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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
gr-qc/0309015 | Eanna E. Flanagan | Eanna E. Flanagan | Higher order gravity theories and scalar tensor theories | 5 pages, no figures, revtex; references added | Class.Quant.Grav. 21 (2003) 417-426 | 10.1088/0264-9381/21/2/006 | null | gr-qc astro-ph hep-th | null | We generalize the known equivalence between higher order gravity theories and
scalar tensor theories to a new class of theories. Specifically, in the context
of a first order or Palatini variational principle where the metric and
connection are treated as independent variables, we consider theories for which
the Lagrangian density is a function f of (i) the Ricci scalar computed from
the metric, and (ii) a second Ricci scalar computed from the connection. We
show that such theories can be written as tensor-multi-scalar theories with two
scalar fields with the following features: (i) the two dimensional sigma-model
metric that defines the kinetic energy terms for the scalar fields has
constant, negative curvature; (ii) the coupling function determining the
coupling to matter of the scalar fields is universal, independent of the choice
of function f; and (iii) if both mass eigenstates are long ranged, then the
Eddington post-Newtonian parameter has value 1/2. Therefore in order to be
compatible with solar system experiments at least one of the mass eigenstates
must be short ranged.
| [
{
"created": "Wed, 3 Sep 2003 05:59:32 GMT",
"version": "v1"
},
{
"created": "Fri, 26 Sep 2003 19:55:26 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Flanagan",
"Eanna E.",
""
]
] | We generalize the known equivalence between higher order gravity theories and scalar tensor theories to a new class of theories. Specifically, in the context of a first order or Palatini variational principle where the metric and connection are treated as independent variables, we consider theories for which the Lagrangian density is a function f of (i) the Ricci scalar computed from the metric, and (ii) a second Ricci scalar computed from the connection. We show that such theories can be written as tensor-multi-scalar theories with two scalar fields with the following features: (i) the two dimensional sigma-model metric that defines the kinetic energy terms for the scalar fields has constant, negative curvature; (ii) the coupling function determining the coupling to matter of the scalar fields is universal, independent of the choice of function f; and (iii) if both mass eigenstates are long ranged, then the Eddington post-Newtonian parameter has value 1/2. Therefore in order to be compatible with solar system experiments at least one of the mass eigenstates must be short ranged. |
1210.6346 | Farook Rahaman | Farook Rahaman, Ayan Banerjee, Irina Radinschi, Sumita Banerjee and
Soumendranath Ruz | Singularity free stars in (2+1) dimensions | 8 pages, 11 figures. Accepted in IJTP | null | 10.1007/s10773-012-1406-1 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present some new types of non-singular model for anisotropic stars with
constant $\Lambda $ and variable $\Lambda$ based on the Krori and Barua (KB)
metric in $(2+1)$ dimensions. The solutions obtained here satisfy all the
regularity conditions and its simple analytical form helps us to study the
various physical properties of the configuration.
| [
{
"created": "Tue, 23 Oct 2012 11:36:59 GMT",
"version": "v1"
}
] | 2015-06-11 | [
[
"Rahaman",
"Farook",
""
],
[
"Banerjee",
"Ayan",
""
],
[
"Radinschi",
"Irina",
""
],
[
"Banerjee",
"Sumita",
""
],
[
"Ruz",
"Soumendranath",
""
]
] | We present some new types of non-singular model for anisotropic stars with constant $\Lambda $ and variable $\Lambda$ based on the Krori and Barua (KB) metric in $(2+1)$ dimensions. The solutions obtained here satisfy all the regularity conditions and its simple analytical form helps us to study the various physical properties of the configuration. |
gr-qc/9510025 | Gerard Clement | G\'erard Cl\'ement | Spinning charged BTZ black holes and self-dual particle-like solutions | 10 pages, LaTex, no figures | Phys.Lett. B367 (1996) 70-74 | 10.1016/0370-2693(95)01464-0 | GCR-95/10/02 | gr-qc hep-th | null | We generate from the static charged BTZ black hole a family of spinning
charged solutions to the Einstein-Maxwell equations in 2+1 dimensions. These
solutions go over, in a suitable limit, to self-dual spinning charged
solutions, which are horizonless and regular, with logarithmically divergent
mass and spin. To cure this divergence, we add a topological Chern-Simons term
to the gauge field action. The resulting self-dual solution is horizonless,
regular, and asymptotic to the extreme BTZ black hole.
| [
{
"created": "Fri, 13 Oct 1995 13:16:49 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Clément",
"Gérard",
""
]
] | We generate from the static charged BTZ black hole a family of spinning charged solutions to the Einstein-Maxwell equations in 2+1 dimensions. These solutions go over, in a suitable limit, to self-dual spinning charged solutions, which are horizonless and regular, with logarithmically divergent mass and spin. To cure this divergence, we add a topological Chern-Simons term to the gauge field action. The resulting self-dual solution is horizonless, regular, and asymptotic to the extreme BTZ black hole. |
gr-qc/0309019 | Vladimir Majernik | V. Majernik | The force exerting on cosmic bodies in a quaternionc field | 8 pages, no figures | Gen.Rel.Grav. 36 (2004) 1143-1150 | 10.1023/B:GERG.0000018280.96739.ae | null | gr-qc | null | The expression of a time-dependent cosmological constant $\lambda \propto
1/t^2$ is interpreted as the energy density of a special type of the
quaternionic field. The Lorenz-like force acting on the moving body in the
presence of this quaternionic field is determined. The astronomical and
terrestrial effects of this field are presented, and the ways how it can be
observably detected is discussed. Finally, a new mechanism of the particle
creation and an alternative cosmological scenario in the presence of the cosmic
quatertionic field is suggested.
| [
{
"created": "Wed, 3 Sep 2003 10:07:57 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Majernik",
"V.",
""
]
] | The expression of a time-dependent cosmological constant $\lambda \propto 1/t^2$ is interpreted as the energy density of a special type of the quaternionic field. The Lorenz-like force acting on the moving body in the presence of this quaternionic field is determined. The astronomical and terrestrial effects of this field are presented, and the ways how it can be observably detected is discussed. Finally, a new mechanism of the particle creation and an alternative cosmological scenario in the presence of the cosmic quatertionic field is suggested. |
2302.11227 | Yuan-Chuan Zou | Hao Wang, Yuan-Chuan Zou, Yu Liu | Phenomenological relationship between eccentric and quasi-circular
orbital binary black hole waveform | 19 pages, 18 figures | null | 10.1103/PhysRevD.107.124061 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Eccentricity, an important parameter of gravitational waves, has been paid
more and more attention because it can reflect the dynamics of compact object
mergers. Obtaining an accurate and fast gravitational waveform template is of
great significance for the estimation of gravitational wave parameters. This
paper aims to do an extended study of the phenomenological fitting model
proposed by Setyawati and Ohme for adding eccentricity to quasi-circular
orbital waveforms. It can be applied to higher eccentricity up to e = 0.4. But
the higher the eccentricity, the less the accuracy. For e in [0, 0.1], it gives
an overlap of more than 99.99%. For e in [0.1, 0.2], it gives an overlap of
more than 99.9%. For e in [0.2, 0.3], it gives an overlap of more than 99%. For
e in [0.3, 0.4], it gives an overlap of more than 90%. The reason for these
phenomena is that the larger the eccentricity, the larger the deviation of the
eccentricity estimator from the cosine function due to the large change in the
morphology of the eccentric waveform, and the worse the fitting effect of the
model. It can be applied to higher-order modes and gives the same overlap
behavior. After adding a shift parameter, it can be applied to spin-aligned or
spin-antialigned waveforms. After obtaining spin-precessing effect, it can be
applied to the spin-precessing case. In summary, non-spining, spin-aligned,
spin-antialigned or spin-precessing waveforms with eccentricity can be
constructed from quasi-circular non-spining waveforms by the phenomenological
model, which is not only helpful for us to quickly construct phenomenological
gravitational wave templates, but also reveals a phenomenological and universal
relationship between eccentric waveform and quasi-circular orbital waveform.
| [
{
"created": "Wed, 22 Feb 2023 09:18:41 GMT",
"version": "v1"
}
] | 2023-07-12 | [
[
"Wang",
"Hao",
""
],
[
"Zou",
"Yuan-Chuan",
""
],
[
"Liu",
"Yu",
""
]
] | Eccentricity, an important parameter of gravitational waves, has been paid more and more attention because it can reflect the dynamics of compact object mergers. Obtaining an accurate and fast gravitational waveform template is of great significance for the estimation of gravitational wave parameters. This paper aims to do an extended study of the phenomenological fitting model proposed by Setyawati and Ohme for adding eccentricity to quasi-circular orbital waveforms. It can be applied to higher eccentricity up to e = 0.4. But the higher the eccentricity, the less the accuracy. For e in [0, 0.1], it gives an overlap of more than 99.99%. For e in [0.1, 0.2], it gives an overlap of more than 99.9%. For e in [0.2, 0.3], it gives an overlap of more than 99%. For e in [0.3, 0.4], it gives an overlap of more than 90%. The reason for these phenomena is that the larger the eccentricity, the larger the deviation of the eccentricity estimator from the cosine function due to the large change in the morphology of the eccentric waveform, and the worse the fitting effect of the model. It can be applied to higher-order modes and gives the same overlap behavior. After adding a shift parameter, it can be applied to spin-aligned or spin-antialigned waveforms. After obtaining spin-precessing effect, it can be applied to the spin-precessing case. In summary, non-spining, spin-aligned, spin-antialigned or spin-precessing waveforms with eccentricity can be constructed from quasi-circular non-spining waveforms by the phenomenological model, which is not only helpful for us to quickly construct phenomenological gravitational wave templates, but also reveals a phenomenological and universal relationship between eccentric waveform and quasi-circular orbital waveform. |
0705.3109 | T. Damour | Thibault Damour | Black Hole and Neutron Star Binaries: Theoretical Challenges | 53 pages, 3 eps figures, to appear in a revised edition of the book:
Neutron Stars, Black Holes and Binary X-Ray Sources by H. Gursky and R.
Ruffini | null | null | null | gr-qc | null | Some of the theoretical challenges posed by the general relativistic
description of binary systems of compact objects (neutron stars or black holes)
are reviewed. We recall the various ways one can use the theory of the motion,
and of the timing, of binary pulsars to test the strong-field and/or radiative
aspects of General Relativity. Recent advances in the theory of the motion and
radiation of binary black holes are discussed. One emphasizes the usefulness of
the Effective One Body approach in providing a quasi-analytical description of
the waveform emitted by coalescing binary black holes.
| [
{
"created": "Tue, 22 May 2007 08:24:16 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Damour",
"Thibault",
""
]
] | Some of the theoretical challenges posed by the general relativistic description of binary systems of compact objects (neutron stars or black holes) are reviewed. We recall the various ways one can use the theory of the motion, and of the timing, of binary pulsars to test the strong-field and/or radiative aspects of General Relativity. Recent advances in the theory of the motion and radiation of binary black holes are discussed. One emphasizes the usefulness of the Effective One Body approach in providing a quasi-analytical description of the waveform emitted by coalescing binary black holes. |
1907.06854 | Luis Granda | L. N. Granda | $\Lambda$CDM-like models with future singularities | 32 pages, 6 figures, to appear in EPJP | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider new models of dark energy with finite time future singularities,
by introducing the pressure density as a function of the scale factor. This
approach gives acceptable phenomenological models of dark energy, practically
indistinguishable from the cosmological constant up to the present, which face
future singularities at finite time and finite scale factor. Exact scalar field
model representation was found for quintessence, Big Rip and type III
singularity models. The simple form of the equation of state allows to
establish a relationship between its current value, $w_0$, and the time or
redshift at which the singularity takes place. The effect on the growth of
matter perturbations was calculated.
| [
{
"created": "Tue, 16 Jul 2019 06:05:49 GMT",
"version": "v1"
}
] | 2019-07-17 | [
[
"Granda",
"L. N.",
""
]
] | We consider new models of dark energy with finite time future singularities, by introducing the pressure density as a function of the scale factor. This approach gives acceptable phenomenological models of dark energy, practically indistinguishable from the cosmological constant up to the present, which face future singularities at finite time and finite scale factor. Exact scalar field model representation was found for quintessence, Big Rip and type III singularity models. The simple form of the equation of state allows to establish a relationship between its current value, $w_0$, and the time or redshift at which the singularity takes place. The effect on the growth of matter perturbations was calculated. |
2302.11915 | Jo\~ao Lu\'is Rosa | Jo\~ao Lu\'is Rosa | Observational properties of relativistic fluid spheres with thin
accretion disks | 22 pages, 25 figures | Phys. Rev. D 107, 084048 (2023) | 10.1103/PhysRevD.107.084048 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we analyze the observational properties of incompressible
relativistic fluid spheres with and without thin-shells, when surrounded by
thin accretion disks. We consider a set of six configurations with different
combinations of the star radius $R$ and the thin-shell radius $r_\Sigma$ to
produce solutions with neither thin-shells nor light-rings, with either of
those features, and with both. Furthermore, we consider three different models
for the intensity profile of the accretion disk, based on the
Gralla-Lupsasca-Marrone (GLM) disk model, for which the peaks of intensity
occur at the Innermost Stable Circular Orbit (ISCO), the Light-Ring (LR), and
the center of the star. The observed images and intensity profiles for an
asymptotic observer are produced using a Mathematica-based ray-tracing code.
Our results indicate that, in the absence of a light-ring, the presence of a
thin-shell produces a negligible effect in the observational properties of the
stars. However, when the spacetime features a light-ring, the portion of the
mass of the star that is stored in the thin-shell has a strong effect on its
observational properties, particularly in the magnitude of the central
gravitational redshift effect responsible for causing a central shadow-like
dimming in the observed images. A comparison with the Schwarzschild spacetime
is also provided and the most compact configurations are shown to produce
observational imprints similar to those of black-hole solutions, with subtle
qualitative differences, most notably extra secondary image components that
decrease the radius of the shadow and are potentially observable.
| [
{
"created": "Thu, 23 Feb 2023 10:45:13 GMT",
"version": "v1"
}
] | 2023-05-01 | [
[
"Rosa",
"João Luís",
""
]
] | In this work we analyze the observational properties of incompressible relativistic fluid spheres with and without thin-shells, when surrounded by thin accretion disks. We consider a set of six configurations with different combinations of the star radius $R$ and the thin-shell radius $r_\Sigma$ to produce solutions with neither thin-shells nor light-rings, with either of those features, and with both. Furthermore, we consider three different models for the intensity profile of the accretion disk, based on the Gralla-Lupsasca-Marrone (GLM) disk model, for which the peaks of intensity occur at the Innermost Stable Circular Orbit (ISCO), the Light-Ring (LR), and the center of the star. The observed images and intensity profiles for an asymptotic observer are produced using a Mathematica-based ray-tracing code. Our results indicate that, in the absence of a light-ring, the presence of a thin-shell produces a negligible effect in the observational properties of the stars. However, when the spacetime features a light-ring, the portion of the mass of the star that is stored in the thin-shell has a strong effect on its observational properties, particularly in the magnitude of the central gravitational redshift effect responsible for causing a central shadow-like dimming in the observed images. A comparison with the Schwarzschild spacetime is also provided and the most compact configurations are shown to produce observational imprints similar to those of black-hole solutions, with subtle qualitative differences, most notably extra secondary image components that decrease the radius of the shadow and are potentially observable. |
2407.05111 | Piyali Bhar | Piyali Bhar, Allah Ditta, and Abdelghani Errehymy | Noncommutative wormhole in de Rham-Gabadadze-Tolley like massive gravity | 16 pages, Accepted in Nuclear Physics B | Nucl. Phys. B 1006 (2024) 116621 | 10.1016/j.nuclphysb.2024.116621 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | The wormhole solution in dRGT massive gravity is examined in this paper in
the background of non-commutative geometry. In order to derive the wormhole
model, along with the zero tidal force, we assume that the matter distribution
is given by the Gaussian and Lorentzian distributions. The shape function in
both models involves the massive gravity parameters m2c1 and m2c2. But the
spacetime loses its asymptotic flatness due to the action of the massive
gravity parameter. It is noticed that the asymptotic flatness is affected by
the repulsive effect induced in the massive gravitons that push the spacetime
geometry very strongly. We observed that each model violates the null energy
criteria, indicating the presence of exotic matter which is necessary to
sustain the wormholes. The exotic matter is measured using the volume integral
quantifier. Moreover, it is discovered that the model is stable under the
hydrostatic equilibrium condition by utilizing the TOV equation. Finally, our
research encompassed an exploration of the repulsive influence exerted by
gravity. Our findings demonstrated that the presence of repulsive gravity
results in a negative deflection angle for photons following null geodesics.
Remarkably, we consistently observed negative values for the deflection angle
across all values of r0 in the two scenarios examined. This consistent
negativity unequivocally signifies the manifestation of the repulsive gravity
effect.
| [
{
"created": "Sat, 6 Jul 2024 15:41:17 GMT",
"version": "v1"
}
] | 2024-07-30 | [
[
"Bhar",
"Piyali",
""
],
[
"Ditta",
"Allah",
""
],
[
"Errehymy",
"Abdelghani",
""
]
] | The wormhole solution in dRGT massive gravity is examined in this paper in the background of non-commutative geometry. In order to derive the wormhole model, along with the zero tidal force, we assume that the matter distribution is given by the Gaussian and Lorentzian distributions. The shape function in both models involves the massive gravity parameters m2c1 and m2c2. But the spacetime loses its asymptotic flatness due to the action of the massive gravity parameter. It is noticed that the asymptotic flatness is affected by the repulsive effect induced in the massive gravitons that push the spacetime geometry very strongly. We observed that each model violates the null energy criteria, indicating the presence of exotic matter which is necessary to sustain the wormholes. The exotic matter is measured using the volume integral quantifier. Moreover, it is discovered that the model is stable under the hydrostatic equilibrium condition by utilizing the TOV equation. Finally, our research encompassed an exploration of the repulsive influence exerted by gravity. Our findings demonstrated that the presence of repulsive gravity results in a negative deflection angle for photons following null geodesics. Remarkably, we consistently observed negative values for the deflection angle across all values of r0 in the two scenarios examined. This consistent negativity unequivocally signifies the manifestation of the repulsive gravity effect. |
1205.3134 | Andrei Lebed G | Andrei Lebed | Breakdown of the Equivalence between Energy Content and Weight in a Weak
Gravitational Field for a Quantum Body | Talk at the American Physical Society April Meeting (Atlanta, USA,
April 1st, 2012) | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown that weight operator of a composite quantum body in a weak
external gravitational field in the post-Newtonian approximation of the General
Relativity does not commute with its energy operator, taken in the absence of
the field. Nevertheless, the weak equivalence between the expectations values
of weight and energy is shown to survive at a macroscopic level for stationary
quantum states for the simplest composite quantum body - a hydrogen atom.
Breakdown of the weak equivalence between weight and energy at a microscopic
level for stationary quantum states can be experimentally detected by studying
unusual electromagnetic radiation, emitted by the atoms, supported and moved in
the Earth gravitational field with constant velocity, using spacecraft or
satellite. For superpositions of stationary quantum states, a breakdown of the
above mentioned equivalence at a macroscopic level leads to time dependent
oscillations of the expectation values of weight, where the equivalence
restores after averaging over time procedure.
| [
{
"created": "Mon, 14 May 2012 18:44:57 GMT",
"version": "v1"
}
] | 2012-05-15 | [
[
"Lebed",
"Andrei",
""
]
] | It is shown that weight operator of a composite quantum body in a weak external gravitational field in the post-Newtonian approximation of the General Relativity does not commute with its energy operator, taken in the absence of the field. Nevertheless, the weak equivalence between the expectations values of weight and energy is shown to survive at a macroscopic level for stationary quantum states for the simplest composite quantum body - a hydrogen atom. Breakdown of the weak equivalence between weight and energy at a microscopic level for stationary quantum states can be experimentally detected by studying unusual electromagnetic radiation, emitted by the atoms, supported and moved in the Earth gravitational field with constant velocity, using spacecraft or satellite. For superpositions of stationary quantum states, a breakdown of the above mentioned equivalence at a macroscopic level leads to time dependent oscillations of the expectation values of weight, where the equivalence restores after averaging over time procedure. |
gr-qc/0412138 | Kirill Bronnikov | K.A. Bronnikov, E.A. Tagirov | Quantum theory of scalar field in isotropic world | 7 pages, gc.sty. Published for the first time in Russian in 1968 as
JINR Preprint. With E.A. Tagirov's comment of September 2004 | Grav.Cosmol. 10 (2004) 249-255 | null | JINR P2-4151, Dubna, 1968 | gr-qc | null | Fock representations are constructed for a free scalar field in the closed
and quasi-Euclidean isotropic cosmological models. Invariance of their cyclic
vector (vacuum) under isometries and the correspondence principle single out a
class of unitarily equivalent representations.
| [
{
"created": "Thu, 30 Dec 2004 18:39:59 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Bronnikov",
"K. A.",
""
],
[
"Tagirov",
"E. A.",
""
]
] | Fock representations are constructed for a free scalar field in the closed and quasi-Euclidean isotropic cosmological models. Invariance of their cyclic vector (vacuum) under isometries and the correspondence principle single out a class of unitarily equivalent representations. |
1905.04586 | Gilles Esposito-Farese | Gilles Esposito-Farese | Hamiltonian vs stability in alternative theories of gravity | 9 pages, 2 figures, uses the LaTeX class file "moriond.cls",
contribution to the 2019 Gravitation session of the 54th Rencontres de
Moriond | Proceedings of the 54th Rencontres de Moriond, La Thuile, ARISF
(2019), 201-8 | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | When a Hamiltonian density is bounded by below, we know that the
lowest-energy state must be stable. One is often tempted to reverse the theorem
and therefore believe that an unbounded Hamiltonian density always implies an
instability. The main purpose of this presentation (which summarizes my work
with E. Babichev, C. Charmousis and A. Leh\'ebel) is to pedagogically explain
why this is erroneous. Stability is indeed a coordinate-independent property,
whereas the Hamiltonian density does depend on the choice of coordinates. In
alternative theories of gravity, like k-essence or Horndeski theories, the
correct stability criterion is a subtler version of the well-known "Weak Energy
Condition" of general relativity. As an illustration, this criterion is applied
to an exact Schwarzschild-de Sitter solution of a Horndeski theory, which is
found to be stable for a given range of its parameters, contrary to a claim in
the literature.
| [
{
"created": "Sat, 11 May 2019 20:31:54 GMT",
"version": "v1"
}
] | 2023-12-08 | [
[
"Esposito-Farese",
"Gilles",
""
]
] | When a Hamiltonian density is bounded by below, we know that the lowest-energy state must be stable. One is often tempted to reverse the theorem and therefore believe that an unbounded Hamiltonian density always implies an instability. The main purpose of this presentation (which summarizes my work with E. Babichev, C. Charmousis and A. Leh\'ebel) is to pedagogically explain why this is erroneous. Stability is indeed a coordinate-independent property, whereas the Hamiltonian density does depend on the choice of coordinates. In alternative theories of gravity, like k-essence or Horndeski theories, the correct stability criterion is a subtler version of the well-known "Weak Energy Condition" of general relativity. As an illustration, this criterion is applied to an exact Schwarzschild-de Sitter solution of a Horndeski theory, which is found to be stable for a given range of its parameters, contrary to a claim in the literature. |
1101.5059 | Anja Marunovic | Anja Marunovic and Tomislav Prokopec | Time transients in the quantum corrected Newtonian potential induced by
a massless nonminimally coupled scalar field | 22 pages, 5 figures; detailed calculation of the graviton vacuum
polarization moved to the new Appendix; matches published version | Phys.Rev.D83:104039,2011 | 10.1103/PhysRevD.83.104039 | ITP-UU-11/04, SPIN-11/02 | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We calculate the one loop graviton vacuum polarization induced by a massless,
nonminimally coupled scalar field on Minkowski background. We make use of the
Schwinger-Keldysh formalism, which allows us to study time dependent phenomena.
