framework in which the notion of a determinant can be easily generalized and used as the lowest-order term in a gravitational lagrangian of a new kind. As a result, we obtain a Born-Infeld-like lagrangian as a root of sufficiently high order of a combination of metric, gauge potentials and the scalar field interactions. We then analyze the behavior of cosmological models based on this lagrangian. It leads to primordial inflation with varying speed, with possibility of early deceleration ruled by the relative strength of the Higgs field. |
1712.03398 | Hugo Ferreira | Hugo R. C. Ferreira, Carlos A. R. Herdeiro | Superradiant instabilities in the Kerr-mirror and Kerr-AdS black holes
with Robin boundary conditions | 10 pages, 6 figures; v2: discussion of Kerr-mirror case revised and
expanded | Phys. Rev. D 97, 084003 (2018) | 10.1103/PhysRevD.97.084003 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been recently observed that a scalar field with Robin boundary
conditions (RBCs) can trigger both a superradiant and a bulk instability for a
BTZ black hole (BH). To understand the generality and scrutinize the origin of
this behavior, we consider here the superradiant instability of a Kerr BH
confined either in a mirror-like cavity or in AdS space, triggered also by a
scalar field with RBCs. These boundary conditions are the most general ones
that ensure the cavity/AdS space is an isolated system, and include, as a
particular case, the commonly considered Dirichlet boundary conditions (DBCs).
Whereas the superradiant modes for some RBCs differ only mildly from the ones
with DBCs, in both cases we find that as we vary the RBCs, the imaginary part
of the frequency may attain arbitrarily large positive values. We interpret
this growth as being sourced by a bulk instability of both confined geometries
when certain RBCs are imposed to either the mirror-like cavity or the AdS
boundary, rather than by energy extraction from the BH, in analogy with the BTZ
behavior.
| [
{
"created": "Sat, 9 Dec 2017 15:05:25 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Feb 2018 17:14:45 GMT",
"version": "v2"
}
] | 2018-04-11 | [
[
"Ferreira",
"Hugo R. C.",
""
],
[
"Herdeiro",
"Carlos A. R.",
""
]
] | It has been recently observed that a scalar field with Robin boundary conditions (RBCs) can trigger both a superradiant and a bulk instability for a BTZ black hole (BH). To understand the generality and scrutinize the origin of this behavior, we consider here the superradiant instability of a Kerr BH confined either in a mirror-like cavity or in AdS space, triggered also by a scalar field with RBCs. These boundary conditions are the most general ones that ensure the cavity/AdS space is an isolated system, and include, as a particular case, the commonly considered Dirichlet boundary conditions (DBCs). Whereas the superradiant modes for some RBCs differ only mildly from the ones with DBCs, in both cases we find that as we vary the RBCs, the imaginary part of the frequency may attain arbitrarily large positive values. We interpret this growth as being sourced by a bulk instability of both confined geometries when certain RBCs are imposed to either the mirror-like cavity or the AdS boundary, rather than by energy extraction from the BH, in analogy with the BTZ behavior. |
1703.10072 | Sharmanthie Fernando | Sharmanthie Fernando | Charged dilaton black hole in 2+1 dimensions as a particle accelerator | Accepted to be published in Modern Physics Letters A | Mod. Phys. Lett. A, Vol. 32, No. 16 (2017) 1750088 | 10.1142/S0217732317500882 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we have studied particle collisions around a charged dilaton
black hole in 2+1 dimensions. This black hole is a solution to the low energy
string action in 2+1 dimensions. Time-like geodesics for charged particles are
studied in detail. The center of mass energy for two charged particles
colliding closer to the horizon is calculated and shown to be infinite if one
of the particles has the critical charge.
| [
{
"created": "Wed, 29 Mar 2017 14:44:30 GMT",
"version": "v1"
}
] | 2017-05-16 | [
[
"Fernando",
"Sharmanthie",
""
]
] | In this paper we have studied particle collisions around a charged dilaton black hole in 2+1 dimensions. This black hole is a solution to the low energy string action in 2+1 dimensions. Time-like geodesics for charged particles are studied in detail. The center of mass energy for two charged particles colliding closer to the horizon is calculated and shown to be infinite if one of the particles has the critical charge. |
1302.6207 | David Garfinkle | David Garfinkle and E.N. Glass | Killing-Yano tensors in spaces admitting a hypersurface orthogonal
Killing vector | null | null | 10.1063/1.4795122 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Methods are presented for finding Killing-Yano tensors, conformal
Killing-Yano tensors, and conformal Killing vectors in spacetimes with a
hypersurface orthogonal Killing vector. These methods are similar to a method
developed by the authors for finding Killing tensors. In all cases one
decomposes both the tensor and the equation it satisfies into pieces along the
Killing vector and pieces orthogonal to the Killing vector. Solving the
separate equations that result from this decomposition requires less computing
than integrating the original equation. In each case, examples are given to
illustrate the method.
| [
{
"created": "Mon, 25 Feb 2013 19:56:15 GMT",
"version": "v1"
}
] | 2015-06-15 | [
[
"Garfinkle",
"David",
""
],
[
"Glass",
"E. N.",
""
]
] | Methods are presented for finding Killing-Yano tensors, conformal Killing-Yano tensors, and conformal Killing vectors in spacetimes with a hypersurface orthogonal Killing vector. These methods are similar to a method developed by the authors for finding Killing tensors. In all cases one decomposes both the tensor and the equation it satisfies into pieces along the Killing vector and pieces orthogonal to the Killing vector. Solving the separate equations that result from this decomposition requires less computing than integrating the original equation. In each case, examples are given to illustrate the method. |
2307.10963 | Zinnat Hassan | Moreshwar Tayde, Zinnat Hassan, P.K. Sahoo | Existence of Wormhole Solutions in $f(Q,T)$ Gravity under
Non-commutative Geometries | Physics of Dark Universe published version | Physics of the Dark Universe, 42 (2023) 101288 | 10.1016/j.dark.2023.101288 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this paper, we have systematically discussed the existence of the
spherically symmetric wormhole solutions in the framework of $f(Q,\,T)$ gravity
under two interesting non-commutative geometries such as Gaussian and
Lorentzian distributions of the string theory. Also, to find the solutions, we
consider two $f(Q,\,T)$ models such as linear $f(Q,\,T)=\alpha\,Q+\beta\,T$ and
non-linear $f(Q,\,T)=Q+\lambda\,Q^2+\eta\,T$ models in our study. We obtained
analytic and numerical solutions for the above models in the presence of both
non-commutative distributions. We discussed wormhole solutions analytically for
the first model and numerically for the second model and graphically showed
their behaviors with the appropriate choice of free parameters. We noticed that
the obtained shape function is compatible with the flare-out conditions under
asymptotic background. Further, we checked energy conditions at the wormhole
throat with throat radius $r_0$ and found that NEC is violated for both models
under non-commutative background. At last, we examine the gravitational lensing
phenomenon for the precise wormhole model and determine that the deflection
angle diverges at the wormhole throat.
| [
{
"created": "Thu, 20 Jul 2023 15:42:34 GMT",
"version": "v1"
}
] | 2023-07-25 | [
[
"Tayde",
"Moreshwar",
""
],
[
"Hassan",
"Zinnat",
""
],
[
"Sahoo",
"P. K.",
""
]
] | In this paper, we have systematically discussed the existence of the spherically symmetric wormhole solutions in the framework of $f(Q,\,T)$ gravity under two interesting non-commutative geometries such as Gaussian and Lorentzian distributions of the string theory. Also, to find the solutions, we consider two $f(Q,\,T)$ models such as linear $f(Q,\,T)=\alpha\,Q+\beta\,T$ and non-linear $f(Q,\,T)=Q+\lambda\,Q^2+\eta\,T$ models in our study. We obtained analytic and numerical solutions for the above models in the presence of both non-commutative distributions. We discussed wormhole solutions analytically for the first model and numerically for the second model and graphically showed their behaviors with the appropriate choice of free parameters. We noticed that the obtained shape function is compatible with the flare-out conditions under asymptotic background. Further, we checked energy conditions at the wormhole throat with throat radius $r_0$ and found that NEC is violated for both models under non-commutative background. At last, we examine the gravitational lensing phenomenon for the precise wormhole model and determine that the deflection angle diverges at the wormhole throat. |
2208.02741 | Maurizio Capriolo | Salvatore Capozziello, Maurizio Capriolo and Gaetano Lambiase | Energy-Momentum Complex in Higher Order Curvature-Based Local Gravity | 33 pages, accepted for publication in Particles | null | 10.3390/particles5030026 | null | gr-qc hep-th math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | In General Relativity, there have been many proposals for defining the
gravitational energy density, notably those proposed by Einstein, Tolman,
Landau and Lifshitz, Papapetrou, M{\o}ller, and Weinberg. In this review, we
firstly explored the energy--momentum complex in an $n^{th}$ order
gravitational Lagrangian $L=L\left(g_{\mu\nu}, g_{\mu\nu,i_{1}},
g_{\mu\nu,i_{1}i_{2}},g_{\mu\nu,i_{1}i_{2}i_{3}},\cdots,
g_{\mu\nu,i_{1}i_{2}i_{3}\cdots i_{n}}\right)$ and then in a gravitational
Lagrangian as \mbox{$L_{g}=(\overline{R}+a_{0}R^{2}+\sum_{k=1}^{p}
a_{k}R\Box^{k}R)\sqrt{-g}$}. Its gravitational part was obtained by invariance
of gravitational action under infinitesimal rigid translations using Noether's
theorem. We also showed that this tensor, in general, is not a covariant object
but only an affine object, that is, a pseudo-tensor. Therefore, the
pseudo-tensor $\tau^{\eta}_{\alpha}$ becomes the one introduced by Einstein if
we limit ourselves to General Relativity and its extended corrections have been
explicitly indicated. The same method was used to derive the energy--momentum
complex in $ f\left (R \right) $ gravity both in Palatini and metric
approaches. Moreover, in the weak field approximation the pseudo-tensor
$\tau^{\eta}_{\alpha}$ to lowest order in the metric perturbation $h$ was
calculated. As a practical application, the power per unit solid angle $\Omega$
emitted by a localized source carried by a gravitational wave in a direction
$\hat{x}$ for a fixed wave number $\mathbf{k}$ under a suitable gauge was
obtained, through the average value of the pseudo-tensor over a suitable
spacetime domain and the local conservation of the pseudo-tensor. As a
cosmological application, in a flat Friedmann--Lema\^itre--Robertson--Walker
spacetime, the gravitational and matter energy density in $f(R)$ gravity both
in Palatini and metric formalism was proposed.
| [
{
"created": "Thu, 4 Aug 2022 16:17:51 GMT",
"version": "v1"
},
{
"created": "Thu, 11 Aug 2022 10:43:40 GMT",
"version": "v2"
}
] | 2022-08-12 | [
[
"Capozziello",
"Salvatore",
""
],
[
"Capriolo",
"Maurizio",
""
],
[
"Lambiase",
"Gaetano",
""
]
] | In General Relativity, there have been many proposals for defining the gravitational energy density, notably those proposed by Einstein, Tolman, Landau and Lifshitz, Papapetrou, M{\o}ller, and Weinberg. In this review, we firstly explored the energy--momentum complex in an $n^{th}$ order gravitational Lagrangian $L=L\left(g_{\mu\nu}, g_{\mu\nu,i_{1}}, g_{\mu\nu,i_{1}i_{2}},g_{\mu\nu,i_{1}i_{2}i_{3}},\cdots, g_{\mu\nu,i_{1}i_{2}i_{3}\cdots i_{n}}\right)$ and then in a gravitational Lagrangian as \mbox{$L_{g}=(\overline{R}+a_{0}R^{2}+\sum_{k=1}^{p} a_{k}R\Box^{k}R)\sqrt{-g}$}. Its gravitational part was obtained by invariance of gravitational action under infinitesimal rigid translations using Noether's theorem. We also showed that this tensor, in general, is not a covariant object but only an affine object, that is, a pseudo-tensor. Therefore, the pseudo-tensor $\tau^{\eta}_{\alpha}$ becomes the one introduced by Einstein if we limit ourselves to General Relativity and its extended corrections have been explicitly indicated. The same method was used to derive the energy--momentum complex in $ f\left (R \right) $ gravity both in Palatini and metric approaches. Moreover, in the weak field approximation the pseudo-tensor $\tau^{\eta}_{\alpha}$ to lowest order in the metric perturbation $h$ was calculated. As a practical application, the power per unit solid angle $\Omega$ emitted by a localized source carried by a gravitational wave in a direction $\hat{x}$ for a fixed wave number $\mathbf{k}$ under a suitable gauge was obtained, through the average value of the pseudo-tensor over a suitable spacetime domain and the local conservation of the pseudo-tensor. As a cosmological application, in a flat Friedmann--Lema\^itre--Robertson--Walker spacetime, the gravitational and matter energy density in $f(R)$ gravity both in Palatini and metric formalism was proposed. |
1305.5991 | Daniel Hemberger | Daniel A. Hemberger, Geoffrey Lovelace, Thomas J. Loredo, Lawrence E.
Kidder, Mark A. Scheel, B\'ela Szil\'agyi, Nicholas W. Taylor, Saul A.
Teukolsky | Final spin and radiated energy in numerical simulations of binary black
holes with equal masses and equal, aligned or anti-aligned spins | 13 pages, 10 figures | Phys. Rev. D 88, 064014 (2013) | 10.1103/PhysRevD.88.064014 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The behavior of merging black holes (including the emitted gravitational
waves and the properties of the remnant) can currently be computed only by
numerical simulations. This paper introduces ten numerical relativity
simulations of binary black holes with equal masses and equal spins aligned or
anti-aligned with the orbital angular momentum. The initial spin magnitudes
have $|\chi_i| \lesssim 0.95$ and are more concentrated in the aligned
direction because of the greater astrophysical interest of this case. We
combine this data with five previously reported simulations of the same
configuration, but with different spin magnitudes, including the highest spin
simulated to date, $\chi_i \approx 0.97$. This data set is sufficiently
accurate to enable us to offer improved analytic fitting formulae for the final
spin and for the energy radiated by gravitational waves as a function of
initial spin. The improved fitting formulae can help to improve our
understanding of the properties of binary black hole merger remnants and can be
used to enhance future approximate waveforms for gravitational wave searches,
such as Effective-One-Body waveforms.
| [
{
"created": "Sun, 26 May 2013 06:33:39 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Sep 2013 19:36:30 GMT",
"version": "v2"
}
] | 2013-09-24 | [
[
"Hemberger",
"Daniel A.",
""
],
[
"Lovelace",
"Geoffrey",
""
],
[
"Loredo",
"Thomas J.",
""
],
[
"Kidder",
"Lawrence E.",
""
],
[
"Scheel",
"Mark A.",
""
],
[
"Szilágyi",
"Béla",
""
],
[
"Taylor",
"Nicholas W.",
""
],
[
"Teukolsky",
"Saul A.",
""
]
] | The behavior of merging black holes (including the emitted gravitational waves and the properties of the remnant) can currently be computed only by numerical simulations. This paper introduces ten numerical relativity simulations of binary black holes with equal masses and equal spins aligned or anti-aligned with the orbital angular momentum. The initial spin magnitudes have $|\chi_i| \lesssim 0.95$ and are more concentrated in the aligned direction because of the greater astrophysical interest of this case. We combine this data with five previously reported simulations of the same configuration, but with different spin magnitudes, including the highest spin simulated to date, $\chi_i \approx 0.97$. This data set is sufficiently accurate to enable us to offer improved analytic fitting formulae for the final spin and for the energy radiated by gravitational waves as a function of initial spin. The improved fitting formulae can help to improve our understanding of the properties of binary black hole merger remnants and can be used to enhance future approximate waveforms for gravitational wave searches, such as Effective-One-Body waveforms. |
2209.15547 | Gregory Ashton | Gregory Ashton | Gaussian Processes for Glitch-robust Gravitational-wave Astronomy | 12 pages, published in MNRAS | null | 10.1093/mnras/stad341 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Interferometric gravitational-wave observatories have opened a new era in
astronomy. The rich data produced by an international network enables detailed
analysis of the curved space-time around black holes. With nearly one hundred
signals observed so far and thousands expected in the next decade, their
population properties enable insights into stellar evolution and the expansion
of our Universe. However, the detectors are afflicted by transient noise
artefacts known as "glitches" which contaminate the signals and bias
inferences. Of the 90 signals detected to date, 18 were contaminated by
glitches. This feasibility study explores a new approach to transient
gravitational-wave data analysis using Gaussian processes, which model the
underlying physics of the glitch-generating mechanism rather than the explicit
realisation of the glitch itself. We demonstrate that if the Gaussian process
kernel function can adequately model the glitch morphology, we can recover the
parameters of simulated signals. Moreover, we find that the Gaussian processes
kernels used in this work are well-suited to modelling long-duration glitches
which are most challenging for existing glitch-mitigation approaches. Finally,
we show how the time-domain nature of our approach enables a new class of
time-domain tests of General Relativity, performing a re-analysis of the
inspiral-merger-ringdown test on the first observed binary black hole merger.
