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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
2207.01276 | Rocco D'Agostino | Salvatore Capozziello, Rocco D'Agostino, Orlando Luongo | The phase-space view of non-local gravity cosmology | 9 pages, 2 figures, 2 tables. Accepted for publication in Physics
Letters B | null | 10.1016/j.physletb.2022.137475 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider non-local Integral Kernel Theories of Gravity in a homogeneous
and isotropic universe background as a possible scenario to drive the cosmic
history. In particular, we investigate the cosmological properties of a
gravitational action containing the inverse d'Alembert operator of the Ricci
scalar proposed to improve Einstein's gravity at both high and low-energy
regimes. In particular, the dynamics of a physically motivated non-local
exponential coupling is analyzed in detail by recasting the cosmological
equations as an autonomous system of first-order differential equations with
dimensionless variables. Consequently, we study the phase-space domain and its
critical points, investigating their stability and main properties. In
particular, saddle points and late-time cosmological attractors are discussed
in terms of the free parameters of the model. Finally, we discuss the main
physical consequences of our approach in view of dark energy behavior and the
$\Lambda$CDM model.
| [
{
"created": "Mon, 4 Jul 2022 09:09:09 GMT",
"version": "v1"
},
{
"created": "Thu, 29 Sep 2022 13:56:16 GMT",
"version": "v2"
}
] | 2022-09-30 | [
[
"Capozziello",
"Salvatore",
""
],
[
"D'Agostino",
"Rocco",
""
],
[
"Luongo",
"Orlando",
""
]
] | We consider non-local Integral Kernel Theories of Gravity in a homogeneous and isotropic universe background as a possible scenario to drive the cosmic history. In particular, we investigate the cosmological properties of a gravitational action containing the inverse d'Alembert operator of the Ricci scalar proposed to improve Einstein's gravity at both high and low-energy regimes. In particular, the dynamics of a physically motivated non-local exponential coupling is analyzed in detail by recasting the cosmological equations as an autonomous system of first-order differential equations with dimensionless variables. Consequently, we study the phase-space domain and its critical points, investigating their stability and main properties. In particular, saddle points and late-time cosmological attractors are discussed in terms of the free parameters of the model. Finally, we discuss the main physical consequences of our approach in view of dark energy behavior and the $\Lambda$CDM model. |
gr-qc/0205131 | Kirill Bronnikov | K.A. Bronnikov and S. Grinyok (Moscow) | Charged wormholes with non-minimally coupled scalar fields. Existence
and stability | Latex2e, 6 pages. Contribution to Festschrift in honour of Prof.
Mario Novello | null | null | null | gr-qc | null | Static, spherically symmetric, traversable wormhole solutions with electric
or magnetic charges are shown to exist in general relativity in the presence of
scalar fields nonminimally coupled to gravity. These wormholes, however, turn
out to be unstable under spherically symmetric perturbations. The instability
is related to blowing-up of the effective gravitational constant on a certain
sphere.
| [
{
"created": "Thu, 30 May 2002 20:35:46 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Bronnikov",
"K. A.",
"",
"Moscow"
],
[
"Grinyok",
"S.",
"",
"Moscow"
]
] | Static, spherically symmetric, traversable wormhole solutions with electric or magnetic charges are shown to exist in general relativity in the presence of scalar fields nonminimally coupled to gravity. These wormholes, however, turn out to be unstable under spherically symmetric perturbations. The instability is related to blowing-up of the effective gravitational constant on a certain sphere. |
gr-qc/0701145 | Matthew D. Duez | Matthew D. Duez, Yuk Tung Liu, Stuart L. Shapiro, Masaru Shibata,
Branson C. Stephens | The Final Fate of Binary Neutron Stars: What Happens After the Merger? | 3 pages. To appear in the Proceedings of the Eleventh Marcel
Grossmann Meeting, Berlin, Germany, 23-29 July 2006, World Scientific,
Singapore (2007) | null | 10.1142/9789812834300_0209 | null | gr-qc astro-ph | null | The merger of two neutron stars usually produces a remnant with a mass
significantly above the single (nonrotating) neutron star maximum mass. In some
cases, the remnant will be stabilized against collapse by rapid, differential
rotation. MHD-driven angular momentum transport eventually leads to the
collapse of the remnant's core, resulting in a black hole surrounded by a
massive accretion torus. Here we present simulations of this process. The
plausibility of generating short duration gamma ray bursts through this
scenario is discussed.
| [
{
"created": "Fri, 26 Jan 2007 21:05:36 GMT",
"version": "v1"
}
] | 2016-11-15 | [
[
"Duez",
"Matthew D.",
""
],
[
"Liu",
"Yuk Tung",
""
],
[
"Shapiro",
"Stuart L.",
""
],
[
"Shibata",
"Masaru",
""
],
[
"Stephens",
"Branson C.",
""
]
] | The merger of two neutron stars usually produces a remnant with a mass significantly above the single (nonrotating) neutron star maximum mass. In some cases, the remnant will be stabilized against collapse by rapid, differential rotation. MHD-driven angular momentum transport eventually leads to the collapse of the remnant's core, resulting in a black hole surrounded by a massive accretion torus. Here we present simulations of this process. The plausibility of generating short duration gamma ray bursts through this scenario is discussed. |
gr-qc/0612027 | Irit Maor | Sourish Dutta and Irit Maor | Voids of dark energy | 9 pages, 13 figures V3: typo in equation (11) corrected | Phys.Rev.D75:063507,2007 | 10.1103/PhysRevD.75.063507 | null | gr-qc astro-ph | null | We investigate the clustering properties of a dynamical dark energy
component. In a cosmic mix of a pressureless fluid and a light scalar field, we
follow the linear evolution of spherical matter perturbations. We find that the
scalar field tends to form underdensities in response to the gravitationally
collapsing matter. We thoroughly investigate these voids for a variety of
initial conditions, explain the physics behind their formation and consider
possible observational implications. Detection of dark energy voids will
clearly rule out the cosmological constant as the main source of the present
acceleration.
| [
{
"created": "Tue, 5 Dec 2006 03:08:09 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Mar 2007 20:37:37 GMT",
"version": "v2"
},
{
"created": "Thu, 15 Nov 2007 19:08:08 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Dutta",
"Sourish",
""
],
[
"Maor",
"Irit",
""
]
] | We investigate the clustering properties of a dynamical dark energy component. In a cosmic mix of a pressureless fluid and a light scalar field, we follow the linear evolution of spherical matter perturbations. We find that the scalar field tends to form underdensities in response to the gravitationally collapsing matter. We thoroughly investigate these voids for a variety of initial conditions, explain the physics behind their formation and consider possible observational implications. Detection of dark energy voids will clearly rule out the cosmological constant as the main source of the present acceleration. |
gr-qc/9912034 | Anatoly Nikishov | A.I.Nikishov (P.N.Lebedev Institute of Physics, Moscow, Russia) | On energy-momentum tensors of gravitational field | 24 pages, 2 figures | Phys.Part.Nucl. 32 (2001) 1-14; Fiz.Elem.Chast.Atom.Yadra 32
(2001) 5-30 | null | null | gr-qc | null | Several energy-momentum "tensors" of gravitational field are considered and
compared in the lowest approximation. Each of them together with
energy-momentum tensor of point-like particles satisfies the conservation laws
when equations of motion of particles are the same as in general relativity. It
is shown that in Newtonian approximation the considered tensors differ one from
the other in the way their energy density is distributed between energy density
of interaction (nonzero only at locations of particles) and energy density of
gravitational field. Starting from Lorentz invariance the Lagrangians for
spin-2, mass-0 field are considered. They differ only by divergences. From
these Lagrangians by Belinfante-Rosenfeld procedure the energy-momentum tensors
are build. Using each of these tensors in 3-graviton vertex we obtain the
corresponding metric of a Newtonian center in $G^2$ approximation. Only one of
these ''field-theretical''tensors (namely the half sum of Thirring tensor and
tensor obtained from Lagrangian given by Misner, Thorne and Wheeler) leads to
correct value of the perihelion shift. This tensor does not coincide with
Weinberg`s one (directly obtainable from Einstein equation) and gives metric of
a spherical body differing (in space part of metric in the first nonlinear
approximation) from Schwarzschild field in harmonic coordinates. As a result a
relativistic particle in such field must move note according general relativity
prescriptions. This approach puts the gravitational energy-momentum tensor on
the same footing as any other energy-momentum tensor.
| [
{
"created": "Thu, 9 Dec 1999 12:26:44 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Nikishov",
"A. I.",
"",
"P.N.Lebedev Institute of Physics, Moscow, Russia"
]
] | Several energy-momentum "tensors" of gravitational field are considered and compared in the lowest approximation. Each of them together with energy-momentum tensor of point-like particles satisfies the conservation laws when equations of motion of particles are the same as in general relativity. It is shown that in Newtonian approximation the considered tensors differ one from the other in the way their energy density is distributed between energy density of interaction (nonzero only at locations of particles) and energy density of gravitational field. Starting from Lorentz invariance the Lagrangians for spin-2, mass-0 field are considered. They differ only by divergences. From these Lagrangians by Belinfante-Rosenfeld procedure the energy-momentum tensors are build. Using each of these tensors in 3-graviton vertex we obtain the corresponding metric of a Newtonian center in $G^2$ approximation. Only one of these ''field-theretical''tensors (namely the half sum of Thirring tensor and tensor obtained from Lagrangian given by Misner, Thorne and Wheeler) leads to correct value of the perihelion shift. This tensor does not coincide with Weinberg`s one (directly obtainable from Einstein equation) and gives metric of a spherical body differing (in space part of metric in the first nonlinear approximation) from Schwarzschild field in harmonic coordinates. As a result a relativistic particle in such field must move note according general relativity prescriptions. This approach puts the gravitational energy-momentum tensor on the same footing as any other energy-momentum tensor. |
1907.02176 | Yujie Tan | Xiao-yu Lu, Yu-Jie Tan, and Cheng-Gang Shao | Testing Lorentz violation by the comparison of atomic clocks | Presented at the Eighth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, May 12-16, 2019 | null | null | null | gr-qc hep-ph | http://creativecommons.org/publicdomain/zero/1.0/ | A more complete theoretical model of testing Lorentz violation by the
comparison of atomic clocks is developed in the Robertson-Mansouri-Sexl
kinematic framework. As this frame postulates the deviation of the coordinate
transformation from the Lorentz transformation, from the viewpoint of the
transformation violations on time and space, the LI violating effect in the
atomic clock comparison can be explained as two parts: time-delay effect
$\alpha \frac {v^2}{c^2}$ and structure effect $-\frac {\beta+2\delta}{3} \frac
{v^2}{c^2}$. Standard model extension is a widely used dynamic frame to
characterize the Lorentz violation, in which a space-orientation dependence
violating background field is regarded as the essential reason for the Lorentz
violation effect. Compared with the RMS frame which only indicates the
kinematic properties with the coordinate transformation, this dynamic frame
provides a more complete and clear description for the Lorentz violation
effect.
| [
{
"created": "Thu, 4 Jul 2019 01:10:26 GMT",
"version": "v1"
}
] | 2019-07-05 | [
[
"Lu",
"Xiao-yu",
""
],
[
"Tan",
"Yu-Jie",
""
],
[
"Shao",
"Cheng-Gang",
""
]
] | A more complete theoretical model of testing Lorentz violation by the comparison of atomic clocks is developed in the Robertson-Mansouri-Sexl kinematic framework. As this frame postulates the deviation of the coordinate transformation from the Lorentz transformation, from the viewpoint of the transformation violations on time and space, the LI violating effect in the atomic clock comparison can be explained as two parts: time-delay effect $\alpha \frac {v^2}{c^2}$ and structure effect $-\frac {\beta+2\delta}{3} \frac {v^2}{c^2}$. Standard model extension is a widely used dynamic frame to characterize the Lorentz violation, in which a space-orientation dependence violating background field is regarded as the essential reason for the Lorentz violation effect. Compared with the RMS frame which only indicates the kinematic properties with the coordinate transformation, this dynamic frame provides a more complete and clear description for the Lorentz violation effect. |
gr-qc/0207005 | Lorenzo Iorio | Lorenzo Iorio | On some gravitomagnetic spin-spin effects for astronomical bodies | LaTex2e, World Scientific macros, no figures, 3 tables, 9 pages.
Accepted for publication in International Journal of Modern Physics D | Int.J.Mod.Phys. D vol.12, no.1, pp. 35-44, 2003. | 10.1142/S021827180300269X | null | gr-qc astro-ph | null | In this paper we look at the gravitational spin--spin interaction between
macroscopic astronomical bodies. In particular, we calculate their
post--Newtonian orbital effects of order $\mathcal{O}(c^{-2})$ on the
trajectory of a spinning particle with proper angular momentum ${\bf s}$ moving
in the external gravitomagnetic field generated by a central spinning mass with
proper angular momentum ${\bf J}$. It turns out that, at order $\mathcal{O}(e)$
in the orbiter's eccentricity, the eccentricity the pericenter and the mean
anomaly rates of the moving particle are affected by long--term harmonic
effects. If, on one hand, they are undetectable in the Solar System, on the
other, maybe that in an astrophysical context like that of the binary
millisecond pulsars there will be some hopes of measuring them in the future.
| [
{
"created": "Sun, 30 Jun 2002 15:07:53 GMT",
"version": "v1"
},
{
"created": "Fri, 6 Sep 2002 12:38:21 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Iorio",
"Lorenzo",
""
]
] | In this paper we look at the gravitational spin--spin interaction between macroscopic astronomical bodies. In particular, we calculate their post--Newtonian orbital effects of order $\mathcal{O}(c^{-2})$ on the trajectory of a spinning particle with proper angular momentum ${\bf s}$ moving in the external gravitomagnetic field generated by a central spinning mass with proper angular momentum ${\bf J}$. It turns out that, at order $\mathcal{O}(e)$ in the orbiter's eccentricity, the eccentricity the pericenter and the mean anomaly rates of the moving particle are affected by long--term harmonic effects. If, on one hand, they are undetectable in the Solar System, on the other, maybe that in an astrophysical context like that of the binary millisecond pulsars there will be some hopes of measuring them in the future. |
0710.4543 | Parampreet Singh | Alejandro Corichi, Parampreet Singh | Quantum bounce and cosmic recall | Some clarifying remarks and references added. To appear in Physical
Review Letters | Phys.Rev.Lett.100:161302,2008 | 10.1103/PhysRevLett.100.161302 | IGC-07/10-02, PI-QG-66 | gr-qc hep-th | null | Loop quantum cosmology predicts that, in simple models, the big bang
singularity of classical general relativity is replaced by a quantum bounce.
Because of the extreme physical conditions near the bounce, a natural question
is whether the universe can retain, after the bounce, its memory about the
previous epoch. More precisely, does the universe retain various properties of
the state after evolving unitarily through the bounce or does it suffer from
some cosmic amnesia as has been recently suggested? Here we show that this
issue can be answered unambiguously at least within an exactly solvable model,
derived from a small simplification of loop quantum cosmology, for which there
is full analytical control on the quantum theory. We show that if there exists
a semiclassical state at late times on one side, peaked around a pair of
canonically conjugate variables, then there are very strong bounds on the
fluctuations on the other side of the bounce, implying semi-classicality. For
such a model universe which grows to a size of 1 megaparsec, at late times, the
change in relative fluctuations of the only non-trivial observable of the model
across the bounce is less than $10^{-56}$ (becoming smaller for universes which
grow larger). The universe maintains (an almost) total recall.
| [
{
"created": "Wed, 24 Oct 2007 19:47:00 GMT",
"version": "v1"
},
{
"created": "Thu, 27 Mar 2008 18:08:23 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Corichi",
"Alejandro",
""
],
[
"Singh",
"Parampreet",
""
]
] | Loop quantum cosmology predicts that, in simple models, the big bang singularity of classical general relativity is replaced by a quantum bounce. Because of the extreme physical conditions near the bounce, a natural question is whether the universe can retain, after the bounce, its memory about the previous epoch. More precisely, does the universe retain various properties of the state after evolving unitarily through the bounce or does it suffer from some cosmic amnesia as has been recently suggested? Here we show that this issue can be answered unambiguously at least within an exactly solvable model, derived from a small simplification of loop quantum cosmology, for which there is full analytical control on the quantum theory. We show that if there exists a semiclassical state at late times on one side, peaked around a pair of canonically conjugate variables, then there are very strong bounds on the fluctuations on the other side of the bounce, implying semi-classicality. For such a model universe which grows to a size of 1 megaparsec, at late times, the change in relative fluctuations of the only non-trivial observable of the model across the bounce is less than $10^{-56}$ (becoming smaller for universes which grow larger). The universe maintains (an almost) total recall. |
gr-qc/0405128 | Sukratu Barve | Sukratu Barve | Conformal transformations near Naked Singularities - I | null | Mod.Phys.Lett. A17 (2002) 1013 | 10.1142/S0217732302007594 | null | gr-qc | null | We show that the behaviour of the outgoing radial null geodesic congruence on
the boundary of the trapped region (suitably defined as a four dimensional
region) is related to the property of nakedness in spherical dust collapse. The
argument involves a conformal transformation which justifies the difference in
the Penrose diagrams in the naked and covered dust collapse scenarios.
| [
{
"created": "Wed, 26 May 2004 06:22:43 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Barve",
"Sukratu",
""
]
] | We show that the behaviour of the outgoing radial null geodesic congruence on the boundary of the trapped region (suitably defined as a four dimensional region) is related to the property of nakedness in spherical dust collapse. The argument involves a conformal transformation which justifies the difference in the Penrose diagrams in the naked and covered dust collapse scenarios. |
2302.03872 | Farshid Soltani | Muxin Han, Carlo Rovelli, Farshid Soltani | On the geometry of the black-to-white hole transition within a single
asymptotic region | 16 pages, 12 figures | Phys. Rev. D 107, 064011 (2023) | 10.1103/PhysRevD.107.064011 | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/4.0/ | We write explicitly the complete Lorentzian metric of a singularity-free
spacetime where a black hole transitions into a white hole located in its same
asymptotic region. In particular, the metric interpolates between the black and
white horizons. The metric satisfies the Einstein field equations up to the
tunneling region. The matter giving rise to the black hole is described by the
Oppenheimer-Snyder model, corrected with loop-quantum-cosmology techniques in
the quantum region. The interior quantum geometry is fixed by a local Killing
symmetry, broken at the horizon transition. At large scale, the geometry is
determined by two parameters: the mass of the hole and the duration of the
transition process. The latter is a global geometrical parameter. We give the
full metric outside the star in a single coordinate patch.
| [
{
"created": "Wed, 8 Feb 2023 04:14:43 GMT",
"version": "v1"
}
] | 2023-03-20 | [
[
"Han",
"Muxin",
""
],
[
"Rovelli",
"Carlo",
""
],
[
"Soltani",
"Farshid",
""
]
] | We write explicitly the complete Lorentzian metric of a singularity-free spacetime where a black hole transitions into a white hole located in its same asymptotic region. In particular, the metric interpolates between the black and white horizons. The metric satisfies the Einstein field equations up to the tunneling region. The matter giving rise to the black hole is described by the Oppenheimer-Snyder model, corrected with loop-quantum-cosmology techniques in the quantum region. The interior quantum geometry is fixed by a local Killing symmetry, broken at the horizon transition. At large scale, the geometry is determined by two parameters: the mass of the hole and the duration of the transition process. The latter is a global geometrical parameter. We give the full metric outside the star in a single coordinate patch. |
1909.11037 | Emilio Elizalde | Emilio Elizalde, Martiros Khurshudyan | Wormhole models in $f(\textit{R}, \textit{T})$ gravity | 15 pages, 7 figures, to appear in IJMPD | null | null | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Models of static wormholes within the $f(\textit{R}, \textit{T})$ extended
theory of gravity are investigated and, in particular, the family
$f(\textit{R}, \textit{T}) = R + \lambda T$, with $T = \rho + P_{r} + 2P_{l}$
being the trace of the energy-momentum tensor. Models corresponding to
different relations for the pressure components (radial and lateral), and
several equations of state (EoS), reflecting different matter content, are
worked out explicitly. The solutions obtained for the shape functions of the
generated wormholes obey the necessary metric conditions, as manifested in
other studies in the literature. The respective energy conditions reveal the
physical nature of the wormhole models thus constructed. It is found, in
particular, that for each of those considered, the parameter space can be
divided into different regions, in which the exact wormhole solutions fulfill
the null~(NEC) and the weak energy conditions~(WEC), respectively, in terms of
the lateral pressure. Moreover, the dominant energy condition~(DEC) in terms of
both pressures is also valid, while $\rho + P_{r} + 2P_{l} = 0$. A similar
solution for the theory $P_{r} = \omega_{1} \rho + \omega_{2} \rho^{2}$ is
found numerically, where $\omega_{1}$ and $\omega_{2}$ are either constant or
functions of $r$, leading to the result that the NEC in terms of the radial
pressure is also valid. For non-constant $\omega_{i}$ models, attention is
focused on the behavior $\omega_{i} \propto r^{m}$. To finish, the question is
addressed, how $f(R) = R+\alpha R^{2}$ will affect the wormhole solutions
corresponding to fluids of the form $P_{r} = \omega_{1} \rho + \omega_{2}
\rho^{2}$, in the three cases mentioned above. Issues concerning the
nonconservation of the matter energy-momentum tensor, the stability of the
solutions obtained, and the observational possibilities for testing these
models are discussed in the last section.
| [
{
"created": "Tue, 24 Sep 2019 16:42:18 GMT",
"version": "v1"
}
] | 2019-09-25 | [
[
"Elizalde",
"Emilio",
""
],
[
"Khurshudyan",
"Martiros",
""
]
] | Models of static wormholes within the $f(\textit{R}, \textit{T})$ extended theory of gravity are investigated and, in particular, the family $f(\textit{R}, \textit{T}) = R + \lambda T$, with $T = \rho + P_{r} + 2P_{l}$ being the trace of the energy-momentum tensor. Models corresponding to different relations for the pressure components (radial and lateral), and several equations of state (EoS), reflecting different matter content, are worked out explicitly. The solutions obtained for the shape functions of the generated wormholes obey the necessary metric conditions, as manifested in other studies in the literature. The respective energy conditions reveal the physical nature of the wormhole models thus constructed. It is found, in particular, that for each of those considered, the parameter space can be divided into different regions, in which the exact wormhole solutions fulfill the null~(NEC) and the weak energy conditions~(WEC), respectively, in terms of the lateral pressure. Moreover, the dominant energy condition~(DEC) in terms of both pressures is also valid, while $\rho + P_{r} + 2P_{l} = 0$. A similar solution for the theory $P_{r} = \omega_{1} \rho + \omega_{2} \rho^{2}$ is found numerically, where $\omega_{1}$ and $\omega_{2}$ are either constant or functions of $r$, leading to the result that the NEC in terms of the radial pressure is also valid. For non-constant $\omega_{i}$ models, attention is focused on the behavior $\omega_{i} \propto r^{m}$. To finish, the question is addressed, how $f(R) = R+\alpha R^{2}$ will affect the wormhole solutions corresponding to fluids of the form $P_{r} = \omega_{1} \rho + \omega_{2} \rho^{2}$, in the three cases mentioned above. Issues concerning the nonconservation of the matter energy-momentum tensor, the stability of the solutions obtained, and the observational possibilities for testing these models are discussed in the last section. |
gr-qc/0601040 | Woei Chet Lim | W. C. Lim, R. J. Deeley, J. Wainwright | Tilted Bianchi VII_0 cosmologies -- the radiation bifurcation | 22 pages, no figures | Class.Quant.Grav.23:3215-3234,2006 | 10.1088/0264-9381/23/9/029 | null | gr-qc | null | We derive the late-time behaviour of tilted Bianchi VII_0 cosmologies with an
irrotational radiation fluid as source, and give the asymptotic form of the
general solution as $t \to +\infty$, making comparisons with the dust-filled
models. At first sight the radiation-filled models appear to approximate the
flat FL model at late times, since the Hubble-normalized shear and the tilt
tend to zero and the density parameter tends to one. The Hubble-normalized Weyl
curvature diverges, however, indicating that physically significant anisotropy
remains. We also discuss the influence of a cosmological constant on this
phenomenon.
| [
{
"created": "Wed, 11 Jan 2006 00:33:07 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Apr 2006 16:37:05 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Lim",
"W. C.",
""
],
[
"Deeley",
"R. J.",
""
],
[
"Wainwright",
"J.",
""
]
] | We derive the late-time behaviour of tilted Bianchi VII_0 cosmologies with an irrotational radiation fluid as source, and give the asymptotic form of the general solution as $t \to +\infty$, making comparisons with the dust-filled models. At first sight the radiation-filled models appear to approximate the flat FL model at late times, since the Hubble-normalized shear and the tilt tend to zero and the density parameter tends to one. The Hubble-normalized Weyl curvature diverges, however, indicating that physically significant anisotropy remains. We also discuss the influence of a cosmological constant on this phenomenon. |
2201.08578 | Elham Nazari | Elham Nazari, Mahmood Roshan, Ivan De Martino | Constraining Energy-Momentum-Squared Gravity by binary pulsar
observations | 21 pages, 5 figures URL:
https://link.aps.org/doi/10.1103/PhysRevD.105.044014 | null | 10.1103/PhysRevD.105.044014 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we introduce the post-Minkowskian approximation of
Energy-Momentum-Squared Gravity (EMSG). This approximation is used to study the
gravitational energy flux in the context of EMSG. As an application of our
results, we investigate the EMSG effect on the first time derivative of the
orbital period of the binary pulsars. Utilizing this post-Keplerian parameter,
the free parameter of the EMSG theory, $f_0'$, is estimated for six known
binary pulsars. Taking the binaries that have the most accurate observations,
it turns out that $-6\times
10^{-37}\text{m}\,\text{s}^2\text{kg}^{-1}<f_0'<+10^{-36}\text{m}\,\text{s}^2\text{kg}^{-1}$.