As an application we compute the leading quantum correction to the Newtonian
potential of a point particle. The novel aspect of the calculation is the use
of the Schwinger-Keldysh formalism, within which we calculate the time
transients induced by switching on of the graviton-scalar coupling.
| [
{
"created": "Wed, 26 Jan 2011 13:50:20 GMT",
"version": "v1"
},
{
"created": "Thu, 8 Sep 2011 16:08:52 GMT",
"version": "v2"
}
] | 2015-03-18 | [
[
"Marunovic",
"Anja",
""
],
[
"Prokopec",
"Tomislav",
""
]
] | We calculate the one loop graviton vacuum polarization induced by a massless, nonminimally coupled scalar field on Minkowski background. We make use of the Schwinger-Keldysh formalism, which allows us to study time dependent phenomena. As an application we compute the leading quantum correction to the Newtonian potential of a point particle. The novel aspect of the calculation is the use of the Schwinger-Keldysh formalism, within which we calculate the time transients induced by switching on of the graviton-scalar coupling. |
1504.04582 | Wen-Biao Liu | Jing-Zhao Qi, Ming-Jian Zhang, Wen-Biao Liu | Dynamical evolution of quintessence cosmology in a physical phase space | Accepted: 21 March 2016, Int J Theor Phys 2016 | null | 10.1007/s10773-016-2996-9 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The phase space analysis of cosmological parameters $\Omega_{\phi}$ and
$\gamma_{\phi}$ is given. Based on this, the well-known quintessence cosmology
is studied with an exponential potential $V(\phi)=V_{0}\exp(-\lambda\phi)$.
Given observational data, the current state of universe could be pinpointed in
the phase diagrams, thus making the diagrams more informative. The scaling
solution of quintessence usually is not supposed to give the cosmic
accelerating expansion, but we prove it could educe the transient acceleration.
We also find that the differential equations of system used widely in study of
scalar field are incomplete, and then a numerical method is used to figure out
the range of application.
| [
{
"created": "Thu, 16 Apr 2015 08:44:56 GMT",
"version": "v1"
},
{
"created": "Thu, 14 May 2015 14:17:47 GMT",
"version": "v2"
},
{
"created": "Sun, 12 Jun 2016 07:31:19 GMT",
"version": "v3"
}
] | 2016-06-14 | [
[
"Qi",
"Jing-Zhao",
""
],
[
"Zhang",
"Ming-Jian",
""
],
[
"Liu",
"Wen-Biao",
""
]
] | The phase space analysis of cosmological parameters $\Omega_{\phi}$ and $\gamma_{\phi}$ is given. Based on this, the well-known quintessence cosmology is studied with an exponential potential $V(\phi)=V_{0}\exp(-\lambda\phi)$. Given observational data, the current state of universe could be pinpointed in the phase diagrams, thus making the diagrams more informative. The scaling solution of quintessence usually is not supposed to give the cosmic accelerating expansion, but we prove it could educe the transient acceleration. We also find that the differential equations of system used widely in study of scalar field are incomplete, and then a numerical method is used to figure out the range of application. |
2111.01064 | Michael Katz | Michael L. Katz | A fully-automated end-to-end pipeline for massive black hole binary
signal extraction from LISA data | 14 pages, 6 figures, 3 tables | null | 10.1103/PhysRevD.105.044055 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The LISA Data Challenges Working Group within the LISA Consortium has started
publishing datasets to benchmark, compare, and build LISA data analysis
infrastructure as the Consortium prepares for the launch of the mission. We
present our solution to the dataset from LISA Data Challenge (LDC) 1A
containing a single massive black hole binary signal. This solution is built
from a fully-automated and GPU-accelerated pipeline consisting of three
segments: a brute-force initial search; a refining search that uses the
efficient Likelihood computation technique of Heterodyning (also called
Relative Binning) to locate the maximum Likelihood point; and a parameter
estimation portion that also takes advantage of the speed of the Heterodyning
method. This pipeline takes tens of minutes to evolve from randomized initial
parameters throughout the prior volume to a converged final posterior
distribution. Final posteriors are shown for both datasets from LDC 1A: one
noiseless data stream and one containing additive noise. A posterior
distribution including higher harmonics is also shown for a self-injected
waveform with the same source parameters as is used in the original LDC 1A
dataset. This higher-mode posterior is shown in order to provide a more
realistic distribution on the parameters of the source.
| [
{
"created": "Mon, 1 Nov 2021 16:22:10 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Jan 2022 23:30:51 GMT",
"version": "v2"
},
{
"created": "Tue, 22 Feb 2022 00:26:42 GMT",
"version": "v3"
}
] | 2022-03-09 | [
[
"Katz",
"Michael L.",
""
]
] | The LISA Data Challenges Working Group within the LISA Consortium has started publishing datasets to benchmark, compare, and build LISA data analysis infrastructure as the Consortium prepares for the launch of the mission. We present our solution to the dataset from LISA Data Challenge (LDC) 1A containing a single massive black hole binary signal. This solution is built from a fully-automated and GPU-accelerated pipeline consisting of three segments: a brute-force initial search; a refining search that uses the efficient Likelihood computation technique of Heterodyning (also called Relative Binning) to locate the maximum Likelihood point; and a parameter estimation portion that also takes advantage of the speed of the Heterodyning method. This pipeline takes tens of minutes to evolve from randomized initial parameters throughout the prior volume to a converged final posterior distribution. Final posteriors are shown for both datasets from LDC 1A: one noiseless data stream and one containing additive noise. A posterior distribution including higher harmonics is also shown for a self-injected waveform with the same source parameters as is used in the original LDC 1A dataset. This higher-mode posterior is shown in order to provide a more realistic distribution on the parameters of the source. |
1408.6983 | Andrea Geralico | Donato Bini, Andrea Geralico, Maria Haney | Refraction index analysis of light propagation in a colliding
gravitational wave spacetime | 16 pages, 6 figures; published version | Gen. Relativ. Gravit. 46, 1644 (2014) | 10.1007/s10714-013-1644-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The optical medium analogy of a given spacetime was developed decades ago and
has since then been widely applied to different gravitational contexts. Here we
consider the case of a colliding gravitational wave spacetime, generalizing
previous results concerning single gravitational pulses. Given the complexity
of the nonlinear interaction of two gravitational waves in the framework of
general relativity, typically leading to the formation of either horizons or
singularities, the optical medium analogy proves helpful to simply capture some
interesting effects of photon propagation.
| [
{
"created": "Fri, 29 Aug 2014 11:18:31 GMT",
"version": "v1"
}
] | 2015-06-22 | [
[
"Bini",
"Donato",
""
],
[
"Geralico",
"Andrea",
""
],
[
"Haney",
"Maria",
""
]
] | The optical medium analogy of a given spacetime was developed decades ago and has since then been widely applied to different gravitational contexts. Here we consider the case of a colliding gravitational wave spacetime, generalizing previous results concerning single gravitational pulses. Given the complexity of the nonlinear interaction of two gravitational waves in the framework of general relativity, typically leading to the formation of either horizons or singularities, the optical medium analogy proves helpful to simply capture some interesting effects of photon propagation. |
0808.0475 | Edward Glass | J.P. Krisch and E.N. Glass | Thin Shell Dynamics and Equations of State | null | Phys.Rev.D78:044003,2008 | 10.1103/PhysRevD.78.044003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A relation between stress-energy and motion is derived for accelerated Israel
layers. The relation, for layers between two Schwarzschild manifolds,
generalizes the equation of state for geodesic collapse. A set of linked layers
is discussed.
| [
{
"created": "Mon, 4 Aug 2008 18:07:00 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Krisch",
"J. P.",
""
],
[
"Glass",
"E. N.",
""
]
] | A relation between stress-energy and motion is derived for accelerated Israel layers. The relation, for layers between two Schwarzschild manifolds, generalizes the equation of state for geodesic collapse. A set of linked layers is discussed. |
1504.07606 | Emmanuil Saridakis | Genly Leon (Valparaiso U., Catolica), Emmanuel N. Saridakis (Natl.
Tech. U., Athens & Valparaiso U., Catolica) | Cosmology in time asymmetric extensions of general relativity | 42 pages, 6 figures, 8 tables, version published in JCAP | JCAP 1511 (2015) 11, 009 | 10.1088/1475-7516/2015/11/009 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the cosmological behavior in a universe governed by time
asymmetric extensions of general relativity, which is a novel modified gravity
based on the addition of new, time-asymmetric, terms on the Hamiltonian
framework, in a way that the algebra of constraints and local physics remain
unchanged. Nevertheless, at cosmological scales these new terms can have
significant effects that can alter the universe evolution, both at early and
late times, and the freedom in the choice of the involved modification function
makes the scenario able to produce a huge class of cosmological behaviors. For
basic ansatzes of modification, we perform a detailed dynamical analysis,
extracting the stable late-time solutions. Amongst others, we find that the
universe can result in dark-energy dominated, accelerating solutions, even in
the absence of an explicit cosmological constant, in which the dark energy can
be quintessence-like, phantom-like, or behave as an effective cosmological
constant. Moreover, it can result to matter-domination, or to a Big Rip, or
experience the sequence from matter to dark energy domination. Additionally, in
the case of closed curvature, the universe may experience a cosmological bounce
or turnaround, or even cyclic behavior. Finally, these scenarios can easily
satisfy the observational and phenomenological requirements. Hence, time
asymmetric cosmology can be a good candidate for the description of the
universe.
| [
{
"created": "Tue, 28 Apr 2015 19:24:09 GMT",
"version": "v1"
},
{
"created": "Mon, 9 Nov 2015 19:21:43 GMT",
"version": "v2"
}
] | 2015-11-11 | [
[
"Leon",
"Genly",
"",
"Valparaiso U., Catolica"
],
[
"Saridakis",
"Emmanuel N.",
"",
"Natl.\n Tech. U., Athens & Valparaiso U., Catolica"
]
] | We investigate the cosmological behavior in a universe governed by time asymmetric extensions of general relativity, which is a novel modified gravity based on the addition of new, time-asymmetric, terms on the Hamiltonian framework, in a way that the algebra of constraints and local physics remain unchanged. Nevertheless, at cosmological scales these new terms can have significant effects that can alter the universe evolution, both at early and late times, and the freedom in the choice of the involved modification function makes the scenario able to produce a huge class of cosmological behaviors. For basic ansatzes of modification, we perform a detailed dynamical analysis, extracting the stable late-time solutions. Amongst others, we find that the universe can result in dark-energy dominated, accelerating solutions, even in the absence of an explicit cosmological constant, in which the dark energy can be quintessence-like, phantom-like, or behave as an effective cosmological constant. Moreover, it can result to matter-domination, or to a Big Rip, or experience the sequence from matter to dark energy domination. Additionally, in the case of closed curvature, the universe may experience a cosmological bounce or turnaround, or even cyclic behavior. Finally, these scenarios can easily satisfy the observational and phenomenological requirements. Hence, time asymmetric cosmology can be a good candidate for the description of the universe. |
2007.01591 | Abdulla Al Mamon | Abdulla Al Mamon | Study of Tsallis holographic dark energy model in the framework of
Fractal cosmology | 6 pages, 5 figures, Accepted for publication in MPLA | null | 10.1142/S021773232050251X | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we study the evolution of a fractal universe composed of
Tsallis holographic dark energy (THDE) and a pressureless dark matter that
interact with each other through a mutual interaction. We then reconstruct the
interaction term of this model by considering the Hubble length as the IR
cut-off scale. We also study the behavior of different cosmological parameters
during the cosmic evolution from the early matter-dominated era until the
late-time acceleration. The present study shows that the universe undergoes a
smooth transition from a decelerated to an accelerated phase of expansion in
the recent past. Moreover, we also shown the evolution of the normalized Hubble
parameter for our model and compared that with the latest cosmic chronometer
data. Finally, we test the viability of the model by exploring its stability
against small perturbation by using the squared of the sound speed.
| [
{
"created": "Fri, 3 Jul 2020 10:11:35 GMT",
"version": "v1"
}
] | 2020-10-28 | [
[
"Mamon",
"Abdulla Al",
""
]
] | In this work, we study the evolution of a fractal universe composed of Tsallis holographic dark energy (THDE) and a pressureless dark matter that interact with each other through a mutual interaction. We then reconstruct the interaction term of this model by considering the Hubble length as the IR cut-off scale. We also study the behavior of different cosmological parameters during the cosmic evolution from the early matter-dominated era until the late-time acceleration. The present study shows that the universe undergoes a smooth transition from a decelerated to an accelerated phase of expansion in the recent past. Moreover, we also shown the evolution of the normalized Hubble parameter for our model and compared that with the latest cosmic chronometer data. Finally, we test the viability of the model by exploring its stability against small perturbation by using the squared of the sound speed. |
2403.16192 | Galin Gyulchev | Eugeny Babichev, Christos Charmousis, Daniela D. Doneva, Galin N.
Gyulchev and Stoytcho S. Yazadjiev | Testing disformal non-circular deformation of Kerr black holes with LISA | 19 pages, 13 figures; v2: references added | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | There is strong observational evidence that almost every large galaxy has a
supermassive black hole at its center. It is of fundamental importance to know
whether such black holes are described by the standard Kerr solution in General
Relativity (GR) or by another black hole solution. An interesting alternative
is the so-called disformal Kerr black holes which exist within the framework of
degenerate higher-order scalar-tensor (DHOST) theories of gravity. The
departure from the standard Kerr black hole spacetime is parametrized by a
parameter $D$, called $\textit{disformal parameter}$. In the present work, we
discuss the capability of LISA to detect the disformal parameter. For this
purpose, we study Extreme Mass Ratio Inspirals (EMRI's) around disformal Kerr
black holes within the framework of the quadrupole hybrid formalism. Even when
the disformal parameter is very small, its effect on the globally accumulated
phase of the gravitational waveform of an EMRI can be significant due to the
large number of cycles in the LISA band made by the small compact object. We
show that LISA will in principle be able to detect and measure extremely small
values of the disformal parameter which in turn, can be seen as an assessment
of LISA's ability to detect very small deviations from the Kerr geometry.
| [
{
"created": "Sun, 24 Mar 2024 15:18:00 GMT",
"version": "v1"
},
{
"created": "Wed, 12 Jun 2024 21:30:54 GMT",
"version": "v2"
}
] | 2024-06-14 | [
[
"Babichev",
"Eugeny",
""
],
[
"Charmousis",
"Christos",
""
],
[
"Doneva",
"Daniela D.",
""
],
[
"Gyulchev",
"Galin N.",
""
],
[
"Yazadjiev",
"Stoytcho S.",
""
]
] | There is strong observational evidence that almost every large galaxy has a supermassive black hole at its center. It is of fundamental importance to know whether such black holes are described by the standard Kerr solution in General Relativity (GR) or by another black hole solution. An interesting alternative is the so-called disformal Kerr black holes which exist within the framework of degenerate higher-order scalar-tensor (DHOST) theories of gravity. The departure from the standard Kerr black hole spacetime is parametrized by a parameter $D$, called $\textit{disformal parameter}$. In the present work, we discuss the capability of LISA to detect the disformal parameter. For this purpose, we study Extreme Mass Ratio Inspirals (EMRI's) around disformal Kerr black holes within the framework of the quadrupole hybrid formalism. Even when the disformal parameter is very small, its effect on the globally accumulated phase of the gravitational waveform of an EMRI can be significant due to the large number of cycles in the LISA band made by the small compact object. We show that LISA will in principle be able to detect and measure extremely small values of the disformal parameter which in turn, can be seen as an assessment of LISA's ability to detect very small deviations from the Kerr geometry. |
gr-qc/0110108 | Adam D. Helfer | Adam D. Helfer | Red-shifts near black holes | 20 pages, plain Tex, IOP macros, 4 eps figures, accepted by CQG | Class.Quant.Grav. 18 (2001) 5413-5428 | 10.1088/0264-9381/18/24/307 | null | gr-qc | null | A simple ordinary differential equation is derived governing the red-shifts
of wave-fronts propagating through a non-stationary spherically symmetric
space-time. Approach to an event horizon corresponds to approach to a fixed
point; in general, the phase portrait of the equation illuminates the
qualitative features of the geometry. In particular, the asymptotics of the
red-shift as a horizon is approached, a critical ingredient of Hawking's
prediction of radiation from black holes, are easily brought out. This
asympotic behavior has elements in common with the universal behavior near
phase transitions in statistical physics. The validity of the Unruh vacuum for
the Hawking process can be understood in terms of this universality. The
concept of surface gravity is extended to to non-stationary spherically
symmetric black holes. Finally, it is shown that in the non-stationary case,
Hawking's predicted flux of radiation from a black hole would be modified.
| [
{
"created": "Wed, 24 Oct 2001 17:13:23 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Helfer",
"Adam D.",
""
]
] | A simple ordinary differential equation is derived governing the red-shifts of wave-fronts propagating through a non-stationary spherically symmetric space-time. Approach to an event horizon corresponds to approach to a fixed point; in general, the phase portrait of the equation illuminates the qualitative features of the geometry. In particular, the asymptotics of the red-shift as a horizon is approached, a critical ingredient of Hawking's prediction of radiation from black holes, are easily brought out. This asympotic behavior has elements in common with the universal behavior near phase transitions in statistical physics. The validity of the Unruh vacuum for the Hawking process can be understood in terms of this universality. The concept of surface gravity is extended to to non-stationary spherically symmetric black holes. Finally, it is shown that in the non-stationary case, Hawking's predicted flux of radiation from a black hole would be modified. |
0907.0696 | Jeffrey Hazboun | Jeffrey S Hazboun and Tevian Dray | The Effect of Negative-Energy Shells on the Schwarzschild Black Hole | 12 pages, 10 figures | Gen.Rel.Grav.42:1457-1467,2010 | 10.1007/s10714-009-0916-5 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct Penrose diagrams for Schwarzschild spacetimes joined by massless
shells of matter, in the process correcting minor flaws in the similar diagrams
drawn by Dray and 't Hooft, and confirming their result that such shells
generate a horizon shift. We then consider shells with negative energy density,
showing that the horizon shift in this case allows for travel between the
heretofore causally separated exterior regions of the Schwarzschild geometry.
These drawing techniques are then used to investigate the properties of
successive shells, joining multiple Schwarzschild regions. Again, the presence
of negative-energy shells leads to a causal connection between the exterior
regions, even in (some) cases with two successive shells of equal but opposite
total energy.
| [
{
"created": "Fri, 3 Jul 2009 18:54:42 GMT",
"version": "v1"
}
] | 2014-11-20 | [
[
"Hazboun",
"Jeffrey S",
""
],
[
"Dray",
"Tevian",
""
]
] | We construct Penrose diagrams for Schwarzschild spacetimes joined by massless shells of matter, in the process correcting minor flaws in the similar diagrams drawn by Dray and 't Hooft, and confirming their result that such shells generate a horizon shift. We then consider shells with negative energy density, showing that the horizon shift in this case allows for travel between the heretofore causally separated exterior regions of the Schwarzschild geometry. These drawing techniques are then used to investigate the properties of successive shells, joining multiple Schwarzschild regions. Again, the presence of negative-energy shells leads to a causal connection between the exterior regions, even in (some) cases with two successive shells of equal but opposite total energy. |
gr-qc/9901025 | Marco Spaans | Marco Spaans (Harvard CfA) | On the Topological Nature of Fundamental Interactions | null | null | null | null | gr-qc astro-ph hep-ph hep-th | null | A thought experiment is proposed to unify quantum mechanics and general
relativity. The central paradigm is that space-time {\it topology} is
ultimately responsible for the Heisenberg uncertaintly principle. It is found
that Plankian space-time exhibits a complicated, but also definite, multiply
connected character. In this framework, an analysis of the interactions in
Nature is presented.
I. The Universal ground state of the constructed theory derives from the
properties of the topological manifold $Q=2T^3\oplus 3S^1\times S^2$, which has
23 intrinsic degrees of freedom, discrete $Z_3$ and $Z_2\times Z_3$ internal
groups, an SU(5) gauge group, and leads to a U(1) symmetry on a lattice. The
structure of $Q$ provides a unique equation motion for the mass-energy and
particle rest mass wave functions. In its excited state the Universe is
characterized by a lattice of three-tori, $L(T^3)$. The topological
identifications present in this structure, a direct reflection of the
Heisenberg uncertainty principle, provide the boundary conditions for solutions
to the equation of motion, and suggest an interpretation for the conceptually
difficult concept of quantum mechanical entanglement. II. In the second half of
the paper the (observable) properties of $Q$ and $L(T^3)$ are investigated. One
reproduces the standard model, and the theory naturally contains a Higgs field
with possible inflation. The electron and its neutrino are identified as
particle ground states and their masses, together with those of all other known
particles, are predicted. A mass of $m_{\rm H}=131.6$ GeV is found for the
Higgs boson. [Abridged]
| [
{
"created": "Sat, 9 Jan 1999 00:35:49 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Apr 2000 08:41:00 GMT",
"version": "v10"
},
{
"created": "Sun, 23 Apr 2000 16:03:22 GMT",
"version": "v11"
},
{
"created": "Fri, 12 May 2000 20:07:26 GMT",
"version": "v12"
},
{
... | 2007-05-23 | [
[
"Spaans",
"Marco",
"",
"Harvard CfA"
]
] | A thought experiment is proposed to unify quantum mechanics and general relativity. The central paradigm is that space-time {\it topology} is ultimately responsible for the Heisenberg uncertaintly principle. It is found that Plankian space-time exhibits a complicated, but also definite, multiply connected character. In this framework, an analysis of the interactions in Nature is presented. I. The Universal ground state of the constructed theory derives from the properties of the topological manifold $Q=2T^3\oplus 3S^1\times S^2$, which has 23 intrinsic degrees of freedom, discrete $Z_3$ and $Z_2\times Z_3$ internal groups, an SU(5) gauge group, and leads to a U(1) symmetry on a lattice. The structure of $Q$ provides a unique equation motion for the mass-energy and particle rest mass wave functions. In its excited state the Universe is characterized by a lattice of three-tori, $L(T^3)$. The topological identifications present in this structure, a direct reflection of the Heisenberg uncertainty principle, provide the boundary conditions for solutions to the equation of motion, and suggest an interpretation for the conceptually difficult concept of quantum mechanical entanglement. II. In the second half of the paper the (observable) properties of $Q$ and $L(T^3)$ are investigated. One reproduces the standard model, and the theory naturally contains a Higgs field with possible inflation. The electron and its neutrino are identified as particle ground states and their masses, together with those of all other known particles, are predicted. A mass of $m_{\rm H}=131.6$ GeV is found for the Higgs boson. [Abridged] |
gr-qc/0608126 | Stephane Fay | Stephane Fay, Morad Amarzguioui | Large-scale structure and the Cardassian fluid | 10 pages, 18 figures, Accepted for publication in A&A | null | 10.1051/0004-6361:20064965 | null | gr-qc astro-ph | null | In this paper, we confront the predictions of the power law cardassian model
for the baryon power spectrum with the observations of the SDSS galaxy survey.
We show that they fit only for very unusual values of the cold dark matter or
baryon density parameters, the Hubble parameter or the spectral index of the
initial power spectrum. Moreover, the best-fit Cardassian models turn out to be
phantom models. If one wants to recover the usual values for these constants,
as quoted by the WMAP team, the power law Cardassian model turns out to be
indistinguishable from a LCDM model.
| [
{
"created": "Tue, 29 Aug 2006 18:07:46 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Fay",
"Stephane",
""
],
[
"Amarzguioui",
"Morad",
""
]
] | In this paper, we confront the predictions of the power law cardassian model for the baryon power spectrum with the observations of the SDSS galaxy survey. We show that they fit only for very unusual values of the cold dark matter or baryon density parameters, the Hubble parameter or the spectral index of the initial power spectrum. Moreover, the best-fit Cardassian models turn out to be phantom models. If one wants to recover the usual values for these constants, as quoted by the WMAP team, the power law Cardassian model turns out to be indistinguishable from a LCDM model. |
gr-qc/0409066 | Kostas Kokkotas D. | Hajime Sotani and Kostas D. Kokkotas | Probing Strong-Field Scalar-Tensor Gravity with Gravitational Wave
Asteroseismology | 14 pages, 7 figures | Phys.Rev. D70 (2004) 084026 | 10.1103/PhysRevD.70.084026 | null | gr-qc astro-ph hep-th | null | We present an alternative way of tracing the existence of a scalar field
based on the analysis of the gravitational wave spectrum of a vibrating neutron
star. Scalar-tensor theories in strong-field gravity can potentially introduce
much greater differences in the parameters of a neutron star than the
uncertainties introduced by the various equations of state. The detection of
gravitational waves from neutron stars can set constraints on the existence and
the strength of scalar fields. We show that the oscillation spectrum is
dramatically affected by the presence of a scalar field, and can provide unique
confirmation of its existence.
| [
{
"created": "Fri, 17 Sep 2004 06:58:41 GMT",
"version": "v1"
},
{
"created": "Sat, 30 Oct 2004 10:28:00 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Sotani",
"Hajime",
""
],
[
"Kokkotas",
"Kostas D.",
""
]
] | We present an alternative way of tracing the existence of a scalar field based on the analysis of the gravitational wave spectrum of a vibrating neutron star. Scalar-tensor theories in strong-field gravity can potentially introduce much greater differences in the parameters of a neutron star than the uncertainties introduced by the various equations of state. The detection of gravitational waves from neutron stars can set constraints on the existence and the strength of scalar fields. We show that the oscillation spectrum is dramatically affected by the presence of a scalar field, and can provide unique confirmation of its existence. |
2406.00506 | Bob Osano | Bob Osano | Dynamics of the transitions epochs in cosmological evolution | null | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We study two transition periods in cosmology: radiation-to-matter and
matter-to-dark energy. In each case, we define a new parameter $\chi$ given by
the ratios of the two energy densities involved in the transition. Our study of
the second epoch is motivated by the need to understand cosmic acceleration.