Our investigation demonstrates the feasibility of the Gaussian processes as an
alternative to the traditional framework but does not yet establish them as a
replacement. Therefore, we conclude with an outlook on the steps needed to
realise the full potential of the Gaussian process approach.
| [
{
"created": "Fri, 30 Sep 2022 15:49:01 GMT",
"version": "v1"
},
{
"created": "Sat, 4 Mar 2023 13:00:48 GMT",
"version": "v2"
}
] | 2023-03-07 | [
[
"Ashton",
"Gregory",
""
]
] | Interferometric gravitational-wave observatories have opened a new era in astronomy. The rich data produced by an international network enables detailed analysis of the curved space-time around black holes. With nearly one hundred signals observed so far and thousands expected in the next decade, their population properties enable insights into stellar evolution and the expansion of our Universe. However, the detectors are afflicted by transient noise artefacts known as "glitches" which contaminate the signals and bias inferences. Of the 90 signals detected to date, 18 were contaminated by glitches. This feasibility study explores a new approach to transient gravitational-wave data analysis using Gaussian processes, which model the underlying physics of the glitch-generating mechanism rather than the explicit realisation of the glitch itself. We demonstrate that if the Gaussian process kernel function can adequately model the glitch morphology, we can recover the parameters of simulated signals. Moreover, we find that the Gaussian processes kernels used in this work are well-suited to modelling long-duration glitches which are most challenging for existing glitch-mitigation approaches. Finally, we show how the time-domain nature of our approach enables a new class of time-domain tests of General Relativity, performing a re-analysis of the inspiral-merger-ringdown test on the first observed binary black hole merger. Our investigation demonstrates the feasibility of the Gaussian processes as an alternative to the traditional framework but does not yet establish them as a replacement. Therefore, we conclude with an outlook on the steps needed to realise the full potential of the Gaussian process approach. |
gr-qc/0701013 | Ujjal Debnath | Anup Kumar Singha and Ujjal Debnath | Varying Speed of Light, Modified Chaplygin Gas and Accelerating Universe | 5 latex pages, RevTeX style, 2 figures | Int.J.Mod.Phys.D16:117-122,2007 | 10.1142/S0218271807009358 | null | gr-qc | null | In this paper, we have considered a model of modified Chaplygin gas in VSL
theory with variable gravitational constant $G$. We have shown that the
evolution of the universe starts from radiation era to phantom model. The whole
evolution of the universe has been shown diagramatically by using statefinder
parameters.
| [
{
"created": "Mon, 1 Jan 2007 10:35:17 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Singha",
"Anup Kumar",
""
],
[
"Debnath",
"Ujjal",
""
]
] | In this paper, we have considered a model of modified Chaplygin gas in VSL theory with variable gravitational constant $G$. We have shown that the evolution of the universe starts from radiation era to phantom model. The whole evolution of the universe has been shown diagramatically by using statefinder parameters. |
1905.04613 | Paul Chesler | Paul M. Chesler | Singularities in rotating black holes coupled to a massless scalar field | 20 pages, 4 figures. arXiv admin note: substantial text overlap with
arXiv:1902.08323 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We employ a late-time expansion to study the interior of rotating black holes
coupled to a massless scalar field in asymptotically flat spacetime. We find
that decaying fluxes of scalar radiation into the black hole necessitate the
existence of a null singularity at the Cauchy horizon and a central spacelike
singularity at radius $r = 0$. In particular, the decaying influxes source a
localized cloud of scalar radiation near $r=0$ whose amplitude grows
unboundedly large as advanced time $v \to \infty$. The scalar cloud inevitably
results in a central spacelike singularity at late times $v$, with the
curvature near $r = 0$ diverging like $r^{-\alpha v}$, where $\alpha > 0$ is a
constant.
| [
{
"created": "Sun, 12 May 2019 00:39:51 GMT",
"version": "v1"
}
] | 2019-05-14 | [
[
"Chesler",
"Paul M.",
""
]
] | We employ a late-time expansion to study the interior of rotating black holes coupled to a massless scalar field in asymptotically flat spacetime. We find that decaying fluxes of scalar radiation into the black hole necessitate the existence of a null singularity at the Cauchy horizon and a central spacelike singularity at radius $r = 0$. In particular, the decaying influxes source a localized cloud of scalar radiation near $r=0$ whose amplitude grows unboundedly large as advanced time $v \to \infty$. The scalar cloud inevitably results in a central spacelike singularity at late times $v$, with the curvature near $r = 0$ diverging like $r^{-\alpha v}$, where $\alpha > 0$ is a constant. |
0811.4548 | Hrvoje Stefancic | Hrvoje Stefancic | The inhomogeneous equation of state and the road towards the solution of
the cosmological constant problem | Contribution to the Brevik anniversary volume of TSPU Vestnik on the
occasion of the 70th birthday of Prof. Iver Brevik (Editor Prof. S.D.
Odintsov) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a cosmological model containing a cosmological constant $\Lambda$
and a component with an inhomogeneous equation of state. We study the form of
the inhomogeneous equation of state for which the model exhibits the relaxation
of the cosmological constant, i.e. it asymptotically tends to the de Sitter
regime characterized by a small positive effective cosmological constant. The
effect of the relaxation of the cosmological constant is observed both for
negative and positive values of $\Lambda$ and for a range of model parameters.
A special emphasis is put on the study of the details of the CC relaxation
mechanism and the robustness of the mechanism to the variation of model
parameters. It is found that within the studied model the effective
cosmological constant at large scale factor values is small because the
absolute value of the real cosmological constant is large.
| [
{
"created": "Thu, 27 Nov 2008 14:15:52 GMT",
"version": "v1"
}
] | 2008-12-01 | [
[
"Stefancic",
"Hrvoje",
""
]
] | We present a cosmological model containing a cosmological constant $\Lambda$ and a component with an inhomogeneous equation of state. We study the form of the inhomogeneous equation of state for which the model exhibits the relaxation of the cosmological constant, i.e. it asymptotically tends to the de Sitter regime characterized by a small positive effective cosmological constant. The effect of the relaxation of the cosmological constant is observed both for negative and positive values of $\Lambda$ and for a range of model parameters. A special emphasis is put on the study of the details of the CC relaxation mechanism and the robustness of the mechanism to the variation of model parameters. It is found that within the studied model the effective cosmological constant at large scale factor values is small because the absolute value of the real cosmological constant is large. |
2302.09371 | Alfredo D. Millano | Alfredo D. Millano (Catolica del Norte U.), Genly Leon (Catolica del
Norte U. and DUT, Durban) and Andronikos Paliathanasis (Catolica del Norte U.
and DUT, Durban) | Phase-space analysis of an Einstein-Gauss-Bonnet scalar field cosmology | 56 pages, 50 compound figures | null | null | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We perform a detailed study of the phase-space of the field equations of an
Einstein-Gauss-Bonnet scalar field cosmology for a spatially flat
Friedmann--Lema\^{\i}tre--Robertson--Walker spacetime. For the scalar field
potential, we consider the exponential function. In contrast, for the coupling
function of the scalar field with the Gauss-Bonnet term, we assume two cases,
the exponential function and the power-law function. We write the field
equations in dimensionless variables and study the equilibrium points using
Poincare variables. For the exponential coupling function, the asymptotic
solutions describe de Sitter universes or spacetimes where the Gauss-Bonnet
term dominates. We recovered previous results but found new asymptotic
solutions not previously studied. For the power-law coupling function,
equilibrium points which describe the scaling solution appear. Finally, the
power-law coupling provides a rich cosmological phenomenology.
| [
{
"created": "Sat, 18 Feb 2023 16:01:24 GMT",
"version": "v1"
}
] | 2023-02-21 | [
[
"Millano",
"Alfredo D.",
"",
"Catolica del Norte U."
],
[
"Leon",
"Genly",
"",
"Catolica del\n Norte U. and DUT, Durban"
],
[
"Paliathanasis",
"Andronikos",
"",
"Catolica del Norte U.\n and DUT, Durban"
]
] | We perform a detailed study of the phase-space of the field equations of an Einstein-Gauss-Bonnet scalar field cosmology for a spatially flat Friedmann--Lema\^{\i}tre--Robertson--Walker spacetime. For the scalar field potential, we consider the exponential function. In contrast, for the coupling function of the scalar field with the Gauss-Bonnet term, we assume two cases, the exponential function and the power-law function. We write the field equations in dimensionless variables and study the equilibrium points using Poincare variables. For the exponential coupling function, the asymptotic solutions describe de Sitter universes or spacetimes where the Gauss-Bonnet term dominates. We recovered previous results but found new asymptotic solutions not previously studied. For the power-law coupling function, equilibrium points which describe the scaling solution appear. Finally, the power-law coupling provides a rich cosmological phenomenology. |
1202.1879 | Tiberiu Harko | Zahra Haghani, Tiberiu Harko, Hamid Reza Sepangi, Shahab Shahidi | Weyl-Cartan-Weitzenb\"{o}ck gravity as a generalization of teleparallel
gravity | 15 pages, 5 figures; title changed, major modifications; accepted for
publication in JCAP | JCAP 10 (2012) 061 | 10.1088/1475-7516/2012/10/061 | null | gr-qc astro-ph.CO hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider a gravitational model in a Weyl-Cartan space-time, in which the
Weitzenb\"{o}ck condition of the vanishing of the sum of the curvature and
torsion scalar is also imposed. Moreover, a kinetic term for the torsion is
also included in the gravitational action. The field equations of the model are
obtained from a Hilbert-Einstein type variational principle, and they lead to a
complete description of the gravitational field in terms of two fields, the
Weyl vector and the torsion, respectively, defined in a curved background. The
cosmological applications of the model are investigated for a particular choice
of the free parameters in which the torsion vector is proportional to the Weyl
vector. Depending on the numerical values of the parameters of the cosmological
model, a large variety of dynamic evolutions can be obtained, ranging from
inflationary/accelerated expansions to non-inflationary behaviors. In
particular we show that a de Sitter type late time evolution can be naturally
obtained from the field equations of the model. Therefore the present model
leads to the possibility of a purely geometrical description of the dark
energy, in which the late time acceleration of the Universe is determined by
the intrinsic geometry of the space-time.
| [
{
"created": "Thu, 9 Feb 2012 03:22:02 GMT",
"version": "v1"
},
{
"created": "Wed, 10 Oct 2012 08:31:41 GMT",
"version": "v2"
}
] | 2013-08-13 | [
[
"Haghani",
"Zahra",
""
],
[
"Harko",
"Tiberiu",
""
],
[
"Sepangi",
"Hamid Reza",
""
],
[
"Shahidi",
"Shahab",
""
]
] | We consider a gravitational model in a Weyl-Cartan space-time, in which the Weitzenb\"{o}ck condition of the vanishing of the sum of the curvature and torsion scalar is also imposed. Moreover, a kinetic term for the torsion is also included in the gravitational action. The field equations of the model are obtained from a Hilbert-Einstein type variational principle, and they lead to a complete description of the gravitational field in terms of two fields, the Weyl vector and the torsion, respectively, defined in a curved background. The cosmological applications of the model are investigated for a particular choice of the free parameters in which the torsion vector is proportional to the Weyl vector. Depending on the numerical values of the parameters of the cosmological model, a large variety of dynamic evolutions can be obtained, ranging from inflationary/accelerated expansions to non-inflationary behaviors. In particular we show that a de Sitter type late time evolution can be naturally obtained from the field equations of the model. Therefore the present model leads to the possibility of a purely geometrical description of the dark energy, in which the late time acceleration of the Universe is determined by the intrinsic geometry of the space-time. |
2405.12296 | Parampreet Singh | Bao-Fei Li, Meysam Motaharfar, Parampreet Singh | Constraining regularization ambiguities in Loop Quantum Cosmology via
CMB | 28 pages, 12 figures | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | In order to investigate the potential observational signals of different
regularization ambiguities in loop quantum cosmological models, we
systematically compute and compare the primordial scalar power spectra and the
resulting angular power spectra in the standard loop quantum cosmology (LQC)
and its Thiemann regularized versions -- modified LQC-I/II (mLQC-I/II), using
both the dressed metric and the hybrid approaches. All three loop quantum
cosmological models yield a non-singular bounce with a post-bounce physics that
converges rapidly in a few Planck seconds. Using Starobinsky potential and the
initial conditions for the background dynamics chosen to yield the same
inflationary e-foldings, which are fixed to be $65$ in all three LQC models, we
require that all three models result in the same scale-invariant regime for the
primordial power spectrum with a relative difference of less than one percent.
This permits us to explore the differences resulting from the deep Planck
regime in the angular power spectrum. For the adiabatic states, our results
demonstrate that the angular power spectrum predicted by the hybrid approach
has a smaller deviation from the angular power spectrum predicted by the
standard $\Lambda$CDM cosmological model at large angles in comparison with the
dressed metric approach for all three models. The angular power spectrum
predicted by mLQC-I in both the hybrid and the dressed metric approaches shows
the smallest deviation from the one predicted by the standard $\Lambda$CDM
cosmological model at large angular scales, except for the case of fourth order
adiabatic initial states in the hybrid approach. On the contrary, mLQC-II
results in the largest deviations for the amplitude of the angular power
spectrum at large angles and is most disfavored.
| [
{
"created": "Mon, 20 May 2024 18:01:29 GMT",
"version": "v1"
}
] | 2024-05-22 | [
[
"Li",
"Bao-Fei",
""
],
[
"Motaharfar",
"Meysam",
""
],
[
"Singh",
"Parampreet",
""
]
] | In order to investigate the potential observational signals of different regularization ambiguities in loop quantum cosmological models, we systematically compute and compare the primordial scalar power spectra and the resulting angular power spectra in the standard loop quantum cosmology (LQC) and its Thiemann regularized versions -- modified LQC-I/II (mLQC-I/II), using both the dressed metric and the hybrid approaches. All three loop quantum cosmological models yield a non-singular bounce with a post-bounce physics that converges rapidly in a few Planck seconds. Using Starobinsky potential and the initial conditions for the background dynamics chosen to yield the same inflationary e-foldings, which are fixed to be $65$ in all three LQC models, we require that all three models result in the same scale-invariant regime for the primordial power spectrum with a relative difference of less than one percent. This permits us to explore the differences resulting from the deep Planck regime in the angular power spectrum. For the adiabatic states, our results demonstrate that the angular power spectrum predicted by the hybrid approach has a smaller deviation from the angular power spectrum predicted by the standard $\Lambda$CDM cosmological model at large angles in comparison with the dressed metric approach for all three models. The angular power spectrum predicted by mLQC-I in both the hybrid and the dressed metric approaches shows the smallest deviation from the one predicted by the standard $\Lambda$CDM cosmological model at large angular scales, except for the case of fourth order adiabatic initial states in the hybrid approach. On the contrary, mLQC-II results in the largest deviations for the amplitude of the angular power spectrum at large angles and is most disfavored. |
gr-qc/9910101 | Abhay Ashtekar | Abhay Ashtekar | Interface of General Relativity, Quantum Physics and Statistical
Mechanics: Some Recent Developments | 20 pages, 5 figures. Based on a talk given at the 99 Journees
Relativistes held at Weimar. To appear in Annalen der Physik | Annalen Phys.9:178-198,2000 | 10.1002/(SICI)1521-3889(200005)9:3/5<178::AID-ANDP178>3.0.CO;2-U | CGPG-99/8-4 | gr-qc hep-th physics.flu-dyn | null | The arena normally used in black holes thermodynamics was recently
generalized to incorporate a broad class of physically interesting situations.
The key idea is to replace the notion of stationary event horizons by that of
`isolated horizons.' Unlike event horizons, isolated horizons can be located in
a space-time quasi-locally. Furthermore, they need not be Killing horizons. In
particular, a space-time representing a black hole which is itself in
equilibrium, but whose exterior contains radiation, admits an isolated horizon.
