id stringlengths 9 13 | submitter stringlengths 1 64 ⌀ | authors stringlengths 5 22.9k | title stringlengths 4 245 | comments stringlengths 1 548 ⌀ | journal-ref stringlengths 4 362 ⌀ | doi stringlengths 12 82 ⌀ | report-no stringlengths 2 281 ⌀ | categories stringclasses 793 values | license stringclasses 9 values | orig_abstract stringlengths 24 1.95k | versions listlengths 1 30 | update_date stringlengths 10 10 | authors_parsed listlengths 1 1.74k | abstract stringlengths 21 1.95k |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1910.00083 | Francisco Nogueira Lima | A. S. Ribeiro and F. N. Lima | An exact solution of the orbit equation for a massive particle in
Schwarzschild metric | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we consider a spherically curved symmetric spacetime to exact
solving the orbit equation of a massive particle by using Jacobi's elliptic
functions. Generally, the solution of the orbit equation provides the
relativistic effects on the massive particle, absents in Newtonian mechanics.
Besides, we investigate the additional physical information introduced by the
exact solution to the orbit equation that is not visible in the approximate
solutions traditionally presented in literature. Here, we exactly solve the
problem by the use an analytical methodology step by step in order to provide
detailed solutions as well as demonstrate with mathematical rigour the geodesic
solution in terms of Jacobi's elliptic functions. We find oscillatory movements
of the orbit of the massive particle at the expected regimes without to
consider any heuristic argument. Bound regions to the solution of the equation
of motion is presented, finding the aspect of the geodesic when the massive
particle is trapped in the gravitational field of the source.
| [
{
"created": "Mon, 30 Sep 2019 20:19:26 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Oct 2019 14:39:48 GMT",
"version": "v2"
},
{
"created": "Fri, 13 Mar 2020 19:37:59 GMT",
"version": "v3"
}
] | 2020-03-17 | [
[
"Ribeiro",
"A. S.",
""
],
[
"Lima",
"F. N.",
""
]
] | In this paper, we consider a spherically curved symmetric spacetime to exact solving the orbit equation of a massive particle by using Jacobi's elliptic functions. Generally, the solution of the orbit equation provides the relativistic effects on the massive particle, absents in Newtonian mechanics. Besides, we investigate the additional physical information introduced by the exact solution to the orbit equation that is not visible in the approximate solutions traditionally presented in literature. Here, we exactly solve the problem by the use an analytical methodology step by step in order to provide detailed solutions as well as demonstrate with mathematical rigour the geodesic solution in terms of Jacobi's elliptic functions. We find oscillatory movements of the orbit of the massive particle at the expected regimes without to consider any heuristic argument. Bound regions to the solution of the equation of motion is presented, finding the aspect of the geodesic when the massive particle is trapped in the gravitational field of the source. |
1706.03596 | Ronaldo Vieira Lobato | G. A. Carvalho, R. V. Lobato, P. H. R. S. Moraes, Jos\'e D. V.
Arba\~nil, R. M. Marinho Jr, E. Otoniel and M. Malheiro | Stellar equilibrium configurations of white dwarfs in the $f(R,T)$
gravity | To be published in EPJC | null | 10.1140/epjc/s10052-017-5413-5 | null | gr-qc astro-ph.SR hep-th nucl-th | http://creativecommons.org/licenses/by-nc-sa/4.0/ | In this work we investigate the equilibrium configurations of white dwarfs in
a modified gravity theory, na\-mely, $f(R,T)$ gravity, for which $R$ and $T$
stand for the Ricci scalar and trace of the energy-momentum tensor,
respectively. Considering the functional form $f(R,T)=R+2\lambda T$, with
$\lambda$ being a constant, we obtain the hydrostatic equilibrium equation for
the theory. Some physical properties of white dwarfs, such as: mass, radius,
pressure and energy density, as well as their dependence on the parameter
$\lambda$ are derived. More massive and larger white dwarfs are found for
negative values of $\lambda$ when it decreases. The equilibrium configurations
predict a maximum mass limit for white dwarfs slightly above the Chandrasekhar
limit, with larger radii and lower central densities when compared to standard
gravity outcomes. The most important effect of $f(R,T)$ theory for massive
white dwarfs is the increase of the radius in comparison with GR and also
$f(R)$ results. By comparing our results with some observational data of
massive white dwarfs we also find a lower limit for $\lambda$, namely, $\lambda
>- 3\times 10^{-4}$.
| [
{
"created": "Mon, 12 Jun 2017 12:29:18 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Nov 2017 16:46:11 GMT",
"version": "v2"
}
] | 2017-12-20 | [
[
"Carvalho",
"G. A.",
""
],
[
"Lobato",
"R. V.",
""
],
[
"Moraes",
"P. H. R. S.",
""
],
[
"Arbañil",
"José D. V.",
""
],
[
"Marinho",
"R. M.",
"Jr"
],
[
"Otoniel",
"E.",
""
],
[
"Malheiro",
"M.",
""
]
] | In this work we investigate the equilibrium configurations of white dwarfs in a modified gravity theory, na\-mely, $f(R,T)$ gravity, for which $R$ and $T$ stand for the Ricci scalar and trace of the energy-momentum tensor, respectively. Considering the functional form $f(R,T)=R+2\lambda T$, with $\lambda$ being a constant, we obtain the hydrostatic equilibrium equation for the theory. Some physical properties of white dwarfs, such as: mass, radius, pressure and energy density, as well as their dependence on the parameter $\lambda$ are derived. More massive and larger white dwarfs are found for negative values of $\lambda$ when it decreases. The equilibrium configurations predict a maximum mass limit for white dwarfs slightly above the Chandrasekhar limit, with larger radii and lower central densities when compared to standard gravity outcomes. The most important effect of $f(R,T)$ theory for massive white dwarfs is the increase of the radius in comparison with GR and also $f(R)$ results. By comparing our results with some observational data of massive white dwarfs we also find a lower limit for $\lambda$, namely, $\lambda >- 3\times 10^{-4}$. |
2109.04209 | Lavinia Heisenberg | Fabio D'Ambrosio, Lavinia Heisenberg and Simon Kuhn | Revisiting Cosmologies in Teleparallelism | 17 pages, no figures | null | 10.1088/1361-6382/ac3f99 | null | gr-qc astro-ph.CO hep-th | http://creativecommons.org/licenses/by/4.0/ | We discuss the most general field equations for cosmological spacetimes for
theories of gravity based on non-linear extensions of the non-metricity scalar
and the torsion scalar. Our approach is based on a systematic
symmetry-reduction of the metric-affine geometry which underlies these
theories. While for the simplest conceivable case the connection disappears
from the field equations and one obtains the Friedmann equations of General
Relativity, we show that in $f(\mathbb{Q})$ cosmology the connection
generically modifies the metric field equations and that some of the connection
components become dynamical. We show that $f(\mathbb{Q})$ cosmology contains
the exact General Relativity solutions and also exact solutions which go
beyond. In $f(\mathbb{T})$~cosmology, however, the connection is completely
fixed and not dynamical.
| [
{
"created": "Thu, 9 Sep 2021 12:29:29 GMT",
"version": "v1"
},
{
"created": "Sun, 12 Sep 2021 06:11:26 GMT",
"version": "v2"
}
] | 2022-01-05 | [
[
"D'Ambrosio",
"Fabio",
""
],
[
"Heisenberg",
"Lavinia",
""
],
[
"Kuhn",
"Simon",
""
]
] | We discuss the most general field equations for cosmological spacetimes for theories of gravity based on non-linear extensions of the non-metricity scalar and the torsion scalar. Our approach is based on a systematic symmetry-reduction of the metric-affine geometry which underlies these theories. While for the simplest conceivable case the connection disappears from the field equations and one obtains the Friedmann equations of General Relativity, we show that in $f(\mathbb{Q})$ cosmology the connection generically modifies the metric field equations and that some of the connection components become dynamical. We show that $f(\mathbb{Q})$ cosmology contains the exact General Relativity solutions and also exact solutions which go beyond. In $f(\mathbb{T})$~cosmology, however, the connection is completely fixed and not dynamical. |
1904.12983 | Luca Visinelli | Cosimo Bambi, Katherine Freese, Sunny Vagnozzi, Luca Visinelli | Testing the rotational nature of the supermassive object M87* from the
circularity and size of its first image | 9 pages, 4 figures, Accepted in PRD | Phys. Rev. D 100 (2019) 044057 | 10.1103/PhysRevD.100.044057 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Event Horizon Telescope (EHT) collaboration has recently released the
first image of a black hole (BH), opening a new window onto tests of general
relativity in the strong field regime. In this paper, we derive constraints on
the nature of M87* (the supermassive object at the centre of the galaxy M87),
exploiting the fact that its shadow appears to be highly circular, and using
measurements of its angular size. We first consider the simple case where M87*
is assumed to be a Kerr BH. We find that the inferred circularity of M87*
excludes Kerr BHs with observation angle $\theta_{\rm obs} \gtrsim 45^{\circ}$
for dimensionless rotational parameter $0.95 \lesssim a_* \leq 1$ whereas the
observation angle is unbounded for $a_* \lesssim 0.9$. We then consider the
possibility that M87* might be a superspinar, i.e. an object described by the
Kerr solution and spinning so fast that it violates the Kerr bound by having
$|a_*| > 1$. We find that, within certain regions of parameter space, the
inferred circularity and size of the shadow of M87* do not exclude the
possibility that this object might be a superspinar.
| [
{
"created": "Mon, 29 Apr 2019 23:04:12 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Aug 2019 12:36:19 GMT",
"version": "v2"
}
] | 2020-02-24 | [
[
"Bambi",
"Cosimo",
""
],
[
"Freese",
"Katherine",
""
],
[
"Vagnozzi",
"Sunny",
""
],
[
"Visinelli",
"Luca",
""
]
] | The Event Horizon Telescope (EHT) collaboration has recently released the first image of a black hole (BH), opening a new window onto tests of general relativity in the strong field regime. In this paper, we derive constraints on the nature of M87* (the supermassive object at the centre of the galaxy M87), exploiting the fact that its shadow appears to be highly circular, and using measurements of its angular size. We first consider the simple case where M87* is assumed to be a Kerr BH. We find that the inferred circularity of M87* excludes Kerr BHs with observation angle $\theta_{\rm obs} \gtrsim 45^{\circ}$ for dimensionless rotational parameter $0.95 \lesssim a_* \leq 1$ whereas the observation angle is unbounded for $a_* \lesssim 0.9$. We then consider the possibility that M87* might be a superspinar, i.e. an object described by the Kerr solution and spinning so fast that it violates the Kerr bound by having $|a_*| > 1$. We find that, within certain regions of parameter space, the inferred circularity and size of the shadow of M87* do not exclude the possibility that this object might be a superspinar. |
0806.0014 | Sean A. Hayward | S. A. Hayward, R. Di Criscienzo, M. Nadalini, L. Vanzo and S. Zerbini | Local Hawking temperature for dynamical black holes | 9 pages | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A local Hawking temperature is derived for any future outer trapping horizon
in spherical symmetry, using a Hamilton-Jacobi variant of the Parikh-Wilczek
tunneling method. It is given by a dynamical surface gravity as defined
geometrically. The operational meaning of the temperature is that Kodama
observers just outside the horizon measure an invariantly redshifted
temperature, diverging at the horizon itself. In static, asymptotically flat
cases, the Hawking temperature as usually defined by the Killing vector agrees
in standard cases, but generally differs by a relative redshift factor between
the horizon and infinity, being the temperature measured by static observers at
infinity. Likewise, the geometrical surface gravity reduces to the Newtonian
surface gravity in the Newtonian limit, while the Killing definition instead
reflects measurements at infinity. This may resolve a longstanding puzzle
concerning the Hawking temperature for the extremal limit of the charged
stringy black hole, namely that it is the local temperature which vanishes. In
general, this confirms the quasi-stationary picture of black-hole evaporation
in early stages. However, the geometrical surface gravity is generally not the
surface gravity of a static black hole with the same parameters.
| [
{
"created": "Fri, 30 May 2008 20:42:47 GMT",
"version": "v1"
},
{
"created": "Wed, 11 Feb 2009 11:48:23 GMT",
"version": "v2"
}
] | 2009-02-11 | [
[
"Hayward",
"S. A.",
""
],
[
"Di Criscienzo",
"R.",
""
],
[
"Nadalini",
"M.",
""
],
[
"Vanzo",
"L.",
""
],
[
"Zerbini",
"S.",
""
]
] | A local Hawking temperature is derived for any future outer trapping horizon in spherical symmetry, using a Hamilton-Jacobi variant of the Parikh-Wilczek tunneling method. It is given by a dynamical surface gravity as defined geometrically. The operational meaning of the temperature is that Kodama observers just outside the horizon measure an invariantly redshifted temperature, diverging at the horizon itself. In static, asymptotically flat cases, the Hawking temperature as usually defined by the Killing vector agrees in standard cases, but generally differs by a relative redshift factor between the horizon and infinity, being the temperature measured by static observers at infinity. Likewise, the geometrical surface gravity reduces to the Newtonian surface gravity in the Newtonian limit, while the Killing definition instead reflects measurements at infinity. This may resolve a longstanding puzzle concerning the Hawking temperature for the extremal limit of the charged stringy black hole, namely that it is the local temperature which vanishes. In general, this confirms the quasi-stationary picture of black-hole evaporation in early stages. However, the geometrical surface gravity is generally not the surface gravity of a static black hole with the same parameters. |
2011.01248 | Francesco Bajardi | Francesco Bajardi, Daniele Vernieri, Salvatore Capozziello | Bouncing Cosmology in f(Q) Symmetric Teleparallel Gravity | 11 pages, 1 figure, 68 references | Eur. Phys. J. Plus 135, no.11, 912 (2020) | 10.1140/epjp/s13360-020-00918-3 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We consider f(Q) extended symmetric teleparallel cosmologies, where Q is the
non-metricity scalar, and constrain its functional form through the order
reduction method. By using this technique, we are able to reduce and integrate
the field equations and thus to select the corresponding models giving rise to
bouncing cosmology. The selected Lagrangian is then used to develop the
Hamiltonian formalism and to obtain the Wave Function of the Universe which
suggests that classical observable universes can be recovered according to the
Hartle Criterion.
| [
{
"created": "Mon, 2 Nov 2020 19:00:04 GMT",
"version": "v1"
}
] | 2020-12-03 | [
[
"Bajardi",
"Francesco",
""
],
[
"Vernieri",
"Daniele",
""
],
[
"Capozziello",
"Salvatore",
""
]
] | We consider f(Q) extended symmetric teleparallel cosmologies, where Q is the non-metricity scalar, and constrain its functional form through the order reduction method. By using this technique, we are able to reduce and integrate the field equations and thus to select the corresponding models giving rise to bouncing cosmology. The selected Lagrangian is then used to develop the Hamiltonian formalism and to obtain the Wave Function of the Universe which suggests that classical observable universes can be recovered according to the Hartle Criterion. |
0806.4239 | Lorenzo Sindoni | Florian Girelli, Stefano Liberati and Lorenzo Sindoni | On the emergence of Lorentzian signature and scalar gravity | 10 pages, revtex4. Replaced with the published version | Phys.Rev.D79:044019,2009 | 10.1103/PhysRevD.79.044019 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In recent years, a growing momentum has been gained by the emergent gravity
framework. Within the latter, the very concepts of geometry and gravitational
interaction are not seen as elementary aspects of Nature but rather as
collective phenomena associated to the dynamics of more fundamental objects. In
this paper we want to further explore this possibility by proposing a model of
emergent Lorentzian signature and scalar gravity. Assuming that the dynamics of
the fundamental objects can give rise in first place to a Riemannian manifold
and a set of scalar fields we show how time (in the sense of hyperbolic
equations) can emerge as a property of perturbations dynamics around some
specific class of solutions of the field equations. Moreover, we show that
these perturbations can give rise to a spin-0 gravity via a suitable
redefinition of the fields that identifies the relevant degrees of freedom. In
particular, we find that our model gives rise to Nordstrom gravity. Since this
theory is invariant under general coordinate transformations, this also shows
how diffeomorphism invariance (albeit of a weaker form than the one of general
relativity) can emerge from much simpler systems.
| [
{
"created": "Thu, 26 Jun 2008 18:46:40 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Feb 2009 11:17:03 GMT",
"version": "v2"
}
] | 2009-04-08 | [
[
"Girelli",
"Florian",
""
],
[
"Liberati",
"Stefano",
""
],
[
"Sindoni",
"Lorenzo",
""
]
] | In recent years, a growing momentum has been gained by the emergent gravity framework. Within the latter, the very concepts of geometry and gravitational interaction are not seen as elementary aspects of Nature but rather as collective phenomena associated to the dynamics of more fundamental objects. In this paper we want to further explore this possibility by proposing a model of emergent Lorentzian signature and scalar gravity. Assuming that the dynamics of the fundamental objects can give rise in first place to a Riemannian manifold and a set of scalar fields we show how time (in the sense of hyperbolic equations) can emerge as a property of perturbations dynamics around some specific class of solutions of the field equations. Moreover, we show that these perturbations can give rise to a spin-0 gravity via a suitable redefinition of the fields that identifies the relevant degrees of freedom. In particular, we find that our model gives rise to Nordstrom gravity. Since this theory is invariant under general coordinate transformations, this also shows how diffeomorphism invariance (albeit of a weaker form than the one of general relativity) can emerge from much simpler systems. |
gr-qc/0110021 | Andrzej Herdegen | Andrzej Herdegen and Jaroslaw Wawrzycki | Is Einstein's equivalence principle valid for a quantum particle? | 5 pages, RevTeX, published version, references and comments added | Phys.Rev. D66 (2002) 044007 | 10.1103/PhysRevD.66.044007 | null | gr-qc quant-ph | null | Einstein's equivalence principle in classical physics is a rule stating that
the effect of gravitation is locally equivalent to the acceleration of an
observer. The principle determines the motion of test particles uniquely
(modulo very broad general assumptions). We show that the same principle
applied to a quantum particle described by a wave function on a Newtonian
gravitational background determines its motion with a similar degree of
uniqueness.
| [
{
"created": "Wed, 3 Oct 2001 09:53:16 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Jan 2003 08:22:53 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Herdegen",
"Andrzej",
""
],
[
"Wawrzycki",
"Jaroslaw",
""
]
] | Einstein's equivalence principle in classical physics is a rule stating that the effect of gravitation is locally equivalent to the acceleration of an observer. The principle determines the motion of test particles uniquely (modulo very broad general assumptions). We show that the same principle applied to a quantum particle described by a wave function on a Newtonian gravitational background determines its motion with a similar degree of uniqueness. |
1009.4544 | Sergey Kozyrev | S. Kozyrev | Composite spherically symmetric configurations in Jordan-Brans-Dicke
theory | 6 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this article, a study of the scalar field shells in relativistic
spherically symmetric configurations has been performed. We construct the
composite solution of Jordan-Brans-Dicke field equation by matching the
conformal Brans solutions at each junction surfaces. This approach allows us to
associate rigorously with all solutions as a single glued "space", which is a
unique differentiable manifold M^4.
| [
{
"created": "Thu, 23 Sep 2010 08:55:50 GMT",
"version": "v1"
}
] | 2010-09-24 | [
[
"Kozyrev",
"S.",
""
]
] | In this article, a study of the scalar field shells in relativistic spherically symmetric configurations has been performed. We construct the composite solution of Jordan-Brans-Dicke field equation by matching the conformal Brans solutions at each junction surfaces. This approach allows us to associate rigorously with all solutions as a single glued "space", which is a unique differentiable manifold M^4. |
gr-qc/0302057 | Kouji Nakamura | Kouji Nakamura | Comparison of the oscillatory behaviors of a gravitating Nambu-Goto
string with a test string | 32 pages, 1 figure, PTPTeX ver.0.8 (LateX2e), Accepted for
publication to Progress of Theoretical Physics | Prog.Theor.Phys. 110 (2003) 201-232 | 10.1143/PTP.110.201 | NAOJ-TH-Ap 2003, No.4 | gr-qc astro-ph hep-ph hep-th | null | Comparison of the oscillatory behavior of a gravitating infinite Nambu-Goto
string and a test string is investigated using the general relativistic gauge
invariant perturbation technique with two infinitesimal parameters on a flat
spacetime background. Due to the existence of the pp-wave exact solution, we
see that the conclusion that the dynamical degree of freedom of an infinite
Nambu-Goto string is completely determined by that of gravitational waves,
which was reached in our previous works [K. Nakamura, A. Ishibashi and H.
Ishihara, Phys. Rev. D{\bf 62} (2002), 101502(R); K. Nakamura and H. Ishihara,
Phys. Rev. D{\bf 63} (2001), 127501.], do not contradict to the dynamics of a
test string. We also briefly discuss the implication of this result.
| [
{
"created": "Fri, 14 Feb 2003 04:45:48 GMT",
"version": "v1"
},
{
"created": "Mon, 24 Mar 2003 08:56:48 GMT",
"version": "v2"
},
{
"created": "Wed, 14 May 2003 08:18:49 GMT",
"version": "v3"
},
{
"created": "Mon, 21 Jul 2003 11:54:41 GMT",
"version": "v4"
}
] | 2009-11-10 | [
[
"Nakamura",
"Kouji",
""
]
] | Comparison of the oscillatory behavior of a gravitating infinite Nambu-Goto string and a test string is investigated using the general relativistic gauge invariant perturbation technique with two infinitesimal parameters on a flat spacetime background. Due to the existence of the pp-wave exact solution, we see that the conclusion that the dynamical degree of freedom of an infinite Nambu-Goto string is completely determined by that of gravitational waves, which was reached in our previous works [K. Nakamura, A. Ishibashi and H. Ishihara, Phys. Rev. D{\bf 62} (2002), 101502(R); K. Nakamura and H. Ishihara, Phys. Rev. D{\bf 63} (2001), 127501.], do not contradict to the dynamics of a test string. We also briefly discuss the implication of this result. |
2103.13824 | Behnam Pourhassan | Mir Hameeda, Behnam Pourhassan, Mario C. Rocca, and Mir Faizal | Finite Tsallis Gravitational Partition Function for a System of Galaxies | Accepted for publication in General Relativity and Gravitation | Gen.Rel.Grav. 53 (2021) 4, 41 | 10.1007/s10714-021-02813-3 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we will study the large scale structure formation using the
gravitational partition function. We will assertively argue that the system of
gravitating galaxies can be analyzed using the Tsallis statistical mechanics.
The divergences in the Tsallis gravitational partition function can be removed
using the mathematical riches of the generalization of the dimensional
regularization (GDR). The finite gravitational partition function thus obtained
will be used to evaluate the thermodynamics of the system of galaxies and thus,
to understand the clustering of galaxies in the universe. The correlation
function which is believed to contain the information of clustering of galaxies
will also be discussed in this formalism.
| [
{
"created": "Wed, 24 Mar 2021 10:27:52 GMT",
"version": "v1"
}
] | 2021-05-13 | [
[
"Hameeda",
"Mir",
""
],
[
"Pourhassan",
"Behnam",
""
],
[
"Rocca",
"Mario C.",
""
],
[
"Faizal",
"Mir",
""
]
] | In this paper, we will study the large scale structure formation using the gravitational partition function. We will assertively argue that the system of gravitating galaxies can be analyzed using the Tsallis statistical mechanics. The divergences in the Tsallis gravitational partition function can be removed using the mathematical riches of the generalization of the dimensional regularization (GDR). The finite gravitational partition function thus obtained will be used to evaluate the thermodynamics of the system of galaxies and thus, to understand the clustering of galaxies in the universe. The correlation function which is believed to contain the information of clustering of galaxies will also be discussed in this formalism. |
gr-qc/9905015 | Winfried Zimdahl | Winfried Zimdahl (Konstanz) and Alexander B. Balakin (Kazan) | Thermodynamic equilibrium in the expanding universe | 10 pages, Latex, to appear in GRG | Gen.Rel.Grav. 31 (1999) 1395-1405 | 10.1023/A:1026741228100 | null | gr-qc astro-ph | null | We show that a relativistic gas may be at ``global'' equilibrium in the
expanding universe for any equation of state $0 < p \leq \rho /3$, provided
that the gas particles move under the influence of a self-interacting,
effective one-particle force in between elastic binary collisions. In the
force-free limit we recover the equilibrium conditions for ultrarelativistic
matter which imply the existence of a conformal timelike Killing vector.
| [
{
"created": "Thu, 6 May 1999 06:50:27 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Zimdahl",
"Winfried",
"",
"Konstanz"
],
[
"Balakin",
"Alexander B.",
"",
"Kazan"
]
] | We show that a relativistic gas may be at ``global'' equilibrium in the expanding universe for any equation of state $0 < p \leq \rho /3$, provided that the gas particles move under the influence of a self-interacting, effective one-particle force in between elastic binary collisions. In the force-free limit we recover the equilibrium conditions for ultrarelativistic matter which imply the existence of a conformal timelike Killing vector. |
gr-qc/0103068 | Cristiano Germani | C. Germani, D. Bini, R.T. Jantzen | A Classical Interpretation of Maxwell's Equations in Curved Spacetime | MGIX proceedings, 2 pages, added a reference | null | null | null | gr-qc | null | We present an integral formulation of observer-dependent Maxwell's equations
in curved spacetime and give a classical interpretation of them.
| [
{
"created": "Sun, 18 Mar 2001 13:26:54 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Mar 2001 08:43:49 GMT",
"version": "v2"
},
{
"created": "Mon, 9 Apr 2001 13:48:08 GMT",
"version": "v3"
},
{
"created": "Fri, 19 Oct 2001 14:22:36 GMT",
"version": "v4"
}
] | 2007-05-23 | [
[
"Germani",
"C.",
""
],
[
"Bini",
"D.",
""
],
[
"Jantzen",
"R. T.",
""
]
] | We present an integral formulation of observer-dependent Maxwell's equations in curved spacetime and give a classical interpretation of them. |
0904.0773 | Sunil Maharaj | A. Beesham, S. V. Chervon, S. D. Maharaj | An emergent universe supported by a nonlinear sigma model | 10 pages, To appear in Class. Quantum. Grav | Class.Quant.Grav.26:075017,2009 | 10.1088/0264-9381/26/7/075017 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We suggest the use of a nonlinear sigma model as the source which supports an
emergent universe. The two-component nonlinear sigma model is considered as the
simplest model containing inflaton and auxiliary chiral fields.
| [
{
"created": "Sun, 5 Apr 2009 14:09:11 GMT",
"version": "v1"
}
] | 2009-05-08 | [
[
"Beesham",
"A.",
""
],
[
"Chervon",
"S. V.",
""
],
[
"Maharaj",
"S. D.",
""
]
] | We suggest the use of a nonlinear sigma model as the source which supports an emergent universe. The two-component nonlinear sigma model is considered as the simplest model containing inflaton and auxiliary chiral fields. |
gr-qc/9711083 | Luis Bel | Lluis Bel | A distinguished set of modes in an accelerated frame of reference | To appear in "Analytical and Numerical Approaches to Relativity:
Sources of Gravitational Radiation", ERE 1997, ed J.Stela, UIB, Palma de
Mallorca, Spain | null | null | null | gr-qc | null | We construct a distinguished set of positive and negative energy modes of the
Klein-Gordon equation for any Born frame of reference in Minkowski's
space-time. Unlike the case of a galilean frame of reference it is unclear
whether this set of modes may be an appropriate basis to define the vacuum of a
quantized scalar field in an accelerated cavity.
| [
{
"created": "Thu, 27 Nov 1997 11:09:03 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Bel",
"Lluis",
""
]
] | We construct a distinguished set of positive and negative energy modes of the Klein-Gordon equation for any Born frame of reference in Minkowski's space-time. Unlike the case of a galilean frame of reference it is unclear whether this set of modes may be an appropriate basis to define the vacuum of a quantized scalar field in an accelerated cavity. |
2105.03744 | Sobhan Kazempour | Amin Rezaei Akbarieh, Sobhan Kazempour and Lijing Shao | Cosmological perturbations in Gauss-Bonnet quasi-dilaton massive gravity | null | Phys. Rev. D 103, 123518 (2021) | 10.1103/PhysRevD.103.123518 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We present the cosmological analysis of the Gauss-Bonnet quasi-dilaton
massive gravity theory. This offers a gravitational theory with a non-zero
graviton mass. We calculate the complete set of background equations of motion.