Assuming a dynamic dark energy is the driving force for cosmic acceleration, we
formulate a new equation of state for the dark energy given in terms of the
ratio $\chi$ and the deceleration parameter, $q$. We have analysed the
resultant system of equations, where we vary different parameters and examine
the effect on the universe's evolution. For cosmic acceleration to occur, the
EoS of the dynamic dark energy must lie in the interval $\omega_{DDE}<-2/3$ at
matter-dynamic dark energy equality( equivalently $\omega_{DDE}<-0.47$ today)
| [
{
"created": "Sat, 1 Jun 2024 17:28:37 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Jun 2024 17:47:20 GMT",
"version": "v2"
}
] | 2024-06-05 | [
[
"Osano",
"Bob",
""
]
] | We study two transition periods in cosmology: radiation-to-matter and matter-to-dark energy. In each case, we define a new parameter $\chi$ given by the ratios of the two energy densities involved in the transition. Our study of the second epoch is motivated by the need to understand cosmic acceleration. Assuming a dynamic dark energy is the driving force for cosmic acceleration, we formulate a new equation of state for the dark energy given in terms of the ratio $\chi$ and the deceleration parameter, $q$. We have analysed the resultant system of equations, where we vary different parameters and examine the effect on the universe's evolution. For cosmic acceleration to occur, the EoS of the dynamic dark energy must lie in the interval $\omega_{DDE}<-2/3$ at matter-dynamic dark energy equality( equivalently $\omega_{DDE}<-0.47$ today) |
gr-qc/0209045 | Uwe Gunther | U. Guenther, P. Moniz, A. Zhuk | Multidimensional cosmology and asymptotical AdS | 6 pages, kluwer.sty; Conf. Proc., 11th EAS Meeting: "JENAM 2002: The
Unsolved Universe", Porto, Portugal | Astrophys.Space Sci. 283 (2003) 679-684 | 10.1023/A:1022532313230 | null | gr-qc | null | A non-linear gravitational model with a multidimensional geometry and
quadratic scalar curvature is considered. For certain parameter ranges, the
extra dimensions are stabilized if the internal spaces have negative curvature.
As a consequence, the 4-dimensional effective cosmological constant as well as
the bulk cosmological constant become negative. The homogeneous and isotropic
external space is asymptotically AdS. The connection between the D-dimensional
and the 4-dimensional fundamental mass scales sets an additional restriction on
the parameters of the considered non-linear models.
| [
{
"created": "Fri, 13 Sep 2002 11:49:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Guenther",
"U.",
""
],
[
"Moniz",
"P.",
""
],
[
"Zhuk",
"A.",
""
]
] | A non-linear gravitational model with a multidimensional geometry and quadratic scalar curvature is considered. For certain parameter ranges, the extra dimensions are stabilized if the internal spaces have negative curvature. As a consequence, the 4-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. The homogeneous and isotropic external space is asymptotically AdS. The connection between the D-dimensional and the 4-dimensional fundamental mass scales sets an additional restriction on the parameters of the considered non-linear models. |
2205.14170 | Vania Vellucci | Vania Vellucci, Edgardo Franzin and Stefano Liberati | Echoes from backreacting exotic compact objects | 12 pages, 5 figures | Phys. Rev. D 107, 044027, 2023 | 10.1103/PhysRevD.107.044027 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The possible detection of echoes in late gravitational-wave signals is the
most promising way to test horizonless alternatives to general relativistic
black holes, and probe the physics of these hypothetical ultra-compact objects.
While there is currently no evidence for the presence of such signatures,
better accuracy is expected with the growing wealth of data from gravitational
waves observatories. So far, several searches for these specific signals have
been performed considering equidistant intervals between consecutive echoes,
i.e. quasi-periodic wave-forms, and ignoring possible backreaction effects of
the incoming waves. Here we study scalar perturbations in exotic compact object
scenarios that account for possible backreaction phenomena. In particular, we
find that if one considers the increase of the central object mass due to the
partial absorption of the energy carried by the perturbation, the echo signal
can be quite different and non-periodic. Apart from this simple scenario, we
also consider the case in which, in order to preserve its compactness above the
black hole limit, the compact object absorption shuts down in a finite amount
of time or leads to an expansion. In both these cases we find interesting new
features that should be taken into account in future searches.
| [
{
"created": "Fri, 27 May 2022 18:00:14 GMT",
"version": "v1"
},
{
"created": "Thu, 9 Feb 2023 10:56:02 GMT",
"version": "v2"
}
] | 2023-02-22 | [
[
"Vellucci",
"Vania",
""
],
[
"Franzin",
"Edgardo",
""
],
[
"Liberati",
"Stefano",
""
]
] | The possible detection of echoes in late gravitational-wave signals is the most promising way to test horizonless alternatives to general relativistic black holes, and probe the physics of these hypothetical ultra-compact objects. While there is currently no evidence for the presence of such signatures, better accuracy is expected with the growing wealth of data from gravitational waves observatories. So far, several searches for these specific signals have been performed considering equidistant intervals between consecutive echoes, i.e. quasi-periodic wave-forms, and ignoring possible backreaction effects of the incoming waves. Here we study scalar perturbations in exotic compact object scenarios that account for possible backreaction phenomena. In particular, we find that if one considers the increase of the central object mass due to the partial absorption of the energy carried by the perturbation, the echo signal can be quite different and non-periodic. Apart from this simple scenario, we also consider the case in which, in order to preserve its compactness above the black hole limit, the compact object absorption shuts down in a finite amount of time or leads to an expansion. In both these cases we find interesting new features that should be taken into account in future searches. |
gr-qc/9904014 | Wai-Mo Suen | Edward Seidel and Wai-Mo Suen | Numerical Relativity As A Tool For Computational Astrophysics | Review for JCAM | null | null | null | gr-qc | null | The astrophysics of compact objects, which requires Einstein's theory of
general relativity for understanding phenomena such as black holes and neutron
stars, is attracting increasing attention. In general relativity, gravity is
governed by an extremely complex set of coupled, nonlinear, hyperbolic-elliptic
partial differential equations. The largest parallel supercomputers are finally
approaching the speed and memory required to solve the complete set of
Einstein's equations for the first time since they were written over 80 years
ago, allowing one to attempt full 3D simulations of such exciting events as
colliding black holes and neutron stars. In this paper we review the
computational effort in this direction, and discuss a new 3D multi-purpose
parallel code called ``Cactus'' for general relativistic astrophysics.
Directions for further work are indicated where appropriate.
| [
{
"created": "Tue, 6 Apr 1999 15:31:09 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Seidel",
"Edward",
""
],
[
"Suen",
"Wai-Mo",
""
]
] | The astrophysics of compact objects, which requires Einstein's theory of general relativity for understanding phenomena such as black holes and neutron stars, is attracting increasing attention. In general relativity, gravity is governed by an extremely complex set of coupled, nonlinear, hyperbolic-elliptic partial differential equations. The largest parallel supercomputers are finally approaching the speed and memory required to solve the complete set of Einstein's equations for the first time since they were written over 80 years ago, allowing one to attempt full 3D simulations of such exciting events as colliding black holes and neutron stars. In this paper we review the computational effort in this direction, and discuss a new 3D multi-purpose parallel code called ``Cactus'' for general relativistic astrophysics. Directions for further work are indicated where appropriate. |
0806.2611 | Marc-Thierry Jaekel | Marc-Thierry Jaekel, Serge Reynaud | Conformal symmetry and quantum localization in space-time | 9 pages | in XXVI Workshop on Geometrical Methods in Physics, Bialowieza
2007, AIP Conference Proceedings, Eds P. Kielanowski,A. Odzijewicz, M.
Schlichenmaier, T. Voronov, New York (2007) 61-72 | 10.1063/1.2820981 | LPTENS 07/44 | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The classical procedures which define the relativistic notion of space-time
can be implemented in the framework of Quantum Field Theory. Only relying on
the conformal symmetries of field propagation, time-frequency transfer and
localization lead to the definition of time-frequency references and positions
in space-time as quantum observables. Quantum positions have a non vanishing
commutator identifying with spin, both observables characterizing quantum
localization in space-time. Frame transformations to accelerated frames differ
from their classical counterparts. Conformal symmetry nevertheless allows to
extend the covariance rules underlying the formalism of general relativity
under an algebraic form suiting the quantum framework.
| [
{
"created": "Mon, 16 Jun 2008 15:34:41 GMT",
"version": "v1"
}
] | 2013-02-27 | [
[
"Jaekel",
"Marc-Thierry",
""
],
[
"Reynaud",
"Serge",
""
]
] | The classical procedures which define the relativistic notion of space-time can be implemented in the framework of Quantum Field Theory. Only relying on the conformal symmetries of field propagation, time-frequency transfer and localization lead to the definition of time-frequency references and positions in space-time as quantum observables. Quantum positions have a non vanishing commutator identifying with spin, both observables characterizing quantum localization in space-time. Frame transformations to accelerated frames differ from their classical counterparts. Conformal symmetry nevertheless allows to extend the covariance rules underlying the formalism of general relativity under an algebraic form suiting the quantum framework. |
1105.1331 | Gaston Giribet | Hideki Maeda, Gaston Giribet | Lifshitz black holes in Brans-Dicke theory | 32 pages, no figure. v2: revised version. Section 3.1 and Appendix B
improved. The argument in Appendix A clarified. v3: References added. v4:
analysis on the black hole thermodynamical properties corrected. Final
version to appear in JHEP | JHEP 11 (2011) 15 | 10.1007/JHEP11(2011)015 | CECS-PHY-11/04 | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present an exact asymptotically Lifshitz black hole solution in
Brans-Dicke theory of gravity in arbitrary $n(\ge 3)$ dimensions in presence of
a power-law potential. In this solution, the dynamical exponent $z$ is
determined in terms of the Brans-Dicke parameter $\omega$ and $n$. Asymptotic
Lifshitz condition at infinity requires $z>1$, which corresponds to
$-(n-1)/(n-2) \le \omega < -n/(n-1)$. On the other hand, the no-ghost condition
for the scalar field in the Einstein frame requires $0<z \le 2(n-2)/(n-3)$. We
compute the Hawking temperature of the black hole solution and discuss the
problems encountered and the proposals in defining its thermodynamic
properties. A generalized solution charged under the Maxwell field is also
presented.
| [
{
"created": "Fri, 6 May 2011 17:07:36 GMT",
"version": "v1"
},
{
"created": "Mon, 16 May 2011 17:32:23 GMT",
"version": "v2"
},
{
"created": "Wed, 18 May 2011 19:59:31 GMT",
"version": "v3"
},
{
"created": "Sun, 1 Jan 2012 22:22:58 GMT",
"version": "v4"
}
] | 2015-05-28 | [
[
"Maeda",
"Hideki",
""
],
[
"Giribet",
"Gaston",
""
]
] | We present an exact asymptotically Lifshitz black hole solution in Brans-Dicke theory of gravity in arbitrary $n(\ge 3)$ dimensions in presence of a power-law potential. In this solution, the dynamical exponent $z$ is determined in terms of the Brans-Dicke parameter $\omega$ and $n$. Asymptotic Lifshitz condition at infinity requires $z>1$, which corresponds to $-(n-1)/(n-2) \le \omega < -n/(n-1)$. On the other hand, the no-ghost condition for the scalar field in the Einstein frame requires $0<z \le 2(n-2)/(n-3)$. We compute the Hawking temperature of the black hole solution and discuss the problems encountered and the proposals in defining its thermodynamic properties. A generalized solution charged under the Maxwell field is also presented. |
1912.03654 | Julia Tchemarina | I.M. Potashov, Ju.V. Tchemarina and A.N. Tsirulev | Bound orbits near black holes with scalar hair | 6 pages, 2 figures, presented at the 4th International Conference on
Particle Physics and Astrophysics (ICPPA-2018) | IOP Conf. Series: Journal of Physics: Conf. Series 1390 (2019)
012097 | 10.1088/1742-6596/1390/1/012097 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We consider spherically symmetric black holes with minimally coupled scalar
fields and concentrate our attention on asymptotically flat self-gravitating
configurations having the event horizons located at radii much smaller than
$2m$. We think of such configurations as rigorous mathematical models of the
gravitating objects, surrounded by dark matter, in the centres of normal
galaxies. It turns out that the radius of the event horizon of a scalar field
black hole always less than the Schwarzschild radius of vacuum black hole of
the same mass and can be arbitrary close to zero. In astronomical observations,
a key role in distinguishing between black holes, wormholes, and naked
singularities plays measuring parameters of bound quasiperiodic orbits, in
particular, the shape of an orbit and the angle of precession of its
pericentre. We consider a typical two-parameter family of compact scalar field
black holes and compute numerically the shapes of some bound orbits. We find
that a key feature of bound orbits around a compact black hole is that the
angle between closest pericentre points is either negative or, at least, less
than that for the Schwarzschild black hole of the same mass.
| [
{
"created": "Sun, 8 Dec 2019 11:02:50 GMT",
"version": "v1"
}
] | 2019-12-10 | [
[
"Potashov",
"I. M.",
""
],
[
"Tchemarina",
"Ju. V.",
""
],
[
"Tsirulev",
"A. N.",
""
]
] | We consider spherically symmetric black holes with minimally coupled scalar fields and concentrate our attention on asymptotically flat self-gravitating configurations having the event horizons located at radii much smaller than $2m$. We think of such configurations as rigorous mathematical models of the gravitating objects, surrounded by dark matter, in the centres of normal galaxies. It turns out that the radius of the event horizon of a scalar field black hole always less than the Schwarzschild radius of vacuum black hole of the same mass and can be arbitrary close to zero. In astronomical observations, a key role in distinguishing between black holes, wormholes, and naked singularities plays measuring parameters of bound quasiperiodic orbits, in particular, the shape of an orbit and the angle of precession of its pericentre. We consider a typical two-parameter family of compact scalar field black holes and compute numerically the shapes of some bound orbits. We find that a key feature of bound orbits around a compact black hole is that the angle between closest pericentre points is either negative or, at least, less than that for the Schwarzschild black hole of the same mass. |
1804.01876 | Patric H\"olscher | Chiara Caprini, Patric H\"olscher, Dominik J. Schwarz | Astrophysical Gravitational Waves in Conformal Gravity | v2: 21 pages, no figures; Uses REVTeX 4.1; added a comment and
references in section 1; corrected sign in eqn. (3) | Phys. Rev. D 98, 084002 (2018) | 10.1103/PhysRevD.98.084002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the gravitational radiation from binary systems in conformal
gravity (CG) and massive conformal gravity (MCG). CG might explain observed
galaxy rotation curves without dark matter, and both models are of interest in
the context of quantum gravity. Here we show that gravitational radiation
emitted by compact binaries allows us to strongly constrain both models. We
work in Weyl gauge, which fixes the rescaling invariance of the models, and
derive the linearized fourth-order equation of motion for the metric, which
describes massless and massive modes of propagation. In the limit of a large
graviton mass, MCG reduces to general relativity (GR), whereas CG does not.
Coordinates are fixed by Teyssandier gauge to show that for a conserved
energy-momentum tensor the gravitational radiation is due to the time-dependent
quadrupole moment of a non-relativistic source and we derive the gravitational
energy-momentum tensor for both models. We apply our findings to the case of
close binaries on circular orbits, which have been used to indirectly infer the
existence of gravitational radiation prior to the direct observation of
gravitational waves. As an example, we analyze the binary system PSR
J1012+5307, chosen for its small eccentricity. When fixing the graviton mass in
CG such that observed galaxy rotation curves could be explained without dark
matter, the gravitational radiation of a binary system is much smaller than in
GR. The same holds for MCG for small masses of the graviton. Thus gravitational
radiation cannot explain the orbital decay of binary systems and replace dark
matter simultaneously. We also analyse MCG for large graviton masses and
conclude that MCG can describe the orbital periods of compact binaries in
agreement with data, as it reduces to GR in that limit.
| [
{
"created": "Thu, 5 Apr 2018 14:29:15 GMT",
"version": "v1"
},
{
"created": "Mon, 23 Apr 2018 08:40:32 GMT",
"version": "v2"
}
] | 2018-10-10 | [
[
"Caprini",
"Chiara",
""
],
[
"Hölscher",
"Patric",
""
],
[
"Schwarz",
"Dominik J.",
""
]
] | We investigate the gravitational radiation from binary systems in conformal gravity (CG) and massive conformal gravity (MCG). CG might explain observed galaxy rotation curves without dark matter, and both models are of interest in the context of quantum gravity. Here we show that gravitational radiation emitted by compact binaries allows us to strongly constrain both models. We work in Weyl gauge, which fixes the rescaling invariance of the models, and derive the linearized fourth-order equation of motion for the metric, which describes massless and massive modes of propagation. In the limit of a large graviton mass, MCG reduces to general relativity (GR), whereas CG does not. Coordinates are fixed by Teyssandier gauge to show that for a conserved energy-momentum tensor the gravitational radiation is due to the time-dependent quadrupole moment of a non-relativistic source and we derive the gravitational energy-momentum tensor for both models. We apply our findings to the case of close binaries on circular orbits, which have been used to indirectly infer the existence of gravitational radiation prior to the direct observation of gravitational waves. As an example, we analyze the binary system PSR J1012+5307, chosen for its small eccentricity. When fixing the graviton mass in CG such that observed galaxy rotation curves could be explained without dark matter, the gravitational radiation of a binary system is much smaller than in GR. The same holds for MCG for small masses of the graviton. Thus gravitational radiation cannot explain the orbital decay of binary systems and replace dark matter simultaneously. We also analyse MCG for large graviton masses and conclude that MCG can describe the orbital periods of compact binaries in agreement with data, as it reduces to GR in that limit. |
0901.4708 | Mohammad Vahid Takook | F. Payandeh, M. Mehrafarin, M. V. Takook | One-loop approximation of Moller scattering in Krein-space quantization | 10 pages | Sci.China G52:212-217,2009 | 10.1007/s11433-009-0039-8 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has been shown that the negative-norm states necessarily appear in a
covariant quantization of the free minimally coupled scalar field in de Sitter
spacetime [1,2]. In this processes ultraviolet and infrared divergences have
been automatically eliminated [3]. A natural renormalization of the one-loop
interacting quantum field in Minkowski spacetime ($\lambda\phi^4$) has been
achieved through the consideration of the negative-norm states defined in Krein
space. It has been shown that the combination of quantum field theory in Krein
space together with consideration of quantum metric fluctuation, results in
quantum field theory without any divergences [4]. Pursuing this approach, we
express Wick's theorem and calculate M{\o}ller scattering in the one-loop
approximation in Krein space. The mathematical consequence of this method is
the disappearance of the ultraviolet divergence in the one-loop approximation.
| [
{
"created": "Thu, 29 Jan 2009 15:50:41 GMT",
"version": "v1"
}
] | 2009-04-13 | [
[
"Payandeh",
"F.",
""
],
[
"Mehrafarin",
"M.",
""
],
[
"Takook",
"M. V.",
""
]
] | It has been shown that the negative-norm states necessarily appear in a covariant quantization of the free minimally coupled scalar field in de Sitter spacetime [1,2]. In this processes ultraviolet and infrared divergences have been automatically eliminated [3]. A natural renormalization of the one-loop interacting quantum field in Minkowski spacetime ($\lambda\phi^4$) has been achieved through the consideration of the negative-norm states defined in Krein space. It has been shown that the combination of quantum field theory in Krein space together with consideration of quantum metric fluctuation, results in quantum field theory without any divergences [4]. Pursuing this approach, we express Wick's theorem and calculate M{\o}ller scattering in the one-loop approximation in Krein space. The mathematical consequence of this method is the disappearance of the ultraviolet divergence in the one-loop approximation. |
1809.00673 | Andrea Maselli | Vitor Cardoso, Gon\c{c}alo Castro, Andrea Maselli | Gravitational waves in massive gravity theories: waveforms, fluxes and
constraints from extreme-mass-ratio mergers | Important clarifications on screening and on our results added.
Accepted for publication in Physical Review Letters | Phys. Rev. Lett. 121, 251103 (2018) | 10.1103/PhysRevLett.121.251103 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Is the graviton massless? This problem was addressed in the literature at a
phenomenological level, using modified dispersion relations for gravitational
waves, in linearized calculations around flat space. Here, we perform a
detailed analysis of the gravitational waveform produced when a small particle
plunges or inspirals into a large non-spinning black hole. Our results should
presumably also describe the gravitational collapse to black holes and
explosive events such as supernovae. In the context of a theory with massive
gravitons and screening, merging objects up to $1\,{\rm Gpc}$ away or
collapsing stars in the nearby galaxy may be used to constrain the mass of the
graviton to be smaller than $\sim 10^{-23}\,{\rm eV}$, with low-frequency
detectors. Our results suggest that the absence of dipolar gravitational waves
from black hole binaries may be used to rule out entirely such theories.
| [
{
"created": "Mon, 3 Sep 2018 18:00:17 GMT",
"version": "v1"
},
{
"created": "Fri, 7 Sep 2018 09:26:14 GMT",
"version": "v2"
},
{
"created": "Mon, 19 Nov 2018 19:00:16 GMT",
"version": "v3"
}
] | 2018-12-26 | [
[
"Cardoso",
"Vitor",
""
],
[
"Castro",
"Gonçalo",
""
],
[
"Maselli",
"Andrea",
""
]
] | Is the graviton massless? This problem was addressed in the literature at a phenomenological level, using modified dispersion relations for gravitational waves, in linearized calculations around flat space. Here, we perform a detailed analysis of the gravitational waveform produced when a small particle plunges or inspirals into a large non-spinning black hole. Our results should presumably also describe the gravitational collapse to black holes and explosive events such as supernovae. In the context of a theory with massive gravitons and screening, merging objects up to $1\,{\rm Gpc}$ away or collapsing stars in the nearby galaxy may be used to constrain the mass of the graviton to be smaller than $\sim 10^{-23}\,{\rm eV}$, with low-frequency detectors. Our results suggest that the absence of dipolar gravitational waves from black hole binaries may be used to rule out entirely such theories. |
gr-qc/0103070 | Robert R. Caldwell | Robert R. Caldwell and David Langlois | Shortcuts in the fifth dimension | 11 pages, 2 figures | Phys.Lett. B511 (2001) 129-135 | 10.1016/S0370-2693(01)00631-1 | null | gr-qc astro-ph hep-ph hep-th | null | If our Universe is a three-brane embedded in a five-dimensional anti-deSitter
spacetime, in which matter is confined to the brane and gravity inhabits an
infinite bulk space, then the causal propagation of luminous and gravitational
signals is in general different. A gravitational signal traveling between two
points on the brane can take a ``shortcut'' through the bulk, and appear
quicker than a photon traveling between the same two points along a geodesic on
the brane. Similarly, in a given time interval, a gravitational signal can
propagate farther than a luminous signal. We quantify this effect, and analyze
the impact of these shortcuts through the fifth dimension on cosmology.
| [
{
"created": "Mon, 19 Mar 2001 20:04:31 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Caldwell",
"Robert R.",
""
],
[
"Langlois",
"David",
""
]
] | If our Universe is a three-brane embedded in a five-dimensional anti-deSitter spacetime, in which matter is confined to the brane and gravity inhabits an infinite bulk space, then the causal propagation of luminous and gravitational signals is in general different. A gravitational signal traveling between two points on the brane can take a ``shortcut'' through the bulk, and appear quicker than a photon traveling between the same two points along a geodesic on the brane. Similarly, in a given time interval, a gravitational signal can propagate farther than a luminous signal. We quantify this effect, and analyze the impact of these shortcuts through the fifth dimension on cosmology. |
gr-qc/0506087 | Jarmo M\"akel\"a Mr. | Jarmo Makela | Accelerating Observers, Area and Entropy | 7 pages, no figures | null | null | null | gr-qc | null | We consider an explicit example of a process, where the entropy carried by
radiation through an accelerating two-plane is proportional to the decrease in
the area of that two-plane even when the two-plane is not a part of any horizon
of spacetime. Our results seem to support the view that entropy proportional to
area is possessed not only by horizons but by all spacelike two-surfaces of
spacetime.
| [
{
"created": "Thu, 16 Jun 2005 12:52:24 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Makela",
"Jarmo",
""
]
] | We consider an explicit example of a process, where the entropy carried by radiation through an accelerating two-plane is proportional to the decrease in the area of that two-plane even when the two-plane is not a part of any horizon of spacetime. Our results seem to support the view that entropy proportional to area is possessed not only by horizons but by all spacelike two-surfaces of spacetime. |
gr-qc/0311017 | Karl Martel | Karl Martel | Gravitational waveforms from a point particle orbiting a Schwarzschild
black hole | revtex4, 24 pages, 23 figures, 3 tables, submitted to PRD | Phys.Rev. D69 (2004) 044025 | 10.1103/PhysRevD.69.044025 | null | gr-qc | null | We numerically solve the inhomogeneous Zerilli-Moncrief and Regge-Wheeler
equations in the time domain. We obtain the gravitational waveforms produced by
a point-particle of mass $\mu$ traveling around a Schwarzschild black hole of
mass M on arbitrary bound and unbound orbits. Fluxes of energy and angular
momentum at infinity and the event horizon are also calculated. Results for
circular orbits, selected cases of eccentric orbits, and parabolic orbits are
presented. The numerical results from the time-domain code indicate that, for
all three types of orbital motion, black hole absorption contributes less than
1% of the total flux, so long as the orbital radius r_p(t) satisfies r_p(t)> 5M
at all times.
| [
{
"created": "Wed, 5 Nov 2003 18:29:10 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Martel",
"Karl",
""
]
] | We numerically solve the inhomogeneous Zerilli-Moncrief and Regge-Wheeler equations in the time domain. We obtain the gravitational waveforms produced by a point-particle of mass $\mu$ traveling around a Schwarzschild black hole of mass M on arbitrary bound and unbound orbits. Fluxes of energy and angular momentum at infinity and the event horizon are also calculated. Results for circular orbits, selected cases of eccentric orbits, and parabolic orbits are presented. The numerical results from the time-domain code indicate that, for all three types of orbital motion, black hole absorption contributes less than 1% of the total flux, so long as the orbital radius r_p(t) satisfies r_p(t)> 5M at all times. |
0712.2861 | Ramin Nowbakht Ghalati | R. N. Ghalati, D. G. C. McKeon | A Reexamination of the Canonical Structure of the Einstein-Hilbert
Action in First-Order Form | 26 pages | null | null | UWO-TH-07/19 | gr-qc | null | A canonical analysis of the Einstein-Hilbert action S_d (d>2) is considered,
using the first order form with the metric and affine connection as independent
fields. We adopt a conservative approach to using the Dirac constraint
formalism; we do not use equations of motion which are independent of time
derivatives and correspond to first class constraints to eliminate fields.