This bound is in agreement with the precedent studies.
| [
{
"created": "Fri, 21 Jan 2022 07:48:12 GMT",
"version": "v1"
},
{
"created": "Fri, 11 Feb 2022 05:20:02 GMT",
"version": "v2"
}
] | 2022-02-14 | [
[
"Nazari",
"Elham",
""
],
[
"Roshan",
"Mahmood",
""
],
[
"De Martino",
"Ivan",
""
]
] | In this paper, we introduce the post-Minkowskian approximation of Energy-Momentum-Squared Gravity (EMSG). This approximation is used to study the gravitational energy flux in the context of EMSG. As an application of our results, we investigate the EMSG effect on the first time derivative of the orbital period of the binary pulsars. Utilizing this post-Keplerian parameter, the free parameter of the EMSG theory, $f_0'$, is estimated for six known binary pulsars. Taking the binaries that have the most accurate observations, it turns out that $-6\times 10^{-37}\text{m}\,\text{s}^2\text{kg}^{-1}<f_0'<+10^{-36}\text{m}\,\text{s}^2\text{kg}^{-1}$. This bound is in agreement with the precedent studies. |
1703.06251 | Hao Zheng | H. Zheng, L. F. Wei, H. Wen, F. Y. Li | Searching for high-frequency gravitational waves by ground high field
magnetic resonant sweepings | null | Phys. Rev. D 98, 064028 (2018) | 10.1103/PhysRevD.98.064028 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | With laser interferometers, LIGO-Virgo collaboration has recently realized
the direct detections of the intermediate-frequency (i.e., from dozens to
hundreds of Hertz) gravitational waves (GWs) by probing their
mechanically-tidal responses. Alternatively, in this letter we propose a
feasible approach to actively search for the high-frequency GWs by probing
their electromagnetic responses (EMRs) in a high alternating magnetic field.
Differing from the original Gertsenshtein-Zeldovich configuration (in which
the EMRs are proportional to the square of the amplitudes of the GWs, and
consequently are too weak to be detected experimentally), the EMRs of the GWs
passing through the present configuration are linearly related to the
amplitudes of the GWs and thus the relevant signals are detectable with the
current weak-light detection technique.
As the wave impedances of the GWs-induced electromagnetic signals (EMSs) are
very different from those the EM radiations in flat space-time, i.e, ($\cong
377 \Omega$), the stronger background noises (without any GWs information)
could be effectively filtered out by using wave-matching technique.
Given the frequency of the applied alternating magnetic field is conveniently
adjustable, the configuration proposed here could be utilized to actively
search for the GWs (if they really exist) in a sufficiently-wide frequency band
(e.g., could be $10^7-10^{12}$Hz), once the scale of the cavity and the
sweeping frequency of the applied alternating magnetic field are experimentally
achievable.
| [
{
"created": "Sat, 18 Mar 2017 04:41:36 GMT",
"version": "v1"
},
{
"created": "Sat, 13 May 2017 04:55:49 GMT",
"version": "v2"
},
{
"created": "Tue, 17 Oct 2017 11:45:48 GMT",
"version": "v3"
}
] | 2018-09-19 | [
[
"Zheng",
"H.",
""
],
[
"Wei",
"L. F.",
""
],
[
"Wen",
"H.",
""
],
[
"Li",
"F. Y.",
""
]
] | With laser interferometers, LIGO-Virgo collaboration has recently realized the direct detections of the intermediate-frequency (i.e., from dozens to hundreds of Hertz) gravitational waves (GWs) by probing their mechanically-tidal responses. Alternatively, in this letter we propose a feasible approach to actively search for the high-frequency GWs by probing their electromagnetic responses (EMRs) in a high alternating magnetic field. Differing from the original Gertsenshtein-Zeldovich configuration (in which the EMRs are proportional to the square of the amplitudes of the GWs, and consequently are too weak to be detected experimentally), the EMRs of the GWs passing through the present configuration are linearly related to the amplitudes of the GWs and thus the relevant signals are detectable with the current weak-light detection technique. As the wave impedances of the GWs-induced electromagnetic signals (EMSs) are very different from those the EM radiations in flat space-time, i.e, ($\cong 377 \Omega$), the stronger background noises (without any GWs information) could be effectively filtered out by using wave-matching technique. Given the frequency of the applied alternating magnetic field is conveniently adjustable, the configuration proposed here could be utilized to actively search for the GWs (if they really exist) in a sufficiently-wide frequency band (e.g., could be $10^7-10^{12}$Hz), once the scale of the cavity and the sweeping frequency of the applied alternating magnetic field are experimentally achievable. |
2301.08074 | Giorgio Mentasti | Giorgio Mentasti, Carlo R. Contaldi, Marco Peloso | Intrinsic limits on the detection of the anisotropies of the Stochastic
Gravitational Wave Background | 5 pages, 2 figures | null | null | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | For any given network of detectors, and for any given integration time, even
in the idealized limit of negligible instrumental noise, the intrinsic time
variation of the isotropic component of the Stochastic Gravitational Wave
Background (SGWB) induces a limit on how accurately the anisotropies in the
SGWB can be measured. We show here how this sample limit can be calculated and
apply this to three separate configurations of ground-based detectors placed at
existing and planned sites. Our results show that in the idealized, best-case
scenario individual multipoles of the anisotropies at $\ell \leq 8$ can only be
measured to $\sim 10^{-5} - 10^{-4}$ level over 5 years of observation as a
fraction of the isotropic component. As the sensitivity improves as the square
root of the observation time, this poses a very serious challenge for the
measurement of the anisotropies of SGWB of cosmological origin, even in the
case of idealised detectors with arbitrarily low instrumental noise.
| [
{
"created": "Thu, 19 Jan 2023 13:42:22 GMT",
"version": "v1"
}
] | 2023-01-20 | [
[
"Mentasti",
"Giorgio",
""
],
[
"Contaldi",
"Carlo R.",
""
],
[
"Peloso",
"Marco",
""
]
] | For any given network of detectors, and for any given integration time, even in the idealized limit of negligible instrumental noise, the intrinsic time variation of the isotropic component of the Stochastic Gravitational Wave Background (SGWB) induces a limit on how accurately the anisotropies in the SGWB can be measured. We show here how this sample limit can be calculated and apply this to three separate configurations of ground-based detectors placed at existing and planned sites. Our results show that in the idealized, best-case scenario individual multipoles of the anisotropies at $\ell \leq 8$ can only be measured to $\sim 10^{-5} - 10^{-4}$ level over 5 years of observation as a fraction of the isotropic component. As the sensitivity improves as the square root of the observation time, this poses a very serious challenge for the measurement of the anisotropies of SGWB of cosmological origin, even in the case of idealised detectors with arbitrarily low instrumental noise. |
1711.10073 | Edward Anderson | Edward Anderson | The Smallest Shape Spaces. II. 4 Points in 1-d Suffices to have a
Complex Background-Independent Theory of Inhomogeneity | 42 pages with 36 figures. Minor changes, a few new references | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The program of understanding Shape Theory layer by layer topologically and
geometrically -- proposed in Part I -- is now addressed for 4 points in 1-$d$.
Topological shape space graphs are far more complex here, whereas metric shape
spaces are (pieces of) spheres which admit an intricate shape-theoretically
significant tessellation. Metric shapes covers a far wider range of notions of
inhomogeneity: collisions, symmetric states, mergers and uniform states are all
distinctly realized in this model. We furthermore provide quantifiers for the
extent to which various ways which configurations maximally and minimally
realize these. Some of the uniform states additionally form cusps and higher
catastrophes in the indistinguishable-particle and Leibniz shape spaces. We
also provide shape-theoretically significant notions of centre for the
indistinguishable-particle and Leibniz shape spaces. 4 points in 1-$d$
constitutes a useful and already highly nontrivial model of inhomogeneity and
of uniformity -- both topics of cosmological interest -- and also of background
independence: of interest in the foundations of physics and in quantum gravity.
We finally give the automorphism groups of the topological shape space graphs
and the metric shape space (pieces of) manifolds, which is a crucial
preliminary toward quantizing the indistinguishable-particle and Leibniz
versions of the model.
| [
{
"created": "Tue, 28 Nov 2017 01:04:29 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Feb 2018 14:28:43 GMT",
"version": "v2"
}
] | 2018-02-15 | [
[
"Anderson",
"Edward",
""
]
] | The program of understanding Shape Theory layer by layer topologically and geometrically -- proposed in Part I -- is now addressed for 4 points in 1-$d$. Topological shape space graphs are far more complex here, whereas metric shape spaces are (pieces of) spheres which admit an intricate shape-theoretically significant tessellation. Metric shapes covers a far wider range of notions of inhomogeneity: collisions, symmetric states, mergers and uniform states are all distinctly realized in this model. We furthermore provide quantifiers for the extent to which various ways which configurations maximally and minimally realize these. Some of the uniform states additionally form cusps and higher catastrophes in the indistinguishable-particle and Leibniz shape spaces. We also provide shape-theoretically significant notions of centre for the indistinguishable-particle and Leibniz shape spaces. 4 points in 1-$d$ constitutes a useful and already highly nontrivial model of inhomogeneity and of uniformity -- both topics of cosmological interest -- and also of background independence: of interest in the foundations of physics and in quantum gravity. We finally give the automorphism groups of the topological shape space graphs and the metric shape space (pieces of) manifolds, which is a crucial preliminary toward quantizing the indistinguishable-particle and Leibniz versions of the model. |
1411.3854 | Helmut Friedrich | Helmut Friedrich | Geometric Asymptotics and Beyond | 34 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss some global and semi-global existence and stability results
obtained with the use of the conformal field equations.
| [
{
"created": "Fri, 14 Nov 2014 10:18:12 GMT",
"version": "v1"
}
] | 2014-11-17 | [
[
"Friedrich",
"Helmut",
""
]
] | We discuss some global and semi-global existence and stability results obtained with the use of the conformal field equations. |
0804.4261 | Roldao da Rocha | J. M. Hoff da Silva and Roldao da Rocha | Braneworld Remarks in Riemann-Cartan Manifolds | 7 pages. A corrected misprint in def.(18), and the respective terms
in Eqs.(20-23). All physical consequences remain unchanged | Class.Quant.Grav. 26 (2009) 055007; 26 (2009) 179801 | 10.1088/0264-9381/26/5/055007 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the projected effective Einstein equation in a 4-dimensional
arbitrary manifold embedded in a 5-dimensional Riemann-Cartan manifold. The
Israel-Darmois matching conditions are investigated, in the context where the
torsion discontinuity is orthogonal to the brane. Unexpectedly, the presence of
torsion terms in the connection does not modify such conditions whatsoever,
despite of the modification in the extrinsic curvature and in the connection.
Then, by imposing the Z_2-symmetry, the Einstein equation obtained via
Gauss-Codazzi formalism is extended, in order to now encompass the torsion
terms. We also show that the factors involving contorsion change drastically
the effective Einstein equation on the brane, as well as the effective
cosmological constant.
| [
{
"created": "Sun, 27 Apr 2008 00:34:08 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Oct 2008 16:04:58 GMT",
"version": "v2"
},
{
"created": "Tue, 17 Feb 2009 14:03:18 GMT",
"version": "v3"
},
{
"created": "Sat, 14 Mar 2009 17:43:09 GMT",
"version": "v4"
}
] | 2009-08-17 | [
[
"da Silva",
"J. M. Hoff",
""
],
[
"da Rocha",
"Roldao",
""
]
] | We analyze the projected effective Einstein equation in a 4-dimensional arbitrary manifold embedded in a 5-dimensional Riemann-Cartan manifold. The Israel-Darmois matching conditions are investigated, in the context where the torsion discontinuity is orthogonal to the brane. Unexpectedly, the presence of torsion terms in the connection does not modify such conditions whatsoever, despite of the modification in the extrinsic curvature and in the connection. Then, by imposing the Z_2-symmetry, the Einstein equation obtained via Gauss-Codazzi formalism is extended, in order to now encompass the torsion terms. We also show that the factors involving contorsion change drastically the effective Einstein equation on the brane, as well as the effective cosmological constant. |
0811.2876 | Francisco Lobo | Orfeu Bertolami, Tiberiu Harko, Francisco S. N. Lobo, Jorge P\'aramos | Non-minimal curvature-matter couplings in modified gravity | 10 pages, 2 figures, contribution to the anniversary volume "The
Problems of Modern Cosmology", on the occasion of the 50th birthday of Prof.
S. D. Odintsov. Editor: Prof. P. M. Lavrov, Tomsk State Pedagogical
University | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Recently, in the context of f(R) modified theories of gravity, it was shown
that a curvature-matter coupling induces a non-vanishing covariant derivative
of the energy-momentum, implying non-geodesic motion and, under appropriate
conditions, leading to the appearance of an extra force. We study the
implications of this proposal and discuss some directions for future research.
| [
{
"created": "Tue, 18 Nov 2008 10:31:23 GMT",
"version": "v1"
}
] | 2008-11-19 | [
[
"Bertolami",
"Orfeu",
""
],
[
"Harko",
"Tiberiu",
""
],
[
"Lobo",
"Francisco S. N.",
""
],
[
"Páramos",
"Jorge",
""
]
] | Recently, in the context of f(R) modified theories of gravity, it was shown that a curvature-matter coupling induces a non-vanishing covariant derivative of the energy-momentum, implying non-geodesic motion and, under appropriate conditions, leading to the appearance of an extra force. We study the implications of this proposal and discuss some directions for future research. |
1108.6320 | Kayll Lake | C\'edric Grenon and Kayll Lake | Generalized Swiss-Cheese Cosmologies II: Spherical Dust | 5 pages revtex 4.1 Final form to appear in Phys. Rev. D | Phys. Rev. D 84, 083506 (2011) | 10.1103/PhysRevD.84.083506 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The generalized Swiss - cheese model, consisting of a Lema\^itre - Tolman
(inhomogeneous dust) region matched, by way of a comoving boundary surface,
onto a Robertson-Walker background of homogeneous dust, has become a standard
construction in modern cosmology. Here we ask if this construction can be made
more realistic by introducing some evolution of the boundary surface. The
answer we find is no. To maintain a boundary surface using the Darmois - Israel
junction conditions, as opposed to the introduction of a surface layer, the
boundary must remain exactly comoving. The options are to drop the assumption
of dust or allow the development of surface layers. Either option fundamentally
changes the original construction.
| [
{
"created": "Wed, 31 Aug 2011 18:52:34 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Sep 2011 17:35:45 GMT",
"version": "v2"
},
{
"created": "Wed, 21 Sep 2011 15:23:02 GMT",
"version": "v3"
}
] | 2013-05-29 | [
[
"Grenon",
"Cédric",
""
],
[
"Lake",
"Kayll",
""
]
] | The generalized Swiss - cheese model, consisting of a Lema\^itre - Tolman (inhomogeneous dust) region matched, by way of a comoving boundary surface, onto a Robertson-Walker background of homogeneous dust, has become a standard construction in modern cosmology. Here we ask if this construction can be made more realistic by introducing some evolution of the boundary surface. The answer we find is no. To maintain a boundary surface using the Darmois - Israel junction conditions, as opposed to the introduction of a surface layer, the boundary must remain exactly comoving. The options are to drop the assumption of dust or allow the development of surface layers. Either option fundamentally changes the original construction. |
gr-qc/0402056 | Ezra Newman | Ezra Newman | Maxwell Fields and Shear-Free Null Geodesic Congruences | 39 | Class.Quant.Grav. 21 (2004) 3197-3222 | 10.1088/0264-9381/21/13/007 | null | gr-qc | null | We study and report on the class of vacuum Maxwell fields in Minkowski space
that possess a non-degenerate, diverging, principle null vector field (null
eigenvector field of the Maxwell tensor) that is tangent to a shear-free null
geodesics congruence. These congruences can be either surface forming (the
tangent vectors proportional to gradients) or not, i.e., the twisting
congruences. In the non-twisting case, the associated Maxwell fields are
precisely the Lienard-Wiechert fields, i.e., those Maxwell fields arising from
an electric monopole moving on an arbitrary worldline. The null geodesic
congruence is given by the generators of the light-cones with apex on the
world-line. The twisting case is much richer, more interesting and far more
complicated. In a twisting subcase, where our main interests lie, it can be
given the following strange interpretation. If we allow the real Minkowski
space to be complexified so that the real Minkowski coordinates x^a take
complex values, i.e., x^a => z^a=x^a+iy^a with complex metric g=eta_abdz^adz^b,
the real vacuum Maxwell equations can be extended into the complex and
rewritten as curlW =iWdot, divW with W =E+iB. This subcase of Maxwell fields
can then be extended into the complex so as to have as source, a complex
analytic world-line, i.e., to now become complex Lienard-Wiechart fields. When
viewed as real fields on the real Minkowski space, z^a=x^a, they possess a real
principle null vector that is shear-free but twisting and diverging. The twist
is a measure of how far the complex world-line is from the real 'slice'. Most
Maxwell fields in this subcase are asymptotically flat with a time-varying set
of electric and magnetic moments, all depending on the complex displacements
and the complex velocities.
| [
{
"created": "Thu, 12 Feb 2004 16:36:50 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Newman",
"Ezra",
""
]
] | We study and report on the class of vacuum Maxwell fields in Minkowski space that possess a non-degenerate, diverging, principle null vector field (null eigenvector field of the Maxwell tensor) that is tangent to a shear-free null geodesics congruence. These congruences can be either surface forming (the tangent vectors proportional to gradients) or not, i.e., the twisting congruences. In the non-twisting case, the associated Maxwell fields are precisely the Lienard-Wiechert fields, i.e., those Maxwell fields arising from an electric monopole moving on an arbitrary worldline. The null geodesic congruence is given by the generators of the light-cones with apex on the world-line. The twisting case is much richer, more interesting and far more complicated. In a twisting subcase, where our main interests lie, it can be given the following strange interpretation. If we allow the real Minkowski space to be complexified so that the real Minkowski coordinates x^a take complex values, i.e., x^a => z^a=x^a+iy^a with complex metric g=eta_abdz^adz^b, the real vacuum Maxwell equations can be extended into the complex and rewritten as curlW =iWdot, divW with W =E+iB. This subcase of Maxwell fields can then be extended into the complex so as to have as source, a complex analytic world-line, i.e., to now become complex Lienard-Wiechart fields. When viewed as real fields on the real Minkowski space, z^a=x^a, they possess a real principle null vector that is shear-free but twisting and diverging. The twist is a measure of how far the complex world-line is from the real 'slice'. Most Maxwell fields in this subcase are asymptotically flat with a time-varying set of electric and magnetic moments, all depending on the complex displacements and the complex velocities. |
gr-qc/0209034 | Helmut Friedrich | Helmut Friedrich | Spin-2 fields on Minkowski space near space-like and null infinity | 18 pages | Class.Quant.Grav. 20 (2003) 101-118 | 10.1088/0264-9381/20/1/308 | null | gr-qc | null | We show that the spin-2 equations on Minkowski space in the gauge of the
`regular finite initial value problem at space-like infinity' imply estimates
which, together with the transport equations on the cylinder at space-like
infinity, allow us to obtain for a certain class of initial data information on
the behaviour of the solution near space-like and null infinity of any desired
precision.
| [
{
"created": "Tue, 10 Sep 2002 11:21:34 GMT",
"version": "v1"
}
] | 2017-08-23 | [
[
"Friedrich",
"Helmut",
""
]
] | We show that the spin-2 equations on Minkowski space in the gauge of the `regular finite initial value problem at space-like infinity' imply estimates which, together with the transport equations on the cylinder at space-like infinity, allow us to obtain for a certain class of initial data information on the behaviour of the solution near space-like and null infinity of any desired precision. |
gr-qc/9709009 | Gen Uchida | Uchida Gen and Tetsuya Shiromizu | Timelike Infinity and Asymptotic Symmetry | 19 pages, LaTex, the final version to appear in J. Math. Phys | J.Math.Phys.39:6573-6592,1998 | 10.1063/1.532666 | UTAP-270, RESCEU-33/97 | gr-qc | null | By extending Ashtekar and Romano's definition of spacelike infinity to the
timelike direction, a new definition of asymptotic flatness at timelike
infinity for an isolated system with a source is proposed. The treatment
provides unit spacelike 3-hyperboloid timelike infinity and avoids the
introduction of the troublesome differentiability conditions which were
necessary in the previous works on asymptotically flat spacetimes at timelike
infinity. Asymptotic flatness is characterized by the fall-off rate of the
energy-momentum tensor at timelike infinity, which makes it easier to
understand physically what spacetimes are investigated. The notion of the order
of the asymptotic flatness is naturally introduced from the rate. The
definition gives a systematized picture of hierarchy in the asymptotic
structure, which was not clear in the previous works. It is found that if the
energy-momentum tensor falls off at a rate faster than $\sim t^{-2}$, the
spacetime is asymptotically flat and asymptotically stationary in the sense
that the Lie derivative of the metric with respect to $\ppp_t$ falls off at the
rate $\sim t^{-2}$. It also admits an asymptotic symmetry group similar to the
Poincar\'e group. If the energy-momentum tensor falls off at a rate faster than
$\sim t^{-3}$, the four-momentum of a spacetime may be defined. On the other
hand, angular momentum is defined only for spacetimes in which the
energy-momentum tensor falls off at a rate faster than $\sim t^{-4}$.
| [
{
"created": "Thu, 4 Sep 1997 08:08:12 GMT",
"version": "v1"
},
{
"created": "Wed, 24 Sep 1997 05:19:03 GMT",
"version": "v2"
},
{
"created": "Sun, 11 Oct 1998 12:25:52 GMT",
"version": "v3"
}
] | 2011-07-19 | [
[
"Gen",
"Uchida",
""
],
[
"Shiromizu",
"Tetsuya",
""
]
] | By extending Ashtekar and Romano's definition of spacelike infinity to the timelike direction, a new definition of asymptotic flatness at timelike infinity for an isolated system with a source is proposed. The treatment provides unit spacelike 3-hyperboloid timelike infinity and avoids the introduction of the troublesome differentiability conditions which were necessary in the previous works on asymptotically flat spacetimes at timelike infinity. Asymptotic flatness is characterized by the fall-off rate of the energy-momentum tensor at timelike infinity, which makes it easier to understand physically what spacetimes are investigated. The notion of the order of the asymptotic flatness is naturally introduced from the rate. The definition gives a systematized picture of hierarchy in the asymptotic structure, which was not clear in the previous works. It is found that if the energy-momentum tensor falls off at a rate faster than $\sim t^{-2}$, the spacetime is asymptotically flat and asymptotically stationary in the sense that the Lie derivative of the metric with respect to $\ppp_t$ falls off at the rate $\sim t^{-2}$. It also admits an asymptotic symmetry group similar to the Poincar\'e group. If the energy-momentum tensor falls off at a rate faster than $\sim t^{-3}$, the four-momentum of a spacetime may be defined. On the other hand, angular momentum is defined only for spacetimes in which the energy-momentum tensor falls off at a rate faster than $\sim t^{-4}$. |
1710.00830 | Miguel Ferreira | Miguel C. Ferreira, Caio F. B. Macedo, Vitor Cardoso | Orbital fingerprints of ultralight scalar fields around black holes | 21 pages, 13 figures. Accepted for publication in Physical Review D,
comments are welcome | null | 10.1103/PhysRevD.96.083017 | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Ultralight scalars have been predicted in a variety of scenarios, and
advocated as a possible component of dark matter. These fields can form compact
regular structures known as boson stars, or---in the presence of
horizons---give rise to nontrivial time-dependent scalar hair and a stationary
geometry. Because these fields can be coherent over large spatial extents,
their interaction with "regular" matter can lead to very peculiar effects, most
notably resonances. Here we study the motion of stars in a background
describing black holes surrounded by non-axially symmetric scalar field
profiles. By analyzing the system in a weak-field approach, we find that the
presence of a scalar field gives rise to secular effects akin to ones existing
in planetary and accretion disks. Particularly, the existence of resonances
between the orbiting stars and the scalar field may enable angular momentum
exchange between them, providing mechanisms similar to planetary migration.