In spite of this generality, the zeroth and first laws of black hole mechanics
extend to isolated horizons. Furthermore, by carrying out a systematic,
non-perturbative quantization, one can explore the quantum geometry of isolated
horizons and account for their entropy from statistical mechanical
considerations. After a general introduction to black hole thermodynamics as a
whole, these recent developments are briefly summarized.
| [
{
"created": "Wed, 27 Oct 1999 19:10:53 GMT",
"version": "v1"
}
] | 2017-09-27 | [
[
"Ashtekar",
"Abhay",
""
]
] | The arena normally used in black holes thermodynamics was recently generalized to incorporate a broad class of physically interesting situations. The key idea is to replace the notion of stationary event horizons by that of `isolated horizons.' Unlike event horizons, isolated horizons can be located in a space-time quasi-locally. Furthermore, they need not be Killing horizons. In particular, a space-time representing a black hole which is itself in equilibrium, but whose exterior contains radiation, admits an isolated horizon. In spite of this generality, the zeroth and first laws of black hole mechanics extend to isolated horizons. Furthermore, by carrying out a systematic, non-perturbative quantization, one can explore the quantum geometry of isolated horizons and account for their entropy from statistical mechanical considerations. After a general introduction to black hole thermodynamics as a whole, these recent developments are briefly summarized. |
1903.08088 | Louis Perenon | Louis Perenon and Hermano Velten | The effective field theory of dark energy diagnostic of linear Horndeski
theories after GW170817 and GRB170817A | Contribution to the Jose Plinio Baptista school on Cosmology held in
2016 | Universe 5 (2019) no.6, 138 | 10.3390/universe5060138 | C16-09-25.1 | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We summarise the effective field theory of dark energy construction to
explore observable predictions of linear Horndeski theories. Based on
\cite{Perenon:2016blf}, we review the diagnostic of these theories on the
correlation of the large-scale structure phenomenological functions: the
effective Newton constant, the light deflection parameter and the growth
function of matter perturbations. We take this opportunity to discuss the
evolution of the bounds the propagation speed of gravitational waves has
undergone and use the most restrictive one to update the diagnostic.
| [
{
"created": "Mon, 18 Mar 2019 14:47:53 GMT",
"version": "v1"
}
] | 2019-06-14 | [
[
"Perenon",
"Louis",
""
],
[
"Velten",
"Hermano",
""
]
] | We summarise the effective field theory of dark energy construction to explore observable predictions of linear Horndeski theories. Based on \cite{Perenon:2016blf}, we review the diagnostic of these theories on the correlation of the large-scale structure phenomenological functions: the effective Newton constant, the light deflection parameter and the growth function of matter perturbations. We take this opportunity to discuss the evolution of the bounds the propagation speed of gravitational waves has undergone and use the most restrictive one to update the diagnostic. |
gr-qc/0607061 | Farook Rahaman | F.Rahaman, M.Kalam and S.Chakraborty | Thin shell wormholes in higher dimensiaonal Einstein-Maxwell theory | 10 pages, accepted in Gen.Rel.Grav | Gen.Rel.Grav. 38 (2006) 1687-1695 | 10.1007/s10714-006-0325-y | null | gr-qc | null | We construct thin shell Lorentzian wormholes in higher dimensional
Einstein-Maxwell theory applying the ' Cut and Paste ' technique proposed by
Visser. The linearized stability is analyzed under radial perturbations around
some assumed higher dimensional spherically symmetric static solution of the
Einstein field equations in presence of Electromagnetic field. We determine the
total amount of exotic matter, which is concentrated at the wormhole throat.
| [
{
"created": "Mon, 17 Jul 2006 11:00:42 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Rahaman",
"F.",
""
],
[
"Kalam",
"M.",
""
],
[
"Chakraborty",
"S.",
""
]
] | We construct thin shell Lorentzian wormholes in higher dimensional Einstein-Maxwell theory applying the ' Cut and Paste ' technique proposed by Visser. The linearized stability is analyzed under radial perturbations around some assumed higher dimensional spherically symmetric static solution of the Einstein field equations in presence of Electromagnetic field. We determine the total amount of exotic matter, which is concentrated at the wormhole throat. |
2205.13052 | Abdellah Touati | Abdellah Touati, Slimane Zaim | On Modified First Law of Black hole Thermodynamics in The
Non-Commutative Gauge Theory | null | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | In this paper, we investigated the thermodynamic properties of Schwarzschild
black hole (SBH) in the non-commutative (NC) gauge theory of gravity. According
to our previous work, we modify the first law of the black hole (BH)
thermodynamics by the physical quantity (NC potential) $\mathcal{A}$ which is
the conjugate to the NC parameter $\Theta$, which leads to this expression
$d\hat{M}=\hat{T}d\hat{S}+\mathcal{A}d\Theta$. Our result shows that the NC SBH
has a phase transition, and the non-commutativity affected this transition. And
the NC potential $\mathcal{A}$ is effective only in the final stage of the BH
evaporation, where it increases the Gibbs free energy at this stage, and the NC
parameter in this study can represent the tension of the spacetime. Then the
study of the pressure of the SBH in the modified first law of the BH
thermodynamic shows a second-order phase transition, and the critical value of
the thermodynamical variables are related to each value of $\Theta$, and that
leads to this parameter to play the same role as a thermodynamical variable.
| [
{
"created": "Wed, 25 May 2022 21:13:14 GMT",
"version": "v1"
}
] | 2023-10-06 | [
[
"Touati",
"Abdellah",
""
],
[
"Zaim",
"Slimane",
""
]
] | In this paper, we investigated the thermodynamic properties of Schwarzschild black hole (SBH) in the non-commutative (NC) gauge theory of gravity. According to our previous work, we modify the first law of the black hole (BH) thermodynamics by the physical quantity (NC potential) $\mathcal{A}$ which is the conjugate to the NC parameter $\Theta$, which leads to this expression $d\hat{M}=\hat{T}d\hat{S}+\mathcal{A}d\Theta$. Our result shows that the NC SBH has a phase transition, and the non-commutativity affected this transition. And the NC potential $\mathcal{A}$ is effective only in the final stage of the BH evaporation, where it increases the Gibbs free energy at this stage, and the NC parameter in this study can represent the tension of the spacetime. Then the study of the pressure of the SBH in the modified first law of the BH thermodynamic shows a second-order phase transition, and the critical value of the thermodynamical variables are related to each value of $\Theta$, and that leads to this parameter to play the same role as a thermodynamical variable. |
1612.03157 | Pedro Ferreira | Pedro G. Ferreira, Christopher T. Hill, Graham G. Ross | No fifth force in a scale invariant universe | 8 pages, submitted to PRD | Phys. Rev. D 95, 064038 (2017) | 10.1103/PhysRevD.95.064038 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We revisit the possibility that the Planck mass is spontaneously generated in
scale invariant scalar-tensor theories of gravity, typically leading to a
"dilaton." The fifth force, arising from the dilaton, is severely constrained
by astrophysical measurements. We explore the possibility that nature is
fundamentally Weyl-scale invariant and argue that, as a consequence, the fifth
force effects are dramatically suppressed and such models are viable. We
discuss possible obstructions to maintaining scale invariance and how these
might be resolved.
| [
{
"created": "Fri, 9 Dec 2016 20:38:46 GMT",
"version": "v1"
}
] | 2017-03-29 | [
[
"Ferreira",
"Pedro G.",
""
],
[
"Hill",
"Christopher T.",
""
],
[
"Ross",
"Graham G.",
""
]
] | We revisit the possibility that the Planck mass is spontaneously generated in scale invariant scalar-tensor theories of gravity, typically leading to a "dilaton." The fifth force, arising from the dilaton, is severely constrained by astrophysical measurements. We explore the possibility that nature is fundamentally Weyl-scale invariant and argue that, as a consequence, the fifth force effects are dramatically suppressed and such models are viable. We discuss possible obstructions to maintaining scale invariance and how these might be resolved. |
0809.2412 | Belinch\'on Jos\'e Antonio | Jos\'e Antonio Belinch\'on | Bianchi I with variable $G$ and $\Lambda$. Self-Similar approach | 15 pages. accepted in IJMPA | Int.J.Mod.Phys.A23:5021-5036,2008 | 10.1142/S0217751X08043127 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study how to attack under the self-similarity hypothesis a
perfect fluid Bianchi I model with variable $G,$and $\Lambda,$ but under the
condition $\operatorname{div}T\neq0.$ We arrive to the conclusion that: $G$ and
$\Lambda$ are decreasing time functions (the sing of $\Lambda$ depends on the
equation of state), while the exponents of the scale factor must satisfy the
conditions $\sum_{i=1}^{3}\alpha_{i}=1$ and $\sum_{i=1}^{3}\alpha_{i}^{2}<1,$
$\forall\omega\in(-1,1) ,$ relaxing in this way the Kasner conditions. We also
show the connection between the behavior of $G$ and the Weyl tensor.
| [
{
"created": "Sun, 14 Sep 2008 18:21:16 GMT",
"version": "v1"
}
] | 2009-02-11 | [
[
"Belinchón",
"José Antonio",
""
]
] | In this paper we study how to attack under the self-similarity hypothesis a perfect fluid Bianchi I model with variable $G,$and $\Lambda,$ but under the condition $\operatorname{div}T\neq0.$ We arrive to the conclusion that: $G$ and $\Lambda$ are decreasing time functions (the sing of $\Lambda$ depends on the equation of state), while the exponents of the scale factor must satisfy the conditions $\sum_{i=1}^{3}\alpha_{i}=1$ and $\sum_{i=1}^{3}\alpha_{i}^{2}<1,$ $\forall\omega\in(-1,1) ,$ relaxing in this way the Kasner conditions. We also show the connection between the behavior of $G$ and the Weyl tensor. |
1806.07909 | Vitor Cardoso | Thiago Assumpcao, Vitor Cardoso, Akihiro Ishibashi, Mauricio Richartz,
Miguel Zilhao | Black hole binaries: ergoregions, photon surfaces, wave scattering, and
quasinormal modes | 13 pages, 11 figures. v3: minor edits, to appear in Physical Review D | Phys. Rev. D 98, 064036 (2018) | 10.1103/PhysRevD.98.064036 | null | gr-qc astro-ph.HE hep-th physics.flu-dyn | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Closed photon orbits around isolated black holes are related to important
aspects of black hole physics, such as strong lensing, absorption cross section
of null particles and the way that black holes relax through quasinormal
ringing. When two black holes are present -- such as during the inspiral and
merger events of interest for gravitational-wave detectors -- the concept of
closed photon orbits still exists, but its properties are basically unknown.
With these applications in mind, we study here the closed photon orbits of two
different static black hole binaries. The first one is the Majumdar-Papapetrou
geometry describing two extremal, charged black holes in equilibrium, while the
second one is the double sink solution of fluid dynamics, which describes (in a
curved-spacetime language) two "dumb" holes. For the latter solution, we also
characterize its dynamical response to external perturbations, and study how it
relates to the photon orbits. In addition, we compute the ergoregion of such
spacetime and show that it does not coincide with the event horizon.
| [
{
"created": "Wed, 20 Jun 2018 18:07:40 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Sep 2018 07:43:23 GMT",
"version": "v2"
},
{
"created": "Thu, 13 Sep 2018 23:49:37 GMT",
"version": "v3"
}
] | 2018-09-26 | [
[
"Assumpcao",
"Thiago",
""
],
[
"Cardoso",
"Vitor",
""
],
[
"Ishibashi",
"Akihiro",
""
],
[
"Richartz",
"Mauricio",
""
],
[
"Zilhao",
"Miguel",
""
]
] | Closed photon orbits around isolated black holes are related to important aspects of black hole physics, such as strong lensing, absorption cross section of null particles and the way that black holes relax through quasinormal ringing. When two black holes are present -- such as during the inspiral and merger events of interest for gravitational-wave detectors -- the concept of closed photon orbits still exists, but its properties are basically unknown. With these applications in mind, we study here the closed photon orbits of two different static black hole binaries. The first one is the Majumdar-Papapetrou geometry describing two extremal, charged black holes in equilibrium, while the second one is the double sink solution of fluid dynamics, which describes (in a curved-spacetime language) two "dumb" holes. For the latter solution, we also characterize its dynamical response to external perturbations, and study how it relates to the photon orbits. In addition, we compute the ergoregion of such spacetime and show that it does not coincide with the event horizon. |
0908.3101 | Matteo Carrera | Matteo Carrera and Domenico Giulini | On the generalization of McVittie's model for an inhomogeneity in a
cosmological spacetime | LaTeX (RevTeX), 15 pages, no figure | Phys.Rev.D81:043521,2010 | 10.1103/PhysRevD.81.043521 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | McVittie's spacetime is a spherically symmetric solution to Einstein's
equation with an energy-momentum tensor of a perfect fluid. It describes the
external field of a single quasi-isolated object with vanishing electric charge
and angular momentum in an environment that asymptotically tends to a
Friedmann--Lemaitre--Robertson--Walker universe. We critically discuss some
recently proposed generalizations of this solution, in which radial matter
accretion as well as heat currents are allowed. We clarify the hitherto
unexplained constraints between these two generalizing aspects as being due to
a geometric property, here called spatial Ricci-isotropy, which forces
solutions covered by the McVittie ansatz to be rather special. We also clarify
other aspects of these solutions, like whether they include geometries which
are in the same conformal equivalence class as the exterior Schwarzschild
solution, which leads us to contradict some of the statements in the recent
literature.
| [
{
"created": "Fri, 21 Aug 2009 11:25:39 GMT",
"version": "v1"
}
] | 2010-05-12 | [
[
"Carrera",
"Matteo",
""
],
[
"Giulini",
"Domenico",
""
]
] | McVittie's spacetime is a spherically symmetric solution to Einstein's equation with an energy-momentum tensor of a perfect fluid. It describes the external field of a single quasi-isolated object with vanishing electric charge and angular momentum in an environment that asymptotically tends to a Friedmann--Lemaitre--Robertson--Walker universe. We critically discuss some recently proposed generalizations of this solution, in which radial matter accretion as well as heat currents are allowed. We clarify the hitherto unexplained constraints between these two generalizing aspects as being due to a geometric property, here called spatial Ricci-isotropy, which forces solutions covered by the McVittie ansatz to be rather special. We also clarify other aspects of these solutions, like whether they include geometries which are in the same conformal equivalence class as the exterior Schwarzschild solution, which leads us to contradict some of the statements in the recent literature. |
gr-qc/9910055 | Wlodzimierz Piechocki | Wlodzimierz Piechocki (Soltan Institute for Nuclear Studies, Warsaw,
Poland) | Topology of the Universe | Presented at the Workshop `Connecting Fundamental Physics and
Cosmology', Cambridge, U.K., 23-27 August 1999; 5 pages, LaTeX2e, no figures | null | null | null | gr-qc | null | General relativity is unable to determine the topology of the Universe. We
propose to apply quantum approach. Quantization of dynamics of a test particle
is sensitive to the spacetime topology. Presented results for a particle in de
Sitter spacetimes favor a finite universe.
| [
{
"created": "Fri, 15 Oct 1999 07:43:21 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Piechocki",
"Wlodzimierz",
"",
"Soltan Institute for Nuclear Studies, Warsaw,\n Poland"
]
] | General relativity is unable to determine the topology of the Universe. We propose to apply quantum approach. Quantization of dynamics of a test particle is sensitive to the spacetime topology. Presented results for a particle in de Sitter spacetimes favor a finite universe. |
1110.0775 | George E. A. Matsas | Raissa F. P. Mendes and George E. A. Matsas | Radiation interference from sources rotating around Schwarzschild black
holes | 7 pages and 7 figures | Phys. Rev. D, vol 84, 124035 (2011) | 10.1103/PhysRevD.84.124035 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the influence of the spacetime curvature on the interference
of the radiation emitted by an ensemble of scalar sources in circular motion
around a Schwarzschild black hole. We pay particular attention to the
transition from the radiating to the non-radiating regime as the number of
sources increases.
| [
{
"created": "Tue, 4 Oct 2011 18:05:25 GMT",
"version": "v1"
}
] | 2013-08-09 | [
[
"Mendes",
"Raissa F. P.",
""
],
[
"Matsas",
"George E. A.",
""
]
] | We investigate the influence of the spacetime curvature on the interference of the radiation emitted by an ensemble of scalar sources in circular motion around a Schwarzschild black hole. We pay particular attention to the transition from the radiating to the non-radiating regime as the number of sources increases. |
1605.01341 | Antoine Klein | Atsushi Nishizawa, Emanuele Berti, Antoine Klein, Alberto Sesana | eLISA eccentricity measurements as tracers of binary black hole
formation | 13 pages, 7 figures, 4 tables, Matches version accepted in Physical
Review D | Phys. Rev. D 94, 064020 (2016) | 10.1103/PhysRevD.94.064020 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Up to hundreds of black hole binaries individually resolvable by eLISA will
coalesce in the Advanced LIGO/Virgo band within ten years, allowing for
multi-band gravitational wave observations. Binaries formed via dynamical
interactions in dense star clusters are expected to have eccentricities
$e_0\sim 10^{-3}$-$10^{-1}$ at the frequencies $f_0=10^{-2}$ Hz where eLISA is
most sensitive, while binaries formed in the field should have negligible
eccentricity in both frequency bands. We estimate that eLISA should always be
able to detect a nonzero $e_0$ whenever $e_0\gtrsim 10^{-2}$; if $e_0\sim
10^{-3}$, eLISA should detect nonzero eccentricity for a fraction $\sim 90\%$
($\sim 25\%$) of binaries when the observation time is $T_{\rm obs}=5$ ($2$)
years, respectively. Therefore eLISA observations of BH binaries have the
potential to distinguish between field and cluster formation scenarios.