Applying the Dirac procedure, we find that the primary constraints lead to
secondary constraints which are equations of motion not involving time
derivatives, and that those secondary constraints which are first class imply
novel tertiary constraints which are also first class. Once the constraints and
their associated gauge conditions are used to eliminate the non-dynamical
degrees of freedom in S_d, there are d(d-3) degrees of freedom left in phase
space. We also consider the simpler limiting case of the non-interacting
graviton in the first order formalism as well as the effect of adding the
action for a massless scalar field to the Einstein-Hilbert action.
| [
{
"created": "Tue, 18 Dec 2007 01:59:15 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Feb 2008 16:50:43 GMT",
"version": "v2"
},
{
"created": "Mon, 2 Jun 2008 15:04:19 GMT",
"version": "v3"
}
] | 2008-06-02 | [
[
"Ghalati",
"R. N.",
""
],
[
"McKeon",
"D. G. C.",
""
]
] | A canonical analysis of the Einstein-Hilbert action S_d (d>2) is considered, using the first order form with the metric and affine connection as independent fields. We adopt a conservative approach to using the Dirac constraint formalism; we do not use equations of motion which are independent of time derivatives and correspond to first class constraints to eliminate fields. Applying the Dirac procedure, we find that the primary constraints lead to secondary constraints which are equations of motion not involving time derivatives, and that those secondary constraints which are first class imply novel tertiary constraints which are also first class. Once the constraints and their associated gauge conditions are used to eliminate the non-dynamical degrees of freedom in S_d, there are d(d-3) degrees of freedom left in phase space. We also consider the simpler limiting case of the non-interacting graviton in the first order formalism as well as the effect of adding the action for a massless scalar field to the Einstein-Hilbert action. |
2102.13358 | Joan Josep Ferrando | Joan Josep Ferrando and Juan Antonio S\'aez | Dimension of the isometry group in three-dimensional Riemannian spaces | 8 pages, 1 figure | Class. Quantum Grav. 38 (2021) 067001 | 10.1088/1361-6382/abdaf4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The necessary and sufficient conditions for a three-dimensional Riemannian
metric to admit a group of isometries of dimension $r$ acting on s-dimensional
orbits are obtained. These conditions are Intrinsic, Deductive, Explicit and
ALgorithmic and they offer an IDEAL labeling that improves previously known
invariant studies.
| [
{
"created": "Fri, 26 Feb 2021 08:36:45 GMT",
"version": "v1"
}
] | 2021-03-01 | [
[
"Ferrando",
"Joan Josep",
""
],
[
"Sáez",
"Juan Antonio",
""
]
] | The necessary and sufficient conditions for a three-dimensional Riemannian metric to admit a group of isometries of dimension $r$ acting on s-dimensional orbits are obtained. These conditions are Intrinsic, Deductive, Explicit and ALgorithmic and they offer an IDEAL labeling that improves previously known invariant studies. |
gr-qc/9403035 | null | I. G. Avramidi | Covariant algebraic calculation of the one-loop effective potential in
non-Abelian gauge theory and a new approach to stability problem | 14 pages, LATeX, University of Greifswald (1994) | J.Math.Phys. 36 (1995) 1557-1571 | 10.1063/1.531139 | null | gr-qc hep-th | null | We use our recently proposed algebraic approach for calculating the heat
kernel associated with the Laplace operator to calculate the one-loop effective
action in the non-Abelian gauge theory. We consider the most general case of
arbitrary space-time dimension, arbitrary compact simple gauge group and
arbitrary matter and assume a covariantly constant gauge field strength of the
most general form, having many independent color and space-time invariants
(Savvidy type chromomagnetic vacuum) and covariantly constant scalar fields as
a background. The explicit formulas for all the needed heat kernels and
zeta-functions are obtained. We propose a new method to study the vacuum
stability and show that the background field configurations with covariantly
constant chromomagnetic fields can be stable only in the case when more than
one independent field invariants are present and the values of these invariants
differ not greatly from each other. The role of space-time dimension is
analyzed in this connection and it is shown that this is possible only in
space-times with dimensions not less than five $d\geq 5$.
| [
{
"created": "Fri, 18 Mar 1994 15:47:46 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Avramidi",
"I. G.",
""
]
] | We use our recently proposed algebraic approach for calculating the heat kernel associated with the Laplace operator to calculate the one-loop effective action in the non-Abelian gauge theory. We consider the most general case of arbitrary space-time dimension, arbitrary compact simple gauge group and arbitrary matter and assume a covariantly constant gauge field strength of the most general form, having many independent color and space-time invariants (Savvidy type chromomagnetic vacuum) and covariantly constant scalar fields as a background. The explicit formulas for all the needed heat kernels and zeta-functions are obtained. We propose a new method to study the vacuum stability and show that the background field configurations with covariantly constant chromomagnetic fields can be stable only in the case when more than one independent field invariants are present and the values of these invariants differ not greatly from each other. The role of space-time dimension is analyzed in this connection and it is shown that this is possible only in space-times with dimensions not less than five $d\geq 5$. |
1907.00295 | Madeleine Burkhart | Madeleine Burkhart and Daniel Pollack | Causal geodesic incompleteness of spacetimes arising from IMP gluing | null | null | 10.1007/s10714-019-2621-3 | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In 2002, Isenberg-Mazzeo-Pollack (IMP) constructed a series of vacuum initial
data sets via a gluing construction. In this paper, we investigate some local
geometry of these initial data sets as well as implications regarding their
spacetime developments. In particular, we state conditions for the existence of
outer trapped surfaces near the center of the IMP gluing neck and thence use a
generalization of the Penrose incompleteness theorem to deduce null
incompleteness of the resulting spacetimes.
| [
{
"created": "Sat, 29 Jun 2019 23:35:36 GMT",
"version": "v1"
}
] | 2020-01-08 | [
[
"Burkhart",
"Madeleine",
""
],
[
"Pollack",
"Daniel",
""
]
] | In 2002, Isenberg-Mazzeo-Pollack (IMP) constructed a series of vacuum initial data sets via a gluing construction. In this paper, we investigate some local geometry of these initial data sets as well as implications regarding their spacetime developments. In particular, we state conditions for the existence of outer trapped surfaces near the center of the IMP gluing neck and thence use a generalization of the Penrose incompleteness theorem to deduce null incompleteness of the resulting spacetimes. |
2012.11304 | Yong Cai | Yong Cai, Yun-Song Piao | Intermittent null energy condition violations during inflation and
primordial gravitational waves | 21 pages, 11 figures; v2, references added, updated to match
published version | Phys. Rev. D 103, 083521 (2021) | 10.1103/PhysRevD.103.083521 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | Primordial null energy condition (NEC) violation would imprint a blue-tilted
spectrum on gravitational wave background (GWB). However, its implications on
the GWB might be far richer than expected. We present a scenario, in which
after a slow-roll (NEC-preserving) inflation with Hubble parameter $H\simeq
H_{inf1}$, the Universe goes through an NEC-violating period and then enters
subsequent slow-roll inflation with a higher $H$ ($=H_{inf2}\gg H_{inf1}$). The
resulting primordial gravitational wave spectrum is nearly flat at the cosmic
microwave background band, as well as at the frequency $f\sim 1/{\rm yr}$ but
with higher amplitude (compatible with the recent NANOGrav result). It is also
highlighted that for the multi-stage inflation if the NEC violations happened
intermittently, we might have a Great Wall-like spectrum of the stochastic GWB
at the corresponding frequency band.
| [
{
"created": "Mon, 21 Dec 2020 13:16:46 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Apr 2021 05:53:45 GMT",
"version": "v2"
}
] | 2021-04-28 | [
[
"Cai",
"Yong",
""
],
[
"Piao",
"Yun-Song",
""
]
] | Primordial null energy condition (NEC) violation would imprint a blue-tilted spectrum on gravitational wave background (GWB). However, its implications on the GWB might be far richer than expected. We present a scenario, in which after a slow-roll (NEC-preserving) inflation with Hubble parameter $H\simeq H_{inf1}$, the Universe goes through an NEC-violating period and then enters subsequent slow-roll inflation with a higher $H$ ($=H_{inf2}\gg H_{inf1}$). The resulting primordial gravitational wave spectrum is nearly flat at the cosmic microwave background band, as well as at the frequency $f\sim 1/{\rm yr}$ but with higher amplitude (compatible with the recent NANOGrav result). It is also highlighted that for the multi-stage inflation if the NEC violations happened intermittently, we might have a Great Wall-like spectrum of the stochastic GWB at the corresponding frequency band. |
2006.12663 | Byon Jayawiguna | Byon N. Jayawiguna | Three Dimensional Black Hole in the Low Energy Heterotic String Theory | 8 pages, 2 figures, under review on Physics letter B Journal | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We study the BTZ black holes (2+1 dimensional space-time) in the low energy
heterotic string theory (BTZ-Sen BH). This concept requires us to include a
non-trivial dilaton $ \phi $ and a 3-form $ H_{\mu\nu\rho} $ field. By using
the Hassan-Sen transformation and BTZ black hole as a seed solution, we obtain
the solution in the string frame. Some properties of the black hole solutions
are discussed.
| [
{
"created": "Mon, 22 Jun 2020 23:20:33 GMT",
"version": "v1"
}
] | 2020-06-24 | [
[
"Jayawiguna",
"Byon N.",
""
]
] | We study the BTZ black holes (2+1 dimensional space-time) in the low energy heterotic string theory (BTZ-Sen BH). This concept requires us to include a non-trivial dilaton $ \phi $ and a 3-form $ H_{\mu\nu\rho} $ field. By using the Hassan-Sen transformation and BTZ black hole as a seed solution, we obtain the solution in the string frame. Some properties of the black hole solutions are discussed. |
gr-qc/0003113 | Carsten Gundlach | David Garfinkle, Carsten Gundlach, James Isenberg and Niall OMurchadha | Existence, uniqueness and other properties of the BCT (minimal strain
lapse and shift) gauge | 5 pages, RevTex | Class.Quant.Grav. 17 (2000) 3899-3904 | 10.1088/0264-9381/17/18/321 | null | gr-qc | null | Brady, Creighton and Thorne have proposed a choice of the lapse and shift for
numerical evolutions in general relativity that extremizes a measure of the
rate of change of the three-metric (BCT gauge). We investigate existence and
uniqueness of this gauge, and comment on its use in numerical time evolutions.
| [
{
"created": "Fri, 31 Mar 2000 08:43:31 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Garfinkle",
"David",
""
],
[
"Gundlach",
"Carsten",
""
],
[
"Isenberg",
"James",
""
],
[
"OMurchadha",
"Niall",
""
]
] | Brady, Creighton and Thorne have proposed a choice of the lapse and shift for numerical evolutions in general relativity that extremizes a measure of the rate of change of the three-metric (BCT gauge). We investigate existence and uniqueness of this gauge, and comment on its use in numerical time evolutions. |
gr-qc/9911014 | Lawrence E. Kidder | Lawrence E. Kidder, Lee Samuel Finn | Spectral Methods for Numerical Relativity. The Initial Data Problem | 15 pages, 5 figures, revtex, submitted to PRD | Phys.Rev. D62 (2000) 084026 | 10.1103/PhysRevD.62.084026 | null | gr-qc | null | Numerical relativity has traditionally been pursued via finite differencing.
Here we explore pseudospectral collocation (PSC) as an alternative to finite
differencing, focusing particularly on the solution of the Hamiltonian
constraint (an elliptic partial differential equation) for a black hole
spacetime with angular momentum and for a black hole spacetime superposed with
gravitational radiation. In PSC, an approximate solution, generally expressed
as a sum over a set of orthogonal basis functions (e.g., Chebyshev
polynomials), is substituted into the exact system of equations and the
residual minimized. For systems with analytic solutions the approximate
solutions converge upon the exact solution exponentially as the number of basis
functions is increased. Consequently, PSC has a high computational efficiency:
for solutions of even modest accuracy we find that PSC is substantially more
efficient, as measured by either execution time or memory required, than finite
differencing; furthermore, these savings increase rapidly with increasing
accuracy. The solution provided by PSC is an analytic function given
everywhere; consequently, no interpolation operators need to be defined to
determine the function values at intermediate points and no special
arrangements need to be made to evaluate the solution or its derivatives on the
boundaries. Since the practice of numerical relativity by finite differencing
has been, and continues to be, hampered by both high computational resource
demands and the difficulty of formulating acceptable finite difference
alternatives to the analytic boundary conditions, PSC should be further pursued
as an alternative way of formulating the computational problem of finding
numerical solutions to the field equations of general relativity.
| [
{
"created": "Wed, 3 Nov 1999 22:21:42 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Kidder",
"Lawrence E.",
""
],
[
"Finn",
"Lee Samuel",
""
]
] | Numerical relativity has traditionally been pursued via finite differencing. Here we explore pseudospectral collocation (PSC) as an alternative to finite differencing, focusing particularly on the solution of the Hamiltonian constraint (an elliptic partial differential equation) for a black hole spacetime with angular momentum and for a black hole spacetime superposed with gravitational radiation. In PSC, an approximate solution, generally expressed as a sum over a set of orthogonal basis functions (e.g., Chebyshev polynomials), is substituted into the exact system of equations and the residual minimized. For systems with analytic solutions the approximate solutions converge upon the exact solution exponentially as the number of basis functions is increased. Consequently, PSC has a high computational efficiency: for solutions of even modest accuracy we find that PSC is substantially more efficient, as measured by either execution time or memory required, than finite differencing; furthermore, these savings increase rapidly with increasing accuracy. The solution provided by PSC is an analytic function given everywhere; consequently, no interpolation operators need to be defined to determine the function values at intermediate points and no special arrangements need to be made to evaluate the solution or its derivatives on the boundaries. Since the practice of numerical relativity by finite differencing has been, and continues to be, hampered by both high computational resource demands and the difficulty of formulating acceptable finite difference alternatives to the analytic boundary conditions, PSC should be further pursued as an alternative way of formulating the computational problem of finding numerical solutions to the field equations of general relativity. |
gr-qc/0012094 | Bob Laughlin | G. Chapline (Los Alamos), E. Hohlfeld, R. B. Laughlin, and D. I.
Santiago (Stanford University) | Quantum Phase Transitions and the Breakdown of Classical General
Relativity | 11 pages of RevTeX, 9 eps figures | Int.J.Mod.Phys. A18 (2003) 3587-3590 | 10.1142/S0217751X03016380 | null | gr-qc cond-mat | null | It is proposed that the event horizon of a black hole is a quantum phase
transition of the vacuum of space-time analogous to the liquid-vapor critical
point of a bose fluid. The equations of classical general relativity remain
valid arbitrarily close to the horizon yet fail there through the divergence of
a characteristic coherence length. The integrity of global time, required for
conventional quantum mechanics to be defined, is maintained. The metric inside
the event horizon is different from that predicted by classical general
relativity and may be de Sitter space. The deviations from classical behavior
lead to distinct spectroscopic and bolometric signatures that can, in
principle, be observed at large distances from the black hole.
| [
{
"created": "Mon, 25 Dec 2000 19:32:07 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Chapline",
"G.",
"",
"Los Alamos"
],
[
"Hohlfeld",
"E.",
"",
"Stanford University"
],
[
"Laughlin",
"R. B.",
"",
"Stanford University"
],
[
"Santiago",
"D. I.",
"",
"Stanford University"
]
] | It is proposed that the event horizon of a black hole is a quantum phase transition of the vacuum of space-time analogous to the liquid-vapor critical point of a bose fluid. The equations of classical general relativity remain valid arbitrarily close to the horizon yet fail there through the divergence of a characteristic coherence length. The integrity of global time, required for conventional quantum mechanics to be defined, is maintained. The metric inside the event horizon is different from that predicted by classical general relativity and may be de Sitter space. The deviations from classical behavior lead to distinct spectroscopic and bolometric signatures that can, in principle, be observed at large distances from the black hole. |
gr-qc/0701173 | Gil Jannes | C. Barcelo, A. Cano, L. J. Garay, G. Jannes | Quasi-normal mode analysis in BEC acoustic black holes | 7 pages, 3 figures | Phys.Rev.D75:084024,2007 | 10.1103/PhysRevD.75.084024 | null | gr-qc | null | We perform a quasi-normal mode analysis of black hole configurations in
Bose-Einstein condensates (BEC). In this analysis we use the full Bogoliubov
dispersion relation, not just the hydrodynamic or geometric approximation. We
restrict our attention to one-dimensional flows in BEC with step-like
discontinuities. For this case we show that in the hydrodynamic approximation
quasi-normal modes do not exist. The full dispersion relation, however, allows
the existence of quasi-normal modes. Remarkably, the spectrum of these modes is
not discrete but continuous.
| [
{
"created": "Wed, 31 Jan 2007 12:17:43 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Barcelo",
"C.",
""
],
[
"Cano",
"A.",
""
],
[
"Garay",
"L. J.",
""
],
[
"Jannes",
"G.",
""
]
] | We perform a quasi-normal mode analysis of black hole configurations in Bose-Einstein condensates (BEC). In this analysis we use the full Bogoliubov dispersion relation, not just the hydrodynamic or geometric approximation. We restrict our attention to one-dimensional flows in BEC with step-like discontinuities. For this case we show that in the hydrodynamic approximation quasi-normal modes do not exist. The full dispersion relation, however, allows the existence of quasi-normal modes. Remarkably, the spectrum of these modes is not discrete but continuous. |
gr-qc/0103061 | Nathaniel Obadia | N. Obadia and R. Parentani | Notes on moving mirrors | 27 pages and 2 figures LaTeX2e | Phys.Rev. D64 (2001) 044019 | 10.1103/PhysRevD.64.044019 | null | gr-qc hep-th | null | The Davies-Fulling (DF) model describes the scattering of a massless field by
a non-inertial mirror in two dimensions. In this paper, we generalize this
model in two different ways. First, we consider partially reflecting mirrors.
We show that the Bogoliubov coefficients relating inertial modes can be
expressed in terms of the frequency dependent reflection factor which is
specified in the rest frame of the mirror and the transformation from the
inertial modes to the modes at rest with respect to the mirror. In this
perspective, the DF model is simply the limiting case when this factor is unity
for all frequencies. In the second part, we introduce an alternative model
which is based on self-interactions described by an action principle. When the
coupling is constant, this model can be solved exactly and gives rise to a
partially reflecting mirror. The usefulness of this dynamical model lies in the
possibility of switching off the coupling between the mirror and the field.
This allows to obtain regularized expressions for the fluxes in situations
where they are singular when using the DF model. Two examples are considered.
The first concerns the flux induced by the disappearance of the reflection
condition, a situation which bears some analogies with the end of the
evaporation of a black hole. The second case concerns the flux emitted by a
uniformly accelerated mirror.
| [
{
"created": "Fri, 16 Mar 2001 12:56:43 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Obadia",
"N.",
""
],
[
"Parentani",
"R.",
""
]
] | The Davies-Fulling (DF) model describes the scattering of a massless field by a non-inertial mirror in two dimensions. In this paper, we generalize this model in two different ways. First, we consider partially reflecting mirrors. We show that the Bogoliubov coefficients relating inertial modes can be expressed in terms of the frequency dependent reflection factor which is specified in the rest frame of the mirror and the transformation from the inertial modes to the modes at rest with respect to the mirror. In this perspective, the DF model is simply the limiting case when this factor is unity for all frequencies. In the second part, we introduce an alternative model which is based on self-interactions described by an action principle. When the coupling is constant, this model can be solved exactly and gives rise to a partially reflecting mirror. The usefulness of this dynamical model lies in the possibility of switching off the coupling between the mirror and the field. This allows to obtain regularized expressions for the fluxes in situations where they are singular when using the DF model. Two examples are considered. The first concerns the flux induced by the disappearance of the reflection condition, a situation which bears some analogies with the end of the evaporation of a black hole. The second case concerns the flux emitted by a uniformly accelerated mirror. |
2207.09458 | Seyed Hamid Reza Fazlollahi | H. R. Fazlollahi | Holographic Dark Energy from Acceleration of Particle Horizon | null | null | 10.1088/1674-1137/aca468 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Following the holographic principle, which suggests that the energy density
of dark energy may be proportional inversely to the area of the event horizon
of the Universe, we have proposed a new energy density of dark energy through
the acceleration of particle horizon scaled by the length of this parameter.
This model depends only on one free parameter beta=0-1.99. For beta's near
zero, the deviation of the model compared with the Lambda CDM model is tangible
while for values beta=1.99, the suggested model has no conflict with Lambda CDM
theory. Regardless of the value of beta, the model presents dark energy that
behaves such as matter with positive pressure in high redshifts =0.33, while
for present and near-future Universe treats like the cosmological constant
model and phantom field. Comparing the model with Ricci dark energy illustrates
our model alleviates Ricci dark energy errors in calculating the age of old
supernovae and the evolution of different cosmic components in high redshifts.
Moreover, we have calculated matter structure formation parameters such as CMB
temperature and matter power spectrum of the model to consider the effects of
matter-like dark energy during the matter-dominated era.
| [
{
"created": "Tue, 19 Jul 2022 14:20:39 GMT",
"version": "v1"
}
] | 2023-01-25 | [
[
"Fazlollahi",
"H. R.",
""
]
] | Following the holographic principle, which suggests that the energy density of dark energy may be proportional inversely to the area of the event horizon of the Universe, we have proposed a new energy density of dark energy through the acceleration of particle horizon scaled by the length of this parameter. This model depends only on one free parameter beta=0-1.99. For beta's near zero, the deviation of the model compared with the Lambda CDM model is tangible while for values beta=1.99, the suggested model has no conflict with Lambda CDM theory. Regardless of the value of beta, the model presents dark energy that behaves such as matter with positive pressure in high redshifts =0.33, while for present and near-future Universe treats like the cosmological constant model and phantom field. Comparing the model with Ricci dark energy illustrates our model alleviates Ricci dark energy errors in calculating the age of old supernovae and the evolution of different cosmic components in high redshifts. Moreover, we have calculated matter structure formation parameters such as CMB temperature and matter power spectrum of the model to consider the effects of matter-like dark energy during the matter-dominated era. |
0911.3862 | Roman Gold | Roman Gold, Bernd Bruegmann | Radiation from low-momentum zoom-whirl orbits | 9 pages, 6 figures, Amaldi8 conference proceedings as published | Class.Quant.Grav.27:084035,2010 | 10.1088/0264-9381/27/8/084035 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study zoom-whirl behaviour of equal mass, non-spinning black hole binaries
in full general relativity. The magnitude of the linear momentum of the initial
data is fixed to that of a quasi-circular orbit, and its direction is varied.
