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 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1110.1356 | Paulo Pitanga | Jair Koiller, Paulo R. Rodrigues and Paulo Pitanga | Non-Holonomic Connections Following \'Elie Cartan | null | Anais da Academia Brasileira de Ciencias 73 (2) 165 (2001) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this note we revisit E. Cartan's address at the 1928 International
Congress of Mathematicians at Bologna, Italy. The distributions considered here
will be of the same class as those considered by Cartan, a special type which
we call strongly non-holonomic. We set up the groundwork for using Cartan's
method of equivalence (a powerful tool for obtaining invariants associated to
geometrical objects), to more general non-holonomic distributions.
| [
{
"created": "Thu, 6 Oct 2011 19:22:52 GMT",
"version": "v1"
}
] | 2011-10-07 | [
[
"Koiller",
"Jair",
""
],
[
"Rodrigues",
"Paulo R.",
""
],
[
"Pitanga",
"Paulo",
""
]
] | In this note we revisit E. Cartan's address at the 1928 International Congress of Mathematicians at Bologna, Italy. The distributions considered here will be of the same class as those considered by Cartan, a special type which we call strongly non-holonomic. We set up the groundwork for using Cartan's method of equivalence (a powerful tool for obtaining invariants associated to geometrical objects), to more general non-holonomic distributions. |
2305.07123 | Bekir Can L\"utf\"uo\u{g}lu | B. Hamil and B. C. L\"utf\"uo\u{g}lu | Thermodynamics and Shadows of quantum-corrected Reissner-Nordstr\"om
black hole surrounded by quintessence | 21 pages, 4 Tables, 7 Figures | Phys. Dark Universe 42, 101293 (2023) | 10.1016/j.dark.2023.101293 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work, we consider the quantum-corrected Reissner-Nordstr\"om black
hole surrounded by quintessence matter and examine its thermodynamics and
shadow. To this end, we handle the quantum-corrected metric of the black hole,
which is given by Wu and Lui in 2022, and couple the quintessence matter field
effects to the lapse function. Then, we obtain the mass, Hawking temperature,
specific heat, and equation of state functions. In all these functions, we
discuss two cases in which the quantum corrections are greater or smaller than
the quintessence matter effects. We observe that within these two scenarios,
the black hole has different characteristic thermal behaviors. Moreover, we
find that the quintessence matter plays an important role in leading to a black
hole remnant. Finally, we investigate the black hole shadow by Carter's
approach. We find that quintessence matter and quantum corrections modify the
shadow of the black hole.
| [
{
"created": "Thu, 11 May 2023 20:23:29 GMT",
"version": "v1"
},
{
"created": "Mon, 21 Aug 2023 15:59:43 GMT",
"version": "v2"
}
] | 2023-08-22 | [
[
"Hamil",
"B.",
""
],
[
"Lütfüoğlu",
"B. C.",
""
]
] | In this work, we consider the quantum-corrected Reissner-Nordstr\"om black hole surrounded by quintessence matter and examine its thermodynamics and shadow. To this end, we handle the quantum-corrected metric of the black hole, which is given by Wu and Lui in 2022, and couple the quintessence matter field effects to the lapse function. Then, we obtain the mass, Hawking temperature, specific heat, and equation of state functions. In all these functions, we discuss two cases in which the quantum corrections are greater or smaller than the quintessence matter effects. We observe that within these two scenarios, the black hole has different characteristic thermal behaviors. Moreover, we find that the quintessence matter plays an important role in leading to a black hole remnant. Finally, we investigate the black hole shadow by Carter's approach. We find that quintessence matter and quantum corrections modify the shadow of the black hole. |
gr-qc/0102034 | Enric Verdaguer | Enric Verdaguer | Stochastic semiclassical gravity and fluctuations during inflation | 9 pages, Proceedings of the conference on Applied and differential
geometry, Lie algebras and general relativity, Thessaloniki 2000 | null | null | null | gr-qc | null | Stochastic semiclassical gravity is a theory for the interaction of gravity
with quantum matter fields which goes beyond the semiclassical limit. The
theory predicts stochastic fluctuations of the classical gravitational field
induced by the quantum fluctuations of the stress energy tensor of the matter
fields. Here we use an axiomatic approach to introduce the Einstein-Langevin
equations as the consistent set of dynamical equations for a first order
perturbative correction to semiclassical gravity and review their main
features. We then describe the application of the theory in a simple chaotic
inflationary model, where the fluctuations of the inflaton field induce
stochastic fluctuations in the gravitational field. The correlation functions
for these gravitational fluctuations lead to an almost Harrison-Zel'dovich
scale invariant spectrum at large scales, in agreement with the standard
theories for structure formation. A summary of recent results and other
applications of the theory is also given.
| [
{
"created": "Thu, 8 Feb 2001 19:05:31 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Verdaguer",
"Enric",
""
]
] | Stochastic semiclassical gravity is a theory for the interaction of gravity with quantum matter fields which goes beyond the semiclassical limit. The theory predicts stochastic fluctuations of the classical gravitational field induced by the quantum fluctuations of the stress energy tensor of the matter fields. Here we use an axiomatic approach to introduce the Einstein-Langevin equations as the consistent set of dynamical equations for a first order perturbative correction to semiclassical gravity and review their main features. We then describe the application of the theory in a simple chaotic inflationary model, where the fluctuations of the inflaton field induce stochastic fluctuations in the gravitational field. The correlation functions for these gravitational fluctuations lead to an almost Harrison-Zel'dovich scale invariant spectrum at large scales, in agreement with the standard theories for structure formation. A summary of recent results and other applications of the theory is also given. |
2211.13604 | Ruxandra Bondarescu | Ruxandra Bondarescu, Helena Ubach, Oleg Bulashenko and Andrew P.
Lundgren | Compact Binaries through a Lens: Silent vs. Detectable Microlensing for
the LIGO-Virgo-KAGRA Gravitational Wave Observatories | 17 pages, 12 Figures. Updated References. Submitted to Phys. Rev. D | Phys. Rev. D 108, (2023) 084033 | 10.1103/PhysRevD.108.084033 | null | gr-qc astro-ph.CO astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Massive objects located between Earth and a compact binary merger can act as
a magnifying glass improving the sensitivity of gravitational wave detectors to
distant events. Depending on the parameters of the system, a point mass lens
between the detector and the source can either lead to a smooth
frequency-dependent amplification of the gravitational wave signal, or
magnification combined with the appearance of a second image that interferes
with the first creating a regular, predictable pattern. We map the increase in
the signal to noise ratio for upcoming LVK observations as a function of the
mass of the lens $M_L$ and dimensionless source position $y$ for any point mass
lens between the detector and the binary source. To quantify detectability, we
compute the optimal match between the lensed waveform and the waveforms in the
unlensed template bank. The higher the mismatch with unlensed templates, the
more detectable lensing is. Furthermore, we estimate the probability of
lensing, and find that the redshift to which binary mergers are visible with
the LVK increases from z = 1 to about 3.2 for a total detected binary mass of
120 $M_\odot$. The overall probability of lensing is $<20\%$ of all detectable
events above the threshold SNR for $120 M_\odot$ and $<5\%$ for more common
events with $60 M_\odot$. We find that there is a selection bias for detectable
lensing that favors events that are close to the line of sight $y \lesssim
0.5$. Black hole binary searches could thus improve their sensitivity by taking
this bias into account. Moreover, the match, the SNR increase due to lensing,
and the probability of lensing are only weakly dependent on the noise curve of
the detector with very similar results for both the O3 and predicted O4 noise
power spectral densities. These results are upper limits that assume all dark
matter is composed of $300 M_\odot$ point mass lenses.
| [
{
"created": "Thu, 24 Nov 2022 13:45:31 GMT",
"version": "v1"
},
{
"created": "Sun, 11 Dec 2022 21:00:56 GMT",
"version": "v2"
},
{
"created": "Thu, 26 Oct 2023 11:57:46 GMT",
"version": "v3"
}
] | 2023-10-27 | [
[
"Bondarescu",
"Ruxandra",
""
],
[
"Ubach",
"Helena",
""
],
[
"Bulashenko",
"Oleg",
""
],
[
"Lundgren",
"Andrew P.",
""
]
] | Massive objects located between Earth and a compact binary merger can act as a magnifying glass improving the sensitivity of gravitational wave detectors to distant events. Depending on the parameters of the system, a point mass lens between the detector and the source can either lead to a smooth frequency-dependent amplification of the gravitational wave signal, or magnification combined with the appearance of a second image that interferes with the first creating a regular, predictable pattern. We map the increase in the signal to noise ratio for upcoming LVK observations as a function of the mass of the lens $M_L$ and dimensionless source position $y$ for any point mass lens between the detector and the binary source. To quantify detectability, we compute the optimal match between the lensed waveform and the waveforms in the unlensed template bank. The higher the mismatch with unlensed templates, the more detectable lensing is. Furthermore, we estimate the probability of lensing, and find that the redshift to which binary mergers are visible with the LVK increases from z = 1 to about 3.2 for a total detected binary mass of 120 $M_\odot$. The overall probability of lensing is $<20\%$ of all detectable events above the threshold SNR for $120 M_\odot$ and $<5\%$ for more common events with $60 M_\odot$. We find that there is a selection bias for detectable lensing that favors events that are close to the line of sight $y \lesssim 0.5$. Black hole binary searches could thus improve their sensitivity by taking this bias into account. Moreover, the match, the SNR increase due to lensing, and the probability of lensing are only weakly dependent on the noise curve of the detector with very similar results for both the O3 and predicted O4 noise power spectral densities. These results are upper limits that assume all dark matter is composed of $300 M_\odot$ point mass lenses. |
gr-qc/0608022 | Farrukh Fattoyev Jabborovich | B. J. Ahmedov, A. V. Khugaev | Remarks on Papapetrou Class of Vacuum Solutions of Einstein Equations | 8 pages | Int.J.Mod.Phys. D13 (2006) 1823-1830 | 10.1142/S0218271804004748 | null | gr-qc astro-ph | null | Class of axially symmetric solutions of vacuum Einstein field equations
including the Papapetrou solution as particular case has been found. It has
been shown that the derived solution describes the external axial symmetric
gravitational field of the source with nonvanishing mass. The general solution
is obtained for this class of functions. As an example of physical application,
the spacetime metric outside a line gravitomagnetic monopole has been obtained
from Papapetrou solution of vacuum equations of gravitational field.
| [
{
"created": "Fri, 4 Aug 2006 09:03:17 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Ahmedov",
"B. J.",
""
],
[
"Khugaev",
"A. V.",
""
]
] | Class of axially symmetric solutions of vacuum Einstein field equations including the Papapetrou solution as particular case has been found. It has been shown that the derived solution describes the external axial symmetric gravitational field of the source with nonvanishing mass. The general solution is obtained for this class of functions. As an example of physical application, the spacetime metric outside a line gravitomagnetic monopole has been obtained from Papapetrou solution of vacuum equations of gravitational field. |
1709.04016 | Santiago Esteban Perez Bergliaffa | Luz Marina Reyes and Santiago Esteban Perez Bergliaffa | On the emergence of the ${\bf\Lambda}$CDM model from self-interacting
Brans-Dicke theory in ${\bf d= 5}$ | 7 pages, 7 figures | null | 10.1140/epjc/s10052-017-5497-y | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate whether a self-interacting Brans-Dicke theory in $d=5$ without
matter and with a time-dependent metric can describe, after dimensional
reduction to $d=4$, the FLRW model with accelerated expansion and
non-relativistic matter. By rewriting the effective 4-dimensional theory as an
autonomous three-dimensional dynamical system and studying its critical points,
we show that the $\Lambda$CDM cosmology cannot emerge from such a model. This
result suggests that a richer structure in $d=5$ may be needed to obtain the
accelerated expansion as well as the matter content of the 4-dimensional
universe.
| [
{
"created": "Tue, 12 Sep 2017 18:49:50 GMT",
"version": "v1"
}
] | 2018-02-14 | [
[
"Reyes",
"Luz Marina",
""
],
[
"Bergliaffa",
"Santiago Esteban Perez",
""
]
] | We investigate whether a self-interacting Brans-Dicke theory in $d=5$ without matter and with a time-dependent metric can describe, after dimensional reduction to $d=4$, the FLRW model with accelerated expansion and non-relativistic matter. By rewriting the effective 4-dimensional theory as an autonomous three-dimensional dynamical system and studying its critical points, we show that the $\Lambda$CDM cosmology cannot emerge from such a model. This result suggests that a richer structure in $d=5$ may be needed to obtain the accelerated expansion as well as the matter content of the 4-dimensional universe. |
1512.08346 | Claus Kiefer | Claus Kiefer | Quantum black hole without singularity | 5 pages, invited contribution to the BH6 session at the Marcel
Grossmann Conference MG14 | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We discuss the quantization of a spherical dust shell in a rigorous manner.
Classically, the shell can collapse to form a black hole with a singularity. In
the quantum theory, we construct a well-defined self-adjoint extension for the
Hamilton operator. As a result, the evolution is unitary and the singularity is
avoided. If we represent the shell initially by a narrow wave packet, it will
first contract until it reaches the region where classically a black hole would
form, but then re-expands to infinity. In a way, the state can be interpreted
as a superposition of a black hole with a white hole.
| [
{
"created": "Mon, 28 Dec 2015 08:50:02 GMT",
"version": "v1"
}
] | 2015-12-29 | [
[
"Kiefer",
"Claus",
""
]
] | We discuss the quantization of a spherical dust shell in a rigorous manner. Classically, the shell can collapse to form a black hole with a singularity. In the quantum theory, we construct a well-defined self-adjoint extension for the Hamilton operator. As a result, the evolution is unitary and the singularity is avoided. If we represent the shell initially by a narrow wave packet, it will first contract until it reaches the region where classically a black hole would form, but then re-expands to infinity. In a way, the state can be interpreted as a superposition of a black hole with a white hole. |
2311.11752 | Jo\~ao Lu\'is Rosa | Jo\~ao Lu\'is Rosa | Junction conditions in gravity theories with extra scalar degrees of
freedom | 29 pages. V2: published version | Phys. Rev. D 109, 064018 (2024) | 10.1103/PhysRevD.109.064018 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this work we present a general method to obtain the junction conditions of
modified theories of gravity whose action can be written in the form
$f\left(X_1,...,X_n\right)$, where $X_1$ to $X_n$ are any combination of scalar
dependencies, e.g. the Ricci scalar $R$, the trace of the stress-energy tensor
$T$, the Gauss-Bonnet invariant $\mathcal G$, among others. We discriminate the
junction conditions into three sub-groups: the immediate conditions, arising
from the imposition of regularity of the relevant quantities in the
distribution formalism; the differential conditions, arising from the
differential terms in the field equations; and the coupling conditions, arising
from the interaction between different scalars $X_i$. Writing the modified
field equations in terms of a linear combination of the different contributions
of the scalars $X_i$ allows one to analyze the direct and differential junction
conditions independently for each of these scalars, whereas the coupling
junction conditions can be analyzed separately afterwards. We show that the
coupling junction conditions induced on a scalar $X_i$ due to a coupling with a
scalar $X_j$ are of the same form as the differential junction conditions of
the scalar $X_j$, but applied to the analogous quantity in the framework of the
scalar $X_i$. We provide a complete analysis of three different types of
spacetime matching, namely smooth matching, matching with a thin-shell, and
matching with double gravitational layers, and we also describe under which
conditions the full sets of junction conditions might be simplified. Our
results are applicable to several well-known theories of gravity e.g.
$f\left(R\right)$, $f\left(T\right)$, and $f\left(\mathcal G\right)$, and can
be straightforwardly extrapolated to other theories with scalar dependencies
and more complicated scenarios where several dependencies are present
simultaneously.
| [
{
"created": "Mon, 20 Nov 2023 13:27:44 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Mar 2024 15:48:21 GMT",
"version": "v2"
}
] | 2024-03-11 | [
[
"Rosa",
"João Luís",
""
]
] | In this work we present a general method to obtain the junction conditions of modified theories of gravity whose action can be written in the form $f\left(X_1,...,X_n\right)$, where $X_1$ to $X_n$ are any combination of scalar dependencies, e.g. the Ricci scalar $R$, the trace of the stress-energy tensor $T$, the Gauss-Bonnet invariant $\mathcal G$, among others. We discriminate the junction conditions into three sub-groups: the immediate conditions, arising from the imposition of regularity of the relevant quantities in the distribution formalism; the differential conditions, arising from the differential terms in the field equations; and the coupling conditions, arising from the interaction between different scalars $X_i$. Writing the modified field equations in terms of a linear combination of the different contributions of the scalars $X_i$ allows one to analyze the direct and differential junction conditions independently for each of these scalars, whereas the coupling junction conditions can be analyzed separately afterwards. We show that the coupling junction conditions induced on a scalar $X_i$ due to a coupling with a scalar $X_j$ are of the same form as the differential junction conditions of the scalar $X_j$, but applied to the analogous quantity in the framework of the scalar $X_i$. We provide a complete analysis of three different types of spacetime matching, namely smooth matching, matching with a thin-shell, and matching with double gravitational layers, and we also describe under which conditions the full sets of junction conditions might be simplified. Our results are applicable to several well-known theories of gravity e.g. $f\left(R\right)$, $f\left(T\right)$, and $f\left(\mathcal G\right)$, and can be straightforwardly extrapolated to other theories with scalar dependencies and more complicated scenarios where several dependencies are present simultaneously. |
gr-qc/9605068 | Eli Hawkins | Eli Hawkins | Hamiltonian Gravity and Noncommutative Geometry | 22 pages, AMS-LaTeX. Some improvements - mainly to sections 8 and 9.
Typographical errors to equations in appendix corrected | Commun.Math.Phys. 187 (1997) 471-489 | 10.1007/s002200050145 | CGPG-96/5-8 | gr-qc hep-th | null | A version of foliated spacetime is constructed in which the spatial geometry
is described as a time dependent noncommutative geometry. The ADM version of
the gravitational action is expressed in terms of these variables. It is shown
that the vector constraint is obtained without the need for an extraneous shift
vector in the action.
| [
{
"created": "Thu, 30 May 1996 21:47:19 GMT",
"version": "v1"
},
{
"created": "Thu, 6 Mar 1997 23:00:58 GMT",
"version": "v2"
},
{
"created": "Thu, 8 May 1997 21:18:46 GMT",
"version": "v3"
}
] | 2009-10-28 | [
[
"Hawkins",
"Eli",
""
]
] | A version of foliated spacetime is constructed in which the spatial geometry is described as a time dependent noncommutative geometry. The ADM version of the gravitational action is expressed in terms of these variables. It is shown that the vector constraint is obtained without the need for an extraneous shift vector in the action. |
gr-qc/0502066 | Brendan Foster | Brendan Z. Foster | Metric Redefinitions in Einstein-Aether Theory | 11 pages; v.2: Some clarifying remarks added, to appear in PRD | Phys.Rev. D72 (2005) 044017 | 10.1103/PhysRevD.72.044017 | null | gr-qc | null | `Einstein-Aether' theory, in which gravity couples to a dynamical, time-like,
unit-norm vector field, provides a means for studying Lorentz violation in a
generally covariant setting. Demonstrated here is the effect of a redefinition
of the metric and vector field in terms of the original fields and two free
parameters. The net effect is a change of the coupling constants appearing in
the action. Using such a redefinition, one of the coupling constants can be set
to zero, simplifying studies of solutions of the theory.
| [
{
"created": "Mon, 14 Feb 2005 20:46:49 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Aug 2005 17:44:22 GMT",
"version": "v2"
}
] | 2009-11-11 | [
[
"Foster",
"Brendan Z.",
""
]
] | `Einstein-Aether' theory, in which gravity couples to a dynamical, time-like, unit-norm vector field, provides a means for studying Lorentz violation in a generally covariant setting. Demonstrated here is the effect of a redefinition of the metric and vector field in terms of the original fields and two free parameters. The net effect is a change of the coupling constants appearing in the action. Using such a redefinition, one of the coupling constants can be set to zero, simplifying studies of solutions of the theory. |
2201.12458 | E. Kyriakopoulos | E. Kyriakopoulos | Regular Interior Solutions to the Solution of Kerr which Satisfy the
Weak and the Strong Energy Conditions | 25 pages, 15 figures | J. Math. Phys. 63, 012501 (2022) | 10.1063/5.0080367 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The line element of a class of solutions which match to the solution of Kerr
on an oblate spheroid if the two functions $ F(r)$ and $H(r)$ on which it
depends satisfy certain matching conditions is presented. The non vanishing
components of the Ricci tensor $R_{\mu\nu}$, the Ricci scalar $ R$, the second
order curvature invariant $K$, the eigenvalues of the Ricci tensor, the energy
density $\mu$, the tangential pressure $P_{\perp}$, and the quantity
$\mu+P_{\perp}$ are calculated. A function $F(r)$ is given for which $R$ and
$K$ and therefore the solutions are regular. The function $ H(r) $ should be
such that the solution it gives satisfies at least the Weak Energy Conditions
(WEC). Several $H(r)$ are given explicitly for which the resulting solutions
satisfy the WEC and also the Strong Energy Conditions (SEC) and the graphs of
their $\mu$, $P_{\perp}$ and $\mu+P_{\perp}$ for certain values of their
parameters are presented. It is shown that all solutions of the class are
anisotropic fluid solutions and that there are no perfect fluid solutions in
the class.
| [
{
"created": "Sat, 29 Jan 2022 00:05:14 GMT",
"version": "v1"
}
] | 2022-02-01 | [
[
"Kyriakopoulos",
"E.",
""
]
] | The line element of a class of solutions which match to the solution of Kerr on an oblate spheroid if the two functions $ F(r)$ and $H(r)$ on which it depends satisfy certain matching conditions is presented. The non vanishing components of the Ricci tensor $R_{\mu\nu}$, the Ricci scalar $ R$, the second order curvature invariant $K$, the eigenvalues of the Ricci tensor, the energy density $\mu$, the tangential pressure $P_{\perp}$, and the quantity $\mu+P_{\perp}$ are calculated. A function $F(r)$ is given for which $R$ and $K$ and therefore the solutions are regular. The function $ H(r) $ should be such that the solution it gives satisfies at least the Weak Energy Conditions (WEC). Several $H(r)$ are given explicitly for which the resulting solutions satisfy the WEC and also the Strong Energy Conditions (SEC) and the graphs of their $\mu$, $P_{\perp}$ and $\mu+P_{\perp}$ for certain values of their parameters are presented. It is shown that all solutions of the class are anisotropic fluid solutions and that there are no perfect fluid solutions in the class. |
1507.05669 | Sumanta Chakraborty | T. Padmanabhan, Sumanta Chakraborty and Dawood Kothawala | Spacetime with zero point length is two-dimensional at the Planck scale | published version | Gen. Rel. Grav. 48, 55 (2016) | 10.1007/s10714-016-2053-2 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is generally believed that any quantum theory of gravity should have a
generic feature --- a quantum of length. We provide a physical ansatz to obtain
an effective non-local metric tensor starting from the standard metric tensor
such that the spacetime acquires a zero-point-length $\ell _{0}$ of the order
of the Planck length $L_{P}$. This prescription leads to several remarkable
consequences. In particular, the Euclidean volume $V_D(\ell,\ell_{0})$ in a
$D$-dimensional spacetime of a region of size $\ell $ scales as $V_D(\ell, \ell
_{0}) \propto \ell_{0}^{D-2} \ell^2$ when $\ell \sim \ell_{0}$, while it
reduces to the standard result $V_D(\ell,\ell_{0}) \propto \ell^D$ at large
scales ($\ell \gg \ell_{0}$). The appropriately defined effective dimension,
$D_{\rm eff} $, decreases continuously from $D_{\rm eff}=D$ (at $\ell \gg
\ell_{0}$) to $D_{\rm eff}=2$ (at $\ell \sim \ell_{0}$). This suggests that the
physical spacetime becomes essentially 2-dimensional near Planck scale.
| [
{
"created": "Thu, 16 Jul 2015 20:00:58 GMT",
"version": "v1"
},
{
"created": "Mon, 3 Aug 2015 06:29:34 GMT",
"version": "v2"
},
{
"created": "Thu, 7 Apr 2016 04:15:31 GMT",
"version": "v3"
}
] | 2016-04-08 | [
[
"Padmanabhan",
"T.",
""
],
[
"Chakraborty",
"Sumanta",
""
],
[
"Kothawala",
"Dawood",
""
]
] | It is generally believed that any quantum theory of gravity should have a generic feature --- a quantum of length. We provide a physical ansatz to obtain an effective non-local metric tensor starting from the standard metric tensor such that the spacetime acquires a zero-point-length $\ell _{0}$ of the order of the Planck length $L_{P}$. This prescription leads to several remarkable consequences. In particular, the Euclidean volume $V_D(\ell,\ell_{0})$ in a $D$-dimensional spacetime of a region of size $\ell $ scales as $V_D(\ell, \ell _{0}) \propto \ell_{0}^{D-2} \ell^2$ when $\ell \sim \ell_{0}$, while it reduces to the standard result $V_D(\ell,\ell_{0}) \propto \ell^D$ at large scales ($\ell \gg \ell_{0}$). The appropriately defined effective dimension, $D_{\rm eff} $, decreases continuously from $D_{\rm eff}=D$ (at $\ell \gg \ell_{0}$) to $D_{\rm eff}=2$ (at $\ell \sim \ell_{0}$). This suggests that the physical spacetime becomes essentially 2-dimensional near Planck scale. |
1703.03710 | Llibert Arest\'e Sal\'o | Jaume Haro, Jaume Amor\'os and Llibert Arest\'e Sal\'o | The matter-ekpyrotic bounce scenario in Loop Quantum Cosmology | 39 pages, 19 figures. Version accepted for publication in JCAP | JCAP 09 (2017) 002 | 10.1088/1475-7516/2017/09/002 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We will perform a detailed study of the matter-ekpyrotic bouncing scenario in
Loop Quantum Cosmology using the methods of the dynamical systems theory. We
will show that when the background is driven by a single scalar field, at very
late times, in the contracting phase, all orbits depict a matter dominated
Universe, which evolves to an ekpyrotic phase. After the bounce the Universe
enters in the expanding phase, where the orbits leave the ekpyrotic regime
going to a kination (also named deflationary) regime. Moreover, this scenario
supports the production of heavy massive particles conformally coupled with
gravity, which reheats the universe at temperatures compatible with the
nucleosynthesis bounds and also the production of massless particles
non-conformally coupled with gravity leading to very high reheating
temperatures but ensuring the nucleosynthesis success. Dealing with
cosmological perturbations, these background dynamics produce a nearly scale
invariant power spectrum for the modes that leave the Hubble radius, in the
contracting phase, when the Universe is quasi-matter dominated, whose spectral
index and corresponding running is compatible with the recent experimental data
obtained by PLANCK's team.