| [
{
"created": "Wed, 4 May 2016 16:47:03 GMT",
"version": "v1"
},
{
"created": "Fri, 27 May 2016 15:48:44 GMT",
"version": "v2"
},
{
"created": "Fri, 19 Aug 2016 13:41:12 GMT",
"version": "v3"
}
] | 2016-09-14 | [
[
"Nishizawa",
"Atsushi",
""
],
[
"Berti",
"Emanuele",
""
],
[
"Klein",
"Antoine",
""
],
[
"Sesana",
"Alberto",
""
]
] | Up to hundreds of black hole binaries individually resolvable by eLISA will coalesce in the Advanced LIGO/Virgo band within ten years, allowing for multi-band gravitational wave observations. Binaries formed via dynamical interactions in dense star clusters are expected to have eccentricities $e_0\sim 10^{-3}$-$10^{-1}$ at the frequencies $f_0=10^{-2}$ Hz where eLISA is most sensitive, while binaries formed in the field should have negligible eccentricity in both frequency bands. We estimate that eLISA should always be able to detect a nonzero $e_0$ whenever $e_0\gtrsim 10^{-2}$; if $e_0\sim 10^{-3}$, eLISA should detect nonzero eccentricity for a fraction $\sim 90\%$ ($\sim 25\%$) of binaries when the observation time is $T_{\rm obs}=5$ ($2$) years, respectively. Therefore eLISA observations of BH binaries have the potential to distinguish between field and cluster formation scenarios. |
0803.2005 | Salvador Robles-Perez | Prado Mart\'in-Moruno, Az-Eddine L. Marrakchi, Salvador Robles-P\'erez
and Pedro F. Gonz\'alez-D\'iaz | Dark Energy Accretion onto black holes in a cosmic scenario | 7 pages, 3 figures | Gen.Rel.Grav.41:2797-2811,2009 | 10.1007/s10714-009-0808-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we study the accretion of dark energy onto a black hole in the
cases that dark energy is equipped with a positive cosmological constant and
when the space-time is described by a Schwarzschild-de Sitter metric. It is
shown that, if confronted with current observational data, the results derived
when no cosmological constant is present are once again obtained in both cases.
| [
{
"created": "Thu, 13 Mar 2008 16:38:36 GMT",
"version": "v1"
}
] | 2009-12-04 | [
[
"Martín-Moruno",
"Prado",
""
],
[
"Marrakchi",
"Az-Eddine L.",
""
],
[
"Robles-Pérez",
"Salvador",
""
],
[
"González-Díaz",
"Pedro F.",
""
]
] | In this paper we study the accretion of dark energy onto a black hole in the cases that dark energy is equipped with a positive cosmological constant and when the space-time is described by a Schwarzschild-de Sitter metric. It is shown that, if confronted with current observational data, the results derived when no cosmological constant is present are once again obtained in both cases. |
2407.16669 | Tathagata Ghosh | Tathagata Ghosh, Bhaskar Biswas, Sukanta Bose, Shasvath J. Kapadia | Joint Inference of Population, Cosmology, and Neutron Star Equation of
State from Gravitational Waves of Dark Binary Neutron Stars | 26 pages, 14 figures, 4 tables | null | null | LIGO-P2400303 | gr-qc astro-ph.CO astro-ph.HE nucl-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational waves (GWs) from binary neutron stars (BNSs) are expected to be
accompanied by electromagnetic (EM) emissions, which help to identify the host
galaxy. Since GW events directly measure their luminosity distances, joint
GW-EM observations from BNSs help to study cosmology, particularly the Hubble
constant, unaffected by cosmic distance ladder systematics. However, detecting
EM counterparts from BNS mergers is not always possible. Additionally, the
tidal deformations of BNS components offer insights into the neutron star (NS)
equation of state (EoS). In such cases, the tidal parameters of NSs, combined
with the knowledge of the NS EoS, can break the degeneracy between mass
parameters and redshift, allowing for the inference of the Hubble constant.
Several efforts have aimed to infer the Hubble constant using the tidal
parameters of BNSs, without EM counterparts, termed dark BNSs. Moreover, some
studies have focused on the joint estimation of population and NS EoS for
unbiased NS EoS estimation. However, none of the works consistently combined
the uncertainties of population, cosmology, and NS EoS within a Bayesian
framework. In this study, we propose a novel Bayesian analysis to jointly
constrain the NS EoS, population, and cosmological parameters using a
population of dark BNSs detected through GW observations. This method can well
constrain the Hubble constant with as few as $5$ BNS observations using
current-generation detectors. This level of precision is unattainable without
incorporating the NS EoS, especially when observing BNS mergers without EM
counterpart information.
| [
{
"created": "Tue, 23 Jul 2024 17:37:43 GMT",
"version": "v1"
}
] | 2024-07-24 | [
[
"Ghosh",
"Tathagata",
""
],
[
"Biswas",
"Bhaskar",
""
],
[
"Bose",
"Sukanta",
""
],
[
"Kapadia",
"Shasvath J.",
""
]
] | Gravitational waves (GWs) from binary neutron stars (BNSs) are expected to be accompanied by electromagnetic (EM) emissions, which help to identify the host galaxy. Since GW events directly measure their luminosity distances, joint GW-EM observations from BNSs help to study cosmology, particularly the Hubble constant, unaffected by cosmic distance ladder systematics. However, detecting EM counterparts from BNS mergers is not always possible. Additionally, the tidal deformations of BNS components offer insights into the neutron star (NS) equation of state (EoS). In such cases, the tidal parameters of NSs, combined with the knowledge of the NS EoS, can break the degeneracy between mass parameters and redshift, allowing for the inference of the Hubble constant. Several efforts have aimed to infer the Hubble constant using the tidal parameters of BNSs, without EM counterparts, termed dark BNSs. Moreover, some studies have focused on the joint estimation of population and NS EoS for unbiased NS EoS estimation. However, none of the works consistently combined the uncertainties of population, cosmology, and NS EoS within a Bayesian framework. In this study, we propose a novel Bayesian analysis to jointly constrain the NS EoS, population, and cosmological parameters using a population of dark BNSs detected through GW observations. This method can well constrain the Hubble constant with as few as $5$ BNS observations using current-generation detectors. This level of precision is unattainable without incorporating the NS EoS, especially when observing BNS mergers without EM counterpart information. |
2103.14750 | Hugo Roussille | David Langlois, Karim Noui, Hugo Roussille | Black hole perturbations in modified gravity | v3: version accepted for publication in Physical Review D | null | 10.1103/PhysRevD.104.124044 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/publicdomain/zero/1.0/ | We study the linear perturbations about nonrotating black holes in the
context of degenerate higher-order scalar-tensor (DHOST) theories, using a
systematic approach that extracts the asymptotic behaviour of perturbations (at
spatial infinity and near the horizon) directly from the first-order radial
differential system governing these perturbations. For axial (odd-parity)
modes, this provides an alternative to the traditional approach based on a
second-order Schr\"odinger-like equation with an effective potential, which we
also discuss for completeness. For polar (even-parity) modes, which contain an
additional degree of freedom in DHOST theories, and are thus more complex, we
use a direct treatment of the four-dimensional first-order differential system
(without resorting to a second order reformulation). We illustrate our study
with two specific types of black hole solutions: 'stealth' Schwarzschild black
holes, with a non trivial scalar hair, as well as a class of non-stealth black
holes whose metric is distinct from Schwarzschild. The knowledge of the
asymptotic behaviours of the perturbations enables us to compute numerically
quasi-normal modes, as we show explicitly for the non-stealth solutions.
Finally, the asymptotic form of the modes also signals some pathologies in the
stealth and non-stealth solutions considered here.
| [
{
"created": "Fri, 26 Mar 2021 21:56:01 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Apr 2021 09:37:09 GMT",
"version": "v2"
},
{
"created": "Tue, 14 Dec 2021 16:22:58 GMT",
"version": "v3"
}
] | 2021-12-15 | [
[
"Langlois",
"David",
""
],
[
"Noui",
"Karim",
""
],
[
"Roussille",
"Hugo",
""
]
] | We study the linear perturbations about nonrotating black holes in the context of degenerate higher-order scalar-tensor (DHOST) theories, using a systematic approach that extracts the asymptotic behaviour of perturbations (at spatial infinity and near the horizon) directly from the first-order radial differential system governing these perturbations. For axial (odd-parity) modes, this provides an alternative to the traditional approach based on a second-order Schr\"odinger-like equation with an effective potential, which we also discuss for completeness. For polar (even-parity) modes, which contain an additional degree of freedom in DHOST theories, and are thus more complex, we use a direct treatment of the four-dimensional first-order differential system (without resorting to a second order reformulation). We illustrate our study with two specific types of black hole solutions: 'stealth' Schwarzschild black holes, with a non trivial scalar hair, as well as a class of non-stealth black holes whose metric is distinct from Schwarzschild. The knowledge of the asymptotic behaviours of the perturbations enables us to compute numerically quasi-normal modes, as we show explicitly for the non-stealth solutions. Finally, the asymptotic form of the modes also signals some pathologies in the stealth and non-stealth solutions considered here. |
1205.3974 | Cenalo Vaz | Kinjalk Lochan and Cenalo Vaz | Statistical analysis of entropy correction from topological defects in
Loop Black Holes | 12 pages, no figures. Version to appear in Phys. Rev. D | Phys. Rev. D 86 (2012) 044035 | 10.1103/PhysRevD.86.044035 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we discuss the entropy of quantum black holes in the LQG
formalism when the number of punctures on the horizon is treated as a quantum
hair, that is we compute the black hole entropy in the grand canonical (area)
ensemble. The entropy is a function of both the average area and the average
number of punctures and bears little resemblance to the Bekenstein-Hawking
entropy. In the thermodynamic limit, both the "temperature" and the chemical
potential can be shown to be functions only of the average area per puncture.
At a fixed temperature, the average number of punctures becomes proportional to
the average area and we recover the Bekenstein-Hawking area-entropy law to
leading order provided that the Barbero-Immirzi parameter, $\gamma$, is
appropriately fixed. This also relates the chemical potential to $\gamma$. We
obtain a sub-leading correction, which differs in signature from that obtained
in the microcanonical and canonical ensembles in its sign but agrees with
earlier results in the grand canonical ensemble.
| [
{
"created": "Thu, 17 May 2012 16:24:35 GMT",
"version": "v1"
},
{
"created": "Mon, 30 Jul 2012 12:06:46 GMT",
"version": "v2"
}
] | 2012-08-30 | [
[
"Lochan",
"Kinjalk",
""
],
[
"Vaz",
"Cenalo",
""
]
] | In this paper we discuss the entropy of quantum black holes in the LQG formalism when the number of punctures on the horizon is treated as a quantum hair, that is we compute the black hole entropy in the grand canonical (area) ensemble. The entropy is a function of both the average area and the average number of punctures and bears little resemblance to the Bekenstein-Hawking entropy. In the thermodynamic limit, both the "temperature" and the chemical potential can be shown to be functions only of the average area per puncture. At a fixed temperature, the average number of punctures becomes proportional to the average area and we recover the Bekenstein-Hawking area-entropy law to leading order provided that the Barbero-Immirzi parameter, $\gamma$, is appropriately fixed. This also relates the chemical potential to $\gamma$. We obtain a sub-leading correction, which differs in signature from that obtained in the microcanonical and canonical ensembles in its sign but agrees with earlier results in the grand canonical ensemble. |
gr-qc/9606031 | Dharam Ahluwalia | D. V. Ahluwalia (Los Alamos Nat'l Lab.) and C. Burgard (DESY) | About the Interpretation of Gravitationally Induced Neutrino Oscillation
Phases | Requires elsart style files. 5 pages | null | null | LA-UR-96-2031 | gr-qc astro-ph hep-ph quant-ph | null | We present some thoughts on how to interpret the gravitionally induced
neutrino oscillation phases presented by us in our 1996 Gravity Research
Foundation Essay.
| [
{
"created": "Fri, 14 Jun 1996 01:51:15 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Ahluwalia",
"D. V.",
"",
"Los Alamos Nat'l Lab."
],
[
"Burgard",
"C.",
"",
"DESY"
]
] | We present some thoughts on how to interpret the gravitionally induced neutrino oscillation phases presented by us in our 1996 Gravity Research Foundation Essay. |
0903.0109 | Wolfgang Hasse | Wolfgang Hasse, Emrah Birsin, Philipp Haehnel | On force-field models of the spacecraft flyby anomaly | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, Anderson et al. published an empirical prediction formula for the
so far unexplained parts of the velocity changes of spacecrafts during Earth
flybys. In the framework of a perturbational approach, we show that there is no
velocity-independent force field of the Earth - in addition to its Newtonian
gravity field - that is to reproduce this formula. However, we give examples
for fields modeling exactly the flyby anomaly which are quadratic functions of
the velocity of the spacecraft.
| [
{
"created": "Sat, 28 Feb 2009 21:16:40 GMT",
"version": "v1"
}
] | 2009-03-03 | [
[
"Hasse",
"Wolfgang",
""
],
[
"Birsin",
"Emrah",
""
],
[
"Haehnel",
"Philipp",
""
]
] | Recently, Anderson et al. published an empirical prediction formula for the so far unexplained parts of the velocity changes of spacecrafts during Earth flybys. In the framework of a perturbational approach, we show that there is no velocity-independent force field of the Earth - in addition to its Newtonian gravity field - that is to reproduce this formula. However, we give examples for fields modeling exactly the flyby anomaly which are quadratic functions of the velocity of the spacecraft. |
gr-qc/0409086 | Sushil Srivastava | S.K.Srivastava | Non-violation of Energy Conditions in the future accelerated universe
due to quantum effects | 11pages. To appear in Int. J. Theo. Phys | null | null | null | gr-qc astro-ph hep-th | null | Here, an accelerated phantom model for the late universe is explored, which
is free from future singularity. It is interseting to see that this model
exhibits strong curvature for all time in future, unlike models with `big-rip
singularity' showing high curvature near singularity time only. So, quantum
gravity effects grow dominant as time increases in the late universe too. More
importantly, it is demonstrated that that quantum corrections to FRW equations
lead to non-violation of `cosmic energy conditions' of general relativity,
which are violated for accelerating universe without these corrections.
| [
{
"created": "Wed, 22 Sep 2004 10:45:21 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Apr 2005 10:16:28 GMT",
"version": "v2"
},
{
"created": "Mon, 10 Apr 2006 12:14:09 GMT",
"version": "v3"
},
{
"created": "Wed, 25 Oct 2006 08:06:36 GMT",
"version": "v4"
}
] | 2007-05-23 | [
[
"Srivastava",
"S. K.",
""
]
] | Here, an accelerated phantom model for the late universe is explored, which is free from future singularity. It is interseting to see that this model exhibits strong curvature for all time in future, unlike models with `big-rip singularity' showing high curvature near singularity time only. So, quantum gravity effects grow dominant as time increases in the late universe too. More importantly, it is demonstrated that that quantum corrections to FRW equations lead to non-violation of `cosmic energy conditions' of general relativity, which are violated for accelerating universe without these corrections. |
0806.0428 | J. Ponce de Leon | J. Ponce de Leon and P.S. Wesson | A Class of Anisotropic Five-Dimensional Solutions for the Early Universe | V2 has some minor editorial changes in the introduction | Europhys.Lett.84:20007,2008 | 10.1209/0295-5075/84/20007 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We solve the Ricci-flat equations of extended general relativity to obtain an
interesting class of cosmological models. The solutions are analogous to the 4D
ones of Bianchi type-I of Kasner type and have significant implications for
astrophysics.
| [
{
"created": "Tue, 3 Jun 2008 03:46:51 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Oct 2008 04:34:41 GMT",
"version": "v2"
}
] | 2008-12-18 | [
[
"de Leon",
"J. Ponce",
""
],
[
"Wesson",
"P. S.",
""
]
] | We solve the Ricci-flat equations of extended general relativity to obtain an interesting class of cosmological models. The solutions are analogous to the 4D ones of Bianchi type-I of Kasner type and have significant implications for astrophysics. |
1806.01297 | T. P. Singh | Tejinder P. Singh | Space and time as a consequence of GRW quantum jumps | v1: 7 pages; v2: 7 pages, references added; v3: 11 pages,
significantly expanded: remarks (i)-(x) added, including a new explanation
for the quantum non-locality puzzle, and `quantum interference in time' as
possible evidence for operator time, references added; v4: references
updated, to appear in Zeitschrift fur Naturforschung A as a Rapid
Communication | Zeitschrift f\"ur Naturforschung A73 (2018) 923 | 10.1515/zna-2018-0351 | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Ghirardi-Rimini-Weber (GRW) theory of spontaneous collapse offers a
possible resolution of the quantum measurement problem. In this theory, the
wave function of a particle spontaneously and repeatedly localises to one or
the other random position in space, as a consequence of the hypothesised
quantum jumps. In between jumps the wave function undergoes the usual
Schr\"{o}dinger evolution. In the present paper we suggest that these jumps
take place in Hilbert space, with no reference to physical space, and physical
three-dimensional space arises as a consequence of localisation of macroscopic
objects in the universe. That is, collapse of the wave-function is responsible
for the origin of space. We then suggest that similar jumps take place for a
hypothetical time operator in Hilbert space, and classical time as we know it
emerges from localisation of this time operator for macroscopic objects. More
generally, the jumps are suggested to take place in an operator space-time in
Hilbert space, leading to an emergent classical space-time.
| [
{
"created": "Mon, 4 Jun 2018 18:03:05 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Jul 2018 14:46:39 GMT",
"version": "v2"
},
{
"created": "Wed, 15 Aug 2018 02:45:50 GMT",
"version": "v3"
},
{
"created": "Thu, 30 Aug 2018 12:40:21 GMT",
"version": "v4"
}
] | 2018-10-02 | [
[
"Singh",
"Tejinder P.",
""
]
] | The Ghirardi-Rimini-Weber (GRW) theory of spontaneous collapse offers a possible resolution of the quantum measurement problem. In this theory, the wave function of a particle spontaneously and repeatedly localises to one or the other random position in space, as a consequence of the hypothesised quantum jumps. In between jumps the wave function undergoes the usual Schr\"{o}dinger evolution. In the present paper we suggest that these jumps take place in Hilbert space, with no reference to physical space, and physical three-dimensional space arises as a consequence of localisation of macroscopic objects in the universe. That is, collapse of the wave-function is responsible for the origin of space. We then suggest that similar jumps take place for a hypothetical time operator in Hilbert space, and classical time as we know it emerges from localisation of this time operator for macroscopic objects. More generally, the jumps are suggested to take place in an operator space-time in Hilbert space, leading to an emergent classical space-time. |
2203.08181 | Mouhssine Koussour | M. Koussour, S.H. Shekh, and M. Bennai | Bianchi type-I Barrow holographic dark energy model in symmetric
teleparallel gravity | IJMPA accepted version | Int. J. Mod. Phys. A, 37.28n29 (2022) 2250184 | 10.1142/S0217751X22501846 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we have discussed a spatially homogeneous and anisotropic
Bianchi type-I space-time in the presence of Barrow holographic dark energy
(infrared cut-off is the Hubble's horizon) proposed by Barrow recently (Physics
Letters B 808 (2020): 135643) and matter in the framework of $f(Q)$ gravity
where the non-metricity $Q$ is responsible for the gravitational interaction
for the specific choice of $f(Q)=\lambda Q^{2}$ (where $\lambda <0$ is a
constant). To find the exact solutions to the field equations we consider the
deceleration parameter $q$ is a function of the Hubble's parameter $H$ i.e.