Also, we obtain the self-accelerating background solutions and we present the
constraints on parameters to indicate the correct sign of parameters. In
addition, we analyse tensor perturbations and calculate the mass of graviton
and find the dispersion relation of gravitational waves for two cases. Finally,
we investigate the propagation of gravitational perturbation in the FLRW
cosmology in the Gauss-Bonnet quasi-dilaton massive gravity.
| [
{
"created": "Sat, 8 May 2021 17:09:13 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Jul 2021 18:43:56 GMT",
"version": "v2"
}
] | 2021-07-14 | [
[
"Akbarieh",
"Amin Rezaei",
""
],
[
"Kazempour",
"Sobhan",
""
],
[
"Shao",
"Lijing",
""
]
] | We present the cosmological analysis of the Gauss-Bonnet quasi-dilaton massive gravity theory. This offers a gravitational theory with a non-zero graviton mass. We calculate the complete set of background equations of motion. Also, we obtain the self-accelerating background solutions and we present the constraints on parameters to indicate the correct sign of parameters. In addition, we analyse tensor perturbations and calculate the mass of graviton and find the dispersion relation of gravitational waves for two cases. Finally, we investigate the propagation of gravitational perturbation in the FLRW cosmology in the Gauss-Bonnet quasi-dilaton massive gravity. |
gr-qc/0108058 | Kayll Lake | Mustapha Ishak and Kayll Lake | Stability of Transparent Spherically Symmetric Thin Shells and Wormholes | 12 pages, 7 figures, revtex. Final form to appear in Phys. Rev. D | Phys.Rev. D65 (2002) 044011 | 10.1103/PhysRevD.65.044011 | null | gr-qc | null | The stability of transparent spherically symmetric thin shells (and
wormholes) to linearized spherically symmetric perturbations about static
equilibrium is examined. This work generalizes and systematizes previous
studies and explores the consequences of including the cosmological constant.
The approach shows how the existence (or not) of a domain wall dominates the
landscape of possible equilibrium configurations.
| [
{
"created": "Fri, 24 Aug 2001 17:16:28 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Dec 2001 15:24:01 GMT",
"version": "v2"
}
] | 2009-11-07 | [
[
"Ishak",
"Mustapha",
""
],
[
"Lake",
"Kayll",
""
]
] | The stability of transparent spherically symmetric thin shells (and wormholes) to linearized spherically symmetric perturbations about static equilibrium is examined. This work generalizes and systematizes previous studies and explores the consequences of including the cosmological constant. The approach shows how the existence (or not) of a domain wall dominates the landscape of possible equilibrium configurations. |
2307.10136 | Antonino Marciano | Matteo Lulli, Antonino Marciano and Kristian Piscicchia | Stochastic Ricci Flow dynamics of the gravitationally induced
wave-function collapse | 14 pages | null | null | null | gr-qc hep-th quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In order to reconcile the wave-function collapse in quantum mechanics with
the finiteness of signals' propagation in general relativity, we delve into a
stochastic version of the Ricci flow and study its non-relativistic limit in
presence of matter. We hence derive the Di\'osi-Penrose collapse model for the
wave-function of a quantum gas. The procedure entails additional parameters
with respect to phenomenological models hitherto accounted for, including the
temperature of the gas and the cosmological constant, in turn related to the
stochastic gravitational noise responsible for the collapse.
| [
{
"created": "Wed, 19 Jul 2023 17:00:48 GMT",
"version": "v1"
}
] | 2023-07-20 | [
[
"Lulli",
"Matteo",
""
],
[
"Marciano",
"Antonino",
""
],
[
"Piscicchia",
"Kristian",
""
]
] | In order to reconcile the wave-function collapse in quantum mechanics with the finiteness of signals' propagation in general relativity, we delve into a stochastic version of the Ricci flow and study its non-relativistic limit in presence of matter. We hence derive the Di\'osi-Penrose collapse model for the wave-function of a quantum gas. The procedure entails additional parameters with respect to phenomenological models hitherto accounted for, including the temperature of the gas and the cosmological constant, in turn related to the stochastic gravitational noise responsible for the collapse. |
2007.14881 | Brian Seymour | Brian C. Seymour, Kent Yagi | Probing Massive Scalar/Vector Fields with Binary Pulsars | minor edits, 12 pages, 3 figures | Phys. Rev. D 102, 104003 (2020) | 10.1103/PhysRevD.102.104003 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Precision tests of general relativity can be conducted by observing binary
pulsars. Theories with massive fields exist to explain a variety of phenomena
from dark energy to the strong CP problem. Existing pulsar binaries, such as
the white dwarf-pulsar binary J1738+0333, have been used to place stringent
bounds on the scalar dipole emission, and radio telescopes may detect a pulsar
orbiting a black hole in the future. In this paper, we study the ability of
pulsar binaries to probe theories involving massive scalar and vector fields
through the measurement of the orbital decay rate. With a generic framework, we
describe corrections to orbital decay rate due to (a) modification of GR
quadrupolar radiation and (b) dipolar radiation of a massive field. We then
consider three concrete examples: (i) massive Brans-Dicke theory, (ii) general
relativity with axions, and (iii) general relativity with bound dark matter and
a dark force. Finally, we apply direct observations of J1738 and simulations of
a black hole-pulsar binary to bound theory parameters such as field's mass and
coupling constant. We find new constraints on bound dark matter interactions
with PSR J1738, and a black hole-pulsar discovery would likely improve these
further. Such bounds are complementary to future gravitational-wave bounds.
Regarding other theories, we find similar constraints to previous pulsar
measurements for massive Brans-Dicke theory and axions. These results show that
new pulsar binaries will continue to allow for more stringent tests of gravity.
| [
{
"created": "Wed, 29 Jul 2020 14:58:17 GMT",
"version": "v1"
},
{
"created": "Fri, 2 Oct 2020 00:47:11 GMT",
"version": "v2"
}
] | 2020-11-11 | [
[
"Seymour",
"Brian C.",
""
],
[
"Yagi",
"Kent",
""
]
] | Precision tests of general relativity can be conducted by observing binary pulsars. Theories with massive fields exist to explain a variety of phenomena from dark energy to the strong CP problem. Existing pulsar binaries, such as the white dwarf-pulsar binary J1738+0333, have been used to place stringent bounds on the scalar dipole emission, and radio telescopes may detect a pulsar orbiting a black hole in the future. In this paper, we study the ability of pulsar binaries to probe theories involving massive scalar and vector fields through the measurement of the orbital decay rate. With a generic framework, we describe corrections to orbital decay rate due to (a) modification of GR quadrupolar radiation and (b) dipolar radiation of a massive field. We then consider three concrete examples: (i) massive Brans-Dicke theory, (ii) general relativity with axions, and (iii) general relativity with bound dark matter and a dark force. Finally, we apply direct observations of J1738 and simulations of a black hole-pulsar binary to bound theory parameters such as field's mass and coupling constant. We find new constraints on bound dark matter interactions with PSR J1738, and a black hole-pulsar discovery would likely improve these further. Such bounds are complementary to future gravitational-wave bounds. Regarding other theories, we find similar constraints to previous pulsar measurements for massive Brans-Dicke theory and axions. These results show that new pulsar binaries will continue to allow for more stringent tests of gravity. |
gr-qc/9606029 | M. B. Paranjape | A. Edery and M. B. Paranjape | Localized Mass and Spin Sources in 2+1 Dimensional Topologically Massive
Gravity | revised version, minor corrections, latex, 8 pages | Phys.Lett.B413:35-40,1997 | 10.1016/S0370-2693(97)01101-5 | UDEM-GPP-TH-96-37 | gr-qc | null | Stationary solutions to the full non-linear topologically massive gravity
(TMG) are obtained for localized sources of mass $m$ and spin $\sigma$. Our
results show that the topological term induces spin and that the total spin J
(which is the spin observed by an asymptotic observer) ranges from 0 to $\sigma
+ \frac{m}{\mu}(\frac{4\pi+m}{4\pi +2m})$ depending on the structure of the
spin source (here $\mu$ is the topological mass). We find that it is
inconsistent to consider actual delta function mass and spin sources. In the
point-like limit, however, we find no condition constraining $m$ and $\sigma$
contrary to a previous analysis by Clement.
| [
{
"created": "Thu, 13 Jun 1996 20:32:02 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Jun 1997 16:21:16 GMT",
"version": "v2"
}
] | 2008-12-30 | [
[
"Edery",
"A.",
""
],
[
"Paranjape",
"M. B.",
""
]
] | Stationary solutions to the full non-linear topologically massive gravity (TMG) are obtained for localized sources of mass $m$ and spin $\sigma$. Our results show that the topological term induces spin and that the total spin J (which is the spin observed by an asymptotic observer) ranges from 0 to $\sigma + \frac{m}{\mu}(\frac{4\pi+m}{4\pi +2m})$ depending on the structure of the spin source (here $\mu$ is the topological mass). We find that it is inconsistent to consider actual delta function mass and spin sources. In the point-like limit, however, we find no condition constraining $m$ and $\sigma$ contrary to a previous analysis by Clement. |
1411.3143 | Arturo Stabile | A. Stabile, S. Capozziello | Self-gravitating systems in Extended Gravity | Review paper; 59 pages, 15 figures | Galaxies 2014, 2(4), 520-576 | 10.3390/galaxies2040520 | null | gr-qc astro-ph.GA astro-ph.SR math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Starting from the weak field limit, we discuss astrophysical applications of
Extended Theories of Gravity where higher order curvature invariants and scalar
fields are considered by generalizing the Hilbert-Einstein action linear in the
Ricci curvature scalar $R$. Results are compared to General Relativity in the
hypothesis that Dark Matter contributions to the dynamics can be neglected
thanks to modified gravity. In particular, we consider stellar hydrostatic
equilibrium, galactic rotation curves, and gravitational lensing. Finally, we
discuss the weak field limit in the Jordan and Einstein frames pointing out how
effective quantities, as gravitational potentials, transform from one frame to
the other and the interpretation of results can completely change accordingly.
| [
{
"created": "Wed, 12 Nov 2014 11:18:46 GMT",
"version": "v1"
}
] | 2015-02-25 | [
[
"Stabile",
"A.",
""
],
[
"Capozziello",
"S.",
""
]
] | Starting from the weak field limit, we discuss astrophysical applications of Extended Theories of Gravity where higher order curvature invariants and scalar fields are considered by generalizing the Hilbert-Einstein action linear in the Ricci curvature scalar $R$. Results are compared to General Relativity in the hypothesis that Dark Matter contributions to the dynamics can be neglected thanks to modified gravity. In particular, we consider stellar hydrostatic equilibrium, galactic rotation curves, and gravitational lensing. Finally, we discuss the weak field limit in the Jordan and Einstein frames pointing out how effective quantities, as gravitational potentials, transform from one frame to the other and the interpretation of results can completely change accordingly. |
2110.05176 | Sandeep S. Cranganore | Sandeep S. Cranganore | The Sugawara-Sommerfield construction including canonical spin current | 26 pages, Latex; typos corrected, title changed, added new subsection
and references in section 7, corrected equations in section 6 | null | 10.1103/PhysRevD.104.124022 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We set up the Sugawara-Sommerfield (SS) construction and generalize it by the
inclusion of canonical spin current. Using the techniques of current algebra,
we infer that the canonical spin current are linear in the vector-axial vector
currents. From a geometric perspective, the underlying manifold has a vanishing
Lorentz curvature and a non-vanishing torsion. This leads to teleparallelism
and the canonical spin current (connection) assume a pure gauge form. Moreover,
this model provides a possibility to unify gravity with strong-interactions by
expressing the gravitational gauge connections in terms of the Yang-Mills gauge
connections.
| [
{
"created": "Thu, 7 Oct 2021 19:27:15 GMT",
"version": "v1"
},
{
"created": "Tue, 9 Nov 2021 21:22:55 GMT",
"version": "v2"
}
] | 2021-12-15 | [
[
"Cranganore",
"Sandeep S.",
""
]
] | We set up the Sugawara-Sommerfield (SS) construction and generalize it by the inclusion of canonical spin current. Using the techniques of current algebra, we infer that the canonical spin current are linear in the vector-axial vector currents. From a geometric perspective, the underlying manifold has a vanishing Lorentz curvature and a non-vanishing torsion. This leads to teleparallelism and the canonical spin current (connection) assume a pure gauge form. Moreover, this model provides a possibility to unify gravity with strong-interactions by expressing the gravitational gauge connections in terms of the Yang-Mills gauge connections. |
1906.05557 | Hoang Nam Cao | Cao Hoang Nam | Heat engine efficiency and Joule-Thomson expansion of non-linear charged
AdS black hole in massive gravity | 22 pages | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we have considered the heat engine and Joule-Thomson expansion
for the charged AdS black hole in the context of the non-linear electrodynamics
and massive gravity. For the black hole heat engine, we obtained the analytical
expression for the efficiency in terms of either the entropies or the
temperatures and pressures in various limits. For the Joule-Thomson expansion
of the black hole, we derived the isenthalpic curves in $T-P$ diagram, the
Joule-Thomson coefficient, and the inversion curves. We also indicated in
detail the effects of the non-linear electrodynamics and massive gravity on the
heat engine efficiency and the Joule-Thomson expansion of the black hole.
| [
{
"created": "Thu, 13 Jun 2019 09:14:59 GMT",
"version": "v1"
}
] | 2019-06-14 | [
[
"Nam",
"Cao Hoang",
""
]
] | In this paper, we have considered the heat engine and Joule-Thomson expansion for the charged AdS black hole in the context of the non-linear electrodynamics and massive gravity. For the black hole heat engine, we obtained the analytical expression for the efficiency in terms of either the entropies or the temperatures and pressures in various limits. For the Joule-Thomson expansion of the black hole, we derived the isenthalpic curves in $T-P$ diagram, the Joule-Thomson coefficient, and the inversion curves. We also indicated in detail the effects of the non-linear electrodynamics and massive gravity on the heat engine efficiency and the Joule-Thomson expansion of the black hole. |
2105.12582 | Emmanuil Saridakis | Emmanuel N. Saridakis, Ruth Lazkoz, Vincenzo Salzano, Paulo Vargas
Moniz, Salvatore Capozziello, Jose Beltr\'an Jim\'enez, Mariafelicia De
Laurentis, Gonzalo J. Olmo, Yashar Akrami, Sebastian Bahamonde, Jose Luis
Bl\'azquez-Salcedo, Christian G. B\"ohmer, Camille Bonvin, Mariam
Bouhmadi-L\'opez, Philippe Brax, Gianluca Calcagni, Roberto Casadio, Jose A.
R. Cembranos, \'Alvaro de la Cruz-Dombriz, Anne-Christine Davis, Adri\`a
Delhom, Eleonora Di Valentino, Konstantinos F. Dialektopoulos, Benjamin
Elder, Jose Mar\'ia Ezquiaga, Noemi Frusciante, Remo Garattini, L\'aszl\'o
\'A. Gergely, Andrea Giusti, Lavinia Heisenberg, Manuel Hohmann, Damianos
Iosifidis, Lavrentios Kazantzidis, Burkhard Kleihaus, Tomi S. Koivisto, Jutta
Kunz, Francisco S. N. Lobo, Matteo Martinelli, Prado Mart\'in-Moruno, Jos\'e
Pedro Mimoso, David F. Mota, Simone Peirone, Leandros Perivolaropoulos,
Valeria Pettorino, Christian Pfeifer, Lorenzo Pizzuti, Diego Rubiera-Garcia,
Jackson Levi Said, Mairi Sakellariadou, Ippocratis D. Saltas, Alessio Spurio
Mancini, Nicoleta Voicu, Aneta Wojnar | Modified Gravity and Cosmology: An Update by the CANTATA Network | 543 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | General Relativity and the $\Lambda$CDM framework are currently the standard
lore and constitute the concordance paradigm. Nevertheless, long-standing open
theoretical issues, as well as possible new observational ones arising from the
explosive development of cosmology the last two decades, offer the motivation
and lead a large amount of research to be devoted in constructing various
extensions and modifications. All extended theories and scenarios are first
examined under the light of theoretical consistency, and then are applied to
various geometrical backgrounds, such as the cosmological and the spherical
symmetric ones. Their predictions at both the background and perturbation
levels, and concerning cosmology at early, intermediate and late times, are
then confronted with the huge amount of observational data that astrophysics
and cosmology are able to offer recently. Theories, scenarios and models that
successfully and efficiently pass the above steps are classified as viable and
are candidates for the description of Nature. This work is a Review of the
recent developments in the fields of gravity and cosmology, presenting the
state of the art, high-lighting the open problems, and outlining the directions
of future research. Its realization was performed in the framework of the COST
European Action ``Cosmology and Astrophysics Network for Theoretical Advances
and Training Actions''.
| [
{
"created": "Thu, 20 May 2021 17:25:53 GMT",
"version": "v1"
},
{
"created": "Fri, 19 May 2023 08:36:12 GMT",
"version": "v2"
}
] | 2023-05-22 | [
[
"Saridakis",
"Emmanuel N.",
""
],
[
"Lazkoz",
"Ruth",
""
],
[
"Salzano",
"Vincenzo",
""
],
[
"Moniz",
"Paulo Vargas",
""
],
[
"Capozziello",
"Salvatore",
""
],
[
"Jiménez",
"Jose Beltrán",
""
],
[
"De Laurentis",
... | General Relativity and the $\Lambda$CDM framework are currently the standard lore and constitute the concordance paradigm. Nevertheless, long-standing open theoretical issues, as well as possible new observational ones arising from the explosive development of cosmology the last two decades, offer the motivation and lead a large amount of research to be devoted in constructing various extensions and modifications. All extended theories and scenarios are first examined under the light of theoretical consistency, and then are applied to various geometrical backgrounds, such as the cosmological and the spherical symmetric ones. Their predictions at both the background and perturbation levels, and concerning cosmology at early, intermediate and late times, are then confronted with the huge amount of observational data that astrophysics and cosmology are able to offer recently. Theories, scenarios and models that successfully and efficiently pass the above steps are classified as viable and are candidates for the description of Nature. This work is a Review of the recent developments in the fields of gravity and cosmology, presenting the state of the art, high-lighting the open problems, and outlining the directions of future research. Its realization was performed in the framework of the COST European Action ``Cosmology and Astrophysics Network for Theoretical Advances and Training Actions''. |
gr-qc/0101030 | Lorenzo Iorio | Lorenzo Iorio and Erricos C. Pavlis | Tidal satellite perturbations and the Lense-Thirring effect | 6 pages, LaTex, to appear in Journal of the Geodetic Society of
Japan, vol. 47, no. 1, special issue for the Proceedings of The XIV
International Symposium on Earth tides (ETS 2000) held at Mizusawa, Iwate,
Japan from August 28 to September 1, 2000 | J.Geodet.Soc.Jap.47:1-7,2001 | 10.11366/sokuchi1954.47.169 | null | gr-qc astro-ph physics.geo-ph physics.space-ph | null | The tiny general relativistic Lense-Thirring effect can be measured by means
of a suitable combination of the orbital residuals of the nodes of LAGEOS and
LAGEOS II and the perigee of LAGEOS II. This observable is affected, among
other factors, by the Earth' s solid and ocean tides. They induce long-period
orbital perturbations that, over observational periods of few years, may alias
the detection of the gravitomagnetic secular trend of interest. In this paper
we calculate explicitly the most relevant tidal perturbations acting upon
LAGEOSs and assess their influence on the detection of the Lense-Thirring
effect. The present day level of knowledge of the solid and ocean tides allow
us to conclude that their influence on it ranges from almost 4% over 4 years to
less than 2% over 7 years.
| [
{
"created": "Tue, 9 Jan 2001 09:39:35 GMT",
"version": "v1"
}
] | 2013-11-12 | [
[
"Iorio",
"Lorenzo",
""
],
[
"Pavlis",
"Erricos C.",
""
]
] | The tiny general relativistic Lense-Thirring effect can be measured by means of a suitable combination of the orbital residuals of the nodes of LAGEOS and LAGEOS II and the perigee of LAGEOS II. This observable is affected, among other factors, by the Earth' s solid and ocean tides. They induce long-period orbital perturbations that, over observational periods of few years, may alias the detection of the gravitomagnetic secular trend of interest. In this paper we calculate explicitly the most relevant tidal perturbations acting upon LAGEOSs and assess their influence on the detection of the Lense-Thirring effect. The present day level of knowledge of the solid and ocean tides allow us to conclude that their influence on it ranges from almost 4% over 4 years to less than 2% over 7 years. |
2407.12954 | Edward Timoshenko G | G. A. Sardanashvily, E. G. Timoshenko | Caustics type of gravitational singularities | 4 pages. Translated from Russian by author on 07.07.2024 | Bulletin of Moscow State University, ISSN 2074-6636, UDC 530.12,
Series 3, Physics and astronomy, Vol. 30, No 3, pp. 75-77 (1989) | 10.6084/m9.figshare.26213036 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We describe a new type of gravitational singularities which are caustics of
spatial-temporal foliations. An example of gravitational wave solution forming
a singularity with caustics is given.
| [
{
"created": "Wed, 17 Jul 2024 18:56:38 GMT",
"version": "v1"
}
] | 2024-07-19 | [
[
"Sardanashvily",
"G. A.",
""
],
[
"Timoshenko",
"E. G.",
""
]
] | We describe a new type of gravitational singularities which are caustics of spatial-temporal foliations. An example of gravitational wave solution forming a singularity with caustics is given. |
1408.3465 | Tiberiu Harko | Tiberiu Harko | Thermodynamic interpretation of the generalized gravity models with
geometry - matter coupling | 12 pages, no figures, accepted for publication in PRD; references
added. arXiv admin note: text overlap with arXiv:gr-qc/0404045 by other
authors without attribution | Physical Review D 90, 044067 (2014) | 10.1103/PhysRevD.90.044067 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Modified gravity theories with geometry - matter coupling, in which the
action is an arbitrary function of the Ricci scalar and the matter Lagrangian
($f\left(R,L_m\right)$ gravity), and of the Ricci scalar and of the trace of
the matter energy-momentum tensor ($f(R,T)$ gravity), respectively, have the
intriguing property that the divergence of the matter energy - momentum tensor
is nonzero. In the present paper, by using the formalism of open thermodynamic
systems, we interpret the generalized conservation equations in these
gravitational theories from a thermodynamic point of view as describing
irreversible matter creation processes, which could be validated by fundamental
particle physics. Thus particle creation corresponds to an irreversible energy
flow from the gravitational field to the created matter constituents, with the
second law of thermodynamics requiring that space-time transforms into matter.