| [
{
"created": "Fri, 10 Mar 2017 15:16:04 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Mar 2017 15:51:38 GMT",
"version": "v2"
},
{
"created": "Sun, 13 Aug 2017 16:01:26 GMT",
"version": "v3"
}
] | 2017-09-04 | [
[
"Haro",
"Jaume",
""
],
[
"Amorós",
"Jaume",
""
],
[
"Saló",
"Llibert Aresté",
""
]
] | We will perform a detailed study of the matter-ekpyrotic bouncing scenario in Loop Quantum Cosmology using the methods of the dynamical systems theory. We will show that when the background is driven by a single scalar field, at very late times, in the contracting phase, all orbits depict a matter dominated Universe, which evolves to an ekpyrotic phase. After the bounce the Universe enters in the expanding phase, where the orbits leave the ekpyrotic regime going to a kination (also named deflationary) regime. Moreover, this scenario supports the production of heavy massive particles conformally coupled with gravity, which reheats the universe at temperatures compatible with the nucleosynthesis bounds and also the production of massless particles non-conformally coupled with gravity leading to very high reheating temperatures but ensuring the nucleosynthesis success. Dealing with cosmological perturbations, these background dynamics produce a nearly scale invariant power spectrum for the modes that leave the Hubble radius, in the contracting phase, when the Universe is quasi-matter dominated, whose spectral index and corresponding running is compatible with the recent experimental data obtained by PLANCK's team. |
2112.14538 | Laszlo B. Szabados | L\'aszl\'o B. Szabados | A note on Penrose's Spin-Geometry Theorem and the geometry of `empirical
quantum angles' | 10 pages; v2: a convention changed to be compatible with the standard
one, the link in ref [5] is added, one reference is updated; v3: references
added, typos corrected, discussion improved; v4: references updated and
added, final version (Foundations of Physics) | Foundations of Physics (2022) 52:96 | 10.1007/s10701-022-00616-3 | null | gr-qc quant-ph | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the traditional formalism of quantum mechanics, a simple direct proof of
(a version of) the Spin Geometry Theorem of Penrose is given; and the structure
of a model of the `space of the quantum directions', defined in terms of
elementary $SU(2)$-invariant observables of the quantum mechanical systems, is
sketched.
| [
{
"created": "Wed, 29 Dec 2021 13:28:27 GMT",
"version": "v1"
},
{
"created": "Thu, 10 Mar 2022 11:37:24 GMT",
"version": "v2"
},
{
"created": "Tue, 12 Jul 2022 19:01:33 GMT",
"version": "v3"
},
{
"created": "Thu, 18 Aug 2022 11:21:41 GMT",
"version": "v4"
}
] | 2022-09-08 | [
[
"Szabados",
"László B.",
""
]
] | In the traditional formalism of quantum mechanics, a simple direct proof of (a version of) the Spin Geometry Theorem of Penrose is given; and the structure of a model of the `space of the quantum directions', defined in terms of elementary $SU(2)$-invariant observables of the quantum mechanical systems, is sketched. |
gr-qc/0411075 | Mihalis Dafermos | Mihalis Dafermos and Alan Rendall | An extension principle for the Einstein-Vlasov system in spherical
symmetry | 19 pages, 2 figures | Annales Henri Poincare 6 (2005) 1137-1155 | 10.1007/s00023-005-0235-7 | null | gr-qc | null | We prove that "first singularities" in the non-trapped region of the maximal
development of spherically symmetric asymptotically flat data for the
Einstein-Vlasov system must necessarily emanate from the center. The notion of
"first" depends only on the causal structure and can be described in the
language of terminal indecomposable pasts (TIPs). This result suggests a local
approach to proving weak cosmic censorship for this system. It can also be used
to give the first proof of the formation of black holes by the collapse of
collisionless matter from regular initial configurations.
| [
{
"created": "Mon, 15 Nov 2004 17:48:06 GMT",
"version": "v1"
}
] | 2009-11-10 | [
[
"Dafermos",
"Mihalis",
""
],
[
"Rendall",
"Alan",
""
]
] | We prove that "first singularities" in the non-trapped region of the maximal development of spherically symmetric asymptotically flat data for the Einstein-Vlasov system must necessarily emanate from the center. The notion of "first" depends only on the causal structure and can be described in the language of terminal indecomposable pasts (TIPs). This result suggests a local approach to proving weak cosmic censorship for this system. It can also be used to give the first proof of the formation of black holes by the collapse of collisionless matter from regular initial configurations. |
2109.02295 | Ying Wang | Wei Sun, Ying Wang, Fuyao Liu, Xin Wu | Applying explicit symplectic integrator to study chaos of charged
particles around magnetized Kerr black hole | 10 pages,20 figures | null | 10.1140/epjc/s10052-021-09579-7 | null | gr-qc astro-ph.IM nlin.CD physics.comp-ph | http://creativecommons.org/licenses/by/4.0/ | In a recent work of Wu, Wang, Sun and Liu, a second-order explicit symplectic
integrator was proposed for the integrable Kerr spacetime geometry. It is still
suited for simulating the nonintegrable dynamics of charged particles moving
around the Kerr black hole embedded in an external magnetic field. Its
successful construction is due to the contribution of a time transformation.
The algorithm exhibits a good long-term numerical performance in stable
Hamiltonian errors and computational efficiency. As its application, the
dynamics of order and chaos of charged particles is surveyed. In some
circumstances, an increase of the dragging effects of the spacetime seems to
weaken the extent of chaos from the global phase-space structure on Poincare
sections. However, an increase of the magnetic parameter strengthens the
chaotic properties. On the other hand, fast Lyapunov indicators show that there
is no universal rule for the dependence of the transition between different
dynamical regimes on the black hole spin. The dragging effects of the spacetime
do not always weaken the extent of chaos from a local point of view.
| [
{
"created": "Mon, 6 Sep 2021 08:54:55 GMT",
"version": "v1"
}
] | 2021-09-07 | [
[
"Sun",
"Wei",
""
],
[
"Wang",
"Ying",
""
],
[
"Liu",
"Fuyao",
""
],
[
"Wu",
"Xin",
""
]
] | In a recent work of Wu, Wang, Sun and Liu, a second-order explicit symplectic integrator was proposed for the integrable Kerr spacetime geometry. It is still suited for simulating the nonintegrable dynamics of charged particles moving around the Kerr black hole embedded in an external magnetic field. Its successful construction is due to the contribution of a time transformation. The algorithm exhibits a good long-term numerical performance in stable Hamiltonian errors and computational efficiency. As its application, the dynamics of order and chaos of charged particles is surveyed. In some circumstances, an increase of the dragging effects of the spacetime seems to weaken the extent of chaos from the global phase-space structure on Poincare sections. However, an increase of the magnetic parameter strengthens the chaotic properties. On the other hand, fast Lyapunov indicators show that there is no universal rule for the dependence of the transition between different dynamical regimes on the black hole spin. The dragging effects of the spacetime do not always weaken the extent of chaos from a local point of view. |
1901.00938 | David Anderson | David Anderson, Paulo Freire, Nicol\'as Yunes | Binary Pulsar constraints on massless scalar-tensor theories using
Bayesian statistics | 15 pages, 7 figures, Submitted to CQG | null | 10.1088/1361-6382/ab3a1c | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Binary pulsars provide some of the tightest current constraints on modified
theories of gravity and these constraints will only get tighter as radio
astronomers continue timing these systems. These binary pulsars are
particularly good at constraining scalar-tensor theories in which gravity is
mediated by a scalar field in addition to the metric tensor. Scalar-tensor
theories can predict large deviations from General Relativity due to the fact
that they allow for violation of the strong-equivalence principle through a
phenomenon known as scalarization. This effect appears directly in the timing
model for binary pulsars, and as such, it can be tightly constrained through
precise timing. In this paper, we investigate these constraints for two
scalar-tensor theories and a large set of realistic equations of state. We
calculate the constraints that can be placed by saturating the current
$1\sigma$ bounds on single post-Keplerian parameters, as well as employing
Bayesian methods through Markov-Chain-Monte-Carlo simulations to explore the
constraints that can be achieved when one considers all measured parameters
simultaneously. Our results demonstrate that both methods are able to place
similar constraints and that they are both indeed dominated by the measurements
of the orbital period decay. The Bayesian approach, however, allows one to
simultaneously explore the posterior distributions of not only the theory
parameters but of the masses as well.
| [
{
"created": "Thu, 3 Jan 2019 23:09:45 GMT",
"version": "v1"
}
] | 2019-12-11 | [
[
"Anderson",
"David",
""
],
[
"Freire",
"Paulo",
""
],
[
"Yunes",
"Nicolás",
""
]
] | Binary pulsars provide some of the tightest current constraints on modified theories of gravity and these constraints will only get tighter as radio astronomers continue timing these systems. These binary pulsars are particularly good at constraining scalar-tensor theories in which gravity is mediated by a scalar field in addition to the metric tensor. Scalar-tensor theories can predict large deviations from General Relativity due to the fact that they allow for violation of the strong-equivalence principle through a phenomenon known as scalarization. This effect appears directly in the timing model for binary pulsars, and as such, it can be tightly constrained through precise timing. In this paper, we investigate these constraints for two scalar-tensor theories and a large set of realistic equations of state. We calculate the constraints that can be placed by saturating the current $1\sigma$ bounds on single post-Keplerian parameters, as well as employing Bayesian methods through Markov-Chain-Monte-Carlo simulations to explore the constraints that can be achieved when one considers all measured parameters simultaneously. Our results demonstrate that both methods are able to place similar constraints and that they are both indeed dominated by the measurements of the orbital period decay. The Bayesian approach, however, allows one to simultaneously explore the posterior distributions of not only the theory parameters but of the masses as well. |
gr-qc/9910085 | null | Jacek Jezierski | Trautman-Bondi Mass for Scalar Field and Gravity | LaTeX2e, 14 pages, to appear in Rep. on Math. Physics | Coherent States, Quantization, and Gravity; Proceedings of the
XVII Workshop on Geometric Methods in Physics, 1998 | null | UW-KMMF-99-03 | gr-qc | null | The energy at null infinity is presented with the help of a simple example of
a massless scalar field in Minkowski spacetime. It is also discussed for
Einstein gravity. In particular, various aspects of the loss of the energy in
the radiating regime are shown.
| [
{
"created": "Mon, 25 Oct 1999 13:25:33 GMT",
"version": "v1"
}
] | 2013-11-12 | [
[
"Jezierski",
"Jacek",
""
]
] | The energy at null infinity is presented with the help of a simple example of a massless scalar field in Minkowski spacetime. It is also discussed for Einstein gravity. In particular, various aspects of the loss of the energy in the radiating regime are shown. |
gr-qc/0204004 | Sawa Manoff | Sawa Manoff | Mechanics of Continuous Media in $(\bar{L}_{n},g)$-Spaces. IV. Stress
(Tension) Tensor | 38 pages, LaTeX | null | null | null | gr-qc | null | Basic notions of continuous media mechanics are introduced for spaces with
affine connections and metrics. Stress (tension) tensors are considered,
obtained by the use of the method of Lagrangians with covariant derivatives
(MLCD). On the basis of the covariant Noether's identities for the
energy-momentum tensors, Navier-Stokes' identities are found and generalized
Navier-Cauchy as well as Navier-Stokes' equations are investigated over spaces
with affine connections and metrics. PACS numbers: 11.10.-z; 11.10.Ef; 7.10.+g;
47.75.+f; 47.90.+a; 83.10.Bb
| [
{
"created": "Mon, 1 Apr 2002 11:23:51 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Manoff",
"Sawa",
""
]
] | Basic notions of continuous media mechanics are introduced for spaces with affine connections and metrics. Stress (tension) tensors are considered, obtained by the use of the method of Lagrangians with covariant derivatives (MLCD). On the basis of the covariant Noether's identities for the energy-momentum tensors, Navier-Stokes' identities are found and generalized Navier-Cauchy as well as Navier-Stokes' equations are investigated over spaces with affine connections and metrics. PACS numbers: 11.10.-z; 11.10.Ef; 7.10.+g; 47.75.+f; 47.90.+a; 83.10.Bb |
gr-qc/9601007 | Jorge Griego | Jorge Griego | Extended knots and the space of states of quantum gravity | 19 pages | Nucl.Phys. B473 (1996) 291-307 | 10.1016/0550-3213(96)00235-0 | IFFC 96-01 | gr-qc | null | In the loop representation the quantum constraints of gravity can be solved.
This fact allowed significant progress in the understanding of the space of
states of the theory. The analysis of the constraints over loop dependent
wavefunctions has been traditionally based upon geometric (in contrast to
analytic) properties of the loops. The reason for this preferred way is
twofold: for one hand the inherent difficulties associated with the analytic
loop calculus, and on the other our limited knowledge about the analytic
properties of knots invariants. Extended loops provide a way to overcome the
difficulties at both levels. For one hand, a systematic method to construct
analytic expressions of diffeomorphism invariants (the extended knots) in terms
of the Chern-Simons propagators can be developed. Extended knots are simply
related to ordinary knots (at least formally). The analytic expressions of knot
invariants could be produced then in a generic way. On the other hand, the
evaluation of the Hamiltonian over extended loop wavefunctions can be
thoroughly accomplished in the extended loop framework. These two ingredients
promote extended loops as a potential resort for answering important questions
about quantum gravity.
| [
{
"created": "Sun, 7 Jan 1996 01:19:30 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Griego",
"Jorge",
""
]
] | In the loop representation the quantum constraints of gravity can be solved. This fact allowed significant progress in the understanding of the space of states of the theory. The analysis of the constraints over loop dependent wavefunctions has been traditionally based upon geometric (in contrast to analytic) properties of the loops. The reason for this preferred way is twofold: for one hand the inherent difficulties associated with the analytic loop calculus, and on the other our limited knowledge about the analytic properties of knots invariants. Extended loops provide a way to overcome the difficulties at both levels. For one hand, a systematic method to construct analytic expressions of diffeomorphism invariants (the extended knots) in terms of the Chern-Simons propagators can be developed. Extended knots are simply related to ordinary knots (at least formally). The analytic expressions of knot invariants could be produced then in a generic way. On the other hand, the evaluation of the Hamiltonian over extended loop wavefunctions can be thoroughly accomplished in the extended loop framework. These two ingredients promote extended loops as a potential resort for answering important questions about quantum gravity. |
1009.4923 | Tanja Hinderer | Eanna E. Flanagan (Cornell), Tanja Hinderer (Caltech) | Transient resonances in the inspirals of point particles into black
holes | 4 pages, 1 figure, minor corrections | null | 10.1103/PhysRevLett.109.071102 | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that transient resonances occur in the two body problem in general
relativity, in the highly relativistic, extreme mass-ratio regime for spinning
black holes. These resonances occur when the ratio of polar and radial orbital
frequencies, which is slowly evolving under the influence of gravitational
radiation reaction, passes through a low order rational number. At such points,
the adiabatic approximation to the orbital evolution breaks down, and there is
a brief but order unity correction to the inspiral rate. Corrections to the
gravitational wave signal's phase due to resonance effects scale as the square
root of the inverse of mass of the small body, and thus become large in the
extreme-mass-ratio limit, dominating over all other post-adiabatic effects. The
resonances make orbits more sensitive to changes in initial data (though not
quite chaotic), and are genuine non-perturbative effects that are not seen at
any order in a standard post-Newtonian expansion. Our results apply to an
important potential source of gravitational waves, the gradual inspiral of
white dwarfs, neutron stars, or black holes into much more massive black holes.
It is hoped to exploit observations of these sources to map the spacetime
geometry of black holes. However, such mapping will require accurate models of
binary dynamics, which is a computational challenge whose difficulty is
significantly increased by resonance effects. We estimate that the resonance
phase shifts will be of order a few tens of cycles for mass ratios $\sim
10^{-6}$, by numerically evolving fully relativistic orbital dynamics
supplemented with an approximate, post-Newtonian self-force.
| [
{
"created": "Fri, 24 Sep 2010 19:52:21 GMT",
"version": "v1"
},
{
"created": "Mon, 27 Sep 2010 20:39:38 GMT",
"version": "v2"
},
{
"created": "Wed, 11 Jul 2012 21:22:42 GMT",
"version": "v3"
}
] | 2013-05-30 | [
[
"Flanagan",
"Eanna E.",
"",
"Cornell"
],
[
"Hinderer",
"Tanja",
"",
"Caltech"
]
] | We show that transient resonances occur in the two body problem in general relativity, in the highly relativistic, extreme mass-ratio regime for spinning black holes. These resonances occur when the ratio of polar and radial orbital frequencies, which is slowly evolving under the influence of gravitational radiation reaction, passes through a low order rational number. At such points, the adiabatic approximation to the orbital evolution breaks down, and there is a brief but order unity correction to the inspiral rate. Corrections to the gravitational wave signal's phase due to resonance effects scale as the square root of the inverse of mass of the small body, and thus become large in the extreme-mass-ratio limit, dominating over all other post-adiabatic effects. The resonances make orbits more sensitive to changes in initial data (though not quite chaotic), and are genuine non-perturbative effects that are not seen at any order in a standard post-Newtonian expansion. Our results apply to an important potential source of gravitational waves, the gradual inspiral of white dwarfs, neutron stars, or black holes into much more massive black holes. It is hoped to exploit observations of these sources to map the spacetime geometry of black holes. However, such mapping will require accurate models of binary dynamics, which is a computational challenge whose difficulty is significantly increased by resonance effects. We estimate that the resonance phase shifts will be of order a few tens of cycles for mass ratios $\sim 10^{-6}$, by numerically evolving fully relativistic orbital dynamics supplemented with an approximate, post-Newtonian self-force. |
1611.09781 | Pantelis Apostolopoulos | Pantelis S. Apostolopoulos | Intrinsic Conformal Symmetries in Szekeres models | 6 pages (uses iopart style/class files); (v2) some minor amendments
to match published version in Modern Physics Letters A | Mod.Phys.Lett. A32 (2017) no.19, 1750099 | 10.1142/S0217732317500997 | null | gr-qc math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We show that Spatially Inhomogeneous (SI) and Irrotational dust models admit
a \emph{6-dimensional algebra } of \emph{Intrinsic Conformal Vector Fields}
(ICVFs) $\mathbf{X}_{\alpha }$ satisfying
$p_{a}^{c}p_{b}^{d}\mathcal{L}_{\mathbf{X}_{\alpha }}p_{cd}=2\phi
(\mathbf{X}_{\alpha })p_{ab}$ where $p_{ab}$ is the associated metric of the 2d
distribution $\mathcal{X}$ normal to the fluid velocity $u^{a}$ and the radial
unit spacelike vector field $x^{a}$. The Intrinsic Conformal (IC) algebra is
determined for each of the curvature value $\epsilon $ that characterizes the
structure of the screen space $\mathcal{X}$. In addition the conformal flatness
of the hypersurfaces $\mathbf{u}=\mathbf{0}$ indicates the existence of a
\emph{% 10-dimensional algebra} of ICVFs of the 3d metric $h_{ab}$. We
illustrate this expectation and propose a method to derive them by giving
explicitly the \emph{7 proper} ICVFs of the Lema\^{\i}tre-Tolman-Bondi (LTB)
model which represents the simplest subclass within the Szekeres family.
| [
{
"created": "Tue, 29 Nov 2016 18:46:37 GMT",
"version": "v1"
},
{
"created": "Mon, 22 May 2017 15:49:53 GMT",
"version": "v2"
}
] | 2017-06-13 | [
[
"Apostolopoulos",
"Pantelis S.",
""
]
] | We show that Spatially Inhomogeneous (SI) and Irrotational dust models admit a \emph{6-dimensional algebra } of \emph{Intrinsic Conformal Vector Fields} (ICVFs) $\mathbf{X}_{\alpha }$ satisfying $p_{a}^{c}p_{b}^{d}\mathcal{L}_{\mathbf{X}_{\alpha }}p_{cd}=2\phi (\mathbf{X}_{\alpha })p_{ab}$ where $p_{ab}$ is the associated metric of the 2d distribution $\mathcal{X}$ normal to the fluid velocity $u^{a}$ and the radial unit spacelike vector field $x^{a}$. The Intrinsic Conformal (IC) algebra is determined for each of the curvature value $\epsilon $ that characterizes the structure of the screen space $\mathcal{X}$. In addition the conformal flatness of the hypersurfaces $\mathbf{u}=\mathbf{0}$ indicates the existence of a \emph{% 10-dimensional algebra} of ICVFs of the 3d metric $h_{ab}$. We illustrate this expectation and propose a method to derive them by giving explicitly the \emph{7 proper} ICVFs of the Lema\^{\i}tre-Tolman-Bondi (LTB) model which represents the simplest subclass within the Szekeres family. |
2008.06728 | Peter K.F. Kuhfittig | Peter K.F. Kuhfittig | Noncommutative-geometry wormholes without exotic matter | 6 pages, no figures | Adv. Stud. Theor. Phys.,vol. 14, 219-225 (2020) | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A fundamental property of Morris-Thorne wormholes is the so-called flare-out
condition that automatically results in a violation of the null energy
condition (NEC) in classical general relativity. By contrast, in $f(R)$
modified gravity, the material threading the wormhole may actually satisfy the
NEC, while, at the same time, the effective stress-energy tensor arising from
the modified theory violates the NEC, thereby sustaining the wormhole. It is
shown in this paper that noncommutative geometry, an offshoot of string theory,
can be viewed as a special case of $f(R)$ gravity and can therefore sustain a
wormhole without the use of exotic matter. It also provides a motivation for
the choice of $f(R)$ in the modified gravitational theory.
| [
{
"created": "Sat, 15 Aug 2020 14:58:23 GMT",
"version": "v1"
},
{
"created": "Wed, 19 Aug 2020 15:52:33 GMT",
"version": "v2"
}
] | 2020-08-20 | [
[
"Kuhfittig",
"Peter K. F.",
""
]
] | A fundamental property of Morris-Thorne wormholes is the so-called flare-out condition that automatically results in a violation of the null energy condition (NEC) in classical general relativity. By contrast, in $f(R)$ modified gravity, the material threading the wormhole may actually satisfy the NEC, while, at the same time, the effective stress-energy tensor arising from the modified theory violates the NEC, thereby sustaining the wormhole. It is shown in this paper that noncommutative geometry, an offshoot of string theory, can be viewed as a special case of $f(R)$ gravity and can therefore sustain a wormhole without the use of exotic matter. It also provides a motivation for the choice of $f(R)$ in the modified gravitational theory. |
gr-qc/9701007 | Renate Loll | R. Loll (AEI, Potsdam and ESI, Vienna) | Latticing quantum gravity | 7 pages, TeX, 1 figure (epsf); contribution to Santa Margherita
Conference on Constrained Dynamics and Quantum Gravity | Nucl.Phys.Proc.Suppl. 57 (1997) 255-258 | 10.1016/S0920-5632(97)00398-8 | null | gr-qc | null | I discuss some aspects of a lattice approach to canonical quantum gravity in
a connection formulation, discuss how it differs from the continuum
construction, and compare the spectra of geometric operators - encoding
information about components of the spatial metric - for some simple lattice
quantum states.