$q=b-\frac{n}{H}$ (where $b$ and $n$ are constants). We have studied the
physical behavior of important cosmological parameters such as the EoS
parameter, BHDE and matter density, skewness parameter, squared sound speed,
and $\omega _{B}-\omega _{B}^{^{\prime }}$ plane. Also, we constrain the values
of the model parameters $b$ and $n$ using $57$ Hubble's parameter measurements.
| [
{
"created": "Tue, 15 Mar 2022 18:18:55 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Oct 2022 12:02:12 GMT",
"version": "v2"
}
] | 2023-02-03 | [
[
"Koussour",
"M.",
""
],
[
"Shekh",
"S. H.",
""
],
[
"Bennai",
"M.",
""
]
] | In this work, we have discussed a spatially homogeneous and anisotropic Bianchi type-I space-time in the presence of Barrow holographic dark energy (infrared cut-off is the Hubble's horizon) proposed by Barrow recently (Physics Letters B 808 (2020): 135643) and matter in the framework of $f(Q)$ gravity where the non-metricity $Q$ is responsible for the gravitational interaction for the specific choice of $f(Q)=\lambda Q^{2}$ (where $\lambda <0$ is a constant). To find the exact solutions to the field equations we consider the deceleration parameter $q$ is a function of the Hubble's parameter $H$ i.e. $q=b-\frac{n}{H}$ (where $b$ and $n$ are constants). We have studied the physical behavior of important cosmological parameters such as the EoS parameter, BHDE and matter density, skewness parameter, squared sound speed, and $\omega _{B}-\omega _{B}^{^{\prime }}$ plane. Also, we constrain the values of the model parameters $b$ and $n$ using $57$ Hubble's parameter measurements. |
2205.15342 | Naritaka Oshita | Naritaka Oshita, Hayato Motohashi, Sousuke Noda | Evaporation of Echoing Black Holes | 15 pages, 10 figures, published version | Phys.Rev.D 106 (2022) 4, 044044 | 10.1103/PhysRevD.106.044044 | RIKEN-iTHEMS-Report-22 | gr-qc hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | We compute the graybody factor and evaporation rate of a rotating black hole
in the presence of a hypothetical reflective surface slightly outside the outer
horizon radius, assuming that it spontaneously emits thermal radiation due to
quantum-gravitational effects such as firewalls or stretched horizons. As a
result of a resonance caused by a cavity between the reflective surface and
angular momentum barrier, the graybody factor is subject to a modulation in the
frequency space. By taking into account this effect for multiangular modes of
neutrinos, photons, and gravitons, we numerically compute the time development
of the mass and angular momentum of the black hole, and show that the excited
reflective surface shortens the lifetime of quantum black holes.
| [
{
"created": "Mon, 30 May 2022 18:00:03 GMT",
"version": "v1"
},
{
"created": "Tue, 30 Aug 2022 08:31:39 GMT",
"version": "v2"
}
] | 2022-08-31 | [
[
"Oshita",
"Naritaka",
""
],
[
"Motohashi",
"Hayato",
""
],
[
"Noda",
"Sousuke",
""
]
] | We compute the graybody factor and evaporation rate of a rotating black hole in the presence of a hypothetical reflective surface slightly outside the outer horizon radius, assuming that it spontaneously emits thermal radiation due to quantum-gravitational effects such as firewalls or stretched horizons. As a result of a resonance caused by a cavity between the reflective surface and angular momentum barrier, the graybody factor is subject to a modulation in the frequency space. By taking into account this effect for multiangular modes of neutrinos, photons, and gravitons, we numerically compute the time development of the mass and angular momentum of the black hole, and show that the excited reflective surface shortens the lifetime of quantum black holes. |
1602.06939 | Massimiliano Rinaldi | Adolfo Cisterna, T\'erence Delsate, Ludovic Ducobu, Massimiliano
Rinaldi | Slowly rotating neutron stars in the nonminimal derivative coupling
sector of Horndeski gravity | 29 pages, 6 figures, revtex preprint style. Few typos corrected, one
reference added. Version accepted for publication in Physical Review D | Phys. Rev. D 93, 084046 (2016) | 10.1103/PhysRevD.93.084046 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This work is devoted to the construction of slowly rotating neutron stars in
the framework of the nonminimal derivative coupling sector of Horndeski theory.
We match the large radius expansion of spherically symmetric solutions with
cosmological solutions and we find that the most viable model has only one free
parameter. Then, by using several tabulated and realistic equations of state,
we establish numerically the upper bound for this parameter in order to
construct neutron stars in the slow rotation approximation with the maximal
mass observed today. We finally study the surface redshift and the inertia of
these objects and compare them with known data.
| [
{
"created": "Mon, 22 Feb 2016 20:56:03 GMT",
"version": "v1"
},
{
"created": "Fri, 18 Mar 2016 18:48:33 GMT",
"version": "v2"
},
{
"created": "Wed, 6 Apr 2016 21:30:46 GMT",
"version": "v3"
}
] | 2016-05-04 | [
[
"Cisterna",
"Adolfo",
""
],
[
"Delsate",
"Térence",
""
],
[
"Ducobu",
"Ludovic",
""
],
[
"Rinaldi",
"Massimiliano",
""
]
] | This work is devoted to the construction of slowly rotating neutron stars in the framework of the nonminimal derivative coupling sector of Horndeski theory. We match the large radius expansion of spherically symmetric solutions with cosmological solutions and we find that the most viable model has only one free parameter. Then, by using several tabulated and realistic equations of state, we establish numerically the upper bound for this parameter in order to construct neutron stars in the slow rotation approximation with the maximal mass observed today. We finally study the surface redshift and the inertia of these objects and compare them with known data. |
gr-qc/0408018 | David Garfinkle | David Garfinkle | The fine structure of Gowdy spacetimes | contribution to A Spacetime Safari: Essays in honor of Vincent
Moncrief | Class.Quant.Grav. 21 (2004) S219 | 10.1088/0264-9381/21/3/012 | null | gr-qc | null | The approach to the singularity in Gowdy spacetimes consists of velocity term
dominated behavior, except at a set of isolated points. At and near these
points, spiky features grow. This paper reviews what is known about these
spikes.
| [
{
"created": "Fri, 6 Aug 2004 19:16:03 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Garfinkle",
"David",
""
]
] | The approach to the singularity in Gowdy spacetimes consists of velocity term dominated behavior, except at a set of isolated points. At and near these points, spiky features grow. This paper reviews what is known about these spikes. |
2304.08333 | Xi-Long Fan | Zhencheng Li, Zhen Jiang, Xi-Long Fan, Yun Chen, Liang Gao, Qi Guo and
Shenghua Yu | Exploring the multiband gravitational wave background with a
semi-analytic galaxy formation model | 12 pages, 5 figures | MNRAS, 527, 3, 2024, 5616-5626 | 10.1093/mnras/stad3576 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An enormous number of compact binary systems, spanning from stellar to
supermassive levels, emit substantial gravitational waves during their final
evolutionary stages, thereby creating a stochastic gravitational wave
background (SGWB). We calculate the merger rates of stellar compact binaries
and massive black hole binaries using a semi-analytic galaxy formation model --
Galaxy Assembly with Binary Evolution (GABE) in a unified and self-consistent
approach, followed by an estimation of the multi-band SGWB contributed by those
systems. We find that the amplitudes of the principal peaks of the SGWB energy
density are within one order of magnitude $\Omega_{GW} \sim 10^{-9}- 10^{-8}$.
This SGWB could easily be detected by the Square Kilometre Array (SKA), as well
as planned interferometric detectors, such as the Einstein Telescope (ET) and
the Laser Interferometer Space Antenna (LISA). The energy density of this
background varies as $\Omega_{GW} \propto f^{2/3}$ in SKA band. The shape of
the SGWB spectrum in the frequency range $\sim[10^{-4}$,$1]$Hz could allow the
LISA to distinguish the black hole seed models. The amplitude of the SGWB from
merging stellar binary black holes (BBHs) at $\sim 100$ Hz is approximately 10
and 100 times greater than those from merging binary neutron stars (BNSs) and
neutron-star-black-hole (NSBH) mergers, respectively. Note that, since the
cosmic star formation rate density predicted by GABE is somewhat lower than
observational results by $\sim 0.2$ dex at z < $\sim 2$, the amplitude of the
SGWB in the frequency range $\sim[1$, $10^{4}]$ Hz may be underestimated by a
similar factor at most.
| [
{
"created": "Mon, 17 Apr 2023 14:52:03 GMT",
"version": "v1"
},
{
"created": "Mon, 4 Dec 2023 12:12:47 GMT",
"version": "v2"
}
] | 2023-12-05 | [
[
"Li",
"Zhencheng",
""
],
[
"Jiang",
"Zhen",
""
],
[
"Fan",
"Xi-Long",
""
],
[
"Chen",
"Yun",
""
],
[
"Gao",
"Liang",
""
],
[
"Guo",
"Qi",
""
],
[
"Yu",
"Shenghua",
""
]
] | An enormous number of compact binary systems, spanning from stellar to supermassive levels, emit substantial gravitational waves during their final evolutionary stages, thereby creating a stochastic gravitational wave background (SGWB). We calculate the merger rates of stellar compact binaries and massive black hole binaries using a semi-analytic galaxy formation model -- Galaxy Assembly with Binary Evolution (GABE) in a unified and self-consistent approach, followed by an estimation of the multi-band SGWB contributed by those systems. We find that the amplitudes of the principal peaks of the SGWB energy density are within one order of magnitude $\Omega_{GW} \sim 10^{-9}- 10^{-8}$. This SGWB could easily be detected by the Square Kilometre Array (SKA), as well as planned interferometric detectors, such as the Einstein Telescope (ET) and the Laser Interferometer Space Antenna (LISA). The energy density of this background varies as $\Omega_{GW} \propto f^{2/3}$ in SKA band. The shape of the SGWB spectrum in the frequency range $\sim[10^{-4}$,$1]$Hz could allow the LISA to distinguish the black hole seed models. The amplitude of the SGWB from merging stellar binary black holes (BBHs) at $\sim 100$ Hz is approximately 10 and 100 times greater than those from merging binary neutron stars (BNSs) and neutron-star-black-hole (NSBH) mergers, respectively. Note that, since the cosmic star formation rate density predicted by GABE is somewhat lower than observational results by $\sim 0.2$ dex at z < $\sim 2$, the amplitude of the SGWB in the frequency range $\sim[1$, $10^{4}]$ Hz may be underestimated by a similar factor at most. |
0808.2574 | Sumit Som | A. Sil and S. Som | A Better Way to Reconstruct Dark Energy Models ? | 17 pages, 5 figures Accepted for publication in `Astrophysics and
Space Science' | Astrophys.Space Sci.318:109-115,2008 | 10.1007/s10509-008-9892-6 | null | gr-qc astro-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | To reconstruct dark energy models the redshift $z_{eq}$, marking the end of
radiation era and the beginning of matter-dominated era, can play a role as
important as $z_{t}$, the redshift at which deceleration parameter experiences
a signature flip. To implement the idea we propose a variable equation of state
for matter that can bring a smooth transition from radiation to
matter-dominated era in a single model. A popular $\Lambda \propto \rho$ dark
energy model is chosen for demonstration but found to be unacceptable. An
alternative $\Lambda \propto \rho a^{3}$ model is proposed and found to be more
close to observation.
| [
{
"created": "Tue, 19 Aug 2008 11:04:28 GMT",
"version": "v1"
}
] | 2009-11-18 | [
[
"Sil",
"A.",
""
],
[
"Som",
"S.",
""
]
] | To reconstruct dark energy models the redshift $z_{eq}$, marking the end of radiation era and the beginning of matter-dominated era, can play a role as important as $z_{t}$, the redshift at which deceleration parameter experiences a signature flip. To implement the idea we propose a variable equation of state for matter that can bring a smooth transition from radiation to matter-dominated era in a single model. A popular $\Lambda \propto \rho$ dark energy model is chosen for demonstration but found to be unacceptable. An alternative $\Lambda \propto \rho a^{3}$ model is proposed and found to be more close to observation. |
gr-qc/9911005 | Jeanette E. Nelson | J.E.Nelson (1) and R.F.Picken (2) ((1)Universita di
Torino,Italy,(2)Instituto Superior Tecnico,Lisboa,Portugal) | Quantum Holonomies in (2+1)-Dimensional Gravity | 10 pages Latex no figures | Phys.Lett. B471 (2000) 367-372 | 10.1016/S0370-2693(99)01407-0 | DFTT/59/99,IST/DM/30/99 | gr-qc hep-th math.QA | null | We describe an approach to the quantisation of (2+1)-dimensional gravity with
topology R x T^2 and negative cosmological constant, which uses two quantum
holonomy matrices satisfying a q-commutation relation. Solutions of diagonal
and upper-triangular form are constructed, which in the latter case exhibit
additional, non-trivial internal relations for each holonomy matrix.
Representations are constructed and a group of transformations - a
quasi-modular group - which preserves this structure, is presented.
| [
{
"created": "Tue, 2 Nov 1999 17:27:28 GMT",
"version": "v1"
},
{
"created": "Wed, 3 Nov 1999 11:11:41 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Nelson",
"J. E.",
""
],
[
"Picken",
"R. F.",
""
]
] | We describe an approach to the quantisation of (2+1)-dimensional gravity with topology R x T^2 and negative cosmological constant, which uses two quantum holonomy matrices satisfying a q-commutation relation. Solutions of diagonal and upper-triangular form are constructed, which in the latter case exhibit additional, non-trivial internal relations for each holonomy matrix. Representations are constructed and a group of transformations - a quasi-modular group - which preserves this structure, is presented. |
2003.12279 | Jinn-Ouk Gong | Inyong Cho, Jinn-Ouk Gong and Seung Hun Oh | Second-order effective energy-momentum tensor of gravitational scalar
perturbations with perfect fluid | 21 pages | Phys. Rev. D 102, 043531 (2020) | 10.1103/PhysRevD.102.043531 | null | gr-qc astro-ph.CO hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the second-order gravitational scalar perturbations for a
barotropic fluid. We derive the effective energy-momentum tensor described by
the quadratic terms of the gravitational and the matter perturbations. We show
that the second-order effective energy-momentum tensor is gauge dependent. We
impose three gauge conditions (longitudinal, spatially-flat, and comoving
gauges) for dust and radiation. The resulting energy-momentum tensor is
described only by a gauge invariant variable, but the functional form depends
on the gauge choice. In the matter-dominated epoch with dust-like fluid
background, the second-order effective energy density and pressure of the
perturbations evolve as 1/a^2 in all three gauge choices, like the curvature
density of the Universe, but they do not provide the correct equation of state.