The equivalent particle number creation rates, the creation pressure and the
entropy production rates are obtained for both $f\left(R,L_m\right)$ and
$f(R,T)$ gravity theories. The temperature evolution laws of the newly created
particles are also obtained. In the case of the $f(R,T)$ gravity theory the
open irreversible thermodynamic interpretation of a simple cosmological model
is presented in detail. It is also shown that due to the geometry--matter
coupling, during the cosmological evolution a large amount of comoving entropy
could be produced.
| [
{
"created": "Fri, 15 Aug 2014 05:04:17 GMT",
"version": "v1"
},
{
"created": "Fri, 22 Aug 2014 02:06:42 GMT",
"version": "v2"
}
] | 2015-06-22 | [
[
"Harko",
"Tiberiu",
""
]
] | Modified gravity theories with geometry - matter coupling, in which the action is an arbitrary function of the Ricci scalar and the matter Lagrangian ($f\left(R,L_m\right)$ gravity), and of the Ricci scalar and of the trace of the matter energy-momentum tensor ($f(R,T)$ gravity), respectively, have the intriguing property that the divergence of the matter energy - momentum tensor is nonzero. In the present paper, by using the formalism of open thermodynamic systems, we interpret the generalized conservation equations in these gravitational theories from a thermodynamic point of view as describing irreversible matter creation processes, which could be validated by fundamental particle physics. Thus particle creation corresponds to an irreversible energy flow from the gravitational field to the created matter constituents, with the second law of thermodynamics requiring that space-time transforms into matter. The equivalent particle number creation rates, the creation pressure and the entropy production rates are obtained for both $f\left(R,L_m\right)$ and $f(R,T)$ gravity theories. The temperature evolution laws of the newly created particles are also obtained. In the case of the $f(R,T)$ gravity theory the open irreversible thermodynamic interpretation of a simple cosmological model is presented in detail. It is also shown that due to the geometry--matter coupling, during the cosmological evolution a large amount of comoving entropy could be produced. |
2404.19423 | De-Cheng Zou | Shan Wu, Kai-Qiang Qian, Rui-Hong Yue, Ming Zhang and De-Cheng Zou | Thermodynamics of charged Lifshitz black holes with scalar hair | 12 pages, 2 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we discuss the generalized Einstein-Maxwell-Dilaton gravity
theory with a nonminimal coupling between the Maxwell field and scalar field.
Considering different geometric properties of black hole horizon structure, the
charged dilaton Lifshitz black hole solutions are presented in 4-dimensional
spacetimes. Later, utilizing the Wald Formalism, we derive the thermodynamic
first law of black hole and conserved quantities. According to the relationship
between the heat capacity and the local stability of black hole, we study the
stability of charged Lifshitz black holes and identify the thermodynamic stable
region of black holes that meet the criteria.
| [
{
"created": "Tue, 30 Apr 2024 10:13:01 GMT",
"version": "v1"
},
{
"created": "Wed, 1 May 2024 01:38:44 GMT",
"version": "v2"
}
] | 2024-05-02 | [
[
"Wu",
"Shan",
""
],
[
"Qian",
"Kai-Qiang",
""
],
[
"Yue",
"Rui-Hong",
""
],
[
"Zhang",
"Ming",
""
],
[
"Zou",
"De-Cheng",
""
]
] | In this work, we discuss the generalized Einstein-Maxwell-Dilaton gravity theory with a nonminimal coupling between the Maxwell field and scalar field. Considering different geometric properties of black hole horizon structure, the charged dilaton Lifshitz black hole solutions are presented in 4-dimensional spacetimes. Later, utilizing the Wald Formalism, we derive the thermodynamic first law of black hole and conserved quantities. According to the relationship between the heat capacity and the local stability of black hole, we study the stability of charged Lifshitz black holes and identify the thermodynamic stable region of black holes that meet the criteria. |
gr-qc/0304025 | Carlos Augusto Romero Filho | A. Barros and C. Romero | Gravitomagnetic time delay and the Lense-Thirring effect in Brans-Dicke
theory of gravity | 10 pages Typeset using REVTEX | Mod.Phys.Lett.A18:2117-2124,2003 | 10.1142/S0217732303011721 | null | gr-qc | null | We discuss the gravitomagnetic time delay and the Lense-Thirring effect in
the context of Brans-Dicke theory of gravity. We compare the theoretical
results obtained with those predicted by general relativity. We show that
within the accuracy of experiments designed to measure these effects both
theories predict essentially the same result.
| [
{
"created": "Sat, 5 Apr 2003 14:08:57 GMT",
"version": "v1"
}
] | 2011-09-13 | [
[
"Barros",
"A.",
""
],
[
"Romero",
"C.",
""
]
] | We discuss the gravitomagnetic time delay and the Lense-Thirring effect in the context of Brans-Dicke theory of gravity. We compare the theoretical results obtained with those predicted by general relativity. We show that within the accuracy of experiments designed to measure these effects both theories predict essentially the same result. |
1501.01053 | Krishnamohan Parattu | Krishnamohan Parattu, Sumanta Chakraborty, Bibhas Ranjan Majhi and T.
Padmanabhan | A Boundary Term for the Gravitational Action with Null Boundaries | 47 pages, no figures, title changed | Gen.Rel.Grav. 48 (2016) no.7, 94 | 10.1007/s10714-016-2093-7 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Constructing a well-posed variational principle is a non-trivial issue in
general relativity. For spacelike and timelike boundaries, one knows that the
addition of the Gibbons-Hawking-York (GHY) counter-term will make the
variational principle well-defined. This result, however, does not directly
generalize to null boundaries on which the 3-metric becomes degenerate. In this
work, we address the following question: What is the counter-term that may be
added on a null boundary to make the variational principle well-defined? We
propose the boundary integral of $2 \sqrt{-g} \left( \Theta+\kappa \right)$ as
an appropriate counter-term for a null boundary. We also conduct a preliminary
analysis of the variations of the metric on the null boundary and conclude that
isolating the degrees of freedom that may be fixed for a well-posed variational
principle requires a deeper investigation.
| [
{
"created": "Tue, 6 Jan 2015 01:09:13 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Aug 2016 17:48:04 GMT",
"version": "v2"
}
] | 2016-08-02 | [
[
"Parattu",
"Krishnamohan",
""
],
[
"Chakraborty",
"Sumanta",
""
],
[
"Majhi",
"Bibhas Ranjan",
""
],
[
"Padmanabhan",
"T.",
""
]
] | Constructing a well-posed variational principle is a non-trivial issue in general relativity. For spacelike and timelike boundaries, one knows that the addition of the Gibbons-Hawking-York (GHY) counter-term will make the variational principle well-defined. This result, however, does not directly generalize to null boundaries on which the 3-metric becomes degenerate. In this work, we address the following question: What is the counter-term that may be added on a null boundary to make the variational principle well-defined? We propose the boundary integral of $2 \sqrt{-g} \left( \Theta+\kappa \right)$ as an appropriate counter-term for a null boundary. We also conduct a preliminary analysis of the variations of the metric on the null boundary and conclude that isolating the degrees of freedom that may be fixed for a well-posed variational principle requires a deeper investigation. |
1407.0744 | Leo Stein | Leo C. Stein | Note on Legendre decomposition of the Pontryagin density in Kerr | 3 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In arXiv:1406.0957v1 ("Scalar field excited around a rapidly rotating black
hole in Chern-Simons modified gravity"), Konno and Takahashi have recently
developed some analytical results for the scalar field about a Kerr black hole
in the decoupling limit of dynamical Chern-Simons gravity. This involved a
decomposition of the source (the Pontryagin density) in terms of Legendre
polynomials. Here we give a two-line expression for this decomposition which
simplifies their quadruple sum. Our expressions are rational polynomials
multiplying Legendre functions of the second kind, or equivalently rational
polynomials multiplying hypergeometric functions.
| [
{
"created": "Wed, 2 Jul 2014 23:43:39 GMT",
"version": "v1"
}
] | 2014-07-04 | [
[
"Stein",
"Leo C.",
""
]
] | In arXiv:1406.0957v1 ("Scalar field excited around a rapidly rotating black hole in Chern-Simons modified gravity"), Konno and Takahashi have recently developed some analytical results for the scalar field about a Kerr black hole in the decoupling limit of dynamical Chern-Simons gravity. This involved a decomposition of the source (the Pontryagin density) in terms of Legendre polynomials. Here we give a two-line expression for this decomposition which simplifies their quadruple sum. Our expressions are rational polynomials multiplying Legendre functions of the second kind, or equivalently rational polynomials multiplying hypergeometric functions. |
2004.08027 | Yen-Kheng Lim PhD | Yen-Kheng Lim | Hypocycloid motion in the Melvin magnetic universe | 18 pages, 4 figures. Typos corrected. Introduction and conclusion
improved thanks to the suggestions of the anonymous referee | Phys. Rev. D 101, 104031 (2020) | 10.1103/PhysRevD.101.104031 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The trajectory of a charged test particle in the Melvin magnetic universe is
shown to take the form of hypocycloids in two different regimes, first of which
is the class of perturbed circular orbits, and secondly in the weak-field
approximation. In the latter case we find a simple relation between the charge
of the particle and the number of cusps. These two regimes are within a
continuously connected family of deformed hypocycloid-like orbits parametrised
by the magnetic flux strength of the Melvin spacetime.
| [
{
"created": "Fri, 17 Apr 2020 01:53:35 GMT",
"version": "v1"
},
{
"created": "Mon, 18 May 2020 01:56:11 GMT",
"version": "v2"
}
] | 2020-05-19 | [
[
"Lim",
"Yen-Kheng",
""
]
] | The trajectory of a charged test particle in the Melvin magnetic universe is shown to take the form of hypocycloids in two different regimes, first of which is the class of perturbed circular orbits, and secondly in the weak-field approximation. In the latter case we find a simple relation between the charge of the particle and the number of cusps. These two regimes are within a continuously connected family of deformed hypocycloid-like orbits parametrised by the magnetic flux strength of the Melvin spacetime. |
1902.07411 | Daniel Pollack | Madeleine Burkhart, Martin Lesourd, and Daniel Pollack | Null geodesic incompleteness of spacetimes with no CMC Cauchy surfaces | All comments welcome! (v3: Dedication and reference added, minor
changes) | null | null | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Chru\'sciel, Isenberg, and Pollack constructed a class of vacuum cosmological
spacetimes that do not admit Cauchy surfaces with constant mean curvature. We
prove that, for sufficiently large values of the gluing parameter, these
examples are both future and past null geodesically incomplete.
The authors are honored to dedicate this paper to Robert Bartnik on the
occasion of his 60th birthday.
| [
{
"created": "Wed, 20 Feb 2019 05:27:40 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Feb 2019 04:42:14 GMT",
"version": "v2"
},
{
"created": "Thu, 28 Feb 2019 07:01:02 GMT",
"version": "v3"
}
] | 2019-03-01 | [
[
"Burkhart",
"Madeleine",
""
],
[
"Lesourd",
"Martin",
""
],
[
"Pollack",
"Daniel",
""
]
] | Chru\'sciel, Isenberg, and Pollack constructed a class of vacuum cosmological spacetimes that do not admit Cauchy surfaces with constant mean curvature. We prove that, for sufficiently large values of the gluing parameter, these examples are both future and past null geodesically incomplete. The authors are honored to dedicate this paper to Robert Bartnik on the occasion of his 60th birthday. |
1605.00497 | Giovanni Amelino-Camelia | Giovanni Amelino-Camelia, Mal\'u Maira da Silva, Michele Ronco,
Lorenzo Cesarini, Orchidea Maria Lecian | Spacetime-noncommutativity regime of Loop Quantum Gravity | null | Phys. Rev. D 95, 024028 (2017) | 10.1103/PhysRevD.95.024028 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A recent study by Bojowald and Paily provided a path toward the
identification of an effective quantum-spacetime picture of Loop Quantum
Gravity, applicable in the "Minkowski regime", the regime where the large-scale
(coarse-grained) spacetime metric is flat. A pivotal role in the analysis is
played by Loop-Quantum-Gravity-based modifications to the hypersurface
deformation algebra, which leave a trace in the Minkowski regime. We here show
that the symmetry-algebra results reported by Bojowald and Paily are consistent
with a description of spacetime in the Minkowski regime given in terms of the
$\kappa$-Minkowski noncommutative spacetime, whose relevance for the study of
the quantum-gravity problem had already been proposed for independent reasons.
| [
{
"created": "Mon, 2 May 2016 14:14:10 GMT",
"version": "v1"
}
] | 2017-01-25 | [
[
"Amelino-Camelia",
"Giovanni",
""
],
[
"da Silva",
"Malú Maira",
""
],
[
"Ronco",
"Michele",
""
],
[
"Cesarini",
"Lorenzo",
""
],
[
"Lecian",
"Orchidea Maria",
""
]
] | A recent study by Bojowald and Paily provided a path toward the identification of an effective quantum-spacetime picture of Loop Quantum Gravity, applicable in the "Minkowski regime", the regime where the large-scale (coarse-grained) spacetime metric is flat. A pivotal role in the analysis is played by Loop-Quantum-Gravity-based modifications to the hypersurface deformation algebra, which leave a trace in the Minkowski regime. We here show that the symmetry-algebra results reported by Bojowald and Paily are consistent with a description of spacetime in the Minkowski regime given in terms of the $\kappa$-Minkowski noncommutative spacetime, whose relevance for the study of the quantum-gravity problem had already been proposed for independent reasons. |
0709.0872 | Golam Mortuza Hossain | Martin Bojowald and Golam Mortuza Hossain | Cosmological vector modes and quantum gravity effects | 20 pages | Class.Quant.Grav.24:4801-4816,2007 | 10.1088/0264-9381/24/18/015 | IGPG-07/6-5 | gr-qc astro-ph hep-th | null | In contrast to scalar and tensor modes, vector modes of linear perturbations
around an expanding Friedmann--Robertson--Walker universe decay. This makes
them largely irrelevant for late time cosmology, assuming that all modes
started out at a similar magnitude at some early stage. By now, however,
bouncing models are frequently considered which exhibit a collapsing phase.
Before this phase reaches a minimum size and re-expands, vector modes grow.
Such modes are thus relevant for the bounce and may even signal the breakdown
of perturbation theory if the growth is too strong. Here, a gauge invariant
formulation of vector mode perturbations in Hamiltonian cosmology is presented.
This lays out a framework for studying possible canonical quantum gravity
effects, such as those of loop quantum gravity, at an effective level. As an
explicit example, typical quantum corrections, namely those coming from inverse
densitized triad components and holonomies, are shown to increase the growth
rate of vector perturbations in the contracting phase, but only slightly.
Effects at the bounce of the background geometry can, however, be much
stronger.
| [
{
"created": "Thu, 6 Sep 2007 14:33:31 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Bojowald",
"Martin",
""
],
[
"Hossain",
"Golam Mortuza",
""
]
] | In contrast to scalar and tensor modes, vector modes of linear perturbations around an expanding Friedmann--Robertson--Walker universe decay. This makes them largely irrelevant for late time cosmology, assuming that all modes started out at a similar magnitude at some early stage. By now, however, bouncing models are frequently considered which exhibit a collapsing phase. Before this phase reaches a minimum size and re-expands, vector modes grow. Such modes are thus relevant for the bounce and may even signal the breakdown of perturbation theory if the growth is too strong. Here, a gauge invariant formulation of vector mode perturbations in Hamiltonian cosmology is presented. This lays out a framework for studying possible canonical quantum gravity effects, such as those of loop quantum gravity, at an effective level. As an explicit example, typical quantum corrections, namely those coming from inverse densitized triad components and holonomies, are shown to increase the growth rate of vector perturbations in the contracting phase, but only slightly. Effects at the bounce of the background geometry can, however, be much stronger. |
2204.06750 | Yun Soo Myung | Yun Soo Myung | Conditions for superradiant instability of the Kerr-Newman black holes | 15 pages, 7 figures, a version to appear in PRD | null | 10.1103/PhysRevD.105.124015 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We find two conditions for superradiant instability of Kerr-Newman black
holes under a charged massive scalar perturbation by analyzing asymptotic
scalar potential and far-region wave function. Actually, they correspond to the
condition for getting a trapping well. Also, we obtain the conditions for
superradiant stability of Kerr-Newman black holes which states that there is no
trapping well. The analysis is applied to Kerr black holes to find a condition
for superradiant instability.
| [
{
"created": "Thu, 14 Apr 2022 04:20:01 GMT",
"version": "v1"
},
{
"created": "Tue, 26 Apr 2022 03:26:38 GMT",
"version": "v2"
},
{
"created": "Wed, 25 May 2022 21:57:12 GMT",
"version": "v3"
}
] | 2022-06-22 | [
[
"Myung",
"Yun Soo",
""
]
] | We find two conditions for superradiant instability of Kerr-Newman black holes under a charged massive scalar perturbation by analyzing asymptotic scalar potential and far-region wave function. Actually, they correspond to the condition for getting a trapping well. Also, we obtain the conditions for superradiant stability of Kerr-Newman black holes which states that there is no trapping well. The analysis is applied to Kerr black holes to find a condition for superradiant instability. |
2204.08113 | Vilson T. Zanchin | Angel D. Masa and Vilson T. Zanchin | Rotating regular black holes and other compact objects with a Tolman
type potential as a regular interior for the Kerr metric | New references added, text improved | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We obtain a new class of stationary axisymmetric spacetimes by using the
G\"urses-G\"ursey metric with an appropriate mass function in order to generate
a rotating core of matter that may be smoothly matched to the exterior Kerr
metric. The same stationary spacetimes may be obtained by applying a slightly
modified version of the Newman-Janis algorithm to a nonrotating spherically
symmetric seed metric. The starting spherically symmetric configuration
represents a nonisotropic de-Sitter type fluid whose radial pressure $p_r$
satisfies an state equation of the form $p_r=-\rho$, where the energy density
$\rho$ is chosen to be the Tolman type-VII energy density [R. C. Tolman, Phys.
Rev. {\bf 55}, 364 (1939)]. The resulting rotating metric is then smoothly
matched to the exterior Kerr metric, and the main properties of the obtained
geometries are investigated. All the solutions considered in the present study
are regular in the sense they are free of curvature singularities. Depending on
the relative values of the total mass $m$ and rotation parameter $a$, the
resulting stationary spacetimes represent different kinds of rotating compact
objects such as regular black holes, extremal regular black holes, and regular
starlike configurations.
| [
{
"created": "Mon, 18 Apr 2022 00:28:21 GMT",
"version": "v1"
},
{
"created": "Wed, 8 Nov 2023 21:29:12 GMT",
"version": "v2"
}
] | 2023-11-10 | [
[
"Masa",
"Angel D.",
""
],
[
"Zanchin",
"Vilson T.",
""
]
] | We obtain a new class of stationary axisymmetric spacetimes by using the G\"urses-G\"ursey metric with an appropriate mass function in order to generate a rotating core of matter that may be smoothly matched to the exterior Kerr metric. The same stationary spacetimes may be obtained by applying a slightly modified version of the Newman-Janis algorithm to a nonrotating spherically symmetric seed metric. The starting spherically symmetric configuration represents a nonisotropic de-Sitter type fluid whose radial pressure $p_r$ satisfies an state equation of the form $p_r=-\rho$, where the energy density $\rho$ is chosen to be the Tolman type-VII energy density [R. C. Tolman, Phys. Rev. {\bf 55}, 364 (1939)]. The resulting rotating metric is then smoothly matched to the exterior Kerr metric, and the main properties of the obtained geometries are investigated. All the solutions considered in the present study are regular in the sense they are free of curvature singularities. Depending on the relative values of the total mass $m$ and rotation parameter $a$, the resulting stationary spacetimes represent different kinds of rotating compact objects such as regular black holes, extremal regular black holes, and regular starlike configurations. |
2107.09536 | Neev Khera | Neev Khera, Abhay Ashtekar, Badri Krishnan | Testing gravitational waveform models using angular momentum | 12 pages, 6 figures. Appendix B added to provide heat maps showing
the degree of violation of the angular momentum balance law in various
non-precessing and precessing models, as functions of the binary parameters | Phys. Rev. D104, 124071 (2021) | 10.1103/PhysRevD.104.124071 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The anticipated enhancements in detector sensitivity and the corresponding
increase in the number of gravitational wave detections will make it possible
to estimate parameters of compact binaries with greater accuracy assuming
general relativity(GR), and also to carry out sharper tests of GR itself.
Crucial to these procedures are accurate gravitational waveform models. The
systematic errors of the models must stay below statistical errors to prevent
biases in parameter estimation and to carry out meaningful tests of GR.
Comparisons of the models against numerical relativity (NR) waveforms provide
an excellent measure of systematic errors. A complementary approach is to use
balance laws provided by Einstein's equations to measure faithfulness of a
candidate waveform against exact GR. Each balance law focuses on a physical
observable and measures the accuracy of the candidate waveform vis a vis that
observable. Therefore, this analysis can provide new physical insights into
sources of errors. In this paper we focus on the angular momentum balance law,
using post-Newtonian theory to calculate the initial angular momentum,
surrogate fits to obtain the remnant spin and waveforms from models to
calculate the flux. The consistency check provided by the angular momentum
balance law brings out the marked improvement in the passage from
\texttt{IMRPhenomPv2} to \texttt{IMRPhenomXPHM} and from \texttt{SEOBNRv3} to
\texttt{SEOBNRv4PHM} and shows that the most recent versions agree quite well
with exact GR. For precessing systems, on the other hand, we find that there is
room for further improvement, especially for the Phenom models.
| [
{
"created": "Tue, 20 Jul 2021 14:50:35 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Dec 2021 18:23:59 GMT",
"version": "v2"
}
] | 2021-12-30 | [
[
"Khera",
"Neev",
""
],
[
"Ashtekar",
"Abhay",
""
],
[
"Krishnan",
"Badri",
""
]
] | The anticipated enhancements in detector sensitivity and the corresponding increase in the number of gravitational wave detections will make it possible to estimate parameters of compact binaries with greater accuracy assuming general relativity(GR), and also to carry out sharper tests of GR itself. Crucial to these procedures are accurate gravitational waveform models. The systematic errors of the models must stay below statistical errors to prevent biases in parameter estimation and to carry out meaningful tests of GR. Comparisons of the models against numerical relativity (NR) waveforms provide an excellent measure of systematic errors. A complementary approach is to use balance laws provided by Einstein's equations to measure faithfulness of a candidate waveform against exact GR. Each balance law focuses on a physical observable and measures the accuracy of the candidate waveform vis a vis that observable. Therefore, this analysis can provide new physical insights into sources of errors. In this paper we focus on the angular momentum balance law, using post-Newtonian theory to calculate the initial angular momentum, surrogate fits to obtain the remnant spin and waveforms from models to calculate the flux. The consistency check provided by the angular momentum balance law brings out the marked improvement in the passage from \texttt{IMRPhenomPv2} to \texttt{IMRPhenomXPHM} and from \texttt{SEOBNRv3} to \texttt{SEOBNRv4PHM} and shows that the most recent versions agree quite well with exact GR. For precessing systems, on the other hand, we find that there is room for further improvement, especially for the Phenom models. |
2406.11626 | Tobias Weinzierl | Han Zhang (1 and 2), Baojiu Li (2), Tobias Weinzierl (1), Cristian
Barrera-Hinojosa (3) ((1) Department of Computer Science, Durham University,
(2) Institute for Computational Cosmology, Durham University (3) Instituto de
F\'isica y Astronom\'ia, Universidad de Valpara\'iso) | ExaGRyPE: Numerical General Relativity Solvers Based upon the Hyperbolic
PDEs Solver Engine ExaHyPE | null | null | null | null | gr-qc astro-ph.HE | http://creativecommons.org/licenses/by-nc-nd/4.0/ | ExaGRyPE describes a suite of solvers for numerical relativity, based upon
ExaHyPE 2, the second generation of our Exascale Hyperbolic PDE Engine. The
presented generation of ExaGRyPE solves the Einstein equations in the CCZ4
formulation under a 3+1 foliation and focuses on black hole spacetimes. It
employs a block-structured Cartesian grid carrying a higher-order order Finite
Difference scheme with adaptive mesh refinement, it facilitates massive
parallelism combining message passing, domain decomposition and task
parallelism, and it supports the injection of particles into the grid as data
probes or tracers. We introduce the ExaGRyPE-specific building blocks within
ExaHyPE 2, and discuss its software architecture and compute-n-feel:
For this, we formalize the creation of any specific simulation with ExaGRyPE
as a sequence of lowering operations, where abstract logical tasks are
successively broken into finer tasks until we obtain an abstraction level that
can be mapped onto a C++ executable. The overall program logic is fully
specified via a domain-specific Python interface, we map this logic onto a more
detailed set of numerical tasks, subsequently lower this representation onto
technical tasks that the underlying ExaHyPE engine uses to parallelize the
application, before eventually the technical tasks are mapped onto task graphs
including the actual PDE term evaluations, initial conditions, boundary
conditions, and so forth. We end up with a rigorous separation of concerns
which shields ExaGRyPE users from technical details and hence simplifies the
development of novel physical models. We present the simulations and data for
the gauge wave, static single black holes and rotating binary black hole
systems, demonstrating that the code base is mature and usable. However, we
also uncover domain-specific numerical challenges that need further study by
the community in future work.
| [
{
"created": "Mon, 17 Jun 2024 15:08:40 GMT",
"version": "v1"
},
{
"created": "Tue, 18 Jun 2024 09:41:55 GMT",
"version": "v2"
}
] | 2024-06-19 | [
[
"Zhang",
"Han",
"",
"1 and 2"
],
[
"Li",
"Baojiu",
""
],
[
"Weinzierl",
"Tobias",
""
],
[
"Barrera-Hinojosa",
"Cristian",
""
]
] | ExaGRyPE describes a suite of solvers for numerical relativity, based upon ExaHyPE 2, the second generation of our Exascale Hyperbolic PDE Engine. The presented generation of ExaGRyPE solves the Einstein equations in the CCZ4 formulation under a 3+1 foliation and focuses on black hole spacetimes. It employs a block-structured Cartesian grid carrying a higher-order order Finite Difference scheme with adaptive mesh refinement, it facilitates massive parallelism combining message passing, domain decomposition and task parallelism, and it supports the injection of particles into the grid as data probes or tracers. We introduce the ExaGRyPE-specific building blocks within ExaHyPE 2, and discuss its software architecture and compute-n-feel: For this, we formalize the creation of any specific simulation with ExaGRyPE as a sequence of lowering operations, where abstract logical tasks are successively broken into finer tasks until we obtain an abstraction level that can be mapped onto a C++ executable. The overall program logic is fully specified via a domain-specific Python interface, we map this logic onto a more detailed set of numerical tasks, subsequently lower this representation onto technical tasks that the underlying ExaHyPE engine uses to parallelize the application, before eventually the technical tasks are mapped onto task graphs including the actual PDE term evaluations, initial conditions, boundary conditions, and so forth. We end up with a rigorous separation of concerns which shields ExaGRyPE users from technical details and hence simplifies the development of novel physical models. We present the simulations and data for the gauge wave, static single black holes and rotating binary black hole systems, demonstrating that the code base is mature and usable. However, we also uncover domain-specific numerical challenges that need further study by the community in future work. |
1308.4306 | Oldrich Semerak | P. Sukov\'a, O. Semer\'ak | Free motion around black holes with discs or rings: between
integrability and chaos - III | 19 pages, 10 figures; accepted in MNRAS | MNRAS 436 (2013) 978-996 | 10.1093/mnras/stt1587 | null | gr-qc astro-ph.GA nlin.CD | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We continue the study of time-like geodesic dynamics in exact static, axially
and reflection symmetric space-times describing the fields of a Schwarzschild
black hole surrounded by thin discs or rings. In the first paper of this
series, the rise (and decline) of geodesic chaos with ring/disc mass and
position and with test particle energy was revealed on Poincar\'e sections and
on time series of position or velocity and their power spectra. In the second
paper we compared these results with those obtained by two recurrence methods,
focusing on "sticky" orbits whose different parts show different degrees of
chaoticity. Here we complement the analysis by using several Lyapunov-type
coefficients which quantify the rate of orbital divergence. After comparing the
results with those obtained by the previous methods, we specifically consider a
system involving a black hole surrounded by a small thin disc or a large ring,
having in mind the configuration which probably occurs in galactic nuclei.