| [
{
"created": "Mon, 6 Jan 1997 22:45:17 GMT",
"version": "v1"
}
] | 2009-10-30 | [
[
"Loll",
"R.",
"",
"AEI, Potsdam and ESI, Vienna"
]
] | I discuss some aspects of a lattice approach to canonical quantum gravity in a connection formulation, discuss how it differs from the continuum construction, and compare the spectra of geometric operators - encoding information about components of the spatial metric - for some simple lattice quantum states. |
2008.10332 | Jianwei Mei | Jianwei Mei, Yan-Zheng Bai, Jiahui Bao, Enrico Barausse, Lin Cai,
Enrico Canuto, Bin Cao, Wei-Ming Chen, Yu Chen, Yan-Wei Ding, Hui-Zong Duan,
Huimin Fan, Wen-Fan Feng, Honglin Fu, Qing Gao, TianQuan Gao, Yungui Gong,
Xingyu Gou, Chao-Zheng Gu, De-Feng Gu, Zi-Qi He, Martin Hendry, Wei Hong,
Xin-Chun Hu, Yi-Ming Hu, Yuexin Hu, Shun-Jia Huang, Xiang-Qing Huang, Qinghua
Jiang, Yuan-Ze Jiang, Yun Jiang, Zhen Jiang, Hong-Ming Jin, Valeriya Korol,
Hong-Yin Li, Ming Li, Ming Li, Pengcheng Li, Rongwang Li, Yuqiang Li, Zhu Li,
Zhulian Li, Zhu-Xi Li, Yu-Rong Liang, Zheng-Cheng Liang, Fang-Jie Liao, Shuai
Liu, Yan-Chong Liu, Li Liu, Pei-Bo Liu, Xuhui Liu, Yuan Liu, Xiong-Fei Lu,
Yang Lu, Ze-Huang Lu, Yan Luo, Zhi-Cai Luo, Vadim Milyukov, Min Ming, Xiaoyu
Pi, Chenggang Qin, Shao-Bo Qu, Alberto Sesana, Chenggang Shao, Changfu Shi,
Wei Su, Ding-Yin Tan, Yujie Tan, Zhuangbin Tan, Liang-Cheng Tu, Bin Wang,
Cheng-Rui Wang, Fengbin Wang, Guan-Fang Wang, Haitian Wang, Jian Wang, Lijiao
Wang, Panpan Wang, Xudong Wang, Yan Wang, Yi-Fan Wang, Ran Wei, Shu-Chao Wu,
Chun-Yu Xiao, Xiao-Shi Xu, Chao Xue, Fang-Chao Yang, Liang Yang, Ming-Lin
Yang, Shan-Qing Yang, Bobing Ye, Hsien-Chi Yeh, Shenghua Yu, Dongsheng Zhai,
Caishi Zhang, Haitao Zhang, Jian-dong Zhang, Jie Zhang, Lihua Zhang, Xin
Zhang, Xuefeng Zhang, Hao Zhou, Ming-Yue Zhou, Ze-Bing Zhou, Dong-Dong Zhu,
Tie-Guang Zi, Jun Luo | The TianQin project: current progress on science and technology | 16 pages, 1 figure, invited article to a special section in PTEP | null | 10.1093/ptep/ptaa114 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | TianQin is a planned space-based gravitational wave (GW) observatory
consisting of three earth orbiting satellites with an orbital radius of about
$10^5~{\rm km}$. The satellites will form a equilateral triangle constellation
the plane of which is nearly perpendicular to the ecliptic plane. TianQin aims
to detect GWs between $10^{-4}~{\rm Hz}$ and $1~{\rm Hz}$ that can be generated
by a wide variety of important astrophysical and cosmological sources,
including the inspiral of Galactic ultra-compact binaries, the inspiral of
stellar-mass black hole binaries, extreme mass ratio inspirals, the merger of
massive black hole binaries, and possibly the energetic processes in the very
early universe or exotic sources such as cosmic strings. In order to start
science operations around 2035, a roadmap called the 0123 plan is being used to
bring the key technologies of TianQin to maturity, supported by the
construction of a series of research facilities on the ground. Two major
projects of the 0123 plan are being carried out. In this process, the team has
created a new generation $17~{\rm cm}$ single-body hollow corner-cube
retro-reflector which has been launched with the QueQiao satellite on 21 May
2018; a new laser ranging station equipped with a $1.2~{\rm m}$ telescope has
been constructed and the station has successfully ranged to all the five
retro-reflectors on the Moon; and the TianQin-1 experimental satellite has been
launched on 20 December 2019 and the first round result shows that the
satellite has exceeded all of its mission requirements.
| [
{
"created": "Mon, 24 Aug 2020 11:45:05 GMT",
"version": "v1"
}
] | 2020-08-25 | [
[
"Mei",
"Jianwei",
""
],
[
"Bai",
"Yan-Zheng",
""
],
[
"Bao",
"Jiahui",
""
],
[
"Barausse",
"Enrico",
""
],
[
"Cai",
"Lin",
""
],
[
"Canuto",
"Enrico",
""
],
[
"Cao",
"Bin",
""
],
[
"Chen",
"Wei-... | TianQin is a planned space-based gravitational wave (GW) observatory consisting of three earth orbiting satellites with an orbital radius of about $10^5~{\rm km}$. The satellites will form a equilateral triangle constellation the plane of which is nearly perpendicular to the ecliptic plane. TianQin aims to detect GWs between $10^{-4}~{\rm Hz}$ and $1~{\rm Hz}$ that can be generated by a wide variety of important astrophysical and cosmological sources, including the inspiral of Galactic ultra-compact binaries, the inspiral of stellar-mass black hole binaries, extreme mass ratio inspirals, the merger of massive black hole binaries, and possibly the energetic processes in the very early universe or exotic sources such as cosmic strings. In order to start science operations around 2035, a roadmap called the 0123 plan is being used to bring the key technologies of TianQin to maturity, supported by the construction of a series of research facilities on the ground. Two major projects of the 0123 plan are being carried out. In this process, the team has created a new generation $17~{\rm cm}$ single-body hollow corner-cube retro-reflector which has been launched with the QueQiao satellite on 21 May 2018; a new laser ranging station equipped with a $1.2~{\rm m}$ telescope has been constructed and the station has successfully ranged to all the five retro-reflectors on the Moon; and the TianQin-1 experimental satellite has been launched on 20 December 2019 and the first round result shows that the satellite has exceeded all of its mission requirements. |
1101.2198 | Travis Garrett | Travis Garrett | The Observer Class Hypothesis | 14 pages, 1 figure | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The discovery of a small cosmological constant has stimulated interest in the
measure problem. One should expect to be a typical observer, but defining such
a thing is difficult in the vastness of an eternally inflating universe. We
propose that a crucial prerequisite is understanding why one should exist as an
observer at all. We assume that the Physical Church Turing Thesis is correct
and therefore all observers (and everything else that exists) can be described
as different types of information. We then argue that the observers
collectively form the largest class of information (where, in analogy with the
Faddeev Popov procedure, we only count over "gauge invariant" forms of
information). The statistical predominance of the observers is due to their
ability to selectively absorb other forms of information from many different
sources. In particular, it is the combinatorics that arise from this selection
process which leads us to equate the observer class $\mathcal{O}$ with the
nontrivial power set $\hat{\mathcal{P}}(\mathcal{U})$ of the set of all
information $\mathcal{U}$. Observers themselves are thus the typical form of
information. If correct, this proposal simplifies the measure problem, and
leads to dramatic long term predictions.
| [
{
"created": "Tue, 11 Jan 2011 20:40:50 GMT",
"version": "v1"
}
] | 2011-01-12 | [
[
"Garrett",
"Travis",
""
]
] | The discovery of a small cosmological constant has stimulated interest in the measure problem. One should expect to be a typical observer, but defining such a thing is difficult in the vastness of an eternally inflating universe. We propose that a crucial prerequisite is understanding why one should exist as an observer at all. We assume that the Physical Church Turing Thesis is correct and therefore all observers (and everything else that exists) can be described as different types of information. We then argue that the observers collectively form the largest class of information (where, in analogy with the Faddeev Popov procedure, we only count over "gauge invariant" forms of information). The statistical predominance of the observers is due to their ability to selectively absorb other forms of information from many different sources. In particular, it is the combinatorics that arise from this selection process which leads us to equate the observer class $\mathcal{O}$ with the nontrivial power set $\hat{\mathcal{P}}(\mathcal{U})$ of the set of all information $\mathcal{U}$. Observers themselves are thus the typical form of information. If correct, this proposal simplifies the measure problem, and leads to dramatic long term predictions. |
2302.10233 | Francisco M. Blanco | Francisco M. Blanco and \'Eanna \'E. Flanagan | Motion of a spinning particle under the conservative piece of the
self-force is Hamiltonian to first order in mass and spin | 7 pages | null | 10.1103/PhysRevD.107.124017 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We consider the motion of a point particle with spin in a stationary
spacetime. We define, following Witzany (2019) and later Ramond (2022), a
twelve dimensional Hamiltonian dynamical system whose orbits coincide with the
solutions of the Mathisson-Papapetrou-Dixon equations of motion with the
Tulczyjew-Dixon spin supplementary condition, to linear order in spin. We then
perturb this system by adding the conservative pieces of the leading order
gravitational self-force and self-torque sourced by the particle's mass and
spin. We show that this perturbed system is Hamiltonian and derive expressions
for the Hamiltonian function and symplectic form. This result extends our
previous result for spinless point particles.
| [
{
"created": "Mon, 20 Feb 2023 19:05:56 GMT",
"version": "v1"
},
{
"created": "Thu, 4 May 2023 04:54:22 GMT",
"version": "v2"
}
] | 2023-06-21 | [
[
"Blanco",
"Francisco M.",
""
],
[
"Flanagan",
"Éanna É.",
""
]
] | We consider the motion of a point particle with spin in a stationary spacetime. We define, following Witzany (2019) and later Ramond (2022), a twelve dimensional Hamiltonian dynamical system whose orbits coincide with the solutions of the Mathisson-Papapetrou-Dixon equations of motion with the Tulczyjew-Dixon spin supplementary condition, to linear order in spin. We then perturb this system by adding the conservative pieces of the leading order gravitational self-force and self-torque sourced by the particle's mass and spin. We show that this perturbed system is Hamiltonian and derive expressions for the Hamiltonian function and symplectic form. This result extends our previous result for spinless point particles. |
1902.08734 | Gauranga Samanta | Karim Mosani and Gauranga C. Samanta | Dynamics of General Barotropic Stellar Fluid in the Framework of
$R+2\alpha T$ Gravity | 14 pages, 17 figures | null | 10.1142/S0217732320500893 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Gravitational collapse of a spherically symmetric homogeneous perfect
barotropic fluid with linear as well as polytropic type Equation of State (EoS)
has been investigated in the framework of a linear model of $f(R,T)$ gravity.
This modified gravity has the potential to explain the observed cosmic
acceleration. The calculations have been done taking the transformed time
coordinate $t \to \sqrt{\frac{\rho_0}{3}} t$, where $\rho_0$ is the initial
density of the fluid. For linear EoS $p=\omega\rho$, the condition for being a
true singularity, along with sufficient condition for the formation of apparent
horizon covering the singularity has been derived. For a polytrope having the
EoS $p=K\rho^{1+\frac{1}{n}}$, the scale factor ($A$) as a function of fluid
density ($\rho$) has been obtained which is then used to study the dynamics of
the fluid. Role of the polytropic index ($n$) and the constant of
proportionality ($K$) in the dynamics of the fluid is also studied. A new type
of exotic matter field having varied dependence of scale factor on the density,
and having the potential to give rise to bouncing cosmology, provided it is the
dominating fluid in the universe, is obtained in this domain and is
investigated. Energy conditions are discussed.
| [
{
"created": "Sat, 23 Feb 2019 04:06:05 GMT",
"version": "v1"
}
] | 2020-05-06 | [
[
"Mosani",
"Karim",
""
],
[
"Samanta",
"Gauranga C.",
""
]
] | Gravitational collapse of a spherically symmetric homogeneous perfect barotropic fluid with linear as well as polytropic type Equation of State (EoS) has been investigated in the framework of a linear model of $f(R,T)$ gravity. This modified gravity has the potential to explain the observed cosmic acceleration. The calculations have been done taking the transformed time coordinate $t \to \sqrt{\frac{\rho_0}{3}} t$, where $\rho_0$ is the initial density of the fluid. For linear EoS $p=\omega\rho$, the condition for being a true singularity, along with sufficient condition for the formation of apparent horizon covering the singularity has been derived. For a polytrope having the EoS $p=K\rho^{1+\frac{1}{n}}$, the scale factor ($A$) as a function of fluid density ($\rho$) has been obtained which is then used to study the dynamics of the fluid. Role of the polytropic index ($n$) and the constant of proportionality ($K$) in the dynamics of the fluid is also studied. A new type of exotic matter field having varied dependence of scale factor on the density, and having the potential to give rise to bouncing cosmology, provided it is the dominating fluid in the universe, is obtained in this domain and is investigated. Energy conditions are discussed. |
1805.11591 | Petya Nedkova | Galin Gyulchev, Petya Nedkova, Vassil Tinchev, Stoytcho Yazadjiev | On the shadow of rotating traversable wormholes | 19 pages; 12 figures | null | 10.1140/epjc/s10052-018-6012-9 | null | gr-qc astro-ph.HE | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We revisit the shadow of rotating traversable wormholes discussing the role
of the wormhole throat in the shadow formation. For certain classes of
wormholes the throat serves as a potential barrier for light rays with
particular impact parameters, thus modifying the shadow shape. We consider a
couple of wormhole solutions and examine the structure of their shadow images,
and the intrinsic mechanisms for their formation. Some of the shadows possess
cuspy edges, which arise due to the interplay of two distinct families of
unstable spherical orbits. These solutions provide examples, in which the
explicit mechanism for cusp formation can be uncovered.
| [
{
"created": "Tue, 29 May 2018 17:18:27 GMT",
"version": "v1"
}
] | 2018-08-01 | [
[
"Gyulchev",
"Galin",
""
],
[
"Nedkova",
"Petya",
""
],
[
"Tinchev",
"Vassil",
""
],
[
"Yazadjiev",
"Stoytcho",
""
]
] | We revisit the shadow of rotating traversable wormholes discussing the role of the wormhole throat in the shadow formation. For certain classes of wormholes the throat serves as a potential barrier for light rays with particular impact parameters, thus modifying the shadow shape. We consider a couple of wormhole solutions and examine the structure of their shadow images, and the intrinsic mechanisms for their formation. Some of the shadows possess cuspy edges, which arise due to the interplay of two distinct families of unstable spherical orbits. These solutions provide examples, in which the explicit mechanism for cusp formation can be uncovered. |
2206.00768 | Arnab Mukherjee | Arnab Mukherjee, Sunandan Gangopadhyay and A. S. Majumdar | Unruh quantum Otto engine in the presence of a reflecting boundary | Version accepted in JHEP | JHEP 09 (2022) 105 | 10.1007/JHEP09(2022)105 | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We introduce a new model of relativistic quantum analogue of the classical
Otto engine in the presence of a perfectly reflecting boundary. A single qubit
acts as the working substance interacting with a massless quantum scalar field,
with the boundary obeying the Dirichlet condition. The quantum vacuum serves as
a thermal bath through the Unruh effect. We observe that the response function
of the qubit gets significantly modified by the presence of the reflecting
boundary. From the structure of the correlation function, we find that three
different cases emerge, namely, the intermediate boundary regime, the near
boundary regime, and the far boundary regime. As expected, the correlation in
the far boundary regime approaches that of the Unruh quantum Otto engine (UQOE)
when the reflecting boundary goes to infinity. The effect of the reflecting
boundary is manifested through the reduction of the critical excitation
probability of the qubit and the work output of the engine. In spite of the
reduced work output, the efficiency of the engine remains unaltered even in the
presence of the boundary.
| [
{
"created": "Fri, 20 May 2022 04:11:51 GMT",
"version": "v1"
},
{
"created": "Sat, 27 Aug 2022 10:04:12 GMT",
"version": "v2"
}
] | 2022-09-19 | [
[
"Mukherjee",
"Arnab",
""
],
[
"Gangopadhyay",
"Sunandan",
""
],
[
"Majumdar",
"A. S.",
""
]
] | We introduce a new model of relativistic quantum analogue of the classical Otto engine in the presence of a perfectly reflecting boundary. A single qubit acts as the working substance interacting with a massless quantum scalar field, with the boundary obeying the Dirichlet condition. The quantum vacuum serves as a thermal bath through the Unruh effect. We observe that the response function of the qubit gets significantly modified by the presence of the reflecting boundary. From the structure of the correlation function, we find that three different cases emerge, namely, the intermediate boundary regime, the near boundary regime, and the far boundary regime. As expected, the correlation in the far boundary regime approaches that of the Unruh quantum Otto engine (UQOE) when the reflecting boundary goes to infinity. The effect of the reflecting boundary is manifested through the reduction of the critical excitation probability of the qubit and the work output of the engine. In spite of the reduced work output, the efficiency of the engine remains unaltered even in the presence of the boundary. |
1111.7231 | Tamerlan Saidov | Tamerlan Saidov | The Compactification Problems of Additional Dimensions in
Multidimensional Cosmological Theories | 126 pages, 33 figures; the PhD thesis for physical and mathematical
science | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Multidimensionality of our Universe is one of the most intriguing assumption
in modern physics. It follows naturally from theories unifying different
fundamental interactions with gravity, e.g. M/string theory. The idea has
received a great deal of renewed attention over the last few years. However, it
also brings a row of additional questions. According to observations the
internal space should be static or nearly static at least from the time of
primordial nucleosynthesis, otherwise the fundamental physical constants would
vary. This means that at the present evolutionary stage of the Universe there
are two possibilities: slow variation or compactification of internal space
scale parameters. In many recent studies the problem of extra dimensions
stabilization was studied for so-called ADD. Under these approaches a massive
scalar fields (gravitons or radions) of external space-time can be presented as
conformal excitations. In above mentioned works it was assumed that
multidimensional action to be linear with respect to curvature. Although as
follows from string theory, the gravity action needs to be extended to
nonlinear one. In order to investigate effects of nonlinearity, in this Thesis
a multidimensional Lagrangian will be studied, having the form L = f(R), where
f(R) is an arbitrary smooth function of the scalar curvature.
| [
{
"created": "Wed, 30 Nov 2011 16:22:32 GMT",
"version": "v1"
}
] | 2011-12-01 | [
[
"Saidov",
"Tamerlan",
""
]
] | Multidimensionality of our Universe is one of the most intriguing assumption in modern physics. It follows naturally from theories unifying different fundamental interactions with gravity, e.g. M/string theory. The idea has received a great deal of renewed attention over the last few years. However, it also brings a row of additional questions. According to observations the internal space should be static or nearly static at least from the time of primordial nucleosynthesis, otherwise the fundamental physical constants would vary. This means that at the present evolutionary stage of the Universe there are two possibilities: slow variation or compactification of internal space scale parameters. In many recent studies the problem of extra dimensions stabilization was studied for so-called ADD. Under these approaches a massive scalar fields (gravitons or radions) of external space-time can be presented as conformal excitations. In above mentioned works it was assumed that multidimensional action to be linear with respect to curvature. Although as follows from string theory, the gravity action needs to be extended to nonlinear one. In order to investigate effects of nonlinearity, in this Thesis a multidimensional Lagrangian will be studied, having the form L = f(R), where f(R) is an arbitrary smooth function of the scalar curvature. |
2207.06429 | Raimon Luna | Raimon Luna, Gabriele Bozzola, Vitor Cardoso, Vasileios Paschalidis,
Miguel Zilh\~ao | Kicks in charged black hole binaries | 12 pages, 10 figures. v2: Matches published version | Phys.Rev.D 106 (2022) 8, 084017 | 10.1103/PhysRevD.106.084017 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We compute the emission of linear momentum (kicks) by both gravitational and
electromagnetic radiation in fully general-relativistic numerical evolutions of
quasi-circular charged black hole binaries. We derive analytical expressions
for slowly moving bodies and explore numerically a variety of mass ratios and
charge-to-mass ratios. We find that for the equal mass case our analytical
expression is in excellent agreement with the observed values and, contrarily
to what happens in the vacuum case, we find that in presence of electromagnetic
fields there is emission of momentum by gravitational waves. We also find that
the strong gravitational kicks of binaries with unequal masses affect the
electromagnetic kicks, causing them to strongly deviate from Keplerian
predictions. For the values of charge-to-mass ratio considered in this work, we
observe that magnitudes of the electromagnetic kicks are always smaller than
the gravitational ones.
| [
{
"created": "Wed, 13 Jul 2022 18:00:01 GMT",
"version": "v1"
},
{
"created": "Wed, 9 Nov 2022 17:31:10 GMT",
"version": "v2"
}
] | 2022-11-10 | [
[
"Luna",
"Raimon",
""
],
[
"Bozzola",
"Gabriele",
""
],
[
"Cardoso",
"Vitor",
""
],
[
"Paschalidis",
"Vasileios",
""
],
[
"Zilhão",
"Miguel",
""
]
] | We compute the emission of linear momentum (kicks) by both gravitational and electromagnetic radiation in fully general-relativistic numerical evolutions of quasi-circular charged black hole binaries. We derive analytical expressions for slowly moving bodies and explore numerically a variety of mass ratios and charge-to-mass ratios. We find that for the equal mass case our analytical expression is in excellent agreement with the observed values and, contrarily to what happens in the vacuum case, we find that in presence of electromagnetic fields there is emission of momentum by gravitational waves. We also find that the strong gravitational kicks of binaries with unequal masses affect the electromagnetic kicks, causing them to strongly deviate from Keplerian predictions. For the values of charge-to-mass ratio considered in this work, we observe that magnitudes of the electromagnetic kicks are always smaller than the gravitational ones. |
2307.06139 | Sheref Nasereldin | Sheref Nasereldin and Kayll Lake | Constructing Maximal Extensions of the Vaidya Metric in Israel
Coordinates: I. Integration of the Field Equations | 8 pages, 1 figure, 2 tables | null | 10.1103/PhysRevD.108.124064 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper explores a complete representation of the Vaidya model, a radial
flux of radiation in the eikonal approximation, used for modeling various
phenomena in both classical and semi-classical General Relativity and
Astrophysics. The majority of the applications of the Vaidya model have been
formulated in an incomplete representation. A complete representation is
obtained here by direct integration of the Einstein field equations. We present
the methodology to obtain this complete representation, and its utility in the
modeling of general relativistic phenomena.
| [
{
"created": "Sun, 9 Jul 2023 04:58:49 GMT",
"version": "v1"
},
{
"created": "Fri, 14 Jul 2023 00:29:45 GMT",
"version": "v2"
},
{
"created": "Mon, 30 Oct 2023 17:35:10 GMT",
"version": "v3"
},
{
"created": "Tue, 26 Dec 2023 14:20:42 GMT",
"version": "v4"
}
] | 2023-12-27 | [
[
"Nasereldin",
"Sheref",
""
],
[
"Lake",
"Kayll",
""
]
] | This paper explores a complete representation of the Vaidya model, a radial flux of radiation in the eikonal approximation, used for modeling various phenomena in both classical and semi-classical General Relativity and Astrophysics. The majority of the applications of the Vaidya model have been formulated in an incomplete representation. A complete representation is obtained here by direct integration of the Einstein field equations. We present the methodology to obtain this complete representation, and its utility in the modeling of general relativistic phenomena. |
1707.07566 | Donald Lynden-Bell Prof | D. Lynden-Bell, S.M. Chitre | Does Viscosity turn inflation into the CMB and $\Lambda$ | 8 pages , 2 figures | null | null | null | gr-qc astro-ph.CO | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Consideration of the entropy production in the creation of the CMB leads to a
simple model of the evolution of the universe during this period which suggests
a connection between the small observed acceleration term and the early
inflation of a closed universe. From this we find an unexpected relationship
between the Omega's of cosmology and calculate the total volume of the
universe.
| [
{
"created": "Mon, 24 Jul 2017 14:11:47 GMT",
"version": "v1"
}
] | 2017-07-25 | [
[
"Lynden-Bell",
"D.",
""
],
[
"Chitre",
"S. M.",
""
]
] | Consideration of the entropy production in the creation of the CMB leads to a simple model of the evolution of the universe during this period which suggests a connection between the small observed acceleration term and the early inflation of a closed universe. From this we find an unexpected relationship between the Omega's of cosmology and calculate the total volume of the universe. |
0712.1313 | Hongbao Zhang | Song He and Hongbao Zhang | The black hole dynamical horizon and generalized second law of
thermodynamics | JHEP style, 8 pages, 2 figures, version to appear in JHEP with typos
corrected | JHEP0712:052,2007 | 10.1088/1126-6708/2007/12/052 | null | gr-qc astro-ph hep-th | null | The generalized second law of thermodynamics for a system containing a black
hole dynamical horizon is proposed in a covariant way. Its validity is also
tested in case of adiabatically collapsing thick light shells.
| [
{
"created": "Sat, 8 Dec 2007 23:16:33 GMT",
"version": "v1"
},
{
"created": "Tue, 11 Dec 2007 16:47:55 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"He",
"Song",
""
],
[
"Zhang",
"Hongbao",
""
]
] | The generalized second law of thermodynamics for a system containing a black hole dynamical horizon is proposed in a covariant way. Its validity is also tested in case of adiabatically collapsing thick light shells. |
1712.05673 | Edward Malec | Janusz Karkowski, Wojciech Kulczycki, Patryk Mach, Edward Malec,
Andrzej Odrzywolek, Michal Pirog | General-relativistic rotation: self-gravitating fluid tori in motion
around black holes | Matches published version | Phys. Rev. D 97, 104034 (2018) | 10.1103/PhysRevD.97.104034 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We obtain from the first principles a general-relativistic Keplerian rotation
law for self-gravitating disks around spinning black holes. This is an
extension of a former rotation law that was designed mainly for toroids around
spin-less black holes. We integrate numerically axial stationary Einstein
equations with self-gravitating disks around spinless or spinning black holes;
that includes the first ever integration of the Keplerian selfgravitating tori.