We find a global maximum in radiated energy for a configuration which completes
roughly one orbit. The radiated energy in this case exceeds the value of a
quasi-circular binary with the same momentum by 15%. The direction parameter
only requires minor tuning for the localization of the maximum. There is
non-trivial dependence of the energy radiated on eccentricity (several local
maxima and minima). Correlations with orbital dynamics shortly before merger
are discussed. While being strongly gauge dependent, these findings are
intuitive from a physical point of view and support basic ideas about the
efficiency of gravitational radiation from a binary system.
| [
{
"created": "Thu, 19 Nov 2009 18:17:46 GMT",
"version": "v1"
},
{
"created": "Mon, 3 May 2010 14:05:15 GMT",
"version": "v2"
}
] | 2010-05-07 | [
[
"Gold",
"Roman",
""
],
[
"Bruegmann",
"Bernd",
""
]
] | We study zoom-whirl behaviour of equal mass, non-spinning black hole binaries in full general relativity. The magnitude of the linear momentum of the initial data is fixed to that of a quasi-circular orbit, and its direction is varied. We find a global maximum in radiated energy for a configuration which completes roughly one orbit. The radiated energy in this case exceeds the value of a quasi-circular binary with the same momentum by 15%. The direction parameter only requires minor tuning for the localization of the maximum. There is non-trivial dependence of the energy radiated on eccentricity (several local maxima and minima). Correlations with orbital dynamics shortly before merger are discussed. While being strongly gauge dependent, these findings are intuitive from a physical point of view and support basic ideas about the efficiency of gravitational radiation from a binary system. |
0907.4528 | Khireddine Nouicer | Khireddine Nouicer | Entropy of cosmological black holes and generalized second law in
phantom energy-dominated universe | 20 pages, 5 figures, Major revision,Submitted to the IJMPD | Int.J.Mod.Phys.D20:233-252,2011 | 10.1142/S0218271811018743 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Adopting the thin-layer improved brick-wall method, we investigate the
thermodynamics of a black hole embedded in a spatially flat
Friedmann-Robertson-Walker universe. We calculate the temperature and the
entropy at every apparent horizon for arbitrary solution of the scale factor.
We show that the temperature and entropy display a non-trivial behavior as
functions of time. In the case of black holes immersed in universe driven by
phantom energy, we show that for specific ranges of the equation-of-state
parameter and apparent horizons the entropy is compatible with the D-bound
conjecture, even the null, dominant and strong energy conditions are violated.
In the case of accretion of phantom energy onto black hole with small
Hawking-Hayward quasi-local mass, we obtain an equation-of-state parameter in
the range $w\leq-5/3$, guaranteeing the validity of the generalized second law.
| [
{
"created": "Sun, 26 Jul 2009 23:07:56 GMT",
"version": "v1"
},
{
"created": "Tue, 6 Apr 2010 12:37:24 GMT",
"version": "v2"
}
] | 2011-03-07 | [
[
"Nouicer",
"Khireddine",
""
]
] | Adopting the thin-layer improved brick-wall method, we investigate the thermodynamics of a black hole embedded in a spatially flat Friedmann-Robertson-Walker universe. We calculate the temperature and the entropy at every apparent horizon for arbitrary solution of the scale factor. We show that the temperature and entropy display a non-trivial behavior as functions of time. In the case of black holes immersed in universe driven by phantom energy, we show that for specific ranges of the equation-of-state parameter and apparent horizons the entropy is compatible with the D-bound conjecture, even the null, dominant and strong energy conditions are violated. In the case of accretion of phantom energy onto black hole with small Hawking-Hayward quasi-local mass, we obtain an equation-of-state parameter in the range $w\leq-5/3$, guaranteeing the validity of the generalized second law. |
gr-qc/0607079 | Nicos Pelavas | A.A. Coley and N. Pelavas | Averaging in Spherically Symmetric Cosmology | null | Phys.Rev.D75:043506,2007 | 10.1103/PhysRevD.75.043506 | null | gr-qc astro-ph | null | In the macroscopic gravity approach to the averaging problem in cosmology,
the Einstein field equations on cosmological scales are modified by appropriate
gravitational correlation terms. We study the averaging problem within the
class of spherically symmetric cosmological models. That is, we shall take the
microscopic equations and effect the averaging procedure to determine the
precise form of the correlation tensor in this case. In particular, by working
in volume preserving coordinates, we calculate the form of the correlation
tensor under some reasonable assumptions on the form for the inhomogeneous
gravitational field and matter distribution. We find that the correlation
tensor in a FLRW background must be of the form of a spatial curvature.
Inhomogeneities and spatial averaging, through this spatial curvature
correction term, can have a very significant dynamical effect on the dynamics
of the Universe and cosmological observations; in particular, we discuss
whether spatial averaging might lead to a more conservative explanation of the
observed acceleration of the Universe (without the introduction of exotic dark
matter fields). We also find that the correlation tensor for a non-FLRW
background can be interpreted as the sum of a spatial curvature and an
anisotropic fluid. This may lead to interesting effects of averaging on
astrophysical scales. We also discuss the results of averaging an inhomogeneous
Lemaitre-Tolman-Bondi solution as well as calculations of linear perturbations
(that is, the back-reaction) in an FLRW background, which support the main
conclusions of the analysis.
| [
{
"created": "Thu, 20 Jul 2006 13:15:41 GMT",
"version": "v1"
},
{
"created": "Sun, 24 Sep 2006 16:12:46 GMT",
"version": "v2"
},
{
"created": "Wed, 21 Feb 2007 04:12:54 GMT",
"version": "v3"
}
] | 2008-11-26 | [
[
"Coley",
"A. A.",
""
],
[
"Pelavas",
"N.",
""
]
] | In the macroscopic gravity approach to the averaging problem in cosmology, the Einstein field equations on cosmological scales are modified by appropriate gravitational correlation terms. We study the averaging problem within the class of spherically symmetric cosmological models. That is, we shall take the microscopic equations and effect the averaging procedure to determine the precise form of the correlation tensor in this case. In particular, by working in volume preserving coordinates, we calculate the form of the correlation tensor under some reasonable assumptions on the form for the inhomogeneous gravitational field and matter distribution. We find that the correlation tensor in a FLRW background must be of the form of a spatial curvature. Inhomogeneities and spatial averaging, through this spatial curvature correction term, can have a very significant dynamical effect on the dynamics of the Universe and cosmological observations; in particular, we discuss whether spatial averaging might lead to a more conservative explanation of the observed acceleration of the Universe (without the introduction of exotic dark matter fields). We also find that the correlation tensor for a non-FLRW background can be interpreted as the sum of a spatial curvature and an anisotropic fluid. This may lead to interesting effects of averaging on astrophysical scales. We also discuss the results of averaging an inhomogeneous Lemaitre-Tolman-Bondi solution as well as calculations of linear perturbations (that is, the back-reaction) in an FLRW background, which support the main conclusions of the analysis. |
gr-qc/9804073 | J. W. van Holten | D. v. Albada, W. v. Amersfoort, H. Boer Rookhuizen, J. Flokstra, G.
Frossati, H. v.d. Graaf, A. Heijboer, G. Heijboer, E. v.d. Heuvel, J.W. v.
Holten, G.J. Nooren, J. Oberski, H. Rogalla, A. de Waele, P. de Witt Huberts | GRAIL, an omni-directional gravitational wave detector | 5 pages, 4 figs., contribution to proceedings GW Data Analysis
Workshop, Paris, nov. 1997 | null | null | NIKHEF/98-009 | gr-qc | null | A cryogenic spherical and omni-directional resonant-mass detector proposed by
the GRAIL collaboration is described.
| [
{
"created": "Mon, 27 Apr 1998 13:32:45 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Albada",
"D. v.",
""
],
[
"Amersfoort",
"W. v.",
""
],
[
"Rookhuizen",
"H. Boer",
""
],
[
"Flokstra",
"J.",
""
],
[
"Frossati",
"G.",
""
],
[
"Graaf",
"H. v. d.",
""
],
[
"Heijboer",
"A.",
""
],
[
... | A cryogenic spherical and omni-directional resonant-mass detector proposed by the GRAIL collaboration is described. |
2204.05469 | Josue De-Santiago | Ruben Cordero, Josue De-Santiago, Omar G. Miranda, and Margarita
Serrano-Crivelli | Perturbations and stability conditions of k-essence and kinetic gravity
braiding models in two-field measure theory | 16 pages, 2 figures | Phys. Scr. 98 115242 (2023) | 10.1088/1402-4896/ad007a | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | We study cosmological perturbations for k-essence and kinetic gravity
braiding models in the context of the two-field measure theory (TMT).
Considering scalar perturbations and the uniform field gauge, we obtain the
sound speed of the fields and present a stability analysis by means of the
kinetic matrix and the mass eigenvalues. For k-essence models, in the two-field
measure theory, the speed of propagation of the field is modified completely
due to the new measure field and it gives rise to crucial differences with
respect to the case without new measure. The stability analysis gives a
physical viable model for the Universe. For the kinetic gravity braiding models
in the two-field measure theory we get that, in general, the speed of
perturbations is equal to the speed of light which is a consequence of the
properties of the new measure field. In the later case, there is always a ghost
field. Furthermore, we calculate general expressions for the mass eigenvalues
and find, for an explicit example, the existence of tachyonic instabilities.
| [
{
"created": "Tue, 12 Apr 2022 01:41:09 GMT",
"version": "v1"
},
{
"created": "Thu, 13 Oct 2022 02:29:07 GMT",
"version": "v2"
}
] | 2023-10-23 | [
[
"Cordero",
"Ruben",
""
],
[
"De-Santiago",
"Josue",
""
],
[
"Miranda",
"Omar G.",
""
],
[
"Serrano-Crivelli",
"Margarita",
""
]
] | We study cosmological perturbations for k-essence and kinetic gravity braiding models in the context of the two-field measure theory (TMT). Considering scalar perturbations and the uniform field gauge, we obtain the sound speed of the fields and present a stability analysis by means of the kinetic matrix and the mass eigenvalues. For k-essence models, in the two-field measure theory, the speed of propagation of the field is modified completely due to the new measure field and it gives rise to crucial differences with respect to the case without new measure. The stability analysis gives a physical viable model for the Universe. For the kinetic gravity braiding models in the two-field measure theory we get that, in general, the speed of perturbations is equal to the speed of light which is a consequence of the properties of the new measure field. In the later case, there is always a ghost field. Furthermore, we calculate general expressions for the mass eigenvalues and find, for an explicit example, the existence of tachyonic instabilities. |
1804.01419 | Gonzalo Garc\'ia-Reyes | Gonzalo Garc\'ia-Reyes | Exact relativistic models of conformastatic charged dust thick disks | 15 pages, 32 figures. Accepted for publication in Gen. Relativ.
Gravit | Gen. Relativ. Gravit. 50, 4, 1-16 (2018) | 10.1007/s10714-018-2366-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct relativistic models of charged dust thick disks for a particular
conformastatic spacetime through a Miyamoto-Nagai transformation used in
Newtonian gravity to model disk like galaxies. Two simple families of thick
disk models and a family of thick annular disks based on the field of an
extreme Reissner-Nordstr\"om black hole and a Morgan-Morgan-like metric are
considered. The electrogeodesic motion of test particles around the structures
are analyzed. Also the stability of the particles against radial perturbation
is studied using an extension of the Rayleigh criteria of stability of a fluid
in rest in a gravitational field. The models built satisfy all the energy
conditions.
| [
{
"created": "Wed, 4 Apr 2018 14:05:10 GMT",
"version": "v1"
}
] | 2018-05-10 | [
[
"García-Reyes",
"Gonzalo",
""
]
] | We construct relativistic models of charged dust thick disks for a particular conformastatic spacetime through a Miyamoto-Nagai transformation used in Newtonian gravity to model disk like galaxies. Two simple families of thick disk models and a family of thick annular disks based on the field of an extreme Reissner-Nordstr\"om black hole and a Morgan-Morgan-like metric are considered. The electrogeodesic motion of test particles around the structures are analyzed. Also the stability of the particles against radial perturbation is studied using an extension of the Rayleigh criteria of stability of a fluid in rest in a gravitational field. The models built satisfy all the energy conditions. |
1008.2540 | Przemyslaw Malkiewicz | Przemyslaw Malkiewicz | Quantization of FRW universe via gauge-fixed action | 15 pages, 2 figures, improved version, submitted for publication | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper is devoted to investigation of the quantum
Friedman-Robertson-Walker universe with matter satisfying the equation of state
$p=w\rho$, where $w$ is an almost arbitrary constant. The procedure starts with
a reduced Lagrangian, which describes the system in a gauge fixed, so that the
evolution parameter corresponds to the cosmological time. Then we construct the
phase space, which is believed to correspond to the reduced phase space
consisting of Dirac's observables. The physically relevant quantities are
mapped into operators. We show that the operators have self-adjoint
realizations and that there exist quantum states for which the evolution across
singularity is well-defined.
| [
{
"created": "Sun, 15 Aug 2010 18:13:03 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Sep 2010 10:34:27 GMT",
"version": "v2"
}
] | 2010-09-23 | [
[
"Malkiewicz",
"Przemyslaw",
""
]
] | This paper is devoted to investigation of the quantum Friedman-Robertson-Walker universe with matter satisfying the equation of state $p=w\rho$, where $w$ is an almost arbitrary constant. The procedure starts with a reduced Lagrangian, which describes the system in a gauge fixed, so that the evolution parameter corresponds to the cosmological time. Then we construct the phase space, which is believed to correspond to the reduced phase space consisting of Dirac's observables. The physically relevant quantities are mapped into operators. We show that the operators have self-adjoint realizations and that there exist quantum states for which the evolution across singularity is well-defined. |
0801.4645 | Andrzej Bialas | A.Bialas and W.Czyz | Renyi entropies of a black hole from Hawking radiation | 10 pages | Europhys.Lett.83:60009,2008 | 10.1209/0295-5075/83/60009 | null | gr-qc | null | Renyi entropies of a black hole are evaluated by counting the states of the
Hawking radiation which fills a thin shell surrounding the horizon. The width
of the shell is determined from its energy content and the corresponding mass
defect. The Bekenstein-Hawking formula for the entropy of the black hole is
correctly reproduced.
| [
{
"created": "Wed, 30 Jan 2008 11:00:32 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Bialas",
"A.",
""
],
[
"Czyz",
"W.",
""
]
] | Renyi entropies of a black hole are evaluated by counting the states of the Hawking radiation which fills a thin shell surrounding the horizon. The width of the shell is determined from its energy content and the corresponding mass defect. The Bekenstein-Hawking formula for the entropy of the black hole is correctly reproduced. |
1401.0181 | Tehani Finch | Tehani K. Finch | Painlev\'{e}-Gullstrand-type coordinates for the five-dimensional
Myers-Perry black hole | 15 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Painleve-Gullstrand coordinates provide a convenient framework for
presenting the Schwarzschild geometry because of their flat constant-time
hypersurfaces, and the fact that they are free of coordinate singularities
outside r=0. Generalizations of Painleve-Gullstrand coordinates suitable for
the Kerr geometry have been presented by Doran and Natario. These coordinate
systems feature a time coordinate identical to the proper time of
zero-angular-momentum observers that are dropped from infinity. Here, the
methods of Doran and Natario are extended to the five-dimensional rotating
black hole found by Myers and Perry. The result is a new formulation of the
Myers-Perry metric. The properties and physical significance of these new
coordinates are discussed.
| [
{
"created": "Tue, 31 Dec 2013 16:56:36 GMT",
"version": "v1"
}
] | 2014-01-03 | [
[
"Finch",
"Tehani K.",
""
]
] | The Painleve-Gullstrand coordinates provide a convenient framework for presenting the Schwarzschild geometry because of their flat constant-time hypersurfaces, and the fact that they are free of coordinate singularities outside r=0. Generalizations of Painleve-Gullstrand coordinates suitable for the Kerr geometry have been presented by Doran and Natario. These coordinate systems feature a time coordinate identical to the proper time of zero-angular-momentum observers that are dropped from infinity. Here, the methods of Doran and Natario are extended to the five-dimensional rotating black hole found by Myers and Perry. The result is a new formulation of the Myers-Perry metric. The properties and physical significance of these new coordinates are discussed. |
1207.0671 | Andrea Dapor | Andrea Dapor, Jerzy Lewandowski, Yaser Tavakoli | Lorentz Symmetry in QFT on Quantum Bianchi I Space-Time | 14 pages, v3. Corrected a reference in the bibliography | Phys. Rev. D 86, 064013 (2012) | 10.1103/PhysRevD.86.064013 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We develop the quantum theory of a scalar field on LQC Bianchi I geometry. In
particular, we focus on single modes of the field: the evolution equation is
derived from the quantum scalar constraint, and it is shown that the same
equation can be obtained from QFT on an "classical" effective geometry. We
investigate the dependence of this effective space-time on the wavevector of
the mode (which could in principle generate a deformation in local
Lorentz-symmetry), focusing our attention on the dispersion relation. We prove
that when we disregard backreaction no Lorentz-violation is present, despite
the effective metric being different than the classical Bianchi I one. A
preliminary analysis of the correction due to inclusion of backreaction is
briefly discussed in the context of Born-Oppenheimer approximation.
| [
{
"created": "Tue, 3 Jul 2012 13:34:11 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Sep 2012 14:11:27 GMT",
"version": "v2"
},
{
"created": "Thu, 25 Oct 2012 09:58:39 GMT",
"version": "v3"
}
] | 2012-10-26 | [
[
"Dapor",
"Andrea",
""
],
[
"Lewandowski",
"Jerzy",
""
],
[
"Tavakoli",
"Yaser",
""
]
] | We develop the quantum theory of a scalar field on LQC Bianchi I geometry. In particular, we focus on single modes of the field: the evolution equation is derived from the quantum scalar constraint, and it is shown that the same equation can be obtained from QFT on an "classical" effective geometry. We investigate the dependence of this effective space-time on the wavevector of the mode (which could in principle generate a deformation in local Lorentz-symmetry), focusing our attention on the dispersion relation. We prove that when we disregard backreaction no Lorentz-violation is present, despite the effective metric being different than the classical Bianchi I one. A preliminary analysis of the correction due to inclusion of backreaction is briefly discussed in the context of Born-Oppenheimer approximation. |
gr-qc/0007021 | Robert M. Wald | Sijie Gao and Robert M. Wald | Theorems on gravitational time delay and related issues | 15 pages, 1 figure. Example of gauge perturbation changed/corrected.
Two footnotes added and one footnote removed | Class.Quant.Grav. 17 (2000) 4999-5008 | 10.1088/0264-9381/17/24/305 | null | gr-qc | null | Two theorems related to gravitational time delay are proven. Both theorems
apply to spacetimes satisfying the null energy condition and the null generic
condition. The first theorem states that if the spacetime is null geodesically
complete, then given any compact set $K$, there exists another compact set $K'$
such that for any $p,q \not\in K'$, if there exists a ``fastest null
geodesic'', $\gamma$, between $p$ and $q$, then $\gamma$ cannot enter $K$. As
an application of this theorem, we show that if, in addition, the spacetime is
globally hyperbolic with a compact Cauchy surface, then any observer at
sufficiently late times cannot have a particle horizon. The second theorem
states that if a timelike conformal boundary can be attached to the spacetime
such that the spacetime with boundary satisfies strong causality as well as a
compactness condition, then any ``fastest null geodesic'' connecting two points
on the boundary must lie entirely within the boundary. It follows from this
theorem that generic perturbations of anti-de Sitter spacetime always produce a
time delay relative to anti-de Sitter spacetime itself.
| [
{
"created": "Tue, 11 Jul 2000 15:12:16 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Jul 2000 22:10:54 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Gao",
"Sijie",
""
],
[
"Wald",
"Robert M.",
""
]
] | Two theorems related to gravitational time delay are proven. Both theorems apply to spacetimes satisfying the null energy condition and the null generic condition. The first theorem states that if the spacetime is null geodesically complete, then given any compact set $K$, there exists another compact set $K'$ such that for any $p,q \not\in K'$, if there exists a ``fastest null geodesic'', $\gamma$, between $p$ and $q$, then $\gamma$ cannot enter $K$. As an application of this theorem, we show that if, in addition, the spacetime is globally hyperbolic with a compact Cauchy surface, then any observer at sufficiently late times cannot have a particle horizon. The second theorem states that if a timelike conformal boundary can be attached to the spacetime such that the spacetime with boundary satisfies strong causality as well as a compactness condition, then any ``fastest null geodesic'' connecting two points on the boundary must lie entirely within the boundary. It follows from this theorem that generic perturbations of anti-de Sitter spacetime always produce a time delay relative to anti-de Sitter spacetime itself. |
gr-qc/0411137 | Peter Diener | Miguel Alcubierre, Bernd Bruegmann, Peter Diener, Frank Herrmann,
Denis Pollney, Edward Seidel, Ryoji Takahashi | Testing excision techniques for dynamical 3D black hole evolutions | REVTeX4, 8 pages, 9 figures | null | null | null | gr-qc | null | We perform both distorted black hole evolutions and binary black hole head on
collisions and compare the results of using a full grid to results obtained by
excising the black hole interiors. In both cases the evolutions are found to
run essentially indefinitely, and produce the same, convergent waveforms.
Further, since both the distorted black holes and the head-on collision of
puncture initial data can be carried out without excision, they provide an
excellent dynamical test-bed for excision codes. This provides a strong
numerical demonstration of the validity of the excision idea, namely the event
horizon can be made to "protect" the spacetime from the excision boundary and
allow an accurate exterior evolution.
| [
{
"created": "Mon, 29 Nov 2004 16:03:39 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Alcubierre",
"Miguel",
""
],
[
"Bruegmann",
"Bernd",
""
],
[
"Diener",
"Peter",
""
],
[
"Herrmann",
"Frank",
""
],
[
"Pollney",
"Denis",
""
],
[
"Seidel",
"Edward",
""
],
[
"Takahashi",
"Ryoji",
""
]
] | We perform both distorted black hole evolutions and binary black hole head on collisions and compare the results of using a full grid to results obtained by excising the black hole interiors. In both cases the evolutions are found to run essentially indefinitely, and produce the same, convergent waveforms. Further, since both the distorted black holes and the head-on collision of puncture initial data can be carried out without excision, they provide an excellent dynamical test-bed for excision codes. This provides a strong numerical demonstration of the validity of the excision idea, namely the event horizon can be made to "protect" the spacetime from the excision boundary and allow an accurate exterior evolution. |
1307.6006 | Iver Brevik | I. Brevik, A. V. Timoshkin, Ye. Rabochaya and S. Zerbini | Turbulence Accelerating Cosmology from an Inhomogeneous Dark Fluid | 14 pages latex2e, no figures. To appear in Astrophys. Space Sci | Astrophysics and Space Science 347, 203 (2013) | 10.1007/s10509-013-1506-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Specific dark energy models with a linear inhomogeneous time-dependent
equation of state, within the framework of 4d Friedman-Robertson-Walker (FRW)
cosmology, are investigated. It is demonstrated that such 4d inhomogeneous
fluid models may lead to a turbulence FRW cosmology. Both one-component and
two-component models from 4d inhomogeneous dark fluid models are considered. In
the one-component model the universe may develop from a viscous era with, for
instance, a constant bulk viscosity, into a turbulent era. In the two-component
model the fluid can be decomposed into two components, one non-turbulent
(ideal) and another turbulent part, obeying two different equations of state.