Additionally, these mechanisms may allow \textit{floating orbits}, which are
stable radiating orbits. We also show, in the full relativistic case, that
these effects also appear when there is a direct coupling between the scalar
field and the stellar matter, which can arise due to the presence of a scalar
core in the star or in alternative theories of gravity.
| [
{
"created": "Mon, 2 Oct 2017 18:00:04 GMT",
"version": "v1"
}
] | 2017-11-22 | [
[
"Ferreira",
"Miguel C.",
""
],
[
"Macedo",
"Caio F. B.",
""
],
[
"Cardoso",
"Vitor",
""
]
] | Ultralight scalars have been predicted in a variety of scenarios, and advocated as a possible component of dark matter. These fields can form compact regular structures known as boson stars, or---in the presence of horizons---give rise to nontrivial time-dependent scalar hair and a stationary geometry. Because these fields can be coherent over large spatial extents, their interaction with "regular" matter can lead to very peculiar effects, most notably resonances. Here we study the motion of stars in a background describing black holes surrounded by non-axially symmetric scalar field profiles. By analyzing the system in a weak-field approach, we find that the presence of a scalar field gives rise to secular effects akin to ones existing in planetary and accretion disks. Particularly, the existence of resonances between the orbiting stars and the scalar field may enable angular momentum exchange between them, providing mechanisms similar to planetary migration. Additionally, these mechanisms may allow \textit{floating orbits}, which are stable radiating orbits. We also show, in the full relativistic case, that these effects also appear when there is a direct coupling between the scalar field and the stellar matter, which can arise due to the presence of a scalar core in the star or in alternative theories of gravity. |
1410.3215 | Carl Kent | Carl Kent, Elizabeth Winstanley | The global rotating scalar field vacuum on anti-de Sitter space-time | Minor changes (inc. title change), version accepted for publication
in Physics Letters B, 4 pages | Phys. Lett. B 740 (2015) 188 - 191 | 10.1016/j.physletb.2014.11.047 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the definition of the global vacuum state of a quantum scalar
field on $n$-dimensional anti-de Sitter space-time as seen by an observer
rotating about the polar axis. Since positive (or negative) frequency scalar
field modes must have positive (or negative) Klein-Gordon norm respectively, we
find that the only sensible choice of positive frequency corresponds to
positive frequency as seen by a static observer. This means that the global
rotating vacuum is identical to the global nonrotating vacuum. For $n\ge 4$, if
the angular velocity of the rotating observer is smaller than the inverse of
the anti-de Sitter radius of curvature, then modes with positive Klein-Gordon
norm also have positive frequency as seen by the rotating observer.We comment
on the implications of this result for the construction of global rotating
thermal states.
| [
{
"created": "Mon, 13 Oct 2014 08:26:25 GMT",
"version": "v1"
},
{
"created": "Thu, 4 Dec 2014 08:58:14 GMT",
"version": "v2"
}
] | 2015-03-16 | [
[
"Kent",
"Carl",
""
],
[
"Winstanley",
"Elizabeth",
""
]
] | We consider the definition of the global vacuum state of a quantum scalar field on $n$-dimensional anti-de Sitter space-time as seen by an observer rotating about the polar axis. Since positive (or negative) frequency scalar field modes must have positive (or negative) Klein-Gordon norm respectively, we find that the only sensible choice of positive frequency corresponds to positive frequency as seen by a static observer. This means that the global rotating vacuum is identical to the global nonrotating vacuum. For $n\ge 4$, if the angular velocity of the rotating observer is smaller than the inverse of the anti-de Sitter radius of curvature, then modes with positive Klein-Gordon norm also have positive frequency as seen by the rotating observer.We comment on the implications of this result for the construction of global rotating thermal states. |
gr-qc/0008001 | Hod Shahar | Shahar Hod | Wave Propagation in Nontrivial Backgrounds | 5 pages. 2 Figures | Class.Quant.Grav. 18 (2001) 1311-1318 | 10.1088/0264-9381/18/7/313 | null | gr-qc | null | It is well known that waves propagating in a nontrivial medium develop
``tails''. However, the exact form of the late-time tail has so far been
determined only for a narrow class of models. We present a systematic analysis
of the tail phenomenon for waves propagating under the influence of a {\it
general} scattering potential $V(x)$. It is shown that, generically, the
late-time tail is determined by spatial {\it derivatives} of the potential. The
central role played by derivatives of the scattering potential appears not to
be widely recognized. The analytical results are confirmed by numerical
calculations.
| [
{
"created": "Tue, 1 Aug 2000 06:42:20 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Hod",
"Shahar",
""
]
] | It is well known that waves propagating in a nontrivial medium develop ``tails''. However, the exact form of the late-time tail has so far been determined only for a narrow class of models. We present a systematic analysis of the tail phenomenon for waves propagating under the influence of a {\it general} scattering potential $V(x)$. It is shown that, generically, the late-time tail is determined by spatial {\it derivatives} of the potential. The central role played by derivatives of the scattering potential appears not to be widely recognized. The analytical results are confirmed by numerical calculations. |
gr-qc/0505076 | Matthew Pitkin | Matthew Pitkin (for the LIGO Scientific Collaboration) | Searching for gravitational waves from known pulsars | Accepted by CQG for the proceeding of GWDAW9, 7 pages, 2 figures | Class.Quant.Grav. 22 (2005) S1277-S1282 | 10.1088/0264-9381/22/18/S41 | null | gr-qc astro-ph | null | We present upper limits on the amplitude of gravitational waves from 28
isolated pulsars using data from the second science run of LIGO. The results
are also expressed as a constraint on the pulsars' equatorial ellipticities. We
discuss a new way of presenting such ellipticity upper limits that takes
account of the uncertainties of the pulsar moment of inertia. We also extend
our previous method to search for known pulsars in binary systems, of which
there are about 80 in the sensitive frequency range of LIGO and GEO 600.
| [
{
"created": "Mon, 16 May 2005 11:42:51 GMT",
"version": "v1"
}
] | 2019-08-14 | [
[
"Pitkin",
"Matthew",
"",
"for the LIGO Scientific Collaboration"
]
] | We present upper limits on the amplitude of gravitational waves from 28 isolated pulsars using data from the second science run of LIGO. The results are also expressed as a constraint on the pulsars' equatorial ellipticities. We discuss a new way of presenting such ellipticity upper limits that takes account of the uncertainties of the pulsar moment of inertia. We also extend our previous method to search for known pulsars in binary systems, of which there are about 80 in the sensitive frequency range of LIGO and GEO 600. |
gr-qc/0505154 | Ding-Fang Zeng | Ding-fang Zeng and Yi-hong Gao | An Ignored Assumption of $\Lambda$CDM Cosmology and An Old Question: Do
We Live On The "Center" of The Universe? | two column style, 4 pages | null | null | null | gr-qc | null | We point out that $\Lambda$CDM cosmology has an ignored assumption. That is,
the $\Lambda$ component of the universe moves synchronously with ordinary
matters on Hubble scales. If cosmological constant is vacuum energy, this
assumption may be very difficult to be understood.
We then propose a new mechanism which can explain the accelerating recession
of super-novaes. That is, considering the pressures originating from the random
moving (including Hubble recession) of galaxy clusters and galaxies. We provide
an new analytical solution of Einstein equation which may describe a universe
whose pressures originating from the random moving of galaxy clusters and
galaxies are considered.
| [
{
"created": "Tue, 31 May 2005 11:25:01 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Zeng",
"Ding-fang",
""
],
[
"Gao",
"Yi-hong",
""
]
] | We point out that $\Lambda$CDM cosmology has an ignored assumption. That is, the $\Lambda$ component of the universe moves synchronously with ordinary matters on Hubble scales. If cosmological constant is vacuum energy, this assumption may be very difficult to be understood. We then propose a new mechanism which can explain the accelerating recession of super-novaes. That is, considering the pressures originating from the random moving (including Hubble recession) of galaxy clusters and galaxies. We provide an new analytical solution of Einstein equation which may describe a universe whose pressures originating from the random moving of galaxy clusters and galaxies are considered. |
gr-qc/0510008 | Lior M. Burko | Alexander Z. Smith and Lior M. Burko | Comment on "High-order contamination in the tail of gravitational
collapse'' | 4 pages, 4 figures | Phys.Rev. D74 (2006) 028501 | 10.1103/PhysRevD.74.028501 | null | gr-qc | null | We confront the predictions of S. Hod, Phys. Rev. D 60, 104053 (1999) for the
late-time decay rate of black hole perturbations with numerical data.
Specifically, we ask two questions: First, are corrections to the Price tail
dominated by logarithmic terms, as predicted by Hod? Second, if there were
logarithmic correction terms, do they take the specific form predicted in Hod's
paper? The answer to both questions is ``no.''
| [
{
"created": "Mon, 3 Oct 2005 16:40:34 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Jun 2006 22:06:06 GMT",
"version": "v2"
},
{
"created": "Wed, 19 Jul 2006 18:12:22 GMT",
"version": "v3"
}
] | 2009-11-11 | [
[
"Smith",
"Alexander Z.",
""
],
[
"Burko",
"Lior M.",
""
]
] | We confront the predictions of S. Hod, Phys. Rev. D 60, 104053 (1999) for the late-time decay rate of black hole perturbations with numerical data. Specifically, we ask two questions: First, are corrections to the Price tail dominated by logarithmic terms, as predicted by Hod? Second, if there were logarithmic correction terms, do they take the specific form predicted in Hod's paper? The answer to both questions is ``no.'' |
1207.0708 | M. Farasat Shamir | M. Farasat Shamir, Adil Jhangeer, Akhlaq Ahmad Bhatti | Exact Solutions of Bianchi Types $I$ and $V$ Models in $f(R,T)$ Gravity | 16 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper is devoted to investigate the exact solutions of Bianchi types I
and V spacetimes in the context of f(R, T) gravity [1]. For this purpose, we
found two exact solutions in each case by using assumption of constant
deceleration parameter and the variation law of Hubble parameter. The obtained
solutions correspond to two different models of this universe. The physical
behavior of these models is also discussed.
| [
{
"created": "Mon, 2 Jul 2012 11:11:36 GMT",
"version": "v1"
}
] | 2012-07-04 | [
[
"Shamir",
"M. Farasat",
""
],
[
"Jhangeer",
"Adil",
""
],
[
"Bhatti",
"Akhlaq Ahmad",
""
]
] | This paper is devoted to investigate the exact solutions of Bianchi types I and V spacetimes in the context of f(R, T) gravity [1]. For this purpose, we found two exact solutions in each case by using assumption of constant deceleration parameter and the variation law of Hubble parameter. The obtained solutions correspond to two different models of this universe. The physical behavior of these models is also discussed. |
0806.1391 | Farook Rahaman | F.Rahaman, M.Kalam and K A Rahman | Thin shell wormhole due to dyadosphere of a charged black hole | 10 pages, 2 figures. Accepted in Mod.Phys.Lett.A | Mod.Phys.Lett.A24:53-61,2009 | 10.1142/S0217732309027406 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | To explain Gamma Ray Bursts, Ruffini argued that the event horizon of a
charged black hole is surrounded by a special region called, the Dyadosphere
where electric field exceeds the critical value for $e^+$ $e^-$ pair
production. In the present work, we construct a thin shell wormhole by
performing a thought surgery between two dadospheres. Several physical
properties of this thin shell wormhole have been analyzed.
| [
{
"created": "Mon, 9 Jun 2008 08:05:48 GMT",
"version": "v1"
}
] | 2009-02-10 | [
[
"Rahaman",
"F.",
""
],
[
"Kalam",
"M.",
""
],
[
"Rahman",
"K A",
""
]
] | To explain Gamma Ray Bursts, Ruffini argued that the event horizon of a charged black hole is surrounded by a special region called, the Dyadosphere where electric field exceeds the critical value for $e^+$ $e^-$ pair production. In the present work, we construct a thin shell wormhole by performing a thought surgery between two dadospheres. Several physical properties of this thin shell wormhole have been analyzed. |
2311.10369 | Z. Yousaf | Z. Yousaf, Kazuharu Bamba, M. Z. Bhatti, U. Farwa | Quasi-static evolution of axially and reflection symmetric large-scale
configuration | 43 pages | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We review recently offered notions of quasi-static evolution of the axial
self-gravitating structures at large-scales and the criteria to characterize
the corresponding evolutionary aspects under the influence of strong curvature
regimes. In doing so, we examine the axial source's dynamic and quasi-static
behavior within the parameters of various modified gravity theories. We address
the formalism of these notions and their possible implications in studying the
dissipative and anisotropic configuration. We initiate by considering
higher-order curvature gravity. The Palatini formalism of $f(R)$ gravity is
also taken into consideration to analyze the behavior of the kinematical as
well as the dynamical variables of the proposed problem. The set of invariant
velocities is defined to comprehend the concept of quasi-static approximation
that enhances the stability of the system in contrast to the dynamic mode. It
is identified that vorticity and distinct versions of the structure scalars
$Y_{I}$, $Y_{II}$ and $Y_{KL}$ play an important role in revealing the
significant effects of a fluid's anisotropy. As another example of evolution,
we check the influence of Palatini-based factors on the shearing motion of the
object. A comparison-based study of the physical nature of distinct curvature
factors on the propagation of the axial source is exhibited. This provides an
intriguing platform to grasp the notion of quasi-static evolution together with
the distinct curvature factors at the current time scenario. The importance of
slowly evolving axially symmetric regimes will be addressed through the
distinct modified gravitational context. Finally, we share a list of queries
that, we believe, deserve to be addressed in the near future.
| [
{
"created": "Fri, 17 Nov 2023 07:46:08 GMT",
"version": "v1"
}
] | 2023-12-05 | [
[
"Yousaf",
"Z.",
""
],
[
"Bamba",
"Kazuharu",
""
],
[
"Bhatti",
"M. Z.",
""
],
[
"Farwa",
"U.",
""
]
] | We review recently offered notions of quasi-static evolution of the axial self-gravitating structures at large-scales and the criteria to characterize the corresponding evolutionary aspects under the influence of strong curvature regimes. In doing so, we examine the axial source's dynamic and quasi-static behavior within the parameters of various modified gravity theories. We address the formalism of these notions and their possible implications in studying the dissipative and anisotropic configuration. We initiate by considering higher-order curvature gravity. The Palatini formalism of $f(R)$ gravity is also taken into consideration to analyze the behavior of the kinematical as well as the dynamical variables of the proposed problem. The set of invariant velocities is defined to comprehend the concept of quasi-static approximation that enhances the stability of the system in contrast to the dynamic mode. It is identified that vorticity and distinct versions of the structure scalars $Y_{I}$, $Y_{II}$ and $Y_{KL}$ play an important role in revealing the significant effects of a fluid's anisotropy. As another example of evolution, we check the influence of Palatini-based factors on the shearing motion of the object. A comparison-based study of the physical nature of distinct curvature factors on the propagation of the axial source is exhibited. This provides an intriguing platform to grasp the notion of quasi-static evolution together with the distinct curvature factors at the current time scenario. The importance of slowly evolving axially symmetric regimes will be addressed through the distinct modified gravitational context. Finally, we share a list of queries that, we believe, deserve to be addressed in the near future. |
1301.6344 | Emilio Elizalde | A. V. Astashenok, E. Elizalde, J. de Haro, S. D. Odintsov, A. V. Yurov | Brane cosmology from observational surveys and its comparison with
standard FRW cosmology | 19 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1206.2192 | null | 10.1007/s10509-013-1484-4 | null | gr-qc astro-ph.CO hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Several dark energy models on the brane are investigated. They are compared
with corresponding theories in the frame of 4d Friedmann-Robertson-Walker
cosmology. To constrain the parameters of the models considered, recent
observational data, including SNIa apparent magnitude measurements, baryon
acoustic oscillation results, Hubble parameter evolution data and matter
density perturbations are used. Explicit formulas of the so-called {\it
state-finder} parameters in teleparallel theories are obtained that could be
useful to test these models and to establish a link between Loop Quantum
Cosmology and Brane Cosmology. It is concluded that a joint analysis as the one
developed here allows to estimate, in a very convenient way, possible deviation
of the real universe cosmology from the standard Friedmann-Robertson-Walker
one.
| [
{
"created": "Sun, 27 Jan 2013 11:01:26 GMT",
"version": "v1"
}
] | 2015-06-12 | [
[
"Astashenok",
"A. V.",
""
],
[
"Elizalde",
"E.",
""
],
[
"de Haro",
"J.",
""
],
[
"Odintsov",
"S. D.",
""
],
[
"Yurov",
"A. V.",
""
]
] | Several dark energy models on the brane are investigated. They are compared with corresponding theories in the frame of 4d Friedmann-Robertson-Walker cosmology. To constrain the parameters of the models considered, recent observational data, including SNIa apparent magnitude measurements, baryon acoustic oscillation results, Hubble parameter evolution data and matter density perturbations are used. Explicit formulas of the so-called {\it state-finder} parameters in teleparallel theories are obtained that could be useful to test these models and to establish a link between Loop Quantum Cosmology and Brane Cosmology. It is concluded that a joint analysis as the one developed here allows to estimate, in a very convenient way, possible deviation of the real universe cosmology from the standard Friedmann-Robertson-Walker one. |
1205.4466 | Richard Woodard | P. J. Mora (U. Florida), N. C. Tsamis (U. Crete) and R. P. Woodard (U.
Florida) | Weyl-Weyl Correlator in de Donder Gauge on de Sitter | 16 pages, no figures, uses LaTeX2e | null | 10.1103/PhysRevD.86.084016 | UFIFT-QG-12-04 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compute the linearized Weyl-Weyl correlator using a new solution for the
graviton propagator on de Sitter background in de Donder gauge. The result
agrees exactly with a previous computation in a noncovariant gauge. We also use
dimensional regularization to compute the one loop expectation value of the
square of the Weyl tensor.
| [
{
"created": "Sun, 20 May 2012 22:13:49 GMT",
"version": "v1"
}
] | 2015-06-05 | [
[
"Mora",
"P. J.",
"",
"U. Florida"
],
[
"Tsamis",
"N. C.",
"",
"U. Crete"
],
[
"Woodard",
"R. P.",
"",
"U.\n Florida"
]
] | We compute the linearized Weyl-Weyl correlator using a new solution for the graviton propagator on de Sitter background in de Donder gauge. The result agrees exactly with a previous computation in a noncovariant gauge. We also use dimensional regularization to compute the one loop expectation value of the square of the Weyl tensor. |
gr-qc/0002053 | Luca Bombelli | Luca Bombelli | Statistical Lorentzian geometry and the closeness of Lorentzian
manifolds | Plain TeX, 19 pages + 3 figures, revised version for publication in
J.Math.Phys., significantly improved content | J.Math.Phys. 41 (2000) 6944-6958 | 10.1063/1.1288494 | null | gr-qc math-ph math.DG math.MP | null | I introduce a family of closeness functions between causal Lorentzian
geometries of finite volume and arbitrary underlying topology. When points are
randomly scattered in a Lorentzian manifold, with uniform density according to
the volume element, some information on the topology and metric is encoded in
the partial order that the causal structure induces among those points; one can
then define closeness between Lorentzian geometries by comparing the sets of
probabilities they give for obtaining the same posets. If the density of points
is finite, one gets a pseudo-distance, which only compares the manifolds down
to a finite volume scale, as illustrated here by a fully worked out example of
two 2-dimensional manifolds of different topology; if the density is allowed to
become infinite, a true distance can be defined on the space of all Lorentzian
geometries. The introductory and concluding sections include some remarks on
the motivation for this definition and its applications to quantum gravity.
| [
{
"created": "Tue, 15 Feb 2000 18:35:07 GMT",
"version": "v1"
},
{
"created": "Sun, 11 Jun 2000 22:41:49 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Bombelli",
"Luca",
""
]
] | I introduce a family of closeness functions between causal Lorentzian geometries of finite volume and arbitrary underlying topology. When points are randomly scattered in a Lorentzian manifold, with uniform density according to the volume element, some information on the topology and metric is encoded in the partial order that the causal structure induces among those points; one can then define closeness between Lorentzian geometries by comparing the sets of probabilities they give for obtaining the same posets. If the density of points is finite, one gets a pseudo-distance, which only compares the manifolds down to a finite volume scale, as illustrated here by a fully worked out example of two 2-dimensional manifolds of different topology; if the density is allowed to become infinite, a true distance can be defined on the space of all Lorentzian geometries. The introductory and concluding sections include some remarks on the motivation for this definition and its applications to quantum gravity. |
2201.00047 | Jahed Abedi | Jahed Abedi, Lu\'is Felipe Longo Micchi, Niayesh Afshordi | GW190521: Search for Echoes due to Stimulated Hawking Radiation from
Black Holes | 17 pages, 13 figures, 3 tables, Codes available at
https://github.com/No-GAP/GW190521echo | null | 10.1103/PhysRevD.108.044047 | null | gr-qc astro-ph.CO astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Being arguably the most massive binary black hole merger event observed to
date, GW190521 deserves special attention. The exceptionally loud ringdown of
this merger makes it an ideal candidate to search for gravitational wave
echoes, a proposed smoking gun for the quantum structure of black hole
horizons. We perform an unprecedented multi-pronged search for echoes via two
well-established and independent pipelines: a template-based search for
stimulated emission of Hawking radiation, or Boltzmann echoes, and the
model-agnostic coherent WaveBurst (cWB) search. Stimulated Hawking radiation
from the merger is expected to lead to post-merger echoes at horizon mode
frequency of $\sim50$ Hz (for quadrupolar gravitational radiation), repeating
at intervals of $\sim1$ second, due to partial reflection off Planckian quantum
structure of the horizon. A careful analysis using dynamic nested sampling
yields a Bayesian evidence of $8^{+4}_{-2}$ (90\% confidence level) for this
signal following GW190521, carrying an excess of $6^{+10}_{-5}\%$ in
gravitational wave energy, relative to the main event (consistent with the
predicted amplitude of Boltzmann echoes). The "look-elsewhere" effect is
estimated by using General Relativity (plus Boltzmann echoes) injections in
real data, around the event, giving a false (true) positive detection
probability for higher Bayes factors of $1.5^{+1.2}_{-0.9}\%$ ($35\pm7\%$).