Within the range of parameters which roughly corresponds to our Galactic
center, we found that the black-hole accretion disc does not have a significant
gravitational effect on the dynamics of free motion at larger radii, while the
inner circumnuclear molecular ring (concentrated above 1 parsec radius) can
only induce some irregularity in motion of stars ("particles") on smaller radii
if its mass reaches 10 to 30% of the central black hole (which is the upper
estimate given in the literature), if it is sufficiently compact (which does
not hold but maybe for its inner rim) and if the stars can get to its close
vicinity. The outer dust ring between 60 and 100 parsecs appears to be less
important for the geodesic dynamics in its interior.
| [
{
"created": "Tue, 20 Aug 2013 13:31:55 GMT",
"version": "v1"
}
] | 2013-11-15 | [
[
"Suková",
"P.",
""
],
[
"Semerák",
"O.",
""
]
] | We continue the study of time-like geodesic dynamics in exact static, axially and reflection symmetric space-times describing the fields of a Schwarzschild black hole surrounded by thin discs or rings. In the first paper of this series, the rise (and decline) of geodesic chaos with ring/disc mass and position and with test particle energy was revealed on Poincar\'e sections and on time series of position or velocity and their power spectra. In the second paper we compared these results with those obtained by two recurrence methods, focusing on "sticky" orbits whose different parts show different degrees of chaoticity. Here we complement the analysis by using several Lyapunov-type coefficients which quantify the rate of orbital divergence. After comparing the results with those obtained by the previous methods, we specifically consider a system involving a black hole surrounded by a small thin disc or a large ring, having in mind the configuration which probably occurs in galactic nuclei. Within the range of parameters which roughly corresponds to our Galactic center, we found that the black-hole accretion disc does not have a significant gravitational effect on the dynamics of free motion at larger radii, while the inner circumnuclear molecular ring (concentrated above 1 parsec radius) can only induce some irregularity in motion of stars ("particles") on smaller radii if its mass reaches 10 to 30% of the central black hole (which is the upper estimate given in the literature), if it is sufficiently compact (which does not hold but maybe for its inner rim) and if the stars can get to its close vicinity. The outer dust ring between 60 and 100 parsecs appears to be less important for the geodesic dynamics in its interior. |
2207.11721 | Shu-Min Wu | Shu-Min Wu, Chun-Xu Wang, Dan-Dan Liu, Xiao-Li Huang, Hao-Sheng Zeng | Would quantum coherence be increased by curvature effect in de Sitter
space? | 24 pages, 5 figures | JHEP 02 (2023) 115 | 10.1007/JHEP02(2023)115 | null | gr-qc hep-th quant-ph | http://creativecommons.org/licenses/by/4.0/ | We study the quantum coherence in de Sitter space for the bipartite system of
Alice and Bob who initially share an entangled state between the two modes of a
free massive scalar field. It is shown that the space-curvature effect can
produce both local coherence and correlated coherence, leading to the increase
of the total coherence of the bipartite system. These results are sharp
different from the Unruh effect or Hawking effect, which, in the single mode
approximation, cannot produce local coherence and at the same time destroy
correlated coherence, leading to the decrease of the total coherence of the
bipartite systems. Interestingly, we find that quantum coherence has the
opposite behavior compared with the quantum correlation in de Sitter space. We
also find that quantum coherence is most severely affected by the curvature
effect of de Sitter space for the cases of conformal invariance and
masslessness. Our result reveals the difference between the curvature effect in
the de Sitter space and the Unruh effect in Rindler spacetime or the Hawking
effect in black hole spacetime on quantum coherence.
| [
{
"created": "Sun, 24 Jul 2022 11:35:06 GMT",
"version": "v1"
},
{
"created": "Sun, 12 Feb 2023 08:25:04 GMT",
"version": "v2"
}
] | 2023-03-01 | [
[
"Wu",
"Shu-Min",
""
],
[
"Wang",
"Chun-Xu",
""
],
[
"Liu",
"Dan-Dan",
""
],
[
"Huang",
"Xiao-Li",
""
],
[
"Zeng",
"Hao-Sheng",
""
]
] | We study the quantum coherence in de Sitter space for the bipartite system of Alice and Bob who initially share an entangled state between the two modes of a free massive scalar field. It is shown that the space-curvature effect can produce both local coherence and correlated coherence, leading to the increase of the total coherence of the bipartite system. These results are sharp different from the Unruh effect or Hawking effect, which, in the single mode approximation, cannot produce local coherence and at the same time destroy correlated coherence, leading to the decrease of the total coherence of the bipartite systems. Interestingly, we find that quantum coherence has the opposite behavior compared with the quantum correlation in de Sitter space. We also find that quantum coherence is most severely affected by the curvature effect of de Sitter space for the cases of conformal invariance and masslessness. Our result reveals the difference between the curvature effect in the de Sitter space and the Unruh effect in Rindler spacetime or the Hawking effect in black hole spacetime on quantum coherence. |
1007.4129 | Diego Pavon | Ninfa Radicella and Diego Pavon | On the $c^{2}$ term in the holographic formula for dark energy | 10 pages, 1 figure | JCAP 1010:005,2010 | 10.1088/1475-7516/2010/10/005 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is argued that the $c^{2}$ term that appears in the conventional formula
for holographic dark energy should not be assumed constant in general.
Notwithstanding, there is at least an exception, namely, when the Ricci scale
is chosen as the infrared cutoff length.
| [
{
"created": "Fri, 23 Jul 2010 13:45:20 GMT",
"version": "v1"
}
] | 2014-11-21 | [
[
"Radicella",
"Ninfa",
""
],
[
"Pavon",
"Diego",
""
]
] | It is argued that the $c^{2}$ term that appears in the conventional formula for holographic dark energy should not be assumed constant in general. Notwithstanding, there is at least an exception, namely, when the Ricci scale is chosen as the infrared cutoff length. |
1407.8139 | Firmin Oliveira | Firmin J. Oliveira | Cosmological General Relativity With Scale Factor and Dark Energy | 28 pages, 9 figures, 1 table. The final publication is available at
springerlink.com | null | 10.1007/s10773-014-2138-1 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper the four-dimensional space-velocity Cosmological General
Relativity of Carmeli is developed by a general solution to the Einstein field
equations. The metric is given in the Tolman form and the vacuum mass density
is included in the energy-momentum tensor. The scale factor redshift equation
is obtained, forming the basis for deriving the various redshift-distance
relations of cosmological analysis. A linear equation of state dependent on the
scale factor is assumed to account for the effects of an evolving dark energy
in the expansion of the universe. Modeling simulations are provided for a few
combinations of mass density, vacuum density and state parameter values over a
sample of high redshift SNe Ia data. Also, the Carmeli cosmological model is
derived as a special case of the general solution.
| [
{
"created": "Wed, 30 Jul 2014 17:41:07 GMT",
"version": "v1"
}
] | 2014-07-31 | [
[
"Oliveira",
"Firmin J.",
""
]
] | In this paper the four-dimensional space-velocity Cosmological General Relativity of Carmeli is developed by a general solution to the Einstein field equations. The metric is given in the Tolman form and the vacuum mass density is included in the energy-momentum tensor. The scale factor redshift equation is obtained, forming the basis for deriving the various redshift-distance relations of cosmological analysis. A linear equation of state dependent on the scale factor is assumed to account for the effects of an evolving dark energy in the expansion of the universe. Modeling simulations are provided for a few combinations of mass density, vacuum density and state parameter values over a sample of high redshift SNe Ia data. Also, the Carmeli cosmological model is derived as a special case of the general solution. |
1310.3949 | Omid Jalili | O.Jalili, S.Rouhani and M.V.Takook | Gravitational wave detection by bounded cold electronic plasma in a long
pipe | 14 pages, 5 figures | International Journal of Theoretical Physics: Volume 49, Issue 1
(2010), Page 84 | 10.1007/s10773-009-0181-0 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We intend to propose an experimental sketch to detect gravitational waves
(GW) directly, using an cold electronic plasma in a long pipe. By considering
an cold electronic plasma in a long pipe, the Maxwell equations in 3+1
formalism will be invoked to relate gravitational waves to the perturbations of
plasma particles. It will be shown that the impact of GW on cold electronic
plasma causes disturbances on the paths of the electrons. Those electrons that
absorb energy from GW will pass through the potential barrier at the end of the
pipe. Therefore, crossing of some electrons over the barrier will imply the
existence of the GW.
| [
{
"created": "Tue, 15 Oct 2013 08:13:56 GMT",
"version": "v1"
}
] | 2015-06-17 | [
[
"Jalili",
"O.",
""
],
[
"Rouhani",
"S.",
""
],
[
"Takook",
"M. V.",
""
]
] | We intend to propose an experimental sketch to detect gravitational waves (GW) directly, using an cold electronic plasma in a long pipe. By considering an cold electronic plasma in a long pipe, the Maxwell equations in 3+1 formalism will be invoked to relate gravitational waves to the perturbations of plasma particles. It will be shown that the impact of GW on cold electronic plasma causes disturbances on the paths of the electrons. Those electrons that absorb energy from GW will pass through the potential barrier at the end of the pipe. Therefore, crossing of some electrons over the barrier will imply the existence of the GW. |
1808.01891 | Everton Murilo Carvalho Abreu | Everton M. C. Abreu, Jorge Ananias Neto, Albert C. R. Mendes and
Rodrigo M. de Paula | Loop Quantum Gravity Immirzi parameter and the Kaniadakis statistics | 7 pages. Preprint format | null | 10.1016/j.chaos.2018.11.033 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this letter we have shown that a possible connection between the LQG
Immirzi parameter and the area of a punctured surface can emerge depending on
the thermostatistics theory previously chosen. Starting from the
Boltzmann-Gibbs entropy, the Immirzi parameter can be reobtained. Using the
Kaniadakis statistics, which is an important non-Gaussian statistics, we have
derived a new relation between the Immirzi parameter, the kappa parameter and
the area of a punctured surface. After that, we have compared our result with
the Immirzi parameter previously obtained in the literature within the context
of Tsallis' statistics. We have demonstrated in an exact way that the LQG
Immirzi parameter can also be used to compare both Kaniadakis and Tsallis
statics.
| [
{
"created": "Tue, 31 Jul 2018 19:29:06 GMT",
"version": "v1"
}
] | 2018-12-26 | [
[
"Abreu",
"Everton M. C.",
""
],
[
"Neto",
"Jorge Ananias",
""
],
[
"Mendes",
"Albert C. R.",
""
],
[
"de Paula",
"Rodrigo M.",
""
]
] | In this letter we have shown that a possible connection between the LQG Immirzi parameter and the area of a punctured surface can emerge depending on the thermostatistics theory previously chosen. Starting from the Boltzmann-Gibbs entropy, the Immirzi parameter can be reobtained. Using the Kaniadakis statistics, which is an important non-Gaussian statistics, we have derived a new relation between the Immirzi parameter, the kappa parameter and the area of a punctured surface. After that, we have compared our result with the Immirzi parameter previously obtained in the literature within the context of Tsallis' statistics. We have demonstrated in an exact way that the LQG Immirzi parameter can also be used to compare both Kaniadakis and Tsallis statics. |
1603.01221 | Niels Warburton | Samuel E. Gralla, Scott A. Hughes, Niels Warburton | Inspiral into Gargantua | 10 pages, 5 figures, updated to journal version | Class. Quant. Grav. 33 155002 (2016) | 10.1088/0264-9381/33/15/155002 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We model the inspiral of a compact object into a more massive black hole
rotating very near the theoretical maximum. We find that once the body enters
the near-horizon regime the gravitational radiation is characterized by a
constant frequency, equal to (twice) the horizon frequency, with an
exponentially damped profile. This contrasts with the usual "chirping" behavior
and, if detected, would constitute a "smoking gun" for a near-extremal black
hole in nature.
| [
{
"created": "Thu, 3 Mar 2016 18:54:59 GMT",
"version": "v1"
},
{
"created": "Mon, 19 Sep 2016 20:45:13 GMT",
"version": "v2"
}
] | 2016-09-21 | [
[
"Gralla",
"Samuel E.",
""
],
[
"Hughes",
"Scott A.",
""
],
[
"Warburton",
"Niels",
""
]
] | We model the inspiral of a compact object into a more massive black hole rotating very near the theoretical maximum. We find that once the body enters the near-horizon regime the gravitational radiation is characterized by a constant frequency, equal to (twice) the horizon frequency, with an exponentially damped profile. This contrasts with the usual "chirping" behavior and, if detected, would constitute a "smoking gun" for a near-extremal black hole in nature. |
2107.09800 | Jian-Hua He | Jian-Hua He | GWsim: a code to simulate gravitational waves propagating in a potential
well | 17 pages, 11 figures, substantial text overlap with arXiv:1912.00325,
accepted for publication in MNRAS | MNRAS, 506, 5278 (2021) | 10.1093/mnras/stab2080 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a code to simulate the propagation of GWs in a potential well in
the time domain. Our code uses the finite element method (FEM) based on the
publicly available code {\it deal.ii}. We test our code using a point source
monochromatic spherical wave. We examine not only the waveform observed by a
local observer but also the global energy conservation of the waves. We find
that our numerical results agree with the analytical predictions very well.
Based on our code, we study the propagation of the leading wavefront of GWs in
a potential well. We find that our numerical results agree with the results
obtained from tracing null geodesics very well. Based on our simulations, we
also test the accuracy of the thin-lens model in predicting the positions of
the wavefront. We find that the analytical formula of the Shapiro-time delay is
only accurate in regimes that are far away from the center of the potential
well. However, near the optic axis, the analytical formula shows significant
differences from the simulated ones. Besides these results, we find that unlike
the conventional images in geometric optics, GWs can not be sheltered by the
scatterer due to wave effects. The signals of GWs can circle around the
scatterer and travel along the optic axis until arrive at a distant observer,
which is an important observational consequence in such a system.
| [
{
"created": "Wed, 21 Jul 2021 00:52:04 GMT",
"version": "v1"
}
] | 2021-08-12 | [
[
"He",
"Jian-Hua",
""
]
] | We present a code to simulate the propagation of GWs in a potential well in the time domain. Our code uses the finite element method (FEM) based on the publicly available code {\it deal.ii}. We test our code using a point source monochromatic spherical wave. We examine not only the waveform observed by a local observer but also the global energy conservation of the waves. We find that our numerical results agree with the analytical predictions very well. Based on our code, we study the propagation of the leading wavefront of GWs in a potential well. We find that our numerical results agree with the results obtained from tracing null geodesics very well. Based on our simulations, we also test the accuracy of the thin-lens model in predicting the positions of the wavefront. We find that the analytical formula of the Shapiro-time delay is only accurate in regimes that are far away from the center of the potential well. However, near the optic axis, the analytical formula shows significant differences from the simulated ones. Besides these results, we find that unlike the conventional images in geometric optics, GWs can not be sheltered by the scatterer due to wave effects. The signals of GWs can circle around the scatterer and travel along the optic axis until arrive at a distant observer, which is an important observational consequence in such a system. |
1804.00594 | Fethi M. Ramazanoglu | Fethi M Ramazano\u{g}lu | Spontaneous growth of spinor fields in gravity | This version incorporates the corrections due to some missing terms
in the equations which were published in the erratum at
10.1103/PhysRevD.100.029903. Conclusions are unchanged | Phys. Rev. D 98, 044011 (2018) | 10.1103/PhysRevD.98.044011 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that spinor fields nonminimally coupled to gravity can grow
spontaneously in the presence of matter. We name this phenomenon spontaneous
spinorization after the spontaneous scalarization scenario in scalar-tensor
theories. Underlying reason for the growth of the spinor is an instability
similar to the tachyon of spontaneous scalarization. We first present the
structure of a tachyonic Dirac equation, and incorporate it into the matter
coupling in gravity. This causes the zero-spinor solution to be unstable and
leads to spontaneous growth. We investigate the behavior of the resulting
theory for a spherically symmetric neutron star that has grown a spinor cloud.
Spontaneous spinorization has the potential to lead to order-of-unity
deviations from general relativity in strong fields in a similar manner to its
close relative spontaneous scalarization. This makes the theory especially
relevant to gravitational wave science and neutron star astrophysics.
| [
{
"created": "Mon, 2 Apr 2018 15:39:01 GMT",
"version": "v1"
},
{
"created": "Wed, 15 Aug 2018 12:36:13 GMT",
"version": "v2"
},
{
"created": "Mon, 7 Oct 2019 14:24:03 GMT",
"version": "v3"
}
] | 2019-10-08 | [
[
"Ramazanoğlu",
"Fethi M",
""
]
] | We show that spinor fields nonminimally coupled to gravity can grow spontaneously in the presence of matter. We name this phenomenon spontaneous spinorization after the spontaneous scalarization scenario in scalar-tensor theories. Underlying reason for the growth of the spinor is an instability similar to the tachyon of spontaneous scalarization. We first present the structure of a tachyonic Dirac equation, and incorporate it into the matter coupling in gravity. This causes the zero-spinor solution to be unstable and leads to spontaneous growth. We investigate the behavior of the resulting theory for a spherically symmetric neutron star that has grown a spinor cloud. Spontaneous spinorization has the potential to lead to order-of-unity deviations from general relativity in strong fields in a similar manner to its close relative spontaneous scalarization. This makes the theory especially relevant to gravitational wave science and neutron star astrophysics. |
0708.2783 | Janusz Garecki Prof | Janusz Garecki | On Energy of the Friedman Universes in Conformally Flat Coordinates | 11 pages, no figures, Revtex4. Abstract extended. Acknowledgements
added. References added | Acta Phys.Polon.B39:781-797,2008 | null | null | gr-qc | null | Recently many authors have calculated the energy of the Friedman universes by
using double index energy-momentum complexes in Cartesian comoving coordinates
$(t,x,y,z)$ and concluded that the flat and closed Friedman universes are
energy-free. We show in this paper by using Einstein canonical energy-momentum
complex and by doing calculations in conformally flat coordinates that such
conclusion is incorrect. The results obtained in this paper are compatible with
the results of the our previous paper \cite{Gar07} where we have used
coordinate-independent averaged relative energy-momentum tensors to analyze
Friedman universes.
| [
{
"created": "Tue, 21 Aug 2007 12:53:32 GMT",
"version": "v1"
},
{
"created": "Fri, 24 Aug 2007 12:45:14 GMT",
"version": "v2"
},
{
"created": "Mon, 3 Sep 2007 12:30:28 GMT",
"version": "v3"
},
{
"created": "Tue, 2 Oct 2007 11:58:35 GMT",
"version": "v4"
}
] | 2011-04-26 | [
[
"Garecki",
"Janusz",
""
]
] | Recently many authors have calculated the energy of the Friedman universes by using double index energy-momentum complexes in Cartesian comoving coordinates $(t,x,y,z)$ and concluded that the flat and closed Friedman universes are energy-free. We show in this paper by using Einstein canonical energy-momentum complex and by doing calculations in conformally flat coordinates that such conclusion is incorrect. The results obtained in this paper are compatible with the results of the our previous paper \cite{Gar07} where we have used coordinate-independent averaged relative energy-momentum tensors to analyze Friedman universes. |
0807.0885 | Ming Lei Tong | Ming-lei Tong, Yang Zhang, Fang-Yu Li | Using polarized maser to detect high-frequency relic gravitational waves | 20 pages, 6 figures, accepted for Phys. Rev. D | Phys.Rev.D78:024041,2008 | 10.1103/PhysRevD.78.024041 | null | gr-qc | http://creativecommons.org/licenses/by-nc-sa/3.0/ | A GHz maser beam with Gaussian-type distribution passing through a homogenous
static magnetic field can be used to detect gravitational waves (GWs) with the
same frequency. The presence of GWs will perturb the electromagnetic (EM)
fields, giving rise to perturbed photon fluxes (PPFs). After being reflected by
a fractal membrane, the perturbed photons suffer little decay and can be
measured by a microwave receiver. This idea has been explored to certain extent
as a method for very high frequency gravitational waves. In this paper, we
examine and develop this method more extensively, and confront the possible
detection with the predicted signal of relic gravitational waves (RGWs). A
maser beam with high linear polarization is used to reduce the background
photon fluxes (BPFs) in the detecting direction as the main noise. As a key
factor of applicability of this method, we give a preliminary estimation of the
sensitivity of a sample detector limited by thermal noise using currently
common technology.
The minimal detectable amplitude of GWs is found to be
$h_{\rm{min}}\sim10^{-30}$. Comparing with the known spectrum of the RGWs in
the accelerating universe for $\beta=-1.9$, there is still roughly a gap of
$4\sim 5$ orders. However, possible improvements on the detector can further
narrow down the gap and make it a feasible method to detect high frequency
RGWs.
| [
{
"created": "Sun, 6 Jul 2008 03:45:11 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Tong",
"Ming-lei",
""
],
[
"Zhang",
"Yang",
""
],
[
"Li",
"Fang-Yu",
""
]
] | A GHz maser beam with Gaussian-type distribution passing through a homogenous static magnetic field can be used to detect gravitational waves (GWs) with the same frequency. The presence of GWs will perturb the electromagnetic (EM) fields, giving rise to perturbed photon fluxes (PPFs). After being reflected by a fractal membrane, the perturbed photons suffer little decay and can be measured by a microwave receiver. This idea has been explored to certain extent as a method for very high frequency gravitational waves. In this paper, we examine and develop this method more extensively, and confront the possible detection with the predicted signal of relic gravitational waves (RGWs). A maser beam with high linear polarization is used to reduce the background photon fluxes (BPFs) in the detecting direction as the main noise. As a key factor of applicability of this method, we give a preliminary estimation of the sensitivity of a sample detector limited by thermal noise using currently common technology. The minimal detectable amplitude of GWs is found to be $h_{\rm{min}}\sim10^{-30}$. Comparing with the known spectrum of the RGWs in the accelerating universe for $\beta=-1.9$, there is still roughly a gap of $4\sim 5$ orders. However, possible improvements on the detector can further narrow down the gap and make it a feasible method to detect high frequency RGWs. |
2403.02119 | Jos\'e De Jes\'us Padua Arg\"uelles | Bianca Dittrich, Ted Jacobson, Jos\'e Padua-Arg\"uelles | De Sitter horizon entropy from a simplicial Lorentzian path integral | 24 pages, 12 figures | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The dimension of the Hilbert space of a quantum gravitational system can be
written formally as a path integral partition function over Lorentzian metrics.