The value of this parameter depends also on the gauge choice. In the
radiation-dominated epoch, the perturbations in the short-wave limit behave in
the same way as the radiation-like fluid in the longitudinal and the
spatially-flat gauges. However, they behave in a different way in the comoving
gauge. As a whole, we conclude that the second-order effective energy-momentum
tensor of the scalar perturbation is strictly gauge dependent.
| [
{
"created": "Fri, 27 Mar 2020 08:40:42 GMT",
"version": "v1"
}
] | 2020-09-09 | [
[
"Cho",
"Inyong",
""
],
[
"Gong",
"Jinn-Ouk",
""
],
[
"Oh",
"Seung Hun",
""
]
] | We investigate the second-order gravitational scalar perturbations for a barotropic fluid. We derive the effective energy-momentum tensor described by the quadratic terms of the gravitational and the matter perturbations. We show that the second-order effective energy-momentum tensor is gauge dependent. We impose three gauge conditions (longitudinal, spatially-flat, and comoving gauges) for dust and radiation. The resulting energy-momentum tensor is described only by a gauge invariant variable, but the functional form depends on the gauge choice. In the matter-dominated epoch with dust-like fluid background, the second-order effective energy density and pressure of the perturbations evolve as 1/a^2 in all three gauge choices, like the curvature density of the Universe, but they do not provide the correct equation of state. The value of this parameter depends also on the gauge choice. In the radiation-dominated epoch, the perturbations in the short-wave limit behave in the same way as the radiation-like fluid in the longitudinal and the spatially-flat gauges. However, they behave in a different way in the comoving gauge. As a whole, we conclude that the second-order effective energy-momentum tensor of the scalar perturbation is strictly gauge dependent. |
gr-qc/9604010 | Carlo Rovelli | Norbert Grot, Carlo Rovelli | Moduli-space structure of knots with intersections | 15 pages, latex-revtex, no figures | J.Math.Phys. 37 (1996) 3014-3021 | 10.1063/1.531527 | null | gr-qc | null | It is well known that knots are countable in ordinary knot theory. Recently,
knots {\it with intersections} have raised a certain interest, and have been
found to have physical applications. We point out that such knots --equivalence
classes of loops in $R^3$ under diffeomorphisms-- are not countable; rather,
they exhibit a moduli-space structure. We characterize these spaces of moduli
and study their dimension. We derive a lower bound (which we conjecture being
actually attained) on the dimension of the (non-degenerate components) of the
moduli spaces, as a function of the valence of the intersection.
| [
{
"created": "Thu, 4 Apr 1996 03:42:05 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Grot",
"Norbert",
""
],
[
"Rovelli",
"Carlo",
""
]
] | It is well known that knots are countable in ordinary knot theory. Recently, knots {\it with intersections} have raised a certain interest, and have been found to have physical applications. We point out that such knots --equivalence classes of loops in $R^3$ under diffeomorphisms-- are not countable; rather, they exhibit a moduli-space structure. We characterize these spaces of moduli and study their dimension. We derive a lower bound (which we conjecture being actually attained) on the dimension of the (non-degenerate components) of the moduli spaces, as a function of the valence of the intersection. |
gr-qc/0405143 | Edward Glass | E.N. Glass and J.P. Krisch | Kottler-Lambda-Kerr Spacetime | 1 eps figure | null | null | null | gr-qc | null | The static Kottler metric is the Schwarzschild vacuum metric extended to
include a cosmological constant. Angular momentum is added to the Kottler
metric by using Newman and Janis' complexifying algorithm. The new metric is
the Lambda generalization of the Kerr spacetime. It is stationary, axially
symmetric, Petrov type II, and has Kerr-Schild form.
| [
{
"created": "Fri, 28 May 2004 21:05:16 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Glass",
"E. N.",
""
],
[
"Krisch",
"J. P.",
""
]
] | The static Kottler metric is the Schwarzschild vacuum metric extended to include a cosmological constant. Angular momentum is added to the Kottler metric by using Newman and Janis' complexifying algorithm. The new metric is the Lambda generalization of the Kerr spacetime. It is stationary, axially symmetric, Petrov type II, and has Kerr-Schild form. |
0804.3806 | R. F. O'Connell | R. F. O'Connell | Gravito-Magnetism in one-body and two-body systems: Theory and
Experiments | Invited Lecture, in "Atom Optics and Space Physics", Proc. of Course
CLXVIII of the International School of Physics "Enrico Fermi", Varenna,
Italy, 2007, ed. E. Arimondo, W. Ertmer and W. Schleich, in press; 15 pages | null | null | Proc. of Course CLXVIII of the International School of
Physics(Societa Italiana di Fisica, 2009) | gr-qc astro-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We survey theoretical and experimental/observational results on
general-relativistic spin (rotation) effects in binary systems. A detailed
discussion is given of the two-body Kepler problem and its first post-Newtonian
generalization, including spin effects. Spin effects result from gravitational
spin-orbit and spin-spin interactions (analogous to the corresponding case in
quantum electrodynamics) and these effects are shown to manifest themselves in
two ways: (a) precession of the spinning bodies per se and (b) precession of
the orbit (which is further broke down into precessions of the argument of the
periastron, the longitude of the ascending node and the inclination of the
orbit). We also note the ambiguity that arises from use of the terminology
frame-dragging, de Sitter precession and Lense-Thirring precession, in contrast
to the unambiguous reference to spin-orbit and spin-spin precessions. Turning
to one-body experiments, we discuss the recent results of the GP-B experiment,
the Ciufolini-Pavlis Lageos experiment and lunar-laser ranging measurements
(which actually involve three bodies). Two-body systems inevitably involve
astronomical observations and we survey results obtained from the first binary
pulsar system, a more recently discovered binary system and, finally, the
highly significant discovery of a double-pulsar binary system.
| [
{
"created": "Wed, 23 Apr 2008 20:32:52 GMT",
"version": "v1"
},
{
"created": "Sat, 12 Sep 2009 15:41:21 GMT",
"version": "v2"
}
] | 2009-09-21 | [
[
"O'Connell",
"R. F.",
""
]
] | We survey theoretical and experimental/observational results on general-relativistic spin (rotation) effects in binary systems. A detailed discussion is given of the two-body Kepler problem and its first post-Newtonian generalization, including spin effects. Spin effects result from gravitational spin-orbit and spin-spin interactions (analogous to the corresponding case in quantum electrodynamics) and these effects are shown to manifest themselves in two ways: (a) precession of the spinning bodies per se and (b) precession of the orbit (which is further broke down into precessions of the argument of the periastron, the longitude of the ascending node and the inclination of the orbit). We also note the ambiguity that arises from use of the terminology frame-dragging, de Sitter precession and Lense-Thirring precession, in contrast to the unambiguous reference to spin-orbit and spin-spin precessions. Turning to one-body experiments, we discuss the recent results of the GP-B experiment, the Ciufolini-Pavlis Lageos experiment and lunar-laser ranging measurements (which actually involve three bodies). Two-body systems inevitably involve astronomical observations and we survey results obtained from the first binary pulsar system, a more recently discovered binary system and, finally, the highly significant discovery of a double-pulsar binary system. |
gr-qc/0602110 | Richard Woodard | Shun-Pei Miao and R. P. Woodard (University of Florida) | Leading Log Solution for Inflationary Yukawa | 35 pages, LaTeX 2epsilon, 4 figures (using axodraw), version 2 has an
updated reference list | Phys.Rev.D74:044019,2006 | 10.1103/PhysRevD.74.044019 | UFIFT-QG-06-03 | gr-qc astro-ph hep-ph | null | We generalize Starobinskii's stochastic technique to the theory of a
massless, minimally coupled scalar interacting with a massless fermion in a
locally de Sitter geometry. The scalar is an ``active'' field that can engender
infrared logarithms. The fermion is a ``passive'' field that cannot cause
infrared logarithms but which can carry them, and which can also induce new
interactions between the active fields. The procedure for dealing with passive
fields is to integrate them out, then stochastically simplify the resulting
effective action following Starobinski\u{\i}. Because Yukawa theory is
quadratic in the fermion this can be done explicitly using the classic solution
of Candelas and Raine. We check the resulting stochastic formulation against an
explicit two loop computation. We also derive a nonperturbative, leading log
result for the stress tensor. Because the scalar effective potential induced by
fermions is unbounded below, back-reaction from this model might dynamically
cancel an arbitrarily large cosmological constant.
| [
{
"created": "Mon, 27 Feb 2006 11:46:26 GMT",
"version": "v1"
},
{
"created": "Sun, 11 May 2008 12:42:57 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Miao",
"Shun-Pei",
"",
"University of Florida"
],
[
"Woodard",
"R. P.",
"",
"University of Florida"
]
] | We generalize Starobinskii's stochastic technique to the theory of a massless, minimally coupled scalar interacting with a massless fermion in a locally de Sitter geometry. The scalar is an ``active'' field that can engender infrared logarithms. The fermion is a ``passive'' field that cannot cause infrared logarithms but which can carry them, and which can also induce new interactions between the active fields. The procedure for dealing with passive fields is to integrate them out, then stochastically simplify the resulting effective action following Starobinski\u{\i}. Because Yukawa theory is quadratic in the fermion this can be done explicitly using the classic solution of Candelas and Raine. We check the resulting stochastic formulation against an explicit two loop computation. We also derive a nonperturbative, leading log result for the stress tensor. Because the scalar effective potential induced by fermions is unbounded below, back-reaction from this model might dynamically cancel an arbitrarily large cosmological constant. |
1412.7832 | Sarbari Guha Dr. | Pinaki Bhattacharya and Sarbari Guha | Confinement and stability of dynamical system in presence of scalar
fields and perturbation in the bulk | 13 pages, 28 figures, minor changes in the text, one reference added | null | null | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we have considered a five-dimensional warped product spacetime
with spacelike extra dimension and with a scalar field source in the bulk. We
have studied the dynamics of the scalar field under different types of
potential in an effort to explain the confinement of particles in the
five-dimensional spacetime. The behavior of the system is determined from the
nature of damping force on the system. We have also examined the nature of the
effective potential under different circumstances. Lastly we have studied the
system to determine whether or not the system attains asymptotically stable
condition for both unperturbed and perturbed conditions. The analysis throws
significant light on the nature confinement of particles and the stability of
the dynamical system under these conditions.
| [
{
"created": "Thu, 25 Dec 2014 16:07:00 GMT",
"version": "v1"
},
{
"created": "Sat, 23 May 2015 10:39:45 GMT",
"version": "v2"
},
{
"created": "Mon, 1 Jun 2015 19:05:21 GMT",
"version": "v3"
}
] | 2015-06-02 | [
[
"Bhattacharya",
"Pinaki",
""
],
[
"Guha",
"Sarbari",
""
]
] | In this paper we have considered a five-dimensional warped product spacetime with spacelike extra dimension and with a scalar field source in the bulk. We have studied the dynamics of the scalar field under different types of potential in an effort to explain the confinement of particles in the five-dimensional spacetime. The behavior of the system is determined from the nature of damping force on the system. We have also examined the nature of the effective potential under different circumstances. Lastly we have studied the system to determine whether or not the system attains asymptotically stable condition for both unperturbed and perturbed conditions. The analysis throws significant light on the nature confinement of particles and the stability of the dynamical system under these conditions. |
gr-qc/9812078 | Jose Pizarro de Sande Lemos | Jose' P. S. Lemos | Collapsing shells of radiation in anti-de Sitter spacetimes and the hoop
and cosmic censorship conjectures | 4 pages, Revtex Journal: to appear in Physical Review D | Phys.Rev. D59 (1999) 044020 | 10.1103/PhysRevD.59.044020 | null | gr-qc | null | Gravitational collapse of radiation in an anti-de Sitter background is
studied. For the spherical case, the collapse proceeds in much the same way as
in the Minkowski background, i.e., massless naked singularities may form for a
highly inhomogeneous collapse, violating the cosmic censorship, but not the
hoop conjecture. The toroidal, cylindrical and planar collapses can be treated
together. In these cases no naked singularity ever forms, in accordance with
the cosmic censorship. However, since the collapse proceeds to form toroidal,
cylindrical or planar black holes, the hoop conjecture in an anti-de Sitter
spacetime is violated.
| [
{
"created": "Mon, 21 Dec 1998 23:00:35 GMT",
"version": "v1"
},
{
"created": "Tue, 22 Dec 1998 19:40:01 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Lemos",
"Jose' P. S.",
""
]
] | Gravitational collapse of radiation in an anti-de Sitter background is studied. For the spherical case, the collapse proceeds in much the same way as in the Minkowski background, i.e., massless naked singularities may form for a highly inhomogeneous collapse, violating the cosmic censorship, but not the hoop conjecture. The toroidal, cylindrical and planar collapses can be treated together. In these cases no naked singularity ever forms, in accordance with the cosmic censorship. However, since the collapse proceeds to form toroidal, cylindrical or planar black holes, the hoop conjecture in an anti-de Sitter spacetime is violated. |
gr-qc/0605100 | Leonid Grishchuk P | D. Baskaran, L. P. Grishchuk, and A. G. Polnarev | Imprints of Relic Gravitational Waves in Cosmic Microwave Background
Radiation | 61 pages including 15 figures, v.2: additional references and
clarifications, to be published in Phys. Rev. D | Phys.Rev. D74 (2006) 083008 | 10.1103/PhysRevD.74.083008 | null | gr-qc astro-ph hep-th | null | A strong variable gravitational field of the very early Universe inevitably
generates relic gravitational waves by amplifying their zero-point quantum
oscillations. We begin our discussion by contrasting the concepts of relic
gravitational waves and inflationary `tensor modes'. We explain and summarize
the properties of relic gravitational waves that are needed to derive their
effects on CMB temperature and polarization anisotropies. The radiation field
is characterized by four invariants I, V, E, B. We reduce the radiative
transfer equations to a single integral equation of Voltairre type and solve it
analytically and numerically. We formulate the correlation functions
C^{XX'}_{\ell} for X, X'= T, E, B and derive their amplitudes, shapes and
oscillatory features. Although all of our main conclusions are supported by
exact numerical calculations, we obtain them, in effect, analytically by
developing and using accurate approximations. We show that the TE correlation
at lower \ell's must be negative (i.e. an anticorrelation), if it is caused by
gravitational waves, and positive if it is caused by density perturbations.
This difference in TE correlation may be a signature more valuable
observationally than the lack or presence of the BB correlation, since the TE
signal is about 100 times stronger than the expected BB signal. We discuss the
detection by WMAP of the TE anticorrelation at \ell \approx 30 and show that
such an anticorrelation is possible only in the presence of a significant
amount of relic gravitational waves (within the framework of all other common
assumptions). We propose models containing considerable amounts of relic
gravitational waves that are consistent with the measured TT, TE and EE
correlations.
| [
{
"created": "Wed, 17 May 2006 16:19:47 GMT",
"version": "v1"
},
{
"created": "Mon, 25 Sep 2006 10:01:12 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Baskaran",
"D.",
""
],
[
"Grishchuk",
"L. P.",
""
],
[
"Polnarev",
"A. G.",
""
]
] | A strong variable gravitational field of the very early Universe inevitably generates relic gravitational waves by amplifying their zero-point quantum oscillations. We begin our discussion by contrasting the concepts of relic gravitational waves and inflationary `tensor modes'. We explain and summarize the properties of relic gravitational waves that are needed to derive their effects on CMB temperature and polarization anisotropies. The radiation field is characterized by four invariants I, V, E, B. We reduce the radiative transfer equations to a single integral equation of Voltairre type and solve it analytically and numerically. We formulate the correlation functions C^{XX'}_{\ell} for X, X'= T, E, B and derive their amplitudes, shapes and oscillatory features. Although all of our main conclusions are supported by exact numerical calculations, we obtain them, in effect, analytically by developing and using accurate approximations. We show that the TE correlation at lower \ell's must be negative (i.e. an anticorrelation), if it is caused by gravitational waves, and positive if it is caused by density perturbations. This difference in TE correlation may be a signature more valuable observationally than the lack or presence of the BB correlation, since the TE signal is about 100 times stronger than the expected BB signal. We discuss the detection by WMAP of the TE anticorrelation at \ell \approx 30 and show that such an anticorrelation is possible only in the presence of a significant amount of relic gravitational waves (within the framework of all other common assumptions). We propose models containing considerable amounts of relic gravitational waves that are consistent with the measured TT, TE and EE correlations. |
2105.07994 | Maria Shubina | Maria Shubina | Exact solutions in two-dimensional metric $f(R)$-gravity | 10 pages | null | null | null | gr-qc nlin.SI | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we consider the two-dimensional metric $f(R)$-gravity model for
the metric tensor depending on two variable: time and one spacelike coordinate.