Conditions for the appearance of the turbulent dark energy universe in terms of
the parameters in the equation of state (EoS) without introducing the
turbulence concept explicitly are are obtained. An equivalent description in
terms of an inhomogeneous fluid for the viscous Little Rip (LR) cosmology is
also developed.
| [
{
"created": "Tue, 23 Jul 2013 10:01:27 GMT",
"version": "v1"
}
] | 2014-01-28 | [
[
"Brevik",
"I.",
""
],
[
"Timoshkin",
"A. V.",
""
],
[
"Rabochaya",
"Ye.",
""
],
[
"Zerbini",
"S.",
""
]
] | Specific dark energy models with a linear inhomogeneous time-dependent equation of state, within the framework of 4d Friedman-Robertson-Walker (FRW) cosmology, are investigated. It is demonstrated that such 4d inhomogeneous fluid models may lead to a turbulence FRW cosmology. Both one-component and two-component models from 4d inhomogeneous dark fluid models are considered. In the one-component model the universe may develop from a viscous era with, for instance, a constant bulk viscosity, into a turbulent era. In the two-component model the fluid can be decomposed into two components, one non-turbulent (ideal) and another turbulent part, obeying two different equations of state. Conditions for the appearance of the turbulent dark energy universe in terms of the parameters in the equation of state (EoS) without introducing the turbulence concept explicitly are are obtained. An equivalent description in terms of an inhomogeneous fluid for the viscous Little Rip (LR) cosmology is also developed. |
0812.4127 | Yousef Sobouti | Yousef Sobouti | Dark companion of baryonic matter in spliral galaxies | 3 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Flat or almost flat rotation curves of spiral galaxies can be explained by
logarithmic gravitational potentials. The field equations of GR admit of
spacetime metrics with such behaviors. The scenario can be interpreted either
as an alternative theory of gravitation or, equivalently, as a dark matter
paradigm. In the latter interpretation, one is led to assign a dark companion
to the baryonic matter who's size and distribution is determined by the mass of
the baryons. The formalism also opens up a way to support Milgrom's idea that
the acceleration of a test object in a gravitational field is not simply the
newtonian gravitational force $g_N$, but rather an involved function of
$(g_N/a_0)$, $a_0$ MOND's universal acceleration. Keywords: Dark matter;
Alternative GR; Spiral galaxies, rotation curves of
| [
{
"created": "Mon, 22 Dec 2008 09:07:56 GMT",
"version": "v1"
},
{
"created": "Thu, 26 Mar 2009 10:57:17 GMT",
"version": "v2"
}
] | 2009-03-26 | [
[
"Sobouti",
"Yousef",
""
]
] | Flat or almost flat rotation curves of spiral galaxies can be explained by logarithmic gravitational potentials. The field equations of GR admit of spacetime metrics with such behaviors. The scenario can be interpreted either as an alternative theory of gravitation or, equivalently, as a dark matter paradigm. In the latter interpretation, one is led to assign a dark companion to the baryonic matter who's size and distribution is determined by the mass of the baryons. The formalism also opens up a way to support Milgrom's idea that the acceleration of a test object in a gravitational field is not simply the newtonian gravitational force $g_N$, but rather an involved function of $(g_N/a_0)$, $a_0$ MOND's universal acceleration. Keywords: Dark matter; Alternative GR; Spiral galaxies, rotation curves of |
2012.05186 | Mohsen Khodadi | Mohsen Khodadi, Emmanuel N. Saridakis | Einstein-\AE ther Gravity in the light of Event Horizon Telescope
Observations of M87* | 29 pages, 10 figures. v2: discussion improved, figures and references
added, matches the version accepted for publication in "Physics of the Dark
Universe" | Phys.Dark Univ. 32 (2021) 100835 | 10.1016/j.dark.2021.100835 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate Einstein-\AE ther gravity in light of the recent Event Horizon
Telescope (EHT) observations of the M87*. The shape and size of the observed
black hole shadow contains information of the geometry in its vicinity, and
thus one can consider it as a potential probe to investigate different
gravitational theories, since the involved calculation framework is enriched
with different size-rotation features as well as with extra model parameters.
In the case of Einstein-\AE ther gravity the black hole solutions include two
classes depending on the involved \ae{}ther parameters. We calculate the
corresponding photon effective potential, the unstable photon sphere radius,
and finally, the induced angular size, which combined with the mass and the
distance can lead to a single prediction that quantifies the black hole shadow,
namely the diameter per unit mass $d$. Since $d_{M87*}$ is observationally
known from the EHT Probe, we extract the corresponding parameter regions in
order to obtain consistency. We find that Einstein-\AE ther black hole
solutions agree with the shadow size of EHT M87*, if the involved \AE ther
parameters are restricted within specific ranges, along with an upper bound on
the dimensionless spin parameter $a$, which is verified by a full scan of the
parameter space within $1\sigma$-error.
| [
{
"created": "Wed, 9 Dec 2020 17:24:07 GMT",
"version": "v1"
},
{
"created": "Tue, 11 May 2021 17:16:33 GMT",
"version": "v2"
}
] | 2021-05-20 | [
[
"Khodadi",
"Mohsen",
""
],
[
"Saridakis",
"Emmanuel N.",
""
]
] | We investigate Einstein-\AE ther gravity in light of the recent Event Horizon Telescope (EHT) observations of the M87*. The shape and size of the observed black hole shadow contains information of the geometry in its vicinity, and thus one can consider it as a potential probe to investigate different gravitational theories, since the involved calculation framework is enriched with different size-rotation features as well as with extra model parameters. In the case of Einstein-\AE ther gravity the black hole solutions include two classes depending on the involved \ae{}ther parameters. We calculate the corresponding photon effective potential, the unstable photon sphere radius, and finally, the induced angular size, which combined with the mass and the distance can lead to a single prediction that quantifies the black hole shadow, namely the diameter per unit mass $d$. Since $d_{M87*}$ is observationally known from the EHT Probe, we extract the corresponding parameter regions in order to obtain consistency. We find that Einstein-\AE ther black hole solutions agree with the shadow size of EHT M87*, if the involved \AE ther parameters are restricted within specific ranges, along with an upper bound on the dimensionless spin parameter $a$, which is verified by a full scan of the parameter space within $1\sigma$-error. |
2306.06177 | Arnab Dhani | Arnab Dhani, David Radice, Jan Sch\"utte-Engel, Susan Gardner,
Bangalore Sathyaprakash, Domenico Logoteta, Albino Perego, Rahul Kashyap | Prospects for Direct Detection of Black Hole Formation in Neutron Star
Mergers with Next-Generation Gravitational-Wave Detectors | null | null | 10.1103/PhysRevD.109.044071 | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | A direct detection of black hole formation in neutron star mergers would
provide invaluable information about matter in neutron star cores and finite
temperature effects on the nuclear equation of state. We study black hole
formation in neutron star mergers using a set of 190 numerical relativity
simulations consisting of long-lived and black-hole-forming remnants. The
postmerger gravitational-wave spectrum of a long-lived remnant has greatly
reduced power at a frequency $f$ greater than $f_{\rm peak}$, for $f \gtrsim
4\,\rm kHz$, with $f_{\rm peak} \in [2.5, 4]\,\rm kHz$. On the other hand,
black-hole-forming remnants exhibit excess power in the same large $f$ region
and manifest exponential damping in the time domain characteristic of a
quasinormal mode. We demonstrate that the gravitational-wave signal from a
collapsed remnant is indeed a quasinormal ringing. We report on the opportunity
for direct detections of black hole formation with next-generation
gravitational-wave detectors such as Cosmic Explorer and Einstein Telescope and
set forth the tantalizing prospect of such observations up to a distance of 100
Mpc for an optimally oriented and located source with an SNR of 4.
| [
{
"created": "Fri, 9 Jun 2023 18:03:04 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Jun 2024 11:40:08 GMT",
"version": "v2"
}
] | 2024-07-03 | [
[
"Dhani",
"Arnab",
""
],
[
"Radice",
"David",
""
],
[
"Schütte-Engel",
"Jan",
""
],
[
"Gardner",
"Susan",
""
],
[
"Sathyaprakash",
"Bangalore",
""
],
[
"Logoteta",
"Domenico",
""
],
[
"Perego",
"Albino",
""
... | A direct detection of black hole formation in neutron star mergers would provide invaluable information about matter in neutron star cores and finite temperature effects on the nuclear equation of state. We study black hole formation in neutron star mergers using a set of 190 numerical relativity simulations consisting of long-lived and black-hole-forming remnants. The postmerger gravitational-wave spectrum of a long-lived remnant has greatly reduced power at a frequency $f$ greater than $f_{\rm peak}$, for $f \gtrsim 4\,\rm kHz$, with $f_{\rm peak} \in [2.5, 4]\,\rm kHz$. On the other hand, black-hole-forming remnants exhibit excess power in the same large $f$ region and manifest exponential damping in the time domain characteristic of a quasinormal mode. We demonstrate that the gravitational-wave signal from a collapsed remnant is indeed a quasinormal ringing. We report on the opportunity for direct detections of black hole formation with next-generation gravitational-wave detectors such as Cosmic Explorer and Einstein Telescope and set forth the tantalizing prospect of such observations up to a distance of 100 Mpc for an optimally oriented and located source with an SNR of 4. |
1704.06524 | Antonio Sanchez Puente | Antonio Sanchez-Puente | Black Holes, Geons, and Singularities in Metric-Affine Gravity | PhD Dissertation, 196 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This thesis deals with the problem of singularities in a family of extensions
of General Relativity in the Metric-Affine formalism. I introduce the
Metric-Affine formalism as a framework in which study extensions of GR. I
review its features and motivate it through its application in Bravais
crystals, where ideal crystals can be described through Riemannian formalism,
but a crystal with defects have to be described with in terms of an independent
connection. The simplest way to construct solutions different from GR in this
formalism is to take a quadratic gravity lagrangian with an electrovacuum
stress-energy tensor. This way, charged black hole solutions are obtained.
The geometry of these new charged black hole solutions is analysed. Far from
the sources, the geometry of these new solutions is equal to the GR one up to
$1/r^4$ corrections. However, instead of a central singularity, they have a
wormhole structure, which can be completely regular or where the curvature
scalars diverge, depending on the mass and charge of the black hole. I study
the geodesics around the wormhole throat and conclude that the geodesics are
always complete even in the case of a curvature divergence. To analyse in more
detail the geometry, I also study the evolution of a scalar wave sent towards
the wormhole. The evolution is shown to be regular and I calculate the
transmission coefficients and transmission cross section for a naked wormhole.
Finally, I study the same case for a Born-Infeld lagrangian in an arbitrary
number of dimension ($d>4$). In this setting, the wormhole structure is also
present and the geodesics are still complete, therefore showing that the
metric-affine formalism can resolve singularities for a variety of models, and
is not a particular feature of the quadratic Lagrangian for $d=4$.
| [
{
"created": "Fri, 21 Apr 2017 13:16:14 GMT",
"version": "v1"
},
{
"created": "Mon, 10 Jul 2017 09:44:17 GMT",
"version": "v2"
},
{
"created": "Fri, 21 Jul 2017 11:29:12 GMT",
"version": "v3"
}
] | 2017-07-24 | [
[
"Sanchez-Puente",
"Antonio",
""
]
] | This thesis deals with the problem of singularities in a family of extensions of General Relativity in the Metric-Affine formalism. I introduce the Metric-Affine formalism as a framework in which study extensions of GR. I review its features and motivate it through its application in Bravais crystals, where ideal crystals can be described through Riemannian formalism, but a crystal with defects have to be described with in terms of an independent connection. The simplest way to construct solutions different from GR in this formalism is to take a quadratic gravity lagrangian with an electrovacuum stress-energy tensor. This way, charged black hole solutions are obtained. The geometry of these new charged black hole solutions is analysed. Far from the sources, the geometry of these new solutions is equal to the GR one up to $1/r^4$ corrections. However, instead of a central singularity, they have a wormhole structure, which can be completely regular or where the curvature scalars diverge, depending on the mass and charge of the black hole. I study the geodesics around the wormhole throat and conclude that the geodesics are always complete even in the case of a curvature divergence. To analyse in more detail the geometry, I also study the evolution of a scalar wave sent towards the wormhole. The evolution is shown to be regular and I calculate the transmission coefficients and transmission cross section for a naked wormhole. Finally, I study the same case for a Born-Infeld lagrangian in an arbitrary number of dimension ($d>4$). In this setting, the wormhole structure is also present and the geodesics are still complete, therefore showing that the metric-affine formalism can resolve singularities for a variety of models, and is not a particular feature of the quadratic Lagrangian for $d=4$. |
2104.14453 | Pardyumn Kumar Sahoo | S. K. J. Pacif, Simran Arora, P.K. Sahoo | Late-time acceleration with a scalar field source: Observational
constraints and statefinder diagnostics | Physics of the Dark Universe published version | Phys. Dark Universe 32, 100804 (2021) | 10.1016/j.dark.2021.100804 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | This article discusses a dark energy cosmological model in the standard
theory of gravity - general relativity with a broad scalar field as a source.
Exact solutions of Einstein's field equations are derived by considering a
particular form of deceleration parameter $q$, which shows a smooth transition
from decelerated to accelerated phase in the evolution of the universe. The
external datasets such as Hubble ($H(z)$) datasets, Supernovae (SN) datasets,
and Baryonic Acoustic Oscillation (BAO) datasets are used for constraining the
model par parameters appearing in the functional form of $q$. The transition
redshift is obtained at $% z_{t}=0.67_{-0.36}^{+0.26}$ for the combined data
set ($H(z)+SN+BAO$), where the model shows signature-flipping and is consistent
with recent observations. Moreover, the present value of the deceleration
parameter comes out to be $q_{0}=-0.50_{-0.11}^{+0.12}$ and the jerk parameter
$% j_{0}=-0.98_{-0.02}^{+0.06}$ (close to 1) for the combined datasets, which
is compatible as per Planck2018 results. The analysis also constrains the omega
value i.e., $\Omega _{m_{0}}\leq 0.269$ for the smooth evolution of the scalar
field EoS parameter. It is seen that energy density is higher for the effective
energy density of the matter field than energy density in the presence of a
scalar field. The evolution of the physical and geometrical parameters is
discussed in some details with the model parameters' numerical constrained
values. Moreover, we have performed the state-finder analysis to investigate
the nature of dark energy.
| [
{
"created": "Fri, 2 Apr 2021 06:19:25 GMT",
"version": "v1"
}
] | 2022-08-23 | [
[
"Pacif",
"S. K. J.",
""
],
[
"Arora",
"Simran",
""
],
[
"Sahoo",
"P. K.",
""
]
] | This article discusses a dark energy cosmological model in the standard theory of gravity - general relativity with a broad scalar field as a source. Exact solutions of Einstein's field equations are derived by considering a particular form of deceleration parameter $q$, which shows a smooth transition from decelerated to accelerated phase in the evolution of the universe. The external datasets such as Hubble ($H(z)$) datasets, Supernovae (SN) datasets, and Baryonic Acoustic Oscillation (BAO) datasets are used for constraining the model par parameters appearing in the functional form of $q$. The transition redshift is obtained at $% z_{t}=0.67_{-0.36}^{+0.26}$ for the combined data set ($H(z)+SN+BAO$), where the model shows signature-flipping and is consistent with recent observations. Moreover, the present value of the deceleration parameter comes out to be $q_{0}=-0.50_{-0.11}^{+0.12}$ and the jerk parameter $% j_{0}=-0.98_{-0.02}^{+0.06}$ (close to 1) for the combined datasets, which is compatible as per Planck2018 results. The analysis also constrains the omega value i.e., $\Omega _{m_{0}}\leq 0.269$ for the smooth evolution of the scalar field EoS parameter. It is seen that energy density is higher for the effective energy density of the matter field than energy density in the presence of a scalar field. The evolution of the physical and geometrical parameters is discussed in some details with the model parameters' numerical constrained values. Moreover, we have performed the state-finder analysis to investigate the nature of dark energy. |
2106.03150 | Masaya Amo | Masaya Amo, Keisuke Izumi, Yoshimune Tomikawa, Hirotaka Yoshino,
Tetsuya Shiromizu | Asymptotic behavior of null geodesics near future null infinity:
Significance of gravitational waves | 23 pages, published version, in v3 minor corrections | Phys. Rev. D 104, 064025 (2021) | 10.1103/PhysRevD.104.064025 | YITP-21-54, KOBE-COSMO-21-11, OCU-PHYS-541, AP-GR-169 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the behavior of null geodesics near future null infinity in
asymptotically flat spacetimes. In particular, we focus on the asymptotic
behavior of null geodesics that correspond to worldlines of photons initially
emitted in the directions tangential to the constant radial surfaces in the
Bondi coordinates. The analysis is performed for general dimensions, and the
difference between the four-dimensional cases and the higher-dimensional cases
is stressed. In four dimensions, some assumptions are required to guarantee the
null geodesics to reach future null infinity, in addition to the conditions of
asymptotic flatness. Without these assumptions, gravitational waves may prevent
photons from reaching null infinity. In higher dimensions, by contrast, such
assumptions are not necessary, and gravitational waves do not affect the
asymptotic behavior of null geodesics.
| [
{
"created": "Sun, 6 Jun 2021 15:10:00 GMT",
"version": "v1"
},
{
"created": "Thu, 17 Jun 2021 05:42:09 GMT",
"version": "v2"
},
{
"created": "Fri, 10 Sep 2021 02:23:03 GMT",
"version": "v3"
}
] | 2021-09-13 | [
[
"Amo",
"Masaya",
""
],
[
"Izumi",
"Keisuke",
""
],
[
"Tomikawa",
"Yoshimune",
""
],
[
"Yoshino",
"Hirotaka",
""
],
[
"Shiromizu",
"Tetsuya",
""
]
] | We investigate the behavior of null geodesics near future null infinity in asymptotically flat spacetimes. In particular, we focus on the asymptotic behavior of null geodesics that correspond to worldlines of photons initially emitted in the directions tangential to the constant radial surfaces in the Bondi coordinates. The analysis is performed for general dimensions, and the difference between the four-dimensional cases and the higher-dimensional cases is stressed. In four dimensions, some assumptions are required to guarantee the null geodesics to reach future null infinity, in addition to the conditions of asymptotic flatness. Without these assumptions, gravitational waves may prevent photons from reaching null infinity. In higher dimensions, by contrast, such assumptions are not necessary, and gravitational waves do not affect the asymptotic behavior of null geodesics. |
2010.13693 | Brandon Mattingly | Brandon Mattingly, Abinash Kar, Matthew Gorban, William Julius, Cooper
Watson, MD Ali, Andrew Baas, Caleb Elmore, Jeff Lee, Bahram Shakerin, Eric
Davis, and Gerald Cleaver | Curvature Invariants for the Alcubierre and Nat\'ario Warp Drives | 41 Pages, 15 figures | Universe 2021, 7, 21 | 10.3390/universe7020021 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A process for using curvature invariants is applied to evaluate the metrics
for the Alcubierre and the Natario warp drives at a constant velocity.Curvature
invariants are independent of coordinate bases, so plotting these invariants
will be free of coordinate mapping distortions. As a consequence, they provide
a novel perspective into complex spacetimes such as warp drives. Warp drives
are the theoretical solutions to Einstein's field equations that allow the
possibility for faster-than-light (FTL) travel. While their mathematics is well
established, the visualisation of such spacetimes is unexplored. This paper
uses the methods of computing and plotting the warp drive curvature invariants
to reveal these spacetimes. The warp drive parameters of velocity, skin depth
and radius are varied individually and then plotted to see each parameter's
unique effect on the surrounding curvature. For each warp drive, this research
shows a safe harbor and how the shape function forms the warp bubble. The
curvature plots for the constant velocity Natario warp drive do not contain a
wake or a constant curvature indicating that these are unique features of the
accelerating Natario warp drive.
| [
{
"created": "Mon, 26 Oct 2020 16:18:25 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Jan 2021 22:12:17 GMT",
"version": "v2"
},
{
"created": "Wed, 14 Apr 2021 15:17:28 GMT",
"version": "v3"
}
] | 2021-04-15 | [
[
"Mattingly",
"Brandon",
""
],
[
"Kar",
"Abinash",
""
],
[
"Gorban",
"Matthew",
""
],
[
"Julius",
"William",
""
],
[
"Watson",
"Cooper",
""
],
[
"Ali",
"MD",
""
],
[
"Baas",
"Andrew",
""
],
[
"Elmore... | A process for using curvature invariants is applied to evaluate the metrics for the Alcubierre and the Natario warp drives at a constant velocity.Curvature invariants are independent of coordinate bases, so plotting these invariants will be free of coordinate mapping distortions. As a consequence, they provide a novel perspective into complex spacetimes such as warp drives. Warp drives are the theoretical solutions to Einstein's field equations that allow the possibility for faster-than-light (FTL) travel. While their mathematics is well established, the visualisation of such spacetimes is unexplored. This paper uses the methods of computing and plotting the warp drive curvature invariants to reveal these spacetimes. The warp drive parameters of velocity, skin depth and radius are varied individually and then plotted to see each parameter's unique effect on the surrounding curvature. For each warp drive, this research shows a safe harbor and how the shape function forms the warp bubble. The curvature plots for the constant velocity Natario warp drive do not contain a wake or a constant curvature indicating that these are unique features of the accelerating Natario warp drive. |
1505.05980 | Yu-Hsiang Lin | Pisin Chen, Yu-Hsiang Lin | What initial condition of inflation would suppress the large-scale CMB
spectrum? | 17 pages, 17 figures; revised to address referee's comment, added
subsection III D and appendix with accompanying figures; matching
coefficients in subsection III D and appendix corrected, other minor
corrections and improvement, published in PRD | Phys. Rev. D 93, 023503 (2016) | 10.1103/PhysRevD.93.023503 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | There is an apparent power deficit relative to the $\Lambda$CDM prediction of
the CMB spectrum at large scales, which, though not yet statistically
significant, persists from WMAP to Planck data. Proposals that invoke some form
of initial condition for the inflation have been made to address this apparent
power suppression, albeit with conflicting conclusions. By studying the
curvature perturbations of a scalar field in the FLRW universe parameterized by
the equation of state parameter $w$, we find that the large-scale spectrum at
the end of inflation reflects the super-horizon spectrum of the initial state.
The large-scale spectrum is suppressed if the universe begins with the
adiabatic vacuum in a super-inflation ($w < -1$) or positive-pressure ($w > 0$)
era. In the latter case, there is however no causal mechanism to establish the
initial adiabatic vacuum. On the other hand, as long as the universe begins
with the adiabatic vacuum in an era with $-1 < w < 0$, even if there exists an
intermediate positive-pressure era, the large-scale spectrum would be enhanced
rather than suppressed. We further calculate the spectrum of a two-stage
inflation model with a two-field potential and show that the result agrees with
that obtained from the ad hoc single-field analysis.
| [
{
"created": "Fri, 22 May 2015 08:10:27 GMT",
"version": "v1"
},
{
"created": "Fri, 4 Sep 2015 19:44:12 GMT",
"version": "v2"
},
{
"created": "Fri, 8 Jan 2016 21:17:52 GMT",
"version": "v3"
}
] | 2016-01-12 | [
[
"Chen",
"Pisin",
""
],
[
"Lin",
"Yu-Hsiang",
""
]
] | There is an apparent power deficit relative to the $\Lambda$CDM prediction of the CMB spectrum at large scales, which, though not yet statistically significant, persists from WMAP to Planck data. Proposals that invoke some form of initial condition for the inflation have been made to address this apparent power suppression, albeit with conflicting conclusions. By studying the curvature perturbations of a scalar field in the FLRW universe parameterized by the equation of state parameter $w$, we find that the large-scale spectrum at the end of inflation reflects the super-horizon spectrum of the initial state. The large-scale spectrum is suppressed if the universe begins with the adiabatic vacuum in a super-inflation ($w < -1$) or positive-pressure ($w > 0$) era. In the latter case, there is however no causal mechanism to establish the initial adiabatic vacuum. On the other hand, as long as the universe begins with the adiabatic vacuum in an era with $-1 < w < 0$, even if there exists an intermediate positive-pressure era, the large-scale spectrum would be enhanced rather than suppressed. We further calculate the spectrum of a two-stage inflation model with a two-field potential and show that the result agrees with that obtained from the ad hoc single-field analysis. |
1105.1091 | Surajit Chattopadhyay | Surajit Chattopadhyay (Pailan College of Management and Technology,
Kolkata) and Ujjal Debnath (Bengal Engineering and Science University,
Shibpur) | Emergent universe in chameleon, f(R) and f(T) gravity theories | International Journal of Modern Physics D, 2011 | Int.J.Mod.Phys.D20:1135-1152,2011 | 10.1142/S0218271811019293 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we consider an emergent universe in generalized gravity
theories like the chameleon, f(R) and f(T) gravities. We reconstruct the
potential of the chameleon field under the emergent scenario of the universe
and observe its increasing nature with the evolution of the universe. We reveal
that in the emergent universe scenario, the equation-of-state parameter behaves
like quintessence in the case of f(R) gravity and like phantom in the case of
f(T) gravity.
| [
{
"created": "Wed, 4 May 2011 08:50:55 GMT",
"version": "v1"
}
] | 2011-07-04 | [
[
"Chattopadhyay",
"Surajit",
"",
"Pailan College of Management and Technology,\n Kolkata"
],
[
"Debnath",
"Ujjal",
"",
"Bengal Engineering and Science University,\n Shibpur"
]
] | In this work, we consider an emergent universe in generalized gravity theories like the chameleon, f(R) and f(T) gravities. We reconstruct the potential of the chameleon field under the emergent scenario of the universe and observe its increasing nature with the evolution of the universe. We reveal that in the emergent universe scenario, the equation-of-state parameter behaves like quintessence in the case of f(R) gravity and like phantom in the case of f(T) gravity. |
1908.04995 | Mustapha Azreg-A\"inou | Mustapha Azreg-A\"inou | Cylindrically symmetric static $n$-dimensional (un)charged (anti-)de
Sitter black holes in generic $f(T)$ gravity | 7 pages, 2 figures, extended version | Europhysics Letters (EPL) vol. 129 (2020) 20003 | 10.1209/0295-5075/129/20003 | null | gr-qc astro-ph.HE math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Given a generic function $f(T)$ we construct in closed forms cylindrically
symmetric static $n$-dimensional uncharged and charged de Sitter and anti-de
Sitter solutions (including black holes, wormholes and possibly other regular
solutions) in $f(T)$ gravity. Applications to some known models are considered.
| [
{
"created": "Wed, 14 Aug 2019 07:30:19 GMT",
"version": "v1"
},
{
"created": "Mon, 17 Feb 2020 16:12:26 GMT",
"version": "v2"
}
] | 2020-02-18 | [
[
"Azreg-Aïnou",
"Mustapha",
""
]
] | Given a generic function $f(T)$ we construct in closed forms cylindrically symmetric static $n$-dimensional uncharged and charged de Sitter and anti-de Sitter solutions (including black holes, wormholes and possibly other regular solutions) in $f(T)$ gravity. Applications to some known models are considered. |
gr-qc/9807050 | Wang Bin | Bin Wang and Ru-Keng Su | Two kinds of extreme black holes and their classification | Latex version, to be published on Phys.Lett.B | Phys.Lett. B432 (1998) 69-73 | 10.1016/S0370-2693(98)00642-X | null | gr-qc | null | According to different topological configurations, we suggest that there are
two kinds of extreme black holes in the nature. We find that the Euler
characteristic plays an essential role to classify these two kinds of extreme
black holes. For the first kind of extreme black holes, Euler characteristic is
zero, and for the second kind, Euler characteristic is two or one provided they
are four dimensional holes or two dimensional holes respectively.
| [
{
"created": "Sun, 19 Jul 1998 13:06:21 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Wang",
"Bin",
""
],
[
"Su",
"Ru-Keng",
""
]
] | According to different topological configurations, we suggest that there are two kinds of extreme black holes in the nature. We find that the Euler characteristic plays an essential role to classify these two kinds of extreme black holes. For the first kind of extreme black holes, Euler characteristic is zero, and for the second kind, Euler characteristic is two or one provided they are four dimensional holes or two dimensional holes respectively. |
1909.02375 | Donato Bini | Donato Bini, Thibault Damour, Andrea Geralico | Novel approach to binary dynamics: application to the fifth
post-Newtonian level | 6 pages, 1 figure | Phys. Rev. Lett. 123, 231104 (2019) | 10.1103/PhysRevLett.123.231104 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We introduce a new methodology for deriving the conservative dynamics of
gravitationally interacting binary systems. Our approach combines, in a novel
way, several theoretical formalisms: post-Newtonian, post-Minkowskian,
multipolar-post-Minkowskian, gravitational self-force, and effective one-body.