This construction can be used for the description of tight black hole-torus
systems produced during coalescences of two neutron stars or modelling of
compact active galactic nuclei.
| [
{
"created": "Fri, 15 Dec 2017 13:50:37 GMT",
"version": "v1"
},
{
"created": "Tue, 13 Mar 2018 12:33:09 GMT",
"version": "v2"
},
{
"created": "Wed, 30 May 2018 12:38:04 GMT",
"version": "v3"
}
] | 2018-06-06 | [
[
"Karkowski",
"Janusz",
""
],
[
"Kulczycki",
"Wojciech",
""
],
[
"Mach",
"Patryk",
""
],
[
"Malec",
"Edward",
""
],
[
"Odrzywolek",
"Andrzej",
""
],
[
"Pirog",
"Michal",
""
]
] | We obtain from the first principles a general-relativistic Keplerian rotation law for self-gravitating disks around spinning black holes. This is an extension of a former rotation law that was designed mainly for toroids around spin-less black holes. We integrate numerically axial stationary Einstein equations with self-gravitating disks around spinless or spinning black holes; that includes the first ever integration of the Keplerian selfgravitating tori. This construction can be used for the description of tight black hole-torus systems produced during coalescences of two neutron stars or modelling of compact active galactic nuclei. |
1210.3022 | Naresh Dadhich | Naresh Dadhich | The gravitational equation in higher dimensions | latex, 5pages, Contribution to the Proceedings of the Conference,
Relativity and Gravitation: 100 years after Einstein in Prague, June 25-28,
2012 | null | null | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Like the Lovelock Lagrangian which is a specific homogeneous polynomial in
Riemann curvature, for an alternative derivation of the gravitational equation
of motion, it is possible to define a specific homogeneous polynomial analogue
of the Riemann curvature, and then the trace of its Bianchi derivative yields
the corresponding polynomial analogue of the divergence free Einstein tensor
defining the differential operator for the equation of motion. We propose that
the general equation of motion is $G^{(n)}_{ab} = -\Lambda g_{ab} +\kappa_n
T_{ab}$ for $d=2n+1, \, 2n+2$ dimensions with the single coupling constant
$\kappa_n$, and $n=1$ is the usual Einstein equation. It turns out that
gravitational behavior is essentially similar in the critical dimensions for
all $n$. All static vacuum solutions asymptotically go over to the Einstein
limit, Schwarzschild-dS/AdS. The thermodynamical parameters bear the same
relation to horizon radius, for example entropy always goes as $r_h^{d-2n}$ and
so for the critical dimensions it always goes as $r_h, \, r_h^2$. In terms of
the area, it would go as $A^{1/n}$. The generalized analogues of the Nariai and
Bertotti-Robinson solutions arising from the product of two constant curvature
spaces, also bear the same relations between the curvatures $k_1=k_2$ and
$k_1=-k_2$ respectively.
| [
{
"created": "Wed, 10 Oct 2012 09:32:46 GMT",
"version": "v1"
}
] | 2012-10-12 | [
[
"Dadhich",
"Naresh",
""
]
] | Like the Lovelock Lagrangian which is a specific homogeneous polynomial in Riemann curvature, for an alternative derivation of the gravitational equation of motion, it is possible to define a specific homogeneous polynomial analogue of the Riemann curvature, and then the trace of its Bianchi derivative yields the corresponding polynomial analogue of the divergence free Einstein tensor defining the differential operator for the equation of motion. We propose that the general equation of motion is $G^{(n)}_{ab} = -\Lambda g_{ab} +\kappa_n T_{ab}$ for $d=2n+1, \, 2n+2$ dimensions with the single coupling constant $\kappa_n$, and $n=1$ is the usual Einstein equation. It turns out that gravitational behavior is essentially similar in the critical dimensions for all $n$. All static vacuum solutions asymptotically go over to the Einstein limit, Schwarzschild-dS/AdS. The thermodynamical parameters bear the same relation to horizon radius, for example entropy always goes as $r_h^{d-2n}$ and so for the critical dimensions it always goes as $r_h, \, r_h^2$. In terms of the area, it would go as $A^{1/n}$. The generalized analogues of the Nariai and Bertotti-Robinson solutions arising from the product of two constant curvature spaces, also bear the same relations between the curvatures $k_1=k_2$ and $k_1=-k_2$ respectively. |
gr-qc/0511031 | Fernando Mendez | R. Aloisio, A. Galante, A. Grillo, S. Liberati, E. Luzio and F. Mendez | Deformed Special Relativity as an effective theory of measurements on
quantum gravitational backgrounds | 11 pages, no figures | Phys.Rev. D73 (2006) 045020 | 10.1103/PhysRevD.73.045020 | null | gr-qc hep-ph hep-th | null | In this article we elaborate on a recently proposed interpretation of DSR as
an effective measurement theory in the presence of non-negligible (albeit
small) quantum gravitational fluctuations. We provide several heuristic
arguments to explain how such a new theory can emerge and discuss the possible
observational consequences of this framework.
| [
{
"created": "Sun, 6 Nov 2005 21:49:20 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Aloisio",
"R.",
""
],
[
"Galante",
"A.",
""
],
[
"Grillo",
"A.",
""
],
[
"Liberati",
"S.",
""
],
[
"Luzio",
"E.",
""
],
[
"Mendez",
"F.",
""
]
] | In this article we elaborate on a recently proposed interpretation of DSR as an effective measurement theory in the presence of non-negligible (albeit small) quantum gravitational fluctuations. We provide several heuristic arguments to explain how such a new theory can emerge and discuss the possible observational consequences of this framework. |
2010.13287 | Thae Hyok Kim | Ok Song An, Jin U Kang, Thae Hyok Kim, Ui Ri Mun | Notes on the post-bounce background dynamics in bouncing cosmologies | 26 pages, 15 figures. Significantly revised and accepted version for
JHEP | null | 10.1007/JHEP10(2021)085 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We investigate the post-bounce background dynamics in a certain class of
single bounce scenarios studied in the literature, in which the cosmic bounce
is driven by a scalar field with negative exponential potential such as the
ekpyrotic potential. We show that those models can actually lead to cyclic
evolutions with repeated bounces. These cyclic evolutions, however, do not
account for the currently observed late-time accelerated expansion and hence
are not cosmologically viable. In this respect we consider a new kind of cyclic
model proposed recently and derive some cosmological constraints on this model.
| [
{
"created": "Mon, 26 Oct 2020 02:28:49 GMT",
"version": "v1"
},
{
"created": "Thu, 16 Sep 2021 06:56:50 GMT",
"version": "v2"
}
] | 2021-10-27 | [
[
"An",
"Ok Song",
""
],
[
"Kang",
"Jin U",
""
],
[
"Kim",
"Thae Hyok",
""
],
[
"Mun",
"Ui Ri",
""
]
] | We investigate the post-bounce background dynamics in a certain class of single bounce scenarios studied in the literature, in which the cosmic bounce is driven by a scalar field with negative exponential potential such as the ekpyrotic potential. We show that those models can actually lead to cyclic evolutions with repeated bounces. These cyclic evolutions, however, do not account for the currently observed late-time accelerated expansion and hence are not cosmologically viable. In this respect we consider a new kind of cyclic model proposed recently and derive some cosmological constraints on this model. |
2406.10436 | Mourad Guenouche | Mourad Guenouche | Effect of the spatial curvature on light bending and time delay in
curved Einstein-Straus-de Sitter solution | 36 pages, 6 figures, 5 tables | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A method of general applicability has been developed, whereby the null
geodesic equations of the Einstein-Straus-de Sitter metric can be integrated
simultaneously in terms of the curvature constant $k$. The purpose is to
generalize the computation of light deflection and time delay by a spherical
mass distribution. Assuming a flat Universe with most recent measurements of
the Hubble constant $H_0$ and the cosmological constant $\Lambda$, five time
delays between the four bright images of the lensed quasar SDSS J1004+4112 have
been forecasted and compared to others in the field. In addition, we have
reviewed the question of the possible contribution of a positive $\Lambda$ to
reduce the light bending, and concluded that the changes are seemingly too
small to be appreciable on cosmological scales. The same conclusion has been
reached regarding the time delay. Having addressed the question of the effect
of the spatial curvature in both closed and open Universe, we have found that
the strong lensing is slightly affected by the expected small curvature density
$\Omega_{k0}$ of the current Universe within its error bar
$|\Omega_{k0}|\lessapprox 0.001$, in such a way that it may safely be
neglected. However, it's only if $\Omega_{k0}$ gets quite larger that the
effect being noticeable. While it is only theoretically possible for
$\Omega_{k0}$ to be higher, it's worthwhile to stress that this should impact
the light bending and time delay, causing them to decrease or increase
depending upon whether the spatial curvature is positive or negative.
Furthermore, one can infer that the observed light deflection and time delay
independently, that are found to be significantly deviated from those of the
flat Universe, may serve as a useful means to provide constraints on $\Omega
_{k0}$, thus making the approach employed in this work more promising than
others.
| [
{
"created": "Fri, 14 Jun 2024 22:58:37 GMT",
"version": "v1"
}
] | 2024-06-18 | [
[
"Guenouche",
"Mourad",
""
]
] | A method of general applicability has been developed, whereby the null geodesic equations of the Einstein-Straus-de Sitter metric can be integrated simultaneously in terms of the curvature constant $k$. The purpose is to generalize the computation of light deflection and time delay by a spherical mass distribution. Assuming a flat Universe with most recent measurements of the Hubble constant $H_0$ and the cosmological constant $\Lambda$, five time delays between the four bright images of the lensed quasar SDSS J1004+4112 have been forecasted and compared to others in the field. In addition, we have reviewed the question of the possible contribution of a positive $\Lambda$ to reduce the light bending, and concluded that the changes are seemingly too small to be appreciable on cosmological scales. The same conclusion has been reached regarding the time delay. Having addressed the question of the effect of the spatial curvature in both closed and open Universe, we have found that the strong lensing is slightly affected by the expected small curvature density $\Omega_{k0}$ of the current Universe within its error bar $|\Omega_{k0}|\lessapprox 0.001$, in such a way that it may safely be neglected. However, it's only if $\Omega_{k0}$ gets quite larger that the effect being noticeable. While it is only theoretically possible for $\Omega_{k0}$ to be higher, it's worthwhile to stress that this should impact the light bending and time delay, causing them to decrease or increase depending upon whether the spatial curvature is positive or negative. Furthermore, one can infer that the observed light deflection and time delay independently, that are found to be significantly deviated from those of the flat Universe, may serve as a useful means to provide constraints on $\Omega _{k0}$, thus making the approach employed in this work more promising than others. |
gr-qc/9603056 | Takeshi Chiba | Takeshi Chiba, Jiro Soda | Critical Behavior in the Brans-Dicke Theory of Gravitation | 6 pages | Prog.Theor.Phys. 96 (1996) 567-574 | 10.1143/PTP.96.567 | KUNS-1386, KUCP-0093 | gr-qc | null | The collapse of a massless scalar field in the Brans-Dicke theory of
gravitation is studied in the analysis of both analytical solution and
numerical one. By conformally transforming the Roberts's solution into the
Brans-Dicke frame, we find for $\omega > -3/2$ that a continuous
self-similarity continues and that the critical exponent does depend on
$\omega$. By conformally transforming the Choptuik's solution into the
Brans-Dicke frame, we find for $\omega > -3/2$ that at the critical solution
shows discrete self-similarity, however, the critical exponent depends strongly
on $\omega$ while the echoing parameter weakly on it.
| [
{
"created": "Thu, 28 Mar 1996 09:21:34 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Chiba",
"Takeshi",
""
],
[
"Soda",
"Jiro",
""
]
] | The collapse of a massless scalar field in the Brans-Dicke theory of gravitation is studied in the analysis of both analytical solution and numerical one. By conformally transforming the Roberts's solution into the Brans-Dicke frame, we find for $\omega > -3/2$ that a continuous self-similarity continues and that the critical exponent does depend on $\omega$. By conformally transforming the Choptuik's solution into the Brans-Dicke frame, we find for $\omega > -3/2$ that at the critical solution shows discrete self-similarity, however, the critical exponent depends strongly on $\omega$ while the echoing parameter weakly on it. |
gr-qc/9806003 | Malcolm MacCallum | M.A.H. MacCallum | Integrability in tetrad formalisms and conservation in cosmology | 10 pages, latex 2.09, uses sprocl.sty To appear in the Proceedings of
the International Seminar on Mathematical Cosmology, Potsdam, Mar-Apr 98, ed.
H.-J. Schmidt and M. Rainer. World Scientific, Singapore | Current Topics in Mathematical Cosmology (Proceedings of the
International Seminar), ed. M. Rainer and H.-J. Schmidt, World Scientific
(1998) | null | null | gr-qc | null | Integrability in general tetrad formalisms is reviewed, following and
clarifying work of Papapetrou and Edgar. The integrability conditions are
(combinations of) the Bianchi equations and their consequences. The
introduction of additional constraints is considered. Recent results on the
conservation of constraints in the 1+3 covariant formulation of cosmology are
shown to follow from the Bianchi equations
| [
{
"created": "Sat, 30 May 1998 16:22:00 GMT",
"version": "v1"
}
] | 2008-02-11 | [
[
"MacCallum",
"M. A. H.",
""
]
] | Integrability in general tetrad formalisms is reviewed, following and clarifying work of Papapetrou and Edgar. The integrability conditions are (combinations of) the Bianchi equations and their consequences. The introduction of additional constraints is considered. Recent results on the conservation of constraints in the 1+3 covariant formulation of cosmology are shown to follow from the Bianchi equations |
1505.01680 | Dirk Puetzfeld | Yuri N. Obukhov, Dirk Puetzfeld | Multipolar test body equations of motion in generalized gravity theories | 54 pages, 3 figures, to appear in "Equations of Motion in
Relativistic Gravity", D. Puetzfeld et al. (eds.), Fundamental theories of
Physics, Springer 2015. arXiv admin note: substantial text overlap with
arXiv:1408.5669 | null | 10.1007/978-3-319-18335-0_2 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We give an overview of the derivation of multipolar equations of motion of
extended test bodies for a wide set of gravitational theories beyond the
standard general relativistic framework. The classes of theories covered range
from simple generalizations of General Relativity, e.g. encompassing additional
scalar fields, to theories with additional geometrical structures which are
needed for the description of microstructured matter. Our unified framework
even allows to handle theories with nonminimal coupling to matter, and thereby
for a systematic test of a very broad range of gravitational theories.
| [
{
"created": "Thu, 7 May 2015 12:30:39 GMT",
"version": "v1"
}
] | 2021-04-07 | [
[
"Obukhov",
"Yuri N.",
""
],
[
"Puetzfeld",
"Dirk",
""
]
] | We give an overview of the derivation of multipolar equations of motion of extended test bodies for a wide set of gravitational theories beyond the standard general relativistic framework. The classes of theories covered range from simple generalizations of General Relativity, e.g. encompassing additional scalar fields, to theories with additional geometrical structures which are needed for the description of microstructured matter. Our unified framework even allows to handle theories with nonminimal coupling to matter, and thereby for a systematic test of a very broad range of gravitational theories. |
2011.08222 | Imanol Albarran | Imanol Albarran, Mariam Bouhmadi-L\'opez, Jo\~ao Marto | A varying Dark Energy effective speed of sound parameter in the phantom
Universe | 15 pages, 6 figures. Improved version with an extended physical
discussion. Version published in EPJC | Eur. Phys. J. C 81 (2021) no.9, 803 | 10.1140/epjc/s10052-021-09546-2 | null | gr-qc astro-ph.CO hep-ph | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We analyse the phenomenological effects of a varying Dark Energy (DE)
effective speed of sound parameter, $c^{2}_{\textrm{sd}}$, on the cosmological
perturbations of three phantom DE models. Each of these models induce a
particular abrupt future event known as Big Rip (BR), Little Rip (LR), and
Little Sibling of the Big Rip (LSBR). In this class of abrupt events, all the
bound structures in the Universe would be ripped apart at a finite cosmic time.
We compute the evolution of the perturbations, $f\sigma_{8}$ growth rate and
forecast the current matter power spectrum. We vary the $c^{2}_{\textrm{sd}}$
parameter in the interval $[0,1]$ and compute the relative deviation with
respect $c^{2}_{\textrm{sd}}=1$. In addition, we analyse the effect of
gravitational potential sign flip that occurs at very large scale factors as
compared with the current one.
| [
{
"created": "Mon, 16 Nov 2020 19:09:16 GMT",
"version": "v1"
},
{
"created": "Fri, 5 Nov 2021 12:23:50 GMT",
"version": "v2"
}
] | 2021-11-08 | [
[
"Albarran",
"Imanol",
""
],
[
"Bouhmadi-López",
"Mariam",
""
],
[
"Marto",
"João",
""
]
] | We analyse the phenomenological effects of a varying Dark Energy (DE) effective speed of sound parameter, $c^{2}_{\textrm{sd}}$, on the cosmological perturbations of three phantom DE models. Each of these models induce a particular abrupt future event known as Big Rip (BR), Little Rip (LR), and Little Sibling of the Big Rip (LSBR). In this class of abrupt events, all the bound structures in the Universe would be ripped apart at a finite cosmic time. We compute the evolution of the perturbations, $f\sigma_{8}$ growth rate and forecast the current matter power spectrum. We vary the $c^{2}_{\textrm{sd}}$ parameter in the interval $[0,1]$ and compute the relative deviation with respect $c^{2}_{\textrm{sd}}=1$. In addition, we analyse the effect of gravitational potential sign flip that occurs at very large scale factors as compared with the current one. |
0707.0588 | Mairi Sakellariadou | William Nelson and Mairi Sakellariadou (King's College, London) | Lattice Refining LQC and the Matter Hamiltonian | 15 pages, 3 figures, revtex style; amended version to match
publication in Phys. Rev. D | Phys.Rev.D76:104003,2007 | 10.1103/PhysRevD.76.104003 | null | gr-qc astro-ph hep-ex hep-ph hep-th | null | In the context of loop quantum cosmology, we parametrise the lattice
refinement by a parameter, $A$, and the matter Hamiltonian by a parameter,
$\delta$. We then solve the Hamiltonian constraint for both a self-adjoint, and
a non-self-adjoint Hamiltonian operator. Demanding that the solutions for the
wave-functions obey certain physical restrictions, we impose constraints on the
two-dimensional, $(A,\delta)$, parameter space, thereby restricting the types
of matter content that can be supported by a particular lattice refinement
model.
| [
{
"created": "Wed, 4 Jul 2007 12:11:43 GMT",
"version": "v1"
},
{
"created": "Thu, 30 Aug 2007 11:17:33 GMT",
"version": "v2"
}
] | 2008-11-26 | [
[
"Nelson",
"William",
"",
"King's College, London"
],
[
"Sakellariadou",
"Mairi",
"",
"King's College, London"
]
] | In the context of loop quantum cosmology, we parametrise the lattice refinement by a parameter, $A$, and the matter Hamiltonian by a parameter, $\delta$. We then solve the Hamiltonian constraint for both a self-adjoint, and a non-self-adjoint Hamiltonian operator. Demanding that the solutions for the wave-functions obey certain physical restrictions, we impose constraints on the two-dimensional, $(A,\delta)$, parameter space, thereby restricting the types of matter content that can be supported by a particular lattice refinement model. |
2204.06267 | Saskia Grunau | Saskia Grunau and Jutta Kunz | Hyperelliptic functions and motion in general relativity | Published in MDPI Mathematics 2022, 10(12), 1958, Special Issue
"Partial Differential Equations and Applications". (Changes made as requested
by the referees and editors.) | Mathematics 2022, 10(12), 1958 | 10.3390/math10121958 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Analysis of black hole spacetimes requires study of the motion of particles
and light in these spacetimes. Here exact solutions of the geodesic equations
are the means of choice. Numerous interesting black hole spacetimes have been
analyzed in terms of elliptic functions. However, the presence of a
cosmological constant, higher dimensions or alternative gravity theories often
necessitate an analysis in terms of hyperelliptic functions. Here we review the
method and current status for solving the geodesic equations for the general
hyperelliptic case, illustrating it with set a of examples of genus $g=2$.
| [
{
"created": "Wed, 13 Apr 2022 09:37:46 GMT",
"version": "v1"
},
{
"created": "Mon, 13 Jun 2022 12:10:18 GMT",
"version": "v2"
}
] | 2022-06-14 | [
[
"Grunau",
"Saskia",
""
],
[
"Kunz",
"Jutta",
""
]
] | Analysis of black hole spacetimes requires study of the motion of particles and light in these spacetimes. Here exact solutions of the geodesic equations are the means of choice. Numerous interesting black hole spacetimes have been analyzed in terms of elliptic functions. However, the presence of a cosmological constant, higher dimensions or alternative gravity theories often necessitate an analysis in terms of hyperelliptic functions. Here we review the method and current status for solving the geodesic equations for the general hyperelliptic case, illustrating it with set a of examples of genus $g=2$. |
gr-qc/9311023 | Andrew Barvinski | A.O.Barvinsky | Tunnelling geometries II. Reduction methods for functional determinants | 23 pages, latex, figures are not included (available on request by
regular mail), report Alberta Thy-41-93 | Phys.Rev. D50 (1994) 5115-5124 | 10.1103/PhysRevD.50.5115 | null | gr-qc | null | The reduction algorithms for functional determinants of differential
operators on spacetime manifolds of different topological types are presented,
which were recently used for the calculation of the no-boundary wavefunction
and the partition function of tunnelling geometries in quantum gravity and
cosmology.
| [
{
"created": "Sun, 14 Nov 1993 04:55:34 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Barvinsky",
"A. O.",
""
]
] | The reduction algorithms for functional determinants of differential operators on spacetime manifolds of different topological types are presented, which were recently used for the calculation of the no-boundary wavefunction and the partition function of tunnelling geometries in quantum gravity and cosmology. |
gr-qc/0209077 | Olga V. Babourova | Olga V. Babourova, Boris N. Frolov | Matter with dilaton charge in Weyl-Cartan spacetime and evolution of the
Universe | LaTex, 23 pages, no figures, uses IOP.sty, misprints and references
corrected | Class.Quant.Grav.20:1423-1442,2003 | 10.1088/0264-9381/20/8/302 | null | gr-qc astro-ph | null | The perfect dilaton-spin fluid (as a model of the dilaton matter, the
particles of which are endowed with intrinsic spin and dilaton charge) is
considered as the source of the gravitational field in a Weyl-Cartan spacetime.