We implement this in a 2+1 dimensional simplicial minisuperspace model in which
the system is a spatial topological disc, and recover by contour deformation
through a Euclidean saddle the entropy of the de Sitter static patch, up to
discretization artifacts. The model illustrates the importance of integration
over both positive and negative lapse to enforce the gravitational constraints,
and of restriction to complex metrics for which the fluctuation integrals would
converge. Although a strictly Lorentzian path integral is oscillatory, an
exponentially large partition function results from unavoidable imaginary
contributions to the action. These arise from analytic continuation of the
simplicial (Regge) action for configurations with codimension-2 simplices where
the metric fails to be Lorentzian. In particular, the dominant contribution
comes from configurations with contractible closed timelike curves that
encircle the boundary of the disc, in close correspondence with recent
continuum results.
| [
{
"created": "Mon, 4 Mar 2024 15:24:22 GMT",
"version": "v1"
}
] | 2024-03-05 | [
[
"Dittrich",
"Bianca",
""
],
[
"Jacobson",
"Ted",
""
],
[
"Padua-Argüelles",
"José",
""
]
] | The dimension of the Hilbert space of a quantum gravitational system can be written formally as a path integral partition function over Lorentzian metrics. We implement this in a 2+1 dimensional simplicial minisuperspace model in which the system is a spatial topological disc, and recover by contour deformation through a Euclidean saddle the entropy of the de Sitter static patch, up to discretization artifacts. The model illustrates the importance of integration over both positive and negative lapse to enforce the gravitational constraints, and of restriction to complex metrics for which the fluctuation integrals would converge. Although a strictly Lorentzian path integral is oscillatory, an exponentially large partition function results from unavoidable imaginary contributions to the action. These arise from analytic continuation of the simplicial (Regge) action for configurations with codimension-2 simplices where the metric fails to be Lorentzian. In particular, the dominant contribution comes from configurations with contractible closed timelike curves that encircle the boundary of the disc, in close correspondence with recent continuum results. |
1410.5104 | Felipe Faria | F. F. Faria | Late cosmology in massive conformal gravity | v2: 11 pages, 1 figure, title changed, cosmological solutions added;
v3: 8 pages, major changes; v4: 11 pages, updated version; v5: title changed,
stability analysis included, matches the published version | Mod. Phys. Lett. A. 36, 2150115 (2021) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper we find the cosmological solutions of the massive conformal
gravity field equations in the presence of matter fields. In particular, we
show that the solution of negative curvature is in good agreement with the late
universe.
| [
{
"created": "Sun, 19 Oct 2014 19:10:09 GMT",
"version": "v1"
},
{
"created": "Fri, 25 Sep 2015 04:11:04 GMT",
"version": "v2"
},
{
"created": "Mon, 14 Aug 2017 01:57:08 GMT",
"version": "v3"
},
{
"created": "Wed, 6 Mar 2019 01:59:39 GMT",
"version": "v4"
},
{
"cr... | 2021-06-14 | [
[
"Faria",
"F. F.",
""
]
] | In this paper we find the cosmological solutions of the massive conformal gravity field equations in the presence of matter fields. In particular, we show that the solution of negative curvature is in good agreement with the late universe. |
2203.13914 | Lavinia Heisenberg | Lavinia Heisenberg, Simon Kuhn and Laurens Walleghem | Wald's entropy in Coincident General Relativity | 30 pages | null | 10.1088/1361-6382/ac987d | null | gr-qc hep-th math-ph math.MP | http://creativecommons.org/licenses/by/4.0/ | The equivalence principle and its universality enables the geometrical
formulation of gravity. In the standard formulation of General Relativity \'a
la Einstein, the gravitational interaction is geometrized in terms of the
spacetime curvature. However, if we embrace the geometrical character of
gravity, two alternative, though equivalent, formulations of General Relativity
emerge in flat spacetimes, in which gravity is fully ascribed either to torsion
or to non-metricity. The latter allows a much simpler formulation of General
Relativity oblivious to the affine spacetime structure, the Coincident General
Relativity. The entropy of a black hole can be computed using the Euclidean
path integral approach, which strongly relies on the addition of boundary or
regulating terms in the standard formulation of General Relativity. A more
fundamental derivation can be performed using Wald's formula, in which the
entropy is directly related to Noether charges and is applicable to general
theories with diffeomorphism invariance. In this work we extend Wald's Noether
charge method for calculating black hole entropy to spacetimes endowed with
non-metricity. Using this method, we show that Coincident General Relativity
with an improved action principle gives the same entropy as the well-known
entropy in standard General Relativity. Furthermore the first law of black hole
thermodynamics holds and an explicit expression for the energy appearing in the
first law is obtained.
| [
{
"created": "Fri, 25 Mar 2022 21:17:32 GMT",
"version": "v1"
}
] | 2022-11-23 | [
[
"Heisenberg",
"Lavinia",
""
],
[
"Kuhn",
"Simon",
""
],
[
"Walleghem",
"Laurens",
""
]
] | The equivalence principle and its universality enables the geometrical formulation of gravity. In the standard formulation of General Relativity \'a la Einstein, the gravitational interaction is geometrized in terms of the spacetime curvature. However, if we embrace the geometrical character of gravity, two alternative, though equivalent, formulations of General Relativity emerge in flat spacetimes, in which gravity is fully ascribed either to torsion or to non-metricity. The latter allows a much simpler formulation of General Relativity oblivious to the affine spacetime structure, the Coincident General Relativity. The entropy of a black hole can be computed using the Euclidean path integral approach, which strongly relies on the addition of boundary or regulating terms in the standard formulation of General Relativity. A more fundamental derivation can be performed using Wald's formula, in which the entropy is directly related to Noether charges and is applicable to general theories with diffeomorphism invariance. In this work we extend Wald's Noether charge method for calculating black hole entropy to spacetimes endowed with non-metricity. Using this method, we show that Coincident General Relativity with an improved action principle gives the same entropy as the well-known entropy in standard General Relativity. Furthermore the first law of black hole thermodynamics holds and an explicit expression for the energy appearing in the first law is obtained. |
1602.04337 | Pedro Bicudo | Pedro Bicudo | Tighter bounds on a hypothetical graviton screening mass from the
gravitational wave observation GW150914 at LIGO | 6 pages, 1 figure, 1 table, new version with more clarified details
and references added | null | null | null | gr-qc hep-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | While quantum gravity is not solved yet, a screening mass for the graviton
remains theoretically possible. If such a mass would screen gravity at
distances of the order of the cluster galaxy radius, it could account for the
universe expansion. The modified Newtonian dynamics model also could be related
to a screening graviton mass at inter-galactic scales. Moreover, massive spin-2
theories constitute a very active theoretical topic. We briefly show how the
very recent LIGO gravitational wave observation GW150914, emitted by a binary
black hole merger distant $\sim 1.3 \times 10^9$ ly from the Earth, tightens
the phenomenological bound on a massive graviton or on the screening of
gravity.
| [
{
"created": "Sat, 13 Feb 2016 14:28:07 GMT",
"version": "v1"
},
{
"created": "Sun, 21 Feb 2016 00:30:51 GMT",
"version": "v2"
},
{
"created": "Tue, 29 Mar 2016 15:38:29 GMT",
"version": "v3"
}
] | 2016-03-30 | [
[
"Bicudo",
"Pedro",
""
]
] | While quantum gravity is not solved yet, a screening mass for the graviton remains theoretically possible. If such a mass would screen gravity at distances of the order of the cluster galaxy radius, it could account for the universe expansion. The modified Newtonian dynamics model also could be related to a screening graviton mass at inter-galactic scales. Moreover, massive spin-2 theories constitute a very active theoretical topic. We briefly show how the very recent LIGO gravitational wave observation GW150914, emitted by a binary black hole merger distant $\sim 1.3 \times 10^9$ ly from the Earth, tightens the phenomenological bound on a massive graviton or on the screening of gravity. |
gr-qc/0504147 | Hanno Sahlmann | Jerzy Lewandowski, Andrzej Okolow, Hanno Sahlmann and Thomas Thiemann | Uniqueness of diffeomorphism invariant states on holonomy-flux algebras | 38 pages, one figure. v2: Minor changes, final version, as published
in CMP | Commun.Math.Phys.267:703-733,2006 | 10.1007/s00220-006-0100-7 | AEI-2005-093, CGPG-04/5-3 | gr-qc hep-th math-ph math.MP | null | Loop quantum gravity is an approach to quantum gravity that starts from the
Hamiltonian formulation in terms of a connection and its canonical conjugate.
Quantization proceeds in the spirit of Dirac: First one defines an algebra of
basic kinematical observables and represents it through operators on a suitable
Hilbert space. In a second step, one implements the constraints. The main
result of the paper concerns the representation theory of the kinematical
algebra: We show that there is only one cyclic representation invariant under
spatial diffeomorphisms.
While this result is particularly important for loop quantum gravity, we are
rather general: The precise definition of the abstract *-algebra of the basic
kinematical observables we give could be used for any theory in which the
configuration variable is a connection with a compact structure group. The
variables are constructed from the holonomy map and from the fluxes of the
momentum conjugate to the connection. The uniqueness result is relevant for any
such theory invariant under spatial diffeomorphisms or being a part of a
diffeomorphism invariant theory.
| [
{
"created": "Fri, 29 Apr 2005 18:34:19 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Sep 2006 09:46:38 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Lewandowski",
"Jerzy",
""
],
[
"Okolow",
"Andrzej",
""
],
[
"Sahlmann",
"Hanno",
""
],
[
"Thiemann",
"Thomas",
""
]
] | Loop quantum gravity is an approach to quantum gravity that starts from the Hamiltonian formulation in terms of a connection and its canonical conjugate. Quantization proceeds in the spirit of Dirac: First one defines an algebra of basic kinematical observables and represents it through operators on a suitable Hilbert space. In a second step, one implements the constraints. The main result of the paper concerns the representation theory of the kinematical algebra: We show that there is only one cyclic representation invariant under spatial diffeomorphisms. While this result is particularly important for loop quantum gravity, we are rather general: The precise definition of the abstract *-algebra of the basic kinematical observables we give could be used for any theory in which the configuration variable is a connection with a compact structure group. The variables are constructed from the holonomy map and from the fluxes of the momentum conjugate to the connection. The uniqueness result is relevant for any such theory invariant under spatial diffeomorphisms or being a part of a diffeomorphism invariant theory. |
1912.10690 | Che-Yu Chen | Che-Yu Chen | Threshold of primordial black hole formation in
Eddington-inspired-Born-Infeld gravity | 14 pages, 1 figure. Updated to match the published version | Int.J.Mod.Phys.D 30 (2021) 02, 2150010 | 10.1142/S0218271821500103 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is believed that primordial black holes (PBHs), if they exist, can serve
as a powerful tool to probe the early stage of the cosmic history. Essentially,
in the radiation dominated universe, PBHs could form by the gravitational
collapse of overdense primordial perturbations produced during inflation. In
this picture, one important ingredient is the threshold of density contrast,
which defines the onset of PBH formation. In the literature, most of the
estimations of threshold, no matter numerically or analytically, are
implemented in the framework of general relativity (GR). In this paper, by
performing analytic estimations, we point out that the threshold for PBH
formation depends on the gravitational theory under consideration. In GR, given
a fixed equation of state, the analytic estimations adopted in this paper give
a constant value of the formation threshold. If the theory is characterized by
additional mass scales other than the Planck mass, the estimated threshold of
density contrast may depend on the energy scale of the universe at the time of
PBH formation. In this paper, we consider the Eddington-inspired-Born-Infeld
gravity as an example. We find that the threshold would be enhanced if the
Born-Infeld coupling constant is positive, and would be suppressed for a
negative coupling constant. Also, we show explicitly that the threshold depends
on the energy scale of the universe at the PBH formation time. This conclusion
is expected to be valid for any gravitational theory characterized by
additional mass scales, suggesting the possibility of testing gravitational
theories with PBHs.
| [
{
"created": "Mon, 23 Dec 2019 08:54:58 GMT",
"version": "v1"
},
{
"created": "Fri, 27 Dec 2019 04:35:36 GMT",
"version": "v2"
},
{
"created": "Thu, 23 Apr 2020 09:55:22 GMT",
"version": "v3"
},
{
"created": "Wed, 10 Feb 2021 06:59:01 GMT",
"version": "v4"
}
] | 2021-02-11 | [
[
"Chen",
"Che-Yu",
""
]
] | It is believed that primordial black holes (PBHs), if they exist, can serve as a powerful tool to probe the early stage of the cosmic history. Essentially, in the radiation dominated universe, PBHs could form by the gravitational collapse of overdense primordial perturbations produced during inflation. In this picture, one important ingredient is the threshold of density contrast, which defines the onset of PBH formation. In the literature, most of the estimations of threshold, no matter numerically or analytically, are implemented in the framework of general relativity (GR). In this paper, by performing analytic estimations, we point out that the threshold for PBH formation depends on the gravitational theory under consideration. In GR, given a fixed equation of state, the analytic estimations adopted in this paper give a constant value of the formation threshold. If the theory is characterized by additional mass scales other than the Planck mass, the estimated threshold of density contrast may depend on the energy scale of the universe at the time of PBH formation. In this paper, we consider the Eddington-inspired-Born-Infeld gravity as an example. We find that the threshold would be enhanced if the Born-Infeld coupling constant is positive, and would be suppressed for a negative coupling constant. Also, we show explicitly that the threshold depends on the energy scale of the universe at the PBH formation time. This conclusion is expected to be valid for any gravitational theory characterized by additional mass scales, suggesting the possibility of testing gravitational theories with PBHs. |
2110.02353 | Gabriela Carvalho | G. C. Carvalho, M. E. X. Guimar\~aes, P. O. Mesquita and J. L. Neto | Formation and Evolution of Wakes in the Spacetime Generated by a Cosmic
String in $f(R)$ Theory of Gravity | null | Journal of High Energy Physics, Gravitation and Cosmology 2021 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The formation and evolution of cosmic string wakes in the framework of a
$f(R)$ theory of gravity are investigated in this work. We consider a simple
model in which baryonic matter flows past a cosmic string. We treat this
problem in the Zel'dovich approximation. We compare our results with previous
results obtained in the context of General Relativity and Scalar-Theories of
Gravity.
| [
{
"created": "Tue, 5 Oct 2021 20:48:59 GMT",
"version": "v1"
}
] | 2021-10-07 | [
[
"Carvalho",
"G. C.",
""
],
[
"Guimarães",
"M. E. X.",
""
],
[
"Mesquita",
"P. O.",
""
],
[
"Neto",
"J. L.",
""
]
] | The formation and evolution of cosmic string wakes in the framework of a $f(R)$ theory of gravity are investigated in this work. We consider a simple model in which baryonic matter flows past a cosmic string. We treat this problem in the Zel'dovich approximation. We compare our results with previous results obtained in the context of General Relativity and Scalar-Theories of Gravity. |
1402.0261 | Friedrich W. Hehl | Friedrich W. Hehl (Cologne and Columbia, MO) | On energy-momentum and spin/helicity of quark and gluon fields | 10 pages latex. Invited talk delivered at the XV Workshop on High
Energy Spin Physics `DSPIN-13' in Dubna, Russia, 08--12 October 2013 | null | null | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In special relativity, quantum matter can be classified according to
mass-energy and spin. The corresponding field-theoretical notions are the
energy-momentum-stress tensor T and the spin angular momentum tensor S. Since
each object in physics carries energy and, if fermionic, also spin, the notions
of T and S can be spotted in all domains of physics. We discuss the T and S
currents in Special Relativity (SR), in General Relativity (GR), and in the
Einstein-Cartan theory of gravity (EC). We collect our results in 4 theses: (i)
The quark energy-momentum and the quark spin are described correctly by the
canonical (Noether) currents T and S, respectively. (ii) The gluon
energy-momentum current is described correctly by the (symmetric and gauge
invariant) Minkowski type current. Its (Lorentz) spin current vanishes, S = 0.
However, it carries helicity of plus or minus one. (iii) GR contradicts thesis
(i), but is compatible with thesis (ii). (iv) Within the viable EC-theory, our
theses (i) and (ii) are fulfilled and, thus, we favor this gravitational
theory.
| [
{
"created": "Sun, 2 Feb 2014 23:32:10 GMT",
"version": "v1"
}
] | 2014-02-04 | [
[
"Hehl",
"Friedrich W.",
"",
"Cologne and Columbia, MO"
]
] | In special relativity, quantum matter can be classified according to mass-energy and spin. The corresponding field-theoretical notions are the energy-momentum-stress tensor T and the spin angular momentum tensor S. Since each object in physics carries energy and, if fermionic, also spin, the notions of T and S can be spotted in all domains of physics. We discuss the T and S currents in Special Relativity (SR), in General Relativity (GR), and in the Einstein-Cartan theory of gravity (EC). We collect our results in 4 theses: (i) The quark energy-momentum and the quark spin are described correctly by the canonical (Noether) currents T and S, respectively. (ii) The gluon energy-momentum current is described correctly by the (symmetric and gauge invariant) Minkowski type current. Its (Lorentz) spin current vanishes, S = 0. However, it carries helicity of plus or minus one. (iii) GR contradicts thesis (i), but is compatible with thesis (ii). (iv) Within the viable EC-theory, our theses (i) and (ii) are fulfilled and, thus, we favor this gravitational theory. |
1108.2650 | Aharon Davidson | Aharon Davidson | Holographic Shell Model: Stack Data Structure inside Black Holes | 4 pages, 3 figures | Int. J. Mod. Phys. D, 23, 1450041 (2014) | 10.1142/S0218271814500412 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We suggest that bits of information inhabit, universally and holographically,
the entire black hole interior, a bit per a light sheet unit interval of order
Planck area difference. The number of distinguishable (tagged by a binary code)
configurations, counted within the context of a discrete holographic shell
model, is given by the Catalan series. The area entropy formula is recovered,
including the universal logarithmic correction, and the equipartition of mass
per degree of freedom is proven. The black hole information storage resembles a
stack data structure.
| [
{
"created": "Fri, 12 Aug 2011 16:00:29 GMT",
"version": "v1"
}
] | 2015-03-19 | [
[
"Davidson",
"Aharon",
""
]
] | We suggest that bits of information inhabit, universally and holographically, the entire black hole interior, a bit per a light sheet unit interval of order Planck area difference. The number of distinguishable (tagged by a binary code) configurations, counted within the context of a discrete holographic shell model, is given by the Catalan series. The area entropy formula is recovered, including the universal logarithmic correction, and the equipartition of mass per degree of freedom is proven. The black hole information storage resembles a stack data structure. |
1210.6833 | Laszlo Arpad Gergely | Marek Dwornik, Zolt\'an Keresztes, L\'aszl\'o \'Arp\'ad Gergely | Modified gravity theories and dark matter models tested by galactic
rotation curves | submitted to the proceedings of the conference on Relativity and
Gravitation: 100 Years after Einstein in Prague | Springer Proceedings in Physics 157, 427-430 (2014) | 10.1007/978-3-319-06761-2_59 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Bose-Einstein condensate dark matter model and Randall-Sundrum type 2
brane-world theory are tested with galactic rotation curves. Analytical
expressions are derived for the rotational velocities of test particles around
the galactic center in both cases. The velocity profiles are fitted to the
observed rotation curve data of high surface brightness and low surface
brightness galaxies. The brane-world model fits better the rotation curves with
asymptotically flat behaviour.
| [
{
"created": "Thu, 25 Oct 2012 13:39:48 GMT",
"version": "v1"
}
] | 2014-09-12 | [
[
"Dwornik",
"Marek",
""
],
[
"Keresztes",
"Zoltán",
""
],
[
"Gergely",
"László Árpád",
""
]
] | Bose-Einstein condensate dark matter model and Randall-Sundrum type 2 brane-world theory are tested with galactic rotation curves. Analytical expressions are derived for the rotational velocities of test particles around the galactic center in both cases. The velocity profiles are fitted to the observed rotation curve data of high surface brightness and low surface brightness galaxies. The brane-world model fits better the rotation curves with asymptotically flat behaviour. |
1812.01809 | Carlos A. S. Almeida | L. J. S. Sousa, J. E. G. Silva, W. T. Cruz and C. A. S. Almeida | Geometric standing wave braneworld and field localization in Lyra
manifold | 16 pages, 1 figure | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we propose a standing wave braneworld based on Lyra geometry
scenario. The Lyra displacement vector provides a modification in Einstein
equations which can be interpreted as a noninteracting phantom scalar. From the
Einstein's equation in Lyra manifold, a 5D standing wave braneworld is
constructed in the presence of a cosmological constant. Unlike other standing
wave solutions presented in the literature, no matter field is necessary to
obtain these new solutions. We analyze the properties of the scalar, gauge
vector and fermionic fields in this model, highlighting the relevance of
geometric structure in the process of trapping matter.
| [
{
"created": "Wed, 5 Dec 2018 04:02:44 GMT",
"version": "v1"
}
] | 2018-12-06 | [
[
"Sousa",
"L. J. S.",
""
],
[
"Silva",
"J. E. G.",
""
],
[
"Cruz",
"W. T.",
""
],
[
"Almeida",
"C. A. S.",
""
]
] | In this work, we propose a standing wave braneworld based on Lyra geometry scenario. The Lyra displacement vector provides a modification in Einstein equations which can be interpreted as a noninteracting phantom scalar. From the Einstein's equation in Lyra manifold, a 5D standing wave braneworld is constructed in the presence of a cosmological constant. Unlike other standing wave solutions presented in the literature, no matter field is necessary to obtain these new solutions. We analyze the properties of the scalar, gauge vector and fermionic fields in this model, highlighting the relevance of geometric structure in the process of trapping matter. |
2112.06821 | Eirini C. Telali | Eirini C. Telali, Emmanuel N. Saridakis | Power-law holographic dark energy and cosmology | 6 pages, 3 figures | null | 10.1140/epjc/s10052-022-10411-z | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We formulate power-law holographic dark energy, which is a modified
holographic dark energy model based on the extended entropy relation arising
from the consideration of state mixing between the ground and the excited ones
in the calculation of the entanglement entropy. We construct two cases of the
scenario, imposing the usual future event horizon choice, as well as the Hubble
one. Thus, the former model is a one-parameter extension of standard
holographic dark energy, recovering it in the limit where power-law extended
entropy recovers Bekenstein-Hawking one, while the latter belongs to the class
of running vacuum models, a feature that may reveal the connection between
holography and the renormalization group running. For both models we extract
the differential equation that determines the evolution of the dark-energy
density parameter and we provide the expression for the corresponding
equation-of-state parameter. We find that the scenario can describe the
sequence of epochs in the Universe evolution, namely the domination of matter
followed by the domination of dark energy. Moreover, the dark-energy equation
of state presents a rich behavior, lying in the quintessence regime or passing
into the phantom one too, depending on the values of the two model parameters,
a behavior that is richer than the one of standard holographic dark energy.
| [
{
"created": "Mon, 13 Dec 2021 17:33:30 GMT",
"version": "v1"
},
{
"created": "Tue, 24 May 2022 08:41:18 GMT",
"version": "v2"
}
] | 2022-05-25 | [
[
"Telali",
"Eirini C.",
""
],
[
"Saridakis",
"Emmanuel N.",
""
]
] | We formulate power-law holographic dark energy, which is a modified holographic dark energy model based on the extended entropy relation arising from the consideration of state mixing between the ground and the excited ones in the calculation of the entanglement entropy. We construct two cases of the scenario, imposing the usual future event horizon choice, as well as the Hubble one. Thus, the former model is a one-parameter extension of standard holographic dark energy, recovering it in the limit where power-law extended entropy recovers Bekenstein-Hawking one, while the latter belongs to the class of running vacuum models, a feature that may reveal the connection between holography and the renormalization group running. For both models we extract the differential equation that determines the evolution of the dark-energy density parameter and we provide the expression for the corresponding equation-of-state parameter. We find that the scenario can describe the sequence of epochs in the Universe evolution, namely the domination of matter followed by the domination of dark energy. Moreover, the dark-energy equation of state presents a rich behavior, lying in the quintessence regime or passing into the phantom one too, depending on the values of the two model parameters, a behavior that is richer than the one of standard holographic dark energy. |
1801.05843 | Zachary Fifer | Zack Fifer, Theo Torres, Sebastian Erne, Anastasios Avgoustidis,
Richard J. A. Hill, and Silke Weinfurtner | Mimicking inflation with 2-fluid systems in a strong gradient magnetic
field | 6 pages, 3 figures | Phys. Rev. E 99, 031101 (2019) | 10.1103/PhysRevE.99.031101 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the standard cosmological picture the Universe underwent a brief period of
near-exponential expansion, known as Inflation. This provides an explanation
for structure formation through the amplification of perturbations by the rapid
expansion of the fabric of space. Although this mech- anism is theoretically
well understood, it cannot be directly observed in nature. We propose a novel
experiment combining fluid dynamics and strong magnetic field physics to
simulate cosmo- logical inflation. Our proposed system consists of two
immiscible, weakly magnetised fluids moving through a strong magnetic field in
the bore of a superconducting magnet. By precisely controlling the propagation
speed of the interface waves, we can capture the essential dynamics of
inflation- ary fluctuations: interface perturbations experience a shrinking
effective horizon and are shown to transition from oscillatory to squeezed and
frozen regimes at horizon crossing.
| [
{
"created": "Wed, 17 Jan 2018 19:47:55 GMT",
"version": "v1"
}
] | 2019-04-03 | [
[
"Fifer",
"Zack",
""
],
[
"Torres",
"Theo",
""
],
[
"Erne",
"Sebastian",
""
],
[
"Avgoustidis",
"Anastasios",
""
],
[
"Hill",
"Richard J. A.",
""
],
[
"Weinfurtner",
"Silke",
""
]
] | In the standard cosmological picture the Universe underwent a brief period of near-exponential expansion, known as Inflation. This provides an explanation for structure formation through the amplification of perturbations by the rapid expansion of the fabric of space. Although this mech- anism is theoretically well understood, it cannot be directly observed in nature. We propose a novel experiment combining fluid dynamics and strong magnetic field physics to simulate cosmo- logical inflation. Our proposed system consists of two immiscible, weakly magnetised fluids moving through a strong magnetic field in the bore of a superconducting magnet. By precisely controlling the propagation speed of the interface waves, we can capture the essential dynamics of inflation- ary fluctuations: interface perturbations experience a shrinking effective horizon and are shown to transition from oscillatory to squeezed and frozen regimes at horizon crossing. |
1505.00714 | Hirotaka Yoshino | Hirotaka Yoshino, Hideo Kodama | Bosenova and Axiverse | 56 pages, 30 figures, Invited contribution to the Focus Issue on
"Black holes and fundamental fields" to appear in Classical and Quantum
Gravity | Class. Quantum Grav. 32 (2015) 214001 | 10.1088/0264-9381/32/21/214001 | KEK-TH-1820, KEK-Cosmo-169 | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We report some new interesting features of the dynamics of a string axion
field (i.e., a (pseudo-)scalar field with tiny mass with sine-Gordon-type
self-interaction) around a rotating black hole in three respects. First, we
revisit the calculation of the growth rate of superradiant instability, and
show that in some cases, overtone modes have larger growth rates than the
fundamental mode with the same angular quantum numbers when the black hole is
rapidly rotating. Next, we study the dynamical evolution of the scalar field
caused by the nonlinear self-interaction, taking attention to the dependence of
the dynamical phenomena on the axion mass and the modes. The cases in which two
superradiantly unstable modes are excited simultaneously are also studied.