Similarly, the reconstructed waveform of the first echo in cWB carries an
energy excess of $13^{+16}_{-7}\%$. While the current evidence for stimulated
Hawking radiation does not reach the gold standard of $5\sigma$ (or p-value
$<3\times10^{-7}$), our findings are in line with expectations for stimulated
Hawking radiation at current detector sensitivities. The next generation of
gravitational wave observatories can thus draw a definitive conclusion on the
quantum nature of black hole horizons.
| [
{
"created": "Fri, 31 Dec 2021 20:12:38 GMT",
"version": "v1"
},
{
"created": "Mon, 29 May 2023 14:27:42 GMT",
"version": "v2"
}
] | 2023-10-09 | [
[
"Abedi",
"Jahed",
""
],
[
"Micchi",
"Luís Felipe Longo",
""
],
[
"Afshordi",
"Niayesh",
""
]
] | Being arguably the most massive binary black hole merger event observed to date, GW190521 deserves special attention. The exceptionally loud ringdown of this merger makes it an ideal candidate to search for gravitational wave echoes, a proposed smoking gun for the quantum structure of black hole horizons. We perform an unprecedented multi-pronged search for echoes via two well-established and independent pipelines: a template-based search for stimulated emission of Hawking radiation, or Boltzmann echoes, and the model-agnostic coherent WaveBurst (cWB) search. Stimulated Hawking radiation from the merger is expected to lead to post-merger echoes at horizon mode frequency of $\sim50$ Hz (for quadrupolar gravitational radiation), repeating at intervals of $\sim1$ second, due to partial reflection off Planckian quantum structure of the horizon. A careful analysis using dynamic nested sampling yields a Bayesian evidence of $8^{+4}_{-2}$ (90\% confidence level) for this signal following GW190521, carrying an excess of $6^{+10}_{-5}\%$ in gravitational wave energy, relative to the main event (consistent with the predicted amplitude of Boltzmann echoes). The "look-elsewhere" effect is estimated by using General Relativity (plus Boltzmann echoes) injections in real data, around the event, giving a false (true) positive detection probability for higher Bayes factors of $1.5^{+1.2}_{-0.9}\%$ ($35\pm7\%$). Similarly, the reconstructed waveform of the first echo in cWB carries an energy excess of $13^{+16}_{-7}\%$. While the current evidence for stimulated Hawking radiation does not reach the gold standard of $5\sigma$ (or p-value $<3\times10^{-7}$), our findings are in line with expectations for stimulated Hawking radiation at current detector sensitivities. The next generation of gravitational wave observatories can thus draw a definitive conclusion on the quantum nature of black hole horizons. |
gr-qc/0610099 | Pui Tang Leung | L.K. Tsui, P.T. Leung and J. Wu | Determination of the internal structure of neutron stars from
gravitational wave spectra | 26 pages, 14 figures, submitted to Physical Review D | Phys.Rev.D74:124025,2006 | 10.1103/PhysRevD.74.124025 | null | gr-qc | null | In this paper the internal structure of a neutron star is shown to be
inferrable from its gravitational-wave spectrum. Iteratively applying the
inverse scheme of the scaled coordinate logarithmic perturbation method for
neutron stars proposed by Tsui and Leung [Astrophys. J. {\bf 631}, 495 (2005)],
we are able to determine the mass, the radius and the mass distribution of a
star from its quasi-normal mode frequencies of stellar pulsation. In addition,
accurate equation of state of nuclear matter can be obtained from such
inversion scheme. Explicit formulas for the case of axial $w$-mode oscillation
are derived here and numerical results for neutron stars characterized by
different equations of state are shown.
| [
{
"created": "Fri, 20 Oct 2006 07:36:54 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Tsui",
"L. K.",
""
],
[
"Leung",
"P. T.",
""
],
[
"Wu",
"J.",
""
]
] | In this paper the internal structure of a neutron star is shown to be inferrable from its gravitational-wave spectrum. Iteratively applying the inverse scheme of the scaled coordinate logarithmic perturbation method for neutron stars proposed by Tsui and Leung [Astrophys. J. {\bf 631}, 495 (2005)], we are able to determine the mass, the radius and the mass distribution of a star from its quasi-normal mode frequencies of stellar pulsation. In addition, accurate equation of state of nuclear matter can be obtained from such inversion scheme. Explicit formulas for the case of axial $w$-mode oscillation are derived here and numerical results for neutron stars characterized by different equations of state are shown. |
1307.1923 | Edward Anderson | Edward Anderson | Kendall's Shape Statistics as a Classical Realization of Barbour-type
Timeless Records Theory approach to Quantum Gravity | 11 pages with 5 figures. Improved text, as Accepted by SHPMP (Studies
in History and Philosophy of Modern Physics) with some new explanations,
minor corrections and updated references | Stud. Hist. Phil. Mod. Phys. 51 (2015) 1-8 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | I previously showed that Kendall's work on shape geometry is in fact also the
geometrical description of Barbour's relational mechanics' reduced
configuration spaces (alias shape spaces). I now describe the extent to which
Kendall's subsequent statistical application to e.g. the `standing stones
problem' realizes further ideas along the lines of Barbour-type timeless
records theories, albeit just at the classical level.
| [
{
"created": "Sun, 7 Jul 2013 21:42:15 GMT",
"version": "v1"
},
{
"created": "Fri, 26 Jul 2013 18:54:37 GMT",
"version": "v2"
},
{
"created": "Wed, 7 Aug 2013 14:06:48 GMT",
"version": "v3"
},
{
"created": "Mon, 25 Nov 2013 02:22:31 GMT",
"version": "v4"
},
{
"cre... | 2015-08-07 | [
[
"Anderson",
"Edward",
""
]
] | I previously showed that Kendall's work on shape geometry is in fact also the geometrical description of Barbour's relational mechanics' reduced configuration spaces (alias shape spaces). I now describe the extent to which Kendall's subsequent statistical application to e.g. the `standing stones problem' realizes further ideas along the lines of Barbour-type timeless records theories, albeit just at the classical level. |
2211.12780 | Antonio C. Guti\'errez-Pi\~neres | Antonio C. Guti\'errez-Pi\~neres | Fermi-normal coordinates for the Newtonian approximation of gravity | Replaced with the version matching the published one in Physica
Scripta | null | 10.1088/1402-4896/ad0fc7 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this work, we compute the metric corresponding to a static and spherically
symmetric mass distribution in the general relativistic weak field
approximation to quadratic order in Fermi-normal coordinates surrounding a
radial geodesic. To construct a geodesic and a convenient tetrad transported
along it, we first introduce a general metric, use the Cartan formalism of
differential forms, and then specialize the space-time by considering the
nearly Newtonian metric. This procedure simplifies the calculations
significantly, and the expression for the radial geodesic admits a simple form.
We conclude that in quadratic order, the effects of a Schwarzschild
gravitational field measured locally by a freely falling observer equals the
measured by an observer in similar conditions in the presence of a Newtonian
approximation of gravitation.
| [
{
"created": "Wed, 23 Nov 2022 08:49:42 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Dec 2022 20:41:14 GMT",
"version": "v2"
},
{
"created": "Sat, 25 Nov 2023 15:07:57 GMT",
"version": "v3"
}
] | 2023-11-28 | [
[
"Gutiérrez-Piñeres",
"Antonio C.",
""
]
] | In this work, we compute the metric corresponding to a static and spherically symmetric mass distribution in the general relativistic weak field approximation to quadratic order in Fermi-normal coordinates surrounding a radial geodesic. To construct a geodesic and a convenient tetrad transported along it, we first introduce a general metric, use the Cartan formalism of differential forms, and then specialize the space-time by considering the nearly Newtonian metric. This procedure simplifies the calculations significantly, and the expression for the radial geodesic admits a simple form. We conclude that in quadratic order, the effects of a Schwarzschild gravitational field measured locally by a freely falling observer equals the measured by an observer in similar conditions in the presence of a Newtonian approximation of gravitation. |
1004.2539 | Matt Visser | Jozef Skakala (Victoria University of Wellington) and Matt Visser
(Victoria University of Wellington) | Semi-analytic results for quasi-normal frequencies | V1: 28 pages, no figures. V2: 3 references added, no physics changes.
V3: 29 pages, 9 references added, no physics changes; V4: reformatted, now 27
pages. Some clarifications, comparison with results obtained by monodromy
techniques. This version accepted for publication in JHEP. V5: Minor typos
fixed. Compatible with published version | JHEP 1008:061,2010 | 10.1007/JHEP08(2010)061 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The last decade has seen considerable interest in the quasi-normal
frequencies [QNFs] of black holes (and even wormholes), both asymptotically
flat and with cosmological horizons. There is wide agreement that the QNFs are
often of the form omega_n = (offset) + i n (gap), though some authors have
encountered situations where this behaviour seems to fail. To get a better
understanding of the general situation we consider a semi-analytic model based
on a piecewise Eckart (Poeschl-Teller) potential, allowing for different
heights and different rates of exponential falloff in the two asymptotic
directions. This model is sufficiently general to capture and display key
features of the black hole QNFs while simultaneously being analytically
tractable, at least for asymptotically large imaginary parts of the QNFs. We
shall derive an appropriate "quantization condition" for the asymptotic QNFs,
and extract as much analytic information as possible. In particular, we shall
explicitly verify that the (offset)+ i n (gap) behaviour is common but not
universal, with this behaviour failing unless the ratio of rates of exponential
falloff on the two sides of the potential is a rational number. (This is
"common but not universal" in the sense that the rational numbers are dense in
the reals.) We argue that this behaviour is likely to persist for black holes
with cosmological horizons.
| [
{
"created": "Thu, 15 Apr 2010 02:11:35 GMT",
"version": "v1"
},
{
"created": "Wed, 21 Apr 2010 03:35:59 GMT",
"version": "v2"
},
{
"created": "Fri, 30 Apr 2010 03:19:27 GMT",
"version": "v3"
},
{
"created": "Thu, 22 Jul 2010 12:17:13 GMT",
"version": "v4"
},
{
"c... | 2010-09-02 | [
[
"Skakala",
"Jozef",
"",
"Victoria University of Wellington"
],
[
"Visser",
"Matt",
"",
"Victoria University of Wellington"
]
] | The last decade has seen considerable interest in the quasi-normal frequencies [QNFs] of black holes (and even wormholes), both asymptotically flat and with cosmological horizons. There is wide agreement that the QNFs are often of the form omega_n = (offset) + i n (gap), though some authors have encountered situations where this behaviour seems to fail. To get a better understanding of the general situation we consider a semi-analytic model based on a piecewise Eckart (Poeschl-Teller) potential, allowing for different heights and different rates of exponential falloff in the two asymptotic directions. This model is sufficiently general to capture and display key features of the black hole QNFs while simultaneously being analytically tractable, at least for asymptotically large imaginary parts of the QNFs. We shall derive an appropriate "quantization condition" for the asymptotic QNFs, and extract as much analytic information as possible. In particular, we shall explicitly verify that the (offset)+ i n (gap) behaviour is common but not universal, with this behaviour failing unless the ratio of rates of exponential falloff on the two sides of the potential is a rational number. (This is "common but not universal" in the sense that the rational numbers are dense in the reals.) We argue that this behaviour is likely to persist for black holes with cosmological horizons. |
2001.06830 | Vasilis Oikonomou | S.D. Odintsov, V.K. Oikonomou | Geometric Inflation and Dark Energy with Axion $F(R)$ Gravity | PRD Accepted | null | 10.1103/PhysRevD.101.044009 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a model of $F(R)$ gravity in the presence of a string theory
motivated misalignment axion like particle materialized in terms of a canonical
scalar field minimally coupled with gravity, and we study the cosmological
phenomenology of the model, emphasizing mainly on the late-time era. The main
result of the paper is that inflation and the dark energy era may be realized
in a geometric way by an $F(R)$ gravity, while the axion is the dark matter
constituent of the Universe. The $F(R)$ gravity model consists of an $R^2$
term, which as we show dominates the evolution during the early time, thus
producing a viable inflationary phenomenology, and a power law term $\sim
R^{\delta}$ with $\delta\ll 1 $ and positive, which eventually controls the
late-time era. The axion field remains frozen during the inflationary era,
which is an effect known for misalignment axions, but as the Universe expands,
the axion starts to oscillate, and its energy density scales eventually as we
show, as $\rho_a\sim a^{-3}$. After appropriately rewriting the gravitational
equations in terms of the redshift $z$, we study in detail the late-time
phenomenology of the model, and we compare the results with the $\Lambda$CDM
model and the latest Planck 2018 data. As we show, the model for small
redshifts $0<z<5$ is phenomenologically similar to the $\Lambda$CDM model,
however at large redshifts and deeply in the matter domination era, the results
are different from those of the $\Lambda$CDM model due to the dark energy
oscillations. For the late-time study we investigate the behavior of several
well-known statefinder quantities, like the deceleration parameter, the jerk
and $Om(z)$, and we demonstrate that the statefinders which contain lower
derivatives of the Hubble rate have similar behavior for both the $\Lambda$CDM
and the axion $F(R)$ gravity model.
| [
{
"created": "Sun, 19 Jan 2020 13:59:51 GMT",
"version": "v1"
}
] | 2020-02-19 | [
[
"Odintsov",
"S. D.",
""
],
[
"Oikonomou",
"V. K.",
""
]
] | We present a model of $F(R)$ gravity in the presence of a string theory motivated misalignment axion like particle materialized in terms of a canonical scalar field minimally coupled with gravity, and we study the cosmological phenomenology of the model, emphasizing mainly on the late-time era. The main result of the paper is that inflation and the dark energy era may be realized in a geometric way by an $F(R)$ gravity, while the axion is the dark matter constituent of the Universe. The $F(R)$ gravity model consists of an $R^2$ term, which as we show dominates the evolution during the early time, thus producing a viable inflationary phenomenology, and a power law term $\sim R^{\delta}$ with $\delta\ll 1 $ and positive, which eventually controls the late-time era. The axion field remains frozen during the inflationary era, which is an effect known for misalignment axions, but as the Universe expands, the axion starts to oscillate, and its energy density scales eventually as we show, as $\rho_a\sim a^{-3}$. After appropriately rewriting the gravitational equations in terms of the redshift $z$, we study in detail the late-time phenomenology of the model, and we compare the results with the $\Lambda$CDM model and the latest Planck 2018 data. As we show, the model for small redshifts $0<z<5$ is phenomenologically similar to the $\Lambda$CDM model, however at large redshifts and deeply in the matter domination era, the results are different from those of the $\Lambda$CDM model due to the dark energy oscillations. For the late-time study we investigate the behavior of several well-known statefinder quantities, like the deceleration parameter, the jerk and $Om(z)$, and we demonstrate that the statefinders which contain lower derivatives of the Hubble rate have similar behavior for both the $\Lambda$CDM and the axion $F(R)$ gravity model. |
1011.2779 | Gianluca Calcagni | Martin Bojowald, Gianluca Calcagni | Inflationary observables in loop quantum cosmology | 41 pages; v2: minor typos corrected, summary of results added | JCAP 1103:032,2011 | 10.1088/1475-7516/2011/03/032 | AEI-2010-161, IGC-10/11-1 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The full set of cosmological observables coming from linear scalar and tensor
perturbations of loop quantum cosmology is computed in the presence of
inverse-volume corrections. Background inflationary solutions are found at
linear order in the quantum corrections; depending on the values of
quantization parameters, they obey an exact or perturbed power-law expansion in
conformal time. The comoving curvature perturbation is shown to be conserved at
large scales, just as in the classical case. Its associated Mukhanov equation
is obtained and solved. Combined with the results for tensor modes, this yields
the scalar and tensor indices, their running, and the tensor-to-scalar ratio,
which are all first order in the quantum correction. The latter could be
sizable in phenomenological scenarios. Contrary to a pure minisuperspace
parametrization, the lattice refinement parametrization is in agreement with
both anomaly cancellation and our results on background solutions and linear
perturbations. The issue of the choice of parametrization is also discussed in
relation with a possible superluminal propagation of perturbative modes, and
conclusions for quantum spacetime structure are drawn.
| [
{
"created": "Thu, 11 Nov 2010 21:39:13 GMT",
"version": "v1"
},
{
"created": "Mon, 21 Mar 2011 15:24:23 GMT",
"version": "v2"
}
] | 2011-03-28 | [
[
"Bojowald",
"Martin",
""
],
[
"Calcagni",
"Gianluca",
""
]
] | The full set of cosmological observables coming from linear scalar and tensor perturbations of loop quantum cosmology is computed in the presence of inverse-volume corrections. Background inflationary solutions are found at linear order in the quantum corrections; depending on the values of quantization parameters, they obey an exact or perturbed power-law expansion in conformal time. The comoving curvature perturbation is shown to be conserved at large scales, just as in the classical case. Its associated Mukhanov equation is obtained and solved. Combined with the results for tensor modes, this yields the scalar and tensor indices, their running, and the tensor-to-scalar ratio, which are all first order in the quantum correction. The latter could be sizable in phenomenological scenarios. Contrary to a pure minisuperspace parametrization, the lattice refinement parametrization is in agreement with both anomaly cancellation and our results on background solutions and linear perturbations. The issue of the choice of parametrization is also discussed in relation with a possible superluminal propagation of perturbative modes, and conclusions for quantum spacetime structure are drawn. |
1811.00814 | Johannes Lumma | Astrid Eichhorn, Tim Koslowski, Johannes Lumma, Antonio D. Pereira | Towards background independent quantum gravity with tensor models | 23 pages plus appendix and references | Class. Quantum Grav. 36 155007 (2019) | 10.1088/1361-6382/ab2545 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We explore whether the phase diagram of tensor models could feature a
pregeometric, discrete and a geometric, continuum phase for the building blocks
of space. The latter are associated to rank $d$ tensors of size $N$. We search
for a universal large $N$ scaling limit in a rank-3 model with real tensors
that could be linked to a transition between the two phases. We extend the
conceptual development and practical implementation of the flow equation for
the pregeometric setting. This provides a pregeometric "coarse-graining" by
going from many microscopic to few effective degrees of freedom by lowering
$N$. We discover several candidates for fixed points of this coarse graining
procedure, and specifically explore the impact of a novel class of interactions
allowed in the real rank-3 model. In particular, we explain how most
universality classes feature dimensional reduction, while one candidate,
involving a tetrahedral interaction, might potentially be of relevance for
three-dimensional quantum gravity.
| [
{
"created": "Fri, 2 Nov 2018 10:54:48 GMT",
"version": "v1"
}
] | 2020-10-07 | [
[
"Eichhorn",
"Astrid",
""
],
[
"Koslowski",
"Tim",
""
],
[
"Lumma",
"Johannes",
""
],
[
"Pereira",
"Antonio D.",
""
]
] | We explore whether the phase diagram of tensor models could feature a pregeometric, discrete and a geometric, continuum phase for the building blocks of space. The latter are associated to rank $d$ tensors of size $N$. We search for a universal large $N$ scaling limit in a rank-3 model with real tensors that could be linked to a transition between the two phases. We extend the conceptual development and practical implementation of the flow equation for the pregeometric setting. This provides a pregeometric "coarse-graining" by going from many microscopic to few effective degrees of freedom by lowering $N$. We discover several candidates for fixed points of this coarse graining procedure, and specifically explore the impact of a novel class of interactions allowed in the real rank-3 model. In particular, we explain how most universality classes feature dimensional reduction, while one candidate, involving a tetrahedral interaction, might potentially be of relevance for three-dimensional quantum gravity. |
1311.0206 | Mariafelicia De Laurentis Dr. | Mariafelicia De Laurentis, Antonio Jesus Lopez-Revelles | Newtonian, Post Newtonian and Parameterized Post Newtonian limits of
f(R, G) gravity | 26 pages | International Journal of Geometric Methods in Modern Physics Vol.
11, No. 10, 1450082 (2014) | 10.1142/S0219887814500820 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss in detail the weak field limit of f(R,G) gravity taking into
account analytic functions of the Ricci scalar R and the Gauss-Bonnet invariant
G. Specifically, we develop, in metric formalism, the Newtonian, Post Newtonian
and Parameterized Post Newtonian limits starting from general f(R, G)
Lagrangian. The special cases of f(R) and f(G) gravities are considered. In the
case of the Newtonian limit of f(R, G) gravity, a general solution in terms of
Green's functions is achieved.
| [
{
"created": "Fri, 1 Nov 2013 15:20:57 GMT",
"version": "v1"
}
] | 2014-11-13 | [
[
"De Laurentis",
"Mariafelicia",
""
],
[
"Lopez-Revelles",
"Antonio Jesus",
""
]
] | We discuss in detail the weak field limit of f(R,G) gravity taking into account analytic functions of the Ricci scalar R and the Gauss-Bonnet invariant G. Specifically, we develop, in metric formalism, the Newtonian, Post Newtonian and Parameterized Post Newtonian limits starting from general f(R, G) Lagrangian. The special cases of f(R) and f(G) gravities are considered. In the case of the Newtonian limit of f(R, G) gravity, a general solution in terms of Green's functions is achieved. |
1112.1005 | Patrick Nash Dr. | Patrick L. Nash | Spinor-Unit Field Representation of Electromagnetism Applied to a Model
Inflationary Cosmology | replaced by "Possible consistent extra time dimensions in the early
universe," http://arxiv.org/abs/1310.0697 | General Relativity and Gravitation, 2012, DOI:
10.1007/s10714-012-1380-1 | 10.1007/s10714-012-1380-1 | null | gr-qc astro-ph.CO hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The new spinor-unit field representation of the electromagnetism
\cite{Nash2010} (with quark and lepton sources) is integrated via minimal
coupling with standard Einstein gravitation, to formulate a Lagrangian model of
the very early universe. The solution of the coupled Euler-Lagrange field
equations yields a scale factor $a(t)$ (comoving coordinates) that initially
exponentially increases $N$ e-folds from $a(0) \approx 0$ to $a_{1} = a(0)
{e}^{N} $ ($N$ = 60 is illustrated), then exponentially decreases, then
exponentially increases to $a_{1}$, and so on almost periodically. (Oscillatory
cosmological models are not knew, and have been derived from string theory and
loop quantum gravity.) It is not known if the scale factor escapes this
periodic trap.
This model is noteworthy in several respects: $\{1\}$ All fundamental fields
other than gravity are realized by spinor fields. $\{2\}$ A plausible
connection between the \emph{unit} field $\mathbf{u}$ and the generalization of
the photon wave function with a form of Dark Energy is described, and a simple
natural scenario is outlined that allocates a fraction of the total energy of
the Universe to this form of Dark Energy. $\{3\}$ A solution of an analog of
the pure Einstein-Maxwell equations is found. This approach is in contrast with
the method followed to obtain a solution of the well known Friedmann model of a
radiation-dominated universe.
| [
{
"created": "Mon, 5 Dec 2011 17:14:23 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Feb 2012 15:03:06 GMT",
"version": "v2"
},
{
"created": "Tue, 27 Mar 2012 12:27:41 GMT",
"version": "v3"
},
{
"created": "Tue, 14 Apr 2015 16:58:28 GMT",
"version": "v4"
}
] | 2015-04-15 | [
[
"Nash",
"Patrick L.",
""
]
] | The new spinor-unit field representation of the electromagnetism \cite{Nash2010} (with quark and lepton sources) is integrated via minimal coupling with standard Einstein gravitation, to formulate a Lagrangian model of the very early universe. The solution of the coupled Euler-Lagrange field equations yields a scale factor $a(t)$ (comoving coordinates) that initially exponentially increases $N$ e-folds from $a(0) \approx 0$ to $a_{1} = a(0) {e}^{N} $ ($N$ = 60 is illustrated), then exponentially decreases, then exponentially increases to $a_{1}$, and so on almost periodically. (Oscillatory cosmological models are not knew, and have been derived from string theory and loop quantum gravity.) It is not known if the scale factor escapes this periodic trap. This model is noteworthy in several respects: $\{1\}$ All fundamental fields other than gravity are realized by spinor fields. $\{2\}$ A plausible connection between the \emph{unit} field $\mathbf{u}$ and the generalization of the photon wave function with a form of Dark Energy is described, and a simple natural scenario is outlined that allocates a fraction of the total energy of the Universe to this form of Dark Energy. $\{3\}$ A solution of an analog of the pure Einstein-Maxwell equations is found. This approach is in contrast with the method followed to obtain a solution of the well known Friedmann model of a radiation-dominated universe. |
2003.02018 | Ebrahim Yusofi Ramneti | A. R. Ziyaee, M. Mohsenzadeh and E. Yusofi | A Covariant Approach for Particle Creation in Non-flat Background | 10 pages, 4 figures, Statements of introduction, abstract and results
were corrected | null | 10.1007/s10773-020-04649-0 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Krein approach is used to study the particle creation during quasi-de Sitter
inflation in different background space-times. In the conventional method for
calculating the created particles spectrum, the background space-time is
automatically considered flat. Selecting a flat background poses two
fundamental problems: First, the method of calculating is not covariant
relative to the curved space-time. Second, the number of created particles
becomes negative. Krein approach can be considered as a covariant method to
calculate two-point functions in curved space-time. So we extend this method
for particle creation during early cosmic inflation. As a new proposal, we
choose the background vacuum based on the smallest number of created particles
in that space-time. The calculations will show that in order to solve the above
mentioned problems, the background space-time must be non-flat and the number
of particles in the background must be minimum.
| [
{
"created": "Wed, 4 Mar 2020 11:53:17 GMT",
"version": "v1"
},
{
"created": "Tue, 17 Mar 2020 09:49:25 GMT",
"version": "v2"
}
] | 2020-12-02 | [
[
"Ziyaee",
"A. R.",
""
],
[
"Mohsenzadeh",
"M.",
""
],
[
"Yusofi",
"E.",
""
]
] | Krein approach is used to study the particle creation during quasi-de Sitter inflation in different background space-times. In the conventional method for calculating the created particles spectrum, the background space-time is automatically considered flat. Selecting a flat background poses two fundamental problems: First, the method of calculating is not covariant relative to the curved space-time. Second, the number of created particles becomes negative. Krein approach can be considered as a covariant method to calculate two-point functions in curved space-time. So we extend this method for particle creation during early cosmic inflation. As a new proposal, we choose the background vacuum based on the smallest number of created particles in that space-time. The calculations will show that in order to solve the above mentioned problems, the background space-time must be non-flat and the number of particles in the background must be minimum. |
gr-qc/9411031 | Steve Carlip | S. Carlip and J.E. Nelson | Comparative Quantizations of (2+1)-Dimensional Gravity | 24 pages, LaTeX, no figures | Phys.Rev.D51:5643-5653,1995 | 10.1103/PhysRevD.51.5643 | UCD-94-37 and DFTT/49/94 | gr-qc hep-th | null | We compare three approaches to the quantization of (2+1)-dimensional gravity
with a negative cosmological constant: reduced phase space quantization with
the York time slicing, quantization of the algebra of holonomies, and
quantization of the space of classical solutions. The relationships among these
quantum theories allow us to define and interpret time-dependent operators in
the ``frozen time'' holonomy formulation.
| [
{
"created": "Sat, 12 Nov 1994 02:18:41 GMT",
"version": "v1"
}
] | 2010-04-28 | [
[
"Carlip",
"S.",
""
],
[
"Nelson",
"J. E.",
""
]
] | We compare three approaches to the quantization of (2+1)-dimensional gravity with a negative cosmological constant: reduced phase space quantization with the York time slicing, quantization of the algebra of holonomies, and quantization of the space of classical solutions. The relationships among these quantum theories allow us to define and interpret time-dependent operators in the ``frozen time'' holonomy formulation. |
1308.3100 | Lydia Bieri | Lydia Bieri, David Garfinkle | Neutrino Radiation Showing a Christodoulou Memory Effect in General
Relativity | 35 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We describe neutrino radiation in general relativity by introducing the
energy-momentum tensor of a null fluid into the Einstein equations.