We apply our method to the derivation of the fifth post-Newtonian dynamics. By
restricting our results to the third post-Minkowskian level, we give the first
independent confirmation of the recent result of Bern {\it et al.}
[Phys.\ Rev.\ Lett.\ {\bf 122}, 201603 (2019)]. We also offer checks for
future fourth post-Minkowskian calculations.
Our technique can, in principle, be extended to higher orders of perturbation
theory.
| [
{
"created": "Thu, 5 Sep 2019 12:59:56 GMT",
"version": "v1"
}
] | 2019-12-11 | [
[
"Bini",
"Donato",
""
],
[
"Damour",
"Thibault",
""
],
[
"Geralico",
"Andrea",
""
]
] | We introduce a new methodology for deriving the conservative dynamics of gravitationally interacting binary systems. Our approach combines, in a novel way, several theoretical formalisms: post-Newtonian, post-Minkowskian, multipolar-post-Minkowskian, gravitational self-force, and effective one-body. We apply our method to the derivation of the fifth post-Newtonian dynamics. By restricting our results to the third post-Minkowskian level, we give the first independent confirmation of the recent result of Bern {\it et al.} [Phys.\ Rev.\ Lett.\ {\bf 122}, 201603 (2019)]. We also offer checks for future fourth post-Minkowskian calculations. Our technique can, in principle, be extended to higher orders of perturbation theory. |
2112.07635 | Mark Ho-Yeuk Cheung | Simon M. C. Yeung, Mark H. Y. Cheung, Joseph A. J. Gais, Otto A.
Hannuksela, Tjonnie G. F. Li | Detectability of microlensed gravitational waves | 11 pages, 15 figures. Matches published version on MNRAS | Monthly Notices of the Royal Astronomical Society, Volume 526,
Issue 2, December 2023, Pages 2230-2240 | 10.1093/mnras/stad2772 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational lensing describes the bending of the trajectories of light and
gravitational waves due to the gravitational potential of a massive object.
Strong lensing by galaxies can create multiple images with different overall
amplifications, arrival times, and image types. If, furthermore, the
gravitational wave encounters a star along its trajectory, microlensing will
take place. Previously, it has been shown that the effects of microlenses on
strongly-lensed type-I images could be negligible in practice, at least in the
low magnification regime. In this work, we study the same effect on type-II
strongly-lensed images by computing the microlensing amplification factor. As
opposed to being magnified, type-II images are typically demagnified. Moreover,
microlensing on top of type-II images induces larger mismatches with
un-microlensed waveforms than type-I images. These results are broadly
consistent with recent literature and serve to confirm the findings. In
addition, we investigate the possibility of detecting and analysing microlensed
signals through Bayesian parameter estimation with an isolated point mass lens
template, which has been adopted in recent parameter estimation literature. In
particular, we simulate gravitational waves microlensed by a microlens embedded
in a galaxy potential near moderately magnified type-I and II macroimages, with
variable lens masses, source parameters and macromagnifcations. Generally, an
isolated point mass model could be used as an effective template to detect a
type-II microlensed image but not for type-I images, demonstrating the
necessity for more realistic microlensing search templates.
| [
{
"created": "Tue, 14 Dec 2021 18:26:58 GMT",
"version": "v1"
},
{
"created": "Thu, 22 Feb 2024 23:20:15 GMT",
"version": "v2"
}
] | 2024-02-26 | [
[
"Yeung",
"Simon M. C.",
""
],
[
"Cheung",
"Mark H. Y.",
""
],
[
"Gais",
"Joseph A. J.",
""
],
[
"Hannuksela",
"Otto A.",
""
],
[
"Li",
"Tjonnie G. F.",
""
]
] | Gravitational lensing describes the bending of the trajectories of light and gravitational waves due to the gravitational potential of a massive object. Strong lensing by galaxies can create multiple images with different overall amplifications, arrival times, and image types. If, furthermore, the gravitational wave encounters a star along its trajectory, microlensing will take place. Previously, it has been shown that the effects of microlenses on strongly-lensed type-I images could be negligible in practice, at least in the low magnification regime. In this work, we study the same effect on type-II strongly-lensed images by computing the microlensing amplification factor. As opposed to being magnified, type-II images are typically demagnified. Moreover, microlensing on top of type-II images induces larger mismatches with un-microlensed waveforms than type-I images. These results are broadly consistent with recent literature and serve to confirm the findings. In addition, we investigate the possibility of detecting and analysing microlensed signals through Bayesian parameter estimation with an isolated point mass lens template, which has been adopted in recent parameter estimation literature. In particular, we simulate gravitational waves microlensed by a microlens embedded in a galaxy potential near moderately magnified type-I and II macroimages, with variable lens masses, source parameters and macromagnifcations. Generally, an isolated point mass model could be used as an effective template to detect a type-II microlensed image but not for type-I images, demonstrating the necessity for more realistic microlensing search templates. |
0903.3423 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | Theoretical construction of stable traversable wormholes | 5 pages; 1 figure | Central Eur. J. Phys.8:364,2010 | 10.2478/s11534-009-0099-4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is shown in this paper that it is possible, at least in principle, to
construct a traversable wormhole that is stable to linearized radial
perturbations by specifying relatively simple conditions on the shape and
redshift functions.
| [
{
"created": "Thu, 19 Mar 2009 20:57:27 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Jun 2010 20:52:44 GMT",
"version": "v2"
},
{
"created": "Mon, 28 Jan 2013 16:04:36 GMT",
"version": "v3"
}
] | 2013-01-29 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | It is shown in this paper that it is possible, at least in principle, to construct a traversable wormhole that is stable to linearized radial perturbations by specifying relatively simple conditions on the shape and redshift functions. |
1911.00881 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig and Vance D. Gladney | Seeking connections between wormholes, gravastars, and black holes via
noncommutative geometry | 9 pages, 1 figure; accepted by MPLA | null | 10.1142/S0217732320500595 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Noncommutative geometry, an offshoot of string theory, replaces point-like
objects by smeared objects. The resulting uncertainty may cause a black hole to
be observationally indistinguishable from a traversable wormhole, while the
latter, in turn, may become observationally indistinguishable from a gravastar.
The same noncommutative-geometry background allows the theoretical construction
of thin-shell wormholes from gravastars and may even serve as a model for dark
energy.
| [
{
"created": "Sun, 3 Nov 2019 13:04:15 GMT",
"version": "v1"
},
{
"created": "Sat, 23 Nov 2019 18:38:52 GMT",
"version": "v2"
}
] | 2020-04-15 | [
[
"Kuhfittig",
"Peter K. F.",
""
],
[
"Gladney",
"Vance D.",
""
]
] | Noncommutative geometry, an offshoot of string theory, replaces point-like objects by smeared objects. The resulting uncertainty may cause a black hole to be observationally indistinguishable from a traversable wormhole, while the latter, in turn, may become observationally indistinguishable from a gravastar. The same noncommutative-geometry background allows the theoretical construction of thin-shell wormholes from gravastars and may even serve as a model for dark energy. |
gr-qc/9403044 | null | Karl-Peter Marzlin | Fermi Coordinates for Weak Gravitational Fields | 7 Pages, Preprint KONS-RGKU-94-04, LaTeX | Phys.Rev. D50 (1994) 888-891 | 10.1103/PhysRevD.50.888 | null | gr-qc | null | A Reference is corrected. (We derive the Fermi coordinate system of an
observer in arbitrary motion in an arbitrary weak gravitational field valid to
all orders in the geodesic distance from the worldline of the observer. In flat
space-time this leads to a generalization of Rindler space for arbitrary
acceleration and rotation. The general approach is applied to the special case
of an observer resting with respect to the weak gravitational field of a static
mass distribution. This allows to make the correspondence between general
relativity and Newtonian gravity more precise.)
| [
{
"created": "Tue, 22 Mar 1994 11:24:09 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Mar 1994 12:33:07 GMT",
"version": "v2"
}
] | 2009-10-22 | [
[
"Marzlin",
"Karl-Peter",
""
]
] | A Reference is corrected. (We derive the Fermi coordinate system of an observer in arbitrary motion in an arbitrary weak gravitational field valid to all orders in the geodesic distance from the worldline of the observer. In flat space-time this leads to a generalization of Rindler space for arbitrary acceleration and rotation. The general approach is applied to the special case of an observer resting with respect to the weak gravitational field of a static mass distribution. This allows to make the correspondence between general relativity and Newtonian gravity more precise.) |
2308.07963 | Nishita Jadoo | Nishita Jadoo, J. David Brown, Charles R. Evans | Extended body dynamics in general relativity: hyperelastic models | Corrected typos | Phys. Rev. D 108, 084020 (2023) | 10.1103/PhysRevD.108.084020 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We present a numerical framework for modeling extended hyperelastic bodies
based on a Lagrangian formulation of general relativistic elasticity theory. We
use finite element methods to discretize the body, then use the semi--discrete
action to derive ordinary differential equations of motion for the discrete
nodes. The nodes are evolved in time using fourth--order Runge--Kutta. We
validate our code against the normal modes of oscillation of a hyperelastic
sphere, which are known analytically in the limit of small (linear), slow
(Newtonian) oscillations. The algorithm displays second order convergence. This
numerical framework can be used to obtain the orbital motion and internal
dynamics of a hyperelastic body of any shape, for any spacetime metric, and for
varying hyperelastic energy models.
| [
{
"created": "Tue, 15 Aug 2023 18:01:26 GMT",
"version": "v1"
},
{
"created": "Tue, 17 Oct 2023 16:54:11 GMT",
"version": "v2"
}
] | 2023-10-18 | [
[
"Jadoo",
"Nishita",
""
],
[
"Brown",
"J. David",
""
],
[
"Evans",
"Charles R.",
""
]
] | We present a numerical framework for modeling extended hyperelastic bodies based on a Lagrangian formulation of general relativistic elasticity theory. We use finite element methods to discretize the body, then use the semi--discrete action to derive ordinary differential equations of motion for the discrete nodes. The nodes are evolved in time using fourth--order Runge--Kutta. We validate our code against the normal modes of oscillation of a hyperelastic sphere, which are known analytically in the limit of small (linear), slow (Newtonian) oscillations. The algorithm displays second order convergence. This numerical framework can be used to obtain the orbital motion and internal dynamics of a hyperelastic body of any shape, for any spacetime metric, and for varying hyperelastic energy models. |
0706.2072 | Iver Brevik | I. Brevik, E. Elizalde, O. Gorbunova, A. V. Timoshkin | A FRW Dark Fluid with a Non-Linear Inhomogeneous Equation of State | 11 pages pdf, 2 figures; to appear in Eur. Phys. J. C | Eur.Phys.J.C52:223-228,2007 | 10.1140/epjc/s10052-007-0357-9 | null | gr-qc | null | A dark Friedman-Robertson-Walker fluid governed by a non-linear inhomogeneous
equation of state is considered which can be viewed as a conveniently simple
paradigm for a whole class of models which exhibit phase transitions from a
non-phantom towards a phantom era (superacceleration transition). From another
side, such dark fluid models may describe also quintessence-like cosmic
acceleration. Thermodynamical considerations for the processes involved, which
are of great importance in the characterization of the global evolution of the
corresponding universe, are given too. Connecting the proposed equation of
state with an anisotropic Kasner universe with viscosity, we are led to the
plausible conjecture of a dark fluid origin of the anisotropies in the early
universe.
| [
{
"created": "Thu, 14 Jun 2007 09:39:11 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Brevik",
"I.",
""
],
[
"Elizalde",
"E.",
""
],
[
"Gorbunova",
"O.",
""
],
[
"Timoshkin",
"A. V.",
""
]
] | A dark Friedman-Robertson-Walker fluid governed by a non-linear inhomogeneous equation of state is considered which can be viewed as a conveniently simple paradigm for a whole class of models which exhibit phase transitions from a non-phantom towards a phantom era (superacceleration transition). From another side, such dark fluid models may describe also quintessence-like cosmic acceleration. Thermodynamical considerations for the processes involved, which are of great importance in the characterization of the global evolution of the corresponding universe, are given too. Connecting the proposed equation of state with an anisotropic Kasner universe with viscosity, we are led to the plausible conjecture of a dark fluid origin of the anisotropies in the early universe. |
1312.5544 | Piotr Bizon | Piotr Bizo\'n | Is AdS stable? | invited review for GRG (based on my plenary lecture at GR20) | Gen. Rel. Grav. 46, 1724 (2014) | 10.1007/s10714-014-1724-0 | null | gr-qc hep-th math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It has recently been conjectured that the Anti-de Sitter space is unstable
under arbitrarily small perturbations. This article (based on my plenary talk
of the same title at the conference GR20 in Warsaw) briefly reviews numerical
and analytical evidence supporting this conjecture, putting emphasis on weak
turbulence as a driving mechanism of instability.
| [
{
"created": "Thu, 19 Dec 2013 13:36:06 GMT",
"version": "v1"
}
] | 2015-06-18 | [
[
"Bizoń",
"Piotr",
""
]
] | It has recently been conjectured that the Anti-de Sitter space is unstable under arbitrarily small perturbations. This article (based on my plenary talk of the same title at the conference GR20 in Warsaw) briefly reviews numerical and analytical evidence supporting this conjecture, putting emphasis on weak turbulence as a driving mechanism of instability. |
1303.4083 | Mehedi Kalam | Mehedi Kalam, Nur Farhad and Sk. Monowar Hossein | Geodesic study of a charged black hole | 6 pages,6 figures | null | 10.1007/s10773-013-1814-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The behavior of the timelike and null geodesics of charged E.
Ay$\acute{o}$n-Beato and A. Garcia (ABG) black hole are investigated. For
circular and radial geodesics, we investigate all the possible motions by
plotting the effective potentials for different parameters. In conclusion, we
have shown that there is no phenomenon of \textit{superradiance} in this case.
| [
{
"created": "Sun, 17 Mar 2013 18:09:14 GMT",
"version": "v1"
}
] | 2015-06-15 | [
[
"Kalam",
"Mehedi",
""
],
[
"Farhad",
"Nur",
""
],
[
"Hossein",
"Sk. Monowar",
""
]
] | The behavior of the timelike and null geodesics of charged E. Ay$\acute{o}$n-Beato and A. Garcia (ABG) black hole are investigated. For circular and radial geodesics, we investigate all the possible motions by plotting the effective potentials for different parameters. In conclusion, we have shown that there is no phenomenon of \textit{superradiance} in this case. |
gr-qc/9907072 | Robert Mann | I.S. Booth and R.B. Mann | Static and Infalling Quasilocal Energy of Charged and Naked Black Holes | 33 pages, 1 figure | Phys. Rev. D:124009, 1999 | 10.1103/PhysRevD.60.124009 | WATPHYS-TH99/04 | gr-qc | null | We extend the quasilocal formalism of Brown and York to include
electromagnetic and dilaton fields and also allow for spatial boundaries that
are not orthogonal to the foliation of the spacetime. The extension allows us
to study the quasilocal energy measured by observers who are moving around in a
spacetime. We show that the quasilocal energy transforms with respect to boosts
by Lorentz-type transformation laws. The resulting formalism can be used to
study spacetimes containing electric or magnetic charge but not both, a
restriction inherent in the formalism. The gauge dependence of the quasilocal
energy is discussed. We use the thin shell formalism of Israel to reinterpret
the quasilocal energy from an operational point of view and examine the
implications for the recently proposed AdS/CFT inspired intrinsic reference
terms. The distribution of energy around Reissner-Nordstr\"{o}m and naked black
holes is investigated as measured by both static and infalling observers. We
see that this proposed distribution matches a Newtonian intuition in the
appropriate limit. Finally the study of naked black holes reveals an alternate
characterization of this class of spacetimes in terms of the quasilocal
energies.
| [
{
"created": "Thu, 22 Jul 1999 16:30:43 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Booth",
"I. S.",
""
],
[
"Mann",
"R. B.",
""
]
] | We extend the quasilocal formalism of Brown and York to include electromagnetic and dilaton fields and also allow for spatial boundaries that are not orthogonal to the foliation of the spacetime. The extension allows us to study the quasilocal energy measured by observers who are moving around in a spacetime. We show that the quasilocal energy transforms with respect to boosts by Lorentz-type transformation laws. The resulting formalism can be used to study spacetimes containing electric or magnetic charge but not both, a restriction inherent in the formalism. The gauge dependence of the quasilocal energy is discussed. We use the thin shell formalism of Israel to reinterpret the quasilocal energy from an operational point of view and examine the implications for the recently proposed AdS/CFT inspired intrinsic reference terms. The distribution of energy around Reissner-Nordstr\"{o}m and naked black holes is investigated as measured by both static and infalling observers. We see that this proposed distribution matches a Newtonian intuition in the appropriate limit. Finally the study of naked black holes reveals an alternate characterization of this class of spacetimes in terms of the quasilocal energies. |
1507.05850 | Jan Harms | Jan Harms | Terrestrial Gravity Fluctuations | 151 pages, 52 figures; submitted to Living Reviews in Relativity | null | 10.1007/s41114-019-0022-2 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The article reviews the current state of the field, and also presents new
analyses especially with respect to the impact of seismic scattering on gravity
perturbations, active gravity noise cancellation, and time-domain models of
gravity perturbations from atmospheric and seismic point sources. Our
understanding of terrestrial gravity fluctuations will have great impact on the
future development of GW detectors and high-precision gravimetry in general,
and many open questions need to be answered still as emphasized in this
article.
| [
{
"created": "Tue, 21 Jul 2015 14:26:54 GMT",
"version": "v1"
}
] | 2020-06-16 | [
[
"Harms",
"Jan",
""
]
] | The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of terrestrial gravity fluctuations will have great impact on the future development of GW detectors and high-precision gravimetry in general, and many open questions need to be answered still as emphasized in this article. |
1704.05997 | Peng-Ming Zhang | P. M. Zhang, C. Duval, G. W. Gibbons, P. A. Horvathy | The Memory Effect for Plane Gravitational Waves | Thoroughly revised version. 11 pages, 4 figures | null | 10.1016/j.physletb.2017.07.050 | null | gr-qc astro-ph.HE hep-th math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | We give an account of the gravitational memory effect in the presence of the
exact plane wave solution of Einstein's vacuum equations. This allows an
elementary but exact description of the soft gravitons and how their presence
may be detected by observing the motion of freely falling particles. The
theorem of Bondi and Pirani on caustics (for which we present a new proof)
implies that the asymptotic relative velocity is constant but not zero, in
contradiction with the permanent displacement claimed by Zel'dovich and
Polnarev. A non-vanishing asymptotic relative velocity might be used to detect
gravitational waves through the "velocity memory effect", considered by
Braginsky, Thorne, Grishchuk, and Polnarev.
| [
{
"created": "Thu, 20 Apr 2017 03:56:28 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Jul 2017 08:24:18 GMT",
"version": "v2"
},
{
"created": "Thu, 20 Jul 2017 14:11:42 GMT",
"version": "v3"
},
{
"created": "Fri, 25 Aug 2017 02:52:59 GMT",
"version": "v4"
}
] | 2017-09-13 | [
[
"Zhang",
"P. M.",
""
],
[
"Duval",
"C.",
""
],
[
"Gibbons",
"G. W.",
""
],
[
"Horvathy",
"P. A.",
""
]
] | We give an account of the gravitational memory effect in the presence of the exact plane wave solution of Einstein's vacuum equations. This allows an elementary but exact description of the soft gravitons and how their presence may be detected by observing the motion of freely falling particles. The theorem of Bondi and Pirani on caustics (for which we present a new proof) implies that the asymptotic relative velocity is constant but not zero, in contradiction with the permanent displacement claimed by Zel'dovich and Polnarev. A non-vanishing asymptotic relative velocity might be used to detect gravitational waves through the "velocity memory effect", considered by Braginsky, Thorne, Grishchuk, and Polnarev. |
1001.0558 | Adrian Melissinos | Adrian Melissinos (for the LSC) | The effect of the Tides on the LIGO Interferometers | To appear in the Proceedings of the 12th Marcel Grossman Meeting,
Paris July 2009 | null | null | LIGO Document P0900257-v3 | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present data on the modulation of the dark port power at the free spectral
range frequency of the LIGO 4 km interferometers. It is found that the power is
modulated exactly at the tidal frequencies to a precision of 6e-9 Hz.
| [
{
"created": "Mon, 4 Jan 2010 20:45:36 GMT",
"version": "v1"
},
{
"created": "Tue, 5 Jan 2010 19:08:11 GMT",
"version": "v2"
}
] | 2010-01-05 | [
[
"Melissinos",
"Adrian",
"",
"for the LSC"
]
] | We present data on the modulation of the dark port power at the free spectral range frequency of the LIGO 4 km interferometers. It is found that the power is modulated exactly at the tidal frequencies to a precision of 6e-9 Hz. |
2112.05054 | Jun Zhang | Claudia de Rham, Andrew J. Tolley, Jun Zhang | Causality Constraints on Gravitational Effective Field Theories | 12 pages, 4 figures, typos corrected, constraints on the dim-6
operators updated | null | 10.1103/PhysRevLett.128.131102 | Imperial/TP/2021/CdR/4 | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider the effective field theory of gravity around black holes, and
show that the coefficients of the dimension-8 operators are tightly constrained
by causality considerations. Those constraints are consistent with -- but
tighter than -- previously derived causality and positivity bounds and imply
that the effects of one of the dimension-8 operators by itself cannot be
observable while remaining consistent with causality. We then establish in
which regime one can expect the generic dimension-8 and lower order operators
to be potentially observable while preserving causality, providing a
theoretical prior for future observations. We highlight the importance of
"infrared causality" and show that the requirement of "asymptotic causality" or
net (sub)luminality would fail to properly diagnose violations of causality.
| [
{
"created": "Thu, 9 Dec 2021 17:27:38 GMT",
"version": "v1"
},
{
"created": "Wed, 22 Dec 2021 12:35:41 GMT",
"version": "v2"
},
{
"created": "Wed, 6 Apr 2022 08:37:03 GMT",
"version": "v3"
},
{
"created": "Fri, 19 Jan 2024 13:49:39 GMT",
"version": "v4"
}
] | 2024-01-22 | [
[
"de Rham",
"Claudia",
""
],
[
"Tolley",
"Andrew J.",
""
],
[
"Zhang",
"Jun",
""
]
] | We consider the effective field theory of gravity around black holes, and show that the coefficients of the dimension-8 operators are tightly constrained by causality considerations. Those constraints are consistent with -- but tighter than -- previously derived causality and positivity bounds and imply that the effects of one of the dimension-8 operators by itself cannot be observable while remaining consistent with causality. We then establish in which regime one can expect the generic dimension-8 and lower order operators to be potentially observable while preserving causality, providing a theoretical prior for future observations. We highlight the importance of "infrared causality" and show that the requirement of "asymptotic causality" or net (sub)luminality would fail to properly diagnose violations of causality. |
gr-qc/0106085 | Omar E. Ortiz | Heinz-O. Kreiss and Omar E. Ortiz | Some Mathematical And Numerical Questions Connected With First And
Second Order Time Dependent Systems Of Partial Differential Equations | 12 pages, LaTeX; corrected typos and added reference | Lect.Notes Phys. 604 (2002) 359 | null | null | gr-qc | null | There is a tendency to write the equations of general relativity as a first
order symmetric system of time dependent partial differential equations.