We obtain exact analytical vacuum solutions for different forms of function $
f(R) $ which are solutions of cosmological type. These solutions are expressed
in terms of arbitrary functions, which, under certain conditions, can be chosen
as new variables.
| [
{
"created": "Mon, 17 May 2021 16:19:15 GMT",
"version": "v1"
}
] | 2021-05-18 | [
[
"Shubina",
"Maria",
""
]
] | In this paper we consider the two-dimensional metric $f(R)$-gravity model for the metric tensor depending on two variable: time and one spacelike coordinate. We obtain exact analytical vacuum solutions for different forms of function $ f(R) $ which are solutions of cosmological type. These solutions are expressed in terms of arbitrary functions, which, under certain conditions, can be chosen as new variables. |
2405.04933 | Antonia Seifert | Antonia Seifert | The Importance of Being Symmetric: Flat Rotation Curves from Exact
Axisymmetric Static Vacuum Spacetimes | 10 pages, 4 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Starting from the vacuum Einstein Field Equations and a static axisymmetric
ansatz, we find two new solutions describing an axisymmetric static vacuum
spacetime with cylindrical symmetry: One of this exhibits an additional
symmetry in $z$-direction and the other has $z$-coordinate dependent
coefficients. In analogy to the Schwarzschild solution, these metrics describe
a static vacuum spacetime and apply in similar settings except for the changed
symmetry conditions. Analyzing the low-velocity limit corresponding to the
Newtonian approximation of the Schwarzschild metric, we find an effective
logarithmic potential. This yields flat rotation curves for test particles
undergoing rotational motion within the spacetime described by the line
elements, in contrast to Newtonian rotation curves. This analysis highlights
how important the symmetry assumptions are for deriving general relativistic
solutions.
One example of physical objects that are generally described in the static
vacuum low-velocity limit (reducing to Newtonian gravity in the spherically
symmetric case) and exhibit axial symmetry are disk galaxies. We show that
symmetries and appropriate line elements that respect them are crucial to
consider in such settings. In particular, the solutions presented here result
in flat rotation curves without any need for dark matter. While these exact
solutions are limited to static vacuum spacetimes, their application to
physical galaxies relies on appropriate approximations. Nonetheless, they offer
valuable insights into explanations for flat rotation curves in galaxies and
their implications for dark matter.
| [
{
"created": "Wed, 8 May 2024 10:00:33 GMT",
"version": "v1"
}
] | 2024-05-09 | [
[
"Seifert",
"Antonia",
""
]
] | Starting from the vacuum Einstein Field Equations and a static axisymmetric ansatz, we find two new solutions describing an axisymmetric static vacuum spacetime with cylindrical symmetry: One of this exhibits an additional symmetry in $z$-direction and the other has $z$-coordinate dependent coefficients. In analogy to the Schwarzschild solution, these metrics describe a static vacuum spacetime and apply in similar settings except for the changed symmetry conditions. Analyzing the low-velocity limit corresponding to the Newtonian approximation of the Schwarzschild metric, we find an effective logarithmic potential. This yields flat rotation curves for test particles undergoing rotational motion within the spacetime described by the line elements, in contrast to Newtonian rotation curves. This analysis highlights how important the symmetry assumptions are for deriving general relativistic solutions. One example of physical objects that are generally described in the static vacuum low-velocity limit (reducing to Newtonian gravity in the spherically symmetric case) and exhibit axial symmetry are disk galaxies. We show that symmetries and appropriate line elements that respect them are crucial to consider in such settings. In particular, the solutions presented here result in flat rotation curves without any need for dark matter. While these exact solutions are limited to static vacuum spacetimes, their application to physical galaxies relies on appropriate approximations. Nonetheless, they offer valuable insights into explanations for flat rotation curves in galaxies and their implications for dark matter. |
gr-qc/9605008 | Henrique | H. P. de Oliveira | Self-Similar Collapse in Brans-Dicke Theory and Critical Behavior | 7 pages, 4 Postscript figures available upon request | null | null | null | gr-qc | null | We use the technique of conformal transformations to generate self-similar
collapse in Brans-Dicke theory. We analyze the solutions concerning the
critical behavior found recently by Choptuik. The critical exponent associated
to the formation of black hole for near critical evolution is obtained. The
role of the coupling parameter is discussed.
| [
{
"created": "Fri, 3 May 1996 22:47:15 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"de Oliveira",
"H. P.",
""
]
] | We use the technique of conformal transformations to generate self-similar collapse in Brans-Dicke theory. We analyze the solutions concerning the critical behavior found recently by Choptuik. The critical exponent associated to the formation of black hole for near critical evolution is obtained. The role of the coupling parameter is discussed. |
0901.3349 | Hector Hernandez-Coronado | C. Chryssomalakos, H. Hernandez-Coronado and E. Okon | Center of mass in special and general relativity and its role in an
effective description of spacetime | Prepared for the procceding of the conference DICE 2008 | J.Phys.Conf.Ser.174:012026,2009 | 10.1088/1742-6596/174/1/012026 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this contribution, we suggest the approach that geometric concepts ought
to be defined in terms of physical operations involving quantum matter. In this
way it is expected that some (presumably nocive) idealizations lying deep
within the roots of the notion of spacetime might be excluded. In particular,
we consider that spacetime can be probed only with physical (and therefore
extended) particles, which can be effectively described by coordinates that
fail to commute by a term proportional to the spin of the particles.
| [
{
"created": "Wed, 21 Jan 2009 20:21:36 GMT",
"version": "v1"
}
] | 2009-07-24 | [
[
"Chryssomalakos",
"C.",
""
],
[
"Hernandez-Coronado",
"H.",
""
],
[
"Okon",
"E.",
""
]
] | In this contribution, we suggest the approach that geometric concepts ought to be defined in terms of physical operations involving quantum matter. In this way it is expected that some (presumably nocive) idealizations lying deep within the roots of the notion of spacetime might be excluded. In particular, we consider that spacetime can be probed only with physical (and therefore extended) particles, which can be effectively described by coordinates that fail to commute by a term proportional to the spin of the particles. |
gr-qc/0104073 | Anzhong Wang | Anzhong Wang | Critical Phenomena in Gravitational Collapse: The Studies So Far | 5 figures, revtex. To appear in Braz. J. Phys. (2001) | Braz.J.Phys.31:188-197,2001 | null | null | gr-qc | null | Studies of black hole formation from gravitational collapse have revealed
interesting non-linear phenomena at the threshold of black hole formation. In
particular, in 1993 Choptuik studied the collapse of a massless scalar field
with spherical symmetry and found some behaviour, which is quite similar to the
critical phenomena well-known in {\em Statistical Mechanics} and {\em Quantum
Field Theory}. Universality and echoing of the critical solution and power-law
scaling of the black hole masses have given rise to the name {\em Critical
Phenomena in Gravitational Collapse}. Choptuik's results were soon confirmed
both numerically and semi-analytically, and have extended to various other
matter fields.
In this paper, we shall give a brief introduction to this fascinating and
relatively new area, and provides an updated publication list. An analytical
"toy" model of critical collapse is presented, and some current investigations
are given.
| [
{
"created": "Mon, 23 Apr 2001 22:44:23 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Wang",
"Anzhong",
""
]
] | Studies of black hole formation from gravitational collapse have revealed interesting non-linear phenomena at the threshold of black hole formation. In particular, in 1993 Choptuik studied the collapse of a massless scalar field with spherical symmetry and found some behaviour, which is quite similar to the critical phenomena well-known in {\em Statistical Mechanics} and {\em Quantum Field Theory}. Universality and echoing of the critical solution and power-law scaling of the black hole masses have given rise to the name {\em Critical Phenomena in Gravitational Collapse}. Choptuik's results were soon confirmed both numerically and semi-analytically, and have extended to various other matter fields. In this paper, we shall give a brief introduction to this fascinating and relatively new area, and provides an updated publication list. An analytical "toy" model of critical collapse is presented, and some current investigations are given. |
gr-qc/0102056 | Joshua Wood | Joshua Wood and William Moreau | Solutions of Conformal Gravity with Dynamical Mass Generation in the
Solar System | 8 pages, 3 figures | null | null | null | gr-qc | null | The field equations of Mannheim's theory of conformal gravity with dynamic
mass generation are solved numerically in the interior and exterior regions of
a model spherically symmetric sun with matched boundary conditions at the
surface. The model consists of a generic fermion field inside the sun, and a
scalar Higgs field in both the interior and exterior regions. From the
conformal geodesic equations it is shown how an asymptotic gradient in the
Higgs field causes an anomalous radial acceleration in qualitative agreement
with that observed on the Pioneer 10/11, Galileo, and Ulysses spacecraft. At
the same time the standard solar system tests of general relativity are
preserved within the limits of observation.
| [
{
"created": "Tue, 13 Feb 2001 05:17:29 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Wood",
"Joshua",
""
],
[
"Moreau",
"William",
""
]
] | The field equations of Mannheim's theory of conformal gravity with dynamic mass generation are solved numerically in the interior and exterior regions of a model spherically symmetric sun with matched boundary conditions at the surface. The model consists of a generic fermion field inside the sun, and a scalar Higgs field in both the interior and exterior regions. From the conformal geodesic equations it is shown how an asymptotic gradient in the Higgs field causes an anomalous radial acceleration in qualitative agreement with that observed on the Pioneer 10/11, Galileo, and Ulysses spacecraft. At the same time the standard solar system tests of general relativity are preserved within the limits of observation. |
0808.2165 | Marcello Ortaggio | Marcello Ortaggio, Vojtech Pravda, Alena Pravdova | Higher dimensional Kerr-Schild spacetimes | 33 pages. v2: minor changes, new references | Class.Quant.Grav.26:025008,2009 | 10.1088/0264-9381/26/2/025008 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate general properties of Kerr-Schild (KS) metrics in n>4
spacetime dimensions. First, we show that the Weyl tensor is of type II or more
special if the null KS vector k is geodetic (or, equivalently, if
T_{ab}k^ak^b=0). We subsequently specialize to vacuum KS solutions, which
naturally split into two families of non-expanding and expanding metrics. After
demonstrating that non-expanding solutions are equivalent to the known class of
vacuum Kundt solutions of type N, we analyze expanding solutions in detail. We
show that they can only be of the type II or D, and we characterize optical
properties of the multiple Weyl aligned null direction (WAND) k. In general, k
has caustics corresponding to curvature singularities. In addition, it is
generically shearing. Nevertheless, we arrive at a possible "weak" n>4
extension of the Goldberg-Sachs theorem, limited to the KS class, which matches
previous conclusions for general type III/N solutions. In passing, properties
of Myers-Perry black holes and black rings related to our results are also
briefly discussed.
| [
{
"created": "Fri, 15 Aug 2008 16:20:14 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Jan 2009 11:02:35 GMT",
"version": "v2"
}
] | 2009-01-12 | [
[
"Ortaggio",
"Marcello",
""
],
[
"Pravda",
"Vojtech",
""
],
[
"Pravdova",
"Alena",
""
]
] | We investigate general properties of Kerr-Schild (KS) metrics in n>4 spacetime dimensions. First, we show that the Weyl tensor is of type II or more special if the null KS vector k is geodetic (or, equivalently, if T_{ab}k^ak^b=0). We subsequently specialize to vacuum KS solutions, which naturally split into two families of non-expanding and expanding metrics. After demonstrating that non-expanding solutions are equivalent to the known class of vacuum Kundt solutions of type N, we analyze expanding solutions in detail. We show that they can only be of the type II or D, and we characterize optical properties of the multiple Weyl aligned null direction (WAND) k. In general, k has caustics corresponding to curvature singularities. In addition, it is generically shearing. Nevertheless, we arrive at a possible "weak" n>4 extension of the Goldberg-Sachs theorem, limited to the KS class, which matches previous conclusions for general type III/N solutions. In passing, properties of Myers-Perry black holes and black rings related to our results are also briefly discussed. |
1506.06799 | Martin Kolo\v{s} | Martin Kolo\v{s}, Zden\v{e}k Stuchl\'ik and Arman Tursunov | Quasi-harmonic oscillatory motion of charged particles around a
Schwarzschild black hole immersed in an uniform magnetic field | accepted for publication in Classical and Quantum Gravity, 16 pages,
13 figures, 3 tables | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In order to test the role of large-scale magnetic fields in quasiperiodic
oscillation phenomena observed in microquasars, we study oscillatory motion of
charged particles in vicinity of a Schwarzschild black hole immersed into an
external asymptotically uniform magnetic field. We determine the fundamental
frequencies of small harmonic oscillations of charged test particles around
stable circular orbits in the equatorial plane of a magnetized black hole, and
discuss the radial profiles of frequencies of the radial and latitudinal
harmonic oscillations in dependence on the mass of the black hole and the
strength of the magnetic field. We demonstrate that assuming relevance of
resonant phenomena of the radial and latitudinal oscillations of charged
particles at their frequency ratio $3:2$, the oscillatory frequencies of
charged particles can be well related to the frequencies of the twin
high-frequency quasi-periodic oscillations observed in the microquasars GRS
1915+105, XTE 1550-564 and GRO 1655-40.
| [
{
"created": "Mon, 22 Jun 2015 21:51:52 GMT",
"version": "v1"
}
] | 2015-06-24 | [
[
"Kološ",
"Martin",
""
],
[
"Stuchlík",
"Zdeněk",
""
],
[
"Tursunov",
"Arman",
""
]
] | In order to test the role of large-scale magnetic fields in quasiperiodic oscillation phenomena observed in microquasars, we study oscillatory motion of charged particles in vicinity of a Schwarzschild black hole immersed into an external asymptotically uniform magnetic field. We determine the fundamental frequencies of small harmonic oscillations of charged test particles around stable circular orbits in the equatorial plane of a magnetized black hole, and discuss the radial profiles of frequencies of the radial and latitudinal harmonic oscillations in dependence on the mass of the black hole and the strength of the magnetic field. We demonstrate that assuming relevance of resonant phenomena of the radial and latitudinal oscillations of charged particles at their frequency ratio $3:2$, the oscillatory frequencies of charged particles can be well related to the frequencies of the twin high-frequency quasi-periodic oscillations observed in the microquasars GRS 1915+105, XTE 1550-564 and GRO 1655-40. |
gr-qc/9709074 | Wlodzimierz Piechocki | George Jorjadze and Wlodzimierz Piechocki | Dynamical Ambiguities in Singular Gravitational Field | 7 pages, latex, no figures, submitted for publication | Class.Quant.Grav.15:L41-L45,1998 | 10.1088/0264-9381/15/5/002 | null | gr-qc | null | We consider particle dynamics in singular gravitational field. In 2d
spacetime the system splits into two independent gravitational systems without
singularity. Dynamical integrals of each system define $sl(2,R)$ algebra, but
the corresponding symmetry transformations are not defined globally.
Quantization leads to ambiguity. By including singularity one can get the
global $SO(2.1)$ symmetry. Quantization in this case leads to unique quantum
theory.
| [
{
"created": "Sat, 27 Sep 1997 14:40:48 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"Jorjadze",
"George",
""
],
[
"Piechocki",
"Wlodzimierz",
""
]
] | We consider particle dynamics in singular gravitational field. In 2d spacetime the system splits into two independent gravitational systems without singularity. Dynamical integrals of each system define $sl(2,R)$ algebra, but the corresponding symmetry transformations are not defined globally. Quantization leads to ambiguity. By including singularity one can get the global $SO(2.1)$ symmetry. Quantization in this case leads to unique quantum theory. |
0704.2861 | Vasileios Paschalidis | Vasileios Paschalidis | Mixed Hyperbolic - Second-Order Parabolic Formulations of General
Relativity | 19 pages, two column, references added, two proofs of well-posedness
added, content changed to agree with submitted version to PRD | Phys.Rev.D78:024002,2008 | 10.1103/PhysRevD.78.024002 | null | gr-qc | null | Two new formulations of general relativity are introduced. The first one is a
parabolization of the Arnowitt, Deser, Misner (ADM) formulation and is derived
by addition of combinations of the constraints and their derivatives to the
right-hand-side of the ADM evolution equations. The desirable property of this
modification is that it turns the surface of constraints into a local attractor
because the constraint propagation equations become second-order parabolic
independently of the gauge conditions employed. This system may be classified
as mixed hyperbolic - second-order parabolic. The second formulation is a
parabolization of the Kidder, Scheel, Teukolsky formulation and is a manifestly
mixed strongly hyperbolic - second-order parabolic set of equations, bearing
thus resemblance to the compressible Navier-Stokes equations. As a first test,
a stability analysis of flat space is carried out and it is shown that the
first modification exponentially damps and smoothes all constraint violating
modes. These systems provide a new basis for constructing schemes for long-term
and stable numerical integration of the Einstein field equations.
| [
{
"created": "Sun, 22 Apr 2007 20:06:57 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Mar 2008 02:29:30 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Paschalidis",
"Vasileios",
""
]
] | Two new formulations of general relativity are introduced. The first one is a parabolization of the Arnowitt, Deser, Misner (ADM) formulation and is derived by addition of combinations of the constraints and their derivatives to the right-hand-side of the ADM evolution equations. The desirable property of this modification is that it turns the surface of constraints into a local attractor because the constraint propagation equations become second-order parabolic independently of the gauge conditions employed. This system may be classified as mixed hyperbolic - second-order parabolic. The second formulation is a parabolization of the Kidder, Scheel, Teukolsky formulation and is a manifestly mixed strongly hyperbolic - second-order parabolic set of equations, bearing thus resemblance to the compressible Navier-Stokes equations. As a first test, a stability analysis of flat space is carried out and it is shown that the first modification exponentially damps and smoothes all constraint violating modes. These systems provide a new basis for constructing schemes for long-term and stable numerical integration of the Einstein field equations. |
1708.00830 | Gaurav Narain | Gaurav Narain | On the Renormalization Group perspective of $\alpha$-attractors | 1+17 pages, 2 figures. Typos corrected, new references added,
additional paragraph added in conclusion. Accepted for publication in JCAP | null | 10.1088/1475-7516/2017/10/032 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this short paper we outline a recipe for the reconstruction of $F(R)$
gravity starting from single field inflationary potentials in the Einstein
frame. For simple potentials one can compute the explicit form of $F(R)$,
whilst for more involved examples one gets a parametric form of $F(R)$. The
$F(R)$ reconstruction algorithm is used to study various examples: power-law
$\phi^n$, exponential and $\alpha$-attractors. In each case it is seen that for
large $R$ (corresponding to large value of inflaton field), $F(R) \sim R^2$.