The variational theory of such fluid is constructed and the dilaton-spin fluid
energy-momentum tensor is obtained. The variational formalism of the
gravitational field in a Weyl-Cartan spacetime ia developed in the exterior
form language. The homogeneous and isotropic Universe filled with the dilaton
matter as the dark matter is considered and one of the field equations is
represented as Einstein-like equation which leads to the modified
Friedmann-Lemaitre equation. From this equation the absence of the initial
singularity in the cosmological solution follows. Also the existence of two
points of inflection of the scale factor function is established, the first of
which corresponds to the early stage of the Universe and the second one
corresponds to the modern era when the expansion with deceleration is replaced
by the expansion with acceleration. The possible equations of state for the
self-interacting cold dark matter are found on the basis of the modern
observational data. The inflation-like solution is obtained.
| [
{
"created": "Sat, 21 Sep 2002 11:30:07 GMT",
"version": "v1"
},
{
"created": "Thu, 19 Dec 2002 17:51:53 GMT",
"version": "v2"
}
] | 2011-07-19 | [
[
"Babourova",
"Olga V.",
""
],
[
"Frolov",
"Boris N.",
""
]
] | The perfect dilaton-spin fluid (as a model of the dilaton matter, the particles of which are endowed with intrinsic spin and dilaton charge) is considered as the source of the gravitational field in a Weyl-Cartan spacetime. The variational theory of such fluid is constructed and the dilaton-spin fluid energy-momentum tensor is obtained. The variational formalism of the gravitational field in a Weyl-Cartan spacetime ia developed in the exterior form language. The homogeneous and isotropic Universe filled with the dilaton matter as the dark matter is considered and one of the field equations is represented as Einstein-like equation which leads to the modified Friedmann-Lemaitre equation. From this equation the absence of the initial singularity in the cosmological solution follows. Also the existence of two points of inflection of the scale factor function is established, the first of which corresponds to the early stage of the Universe and the second one corresponds to the modern era when the expansion with deceleration is replaced by the expansion with acceleration. The possible equations of state for the self-interacting cold dark matter are found on the basis of the modern observational data. The inflation-like solution is obtained. |
gr-qc/9501037 | Sujan Sengupta | Sujan Sengupta (Indian Institute Of Astrophysics, Bangalore 560034) | TOWARDS A PHYSICAL INTERPRETATION OF THE ANGULAR MOMENTUM PARAMETER
ASSOCIATED WITH THE KERR METRIC | 9 pages, LATEX, no figure | null | null | IIA-TH/95-4 | gr-qc | null | The role of the parameter `$a$' associated with the Kerr metric which
represents the angular momentum per unit mass of a rotating massive object has
been converted into determining the rotationally induced quadrapole electric
field outside a rotating massive object with external dipole magnetic field. A
comparison of the result with that of the Newtonian case implies that the
parameter `$a$' represents the angular momentum per unit mass of a rotating
hollow object.
| [
{
"created": "Fri, 27 Jan 1995 08:38:54 GMT",
"version": "v1"
}
] | 2016-08-31 | [
[
"Sengupta",
"Sujan",
"",
"Indian Institute Of Astrophysics, Bangalore 560034"
]
] | The role of the parameter `$a$' associated with the Kerr metric which represents the angular momentum per unit mass of a rotating massive object has been converted into determining the rotationally induced quadrapole electric field outside a rotating massive object with external dipole magnetic field. A comparison of the result with that of the Newtonian case implies that the parameter `$a$' represents the angular momentum per unit mass of a rotating hollow object. |
1101.2147 | Mauricio Cataldo MC | Mauricio Cataldo, Fabiola Arevalo and Patricio Mella | Interacting Kasner-type cosmologies | Accepted for publication in Astrophysics &Space Science, 8 pages | Astrophys.Space Sci.333:287-293,2011 | 10.1007/s10509-011-0596-y | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | It is well known that Kasner-type cosmologies provide a useful framework for
analyzing the three-dimensional anisotropic expansion because of the
simplification of the anisotropic dynamics. In this paper relativistic
multi-fluid Kasner-type scenarios are studied. We first consider the general
case of a superposition of two ideal cosmic fluids, as well as the particular
cases of non-interacting and interacting ones, by introducing a
phenomenological coupling function $q(t)$. For two-fluid cosmological scenarios
there exist only cosmological scaling solutions, while for three-fluid
configurations there exist not only cosmological scaling ones, but also more
general solutions. In the case of triply interacting cosmic fluids we can have
energy transfer from two fluids to a third one, or energy transfer from one
cosmic fluid to the other two. It is shown that by requiring the positivity of
energy densities there always is a matter component which violates the dominant
energy condition in this kind of anisotropic cosmological scenarios.
| [
{
"created": "Tue, 11 Jan 2011 15:47:26 GMT",
"version": "v1"
}
] | 2015-03-17 | [
[
"Cataldo",
"Mauricio",
""
],
[
"Arevalo",
"Fabiola",
""
],
[
"Mella",
"Patricio",
""
]
] | It is well known that Kasner-type cosmologies provide a useful framework for analyzing the three-dimensional anisotropic expansion because of the simplification of the anisotropic dynamics. In this paper relativistic multi-fluid Kasner-type scenarios are studied. We first consider the general case of a superposition of two ideal cosmic fluids, as well as the particular cases of non-interacting and interacting ones, by introducing a phenomenological coupling function $q(t)$. For two-fluid cosmological scenarios there exist only cosmological scaling solutions, while for three-fluid configurations there exist not only cosmological scaling ones, but also more general solutions. In the case of triply interacting cosmic fluids we can have energy transfer from two fluids to a third one, or energy transfer from one cosmic fluid to the other two. It is shown that by requiring the positivity of energy densities there always is a matter component which violates the dominant energy condition in this kind of anisotropic cosmological scenarios. |
1703.09149 | Alejandro Perez | Alejandro Perez | Black Holes in Loop Quantum Gravity | Typos corrected, references corrected. To appear in Reports on
Progress in Physics | null | 10.1088/1361-6633/aa7e14 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This is a review of the results on black hole physics in the framework of
loop quantum gravity. The key feature underlying the results is the
discreteness of geometric quantities at the Planck scale predicted by this
approach to quantum gravity. Quantum discreteness follows directly from the
canonical quantization prescription when applied to the action of general
relativity that is suitable for the coupling of gravity with gauge fields and
specially with fermions. Planckian discreteness and causal considerations
provide the basic structure for the understanding of the thermal properties of
black holes close to equilibrium. Discreteness also provides a fresh new look
at more (at the moment) speculative issues such as those concerning the fate of
information in black hole evaporation. The hypothesis of discreteness leads
also to interesting phenomenology with possible observational consequences. The
theory of loop quantum gravity is a developing program. This review reports its
achievements and open questions in a pedagogical manner with an emphasis on
quantum aspects of black hole physics.
| [
{
"created": "Mon, 27 Mar 2017 15:38:15 GMT",
"version": "v1"
},
{
"created": "Fri, 8 Sep 2017 13:12:36 GMT",
"version": "v2"
}
] | 2017-11-22 | [
[
"Perez",
"Alejandro",
""
]
] | This is a review of the results on black hole physics in the framework of loop quantum gravity. The key feature underlying the results is the discreteness of geometric quantities at the Planck scale predicted by this approach to quantum gravity. Quantum discreteness follows directly from the canonical quantization prescription when applied to the action of general relativity that is suitable for the coupling of gravity with gauge fields and specially with fermions. Planckian discreteness and causal considerations provide the basic structure for the understanding of the thermal properties of black holes close to equilibrium. Discreteness also provides a fresh new look at more (at the moment) speculative issues such as those concerning the fate of information in black hole evaporation. The hypothesis of discreteness leads also to interesting phenomenology with possible observational consequences. The theory of loop quantum gravity is a developing program. This review reports its achievements and open questions in a pedagogical manner with an emphasis on quantum aspects of black hole physics. |
gr-qc/9903054 | L. Sriramkumar | L. Sriramkumar and T. Padmanabhan | Probes of the vacuum structure of quantum fields in classical
backgrounds | 43 pages, LaTeX2e (uses ajour.cls); Discussions added in sections
3.3, 5.2 and 6.2 | Int.J.Mod.Phys. D11 (2002) 1-34 | 10.1142/S0218271802001354 | null | gr-qc hep-th | null | We compare the different approaches presently available in literature to
probe the vacuum structure of quantum fields in classical electromagnetic and
gravitational backgrounds. We compare the results from the Bogolubov
transformations and the effective Lagrangian approach with the response of
monopole detectors (of the Unruh-DeWitt type) in non-inertial frames in flat
spacetime and in inertial frames in different types of classical
electromagnetic backgrounds. We also carry out such a comparison in inertial
and rotating frames when boundaries are present in flat spacetime. We find that
the results from these different approaches do not, in general, agree with each
other. We attempt to identify the origin of these differences and then go on to
discuss its implications for classical gravitational backgrounds.
| [
{
"created": "Sun, 14 Mar 1999 17:14:13 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Sep 2000 00:27:19 GMT",
"version": "v2"
},
{
"created": "Fri, 23 Feb 2001 03:02:15 GMT",
"version": "v3"
}
] | 2009-10-31 | [
[
"Sriramkumar",
"L.",
""
],
[
"Padmanabhan",
"T.",
""
]
] | We compare the different approaches presently available in literature to probe the vacuum structure of quantum fields in classical electromagnetic and gravitational backgrounds. We compare the results from the Bogolubov transformations and the effective Lagrangian approach with the response of monopole detectors (of the Unruh-DeWitt type) in non-inertial frames in flat spacetime and in inertial frames in different types of classical electromagnetic backgrounds. We also carry out such a comparison in inertial and rotating frames when boundaries are present in flat spacetime. We find that the results from these different approaches do not, in general, agree with each other. We attempt to identify the origin of these differences and then go on to discuss its implications for classical gravitational backgrounds. |
1210.3372 | Si Chen | Si Chen and Steven S. Plotkin | Statistical mechanics of graph models and their implications for
emergent spacetime manifolds | 21 pages, 20 figures, 1 table; v2: References added; Figure added;
Discussion expanded; v3: minor corrections, published version | Phys. Rev. D 87, 084011 (2013) | 10.1103/PhysRevD.87.084011 | null | gr-qc cond-mat.dis-nn cond-mat.stat-mech hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Inspired by "quantum graphity" models for spacetime, a statistical model of
graphs is proposed to explore possible realizations of emergent manifolds.
Graphs with given numbers of vertices and edges are considered, governed by a
very general Hamiltonian that merely favors graphs with near-constant valency
and local rotational symmetry. The ratio of vertices to edges controls the
dimensionality of the emergent manifold. The model is simulated numerically in
the canonical ensemble for a given vertex to edge ratio, where it is found that
the low-energy states are almost triangulations of two-dimensional manifolds.
The resulting manifold shows topological "handles" and surface intersections in
a higher embedding space, as well as non-trivial fractal dimension consistent
with previous spectral analysis, and nonlocal links consistent with models of
disordered locality. The transition to an emergent manifold is first order, and
thus dependent on microscopic structure. Issues involved in interpreting
nearly-fixed valency graphs as Feynman diagrams dual to a triangulated manifold
as in matrix models are discussed. Another interesting phenomenon is that the
entropy of the graphs are super-extensive, a fact known since Erd\H{o}s, which
results in a transition temperature of zero in the limit of infinite system
size: infinite manifolds are always disordered. Aside from a finite universe or
diverging coupling constraints as possible solutions to this problem,
long-range interactions between vertex defects also resolve the problem and
restore a nonzero transition temperature, in a manner similar to that in
low-dimensional condensed-matter systems.
| [
{
"created": "Thu, 11 Oct 2012 20:50:29 GMT",
"version": "v1"
},
{
"created": "Mon, 18 Feb 2013 00:54:36 GMT",
"version": "v2"
},
{
"created": "Fri, 5 Apr 2013 21:18:35 GMT",
"version": "v3"
}
] | 2013-04-09 | [
[
"Chen",
"Si",
""
],
[
"Plotkin",
"Steven S.",
""
]
] | Inspired by "quantum graphity" models for spacetime, a statistical model of graphs is proposed to explore possible realizations of emergent manifolds. Graphs with given numbers of vertices and edges are considered, governed by a very general Hamiltonian that merely favors graphs with near-constant valency and local rotational symmetry. The ratio of vertices to edges controls the dimensionality of the emergent manifold. The model is simulated numerically in the canonical ensemble for a given vertex to edge ratio, where it is found that the low-energy states are almost triangulations of two-dimensional manifolds. The resulting manifold shows topological "handles" and surface intersections in a higher embedding space, as well as non-trivial fractal dimension consistent with previous spectral analysis, and nonlocal links consistent with models of disordered locality. The transition to an emergent manifold is first order, and thus dependent on microscopic structure. Issues involved in interpreting nearly-fixed valency graphs as Feynman diagrams dual to a triangulated manifold as in matrix models are discussed. Another interesting phenomenon is that the entropy of the graphs are super-extensive, a fact known since Erd\H{o}s, which results in a transition temperature of zero in the limit of infinite system size: infinite manifolds are always disordered. Aside from a finite universe or diverging coupling constraints as possible solutions to this problem, long-range interactions between vertex defects also resolve the problem and restore a nonzero transition temperature, in a manner similar to that in low-dimensional condensed-matter systems. |
gr-qc/0406118 | Bahram Mashhoon | C. Chicone and B. Mashhoon | Significance of c/sqrt(2) in Relativistic Physics | 7 pages, 1 figure, slightly expanded version accepted for publication
in Class. Quantum Grav | Class.Quant.Grav. 21 (2004) L139 | 10.1088/0264-9381/21/24/L01 | null | gr-qc astro-ph | null | In the description of \emph{relative} motion in accelerated systems and
gravitational fields, inertial and tidal accelerations must be taken into
account, respectively. These involve a critical speed that in the first
approximation can be simply illustrated in the case of motion in one dimension.
For one-dimensional motion, such first-order accelerations are multiplied by
$(1-V^2/V_c^2)$, where $V_c=c/\sqrt{2}$ is the critical speed. If the speed of
relative motion exceeds $V_c$, there is a sign reversal with consequences that
are contrary to Newtonian expectations.
| [
{
"created": "Tue, 29 Jun 2004 23:03:15 GMT",
"version": "v1"
},
{
"created": "Thu, 21 Oct 2004 23:48:53 GMT",
"version": "v2"
}
] | 2009-11-10 | [
[
"Chicone",
"C.",
""
],
[
"Mashhoon",
"B.",
""
]
] | In the description of \emph{relative} motion in accelerated systems and gravitational fields, inertial and tidal accelerations must be taken into account, respectively. These involve a critical speed that in the first approximation can be simply illustrated in the case of motion in one dimension. For one-dimensional motion, such first-order accelerations are multiplied by $(1-V^2/V_c^2)$, where $V_c=c/\sqrt{2}$ is the critical speed. If the speed of relative motion exceeds $V_c$, there is a sign reversal with consequences that are contrary to Newtonian expectations. |
2212.08865 | Jiri Podolsky | Jiri Podolsky, Adam Vratny | New form of all black holes of type D with a cosmological constant | 38 pages, 3 figures. arXiv admin note: text overlap with
arXiv:2108.02239. Final version accepted for publication in Phys. Rev. D,
with corrected electromagnetic field (in agreement with the results presented
in Astorino and Boldi, JHEP 08 (2023) 085, arxiv.org/abs/2305.03744) | Phys. Rev. D 107, 084034 (2023) | 10.1103/PhysRevD.107.084034 | null | gr-qc hep-th | http://creativecommons.org/licenses/by-nc-nd/4.0/ | We present an improved metric form of the complete family of exact black hole
spacetimes of algebraic type D, including any cosmological constant. This class
was found by Debever in 1971, Plebanski and Demianski in 1976, and conveniently
reformulated by Griffiths and Podolsky in 2005. In our new form of this metric
the key functions are simplified, partially factorized, and fully explicit.
They depend on seven parameters with direct physical meanings, namely m, a, l,
alpha, e, g, Lambda which characterize mass, Kerr-like rotation, NUT parameter,
acceleration, electric and magnetic charges of the black hole, and the
cosmological constant, respectively. Moreover, this general metric reduces
directly to the familiar forms of (possibly accelerating) Kerr-Newman-(anti-)de
Sitter spacetime, charged Taub-NUT-(anti-)de Sitter solution, or (possibly
rotating and charged) C-metric with a cosmological constant by simply setting
the corresponding parameters to zero. In addition, it shows that the
Plebanski-Demianski family does not involve accelerating NUT black holes
without the Kerr-like rotation. The new improved metric also enables us to
study various physical and geometrical properties, namely the character of
singularities, two black-hole and two cosmo-acceleration horizons (in a generic
situation), the related ergoregions, global structure including the Penrose
conformal diagrams, parameters of cosmic strings causing the acceleration of
the black holes, their rotation, pathological regions with closed timelike
curves, or thermodynamic quantities.
| [
{
"created": "Sat, 17 Dec 2022 13:21:33 GMT",
"version": "v1"
},
{
"created": "Fri, 10 Mar 2023 20:40:40 GMT",
"version": "v2"
},
{
"created": "Sun, 26 Nov 2023 13:41:33 GMT",
"version": "v3"
}
] | 2024-07-24 | [
[
"Podolsky",
"Jiri",
""
],
[
"Vratny",
"Adam",
""
]
] | We present an improved metric form of the complete family of exact black hole spacetimes of algebraic type D, including any cosmological constant. This class was found by Debever in 1971, Plebanski and Demianski in 1976, and conveniently reformulated by Griffiths and Podolsky in 2005. In our new form of this metric the key functions are simplified, partially factorized, and fully explicit. They depend on seven parameters with direct physical meanings, namely m, a, l, alpha, e, g, Lambda which characterize mass, Kerr-like rotation, NUT parameter, acceleration, electric and magnetic charges of the black hole, and the cosmological constant, respectively. Moreover, this general metric reduces directly to the familiar forms of (possibly accelerating) Kerr-Newman-(anti-)de Sitter spacetime, charged Taub-NUT-(anti-)de Sitter solution, or (possibly rotating and charged) C-metric with a cosmological constant by simply setting the corresponding parameters to zero. In addition, it shows that the Plebanski-Demianski family does not involve accelerating NUT black holes without the Kerr-like rotation. The new improved metric also enables us to study various physical and geometrical properties, namely the character of singularities, two black-hole and two cosmo-acceleration horizons (in a generic situation), the related ergoregions, global structure including the Penrose conformal diagrams, parameters of cosmic strings causing the acceleration of the black holes, their rotation, pathological regions with closed timelike curves, or thermodynamic quantities. |
2302.10938 | Shahar Hod | Shahar Hod | Comment on: "Possible Relation between the Cosmological Constant and
Standard Model Parameters" | 2 pages | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | It has recently been proposed [M. P. Hertzberg and A. Loeb, arXiv:2302.09090]
that the observed value of the cosmological constant can be related to the
physical parameters of the Standard Model. In the present compact note we point
out that the derivation of the claimed cosmological-constant-standard-model
relation presented in \cite{HL} is, unfortunately, erroneous.
| [
{
"created": "Tue, 21 Feb 2023 19:00:08 GMT",
"version": "v1"
}
] | 2023-02-23 | [
[
"Hod",
"Shahar",
""
]
] | It has recently been proposed [M. P. Hertzberg and A. Loeb, arXiv:2302.09090] that the observed value of the cosmological constant can be related to the physical parameters of the Standard Model. In the present compact note we point out that the derivation of the claimed cosmological-constant-standard-model relation presented in \cite{HL} is, unfortunately, erroneous. |
gr-qc/9912104 | Garcia | L.C.Garcia de Andrade | On de Sitter gravitationally from the spin-torsion primordial density | Latex file | null | null | null | gr-qc | null | Fluctuations on de Sitter solution of Einstein-Cartan field equations are
obtained in terms of the matter density primordial density fluctuations and
spin-torsion density and matter density fluctuations obtained from COBE data.
Einstein-de Sitter solution is shown to be unstable even in the absence of
torsion.The spin-torsion density fluctuation is simply computed from the
Einstein-Cartan equations and from COBE data.
| [
{
"created": "Fri, 24 Dec 1999 09:00:35 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"de Andrade",
"L. C. Garcia",
""
]
] | Fluctuations on de Sitter solution of Einstein-Cartan field equations are obtained in terms of the matter density primordial density fluctuations and spin-torsion density and matter density fluctuations obtained from COBE data. Einstein-de Sitter solution is shown to be unstable even in the absence of torsion.The spin-torsion density fluctuation is simply computed from the Einstein-Cartan equations and from COBE data. |
gr-qc/0605026 | Tomasz Pawlowski | Jerzy Lewandowski, Tomasz Pawlowski | Symmetric non-expanding horizons | Revtex4, 36 pages | Class.Quant.Grav. 23 (2006) 6031-6058 | 10.1088/0264-9381/23/20/022 | IGPG-06/5-1 | gr-qc | null | Symmetric non-expanding horizons are studied in arbitrary dimension. The
global properties -as the zeros of infinitesimal symmetries- are analyzed
particularly carefully. For the class of NEH geometries admitting helical
symmetry a quasi-local analog of Hawking's rigidity theorem is formulated and
proved: the presence of helical symmetry implies the presence of two
symmetries: null, and cyclic.
The results valid for arbitrary-dimensional horizons are next applied in a
complete classification of symmetric NEHs in 4-dimensional space-times (the
existence of a 2-sphere crossection is assumed). That classification divides
possible NEH geometries into classes labeled by two numbers - the dimensions
of, respectively, the group of isometries induced in the horizon base space and
the group of null symmetries of the horizon.
| [
{
"created": "Thu, 4 May 2006 15:23:37 GMT",
"version": "v1"
}
] | 2009-11-11 | [
[
"Lewandowski",
"Jerzy",
""
],
[
"Pawlowski",
"Tomasz",
""
]
] | Symmetric non-expanding horizons are studied in arbitrary dimension. The global properties -as the zeros of infinitesimal symmetries- are analyzed particularly carefully. For the class of NEH geometries admitting helical symmetry a quasi-local analog of Hawking's rigidity theorem is formulated and proved: the presence of helical symmetry implies the presence of two symmetries: null, and cyclic. The results valid for arbitrary-dimensional horizons are next applied in a complete classification of symmetric NEHs in 4-dimensional space-times (the existence of a 2-sphere crossection is assumed). That classification divides possible NEH geometries into classes labeled by two numbers - the dimensions of, respectively, the group of isometries induced in the horizon base space and the group of null symmetries of the horizon. |
2106.09044 | Anzhong Wang | Jacob Oost, Shinji Mukohyama, and Anzhong Wang | Spherically symmetric exact vacuum solutions in Einstein-aether theory | revtex4-1, one figure and no tables. Some typos are corrected.
Universe 7 (2021) 272 | Universe 7 (2021) 272 | 10.3390/universe7080272 | YITP-21-59, IPMU21-0036 | gr-qc astro-ph.GA hep-ph hep-th | http://creativecommons.org/licenses/by/4.0/ | We study spherically symmetric spacetimes in Einstein-aether theory in three
different coordinate systems, the isotropic, Painlev\`e-Gullstrand, and
Schwarzschild coordinates, in which the aether is always comoving, and present
both time-dependent and time-independent exact vacuum solutions. In particular,
in the isotropic coordinates we find a class of exact static solutions
characterized by a single parameter $c_{14}$ in closed forms, which satisfies
all the current observational constraints of the theory, and reduces to the
Schwarzschild vacuum black hole solution in the decoupling limit ($c_{14} =
0$). However, as long as $c_{14} \not= 0$, a marginally trapped throat with a
finite non-zero radius always exists, and in one side of it the spacetime is
asymptotically flat, while in the other side the spacetime becomes singular
within a finite proper distance from the throat, although the geometric area is
infinitely large at the singularity. Moreover, the singularity is a strong and
spacetime curvature singularity, at which both of the Ricci and Kretschmann
scalars become infinitely large.
| [
{
"created": "Wed, 16 Jun 2021 18:00:04 GMT",
"version": "v1"
},
{
"created": "Thu, 1 Jul 2021 13:30:58 GMT",
"version": "v2"
},
{
"created": "Thu, 22 Jul 2021 19:44:22 GMT",
"version": "v3"
},
{
"created": "Wed, 28 Jul 2021 20:00:02 GMT",
"version": "v4"
}
] | 2021-07-30 | [
[
"Oost",
"Jacob",
""
],
[
"Mukohyama",
"Shinji",
""
],
[
"Wang",
"Anzhong",
""
]
] | We study spherically symmetric spacetimes in Einstein-aether theory in three different coordinate systems, the isotropic, Painlev\`e-Gullstrand, and Schwarzschild coordinates, in which the aether is always comoving, and present both time-dependent and time-independent exact vacuum solutions. In particular, in the isotropic coordinates we find a class of exact static solutions characterized by a single parameter $c_{14}$ in closed forms, which satisfies all the current observational constraints of the theory, and reduces to the Schwarzschild vacuum black hole solution in the decoupling limit ($c_{14} = 0$). However, as long as $c_{14} \not= 0$, a marginally trapped throat with a finite non-zero radius always exists, and in one side of it the spacetime is asymptotically flat, while in the other side the spacetime becomes singular within a finite proper distance from the throat, although the geometric area is infinitely large at the singularity. Moreover, the singularity is a strong and spacetime curvature singularity, at which both of the Ricci and Kretschmann scalars become infinitely large. |
gr-qc/0105103 | Vitor Cardoso | Vitor Cardoso, Jose' P. S. Lemos | Quasi-Normal Modes of Schwarzschild Anti-De Sitter Black Holes:
Electromagnetic and Gravitational Perturbations | 2 figures | Phys.Rev. D64 (2001) 084017 | 10.1103/PhysRevD.64.084017 | null | gr-qc hep-th | null | We study the quasi-normal modes (QNM) of electromagnetic and gravitational
perturbations of a Schwarzschild black hole in an asymptotically Anti-de Sitter
(AdS) spacetime. Some of the electromagnetic modes do not oscillate, they only
decay, since they have pure imaginary frequencies. The gravitational modes show
peculiar features: the odd and even gravitational perturbations no longer have
the same characteristic quasinormal frequencies. There is a special mode for
odd perturbations whose behavior differs completely from the usual one in
scalar and electromagnetic perturbation in an AdS spacetime, but has a similar
behavior to the Schwarzschild black hole in an asymptotically flat spacetime:
the imaginary part of the frequency goes as 1/r+, where r+ is the horizon
radius. We also investigate the small black hole limit showing that the
imaginary part of the frequency goes as r+^2. These results are important to
the AdS/CFT conjecture since according to it the QNMs describe the approach to
equilibrium in the conformal field theory.
| [
{
"created": "Mon, 28 May 2001 19:20:39 GMT",
"version": "v1"
}
] | 2009-11-07 | [
[
"Cardoso",
"Vitor",
""
],
[
"Lemos",
"Jose' P. S.",
""
]
] | We study the quasi-normal modes (QNM) of electromagnetic and gravitational perturbations of a Schwarzschild black hole in an asymptotically Anti-de Sitter (AdS) spacetime. Some of the electromagnetic modes do not oscillate, they only decay, since they have pure imaginary frequencies. The gravitational modes show peculiar features: the odd and even gravitational perturbations no longer have the same characteristic quasinormal frequencies. There is a special mode for odd perturbations whose behavior differs completely from the usual one in scalar and electromagnetic perturbation in an AdS spacetime, but has a similar behavior to the Schwarzschild black hole in an asymptotically flat spacetime: the imaginary part of the frequency goes as 1/r+, where r+ is the horizon radius. We also investigate the small black hole limit showing that the imaginary part of the frequency goes as r+^2. These results are important to the AdS/CFT conjecture since according to it the QNMs describe the approach to equilibrium in the conformal field theory. |
1902.04616 | Rossella Gamba | Rossella Gamba, Jocelyn S. Read, Leslie E. Wade | The impact of the crust equation of state on the analysis of GW170817 | 11 pages, 6 figures | Class. Quantum Grav. 37 025008 (2020) | 10.1088/1361-6382/ab5ba4 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The detection of GW170817, the first neutron star-neutron star merger
observed by Advanced LIGO and Virgo, and its following analyses represent the
first contributions of gravitational wave (GW) data to understanding dense
matter. Parameterizing the high density section of the equation of state (EOS)
of both neutron stars through spectral decomposition, and imposing a lower
limit on the maximum mass value, led to an estimate of the stars' radii of $R_1
= 11.9_{- 1.4}^{+ 1.4}$ km and $R_2 = 11.9_{- 1.4}^{+ 1.4}$ km. These values do
not, however, take into account any uncertainty owed to the choice of the crust
low-density EOS, which was fixed to reproduce the SLy EOS model. We here
re-analyze GW170817 data and establish that different crust models do not
strongly impact the mass or tidal deformability of a neutron star: it is
impossible to distinguish between low-density models with GW analysis. However,
the crust does have an effect on the inferred radius. We predict the systematic
error due to this effect using neutron star structure equations, and compare
the prediction to results from full parameter estimation runs. For GW170817,
this systematic error affects the radius estimate by 0.3 km, approximately
$3\%$ of the NS radii.
| [
{
"created": "Tue, 12 Feb 2019 20:12:23 GMT",
"version": "v1"
}
] | 2021-11-08 | [
[
"Gamba",
"Rossella",
""
],
[
"Read",
"Jocelyn S.",
""
],
[
"Wade",
"Leslie E.",
""
]
] | The detection of GW170817, the first neutron star-neutron star merger observed by Advanced LIGO and Virgo, and its following analyses represent the first contributions of gravitational wave (GW) data to understanding dense matter. Parameterizing the high density section of the equation of state (EOS) of both neutron stars through spectral decomposition, and imposing a lower limit on the maximum mass value, led to an estimate of the stars' radii of $R_1 = 11.9_{- 1.4}^{+ 1.4}$ km and $R_2 = 11.9_{- 1.4}^{+ 1.4}$ km. These values do not, however, take into account any uncertainty owed to the choice of the crust low-density EOS, which was fixed to reproduce the SLy EOS model. We here re-analyze GW170817 data and establish that different crust models do not strongly impact the mass or tidal deformability of a neutron star: it is impossible to distinguish between low-density models with GW analysis. However, the crust does have an effect on the inferred radius. We predict the systematic error due to this effect using neutron star structure equations, and compare the prediction to results from full parameter estimation runs. For GW170817, this systematic error affects the radius estimate by 0.3 km, approximately $3\%$ of the NS radii. |
gr-qc/9605055 | Jose Ademir Sales de Lima | J.A.S. Lima (Brown Univ. and Univ. Federal do Rio Grande do Norte,
Natal, Brazil) | Thermodynamics of Decaying Vacuum Cosmologies | 21 pages, uses LATEX | Phys.Rev. D54 (1996) 2571-2577 | 10.1103/PhysRevD.54.2571 | BROWN-HET-1013 | gr-qc | null | The thermodynamic behavior of vacuum decaying cosmologies is investigated
within a manifestly covariant formulation. Such a process corresponds to a
continuous irreversible energy flow from the vacuum component to the created
matter constituents. It is shown that if the specific entropy per particle
remains constant during the process, the equilibrium relations are preserved.