Finally, we report on our preliminary simulations for gravitational wave
emission from the dynamical axion cloud in the Schwarzschild background
approximation. Our result suggests that fairly strong gravitational wave burst
is emitted during the bosenova, which could be detected by the ground-based
detectors if it happens in Our Galaxy or nearby galaxies.
| [
{
"created": "Mon, 4 May 2015 17:03:43 GMT",
"version": "v1"
}
] | 2015-10-19 | [
[
"Yoshino",
"Hirotaka",
""
],
[
"Kodama",
"Hideo",
""
]
] | We report some new interesting features of the dynamics of a string axion field (i.e., a (pseudo-)scalar field with tiny mass with sine-Gordon-type self-interaction) around a rotating black hole in three respects. First, we revisit the calculation of the growth rate of superradiant instability, and show that in some cases, overtone modes have larger growth rates than the fundamental mode with the same angular quantum numbers when the black hole is rapidly rotating. Next, we study the dynamical evolution of the scalar field caused by the nonlinear self-interaction, taking attention to the dependence of the dynamical phenomena on the axion mass and the modes. The cases in which two superradiantly unstable modes are excited simultaneously are also studied. Finally, we report on our preliminary simulations for gravitational wave emission from the dynamical axion cloud in the Schwarzschild background approximation. Our result suggests that fairly strong gravitational wave burst is emitted during the bosenova, which could be detected by the ground-based detectors if it happens in Our Galaxy or nearby galaxies. |
1807.09787 | Adam Rebei | Adam Rebei, E. A. Huerta, Sibo Wang, Sarah Habib, Roland Haas, Daniel
Johnson, Daniel George | Fusing numerical relativity and deep learning to detect higher-order
multipole waveforms from eccentric binary black hole mergers | 17 pages, 11 figures, 1 appendix, accepted to Phys. Rev. D | Phys. Rev. D 100, 044025 (2019) | 10.1103/PhysRevD.100.044025 | null | gr-qc astro-ph.HE physics.comp-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We determine the mass-ratio, eccentricity and binary inclination angles that
maximize the contribution of the higher-order waveform multipoles $(\ell, \,
|m|)= \{(2,\,2),\, (2,\,1),\, (3,\,3),\, (3,\,2), \, (3,\,1),\, (4,\,4),\,
(4,\,3),\, (4,\,2),\,(4,\,1)\}$ for the gravitational wave detection of
eccentric binary black hole mergers. We carry out this study using numerical
relativity waveforms that describe non-spinning black hole binaries with
mass-ratios $1\leq q \leq 10$, and orbital eccentricities as high as $e_0=0.18$
fifteen cycles before merger. For stellar-mass, asymmetric mass-ratio, binary
black hole mergers, and assuming LIGO's Zero Detuned High Power configuration,
we find that in regions of parameter space where black hole mergers modeled
with $\ell=|m|=2$ waveforms have vanishing signal-to-noise ratios, the
inclusion of $(\ell, \, |m|)$ modes enables the observation of these sources
with signal-to-noise ratios that range between 30\% to 45\% the signal-to-noise
ratio of optimally oriented binary black hole mergers modeled with $\ell=|m|=2$
numerical relativity waveforms. Having determined the parameter space where
$(\ell, \, |m|)$ modes are important for gravitational wave detection, we
construct waveform signals that describe these astrophysically motivate
scenarios, and demonstrate that these topologically complex signals can be
detected and characterized in real LIGO noise with deep learning algorithms.
| [
{
"created": "Wed, 25 Jul 2018 18:00:05 GMT",
"version": "v1"
},
{
"created": "Thu, 15 Aug 2019 20:47:44 GMT",
"version": "v2"
}
] | 2019-08-19 | [
[
"Rebei",
"Adam",
""
],
[
"Huerta",
"E. A.",
""
],
[
"Wang",
"Sibo",
""
],
[
"Habib",
"Sarah",
""
],
[
"Haas",
"Roland",
""
],
[
"Johnson",
"Daniel",
""
],
[
"George",
"Daniel",
""
]
] | We determine the mass-ratio, eccentricity and binary inclination angles that maximize the contribution of the higher-order waveform multipoles $(\ell, \, |m|)= \{(2,\,2),\, (2,\,1),\, (3,\,3),\, (3,\,2), \, (3,\,1),\, (4,\,4),\, (4,\,3),\, (4,\,2),\,(4,\,1)\}$ for the gravitational wave detection of eccentric binary black hole mergers. We carry out this study using numerical relativity waveforms that describe non-spinning black hole binaries with mass-ratios $1\leq q \leq 10$, and orbital eccentricities as high as $e_0=0.18$ fifteen cycles before merger. For stellar-mass, asymmetric mass-ratio, binary black hole mergers, and assuming LIGO's Zero Detuned High Power configuration, we find that in regions of parameter space where black hole mergers modeled with $\ell=|m|=2$ waveforms have vanishing signal-to-noise ratios, the inclusion of $(\ell, \, |m|)$ modes enables the observation of these sources with signal-to-noise ratios that range between 30\% to 45\% the signal-to-noise ratio of optimally oriented binary black hole mergers modeled with $\ell=|m|=2$ numerical relativity waveforms. Having determined the parameter space where $(\ell, \, |m|)$ modes are important for gravitational wave detection, we construct waveform signals that describe these astrophysically motivate scenarios, and demonstrate that these topologically complex signals can be detected and characterized in real LIGO noise with deep learning algorithms. |
1103.4121 | Mona Kamal | M. I. Wanas and Mona M. Kamal | An AP-Structure with Finslerian Flavor II: Torsion, Curvature and Other
Objects | 15 pages, LaTeX file, revised version, Journal reference inserted | Mod.Phys.Lett.A26:2065-2078,2011 | 10.1142/S021773231103653X | null | gr-qc math.DG | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | An absolute parallelism (AP-) space having Finslerian properties is called
FAP-space. This FAP-structure is more wider than both conventional AP and
Finsler structures. In the present work, more geometric objects as curvature
and torsion tensors are derived in the context of this structure. Also second
order tensors, usually needed for physical applications, are derived and
studied. Furthermore, the anti-curvature and the W-tensor are defined for the
FAP-structure. Relations between Riemannian, AP, Finsler and FAP structures are
given. These relations facilitate comparison between results of applications
carried out in the framework of these structures. We hope that the use of the
FAP-structure, in applications may throw some light on some of the problems
facing geometric field theories.
| [
{
"created": "Mon, 21 Mar 2011 19:42:02 GMT",
"version": "v1"
},
{
"created": "Wed, 14 Sep 2011 10:05:42 GMT",
"version": "v2"
}
] | 2011-09-15 | [
[
"Wanas",
"M. I.",
""
],
[
"Kamal",
"Mona M.",
""
]
] | An absolute parallelism (AP-) space having Finslerian properties is called FAP-space. This FAP-structure is more wider than both conventional AP and Finsler structures. In the present work, more geometric objects as curvature and torsion tensors are derived in the context of this structure. Also second order tensors, usually needed for physical applications, are derived and studied. Furthermore, the anti-curvature and the W-tensor are defined for the FAP-structure. Relations between Riemannian, AP, Finsler and FAP structures are given. These relations facilitate comparison between results of applications carried out in the framework of these structures. We hope that the use of the FAP-structure, in applications may throw some light on some of the problems facing geometric field theories. |
1110.1018 | Miguel Socolovsky | Miguel Socolovsky | Fibre bundles, connections, general relativity, and Einstein-Cartan
theory | 60 pages | null | null | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present in the most natural way, that is, in the context of the theory of
vector and principal bundles and connections in them, fundamental geometrical
concepts related to General Relativity and one of its extensions, the
Einstein-Cartan theory.
| [
{
"created": "Wed, 5 Oct 2011 15:12:15 GMT",
"version": "v1"
}
] | 2015-03-13 | [
[
"Socolovsky",
"Miguel",
""
]
] | We present in the most natural way, that is, in the context of the theory of vector and principal bundles and connections in them, fundamental geometrical concepts related to General Relativity and one of its extensions, the Einstein-Cartan theory. |
1602.01152 | George F. Chapline | George Chapline and James Barbieri | Was there a negative vacuum energy in your past? | 16 pages, 3 figures | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A model for gravitational collapse where the event horizon is a quantum
critical phase transition is extended to provide an explanation for the origin
of the observable universe, where the expanding universe that we observe today
was proceeded by a flat universe with a negative cosmological constant. In
principal this allows one derive all the features of our universe from a single
parameter: the magnitude of the pre-big bang negative vacuum energy density. In
this paper a simple model for the big bang is introduced which allows us to
relate the present day energy density and temperature fluctuations of the CMB,
to the present day density of dark matter. This model for the big bang also
makes a dramatic prediction: dark matter mostly consists of compact objects
with a masses on the order of 10^4 solar masses. Remarkably this is consistent
with numerical simulations for how primordial fluctuations in the density of
dark give rise to the observed inhomogeneous distribution of matter in our
universe. Our model for the big bang also allows for the production of some
compact objects with masses greater than 10^4 solar masses, which is consistent
with numerical simulations of structure formation which require massive
primordial comapact objects as the seeds for galaxies in order to explain
galactic morphologies.
| [
{
"created": "Tue, 2 Feb 2016 23:12:25 GMT",
"version": "v1"
},
{
"created": "Sat, 6 Feb 2016 01:57:57 GMT",
"version": "v2"
}
] | 2016-02-09 | [
[
"Chapline",
"George",
""
],
[
"Barbieri",
"James",
""
]
] | A model for gravitational collapse where the event horizon is a quantum critical phase transition is extended to provide an explanation for the origin of the observable universe, where the expanding universe that we observe today was proceeded by a flat universe with a negative cosmological constant. In principal this allows one derive all the features of our universe from a single parameter: the magnitude of the pre-big bang negative vacuum energy density. In this paper a simple model for the big bang is introduced which allows us to relate the present day energy density and temperature fluctuations of the CMB, to the present day density of dark matter. This model for the big bang also makes a dramatic prediction: dark matter mostly consists of compact objects with a masses on the order of 10^4 solar masses. Remarkably this is consistent with numerical simulations for how primordial fluctuations in the density of dark give rise to the observed inhomogeneous distribution of matter in our universe. Our model for the big bang also allows for the production of some compact objects with masses greater than 10^4 solar masses, which is consistent with numerical simulations of structure formation which require massive primordial comapact objects as the seeds for galaxies in order to explain galactic morphologies. |
2310.12138 | Dallas DeGan | Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven
Arzoumanian, Jeremy Baier, Paul T. Baker, Bence B\'ecsy, Laura Blecha, Adam
Brazier, Paul R. Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, J.
Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M.
Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn
Crowter, Megan E. DeCesar, Dallas DeGan, Paul B. Demorest, Timothy Dolch,
Brendan Drachler, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca,
Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser,
Deborah C. Good, Kayhan G\"ultekin, Jeffrey S. Hazboun, Ross J. Jennings,
Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke
Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William
G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R.
Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander
McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W.
Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Priyamvada Natarajan,
Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T.
Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M.
Ransom, Paul S. Ray, Joseph D. Romano, Alexander Saffer, Shashwat C.
Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Brent J.
Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H.
Stairs, Daniel R. Stinebring, Kevin Stovall, Jerry P. Sun, Abhimanyu
Susobhanan, Joseph K. Swiggum, Jacob A. Taylor, Stephen R. Taylor, E. Turner,
Caner Unal, Michele Vallisneri, Sarah J. Vigeland, Haley M. Wahl, Caitlin A.
Witt, Olivia Young | The NANOGrav 15-year data set: Search for Transverse Polarization Modes
in the Gravitational-Wave Background | 11 pages, 5 figures | null | null | null | gr-qc astro-ph.GA astro-ph.HE | http://creativecommons.org/licenses/by/4.0/ | Recently we found compelling evidence for a gravitational wave background
with Hellings and Downs (HD) correlations in our 15-year data set. These
correlations describe gravitational waves as predicted by general relativity,
which has two transverse polarization modes. However, more general metric
theories of gravity can have additional polarization modes which produce
different interpulsar correlations. In this work we search the NANOGrav 15-year
data set for evidence of a gravitational wave background with quadrupolar
Hellings and Downs (HD) and Scalar Transverse (ST) correlations. We find that
HD correlations are the best fit to the data, and no significant evidence in
favor of ST correlations. While Bayes factors show strong evidence for a
correlated signal, the data does not strongly prefer either correlation
signature, with Bayes factors $\sim 2$ when comparing HD to ST correlations,
and $\sim 1$ for HD plus ST correlations to HD correlations alone. However,
when modeled alongside HD correlations, the amplitude and spectral index
posteriors for ST correlations are uninformative, with the HD process
accounting for the vast majority of the total signal. Using the optimal
statistic, a frequentist technique that focuses on the pulsar-pair
cross-correlations, we find median signal-to-noise-ratios of 5.0 for HD and 4.6
for ST correlations when fit for separately, and median signal-to-noise-ratios
of 3.5 for HD and 3.0 for ST correlations when fit for simultaneously. While
the signal-to-noise-ratios for each of the correlations are comparable, the
estimated amplitude and spectral index for HD are a significantly better fit to
the total signal, in agreement with our Bayesian analysis.
| [
{
"created": "Wed, 18 Oct 2023 17:49:33 GMT",
"version": "v1"
}
] | 2023-10-19 | [
[
"Agazie",
"Gabriella",
""
],
[
"Anumarlapudi",
"Akash",
""
],
[
"Archibald",
"Anne M.",
""
],
[
"Arzoumanian",
"Zaven",
""
],
[
"Baier",
"Jeremy",
""
],
[
"Baker",
"Paul T.",
""
],
[
"Bécsy",
"Bence",
""
... | Recently we found compelling evidence for a gravitational wave background with Hellings and Downs (HD) correlations in our 15-year data set. These correlations describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more general metric theories of gravity can have additional polarization modes which produce different interpulsar correlations. In this work we search the NANOGrav 15-year data set for evidence of a gravitational wave background with quadrupolar Hellings and Downs (HD) and Scalar Transverse (ST) correlations. We find that HD correlations are the best fit to the data, and no significant evidence in favor of ST correlations. While Bayes factors show strong evidence for a correlated signal, the data does not strongly prefer either correlation signature, with Bayes factors $\sim 2$ when comparing HD to ST correlations, and $\sim 1$ for HD plus ST correlations to HD correlations alone. However, when modeled alongside HD correlations, the amplitude and spectral index posteriors for ST correlations are uninformative, with the HD process accounting for the vast majority of the total signal. Using the optimal statistic, a frequentist technique that focuses on the pulsar-pair cross-correlations, we find median signal-to-noise-ratios of 5.0 for HD and 4.6 for ST correlations when fit for separately, and median signal-to-noise-ratios of 3.5 for HD and 3.0 for ST correlations when fit for simultaneously. While the signal-to-noise-ratios for each of the correlations are comparable, the estimated amplitude and spectral index for HD are a significantly better fit to the total signal, in agreement with our Bayesian analysis. |
0712.4301 | J. Ponce de Leon | J. Ponce de Leon | Embeddings for 4D Einstein equations with a cosmological constant | null | Grav.Cosmol.14:241-247,2008 | 10.1134/S0202289308030067 | null | gr-qc | null | There are many ways of embedding a 4D spacetime in a given higher-dimensional
manifold while, satisfying the field equations. In this work we extend and
generalize a recent paper by Mashhoon and Wesson ({\it Gen. Rel. Gravit.} {\bf
39}, 1403(2007)) by showing different ways of embedding a solution of the 4D
Einstein equations, in vacuum with a cosmological constant, in a Ricci-flat, as
well as in an anti-de Sitter, 5D manifold. These embeddings lead to different
physics in 4D. In particular, to non-equivalent cosmological terms as functions
of the extra coordinate. We study the motion of test particles for different
embeddings and show that there is a complete equivalence between several
definitions for the effective mass of test particles measured in 4D, obtained
from different theoretical approaches like the Hamilton-Jacobi formalism and
the principle of least action. For the case under consideration, we find that
the effective mass observed in 4D is the same regardless of whether we consider
null or non-null motion in 5D.
| [
{
"created": "Fri, 28 Dec 2007 01:43:28 GMT",
"version": "v1"
},
{
"created": "Mon, 31 Dec 2007 02:23:54 GMT",
"version": "v2"
}
] | 2009-11-13 | [
[
"de Leon",
"J. Ponce",
""
]
] | There are many ways of embedding a 4D spacetime in a given higher-dimensional manifold while, satisfying the field equations. In this work we extend and generalize a recent paper by Mashhoon and Wesson ({\it Gen. Rel. Gravit.} {\bf 39}, 1403(2007)) by showing different ways of embedding a solution of the 4D Einstein equations, in vacuum with a cosmological constant, in a Ricci-flat, as well as in an anti-de Sitter, 5D manifold. These embeddings lead to different physics in 4D. In particular, to non-equivalent cosmological terms as functions of the extra coordinate. We study the motion of test particles for different embeddings and show that there is a complete equivalence between several definitions for the effective mass of test particles measured in 4D, obtained from different theoretical approaches like the Hamilton-Jacobi formalism and the principle of least action. For the case under consideration, we find that the effective mass observed in 4D is the same regardless of whether we consider null or non-null motion in 5D. |
2204.05996 | Jainendra Kumar Singh Dr. | Ashima Sood, Arun Kumar, J. K. Singh and Sushant G. Ghosh | Thermodynamic stability and P-V criticality of nonsingular-AdS black
holes endowed with clouds of strings | 12 pages, 16 figures | European Physical Journal C, (2022) 82:227 | 10.1140/epjc/s10052-022-10181-8 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We investigate the extended phase space thermodynamics of nonsingular-AdS
black holes minimally coupled to clouds of strings in which we consider the
cosmological constant ($\Lambda$) as the pressure ($P$) of the black holes and
its conjugate variable thermodynamical volume ($V$) of the black holes. Owing
to the background clouds of strings parameter ($a$), we analyse the Hawking
temperature, entropy and specific heat on horizon radius for fixed-parameter
$k$. We find that the strings clouds background does not alter small/large
black hole (SBH/LBH) phase transition but occurs at a larger horizon radius,
and two second-order phase transitions occur at a smaller horizon radius.
Indeed, the $G$--$T$ plots exhibit a swallowtail below the critical pressure,
implying that the first-order phase transition is analogous to the liquid-gas
phase transition at a lower temperature and lower critical pressure. To further
examine the analogy between nonsingular-AdS black holes and a liquid-gas
system, we derive the exact critical points and probe the effects of a cloud of
strings on $P-V$ criticality to find that the isotherms undergo liquid-gas like
phase transition for $\tilde{T}\,<\,\tilde{T}_c$ at lower $\tilde{T}_c$. We
have also calculated the critical exponents identical with Van der Walls fluid,
i.e., same as those obtained before for arbitrary other AdS black holes, which
implies that the background clouds of strings do not change the critical
exponents.
| [
{
"created": "Tue, 12 Apr 2022 12:04:06 GMT",
"version": "v1"
}
] | 2022-04-14 | [
[
"Sood",
"Ashima",
""
],
[
"Kumar",
"Arun",
""
],
[
"Singh",
"J. K.",
""
],
[
"Ghosh",
"Sushant G.",
""
]
] | We investigate the extended phase space thermodynamics of nonsingular-AdS black holes minimally coupled to clouds of strings in which we consider the cosmological constant ($\Lambda$) as the pressure ($P$) of the black holes and its conjugate variable thermodynamical volume ($V$) of the black holes. Owing to the background clouds of strings parameter ($a$), we analyse the Hawking temperature, entropy and specific heat on horizon radius for fixed-parameter $k$. We find that the strings clouds background does not alter small/large black hole (SBH/LBH) phase transition but occurs at a larger horizon radius, and two second-order phase transitions occur at a smaller horizon radius. Indeed, the $G$--$T$ plots exhibit a swallowtail below the critical pressure, implying that the first-order phase transition is analogous to the liquid-gas phase transition at a lower temperature and lower critical pressure. To further examine the analogy between nonsingular-AdS black holes and a liquid-gas system, we derive the exact critical points and probe the effects of a cloud of strings on $P-V$ criticality to find that the isotherms undergo liquid-gas like phase transition for $\tilde{T}\,<\,\tilde{T}_c$ at lower $\tilde{T}_c$. We have also calculated the critical exponents identical with Van der Walls fluid, i.e., same as those obtained before for arbitrary other AdS black holes, which implies that the background clouds of strings do not change the critical exponents. |
gr-qc/0607088 | Christian Boehmer | Christian G. Boehmer | The Einstein-Cartan-Elko system | 12 pages, no figures | AnnalenPhys.16:38-44,2007 | 10.1002/andp.200610216 | null | gr-qc hep-th | null | The present paper analyses the Einstein-Cartan theory of gravitation with
Elko spinors as sources of curvature and torsion. After minimally coupling the
Elko spinors to torsion, the spin angular momentum tensor is derived and its
structure is discussed. It shows a much richer structure than the Dirac
analogue and hence it is demonstrated that spin one half particles do not
necessarily yield only an axial vector torsion component. Moreover, it is
argued that the presence of Elko spinors partially solves the problem of
minimally coupling Maxwell fields to Einstein-Cartan theory.
| [
{
"created": "Fri, 21 Jul 2006 14:30:50 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Boehmer",
"Christian G.",
""
]
] | The present paper analyses the Einstein-Cartan theory of gravitation with Elko spinors as sources of curvature and torsion. After minimally coupling the Elko spinors to torsion, the spin angular momentum tensor is derived and its structure is discussed. It shows a much richer structure than the Dirac analogue and hence it is demonstrated that spin one half particles do not necessarily yield only an axial vector torsion component. Moreover, it is argued that the presence of Elko spinors partially solves the problem of minimally coupling Maxwell fields to Einstein-Cartan theory. |
gr-qc/9812091 | Mark D. Roberts | Mark D. Roberts | Non Metric Mass | 37 pages, no diagrams, LaTex2e | null | null | null | gr-qc hep-th | null | In general relativity g_ab;c=0 implies that the wave equation
(\Box^2-M)g_ab=0 always has M=0. If the underlying geometry is generalized to
include non-metricity this incurs M \neq 0, and the above wave equation can be
rewritten as M(x)+\td{\na}_a Q_.^a+(\ep+\fr{d}{2}-2)Q_a Q_.^a=0, where \ep=0,
1, 2, or 3, d is the dimension of the spacetime, and Q is the object of
non-metricity. The consequences of this equation and the properties of M are
investigated.
| [
{
"created": "Tue, 29 Dec 1998 16:49:17 GMT",
"version": "v1"
},
{
"created": "Wed, 30 Dec 1998 14:27:52 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Roberts",
"Mark D.",
""
]
] | In general relativity g_ab;c=0 implies that the wave equation (\Box^2-M)g_ab=0 always has M=0. If the underlying geometry is generalized to include non-metricity this incurs M \neq 0, and the above wave equation can be rewritten as M(x)+\td{\na}_a Q_.^a+(\ep+\fr{d}{2}-2)Q_a Q_.^a=0, where \ep=0, 1, 2, or 3, d is the dimension of the spacetime, and Q is the object of non-metricity. The consequences of this equation and the properties of M are investigated. |
1509.06967 | S Habib Mazharimousavi | Z. Amirabi, M. Halilsoy and S. Habib Mazharimousavi | Generation of spherically symmetric metrics in $f\left( R\right) $
gravity | 8 pages, no figure, revised version accepted for publication in EPJC | Eur. Phys. J. C 76, 338 (2016) | 10.1140/epjc/s10052-016-4164-z | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In $D-$dimensional spherically symmetric $f\left( R\right) $ gravity there
are three unknown functions to be determined from the fourth order differential
equations. It is shown that the system remarkably integrates to relate two
functions through the third one to provide reduction to second order equations
accompanied with a large class of potential solutions. The third function which
acts as the generator of the process is $F\left( R\right) =\frac{df\left(
R\right) }{dR}.$ We recall that our generating function has been employed as a
scalar field with an accompanying self-interacting potential previously which
is entirely different from our approach. Reduction of $f\left( R\right) $
theory into system of equations seems to be efficient enough to generate a
solution corresponding to each generating function. As particular examples,
besides known ones, we obtain new black hole solutions in any dimension $D$. We
further extend our analysis to cover non-zero energy-momentum tensors. Global
monopole and Maxwell sources are given as examples.
| [
{
"created": "Wed, 16 Sep 2015 09:03:55 GMT",
"version": "v1"
},
{
"created": "Tue, 29 Sep 2015 07:59:55 GMT",
"version": "v2"
},
{
"created": "Mon, 30 May 2016 06:05:49 GMT",
"version": "v3"
}
] | 2016-06-23 | [
[
"Amirabi",
"Z.",
""
],
[
"Halilsoy",
"M.",
""
],
[
"Mazharimousavi",
"S. Habib",
""
]
] | In $D-$dimensional spherically symmetric $f\left( R\right) $ gravity there are three unknown functions to be determined from the fourth order differential equations. It is shown that the system remarkably integrates to relate two functions through the third one to provide reduction to second order equations accompanied with a large class of potential solutions. The third function which acts as the generator of the process is $F\left( R\right) =\frac{df\left( R\right) }{dR}.$ We recall that our generating function has been employed as a scalar field with an accompanying self-interacting potential previously which is entirely different from our approach. Reduction of $f\left( R\right) $ theory into system of equations seems to be efficient enough to generate a solution corresponding to each generating function. As particular examples, besides known ones, we obtain new black hole solutions in any dimension $D$. We further extend our analysis to cover non-zero energy-momentum tensors. Global monopole and Maxwell sources are given as examples. |
0709.1603 | Jose Geraldo Pereira | R. Aldrovandi, J. G. Pereira, K. H. Vu | The Nonlinear Essence of Gravitational Waves | Plain Latex, 13 pages, no figures. Accepted for publication in
Foundations of Physiscs | Found.Phys.37:1503-1517,2007 | 10.1007/s10701-007-9180-2 | null | gr-qc hep-th | null | A critical review of gravitational wave theory is made. It is pointed out
that the usual linear approach to the gravitational wave theory is neither
conceptually consistent nor mathematically justified. Relying upon that
analysis it is then argued that -- analogously to a Yang-Mills propagating
field, which must be nonlinear to carry its gauge charge -- a gravitational
wave must necessarily be nonlinear to transport its own charge -- that is,
energy-momentum.