Investigating the geometry and analysis at null infinity, we prove that a
component of the null fluid enlarges the Christodoulou memory effect of
gravitational waves. The description of neutrinos in general relativity as a
null fluid can be regarded as a limiting case of a more general description
using the massless limit of the Einstein-Vlasov system. The present authors
with co-authors have work in progress to generalize the results of this paper
using this more general description. Gigantic neutrino bursts occur in our
universe in core-collapse supernovae and in the mergers of neutron star
binaries.
| [
{
"created": "Wed, 14 Aug 2013 12:17:32 GMT",
"version": "v1"
}
] | 2013-08-15 | [
[
"Bieri",
"Lydia",
""
],
[
"Garfinkle",
"David",
""
]
] | We describe neutrino radiation in general relativity by introducing the energy-momentum tensor of a null fluid into the Einstein equations. Investigating the geometry and analysis at null infinity, we prove that a component of the null fluid enlarges the Christodoulou memory effect of gravitational waves. The description of neutrinos in general relativity as a null fluid can be regarded as a limiting case of a more general description using the massless limit of the Einstein-Vlasov system. The present authors with co-authors have work in progress to generalize the results of this paper using this more general description. Gigantic neutrino bursts occur in our universe in core-collapse supernovae and in the mergers of neutron star binaries. |
gr-qc/0401032 | M. D. Maia | M. D. Maia | Brane-worlds and Cosmology | Essay in honor of Mario Novello, 8 pages, latex. Typo corrected | Inquiring the Universe. Frontiers Group, (2003) J.M. Salim,
S.P.Bergliaffa, L.A. Oliveira and V. De Lorenci (editors) | null | null | gr-qc | null | The Friedmann equation for a FRW-brane-world in a flat bulk is derived and
applied to the accelerated expansion of the universe.
| [
{
"created": "Fri, 9 Jan 2004 16:32:28 GMT",
"version": "v1"
},
{
"created": "Wed, 3 Mar 2004 15:39:41 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Maia",
"M. D.",
""
]
] | The Friedmann equation for a FRW-brane-world in a flat bulk is derived and applied to the accelerated expansion of the universe. |
1003.3102 | Hyeong-Chan Kim | Bogeun Gwak, Bum-Hoon Lee, Wonwoo Lee, and Hyeong-Chan Kim | Geodesic motions in extraordinary string geometry | 15 pages, 11 figures | null | 10.1007/s10714-011-1183-9 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The geodesic properties of the extraordinary vacuum string solution in (4+1)
dimensions are analyzed by using Hamilton-Jacobi method. The geodesic motions
show distinct properties from those of the static one. Especially, any freely
falling particle can not arrive at the horizon or singularity. There exist
stable null circular orbits and bouncing timelike and null geodesics. To get
into the horizon {or singularity}, a particle need to follow a non-geodesic
trajectory. We also analyze the orbit precession to show that the precession
angle has distinct features for each geometry such as naked singularity, black
string, and wormhole.
| [
{
"created": "Tue, 16 Mar 2010 08:39:35 GMT",
"version": "v1"
},
{
"created": "Mon, 31 May 2010 12:22:06 GMT",
"version": "v2"
}
] | 2015-05-18 | [
[
"Gwak",
"Bogeun",
""
],
[
"Lee",
"Bum-Hoon",
""
],
[
"Lee",
"Wonwoo",
""
],
[
"Kim",
"Hyeong-Chan",
""
]
] | The geodesic properties of the extraordinary vacuum string solution in (4+1) dimensions are analyzed by using Hamilton-Jacobi method. The geodesic motions show distinct properties from those of the static one. Especially, any freely falling particle can not arrive at the horizon or singularity. There exist stable null circular orbits and bouncing timelike and null geodesics. To get into the horizon {or singularity}, a particle need to follow a non-geodesic trajectory. We also analyze the orbit precession to show that the precession angle has distinct features for each geometry such as naked singularity, black string, and wormhole. |
gr-qc/9901056 | Luis Lehner | N.T. Bishop, R. Gomez, L. Lehner, M. Maharaj and J. Winicour | The incorporation of matter into characteristic numerical relativity | 15 pages + 4 (eps) figures | Phys.Rev.D60:024005,1999 | 10.1103/PhysRevD.60.024005 | null | gr-qc | null | A code that implements Einstein equations in the characteristic formulation
in 3D has been developed and thoroughly tested for the vacuum case. Here, we
describe how to incorporate matter, in the form of a perfect fluid, into the
code. The extended code has been written and validated in a number of cases. It
is stable and capable of contributing towards an understanding of a number of
problems in black hole astrophysics.
| [
{
"created": "Wed, 20 Jan 1999 22:46:37 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Bishop",
"N. T.",
""
],
[
"Gomez",
"R.",
""
],
[
"Lehner",
"L.",
""
],
[
"Maharaj",
"M.",
""
],
[
"Winicour",
"J.",
""
]
] | A code that implements Einstein equations in the characteristic formulation in 3D has been developed and thoroughly tested for the vacuum case. Here, we describe how to incorporate matter, in the form of a perfect fluid, into the code. The extended code has been written and validated in a number of cases. It is stable and capable of contributing towards an understanding of a number of problems in black hole astrophysics. |
1405.2402 | Sunil Maharaj | Y. Nyonyi, S. D. Maharaj, K. S. Govinder | Higher dimensional charged shear-free relativistic models with heat flux | 21 pages, submitted for publication | Eur. Phys. J. C 74, 2952 (2014) | 10.1140/epjc/s10052-014-2952-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyse shear-free spherically symmetric relativistic models of
gravitating fluids with heat flow and electric charge defined on higher
dimensional manifolds. The solution to the Einstein-Maxwell system is governed
by the pressure isotropy condition which depends on the spacetime dimension. We
study this highly nonlinear partial differential equation using Lie's group
theoretic approach. The Lie symmetry generators that leave the equation
invariant are determined. We provide exact solutions to the gravitational
potentials using the first symmetry admitted by the equation. Our new exact
solutions contain the earlier results for the four-dimensional case. Using the
other Lie generators, we are able to provide solutions to the gravitational
potentials or reduce the order of the master equation to a first order
nonlinear differential equation. We derive the temperature transport equation
in higher dimensions and find expressions for the causal and Eckart
temperatures showing their explicit dependance on the dimension. We analyse a
particular solution, obtained via group techniques, to show its physical
applicability.
| [
{
"created": "Sat, 10 May 2014 07:10:22 GMT",
"version": "v1"
}
] | 2015-06-19 | [
[
"Nyonyi",
"Y.",
""
],
[
"Maharaj",
"S. D.",
""
],
[
"Govinder",
"K. S.",
""
]
] | We analyse shear-free spherically symmetric relativistic models of gravitating fluids with heat flow and electric charge defined on higher dimensional manifolds. The solution to the Einstein-Maxwell system is governed by the pressure isotropy condition which depends on the spacetime dimension. We study this highly nonlinear partial differential equation using Lie's group theoretic approach. The Lie symmetry generators that leave the equation invariant are determined. We provide exact solutions to the gravitational potentials using the first symmetry admitted by the equation. Our new exact solutions contain the earlier results for the four-dimensional case. Using the other Lie generators, we are able to provide solutions to the gravitational potentials or reduce the order of the master equation to a first order nonlinear differential equation. We derive the temperature transport equation in higher dimensions and find expressions for the causal and Eckart temperatures showing their explicit dependance on the dimension. We analyse a particular solution, obtained via group techniques, to show its physical applicability. |
2310.10718 | Boris Goncharov | Boris Goncharov, Laura Donnay, Jan Harms | Inferring fundamental spacetime symmetries with gravitational-wave
memory: from LISA to the Einstein Telescope | 13 pages, 6 figures, 1 table | null | 10.1103/PhysRevLett.132.241401 | null | gr-qc astro-ph.CO | http://creativecommons.org/licenses/by/4.0/ | We revisit gravitational wave (GW) memory as the key to measuring spacetime
symmetries, extending beyond its traditional role in GW searches. In
particular, we show how these symmetries may be probed via displacement and
spin memory observations, respectively. We further find that the Einstein
Telescope's (ET) sensitivity enables constraining the strain amplitude of a
displacement memory to 2% and that of spin memory to 22%. Finally, we point out
that neglecting memory could lead to an overestimation of measurement
uncertainties for parameters of binary black hole (BBH) mergers by about 10% in
ET.
| [
{
"created": "Mon, 16 Oct 2023 18:00:01 GMT",
"version": "v1"
},
{
"created": "Thu, 9 May 2024 16:34:25 GMT",
"version": "v2"
}
] | 2024-06-17 | [
[
"Goncharov",
"Boris",
""
],
[
"Donnay",
"Laura",
""
],
[
"Harms",
"Jan",
""
]
] | We revisit gravitational wave (GW) memory as the key to measuring spacetime symmetries, extending beyond its traditional role in GW searches. In particular, we show how these symmetries may be probed via displacement and spin memory observations, respectively. We further find that the Einstein Telescope's (ET) sensitivity enables constraining the strain amplitude of a displacement memory to 2% and that of spin memory to 22%. Finally, we point out that neglecting memory could lead to an overestimation of measurement uncertainties for parameters of binary black hole (BBH) mergers by about 10% in ET. |
1912.03471 | Natalia Konobeeva | Natalia N. Konobeeva and Mikhail B. Belonenko | Zitterbewegung in the vicinity of the Chern-Simons black hole | 8 pages, 4 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider zitterbewegung (ZB) effect in four and five-dimensional space in
the vicinity of the Chern-Simons black hole with torsion. The metric is taken
in the traditional spherically symmetric form. We consider the equation for the
current in the framework of the Schr\"odinger representation. Dependences of
the electric current density on time is calculated for different dimension of
space. In particular, it is shown that, with an increase in the space
dimension, the effect of trembling motion qualitatively coincides. As the
dimension increases, the amplitude of this effect decreases. Also, we
investigate the dependence of the current on the radial coordinate for
different dimensions of space. We obtain that when away from the event horizon
the current ZB increases.
| [
{
"created": "Sat, 7 Dec 2019 09:14:51 GMT",
"version": "v1"
}
] | 2019-12-10 | [
[
"Konobeeva",
"Natalia N.",
""
],
[
"Belonenko",
"Mikhail B.",
""
]
] | We consider zitterbewegung (ZB) effect in four and five-dimensional space in the vicinity of the Chern-Simons black hole with torsion. The metric is taken in the traditional spherically symmetric form. We consider the equation for the current in the framework of the Schr\"odinger representation. Dependences of the electric current density on time is calculated for different dimension of space. In particular, it is shown that, with an increase in the space dimension, the effect of trembling motion qualitatively coincides. As the dimension increases, the amplitude of this effect decreases. Also, we investigate the dependence of the current on the radial coordinate for different dimensions of space. We obtain that when away from the event horizon the current ZB increases. |
1610.01453 | Vasilis Oikonomou | V.K. Oikonomou, Supriya Pan, Rafael C. Nunes | Gravitational Baryogenesis in Running Vacuum models | 9 pages, IJMPA Accepted | null | 10.1142/S0217751X17501299 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the gravitational baryogenesis mechanism for generating baryon
asymmetry in the context of running vacuum models. Regardless if these models
can produce a viable cosmological evolution, we demonstrate that they produce a
non-zero baryon-to-entropy ratio even if the universe is filled with conformal
matter. This is a sound difference between the running vacuum gravitational
baryogenesis and the Einstein-Hilbert one, since in the latter case, the
predicted baryon-to-entropy ratio is zero. We consider two well known and most
used running vacuum models and show that the resulting baryon-to-entropy ratio
is compatible with the observational data. Moreover, we also show that the
mechanism of gravitational baryogenesis may constrain the running vacuum
models.
| [
{
"created": "Wed, 5 Oct 2016 14:41:22 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Jul 2017 22:45:57 GMT",
"version": "v2"
}
] | 2017-09-06 | [
[
"Oikonomou",
"V. K.",
""
],
[
"Pan",
"Supriya",
""
],
[
"Nunes",
"Rafael C.",
""
]
] | We study the gravitational baryogenesis mechanism for generating baryon asymmetry in the context of running vacuum models. Regardless if these models can produce a viable cosmological evolution, we demonstrate that they produce a non-zero baryon-to-entropy ratio even if the universe is filled with conformal matter. This is a sound difference between the running vacuum gravitational baryogenesis and the Einstein-Hilbert one, since in the latter case, the predicted baryon-to-entropy ratio is zero. We consider two well known and most used running vacuum models and show that the resulting baryon-to-entropy ratio is compatible with the observational data. Moreover, we also show that the mechanism of gravitational baryogenesis may constrain the running vacuum models. |
2009.06518 | Krzysztof Andrzejewski | K. Andrzejewski, P. Kosinski | Global propagation of massive quantum fields in the plane gravitational
waves and electromagnetic backgrounds | 29 pages, version accepted for publication in CQG (title modified and
some explanations added) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The behavior of massive quantum fields in the general plane wave spacetime
and external, non-plane, electromagnetic waves is studied. The asymptotic
conditions, the "in" ("out") states and the cross sections are analysed. It is
observed that, despite of the singularities encountered, the global form of
these states can be obtained: at the singular points the Dirac delta-like
behavior emerges and there is a discrete change of phase of the wave function
after passing through each singular point. The relations between these phase
corrections and local charts are discussed. Some examples of waves of infinite
range (including the circularly polarized ones) are presented for which the
explicit form of solutions can be obtained. All these results concern both the
scalar as well as spin one-half fields; in the latter case the change of the
spin polarization after the general sandwich wave has passed is studied.
| [
{
"created": "Mon, 14 Sep 2020 15:27:10 GMT",
"version": "v1"
},
{
"created": "Wed, 19 May 2021 14:56:14 GMT",
"version": "v2"
},
{
"created": "Thu, 16 Dec 2021 14:30:58 GMT",
"version": "v3"
}
] | 2021-12-17 | [
[
"Andrzejewski",
"K.",
""
],
[
"Kosinski",
"P.",
""
]
] | The behavior of massive quantum fields in the general plane wave spacetime and external, non-plane, electromagnetic waves is studied. The asymptotic conditions, the "in" ("out") states and the cross sections are analysed. It is observed that, despite of the singularities encountered, the global form of these states can be obtained: at the singular points the Dirac delta-like behavior emerges and there is a discrete change of phase of the wave function after passing through each singular point. The relations between these phase corrections and local charts are discussed. Some examples of waves of infinite range (including the circularly polarized ones) are presented for which the explicit form of solutions can be obtained. All these results concern both the scalar as well as spin one-half fields; in the latter case the change of the spin polarization after the general sandwich wave has passed is studied. |
1003.5352 | Tao Mei | T. Mei | General Relativity as a fully singular Lagrange system | 25 pages, no figure | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present some gauge conditions to eliminate all second time derivative
terms in the vierbein forms of the ten Einstein equations of general
relativity; at the same time, we present the corresponding Lagrangian in which
there is not any quadratic term of first time derivative that can leads to
those vierbein forms of the Einstein equations without second time derivative
term by the corresponding Euler-Lagrange equations. General relativity thus
becomes a fully singular Lagrange system.
| [
{
"created": "Sun, 28 Mar 2010 08:51:11 GMT",
"version": "v1"
},
{
"created": "Wed, 27 Oct 2010 01:59:54 GMT",
"version": "v2"
}
] | 2010-10-28 | [
[
"Mei",
"T.",
""
]
] | We present some gauge conditions to eliminate all second time derivative terms in the vierbein forms of the ten Einstein equations of general relativity; at the same time, we present the corresponding Lagrangian in which there is not any quadratic term of first time derivative that can leads to those vierbein forms of the Einstein equations without second time derivative term by the corresponding Euler-Lagrange equations. General relativity thus becomes a fully singular Lagrange system. |
1504.04108 | Sanjay Jhingan | Remya Nair, Sanjay Jhingan, Takahiro Tanaka | Synergy between ground and space based gravitational wave detectors for
estimation of binary coalescence parameters | 12 pages, 9 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the advantage of the co-existence of future ground and space based
gravitational wave detectors, in estimating the parameters of a binary
coalescence. Using the post-Newtonian waveform for the inspiral of non-spinning
neutron star-black hole pairs in circular orbits, we study how the estimates
for chirp mass, symmetric mass ratio, and time and phase at coalescence are
improved by combining the data from different space-ground detector pairs.
Since the gravitational waves produced by binary coalescence also provide a
suitable domain where we can study strong field gravity, we also study the
deviations from general relativity using the parameterized post-Einsteinian
framework. As an example, focusing on the Einstein telescope and DECIGO pair,
we demonstrate that there exists a sweet spot range of sensitivity in the
pre-DECIGO phase where the best enhancement due to the synergy effect can be
obtained for the estimates of the post-Newtonian waveform parameters as well as
the modification parameters to general relativity.
| [
{
"created": "Thu, 16 Apr 2015 06:58:21 GMT",
"version": "v1"
}
] | 2015-04-17 | [
[
"Nair",
"Remya",
""
],
[
"Jhingan",
"Sanjay",
""
],
[
"Tanaka",
"Takahiro",
""
]
] | We study the advantage of the co-existence of future ground and space based gravitational wave detectors, in estimating the parameters of a binary coalescence. Using the post-Newtonian waveform for the inspiral of non-spinning neutron star-black hole pairs in circular orbits, we study how the estimates for chirp mass, symmetric mass ratio, and time and phase at coalescence are improved by combining the data from different space-ground detector pairs. Since the gravitational waves produced by binary coalescence also provide a suitable domain where we can study strong field gravity, we also study the deviations from general relativity using the parameterized post-Einsteinian framework. As an example, focusing on the Einstein telescope and DECIGO pair, we demonstrate that there exists a sweet spot range of sensitivity in the pre-DECIGO phase where the best enhancement due to the synergy effect can be obtained for the estimates of the post-Newtonian waveform parameters as well as the modification parameters to general relativity. |
2406.01498 | Benito A. Ju\'arez-Aubry | Benito A. Ju\'arez-Aubry, Bernard S. Kay, Tonatiuh Miramontes and
Daniel Sudarsky | The Hadamard condition on a Cauchy surface and the renormalized
stress-energy tensor | 64 pages | null | null | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Given a Cauchy surface in a curved spacetime and a suitably defined quantum
state on the CCR algebra of the Klein Gordon quantum field on that surface, we
show, by expanding the squared spacetime geodesic distance and the '$U$' and
'$V$' Hadamard coefficients (and suitable derivatives thereof) in sufficiently
accurate covariant Taylor expansions on the surface that the renormalized
expectation value of the quantum stress-energy tensor on the surface is
determined by the geometry of the surface and the first 4 time derivatives of
the metric off the surface, in addition to the Cauchy data for the field's
two-point function. This result has been anticipated in and is motivated by a
previous investigation by the authors on the initial value problem in
semiclassical gravity, for which the geometric initial data corresponds {\it a
priori} to the metric on the surface and up to 3 time derivatives off the
surface, but where it was argued that the fourth derivative can be obtained
with aid of the field equations on the initial surface.
| [
{
"created": "Mon, 3 Jun 2024 16:24:35 GMT",
"version": "v1"
}
] | 2024-06-04 | [
[
"Juárez-Aubry",
"Benito A.",
""
],
[
"Kay",
"Bernard S.",
""
],
[
"Miramontes",
"Tonatiuh",
""
],
[
"Sudarsky",
"Daniel",
""
]
] | Given a Cauchy surface in a curved spacetime and a suitably defined quantum state on the CCR algebra of the Klein Gordon quantum field on that surface, we show, by expanding the squared spacetime geodesic distance and the '$U$' and '$V$' Hadamard coefficients (and suitable derivatives thereof) in sufficiently accurate covariant Taylor expansions on the surface that the renormalized expectation value of the quantum stress-energy tensor on the surface is determined by the geometry of the surface and the first 4 time derivatives of the metric off the surface, in addition to the Cauchy data for the field's two-point function. This result has been anticipated in and is motivated by a previous investigation by the authors on the initial value problem in semiclassical gravity, for which the geometric initial data corresponds {\it a priori} to the metric on the surface and up to 3 time derivatives off the surface, but where it was argued that the fourth derivative can be obtained with aid of the field equations on the initial surface. |
1605.06140 | Monica Forte | M\'onica Forte | Holographik, the k-essential approach to interactive models with
modified holographic Ricci dark energy | 16 pages, 6 figures, minor revision, references added | null | 10.1140/epjc/s10052-016-4572-0 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We make a scalar representation of interactive models with cold dark matter
and modified holographic Ricci dark energy through unified models driven by
scalar fields with non-canonical kinetic term. These models are applications of
the formalism of exotic k-essences generated by the global description of
cosmological models with two interactive fluids in the dark sector and in these
cases they correspond to usual k-essences. The formalism is applied to the
cases of constant potential in Friedmann-Robertson-Walker geometries.
| [
{
"created": "Thu, 19 May 2016 20:55:44 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Nov 2016 15:36:32 GMT",
"version": "v2"
}
] | 2017-02-01 | [
[
"Forte",
"Mónica",
""
]
] | We make a scalar representation of interactive models with cold dark matter and modified holographic Ricci dark energy through unified models driven by scalar fields with non-canonical kinetic term. These models are applications of the formalism of exotic k-essences generated by the global description of cosmological models with two interactive fluids in the dark sector and in these cases they correspond to usual k-essences. The formalism is applied to the cases of constant potential in Friedmann-Robertson-Walker geometries. |
1204.2468 | Chen Songbai | Songbai Chen, Jiliang Jing | Strong gravitational lensing by a rotating non-Kerr compact object | 16 pages, 10 figures. The corrected version to be appeared in Phys.