In particular, if the vacuum decays into photons, the energy density $\rho$ and
average number density of photons $n$ scale with the temperature as $\rho \sim
T^{4}$ and $n \sim T^{3}$. The temperature law is determined and a generalized
Planckian type form of the spectrum, which is preserved in the course of the
evolution, is also proposed. Some consequences of these results for decaying
vacuum FRW type cosmologies as well as for models with ``adiabatic'' photon
creation are discussed.
| [
{
"created": "Sun, 26 May 1996 03:05:48 GMT",
"version": "v1"
}
] | 2009-10-28 | [
[
"Lima",
"J. A. S.",
"",
"Brown Univ. and Univ. Federal do Rio Grande do Norte,\n Natal, Brazil"
]
] | The thermodynamic behavior of vacuum decaying cosmologies is investigated within a manifestly covariant formulation. Such a process corresponds to a continuous irreversible energy flow from the vacuum component to the created matter constituents. It is shown that if the specific entropy per particle remains constant during the process, the equilibrium relations are preserved. In particular, if the vacuum decays into photons, the energy density $\rho$ and average number density of photons $n$ scale with the temperature as $\rho \sim T^{4}$ and $n \sim T^{3}$. The temperature law is determined and a generalized Planckian type form of the spectrum, which is preserved in the course of the evolution, is also proposed. Some consequences of these results for decaying vacuum FRW type cosmologies as well as for models with ``adiabatic'' photon creation are discussed. |
gr-qc/0012035 | Daniele Oriti | Tullio Regge and Ruth M. Williams | Discrete structures in gravity | 30 pages, 4 figures | J.Math.Phys.41:3964-3984,2000 | 10.1063/1.533333 | DAMTP-2000-101 | gr-qc | null | Discrete approaches to gravity, both classical and quantum, are reviewed
briefly, with emphasis on the method using piecewise-linear spaces. Models of
3-dimensional quantum gravity involving 6j-symbols are then described, and
progress in generalising these models to four dimensions is discussed, as is
the relationship of these models in both three and four dimensions to
topological theories. Finally, the repercussions of the generalisations are
explored for the original formulation of discrete gravity using edge-length
variables.
| [
{
"created": "Sat, 9 Dec 2000 15:10:53 GMT",
"version": "v1"
}
] | 2011-07-19 | [
[
"Regge",
"Tullio",
""
],
[
"Williams",
"Ruth M.",
""
]
] | Discrete approaches to gravity, both classical and quantum, are reviewed briefly, with emphasis on the method using piecewise-linear spaces. Models of 3-dimensional quantum gravity involving 6j-symbols are then described, and progress in generalising these models to four dimensions is discussed, as is the relationship of these models in both three and four dimensions to topological theories. Finally, the repercussions of the generalisations are explored for the original formulation of discrete gravity using edge-length variables. |
2312.00318 | Junji Jia | Zonghai Li and Junji Jia | Deflection of charged signals in a dipole magnetic field in Kerr
background | 10 pages, 1 figure | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This paper investigates charged particle deflection in a Kerr spacetime
background with a dipole magnetic field, focusing on the equatorial plane and
employing the weak field approximation. We employ the Jacobi-Randers metric to
unify the treatment of the gravitational and electromagnetic effects on charged
particles. Furthermore, we utilize the Gauss-Bonnet theorem to calculate the
deflection angle through curvature integrals. The difference between the
prograde and retrograde deflection angles is linked to the non-reversibility of
metrics and geodesics in Finsler geometry, revealing that this difference can
be considered a Finslerian effect. We analyze the impact of both
gravitomagnetic field and dipole magnetic field on particle motion and
deflection using the Jacobi-Randers magnetic field. The model considered in
this paper exhibits interesting features in the second-order approximation of
($M/b$). When $q\mu=2MaE$, the Jacobi-Randers metric possesses reversible
geodesics, leading to equal prograde and retrograde deflection angles. In this
case, the gravitomagnetic field and dipole magnetic field cancel each other
out, distinguishing it from scenarios involving only the gravitomagnetic field
or the dipole magnetic field. We also explore the magnetic field's impact on
gravitational lensing of charged particles.
| [
{
"created": "Fri, 1 Dec 2023 03:19:02 GMT",
"version": "v1"
}
] | 2023-12-04 | [
[
"Li",
"Zonghai",
""
],
[
"Jia",
"Junji",
""
]
] | This paper investigates charged particle deflection in a Kerr spacetime background with a dipole magnetic field, focusing on the equatorial plane and employing the weak field approximation. We employ the Jacobi-Randers metric to unify the treatment of the gravitational and electromagnetic effects on charged particles. Furthermore, we utilize the Gauss-Bonnet theorem to calculate the deflection angle through curvature integrals. The difference between the prograde and retrograde deflection angles is linked to the non-reversibility of metrics and geodesics in Finsler geometry, revealing that this difference can be considered a Finslerian effect. We analyze the impact of both gravitomagnetic field and dipole magnetic field on particle motion and deflection using the Jacobi-Randers magnetic field. The model considered in this paper exhibits interesting features in the second-order approximation of ($M/b$). When $q\mu=2MaE$, the Jacobi-Randers metric possesses reversible geodesics, leading to equal prograde and retrograde deflection angles. In this case, the gravitomagnetic field and dipole magnetic field cancel each other out, distinguishing it from scenarios involving only the gravitomagnetic field or the dipole magnetic field. We also explore the magnetic field's impact on gravitational lensing of charged particles. |
2301.03568 | Hannes R\"uter | Hannes R. R\"uter, Violetta Sagun, Wolfgang Tichy, Tim Dietrich | Quasi-equilibrium configurations of binary systems of dark matter
admixed neutron stars | 13 pages, 11 figures, v2: Added investigation of dependence on dark
matter particle mass | null | null | null | gr-qc astro-ph.HE nucl-th | http://creativecommons.org/licenses/by/4.0/ | Using an adapted version of the SGRID code, we construct for the first time
consistent quasi-equilibrium configurations for a binary system consisting of
two neutron stars in which each is admixed with dark matter. The stars are
modelled as a system of two non-interacting fluids minimally coupled to
gravity. For the fluid representing baryonic matter the SLy equation of state
is used, whereas the second fluid, which corresponds to dark matter, is
described using the equation of state of a degenerate Fermi gas. We consider
two different scenarios for the distribution of the dark matter. In the first
scenario the dark matter is confined to the core of the star, whereas in the
second scenario the dark matter extends beyond the surface of the baryonic
matter, forming a halo around the baryonic star. The presence of dark matter
alters the star's reaction to the companion's tidal forces, which we
investigate in terms of the coordinate deformation and mass shedding
parameters. The constructed quasi-equilibrium configurations mark the first
step towards consistent numerical-relativity simulations of dark matter admixed
neutron star binaries.
| [
{
"created": "Mon, 9 Jan 2023 18:39:21 GMT",
"version": "v1"
},
{
"created": "Wed, 20 Sep 2023 19:14:39 GMT",
"version": "v2"
}
] | 2023-09-22 | [
[
"Rüter",
"Hannes R.",
""
],
[
"Sagun",
"Violetta",
""
],
[
"Tichy",
"Wolfgang",
""
],
[
"Dietrich",
"Tim",
""
]
] | Using an adapted version of the SGRID code, we construct for the first time consistent quasi-equilibrium configurations for a binary system consisting of two neutron stars in which each is admixed with dark matter. The stars are modelled as a system of two non-interacting fluids minimally coupled to gravity. For the fluid representing baryonic matter the SLy equation of state is used, whereas the second fluid, which corresponds to dark matter, is described using the equation of state of a degenerate Fermi gas. We consider two different scenarios for the distribution of the dark matter. In the first scenario the dark matter is confined to the core of the star, whereas in the second scenario the dark matter extends beyond the surface of the baryonic matter, forming a halo around the baryonic star. The presence of dark matter alters the star's reaction to the companion's tidal forces, which we investigate in terms of the coordinate deformation and mass shedding parameters. The constructed quasi-equilibrium configurations mark the first step towards consistent numerical-relativity simulations of dark matter admixed neutron star binaries. |
1402.5894 | Peter Horvathy | C. Duval, G. W. Gibbons, P. A. Horvathy | Conformal Carroll groups and BMS symmetry | 10 pages, no figure. Fast Track COmmunication, to appear in Class.
Quant. Grav | null | 10.1088/0264-9381/31/9/092001 | null | gr-qc hep-th math-ph math.MP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The Bondi-Metzner-Sachs (BMS) group is shown to be the conformal extension of
Levy-Leblond's "Carroll" group. Further extension to the Newman-Unti (NU) group
is also discussed in the Carroll framework.
| [
{
"created": "Mon, 24 Feb 2014 17:10:17 GMT",
"version": "v1"
},
{
"created": "Thu, 3 Apr 2014 08:10:10 GMT",
"version": "v2"
}
] | 2015-06-18 | [
[
"Duval",
"C.",
""
],
[
"Gibbons",
"G. W.",
""
],
[
"Horvathy",
"P. A.",
""
]
] | The Bondi-Metzner-Sachs (BMS) group is shown to be the conformal extension of Levy-Leblond's "Carroll" group. Further extension to the Newman-Unti (NU) group is also discussed in the Carroll framework. |
1908.04690 | Pedro Ca\~nate Casseres | Pedro Ca\~nate, Nora Breton | New exact traversable wormhole solution to the
Einstein-scalar-Gauss-Bonnet Equations coupled to a power-Maxwell
electrodynamics | 8 pages, 2 figures | Phys. Rev. D 100, 064067 (2019) | 10.1103/PhysRevD.100.064067 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a novel, exact, traversable wormhole (T-WH) solution for
$(3+1)$-dimensional Einstein-scalar-Gauss-Bonnet theory (EsGB) coupled to a
power-Maxwell nonlinear electrodynamics (NLED). The solution is characterized
by two parameters, $\mathcal{Q}\!_{\rm e}$ and $\mathcal{Q}\!_{_{ \mathcal{S}
}}$, associated respectively with the electromagnetic field and the scalar
field. We show that for $\mathcal{Q}^2_{\rm e} - \mathcal{Q}\!_{_{ \mathcal{S}
}}>0$ the solution can be interpreted as a traversable wormhole. In the general
case, with non-vanishing electromagnetic field, the scalar-Gauss-Bonnet term
(sGB) is the only responsible for the negative energy density necessary for the
traversability. In the limiting case of vanishing electromagnetic field, the
scalar field becomes a phantom one keeping the WH throat open and in this case
the Ellis WH solution \cite{Ellis} is recovered.
| [
{
"created": "Tue, 13 Aug 2019 14:59:37 GMT",
"version": "v1"
}
] | 2019-10-09 | [
[
"Cañate",
"Pedro",
""
],
[
"Breton",
"Nora",
""
]
] | We present a novel, exact, traversable wormhole (T-WH) solution for $(3+1)$-dimensional Einstein-scalar-Gauss-Bonnet theory (EsGB) coupled to a power-Maxwell nonlinear electrodynamics (NLED). The solution is characterized by two parameters, $\mathcal{Q}\!_{\rm e}$ and $\mathcal{Q}\!_{_{ \mathcal{S} }}$, associated respectively with the electromagnetic field and the scalar field. We show that for $\mathcal{Q}^2_{\rm e} - \mathcal{Q}\!_{_{ \mathcal{S} }}>0$ the solution can be interpreted as a traversable wormhole. In the general case, with non-vanishing electromagnetic field, the scalar-Gauss-Bonnet term (sGB) is the only responsible for the negative energy density necessary for the traversability. In the limiting case of vanishing electromagnetic field, the scalar field becomes a phantom one keeping the WH throat open and in this case the Ellis WH solution \cite{Ellis} is recovered. |
gr-qc/9506048 | null | Giampiero Esposito | Asymptotic Heat Kernels in Quantum Field Theory | 15 pages, plain-tex, appearing in Problems on High Energy Physics and
Field Theory, Proceedings of the XVII Workshop, Dedicated to the 140th
Anniversary of Henri Poincare, pp. 127-134 (Protvino: IHEP Pub. 1995) | null | null | DSF preprint 95/29 | gr-qc | null | Asymptotic expansions were first introduced by Henri Poincare in 1886. This
paper describes their application to the semi-classical evaluation of
amplitudes in quantum field theory with boundaries. By using zeta-function
regularization, the conformal anomaly for a massless spin-${1\over 2}$ field in
flat Euclidean backgrounds with boundary is obtained on imposing locally
supersymmetric boundary conditions. The quantization program for gauge fields
and gravitation in the presence of boundaries is then introduced by focusing on
conformal anomalies for higher-spin fields. The conditions under which the
covariant Schwinger-DeWitt and the non-covariant, mode-by-mode analysis of
quantum amplitudes agree are described.
| [
{
"created": "Fri, 23 Jun 1995 06:38:23 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Esposito",
"Giampiero",
""
]
] | Asymptotic expansions were first introduced by Henri Poincare in 1886. This paper describes their application to the semi-classical evaluation of amplitudes in quantum field theory with boundaries. By using zeta-function regularization, the conformal anomaly for a massless spin-${1\over 2}$ field in flat Euclidean backgrounds with boundary is obtained on imposing locally supersymmetric boundary conditions. The quantization program for gauge fields and gravitation in the presence of boundaries is then introduced by focusing on conformal anomalies for higher-spin fields. The conditions under which the covariant Schwinger-DeWitt and the non-covariant, mode-by-mode analysis of quantum amplitudes agree are described. |
2111.06421 | Saeed Noori Gashti | S. Noori Gashti | Two-Field Inflationary Model and Swampland de Sitter Conjecture | 11 page. 5 figure, Accepted for publication in Journal of Holography
Applications in Physics | Journal of Holography Applications in Physics 2 (1), 13-24 (2022) | 10.22128/JHAP.2021.452.1002 | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | In this paper, we are going to investigate a new perspective of the two-field
inflation model with respect to the swampland dS conjecture. At the first step,
we study the two-fields inflation model, and apply the swampland conjecture to
our model. Then, we calculate some cosmological parameters such as scalar
spectrum index, tensor-to-scalar ratio, and compare our results with the recent
observational data. Also, we give numerical analysis to show agreement with
observational data.
| [
{
"created": "Thu, 11 Nov 2021 19:06:25 GMT",
"version": "v1"
}
] | 2023-02-14 | [
[
"Gashti",
"S. Noori",
""
]
] | In this paper, we are going to investigate a new perspective of the two-field inflation model with respect to the swampland dS conjecture. At the first step, we study the two-fields inflation model, and apply the swampland conjecture to our model. Then, we calculate some cosmological parameters such as scalar spectrum index, tensor-to-scalar ratio, and compare our results with the recent observational data. Also, we give numerical analysis to show agreement with observational data. |
1204.4344 | Alejandro Perez | Amit Ghosh and Alejandro Perez | Reply to the comment on "Black hole entropy and isolated horizons
thermodynamics" | null | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The comment arXiv:1204.2729v1 is completely wrong. The author makes serious
mistakes in calculations and judgement. The errors are made at the level of
basic undergraduate statistical mechanics.
| [
{
"created": "Thu, 19 Apr 2012 13:13:39 GMT",
"version": "v1"
}
] | 2012-04-20 | [
[
"Ghosh",
"Amit",
""
],
[
"Perez",
"Alejandro",
""
]
] | The comment arXiv:1204.2729v1 is completely wrong. The author makes serious mistakes in calculations and judgement. The errors are made at the level of basic undergraduate statistical mechanics. |
2101.01374 | Haoran Zhang | Hao-Ran Zhang, Peng-Zhang He, Lei-Shao, Yuan Chen, and Xian-Ru Hu | Shadow of topologically charged rotating braneworld black hole | null | null | 10.1142/S0217732322501450 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we discuss optical properties of the topologically charged
rotating black hole. We study the horizon, the photon region, the shadow of the
black hole and other observables. The results show that in addition to the
black hole spin parameter $a$, the other two parameters, tidal charge $\beta$
and electric charge $q$, are also found to affect the horizon, the photon
region and the black hole shadow. In a certain range, with the increase of the
three parameters, the horizon distance, shape of the photon region and the
black hole shadow will all shrink. Moreover, with the increase of these three
parameters, the distortion parameter $\delta_{s}$ gradually increases, while
the peak of the black hole energy emission rate decreases.
| [
{
"created": "Tue, 5 Jan 2021 06:55:55 GMT",
"version": "v1"
},
{
"created": "Sun, 21 Mar 2021 17:53:41 GMT",
"version": "v2"
}
] | 2022-11-09 | [
[
"Zhang",
"Hao-Ran",
""
],
[
"He",
"Peng-Zhang",
""
],
[
"Lei-Shao",
"",
""
],
[
"Chen",
"Yuan",
""
],
[
"Hu",
"Xian-Ru",
""
]
] | In this paper, we discuss optical properties of the topologically charged rotating black hole. We study the horizon, the photon region, the shadow of the black hole and other observables. The results show that in addition to the black hole spin parameter $a$, the other two parameters, tidal charge $\beta$ and electric charge $q$, are also found to affect the horizon, the photon region and the black hole shadow. In a certain range, with the increase of the three parameters, the horizon distance, shape of the photon region and the black hole shadow will all shrink. Moreover, with the increase of these three parameters, the distortion parameter $\delta_{s}$ gradually increases, while the peak of the black hole energy emission rate decreases. |
1005.5491 | Abhay Ashtekar | Abhay Ashtekar | The Big Bang and the Quantum | 18 pages, 6 figures. Plenary talk at the Invisible Universe
conference held in Paris in July 2009. To appear in the Proceedings, edited
by J. M. Alimi et al (AIP Publications) | AIP Conf.Proc.1241:109-121,2010 | 10.1063/1.3462605 | null | gr-qc astro-ph.CO hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | This short review is addressed to cosmologists.
General relativity predicts that space-time comes to an end and physics comes
to a halt at the big-bang. Recent developments in loop quantum cosmology have
shown that these predictions cannot be trusted. Quantum geometry effects can
resolve singularities, thereby opening new vistas. Examples are: The big bang
is replaced by a quantum bounce; the `horizon problem' disappears; immediately
after the big bounce, there is a super-inflationary phase with its own
phenomenological ramifications; and, in presence of a standard inflaton
potential, initial conditions are naturally set for a long, slow roll inflation
independently of what happens in the pre-big bang branch.
| [
{
"created": "Sat, 29 May 2010 23:02:55 GMT",
"version": "v1"
}
] | 2011-01-25 | [
[
"Ashtekar",
"Abhay",
""
]
] | This short review is addressed to cosmologists. General relativity predicts that space-time comes to an end and physics comes to a halt at the big-bang. Recent developments in loop quantum cosmology have shown that these predictions cannot be trusted. Quantum geometry effects can resolve singularities, thereby opening new vistas. Examples are: The big bang is replaced by a quantum bounce; the `horizon problem' disappears; immediately after the big bounce, there is a super-inflationary phase with its own phenomenological ramifications; and, in presence of a standard inflaton potential, initial conditions are naturally set for a long, slow roll inflation independently of what happens in the pre-big bang branch. |
gr-qc/9510016 | Moretti Walter | Valter Moretti (Dept. Phys. Uni. Trento, Italy) | Hessling's Quantum Equivalence Principle and the Temperature of an
Extremal Reissner-Nordstr\"{o}m Black Hole | 8 pages, standard LaTex, no figures | null | null | preprint - UTF 363 | gr-qc hep-th | null | The Hessling improvement of the Haag, Narnhofer and Stein principle is
analysed in the case of a massless scalar field propagating outside of an
extremal R-N black hole. It is found that this sort of ``Quantum (Einstein's)
Equivalence Principle'' selects only the R-N vacuum as a physically sensible
state, i.e., it selects the temperature $T=0$ only.
| [
{
"created": "Tue, 10 Oct 1995 12:38:48 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Moretti",
"Valter",
"",
"Dept. Phys. Uni. Trento, Italy"
]
] | The Hessling improvement of the Haag, Narnhofer and Stein principle is analysed in the case of a massless scalar field propagating outside of an extremal R-N black hole. It is found that this sort of ``Quantum (Einstein's) Equivalence Principle'' selects only the R-N vacuum as a physically sensible state, i.e., it selects the temperature $T=0$ only. |
gr-qc/0309113 | Zuxiang Dai | Zuxiang Dai | Cosmological magnetic fields: generation during inflation and evolution | 43 pages, paper also at
http://www.slac.stanford.edu/spires/find/hep/www?irn=5513243 | null | null | null | gr-qc | null | This paper concerns the generation and evolution of the cosmological
(large-scale $\sim Mpc$) magnetic fields in an inflationary universe. The
universe during inflation is represented by de Sitter space-time. We started
with the Maxwell equations in spatially flat Friedmann-Robertson-Walker (FRW)
Cosmologies. Then we calculated the wave equations of the magnetic field and
electric field for the evolution. We consider the input current that was
produced from a massless charged scalar complex field. This field minimally
coupled to both gravity and the electromagnetic fields. The Lagrangian for
massless scalar electrodynamics is then
$L=\sqrt{-g}(D_\mu\phi(D^\mu\phi)^*-{1/4}F_{\mu\nu}F^{\mu\nu})$ . The complex
scalar field couples to electromagnetism through the usual gauge covariant
derivative $D_\mu=\partial_\mu-ieA_\mu$ . After the quantum field theoretical
deduction for the current, we put it back into the wave equation of the
magnetic field.
After solving this wave equation, our result is $a^2B\sim
\frac{eH}{\sqrt{2}k^2}\mid\sin\sqrt{2}k\eta\mid$ . At the time $\eta_{RH}$ we
have $B_{RH}=\frac{e}{k_{phys}}$. This may imply that the breaking of the
conformal invariance due to the minimal coupling of a massless charged scalar
complex field to both gravitational and electromagnetic fields is not
sufficient for the production of seed galactic magnetic fields during
inflation. But since we are interested in the large-scale cosmological magnetic
field, this could be still a candidate, because of the $1/k$ factor.
| [
{
"created": "Tue, 23 Sep 2003 15:27:49 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Dai",
"Zuxiang",
""
]
] | This paper concerns the generation and evolution of the cosmological (large-scale $\sim Mpc$) magnetic fields in an inflationary universe. The universe during inflation is represented by de Sitter space-time. We started with the Maxwell equations in spatially flat Friedmann-Robertson-Walker (FRW) Cosmologies. Then we calculated the wave equations of the magnetic field and electric field for the evolution. We consider the input current that was produced from a massless charged scalar complex field. This field minimally coupled to both gravity and the electromagnetic fields. The Lagrangian for massless scalar electrodynamics is then $L=\sqrt{-g}(D_\mu\phi(D^\mu\phi)^*-{1/4}F_{\mu\nu}F^{\mu\nu})$ . The complex scalar field couples to electromagnetism through the usual gauge covariant derivative $D_\mu=\partial_\mu-ieA_\mu$ . After the quantum field theoretical deduction for the current, we put it back into the wave equation of the magnetic field. After solving this wave equation, our result is $a^2B\sim \frac{eH}{\sqrt{2}k^2}\mid\sin\sqrt{2}k\eta\mid$ . At the time $\eta_{RH}$ we have $B_{RH}=\frac{e}{k_{phys}}$. This may imply that the breaking of the conformal invariance due to the minimal coupling of a massless charged scalar complex field to both gravitational and electromagnetic fields is not sufficient for the production of seed galactic magnetic fields during inflation. But since we are interested in the large-scale cosmological magnetic field, this could be still a candidate, because of the $1/k$ factor. |
2206.13227 | Arnau Mas | Jordi Gaset, Arnau Mas | A variational derivation of the field equations of an action-dependent
Einstein-Hilbert Lagrangian | 22 pp; v1: initial submission; v2: minor changes; v3: submitted to
Journal of Geometric Mechanics, updated to reflect changes after peer review | null | 10.3934/jgm.2023014 | null | gr-qc math-ph math.MP physics.class-ph | http://creativecommons.org/licenses/by/4.0/ | We derive the equations of motion of an action-dependent version of the
Einstein-Hilbert Lagrangian, as a specific instance of the Herglotz variational
problem. Action-dependent Lagrangians lead to dissipative dynamics, which
cannot be obtained with the standard method of Lagrangian field theory.