| [
{
"created": "Tue, 11 Sep 2007 12:33:40 GMT",
"version": "v1"
}
] | 2008-11-26 | [
[
"Aldrovandi",
"R.",
""
],
[
"Pereira",
"J. G.",
""
],
[
"Vu",
"K. H.",
""
]
] | A critical review of gravitational wave theory is made. It is pointed out that the usual linear approach to the gravitational wave theory is neither conceptually consistent nor mathematically justified. Relying upon that analysis it is then argued that -- analogously to a Yang-Mills propagating field, which must be nonlinear to carry its gauge charge -- a gravitational wave must necessarily be nonlinear to transport its own charge -- that is, energy-momentum. |
1911.04482 | Alexander Oliveros < | A. Oliveros and Mario A. Acero | Inflation driven by a holographic energy density | 7 pages, 2 figures, references added, minor changes, accepted for
publication in EPL | EPL 128 (2019) 5, 59001 | 10.1209/0295-5075/128/59001 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this letter we study a model of inflation in which the inflationary
regimen comes from a type of holographic energy density. In particular, we
consider the Granda-Oliveros proposal for the holographic energy density, which
contains two free dimensionless parameters, $\alpha$ and $\beta$. This
holographic energy density is associated to the so-called Granda-Oliveros
infrared cutoff (G-O cutoff). Additionally, since in the inflationary regimen
the energy scales are very high, it is necessary to modify the G-O cutoff
taking into account a correction due to the ultraviolet cutoff. In this way, we
obtain an algebraic equation which implicitly includes the Hubble parameter (as
a function of e-folding number, $N$) and from this, we calculate the Hubble
slow-roll parameters and the values of the inflationary observables: the scalar
spectral index of the curvature perturbations and its running, the tensor
spectral index and the tensor-to-scalar ratio. Finally, since the values for
these inflationary observables are known (Planck 2018 observations), we present
constraints on the parameters $\alpha$ and $\beta$ to make this a viable model.
| [
{
"created": "Mon, 11 Nov 2019 13:42:10 GMT",
"version": "v1"
},
{
"created": "Thu, 23 Jan 2020 19:26:52 GMT",
"version": "v2"
}
] | 2023-02-15 | [
[
"Oliveros",
"A.",
""
],
[
"Acero",
"Mario A.",
""
]
] | In this letter we study a model of inflation in which the inflationary regimen comes from a type of holographic energy density. In particular, we consider the Granda-Oliveros proposal for the holographic energy density, which contains two free dimensionless parameters, $\alpha$ and $\beta$. This holographic energy density is associated to the so-called Granda-Oliveros infrared cutoff (G-O cutoff). Additionally, since in the inflationary regimen the energy scales are very high, it is necessary to modify the G-O cutoff taking into account a correction due to the ultraviolet cutoff. In this way, we obtain an algebraic equation which implicitly includes the Hubble parameter (as a function of e-folding number, $N$) and from this, we calculate the Hubble slow-roll parameters and the values of the inflationary observables: the scalar spectral index of the curvature perturbations and its running, the tensor spectral index and the tensor-to-scalar ratio. Finally, since the values for these inflationary observables are known (Planck 2018 observations), we present constraints on the parameters $\alpha$ and $\beta$ to make this a viable model. |
2303.12656 | Mohamed Ould El Hadj | Mohamed Ould El Hadj | Scattering and conversion of electromagnetic and gravitational waves by
Reissner-Nordstr\"om black holes: The Regge pole description | v2: minor changes and a few typos corrected in the text to match the
published version | Phys. Rev. D 107, 104051 (2023) | 10.1103/PhysRevD.107.104051 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the problem of scattering and conversion of monochromatic
planar gravitational and electromagnetic waves impinging upon a
Reissner-Nordstr\"om black hole using a Regge pole description, i.e., a complex
angular momentum approach. For this purpose, we first compute numerically the
Regge pole spectrum for various charge-to-mass ratio configurations. We then
derive an asymptotic expressions for the lowest Regge poles, and by considering
Bohr-Sommerfeld-type quantization conditions, obtain the spectrum of weakly
damped quasinormal frequencies from the Regge trajectories. Next, we construct
the scattering and conversion amplitudes as well as the total differential
cross sections for different processes using both a complex angular momentum
representation and a partial wave expansion method. Finally, we provide an
analytical approximation of the scattering and conversion cross sections of
different processes from asymptotic expressions for the lowest Regge poles and
the associated residues based on the correspondence Regge poles, "surface
waves" propagating close to the photon (graviton) sphere. This allows us to
extract the physical interpretation encoded in the partial wave expansions in
the high-frequency regime (i.e., in the short-wavelength regime), and to
describe semiclassically with very good agreement both black hole glory and a
large part of the orbiting oscillations, thus unifying these two phenomena from
a purely wave point of view.
| [
{
"created": "Wed, 22 Mar 2023 15:34:16 GMT",
"version": "v1"
},
{
"created": "Thu, 25 May 2023 14:16:26 GMT",
"version": "v2"
}
] | 2023-05-26 | [
[
"Hadj",
"Mohamed Ould El",
""
]
] | We investigate the problem of scattering and conversion of monochromatic planar gravitational and electromagnetic waves impinging upon a Reissner-Nordstr\"om black hole using a Regge pole description, i.e., a complex angular momentum approach. For this purpose, we first compute numerically the Regge pole spectrum for various charge-to-mass ratio configurations. We then derive an asymptotic expressions for the lowest Regge poles, and by considering Bohr-Sommerfeld-type quantization conditions, obtain the spectrum of weakly damped quasinormal frequencies from the Regge trajectories. Next, we construct the scattering and conversion amplitudes as well as the total differential cross sections for different processes using both a complex angular momentum representation and a partial wave expansion method. Finally, we provide an analytical approximation of the scattering and conversion cross sections of different processes from asymptotic expressions for the lowest Regge poles and the associated residues based on the correspondence Regge poles, "surface waves" propagating close to the photon (graviton) sphere. This allows us to extract the physical interpretation encoded in the partial wave expansions in the high-frequency regime (i.e., in the short-wavelength regime), and to describe semiclassically with very good agreement both black hole glory and a large part of the orbiting oscillations, thus unifying these two phenomena from a purely wave point of view. |
1006.4806 | Sunil Maharaj | S. Thirukkanesh, S. D. Maharaj | Mixed potentials in radiative stellar collapse | 10 pages, To appear in J. Math. Phys | J.Math.Phys.51:072502,2010 | 10.1063/1.3456081 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the behaviour of a radiating star when the interior expanding,
shearing fluid particles are traveling in geodesic motion. We demonstrate that
it is possible to obtain new classes of exact solutions in terms of elementary
functions without assuming a separable form for the gravitational potentials or
initially fixing the temporal evolution of the model unlike earlier treatments.
A systematic approach enables us to write the junction condition as a Riccati
equation which under particular conditions may be transformed into a separable
equation. New classes of solutions are generated which allow for mixed spatial
and temporal dependence in the metric functions. We regain particular models
found previously from our general classes of solutions.
| [
{
"created": "Thu, 24 Jun 2010 14:50:27 GMT",
"version": "v1"
}
] | 2011-08-23 | [
[
"Thirukkanesh",
"S.",
""
],
[
"Maharaj",
"S. D.",
""
]
] | We study the behaviour of a radiating star when the interior expanding, shearing fluid particles are traveling in geodesic motion. We demonstrate that it is possible to obtain new classes of exact solutions in terms of elementary functions without assuming a separable form for the gravitational potentials or initially fixing the temporal evolution of the model unlike earlier treatments. A systematic approach enables us to write the junction condition as a Riccati equation which under particular conditions may be transformed into a separable equation. New classes of solutions are generated which allow for mixed spatial and temporal dependence in the metric functions. We regain particular models found previously from our general classes of solutions. |
0806.3066 | Nicoleta Brinzei | Sergey Siparov (1), Nicoleta Brinzei (2) ((1) State University of
civil aviation, St-Petersburg, Russia, (2) "Transilvania" University, Brasov,
Romania) | Space-time anisotropy: theoretical issues and the possibility of an
observational test | 17 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The specific astrophysical data collected during the last decade causes the
need for the modification of the expression for the Einstein-Hilbert action,
and several attempts sufficing this need are known. The modification suggested
in this paper stems from the possible anisotropy of space-time and this means
the natural change of the simplest scalar in the least action principle. To
provide the testable support to this idea, the optic-metrical parametric
resonance is regarded - an experiment on the galactic scale based on the
interaction between the electromagnetic radiation of cosmic masers and
periodical gravitational waves emitted by close double systems or pulsars.
Since the effect depends on the space-time metric, the possible anisotropy
could reveal itself through observations. To give the corresponding theory
predicting the corrections to the expected results of the experiment, the
specific mathematical formalism of Finsler geometry was chosen. It was found
that in case the anisotropy of the space-time exists, the orientation of the
astrophysical systems suitable for observations would show it. In the obtained
geodesics equation there is a direction dependent term.
| [
{
"created": "Wed, 18 Jun 2008 19:04:04 GMT",
"version": "v1"
},
{
"created": "Sat, 2 Aug 2008 16:59:59 GMT",
"version": "v2"
}
] | 2012-07-04 | [
[
"Siparov",
"Sergey",
""
],
[
"Brinzei",
"Nicoleta",
""
]
] | The specific astrophysical data collected during the last decade causes the need for the modification of the expression for the Einstein-Hilbert action, and several attempts sufficing this need are known. The modification suggested in this paper stems from the possible anisotropy of space-time and this means the natural change of the simplest scalar in the least action principle. To provide the testable support to this idea, the optic-metrical parametric resonance is regarded - an experiment on the galactic scale based on the interaction between the electromagnetic radiation of cosmic masers and periodical gravitational waves emitted by close double systems or pulsars. Since the effect depends on the space-time metric, the possible anisotropy could reveal itself through observations. To give the corresponding theory predicting the corrections to the expected results of the experiment, the specific mathematical formalism of Finsler geometry was chosen. It was found that in case the anisotropy of the space-time exists, the orientation of the astrophysical systems suitable for observations would show it. In the obtained geodesics equation there is a direction dependent term. |
1804.05883 | Changqing Liu Lcqliu | Changqing Liu, Chikun Ding, Jiliang Jing | Periodic orbits around Kerr Sen black holes | 14 pages 8 figures | Commun. Theor. Phys. 71 (12), 1461, 2019 | 10.1088/0253-6102/71/12/1461 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate periodic orbits and zoom-whirl behaviors around a Kerr Sen
black hole with a rational number $q$ in terms of three integers $(z,w,v)$,
from which one can immediately read off the number of leaves(or zooms), the
ordering of the leaves, and the number of whirls. The characteristic of
zoom-whirl periodic orbits is the precession of multi-leaf orbits in the strong
field regime. This feature is analogous to the counterpart in the Kerr
space-time. Finally, we analyze the impact of the charge parameter $b$ on the
zoom-whirl periodic orbits. Compared to the periodic orbits around the Kerr
black hole, it is found that typically lower energies are required for the same
orbits in the Kerr Sen black hole.
| [
{
"created": "Mon, 16 Apr 2018 18:29:50 GMT",
"version": "v1"
},
{
"created": "Sat, 23 Nov 2019 01:58:51 GMT",
"version": "v2"
}
] | 2019-12-10 | [
[
"Liu",
"Changqing",
""
],
[
"Ding",
"Chikun",
""
],
[
"Jing",
"Jiliang",
""
]
] | We investigate periodic orbits and zoom-whirl behaviors around a Kerr Sen black hole with a rational number $q$ in terms of three integers $(z,w,v)$, from which one can immediately read off the number of leaves(or zooms), the ordering of the leaves, and the number of whirls. The characteristic of zoom-whirl periodic orbits is the precession of multi-leaf orbits in the strong field regime. This feature is analogous to the counterpart in the Kerr space-time. Finally, we analyze the impact of the charge parameter $b$ on the zoom-whirl periodic orbits. Compared to the periodic orbits around the Kerr black hole, it is found that typically lower energies are required for the same orbits in the Kerr Sen black hole. |
1604.06576 | J.J.L. Velazquez | Alan D. Rendall and Juan J. L. Vel\'azquez | Veiled singularities for the spherically symmetric massless
Einstein-Vlasov system | 67 pages, 1 figure | null | 10.1007/s00023-017-0607-9 | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper continues the investigation of the formation of naked
singularities in the collapse of collisionless matter initiated in [RV]. There
the existence of certain classes of non-smooth solutions of the Einstein-Vlasov
system was proved. Those solutions are self-similar and hence not
asymptotically flat. To obtain solutions which are more physically relevant it
makes sense to attempt to cut off these solutions in a suitable way so as to
make them asymptotically flat. This task, which turns out to be technically
challenging, will be carried out in this paper.
[RV] A. D. Rendall and J. J. L. Vel\'{a}zquez, A class of dust-like
self-similar solutions of the massless Einstein-Vlasov system. Annales Henri
Poincare 12, 919-964, (2011).
| [
{
"created": "Fri, 22 Apr 2016 08:58:51 GMT",
"version": "v1"
}
] | 2018-03-28 | [
[
"Rendall",
"Alan D.",
""
],
[
"Velázquez",
"Juan J. L.",
""
]
] | This paper continues the investigation of the formation of naked singularities in the collapse of collisionless matter initiated in [RV]. There the existence of certain classes of non-smooth solutions of the Einstein-Vlasov system was proved. Those solutions are self-similar and hence not asymptotically flat. To obtain solutions which are more physically relevant it makes sense to attempt to cut off these solutions in a suitable way so as to make them asymptotically flat. This task, which turns out to be technically challenging, will be carried out in this paper. [RV] A. D. Rendall and J. J. L. Vel\'{a}zquez, A class of dust-like self-similar solutions of the massless Einstein-Vlasov system. Annales Henri Poincare 12, 919-964, (2011). |
gr-qc/0703121 | Roy Maartens | George Ellis, Roy Maartens, Malcolm MacCallum | Causality and the speed of sound | v2: additional discussion on models that appear to have superluminal
signal speeds; version to appear in GRG | Gen.Rel.Grav.39:1651-1660,2007 | 10.1007/s10714-007-0479-2 | null | gr-qc astro-ph hep-th | null | A usual causal requirement on a viable theory of matter is that the speed of
sound be at most the speed of light. In view of various recent papers querying
this limit, the question is revisited here. We point to various issues
confronting theories that violate the usual constraint.
| [
{
"created": "Sun, 25 Mar 2007 20:20:00 GMT",
"version": "v1"
},
{
"created": "Tue, 29 May 2007 12:16:24 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Ellis",
"George",
""
],
[
"Maartens",
"Roy",
""
],
[
"MacCallum",
"Malcolm",
""
]
] | A usual causal requirement on a viable theory of matter is that the speed of sound be at most the speed of light. In view of various recent papers querying this limit, the question is revisited here. We point to various issues confronting theories that violate the usual constraint. |
1505.01990 | Izzet Sakalli | I. Sakalli and H. Gursel | Quantum tunneling from rotating black holes with scalar hair in three
dimensions | null | European Physical Journal C Volume: 76 Issue: 6 Article Number:
318 (2016) | 10.1140/epjc/s10052-016-4158-x | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the Hawking radiation (HR) of scalar and Dirac particles (fermions)
emitted from a rotating scalar hair black hole (RSHBH) within the context of
three dimensional ($3D$) Einstein gravity using non-minimally coupled scalar
field theory. Amalgamating the quantum tunneling approach with the
Wentzel--Kramers--Brillouin (WKB) approximation, we obtain the tunneling rates
of the outgoing particles across the event horizon. Inserting the resultant
tunneling rates into the Boltzmann formula, we then obtain the Hawking
temperature ($T_{H}$) of the $3D$ RSHBH.
| [
{
"created": "Fri, 8 May 2015 10:49:02 GMT",
"version": "v1"
}
] | 2016-10-24 | [
[
"Sakalli",
"I.",
""
],
[
"Gursel",
"H.",
""
]
] | We study the Hawking radiation (HR) of scalar and Dirac particles (fermions) emitted from a rotating scalar hair black hole (RSHBH) within the context of three dimensional ($3D$) Einstein gravity using non-minimally coupled scalar field theory. Amalgamating the quantum tunneling approach with the Wentzel--Kramers--Brillouin (WKB) approximation, we obtain the tunneling rates of the outgoing particles across the event horizon. Inserting the resultant tunneling rates into the Boltzmann formula, we then obtain the Hawking temperature ($T_{H}$) of the $3D$ RSHBH. |
2312.07486 | Stylianos A. Tsilioukas | Stylianos A. Tsilioukas, Emmanuel N. Saridakis, Charalampos Tzerefos | Dark energy from topology change induced by microscopic Gauss-Bonnet
wormholes | 9 pages, 1 figure, version to appear in Phys. Rev. D | Phys.Rev.D 109 (2024), 084010 | 10.1103/PhysRevD.109.084010 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is known that the appearance of microscopic objects with distinct
topologies and different Euler characteristics, such as instatons and
wormholes, at the spacetime-foam level in Euclidean quantum gravity approaches,
leads to spacetime topology changes. Such changes, in principle, may affect the
field equations that arise through the semiclassical variation procedure of
gravitational actions. Although in the case of Einstein-Hilbert action the
presence of microscopic wormholes does not lead to any non-trivial result, when
the Gauss-Bonnet term is added in the gravitational action, the above effective
topological variation procedure induces an effective cosmological constant that
depends on the Gauss-Bonnet coupling and the wormhole density. Since the later
in a dynamical spacetime is in general time-dependent, one obtains an effective
dark energy sector of topological origin.
| [
{
"created": "Tue, 12 Dec 2023 18:21:41 GMT",
"version": "v1"
},
{
"created": "Wed, 28 Feb 2024 14:54:28 GMT",
"version": "v2"
}
] | 2024-04-08 | [
[
"Tsilioukas",
"Stylianos A.",
""
],
[
"Saridakis",
"Emmanuel N.",
""
],
[
"Tzerefos",
"Charalampos",
""
]
] | It is known that the appearance of microscopic objects with distinct topologies and different Euler characteristics, such as instatons and wormholes, at the spacetime-foam level in Euclidean quantum gravity approaches, leads to spacetime topology changes. Such changes, in principle, may affect the field equations that arise through the semiclassical variation procedure of gravitational actions. Although in the case of Einstein-Hilbert action the presence of microscopic wormholes does not lead to any non-trivial result, when the Gauss-Bonnet term is added in the gravitational action, the above effective topological variation procedure induces an effective cosmological constant that depends on the Gauss-Bonnet coupling and the wormhole density. Since the later in a dynamical spacetime is in general time-dependent, one obtains an effective dark energy sector of topological origin. |
2102.09456 | Orfeu Bertolami | Orfeu Bertolami | Inflation, phase transitions and the cosmological constant | 9 pages. Version to match to one to be published in General
Relativity and Gravitation | null | 10.1007/s10714-021-02877-1 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | Cosmological phase transitions are thought to have taken place at the early
Universe imprinting their properties on the observable Universe. There is
strong evidence that, through the dynamics of a scalar field that lead a second
order phase transition, inflation shaped the Universe accounting for the most
conspicuous features of the observed Universe. It is argued that inflation has
also striking implications for the vacuum energy. Considerations for subsequent
second order phase transitions are also discussed.
| [
{
"created": "Wed, 17 Feb 2021 14:52:01 GMT",
"version": "v1"
},
{
"created": "Sat, 15 May 2021 09:32:28 GMT",
"version": "v2"
},
{
"created": "Wed, 3 Nov 2021 18:21:39 GMT",
"version": "v3"
}
] | 2021-12-08 | [
[
"Bertolami",
"Orfeu",
""
]
] | Cosmological phase transitions are thought to have taken place at the early Universe imprinting their properties on the observable Universe. There is strong evidence that, through the dynamics of a scalar field that lead a second order phase transition, inflation shaped the Universe accounting for the most conspicuous features of the observed Universe. It is argued that inflation has also striking implications for the vacuum energy. Considerations for subsequent second order phase transitions are also discussed. |
1807.01381 | Lee Smolin | Stephon Alexander, Joao Magueijo and Lee Smolin | The quantum cosmological constant | 15 pages. no figures, minor improvments | null | null | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present an extension of general relativity in which the cosmological
constant becomes dynamical and turns out to be conjugate to the Chern-Simons
invariant of the Ashtekar connection on a spatial slicing. The latter has been
proposed in \cite{Chopin-Lee} as a time variable for quantum gravity: the
Chern-Simons time. In the quantum theory the inverse cosmological constant and
Chern-Simons time will then become conjugate operators. The "Kodama state" gets
a new interpretation as a family of transition functions. These results imply
an uncertainty relation between $\Lambda$ and Chern-Simons time; the
consequences of which will be discussed elsewhere.
| [
{
"created": "Tue, 3 Jul 2018 21:58:47 GMT",
"version": "v1"
},
{
"created": "Sat, 21 Jul 2018 16:02:09 GMT",
"version": "v2"
}
] | 2018-07-24 | [
[
"Alexander",
"Stephon",
""
],
[
"Magueijo",
"Joao",
""
],
[
"Smolin",
"Lee",
""
]
] | We present an extension of general relativity in which the cosmological constant becomes dynamical and turns out to be conjugate to the Chern-Simons invariant of the Ashtekar connection on a spatial slicing. The latter has been proposed in \cite{Chopin-Lee} as a time variable for quantum gravity: the Chern-Simons time. In the quantum theory the inverse cosmological constant and Chern-Simons time will then become conjugate operators. The "Kodama state" gets a new interpretation as a family of transition functions. These results imply an uncertainty relation between $\Lambda$ and Chern-Simons time; the consequences of which will be discussed elsewhere. |
gr-qc/0210045 | Thomas Buchert | Thomas Buchert and Mauro Carfora | Cosmological parameters are dressed | LateX, PRLstyle, 4 pages; submitted to PRL | Phys.Rev.Lett.90:031101,2003 | 10.1103/PhysRevLett.90.031101 | null | gr-qc astro-ph hep-ph hep-th | null | In the context of the averaging problem in relativistic cosmology, we provide
a key to the interpretation of cosmological parameters by taking into account
the actual inhomogeneous geometry of the Universe. We discuss the relation
between `bare' cosmological parameters determining the cosmological model, and
the parameters interpreted by observers with a ``Friedmannian bias'', which are
`dressed' by the smoothed-out geometrical inhomogeneities of the surveyed
spatial region.
| [
{
"created": "Tue, 15 Oct 2002 08:04:14 GMT",
"version": "v1"
}
] | 2009-07-10 | [
[
"Buchert",
"Thomas",
""
],
[
"Carfora",
"Mauro",
""
]
] | In the context of the averaging problem in relativistic cosmology, we provide a key to the interpretation of cosmological parameters by taking into account the actual inhomogeneous geometry of the Universe. We discuss the relation between `bare' cosmological parameters determining the cosmological model, and the parameters interpreted by observers with a ``Friedmannian bias'', which are `dressed' by the smoothed-out geometrical inhomogeneities of the surveyed spatial region. |
2307.02567 | Yuri Obukhov | Yuri N. Obukhov | Spin as a probe of axion physics in general relativity | 14 pages, Revtex, no figures. Accepted for publication in
International Journal of Modern Physics A | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The dynamics of spin in external electromagnetic, gravitational, and axion
fields is analysed in the framework of the gravitoelectromagnetism approach in
Einstein's general relativity theory. We consistently extend the recent studies
from the flat Minkowski geometry to the curved spacetime manifolds,
contributing to the discussion of the possible new role of a precessing spin as
an ``axion antenna'' that can be used to detect the hypothetical axion-like
dark matter. The formalism developed helps to clarify the subtle influence of
the gravitational/inertial and axion fields in the ultra-sensitive high-energy
spin experiments with charged particles and neutrons at accelerators and
storage rings devoted to testing fundamental physical symmetries, including
attempts to establish the nature of dark matter in the Universe.
| [
{
"created": "Wed, 5 Jul 2023 18:08:15 GMT",
"version": "v1"
}
] | 2023-07-07 | [
[
"Obukhov",
"Yuri N.",
""
]
] | The dynamics of spin in external electromagnetic, gravitational, and axion fields is analysed in the framework of the gravitoelectromagnetism approach in Einstein's general relativity theory. We consistently extend the recent studies from the flat Minkowski geometry to the curved spacetime manifolds, contributing to the discussion of the possible new role of a precessing spin as an ``axion antenna'' that can be used to detect the hypothetical axion-like dark matter. The formalism developed helps to clarify the subtle influence of the gravitational/inertial and axion fields in the ultra-sensitive high-energy spin experiments with charged particles and neutrons at accelerators and storage rings devoted to testing fundamental physical symmetries, including attempts to establish the nature of dark matter in the Universe. |
1312.2866 | Marc Lachieze-Rey | Marc Lachieze-Rey (APC) | In search of relativistic time | to appear in Studies in History and Philosophy of Science Part B:
Studies in History and Philosophy of Modern Physics | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper explores the status of some notions which are usually associated
to time, like datations, chronology, durations, causality, cosmic time and time
functions in the Einsteinian relativistic theories. It shows how, even if some
of these notions do exist in the theory or for some particular solution of it,
they appear usually in mutual conflict: they cannot be synthesized coherently,
and this is interpreted as the impossibility to construct a common entity which
could be called time. This contrasts with the case in Newtonian physics where
such a synthesis precisely constitutes Newtonian time. After an illustration by
comparing the status of time in Einsteinian physics with that of the vertical
direction in Newtonian physics, I will conclude that there is no pertinent
notion of time in Einsteinian theories.
| [
{
"created": "Mon, 9 Dec 2013 20:18:35 GMT",
"version": "v1"
}
] | 2013-12-11 | [
[
"Lachieze-Rey",
"Marc",
"",
"APC"
]
] | This paper explores the status of some notions which are usually associated to time, like datations, chronology, durations, causality, cosmic time and time functions in the Einsteinian relativistic theories. It shows how, even if some of these notions do exist in the theory or for some particular solution of it, they appear usually in mutual conflict: they cannot be synthesized coherently, and this is interpreted as the impossibility to construct a common entity which could be called time. This contrasts with the case in Newtonian physics where such a synthesis precisely constitutes Newtonian time. After an illustration by comparing the status of time in Einsteinian physics with that of the vertical direction in Newtonian physics, I will conclude that there is no pertinent notion of time in Einsteinian theories. |
2111.02462 | Charis Anastopoulos | Charis Anastopoulos and Bei-Lok Hu | Gravitational Decoherence: A Thematic Overview | 26 pages, Article prepared for the Special Topic Collection
"Celebrating Sir Roger Penrose's Nobel Prize" | null | 10.1116/5.0077536 | null | gr-qc hep-th quant-ph | http://creativecommons.org/licenses/by/4.0/ | Gravitational decoherence (GD) refers to the effects of gravity in actuating
the classical appearance of a quantum system. Because the underlying processes
involve issues in general relativity (GR), quantum field theory (QFT) and
quantum information, GD has fundamental theoretical significance. There is a
great variety of GD models, many of them involving physics that diverge from GR
and/or QFT. This overview has two specific goals along one central theme: (i)
present theories of GD based on GR and QFT and explore their experimental
predictions; (ii) place other theories of GD under the scrutiny of GR and QFT,
and point out their theoretical differences. We also describe how GD
experiments in space in the coming decades can provide evidences at two levels:
a) discriminate alternative quantum theories and non-GR theories; b) discern
whether gravity is a fundamental or an effective theory.
| [
{
"created": "Wed, 3 Nov 2021 18:37:40 GMT",
"version": "v1"
}
] | 2024-06-19 | [
[
"Anastopoulos",
"Charis",
""
],
[
"Hu",
"Bei-Lok",
""
]
] | Gravitational decoherence (GD) refers to the effects of gravity in actuating the classical appearance of a quantum system. Because the underlying processes involve issues in general relativity (GR), quantum field theory (QFT) and quantum information, GD has fundamental theoretical significance. There is a great variety of GD models, many of them involving physics that diverge from GR and/or QFT. This overview has two specific goals along one central theme: (i) present theories of GD based on GR and QFT and explore their experimental predictions; (ii) place other theories of GD under the scrutiny of GR and QFT, and point out their theoretical differences. We also describe how GD experiments in space in the coming decades can provide evidences at two levels: a) discriminate alternative quantum theories and non-GR theories; b) discern whether gravity is a fundamental or an effective theory. |
2204.06420 | Francesco Pace | Francesco Pace and Noemi Frusciante | A 3D Phase Space Analysis of Scalar Field Potentials | 23 pages, 3 figures. 4 tables. Accepted for publication on Universe
for the Special Issue entitled "Large Scale Structure of the Universe", led
by the authors, and belongs to the section "Cosmology" | Universe 2022, 8(3), 145 | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this study, we present the phase-space analysis of Quintessence models
specified by the choice of two potentials, namely the Recliner potential and
what we call the broken exponential-law potential, which is a new proposal.