Rev. D | Phys. Rev. D 85, 124029 (2012) | 10.1103/PhysRevD.85.124029 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the strong gravitational lensing in the background of a rotating
non-Kerr compact object with a deformed parameter $\epsilon$ and an unbound
rotation parameter $a$. We find that the photon sphere radius and the
deflection angle depend sharply on the parameters $\epsilon$ and $a$. For the
case in which the black hole is more prolate than a Kerr black hole, the photon
sphere exists only in the regime $\epsilon\leq\epsilon_{max}$ for prograde
photon. The upper limit $\epsilon_{max}$ is a function of the rotation
parameter $a$. As $\epsilon>\epsilon_{max}$, the deflection angle of the light
ray closing very to the naked singularity is a positive finite value, which is
different from those in both the usual Kerr black hole spacetime and in the
rotating naked singularity described by Janis-Newman-Winicour metric. For the
oblate black hole and the retrograde photon, there does not exist such a
threshold value. Modelling the supermassive central object of the Galaxy as a
rotating non-Kerr compact object, we estimated the numerical values of the
coefficients and observables for gravitational lensing in the strong field
limit.
| [
{
"created": "Wed, 11 Apr 2012 14:54:44 GMT",
"version": "v1"
},
{
"created": "Tue, 12 Jun 2012 15:29:58 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Chen",
"Songbai",
""
],
[
"Jing",
"Jiliang",
""
]
] | We study the strong gravitational lensing in the background of a rotating non-Kerr compact object with a deformed parameter $\epsilon$ and an unbound rotation parameter $a$. We find that the photon sphere radius and the deflection angle depend sharply on the parameters $\epsilon$ and $a$. For the case in which the black hole is more prolate than a Kerr black hole, the photon sphere exists only in the regime $\epsilon\leq\epsilon_{max}$ for prograde photon. The upper limit $\epsilon_{max}$ is a function of the rotation parameter $a$. As $\epsilon>\epsilon_{max}$, the deflection angle of the light ray closing very to the naked singularity is a positive finite value, which is different from those in both the usual Kerr black hole spacetime and in the rotating naked singularity described by Janis-Newman-Winicour metric. For the oblate black hole and the retrograde photon, there does not exist such a threshold value. Modelling the supermassive central object of the Galaxy as a rotating non-Kerr compact object, we estimated the numerical values of the coefficients and observables for gravitational lensing in the strong field limit. |
2205.10719 | Robert van den Hoogen | A. A. Coley and R. J. van den Hoogen and D. D. McNutt | Symmetric Teleparallel Geometries | 15 pages | Class. Quantum Grav., 39, 22LT01 (2022) | 10.1088/1361-6382/ac994a | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In teleparallel gravity and, in particular, in $F(T)$ teleparallel gravity,
there is a challenge in determining an appropriate (co-)frame and its
corresponding spin connection to describe the geometry. Very often, the
"proper" frame, the frame in which all inertial effects are absent, is not the
simplest (e.g, diagonal) (co-)frame. The determination of the frame and its
corresponding spin connection for $F(T)$ teleparallel gravity theories when
there exist affine symmetries is of much interest. In this paper we present the
general form of the coframe and its corresponding spin connection for
teleparallel geometries which are invariant under a $G_6$ group of affine
symmetries. The proper coframe and the corresponding $F(T)$ field equations are
also shown for these Teleparallel Robertson Walker (TRW) geometries. Further,
with the addition of an additional affine symmetry, it is possible to define a
Teleparallel de Sitter (TdS) geometry.
| [
{
"created": "Sun, 22 May 2022 03:08:15 GMT",
"version": "v1"
},
{
"created": "Sun, 5 Jun 2022 11:41:42 GMT",
"version": "v2"
},
{
"created": "Tue, 23 Aug 2022 11:17:27 GMT",
"version": "v3"
}
] | 2022-11-17 | [
[
"Coley",
"A. A.",
""
],
[
"Hoogen",
"R. J. van den",
""
],
[
"McNutt",
"D. D.",
""
]
] | In teleparallel gravity and, in particular, in $F(T)$ teleparallel gravity, there is a challenge in determining an appropriate (co-)frame and its corresponding spin connection to describe the geometry. Very often, the "proper" frame, the frame in which all inertial effects are absent, is not the simplest (e.g, diagonal) (co-)frame. The determination of the frame and its corresponding spin connection for $F(T)$ teleparallel gravity theories when there exist affine symmetries is of much interest. In this paper we present the general form of the coframe and its corresponding spin connection for teleparallel geometries which are invariant under a $G_6$ group of affine symmetries. The proper coframe and the corresponding $F(T)$ field equations are also shown for these Teleparallel Robertson Walker (TRW) geometries. Further, with the addition of an additional affine symmetry, it is possible to define a Teleparallel de Sitter (TdS) geometry. |
1212.1755 | Henrique de Andrade Gomes | Henrique Gomes | Poincar\'e invariance and asymptotic flatness in Shape Dynamics | 22 pages, matches accepted version | Phys. Rev. D 88, 024047 (2013) | 10.1103/PhysRevD.88.024047 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Shape Dynamics is a theory of gravity that waives refoliation invariance in
favor of spatial Weyl invariance. It is a canonical theory, constructed from a
Hamiltonian, 3+1 perspective. One of the main deficits of Shape Dynamics is
that its Hamiltonian is only implicitly constructed as a functional of the
phase space variables. In this paper, I write down the equations of motion for
Shape Dynamics to show that over a curve in phase space representing a
Minkowski spacetime, Shape Dynamics possesses Poincar\'e symmetry for
appropriate boundary conditions. The proper treatment of such boundary
conditions leads us to completely formulate Shape Dynamics for open manifolds
in the asymptotically flat case. We study the charges arising in this case and
find a new definition of total energy, which is completely invariant under
spatial Weyl transformations close to the boundary. We then use the equations
of motion once again to find a non-trivial solution of Shape Dynamics,
consisting of a flat static Universe with a point-like mass at the center. We
calculate its energy through the new formula and rederive the usual
Schwarzschild mass.
| [
{
"created": "Sat, 8 Dec 2012 03:03:04 GMT",
"version": "v1"
},
{
"created": "Wed, 31 Jul 2013 02:51:52 GMT",
"version": "v2"
}
] | 2015-06-12 | [
[
"Gomes",
"Henrique",
""
]
] | Shape Dynamics is a theory of gravity that waives refoliation invariance in favor of spatial Weyl invariance. It is a canonical theory, constructed from a Hamiltonian, 3+1 perspective. One of the main deficits of Shape Dynamics is that its Hamiltonian is only implicitly constructed as a functional of the phase space variables. In this paper, I write down the equations of motion for Shape Dynamics to show that over a curve in phase space representing a Minkowski spacetime, Shape Dynamics possesses Poincar\'e symmetry for appropriate boundary conditions. The proper treatment of such boundary conditions leads us to completely formulate Shape Dynamics for open manifolds in the asymptotically flat case. We study the charges arising in this case and find a new definition of total energy, which is completely invariant under spatial Weyl transformations close to the boundary. We then use the equations of motion once again to find a non-trivial solution of Shape Dynamics, consisting of a flat static Universe with a point-like mass at the center. We calculate its energy through the new formula and rederive the usual Schwarzschild mass. |
gr-qc/0406072 | Niklas Rohr | J. Mark Heinzle, N. Rohr, C. Uggla | Matter and dynamics in closed cosmologies | 23 pages, 24 figures (compressed), LaTeX | Phys.Rev. D71 (2005) 083506 | 10.1103/PhysRevD.71.083506 | null | gr-qc | null | To systematically analyze the dynamical implications of the matter content in
cosmology, we generalize earlier dynamical systems approaches so that perfect
fluids with a general barotropic equation of state can be treated. We focus on
locally rotationally symmetric Bianchi type IX and Kantowski-Sachs orthogonal
perfect fluid models, since such models exhibit a particularly rich dynamical
structure and also illustrate typical features of more general cases. For these
models, we recast Einstein's field equations into a regular system on a compact
state space, which is the basis for our analysis. We prove that models expand
from a singularity and recollapse to a singularity when the perfect fluid
satisfies the strong energy condition. When the matter source admits Einstein's
static model, we present a comprehensive dynamical description, which includes
asymptotic behavior, of models in the neighborhood of the Einstein model; these
results make earlier claims about ``homoclinic phenomena and chaos'' highly
questionable. We also discuss aspects of the global asymptotic dynamics, in
particular, we give criteria for the collapse to a singularity, and we describe
when models expand forever to a state of infinite dilution; possible initial
and final states are analyzed. Numerical investigations complement the
analytical results.
| [
{
"created": "Fri, 18 Jun 2004 13:52:53 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Heinzle",
"J. Mark",
""
],
[
"Rohr",
"N.",
""
],
[
"Uggla",
"C.",
""
]
] | To systematically analyze the dynamical implications of the matter content in cosmology, we generalize earlier dynamical systems approaches so that perfect fluids with a general barotropic equation of state can be treated. We focus on locally rotationally symmetric Bianchi type IX and Kantowski-Sachs orthogonal perfect fluid models, since such models exhibit a particularly rich dynamical structure and also illustrate typical features of more general cases. For these models, we recast Einstein's field equations into a regular system on a compact state space, which is the basis for our analysis. We prove that models expand from a singularity and recollapse to a singularity when the perfect fluid satisfies the strong energy condition. When the matter source admits Einstein's static model, we present a comprehensive dynamical description, which includes asymptotic behavior, of models in the neighborhood of the Einstein model; these results make earlier claims about ``homoclinic phenomena and chaos'' highly questionable. We also discuss aspects of the global asymptotic dynamics, in particular, we give criteria for the collapse to a singularity, and we describe when models expand forever to a state of infinite dilution; possible initial and final states are analyzed. Numerical investigations complement the analytical results. |
gr-qc/9607023 | Roland Puntigam | Roland A. Puntigam, Claus L\"ammerzahl, Friedrich W. Hehl (Theoretical
Physics, University of Cologne, Germany) | Maxwell's theory on a post-Riemannian spacetime and the equivalence
principle | 9 pages, REVTeX, no figures; minor changes, version to be published
in Class. Quantum Grav | Class.Quant.Grav. 14 (1997) 1347-1356 | 10.1088/0264-9381/14/5/033 | Cologne-thp-1996-H15 | gr-qc | null | The form of Maxwell's theory is well known in the framework of general
relativity, a fact that is related to the applicability of the principle of
equivalence to electromagnetic phenomena. We pose the question whether this
form changes if torsion and/or nonmetricity fields are allowed for in
spacetime. Starting from the conservation laws of electric charge and magnetic
flux, we recognize that the Maxwell equations themselves remain the same, but
the constitutive law must depend on the metric and, additionally, may depend on
quantities related to torsion and/or nonmetricity. We illustrate our results by
putting an electric charge on top of a spherically symmetric exact solution of
the metric-affine gauge theory of gravity (comprising torsion and
nonmetricity). All this is compared to the recent results of Vandyck.
| [
{
"created": "Wed, 10 Jul 1996 10:25:22 GMT",
"version": "v1"
},
{
"created": "Sun, 22 Sep 1996 09:11:12 GMT",
"version": "v2"
},
{
"created": "Wed, 12 Feb 1997 14:53:44 GMT",
"version": "v3"
}
] | 2016-08-15 | [
[
"Puntigam",
"Roland A.",
"",
"Theoretical\n Physics, University of Cologne, Germany"
],
[
"Lämmerzahl",
"Claus",
"",
"Theoretical\n Physics, University of Cologne, Germany"
],
[
"Hehl",
"Friedrich W.",
"",
"Theoretical\n Physics, University of Cologne, Ge... | The form of Maxwell's theory is well known in the framework of general relativity, a fact that is related to the applicability of the principle of equivalence to electromagnetic phenomena. We pose the question whether this form changes if torsion and/or nonmetricity fields are allowed for in spacetime. Starting from the conservation laws of electric charge and magnetic flux, we recognize that the Maxwell equations themselves remain the same, but the constitutive law must depend on the metric and, additionally, may depend on quantities related to torsion and/or nonmetricity. We illustrate our results by putting an electric charge on top of a spherically symmetric exact solution of the metric-affine gauge theory of gravity (comprising torsion and nonmetricity). All this is compared to the recent results of Vandyck. |
1408.5260 | Andrea Geralico | Donato Bini, Andrea Geralico, Maria Haney, Robert T. Jantzen | Scattering of particles by radiation fields: a comparative analysis | 13 pages, 1 figure; published version | Phys. Rev. D 86, 064016 (2012) | 10.1103/PhysRevD.86.064016 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The features of the scattering of massive neutral particles propagating in
the field of a gravitational plane wave are compared with those characterizing
their interaction with an electromagnetic radiation field. The motion is
geodesic in the former case, whereas in the case of an electromagnetic pulse it
is accelerated by the radiation field filling the associated spacetime region.
The interaction with the radiation field is modeled by a force term entering
the equations of motion proportional to the 4-momentum density of radiation
observed in the particle's rest frame. The corresponding classical scattering
cross sections are evaluated too.
| [
{
"created": "Fri, 22 Aug 2014 10:53:45 GMT",
"version": "v1"
}
] | 2015-06-22 | [
[
"Bini",
"Donato",
""
],
[
"Geralico",
"Andrea",
""
],
[
"Haney",
"Maria",
""
],
[
"Jantzen",
"Robert T.",
""
]
] | The features of the scattering of massive neutral particles propagating in the field of a gravitational plane wave are compared with those characterizing their interaction with an electromagnetic radiation field. The motion is geodesic in the former case, whereas in the case of an electromagnetic pulse it is accelerated by the radiation field filling the associated spacetime region. The interaction with the radiation field is modeled by a force term entering the equations of motion proportional to the 4-momentum density of radiation observed in the particle's rest frame. The corresponding classical scattering cross sections are evaluated too. |
gr-qc/0309079 | Carlos Molina Mendes | C. Molina, D. Giugno, E. Abdalla and A. Saa | Field propagation in de Sitter black holes | 15 pages, 16 figures, published version | Phys.Rev. D69 (2004) 104013 | 10.1103/PhysRevD.69.104013 | null | gr-qc astro-ph hep-th | null | We present an exhaustive analysis of scalar, electromagnetic and
gravitational perturbations in the background of Schwarzchild-de Sitter and
Reissner-Nordstrom-de Sitter spacetimes. The field propagation is considered by
means of a semi-analytical (WKB) approach and two numerical schemes: the
characteristic and general initial value integrations. The results are compared
near the extreme cosmological constant regime, where analytical results are
presented. A unifying picture is established for the dynamics of different spin
fields.
| [
{
"created": "Wed, 17 Sep 2003 18:11:41 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Feb 2004 01:40:31 GMT",
"version": "v2"
},
{
"created": "Sun, 9 Apr 2006 00:24:41 GMT",
"version": "v3"
}
] | 2009-11-10 | [
[
"Molina",
"C.",
""
],
[
"Giugno",
"D.",
""
],
[
"Abdalla",
"E.",
""
],
[
"Saa",
"A.",
""
]
] | We present an exhaustive analysis of scalar, electromagnetic and gravitational perturbations in the background of Schwarzchild-de Sitter and Reissner-Nordstrom-de Sitter spacetimes. The field propagation is considered by means of a semi-analytical (WKB) approach and two numerical schemes: the characteristic and general initial value integrations. The results are compared near the extreme cosmological constant regime, where analytical results are presented. A unifying picture is established for the dynamics of different spin fields. |
1805.04987 | Ednilton S. de Oliveira Ph.D. | Ednilton S. de Oliveira | Scalar scattering from black holes with tidal charge | null | Eur. Phys. J. C (2018) 78:876 | 10.1140/epjc/s10052-018-6316-9 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The cross sections of black holes with tidal charge predicted in the context
of the Randall--Sundrum brane-world scenario are computed considering the
massless scalar field. Results obtained for black holes with different
tidal-charge intensities are compared in order to study how this charge
modifies the black hole cross sections. Such results are also compared with the
ones for Schwarzschild and extreme Reissner--Nordstr\"om black holes. The
increase of the tidal-charge intensity makes the black hole absorb more and can
also be measured by the narrowing of interference fringes of the differential
scattering cross section. These results indicate that the effects of the tidal
charge are very important in phenomena which take place near the black hole,
but can be neglected in the far region. Analytical results are obtained in the
high-frequency limit and are shown to excellently agree with the numeric
results obtained via the partial-wave method. It is shown numerically that
black holes with tidal charge obey the universality of the low-frequency
absorption cross section of stationary black holes for the massless scalar
field.
| [
{
"created": "Mon, 14 May 2018 02:16:27 GMT",
"version": "v1"
},
{
"created": "Mon, 28 May 2018 21:06:20 GMT",
"version": "v2"
}
] | 2018-11-06 | [
[
"de Oliveira",
"Ednilton S.",
""
]
] | The cross sections of black holes with tidal charge predicted in the context of the Randall--Sundrum brane-world scenario are computed considering the massless scalar field. Results obtained for black holes with different tidal-charge intensities are compared in order to study how this charge modifies the black hole cross sections. Such results are also compared with the ones for Schwarzschild and extreme Reissner--Nordstr\"om black holes. The increase of the tidal-charge intensity makes the black hole absorb more and can also be measured by the narrowing of interference fringes of the differential scattering cross section. These results indicate that the effects of the tidal charge are very important in phenomena which take place near the black hole, but can be neglected in the far region. Analytical results are obtained in the high-frequency limit and are shown to excellently agree with the numeric results obtained via the partial-wave method. It is shown numerically that black holes with tidal charge obey the universality of the low-frequency absorption cross section of stationary black holes for the massless scalar field. |
1907.08682 | Pardyumn Kumar Sahoo | Parbati Sahoo, S. Bhattacharjee, S. K. Tripathy, P.K. Sahoo | Bouncing scenario in $f(R,T)$ gravity | Accepted version at MPLA | Modern Physics Letters A, 35 (2020) 2050095 | 10.1142/S0217732320500959 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The present manuscript presents modeling of matter bounce in the framework of
$f(R,T)$ gravity where $f(R,T) = R + 2 \lambda T$. We start by defining a
parametrization of scale factor which is non-vanishing. The geometrical
parameters such as the Hubble parameter and deceleration parameter are derived,
from which expressions of pressure, density and Equation of State (EoS)
parameter and a qualitative understanding of the initial conditions of the
universe at the bounce are ascertained. We found that the initial conditions of
the universe are finite owing to the non-vanishing nature of the scale factor
thus eliminates the initial singularity problem. Furthermore, we show the
violation of energy conditions near the bouncing region and analyzed the
stability of our model with respect to linear homogeneous perturbations in
Friedmann-Lema\^tre-Robertson-Walker (FLRW) spacetime. We found that our model
and hence matter bounce scenarios in general are highly unstable at the bounce
in the framework of $f(R,T)$ gravity but the perturbations decay out rapidly
away from the bounce safeguarding its stability at late times.
| [
{
"created": "Thu, 18 Jul 2019 11:20:03 GMT",
"version": "v1"
},
{
"created": "Tue, 22 Oct 2019 04:42:45 GMT",
"version": "v2"
},
{
"created": "Tue, 28 Jan 2020 03:57:25 GMT",
"version": "v3"
}
] | 2020-02-04 | [
[
"Sahoo",
"Parbati",
""
],
[
"Bhattacharjee",
"S.",
""
],
[
"Tripathy",
"S. K.",
""
],
[
"Sahoo",
"P. K.",
""
]
] | The present manuscript presents modeling of matter bounce in the framework of $f(R,T)$ gravity where $f(R,T) = R + 2 \lambda T$. We start by defining a parametrization of scale factor which is non-vanishing. The geometrical parameters such as the Hubble parameter and deceleration parameter are derived, from which expressions of pressure, density and Equation of State (EoS) parameter and a qualitative understanding of the initial conditions of the universe at the bounce are ascertained. We found that the initial conditions of the universe are finite owing to the non-vanishing nature of the scale factor thus eliminates the initial singularity problem. Furthermore, we show the violation of energy conditions near the bouncing region and analyzed the stability of our model with respect to linear homogeneous perturbations in Friedmann-Lema\^tre-Robertson-Walker (FLRW) spacetime. We found that our model and hence matter bounce scenarios in general are highly unstable at the bounce in the framework of $f(R,T)$ gravity but the perturbations decay out rapidly away from the bounce safeguarding its stability at late times. |
gr-qc/0407060 | Alexander Poltorak | Alexander Poltorak | Gravity as Nonmetricity: General Relativity in Metric-Affine Space
(Ln,g) | 15 pages. LaTeX. Was presented at the 17th International Conference
on General Relativity and Gravitation (GR17), Dublin 2004. Typos corrected | null | null | null | gr-qc | null | A new geometric interpretation for General Relativity (GR) is proposed. We
show that in the presence of an arbitrary affine connection, the gravitational
field is described as nonmetricity of the affine connection. An affine
connection can be interpreted as induced by a frame of reference (FR). Although
the gravitational field equations are identical to Einstein's equations of GR,
this formulation leads to a covariant tensor (instead of the pseudotensor) of
energy-momentum of the gravitational field and covariant conservation laws. We
further develop a geometric representation of FR as a metric-affine space, with
transition between FR represented as affine deformation of the connection.
Geodesic and autoparallel worldlines are considered. We show that the affine
connection of a NIFR has curvature and may have torsion. We calculate the
curvature for the uniformly accelerated FR. Finally, we show that GR is
inadequate to describe the gravitational field in a NIFR. We propose a
generalization of GR, which describes gravity as nonmetricity of the affine
connection induced in a FR. This generalization contains GR as a special case
of the inertial FR.
| [
{
"created": "Thu, 15 Jul 2004 22:32:38 GMT",
"version": "v1"
},
{
"created": "Fri, 30 Jul 2004 20:00:16 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Poltorak",
"Alexander",
""
]
] | A new geometric interpretation for General Relativity (GR) is proposed. We show that in the presence of an arbitrary affine connection, the gravitational field is described as nonmetricity of the affine connection. An affine connection can be interpreted as induced by a frame of reference (FR). Although the gravitational field equations are identical to Einstein's equations of GR, this formulation leads to a covariant tensor (instead of the pseudotensor) of energy-momentum of the gravitational field and covariant conservation laws. We further develop a geometric representation of FR as a metric-affine space, with transition between FR represented as affine deformation of the connection. Geodesic and autoparallel worldlines are considered. We show that the affine connection of a NIFR has curvature and may have torsion. We calculate the curvature for the uniformly accelerated FR. Finally, we show that GR is inadequate to describe the gravitational field in a NIFR. We propose a generalization of GR, which describes gravity as nonmetricity of the affine connection induced in a FR. This generalization contains GR as a special case of the inertial FR. |
1808.05015 | Sandro Marcio Rodrigues Micheletti | Sandro M. R. Micheletti | Quintessence and tachyon dark energy in interaction with dark matter:
Observational constraints and model selection | To be published in the International Journal of Modern Physics D | Int. J. Mod. Phys. D 29, no. 8, 2050057 (2020) | 10.1142/S0218271820500571 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We derive two field theory models of interacting dark energy, one in which
dark energy is associated with the quintessence and another in which it is
associated with the tachyon. In both, instead of choosing arbitrarily the
potential of scalar fields, these are specified implicitly by imposing that the
dark energy fields must behave as the new agegraphic dark energy. The resulting
models are compared with the Pantheon supernovae sample, CMB distance
information from Planck 2015 data, baryonic acoustic oscillations (BAO) and
Hubble parameter data. For comparison, the noninteracting case and the $\Lambda
CDM$ model also are considered. By use of the $ AIC $ and $ BIC $ criteria, we
obtain strong evidence in favor of the two interacting models, and the coupling
constants are nonvanishing at more than $3\sigma$ confidence level.
| [
{
"created": "Wed, 15 Aug 2018 09:42:33 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Aug 2018 12:36:07 GMT",
"version": "v2"
},
{
"created": "Sun, 21 Jun 2020 02:54:48 GMT",
"version": "v3"
}
] | 2020-07-10 | [
[
"Micheletti",
"Sandro M. R.",
""
]
] | We derive two field theory models of interacting dark energy, one in which dark energy is associated with the quintessence and another in which it is associated with the tachyon. In both, instead of choosing arbitrarily the potential of scalar fields, these are specified implicitly by imposing that the dark energy fields must behave as the new agegraphic dark energy. The resulting models are compared with the Pantheon supernovae sample, CMB distance information from Planck 2015 data, baryonic acoustic oscillations (BAO) and Hubble parameter data. For comparison, the noninteracting case and the $\Lambda CDM$ model also are considered. By use of the $ AIC $ and $ BIC $ criteria, we obtain strong evidence in favor of the two interacting models, and the coupling constants are nonvanishing at more than $3\sigma$ confidence level. |
1010.1928 | Vjacheslav Dorofeev | V. Yu. Dorofeev | The Riemann-Cartan space in the O-theory | 12 pages | null | 10.1134/S0202289312020065 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Nonrelativistic equation of particle with a spin for the Lagrangian on a
nonassociative algebra is obtained. It is shown that in this model arises
Riemann-Cartan space. In the case of central symmetry in addition to the
pseudo-curvature appears torsion as pseudovector that interacts with the spin
of the particle. An estimation of the influence of torsion on the strength of
gravitational attraction in the central gravitational field is given.
| [
{
"created": "Sun, 10 Oct 2010 15:18:19 GMT",
"version": "v1"
}
] | 2015-05-20 | [
[
"Dorofeev",
"V. Yu.",
""
]
] | Nonrelativistic equation of particle with a spin for the Lagrangian on a nonassociative algebra is obtained. It is shown that in this model arises Riemann-Cartan space. In the case of central symmetry in addition to the pseudo-curvature appears torsion as pseudovector that interacts with the spin of the particle. An estimation of the influence of torsion on the strength of gravitational attraction in the central gravitational field is given. |
2308.03716 | Iarley P. Lobo Dr | Pedro H. Morais, Iarley P. Lobo, Christian Pfeifer, Rafael Alves
Batista, Valdir B. Bezerra | Modified particle lifetimes as a signature of deformed relativity | 5 pages. Acknowledgments added. Matches published version | Phys.Lett.B 848 (2024) 138380 | 10.1016/j.physletb.2023.138380 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We demonstrate a compatibility between the relativity principle and the clock
postulate in deformed special relativity, by identifying the relevant deformed
Lorentz transformations in position space between arbitrary frames. This result
leads to a first-principles correction to the dilated lifetime of fundamental
particles. It turns out that these modified time dilations offer a way to
scrutinize Lorentz invariance (or deviations thereof) to high precision.
| [
{
"created": "Mon, 7 Aug 2023 16:38:07 GMT",
"version": "v1"
},
{
"created": "Tue, 8 Aug 2023 17:46:05 GMT",
"version": "v2"
},
{
"created": "Thu, 14 Dec 2023 23:10:52 GMT",
"version": "v3"
}
] | 2023-12-18 | [
[
"Morais",
"Pedro H.",
""
],
[
"Lobo",
"Iarley P.",
""
],
[
"Pfeifer",
"Christian",
""
],
[
"Batista",
"Rafael Alves",
""
],
[
"Bezerra",
"Valdir B.",
""
]
] | We demonstrate a compatibility between the relativity principle and the clock postulate in deformed special relativity, by identifying the relevant deformed Lorentz transformations in position space between arbitrary frames. This result leads to a first-principles correction to the dilated lifetime of fundamental particles. It turns out that these modified time dilations offer a way to scrutinize Lorentz invariance (or deviations thereof) to high precision. |
1909.07033 | Ming Zhang | Ming Zhang, Minyong Guo | Can shadows reflect phase structures of black holes? | 9 pages, 8 captioned figures, to appear in EPJC | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by-sa/4.0/ | The relation between the black hole shadow and the black hole thermodynamics
is investigated. We find that the phase structure can be reflected by the
shadow radius for the spherically symmetric black hole. We also find that the
shadow size gives correct information but the distortion of the shadow gives
wrong information of the phase structure for the axially symmetric black hole.