First-order theories of this kind are relatively well understood, but examples
of singular or higher-order action-dependent field theories are scarce. This
work constitutes an example of such a theory. By casting the problem in clear
geometric terms we are able to obtain a Lorentz invariant set of equations,
which contrasts with previous attempts.
| [
{
"created": "Thu, 23 Jun 2022 20:56:28 GMT",
"version": "v1"
},
{
"created": "Thu, 7 Jul 2022 11:53:05 GMT",
"version": "v2"
},
{
"created": "Mon, 30 Jan 2023 16:44:44 GMT",
"version": "v3"
}
] | 2023-03-08 | [
[
"Gaset",
"Jordi",
""
],
[
"Mas",
"Arnau",
""
]
] | We derive the equations of motion of an action-dependent version of the Einstein-Hilbert Lagrangian, as a specific instance of the Herglotz variational problem. Action-dependent Lagrangians lead to dissipative dynamics, which cannot be obtained with the standard method of Lagrangian field theory. First-order theories of this kind are relatively well understood, but examples of singular or higher-order action-dependent field theories are scarce. This work constitutes an example of such a theory. By casting the problem in clear geometric terms we are able to obtain a Lorentz invariant set of equations, which contrasts with previous attempts. |
1710.01822 | Ivan Gentile De Austria | Ivan Gentile de Austria | Bounds for the metric and shift vector on extreme Kerr under linear
axially symmetric gravitational perturbations | 14 pages | null | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present integral estimates for the shift and induced metric in the maximal
isothermal gauge, corresponding to linear axially symmetric gravitational
perturbations over the Minkowski and extreme Kerr metric. These bounds are a
step towards finding pointwise bounds for the perturbations. In particular the
presented estimate for the shift includes the horizon for the extreme Kerr
case.
| [
{
"created": "Wed, 4 Oct 2017 22:59:01 GMT",
"version": "v1"
}
] | 2017-10-06 | [
[
"de Austria",
"Ivan Gentile",
""
]
] | We present integral estimates for the shift and induced metric in the maximal isothermal gauge, corresponding to linear axially symmetric gravitational perturbations over the Minkowski and extreme Kerr metric. These bounds are a step towards finding pointwise bounds for the perturbations. In particular the presented estimate for the shift includes the horizon for the extreme Kerr case. |
gr-qc/9810041 | Korotkin Dmitrii | D.Korotkin and V.Matveev | Solutions of Schlesinger system and Ernst equation in terms of
theta-functions | null | null | null | AEI-087, august 1998 | gr-qc | null | We discuss the relationship between Schlesinger system and stationary
axisymmetric Einstein's equation on the level of algebro-geometric solutions.
In particular, we calculate all metric coefficients corresponding to solutions
of Ernst equation in terms of theta-functions.
| [
{
"created": "Mon, 12 Oct 1998 09:58:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Korotkin",
"D.",
""
],
[
"Matveev",
"V.",
""
]
] | We discuss the relationship between Schlesinger system and stationary axisymmetric Einstein's equation on the level of algebro-geometric solutions. In particular, we calculate all metric coefficients corresponding to solutions of Ernst equation in terms of theta-functions. |
gr-qc/9306020 | null | Gerhard Rein, Alan D. Rendall, and Jack Schaeffer | A regularity theorem for solutions of the spherically symmetric
Vlasov-Einstein system | 15 pages, Latex, report # 2 | Commun.Math.Phys. 168 (1995) 467-478 | 10.1007/BF02101839 | null | gr-qc | null | In a previous paper two of the authors (G. R. and A. D. R.) showed that there
exist global, classical solutions of the spherically symmetric Vlasov-Einstein
system for small initial data. The present paper continues this investigation
and allows also large initial data. It is shown that if a solution of the
spherically symmetric Vlasov-Einstein system develops a singularity at all then
the first singularity has to appear at the center of symmetry. The result adds
weight to the conjecture that cosmic censorship holds if one replaces dust as
matter model for which naked singularities do form by a collisionless gas
described by the Vlasov equation. The main tool is an estimate which shows that
a solution is global if all the matter remains away from the center of
symmetry.
| [
{
"created": "Wed, 16 Jun 1993 09:18:47 GMT",
"version": "v1"
}
] | 2015-06-25 | [
[
"Rein",
"Gerhard",
""
],
[
"Rendall",
"Alan D.",
""
],
[
"Schaeffer",
"Jack",
""
]
] | In a previous paper two of the authors (G. R. and A. D. R.) showed that there exist global, classical solutions of the spherically symmetric Vlasov-Einstein system for small initial data. The present paper continues this investigation and allows also large initial data. It is shown that if a solution of the spherically symmetric Vlasov-Einstein system develops a singularity at all then the first singularity has to appear at the center of symmetry. The result adds weight to the conjecture that cosmic censorship holds if one replaces dust as matter model for which naked singularities do form by a collisionless gas described by the Vlasov equation. The main tool is an estimate which shows that a solution is global if all the matter remains away from the center of symmetry. |
gr-qc/9305007 | Don N. Page | Don N. Page | Average Entropy of a Subsystem | 10 pages, LaTeX. Title change and minor corrections added before
publication in Phys. Rev. Lett. 71 (1993) 1291. Alberta-Thy-22-93 | Phys.Rev.Lett.71:1291-1294,1993 | 10.1103/PhysRevLett.71.1291 | null | gr-qc hep-th | null | If a quantum system of Hilbert space dimension $mn$ is in a random pure
state, the average entropy of a subsystem of dimension $m\leq n$ is conjectured
to be $S_{m,n}=\sum_{k=n+1}^{mn}\frac{1}{k}-\frac{m-1}{2n}$ and is shown to be
$\simeq \ln m - \frac{m}{2n}$ for $1\ll m\leq n$. Thus there is less than
one-half unit of information, on average, in the smaller subsystem of a total
system in a random pure state.
| [
{
"created": "Fri, 7 May 1993 17:14:41 GMT",
"version": "v1"
},
{
"created": "Tue, 31 Aug 1993 23:23:25 GMT",
"version": "v2"
}
] | 2014-11-17 | [
[
"Page",
"Don N.",
""
]
] | If a quantum system of Hilbert space dimension $mn$ is in a random pure state, the average entropy of a subsystem of dimension $m\leq n$ is conjectured to be $S_{m,n}=\sum_{k=n+1}^{mn}\frac{1}{k}-\frac{m-1}{2n}$ and is shown to be $\simeq \ln m - \frac{m}{2n}$ for $1\ll m\leq n$. Thus there is less than one-half unit of information, on average, in the smaller subsystem of a total system in a random pure state. |
1501.04773 | Francisco Lobo | Mohammad Reza Mehdizadeh, Mahdi Kord Zangeneh, Francisco S. N. Lobo | Einstein-Gauss-Bonnet traversable wormholes satisfying the weak energy
condition | 8 pages, 6 figures. V2: 9 pages, minor modifications, references
added and typo corrected; to appear in PRD | Phys.Rev.D91:084004,2015 | 10.1103/PhysRevD.91.084004 | null | gr-qc astro-ph.HE hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we explore higher-dimensional asymptotically flat wormhole
geometries in the framework of Gauss-Bonnet (GB) gravity and investigate the
effects of the GB term, by considering a specific radial-dependent redshift
function and by imposing a particular equation of state. This work is motivated
by previous assumptions that wormhole solutions were not possible for the $k=1$
and $\alpha < 0$ case, where $k$ is the sectional curvature of an
$(n-2)$-dimensional maximally symmetric space, and $\alpha$ is the Gauss-Bonnet
coupling constant. However, we emphasize that this discussion is purely based
on a nontrivial assumption that is only valid at the wormhole throat, and
cannot be extended to the entire radial-coordinate range. In this work, we
provide a counterexample to this claim, and find for the first time specific
solutions that satisfy the weak energy condition throughout the entire
spacetime, for $k=1$ and $\alpha < 0$. In addition to this, we also present
other wormhole solutions which alleviate the violation of the WEC in the
vicinity of the wormhole throat.
| [
{
"created": "Tue, 20 Jan 2015 12:14:31 GMT",
"version": "v1"
},
{
"created": "Mon, 16 Mar 2015 19:32:17 GMT",
"version": "v2"
}
] | 2015-04-06 | [
[
"Mehdizadeh",
"Mohammad Reza",
""
],
[
"Zangeneh",
"Mahdi Kord",
""
],
[
"Lobo",
"Francisco S. N.",
""
]
] | In this paper, we explore higher-dimensional asymptotically flat wormhole geometries in the framework of Gauss-Bonnet (GB) gravity and investigate the effects of the GB term, by considering a specific radial-dependent redshift function and by imposing a particular equation of state. This work is motivated by previous assumptions that wormhole solutions were not possible for the $k=1$ and $\alpha < 0$ case, where $k$ is the sectional curvature of an $(n-2)$-dimensional maximally symmetric space, and $\alpha$ is the Gauss-Bonnet coupling constant. However, we emphasize that this discussion is purely based on a nontrivial assumption that is only valid at the wormhole throat, and cannot be extended to the entire radial-coordinate range. In this work, we provide a counterexample to this claim, and find for the first time specific solutions that satisfy the weak energy condition throughout the entire spacetime, for $k=1$ and $\alpha < 0$. In addition to this, we also present other wormhole solutions which alleviate the violation of the WEC in the vicinity of the wormhole throat. |
1903.01726 | Tomas Ledvinka | Tom\'a\v{s} Ledvinka and Ji\v{r}\'i Bi\v{c}\'ak | Disk sources of the Kerr and Tomimatsu-Sato spacetimes: construction and
physical properties | null | null | 10.1103/PhysRevD.99.064046 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We construct the disk sources matched to the exact vacuum Kerr and to the two
classes of Tomimatsu-Sato spacetimes. We analyze two models of the matter
forming these disks. At each radius we consider either a rotating massive ring
with pressure or two counter-rotating streams of particles in circular geodesic
motion. Dragging effects present in such spacetimes lead either to rotation of
rings or asymmetry of both streams. We demonstrate that the model of rotating
rings is general enough to describe all axisymmetric stationary disk sources
with vanishing radial pressure which satisfy weak energy condition, and that
centrifugal effects present in the disk sources of spacetimes with large
angular momentum prevent the construction of highly compact sources made of
counter-rotating streams of geodesic particles. We illustrate the radial
distribution of the mass inside the disks and the angular velocities of both
geodesic streams.
| [
{
"created": "Tue, 5 Mar 2019 08:46:07 GMT",
"version": "v1"
}
] | 2019-04-17 | [
[
"Ledvinka",
"Tomáš",
""
],
[
"Bičák",
"Jiří",
""
]
] | We construct the disk sources matched to the exact vacuum Kerr and to the two classes of Tomimatsu-Sato spacetimes. We analyze two models of the matter forming these disks. At each radius we consider either a rotating massive ring with pressure or two counter-rotating streams of particles in circular geodesic motion. Dragging effects present in such spacetimes lead either to rotation of rings or asymmetry of both streams. We demonstrate that the model of rotating rings is general enough to describe all axisymmetric stationary disk sources with vanishing radial pressure which satisfy weak energy condition, and that centrifugal effects present in the disk sources of spacetimes with large angular momentum prevent the construction of highly compact sources made of counter-rotating streams of geodesic particles. We illustrate the radial distribution of the mass inside the disks and the angular velocities of both geodesic streams. |
1309.6622 | Seyed Meraj Mousavi Rasouli | S. M. M. Rasouli, A. H. Ziaie, J. Marto and P. V. Moniz | Gravitational Collapse of a Homogeneous Scalar Field in Deformed Phase
Space | 17 pages, 17 figures | Phys. Rev. D 89, 044028 (2014) | 10.1103/PhysRevD.89.044028 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the gravitational collapse of a homogeneous scalar field, minimally
coupled to gravity, in the presence of a particular type of dynamical
deformation between the canonical momenta of the scale factor and of the scalar
field. In the absence of such a deformation, a class of solutions can be found
in the literature [R. Goswami and P. S. Joshi, arXiv:gr-qc/0410144],
%\cite{JG04}, whereby a curvature singularity occurs at the collapse end state,
which can be either hidden behind a horizon or be visible to external
observers. However, when the phase-space is deformed, as implemented herein
this paper, we find that the singularity may be either removed or instead,
attained faster. More precisely, for negative values of the deformation
parameter, we identify the emergence of a negative pressure term, which slows
down the collapse so that the singularity is replaced with a bounce. In this
respect, the formation of a dynamical horizon can be avoided depending on the
suitable choice of the boundary surface of the star. Whereas for positive
values, the pressure that originates from the deformation effects assists the
collapse toward the singularity formation. In this case, since the collapse
speed is unbounded, the condition on the horizon formation is always satisfied
and furthermore the dynamical horizon develops earlier than when the
phase-space deformations are absent. These results are obtained by means of a
thoroughly numerical discussion.
| [
{
"created": "Wed, 25 Sep 2013 19:44:41 GMT",
"version": "v1"
},
{
"created": "Tue, 4 Mar 2014 00:21:55 GMT",
"version": "v2"
}
] | 2014-03-05 | [
[
"Rasouli",
"S. M. M.",
""
],
[
"Ziaie",
"A. H.",
""
],
[
"Marto",
"J.",
""
],
[
"Moniz",
"P. V.",
""
]
] | We study the gravitational collapse of a homogeneous scalar field, minimally coupled to gravity, in the presence of a particular type of dynamical deformation between the canonical momenta of the scale factor and of the scalar field. In the absence of such a deformation, a class of solutions can be found in the literature [R. Goswami and P. S. Joshi, arXiv:gr-qc/0410144], %\cite{JG04}, whereby a curvature singularity occurs at the collapse end state, which can be either hidden behind a horizon or be visible to external observers. However, when the phase-space is deformed, as implemented herein this paper, we find that the singularity may be either removed or instead, attained faster. More precisely, for negative values of the deformation parameter, we identify the emergence of a negative pressure term, which slows down the collapse so that the singularity is replaced with a bounce. In this respect, the formation of a dynamical horizon can be avoided depending on the suitable choice of the boundary surface of the star. Whereas for positive values, the pressure that originates from the deformation effects assists the collapse toward the singularity formation. In this case, since the collapse speed is unbounded, the condition on the horizon formation is always satisfied and furthermore the dynamical horizon develops earlier than when the phase-space deformations are absent. These results are obtained by means of a thoroughly numerical discussion. |
2007.02409 | Mushtaq Ahmad Sial | G. Mustafa, M. Farasat Shamir, Mushtaq Ahmad | Bardeen Stellar Structures with Karmarkar Condition | 23 pages, 17 figures | Phys. Dark Universe 30, 100652 (2020) | 10.1016/j.dark.2020.100652 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Current study is focussed to discuss the existence of a new family of compact
star solutions by adopting the Karmarkar condition in the background of Bardeen
black hole geometry. For this purpose, we consider static spherically symmetric
spacetime with anisotropic fluid distribution in the presence of electric
charge. We consider a specific model of $g_{rr}$ metric function, to describe a
new family of solutions which satisfies the Karmarkar condition. Further, we
investigate the interior solutions for two different models of compact stars
with observational mass and radii, i.e., $(M=1.77M_{\odot}, \;R_{b}=9.56km)$
and $(M=1.97M_{\odot}, \;R_{b}=10.3km)$. It is found that these solutions
fulfill all the necessary conditions for a charged star. Through graphical
discussion, it is noticed that our calculated solutions are physically arguable
with a best degree of accuracy for $n\in[1.8,7)$, where parameter $n$ is
involved in the model under discussion. However, it is perceived that the
presented model violates all the physical conditions for $n\in\{2,4,6\}$.
Finally, it is concluded that the parameter $n$ has a strong impact on the
obtained solutions in the context of Bardeen stellar structures.
| [
{
"created": "Sun, 5 Jul 2020 18:26:08 GMT",
"version": "v1"
}
] | 2020-07-07 | [
[
"Mustafa",
"G.",
""
],
[
"Shamir",
"M. Farasat",
""
],
[
"Ahmad",
"Mushtaq",
""
]
] | Current study is focussed to discuss the existence of a new family of compact star solutions by adopting the Karmarkar condition in the background of Bardeen black hole geometry. For this purpose, we consider static spherically symmetric spacetime with anisotropic fluid distribution in the presence of electric charge. We consider a specific model of $g_{rr}$ metric function, to describe a new family of solutions which satisfies the Karmarkar condition. Further, we investigate the interior solutions for two different models of compact stars with observational mass and radii, i.e., $(M=1.77M_{\odot}, \;R_{b}=9.56km)$ and $(M=1.97M_{\odot}, \;R_{b}=10.3km)$. It is found that these solutions fulfill all the necessary conditions for a charged star. Through graphical discussion, it is noticed that our calculated solutions are physically arguable with a best degree of accuracy for $n\in[1.8,7)$, where parameter $n$ is involved in the model under discussion. However, it is perceived that the presented model violates all the physical conditions for $n\in\{2,4,6\}$. Finally, it is concluded that the parameter $n$ has a strong impact on the obtained solutions in the context of Bardeen stellar structures. |
1801.08944 | Jose Natario | Jo\~ao L. Costa, Jos\'e Nat\'ario, Pedro Oliveira | Decay of solutions of the wave equation in expanding cosmological
spacetimes | 25 pages, 3 figures; v2: small corrections; v3: typos corrected,
matches final published version; v4: typo in the statement of Theorem 2
corrected; v5: sign error in the conformally invariant wave equation fixed | J. Hyperbolic Differ. Equ. 16 (2019) 35-58 | 10.1142/S0219891619500024 | null | gr-qc math.AP | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We study the decay of solutions of the wave equation in some expanding
cosmological spacetimes, namely flat Friedmann-Lema\^itre-Robertson-Walker
(FLRW) models and the cosmological region of the Reissner-Nordstr\"om-de Sitter
(RNdS) solution. By introducing a partial energy and using an iteration scheme,
we find that, for initial data with finite higher order energies, the decay
rate of the time derivative is faster than previously existing estimates. For
models undergoing accelerated expansion, our decay rate appears to be (almost)
sharp.
| [
{
"created": "Fri, 26 Jan 2018 19:00:08 GMT",
"version": "v1"
},
{
"created": "Mon, 12 Nov 2018 17:11:00 GMT",
"version": "v2"
},
{
"created": "Wed, 3 Jul 2019 13:13:28 GMT",
"version": "v3"
},
{
"created": "Mon, 22 Jul 2019 10:55:39 GMT",
"version": "v4"
},
{
"cr... | 2020-05-06 | [
[
"Costa",
"João L.",
""
],
[
"Natário",
"José",
""
],
[
"Oliveira",
"Pedro",
""
]
] | We study the decay of solutions of the wave equation in some expanding cosmological spacetimes, namely flat Friedmann-Lema\^itre-Robertson-Walker (FLRW) models and the cosmological region of the Reissner-Nordstr\"om-de Sitter (RNdS) solution. By introducing a partial energy and using an iteration scheme, we find that, for initial data with finite higher order energies, the decay rate of the time derivative is faster than previously existing estimates. For models undergoing accelerated expansion, our decay rate appears to be (almost) sharp. |
gr-qc/9208010 | Kiyoshi Kamimura | K.Kamimura and T.Fukuyama | Massive Analogue of Ashtekar-CJD Action | 6p. Tex | null | 10.1016/0083-6656(93)90105-S | TOHO-FP-9243 | gr-qc hep-th | null | The action of Ashtekar gravity have been found by Cappovilla, Jacobson and
Dell. It does not depend on the metric nor the signature of the space-time. The
action has a similar structure as that of a massless relativistic particle. The
former is naturally generalized by adding a term analogous to a mass term of
the relativistic particle. The new action possesses a constant parameter
regarded as a kind of a cosmological constant. It is interesting to find a
covariant Einstein equation from the action. In order to do it we will examine
how the geometrical quantities are determined from the non-metric action and
how the Einstein equation follows from it.
| [
{
"created": "Tue, 25 Aug 1992 02:25:20 GMT",
"version": "v1"
}
] | 2009-10-22 | [
[
"Kamimura",
"K.",
""
],
[
"Fukuyama",
"T.",
""
]
] | The action of Ashtekar gravity have been found by Cappovilla, Jacobson and Dell. It does not depend on the metric nor the signature of the space-time. The action has a similar structure as that of a massless relativistic particle. The former is naturally generalized by adding a term analogous to a mass term of the relativistic particle. The new action possesses a constant parameter regarded as a kind of a cosmological constant. It is interesting to find a covariant Einstein equation from the action. In order to do it we will examine how the geometrical quantities are determined from the non-metric action and how the Einstein equation follows from it. |
1810.12336 | K\'evin Nguyen | Oleg Evnin and K\'evin Nguyen | A Graceful Exit for the Cosmological Constant Damping Scenario | v2: 16 pages, minor improvements, discussion added, typos corrected | Phys. Rev. D 98, 124031 (2018) | 10.1103/PhysRevD.98.124031 | null | gr-qc hep-ph hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | We present a broad and simple class of scalar-tensor scenarios that
successfully realize dynamical damping of the effective cosmological constant,
therefore providing a viable dynamical solution to the fine-tuning or "old"
cosmological constant problem. In contrast to early versions of this approach,
pioneered in the works of A. Dolgov in the 1980es, these do not suffer from
unacceptable variations of Newton's constant, as one aims at a small but
strictly positive (rather than zero) late-time curvature. In our approach, the
original fine-tuning issue is traded for a hierarchy of couplings, and we
further suggest a way to naturally generate this hierarchy based on fermion
condensation and softly broken field shift symmetry.
| [
{
"created": "Mon, 29 Oct 2018 18:19:12 GMT",
"version": "v1"
},
{
"created": "Mon, 26 Nov 2018 09:04:45 GMT",
"version": "v2"
}
] | 2018-12-27 | [
[
"Evnin",
"Oleg",
""
],
[
"Nguyen",
"Kévin",
""
]
] | We present a broad and simple class of scalar-tensor scenarios that successfully realize dynamical damping of the effective cosmological constant, therefore providing a viable dynamical solution to the fine-tuning or "old" cosmological constant problem. In contrast to early versions of this approach, pioneered in the works of A. Dolgov in the 1980es, these do not suffer from unacceptable variations of Newton's constant, as one aims at a small but strictly positive (rather than zero) late-time curvature. In our approach, the original fine-tuning issue is traded for a hierarchy of couplings, and we further suggest a way to naturally generate this hierarchy based on fermion condensation and softly broken field shift symmetry. |
1202.4639 | Thomas W. Baumgarte | Thomas W. Baumgarte | An alternative approach to solving the Hamiltonian constraint | 5 pages, 4 figures, matches version published in PRD | Phys.Rev.D85:084013,2012 | 10.1103/PhysRevD.85.084013 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Solving Einstein's constraint equations for the construction of black hole
initial data requires handling the black hole singularity. Typically, this is
done either with the excision method, in which the black hole interior is
excised from the numerical grid, or with the puncture method, in which the
singular part of the conformal factor is expressed in terms of an analytical
background solution, and the Hamiltonian constraint is then solved for a
correction to the background solution that, usually, is assumed to be regular
everywhere. We discuss an alternative approach in which the Hamiltonian
constraint is solved for an inverse power of the conformal factor. This new
function remains finite everywhere, so that this approach requires neither
excision nor a split into background and correction. In particular, this method
can be used without modification even when the correction to the conformal
factor is singular itself. We demonstrate this feature for rotating black holes
in the trumpet topology.
| [
{
"created": "Tue, 21 Feb 2012 13:52:41 GMT",
"version": "v1"
},
{
"created": "Tue, 24 Apr 2012 12:45:53 GMT",
"version": "v2"
}
] | 2015-06-04 | [
[
"Baumgarte",
"Thomas W.",
""
]
] | Solving Einstein's constraint equations for the construction of black hole initial data requires handling the black hole singularity. Typically, this is done either with the excision method, in which the black hole interior is excised from the numerical grid, or with the puncture method, in which the singular part of the conformal factor is expressed in terms of an analytical background solution, and the Hamiltonian constraint is then solved for a correction to the background solution that, usually, is assumed to be regular everywhere. We discuss an alternative approach in which the Hamiltonian constraint is solved for an inverse power of the conformal factor. This new function remains finite everywhere, so that this approach requires neither excision nor a split into background and correction. In particular, this method can be used without modification even when the correction to the conformal factor is singular itself. We demonstrate this feature for rotating black holes in the trumpet topology. |
1311.0268 | N\'estor Ortiz | N\'estor Ortiz and Olivier Sarbach | Cauchy horizon stability in a collapsing spherical dust cloud I:
geometric optic approximation and spherically symmetric test fields | 15 pages, 7 figures | Class.Quant.Grav. 31 (2014) 075003 | 10.1088/0264-9381/31/7/075003 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | A spherical dust cloud which is initially at rest and which has a
monotonously decaying density profile collapses and forms a shell-focussing
singularity. Provided the density profile is not too flat, meaning that its
second radial derivative is negative at the center, this singularity is visible
to local, and sometimes even to global observers. According to the strong
cosmic censorship conjecture, such naked singularities should be unstable under
generic, nonspherical perturbations of the initial data or when more realistic
matter models are considered.