However, for numerical reasons, it might be advantageous to use a second order
formulation like one obtained from the ADM equations. Unfortunately, the type
of the ADM equations is not well understood and therefore we shall discuss, in
the next section, the concept of wellposedness. We have to distinguish between
weakly and strongly hyperbolic systems. Strongly hyperbolic systems are well
behaved even if we add lower order terms. In contrast; for every weakly
hyperbolic system we can find lower order terms which make the problem totally
illposed. Thus, for weakly hyperbolic systems, there is only a restricted class
of lower order perturbations which do not destroy the wellposedness. To
identify that class can be very difficult, especially for nonlinear
perturbations. In Section 3 we will show that the ADM equations, linearized
around flat with constant lapse function and shift vector, are only weakly
hyperbolic. However, we can use the trace of the metric as a lapse function to
make the equations into a strongly second order hyperbolic system. Using simple
models we shall, in section 4, demonstrate that approximations of second order
equations have better accuracy properties than the corresponding approximations
of first order equations. Also, we avoid spurious waves which travel against
the characteristic direction. In the last section we discuss some difficulties
connected with the preservation of constraints.
| [
{
"created": "Tue, 26 Jun 2001 19:47:59 GMT",
"version": "v1"
},
{
"created": "Sat, 7 Jul 2001 17:27:46 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Kreiss",
"Heinz-O.",
""
],
[
"Ortiz",
"Omar E.",
""
]
] | There is a tendency to write the equations of general relativity as a first order symmetric system of time dependent partial differential equations. However, for numerical reasons, it might be advantageous to use a second order formulation like one obtained from the ADM equations. Unfortunately, the type of the ADM equations is not well understood and therefore we shall discuss, in the next section, the concept of wellposedness. We have to distinguish between weakly and strongly hyperbolic systems. Strongly hyperbolic systems are well behaved even if we add lower order terms. In contrast; for every weakly hyperbolic system we can find lower order terms which make the problem totally illposed. Thus, for weakly hyperbolic systems, there is only a restricted class of lower order perturbations which do not destroy the wellposedness. To identify that class can be very difficult, especially for nonlinear perturbations. In Section 3 we will show that the ADM equations, linearized around flat with constant lapse function and shift vector, are only weakly hyperbolic. However, we can use the trace of the metric as a lapse function to make the equations into a strongly second order hyperbolic system. Using simple models we shall, in section 4, demonstrate that approximations of second order equations have better accuracy properties than the corresponding approximations of first order equations. Also, we avoid spurious waves which travel against the characteristic direction. In the last section we discuss some difficulties connected with the preservation of constraints. |
gr-qc/9512032 | BoB | Roberto Casadio and Giovanni Venturi (Department of Physics University
of Bologna and Istituto Nazionale di Fisica Nucleare, Sezione di Bologna) | Semiclassical collapse of a sphere of dust | LaTeX, 25 pages, no figures, final version accepted for publication
in Class. and Quantum Grav | Class.Quant.Grav. 13 (1996) 2715-2734 | 10.1088/0264-9381/13/10/011 | null | gr-qc hep-th | null | The semiclassical collapse of a homogeneous sphere of dust is studied. After
identifying the independent dynamical variables, the system is canonically
quantised and coupled equations describing matter (dust) and gravitation are
obtained. The conditions for the validity of the adiabatic (Born--Oppenheimer)
and semiclassical approximations are derived. Further on neglecting
back--reaction effects, it is shown that in the vicinity of the horizon and
inside the dust the Wightman function for a conformal scalar field coupled to a
monopole emitter is thermal at the characteristic Hawking temperature.
| [
{
"created": "Mon, 18 Dec 1995 09:28:14 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Jul 1996 09:52:47 GMT",
"version": "v2"
}
] | 2009-10-28 | [
[
"Casadio",
"Roberto",
"",
"Department of Physics University\n of Bologna and Istituto Nazionale di Fisica Nucleare, Sezione di Bologna"
],
[
"Venturi",
"Giovanni",
"",
"Department of Physics University\n of Bologna and Istituto Nazionale di Fisica Nucleare, Sezione di Bologna... | The semiclassical collapse of a homogeneous sphere of dust is studied. After identifying the independent dynamical variables, the system is canonically quantised and coupled equations describing matter (dust) and gravitation are obtained. The conditions for the validity of the adiabatic (Born--Oppenheimer) and semiclassical approximations are derived. Further on neglecting back--reaction effects, it is shown that in the vicinity of the horizon and inside the dust the Wightman function for a conformal scalar field coupled to a monopole emitter is thermal at the characteristic Hawking temperature. |
1804.00249 | Yu Tian | Yu Tian | A topological charge of black holes | 8 pages, 1 table; v2: title changed from "The last (lost) charge of a
black hole" to "A topological charge of black holes", version published in
CQG | Class. Quantum Grav. 36 (2019) 245001 | 10.1088/1361-6382/ab5343 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The topological charge of a maximally symmetric black hole naturally arises
in holography, which can be viewed as the last charge of the black hole in the
sense that it together with all other known charges satisfies the holographic
Gibbs-Duhem-like relation as a completeness relation. It is then observed that
this topological charge, which we have missed before, fits perfectly into the
black hole thermodynamics from two different approaches, not only in Einstein's
gravity, but also in the general Lovelock-Maxwell theory.
| [
{
"created": "Sun, 1 Apr 2018 02:17:34 GMT",
"version": "v1"
},
{
"created": "Sun, 3 Nov 2019 03:11:41 GMT",
"version": "v2"
}
] | 2019-11-28 | [
[
"Tian",
"Yu",
""
]
] | The topological charge of a maximally symmetric black hole naturally arises in holography, which can be viewed as the last charge of the black hole in the sense that it together with all other known charges satisfies the holographic Gibbs-Duhem-like relation as a completeness relation. It is then observed that this topological charge, which we have missed before, fits perfectly into the black hole thermodynamics from two different approaches, not only in Einstein's gravity, but also in the general Lovelock-Maxwell theory. |
0906.3825 | Lukasz Glinka | Lukasz Andrzej Glinka | Novel Solution of Wheeler-DeWitt Theory | 20 pages | in L.A. Glinka (Ed.) "Towards New Cosmology From Quantum Gravity &
Particle Physics", Applied Mathematics and Physics, vol. 2, no. 3 (2014):
73-81 | 10.12691/amp-2-3-3 | null | gr-qc | http://creativecommons.org/licenses/by/3.0/ | Taking into account the global one-dimensionality conjecture recently
proposed by the author, the Cauchy-like analytical wave functional of the
Wheeler-DeWitt theory is derived. The crucial point of the integration strategy
is canceling of the singular behavior of the effective potential, which is
performed through the suitable change of variables introducing the invariant
global dimension. In addition, the conjecture is extended onto the wave
functionals dependent on both Matter felids as well as the invariant global
dimension. Through application of the reduction within the quantum gravity
model, the appropriate Dirac equation is obtained and than solved. The case of
superposition is also briey discussed.
| [
{
"created": "Sat, 20 Jun 2009 20:47:26 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Jun 2014 15:28:44 GMT",
"version": "v2"
}
] | 2014-06-11 | [
[
"Glinka",
"Lukasz Andrzej",
""
]
] | Taking into account the global one-dimensionality conjecture recently proposed by the author, the Cauchy-like analytical wave functional of the Wheeler-DeWitt theory is derived. The crucial point of the integration strategy is canceling of the singular behavior of the effective potential, which is performed through the suitable change of variables introducing the invariant global dimension. In addition, the conjecture is extended onto the wave functionals dependent on both Matter felids as well as the invariant global dimension. Through application of the reduction within the quantum gravity model, the appropriate Dirac equation is obtained and than solved. The case of superposition is also briey discussed. |
gr-qc/0207009 | Vitor Cardoso | Vitor Cardoso, Jose' P. S. Lemos | The radial infall of a highly relativistic point particle into a Kerr
black hole along the symmetry axis | 1 figure | Gen.Rel.Grav. 35 (2003) 327-333 | 10.1023/A:1022301412348 | null | gr-qc astro-ph hep-ph hep-th | null | In this Letter we consider the radial infall along the symmetry axis of an
ultra-relativistic point particle into a rotating Kerr black hole. We use the
Sasaki-Nakamura formalism to compute the waveform, energy spectra and total
energy radiated during this process. We discuss possible connections between
these results and the black hole-black hole collision at the speed of light
process.
| [
{
"created": "Mon, 1 Jul 2002 10:34:37 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Cardoso",
"Vitor",
""
],
[
"Lemos",
"Jose' P. S.",
""
]
] | In this Letter we consider the radial infall along the symmetry axis of an ultra-relativistic point particle into a rotating Kerr black hole. We use the Sasaki-Nakamura formalism to compute the waveform, energy spectra and total energy radiated during this process. We discuss possible connections between these results and the black hole-black hole collision at the speed of light process. |
1911.01496 | Le\"ila Haegel | Le\"ila Haegel, Sascha Husa | Predicting the properties of black holes merger remnants with Deep
Neural Networks | 16 pages, 5 figures | Class.Quant.Grav. 37 (2020) 13, 135005 | 10.1088/1361-6382/ab905c | null | gr-qc stat.ML | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present the first estimation of the mass and spin magnitude of Kerr black
holes resulting from the coalescence of binary black holes using a deep neural
network. The network is trained on a dataset containing 80\% of the full
publicly available catalog of numerical simulations of gravitational waves
emission by binary black hole systems, including full precession effects for
spinning binaries. The network predicts the remnant black holes mass and spin
with an error less than 0.04\% and 0.3\% respectively for 90\% of the values in
the non-precessing test dataset, it is 0.1\% and 0.3\% respectively in the
precessing test dataset. When compared to existing fits in the LIGO algorithm
software library, the network enables to reduce the remnant mass root mean
square error to one half in the non-precessing case. In the precessing case,
both remnant mass and spin mean square errors are decreased to one half, and
the network corrects the bias observed in available fits.
| [
{
"created": "Mon, 4 Nov 2019 21:30:17 GMT",
"version": "v1"
},
{
"created": "Wed, 6 May 2020 09:09:18 GMT",
"version": "v2"
}
] | 2021-10-13 | [
[
"Haegel",
"Leïla",
""
],
[
"Husa",
"Sascha",
""
]
] | We present the first estimation of the mass and spin magnitude of Kerr black holes resulting from the coalescence of binary black holes using a deep neural network. The network is trained on a dataset containing 80\% of the full publicly available catalog of numerical simulations of gravitational waves emission by binary black hole systems, including full precession effects for spinning binaries. The network predicts the remnant black holes mass and spin with an error less than 0.04\% and 0.3\% respectively for 90\% of the values in the non-precessing test dataset, it is 0.1\% and 0.3\% respectively in the precessing test dataset. When compared to existing fits in the LIGO algorithm software library, the network enables to reduce the remnant mass root mean square error to one half in the non-precessing case. In the precessing case, both remnant mass and spin mean square errors are decreased to one half, and the network corrects the bias observed in available fits. |
2007.00580 | Philipp Hoehn | Philipp A. Hoehn, Alexander R. H. Smith and Maximilian P. E. Lock | Equivalence of approaches to relational quantum dynamics in relativistic
settings | 28+7 pages | Front. Phys. 9, 587083 (2021) | 10.3389/fphy.2021.587083 | null | gr-qc hep-th math-ph math.MP quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We have previously shown (arXiv:1912.00033) that three approaches to
relational quantum dynamics -- relational Dirac observables, the Page-Wootters
formalism and quantum deparametrizations -- are equivalent. Here we show that
this `trinity' of relational quantum dynamics holds in relativistic settings
per frequency superselection sector. We ascribe the time according to the clock
subsystem to a POVM which is covariant with respect to its (quadratic)
Hamiltonian. This differs from the usual choice of a self-adjoint clock
observable conjugate to the clock momentum. It also resolves Kucha\v{r}'s
criticism that the Page-Wootters formalism yields incorrect localization
probabilities for the relativistic particle when conditioning on a Minkowski
time operator. We show that conditioning instead on the covariant clock POVM
results in a Newton-Wigner type localization probability commonly used in
relativistic quantum mechanics. By establishing the equivalence mentioned
above, we also assign a consistent conditional-probability interpretation to
relational observables and deparametrizations. Finally, we expand a recent
method of changing temporal reference frames, and show how to transform states
and observables frequency-sector-wise. We use this method to discuss an
indirect clock self-reference effect and explore the state and temporal
frame-dependence of the task of comparing and synchronizing different quantum
clocks.
| [
{
"created": "Wed, 1 Jul 2020 16:12:24 GMT",
"version": "v1"
}
] | 2022-08-24 | [
[
"Hoehn",
"Philipp A.",
""
],
[
"Smith",
"Alexander R. H.",
""
],
[
"Lock",
"Maximilian P. E.",
""
]
] | We have previously shown (arXiv:1912.00033) that three approaches to relational quantum dynamics -- relational Dirac observables, the Page-Wootters formalism and quantum deparametrizations -- are equivalent. Here we show that this `trinity' of relational quantum dynamics holds in relativistic settings per frequency superselection sector. We ascribe the time according to the clock subsystem to a POVM which is covariant with respect to its (quadratic) Hamiltonian. This differs from the usual choice of a self-adjoint clock observable conjugate to the clock momentum. It also resolves Kucha\v{r}'s criticism that the Page-Wootters formalism yields incorrect localization probabilities for the relativistic particle when conditioning on a Minkowski time operator. We show that conditioning instead on the covariant clock POVM results in a Newton-Wigner type localization probability commonly used in relativistic quantum mechanics. By establishing the equivalence mentioned above, we also assign a consistent conditional-probability interpretation to relational observables and deparametrizations. Finally, we expand a recent method of changing temporal reference frames, and show how to transform states and observables frequency-sector-wise. We use this method to discuss an indirect clock self-reference effect and explore the state and temporal frame-dependence of the task of comparing and synchronizing different quantum clocks. |
gr-qc/0312015 | Ashutosh Mahajan | Ashutosh Mahajan, Rituparno Goswami, Pankaj S.Joshi | Gravitational collapse from smooth initial data with vanishing radial
pressure | 10 pages,3 figures,revtex4,Revised Version | Class.Quant.Grav. 22 (2005) 271-282 | 10.1088/0264-9381/22/2/002 | null | gr-qc | null | We study here the spherical gravitational collapse assuming initial data to
be necessarily smooth, as motivated by the requirements based on physical
reasonableness. A tangential pressure model is constructed and analyzed in
order to understand the final fate of collapse explicitly in terms of the
density and pressure parameters at the initial epoch from which the
collapsedevelops. It is seen that both black holes and naked singularities are
produced as collapse end states even when the initial data is smooth. We show
that the outcome is decided entirely in terms of the initial data, as given by
density, pressure and velocity profiles at the initial epoch, from which the
collapse evolves.
| [
{
"created": "Tue, 2 Dec 2003 12:00:28 GMT",
"version": "v1"
},
{
"created": "Fri, 17 Dec 2004 15:22:37 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Mahajan",
"Ashutosh",
""
],
[
"Goswami",
"Rituparno",
""
],
[
"Joshi",
"Pankaj S.",
""
]
] | We study here the spherical gravitational collapse assuming initial data to be necessarily smooth, as motivated by the requirements based on physical reasonableness. A tangential pressure model is constructed and analyzed in order to understand the final fate of collapse explicitly in terms of the density and pressure parameters at the initial epoch from which the collapsedevelops. It is seen that both black holes and naked singularities are produced as collapse end states even when the initial data is smooth. We show that the outcome is decided entirely in terms of the initial data, as given by density, pressure and velocity profiles at the initial epoch, from which the collapse evolves. |
gr-qc/0211017 | Miguel S\'anchez | A. M. Candela (1), J.L. Flores (2), Miguel Sanchez (2) ((1) Univ.
Bari, (2) Univ. Granada) | On General Plane Fronted Waves. Geodesics | Final version with minor errata corrected. 19 pages, Latex. To appear
in Gen. Relat. Gravit. (2003) | Gen.Rel.Grav. 35 (2003) 631-649 | 10.1023/A:1022962017685 | null | gr-qc math.DG | null | A general class of Lorentzian metrics, $M_0 x R^2$, $ds^2 = <.,.> + 2 du dv +
H(x,u) du^2$, with $(M_0, <.,.>$ any Riemannian manifold, is introduced in
order to generalize classical exact plane fronted waves. Here, we start a
systematic study of their main geodesic properties: geodesic completeness,
geodesic connectedness and multiplicity, causal character of connecting
geodesics. These results are independent of the possibility of a full
integration of geodesic equations. Variational and geometrical techniques are
applied systematically.
In particular, we prove that the asymptotic behavior of $H(x,u)$ with $x$ at
infinity determines many properties of geodesics. Essentially, a subquadratic
growth of $H$ ensures geodesic completeness and connectedness, while the
critical situation appears when $H(x,u)$ behaves in some direction as $|x|^2$,
as in the classical model of exact gravitational waves
| [
{
"created": "Tue, 5 Nov 2002 17:00:01 GMT",
"version": "v1"
},
{
"created": "Wed, 5 Mar 2003 10:24:14 GMT",
"version": "v2"
}
] | 2015-06-25 | [
[
"Candela",
"A. M.",
""
],
[
"Flores",
"J. L.",
""
],
[
"Sanchez",
"Miguel",
""
]
] | A general class of Lorentzian metrics, $M_0 x R^2$, $ds^2 = <.,.> + 2 du dv + H(x,u) du^2$, with $(M_0, <.,.>$ any Riemannian manifold, is introduced in order to generalize classical exact plane fronted waves. Here, we start a systematic study of their main geodesic properties: geodesic completeness, geodesic connectedness and multiplicity, causal character of connecting geodesics. These results are independent of the possibility of a full integration of geodesic equations. Variational and geometrical techniques are applied systematically. In particular, we prove that the asymptotic behavior of $H(x,u)$ with $x$ at infinity determines many properties of geodesics. Essentially, a subquadratic growth of $H$ ensures geodesic completeness and connectedness, while the critical situation appears when $H(x,u)$ behaves in some direction as $|x|^2$, as in the classical model of exact gravitational waves |
1401.8282 | Jong-Ping Hsu | Leonardo Hsu, Jong-Ping Hsu | Thim's Experiment and Exact Rotational Space-Time Transformations | 8 pages | Eur. Phys. J. Plus (2014) 129: 16 | 10.1140/epjp/i2014-14016-4 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Thim measured the transverse Doppler shift using a system consisting of a
stationary antenna and pickup, in addition to a number of intermediate antennas
mounted on the rim of a rotating disk. No such shift was detected, although the
experiment should have had enough sensitivity to measure it, as predicted by
the Lorentz transformations. However, using the Lorentz transformations to
analyze the results of experiments involving circular motion, while commonly
done, is inappropriate because such an analysis involves non-inertial frames,
which are outside the range of validity of special relativity. In this paper,
we re-analyze Thim's experiment using exact rotational space-time
transformations, finding that his null result is consistent with theoretical
predictions.
| [
{
"created": "Thu, 30 Jan 2014 14:51:15 GMT",
"version": "v1"
}
] | 2014-02-26 | [
[
"Hsu",
"Leonardo",
""
],
[
"Hsu",
"Jong-Ping",
""
]
] | Thim measured the transverse Doppler shift using a system consisting of a stationary antenna and pickup, in addition to a number of intermediate antennas mounted on the rim of a rotating disk. No such shift was detected, although the experiment should have had enough sensitivity to measure it, as predicted by the Lorentz transformations. However, using the Lorentz transformations to analyze the results of experiments involving circular motion, while commonly done, is inappropriate because such an analysis involves non-inertial frames, which are outside the range of validity of special relativity. In this paper, we re-analyze Thim's experiment using exact rotational space-time transformations, finding that his null result is consistent with theoretical predictions. |
gr-qc/0610104 | Neven Bilic | Neven Bilic, Gary B. Tupper and Raoul D. Viollier | Chaplygin Gas Cosmology - Unification of Dark Matter and Dark Energy | 7 pages, presented by N. B. at IRGAC 2006, Barcelona, 11-15 July
2006, typos corrected, concluding paragraph slightly expanded, final version,
accepted in J. Phys. A, special issue | J.Phys.A40:6877-6882,2007 | 10.1088/1751-8113/40/25/S33 | null | gr-qc astro-ph hep-th | null | The models that unify dark matter and dark energy based upon the Chaplygin
gas fail owing to the suppression of structure formation by the adiabatic speed
of sound. Including string theory effects, in particular the Kalb-Ramond field,
we show how nonadiabatic perturbations allow a successful structure formation.
| [
{
"created": "Mon, 23 Oct 2006 14:58:17 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Dec 2006 10:10:51 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Bilic",
"Neven",
""
],
[
"Tupper",
"Gary B.",
""
],
[
"Viollier",
"Raoul D.",
""
]
] | The models that unify dark matter and dark energy based upon the Chaplygin gas fail owing to the suppression of structure formation by the adiabatic speed of sound. Including string theory effects, in particular the Kalb-Ramond field, we show how nonadiabatic perturbations allow a successful structure formation. |
gr-qc/0512054 | Sa\v{s}a Iliji\'c | Dubravko Horvat, Sasa Ilijic | Regular and singular solutions for charged dust distributions in the
Einstein--Maxwell theory | LaTeX/RevTeX, 7 pages 2 figures, changes wrt v1: results unchanged
but discussion considerably extended and several references added | Can. J. Phys. 85 (2007) 957-965 | 10.1139/P07-090 | null | gr-qc | null | Solutions for the static spherically symmetric extremally charged dust in the
Majumdar--Papapetrou system have been found. For a certain amount of the
allocated mass/charge, the solutions have singularities of a type which could
render them physically unacceptable, since the corresponding physically
relevant quantities are singular as well. These solutions, with a number of
zero-nodes in the metric tensor, are regularized through the $\delta$-shell
formalism, thus redefining the mass/charge distributions. The bifurcating
behaviour of regular solutions found before is no longer present in these
singular solutions, but quantized-like behaviour in the total mass is observed.
Spectrum of regularized solutions restores the equality of the
Tolman--Whittaker and ADM mass, as well the equality of the net charge and ADM
mass, which is the distinctive feature of Majumdar--Papapetrou systems.
| [
{
"created": "Thu, 8 Dec 2005 19:50:30 GMT",
"version": "v1"
},
{
"created": "Fri, 28 Sep 2007 07:12:53 GMT",
"version": "v2"
}
] | 2011-11-09 | [
[
"Horvat",
"Dubravko",
""
],
[
"Ilijic",
"Sasa",
""
]
] | Solutions for the static spherically symmetric extremally charged dust in the Majumdar--Papapetrou system have been found. For a certain amount of the allocated mass/charge, the solutions have singularities of a type which could render them physically unacceptable, since the corresponding physically relevant quantities are singular as well. These solutions, with a number of zero-nodes in the metric tensor, are regularized through the $\delta$-shell formalism, thus redefining the mass/charge distributions. The bifurcating behaviour of regular solutions found before is no longer present in these singular solutions, but quantized-like behaviour in the total mass is observed. Spectrum of regularized solutions restores the equality of the Tolman--Whittaker and ADM mass, as well the equality of the net charge and ADM mass, which is the distinctive feature of Majumdar--Papapetrou systems. |
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