| [
{
"created": "Mon, 16 Sep 2019 07:29:11 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Sep 2019 06:26:46 GMT",
"version": "v2"
},
{
"created": "Tue, 28 Apr 2020 14:37:46 GMT",
"version": "v3"
},
{
"created": "Tue, 2 Jun 2020 13:35:26 GMT",
"version": "v4"
},
{
"cr... | 2020-08-28 | [
[
"Zhang",
"Ming",
""
],
[
"Guo",
"Minyong",
""
]
] | The relation between the black hole shadow and the black hole thermodynamics is investigated. We find that the phase structure can be reflected by the shadow radius for the spherically symmetric black hole. We also find that the shadow size gives correct information but the distortion of the shadow gives wrong information of the phase structure for the axially symmetric black hole. |
1901.07524 | Emilio Rub\'in de Celis | C. Tomasini, E. Rub\'in de Celis and C. Simeone | Arbitrarily coupled massive scalar field in conical thin-shell
spacetimes | 17 pages | null | 10.1140/epjc/s10052-019-6722-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the massive scalar field of a charged particle held at rest in
conical thin-shell spacetimes with one or two asymptotic regions. Resonant and
stable scalar Green's functions are characterized in terms of the coupling of
the field to the trace of the extrinsic curvature jump at the shell. Stable
coupling values, within the safety domain of the configuration parameters, are
used to analyze the self-force of static point charges.
| [
{
"created": "Tue, 22 Jan 2019 18:57:32 GMT",
"version": "v1"
}
] | 2019-03-27 | [
[
"Tomasini",
"C.",
""
],
[
"de Celis",
"E. Rubín",
""
],
[
"Simeone",
"C.",
""
]
] | We study the massive scalar field of a charged particle held at rest in conical thin-shell spacetimes with one or two asymptotic regions. Resonant and stable scalar Green's functions are characterized in terms of the coupling of the field to the trace of the extrinsic curvature jump at the shell. Stable coupling values, within the safety domain of the configuration parameters, are used to analyze the self-force of static point charges. |
1510.02573 | Sudipta Das | Sudipta Das, Ujjal Debnath, Abdulla Al Mamon | Generalized Second Law of Thermodynamics for Non-canonical Scalar Field
Model with Corrected-Entropy | 15 pages, 8 figures, Accepted for publication in EPJC | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we have considered a non-canonical scalar field dark energy
model in the framework of flat FRW background. It has also been assumed that
the dark matter sector interacts with the non-canonical dark energy sector
through some interaction term. Using the solutions for this interacting
non-canonical scalar field dark energy model, we have investigated the validity
of generalized second law (GSL) of thermodynamics in various scenarios using
first law and area law of thermodynamics. For this purpose, we have assumed two
types of horizons viz apparent horizon and event horizon for the universe and
using first law of thermodynamics, we have examined the validity of GSL on both
apparent and event horizons. Next, we have considered two types of
entropy-corrections on apparent and event horizons. Using the modified area
law, we have examined the validity of GSL of thermodynamics on apparent and
event horizons under some restrictions of model parameters.
| [
{
"created": "Fri, 9 Oct 2015 05:25:52 GMT",
"version": "v1"
}
] | 2015-10-12 | [
[
"Das",
"Sudipta",
""
],
[
"Debnath",
"Ujjal",
""
],
[
"Mamon",
"Abdulla Al",
""
]
] | In this work, we have considered a non-canonical scalar field dark energy model in the framework of flat FRW background. It has also been assumed that the dark matter sector interacts with the non-canonical dark energy sector through some interaction term. Using the solutions for this interacting non-canonical scalar field dark energy model, we have investigated the validity of generalized second law (GSL) of thermodynamics in various scenarios using first law and area law of thermodynamics. For this purpose, we have assumed two types of horizons viz apparent horizon and event horizon for the universe and using first law of thermodynamics, we have examined the validity of GSL on both apparent and event horizons. Next, we have considered two types of entropy-corrections on apparent and event horizons. Using the modified area law, we have examined the validity of GSL of thermodynamics on apparent and event horizons under some restrictions of model parameters. |
1901.06638 | Spyros Basilakos | Spyros Basilakos, Nick E. Mavromatos, Joan Sola | Scalar Field Theory Description of the Running Vacuum Model: the
Vacuumon | 15 pages, 3 figures, JCAP, 025, 12 (2019) | null | 10.1088/1475-7516/2019/12/025 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the running vacuum model (RVM) in the framework of scalar
field theory.This dynamical vacuum model provides an elegant global explanation
of the cosmic history, namely the universe starts from a non-singular initial
de Sitter vacuum stage, it passes smoothly from an early inflationary era to a
radiation epoch ("graceful exit") and finally it enters the dark matter and
dark energy (DE) dominated epochs, where it can explain the large entropy
problem and predicts a mild dynamical evolution of the DE. Within this
phenomenologically appealing context, we formulate an effective {\it classical}
scalar field description of the RVM through a field $\phi$, called the {\it
vacuumon}, which turns out to be very helpful for an understanding and
practical implementation of the physical mechanisms of the running vacuum
during both the early universe and the late time cosmic acceleration. In the
early universe the potential for the vacuumon may be mapped to a potential that
behaves similarly to that of the scalaron field of Starobinsky-type inflation
at the {\it classical} level, whilst in the late universe it provides an
effective scalar field description of DE. The two representations, however, are
not physically equivalent since the mechanisms of inflation are entirely
different. Moreover, unlike the scalaron, vacuumon is treated as a classical
background field, and not a fully fledged quantum field, hence cosmological
perturbations will be different between the two pictures of inflation.
| [
{
"created": "Sun, 20 Jan 2019 08:02:29 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Jan 2019 09:57:53 GMT",
"version": "v2"
},
{
"created": "Thu, 21 Nov 2019 08:45:01 GMT",
"version": "v3"
},
{
"created": "Tue, 10 Dec 2019 14:04:05 GMT",
"version": "v4"
}
] | 2019-12-18 | [
[
"Basilakos",
"Spyros",
""
],
[
"Mavromatos",
"Nick E.",
""
],
[
"Sola",
"Joan",
""
]
] | We investigate the running vacuum model (RVM) in the framework of scalar field theory.This dynamical vacuum model provides an elegant global explanation of the cosmic history, namely the universe starts from a non-singular initial de Sitter vacuum stage, it passes smoothly from an early inflationary era to a radiation epoch ("graceful exit") and finally it enters the dark matter and dark energy (DE) dominated epochs, where it can explain the large entropy problem and predicts a mild dynamical evolution of the DE. Within this phenomenologically appealing context, we formulate an effective {\it classical} scalar field description of the RVM through a field $\phi$, called the {\it vacuumon}, which turns out to be very helpful for an understanding and practical implementation of the physical mechanisms of the running vacuum during both the early universe and the late time cosmic acceleration. In the early universe the potential for the vacuumon may be mapped to a potential that behaves similarly to that of the scalaron field of Starobinsky-type inflation at the {\it classical} level, whilst in the late universe it provides an effective scalar field description of DE. The two representations, however, are not physically equivalent since the mechanisms of inflation are entirely different. Moreover, unlike the scalaron, vacuumon is treated as a classical background field, and not a fully fledged quantum field, hence cosmological perturbations will be different between the two pictures of inflation. |
gr-qc/0606043 | Valerii Dryuma sem | Valery Dryuma | 10-Dim Einstein spaces made up on basis of 6-Dim Ricci-flat spaces and
4-Dim Einstein spaces | 8 pages | null | null | null | gr-qc | null | Some examples of ten-dimensional vacuum Einstein spaces made up on basis of
four-dimensional Ricci-flat spaces and six-dimensional Ricci-flat spaces
defined by solutions of the Sin-Gordon equation are constructed. The properties
of geodesics for such type of the spaces are discussed
| [
{
"created": "Fri, 9 Jun 2006 19:29:53 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Dryuma",
"Valery",
""
]
] | Some examples of ten-dimensional vacuum Einstein spaces made up on basis of four-dimensional Ricci-flat spaces and six-dimensional Ricci-flat spaces defined by solutions of the Sin-Gordon equation are constructed. The properties of geodesics for such type of the spaces are discussed |
1805.02328 | Jiliang Jing | Weiping Yao, Chaohui Yang, Jiliang Jing | Holographic insulator/superconductor transition with exponential
nonlinear electrodynamics probed by entanglement entropy | 15 pages, 6 figures | Eur. Phys. J. C. (2018) 78: 353 | 10.1140/epjc/s10052-018-5836-7 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | From the viewpoint of holography, we study the behaviors of the entanglement
entropy in insulator/superconductor transition with exponential nonlinear
electrodynamics (ENE). We find that the entanglement entropy is a good probe to
the properties of the holographic phase transition. Both in the half space and
the belt space, the non-monotonic behavior of the entanglement entropy in
superconducting phase versus the chemical potential is general in this model.
Furthermore, the behavior of the entanglement entropy for the strip geometry
shows that the confinement/deconfinement phase transition appears in both
insulator and superconductor phases. And the critical width of the the
confinement/deconfinement phase transition depends on the chemical potential
and the exponential coupling term. More interestingly, the behaviors of the
entanglement entropy in their corresponding insulator phases are independent of
the exponential coupling factor but depends on the the width of the subsystem
$\mathcal{A}$.
| [
{
"created": "Mon, 7 May 2018 03:04:54 GMT",
"version": "v1"
}
] | 2018-05-23 | [
[
"Yao",
"Weiping",
""
],
[
"Yang",
"Chaohui",
""
],
[
"Jing",
"Jiliang",
""
]
] | From the viewpoint of holography, we study the behaviors of the entanglement entropy in insulator/superconductor transition with exponential nonlinear electrodynamics (ENE). We find that the entanglement entropy is a good probe to the properties of the holographic phase transition. Both in the half space and the belt space, the non-monotonic behavior of the entanglement entropy in superconducting phase versus the chemical potential is general in this model. Furthermore, the behavior of the entanglement entropy for the strip geometry shows that the confinement/deconfinement phase transition appears in both insulator and superconductor phases. And the critical width of the the confinement/deconfinement phase transition depends on the chemical potential and the exponential coupling term. More interestingly, the behaviors of the entanglement entropy in their corresponding insulator phases are independent of the exponential coupling factor but depends on the the width of the subsystem $\mathcal{A}$. |
2106.08836 | Takuya Takahashi | Takuya Takahashi and Takahiro Tanaka | Axion clouds may survive the perturbative tidal interaction over the
early inspiral phase of black hole binaries | 15 pages, 4 figures | null | 10.1088/1475-7516/2021/10/031 | null | gr-qc astro-ph.CO hep-ph | http://creativecommons.org/licenses/by/4.0/ | Gravitational wave observation has the potential of probing ultralight
bosonic fields such as axion. Axion forms a cloud around a rotating black hole
(BH) by superradiant instability and should affect the gravitational waveform
from binary BHs. On the other hand, considering the cloud associated with a BH
in a binary system, tidal interaction depletes the cloud in some cases during
the inspiral phase. We made the exhaustive study of cloud depletion numerically
in a wide parameter range for equal mass binaries, assuming only the
quadrupolar tidal perturbation is at work. We found that clouds can avoid
disappearing due to the tidal effect only when $l=1$ mode is the fastest
growing mode and when the binary orbit is counter-rotating in the
non-relativistic parameter region.
| [
{
"created": "Wed, 16 Jun 2021 14:55:11 GMT",
"version": "v1"
},
{
"created": "Wed, 23 Jun 2021 14:22:33 GMT",
"version": "v2"
},
{
"created": "Wed, 25 Aug 2021 12:22:45 GMT",
"version": "v3"
}
] | 2021-10-20 | [
[
"Takahashi",
"Takuya",
""
],
[
"Tanaka",
"Takahiro",
""
]
] | Gravitational wave observation has the potential of probing ultralight bosonic fields such as axion. Axion forms a cloud around a rotating black hole (BH) by superradiant instability and should affect the gravitational waveform from binary BHs. On the other hand, considering the cloud associated with a BH in a binary system, tidal interaction depletes the cloud in some cases during the inspiral phase. We made the exhaustive study of cloud depletion numerically in a wide parameter range for equal mass binaries, assuming only the quadrupolar tidal perturbation is at work. We found that clouds can avoid disappearing due to the tidal effect only when $l=1$ mode is the fastest growing mode and when the binary orbit is counter-rotating in the non-relativistic parameter region. |
0909.3341 | Jan Harms | Jan Harms, Riccardo DeSalvo, Steven Dorsher and Vuk Mandic | Simulation of underground gravity gradients from stochastic seismic
fields | 24 pages, 12 figures | null | 10.1103/PhysRevD.80.122001 | null | gr-qc physics.geo-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present results obtained from a finite-element simulation of seismic
displacement fields and of gravity gradients generated by those fields. The
displacement field is constructed by a plane wave model with a 3D isotropic
stochastic field and a 2D fundamental Rayleigh field. The plane wave model
provides an accurate representation of stationary fields from distant sources.
Underground gravity gradients are calculated as acceleration of a free test
mass inside a cavity. The results are discussed in the context of
gravity-gradient noise subtraction in third generation gravitational-wave
detectors. Error analysis with respect to the density of the simulated grid
leads to a derivation of an improved seismometer placement inside a 3D array
which would be used in practice to monitor the seismic field.
| [
{
"created": "Fri, 18 Sep 2009 00:57:05 GMT",
"version": "v1"
}
] | 2013-05-29 | [
[
"Harms",
"Jan",
""
],
[
"DeSalvo",
"Riccardo",
""
],
[
"Dorsher",
"Steven",
""
],
[
"Mandic",
"Vuk",
""
]
] | We present results obtained from a finite-element simulation of seismic displacement fields and of gravity gradients generated by those fields. The displacement field is constructed by a plane wave model with a 3D isotropic stochastic field and a 2D fundamental Rayleigh field. The plane wave model provides an accurate representation of stationary fields from distant sources. Underground gravity gradients are calculated as acceleration of a free test mass inside a cavity. The results are discussed in the context of gravity-gradient noise subtraction in third generation gravitational-wave detectors. Error analysis with respect to the density of the simulated grid leads to a derivation of an improved seismometer placement inside a 3D array which would be used in practice to monitor the seismic field. |
2307.12244 | Xiangyu Lyu | Xiangyu Lyu, En-Kun Li, Yi-Ming Hu | Parameter Estimation of Stellar Mass Binary Black Holes under the
Network of TianQin and LISA | 17 pages, 6 figures, | Phys. Rev. D 2023 | 10.1103/PhysRevD.108.083023 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a Bayesian parameter estimation progress to infer the stellar mass
binary black hole properties by TianQin, LISA, and TianQin+LISA.Two typical
stellar mass black hole binary systems, GW150914 and GW190521 are chosen as the
fiducial sources. In this work, we establish the ability of TianQin to infer
the parameters of those systems and first apply the full frequency response in
TianQin's data analysis. We obtain the parameter estimation results and explain
the correlation between them. We also find the TianQin+LISA could marginally
increase the parameter estimation precision and narrow the $1\sigma$ area
compared with TianQin and LISA individual observations. We finally demonstrate
the importance of considering the effect of spin when the binaries have a
nonzero component spin and great deviation will appear especially on mass,
coalescence time and sky location.
| [
{
"created": "Sun, 23 Jul 2023 06:58:49 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Dec 2023 08:40:44 GMT",
"version": "v2"
}
] | 2023-12-08 | [
[
"Lyu",
"Xiangyu",
""
],
[
"Li",
"En-Kun",
""
],
[
"Hu",
"Yi-Ming",
""
]
] | We present a Bayesian parameter estimation progress to infer the stellar mass binary black hole properties by TianQin, LISA, and TianQin+LISA.Two typical stellar mass black hole binary systems, GW150914 and GW190521 are chosen as the fiducial sources. In this work, we establish the ability of TianQin to infer the parameters of those systems and first apply the full frequency response in TianQin's data analysis. We obtain the parameter estimation results and explain the correlation between them. We also find the TianQin+LISA could marginally increase the parameter estimation precision and narrow the $1\sigma$ area compared with TianQin and LISA individual observations. We finally demonstrate the importance of considering the effect of spin when the binaries have a nonzero component spin and great deviation will appear especially on mass, coalescence time and sky location. |
gr-qc/0001016 | Hiromi Saida | Hiromi Saida & Jiro Soda | BTZ Black Hole Entropy in Higher Curvature Gravity | Appeared in The Proceedings of the 9th Workshop on General Relativity
and Gravitation (Japan), 8pages, no figure | null | null | null | gr-qc | null | For the BTZ black hole in the Einstein gravity, a statistical entropy has
been calculated. It is equal to the Bekenstein-Hawking entropy. In this
article, its statistical entropy in the higer curvature gravity is calculated
and shown to be equal to one derived by using the Noether charge method. This
suggests that the equivalence between the geometrical and statistical entropies
of the black hole is retained in the general diffeomorphism invariant theories
of gravity. A relation between the cosmic censorship conjecture and the
unitarity of the conformal field theory on the boundary of AdS_3 is also
discussed.
| [
{
"created": "Fri, 7 Jan 2000 07:38:28 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Jan 2000 10:02:56 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Saida",
"Hiromi",
""
],
[
"Soda",
"Jiro",
""
]
] | For the BTZ black hole in the Einstein gravity, a statistical entropy has been calculated. It is equal to the Bekenstein-Hawking entropy. In this article, its statistical entropy in the higer curvature gravity is calculated and shown to be equal to one derived by using the Noether charge method. This suggests that the equivalence between the geometrical and statistical entropies of the black hole is retained in the general diffeomorphism invariant theories of gravity. A relation between the cosmic censorship conjecture and the unitarity of the conformal field theory on the boundary of AdS_3 is also discussed. |
gr-qc/9309004 | null | Sean A. Hayward, Tetsuya Shiromizu & Ken-ichi Nakao | A Cosmological Constant Limits the Size of Black Holes | 10 pages | Phys.Rev. D49 (1994) 5080-5085 | 10.1103/PhysRevD.49.5080 | null | gr-qc | null | In a space-time with cosmological constant $\Lambda>0$ and matter satisfying
the dominant energy condition, the area of a black or white hole cannot exceed
$4\pi/\Lambda$. This applies to event horizons where defined, i.e. in an
asymptotically deSitter space-time, and to outer trapping horizons (cf.
apparent horizons) in any space-time. The bound is attained if and only if the
horizon is identical to that of the degenerate `Schwarzschild-deSitter'
solution. This yields a topological restriction on the event horizon, namely
that components whose total area exceeds $4\pi/\Lambda$ cannot merge. We
discuss the conjectured isoperimetric inequality and implications for the
cosmic censorship conjecture.
| [
{
"created": "Thu, 2 Sep 1993 13:48:35 GMT",
"version": "v1"
},
{
"created": "Wed, 25 May 1994 06:08:35 GMT",
"version": "v2"
}
] | 2009-10-22 | [
[
"Hayward",
"Sean A.",
""
],
[
"Shiromizu",
"Tetsuya",
""
],
[
"Nakao",
"Ken-ichi",
""
]
] | In a space-time with cosmological constant $\Lambda>0$ and matter satisfying the dominant energy condition, the area of a black or white hole cannot exceed $4\pi/\Lambda$. This applies to event horizons where defined, i.e. in an asymptotically deSitter space-time, and to outer trapping horizons (cf. apparent horizons) in any space-time. The bound is attained if and only if the horizon is identical to that of the degenerate `Schwarzschild-deSitter' solution. This yields a topological restriction on the event horizon, namely that components whose total area exceeds $4\pi/\Lambda$ cannot merge. We discuss the conjectured isoperimetric inequality and implications for the cosmic censorship conjecture. |
gr-qc/9812095 | Walter J. Wild | Walter J. Wild | A Matrix Formulation of Einstein's Vacuum Field Equations | 8 pages | null | null | null | gr-qc | null | We develop a correspondence between arbitrary tensors and matrices based on
the use of Kronecker products and associated identities.
Utilizing the rules of matrix differentiation we derive the vacuum Einstein
field equations as a differential-matrix equation. This formulation may
facilitate their efficient use in numerical relativistic models.
| [
{
"created": "Thu, 31 Dec 1998 08:53:28 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Wild",
"Walter J.",
""
]
] | We develop a correspondence between arbitrary tensors and matrices based on the use of Kronecker products and associated identities. Utilizing the rules of matrix differentiation we derive the vacuum Einstein field equations as a differential-matrix equation. This formulation may facilitate their efficient use in numerical relativistic models. |
1409.3758 | Ram Gopal Vishwakarma | Ram Gopal Vishwakarma | A New Solution of Einstein Vacuum Field Equations | Pramana - J. Phys. (in press) | null | 10.1007/s12043-015-0946-3 | null | gr-qc astro-ph.CO math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A new solution of Einstein's vacuum field equations is discovered which
appears as a generalization of the well-known Ozsvath-Schucking solution and
explains its source of curvature which has otherwise remained hidden.
Curiously, the new solution has a vanishing Kretschmann scalar and is
singularity-free despite being curved.
The discovery of the new solution is facilitated by a new insight which
reveals that it is always possible to define the source of curvature in a
vacuum solution in terms of some dimensional parameters. As the parameters
vanish, so does the curvature. The new insight also helps to make the vacuum
solutions Machian.
| [
{
"created": "Thu, 11 Sep 2014 17:34:21 GMT",
"version": "v1"
}
] | 2015-09-22 | [
[
"Vishwakarma",
"Ram Gopal",
""
]
] | A new solution of Einstein's vacuum field equations is discovered which appears as a generalization of the well-known Ozsvath-Schucking solution and explains its source of curvature which has otherwise remained hidden. Curiously, the new solution has a vanishing Kretschmann scalar and is singularity-free despite being curved. The discovery of the new solution is facilitated by a new insight which reveals that it is always possible to define the source of curvature in a vacuum solution in terms of some dimensional parameters. As the parameters vanish, so does the curvature. The new insight also helps to make the vacuum solutions Machian. |
1401.7622 | Aur\'elien Hees | A. Hees, S. Bertone, C. Le Poncin-Lafitte | Relativistic formulation of coordinate light time, Doppler and
astrometric observables up to the second post-Minkowskian order | 22 pages, 5 figures, accepted in Phys. Rev. D | Phys. Rev. D 89, 064045, 2014 | 10.1103/PhysRevD.89.064045 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Given the extreme accuracy of modern space science, a precise relativistic
modeling of observations is required. In particular, it is important to
describe properly light propagation through the Solar System. For two decades,
several modeling efforts based on the solution of the null geodesic equations
have been proposed but they are mainly valid only for the first order
Post-Newtonian approximation. However, with the increasing precision of ongoing
space missions as Gaia, GAME, BepiColombo, JUNO or JUICE, we know that some
corrections up to the second order have to be taken into account for future
experiments. We present a procedure to compute the relativistic coordinate time
delay, Doppler and astrometric observables avoiding the integration of the null
geodesic equation. This is possible using the Time Transfer Function formalism,
a powerful tool providing key quantities such as the time of flight of a light
signal between two point-events and the tangent vector to its null-geodesic.