For the case of $\alpha$-attractors $F(R) \sim R^2$ for all values of inflaton
field (for all values of $R$) as $\alpha\to0$. For generic inflaton potential
$V(\phi)$, it is seen that if $V^\prime/V \to0$ (for some $\phi$) then the
corresponding $F(R) \sim R^2$. We then study $\alpha$-attractors in more detail
using non-perturbative renormalisation group methods to analyse the
reconstructed $F(R)$. It is seen that $\alpha\to0$ is an ultraviolet stable
fixed point of the renormalisation group trajectories.
| [
{
"created": "Wed, 2 Aug 2017 17:08:07 GMT",
"version": "v1"
},
{
"created": "Fri, 20 Oct 2017 06:27:08 GMT",
"version": "v2"
}
] | 2017-11-01 | [
[
"Narain",
"Gaurav",
""
]
] | In this short paper we outline a recipe for the reconstruction of $F(R)$ gravity starting from single field inflationary potentials in the Einstein frame. For simple potentials one can compute the explicit form of $F(R)$, whilst for more involved examples one gets a parametric form of $F(R)$. The $F(R)$ reconstruction algorithm is used to study various examples: power-law $\phi^n$, exponential and $\alpha$-attractors. In each case it is seen that for large $R$ (corresponding to large value of inflaton field), $F(R) \sim R^2$. For the case of $\alpha$-attractors $F(R) \sim R^2$ for all values of inflaton field (for all values of $R$) as $\alpha\to0$. For generic inflaton potential $V(\phi)$, it is seen that if $V^\prime/V \to0$ (for some $\phi$) then the corresponding $F(R) \sim R^2$. We then study $\alpha$-attractors in more detail using non-perturbative renormalisation group methods to analyse the reconstructed $F(R)$. It is seen that $\alpha\to0$ is an ultraviolet stable fixed point of the renormalisation group trajectories. |
2212.07293 | Pedro Fernandes | Pedro G. S. Fernandes and David J. Mulryne | A new approach and code for spinning black holes in modified gravity | 40 pages, 14 figures. GitHub repository:
https://github.com/pgsfernandes/SpinningBlackHoles.jl ; v2: added references,
accepted for publication in Classical and Quantum Gravity | Class. Quantum Grav. (2023) 40 165001 | 10.1088/1361-6382/ace232 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss and implement a spectral method approach to computing stationary
and axisymmetric black hole solutions and their properties in modified theories
of gravity. The resulting code is written in the Julia language and is
transparent and easily adapted to new settings. We test the code on both
general relativity and on Einstein-Scalar-Gauss-Bonnet gravity. It is accurate
and fast, converging on a spinning solution in these theories with tiny errors
($\sim \mathcal{O}\left(10^{-13}\right)$ in most cases) in a matter of seconds.
| [
{
"created": "Wed, 14 Dec 2022 15:54:31 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Jul 2023 11:20:54 GMT",
"version": "v2"
}
] | 2023-07-12 | [
[
"Fernandes",
"Pedro G. S.",
""
],
[
"Mulryne",
"David J.",
""
]
] | We discuss and implement a spectral method approach to computing stationary and axisymmetric black hole solutions and their properties in modified theories of gravity. The resulting code is written in the Julia language and is transparent and easily adapted to new settings. We test the code on both general relativity and on Einstein-Scalar-Gauss-Bonnet gravity. It is accurate and fast, converging on a spinning solution in these theories with tiny errors ($\sim \mathcal{O}\left(10^{-13}\right)$ in most cases) in a matter of seconds. |
2212.12518 | Filipe Mena | Jo\~ao L. Costa, Rodrigo Duarte and Filipe C. Mena | Improved decay estimates and $C^2$-asymptotic stability of solutions to
the Einstein-scalar field system in spherical symmetry | 42 pages | null | null | null | gr-qc math-ph math.AP math.MP | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We investigate the asymptotic stability of solutions to the characteristic
initial value problem for the Einstein (massless) scalar field system with a
positive cosmological constant. We prescribe spherically symmetric initial data
on a future null cone with a wider range of decaying profiles than previously
considered. New estimates are then derived in order to prove that, for small
data, the system has a unique global classical solution. We also show that the
solution decays exponentially in (Bondi) time and that the radial decay is
essentially polynomial, although containing logarithmic factors in some special
cases. This improved asymptotic analysis allows us to show that, under
appropriate and natural decaying conditions on the initial data, the future
asymptotic solution is differentiable, up to and including spatial
null-infinity, and approaches the de Sitter solution, uniformly, in a
neighborhood of infinity. Moreover, we analyze the decay of derivatives of the
solution up to second order showing the (uniform) $C^2$-asymptotic stability of
the de Sitter attractor in this setting. This corresponds to a surprisingly
strong realization of the cosmic no-hair conjecture.
| [
{
"created": "Fri, 23 Dec 2022 18:27:54 GMT",
"version": "v1"
}
] | 2022-12-26 | [
[
"Costa",
"João L.",
""
],
[
"Duarte",
"Rodrigo",
""
],
[
"Mena",
"Filipe C.",
""
]
] | We investigate the asymptotic stability of solutions to the characteristic initial value problem for the Einstein (massless) scalar field system with a positive cosmological constant. We prescribe spherically symmetric initial data on a future null cone with a wider range of decaying profiles than previously considered. New estimates are then derived in order to prove that, for small data, the system has a unique global classical solution. We also show that the solution decays exponentially in (Bondi) time and that the radial decay is essentially polynomial, although containing logarithmic factors in some special cases. This improved asymptotic analysis allows us to show that, under appropriate and natural decaying conditions on the initial data, the future asymptotic solution is differentiable, up to and including spatial null-infinity, and approaches the de Sitter solution, uniformly, in a neighborhood of infinity. Moreover, we analyze the decay of derivatives of the solution up to second order showing the (uniform) $C^2$-asymptotic stability of the de Sitter attractor in this setting. This corresponds to a surprisingly strong realization of the cosmic no-hair conjecture. |
gr-qc/0011050 | Domenico Giulini | Domenico Giulini (University of Zuerich, Switzerland) | Uniqueness of Simultaneity | LeTeX-2e, 18 pages, no figures | The British Journal for the Philosophy of Science, year 2001,
volume 52, number 4 , pages 651-670 | null | ZU-TH 25/00 | gr-qc math-ph math.MP physics.space-ph | null | We consider the problem of uniqueness of certain simultaneity structures in
flat spacetime. Absolute simultaneity is specified to be a non-trivial
equivalence relation which is invariant under the automorphism group Aut of
spacetime. Aut is taken to be the identity-component of either the
inhomogeneous Galilei group or the inhomogeneous Lorentz group. Uniqueness of
standard simultaneity in the first, and absence of any absolute simultaneity in
the second case are demonstrated and related to certain group theoretic
properties. Relative simultaneity with respect to an additional structure X on
spacetime is specified to be a non-trivial equivalence relation which is
invariant under the subgroup in Aut that stabilises X. Uniqueness of standard
Einstein simultaneity is proven in the Lorentzian case when X is an inertial
frame. We end by discussing the relation to previous work of others.
| [
{
"created": "Tue, 14 Nov 2000 16:58:46 GMT",
"version": "v1"
}
] | 2015-06-03 | [
[
"Giulini",
"Domenico",
"",
"University of Zuerich, Switzerland"
]
] | We consider the problem of uniqueness of certain simultaneity structures in flat spacetime. Absolute simultaneity is specified to be a non-trivial equivalence relation which is invariant under the automorphism group Aut of spacetime. Aut is taken to be the identity-component of either the inhomogeneous Galilei group or the inhomogeneous Lorentz group. Uniqueness of standard simultaneity in the first, and absence of any absolute simultaneity in the second case are demonstrated and related to certain group theoretic properties. Relative simultaneity with respect to an additional structure X on spacetime is specified to be a non-trivial equivalence relation which is invariant under the subgroup in Aut that stabilises X. Uniqueness of standard Einstein simultaneity is proven in the Lorentzian case when X is an inertial frame. We end by discussing the relation to previous work of others. |
gr-qc/0410044 | Slava G. Turyshev | Slava G. Turyshev, Michael Shao, Kenneth L. Nordtvedt | Experimental Design for the LATOR Mission | 16 pages, 17 figures, invited talk given at ``The 2004 NASA/JPL
Workshop on Physics for Planetary Exploration.'' April 20-22, 2004, Solvang,
CA | Int.J.Mod.Phys. D13 (2004) 2035-2064 | 10.1142/S0218271804006528 | null | gr-qc astro-ph physics.space-ph | null | This paper discusses experimental design for the Laser Astrometric Test Of
Relativity (LATOR) mission. LATOR is designed to reach unprecedented accuracy
of 1 part in 10^8 in measuring the curvature of the solar gravitational field
as given by the value of the key Eddington post-Newtonian parameter \gamma.
This mission will demonstrate the accuracy needed to measure effects of the
next post-Newtonian order (~G^2) of light deflection resulting from gravity's
intrinsic non-linearity. LATOR will provide the first precise measurement of
the solar quadrupole moment parameter, J2, and will improve determination of a
variety of relativistic effects including Lense-Thirring precession. The
mission will benefit from the recent progress in the optical communication
technologies -- the immediate and natural step above the standard radio-metric
techniques. The key element of LATOR is a geometric redundancy provided by the
laser ranging and long-baseline optical interferometry. We discuss the mission
and optical designs, as well as the expected performance of this proposed
mission. LATOR will lead to very robust advances in the tests of Fundamental
physics: this mission could discover a violation or extension of general
relativity, or reveal the presence of an additional long range interaction in
the physical law. There are no analogs to the LATOR experiment; it is unique
and is a natural culmination of solar system gravity experiments.
| [
{
"created": "Fri, 8 Oct 2004 19:37:21 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Turyshev",
"Slava G.",
""
],
[
"Shao",
"Michael",
""
],
[
"Nordtvedt",
"Kenneth L.",
""
]
] | This paper discusses experimental design for the Laser Astrometric Test Of Relativity (LATOR) mission. LATOR is designed to reach unprecedented accuracy of 1 part in 10^8 in measuring the curvature of the solar gravitational field as given by the value of the key Eddington post-Newtonian parameter \gamma. This mission will demonstrate the accuracy needed to measure effects of the next post-Newtonian order (~G^2) of light deflection resulting from gravity's intrinsic non-linearity. LATOR will provide the first precise measurement of the solar quadrupole moment parameter, J2, and will improve determination of a variety of relativistic effects including Lense-Thirring precession. The mission will benefit from the recent progress in the optical communication technologies -- the immediate and natural step above the standard radio-metric techniques. The key element of LATOR is a geometric redundancy provided by the laser ranging and long-baseline optical interferometry. We discuss the mission and optical designs, as well as the expected performance of this proposed mission. LATOR will lead to very robust advances in the tests of Fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law. There are no analogs to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments. |
0908.3367 | Nurettin Pirinccioglu | Nurettin Pirinccioglu | Gravitational Higgs Mechanism: The Role of Determinantal Invariants | 7 pages, no figure | null | 10.1007/s10714-012-1414-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Higgs mechanism for gravity, as proposed by 't Hooft in arXiv:0708.3184
[hep-th], can be augmented by including determinantal invariants. We analyze
the effects of determinantal invariants in such a set up. We find that the part
of the potential that depends on the determinantal invariants, if obtains a
specific exponential form in terms of its argument, may not affect the graviton
mass calculated.
| [
{
"created": "Mon, 24 Aug 2009 06:28:08 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Jan 2010 13:49:08 GMT",
"version": "v2"
},
{
"created": "Wed, 15 Dec 2010 08:36:24 GMT",
"version": "v3"
}
] | 2015-05-14 | [
[
"Pirinccioglu",
"Nurettin",
""
]
] | The Higgs mechanism for gravity, as proposed by 't Hooft in arXiv:0708.3184 [hep-th], can be augmented by including determinantal invariants. We analyze the effects of determinantal invariants in such a set up. We find that the part of the potential that depends on the determinantal invariants, if obtains a specific exponential form in terms of its argument, may not affect the graviton mass calculated. |
gr-qc/9903107 | Lee Samuel Finn | Lee Samuel Finn | Gravitational radiation sources and signatures | 85 pages, 13 figures. Uses ssi.sty macros (included). Written version
of lectures given at XXVI SLAC Summer Institute on Particle Physics
``Gravity: From the Hubble Length to the Planck Length'', August 3-14, 1998 | ECONFC9808031:07,1998 | null | null | gr-qc astro-ph | null | The goal of these lecture notes is to introduce the developing research area
of gravitational-wave phenomenology. In more concrete terms, they are meant to
provide an overview of gravitational-wave sources and an introduction to the
interpretation of real gravitational wave detector data. They are, of course,
limited in both regards. Either topic could be the subject of one or more
books, and certainly more than the few lectures possible in a summer school.
Nevertheless, it is possible to talk about the problems of data analysis and
give something of their flavor, and do the same for gravitational wave sources
that might be observed in the upcoming generation of sensitive detectors. These
notes are an attempt to do just that.
| [
{
"created": "Tue, 30 Mar 1999 20:59:25 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Finn",
"Lee Samuel",
""
]
] | The goal of these lecture notes is to introduce the developing research area of gravitational-wave phenomenology. In more concrete terms, they are meant to provide an overview of gravitational-wave sources and an introduction to the interpretation of real gravitational wave detector data. They are, of course, limited in both regards. Either topic could be the subject of one or more books, and certainly more than the few lectures possible in a summer school. Nevertheless, it is possible to talk about the problems of data analysis and give something of their flavor, and do the same for gravitational wave sources that might be observed in the upcoming generation of sensitive detectors. These notes are an attempt to do just that. |
1212.2929 | Rodrigo Maier | Rodrigo Maier and Felipe Tovar Falciano | Brane world in Non-Riemannian Geometry | Physical Review D (2011) | Phys. Rev. D 83, 064019 (2011) | 10.1103/PhysRevD.83.064019 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We carefully investigate the modified Einstein's field equation in a four
dimensional (3-brane) arbitrary manifold embedded in a five dimensional
Non-Riemannian bulk spacetime with a noncompact extra dimension. In this
context the Israel-Darmois matching conditions are extended assuming that the
torsion in the bulk is continuous. The discontinuity in the torsion first
derivatives are related to the matter distribution through the field equation.
In addition, we develop a model that describes a flat FLRW model embedded in a
5-dimensional de Sitter or Anti de Sitter, where a 5-dimensional cosmological
constant emerges from the torsion.
| [
{
"created": "Wed, 12 Dec 2012 18:54:05 GMT",
"version": "v1"
}
] | 2013-01-23 | [
[
"Maier",
"Rodrigo",
""
],
[
"Falciano",
"Felipe Tovar",
""
]
] | We carefully investigate the modified Einstein's field equation in a four dimensional (3-brane) arbitrary manifold embedded in a five dimensional Non-Riemannian bulk spacetime with a noncompact extra dimension. In this context the Israel-Darmois matching conditions are extended assuming that the torsion in the bulk is continuous. The discontinuity in the torsion first derivatives are related to the matter distribution through the field equation. In addition, we develop a model that describes a flat FLRW model embedded in a 5-dimensional de Sitter or Anti de Sitter, where a 5-dimensional cosmological constant emerges from the torsion. |
gr-qc/0110039 | Wu Shuangqin | S. Q. Wu and X. Cai | Addendum: Hawking Radiation of Photons in a Variable-mass Kerr Black
Hole | 8 pages, no figures, Latex(use kluwer.cls), to appear in Gen. Rel.
Grav. 34 (2002) No. 4 | Gen.Rel.Grav. 34 (2002) 557-564 | 10.1023/A:1015548909824 | null | gr-qc | null | Hawking evaporation of photons in a variable-mass Kerr space-time is
investigated by using a method of the generalized tortoise coordinate
transformation. The blackbody radiant spectrum of photons displays a new
spin-rotation coupling effect obviously dependent on different helicity states
of photons.
| [
{
"created": "Mon, 8 Oct 2001 13:52:46 GMT",
"version": "v1"
}
] | 2021-10-20 | [
[
"Wu",
"S. Q.",
""
],
[
"Cai",
"X.",
""
]
] | Hawking evaporation of photons in a variable-mass Kerr space-time is investigated by using a method of the generalized tortoise coordinate transformation. The blackbody radiant spectrum of photons displays a new spin-rotation coupling effect obviously dependent on different helicity states of photons. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.