Using a dynamical system analysis we provide a systematic study of the
cosmological evolution of the two models and their properties. We find new
scaling solutions characterised by a constant ratio between the energy density
of the scalar field and that of the matter component. These solutions are of
high interest in light of the possibility to alleviate the coincidence problem.
Additionally, the models also show attractor solutions. We finally construct
concrete models built using a double potential according to which one potential
realises the early-time scaling regime and the second one allows to exit this
regime and to enter in the epoch of cosmic acceleration driven by a
scalar-field dominated attractor point.
| [
{
"created": "Wed, 13 Apr 2022 14:30:48 GMT",
"version": "v1"
}
] | 2022-04-14 | [
[
"Pace",
"Francesco",
""
],
[
"Frusciante",
"Noemi",
""
]
] | In this study, we present the phase-space analysis of Quintessence models specified by the choice of two potentials, namely the Recliner potential and what we call the broken exponential-law potential, which is a new proposal. Using a dynamical system analysis we provide a systematic study of the cosmological evolution of the two models and their properties. We find new scaling solutions characterised by a constant ratio between the energy density of the scalar field and that of the matter component. These solutions are of high interest in light of the possibility to alleviate the coincidence problem. Additionally, the models also show attractor solutions. We finally construct concrete models built using a double potential according to which one potential realises the early-time scaling regime and the second one allows to exit this regime and to enter in the epoch of cosmic acceleration driven by a scalar-field dominated attractor point. |
2104.09972 | Justin Ripley | Justin L. Ripley | A symmetric hyperbolic formulation of the vacuum Einstein equations in
affine-null coordinates | updated to match journal version | Journal of Mathematical Physics 62, 062501 (2021) | 10.1063/5.0055561 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a symmetric hyperbolic formulation of the Einstein equations in
affine-null coordinates. Giannakopoulos et. al. (arXiv:2007.06419) recently
showed that the most commonly numerically implemented formulations of the
Einstein equations in affine-null coordinates (and other single-null coordinate
systems) are only weakly-but not strongly-hyperbolic. By making use of the
tetrad-based Newman-Penrose formalism, our formulation avoids the hyperbolicity
problems of the formulations investigated by Giannakopoulos et. al. We discuss
a potential application of our formulation for studying gravitational wave
scattering.
| [
{
"created": "Tue, 20 Apr 2021 14:04:03 GMT",
"version": "v1"
},
{
"created": "Wed, 2 Jun 2021 20:37:16 GMT",
"version": "v2"
}
] | 2021-06-04 | [
[
"Ripley",
"Justin L.",
""
]
] | We present a symmetric hyperbolic formulation of the Einstein equations in affine-null coordinates. Giannakopoulos et. al. (arXiv:2007.06419) recently showed that the most commonly numerically implemented formulations of the Einstein equations in affine-null coordinates (and other single-null coordinate systems) are only weakly-but not strongly-hyperbolic. By making use of the tetrad-based Newman-Penrose formalism, our formulation avoids the hyperbolicity problems of the formulations investigated by Giannakopoulos et. al. We discuss a potential application of our formulation for studying gravitational wave scattering. |
1705.09470 | Alexander Kamenshchik | A.O. Barvinsky and A.Yu. Kamenshchik | Darkness without dark matter and energy -- generalized unimodular
gravity | 11 pages, final version, to be published in Physics Letters B | Physics Letters B 774, 59-63 (2017) | 10.1016/j.physletb.2017.09.045 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We suggest a Lorentz non-invariant generalization of the unimodular gravity
theory, which is classically equivalent to general relativity with a locally
inert (devoid of local degrees of freedom) perfect fluid having an equation of
state with a constant parameter $w$. For the range of $w$ near $-1$ this dark
fluid can play the role of dark energy, while for $w=0$ this dark dust admits
spatial inhomogeneities and can be interpreted as dark matter. We discuss
possible implications of this model in the cosmological initial conditions
problem. In particular, this is the extension of known microcanonical density
matrix predictions for the initial quantum state of the closed cosmology to the
case of spatially open Universe, based on the imitation of the spatial
curvature by the dark fluid density. We also briefly discuss quantization of
this model necessarily involving the method of gauge systems with reducible
constraints and the effect of this method on the treatment of recently
suggested mechanism of vacuum energy sequestering.
| [
{
"created": "Fri, 26 May 2017 08:17:11 GMT",
"version": "v1"
},
{
"created": "Fri, 15 Sep 2017 13:30:05 GMT",
"version": "v2"
}
] | 2017-10-02 | [
[
"Barvinsky",
"A. O.",
""
],
[
"Kamenshchik",
"A. Yu.",
""
]
] | We suggest a Lorentz non-invariant generalization of the unimodular gravity theory, which is classically equivalent to general relativity with a locally inert (devoid of local degrees of freedom) perfect fluid having an equation of state with a constant parameter $w$. For the range of $w$ near $-1$ this dark fluid can play the role of dark energy, while for $w=0$ this dark dust admits spatial inhomogeneities and can be interpreted as dark matter. We discuss possible implications of this model in the cosmological initial conditions problem. In particular, this is the extension of known microcanonical density matrix predictions for the initial quantum state of the closed cosmology to the case of spatially open Universe, based on the imitation of the spatial curvature by the dark fluid density. We also briefly discuss quantization of this model necessarily involving the method of gauge systems with reducible constraints and the effect of this method on the treatment of recently suggested mechanism of vacuum energy sequestering. |
1604.07213 | Muhammad Zubair | M. Zubair, Farzana Kousar and Sebastian Bahamonde | Thermodynamics in $f(R,R_{\alpha\beta}R^{\alpha\beta},\phi)$ theory of
gravity | 29 pages, 4 figures | Physics of the Dark Universe Vol. 14, (2016)116-125 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | First and second laws of black hole thermodynamics are examined at the
apparent horizon of FRW spacetime in $f(R,R_{\alpha\beta}R^{\alpha\beta}
,\phi)$ gravity, where $R$, $R_{\alpha\beta}R^{\alpha\beta}$ and $\phi$ are the
Ricci scalar, Ricci invariant and the scalar field respectively. In this
modified theory, Friedmann equations are formulated for any spatial curvature.
These equations can be presented into the form of first law of thermodynamics
for $T_{h}d\hat{S}_{h}+ T_{h}d_{i}\hat{S}_{h}+W dV=dE$, where
$d_{i}\hat{S}_{h}$ is an extra entropy term because of the non-equilibrium
presentation of the equations and $T_{h}d\hat{S}_{h}+W dV=dE$ for the
equilibrium presentation. The generalized second law of thermodynamics (GSLT)
is expressed in an inclusive form where these results can be represented in GR
$f(R)$ and $f(R, \phi)$ gravities. Finally to check the validity of GSLT, we
take some particular models and produce constraints of the parameters.
| [
{
"created": "Mon, 25 Apr 2016 11:47:38 GMT",
"version": "v1"
},
{
"created": "Wed, 16 Nov 2016 15:02:07 GMT",
"version": "v2"
}
] | 2016-11-17 | [
[
"Zubair",
"M.",
""
],
[
"Kousar",
"Farzana",
""
],
[
"Bahamonde",
"Sebastian",
""
]
] | First and second laws of black hole thermodynamics are examined at the apparent horizon of FRW spacetime in $f(R,R_{\alpha\beta}R^{\alpha\beta} ,\phi)$ gravity, where $R$, $R_{\alpha\beta}R^{\alpha\beta}$ and $\phi$ are the Ricci scalar, Ricci invariant and the scalar field respectively. In this modified theory, Friedmann equations are formulated for any spatial curvature. These equations can be presented into the form of first law of thermodynamics for $T_{h}d\hat{S}_{h}+ T_{h}d_{i}\hat{S}_{h}+W dV=dE$, where $d_{i}\hat{S}_{h}$ is an extra entropy term because of the non-equilibrium presentation of the equations and $T_{h}d\hat{S}_{h}+W dV=dE$ for the equilibrium presentation. The generalized second law of thermodynamics (GSLT) is expressed in an inclusive form where these results can be represented in GR $f(R)$ and $f(R, \phi)$ gravities. Finally to check the validity of GSLT, we take some particular models and produce constraints of the parameters. |
2208.01987 | Guillermo A. Mena Marugan | Simon Iteanu and Guillermo A. Mena Marug\'an | Mass of cosmological perturbations in the hybrid and dressed metric
formalisms of Loop Quantum Cosmology for the Starobinsky and exponential
potentials | 13 pages | Universe 8, 463 (2022) | 10.3390/universe8090463 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The hybrid and the dressed metric formalisms for the study of primordial
perturbations in Loop Quantum Cosmology lead to dynamical equations for the
modes of these perturbations that are of a generalized harmonic-oscillator
type, with a mass that depends on the background but is the same for all modes.
For quantum background states that are peaked on trajectories of the effective
description of Loop Quantum Cosmology, the main difference between the two
considered formalisms is found in the expression of this mass. The value of the
mass at the bounce is especially important, since it is only in a short
interval around this event that the quantum geometry effects on the
perturbations are relevant. In a previous article, the properties of this mass
were discussed for an inflaton potential of quadratic form, or with similar
characteristics. In the present work, we extend this study to other interesting
potentials in cosmology, namely the Starobinsky and the exponential potentials.
We prove that there exists a finite interval of values of the potential (which
includes the zero but typically goes beyond the sector of kinetically dominated
inflaton energy density) for which the hybrid mass is positive at the bounce
whereas the dressed metric mass is negative.
| [
{
"created": "Wed, 3 Aug 2022 11:28:21 GMT",
"version": "v1"
},
{
"created": "Fri, 23 Sep 2022 09:17:23 GMT",
"version": "v2"
}
] | 2022-09-26 | [
[
"Iteanu",
"Simon",
""
],
[
"Marugán",
"Guillermo A. Mena",
""
]
] | The hybrid and the dressed metric formalisms for the study of primordial perturbations in Loop Quantum Cosmology lead to dynamical equations for the modes of these perturbations that are of a generalized harmonic-oscillator type, with a mass that depends on the background but is the same for all modes. For quantum background states that are peaked on trajectories of the effective description of Loop Quantum Cosmology, the main difference between the two considered formalisms is found in the expression of this mass. The value of the mass at the bounce is especially important, since it is only in a short interval around this event that the quantum geometry effects on the perturbations are relevant. In a previous article, the properties of this mass were discussed for an inflaton potential of quadratic form, or with similar characteristics. In the present work, we extend this study to other interesting potentials in cosmology, namely the Starobinsky and the exponential potentials. We prove that there exists a finite interval of values of the potential (which includes the zero but typically goes beyond the sector of kinetically dominated inflaton energy density) for which the hybrid mass is positive at the bounce whereas the dressed metric mass is negative. |
gr-qc/9212009 | null | Peter C. Aichelburg and Piotr Bizon | Magnetically Charged Black Holes and their Stability | 19 pages, 5 figures available upon request, Latex | Phys.Rev.D48:607-615,1993 | 10.1103/PhysRevD.48.607 | UWThPh-1992-63 | gr-qc hep-th | null | We study magnetically charged black holes in the Einstein-Yang-Mills-Higgs
theory in the limit of infinitely strong coupling of the Higgs field. Using
mixed analytical and numerical methods we give a complete description of static
spherically symmetric black hole solutions, both abelian and nonabelian. In
particular, we find a new class of extremal nonabelian solutions. We show that
all nonabelian solutions are stable against linear radial perturbations. The
implications of our results for the semiclassical evolution of magnetically
charged black holes are discussed.
| [
{
"created": "Mon, 14 Dec 1992 14:17:00 GMT",
"version": "v1"
}
] | 2010-11-01 | [
[
"Aichelburg",
"Peter C.",
""
],
[
"Bizon",
"Piotr",
""
]
] | We study magnetically charged black holes in the Einstein-Yang-Mills-Higgs theory in the limit of infinitely strong coupling of the Higgs field. Using mixed analytical and numerical methods we give a complete description of static spherically symmetric black hole solutions, both abelian and nonabelian. In particular, we find a new class of extremal nonabelian solutions. We show that all nonabelian solutions are stable against linear radial perturbations. The implications of our results for the semiclassical evolution of magnetically charged black holes are discussed. |
gr-qc/0309063 | Edward Anderson | Edward Anderson and Reza Tavakol | PDE System Approach to Large Extra Dimensions | 33 pages and 9 figures | null | null | null | gr-qc hep-th | null | We explore some fundational issues regarding the splitting of D-dimensional
EFE's w.r.t timelike and spacelike (D-1)-dimensional hypersurfaces, first
without and then with thin matter sheets such as branes. We begin to implement
methodology, that is well-established for the GR CP and IVP, in the new field
of GR-based braneworlds, identifying and comparing many different choices of
procedure. We abridge fragmentary parts of the literature of embeddings,
putting the Campbell--Magaard theorem into context. We recollect and refine
arguments why York and not elimination methods are used for the GR IVP. We
compile a list of numerous mathematical and physical impasses to using timelike
splits, whereas spacelike splits are known to be well-behaved. We however
pursue both options to make contact with the current braneworld literature
which is almost entirely based on timelike splits. We look at the
Shiromizu-Maeda -Sasaki braneworld by means of reformulations which emphasize
different aspects from the original formulation. We show that what remains of
the York method in the timelike case generalizes heuristic bulk construction
schemes. We formulate timelike (brane) versions of the thin sandwich
conjecture. We discuss whether it is plausible to remove singularities by
timelike embeddings. We point out how the braneworld geodesic postulates lead
to further difficulties with the notion of singularities than in GR where these
postulates are simpler. Having argued for the use of the spacelike split, we
study how to progress to the construction of more general data sets for spaces
partially bounded by branes. Boundary conditions are found and algorithms
provided. Working with (finitely) thick branes would appear to facilitate such
a study.
| [
{
"created": "Fri, 12 Sep 2003 16:21:16 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Anderson",
"Edward",
""
],
[
"Tavakol",
"Reza",
""
]
] | We explore some fundational issues regarding the splitting of D-dimensional EFE's w.r.t timelike and spacelike (D-1)-dimensional hypersurfaces, first without and then with thin matter sheets such as branes. We begin to implement methodology, that is well-established for the GR CP and IVP, in the new field of GR-based braneworlds, identifying and comparing many different choices of procedure. We abridge fragmentary parts of the literature of embeddings, putting the Campbell--Magaard theorem into context. We recollect and refine arguments why York and not elimination methods are used for the GR IVP. We compile a list of numerous mathematical and physical impasses to using timelike splits, whereas spacelike splits are known to be well-behaved. We however pursue both options to make contact with the current braneworld literature which is almost entirely based on timelike splits. We look at the Shiromizu-Maeda -Sasaki braneworld by means of reformulations which emphasize different aspects from the original formulation. We show that what remains of the York method in the timelike case generalizes heuristic bulk construction schemes. We formulate timelike (brane) versions of the thin sandwich conjecture. We discuss whether it is plausible to remove singularities by timelike embeddings. We point out how the braneworld geodesic postulates lead to further difficulties with the notion of singularities than in GR where these postulates are simpler. Having argued for the use of the spacelike split, we study how to progress to the construction of more general data sets for spaces partially bounded by branes. Boundary conditions are found and algorithms provided. Working with (finitely) thick branes would appear to facilitate such a study. |
2307.14862 | Artyom Astashenok V | Artyom V. Astashenok, Sergey D. Odintsov, Vasilis K. Oikonomou | Compact Stars with Dark Energy in General Relativity and Modified
Gravity | accepted in Phys. Dark Univ | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate realistic models of compact objects, focusing on neutron and
strange stars, composed by dense matter and dark energy in the form of a simple
fluid or scalar field interacting with matter. For the dark energy component,
we use equations of state compatible with cosmological observations. This
requirement strongly constrains possible deviations from the simple
$\Lambda$-Cold Dark-Matter model with EoS $p_{d}=-\rho_{d}$ at least for small
densities of the dark component. But we can propose that the density of dark
energy interacting with matter can reach large values in relativistic stars and
affects the star parameters such as the mass and radius. Simple models of dark
energy are considered. Then we investigated possible effects from modified
gravity choosing to study the $R^2$ model combined with dark energy. Finally,
the case of dark energy as scalar field non-minimally interacting with gravity
is considered.
| [
{
"created": "Thu, 27 Jul 2023 13:46:30 GMT",
"version": "v1"
}
] | 2023-08-01 | [
[
"Astashenok",
"Artyom V.",
""
],
[
"Odintsov",
"Sergey D.",
""
],
[
"Oikonomou",
"Vasilis K.",
""
]
] | We investigate realistic models of compact objects, focusing on neutron and strange stars, composed by dense matter and dark energy in the form of a simple fluid or scalar field interacting with matter. For the dark energy component, we use equations of state compatible with cosmological observations. This requirement strongly constrains possible deviations from the simple $\Lambda$-Cold Dark-Matter model with EoS $p_{d}=-\rho_{d}$ at least for small densities of the dark component. But we can propose that the density of dark energy interacting with matter can reach large values in relativistic stars and affects the star parameters such as the mass and radius. Simple models of dark energy are considered. Then we investigated possible effects from modified gravity choosing to study the $R^2$ model combined with dark energy. Finally, the case of dark energy as scalar field non-minimally interacting with gravity is considered. |
2009.07732 | Tanmoy Paul | Tanmoy Paul | Antisymmetric tensor fields in modified gravity: a summary | Invited review paper from Symmetry for special issue Feature Papers
2020, Symmetry Accepted | null | null | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We provide various aspects of second rank antisymmetric Kalb-Ramond (KR)
field in modified theories of gravity. The KR field energy density is found to
decrease with the expansion of our universe at a faster rate in comparison to
radiation and matter components. Thus as the Universe evolves and cools down,
the contribution of the KR field on the evolutionary process reduces
significantly, and at present it almost does not affect the universe evolution.
However the KR field has a significant contribution during early universe, in
particular, it affects the beginning of inflation as well as increases the
amount of primordial gravitational radiation and hence enlarges the value of
tensor to scalar ratio in respect to the case when the KR field is absent. In
regard to the KR field couplings, it turns out that in four dimensional higher
curvature inflationary model the couplings of the KR field to other matter
fields is given by $1/M_{Pl}$ i.e same as the usual gravity-matter coupling.
However in higher dimensional higher curvature model the KR couplings get an
additional suppression over $1/M_{Pl}$ and thus gives a better explanation of
why the present universe carries practically no footprint of the Kalb-Ramond
field in comparison to the 4D higher curvature model. The higher curvature term
in 5D action acts as a suitable stabilizing agent in the dynamical
stabilization mechanism of the extra dimensional modulus field from the
perspective of effective on-brane theory. Based on the evolution of KR field,
one intriguing question can be - sitting in present day universe, how do we
confirm the existence of the Kalb-Ramond field which has considerably low
energy density in our present universe but has a significant impact during
early universe ? We try to answer this question by the phenomena "cosmological
quantum entanglement" which indeed carries the information of early universe.
| [
{
"created": "Wed, 16 Sep 2020 15:05:21 GMT",
"version": "v1"
}
] | 2020-09-17 | [
[
"Paul",
"Tanmoy",
""
]
] | We provide various aspects of second rank antisymmetric Kalb-Ramond (KR) field in modified theories of gravity. The KR field energy density is found to decrease with the expansion of our universe at a faster rate in comparison to radiation and matter components. Thus as the Universe evolves and cools down, the contribution of the KR field on the evolutionary process reduces significantly, and at present it almost does not affect the universe evolution. However the KR field has a significant contribution during early universe, in particular, it affects the beginning of inflation as well as increases the amount of primordial gravitational radiation and hence enlarges the value of tensor to scalar ratio in respect to the case when the KR field is absent. In regard to the KR field couplings, it turns out that in four dimensional higher curvature inflationary model the couplings of the KR field to other matter fields is given by $1/M_{Pl}$ i.e same as the usual gravity-matter coupling. However in higher dimensional higher curvature model the KR couplings get an additional suppression over $1/M_{Pl}$ and thus gives a better explanation of why the present universe carries practically no footprint of the Kalb-Ramond field in comparison to the 4D higher curvature model. The higher curvature term in 5D action acts as a suitable stabilizing agent in the dynamical stabilization mechanism of the extra dimensional modulus field from the perspective of effective on-brane theory. Based on the evolution of KR field, one intriguing question can be - sitting in present day universe, how do we confirm the existence of the Kalb-Ramond field which has considerably low energy density in our present universe but has a significant impact during early universe ? We try to answer this question by the phenomena "cosmological quantum entanglement" which indeed carries the information of early universe. |
1910.08756 | Thomas B\"ackdahl | Steffen Aksteiner, Lars Andersson, Thomas B\"ackdahl, Igor Khavkine,
Bernard Whiting | Compatibility complex for black hole spacetimes | 23 pages. Some remarks added | Commun. Math. Phys. (2021) | 10.1007/s00220-021-04078-y | null | gr-qc math-ph math.DG math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The set of local gauge invariant quantities for linearized gravity on the
Kerr spacetime presented by two of the authors (S.A, T.B.) in
(arXiv:1803.05341) is shown to be complete. In particular, any gauge invariant
quantity for linearized gravity on Kerr that is local and of finite order in
derivatives can be expressed in terms of these gauge invariants and derivatives
thereof. The proof is carried out by constructing a complete compatibility
complex for the Killing operator, and demonstrating the equivalence of the
gauge invariants from (arXiv:1803.05341) with the first compatibility operator
from that complex.
| [
{
"created": "Sat, 19 Oct 2019 11:54:12 GMT",
"version": "v1"
},
{
"created": "Mon, 10 May 2021 05:14:08 GMT",
"version": "v2"
}
] | 2021-05-11 | [
[
"Aksteiner",
"Steffen",
""
],
[
"Andersson",
"Lars",
""
],
[
"Bäckdahl",
"Thomas",
""
],
[
"Khavkine",
"Igor",
""
],
[
"Whiting",
"Bernard",
""
]
] | The set of local gauge invariant quantities for linearized gravity on the Kerr spacetime presented by two of the authors (S.A, T.B.) in (arXiv:1803.05341) is shown to be complete. In particular, any gauge invariant quantity for linearized gravity on Kerr that is local and of finite order in derivatives can be expressed in terms of these gauge invariants and derivatives thereof. The proof is carried out by constructing a complete compatibility complex for the Killing operator, and demonstrating the equivalence of the gauge invariants from (arXiv:1803.05341) with the first compatibility operator from that complex. |
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