Indeed we show how to compute the Time Transfer Functions and their derivatives
(and thus range, Doppler and astrometric observables) up to the second
post-Minkowskian order. We express these quantities as quadratures of some
functions that depend only on the metric and its derivatives evaluated along a
Minkowskian straight line. This method is particularly well adapted for
numerical estimations. As an illustration, we provide explicit expressions in
static and spherically symmetric space-time up to second post-Minkowskian
order. Then we give the order of magnitude of these corrections for the
range/Doppler on the BepiColombo mission and for astrometry in a GAME-like
observation.
| [
{
"created": "Wed, 29 Jan 2014 18:56:24 GMT",
"version": "v1"
}
] | 2014-03-21 | [
[
"Hees",
"A.",
""
],
[
"Bertone",
"S.",
""
],
[
"Poncin-Lafitte",
"C. Le",
""
]
] | Given the extreme accuracy of modern space science, a precise relativistic modeling of observations is required. In particular, it is important to describe properly light propagation through the Solar System. For two decades, several modeling efforts based on the solution of the null geodesic equations have been proposed but they are mainly valid only for the first order Post-Newtonian approximation. However, with the increasing precision of ongoing space missions as Gaia, GAME, BepiColombo, JUNO or JUICE, we know that some corrections up to the second order have to be taken into account for future experiments. We present a procedure to compute the relativistic coordinate time delay, Doppler and astrometric observables avoiding the integration of the null geodesic equation. This is possible using the Time Transfer Function formalism, a powerful tool providing key quantities such as the time of flight of a light signal between two point-events and the tangent vector to its null-geodesic. Indeed we show how to compute the Time Transfer Functions and their derivatives (and thus range, Doppler and astrometric observables) up to the second post-Minkowskian order. We express these quantities as quadratures of some functions that depend only on the metric and its derivatives evaluated along a Minkowskian straight line. This method is particularly well adapted for numerical estimations. As an illustration, we provide explicit expressions in static and spherically symmetric space-time up to second post-Minkowskian order. Then we give the order of magnitude of these corrections for the range/Doppler on the BepiColombo mission and for astrometry in a GAME-like observation. |
1402.2256 | Giovanni Otalora | Giovanni Otalora | A novel teleparallel dark energy model | 15 pages, 2 figures, 3 tables | International Journal of Modern Physics D International Journal of
Modern Physics D, Vol. 25, No. 2 (2016) 1650025 (15 pages) | 10.1142/S0218271816500255 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Although equivalent to general relativity, teleparallel gravity is
conceptually speaking a completely different theory. In this theory, the
gravitational field is described by torsion, not by curvature. By working in
this context, a new model is proposed in which the four-derivative of a
canonical scalar field representing dark energy is nonminimally coupled to the
"vector torsion". This type of coupling is motivated by the fact that a scalar
field couples to torsion through its four-derivative, which is consistent with
local spacetime kinematics regulated by the de Sitter group $SO(1,4)$. It is
found that the current state of accelerated expansion of the Universe
corresponds to a late-time attractor that can be (i) a dark-energy-dominated de
Sitter solution ($\omega_{\phi}=-1$), (ii) a quintessence-type solution with
$\omega_{\phi}\geq-1$, or (iii) a phantom-type $\omega_{\phi}<-1$ dark energy.
| [
{
"created": "Mon, 10 Feb 2014 20:25:16 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Nov 2015 17:35:09 GMT",
"version": "v2"
}
] | 2015-11-30 | [
[
"Otalora",
"Giovanni",
""
]
] | Although equivalent to general relativity, teleparallel gravity is conceptually speaking a completely different theory. In this theory, the gravitational field is described by torsion, not by curvature. By working in this context, a new model is proposed in which the four-derivative of a canonical scalar field representing dark energy is nonminimally coupled to the "vector torsion". This type of coupling is motivated by the fact that a scalar field couples to torsion through its four-derivative, which is consistent with local spacetime kinematics regulated by the de Sitter group $SO(1,4)$. It is found that the current state of accelerated expansion of the Universe corresponds to a late-time attractor that can be (i) a dark-energy-dominated de Sitter solution ($\omega_{\phi}=-1$), (ii) a quintessence-type solution with $\omega_{\phi}\geq-1$, or (iii) a phantom-type $\omega_{\phi}<-1$ dark energy. |
1805.08064 | Roman Sverdlov | Roman Sverdlov | Electromagnetic Lagrangian on a causal set that resides on edges rather
than points | 40 pages, no figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The goal of this paper is to introduce one of the versions of the
electromagnetic Lagrangian on a causal set in such a way that would address the
non-locality issues inherent to causal set theory. The key idea is that
Lagrangian density is assigned to the edges rather than points, and there is a
way of defining the concept of "neighboring edges" of a given edge in such a
way that each edge has only finitely many neighboring edges which would
ultimately allow for the theory to be local. That is to be contrasted with
points where every point has infinitely many direct neighbors which is a source
of non-locality. The edges are needed in order to define electromagnetic
Lagrangian anyway, regardless of the consideration of locality; the novelty of
this paper is to assign Lagrangian density to the edges as well. Also, in the
other papers edges were both spacelike and timelike, while in this paper they
are only timelike. This makes calculations considerably more complicated, but
it is crucial in preserving locality since the Lorentz group in a hyperplane
perpendicular to the edge is compact only if the edge is timelike.
| [
{
"created": "Thu, 17 May 2018 22:05:10 GMT",
"version": "v1"
},
{
"created": "Wed, 23 May 2018 17:16:49 GMT",
"version": "v2"
}
] | 2018-05-24 | [
[
"Sverdlov",
"Roman",
""
]
] | The goal of this paper is to introduce one of the versions of the electromagnetic Lagrangian on a causal set in such a way that would address the non-locality issues inherent to causal set theory. The key idea is that Lagrangian density is assigned to the edges rather than points, and there is a way of defining the concept of "neighboring edges" of a given edge in such a way that each edge has only finitely many neighboring edges which would ultimately allow for the theory to be local. That is to be contrasted with points where every point has infinitely many direct neighbors which is a source of non-locality. The edges are needed in order to define electromagnetic Lagrangian anyway, regardless of the consideration of locality; the novelty of this paper is to assign Lagrangian density to the edges as well. Also, in the other papers edges were both spacelike and timelike, while in this paper they are only timelike. This makes calculations considerably more complicated, but it is crucial in preserving locality since the Lorentz group in a hyperplane perpendicular to the edge is compact only if the edge is timelike. |
2004.07476 | Hakan Cebeci | Hakan Cebeci | Matter coupling in Minimal Massive 3D Gravity and spinor-matter
interactions in exterior algebra formalism | Updated version, Title and Abstract changed, accepted for publication | null | 10.1088/1361-6382/ac43d4 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, by employing the exterior algebra formalism, we study the
matter coupling in Minimal Massive 3D Gravity (MMG) by first considering that
the matter Lagrangian is connection-independent and then considering that the
matter coupling is connection-dependent. The matter coupling in MMG has been
previously investigated in the work Arvanitakis {\it et al} (2014 {\it Class.
Quantum Grav.} {\bf 31} 235012) in tensorial notation where the matter
Lagrangian is considered to be connection-independent. In the first part of the
present paper, we revisit the connection-independent matter coupling by using
the language of differential forms. We derive the MMG field equation and
construct the related source 2-form. We also obtain the consistency relation
within this formalism. Next, we examine the case where the matter Lagrangian is
connection-dependent. In particular, we concentrate on the spinor-matter
coupling and obtain the MMG field equation by explicitly constructing the
source term. We also get the consistency relation that the source term should
satisfy in order that spinor-matter coupled MMG equation be consistent.
| [
{
"created": "Thu, 16 Apr 2020 06:29:39 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Jul 2020 07:16:53 GMT",
"version": "v2"
},
{
"created": "Wed, 5 Jan 2022 19:08:05 GMT",
"version": "v3"
}
] | 2022-01-07 | [
[
"Cebeci",
"Hakan",
""
]
] | In this work, by employing the exterior algebra formalism, we study the matter coupling in Minimal Massive 3D Gravity (MMG) by first considering that the matter Lagrangian is connection-independent and then considering that the matter coupling is connection-dependent. The matter coupling in MMG has been previously investigated in the work Arvanitakis {\it et al} (2014 {\it Class. Quantum Grav.} {\bf 31} 235012) in tensorial notation where the matter Lagrangian is considered to be connection-independent. In the first part of the present paper, we revisit the connection-independent matter coupling by using the language of differential forms. We derive the MMG field equation and construct the related source 2-form. We also obtain the consistency relation within this formalism. Next, we examine the case where the matter Lagrangian is connection-dependent. In particular, we concentrate on the spinor-matter coupling and obtain the MMG field equation by explicitly constructing the source term. We also get the consistency relation that the source term should satisfy in order that spinor-matter coupled MMG equation be consistent. |
gr-qc/9906097 | Chris Clarkson | Chris Clarkson and Richard Barrett | Does the Isotropy of the CMB Imply a Homogeneous Universe? Some
Generalised EGS Theorems | replaced with final version. Added discusion and refs | Class.Quant.Grav. 16 (1999) 3781-3794 | 10.1088/0264-9381/16/12/302 | null | gr-qc astro-ph | null | We demonstrate that the high isotropy of the Cosmic Microwave Background
(CMB), combined with the Copernican principle, is not sufficient to prove
homogeneity of the universe -- in contrast to previous results on this subject.
The crucial additional factor not included in earlier work is the acceleration
of the fundamental observers. We find the complete class of irrotational
perfect fluid spacetimes admitting an exactly isotropic radiation field for
every fundamental observer and show that are FLRW if and only if the
acceleration is zero. While inhomogeneous in general, these spacetimes all
possess three-dimensional symmetry groups, from which it follows that they also
admit a thermodynamic interpretation. In addition to perfect fluids models we
also consider multi-component fluids containing non-interacting radiation, dust
and a quintessential scalar field or cosmological constant in which the
radiation is isotropic for the geodesic (dust) observers. It is shown that the
non-acceleration of the fundamental observers forces these spacetimes to be
FLRW. While it is plausible that fundamental observers (galaxies) in the real
universe follow geodesics, it is strictly necessary to determine this from
local observations for the cosmological principle to be more than an
assumption. We discuss how observations may be used to test this.
| [
{
"created": "Wed, 23 Jun 1999 23:25:34 GMT",
"version": "v1"
},
{
"created": "Tue, 14 Dec 1999 17:03:13 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Clarkson",
"Chris",
""
],
[
"Barrett",
"Richard",
""
]
] | We demonstrate that the high isotropy of the Cosmic Microwave Background (CMB), combined with the Copernican principle, is not sufficient to prove homogeneity of the universe -- in contrast to previous results on this subject. The crucial additional factor not included in earlier work is the acceleration of the fundamental observers. We find the complete class of irrotational perfect fluid spacetimes admitting an exactly isotropic radiation field for every fundamental observer and show that are FLRW if and only if the acceleration is zero. While inhomogeneous in general, these spacetimes all possess three-dimensional symmetry groups, from which it follows that they also admit a thermodynamic interpretation. In addition to perfect fluids models we also consider multi-component fluids containing non-interacting radiation, dust and a quintessential scalar field or cosmological constant in which the radiation is isotropic for the geodesic (dust) observers. It is shown that the non-acceleration of the fundamental observers forces these spacetimes to be FLRW. While it is plausible that fundamental observers (galaxies) in the real universe follow geodesics, it is strictly necessary to determine this from local observations for the cosmological principle to be more than an assumption. We discuss how observations may be used to test this. |
2212.12144 | Teng Zhang | Teng Zhang, Huan Yang, Denis Martynov, Patricia Schmidt, Haixing Miao | A Gravitational Wave Detector for Post Merger Neutron Stars: Beyond the
Quantum Loss Limit of Michelson Fabry Perot Interferometer | 12 pages, 9 figures | Phys. Rev. X. 13, 021019 (2023) | 10.1103/PhysRevX.13.021019 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Advanced gravitational-wave detectors that have made groundbreaking
discoveries are Michelson interferometers with resonating optical cavities as
their arms. As light travels at finite speed, these cavities are optimal for
enhancing signals at frequencies below their bandwidth frequency. A small
amount of optical loss will, however, significantly impact the high-frequency
signals which are not optimally amplified. We find an elegant interferometer
configuration with an "L-resonator" as the core, significantly surpassing the
loss limited sensitivity of dual recycled Fabry Perot Michelson interferometers
at high frequencies. Following this concept, we provide a broadband design of a
25 km detector with outstanding sensitivity between 2-4 kHz. We have performed
Monte-Carlo population studies of binary neutron star mergers, given the most
recent merger rate from the GWTC-3 catalog and several representative neutron
star equations of state. We find that the new interferometer configuration
significantly outperforms other third-generation detectors by a factor of 3 to
7 in the signal-to-noise ratio of the post-merger signal. Assuming a detection
threshold with signal-to-noise ratio >5 and for the cases we have explored, the
new design is the only detector that confidently achieves a detection rate
larger than one per year, with the rate being 1 to 30 events per year.
| [
{
"created": "Fri, 23 Dec 2022 04:36:29 GMT",
"version": "v1"
},
{
"created": "Sun, 1 Jan 2023 00:58:04 GMT",
"version": "v2"
},
{
"created": "Fri, 13 Jan 2023 14:13:12 GMT",
"version": "v3"
},
{
"created": "Thu, 2 Feb 2023 11:57:18 GMT",
"version": "v4"
},
{
"cre... | 2023-05-30 | [
[
"Zhang",
"Teng",
""
],
[
"Yang",
"Huan",
""
],
[
"Martynov",
"Denis",
""
],
[
"Schmidt",
"Patricia",
""
],
[
"Miao",
"Haixing",
""
]
] | Advanced gravitational-wave detectors that have made groundbreaking discoveries are Michelson interferometers with resonating optical cavities as their arms. As light travels at finite speed, these cavities are optimal for enhancing signals at frequencies below their bandwidth frequency. A small amount of optical loss will, however, significantly impact the high-frequency signals which are not optimally amplified. We find an elegant interferometer configuration with an "L-resonator" as the core, significantly surpassing the loss limited sensitivity of dual recycled Fabry Perot Michelson interferometers at high frequencies. Following this concept, we provide a broadband design of a 25 km detector with outstanding sensitivity between 2-4 kHz. We have performed Monte-Carlo population studies of binary neutron star mergers, given the most recent merger rate from the GWTC-3 catalog and several representative neutron star equations of state. We find that the new interferometer configuration significantly outperforms other third-generation detectors by a factor of 3 to 7 in the signal-to-noise ratio of the post-merger signal. Assuming a detection threshold with signal-to-noise ratio >5 and for the cases we have explored, the new design is the only detector that confidently achieves a detection rate larger than one per year, with the rate being 1 to 30 events per year. |
0805.3469 | Dr. Anirudh Pradhan | Anirudh Pradhan and Raj Bali | Magnetized Bianchi Type $VI_{0}$ Barotropic Massive String Universe with
Decaying Vacuum Energy Density $\Lambda$ | 14 pages, no figures | Elect. J. Theor. Phys. 15:91-104,2008 | 10.1007/s10773-008-9918-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bianchi type $VI_{0}$ massive string cosmological models using the technique
given by Letelier (1983) with magnetic field are investigated. To get the
deterministic models, we assume that the expansion ($\theta$) in the model is
proportional to the shear ($\sigma$) and also the fluid obeys the barotropic
equation of state. It was found that vacuum energy density $\Lambda \propto
\frac{1}{t^{2}}$ which matches with natural units. The behaviour of the models
from physical and geometrical aspects in presence and absence of magnetic field
is also discussed.
| [
{
"created": "Thu, 22 May 2008 14:31:53 GMT",
"version": "v1"
}
] | 2015-06-30 | [
[
"Pradhan",
"Anirudh",
""
],
[
"Bali",
"Raj",
""
]
] | Bianchi type $VI_{0}$ massive string cosmological models using the technique given by Letelier (1983) with magnetic field are investigated. To get the deterministic models, we assume that the expansion ($\theta$) in the model is proportional to the shear ($\sigma$) and also the fluid obeys the barotropic equation of state. It was found that vacuum energy density $\Lambda \propto \frac{1}{t^{2}}$ which matches with natural units. The behaviour of the models from physical and geometrical aspects in presence and absence of magnetic field is also discussed. |
gr-qc/9406014 | Roberto De Pietri | Roberto De Pietri & Carlo Rovelli | Eigenvalues of the Weyl operator as observables of general relativity | 15 pages, LaTex style, preprint UPRF-94-399 | Class.Quant.Grav.12:1279-1286,1995 | 10.1088/0264-9381/12/5/017 | null | gr-qc | null | We consider the eigenvalues of the three-dimensional Weyl operator defined in
terms of the (Euclidean) Ashtekar variables, and we study their dependence on
the gravitational field. We notice that these eigenvalues can be used as
gravitational variables, and derive explicit formulas for their Poisson
brackets and their time evolution.
| [
{
"created": "Wed, 8 Jun 1994 11:38:13 GMT",
"version": "v1"
}
] | 2010-04-06 | [
[
"De Pietri",
"Roberto",
""
],
[
"Rovelli",
"Carlo",
""
]
] | We consider the eigenvalues of the three-dimensional Weyl operator defined in terms of the (Euclidean) Ashtekar variables, and we study their dependence on the gravitational field. We notice that these eigenvalues can be used as gravitational variables, and derive explicit formulas for their Poisson brackets and their time evolution. |
1612.08517 | Sunil Maharaj | R. Mohanlal, S. D. Maharaj, A. K. Tiwari, R. Narain | Radiating stars with exponential Lie symmetries | 14 pages, submitted for publication | Gen. Relativ. Gravit. 48, 87 (2016) | 10.1007/s10714-016-2081-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We analyze the general model of a radiating star in general relativity. A
group analysis of the under determined, nonlinear partial differential equation
governing the model's gravitational potentials is performed. This analysis is
an extension of previous group analyses carried out and produces new group
invariant solutions. We find that the gravitational potentials depend on
exponential functions owing to the choice of the Lie symmetry generator. The
fundamental boundary equation to be solved is in general a Riccati equation.
Several new exact families of solutions to the boundary condition are
generated. Earlier models of Euclidean stars and generalized Euclidean stellar
models are regained as special cases. Linear equations of state can be found
for shear-free and shearing spacetimes.
| [
{
"created": "Tue, 27 Dec 2016 07:04:49 GMT",
"version": "v1"
}
] | 2017-01-04 | [
[
"Mohanlal",
"R.",
""
],
[
"Maharaj",
"S. D.",
""
],
[
"Tiwari",
"A. K.",
""
],
[
"Narain",
"R.",
""
]
] | We analyze the general model of a radiating star in general relativity. A group analysis of the under determined, nonlinear partial differential equation governing the model's gravitational potentials is performed. This analysis is an extension of previous group analyses carried out and produces new group invariant solutions. We find that the gravitational potentials depend on exponential functions owing to the choice of the Lie symmetry generator. The fundamental boundary equation to be solved is in general a Riccati equation. Several new exact families of solutions to the boundary condition are generated. Earlier models of Euclidean stars and generalized Euclidean stellar models are regained as special cases. Linear equations of state can be found for shear-free and shearing spacetimes. |
2211.07023 | Wei-Liang Qian | Shui-Fa Shen, Wei-Liang Qian, Hong Guo, Shao-Jun Zhang, Jin Li | An implementation of the matrix method using Chebyshev grid | 13 pages, 6 tables | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this work, we explore the properties of the matrix method for black hole
quasinormal modes on the nonuniform grid. In particular, the method is
implemented to be adapted to the Chebyshev grid, aimed at effectively
suppressing Runge's phenomenon. It is found that while such an implementation
is favorable from a mathematical point of view, in practice, the increase in
precision does not necessarily compensate for the penalty in computational
time. On the other hand, the original matrix method, though subject to Runge's
phenomenon, is shown to be reasonably robust and suffices for most applications
with a moderate grid number. In terms of computational time and obtained
significant figures, we carried out an analysis regarding the trade-off between
the two aspects. The implications of the present study are also addressed.
| [
{
"created": "Sun, 13 Nov 2022 21:49:56 GMT",
"version": "v1"
}
] | 2022-11-15 | [
[
"Shen",
"Shui-Fa",
""
],
[
"Qian",
"Wei-Liang",
""
],
[
"Guo",
"Hong",
""
],
[
"Zhang",
"Shao-Jun",
""
],
[
"Li",
"Jin",
""
]
] | In this work, we explore the properties of the matrix method for black hole quasinormal modes on the nonuniform grid. In particular, the method is implemented to be adapted to the Chebyshev grid, aimed at effectively suppressing Runge's phenomenon. It is found that while such an implementation is favorable from a mathematical point of view, in practice, the increase in precision does not necessarily compensate for the penalty in computational time. On the other hand, the original matrix method, though subject to Runge's phenomenon, is shown to be reasonably robust and suffices for most applications with a moderate grid number. In terms of computational time and obtained significant figures, we carried out an analysis regarding the trade-off between the two aspects. The implications of the present study are also addressed. |
1506.06228 | Seyyed Shahrokh Assyyaee | N. Riazi and Sh. Assyyaee | A new look at dark energy | 6 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The origin of the dark energy which is assumed to be responsible for the
observed accelerated expansion of the universe still remains a scientific
dilemma. Here we propose a tentative origin for this energy, if it is coming
from a distribution of specific quantum particles.
| [
{
"created": "Sat, 20 Jun 2015 11:04:20 GMT",
"version": "v1"
}
] | 2015-06-23 | [
[
"Riazi",
"N.",
""
],
[
"Assyyaee",
"Sh.",
""
]
] | The origin of the dark energy which is assumed to be responsible for the observed accelerated expansion of the universe still remains a scientific dilemma. Here we propose a tentative origin for this energy, if it is coming from a distribution of specific quantum particles. |
gr-qc/0212080 | Jose Geraldo Pereira | Yu. N. Obukhov and J. G. Pereira | Metric-affine approach to teleparallel gravity | Revtex4, 22 pages, no figures. Accepted for publication in Phys. Rev.
D | Phys.Rev. D67 (2003) 044016 | 10.1103/PhysRevD.67.044016 | IFT.P-94/2002 | gr-qc | null | The teleparallel gravity theory, treated physically as a gauge theory of
translations, naturally represents a particular case of the most general
gauge-theoretic model based on the general affine group of spacetime. On the
other hand, geometrically, the Weitzenboeck spacetime of distant parallelism is
a particular case of the general metric-affine spacetime manifold. These
physical and geometrical facts offer a new approach to the teleparallelism. We
present a systematic treatment of the teleparallel gravity within the framework
of the metric-affine theory. The symmetries, conservation laws and the field
equations are consistently derived, and the physical consequences are discussed
in detail. We demonstrate that the so-called teleparallel GR-equivalent model
has a number of attractive features which distinguishes it among the general
teleparallel theories, although it has a consistency problem when dealing with
spinning matter sources.
| [
{
"created": "Thu, 19 Dec 2002 15:20:07 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Obukhov",
"Yu. N.",
""
],
[
"Pereira",
"J. G.",
""
]
] | The teleparallel gravity theory, treated physically as a gauge theory of translations, naturally represents a particular case of the most general gauge-theoretic model based on the general affine group of spacetime. On the other hand, geometrically, the Weitzenboeck spacetime of distant parallelism is a particular case of the general metric-affine spacetime manifold. These physical and geometrical facts offer a new approach to the teleparallelism. We present a systematic treatment of the teleparallel gravity within the framework of the metric-affine theory. The symmetries, conservation laws and the field equations are consistently derived, and the physical consequences are discussed in detail. We demonstrate that the so-called teleparallel GR-equivalent model has a number of attractive features which distinguishes it among the general teleparallel theories, although it has a consistency problem when dealing with spinning matter sources. |
gr-qc/0601078 | David Wands | David Wands (ICG, Portsmouth) | Brane-world cosmology | 16 pages, 4 figures, to appear in proceedings of ERE2005, the XXVIII
Spanish Relativity Meeting, Oviedo, Spain | null | 10.1063/1.2218177 | PU-ICG-06/01 | gr-qc astro-ph hep-th | null | Brane-world models, where observers are restricted to a brane in a
higher-dimensional spacetime, offer a novel perspective on cosmology. I discuss
some approaches to cosmology in extra dimensions and some interesting aspects
of gravity and cosmology in brane-world models.
| [
{
"created": "Thu, 19 Jan 2006 11:05:44 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Wands",
"David",
"",
"ICG, Portsmouth"
]
] | Brane-world models, where observers are restricted to a brane in a higher-dimensional spacetime, offer a novel perspective on cosmology. I discuss some approaches to cosmology in extra dimensions and some interesting aspects of gravity and cosmology in brane-world models. |
0912.0115 | A. Tawfik | A. Tawfik (ECTP & Mti U), H. Mansour (Cairo U), M. Wahba (ECTP & Mti
U) | Hubble Parameter in Bulk Viscous Cosmology | 4 pages, 2 eps figure, Talk given at 12th Marcel Grossmann Meeting on
"General Relativity", Paris-France, 12-18 July 2009 | null | null | ECTP-2009-9 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss influences of bulk viscosity on the Early Universe, which is
modeled by Friedmann-Robertson-Walker metric and Einstein field equations. We
assume that the matter filling the isotropic and homogeneous background is
relativistic viscous characterized by ultra-relativistic equations of state
deduced from recent lattice QCD simulations. We obtain a set of complicated
differential equations, for which we suggest approximate solutions for Hubble
parameter $H$. We find that finite viscosity in Eckart and Israel-Stewart
fluids would significantly modify our picture about the Early Universe.
| [
{
"created": "Tue, 1 Dec 2009 10:25:08 GMT",
"version": "v1"
}
] | 2009-12-02 | [
[
"Tawfik",
"A.",
"",
"ECTP & Mti U"
],
[
"Mansour",
"H.",
"",
"Cairo U"
],
[
"Wahba",
"M.",
"",
"ECTP & Mti\n U"
]
] | We discuss influences of bulk viscosity on the Early Universe, which is modeled by Friedmann-Robertson-Walker metric and Einstein field equations. We assume that the matter filling the isotropic and homogeneous background is relativistic viscous characterized by ultra-relativistic equations of state deduced from recent lattice QCD simulations. We obtain a set of complicated differential equations, for which we suggest approximate solutions for Hubble parameter $H$. We find that finite viscosity in Eckart and Israel-Stewart fluids would significantly modify our picture about the Early Universe. |
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