In an attempt to gain some understanding about this stability issue, in this
work we initiate the analysis of a simpler but related problem. We discuss the
stability of test fields propagating in the vicinity of the Cauchy horizon
associated to the naked central singularity. We first study the high-frequency
limit and show that the fields undergo a blueshift as they approach the Cauchy
horizon. However, in contrast to what occurs at inner horizons of black holes,
we show that the blueshift is uniformly bounded along incoming and outgoing
null rays. Motivated by this boundedness result, we take a step beyond the
geometric optic approximation and consider the Cauchy evolution of spherically
symmetric test scalar fields. We prove that under reasonable conditions on the
initial data a suitable rescaled field can be continuously extended to the
Cauchy horizon. In particular, this result implies that the physical field is
everywhere finite on the Cauchy horizon away from the central singularity.
| [
{
"created": "Fri, 1 Nov 2013 19:30:11 GMT",
"version": "v1"
}
] | 2014-06-17 | [
[
"Ortiz",
"Néstor",
""
],
[
"Sarbach",
"Olivier",
""
]
] | A spherical dust cloud which is initially at rest and which has a monotonously decaying density profile collapses and forms a shell-focussing singularity. Provided the density profile is not too flat, meaning that its second radial derivative is negative at the center, this singularity is visible to local, and sometimes even to global observers. According to the strong cosmic censorship conjecture, such naked singularities should be unstable under generic, nonspherical perturbations of the initial data or when more realistic matter models are considered. In an attempt to gain some understanding about this stability issue, in this work we initiate the analysis of a simpler but related problem. We discuss the stability of test fields propagating in the vicinity of the Cauchy horizon associated to the naked central singularity. We first study the high-frequency limit and show that the fields undergo a blueshift as they approach the Cauchy horizon. However, in contrast to what occurs at inner horizons of black holes, we show that the blueshift is uniformly bounded along incoming and outgoing null rays. Motivated by this boundedness result, we take a step beyond the geometric optic approximation and consider the Cauchy evolution of spherically symmetric test scalar fields. We prove that under reasonable conditions on the initial data a suitable rescaled field can be continuously extended to the Cauchy horizon. In particular, this result implies that the physical field is everywhere finite on the Cauchy horizon away from the central singularity. |
gr-qc/9906078 | Alejandro Corichi | Alejandro Corichi and Andres Gomberoff | On a spacetime duality in 2+1 gravity | 23 pages, 2 figures, Revtex file | Class.Quant.Grav. 16 (1999) 3579-3598 | 10.1088/0264-9381/16/11/309 | NSF-ITP-99-061, SU-GP-99/6-1 | gr-qc hep-th math-ph math.MP | null | We consider 2+1 dimensional gravity with a cosmological constant, and explore
a duality that exists between space-times that have the De Sitter group SO(3,1)
as its local isometry group. In particular, the Lorentzian theory with a
positive cosmological constant is dual to the Euclidean theory with a negative
cosmological constant. We use this duality to construct a mapping between
apparently unrelated space-times. More precisely, we exhibit a relation between
the Euclidean BTZ family and some $T^2$-cosmological solutions, and between
De-Sitter point particle space-times and the analytic continuations of Anti-De
Sitter point particles. We discuss some possible applications for BH and AdS
thermodynamics.
| [
{
"created": "Thu, 17 Jun 1999 23:06:13 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Oct 1999 16:22:21 GMT",
"version": "v2"
}
] | 2009-10-31 | [
[
"Corichi",
"Alejandro",
""
],
[
"Gomberoff",
"Andres",
""
]
] | We consider 2+1 dimensional gravity with a cosmological constant, and explore a duality that exists between space-times that have the De Sitter group SO(3,1) as its local isometry group. In particular, the Lorentzian theory with a positive cosmological constant is dual to the Euclidean theory with a negative cosmological constant. We use this duality to construct a mapping between apparently unrelated space-times. More precisely, we exhibit a relation between the Euclidean BTZ family and some $T^2$-cosmological solutions, and between De-Sitter point particle space-times and the analytic continuations of Anti-De Sitter point particles. We discuss some possible applications for BH and AdS thermodynamics. |
gr-qc/0408048 | Guoying Chee | G. Y. Chee | Self-dual teleparallel gravity and the positive energy theorem | 11 pages, no figure | null | null | null | gr-qc | null | A self-dual and anti-self-dual decomposition of the teleparallel gravity is
carried out and the self-dual Lagrangian of the teleparallel gravity which is
equivalent to the Ashtekar Lagrangian in vacuum is obtained. Its Hamiltonian
formulation and the constraint analysis are developed. Starting from Witten's
equation Nester's gauge condition is derived directly and a new expression of
the boundary term is obtained. Using this expression and Witten's identity the
proof of the positive energy theorem by Nester et al is extended to a case
including momentum.
| [
{
"created": "Mon, 16 Aug 2004 16:20:52 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"Chee",
"G. Y.",
""
]
] | A self-dual and anti-self-dual decomposition of the teleparallel gravity is carried out and the self-dual Lagrangian of the teleparallel gravity which is equivalent to the Ashtekar Lagrangian in vacuum is obtained. Its Hamiltonian formulation and the constraint analysis are developed. Starting from Witten's equation Nester's gauge condition is derived directly and a new expression of the boundary term is obtained. Using this expression and Witten's identity the proof of the positive energy theorem by Nester et al is extended to a case including momentum. |
2405.09271 | Bobby Eka Gunara | Golfin Ekatria, Andy Octavian Latief, Fiki Taufik Akbar, and Bobby Eka
Gunara | Gravitational Collapse in Higher-Dimensional Rastall Gravity with and
without Cosmological Constant | 13 pages, 6 figures, comments are welcome | null | null | null | gr-qc hep-th | http://creativecommons.org/licenses/by/4.0/ | We consider a spherically symmetric homogeneous perfect fluid undergoing a
gravitational collapse to singularity in the framework of higher-dimensional
Rastall gravity in the cases of vanishing and nonvanishing cosmological
constants. The possible final states of the collapse in any finite dimension
are black hole and naked singularity, hence violating the cosmic censorship
conjecture, but the naked singularity formation becomes less favored when the
dimension is increased, such that the conjecture is fully restored in the limit
of very high dimensions. We find that there are two physically distinct
solutions for the collapse evolution in the case of nonzero cosmological
constant: trigonometric and exponential solutions. The effective energy density
of the fluid is decreasing (increasing) in the former (latter) when the
magnitude of the cosmological constant is increased, which implies that the
former undergoes a slower collapse than the latter. Furthermore, we find that a
temporary trapped surface is possible to emerge in the case of trigonometric
solution in the naked singularity region only. Therefore, faraway observers
with observational time shorter than the collapse duration may conclude that a
black hole is formed, although the collapse will eventually lead to a naked
singularity formation.
| [
{
"created": "Wed, 15 May 2024 11:40:02 GMT",
"version": "v1"
}
] | 2024-05-16 | [
[
"Ekatria",
"Golfin",
""
],
[
"Latief",
"Andy Octavian",
""
],
[
"Akbar",
"Fiki Taufik",
""
],
[
"Gunara",
"Bobby Eka",
""
]
] | We consider a spherically symmetric homogeneous perfect fluid undergoing a gravitational collapse to singularity in the framework of higher-dimensional Rastall gravity in the cases of vanishing and nonvanishing cosmological constants. The possible final states of the collapse in any finite dimension are black hole and naked singularity, hence violating the cosmic censorship conjecture, but the naked singularity formation becomes less favored when the dimension is increased, such that the conjecture is fully restored in the limit of very high dimensions. We find that there are two physically distinct solutions for the collapse evolution in the case of nonzero cosmological constant: trigonometric and exponential solutions. The effective energy density of the fluid is decreasing (increasing) in the former (latter) when the magnitude of the cosmological constant is increased, which implies that the former undergoes a slower collapse than the latter. Furthermore, we find that a temporary trapped surface is possible to emerge in the case of trigonometric solution in the naked singularity region only. Therefore, faraway observers with observational time shorter than the collapse duration may conclude that a black hole is formed, although the collapse will eventually lead to a naked singularity formation. |
gr-qc/0303104 | Roberto Gomez | Roberto Gomez (Pittsburgh Supercomputing Center) and Simonetta
Frittelli (Duquesne University) | First-order quasilinear canonical representation of the characteristic
formulation of the Einstein equations | revtex4, 7 pages, text and references added, typos corrected, to
appear in Phys. Rev. D | Phys.Rev.D68:084013,2003 | 10.1103/PhysRevD.68.084013 | NSF-KITP-03-58 | gr-qc | null | We prescribe a choice of 18 variables in all that casts the equations of the
fully nonlinear characteristic formulation of general relativity in
first--order quasi-linear canonical form. At the analytical level, a
formulation of this type allows us to make concrete statements about existence
of solutions. In addition, it offers concrete advantages for numerical
applications as it now becomes possible to incorporate advanced numerical
techniques for first order systems, which had thus far not been applicable to
the characteristic problem of the Einstein equations, as well as in providing a
framework for a unified treatment of the vacuum and matter problems. This is of
relevance to the accurate simulation of gravitational waves emitted in
astrophysical scenarios such as stellar core collapse.
| [
{
"created": "Wed, 26 Mar 2003 15:12:19 GMT",
"version": "v1"
},
{
"created": "Tue, 19 Aug 2003 17:33:17 GMT",
"version": "v2"
}
] | 2011-07-19 | [
[
"Gomez",
"Roberto",
"",
"Pittsburgh Supercomputing Center"
],
[
"Frittelli",
"Simonetta",
"",
"Duquesne University"
]
] | We prescribe a choice of 18 variables in all that casts the equations of the fully nonlinear characteristic formulation of general relativity in first--order quasi-linear canonical form. At the analytical level, a formulation of this type allows us to make concrete statements about existence of solutions. In addition, it offers concrete advantages for numerical applications as it now becomes possible to incorporate advanced numerical techniques for first order systems, which had thus far not been applicable to the characteristic problem of the Einstein equations, as well as in providing a framework for a unified treatment of the vacuum and matter problems. This is of relevance to the accurate simulation of gravitational waves emitted in astrophysical scenarios such as stellar core collapse. |
2107.02077 | Mitja Fridman Mr. | Saurya Das, Mitja Fridman, Gaetano Lambiase and Elias C. Vagenas | Baryon Asymmetry from the Generalized Uncertainty Principle | 13 pages, 0 figures | Phys. Lett. B 824, 136841 (2022) | 10.1016/j.physletb.2021.136841 | null | gr-qc hep-th | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | The unexplained observed baryon asymmetry in the Universe is a long-standing
problem in physics, with no satisfactory resolution so far. To explain this
asymmetry, three Sakharov conditions must be met. An interaction term which
couples space-time and the baryon current is considered, which satisfies the
first two Sakharov conditions. Furthermore, it is shown that the Generalized
Uncertainty Principle (GUP) from quantum gravity induces corrections to the
Friedmann equations in cosmology, via the holographic principle. GUP also
induces variations of energy and pressure density in the radiation dominated
era, which satisfies the third Sakharov condition. Therefore, this construction
provides a viable explanation for the observed baryon asymmetry. This also
fixes the GUP parameters to $\alpha_0\approx10^4$ and $\beta_0\approx-10^8$.
| [
{
"created": "Mon, 5 Jul 2021 15:17:19 GMT",
"version": "v1"
},
{
"created": "Mon, 1 Nov 2021 14:29:35 GMT",
"version": "v2"
}
] | 2022-08-16 | [
[
"Das",
"Saurya",
""
],
[
"Fridman",
"Mitja",
""
],
[
"Lambiase",
"Gaetano",
""
],
[
"Vagenas",
"Elias C.",
""
]
] | The unexplained observed baryon asymmetry in the Universe is a long-standing problem in physics, with no satisfactory resolution so far. To explain this asymmetry, three Sakharov conditions must be met. An interaction term which couples space-time and the baryon current is considered, which satisfies the first two Sakharov conditions. Furthermore, it is shown that the Generalized Uncertainty Principle (GUP) from quantum gravity induces corrections to the Friedmann equations in cosmology, via the holographic principle. GUP also induces variations of energy and pressure density in the radiation dominated era, which satisfies the third Sakharov condition. Therefore, this construction provides a viable explanation for the observed baryon asymmetry. This also fixes the GUP parameters to $\alpha_0\approx10^4$ and $\beta_0\approx-10^8$. |
1512.06829 | Neil J. Cornish | Neil J. Cornish and Laura M. Sampson | Towards Robust Gravitational Wave Detection with Pulsar Timing Arrays | 11 pages, 12 figures | Phys. Rev. D 93, 104047 (2016) | 10.1103/PhysRevD.93.104047 | null | gr-qc astro-ph.IM | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | Precision timing of highly stable milli-second pulsars is a promising
technique for the detection of very low frequency sources of gravitational
waves. In any single pulsar, a stochastic gravitational wave signal appears as
an additional source of timing noise that can be absorbed by the noise model,
and so it is only by considering the coherent response across a network of
pulsars that the signal can be distinguished from other sources of noise. In
the limit where there are many gravitational wave sources in the sky, or many
pulsars in the array, the signals produce a unique tensor correlation pattern
that depends only on the angular separation between each pulsar pair. It is
this distinct fingerprint that is used to search for gravitational waves using
pulsar timing arrays. Here we consider how the prospects for detection are
diminished when the statistical isotropy of the timing array or the
gravitational wave signal is broken by having a finite number of pulsars and a
finite number of sources. We find the standard tensor-correlation analysis to
be remarkably robust, with a mild impact on detectability compared to the
isotropic limit. Only when there are very few sources and very few pulsars does
the standard analysis begin to fail. Having established that the tensor
correlations are a robust signature for detection, we study the use of
"sky-scrambles" to break the correlations as a way to increase confidence in a
detection. This approach is analogous to the use of "time-slides" in the
analysis of data from ground based interferometric detectors.
| [
{
"created": "Mon, 21 Dec 2015 20:54:18 GMT",
"version": "v1"
}
] | 2016-06-01 | [
[
"Cornish",
"Neil J.",
""
],
[
"Sampson",
"Laura M.",
""
]
] | Precision timing of highly stable milli-second pulsars is a promising technique for the detection of very low frequency sources of gravitational waves. In any single pulsar, a stochastic gravitational wave signal appears as an additional source of timing noise that can be absorbed by the noise model, and so it is only by considering the coherent response across a network of pulsars that the signal can be distinguished from other sources of noise. In the limit where there are many gravitational wave sources in the sky, or many pulsars in the array, the signals produce a unique tensor correlation pattern that depends only on the angular separation between each pulsar pair. It is this distinct fingerprint that is used to search for gravitational waves using pulsar timing arrays. Here we consider how the prospects for detection are diminished when the statistical isotropy of the timing array or the gravitational wave signal is broken by having a finite number of pulsars and a finite number of sources. We find the standard tensor-correlation analysis to be remarkably robust, with a mild impact on detectability compared to the isotropic limit. Only when there are very few sources and very few pulsars does the standard analysis begin to fail. Having established that the tensor correlations are a robust signature for detection, we study the use of "sky-scrambles" to break the correlations as a way to increase confidence in a detection. This approach is analogous to the use of "time-slides" in the analysis of data from ground based interferometric detectors. |
gr-qc/0006041 | Santiago Esteban Perez Bergliaffa | S. E. Perez Bergliaffa and K. E. Hibberd | On the stress-energy tensor of a rotating wormhole | 4 pages, LaTex. Revised version, with several changes | null | null | null | gr-qc | null | We analyze the stress-energy tensor necessary to generate a general
stationary and axisymmetric spacetime. The constraints on the geometry arising
from considering a perfect fluid as a source are derived. For a fluid with a
nonzero stress tensor, we obtain two necessary conditions on the metric. As an
example, we show that the rotating wormhole presented in the literature can not
be described by either a perfect fluid or by a fluid with anisotropic stresses.
| [
{
"created": "Mon, 12 Jun 2000 14:40:22 GMT",
"version": "v1"
},
{
"created": "Wed, 26 Jul 2000 16:08:19 GMT",
"version": "v2"
}
] | 2007-05-23 | [
[
"Bergliaffa",
"S. E. Perez",
""
],
[
"Hibberd",
"K. E.",
""
]
] | We analyze the stress-energy tensor necessary to generate a general stationary and axisymmetric spacetime. The constraints on the geometry arising from considering a perfect fluid as a source are derived. For a fluid with a nonzero stress tensor, we obtain two necessary conditions on the metric. As an example, we show that the rotating wormhole presented in the literature can not be described by either a perfect fluid or by a fluid with anisotropic stresses. |
1810.01286 | Muhammad Sharif | M. Sharif and Sara Ashraf | Thermodynamics of Modified Cosmic Chaplygin Gas | 16 pages, 6 figures, to appear in AHEP | Ad. High Energy Phys. 2018(2018)8949252 | null | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In this paper, we examine the thermodynamic features of an exotic fluid known
as modified cosmic Chaplygin gas in the context of homogeneous isotropic
universe model. For this purpose, the behavior of physical parameters are
discussed that help to analyze nature of the universe. Using specific heat
formalism, the validity of third law of thermodynamics is checked. Furthermore,
with the help of thermodynamic entities, the thermal equation of state is also
discussed. The thermodynamic stability is explored by means of adiabatic,
specific heat and isothermal conditions from classical thermodynamics. It is
concluded that the considered fluid configuration is thermodynamically stable
and expands adiabatically for an appropriate choice of parameters.
| [
{
"created": "Mon, 1 Oct 2018 09:18:43 GMT",
"version": "v1"
}
] | 2018-10-05 | [
[
"Sharif",
"M.",
""
],
[
"Ashraf",
"Sara",
""
]
] | In this paper, we examine the thermodynamic features of an exotic fluid known as modified cosmic Chaplygin gas in the context of homogeneous isotropic universe model. For this purpose, the behavior of physical parameters are discussed that help to analyze nature of the universe. Using specific heat formalism, the validity of third law of thermodynamics is checked. Furthermore, with the help of thermodynamic entities, the thermal equation of state is also discussed. The thermodynamic stability is explored by means of adiabatic, specific heat and isothermal conditions from classical thermodynamics. It is concluded that the considered fluid configuration is thermodynamically stable and expands adiabatically for an appropriate choice of parameters. |
1410.5276 | Hanno Sahlmann | Jerzy Lewandowski and Hanno Sahlmann | A symmetric scalar constraint for loop quantum gravity | 10 pages, v2: added some references and explanations. This version is
identical to the published one up to cosmetics | Phys. Rev. D 91, 044022 (2015) | 10.1103/PhysRevD.91.044022 | null | gr-qc | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ | In the framework of loop quantum gravity, we define a new Hilbert space of
states which are solutions of a large number of components of the
diffeomorphism constraint. On this Hilbert space, using the methods of
Thiemann, we obtain a family of gravitational scalar constraints. They preserve
the Hilbert space for every choice of lapse function. Thus adjointness and
commutator properties of the constraint can be investigated in a
straightforward manner. We show how the space of solutions of the symmetrized
constraint can be defined by spectral decomposition, and the Hilbert space of
physical states by subsequently fully implementing the diffeomorphism
constraint. The relationship of the solutions to those resulting from a
proposal for a symmetric constraint operator by Thiemann remains to be
elucidated.
| [
{
"created": "Mon, 20 Oct 2014 13:56:16 GMT",
"version": "v1"
},
{
"created": "Tue, 10 Feb 2015 07:49:07 GMT",
"version": "v2"
}
] | 2015-03-05 | [
[
"Lewandowski",
"Jerzy",
""
],
[
"Sahlmann",
"Hanno",
""
]
] | In the framework of loop quantum gravity, we define a new Hilbert space of states which are solutions of a large number of components of the diffeomorphism constraint. On this Hilbert space, using the methods of Thiemann, we obtain a family of gravitational scalar constraints. They preserve the Hilbert space for every choice of lapse function. Thus adjointness and commutator properties of the constraint can be investigated in a straightforward manner. We show how the space of solutions of the symmetrized constraint can be defined by spectral decomposition, and the Hilbert space of physical states by subsequently fully implementing the diffeomorphism constraint. The relationship of the solutions to those resulting from a proposal for a symmetric constraint operator by Thiemann remains to be elucidated. |
gr-qc/0006076 | Remo Garattini | Remo Garattini | Casimir energy and variational methods in AdS spacetime | Submitted to Classical and Quantum Gravity | Class.Quant.Grav. 17 (2000) 3335-3352 | 10.1088/0264-9381/17/16/316 | null | gr-qc hep-th | null | Following the subtraction procedure for manifolds with boundaries, we
calculate by variational methods, the Schwarzschild-Anti-de Sitter and the
Anti-de Sitter space energy difference. By computing the one loop approximation
for TT tensors we discover the existence of an unstable mode at zero
temperature, which can be stabilized by the boundary reduction method.
Implications on a foam-like space are discussed.
| [
{
"created": "Wed, 21 Jun 2000 16:25:18 GMT",
"version": "v1"
}
] | 2009-10-31 | [
[
"Garattini",
"Remo",
""
]
] | Following the subtraction procedure for manifolds with boundaries, we calculate by variational methods, the Schwarzschild-Anti-de Sitter and the Anti-de Sitter space energy difference. By computing the one loop approximation for TT tensors we discover the existence of an unstable mode at zero temperature, which can be stabilized by the boundary reduction method. Implications on a foam-like space are discussed. |
2309.00865 | Lorenzo Fatibene | S.Carloni, L.Fatibene, M.Ferraris, R.G.McLenaghan, A.Orizzonte | Relativistic GPS in 3-dimensions | 29 pages, 8 figures | null | null | null | gr-qc | http://creativecommons.org/licenses/by/4.0/ | We extend to three dimensions the proposal of a completely relativistic
positioning system (rPS). The system does not rely on approximations, in fact,
it works at a few Schwarzschild radii from a black hole, and it does not rely
on Newtonian physics or special relativity. Since general relativity (GR)
claims to be our fundamental framework to describe classical physics, it must
provide tools to bootstrap physics within the theory itself, without relying on
previous approximated frameworks. The rPS is able to self-diagnose, that is, it
detects deviations from assumptions about the gravitational field and
consequently stops operations; in addition it is robust, i.e., it is able to
autonomously restore operations when assumptions are restored. From a more
general viewpoint, the rPS is equivalent to geodesy in spacetime, which
establishes a (conventional) coordinate system on a surface by means of
measurements within the surface itself, as well as allowing it to extract
information about the intrinsic geometry of the same surface. In other words,
the positioning system is potentially able to extract information about the
gravitational field (which in fact is identified with the geometry of
spacetime) in addition to the gravitational theory, which describes its
dynamics. Thus, it becomes a framework within which one can operationally
distinguish different theories of gravitation.
| [
{
"created": "Sat, 2 Sep 2023 08:42:57 GMT",
"version": "v1"
}
] | 2023-09-06 | [
[
"Carloni",
"S.",
""
],
[
"Fatibene",
"L.",
""
],
[
"Ferraris",
"M.",
""
],
[
"McLenaghan",
"R. G.",
""
],
[
"Orizzonte",
"A.",
""
]
] | We extend to three dimensions the proposal of a completely relativistic positioning system (rPS). The system does not rely on approximations, in fact, it works at a few Schwarzschild radii from a black hole, and it does not rely on Newtonian physics or special relativity. Since general relativity (GR) claims to be our fundamental framework to describe classical physics, it must provide tools to bootstrap physics within the theory itself, without relying on previous approximated frameworks. The rPS is able to self-diagnose, that is, it detects deviations from assumptions about the gravitational field and consequently stops operations; in addition it is robust, i.e., it is able to autonomously restore operations when assumptions are restored. From a more general viewpoint, the rPS is equivalent to geodesy in spacetime, which establishes a (conventional) coordinate system on a surface by means of measurements within the surface itself, as well as allowing it to extract information about the intrinsic geometry of the same surface. In other words, the positioning system is potentially able to extract information about the gravitational field (which in fact is identified with the geometry of spacetime) in addition to the gravitational theory, which describes its dynamics. Thus, it becomes a framework within which one can operationally distinguish different theories of gravitation. |
gr-qc/0102043 | Maurice H. P. M. van Putten | Maurice H.P.M. van Putten | Gravitational radiation from long gamma-ray bursts | submitted; Presented at the 2001 Aspen Winter Conference on
Gravitational Waves, Feb. 4-10, 2001, Aspen | null | null | null | gr-qc astro-ph | null | Long gamma-ray bursts (GRBs) are probably powered by high-angular momentum
black hole-torus systems in suspended accretion. The torus will radiate
gravitational waves as non-axisymmetric instabilities develop. The luminosity
in gravitational-wave emissions is expected to compare favorably with the
observed isotropic equivalent luminosity in GRB-afterglow emissions. This
predicts that long GRBs are potentially the most powerful LIGO/VIRGO
burst-sources in the Universe. Their frequency-dynamics is characterized by a
horizontal branch in the $\dot{f}(f)-$diagram.
| [
{
"created": "Sun, 11 Feb 2001 19:31:00 GMT",
"version": "v1"
}
] | 2007-05-23 | [
[
"van Putten",
"Maurice H. P. M.",
""
]
] | Long gamma-ray bursts (GRBs) are probably powered by high-angular momentum black hole-torus systems in suspended accretion. The torus will radiate gravitational waves as non-axisymmetric instabilities develop. The luminosity in gravitational-wave emissions is expected to compare favorably with the observed isotropic equivalent luminosity in GRB-afterglow emissions. This predicts that long GRBs are potentially the most powerful LIGO/VIRGO burst-sources in the Universe. Their frequency-dynamics is characterized by a horizontal branch in the $\dot{f}(f)-$diagram. |
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